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Reform des Osterdatums

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A '''reform of the date of Easter''' has been proposed several times because the current system for determining the date of [[Easter]] is seen as presenting two significant problems:

* Its [[moveable feast|date varies from year to year]]. It can fall on up to 35 different days in March and April of the respective calendar. While many Christians do not consider this to be a problem, it can cause frequent difficulties of co-ordination with [[civil calendar]]s, for example [[academic term]]s. Many countries have [[public holiday]]s around Easter weekend or tied to the date of Easter but spread from February to June, such as [[Shrove Tuesday]] or [[Feast of the Ascension|Ascension]] and [[Pentecost]].
* Many [[Eastern Christianity|Eastern churches]] calculate the date of Easter using the [[Julian calendar]], whereas some Eastern churches use the [[Revised Julian calendar]] and all [[Western Christianity|Western churches]] and civil authorities have adopted the [[Gregorian calendar|Gregorian reforms]] for all calendrical purposes. Hence in most years, Easter is celebrated on a later date in the East than in the West.

There have been [[Easter controversy|controversies about the "correct" date of Easter]] since antiquity, leading to [[schism]]s and excommunications or even executions due to [[Heresy in Christianity|heresy]], but most Christian churches today agree on certain points. Easter (Day) should therefore be celebrated …

* on a [[Sunday]] (according to the [[First Council of Nicaea#Separation of Easter computation from Jewish calendar|First Council of Nicaea in 325]]),
* after the [[Northward equinox]] (around Gregorian 20 March), i.e. in Northern spring,
* after the nominal "Paschal" [[full moon]].

There is less agreement whether Easter also should occur …

* so that [[Feast of the Annunciation|Annunciation]] – usually celebrated 25 March, 9 months before [[Christmas]] – does not fall on any day from the [[Palm Sunday|Sunday before Easter]] to the [[Octave of Easter|Sunday after]],
* on or after the [[Quartodecimanism|14th day]] of the lunar month of [[Nisan]],
* not before [[Passover|Jewish Pesach]]. (Easter is after [[passover (Christian holiday)|Christian Passover]] by definition.)

The disagreements have been particularly about the determination of moon phases and the equinox, some still preferring astronomical observation from a certain location (usually Jerusalem, Alexandria, Rome or local), most others following nominal approximations of these in either the [[Hebrew calendar|Hebrew]], Julian or Gregorian calendar using different lookup tables and cycles in their algorithms.

== Fixed date ==

It has been proposed that the first problem could be resolved by making Easter occur on a date fixed relative to the western [[Gregorian calendar]] every year, or alternatively on a Sunday within a fixed range of seven dates. While tying Easter to one fixed date would serve to underline the belief that it commemorates an actual historical event, without an accompanying [[calendar reform]] that changes the pattern of the days of the week (itself a subject of [[World Calendar#Religious objections|religious controversy]]) it would also break the tradition of Easter always being on a Sunday, established since the 2nd century AD and by now deeply embedded in the [[Liturgy|liturgical]] practice and [[Theology|theological]] understanding of almost all [[Christian denomination]]s.

The Second Ecumenical Council of the Vatican agreed in 1963 to accept a fixed Sunday in the Gregorian calendar as the date for Easter as long as other Christian churches agreed on it as well. They also agreed in principle to adopt a civil calendar reform as long as there were never any days outside the cycle of seven days per week.<ref name="vatican">{{cite| title = Constitution on the Sacred Liturgy ''Sacrosanctum Concilium'' | editor = [[Pope Paul VI]] | date = 4 December 1963 | url = http://www.vatican.va/archive/hist_councils/ii_vatican_council/documents/vat-ii_const_19631204_sacrosanctum-concilium_en.html | chapter = Appendix}}</ref>

{{Cal|6 April next Sunday|holiday=Pepuzite Easter}}
The Pepuzites, a 5th-century sect, celebrated Easter on the Sunday following April 6 (in the [[Julian calendar]]).<ref name="Sozomen1846">{{cite book |author=Sozomen |authorlink=Sozomen |title=Ecclesiastical History: A History of the Church : in Nine Books, from A.D. 324 to A.D. 440 : a New Translation from the Greek, with a Memoir of the Author |url=https://books.google.com/books?id=HMoCAAAAQAAJ&pg=353 |year=1846 |publisher=Bagster |page=353}}</ref> This is equivalent to the Sunday closest to April 9. The April 6 date was apparently arrived at because it was equivalent to the 14th of the month of [[Artemisios]] in an earlier calendar used in the area, hence, the 14th of the first month of spring.<ref name=Talley>{{cite book|last=Talley|first= Thomas J|chapter=Afterthoughts on The Origins of the Liturgical Year|title=Western Plainchant in the First Millennium: Studies in the Medieval Liturgy and Its Music |pages=1–10 |publisher=Ashgate |location=Aldershot|date=2003 |editor1=Sean Gallagher|editor2=et al|url=https://books.google.com/books?id=hM16rgEACAAJ|isbn=9780754603894}}</ref>

{{Cal|second Sunday of April|holiday=fixed Easter}}
The two most widespread proposals for fixing the date of Easter would set it on either the second Sunday in April (8 to 14, [[ISO 8601|week]] 14 or 15), or the Sunday after the second Saturday in April (9 to 15), affecting years with dominical letter G or AG where 1 April is a Sunday. In both schemes, account has been taken of the fact that—in spite of the many difficulties in establishing the dates of the historical events involved—many scholars attribute a high degree of probability to [[Good Friday|Friday]] 7 April 30, as the date of the [[crucifixion]] of [[Jesus]], which would make 9 April the date of the [[Resurrection]]. Another date which is supported by many scholars is 3 April 33,<ref>{{cite journal |last=Schaefer |first=B. E. |year=1990 |title=Lunar Visibility and the Crucifixion |journal=Journal of the Royal Astronomical Society |volume=31 |issue=1 |pages=53–67 |bibcode=1990QJRAS..31...53S}}</ref><ref name="humphreys">
* {{cite journal |last1=Humphreys |first1=Colin J. |last2=Waddington |first2=W. G. |title=Dating the Crucifixion |journal=Nature |volume=306 |issue=5945 |year=1983 |pages=743–746 |issn=0028-0836 |doi=10.1038/306743a0 |author-link1=Colin Humphreys|bibcode=1983Natur.306..743H }}
* {{cite web | title = The Date of the Crucifixion |last1=Humphreys|first1=Colin J.|last2=Waddington|first2=W. G.|author-link1=Colin Humphreys | work = Journal of the American Scientific Affiliation |volume=37 | date = March 1985 | accessdate = 2016-01-24 | url = http://www.asa3.org/ASA/PSCF/1985/JASA3-85Humphreys.html.ori.html }}
* {{cite book |last=Humphreys |first=Colin J. |authorlink=Colin Humphreys |title=The Mystery of the Last Supper: Reconstructing the Final Days of Jesus |url=https://books.google.com/books?id=gNQfLwEACAAJ |year=2011 |publisher=Cambridge University Press |isbn=978-0-521-73200-0 |page=193}}</ref> making 5 April the date of the [[Resurrection of Jesus|Resurrection]].

In the late 1920s and 1930s, this idea gained some momentum along with other calendar reform proposals, such as the [[International Fixed Calendar]] and the [[World Calendar]]. In 1928, [[Easter Act 1928|a law]] was passed in the United Kingdom authorising an Order in Council which would fix the date of Easter in that country as the Sunday after the second Saturday in April.<ref name="Richards1998">{{cite book|last=Richards|first=Edward Graham|title=Mapping Time: The Calendar and Its History|url=https://books.google.com/books?id=GqXDQgAACAAJ|year=1998|publisher=Oxford University Press|isbn=978-0-19-286205-1|page=122}}</ref> However, this was never implemented.

{{Cal|{{CURRENTYEAR}}-W14-7|holiday=fixed week Easter}}
The Sunday after the first Wednesday in April would always be in ISO week 14, except for leap years starting on Thursday (DC) where the week count is one higher than in otherwise equivalent common years after February. The [[Symmetry454 Calendar]] proposes a fixed date of Easter in week 14, which would agree with the aforementioned proposals in most years, but would be 1 week earlier in F/GF years (like the only deviation of the Pepuzite definition) and also in DC, D/ED and E/FE years. The Sunday of an ordinal ISO week ''n'' is also the ''n''th Sunday of the year, except in A/AG, B/BA and C/CB years where it is the ''n''+1st Sunday, so both major proposals put Easter on the 15th Sunday of the year except either in common years starting on Monday (G), where 8 April, i.e. the second Sunday in April, is the 14th Sunday of the year, or in leap years starting on Sunday (AG), where 15 April, i.e. the Sunday after the second Saturday in April, is the 16th Sunday of the year.

{| class="wikitable"
|+ Weeks for currently possible dates of Easter Sunday, proposed and special dates highlighted
|-
!scope=col| Month
!scope=col| [[Week#Week numbering|Sunday]]
| [[Dominical letter AG|AG]] || [[Dominical letter A|A]] || [[Dominical letter BA|BA]] || [[Dominical letter B|B]] || [[Dominical letter CB|CB]] || [[Dominical letter C|C]]
| [[Dominical letter DC|DC]] || [[Dominical letter D|D]] || [[Dominical letter ED|ED]] || [[Dominical letter E|E]] || [[Dominical letter FE|FE]] || [[Dominical letter F|F]] || [[Dominical letter GF|GF]] || [[Dominical letter G|G]]
!scope=col| [[ISO week date|Week]]
|-
!rowspan=3| March
! 12th
|colspan=7| — ||colspan=2| M 22 ||colspan=2| M 23 ||colspan=2| M 24 ||title="Annunciation"| '''M 25'''
!rowspan=2| W12
|-
!rowspan=2| 13th
|title="Annunciation"| '''M 25''' ||colspan=2| M 26 ||colspan=2| M 27 || M 28
|colspan=8|
|-
|colspan=6|
| M 28 ||colspan=2| M 29 ||colspan=2| M 30 ||colspan=2| M 31 ||title="April"| A 01
!rowspan=2| W13
|-
!rowspan=8| April
!rowspan=2| 14th
| A 01 ||colspan=2| A 02 ||colspan=2| A 03 || A 04
|colspan=8|
|-
|colspan=6|
| title="Sym454" {{proprietary|A 04}} ||colspan=2 title="Sym454; historical date if in year 0033" {{proprietary|'''A 05'''}} ||colspan=2 title="Sym454" {{proprietary|A 06}} ||colspan=2 title="Pepuzite, Sym454" {{proprietary|A 07}} ||title="Pepuzite, Sym454, 2nd April Sunday" {{yes2|A 08}}
!rowspan=2| W14
|-
!rowspan=2| 15th
|title="in all major proposals" {{yes|A 08}} ||colspan=2 title="in all major proposals; historical date if in year 0030" {{yes|'''A 09'''}} ||colspan=2 title="in all major proposals" {{yes|A 10}} ||title="in all major proposals" {{yes|A 11}}
|colspan=8 {{yes|}}
|-
|colspan=6 {{yes|}}
|title="2nd April Sunday, Sunday after 2nd April Saturday, Pepuzite" {{yes|A 11}} ||colspan=2 title="2nd April Sunday, Sunday after 2nd April Saturday, Pepuzite" {{yes|A 12}} ||colspan=2 title="2nd April Sunday, Sunday after 2nd April Saturday, Pepuzite" {{yes|A 13}} ||colspan=2 title="2nd April Sunday, Sunday after 2nd April Saturday" {{yes|A 14}} || title="2nd April Sunday, Sunday after 2nd April Saturday" {{yes|A 15}}
!rowspan=2| W15
|-
!rowspan=2| 16th
|title="Sunday after 2nd April Saturday" {{yes2|A 15}} ||colspan=2| A 16 ||colspan=2| A 17 || A 18
|colspan=8|
|-
|colspan=6|
| A 18 ||colspan=2| A 19 ||colspan=2| A 20 ||colspan=2| A 21 || A 22
!rowspan=2| W16
|-
!rowspan=2| 17th
| A 22 ||colspan=2| A 23 ||colspan=2| A 24 || A 25
|colspan=8|
|-
|colspan=6| —
| A 25
|colspan=7| —
! W17
|}

In 1977, some Eastern Orthodox representatives objected to separating the date of Easter from lunar phases.<ref name="byzcath.org">[http://www.byzcath.org/index.php/news-mainmenu-49/2689-ukrainian-catholic-university-organizes-seminar-on-easter-date Ukrainian Catholic University Organizes Seminar on Easter Date]</ref>

== Unified date ==

Proposals to resolve the second problem have made greater progress, but they are yet to be adopted.
{{Table of dates of Easter|class=floatright|format=dmy}}

=== 1923 proposal ===

An astronomical rule for Easter was proposed by the 1923 {{Interlanguage link multi|Pan-Orthodox Congress of Constantinople|fr|3=Congrès « panorthodoxe » de Constantinople de 1923}} that also proposed the [[Revised Julian calendar]]: Easter was to be the Sunday after the midnight-to-midnight day at the meridian of the [[Church of the Holy Sepulchre]] in [[Jerusalem]] (35°13'47.2"E or UT+2h20m55s for the small dome) during which the first [[full moon]] after the vernal equinox occurs.<ref name="Milankovitch1923">{{cite journal|last1=Milankovitch|first1=M.|title=Das Ende des julianischen Kalenders und der neue Kalender der orientalischen Kirchen|journal=Astronomische Nachrichten |volume=220 |issue=23|year=1923 |pages=379–384|issn=0004-6337 |doi=10.1002/asna.19232202303 |language=de|ref=harve|bibcode=1924AN....220..379M}}</ref><ref name="Shields1924">{{Cite journal | title = The new calendar of the eastern churches | last = Shields | first = Miriam Nancy | journal= Popular Astronomy|volume=32|page=407 | date = 1924 | url = |bibcode=1924PA.....32..407S | language = | quote = This is a translation of Milankovitch, 1923 }}</ref>

Although the instant of the full moon must occur after the instant of the vernal equinox, it may occur on the same day. If the full moon occurs on a Sunday, Easter is the following Sunday. This proposed astronomical rule was rejected by all Orthodox churches and was never considered by any Western church.

=== 1997 proposal ===

{{main|Aleppo Easter dating method}}
The [[World Council of Churches]] (WCC) proposed a [[Aleppo Easter dating method|reform of the method of determining the date of Easter]] at a summit in [[Aleppo]], [[Syria]], in 1997:<ref>{{cite web|url=http://www.oikoumene.org/en/resources/documents/commissions/faith-and-order/i-unity-the-church-and-its-mission/towards-a-common-date-for-easter/index|title=Towards a Common Date of Easter - World Council of Churches/Middle East Council of Churches Consultation Aleppo, Syria, March 5–10, 1997|publisher=[[World Council of Churches]]|date=10 March 1997}}</ref> Easter would be defined as the first Sunday following the first [[Astronomy|astronomical]] [[full moon]] following the astronomical [[vernal equinox]], as determined from the [[meridian (geography)|meridian]] of [[Jerusalem in Christianity|Jerusalem]].<ref>{{cite web|title=World Council of Churches Press Release: THE DATE OF EASTER: SCIENCE OFFERS SOLUTION TO ANCIENT RELIGIOUS PROBLEM|url=http://www.smart.net/~mmontes/pr.wcc.19970324.html|date=24 March 1997|archive-url=https://web.archive.org/web/20120626033549/http://www.smart.net/~mmontes/pr.wcc.19970324.html |archive-date=2012-06-26}}</ref> The reform would have been implemented starting in 2001, since in that year the Eastern and Western dates of Easter would coincide.

This reform has not been implemented. It would have relied mainly on the co-operation of the [[Eastern Orthodox Church]], since the date of Easter would change for them immediately; whereas for the Western churches, the new system would not differ from that currently in use until 2019. However, Eastern Orthodox support was not forthcoming, and the reform failed.<ref>{{cite web|author=Luke Luhl|title=The Proposal for a Common Date to Celebrate Pascha and Easter|url=http://www.orthodoxinfo.com/ecumenism/common_luhl.aspx|publisher=Orthodox Christian Information Center|year=1997}}</ref> The much greater impact that this reform would have had on the Eastern churches in comparison with those of the West led some Orthodox to suspect that the WCC's decision was an attempt by the West to impose its viewpoint unilaterally on the rest of the world under the guise of [[ecumenism]]. However, it could also be argued that it is fair to ask a significant change of Eastern Christians, as they would be simply making the same substantial changes the various Western Churches have already made in 1582 (when the Catholic Church first adopted the Gregorian calendar) and subsequent years so as to bring the calendar and Easter more in line with the seasons.

=== 2008–2009 proposals ===

In 2008 and 2009, there was a new attempt to reach a consensus on a unified date on the part of Catholic, Orthodox and Protestant leaders.<ref name="Sandri">{{Cite web | title = New attempt to achieve a common date for Easter | last = Sandri | first = Luigi | work = Ekklesia | date = 6 December 2008 | accessdate = 2016-01-24 | url = http://www.ekklesia.co.uk/node/8130 | quote = }}</ref><ref name="Ekklesia">{{Cite web | title = Hope for a common date for Easter affirmed again | author = | work = Ekklesia | date = 29 May 2009 | accessdate = 2016-01-24 | url = http://www.ekklesia.co.uk/node/9553 | quote = }}</ref> This effort largely relies on earlier work carried out during the 1997 Aleppo conference.<ref name="byzcath.org"/><ref name="Christianpost">{{cite web |url=http://www.christianpost.com/news/ecumenical-christians-look-forward-to-shared-easter-dates-38932/ |title=Ecumenical Christians Look Forward to Shared Easter Dates |newspaper=Christianpost.com |date=1 June 2009 |author= Aaron J. Leichman |accessdate= 2016-01-24}}</ref> It was organized by academics working at the Institute of Ecumenical Studies of [[Lviv University]].<ref name="CathNews ">{{Cite web|title=Hopes rise for East-West common Easter |author= |work=CathNews |date=29 May 2009 |accessdate=2016-01-24 |url=http://cathnews.com/article.aspx?aeid=14084 |archive-date=February 9, 2013 |language= |quote= |deadurl=yes |archiveurl=https://web.archive.org/web/20130209094946/http://cathnews.com/article.aspx?aeid=14084 }}</ref>

Part of this attempt was reportedly influenced by ecumenical efforts in Syria and Lebanon, where the [[Melkite Greek Catholic Church|Greek-Melkite Church]] has played an important role in improving ties with the Orthodox.<ref>[http://www.soufanieh.com/PETITION/19820107.lettre.unite.eveques.htm 1982 petition for a unified Easter date]</ref><ref name="Spero">{{Cite web | title = Christians eye common date for Easter | author = | work = Spero News | date = 8 December 2008 | accessdate = 2016-01-24 | url = http://www.speroforum.com/a/16989/Christians-eye-common-date-for-Easter#.VqTRtlnwhek | quote = }}</ref> There is also a series of apparition phenomena known as [[Our Lady of Soufanieh]] that has urged for a common date of Easter.<ref>[http://www.soufanieh.com/PETITION/petition.htm Petition for a Common date of Easter]</ref>

=== 2014–2016 proposals ===

In May 2014, on the anniversary of the meeting between himself and Pope Francis, [[Coptic Orthodox|Coptic]] [[Pope Tawadros II]] wrote a letter to Pope Francis asking for him to consider making renewed effort at a unified date for Easter.<ref name="2015-06-19_CNA">[http://www.catholicnewsagency.com/news/will-pope-francis-change-the-date-of-easter-87684/ Will Pope Francis change the date of Easter?], [[Catholic News Agency]], 19 June 2015, accessed 21 June 2015</ref>

In response, on 12 June 2015, Catholic [[Pope Francis]] remarked to the [[Catholic Charismatic Renewal|International Catholic Charismatic Renewal Services]] 3rd World Retreat of Priests at the [[Basilica of Saint John Lateran]] in [[Rome]] that "we have to come to an agreement" for a common date on Easter, the date calculated under the Orthodox churches' [[Gregorian Calendar]]. {{Interlanguage link multi|Lucetta Scaraffia|it}}, an historian, writing in the Vatican daily newspaper [[L'Osservatore Romano]], said the Pope is offering this initiative to change the date of Easter "as a gift of unity with the other Christian churches" adding that a common date for Easter would encourage "reconciliation between the Christian churches and …a sort of making sense out of the calendar". A week later [[Aphrem II]], the [[Syriac Orthodox Church|Syriac Orthodox]] [[Patriarch of Antioch#Current patriarchs|Patriarch of Antioch]], met with Pope Francis and noted that the celebration of Easter "on two different dates is a source of great discomfort and weakens the common witness of the church in the world."<ref>{{Citation | last = Ieraci | first = Laura | date = June 19, 2015 | title = Pope, Orthodox patriarch express commitment for unity | periodical = National Catholic Reporter | url = http://ncronline.org/blogs/francis-chronicles/pope-orthodox-patriarch-express-commitment-unity | accessdate = 16 January 2016}}</ref>

In January 2016, the [[Archbishop of Canterbury]] [[Justin Welby]] announced that he on behalf of the [[Anglican Communion]] had joined discussions with Catholic, Coptic and Orthodox representatives over a fixed date for Easter, and that he hoped it would happen within the next five to ten years.<ref>{{Cite web|title = Archbishop Justin Welby hopes for fixed Easter date|url = https://www.bbc.co.uk/news/uk-35326237|website = BBC News|access-date = 2016-01-16}}</ref> Welby has suggested that Easter be fixed on either the second or third Sunday of April relative to the Gregorian calendar.<ref name="Telegraph ">{{Cite web | title = Easter date to be fixed 'within next five to 10 years' | last = Bingham | first = John | last2 = Jamieson | first2 = Sophie | work = The Telegraph | date = 16 January 2016 | accessdate = 2016-01-24 | url = https://www.telegraph.co.uk/news/religion/12102278/Easter-date-to-be-fixed-within-next-five-to-10-years.html | quote = He said that Easter should most likely be fixed for the second or third Sunday of April }}</ref> This proposal remains to be approved, especially by Eastern churches which currently determine Easter using the Julian calendar.

According to [[ISO week date|international standards]], Easter Sunday ends the week containing Good Friday and the week of the second Sunday in April has the ordinal number 14 or 15 ([[dominical letter]]s D/DC, E/ED, F/FE and GF, i.e. 46.25% of years), hence the third Sunday is one respective week later. There currently is no public proposal under discussion that used a fixed [[week]] of the year for Easter and dependent feasts. The second Sunday in April is usually the 15th Sunday of the year (except for dominical letter G, 10.75%), which is almost always also the Sunday after the second Saturday in April (except for dominical letter AG, 3.75%).

== See also ==

*[[Computus]]
*[[Easter controversy]]

== References ==

{{Reflist|30em}}

== External links ==

*{{cite web |url=http://www.oikoumene.org/en/resources/documents/commissions/faith-and-order/i-unity-the-church-and-its-mission/frequently-asked-questions-about-the-date-of-easter |date=2007-01-31 |title=Frequently asked questions about the date of Easter |publisher=World Council of Churches (WCC) Faith and Order Commission}}
*{{webarchive |url=https://web.archive.org/web/20000304132803/http://www.smart.net/~mmontes/ortheast.html |date=March 4, 2000 |title=Notes on calculating Orthodox Pascha ("Easter") }}
*[http://www.orthodoxinfo.com/ecumenism/calendar_bond.aspx An Orthodox article arguing for preservation of the current method of calculating the date of Pascha]
*[http://sor.cua.edu/Ecumenism/19970324easterdateproposal.html The Date of Easter: Science offers solution to ancient religious problem]

{{Easter}}
{{Time in religion and mythology}}

{{DEFAULTSORT:Easter, Reform Of The Date Of}}
[[Category:Calendars]]
[[Category:Easter date]]

Olympic-Wallowa-Lineament

2018-06-25T18:20:16Z

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[[File:OWL-location.png|right|frame|Location of the Olympic-Wallowa Lineament]]
[[File:OWL-shadedrelief.png|right|frame|Is the OWL an optical illusion?]]
The '''Olympic-Wallowa lineament''' (OWL) – first reported by cartographer [[Erwin Raisz]] in 1945<ref>{{Harvnb|Raisz|1945}}. Now available on-line; see citation.</ref> on a relief map of the continental United States – is a physiographic feature of unknown origin in the state of Washington (northwestern U.S.) running approximately from the town of [[Port Angeles, Washington|Port Angeles]], on the Olympic Peninsula to the [[Wallowa Mountains]] of eastern Oregon.


==Location==
Raisz located the OWL particularly from [[Cape Flattery (Washington)|Cape Flattery]] (the northwest corner of the Olympic Peninsula) and along the north shore of Lake Crescent, thence the Little River (south of [[Port Angeles, Washington|Port Angeles]]), Liberty Bay (Poulsbo), Elliott Bay (setting the orientation of the streets in downtown Seattle), the north shore of Mercer Island, the Cedar River (Chester Morse Reservoir), Stampede Pass (Cascade crest), the south side of the Kittitas Valley (I-90), [[Manastash Ridge]], the [[Wallula Gap]] (on the Columbia River where it approaches the Oregon state line), and then the South Fork of the Walla Walla River into the northeastern corner of Oregon. After crossing the [[Blue Mountains (Oregon)|Blue Mountains]] Riasz associated the OWL with a dramatic scarp on the north side of the [[Wallowa Mountains]]. Riasz observed that the OWL tends to have basins on the north side (Seattle Basin, Kittitas Valley, Pasco Basin, Walla Walla Basin) and mountains on the southern side (the Olympics, Manastash and Umtanum ridges, Rattlesnake Mountain, the Horseheaven Hills, the Wallowa Mountains), and noted parallel alignments at various points, generally about four miles north or south of the main line. The alignment of these particular features is somewhat irregular; modern maps with much more detail show a broad zone of more regular alignments. Subsequent geological investigations have suggested various refinements and adjustments.

==Introduction to a puzzle==
[[File:Kanizsa triangle.svg|thumb|What triangle?]]
Most geological features are initially identified or characterized from a local expression of that feature. The OWL was first identified as a perceptual effect, a pattern perceived by the human visual system in a broad field of many seemingly random elements. But is it real? Or just an [[optical illusion]], such as the [[Kanizsa triangle]] (see image), where we "see" a triangle that does not really exist?

Raisz considered whether the OWL might be just a chance alignment of random elements, and geologists since have not been able to find any common unitary feature, nor identify any connection between the various local elements. {{Harvtxt|Davis|1977}} called it a "fictional structural element". Yet it has been found to be coincide with many faults and fault zones, and to delineate significant differences of geology.<ref>
Such as the older "crystalline" plutonic rock of the North Cascades from the younger basaltic rocks of the South Cascades.{{Harv|McKee|1972|p=83}} There are also more subtle differences, such as in the [[Columbia Plateau]] where the OWL marks a difference in structural expression, with strike-slip faulting and
rotation predominate to the southwest but subordinate to the northeast {{Harv|Hooper|Camp|1981}}. See also {{Harvnb|Hooper|Conrey|1989}}, pp. 297–300.</ref> These are much too correlated to be dismissed as random alignments. But for all of its prominence, there is as yet no understanding of what the OWL is or how it came to be.

The OWL piques the interest of geologically minded persons in part because its characteristic NW-SE angle of orientation – approximately 50 to 60 degrees west of north (a little short of northwest)<ref>Estimating the northing and westing from a map and applying the usual trigonometric methods gives an angle of 59 degrees west of north (N59W, azimuth 301°) from Wallula Gap to Cape Flattery. There is a bit of a bend east of Port Angeles – the shore line between Pillar Point to Slip Point has a more westerly angle of 65 degrees – but that section is so short that the angle from Wallula Gap to Port Angeles is still 57 degrees. A line run from the strong relief at Gold Creek to the mouth of Liberty Bay and beyond – a line that runs along several seeming OWL features – has an angle of 52 deg. In Seattle the angle of the Ship Canal (which is a reasonably close proxy for the natural feature it lies in) has an angle of 55 degrees...

It is possible that whatever causes the OWL is straight, but at depth, and its expression towards the surface is deflected by other structures. E.g., the Olympic Mountain batholith might be pushing Gold Creek out of alignment. And perhaps the Blue Mountains cause a similar bend. But this is entirely speculative.</ref> – is shared by many other seeming local features across a broad swath of geography. Around Seattle these include strikingly parallel alignments at the south end of Lake Washington, the north side of Elliott Bay, the valley of the Ship Canal, the bluff along Interlaken Blvd. (aligned with the Ship Canal, but offset slightly to the north), the alignment of Ravenna Creek (draining Green Lake southeast into Union Bay) and Carkeek Creek (northwest into Puget Sound), various stream drainages around Lake Forest Park (north end of Lake Washington), and (on the Eastside) the Northrup Valley (Hwy. 520 from Yarrow Bay to the Overlake area), and various smaller details too numerous to mention. All of these are carved into "recent" (less than 18,000 years old) glacial deposits, and it is difficult to conceive of how these could be controlled by anything other than a recent glacial process.

Yet the same orientation shows up in the Brothers, Eugene-Denio, and McLoughlin fault zones in Oregon (see [[#regional-map|map]], below), which are geological features tens of millions of years old, and the [[Walker Lane]] lineament in Nevada.

Likewise to the east, where both the OWL and the Brothers Fault Zone become less distinct in Idaho where they hit the old North American continental craton and the track of [[Yellowstone hotspot]]. But some 50 miles to the north is the parallel Trans-Idaho Discontinuity, and further north, the Osburn fault (Lewis and Clark line) running roughly from Missoula to Spokane. And [[aeromagnetic survey|aeromagnetic]]<ref>{{Harvnb|Zietz|others|1971}}; {{Harvnb|Sims|Lund|Anderson|2005}}.</ref> and [[Bouguer anomaly|gravitational anomaly]] <ref>{{Harvnb|Simpson|others|1986}}, see figure 9.</ref> surveys suggest extension into the interior of the continent.

==Structural relationships with other features==
{{anchor|regional-map}}

A problem in evaluating any hypothesis regarding the OWL is a dearth of evidence.
Raisz suggested that the OWL might be a "transcurrent fault" (long strike-slip faults at what are now known to be plate boundaries), but lacked both data and competence to assess it. One of the first speculations that the OWL might be a major geological structure {{Harv|Wise|1963}} – written when the theory of [[plate tectonics]] was still new and not entirely accepted<ref>As late as 1976 {{Harvtxt|Thomas|1976}} referred to the "presently
popular plate tectonics theory".</ref> – was called by the author "an outrageous hypothesis". Modern investigation is still largely balked by the immense span of geography involved and lack of continuous structures, the lack of clearly cross-cutting features, and a confusing expression in both rock millions of years old and glacial sediments only 16,000 years old.

[[Image:Geofeatures-PacificNW.png|right|frame|'''Major geological structures in Washington and Oregon:''' 
SCF – Straight Creek fault;
SB – Snoqualmie batholith (dotted area to the left);
OWL – Olympic-Wallowa lineament;
L&C – Lewis and Clark line (gravity anomaly);
HF – Hite fault;
KBML – Klamath-Blue Mountains lineament (slightly misplaced);
NC – Newberry caldera;
BFZ – Brothers Fault zone;
EDFZ –Eugene-Denio fault zone;
MFZ – McLoughlin fault zone; 
WSRP – western Snake River Plain;
NR –  Nevada Rift zone;
OIG – Oregon-Idaho graben;
CE – Clearwater Embayment;
(From {{Harvnb|Martin|others|2005}}, Fig. 1, courtesy of [http://www.pnl.gov/notices.asp PNNL])]]
Geological investigation of a feature begins with determining its structure, composition, age, and relationship with other features. The OWL does not cooperate. It is expressed as an orientation in many elements of diverse structure and compositions, and even as a boundary between areas of differing structure and composition; there is yet no understanding of what kind of feature or process – the "ur-OWL" – could control this. Nor are there particular "OWL" rocks which can be examined and radiometrically dated. We are left with determining its age by looking at its relationship with other features, such as which features overlap or cross-cut other (presumably older) features. In the following sections we will look at several features which might be expected to have some kind of structural relationship with the OWL, and consider what they might tell us about the OWL.

===Cascade Range===
The most notable geological feature crossing the OWL is the [[Cascade Range]], raised up in the [[Pliocene]] (two to five million years ago) as a result of the [[Cascadia subduction zone]]. These mountains are distinctly different on either side of the OWL, the material of the South Cascades being [[Cenozoic]] (<66 [[annum|Ma]]) volcanic and sedimentary rock, and the North Cascades being much older [[Paleozoic]] (hundreds of millions of years) metamorphic and plutonic rocks.<ref>{{Harvnb|McKee|1972}}, p.83. See also {{Harvnb|Mitchell|Montgomery|2006}}.</ref> It is unknown whether this difference is in any way linked with the OWL, or is simply a coincidental regional difference.

Raisz judged the Cascades on the north side of the OWL to be offset about six miles to the west, and similarly for the Blue Mountains, but this is questionable, and similar offsets are not apparent in the older – up to 17 Ma ([[annum|millions of years]]) old – [[Columbia River Basalt Group|Columbia River basalt flows]]. In general, there are no clear indications of structures offset by the OWL, but neither are there any distinct features crossing the OWL (and older than 17 Ma) that positively demonstrate a lack of offsetting.

===Straight Creek Fault===
[[File:SCF-terminus.png|frame|Geological topography where the SCF meets the OWL, showing general curvature to the southeast around Lakes Keechelus, Kachess, and Cle Elum. Red line is Interstate 90, Snoqualmie Pass is at upper left corner, [[Easton, Washington|Easton]] is near center. The White River—Naches Fault Zone, at the bottom of the red area, appears to be the southern edge of the OWL. Excerpted from {{Harvnb|Haugerud|Tabor|2009}}.]]

The [[Straight Creek Fault]] (SCF) – just east of Snoqualmie Pass and running nearly due north into Canada – is a major fault notable for considerable identified dextral strike-slip offset (opposite side moving laterally to the right) of at least {{convert|90|km|mi|abbr=on}}.<ref>{{Harvnb|Vance|Miller|1994}}; {{Harvnb|Umhoefer|Miller|1996}}. Estimates of offset vary; this is the minimum.</ref> Its intersection with the OWL (near [[Kachess Lake]]) is the geological equivalent of an atom smasher, and the results should be informative. For example, that the OWL is not offset suggests that it must be younger than the last strike-slip motion on the SCF,<ref>Alternately, could the OWL be a reflection of some kind of structure – perhaps in the [[lithosphere]] – that is not affected by the SCF?</ref> anywhere from around 44 to about 41 million years ago<ref>{{Harvnb|Tabor|others|1984}}; {{Harvnb|Vance|Miller|1994}}; {{Harvnb|Tabor|1994}}, pp 224, 230.</ref> (i.e., during the middle-[[Eocene]] epoch). And if the OWL is a strike-slip fault or megashear, as many have speculated,<ref>{{Harvnb|Raisz|1945}}; {{Harvnb|Wise|1963}}; {{Harvnb|Hooper|Conrey|1989}}.</ref> then it should offset the SCF, and whether the OWL offsets the SCF, or not, becomes an important test of just what the OWL is.

So does the OWL offset the SCF, or not? It is hard to say, as no trace whatsoever has been found of the SCF anywhere south of the OWL. While some geologists have speculated that it does continue directly south, albeit hidden under younger deposits,<ref>{{Harvnb|Davis|1977}}; {{Harvnb|Wyld|others|2006}}, p. 282.</ref> not a trace has been found.

If the SCF fault does not continue directly southward<ref>{{Harvnb|Tabor|others|1984}}, p.30; {{Harvnb|Campbell|1989}}, p.216.</ref> – and the utter lack of evidence that it does makes a case for evidence of lack – then where else might it be? {{Harvtxt|Heller|others|1987}} suggest some possibilities: it may curve to the east, it may curve to the west, or it may just end.

Tabor mapped the SCF turning and merging with the Taneum fault (coincident with the OWL) south of Kachess Lake.<ref>{{Harvnb|Tabor|others|1984}}, p. 27; {{Harvnb|Tabor|others|2000}}, p. 1.</ref> This conforms with the general pattern seen in Lakes Keechelus, Kachess, and Cle Elum, and associated geological units and faults (see image, right): each is aligned north—south at the north end, but turns to the southeast where it approaches the OWL.<ref>Downloadable maps available; see {{Harvnb|Haugerud|Tabor|2009}}, {{Harvnb|Tabor|others|1984}}, and {{Harvnb|Tabor|others|2000}}.</ref> This is suggestive of the OWL being a ''left'' lateral (sinistral) strike-slip fault that has distorted and offset the SCF. But that is inconsistent with the SCF itself and most other strike-slip faults associated with the OWL being ''right'' lateral (dextral), and incompatible with the geology to the southeast. Particularly, studies of the region to the southeast (in connection with Department of Energy activities at the [[Hanford Reservation]]) show no indication of any fault or other structure comparable to the SCF.<ref>E.g., {{Harvnb|Caggiano|Duncan|1983}}, generally, and {{Harvnb|Reidel|Campbell|1989}}.</ref>

[[File:Straight Creek Fault.gif|Figure 1 from USGS Map I-2538 {{Harv|Tabor|others|2000}}.|left]]
On the other hand, {{Harvtxt|Cheney|1999}} maps the SCF as proceeding southerly (without addressing the situation south of the OWL). (He has subsequently speculated<ref>{{Harvnb|Cheney|2003}}, {{Harvnb|Cheney|Hayman|2007}}.</ref> that the missing part of the SCF may have been dextrally offset to become a southerly trending fault in the Puget Lowland. But same problem: later deposits cover any traces.) The seeming southeasterly curvature is possibly explained as a geometrical effect of foreshortening: it occurs in a belt of intense folding (much resembling a rug which has slid against a wall) which, if unfolded, could restore some of the "curves" to a linear position along the southerly extension of the SCF.<ref>See the maps of {{Harvnb|Cheney|1999}} (DGER OFR 99-4) and {{Harvnb|Tabor|others|2000}} (USGS Map I-2538); see also {{Harvnb|Haugerud|Tabor|2009}} (USGS Map I-2940).</ref>

There seem to be no indications that the SCF ''turns'' to the west. Although such indications would mostly be buried, the general sense of the topography suggests no such turn. Displacement, to either the west or the east, seems unlikely in that certain effects that would be expected are not found.<ref>E.g., displacement of the Olympic Mountains is not observed, so the block moving away from the Olympics should leave a gap, and likely [[graben]]s. There is a basin – the Seattle Basin – just immediately north of the [[Seattle Fault]], but it appears no one has attributed it to movement on the OWL.
</ref>

Could the SCF just end? This is difficult to comprehend. If there is displacement along this fault, where did it come from? To quote Wyld et al.<ref>{{Harvnb|Wyld|others|2006}}, p. 282.</ref> (albeit in the context of a different fault): "it cannot just end". Although the SCF has had substantial strike-slip displacement, {{Harvtxt|Vance|Miller|1994}} claim that final major movement on the SCF (about 40 Ma ago) was dominantly dip-slip (vertical displacement). So perhaps the displacement came from the depths, and, as it was extruded, was eroded and redistributed as sediments. But this has not been established.

Another possibility is that the missing southern segment of the SCF is on a [[crustal block]] that rotated away from the OWL. There is evidence that around 45 million years ago much of Oregon and southwestern
Washington rotated some 60° or more about a pivot somewhere in the Olympic Peninsula (see [[#Oregon rotation|Oregon rotation]], below). This would have left a large gap south of the OWL, which could explain why Cenozoic rocks are not found immediately south of the OWL. This suggests that a continuation of the SCF, if any, and the missing Cenozoic, might be somewhere southwest of [[Mount Saint Helens]], but this has not been observed.

===Darrington–Devils Mountain Fault Zone===
The interaction of the Straight Creek Fault with the OWL has yielded practically no intelligible information, and remains as enigmatic as the OWL itself. More informative is the closely related Darrington—Devils Mountain Fault Zone (DDMFZ). It runs east from a complex of faults on the southern end of [[Vancouver Island]] to the town of Darrington, where it turns south to converge with the SCF (see map, above).<ref>{{Harvnb|Dragovich|Stanton|2007}}.</ref>

North of the DDMFZ (and west of the SCF) is the [[Chuckanut Formation]] (part of the "Northwest Cascade System" of rocks shown in green on the map), an [[Eocene]] sedimentary formation which formed adjacent to the Swauk, Roslyn and other formations (also in green) south of [[Mount Stuart]]; their wide separation is attributed to right-lateral strike-slip movement along the SCF.<ref>{{Harvnb|Johnson|1984}}, p. 102.</ref> That the northern part of the DDMFZ shows ''left''-lateral strike-slip movement<ref>{{Harvnb|Dragovich|others|2003}}.</ref> is not the inconsistency it may initially seem – think of the motion on either side of an arrowhead.

It appears that what is now the DDMFZ was originally aligned on the OWL. Then about 50 Ma ago North America crashed into what is now the Olympic Peninsula along an axis nearly perpendicular to the OWL, pushing the rock of the Mesozoic (pre-Cenozoic) Western and Eastern Melange Belts (WEMB, blue on the map) across the OWL, bowing the DDMFZ, and initiating the SCF and thereby splitting the Chuckanut Formation. On the north side of the DDMFZ, and wrapping around a bit to the east side, is a suite of distinctive rocks – the Helena—Haystack mélange ("HH Melange" on the map) – which was collapsed into vertical folds. Similarly distinctive rock is found in [[Manastash Ridge]] (shown on the map, but almost too small to see) still lying on the OWL, just ''east'' of the SCF.<ref>{{Harvnb|Tabor|1994}}.</ref>

This can explain an early puzzle<ref>See {{Harvnb|Davis|1977}}, p. C-33 and Figure C-10.</ref> as to why the Mesozoic rocks just south of the DDMFZ – the Western and Eastern Melange Belts – have no counterpart on the east side of the OWL and offset to the south: they were not faulted by the SCF, but were pushed against it from the southwest.

Then it gets curiouser. Rock very similar to the WEMB (including a type called [[blueschist]]) is also found in the San Juan Islands, and along the West Coast fault on the west side of Vancouver Island. This suggests that the OWL was once a strike-slip fault, possibly a continental margin, along which terranes moved from the southeast. But similar rock also occurs in the Rimrock Lake Inlier, about 75 km south of the OWL and just west of the projected trace of the SCF, and also in the Klamath Mountains of southwestern Oregon.<ref>{{Harvnb|Tabor|1994}}; {{Harvnb|Brandon|1985}}; {{Harvnb|Miller|1989}}.</ref> To account for the wide dispersal of this rock is difficult; many geologists see no alternative to transport along an extended SCF. But that upsets some of the "solutions" described above, and there is yet no consensus on this.

===CLEW and Columbia Plateau===
Further east is the "CLEW", the segment of the OWL from approximately the town of Cle Elum (marking the western limit of the Columbia River basalts) to the [[Wallula Gap]] (a narrow gap on the Columbia River just north of the Oregon border). This segment, and the associated [[Yakima Fold Belt|Yakima fold belts]], do include many northeast-trending faults crossing the
OWL. However, these are largely [[Dip-slip faults#Dip-slip faults|dip-slip]] (vertical) faults, associated with compressional folding of the overlying basalt. As there is typically 3 km of sedimentary deposits separating the basalts
(also about 3 km thick) from the [[basement rock]],<ref>{{Harvnb|Rohay|Davis|1983}}.
</ref> these faults are somewhat isolated from the deeper structure. The geological consensus is that any strike-slip activity on the OWL predates the 17 Ma old [[Columbia River Basalt Group]].<ref>{{Harvnb|Caggiano|Duncan|1983}}.</ref>

There is some evidence that some of the northwest-trending ridges may have some continuity with the basement structure, but the nature and details of the deeper structure is not known.<ref>{{Harvnb|Caggiano|Duncan|1983}}.</ref>
A 260 km long [[seismic refraction]] profile<ref>
{{Harvnb|Catchings|Mooney|1988}}.
</ref>
showed a rise in the crustal basement beneath the OWL, but was unable to determine if that rise was aligned with the OWL, or just coincidentally crossed the OWL at the same location as the profile; gravity data suggested the latter. The seismic data showed a uniformity of rock type and thickness across the OWL that discounts the possibility of it being a boundary between continental and oceanic crust. The results were interpreted as suggesting [[continental rifting]] during the Eocene, perhaps a failed [[rift basin]],<ref>
But questioned by others. See {{Harvnb|Reidel|others|1993}}, p. 9, and also {{Harvnb|Saltus|1993}}.</ref> possibly connected with the rotation of the Klamath Mountain block away from the [[Idaho Batholith]] (see [[#Oregon rotation|Oregon rotation]], below).

There is a curious change of character of the OWL in the center of the CLEW where it crosses the roughly north-trending Hog Ranch—Naneum Anticline. West of there the OWL seems to follow a ridge in the basement structure, to the east it follows a gravity gradient, much like the Klamath–Blue Mountain LIneament (see [[#Columbia Embayment and KBML|below]]) does.<ref>{{Harvnb|Saltus|1993}}, p. 1258.</ref>
The significance of all this is not known.

===Hite Fault System===
Past the Wallula Gap the OWL is identified with the Wallula Fault Zone, which heads towards the [[Blue Mountains (Oregon)|Blue Mountains]]. The Wallula Fault Zone is active, but whether that can be attributed to the OWL is unknown: it may be that, like the Yakima Fold Belt, it is a result of regional stresses, and is expressed only in the superficial basalt, quite independently of what ever is happening in the basement rock.

At the western edge of the Blue Mountains the Wallula Fault zone intersects the northeast-striking Hite Fault System (HFS). This system is complex and has been variously interpreted.<ref>
{{Harvnb|Kuehn|1995}}, p. 9.</ref>
Although seismically active it appears to be offset by, and thus should be older than, the Wallula fault.<ref>
{{Harvnb|Caggiano|Duncan|1983}}; {{Harvnb|Kuehn|1995}}, p. 97. But see also {{Harvnb|Kuehn|1995}}, p. 90.
</ref>
On the other hand, a later study found "no obvious displacement" of either the OWL or HFS–related faults.<ref>{{Harvtxt|Hooper|Conrey|1989}}, p. 297.</ref> Reidel et al.<ref>{{Harvnb|Reidel|others|1993}}, see figure 3 (p. 5), and p. 9.</ref> suggested that the HFS reflects the ''eastern'' margin of a piece of old continental craton (centered around the "HF" – Hite Fault – on the [[#Cascade Range|map]]) that has slipped south; Kuehn<ref>{{Harvnb|Kuehn|1995}}, p. 95.</ref> attributed 80 to 100 kilometers of left-lateral displacement along the HFS (and significant vertical displacements).

The interaction of the Wallula and Hite Fault systems is not yet understood. Past the Hite Fault System the OWL enters a region of geological complexity and confusion, where even the trace of the OWL is less clear, even to the point where it has been suggested that both the topographic feature and the Wallula fault are terminated by the Hite fault.<ref>{{Harvnb|Caggiano|Duncan|1983}}, p. 2-17.</ref>
The original topographic lineament as described by Raisz is along the scarp on the northeast side of the Wallowa Mountains. However, there is a sense that the trend of the faulting in that area turns more to the south; it has been suggested the faulting associated with the OWL takes a large step south to the Vale Fault Zone,<ref>
{{Harvnb|Kuehn|1995}}.</ref> which connects with the Snake River Fault Zone in Idaho.<ref>
{{Harvnb|Sims|Lund|Anderson|2005}}.
</ref>
Both of these lines introduce a bend into the OWL. The Imnaha Fault (striking towards [[Riggins, Idaho]]) is more nearly in line with the rest of the OWL, and in line with the previously mentioned gravitational anomalies that run into the continent.<ref>{{Harvnb|Simpson|others|1986}}.</ref>
Which ever way is deemed correct, it is notable that the OWL seems to change character after it crosses the Hite Fault System. What this says about the nature of the OWL is unclear, although Kuehn concluded that, in northeastern Oregon or western Idaho, it is not a tectonically significant structure.

===Wallowa terrane===
{{anchor|Kuehn-map}}
As described above, the trace of the OWL becomes faint and somewhat confused between the Blue Mountains and the margin of the North American [[craton]] (the thick orange line on the [[#regional-map|map]], just beyond the Oregon—Idaho border; the dashed line on the diagram below). This is the Wallowa terrane, a piece of crust that drifted in from somewhere else and got jammed between the Columbia Embayment to the west and the North American continent to the east and north. A notable feature is the anomalously elevated [[Wallowa Mountains]], to the east is [[Hells Canyon]] (Snake River) on the Oregon—Idaho border. Northeast of the OWL (Wallowa Mountains) is the Clearwater Embayment ("CE" on the [[#regional-map|map]]), delineated by ancient rock of the craton. Southwest of this section of the OWL is a region of [[graben]]s (where large blocks of crust have dropped) extending about {{convert|60|mi|km}} south to the nearly parallel Vale Fault Zone (see diagram, below).

[[File:Kuehn95-fig46a.png|right|frame|Wallula-Vale Transfer Zone and environs.
WFZ – Wallula Fault Zone;
IF – Imnaha Fault;
WF – Wallowa Fault;
LG – La Grande Graben;
BG – Baker Graben
PG – Pine Valley Graben.

Map courtesy of [https://www.ualberta.ca/~skuehn/msthesis/Kuehn_1995_MS.pdf S. C. Kuehn.] ]]
[[Graben]]s form where the crust is being stretched or extended. Several explanations have been offered as to why this is happening here. {{Harvtxt|Kuehn|1995}} theorized that right-lateral slip on the Wallula Fault is being transferred to more southerly faults such as the Vale Fault, wherefore he labelled this region the Wallula–Vale Transfer Zone. {{Harvtxt|Essman|2003}} suggested that crustal deformation in this region is a continuation of the [[Basin and Range Province|Basin and Range]] region immediately to the south, with any connection to the OWL deemed circumstantial. Another explanation is that clock-wise rotation of part of Oregon (discussed below) about a point near the Wallula Gap has pulled the Blue Mountains away from the OWL;<ref>
{{Harvnb|McCaffrey|others|2000}}; {{Harvnb|Pezzopane|Weldon|1993}}; {{Harvnb|Dickinson|2004}}.
</ref> this might also explain why the OWL seems to be bending here.

These theories may all have some truth to them, but what they might imply regarding the genesis and structure of the OWL has not been worked out.

[[Hells Canyon]] – North America's deepest river gorge – is so deep because the terrain it cuts through is so high. This is generally attributed to thinning of the crust, which allows the hotter, and therefore lighter and more buoyant, [[mantle (geology)|mantle]] material to rise higher. This is believed by many to be involved with the [[Yellowstone hotspot]] and [[Columbia River Basalt Group|Columbia River Basalts]]; the nature of such involvement, if any, is hotly debated.<ref>
See {{Harvtxt|Christiansen|others|2002}},
[http://www.mantleplumes.org/Coffin.html "The plume coffin?"], [http://www.semp.us/publications/biot_reader.php?BiotID=218 "The Great Mantle Plume Debate"], and [ftp://rock.geosociety.org/pub/GSAToday/gt0012.pdf "Beneath Yellowstone"] ({{Harvnb|Humphreys|others|2000}}). See {{Harvtxt|Xue|Allen|2006|p=316}} for additional references.
</ref>
While the Yellowstone hotspot and Columbia River Basalts do not seem to directly interact with the OWL, clarification of their origin and context might explain some of the OWL's context, and even constrain possible models. Likewise, clarification of the nature and history of the Wallowa terrane, and particularly of the nature and causes of the apparent bending and multiple alignments of the OWL in this region, would be a major step in understanding the OWL.

===Columbia Embayment and KBML===
The bedrock of Washington and Oregon, like most of the continent, is nearly all pre-Cenozoic rock, older than 66 million years. The exception is southwestern Washington and Oregon, which has virtually no pre-Cenozoic strata. This is the Columbia Embayment, a large indentation into the North American continent characterized by oceanic crust covered by thick sedimentary deposits.<ref>{{Harvnb|McKee|1972}}, p. 154; {{Harvnb|Riddihough|others|1986}}.</ref> ("Embayment" is perhaps a misleading term, in that it suggests a bowing of a coast line, which only seems so in the context of the modern coast. In the geological past, the coast of North America was in Idaho and Nevada, as will be described later.)

The Columbia Embayment is of interest here because its northern margin is approximately delineated by the OWL. The variations are mainly in the region of the [[#CLEW and Columbia Plateau|CLEW]], where sediments are buried under the basalts of the [[Columbia River Drainage Basin|Columbia Basin]], and in Puget Sound, where the Cenozoic geology extends as far north as Vancouver Island.<ref>The contact between oceanic and continental crust seems to be the [[#Southern Whidbey Island Fault and RMFZ|Southern Whidbey Island Fault]], discussed below. Whether this contact extends south of the OWL is not yet known.</ref> Whether the OWL might reflect a deeper crustal boundary has been
questioned by geophysical studies which may – or may not – see the characteristics expected of such a boundary.<ref>
E.g., {{Harvtxt|Cantwell|others|1965}} sees some kind of boundary, {{Harvtxt|Catchings|Mooney|1988}} do not.</ref>

The southern edge of the Columbia Embayment is along a line from the Klamath Mountains on the Oregon coast to a point in the Blue Mountains just east of the Wallula Gap. Unlike the OWL, this line has little topographical expression,<ref>The lack of topographical relief may be due to in-filling by the Grande Ronde and Picture Gorge basalt flows (related to the Columbia River Basalts).
{{Harvnb|Hooper|Conrey|1989}}, p. 297.</ref> and aside from the Hite Fault System is not associated with any major fault systems. But mapping of gravitational anomalies shows a definite lineament, some 700 km (about 400 miles) long, called the [[Klamath-Blue Mountain Lineament]] (KBML).<ref>{{Harvnb|Riddihough|others|1986}}.</ref> This lineament is of interest here because of the possibility it was formerly conjugate with OWL, discussed in the next section.

===Oregon rotation===
Then the situation gets very interesting. Measurements of [[paleomagnetism]] (the record of the direction the rock was pointed when it cooled) from a variety of sites in the Coast Range – from the Klamath Mountains to the Olympic Peninsula – consistently measure clockwise rotations of 50 to 70 degrees.<ref>
{{Harvnb|Simpson|Cox|1977 }};
{{Harvnb|Hammond|1979 }};
{{Harvnb|Magill|Cox|1981 }};
{{Harvnb|Wells|others|1998 }};
{{Harvnb|McCaffrey|others|2000 }};
{{Harvnb|Wells|Simpson|2001 }}.
Geologists are often disturbed by the results from [[geophysical]] methods, which they attribute to various kinds of errors. Geophysicists claim their results have a consistency that precludes such errors.</ref> (See map, below.)

One interpretation of this is that western Oregon and southwestern Washington have swung as a rigid block about a pivot point at the northern end, near the Olympic Peninsula.<ref>
{{Harvnb|Simpson|Cox|1977 }};
{{Harvnb|Hammond|1979 }};
</ref>

[[File:Oregon rotation.png|right|frame|Rotation of Coast Range (light green) and Blue Mountains shown by red lines. (Authorities differ on amount and location of poles; see text.) Dashed red line is OWL; dashed blue line is KBML; intersection is approximate location of Wallula Gap.

Original map courtesy of William R. Dickinson.<ref>See {{Harvnb|Dickinson|2004}}, Fig. 8, p. 30, for an earliar version.</ref>
]]
The interesting thing is: backing out this rotation restores the Coast Range to an earlier position nearly juxtaposed against the OWL. {{Harvtxt|Hammond|1979}} argues that the Coast Range (believed to be seamounts that had previously accreted to the continent) were rifted away from the continent starting about 50 Ma ago (mid-[[Eocene]]). This interpretation implies a "[[back arc]]" of magmatism, probably fed by a subduction zone, and possibly implicated with the intrusion of various plutons in the North Cascades around 50 Ma. Curiously, this is just when the Kula–Farallon [[spreading ridge]] passed under the OWL (discussed [[#Kula|below]]). {{Harvtxt|Magill|Cox|1981}} found a spurt of rapid rotation around 45 Ma ago. This may be when this block was impinged by the Sierra Nevada block of California; {{Harvtxt|Simpson|Cox|1977}} note that around 40 Ma ago there was a change in the direction of the Pacific Plate (possibly due to collision with another plate). (The cause and nature of the rifting does not seem to have been worked out yet. Certain complications in the subduction of the Kula and Farallon plates may have been involved.)

During this rotation of the Coast Range the block of continental crust that is now the Blue Mountains (on the eastern side of the KBML) was also rifted away from the Idaho batholith, and also rotated about 50 degrees, but about a point near the Wallula Gap (or perhaps further east).<ref>{{Harvnb|Simpson|Cox|1977 }}; {{Harvnb|Dickinson|2004}}. In a later work {{Harvtxt|Dickinson|2009}} [?] leans towards a more eastern location of the hinge point, as indicated on the map.
</ref>
In the resulting gap the crust was stretched and thinned; the buoyancy of the hotter mantle have contributed to the subsequent rise of the Wallowa and Seven Devils Mountains, and perhaps also with the irruption of the [[Columbia River Basalt Group|Columbia River basalts]] and other basalt flows.

While the rigid-block rotation model has much appeal, many geologists prefer another interpretation that minimizes whole–block rotation, and instead of rifting invokes "dextral shear" (resulting from the relative motion of the Pacific plate past the North American plate, or possibly from the extension of the [[Basin and Range province]]) as the primary driving force. The large values of paleomagnetic rotation are explained by a "ball bearing" model:<ref>
{{Harvnb|Beck|1976}}.
</ref> the entire Oregon block (western Oregon including the Cascades and southwestern Washington) are deemed to be composed of many smaller blocks (on the scale of tens of kilometers), each of which rotates independently on its own axis.
Evidence of such small blocks (at least in southwestern Washington) has been claimed.<ref>
{{Harvnb|Wells|Coe|1985}}.
</ref>
Later work has attempted to work out how much of the paleomagnetic rotation reflects actual block rotation;<ref>
{{Harvnb|Wells|Heller|1988}}.
</ref>
although the amount of rotation has been reduced (to perhaps only 28°), it seems it will not entirely go away. How this affects the postulated rifting does not seem to have been addressed. A more recent work based on analysis of GPS measurements concluded that "most of the Pacific Northwest can be described by a few large, rotating, elastic crustal blocks",<ref>{{Harvnb|McCaffrey|others|2007}}, p.1338.</ref> but noted that in a zone about 50 km wide on the Oregon coast the apparent rotation rate seems to double; this suggests that multiple models may be applicable.

Modern measurements show that the central Oregon is still rotating, with the calculated rotation poles bracketing the Wallula Gap.,<ref>{{Harvnb|Wells|others|1998}}; {{Harvnb|McCaffrey|others|2000}}; {{Harvnb|Wells|Simpson|2001}}.</ref> which is approximately the intersection of the OWL and KBML. It is intriguing to consider whether the KBML has participated in this rotation, but this is unclear; that it is unbent where it crosses the OWL suggests it is not. The OWL seems to be the northern edge of the rotating block,<ref>{{Harvnb|McCaffrey|others|2000}}, p.3120, Conclusions.</ref> and the paucity of paleomagnetic data to the southeast of the KBML suggests it might be the southern edge. But the details of all this remain murky.

===Puget Sound===
[[File:Puget Sound offset.png|thumb|The west side of central Puget Sound, Holmes Harbor, and Saratoga Passage forms a lineament (between blue bars) that is offset at Port Madison (red bar).]]
Another notable feature that crosses the OWL is [[Puget Sound]], and it is curious to consider the possible implications of a Puget Sound Fault. (Such a fault was once proposed<ref>{{Harvnb|Johnson|others|1999}}.</ref> on the basis of certain marine seismic data, but the proposal was stiffly rejected, and now seems to have been abandoned.) Combined terrestrial and bathymetric topography shows a distinct lineament along the west side of Puget Sound from Vashon Island (just north of Tacoma) north to the west side of Holmes Harbor and Saratoga Passage on [[Whidbey Island]] (see image). But at [[Port Madison]] (at the red bar in the image) it is split by a distinct offset of several miles.

Curiously, the southern section lies in the approximate zone of the OWL. (Note OWL–associated lineaments running parallel to the red line.) This suggests dextral offset along a strike-slip fault. But if that is the case then there should be a major fault in the vicinity of Port Madison and crossing to Seattle (perhaps at the Ship Canal, aligned with the red line) – but for this there is even less evidence than there was for the Puget Sound fault.<ref>The southern segment of this lineament is where {{Harvtxt|Brandon|1989}} located the boundary of the Cascade orogen (the "Cenozoic Truncation Scar" in his Fig. 1). But this boundary is now known to be the South Whidbey Island Fault, which crosses Whidbey Island near Holmes Harbor and strikes southeast.
</ref>
The significance of this lineament and its offset is entirely unknown. That it seems to be expressed in Ice Age (16 Ka) deposits implies a very recent but entirely unknown event; but perhaps these recent deposits are only draped over a much older topography. A recent offset might explain the apparent offsetting of north–south glacial [[drumlins]] bisected by the Ship Canal, but is not evident in more eastern segments.

Alternately – and this would seem very pertinent in regard of the OWL – perhaps some mechanism other than strike-slip faulting creates these lineaments.

===Seattle Fault===
{{Main|Seattle Fault}}
A locally notable feature that crosses the zone of the OWL is the west-east [[Seattle Fault]]. This is not a strike-slip fault, but a [[thrust fault]], where a relatively shallow slab of rock from the south is being pushed against and over the northern part. (And over the OWL.) One model has the slab of rock being forced up by some structure about 8 km deep. Another model has the base of the slab (again, about 8 km deep) catching on something, which causes the leading edge to roll.<ref>{{Harvnb|Kelsey|others|2008}}. See {{Harvnb|Johnson|others|2004}} Fig. 17 for cross-sections of several models.</ref> The nature of the underlying structure is not known; geophysical data does not indicate a major fault nor any kind of crustal boundary along the front of the Seattle Fault, nor along the OWL, but this could be due to the limited reach of geophysical methods. Recent geological mapping at the eastern side of the Seattle Fault<ref>DGER Geological Map {{Harvnb|GM73|p. 24+}}.</ref> suggests a [[decollement]] (horizontal plane) about 18 km deep.

These models were developed in study of the western segment of the Seattle Fault. In the center segment, where it crosses surface exposures of Eocene rock associated with the OWL, the various strands of the fault – elsewhere fairly orderly – meander. The significance of this and the nature of the interaction with the Eocene rock are also not known.<ref>{{Harvnb|Blakely|others|2002}}.</ref>

Examination of the various strands of the Seattle Fault, particularly in the central section, is similarly suggestive of ripples in a flow that is obliquely crossing some deeper sill. This is an intriguing idea that could explain how local and seemingly independent features could be organized from depth, and even across a large scale, but it does not seem to have been considered. This is likely due, in part, to a paucity of information on the nature and structure of the lower crust where such a sill would exist.

===Southern Whidbey Island Fault and RMFZ ===
The Southern Whidbey Island Fault (SWIF), running nearly parallel to the OWL from Victoria, B.C., southeast to the Cascade foothills to a point northeast of Seattle, is notable as the contact between the Coast Range block of oceanic crust to the west and the Cascades block of pre-Cenozoic continental crust to the east.<ref>{{Harvnb|Johnson|others|1996}}.</ref>
It appears to connect with the more southerly oriented right-lateral Rattlesnake Mountain Fault Zone (RMFZ) straddling Rattlesnake Mountain (near North Bend), which shows a similar deep-seated contact between different kinds of basement rock.<ref>DGER Geological Map {{Harvnb|GM67}}.</ref> At the southern end of Rattlesnake Mountain – exactly where the first lineament of the OWL is encountered – at least one strand of the RMFZ (the others are hidden) turns to run by Cedar Falls and up the Cedar River. Other faults to the south also show a similar turn,<ref>DGER Geological Map {{Harvnb|GM50}}. Recent mapping (DGER Geological Map {{Harvnb|GM73}}) shows a multiplicity of fault strands; it is possible that these seemingly arcuate faults may be artefacts of slightly confused mapping.</ref> suggesting a general turning or bending across the OWL, yet such a bend is not apparent in the pattern of physiographic features that express the OWL. With awareness that the Seattle Fault and the RMFZ are the edges of a large sheet of material which is moving north, there is a distinct impression that these faults, and even some of the topographical features, are flowing around the corner of the Snoqualmie Valley. If it seems odd that a mountain should "float" around a valley: bear in mind that while the surface relief is about three-quarters of a kilometer (half a mile) in height, the material flowing could be as much as eighteen kilometers deep.<ref>DGER Geological Map {{Harvnb|GM73|p=13}}.</ref> (The analogy of icebergs moving around a submerged sandbar is quite apt.) It is worth noting that [http://www.scn.org/cedar_butte Cedar Butte] – a minor prominence just east of Cedar Falls – is the southwestern-most exposure in the region of some very old Cretaceaous (pre-Cenozoic) metamorphic rock.<ref>DGER Geological Map {{Harvnb|GM50}}.</ref> It seems quite plausible that there is some well-founded and obdurate obstruction at depth, around which the shallower and younger sedimentary formations are flowing. In such a context the observed arcuate fault bends would be very natural.

==Broader context==
It is generally assumed{{by whom|date=August 2014}} that the pattern of the OWL is a manifestation of some deeper physical structure or process (the "ur-OWL"), which might be elucidated by studying the effects it has on other structures. As has been shown, study of features that should interact with OWL has yielded very little: a tentative age range (between 45 and 17 million years), suggestions that the ur-OWL arises from deep in the crust, and evidence that the OWL is not (contrary to expectations) itself a boundary between oceanic and continental crust.

The lack of results so far suggests that the broader context of the OWL should be considered. Following are some elements of that broader context, which may – or may not – relate in some way to the OWL.


===Plate tectonics===
{{Main|Plate tectonics}}
The broadest and fullest context of the OWL is the global system of [[plate tectonics]], driven by convective flows in the Earth's mantle. The primary story on the western margin of North America is the accretion, subduction, obduction, and translation of plates,
micro-plates, terranes, and crustal blocks between the converging Pacific and North American plates. (For an excellent geological history of Washington, including plate tectonics, see the [http://www.washington.edu/burkemuseum/geo_history_wa Burke Museum web site].)

The principal tectonic plate in this region (Washington, Oregon, Idaho) is the [[North American plate]], consisting of a [[craton]] of ancient, relatively stable [[continental crust]] and various additional parts that have been accreted; this is essentially the whole of the North American continent. The interaction of the North American plate with various other plates, terranes, etc., along its western margin is the primary engine of geology in this region.

Since the breakup of the [[Pangaea]] supercontinent in the [[Jurassic]] (about 250 million years ago) the main tectonic story here has been the North American Plate's subduction of the [[Farallon Plate]] (see below) and its remaining fragments (such as the [[Kula Plate|Kula]], [[Juan de Fuca Plate|Juan de Fuca]], [[Gorda Plate|Gorda]], and [[Explorer Plate|Explorer]] plates). As the North American plate overrides the last of each remnant it comes into contact with the Pacific Plate, generally forming a [[transform fault]], such as the [[Queen Charlotte Fault]] running north of [[Vancouver Island]], and the [[San Andreas Fault]] on the coast of California. Between these is the [[Cascadia subduction zone]], the last portion of a subduction zone that once stretched from Central America to Alaska.

This has not been a steady process. 50 Ma (million years) ago<ref>{{Harvnb|Sharp|Clague|2006}}.</ref> there was a change in the direction of motion of the Pacific plate (as recorded in the bend in the [[Hawaiian-Emperor seamount chain]]). This had repercussions on all the adjoining plates, and may have had something to do with initiation of the Straight Creek Fault,<ref>{{Harvnb|Vance|Miller|1994}}.</ref> and the end of the [[Laramide orogeny]] (the uplift of the [[Geology of the Rocky Mountains|Rocky Mountains]]). This event may have set the stage for the OWL, as much of the crust in which it is expressed was formed around that epoch (the early [[Eocene]]); this may be when the story of the OWL starts. Other evidence suggests a similar plate reorganization around 80 Ma,<ref>{{Harvnb|Umhoefer|Miller|1996}}, p.561.</ref> possibly connected with the start of the Laramide orogeny. {{Harvtxt|Ward|1995}} claimed at least five "major chaotic tectonic events since the Triassic". Each of these events is a possible candidate for creating some condition or structure that affected the OWL or ur-OWL, but knowledge of what these events were or their effects is itself still chaotic.

Complicating the geology is a stream of [[terranes]] – crustal blocks – that have been streaming north along the continental margin<ref>{{Harvnb|Jones|others|1977}};{{Harvnb|Jones|others|1982}}; {{Harvnb|Cowan|1982}}.</ref> for over 120 Ma<ref>{{Harvnb|McClelland|Oldow|2007}} [?].</ref> (and probably much, much earlier), what has recently been called the ''North Pacific Rim orgenic Stream'' (NPRS).<ref>{{Harvnb|Redfield|others|2007}}.</ref> However, these terranes may be incidental to the OWL, as there are suggestions that local tectonic structures may be substantially affected by deeper and much older (e.g., [[Precambrian]]) basement rock, and even lithospheric mantle structures.<ref>{{Harvnb|Sims|Lund|Anderson|2005}}; {{Harvnb|Karlstrom|Humphreys|1998}}.</ref>

===Subduction of the Farallon and Kula Plates===

{{anchor|Kula}}
Roughly 205 million years ago (during the [[Jurassic]] period) the [[Pangaea]] supercontinent began to break up as a [[rift]] separated the [[North American Plate]] from what is now Europe, and pushed it west against the [[Farallon Plate]]. During the subsequent [[Cretaceous Period]] (144 to 66 Ma ago) the entire Pacific coast of North America, from Alaska to Central America, was a [[subduction zone]]. The Farallon plate is notable for having been very large, and for subducting nearly horizontally under much of the United States and Mexico; it is likely connected with the [[Laramide Orogeny]].<ref>
{{Harvnb|Riddihough|1982}};
[http://www.washington.edu/burkemuseum/geo_history_wa/ Burke Museum].
</ref> About 85 Ma ago the part of the Farallon plate from approximately California to the Gulf of Alaska separated to form the [[Kula Plate]].<ref>
{{Harvnb|Stock|Molnar|1988}};
{{Harvnb|Woods|Davies|1982}};
{{Harvnb|Haeussler|others|2003}};
{{Harvnb|Norton|2006}};
{{Harvnb|Wyld|others|2006}}.
</ref>

The period 48–50 Ma (mid-Eocene) is especially interesting as this is when the subducted Kula—Farallon [[spreading ridge]] passed below what is now the OWL.<ref>{{Harvnb|Breitsprecher|others|2003}}. A slightly variant view is that this piece of the Kula plate had broken off to form the Resurrection Plate {{Harv|Haeussler|others|2003}}, so this was actually the ''Resurrection''—Farallon spreading ridge.</ref> (The Burke Museum has some [http://www.washington.edu/burkemuseum/geo_history_wa/The%20Challis%20Episode.htm nice diagrams] of this.) This also marks the onset of the [[#Oregon rotation|Oregon rotation]], possibly with rifting along the OWL,<ref>{{Harvnb|Simpson||Cox|1977}}; {{Harvnb|Hammond|1979}}.</ref> and the initiation of the Queen Charlotte and Straight Creek Faults.<ref>{{Harvnb|Vance|Miller|1994}}.</ref> The timing seems significant, but how all of these might be connected is unknown.

Around 30 Ma ago part of the spreading center between the Farallon Plate and [[Pacific Plate]] was subducted under California, putting the Pacific plate into direct contact with the North American plate and creating the [[San Andreas Fault]]. The remainder of the Farallon Plate split, with the part to the north becoming the [[Juan de Fuca Plate]]; parts of this subsequently broke off to form the [[Gorda Plate]] and [[Explorer Plate]]. By this time the last of the [[Kula Plate]] had been subducted, initiating the [[Queen Charlotte Fault|Queen Charlotte]] transform fault on the coast of British Columbia; coastal subduction has been reduced to just the [[Cascadia Subduction Zone]] under Oregon and Washington.<ref>{{Harvnb|Riddihough|1982}}; {{Harvnb|Wyld|others|2006}};
[http://www.washington.edu/burkemuseum/geo_history_wa/ Burke Museum].</ref>

===Newberry Hotspot Track – Brothers Fault Zone===
[[File:Newberry-Yellowstone tracks.png|thumbnail|350px|Age progressive rhyolitic lavas (light blue) from the McDermitt Caldera (MC) to the Yellowstone Caldera (YC) track the movement of the North American plate over the Yellowstone Hotspot. Similar age progressive lavas across the High Lava Plains (HLP) towards the Newberry Caldera (NC) have been termed the Newberry Hotspot Track, but this goes the wrong direction to be attributed to movement of the plate over a hotspot. Numbers are ages in millions of years. VF = Vale Fault, SMF = Steens Mountain Fault, NNR = North Nevada Rift.]]
The Newberry Hotspot Track – a series of volcanic domes and lava flows closely coincident with the [[Brothers Fault Zone]] (BFZ) – is of interest because it is parallel to the OWL. Unlike anything on the OWL, these lava flows can be dated, and they show a westward age progression from an origin at the McDermitt Caldera on the Oregon-Nevada border to the [[Newberry Volcano]]. Curiously, the [[Yellowstone hotspot]] also appears to have originated in the vicinity of the McDermitt Caldera, and is generally considered to be closely associated with the Newberry magmatism.<ref>{{Harvnb|Xue|Allen|2006}}; {{Harvnb|Christiansen|others|2002}}; {{Harvnb|Shervais|Hanan|2008}}.</ref>
But while the track of the Yellowstone hotspot across the Snake River Plain conforms to what is expected from the motion of the [[North American Plate]] across some sort of "hotspot" fixed in the underlying mantle, the Newberry "hotspot" track is oblique to the motion of the North American Plate; this is inconsistent with the [[hotspot (geology)|hotspot model]].

Alternative models include:<ref>{{Harvnb|Xue|Allen|2006}}</ref> 1) flow of material from the top layer of the mantle (asthenosphere) around the edge of the Juan de Fuca Plate (a.k.a. "Vancouver slab"), 2) flows reflecting lithospheric topography (such as the edge of the craton), 3) faulting in the [[lithosphere]], or 4) extension of the [[Basin and Range province]] (which in turn may be due to interactions between the North American, Pacific, and Farallon Plates, and possibly with the subduction of the [[triple point]] where the three plates came together), but none is yet fully accepted.<ref>E.g., {{Harvtxt|Xue|Allen|2006}} concluded that the Newberry track is the product of a lithosphere-controlled process (such as lithospheric faulting or Basin and Range extension); {{Harvtxt|Zandt|Humphreys|2008}} disagree, arguing for mantle flow around the sinking Gorda—Juan de Fuca slab.</ref>
These models generally attempt to account only for the source of the Newberry magmatism, attributing the "track" to pre-existing weakness in the crust. No model yet accounts for the particular orientation of the BFZ, or the parallel Eugene-Denio or Mendocino Fault Zones (see [[#regional-map|map]]).

===Bermuda Hotspot Track?===
It was noted as early as 1963<ref>{{Harvnb|Wise|1963}}, see figure 2.</ref> that the OWL seems to align with the [[Kodiak-Bowie Seamount chain]]. A 1983 paper by Morgan<ref>{{Harvnb|Morgan|1983}}, recapitulated by {{Harvtxt|Vink|Morgan|Vogt|1985}} in a popular article in ''Scientific American''.</ref> suggested that this seamount—OWL alignment marks the passage some 150 Ma ago of the [[Bermuda hotspot]]. (This same passage has also been invoked to explain the [[Mississippi Embayment]].<ref>{{Harvnb|Cox|Van Arsdale|2002}}.</ref>) However, substantial doubt has been raised as to whether Bermuda is truly a "hotspot",<ref>{{Harvnb|Vogt|Jung|2007a}}.</ref> and lacking any supporting evidence this putative hotspot track is entirely speculative.

The 1983 paper also suggested that passage of a hot spot weakens the continental crust, leaving it vulnerable to rifting. But might the relation actually run the other way: do some of these "hotspots" accumulate in zones where the crust is already weakened (by means as yet unknown)? The supposed Newberry hotspot track may exemplify this (see Megashears, below), but application of this concept more generally is not yet accepted. Application to the OWL would require resolving some other questions, such as how traces of a ca. 150 Ma event resisted being swept north into Alaska to influence a structure believed to be no older than 41 Ma (see [[#Straight Creek Fault|Straight Creek Fault]]). Possibly there is some explanation, but geology has not yet found it.

===Orofino Shear Zone===
The OWL gets faint, perhaps even terminates, just east of the Oregon—Idaho border where it hits the north-trending ''Western Idaho Shear Zone'' (WISZ),<ref>Also known as the western Idaho ''suture'' zone, or the Salmon River suture zone, depending on what portion of its long history is being addressed. {{Harvnb|Fleck|Criss|2004}}, pp. 2—3; {{Harvnb|Giorgis|others|2008}}, pp. 1119—1120.</ref> a nearly vertical tectonic boundary between the accreted oceanic terranes to the west and the plutonic and metamorphic rock of the North American [[craton]] (the ancient continental core) to the east. From the [[Mesozoic]] till about 90 Ma (mid-[[Cretaceous]]) this was the western margin of the North American continent, into which various off-shore terranes were crashing into and then sliding to the north.

Near the town of Orofino (just east of Lewiston, Idaho) something curious happens: the craton margin makes a sharp right-angle bend to the west. What actually happens is the truncation of the WISZ by the WNW-trending ''Orofino Shear Zone'' (OSZ), which can be traced west roughly parallel with the OWL until it disappears below the Columbia River Basalts, and southeast across Idaho and possibly beyond. The truncation occurred between 90 and 70 Ma ago, possibly due to the docking of the [[Insular Belt|Insular super-terrane]] (now the coast of British Columbia).<ref>{{Harvnb|McClelland|Oldow|2007}}; {{Harvnb|Giorgis|others|2008}}, pp. 1119, 1129, 1131.</ref> This was a major left-lateral transform fault, with the northern continuation of the WISZ believed to be one of the faults in the North Cascades. A similar offset is seen between the Canadian Rocky Mountains in British Columbia and the American Rocky Mountains in southern Idaho and western Wyoming.<ref>{{Harvnb|Wise|1963}}, p. 357, and figure 1. See also figure 1 of {{Harvnb|O'Neil|others|2007}} and figure 1 of {{Harvnb|Hildebrand|2009}}.</ref>

Then another curious thing happens: before the west-trending craton margin turns north, it seems to loop south towards Walla Walla (near the Oregon border) and the Wallula Gap (see [[#regional-map|orange-line here]], or [[#Kuehn-map|dashed-line here]]). (Although southeastern Washington is pretty thoroughly covered by the Columbia River Basalts, a borehole in this loop recovered rock characteristic of the craton.<ref>{{Harvnb|Reidel|others|1993}}, p.9, and see figure 3 (p. 5).</ref>) It seems that the OSZ may have been offset, perhaps by the [[#Hite Fault System|Hite Fault]], but, contrary to the regional trend, headed south. If this is a cross-cutting offset it would have to be younger than the OFZ (less than 70 Ma), and older than the OWL, which it does not offset. That the OWL and the OFZ are parallel (along with many other structures) suggests something in common, perhaps a connection at a deeper level. But this offsetting relationship indicates that they were created separately.

===Megashears===
The OFZ (also called the Trans-Idaho Discontinuity) is a local segment of a larger structure that has only recently been recognized, the ''Great Divide Megashear''.<ref>{{Harvnb|O'Neil|others|2007}}.</ref> East of the WISZ this turns to the southeast (much as the OWL may be doing past the Wallula Gap) to follow the Clearwater fault zone down the continental divide near the Idaho—Montana border to the northwestern corner of Wyoming. From there it seems to connect with the Snake River—Wichita fault zone, which passes through Colorado, and Oklahoma.,<ref>{{Harvnb|Sims|others|2001}}; {{Harvnb|Sims|Lund|Anderson|2005}}. A few sources have described this general trend the Olympic—''Wichita'' Lineament (e.g., see {{Harvnb|Vanden Berg|2005}}, or the
[http://www.colorado.edu/GeolSci/Resources/WUSTectonics/AncestralRockies/transtension.html Transtension in the West] article). This is inaccurate. The Great Divide Megashear, even if it existed past the Cascades, would be well north of the Olympic Peninsula, while the OWL, if it is presumed to connect with the Snake Fault zone (via the Vale zone) misses the Great Divide Megashear, and likely Wichita as well. This lineament is said to dextrally offset the ''Colorado Lineament'', said to run from the Grand Canyon to Lake Superior.{{Harv|Vanden Berg|2005}}.</ref> and possibly further.<ref>A "Montana—Florida Lineament" and even a "Mackenzie—Missouri Lineament" (from the Mackenzie River valley in the Yukon to Florida) have been claimed by Carey (see [https://web.archive.org/web/20091026204116/http://www.geocities.com/CapeCanaveral/Launchpad/8098/2.htm excerpts from his book]), but are not generally recognized. For an interesting trip outside of mainstream science read about the [[Expanding Earth]] theory.
</ref>
There is a significant age discrepancy here. Whereas the OFZ is a mere 90 to 70 Ma old, this megashear is ancient, having been dated to the [[Mesoproterozoic]] – about a billion years ago. The Snake River—Wichita fault zone is of a similar age. What appears to be happening is exploitation of ancient weaknesses in the crust. This could explain the Newberry "hotspot track": parallel weaknesses in the crust open as the Brothers, Eugene—Denio, and Mendocino Fault Zones in response to development of the [[Basin and Range Province]]; magma from the event that initiated the Yellowstone hotspot (and possibly the Columbia River and other basalt flows) simply exploits the faults of the Brothers Fault Zone. The other faults do not develop as "hotspot tracks" simply because there is no magma source nearby. Similarly, it may be that the OWL reflects a similar zone of weakness, but does not develop as a major fault zone because it is too far from the stresses of the Basin and Range Province.

This could also explain why the OWL seems possibly aligned with the [[Kodiak-Bowie Seamount chain]] in the Gulf of Alaska, especially as the apparent motion is the wrong direction for the OWL to be a mark of their past passage. They are also on the other side of the spreading centers, though that does suggest a pure speculation that these postulated zones of weakness could be related to transform faults from the spreading center.

===Precambrian basement===
Following the Great Divide Megashear into the mid-continent reveals something interesting: a widespread pattern of similarly trending (roughly NW-SE) fault zones, rifts, and aeromagnetic and gravitational anomalies.<ref>Especially dramatic is the 2005 "Precambrian Crystalline Basement Map of Idaho" {{Harv|Sims|Lund|Anderson|2005}}. See also {{Harvnb|Marshak|Paulsen|1996}}, {{Harvnb|Sims|others|2001}}, {{Harvnb|Vanden Berg|2005}}, and numerous others.
</ref> Although some of the faults are recent, the NW trending zones themselves have been attributed to continental-scale transcurrent shearing at about 1.5 [[annum|Ga]] – that's ''billions'' of years ago – during the assembly of [[Laurentia]] (the North American continent).<ref>{{Harvnb|Sims|Lund|Anderson|2005}}; {{Harvnb|Sims|Saltus|Anderson|2005}}.</ref>

Curiously, there is another widespread pattern of parallel fault zones, etc., of various ages trending roughly NE-SW, including the [[Midcontinent Rift System]], the [[Reelfoot Rift]] (in the [[New Madrid Seismic Zone]]), and others.<ref>The [[#Columbia Embayment and KBML|KBML]] and other less well known trends in Oregon and Washington have a similar orientation, but
the context is so different that they are generally excluded from studies of midcontinental geology.</ref> These fault zones and rifts occur on tectonic boundaries that date to the [[Proterozoic]] – that is, 1.8 to 1.6 billions of years old.<ref>{{Harvnb|Karlstrom|Humphreys|1998}}, p. 161.</ref> They are also roughly parallel to the [[Ouachita orogeny|Ouachita]]— [[Alleghenian orogeny|Appalachian mountains]], raised when [[Laurentia]] merged with the other continents to form the [[Pangaea]] supercontinent some 350 million years ago. It is now believed that these two predominant patterns reflect ancient weaknesses in the underlying [[Precambrian]] [[basement (geology)|basement]] rock,<ref>{{Harvnb|Sims|Saltus|Anderson|2005}}.</ref> which can be reactivated to control the orientation of features formed much later.<ref>{{Harvnb|Holdsworth|others|1997}}.</ref>

Such linkage of older and younger features seems very relevant to the OWL's troubling age relationships. The possible involvement of the deep Precambrian basement does suggest that what we see as the OWL might be just the expression in shallower and transitory terranes and surface processes of a deeper and persistent ur-OWL, just as ripples in a stream may reflect a submerged rock, and suggests that surficial expression of the OWL may need to be distinguished from a deepr ur-OWL. But neither the applicability of this to the OWL nor any details have been worked out.

==Summary: What we know about the OWL==
* First reported by Erwin Raisz in 1945.
* Seems to have more depressions and basins on the north side.
* Associated with many right-lateral strike-slip fault zones.
* Seems to be expressed in Quaternary (recent) glacial deposits.
* Does not offset Columbia River Basalts, so older than 17 million years.
* Not offset by the Straight Creek Fault, so probably younger than 41 million years. (Maybe.)
* Approximately separates oceanic-continental provinces.
* Not an oceanic-continental crustal boundary. (Maybe.)
* Not a hotspot track. (Maybe.)
* Seems to be aligned with lithospheric flow from the Juan de Fuca Ridge.
* Seems to be faint and confused in Oregon.

==See also==
*[[Geology of the Pacific Northwest]]

==Notes==
{{reflist|24em}}

==References==
{{bots|deny=Citation bot}}

OSTI: DOE's [http://www.osti.gov/bridge Office of Scientific and Technical Information].
See also [http://www.osti.gov/energycitations/ Energy Citations Database].

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==External links==
*[http://www.washington.edu/burkemuseum/geo_history_wa Burke Museum web site] Geologic history of Washington.
*[https://web.archive.org/web/20091219063341/http://www.northwestgeology.com/ Evolution of the Pacific Northwest] Good text on the geology of Cascadia.

{{North American faults}}

[[Category:Geology of Oregon]]
[[Category:Geology of Washington (state)]]

Coywolf

2018-06-23T06:28:33Z

Bibcode Bot: Adding 0 arxiv eprint(s), 3 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Use mdy dates|date=February 2015}}
{{Hybridbox
| name = Coywolf
| image = Coywolf hybrids.jpg
| image_caption = Captive-bred [[F1 hybrid|F1]] gray wolf-coyote hybrids, Wildlife Science Center in [[Forest Lake, Minnesota]]
| genus = Canis
| species1 = latrans
| link1 = Coyote
| species2 = lupus
| link2 = Gray wolf
| synonyms =
}}

'''Coywolf''' (sometimes called '''woyote''') is an informal term for a [[canid hybrid]] descended from [[coyote]]s and [[Gray wolf|gray wolves]]. Hybridization between the two species is facilitated by the fact that they diverged relatively recently (around 55,000–117,000 years ago). Genomic studies indicate that nearly all North American gray wolf populations possess some degree of admixture with coyotes following a geographic [[Cline_(biology)|cline]], with the lowest levels occurring in [[Alaska]], and the highest in [[Ontario]] and [[Quebec]], as well as [[Atlantic Canada]].<ref name="vonHoldt2016">{{cite journal|last1=vonHoldt|first1=B. M.|last2= Cahill|first2=J. A.|last3=Fan|first3= Z.|last4=Gronau|first4= I.|last5= Robinson|first5= J.|last6=Pollinger|first6=J. P.|last7=Shapiro|first7= B.|last8=Wall|first8=J.|last9=Wayne|first9=R. K.|title=Whole-genome sequence analysis shows that two endemic species of North American wolf are admixtures of the coyote and gray wolf|journal=Science Advances|volume= 2|issue=7|year= 2016|pages= e1501714–e1501714|doi=10.1126/sciadv.1501714|bibcode=2016SciA....2E1714V}}</ref>

==Description==
Hybrids of any combination tend to be larger than coyotes but smaller than wolves, they show behaviors intermediate between coyotes and the other parent's species.<ref name=mech2014>{{Cite journal | doi = 10.1371/journal.pone.0088861| pmid = 24586418|pmc=3934856| title = Production of Hybrids between Western Gray Wolves and Western Coyotes| journal = PLoS ONE| volume = 9| issue = 2| pages = e88861| year = 2014| last1 = Mech | first1 = L. D. | last2 = Christensen | first2 = B. W. | last3 = Asa | first3 = C. S. | last4 = Callahan | first4 = M. | last5 = Young | first5 = J. K. |bibcode = 2014PLoSO...988861M }}</ref><ref name="way2007">{{cite journal | author = Way J. G. | year = 2007 | title = A comparison of body mass of ''Canis latrans'' (Coyotes) between eastern and western North America | url = http://easterncoyoteresearch.com/downloads/BodyMassWay.PDF | journal = Northeastern Naturalist | volume = 14 | issue = 1| pages = 111–24 | doi=10.1656/1092-6194(2007)14[111:acobmo]2.0.co;2}}</ref> In one captive hybrid experiment, six F1 hybrid pups from a male northwestern gray wolf and a female coyote were measured shortly after birth with an average on their weights, total lengths, head lengths, body lengths, hind foot lengths, shoulder circumferences, and head circumferences compared with those on pure coyote pups at birth. Despite being delivered by a female coyote, the hybrid pups at birth were much larger and heavier than regular coyote pups born and measured around the same time.<ref name=mech2014/> At six months of age, these hybrids were closely monitored at the Wildlife Science Center. Executive Director Peggy Callahan at the facility states that the howls of these hybrids are said to start off much like regular gray wolves with a deep strong vocalization, but changes partway into a coyote-like high pitched yipping.<ref>Riese, Clive (March 19, 2014), [http://forestlaketimes.com/2014/03/19/wildlife-science-center-partners-in-study-impacting-wolf-controversy/ Wildlife Science Center partners in study impacting wolf controversy], ''Forest Lake Times''</ref>

Compared with pure coyotes, [[eastern coyote|eastern wolf-coyote]] hybrids form more cooperative social groups and are generally less aggressive with each other while playing.<ref name="bekoff1978">Bekoff, M. (1978). "Behavioral Development in Coyotes and Eastern Coyotes", pp. 97–124 in M. Bekoff, (ed.) ''Coyotes: Biology, Behavior, and Management''. Academic Press, New York. {{ISBN|1930665423}}.</ref> Hybrids also reach [[sexual maturity]] when they are two years old, which is much later than occurs in pure coyotes.<ref name="way2010">{{cite journal | author = Way J.G.|author2= Rutledge L.|author3= Wheeldon T.|author4= White B.N. | year = 2010 | title = Genetic characterization of Eastern "Coyotes" in eastern Massachusetts | url = http://www.easterncoyoteresearch.com/downloads/GeneticsOfEasternCoywolfFinalInPrint.pdf | format = PDF | journal = Northeastern Naturalist | volume = 17 | issue = 2| pages = 189–204 | doi=10.1656/045.017.0202}}</ref>

==Varieties==

===Eastern coyotes===
[[File:Coyote-face-snow - Virginia - ForestWander.jpg|thumb|left|[[Eastern coyote]], a coyote-wolf hybrid in [[West Virginia]] near the [[Virginia]] state line.]]
Eastern coyotes range from [[New England]], [[New York (state)|New York]], [[New Jersey]], [[Pennsylvania]],<ref>{{cite news|url=https://www.economist.com/news/science-and-technology/21677188-it-rare-new-animal-species-emerge-front-scientists-eyes?fsrc=scn/fb/te/pe/ed/greaterthanthesumofitsparts|title=Greater than the sum of its parts|publisher=[[The Economist]]|date=October 31, 2015|accessdate=October 30, 2015}}</ref> [[Ohio]],<ref>http://ocj.com/2014/12/update-on-coy-wolf-sightings-in-ohio/</ref> [[West Virginia]],<ref>http://www.wvdnr.gov/hunting/coyoteresearch.shtm</ref> [[Maryland]],<ref>http://dnr2.maryland.gov/wildlife/Pages/hunt_trap/coyote.aspx</ref> [[Delaware]], and [[Virginia]].<ref>http://news.nationalgeographic.com/news/2011/11/111107-hybrids-coyotes-wolf-virginia-dna-animals-science/</ref> Their range also occurs in the Canadian provinces of [[Ontario]], [[Quebec]], [[New Brunswick]],<ref name=gnb>{{cite web|title=Living with Wildlife – Eastern coyotes|url=http://www2.gnb.ca/content/dam/gnb/Departments/nr-rn/pdf/en/Wildlife/Coyotes.pdf|work=Natural Resources website|publisher=[[Government of New Brunswick]]|accessdate=February 2, 2014}}</ref> [[Nova Scotia]],<ref name=nsdnr>{{cite web|title=Frequently Asked Questions about Eastern Coyote in Nova Scotia|url=https://novascotia.ca/natr/wildlife/nuisance/coyotes-faq.asp|work=Department of Natural Resources website|publisher=[[Government of Nova Scotia]]|accessdate=February 2, 2014}}</ref> and [[Newfoundland and Labrador]].<ref name=NL>{{cite web|title=Living with Coyotes in Newfoundland and Labrador|url=http://www.env.gov.nl.ca/env/wildlife/all_species/coyotes.html|work=The Department of Environment and Conservation website|publisher=Government of Newfoundland and Labrador|accessdate=February 2, 2014}}</ref> Coyotes and wolves hybridized in the Great Lakes region, followed by an eastern coyote expansion, creating the largest mammalian hybrid zone known.<ref>{{cite journal|doi=10.1111/mec.13667|pmid=27106273|title=Admixture mapping identifies introgressed genomic regions in North American canids|journal=Molecular Ecology|volume=25|issue=11|pages=2443–53 |year=2016|last1=Vonholdt|first1=Bridgett M.|last2=Kays|first2=Roland|last3=Pollinger|first3=John P.|last4=Wayne|first4=Robert K.}}</ref> Extensive hunting of gray wolves over a period of 400 years caused a population decline that reduced the number of suitable mates, thus facilitating coyote genes swamping into the eastern wolf population. This has caused concern over the purity of remaining wolves in the area, and the resulting eastern coyotes are too small to substitute for pure wolves as [[apex predator]]s of moose and deer. The main nucleus of pure eastern wolves is currently concentrated within [[Algonquin Provincial Park]]. This susceptibility to hybridization led to the eastern wolf being listed as Special Concern under the Canadian Committee on the Status of Endangered Wildlife and with the Committee on the Status of Species at Risk in Ontario. By 2001, protection was extended to eastern wolves occurring on the outskirts of the park, thus no longer depriving Park eastern wolves of future pure-blooded mates. By 2012, the genetic composition of the park's eastern wolves was roughly restored to what it was in the mid-1960s, rather than in the 1980s–1990s, when the majority of wolves had large amounts of coyote DNA.<ref name=rutledge>{{Cite journal | doi = 10.1002/ece3.61| pmid = 22408723| title = Intense harvesting of eastern wolves facilitated hybridization with coyotes| journal = Ecology and Evolution| volume = 2| issue = 1| pages = 19–33| year = 2012| last1 = Rutledge | first1 = L. Y. | last2 = White | first2 = B. N. | last3 = Row | first3 = J. R. | last4 = Patterson | first4 = B. R. | pmc = 3297175}}</ref>

Aside from the combinations of coyotes and eastern wolves making up most of the modern day eastern coyote's gene pools, some of the coyotes in the northeastern USA also have mild domestic dog (''C. lupus familiaris'') and western Great Plains gray wolf (''C. l. nubilus'') influences in their gene pool, thus suggesting that the eastern coyote is actually a four-in-one hybrid of coyotes, eastern wolves, western gray wolves, and dogs, and that the hybrids living in areas with higher white-tailed deer density often have higher degrees of wolf genes than those living in urban environments. The addition of domestic dog genes may have played a minor role in facilitating the eastern hybrids' adaptability to survive in human-developed areas.<ref>{{Cite journal|pmc=3899836|title=Assessment of coyote-wolf-dog admixture using ancestry-informative diagnostic SNPs|journal=Molecular Ecology|volume=23|issue=1|pages=182–197|doi=10.1111/mec.12570|year=2013|author1=Monzón|first1=J|last2=Kays|first2=R|last3=Dykhuizen|first3=D. E.|pmid=24148003}}</ref> The four-in-one hybrid theory was further explored in 2014, when Monzón and his team subsequently reanalyzed the tissue and SNP samples taken from 425 eastern coyotes to determine the degree of wolf and dog introgressions involved in each geographic range.<ref>{{cite web|last1=Monzon|first1=Javier|title=It’s a "Coyote-Wolf-Dog Eat Dog" World|url=http://www.gothamcoyote.com/news/its-a-coyote-wolf-dog-eat-dog-world|website=Gotham Coyote Project|date=22 January 2014}}</ref> The domestic dog allele averages 10% of the eastern coyote's genepool, while 26% is contributed by a cluster of both eastern wolves and western gray wolves. The remaining 64% matched mostly with coyotes. This analysis suggested that prior to the uniformity of its modern-day genetic makeup, multiple swarms of genetic exchanges between the coyotes, feral dogs, and the two distinct wolf populations present in the Great Lakes region may have occurred, and urban environments often favor coyote genes, while the ones in the rural and deep forest areas maintain higher levels of wolf content. A 2016 meta-analysis of 25 genetics studies from 1995–2013 found that the northeastern coywolf is 60% western coyote, 30% eastern wolf, and 10% domestic dog. However, this hybrid canid is only now coming into contact with the southern wave of coyote migration into the southern United States.<ref name=Ways&Lynn>{{cite journal |title=Northeastern coyote/coywolf taxonomy and admixture: A meta-analysis |journal=Canid Biology & Conservation |volume=19 |issue=1 |pages=1–7 |url=http://canids.org/CBC/19/Northeastern_coyote_taxonomy.pdf |accessdate=2016-03-20 }}</ref>

===Red and eastern wolves===
[[File:Bartel USFWS pdza rw8.jpg|thumb|[[Red wolf]]]]
The taxonomy of the red and eastern wolf of the Southeastern United States and the [[Great Lakes]] region, respectively, has been long debated, with various schools of thought advocating that they represent either unique species or results of varying degrees of gray wolf-coyote admixture.

In May 2011, an examination of 48,000 [[single nucleotide polymorphisms]] in red wolves, eastern wolves, gray wolves, and dogs indicated that the red and eastern wolves were hybrid species, with the red wolf being 76% coyote and only 20% gray wolf, and the eastern wolf being 58% gray wolf and 42% coyote, finding no evidence of being distinct species in either.<ref name=VonHolt>{{cite journal|last=VonHolt|first=BM|display-authors=etal |title=A genome-wide perspective on the evolutionary history of enigmatic wolf-like canids|journal=Genome Res|date=12 May 2011|pmid=21566151|doi=10.1101/gr.116301.110|pmc=3149496|volume=21|issue=8|pages=1294–305}}</ref> The study was criticized for having used red wolves with recent coyote ancestry,<ref name=Beeland>{{cite book |title=The Secret World of Red Wolves |author=T. DeLene Beeland |year=2013 |publisher=University of North Carolina Press |location=Chapel Hill, NC |isbn= 9781469601991 }}</ref> and a reanalysis in 2012 indicated that it suffered from insufficient sampling.<ref name=Rutledge2>{{cite journal |title=RAD sequencing and genomic simulations resolve hybrid origins within North American ''Canis'' |authors=L. Y. Rutledge, S. Devillard, J. Q. Boone, P. A. Hohenlohe, B. N. White |journal=Biology Letters |date=July 2015 |volume=11 |issue=7 |pages=1–4 |url=http://rsbl.royalsocietypublishing.org/content/11/7/20150303 |accessdate=2015-08-16 |doi=10.1098/rsbl.2015.0303 |pmid=26156129 |pmc=4528444}}</ref> A comprehensive review in 2012 further argued that the study's dog samples were unrepresentative of the species' global diversity, having been limited to boxers and poodles, and that the red wolf samples came from modern rather than historical specimens.<ref name=Chambers>{{cite journal |title=An account of the taxonomy of North American wolves from morphological and genetic analyses |year=2012 |journal=North American Fauna |volume=77 |pages=1–67 |url=http://www.fwspubs.org/doi/pdf/10.3996/nafa.77.0001 |accessdate=2013-07-02 |doi=10.3996/nafa.77.0001|last1=Chambers |first1=Steven M. |last2=Fain |first2=Steven R. |last3=Fazio |first3=Bud |last4=Amaral |first4=Michael }}</ref> The review was itself criticized by a panel of scientists selected for an independent peer review of its findings by the [[USFWS]], which noted that the study's conclusion that the eastern wolf's two unique nonrecombining markers were insufficient to justify full-species status for the animal.<ref name=nceas>Dumbacher, J., [http://www.fws.gov/home/wolfrecovery/pdf/Final_Review_of_Proposed_rule_regarding_wolves2014.pdf Review of Proposed Rule Regarding Status of the Wolf Under the Endangered Species Act], NCEAS (January 2014)</ref>

In 2016, a [[Whole genome sequencing|whole-genome]] DNA study suggested that all of the North American canids, both wolves and coyotes, diverged from a common ancestor 6,000–117,000 years ago. The whole-genome sequence analysis shows that two endemic species of North American wolf, the red wolf and eastern wolf, are [[Genetic admixture|admixtures]] of the coyote and gray wolf.<ref>{{cite journal|doi=10.1126/sciadv.1501714|title=Whole-genome sequence analysis shows that two endemic species of North American wolf are admixtures of the coyote and gray wolf|journal=Science Advances|volume=2|issue=7|pages=e1501714|year=2016|last1=Vonholdt|first1=B. M.|last2=Cahill|first2=J. A.|last3=Fan|first3=Z.|last4=Gronau|first4=I.|last5=Robinson|first5=J.|last6=Pollinger|first6=J. P.|last7=Shapiro|first7=B.|last8=Wall|first8=J.|last9=Wayne|first9=R. K.|bibcode=2016SciA....2E1714V}}</ref><ref>{{cite journal|doi= 10.1126/science.aag0699|title= How do you save a wolf that's not really a wolf?|journal= Science|year= 2016|last1= Morell|first1= Virginia}}</ref>

====Mexican gray wolf-coyote hybrids====
In a study that analyzed the molecular genetics of coyotes, as well as samples of historical red wolves and [[Mexican wolf|Mexican gray wolves]] from Texas, a few coyote genetic markers have been found in the historical samples of some isolated Mexican gray wolf individuals. Likewise, gray wolf Y chromosomes have also been found in a few individual male Texan coyotes.<ref>{{cite journal|doi=10.1371/journal.pone.0003333|pmid=18841199|pmc=2556088|year=2008|author1=Hailer|first1=F|title=Hybridization among three native North American ''Canis'' species in a region of natural sympatry|journal=PLOS ONE|volume=3|issue=10|pages=e3333|last2=Leonard|first2=J. A.|bibcode=2008PLoSO...3.3333H}}</ref> This study suggested that although the Mexican gray wolf is generally less prone to hybridizations with coyotes, exceptional genetic exchanges with the Texan coyotes may have occurred among individual gray wolves from historical remnants before the population was completely extirpated in Texas. The resulting hybrids would later on melt back into the coyote populations as the wolves disappeared. However, the same study also discussed an alternative possibility that the red wolves, which in turn also once overlapped with both species in the central Texas, were involved in circuiting the gene flows between the coyotes and gray wolves much like how the eastern wolf is suspected to have bridged gene flows between gray wolves and coyotes in the Great Lakes region since direct hybridizations between coyotes and gray wolves is considered rare. In tests performed on a stuffed carcass of what was initially labelled a [[chupacabra]], mitochondrial DNA analysis conducted by [[Texas State University]] showed that it was a coyote, though subsequent tests revealed that it was a coyote–gray wolf hybrid sired by a male Mexican gray wolf.<ref>Ardizzoni, S. (September 1, 2013), [http://bionews-tx.com/news/2013/09/01/texas-state-university-researcher-helps-unravel-mystery-of-texas-blue-dog-claimed-to-be-chupacabra/ "Texas State University Researcher Helps Unravel Mystery of Texas ‘Blue Dog’ Claimed to be Chupacabra"], ''Bio News Texas''.</ref>

===Northwestern gray wolf-coyote hybrids===
[[File:Captivecoywolfhybrid.jpg|left|thumb|[[F1 hybrid|F1 hybrid]] coyote-gray wolf hybrid, conceived in captivity]]
In 2013, the U.S. Department of Agriculture Wildlife Services conducted a captive-breeding experiment at their National Wildlife Research Center Predator Research Facility in Logan, Utah. Using gray wolves from British Columbia and western coyotes, they produced six hybrids, making this the first hybridization case between pure coyotes and [[Northwestern wolf|northwestern gray wolves]]. The experiment, which used artificial insemination, was intended to determine whether or not the sperm of the larger gray wolves in the west was capable of fertilizing the [[egg cell]]s of western coyotes. Aside from the historical hybridizations between coyotes and the smaller Mexican gray wolves in the south, as well as with eastern wolves and red wolves, grays wolves from the northwestern USA and western provinces of Canada were not known to interbreed with coyotes in the wild, thus prompting the experiment. The six resulting hybrids included four males and two females. At six months of age, the hybrids were closely monitored and were shown to display both physical and behavioral characteristics from both species, as well as some physical similarities to the eastern wolves, whose status as a distinct wolf species or as a genetically distinct subspecies of the gray wolf is controversial. Regardless, the result of this experiment concluded that northwestern gray wolves, much like the eastern wolves, red wolves, Mexican gray wolves, and domestic dogs, are capable of hybridizing with coyotes.<ref name=mech2014/>{{clear}}

In 2015, a research team from the cell and microbiology department of Anoka-Ramsey Community College revealed that an F2 litter of two pups had been produced from two of the original hybrids. At the same time, despite the six F1's successful delivery from the same coyote, they were not all full siblings because multiple sperm from eight different northwestern gray wolves were used in their production. The successful production of the F2 litter, nonetheless, confirmed that hybrids of coyotes and northwestern gray wolves are just as fertile as hybrids of coyotes to eastern and red wolves. Both the F1 and F2 hybrids were found to be phenotypically intermediate between the western gray wolves and coyotes. Unlike the F1 hybrids, which were produced via artificial insemination, the F2 litter was produced from a natural breeding.<ref>{{cite web|url=https://ncurdb.cur.org/ncur2015/search/display_ncur.aspx?id=93115|title=NCUR|publisher=|accessdate=April 1, 2016}}</ref> The study also discovered through sequencing 16S ribosomal RNA encoding genes that the F1 hybrids all have an intestinal microbiome distinct from both parent species, but were once reported to be present in some gray wolves. Moreover, analysis of their complementary DNA and ribosomal RNA revealed that the hybrids have very differential gene expressions compared to those in gray wolf controls.

====Coydogs====
{{main article|Coydog}}
[[File:The Clever Coyote (1951) Coydogs.jpg|thumb|Coydogs in [[Wyoming]]]]
Hybrids between coyotes and domestic dogs have been bred in captivity dating back to the pre-Columbian Mexico.<ref>{{cite book|url=http://www.colegionacional.org.mx/SACSCMS/XStatic/colegionacional/docs/espanol/lmza/lmza_icaz_2002.pdf|chapter=13. Dog-wolf Hybrid Biotype Reconstruction from the Archaeological City of Teotihuacan in Prehispanic Central Mexico|author1=Valadez, Raúl |author2=Rodríguez, Bernardo |author3=Manzanilla, Linda |author4=Tejeda, Samuel |title=9th ICAZ Conference, Durham 2002: Dogs and People in Social, Working, Economic or Symbolic Interaction|editor=Snyder, Lynn M |editor2=Moore, Elizabeth A. |pages=120–130}}</ref> Other specimens were later produced by mammalian biologists mostly for research purposes. Although the latter species are not often considered wolves outside of the scientific community, domestic dogs are still subsumed into the gray wolf species<ref>{{cite web|url=http://animaldiversity.org/site/accounts/information/Canis_lupus_familiaris.html|title=ADW: Canis lupus familiaris: INFORMATION|work=Animal Diversity Web|accessdate=April 1, 2016}}</ref> hence coydogs are another biological sub-variations of hybrids between coyotes and gray wolves; the latter considered the domesticated form of ''Canis lupus''.<ref>{{Cite journal
| last1 = Anderson | first1 = T. M.
| last2 = Vonholdt | first2 = B. M.
| last3 = Candille | first3 = S. I.
| last4 = Musiani | first4 = M.
| last5 = Greco | first5 = C.
| last6 = Stahler | first6 = D. R.
| last7 = Smith | first7 = D. W.
| last8 = Padhukasahasram | first8 = B.
| last9 = Randi | first9 = E.
| doi = 10.1126/science.1165448
| last10 = Leonard | first10 = J. A.
| last11 = Bustamante | first11 = C. D.
| last12 = Ostrander | first12 = E. A.
| last13 = Tang | first13 = H.
| last14 = Wayne | first14 = R. K.
| last15 = Barsh | first15 = G. S.
| title = Molecular and Evolutionary History of Melanism in North American Gray Wolves
| journal = Science
| volume = 323
| issue = 5919
| pages = 1339–1343
| year = 2009
| pmid = 19197024
| pmc =2903542
|bibcode = 2009Sci...323.1339A }}</ref> Some roaming primitive dogs in North America, such as the [[Carolina dog]]s from the [[southeastern United States]], are also suspected to have had historical genetic exchanges with coyotes.<ref>{{cite web|url=http://news.nationalgeographic.com/news/2003/03/0311_030311_firstdog_2.html|title=Did Carolina Dogs Arrive With Ancient Americans?|work=National Geographic News|author=Handwerk, Brian |date=March 11, 2003}}</ref> Unlike other gray wolf subspecies, dogs have been known to freely hybridize with any ''Canis '' species that come into contact with them during the breeding seasons, which gives them the potential to introgress into various wild wolf and coyote populations.{{Citation needed|date=September 2016}}

{{clear}}

==See also==
{{Portal|Dogs|Mammals}}
* [[Canid hybrid]]
* [[Coydog]]
* [[Jackal-dog hybrid]]
* [[Wolfdog]]

==References==
{{Reflist|30em}}

==Further reading==
* {{cite journal | last1 = Adams | first1 = J.R. | last2 = Kelly | first2 = B.T. | last3 = Waits | first3 = L.P. | year = 2003 | title = Using faecal DNA sampling and GIS to monitor hybridization between red wolves (''Canis rufus'') and coyote (''Canis latrans'') | journal = Mol. Ecol. | volume = 12 | issue = 8 | pages = 2175–2186 | doi=10.1046/j.1365-294x.2003.01895.x| pmid = 12859637 }}
* {{cite journal | last1 = McCarley | first1 = H. | title = The taxonomic status of wild ''Canis'' (Canidae) in the south central United States | journal = Southwest. Nat. | volume = 1962 | issue = 7| pages = 227–235 }}
* {{cite journal | last1 = Wayne | first1 = R.K. | last2 = Jenks | first2 = S.M. | year =1991 | title = Mitochondrial DNA analysis implying extensive hybridization of the endangered red wolf ''Canis rufus'' | journal = Nature | volume = 351| pages = 565–568 | doi=10.1038/351565a0 | issue=6327| bibcode = 1991Natur.351..565W }}

== External links ==
* {{cite web |url= https://www.nytimes.com/2010/09/28/science/28coyotes.html |title= Mysteries That Howl and Hunt |first= Carol Kaesuk |last= Yoon |publisher= NY Times |date= Sep 28, 2010 }}
* {{cite web |url= http://news.nationalgeographic.com/news/2002/12/1217_021226_tvinterbreeding.html |title= Interbreeding Threatens Rare Species, Experts Say |website= National Geographic |date= Dec 2002 }}
* [http://www.easterncoyoteresearch.com/ Eastern Coyote/Coywolf Research]
* {{cite web |url= https://www.pbs.org/wnet/nature/coywolf-meet-the-coywolf/8605/ |title= Meet the Coywolf |publisher= PBS |series= Nature |date= 22 Jan 2014 |subscription= yes |format= Video }}

{{Mammal hybrids}}

[[Category:Canid hybrids]]

Benutzer:Tino Cannst/Minkowski'schen Fragezeichenfunktion

2018-06-20T07:59:57Z

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{{Use dmy dates|date=October 2017}}
{{more footnotes|date=April 2013}}
[[Image:Minkowski question mark.svg|300px|thumb|Minkowski question-mark function.]]
[[File:Minkowski qn mark fcn.gif|500px|thumb|Left: {{math|?(''x'')}}. Right: {{math|?(''x'') − ''x''}}.]]

In [[mathematics]], the '''Minkowski question-mark function''' (or the '''slippery [[Cantor function|devil's staircase]]'''), denoted by {{math|size=120%|?(''x'')}}, is a [[Function (mathematics)|function]] possessing various unusual [[fractal]] properties, defined by {{harvs|txt|authorlink=Hermann Minkowski|first=Hermann |last=Minkowski|year= 1904|loc=pages 171–172}}. It maps [[quadratic irrational]]s to [[rational number]]s on the [[unit interval]], via an expression relating the [[continued fraction]] expansions of the quadratics to the [[binary expansion]]s of the rationals, given by [[Arnaud Denjoy]] in 1938. In addition, it maps rational numbers to [[dyadic rational]]s, as can be seen by a recursive definition closely related to the [[Stern–Brocot tree]].

==Definition==
If <math>[a_0; a_1, a_2, \ldots]</math> is the [[continued fraction|continued fraction representation]] of an [[irrational number]] {{mvar|x}}, then

:<math>{\rm ?}(x) = a_0 + 2 \sum_{n=1}^\infty \frac{(-1)^{n+1}}{2^{a_1 + \cdots + a_n}}</math>

whereas:

If <math>[a_0; a_1, a_2, \ldots, a_m]</math> is a continued fraction representation of a [[rational number]] {{mvar|x}}, then

:<math>{\rm ?}(x) = a_0 + 2 \sum_{n=1}^m \frac{(-1)^{n+1}}{2^{a_1 + \cdots + a_n}}</math>

==Intuitive explanation==
To get some intuition for the definition above, consider the different ways
of interpreting an infinite string of bits beginning with 0 as a real number in {{closed-closed|size=100%|0,1}}.
One obvious way to interpret such a string is to place a binary point after the first 0 and read the string as a [[binary numeral system|binary]] expansion: thus, for instance, the string 001001001001001001001001...
represents the binary number 0.010010010010..., or {{math|size=100%|2/7}}. Another interpretation
views a string as the [[continued fraction]] {{math|size=100%|[0; ''a''1, ''a''2, … ]}}, where the integers {{mvar|size=100%|ai}} are the run lengths in a [[run-length encoding]] of the string. The same example string 001001001001001001001001... then
corresponds to {{math|size=100%|1=[0; 2, 1, 2, 1, 2, 1, …] = ({{sqrt|3}} − 1)/2}}. If the string ends in an infinitely long run of the same bit, we ignore it and terminate the representation; this is suggested by the formal "identity":
: {{math|size=120%|1=[0; ''a''1, … ,''a''''n'', ∞] = [0; ''a''1, … ,''a''''n''+1/∞] = [0; ''a''1, … ,''a''''n''+0] = [0; ''a''1, … ,''a''''n'']}}.

The effect of the question-mark function on {{closed-closed|size=100%|0,1}} can then be understood as mapping the second interpretation of a string to the first interpretation of the same string,<ref name=Fin4412>Finch (2003) pp. 441–442</ref><ref name=PF95/> just as the [[Cantor function]] can be understood as mapping a triadic [[base 3]] representation to a base 2 representation. Our example string gives the equality
:<math>?\left(\frac{\sqrt3-1}{2}\right)=\frac{2}{7}.</math>

==Recursive definition for rational arguments==
For rational numbers in the unit interval, the function may also be defined [[recursion|recursively]]; if {{math|''p/q''}} and {{math|''r/s''}} are [[reduced fraction]]s such that {{math|1={{!}} ''ps'' − ''rq'' {{!}} = 1}} (so that they are adjacent elements of a row of the [[Farey sequence]]) then<ref name=PF95>Pytheas Fogg (2002) p. 95</ref>

:<math>?\left(\frac{p+r}{q+s}\right) = \frac12 \left(?\bigg(\frac pq\bigg) + {}?\bigg(\frac rs\bigg)\right)</math>

Using the base cases
:<math>?\left(\frac{0}{1}\right) = 0 \quad \mbox{ and } \quad ?\left(\frac{1}{1}\right)=1</math>
it is then possible to compute {{math|?(''x'')}} for any rational {{mvar|x}}, starting with the [[Farey sequence]] of order 2, then 3, etc.

If <math>p_{n-1}/q_{n-1}</math> and <math>p_n/q_n</math> are two successive convergents of a [[continued fraction]], then the matrix

:<math>\begin{pmatrix} p_{n-1} & p_n \\ q_{n-1} & q_n \end{pmatrix}</math>

has [[determinant]] ±1. Such a matrix is an element of ''SL''(2,'''Z'''), the group of two-by-two matrices with determinant ±1. This group is related to the [[modular group]].

===Algorithm===
This recursive definition naturally lends itself to an [[algorithm]] for computing the function to any desired degree of accuracy for any real number, as the following [[C (programming language)|C]] function demonstrates. The algorithm descends the [[Stern–Brocot tree]] in search of the input {{mvar|x}}, and sums the terms of the binary expansion of ''y'' = ?(''x'') on the way. As long as the '''[[loop invariant]]''' <math>qr-ps=1</math> remains satisfied there is no need to reduce the fraction <math>\frac m n = \frac{p+r}{q+s},</math> since it is already in lowest terms. Another invariant is <math>\frac p q \le x < \frac r s.</math> The '''for''' loop in this program may be analyzed somewhat like a '''while''' loop, with the conditional break statements in the first three lines making out the condition. The only statements in the loop that can possibly affect the invariants are in the last two lines, and these can be shown to preserve the truth of both invariants as long as the first three lines have executed successfully without breaking out of the loop. A third invariant for the body of the loop (up to floating point precision) is <math>y \le \; ?(x) < y + d,</math> but since {{mvar|d}} is [[division by two|halved]] at the beginning of the loop before any conditions are tested, our conclusion is only that <math>y \le \; ?(x) < y + 2d</math> at the termination of the loop.

To [[Loop variant|prove termination]], it is sufficient to note that the sum <math>q+s</math> increases by at least 1 with every iteration of the loop, and that the loop will terminate when this sum is too large to be represented in the primitive C data type '''long'''. However, in practice, the conditional break when "y+d==y" is what ensures the termination of the loop in a reasonable amount of time.

<source lang="c">
/* Minkowski's question-mark function */
double minkowski(double x) {
long p=x; if ((double)p>x) --p; /* p=floor(x) */
long q=1, r=p+1, s=1, m, n;
double d=1, y=p;
if (x<(double)p||(p<0)^(r<=0)) return x; /* out of range ?(x) =~ x */
for (;;) /* invariants: q*r-p*s==1 && (double)p/q <= x && x < (double)r/s */
{
d/=2; if (y+d==y) break; /* reached max possible precision */
m=p+r; if ((m<0)^(p<0)) break; /* sum overflowed */
n=q+s; if (n<0) break; /* sum overflowed */

if (x<(double)m/n) r=m, s=n;
else y+=d, p=m, q=n;
}
return y+d; /* final round-off */
}
</source>

==Self-symmetry==
The question mark is clearly visually self-similar. A [[monoid]] of self-similarities may be generated by two operators {{mvar|S}} and {{mvar|R}} acting on the unit square and defined as follows:

:<math>\begin{align}
S(x, y) &= \left( \frac x {x+1}, \frac y 2 \right) \\[5pt]
R(x, y) &= (1-x, 1-y).
\end{align}</math>

Visually, {{mvar|S}} shrinks the unit square to its bottom-left quarter, while {{mvar|R}} performs a [[point reflection]] through its center.

A point on the [[function graph|graph]] of ? has coordinates {{math|(''x'', ?(''x''))}} for some {{mvar|x}} in the unit interval. Such a point is transformed by {{mvar|S}} and {{mvar|R}} into another point of the graph, because ? satisfies the following identities for all <math>x\in [0,1]</math>:

:<math>
\begin{align}
?\left(\frac x {x+1}\right) &= \frac{?(x)} 2 \\[5pt]
?(1-x) &= 1-?(x)\,.
\end{align}
</math>

These two operators may be repeatedly combined, forming a monoid. A general element of the monoid is then

:<math>S^{a_1} R S^{a_2} R S^{a_3} \cdots</math>

for positive integers <math>a_1, a_2, a_3, \ldots</math>. Each such element describes a [[self-similarity]] of the question-mark function. This monoid is sometimes called the '''[[period-doubling monoid]]''', and all period-doubling fractal curves have a self-symmetry described by it (the [[de Rham curve]], of which the question mark is a special case, is a category of such curves). Note also that the elements of the monoid are in correspondence with the rationals, by means of the identification of <math>a_1, a_2, a_3, \ldots</math> with the continued fraction <math>[0; a_1, a_2, a_3, \ldots]</math>. Since both

:<math>S: x \mapsto \frac{x}{x+1}</math>

and

:<math>T: x \mapsto 1-x</math>

are [[linear fractional transformation]]s with integer coefficients, the monoid may be regarded as a subset of the [[modular group]] PSL(2,'''Z''').

==Properties of ?(''x'')==
{{wide image|Minkowski'sQuestionMarkLessTheIdentity.png|1024px|align-cap=center|alt=?(''x'') − ''x''}}
The question-mark function is a [[strictly increasing]] and continuous,<ref name=Fin442>Finch (2003) p. 442</ref> but not [[absolutely continuous]] function. The [[derivative]] vanishes on the [[rational number]]s. There are several constructions for a [[measure (mathematics)|measure]] that, when integrated, yields the question-mark function. One such construction is obtained by measuring the density of the [[Farey sequence|Farey numbers]] on the real number line. The question-mark measure is the prototypical example of what are sometimes referred to as [[multifractal|multi-fractal measure]]s.

The question-mark function maps rational numbers to [[dyadic rational|dyadic rational number]]s, meaning those whose [[Binary numeral system|base two]] representation terminates, as may be proven by induction from the recursive construction outlined above. It maps [[quadratic irrational]]s to non-dyadic rational numbers. It is an [[odd function]], and satisfies the functional equation {{math|1=?(''x'' + 1) = ?(''x'') + 1}}; consequently {{math|''x'' → ?(''x'') − ''x''}} is an odd [[periodic function]] with period one. If {{math|?(''x'')}} is irrational, then {{mvar|x}} is either [[algebraic number|algebraic]] of degree greater than two, or [[transcendental number|transcendental]].

The question-mark function has [[Fixed point (mathematics)|fixed point]]s at 0, 1/2 and 1, and at least two more, symmetric about the midpoint. One is approximately 0.42037.<ref name=Fin442/>

In 1943, [[Raphaël Salem]] raised the question of whether the Fourier–Stieltjes coefficients of the question-mark function vanish at infinity.<ref>Salem (1943)</ref> In other words, he wanted to know whether or not

:<math>\lim_{n \to \infty}\int_0^1 e^{2\pi inx} \, d?(x)=0.</math>

This was answered affirmatively by Jordan and Sahlsten,<ref>Jordan and Sahlsten (2013)</ref> as a special case of a result on [[Gibbs measure]]s.

The graph of Minkowski question mark function is a special case of fractal curves known as [[de Rham curve]]s.

==Conway box function==
{{See also|Sawtooth wave}}

The ? is invertible, and the [[inverse function]] has also attracted the attention of various mathematicians, in particular [[John Horton Conway|John Conway]], who discovered it independently, and whose notation for {{math|?−1(''x'')}} is {{mvar|x}} with a box drawn around it: {{mvar|x}} The box function can be computed as an encoding of the [[binary numeral system|base two]] expansion of <math>(x-\lfloor x \rfloor)/2</math>, where <math>\lfloor x \rfloor</math> denotes the [[floor function]]. To the right of the point, this will have {{math|size=120%|''n''1}} 0s, followed by {{math|size=120%|''n''2}} 1s, then {{math|size=120%|''n''3}} 0s and so on. For <math>n_0 = \lfloor x \rfloor</math>,

:{{bigmath|1=''x'' = [''n''0; ''n''1, ''n''2, ''n''3, … ],}}

where the term on the right is a [[continued fraction]].

==See also==
* [[Pompeiu derivative]]

==Notes==
{{reflist}}

==Historical references==

*{{citation|url=http://ada00.math.uni-bielefeld.de/ICM/ICM1904/|archive-url=https://web.archive.org/web/20150104205306/http://ada00.math.uni-bielefeld.de/ICM/ICM1904/|dead-url=yes|archive-date=2015-01-04|first=Hermann|last=Minkowski|authorlink=Hermann Minkowski|title=Verhandlungen des III. internationalen Mathematiker-Kongresses in Heidelberg|year=1904|place=Berlin|chapter=Zur Geometrie der Zahlen|pages=164–173|jfm=36.0281.01}}
* {{citation | last=Denjoy | first=Arnaud | authorlink=Arnaud Denjoy | title=Sur une fonction réelle de Minkowski | language=French | zbl=0018.34602 | journal=J. Math. Pures Appl., IX. Sér. | volume=17 | pages=105–151 | year=1938 }}

==References==
*{{citation
| last = Alkauskas | first = Giedrius
| publisher = [[University of Nottingham]]
| series = PhD thesis
| title = Integral transforms of the Minkowski question mark function
| url = http://eprints.nottingham.ac.uk/10641/
| year = 2008}}.
*{{citation
|last1 = Bibiloni
|first1 = L.
|last2 = Paradis
|first2 = J.
|last3 = Viader
|first3 = P.
|doi = 10.1006/jnth.1998.2294
|journal = Journal of Number Theory
|pages = 212–227
|title = A new light on Minkowski's ?(x) function
|issue = 2
|url = http://www.econ.upf.es/en/research/onepaper.php?id=226
|volume = 73
|year = 1998
|zbl = 0928.11006
|deadurl = yes
|archiveurl = https://web.archive.org/web/20150622194657/http://www.econ.upf.es/en/research/onepaper.php?id=226
|archivedate = 22 June 2015
|df = dmy-all
}}.
*{{citation
|last1 = Bibiloni
|first1 = L.
|last2 = Paradis
|first2 = J.
|last3 = Viader
|first3 = P.
|journal = Journal of Mathematical Analysis and Applications
|pages = 107–125
|title = The derivative of Minkowski's singular function
|issue = 1
|url = http://www.econ.upf.es/en/research/onepaper.php?id=378
|volume = 253
|year = 2001
|doi = 10.1006/jmaa.2000.7064
|zbl = 0995.26005
|deadurl = yes
|archiveurl = https://web.archive.org/web/20150622192620/http://www.econ.upf.es/en/research/onepaper.php?id=378
|archivedate = 22 June 2015
|df = dmy-all
}}.
*{{citation
| last = Conley | first = R. M.
| publisher = [[West Virginia University]]
| series = Masters thesis
| title = A Survey of the Minkowski ?(x) Function
| year = 2003}}.
*{{citation
| last = Conway | first = J. H. | author-link = John Horton Conway
| contribution = Contorted fractions
| edition = 2nd
| location = Wellesley, MA
| pages = 82–86
| publisher = A K Peters
| title = On Numbers and Games
| year = 2000}}.
*{{citation | last=Finch | first=Steven R. | title=Mathematical constants | series=Encyclopedia of Mathematics and Its Applications | volume=94 | location=[[Cambridge]] | publisher=[[Cambridge University Press]] | year=2003 | isbn=0-521-81805-2 | zbl=1054.00001 }}
*{{citation | last1=Jordan | first1=Thomas | last2= Sahlsten | first2=Tuomas | title= Fourier transforms of Gibbs measures for the Gauss map | journal = [[Mathematische Annalen]] (to appear) | year=2013 | arxiv= 1312.3619 | bibcode=2013arXiv1312.3619J }}
*{{citation | last=Pytheas Fogg | first=N. | editor1-first=Valérie | editor1-last = Berthé |editor1-link = Valérie Berthé| editor2-last = Ferenczi | editor2-first= Sébastien | editor3-last= Mauduit | editor3-first= Christian | editor4-last= Siegel | editor4-first= A. | title=Substitutions in dynamics, arithmetics and combinatorics | series=Lecture Notes in Mathematics | volume=1794 | location=Berlin | publisher=[[Springer-Verlag]] | year=2002 | isbn=3-540-44141-7 | zbl=1014.11015 }}
*{{citation | last = Salem | first = Raphaël | author-link = Raphaël Salem | journal = [[Transactions of the American Mathematical Society]] | pages = 427–439 | volume = 53 | issue = 3 | url = http://www.ams.org/journals/tran/1943-053-03/S0002-9947-1943-0007929-6/S0002-9947-1943-0007929-6.pdf | title = On some singular monotonic functions which are strictly increasing | year = 1943 | doi=10.2307/1990210}}
*{{citation
| last = Vepstas | first = L.
| title = The Minkowski Question Mark and the Modular Group SL(2,Z)
| url = http://www.linas.org/math/chap-minkowski.pdf
| year = 2004}}
*{{citation
| last = Vepstas | first = L.
| title = On the Minkowski Measure
| arxiv = 0810.1265
| series= arXiv:0810.1265
| year = 2008| bibcode = 2008arXiv0810.1265V}}

==External links==
* [http://uosis.mif.vu.lt/~alkauskas/minkowski.htm An extensive bibliography list]
*{{mathworld|urlname=MinkowskisQuestionMarkFunction|title=Minkowski's Question Mark Function}}
* [https://gist.github.com/pallas/5565556 Simple IEEE 754 implementation in C++]

[[Category:Fractal curves]]
[[Category:Continued fractions]]
[[Category:Special functions]]
[[Category:Continuous mappings]]
[[Category:Articles with example C code]]
[[Category:Hermann Minkowski]]

Hilda-Gruppe

2018-06-19T23:57:23Z

Bibcode Bot: Adding 0 arxiv eprint(s), 0 bibcode(s), 0 doi(s), and updating 1 bibcode(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

[[Image:InnerSolarSystem-en.png|300px|thumb|The asteroids of the [[inner Solar System]] and [[Jupiter]]: The ''Hilda group'' is located between the asteroid belt and the orbit of Jupiter.
{| style="width:100%;"
|-
| valign=top |
{{legend2|#6ad768|border=1px solid #2B9929|[[Jupiter trojan]]s}} 
{{legend2|#007DD6|border=1px solid #00508A|[[Orbit]]s of [[planet]]s}} 
{{legend2|#FFFF00|border=1px solid #B3B300|[[Sun]]}}
| valign=top |
{{legend2|#d39300|border=1px solid #855D00|'''''Hilda group'''''}} 
{{legend2|#e9e9e9|border=1px solid #999999|[[Asteroid belt]]}} 
{{legend2|#c90000|border=1px solid #940000|[[Near-Earth object]]s {{small|(selection)}}}}
|}
]]

The '''Hilda asteroids''' (adj. ''Hildian'') are a [[List of minor-planet groups|dynamical group]]<ref name=Broz2008>{{cite journal |last=Brož |first=M. |author2=Vokrouhlický, D. |title=Asteroid families in the first-order resonances with Jupiter |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=390 |issue=2 |pages=715–732 |date=2008 |doi=10.1111/j.1365-2966.2008.13764.x |bibcode=2008MNRAS.390..715B
|arxiv=1104.4004 }}</ref> of [[asteroid]]s in a 3:2 [[orbital resonance]] with [[Jupiter]]. The namesake is the asteroid [[153 Hilda]]. Hildas move in their elliptical orbits so that their [[apsis|aphelia]] put them opposite Jupiter (at {{L3}}), or 60 degrees ahead of or behind Jupiter at the {{L4}} and {{L5}} [[Lagrangian point]]s.<ref name="easysky">{{cite web |title=The triangle formed by the Hilda asteroids |publisher=EasySky |author=Matthias Busch |url=http://www.easysky.de/eng/screenshots/Hildas.htm |accessdate=2009-12-15
}}</ref> Over three successive orbits each Hilda asteroid approaches all of these three points in sequence. A Hilda's orbit has a [[semi-major axis]] between 3.7 AU and 4.2 AU (the average over a long time span is 3.97), an [[eccentricity (orbit)|eccentricity]] less than 0.3, and an [[inclination]] less than 20°.<ref name="Ohtsukaetal2008">{{cite journal |bibcode = 2008A&A...489.1355O |title = Quasi-Hilda comet 147P/Kushida-Muramatsu. Another long temporary satellite capture by Jupiter |last1 = Ohtsuka |first1 = Katsuhito |last2 = Yoshikawa |first2 = M. |last3 = Asher |first3 = D. J. |last4 = Arakida |first4 = H. |journal = Astronomy and Astrophysics |volume = 489 |issue = 3 |date = October 2008 |pages = 1355–1362 |doi = 10.1051/0004-6361:200810321 |last5 = Arakida |first5 = H.
|arxiv = 0808.2277 }}</ref> Two [[asteroid family|collisional families]] exist within the Hilda group: the '''Hilda family''' and the [[Schubart family]].<ref name=Broz_Vokrouhlicky>{{cite journal|last=Brož|first=M.|author2=Vokrouhlický, D.|title=Asteroid families in the first-order resonances with Jupiter|journal=Monthly Notices of the Royal Astronomical Society|date=2008|volume=390|issue=2|pages=715–732|doi=10.1111/j.1365-2966.2008.13764.x|arxiv=1104.4004|bibcode=2008MNRAS.390..715B}}</ref> The namesake for the latter family is [[1911 Schubart]]. There are more than 4,000 known Hilda asteroids including unnumbered objects.<ref name=Broz2008/><ref name="Ohtsukaetal2008" />

Hildas' surface colors often correspond to the low-albedo [[D-type asteroid|D-type]] and [[P-type asteroid|P-type]]; however, a small portion are [[C-type asteroid|C-type]]. D-type and P-type asteroids have surface colors, and thus also surface mineralogies, similar to those of [[cometary nuclei]]. This implies that they share a common origin.<ref name="Ohtsukaetal2008"/><ref>{{cite journal|last=Gil-Hutton|first=R.|author2=Brunini, Adrián|title=Surface composition of Hilda asteroids from the analysis of the Sloan Digital Sky Survey colors|journal=Icarus|volume=193|issue=2|pages=567–571|url=http://sedici.unlp.edu.ar/handle/10915/2097|accessdate=14 April 2014|doi=10.1016/j.icarus.2007.08.026|bibcode=2008Icar..193..567G}}</ref>

== Dynamics ==
The asteroids of the Hilda group (Hildas) are in 3:2 [[orbital resonance|mean-motion resonance]] with Jupiter.<ref name="Ohtsukaetal2008" /> That is, their [[orbital period]]s are 2/3 that of Jupiter. They move along the orbits with a semimajor axis near 4.0 AU and moderate values of eccentricity (up to 0.3) and inclination (up to 20°). Unlike the [[Jupiter trojan]]s they may have any difference in longitude with Jupiter, nevertheless avoiding dangerous approaches to the planet.

The Hildas taken together constitute a dynamic triangular figure with slightly convex sides and trimmed apexes in the triangular libration points of Jupiter—the "Hildas Triangle".<ref name="easysky"/> The "asteroidal stream" within the sides of the triangle is about 1 [[astronomical unit|AU]] wide, and in the apexes this value is 20-40% greater. Figure 1 shows the positions of the Hildas (black) against a background of all known asteroids (gray) up to Jupiter's orbit at January 1, 2005.<ref>L'vov V.N., Smekhacheva R.I., Smirnov S.S., Tsekmejster S.D. Some peculiarities in the Hildas motion. Izv. Pulkovo Astr. Obs., 2004, 217, 318-324 (in Russian)</ref>

Each of the Hilda objects moves along its own [[Kepler's laws of planetary motion|elliptic orbit]]. However, at any moment the Hildas together constitute this triangular configuration, and all the orbits together form a predictable ring. Figure 2 illustrates this with the Hildas positions (black) against a background of their orbits (gray). For the majority of these asteroids, their position in orbit may be arbitrary, except for the external parts of the apexes (the objects near aphelion) and the middles of the sides (the objects near perihelion). The Hildas Triangle has proven to be dynamically stable over a long time span.

[[Image:Hildas01.jpg|thumb|left|525px|Left: The Hildas Triangle against a background of all known asteroids up to Jupiter's orbit. Right: The positions of the Hildas against a background of their orbits.]]

The typical Hilda object has a [[Retrograde motion|retrograde perihelion motion]]. On average, the velocity of perihelion motion is greater when the orbital eccentricity is lesser, while the nodes move more slowly. All typical objects in aphelion would seemingly approach closely to Jupiter, which should be destabilising for them—but the variation of the orbital elements over time prevents this, and [[conjunction (astronomy and astrology)|conjunctions]] with Jupiter occur only near the perihelion of Hilda asteroids. Moreover, the [[Apsis|apsidal]] line oscillates near the line of conjunction with different amplitude and a period of 2.5 to 3.0 centuries.

[[File:HildasOrbitWithLagrangePointsLousy.gif|frame|right|A schematic of the orbit of [[153 Hilda]] (green), with [[Jupiter]] (red)]][[Image:hildas02.gif|thumb|300px|Hildas (black) and Trojans viewed from the ecliptic plane near 190 degrees longitude on Jan. 1, 2005]]
In addition to the fact that the Hildas triangle revolves in sync with Jupiter, the density of asteroids in the stream exhibits quasi-periodical waves. At any time, the density of objects in the triangle's apexes is more than twice the density within the sides. The Hildas "rest" at their aphelia in the apexes for an average of 5.0-5.5 years, whereas they move along the sides more quickly, averaging 2.5 to 3.0 years. The [[orbital period]]s of these asteroids are approximately 7.9 years, or two thirds that of Jupiter.

Although the triangle is nearly [[equilateral]], some asymmetry exists. Due to the eccentricity of Jupiter's orbit, the side {{L4}}-{{L5}} slightly differs from the two other sides. When Jupiter is in [[aphelion]], the mean velocity of the objects moving along this side is somewhat smaller than that of the objects moving along the other two sides. When Jupiter is in [[perihelion]], the reverse is true.

At the apexes of the triangle corresponding to the points {{L4}} and {{L5}} of Jupiter's orbit, the Hildas approach the [[Trojan asteroid|Trojans]]. At the mid-sides of the triangle, they are close to the asteroids of the external part of the [[asteroid belt]]. The velocity dispersion of Hildas is more evident than that of Trojans in the regions where they intersect. It should also be noted that the dispersion of Trojans in [[inclination]] is twice that of the Hildas. Due to this, as much as one quarter of the Trojans cannot intersect with the Hildas, and at all times many Trojans are located outside Jupiter's orbit. Therefore, the regions of intersection are limited. This is illustrated by the adjacent figure that shows the Hildas (black) and the Trojans (gray) along the [[plane of the ecliptic|ecliptic plane]]. One can see the spherical form of the Trojan swarms.

When moving along each side of the triangle, the Hildas travel more slowly than the Trojans, but encounter a denser neighborhood of outer-asteroid-belt asteroids. Here, the velocity dispersion is much smaller.

[[File:Hilda asteroid as seen from Jupiter.png|thumb|Orbits of two idealized asteroids of the Hilda family, in the rotating reference frame of Jupiter's orbit. Black: eccentricity 0.310; aphelion at Jupiter's orbit. Red: eccentricity 0.211.]]

== Research ==
The observed peculiarities in the Hildas' motion are based on data for a few hundred objects known to date and generate still more questions. Further observations are needed to expand on the list of Hildas. Such observations are most favorable when Earth is near [[conjunction (astronomy and astrology)|conjunction]] with the mid-sides of the Hildas Triangle. These moments occur each 4 and 1/3 months. In these circumstances the [[luminosity#In astronomy|brilliance]] of objects of similar size could run up to 2.5 magnitudes as compared to the apexes.{{cn|date=September 2017}}

The Hildas traverse regions of the Solar system from approximately 2 AU up to Jupiter's orbit. This entails a variety of physical conditions and the neighborhood of various groups of asteroids. On further observation some theories on the Hildas may have to be revised.{{cn|date=September 2017}}

==References==
{{reflist}}

{{Small Solar System bodies}}

{{DEFAULTSORT:Hilda Family}}
[[Category:Hilda asteroids|*]]
[[Category:Jupiter]]

Rishonen-Modell

2018-06-08T02:27:26Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 1 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Use dmy dates|date=July 2013}}
The '''Harari–Shupe preon model''' (also known as '''rishon model''', RM) is the earliest effort to develop a [[preon]] model to explain the phenomena appearing in the [[Standard Model]] (SM) of [[particle physics]].<ref name=Harari1979>{{cite journal |last=Harari |first=H. |year=1979 |title=A schematic model of quarks and leptons |url=http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-2310.pdf |journal=[[Physics Letters B]] |volume=86 |issue=1 |pages=83–86 |doi=10.1016/0370-2693(79)90626-9 |bibcode=1979PhLB...86...83H }}</ref> It was first developed independently by [[Haim Harari]] and by [[Michael A. Shupe]]<ref name=Shupe1979>{{cite journal |last=Shupe |first=M. A. |year=1979 |title=A composite model of leptons and quarks |journal=[[Physics Letters B]] |volume=86 |issue=1 |pages=87–92 |doi=10.1016/0370-2693(79)90627-0 |bibcode=1979PhLB...86...87S }}
</ref> and later expanded by Harari and his then-student [[Nathan Seiberg]].<ref name=HarariSeiberg1984/>

==The model==
The model has two kinds of fundamental particles called '''rishons''' (which means "primary" in [[Hebrew]]). They are '''T''' ("Third" since it has an electric charge of +⅓ [[elementary charge|''e'']], or [[Tohu Rishon|Tohu]] which means [[Tohu va bohu|"unformed"]] in [[Book of Genesis|Hebrew Genesis]]) and '''V''' ("Vanishes", since it is electrically neutral, or [[Vohu Rishon|Vohu]] which means "void" in Hebrew Genesis). All [[lepton]]s and all [[flavour (particle physics)|flavour]]s of [[quark]]s are three-rishon ordered triplets. These groups of three rishons have [[spin-½]]. They are as follows:
* TTT = [[positron]] (anti-electron);
* VVV = [[electron neutrino]];
* TTV, TVT and VTT = three [[color charge|colour]]s of [[up quark]]s;
* TVV, VTV and VVT = three colours of [[down quark|down antiquarks]].

Each rishon has a corresponding antiparticle. Hence:
* {{overline|TTT}} = [[electron]];
* {{overline|VVV}} = [[electron antineutrino]];
* {{overline|TTV}}, {{overline|TVT}}, {{overline|VTT}} = three colours of [[up quark|up antiquarks]];
* {{overline|TVV}}, {{overline|VTV}}, {{overline|VVT}} = three colours of [[down quark]]s.

The [[W and Z bosons|W+ boson]] = TTTVVV;
The [[W and Z bosons|W− boson]] = {{overline|TTTVVV}}.

[[Baryon number]] (''B'') and [[lepton number]] (''L'') are not conserved, but the quantity [[B−L|''B''−''L'']] is conserved. A baryon number violating process (such as [[proton decay]]) in the model would be 
<tt> {{nowrap|u  +  u  →  {{overline|d}}  +  e+}} 
/|\   /|\   /|\   /|\ 
{{nowrap|TTV + TTV → TVV + TTT}}</tt>

*[[Matter]] and [[antimatter]] are equally abundant in nature in the RM.
*[[Generation (particle physics)|Higher generation]] leptons and quarks are presumed to be excited states of first generation leptons and quarks.
*[[Mass]] is not explained.

In the expanded Harari–Seiberg version the rishons possess color and hypercolor, explaining why the only composites are the observed quarks and leptons.<ref name=HarariSeiberg1984>{{cite journal |last1=Harari |first1=Haim |last2=Seiberg |first2=Nathan |url=http://www.weizmann.ac.il/home/harari/files/Nuclear_PhysicsB_Vol204.pdf |year=1982 |title=The Rishon Model |journal=Nuclear Physics B |volume=204 |pages=141–167 |publisher=North-Holland Publishing |access-date=2018-06-02 |dead-url=no|bibcode=1982NuPhB.204..141H |doi=10.1016/0550-3213(82)90426-6 }}</ref> Under certain assumptions, it is possible to show that the model allows exactly for three generations of quarks and leptons.

==Evidence==
Currently, there is no [[scientific evidence]] for the existence of substructure within quarks and leptons, but there is no profound reason why such a substructure may not be revealed at shorter distances. In 2008, [[Piotr Zenczykowski]] has derived the RM by starting from a non-relativistic [[O(6)]] [[phase space]].<ref name=Zenczykowski2008>{{cite journal |author=Zenczykowski, P. |year=2008 |title=The Harari–Shupe preon model and nonrelativistic quantum phase space |journal=[[Physics Letters B]] |volume=660 |issue=5 |pages=567–572 |doi=10.1016/j.physletb.2008.01.045 |bibcode=2008PhLB..660..567Z |arxiv=0803.0223 }}</ref> Such model is based on fundamental principles and the structure of [[Clifford algebras]], and fully recovers the RM by naturally explaining several obscure and otherwise artificial features of the original model.

==In popular culture==
* Science fiction author [[Vonda McIntyre]], in her novelizations of the scripts of the movies ''[[Star Trek II: The Wrath of Khan]]'' and ''[[Star Trek III: The Search for Spock]]'' suggested that the [[Project Genesis (Star Trek)|Genesis effect]] was a result of a newly discovered rishon-like substructure to matter.
* Science fiction author [[James P. Hogan (writer)|James P. Hogan]] in his novel ''[[Voyage from Yesteryear]]'' explicitly postulated a rishon-like model in the development of antimatter weapons and energy sources.

==References==
{{reflist}}

[[Category:Particle physics]]
[[Category:Hypothetical elementary particles]]

No-go-Theorem

2018-06-07T18:15:50Z

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{{Distinguish|No-ghost theorem}}
{{Refimprove|date=September 2012}}

In [[theoretical physics]], a '''no-go theorem''' is a [[theorem]] that states that a particular situation is not physically possible. Specifically, the term describes results in [[quantum mechanics]] like [[Bell's theorem]] and the [[Kochen–Specker theorem]] that constrain the permissible types of [[Hidden variable theory|hidden variable theories]] which try to explain the apparent randomness of quantum mechanics as a deterministic model featuring hidden states.<ref>{{cite book |title=Interpreting the Quantum World |last=Bub |first=Jeffrey |authorlink=Jeffrey Bub |year=1999 |edition=revised paperback |publisher=Cambridge University Press |isbn=978-0-521-65386-2 }}</ref><ref>{{cite book |title=Probabilistic and Statistical Aspects of Quantum Theory |last=Holevo |first=Alexander |authorlink=Alexander Holevo|year=2011 |edition=2nd English |publisher=Edizioni della Normale |location=Pisa |isbn=978-8876423758}}</ref>{{Failed verification|talk=Notable?|date=April 2017}}

==Examples==
The [[Weinberg–Witten theorem]] states that massless particles (either composite or elementary) with spin ''j'' > {{frac|1|2}} cannot carry a [[Lorentz covariance|Lorentz-covariant]] current, while massless particles with spin ''j'' > 1 cannot carry a Lorentz-covariant [[Stress–energy tensor|stress-energy]]. The theorem is usually interpreted to mean that the [[graviton]] (''j'' = 2) cannot be a composite particle in a relativistic [[quantum field theory]].

In [[quantum information theory]], a [[no-communication theorem]] is a result that gives conditions under which instantaneous transfer of information between two observers is impossible.

Other examples:
* [[Antidynamo theorem]]s (e.g. Cowling's theorem)
* [[Coleman–Mandula theorem]]
* [[Earnshaw's theorem]] (it states that a collection of [[point charge]]s cannot be maintained in a stable stationary [[mechanical equilibrium|equilibrium]] configuration solely by the [[electrostatic]] interaction of the charges)
* [[Haag–Łopuszański–Sohnius theorem]] as a generalisation of the [[Coleman–Mandula theorem]] stating that "space-time and internal symmetries cannot be combined in any but a trivial way"
* [[Haag's theorem]]
* [[Nielsen–Ninomiya theorem]]
* [[No-broadcast theorem]]
* [[No-cloning theorem]]
* [[Quantum no-deleting theorem|No-deleting theorem]]
* [[No-hiding theorem]]
* [[No-teleportation theorem]]
* [[No-programming theorem]]<ref>{{Cite journal|last=Nielsen|first=M. A.|last2=Chuang|first2=Isaac L.|date=1997-07-14|title=Programmable Quantum Gate Arrays|url=https://link.aps.org/doi/10.1103/PhysRevLett.79.321|journal=Physical Review Letters|volume=79|issue=2|pages=321–324|doi=10.1103/PhysRevLett.79.321|arxiv=quant-ph/9703032|bibcode=1997PhRvL..79..321N}}</ref>

== See also ==

* [[Proof of impossibility]]

==References==
{{reflist|2}}

==External links==
*[https://arxiv.org/abs/1406.7239 Beating no-go theorems by engineering defects in quantum spin models (2014)]

{{DEFAULTSORT:No-Go Theorem}}
[[Category:Quantum field theory]]
[[Category:Supersymmetry]]

{{Physics-stub}}

Effektiv-Medium-Theorie

2018-06-07T06:20:36Z

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'''Effective medium approximations''' or '''effective medium theory''' (sometimes abbreviated as '''EMA''' or '''EMT''') pertains to [[computer modeling|analytical]] or [[scientific theory|theoretical]] modeling that describes the [[macroscopic]] properties of [[Advanced composite materials (engineering)|composite material]]s. EMAs or EMTs are developed from averaging the multiple values of the constituents that directly make up the composite material. At the constituent level, the values of the materials vary and are [[homogeneous|inhomogeneous]]. Precise calculation of the many constituent values is nearly impossible. However, theories have been developed that can produce acceptable approximations which in turn describe useful parameters and properties of the composite material as a whole. In this sense, effective medium approximations are descriptions of a medium (composite material) based on the properties and the relative fractions of its components and are derived from calculations.<ref name=Cai-book>
{{Cite book
| last1 = Wenshan | first1 = Cai
| first2 = Vladimir | last2 = Shalaev
| authorlink = Vladimir Shalaev
| title =Optical Metamaterials: Fundamentals and Applications
| publisher =Springer
| date =November 2009
| pages =Chapter 2.4
| url =https://books.google.com/books?id=q8gDF2pbKXsC&pg=PA59&dq=artificial+dielectrics#v=onepage&q=artificial%20dielectrics&f=false
| isbn =978-1-4419-1150-6}}</ref><ref name= wang-pan>
{{cite journal
| doi=10.1016/j.mser.2008.07.001
| url= http://ningpan.net/publications/151-200/156.pdf
| format=Free PDF download
| title=Predictions of effective physical properties of complex multiphase materials
| year=2008
| last1=Wang
| first1=M
| last2=Pan
| first2=N
| journal=Materials Science and Engineering: R: Reports
| volume=63
| pages=1}}</ref>

==Applications==
They can be discrete models such as applied to resistor networks or continuum theories as applied to elasticity or viscosity but most of the current theories have difficulty in describing percolating systems. Indeed, among the numerous effective medium approximations, only Bruggeman’s symmetrical theory is able to predict a threshold. This characteristic feature of the latter theory puts it in the same category as other mean field theories of [[critical phenomena]].

There are many different effective medium approximations,<ref>{{cite journal |last1=Tinga |first1=W. R. |last2=Voss |first2=W. A. G.|last3=Blossey|first3=D. F. |year=1973 |title=Generalized approach to multiphase dielectric mixture theory |journal=J. Appl. Phys. |volume=44 |issue= 9|pages=3897 |url=http://link.aip.org/link/?JAPIAU/44/3897/1 |doi=10.1063/1.1662868|bibcode = 1973JAP....44.3897T }}</ref> each of them being more or less accurate in distinct conditions. Nevertheless, they all assume that the macroscopic system is homogeneous and typical of all mean field theories, they fail to predict the properties of a multiphase medium close to the percolation threshold due to the absence of long-range correlations or critical fluctuations in the theory.

The properties under consideration are usually the [[electrical conductivity|conductivity]] <math>\sigma</math> or the [[dielectric constant]] <math>\epsilon</math> of the medium. These parameters are interchangeable in the formulas in a whole range of models due to the wide applicability of the Laplace equation. The problems that fall outside of this class are mainly in the field of elasticity and hydrodynamics, due to the higher order tensorial character of the effective medium constants.

== Bruggeman's model ==

=== Formulas ===
Without any loss of generality, we shall consider the study of the effective conductivity (which can be either dc or ac) for a system made up of spherical multicomponent inclusions with different arbitrary conductivities. Then the Bruggeman formula takes the form:

==== Circular and spherical inclusions ====
<math>\sum_i\,\delta_i\,\frac{\sigma_i - \sigma_e}{\sigma_i + (n-1) \sigma_e}\,=\,0\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(1)</math>

In a system of Euclidean spatial dimension <math> n </math> that has an arbitrary number of components,<ref name=landauer>{{cite conference |url=http://link.aip.org/link/?APCPCS/40/2/1 |title=Electrical conductivity in inhomogeneous media |last1=Landauer |first1=Rolf |date=April 1978 |publisher=American Institute of Physics |accessdate=2010-02-07 |booktitle=AIP Conference Proceedings |volume=40 |pages=2–45 |location=|doi=10.1063/1.31150}}</ref> the sum is made over all the constituents. <math>\delta_i</math> and <math>\sigma_i</math> are respectively the fraction and the conductivity of each component, and <math>\sigma_e</math> is the effective conductivity of the medium. (The sum over the <math>\delta_i</math>'s is unity.)

==== Elliptical and ellipsoidal inclusions ====
<math>\frac{1}{n}\,\delta\alpha+\frac{(1-\delta)(\sigma_m - \sigma_e)}{\sigma_m + (n-1)\sigma_e}\,=\,0\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(2)</math>

This is a generalization of Eq. (1) to a biphasic system with ellipsoidal inclusions of conductivity <math>\sigma</math> into a matrix of conductivity <math>\sigma_m</math>.<ref>{{cite journal|last1=Granqvist|first1=C. G. |last2=Hunderi |first2=O. |year=1978 |title=Conductivity of inhomogeneous materials: Effective-medium theory with dipole-dipole interaction |journal=Phys. Rev. B |volume=18 |issue=4 |pages=1554–1561 |url=http://link.aps.org/doi/10.1103/PhysRevB.18.1554 |doi=10.1103/PhysRevB.18.1554|bibcode = 1978PhRvB..18.1554G }}</ref> The fraction of inclusions is <math>\delta</math> and the system is <math>n</math> dimensional. For randomly oriented inclusions,

<math>\alpha\,=\,\frac{1}{n}\sum_{j=1}^{n}\,\frac{\sigma - \sigma_e}{\sigma_e + L_j(\sigma - \sigma_e)}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(3)</math>

where the <math>L_j</math>'s denote the appropriate doublet/triplet of depolarization factors which is governed by the ratios between the axis of the ellipse/ellipsoid. For example: in the case of a circle {<math>L_1=1/2</math>, <math>L_2=1/2</math>} and in the case of a sphere {<math>L_1=1/3</math>, <math>L_2=1/3</math>, <math>L_3=1/3</math>}. (The sum over the <math>L_j</math> 's is unity.)

The most general case to which the Bruggeman approach has been applied involves bianisotropic ellipsoidal inclusions.<ref name="www3.interscience.wiley">{{cite journal|last1=Weiglhofer|first1=W. S. |last2=Lakhtakia |first2=A. |last3=Michel |first3=B. |year=1998 |title=Maxwell Garnett and Bruggeman formalisms for a particulate composite with bianisotropic host medium|journal=Microw. Opt. Technol. Lett. |volume=15 |issue=4 |pages=263–266 |url=http://www3.interscience.wiley.com/journal/53983/abstract?CRETRY=1&SRETRY=0 |doi=10.1002/(SICI)1098-2760(199707)15:4<263::AID-MOP19>3.0.CO;2-8}}</ref>

=== Derivation ===
The figure illustrates a two-component medium.<ref name=landauer/> Let us consider the cross-hatched volume of conductivity <math>\sigma_1</math>, take it as a sphere of volume <math>V</math> and assume it is embedded in a uniform medium with an effective conductivity <math>\sigma_e</math>. If the [[electric field]] far from the inclusion is <math>\overline{E_0}</math> then elementary considerations lead to a [[Electric dipole moment|dipole moment]] associated with the volume

<math>\overline{p}\, \propto \,V\,\frac{\sigma_1 - \sigma_e}{\sigma_1 + 2\sigma_e}\,\overline{E_0}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(4)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,.</math>

This [[polarization density|polarization]] produces a deviation from <math>\overline{E_0}</math>. If the average deviation is to vanish, the total polarization summed over the two types of inclusion must vanish. Thus

<math>\delta_1\frac{\sigma_1 - \sigma_e}{\sigma_1 + 2\sigma_e}\,+\,\delta_2\frac{\sigma_2 - \sigma_e}{\sigma_2 + 2\sigma_e}\,=\,0\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(5)</math>

where <math>\delta_1</math> and <math>\delta_2</math> are respectively the volume fraction of material 1 and 2. This can be easily extended to a system of dimension <math>n</math> that has an arbitrary number of components. All cases
can be combined to yield Eq. (1).

Eq. (1) can also be obtained by requiring the deviation in current to vanish
<ref>{{cite journal |last1=Stroud |first1=D. |year=1975 |title=Generalized effective-medium approach to the conductivity of an inhomogeneous material |journal=Phys. Rev. B |volume=12 |issue=8 |pages=3368–3373 |url=http://link.aps.org/doi/10.1103/PhysRevB.12.3368 |doi=10.1103/PhysRevB.12.3368 |bibcode = 1975PhRvB..12.3368S }}</ref>
<ref>{{cite journal |last1=Davidson |first1=A. |last2=Tinkham |first2=M. |year=1976 |title=Phenomenological equations for the electrical conductivity of microscopically inhomogeneous materials |journal=Phys. Rev. B |volume=13 |issue=8 |pages=3261–3267 |url=http://link.aps.org/doi/10.1103/PhysRevB.13.3261 |doi=10.1103/PhysRevB.13.3261 |bibcode = 1976PhRvB..13.3261D }}</ref>
. It has been derived here from the assumption that the inclusions are spherical and it can be modified for shapes with other depolarization factors; leading to Eq. (2).

A more general derivation applicable to bianisotropic materials is also available.<ref name="www3.interscience.wiley" />

=== Modeling of percolating systems ===
The main approximation is that all the domains are located in an equivalent mean field.
Unfortunately, it is not the case close to the percolation threshold where the system is governed by the largest cluster of conductors, which is a fractal, and long-range correlations that are totally absent from Bruggeman's simple formula.
The threshold values are in general not correctly predicted. It is 33% in the EMA, in three dimensions, far
from the 16% expected from percolation theory and observed in experiments. However, in
two dimensions, the EMA gives a threshold of 50% and has been proven to model percolation
relatively well.<ref>{{cite journal |last1=Kirkpatrick |first1=Scott |year=1973 |title=Percolation and conduction |journal=Rev. Mod. Phys. |volume=45 |issue=4 |pages=574–588 |url=http://link.aps.org/doi/10.1103/RevModPhys.45.574 |doi=10.1103/RevModPhys.45.574 |bibcode = 1973RvMP...45..574K }}</ref>
<ref>{{cite book |title=The Physics of Amorphous Solids |last=Zallen |first=Richard |authorlink= |year=1998 |publisher=Wiley-Interscience |isbn= 978-0-471-29941-7 |page= |pages= }}</ref><ref>{{cite journal |last1=Rozen |first1=John |last2=Lopez |first2=René |last3=Haglund |first3=Richard F. Jr. |last4=Feldman |first4=Leonard C. |year=2006 |title=Two-dimensional current percolation in nanocrystalline vanadium dioxide films |journal=Appl. Phys. Lett. |volume=88 |issue=8 |pages=081902 |url=http://link.aip.org/link/?APPLAB/88/081902/1 |doi=10.1063/1.2175490 |bibcode = 2006ApPhL..88h1902R }}</ref>

== Maxwell Garnett equation ==
In the Maxwell Garnett approximation, the effective medium consists of a matrix medium with <math>\varepsilon_m</math> and inclusions with <math>\varepsilon_i</math>.

=== Formula ===
The Maxwell Garnett equation reads:<ref name=TuckChoy>{{cite book|last=Choy|first=Tuck C.|title=Effective Medium Theory|year=1999|publisher=Clarendon Press|location=Oxford|isbn=978-0-19-851892-1}}</ref>
:<math>\left( \frac{\varepsilon_\mathrm{eff}-\varepsilon_m}{\varepsilon_\mathrm{eff}+2\varepsilon_m} \right) =\delta_i \left( \frac{\varepsilon_i-\varepsilon_m}{\varepsilon_i+2\varepsilon_m}\right),\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(6)</math>
where <math>\varepsilon_\mathrm{eff}</math> is the effective dielectric constant of the medium, <math>\varepsilon_i</math> is the one of the inclusions and <math>\varepsilon_m</math> is the one of the matrix; <math>\delta_i</math> is the volume fraction of the inclusions.

The Maxwell Garnett equation is solved by:
:<math>\varepsilon_\mathrm{eff}\,=\,\varepsilon_m\,\frac{2\delta_i(\varepsilon_i - \varepsilon_m) + \varepsilon_i + 2\varepsilon_m}{2\varepsilon_m + \varepsilon_i + \delta_i(\varepsilon_m-\varepsilon_i)},\,\,\,\,\,\,\,\,(7)</math><ref>Levy, O., & Stroud, D. (1997). Maxwell Garnett theory for mixtures of anisotropic inclusions: Application to conducting polymers. Physical Review B, 56(13), 8035.</ref><ref>Liu, Tong, et al. "Microporous Co@ CoO nanoparticles with superior microwave absorption properties." Nanoscale 6.4 (2014): 2447-2454.</ref>
so long as the denominator does not vanish. A simple MATLAB calculator using this formula is as follows.
<source lang="matlab">
% This simple MATLAB calculator computes the effective dielectric
% constant of a mixture of an inclusion material in a base medium
% according to the Maxwell Garnett theory as introduced in:
% http://en.wikipedia.org/wiki/Effective_Medium_Approximations
% INPUTS:
% eps_base: dielectric constant of base material;
% eps_incl: dielectric constant of inclusion material;
% vol_incl: volume portion of inclusion material;
% OUTPUT:
% eps_mean: effective dielectric constant of the mixture.

function [eps_mean] = MaxwellGarnettFormula(eps_base, eps_incl, vol_incl)

small_number_cutoff = 1e-6;

if vol_incl < 0 || vol_incl > 1
disp(['WARNING: volume portion of inclusion material is out of range!']);
end
factor_up = 2*(1-vol_incl)*eps_base+(1+2*vol_incl)*eps_incl;
factor_down = (2+vol_incl)*eps_base+(1-vol_incl)*eps_incl;
if abs(factor_down) < small_number_cutoff
disp(['WARNING: the effective medium is singular!']);
eps_mean = 0;
else
eps_mean = eps_base*factor_up/factor_down;
end
</source>

=== Derivation ===
For the derivation of the Maxwell Garnett equation we start with an array of polarizable particles. By using the Lorentz local field concept, we obtain the [[Clausius-Mossotti relation]]:
:<math>\frac{\varepsilon-1}{\varepsilon+2}= \frac{4\pi}{3} \sum_j N_j \alpha_j</math>
Where <math>N_j</math> is the number of particles per unit volume. By using elementary electrostatics, we get for a spherical inclusion with dielectric constant <math>\varepsilon_i</math> and a radius <math>a</math> a polarisability <math>\alpha</math>:
:<math> \alpha = \left( \frac{\varepsilon_i-1}{\varepsilon_i+2} \right) a^{3}</math>
If we combine <math>\alpha</math> with the Clausius Mosotti equation, we get:
:<math> \left( \frac{\varepsilon_\mathrm{eff}-1}{\varepsilon_\mathrm{eff}+2} \right) = \delta_i \left( \frac{\varepsilon_i-1}{\varepsilon_i+2} \right)</math>
Where <math>\varepsilon_\mathrm{eff}</math> is the effective dielectric constant of the medium, <math>\varepsilon_i</math> is the one of the inclusions; <math>\delta_i</math> is the volume fraction of the inclusions. 
As the model of Maxwell Garnett is a composition of a matrix medium with inclusions we enhance the equation:
:<math>\left( \frac{\varepsilon_\mathrm{eff}-\varepsilon_m}{\varepsilon_\mathrm{eff}+2\varepsilon_m} \right) =\delta_i \left( \frac{\varepsilon_i-\varepsilon_m}{\varepsilon_i+2\varepsilon_m}\right)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(8)</math>

=== Validity ===
In general terms, the Maxwell Garnett EMA is expected to be valid at low volume fractions <math>\delta_i </math> since it is assumed that the domains are spatially separated.<ref>{{cite journal |last1=Jepsen |first1=Peter Uhd |last2=Fischer |first2=Bernd M. |last3=Thoman|first3=Andreas |last4=Helm|first4=Hanspeter |last5=Suh |first5=J. Y. |last6=Lopez |first6=René | last7= Haglund |first7=R. F. Jr. |year=2006 |title=Metal-insulator phase transition in a VO2 thin film observed with terahertz spectroscopy |journal=Phys. Rev. B |volume=74 |issue=20 |pages=205103 |url=http://link.aps.org/doi/10.1103/PhysRevB.74.205103 |doi=10.1103/PhysRevB.74.205103 |bibcode = 2006PhRvB..74t5103J }}</ref>

==Effective medium theory for resistor networks==
For a network consisting of a high density of random resistors, an exact solution for each individual element may be impractical or impossible. In such case, a random resistor network can be considered as a two-dimensional [[Graph (discrete mathematics)|graph]]
and the effective resistance can be modelled in terms of graph measures and geometrical properties of networks. <ref>{{Cite journal|last=Kumar|first=Ankush|last2=Vidhyadhiraja|first2=N. S.|last3=Kulkarni|first3=G. U .|date=|year=2017|title=Current distribution in conducting nanowire networks|url=http://aip.scitation.org/doi/full/10.1063/1.4985792|journal=Journal of Applied Physics|volume=122|pages=045101|doi=10.1063/1.4985792|issn=|via=|bibcode=2017JAP...122d5101K}}</ref>
Assuming, edge length << electrode spacing and edges to be uniformly distributed, the potential can be considered to drop uniformly from one electrode to another.
Sheet resistance of such a random network (<math>R_{sn}</math>) can be written in terms of edge (wire) density (<math>N_E</math>), resistivity (<math>\rho</math>), width (<math>w</math>) and thickness (<math>t</math>) of edges (wires) as:

<math>R_{sn}\,=\,\frac{\pi}{2}\frac{\rho}{w\,t\,\sqrt{N_E}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(9)</math>

==See also==
* [[Constitutive equation]]
* [[Percolation threshold]]

==References==
{{reflist}}

==Further reading==
* {{cite book |title=Selected Papers on Linear Optical Composite Materials [Milestone Vol. 120]|last=Lakhtakia (Ed.) |first=A. |year=1996 |publisher=SPIE Press |location=Bellingham, WA, USA|isbn=0-8194-2152-9 }}
* {{cite book |title=Effective Medium Theory|last=Tuck |first=Choy |edition=1st |year=1999 |publisher=Oxford University Press |location=Oxford|isbn=978-0-19-851892-1 }}
* {{cite book |title=Electromagnetic Fields in Unconventional Materials and Structures|last=Lakhtakia (Ed.) |first=A. |authorlink=Akhlesh Lakhtakia |year=2000 |publisher=Wiley-Interscience|location=New York|isbn=0-471-36356-1 }}
* {{cite book |title=Introduction to Complex Mediums for Optics and Electromagnetics |last1=Weiglhofer (Ed.) |first2=A.|last2=Lakhtakia (Ed.) |authorlink=Akhlesh Lakhtakia |year=2003 |publisher=SPIE Press |location=Bellingham, WA, USA|isbn=0-8194-4947-4 }}
* {{cite book |title=Electromagnetic Anisotropy and Bianisotropy: A Field Guide|last1=Mackay |first1=T. G. |last2=Lakhtakia |first2=A. |authorlink=Akhlesh Lakhtakia|edition=1st |year=2010 |publisher=World Scientific |location=Singapore|isbn=978-981-4289-61-0 }}

[[Category:Condensed matter physics]]
[[Category:Physical chemistry]]

Dunkles Photon

2018-06-07T05:26:49Z

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{{Beyond the Standard Model}}

The '''dark photon''' (also hidden, heavy, para- or secluded photon) is a hypothetical [[hidden sector]] [[elementary particle|particle]], proposed as a [[force carrier]] similar to the [[photon]] of [[electromagnetism]] but potentially connected to [[dark matter]].<ref name=":0">{{cite arxiv|last=Essig|first=R.|last2=Jaros|first2=J. A.|last3=Wester|first3=W.|last4=Adrian|first4=P. Hansson|last5=Andreas|first5=S.|last6=Averett|first6=T.|last7=Baker|first7=O.|last8=Batell|first8=B.|last9=Battaglieri|first9=M.|date=2013-10-31|title=Dark Sectors and New, Light, Weakly-Coupled Particles|eprint=1311.0029|class=hep-ph}}</ref> In a minimal scenario, this new force can be introduced by extending the gauge group of the [[Standard Model|Standard Model of Particle Physics]] with a new [[Abelian group|abelian]] [[U(1)]] [[gauge symmetry]]. The corresponding new [[Spin 1 particles|spin-1]] [[gauge boson]] (i.e. the dark photon) can then couple very weakly to electrically charged particles through kinetic mixing with the ordinary photon<ref name=":1">{{Cite journal|date=1986-01-09|title=Two U(1)'s and ϵ charge shifts|url=https://www.sciencedirect.com/science/article/pii/0370269386913778|journal=Physics Letters B|language=en|volume=166|issue=2|pages=196–198|doi=10.1016/0370-2693(86)91377-8|issn=0370-2693|last1=Holdom|first1=Bob|bibcode=1986PhLB..166..196H}}</ref> and could thus be detected. Other types of couplings beyond kinetic mixing are also possible.<ref>{{Cite journal|date=1984-03-08|title=Two Z's or not two Z's?|url=https://www.sciencedirect.com/science/article/pii/0370269384911614|journal=Physics Letters B|language=en|volume=136|issue=4|pages=279–283|doi=10.1016/0370-2693(84)91161-4|issn=0370-2693|last1=Galison|first1=Peter|last2=Manohar|first2=Aneesh|bibcode=1984PhLB..136..279G}}</ref>

== Motivation ==
Observations of gravitational effects, that cannot be explained by [[Baryonic matter|visible matter]] alone, imply the existence of matter which does not or does only very weakly couple to the known forces of Nature. This dark matter dominates the matter density of the Universe, but its particles (if there are any) have eluded direct and indirect detection so far. Given the rich interaction structure of the well-known Standard Model particles, which make up only the subdominant component of the Universe, it is natural to think about a similarly interactive behaviour of dark sector particles. Dark photons could be part of these interactions among dark matter particles and provide a non-gravitational window (a so-called vector portal) into their existence by kinematically mixing with the Standard Model photon.<ref name=":0" /><ref>{{cite arxiv|last=Battaglieri|first=Marco|last2=Belloni|first2=Alberto|last3=Chou|first3=Aaron|last4=Cushman|first4=Priscilla|last5=Echenard|first5=Bertrand|last6=Essig|first6=Rouven|last7=Estrada|first7=Juan|last8=Feng|first8=Jonathan L.|last9=Flaugher|first9=Brenna|date=2017-07-14|title=US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report|eprint=1707.04591|class=hep-ph}}</ref> Further motivation for the search for dark photons comes from several observed anomalies in astrophysics (e.g. in [[cosmic ray]]s) that could be related to dark matter interacting with a dark photon.<ref>{{Cite journal|last=Pospelov|first=Maxim|last2=Ritz|first2=Adam|date=January 2009|title=Astrophysical Signatures of Secluded Dark Matter|journal=Physics Letters B|volume=671|issue=3|pages=391–397|doi=10.1016/j.physletb.2008.12.012|arxiv=0810.1502|bibcode=2009PhLB..671..391P}}</ref><ref>{{Cite journal|last=Arkani-Hamed|first=Nima|last2=Finkbeiner|first2=Douglas P.|last3=Slatyer|first3=Tracy R.|last4=Weiner|first4=Neal|date=2009-01-27|title=A Theory of Dark Matter|journal=Physical Review D|volume=79|issue=1|doi=10.1103/PhysRevD.79.015014|issn=1550-7998|arxiv=0810.0713|bibcode=2009PhRvD..79a5014A}}</ref> Arguably the most interesting application of dark photons arises in the explanation of the discrepancy between the measured and the calculated [[Anomalous magnetic dipole moment|anomalous magnetic moment of the muon]].<ref>{{Cite journal|last=Pospelov|first=Maxim|date=2009-11-02|title=Secluded U(1) below the weak scale|journal=Physical Review D|volume=80|issue=9|doi=10.1103/PhysRevD.80.095002|issn=1550-7998|arxiv=0811.1030|bibcode=2009PhRvD..80i5002P}}</ref><ref>{{Cite journal|last=Endo|first=Motoi|last2=Hamaguchi|first2=Koichi|last3=Mishima|first3=Go|date=2012-11-27|title=Constraints on Hidden Photon Models from Electron g-2 and Hydrogen Spectroscopy|journal=Physical Review D|volume=86|issue=9|doi=10.1103/PhysRevD.86.095029|issn=1550-7998|arxiv=1209.2558|bibcode=2012PhRvD..86i5029E}}</ref><ref>{{Cite journal|last=Giusti|first=D.|last2=Lubicz|first2=V.|last3=Martinelli|first3=G.|last4=Sanfilippo|first4=F.|last5=Simula|first5=S.|date=October 2017|title=Strange and charm HVP contributions to the muon ($g - 2)$ including QED corrections with twisted-mass fermions|journal=Journal of High Energy Physics|volume=2017|issue=10|doi=10.1007/JHEP10(2017)157|issn=1029-8479|arxiv=1707.03019|bibcode=2017JHEP...10..157G}}</ref> This discrepancy is usually thought of as a persisting hint for [[physics beyond the Standard Model]] and should be accounted for by general [[New Physics|new physics]] models. Beside the effect on electromagnetism via kinetic mixing and possible interactions with dark matter particles, dark photons (if massive) can also play the role of a dark matter candidate themselves. This is theoretically possible through the [[misalignment mechanism]].<ref>{{Cite journal|last=Arias|first=Paola|last2=Cadamuro|first2=Davide|last3=Goodsell|first3=Mark|last4=Jaeckel|first4=Joerg|last5=Redondo|first5=Javier|last6=Ringwald|first6=Andreas|date=2012-06-08|title=WISPy Cold Dark Matter|journal=Journal of Cosmology and Astroparticle Physics|volume=2012|issue=6|pages=013–013|doi=10.1088/1475-7516/2012/06/013|issn=1475-7516|arxiv=1201.5902|bibcode=2012JCAP...06..013A}}</ref>

== Theory ==
Adding a sector containing dark photons to the [[Lagrangian (field theory)|Lagrangian]] of the Standard Model can be done in a straightforward and minimal way by introducing a new U(1) [[gauge field]].<ref name=":1" /> The specifics of the interaction between this new field, potential new particle content (e.g. a [[Dirac fermion]] for dark matter) and the Standard Model particles are virtually only limited by the creativity of the theorist and the constraints that have already been put on certain kinds of couplings. The arguably most popular basic model involves a single new broken U(1) gauge symmetry and kinetic mixing between the corresponding dark photon field <math>A^{\prime}</math> and the [[Electroweak interaction|Standard Model hypercharge fields]]. The operator at play is <math>F_{\mu\nu}^\prime B^{\mu\nu}</math>, where <math>F_{\mu\nu}^{\prime}</math> is the [[field strength tensor]] of the dark photon field and <math>B^{\mu\nu}
</math>denotes the field strength tensor of the Standard Model weak hypercharge fields. This term arises naturally by writing down all terms allowed by the gauge symmetry. After [[electroweak symmetry breaking]] and diagonalising the terms containing the field strength tensors (kinetic terms) by redefining the fields, the relevant terms in the Lagrangian are

<math display="block" id="lagrange">\mathcal{L}\supset-\frac{1}{4}F^{\prime\mu\nu}F^{\prime}_{\mu\nu}+\frac{1}{2}m_{A^\prime}^{2}A^{\prime\mu}A^{\prime}_\mu+\epsilon e A^{\prime\mu}J_{\mu}^{EM}</math>

where <math>m_{A^\prime}</math>is the mass of the dark photon (in this case it can be thought of as being generated by the [[Higgs mechanism|Higgs]] or [[Stueckelberg action|Stueckelberg mechansim]]), <math>\epsilon</math> is the parameter describing the kinetic mixing strength and <math>J_{\mu}^{EM}</math>denotes the [[Four-current|electromagnetic current]] with its coupling <math>e</math>. The fundamental parameters of this model are thus the mass of the dark photon and the strength of the kinetic mixing. Other models leave the new U(1) gauge symmetry unbroken, resulting in a massless dark photon carrying a long-range interaction.<ref>{{Cite journal|last=Ackerman|first=Lotty|last2=Buckley|first2=Matthew R.|last3=Carroll|first3=Sean M.|last4=Kamionkowski|first4=Marc|date=2009-01-23|title=Dark Matter and Dark Radiation|journal=Physical Review D|volume=79|issue=2|doi=10.1103/PhysRevD.79.023519|issn=1550-7998|arxiv=0810.5126|bibcode=2009PhRvD..79b3519A}}</ref> A massless dark photon, however, will experimentally be hard to distinguish from the Standard Model photon. The incorporation of new Dirac fermions as dark matter particles in this theory is uncomplicated and can be achieved by simply adding the [[Dirac equation|Dirac terms]] to the Lagrangian.<ref>{{cite arxiv|last=Ilten|first=Philip|last2=Soreq|first2=Yotam|last3=Williams|first3=Mike|last4=Xue|first4=Wei|date=2018-01-15|title=Serendipity in dark photon searches|eprint=1801.04847|class=hep-ph}}</ref>

== See also ==
* [[Dark radiation]]
* [[Fifth force#Possible evidence|Fifth force]]
* [[Dual photon]]
* [[Photino]]

== References ==
{{reflist}}

{{Dark matter}}

[[Category:Bosons]]
[[Category:Dark matter]]
[[Category:Hypothetical elementary particles]]
[[Category:Physics beyond the Standard Model]]

Popular Astronomy (US-Zeitschrift)

2018-02-02T22:06:10Z

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{{Infobox magazine
| logo =
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| editor = 
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| firstdate = September 1893
| finaldate = 1951
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{{about|American magazine published from 1893-1951|the British magazine|Popular Astronomy (UK magazine)}}
'''''Popular Astronomy''''' is an American magazine published by John August Media, LLC and hosted at TechnicaCuriosa.com for [[amateur astronomy|amateur astronomers]]. Prior to its revival in 2009, the title was published between 1893 and 1951.<ref name=has/> It was the successor to ''The Sidereal Messenger'', which was published from March 1882 to 1892.<ref name=has>{{cite journal|author=Smith, H. A.|title=Popular Astronomy Magazine and the Development of Variable Star Observing in the United States|journal=The Journal of the American Association of Variable Star Observers|url=http://adsabs.harvard.edu/full/1980JAVSO...9...40S|date=1980|volume=9|issue=1|pages=40-42|accessdate=30 October 2016|bibcode=1980JAVSO...9...40S}}</ref> The first issue of ''Popular Astronomy'' appeared in September 1893.<ref name="gin"/> Each yearly volume of ''Popular Astronomy'' contained 10 issues,<ref name=has/> for a total of 59 volumes.

The first editor, from 1893-1909, was [[William W. Payne (astronomer)|William W. Payne]] of [[Carleton College]].<ref name=gin>{{cite journal|author=Gingrich, C. H.|title=Popular Astronomy-The first fifty years|journal=Popular Astronomy|date=1943|volume=51|issue=1|url=http://articles.adsabs.harvard.edu//full/1943PA.....51....1G/0000001P001.html|accessdate=30 October 2016}}</ref> Charlotte R. Willard served as co-editor from 1893-1905. He was followed by [[Herbert Couper Wilson|Herbert C. Wilson]], who served in the post between 1909 and 1926.<ref name=gin/>

The magazine played an important role in the development of amateur [[variable star]] observing in the United States.<ref>{{Citation|last=Smith|first=Horace A.|title=''Popular Astronomy'' Magazine and the Development of Variable Star Observing in the United States|magazine=The Journal of the American Association of Variable Star Observers|volume=9|pages=40–42|date=October 1980}}</ref>

In 2017 ''Popular Astronomy'' has returned as part of TechnicaCuriosa.com, along with sister titles Popular Electronics and Mechanix Illustrated.

==References==
{{Reflist}}

[[Category:1893 establishments in the United States]]
[[Category:1951 disestablishments in the United States]]
[[Category:American science and technology magazines]]
[[Category:Astronomy magazines]]
[[Category:Defunct science fiction magazines of the United States]]
[[Category:Magazines established in 1893]]
[[Category:Magazines disestablished in 1951]]
[[Category:Magazines published in Minnesota]]

{{sci-mag-stub}}

Hilda-Gruppe

2018-02-02T03:08:04Z

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[[Image:InnerSolarSystem-en.png|300px|thumb|The asteroids of the [[inner Solar System]] and [[Jupiter]]: The ''Hilda group'' is located between the asteroid belt and the orbit of Jupiter.
{| style="width:100%;"
|-
| valign=top |
{{legend2|#6ad768|border=1px solid #2B9929|[[Jupiter trojan]]s}} 
{{legend2|#007DD6|border=1px solid #00508A|[[Orbit]]s of [[planet]]s}} 
{{legend2|#FFFF00|border=1px solid #B3B300|[[Sun]]}}
| valign=top |
{{legend2|#d39300|border=1px solid #855D00|'''''Hilda group'''''}} 
{{legend2|#e9e9e9|border=1px solid #999999|[[Asteroid belt]]}} 
{{legend2|#c90000|border=1px solid #940000|[[Near-Earth object]]s {{small|(selection)}}}}
|}
]]

The '''Hilda''' or '''Hildian asteroids''' are a ''[[List of minor-planet groups|dynamical group]]''<ref name=Broz2008>{{cite journal |last=Brož |first=M. |author2=Vokrouhlický, D. |title=Asteroid families in the first-order resonances with Jupiter |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=390 |issue=2 |pages=715–732 |date=2008 |doi=10.1111/j.1365-2966.2008.13764.x |bibcode=2008MNRAS.tmp.1068B
}}</ref> of [[asteroid]]s in a 3:2 [[orbital resonance]] with [[Jupiter]]. The namesake is the asteroid [[153 Hilda]]. Hildas move in their elliptical orbits so that their [[apsis|aphelia]] put them opposite Jupiter (at {{L3}}), or 60 degrees ahead of or behind Jupiter at the {{L4}} and {{L5}} [[Lagrangian point]]s.<ref name="easysky">{{cite web |title=The triangle formed by the Hilda asteroids |publisher=EasySky |author=Matthias Busch |url=http://www.easysky.de/eng/screenshots/Hildas.htm |accessdate=2009-12-15
}}</ref> Over three successive orbits each Hilda asteroid approaches all of these three points in sequence. A Hilda's orbit has a [[semi-major axis]] between 3.7 AU and 4.2 AU (the average over a long time span is 3.97), an [[eccentricity (orbit)|eccentricity]] less than 0.3, and an [[inclination]] less than 20°.<ref name="Ohtsukaetal2008">{{cite journal |bibcode = 2008A&A...489.1355O |title = Quasi-Hilda comet 147P/Kushida-Muramatsu. Another long temporary satellite capture by Jupiter |last1 = Ohtsuka |first1 = Katsuhito |last2 = Yoshikawa |first2 = M. |last3 = Asher |first3 = D. J. |last4 = Arakida |first4 = H. |journal = Astronomy and Astrophysics |volume = 489 |issue = 3 |date = October 2008 |pages = 1355–1362 |doi = 10.1051/0004-6361:200810321 |last5 = Arakida |first5 = H.
|arxiv = 0808.2277 }}</ref> Two [[asteroid family|collisional families]] exist within the Hilda group: the Hilda family and the Schubart family.<ref name=Broz_Vokrouhlicky>{{cite journal|last=Brož|first=M.|author2=Vokrouhlický, D.|title=Asteroid families in the first-order resonances with Jupiter|journal=Monthly Notices of the Royal Astronomical Society|date=2008|volume=390|issue=2|pages=715–732|doi=10.1111/j.1365-2966.2008.13764.x|arxiv=1104.4004|bibcode=2008MNRAS.390..715B}}</ref> The namesake for the latter family is [[1911 Schubart]]. There are more than 1,100 known Hilda asteroids including unnumbered objects.<ref name=Broz2008/><ref name="Ohtsukaetal2008" />

Hildas' surface colors often correspond to the low-albedo [[D-type asteroid|D-type]] and [[P-type asteroid|P-type]]; however, a small portion are [[C-type asteroid|C-type]]. D-type and P-type asteroids have surface colors, and thus also surface mineralogies, similar to those of [[cometary nuclei]]. This implies that they share a common origin.<ref name="Ohtsukaetal2008"/><ref>{{cite journal|last=Gil-Hutton|first=R.|author2=Brunini, Adrián|title=Surface composition of Hilda asteroids from the analysis of the Sloan Digital Sky Survey colors|journal=Icarus|volume=193|issue=2|pages=567–571|url=http://sedici.unlp.edu.ar/handle/10915/2097|accessdate=14 April 2014|doi=10.1016/j.icarus.2007.08.026|bibcode=2008Icar..193..567G}}</ref>

== Dynamics ==
The asteroids of the Hilda group (Hildas) are in 3:2 [[orbital resonance|mean-motion resonance]] with Jupiter.<ref name="Ohtsukaetal2008" /> That is, their [[orbital period]]s are 2/3 that of Jupiter. They move along the orbits with a semimajor axis near 4.0 AU and moderate values of eccentricity (up to 0.3) and inclination (up to 20°). Unlike the [[Jupiter trojan]]s they may have any difference in longitude with Jupiter, nevertheless avoiding dangerous approaches to the planet.

The Hildas taken together constitute a dynamic triangular figure with slightly convex sides and trimmed apexes in the triangular libration points of Jupiter—the "Hildas Triangle".<ref name="easysky"/> The "asteroidal stream" within the sides of the triangle is about 1 [[astronomical unit|AU]] wide, and in the apexes this value is 20-40% greater. Figure 1 shows the positions of the Hildas (black) against a background of all known asteroids (gray) up to Jupiter's orbit at January 1, 2005.<ref>L'vov V.N., Smekhacheva R.I., Smirnov S.S., Tsekmejster S.D. Some peculiarities in the Hildas motion. Izv. Pulkovo Astr. Obs., 2004, 217, 318-324 (in Russian)</ref>

Each of the Hilda objects moves along its own [[Kepler's laws of planetary motion|elliptic orbit]]. However, at any moment the Hildas together constitute this triangular configuration, and all the orbits together form a predictable ring. Figure 2 illustrates this with the Hildas positions (black) against a background of their orbits (gray). For the majority of these asteroids, their position in orbit may be arbitrary, except for the external parts of the apexes (the objects near aphelion) and the middles of the sides (the objects near perihelion). The Hildas Triangle has proven to be dynamically stable over a long time span.

[[Image:Hildas01.jpg|thumb|left|525px|Left: The Hildas Triangle against a background of all known asteroids up to Jupiter's orbit. Right: The positions of the Hildas against a background of their orbits.]]

The typical Hilda object has a [[Retrograde motion|retrograde perihelion motion]]. On average, the velocity of perihelion motion is greater when the orbital eccentricity is lesser, while the nodes move more slowly. All typical objects in aphelion would seemingly approach closely to Jupiter, which should be destabilising for them—but the variation of the orbital elements over time prevents this, and [[conjunction (astronomy and astrology)|conjunctions]] with Jupiter occur only near the perihelion of Hilda asteroids. Moreover, the [[Apsis|apsidal]] line oscillates near the line of conjunction with different amplitude and a period of 2.5 to 3.0 centuries.

[[File:HildasOrbitWithLagrangePointsLousy.gif|frame|right|A schematic of the orbit of [[153 Hilda]] (green), with [[Jupiter]] (red)]][[Image:hildas02.gif|thumb|300px|Hildas (black) and Trojans viewed from the ecliptic plane near 190 degrees longitude on Jan. 1, 2005]]
In addition to the fact that the Hildas triangle revolves in sync with Jupiter, the density of asteroids in the stream exhibits quasi-periodical waves. At any time, the density of objects in the triangle's apexes is more than twice the density within the sides. The Hildas "rest" at their aphelia in the apexes for an average of 5.0-5.5 years, whereas they move along the sides more quickly, averaging 2.5 to 3.0 years. The [[orbital period]]s of these asteroids are approximately 7.9 years, or two thirds that of Jupiter.

Although the triangle is nearly [[equilateral]], some asymmetry exists. Due to the eccentricity of Jupiter's orbit, the side {{L4}}-{{L5}} slightly differs from the two other sides. When Jupiter is in [[aphelion]], the mean velocity of the objects moving along this side is somewhat smaller than that of the objects moving along the other two sides. When Jupiter is in [[perihelion]], the reverse is true.

At the apexes of the triangle corresponding to the points {{L4}} and {{L5}} of Jupiter's orbit, the Hildas approach the [[Trojan asteroid|Trojans]]. At the mid-sides of the triangle, they are close to the asteroids of the external part of the [[asteroid belt]]. The velocity dispersion of Hildas is more evident than that of Trojans in the regions where they intersect. It should also be noted that the dispersion of Trojans in [[inclination]] is twice that of the Hildas. Due to this, as much as one quarter of the Trojans cannot intersect with the Hildas, and at all times many Trojans are located outside Jupiter's orbit. Therefore, the regions of intersection are limited. This is illustrated by the adjacent figure that shows the Hildas (black) and the Trojans (gray) along the [[plane of the ecliptic|ecliptic plane]]. One can see the spherical form of the Trojan swarms.

When moving along each side of the triangle, the Hildas travel more slowly than the Trojans, but encounter a denser neighborhood of outer-asteroid-belt asteroids. Here, the velocity dispersion is much smaller.

[[File:Hilda asteroid as seen from Jupiter.png|thumb|Orbits of two idealized asteroids of the Hilda family, in the rotating reference frame of Jupiter's orbit. Black: eccentricity 0.310; aphelion at Jupiter's orbit. Red: eccentricity 0.211.]]

== Research ==
The observed peculiarities in the Hildas' motion are based on data for a few hundred objects known to date and generate still more questions. Further observations are needed to expand on the list of Hildas. Such observations are most favorable when Earth is near [[conjunction (astronomy and astrology)|conjunction]] with the mid-sides of the Hildas Triangle. These moments occur each 4 and 1/3 months. In these circumstances the [[luminosity#In astronomy|brilliance]] of objects of similar size could run up to 2.5 magnitudes as compared to the apexes.{{cn|date=September 2017}}

The Hildas traverse regions of the Solar system from approximately 2 AU up to Jupiter's orbit. This entails a variety of physical conditions and the neighborhood of various groups of asteroids. On further observation some theories on the Hildas may have to be revised.{{cn|date=September 2017}}

==References==
{{reflist}}

{{Small Solar System bodies}}

{{DEFAULTSORT:Hilda Family}}
[[Category:Hilda asteroids|*]]
[[Category:Jupiter]]

Biosignatur

2018-02-01T10:49:18Z

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{{other uses2|Biomarker}}
A '''biosignature''' (sometimes called '''chemical fossil''' or '''molecular fossil''') is any substance – such as an element, [[isotope]], [[molecule]], or [[phenomenon]] – that provides [[scientific evidence]] of past or present [[life]].<ref name=SSG >{{Cite book| last2=Beaty | last=Steele| contribution=Final report of the MEPAG Astrobiology Field Laboratory Science Steering Group (AFL-SSG)| title=The Astrobiology Field Laboratory | publisher=the Mars Exploration Program Analysis Group (MEPAG) - NASA| place=U.S.A.| pages=72| date=September 26, 2006| id= | contribution-url=http://mepag.jpl.nasa.gov/reports/AFL_SSG_WHITE_PAPER_v3.doc| chapter-format=.doc| postscript=. |display-authors=etal}}</ref><ref>{{cite web | url = http://www.science-dictionary.com/definition/biosignature.html | archive-url = https://web.archive.org/web/20100316062919/http://www.science-dictionary.com/definition/biosignature.html | dead-url = yes | archive-date = 2010-03-16 | title = Biosignature - definition | accessdate = 2011-01-12 | year = 2011 | work = Science Dictionary }}</ref><ref name='Biosignatures 2011'>{{cite journal | title = Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group | journal = Astrobiology | date = 23 February 2011 | first = Roger E. | last = Summons |author2=Jan P. Amend |author3=David Bish |author4=Roger Buick |author5=George D. Cody |author6=David J. Des Marais | volume = 11 | issue = 2 | pages = 157–81 | doi = 10.1089/ast.2010.0506 | url = http://eaps.mit.edu/geobiology/recent%20pubs/AST-2010-0506-Summons_Mars%20Taphonomy.pdf | accessdate = 2013-06-22|bibcode = 2011AsBio..11..157S | pmid=21417945| last7 = Dromart | first7 = G | last8 = Eigenbrode | first8 = J. L. | last9 = Knoll | first9 = A. H. | last10 = Sumner | first10 = D. Y. }}</ref> Measurable attributes of life include its complex physical and chemical structures and also its utilization of [[Thermodynamic free energy|free energy]] and the production of [[biomass]] and [[Cellular waste product|wastes]]. Due to its unique characteristics, a biosignature can be interpreted as having been produced by living [[organisms]]; however, it is important that they not be considered definitive because there is no way of knowing in advance which ones are universal to life and which ones are unique to the peculiar circumstances of life on Earth.<ref>{{cite web | url = http://astrobiology.nasa.gov/nai/library-of-resources/annual-reports/2003/cub/projects/philosophical-issues-in-astrobiology/ | title = Philosophical Issues in Astrobiology | accessdate = 2011-04-15 | author = Carol Cleland | author2 = Gamelyn Dykstra | author3 = Ben Pageler | year = 2003 | publisher = NASA Astrobiology Institute | deadurl = yes | archiveurl = https://web.archive.org/web/20110721213308/http://astrobiology.nasa.gov/nai/library-of-resources/annual-reports/2003/cub/projects/philosophical-issues-in-astrobiology/ | archivedate = 2011-07-21 | df = }}</ref> Nonetheless, [[life forms]] are known to shed unique chemicals, including [[DNA]], into the [[Natural environment|environment]] as evidence of their presence in a particular location.<ref name="NYT-20150122">{{cite news |last=Zimmer |first=Carl |authorlink=Carl Zimmer |title=Even Elusive Animals Leave DNA, and Clues, Behind |url=https://www.nytimes.com/2015/01/27/science/even-elusive-animals-leave-dna-and-clues-behind.html |date=January 22, 2015 |work=[[New York Times]] |accessdate=January 23, 2015 }}</ref>

==In geomicrobiology==
{{Life timeline}}
[[File:Calcidiscus leptoporus 05.jpg|thumb|left|200px|Electron micrograph of microfossils from a sediment core obtained by the [[Deep Sea Drilling Program]] ]]
The ancient record on Earth provides an opportunity to see what geochemical signatures are produced by microbial life and how these signatures are preserved over geologic time. Some related disciplines such as [[geochemistry]], [[geobiology]], and [[geomicrobiology]] often use biosignatures to determine if living [[organism]]s are or were present in a sample. These possible biosignatures include: (a) [[microfossils]] and [[stromatolites]]; (b) molecular structures ([[biomarkers]]) and [[Isotope|isotopic compositions]] of carbon, nitrogen and hydrogen in [[organic matter]]; (c) multiple sulfur and oxygen isotope ratios of minerals; and (d) abundance relationships and isotopic compositions of redox sensitive metals (e.g., Fe, Mo, Cr, and rare earth elements).<ref name='PSARC'>{{cite web | url = http://php.scripts.psu.edu/dept/psarc/index.php?page=executive-summary | title = SIGNATURES OF LIFE FROM EARTH AND BEYOND | accessdate = 2011-01-14 | year = 2009 | work = Penn State Astrobiology Research Center (PSARC) | publisher = Penn State}}</ref><ref>{{cite web | url = http://astrobiology.nasa.gov/articles/2008/7/30/reading-archaean-biosignatures/ | title = Reading Archaean Biosignatures | accessdate = 2014-11-23 | first1 = David | last1 = Tenenbaum | date = July 30, 2008 | publisher = NASA | deadurl = yes | archiveurl = https://web.archive.org/web/20141129094552/http://astrobiology.nasa.gov/articles/2008/7/30/reading-archaean-biosignatures/ | archivedate = November 29, 2014 | df = }}</ref>

For example, the particular [[fatty acids]] measured in a sample can indicate which types of [[bacterium|bacteria]] and [[archaea]] live in that environment. Another example are the long-chain [[fatty alcohol]]s with more than 23 atoms that are produced by [[plankton]]ic [[bacteria]].<ref>[http://www.cyberlipid.org/simple/simp0003.htm Fatty alcohols]</ref> When used in this sense, geochemists often prefer the term [[biomarker]]. Another example is the presence of straight-chain [[lipids]] in the form of [[alkanes]], [[alcohols]] an [[fatty acids]] with 20-36 [[carbon]] atoms in soils or sediments. [[Peat]] deposits are an indication of originating from the [[epicuticular wax]] of higher [[plant]]s.

Life processes may produce a range of biosignatures such as [[nucleic acids]], [[lipid]]s, [[protein]]s, [[amino acid]]s, [[kerogen]]-like material and various morphological features that are detectable in rocks and sediments.<ref name=Beegle >{{cite journal|title=A Concept for NASA's Mars 2016 Astrobiology Field Laboratory |journal=Astrobiology|date=August 2007|first=Luther W.|last=Beegle|volume=7 |issue=4|pages=545–577|id= |url=http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0153?cookieSet=1|accessdate=2009-07-20|doi=10.1089/ast.2007.0153|postscript=. |pmid=17723090 |bibcode=2007AsBio...7..545B|first2=Michael G.|last2=Wilson |last3=Abilleira|first3=Fernando|last4=Jordan|first4=James F.|last5=Wilson|first5=Gregory R.|display-authors=etal}}</ref>
[[Microbes]] often interact with geochemical processes, leaving features in the rock record indicative of biosignatures. For example, bacterial micrometer-sized pores in [[carbonate rock]]s resemble inclusions under transmitted light, but have distinct size, shapes and patterns (swirling or dendritic) and are distributed differently from common fluid inclusions.<ref>{{cite journal | title = Micrometer-scale porosity as a biosignature in carbonate crusts | last1 = Bosak | journal = Geology | date = May 18, 2004 | first = Tanja Bosak | author2 = Virginia Souza-Egipsy | author3 = Frank A. Corsetti | author4 = Dianne K. Newman | last-author-amp = yes | volume = 32 | issue = 9 | pages = 781–784 | doi = 10.1130/G20681.1 | url = http://geology.gsapubs.org/content/32/9/781.abstract | accessdate = 2011-01-14 | bibcode=2004Geo....32..781B}}</ref> A potential biosignature is a phenomenon that ''may'' have been produced by life, but for which alternate [[Abiotic component|abiotic]] origins may also be possible.

==In astrobiology==

[[Astrobiology|Astrobiological exploration]] is founded upon the premise that biosignatures encountered in space will be recognizable as [[extraterrestrial life]]. The usefulness of a biosignature is determined, not only by the probability of life creating it, but also by the improbability of nonbiological (abiotic) processes producing it.<ref name=astrobiology>{{cite web|url=http://astrobiology.arc.nasa.gov/roadmap/g5.html |title=Understand the evolutionary mechanisms and environmental limits of life |accessdate=2009-07-13 |last=Rothschild |first=Lynn |date=September 2003 |publisher=NASA |deadurl=yes |archiveurl=https://web.archive.org/web/20110126083203/http://astrobiology.arc.nasa.gov/roadmap/g5.html |archivedate=2011-01-26 |df= }}</ref> Concluding that evidence of an extraterrestrial life form (past or present) has been discovered, requires proving that a possible biosignature was produced by the activities or remains of life.<ref name=SSG /> As with most scientific discoveries, discovery of a biosignature will require of evidence building up until no other explanation exists.

Possible examples of a biosignature might be complex [[Organic compound|organic molecules]] and/or structures whose formation is virtually unachievable in the absence of life. For example, cellular and extracellular morphologies, [[biomolecule]]s in rocks, bio-organic molecular structures, [[chirality]], [[Biogenic silica|biogenic minerals]], biogenic stable isotope patterns in minerals and organic compounds, atmospheric gases, and remotely detectable features on planetary surfaces, such as [[photosynthetic pigment]]s, etc.<ref name=astrobiology />

;Categories
In general, biosignatures and habitable environment signatures can be grouped into ten broad categories: <ref name='NASA strategy 2015'/>
#Stable [[isotope]] patterns: Isotopic evidence or patterns that require biological processes.
#Chemistry: Chemical features that require biological activity.
#[[Organic matter]]: Organics formed by biological processes.
#Minerals: Minerals or biomineral-phases whose composition and/or morphology indicate biological activity (e.g., [[Magnetite|biomagnetite]]).
#Microscopic structures and textures: Biologically formed cements, microtextures, microfossils, and films.
#Macroscopic physical structures and textures: Structures that indicate microbial ecosystems, biofilms (e.g., [[stromatolite]]s), or [[fossil]]s of larger organisms.
#Temporal variability: Variations in time of atmospheric gases, reflectivity, or macroscopic appearance that indicate the presence of life.
#Surface reflectance features: Large-scale reflectance features due to biological pigments, which could be detected remotely.
#Atmospheric gases: Gases formed by metabolic and/or aqueous processes, which may be present on a planet-wide scale.
#Technosignatures: Biosignatures that indicate a technologically advanced civilization.

===Chemical===

No single compound will prove life once existed. Rather, it will be distinctive patterns present in any organic compounds showing a process of selection.<ref name='PhysOrg Cousins 2018'>[https://phys.org/news/2018-01-rover-life-mars-proveit.html Rover could discover life on Mars – here's what it would take to prove it]. Claire Cousins, ''PhysOrg''. 5 January 2018.</ref> For example, [[membrane lipid]]s left behind by degraded cells will be concentrated, have a limited size range, and comprise an even number of carbons. Similarly, life only uses left-handed amino acids.<ref name='PhysOrg Cousins 2018'/> Biosignatures need not be chemical, however, and can also be suggested by a distinctive [[magnetic]] biosignature.<ref name="Wall-20111213">{{cite web |last=Wall |first=Mike |title=Mars Life Hunt Could Look for Magnetic Clues |url=http://www.space.com/13911-mars-life-search-magnetic-signatures.html |date=13 December 2011 |publisher=[[Space.com]] |accessdate=2011-12-15 }}</ref>

On [[Mars]], surface oxidants and UV radiation will have altered or destroyed organic molecules at or near the surface.<ref name='Biosignatures 2011'/> One issue that may add ambiguity in such a search is the fact that, throughout Martian history, abiogenic organic-rich [[Chondrite|chondritic meteorite]]s have undoubtedly rained upon the Martian surface. At the same time, strong [[Oxidizing agent|oxidants]] in [[Martian soil]] along with exposure to [[ionizing radiation]] might alter or destroy molecular signatures from meteorites or organisms.<ref name='Biosignatures 2011'/> An alternative approach would be to seek concentrations of buried crystalline minerals, such as [[clay]]s and [[evaporite]]s, which may protect organic matter from the destructive effects of [[ionizing radiation]] and strong oxidants.<ref name='Biosignatures 2011'/> The search for Martian biosignatures has become
more promising due to the discovery that surface and near-surface aqueous environments existed on Mars at the same time when biological organic matter was being preserved in ancient aqueous sediments on Earth.<ref name='Biosignatures 2011'/>

===Morphology===

[[File:ALH84001 structures.jpg|thumb|left|200px|Some researchers suggested that these microscopic structures on the Martian [[ALH84001]] meteorite could be fossilized bacteria.<ref name=disbelief>{{cite web | title=After 10 years, few believe life on Mars | url=https://www.usatoday.com/tech/science/space/2006-08-06-mars-life_x.htm | last=Crenson | first=Matt | publisher=[[Associated Press]] (on usatoday.com) | date=2006-08-06 | accessdate=2009-12-06}}</ref><ref name="life">{{cite journal |last=McKay |first=David S. |year=1996 |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |journal=Science |pmid=8688069 |volume=273 |issue=5277 |pages=924–930 |doi=10.1126/science.273.5277.924 |url= |accessdate= |bibcode=1996Sci...273..924M|first2=Everett K.|last2= Gibson Jr|last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |display-authors=etal}}</ref>]]

Another possible biosignature might be [[Morphology (biology)|morphology]] since the shape and size of certain objects may potentially indicate the presence of past or present life. For example, microscopic [[magnetite]] crystals in the Martian [[meteorite]] [[ALH84001]] were the longest-debated of several potential biosignatures in that specimen because it was believed until recently that only bacteria could create crystals of their specific shape. For example, the possible [[Biomineralisation|biomineral]] studied in the Martian [[ALH84001|ALH84001 meteorite]] includes putative microbial [[fossils]], tiny rock-like structures whose shape was a potential biosignature because it resembled known bacteria. Most scientists ultimately concluded that these were far too small to be fossilized [[cell (biology)|cell]]s. A consensus that has emerged from these discussions, and is now seen as a critical requirement, is the demand for further lines of evidence in addition to any morphological data that supports such extraordinary claims.<ref name=SSG /> Currently, the scientific consensus is that "morphology alone cannot be used unambiguously as a tool for primitive life detection."<ref name=morphology>{{cite journal | title = Morphological behavior of inorganic precipitation systems – Instruments, Methods, and Missions for Astrobiology II | journal = SPIE Proceedings | date = December 30, 1999 | first = Juan-Manuel Garcia-Ruiz | volume = Proc. SPIE 3755 | pages = 74 | doi = 10.1117/12.375088 | url = http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=995013 | accessdate = 2013-01-15 | quote = It is concluded that "morphology cannot be used unambiguously as a tool for primitive life detection."| series = Instruments, Methods, and Missions for Astrobiology II | last1 = Garcia-Ruiz }}</ref><ref>{{cite news|author=Agresti|author2=House|author3=Jögi|author4=Kudryavstev|author5=McKeegan|author6=Runnegar|author7=Schopf|author8=Wdowiak|title=Detection and geochemical characterization of Earth's earliest life|date=3 December 2008|publisher=NASA|url=http://astrobiology.ucla.edu/pages/res3e.html|work=NASA Astrobiology Institute|accessdate=2013-01-15|deadurl=yes|archiveurl=https://web.archive.org/web/20130123132429/http://astrobiology.ucla.edu/pages/res3e.html|archivedate=23 January 2013|df=}}</ref><ref>{{cite journal | title = Evidence of Archean life: Stromatolites and microfossils | journal = Precambrian Research | date = 28 April 2007 | first = J. William|last= Schopf |first2=Anatoliy B.|last2=Kudryavtsev|first3=Andrew D.|last3=Czaja|first4=Abhishek B.|last4=Tripathi| volume = 158 | issue = 3–4 | pages = 141–155 | url = http://www.cornellcollege.edu/geology/courses/greenstein/paleo/schopf_07.pdf | format = PDF | accessdate = 2013-01-15 | doi=10.1016/j.precamres.2007.04.009|bibcode = 2007PreR..158..141S }}</ref> Interpretation of morphology is notoriously subjective, and its use alone has led to numerous errors of interpretation.<ref name=morphology/>

===Atmospheric properties and composition===

[[File:PIA19088-MarsCuriosityRover-MethaneSource-20141216.png|thumb|250px|[[Atmosphere of Mars#Methane|Methane]] (CH4) on Mars - potential sources and sinks.]]
The atmospheric properties of exoplanets are of particular importance, as atmospheres provide the most likely observables for the near future, including habitability indicators and biosignatures. Over billions of years, the processes of life on a planet would result in a mixture of chemicals unlike anything that could form in an ordinary chemical equilibrium.<ref>{{cite web | url = https://www.technologyreview.com/blog/arxiv/26247/ | title = Artificial Life Shares Biosignature With Terrestrial Cousins | accessdate = 2011-01-14 | date = 10 January 2011 | work = The Physics arXiv Blog | publisher = MIT}}</ref><ref name="Seager 2017">{{cite journal |title=Toward a List of Molecules as Potential Biosignature Gases for the Search for Life on Exoplanets and Applications to Terrestrial Biochemistry |journal=Astrobiology |volume=16 |issue=6 |pages=465–85 |date=20 April 2016 |last=Seager |first=Sara |last2=Bains |first2=William |last3=Petkowski |first3=Janusz |doi=10.1089/ast.2015.1404 |pmid=27096351 |url=http://online.liebertpub.com/doi/full/10.1089/ast.2015.1404 |accessdate=2016-05-07 |bibcode=2016AsBio..16..465S }}</ref> For example, large amounts of [[oxygen]] and small amounts of [[methane]] are generated by life on Earth.

Also, an exoplanet's color —or reflectance spectrum— might give away the presence of vast colonies of life forms at its surface.<ref name="Berdyugina 2016">{{cite journal |title=Remote sensing of life: polarimetric signatures of photosynthetic pigments as sensitive biomarkers |journal=International Joural of Astrobiology |date=January 2016 |last=Berdyugina |first=Svetlana V. |last2=Kuhn |first2=Jeff |last3=Harrington |first3=David |last4=Santl-Temkiv |first4= Tina |last5=Messersmith |first5=E. John |volume=15 |issue=1 |pages=45–56 |doi=10.1017/S1473550415000129 |bibcode=2016IJAsB..15...45B }}</ref><ref>{{cite journal |title=Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life |journal=PNAS|date=31 March 2015 |last=Hegde |first=Siddharth |last2=Paulino-Lima |first2=Ivan G. |last3=Kent |first3=Ryan |last4=Kaltenegger |first4=Lisa |last5= Rothschild |first5=Lynn |volume=112 |issue=13 |pages=3886–3891 |doi=10.1073/pnas.1421237112 |pmid=25775594|url=http://www.pnas.org/content/112/13/3886.short |accessdate=2015-05-11 |bibcode = 2015PNAS..112.3886H |pmc=4386386}}</ref><ref name="ColorCatalog">{{cite news |last=Cofield |first=Calla |url=http://www.space.com/28906-alien-life-earth-microbe-catalog.html |title=Catalog of Earth Microbes Could Help Find Alien Life |work=Space.com |date=30 March 2015 |accessdate=2015-05-11 }}</ref><ref>{{cite web |url=https://www.researchgate.net/profile/Marco_Sergio_Erculiani/publication/277174176_SIMULATING_SUPER_EARTH_ATMOSPHERES_IN_THE_LABORATORY/links/5564386708ae8c0cab3706e9.pdf |format=PDF |title=SIMULATING SUPER EARTH ATMOSPHERES IN THE LABORATORY |last=Claudi |first=R. |last2=Erculiani |first2=M.S. |date=January 2015 |accessdate=2016-05-07 }}</ref>

The presence of [[Atmospheric methane|methane in the atmosphere]] of [[Mars]] indicates that there must be an active source on the planet, as it is an unstable [[gas]]. Furthermore, current photochemical models cannot explain the presence of methane in the atmosphere of Mars and its reported rapid variations in space and time. Neither its fast appearance nor disappearance can be explained yet.<ref>[http://mepag.jpl.nasa.gov/decadal/TGM_Mars_Panel-cleared-9-4-09.ppt Mars Trace Gas Mission] {{webarchive|url=https://web.archive.org/web/20110721052957/http://mepag.jpl.nasa.gov/decadal/TGM_Mars_Panel-cleared-9-4-09.ppt |date=2011-07-21 }} (September 10, 2009)</ref> To rule out a biogenic origin for the methane, a future probe or lander hosting a [[mass spectrometer]] will be needed, as the isotopic proportions of [[carbon-12]] to [[carbon-14]] in methane could distinguish between a biogenic and non-biogenic origin, similarly to the use of the [[δ13C]] standard for recognizing biogenic methane on Earth.<ref name="nasa">[http://rst.gsfc.nasa.gov/Sect19/Sect19_13a.html Remote Sensing Tutorial, Section 19-13a] {{webarchive|url=https://web.archive.org/web/20111021072805/http://rst.gsfc.nasa.gov/Sect19/Sect19_13a.html |date=2011-10-21 }} - Missions to Mars during the Third Millennium, Nicholas M. Short, Sr., et al., NASA</ref> In June, 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of [[life on Mars (planet)|life on Mars]].<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |url=http://www.pnas.org/content/109/25/9750.abstract |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |accessdate=June 27, 2012 |bibcode = 2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web|author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> The planned [[ExoMars Trace Gas Orbiter]], launched in March 2016 to Mars, will study [[Atmosphere of Mars|atmospheric trace gases]] and will attempt to characterize potential biochemical and geochemical processes at work.<ref name='June 2011'>{{citation |author1= Mark Allen |author2= = Olivier Witasse | contribution = 2016 ESA/NASA ExoMars Trace Gas Orbiter | title = MEPAG June 2011 | publisher = Jet Propulsion Laboratory | date = June 16, 2011| id = | contribution-url = http://mepag.jpl.nasa.gov/meeting/jun-11/13-EMTGO_MEPAG_June2011_presentation-rev2.pdf }} (PDF)</ref>

Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet t Boötis b |url=http://www.nature.com/nature/journal/v486/n7404/full/nature11161.html?WT.ec_id=NATURE-20120628 |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |accessdate=June 28, 2012 |arxiv = 1206.6109 |bibcode = 2012Natur.486..502B |issue=7404 |pmid=22739313}}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=https://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)|Wired]] |accessdate=June 28, 2012 }}</ref> Habitability indicators and biosignatures must be interpreted within a planetary and environmental context.<ref name='NASA strategy 2015'>[https://nai.nasa.gov/media/medialibrary/2015/10/NASA_Astrobiology_Strategy_2015_151008.pdf NASA Astrobiology Strategy 2015].(PDF), NASA </ref> For example, the presence of oxygen and methane together could indicate the kind of extreme thermochemical disequilibrium generated by life.<ref>[http://www.physics.umd.edu/courses/Phys371/AnlageSpring17/Where%20are%20they.pdf Where are they?] (PDF) Mario Livio and Joseph Silk. ''Physics Today'', March 2017.</ref> Two of the top 14,000 proposed atmospheric biosignatures are [[dimethyl sulfide]] and chloromethane ({{chem|CH|3|Cl}}).<ref name="Seager 2017"/> An alternative biosignature is the combination of methane and carbon dioxide.<ref name="SPC-20180124">{{cite web |last=Wall |first=Mike |title=Alien Life Hunt: Oxygen Isn't the Only Possible Sign of Life |url=https://www.space.com/39476-alien-life-biosignature-gases-oxygen.html |date=24 January 2018 |work=[[Space.com]] |accessdate=24 January 2018 }}</ref><ref name="SA-20180124">{{cite journal |last1=Krissansen-Totton |first1=Joshua |last2=Olson |first2=Stephanie |last3=Catlig |first3=David C. |title=Disequilibrium biosignatures over Earth history and implications for detecting exoplanet life |url=http://advances.sciencemag.org/content/4/1/eaao5747 |date=24 January 2018 |volume=4 |number=1, eaao5747 |doi=10.1126/scidv.aao5747 |accessdate=24 January 2018 }}</ref>

===Indirect evidence===

Scientific observations include the possible identification of biosignatures through indirect observation. For example, [[Electromagnetic radiation|electromagnetic]] information through infrared radiation telescopes, radio-telescopes, space telescopes, etc.<ref name='Gardner'>{{cite web | url = http://www.kurzweilai.net/the-physical-constants-as-biosignature-an-anthropic-retrodiction-of-the-selfish-biocosm-hypothesis | title = The Physical Constants as Biosignature: An anthropic retrodiction of the Selfish Biocosm Hypothesis | accessdate = 2011-01-14 | last = Gardner | first = James N. | date = February 28, 2006 | publisher = Kurzweil}}</ref><ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> From this discipline, the hypothetical electromagnetic radio signatures that [[SETI]] scans for would be a biosignature, since a message from intelligent aliens would certainly demonstrate the existence of extraterrestrial life.

===Robotic surface missions===
;The ''Viking'' missions to Mars
{{Main article|Viking biological experiments}}
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] with a model of the ''Viking'' lander]]
The [[Viking Lander|''Viking'' missions]] to Mars in the 1970s conducted the first experiments which were explicitly designed to look for biosignatures on another planet. Each of the two [[Viking program|''Viking'' landers]] carried three [[Viking Biological Experiments|life-detection experiments]] which looked for signs of [[metabolism]]; however, the results were declared inconclusive.<ref name=Beegle /><ref>Levin, G and P. Straaf. 1976. Viking Labeled Release Biology Experiment: Interim Results. Science: vol: 194. pp: 1322-1329.</ref><ref name="Chambers">{{Cite book| first = Paul | last = Chambers| title = Life on Mars; The Complete Story|place = London| publisher = Blandford| year = 1999 |isbn = 0-7137-2747-0}}</ref><ref>{{cite journal | title = The Viking Biological Investigation: Preliminary Results |journal = Science|date = 1976-10-01 |first = Harold P. | last = Klein|author2=Levin, Gilbert V. | volume = 194 | issue = 4260 | pages = 99–105 | doi = 10.1126/science.194.4260.99 | url = http://www.sciencemag.org/cgi/content/abstract/194/4260/99 | accessdate = 2008-08-15
| pmid = 17793090 | bibcode=1976Sci...194...99K|last3 = Levin|first3 = Gilbert V.|last4 = Oyama|first4 = Vance I.|last5 = Lederberg|first5 = Joshua|last6 = Rich|first6 = Alexander|last7 = Hubbard|first7 = Jerry S.|last8 = Hobby|first8 = George L.|last9 = Straat|first9 = Patricia A.|last10 = Berdahl|first10 = Bonnie J.|last11 = Carle|first11 = Glenn C.|last12 = Brown|first12 = Frederick S.|last13 = Johnson|first13 = Richard D.}}</ref><ref name=ExoMars>[http://www.esa.int/SPECIALS/ExoMars/SEMK39JJX7F_0.html ExoMars rover]</ref>

;Mars Science Laboratory
{{Main article|Timeline of Mars Science Laboratory}}
The ''Curiosity'' rover from the [[Mars Science Laboratory]] mission, with its [[Curiosity rover|''Curiosity'' rover]] is currently assessing the potential past and present [[planetary habitability|habitability]] of the Martian environment and is attempting to detect biosignatures on the surface of Mars.<ref name='Biosignatures 2011'/> Considering the MSL instrument payload package, the following classes of biosignatures are within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases.<ref name='Biosignatures 2011'/> The ''Curiosity'' rover targets [[outcrop]]s to maximize the probability of detecting 'fossilized' [[organic matter]] preserved in sedimentary deposits.

;ExoMars rover
The 2016 ExoMars [[Trace Gas Orbiter]] (TGO) is a Mars telecommunications orbiter and atmospheric gas analyzer mission. It delivered the [[Schiaparelli EDM lander|''Schiaparelli'' EDM lander]] and then began to settle into its science orbit to map the sources of [[Atmosphere of Mars#Methane|methane on Mars]] and other gases, and in doing so, will help select the landing site for the [[ExoMars (rover)|ExoMars rover]] to be launched in 2020.<ref>{{cite news | first = Boris | last = Pavlishchev | title = ExoMars program gathers strength | date = Jul 15, 2012 | url = http://english.ruvr.ru/2012_07_15/ExoMars-program-gathers-strength/ | work = The Voice of Russia | accessdate = 2012-07-15}}</ref> The primary objective of the ExoMars rover mission is the search for biosignatures on the surface and subsurface by using a drill able to collect samples down to a depth of {{convert|2|m|ft}}, away from the destructive radiation that bathes the surface.<ref name=ExoMars/><ref name="MSL-main_page">{{cite web|title=Mars Science Laboratory: Mission |url= http://marsprogram.jpl.nasa.gov/msl/mission/ |publisher=NASA/JPL |accessdate=2010-03-12 }}</ref>

;Mars 2020 Rover

The [[Mars 2020]] rover, planned to launch in 2020, is intended to investigate an [[astrobiology|astrobiologically]] relevant ancient environment on Mars, investigate its surface [[Geology of Mars|geological processes]] and history, including the assessment of its past [[Planetary habitability|habitability]], the possibility of past [[life on Mars]], and potential for preservation of biosignatures within accessible geological materials.<ref name="AP-20130709">{{cite news |last=Chang |first=Alicia |title=Panel: Next Mars rover should gather rocks, soil |url=http://apnews.excite.com/article/20130709/DA7EA0K83.html |date=July 9, 2013 |agency=[[Associated Press]] |accessdate=July 12, 2013}}</ref><ref name="nasa-letapp20121220">{{cite web |url=https://mepag.jpl.nasa.gov/announcements/Call_for_2020_Mars_Science_Rover-G.pdf |title=Call for ''Letters of Application'' for Membership on the Science Definition Team for the 2020 Mars Science Rover |publisher=NASA |first=Mitch |last=Schulte |date=December 20, 2012 |id=NNH13ZDA003L}}</ref> In addition, it will cache the most interesting samples for possible future transport to Earth.

;Titan Dragonfly
The planned [[Dragonfly (spacecraft)|Dragonfly]] lander/aircraft to launch in 2025, would seek evidence of biosignatures on the organic-rich surface and atmosphere of [[Titan (moon)|Titan]], as well as study its possible prebiotic [[primordial soup]].<ref>[http://adsabs.harvard.edu/abs/2017DPS....4921902B Dragonfly: Exploring Titan's Surface with a New Frontiers Relocatable Lander]. American Astronomical Society, DPS meeting #49, id.219.02. October 2017.</ref><ref name='LPSC 2017'>[https://www.hou.usra.edu/meetings/lpsc2017/eposter/1958.pdf Dragonfly: Exploring Titan's Prebiotic Organic Chemistry and Habitability] (PDF). E. P. Turtle, J. W. Barnes, M. G. Trainer, R. D. Lorenz, S. M. MacKenzie, K. E. Hibbard, D. Adams, P. Bedini, J. W. Langelaan, K. Zacny, and the Dragonfly Team. ''Lunar and Planetary Science Conference 2017''.</ref>

==See also==
{{div col|2}}
* [[Bioindicator]]
* [[Biomarker]]
* [[Biomolecule]]
* [[Template:Life timeline|Life timeline]]
* [[Template:Nature timeline|Nature timeline]]
* [[Planetary habitability]]
* [[Taphonomy]]
* [[Technosignature]]
{{div col end}}

== References ==
{{reflist|colwidth=30em}}

{{Astrobiology}}
{{Extraterrestrial life}}
{{Portal bar|Astrobiology}}

[[Category:Astrobiology]]
[[Category:Astrochemistry]]
[[Category:Bioindicators]]
[[Category:Biology terminology]]

Erdbeben von Istanbul 1509

2018-01-30T16:03:36Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Earthquake
|title= 1509 Constantinople earthquake
|date= {{Start date|1509|9|10|df=yes}}
|map2 = {{Location map | Turkey |relief=1
| label=
| lat=40.9
| long=28.7
| mark=Bullseye1.png
| marksize=40
| position=top
| width= 260
| float=right
| caption=}}
|magnitude = 7.2 [[Surface wave magnitude|Ms]]
|depth=
|location={{coord|40.9|28.7|display=inline,title}}<ref name="GJI2000">{{cite journal|last=Ambraseys|first=N.N.|author2=Jackson J.A.|year=2000|title=Seismicity of the Sea of Marmara (Turkey) since 1500|journal=[[Geophysical Journal International]]|volume=141|issue=3|pages=F1–F6|bibcode=2000GeoJI.141F...1A|doi=10.1046/j.1365-246x.2000.00137.x}}</ref>
|countries affected = [[Ottoman Empire]]
|casualties = 10,000
|image = 1509 Great Istanbul Earthquake.jpg}}

The '''1509 Constantinople earthquake''', referred to as "The Lesser [[Judgment Day]]" ({{lang-tr|Küçük Kıyamet}} or {{lang-tr|Kıyamet-i Suğra}}) by contemporaries, occurred in the [[Sea of Marmara]] on 10 September 1509 at about 10pm. The earthquake had an estimated magnitude of 7.2 ± 0.3 on the [[surface wave magnitude]] scale.<ref name="Nick">{{cite journal|last=Ambraseys|first=N. N.|authorlink=Nicholas Ambraseys|date=December 2001| journal = Bulletin of the Seismological Society of America|publisher=[[Seismological Society of America]]|url=ftp://ftp.gfz-potsdam.de/pub/home/vst/lau/tsunami/Tsunami-Mittelmeer/Literatur/pdf/Ambraseys.2001.The%20Earthquake%20of%201509%20in%20the%20Sea%20of%20Marmara,.pdf| doi = 10.1785/0120000305| title = The Earthquake of 1509 in the Sea of Marmara, Turkey, Revisited| volume = 91|issue=6| pages = 1397|bibcode = 2001BuSSA..91.1397A }}</ref> A [[tsunami]] and forty-five days of [[aftershocks]] followed the earthquake. Over a thousand houses and 109 [[mosque]]s were destroyed, and an estimated 10,000 people died.

==Background==
The [[Sea of Marmara]] is a [[pull-apart basin]] formed at a [[Extensional tectonics#Releasing bends along strike-slip faults|releasing bend]] in the [[North Anatolian Fault]], a right-lateral [[Fault (geology)#Strike-slip faults|strike-slip fault]]. This local zone of extension occurs where this [[Transform fault|transform]] boundary between the [[Anatolian Plate]] and the [[Eurasian Plate]] steps northwards to the west of [[Izmit]] from the Izmit Fault to the Ganos Fault. The pattern of faults within the Sea of Marmara basin is complex but near [[Istanbul]] there is a single main fault segment with a sharp bend. To the west, the fault trends west-east and is pure strike-slip in type. To the east, the fault is NW-SE trending and shows evidence of [[Transtension|both normal and strike-slip]] motion.<ref name="Armijo">{{cite journal|last=Armijo|first=R.|author2=Meyer B.|author3=Navarro S.|author4=King G.|author5=Narka A.|last-author-amp=yes|year=2002|title=Asymmetric slip partitioning in the Sea of Marmara pull-apart: a clue to propagation processes of the North Anatolian Fault?|journal=Terra Nova|volume=14|issue=2|pages=80–86|url=http://www.ipgp.fr/~armijo/ArmijoPDF/ArmijoTN02.pdf|accessdate=2010-02-06|doi=10.1046/j.1365-3121.2002.00397.x|bibcode=2002TeNov..14...80A}}</ref> Movement on this fault, which bounds the Çınarcık Basin, was the most likely cause of the 1509 event.<ref name="Nick"/>
[[File:Earthquake of 1509 in the Sea of Marmara.gif|thumb|left|A 1529 woodcut showing damage to the [[Fatih Mosque, Istanbul|Fatih Mosque]]]]

==Damage==
The area of significant damage (greater than [[Medvedev–Sponheuer–Karnik scale|VII (''Very strong'')]]) extended from [[Çorlu]] in the west to [[Izmit]] in the east. [[Galata]] and [[Büyükçekmece]] also suffered severe damage. In Constantinople many houses collapsed, chimneys fell and walls cracked. The newly built [[Bayezid II Mosque]] was badly damaged; the main dome was destroyed and a [[minaret]] collapsed. The [[Fatih Mosque]] suffered damage to its four great columns and the dome was split. The former church of [[Hagia Sophia]] survived almost unscathed, although a minaret collapsed. Inside the mosque, the plaster that had been used to cover up the [[Byzantine]] [[mosaic]]s inside the dome fell off, revealing the Christian images.<ref name="Nick"/>

The number of dead and injured is hard to estimate, with different sources giving accounts varying from 1,000 to 13,000.{{cn|date=September 2017}} It is believed that some members of the [[Ottoman dynasty]] died in this earthquake. Earthquake shocks continued for 45 days after the big earthquake, and people were unable to return to their homes for two months.{{cn|date=September 2017}}

[[File:Marmara earthquake 1509.jpg|thumb|Woodcut depicting the effects of the 1509 earthquake]]

==Characteristics==

===Earthquake===
From the area and intensity of shaking, a {{convert|70|km|mi|abbr=on}} fault rupture has been estimated.<ref name="Nick"/>

===Tsunami===
A tsunami is mentioned in some sources with a run-up of greater than {{convert|6.0|m|ft|abbr=on}}, but discounted in others.<ref name="Nick"/> A [[turbidite]] bed whose deposition matches the date of the earthquake has been recognised in the [[Çınarcık]] Basin.<ref name="Lozefski">{{cite web|url=http://gsa.confex.com/gsa/2004NE/finalprogram/abstract_70181.htm|title=Provenance of turbidite sands in the Marmara Sea, Turkey: a tool for submarine paleoseismology|last=Lozefski|first=G.|author2=McHugh C.|author3=Cormier M-H.|author4=Seeber L.|author5=Çagatay N.|author6=Okay N. |year=2004|accessdate=6 February 2010}}</ref>

==See also==
*[[List of earthquakes in Turkey]]
*[[List of historical earthquakes]]

==References==
{{Reflist|30em}}

{{Earthquakes in Turkey}}

{{DEFAULTSORT:1509 Constantinople earthquake}}
[[Category:16th-century earthquakes]]
[[Category:Earthquakes in Turkey]]
[[Category:History of Istanbul]]
[[Category:1509 in science]]
[[Category:1509 in Europe]]
[[Category:1509 in Asia]]
[[Category:1509 in the Ottoman Empire]]
[[Category:Tsunamis in Turkey]]

Radikalische Polymerisation mit reversibler Deaktivierung

2017-09-16T20:19:34Z

Bibcode Bot: Adding 0 arxiv eprint(s), 6 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Quote box
|title = [[International Union of Pure and Applied Chemistry|IUPAC]] definition for Reversible-deactivation radical polymerization
|quote = [[Chain-growth polymerization|Chain (growth) polymerization]], propagated by radicals that are deactivated reversibly, bringing them into active/dormant [[Chemical equilibrium|equilibria]] of which there might be more than one.<ref name="JenkinsJones2009">{{cite journal|vauthors=Jenkins AD, Jones RG, Moad G|title=Terminology for reversible-deactivation radical polymerization previously called "controlled" radical or "living" radical polymerization (IUPAC Recommendations 2010)|journal=Pure and Applied Chemistry|volume=82|issue=2|year=2009|issn=1365-3075|doi=10.1351/PAC-REP-08-04-03}}</ref> See also [[reversible-deactivation polymerization]] RDP.
}}
'''Reversible deactivation radical polymerizations''' are members of the class of [[reversible deactivation polymerization]]s which exhibit much of the character of [[living polymerization]]s, but cannot be categorized as such as they are not without chain transfer or chain termination reactions.<ref name=Szwarz1956>{{Cite journal
| author = Szwarz, M.
| year = 1956
| title = ‘Living’ Polymers
| journal = Nature
| volume = 178
| issue = 1
| pages = 1168–1169
| id =
| url =
| doi = 10.1038/1781168a0
| pmid =
| bibcode =1956Natur.178.1168S}}</ref><ref name=Szwarz2000>{{Cite journal
| author = Szwarz, M.
| year = 2000
| title = Comments on “Living Polymerization: Rationale for Uniform Terminology” by Darling et al.
| journal = J. Polym. Sci. A
| volume = 38
| issue = 10
| pages = 1710
| id =
| url =
| doi =
| pmid =
}}</ref>
Several different names have been used in literature, which are:
*Living Radical Polymerization
*Living Free Radical Polymerization
*Controlled/"Living" Radical Polymerization
*Controlled Radical Polymerization
*Reversible Deactivation Radical Polymerization
Though the term "living" radical polymerization was used in early days, it has been discouraged by IUPAC, because radical polymerization cannot be a truly living process due to unavoidable termination reactions between two radicals. The commonly used term controlled radical polymerization is permitted, but reversible-deactivated radical polymerization or controlled reversible-deactivation radical polymerization (RDRP) is recommended.

==History and character==
RDRP – sometimes misleadingly called 'free' radical polymerization – is one of the most widely used polymerization processes since it can be applied
*to a great variety of monomers
*it can be carried out in the presence of certain functional groups
*the technique is rather simple and easy to control
*the reaction conditions can vary from bulk over solution, emulsion, miniemulsion to suspension
*it is relatively inexpensive compared with competitive techniques

The [[steady-state]] concentration of the growing polymer chains is 10−7 M by order of magnitude, and the average life time of an individual polymer radical before termination is about 5–10 s. A drawback of the conventional radical polymerization is the limited control of chain architecture, molecular weight distribution, and composition. In the late 20th century it was observed that when certain components were added to systems polymerizing by a chain mechanism they are able to react reversibly with the (radical) chain carriers, putting them temporarily into a 'dormant' state.<ref name=Solomon1986>
{{ cite patent
| country = US
| number = 4581429
| status = patent
| title = title
| inventor = D. H. Solomon, E. Rizzardo, P. Cacioli
}}</ref>
<ref name=Moad1995>{{Cite journal
| author = G. Moad
|author2=E. Rizzardo
| year = 1995
| title = Alkoxyamine-Initiated Living Radical Polymerization: Factors Affecting Alkoxyamine Homolysis Rates
| journal = Macromolecules
| volume = 28
| issue =
| pages = 8722–8728
| id =
| url =
| doi = 10.1021/MA00130A003
| pmid =
| bibcode =1995MaMol..28.8722M}}</ref>
This had the effect of prolonging the lifetime of the growing polymer chains (see above) to values comparable with the duration of the experiment. At any instant most of the radicals are in the inactive (dormant) state, however, they are not irreversibly terminated (‘dead’). Only a small fraction of them are active (growing), yet with a fast rate of interconversion of active and dormant forms, faster than the growth rate, the same probability of growth is ensured for all chains, i.e., on average, all chains are growing at the same rate. Consequently, rather than a most probable distribution, the molecular masses (degrees of polymerization) assume a much narrower [[Poisson distribution]], and a lower [[dispersity]] prevails.

IUPAC also recognizes the alternative name, ‘controlled reversible-deactivation radical polymerization’ as acceptable, "provided the controlled context is specified, which in this instance comprises molecular mass and molecular mass distribution." These types of radical polymerizations are not necessarily ‘living’ polymerizations, since chain termination reactions are not precluded".<ref name="JenkinsJones2009"/><ref name=Szwarz1956 /><ref name=Szwarz2000 />

The adjective ‘controlled’ indicates that a certain kinetic feature of a polymerization or structural aspect of the polymer molecules formed is controlled (or both). The expression ‘controlled polymerization’ is sometimes used to describe a [[Radical polymerization|radical]] or [[ionic polymerization]] in which reversible-deactivation of the [[chain carrier]]s is an essential component of the mechanism and interrupts the propagation that secures control of one or more kinetic features of the [[polymerization]] or one or more structural aspects of the [[macromolecule]]s formed, or both. The expression ‘controlled radical polymerization’ is sometimes used to describe a radical polymerization that is conducted in the presence of agents that lead to e.g. atom-transfer radical polymerization (ATRP), nitroxide-(aminoxyl) mediated polymerization (NMP), or reversible-addition-fragmentation chain transfer (RAFT) polymerization. All these and further controlled polymerizations are included in the class of reversible-deactivation radical polymerizations. Whenever the adjective ‘controlled’ is used in this context the particular kinetic or the structural features that are controlled have to be specified.

==Reversible-deactivation polymerization==
There is a mode of polymerization referred to as '''[[reversible-deactivation polymerization]]''' which is distinct from living polymerization, despite some common features. Living polymerization requires a complete absence of termination reactions, whereas reversible-deactivation polymerization may contain a similar fraction of termination as conventional polymerization with the same concentration of active species.<ref name="JenkinsJones2009"/> Some important aspects of these are compared in the table:
{| class="wikitable"
|+'''Comparison of radical polymerization processes'''
|-
! Property !! Standard radical polymerization !! Living polymerization !! Reversible-deactivation polymerization
|-
| Concn. of initiating species
| Falls off only slowly
| Falls off very rapidly
| Falls off very rapidly
|-
| Concn. of chain carriers (Number of growing chains)
| Instantaneous steady state ([[Bodenstein approximation]] applies) decreasing throughout reaction
| Constant throughout reaction
| Constant throughout reaction
|-
| Lifetime of growing chains
| ~ 10−3 s
| Same as reaction duration
| Same as reaction duration
|-
| Main form of [[Radical (chemistry)#Depiction in chemical reactions|termination]]
| Radical combination or radical disproportionation
| Termination reactions are precluded
| Termination reactions are '''not''' precluded
|-
| [[Degree of polymerization]]
| Broad range (Ð >=1.5), Schulz-Zimm distribution
| Narrow range(Ð <1.5), [[Poisson distribution]]
| Narrow range(Ð <1.5), [[Poisson distribution]]
|-
| Dormant states
| None
| Rare
| Predominant
|}

==Common features==
As the name suggests, the prerequisite of a successful RDRP is fast and reversible activation/deactivation of propagating chains. There are three types of RDRP; namely deactivation by catalyzed reversible coupling, deactivation by spontaneous reversible coupling and deactivation by degenerative transfer (DT). A mixture of different mechanisms is possible; e.g. a transition metal mediated RDRP could switch among ATRP, OMRP and DT mechanisms depending on the reaction conditions and reagents used.

In any RDRP processes, the radicals can propagate with the rate coefficient ''k''p by addition of a few monomer units before the deactivation reaction occurs to regenerate the dormant species. Concurrently, two radicals may react with each other to form dead chains with the rate coefficient ''k''t. The rates of propagation and termination between two radicals are not influenced by the mechanism of deactivation or the catalyst used in the system. Thus it is possible to estimate how fast a RDRP can be conducted with preserved chain end functionality?<ref name="Zhong-Matyja 2011 macromolecules">{{cite journal
|journal = [[Macromolecules (journal)|Macromolecules]]|year = 2011|volume = 44|pages = 2668–2677|doi = 10.1021/ma102834s
|title = How Fast Can a CRP Be Conducted with Preserved Chain End Functionality?
|author1 = Zhong, M|author2 = Matyjaszewski, K|bibcode = 2011MaMol..44.2668Z}}</ref>

In addition, other chain breaking reactions such as irreversible chain transfer/termination reactions of the propagating radicals with solvent, monomer, polymer, catalyst, additives, etc. would introduce additional loss of chain end functionality (CEF).<ref name="Wang-Matyja 2013 macromolecules">{{cite journal
|journal = [[Macromolecules (journal)|Macromolecules]]|year = 2013|volume = 46|pages = 683–691|doi = 10.1021/ma3024393
|title = Improving the "Livingness" of ATRP by Reducing Cu Catalyst Concentration
|author1 = Wang, Y|author2 = Soerensen, N|author3 = Zhong, M|author4 = Schroeder, H|author5 = Buback, M|author6 = Matyjaszewski, K|bibcode = 2013MaMol..46..683W}}</ref> The overall rate coefficient of chain breaking reactions besides the direct termination between two radicals is represented as ''k''tx.

[[File:Three types of mechanisms of RDRP.svg|Three types of mechanisms of RDRP]]

In all RDRP methods, the theoretical number average molecular weight of obtained polymers, ''M''n, can be defined by following equation:

<math>M_\text{n}=M_\text{m}\times\frac{[\text{M}]_0-[\text{M}]_t}{[\text{R-X}]_0}</math>

where ''M''m is the molecular weight of monomer; [M]0 and [M]t are the monomer concentrations at time 0 and time ''t''; [R-X]0 is the initial concentration of the initiator.

Besides the designed molecular weight, a well controlled RDRP should give polymers with narrow molecular distributions, which can be quantified by ''M''w/''M''n values, and well preserved chain end functionalities.

[[File:Retention of Chain End Functionality in RDRP.svg|Retention of Chain End Functionality in RDRP]]

A well controlled RDRP process requires: 1) the reversible deactivation process should be sufficiently fast; 2) the chain breaking reactions which cause the loss of chain end functionalities should be limited; 3) properly maintained radical concentration; 4) the initiator should have proper activity.

==Examples==

===Atom-transfer radical polymerization (ATRP)===
{{Main|Atom-transfer radical-polymerization}}
The initiator of the polymerization is usually an organohalogenid and the dormant state is achieved in a metal complex of a transition metal (‘radical buffer’). This method is very versatile but requires unconventional initiator systems that are sometimes poorly compatible with the polymerization media.

===Nitroxide-mediated polymerization (NMP)===
{{Main|Nitroxide mediated radical polymerization}}
Given certain conditions a homolytic splitting of the C-O bond in alkoxylamines can occur and a stable 2-centre 3 electron N-O radical can be formed that is able to initiate a polymerization reaction. The preconditions for an alkoxylamine suitable to initiate a polymerization are bulky, sterically obstructive substituents on the secondary amine, and the substituent on the oxygen should be able to form a stable radical, e.g. benzyl.
[[File:ReversibleDeactivationReaction.png|thumb|center|500px|Example of a reversible deactivation reaction]]

===Reversible addition-fragmentation chain transfer (RAFT)===
{{Main|Reversible addition−fragmentation chain-transfer polymerization}}
RAFT is one of the most versatile and convenient techniques in this context. The most common RAFT-processes are carried out in the presence of thiocarbonylthio compounds that act as radical buffers.
While in ATRP and NMP reversible deactivation of propagating radical-radical reactions takes place and the dormant structures are a halo-compound in ATRP and the alkoxyamine in NMP, both being a sink for radicals and source at the same time and described by the corresponding equilibria. RAFT on the contrary, is controlled by chain-transfer reactions that are in a deactivation-activation equilibrium. Since no radicals are generated or destroyed an external source of radicals is necessary for initiation and maintenance of the propagation reaction.
;Initiation step of a RAFT polymerization
:<ce title="Initiation step">I -> I^. ->[\ce M]->[\ce M] P_\mathit{n}^.</ce>
;Reversible chain transfer
:[[File:RAFT ReversibleChainTransfer.png|500px|Reversible chain transfer]]
;Reinitiation step
:<ce title="Reinitiation step">R^. ->[\ce M] RM^. ->[\ce M]->[\ce M] P^._\mathit{m}</ce>
;Chain equilibration step
:[[File:RAFT ChainEquilibration.png|450px|Chain equilibration step]]
;Termination step
:<ce title="Termination step">{P_\mathit{m}^.} + P_\mathit{n}^. -> P_\mathit{m}P_\mathit{n}</ce>

=== Catalytic chain transfer and cobalt mediated radical polymerization===
{{Main|Catalytic Chain Transfer|Cobalt Mediated Radical Polymerization}}
Although not a strictly living form of polymerization '''catalytic chain transfer polymerization''' must be mentioned as it figures significantly in the development of later forms of living free radical polymerization.
Discovered in the late 1970s in the USSR it was found that [[cobalt]] [[porphyrin]]s were able to reduce the [[molecular weight]] during [[polymerization]] of [[Methyl methacrylate|methacrylate]]s.
Later investigations showed that the cobalt [[glyoxime]] complexes were as effective as the porphyrin catalysts and also less oxygen sensitive. Due to their lower oxygen sensitivity these catalysts have been investigated much more thoroughly than the porphyrin catalysts.

The major products of catalytic chain transfer polymerization are [[Vinyl group|vinyl]]-terminated polymer chains. One of the major drawbacks of the process is that catalytic chain transfer polymerization does not produce [[macromonomer]]s but instead produces addition fragmentation agents. When a growing polymer chain reacts with the addition fragmentation agent the radical [[end-group]] attacks the vinyl bond and forms a bond. However, the resulting product is so [[steric hindrance|hindered]] that the species undergoes fragmentation, leading eventually to [[telechelic polymer|telechelic species]].

These addition fragmentation chain transfer agents do form [[graft copolymer]]s with [[styrene|styrenic]] and [[acrylate]] species however they do so by first forming [[block copolymer]]s and then incorporating these block copolymers into the main polymer backbone.

While high [[chemical yield|yields]] of macromonomers are possible with methacrylate [[monomer]]s, low yields are obtained when using catalytic chain transfer agents during the polymerization of acrylate and stryenic monomers. This has been seen to be due to the interaction of the radical centre with the catalyst during these polymerization reactions.

The [[reversible reaction]] of the cobalt [[macrocycle]] with the growing radical is known as '''cobalt carbon bonding''' and in some cases leads to living polymerization reactions.

=== Iniferter polymerization ===
An '''iniferter''' is a [[chemical compound]] that simultaneously acts as [[Radical initiator|initiator]], transfer agent, and terminator (hence the name ini-fer-ter) in controlled free radical iniferter polymerizations, the most common is the [[dithiocarbamate]] type.<ref>''Role of initiator-transfer agent-terminator (iniferter) in radical polymerizations: Polymer design by organic disulfides as iniferters'' Die Makromolekulare Chemie, Rapid Communications Volume 3, Issue 2, Date: 16 February 1982, Pages: 127-132 {{DOI|10.1002/marc.1982.030030208}}</ref><ref>''A model for living radical polymerization'' Die Makromolekulare Chemie, Rapid Communications Volume 3, Issue 2, Date: 16 February 1982, Pages: 133-140 Takayuki Otsu, Masatoshi Yoshida, Toshinori Tazaki {{DOI|10.1002/marc.1982.030030209}}</ref>

=== Iodine-transfer polymerization (ITP)===
'''Iodine-transfer polymerization (ITP''', also called '''ITRP'''), developed by Tatemoto and coworkers in the 1970s<ref>US 4 243 770 (priority date 04/08/1977).</ref> gives relatively low polydispersities for [[fluoroolefin]] polymers. While it has received relatively little academic attention, this chemistry has served as the basis for several industrial patents and products and may be the most commercially successful form of living free radical polymerization.<ref>{{cite journal | last1 = Ameduri | first1 = B | last2 = Boutevin | first2 = B | year = 1999 | title = Use of telechelic fluorinated diiodides to obtain well-defined fluoropolymers| url = | journal = J. Fluorine Chem. | volume = 100 | issue = | pages = 97–116 | doi=10.1016/s0022-1139(99)00220-1}}</ref> It has primarily been used to incorporate [[iodine]] cure sites into [[FKM|fluoroelastomers]].

The mechanism of ITP involves thermal decomposition of the radical initiator (typically [[persulfate]]), generating the initiating radical In•. This radical adds to the monomer M to form the species P1•, which can propagate to Pm•. By exchange of iodine from the transfer agent R-I to the propagating radical Pm• a new radical R• is formed and Pm• becomes dormant. This species can propagate with monomer M to Pn•. During the polymerization exchange between the different polymer chains and the transfer agent occurs, which is typical for a degenerative transfer process.

:[[File:iodine transfer RP.png|400px]]

Typically, iodine transfer polymerization uses a mono- or diiodo-per[[fluoroalkane]] as the initial [[chain transfer]] agent. This fluoroalkane may be partially substituted with hydrogen or chlorine. The energy of the iodine-perfluoroalkane bond is low and, in contrast to iodo-hydrocarbon bonds, its polarization small.<ref>US 5 037 921 (priority date 03/01/1990).</ref> Therefore, the iodine is easily abstracted in the presence of free radicals. Upon encountering an iodoperfluoroalkane, a growing poly(fluoroolefin) chain will abstract the iodine and terminate, leaving the now-created perfluoroalkyl radical to add further monomer. But the iodine-terminated poly(fluoroolefin) itself acts as a chain transfer agent. As in RAFT processes, as long as the rate of initiation is kept low, the net result is the formation of a monodisperse molecular weight distribution.

Use of conventional hydrocarbon monomers with iodoperfluoroalkane chain transfer agents has been described.<ref>US 5 585 449 (priority date 12/29/1993).</ref> The resulting molecular weight distributions have not been narrow since the energetics of an iodine-hydrocarbon bond are considerably different from that of an iodine-fluorocarbon bond and abstraction of the iodine from the terminated polymer difficult. The use of [[hydrocarbon]] [[iodides]] has also been described, but again the resulting molecular weight distributions were not narrow.<ref>{{cite journal | last1 = Banus | first1 = J. | last2 = Emeleus | first2 = H. J. | last3 = Haszeldine | first3 = R. N. | year = 1951 | title = 12. The heterolytic fission of the carbon?iodine bond in trifluoroiodomethane| url = | journal = J. Chem. Soc. | page = 60 | issue = | doi = 10.1039/jr9510000060 }}</ref>

Preparation of block copolymers by iodine-transfer polymerization was also described by Tatemoto and coworkers in the 1970s.<ref>{{cite journal | last1 = Lansalot | first1 = M. | last2 = Farcet | first2 = C. | last3 = Charleux | first3 = B. | last4 = Vairon | first4 = J.-P. | year =1999 | title = Controlled Free-Radical Miniemulsion Polymerization of Styrene Using Degenerative Transfer| journal =Macromolecules | volume = 32 | issue = | pages = 7354–7360 | doi=10.1021/ma990447w| bibcode = 1999MaMol..32.7354L }}</ref>

Although use of living free radical processes in emulsion polymerization has been characterized as difficult,<ref>{{cite journal | last1 = Matyjaszewski | first1 = K. | last2 = Gaynor | first2 = S. | last3 = Wang | first3 = J.-S. | year = 1995 | title = Controlled Radical Polymerizations: The Use of Alkyl Iodides in Degenerative Transfer| url = | journal = Macromolecules | volume = 28 | issue = | pages = 2093–2095 | doi=10.1021/ma00110a050| bibcode = 1995MaMol..28.2093M}}</ref> all examples of iodine-transfer polymerization have involved emulsion polymerization. Extremely high molecular weights have been claimed.<ref name="ref3" >{{cite journal | last1 = Ziegler | first1 = K | year = 1936 | title = Die Bedeutung der alkalimetallorganischen Verbindungen für die Synthese| url = | journal = Angew. Chem. | volume = 49 | issue = | pages = 499–502 | doi=10.1002/ange.19360493003}}</ref>

Listed below are some other less described but to some extent increasingly important living radical polymerization techniques.

=== Selenium-centered radical-mediated polymerization ===
Diphenyl diselenide and several benzylic selenides have been explored by Kwon ''et al.'' as photoiniferters in polymerization of styrene and methyl methacrylate. Their mechanism of control over polymerization is proposed to be similar to the dithiuram disulfide iniferters. However, their low transfer constants allow them to be used for block copolymer synthesis but give limited control over the molecular weight distribution.

=== Telluride-mediated polymerization (TERP) ===
'''Telluride-mediated polymerization''' or TERP first appeared to mainly operate under a reversible chain transfer mechanism by homolytic substitution under thermal initiation. However, in a kinetic study it was found that TERP predominantly proceeds by degenerative transfer rather than 'dissociation combination'.<ref>{{cite journal |vauthors=Goto A, Kwak Y, Fukuda T, Yamago S, Iida K, Nakajima M, Yoshida J |title=Mechanism-based invention of high-speed living radical polymerization using organotellurium compounds and azo-initiators |journal=J. Am. Chem. Soc. |volume=125 |issue=29 |pages=8720–1 |year=2003 |pmid=12862455 |doi=10.1021/ja035464m }}</ref>

:[[File:TeMRP.png|600px]]

Alkyl tellurides of the structure Z-X-R, were Z=methyl and R= a good free radical leaving group, give the better control for a wide range of monomers, phenyl tellurides (Z=phenyl) giving poor control. Polymerization of methyl methacrylates are only controlled by ditellurides. The importance of X to chain transfer increases in the series O<S<Se<Te, makes alkyl tellurides effective in mediating control under thermally initiated conditions and the alkyl selenides and sulfides effective only under photoinitiated polymerization.

=== Stibine-mediated polymerization ===
More recently Yamago ''et al.'' reported stibine-mediated polymerization, using an organostibine transfer agent with the general structure Z(Z')-Sb-R (where Z= activating group and R= free radical leaving group). A wide range of monomers (styrenics, (meth)acrylics and vinylics) can be controlled, giving narrow molecular weight distributions and predictable molecular weights under thermally initiated conditions.<ref>{{cite journal |vauthors=Yamago S, Ray B, Iida K, Yoshida J, Tada T, Yoshizawa K, Kwak Y, Goto A, Fukuda T |title=Highly versatile organostibine mediators for living radical polymerization |journal=J. Am. Chem. Soc. |volume=126 |issue=43 |pages=13908–9 |year=2004 |pmid=15506736 |doi=10.1021/ja044787v }}</ref><ref>{{cite journal |vauthors=Yamago S, Kayahara E, Kotani M, Ray B, Kwak Y, Goto A, Fukuda T |title=Highly controlled living radical polymerization through dual activation of organobismuthines |journal=Angew. Chem. Int. Ed. Engl. |volume=46 |issue=8 |pages=1304–6 |year=2007 |pmid=17205592 |doi=10.1002/anie.200604473}}</ref> Yamago has also published a patent indicating that bismuth alkyls can also control radical polymerizations via a similar mechanism.

=== Copper mediated polymerization===
{{Main|Copper(0)-mediated reversible-deactivation radical polymerization}}
More reversible-deactivation radical polymerizations are known to be catalysed by [[copper]].

== References ==
{{Reflist|30em}}

[[Category:Polymers]]
[[Category:Polymer chemistry]]
[[Category:Free radicals]]
[[Category:Polymerization reactions]]

Mechanisch verzahnte Moleküle

2017-09-16T10:48:27Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

'''Mechanically interlocked molecular architectures''' (MIMAs) are molecules that are connected as a consequence of their [[topology (chemistry)|topology]]. This connection of molecules is analogous to keys on a [[key chain]] loop. The keys are not directly connected to the key chain loop but they cannot be separated without breaking the loop. On the molecular level the interlocked molecules cannot be separated without the breaking of the [[covalent bond]]s that comprise the conjoined molecules. Examples of mechanically interlocked molecular architectures include [[catenane]]s, [[rotaxane]]s, [[molecular knot]]s, and [[molecular Borromean rings]]. Work in this area was recognized with the 2016 [[Nobel Prize in Chemistry]] to [[Bernard L. Feringa]], [[Jean-Pierre Sauvage]], and [[J. Fraser Stoddart]].<ref>{{cite journal | last1 = Browne | first1 = Wesley R. | last2 = Feringa | first2 = Ben L. | year = 2006 | title = Making molecular machines work | url = | journal = [[Nature Nanotechnology]] | volume = 1 | issue = | pages = 25–35 | doi = 10.1038/nnano.2006.45 | bibcode = 2006NatNa...1...25B }}</ref><ref>{{cite journal | last1 = Stoddart | first1 = J. F. | year = 2009 | title = The chemistry of the mechanical bond | url = | journal = Chem. Soc. Rev. | volume = 38 | issue = | pages = 1802–1820 | doi = 10.1039/b819333a }}</ref><ref>{{cite journal | last1 = Coskun | first1 = A. | last2 = Banaszak | first2 = M. | last3 = Astumian | first3 = R. D. | last4 = Stoddart | first4 = J. F. | last5 = Grzybowski | first5 = B. A. | year = 2012 | title = Great expectations: can artificial molecular machines deliver on their promise? | url = | journal = [[Chem. Soc. Rev.]] | volume = 41 | issue = 1| pages = 19–30 | doi = 10.1039/C1CS15262A }}</ref><ref>{{cite journal | last1 = Durola | first1 = Fabien | last2 = Heitz | first2 = Valerie | last3 = Reviriego | first3 = Felipe | last4 = Roche | first4 = Cecile | last5 = Sauvage | first5 = Jean-Pierre | last6 = Sour | first6 = Angelique | last7 = Trolez | first7 = Yann | year = 2014 | title = Cyclic [4]Rotaxanes Containing Two Parallel Porphyrinic Plates: Toward Switchable Molecular Receptors and Compressors | url = | journal = [[Accounts of Chemical Research]] | volume = 47 | issue = 2| pages = 633–645 | doi = 10.1021/ar4002153 }}</ref>

The synthesis of such entangled architectures has been made efficient by combining [[supramolecular chemistry]] with traditional covalent synthesis, however mechanically interlocked molecular architectures have properties that differ from both “[[supramolecular assemblies]]” and “covalently bonded molecules”. The terminology "mechanical bond" has been coined to describe the connection between the components of mechanically interlocked molecular architectures. Although research into mechanically interlocked molecular architectures is primarily focused on artificial compounds, many examples have been found in biological systems including: [[cytokine|cystine knot]]s, [[cyclotide]]s or lasso-peptides such as [[microcin]] J25 which are [[protein]], and a variety of [[peptide]]s.

== Mechanical bonding and chemical reactivity ==
The introduction of a mechanical bond alters the chemistry of the sub components of rotaxanes and catenanes. [[Steric hindrance]] of reactive functionalities is increased and the strength of [[non-covalent interactions]] between the components are altered.<ref name=":02">{{Cite journal|last=Neal|first=Edward A.|last2=Goldup|first2=Stephen M.|date=2014-04-22|title=Chemical consequences of mechanical bonding in catenanes and rotaxanes: isomerism, modification, catalysis and molecular machines for synthesis|url=http://xlink.rsc.org/?DOI=c3cc47842d|journal=[[Chemical Communications]]|language=en|volume=50|issue=40|doi=10.1039/c3cc47842d|issn=1364-548X|page=5128}}</ref>

=== Mechanical bonding effects on non-covalent interactions ===
The strength of non-covalent interactions in a mechanically interlocked molecular architecture increases as compared to the non-mechanically bonded analogues. This increased strength is demonstrated by the necessity of harsher conditions to remove a metal template ion from catenanes as opposed to their non-mechanically bonded analogues. This effect is referred to as the "catenand effect".<ref>{{Cite journal|last=Albrecht-Gary|first=Anne Marie|last2=Saad|first2=Zeinab|last3=Dietrich-Buchecker|first3=Christiane O.|last4=Sauvage|first4=Jean Pierre|date=1985-05-01|title=Interlocked macrocyclic ligands: a kinetic catenand effect in copper(I) complexes|url=https://dx.doi.org/10.1021/ja00297a028|journal=[[Journal of the American Chemical Society]]|volume=107|issue=11|pages=3205–3209|doi=10.1021/ja00297a028|issn=0002-7863}}</ref><ref>{{Cite book|title=The Nature of the Mechanical Bond: From Molecules to Machines|last=Stoddart |last2= Bruns|first=J. Fraser |first2= Carson J|publisher=Wiley|year=2016|isbn=978-1-119-04400-0|location=|pages=90|quote=|via=}}</ref> This increase in strength of non-covalent interactions is attributed to the loss of [[Degrees of freedom (physics and chemistry)|degrees of freedom]] upon the formation of a mechanical bond. The increase in strength of non-covalent interactions is more pronounced on smaller interlocked systems, where more degrees of freedom are lost, as compared to larger mechanically interlocked systems where the change in degrees of freedom is lower. Therefore if the ring in a rotaxane is made smaller the strength of non-covalent interactions increases, the same effect is observed if the thread is made smaller as well.<ref>{{Cite journal|last=Lahlali|first=Hicham|last2=Jobe|first2=Kajally|last3=Watkinson|first3=Michael|last4=Goldup|first4=Stephen M.|date=2011-04-26|title=Macrocycle Size Matters: "Small" Functionalized Rotaxanes in Excellent Yield Using the CuAAC Active Template Approach|url=http://onlinelibrary.wiley.com/doi/10.1002/anie.201100415/abstract|journal=[[Angewandte Chemie International Edition]]|language=en|volume=50|issue=18|pages=4151–4155|doi=10.1002/anie.201100415|issn=1521-3773|pmid=21462287}}</ref>

=== Mechanical bonding effects on chemical reactivity ===
The mechanical bond can reduce the kinetic reactivity of the products, this is ascribed to the increased steric hindrance. Because of this effect [[hydrogenation]] of an alkene on the thread of a rotaxane is significantly slower as compared to the equivalent non interlocked thread.<ref>{{Cite journal|last=Parham|first=Amir Hossain|last2=Windisch|first2=Björna|last3=Vögtle|first3=Fritz|date=1999-05-01|title=Chemical Reactions in the Axle of Rotaxanes – Steric Hindrance by the Wheel|url=http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1099-0690(199905)1999:53.0.CO;2-Q/abstract|journal=[[European Journal of Organic Chemistry]]|language=en|volume=1999|issue=5|pages=1233–1238|doi=10.1002/(SICI)1099-0690(199905)1999:53.0.CO;2-Q|issn=1099-0690}}</ref> This effect has allowed for the isolation of otherwise reactive intermediates.

The ability to alter reactivity without altering covalent structure has led to MIMAs being investigated for a number of technological applications.

=== Applications of mechanical bonding in controlling chemical reactivity ===
The ability for a mechanical bond to reduce reactivity and hence prevent unwanted reactions has been exploited in a number of areas. One of the earliest applications was in the protection of [[organic dyes]] from [[Industrial dye degradation|environmental degradation]].

==Examples of mechanically interlocked molecular architectures==
<gallery>
Image:Rotaxane cartoon.jpg|[[Rotaxane]]
Image:CatenaneScheme.svg|[[Catenane]]
Image:Trefoil knot arb.png|[[Molecular knot]]
Image:Molecular Borromean Ring.png|[[Molecular Borromean rings]]
</gallery>

== References ==
<references />

==Further reading==
*{{cite journal |author = G. A. Breault, C. A. Hunter and P. C. Mayers |year = 1999 |title = Supramolecular topology |journal = Tetrahedron |volume = 55 |issue = 17 |pages = 5265–5293 |doi = 10.1016/S0040-4020(99)00282-3}}

[[Category:Supramolecular chemistry]]
[[Category:Molecular topology]]

Hindered Amine Light Stabilizers

2017-09-16T04:55:14Z

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[[File:HALSgeneric.png|thumb|Partial structure of a typical hindered amine light stabilizer.]]
'''Hindered amine light stabilizers''' (HALS) are chemical compounds containing an [[amine]] [[functional group]] that are used as [[Stabilizer (chemistry)|stabilizers]] in plastics and polymers. These compounds are typically derivatives of [[tetramethylpiperidine]] and are primarily used to protect the polymers from the effects of [[Photo-oxidation of polymers|photo-oxidation]]; as opposed to other forms of [[polymer degradation]] such as [[ozonolysis]].<ref>{{cite book|chapter=Photostabilisation of Polymer Materials|authors=Pieter Gijsman|year=2010|doi=10.1002/9780470594179.ch17 |publisher=John Wiley & Sons|place=Hoboken|title=Photochemistry and Photophysics of Polymer Materials Photochemistry|editor=Norman S. Allen}}.</ref><ref>{{cite encyclopedia|title=Paints and Coatings, 4. Pigments, Extenders, and Additives|encyclopedia=Ullmann's Encyclopedia Of Industrial Chemistry|author1=Klaus Köhler|author2=Peter Simmendinger|author3=Wolfgang Roelle|author4=Wilfried Scholz|author5=Andreas Valet|author6=Mario Slongo|year=2010|doi=10.1002/14356007.o18_o03}}</ref>

==Mechanism of action==

HALS do not absorb UV radiation, but act to inhibit degradation of the polymer by continuously and cyclically removing [[free radical]]s that are produced by photo-oxidation of the polymer. The overall process is sometimes referred to as the '''Denisov cycle''', after Evguenii T. Denisov<ref>{{cite journal|last1=Denisov|first1=E.T.|title=The role and reactions of nitroxyl radicals in hindered piperidine light stabilisation|journal=Polymer Degradation and Stability|date=January 1991|volume=34|issue=1-3|pages=325–332|doi=10.1016/0141-3910(91)90126-C}}</ref> and is exceedingly complex.<ref>{{cite journal|last1=Hodgson|first1=Jennifer L.|last2=Coote|first2=Michelle L.|title=Clarifying the Mechanism of the Denisov Cycle: How do Hindered Amine Light Stabilizers Protect Polymer Coatings from Photo-oxidative Degradation?|journal=Macromolecules|date=25 May 2010|volume=43|issue=10|pages=4573–4583|doi=10.1021/ma100453d|bibcode=2010MaMol..43.4573H}}</ref> Broadly, HALS react with the initial polymer peroxy radical (POO•) and alkyl polymer radicals (P•) formed by the reaction of the polymer and oxygen. By these reactions HALS are oxidised to their corresponding [[aminoxyl radicals]] (c.f. [[TEMPO]]), however they are able to return to their initial amine form via a series of additional radical reactions. HALS's high efficiency and longevity are due to this cyclic process wherein the HALS are regenerated rather than consumed during the stabilization process.

==References==
<references />

==External links==
*[http://www.specialchem4adhesives.com/tc/uv-light-stabilizers/index.aspx?id=hals] Hindered amine light stabilizers
*[http://www.exxonmobil.com/refiningtechnologies/fuels/mn_flexsorb.html] Gas treating

[[Category:Amines]]

Photoelektrochemischer Prozess

2017-09-16T03:44:21Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 1 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

'''Photoelectrochemical processes''' are processes in [[photoelectrochemistry]]; they usually involve transforming light into other forms of energy.<ref name=photochemelec-process>
{{Cite book
| last=Gerischer| first=Heinz
| chapter=Semiconductor electrodes and their interaction with light
| date=1985
| editor-last=Schiavello | editor-first=Mario
| title=Photoelectrochemistry, Photocatalysis and Photoreactors Fundamentals and Developments
| publisher=[[Springer (publisher)|Springer]]
| pages=39
| url=https://books.google.com/books?id=rLRMeP1KGhsC&pg=PA39#v=onepage&f=false
| isbn=978-90-277-1946-1
}}</ref> These processes apply to photochemistry, optically pumped lasers, sensitized solar cells, luminescence, and photochromism.

==Electron excitation==
[[Image:Energy levels.svg|thumb|210px|right| After absorbing energy, an electron may jump from the ground state to a higher energy excited state.]]

[[Electron excitation]] is the movement of an [[electron]] to a higher [[energy state]]. This can either be done by photoexcitation (PE), where the original electron absorbs the photon and gains all the photon's energy or by electrical [[Excited state|excitation]] (EE), where the original electron absorbs the energy of another, energetic electron. Within a semiconductor crystal lattice, thermal excitation is a process where lattice vibrations provide enough energy to move electrons to a higher [[energy band]]. When an excited electron falls back to a lower energy state again, it is called electron relaxation. This can be done by radiation of a photon or giving the energy to a third spectator particle as well.<ref name=2-electron>
{{Cite journal
|last=Madden | first=R. P.
|last2=Codling| first2=K.
|date=1965
|title=Two electron states in Helium
|journal=[[Astrophysical Journal]]
|volume=141 |pages=364
|bibcode=1965ApJ...141..364M
|doi=10.1086/148132
}}</ref>

In physics there is a specific technical definition for [[energy level]] which is often associated with an atom being excited to an [[excited state]]. The excited state, in general, is in relation to the [[ground state]], where the excited state is at a higher [[energy level]] than the ground state.

==Photoexcitation==
{{See also|Photoelectric effect}}

[[Photoexcitation]] is the mechanism of [[electron excitation]] by [[photon]] absorption, when the energy of the photon is too low to cause photoionization. The absorption of the photon takes place in accordance with Planck's quantum theory.

Photoexcitation plays role in photoisomerization. Photoexcitation is exploited in [[dye-sensitized solar cell]]s, [[photochemistry]], [[luminescence]], optically [[laser pumping|pumped]] lasers, and in some [[photochromic]] applications.
[[file:Military laser experiment.jpg|Military laser experiment|thumb]]

==Photoisomerization==
[[File:Azobenzene isomerization.svg|thumb|Photoisomerization of azobenzene]]
In [[chemistry]], '''photoisomerization''' is [[molecule|molecular]] behavior in which structural change between [[isomer]]s is caused by photoexcitation. Both reversible and irreversible photoisomerization reactions exist. However, the word "photoisomerization" usually indicates a reversible process. Photoisomerizable molecules are already put to practical use, for instance, in [[pigment]]s for [[CD-RW|rewritable CDs]], [[DVD-RW|DVDs]], and [[3D optical data storage]] solutions. In addition, recent interest in photoisomerizable molecules has been aimed at molecular devices, such as molecular switches,<ref>
{{Cite journal
|last1=Mammana |first1=A.
|display-authors=etal
|date=2011
|title=A Chiroptical Photoswitchable DNA Complex
|journal=[[Journal of Physical Chemistry B]]
|volume=115 |issue=40 |pages=11581–11587
|doi=10.1021/jp205893y
}}</ref> molecular motors,<ref>{{Cite journal
|last1=Vachon |first1=J.
|display-authors=etal
|date=2014
|title=An ultrafast surface-bound photo-active molecular motor
|journal=[[Photochemical and Photobiological Sciences]]
|volume=13 |issue=2 |pages=241–246
|doi=10.1039/C3PP50208B
}}</ref> and molecular electronics.

Photoisomerization behavior can be roughly categorized into several classes. Two major classes are ''trans-cis'' (or 'E-'Z) conversion, and open-closed ring transition. Examples of the former include [[stilbene]] and [[azobenzene]]. This type of compounds has a double [[chemical bond|bond]], and rotation or inversion around the double bond affords isomerization between the two states. Examples of the latter include [[fulgide]] and [[diarylethene]]. This type of compounds undergoes bond cleavage and bond creation upon irradiation with particular wavelengths of light. Still another class is the [[Di-pi-methane rearrangement]].

==Photoionization==
{{See also|Ultraviolet photoelectron spectroscopy}}

[[Photoionization]] is the physical process in which an incident [[photon]] ejects one or more [[electron]]s from an [[atom]], [[ion]] or [[molecule]]. This is essentially the same process that occurs with the photoelectric effect with metals. In the case of a gas or single atoms, the term photoionization is more common.<ref name="Grotthuss–Draper-law">
{{Cite web
| title=Radiation
| work=[[Encyclopædia Britannica Online]]
| url=http://www.britannica.com/EBchecked/topic/488507/radiation
| accessdate =2009-11-09
}}</ref>

The ejected electrons, known as [[photoelectron]]s, carry information about their pre-ionized states. For example, a single electron can have a [[kinetic energy]] equal to the energy of the incident photon minus the [[electron binding energy]] of the state it left. Photons with energies less than the electron binding energy may be absorbed or [[scattering|scattered]] but will not photoionize the atom or ion.<ref name="Grotthuss–Draper-law"/>

For example, to ionize [[hydrogen]], photons need an energy greater than 13.6 [[electronvolt]]s, which corresponds to a wavelength of 91.2 [[nanometer|nm]].<ref>
{{Cite book
|last=Carroll |first=B. W.
|last2=Ostlie |first2=D. A.
|date=2007
|title=An Introduction to Modern Astrophysics
|page=121
|publisher=[[Addison-Wesley]]
|isbn=0-321-44284-9
}}</ref> For photons with greater energy than this, the energy of the emitted photoelectron is given by:

: <math> { mv^2 \over 2 } = h \nu - 13.6 eV</math>

where ''h'' is [[Planck's constant]] and ''ν'' is the [[frequency]] of the photon.

This formula defines the [[photoelectric effect]].

Not every photon which encounters an atom or ion will photoionize it. The probability of photoionization is related to the [[Photoionisation cross section|photoionization cross-section]], which depends on the energy of the photon and the target being considered. For photon energies below the ionization threshold, the photoionization cross-section is near zero. But with the development of pulsed lasers it has become possible to create extremely intense, coherent light where multi-photon ionization may occur. At even higher intensities (around 1015 - 1016 W/cm2 of infrared or visible light), [[non-perturbative]] phenomena such as ''barrier suppression ionization''<ref>
{{cite journal
| last1=Delone | first1=N. B.
| last2=Krainov | first2=V. P.
| date=1998
| title=Tunneling and barrier-suppression ionization of atoms and ions in a laser radiation field
| journal=[[Physics-Uspekhi]]
| volume=41 | issue=5 | pages=469–485
| doi=10.1070/PU1998v041n05ABEH000393
|bibcode = 1998PhyU...41..469D }}</ref> and ''rescattering ionization''<ref>
{{cite conference
|last1=Dichiara |first1=A.
|display-authors=etal
|date=2005
|title=Cross-shell multielectron ionization of xenon by an ultrastrong laser field
|booktitle=Proceedings of the Quantum Electronics and Laser Science Conference
|volume=3 |pages=1974–1976
|publisher=[[Optical Society of America]]
|doi=10.1109/QELS.2005.1549346
|isbn=1-55752-796-2
}}</ref> are observed.

===Multi-photon ionization===
{{See also|Fluorescence spectroscopy| Fluorescence| Photoionization mode}}

Several photons of energy below the ionization threshold may actually combine their energies to ionize an atom. This probability decreases rapidly with the number of photons required, but the development of very intense, pulsed lasers still makes it possible. In the perturbative regime (below about 1014 W/cm2 at optical frequencies), the probability of absorbing ''N'' photons depends on the laser-light intensity ''I'' as ''I''''N'' .<ref>
{{Cite journal
|last1=Deng|first1=Z.
|last2=Eberly|first2=J. H.
|date=1985
|title=Multiphoton absorption above ionization threshold by atoms in strong laser fields
|journal=[[Journal of the Optical Society of America B]]
|volume=2 |issue=3 |pages=491
|doi=10.1364/JOSAB.2.000486
|bibcode = 1985JOSAB...2..486D }}</ref>

[[Above threshold ionization]] (ATI) <ref>
{{Cite journal
|last1=Agostini |first1=P.
|display-authors=etal
|date=1979
|title=Free-Free Transitions Following Six-Photon Ionization of Xenon Atoms
|journal=[[Physical Review Letters]]
|volume=42 |issue=17 |pages=1127–1130
|doi=10.1103/PhysRevLett.42.1127
|bibcode=1979PhRvL..42.1127A
}}</ref> is an extension of multi-photon ionization where even more photons are absorbed than actually would be necessary to ionize the atom. The excess energy gives the released electron higher [[kinetic energy]] than the usual case of just-above threshold ionization. More precisely, The system will have multiple peaks in its [[photoelectron spectrum]] which are separated by the photon energies, this indicates that the emitted electron has more kinetic energy than in the normal (lowest possible number of photons) ionization case. The electrons released from the target will have approximately an integer number of photon-energies more kinetic energy. In intensity regions between 1014 W/cm2 and 1018 W/cm2, each of MPI, ATI, and barrier suppression ionization can occur simultaneously, each contributing to the overall ionization of the atoms involved.<ref name=mpi>
{{Cite journal
|last1=Nandor |first1=M.
|display-authors=etal
|date=1999
|title=Detailed comparison of above-threshold-ionization spectra from accurate numerical integrations and high-resolution measurements
|journal=[[Physical Review A]]
|volume=60 |pages=1771–1774|bibcode=1999PhRvA..60.1771N|doi=10.1103/PhysRevA.60.R1771}}</ref>

==Photo-Dember==
{{Main|Photo-Dember}}

In semiconductor physics the [[Photo-Dember]] effect (named after its discoverer H. Dember) consists in the formation of a charge [[dipole]] in the vicinity of a [[semiconductor]] surface after ultra-fast photo-generation of charge carriers. The dipole forms owing to the difference of mobilities (or diffusion constants) for holes and electrons which combined with the break of symmetry provided by the surface lead to an effective charge separation in the direction perpendicular to the surface.<ref name=photodember>
{{Cite journal
|last1=Dekorsy |first1=T.
|display-authors=etal
|date=1996
|title=THz electromagnetic emission by coherent infrared-active phonons
|journal=[[Physical Review B]]
|volume=53 |issue=7 |pages=4005
|doi=10.1103/PhysRevB.53.4005
|bibcode = 1996PhRvB..53.4005D }}</ref>

==Grotthuss–Draper law==
The '''Grotthuss–Draper law''' (also called the '''Principle of Photochemical Activation''') states that only that light which is absorbed by a system can bring about a photochemical change. Materials such as [[dye]]s and [[phosphor]]s must be able to absorb "light" at optical frequencies. This law provides a basis for [[fluorescence]] and [[phosphorescence]]. The law was first proposed in 1817 by [[Theodor Grotthuss]] and in 1842, independently, by [[John William Draper]].<ref name="Grotthuss–Draper-law"/>

This is considered to be one of the two basic laws of [[photochemistry]]. The second law is the [[Photoelectrochemical processes#Stark–Einstein law|Stark–Einstein law]], which says that primary chemical or physical reactions occur with each [[photon]] absorbed.<ref name="Grotthuss–Draper-law"/>

==Stark–Einstein law==
The '''Stark–Einstein law''' is named after German-born physicists [[Johannes Stark]] and [[Albert Einstein]], who independently formulated the law between 1908 and 1913. It is also known as the '''photochemical equivalence law''' or '''photoequivalence law'''. In essence it says that every photon that is absorbed will cause a (primary) chemical or physical reaction.<ref name=StarkEinsteinlaw>
{{Cite web
|title=Photochemical equivalence law
|url=http://www.britannica.com/EBchecked/topic/457732/photochemical-equivalence-law
|work=[[Encyclopædia Britannica Online]]
|accessdate=2009-11-07
}}</ref>

The photon is a quantum of radiation, or one unit of radiation. Therefore, this is a single unit of EM radiation that is equal to Planck's constant (h) times the frequency of light. This quantity is symbolized by γ, hν, or ħω.

The photochemical equivalence law is also restated as follows: for every [[mole (unit)|mole]] of a substance that reacts, an equivalent mole of quanta of light are absorbed. The formula is:<ref name=StarkEinsteinlaw/>

:<math> \Delta E_{mol} = N_A h \nu </math>

where NA is [[Avogadro's number]].

The photochemical equivalence law applies to the part of a light-induced reaction that is referred to as the primary process (i.e. [[absorption (electromagnetic radiation)|absorption]] or [[fluorescence]]).<ref name=StarkEinsteinlaw/>

In most photochemical reactions the primary process is usually followed by so-called secondary photochemical processes that are normal interactions between reactants not requiring absorption of light. As a result, such reactions do not appear to obey the one quantum–one molecule reactant relationship.<ref name=StarkEinsteinlaw/>

The law is further restricted to conventional photochemical processes using light sources with moderate intensities; high-intensity light sources such as those used in [[flash photolysis]] and in laser experiments are known to cause so-called biphotonic processes; i.e., the absorption by a molecule of a substance of two photons of light.<ref name=StarkEinsteinlaw/>

==Absorption==
{{Main|Absorption (electromagnetic radiation)}}

In [[physics]], [[Absorption (electromagnetic radiation)|absorption]] of electromagnetic radiation is the way by which the [[energy]] of a [[photon]] is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy, for example, to heat. The absorption of light during [[wave propagation]] is often called [[attenuation (electromagnetic radiation)|attenuation]]. Usually, the absorption of waves does not depend on their intensity (linear absorption), although in certain conditions (usually, in [[optics]]), the medium changes its transparency dependently on the intensity of waves going through, and the [[Saturable absorption]] (or nonlinear absorption) occurs.

==Photosensitization==
[[Photosensitization]] is a process of transferring the [[energy]] of absorbed light. After absorption, the energy is transferred to the (chosen) [[reactant]]s. This is part of the work of [[photochemistry]] in general. In particular this process is commonly employed where reactions require light sources of certain [[wavelength]]s that are not readily available.<ref name=Photosensitization/>

For example, [[mercury (element)|mercury]] absorbs radiation at 1849 and 2537 [[angstrom]]s, and the source is often high-intensity [[arc lamp|mercury lamps]]. It is a commonly used sensitizer. When mercury vapor is mixed with [[ethylene]], and the compound is [[irradiated]] with a mercury lamp, this results in the photodecomposition of ethylene to acetylene. This occurs on absorption of light to yield excited state mercury atoms, which are able to transfer this energy to the ethylene molecules, and are in turn deactivated to their initial energy state.<ref name=Photosensitization/>

[[Cadmium]]; some of the [[noble gas]]es, for example [[xenon]]; [[zinc]]; [[benzophenone]]; and a large number of organic dyes, are also used as sensitizers.<ref name=Photosensitization>
{{Cite web
|title =Photosensitization
|url=http://www.britannica.com/EBchecked/topic/458153/photosensitization
|work=[[Encyclopædia Britannica Online]]
|accessdate =2009-11-10
}}</ref>

[[Photosensitiser]]s are a key component of [[photodynamic therapy]] used to treat cancers.

==Sensitizer==
{{For|the particulate material used to create voids that aid in the initiation or propagation of an explosive's detonation wave|Explosive sensitiser}}

A '''sensitizer''' in [[chemiluminescence]] is a chemical compound, capable of [[light emission]] after it has received energy from a molecule, which became excited previously in the chemical reaction. A good example is this:

When an alkaline solution of [[sodium hypochlorite]] and a concentrated solution of [[hydrogen peroxide]] are mixed, a reaction occurs:

:ClO−(aq) + H2O2(aq) → O2*(g) + H+(aq) + Cl−(aq) + OH−(aq)

O2*is excited oxygen – meaning, one or more electrons in the O2 molecule have been promoted to higher-energy [[molecular orbital]]s. Hence, oxygen produced by this chemical reaction somehow 'absorbed' the energy released by the reaction and became excited. This energy state is unstable, therefore it will return to the [[ground state]] by lowering its energy. It can do that in more than one way:

*it can react further, without any light emission
*it can lose energy without emission, for example, giving off heat to the surroundings or transferring energy to another molecule
*it can emit light

The intensity, duration and color of emitted light depend on [[quantum mechanics|quantum]] and [[chemical kinetics|kinetical]] factors. However, excited molecules are frequently less capable of light emission in terms of brightness and duration when compared to sensitizers. This is because sensitizers can store energy (that is, be excited) for longer periods of time than other excited molecules. The energy is stored through means of [[quantum vibration]], so sensitizers are usually compounds which either include systems of [[Aromaticity|aromatic]] rings or many conjugated double and triple [[covalent bond|bonds]] in their structure. Hence, if an excited molecule transfers its energy to a sensitizer thus exciting it, longer and easier to quantify light emission is often observed.

The color (that is, the [[wavelength]]), brightness and duration of emission depend upon the sensitizer used. Usually, for a certain chemical reaction, many different sensitizers can be used.

===List of some common sensitizers===
*[[Violanthrone]]
*[[Isoviolanthrone]]
*[[Fluorescein]]
*[[Rubrene]]
*[[9,10-Diphenylanthracene]]
*[[Tetracene]]
*[[13,13'-Dibenzantronile]]
*[[Levulinic acid|Levulinic Acid]]

==Fluorescence spectroscopy==
[[Fluorescence spectroscopy]] aka fluorometry or spectrofluorometry, is a type of [[electromagnetic spectroscopy]] which analyzes [[fluorescence]] from a sample. It involves using a beam of light, usually [[ultraviolet light]], that excites the electrons in [[molecules]] of certain compounds and causes them to emit light of a lower energy, typically, but not necessarily, [[visible light]]. A complementary technique is [[absorption spectroscopy]].<ref name=Modern-spectroscopy/><ref name=sym-spectroscopy/>

Devices that measure [[fluorescence]] are called [[fluorometer]]s or fluorimeters.

==Absorption spectroscopy==
[[Absorption spectroscopy]] refers to [[spectroscopy|spectroscopic]] techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the [[absorption spectrum]]. Absorption spectroscopy is performed across the [[electromagnetic spectrum]].<ref name=Modern-spectroscopy>
{{cite book
|author=Hollas |first=J. M.
|date=2004
|title=Modern Spectroscopy
|edition=4th
|publisher=[[John Wiley & Sons]]
|isbn=0-470-84416-7
}}</ref><ref name=sym-spectroscopy>
{{cite book
|last=Harris |first=D. C.
|last2=Bertolucci |first2=M. D.
|date=1978
|title=Symmetry and Spectroscopy: An introduction to vibrational and electronic spectroscopy
|edition=Reprint
|publisher=[[Dover Publications]]
|isbn=0-486-66144-X
}}</ref>

==See also==
*[[Photoelectrochemistry]]
*[[Ionization energy]]
*[[Isomerization]]
*[[Photoionization mode]]
*[[Photochromism]]
*[[Photoelectric effect]]
*[[Photoionization detector]]

==References==
{{Reflist|30em}}

{{Use dmy dates|date=September 2010}}

{{DEFAULTSORT:Photoelectrochemical Processes}}
[[Category:Astrochemistry]]
[[Category:Chemical reactions]]
[[Category:Electron]]
[[Category:Luminescence]]
[[Category:Materials science]]
[[Category:Optics]]
[[Category:Photochemistry]]
[[Category:Physical chemistry]]
[[Category:Reaction mechanisms]]
[[Category:Semiconductors]]
[[Category:Albert Einstein]]

Graphitinterkalationsverbindungen

2017-09-16T03:37:01Z

Bibcode Bot: Adding 2 arxiv eprint(s), 4 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{multiple image
| align = right
| total_width = 300

| image1 = Potassium-graphite-xtal-3D-SF-A.png
| alt1 = KC8 (side view)
| caption1 = (side view)

| image2 = Potassium-graphite-xtal-3D-SF-B.png
| alt2 = KC8 (top view)
| link2 =
| caption2 = (top view)

| footer = Space-filling model of potassium graphite KC8.
}}

'''Graphite intercalation compounds''' ('''GICs''') are complex materials having a formula CXm where the ion Xn+ or Xn− is inserted ([[intercalation (chemistry)|intercalated]]) between the oppositely charged carbon layers. Typically m is much less than 1.<ref name=greenwood>{{Greenwood&Earnshaw2nd}}</ref><ref>{{cite journal|doi=10.1351/pac199466091893 |author=H-P Boehm |title=Nomenclature and terminology of graphite intercalation compounds |journal=Pure & Appl. Chem. |volume=66 |year=1994 |page=1893 |url=http://www.iupac.org/publications/pac/1994/pdf/6609x1893.pdf |type=PDF |issue=9 |last2=Setton |first2=R. |last3=Stumpp |first3=E. |display-authors=etal |deadurl=yes |archiveurl=https://web.archive.org/web/20120406105828/http://www.iupac.org/publications/pac/1994/pdf/6609x1893.pdf |archivedate=2012-04-06 |df= }}</ref> These materials are deeply colored solids that exhibit a range of electrical and redox properties of potential applications.

==Preparation and structure==
These materials are prepared by treating graphite with a strong oxidant or a strong reducing agent:
:C + m X → CXm
The reaction is reversible.

The host (graphite) and the guest X interact by [[charge transfer complex|charge transfer]]. An analogous process is the basis of commercial [[Lithium-ion battery|lithium-ion batteries]].

In a graphite intercalation compound not every layer is necessarily occupied by guests. In so-called ''stage 1 compounds'', graphite layers and intercalated layers alternate and in ''stage 2 compounds'', two graphite layers with no guest material in between alternate with an intercalated layer. The actual composition may vary and therefore these compounds are an example of [[stoichiometry|non-stoichiometric]] compounds. It is customary to specify the composition together with the stage. The layers are pushed apart upon incorporation of the guest ions.

==Examples==

===Alkali and alkaline earth derivatives===
[[File:Potassium graphite.jpg|thumb|Potassium graphite under argon in a [[Schlenk flask]]. A glass-coated magnetic stir bar is also present.]]
One of the best studied graphite intercalation compounds, KC8, is prepared by melting [[potassium]] over graphite powder. The potassium is absorbed into the graphite and the material changes color from black to bronze.<ref name="OttmersRase1966">{{cite journal|last1=Ottmers|first1=D.M.|last2=Rase|first2=H.F.|title=Potassium graphites prepared by mixed-reaction technique|journal=Carbon|volume=4|issue=1|year=1966|pages=125–127|issn=0008-6223|doi=10.1016/0008-6223(66)90017-0}}</ref> The resulting solid is [[pyrophoric]].<ref name="InorgChem" /> The composition is explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between anionic graphite layers and potassium cations is ionic. The electrical conductivity of the material is greater than that of α-graphite.<ref name="InorgChem" /><ref>[https://web.archive.org/web/20061006232058/http://physics.nist.gov/TechAct.2001/Div846/div846h.html NIST Ionizing Radiation Division 2001 – Major Technical Highlights]. physics.nist.gov</ref> KC8 is a [[superconductor]] with a very low critical temperature Tc = 0.14 K.<ref name=cac6>{{cite journal|author=Emery, N. |title=Review: Synthesis and superconducting properties of CaC6|journal=Sci. Technol. Adv. Mater.|type=PDF|volume=9|year=2008|page=044102|doi=10.1088/1468-6996/9/4/044102|bibcode=2008STAdM...9d4102E|issue=4|last2=Hérold|first2=Claire|last3=Marêché|first3=Jean-François|last4=Lagrange|first4=Philippe|display-authors=etal|pmc=5099629|pmid=27878015}}</ref> Heating KC8 leads to the formation of a series of decomposition products as the K atoms are eliminated:{{citation needed|date=April 2016}}

: 3 KC8 → KC24 + 2 K
Via the intermediates KC24 (blue in color),<ref name="OttmersRase1966"/> KC36, KC48, ultimately the compound KC60 results.

The stoichiometry MC8 is observed for M = K, Rb and Cs. For smaller ions M = Li+, Sr2+, Ba2+, Eu2+, Yb3+, and Ca2+, the limiting stoichiometry is MC6.<ref name=cac6/> Calcium graphite {{chem|CaC|6}} is obtained by immersing highly oriented [[pyrolytic graphite]] in liquid Li–Ca alloy for 10 days at 350 °C. The crystal structure of {{chem|CaC|6}} belongs to the R{{overline|3}}m space group. The graphite interlayer distance increases upon Ca intercalation from 3.35 to 4.524 Å, and the carbon-carbon distance increases from 1.42 to 1.444 Å.
[[File:CaC6structure.jpg|thumb|Structure of {{chem|CaC|6}}]]

With [[barium]] and [[ammonia]], the cations are solvated, giving the stoichiometry (Ba(NH3)2.5C10.9(stage 1)) or those with [[caesium]], [[hydrogen]] and [[potassium]] (CsC8·K2H4/3C8(stage 1)).

Interestingly, different from other alkali metals, the amount of Na intercalation is very small. Quantum-mechanical calculations show that this originate from a quite general phenomenon: among the alkali and alkaline earth metals, Na and Mg generally have the weakest chemical binding to a given substrate, compared with the other elements in the same group of the periodic table.<ref name="PNAS 2016">{{cite journal|last1=Liu|first1=Yuanyue|last2=Merinov|first2=Boris V.|last3=Goddard|first3=William A.|title=Origin of low sodium capacity in graphite and generally weak substrate binding of Na and Mg among alkali and alkaline earth metals|journal=Proceedings of the National Academy of Sciences|date=5 April 2016|volume=113|issue=14|pages=3735–3739|doi=10.1073/pnas.1602473113|pmid=27001855|pmc=4833228|arxiv=1604.03602|bibcode=2016PNAS..113.3735L}}</ref> The phenomenon arises from the competition between trends in the ionization energy and the ion–substrate coupling, down the columns of the periodic table.<ref name="PNAS 2016"/> However, considerable Na intercalation into graphite can occur in cases when the ion is wrapped in a solvent shell through the process of co-intercalation.

===Graphite bisulfate, perchlorate, hexafluoroarsenate: oxidized carbons===
The intercalation compounds graphite bisulfate and graphite perchlorate can be prepared by treating graphite with strong oxidizing agents in the presence of strong acids. In contrast to the potassium and calcium graphites, the carbon layers are oxidized in this process:
48 C + 0.25 O2 + 3 H2SO4 → [C24]+[HSO4]−·2H2SO4 + 0.5 H2O

In graphite perchlorate, planar layers of carbon atoms are 794 [[Picometre|picometers]] apart, separated by ClO4− ions. Cathodic reduction of graphite perchlorate is analogous to heating KC8, which leads to a sequential elimination of HClO4.

Both graphite bisulfate and graphite perchlorate are better conductors as compared to graphite, as predicted by using a positive-hole mechanism.<ref name="InorgChem">{{cite book
| title = Inorganic Chemistry, 3rd Edition
| chapter = Chapter 14: The group 14 elements
| author1 = Catherine E. Housecroft
| author2 = Alan G. Sharpe
| publisher = Pearson
| year = 2008
| isbn = 978-0-13-175553-6
| page = 386
}}</ref>
Reaction of graphite with [O2]+[AsF6]− affords the salt [C8]+[AsF6]−.<ref name="InorgChem" />

===Metal halide derivatives===
A number of metal halides intercalate into graphite. The chloride derivatives have been most extensively studied. Examples include MCl2 (M = Zn, Ni, Cu, Mn), MCl3 (M = Al, Fe, Ga), MCl4 (M = Zr, Pt), etc.<ref name=greenwood/> The materials consists of layers of close-packed metal halide layers between sheets of carbon. The derivative C~8FeCl3 exhibits [[spin glass]] behavior.<ref>{{cite journal|doi=10.1088/0022-3719/16/4/001 |title=Observation of spin glass state in FeCl3: intercalated graphite |journal=Journal of Physics C: Solid State Physics |volume=16 |issue=4 |pages=L89 |year=1983 |last1=Millman |first1=S E |last2=Zimmerman |first2=G O |bibcode=1983JPhC...16L..89M }}</ref> It proved to be a particularly fertile system on which to study phase transitions.{{citation needed|date=April 2015}} A stage n magnetic GIC has n graphite layers separating successive magnetic layers. As the stage number increases the interaction between spins in successive magnetic layers becomes weaker and 2D magnetic behaviour may arise.

===Halogen- and oxide-graphite compounds===
Chlorine and bromine reversibly intercalate into graphite. Iodine does not. Fluorine reacts irreversibly. In the case of bromine, the following stoichiometries are known: CnBr for n = 8, 12, 14, 16, 20, and 28.

Because it forms irreversibly, [[carbon monofluoride]] is often not classified as an intercalation compound. It has the formula (CF)x. It is prepared by reaction of gaseous [[fluorine]] with graphitic carbon at 215–230 °C. The color is greyish, white, or yellow. The bond between the carbon and fluorine atoms is covalent. Tetracarbon monofluoride (C4F) is prepared by treating graphite with a mixture of fluorine and [[hydrogen fluoride]] at room temperature. The compound has a blackish-blue color. Carbon monofluoride is not electrically conductive. It has been studied as a [[cathode]] material in one type of primary (non-rechargeable) [[lithium battery|lithium batteries]].

[[Graphite oxide]] is an unstable yellow solid.

==Properties and applications==
Graphite intercalation compounds have fascinated materials scientists for many years owing to their diverse electronic and electrical properties.

===Superconductivity===
Among the superconducting graphite intercalation compounds, {{chem|CaC|6}} exhibits the highest critical temperature Tc = 11.5 K, which further increases under applied pressure (15.1 K at 8 GPa).<ref name=cac6/> Superconductivity in these compounds is thought to be related to the role of an interlayer state, a free electron like band lying roughly {{convert|2|eV|aJ|abbr=on}} above the [[Fermi level]]; superconductivity only occurs if the interlayer state is occupied.<ref name=Yang>{{cite journal|author=Csányi|title=The role of the interlayer state in the electronic structure of superconducting graphite intercalated compounds|doi=10.1038/nphys119|journal=Nature Physics|volume=1|year=2005|pages=42–45|bibcode = 2005NatPh...1...42C |last2=Littlewood|first2=P. B.|last3=Nevidomskyy|first3=Andriy H.|last4=Pickard|first4=Chris J.|last5=Simons|first5=B. D.|issue=1|display-authors=etal|arxiv=cond-mat/0503569}}</ref> Analysis of pure {{chem|CaC|6}} using a high quality [[ultraviolet light]] revealed to conduct [[angle-resolved photoemission spectroscopy]] measurements. The opening of a superconducting gap in the π* band revealed a substantial contribution to the total electron–phonon-coupling strength from the π*-interlayer interband interaction.<ref name=Yang/>

===Reagents in chemical synthesis: KC8===
The bronze-colored material KC8 is one of the strongest [[reducing agents]] known. It has also been used as a [[catalyst]] in [[polymerization]]s and as a [[coupling reaction|coupling reagent]] for [[aryl halide]]s to [[biphenyl]]s.<ref name=Chakraborty/> In one study, freshly prepared KC8 was treated with 1-iodododecane delivering a modification ([[micrometre]] scale carbon platelets with long alkyl chains sticking out providing solubility) that is soluble in [[chloroform]].<ref name=Chakraborty>{{cite journal|author=Chakraborty, S. |title=Functionalization of Potassium Graphite|doi=10.1002/anie.200605175|journal=Angew. Chem. Int. Ed.|volume=46|year=2007|pages=4486–8|pmid=17477336|issue=24|last2=Chattopadhyay|first2=Jayanta|last3=Guo|first3=Wenhua|last4=Billups|first4=W. Edward|display-authors=etal}}</ref> Another potassium graphite compound, KC24, has been used as a neutron monochromator. A new essential application for potassium graphite was introduced by the invention of the [[potassium-ion battery]]. Like the [[lithium-ion battery]], the [[potassium-ion battery]] should use a carbon-based anode instead of a metallic anode. In this circumstance, the stable structure of potassium graphite is an important advantage.

==See also==
*[[Covalent superconductors]]
*[[Magnesium diboride]], which uses hexagonal planar [[boron]] sheets instead of carbon
*[[Pyrolytic graphite]]

== References ==
{{reflist|30em}}

==Further reading==
{{refbegin}}
*{{cite book| author =T. Enoki, M. Suzuki and M. Endo |title= Graphite intercalation compounds and applications| publisher =Oxford University Press |year =2003| isbn =0-19-512827-3}}
*{{cite journal|author=M.S. Dresselhaus and G. Dresselhaus Review:|title=Intercalation compounds of graphite|doi=10.1080/00018738100101367|journal=Advances in Physics|volume=30|year=1981|pages=139–326|bibcode = 1981AdPhy..30..139D|issue=2 }} (187 pages), also reprinted as {{cite journal|last1=Dresselhaus|first1=M. S.|last2=Dresselhaus|first2=G.|title=Intercalation compounds of graphite|doi=10.1080/00018730110113644|journal=Advances in Physics|volume=51|year=2002|pages=1–186|bibcode=2002AdPhy..51....1D}}
*{{cite journal|doi=10.1351/pac198557121887|author=D. Savoia|title=Applications of potassium-graphite and metals dispersed on graphite in organic synthesis|journal=Pure & Appl. Chem.|volume=57|year=1985|page=1887|url=http://www.iupac.org/publications/pac/1985/pdf/5712x1887.pdf|type=PDF|issue=12|last2=Trombini|first2=C.|last3=Umani-Ronchi|first3=A.|display-authors=etal}}
*{{cite journal|last=Suzuki|first=Itsuko S. |author2=Ting-Yu Huang |author3=Masatsugu Suzuki|title=Magnetic phase diagram of the stage-1 CoCl2 graphite intercalation compound: Existence of metamagnetic transition and spin-flop transitions|journal=Phys. Rev. B|date=13 June 2002|volume=65|issue=22 |page=224432|doi=10.1103/PhysRevB.65.224432|bibcode=2002PhRvB..65v4432S}}
*{{cite journal|last=Rancourt|first=DG|author2=C Meschi |author3=S Flandrois |title=S=1/2 antiferromagnetic finite chains effectively isolated by frustration: CuCl2-intercalated graphite.|journal=Phys Rev B|date=1986|volume=33|issue=1|pages=347–355|doi=10.1103/PhysRevB.33.347|pmid=9937917|bibcode=1986PhRvB..33..347R}}
{{refend}}

== External links ==
{{Commons category|Graphite intercalation compounds}}

{{DEFAULTSORT:Graphite Intercalation Compound}}
[[Category:Inorganic carbon compounds]]
[[Category:Supramolecular chemistry]]

CarbFix

2017-09-15T18:01:21Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Update|date=April 2016}}

'''CarbFix''' is a project in Iceland intended to lock away [[carbon dioxide]] by reacting it with [[basalt]]ic rocks.<ref name=carbfix/> Work on the project began in 2007. The CarbFix team involves American and Icelandic researchers including [[Iceland]] geologist Sigurdur Reynir Gislason serving as chief scientist, project technical manager Bergur Sigfusson, manager Juerg Matter who works with Columbia University's [[Lamont-Doherty Earth Observatory]] and scientific overseer, [[Wallace S. Broecker]] (also with Columbia). Reykjavik Energy has supplied almost half the $10 million spent thus far on CarbFix. Other sponsors include U.S. and Icelandic universities. In addition to finding a new method for permanent [[Carbon capture and storage|carbon dioxide storage]], another objective of the project is to train scientists for years of work to come.<ref>{{Cite news|title=That CO2 warming the world: Lock it in a rock |url=http://www.mercurynews.com/science-headlines/ci_18773956|accessdate =11 October 2011}}</ref>

==Theory==
Carbonated water is injected into the rock and hopefully reacts with the Ca and Mg present.<ref name=carbfix/>
This is called [[enhanced weathering]], calcium and magnesium are present in basalt - but rarely as simple oxides where the equations would be simple:
* CaO + {{CO2|link=yes}} → CaCO3
* MgO + CO2 → MgCO3

However [[silicate mineral]]s of these elements are common in [[basalt]], so an example reaction might be:
* Mg2SiO4 + 2CO2 → 2MgCO3 + SiO2
as a result CO2 is locked away with no dangerous byproducts.

==Practicalities==
Drilling and injecting carbonated water at high pressure into basaltic rocks at [[Hellisheiði Power Station|Hellisheidi]] <ref name=carbfix>{{Cite web|title=CarbFix: About the Project |url=http://www.or.is/English/Projects/CarbFix/AbouttheProject/ |accessdate=15 September 2011 |deadurl=yes |archiveurl=https://web.archive.org/web/20111021093135/http://www.or.is/English/Projects/CarbFix/AbouttheProject/ |archivedate=21 October 2011 |df= }}</ref> is not without cost.

This 10 million dollar project is due to commence carbon injection in October 2011.<ref name=co2starts/> The funding was supplied by the [[University of Iceland]], [[Columbia University]], France's [[Centre National de la Recherche Scientifique|National Centre of Scientific Research]], the [[United States Department of Energy]], the [[European Union|EU]], [[Scandinavia]]n funds and [[Reykjavik Energy]].<ref name=co2starts>{{cite news|title=Iceland’s Hellisheidi prepares to start injection at carbon storage project|url=http://www.ifandp.com/article/0013593.html|date=9 September 2011 }}</ref>

==Possible problems==
These reactions are [[exothermic]] and [[reversible reaction|reversible]] if the rock is later heated.

The nearby [[Hengill]] volcano, generated a [[earthquake swarm|swarm]] of low magnitude [[earthquakes]] as a result of pumping water without the CO2, with 250 quakes being reported on 13 September 2011.<ref name=othergases>{{Cite news|url=http://www.ruv.is/frett/vatnsdaeling-veldur-skjalftum|title=Water pumping causes tremor|date=13 September 2011|language=Icelandic}}</ref>
There have been earthquakes reported there due to the water pumping previously.<ref>{{Cite news|url=http://www.visir.is/orkuveitan-framkallar-jardskjalfta-i-henglinum/article/2011110229859|title=Orkuveitan framkallar jarðskjálfta í Henglinum|date=21 February 2011|language=Icelandic}}</ref><ref>{{Cite web|url=http://www.jonfr.com/volcano/?p=570 |title=Human made earthquakes in Hengill volcano |date=21 February 2011 }}</ref> Proceedings at the [[2010 World Geothermal Congress]] reported that reinjection at Hellisheidi had [[induced seismicity|induced seismic]] activity.<ref>{{Cite web|url=http://b-dig.iie.org.mx/BibDig/P10-0464/pdf/2308.pdf |title=Geothermal Reinjection at the Hengill Triple Junction, SW Iceland |accessdate=27 September 2011 }}{{dead link|date=November 2016 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

===Other gases===
There are reports that not only CO2 is intended to be fixed. [[Hydrogen sulfide]] may also be injected.<ref name=othergases/>

==Current status==
The CarbFix project showed in 2016 that 95% of the injected 250 tonnes of CO2 were solidified into [[calcite]] in 2 years, using 25 tonnes of water per tonne of CO2.<ref name=Matter>{{cite journal |last1=Matter |first1=Juerg M. |last2=Stute |first2=Martin |last3=Snæbjörnsdottir |first3=Sandra O. |last4=Oelkers |first4=Eric H. |last5=Gislason|first5=Sigurdur R. |last6=Aradottir|first6=Edda S.|last7=Sigfusson|first7=Bergur|last8=Gunnarsson|first8=Ingvi|last9=Sigurdardottir|first9=Holmfridur|last10=Gunlaugsson|first10=Einar|last11=Axelsson|first11=Gudni|last12=Alfredsson|first12=Helgi A.|last13=Wolff-Boenisch|first13=Domenik|last14=Mesfin|first14=Kiflom|last15=Fernandez de la Reguera Taya|first15=Diana|last16=Hall|first16=Jennifer|last17=Dideriksen|first17=Knud|last18=Broecker|first18=Wallace S.|title=Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions |journal=Science |date=June 10, 2016 |volume=352 |issue=6291 |pages=1312–1314 |doi=10.1126/science.aad8132|url=http://science.sciencemag.org/content/352/6291/1312|accessdate=10 June 2016 |pmid=27284192|bibcode=2016Sci...352.1312M}}</ref><ref>{{cite web|url=https://www.theverge.com/2016/6/10/11901368/carbon-dioxide-capture-storage-stone-climate-change-study|title=Scientists turn carbon dioxide into stone to combat global warming|date=10 June 2016|publisher=Vox Media|work=The Verge|accessdate=11 June 2016}}</ref>

==References==
{{Reflist}}

==External links==
*{{YouTube|0iqBUSvnsAg|To combat climate change, these scientists are turning CO2 into rock}}, Aug 23, 2016 [[PBS NewsHour]]

[[Category:Emissions reduction]]
[[Category:Environment of Iceland]]
[[Category:Climate engineering]]

Basissatz (Chemie)

2017-09-15T16:18:49Z

Bibcode Bot: Adding 0 arxiv eprint(s), 2 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

A '''basis set''' in [[theoretical chemistry|theoretical]] and [[computational chemistry]] is a set of [[Function (mathematics)|functions]] (called basis functions) that is used to represent the electronic wave function in the [[Hartree–Fock method]] or [[Density functional theory|density-functional theory]] in order to turn the partial differential equations of the model into algebraic equations suitable for efficient implementation on a computer.

The use of basis sets is equivalent to the use of an approximate resolution of the identity. The single-particle states ([[molecular orbital]]s) are then expressed as linear combinations of the basis functions.

The basis set can either be composed of [[atomic orbital]]s (yielding the [[linear combination of atomic orbitals]] approach), which is the usual choice within the quantum chemistry community, or [[plane wave]]s which are typically used within the solid state community. Several types of atomic orbitals can be used: [[Gaussian orbital|Gaussian-type orbitals]], [[Slater-type orbital]]s, or numerical atomic orbitals. Out of the three, Gaussian-type orbitals are by far the most often used, as they allow efficient implementations of [[Post-Hartree–Fock]] methods.

==Introduction==

In modern [[computational chemistry]], [[Quantum chemistry|quantum chemical]] calculations are performed using a finite set of [[basis function]]s. When the finite basis is expanded towards an (infinite) complete set of functions, calculations using such a basis set are said to approach the complete basis set (CBS) limit. In this article, ''basis function'' and ''atomic orbital'' are sometimes used interchangeably, although it should be noted that the basis functions are usually not true atomic orbitals, because many basis functions are used to describe polarization effects in molecules.

Within the basis set, the [[wavefunction]] is represented as a [[vector (geometric)|vector]], the components of which correspond to coefficients of the basis functions in the linear expansion. One-electron [[operator (physics)|Operators]] correspond to [[matrix (mathematics)|matrices]], (rank two [[tensors]]), in this basis, whereas two-electron operators are rank four tensors.

When molecular calculations are performed, it is common to use a basis composed of [[atomic orbital]]s, centered at each nucleus within the molecule ([[linear combination of atomic orbitals]] [[ansatz]]). The physically best motivated basis set are [[Slater-type orbitals]] (STOs),
which are solutions to the [[Schrödinger equation]] of [[hydrogen-like atom]]s, and decay exponentially far away from the nucleus. While hydrogen-like atoms lack many-electron interactions, it can be shown that the [[molecular orbital]]s of [[Hartree-Fock method|Hartree-Fock]] and [[density-functional theory]] also exhibit exponential decay. Furthermore, S-type STOs also satisfy [[Kato theorem|Kato's cusp condition]] at the nucleus, meaning that they are able to accurately describe electron density near the nucleus.

However, calculating integrals with STOs is computationally difficult and it was later realized by [[S. Francis Boys|Frank Boys]] that STOs could be approximated as linear combinations of [[Gaussian orbital|Gaussian-type orbitals]] (GTOs) instead. Because the product of two GTOs can be written as a linear combination of GTOs, integrals with Gaussian basis functions can be written in closed form, which leads to huge computational savings (see [[John Pople]]).

Dozens of Gaussian-type orbital basis sets have been published in the literature.<ref>{{cite journal|last=Jensen|first=Frank|title=Atomic orbital basis sets|journal=WIREs Comput. Mol. Sci.|year=2013|volume=3|pages=273–295|doi=10.1002/wcms.1123}}</ref> Basis sets typically come in hierarchies of increasing size, giving a controlled way to obtain a more accurate solutions, however at a higher cost.

The smallest basis sets are called ''minimal basis sets''. A minimal basis set is one in which, on each atom in the molecule, a single basis function is used for each orbital in a [[Hartree–Fock]] calculation on the free atom. For atoms such as lithium, basis functions of p type are also added to the basis functions that correspond to the 1s and 2s orbitals of the free atom, because lithium also has a 1s2p bound state. For example, each atom in the second period of the periodic system (Li - Ne) would have a basis set of five functions (two s functions and three p functions).

[[File:D-polarization function.png|thumb|200px|right|A d-polarization function added to a p orbital<ref>{{cite book | title = Computational Chemistry: Introduction to the Theory and Applications of Molecular and Quantum Mechanics | isbn = 978-1402072857 | edition = 1st | author = Errol G. Lewars | publisher = Springer}}</ref>]]

The minimal basis set is close to exact for the gas-phase atom. In the next level, additional functions are added to describe polarization of the electron density of the atom in molecules. These are called '''polarization functions'''. For example, while the minimal basis set for hydrogen is one function approximating the 1s atomic orbital, a simple polarized basis set typically has two s- and one p-function (which consists of three basis functions: px, py and pz). This adds flexibility to the basis set, effectively allowing molecular orbitals involving the hydrogen atom to be more asymmetric about the hydrogen nucleus. This is very important for modeling chemical bonding, because the bonds are often polarized. Similarly, d-type functions can be added to a basis set with valence p orbitals, and f-functions to a basis set with d-type orbitals, and so on.

Another common addition to basis sets is the addition of '''diffuse functions'''. These are extended Gaussian basis functions with a small exponent, which give flexibility to the "tail" portion of the atomic orbitals, far away from the nucleus. Diffuse basis functions are important for describing anions or dipole moments, but they can also be important for accurate modeling of intra- and intermolecular bonding.

== Minimal basis sets ==

The most common minimal basis set is [[STO-nG basis sets|STO-nG]], where n is an integer. This ''n'' value represents the number of Gaussian primitive functions comprising a single basis function. In these basis sets, the same number of Gaussian primitives comprise core and valence orbitals. Minimal basis sets typically give rough results that are insufficient for research-quality publication, but are much cheaper than their larger counterparts. Commonly used minimal basis sets of this type are:

* STO-3G
* STO-4G
* STO-6G
* STO-3G* - Polarized version of STO-3G

There are several other minimum basis sets that have been used such as the MidiX basis sets.

== Split-valence basis sets ==

During most molecular bonding, it is the valence electrons which principally take part in the bonding. In recognition of this fact, it is common to represent valence orbitals by more than one basis function (each of which can in turn be composed of a fixed linear combination of primitive Gaussian functions). Basis sets in which there are multiple basis functions corresponding to each valence atomic orbital are called valence double, triple, quadruple-zeta, and so on, basis sets (zeta, ζ, was commonly used to represent the exponent of an STO basis function<ref>{{cite journal | last = Davidson | first = Ernest |author2=Feller, David | authorlink = Ernest R. Davidson | journal = Chem. Rev. | title = Basis set selection for molecular calculations | year = 1986 | volume = 86 | issue = 4 | pages = 681–696 | doi = 10.1021/cr00074a002 }}</ref>). Since the different orbitals of the split have different spatial extents, the combination allows the electron density to adjust its spatial extent appropriate to the particular molecular environment. In contrast, minimal basis sets lack the flexibility to adjust to different molecular environments.

=== Pople basis sets ===

The notation for the ''split-valence'' basis sets arising from the group of [[John Pople]] is typically ''X-YZg''.<ref>{{cite journal|last=Ditchfield|first=R|author2=Hehre, W.J|author3= Pople, J. A.|title=Self-Consistent Molecular-Orbital Methods. IX. An Extended Gaussian-Type Basis for Molecular-Orbital Studies of Organic Molecules|journal=J. Chem. Phys.|year=1971|volume=54|issue=2|pages=724–728|doi=10.1063/1.1674902|bibcode = 1971JChPh..54..724D }}</ref> In this case, ''X'' represents the number of primitive Gaussians comprising each core atomic orbital basis function. The ''Y'' and ''Z'' indicate that the valence orbitals are composed of two basis functions each, the first one composed of a linear combination of ''Y'' primitive Gaussian functions, the other composed of a linear combination of ''Z'' primitive Gaussian functions. In this case, the presence of two numbers after the hyphens implies that this basis set is a ''split-valence double-zeta'' basis set. Split-valence triple- and quadruple-zeta basis sets are also used, denoted as ''X-YZWg'', ''X-YZWVg'', etc. Here is a list of commonly used split-valence basis sets of this type:

* 3-21G
* 3-21G* - Polarization functions on heavy atoms
* 3-21G** - Polarization functions on heavy atoms and hydrogen
* 3-21+G - Diffuse functions on heavy atoms
* 3-21++G - Diffuse functions on heavy atoms and hydrogen
* 3-21+G* - Polarization ''and'' diffuse functions on heavy atoms
* 3-21+G** - Polarization functions on heavy atoms and hydrogen, as well as diffuse functions on heavy atoms
* 4-21G
* 4-31G
* 6-21G
* 6-31G
* 6-31G*
* 6-31+G*
* 6-31G(3df, 3pd)
* 6-311G
* 6-311G*
* 6-311+G*
The 6-31G* basis set (defined for the atoms H through Zn) is a valence double-zeta polarized basis set that adds to the 6-31G set six ''d''-type Cartesian-Gaussian polarization functions on each of the atoms Li through Ca and ten ''f''-type Cartesian Gaussian polarization functions on each of the atoms Sc through Zn.

Pople basis sets are somewhat outdated, as correlation-consistent or polarization-consistent basis sets typically yield better results with similar resources. Also note that some Pople basis sets have grave deficiencies that may lead to incorrect results.<ref>{{cite journal|last=Moran|first=Damian|last2=Simmonett|first2=Andrew C.|last3=Leach|first3=Franklin E. III|last4=Allen|first4=Wesley D.|last5=Schleyer|first5=Paul v. R.|last6=Schaefer|first6=Henry F.|title=Popular theoretical methods predict benzene and arenes to be nonplanar|journal=J. Am. Chem. Soc.|year=2006|volume=128|pages=9342–9343|doi=10.1021/ja0630285}}</ref>

== Correlation-consistent basis sets ==
Ones of the most widely used basis sets are those developed by [[Thom H. Dunning, Jr.|Dunning]] and coworkers,<ref>{{cite journal|last=Dunning|first=Thomas H.|title=Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen|journal=J. Chem. Phys.|year=1989|volume=90|issue=2|pages=1007–1023|doi=10.1063/1.456153|bibcode = 1989JChPh..90.1007D }}</ref> since they are designed for converging [[Post-Hartree–Fock]] calculations systematically to the complete basis set limit using empirical extrapolation techniques.

For first- and second-row atoms, the basis sets are cc-pVNZ where N=D,T,Q,5,6,... (D=double, T=triples, etc.). The 'cc-p', stands for 'correlation-consistent polarized' and the 'V' indicates they are valence-only basis sets. They include successively larger shells of polarization (correlating) functions (''d'', ''f'', ''g'', etc.). More recently these 'correlation-consistent polarized' basis sets have become widely used and are the current state of the art for correlated or [[post-Hartree–Fock]] calculations. Examples of these are:

* cc-pVDZ - Double-zeta
* cc-pVTZ - Triple-zeta
* cc-pVQZ - Quadruple-zeta
* cc-pV5Z - Quintuple-zeta, etc.
* aug-cc-pVDZ, etc. - Augmented versions of the preceding basis sets with added diffuse functions.
* cc-pCVDZ - Double-zeta with core correlation

For period-3 atoms (Al-Ar), additional functions have turned out to be necessary; these are the cc-pV(N+d)Z basis sets. Even larger atoms may employ pseudopotential basis sets, cc-pVNZ-PP, or relativistic-contracted Douglas-Kroll basis sets, cc-pVNZ-DK.

While the usual Dunning basis sets are for valence-only calculations, the sets can be augmented with further functions that describe core electron correlation. These core-valence sets (cc-pCVXZ) can be used to approach the exact solution to the all-electron problem, and they are necessary for accurate geometric and nuclear property calculations.

Weighted core-valence sets (cc-pwCVXZ) have also been recently suggested. The weighted sets aim to capture core-valence correlation, while neglecting most of core-core correlation, in order to yield accurate geometries with smaller cost than the cc-pCVXZ sets.

Diffuse functions can also be added for describing anions and long-range interactions such as Van der Waals forces, or to perform electronic excited-state calculations, electric field property calculations. A recipe for constructing additional augmented functions exists; as many as five augmented functions have been used in second hyperpolarizability calculations in the literature. Because of the rigorous construction of these basis sets, extrapolation can be done for almost any energetic property. However, care must be taken when extrapolating energy differences as the individual energy components converge at different rates: the Hartree-Fock energy converges exponentially, whereas the correlation energy converges only polynomially.

{| class="wikitable"
|-
!
! H-He
! Li-Ne
! Na-Ar
|-
| cc-pVDZ
| [2''s''1''p''] → 5 func.
| [3''s''2''p''1''d''] → 14 func.
| [4''s''3''p''1''d''] → 18 func.
|-
| cc-pVTZ
| [3''s''2''p''1''d''] → 14 func.
| [4''s''3''p''2''d''1''f''] → 30 func.
| [5''s''4''p''2''d''1''f''] → 34 func.
|-
| cc-pVQZ
| [4''s''3''p''2''d''1''f''] → 30 func.
| [5''s''4''p''3''d''2''f''1''g''] → 55 func.
| [6''s''5''p''3''d''2''f''1''g''] → 59 func.
|-
|}
To understand how to get the number of functions take the cc-pVDZ basis set for H:
There are two ''s'' (''L'' = 0) orbitals and one ''p'' (''L'' = 1) orbital that has 3 [[angular momentum#Angular momentum in quantum mechanics|components]] along the ''z''-axis (''m''L = -1,0,1) corresponding to ''p''''x'', ''p''''y'' and ''p''''z''. Thus, five spatial orbitals in total. Note that each orbital can hold two electrons of opposite spin.

For example, Ar [1s, 2s, 2p, 3s, 3p] has 3 s orbitals (L=0) and 2 sets of p orbitals (L=1). Using cc-pVDZ, orbitals are [1s, 2s, 2p, 3s, 3s', 3p, 3p', 3d'] (where ' represents the added in polarisation orbitals), with 4 s orbitals, 3 sets of p orbitals and 1 set of d orbitals.

== Polarization-consistent basis sets ==

[[Density-functional theory]] has recently become widely used in [[computational chemistry]]. However, the correlation-consistent basis sets described above are suboptimal for density-functional theory, because the correlation-consistent sets have been designed for [[Post-Hartree–Fock]], while density-functional theory exhibits much more rapid basis set convergence than wave function methods.

Adopting a similar methodology to the correlation-consistent series, Frank Jensen introduced polarization-consistent (pc-n) basis sets as a way to quickly converge density functional theory calculations to the complete basis set limit.<ref>{{cite journal|last=Jensen|first=Frank|title=Polarization consistent basis sets: Principles|journal=J. Chem. Phys.|year=2001|volume=115|issue=20|pages=9113–9125|doi=10.1063/1.1413524|bibcode=2001JChPh.115.9113J}}</ref> Like the Dunning sets, the pc-n sets can be combined with basis set extrapolation techniques to obtain CBS values.

The pc-n sets can be augmented with diffuse functions to obtain augpc-n sets.

== Karlsruhe basis sets ==

Karlsruhe basis sets come in various flavors

* def2-SV(P) - Split valence with polarization functions on heavy atoms (not hydrogen)
* def2-SVP - Split valence polarization
* def2-SVPD - Split valence polarization with diffuse functions
* def2-TZVP - Valence triple-zeta polarization
* def2-TZVPD - Valence triple-zeta polarization with diffuse functions
* def2-TZVPP - Valence triple-zeta with two sets of polarization functions
* def2-TZVPPD - Valence triple-zeta with two sets of polarization functions and a set of diffuse functions
* def2-QZVP - Valence quadruple-zeta polarization
* def2-QZVPD - Valence quadruple-zeta polarization with diffuse functions
* def2-QZVPP - Valence quadruple-zeta with two sets of polarization functions
* def2-QZVPPD - Valence quadruple-zeta with two sets of polarization functions and a set of diffuse functions

== Completeness-optimized basis sets ==

Gaussian-type orbital basis sets are typically optimized to reproduce the lowest possible energy for the systems used to train the basis set. However, the convergence of the energy does not imply convergence of other properties, such as nuclear magnetic shieldings, the dipole moment, or the electron momentum density, which probe different aspects of the electronic wave function.

Manninen and Vaara have proposed completeness-optimized basis sets,<ref>{{cite journal|last=Manninen|first=Pekka|last2=Vaara|first2=Juha|title=Systematic Gaussian basis-set limit using completeness-optimized primitive sets. A case for magnetic properties|journal=J. Comput. Chem.|year=2006|volume=27|issue=4|pages=434–445|doi=10.1002/jcc.20358}}</ref> where the exponents are obtained by maximization of the one-electron completeness profile<ref>{{cite journal|last=Chong|first=Delano P.|title=Completeness profiles of one-electron basis sets|journal=Can. J. Chem.|year=1995|volume=73|issue=1|pages=79–83|doi=10.1139/v95-011}}</ref> instead of minimization of the energy. Complenetess-optimized basis sets are a way to easily approach the complete basis set limit of any property at any level of theory, and the procedure is simple to automatize.<ref>{{cite journal|last=Lehtola|first=Susi|title=Automatic algorithms for completeness-optimization of Gaussian basis sets|journal=J. Comput. Chem.|year=2015|volume=36|issue=5|pages=335–347|doi=10.1002/jcc.23802}}</ref>

Completeness-optimized basis sets are tailored to a specific property. This way, the flexibility of the basis set can be focused on the computational demands of the chosen property, typically yielding much faster convergence to the complete basis set limit than is achievable with energy-optimized basis sets.

== Plane-wave basis sets ==

In addition to localized basis sets, [[plane wave|plane-wave]] basis sets can also be used in quantum-chemical simulations. Typically, the choice of the plane wave basis set is based on a cutoff energy. The plane waves in the simulation cell that fit below the energy criterion are then included in the calculation. These basis sets are popular in calculations involving three-dimensional [[periodic boundary conditions]].

The main advantage of a plane-wave basis is that it is guaranteed to converge in a ''smooth, monotonic manner'' to the target wavefunction. In contrast, when localized basis sets are used, monotonic convergence to the basis set limit may be difficult due to problems with over-completeness: in a large basis set, functions on different atoms start to look alike, and many eigenvalues of the overlap matrix approach zero.

In addition, certain integrals and operations are much easier to program and carry out with plane-wave basis functions than with their localized counterparts. For example, the kinetic energy operator is diagonal in the reciprocal space. Integrals over real-space operators can be efficiently carried out using [[Fast Fourier Transform|fast Fourier transforms]]. The properties of the Fourier Transform allow a vector representing the gradient of the total energy with respect to the plane-wave coefficients to be calculated with a computational effort that scales as NPW*ln(NPW) where NPW is the number of plane-waves. When this property is combined with separable pseudopotentials of the Kleinman-Bylander type and pre-conditioned conjugate gradient solution techniques, the dynamic simulation of periodic problems containing hundreds of atoms becomes possible.

In practice, plane-wave basis sets are often used in combination with an 'effective core potential' or [[pseudopotential]], so that the plane waves are only used to describe the valence charge density. This is because core electrons tend to be concentrated very close to the atomic nuclei, resulting in large wavefunction and density gradients near the nuclei which are not easily described by a plane-wave basis set unless a very high energy cutoff, and therefore small wavelength, is used. This combined method of a plane-wave basis set with a core [[pseudopotential]] is often abbreviated as a ''PSPW'' calculation.

Furthermore, as all functions in the basis are mutually orthogonal and are not associated with any particular atom, plane-wave basis sets do not exhibit [[basis set superposition error|basis-set superposition error]]. However, the plane-wave basis set is dependent on the size of the simulation cell, complicating cell size optimization.

Due to the assumption of periodic boundary conditions, plane-wave basis sets are less well suited to gas-phase calculations than localized basis sets. Large regions of vacuum need to be added on all sides of the gas-phase molecule in order to avoid interactions with the molecule and its periodic copies. However, the plane waves use a similar accuracy to describe the vacuum region as the region where the molecule is, meaning that obtaining the truly noninteracting limit may be computationally costly.

== Real-space basis sets ==
Analogous to the plane wave basis sets, where the basis functions are eigenfunctions of the momentum operator, there are basis sets whose functions are eigenfunctions of the position operator, that is, points on a uniform mesh in real space. The actual implementation may use [[finite difference]]s, or interpolation with [[sinc function]]s (a.k.a. Lagrange functions) or [[wavelets]].

Sinc functions form an orthonormal, analytical, and complete basis set. The convergence to the complete basis set limit is systematic and relatively simple. Similarly to plane wave basis sets, the accuracy of sinc basis sets is controlled by an energy cutoff criterion.{{citation needed|date=August 2016}}

In the wavelet case, it is possible to make the mesh adaptive, so that more points are used close to the nuclei. Wavelets rely on the use of localized functions that allow for the development of linear-scaling methods.

== See also ==

* [[Basis set superposition error]]
* [[Angular momentum]]
* [[Atomic orbitals]]
* [[Molecular orbitals]]
* [[List of quantum chemistry and solid state physics software]]

==References==
{{reflist}}

All the many basis sets discussed here along with others are discussed in the references below which themselves give references to the original journal articles:
*{{cite book
| last = Levine | first = Ira N.
| title = Quantum Chemistry
| publisher = Prentice Hall | year = 1991 | location = Englewood Cliffs, New jersey
| pages = 461–466 | isbn = 0-205-12770-3}}
*{{cite book
| last = Cramer | first = Christopher J.
| title = Essentials of Computational Chemistry
| publisher = John Wiley & Sons, Ltd. | year = 2002 | location = Chichester
| pages = 154–168 | isbn = 0-471-48552-7}}
*{{cite book
| last = Jensen
| first = Frank
| title = Introduction to Computational Chemistry
| publisher = John Wiley and Sons
| year = 1999
| pages = 150–176
| isbn = 978-0471980858}}
* {{cite book | last = Leach | first = Andrew R.
| title = Molecular Modelling: Principles and Applications
| publisher = Longman | year = 1996 | location = Singapore | pages = 68–77 | isbn = 0-582-23933-8 }}
*{{cite book
| last = Hehre | first = Warren J..
| title = A Guide to Molecular Mechanics and Quantum Chemical Calculations
| publisher = Wavefunction, Inc. | year = 2003 | location = Irvine, California
| pages = 40–47 | isbn = 1-890661-18-X}}
* https://web.archive.org/web/20070830043639/http://www.chem.swin.edu.au/modules/mod8/basis1.html
*{{cite journal
| doi = 10.1021/ja0630285
| title = Popular Theoretical Methods Predict Benzene and Arenes To Be Nonplanar
| pmid = 16848464
| year = 2006
| last1 = Moran
| first1 = Damian
| last2 = Simmonett
| first2 = Andrew C.
| last3 = Leach
| first3 = Franklin E.
| last4 = Allen
| first4 = Wesley D.
| last5 = Schleyer
| first5 = Paul v. R.
| last6 = Schaefer
| first6 = Henry F.
| journal = Journal of the American Chemical Society
| volume = 128
| issue = 29
| pages = 9342–3 }}
*{{cite journal
| doi = 10.1063/1.4913569
| title = Accuracy of Lagrange-sinc functions as a basis set for electronic structure calculations of atoms and molecules
| year = 2015
| last1 = Choi
| first1 = Sunghwan
| last2 = Kwangwoo
| first2 = Hong
| last3 = Jaewook
| first3 = Kim
| last4 = Woo Youn
| first4 = Kim
| journal = The Journal of Chemical Physics | bibcode = 2015JChPh.142i4116C}}

== External links ==
* [https://bse.pnl.gov/bse/portal EMSL Basis Set Exchange]
* [http://cosmologic-services.de/basis-sets/basissets.php TURBOMOLE basis set library]
* [http://www.crystal.unito.it/basis-sets.php CRYSTAL - Basis Sets Library]
* [http://dirac.chem.sdu.dk/basisarchives/dyall/index.html Dyall Basis Sets Library]
* [http://tyr0.chem.wsu.edu/~kipeters/basis.html Peterson Group Correlation Consistent Basis Sets]
* [http://sapporo.center.ims.ac.jp:8080/sapporo/Order.do Sapporo Segmented Gaussian Basis Sets Library]
* [http://www.tc.uni-koeln.de/PP/index.en.html Stuttgart/Cologne energy-consistent (ab initio) pseudopotentials Library]
* [http://www.shodor.org/chemviz/basis/index.html ChemViz - Basis Sets Lab Activity]

[[Category:Quantum chemistry]]
[[Category:Computational chemistry]]
[[Category:Theoretical chemistry]]

[[pl:Baza funkcyjna]]

Plasmonische Solarzelle

2017-09-13T10:43:24Z

Bibcode Bot: Adding 0 arxiv eprint(s), 7 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{expert needed|date=December 2014}}
A '''plasmonic solar cell''' is a type of [[thin film solar cell]] that converts light into electricity with the assistance of [[plasmon]]s.<ref>{{Cite book
| url = http://onlinelibrary.wiley.com/doi/10.1002/9781118845721.ch10/summary
| title = Advances in Plasmonic Light Trapping in Thin-Film Solar Photovoltaic Devices
| last = Gwamuri
| first = J.
| last2 = Güney
| first2 = D. Ö.
| last3 = Pearce
| first3 = J. M.
| date = 2013-01-01
| publisher = John Wiley & Sons, Inc.
| isbn = 9781118845721
| editor-last = Tiwari
| editor-first = Atul
| pages = 241–269
| language = en
| doi = 10.1002/9781118845721.ch10
| editor-last2 = Boukherroub
| editor-first2 = Rabah
| editor-last3 = Sharon
| editor-first3 = heshwar
}}</ref> They are typically less than 2 μm thick and theoretically could be as thin as 100 nm.<ref name=":0" /> They can use [[Substrate (materials science)|substrates]] which are cheaper than [[silicon]], such as [[glass]], [[plastic]] or [[steel]]. One of the challenges for thin film solar cells is that they do not absorb as much light as thicker solar cells made with materials with the same [[absorption coefficient]]. Methods for light trapping are important for thin film solar cells.<ref>{{Cite journal
| last = Müller
| first = Joachim
| last2 = Rech
| first2 = Bernd
| last3 = Springer
| first3 = Jiri
| last4 = Vanecek
| first4 = Milan
| date = 2004-12-01
| title = TCO and light trapping in silicon thin film solar cells
| url = http://www.sciencedirect.com/science/article/pii/S0038092X04000647
| journal = Solar Energy
| series = Thin Film PV
| volume = 77
| issue = 6
| pages = 917–930
| doi = 10.1016/j.solener.2004.03.015
|bibcode = 2004SoEn...77..917M }}</ref> Plasmonic cells improve absorption by scattering light using metal [[nanoparticle|nano-particle]]s excited at their [[surface plasmon resonance]].<ref name=Catchpole>K. R. Catchpole and A. Polman, "Plasmonic solar cells," Opt. Express 16, 21793-21800 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-26-21793</ref> Incoming light at the plasmon resonance frequency induces electron oscillations at the surface of the nanoparticles. The oscillation electrons can then be captured by a conductive layer producing an electrical current. The voltage produced is dependent on the bandgap of the conductive layer and the potential of the electrolyte in contact with the nanoparticles. There is still considerable research necessary to enable the technology to reach its full potential and commercialization of plasmonic enhanced solar cells.<ref name=":0">{{Cite journal
| last = Atwater
| first = Harry A.
| last2 = Polman
| first2 = Albert
| title = Plasmonics for improved photovoltaic devices
| url = http://www.nature.com/doifinder/10.1038/nmat2629
| journal = Nature Materials
| volume = 9
| issue = 3
| pages = 205–213
| doi = 10.1038/nmat2629
|bibcode = 2010NatMa...9..205A
| pmid=20168344
| date=March 2010}}</ref>

== History ==

=== Devices ===

There are currently three different generations of SCs. The first generation (those in the market today) are made with crystalline [[semiconductor wafer]]s, typically silicon. These are the SCs everybody thinks of when they hear "Solar Cell".{{Citation needed|date=March 2016}}

Current SCs trap light by creating [[pyramid]]s on the surface which have dimensions bigger than most thin film SCs. Making the surface of the substrate rough (typically by growing SnO2 or ZnO on surface) with dimensions on the order of the incoming [[wavelength]]s and depositing the SC on top has been explored. This method increases the [[photocurrent]], but the thin film SC would then have poor material quality.
<ref name=Muller>{{cite journal | doi = 10.1016/j.solener.2004.03.015 | title = TCO and light trapping in silicon thin film solar cells | year = 2004 | last1 = Müller | first1 = Joachim | last2 = Rech | first2 = Bernd | last3 = Springer | first3 = Jiri | last4 = Vanecek | first4 = Milan | journal = Solar Energy | volume = 77 | issue = 6 | pages = 917–930 |bibcode = 2004SoEn...77..917M }}</ref>

The second generation SCs are based on [[thin film]] technologies such as those presented here. These SCs focus on lowering the amount of material used as well as increasing the energy production. Third generation SCs are currently being researched. They focus on reducing the cost of the second generation SCs.
<ref name=Conibeer>Gavin Conibeer, Third generation photovoltaics, Proc. SPIE Vol. 7411, 74110D (Aug. 20, 2009)</ref>
The third generation SCs are discussed in more detail under recent advancement.

== Design ==
The design for a PSC varies depending on the method being used to trap and scatter light across the surface and through the material.

=== Nanoparticle cells ===
[[File:PSC using Metal Nanoparticles.png|thumb|alt=A plasmonic solar cell utilizing metal nanoparticles to distribute light and enhance absorption.|PSC using metal nano-particles.]]
A common design is to deposit metal nano-particles on the top surface of the thin film SC. When light hits these metal nano-particles at their surface plasmon resonance, the light is scattered in many different directions. This allows light to travel along the SC and bounce between the substrate and the nano-particles enabling the SC to absorb more light.<ref name=Tanabe>{{cite journal | last1 = Tanabe | first1 = K. | year = 2009 | title = A Review of Ultrahigh Efficiency III-V Semiconductor Compound Solar Cells: Multijunction Tandem, Lower Dimensional, Photonic Up/Down Conversion and Plasmonic Nanometallic Structures | url = | journal = Energies | volume = 2 | issue = 3| pages = 504–530 | doi = 10.3390/en20300504 }}</ref> The concentrated near field intensity induced by localized surface plasmon of the metal nanoparticles will promote the optical absorption of semiconductors. Recently, the plasmonic asymmetric modes of nano particles have found to favor the broadband optical absorption and promote the electrical properties of solar cells.<ref name="Volume 12, Issue 37, pages 5200–5207, 2016">{{cite journal|last1=Ren|first1=Xingang etl.|title=High Efficiency Organic Solar Cells Achieved by the Simultaneous Plasmon-Optical and Plasmon-Electrical Effects from Plasmonic Asymmetric Modes of Gold Nanostars|journal=Small|date=2016|volume=12|issue=37|pages=5200–5207|doi=10.1002/smll.201601949|url=http://onlinelibrary.wiley.com/wol1/doi/10.1002/smll.201601949/abstract}}</ref> The simultaneously plasmon-optical and plasmon-electrical effects of nanoparticles reveal a promising feature of nanoparticle plasmon.

Recently, the core (metal)-shell (dielectric) nanoparticle has demonstrated a zero backward scattering with enhanced forward scattering on Si substrate when surface plasmon is located in front of a solar cell.<ref name=":1">{{Cite journal|last=Yu|first=Peng|last2=Yao|first2=Yisen|last3=Wu|first3=Jiang|last4=Niu|first4=Xiaobin|last5=Rogach|first5=Andrey L.|last6=Wang|first6=Zhiming|date=2017-08-09|title=Effects of Plasmonic Metal Core -Dielectric Shell Nanoparticles on the Broadband Light Absorption Enhancement in Thin Film Solar Cells|url=https://www.nature.com/articles/s41598-017-08077-9|journal=Scientific Reports|language=En|volume=7|issue=1|doi=10.1038/s41598-017-08077-9|issn=2045-2322}}</ref> The core-shell nanoparticles can support simultaneously both electric and magnetic resonances, demonstrating entirely new properties when compared with bare metallic nanoparticles if the resonances are properly engineered.

=== Metal film cells ===

Other methods utilizing surface plasmons for harvesting solar energy are available. One other type of structure is to have a thin film of silicon and a thin layer of metal deposited on the lower surface. The light will travel through the silicon and generate surface plasmons on the interface of the silicon and metal. This generates electric fields inside of the silicon since electric fields do not travel very far into metals. If the [[electric field]] is strong enough, electrons can be moved and collected to produce a photocurrent. The thin film of metal in this design must have nanometer sized grooves which act as [[waveguide]]s for the incoming light in order to excite as many photons in the silicon thin film as possible.
<ref name=Ferry>{{cite journal | doi = 10.1021/nl8022548 | pages= 4391–4397 | title = Plasmonic Nanostructure Design for Efficient Light Coupling into Solar Cells | year = 2008 | last1 = Ferry | first1 = Vivian E. | last2 = Sweatlock | first2 = Luke A. | last3 = Pacifici | first3 = Domenico | last4 = Atwater | first4 = Harry A. | journal = Nano Letters | volume = 8 | issue = 12 | pmid = 19367883 |bibcode = 2008NanoL...8.4391F }}</ref>

== Principles ==

=== General ===
[[File:Thin vs Thick SC.png|thumb|alt=Light effects on thin and thick solar cells.|Thin film SC (left) and Typical SC (right).]]
When a photon is excited in the substrate of a SC, an electron and hole are separated. Once the electrons and holes are separated, they will want to recombine since they are of opposite charge. If the electrons can be collected prior to this happening they can be used as a current for an external circuit. Designing the thickness of a solar cell is always a trade-off between minimizing this recombination (thinner layers) and absorbing more photons (thicker layer).<ref name=Tanabe/>

=== Nano-particles ===

==== Scattering and Absorption ====
The basic principles for the functioning of plasmonic solar cells include scattering and absorption of light due to the deposition of metal nano-particles. Silicon does not absorb light very well. For this reason, more light needs to be scattered across the surface in order to increase the absorption. It has been found that metal nano-particles help to scatter the incoming light across the surface of the silicon substrate. The equations that govern the scattering and absorption of light can be shown as:
*<math>C_{scat}=\frac{1}{6\pi}\left(\frac{2\pi}{\lambda}\right)^4|\alpha|^2</math>
This shows the scattering of light for particles which have diameters below the wavelength of light.
*<math>C_{abs}=\frac{2\pi}{\lambda}\text{Im}[\alpha]</math>
This shows the absorption for a point dipole model.
*<math>\alpha=3V\left[\frac{\epsilon_p/\epsilon_m-1}{\epsilon_p/\epsilon_m+2}\right]</math>
This is the polarizability of the particle. V is the particle volume. <math>\epsilon_p</math> is the dielectric function of the particle. <math>\epsilon_m</math> is the [[dielectric function]] of the embedding medium. When <math>\epsilon_p=-2\epsilon_m</math> the [[polarizability]] of the particle becomes large. This polarizability value is known as the surface plasmon resonance. The dielectric function for metals with low absorption can be defined as:
*<math>\epsilon=1-\frac{\omega_p^2}{\omega^2+i\gamma\omega}</math>
In the previous equation, <math>\omega_p</math> is the bulk plasma frequency. This is defined as:
*<math>\omega_p^2=Ne^2/m\epsilon_0</math>
N is the density of free electrons, e is the [[Electrical resistivity and conductivity|electronic charge]] and m is the [[Effective mass (solid-state physics)|effective mass]] of an electron. <math>\epsilon_0</math> is the dielectric constant of free space. The equation for the surface plasmon resonance in free space can therefore be represented by:
*<math>\alpha=3V\frac{\omega_p^2}{\omega_p^2-3\omega^2-i\gamma\omega}</math>
Many of the plasmonic solar cells use nano-particles to enhance the scattering of light. These nano-particles take the shape of spheres, and therefore the surface plasmon resonance frequency for spheres is desirable. By solving the previous [[equation]]s, the surface plasmon resonance frequency for a sphere in free space can be shown as:
*<math>\omega_{sp}=\sqrt{3}\omega_p</math>

As an example, at the surface plasmon resonance for a silver nanoparticle, the scattering cross-section is about 10x the cross-section of the nanoparticle. The goal of the nano-particles is to trap light on the surface of the SC. The absorption of light is not important for the nanoparticle, rather, it is important for the SC. One would think that if the nanoparticle is increased in size, then the scattering cross-section becomes larger. This is true, however, when compared with the size of the nanoparticle, the ratio (<math>CS_{scat}/CS_{particle}</math>) is reduced. Particles with a large scattering cross section tend to have a broader plasmon resonance range.

==== Wavelength dependence ====
Surface plasmon resonance mainly depends on the density of free electrons in the particle. The order of densities of electrons for different metals is shown below along with the type of light which corresponds to the resonance.
*[[Aluminum]] - Ultra-violet
*[[Silver]] - Ultra-violet
*[[Gold]] - Visible
*[[Copper]] - Visible

If the dielectric constant for the embedding medium is varied, the [[resonant frequency]] can be shifted. Higher indexes of refraction will lead to a longer wavelength frequency.

==== Light trapping ====
The metal nano-particles are deposited at a distance from the substrate in order to trap the light between the substrate and the particles. The particles are embedded in a material on top of the substrate. The material is typically a [[dielectric]], such as silicon or [[silicon nitride]]. When performing experiment and simulations on the amount of light scattered into the substrate due to the distance between the particle and substrate, air is used as the embedding material as a reference. It has been found that the amount of light radiated into the substrate decreases with distance from the substrate. This means that nano-particles on the surface are desirable for radiating light into the substrate, but if there is no distance between the particle and substrate, then the light is not trapped and more light escapes.

The surface plasmons are the excitations of the conduction electrons at the interface of metal and the dielectric. Metallic nano-particles can be used to couple and trap freely propagating plane waves into the semiconductor thin film layer. Light can be folded into the absorbing layer to increase the absorption. The localized surface plasmons in metal nano-particles and the surface plasmon polaritons at the interface of metal and semiconductor are of interest in the current research. In recent reported papers, the shape and size of the metal nano-particles are key factors to determine the incoupling efficiency. The smaller particles have larger incoupling efficiency due to the enhanced near-field coupling. However, very small particles suffer from large ohmic losses. <ref>{{cite journal|last=Atwater|first=Harry|author2=A. Polman |title=Plasmonics for improved photovoltaic devices|journal=Nature Materials|date=19 February 2010|volume=9|pages=205–13|bibcode=2010NatMa...9..205A|doi=10.1038/nmat2629|issue=3|pmid=20168344}}</ref>

Recently, the plasmonic asymmetric modes of nano particles have found to favor the broadband optical absorption and promote the electrical properties of solar cells. The simultaneously plasmon-optical and plasmon-electrical effects of nanoparticles reveal a promising feature of nanoparticle plasmon.<ref name="Volume 12, Issue 37, pages 5200–5207, 2016" />

=== Metal film ===
As light is incident upon the surface of the metal film, it excites surface plasmons. The surface plasmon frequency is specific for the material, but through the use of [[grating]]s on the surface of the film, different frequencies can be obtained. The surface plasmons are also preserved through the use of waveguides as they make the surface plasmons easier to travel on the surface and the losses due to resistance and radiation are minimized. The electric field generated by the surface plasmons influences the electrons to travel toward the collecting substrate.
<ref name=Huag>{{cite journal | doi = 10.1063/1.2981194 | title = Plasmonic absorption in textured silver back reflectors of thin film solar cells | year = 2008 | last1 = Haug | first1 = F.-J. | last2 = SöDerström | first2 = T. | last3 = Cubero | first3 = O. | last4 = Terrazzoni-Daudrix | first4 = V. | last5 = Ballif | first5 = C. | journal = Journal of Applied Physics | volume = 104 | issue = 6 | pages = 064509 |bibcode = 2008JAP...104f4509H }}</ref>

== Materials ==
{| class="wikitable" border="1"
|-
! First Generation
! Second Generation
! Third Generation
|-
| Single-crystal silicon
| CuInSe2
| Gallium Indium Phosphide
|-
| Multicrystalline silicon
| amorphous silicon
| Gallium Indium Arsenide
|-
| Polycrystalline silicon
| thin film crystalline Si
| Germanium
|}<ref name=Conibeer/><ref>http://www1.eere.energy.gov/solar/solar_cell_materials.html</ref>

== Applications ==
The applications for plasmonic solar cells are endless. The need for cheaper and more efficient solar cells is huge. In order for solar cells to be considered cost effective, they need to provide energy for a smaller price than that of traditional power sources such as [[coal]] and [[gasoline]]. The movement toward a more green world has helped to spark research in the area of plasmonic solar cells. Currently, solar cells cannot exceed efficiencies of about 30% (First Generation). With new technologies (Third Generation), efficiencies of up to 40-60% can be expected. With a reduction of materials through the use of thin film technology (Second Generation), prices can be driven lower.

Certain applications for plasmonic solar cells would be for [[space exploration]] vehicles. A main contribution for this would be the reduced weight of the solar cells. An external fuel source would also not be needed if enough power could be generated from the solar cells. This would drastically help to reduce the weight as well.

Solar cells have a great potential to help rural [[electrification]]. An estimated two million villages near the equator have limited access to electricity and fossil fuels and that approximately 25%<ref>http://www.globalissues.org/article/26/poverty-facts-and-stats</ref> of people in the world do not have access to electricity. When the cost of extending [[power grid]]s, running rural electricity and using diesel generators is compared with the cost of solar cells, many times the solar cells win. If the efficiency and cost of the current solar cell technology is decreased even further, then many rural communities and villages around the world could obtain electricity when current methods are out of the question. Specific applications for rural communities would be water pumping systems, residential electric supply and street lights. A particularly interesting application would be for health systems in countries where motorized vehicles are not overly abundant. Solar cells could be used to provide the power to refrigerate [[medication]]s in coolers during transport.

Solar cells could also provide power to [[lighthouse]]s, [[buoy]]s, or even [[battleship]]s out in the ocean. Industrial companies could use them to power [[telecommunications]] systems or monitoring and control systems along pipelines or other system.<ref name=web/>

If the solar cells could be produced on a large scale and be cost effective then entire [[power station]]s could be built in order to provide power to the electrical grids. With a reduction in size, they could be implemented on both commercial and residential buildings with a much smaller footprint. They might not even seem like an [[eyesore]].
<ref name=web>http://www.soton.ac.uk/~solar/intro/appso.htm</ref>

Other areas are in hybrid systems. The solar cells could help to power high consumption devices such as [[automobile]]s in order to reduce the amount of fossil fuels used and to help improve the environmental conditions of the earth.

In consumer electronics devices, solar cells could be used to replace batteries for low power electronics. This would save everyone a lot of money and it would also help to reduce the amount of waste going into [[landfill]]s.<ref>http://blog.coolerplanet.com/2009/01/23/the-4-basic-types-of-solar-cell-applications/</ref>

== Recent advancements ==

=== Choice of plasmonic metal nano-particles ===

Proper choice of plasmatic metal nano-particles is crucial for the maximum light absorption in the active layer. Front surface located nano-particles Ag and Au are the most widely used materials due to their surface plasmon resonances located in the visible range and therefore interact more strongly with the peak solar intensity. However, such noble metal nano-particles always introduce reduced light coupling into Si at the short wavelengths below the surface plasmon resonance due to the detrimental Fano effect, i.e. the destructive interference between the scattered and unscattered light. Moreover, the noble metal nano-particles are impractical to implement for large-scale solar cell manufacture due to their high cost and scarcity in the earth's crust. Recently, Zhang et al. have demonstrated the low cost and earth abundant materials Al nano-particles to be able to outperform the widely used Ag and Au nano-particles. Al nano-particles, with their surface plasmon resonances located in the UV region below the desired solar spectrum edge at 300 nm, can avoid the reduction and introduce extra enhancement in the shorter wavelength range.<ref>{{cite journal| title=Low cost and high performance Al nanoparticles for broadband light trapping in Si wafer solar cells| year=2012 | last1=Yinan | first1=Zhang| journal=Applied Physics Letters | volume=100 | issue=12 | pages=151101 |bibcode = 2012ApPhL.100b1101N |doi = 10.1063/1.3675451 |display-authors=etal}}</ref><ref>{{cite journal| title=Improved multicrystalline Si solar cells by light trapping from Al nanoparticle enhanced antireflection coating| year=2013 | last1=Yinan | first1=Zhang| journal=Opt. Mater. Express| volume=3 | issue=4 | pages=489 |display-authors=etal}}</ref>

==== Shape choice of nano-particles ====
{| class="wikitable"
!Shape
!Ref.
|-
|Nanosphere
|<ref>{{Cite journal|last=Nakayama|first=Keisuke|last2=Tanabe|first2=Katsuaki|last3=Atwater|first3=Harry A.|date=2008-09-22|title=Plasmonic nanoparticle enhanced light absorption in GaAs solar cells|url=http://aip.scitation.org/doi/abs/10.1063/1.2988288|journal=Applied Physics Letters|volume=93|issue=12|pages=121904|doi=10.1063/1.2988288|issn=0003-6951|bibcode=2008ApPhL..93l1904N}}</ref>
|-
|Nanostar
|<ref>{{Cite journal|last=Wu|first=Jiang|last2=Yu|first2=Peng|last3=Susha|first3=Andrei S.|last4=Sablon|first4=Kimberly A.|last5=Chen|first5=Haiyuan|last6=Zhou|first6=Zhihua|last7=Li|first7=Handong|last8=Ji|first8=Haining|last9=Niu|first9=Xiaobin|date=2015-04-01|title=Broadband efficiency enhancement in quantum dot solar cells coupled with multispiked plasmonic nanostars|url=http://www.sciencedirect.com/science/article/pii/S2211285515000713|journal=Nano Energy|volume=13|pages=827–835|doi=10.1016/j.nanoen.2015.02.012}}</ref>
|-
|Core-shell nanoparticle
|<ref name=":1" />
|-
|Nanodisk
|<ref>{{Cite journal|last=Hägglund|first=Carl|last2=Zäch|first2=Michael|last3=Petersson|first3=Göran|last4=Kasemo|first4=Bengt|date=2008-02-04|title=Electromagnetic coupling of light into a silicon solar cell by nanodisk plasmons|url=http://aip.scitation.org/doi/abs/10.1063/1.2840676|journal=Applied Physics Letters|volume=92|issue=5|pages=053110|doi=10.1063/1.2840676|issn=0003-6951|bibcode=2008ApPhL..92e3110H}}</ref>
|-
|Nanocavity
|<ref>{{Cite journal|last=Lindquist|first=Nathan C.|last2=Luhman|first2=Wade A.|last3=Oh|first3=Sang-Hyun|last4=Holmes|first4=Russell J.|date=2008-09-22|title=Plasmonic nanocavity arrays for enhanced efficiency in organic photovoltaic cells|url=http://aip.scitation.org/doi/abs/10.1063/1.2988287|journal=Applied Physics Letters|volume=93|issue=12|pages=123308|doi=10.1063/1.2988287|issn=0003-6951|bibcode=2008ApPhL..93l3308L}}</ref>
|-
|Nanovoid
|<ref>{{Cite journal|last=Lal|first=N. N.|last2=Soares|first2=B. F.|last3=Sinha|first3=J. K.|last4=Huang|first4=F.|last5=Mahajan|first5=S.|last6=Bartlett|first6=P. N.|last7=Greenham|first7=N. C.|last8=Baumberg|first8=J. J.|date=2011-06-06|title=Enhancing solar cells with localized plasmons in nanovoids|url=https://www.osapublishing.org/abstract.cfm?uri=oe-19-12-11256|journal=Optics Express|language=EN|volume=19|issue=12|pages=11256–11263|doi=10.1364/OE.19.011256|issn=1094-4087|bibcode=2011OExpr..1911256L}}</ref>
|-
|Nucleated nanoparticle
|<ref>{{Cite journal|last=Chen|first=Xi|last2=Jia|first2=Baohua|last3=Saha|first3=Jhantu K.|last4=Cai|first4=Boyuan|last5=Stokes|first5=Nicholas|last6=Qiao|first6=Qi|last7=Wang|first7=Yongqian|last8=Shi|first8=Zhengrong|last9=Gu|first9=Min|date=2012-05-09|title=Broadband Enhancement in Thin-Film Amorphous Silicon Solar Cells Enabled by Nucleated Silver Nanoparticles|url=http://dx.doi.org/10.1021/nl203463z|journal=Nano Letters|volume=12|issue=5|pages=2187–2192|doi=10.1021/nl203463z|issn=1530-6984|bibcode=2012NanoL..12.2187C}}</ref>
|-
|Nanocage
|<ref>{{Cite journal|last=Song|first=Kwang Hyun|last2=Kim|first2=Chulhong|last3=Cobley|first3=Claire M.|last4=Xia|first4=Younan|last5=Wang|first5=Lihong V.|date=2009-01-14|title=Near-Infrared Gold Nanocages as a New Class of Tracers for Photoacoustic Sentinel Lymph Node Mapping on a Rat Model|url=http://dx.doi.org/10.1021/nl802746w|journal=Nano Letters|volume=9|issue=1|pages=183–188|doi=10.1021/nl802746w|issn=1530-6984|bibcode=2009NanoL...9..183S}}</ref>
|}

=== Light trapping ===

As discussed earlier, being able to concentrate and scatter light across the surface of the plasmonic solar cell will help to increase efficiencies. Recently, research at [[Sandia National Laboratories]] has discovered a photonic waveguide which collects light at a certain wavelength and traps it within the structure. This new structure can contain 95% of the light that enters it compared to 30% for other traditional waveguides. It can also direct the light within one wavelength which is ten times greater than traditional waveguides. The wavelength this device captures can be selected by changing the structure of the lattice which comprises the structure. If this structure is used to trap light and keep it in the structure until the solar cell can absorb it, the efficiency of the solar cell could be increased dramatically.<ref>http://www.sandia.gov/media/photonic.htm</ref>

=== Absorption ===

Another recent advancement in plasmonic solar cells is using other methods to aid in the absorption of light. One way being researched is the use of metal wires on top of the substrate to scatter the light. This would help by utilizing a larger area of the surface of the solar cell for light scattering and absorption. The danger in using lines instead of dots would be creating a reflective layer which would reject light from the system. This is very undesirable for solar cells. This would be very similar to the thin metal film approach, but it also utilizes the scattering effect of the nano-particles.
<ref>{{cite journal | doi = 10.1002/adma.200900331 | title = Design of Plasmonic Thin-Film Solar Cells with Broadband Absorption Enhancements | year = 2009 | last1 = Pala | first1 = Ragip A. | last2 = White | first2 = Justin | last3 = Barnard | first3 = Edward | last4 = Liu | first4 = John | last5 = Brongersma | first5 = Mark L. | journal = Advanced Materials | volume = 21 | issue = 34 | pages = 3504–3509 }}</ref> Yue, et al. used a type of new materials, called topological insulators, to increase the absorption of ultrathin a-Si solar cells. The topological insulator nanostructure has intrinsically core-shell configuration. The core is dielectric and has ultrahigh refractive index. The shell is metallic and support surface plasmon resonances. Through integrating the nanocone arrays into a-Si thin film solar cells, up to 15% enhancement of light absorption was predicted in the ultraviolet and visible ranges.<ref>{{Cite journal|last=Yue|first=Zengji|last2=Cai|first2=Boyuan|last3=Wang|first3=Lan|last4=Wang|first4=Xiaolin|last5=Gu|first5=Min|date=2016-03-01|title=Intrinsically core-shell plasmonic dielectric nanostructures with ultrahigh refractive index|url=http://advances.sciencemag.org/content/2/3/e1501536|journal=Science Advances|language=en|volume=2|issue=3|pages=e1501536|doi=10.1126/sciadv.1501536|issn=2375-2548|pmc=4820380|pmid=27051869|bibcode=2016SciA....2E1536Y}}</ref>

=== Third generation ===

The goal of third generation solar cells is to increase the efficiency using second generation solar cells (thin film) and using materials that are found abundantly on earth. This has also been a goal of the thin film solar cells. With the use of common and safe materials, third generation solar cells should be able to be manufactured in mass quantities further reducing the costs. The initial costs would be high in order to produce the manufacturing processes, but after that they should be cheap. The way third generation solar cells will be able to improve efficiency is to absorb a wider range of frequencies. The current thin film technology has been limited to one frequency due to the use of single band gap devices.<ref name=Conibeer/>

==== Multiple energy levels ====

The idea for multiple energy level solar cells is to basically stack thin film solar cells on top of each other. Each thin film solar cell would have a different band gap which means that if part of the solar spectrum was not absorbed by the first cell then the one just below would be able to absorb part of the spectrum. These can be stacked and an optimal band gap can be used for each cell in order to produce the maximum amount of power. Options for how each cell is connected are available, such as serial or parallel. The serial connection is desired because the output of the solar cell would just be two leads.

The lattice structure in each of the thin film cells needs to be the same. If it is not then there will be losses. The processes used for depositing the layers are complex. They include Molecular Beam Epitaxy and Metal Organic Vapour Phase Epitaxy. The current efficiency record is made with this process but doesn't have exact matching lattice constants. The losses due to this are not as effective because the differences in lattices allows for more optimal band gap material for the first two cells. This type of cell is expected to be able to be 50% efficient.

Lower quality materials that use cheaper deposition processes are being researched as well. These devices are not as efficient, but the price, size and power combined allow them to be just as cost effective. Since the processes are simpler and the materials are more readily available, the mass production of these devices is more economical.

==== Hot carrier cells ====

A problem with solar cells is that the high energy photons that hit the surface are converted to heat. This is a loss for the cell because the incoming photons are not converted into usable energy. The idea behind the hot carrier cell is to utilize some of that incoming energy which is converted to heat. If the electrons and holes can be collected while hot, a higher voltage can be obtained from the cell. The problem with doing this is that the contacts which collect the electrons and holes will cool the material. Thus far, keeping the contacts from cooling the cell has been theoretical. Another way of improving the efficiency of the solar cell using the heat generated is to have a cell which allows lower energy photons to excite electron and hole pairs. This requires a small bandgap. Using a selective contact, the lower energy electrons and holes can be collected while allowing the higher energy ones to continue moving through the cell. The selective contacts are made using a double barrier resonant tunneling structure. The carriers are cooled which they scatter with phonons. If a material with a large bandgap of phonons then the carriers will carry more of the heat to the contact and it won't be lost in the lattice structure. One material which has a large bandgap of phonons is indium nitride. The hot carrier cells are in their infancy but are beginning to move toward the experimental stage.

==== Plasmonic-electrical solar cells ====

Having unique features of tunable resonances and unprecedented near-field enhancement, [[plasmon]] is an enabling technique for light management. Recently, performances of [[thin-film solar cells]] have been pronouncedly improved by introducing metallic nanostructures. The improvements are mainly attributed to the plasmonic-optical effects for manipulating light propagation, absorption, and scattering. The plasmonic-optical effects could: (1) boost optical absorption of active materials; (2) spatially redistribute light absorption at the active layer due to the localized near-field enhancement around metallic nanostructures. Except for the plasmonic-optical effects, the effects of plasmonically modified [[Genetic recombination|recombination]], transport and collection of photocarriers (electrons and holes), hereafter named plasmonic-electrical effects, have been proposed by Sha, etal.<ref name=Plasmonic_Electrical_1>{{cite journal | doi = 10.1038/srep06236 | title = Breaking the Space Charge Limit in Organic Solar Cells by a Novel Plasmonic-Electrical Concept | year = 2014 | last1 = Sha | first1 = Wei E. I. | last2 = Li | first2 = Xuanhua | last3 = Choy | first3 = Wallace C. H. | journal = Scientific Reports | volume = 4 | pages=6236 |bibcode = 2014NatSR...4E6236S | pmid=25168122 | pmc=4148652}}</ref><ref name=Plasmonic_Electrical_2>{{cite journal | doi = 10.1038/srep08525 | title = A General Design Rule to Manipulate Photocarrier Transport Path in Solar Cells and Its Realization by the Plasmonic-Electrical Effect | year = 2015 | last1 = Sha | first1 = Wei E. I. | last2 = Zhu | first2 = Hugh L. | last3 = Chen | first3 = Luzhou | last4 = Chew | first4 = Weng Cho | last5 = Choy | first5 = Wallace C. H. | journal = Scientific Reports | volume = 5 | pages=8525|bibcode = 2015NatSR...5E8525S | pmid=25686578 | pmc=4330524}}</ref> For boosting device performance, they conceived a general design rule, tailored to arbitrary electron to hole mobility ratio, to decide the transport paths of photocarriers.<ref name="Plasmonic_Electrical_2"/> The design rule suggests that electron to hole transport length ratio should be balanced with electron to hole mobility ratio. In other words, the transport time of electrons and holes (from initial generation sites to corresponding electrodes) should be the same. The general design rule can be realized by spatially redistributing light absorption at the active layer of devices (with the plasmonic-electrical effect). They also demonstrated the breaking of [[space charge]] limit in plasmonic-electrical organic solar cell.<ref name="Plasmonic_Electrical_1"/>
Recently, the plasmonic asymmetric modes of nano particles have found to favor the broadband optical absorption and promote the electrical properties of solar cells. The simultaneously plasmon-optical and plasmon-electrical effects of nanoparticles reveal a promising feature of nanoparticle plasmon.<ref name="Volume 12, Issue 37, pages 5200–5207, 2016" /><ref>{{Cite journal|last=Choy|first=W. C. H.|last2=Ren|first2=X.|date=2016-01-01|title=Plasmon-Electrical Effects on Organic Solar Cells by Incorporation of Metal Nanostructures|url=http://ieeexplore.ieee.org/document/7119560/|journal=IEEE Journal of Selected Topics in Quantum Electronics|volume=22|issue=1|pages=1–9|doi=10.1109/JSTQE.2015.2442679|issn=1077-260X}}</ref>

==== Ultra-thin plasmonic wafer solar cells ====
Reducing the silicon wafer thickness at a minimized efficiency loss represents a mainstream trend in increasing the cost-effectiveness of wafer-based solar cells. Recently, Zhang et al. have demonstrated that, using the advanced light trapping strategy with a properly designed nano-particle architecture, the wafer thickness can be dramatically reduced to only around 1/10 of the current thickness (180 µm) without any solar cell efficiency loss at 18.2%. Nano-particle integrated ultra-thin solar cells with only 3% of the current wafer thickness can potentially achieve 15.3% efficiency combining the absorption enhancement with the benefit of thinner wafer induced open circuit voltage increase. This represents a 97% material saving with only 15% relative efficiency loss. These results demonstrate the feasibility and prospect of achieving high-efficiency ultra-thin silicon wafer cells with plasmonic light trapping.<ref>{{cite journal| title=Towards ultra-thin plasmonic silicon wafer solar cells with minimized efficiency loss| year=2014 | last1=Yinan | first1=Zhang| journal=Scientific Reports | volume=4 | pages=4939 |doi=10.1038/srep04939|bibcode = 2014NatSR...4E4939Z |display-authors=etal | pmid=24820403 | pmc=4018607}}</ref>

== References ==
{{Portal|Renewable energy|Energy}}
{{Reflist|2}}

{{Photovoltaics}}

{{DEFAULTSORT:Plasmonic Solar Cell}}
[[Category:Solar cells]]

Atmosphärische Elektrizität

2017-09-11T22:02:19Z

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{{Use mdy dates|date=June 2013}}

[[File:Lightning over Oradea Romania 3.jpg|thumb|300px|Cloud to ground [[lightning]]. Typically, lightning discharges 30,000 [[ampere]]s, at up to 100 million [[volt]]s, and emits light, radio waves, [[x-ray]]s and even [[gamma ray]]s.<ref>See [http://www.nasa.gov/vision/universe/solarsystem/rhessi_tgf.html Flashes in the Sky: Earth's Gamma-Ray Bursts Triggered by Lightning]</ref> Plasma temperatures in lightning can approach 28,000 [[kelvin]]s.]]

'''Atmospheric electricity''' is the study of [[electrical charge]]s in the Earth's [[atmosphere]] (or that of another [[planet]]). The movement of charge between the Earth's surface, the atmosphere, and the [[ionosphere]] is known as the [[global atmospheric electrical circuit]]. Atmospheric electricity is an interdisciplinary topic, involving concepts from [[electrostatics]], [[atmospheric physics]], [[meteorology]] and [[Earth science]].<ref>{{Cite book|title=Atmospheric Electricity|last=Chalmers|first=J. Alan|publisher=Pergamon Press|year=1967|isbn=|location=|pages=}}</ref>

Thunderstorms act as a giant battery in the atmosphere, charging up the ionosphere to about 400,000 [[volt]]s with respect to the surface. This sets up an electric field throughout the atmosphere, which decreases with increase in [[altitude]]. Atmospheric ions created by cosmic rays and natural radioactivity move in the electric field, so a very small current flows through the atmosphere, even away from thunderstorms. Near the surface of the earth, the magnitude of the field is around 100 V/m.<ref name=":0">{{Cite journal|last=Harrison|first=R. G.|date=2011-01-01|title=Fair weather atmospheric electricity|url=http://stacks.iop.org/1742-6596/301/i=1/a=012001|journal=Journal of Physics: Conference Series|language=en|volume=301|issue=1|pages=012001|doi=10.1088/1742-6596/301/1/012001|issn=1742-6596}}</ref>

Atmospheric electricity involves both [[thunderstorm]]s, which create lightning bolts to rapidly discharge huge amounts of atmospheric charge stored in storm clouds, and the continual electrification of the air due to ionization from [[cosmic ray]]s and [[Background radiation|natural radioactivity]], which ensure that the atmosphere is never quite neutral.

==History==
{{Main article|History of electromagnetic theory}}
[[Electric spark|Sparks]] drawn from electrical machines and from [[Leyden jar]]s suggested to the early experimenters, [[Francis Hauksbee (scientist)|Hauksbee]], [[Isaac Newton|Newton]], Wall, [[Jean-Antoine Nollet|Nollet]], and [[Stephen Gray (scientist)|Gray]], that lightning was caused by electric discharges. In 1708, Dr. [[William Wall (theologian)|William Wall]] was one of the first to observe that spark discharges resembled miniature lightning, after observing the sparks from a charged piece of [[amber]].

[[Benjamin Franklin]]'s experiments showed that electrical phenomena of the atmosphere were not fundamentally different from those produced in the [[laboratory]], by listing many similarities between electricity and lightning. By 1749, Franklin observed lightning to possess almost all the properties observable in electrical machines.

In July 1750, Franklin hypothesized that electricity could be taken from clouds via a tall metal [[Antenna (radio)|aerial]] with a sharp point. Before Franklin could carry out his experiment, in 1752 [[Thomas-François Dalibard]] erected a {{convert|40|ft|m|adj=on}} [[iron]] rod at [[Marly-la-Ville]], near Paris, drawing sparks from a passing cloud. With [[Ground (electricity)|ground]]-[[Insulator (electrical)|insulated]] aerials, an experimenter could bring a grounded lead with an insulated wax handle close to the aerial, and observe a spark discharge from the aerial to the grounding wire. In May 1752, Dalibard affirmed that Franklin's theory was correct.

Around June 1752, Franklin reportedly performed his famous kite experiment. The kite experiment was repeated by Romas, who drew from a metallic string sparks {{convert|9|ft|m}} long, and by [[Tiberius Cavallo|Cavallo]], who made many important observations on atmospheric electricity. [[L. G. Lemonnier|Lemonnier]] (1752) also reproduced Franklin's experiment with an aerial, but substituted the ground wire with some dust particles (testing attraction). He went on to document the ''[[fair weather condition]]'', the clear-day electrification of the atmosphere, and its [[Diurnal phase shift|diurnal]] variation. [[Giovanni Battista Beccaria|Beccaria]] (1775) confirmed Lemonnier's diurnal variation data and determined that the atmosphere's charge [[Electrical polarity|polarity]] was positive in fair weather. [[Horace-Bénédict de Saussure|Saussure]] (1779) recorded data relating to a conductor's induced charge in the atmosphere. Saussure's instrument (which contained two small spheres suspended in parallel with two thin wires) was a precursor to the [[electrometer]]. Saussure found that the atmospheric electrification under clear weather conditions had an annual variation, and that it also varied with height. In 1785, [[Charles-Augustin de Coulomb|Coulomb]] discovered the electrical conductivity of air. His discovery was contrary to the prevailing thought at the time, that the atmospheric gases were insulators (which they are to some extent, or at least not very good conductors when not [[ionization|ionized]]). [[Paul Erman|Erman]] (1804) theorized that the Earth was negatively charged, and [[Jean Charles Athanase Peltier|Peltier]] (1842) tested and confirmed Erman's idea.

Several researchers contributed to the growing body of knowledge about atmospheric electrical phenomena. [[Francis Ronalds]] began observing the [[potential gradient]] and air-earth currents around 1810, including making continuous [[electrometer#Electrograph|automated recordings]].<ref>{{Cite book|title=Sir Francis Ronalds: Father of the Electric Telegraph|last=Ronalds|first=B.F.|publisher=Imperial College Press|year=2016|isbn=978-1-78326-917-4|location=London|pages=}}</ref> He resumed his research in the 1840s as the inaugural Honorary Director of the [[King's Observatory|Kew Observatory]], where the first extended and comprehensive dataset of electrical and associated meteorological parameters was created. He also supplied his equipment to other facilities around the world with the goal of delineating atmospheric electricity on a global scale.<ref>{{Cite journal|last=Ronalds|first=B.F.|date=June 2016|title=Sir Francis Ronalds and the Early Years of the Kew Observatory|url=|journal=Weather|doi=10.1002/wea.2739|pmid=|access-date=|volume=71|pages=131–134|bibcode = 2016Wthr...71..131R }}</ref> [[William Thomson, 1st Baron Kelvin|Kelvin]]'s new water dropper collector and divided-ring [[electrometer]] <ref>{{Cite journal|last=Aplin|first=K. L.|last2=Harrison|first2=R. G.|date=2013-09-03|title=Lord Kelvin's atmospheric electricity measurements|url=http://www.hist-geo-space-sci.net/4/83/2013/hgss-4-83-2013.html|journal=History of Geo- and Space Sciences|language=English|volume=4|issue=2|pages=83–95|doi=10.5194/hgss-4-83-2013|issn=2190-5010|arxiv = 1305.5347 |bibcode = 2013HGSS....4...83A }}</ref> were introduced at Kew Observatory in the 1860s, and atmospheric electricity remained a speciality of the observatory until its closure. For high-altitude measurements, [[kite]]s were once used, and weather balloons or [[aerostat]]s are still used, to lift experimental equipment into the air. Early experimenters even went aloft themselves in [[hot-air balloon]]s.

[[H. H. Hoffert|Hoffert]] (1888) identified individual lightning downward strokes using early cameras.<ref>Proceedings of the Physical Society: Volumes 9-10. Institute of Physics and the Physical Society, Physical Society (Great Britain), Physical Society of London, 1888. Intermittent Lightning-Flashes. By HH Hoffert. [https://books.google.com/books?id=EHwEAAAAYAAJ&pg=RA1-PA176 Page 176].</ref> [[J. Elster|Elster]] and [[H. F. Geitel|Geitel]], who also worked on [[thermionic emission]], proposed a theory to explain thunderstorms' electrical structure (1885) and, later, discovered atmospheric [[radioactivity]] (1899) from the existence of positive and negative [[ion]]s in the atmosphere.<ref>{{Cite journal|last=Fricke|first=Rudolf G. A.|last2=Schlegel|first2=Kristian|date=2017-01-04|title=Julius Elster and Hans Geitel – Dioscuri of physics and pioneer investigators in atmospheric electricity|url=http://www.hist-geo-space-sci.net/8/1/2017/|journal=History of Geo- and Space Sciences|language=English|volume=8|issue=1|pages=1–7|doi=10.5194/hgss-8-1-2017|issn=2190-5010|bibcode = 2017HGSS....8....1F }}</ref> [[Friedrich Carl Alwin Pockels|Pockels]] (1897) estimated lightning [[Electric current|current]] intensity by analyzing lightning flashes in [[basalt]] (c. 1900)<ref name=":1">Vladimir A. Rakov, Martin A. Uman (2003) ''Lightning: Physics and Effects''. Cambridge University Press</ref> and studying the left-over [[magnetic field]]s caused by lightning.<ref>Basalt, being a [[ferromagnetic]] mineral, becomes magnetically polarised when exposed to a large external field such as those generated in a lightning strike. See ''Anomalous Remanent Magnetization of Basalt'' pubs.usgs.gov/bul/1083e/report.pdf for more.</ref> Discoveries about the electrification of the atmosphere via sensitive electrical instruments and ideas on how the Earth's negative charge is maintained were developed mainly in the 20th century, with [[Charles Thomson Rees Wilson|CTR Wilson]] playing an important part.<ref>[https://books.google.com/books?id=O-wA0ocxAiIC Encyclopedia of Geomagnetism and Paleomagnetism] - Page 359</ref><ref>{{Cite journal|last=Harrison|first=Giles|date=2011-10-01|title=The cloud chamber and CTR Wilson's legacy to atmospheric science|url=http://onlinelibrary.wiley.com/doi/10.1002/wea.830/abstract|journal=Weather|language=en|volume=66|issue=10|pages=276–279|doi=10.1002/wea.830|issn=1477-8696|bibcode = 2011Wthr...66..276H }}</ref> Current research on atmospheric electricity focuses mainly on lightning, particularly high-energy particles and transient luminous events, and the role of non-thunderstorm electrical processes in weather and climate.

[[Nikola Tesla]] and [[Hermann Plauson]] investigated the production of [[energy]] and [[Power (physics)|power]] via atmospheric electricity.<ref>Nikola Tesla, [[The Problem of Increasing Human Energy]].</ref> Tesla also proposed to use the atmospheric electrical circuit to transceive wireless energy over large distances, but no feasible apparatus to extract energy from atmospheric electricity has been built.<ref>Thomas Valone [https://books.google.com/books?id=ZNqo1zaZRTYC Harnessing the wheelwork of nature: Tesla's science of energy]</ref><ref>See his [[Wardenclyffe Tower]] and [[Magnifying Transmitter]])</ref>

==Description==
Atmospheric electricity is always present, and during fine weather away from thunderstorms, the air above the surface of Earth is positively charged, while the Earth's surface charge is negative. It can be understood in terms of a [[difference of potential]] between a point of the Earth's surface, and a point somewhere in the air above it. Because the atmospheric electric field is negatively directed in fair weather, the convention is to refer to the potential gradient, which has the opposite sign and is about 100V/m at the surface. There is a weak conduction current of atmospheric ions moving in the atmospheric electric field, about 2 [[Picoampere|picoAmperes]] per square metre, and the air is weakly conductive due to the presence of these atmospheric ions.

===Variations===
Global daily cycles in the atmospheric electric field, with a minimum around 03 [[Universal Time|UT]] and peaking roughly 16 hours later, were researched by the Carnegie Institution of Washington in the 20th century. This [[Carnegie curve]]<ref>{{cite journal|title=The Carnegie Curve|url=https://link.springer.com/article/10.1007%2Fs10712-012-9210-2|journal=Surveys in Geophysics|volume=34|pages=209–232|doi=10.1007/s10712-012-9210-2|bibcode = 2013SGeo...34..209H }}</ref> variation has been described as "the fundamental electrical heartbeat of the planet".<ref>Atmospheric electricity affects cloud height - physicsworld.com http://physicsworld.com/cws/article/news/2013/mar/06/atmospheric-electricity-affects-cloud-height</ref>

Even away from thunderstorms, atmospheric electricity can be highly variable, but, generally, the electric field is enhanced in fogs and dust whereas the atmospheric electrical conductivity is diminished.

===Near space===

The [[electrosphere]] layer (from tens of kilometers above the surface of the earth to the ionosphere) has a high electrical conductivity and is essentially at a constant electric potential. The [[ionosphere]] is the inner edge of the [[magnetosphere]] and is the part of the atmosphere that is ionized by solar radiation. ([[Photoionization]] is a physical process in which a photon is incident on an atom, ion or molecule, resulting in the ejection of one or more electrons.)

===Cosmic radiation===
{{main article|Background radiation|Cosmic ray}}

The Earth, and almost all living things on it, are constantly bombarded by radiation from outer space. This radiation primarily consists of positively charged ions from [[proton]]s to [[iron]] and larger [[atomic nucleus|nuclei]] derived sources outside our [[solar system]]. This radiation interacts with atoms in the atmosphere to create an [[air shower (physics)|air shower]] of secondary ionising radiation, including [[X-ray]]s, [[muon]]s, [[proton]]s, [[alpha particle]]s, [[pion]]s, and [[electron]]s. Ionization from this secondary radiation ensures that the atmosphere is weakly conductive, and that the slight current flow from these ions over the Earth's surface balances the current flow from thunderstorms.<ref name=":0" /> Ions have characteristic parameters such as [[Electron mobility|mobility]], lifetime, and generation rate that vary with [[altitude]].

===Earth-Ionosphere cavity===
{{Main article|Schumann resonance}}
The [[potential difference]] between the [[ionosphere]] and the Earth is maintained by [[thunderstorm]]s. In the [[earth-ionosphere cavity resonance|Earth-ionosphere cavity]], the [[electric field]] and conduction [[current (electricity)|current]] in the lower atmosphere are primarily controlled by [[ion]]s.

The [[Schumann resonance]] is a set of spectrum peaks in the extremely low frequency (ELF) portion of the Earth's electromagnetic field spectrum. Schumann resonance is due to the space between the surface of the Earth and the conductive ionosphere acting as a waveguide. The limited dimensions of the earth cause this waveguide to act as a resonant cavity for electromagnetic waves. The cavity is naturally excited by energy from lightning strikes.

===Thunderstorms and lightning===
{{Main article|Thunderstorms|lightning}}
[[File:Global lightning strikes.png|thumb|right|World map showing frequency of lightning strikes, in flashes per km² per year (equal-area projection). Lightning strikes most frequently in the [[Democratic Republic of the Congo]]. Combined 1995–2003 data from the Optical Transient Detector and 1998–2003 data from the Lightning Imaging Sensor.]]
If the quantity of water that is condensed in and subsequently precipitated from a cloud is known, then the total energy of a thunderstorm can be calculated. In an average thunderstorm, the energy released amounts to about 10,000,000 kilowatt-hours (3.6{{e|13}} [[joule]]), which is equivalent to a 20-kiloton [[nuclear weapon|nuclear warhead]]. A large, severe thunderstorm might be 10 to 100 times more energetic.

Collisions between ice and soft hail (graupel) inside cumulonimbus clouds causes separation of positive and negative [[charge carrier|charge]]s within the cloud, essential for the generation of lightning. How lightning initially forms is still a matter of debate: Scientists have studied root causes ranging from atmospheric perturbations (wind, humidity, and [[atmospheric pressure]]) to the impact of [[solar wind]] and energetic particles.

An average bolt of lightning carries a negative electric current of 40 [[ampere|kiloamperes (kA)]] (although some bolts can be up to 120 kA), and transfers a charge of five [[coulomb]]s and energy of 500 [[joule|MJ]], or enough energy to power a 100-watt lightbulb for just under two months. The voltage depends on the length of the bolt, with the [[dielectric breakdown]] of air being three million volts per meter, and lightning bolts often being several hundred meters long. However, lightning leader development is not a simple matter of dielectric breakdown, and the ambient electric fields required for lightning leader propagation can be a few orders of magnitude less than dielectric breakdown strength. Further, the potential gradient inside a well-developed return-stroke channel is on the order of hundreds of volts per meter or less due to intense channel ionization, resulting in a true power output on the order of megawatts per meter for a vigorous return-stroke current of 100 kA .<ref name=":1" />

[[File:Lightnings sequence 1.jpg|thumbnail|center|555px|Lightning sequence (Duration: 0.32 seconds)]]

===Corona discharges===
[[File:151990main elec dust storm lg.jpg|thumb|400px|A depiction of atmospheric electricity in a Martian dust storm, which has been suggested as a possible explanation for enigmatic chemistry results from Mars (see also [[Viking lander biological experiments]])<ref>{{Cite journal|last=Harrison|first=R. G.|last2=Barth|first2=E.|last3=Esposito|first3=F.|last4=Merrison|first4=J.|last5=Montmessin|first5=F.|last6=Aplin|first6=K. L.|last7=Borlina|first7=C.|last8=Berthelier|first8=J. J.|last9=Déprez|first9=G.|date=2016-04-12|title=Applications of Electrified Dust and Dust Devil Electrodynamics to Martian Atmospheric Electricity|url=https://link.springer.com/article/10.1007/s11214-016-0241-8|journal=Space Science Reviews|language=en|volume=203|issue=1–4|pages=299–345|doi=10.1007/s11214-016-0241-8|issn=0038-6308|bibcode = 2016SSRv..203..299H }}</ref>]]
''[[St. Elmo's Fire]]'' is an electrical phenomenon in which luminous [[Plasma (physics)|plasma]] is created by a [[coronal discharge]] originating from a [[Ground (electricity)|grounded object]]. [[Ball lightning]] is often erroneously identified as St. Elmo's Fire, whereas they are separate and distinct phenomena.<ref name="Barry">Barry, J.D. (1980a) ''[https://books.google.com/books?id=KHdIE3_lv1cC Ball Lightning and Bead Lightning: Extreme Forms of Atmospheric Electricity]''. 8–9. New York and London: Plenum Press. {{ISBN|0-306-40272-6}}</ref> Although referred to as "fire", St. Elmo's Fire is, in fact, [[plasma (physics)|plasma]], and is observed, usually during a [[thunderstorm]], at the tops of trees, spires or other tall objects, or on the heads of animals, as a brush or star of light.

Corona is caused by the electric field around the object in question [[ionization|ionizing]] the air molecules, producing a [[ionized air glow|faint glow]] easily visible in low-light conditions. Approximately 1,000 – 30,000 [[volts]] per centimetre is required to induce St. Elmo's Fire; however, this is dependent on the [[geometry]] of the object in question. Sharp points tend to require lower voltage levels to produce the same result because electric fields are more concentrated in areas of high curvature, thus discharges are more intense at the end of pointed objects. St. Elmo's Fire and normal sparks both can appear when high electrical voltage affects a gas. St. Elmo's fire is seen during thunderstorms when the ground below the storm is electrically charged, and there is high voltage in the air between the cloud and the ground. The voltage tears apart the air molecules and the gas begins to glow. The nitrogen and oxygen in the Earth's atmosphere causes St. Elmo's Fire to fluoresce with blue or violet light; this is similar to the mechanism that causes neon signs to glow.

=== Electrical system grounding ===
{{main article|Earthing system}}
Atmospheric charges can cause undesirable, dangerous, and potentially lethal charge potential buildup in suspended electric wire power distribution systems. Bare wires suspended in the air spanning many kilometers and isolated from the ground can collect very large stored capacitance at high voltage static charge potentials, even when there is no thunderstorm or lightning occurring. This charge potential will seek to discharge itself through the path of least insulation, which can occur when a person reaches out to activate a power switch or to use an electric device.

To dissipate atmospheric charge buildup, one side of the electrical distribution system is connected to the earth at many points throughout the distribution system, as often as on every support [[electricity pylon|pole]]. The one earth-connected wire is commonly referred to as the "protective earth", and provides path for the charge potential to dissipate without causing damage, and provides redundancy in case any one of the ground paths is poor due to corrosion or poor ground conductivity. The additional electric grounding wire that carries no power serves a secondary role, providing a high-current short-circuit path to rapidly blow fuses and render a damaged device safe, rather than have an ungrounded device with damaged insulation become "electrically live" via the grid power supply, and hazardous to touch.

Each [[transformer]] in an alternating current distribution grid segments the grounding system into a new separate circuit loop. These separate grids must also be grounded on one side to prevent charge buildup within them relative to the rest of the system, and which could cause damage from charge potentials discharging across the transformer coils to the other grounded side of the distribution network.

== See also ==
;General: [[Geophysics]], [[Atmospheric sciences]], [[Atmospheric physics]], [[Atmospheric dynamics]], [[Journal of Geophysical Research]], [[Earth system model]], [[Atmospheric chemistry]], [[Ionosphere]], [[Air quality]], [[Lightning rocket]]
;Electromagnetism: [[Earth's magnetic field]], [[Lightning|Sprites and lightning]], [[Whistler (radio)]], [[Telluric current]]s, [[relaxation time]], [[electrode effect]], [[potential gradient]]
;Other: [[Charles Chree Medal]], [[Electrodynamic tether]]s, [[Solar radiation]]
;People: [[Egon Schweidler]], [[Charles Chree]], [[Nikola Tesla]], [[Hermann Plauson]], [[Joseph Dwyer]], [[Giles Harrison]], [[Michael Rycroft]], [[Charles Thomson Rees Wilson]]

==References and external articles==

===Citations and notes===
{{Reflist|30em}}

===General references===

====Journals====
:Articles{{refbegin|2}}
* {{cite journal | last1 = Anderson | first1 = F. J. | last2 = Freier | first2 = G. D. | title = Interactions of the thunderstorm with a conducting atmosphere | doi = 10.1029/jc074i023p05390 | journal = J. Geophys. Res. | volume = 74 | pages = 5390–5396| year = 1969 | bibcode=1969JGR....74.5390A}}
* Brook, M., "''Thunderstorm electrification''", Problems of Atmospheric and Space Electricity. S. C. Coroniti (Ed.), Elsevier, Amsterdam, pp. 280–283, 1965.
* {{cite journal | last1 = Farrell | first1 = W. M. | last2 = Aggson | first2 = T. L. | last3 = Rodgers | first3 = E. B. | last4 = Hanson | first4 = W. B. | year = 1994 | title = Observations of ionospheric electric fields above atmospheric weather systems | url = | journal = J. Geophys. Res. | volume = 99 | issue = | pages = 19475–19484 | doi=10.1029/94ja01135 | bibcode=1994JGR....9919475F}}
* {{cite journal | last1 = Fernsler | first1 = R. F. | last2 = Rowland | first2 = H. L. | year = 1996 | title = Models of lightning-produced sprites and elves | url = | journal = J. Geophys. Res. | volume = 101 | issue = | pages = 29653–29662 | doi=10.1029/96jd02159 | bibcode=1996JGR...10129653F}}
* {{cite journal | last1 = Fraser-Smith | first1 = A. C. | year = | title = ''ULF magnetic fields generated by electrical storms and their significance to geomagnetic pulsation generation'' | url = | journal = Geophys. Res. Lett. | volume = 20 | issue = 467–470| page = 1993 }}
* {{cite journal | last1 = Krider | first1 = E. P. | last2 = Blakeslee | first2 = R. J. | year = 1985 | title = The electric currents produced by thunderclouds | url = | journal = J. Electrostatics | volume = 16 | issue = | pages = 369–378 | doi=10.1016/0304-3886(85)90059-2}}
* {{cite journal | last1 = Lazebnyy | first1 = B. V. | last2 = Nikolayenko | first2 = A. P. | last3 = Rafal'skiy | first3 = V. A. | last4 = Shvets | first4 = A. V. | year = 1988 | title = Detection of transverse resonances of the Earth-ionosphere cavity in the average spectrum of VLF atmospherics | url = | journal = Geomagn. Aeron | volume = 28 | issue = | pages = 281–282 }}
* {{cite journal | last1 = Ogawa | first1 = T | title = Fair-weather electricity | doi = 10.1029/jd090id04p05951 | journal = J. Geophys. Res. | volume = 90 | pages = 5951–5960| year = 1985 | bibcode=1985JGR....90.5951O}}
* {{cite journal | last1 = Sentman | first1 = D. D. | title = Schumann resonance spectra in a two-scale-height Earth-ionosphere cavity | url = | journal = J. Geophys. Res. | volume = 101 | pages = 9479–9487| year = 1996 | doi=10.1029/95jd03301 | bibcode=1996JGR...101.9479S}}
* {{cite journal | last1 = Wåhlin | first1 = L | year = 1994 | title = Elements of fair weather electricity | url = | journal = J. Geophys. Res. | volume = 99 | issue = | pages = 10767–10772 | doi=10.1029/93jd03516 | bibcode=1994JGR....9910767W}}
{{refend}}

===Other reading===
{{refbegin|2}}
* Richard E. Orville (ed.), "''Atmospheric and Space Electricity''". ("Editor's Choice" virtual [[Academic publishing|journal]]) – "''[http://www.agu.org/ American Geophysical Union]''". ([[American Geophysical Union|AGU]]) Washington, DC 20009-1277 USA
* Schonland, B. F. J., "''Atmospheric Electricity''". Methuen and Co., Ltd., London, 1932.
* MacGorman, Donald R., W. David Rust, D. R. Macgorman, and W. D. Rust, "''The Electrical Nature of Storms''". Oxford University Press, March 1998. {{ISBN|0-19-507337-1}}
* Cowling, Thomas Gilbert, "''On Alfven's theory of magnetic storms and of the aurora''", Terrestrial Magnetism and Atmospheric Electricity, 47, 209–214, 1942.
* H. H. Hoffert, "''Intermittent Lightning-Flashes''". Proc. Phys. Soc. London 10 No 1 (June 1888) 176–180.
* Volland, H., "''Atmospheric Electrodynamics"'', Springer, Berlin, 1984.
{{refend}}

===Websites===
{{refbegin|2}}
* Bateman, Monte, "''[https://web.archive.org/web/20060914174216/http://ae.nsstc.uah.edu/ Atmospheric Electricity Homepage]''".
* "''[http://www.atmospheric-electricity.org/ International Commission on Atmospheric Electricity]''". Commission of the International Association of Meteorology And Atmospheric Physics.
* "''[http://thunder.msfc.nasa.gov/ Lightning and Atmospheric Electricity]''". Global Hydrology and Climate Center, [[NASA]].
* Kieft, Sandy, "''[http://www.ee.nmt.edu/~langmuir/ The Langmuir Laboratory for Atmospheric Research]''". New Mexico Institute of Mining & Technology.
* "''[http://www.nuenergy.org/alt/GernsbackOnPlausonFebruary1922.htm Power from the Air]''". Science and invention (Formerly [[Electrical Experimenter]]), Feb. 1922, no. 10. Vol IX, Whole No. 106. New York. (nuenergy.org)
* "''[http://www.nuenergy.org/alt/PlausonMarch1922.htm Power from the Air]''". Science and invention (Formerly [[Electrical Experimenter]]), March 1922. (nuenergy.org).
* "''[http://home.netcom.com/~sbyers11/RFenergy_Iono.html RF Energy via Ionosphere]''". RF Energy Concepts Sec. 101 Rev. Nov., 2003
* Peter Winkler, "''[http://www.meteohistory.org/2004polling_preprints/docs/abstracts/winkler_abstract.pdf Early observations of and knowledge on air electricity and magnetism at Hohenpeißenberg during the Palatina]''". German Weather Service, Meteorological Observatory. ([[PDF]])
* "''[http://www.meridian-int-res.com/Energy/Atmospheric.htm Atmospheric Electricity]''". Meridian International Research.
*"[https://web.archive.org/web/20100311182903/http://www.maverickexperiments.com/AtmosElec/AtmsoElec.html Atmospheric Electricity and Plants]"
* [http://www.sciam.com/article.cfm?id=experts-do-cosmic-rays-cause-lightning Do cosmic rays cause lightning?] Ask the Experts – sciam.com January 24, 2008
* "''[http://www.nap.edu/openbook.php?record_id=898&page=206 The Earth's Electrical Environment]''". CPSMA, USA National Academies Press.
{{refend}}

==Further reading==
* [[James R. Wait]], ''Some basic electromagnetic aspects of ULF field variations in the atmosphere''. Journal Pure and Applied Geophysics, Volume 114, Number 1 / January, 1976 Pages 15–28 Birkhäuser Basel ISSN 0033-4553 (Print) 1420-9136 (Online) DOI 10.1007/BF00875488
* National Research Council (U.S.)., & American Geophysical Union. (1986). [https://books.google.com/books?id=7j4rAAAAYAAJ The Earth's electrical environment]. Washington, D.C: National Academy Pres
* [https://books.google.com/books?id=yXgF1ugrr6YCh Solar Dynamics and Its Effects on the Heliosphere and Earth] By D. N. Baker, International Space Science Institute
* [https://books.google.com/books?id=tUQrAAAAYAAJ Solar variability, weather, and climate] By National Research Council (U.S.). Geophysics Study Committee

==External links==
* [http://hypertextbook.com/facts/2006/TerryMathew.shtml Electric Current through the Atmosphere]
* [http://globalcircuit.phys.uh.edu/ The Global Circuit], phys.uh.edu
* [https://web.archive.org/web/20080317074712/http://science.nasa.gov/newhome/headlines/essd15jun99_1.htm Soaking in atmospheric electricity] 'Fair weather' measurements important to understanding thunderstorms. science.nasa.gov
* [https://web.archive.org/web/20060914174216/http://ae.nsstc.uah.edu/ Atmospheric Electricity HomePage], uah.edu
* Tjt, [https://web.archive.org/web/20070523235301/http://www.ava.fmi.fi/~tjt/fairw.html Fair-weather atmospheric electricity]. ava.fmi.fi
* [[ICAE]] – [[International Commission on Atmospheric Electricity]] [http://icae.jp/ Homepage]

{{Atmospheric electricity}}

{{Authority control}}

{{DEFAULTSORT:Atmospheric Electricity}}
[[Category:Atmospheric electricity| ]]
[[Category:Electrical phenomena]]

3j-Symbol

2017-09-11T19:35:22Z

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In [[quantum mechanics]], the '''Wigner 3-j symbols''', also called 3''-jm'' symbols, are an alternative to [[Clebsch–Gordan coefficients]] for the purpose of adding angular momenta.<ref name="Wigner1951">{{cite book |last=Wigner |first=E. P. |editor1-last=Wightman |editor1-first=Arthur S. |date=1951 |chapter=On the Matrices Which Reduce the Kronecker Products of Representations of S. R. Groups |title=The Collected Works of Eugene Paul Wigner |volume=3 |pages=608–654 |doi=10.1007/978-3-662-02781-3_42 |url=https://link.springer.com/chapter/10.1007%2F978-3-662-02781-3_42 |deadurl=no |accessdate=2017-07-23}}</ref> While the two approaches address exactly the same physical problem, the 3-''j'' symbols do so more symmetrically, and thus have greater and simpler symmetry properties than the Clebsch-Gordan coefficients.

== Mathematical relation to Clebsch-Gordan coefficients ==

The 3-''j'' symbols are given in terms of the Clebsch-Gordon coefficients by
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3 \\
m_1 & m_2 & m_3
\end{pmatrix}
\equiv
\frac{(-1)^{j_1 - j_2 - m_3}}{\sqrt{2 j_3 + 1}}
\langle j_1 \, m_1 \, j_2 \, m_2 | j_3 \, (-m_3) \rangle.
</math>
The ''j'' 's and ''m'' 's are angular momentum quantum numbers, i.e., every {{math|''j''}} (and every corresponding {{math|''m''}}) is either a nonnegative integer or half-odd-integer. The exponent of the sign factor is always an integer, so it remains the same when transposed to the left hand side, and the inverse relation follows upon making the substitution {{math|''m''3 → −''m''3}}:
:<math>
\langle j_1 \, m_1 \, j_2 \, m_2 | j_3 \, m_3 \rangle
= (-1)^{j_1 - j_2 + m_3} \sqrt{2 j_3 + 1}
\begin{pmatrix}
j_1 & j_2 & j_3 \\
m_1 & m_2 & -m_3
\end{pmatrix}
</math>.

== Definitional relation to Clebsch-Gordan coefficients ==

The C-G coefficients are defined so as to express the addition of two angular momenta in terms of a third:
:<math>
|j_3\, m_3\rangle
= \sum_{m_1=-j_1}^{j_1} \sum_{m_2=-j_2}^{j_2}
\langle j_1 \, m_1 \, j_2 \, m_2 | j_3 \, m_3 \rangle
|j_1 \, m_1 \, j_2 \, m_2 \rangle.
</math>
The 3-''j'' symbols, on the other hand, are the coefficients with which three angular momenta must be added so that the resultant is zero:
:<math>
\sum_{m_1=-j_1}^{j_1} \sum_{m_2=-j_2}^{j_2} \sum_{m_3=-j_3}^{j_3}
|j_1 m_1\rangle |j_2 m_2\rangle |j_3 m_3\rangle
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
= |0\,0\rangle.
</math>
Here, <math>|0\,0\rangle</math> is the zero angular momentum state (<math> j = m = 0</math>). It is apparent that the 3-''j'' symbol treats all three angular momenta involved in the addition problem on an equal footing, and is therefore more symmetrical than the C-G coefficient.

Since the state <math>|0\,0\rangle</math> is unchanged by rotation, one also says that the contraction of the product of three rotational states with a 3-''j'' symbol is invariant under rotations.

== Selection rules ==

The Wigner 3-''j'' symbol is zero unless all these conditions are satisfied:

:<math>\begin{align}
&m_i \in \{-j_i, -j_i + 1, -j_i + 2, \ldots, j_i\}, \quad (i = 1, 2, 3).\\
&m_1 + m_2 + m_3 = 0 \\
&|j_1 - j_2| \le j_3 \le j_1 + j_2 \\
&(j_1 + j_2 + j_3) \text{ is an integer (and, moreover, an even integer if } m_1 = m_2 = m_3 = 0 \text{)} \\
\end{align}</math>

== Symmetry properties ==
A 3-''j'' symbol is invariant under an even permutation of its columns:
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
=
\begin{pmatrix}
j_2 & j_3 & j_1\\
m_2 & m_3 & m_1
\end{pmatrix}
=
\begin{pmatrix}
j_3 & j_1 & j_2\\
m_3 & m_1 & m_2
\end{pmatrix}.
</math>
An odd permutation of the columns gives a phase factor:
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
=
(-1)^{j_1+j_2+j_3}
\begin{pmatrix}
j_2 & j_1 & j_3\\
m_2 & m_1 & m_3
\end{pmatrix}
=
(-1)^{j_1+j_2+j_3}
\begin{pmatrix}
j_1 & j_3 & j_2\\
m_1 & m_3 & m_2
\end{pmatrix}.
</math>
Changing the sign of the <math>m</math> quantum numbers (time-reversal) also gives a phase:
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
-m_1 & -m_2 & -m_3
\end{pmatrix}
=
(-1)^{j_1+j_2+j_3}
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}.
</math>
The 3-''j'' symbols also have so-called Regge symmetries, which are not due to permutations or time-reversal.<ref>{{cite journal |first1=T. |last1=Regge|title=Symmetry Properties of Clebsch-Gordan Coefficients |journal=Nuovo Cimento |year=1958|volume=10 |issue=3|page=544 |doi=10.1007/BF02859841|bibcode=1958NCim...10..544R}}</ref> These symmetries are,
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
=
\begin{pmatrix}
j_1 & \frac{j_2+j_3-m_1}{2} & \frac{j_2+j_3+m_1}{2}\\
j_3-j_2 & \frac{j_2-j_3-m_1}{2}-m_3 & \frac{j_2-j_3+m_1}{2}+m_3
\end{pmatrix}.
</math>
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
=
(-1)^{j_1+j_2+j_3}
\begin{pmatrix}
\frac{j_2+j_3+m_1}{2} & \frac{j_1+j_3+m_2}{2} & \frac{j_1+j_2+m_3}{2}\\
j_1 - \frac{j_2+j_3-m_1}{2} & j_2 - \frac{j_1+j_3-m_2}{2} & j_3-\frac{j_1+j_2-m_3}{2}
\end{pmatrix}.
</math>
With the Regge symmetries, the 3-''j'' symbol has a total of 72 symmetries. These are best displayed by the definition of a Regge symbol which is a one-to-one correspondence between it and a 3-''j'' symbol and assumes the properties of a semi-magic square<ref>{{Cite journal |first1=J. |last1=Rasch
|first2=A. C. H. |last2=Yu |title=Efficient Storage Scheme for Pre-calculated Wigner 3j, 6j and Gaunt Coefficients |journal=SIAM J. Sci. Comput. |volume=25 |issue=4 |year=2003 |pages=1416–1428 |doi=10.1137/s1064827503422932
}}</ref>
:<math>
R=
\begin{array}{|ccc|}
\hline
-j_1+j_2+j_3 & j_1-j_2+j_3 & j_1+j_2-j_3\\
j_1-m_1 & j_2-m_2 & j_3-m_3\\
j_1+m_1 & j_2+m_2 & j_3+m_3\\
\hline
\end{array}
</math>
whereby the 72 symmetries now correspond to 3! row and 3! column interchanges plus a transposition of the matrix. These facts can be used to devise an effective storage scheme.<ref>{{Cite journal |first1=J. |last1=Rasch |first2=A. C. H. |last2=Yu |title=Efficient Storage Scheme for Pre-calculated Wigner 3j, 6j and Gaunt Coefficients |journal=SIAM J. Sci. Comput. |volume=25 |issue=4 |year=2003 |pages=1416–1428 |doi=10.1137/s1064827503422932}}</ref>

== Orthogonality relations ==
A system of two angular momenta with magnitudes {{math|''j''1}} and {{math|''j''2}}, say, can be described either in terms of the uncoupled basis states (labeled by the quantum numbers {{math|''m''1}} and {{math|''m''2}}), or the coupled basis states (labeled by {{math|''j''3}} and {{math|''m''3}}). The 3-''j'' symbols constitute a unitary transformation between these two bases, and this unitarity implies the orthogonality relations,
:<math>
(2 j_3 + 1)\sum_{m_1 m_2}
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\begin{pmatrix}
j_1 & j_2 & j'_3\\
m_1 & m_2 & m'_3
\end{pmatrix}
=\delta_{j_3, j'_3} \delta_{m_3, m'_3} \begin{Bmatrix} j_1 & j_2 & j_3 \end{Bmatrix}.
</math>
:<math>
\sum_{j_3 m_3} (2 j_3 + 1)
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1' & m_2' & m_3
\end{pmatrix}
=\delta_{m_1, m_1'} \delta_{m_2, m_2'}.
</math>
The ''triangular delta'' {{math|{''j''1  ''j''2  ''j''3}}} is equal to 1 when the triad (''j''1, ''j''2, ''j''3) satisfies the triangle conditions, and zero otherwise. The triangular delta itself is sometimes confusingly called<ref name="WormerPaldus2006">{{cite article|title=Angular Momentum Diagrams|author1=P.E.S. Wormer |author2=J. Paldus |journal=Advances in Quantum Chemistry|publisher=Elsevier|volume=51|pages=59–124|year=2006|issn=0065-3276|doi=10.1016/S0065-3276(06)51002-0|url=http://www.sciencedirect.com/science/article/pii/S0065327606510020|bibcode = 2006AdQC...51...59W }}</ref> a “3-j symbol” (without the “m”) in analogy to [[6-j symbol|6-j]] and [[9-j symbol|9-j]] symbols, all of which are irreducible summations of 3-jm symbols where no {{math|''m''}} variables remain.

==Relation to spherical harmonics==
The 3-''jm'' symbols give the integral of the products of three [[spherical harmonics]]
:<math>
\begin{align}
& {} \quad \int Y_{l_1m_1}(\theta,\varphi)Y_{l_2m_2}(\theta,\varphi)Y_{l_3m_3}(\theta,\varphi)\,\sin\theta\,\mathrm{d}\theta\,\mathrm{d}\varphi \\
& =
\sqrt{\frac{(2l_1+1)(2l_2+1)(2l_3+1)}{4\pi}}
\begin{pmatrix}
l_1 & l_2 & l_3 \\
0 & 0 & 0
\end{pmatrix}
\begin{pmatrix}
l_1 & l_2 & l_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\end{align}
</math>
with <math>l_1</math>, <math>l_2</math> and <math>l_3</math> integers.

=== Relation to integrals of spin-weighted spherical harmonics ===

Similar relations exist for the [[spin-weighted spherical harmonics]] if <math>s_1+s_2+s_3=0</math>:
:<math>
\begin{align}
& {} \quad \int d{\mathbf{\hat n}}\,{}_{s_1} Y_{j_1 m_1}({\mathbf{\hat n}})
\,{}_{s_2} Y_{j_2m_2}({\mathbf{\hat n}})\, {}_{s_3} Y_{j_3m_3}({\mathbf{\hat
n}}) \\[8pt]
& = \sqrt{\frac{(2j_1+1)(2j_2+1)(2j_3+1)}{4\pi}}
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\begin{pmatrix}
j_1 & j_2 & j_3\\
-s_1 & -s_2 & -s_3
\end{pmatrix}
\end{align}
</math>

== Recursion relations ==
:<math>
\begin{align}
& {} \quad -\sqrt{(l_3\mp s_3)(l_3\pm s_3+1)}
\begin{pmatrix}
l_1 & l_2 & l_3\\
s_1 & s_2 & s_3\pm 1
\end{pmatrix}
\\
& = \sqrt{(l_1\mp s_1)(l_1\pm s_1+1)}
\begin{pmatrix}
l_1 & l_2 & l_3\\
s_1 \pm 1 & s_2 & s_3
\end{pmatrix}
+\sqrt{(l_2\mp s_2)(l_2\pm s_2+1)}
\begin{pmatrix}
l_1 & l_2 & l_3\\
s_1 & s_2 \pm 1 & s_3
\end{pmatrix}
\end{align}
</math>

== Asymptotic expressions ==
For <math>l_1\ll l_2,l_3</math> a non-zero 3-''j'' symbol has
:<math>
\begin{pmatrix}
l_1 & l_2 & l_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\approx (-1)^{l_3+m_3} \frac{ d^{l_1}_{m_1, l_3-l_2}(\theta)}{\sqrt{2l_3+1}}
</math>
where <math>\cos(\theta) = -2m_3/(2l_3+1)</math> and <math>d^l_{mn}</math> is a Wigner function. Generally a better approximation obeying the Regge symmetry is given by
:<math>
\begin{pmatrix}
l_1 & l_2 & l_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\approx (-1)^{l_3+m_3} \frac{ d^{l_1}_{m_1, l_3-l_2}(\theta)}{\sqrt{l_2+l_3+1}}
</math>
where <math>\cos(\theta) = (m_2-m_3)/(l_2+l_3+1)</math>.

== Metric tensor ==

The following quantity acts as a [[metric tensor]] in angular momentum theory and is also known as a ''Wigner 1-jm symbol'',<ref name="Wigner1951"/>
:<math>\begin{pmatrix}
j \\
m \quad m'
\end{pmatrix}
:= \frac{1}{\sqrt{2 j + 1}}
\begin{pmatrix}
j & 0 & j \\
m & 0 & m'
\end{pmatrix}
= (-1)^{j - m'} \delta_{m, -m'}
</math>
It can be used to perform time-reversal on angular momenta.

== Other properties ==
:<math>\sum_m (-1)^{j - m}
\begin{pmatrix}
j & j & J\\
m & -m & 0
\end{pmatrix} = \sqrt{2 j + 1} ~ \delta_{J, 0}
</math>

:<math>
\frac{1}{2} \int_{-1}^1 P_{l_1}(x)P_{l_2}(x)P_{l}(x) \, dx =
\begin{pmatrix}
l & l_1 & l_2 \\
0 & 0 & 0
\end{pmatrix} ^2
</math>

== Relation to Racah {{math|''V''}}-coefficients ==

Wigner 3-j symbols are related to [[Giulio Racah|Racah]] {{math|''V''}}-coefficients<ref>{{Cite journal |first=G. |last=Racah |title=Theory of Complex Spectra II |journal=[[Physical Review]] |volume=62 |issue=9–10 |pages=438–462 |year=1942 |doi=10.1103/PhysRev.62.438 |bibcode = 1942PhRv...62..438R }}</ref> by a simple phase:

:<math>
V(j_1 j_2 j_3; m_1 m_2 m_3) = (-1)^{j_1 - j_2 - j_3} \begin{pmatrix}
j_1 & j_2 & j_3 \\
m_1 & m_2 & m_3
\end{pmatrix}
</math>

==See also==
*[[Clebsch–Gordan coefficients]]
*[[Spherical harmonics]]
*[[6-j symbol]]
*[[9-j symbol]]

==References==
<references />

<div class="references">
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* A. R. Edmonds, ''Angular Momentum in Quantum Mechanics'', 2nd edition, Princeton University Press, Princeton, 1960.
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*{{ cite journal
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</div>

==External links==
* {{cite web
|first1=Anthony
|last1=Stone
|url=http://www-stone.ch.cam.ac.uk/wigner.shtml
|title=Wigner coefficient calculator
}}
* {{cite web
|first1=A.
|last1=Volya
|url=http://www.volya.net/vc/vc.php
|title=Clebsch-Gordan, 3-j and 6-j Coefficient Web Calculator
}} (Numerical)
* {{cite journal
|first1=Paul
|last1=Stevenson
|url=http://personal.ph.surrey.ac.uk/~phs3ps/cleb.html
|title=Clebsch-O-Matic
|journal=Computer Physics Communications
|volume=147
|issue=3
|pages=853
|doi=10.1016/S0010-4655(02)00462-9
|bibcode = 2002CoPhC.147..853S |year=2002
}}
* [http://plasma-gate.weizmann.ac.il/369j.html 369j-symbol calculator at the Plasma Laboratory of Weizmann Institute of Science] (Numerical)
* [http://geoweb.princeton.edu/people/simons/software.html Frederik J Simons: Matlab software archive, the code THREEJ.M]
* [http://www.sagemath.org/ Sage (mathematics software)] Gives exact answer for any value of j, m
* {{cite web
|first1=H.T.
|last1=Johansson
|first2=C.
|last2=Forssén
|title=(WIGXJPF)
|url=http://fy.chalmers.se/subatom/wigxjpf/
}} (accurate; C, fortran, python)
* {{cite web
|first1=H.T.
|last1=Johansson
|title=(FASTWIGXJ)
|url=http://fy.chalmers.se/subatom/fastwigxj/
}} (fast lookup, accurate; C, fortran)

[[Category:Rotational symmetry]]
[[Category:Representation theory of Lie groups]]
[[Category:Quantum mechanics]]

Benutzer:Poldi jungdrache/Supernova Typ II

2017-09-09T15:39:59Z

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[[File:HST SN 1987A 20th anniversary.jpg|right|thumb|320px|The expanding remnant of [[SN 1987A]], a Type II-P supernova in the [[Large Magellanic Cloud]]. ''[[NASA]] image.'']]
A '''Type II supernova''' (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive [[star]]. A star must have at least 8 times, but no more than 40 to 50 times, the [[solar mass|mass of the Sun]] ({{Solar mass|link=y}}) to undergo this type of explosion.<ref name="science304">{{cite journal
| last = Gilmore | first = Gerry
| title=The Short Spectacular Life of a Superstar
| journal=Science | date=2004 | volume=304
| issue=5697 | pages=1915–1916 | doi=10.1126/science.1100370
| pmid = 15218132 }}</ref> Type II supernovae are distinguished from other types of [[supernova]]e by the presence of hydrogen in their [[spectrum|spectra]]. They are usually observed in the [[spiral arm]]s of [[galaxies]] and in [[H II region]]s, but not in [[elliptical galaxies]].

Stars generate energy by the [[nuclear fusion]] of elements. Unlike the Sun, massive stars possess the mass needed to fuse elements that have an [[atomic mass]] greater than hydrogen and helium, albeit at increasingly higher [[temperature]]s and [[pressure]]s, causing increasingly shorter stellar life spans. The [[degeneracy pressure]] of electrons and the energy generated by these [[nuclear fusion|fusion reactions]] are sufficient to counter the force of gravity and prevent the star from collapsing, maintaining stellar equilibrium. The star fuses increasingly higher mass elements, starting with [[hydrogen]] and then [[helium]], progressing up through the periodic table until a core of [[iron]] and [[nickel]] is produced. Fusion of iron or nickel produces no net energy output, so no further fusion can take place, leaving the nickel-iron core inert. Due to the lack of energy output creating outward pressure, equilibrium is broken and the core is compressed by the overlying mass of the star.

When the compacted mass of the inert core exceeds the [[Chandrasekhar limit]] of about {{Solar mass|1.4|link=y}}, electron degeneracy is no longer sufficient to counter the gravitational compression. A cataclysmic [[Implosion (mechanical process)|implosion]] of the core takes place within seconds. Without the support of the now-imploded inner core, the outer core collapses inwards under gravity and reaches a [[velocity]] of up to 23% of the [[speed of light]] and the sudden compression increases the temperature of the inner core to up to 100 billion [[kelvin]]s. [[Neutron]]s and [[neutrino]]s are formed via [[Electron capture|reversed beta-decay]], releasing about 1046 joules (100 [[foe (unit)|foe]]) in a ten-second burst. Also, the collapse of the inner core is halted by [[neutron degeneracy]], causing the implosion to rebound and bounce outward. The energy of this expanding [[shock wave]] is sufficient to disrupt the overlying stellar material and accelerate it to escape velocity, forming a supernova explosion. The shock wave and extremely high temperature and pressure rapidly dissipate but are present for long enough to allow for a brief period during which the
[[Supernova nucleosynthesis|production of elements]] heavier than iron occurs.<ref>{{cite web
| author=Staff | date=2006-09-07 | url=http://heasarc.gsfc.nasa.gov/docs/objects/snrs/snrstext.html
| title=Introduction to Supernova Remnants
| publisher=NASA Goddard/SAO | accessdate=2007-05-01
}}</ref> Depending on initial size of the star, the remnants of the core form a [[neutron star]] or a [[black hole]]. Because of the underlying mechanism, the resulting [[variable star|nova]] is also described as a core-collapse supernova.

There exist several categories of Type II supernova explosions, which are categorized based on the resulting [[light curve]]—a graph of luminosity versus time—following the explosion. Type II-L supernovae show a steady ([[linear]]) decline of the light curve following the explosion, whereas Type II-P display a period of slower decline (a plateau) in their light curve followed by a normal decay. [[Type Ib and Ic supernovae]] are a type of core-collapse supernova for a massive star that has shed its outer envelope of hydrogen and (for Type Ic) helium. As a result, they appear to be lacking in these elements.

==Formation==
[[File:Evolved star fusion shells.svg|right|280px|thumb|The onion-like layers of a massive, evolved star just before core collapse. (Not to scale.)]]
Stars far more massive than the sun evolve in more complex ways. In the core of the star, hydrogen is [[thermonuclear fusion|fused]] into helium, releasing [[thermal energy]] that heats the sun's core and provides outward [[pressure]] that supports the sun's layers against collapse in a process known as stellar or [[hydrostatic equilibrium]]. The helium produced in the core accumulates there since temperatures in the core are not yet high enough to cause it to fuse. Eventually, as the hydrogen at the core is exhausted, fusion starts to slow down, and [[Gravitation|gravity]] causes the core to contract. This contraction raises the temperature high enough to initiate a shorter phase of helium fusion, which accounts for less than 10% of the star's total lifetime. In stars with fewer than eight solar masses, the [[carbon]] produced by helium fusion does not fuse, and the star gradually cools to become a [[white dwarf]].<ref name="late stages">{{cite web
| last = Richmond | first = Michael
| url = http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html
| title = Late stages of evolution for low-mass stars
| publisher = [[Rochester Institute of Technology]]
| accessdate = 2006-08-04 }}
</ref><ref name="hinshaw">
{{cite web
| last = Hinshaw | first = Gary
| date = 2006-08-23 | url = http://map.gsfc.nasa.gov/m_uni/uni_101stars.html
| title = The Life and Death of Stars | publisher = [[NASA]] [[Wilkinson Microwave Anisotropy Probe]] (WMAP) Mission
| accessdate = 2006-09-01 }}</ref> White dwarf stars, if they have a near companion, may then become [[Type Ia supernova]]e.

A much larger star, however, is massive enough to create temperatures and pressures needed to cause the carbon in the core to begin to fuse when the star contracts at the end of the helium-burning stage. The cores of these massive stars become layered like onions as progressively heavier atomic nuclei build up at the center, with an outermost layer of hydrogen gas, surrounding a layer of hydrogen fusing into helium, surrounding a layer of helium fusing into carbon via the [[triple-alpha process]], surrounding layers that fuse to progressively heavier elements. As a star this massive evolves, it undergoes repeated stages where fusion in the core stops, and the core collapses until the pressure and temperature are sufficient to begin the next stage of fusion, reigniting to halt collapse.<ref name="late stages"/><ref name="hinshaw"/>

:{| class="wikitable"
|+ Core-burning nuclear fusion stages for a 25-[[solar mass]] star
!rowspan="2"| Process
!rowspan="2"| Main fuel
!rowspan="2"| Main products
!colspan="3"| {{Solar mass|25|link=y}} star<ref name="WoosleyJanka">{{cite journal
| last=Woosley | first=S. |author2=Janka, H.-T.
| bibcode=2005NatPh...1..147W
| title=The Physics of Core-Collapse Supernovae
| journal=Nature Physics
|date=December 2005
| volume=1 | issue=3 | pages=147–154
| doi=10.1038/nphys172|arxiv = astro-ph/0601261 }}</ref>
|-
!style="font-weight: normal"| Temperature ([[Kelvin|K]])
!style="font-weight: normal"| Density (g/cm3)
!style="font-weight: normal"| Duration
|-
|| [[Hydrogen burning process|hydrogen burning]]
|| [[hydrogen]]
|| [[helium]]
| style="text-align:center;"| 7×107
| style="text-align:center;"| 10
| style="text-align:center;"| 107 years
|-
|| [[triple-alpha process]]
|| [[helium]]
|| [[carbon]], [[oxygen]]
| style="text-align:center;"| 2×108
| style="text-align:center;"| 2000
| style="text-align:center;"| 106 years
|-
|| [[carbon burning process]]
|| [[carbon]]
|| [[neon|Ne]], [[sodium|Na]], [[magnesium|Mg]], [[aluminium|Al]]
| style="text-align:center;"| 8×108
| style="text-align:center;"| 106
| style="text-align:center;"| 103 years
|-
|| [[neon burning process]]
|| [[neon]]
|| [[oxygen|O]], [[magnesium|Mg]]
| style="text-align:center;"| 1.6×109
| style="text-align:center;"| 107
| style="text-align:center;"| 3 years
|-
|| [[oxygen burning process]]
|| [[oxygen]]
|| [[silicon|Si]], [[sulfur|S]], [[argon|Ar]], [[calcium|Ca]]
| style="text-align:center;"| 1.8×109
| style="text-align:center;"| 107
| style="text-align:center;"| 0.3 years
|-
|| [[silicon burning process]]
|| [[silicon]]
|| [[nickel]] (decays into [[iron]])
| style="text-align:center;"| 2.5×109
| style="text-align:center;"| 108
| style="text-align:center;"| 5 days
|}

==Core collapse==
The factor limiting this process is the amount of energy that is released through fusion, which is dependent on the [[binding energy]] that holds together these atomic nuclei. Each additional step produces progressively heavier nuclei, which release progressively less energy when fusing. In addition, from [[Carbon-burning process|carbon-burning]] onwards, energy loss via [[neutrino]] production becomes significant, leading to a higher rate of reaction than would otherwise take place.<ref name="Clayton">{{cite book|last=Clayton|first=Donald| url=https://books.google.com/books?id=8HSGFThnbvkC|title=Principles of Stellar Evolution and Nucleosynthesis|date=1983|publisher=University of Chicago Press|isbn=978-0-226-10953-4}}</ref> This continues until [[Silicon burning process|nickel-56]] is produced, which decays radioactively into [[Cobalt|cobalt-56]] and then [[Iron|iron-56]] over the course of a few months. As iron and nickel have the highest [[binding energy]] per nucleon of all the elements,<ref>
{{cite journal
| last = Fewell | first = M. P. | title=The atomic nuclide with the highest mean binding energy
| journal=[[American Journal of Physics]]
| date=1995 | volume=63 | issue=7 | pages=653–658
| bibcode=1995AmJPh..63..653F | doi=10.1119/1.17828 }}</ref> energy cannot be produced at the core by fusion, and a nickel-iron core grows.<ref name="hinshaw" /><ref>{{cite web
| last=Fleurot | first=Fabrice | url=http://nu.phys.laurentian.ca/~fleurot/evolution/
| title=Evolution of Massive Stars
| publisher=Laurentian University
| accessdate=2007-08-13 }}</ref> This core is under huge gravitational pressure. As there is no fusion to further raise the star's temperature to support it against collapse, it is supported only by [[degeneracy pressure]] of [[electrons]]. In this state, matter is so dense that further compaction would require electrons to occupy the same [[energy level|energy states]]. However, this is forbidden for identical [[fermion]] particles, such as the electron – a phenomenon called the [[Pauli exclusion principle]].

When the core's mass exceeds the [[Chandrasekhar limit]] of about {{Solar mass|1.4|link=y}}, degeneracy pressure can no longer support it, and catastrophic collapse ensues.<ref name="Chandrasekhar">
{{cite journal
| first=E. H. | last=Lieb |author2=Yau, H.-T. | title=A rigorous examination of the Chandrasekhar theory of stellar collapse
| journal=[[Astrophysical Journal]]
| date=1987 | volume=323 | issue=1 | pages=140–144
| bibcode=1987ApJ...323..140L | doi=10.1086/165813 }}</ref> The outer part of the core reaches velocities of up to 70,000 km/s (23% of the [[speed of light]]) as it collapses toward the center of the star.<ref name="grav_waves">
{{cite web
| first=C. L. | last=Fryer |author2=New, K. C. B.
| date =2006-01-24 | url = http://relativity.livingreviews.org/Articles/lrr-2003-2/
| title = Gravitational Waves from Gravitational Collapse
| publisher = [[Max Planck Institute for Gravitational Physics]]
| accessdate = 2006-12-14 }}
</ref> The rapidly shrinking core heats up, producing high-energy [[gamma rays]] that decompose iron [[atomic nucleus|nuclei]] into helium nuclei and free [[neutron]]s via [[photodisintegration]]. As the core's [[density]] increases, it becomes energetically favorable for [[electron]]s and [[proton]]s to merge via inverse [[beta decay]], producing neutrons and [[elementary particle]]s called [[neutrino]]s. Because neutrinos rarely interact with normal matter, they can escape from the core, carrying away energy and further accelerating the collapse, which proceeds over a timescale of milliseconds. As the core detaches from the outer layers of the star, some of these neutrinos are absorbed by the star's outer layers, beginning the supernova explosion.<ref name="hayakawa">
{{cite journal
| last=Hayakawa|first=T.
| last2=Iwamoto|first2=N.
| last3=Kajino|first3=T.
| last4=Shizuma|first4=T.
| last5=Umeda|first5=H.
| last6=Nomoto|first6=K.
| title=Principle of Universality of Gamma-Process Nucleosynthesis in Core-Collapse Supernova Explosions
| journal=The Astrophysical Journal
| volume=648
| issue=1 | pages=L47–L50
| date=2006 | doi = 10.1086/507703
| bibcode=2006ApJ...648L..47H}}</ref>

For Type II supernovae, the collapse is eventually halted by short-range repulsive neutron-neutron interactions, mediated by the [[strong force]], as well as by [[degeneracy pressure]] of neutrons, at a density comparable to that of an atomic nucleus. When the collapse stops, the infalling matter rebounds, producing a [[shock wave]] that propagates outward. The energy from this shock dissociates heavy elements within the core. This reduces the energy of the shock, which can stall the explosion within the outer core.<ref name="collapse scenario">
{{cite web
| first=C. L. | last=Fryer |author2=New, K. B. C.
| date=2006-01-24 | url = http://relativity.livingreviews.org/open?pubNo=lrr-2003-2&page=articlesu6.html
| title = Gravitational Waves from Gravitational Collapse, section 3.1
| publisher = [[Los Alamos National Laboratory]]
| accessdate = 2006-12-09 }}</ref>

The core collapse phase is so dense and energetic that only neutrinos are able to escape. As the protons and electrons combine to form neutrons by means of [[electron capture]], an electron neutrino is produced. In a typical Type II supernova, the newly formed neutron core has an initial temperature of about 100 billion [[kelvin]]s, 104 times the temperature of the Sun's core. Much of this thermal energy must be shed for a stable neutron star to form, otherwise the neutrons would "boil away". This is accomplished by a further release of neutrinos.<ref name=akmann>{{cite book
| last=Mann | first=Alfred K.
| title=Shadow of a star: The neutrino story of Supernova 1987A
| publisher=W. H. Freeman
| date=1997 | location=New York | page=122
| url = http://www.whfreeman.com/GeneralReaders/book.asp?disc=TRAD&id_product=1058001008&@id_course=1058000240
| isbn = 0-7167-3097-9 }}</ref> These 'thermal' neutrinos form as neutrino-antineutrino pairs of all [[Neutrino oscillation|flavors]], and total several times the number of electron-capture neutrinos.<ref>{{cite book
| last = Gribbin | first = John R.
| authorlink = John Gribbin
| last2 = Gribbin | first2 = Mary
| title = Stardust: Supernovae and Life – The Cosmic Connection
| publisher = [[Yale University Press]]
| date = 2000 | location = New Haven | page = 173
| url = http://yalepress.yale.edu/yupbooks/book.asp?isbn=9780300090970
| isbn = 978-0-300-09097-0 }}</ref> The two neutrino production mechanisms convert the gravitational [[potential energy]] of the collapse into a ten-second neutrino burst, releasing about 1046 joules (100 [[foe (unit)|foe]]).<ref name="APS_study">
{{cite web
| first=S. | last=Barwick
|author2=Beacom, J.
|display-authors=etal
| date=2004-10-29 | url = http://www.aps.org/policy/reports/multidivisional/neutrino/upload/Neutrino_Astrophysics_and_Cosmology_Working_Group.pdf
| title = APS Neutrino Study: Report of the Neutrino Astrophysics and Cosmology Working Group
| publisher = [[American Physical Society]]
| format=PDF | accessdate = 2006-12-12 }}</ref>

Through a process that is not clearly understood, about 1%, or 1044 joules (1 foe), of the energy released (in the form of neutrinos) is reabsorbed by the stalled shock, producing the supernova explosion.{{Ref label|A|a|none}}<ref name="collapse scenario" /> Neutrinos generated by a supernova were observed in the case of [[Supernova 1987A]], leading astrophysicists to conclude that the core collapse picture is basically correct. The water-based [[Kamioka Observatory|Kamiokande II]] and [[Irvine-Michigan-Brookhaven (detector)|IMB]] instruments detected antineutrinos of thermal origin,<ref name=akmann/> while the [[gallium]]-71-based [[Baksan Neutrino Observatory|Baksan]] instrument detected neutrinos ([[lepton number]] = 1) of either thermal or electron-capture origin.

[[File:Core collapse scenario.svg|480px|thumb|center| Within a massive, evolved star (a) the onion-layered shells of elements undergo fusion, forming a nickel-iron core (b) that reaches Chandrasekhar-mass and starts to collapse. The inner part of the core is compressed into neutrons (c), causing infalling material to bounce (d) and form an outward-propagating shock front (red). The shock starts to stall (e), but it is re-invigorated by neutrino interaction. The surrounding material is blasted away (f), leaving only a degenerate remnant.]]

When the progenitor star is below about {{Solar mass|20}} – depending on the strength of the explosion and the amount of material that falls back – the degenerate remnant of a core collapse is a [[neutron star]].<ref name="grav_waves" /> Above this mass, the remnant collapses to form a [[black hole]].<ref name="hinshaw" /><ref>
{{cite journal
| last=Fryer | first=Chris L.
| title=Black Hole Formation from Stellar Collapse
| journal=Classical and Quantum Gravity
| date=2003 | volume=20 | issue=10 | pages=S73–S80
| bibcode=2003CQGra..20S..73F | doi=10.1088/0264-9381/20/10/309 }}</ref> The theoretical limiting mass for this type of core collapse scenario is about {{Solar mass|40–50}}. Above that mass, a star is believed to collapse directly into a black hole without forming a supernova explosion,<ref name="fryer">
{{cite journal
| last = Fryer | first = Chris L.
| title=Mass Limits For Black Hole Formation
| journal=The Astrophysical Journal
| date=1999 | volume=522 | issue=1 | pages=413–418
| bibcode=1999ApJ...522..413F | doi=10.1086/307647 |arxiv = astro-ph/9902315 }}</ref> although uncertainties in models of supernova collapse make calculation of these limits uncertain.

==Theoretical models==
The [[Standard Model]] of [[particle physics]] is a theory which describes three of the four known [[fundamental interaction]]s between the [[elementary particles]] that make up all [[matter]]. This theory allows predictions to be made about how particles will interact under many conditions. The energy per particle in a supernova is typically one to one hundred and fifty [[picojoule]]s (tens to hundreds of [[MeV]]).<ref name="izzard">
{{cite journal
| first=R. G. | last=Izzard
|author2=Ramirez-Ruiz, E. |author3=Tout, C. A.
| title = Formation rates of core-collapse supernovae and gamma-ray bursts
| journal = [[Monthly Notices of the Royal Astronomical Society]]
| volume=348 | issue=4 | page=1215 | date=2004
| doi = 10.1111/j.1365-2966.2004.07436.x | bibcode=2004MNRAS.348.1215I|arxiv = astro-ph/0311463 }}
</ref> The per-particle energy involved in a supernova is small enough that the predictions gained from the Standard Model of particle physics are likely to be basically correct. But the high densities may require corrections to the Standard Model.<ref name="cc_sims">
{{cite conference
| first=M. | last=Rampp
|author2=Buras, R. |author3=Janka, H.-Th. |author4= Raffelt, G.
| title = Core-collapse supernova simulations: Variations of the input physics
| booktitle = Proceedings of the 11th Workshop on "Nuclear Astrophysics"
| pages = 119–125 | date = February 11–16, 2002
| location = Ringberg Castle, Tegernsee, Germany
| bibcode = 2002nuas.conf..119R
|arxiv = astro-ph/0203493 }}</ref> In particular, Earth-based [[particle accelerator]]s can produce particle interactions which are of much higher energy than are found in supernovae,<ref>
{{cite journal
| author=The OPAL Collaboration
| author2=Ackerstaff, K.
| display-authors=etal
| title=Tests of the Standard Model and Constraints on New Physics from Measurements of Fermion-pair Production at 189 GeV at LEP
| journal=Submitted to [[The European Physical Journal C]]
| date=1998 | volume=2
| issue=3 | pages=441–472 | url=http://publish.edpsciences.com/articles/epjc/abs/1998/05/epjc851/epjc851.html
| accessdate = 2007-03-18 | doi=10.1007/s100529800851 }}
</ref> but these experiments involve individual particles interacting with individual particles, and it is likely that the high densities within the supernova will produce novel effects. The interactions between neutrinos and the other particles in the supernova take place with the [[weak nuclear force]], which is believed to be well understood. However, the interactions between the protons and neutrons involve the [[strong nuclear force]], which is much less well understood.<ref>{{cite web
| author=Staff | date=2004-10-05
| url =http://nobelprize.org/nobel_prizes/physics/laureates/2004/public.html
| title=The Nobel Prize in Physics 2004
| publisher=Nobel Foundation
| accessdate=2007-05-30 }}</ref>

The major unsolved problem with Type II supernovae is that it is not understood how the burst of [[neutrino]]s transfers its energy to the rest of the star producing the shock wave which causes the star to explode. From the above discussion, only one percent of the energy needs to be transferred to produce an explosion, but explaining how that one percent of transfer occurs has proven very difficult, even though the particle interactions involved are believed to be well understood. In the 1990s, one model for doing this involved [[convective overturn]], which suggests that convection, either from [[neutrino]]s from below, or infalling matter from above, completes the process of destroying the progenitor star. Heavier elements than iron are formed during this explosion by neutron capture, and from the pressure of the neutrinos pressing into the boundary of the "neutrinosphere", seeding the surrounding space with a cloud of gas and dust which is richer in heavy elements than the material from which the star originally formed.<ref name="pop-sci-dec-2006">
{{cite journal
| last=Stover | first=Dawn | title=Life In A Bubble
| journal=[[Popular Science]] | volume=269 | issue=6
| date=2006 | page=16 }}</ref>

[[Weak interaction|Neutrino physics]], which is modeled by the Standard Model, is crucial to the understanding of this process.<ref name="cc_sims" /> The other crucial area of investigation is the [[hydrodynamics]] of the plasma that makes up the dying star; how it behaves during the core collapse determines when and how the "shock wave" forms and when and how it "stalls" and is reenergized.<ref>
{{cite journal
| doi=10.1016/0022-1694(93)90012-X
| last=Janka | first=H.-Th.
|author2=Langanke, K. |author3=Marek, A. |author4=Martinez-Pinedo, G. |author5= Mueller, B.
| title=Theory of Core-Collapse Supernovae
| journal=Bethe Centennial Volume of Physics Reports (submitted)
| volume=142
| issue=1–4
| page=229
| date=2006
| arxiv=astro-ph/0612072
|bibcode = 1993JHyd..142..229H }}</ref>

In fact, some theoretical models incorporate a hydrodynamical instability in the stalled shock known as the "Standing Accretion Shock Instability" (SASI). This instability comes about as a consequence of non-spherical perturbations oscillating the stalled shock thereby deforming it. The SASI is often used in tandem with neutrino theories in computer simulations for re-energizing the stalled shock.<ref>
{{cite web
|title=3D Simulations of Standing Accretion Shock Instability in Core-Collapse Supernovae
|url=http://www.mpa-garching.mpg.de/hydro/NucAstro/PDF_08/iwakami.pdf
|work=3D Simulations of Standing Accretion Shock Instability in Core-Collapse Supernovae|publisher=14th Workshop on “Nuclear Astrophysics”
|accessdate=30 January 2013
|author=Wakana Iwakami|author2=Kei Kotake |author3=Naofumi Ohnishi |author4=Shoichi Yamada |author5=Keisuke Sawada
|date=March 10–15, 2008
}}</ref>

[[Computer model]]s have been very successful at calculating the behavior of Type II supernovae when the shock has been formed. By ignoring the first second of the explosion, and assuming that an explosion is started, [[astrophysicist]]s have been able to make detailed predictions about the elements produced by the supernova and of the expected [[light curve]] from the supernova.<ref>{{cite journal
| first=S.I. | last=Blinnikov
|author2=Röpke, F. K. |author3=Sorokina, E. I. |author4=Gieseler, M. |author5=Reinecke, M. |author6=Travaglio, C. |author7=Hillebrandt, W. |author8= Stritzinger, M.
| title=Theoretical light curves for deflagration models of type Ia supernova
| journal=Astronomy and Astrophysics
| date=2006 | volume=453 | issue=1 | pages=229–240
| bibcode=2006A&A...453..229B
| doi=10.1051/0004-6361:20054594 |arxiv = astro-ph/0603036 }}
</ref><ref>
{{cite journal
| last=Young | first=Timothy R. | title=A Parameter Study of Type II Supernova Light Curves Using 6 M He Cores
| journal=[[The Astrophysical Journal]]
| date=2004 | volume=617 | issue=2 | pages=1233–1250
| doi=10.1086/425675 | bibcode=2004ApJ...617.1233Y|arxiv = astro-ph/0409284 }}
</ref><ref>
{{cite journal
| first=T. | last=Rauscher
|author2=Heger, A. |author3=Hoffman, R. D. |author4= Woosley, S. E.
| title=Nucleosynthesis in Massive Stars With Improved Nuclear and Stellar Physics
| journal=[[The Astrophysical Journal]]
| date=2002 | volume=576 | issue=1 | pages = 323–348
| doi=10.1086/341728 | bibcode=2002ApJ...576..323R|arxiv = astro-ph/0112478 }}
</ref>

==Light curves for Type II-L and Type II-P supernovae==
[[File:SNIIcurva.png|right|thumb|280px|This graph of the luminosity as a function of time shows the characteristic shapes of the light curves for a Type II-L and II-P supernova.]]
When the [[spectrum]] of a Type II supernova is examined, it normally displays [[Balmer series|Balmer absorption lines]] – reduced flux at the characteristic [[frequency|frequencies]] where hydrogen atoms absorb energy. The presence of these lines is used to distinguish this category of supernova from a [[Type Ia supernova|Type I supernova]].

When the luminosity of a Type II supernova is plotted over a period of time, it shows a characteristic rise to a peak brightness followed by a decline. These light curves have an average decay rate of 0.008 [[absolute magnitude|magnitudes]] per day; much lower than the decay rate for Type Ia supernovae. Type II are sub-divided into two classes, depending on the shape of the light curve. The light curve for a Type II-L supernova shows a steady ([[linear]]) decline following the peak brightness. By contrast, the light curve of a Type II-P supernova has a distinctive flat stretch (called a [[plateau]]) during the decline; representing a period where the luminosity decays at a slower rate. The net luminosity decay rate is lower, at 0.0075 magnitudes per day for Type II-P, compared to 0.012 magnitudes per day for Type II-L.<ref name="comparative_study">
{{cite journal
| first=J. B. | last=Doggett |author2=Branch, D.
| title=A Comparative Study of Supernova Light Curves
| journal=Astronomical Journal
| date=1985 | volume=90 | pages=2303–2311
| bibcode=1985AJ.....90.2303D | doi=10.1086/113934 }}
</ref>

The difference in the shape of the light curves is believed to be caused, in the case of Type II-L supernovae, by the expulsion of most of the hydrogen envelope of the progenitor star.<ref name="comparative_study" /> The plateau phase in Type II-P supernovae is due to a change in the [[opacity (optics)|opacity]] of the exterior layer. The shock wave [[ionize]]s the hydrogen in the outer envelope – stripping the electron from the hydrogen atom – resulting in a significant increase in the [[Opacity (optics)|opacity]]. This prevents photons from the inner parts of the explosion from escaping. When the hydrogen cools sufficiently to recombine, the outer layer becomes transparent.<ref>
{{cite web
| url = http://cosmos.swin.edu.au/lookup.html?e=typeiisupernovalightcurves
| title = Type II Supernova Light Curves
| publisher = [[Swinburne University of Technology]]
| accessdate = 2007-03-17 }}
</ref>

==Type IIn supernovae==
The "n" denotes narrow, which indicates the presence of intermediate or very narrow width H emission lines in the spectra. In the intermediate width case, the ejecta from the explosion may be interacting strongly with gas around the star – the circumstellar medium.<ref>{{Cite journal| pages = 309–330| year = 1997| doi = 10.1146/annurev.astro.35.1.309| volume = 35| journal = Annual Review of Astronomy and Astrophysics | first1 = A. V.| title = Optical Spectra of Supernovae| last1 = Filippenko| bibcode=1997ARA&A..35..309F}}</ref><ref>{{cite journal
| first=A. | last=Pastorello
|author2=Turatto, M. |author3=Benetti, S. |author4=Cappellaro, E. |author5=Danziger, I. J. |author6=Mazzali, P. A. |author7=Patat, F. |author8=Filippenko, A. V. |author9=Schlegel, D. J. |author10= Matheson, T.
| title=The type IIn supernova 1995G: interaction with the circumstellar medium
| journal=Monthly Notices of the Royal Astronomical Society
| date=2002 | volume=333 | issue=1 | pages=27–38
| bibcode=2002MNRAS.333...27P
| doi=10.1046/j.1365-8711.2002.05366.x |arxiv = astro-ph/0201483 }}</ref> The estimated circumstellar density required to explain the observational properties is much higher than that expected from the standard stellar evolution theory.<ref>{{cite journal|last1=Langer|first1=N.|title=Presupernova Evolution of Massive Single and Binary Stars|journal=Annual Review of Astronomy and Astrophysics|date=22 September 2012|volume=50|issue=1|pages=107–164|doi=10.1146/annurev-astro-081811-125534|arxiv = 1206.5443 |bibcode = 2012ARA&A..50..107L }}</ref> It is
generally assumed that the high circumstellar density is due to the high mass-loss rates of the SN IIn progenitors. The estimated mass-loss rates are typically higher
than 10{{sup|−3}} M{{sub|⊙}} yr{{sup|−1}}. There are indications that they originate as stars similar to [[Luminous blue variable]]s with large mass losses before exploding.<ref>{{cite journal |author1=Michael Kiewe |author2=Avishay Gal-Yam |author3=Iair Arcavi |author4=Leonard |author5=Emilio Enriquez |author6=Bradley Cenko |author7=Fox |author8=Dae-Sik Moon |author9=Sand |title=Caltech Core-Collapse Project (CCCP) observations of type IIn supernovae: typical properties and implications for their progenitor stars |date=2010 |volume=744 |issue=10 |pages=10 |journal=ApJ |arxiv=1010.2689|bibcode = 2012ApJ...744...10K |doi = 10.1088/0004-637X/744/1/10 |last10=Soderberg |first10=Alicia M. |last11=Cccp |first11=The }}</ref> [[SN 1998S]] and [[SN 2005gl]] are famous examples of Type IIn; [[SN 2006gy]], an extremely energetic supernova, may be another example.<ref>{{Cite journal| last1 = Smith | first1 = N.| last2 = Chornock | first2 = R.| last3 = Silverman | first3 = J. M.| last4 = Filippenko | first4 = A. V.| last5 = Foley | first5 = R. J.| title = Spectral Evolution of the Extraordinary Type IIn Supernova 2006gy| journal = The Astrophysical Journal| volume = 709| issue = 2| pages = 856–883| year = 2010| doi = 10.1088/0004-637X/709/2/856 | bibcode=2010ApJ...709..856S| arxiv = 0906.2200}}</ref>

==Type IIb supernovae==
A ''Type IIb supernova'' has a weak hydrogen line in its initial spectrum, which is why it is classified as a Type II. However, later on the H emission becomes undetectable, and there is also a second peak in the light curve that has a spectrum which more closely resembles a [[Type Ib and Ic supernovae|Type Ib supernova]]. The progenitor could have been a massive star that expelled most of its outer layers, or one which lost most of its hydrogen envelope due to interactions with a companion in a binary system, leaving behind the core that consisted almost entirely of helium.<ref name=Utrobin>{{cite journal | last=Utrobin | first=V. P. | title=Nonthermal ionization and excitation in Type IIb supernova 1993J | journal=Astronomy and Astrophysics | date=1996 | volume=306 | issue=5940 | pages=219–231 | bibcode=1996A&A...306..219U }}</ref> As the ejecta of a Type IIb expands, the hydrogen layer quickly becomes [[Optical thickness|more transparent]] and reveals the deeper layers.<ref name=Utrobin/>
The classic example of a Type IIb supernova is [[SN 1993J|Supernova 1993J]],<ref>{{Cite journal| last1 = Nomoto | first1 = K.| last2 = Suzuki | first2 = T.| last3 = Shigeyama | first3 = T.| last4 = Kumagai | first4 = S.| last5 = Yamaoka | first5 = H.| last6 = Saio | first6 = H.| title = A type IIb model for supernova 1993J| journal = Nature| volume = 364| pages = 507| year = 1993| doi = 10.1038/364507a0|bibcode = 1993Natur.364..507N | issue=6437}}</ref><ref>{{Cite journal| last1 = Chevalier | first1 = R. A.| last2 = Soderberg | first2 = A. M.| title = Type IIb Supernovae with Compact and Extended Progenitors| journal = The Astrophysical Journal| volume = 711| pages = L40| year = 2010| doi = 10.1088/2041-8205/711/1/L40|bibcode = 2010ApJ...711L..40C |arxiv = 0911.3408 }}</ref> while another example is [[Cassiopeia A]].<ref>{{Cite journal| journal = Science| title = The Cassiopeia A supernova was of type IIb | first7 = K.| last7 = Misselt| volume = 320| issue = 5880| doi = 10.1126/science.1155788| pmid = 18511684| year = 2008| pages = 1195–1197 | first6 = G.| last6 = Rieke| last3 = Usuda | first2 = S.| last2 = Birkmann | first1 = O. | first3 = T.| last4 = Hattori | first5 = M.| last5 = Goto | first4 = T.| last1 = Krause|bibcode = 2008Sci...320.1195K |arxiv = 0805.4557 }}</ref> The IIb class was first introduced (as a theoretical concept) by Woosley et al. in 1987,<ref name=woosley1987>{{cite journal|bibcode=1987ApJ...318..664W|title=Supernova 1987A in the Large Magellanic Cloud - the explosion of an approximately 20 solar mass star which has experienced mass loss?|journal=Astrophysical Journal|volume=318|pages=664|author1=Woosley|first1=S. E.|last2=Pinto|first2=P. A.|last3=Martin|first3=P. G.|last4=Weaver|first4=Thomas A.|year=1987|doi=10.1086/165402}}</ref> and the class was soon applied to [[SN 1987K]]<ref name=filippenko1988>{{cite journal|bibcode=1988AJ.....96.1941F|title=Supernova 1987K - Type II in youth, type Ib in old age|journal=Astronomical Journal |volume=96|pages=1941|author1=Filippenko|first1=Alexei V.|year=1988|doi=10.1086/114940}}</ref> and [[SN 1993J]].<ref name=filippenko>{{cite journal|bibcode=1993ApJ...415L.103F|title=The ''Type IIb'' Supernova 1993J in M81: A Close Relative of Type Ib Supernovae|journal=Astrophysical Journal Letters v.415|volume=415|pages=L103|author1=Filippenko|first1=Alexei V.|last2=Matheson|first2=Thomas|last3=Ho|first3=Luis C.|year=1993|doi=10.1086/187043}}</ref>

==Hypernovae==
{{main article|Hypernova}}
[[Hypernovae]] are a rare type of supernova substantially more luminous and energetic than standard supernovae. Examples are [[1997ef]] (type Ic) and [[1997cy]] (type IIn). Hypernovae are produced by more than one type of event: relativistic jets during formation of a black hole from fallback of material onto the neutron star core, the collapsar model; interaction with a dense envelope of circumstellar material, the CSM model; the highest mass [[Pair-instability supernova|pair instability supernovae]]; possibly others such as [[binary star|binary]] and [[quark star]] model.

Stars with initial masses between about 25 and 90 times the sun develop cores large enough that after a supernova explosion, some material will fall back onto the neutron star core and create a black hole. In many cases this reduces the luminosity of the supernova, and above {{Solar mass|90}} the star collapses directly into a black hole without a supernova explosion. However, if the progenitor is spinning quickly enough the infalling material generates relativistic jets that emit more energy than the original explosion.<ref name="nomoto">{{Cite journal | last1 = Nomoto | first1 = K. I. | last2 = Tanaka | first2 = M. | last3 = Tominaga | first3 = N. | last4 = Maeda | first4 = K. | title = Hypernovae, gamma-ray bursts, and first stars | doi = 10.1016/j.newar.2010.09.022 | journal = New Astronomy Reviews | volume = 54 | issue = 3–6 | pages = 191 | year = 2010 | pmid = | pmc = |bibcode = 2010NewAR..54..191N }}</ref> They may also be seen directly if beamed towards us, giving the impression of an even more luminous object. In some cases these can produce [[gamma-ray bursts]], although not all gamma-ray bursts are from supernovae.<ref>
{{cite news
| title=Cosmological Gamma-Ray Bursts and Hypernovae Conclusively Linked
| publisher=[[European Organisation for Astronomical Research in the Southern Hemisphere]] (ESO)
| date=2003-06-18
| url=http://www.eso.org/outreach/press-rel/pr-2003/pr-16-03.html
| accessdate=2006-10-30 }}
</ref>

In some cases a type II supernova occurs when the star is surrounded by a very dense cloud of material, most likely expelled during [[luminous blue variable]] eruptions. This material is shocked by the explosion and becomes more luminous than a standard supernova. It is likely that there is a range of luminosities for these type IIn supernovae with only the brightest qualifying as a hypernova.

Pair instability supernovae occur when an oxygen core in an extremely massive star becomes hot enough that gamma rays spontaneously produce electron-positron pairs.<ref name="kasen">{{Cite journal | last1 = Kasen | first1 = D. | last2 = Woosley | first2 = S. E. | last3 = Heger | first3 = A. | doi = 10.1088/0004-637X/734/2/102 | title = Pair Instability Supernovae: Light Curves, Spectra, and Shock Breakout | journal = The Astrophysical Journal | volume = 734 | issue = 2 | pages = 102 | year = 2011 | arxiv = 1101.3336| url = http://iopscience.iop.org/0004-637X/734/2/102/pdf/0004-637X_734_2_102.pdf | format = pdf|bibcode = 2011ApJ...734..102K }}</ref> This causes the core to collapse, but where the collapse of an iron core causes [[endothermic]] fusion to heavier elements, the collapse of an oxygen core creates runaway [[exothermic]] fusion which completely unbinds the star. The total energy emitted depends on the initial mass, with much of the core being converted to 56Ni and ejected which then powers the supernova for many months. At the lower end stars of about {{Solar mass|140}} produce supernovae that are long-lived but otherwise typical, while the highest mass stars of around {{Solar mass|250}} produce supernovae that are extremely luminous and also very long lived; hypernovae. More massive stars die by [[photodisintegration]]. Only [[population III]] stars, with very low metallicity, can reach this stage. Stars with more heavy elements are more opaque and blow away their outer layers until they are small enough to explode as a normal type Ib/c supernova. It is thought that even in our own galaxy, mergers of old low metallicity stars may form massive stars capable of creating a pair instability supernova.

==See also==
{{Portal|Astronomy}}
{{Wikipedia books|Classes of supernovae}}
* [[History of supernova observation]]
* [[Supernova nucleosynthesis]]
* [[Supernova remnant]]
{{Clear}}

==References==
{{Reflist|30em}}

==External links==
*[https://sne.space/?claimedtype=ii List of all known Type II supernovae] at [https://sne.space The Open Supernova Catalog].
* {{cite web|last=Merrifield|first=Michael|title=Type II Supernova|url=http://www.sixtysymbols.com/videos/supernova.htm|work=Sixty Symbols|publisher=[[Brady Haran]] for the [[University of Nottingham]]}}
{{Supernovae}}
{{good article}}

[[Category:Supernovae|Type 2]]

Lokales Void

2017-09-09T05:28:54Z

Bibcode Bot: Adding 1 arxiv eprint(s), 2 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Use dmy dates|date=May 2013}}
{{sky|18|38|0|+|18|0|0}}
{{Infobox astronomical object
|epoch= [[J2000.0]] <ref name=SIMBAD>{{cite web |url= http://simbad.u-strasbg.fr/simbad/sim-id?Ident=NAME+LOCAL+VOID |title= NAME LOCAL VOID -- Underdense region of the Universe |accessdate= 21 December 2014 |publisher= SIMBAD }}</ref>
|ra= {{RA|18|38}} <ref name=SIMBAD/>
|dec= {{DEC|+18.0}} <ref name=SIMBAD/>
|size_v= {{convert|60|Mpc|Mly|abbr=on|lk=off}} <ref name=1997ApJS..112..245N>{{cite journal |author1=Nakanishi, Kouichiro |author2=Takata, Tadafumi |author3=Yamada, Toru |author4=Takeuchi, Tsutomu T. |author5=Shiroya, Ryuichi |author6=Miyazawa, Morio |author7=Watanabe, Shigeo |author8=Saito, Mamoru |date= 1997 |url= http://www.iop.org/EJ/article/0067-0049/112/2/245/35514.pdf?request-id=ac623b35-5b3d-4c0d-947f-4778e8b92bef |title= Search and Redshift Survey for IRAS Galaxies behind the Milky Way and Structure of the Local Void |journal= Astrophysical Journal Supplement |volume= 112 |issue=2 |page= 245 |bibcode= 1997ApJS..112..245N |doi= 10.1086/313039 }}</ref>
}}

The '''Local Void''' is a vast, [[Void (astronomy)|empty region]] of [[Interstellar medium|space]], lying adjacent to the [[Local Group]].<ref name="NewScientist">{{cite web|url=https://www.newscientist.com/article/dn11971-dwarfflinging-void-is-larger-than-thought.html|title=Dwarf-flinging void is larger than thought|last=Shiga|first=David|date=1 June 2007 |publisher=NewScientist.com news service|accessdate=2008-10-13}}</ref><ref name="journal">{{Cite journal | last1 = Tully | first1 = R. B. | last2 = Shaya | first2 = E. J. | last3 = Karachentsev | first3 = I. D. | last4 = Courtois | first4 = H. M.| last5 = Kocevski | first5 = D. D. | last6 = Rizzi | first6 = L. | last7 = Peel | first7 = A. | title = Our Peculiar Motion Away from the Local Void | journal = The Astrophysical Journal | volume = 676 | pages = 184–205 | year = 2008 | doi = 10.1086/527428 | bibcode=2008ApJ...676..184T|arxiv = 0705.4139 }}</ref> Discovered by [[Brent Tully]] and [[J. Richard Fisher|Rick Fisher]] in 1987,<ref name="atlas">{{cite book | last1 = Tully | first1 = R. Brent | last2 = Fisher | first2 = J. Richard | title = Nearby Galaxy Atlas | publisher = Cambridge University Press | url = http://ned.ipac.caltech.edu/level5/March04/Virgo_cluster/frames.html | date = 1987}}</ref> the Local Void is now known to be composed of three separate sectors, separated by bridges of "wispy [[Galaxy filament|filament]]s".<ref name="journal" /> The precise extent of the void is unknown, but it is at least 45 [[parsec|Mpc]] (150 million [[light-year]]s) across,<ref name="astronomy">{{cite web|url=http://www.astronomy.com/asy/default.aspx?c=a&id=5669|title=Milky Way moving away from void|last=Univ. of Hawaii Institute for Astronomy|date=12 June 2007 |publisher=astronomy.com|accessdate=2008-10-13}}</ref> and possibly 150 to 300 h−1 MPc.<ref name=whitbourn>{{cite journal|doi=10.1093/mnras/stw555|title=The galaxy luminosity function and the Local Hole|journal=Monthly Notices of the Royal Astronomical Society|volume=459|pages=496|year=2016|last1=Whitbourn|first1=J. R.|last2=Shanks|first2=T.|arxiv = 1603.02322 |bibcode = 2016MNRAS.459..496W }}</ref><ref name=kbc>{{Cite journal | last1 = Keenan | first1 = Ryan C. | last2 = Barger | first2 = Amy J. | last3 = Cowie | first3 = Lennox L. | title = Evidence for a ~300 Mpc Scale Under-density in the Local Galaxy Distribution | journal = The Astrophysical Journal | volume = 775 | pages = 62 | year = 2013 | doi = 10.1088/0004-637X/775/1/62 |arxiv = 1304.2884 |bibcode = 2013ApJ...775...62K }}</ref> The Local Void also appears to have significantly fewer [[Galaxy|galaxies]] than expected from standard cosmology.<ref>{{Cite journal | last1 = Peebles | first1 = P. J. E. | last2 = Nusser | first2 = A. | title = Nearby galaxies as pointers to a better theory of cosmic evolution | journal = Nature | volume = 465 | issue = 7298 | pages = 565–569 | year = 2010 | pmid = 20520705 | doi = 10.1038/nature09101|bibcode = 2010Natur.465..565P |arxiv = 1001.1484 }}</ref>

==Location and dimensions==
Voids are the result of the way gravity causes matter in the [[universe]] to "clump together", herding galaxies into [[Galaxy groups and clusters|clusters]] and chains, which are separated by regions mostly devoid of galaxies.<ref name="NewScientist"/><ref name="Iwata"/>

[[Astronomer]]s have previously noticed that the Milky Way sits in a large, flat array of galaxies called the [[Local Sheet]], which bounds the Local Void.<ref name="NewScientist"/> The Local Void extends approximately {{convert|60|Mpc|lk=in}}, beginning at the edge of the [[Local Group]].<ref name="PPT">{{cite web|url=http://www.astro.rug.nl/~weygaert/tim1publication/knawvoid/voidknaw.tully.ppt|title=Our CMB Motion: The Local Void influence|last=Tully|first=Brent|publisher=University of Hawaii, Institute for Astronomy |accessdate=2008-10-13}}</ref> It is believed that the distance from [[Earth]] to the centre of the Local Void must be at least {{convert|23|Mpc}}.<ref name="journal"/>

The size of the Local Void was calculated due to an isolated [[dwarf galaxy]] located inside it. The bigger and emptier the void, the weaker its [[gravity]], and the faster the dwarf should be fleeing the void towards concentrations of matter.<ref name="journal"/> [[Dark energy]] has been suggested as an alternative explanation for the speedy expulsion of the dwarf galaxy.<ref name="NewScientist"/>

An earlier "[[Hubble Bubble (astronomy)|Hubble Bubble]]" model, based on measured velocities of [[Type 1a supernovae]], proposed a relative void centred on the Milky Way. Recent analysis of that data, however, suggested that interstellar dust had resulted in misleading measurements.<ref name=moss>{{cite journal|last=Moss|first=Adam|author2=James P Zibin |author3=Douglas Scott |title=Precision Cosmology Defeats Void Models for Acceleration|doi=10.1103/PhysRevD.83.103515|date=2011|journal=Physical Review D|volume=83|issue=10|pages=103515|arxiv=1007.3725|bibcode = 2011PhRvD..83j3515M }}</ref>

Several authors have shown that the local universe up to 300 MPc from the Milky Way is less dense than surrounding areas, by 15-50%. This has been called the Local Void or Local Hole.<ref name=whitbourn/><ref name=kbc/> Some media reports have dubbed it the KBC Void, although this name has not been taken up in other publications.<ref name=forbes>{{cite web|url=https://www.forbes.com/sites/startswithabang/2017/06/07/were-way-below-average-astronomers-say-milky-way-resides-in-a-great-cosmic-void/#4d53c7cd6d05|title=We're Way Below Average! Astronomers Say Milky Way Resides In A Great Cosmic Void|last=Siegel|first=Ethan|publisher=Forbes|accessdate=2017-06-09}}</ref>

==Effect on surrounds==
Scientists believe that the Local Void is growing and the [[Local Sheet]], which makes up one wall of the void, is rushing away from the void's centre at 260 kilometres per second.<ref name="Iwata">{{cite book|last=I|first=Iwata|author2=Ohta, K. |author3=Nakanishi, K. |author4=Chamaraux, P. |author5= Roman, A.T. |title=The Growth of the Local Void and the Origin of the Local Velocity Anomaly|publisher=Astronomical Society of the Pacific|edition=329|volume=Nearby Large-Scale Structures and the Zone of Avoidance |pages=59|url=http://www.aspbooks.org/a/volumes/article_details/?paper_id=1483}}</ref> Concentrations of matter normally pull together, creating a larger void where matter is rushing away. The Local Void is surrounded uniformly by matter in all directions, except for one sector in which there is nothing, which has the effect of taking more matter away from that sector. The effect on the nearby galaxy is astonishingly large.<ref name="journal"/> The Milky Way's velocity away from the Local Void is {{convert|600000|mph|km/s|disp=flip}}.<ref name="NewScientist"/><ref name="astronomy" />

==List of void galaxies==
Several [[void galaxy|void galaxies]] have been found within the Local Void, these include:

{{expand list|date=August 2016}}

{| class=wikitable
|-
! Galaxy
! Void
! Filament
! Notes
! Comments
|-
| [[PC 1357+4641]]
| [[Boötes void]]
|
| <ref name="10.1086/318868"/>
| [[Emission-line Galaxy]]
|-
| [[IRAS 14288+5255]]
| [[Boötes void]]
|
| <ref name="10.1086/318868"> The Astrophysical Journal Letters, "Detection of X-Ray Emission from Galaxies inside the Bootes Void", '''Chulhee Kim, Th. Boller, Kajal K. Ghosh, Douglas A. Swartz, Brian D. Ramsey''', 'Volume 546, Number 2', ''10 January 2001'', {{doi|10.1086/318868}}</ref>
| [[Active galactic nucleus|AGN]] [[Astrophysical X-ray source|X-ray source]]
|-
| [[G 1432+5302]]
| [[Boötes void]]
|
| <ref name="10.1086/324739"> The Astronomical Journal, "Spectroscopy of Galaxies in the Bootes Void", '''Shawn Cruzen 1, Tara Wehr, Donna Weistrop, Ronald J. Angione, Charles Hoopes''', 'Volume 123, Number 1', ''2002 January'', {{doi|10.1086/324739}}</ref>
| [[Starburst galaxy]]
|-
| [[G 1458+4944]]
| [[Boötes void]]
|
| <ref name="10.1086/324739"/>
| [[LINER galaxy]]
|-
| [[G 1507+4554]]
| [[Boötes void]]
|
| <ref name="10.1086/324739"/>
| [[Starburst galaxy]]
|-
| [[G 1510+4727A]] & [[G 1510+4727B]]
| [[Boötes void]]
|
| <ref name="10.1086/324739"/>
| [[Interacting galaxies|Interacting]] [[galaxy pair]]
|-
| [[BHI 1514+3819]]
| [[Boötes void]]
|
| <ref name="10.1086/318868"/>
|
|-
| [[FSS 1515+3823]]
| [[Boötes void]]
|
| <ref name="10.1086/318868"/>
|
|-
| [[G 1517+3949]]
| [[Boötes void]]
|
| <ref name="10.1086/324739"/>
| [[Starburst galaxy]]
|-
| [[G 1517+3956A]] & [[G 1517+3956B]]
| [[Boötes void]]
|
| <ref name="10.1086/324739"/>
| [[Interacting galaxies|Interacting]] [[galaxy pair]]
|-
| [[IRAS 15195+5050]]
| [[Boötes void]]
|
| <ref name="10.1086/318868"/>
| [[Active galactic nucleus|AGN]] [[Astrophysical X-ray source|X-ray source]]
|-
| [[Markarian 845]]
| [[Boötes void]]
|
| <ref name="10.1086/318868"/>
| [[Seyfert galaxy|Seyfert 1]] ([[Astrophysical X-ray source|X-ray source]])
|-
| [[CG 547]]
| [[Boötes void]]
|
| <ref name="10.1086/318868"/>
| [[Emission-line Galaxy]]
|-
| [[CG 637]]
| [[Boötes void]]
|
| <ref name="10.1086/318868"/>
| [[Emission-line Galaxy]]
|-
| [[CG 922]]
| [[Boötes void]]
|
| <ref name="10.1086/318868"/>
| [[Emission-line Galaxy]]
|-
|[[MCG+01-02-015]]
|
|
|<ref name="SIMBBAD-MCG+01-02-015">SIMBAD, [http://simbad.u-strasbg.fr/simbad/sim-id?Ident=MCG%2B01-02-015 MCG+01-02-015]</ref><ref name=HST-potw1545a>{{cite web|title=The loneliest of galaxies|url=http://www.spacetelescope.org/images/potw1545a/|date=9 November 2015|accessdate=10 November 2015|publisher=Hubble Space Telescope}}</ref><ref name=SciNews->Sci-News, [http://www.sci-news.com/astronomy/science-nasas-hubble-lonely-galaxy-03417.html "NASA’s Hubble Space Telescope Focuses on Lonely Galaxy"], 9 November 2015</ref><ref name=SpaceDaily-2015-11-18>SpaceDaily, [http://www.spacedaily.com/reports/Hubble_Views_a_Lonely_Galaxy_999.html "Hubble Views a Lonely Galaxy"], 18 November 2015</ref>
|LEDA 1852 (Pisces)
|-
| [[Pisces A]]
| Local Void
|
| <ref name=SciNews-2016-08-15>{{cite news |url= http://www.sci-news.com/astronomy/hubble-dwarf-galaxies-pisces-04103.html |title= Hubble Sees Two Dwarf Galaxies in Pisces |publisher= Sci-News |date= 15 August 2016 }}</ref>
|
|-
| [[Pisces B]]
| Local Void
|
| <ref name=SciNews-2016-08-15/>
|
|-
|}

==References==
{{reflist|30em}}

[[Category:Voids (astronomy)]]
[[Category:Interstellar media| ]]
[[Category:Astrochemistry]]

Durham University Observatory

2017-09-07T20:39:01Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{EngvarB|date=September 2013}}
{{Use dmy dates|date=September 2013}}
{{Infobox building
| name = Durham Observatory
| native_name=
| former_names =
| alternate_names =
| image = Durham Observatory.jpg
| caption = Observatory front view
| map_type = United Kingdom Durham
| altitude =
| building_type = [[Observatory]]
| architectural_style =
| structural_system =
| cost =
| ren_cost =
| location = Potters Bank, [[Durham, England|Durham]]
| owner = [[Durham University]]
| coordinates = {{coord|54.768|-1.586|display=inline}}
| start_date = 1839
| completion_date = 1840
| inauguration_date =
| renovation_date =
| demolition_date =
| destruction_date =
| height =
| diameter =
| other_dimensions =
| floor_count =
| floor_area =
| main_contractor =
| architect = [[Anthony Salvin]]
| architecture_firm =
| structural_engineer =
| services_engineer =
| civil_engineer =
| other_designers =
| quantity_surveyor =
| awards =
| ren_architect =
| ren_firm =
| ren_str_engineer =
| ren_serv_engineer =
| ren_civ_engineer =
| ren_oth_designers =
| ren_qty_surveyor =
| ren_awards =
| references =
}}

The '''Durham University Observatory''' is a weather [[observatory]] owned and operated by the [[University of Durham]]. It is a Grade II listed building<ref>{{Cite web|url=http://www.heritagegateway.org.uk/Gateway/Results_Single.aspx?uid=110427&resourceID=5|title=Durham Observatory|publisher=Heritage Gateway|accessdate=3 October 2009}}</ref> located at Potters Bank, Durham and was founded in 1839 initially as an [[astronomical]] and [[meteorological]] observatory (owing to the need to calculate [[refraction]] from the air temperature) by [[Temple Chevallier]], until 1937 when the observatory moved purely to meteorological recording.<ref>[http://www.aip.org/history/newsletter/spr98/doc-98a.htm Documentation Preserved – Spr. 1998]</ref>

The observatory's current Director is Professor [[Tim Burt]] of the Geography Department, who is also Master of [[Hatfield College]].

After the [[Radcliffe Observatory]], Durham has the longest unbroken meteorological record of any University in the UK, with records dating back to the 1840s,<ref>[http://www.geography.dur.ac.uk/projects/weather/Home/tabid/666/Default.aspx Weather > Home ( DNN 3.0.12 )]</ref> principally due to the work of [[Gordon Manley]] in creating a temperature record that would be comparable to Oxford's.<ref>http://www.geography.dur.ac.uk/projects/weather/TheHistory/tabid/2212/Default.aspx The Observatory's History</ref> At present the observatory contributes to the [[Met Office]]'s forecasts by providing automated records.

==Former observers==
*1840 – 1841 [[Temple Chevallier]]<ref name="Durham University: Earlier Foundations and Present Colleges">{{cite web|url=https://archive.org/download/durhamuniversity00fowluoft/durhamuniversity00fowluoft.pdf|title=Durham University: Earlier Foundations and Present Colleges, Fowler, Joseph Thomas (1904)|publisher=Kessinger Publishing|accessdate=25 February 2009}}</ref>
*1841 [[John Stewart Browne]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1842 – 1846 [[Arthur Beanlands]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1846 – 1849 [[Robert Anchor Thompson]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1849 [[Le Jeune]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1849 [[Robert Healey Blakey]] (acting)<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1849 – 1852 [[Richard Christopher Carrington|Richard Carrington]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1852 – 1853 [[William Ellis (astronomer)|William Ellis]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1854 – 1855 [[Georg Friedrich Wilhelm Rümker]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1856 – 1863 [[Albert Marth]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1863 – 1864 [[Edward Gleadowe Marshall]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1865 – 1867 [[Mondeford Reginald Dolman]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1867 – 1874 [[John Isaac Plummer]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1874 – 1885 [[Gabriel Alphonsus Goldney]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1885 – 1900 [[Henry James Carpenter]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1900 – 1919 [[Frederick Charles Hampshire Carpenter]]<ref name="Durham University: Earlier Foundations and Present Colleges"/>
*1919 – 1938 Frank Sargent <ref name="The History of Astronomy in the University of Durham from 1835 TO 1939">{{cite web|url=http://articles.adsabs.harvard.edu//full/1980QJRAS..21..369R/0000378.000.html|title=The History of Astronomy in the University of Durham from 1835 TO 1939|publisher=ROYAL ASTRON. SOC. QUARTERLY JOURNAL V. 21, P. 369, 1980|accessdate=5 May 2009}}</ref>
*1938 – 1939 E. Gluckauf<ref name="Durham University Observatory and its meteorological record">{{cite journal|url=http://onlinelibrary.wiley.com/doi/10.1002/wea.86/abstract|title=Durham University Observatory and its meteorological record|accessdate=5 May 2009|doi=10.1002/wea.86|volume=62|journal=Weather|pages=265–269|bibcode = 2007Wthr...62..265K }}</ref>
*1940 – 1945 A. Beecroft<ref name="Durham University Observatory and its meteorological record"/>
*1945 – 1948 L. S. Joyce<ref name="Durham University Observatory and its meteorological record"/>
*1949 – 1951 K. F. and G. A. Chackett<ref name="Durham University Observatory and its meteorological record"/>
*1951 – 1957 J. Musgrave<ref name="Durham University Observatory and its meteorological record"/>
*1957 – 1968 F. and D. Glockling<ref name="Durham University Observatory and its meteorological record"/>
*1969 – 1990 A. Warner<ref name="Durham University Observatory and its meteorological record"/>

==References==
{{reflist|colwidth=30em}}

==External links==
* [http://www.geography.dur.ac.uk/projects/weather/Home/tabid/666/Default.aspx The Observatory's Homepage]
* [http://www.dur.ac.uk/news/newsitem/?itemno=4124 News Article on rising temperatures at Durham]
* [http://www.keystothepast.info/durhamcc/K2P.nsf/K2PDetail?readform&PRN=D12425 Observatory, Potters Bank, Durham; Listed building (Durham City)]
* [http://storing.ingv.it/es_web/Data/Collection/300282.htm Durham Observatory – Durham (UNITED KINGDOM)]

{{University of Durham}}

[[Category:Buildings and structures of Durham University]]
[[Category:Astronomical observatories in England]]
[[Category:1839 establishments in England]]
[[Category:Meteorological observatories]]
[[Category:Anthony Salvin buildings]]

Benutzer:Molinarius/Silicon photonics

2016-05-12T03:01:57Z

Bibcode Bot: Adding 0 arxiv eprint(s), 2 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Use dmy dates|date=November 2014}}
'''Silicon photonics''' is the study and application of [[photonics|photonic]] systems which use [[silicon]] as an [[optical medium]].<ref name="lipson_2005">{{cite journal
|doi = 10.1109/JLT.2005.858225
|title = Guiding, Modulating, and Emitting Light on Silicon – Challenges and Opportunities
|journal = [[Journal of Lightwave Technology]]
|year = 2005
|volume = 23
|issue = 12
|pages = 4222–4238
|author = Lipson, Michal
| bibcode = 2005JLwT...23.4222L }}</ref><ref name="jalali_2006">{{cite journal
|doi = 10.1109/JLT.2006.885782
|title = Silicon photonics
|journal = [[Journal of Lightwave Technology]]
|year = 2006
|volume = 24
|issue = 12
|pages = 4600–4615
| bibcode = 2006JLwT...24.4600J |last1 = Jalali
|first1 = Bahram
|last2 = Fathpour
|first2 = Sasan
}}</ref><ref name="almeida_2004">{{cite journal
|title = All-optical control of light on a silicon chip
|journal = [[Nature (journal)|Nature]]
|year = 2004
|volume = 431
|issue = 7012
|pages = 1081–1084
|doi = 10.1038/nature02921
|pmid=15510144
| bibcode = 2004Natur.431.1081A |author1 = Almeida
|first1 = V. R.
|last2 = Barrios
|first2 = C. A.
|last3 = Panepucci
|first3 = R. R.
|last4 = Lipson
|first4 = M
}}</ref><ref name="pavesi_book">{{cite book
|title = Silicon photonics
|isbn = 3-540-21022-9
|publisher = [[Springer Science+Business Media|Springer]]
|year = 2004
}}</ref><ref name="reed_book">{{cite book
|title = Silicon photonics: an introduction
|isbn = 0-470-87034-6
|publisher = [[John Wiley and Sons]]
|year = 2004
}}</ref> The silicon is usually patterned with [[nanoscale|sub-micrometre]] precision, into [[microphotonics|microphotonic]] components.<ref name="pavesi_book" /> These operate in the [[infrared]], most commonly at the 1.55 micrometre [[wavelength]] used by most [[fiber optic telecommunication]] systems.<ref name="lipson_2005" /> The silicon typically lies on top of a layer of silica in what (by analogy with [[silicon on insulator|a similar construction]] in [[microelectronics]]) is known as '''silicon on insulator''' (SOI).<ref name="pavesi_book" /><ref name="reed_book" />

[[File:Silicon Photonics 300mm wafer.JPG|thumb|upright|right|Silicon Photonics 300mm wafer]]

Silicon photonic devices can be made using existing [[semiconductor fabrication]] techniques, and because silicon is already used as the substrate for most [[integrated circuit]]s, it is possible to create hybrid devices in which the [[optics|optical]] and [[electronics|electronic]] components are integrated onto a single microchip.<ref name="lipson_2005" /> Consequently, silicon photonics is being actively researched by many electronics manufacturers including [[IBM]] and [[Intel]], as well as by academic research groups such as those of Prof. [[Michal Lipson]] and [[Roel Baets]], who see it is a means for keeping on track with [[Moore's Law]], by using [[optical interconnect]]s to provide faster [[data transfer]] both between and within [[Integrated circuit|microchip]]s.<ref name="ibm_silicon">{{cite web
|title = Silicon Integrated Nanophotonics
|publisher = [[IBM]] Research
|url = http://domino.research.ibm.com/comm/research_projects.nsf/pages/photonics.index.html
|accessdate = 14 July 2009
}}</ref><ref name="intel_silicon">{{cite web
|title = Silicon Photonics
|publisher = [[Intel]]
|url = http://techresearch.intel.com/articles/Tera-Scale/1419.htm
|accessdate = 14 July 2009
}}</ref><ref>{{cite journal|last1=SPIE|title=Yurii A. Vlasov plenary presentation: Silicon Integrated Nanophotonics: From Fundamental Science to Manufacturable Technology|journal=SPIE Newsroom|date=5 March 2015|doi=10.1117/2.3201503.15}}</ref>

The propagation of [[light]] through silicon devices is governed by a range of [[nonlinear optics|nonlinear optical]] phenomena including the [[Kerr effect]], the [[Raman effect]], [[two photon absorption]] and interactions between [[photons]] and [[free charge carriers]].<ref name="dekker_2008" >{{cite journal
|title = Ultrafast nonlinear all-optical processes in silicon-on-insulator waveguides
|journal = [[Journal of Physics D]]
|year = 2008
|volume = 40
|issue = 14
|page = R249–R271
|doi=10.1088/0022-3727/40/14/r01
|bibcode = 2007JPhD...40..249D |last1 = Dekker
|first1 = R
|last2 = Usechak
|first2 = N
|last3 = Först
|first3 = M
|last4 = Driessen
|first4 = A
}}</ref> The presence of nonlinearity is of fundamental importance, as it enables light to interact with light,<ref name="butcher_book">{{cite book
|title = The elements of nonlinear optics
|isbn = 0-521-42424-0
|publisher = [[Cambridge University Press]]
|year = 1991
|author1 = Butcher, Paul N. |author2 = Cotter, David
}}</ref> thus permitting applications such as wavelength conversion and all-optical signal routing, in addition to the passive transmission of light.

Silicon [[waveguide]]s are also of great academic interest, due to their ability to support exotic nonlinear optical phenomena such as [[Soliton (optics)|soliton propagation]].<ref name="hsieh_2006" >{{cite journal
|doi = 10.1364/OE.14.012380
|title = Ultrafast-pulse self-phase modulation and third-order dispersion in Si photonic wire-waveguides
|journal = [[Optics Express]]
|year = 2006
|volume = 14
|issue = 25
|pages = 12380–12387
| bibcode = 2006OExpr..1412380H |last1 = Hsieh
|first1 = I-Wei
|last2 = Chen
|first2 = Xiaogang
|last3 = Dadap
|first3 = Jerry I.
|last4 = Panoiu
|first4 = Nicolae C.
|last5 = Osgood
|first5 = Richard M.
|last6 = McNab
|first6 = Sharee J.
|last7 = Vlasov
|first7 = Yurii A.
}}</ref><ref name="zhang_2007">{{cite journal
|doi = 10.1364/OE.15.007682
|title = Optical solitons in a silicon waveguide
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 12
|pages = 7682–7688
| bibcode = 2007OExpr..15.7682Z |last1 = Zhang
|first1 = Jidong
|last2 = Lin
|first2 = Qiang
|last3 = Piredda
|first3 = Giovanni
|last4 = Boyd
|first4 = Robert W.
|last5 = Agrawal
|first5 = Govind P.
|last6 = Fauchet
|first6 = Philippe M.
}}</ref><ref name="ding_2008">{{cite journal
|doi = 10.1364/OE.16.003310
|title = Solitons and spectral broadening in long silicon-on- insulator photonic wires
|journal = [[Optics Express]]
|year = 2008
|volume = 16
|issue = 5
|pages = 3310–3319
| bibcode = 2008OExpr..16.3310D |last1 = Ding
|first1 = W.
|last2 = Benton
|first2 = C.
|last3 = Gorbach
|first3 = A. V.
|last4 = Wadsworth
|first4 = W. J.
|last5 = Knight
|first5 = J. C.
|last6 = Skryabin
|first6 = D. V.
|last7 = Gnan
|first7 = M.
|last8 = Sorrel
|first8 = M.
|last9 = de la Rue
|first9 = R. M.

}}</ref>

== Applications ==

=== Optical interconnects ===

Progress in computer technology (and the continuation of [[Moore's Law]]) is becoming increasingly dependent on faster [[data transfer]] between and within [[Integrated circuit|microchips]].<ref name="meindl_2003">{{cite journal
|doi = 10.1109/MCISE.2003.1166548
|title = Beyond Moore's Law: the interconnect era
|journal = Computing in Science & Engineering
|year = 2003
|volume = 5
|issue = 1
|pages = 20–24
|author = Meindl, J. D.
}}</ref> [[Optical interconnect]]s may provide a way forward, and silicon photonics may prove particularly useful, once integrated on the standard silicon chips.<ref name="lipson_2005" /><ref name="barwicz_2006">{{cite journal
|doi = 10.1364/JON.6.000063
|title = Silicon photonics for compact, energy-efficient interconnects
|journal = Journal of Optical Networking
|year = 2006
|volume = 6
|issue = 1
|pages = 63–73
| bibcode = 2007JON.....6...63B |last1 = Barwicz
|first1 = T.
|last2 = Byun
|first2 = H.
|last3 = Gan
|first3 = F.
|last4 = Holzwarth
|first4 = C. W.
|last5 = Popovic
|first5 = M. A.
|last6 = Rakich
|first6 = P. T.
|last7 = Watts
|first7 = M. R.
|last8 = Ippen
|first8 = E. P.
|last9 = Kärtner
|first9 = F. X.
|last10 = Smith
|first10 = H. I.
|last11 = Orcutt
|first11 = J. S.
|last12 = Ram
|first12 = R. J.
|last13 = Stojanovic
|first13 = V.
|last14 = Olubuyide
|first14 = O. O.
|last15 = Hoyt
|first15 = J. L.
|last16 = Spector
|first16 = S.
|last17 = Geis
|first17 = M.
|last18 = Grein
|first18 = M.
|last19 = Lyszczarz
|first19 = T.
|last20 = Yoon
|first20 = J. U.
}}</ref><ref name="orcutt_2008">{{cite conference
|authors = Orcutt, J. S.
|title = Demonstration of an Electronic Photonic Integrated Circuit in a Commercial Scaled Bulk CMOS Process
|conference = Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies
|year = 2008
|display-authors=etal}}</ref> In 2006 Former [[Intel]] senior vice president [[Pat Gelsinger]] stated that, "Today, optics is a niche technology. Tomorrow, it's the mainstream of every chip that we build."<ref name="intel_silicon" />

Optical interconnects require multiple advances.

Many researchers believe an on-chip [[laser]] source is required. One such device is the [[hybrid silicon laser]], in which the silicon is bonded to a different [[semiconductor]] (such as [[indium phosphide]]) as the [[lasing medium]].<ref name="intel_hybrid">{{cite web
|url = http://techresearch.intel.com/articles/Tera-Scale/1448.htm
|title = Hybrid Silicon Laser – Intel Platform Research
|publisher = [[Intel]]
|accessdate = 14 July 2009
}}</ref> Another possibility is the all-silicon [[Raman laser]], in which silicon is the lasing medium.<ref name="rong_2005">{{cite journal
|title = An all-silicon Raman laser
|doi = 10.1038/nature03273
|journal = [[Nature (journal)|Nature]]
|pmid = 15635371
|year = 2005
|volume = 433
|issue = 7023
|pages = 292–294
| bibcode = 2005Natur.433..292R |author1 = Rong
|first1 = H
|last2 = Liu
|first2 = A
|last3 = Jones
|first3 = R
|last4 = Cohen
|first4 = O
|last5 = Hak
|first5 = D
|last6 = Nicolaescu
|first6 = R
|last7 = Fang
|first7 = A
|last8 = Paniccia
|first8 = M
}}</ref>

The light must be [[modulation|modulated]] to encode data in the form of optical pulses. One such technique is to control the density of free charge carriers, which (as described below) alter the waveguide's optical properties. Some modulators pass light through the [[intrinsic semiconductor|intrinsic region]] of a [[PIN diode]], into which carriers can be injected or removed by altering the [[Electrical polarity|polarity]] of an applied [[voltage]].<ref name="barrios_2003">{{cite journal
|doi = 10.1109/JLT.2003.818167
|title = Electrooptic Modulation of Silicon-on-Insulator Submicrometer-Size Waveguide Devices
|journal = [[Journal of Lightwave Technology]]
|year = 2003
|volume = 21
|issue = 10
|pages = 2332–2339
| bibcode = 2003JLwT...21.2332B |last1 = Barrios
|first1 = C.A.
|last2 = Almeida
|first2 = V.R.
|last3 = Panepucci
|first3 = R.
|last4 = Lipson
|first4 = M.
}}</ref> In 2007 an [[optical ring resonator]] with a built in PIN diode achieved data transmission rates of 18 [[Gbit/s]].<ref name="xu_2007">{{cite journal
|title = High Speed Carrier Injection 18 Gbit/s Silicon Micro-ring Electro-optic Modulator
|journal = Proceedings of Lasers and Electro-Optics Society
|year = 2007
|volume =
|pages = 537–538
|last1 = Manipatruni
|first1 = Sasikanth
|author2 = Qianfan Xu
|last3 = Schmidt
|first3 = B.
|last4 = Shakya
|first4 = J.
|last5 = Lipson
|first5 = M.
|displayauthors = 1
|doi=10.1109/leos.2007.4382517
}}</ref> Devices where the electrical signal co-moves with the light, allowed data rates of 30 Gbit/s.<ref name="liu_2007">{{cite journal
|doi = 10.1364/OE.15.000660
|last1 = Liu
|first1 = Ansheng
|last2 = Liao
|first2 = Ling
|last3 = Rubin
|first3 = Doron
|last4 = Nguyen
|first4 = Hat
|last5 = Ciftcioglu
|first5 = Berkehan
|last6 = Chetrit
|first6 = Yoel
|last7 = Izhaky
|first7 = Nahum
|last8 = Paniccia
|first8 = Mario
|title = High-speed optical modulation based on carrier depletion in a silicon waveguide
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 2
|pages = 660–668 |bibcode = 2007OExpr..15..660L
}}
</ref> Using multiple wavelengths scaled allowed 50 Gbit/s.<ref name="Manipatruni_2009">{{cite journal
|title = 50 Gbit/s wavelength division multiplexing using silicon microring modulators
|journal = [Group IV Photonics, 2009. GFP '09. 6th IEEE International Conference on]
|year = 2009
|doi = 10.1109/GROUP4.2009.5338375
|pages = 244–246
|author = Manipatruni, Sasikanth; Chen, Long; Lipson, Michal;
|isbn = 978-1-4244-4402-1
}}
</ref> A prototype optical interconnect with microring modulators integrated with germanium detectors has been demonstrated.<ref name="Long Chen_2009">{{cite journal
|doi = 10.1364/OE.17.015248
|title = Integrated GHz silicon photonic interconnect with micrometer-scale modulators and detectors
|journal = [[Optics Express]]
|year = 2009
|volume = 17
|issue = 17
|pages = 15248–15256
| bibcode = 2009OExpr..1715248C |arxiv = 0907.0022 |last1 = Chen
|first1 = Long
|last2 = Preston
|first2 = Kyle
|last3 = Manipatruni
|first3 = Sasikanth
|last4 = Lipson
|first4 = Michal
}}
</ref><ref name="register_vance">{{cite news
|title = Intel cranks up next-gen chip-to-chip play
|publisher = The Register
|author = Vance, Ashlee
|url = http://www.theregister.co.uk/2007/01/27/intel_silicon_modulator/print.html
|accessdate = 26 July 2009
}}</ref>

After passage through a silicon [[waveguide]] to a different chip (or region of the same chip) the light must be [[photodetector|detected]], to reconvert the data into electronic form.<ref>{{cite journal |last1=Kucharski |first1=D. |last2=Guckenberger |first2=D. |last3=Masini |first3=G. |last4=Abdalla |first4=S. |last5=Witzens |first5=J. |last6=Sahni |first6=S. |displayauthors=1 |year=2010 |title=10 Gb/s 15mW optical receiver with integrated Germanium photodetector and hybrid inductor peaking in 0.13µm SOI CMOS technology |journal= Solid-State Circuits Conference Digest of Technical Papers (ISSCC) |pages=360–361}}</ref><ref>{{cite journal|year = 2006|title=CMOS photonics using germanium photodetectors|journal=ECS Transactions|volume=3|issue=7|pages=17–24|doi=10.1149/1.2355790|url=http://ecst.ecsdl.org/content/3/7/17.abstract|last1=Gunn|first1=Cary|last2=Masini|first2=Gianlorenzo|last3=Witzens|first3=J.|last4=Capellini|first4=G.}}</ref> Detectors based on [[metal-semiconductor junction]]s (with [[germanium]] as the semiconductor) have been integrated into silicon waveguides.<ref name="vivien_2007">{{cite journal
|doi = 10.1364/OE.15.009843
|title = High speed and high responsivity germanium photodetector integrated in a Silicon-On-Insulator microwaveguide
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 15
|pages = 9843–9848
| bibcode = 2007OExpr..15.9843V |last1 = Vivien
|first1 = Laurent
|last2 = Rouvière
|first2 = Mathieu
|last3 = Fédéli
|first3 = Jean-Marc
|last4 = Marris-Morini
|first4 = Delphine
|last5 = Damlencourt
|first5 = Jean François
|last6 = Mangeney
|first6 = Juliette
|last7 = Crozat
|first7 = Paul
|last8 = El Melhaoui
|first8 = Loubna
|last9 = Cassan
|first9 = Eric
|last10 = Le Roux
|first10 = Xavier
|last11 = Pascal
|first11 = Daniel
|last12 = Laval
|first12 = Suzanne
}}</ref> More recently, silicon-germanium [[avalanche photodiode]]s capable of operating at 40 Gbit/s have been fabricated.<ref name="kang_2008">{{cite journal
|doi = 10.1038/nnano.2008.25
|title = Monolithic germanium/silicon avalanche photodiodes with 340 GHz gain–bandwidth product
|journal = [[Nature Photonics]]
|year = 2008
|volume = 3
|issue = 2
|pages = 59–63
|pmid = 18654454
| bibcode = 2008NatNa...3...59. }}</ref><ref name="register_modine">{{cite news
|title = Intel trumpets world's fastest silicon photonic detector
|publisher = The Register
|author = Modine, Austin
|url = http://www.theregister.co.uk/2008/12/08/intel_world_record_apd_research/
|date = 8 December 2008
}}</ref>
Complete transceivers have been commercialized in the form of active optical cables.<ref>{{cite journal|author = Narasimha, A. |title = A 40-Gb/s QSFP optoelectronic transceiver in a 0.13 µm CMOS silicon-on-insulator technology|year = 2008|journal = Proceedings of the Optical Fiber Communication Conference (OFC)|page = OMK7|url=http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2008-OMK7|isbn=978-1-55752-859-9}}</ref>

In 2012, IBM announced that it had achieved optical components at the 90 nanometer scale that can be manufactured using standard techniques and incorporated into conventional chips.<ref name="ibm_silicon" /><ref>{{cite web|url=http://www.gizmag.com/ibm-silicon-nanophotonics/25446/?utm_source=Gizmag+Subscribers&utm_campaign=59593484e3-UA-2235360-4&utm_medium=email |title=IBM integrates optics and electronics on a single chip |publisher=Gizmag.com |date= 13 December 2012|author=Borghino, Dario }}</ref> In September 2013, Intel announced technology to transmit data at speeds of 100 gigabits per second along a cable approximately five millimeters in diameter for connecting servers inside data centers. Conventional PCI-E data cables carry data at up to eight gigabits per second, while networking cables reach 40 Gb. The latest version of the [[USB]] standard tops out at five Gb. The technology does not directly replace existing cables in that it requires the a separate circuit board to interconvert electrical and optical signals. Its advanced speed offers the potential of reducing the number of cables that connect blades on a rack and even of separating processor, storage and memory into separate blades to allow more efficient cooling and dynamic configuration<ref>{{cite web|last=Simonite |first=Tom |url=http://www.technologyreview.com/news/518941/intels-laser-chips-could-make-data-centers-run-better |title=Intel Unveils Optical Technology to Kill Copper Cables and Make Data Centers Run Faster | MIT Technology Review |publisher=Technologyreview.com |date= |accessdate=4 September 2013}}</ref>

[[Graphene]] photodetectors have the potential to surpass germanium devices in several important aspects, although they remain about one order of magnitude behind current generation capacity, despite rapid improvement.
Graphene devices can work at very high frequencies, and could in principle reach higher bandwidths. Graphene can absorb a broader range of wavelengths than germanium. That property could be exploited to transmit more data streams simultaneously in the same beam of light. Unlike germanium detectors, graphene photodetectors do not require applied voltage, which could reduce energy needs. Finally, graphene detectors in principle permit a simpler and less expensive on-chip integration. However, graphene does not strongly absorb light. Pairing a silicon waveguide with a graphene sheet better routes light and maximizes interaction. The first such device was demonstrated in 2011. Manufacturing such devices using conventional manufacturing techniques has not been demonstrated.<ref>Orcutt, Mike (2 October 2013) [http://www.technologyreview.com/news/519441/graphene-could-make-data-centers-and-supercomputers-more-efficient "Graphene-Based Optical Communication Could Make Computing More Efficient]. ''MIT Technology Review''.</ref>

In 2013 researchers demonstrated two different depletion-mode carrier-plasma optical modulators that can be fabricated using standard Silicon-on-Insulator Complementary Metal-Oxide-Semiconductor (SOI CMOS) manufacturing processes. The researchers also detailed a second modulator that could be used in bulk CMOS.<ref>{{cite web|url=http://www.kurzweilai.net/major-silicon-photonics-breakthrough-could-allow-for-continued-exponential-growth-in-microprocessors |title=Major silicon photonics breakthrough could allow for continued exponential growth in microprocessors |publisher=KurzweilAI |date= 8 October 2013}}</ref><ref>{{Cite journal | last1 = Shainline | first1 = J. M. | last2 = Orcutt | first2 = J. S. | last3 = Wade | first3 = M. T. | last4 = Nammari | first4 = K. | last5 = Moss | first5 = B. | last6 = Georgas | first6 = M. | last7 = Sun | first7 = C. | last8 = Ram | first8 = R. J. | last9 = Stojanović | first9 = V. | last10 = Popović | first10 = M. A. | doi = 10.1364/OL.38.002657 | title = Depletion-mode carrier-plasma optical modulator in zero-change advanced CMOS | journal = Optics Letters | volume = 38 | issue = 15 | pages = 2657–2659 | year = 2013 | pmid = 23903103| pmc = |bibcode = 2013OptL...38.2657S }}</ref><ref>{{Cite journal | last1 = Shainline | first1 = J. M. | last2 = Orcutt | first2 = J. S. | last3 = Wade | first3 = M. T. | last4 = Nammari | first4 = K. | last5 = Tehar-Zahav | first5 = O. | last6 = Sternberg | first6 = Z. | last7 = Meade | first7 = R. | last8 = Ram | first8 = R. J. | last9 = Stojanović | first9 = V. | last10 = Popović | first10 = M. A. | doi = 10.1364/OL.38.002729 | title = Depletion-mode polysilicon optical modulators in a bulk complementary metal-oxide semiconductor process | journal = Optics Letters | volume = 38 | issue = 15 | pages = 2729–2731 | year = 2013 | pmid = 23903125| pmc = |bibcode = 2013OptL...38.2729S }}</ref>

=== Optical routers and signal processors ===

Another application of silicon photonics is in signal routers for [[fiber optic telecommunication|optical communication]]. Construction can be greatly simplified by fabricating the optical and electronic parts on the same chip, rather than having them spread across multiple components.<ref name="analui_2006">{{cite journal
|doi = 10.1109/JSSC.2006.884388
|title = A Fully Integrated 20-Gb/s Optoelectronic Transceiver Implemented in a Standard 0.13- μm CMOS SOI Technology
|journal = [[IEEE]] Journal of Solid-State Circuits
|year = 2006
|volume = 41
|issue = 12
|pages = 2945–2955
|last1 = Analui
|first1 = Behnam
|last2 = Guckenberger
|first2 = Drew
|last3 = Kucharski
|first3 = Daniel
|last4 = Narasimha
|first4 = Adithyaram
}}</ref> A wider aim is all-optical signal processing, whereby tasks which are conventionally performed by manipulating signals in electronic form are done directly in optical form.<ref name="almeida_2004" /><ref name="boyraz_2004">{{cite journal
|doi = 10.1364/OPEX.12.004094
|title = All optical switching and continuum generation in silicon waveguides
|journal = [[Optics Express]]
|year = 2004
|volume = 12
|issue = 17
|pages = 4094–4102
| bibcode = 2004OExpr..12.4094B |last1 = Boyraz
|first1 = ÖZdal
|last2 = Koonath
|first2 = Prakash
|last3 = Raghunathan
|first3 = Varun
|last4 = Jalali
|first4 = Bahram
}}</ref> An important example is all-[[optical switching]], whereby the routing of optical signals is directly controlled by other optical signals.<ref name="vlasov_2008">{{cite journal
|doi = 10.1038/nphoton.2008.31
|title = High-throughput silicon nanophotonic wavelength-insensitive switch for on-chip optical networks
|journal = [[Nature Photonics]]
|year = 2008
|volume = 2
|issue = 4
|pages = 242–246
|last1 = Vlasov
|first1 = Yurii
|last2 = Green
|first2 = William M. J.
|last3 = Xia
|first3 = Fengnian
}}</ref> Another example is all-optical wavelength conversion.<ref name="foster_2007">{{cite journal
|doi = 10.1364/OE.15.012949
|title = Broad-band continuous-wave parametric wavelength conversion in silicon nanowaveguides
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 20
|pages = 12949–12958
| bibcode = 2007OExpr..1512949F |last1 = Foster
|first1 = Mark A.
|last2 = Turner
|first2 = Amy C.
|last3 = Salem
|first3 = Reza
|last4 = Lipson
|first4 = Michal
|last5 = Gaeta
|first5 = Alexander L.
}}</ref>

In 2013, a [[startup company]] named "[[Compass-EOS]]", based in [[California]] and in [[Israel]], was the first to present a commercial silicon-to-photonics router.<ref>{{cite web|url=http://venturebeat.com/2013/03/12/after-six-years-of-planning-compass-eos-takes-on-cisco-to-make-blazing-fast-routers/ |title=After six years of planning, Compass-EOS takes on Cisco to make blazing-fast routers |publisher=venturebeat.com |date=12 March 2013|accessdate=25 April 2013}}</ref>

=== Long range telecommunications using silicon photonics ===

Silicon microphotonics can potentially increase the [[Internet]]'s bandwidth capacity by providing micro-scale, ultra low power devices. Furthermore, the power consumption of [[datacenter]]s may be significantly reduced if this is successfully achieved. Researchers at [[Sandia National Laboratories|Sandia]],<ref name="Sandia_2010">{{cite journal
|title = Power penalty measurement and frequency chirp extraction in silicon microdisk resonator modulators
|journal = Proc. Optical Fiber Communication Conference (OFC)
|year = 2010
|issue = OMI7
|author = Zortman, W. A.
}}</ref> Kotura, [[Nippon Telegraph and Telephone|NTT]], [[Fujitsu]] and various academic institutes have been attempting to prove this functionality. A 2010 paper reported on a prototype 80 km, 12.5 Gbit/s transmission using microring silicon devices.<ref name="Biberman_Manipatruni_2010">{{cite journal
|doi = 10.1364/OE.18.015544
|title = First demonstration of long-haul transmission using silicon microring modulators
|journal = [[Optics Express]]
|year = 2010
|volume = 18
|issue = 15
|pages = 15544–15552
| bibcode = 2010OExpr..1815544B
|last1 = Biberman
|first1 = Aleksandr
|last2 = Manipatruni
|first2 = Sasikanth
|last3 = Ophir
|first3 = Noam
|last4 = Chen
|first4 = Long
|last5 = Lipson
|first5 = Michal
|last6 = Bergman
|first6 = Keren
}}</ref>

=== Light-field displays ===
As of 2015, US startup company [[Magic Leap]] is working on a [[Light field|light-field]] chip using silicon photonics for the purpose of an [[augmented reality]] display.<ref name=":3">{{Cite web|title = Can Magic Leap Do What It Claims with $592 Million?|url = http://www.technologyreview.com/news/538146/magic-leap-needs-to-engineer-a-miracle/|accessdate = 2015-06-13|publisher = MIT Technology Review|last = Bourzac|first = Katherine|date = 2015-06-11}}</ref>

== Physical properties ==

=== Optical guiding and dispersion tailoring ===

Silicon is [[transparency (optics)|transparent]] to [[infrared light]] with wavelengths above about 1.1 micrometres.<ref name="reading_lab">{{cite web
|url = http://www.rdg.ac.uk/infrared/library/infraredmaterials/ir-infraredmaterials-si.aspx
|title = Silicon (Si)
|publisher = [[University of Reading]] Infrared Multilayer Laboratory
|accessdate = 17 July 2009
}}</ref> Silicon also has a very high [[refractive index]], of about 3.5.<ref name="reading_lab" /> The tight optical confinement provided by this high index allows for microscopic [[optical waveguide]]s, which may have cross-sectional dimensions of only a few hundred [[nanometer]]s.<ref name="dekker_2008" /> This is substantially less than the wavelength of the light itself, and is analogous to a [[subwavelength-diameter optical fibre]]. Single mode propagation can be achieved,<ref name="dekker_2008" /> thus (like [[single-mode optical fiber]]) eliminating the problem of [[modal dispersion]].

The strong [[Interface conditions for electromagnetic fields|dielectric boundary effects]] that result from this tight confinement substantially alter the [[dispersion (optics)|optical dispersion relation]]. By selecting the waveguide geometry, it is possible to tailor the dispersion to have desired properties, which is of crucial importance to applications requiring ultrashort pulses.<ref name="dekker_2008" /> In particular, the ''group velocity dispersion'' (that is, the extent to which [[group velocity]] varies with wavelength) can be closely controlled. In bulk silicon at 1.55 micrometres, the group velocity dispersion (GVD) is ''normal'' in that pulses with longer wavelengths travel with higher group velocity than those with shorter wavelength. By selecting a suitable waveguide geometry, however, it is possible to reverse this, and achieve ''anomalous'' GVD, in which pulses with shorter wavelengths travel faster.<ref name="yin_2006" >{{cite journal
|doi = 10.1364/OL.31.001295
|title = Dispersion tailoring and soliton propagation in silicon waveguides
|journal = [[Optics Letters]]
|year = 2006
|volume = 31
|issue = 9
|pages = 1295–1297
| bibcode = 2006OptL...31.1295Y |last1 = Yin
|first1 = Lianghong
|last2 = Lin
|first2 = Q.
|last3 = Agrawal
|first3 = Govind P.
}}</ref><ref name="turner_2006" >{{cite journal
|doi = 10.1364/OE.14.004357
|title = Tailored anomalous group-velocity dispersion in silicon channel waveguides
|journal = [[Optics Express]]
|year = 2006
|volume = 14
|issue = 10
|pages = 4357–4362
| bibcode = 2006OExpr..14.4357T |last1 = Turner
|first1 = Amy C.
|last2 = Manolatou
|first2 = Christina
|last3 = Schmidt
|first3 = Bradley S.
|last4 = Lipson
|first4 = Michal
|last5 = Foster
|first5 = Mark A.
|last6 = Sharping
|first6 = Jay E.
|last7 = Gaeta
|first7 = Alexander L.
}}</ref> Anomalous dispersion is significant, as it is a prerequisite for [[soliton]] propagation, and [[modulational instability]].<ref name="agrawal_book">{{cite book
|last = Agrawal
|first = Govind P.
|year = 1995
|title = Nonlinear fiber optics
|place = San Diego (California)
|publisher = Academic Press
|edition =2nd
|isbn = 0-12-045142-5
}}</ref>

In order for the silicon photonic components to remain optically independent from the bulk silicon of the [[wafer (electronics)|wafer]] on which they are fabricated, it is necessary to have a layer of intervening material. This is usually [[silica]], which has a much lower refractive index (of about 1.44 in the wavelength region of interest<ref name="malitson_1965">{{cite journal
|doi = 10.1364/JOSA.55.001205
|title = Interspecimen Comparison of the Refractive Index of Fused Silica
|journal = [[Journal of the Optical Society of America]]
|year = 1965
|volume = 55
|issue = 10
|pages = 1205–1209
|author = Malitson, I. H.
}}</ref>), and thus light at the silicon-silica interface will (like light at the silicon-air interface) undergo [[total internal reflection]], and remain in the silicon. This construct is known as silicon on insulator.<ref name="pavesi_book" /><ref name="reed_book" /> It is named after the technology of [[silicon on insulator]] in electronics, whereby components are built upon a layer of [[insulator (electrical)|insulator]] in order to reduce [[parasitic capacitance]] and so improve performance.<ref name="celler_2003">{{cite journal
|title = Frontiers of silicon-on-insulator
|journal = [[Journal of Applied Physics]]
|year = 2003
|volume = 93
|page = 4955
| bibcode = 2003JAP....93.4955C |doi = 10.1063/1.1558223
|issue = 9 |last1 = Celler
|first1 = G. K.
|last2 = Cristoloveanu
|first2 = Sorin
}}</ref>

=== Kerr nonlinearity ===

Silicon has a focusing [[Kerr nonlinearity]], in that the [[refractive index]] increases with optical intensity.<ref name="dekker_2008" /> This effect is not especially strong in bulk silicon, but it can be greatly enhanced by using a silicon waveguide to concentrate light into a very small cross-sectional area.<ref name="hsieh_2006" /> This allows [[nonlinear optics|nonlinear optical]] effects to be seen at low powers. The nonlinearity can be enhanced further by using a [[slot waveguide]], in which the high refractive index of the silicon is used to confine light into a central region filled with a strongly nonlinear [[polymer]].<ref name="koos_2007" >{{cite journal
|doi = 10.1364/OE.15.005976
|title = Nonlinear silicon-on-insulator waveguides for all-optical signal processing
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 10
|pages = 5976–5990
| bibcode = 2007OExpr..15.5976K
|pmid=19546900|author1 = Koos
|first1 = C
|last2 = Jacome
|first2 = L
|last3 = Poulton
|first3 = C
|last4 = Leuthold
|first4 = J
|last5 = Freude
|first5 = W
}}</ref>

Kerr nonlinearity underlies a wide variety of optical phenomena.<ref name="agrawal_book" /> One example is [[four wave mixing]], which has been applied in silicon to realise [[optical parametric amplification]],<ref name="foster_2006">{{cite journal
|title = Broad-band optical parametric gain on a silicon photonic chip
|journal = [[Nature (journal)|Nature]]
|year = 2006
|volume = 441
|issue = 7096
|pages = 960–3
|pmid = 16791190
|doi = 10.1038/nature04932
| bibcode = 2006Natur.441..960F |author1 = Foster
|first1 = M. A.
|last2 = Turner
|first2 = A. C.
|last3 = Sharping
|first3 = J. E.
|last4 = Schmidt
|first4 = B. S.
|last5 = Lipson
|first5 = M
|last6 = Gaeta
|first6 = A. L.
}}</ref> parametric wavelength conversion,<ref name="foster_2007" /> and frequency comb generation.,<ref>{{cite journal|last1=Griffith|first1=Austin G.|last2=Lau|first2=Ryan K.W.|last3=Cardenas|first3=Jaime|last4=Okawachi|first4=Yoshitomo|last5=Mohanty|first5=Aseema|last6=Fain|first6=Romy|last7=Lee|first7=Yoon Ho Daniel|last8=Yu|first8=Mengjie|last9=Phare|first9=Christopher T.|last10=Poitras|first10=Carl B.|last11=Gaeta|first11=Alexander L.|last12=Lipson|first12=Michal|title=Silicon-chip mid-infrared frequency comb generation|journal=Nature Communications|date=24 February 2015|volume=6|pages=6299|doi=10.1038/ncomms7299|arxiv = 1408.1039 |bibcode = 2015NatCo...6E6299G }}</ref><ref>{{cite journal|last1=Kuyken|first1=Bart|last2=Ideguchi|first2=Takuro|last3=Holzner|first3=Simon|last4=Yan|first4=Ming|last5=Hänsch|first5=Theodor W.|last6=Van Campenhout|first6=Joris|last7=Verheyen|first7=Peter|last8=Coen|first8=Stéphane|last9=Leo|first9=Francois|last10=Baets|first10=Roel|last11=Roelkens|first11=Gunther|last12=Picqué|first12=Nathalie|title=An octave-spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide|journal=Nature Communications|date=20 February 2015|volume=6|pages=6310|doi=10.1038/ncomms7310|arxiv = 1405.4205 |bibcode = 2015NatCo...6E6310K }}</ref>

Kerr nonlinearity can also cause [[modulational instability]], in which it reinforces deviations from an optical waveform, leading to the generation of [[Frequency spectrum|spectral]]-sidebands and the eventual breakup of the waveform into a train of pulses.<ref name="panoiu_2006">{{cite journal
|title = Modulation instability in silicon photonic nanowires
|journal = [[Optics Letters]]
|year = 2006
|volume = 31
|pages = 3609–11
|pmid=17130919
| bibcode = 2006OptL...31.3609P |doi = 10.1364/OL.31.003609
|issue = 24 |last1 = Panoiu
|first1 = Nicolae C.
|last2 = Chen
|first2 = Xiaogang
|last3 = Osgood, Jr.
|first3 = Richard M.
}}</ref> Another example (as described below) is soliton propagation.

=== Two-photon absorption ===

Silicon exhibits [[two-photon absorption]] (TPA), in which a pair of [[photon]]s can act to excite an [[electron-hole pair]].<ref name="dekker_2008" /> This process is related to the Kerr effect, and by analogy with [[Mathematical descriptions of opacity|complex refractive index]], can be thought of as the [[Imaginary number|imaginary]]-part of a [[Complex number|complex]] Kerr nonlinearity.<ref name="dekker_2008" /> At the 1.55 micrometre telecommunication wavelength, this imaginary part is approximately 10% of the real part.<ref name="yin_2006_2">{{cite journal
|doi = 10.1364/OL.32.002031
|title = Impact of two-photon absorption on self-phase modulation in silicon waveguides: Free-carrier effects
|journal = [[Optics Letters]]
|year = 2006
|volume = 32
|issue = 14
|pages = 2031–2033
|last1 = Yin
|first1 = Lianghong
|last2 = Agrawal
|first2 = Govind P.
|bibcode = 2007OptL...32.2031Y
}}</ref>

The influence of TPA is highly disruptive, as it both wastes light, and generates unwanted [[heat]].<ref name="nikbin_article">{{cite news
|author = Nikbin, Darius
|title = Silicon photonics solves its "fundamental problem"
|publisher = IOP publishing
|url = http://optics.org/cws/article/research/25379
|date = 20 July 2006
}}</ref> It can be mitigated, however, either by switching to longer wavelengths (at which the TPA to Kerr ratio drops),<ref name="bristow_2007">{{cite journal
|title = Two-photon absorption and Kerr coefﬁcients of silicon for 850– {{convert|2200|nmi|km|abbr=on}}
|journal = [[Applied Physics Letters]]
|year = 2007
|volume = 90
|page = 191104
| bibcode = 2007ApPhL..90b1104R |doi = 10.1063/1.2430400
|issue = 2 |last1 = Rybczynski
|first1 = J.
|last2 = Kempa
|first2 = K.
|last3 = Herczynski
|first3 = A.
|last4 = Wang
|first4 = Y.
|last5 = Naughton
|first5 = M. J.
|last6 = Ren
|first6 = Z. F.
|last7 = Huang
|first7 = Z. P.
|last8 = Cai
|first8 = D.
|last9 = Giersig
|first9 = M.

}}</ref> or by using slot waveguides (in which the internal nonlinear material has a lower TPA to Kerr ratio).<ref name="koos_2007" /> Alternatively, the energy lost through TPA can be partially recovered (as is described below) by extracting it from the generated charge carriers.<ref name="tsia_2006">{{cite conference
|authors = Tsia, K. M.
|title = Energy Harvesting in Silicon Raman Amplifiers
|conference = 3rd [[IEEE]] International Conference on Group IV Photonics
|year = 2006
}}</ref>

=== Free charge carrier interactions ===

The [[Charge carriers in semiconductors|free charge carriers]] within silicon can both absorb photons and change its refractive index.<ref name="soref_1987">{{cite journal
|doi = 10.1109/JQE.1987.1073206
|title = Electrooptical Effects in Silicon
|journal = [[IEEE Journal of Quantum Electronics]]
|year = 1987
|volume = 23
|issue = 1
|pages = 123–129
| bibcode = 1987IJQE...23..123S |last1 = Soref
|first1 = R.
|last2 = Bennett
|first2 = B.
}}</ref> This is particularly significant at high intensities and for long durations, due to the carrier concentration being built up by TPA. The influence of free charge carriers is often (but not always) unwanted, and various means have been proposed to remove them. One such scheme is to [[ion implantation|implant]] the silicon with [[helium]] in order to enhance [[carrier recombination]].<ref name="liu_2006">{{cite journal
|doi = 10.1364/OL.31.001714
|title = Nonlinear absorption and Raman gain in helium-ion-implanted silicon waveguides
|journal = [[Optics Letters]]
|year = 2006
|volume = 31
|issue = 11
|pages = 1714–1716
| bibcode = 2006OptL...31.1714L |last1 = Liu
|first1 = Y.
|last2 = Tsang
|first2 = H. K.
}}</ref> A suitable choice of geometry can also be used to reduce the carrier lifetime. [[Rib waveguide]]s (in which the waveguides consist of thicker regions in a wider layer of silicon) enhance both the carrier recombination at the silica-silicon interface and the [[diffusion]] of carriers from the waveguide core.<ref name="dimitropoulos_2005">{{cite journal
|title = Lifetime of photogenerated carriers in silicon-on-insulator rib waveguides
|journal = [[Applied Physics Letters]]
|year = 2005
|volume = 86
|page = 071115
| bibcode = 2005ApPhL..86a1115Z |doi = 10.1063/1.1846145 |last1 = Zevallos l.
|first1 = Manuel E.
|last2 = Gayen
|first2 = S. K.
|last3 = Alrubaiee
|first3 = M.
|last4 = Alfano
|first4 = R. R.
}}</ref>

A more advanced scheme for carrier removal is to integrate the waveguide into the [[intrinsic semiconductor|intrinsic region]] of a [[PIN diode]], which is [[reverse bias]]ed so that the carriers are attracted away from the waveguide core.<ref name="jones_2005">{{cite journal
|doi = 10.1364/OPEX.13.000519
|title = Net continuous wave optical gain in a low loss silicon-on-insulator waveguide by stimulated Raman scattering
|journal = [[Optics Express]]
|year = 2005
|volume = 13
|issue = 2
|pages = 519–525
| bibcode = 2005OExpr..13..519J |last1 = Jones
|first1 = Richard
|last2 = Rong
|first2 = Haisheng
|last3 = Liu
|first3 = Ansheng
|last4 = Fang
|first4 = Alexander W.
|last5 = Paniccia
|first5 = Mario J.
|last6 = Hak
|first6 = Dani
|last7 = Cohen
|first7 = Oded
}}</ref> A more sophisticated scheme still, is to use the diode as part of a circuit in which [[voltage]] and [[Electric current|current]] are out of phase, thus allowing power to be extracted from the waveguide.<ref name="tsia_2006" /> The source of this power is the light lost to two photon absorption, and so by recovering some of it, the net loss (and the rate at which heat is generated) can be reduced.

As is mentioned above, free charge carrier effects can also be used constructively, in order to modulate the light.<ref name="barrios_2003" /><ref name="xu_2007" /><ref name="liu_2007" />

=== Second-order nonlinearity ===

Second-order nonlinearities cannot exist in bulk silicon because of the [[centrosymmetry]] of its crystalline structure. By applying strain however, the inversion symmetry of silicon can be broken. This can be obtained for example by depositing a [[silicon nitride]] layer on a thin silicon film.<ref name="JacobsenAndersen2006">{{cite journal|last1=Jacobsen|first1=Rune S.|last2=Andersen|first2=Karin N.|last3=Borel|first3=Peter I.|last4=Fage-Pedersen|first4=Jacob|last5=Frandsen|first5=Lars H.|last6=Hansen|first6=Ole|last7=Kristensen|first7=Martin|last8=Lavrinenko|first8=Andrei V.|last9=Moulin|first9=Gaid|last10=Ou|first10=Haiyan|last11=Peucheret|first11=Christophe|last12=Zsigri|first12=Beáta|last13=Bjarklev|first13=Anders|title=Strained silicon as a new electro-optic material|journal=Nature|volume=441|issue=7090|year=2006|pages=199–202|issn=0028-0836|doi=10.1038/nature04706|pmid=16688172|bibcode = 2006Natur.441..199J }}</ref>
Second-order nonlinear phenomena can be exploited for [[Pockels effect|optical modulation]], [[spontaneous parametric down-conversion]], [[Optical parametric amplifier|parametric amplification]], [[Optical computing|ultra-fast optical signal processing]] and [[Infrared|mid-infrared]] generation. Efficient nonlinear conversion however requires [[Phase matching#Phase matching|phase matching]] between the optical waves involved. Second-order nonlinear waveguides based on strained silicon can achieve [[Phase matching#Phase matching|phase matching]] by [[Modal dispersion|dispersion-engineering]].<ref name="AvrutskySoref2011">{{cite journal|last1=Avrutsky|first1=Ivan|last2=Soref|first2=Richard|title=Phase-matched sum frequency generation in strained silicon waveguides using their second-order nonlinear optical susceptibility|journal=Optics Express|volume=19|issue=22|year=2011|page=21707|issn=1094-4087|doi=10.1364/OE.19.021707|bibcode = 2011OExpr..1921707A }}</ref>
So far, however, experimental demonstrations are based only on designs which are not [[Phase matching#Phase matching|phase matched]].<ref name="CazzanelliBianco2011">{{cite journal|last1=Cazzanelli|first1=M.|last2=Bianco|first2=F.|last3=Borga|first3=E.|last4=Pucker|first4=G.|last5=Ghulinyan|first5=M.|last6=Degoli|first6=E.|last7=Luppi|first7=E.|last8=Véniard|first8=V.|last9=Ossicini|first9=S.|last10=Modotto|first10=D.|last11=Wabnitz|first11=S.|last12=Pierobon|first12=R.|last13=Pavesi|first13=L.|title=Second-harmonic generation in silicon waveguides strained by silicon nitride|journal=Nature Materials|volume=11|issue=2|year=2011|pages=148–154|issn=1476-1122|doi=10.1038/nmat3200|pmid=22138793|bibcode = 2012NatMa..11..148C }}</ref>
It has been shown that [[Phase matching#Phase matching|phase matching]] can be obtained as well in silicon double [[slot waveguide]]s coated with a highly nonlinear organic cladding<ref name="AlloattiKorn2012">{{cite journal|last1=Alloatti|first1=L.|last2=Korn|first2=D.|last3=Weimann|first3=C.|last4=Koos|first4=C.|last5=Freude|first5=W.|last6=Leuthold|first6=J.|title=Second-order nonlinear silicon-organic hybrid waveguides|journal=Optics Express|volume=20|issue=18|year=2012|page=20506|issn=1094-4087|doi=10.1364/OE.20.020506|bibcode = 2012OExpr..2020506A }}</ref>
and in periodically strained silicon waveguides.<ref name="HonTsia2009">{{cite journal|last1=Hon|first1=Nick K.|last2=Tsia|first2=Kevin K.|last3=Solli|first3=Daniel R.|last4=Jalali|first4=Bahram|title=Periodically poled silicon|journal=Applied Physics Letters|volume=94|issue=9|year=2009|page=091116|issn=0003-6951|doi=10.1063/1.3094750|arxiv = 0812.4427 |bibcode = 2009ApPhL..94i1116H }}</ref>

=== The Raman effect ===

Silicon exhibits the [[Raman effect]], in which a photon is exchanged for a photon with a slightly different energy, corresponding to an excitation or a relaxation of the material. Silicon's Raman transition is dominated by a single, very narrow frequency peak, which is problematic for broadband phenomena such as [[Raman amplification]], but is beneficial for narrowband devices such as [[Raman laser]]s.<ref name="dekker_2008" /> Early studies of Raman amplification and Raman lasers started at UCLA which led to demonstration of net gain Silicon Raman amplifiers and silicon pulsed Raman laser with fiber resonator (Optics express 2004). Consequently, all-silicon Raman lasers have been fabricated in 2005.<ref name="rong_2005" />

== Solitons ==

The evolution of light through silicon waveguides can be approximated with a cubic [[Nonlinear Schrödinger equation]],<ref name="dekker_2008" /> which is notable for admitting [[hyperbolic secant|sech]]-like [[soliton]] solutions.<ref name="drazin_book">{{cite book
|title = Solitons: an introduction
|publisher = [[Cambridge University Press]]
|year = 1989
|isbn = 0-521-33655-4
|author = Drazin, P. G. and Johnson, R. S.
}}</ref> These [[optical soliton]]s (which are also known in [[optical fiber]]) result from a balance between [[self phase modulation]] (which causes the leading edge of the pulse to be [[Redshifted#Effects due to physical optics or radiative transfer|redshifted]] and the trailing edge blueshifted) and anomalous group velocity dispersion.<ref name="agrawal_book" /> Such solitons have been observed in silicon waveguides, by groups at the universities of [[Columbia University|Columbia]],<ref name="hsieh_2006" /> [[Rochester University|Rochester]],<ref name="zhang_2007" /> and [[University of Bath|Bath]].<ref name="ding_2008" />

== References ==
{{reflist|30em}}

== External links ==
* [http://domino.research.ibm.com/comm/research_projects.nsf/pages/photonics.index.html IBM's page on silicon integrated nanophotonics]
* [https://www-ssl.intel.com/content/www/us/en/research/intel-labs-silicon-photonics-research.html Intel's page on silicon photonics]
* [http://nanophotonics.ece.cornell.edu Michal Lipson's page on silicon photonics]
* [http://www.rle.mit.edu/pmg/ Michael Watts' MIT group working on silicon photonics]
* [http://www.analogphotonics.com/ MIT spin-off company offering silicon photonics design and [MPW]]
* [http://www.uksiliconphotonics.co.uk/ Uk based project website on silicon photonics]
* [http://www.helios-project.eu/ European project website on silicon photonics]
* [http://www.siliconphotonics.co.uk/ UK based group working on silicon photonics]
* [http://silicon-photonics.ief.u-psud.fr/ French based group working on silicon photonics]
* [http://photonics.intec.ugent.be/ Belgian group working on silicon photonics]
* [http://www.ipq.kit.edu/english/index.php Silicon photonics at KIT]
* [http://photontransfer.com/ Photon Transfer]

{{DEFAULTSORT:Silicon Photonics}}
[[Category:Nonlinear optics]]
[[Category:Photonics]]
[[Category:Silicon]]

Plasmonische Solarzelle

2016-05-11T01:40:14Z

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{{expert subject|date=December 2014}}
A '''Plasmonic solar cell''' is a type of [[thin film solar cell]] that converts light into electricity with the assistance of [[plasmon]]s.<ref>{{Cite book
| url = http://onlinelibrary.wiley.com/doi/10.1002/9781118845721.ch10/summary
| title = Advances in Plasmonic Light Trapping in Thin-Film Solar Photovoltaic Devices
| last = Gwamuri
| first = J.
| last2 = Güney
| first2 = D. Ö.
| last3 = Pearce
| first3 = J. M.
| date = 2013-01-01
| publisher = John Wiley & Sons, Inc.
| isbn = 9781118845721
| editor-last = Tiwari
| editor-first = Atul
| pages = 241–269
| language = en
| doi = 10.1002/9781118845721.ch10
| editor-last2 = Boukherroub
| editor-first2 = Rabah
| editor-last3 = Sharon
| editor-first3 = heshwar
}}</ref> They are typically less than 2 μm thick and theoretically could be as thin as 100 nm.<ref name=":0" /> They can use [[Substrate (materials science)|substrates]] which are cheaper than [[silicon]], such as [[glass]], [[plastic]] or [[steel]]. One of the challenges for thin film solar cells is that they do not absorb as much light as thicker solar cells made with materials with the same [[absorption coefficient]]. Methods for light trapping are important for thin film solar cells.<ref>{{Cite journal
| last = Müller
| first = Joachim
| last2 = Rech
| first2 = Bernd
| last3 = Springer
| first3 = Jiri
| last4 = Vanecek
| first4 = Milan
| date = 2004-12-01
| title = TCO and light trapping in silicon thin film solar cells
| url = http://www.sciencedirect.com/science/article/pii/S0038092X04000647
| journal = Solar Energy
| series = Thin Film PV
| volume = 77
| issue = 6
| pages = 917–930
| doi = 10.1016/j.solener.2004.03.015
|bibcode = 2004SoEn...77..917M }}</ref> Plasmonic cells improve absorption by scattering light using metal [[nanoparticle|nano-particle]]s excited at their [[surface plasmon resonance]].<ref name=Catchpole>K. R. Catchpole and A. Polman, "Plasmonic solar cells," Opt. Express 16, 21793-21800 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-26-21793</ref> This allows light to be absorbed more directly without the relatively thick absorber layer required in other types of thin-film solar cells. However, this type of solar cell also normally demands a thin [[transparent conducting oxide]] (TCO) to function for realistic photovoltaic [[absorber]] thicknesses and only recently have methods been advanced that allow high [[Electrical resistivity and conductivity|conductivity]] while maintaining high optical transmission of the TCO.<ref>{{Cite journal
| last = Gwamuri
| first = Jephias
| last2 = Vora
| first2 = Ankit
| last3 = Mayandi
| first3 = Jeyanthinath
| last4 = Güney
| first4 = Durdu Ö.
| last5 = Bergstrom
| first5 = Paul L.
| last6 = Pearce
| first6 = Joshua M.
| date = 2016-05-01
| title = A new method of preparing highly conductive ultra-thin indium tin oxide for plasmonic-enhanced thin film solar photovoltaic devices
| url = https://www.academia.edu/21828389/A_New_Method_of_Preparing_Highly_Conductive_Ultra-Thin_Indium_Tin_Oxide_for_Plasmonic-Enhanced_Thin_Film_Solar_Photovoltaic_Devices
| journal = Solar Energy Materials and Solar Cells
| volume = 149
| pages = 250–257
| doi = 10.1016/j.solmat.2016.01.028
}}</ref> There is still considerable research necessary to enable the technology to reach its full potential and commercialization of plasmonic enhanced solar cells.<ref name=":0">{{Cite journal
| last = Atwater
| first = Harry A.
| last2 = Polman
| first2 = Albert
| title = Plasmonics for improved photovoltaic devices
| url = http://www.nature.com/doifinder/10.1038/nmat2629
| journal = Nature Materials
| volume = 9
| issue = 3
| pages = 205–213
| doi = 10.1038/nmat2629
|bibcode = 2010NatMa...9..205A }}</ref>

== History ==

=== Devices ===

There are currently three different generations of SCs. The first generation (those in the market today) are made with crystalline [[semiconductor wafer]]s, typically silicon. These are the SCs everybody thinks of when they hear "Solar Cell".{{Citation needed|date=March 2016}}

Current SCs trap light by creating [[pyramid]]s on the surface which have dimensions bigger than most thin film SCs. Making the surface of the substrate rough (typically by growing SnO2 or ZnO on surface) with dimensions on the order of the incoming [[wavelength]]s and depositing the SC on top has been explored. This method increases the [[photocurrent]], but the thin film SC would then have poor material quality.
<ref name=Muller>{{cite journal | doi = 10.1016/j.solener.2004.03.015 | title = TCO and light trapping in silicon thin film solar cells | year = 2004 | last1 = Müller | first1 = Joachim | last2 = Rech | first2 = Bernd | last3 = Springer | first3 = Jiri | last4 = Vanecek | first4 = Milan | journal = Solar Energy | volume = 77 | issue = 6 | pages = 917–930 |bibcode = 2004SoEn...77..917M }}</ref>

The second generation SCs are based on [[thin film]] technologies such as those presented here. These SCs focus on lowering the amount of material used as well as increasing the energy production. Third generation SCs are currently being researched. They focus on reducing the cost of the second generation SCs.
<ref name=Conibeer>Gavin Conibeer, Third generation photovoltaics, Proc. SPIE Vol. 7411, 74110D (Aug. 20, 2009)</ref>
The third generation SCs are discussed in more detail under recent advancement.

== Design ==
The design for a PSC varies depending on the method being used to trap and scatter light across the surface and through the material.

=== Nanoparticle cells ===
[[File:PSC using Metal Nanoparticles.png|thumb|alt=A plasmonic solar cell utilizing metal nanoparticles to distribute light and enhance absorption.|PSC using metal nano-particles.]]
A common design is to deposit metal nano-particles on the top surface of the thin film SC. When light hits these metal nano-particles at their surface plasmon resonance, the light is scattered in many different directions. This allows light to travel along the SC and bounce between the substrate and the nano-particles enabling the SC to absorb more light.
<ref name=Tanabe>{{cite journal | last1 = Tanabe | first1 = K. | year = 2009 | title = A Review of Ultrahigh Efficiency III-V Semiconductor Compound Solar Cells: Multijunction Tandem, Lower Dimensional, Photonic Up/Down Conversion and Plasmonic Nanometallic Structures | url = | journal = Energies | volume = 2 | issue = 3| pages = 504–530 | doi = 10.3390/en20300504 }}</ref>

=== Metal film cells ===

Other methods utilizing surface plasmons for harvesting solar energy are available. One other type of structure is to have a thin film of silicon and a thin layer of metal deposited on the lower surface. The light will travel through the silicon and generate surface plasmons on the interface of the silicon and metal. This generates electric fields inside of the silicon since electric fields do not travel very far into metals. If the [[electric field]] is strong enough, electrons can be moved and collected to produce a photocurrent. The thin film of metal in this design must have nanometer sized grooves which act as [[waveguide]]s for the incoming light in order to excite as many photons in the silicon thin film as possible.
<ref name=Ferry>{{cite journal | doi = 10.1021/nl8022548 | pages= 4391–4397 | title = Plasmonic Nanostructure Design for Efficient Light Coupling into Solar Cells | year = 2008 | last1 = Ferry | first1 = Vivian E. | last2 = Sweatlock | first2 = Luke A. | last3 = Pacifici | first3 = Domenico | last4 = Atwater | first4 = Harry A. | journal = Nano Letters | volume = 8 | issue = 12 | pmid = 19367883 |bibcode = 2008NanoL...8.4391F }}</ref>

== Principles ==

=== General ===
[[File:Thin vs Thick SC.png|thumb|alt=Light effects on thin and thick solar cells.|Thin film SC (left) and Typical SC (right).]]
When a photon is excited in the substrate of a SC, an electron and hole are separated. Once the electrons and holes are separated, they will want to recombine since they are of opposite charge. If the electrons can be collected prior to this happening they can be used as a current for an external circuit. Designing the thickness of a solar cell is always a trade-off between minimizing this recombination (thinner layers) and absorbing more photons (thicker layer).<ref name=Tanabe/>

=== Nano-particles ===

==== Scattering and Absorption ====
The basic principles for the functioning of plasmonic solar cells include scattering and absorption of light due to the deposition of metal nano-particles. Silicon does not absorb light very well. For this reason, more light needs to be scattered across the surface in order to increase the absorption. It has been found that metal nano-particles help to scatter the incoming light across the surface of the silicon substrate. The equations that govern the scattering and absorption of light can be shown as:
*<math>C_{scat}=\frac{1}{6\pi}\left(\frac{2\pi}{\lambda}\right)^4|\alpha|^2</math>
This shows the scattering of light for particles which have diameters below the wavelength of light.
*<math>C_{abs}=\frac{2\pi}{\lambda}\text{Im}[\alpha]</math>
This shows the absorption for a point dipole model.
*<math>\alpha=3V\left[\frac{\epsilon_p/\epsilon_m-1}{\epsilon_p/\epsilon_m+2}\right]</math>
This is the polarizability of the particle. V is the particle volume. <math>\epsilon_p</math> is the dielectric function of the particle. <math>\epsilon_m</math> is the [[dielectric function]] of the embedding medium. When <math>\epsilon_p=-2\epsilon_m</math> the [[polarizability]] of the particle becomes large. This polarizability value is known as the surface plasmon resonance. The dielectric function for metals with low absorption can be defined as:
*<math>\epsilon=1-\frac{\omega_p^2}{\omega^2+i\gamma\omega}</math>
In the previous equation, <math>\omega_p</math> is the bulk plasma frequency. This is defined as:
*<math>\omega_p^2=Ne^2/m\epsilon_0</math>
N is the density of free electrons, e is the [[Electrical resistivity and conductivity|electronic charge]] and m is the [[Effective mass (solid-state physics)|effective mass]] of an electron. <math>\epsilon_0</math> is the dielectric constant of free space. The equation for the surface plasmon resonance in free space can therefore be represented by:
*<math>\alpha=3V\frac{\omega_p^2}{\omega_p^2-3\omega^2-i\gamma\omega}</math>
Many of the plasmonic solar cells use nano-particles to enhance the scattering of light. These nano-particles take the shape of spheres, and therefore the surface plasmon resonance frequency for spheres is desirable. By solving the previous [[equation]]s, the surface plasmon resonance frequency for a sphere in free space can be shown as:
*<math>\omega_{sp}=\sqrt{3}\omega_p</math>

As an example, at the surface plasmon resonance for a silver nanoparticle, the scattering cross-section is about 10x the cross-section of the nanoparticle. The goal of the nano-particles is to trap light on the surface of the SC. The absorption of light is not important for the nanoparticle, rather, it is important for the SC. One would think that if the nanoparticle is increased in size, then the scattering cross-section becomes larger. This is true, however, when compared with the size of the nanoparticle, the ratio (<math>CS_{scat}/CS_{particle}</math>) is reduced. Particles with a large scattering cross section tend to have a broader plasmon resonance range.

==== Wavelength dependence ====
Surface plasmon resonance mainly depends on the density of free electrons in the particle. The order of densities of electrons for different metals is shown below along with the type of light which corresponds to the resonance.
*[[Aluminum]] - Ultra-violet
*[[Silver]] - Ultra-violet
*[[Gold]] - Visible
*[[Copper]] - Visible

If the dielectric constant for the embedding medium is varied, the [[resonant frequency]] can be shifted. Higher indexes of refraction will lead to a longer wavelength frequency.

==== Light trapping ====
The metal nano-particles are deposited at a distance from the substrate in order to trap the light between the substrate and the particles. The particles are embedded in a material on top of the substrate. The material is typically a [[dielectric]], such as silicon or [[silicon nitride]]. When performing experiment and simulations on the amount of light scattered into the substrate due to the distance between the particle and substrate, air is used as the embedding material as a reference. It has been found that the amount of light radiated into the substrate decreases with distance from the substrate. This means that nano-particles on the surface are desirable for radiating light into the substrate, but if there is no distance between the particle and substrate, then the light is not trapped and more light escapes.

The surface plasmons are the excitations of the conduction electrons at the interface of metal and the dielectric. Metallic nano-particles can be used to couple and trap freely propagating plane waves into the semiconductor thin film layer. Light can be folded into the absorbing layer to increase the absorption. The localized surface plasmons in metal nano-particles and the surface plasmon polaritons at the interface of metal and semiconductor are of interest in the current research. In recent reported papers, the shape and size of the metal nano-particles are key factors to determine the incoupling efficiency. The smaller particles have larger incoupling efficiency due to the enhanced near-field coupling. However, very small particles suffer from large ohmic losses.
<ref>{{cite journal|last=Atwater|first=Harry|author2=A. Polman |title=Plasmonics for improved photovoltaic devices|journal=Nature Materials|date=19 February 2010|volume=9|pages=205–13|bibcode=2010NatMa...9..205A|doi=10.1038/nmat2629|issue=3|pmid=20168344}}</ref>

=== Metal film ===
As light is incident upon the surface of the metal film, it excites surface plasmons. The surface plasmon frequency is specific for the material, but through the use of [[grating]]s on the surface of the film, different frequencies can be obtained. The surface plasmons are also preserved through the use of waveguides as they make the surface plasmons easier to travel on the surface and the losses due to resistance and radiation are minimized. The electric field generated by the surface plasmons influences the electrons to travel toward the collecting substrate.
<ref name=Huag>{{cite journal | doi = 10.1063/1.2981194 | title = Plasmonic absorption in textured silver back reflectors of thin film solar cells | year = 2008 | last1 = Haug | first1 = F.-J. | last2 = SöDerström | first2 = T. | last3 = Cubero | first3 = O. | last4 = Terrazzoni-Daudrix | first4 = V. | last5 = Ballif | first5 = C. | journal = Journal of Applied Physics | volume = 104 | issue = 6 | pages = 064509 |bibcode = 2008JAP...104f4509H }}</ref>

== Materials ==
{| class="wikitable" border="1"
|-
! First Generation
! Second Generation
! Third Generation
|-
| Single-crystal silicon
| CuInSe2
| Gallium Indium Phosphide
|-
| Multicrystalline silicon
| amorphous silicon
| Gallium Indium Arsenide
|-
| Polycrystalline silicon
| thin film crystalline Si
| Germanium
|}<ref name=Conibeer/><ref>http://www1.eere.energy.gov/solar/solar_cell_materials.html</ref>

== Applications ==
The applications for plasmonic solar cells are endless. The need for cheaper and more efficient solar cells is huge. In order for solar cells to be considered cost effective, they need to provide energy for a smaller price than that of traditional power sources such as [[coal]] and [[gasoline]]. The movement toward a more green world has helped to spark research in the area of plasmonic solar cells. Currently, solar cells cannot exceed efficiencies of about 30% (First Generation). With new technologies (Third Generation), efficiencies of up to 40-60% can be expected. With a reduction of materials through the use of thin film technology (Second Generation), prices can be driven lower.

Certain applications for plasmonic solar cells would be for [[space exploration]] vehicles. A main contribution for this would be the reduced weight of the solar cells. An external fuel source would also not be needed if enough power could be generated from the solar cells. This would drastically help to reduce the weight as well.

Solar cells have a great potential to help rural [[electrification]]. An estimated two million villages near the equator have limited access to electricity and fossil fuels and that approximately 25%<ref>http://www.globalissues.org/article/26/poverty-facts-and-stats</ref> of people in the world do not have access to electricity. When the cost of extending [[power grid]]s, running rural electricity and using diesel generators is compared with the cost of solar cells, many times the solar cells win. If the efficiency and cost of the current solar cell technology is decreased even further, then many rural communities and villages around the world could obtain electricity when current methods are out of the question. Specific applications for rural communities would be water pumping systems, residential electric supply and street lights. A particularly interesting application would be for health systems in countries where motorized vehicles are not overly abundant. Solar cells could be used to provide the power to refrigerate [[medication]]s in coolers during transport.

Solar cells could also provide power to [[lighthouse]]s, [[buoy]]s, or even [[battleship]]s out in the ocean. Industrial companies could use them to power [[telecommunications]] systems or monitoring and control systems along pipelines or other system.<ref name=web/>

If the solar cells could be produced on a large scale and be cost effective then entire [[power station]]s could be built in order to provide power to the electrical grids. With a reduction in size, they could be implemented on both commercial and residential buildings with a much smaller footprint. They might not even seem like an [[eyesore]].
<ref name=web>http://www.soton.ac.uk/~solar/intro/appso.htm</ref>

Other areas are in hybrid systems. The solar cells could help to power high consumption devices such as [[automobile]]s in order to reduce the amount of fossil fuels used and to help improve the environmental conditions of the earth.

In consumer electronics devices, solar cells could be used to replace batteries for low power electronics. This would save everyone a lot of money and it would also help to reduce the amount of waste going into [[landfill]]s.<ref>http://blog.coolerplanet.com/2009/01/23/the-4-basic-types-of-solar-cell-applications/</ref>

== Recent advancements ==

=== Choice of plasmonic metal nano-particles ===

Proper choice of plasmatic metal nano-particles is crucial for the maximum light absorption in the active layer. Front surface located nano-particles Ag and Au are the most widely used materials due to their surface plasmon resonances located in the visible range and therefore interact more strongly with the peak solar intensity. However, such noble metal nano-particles always introduce reduced light coupling into Si at the short wavelengths below the surface plasmon resonance due to the detrimental Fano effect, i.e. the destructive interference between the scattered and unscattered light. Moreover, the noble metal nano-particles are impractical to implement for large-scale solar cell manufacture due to their high cost and scarcity in earth crest. Recently, Zhang et al. have demonstrated the low cost and earth abundant materials Al nano-particles to be able to outperform the widely used Ag and Au nano-particles. Al nano-particles, with their surface plasmon resonances located in the UV region below the desired solar spectrum edge at 300 nm, can avoid the reduction and introduce extra enhancement in the shorter wavelength range.<ref>{{cite journal| title=Low cost and high performance Al nanoparticles for broadband light trapping in Si wafer solar cells| year=2012 | last1=Yinan | first1=Zhang| journal=Applied Physics Letters | volume=100 | issue=12 | pages=151101 |bibcode = 2012ApPhL.100b1101N |doi = 10.1063/1.3675451 |display-authors=etal}}</ref><ref>{{cite journal| title=Improved multicrystalline Si solar cells by light trapping from Al nanoparticle enhanced antireflection coating| year=2013 | last1=Yinan | first1=Zhang| journal=Opt. Mater. Express| volume=3 | issue=4 | pages=489 |display-authors=etal}}</ref>

=== Light trapping ===

As discussed earlier, being able to concentrate and scatter light across the surface of the plasmonic solar cell will help to increase efficiencies. Recently, research at [[Sandia National Laboratories]] has discovered a photonic waveguide which collects light at a certain wavelength and traps it within the structure. This new structure can contain 95% of the light that enters it compared to 30% for other traditional waveguides. It can also direct the light within one wavelength which is ten times greater than traditional waveguides. The wavelength this device captures can be selected by changing the structure of the lattice which comprises the structure. If this structure is used to trap light and keep it in the structure until the solar cell can absorb it, the efficiency of the solar cell could be increased dramatically.<ref>http://www.sandia.gov/media/photonic.htm</ref>

=== Absorption ===

Another recent advancement in plasmonic solar cells is using other methods to aid in the absorption of light. One way being researched is the use of metal wires on top of the substrate to scatter the light. This would help by utilizing a larger area of the surface of the solar cell for light scattering and absorption. The danger in using lines instead of dots would be creating a reflective layer which would reject light from the system. This is very undesirable for solar cells. This would be very similar to the thin metal film approach, but it also utilizes the scattering effect of the nano-particles.
<ref>{{cite journal | doi = 10.1002/adma.200900331 | title = Design of Plasmonic Thin-Film Solar Cells with Broadband Absorption Enhancements | year = 2009 | last1 = Pala | first1 = Ragip A. | last2 = White | first2 = Justin | last3 = Barnard | first3 = Edward | last4 = Liu | first4 = John | last5 = Brongersma | first5 = Mark L. | journal = Advanced Materials | volume = 21 | issue = 34 | pages = 3504–3509 }}</ref>

=== Third generation ===

The goal of third generation solar cells is to increase the efficiency using second generation solar cells (thin film) and using materials that are found abundantly on earth. This has also been a goal of the thin film solar cells. With the use of common and safe materials, third generation solar cells should be able to be manufactured in mass quantities further reducing the costs. The initial costs would be high in order to produce the manufacturing processes, but after that they should be cheap. The way third generation solar cells will be able to improve efficiency is to absorb a wider range of frequencies. The current thin film technology has been limited to one frequency due to the use of single band gap devices.<ref name=Conibeer/>

==== Multiple energy levels ====

The idea for multiple energy level solar cells is to basically stack thin film solar cells on top of each other. Each thin film solar cell would have a different band gap which means that if part of the solar spectrum was not absorbed by the first cell then the one just below would be able to absorb part of the spectrum. These can be stacked and an optimal band gap can be used for each cell in order to produce the maximum amount of power. Options for how each cell is connected are available, such as serial or parallel. The serial connection is desired because the output of the solar cell would just be two leads.

The lattice structure in each of the thin film cells needs to be the same. If it is not then there will be losses. The processes used for depositing the layers are complex. They include Molecular Beam Epitaxy and Metal Organic Vapour Phase Epitaxy. The current efficiency record is made with this process but doesn't have exact matching lattice constants. The losses due to this are not as effective because the differences in lattices allows for more optimal band gap material for the first two cells. This type of cell is expected to be able to be 50% efficient.

Lower quality materials that use cheaper deposition processes are being researched as well. These devices are not as efficient, but the price, size and power combined allow them to be just as cost effective. Since the processes are simpler and the materials are more readily available, the mass production of these devices is more economical.

==== Hot carrier cells ====

A problem with solar cells is that the high energy photons that hit the surface are converted to heat. This is a loss for the cell because the incoming photons are not converted into usable energy. The idea behind the hot carrier cell is to utilize some of that incoming energy which is converted to heat. If the electrons and holes can be collected while hot, a higher voltage can be obtained from the cell. The problem with doing this is that the contacts which collect the electrons and holes will cool the material. Thus far, keeping the contacts from cooling the cell has been theoretical. Another way of improving the efficiency of the solar cell using the heat generated is to have a cell which allows lower energy photons to excite electron and hole pairs. This requires a small bandgap. Using a selective contact, the lower energy electrons and holes can be collected while allowing the higher energy ones to continue moving through the cell. The selective contacts are made using a double barrier resonant tunneling structure. The carriers are cooled which they scatter with phonons. If a material with a large bandgap of phonons then the carriers will carry more of the heat to the contact and it won't be lost in the lattice structure. One material which has a large bandgap of phonons is indium nitride. The hot carrier cells are in their infancy but are beginning to move toward the experimental stage.

==== Plasmonic-electrical solar cells ====

Having unique features of tunable resonances and unprecedented near-field enhancement, [[plasmon]] is an enabling technique for light management. Recently, performances of [[thin-film solar cells]] have been pronouncedly improved by introducing metallic nanostructures. The improvements are mainly attributed to the plasmonic-optical effects for manipulating light propagation, absorption, and scattering. The plasmonic-optical effects could: (1) boost optical absorption of active materials; (2) spatially redistribute light absorption at the active layer due to the localized near-field enhancement around metallic nanostructures. Except for the plasmonic-optical effects, the effects of plasmonically modified [[Genetic recombination|recombination]], transport and collection of photocarriers (electrons and holes), hereafter named plasmonic-electrical effects, have been proposed by Sha, etal.<ref name=Plasmonic_Electrical_1>{{cite journal | doi = 10.1038/srep06236 | title = Breaking the Space Charge Limit in Organic Solar Cells by a Novel Plasmonic-Electrical Concept | year = 2014 | last1 = Sha | first1 = Wei E. I. | last2 = Li | first2 = Xuanhua | last3 = Choy | first3 = Wallace C. H. | journal = Scientific Reports | volume = 4 | pages=6236 |bibcode = 2014NatSR...4E6236S }}</ref><ref name=Plasmonic_Electrical_2>{{cite journal | doi = 10.1038/srep08525 | title = A General Design Rule to Manipulate Photocarrier Transport Path in Solar Cells and Its Realization by the Plasmonic-Electrical Effect | year = 2015 | last1 = Sha | first1 = Wei E. I. | last2 = Zhu | first2 = Hugh L. | last3 = Chen | first3 = Luzhou | last4 = Chew | first4 = Weng Cho | last5 = Choy | first5 = Wallace C. H. | journal = Scientific Reports | volume = 5 | pages=8525|bibcode = 2015NatSR...5E8525S }}</ref> For boosting device performance, they conceived a general design rule, tailored to arbitrary electron to hole mobility ratio, to decide the transport paths of photocarriers.<ref name="Plasmonic_Electrical_2"/> The design rule suggests that electron to hole transport length ratio should be balanced with electron to hole mobility ratio. In other words, the transport time of electrons and holes (from initial generation sites to corresponding electrodes) should be the same. The general design rule can be realized by spatially redistributing light absorption at the active layer of devices (with the plasmonic-electrical effect). They also demonstrated the breaking of [[space charge]] limit in plasmonic-electrical organic solar cell.<ref name="Plasmonic_Electrical_1"/>

==== Ultra-thin plasmonic wafer solar cells ====
Reducing the silicon wafer thickness at a minimized efficiency loss represents a mainstream trend in increasing the cost-effectiveness of wafer-based solar cells. Recently, Zhang et al. have demonstrated that, using the advanced light trapping strategy with a properly designed nano-particle architecture, the wafer thickness can be dramatically reduced to only around 1/10 of the current thickness (180 µm) without any solar cell efficiency loss at 18.2%. Nano-particle integrated ultra-thin solar cells with only 3% of the current wafer thickness can potentially achieve 15.3% efficiency combining the absorption enhancement with the benefit of thinner wafer induced open circuit voltage increase. This represents a 97% material saving with only 15% relative efficiency loss. These results demonstrate the feasibility and prospect of achieving high-efficiency ultra-thin silicon wafer cells with plasmonic light trapping.<ref>{{cite journal| title=Towards ultra-thin plasmonic silicon wafer solar cells with minimized efficiency loss| year=2014 | last1=Yinan | first1=Zhang| journal=Scientific Reports | volume=4 | pages=4939 |doi=10.1038/srep04939|bibcode = 2014NatSR...4E4939Z |display-authors=etal}}</ref>

== References ==
{{Portal|Renewable energy|Energy}}
{{Reflist|2}}

{{Photovoltaics}}

{{DEFAULTSORT:Plasmonic Solar Cell}}
[[Category:Solar cells]]

Dunkles Photon

2016-05-06T20:22:22Z

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{{expert|physics|date=February 2015}}

{{Beyond the Standard Model}}
The '''dark photon''' is a hypothetical [[elementary particle]], proposed as an [[electromagnetic force|electromagnetic]] [[force carrier]] for [[dark matter]].<ref name=walsh>{{cite news|last1=Walsh|first1=Karen McNulty|title=Data from RHIC, other experiments nearly rule out role of 'dark photons' as explanation for 'g-2' anomaly|url=http://phys.org/news/2015-02-rhic-role-dark-photons-explanation.html|accessdate=23 February 2015|publisher=PhysOrg|date=February 19, 2015}}</ref> Dark photons would theoretically be detectable via their [[Mixing (physics)|mixing]] with ordinary [[photon]]s, and subsequent effect on the interactions of known particles.<ref name=walsh/>

Dark photons were proposed in 2008 by [[Lotty Ackerman]], [[Matthew R. Buckley]], [[Sean M. Carroll]], and [[Marc Kamionkowski]] as the force carrier of a new long-range [[U(1)]] [[gauge field]], "dark electromagnetism", acting on dark matter.<ref name=carroll>{{cite web|last1=Carroll|first1=Sean M.|title=Dark photons|url=http://www.preposterousuniverse.com/blog/2008/10/29/dark-photons/|accessdate=23 February 2015|date=October 29, 2008}}</ref> Like the ordinary photon, dark photons would be massless.<ref name=carroll/>

Dark photons were suggested to be a possible cause of the so-called [[Anomalous magnetic dipole moment|'g–2 anomaly']] obtained by experiment E821 at [[Brookhaven National Laboratory]],<ref>{{Cite journal|title = Final report of the E821 muon anomalous magnetic moment measurement at BNL|url = http://link.aps.org/doi/10.1103/PhysRevD.73.072003|journal = Physical Review D|date = 2006-04-07|pages = 072003|volume = 73|issue = 7|doi = 10.1103/PhysRevD.73.072003|first1 = G. W.|last1 = Bennett|first2 = B.|last2 = Bousquet|first3 = H. N.|last3 = Brown|first4 = G.|last4 = Bunce|first5 = R. M.|last5 = Carey|first6 = P.|last6 = Cushman|first7 = G. T.|last7 = Danby|first8 = P. T.|last8 = Debevec|arxiv = hep-ex/0602035 |bibcode = 2006PhRvD..73g2003B }}</ref> which appears to be three to four standard deviations above the Standard-Model values of Hagawara et al.<ref name=hagawara>{{cite journal|last1=Hagawara|first1=Kaoru|last2=Liao|first2=Ruofan|last3=Martin|first3=Alan D.|last4=Nomura|first4=Daisuke|last5=Teubner|first5=Thomas|title=(g − 2)μ and α(M2Z) re-evaluated using new precise data|journal=Journal of Physics G: Nuclear and Particle Physics|date=June 23, 2011|volume=38|issue=8|doi=10.1088/0954-3899/38/8/085003|url=http://iopscience.iop.org/article/10.1088/0954-3899/38/8/085003/meta|accessdate=10 December 2015|publisher=IOP Publishing|arxiv = 1105.3149 |bibcode = 2011JPhG...38h5003H }}</ref> and Davier et al.<ref name=davier>{{cite journal|last1=Davier|first1=M.|last2=Hoecker|first2=A.|last3=Malaescu|first3=B.|last4=Zhang|first4=Z.|title=Reevaluation of the hadronic contributions to the muon g−2 and to α(M2Z)|journal=The European Physical Journal C|date=January 2011|volume=71|doi=10.1140/epjc/s10052-010-1515-z|url=http://link.springer.com/article/10.1140%2Fepjc%2Fs10052-010-1515-z|accessdate=10 December 2015|publisher=Springer-Verlag|issn=1434-6052|arxiv = 1010.4180 |bibcode = 2011EPJC...71.1515D }}</ref> However, dark photons were largely ruled out as a cause of the anomaly by several experiments, including the [[PHENIX detector]] at the [[Relativistic Heavy Ion Collider]] at Brookhaven.<ref name="walsh" /> A new experiment at [[Fermilab]], the [[Fermilab#g−2|Muon g-2]] experiment, expects to produce a precision four times better than the Brookhaven experiment.<ref name=muon_g-2>{{cite web|title=Muon g-2 Experiment|url=http://muon-g-2.fnal.gov/|publisher=Fermilab|accessdate=10 December 2015}}</ref>

==See also==
*[[Dark radiation]]
*[[Photino]]

==References==
{{reflist}}

[[Category:Bosons]]
[[Category:Dark matter]]
[[Category:Hypothetical elementary particles]]
[[Category:Physics beyond the Standard Model]]
{{particle-stub}}

{{Dark matter}}

Royal Observatory, Cape of Good Hope

2016-05-05T00:54:26Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Use British English|date=October 2013}}
{{Use dmy dates|date=October 2013}}
{{Infobox Observatory
|name = Royal Observatory, Cape of Good Hope
|background =
|image = [[File:RO main building plan.jpg|300px]]
|caption = Plan of the Main Building of the Royal Observatory, ca 1840.
|organization = [[South African Astronomical Observatory]]
|location = [[Observatory, Cape Town]]
|coords = {{coord|33.9347|S|18.4776|E|display=inline,title}}
|altitude = 6m
|established = 20 October 1820
|closed = 31 December 1971

}}

The '''Royal Observatory, Cape of Good Hope''', is the oldest continuously existing scientific institution in South Africa.<ref name="ACBrown">{{cite book
|title=A History of Scientific Endeavour in South Africa: A Collection of Essays Published on the Occasion of the Centenary of the Royal Society of South Africa
|editor1-last=Brown
|editor1-first=Alexander Claude
|publisher=Royal Society of South Africa
|date=1977
|location=Cape Town
|author=Royal Society of South Africa
|url=http://books.google.com/?id=-X4IAAAAMAAJ&dq=History+of+Scientific+Endeavour+in+South+Africa&q=founded+1820
|page=60}}</ref>

It is located on a small hill 5 km from central Cape Town in the eponymous suburb of [[Observatory, Cape Town|Observatory]].  It has also been the subject of an ICOMOS/IAU Case Study.<ref name="unesco">{{cite web |url = http://www2.astronomicalheritage.net/index.php/show-entity?identity=52&idsubentity=1|title = Royal Observatory, Cape of Good Hope, Republic of South Africa|publisher=UNESCO}}</ref>

== History ==

The Royal Observatory was founded in 1820<ref name="ACBrown" /> by an [[Order in Council]] of [[George IV of the United Kingdom|King George IV]] of the United Kingdom. It remained a separate entity until 1972 when it was amalgamated with the [[Union Observatory|Republic Observatory]] Johannesburg to form the present-day [[South African Astronomical Observatory]]. Its site is now the headquarters of the South African Astronomical Observatory.

In accordance with its mandate, the principal activity of the Observatory was [[Astrometry]] and it was over its existence responsible for publishing many catalogues of star positions. In the 20th century it turned in part towards [[Astrophysics]] but by the nineteen-fifties the city lights of Cape Town had rendered work on faint objects impossible and a new site in the [[Karoo]] semi-desert was sought. An agreement to facilitate this was ratified on 23 September 1970.<ref>{{cite web|title=ASSA Historical Section|url=http://assa.saao.ac.za/html/his-obs-radcliffe.html|publisher=Astronomical Society of South Africa|accessdate=10 November 2013|author=Chris de Coning}}</ref> Nevertheless, several telescopes remained in operation until the 1990s. These are rarely made use of today except for public outreach events. [[Alan William James Cousins|Alan Cousins]] was the last serious observer to work from the Royal Observatory site.

The Royal Observatory was responsible for a number of significant events in the history of astronomy. The second HM Astronomer, Thomas Henderson, aided by his assistant, Lieutenant William Meadows, made the first observations that led to a believable stellar parallax, namely of [[Alpha Centauri]]. However, he lost priority as the discoverer of [[Stellar Parallax|stellar parallax]] to [[Friedrich Bessel|Friedrich Wilhelm Bessel]] who published his own (later) observations of 61 Cygni before Henderson got around to his.<ref>{{cite journal|last=Henderson|first=T.|date=1840|title=On the Parallax of α Centauri |journal=Memoirs of the Royal Astronomical Society|volume=XI |pages=61–68}}</ref><ref>{{cite book |last=Glass|first=I.S.|url=http://www.saao.ac.za/~isg/proxima.html|date= 2008|title= Proxima: The Nearest Star (other than the Sun)|publisher=Mons Mensa|location=Cape Town}}</ref>
Around 1840, Thomas Maclear re-measured the controversial meridian of [[Nicolas Louis de Lacaille|Nicolas-Louis de La Caille]], showing that the latter's geodetic measurements had been correct but that nearby mountains had affected his latitude determinations<ref>{{cite book|last=Maclear|first=Sir Thomas|date=1866|title=Verification and Extension of La Caille's Arc of Meridian at the Cape of Good Hope|publisher=Lords Commissioners of the Admiralty}}</ref><ref>{{cite book|last=Glass|first=I.S.|date=2012|title=Nicolas-Louis de La Caille, Astronomer and Geodesist|publisher=Oxford University Press}}</ref>
In 1882 David Gill obtained long-exposure photographs of the [[Great Comet of 1882|great comet of that year]] showing the presence of stars in the background. This led him to undertake in collaboration with [[Jacobus Kapteyn|J.C. Kapteyn]] of Groningen the Cape Photographic [[Durchmusterung]], the first stellar catalogue prepared by photographic means. In 1886 he proposed to [[Amédée Mouchez|Admiral A.E.B. Mouchez]] of Paris Observatory the holding of an international congress to promote a photographic catalogue of the whole sky. In 1887 this congress took place in Paris and resulted in the [[Carte du Ciel]] project. The Cape Observatory was assigned the zone between declinations −40° and −52°. The Carte du Ciel is regarded as the precursor of the [[International Astronomical Union]].

In 1897 Frank McClean, a close friend of Gill's and the donor of the McClean telescope, discovered the presence of oxygen in a number of stars using an objective prism attached to the Astrographic Telescope.<ref name="mcclean">{{cite journal|last=McClean|first=F.|title=Comparison of Oxygen with the extra lines in the Spectra in the Helium Stars β Crucis &c....|journal=Proc. Roy. Soc. London|volume=62|pages=417–423|doi=10.1098/rspl.1897.0130}}</ref>

In 1911, J.K.E. Halm, then the Chief Assistant, put forward a pioneering paper on [[stellar dynamics]] in which he hypothesized that the star streams discovered by Kapteyn arose from a [[Maxwell–Boltzmann distribution|Maxwellian]] distribution of stellar velocities. This paper also contains the first suggestion that stars obey a mass-luminosity relationship. <ref name="halm">{{cite journal|last=Halm|first=J.|title=Stars, motion in space, etc. Further considerations relating to the systematic motions of the stars|journal=[[Monthly Notices of the Royal Astronomical Society]]|volume= 71| page=610|date=1911|bibcode=1911MNRAS..71..610H|doi=10.1093/mnras/71.8.610 }}</ref>

A later 20th-century HM Astronomer, H. Spencer Jones, was active in an international project for determining the solar parallax through observations of the minor planet [[433 Eros|Eros]].<ref>{{Cite journal | last = Jones | first = H. Spencer | title = The Solar Parallax and the Mass of the Moon from Observations of Eros at the Opposition of 1931 | journal = Mem. Roy. Astron. Soc. | volume = 66 | date = 1941 | pages = 11–66}}</ref>

In the second half of the twentieth century Alan Cousins set up very precise southern standards for [[UBV photometric system|UBV]] and introduced a widely used system of [[Photometric system|VRI]] photometry that enjoyed international recognition for precision.<ref name="kilkenny">{{cite conference|last=Kilkenny|first=D.|title=Alan Cousins (1903-2001): a life in astronomy|series=ASP Conference Proceedings|volume=256|page=1}}</ref>

In 1977 the occultation of the star SAO 158687 was observed by Joseph Churms from the former Royal Observatory and these observations provided needed confirmation of the [[Rings of Uranus|Uranian rings]] discovered from the Kuiper aeroplane by Elliot et al.<ref>{{cite journal|last=Booth|first=Pat|title= Presidential Address: The Rings of Uranus – the South African Story|journal=Monthly Notes of the Astronomical Society of South Africa| volume= 64|page=165|date=2005|bibcode=2005MNSSA..64..165B}}</ref>
During the 19th century the Observatory was regarded as the main advisor to the colonial government on scientific matters. it served as the repository for standard weights and measures of the Colony and was responsible for timekeeping and geodetic surveying. A magnetic observatory was constructed in 1841 but burned down during the following decade. The Observatory also possesses a long series of meteorological records.

The history of the Royal Observatory has been the subject of several works.<ref name="dgill">{{cite book|last=Gill|first=Sir D.|title= History and Description of the Royal Observatory, Cape of Good Hope|publisher= HMSO|location=London|date=1913}}</ref><ref>{{cite book |last=Laing|first= J.D.|date= 1970|title= The Royal Observatory, Cape of Good Hope 1820–1970|publisher=Royal Observatory|location=Cape Town}}</ref><ref name="bwarner">{{cite book |last=Warner|first= B.|date= 1979|title= Astronomers at the Royal Observatory, Cape of Good Hope|publisher= Balkema|location= Cape Town and Rotterdam}}</ref><ref>{{cite book |last=Warner|first=B.|title=Royal Observatory, Cape of Good Hope 1820-1831: The Founding of a Colonial Observatory Incorporating a biography of Fearon Fallows |date=1995|publisher= Springer|isbn=978-0-7923-3527-6|oclc=32465151}}</ref>

== Her Majesty's astronomers at the Cape ==
The Royal Observatory's directors were known as His or Her Majesty's Astronomers at the Cape. They were as follows:<ref name="bwarner" />
*[[Fearon Fallows|Rev Fearon Fallows]] 1820–1831
*[[Thomas Henderson (astronomer)|Thomas Henderson]] 1831–1833
*[[Thomas Maclear]] 1833–1879
*[[Edward James Stone]] 1870–1879
*[[David Gill (astronomer)|David Gill]] 1879–1907
*Sydney Samuel Hough 1907–1923
*[[Harold Spencer Jones]] 1923–1933
*[[John Jackson (astronomer)|John Jackson]] 1933–1950
*Richard Hugh Stoy 1950–1968
*George Alfred Harding was Officer-in-charge 1969-1971

== Some astronomers who worked at the Royal Observatory ==

A full list of people who worked at the Royal Observatory and their publications, up to 1913, is given in Gill (1913).<ref name="dgill"/>
*[[Charles Piazzi Smyth]] 1835–1845. Later Astronomer Royal for Scotland.
*[[William Lewis Elkin]] 1881–1883. Later director of [[Yale University Observatory]].
*[[Frank McClean]]<ref name="mcclean"/> 1895–1897. Discoverer of oxygen in stars.
*[[Willem de Sitter]] 1897–1899. Later a famous cosmologist and director of [[Leiden Observatory]].
*[[Robert T. A. Innes|Robert Thorburn Ayton Innes]] 1897–1903. Discoverer of the nearest star and later director of the Union (Republic) Observatory
*[[Jakob Karl Ernst Halm]]<ref name="halm"/> 1907–1927. Discoverer of the mass-luminosity relation and pioneer of stellar dynamics.
*[[Joan Voûte|Joan George Erardus Gijsbertus Voûte]]. Later founder and director of [[Bosscha Observatory]].
*[[Alan William James Cousins]]<ref name="kilkenny"/> 1947–1971. Noted photometrist.
*[[David Stanley Evans]] 1951–1968. Known for Barnes-Evans relation.

== Principal buildings ==
A heritage survey was recorded in 2011 of a complete list of the buildings at the Observatory.<ref>{{cite book|last1=Baumann|first1=N.|last2=Winter|first2=S.|title=The South African Astronomical Observatory, A Heritage Survey| publisher=South African Astronomical Observatory|location= Observatory|date=2011}}</ref> They include:
[[File:Main building of Royal Observatory, Cape of Good Hope.jpg|thumb|Main Building]] [[File:Aerial view of McClean telescope building.jpg|thumb|McClean building]]
*Main Building, completed 1828. Greek revival style; Architect [[John Rennie the Elder|John Rennie]]. This contains today offices and a notable astronomical library.
*Photoheliograph building, 1849 (formerly 7-inch Merz telescope building). Its dome rotates on cannon balls.
*Heliometer, 1888 (now containing 18-inch reflector). Its dome (by [[Howard Grubb]]) was designed for flow-through ventilation.
*McClean, 1896, designed by [[Herbert Baker]] and laboratory (now Astronomical Museum). Hydraulically driven rising floor. Dome by [[T. Cooke & Sons|T. Cooke and Sons]] of York.
*Astrographic, 1889. Dome by [[Howard Grubb]].
*Reversible Transit Circle 1905 (6-inch). Two each Collimator and Mark houses.
*Technical Building (ca 1987)
*Auditorium, constructed originally as an optical instrument repair workshop during World War II.

== Principal telescopes ==
Historically, the main building contained a 10 feet focal length Transit by [[Peter Dollond|Dollond]] and a 6-feet Mural Circle by Thomas Jones. These were replaced by in 1855 by an 8-inch Transit Circle designed by [[George Biddell Airy]], Astronomer Royal at Greenwich. The Airy instrument was removed in 1950.<ref name="unesco" /> Some parts of these telescopes are in the Observatory's Astronomical Museum.

* 4-inch Photoheliograph (1875) by [[John Henry Dallmeyer|Dallmeyer]]
* 6-inch visual refractor (1882) [[Howard Grubb]]
* Astrographic, 1889 (13-inch photographic and 10-inch guide refractors by [[Howard Grubb]]). Used for the Cape Astrographic Zone (see above) and by F. McClean for spectroscopy.
* McClean or Victoria telescope (18-inch visual, 24-inch photographic and 8-inch guide refractors by [[Howard Grubb]])<ref>{{cite journal|title=Royal Observatory, Cape of Good Hope|journal=The Observatory|date=August 1902|volume=XXV|url=http://archive.org/stream/observatory03unkngoog#page/n373/mode/1up}}</ref>
* 6-inch Reversible Transit Circle 1905. Designed by Sir David Gill and constructed by [[Troughton & Simms|Troughton and Simms]]. Used inter alia for the southern part of the [[Catalogues of Fundamental Stars|Fundamental Katalog]] FK4.
* 18-inch reflector by Cox, Hargreaves and Thomson, 1955. Guide telescope is 7-inch Merz

A 40-inch reflector by [[Sir Howard Grubb, Parsons and Co|Grubb Parsons]] was installed in 1964 but was removed to Sutherland in 1972.

== Astronomical Museum ==

The former spectroscopic laboratory of the McClean telescope was converted into a museum in 1987, retaining the original 19th-century fittings. The building still contains the original hydraulic apparatus for raising the observing floor and a darkroom which contains specimens of darkroom equipment taken from various domes after photography went out of use.<ref>{{cite journal |last= Glass|first=I.S. |date=2010|title= The Astronomical Museum of the SAAO|journal=Monthly Notes of the Astronomical Society of Southern Africa |volume=69|page=20|bibcode = 2010MNSSA..69...20G }}</ref> Items on display include telescope models, measuring machines, altazimuth instruments by Dollond (1820) and Bamberg (ca 1900), calculating machines, early office equipment, early electronic devices, lenses from early telescopes including the photographic telescopes of Gill, a clockwork telescope drive, a signal pistol, chemistry equipment etc.

== Natural history ==

The Royal Observatory site is situated in the Two Rivers Urban Park, a wetland area. The underlying rock is Malmesbury shale with a zone of greywacke and quartzitic limestone. Some of its original ecology is preserved and it supports a wide variety of animals and plant life. It is the northern limit of the [[Western Leopard Toad]] (Bufo Pantherinus) and the only remaining natural habitat of the rare iris, [[Moraea aristata]].<ref>{{cite web|title=Red List of South African Plants - Moraea aristata (D.Delaroche) Asch. & Graebn|url=http://redlist.sanbi.org/species.php?species=1556-10|publisher=South African National Biodiversity Institute}}</ref>

==Further reading==
* {{cite book|last=Glass|first=I.S.|title=The Royal Observatory at the Cape of Good Hope|publisher=Mons Mensa (self published)|url=http://www.facebook.com/royal.observatory.cape|date=2015}}
* {{cite book|last=Gill|first=David|title=Heliometer observations for determination of stellar parallax made at the Royal Observatory, Cape of Good Hope|publisher=Eyre and Spottiswoode|url=http://www.archive.org/details/heliometerobserv00gillrich|date=1893}}* {{cite book|last=Stone|first=Edward James|title=The Cape catalogue of 1159 stars, deduced from observations at the Royal Observatory, Cape of Good Hope, 1856-1861, reduced to the epoch 1860|date=1873|publisher=S Solomon|location=Cape Town|url=http://archive.org/details/capecatalogueofs00royaiala}}
* {{cite book|title=Results of Astronomical Observations Made at the Royal Observatory, Cape of Good Hope in the year 1856|date=1871|publisher=S Solomon|url=http://archive.org/details/resultsastronom00admigoog|last1=Stone|first1=Edward James|last2=Maclear|first2=Thomas}}
* {{cite book|title=Astronomers at the Royal Observatory, Cape of Good Hope|date=1979|publisher=AA Balkema|last=Warner|first=Brian}}

== Notes ==

{{reflist}}

== References ==
{{commons category}}
*Glass, I.S., 2009. The Royal Observatory, Cape of Good Hope, a Valuable Cultural Property, in Wolfschmidt,G. (ed), Cultural Heritage of Astronomical Observatories from Classical Antiquity to Modern Astrophysics, Proceedings of the International ICOMOS Symposium in Hamburg, 14–17 October 2008. Monuments and Sites XVIII, ICOMOS/Hendrik Bäßler-Verlag, Berlin.
*Glass, I.S., 2011. The Royal Observatory, Cape of Good Hope, Republic of South Africa, in Ruggles, C. and Cotte, M. (eds) Heritage Sites of Astronomy and Archaeoastronomy in the Context of the UNESCO World Heritage Convention, ICOMOS and IAU, Paris.
*Van der Walt, L., Strong, N. 2010. Observatory Landscape Framework, South African Astronomical Observatory, Observatory.

{{Cape Town}}
[[Category:Astronomical observatories in South Africa]]
[[Category:1820 establishments in the Cape Colony]]
[[Category:Museums in Cape Town]]

Trumpler 16

2016-04-27T23:55:19Z

Bibcode Bot: Adding 2 arxiv eprint(s), 0 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Infobox cluster
| name = Trumpler 16
| image = [[File:ESO - The Carina Nebula (by).jpg|240 px]]
| caption = The inner region of the [[Carina Nebula]] as seen in near-infrared. Trumpler 16 is the cluster of stars at the left, around [[Eta Carinae]] (the brightest star in the image).
| credit = [[European Southern Observatory]]
| epoch = [[Epoch (astronomy)#Julian years and J2000|J2000]]
| constellation = [[Carina (constellation)|Carina]]
| ra = {{RA|10|49|10}}<ref name=wu>{{cite journal|bibcode=2009MNRAS.399.2146W|title=The orbits of open clusters in the Galaxy|journal=Monthly Notices of the Royal Astronomical Society|volume=399|issue=4|pages=2146|author1=Wu|first1=Zhen-Yu|last2=Zhou|first2=Xu|last3=Ma|first3=Jun|last4=Du|first4=Cui-Hua|year=2009|doi=10.1111/j.1365-2966.2009.15416.x|arxiv = 0909.3737 }}</ref>
| dec = {{DEC|-59|43.0}}<ref name=wu/>
| dist_ly = 7,500 [[light-year]]s
| dist_pc = 2,300 [[parsec]]s<ref name=scott/>
| appmag_v =
| names = C 1043-594
}}

[[File:NGC 3372d.jpg|upright=1.6|thumb|left|[[Carina OB1]] association, with Trumpler 16]]
'''Trumpler 16''' is a massive [[open cluster]] that is home to some of the most luminous stars in the [[Milky Way]] Galaxy. It is situated within the [[Carina Nebula]] ([[Caldwell 92]]) complex in the [[Carina-Sagittarius Arm]], located approximately 7,500 light-years from Earth. The cluster has one naked eye member star, [[Eta Carinae]].

[[File:Carina Nebula by ESO.jpg|left|thumb|Image of [[Carina OB1]] showing Trumpler 16 with [[Trumpler 14]] and [[Collinder 228]]]]
Its most luminous members are Eta Carinae and [[WR 25]], with both having luminosities several million times that of the Sun, and there are six other extreme stars with O3 spectral classes.<ref name=scott>{{cite journal |title=The Chandra Carina Complex Project View of Trumpler 16 |display-authors=4 |author=Wolk, Scott J. |author2=Broos, Patrick S. |author3=Getman, Konstantin V. |author4=Feigelson, Eric D. |author5=Preibisch, Thomas |author6=Townsley, Leisa K. |author7=Wang, Junfeng |author8=Stassun, Keivan G. |author9=King, Robert R. |author10=McCaughrean, Mark J. |author11=Moffat, Anthony F. J. |author12=Zinnecker, Hans | journal=The Astrophysical Journal Supplement|volume=194| issue=1| id=12| pages=15 |date=2011 |doi= 10.1088/0067-0049/194/1/12 | bibcode=2011ApJS..194...12W|arxiv = 1103.1126 }}</ref> Both η Carinae and WR 25 are binaries, with the primary stars contributing most of the luminosity, but with companions which are themselves more massive and luminous than most stars. Across all wavelengths, WR 25 is estimated to be the more luminous of the two, 6,300,000 times the Sun's luminosity (absolute bolometric magnitude -12.25) compared to Eta Carinae at 5,000,000 times the Sun's luminosity (absolute bolometric magnitude -12.0). However in the image on the right Eta Carinae appears by far the brightest object, both because it is brighter in visual wavelengths and because it is embedded in nebulosity which is exaggerated in this type of image. WR 25 is very hot and emits most of its radiation as ultraviolet. It can be seen in the image below and to the right of Eta Carinae, just beyond the edge of the brightest nebulosity and to the right of an orange foreground star.

Trumpler 16 and Trumpler 14 are the most prominent star clusters in [[Carina OB1]], a giant stellar association in the Carina spiral arm. Another cluster within Carina OB1, [[Collinder catalog|Collinder]] 228, is thought to be an extension of Trumpler 16 appearing visually separated only because of an intervening dust lane. The spectral types of the stars indicate that Trumpler 16 formed by a single wave of star formation. Because of the extreme luminosity of the stars formed, their stellar winds push away the clouds of dust, similar to the [[Pleiades]]. In a few million years, after the brightest stars have exploded as [[supernova]]e, the cluster will slowly die away. Trumpler 16 includes most of the stars in the left (east) half of the nebulosity in this image. Trumpler 14 is younger and more compact, visible just right (west) of the centre of this frame.<ref name=carrago>{{cite journal|bibcode= 2004A&A...418..525C |title= The star cluster Collinder 232 in the Carina complex and its relation to Trumpler 14/16 |journal= Astronomy and Astrophysics |volume= 418 |issue= 2 |pages= 525 |author1= Carraro |first1= G. |last2= Romaniello |first2= M. |last3= Ventura |first3= P. |last4= Patat |first4= F. |year= 2004 |doi= 10.1051/0004-6361:20034335 |arxiv = astro-ph/0401144 }}</ref>

==See also==
*[[Trumpler 10]]
*[[Carina OB2]]

==References==
{{reflist}}

==Further reading==
{{cite journal|title=η Carinae and the Trumpler 16 Cluster|journal=Publications of the Astronomical Society of the Pacific|page=492|number=447|volume=75|date=December 1963|doi=10.1086/128013|author=Feinstein, Alejandro|bibcode=1963PASP...75..492F}}

[[Category:Carina Nebula]]
[[Category:Open clusters]]
[[Category:Carina (constellation)]]
[[Category:Trumpler catalog]]

Coywolf

2015-09-30T03:24:48Z

Bibcode Bot: Adding 0 arxiv eprint(s), 3 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Use mdy dates|date=February 2015}}
{{Taxobox
| image = Coywolf hybrids.jpg
| image_width= 260px
| image_caption = Captive-bred [[F1 hybrid|F1]] gray wolf-coyote hybrids, Wildlife Science Center in Forest Lake, [[Minnesota]]
| name = Coywolf
| status = NE
| status_system = iucn3.1
| regnum = [[Animal]]ia
| phylum = [[Chordate|Chordata]]
| classis = [[Mammal]]ia
| ordo = [[Carnivora]]
| familia = [[Canidae]]
| genus = ''[[Canis]]''
| species = ''[[Canis latrans|C. latrans]]'' × ''[[Canis lupus|C. lupus]]/[[Canis lycaon|lycaon]]/[[Canis rufus|rufus]]''
| binomial =
| synonyms=
}}
'''Coywolf''' (sometimes called '''woyote''') is an informal term for a [[canid hybrid]] descended from [[coyote]]s and one of three other North American ''[[Canis]]'' species, the [[Gray wolf|gray]], [[Eastern wolf|eastern]] and [[red wolf]]. Coyotes are closely related to eastern and red wolves, having diverged 150,000–300,000 years ago and evolved side by side in North America, thus facilitating hybridization.<ref name=wilson2000/> In contrast, hybrids between coyotes and gray wolves, which are [[Eurasia]]n in origin and diverged from coyotes 1–2 million years ago, are extremely rare. Such hybridization in the wild has only been confirmed in isolated gray wolf populations in the southern USA,<ref name="hailer2008">{{Cite journal | last1 = Hailer | first1 = F. | last2 = Leonard | first2 = J. A. | editor1-last = Harpending | editor1-first = Henry | doi = 10.1371/journal.pone.0003333 | title = Hybridization among Three Native North American Canis Species in a Region of Natural Sympatry | journal = PLoS ONE | volume = 3 | issue = 10 | pages = e3333 | year = 2008 | pmid = 18841199| pmc =2556088 |bibcode = 2008PLoSO...3.3333H }}</ref> while several specimens were produced in captivity via [[artificial insemination]] from sperm extracted from northwestern gray wolves introduced to female western coyotes.<ref name=mech2014>{{Cite journal | doi = 10.1371/journal.pone.0088861| pmid = 24586418|pmc=3934856| title = Production of Hybrids between Western Gray Wolves and Western Coyotes| journal = PLoS ONE| volume = 9| issue = 2| pages = e88861| year = 2014| last1 = Mech | first1 = L. D. | last2 = Christensen | first2 = B. W. | last3 = Asa | first3 = C. S. | last4 = Callahan | first4 = M. | last5 = Young | first5 = J. K. |bibcode = 2014PLoSO...988861M }}</ref>

==Description==
Hybrids of any combination tend to be larger than coyotes, and show behaviors intermediate between coyotes and the other parent's species.<ref name=mech2014/><ref name="way2007">{{cite journal | author = Way J. G. | year = 2007 | title = A comparison of body mass of Canis latrans (Coyotes) between eastern and western North America | url = http://easterncoyoteresearch.com/downloads/BodyMassWay.PDF | journal = Northeastern Naturalist | volume = 14 | issue = 1| pages = 111–24 | doi=10.1656/1092-6194(2007)14[111:acobmo]2.0.co;2}}</ref> In one captive hybrid experiment, six F1 hybrid pups from a male northwestern gray wolf and a female coyote were measured shortly after birth with an average on their weights, total lengths, head lengths, body lengths, hind foot lengths, shoulder circumferences, and head circumferences compared with those on pure coyote pups at birth. The results found that, despite being delivered by a female coyote, the hybrid pups at birth were much larger and heavier than regular coyote pups born and measured around the same time.<ref name=mech2014/> At six months of age, these hybrids were closely monitored at the Wildlife Science Center. Executive Director Peggy Callahan at the facility states that the howls of these hybrids are said to start off much like regular gray wolves with a deep strong vocalization, but changes partway into a coyote-like high pitched yipping.<ref>Riese, Clive (March 19, 2014), [http://forestlaketimes.com/2014/03/19/wildlife-science-center-partners-in-study-impacting-wolf-controversy/ Wildlife Science Center partners in study impacting wolf controversy], ''Forest Lake Times''</ref>

Compared with pure coyotes, [[Eastern wolf-coyote hybrid]]s have been recorded forming more cooperative social groups and are generally less aggressive with each other while playing.<ref name="bekoff1978">Bekoff, M. (1978). "Behavioral Development in Coyotes and Eastern Coyotes", pp. 97–124 in M. Bekoff, (ed.) ''Coyotes: Biology, Behavior, and Management''. Academic Press, New York. ISBN 1930665423.</ref> Hybrids also reach [[sexual maturity]] when they are two years old, which is much later than occurs in pure coyotes.<ref name="way2010">{{cite journal | author = Way J.G.|author2= Rutledge L.|author3= Wheeldon T.|author4= White B.N. | year = 2010 | title = Genetic characterization of Eastern "Coyotes" in eastern Massachusetts | url = http://www.easterncoyoteresearch.com/downloads/GeneticsOfEasternCoywolfFinalInPrint.pdf | format = PDF | journal = Northeastern Naturalist | volume = 17 | issue = 2| pages = 189–204 | doi=10.1656/045.017.0202}}</ref>

==Varieties==

===Gray wolf-coyote hybrids===
[[File:Captivecoywolfhybrid.jpg|left|thumb|[[F1 hybrid|F1 hybrid]] coyote-gray wolf hybrid, conceived in captivity.]]

====Mexican gray wolf-coyote hybrids====

Despite the nature of hybridization between coyotes and gray wolves being extremely rare, there has been speculation for a long time that hybrids of southern coyotes and isolated Mexican gray wolves have been roaming the south-central USA after the latter species was depleted from persecutions. However, the existence of such hybrids was not confirmed until 2007, following the analysis of several specimens of large coyotes collected in central and western Texas. One analysis of controlled-region [[haplotype]]s of the [[mitochondrial DNA]] and sex chromosomes of [[Mexican wolf|Mexican gray wolves]] by [[Uppsala University]] detected the presence of coyote markers in some specimens. However, these markers were absent in captive Mexican gray wolf populations, thus suggesting that some male gray wolves from remnant wild populations began mating with female coyotes and coywolf hybrids, later backcrossing to other male wolves. Analysis on Texan coyote haplotypes also detected the presence of male gray wolf introgression, such as gray wolf Y-chromosomes in some of the male coyotes. In an extremely rare case, the study found that one coyote out of seventy individuals from Texas was discovered to carry a mtDNA haplotype derived from a female Mexican gray wolf, thus indicating that a male coyote had also managed to breed with a female Mexican gray wolf in the wild. The Mexican gray wolf may be the only gray wolf in the southern states besides domestic and feral dogs to have hybridized with coyotes.<ref name="hailer2008"/> In tests performed on a stuffed carcass of what was initially labelled a [[chupacabra]], mitochondrial DNA analysis conducted by [[Texas State University]] showed that it was a coyote, though subsequent tests revealed that it was a coyote–gray wolf hybrid sired by a male Mexican gray wolf.<ref>Ardizzoni, S. (September 1, 2013), [http://bionews-tx.com/news/2013/09/01/texas-state-university-researcher-helps-unravel-mystery-of-texas-blue-dog-claimed-to-be-chupacabra/ "Texas State University Researcher Helps Unravel Mystery of Texas ‘Blue Dog’ Claimed to be Chupacabra"], ''Bio News Texas''.</ref>

====Northwestern gray wolf-coyote hybrids====
In 2013, the U.S. Department of Agriculture Wildlife Services conducted a captive breeding experiment at their National Wildlife Research Center Predator Research Facility in Logan, Utah. Using gray wolves from British Columbia and western coyotes, they produced six hybrids, making this the very first hybridization case between pure coyotes and [[Northwestern wolf|northwestern gray wolves]]. The experiment, which used artificial insemination, was intended to determine whether or not the sperm of the larger gray wolves in the west was capable of fertilizing the [[egg cell]]s of western coyotes. Aside from the historical hybridizations between coyotes and the smaller Mexican gray wolves in the south, as well as with eastern wolves and red wolves, grays wolves from the northwestern USA and western provinces of Canada are not known to interbreed with coyotes in the wild, thus prompting the experiment. The six resulting hybrids included four males and two females. At six months of age, the hybrids were closely monitored and were shown to display both physical and behavioral characteristics from both species, as well as some physical similarities to the eastern wolves, whose status as a distinct wolf species or as a genetically distinct subspecies of the gray wolf is controversial. Regardless, the result of this experiment concluded that northwestern gray wolves, much like the eastern wolves, red wolves, Mexican gray wolves, and domestic dogs, are capable of hybridizing with coyotes.<ref name=mech2014/>{{clear}}

In 2015, a research team from the cell and microbiology department of Anoka-Ramsey Community College revealed that an F2 litter of two pups had been produced from two of the original hybrids. At the same time, it was also revealed that, despite the six F1's successful delivery from the same coyote, they were not all full siblings because multiple sperms from eight different northwestern gray wolves were used in their production. The successful production of the F2 litter, nonetheless, confirmed that hybrids of coyotes and northwestern gray wolves are just as fertile as hybrids of coyotes to eastern and red wolves. Both the F1 and F2 hybrids were found to be phenotypically intermediate between the western gray wolves and coyotes. Unlike the F1 hybrids, which were produced via artificial insemination, the F2 litter was produced from a natural breeding.<ref>https://ncurdb.cur.org/ncur2015/search/display_ncur.aspx?id=93115</ref> The study also discovered through sequencing 16S ribosomal RNA encoding genes that the F1 hybrids all have an intestinal microbiome distinct from both parent species but were once reported to be present in some gray wolves. Moreover, analysis of their complementary DNA and ribosomal RNA revealed that the hybrids have very differential gene expressions compared to those in gray wolf controls.

====Coydogs====
{{main|Coydog}}
[[File:The Clever Coyote (1951) Coydogs.jpg|thumb|Coydogs in [[Wyoming]]]]
Hybrids between coyotes and domestic dogs have been bred in captivity dating back to the Pre-Columbian Mexico.<ref>{{cite book|url=http://www.colegionacional.org.mx/SACSCMS/XStatic/colegionacional/docs/espanol/lmza/lmza_icaz_2002.pdf|chapter=13. Dog-wolf Hybrid Biotype Reconstruction from the Archaeological City of Teotihuacan in Prehispanic Central Mexico|author=Valadez, Raúl; Rodríguez, Bernardo; Manzanilla, Linda and Tejeda, Samuel |title=9th ICAZ Conference, Durham 2002: Dogs and People in Social, Working, Economic or Symbolic Interaction|editor=Snyder, Lynn M and Moore, Elizabeth A. |pages=120–130}}</ref> Other specimens were later produced by mammalian biologists mostly for research purposes. Although the latter species are not often considered wolves outside of the scientific community, domestic dogs are still subsumed into the gray wolf species<ref>http://animaldiversity.org/site/accounts/information/Canis_lupus_familiaris.html</ref> hence coydogs are another biological sub-variations of hybrids between coyotes and gray wolves; the latter considered the domesticated form of ''Canis lupus''.<ref>{{Cite journal
| last1 = Anderson | first1 = T. M.
| last2 = Vonholdt | first2 = B. M.
| last3 = Candille | first3 = S. I.
| last4 = Musiani | first4 = M.
| last5 = Greco | first5 = C.
| last6 = Stahler | first6 = D. R.
| last7 = Smith | first7 = D. W.
| last8 = Padhukasahasram | first8 = B.
| last9 = Randi | first9 = E.
| doi = 10.1126/science.1165448
| last10 = Leonard | first10 = J. A.
| last11 = Bustamante | first11 = C. D.
| last12 = Ostrander | first12 = E. A.
| last13 = Tang | first13 = H.
| last14 = Wayne | first14 = R. K.
| last15 = Barsh | first15 = G. S.
| title = Molecular and Evolutionary History of Melanism in North American Gray Wolves
| journal = Science
| volume = 323
| issue = 5919
| pages = 1339–1343
| year = 2009
| pmid = 19197024
| pmc =2903542
|bibcode = 2009Sci...323.1339A }}</ref> Some roaming primitive dogs in North America, such as the [[Carolina dog]]s from the south-eastern USA, are also suspected to have had historical genetic exchanges with coyotes.<ref>{{cite web|url=http://news.nationalgeographic.com/news/2003/03/0311_030311_firstdog_2.html|title=Did Carolina Dogs Arrive With Ancient Americans?|work=National Geographic News|author=Handwerk, Brian |date=March 11, 2003}}</ref> Unlike other gray wolf subspecies, dogs have been known to freely hybridize with any Canis that come into contact with them during the breeding seasons, which gives them the potential to introgress into various wild wolf and coyote populations.

===Eastern wolf-coyote hybrids===

====Eastern coyotes====
[[File:Coyote-face-snow - Virginia - ForestWander.jpg|thumb|left|[[Eastern coyote]], an eastern wolf-coyote hybrid, [[West Virginia]].]]
[[Eastern wolf-coyote hybrid]]s, termed eastern coyotes, occur in [[Michigan]], [[New England]], [[New York]], [[New Jersey]], [[Pennsylvania]], [[Ontario]], [[Quebec]], [[New Brunswick]],<ref name=gnb>{{cite web|title=Living with Wildlife – Eastern coyotes|url=http://www2.gnb.ca/content/dam/gnb/Departments/nr-rn/pdf/en/Wildlife/Coyotes.pdf|work=Natural Resources website|publisher=[[Government of New Brunswick]]|accessdate=February 2, 2014}}</ref> [[Nova Scotia]],<ref name=nsdnr>{{cite web|title=Frequently Asked Questions about Eastern Coyote in Nova Scotia|url=http://novascotia.ca/natr/wildlife/nuisance/coyotes-faq.asp|work=Department of Natural Resources website|publisher=[[Government of Nova Scotia]]|accessdate=February 2, 2014}}</ref> and [[Newfoundland and Labrador]].<ref name=NL>{{cite web|title=Living with Coyotes in Newfoundland and Labrador|url=http://www.env.gov.nl.ca/env/wildlife/all_species/coyotes.html|work=The Department of Environment and Conservation website|publisher=Government of Newfoundland and Labrador|accessdate=February 2, 2014}}</ref> The eastern wolf is particularly susceptible to hybridization with the coyote, due to its close relationship to it and its ability to bridge [[gene flow]] between both coyotes and gray wolves. Furthermore, hunting over a period of 400 years caused a population decline that reduced the number of suitable mates, thus facilitating coyote genes swamping into the eastern wolf population. Aside from posing a threat to a unique species, the resulting eastern wolf-coyote hybrids are too small to substitute for pure eastern wolves as [[apex predator]]s of moose and deer. The main nucleus of pure eastern wolves is currently concentrated within [[Algonquin Provincial Park]]. This susceptibility to hybridization led to the eastern wolf being listed as Special Concern under the Canadian Committee on the Status of Endangered Wildlife (COSEWIC) and with the Committee on the Status of Species at Risk in Ontario (COSSARO). By 2001, protection was extended to eastern wolves occurring on the outskirts of the Park, thus no longer depriving Park eastern wolves of future pure-blooded mates. By 2012, the genetic composition of the Park's eastern wolves was roughly restored to what it was in the mid-1960s, rather than in the 1980s–1990s, when the majority of wolves had large amounts of coyote DNA.<ref name=rutledge>{{Cite journal | doi = 10.1002/ece3.61| pmid = 22408723| title = Intense harvesting of eastern wolves facilitated hybridization with coyotes| journal = Ecology and Evolution| volume = 2| issue = 1| pages = 19–33| year = 2012| last1 = Rutledge | first1 = L. Y. | last2 = White | first2 = B. N. | last3 = Row | first3 = J. R. | last4 = Patterson | first4 = B. R. | pmc = 3297175}}</ref>{{clear}}

Aside from the combinations of coyotes and eastern wolves making up most of the modern day eastern coyote's genepools, a study in 2013 by mammalian biologist Dr. Javier Monzón revealed that some of the coyotes in the northeastern USA also have mild domestic dogs (Canis lupus familiaris) and western Great Plains gray wolf (Canis lupus nubilus) influences in their genepool, thus suggesting that the eastern coyote is actually a four-in-one hybrid of coyotes, eastern wolves, western gray wolves, and dogs; and that the hybrids living in areas with higher white-tailed deer density often have higher degrees of wolf genes than those living in urban environments. The addition of domestic dog genes may have played a minor role in facilitating the eastern hybrids' adaptability to survive in human developed areas.<ref>http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3899836/</ref> The four-in-one hybrid theory was further explored in 2014, when Monzón and his team subsequently re-analyzed the tissue and SNP samples taken from 425 eastern coyotes to determine the degree of wolf and dog introgressions involved in each geographic range.<ref>http://www.gothamcoyote.com/2014/01/its-coyote-wolf-dog-eat-dog-world.html</ref> The team discovered that the domestic dog allele averages 10% of the eastern coyote's genepool, while the eastern wolf alleles averages 13% and western gray wolves contribute another 13%. The remaining 64% matched mostly with coyotes. This analysis suggested that there may have been multiple swarms of genetic exchanges between the coyotes, feral dogs, and the other two distinct wolf populations present in the Great Lakes region.

====Great Lakes boreal hybrids====

The taxonomy of the [[Great Lakes boreal wolf]] has long been debated by many North American mammalian biologists. Studies of the molecular-genetic literature on the wolf-like canids in the Great Lakes region have given rise to two disparate schools of thought: one group has argued that the animals are hybrids between western gray wolves and eastern wolves,<ref name=wilson2000>{{Cite journal | doi = 10.1139/z00-158|url=https://www.researchgate.net/publication/229189481_DNA_profiles_of_the_eastern_Canadian_wolf_and_the_red_wolf_provide_evidence_for_a_common_evolutionary_history_independent_of_the_gray_wolf| title = DNA profiles of the eastern Canadian wolf and the red wolf provide evidence for a common evolutionary history independent of the gray wolf| journal = Canadian Journal of Zoology| volume = 78| issue = 12| pages = 2156| year = 2000| last1 = Wilson | first1 = P. J. | last2 = Grewal | first2 = S. | last3 = Lawford | first3 = I. D. | last4 = Heal | first4 = J. N. | last5 = Granacki | first5 = A. G. | last6 = Pennock | first6 = D. | last7 = Theberge | first7 = J. B. | last8 = Theberge | first8 = M. T. | last9 = Voigt | first9 = D. R. | last10 = Waddell | first10 = W. | last11 = Chambers | first11 = R. E. | last12 = Paquet | first12 = P. C. | last13 = Goulet | first13 = G. | last14 = Cluff | first14 = D. | last15 = White | first15 = B. N. }}</ref><ref>{{Cite journal | doi = 10.1139/z11-097|url=http://www.wolf.org/wp-content/uploads/2013/08/329usecranialcharacters_mnwolves.pdf| title = Use of cranial characters in taxonomy of the Minnesota wolf (''Canis'' sp.)| journal = Canadian Journal of Zoology| volume = 89| issue = 12| pages = 1188| year = 2011| last1 = Mech | first1 = L. D. | last2 = Nowak | first2 = R. M. | last3 = Weisberg | first3 = S. }}</ref> the other that the hybrids derive from an extinct Pre-Columbian coyote population and a unique population of ecotype gray wolves.<ref>{{Cite journal | doi = 10.2307/2409486| jstor = 2409486| title = Introgression of Coyote Mitochondrial DNA into Sympatric North American Gray Wolf Populations| journal = Evolution| volume = 45| pages = 104| year = 1991| last1 = Lehman | first1 = N. | last2 = Eisenhawer | first2 = A. | last3 = Hansen | first3 = K. | last4 = Mech | first4 = L. D. | last5 = Peterson | first5 = R. O. | last6 = Gogan | first6 = P. J. P. | last7 = Wayne | first7 = R. K. }}</ref><ref>{{Cite journal | doi = 10.1111/j.1365-294X.2009.04176.x| title = Origin and status of the Great Lakes wolf| journal = Molecular Ecology| volume = 18| issue = 11| pages = 2313| year = 2009| last1 = Koblmüller | first1 = S. | last2 = Nord | first2 = M. | last3 = Wayne | first3 = R. K. | last4 = Leonard | first4 = J. A. }}</ref> The latter group asserts that the eastern wolf is a genetically distinct subspecies of the gray wolf with mild coyote introgression. Evolutionary biologists who analyzed 48,000 [[single nucleotide polymorphism]] detected patterns of gray wolf and coyote admixture in the Great Lakes boreal wolves and thus interpreted these findings as evidences of ancient hybridizations between gray wolves and coyotes.<ref>{{Cite journal
| last1 = Vonholdt | first1 = B. M.
| last2 = Pollinger | first2 = J. P.
| last3 = Earl | first3 = D. A.
| last4 = Knowles | first4 = J. C.
| last5 = Boyko | first5 = A. R.
| last6 = Parker | first6 = H.
| last7 = Geffen | first7 = E.
| last8 = Pilot | first8 = M.
| last9 = Jedrzejewski | first9 = W.
| last10 = Jedrzejewska
| doi = 10.1101/gr.116301.110 | first10 = B.
| last11 = Sidorovich | first11 = V.
| last12 = Greco | first12 = C.
| last13 = Randi | first13 = E.
| last14 = Musiani | first14 = M.
| last15 = Kays | first15 = R.
| last16 = Bustamante | first16 = C. D.
| last17 = Ostrander | first17 = E. A.
| last18 = Novembre | first18 = J.
| last19 = Wayne | first19 = R. K.
| title = A genome-wide perspective on the evolutionary history of enigmatic wolf-like canids
| journal = Genome Research
| volume = 21
| issue = 8
| pages = 1294–1305
| year = 2011
| pmid = 21566151
| pmc =3149496
}}</ref> Those who were critical of the genome research's interpretation, however, re-analyzed the data and compared them to samples taken from eastern wolves in [[Algonquin Provincial Park]]. This group found that some of the gray wolf genes were also admixed with eastern wolves and interpreted the coyote-like haplotypes as eastern wolf DNA. However, subsequent analysis on mtDNA, autosomal and sex chromosomes suggests that the wolves in the Great Lakes boreal forests are actually hybrids of all three Canis species.<ref name=rutledge2>Rutledge, L. Y. (May 2010). [http://people.trentu.ca/~brentpatterson/index_files/Rutledge_PhD_COMPLETE_Jan27_10.pdf Evolutionary origins, social structure, and hybridization of the eastern wolf (''Canis lycaon'')], [thesis], Trent University, Peterborough, Ontario, Canada</ref> Since pure gray wolves in the wild rarely interbreed with pure coyotes, it is suspected that earlier hybrids between gray and eastern wolves from the western Great Lakes boreal forests may had hybridized with hybrids between eastern wolves and coyotes on the eastern half, thus forming the modern day hybrids in the Great Lakes region.

===Red wolf-coyote hybrids===
Due to intensive persecution, forest clearing, road building, and perhaps the decline in deer populations throughout the 1900s, red wolves were eliminated from most of their historic range, being reduced to a small population in [[Louisiana]] and [[Texas]] by the 1960s. This limited range was also occupied by coyotes, which began to hybridize with the remaining red wolves, to the point that the [[U.S. Fish and Wildlife Service]] listed the species as [[endangered]] in 1967. The Service initiated a captive breeding program in 1973, with over 400 wild canids being captured for the purpose, though only 10% of this stock was determined to be of pure red wolf stock. Fourteen of the captured animals were ultimately released into northeastern [[North Carolina]] in 1986, though coyotes began to colonize the area in the early 1990s, resulting in the creation of hybrid offspring. The Wildlife Service's current management strategy consists of sterilizing hybrids, though the identification of hybrids with more than 50% red wolf ancestry is difficult based on appearance alone, so they are instead identified through assignment tests based on microsatellite
loci.<ref name="fredrickson2005">{{cite journal | author = Fredrickson R. J.|author2= Hedrick P. W. | year = 2005 | title = Dynamics of Hybridization and Introgression in Red Wolves and Coyotes | journal = Conservation Biology | volume = 20 | issue = 4| pages = 1272–1283 | doi=10.1111/j.1523-1739.2006.00401.x| pmid = 16922243 }}</ref>
{{clear}}

==See also==
{{Portal|Dogs|Mammals}}
*[[Canid hybrid]]
*[[Jackal-dog hybrid]]
*[[Wolf-dog hybrid]]
*[[Coydog]]

==References==
{{reflist|colwidth=30em}}

==Further reading==
* {{cite journal | last1 = Adams | first1 = J.R. | last2 = Kelly | first2 = B.T. | last3 = Waits | first3 = L.P. | year = 2003 | title = Using faecal DNA sampling and GIS to monitor hybridization between red wolves (''Canis rufus'') and coyote (''Canis latrans'') | journal = Mol. Ecol. | volume = 12 | issue = 8 | pages = 2175–2186 | doi=10.1046/j.1365-294x.2003.01895.x| pmid = 12859637 }}
* {{cite journal | last1 = McCarley | first1 = H. | title = The taxonomic status of wild ''Canis'' (Canidae) in the south central United States | journal = Southwest. Nat. | volume = 1962 | issue = 7| pages = 227–235 }}
* {{cite journal | last1 = Wayne | first1 = R.K. | last2 = Jenks | first2 = S.M. | year =1991 | title = Mitochondrial DNA analysis implying extensive hybridization of the endangered red wolf ''Canis rufus'' | journal = Nature | volume = 351| pages = 565–568 | doi=10.1038/351565a0 | issue=6327| bibcode = 1991Natur.351..565W }}

== External links ==
* The complicated science of studying coyotes and hybrid species: [http://www.nytimes.com/2010/09/28/science/28coyotes.html Mysteries That Howl and Hunt]
* [http://news.nationalgeographic.com/news/2002/12/1217_021226_tvinterbreeding.html Interbreeding Threatens Rare Species, Experts Say]
* [http://www.easterncoyoteresearch.com/ Eastern Coyote/Coywolf Research]
* [http://www.pbs.org/wnet/nature/coywolf-meet-the-coywolf/8605/ "Meet the Coywolf" episode of PBS' Nature series (premiere 22 Jan 2014)]

{{Mammal hybrids}}

[[Category:Canid hybrids]]
[[Category:Mammal hybrids]]

Biosignatur

2015-09-26T15:19:55Z

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{{other uses2|Biomarker}}
A '''biosignature''' is any substance – such as an element, [[isotope]], [[molecule]], or [[phenomenon]] – that provides [[scientific evidence]] of past or present [[life]].<ref name=SSG >{{Cite book| last2=Beaty | last=Steele| contribution=Final report of the MEPAG Astrobiology Field Laboratory Science Steering Group (AFL-SSG)| title=The Astrobiology Field Laboratory | publisher=the Mars Exploration Program Analysis Group (MEPAG) - NASA| place=U.S.A.| pages=72| date=September 26, 2006| id= | contribution-url=http://mepag.jpl.nasa.gov/reports/AFL_SSG_WHITE_PAPER_v3.doc| chapter-format=.doc| postscript=. |display-authors=etal}}</ref><ref>{{cite web | url = http://www.science-dictionary.com/definition/biosignature.html | title = Biosignature - definition | accessdate = 2011-01-12 | year = 2011 | work = Science Dictionary}}</ref><ref name='Biosignatures 2011'>{{cite journal | title = Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group | journal = The Astrobiology Journal | date = 23 February 2011 | first = Roger E. | last = Summons |author2=Jan P. Amend |author3=David Bish |author4=Roger Buick |author5=George D. Cody |author6=David J. Des Marais | volume = 11 | issue = 2 | pages = 157–81 | doi = 10.1089/ast.2010.0506 | url = http://eaps.mit.edu/geobiology/recent%20pubs/AST-2010-0506-Summons_Mars%20Taphonomy.pdf | accessdate = 2013-06-22|bibcode = 2011AsBio..11..157S | pmid=21417945| last7 = Dromart | first7 = G | last8 = Eigenbrode | first8 = J. L. | last9 = Knoll | first9 = A. H. | last10 = Sumner | first10 = D. Y. }}</ref> Measurable attributes of life include its complex physical and chemical structures and also its utilization of [[Thermodynamic free energy|free energy]] and the production of [[biomass]] and [[Cellular waste product|wastes]]. Due to its unique characteristics, a biosignature can be interpreted as having been produced by living [[organisms]]; however, it is important that they not be considered definitive because there is no way of knowing in advance which ones are universal to life and which ones are unique to the peculiar circumstances of life on Earth.<ref>{{cite web | url = http://astrobiology.nasa.gov/nai/library-of-resources/annual-reports/2003/cub/projects/philosophical-issues-in-astrobiology/ | title = Philosophical Issues in Astrobiology | accessdate = 2011-04-15 | last = Carol Cleland |author2=Gamelyn Dykstra|author3=Ben Pageler | year = 2003 | publisher = NASA Astrobiology Institute}}</ref> Nonetheless, [[life forms]] are known to shed unique chemicals, including [[DNA]], into the [[Natural environment|environment]] as evidence of their presence in a particular location.<ref name="NYT-20150122">{{cite news |last=Zimmer |first=Carl |authorlink=Carl Zimmer |title=Even Elusive Animals Leave DNA, and Clues, Behind |url=http://www.nytimes.com/2015/01/27/science/even-elusive-animals-leave-dna-and-clues-behind.html |date=January 22, 2015 |work=[[New York Times]] |accessdate=January 23, 2015 }}</ref>

==In geomicrobiology==
[[File:Calcidiscus leptoporus 05.jpg|thumb|Electron micrograph of microfossils from a sediment core obtained by the [[Deep Sea Drilling Program]] ]]
The ancient record on Earth provides an opportunity to see what geochemical signatures are produced by microbial life and how these signatures are preserved over geologic time. Some related disciplines such as [[geochemistry]], [[geobiology]], and [[geomicrobiology]] often use biosignatures to determine if living [[organism]]s are or were present in a sample. These possible biosignatures include: (a) [[microfossils]] and [[stromatolites]]; (b) molecular structures ([[biomarkers]]) and [[Isotope|isotopic compositions]] of carbon, nitrogen and hydrogen in [[organic matter]]; (c) multiple sulfur and oxygen isotope ratios of minerals; and (d) abundance relationships and isotopic compositions of redox sensitive metals (e.g., Fe, Mo, Cr, and rare earth elements).<ref name='PSARC'>{{cite web | url = http://php.scripts.psu.edu/dept/psarc/index.php?page=executive-summary | title = SIGNATURES OF LIFE FROM EARTH AND BEYOND | accessdate = 2011-01-14 | year = 2009 | work = Penn State Astrobiology Research Center (PSARC) | publisher = Penn State}}</ref><ref>{{cite web | url = http://astrobiology.nasa.gov/articles/2008/7/30/reading-archaean-biosignatures/ | title = Reading Archaean Biosignatures | accessdate = 2014-11-23 | first1 = David | last1 = Tenenbaum | date = July 30, 2008 | publisher = NASA}}</ref>

For example, the particular [[fatty acids]] measured in a sample can indicate which types of [[bacterium|bacteria]] and [[archaea]] live in that environment. Another example are the long-chain [[fatty alcohol]]s with more than 23 atoms that are produced by [[plankton]]ic [[bacteria]].<ref>[http://www.cyberlipid.org/simple/simp0003.htm Fatty alcohols]</ref> When used in this sense, geochemists often prefer the term [[biomarker]]. An other example is the presence of straight-chain [[lipids]] in the form of [[alkanes]], [[alcohols]] an [[fatty acids]] with 20-36 [[carbon]] atoms in soils or sediments. [[Peat]] deposits are an indication of originating from the [[epicuticular wax]] of higher [[plant]]s.

Life processes may produce a range of biosignatures such as [[nucleic acids]], [[lipid]]s, [[protein]]s, [[amino acid]]s, [[kerogen]]-like material and various morphological features that are detectable in rocks and sediments.<ref name=Beegle >{{cite journal|title=A Concept for NASA's Mars 2016 Astrobiology Field Laboratory |journal=Astrobiology|date=August 2007|first=Luther W.|last=Beegle|volume=7 |issue=4|pages=545–577|id= |url=http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0153?cookieSet=1|format=|accessdate=2009-07-20|doi=10.1089/ast.2007.0153|postscript=. |pmid=17723090 |bibcode=2007AsBio...7..545B|last3=Abilleira|first3=Fernando|last4=Jordan|first4=James F.|last5=Wilson|first5=Gregory R.|display-authors=etal}}</ref>
[[Microbes]] often interact with geochemical processes, leaving features in the rock record indicative of biosignatures. For example, bacterial micrometer-sized pores in [[carbonate rock]]s resemble inclusions under transmitted light, but have distinct size, shapes and patterns (swirling or dendritic) and are distributed differently from common fluid inclusions.<ref>{{cite journal | title = Micrometer-scale porosity as a biosignature in carbonate crusts | last1 = Bosak | journal = Geology | date = May 18, 2004 | first = Tanja Bosak | author2 = Virginia Souza-Egipsy, Frank A. Corsetti and Dianne K. Newman | volume = 32 | issue = 9 | pages = 781–784 | doi = 10.1130/G20681.1 | url = http://geology.gsapubs.org/content/32/9/781.abstract | accessdate = 2011-01-14 | bibcode=2004Geo....32..781B| last3 = Corsetti | first3 = Frank A. | last4 = Newman | first4 = Dianne K. }}</ref> A potential biosignature is a phenomenon that ''may'' have been produced by life, but for which alternate [[Abiotic component|abiotic]] origins may also be possible.

==In astrobiology==
[[File:ALH84001 structures.jpg|thumb|left|200px|Some researchers suggested that these microscopic structures on the Martian [[ALH84001]] meteorite could be fossilized bacteria.<ref name=disbelief>{{cite web | title=After 10 years, few believe life on Mars | url=http://www.usatoday.com/tech/science/space/2006-08-06-mars-life_x.htm | last=Crenson | first=Matt | publisher=[[Associated Press]] (on [http://www.usatoday.com/ usatoday.com]) | date=2006-08-06 | accessdate=2009-12-06}}</ref><ref name="life">{{cite journal |last=McKay |first=David S. |authorlink= |year=1996 |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |journal=Science |pmid=8688069 |volume=273 |issue=5277 |pages=924–930 |doi=10.1126/science.273.5277.924 |url= |accessdate= |quote= |bibcode=1996Sci...273..924M|last3=Thomas-Keprta |first3=Kathie L. |last4=Vali |first4=Hojatollah |last5=Romanek |first5=Christopher S. |last6=Clemett |first6=Simon J. |last7=Chillier |first7=Xavier D. F. |last8=Maechling |first8=Claude R. |last9=Zare |first9=Richard N. |display-authors=etal}}</ref>]]
[[Astrobiology|Astrobiological exploration]] is founded upon the premise that biosignatures encountered in space will be recognizable as [[extraterrestrial life]]. The usefulness of a biosignature is determined, not only by the probability of life creating it, but also by the improbability of nonbiological (abiotic) processes producing it.<ref name=astrobiology >{{cite web|url=http://astrobiology.arc.nasa.gov/roadmap/g5.html |title=Understand the evolutionary mechanisms and environmental limits of life |accessdate=2009-07-13 |last=Rothschild |first=Lynn |date=September 2003 |publisher=NASA }}</ref> An example of such a biosignature might be complex [[Organic compound|organic molecules]] and/or structures whose formation is virtually unachievable in the absence of life. For example, some categories of biosignatures can include the following: cellular and extracellular morphologies, [[biogenic substance]] in rocks, bio-organic molecular structures, [[chirality]], [[Biogenic silica|biogenic minerals]], biogenic stable isotope patterns in minerals and organic compounds, atmospheric gases, and remotely detectable features on planetary surfaces, such as [[photosynthetic pigment]]s, etc.<ref name=astrobiology />

Biosignatures need not be chemical, however, and can also be suggested by a distinctive [[magnetic]] biosignature.<ref name="Wall-20111213">{{cite web |last=Wall |first=Mike |title=Mars Life Hunt Could Look for Magnetic Clues |url=http://www.space.com/13911-mars-life-search-magnetic-signatures.html |date=13 December 2011 |publisher=[[Space.com]] |accessdate=2011-12-15 }}</ref> Another possible biosignature might be [[Morphology (biology)|morphology]] since the shape and size of certain objects may potentially indicate the presence of past or present life. For example, microscopic [[magnetite]] crystals in the Martian [[meteorite]] [[ALH84001]] were the longest-debated of several potential biosignatures in that specimen because it was believed until recently that only bacteria could create crystals of their specific shape. However, anomalous features discovered that are "possible biosignatures" for life forms would be investigated as well. Such features constitute a working [[hypothesis]], not a confirmation of detection of life. Concluding that evidence of an extraterrestrial life form (past or present) has been discovered, requires proving that a possible biosignature was produced by the activities or remains of life.<ref name=SSG /> For example, the possible [[Biomineralisation|biomineral]] studied in the Martian [[ALH84001|ALH84001 meteorite]] includes putative microbial [[fossils]], tiny rock-like structures whose shape was a potential biosignature because it resembled known bacteria. Most scientists ultimately concluded that these were far too small to be fossilized [[cell (biology)|cell]]s. A consensus that has emerged from these discussions, and is now seen as a critical requirement, is the demand for further lines of evidence in addition to any morphological data that supports such extraordinary claims.<ref name=SSG />
[[File:PIA19088-MarsCuriosityRover-MethaneSource-20141216.png|thumb|right|300px|[[Atmosphere of Mars#Methane|Methane]] (CH4) on Mars - potential sources and sinks.]]
Scientific observations include the possible identification of biosignatures through indirect observation. For example, [[Electromagnetic radiation|electromagnetic]] information through infrared radiation telescopes, radio-telescopes, space telescopes, etc.<ref name='Gardner'>{{cite web | url = http://www.kurzweilai.net/the-physical-constants-as-biosignature-an-anthropic-retrodiction-of-the-selfish-biocosm-hypothesis | title = The Physical Constants as Biosignature: An anthropic retrodiction of the Selfish Biocosm Hypothesis | accessdate = 2011-01-14 | last = Gardner | first = James N. | date = February 28, 2006 | publisher = Kurzweil}}</ref><ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> From this discipline, the hypothetical electromagnetic radio signatures that [[SETI]] scans for would be a biosignature, since a message from intelligent aliens would certainly demonstrate the existence of extraterrestrial life.

On [[Mars]], surface oxidants and UV radiation will have altered or destroyed organic molecules at or near the surface.<ref name='Biosignatures 2011'/> One issue that may add ambiguity in such a search is the fact that, throughout Martian history, abiogenic organic-rich [[Chondrite|chondritic meteorite]]s have undoubtedly rained upon the Martian surface. At the same time, strong [[Oxidizing agent|oxidants]] in [[Martian soil]] along with exposure to [[ionizing radiation]] might alter or destroy molecular signatures from meteorites or organisms.<ref name='Biosignatures 2011'/> An alternative approach would be to seek concentrations of buried crystalline minerals, such as [[clay]]s and [[evaporite]]s, which may protect organic matter from the destructive effects of [[ionizing radiation]] and strong oxidants.<ref name='Biosignatures 2011'/> The search for Martian biosignatures has become
more promising due to the discovery that surface and near-surface aqueous environments existed on Mars at the same time when biological organic matter was being preserved in ancient aqueous sediments on Earth.<ref name='Biosignatures 2011'/>

;Atmosphere
Over billions of years, the processes of life on a planet would result in a mixture of chemicals unlike anything that could form in an ordinary chemical equilibrium.<ref>{{cite web | url = https://www.technologyreview.com/blog/arxiv/26247/ | title = Artificial Life Shares Biosignature With Terrestrial Cousins | accessdate = 2011-01-14 | date = 10 January 2011 | work = The Physics arXiv Blog | publisher = MIT}}</ref> For example, large amounts of [[oxygen]] and small amounts of [[methane]] are generated by life on Earth. The presence of methane in the atmosphere of [[Mars]] indicates that there must be an active source on the planet, as it is an unstable [[gas]]. Furthermore, current photochemical models cannot explain the presence of methane in the atmosphere of Mars and its reported rapid variations in space and time. Neither its fast appearance nor disappearance can be explained yet.<ref>[http://mepag.jpl.nasa.gov/decadal/TGM_Mars_Panel-cleared-9-4-09.ppt Mars Trace Gas Mission] (September 10, 2009)</ref> To rule out a biogenic origin for the methane, a future probe or lander hosting a [[mass spectrometer]] will be needed, as the isotopic proportions of [[carbon-12]] to [[carbon-14]] in methane could distinguish between a biogenic and non-biogenic origin.<ref name="nasa">[http://rst.gsfc.nasa.gov/Sect19/Sect19_13a.html Remote Sensing Tutorial, Section 19-13a] - Missions to Mars during the Third Millennium, Nicholas M. Short, Sr., et al., NASA</ref> In June, 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of [[life on Mars (planet)|life on Mars]].<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |url=http://www.pnas.org/content/109/25/9750.abstract |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |accessdate=June 27, 2012 |bibcode = 2012PNAS..109.9750O |pmid=22679287 |pmc=3382529}}</ref><ref name="Space-20120625">{{cite web|author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet t Boötis b |url=http://www.nature.com/nature/journal/v486/n7404/full/nature11161.html?WT.ec_id=NATURE-20120628 |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |accessdate=June 28, 2012 |arxiv = 1206.6109 |bibcode = 2012Natur.486..502B |issue=7404}}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref> The planned [[ExoMars Trace Gas Orbiter]] to be launched in 2016 to Mars, will study [[Atmosphere of Mars|atmospheric trace gases]] and will attempt to characterize potential biochemical and geochemical processes at work.<ref name='June 2011'>{{citation |author1= Mark Allen |author2= = Olivier Witasse | contribution = 2016 ESA/NASA ExoMars Trace Gas Orbiter | title = MEPAG June 2011 | publisher = Jet Propulsion Laboratory | date = June 16, 2011| id = | contribution-url = http://mepag.jpl.nasa.gov/meeting/jun-11/13-EMTGO_MEPAG_June2011_presentation-rev2.pdf }} (PDF)</ref>

===The Viking missions to Mars===
{{Main|Viking biological experiments}}
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] with a model of the Viking lander]]
The [[Viking Lander|Viking missions]] to Mars in the 1970s conducted the first experiments which were explicitly designed to look for biosignatures on another planet. Each of the two [[Viking landers]] carried three [[Viking Biological Experiments|life-detection experiments]] which looked for signs of [[metabolism]]; however, the results were declared 'inconclusive'.<ref name=Beegle >{{cite journal|title=A Concept for NASA's Mars 2016 Astrobiology Field Laboratory |journal=Astrobiology|date=August 2007|first=LUTHER W.|last=BEEGLE |volume=7 | issue = 4|pmid=17723090 |pages=545–577|id= | url=http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0153?cookieSet=1 |format= |accessdate=2009-07-20| doi=10.1089/ast.2007.0153 | bibcode=2007AsBio...7..545B|last3=Abilleira|first3=Fernando|last4=Jordan|first4=James F.|last5=Wilson|first5=Gregory R.|display-authors=etal}}</ref><ref>Levin, G and P. Straaf. 1976. Viking Labeled Release Biology Experiment: Interim Results. Science: vol: 194. pp: 1322-1329.</ref><ref name="Chambers">{{Cite book| first = Paul | last = Chambers| title = Life on Mars; The Complete Story|place = London| publisher = Blandford| year = 1999 |isbn = 0-7137-2747-0}}</ref><ref>{{cite journal | title = The Viking Biological Investigation: Preliminary Results |journal = Science|date = 1976-10-01 |first = Harold P. | last = Klein|author2=Levin, Gilbert V. | volume = 194 | issue = 4260 | pages = 99–105 | doi = 10.1126/science.194.4260.99 | url = http://www.sciencemag.org/cgi/content/abstract/194/4260/99 | accessdate = 2008-08-15
| pmid = 17793090 | bibcode=1976Sci...194...99K|last3 = Levin|first3 = Gilbert V.|last4 = Oyama|first4 = Vance I.|last5 = Lederberg|first5 = Joshua|last6 = Rich|first6 = Alexander|last7 = Hubbard|first7 = Jerry S.|last8 = Hobby|first8 = George L.|last9 = Straat|first9 = Patricia A.|last10 = Berdahl|first10 = Bonnie J.|last11 = Carle|first11 = Glenn C.|last12 = Brown|first12 = Frederick S.|last13 = Johnson|first13 = Richard D.}}</ref><ref name=ExoMars>[http://www.esa.int/SPECIALS/ExoMars/SEMK39JJX7F_0.html ExoMars rover]</ref>

===Mars Science Laboratory===
{{Main|Timeline of Mars Science Laboratory}}
The ''Curiosity'' rover from the [[Mars Science Laboratory]] mission, is currently assessing the potential past and present [[planetary habitability|habitability]] of the Martian environment and is attempting to detect biosignatures on the surface of Mars.<ref name='Biosignatures 2011'/> Considering the MSL instrument payload package, the following classes of biosignatures are within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.<ref name='Biosignatures 2011'/> The ''Curiosity'' rover targets [[outcrop]]s to maximize the probability of detecting 'fossilized’ [[organic matter]] preserved in sedimentary deposits.

On January 24, 2014, NASA reported that current studies by the [[Curiosity (rover)|''Curiosity'']] and [[Opportunity (rover)|''Opportunity'']] [[Mars rover|rovers]] on the planet Mars will now be searching for evidence of ancient life, including a [[biosphere]] based on [[autotroph]]ic, [[chemotroph]]ic and/or [[Lithotroph#Chemolithotrophs|chemolithoautotrophic]] [[microorganism]]s, as well as ancient water, including [[Lacustrine plain|fluvio-lacustrine environments]] ([[plain]]s related to ancient [[river]]s or [[lake]]s) that may have been [[Planetary habitability|habitable]].<ref name="SCI-20140124a">{{cite journal |last=Grotzinger |first=John P.|title=Introduction to Special Issue - Habitability, Taphonomy, and the Search for Organic Carbon on Mars|url=http://www.sciencemag.org/content/343/6169/386 |journal=[[Science (journal)|Science]] |date=January 24, 2014 |volume=343 |number=6169 |pages=386–387 |doi=10.1126/science.1249944 |accessdate=January 24, 2014 |bibcode=2014Sci...343..386G}}</ref><ref name="SCI-20140124special">{{cite journal |authors=Various |title=Special Issue - Table of Contents - Exploring Martian Habitability |url=http://www.sciencemag.org/content/343/6169.toc#SpecialIssue|date=January 24, 2014|journal=[[Science (journal)|Science]] |volume=343 |number=6169 |pages=345–452|accessdate=January 24, 2014 }}</ref><ref name="SCI-20140124">{{cite journal |authors=Various |title=Special Collection - Curiosity - Exploring Martian Habitability|url=http://www.sciencemag.org/site/extra/curiosity/|date=January 24, 2014 |journal=[[Science (journal)|Science]] |accessdate=January 24, 2014 }}</ref><ref name="SCI-20140124c">{{cite journal |title=A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars |url=http://www.sciencemag.org/content/343/6169/1242777 |date=January 24, 2014 |journal=[[Science (journal)|Science]] |volume=343 |number=6169 |pages=1242777 |doi=10.1126/science.1242777 |accessdate=January 24, 2014 |last1=Grotzinger |first1=J. P. |last2=Sumner |first2=D. Y. |last3=Kah |first3=L. C. |last4=Stack |first4=K. |last5=Gupta |first5=S. |last6=Edgar |first6=L. |last7=Rubin |first7=D. |last8=Lewis |first8=K. |last9=Schieber |first9=J. |last10=Mangold |first10=N. |last11=Milliken |first11=R. |last12=Conrad |first12=P. G. |last13=Desmarais |first13=D. |last14=Farmer |first14=J. |last15=Siebach |first15=K. |last16=Calef |first16=F. |last17=Hurowitz |first17=J. |last18=McLennan |first18=S. M. |last19=Ming |first19=D. |last20=Vaniman |first20=D. |last21=Crisp |first21=J. |last22=Vasavada |first22=A. |last23=Edgett |first23=K. S. |last24=Malin |first24=M. |last25=Blake |first25=D. |last26=Gellert |first26=R. |last27=Mahaffy |first27=P. |last28=Wiens |first28=R. C. |last29=Maurice |first29=S. |last30=Grant |first30=J. A. |displayauthors=1 |bibcode = 2014Sci...343A.386G }}</ref> The search for evidence of [[Planetary habitability|habitability]], [[taphonomy]] (related to [[fossils]]), and [[organic carbon]] on the planet Mars is now a primary [[NASA]] objective.<ref name="SCI-20140124a">{{cite journal |last=Grotzinger |first=John P.|title=Introduction to Special Issue - Habitability, Taphonomy, and the Search for Organic Carbon on Mars|url=http://www.sciencemag.org/content/343/6169/386 |journal=[[Science (journal)|Science]] |date=January 24, 2014 |volume=343 |number=6169 |pages=386–387 |doi=10.1126/science.1249944 |accessdate=January 24, 2014 |bibcode=2014Sci...343..386G}}</ref><ref name="SCI-20140124special">{{cite journal |authors=Various |title=Special Issue - Table of Contents - Exploring Martian Habitability |url=http://www.sciencemag.org/content/343/6169.toc#SpecialIssue|date=January 24, 2014|journal=[[Science (journal)|Science]] |volume=343 |number=6169 |pages=345–452|accessdate=January 24, 2014 }}</ref>

===ExoMars===
The 2016 [[Trace Gas Orbiter]] (TGO) will be a Mars telecommunications orbiter and atmospheric gas analyzer mission. It will deliver the ExoMars EDM lander and then proceed to map the sources of [[Atmosphere of Mars#Methane|methane on Mars]] and other gases, and in doing so, help select the landing site for the ExoMars [[Rover (space exploration)|rover]] to be launched on 2018.<ref>{{cite news | first = Boris | last = Pavlishchev | title = ExoMars program gathers strength | date = Jul 15, 2012 | url = http://english.ruvr.ru/2012_07_15/ExoMars-program-gathers-strength/ | work = The Voice of Russia | accessdate = 2012-07-15}}</ref> The primary objective of the 2018 [[ExoMars]] rover mission is the search for biosignatures on the surface and subsurface by using a drill able to collect samples down to a depth of {{convert|2|m|ft}}.<ref name=ExoMars/><ref name="MSL-main_page">{{cite web|title=Mars Science Laboratory: Mission |url= http://marsprogram.jpl.nasa.gov/msl/mission/ |publisher=NASA/JPL |accessdate=2010-03-12 }}</ref>

==See also==
{{Portal|Astrobiology}}
{{cmn|2|
*[[Bioindicator]]
*[[Biomarker]]
*[[Planetary habitability]]
*[[Taphonomy]]
*[[Technosignature]]
}}

== References ==
{{reflist|30em}}
{{Extraterrestrial life}}

[[Category:Astrobiology]]
[[Category:Bioindicators]]
[[Category:Biology terminology]]
[[Category:Astrochemistry]]

AS 314

2015-09-12T18:11:48Z

Bibcode Bot: Adding 1 arxiv eprint(s), 0 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Starbox begin
| name = V452 Scuti}}
{{Starbox observe
| epoch = J2000
| ra = {{nowrap|{{RA|18|39|26.10612}}<ref name=hipparcos>{{cite journal|bibcode=2007A&A...474..653V|title=Validation of the new Hipparcos reduction|journal=Astronomy and Astrophysics|volume=474|issue=2|pages=653|author1=Van Leeuwen|first1=F.|year=2007|doi=10.1051/0004-6361:20078357|arxiv = 0708.1752 }}</ref>}}
| dec = {{DEC|-13|50|47.1892}}<ref name=hipparcos/>
| appmag_v = 9.85<ref name=kozok>{{cite journal|bibcode=1985A&AS...61..387K|title=Photometric observations of emission B-stars in the southern Milky Way|journal=Astronomy and Astrophysics Supplement Series (ISSN 0365-0138)|volume=61|pages=387|author1=Kozok|first1=J. R.|year=1985}}</ref>
| constell = [[Scutum]]
}}
{{Starbox character
| class = A0Ia+<ref name=miroshnichenko>{{Cite journal | author = Miroshnichenko, A. S.; Chentsov, E. L.; Klochkova, V. G. | date = June 2000 | journal = [[Astronomy and Astrophysics]] | volume = 144 | pages = 379–389 | title = AS 314: A dusty A-type hypergiant | bibcode = 2000A&AS..144..379M | doi = 10.1051/aas:2000216 | postscript = |arxiv = }}</ref>
| b-v=+0.89<ref name=kozok/>
| u-b=+0.12<ref name=kozok/>
| v-r=
| variable=[[Luminous blue variable|cLBV]]<ref name=naze>{{cite journal|doi=10.1051/0004-6361/201118040|title=The first X-ray survey of Galactic luminous blue variables|journal=Astronomy & Astrophysics|volume=538|pages=A47|year=2012|last1=Nazé|first1=Y.|last2=Rauw|first2=G.|last3=Hutsemékers|first3=D.|bibcode=2012A&A...538A..47N|arxiv = 1111.6375 }}</ref>
}}
{{Starbox astrometry
| radial_v=−50.00<ref name=miroshnichenko/>
| prop_mo_ra=1.87<ref name=hipparcos/>
| prop_mo_dec=-9.55<ref name=hipparcos/>
| parallax=4,29
| p_error=1.68
| parallax_footnote=<ref name=hipparcos/>
| dist_pc=8,000<ref name=vangenderen2001/>
| dist_ly=
| absmag_v=−8.0<ref name=miroshnichenko/>
}}
{{Starbox detail
| luminosity = 79,400<ref name=vangenderen2001/>
| temperature = 10,200<ref name=vangenderen2001>
{{cite journal
|last1=van Genderen |first1=A.M.
|date=2001
|title=S Doradus variables in the Galaxy and the Magellanic Clouds
|journal=[[Astronomy & Astrophysics]]
|volume=366 |issue=2
|pages=508–531
|bibcode=2001A&A...366..508V
|doi=10.1051/0004-6361:20000022
}}</ref>
}}
{{Starbox catalog
| names = [[Variable star designation|V452]] Sct, [[Bonner Durchmusterung|BD -13°5061]], [[Hipparcos catalogue|HIP]] 91477, [[2MASS]] J18392610-1350470
}}
{{Starbox reference
| Simbad = V452+Sct
}}
{{Starbox end}}

'''AS 314''', also known as '''V452 Scuti''', is a white [[hypergiant]] [[star]] and [[luminous blue variable]] candidate located in the [[constellation]] of [[Scutum]]. It has an [[apparent magnitude]] of 9.85 and can be seen with small [[telescope]]s.

==Characteristics==
AS 314 was poorly studied until the year 2000, when Miroshnichenko ''et al.'' determined a distance for this star of around 10 kilo[[parsec]]s (32,600 [[light year]]s), a [[bolometric luminosity|luminosity]] 160,000 times that of [[Sun luminosity|Sun]] ({{Solar luminosity|link=y}}), a radius 200 times the [[Sun radius|solar radius]] ({{Solar radius|link=y}}), and an initial mass of 20 [[solar mass|solar masses]] ({{Solar mass|link=y}}). It's losing {{Solar mass|2 × 10−5|link=y}} each year (in other words, {{Solar mass|1}} every 50,000 years) through a very strong [[stellar wind]].<ref name=miroshnichenko/>

It has an [[infrared excess]], suggesting that it's shrouded in a [[circumstellar envelope]] of [[interstellar dust|dust]], which perhaps produced outbursts in the past as a [[luminous blue variable]], because its location in the [[Hertzsprung-Russell diagram]] places it near the zone occupied by those stars;<ref name=miroshnichenko/><ref name="Clark2005">{{Cite journal
| author = Clark, J. S.; Larionov, V. M.; Arkharov, A.
| date = May 2005
| journal = Astronomy and Astrophysics
| volume = 435
| issue = 1
| pages = 239–246
| title = On the population of galactic Luminous Blue Variables
| bibcode = 2005A&A...435..239C
| doi = 10.1051/0004-6361:20042563
| postscript =
|arxiv = }}</ref> however, it has not been classified as a ''bona fide'' luminous blue variable, but as a candidate.<ref name=naze/>

The Hipparcos parallax and proper motions are large and imply a much closer, and hence less luminous, star.<ref name=hipparcos/>

==References==
{{reflist}}

{{Stars of Scutum}}

[[Category:A-type hypergiants]]
[[Category:Luminous blue variables]]
[[Category:Scutum (constellation)]]
[[Category:Objects named with variable star designations|Scuti, V452]]
[[Category:Durchmusterung objects]]
[[Category:Hipparcos objects]]

Glacial Lake Columbia

2015-08-01T16:04:07Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

[[File:Map missoula floods.gif|thumb|{{legend|#00CEFF|Cordilleran Ice Sheet}}
{{legend|#FFFF00|maximum extent of Glacial Lake Missoula (eastern) and Glacial Lake Columbia (western)}}
{{legend|#FFCE00|areas swept by Missoula and Columbia floods}}]]
[[File:Lakes-Washington-Oregon-9.GIF|thumb|240px|alt= Figure showing topographic maps of Washington and northern Oregon with the lowlands flooded by the Missoula Floods marked. |Location of Glacial Lake Columbia]]
'''Glacial Lake Columbia''' was the lake formed on the ice-dammed [[Columbia River]] behind the [[Okanogan lobe]] of the [[Cordilleran Ice Sheet]] when the lobe covered {{convert|500|sqmi|km2}} of the [[Waterville Plateau]] west of [[Grand Coulee]] in central [[Washington (U.S. state)|Washington state]] during the [[Wisconsin glaciation]].<ref>The Wisconsin glaciation began about 80,000 years ago and ended around 10,000 years ago.</ref> Lake Columbia was a substantially larger version of the modern-day lake behind the [[Grand Coulee Dam]]. Lake Columbia's overflow – the diverted Columbia River – drained first through [[Foster Coulee]], and as the ice dam grew, through first [[Moses Coulee]], and finally, the [[Grand Coulee]].<ref name=usgs>{{Cite document | last = | first = | contribution = | year = | title = DESCRIPTION: Ice Sheets and Glaciations | editor-last = | editor-first = | volume = | pages = | place = | publisher = USGS | url = http://vulcan.wr.usgs.gov/Glossary/Glaciers/IceSheets/description_ice_sheets.html | accessdate = 14 November 2009 | id = | postscript = {{inconsistent citations}} }}</ref><ref name=Atwater>{{Cite journal | last = Atwater | first = Brian F. | authorlink = | coauthors = | title = Periodic floods from glacial Lake Missoula into the Sanpoil arm from of glacial Lake Columbia, northeastern Washington | journal = Geology | volume = 12 | issue = 8| pages = 464–467 | publisher = The Geological Society of America | location = | year = 1984 | url = | doi = 10.1130/0091-7613(1984)12<464:PFFGLM>2.0.CO;2 | id = | accessdate = |bibcode = 1984Geo....12..464A }}</ref>

==Glacial Lake Missoula==
The Cordilleran ice sheet also blocked the [[Clark Fork River]] and created [[Glacial Lake Missoula]], rising behind a {{convert|2000|ft|m}} high ice dam in flooded valleys of western Montana. Over 2000 years the ice dam periodically failed, releasing approximately 40 high-volume [[Missoula Floods]] of water down the Columbia River drainage, passing through glacial Lake Columbia. The largest flood is estimated to be the initial flood at 2,500 km3 (600 mi3), with subsequent floods occurring at roughly 20 to 80 year intervals.<ref name=Hendy>{{Cite journal | last = Hendy | first = Ingrid | authorlink = | coauthors = | title = A fresh perspective on the Cordilleran Ice Sheet | journal = Geology | volume = 37 | issue = | pages = 464–467 | publisher = The Geological Society of America | location = | year = 2009 | url = http://geology.gsapubs.org/content/37/1/95.full| doi =10.1130/focus012009.1 | id = | accessdate = 14 Nov 2009|bibcode = 2009Geo....37...95H }}</ref> Since Lake Columbia was impounded behind the Okanogan lobe, which rose to {{convert|1300|m|ft|sp=us}}, this lobe effectively blocked the normal course of the Columbia River, blocking the Missoula Floods and diverting water to flow across much of eastern Washington state. The erosion from the floods created the Grand Coulee as well as the [[Dry Falls]], [[Palouse Falls]], and the [[Channeled Scablands]] features of eastern Washington state.<ref name=Atwater/>

==Flood deposits==
Flood beds on the Sanpoil arm of glacial Lake Columbia show episodic flood deposits as well as deposit grading and rhythmical repetition. Since Glacial Lake Columbia remained filled between Missoula floods, annual deposits ([[varve]]s) can be observed between the Missoula flood deposits, they help to establish the periodicity of these major floods. The flood deposits can be distinguished from annually-deposited varves by both their thickness and the presence of materials foreign to the immediate drainage. Atwater reports from 35 to 55 annual varves between flood deposits in Lake Columbia, supporting a period of 35 to 55 years between ice dam failures.<ref name=Atwater/>

==References==
{{reflist|2}}

{{Ice Age Floods}}
{{Pleistocene Lakes and Seas}}

{{coord missing|Washington}}

[[Category:Former lakes|Columbia]]
[[Category:Lakes of Washington (state)|Columbia]]
[[Category:Geology of Washington (state)]]
[[Category:Glacial lakes of the United States|Columbia]]

3j-Symbol

2015-06-10T13:17:14Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

In [[quantum mechanics]], the '''Wigner 3-j symbols''', also called 3''j'' or 3''-jm'' symbols,
are related to [[Clebsch–Gordan coefficients]]
through
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\equiv \frac{(-1)^{j_1-j_2-m_3}}{\sqrt{2j_3+1}} \langle j_1 m_1 j_2 m_2 | j_3 \, {-m_3} \rangle.
</math>

== Inverse relation ==
The inverse relation can be found by noting that ''j''1 − ''j''2 − ''m''3 is an integer and making the substitution <math> m_3 \rightarrow -m_3 </math>:
:<math>
\langle j_1 m_1 j_2 m_2 | j_3 m_3 \rangle = (-1)^{-j_1+j_2-m_3}\sqrt{2j_3+1}
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & -m_3
\end{pmatrix}.
</math>

== Symmetry properties ==
The symmetry properties of 3''j'' symbols are more convenient than those of
[[Clebsch–Gordan coefficients]]. A 3''j'' symbol is invariant under an even
permutation of its columns:
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
=
\begin{pmatrix}
j_2 & j_3 & j_1\\
m_2 & m_3 & m_1
\end{pmatrix}
=
\begin{pmatrix}
j_3 & j_1 & j_2\\
m_3 & m_1 & m_2
\end{pmatrix}.
</math>
An odd permutation of the columns gives a phase factor:
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
=
(-1)^{j_1+j_2+j_3}
\begin{pmatrix}
j_2 & j_1 & j_3\\
m_2 & m_1 & m_3
\end{pmatrix}
=
(-1)^{j_1+j_2+j_3}
\begin{pmatrix}
j_1 & j_3 & j_2\\
m_1 & m_3 & m_2
\end{pmatrix}.
</math>
Changing the sign of the <math>m</math> quantum numbers also gives a phase:
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
-m_1 & -m_2 & -m_3
\end{pmatrix}
=
(-1)^{j_1+j_2+j_3}
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}.
</math>
Regge symmetries also give
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
=
\begin{pmatrix}
j_1 & \frac{j_2+j_3-m_1}{2} & \frac{j_2+j_3+m_1}{2}\\
j_3-j_2 & \frac{j_2-j_3-m_1}{2}-m_3 & \frac{j_2-j_3+m_1}{2}+m_3
\end{pmatrix}.
</math>
:<math>
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
=
(-1)^{j_1+j_2+j_3}
\begin{pmatrix}
\frac{j_2+j_3+m_1}{2} & \frac{j_1+j_3+m_2}{2} & \frac{j_1+j_2+m_3}{2}\\
j_1 - \frac{j_2+j_3-m_1}{2} & j_2 - \frac{j_1+j_3-m_2}{2} & j_3-\frac{j_1+j_2-m_3}{2}
\end{pmatrix}.
</math>
Regge symmetries account for a total of 72 symmetries.<ref>{{cite journal |first1=T. |last1=Regge
|title=Symmetry Properties of Clebsch-Gordan Coefficients |journal=Nuovo Cimento |year=1958
|volume=10 |page=544 |doi=10.1007/BF02859841}}</ref> These are best displayed by the definition of a Regge symbol
which is a one to one correspondence between it and a 3j symbol and assumes the properties of a semi-magic square<ref>{{Cite journal |first1=J. |last1=Rasch
|first2=A. C. H. |last2=Yu |title=Efficient Storage Scheme for Pre-calculated Wigner 3j, 6j and Gaunt Coefficients |journal=SIAM J. Sci. Comput. |volume=25 |issue=4 |year=2003 |pages=1416–1428 |doi=10.1137/s1064827503422932
}}</ref>
:<math>
R=
\begin{array}{|ccc|}
\hline
-j_1+j_2+j_3 & j_1-j_2+j_3 & j_1+j_2-j_3\\
j_1-m_1 & j_2-m_2 & j_3-m_3\\
j_1+m_1 & j_2+m_2 & j_3+m_3\\
\hline
\end{array}
</math>
whereby the 72 symmetries now correspond to 3! row and 3! column interchanges plus a transposition of the matrix. This can be used to devise an effective storage scheme.<ref>{{Cite journal |first1=J. |last1=Rasch |first2=A. C. H. |last2=Yu |title=Efficient Storage Scheme for Pre-calculated Wigner 3j, 6j and Gaunt Coefficients |journal=SIAM J. Sci. Comput. |volume=25 |issue=4 |year=2003 |pages=1416–1428 |doi=10.1137/s1064827503422932}}</ref>

== Selection rules ==

The Wigner 3''j'' is zero unless all these conditions are satisfied:

:<math>m_1+m_2+m_3=0\,</math>

:<math>j_1+j_2 + j_3\text{ is an integer} \, \text{(or an even integer if} \,m_1=m_2=m_3=0)\, </math>

:<math>|m_i| \le j_i \, </math>

:<math>|j_1-j_2|\le j_3 \le j_1+j_2. \, </math>

== Scalar invariant ==
The contraction of the product of three rotational states with a 3''j'' symbol,
:<math>
\sum_{m_1=-j_1}^{j_1} \sum_{m_2=-j_2}^{j_2} \sum_{m_3=-j_3}^{j_3}
|j_1 m_1\rangle |j_2 m_2\rangle |j_3 m_3\rangle
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix},
</math>
is invariant under rotations.

== Orthogonality relations ==
:<math>
(2j+1)\sum_{m_1 m_2}
\begin{pmatrix}
j_1 & j_2 & j\\
m_1 & m_2 & m
\end{pmatrix}
\begin{pmatrix}
j_1 & j_2 & j'\\
m_1 & m_2 & m'
\end{pmatrix}
=\delta_{j j'}\delta_{m m'}.
</math>

:<math>
\sum_{j m} (2j+1)
\begin{pmatrix}
j_1 & j_2 & j\\
m_1 & m_2 & m
\end{pmatrix}
\begin{pmatrix}
j_1 & j_2 & j\\
m_1' & m_2' & m
\end{pmatrix}
=\delta_{m_{1} m_1'}\delta_{m_{2} m_2'}.
</math>

==Relation to spherical harmonics==
The 3jm symbols give the integral of the products of three [[spherical harmonics]]
:<math>
\begin{align}
& {} \quad \int Y_{l_1m_1}(\theta,\varphi)Y_{l_2m_2}(\theta,\varphi)Y_{l_3m_3}(\theta,\varphi)\,\sin\theta\,\mathrm{d}\theta\,\mathrm{d}\varphi \\
& =
\sqrt{\frac{(2l_1+1)(2l_2+1)(2l_3+1)}{4\pi}}
\begin{pmatrix}
l_1 & l_2 & l_3 \\[8pt]
0 & 0 & 0
\end{pmatrix}
\begin{pmatrix}
l_1 & l_2 & l_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\end{align}
</math>

with <math>l_1</math>, <math>l_2</math> and <math>l_3</math> integers.

=== Relation to integrals of spin-weighted spherical harmonics ===

Similar relations exist for the [[spin-weighted spherical harmonics]]:
:<math>
\begin{align}
& {} \quad \int d{\mathbf{\hat n}}\,{}_{s_1} Y_{j_1 m_1}({\mathbf{\hat n}})
\,{}_{s_2} Y_{j_2m_2}({\mathbf{\hat n}})\, {}_{s_3} Y_{j_3m_3}({\mathbf{\hat
n}}) \\[8pt]
& = \sqrt{\frac{(2j_1+1)(2j_2+1)(2j_3+1)}{4\pi}}
\begin{pmatrix}
j_1 & j_2 & j_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\begin{pmatrix}
j_1 & j_2 & j_3\\
-s_1 & -s_2 & -s_3
\end{pmatrix}
\end{align}
</math>

== Recursion relations ==
:<math>
\begin{align}
& {} \quad -\sqrt{(l_3\mp s_3)(l_3\pm s_3+1)}
\begin{pmatrix}
l_1 & l_2 & l_3\\
s_1 & s_2 & s_3\pm 1
\end{pmatrix}
\\
& = \sqrt{(l_1\mp s_1)(l_1\pm s_1+1)}
\begin{pmatrix}
l_1 & l_2 & l_3\\
s_1 \pm 1 & s_2 & s_3
\end{pmatrix}
+\sqrt{(l_2\mp s_2)(l_2\pm s_2+1)}
\begin{pmatrix}
l_1 & l_2 & l_3\\
s_1 & s_2 \pm 1 & s_3
\end{pmatrix}
\end{align}
</math>

== Asymptotic expressions ==
For <math>l_1\ll l_2,l_3</math> a non-zero 3-j symbol has
:<math>
\begin{pmatrix}
l_1 & l_2 & l_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\approx (-1)^{l_3+m_3} \frac{ d^{l_1}_{m_1, l_3-l_2}(\theta)}{\sqrt{2l_3+1}}
</math>
where <math>\cos(\theta) = -2m_3/(2l_3+1)</math> and <math>d^l_{mn}</math> is a Wigner function. Generally a better approximation obeying the Regge symmetry is given by
:<math>
\begin{pmatrix}
l_1 & l_2 & l_3\\
m_1 & m_2 & m_3
\end{pmatrix}
\approx (-1)^{l_3+m_3} \frac{ d^{l_1}_{m_1, l_3-l_2}(\theta)}{\sqrt{l_2+l_3+1}}
</math>
where <math>\cos(\theta) = (m_2-m_3)/(l_2+l_3+1)</math>.

== Other properties ==
:<math>\sum_m (-1)^{j-m}
\begin{pmatrix}
j & j & J\\
m & -m & 0
\end{pmatrix} = \sqrt{2j+1}~ \delta_{J0}
</math>

:<math>
\frac{1}{2} \int_{-1}^1 P_{l_1}(x)P_{l_2}(x)P_{l}(x) \, dx =
\begin{pmatrix}
l & l_1 & l_2 \\
0 & 0 & 0
\end{pmatrix} ^2
</math>

==See also==
*[[Clebsch–Gordan coefficients]]
*[[Spherical harmonics]]
*[[6-j symbol]]
*[[9-j symbol]]

==References==
<references />

<div class="references">
*[[Lawrence Biedenharn|L. C. Biedenharn]] and J. D. Louck, ''Angular Momentum in Quantum Physics'', volume 8 of Encyclopedia of Mathematics, Addison-Wesley, Reading, 1981.
* D. M. Brink and G. R. Satchler, ''Angular Momentum'', 3rd edition, Clarendon, Oxford, 1993.
* A. R. Edmonds, ''Angular Momentum in Quantum Mechanics'', 2nd edition, Princeton University Press, Princeton, 1960.
*{{dlmf|id=34 |title=3j,6j,9j Symbols|first=Leonard C.|last= Maximon}}
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* E. P. Wigner, "On the Matrices Which Reduce the Kronecker Products of Representations of Simply Reducible Groups", unpublished (1940). Reprinted in: L. C. Biedenharn and H. van Dam, ''Quantum Theory of Angular Momentum'', Academic Press, New York (1965).
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|title=Unitary-group approach to the many-electron correlation problem: Relation of Gelfand and Weyl tableau formulations
|journal=Phys. Rev. A
|volume=14
|year=1976
|page=1620
|doi=10.1103/PhysRevA.14.1620
|issue=5
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|journal=J. Phys. A
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|year=1982
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|doi=10.1137/s1064827503422932
}}
</div>

==External links==
* {{cite web
|first1=Anthony
|last1=Stone
|url=http://www-stone.ch.cam.ac.uk/wigner.shtml
|title=Wigner coefficient calculator
}}
* {{cite web
|first1=A.
|last1=Volya
|url=http://www.volya.net/vc/vc.php
|title=Clebsch-Gordan, 3-j and 6-j Coefficient Web Calculator
}} (Numerical)
* {{cite journal
|first1=Paul
|last1=Stevenson
|url=http://personal.ph.surrey.ac.uk/~phs3ps/cleb.html
|title=Clebsch-O-Matic
|doi=10.1016/S0010-4655(02)00462-9
|bibcode = 2002CoPhC.147..853S }}
* [http://plasma-gate.weizmann.ac.il/369j.html 369j-symbol calculator at the Plasma Laboratory of Weizmann Institute of Science] (Numerical)
* [http://geoweb.princeton.edu/people/simons/software.html Frederik J Simons: Matlab software archive, the code THREEJ.M]
* [http://www.sagemath.org/ Sage (mathematics software)] Gives exact answer for any value of j, m
* {{cite web
|first1=H.T.
|last1=Johansson
|first2=C.
|last2=Forssén
|title=(WIGXJPF)
|url=http://fy.chalmers.se/subatom/wigxjpf/
}} (accurate; C, fortran, python)

[[Category:Rotational symmetry]]
[[Category:Representation theory of Lie groups]]
[[Category:Quantum mechanics]]

Weber-Elektrodynamik

2015-06-10T00:55:19Z

Bibcode Bot: Adding 0 arxiv eprint(s), 4 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Electromagnetism|cTopic=[[Classical electromagnetism|Electrodynamics]]}}

'''Weber electrodynamics''' is an alternative to [[Maxwell's Equations|Maxwell electrodynamics]] developed by [[Wilhelm Eduard Weber]]. In this theory, [[Coulomb's Law]] becomes velocity dependent. The theory is widely rejected and ignored by contemporary physicists, and is not even mentioned in mainstream textbooks on [[classical electromagnetism]].

==Mathematical Description==

According to Weber electrodynamics, the force (F) acting simultaneously on point charges <math>q_1</math> and <math>q_2</math>, is given by

<math> \mathbf{F} = \frac{q_1 q_2 \mathbf{\hat{r}}}{4 \pi \epsilon_0 r^2}\left(1-\frac{\dot{r}^2}{2 c^2}+\frac{r\ddot{r}}{c^2}\right) </math>

where <math>\mathbf{r}</math> is the vector connecting <math>q_1</math> and <math>q_2</math>, the dots over <math>r</math> denote time [[derivative]]s and <math>c</math> is the [[speed of light]]. In the limit that speeds and accelerations are small (i.e. <math>\dot{r}\ll c</math>), this reduces to the usual Coulomb's law.<ref name=assis>{{cite journal|last=Assis|first=AKT|author2=HT Silva |title=Comparison between Weber’s electrodynamics and classical electrodynamics|journal=Pramana - journal of physics|date=September 2000|volume=55|issue=3|pages=393–404|doi=10.1007/s12043-000-0069-2|bibcode = 2000Prama..55..393A }}</ref>

This can be derived from the [[potential energy]]

<math> U_{Web} = \frac{q_1 q_2}{4 \pi \epsilon_0 r}\left(1-\frac{\dot{r}^2}{2 c^2}\right) </math>

This can be contrasted with the approximate potential energy from Maxwellian electrodynamics (where <math>v_1</math> and <math>v_2</math> are the velocities of <math>q_1</math> and <math>q_2</math>, respectively):<ref name=assis/>

<math> U_{Max} =\frac{q_1 q_2}{4 \pi \epsilon_0 r}\left(1-\frac{\mathbf{v_1}\cdot\mathbf{v_2}+(\mathbf{v_1}\cdot\mathbf{\hat{r}})(\mathbf{v_2}\cdot\mathbf{\hat{r}})}{2 c^2}\right) </math>

(This only includes terms up to order <math>(v/c)^2</math> and therefore neglects relativistic and retardation effects; see [[Darwin Lagrangian]].)

Using these expressions, the regular form of [[Ampere's law]] and [[Faraday's law of induction|Faraday's law]] can be derived. Importantly, this theory does not predict an expression like the [[Biot–Savart law]] and testing differences between Ampere's law and the Biot–Savart law is one way to test Weber electrodynamics.<ref name=AssisPLA>{{cite journal|last=Assis|first=AKT|author2=JJ Caluzi |title=A limitation of Weber's law|journal=Physics Letters A|year=1991|volume=160|issue=1|pages=25–30|bibcode = 1991PhLA..160...25A |doi = 10.1016/0375-9601(91)90200-R }}</ref>

==Newton's third law in Maxwell and Weber electrodynamics==
In [[Maxwell's equations|Maxwell electrodynamics]], [[Newton's third law]] does not hold for particles. Instead, particles exert forces on electromagnetic fields, and fields exert forces on particles, but particles do not ''directly'' exert forces on other particles. Therefore, two nearby particles need not experience equal and opposite forces. Related to this, Maxwell electrodynamics predicts that the laws of [[conservation of momentum]] and [[conservation of angular momentum]] are valid ''only'' if the momentum of particles ''and'' the momentum of surrounding electromagnetic fields are taken into account. The total momentum of all particles is not necessarily conserved, because the particles may transfer some of their momentum to electromagnetic fields or vice versa. The well-known phenomenon of [[radiation pressure]] proves that electromagnetic waves are indeed able to "push" on matter. See [[Maxwell stress tensor]] and [[Poynting vector]] for further details.

The Weber force law is quite different: All particles, regardless of size and mass, will exactly follow [[Newton's third law]]. Therefore, Weber electrodynamics, unlike Maxwell electrodynamics, has conservation of ''particle'' momentum and conservation of ''particle'' angular momentum.

==Predictions==
Weber dynamics has been used to explain various phenomena such as wires exploding when exposed to high [[Electric current|current]]s.<ref name=Wesley>{{cite journal|last=Wesley|first=JP|title=Weber electrodynamics, part I. general theory, steady current effects|journal=Foundations of Physics Letters|year=1990|volume=3|issue=5|pages=443–469|doi=10.1007/BF00665929|bibcode = 1990FoPhL...3..443W }}</ref>

==Limitations==

Despite various efforts, a velocity and/or acceleration dependent correction to Coulomb's law has never been [[Tests of electromagnetism|observed]], as described in the next section. Moreover, [[Helmholtz]] observed that Weber electrodynamics predicted that under certain configurations charges can act as if they had negative [[inertial mass]], which has also never been observed. (Some scientists have, however, disputed Helmholtz's argument.<ref>{{cite journal|author1=JJ Caluzi|author2=AKT Assis|title=A critical analysis of Helmholtz's argument against Weber's electrodynamics|journal=Foundations of physics|year=1997|volume=27|issue=10|pages=1445–1452 |doi = 10.1007/BF02551521 |bibcode = 1997FoPh...27.1445C }}</ref>)

==Experimental tests==

===Velocity Dependent Tests===
[[Velocity]] and [[acceleration]] dependent corrections to Maxwell's equations arise in Weber electrodynamics. The strongest limits on a new velocity dependent term come from evacuating gasses from containers and observing whether the [[electrons]] become [[Electric charge|charge]]d. However, because the electrons used to set these limits are [[atom|Coulomb bound]], [[renormalization]] effects may cancel the velocity dependent corrections. Other searches have spun current-carrying [[solenoids]], observed metals as they cooled, and used [[superconductors]] to obtain a large drift velocity.<ref>{{cite journal|last=Lemon|first=DK|author2=WF Edwards |author3=CS Kenyon |title=Electric potentials associated with steady currents in superconducting coils|journal=Physics Letters A|year=1992|volume=162|issue=2|pages=105–114|bibcode = 1992PhLA..162..105L |doi = 10.1016/0375-9601(92)90985-U }}</ref> None of these searches have observed any discrepancy from Coulomb's law. Observing the charge of [[particle beams]] provides weaker bounds, but tests the velocity dependent corrections to Maxwell's equations for particles with higher velocities.<ref>{{cite journal|last=Walz|first=DR|author2=HR Noyes |title=Calorimetric test of special relativity|journal=Physical Review A|date=April 1984|volume=29|issue=1|pages=2110–2114|bibcode = 1984PhRvA..29.2110W |doi = 10.1103/PhysRevA.29.2110 }}</ref><ref>{{cite journal|last=Bartlett|first=DF|author2=BFL Ward |title=Is an electron's charge independent of its velocity?|journal=Physical Review D|date=15 December 1997|volume=16|issue=12|pages=3453–3458|doi=10.1103/physrevd.16.3453|bibcode = 1977PhRvD..16.3453B }}</ref>

===Acceleration Dependent Tests===
Test charges inside a spherical conducting shell will experience different behaviors depending on the force law the test charge is subject to.<ref name=Junginger>{{cite journal|last=Junginger|first=JE|author2=ZD Popovic |title=An experimental investigation of the influence of an electrostatic potential on electron mass as predicted by Weber’s force law|journal=Can. J. Phys.|year=2004|volume=82|pages=731–735|doi=10.1139/p04-046|bibcode = 2004CaJPh..82..731J }}</ref> By measuring the [[oscillation frequency]] of a [[neon lamp]] inside a spherical conductor biased to a high voltage, this can be tested. Again, no significant deviations from the Maxwell theory have been observed.

===Relation to quantum electrodynamics===
[[Quantum electrodynamics]] (QED) is perhaps the most stringently tested theory in physics, with highly nontrivial predictions verified to an accuracy better than 10 parts per billion: See [[precision tests of QED]]. Since Maxwell's equations can be derived as the classical limit of the equations of QED,<ref>Peskin, M.; Schroeder, D. (1995). An Introduction to Quantum Field Theory. Westview Press. ISBN 0-201-50397-2. Section 4.1.</ref> it follows that ''if'' QED is correct (as is widely believed by mainstream physicists), then Maxwell's equations and the Lorentz force law are correct too.

Although it is has been demonstrated that, in certain aspects, the Weber force formula is consistent with Maxwell’s equations and the Lorentz force,<ref>{{cite journal |authors=E.T. Kinzer and J. Fukai |title=Weber's force and Maxwell's equations |journal=Found. Phys. Lett. |volume=9 |page=457 |year=1996 |doi=10.1007/BF02190049|bibcode = 1996FoPhL...9..457K }}</ref> they are not exactly equivalent—and more specifically, they make various contradictory predictions<ref name=assis/><ref name=AssisPLA/><ref name=Wesley/><ref name=Junginger/> as described above. Therefore they cannot both be correct.

==References==

{{Reflist}}

[[Category:Electrodynamics]]
[[Category:Electromagnetism]]

Verschmutzung gegen den Strom

2015-06-09T11:44:35Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

[[File:Upstream contamination in mate beverage.jpg|thumb|Particles can climb up the falling water while preparing a mate beverage.]]
'''Upstream contamination''' by floating particles is a [[paradox|counterintuitive phenomenon]] in [[fluid dynamics]]. When pouring water from a higher container to a lower one, particles floating in the latter can climb upstream into the upper container. A definitive explanation is still lacking: experimental and computational evidence indicates that the contamination is chiefly driven by [[surface tension]] gradients, however the phenomenon is also affected by the dynamics of swirling flows that remain to be fully investigated.

==Origins==
[[File:Experimental setup for upstream contamination.gif|thumb|Experimental setup for creating a constant flow of water falling from a higher to a lower recipient.]]

The phenomenon was first observed in 2008 by the Argentinian
S. Bianchini during mate tea preparation, while studying Physics
at the [[University of Havana]].

It rapidly attracted the interest of Prof. A. Lage, who performed,
with Bianchini, a series of controlled experiments. Later on
Prof. E. Altshuler completed the trio in [[Havana]], which resulted in the
Diploma thesis of Bianchini and
a short original paper posted in the web arxiv<ref>{{Cite arXiv|author=Bianchini S. |display-authors=etal |title=Upstream contamination in water pouring |date=2011 |arxiv=1105.2585}}</ref> and commented as a surprising fact in some online journals.<ref>{{cite web| date=2011 |title=Contaminants Can Flow Up Waterfalls, Say Physicists |url=http://www.technologyreview.com/view/424026/contaminants-can-flow-up-waterfalls-say-physicists/ }}</ref><ref>{{cite web| date=2011 |title=Small Particles Can Flow Up Waterfalls, Say Tea-Drinking Physicists |url=http://blogs.discovermagazine.com/discoblog/2011/05/17/small-particles-can-flow-up-waterfalls-say-tea-drinking-physicists}}</ref>
<ref>{{cite web |date=2011 |title= Some particles are able to flow up small waterfalls, physicists show |url=http://phys.org/news/2011-05-particles-small-waterfalls-physicists.html}}</ref>
<ref>{{cite web| date=2013| title= Particles defy gravity, float upstream|url=https://www.sciencenews.org/article/particles-defy-gravity-float-upstream}}</ref>

Bianchini's Diploma thesis showed that the phenomenon could be reproduced
in a controlled laboratory setting using mate leaves or chalk powder as contaminants,
and that temperature gradients (hot in the top, cold in the bottom) were not necessary
to generate the effect. The research also showed that surface tension was
a key element to the explanation through the so-called [[Marangoni effect]], which was
suggested by two facts: (a) both mate and
chalk lowered the surface tension of water, and (b) if an industrial surfactant was
added on the upper reservoir, the upstream motion of particles would stop.

==Confirmation==
After a talk by A. Lage at the First Workshop on Complex Matter Physics
in Havana (MarchCOMeeting'2012), Prof. T Shinbrot ([[Rutgers University]])
got interested in the subject. Together with student T. Siu,
Cuban results were confirmed and expanded with new experiments and numerical
simulations at Rutgers,
which resulted in a joint peer-reviewed paper.<ref>{{cite journal|author=Bianchini S. |display-authors=etal |title=Upstream contamination by floating particles |journal=Proceedings of the Royal Society A|date=2013 |url=http://rspa.royalsocietypublishing.org/content/469/2157/20130067|doi=10.1098/rspa.2013.0067 |volume=469 |pages=20130067|bibcode = 2013RSPSA.46930067B }}</ref>

Later on, the phenomenon has been confirmed independently by others.<ref>{{cite web|title=Upstream Contamination by Floating Particles |date=2014 |url=https://www.youtube.com/watch?v=PCKu_mwTTI0}}</ref>
Whether it is caused solely by surface tension gardients or depends also on dynamical
behaviors of the falling water still remains as an open question.

Videos of the effect are available on YouTube.<ref>{{cite web|title=Upstream contamination in water pouring|author=A. Lage-Castellanos |date=2013 |url=https://www.youtube.com/watch?v=Jk-qAIcZk74}}</ref><ref>{{cite web|title=Upstream Contamination by Floating Particles |date=2014 |url=https://www.youtube.com/watch?v=PCKu_mwTTI0}}</ref>

==Implications==
The phenomenon of upstream contamination could be relevant to industrial and biotechnological pocesses, and may be
connected even to movements of the [[protoplasm]]. It could imply that some of the ''good practices'' in industrial and biotechnological procedures need revision.

==References==
{{Reflist}}

[[Category:Physical paradoxes]]
[[Category:Physical phenomena]]

Benutzer:Molinarius/Silicon photonics

2015-06-09T01:36:37Z

Bibcode Bot: Adding 2 arxiv eprint(s), 2 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Use dmy dates|date=November 2014}}
'''Silicon photonics''' is the study and application of [[photonics|photonic]] systems which use [[silicon]] as an [[optical medium]].<ref name="lipson_2005">{{cite journal
|doi = 10.1109/JLT.2005.858225
|title = Guiding, Modulating, and Emitting Light on Silicon – Challenges and Opportunities
|journal = [[Journal of Lightwave Technology]]
|year = 2005
|volume = 23
|issue = 12
|pages = 4222–4238
|author = Lipson, Michal
| bibcode = 2005JLwT...23.4222L }}</ref><ref name="jalali_2006">{{cite journal
|doi = 10.1109/JLT.2006.885782
|title = Silicon photonics
|journal = [[Journal of Lightwave Technology]]
|year = 2006
|volume = 24
|issue = 12
|pages = 4600–4615
| bibcode = 2006JLwT...24.4600J |last1 = Jalali
|first1 = Bahram
|last2 = Fathpour
|first2 = Sasan
}}</ref><ref name="almeida_2004">{{cite journal
|title = All-optical control of light on a silicon chip
|journal = [[Nature (journal)|Nature]]
|year = 2004
|volume = 431
|issue = 7012
|pages = 1081–1084
|doi = 10.1038/nature02921
|pmid=15510144
| bibcode = 2004Natur.431.1081A |author1 = Almeida
|first1 = V. R.
|last2 = Barrios
|first2 = C. A.
|last3 = Panepucci
|first3 = R. R.
|last4 = Lipson
|first4 = M
}}</ref><ref name="pavesi_book">{{cite book
|title = Silicon photonics
|isbn = 3-540-21022-9
|publisher = [[Springer Science+Business Media|Springer]]
|year = 2004
}}</ref><ref name="reed_book">{{cite book
|title = Silicon photonics: an introduction
|isbn = 0-470-87034-6
|publisher = [[John Wiley and Sons]]
|year = 2004
}}</ref> The silicon is usually patterned with [[nanoscale|sub-micrometre]] precision, into [[microphotonics|microphotonic]] components.<ref name="pavesi_book" /> These operate in the [[infrared]], most commonly at the 1.55 micrometre [[wavelength]] used by most [[fiber optic telecommunication]] systems.<ref name="lipson_2005" /> The silicon typically lies on top of a layer of silica in what (by analogy with [[silicon on insulator|a similar construction]] in [[microelectronics]]) is known as '''silicon on insulator''' (SOI).<ref name="pavesi_book" /><ref name="reed_book" />

[[File:Silicon Photonics 300mm wafer.JPG|thumb|upright|right|Silicon Photonics 300mm wafer]]

Silicon photonic devices can be made using existing [[semiconductor fabrication]] techniques, and because silicon is already used as the substrate for most [[integrated circuit]]s, it is possible to create hybrid devices in which the [[optics|optical]] and [[electronics|electronic]] components are integrated onto a single microchip.<ref name="lipson_2005" /> Consequently, silicon photonics is being actively researched by many electronics manufacturers including [[IBM]] and [[Intel]], as well as by academic research groups such as that of Prof. [[Michal Lipson]], who see it is a means for keeping on track with [[Moore's Law]], by using [[optical interconnect]]s to provide faster [[data transfer]] both between and within [[Integrated circuit|microchip]]s.<ref name="ibm_silicon">{{cite web
|title = Silicon Integrated Nanophotonics
|publisher = [[IBM]] Research
|url = http://domino.research.ibm.com/comm/research_projects.nsf/pages/photonics.index.html
|accessdate = 14 July 2009
}}</ref><ref name="intel_silicon">{{cite web
|title = Silicon Photonics
|publisher = [[Intel]]
|url = http://techresearch.intel.com/articles/Tera-Scale/1419.htm
|accessdate = 14 July 2009
}}</ref><ref>{{cite journal|last1=SPIE|title=Yurii A. Vlasov plenary presentation: Silicon Integrated Nanophotonics: From Fundamental Science to Manufacturable Technology|journal=SPIE Newsroom|date=5 March 2015|doi=10.1117/2.3201503.15}}</ref>

The propagation of [[light]] through silicon devices is governed by a range of [[nonlinear optics|nonlinear optical]] phenomena including the [[Kerr effect]], the [[Raman effect]], [[two photon absorption]] and interactions between [[photons]] and [[free charge carriers]].<ref name="dekker_2008" >{{cite journal
|title = Ultrafast nonlinear all-optical processes in silicon-on-insulator waveguides
|journal = [[Journal of Physics D]]
|year = 2008
|volume = 40
|issue = 14
|page = R249–R271
|doi=10.1088/0022-3727/40/14/r01
|bibcode = 2007JPhD...40..249D |last1 = Dekker
|first1 = R
|last2 = Usechak
|first2 = N
|last3 = Först
|first3 = M
|last4 = Driessen
|first4 = A
}}</ref> The presence of nonlinearity is of fundamental importance, as it enables light to interact with light,<ref name="butcher_book">{{cite book
|title = The elements of nonlinear optics
|isbn = 0-521-42424-0
|publisher = [[Cambridge University Press]]
|year = 1991
|author1 = Butcher, Paul N. |author2 = Cotter, David
}}</ref> thus permitting applications such as wavelength conversion and all-optical signal routing, in addition to the passive transmission of light.

Silicon waveguides are also of great academic interest, due to their ability to support exotic nonlinear optical phenomena such as [[Soliton (optics)|soliton propagation]].<ref name="hsieh_2006" >{{cite journal
|doi = 10.1364/OE.14.012380
|title = Ultrafast-pulse self-phase modulation and third-order dispersion in Si photonic wire-waveguides
|journal = [[Optics Express]]
|year = 2006
|volume = 14
|issue = 25
|pages = 12380–12387
| bibcode = 2006OExpr..1412380H |last1 = Hsieh
|first1 = I-Wei
|last2 = Chen
|first2 = Xiaogang
|last3 = Dadap
|first3 = Jerry I.
|last4 = Panoiu
|first4 = Nicolae C.
|last5 = Osgood
|first5 = Richard M.
|last6 = McNab
|first6 = Sharee J.
|last7 = Vlasov
|first7 = Yurii A.
}}</ref><ref name="zhang_2007">{{cite journal
|doi = 10.1364/OE.15.007682
|title = Optical solitons in a silicon waveguide
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 12
|pages = 7682–7688
| bibcode = 2007OExpr..15.7682Z |last1 = Zhang
|first1 = Jidong
|last2 = Lin
|first2 = Qiang
|last3 = Piredda
|first3 = Giovanni
|last4 = Boyd
|first4 = Robert W.
|last5 = Agrawal
|first5 = Govind P.
|last6 = Fauchet
|first6 = Philippe M.
}}</ref><ref name="ding_2008">{{cite journal
|doi = 10.1364/OE.16.003310
|title = Solitons and spectral broadening in long silicon-on- insulator photonic wires
|journal = [[Optics Express]]
|year = 2008
|volume = 16
|issue = 5
|pages = 3310–3319
| bibcode = 2008OExpr..16.3310D |last1 = Ding
|first1 = W.
|last2 = Benton
|first2 = C.
|last3 = Gorbach
|first3 = A. V.
|last4 = Wadsworth
|first4 = W. J.
|last5 = Knight
|first5 = J. C.
|last6 = Skryabin
|first6 = D. V.
|last7 = Gnan
|first7 = M.
|last8 = Sorrel
|first8 = M.
|last9 = de la Rue
|first9 = R. M.

}}</ref>

== Applications ==

=== Optical interconnects ===

Progress in computer technology (and the continuation of [[Moore's Law]]) is becoming increasingly dependent on faster [[data transfer]] between and within [[Integrated circuit|microchips]].<ref name="meindl_2003">{{cite journal
|doi = 10.1109/MCISE.2003.1166548
|title = Beyond Moore's Law: the interconnect era
|journal = Computing in Science & Engineering
|year = 2003
|volume = 5
|issue = 1
|pages = 20–24
|author = Meindl, J. D.
}}</ref> [[Optical interconnect]]s may provide a way forward, and silicon photonics may prove particularly useful, once integrated on the standard silicon chips.<ref name="lipson_2005" /><ref name="barwicz_2006">{{cite journal
|doi = 10.1364/JON.6.000063
|title = Silicon photonics for compact, energy-efficient interconnects
|journal = Journal of Optical Networking
|year = 2006
|volume = 6
|issue = 1
|pages = 63–73
| bibcode = 2007JON.....6...63B |last1 = Barwicz
|first1 = T.
|last2 = Byun
|first2 = H.
|last3 = Gan
|first3 = F.
|last4 = Holzwarth
|first4 = C. W.
|last5 = Popovic
|first5 = M. A.
|last6 = Rakich
|first6 = P. T.
|last7 = Watts
|first7 = M. R.
|last8 = Ippen
|first8 = E. P.
|last9 = Kärtner
|first9 = F. X.
|last10 = Smith
|first10 = H. I.
|last11 = Orcutt
|first11 = J. S.
|last12 = Ram
|first12 = R. J.
|last13 = Stojanovic
|first13 = V.
|last14 = Olubuyide
|first14 = O. O.
|last15 = Hoyt
|first15 = J. L.
|last16 = Spector
|first16 = S.
|last17 = Geis
|first17 = M.
|last18 = Grein
|first18 = M.
|last19 = Lyszczarz
|first19 = T.
|last20 = Yoon
|first20 = J. U.
}}</ref><ref name="orcutt_2008">{{cite conference
|authors = Orcutt, J. S. ''et al.''
|title = Demonstration of an Electronic Photonic Integrated Circuit in a Commercial Scaled Bulk CMOS Process
|conference = Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies
|year = 2008
}}</ref> In 2006 Former [[Intel]] senior vice president [[Pat Gelsinger]] stated that, "Today, optics is a niche technology. Tomorrow, it's the mainstream of every chip that we build."<ref name="intel_silicon" />

Optical interconnects require multiple advances.

An on-chip [[laser]] source is required. One such device is the [[hybrid silicon laser]], in which the silicon is bonded to a different [[semiconductor]] (such as [[indium phosphide]]) as the [[lasing medium]].<ref name="intel_hybrid">{{cite web
|url = http://techresearch.intel.com/articles/Tera-Scale/1448.htm
|title = Hybrid Silicon Laser – Intel Platform Research
|publisher = [[Intel]]
|accessdate = 14 July 2009
}}</ref> Another possibility is the all-silicon [[Raman laser]], in which silicon is the lasing medium.<ref name="rong_2005">{{cite journal
|title = An all-silicon Raman laser
|doi = 10.1038/nature03273
|journal = [[Nature (journal)|Nature]]
|pmid = 15635371
|year = 2005
|volume = 433
|issue = 7023
|pages = 292–294
| bibcode = 2005Natur.433..292R |author1 = Rong
|first1 = H
|last2 = Liu
|first2 = A
|last3 = Jones
|first3 = R
|last4 = Cohen
|first4 = O
|last5 = Hak
|first5 = D
|last6 = Nicolaescu
|first6 = R
|last7 = Fang
|first7 = A
|last8 = Paniccia
|first8 = M
}}</ref>

The light must be [[modulation|modulated]] to encode data in the form of optical pulses. One such technique is to control the density of free charge carriers, which (as described below) alter the waveguide's optical properties. Some modulators pass light through the [[intrinsic semiconductor|intrinsic region]] of a [[PIN diode]], into which carriers can be injected or removed by altering the [[Electrical polarity|polarity]] of an applied [[voltage]].<ref name="barrios_2003">{{cite journal
|doi = 10.1109/JLT.2003.818167
|title = Electrooptic Modulation of Silicon-on-Insulator Submicrometer-Size Waveguide Devices
|journal = [[Journal of Lightwave Technology]]
|year = 2003
|volume = 21
|issue = 10
|pages = 2332–2339
| bibcode = 2003JLwT...21.2332B |last1 = Barrios
|first1 = C.A.
|last2 = Almeida
|first2 = V.R.
|last3 = Panepucci
|first3 = R.
|last4 = Lipson
|first4 = M.
}}</ref> In 2007 an [[optical ring resonator]] with a built in PIN diode achieved data transmission rates of 18 [[Gbit/s]].<ref name="xu_2007">{{cite journal
|title = High Speed Carrier Injection 18 Gbit/s Silicon Micro-ring Electro-optic Modulator
|journal = Proceedings of Lasers and Electro-Optics Society
|year = 2007
|volume =
|pages = 537–538
|last1 = Manipatruni
|first1 = Sasikanth
|author2 = Qianfan Xu
|last3 = Schmidt
|first3 = B.
|last4 = Shakya
|first4 = J.
|last5 = Lipson
|first5 = M.
|displayauthors = 1
|doi=10.1109/leos.2007.4382517
}}</ref> Devices where the electrical signal co-moves with the light, allowed data rates of 30 Gbit/s.<ref name="liu_2007">{{cite journal
|doi = 10.1364/OE.15.000660
|last1 = Liu
|first1 = Ansheng
|last2 = Liao
|first2 = Ling
|last3 = Rubin
|first3 = Doron
|last4 = Nguyen
|first4 = Hat
|last5 = Ciftcioglu
|first5 = Berkehan
|last6 = Chetrit
|first6 = Yoel
|last7 = Izhaky
|first7 = Nahum
|last8 = Paniccia
|first8 = Mario
|title = High-speed optical modulation based on carrier depletion in a silicon waveguide
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 2
|pages = 660–668 |bibcode = 2007OExpr..15..660L
}}
</ref> Using multiple wavelengths scaled allowed 50 Gbit/s.<ref name="Manipatruni_2009">{{cite journal
|title = 50 Gbit/s wavelength division multiplexing using silicon microring modulators
|journal = [Group IV Photonics, 2009. GFP '09. 6th IEEE International Conference on]
|year = 2009
|doi = 10.1109/GROUP4.2009.5338375
|pages = 244–246
|author = Manipatruni, Sasikanth; Chen, Long; Lipson, Michal;
|isbn = 978-1-4244-4402-1
}}
</ref> A prototype optical interconnect with microring modulators integrated with germanium detectors has been demonstrated.<ref name="Long Chen_2009">{{cite journal
|doi = 10.1364/OE.17.015248
|title = Integrated GHz silicon photonic interconnect with micrometer-scale modulators and detectors
|journal = [[Optics Express]]
|year = 2009
|volume = 17
|issue = 17
|pages = 15248–15256
| bibcode = 2009OExpr..1715248C |arxiv = 0907.0022 |last1 = Chen
|first1 = Long
|last2 = Preston
|first2 = Kyle
|last3 = Manipatruni
|first3 = Sasikanth
|last4 = Lipson
|first4 = Michal
}}
</ref><ref name="register_vance">{{cite news
|title = Intel cranks up next-gen chip-to-chip play
|publisher = The Register
|author = Vance, Ashlee
|url = http://www.theregister.co.uk/2007/01/27/intel_silicon_modulator/print.html
|accessdate = 26 July 2009
}}</ref>

After passage through a silicon [[waveguide]] to a different chip (or region of the same chip) the light must be [[photodetector|detected]], to reconvert the data into electronic form.<ref>{{cite journal |last1=Kucharski |first1=D. |last2=Guckenberger |first2=D. |last3=Masini |first3=G. |last4=Abdalla |first4=S. |last5=Witzens |first5=J. |last6=Sahni |first6=S. |displayauthors=1 |year=2010 |title=10 Gb/s 15mW optical receiver with integrated Germanium photodetector and hybrid inductor peaking in 0.13µm SOI CMOS technology |journal= Solid-State Circuits Conference Digest of Technical Papers (ISSCC) |pages=360–361}}</ref><ref>{{cite journal|year = 2006|title=CMOS photonics using germanium photodetectors|journal=ECS Transactions|volume=3|issue=7|pages=17–24|doi=10.1149/1.2355790|url=http://ecst.ecsdl.org/content/3/7/17.abstract|last1=Gunn|first1=Cary|last2=Masini|first2=Gianlorenzo|last3=Witzens|first3=J.|last4=Capellini|first4=G.}}</ref> Detectors based on [[metal-semiconductor junction]]s (with [[germanium]] as the semiconductor) have been integrated into silicon waveguides.<ref name="vivien_2007">{{cite journal
|doi = 10.1364/OE.15.009843
|title = High speed and high responsivity germanium photodetector integrated in a Silicon-On-Insulator microwaveguide
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 15
|pages = 9843–9848
| bibcode = 2007OExpr..15.9843V |last1 = Vivien
|first1 = Laurent
|last2 = Rouvière
|first2 = Mathieu
|last3 = Fédéli
|first3 = Jean-Marc
|last4 = Marris-Morini
|first4 = Delphine
|last5 = Damlencourt
|first5 = Jean François
|last6 = Mangeney
|first6 = Juliette
|last7 = Crozat
|first7 = Paul
|last8 = El Melhaoui
|first8 = Loubna
|last9 = Cassan
|first9 = Eric
|last10 = Le Roux
|first10 = Xavier
|last11 = Pascal
|first11 = Daniel
|last12 = Laval
|first12 = Suzanne
}}</ref> More recently, silicon-germanium [[avalanche photodiode]]s capable of operating at 40 Gbit/s have been fabricated.<ref name="kang_2008">{{cite journal
|doi = 10.1038/nnano.2008.25
|title = Monolithic germanium/silicon avalanche photodiodes with 340 GHz gain–bandwidth product
|journal = [[Nature Photonics]]
|year = 2008
|volume = 3
|issue = 2
|pages = 59–63
|pmid = 18654454
| bibcode = 2008NatNa...3...59. }}</ref><ref name="register_modine">{{cite news
|title = Intel trumpets world's fastest silicon photonic detector
|publisher = The Register
|author = Modine, Austin
|url = http://www.theregister.co.uk/2008/12/08/intel_world_record_apd_research/
|date = 8 December 2008
}}</ref>
Complete transceivers have been commercialized in the form of active optical cables.<ref>{{cite journal|author = Narasimha, A. |title = A 40-Gb/s QSFP optoelectronic transceiver in a 0.13 µm CMOS silicon-on-insulator technology|year = 2008|journal = Proceedings of the Optical Fiber Communication Conference (OFC)|page = OMK7|url=http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2008-OMK7|isbn=978-1-55752-859-9}}</ref>

In 2012, IBM announced that it had achieved optical components at the 90 nanometer scale that can be manufactured using standard techniques and incorporated into conventional chips.<ref name="ibm_silicon" /><ref>{{cite web|url=http://www.gizmag.com/ibm-silicon-nanophotonics/25446/?utm_source=Gizmag+Subscribers&utm_campaign=59593484e3-UA-2235360-4&utm_medium=email |title=IBM integrates optics and electronics on a single chip |publisher=Gizmag.com |date= 13 December 2012|author=Borghino, Dario }}</ref> In September 2013, Intel announced technology to transmit data at speeds of 100 gigabits per second along a cable approximately five millimeters in diameter for connecting servers inside data centers. Conventional PCI-E data cables carry data at up to eight gigabits per second, while networking cables reach 40 Gb. The latest version of the [[USB]] standard tops out at five Gb. The technology does not directly replace existing cables in that it requires the a separate circuit board to interconvert electrical and optical signals. Its advanced speed offers the potential of reducing the number of cables that connect blades on a rack and even of separating processor, storage and memory into separate blades to allow more efficient cooling and dynamic configuration<ref>{{cite web|last=Simonite |first=Tom |url=http://www.technologyreview.com/news/518941/intels-laser-chips-could-make-data-centers-run-better |title=Intel Unveils Optical Technology to Kill Copper Cables and Make Data Centers Run Faster | MIT Technology Review |publisher=Technologyreview.com |date= |accessdate=4 September 2013}}</ref>

[[Graphene]] photodetectors have the potential to surpass germanium devices in several important aspects, although they remain about one order of magnitude behind current generation capacity, despite rapid improvement.
Graphene devices can work at very high frequencies, and could in principle reach higher bandwidths. Graphene can absorb a broader range of wavelengths than germanium. That property could be exploited to transmit more data streams simultaneously in the same beam of light. Unlike germanium detectors, graphene photodetectors do not require applied voltage, which could reduce energy needs. Finally, graphene detectors in principle permit a simpler and less expensive on-chip integration. However, graphene does not strongly absorb light. Pairing a silicon waveguide with a graphene sheet better routes light and maximizes interaction. The first such device was demonstrated in 2011. Manufacturing such devices using conventional manufacturing techniques has not been demonstrated.<ref>Orcutt, Mike (2 October 2013) [http://www.technologyreview.com/news/519441/graphene-could-make-data-centers-and-supercomputers-more-efficient "Graphene-Based Optical Communication Could Make Computing More Efficient]. ''MIT Technology Review''.</ref>

In 2013 researchers demonstrated two different depletion-mode carrier-plasma optical modulators that can be fabricated using standard Silicon-on-Insulator Complementary Metal-Oxide-Semiconductor (SOI CMOS) manufacturing processes. The researchers also detailed a second modulator that could be used in bulk CMOS.<ref>{{cite web|url=http://www.kurzweilai.net/major-silicon-photonics-breakthrough-could-allow-for-continued-exponential-growth-in-microprocessors |title=Major silicon photonics breakthrough could allow for continued exponential growth in microprocessors |publisher=KurzweilAI |date= 8 October 2013}}</ref><ref>{{cite doi|10.1364/OL.38.002657}}</ref><ref>{{cite doi|10.1364/OL.38.002729}}</ref>

=== Optical routers and signal processors ===

Another application of silicon photonics is in signal routers for [[fiber optic telecommunication|optical communication]]. Construction can be greatly simplified by fabricating the optical and electronic parts on the same chip, rather than having them spread across multiple components.<ref name="analui_2006">{{cite journal
|doi = 10.1109/JSSC.2006.884388
|title = A Fully Integrated 20-Gb/s Optoelectronic Transceiver Implemented in a Standard 0.13- μm CMOS SOI Technology
|journal = [[IEEE]] Journal of Solid-State Circuits
|year = 2006
|volume = 41
|issue = 12
|pages = 2945–2955
|last1 = Analui
|first1 = Behnam
|last2 = Guckenberger
|first2 = Drew
|last3 = Kucharski
|first3 = Daniel
|last4 = Narasimha
|first4 = Adithyaram
}}</ref> A wider aim is all-optical signal processing, whereby tasks which are conventionally performed by manipulating signals in electronic form are done directly in optical form.<ref name="almeida_2004" /><ref name="boyraz_2004">{{cite journal
|doi = 10.1364/OPEX.12.004094
|title = All optical switching and continuum generation in silicon waveguides
|journal = [[Optics Express]]
|year = 2004
|volume = 12
|issue = 17
|pages = 4094–4102
| bibcode = 2004OExpr..12.4094B |last1 = Boyraz
|first1 = ÖZdal
|last2 = Koonath
|first2 = Prakash
|last3 = Raghunathan
|first3 = Varun
|last4 = Jalali
|first4 = Bahram
}}</ref> An important example is all-[[optical switching]], whereby the routing of optical signals is directly controlled by other optical signals.<ref name="vlasov_2008">{{cite journal
|doi = 10.1038/nphoton.2008.31
|title = High-throughput silicon nanophotonic wavelength-insensitive switch for on-chip optical networks
|journal = [[Nature Photonics]]
|year = 2008
|volume = 2
|issue = 4
|pages = 242–246
|last1 = Vlasov
|first1 = Yurii
|last2 = Green
|first2 = William M. J.
|last3 = Xia
|first3 = Fengnian
}}</ref> Another example is all-optical wavelength conversion.<ref name="foster_2007">{{cite journal
|doi = 10.1364/OE.15.012949
|title = Broad-band continuous-wave parametric wavelength conversion in silicon nanowaveguides
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 20
|pages = 12949–12958
| bibcode = 2007OExpr..1512949F |last1 = Foster
|first1 = Mark A.
|last2 = Turner
|first2 = Amy C.
|last3 = Salem
|first3 = Reza
|last4 = Lipson
|first4 = Michal
|last5 = Gaeta
|first5 = Alexander L.
}}</ref>

In 2013, a [[startup company]] named "[[Compass-EOS]]", based in [[California]] and in [[Israel]], was the first to present a commercial silicon-to-photonics router.<ref>{{cite web|url=http://venturebeat.com/2013/03/12/after-six-years-of-planning-compass-eos-takes-on-cisco-to-make-blazing-fast-routers/ |title=After six years of planning, Compass-EOS takes on Cisco to make blazing-fast routers |publisher=venturebeat.com |date=12 March 2013|accessdate=25 April 2013}}</ref>

=== Long range telecommunications using silicon photonics ===

Silicon microphotonics can potentially increase the [[Internet]]'s bandwidth capacity by providing micro-scale, ultra low power devices. Furthermore, the power consumption of [[datacenter]]s may be significantly reduced if this is successfully achieved. Researchers at [[Sandia National Laboratories|Sandia]],<ref name="Sandia_2010">{{cite journal
|title = Power penalty measurement and frequency chirp extraction in silicon microdisk resonator modulators
|journal = Proc. Optical Fiber Communication Conference (OFC)
|year = 2010
|issue = OMI7
|author = Zortman, W. A.
}}</ref> Kotura, [[Nippon Telegraph and Telephone|NTT]], [[Fujitsu]] and various academic institutes have been attempting to prove this functionality. A prototype 80 km, 12.5 Gbit/s transmission has recently been reported using microring silicon devices.<ref name="Biberman_Manipatruni_2010">{{cite journal
|doi = 10.1364/OE.18.015544
|title = First demonstration of long-haul transmission using silicon microring modulators
|journal = [[Optics Express]]
|year = 2010
|volume = 18
|issue = 15
|pages = 15544–15552
| bibcode = 2010OExpr..1815544B
|last1 = Biberman
|first1 = Aleksandr
|last2 = Manipatruni
|first2 = Sasikanth
|last3 = Ophir
|first3 = Noam
|last4 = Chen
|first4 = Long
|last5 = Lipson
|first5 = Michal
|last6 = Bergman
|first6 = Keren
}}</ref>

== Physical properties ==

=== Optical guiding and dispersion tailoring ===

Silicon is [[transparency (optics)|transparent]] to [[infrared light]] with wavelengths above about 1.1 micrometres.<ref name="reading_lab">{{cite web
|url = http://www.rdg.ac.uk/infrared/library/infraredmaterials/ir-infraredmaterials-si.aspx
|title = Silicon (Si)
|publisher = [[University of Reading]] Infrared Multilayer Laboratory
|accessdate = 17 July 2009
}}</ref> Silicon also has a very high [[refractive index]], of about 3.5.<ref name="reading_lab" /> The tight optical confinement provided by this high index allows for microscopic [[optical waveguide]]s, which may have cross-sectional dimensions of only a few hundred [[nanometer]]s.<ref name="dekker_2008" /> This is substantially less than the wavelength of the light itself, and is analogous to a [[subwavelength-diameter optical fibre]]. Single mode propagation can be achieved,<ref name="dekker_2008" /> thus (like [[single-mode optical fiber]]) eliminating the problem of [[modal dispersion]].

The strong [[Interface conditions for electromagnetic fields|dielectric boundary effects]] that result from this tight confinement substantially alter the [[dispersion (optics)|optical dispersion relation]]. By selecting the waveguide geometry, it is possible to tailor the dispersion to have desired properties, which is of crucial importance to applications requiring ultrashort pulses.<ref name="dekker_2008" /> In particular, the ''group velocity dispersion'' (that is, the extent to which [[group velocity]] varies with wavelength) can be closely controlled. In bulk silicon at 1.55 micrometres, the group velocity dispersion (GVD) is ''normal'' in that pulses with longer wavelengths travel with higher group velocity than those with shorter wavelength. By selecting a suitable waveguide geometry, however, it is possible to reverse this, and achieve ''anomalous'' GVD, in which pulses with shorter wavelengths travel faster.<ref name="yin_2006" >{{cite journal
|doi = 10.1364/OL.31.001295
|title = Dispersion tailoring and soliton propagation in silicon waveguides
|journal = [[Optics Letters]]
|year = 2006
|volume = 31
|issue = 9
|pages = 1295–1297
| bibcode = 2006OptL...31.1295Y |last1 = Yin
|first1 = Lianghong
|last2 = Lin
|first2 = Q.
|last3 = Agrawal
|first3 = Govind P.
}}</ref><ref name="turner_2006" >{{cite journal
|doi = 10.1364/OE.14.004357
|title = Tailored anomalous group-velocity dispersion in silicon channel waveguides
|journal = [[Optics Express]]
|year = 2006
|volume = 14
|issue = 10
|pages = 4357–4362
| bibcode = 2006OExpr..14.4357T |last1 = Turner
|first1 = Amy C.
|last2 = Manolatou
|first2 = Christina
|last3 = Schmidt
|first3 = Bradley S.
|last4 = Lipson
|first4 = Michal
|last5 = Foster
|first5 = Mark A.
|last6 = Sharping
|first6 = Jay E.
|last7 = Gaeta
|first7 = Alexander L.
}}</ref> Anomalous dispersion is significant, as it is a prerequisite for [[soliton]] propagation, and [[modulational instability]].<ref name="agrawal_book">{{cite book
|last = Agrawal
|first = Govind P.
|year = 1995
|title = Nonlinear fiber optics
|place = San Diego (California)
|publisher = Academic Press
|edition =2nd
|isbn = 0-12-045142-5
}}</ref>

In order for the silicon photonic components to remain optically independent from the bulk silicon of the [[wafer (electronics)|wafer]] on which they are fabricated, it is necessary to have a layer of intervening material. This is usually [[silica]], which has a much lower refractive index (of about 1.44 in the wavelength region of interest<ref name="malitson_1965">{{cite journal
|doi = 10.1364/JOSA.55.001205
|title = Interspecimen Comparison of the Refractive Index of Fused Silica
|journal = [[Journal of the Optical Society of America]]
|year = 1965
|volume = 55
|issue = 10
|pages = 1205–1209
|author = Malitson, I. H.
}}</ref>), and thus light at the silicon-silica interface will (like light at the silicon-air interface) undergo [[total internal reflection]], and remain in the silicon. This construct is known as silicon on insulator.<ref name="pavesi_book" /><ref name="reed_book" /> It is named after the technology of [[silicon on insulator]] in electronics, whereby components are built upon a layer of [[insulator (electrical)|insulator]] in order to reduce [[parasitic capacitance]] and so improve performance.<ref name="celler_2003">{{cite journal
|title = Frontiers of silicon-on-insulator
|journal = [[Journal of Applied Physics]]
|year = 2003
|volume = 93
|page = 4955
| bibcode = 2003JAP....93.4955C |doi = 10.1063/1.1558223
|issue = 9 |last1 = Celler
|first1 = G. K.
|last2 = Cristoloveanu
|first2 = Sorin
}}</ref>

=== Kerr nonlinearity ===

Silicon has a focusing [[Kerr nonlinearity]], in that the [[refractive index]] increases with optical intensity.<ref name="dekker_2008" /> This effect is not especially strong in bulk silicon, but it can be greatly enhanced by using a silicon waveguide to concentrate light into a very small cross-sectional area.<ref name="hsieh_2006" /> This allows [[nonlinear optics|nonlinear optical]] effects to be seen at low powers. The nonlinearity can be enhanced further by using a [[slot waveguide]], in which the high refractive index of the silicon is used to confine light into a central region filled with a strongly nonlinear [[polymer]].<ref name="koos_2007" >{{cite journal
|doi = 10.1364/OE.15.005976
|title = Nonlinear silicon-on-insulator waveguides for all-optical signal processing
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 10
|pages = 5976–5990
| bibcode = 2007OExpr..15.5976K
|pmid=19546900|author1 = Koos
|first1 = C
|last2 = Jacome
|first2 = L
|last3 = Poulton
|first3 = C
|last4 = Leuthold
|first4 = J
|last5 = Freude
|first5 = W
}}</ref>

Kerr nonlinearity underlies a wide variety of optical phenomena.<ref name="agrawal_book" /> One example is [[four wave mixing]], which has been applied in silicon to realise [[optical parametric amplification]],<ref name="foster_2006">{{cite journal
|title = Broad-band optical parametric gain on a silicon photonic chip
|journal = [[Nature (journal)|Nature]]
|year = 2006
|volume = 441
|issue = 7096
|pages = 960–3
|pmid = 16791190
|doi = 10.1038/nature04932
| bibcode = 2006Natur.441..960F |author1 = Foster
|first1 = M. A.
|last2 = Turner
|first2 = A. C.
|last3 = Sharping
|first3 = J. E.
|last4 = Schmidt
|first4 = B. S.
|last5 = Lipson
|first5 = M
|last6 = Gaeta
|first6 = A. L.
}}</ref> parametric wavelength conversion,<ref name="foster_2007" /> and frequency comb generation.,<ref>{{cite journal|last1=Griffith|first1=Austin G.|last2=Lau|first2=Ryan K.W.|last3=Cardenas|first3=Jaime|last4=Okawachi|first4=Yoshitomo|last5=Mohanty|first5=Aseema|last6=Fain|first6=Romy|last7=Lee|first7=Yoon Ho Daniel|last8=Yu|first8=Mengjie|last9=Phare|first9=Christopher T.|last10=Poitras|first10=Carl B.|last11=Gaeta|first11=Alexander L.|last12=Lipson|first12=Michal|title=Silicon-chip mid-infrared frequency comb generation|journal=Nature Communications|date=24 February 2015|volume=6|pages=6299|doi=10.1038/ncomms7299|arxiv = 1408.1039 |bibcode = 2015NatCo...6E6299G }}</ref><ref>{{cite journal|last1=Kuyken|first1=Bart|last2=Ideguchi|first2=Takuro|last3=Holzner|first3=Simon|last4=Yan|first4=Ming|last5=Hänsch|first5=Theodor W.|last6=Van Campenhout|first6=Joris|last7=Verheyen|first7=Peter|last8=Coen|first8=Stéphane|last9=Leo|first9=Francois|last10=Baets|first10=Roel|last11=Roelkens|first11=Gunther|last12=Picqué|first12=Nathalie|title=An octave-spanning mid-infrared frequency comb generated in a silicon nanophotonic wire waveguide|journal=Nature Communications|date=20 February 2015|volume=6|pages=6310|doi=10.1038/ncomms7310|arxiv = 1405.4205 |bibcode = 2015NatCo...6E6310K }}</ref>

Kerr nonlinearity can also cause [[modulational instability]], in which it reinforces deviations from an optical waveform, leading to the generation of [[Frequency spectrum|spectral]]-sidebands and the eventual breakup of the waveform into a train of pulses.<ref name="panoiu_2006">{{cite journal
|title = Modulation instability in silicon photonic nanowires
|journal = [[Optics Letters]]
|year = 2006
|volume = 31
|pages = 3609–11
|pmid=17130919
| bibcode = 2006OptL...31.3609P |doi = 10.1364/OL.31.003609
|issue = 24 |last1 = Panoiu
|first1 = Nicolae C.
|last2 = Chen
|first2 = Xiaogang
|last3 = Osgood, Jr.
|first3 = Richard M.
}}</ref> Another example (as described below) is soliton propagation.

=== Two-photon absorption ===

Silicon exhibits [[two-photon absorption]] (TPA), in which a pair of [[photon]]s can act to excite an [[electron-hole pair]].<ref name="dekker_2008" /> This process is related to the Kerr effect, and by analogy with [[Mathematical descriptions of opacity|complex refractive index]], can be thought of as the [[Imaginary number|imaginary]]-part of a [[Complex number|complex]] Kerr nonlinearity.<ref name="dekker_2008" /> At the 1.55 micrometre telecommunication wavelength, this imaginary part is approximately 10% of the real part.<ref name="yin_2006_2">{{cite journal
|doi = 10.1364/OL.32.002031
|title = Impact of two-photon absorption on self-phase modulation in silicon waveguides: Free-carrier effects
|journal = [[Optics Letters]]
|year = 2006
|volume = 32
|issue = 14
|pages = 2031–2033
|last1 = Yin
|first1 = Lianghong
|last2 = Agrawal
|first2 = Govind P.
|bibcode = 2007OptL...32.2031Y
}}</ref>

The influence of TPA is highly disruptive, as it both wastes light, and generates unwanted [[heat]].<ref name="nikbin_article">{{cite news
|author = Nikbin, Darius
|title = Silicon photonics solves its "fundamental problem"
|publisher = IOP publishing
|url = http://optics.org/cws/article/research/25379
|date = 20 July 2006
}}</ref> It can be mitigated, however, either by switching to longer wavelengths (at which the TPA to Kerr ratio drops),<ref name="bristow_2007">{{cite journal
|title = Two-photon absorption and Kerr coefﬁcients of silicon for 850– {{convert|2200|nmi|km|abbr=on}}
|journal = [[Applied Physics Letters]]
|year = 2007
|volume = 90
|page = 191104
| bibcode = 2007ApPhL..90b1104R |doi = 10.1063/1.2430400
|issue = 2 |last1 = Rybczynski
|first1 = J.
|last2 = Kempa
|first2 = K.
|last3 = Herczynski
|first3 = A.
|last4 = Wang
|first4 = Y.
|last5 = Naughton
|first5 = M. J.
|last6 = Ren
|first6 = Z. F.
|last7 = Huang
|first7 = Z. P.
|last8 = Cai
|first8 = D.
|last9 = Giersig
|first9 = M.

}}</ref> or by using slot waveguides (in which the internal nonlinear material has a lower TPA to Kerr ratio).<ref name="koos_2007" /> Alternatively, the energy lost through TPA can be partially recovered (as is described below) by extracting it from the generated charge carriers.<ref name="tsia_2006">{{cite conference
|authors = Tsia, K. M.
|title = Energy Harvesting in Silicon Raman Amplifiers
|conference = 3rd [[IEEE]] International Conference on Group IV Photonics
|year = 2006
}}</ref>

=== Free charge carrier interactions ===

The [[Charge carriers in semiconductors|free charge carriers]] within silicon can both absorb photons and change its refractive index.<ref name="soref_1987">{{cite journal
|doi = 10.1109/JQE.1987.1073206
|title = Electrooptical Effects in Silicon
|journal = [[IEEE Journal of Quantum Electronics]]
|year = 1987
|volume = 23
|issue = 1
|pages = 123–129
| bibcode = 1987IJQE...23..123S |last1 = Soref
|first1 = R.
|last2 = Bennett
|first2 = B.
}}</ref> This is particularly significant at high intensities and for long durations, due to the carrier concentration being built up by TPA. The influence of free charge carriers is often (but not always) unwanted, and various means have been proposed to remove them. One such scheme is to [[ion implantation|implant]] the silicon with [[helium]] in order to enhance [[carrier recombination]].<ref name="liu_2006">{{cite journal
|doi = 10.1364/OL.31.001714
|title = Nonlinear absorption and Raman gain in helium-ion-implanted silicon waveguides
|journal = [[Optics Letters]]
|year = 2006
|volume = 31
|issue = 11
|pages = 1714–1716
| bibcode = 2006OptL...31.1714L |last1 = Liu
|first1 = Y.
|last2 = Tsang
|first2 = H. K.
}}</ref> A suitable choice of geometry can also be used to reduce the carrier lifetime. [[Rib waveguide]]s (in which the waveguides consist of thicker regions in a wider layer of silicon) enhance both the carrier recombination at the silica-silicon interface and the [[diffusion]] of carriers from the waveguide core.<ref name="dimitropoulos_2005">{{cite journal
|title = Lifetime of photogenerated carriers in silicon-on-insulator rib waveguides
|journal = [[Applied Physics Letters]]
|year = 2005
|volume = 86
|page = 071115
| bibcode = 2005ApPhL..86a1115Z |doi = 10.1063/1.1846145 |last1 = Zevallos l.
|first1 = Manuel E.
|last2 = Gayen
|first2 = S. K.
|last3 = Alrubaiee
|first3 = M.
|last4 = Alfano
|first4 = R. R.
}}</ref>

A more advanced scheme for carrier removal is to integrate the waveguide into the [[intrinsic semiconductor|intrinsic region]] of a [[PIN diode]], which is [[reverse bias]]ed so that the carriers are attracted away from the waveguide core.<ref name="jones_2005">{{cite journal
|doi = 10.1364/OPEX.13.000519
|title = Net continuous wave optical gain in a low loss silicon-on-insulator waveguide by stimulated Raman scattering
|journal = [[Optics Express]]
|year = 2005
|volume = 13
|issue = 2
|pages = 519–525
| bibcode = 2005OExpr..13..519J |last1 = Jones
|first1 = Richard
|last2 = Rong
|first2 = Haisheng
|last3 = Liu
|first3 = Ansheng
|last4 = Fang
|first4 = Alexander W.
|last5 = Paniccia
|first5 = Mario J.
|last6 = Hak
|first6 = Dani
|last7 = Cohen
|first7 = Oded
}}</ref> A more sophisticated scheme still, is to use the diode as part of a circuit in which [[voltage]] and [[Electric current|current]] are out of phase, thus allowing power to be extracted from the waveguide.<ref name="tsia_2006" /> The source of this power is the light lost to two photon absorption, and so by recovering some of it, the net loss (and the rate at which heat is generated) can be reduced.

As is mentioned above, free charge carrier effects can also be used constructively, in order to modulate the light.<ref name="barrios_2003" /><ref name="xu_2007" /><ref name="liu_2007" />

=== Second-order nonlinearity ===

Second-order nonlinearities cannot exist in bulk silicon because of the [[centrosymmetry]] of its crystalline structure. By applying strain however, the inversion symmetry of silicon can be broken. This can be obtained for example by depositing a [[silicon nitride]] layer on a thin silicon film.<ref name="JacobsenAndersen2006">{{cite journal|last1=Jacobsen|first1=Rune S.|last2=Andersen|first2=Karin N.|last3=Borel|first3=Peter I.|last4=Fage-Pedersen|first4=Jacob|last5=Frandsen|first5=Lars H.|last6=Hansen|first6=Ole|last7=Kristensen|first7=Martin|last8=Lavrinenko|first8=Andrei V.|last9=Moulin|first9=Gaid|last10=Ou|first10=Haiyan|last11=Peucheret|first11=Christophe|last12=Zsigri|first12=Beáta|last13=Bjarklev|first13=Anders|title=Strained silicon as a new electro-optic material|journal=Nature|volume=441|issue=7090|year=2006|pages=199–202|issn=0028-0836|doi=10.1038/nature04706|pmid=16688172|bibcode = 2006Natur.441..199J }}</ref>
Second-order nonlinear phenomena can be exploited for [[Pockels effect|optical modulation]], [[spontaneous parametric down-conversion]], [[Optical parametric amplifier|parametric amplification]], [[Optical computing|ultra-fast optical signal processing]] and [[Infrared|mid-infrared]] generation. Efficient nonlinear conversion however requires [[Phase matching#Phase matching|phase matching]] between the optical waves involved. Second-order nonlinear waveguides based on strained silicon can achieve [[Phase matching#Phase matching|phase matching]] by [[Modal dispersion|dispersion-engineering]].<ref name="AvrutskySoref2011">{{cite journal|last1=Avrutsky|first1=Ivan|last2=Soref|first2=Richard|title=Phase-matched sum frequency generation in strained silicon waveguides using their second-order nonlinear optical susceptibility|journal=Optics Express|volume=19|issue=22|year=2011|page=21707|issn=1094-4087|doi=10.1364/OE.19.021707|bibcode = 2011OExpr..1921707A }}</ref>
So far, however, experimental demonstrations are based only on designs which are not [[Phase matching#Phase matching|phase matched]].<ref name="CazzanelliBianco2011">{{cite journal|last1=Cazzanelli|first1=M.|last2=Bianco|first2=F.|last3=Borga|first3=E.|last4=Pucker|first4=G.|last5=Ghulinyan|first5=M.|last6=Degoli|first6=E.|last7=Luppi|first7=E.|last8=Véniard|first8=V.|last9=Ossicini|first9=S.|last10=Modotto|first10=D.|last11=Wabnitz|first11=S.|last12=Pierobon|first12=R.|last13=Pavesi|first13=L.|title=Second-harmonic generation in silicon waveguides strained by silicon nitride|journal=Nature Materials|volume=11|issue=2|year=2011|pages=148–154|issn=1476-1122|doi=10.1038/nmat3200|pmid=22138793|bibcode = 2012NatMa..11..148C }}</ref>
It has been shown that [[Phase matching#Phase matching|phase matching]] can be obtained as well in silicon double [[slot waveguide]]s coated with a highly nonlinear organic cladding<ref name="AlloattiKorn2012">{{cite journal|last1=Alloatti|first1=L.|last2=Korn|first2=D.|last3=Weimann|first3=C.|last4=Koos|first4=C.|last5=Freude|first5=W.|last6=Leuthold|first6=J.|title=Second-order nonlinear silicon-organic hybrid waveguides|journal=Optics Express|volume=20|issue=18|year=2012|page=20506|issn=1094-4087|doi=10.1364/OE.20.020506|bibcode = 2012OExpr..2020506A }}</ref>
and in periodically strained silicon waveguides.<ref name="HonTsia2009">{{cite journal|last1=Hon|first1=Nick K.|last2=Tsia|first2=Kevin K.|last3=Solli|first3=Daniel R.|last4=Jalali|first4=Bahram|title=Periodically poled silicon|journal=Applied Physics Letters|volume=94|issue=9|year=2009|page=091116|issn=00036951|doi=10.1063/1.3094750|arxiv = 0812.4427 |bibcode = 2009ApPhL..94i1116H }}</ref>

=== The Raman effect ===

Silicon exhibits the [[Raman effect]], in which a photon is exchanged for a photon with a slightly different energy, corresponding to an excitation or a relaxation of the material. Silicon's Raman transition is dominated by a single, very narrow frequency peak, which is problematic for broadband phenomena such as [[Raman amplification]], but is beneficial for narrowband devices such as [[Raman laser]]s.<ref name="dekker_2008" /> Early studies of Raman amplification and Raman lasers started at UCLA which led to demonstration of net gain Silicon Raman amplifiers and silicon pulsed Raman laser with fiber resonator (Optics express 2004). Consequently, all-silicon Raman lasers have been fabricated in 2005.<ref name="rong_2005" />

== Solitons ==

The evolution of light through silicon waveguides can be approximated with a cubic [[Nonlinear Schrödinger equation]],<ref name="dekker_2008" /> which is notable for admitting [[hyperbolic secant|sech]]-like [[soliton]] solutions.<ref name="drazin_book">{{cite book
|title = Solitons: an introduction
|publisher = [[Cambridge University Press]]
|year = 1989
|isbn = 0-521-33655-4
|author = Drazin, P. G. and Johnson, R. S.
}}</ref> These [[optical soliton]]s (which are also known in [[optical fiber]]) result from a balance between [[self phase modulation]] (which causes the leading edge of the pulse to be [[Redshifted#Effects due to physical optics or radiative transfer|redshifted]] and the trailing edge blueshifted) and anomalous group velocity dispersion.<ref name="agrawal_book" /> Such solitons have been observed in silicon waveguides, by groups at the universities of [[Columbia University|Columbia]],<ref name="hsieh_2006" /> [[Rochester University|Rochester]],<ref name="zhang_2007" /> and [[University of Bath|Bath]].<ref name="ding_2008" />

== References ==
{{reflist|30em}}

== External links ==
* [http://domino.research.ibm.com/comm/research_projects.nsf/pages/photonics.index.html IBM's page on silicon integrated nanophotonics]
* [https://www-ssl.intel.com/content/www/us/en/research/intel-labs-silicon-photonics-research.html Intel's page on silicon photonics]
* [http://nanophotonics.ece.cornell.edu Michal Lipson's page on silicon photonics]
* [http://www.rle.mit.edu/pmg/ Michael Watts' MIT group working on silicon photonics]
* [http://www.analogphotonics.com/ MIT spin-off company offering silicon photonics design and [MPW]]
* [http://www.uksiliconphotonics.co.uk/ Uk based project website on silicon photonics]
* [http://www.helios-project.eu/ European project website on silicon photonics]
* [http://www.siliconphotonics.co.uk/ UK based group working on silicon photonics]
* [http://silicon-photonics.ief.u-psud.fr/ French based group working on silicon photonics]
* [http://photonics.intec.ugent.be/ Belgian group working on silicon photonics]
* [http://www.ipq.kit.edu/english/index.php Silicon photonics at KIT]
* [http://photontransfer.com/ Photon Transfer]

{{DEFAULTSORT:Silicon Photonics}}
[[Category:Nonlinear optics]]
[[Category:Photonics]]
[[Category:Silicon]]

Plasmonische Solarzelle

2015-06-06T15:15:04Z

Bibcode Bot: Adding 0 arxiv eprint(s), 5 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{expert|date=December 2014}}
'''Plasmonic solar cells''' are a class of [[photovoltaic device]]s that convert light into electricity by using [[plasmon]]s. Plasmonic solar cells are a type of [[thin film solar cell]] which are typically 1-2μm thick. They can use [[Substrate (materials science)|substrates]] which are cheaper than [[silicon]], such as [[glass]], [[plastic]] or [[steel]]. The biggest problem for thin film solar cells is that they don’t absorb as much light as thicker solar cells. Methods for trapping light are crucial in order to make thin film solar cells viable. Plasmonic cells improve absorption by scattering light using metal [[nanoparticle]]s excited at their [[surface plasmon resonance]].
<ref name=Catchpole>K. R. Catchpole and A. Polman, "Plasmonic solar cells," Opt. Express 16, 21793-21800 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-26-21793</ref>
This allows light to be absorbed more directly without the relatively thick additional layer required in other types of thin-film solar cells.

== History ==

=== People ===

There have been quite a few pioneers working with plasmonic solar cells.<ref name=Catchpole/> One of the main focuses has been on improving the thin film SC through the use of metal nanoparticles distributed on the surface. It has been found that the [[Raman scattering]] can be increased by [[order of magnitude]] when using metal nanoparticles. The increased Raman scattering provides more [[photon]]s to become available to excite [[surface plasmon]]s which cause [[electron]]s to be excited and travel through the thin film SC to create a [[Current (electricity)|current]]. The list below shows a few of research which has been done to improve PSCs.

*Stuart and Hall: Photocurrent enhancement by 18x with 165 nm SOI [[photodetector]] with wavelength of 800 nm using silver nanoparticles used for scattering and absorption of light.<ref>{{cite journal | bibcode=1998ApPhL..73.3815S | doi = 10.1063/1.122903 | title=Island size effects in nanoparticle-enhanced photodetectors | year=1998 | last1=Stuart | first1=Howard R. | last2=Hall | first2=Dennis G. | journal=Applied Physics Letters | volume=73 | issue=26 | pages=3815 }}</ref>

*Schaadt: Gold nanoparticles used for scattering and absorption of light on doped silicon obtaining 80% enhancements with 500 nm wavelength.<ref>{{cite journal | doi = 10.1063/1.1855423 | title = Enhanced semiconductor optical absorption via surface plasmon excitation in metal nanoparticles | year = 2005 | last1 = Schaadt | first1 = D. M. | last2 = Feng | first2 = B. | last3 = Yu | first3 = E. T. | journal = Applied Physics Letters | volume = 86 | issue = 6 | pages = 063106 |bibcode = 2005ApPhL..86f3106S }}</ref>

*Derkacs: Gold nanoparticles on [[thin-film silicon]] gaining 8% on [[conversion efficiency]].<ref>{{cite journal | doi = 10.1063/1.2336629 | title = Improved performance of amorphous silicon solar cells via scattering from surface plasmon polaritons in nearby metallic nanoparticles | year = 2006 | last1 = Derkacs | first1 = D. | last2 = Lim | first2 = S. H. | last3 = Matheu | first3 = P. | last4 = Mar | first4 = W. | last5 = Yu | first5 = E. T. | journal = Applied Physics Letters | volume = 89 | issue = 9 | pages = 093103 |bibcode = 2006ApPhL..89i3103D }}</ref>

*Pillai: Silver particles on SOI obtaining 33% photocurrent increase.<ref>{{cite journal | doi = 10.1063/1.2734885 | bibcode= 2007JAP...101i3105P | title = Surface plasmon enhanced silicon solar cells | year = 2007 | last1 = Pillai | first1 = S. | last2 = Catchpole | first2 = K. R. | last3 = Trupke | first3 = T. | last4 = Green | first4 = M. A. | journal = Journal of Applied Physics | volume = 101 | issue = 9 | pages = 093105 }}</ref><ref>{{cite journal | doi = 10.1063/1.2195695 | title = Enhanced emission from Si-based light-emitting diodes using surface plasmons | year = 2006 | last1 = Pillai | first1 = S. | last2 = Catchpole | first2 = K. R. | last3 = Trupke | first3 = T. | last4 = Zhang | first4 = G. | last5 = Zhao | first5 = J. | last6 = Green | first6 = M. A. | journal = Applied Physics Letters | volume = 88 | issue = 16 | pages = 161102 |bibcode = 2006ApPhL..88p1102P }}</ref>

*Stenzel: Enhancements in photocurrent by a factor of 2.7 for ITO-copper [[phthalocyanine]]-[[indium]] structures.

*Westphalen: Enhancement for silver clusters incorporated into ITO and [[zinc]] phthalocyanine solar cells.<ref>{{cite journal | doi = 10.1016/S0927-0248(99)00100-2 | title = Metal cluster enhanced organic solar cells | year = 2000 | last1 = Westphalen | first1 = M | last2 = Kreibig | first2 = U | last3 = Rostalski | first3 = J | last4 = Lüth | first4 = H | last5 = Meissner | first5 = D | journal = Solar Energy Materials and Solar Cells | volume = 61 | pages = 97}}</ref>

*Rand: Enhanced efficiencies for ultra thin film organic solar cells due to 5 nm diameter silver nanoparticles.<ref>{{cite journal | doi = 10.1063/1.1812589|bibcode=2004JAP....96.7519R | title = Long-range absorption enhancement in organic tandem thin-film solar cells containing silver nanoclusters | year = 2004 | last1 = Rand | first1 = Barry P. | last2 = Peumans | first2 = Peter | last3 = Forrest | first3 = Stephen R. | journal = Journal of Applied Physics | volume = 96 | issue = 12 | pages = 7519 }}</ref><ref>http://www.prima-ict.eu</ref>

*Brown: Enhanced photocurrent and efficiencies in dye-sensitized solar cells incorporating metal-insulator core-shell nanoparticle geometries.<ref>{{cite journal | doi = 10.1021/nl1031106 | title = Plasmonic Dye-Sensitized Solar Cells Using Core−Shell Metal−Insulator Nanoparticles | year = 2010 | last1= Brown | first1 = M. D. | last2 = Suteewong | first2 = T. | last3 = Kumar | first3 = R.S.S. | last4 = D'Innocenzo | first4 = V | last5 = Petrozza | first5 = A | last6 = Lee | first6 = M | last7 = Wiesner | first7 = U. | last8 = Snaith | first8 = H | | authorlink8 = Henry Snaith |journal = Nano Letters | volume = 11 | issue = 2 | pages = 438–445|bibcode = 2011NanoL..11..438B }}</ref>

*Li: [[Solar cell efficiency | Power conversion efficiency]] of 8.8% has been reached with a single-junction bulk-heterojunction [[polymer solar cell]] by incorporating dual plasmonic nanostructures (nanograting and nanoparticles) <ref name=Dual_Plasmonics>{{cite journal | doi = 10.1002/adma.201200120| title = Dual Plasmonic Nanostructures for High Performance Inverted Organic Solar Cells | year = 2012| last1 = Li | first1 = Xuanhua | last2 = Choy| first2 = Wallace C. H. | last3 = Huo| first3 = Lijun | last4 = Xie | first4 = Fengxian | last5 = Sha | first5 = Wei E. I. | last6 = Ding | first6 = Baofu | last7 = Guo | first7 = Xia | last8 = Li | first8 = Yongfang | last9 = Hou | first9 = Jianhui | last10 = You | first10 = Jingbi | last11 = Yang | first11 = Yang | journal = Advanced Materials | volume = 24 | issue=22 | pages=3046-3052 }}</ref>

*Zhang, Saliba: Enhanced photocurrent in [[perovskite solar cell]]s utilizing plasmonic core-shell (gold-silica) nanoparticles.<ref>{{cite journal|last1=Zhang|first1=Wei|last2=Saliba|first2=Michael|last3=Stranks|first3=Samuel D.|last4=Sun|first4=Yao|last5=Shi|first5=Xian|last6=Wiesner|first6=Ulrich|last7=Snaith|first7=Henry J.|authorlink7 = Henry Snaith|title=Enhancement of Perovskite-Based Solar Cells Employing Core–Shell Metal Nanoparticles|journal=Nano Letters|date=11 September 2013|volume=13|issue=9|pages=4505–4510|doi=10.1021/nl4024287}}</ref>

=== Devices ===

There are currently three different generations of SCs. The first generation (those in the market today) are made with crystalline [[semiconductor wafer]]s, typically silicon. These are the SCs everybody thinks of when they hear "Solar Cell".

Current SCs trap light by creating [[pyramid]]s on the surface which have dimensions bigger than most thin film SCs. Making the surface of the substrate rough (typically by growing SnO2 or ZnO on surface) with dimensions on the order of the incoming [[wavelength]]s and depositing the SC on top has been explored. This method increases the [[photocurrent]], but the thin film SC would then have poor material quality.
<ref name=Muller>{{cite journal | doi = 10.1016/j.solener.2004.03.015 | title = TCO and light trapping in silicon thin film solar cells | year = 2004 | last1 = Müller | first1 = Joachim | last2 = Rech | first2 = Bernd | last3 = Springer | first3 = Jiri | last4 = Vanecek | first4 = Milan | journal = Solar Energy | volume = 77 | issue = 6 | pages = 917 |bibcode = 2004SoEn...77..917M }}</ref>

The second generation SCs are based on [[thin film]] technologies such as those presented here. These SCs focus on lowering the amount of material used as well as increasing the energy production. Third generation SCs are currently being researched. They focus on reducing the cost of the second generation SCs.
<ref name=Conibeer>Gavin Conibeer, Third generation photovoltaics, Proc. SPIE Vol. 7411, 74110D (Aug. 20, 2009)</ref>
The third generation SCs are discussed in more detail under recent advancement.

== Design ==
The design for a PSC varies depending on the method being used to trap and scatter light across the surface and through the material.

=== Nanoparticle cells ===
[[File:PSC using Metal Nanoparticles.png|thumb|alt=A plasmonic solar cell utilizing metal nanoparticles to distribute light and enhance absorption.|PSC using metal nanoparticles.]]
A common design is to deposit metal nanoparticles on the top surface of the thin film SC. When light hits these metal nanoparticles at their surface plasmon resonance, the light is scattered in many different directions. This allows light to travel along the SC and bounce between the substrate and the nanoparticles enabling the SC to absorb more light.
<ref name=Tanabe>{{cite journal | last1 = Tanabe | first1 = K. | year = 2009 | title = A Review of Ultrahigh Efficiency III-V Semiconductor Compound Solar Cells: Multijunction Tandem, Lower Dimensional, Photonic Up/Down Conversion and Plasmonic Nanometallic Structures | url = | journal = Energies | volume = 2 | issue = 3| pages = 504–530 | doi = 10.3390/en20300504 }}</ref>

=== Metal film cells ===

Other methods utilizing surface plasmons for harvesting solar energy are available. One other type of structure is to have a thin film of silicon and a thin layer of metal deposited on the lower surface. The light will travel through the silicon and generate surface plasmons on the interface of the silicon and metal. This generates electric fields inside of the silicon since electric fields do not travel very far into metals. If the [[electric field]] is strong enough, electrons can be moved and collected to produce a photocurrent. The thin film of metal in this design must have nanometer sized grooves which act as [[waveguide]]s for the incoming light in order to excite as many photons in the silicon thin film as possible.
<ref name=Ferry>{{cite journal | doi = 10.1021/nl8022548 | pages= 4391–4397 | title = Plasmonic Nanostructure Design for Efficient Light Coupling into Solar Cells | year = 2008 | last1 = Ferry | first1 = Vivian E. | last2 = Sweatlock | first2 = Luke A. | last3 = Pacifici | first3 = Domenico | last4 = Atwater | first4 = Harry A. | journal = Nano Letters | volume = 8 | issue = 12 | pmid = 19367883 |bibcode = 2008NanoL...8.4391F }}</ref>

== Principles ==

=== General ===
[[File:Thin vs Thick SC.png|thumb|alt=Light effects on thin and thick solar cells.|Thin film SC (left) and Typical SC (right).]]
When a photon is excited in the substrate of a SC, an electron and hole are separated. Once the electrons and holes are separated, they will want to recombine since they are of opposite charge. If the electrons can be collected prior to this happening they can be used as a current for an external circuit. Designing the thickness of a solar cell is always a trade-off between minimizing this recombination (thinner layers) and absorbing more photons (thicker layer).<ref name=Tanabe/>

=== Nanoparticles ===

==== Scattering and Absorption ====
The basic principles for the functioning of plasmonic solar cells include scattering and absorption of light due to the deposition of metal nanoparticles. Silicon does not absorb light very well. For this reason, more light needs to be scattered across the surface in order to increase the absorption. It has been found that metal nanoparticles help to scatter the incoming light across the surface of the silicon substrate. The equations that govern the scattering and absorption of light can be shown as:
*<math>C_{scat}=\frac{1}{6\pi}\left(\frac{2\pi}{\lambda}\right)^4|\alpha|^2</math>
This shows the scattering of light for particles which have diameters below the wavelength of light.
*<math>C_{abs}=\frac{2\pi}{\lambda}Im[\alpha]</math>
This shows the absorption for a point dipole model.
*<math>\alpha=3V\left[\frac{\epsilon_p/\epsilon_m-1}{\epsilon_p/\epsilon_m+2}\right]</math>
This is the polarizability of the particle. V is the particle volume. <math>\epsilon_p</math> is the dielectric function of the particle. <math>\epsilon_m</math> is the [[dielectric function]] of the embedding medium. When <math>\epsilon_p=-2\epsilon_m</math> the [[polarizability]] of the particle becomes large. This polarizability value is known as the surface plasmon resonance. The dielectric function for metals with low absorption can be defined as:
*<math>\epsilon=1-\frac{\omega_p^2}{\omega^2+i\gamma\omega}</math>
In the previous equation, <math>\omega_p</math> is the bulk plasma frequency. This is defined as:
*<math>\omega_p^2=Ne^2/m\epsilon_0</math>
N is the density of free electrons, e is the [[Electrical resistivity and conductivity|electronic charge]] and m is the [[Effective mass (solid-state physics)|effective mass]] of an electron. <math>\epsilon_0</math> is the dielectric constant of free space. The equation for the surface plasmon resonance in free space can therefore be represented by:
*<math>\alpha=3V\frac{\omega_p^2}{\omega_p^2-3\omega^2-i\gamma\omega}</math>
Many of the plasmonic solar cells use nanoparticles to enhance the scattering of light. These nanoparticles take the shape of spheres, and therefore the surface plasmon resonance frequency for spheres is desirable. By solving the previous [[equation]]s, the surface plasmon resonance frequency for a sphere in free space can be shown as:
*<math>\omega_{sp}=\sqrt{3}\omega_p</math>

As an example, at the surface plasmon resonance for a silver nanoparticle, the scattering cross-section is about 10x the cross-section of the nanoparticle. The goal of the nanoparticles is to trap light on the surface of the SC. The absorption of light is not important for the nanoparticle, rather, it is important for the SC. One would think that if the nanoparticle is increased in size, then the scattering cross-section becomes larger. This is true, however, when compared with the size of the nanoparticle, the ratio (<math>\frac{CS_{scat}}{CS_{particle}}</math>) is reduced. Particles with a large scattering cross section tend to have a broader plasmon resonance range.

==== Wavelength dependence ====
Surface plasmon resonance mainly depends on the density of free electrons in the particle. The order of densities of electrons for different metals is shown below along with the type of light which corresponds to the resonance.
*[[Aluminum]] - Ultra-violet
*[[Silver]] - Ultra-violet
*[[Gold]] - Visible
*[[Copper]] - Visible

If the dielectric constant for the embedding medium is varied, the [[resonant frequency]] can be shifted. Higher indexes of refraction will lead to a longer wavelength frequency.

==== Light trapping ====
The metal nanoparticles are deposited at a distance from the substrate in order to trap the light between the substrate and the particles. The particles are embedded in a material on top of the substrate. The material is typically a [[dielectric]], such as silicon or [[silicon nitride]]. When performing experiment and simulations on the amount of light scattered into the substrate due to the distance between the particle and substrate, air is used as the embedding material as a reference. It has been found that the amount of light radiated into the substrate decreases with distance from the substrate. This means that nanoparticles on the surface are desirable for radiating light into the substrate, but if there is no distance between the particle and substrate, then the light is not trapped and more light escapes.

The surface plasmons are the excitations of the conduction electrons at the interface of metal and the dielectric. Metallic nanoparticles can be used to couple and trap freely propagating plane waves into the semiconductor thin film layer. Light can be folded into the absorbing layer to increase the absorption. The localized surface plasmons in metal nanoparticles and the surface plasmon polaritons at the interface of metal and semiconductor are of interest in the current research. In recent reported papers, the shape and size of the metal nanoparticles are key factors to determine the incoupling efficiency. The smaller particles have larger incoupling efficiency due to the enhanced near-field coupling. However, very small particles suffer from large ohmic losses.
<ref>{{cite journal|last=Atwater|first=Harry|author2=A. Polman |title=Plasmonics for improved photovoltaic devices|journal=Nature materials|date=19 February 2010|volume=9|pages=205–13|bibcode=2010NatMa...9..205A|doi=10.1038/nmat2629|issue=3|pmid=20168344}}</ref>

=== Metal film ===
As light is incident upon the surface of the metal film, it excites surface plasmons. The surface plasmon frequency is specific for the material, but through the use of [[grating]]s on the surface of the film, different frequencies can be obtained. The surface plasmons are also preserved through the use of waveguides as they make the surface plasmons easier to travel on the surface and the losses due to resistance and radiation are minimized. The electric field generated by the surface plasmons influences the electrons to travel toward the collecting substrate.
<ref name=Huag>{{cite journal | doi = 10.1063/1.2981194 | title = Plasmonic absorption in textured silver back reflectors of thin film solar cells | year = 2008 | last1 = Haug | first1 = F.-J. | last2 = SöDerström | first2 = T. | last3 = Cubero | first3 = O. | last4 = Terrazzoni-Daudrix | first4 = V. | last5 = Ballif | first5 = C. | journal = Journal of Applied Physics | volume = 104 | issue = 6 | pages = 064509 |bibcode = 2008JAP...104f4509H }}</ref>

== Materials ==
{| class="wikitable" border="1"
|-
! First Generation
! Second Generation
! Third Generation
|-
| Single-crystal silicon
| CuInSe2
| Gallium Indium Phosphide
|-
| Multicrystalline silicon
| amorphous silicon
| Gallium Indium Arsenide
|-
| Polycrystalline silicon
| thin film crystalline Si
| Germanium
|}<ref name=Conibeer/><ref>http://www1.eere.energy.gov/solar/solar_cell_materials.html</ref>

== Applications ==
The applications for plasmonic solar cells are endless. The need for cheaper and more efficient solar cells is huge. In order for solar cells to be considered cost effective, they need to provide energy for a smaller price than that of traditional power sources such as [[coal]] and [[gasoline]]. The movement toward a more green world has helped to spark research in the area of plasmonic solar cells. Currently, solar cells cannot exceed efficiencies of about 30% (First Generation). With new technologies (Third Generation), efficiencies of up to 40-60% can be expected. With a reduction of materials through the use of thin film technology (Second Generation), prices can be driven lower.

Certain applications for plasmonic solar cells would be for [[space exploration]] vehicles. A main contribution for this would be the reduced weight of the solar cells. An external fuel source would also not be needed if enough power could be generated from the solar cells. This would drastically help to reduce the weight as well.

Solar cells have a great potential to help rural [[electrification]]. An estimated two million villages near the equator have limited access to electricity and fossil fuels and that approximately 25%<ref>http://www.globalissues.org/article/26/poverty-facts-and-stats</ref> of people in the world do not have access to electricity. When the cost of extending [[power grid]]s, running rural electricity and using diesel generators is compared with the cost of solar cells, many times the solar cells win. If the efficiency and cost of the current solar cell technology is decreased even further, then many rural communities and villages around the world could obtain electricity when current methods are out of the question. Specific applications for rural communities would be water pumping systems, residential electric supply and street lights. A particularly interesting application would be for health systems in countries where motorized vehicles are not overly abundant. Solar cells could be used to provide the power to refrigerate [[medication]]s in coolers during transport.

Solar cells could also provide power to [[lighthouse]]s, [[buoy]]s, or even [[battleship]]s out in the ocean. Industrial companies could use them to power [[telecommunications]] systems or monitoring and control systems along pipelines or other system.<ref name=web/>

If the solar cells could be produced on a large scale and be cost effective then entire [[power station]]s could be built in order to provide power to the electrical grids. With a reduction in size, they could be implemented on both commercial and residential buildings with a much smaller footprint. They might not even seem like an [[eyesore]].
<ref name=web>http://www.soton.ac.uk/~solar/intro/appso.htm</ref>

Other areas are in hybrid systems. The solar cells could help to power high consumption devices such as [[automobile]]s in order to reduce the amount of fossil fuels used and to help improve the environmental conditions of the earth.

In consumer electronics devices, solar cells could be used to replace batteries for low power electronics. This would save everyone a lot of money and it would also help to reduce the amount of waste going into [[landfill]]s.<ref>http://blog.coolerplanet.com/2009/01/23/the-4-basic-types-of-solar-cell-applications/</ref>

== Recent advancements ==

=== Choice of plasmonic metal nanoparticles ===

Proper choice of plasmatic metal nanoparticles is crucial for the maximum light absorption in the active layer. Front surface located nanoparticles Ag and Au are the most widely used materials due to their surface plasmon resonances located in the visible range and therefore interact more strongly with the peak solar intensity. However, such noble metal nanoparticles always introduce reduced light coupling into Si at the short wavelengths below the surface plasmon resonance due to the detrimental Fano effect, i.e. the destructive interference between the scattered and unscattered light. Moreover, the noble metal nanoparticles are impractical to implement for large-scale solar cell manufacture due to their high cost and scarcity in earth crest. Recently, Zhang et al. have demonstrated the low cost and earth abundant materials Al nanoparticles to be able to outperform the widely used Ag and Au nanoparticles. Al nanoparticles, with their surface plasmon resonances located in the UV region below the desired solar spectrum edge at 300 nm, can avoid the reduction and introduce extra enhancement in the shorter wavelength range.<ref>{{cite journal| title=Low cost and high performance Al nanoparticles for broadband light trapping in Si wafer solar cells| year=2012 | last1=Yinan | first1=Zhang et al| journal=Applied Physics Letters | volume=100 | issue=12 | pages=151101 |bibcode = 2012ApPhL.100b1101N |doi = 10.1063/1.3675451 }}</ref><ref>{{cite journal| title=Improved multicrystalline Si solar cells by light trapping from Al nanoparticle enhanced antireflection coating| year=2013 | last1=Yinan | first1=Zhang et al| journal=Opt. Mater. Express| volume=3 | issue=4 | pages=489 }}</ref>

=== Light trapping ===

As discussed earlier, being able to concentrate and scatter light across the surface of the plasmonic solar cell will help to increase efficiencies. Recently, research at [[Sandia National Laboratories]] has discovered a photonic waveguide which collects light at a certain wavelength and traps it within the structure. This new structure can contain 95% of the light that enters it compared to 30% for other traditional waveguides. It can also direct the light within one wavelength which is ten times greater than traditional waveguides. The wavelength this device captures can be selected by changing the structure of the lattice which comprises the structure. If this structure is used to trap light and keep it in the structure until the solar cell can absorb it, the efficiency of the solar cell could be increased dramatically.<ref>http://www.sandia.gov/media/photonic.htm</ref>

=== Absorption ===

Another recent advancement in plasmonic solar cells is using other methods to aid in the absorption of light. One way being researched is the use of metal wires on top of the substrate to scatter the light. This would help by utilizing a larger area of the surface of the solar cell for light scattering and absorption. The danger in using lines instead of dots would be creating a reflective layer which would reject light from the system. This is very undesirable for solar cells. This would be very similar to the thin metal film approach, but it also utilizes the scattering effect of the nanoparticles.
<ref>{{cite journal | doi = 10.1002/adma.200900331 | title = Design of Plasmonic Thin-Film Solar Cells with Broadband Absorption Enhancements | year = 2009 | last1 = Pala | first1 = Ragip A. | last2 = White | first2 = Justin | last3 = Barnard | first3 = Edward | last4 = Liu | first4 = John | last5 = Brongersma | first5 = Mark L. | journal = Advanced Materials | volume = 21 | issue = 34 | pages = 3504 }}</ref>

=== Third generation ===

The goal of third generation solar cells is to increase the efficiency using second generation solar cells (thin film) and using materials that are found abundantly on earth. This has also been a goal of the thin film solar cells. With the use of common and safe materials, third generation solar cells should be able to be manufactured in mass quantities further reducing the costs. The initial costs would be high in order to produce the manufacturing processes, but after that they should be cheap. The way third generation solar cells will be able to improve efficiency is to absorb a wider range of frequencies. The current thin film technology has been limited to one frequency due to the use of single band gap devices.<ref name=Conibeer/>

==== Multiple energy levels ====

The idea for multiple energy level solar cells is to basically stack thin film solar cells on top of each other. Each thin film solar cell would have a different band gap which means that if part of the solar spectrum was not absorbed by the first cell then the one just below would be able to absorb part of the spectrum. These can be stacked and an optimal band gap can be used for each cell in order to produce the maximum amount of power. Options for how each cell is connected are available, such as serial or parallel. The serial connection is desired because the output of the solar cell would just be two leads.

The lattice structure in each of the thin film cells needs to be the same. If it is not then there will be losses. The processes used for depositing the layers are complex. They include Molecular Beam Epitaxy and Metal Organic Vapour Phase Epitaxy. The current efficiency record is made with this process but doesn't have exact matching lattice constants. The losses due to this are not as effective because the differences in lattices allows for more optimal band gap material for the first two cells. This type of cell is expected to be able to be 50% efficient.

Lower quality materials that use cheaper deposition processes are being researched as well. These devices are not as efficient, but the price, size and power combined allow them to be just as cost effective. Since the processes are simpler and the materials are more readily available, the mass production of these devices is more economical.

==== Hot carrier cells ====

A problem with solar cells is that the high energy photons that hit the surface are converted to heat. This is a loss for the cell because the incoming photons are not converted into usable energy. The idea behind the hot carrier cell is to utilize some of that incoming energy which is converted to heat. If the electrons and holes can be collected while hot, a higher voltage can be obtained from the cell. The problem with doing this is that the contacts which collect the electrons and holes will cool the material. Thus far, keeping the contacts from cooling the cell has been theoretical. Another way of improving the efficiency of the solar cell using the heat generated is to have a cell which allows lower energy photons to excite electron and hole pairs. This requires a small bandgap. Using a selective contact, the lower energy electrons and holes can be collected while allowing the higher energy ones to continue moving through the cell. The selective contacts are made using a double barrier resonant tunneling structure. The carriers are cooled which they scatter with phonons. If a material with a large bandgap of phonons then the carriers will carry more of the heat to the contact and it won't be lost in the lattice structure. One material which has a large bandgap of phonons is indium nitride. The hot carrier cells are in their infancy but are beginning to move toward the experimental stage.

==== Plasmonic-electrical solar cells ====

Having unique features of tunable resonances and unprecedented near-field enhancement, [[plasmon]] is an enabling technique for light management. Recently, performances of [[thin-film solar cells]] have been pronouncedly improved by introducing metallic nanostructures. The improvements are mainly attributed to the plasmonic-optical effects for manipulating light propagation, absorption, and scattering. The plasmonic-optical effects could: (1) boost optical absorption of active materials; (2) spatially redistribute light absorption at the active layer due to the localized near-field enhancement around metallic nanostructures. Except for the plasmonic-optical effects, the effects of plasmonically modified [[Genetic recombination|recombination]], transport and collection of photocarriers (electrons and holes), hereafter named plasmonic-electrical effects, have been proposed by Sha, etal. <ref name=Plasmonic_Electrical_1>{{cite journal | doi = 10.1038/srep06236 | title = Breaking the Space Charge Limit in Organic Solar Cells by a Novel Plasmonic-Electrical Concept | year = 2014 | last1 = Sha | first1 = Wei E. I. | last2 = Li | first2 = Xuanhua | last3 = Choy | first3 = Wallace C. H. | journal = Scientific Reports | volume = 4 | pages=6236 |bibcode = 2014NatSR...4E6236S }}</ref><ref name=Plasmonic_Electrical_2>{{cite journal | doi = 10.1038/srep08525 | title = A General Design Rule to Manipulate Photocarrier Transport Path in Solar Cells and Its Realization by the Plasmonic-Electrical Effect | year = 2015 | last1 = Sha | first1 = Wei E. I. | last2 = Zhu | first2 = Hugh L. | last3 = Chen | first3 = Luzhou | last4 = Chew | first4 = Weng Cho | last5 = Choy | first5 = Wallace C. H. | journal = Scientific Reports | volume = 5 | pages=8525|bibcode = 2015NatSR...5E8525S }}</ref> For boosting device performance, they conceived a general design rule, tailored to arbitrary electron to hole mobility ratio, to decide the transport paths of photocarriers. <ref name=Plasmonic_Electrical_2>{{cite journal | doi = 10.1038/srep08525 | title = A General Design Rule to Manipulate Photocarrier Transport Path in Solar Cells and Its Realization by the Plasmonic-Electrical Effect | year = 2015 | last1 = Sha | first1 = Wei E. I. | last2 = Zhu | first2 = Hugh L. | last3 = Chen | first3 = Luzhou | last4 = Chew | first4 = Weng Cho | last5 = Choy | first5 = Wallace C. H. | journal = Scientific Reports | volume = 5 | pages=8525|bibcode = 2015NatSR...5E8525S }}</ref> The design rule suggests that electron to hole transport length ratio should be balanced with electron to hole mobility ratio. In other words, the transport time of electrons and holes (from initial generation sites to corresponding electrodes) should be the same. The general design rule can be realized by spatially redistributing light absorption at the active layer of devices (with the plasmonic-electrical effect). They also demonstrated the breaking of [[space charge]] limit in plasmonic-electrical organic solar cell. <ref name=Plasmonic_Electrical_1>{{cite journal | doi = 10.1038/srep06236 | title = Breaking the Space Charge Limit in Organic Solar Cells by a Novel Plasmonic-Electrical Concept | year = 2014 | last1 = Sha | first1 = Wei E. I. | last2 = Li | first2 = Xuanhua | last3 = Choy | first3 = Wallace C. H. | journal = Scientific Reports | volume = 4 | pages=6236 |bibcode = 2014NatSR...4E6236S }}</ref>

==== Ultra-thin plasmonic wafer solar cells ====
Reducing the silicon wafer thickness at a minimized efficiency loss represents a mainstream trend in increasing the cost-effectiveness of wafer-based solar cells. Recently, Zhang et al. have demonstrated that, using the advanced light trapping strategy with a properly designed nanoparticle architecture, the wafer thickness can be dramatically reduced to only around 1/10 of the current thickness (180 µm) without any solar cell efficiency loss at 18.2%. Nanoparticle integrated ultra-thin solar cells with only 3% of the current wafer thickness can potentially achieve 15.3% efficiency combining the absorption enhancement with the benefit of thinner wafer induced open circuit voltage increase. This represents a 97% material saving with only 15% relative efficiency loss. These results demonstrate the feasibility and prospect of achieving high-efficiency ultra-thin silicon wafer cells with plasmonic light trapping. <ref>{{cite journal| title=Towards ultra-thin plasmonic silicon wafer solar cells with minimized efficiency loss| year=2014 | last1=Yinan | first1=Zhang et al| journal=Scientific Reports | volume=4 | pages=4939 |doi=10.1038/srep04939|bibcode = 2014NatSR...4E4939Z }}</ref>

== References ==
{{Portal|Renewable energy|Energy}}
{{Reflist|2}}

{{Photovoltaics}}

{{DEFAULTSORT:Plasmonic Solar Cell}}
[[Category:Solar cells]]

Gravitation (Buch)

2015-06-03T22:11:28Z

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{{Infobox book
| name = Gravitation
| image =
| image_caption =
| authors = [[Charles W. Misner]], [[Kip Thorne|Kip S. Thorne]], and [[John Archibald Wheeler]]
| illustrator =
| cover_artist = Kenneth Gwin
| country = United States
| language = [[English language|English]]
| subject = [[Physics]]
| publisher = [[W. H. Freeman]]
| pub_date = {{Start date|1973}}
| media_type = Print
| pages = xxvi, 1279
| isbn = 0-7167-0344-0
| dewey = 531/.14
| congress = QC178 .M57
| oclc = 585119
}}

In [[physics]], '''''Gravitation''''' is a well-known compendium on [[Einstein]]'s theory of gravity by [[Charles W. Misner]], [[Kip Thorne|Kip S. Thorne]], and [[John Archibald Wheeler]], originally published by [[W. H. Freeman and Company]] in 1973. It is often considered the early "bible" of [[general relativity]] by researchers for its prominence and is frequently called '''MTW''' after its authors' initials.<ref>{{cite web |last=Ehrlich |first=Ed |title=Gravitation - Book Review |website=sky-watch.com |quote='Gravitation' is such a prominent book on relativity that the initials of its authors MTW can be used by other books on relativity without explanation. |url=http://www.sky-watch.com/books/misner1.html |accessdate=1 January 2015}}</ref>

The book, whose size and shape at over 1200 pages is similar to that of a large telephone book, covers many aspects of general relativity and also considers [[alternatives to general relativity|some extensions of it]] as well as experimental confirmations. The book is divided into two "tracks", the second of which covers more advanced topics. MTW uses the [[Sign convention|−+++ metric convention]]. A substantial fraction of the book consists of boxes which add supplementary substance to the already thorough main text.

Here is an example of how it can be cited:
* {{citation
| last1=Misner |first1=Charles W. |authorlink1=Charles W. Misner
| last2=Thorne |first2=Kip S. |authorlink2=Kip Thorne
| last3=Wheeler |first3=John Archibald |authorlink3=John Archibald Wheeler
| year=1973
| title=Gravitation
| publisher=[[W. H. Freeman]]
| location=San Francisco
| isbn=978-0-7167-0344-0
}}.

==See also==
*''[[The Large Scale Structure of Space-Time]]'' 

==References==
{{Reflist}}

==Further reading==
*{{cite journal |last=Kaiser |first=David |date=March 2012 |title=A Tale of Two Textbooks: Experiments in Genre |journal=Isis |publisher=The University of Chicago Press |volume=103 |number=1 |pages=126–138 |doi=10.1086/664983}}
*{{cite journal |last1=Braginskii |first1=V. B. |last2=Novikov |first2=I. D. |date=March–April 1975 |title=C. Misner, K. Thorne, J. Wheeler. Gravitation: Reviewed by V. B. Braginskii and I. D. Novikov |journal=Astronomicheskii Zhurnal |volume=52 |pages=447–449 |url=http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975SvA....19..273B&link_type=ARTICLE&db_key=AST&high=54a582219127834|bibcode = 1975AZh....52..447B }}

==External links==
*[http://www.whfreeman.com/Catalog/product/gravitation-firstedition-misner Gravitation] catalog listing at the W. H. Freeman website

[[Category:General relativity]]
[[Category:Physics books]]

{{physics-book-stub}}

Benutzer:Poldi jungdrache/Supernova Typ II

2015-05-10T01:51:31Z

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[[File:HST SN 1987A 20th anniversary.jpg|right|thumb|320px|The expanding remnant of [[SN 1987A]], a Type II-P supernova in the [[Large Magellanic Cloud]]. ''[[NASA]] image.'']]
A '''Type II [[supernova]]''' (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive [[star]]. A star must have at least 8 times, and no more than 40–50 times, the [[solar mass|mass of the Sun]] ({{Solar mass|link=y}}) for this type of explosion.<ref name="science304">{{cite journal
| last = Gilmore | first = Gerry
| title=The Short Spectacular Life of a Superstar
| journal=Science | date=2004 | volume=304
| issue=5697 | pages=1915–1916 | doi=10.1126/science.1100370
| pmid = 15218132 }}</ref> It is distinguished from other types of supernovae by the presence of hydrogen in its [[spectrum]]. Type II supernovae are mainly observed in the [[spiral arm]]s of [[galaxies]] and in [[H II region]]s, but not in [[elliptical galaxies]].

Stars generate energy by the [[nuclear fusion]] of elements. Unlike the Sun, massive stars possess the mass needed to fuse elements that have an [[atomic mass]] greater than hydrogen and helium, albeit at increasingly higher [[temperature]]s and [[pressure]]s, causing increasingly shorter stellar life spans. The [[degeneracy pressure]] of electrons and the energy generated by these [[nuclear fusion|fusion reactions]] are sufficient to counter the force of gravity and prevent the star from collapsing, maintaining stellar equilibrium. The star fuses increasingly higher mass elements, starting with [[hydrogen]] and then [[helium]], progressing up through the periodic table until a core of iron and nickel is produced. Fusion of iron or nickel produces no net energy output, so no further fusion can take place, leaving the nickel-iron core inert. Due to the lack of energy output allowing outward pressure, equilibrium is broken.

When the mass of the inert core exceeds the [[Chandrasekhar limit]] of about {{Solar mass|1.4|link=y}}, electron degeneracy alone is no longer sufficient to counter gravity and maintain stellar equilibrium. A cataclysmic [[Implosion (mechanical process)|implosion]] takes place within seconds, in which the outer core reaches an inward [[velocity]] of up to 23% of the [[speed of light]] and the inner core reaches temperatures of up to 100 billion [[kelvin]]. [[Neutron]]s and [[neutrino]]s are formed via [[beta-decay|reversed beta-decay]], releasing about 1046 joules (100 [[foe (unit)|foes]]) in a ten-second burst. The collapse is halted by [[neutron degeneracy]], causing the implosion to rebound and bounce outward. The energy of this expanding [[shock wave]] is sufficient to accelerate the surrounding stellar material to escape velocity, forming a supernova explosion, while the shock wave and extremely high temperature and pressure briefly allow for the
[[Supernova nucleosynthesis|production of elements]] heavier than iron.<ref>{{cite web
| author=Staff | date=2006-09-07 | url=http://heasarc.gsfc.nasa.gov/docs/objects/snrs/snrstext.html
| title=Introduction to Supernova Remnants
| publisher=NASA Goddard/SAO | accessdate=2007-05-01
}}</ref> Depending on initial size of the star, the remnants of the core form a [[neutron star]] or a [[black hole]]. Because of the underlying mechanism, the resulting [[variable star|nova]] is also described as a core-collapse supernova.

There exist several categories of Type II supernova explosions, which are categorized based on the resulting [[light curve]]—a graph of luminosity versus time—following the explosion. Type II-L supernovae show a steady ([[linear]]) decline of the light curve following the explosion, whereas Type II-P display a period of slower decline (a [[plateau]]) in their light curve followed by a normal decay. [[Type Ib and Ic supernovae]] are a type of core-collapse supernova for a massive star that has shed its outer envelope of hydrogen and (for Type Ic) helium. As a result, they appear to be lacking in these elements.

==Formation==
[[File:Evolved star fusion shells.svg|right|280px|thumb|The onion-like layers of a massive, evolved star just before core collapse. (Not to scale.)]]
Stars far more massive than the sun evolve in more complex ways. In the core of the star, hydrogen is [[thermonuclear fusion|fused]] into helium, releasing [[thermal energy]] that heats the sun's core and provides outward [[pressure]] that supports the sun's layers against collapse in a process known as stellar or [[hydrostatic equilibrium]]. The helium produced in the core accumulates there since temperatures in the core are not yet high enough to cause it to fuse. Eventually, as the hydrogen at the core is exhausted, fusion starts to slow down, and [[Gravitation|gravity]] causes the core to contract. This contraction raises the temperature high enough to initiate a shorter phase of helium fusion, which accounts for less than 10% of the star's total lifetime. In stars with fewer than eight solar masses, the [[carbon]] produced by helium fusion does not fuse, and the star gradually cools to become a [[white dwarf]].<ref name="late stages">{{cite web
| last = Richmond | first = Michael
| url = http://spiff.rit.edu/classes/phys230/lectures/planneb/planneb.html
| title = Late stages of evolution for low-mass stars
| publisher = [[Rochester Institute of Technology]]
| accessdate = 2006-08-04 }}
</ref><ref name="hinshaw">
{{cite web
| last = Hinshaw | first = Gary
| date = 2006-08-23 | url = http://map.gsfc.nasa.gov/m_uni/uni_101stars.html
| title = The Life and Death of Stars | publisher = [[NASA]] [[Wilkinson Microwave Anisotropy Probe]] (WMAP) Mission
| accessdate = 2006-09-01 }}</ref> White dwarf stars, if they have a near companion, may then become [[Type Ia supernova]]e.

A much larger star, however, is massive enough to create temperatures and pressures needed to cause the carbon in the core to begin to fuse once the star contracts at the end of the helium-burning stage. The cores of these massive stars become layered like onions as progressively heavier atomic nuclei build up at the center, with an outermost layer of hydrogen gas, surrounding a layer of hydrogen fusing into helium, surrounding a layer of helium fusing into carbon via the [[triple-alpha process]], surrounding layers that fuse to progressively heavier elements. As a star this massive evolves, it undergoes repeated stages where fusion in the core stops, and the core collapses until the pressure and temperature are sufficient to begin the next stage of fusion, reigniting to halt collapse.<ref name="late stages"/><ref name="hinshaw"/>

:{| class="wikitable"
|+ Core-burning nuclear fusion stages for a 25-[[solar mass]] star
!rowspan="2"| Process
!rowspan="2"| Main fuel
!rowspan="2"| Main products
!colspan="3"| {{Solar mass|25|link=y}} star<ref name="WoosleyJanka">{{cite journal
| last=Woosley | first=S. |author2=Janka, H.-T.
| bibcode=2005NatPh...1..147W
| title=The Physics of Core-Collapse Supernovae
| journal=Nature Physics
|date=December 2005
| volume=1 | issue=3 | pages=147–154
| doi=10.1038/nphys172|arxiv = astro-ph/0601261 }}</ref>
|-
!style="font-weight: normal"| Temperature ([[Kelvin]])
!style="font-weight: normal"| Density (g/cm3)
!style="font-weight: normal"| Duration
|-
|| [[Hydrogen burning process|hydrogen burning]]
|| [[hydrogen]]
|| [[helium]]
| style="text-align:center;"| 7×107
| style="text-align:center;"| 10
| style="text-align:center;"| 107 years
|-
|| [[triple-alpha process]]
|| [[helium]]
|| [[carbon]], [[oxygen]]
| style="text-align:center;"| 2×108
| style="text-align:center;"| 2000
| style="text-align:center;"| 106 years
|-
|| [[carbon burning process]]
|| [[carbon]]
|| [[neon|Ne]], [[sodium|Na]], [[magnesium|Mg]], [[aluminium|Al]]
| style="text-align:center;"| 8×108
| style="text-align:center;"| 106
| style="text-align:center;"| 103 years
|-
|| [[neon burning process]]
|| [[neon]]
|| [[oxygen|O]], [[magnesium|Mg]]
| style="text-align:center;"| 1.6×109
| style="text-align:center;"| 107
| style="text-align:center;"| 3 years
|-
|| [[oxygen burning process]]
|| [[oxygen]]
|| [[silicon|Si]], [[sulfur|S]], [[argon|Ar]], [[calcium|Ca]]
| style="text-align:center;"| 1.8×109
| style="text-align:center;"| 107
| style="text-align:center;"| 0.3 years
|-
|| [[silicon burning process]]
|| [[silicon]]
|| [[nickel]] (decays into [[iron]])
| style="text-align:center;"| 2.5×109
| style="text-align:center;"| 108
| style="text-align:center;"| 5 days
|}

==Core collapse==
The factor limiting this process is the amount of energy that is released through fusion, which is dependent on the [[binding energy]] that holds together these atomic nuclei. Each additional step produces progressively heavier nuclei, which release progressively less energy when fusing. In addition, from [[Carbon-burning process|carbon-burning]] onwards, energy loss via [[neutrino]] production becomes significant, leading to a higher rate of reaction than would otherwise take place.<ref name="Clayton">{{cite book|last=Clayton|first=Donald| url=http://books.google.com/books?id=8HSGFThnbvkC|title=Principles of Stellar Evolution and Nucleosynthesis|date=1983|publisher=University of Chicago Press|isbn=978-0-226-10953-4}}</ref> This continues until [[Silicon burning process|nickel-56]] is produced, which decays radioactively into [[Cobalt|cobalt-56]] and then [[Iron|iron-56]] over the course of a few months. As iron and nickel have the highest [[binding energy]] per nucleon of all the elements,<ref>
{{cite journal
| last = Fewell | first = M. P. | title=The atomic nuclide with the highest mean binding energy
| journal=[[American Journal of Physics]]
| date=1995 | volume=63 | issue=7 | pages=653–658
| bibcode=1995AmJPh..63..653F | doi=10.1119/1.17828 }}</ref> energy cannot be produced at the core by fusion, and a nickel-iron core grows.<ref name="hinshaw" /><ref>{{cite web
| last=Fleurot | first=Fabrice | url=http://nu.phys.laurentian.ca/~fleurot/evolution/
| title=Evolution of Massive Stars
| publisher=Laurentian University
| accessdate=2007-08-13 }}</ref> This core is under huge gravitational pressure. As there is no fusion to further raise the star's temperature to support it against collapse, it is supported only by [[degeneracy pressure]] of [[electrons]]. In this state, matter is so dense that further compaction would require electrons to occupy the same [[energy level|energy states]]. However, this is forbidden for identical [[fermion]] particles, such as the electron – a phenomenon called the [[Pauli exclusion principle]].

When the core's mass exceeds the [[Chandrasekhar limit]] of about {{Solar mass|1.4|link=y}}, degeneracy pressure can no longer support it, and catastrophic collapse ensues.<ref name="Chandrasekhar">
{{cite journal
| first=E. H. | last=Lieb |author2=Yau, H.-T. | title=A rigorous examination of the Chandrasekhar theory of stellar collapse
| journal=[[Astrophysical Journal]]
| date=1987 | volume=323 | issue=1 | pages=140–144
| bibcode=1987ApJ...323..140L | doi=10.1086/165813 }}</ref> The outer part of the core reaches velocities of up to 70,000 km/s (23% of the [[speed of light]]) as it collapses toward the center of the star.<ref name="grav_waves">
{{cite web
| first=C. L. | last=Fryer |author2=New, K. C. B.
| date =2006-01-24 | url = http://relativity.livingreviews.org/Articles/lrr-2003-2/
| title = Gravitational Waves from Gravitational Collapse
| publisher = [[Max Planck Institute for Gravitational Physics]]
| accessdate = 2006-12-14 }}
</ref> The rapidly shrinking core heats up, producing high-energy [[gamma rays]] that decompose iron [[atomic nucleus|nuclei]] into helium nuclei and free [[neutron]]s via [[photodisintegration]]. As the core's [[density]] increases, it becomes energetically favorable for [[electron]]s and [[proton]]s to merge via inverse [[beta decay]], producing neutrons and [[elementary particle]]s called [[neutrino]]s. Because neutrinos rarely interact with normal matter, they can escape from the core, carrying away energy and further accelerating the collapse, which proceeds over a timescale of milliseconds. As the core detaches from the outer layers of the star, some of these neutrinos are absorbed by the star's outer layers, beginning the supernova explosion.<ref name="hayakawa">
{{cite journal
| last=Hayakawa|first=T.
| last2=Iwamoto|first2=N.
| last3=Kajino|first3=T.
| last4=Shizuma|first4=T.
| last5=Umeda|first5=H.
| last6=Nomoto|first6=K.
| title=Principle of Universality of Gamma-Process Nucleosynthesis in Core-Collapse Supernova Explosions
| journal=The Astrophysical Journal
| volume=648
| issue=1 | pages=L47–L50
| date=2006 | doi = 10.1086/507703
| bibcode=2006ApJ...648L..47H}}</ref>

For Type II supernovae, the collapse is eventually halted by short-range repulsive neutron-neutron interactions, mediated by the [[strong force]], as well as by [[degeneracy pressure]] of neutrons, at a density comparable to that of an atomic nucleus. Once collapse stops, the infalling matter rebounds, producing a [[shock wave]] that propagates outward. The energy from this shock dissociates heavy elements within the core. This reduces the energy of the shock, which can stall the explosion within the outer core.<ref name="collapse scenario">
{{cite web
| first=C. L. | last=Fryer |author2=New, K. B. C.
| date=2006-01-24 | url = http://relativity.livingreviews.org/open?pubNo=lrr-2003-2&page=articlesu6.html
| title = Gravitational Waves from Gravitational Collapse, section 3.1
| publisher = [[Los Alamos National Laboratory]]
| accessdate = 2006-12-09 }}</ref>

The core collapse phase is so dense and energetic that only neutrinos are able to escape. As the protons and electrons combine to form neutrons by means of [[electron capture]], an electron neutrino is produced. In a typical Type II supernova, the newly formed neutron core has an initial temperature of about 100 billion [[kelvin]], 104 times the temperature of the sun's core. Much of this thermal energy must be shed for a stable neutron star to form, otherwise the neutrons would "boil away". This is accomplished by a further release of neutrinos.<ref name=akmann>{{cite book
| last=Mann | first=Alfred K.
| title=Shadow of a star: The neutrino story of Supernova 1987A
| publisher=W. H. Freeman
| date=1997 | location=New York | page=122
| url = http://www.whfreeman.com/GeneralReaders/book.asp?disc=TRAD&id_product=1058001008&@id_course=1058000240
| isbn = 0-7167-3097-9 }}</ref> These 'thermal' neutrinos form as neutrino-antineutrino pairs of all [[Neutrino oscillation|flavors]], and total several times the number of electron-capture neutrinos.<ref>{{cite book
| last = Gribbin | first = John R.
| authorlink = John Gribbin
| last2 = Gribbin | first2 = Mary
| title = Stardust: Supernovae and Life – The Cosmic Connection
| publisher = [[Yale University Press]]
| date = 2000 | location = New Haven | page = 173
| url = http://yalepress.yale.edu/yupbooks/book.asp?isbn=9780300090970
| isbn = 978-0-300-09097-0 }}</ref> The two neutrino production mechanisms convert the gravitational [[potential energy]] of the collapse into a ten-second neutrino burst, releasing about 1046 joules (100 [[foe (unit)|foes]]).<ref name="APS_study">
{{cite web
| first=S. | last=Barwick
|author2=Beacom, J.
|display-authors=etal
| date=2004-10-29 | url = http://www.aps.org/policy/reports/multidivisional/neutrino/upload/Neutrino_Astrophysics_and_Cosmology_Working_Group.pdf
| title = APS Neutrino Study: Report of the Neutrino Astrophysics and Cosmology Working Group
| publisher = [[American Physical Society]]
| format=PDF | accessdate = 2006-12-12 }}</ref>

Through a process that is not clearly understood, about 1044 joules (1 foe) is reabsorbed by the stalled shock, producing an explosion.{{Ref label|A|a|none}}<ref name="collapse scenario" /> The neutrinos generated by a supernova were actually observed in the case of [[Supernova 1987A]], leading astronomers to conclude that the core collapse picture is basically correct. The water-based [[Kamioka Observatory|Kamiokande II]] and [[Irvine-Michigan-Brookhaven (detector)|IMB]] instruments detected antineutrinos of thermal origin,<ref name=akmann/> while the [[gallium]]-71-based [[Baksan Neutrino Observatory|Baksan]] instrument detected neutrinos ([[lepton number]] = 1) of either thermal or electron-capture origin.

[[File:Core collapse scenario.png|480px|thumb|center| Within a massive, evolved star (a) the onion-layered shells of elements undergo fusion, forming a nickel-iron core (b) that reaches Chandrasekhar-mass and starts to collapse. The inner part of the core is compressed into neutrons (c), causing infalling material to bounce (d) and form an outward-propagating shock front (red). The shock starts to stall (e), but it is re-invigorated by neutrino interaction. The surrounding material is blasted away (f), leaving only a degenerate remnant.]]

When the progenitor star is below about {{Solar mass|20}} – depending on the strength of the explosion and the amount of material that falls back – the degenerate remnant of a core collapse is a [[neutron star]].<ref name="grav_waves" /> Above this mass, the remnant collapses to form a [[black hole]].<ref name="hinshaw" /><ref>
{{cite journal
| last=Fryer | first=Chris L.
| title=Black Hole Formation from Stellar Collapse
| journal=Classical and Quantum Gravity
| date=2003 | volume=20 | issue=10 | pages=S73–S80
| bibcode=2003CQGra..20S..73F | doi=10.1088/0264-9381/20/10/309 }}</ref> The theoretical limiting mass for this type of core collapse scenario is about {{Solar mass|40–50}}. Above that mass, a star is believed to collapse directly into a black hole without forming a supernova explosion,<ref name="fryer">
{{cite journal
| last = Fryer | first = Chris L.
| title=Mass Limits For Black Hole Formation
| journal=The Astrophysical Journal
| date=1999 | volume=522 | issue=1 | pages=413–418
| bibcode=1999ApJ...522..413F | doi=10.1086/307647 |arxiv = astro-ph/9902315 }}</ref> although uncertainties in models of supernova collapse make calculation of these limits uncertain.

==Theoretical models==
The [[Standard Model]] of [[particle physics]] is a theory which describes three of the four known [[fundamental interaction]]s between the [[elementary particles]] that make up all [[matter]]. This theory allows predictions to be made about how particles will interact under many conditions. The energy per particle in a supernova is typically one to one hundred and fifty [[picojoule]]s (tens to hundreds of [[MeV]]).<ref name="izzard">
{{cite journal
| first=R. G. | last=Izzard
|author2=Ramirez-Ruiz, E. |author3=Tout, C. A.
| title = Formation rates of core-collapse supernovae and gamma-ray bursts
| journal = [[Monthly Notices of the Royal Astronomical Society]]
| volume=348 | issue=4 | page=1215 | date=2004
| doi = 10.1111/j.1365-2966.2004.07436.x | bibcode=2004MNRAS.348.1215I|arxiv = astro-ph/0311463 }}
</ref> The per-particle energy involved in a supernova is small enough that the predictions gained from the Standard Model of particle physics are likely to be basically correct. But the high densities may require corrections to the Standard Model.<ref name="cc_sims">
{{cite conference
| first=M. | last=Rampp
|author2=Buras, R. |author3=Janka, H.-Th. |author4= Raffelt, G.
| title = Core-collapse supernova simulations: Variations of the input physics
| booktitle = Proceedings of the 11th Workshop on "Nuclear Astrophysics"
| pages = 119–125 | date = February 11–16, 2002
| location = Ringberg Castle, Tegernsee, Germany
| bibcode = 2002nuas.conf..119R
}}</ref> In particular, Earth-based [[particle accelerator]]s can produce particle interactions which are of much higher energy than are found in supernovae,<ref>
{{cite journal
| author=The OPAL Collaboration; Ackerstaff, K.
| display-authors=etal
| title=Tests of the Standard Model and Constraints on New Physics from Measurements of Fermion-pair Production at 189 GeV at LEP
| journal=Submitted to [[The European Physical Journal C]]
| date=1998 | volume=2
| issue=3 | pages=441–472 | url=http://publish.edpsciences.com/articles/epjc/abs/1998/05/epjc851/epjc851.html
| accessdate = 2007-03-18 | doi=10.1007/s100529800851 }}
</ref> but these experiments involve individual particles interacting with individual particles, and it is likely that the high densities within the supernova will produce novel effects. The interactions between neutrinos and the other particles in the supernova take place with the [[weak nuclear force]], which is believed to be well understood. However, the interactions between the protons and neutrons involve the [[strong nuclear force]], which is much less well understood.<ref>{{cite web
| author=Staff | date=2004-10-05
| url =http://nobelprize.org/nobel_prizes/physics/laureates/2004/public.html
| title=The Nobel Prize in Physics 2004
| publisher=Nobel Foundation
| accessdate=2007-05-30 }}</ref>

The major unsolved problem with Type II supernovae is that it is not understood how the burst of [[neutrino]]s transfers its energy to the rest of the star producing the shock wave which causes the star to explode. From the above discussion, only one percent of the energy needs to be transferred to produce an explosion, but explaining how that one percent of transfer occurs has proven very difficult, even though the particle interactions involved are believed to be well understood. In the 1990s, one model for doing this involved [[convective overturn]], which suggests that convection, either from [[neutrino]]s from below, or infalling matter from above, completes the process of destroying the progenitor star. Heavier elements than iron are formed during this explosion by neutron capture, and from the pressure of the neutrinos pressing into the boundary of the "neutrinosphere", seeding the surrounding space with a cloud of gas and dust which is richer in heavy elements than the material from which the star originally formed.<ref name="pop-sci-dec-2006">
{{cite journal
| last=Stover | first=Dawn | title=Life In A Bubble
| journal=[[Popular Science]] | volume=269 | issue=6
| date=2006 | page=16 }}</ref>

[[Weak interaction|Neutrino physics]], which is modeled by the Standard Model, is crucial to the understanding of this process.<ref name="cc_sims" /> The other crucial area of investigation is the [[hydrodynamics]] of the plasma that makes up the dying star; how it behaves during the core collapse determines when and how the "shock wave" forms and when and how it "stalls" and is reenergized.<ref>
{{cite journal
| doi=10.1016/0022-1694(93)90012-X
| last=Janka | first=H.-Th.
|author2=Langanke, K. |author3=Marek, A. |author4=Martinez-Pinedo, G. |author5= Mueller, B.
| title=Theory of Core-Collapse Supernovae
| journal=Bethe Centennial Volume of Physics Reports (submitted)
| volume=142
| issue=1–4
| page=229
| date=2006
| arxiv=astro-ph/0612072
|bibcode = 1993JHyd..142..229H }}</ref>

In fact, some theoretical models incorporate a hydrodynamical instability in the stalled shock known as the "Standing Accretion Shock Instability" (SASI). This instability comes about as a consequence of non-spherical perturbations oscillating the stalled shock thereby deforming it. The SASI is often used in tandem with neutrino theories in computer simulations for re-energizing the stalled shock.<ref>
{{cite web
|title=3D Simulations of Standing Accretion Shock Instability in Core-Collapse Supernovae
|url=http://www.mpa-garching.mpg.de/hydro/NucAstro/PDF_08/iwakami.pdf
|work=3D Simulations of Standing Accretion Shock Instability in Core-Collapse Supernovae|publisher=14th Workshop on “Nuclear Astrophysics”
|accessdate=30 January 2013
|author=Wakana Iwakami|author2=Kei Kotake |author3=Naofumi Ohnishi |author4=Shoichi Yamada |author5=Keisuke Sawada
|date=March 10–15, 2008
}}</ref>

[[Computer model]]s have been very successful at calculating the behavior of Type II supernovae once the shock has been formed. By ignoring the first second of the explosion, and assuming that an explosion is started, [[astrophysicist]]s have been able to make detailed predictions about the elements produced by the supernova and of the expected [[light curve]] from the supernova.<ref>{{cite journal
| first=S.I. | last=Blinnikov
|author2=Röpke, F. K. |author3=Sorokina, E. I. |author4=Gieseler, M. |author5=Reinecke, M. |author6=Travaglio, C. |author7=Hillebrandt, W. |author8= Stritzinger, M.
| title=Theoretical light curves for deflagration models of type Ia supernova
| journal=Astronomy and Astrophysics
| date=2006 | volume=453 | issue=1 | pages=229–240
| bibcode=2006A&A...453..229B
| doi=10.1051/0004-6361:20054594 |arxiv = astro-ph/0603036 }}
</ref><ref>
{{cite journal
| last=Young | first=Timothy R. | title=A Parameter Study of Type II Supernova Light Curves Using 6 M He Cores
| journal=[[The Astrophysical Journal]]
| date=2004 | volume=617 | issue=2 | pages=1233–1250
| doi=10.1086/425675 | bibcode=2004ApJ...617.1233Y|arxiv = astro-ph/0409284 }}
</ref><ref>
{{cite journal
| first=T. | last=Rauscher
|author2=Heger, A. |author3=Hoffman, R. D. |author4= Woosley, S. E.
| title=Nucleosynthesis in Massive Stars With Improved Nuclear and Stellar Physics
| journal=[[The Astrophysical Journal]]
| date=2002 | volume=576 | issue=1 | pages = 323–348
| doi=10.1086/341728 | bibcode=2002ApJ...576..323R|arxiv = astro-ph/0112478 }}
</ref>

==Light curves for Type II-L and Type II-P supernovae==
[[File:SNIIcurva.png|right|thumb|280px|This graph of the luminosity as a function of time shows the characteristic shapes of the light curves for a Type II-L and II-P supernova.]]
When the [[spectrum]] of a Type II supernova is examined, it normally displays [[Balmer series|Balmer absorption lines]] – reduced flux at the characteristic [[frequency|frequencies]] where hydrogen atoms absorb energy. The presence of these lines is used to distinguish this category of supernova from a [[Type Ia supernova|Type I supernova]].

When the luminosity of a Type II supernova is plotted over a period of time, it shows a characteristic rise to a peak brightness followed by a decline. These light curves have an average decay rate of 0.008 [[absolute magnitude|magnitudes]] per day; much lower than the decay rate for Type Ia supernovae. Type II are sub-divided into two classes, depending on the shape of the light curve. The light curve for a Type II-L supernova shows a steady ([[linear]]) decline following the peak brightness. By contrast, the light curve of a Type II-P supernova has a distinctive flat stretch (called a [[plateau]]) during the decline; representing a period where the luminosity decays at a slower rate. The net luminosity decay rate is lower, at 0.0075 magnitudes per day for Type II-P, compared to 0.012 magnitudes per day for Type II-L.<ref name="comparative_study">
{{cite journal
| first=J. B. | last=Doggett |author2=Branch, D.
| title=A Comparative Study of Supernova Light Curves
| journal=Astronomical Journal
| date=1985 | volume=90 | pages=2303–2311
| bibcode=1985AJ.....90.2303D | doi=10.1086/113934 }}
</ref>

The difference in the shape of the light curves is believed to be caused, in the case of Type II-L supernovae, by the expulsion of most of the hydrogen envelope of the progenitor star.<ref name="comparative_study" /> The plateau phase in Type II-P supernovae is due to a change in the [[opacity (optics)|opacity]] of the exterior layer. The shock wave [[ionize]]s the hydrogen in the outer envelope – stripping the electron from the hydrogen atom – resulting in a significant increase in the [[Opacity (optics)|opacity]]. This prevents photons from the inner parts of the explosion from escaping. Once the hydrogen cools sufficiently to recombine, the outer layer becomes transparent.<ref>
{{cite web
| url = http://cosmos.swin.edu.au/lookup.html?e=typeiisupernovalightcurves
| title = Type II Supernova Light Curves
| publisher = [[Swinburne University of Technology]]
| accessdate = 2007-03-17 }}
</ref>

==Type IIn supernovae==
The "n" denotes narrow, which indicates the presence of intermediate or very narrow width H emission lines in the spectra. In the intermediate width case, the ejecta from the explosion may be interacting strongly with gas around the star – the circumstellar medium.
<ref>{{cite doi|10.1146/annurev.astro.35.1.309}}</ref><ref>{{cite journal
| first=A. | last=Pastorello
|author2=Turatto, M. |author3=Benetti, S. |author4=Cappellaro, E. |author5=Danziger, I. J. |author6=Mazzali, P. A. |author7=Patat, F. |author8=Filippenko, A. V. |author9=Schlegel, D. J. |author10= Matheson, T.
| title=The type IIn supernova 1995G: interaction with the circumstellar medium
| journal=Monthly Notices of the Royal Astronomical Society
| date=2002 | volume=333 | issue=1 | pages=27–38
| bibcode=2002MNRAS.333...27P
| doi=10.1046/j.1365-8711.2002.05366.x |arxiv = astro-ph/0201483 }}</ref> The estimated circumstellar density required to explain the observational properties is much higher than that expected from the standard stellar evolution theory.<ref>{{cite journal|last1=Langer|first1=N.|title=Presupernova Evolution of Massive Single and Binary Stars|journal=Annual Review of Astronomy and Astrophysics|date=22 September 2012|volume=50|issue=1|pages=107–164|doi=10.1146/annurev-astro-081811-125534|arxiv = 1206.5443 |bibcode = 2012ARA&A..50..107L }}</ref> It is
generally assumed that the high circumstellar density is due to the high mass-loss rates of the SN IIn progenitors. The estimated mass-loss rates are typically higher
than 10{{sup|−3}} M{{sub|⊙}} yr{{sup|−1}}. There are indications that they originate as stars similar to [[Luminous blue variable]]s with large mass losses before exploding.<ref>{{cite journal |author1=Michael Kiewe |author2=Avishay Gal-Yam |author3=Iair Arcavi |author4=Leonard |author5=Emilio Enriquez |author6=Bradley Cenko |author7=Fox |author8=Dae-Sik Moon |author9=Sand |title=Caltech Core-Collapse Project (CCCP) observations of type IIn supernovae: typical properties and implications for their progenitor stars |date=2010 |volume=744 |issue=10 |pages=10 |journal=ApJ |arxiv=1010.2689|bibcode = 2012ApJ...744...10K |doi = 10.1088/0004-637X/744/1/10 |last10=Soderberg |first10=Alicia M. |last11=Cccp |first11=The }}</ref> [[SN 1998S]] and [[SN 2005gl]] are famous examples of Type IIn; [[SN 2006gy]], an extremely energetic supernova, may be another example.<ref>{{cite doi |10.1088/0004-637X/709/2/856}}</ref>

==Type IIb supernovae==
A ''Type IIb supernova'' has a weak hydrogen line in its initial spectrum, which is why it is classified as a Type II. However, later on the H emission becomes undetectable, and there is also a second peak in the light curve that has a spectrum which more closely resembles a [[Type Ib and Ic supernovae|Type Ib supernova]]. The progenitor could have been a giant star which lost most of its hydrogen envelope due to interactions with a companion in a binary system, leaving behind the core that consisted almost entirely of helium.<ref name=Utrobin>{{cite journal | doi= | last=Utrobin | first=V. P. | title=Nonthermal ionization and excitation in Type IIb supernova 1993J | journal=Astronomy and Astrophysics | date=1996 | volume=306 | issue=5940 | pages=219–231 | bibcode=1996A&A...306..219U }}</ref> As the ejecta of a Type IIb expands, the hydrogen layer quickly becomes [[Optical thickness|more transparent]] and reveals the deeper layers.<ref name=Utrobin/>
The classic example of a Type IIb supernova is [[SN 1993J|Supernova 1993J]],<ref>{{cite doi|10.1038/364507a0}}</ref><ref>{{cite doi|10.1088/2041-8205/711/1/L40}}</ref> while another example is [[Cassiopeia A]].<ref>{{cite doi|10.1126/science.1155788}}</ref> The IIb class was first introduced (as a theoretical concept) by Ensman & Woosley 1987.

==Hypernovae (collapsars)==
{{main|Hypernova}}
[[Hypernovae]] are a rare type of supernova substantially more luminous and energetic than standard supernovae. Examples are [[1997ef]] (type Ic) and [[1997cy]] (type IIn). Hypernovae are produced by more than one type of event: relativistic jets during formation of a black hole from fallback of material onto the neutron star core, the collapsar model; interaction with a dense envelope of circumstellar material, the CSM model; the highest mass [[Pair-instability supernova|pair instability supernovae]]; possibly others such as [[binary star|binary]] and [[quark star]] model.

Stars with initial masses between about 25 and 90 times the sun develop cores large enough that after a supernova explosion, some material will fall back onto the neutron star core and create a black hole. In many cases this reduces the luminosity of the supernova, and above {{Solar mass|90}} the star collapses directly into a black hole without a supernova explosion. However if the progenitor is spinning quickly enough the infalling material generates relativistic jets that emit more energy than the original explosion.<ref name="nomoto">{{cite doi|10.1016/j.newar.2010.09.022}}</ref> They may also be seen directly if beamed towards us, giving the impression of an even more luminous object. In some cases these can produce [[gamma-ray bursts]], although not all gamma-ray bursts are from supernovae.<ref>
{{cite news
| title=Cosmological Gamma-Ray Bursts and Hypernovae Conclusively Linked
| publisher=[[European Organisation for Astronomical Research in the Southern Hemisphere]] (ESO)
| date=2003-06-18
| url=http://www.eso.org/outreach/press-rel/pr-2003/pr-16-03.html
| accessdate=2006-10-30 }}
</ref>

In some cases a type II supernova occurs when the star is surrounded by a very dense cloud of material, most likely expelled during [[luminous blue variable]] eruptions. This material is shocked by the explosion and becomes more luminous than a standard supernova. It is likely that there is a range of luminosities for these type IIn supernovae with only the brightest qualifying as a hypernova.

Pair instability supernovae occur when an oxygen core in an extremely massive star becomes hot enough that gamma rays spontaneously produce electron-positron pairs.<ref name="kasen">{{cite doi|10.1088/0004-637X/734/2/102}}</ref> This causes the core to collapse, but where the collapse of an iron core causes [[endothermic]] fusion to heavier elements, the collapse of an oxygen core creates runaway [[exothermic]] fusion which completely unbinds the star. The total energy emitted depends on the initial mass, with much of the core being converted to 56Ni and ejected which then powers the supernova for many months. At the lower end stars of about {{Solar mass|140}} produce supernovae that are long-lived but otherwise typical, while the highest mass stars of around {{Solar mass|250}} produce supernovae that are extremely luminous and also very long lived; hypernovae. More massive stars die by [[photodisintegration]]. Only [[population III]] stars, with very low metallicity, can reach this stage. Stars with more heavy elements are more opaque and blow away their outer layers until they are small enough to explode as a normal type Ib/c supernova. It is thought that even in our own galaxy, mergers of old low metallicity stars may form massive stars capable of creating a pair instability supernova.

==See also==
{{Portal|Astronomy}}
{{Wikipedia books|Classes of supernovae}}
* [[History of supernova observation]]
* [[Supernova nucleosynthesis]]
* [[Supernova remnant]]
{{-}}

==References==
{{reflist|2}}

==External links==
* {{cite web|last=Merrifield|first=Michael|title=Type II Supernova|url=http://www.sixtysymbols.com/videos/supernova.htm|work=Sixty Symbols|publisher=[[Brady Haran]] for the [[University of Nottingham]]}}
{{Supernovae}}
{{good article}}

[[Category:Supernovae|Type 2 Supernova]]

Trumpler 16

2015-05-10T01:50:11Z

Bibcode Bot: Adding 1 arxiv eprint(s), 0 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

{{Infobox cluster
| name = Trumpler 16
| image = [[File:ESO - The Carina Nebula (by).jpg|240 px]]
| caption = The inner region of the [[Carina Nebula]] as seen in near-infrared. Trumpler 16 is the cluster of stars at the left, around [[Eta Carinae]] (the brightest star in the image).
| credit = [[European Southern Observatory]]
| epoch = [[Epoch (astronomy)#Julian years and J2000|J2000]]
| constellation = [[Carina (constellation)|Carina]]
| ra = {{RA|10|49|10}}<ref name=A>{{cite web
| title = SIMBAD Astronomical Database
| work = Basic data for C 1043-594
| url = http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=C+1043-594&submit=SIMBAD+search}}</ref>
| dec = {{DEC|-59|43.0}}<ref name=A />
| dist_ly = 7,500 [[light-year]]s
| dist_pc = 2,300 [[parsec]]s
| appmag_v = 5.0<ref name=A />
| names = C 1043-594
}}

'''Trumpler 16''' is a massive [[open cluster]]<ref name=A/> that is home to some of the most luminous stars in the [[Milky Way]] Galaxy.<ref>{{cite journal |title=The Chandra Carina Complex Project View of Trumpler 16 |display-authors=4 |author=Wolk, Scott J. |author2=Broos, Patrick S. |author3=Getman, Konstantin V. |author4=Feigelson, Eric D. |author5=Preibisch, Thomas |author6=Townsley, Leisa K. |author7=Wang, Junfeng |author8=Stassun, Keivan G. |author9=King, Robert R. |author10=McCaughrean, Mark J. |author11=Moffat, Anthony F. J. |author12=Zinnecker, Hans | journal=The Astrophysical Journal Supplement|volume=194| issue=1| id=12| pages=15 |date=2011 |doi= 10.1088/0067-0049/194/1/12 | bibcode=2011ApJS..194...12W|arxiv = 1103.1126 }}</ref> It is situated within the [[Carina Nebula]] ([[Caldwell 92]]) complex in the [[Carina-Sagittarius Arm]], located approximately 7,500 light-years from Earth. With the visual magnitude of 5,<ref name=A /> it is bright enough to be seen by the naked eye, but the individual stars can be resolved through a small binoculars.

Its most luminous members are [[Eta Carinae]] and [[WR 25]],<ref name=A /> with both having luminosities several million times that of the Sun. Both stars are binaries, with the primary stars contributing most of the luminosity, but with companions which are themselves more massive and luminous than most stars. Across all wavelengths, WR 25 is estimated to be the more luminous of the two, 6,300,000 times the Sun's luminosity (absolute bolometric magnitude -12.25) compared to Eta Carinae at 5,000,000 times the Sun's luminosity (absolute bolometric magnitude -12.0). However in the image on the right Eta Carinae appears by far the brightest object, both because it is brighter in visual wavelengths and because it is embedded in nebulosity which is exaggerated in this type of image. WR 25 is very hot and emits most of its radiation as ultraviolet. It can be seen in the image below and to the right of Eta Carinae, just beyond the edge of the brightest nebulosity and to the right of an orange foreground star.

Trumpler 16 and Trumpler 14 are the most prominent star clusters in [[Carina OB1]], a giant stellar association in the Carina spiral arm. Another cluster within Carina OB1, Collinder 228, is thought to be an extension of Trumpler 16 appearing visually separated only because of an intervening dust lane. The spectral types of the stars indicate that Trumpler 16 formed by a single wave of star formation. Because of the extreme luminosity of the stars formed, their stellar winds push away the clouds of dust, similar to the [[Pleiades]]. In a few million years, after the brightest stars have exploded as [[supernova]]e, the cluster will slowly die away. Trumpler 16 includes most of the stars in the left (east) half of the nebulosity in this image. Trumpler 14 is younger and more compact, visible just right (west) of the centre of this frame<ref>{{cite web|title=The Carina Nebula in Infrared|url=http://apod.nasa.gov/apod/ap000613.html|accessdate=18 January 2014}}</ref>

==Photos==
<gallery style="margin:auto;">
File:Eta Carinae winds&radiation.jpg|A part of Trumpler 16 as seen by the Wide Field Planetary Camera 2.
File:Carina Nebula by ESO.jpg|Image of [[Carina OB1]] showing Trumpler 16 with [[Trumpler 14]] and [[Collinder 228]].
File:NGC 3372d.jpg|[[Carina OB1]] association, with Trumpler 16.
</gallery>

==See also==
*[[Trumpler 10]]
*[[Trumpler 14]]

==References==
{{reflist}}

===Notes===
* {{cite journal|title=η Carinae and the Trumpler 16 Cluster|journal=Publications of the Astronomical Society of the Pacific|page=492|number=447|volume=75|date=December 1963|doi=10.1086/128013|url=http://adsabs.harvard.edu/full/1963PASP...75..492F|accessdate=18 January 2014|author=Feinstein, Alejandro|bibcode=1963PASP...75..492F}}

[[Category:Open clusters]]
[[Category:Carina (constellation)]]
[[Category:Trumpler catalog]]

Benutzer:Molinarius/Silicon photonics

2014-07-17T07:06:41Z

Bibcode Bot: Adding 0 arxiv eprint(s), 1 bibcode(s) and 0 doi(s). Did it miss something? Report bugs, errors, and suggestions at User talk:Bibcode Bot

'''Silicon photonics''' is the study and application of [[photonics|photonic]] systems which use [[silicon]] as an [[optical medium]].<ref name="lipson_2005">{{cite journal
|doi = 10.1109/JLT.2005.858225
|title = Guiding, Modulating, and Emitting Light on Silicon -- Challenges and Opportunities
|journal = [[Journal of Lightwave Technology]]
|year = 2005
|volume = 23
|issue = 12
|pages = 4222–4238
|author = Michal Lipson
| bibcode = 2005JLwT...23.4222L }}</ref><ref name="jalali_2006">{{cite journal
|doi = 10.1109/JLT.2006.885782
|title = Silicon photonics
|journal = [[Journal of Lightwave Technology]]
|year = 2006
|volume = 24
|issue = 12
|pages = 4600–4615
|author = B Jalali and S Fathpour
| bibcode = 2006JLwT...24.4600J }}</ref><ref name="almeida_2004">{{cite journal
|title = All-optical control of light on a silicon chip
|journal = [[Nature (journal)|Nature]]
|year = 2004
|volume = 431
|issue = 7012
|pages = 1081–1084
|doi = 10.1038/nature02921
|author = Vilson R. Almeida, Carlos A. Barrios, Roberto R. Panepucci and Michal Lipson
|pmid=15510144
| bibcode = 2004Natur.431.1081A }}</ref><ref name="pavesi_book">{{cite book
|title = Silicon photonics
|isbn = 3-540-21022-9
|publisher = [[Springer Science+Business Media|Springer]]
|year = 2004
|author = Lorenzo Pavesi and David J. Lockwood
}}</ref><ref name="reed_book">{{cite book
|title = Silicon photonics: an introduction
|isbn = 0-470-87034-6
|publisher = [[John Wiley and Sons]]
|year = 2004
|author = Graham T. Reed and Andrew P. Knight
}}</ref> The silicon is usually patterned with [[nanoscale|sub-micrometre]] precision, into [[microphotonics|microphotonic]] components.<ref name="pavesi_book" /> These operate in the [[infrared]], most commonly at the 1.55 micrometre [[wavelength]] used by most [[fiber optic telecommunication]] systems.<ref name="lipson_2005" /> The silicon typically lies on top of a layer of silica in what (by analogy with [[silicon on insulator|a similar construction]] in [[microelectronics]]) is known as '''silicon on insulator''' (SOI).<ref name="pavesi_book" /><ref name="reed_book" />

Silicon photonic devices can be made using existing [[semiconductor fabrication]] techniques, and because silicon is already used as the substrate for most [[integrated circuit]]s, it is possible to create hybrid devices in which the [[optics|optical]] and [[electronics|electronic]] components are integrated onto a single microchip.<ref name="lipson_2005" /> Consequently, silicon photonics is being actively researched by many electronics manufacturers including [[IBM]] and [[Intel]], as well as by academic research groups such as that of Prof. [[Michal Lipson]], who see it is a means for keeping on track with [[Moore's Law]], by using [[optical interconnect]]s to provide faster [[data transfer]] both between and within [[Integrated circuit|microchip]]s.<ref name="ibm_silicon">{{cite web
|title = Silicon Integrated Nanophotonics
|publisher = [[IBM]] Research
|url = http://domino.research.ibm.com/comm/research_projects.nsf/pages/photonics.index.html
|accessdate = 2009-07-14
}}</ref><ref name="intel_silicon">{{cite web
|title = Silicon Photonics
|publisher = [[Intel]]
|url = http://techresearch.intel.com/articles/Tera-Scale/1419.htm
|accessdate = 2009-07-14
}}</ref>

The propagation of [[light]] through silicon devices is governed by a range of [[nonlinear optics|nonlinear optical]] phenomena including the [[Kerr effect]], the [[Raman effect]], [[two photon absorption]] and interactions between [[photons]] and [[free charge carriers]].<ref name="dekker_2008" >{{cite journal
|title = Ultrafast nonlinear all-optical processes in silicon-on-insulator waveguides
|journal = [[Journal of Physics D]]
|year = 2008
|volume = 40
|page = R249–R271
|author = R. Dekker, N. Usechak, M. Först and A. Driessen
|doi=10.1088/0022-3727/40/14/r01
|bibcode = 2007JPhD...40..249D }}</ref> The presence of nonlinearity is of fundamental importance, as it enables light to interact with light,<ref name="butcher_book">{{cite book
|title = The elements of nonlinear optics
|isbn = 0-521-42424-0
|publisher = [[Cambridge University Press]]
|year = 1991
|author = Paul N. Butcher and David Cotter
}}</ref> thus permitting applications such as wavelength conversion and all-optical signal routing, in addition to the passive transmission of light.

Silicon waveguides are also of great academic interest, due to their ability to support exotic nonlinear optical phenomena such as [[Soliton (optics)|soliton propagation]].<ref name="hsieh_2006" >{{cite journal
|doi = 10.1364/OE.14.012380
|title = Ultrafast-pulse self-phase modulation and third-order dispersion in Si photonic wire-waveguides
|journal = [[Optics Express]]
|year = 2006
|volume = 14
|issue = 25
|pages = 12380–12387
|author = I-Wei Hsieh, Xiaogang Chen, Jerry I. Dadap, Nicolae C. Panoiu and Richard M. Osgood,
| bibcode = 2006OExpr..1412380H }}</ref><ref name="zhang_2007">{{cite journal
|doi = 10.1364/OE.15.007682
|title = Optical solitons in a silicon waveguide
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 12
|pages = 7682–7688
|author = Jidong Zhang, Qiang Lin, Giovanni Piredda, Robert W. Boyd, Govind P. Agrawal and Philippe M. Fauchet
| bibcode = 2007OExpr..15.7682Z }}</ref><ref name="ding_2008">{{cite journal
|doi = 10.1364/OE.16.003310
|title = Solitons and spectral broadening in long silicon-on- insulator photonic wires
|journal = [[Optics Express]]
|year = 2008
|volume = 16
|issue = 5
|pages = 3310–3319
|author = W. Ding, C. Benton, A. V. Gorbach, W. J. Wadsworth, J.C. Knight, D. V. Skryabin, M. Gnan, M. Sorrel and R. M. De-La-Rue
| bibcode = 2008OExpr..16.3310D }}</ref>

== Applications ==

=== Optical interconnects ===

Progress in computer technology (and the continuation of [[Moore's Law]]) is becoming increasingly dependent on faster [[data transfer]] between and within [[Integrated circuit|microchips]].<ref name="meindl_2003">{{cite journal
|doi = 10.1109/MCISE.2003.1166548
|title = Beyond Moore's Law: the interconnect era
|journal = Computing in Science & Engineering
|year = 2003
|volume = 5
|issue = 1
|pages = 20–24
|author = J. D. Meindl
}}</ref> [[Optical interconnect]]s may provide a way forward, and silicon photonics may prove particularly useful, once integrated on the standard silicon chips.<ref name="lipson_2005" /><ref name="barwicz_2006">{{cite journal
|doi = 10.1364/JON.6.000063
|title = Silicon photonics for compact, energy-efficient interconnects
|journal = Journal of Optical Networking
|year = 2006
|volume = 6
|issue = 1
|pages = 63–73
|author = T. Barwicz, H. Byun, F. Gan, C. W. Holzwarth, M. A. Popovic, P. T. Rakich, M. R. Watts, E. P. Ippen, F. X. Kärtner, H. I. Smith, J. S. Orcutt, R. J. Ram, V. Stojanovic, O. O. Olubuyide, J. L. Hoyt, S. Spector, M. Geis, M. Grein, T. Lyszczarz and J. U. Yoon
| bibcode = 2007JON.....6...63B }}</ref><ref name="orcutt_2008">{{cite conference
|authors = J. S. Orcutt, A. Khilo, M. A. Popovic, C. W. Holzwarth, B. Moss, H. Li, M. S. Dahlem, T. D. Bonifield, F. X. Kaertner, E. P. Ippen, J. L. Hoyt, R. J. Ram, and V. Stojanovic
|title = Demonstration of an Electronic Photonic Integrated Circuit in a Commercial Scaled Bulk CMOS Process
|conference = Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies
|year = 2008
}}</ref> In 2006 Former [[Intel]] senior vice president [[Pat Gelsinger]] stated that, "Today, optics is a niche technology. Tomorrow, it's the mainstream of every chip that we build."<ref name="intel_silicon" />

Optical interconnects require multiple advances.

An on-chip [[laser]] source is required. One such device is the [[hybrid silicon laser]], in which the silicon is bonded to a different [[semiconductor]] (such as [[indium phosphide]]) as the [[lasing medium]].<ref name="intel_hybrid">{{cite web
|url = http://techresearch.intel.com/articles/Tera-Scale/1448.htm
|title = Hybrid Silicon Laser - Intel Platform Research
|publisher = [[Intel]]
|accessdate = 2009-07-14
}}</ref> Another possibility is the all-silicon [[Raman laser]], in which silicon is the lasing medium.<ref name="rong_2005">{{cite journal
|title = An all-silicon Raman laser
|doi = 10.1038/nature03273
|journal = [[Nature (journal)|Nature]]
|pmid = 15635371
|year = 2005
|volume = 433
|issue = 7023
|pages = 292–294
|author = Haisheng Rong, Ansheng Liu, Richard Jones, Oded Cohen, Dani Hak, Remus Nicolaescu, Alexander Fang and Mario Paniccia
| bibcode = 2005Natur.433..292R }}</ref>

The light must be [[modulation|modulated]] to encode data in the form of optical pulses. One such technique is to control the density of free charge carriers, which (as described below) alter the waveguide's optical properties. Some modulators pass light through the [[intrinsic semiconductor|intrinsic region]] of a [[PIN diode]], into which carriers can be injected or removed by altering the [[Electrical polarity|polarity]] of an applied [[voltage]].<ref name="barrios_2003">{{cite journal
|doi = 10.1109/JLT.2003.818167
|title = Electrooptic Modulation of Silicon-on-Insulator Submicrometer-Size Waveguide Devices
|journal = [[Journal of Lightwave Technology]]
|year = 2003
|volume = 21
|issue = 10
|pages = 2332–2339
|author = C. Angulo Barrios, V. R. Almeida, R. Panepucci and M. Lipson
| bibcode = 2003JLwT...21.2332B }}</ref> In 2007 an [[optical ring resonator]] with a built in PIN diode achieved data transmission rates of 18 [[Gbit/s]].<ref name="xu_2007">{{cite journal
|title = High Speed Carrier Injection 18 Gbit/s Silicon Micro-ring Electro-optic Modulator
|journal = [in Proceedings of Lasers and Electro-Optics Society (IEEE, 2007)]
|year = 2007
|volume =
|page = pp.537–538
|author = Sasikanth Manipatruni, Qianfan Xu, Brad Schmidt, Jagat Shakya and Michal Lipson
}}</ref> Devices where the electrical signal co-moves with the light, allowed data rates of 30 Gbit/s.<ref name="liu_2007">{{cite journal
|doi = 10.1364/OE.15.000660
|last1 = Liu
|first1 = Ansheng
|last2 = Liao
|first2 = Ling
|last3 = Rubin
|first3 = Doron
|last4 = Nguyen
|first4 = Hat
|last5 = Ciftcioglu
|first5 = Berkehan
|last6 = Chetrit
|first6 = Yoel
|last7 = Izhaky
|first7 = Nahum
|last8 = Paniccia
|first8 = Mario
|author9 = Ansheng Liu, Ling Liao, Doron Rubin, Hat Nguyen, Berkehan Ciftcioglu, Yoel Chetrit, Nahum Izhaky and Mario Paniccia
|title = High-speed optical modulation based on carrier depletion in a silicon waveguide
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 2
|pages = 660–668 |bibcode = 2007OExpr..15..660L |display-authors = 9
}}
</ref> Using multiple wavelengths scaled allowed 50 Gbit/s.<ref name="Manipatruni_2009">{{cite journal
|title = 50 Gbit/s wavelength division multiplexing using silicon microring modulators
|journal = [Group IV Photonics, 2009. GFP '09. 6th IEEE International Conference on]
|year = 2009
|doi = 10.1109/GROUP4.2009.5338375
|pages = 244–246
|author = Sasikanth Manipatruni; Long Chen; Lipson, Michal;
|isbn = 978-1-4244-4402-1
}}
</ref> A prototype optical interconnect with microring modulators integrated with germanium detectors has been demonstrated.<ref name="Long Chen_2009">{{cite journal
|doi = 10.1364/OE.17.015248
|title = Integrated GHz silicon photonic interconnect with micrometer-scale modulators and detectors
|journal = [[Optics Express]]
|year = 2009
|volume = 17
|issue = 17
|pages = 15248–15256
|author = Long Chen, Kyle Preston, Sasikanth Manipatruni, and Michal Lipson,
| bibcode = 2009OExpr..1715248C |arxiv = 0907.0022 }}
</ref><ref name="register_vance">{{cite news
|title = Intel cranks up next-gen chip-to-chip play
|publisher = The Register
|author = [[Ashlee Vance]]
|url = http://www.theregister.co.uk/2007/01/27/intel_silicon_modulator/print.html
|accessdate = 2009-07-26
}}</ref>

After passage through a silicon [[waveguide]] to a different chip (or region of the same chip) the light must be [[photodetector|detected]], to reconvert the data into electronic form.<ref>{{cite journal|author = D Kucharski, D Guckenberger, G Masini, S Abdalla, J Witzens, S Sahni|year = 2010|title = 10 Gb/s 15mW optical receiver with integrated Germanium photodetector and hybrid inductor peaking in 0.13µm SOI CMOS technology|journal = Solid-State Circuits Conference Digest of Technical Papers (ISSCC)|pages=360–361}}</ref><ref>{{cite journal|author = C Gunn, G Masini, J Witzens, G Capellini|year = 2006|title=CMOS photonics using germanium photodetectors|journal=ECS Transactions|volume=3|issue=7|pages=17–24|doi=10.1149/1.2355790|url=http://ecst.ecsdl.org/content/3/7/17.abstract}}</ref> Detectors based on [[metal-semiconductor junction]]s (with [[germanium]] as the semiconductor) have been integrated into silicon waveguides.<ref name="vivien_2007">{{cite journal
|doi = 10.1364/OE.15.009843
|title = High speed and high responsivity germanium photodetector integrated in a Silicon-On-Insulator microwaveguide
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 15
|pages = 9843–9848
|author = Laurent Vivien, Mathieu Rouvière, Jean-Marc Fédéli, Delphine Marris-Morini, Jean François Damlencourt, Juliette Mangeney, Paul Crozat, Loubna El Melhaoui, Eric Cassan, Xavier Le Roux, Daniel Pascal and Suzanne Laval
| bibcode = 2007OExpr..15.9843V }}</ref> More recently, silicon-germanium [[avalanche photodiode]]s capable of operating at 40 Gbit/s have been fabricated.<ref name="kang_2008">{{cite journal
|doi = 10.1038/nnano.2008.25
|title = Monolithic germanium/silicon avalanche photodiodes with 340 GHz gain–bandwidth product
|journal = [[Nature Photonics]]
|year = 2008
|volume = 3
|issue = 2
|pages = 59–63
|author = Yimin Kang, Han-Din Liu, Mike Morse, Mario J. Paniccia, Moshe Zadka, Stas Litski, Gadi Sarid, Alexandre Pauchard, Ying-Hao Kuo, Hui-Wen Chen, Wissem Sfar Zaoui, John E. Bowers, Andreas Beling, Dion C. McIntosh, Xiaoguang Zheng and Joe C. Campbell
|pmid = 18654454
| bibcode = 2008NatNa...3...59. }}</ref><ref name="register_modine">{{cite news
|title = Intel trumpets world's fastest silicon photonic detector
|publisher = The Register
|author = Austin Modine
|url = http://www.theregister.co.uk/2008/12/08/intel_world_record_apd_research/
|accessdate = 2009-07-26
}}</ref>
Complete transceivers have been commercialized in the form of active optical cables.<ref>{{cite journal|author = A. Narasimha et al.|title = A 40-Gb/s QSFP optoelectronic transceiver in a 0.13 µm CMOS silicon-on-insulator technology|year = 2008|journal = Proceedings of the Optical Fiber Communication Conference (OFC)|page = OMK7|url=http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2008-OMK7}}</ref>

In 2012, IBM announced that it had achieved optical components at the 90 nanometer scale that can be manufactured using standard techniques and incorporated into conventional chips.<ref name="ibm_silicon" /><ref>{{cite web|url=http://www.gizmag.com/ibm-silicon-nanophotonics/25446/?utm_source=Gizmag+Subscribers&utm_campaign=59593484e3-UA-2235360-4&utm_medium=email |title=IBM integrates optics and electronics on a single chip |publisher=Gizmag.com |date= |accessdate=2013-04-20}}</ref> In September 2013, Intel announced technology to transmit data at speeds of 100 gigabits per second along a cable approximately five millimeters in diameter for connecting servers inside data centers. Conventional PCI-E data cables carry data at up to eight gigabits per second, while networking cables reach 40 Gb. The latest version of the [[USB]] standard tops out at five Gb. The technology does not directly replace existing cables in that it requires the a separate circuit board to interconvert electrical and optical signals. Its advanced speed offers the potential of reducing the number of cables that connect blades on a rack and even of separating processor, storage and memory into separate blades to allow more efficient cooling and dynamic configuration<ref>{{cite web|last=Simonite |first=Tom |url=http://www.technologyreview.com/news/518941/intels-laser-chips-could-make-data-centers-run-better |title=Intel Unveils Optical Technology to Kill Copper Cables and Make Data Centers Run Faster | MIT Technology Review |publisher=Technologyreview.com |date= |accessdate=2013-09-04}}</ref>

[[Graphene]] photodetectors have the potential to surpass germanium devices in several important aspects, although they remain about one order of magnitude behind current generation capacity, despite rapid improvement.
Graphene devices can work at very high frequencies, and could in principle reach higher bandwidths. Graphene can absorb a broader range of wavelengths than germanium. That property could be exploited to transmit more data streams simultaneously in the same beam of light. Unlike germanium detectors, graphene photodetectors do not require applied voltage, which could reduce energy needs. Finally, graphene detectors in principle permit a simpler and less expensive on-chip integration. However, graphene does not strongly absorb light. Pairing a silicon waveguide with a graphene sheet better routes light and maximizes interaction. The first such device was demonstrated in 2011. Manufacturing such devices using conventional manufacturing techniques has not been demonstrated.<ref>[http://www.technologyreview.com/news/519441/graphene-could-make-data-centers-and-supercomputers-more-efficient]</ref>

In 2013 researchers demonstrated two different depletion-mode carrier-plasma optical modulators that can be fabricated using standard Silicon-on-Insulator Complementary Metal-Oxide-Semiconductor (SOI CMOS) manufacturing processes. The researchers also detailed a second modulator that could be used in bulk CMOS.<ref>{{cite web|url=http://www.kurzweilai.net/major-silicon-photonics-breakthrough-could-allow-for-continued-exponential-growth-in-microprocessors |title=Major silicon photonics breakthrough could allow for continued exponential growth in microprocessors |publisher=KurzweilAI |date= |accessdate=2013-10-08}}</ref><ref>{{cite doi|10.1364/OL.38.002657}}</ref><ref>{{cite doi|10.1364/OL.38.002729}}</ref>

=== Optical routers and signal processors ===

Another application of silicon photonics is in signal routers for [[fiber optic telecommunication|optical communication]]. Construction can be greatly simplified by fabricating the optical and electronic parts on the same chip, rather than having them spread across multiple components.<ref name="analui_2006">{{cite journal
|doi = 10.1109/JSSC.2006.884388
|title = A Fully Integrated 20-Gb/s Optoelectronic Transceiver Implemented in a Standard 0.13- μm CMOS SOI Technology
|journal = [[IEEE]] Journal of Solid-State Circuits
|year = 2006
|volume = 41
|issue = 12
|pages = 2945–2955
|author = B. Analui, D. Guckenberger, D. Kucharski and A. Narasimha
}}</ref> A wider aim is all-optical signal processing, whereby tasks which are conventionally performed by manipulating signals in electronic form are done directly in optical form.<ref name="almeida_2004" /><ref name="boyraz_2004">{{cite journal
|doi = 10.1364/OPEX.12.004094
|title = All optical switching and continuum generation in silicon waveguides
|journal = [[Optics Express]]
|year = 2004
|volume = 12
|issue = 17
|pages = 4094–4102
|author = Özdal Boyraz, Prakash Koonath, Varun Raghunathan and Bahram Jalali
| bibcode = 2004OExpr..12.4094B }}</ref> An important example is all-[[optical switching]], whereby the routing of optical signals is directly controlled by other optical signals.<ref name="vlasov_2008">{{cite journal
|doi = 10.1038/nphoton.2008.31
|title = High-throughput silicon nanophotonic wavelength-insensitive switch for on-chip optical networks
|journal = [[Nature Photonics]]
|year = 2008
|volume = 2
|issue = 4
|pages = 242–246
|author = Y. Vlasov, W. M. J. Green and F. Xia
}}</ref> Another example is all-optical wavelength conversion.<ref name="foster_2007">{{cite journal
|doi = 10.1364/OE.15.012949
|title = Broad-band continuous-wave parametric wavelength conversion in silicon nanowaveguides
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 20
|pages = 12949–12958
|author = Mark A. Foster, Amy C. Turner, Reza Salem, Michal Lipson and Alexander L. Gaeta
| bibcode = 2007OExpr..1512949F }}</ref>

In 2013, a [[startup company]] named "[[Compass-EOS]]", based in [[California]] and in [[Israel]], was the first to present a commercial silicon-to-photonics router.<ref>{{cite web|url=http://venturebeat.com/2013/03/12/after-six-years-of-planning-compass-eos-takes-on-cisco-to-make-blazing-fast-routers/ |title=After six years of planning, Compass-EOS takes on Cisco to make blazing-fast routers |publisher=venturebeat.com |date=2013-03-12|accessdate=2013-04-25}}</ref>

=== Long range telecommunications using silicon photonics ===

Silicon microphotonics can potentially increase the [[Internet]]'s bandwidth capacity by providing micro-scale, ultra low power devices. Furthermore, the power consumption of [[datacenter]]s may be significantly reduced if this is successfully achieved. Researchers at [[Sandia National Laboratories|Sandia]],<ref name="Sandia_2010">{{cite journal
|title = Power penalty measurement and frequency chirp extraction in silicon microdisk resonator modulators
|journal = Proc. Optical Fiber Communication Conference (OFC)
|year = 2010
|issue = OMI7
|author = W. A. Zortman, A. L. Lentine, M. R. Watts, and D. C. Trotter
}}</ref> Kotura, [[Nippon Telegraph and Telephone|NTT]], [[Fujitsu]] and various academic institutes have been attempting to prove this functionality. A prototype 80 km, 12.5 Gbit/s transmission has recently been reported using microring silicon devices.<ref name="Biberman_Manipatruni_2010">{{cite journal
|doi = 10.1364/OE.18.015544
|title = First demonstration of long-haul transmission using silicon microring modulators
|journal = [[Optics Express]]
|year = 2010
|volume = 18
|issue = 15
|pages = 15544–15552
|author = A. Biberman, S. Manipatruni, N. Ophir, L.Chen, M.Lipson, K.Bergman
|url = http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-18-15-15544
| bibcode = 2010OExpr..1815544B |last2 = Manipatruni
|last3 = Ophir
|last4 = Chen
|last5 = Lipson
|last6 = Bergman
}}</ref>

== Physical properties ==

=== Optical guiding and dispersion tailoring ===

Silicon is [[transparency (optics)|transparent]] to [[infrared light]] with wavelengths above about 1.1 micrometres.<ref name="reading_lab">{{cite web
|url = http://www.rdg.ac.uk/infrared/library/infraredmaterials/ir-infraredmaterials-si.aspx
|title = Silicon (Si)
|publisher = [[University of Reading]] Infrared Multilayer Laboratory
|accessdate = 2009-07-17
}}</ref> Silicon also has a very high [[refractive index]], of about 3.5.<ref name="reading_lab" /> The tight optical confinement provided by this high index allows for microscopic [[optical waveguide]]s, which may have cross-sectional dimensions of only a few hundred [[nanometer]]s.<ref name="dekker_2008" /> This is substantially less than the wavelength of the light itself, and is analogous to a [[subwavelength-diameter optical fibre]]. Single mode propagation can be achieved,<ref name="dekker_2008" /> thus (like [[single-mode optical fiber]]) eliminating the problem of [[modal dispersion]].

The strong [[Interface conditions for electromagnetic fields|dielectric boundary effects]] that result from this tight confinement substantially alter the [[dispersion (optics)|optical dispersion relation]]. By selecting the waveguide geometry, it is possible to tailor the dispersion to have desired properties, which is of crucial importance to applications requiring ultrashort pulses.<ref name="dekker_2008" /> In particular, the ''group velocity dispersion'' (that is, the extent to which [[group velocity]] varies with wavelength) can be closely controlled. In bulk silicon at 1.55 micrometres, the group velocity dispersion (GVD) is ''normal'' in that pulses with longer wavelengths travel with higher group velocity than those with shorter wavelength. By selecting a suitable waveguide geometry, however, it is possible to reverse this, and achieve ''anomalous'' GVD, in which pulses with shorter wavelengths travel faster.<ref name="yin_2006" >{{cite journal
|doi = 10.1364/OL.31.001295
|title = Dispersion tailoring and soliton propagation in silicon waveguides
|journal = [[Optics Letters]]
|year = 2006
|volume = 31
|issue = 9
|pages = 1295–1297
|author = L. H. Yin, Q. Lin, and G. P. Agrawal.
| bibcode = 2006OptL...31.1295Y }}</ref><ref name="turner_2006" >{{cite journal
|doi = 10.1364/OE.14.004357
|title = Tailored anomalous group-velocity dispersion in silicon channel waveguides
|journal = [[Optics Express]]
|year = 2006
|volume = 14
|issue = 10
|pages = 4357–4362
|author = Amy C. Turner, Christina Manolatou, Bradley S. Schmidt, Michal Lipson, Mark A. Foster, Jay E. Sharping and Alexander L. Gaeta
| bibcode = 2006OExpr..14.4357T }}</ref> Anomalous dispersion is significant, as it is a prerequisite for [[soliton]] propagation, and [[modulational instability]].<ref name="agrawal_book">{{cite book
|last = Agrawal
|first = Govind P.
|year = 1995
|title = Nonlinear fiber optics
|place = San Diego (California)
|publisher = Academic Press
|edition =2nd
|isbn = 0-12-045142-5
}}</ref>

In order for the silicon photonic components to remain optically independent from the bulk silicon of the [[wafer (electronics)|wafer]] on which they are fabricated, it is necessary to have a layer of intervening material. This is usually [[silica]], which has a much lower refractive index (of about 1.44 in the wavelength region of interest<ref name="malitson_1965">{{cite journal
|doi = 10.1364/JOSA.55.001205
|title = Interspecimen Comparison of the Refractive Index of Fused Silica
|journal = [[Journal of the Optical Society of America]]
|year = 1965
|volume = 55
|issue = 10
|pages = 1205–1209
|author = I. H. Malitson
}}</ref>), and thus light at the silicon-silica interface will (like light at the silicon-air interface) undergo [[total internal reflection]], and remain in the silicon. This construct is known as silicon on insulator.<ref name="pavesi_book" /><ref name="reed_book" /> It is named after the technology of [[silicon on insulator]] in electronics, whereby components are built upon a layer of [[insulator (electrical)|insulator]] in order to reduce [[parasitic capacitance]] and so improve performance.<ref name="celler_2003">{{cite journal
|title = Frontiers of silicon-on-insulator
|journal = [[Journal of Applied Physics]]
|year = 2003
|volume = 93
|page = 4955
|author = G. K. Celler and S. Cristoloveanu
| bibcode = 2003JAP....93.4955C |doi = 10.1063/1.1558223
|issue = 9 }}</ref>

=== Kerr nonlinearity ===

Silicon has a focusing [[Kerr nonlinearity]], in that the [[refractive index]] increases with optical intensity.<ref name="dekker_2008" /> This effect is not especially strong in bulk silicon, but it can be greatly enhanced by using a silicon waveguide to concentrate light into a very small cross-sectional area.<ref name="hsieh_2006" /> This allows [[nonlinear optics|nonlinear optical]] effects to be seen at low powers. The nonlinearity can be enhanced further by using a [[slot waveguide]], in which the high refractive index of the silicon is used to confine light into a central region filled with a strongly nonlinear [[polymer]].<ref name="koos_2007" >{{cite journal
|doi = 10.1364/OE.15.005976
|title = Nonlinear silicon-on-insulator waveguides for all-optical signal processing
|journal = [[Optics Express]]
|year = 2007
|volume = 15
|issue = 10
|pages = 5976–5990
|author = C. Koos and L. Jacome and C. Poulton and J. Leuthold and W. Freude
| bibcode = 2007OExpr..15.5976K
|pmid=19546900}}</ref>

Kerr nonlinearity underlies a wide variety of optical phenomena.<ref name="agrawal_book" /> One example is [[four wave mixing]], which has been applied in silicon to realise both [[optical parametric amplification]]<ref name="foster_2006">{{cite journal
|title = Broad-band optical parametric gain on a silicon photonic chip
|journal = [[Nature (journal)|Nature]]
|year = 2006
|volume = 441
|issue = 7096
|page = 04932
|pmid = 16791190
|doi = 10.1038/nature04932
|author = Mark A. Foster, Amy C. Turner, Jay E. Sharping, Bradley S. Schmidt, Michael Lipson and Alexander L. Gaeta
| bibcode = 2006Natur.441..960F }}</ref> and parametric wavelength conversion.<ref name="foster_2007" /> Kerr nonlinearity can also cause [[modulational instability]], in which it reinforces deviations from an optical waveform, leading to the generation of [[Frequency spectrum|spectral]]-sidebands and the eventual breakup of the waveform into a train of pulses.<ref name="panoiu_2006">{{cite journal
|title = Modulation instability in silicon photonic nanowires
|journal = [[Optics Letters]]
|year = 2006
|volume = 31
|page = 3609
|author = Nicolae C. Panoiu, Xiaogang Chen and Richard M. Osgood, Jr.
| pmid=17130919
| bibcode = 2006OptL...31.3609P |doi = 10.1364/OL.31.003609
|issue = 24 }}</ref> Another example (as described below) is soliton propagation.

=== Two-photon absorption ===

Silicon exhibits [[two-photon absorption]] (TPA), in which a pair of [[photon]]s can act to excite an [[electron-hole pair]].<ref name="dekker_2008" /> This process is related to the Kerr effect, and by analogy with [[Mathematical descriptions of opacity|complex refractive index]], can be thought of as the [[Imaginary number|imaginary]]-part of a [[Complex number|complex]] Kerr nonlinearity.<ref name="dekker_2008" /> At the 1.55 micrometre telecommunication wavelength, this imaginary part is approximately 10% of the real part.<ref name="yin_2006_2">{{cite journal
|doi = 10.1364/OL.32.002031
|title = Impact of two-photon absorption on self-phase modulation in silicon waveguides: Free-carrier effects
|journal = [[Optics Letters]]
|year = 2006
|volume = 32
|issue = 14
|pages = 2031–2033
|author = Lianghong Yin and Govind Agrawal
| bibcode = 2007OptL...32.2031Y }}</ref>

The influence of TPA is highly disruptive, as it both wastes light, and generates unwanted [[heat]].<ref name="nikbin_article">{{cite news
|author = Darius Nikbin
|title = Silicon photonics solves its "fundamental problem"
|publisher = IOP publishing
|url = http://optics.org/cws/article/research/25379
|accessdate = 2009-07-14
}}</ref> It can be mitigated, however, either by switching to longer wavelengths (at which the TPA to Kerr ratio drops),<ref name="bristow_2007">{{cite journal
|title = Two-photon absorption and Kerr coefﬁcients of silicon for 850– {{convert|2200|nmi|km|abbr=on}}
|journal = [[Applied Physics Letters]]
|year = 2007
|volume = 90
|page = 191104
|author = Alan D. Bristow, Nir Rotenberg and Henry M. van Driel
| bibcode = 2007ApPhL..90b1104R |doi = 10.1063/1.2430400
|issue = 2 }}</ref> or by using slot waveguides (in which the internal nonlinear material has a lower TPA to Kerr ratio).<ref name="koos_2007" /> Alternatively, the energy lost through TPA can be partially recovered (as is described below) by extracting it from the generated charge carriers.<ref name="tsia_2006">{{cite conference
|authors = K. M. Tsia, S. Fathpour and B. Jalali
|title = Energy Harvesting in Silicon Raman Amplifiers
|conference = 3rd [[IEEE]] International Conference on Group IV Photonics
|year = 2006
}}</ref>

=== Free charge carrier interactions ===

The [[Charge carriers in semiconductors|free charge carriers]] within silicon can both absorb photons and change its refractive index.<ref name="soref_1987">{{cite journal
|doi = 10.1109/JQE.1987.1073206
|title = Electrooptical Effects in Silicon
|journal = [[IEEE Journal of Quantum Electronics]]
|year = 1987
|volume = 23
|issue = 1
|pages = 123–129
|author = R. A. Soref and B. R. Bennett
| bibcode = 1987IJQE...23..123S }}</ref> This is particularly significant at high intensities and for long durations, due to the carrier concentration being built up by TPA. The influence of free charge carriers is often (but not always) unwanted, and various means have been proposed to remove them. One such scheme is to [[ion implantation|implant]] the silicon with [[helium]] in order to enhance [[carrier recombination]].<ref name="liu_2006">{{cite journal
|doi = 10.1364/OL.31.001714
|title = Nonlinear absorption and Raman gain in helium-ion-implanted silicon waveguides
|journal = [[Optics Letters]]
|year = 2006
|volume = 31
|issue = 11
|pages = 1714–1716
|author = Y. Liu and H. K. Tsang
| bibcode = 2006OptL...31.1714L }}</ref> A suitable choice of geometry can also be used to reduce the carrier lifetime. [[Rib waveguide]]s (in which the waveguides consist of thicker regions in a wider layer of silicon) enhance both the carrier recombination at the silica-silicon interface and the [[diffusion]] of carriers from the waveguide core.<ref name="dimitropoulos_2005">{{cite journal
|title = Lifetime of photogenerated carriers in silicon-on-insulator rib waveguides
|journal = [[Applied Physics Letters]]
|year = 2005
|volume = 86
|page = 071115
|author = D. Dimitropoulos, R. Jhaveri, R. Claps, J.C.S Woo and B. Jalali
| bibcode = 2005ApPhL..86a1115Z |doi = 10.1063/1.1846145 }}</ref>

A more advanced scheme for carrier removal is to integrate the waveguide into the [[intrinsic semiconductor|intrinsic region]] of a [[PIN diode]], which is [[reverse bias]]ed so that the carriers are attracted away from the waveguide core.<ref name="jones_2005">{{cite journal
|doi = 10.1364/OPEX.13.000519
|title = Net continuous wave optical gain in a low loss silicon-on-insulator waveguide by stimulated Raman scattering
|journal = [[Optics Express]]
|year = 2005
|volume = 13
|issue = 2
|pages = 519–525
|author = Richard Jones, Haisheng Rong, Ansheng Liu, Alexander W. Fang and Mario J. Paniccia
| bibcode = 2005OExpr..13..519J }}</ref> A more sophisticated scheme still, is to use the diode as part of a circuit in which [[voltage]] and [[Electric current|current]] are out of phase, thus allowing power to be extracted from the waveguide.<ref name="tsia_2006" /> The source of this power is the light lost to two photon absorption, and so by recovering some of it, the net loss (and the rate at which heat is generated) can be reduced.

As is mentioned above, free charge carrier effects can also be used constructively, in order to modulate the light.<ref name="barrios_2003" /><ref name="xu_2007" /><ref name="liu_2007" />

=== Second-order nonlinearity ===

Second-order nonlinearities cannot exist in bulk silicon because of the [[centrosymmetry]] of its crystalline structure. By applying strain however, the inversion symmetry of silicon can be broken. This can be obtained for example by depositing a [[silicon nitride]] layer on a thin silicon film.<ref name="JacobsenAndersen2006">{{cite journal|last1=Jacobsen|first1=Rune S.|last2=Andersen|first2=Karin N.|last3=Borel|first3=Peter I.|last4=Fage-Pedersen|first4=Jacob|last5=Frandsen|first5=Lars H.|last6=Hansen|first6=Ole|last7=Kristensen|first7=Martin|last8=Lavrinenko|first8=Andrei V.|last9=Moulin|first9=Gaid|last10=Ou|first10=Haiyan|last11=Peucheret|first11=Christophe|last12=Zsigri|first12=Beáta|last13=Bjarklev|first13=Anders|title=Strained silicon as a new electro-optic material|journal=Nature|volume=441|issue=7090|year=2006|pages=199–202|issn=0028-0836|doi=10.1038/nature04706|pmid=16688172|bibcode = 2006Natur.441..199J }}</ref>
Second-order nonlinear phenomena can be exploited for [[Pockels effect|optical modulation]], [[spontaneous parametric down-conversion]], [[Optical parametric amplifier|parametric amplification]], [[Optical computing|ultra-fast optical signal processing]] and [[Infrared|mid-infrared]] generation. Efficient nonlinear conversion however requires [[Phase matching#Phase matching|phase matching]] between the optical waves involved. Second-order nonlinear waveguides based on strained silicon can achieve [[Phase matching#Phase matching|phase matching]] by [[Modal dispersion|dispersion-engineering]].<ref name="AvrutskySoref2011">{{cite journal|last1=Avrutsky|first1=Ivan|last2=Soref|first2=Richard|title=Phase-matched sum frequency generation in strained silicon waveguides using their second-order nonlinear optical susceptibility|journal=Optics Express|volume=19|issue=22|year=2011|page=21707|issn=1094-4087|doi=10.1364/OE.19.021707|bibcode = 2011OExpr..1921707A }}</ref>
So far, however, experimental demonstrations are based only on designs which are not [[Phase matching#Phase matching|phase matched]].<ref name="CazzanelliBianco2011">{{cite journal|last1=Cazzanelli|first1=M.|last2=Bianco|first2=F.|last3=Borga|first3=E.|last4=Pucker|first4=G.|last5=Ghulinyan|first5=M.|last6=Degoli|first6=E.|last7=Luppi|first7=E.|last8=Véniard|first8=V.|last9=Ossicini|first9=S.|last10=Modotto|first10=D.|last11=Wabnitz|first11=S.|last12=Pierobon|first12=R.|last13=Pavesi|first13=L.|title=Second-harmonic generation in silicon waveguides strained by silicon nitride|journal=Nature Materials|volume=11|issue=2|year=2011|pages=148–154|issn=1476-1122|doi=10.1038/nmat3200|pmid=22138793|bibcode = 2012NatMa..11..148C }}</ref>
It has been shown that [[Phase matching#Phase matching|phase matching]] can be obtained as well in silicon double [[slot waveguide]]s coated with a highly nonlinear organic cladding<ref name="AlloattiKorn2012">{{cite journal|last1=Alloatti|first1=L.|last2=Korn|first2=D.|last3=Weimann|first3=C.|last4=Koos|first4=C.|last5=Freude|first5=W.|last6=Leuthold|first6=J.|title=Second-order nonlinear silicon-organic hybrid waveguides|journal=Optics Express|volume=20|issue=18|year=2012|page=20506|issn=1094-4087|doi=10.1364/OE.20.020506|bibcode = 2012OExpr..2020506A }}</ref>
and in periodically strained silicon waveguides.<ref name="HonTsia2009">{{cite journal|last1=Hon|first1=Nick K.|last2=Tsia|first2=Kevin K.|last3=Solli|first3=Daniel R.|last4=Jalali|first4=Bahram|title=Periodically poled silicon|journal=Applied Physics Letters|volume=94|issue=9|year=2009|page=091116|issn=00036951|doi=10.1063/1.3094750|arxiv = 0812.4427 |bibcode = 2009ApPhL..94i1116H }}</ref>

=== The Raman effect ===

Silicon exhibits the [[Raman effect]], in which a photon is exchanged for a photon with a slightly different energy, corresponding to an excitation or a relaxation of the material. Silicon's Raman transition is dominated by a single, very narrow frequency peak, which is problematic for broadband phenomena such as [[Raman amplification]], but is beneficial for narrowband devices such as [[Raman laser]]s.<ref name="dekker_2008" /> Early studies of Raman amplification and Raman lasers started at UCLA which led to demonstration of net gain Silicon Raman amplifiers and silicon pulsed Raman laser with fiber resonator (Optics express 2004). Consequently, all-silicon Raman lasers have been fabricated in 2005.<ref name="rong_2005" />

== Solitons ==

The evolution of light through silicon waveguides can be approximated with a cubic [[Nonlinear Schrödinger equation]],<ref name="dekker_2008" /> which is notable for admitting [[hyperbolic secant|sech]]-like [[soliton]] solutions.<ref name="drazin_book">{{cite book
|title = Solitons: an introduction
|publisher = [[Cambridge University Press]]
|year = 1989
|isbn = 0-521-33655-4
|author = P. G. Drazin and R. S. Johnson
}}</ref> These [[optical soliton]]s (which are also known in [[optical fiber]]) result from a balance between [[self phase modulation]] (which causes the leading edge of the pulse to be [[Redshifted#Effects due to physical optics or radiative transfer|redshifted]] and the trailing edge blueshifted) and anomalous group velocity dispersion.<ref name="agrawal_book" /> Such solitons have been observed in silicon waveguides, by groups at the universities of [[Columbia University|Columbia]],<ref name="hsieh_2006" /> [[Rochester University|Rochester]],<ref name="zhang_2007" /> and [[University of Bath|Bath]].<ref name="ding_2008" />

== External links ==
* [http://domino.research.ibm.com/comm/research_projects.nsf/pages/photonics.index.html IBM's page on silicon integrated nanophotonics]
* [https://www-ssl.intel.com/content/www/us/en/research/intel-labs-silicon-photonics-research.html Intel's page on silicon photonics]
* [http://nanophotonics.ece.cornell.edu Michal Lipson's page on silicon photonics]
* [http://www.uksiliconphotonics.co.uk/ Uk based project website on silicon photonics]
* [http://www.helios-project.eu/ European project website on silicon photonics]
* [http://www.siliconphotonics.co.uk/ UK based group working on silicon photonics]
* [http://silicon-photonics.ief.u-psud.fr/ French based group working on silicon photonics]
* [http://photonics.intec.ugent.be/ Belgian group working on silicon photonics]
* [http://www.ipq.kit.edu/english/index.php Silicon photonics at KIT]

== References ==
{{reflist|2}}

{{DEFAULTSORT:Silicon Photonics}}
[[Category:Nonlinear optics]]
[[Category:Photonics]]
[[Category:Silicon]]

Plasmonische Solarzelle

2014-07-10T04:54:12Z

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'''Plasmonic solar cells''' (PSC) are a class of [[photovoltaic device]]s that convert light into electricity by using [[plasmon]]s. PSCs are a type of [[Thin film solar cell|thin-film SC]] which are typically 1-2μm thick. They can use [[Substrate (materials science)|substrates]] which are cheaper than [[silicon]], such as [[glass]], [[plastic]] or [[steel]]. The biggest problem for thin film solar cells is that they don’t absorb as much light as the current solar cells. Methods for trapping light on the surface, or in the SC are crucial in order to make thin film SCs viable. One method which has been explored over the past few years is to scatter light using metal [[nanoparticle]]s excited at their [[surface plasmon resonance]].
<ref name=Catchpole>K. R. Catchpole and A. Polman, "Plasmonic solar cells," Opt. Express 16, 21793-21800 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-26-21793</ref>
This allows light to be absorbed more directly without the relatively thick additional layer required in other types of thin-film solar cells.

== History ==

=== People ===

There have been quite a few pioneers working with plasmonic solar cells.<ref name=Catchpole/> One of the main focuses has been on improving the thin film SC through the use of metal nanoparticles distributed on the surface. It has been found that the [[Raman scattering]] can be increased by [[order of magnitude]] when using metal nanoparticles. The increased Raman scattering provides more [[photon]]s to become available to excite [[surface plasmon]]s which cause [[electron]]s to be excited and travel through the thin film SC to create a [[Current (electricity)|current]]. The list below shows a few of research which has been done to improve PSCs.

*Stuart and Hall: Photocurrent enhancement by 18x with 165 nm SOI [[photodetector]] with wavelength of 800 nm using silver nanoparticles used for scattering and absorption of light.<ref>{{cite journal | bibcode=1998ApPhL..73.3815S | doi = 10.1063/1.122903 | title=Island size effects in nanoparticle-enhanced photodetectors | year=1998 | last1=Stuart | first1=Howard R. | last2=Hall | first2=Dennis G. | journal=Applied Physics Letters | volume=73 | issue=26 | pages=3815 }}</ref>

*Schaadt: Gold nanoparticles used for scattering and absorption of light on doped silicon obtaining 80% enhancements with 500 nm wavelength.<ref>{{cite journal | doi = 10.1063/1.1855423 | title = Enhanced semiconductor optical absorption via surface plasmon excitation in metal nanoparticles | year = 2005 | last1 = Schaadt | first1 = D. M. | last2 = Feng | first2 = B. | last3 = Yu | first3 = E. T. | journal = Applied Physics Letters | volume = 86 | issue = 6 | pages = 063106 |bibcode = 2005ApPhL..86f3106S }}</ref>

*Derkacs: Gold nanoparticles on [[thin-film silicon]] gaining 8% on [[conversion efficiency]].<ref>{{cite journal | doi = 10.1063/1.2336629 | title = Improved performance of amorphous silicon solar cells via scattering from surface plasmon polaritons in nearby metallic nanoparticles | year = 2006 | last1 = Derkacs | first1 = D. | last2 = Lim | first2 = S. H. | last3 = Matheu | first3 = P. | last4 = Mar | first4 = W. | last5 = Yu | first5 = E. T. | journal = Applied Physics Letters | volume = 89 | issue = 9 | pages = 093103 |bibcode = 2006ApPhL..89i3103D }}</ref>

*Pillai: Silver particles on SOI obtaining 33% photocurrent increase.<ref>{{cite journal | doi = 10.1063/1.2734885 | bibcode= 2007JAP...101i3105P | title = Surface plasmon enhanced silicon solar cells | year = 2007 | last1 = Pillai | first1 = S. | last2 = Catchpole | first2 = K. R. | last3 = Trupke | first3 = T. | last4 = Green | first4 = M. A. | journal = Journal of Applied Physics | volume = 101 | issue = 9 | pages = 093105 }}</ref><ref>{{cite journal | doi = 10.1063/1.2195695 | title = Enhanced emission from Si-based light-emitting diodes using surface plasmons | year = 2006 | last1 = Pillai | first1 = S. | last2 = Catchpole | first2 = K. R. | last3 = Trupke | first3 = T. | last4 = Zhang | first4 = G. | last5 = Zhao | first5 = J. | last6 = Green | first6 = M. A. | journal = Applied Physics Letters | volume = 88 | issue = 16 | pages = 161102 |bibcode = 2006ApPhL..88p1102P }}</ref>

*Stenzel: Enhancements in photocurrent by a factor of 2.7 for ITO-copper [[phthalocyanine]]-[[indium]] structures.

*Westphalen: Enhancement for silver clusters incorporated into ITO and [[zinc]] phthalocyanine solar cells.<ref>{{cite journal | doi = 10.1016/S0927-0248(99)00100-2 | title = Metal cluster enhanced organic solar cells | year = 2000 | last1 = Westphalen | first1 = M | last2 = Kreibig | first2 = U | last3 = Rostalski | first3 = J | last4 = Lüth | first4 = H | last5 = Meissner | first5 = D | journal = Solar Energy Materials and Solar Cells | volume = 61 | pages = 97}}</ref>

*Rand: Enhanced efficiencies for ultra thin film organic solar cells due to 5 nm diameter silver nanoparticles.<ref>{{cite journal | doi = 10.1063/1.1812589|bibcode=2004JAP....96.7519R | title = Long-range absorption enhancement in organic tandem thin-film solar cells containing silver nanoclusters | year = 2004 | last1 = Rand | first1 = Barry P. | last2 = Peumans | first2 = Peter | last3 = Forrest | first3 = Stephen R. | journal = Journal of Applied Physics | volume = 96 | issue = 12 | pages = 7519 }}</ref><ref>http://www.prima-ict.eu</ref>

*Brown: Enhanced photocurrent and efficiencies in dye-sensitized solar cells incorporating metal-insulator core-shell nanoparticle geometries.<ref>{{cite journal | doi = 10.1021/nl1031106 | title = Plasmonic Dye-Sensitized Solar Cells Using Core−Shell Metal−Insulator Nanoparticles | year = 2010 | last1= Brown | first1 = M. D. | last2 = Suteewong | first2 = T. | last3 = Kumar | first3 = R.S.S. | last4 = D'Innocenzo | first4 = V | last5 = Petrozza | first5 = A | last6 = Lee | first6 = M | last7 = Wiesner | first7 = U. | last8 = Snaith | first8 = H | journal = Nano Letters | volume = 11 | issue = 2 | pages = 438–445|bibcode = 2011NanoL..11..438B }}</ref>

=== Devices ===

There are currently three different generations of SCs. The first generation (those in the market today) are made with crystalline [[semiconductor wafer]]s, typically silicon. These are the SCs everybody thinks of when they hear "Solar Cell".

Current SCs trap light by creating [[pyramid]]s on the surface which have dimensions bigger than most thin film SCs. Making the surface of the substrate rough (typically by growing SnO2 or ZnO on surface) with dimensions on the order of the incoming [[wavelength]]s and depositing the SC on top has been explored. This method increases the [[photocurrent]], but the thin film SC would then have poor material quality.
<ref name=Muller>{{cite journal | doi = 10.1016/j.solener.2004.03.015 | title = TCO and light trapping in silicon thin film solar cells | year = 2004 | last1 = Müller | first1 = Joachim | last2 = Rech | first2 = Bernd | last3 = Springer | first3 = Jiri | last4 = Vanecek | first4 = Milan | journal = Solar Energy | volume = 77 | issue = 6 | pages = 917 |bibcode = 2004SoEn...77..917M }}</ref>

The second generation SCs are based on [[thin film]] technologies such as those presented here. These SCs focus on lowering the amount of material used as well as increasing the energy production. Third generation SCs are currently being researched. They focus on reducing the cost of the second generation SCs.
<ref name=Conibeer>Gavin Conibeer, Third generation photovoltaics, Proc. SPIE Vol. 7411, 74110D (Aug. 20, 2009)</ref>
The third generation SCs are discussed in more detail under recent advancement.

== Design ==
The design for a PSC varies depending on the method being used to trap and scatter light across the surface and through the material.

=== Metal Nanoparticle Plasmonic Solar Cell ===
[[Image:PSC using Metal Nanoparticles.png|thumb|alt=A plasmonic solar cell utilizing metal nanoparticles to distribute light and enhance absorption.|PSC using metal nanoparticles.]]
A common design is to deposit metal nanoparticles on the top surface of the thin film SC. When light hits these metal nanoparticles at their surface plasmon resonance, the light is scattered in many different directions. This allows light to travel along the SC and bounce between the substrate and the nanoparticles enabling the SC to absorb more light.
<ref name=Tanabe>{{cite journal | last1 = Tanabe | first1 = K. | year = 2009 | title = A Review of Ultrahigh Efficiency III-V Semiconductor Compound Solar Cells: Multijunction Tandem, Lower Dimensional, Photonic Up/Down Conversion and Plasmonic Nanometallic Structures | url = | journal = Energies | volume = 2 | issue = 3| pages = 504–530 | doi = 10.3390/en20300504 }}</ref>

=== Metal Film Plasmonic Solar Cell ===

Other methods utilizing surface plasmons for harvesting solar energy are available. One other type of structure is to have a thin film of silicon and a thin layer of metal deposited on the lower surface. The light will travel through the silicon and generate surface plasmons on the interface of the silicon and metal. This generates electric fields inside of the silicon since electric fields do not travel very far into metals. If the [[electric field]] is strong enough, electrons can be moved and collected to produce a photocurrent. The thin film of metal in this design must have nanometer sized grooves which act as [[waveguide]]s for the incoming light in order to excite as many photons in the silicon thin film as possible.
<ref name=Ferry>{{cite journal | doi = 10.1021/nl8022548 | pages= 4391–4397 | title = Plasmonic Nanostructure Design for Efficient Light Coupling into Solar Cells | year = 2008 | last1 = Ferry | first1 = Vivian E. | last2 = Sweatlock | first2 = Luke A. | last3 = Pacifici | first3 = Domenico | last4 = Atwater | first4 = Harry A. | journal = Nano Letters | volume = 8 | issue = 12 | pmid = 19367883 |bibcode = 2008NanoL...8.4391F }}</ref>

== Basic Principles ==

=== General ===
[[Image:Thin vs Thick SC.png|thumb|alt=Light effects on thin and thick solar cells.|Thin film SC (left) and Typical SC (right).]]
When a photon is excited in the substrate of a SC, an electron and hole are separated. Once the electrons and holes are separated, they will want to recombine since they are of opposite charge. If the electrons can be collected prior to this happening then the SC is pretty efficient. The way to collect the electrons quickly would be to make the conducting material very thin. If the surface is made very thin, there will be less light absorbed by the device. A thick device absorbs more light.
<ref name=Tanabe/>

=== Metal Nanoparticles<ref name=Catchpole/> ===

==== Scattering and Absorption ====
The basic principles for the functioning of plasmonic solar cells include scattering and absorption of light due to the deposition of metal nanoparticles. Silicon does not absorb light very well. For this reason, more light needs to be scattered across the surface in order to increase the absorption. It has been found that metal nanoparticles help to scatter the incoming light across the surface of the silicon substrate. The equations that govern the scattering and absorption of light can be shown as:
*<math>C_{scat}=\frac{1}{6\pi}\left(\frac{2\pi}{\lambda}\right)^4|\alpha|^2</math>
This shows the scattering of light for particles which have diameters below the wavelength of light.
*<math>C_{abs}=\frac{2\pi}{\lambda}Im[\alpha]</math>
This shows the absorption for a point dipole model.
*<math>\alpha=3V\left[\frac{\epsilon_p/\epsilon_m-1}{\epsilon_p/\epsilon_m+2}\right]</math>
This is the polarizability of the particle. V is the particle volume. <math>\epsilon_p</math> is the dielectric function of the particle. <math>\epsilon_m</math> is the [[dielectric function]] of the embedding medium. When <math>\epsilon_p=-2\epsilon_m</math> the [[polarizability]] of the particle becomes large. This polarizability value is known as the surface plasmon resonance. The dielectric function for metals with low absorption can be defined as:
*<math>\epsilon=1-\frac{\omega_p^2}{\omega^2+i\gamma\omega}</math>
In the previous equation, <math>\omega_p</math> is the bulk plasma frequency. This is defined as:
*<math>\omega_p^2=Ne^2/m\epsilon_0</math>
N is the density of free electrons, e is the [[Electrical resistivity and conductivity|electronic charge]] and m is the [[Effective mass (solid-state physics)|effective mass]] of an electron. <math>\epsilon_0</math> is the dielectric constant of free space. The equation for the surface plasmon resonance in free space can therefore be represented by:
*<math>\alpha=3V\frac{\omega_p^2}{\omega_p^2-3\omega^2-i\gamma\omega}</math>
Many of the plasmonic solar cells use nanoparticles to enhance the scattering of light. These nanoparticles take the shape of spheres, and therefore the surface plasmon resonance frequency for spheres is desirable. By solving the previous [[equation]]s, the surface plasmon resonance frequency for a sphere in free space can be shown as:
*<math>\omega_{sp}=\sqrt{3}\omega_p</math>

As an example, at the surface plasmon resonance for a silver nanoparticle, the scattering cross-section is about 10x the cross-section of the nanoparticle. The goal of the nanoparticles is to trap light on the surface of the SC. The absorption of light is not important for the nanoparticle, rather, it is important for the SC. One would think that if the nanoparticle is increased in size, then the scattering cross-section becomes larger. This is true, however, when compared with the size of the nanoparticle, the ratio (<math>\frac{CS_{scat}}{CS_{particle}}</math>) is reduced. Particles with a large scattering cross section tend to have a broader plasmon resonance range.

==== Wavelength Dependence ====
Surface plasmon resonance mainly depends on the density of free electrons in the particle. The order of densities of electrons for different metals is shown below along with the type of light which corresponds to the resonance.
*[[Aluminum]] - Ultra-violet
*[[Silver]] - Ultra-violet
*[[Gold]] - Visible
*[[Copper]] - Visible

If the dielectric constant for the embedding medium is varied, the [[resonant frequency]] can be shifted. Higher indexes of refraction will lead to a longer wavelength frequency.

==== Light Trapping ====
The metal nanoparticles are deposited at a distance from the substrate in order to trap the light between the substrate and the particles. The particles are embedded in a material on top of the substrate. The material is typically a [[dielectric]], such as silicon or [[silicon nitride]]. When performing experiment and simulations on the amount of light scattered into the substrate due to the distance between the particle and substrate, air is used as the embedding material as a reference. It has been found that the amount of light radiated into the substrate decreases with distance from the substrate. This means that nanoparticles on the surface are desirable for radiating light into the substrate, but if there is no distance between the particle and substrate, then the light is not trapped and more light escapes.

The surface plasmons are the excitations of the conduction electrons at the interface of metal and the dielectric. Metallic nanoparticles can be used to couple and trap freely propagating plane waves into the semiconductor thin film layer. Light can be folded into the absorbing layer to increase the absorption. The localized surface plasmons in metal nanoparticles and the surface plasmon polaritons at the interface of metal and semiconductor are of interest in the current research. In recent reported papers, the shape and size of the metal nanoparticles are key factors to determine the incoupling efficiency. The smaller particles have larger incoupling efficiency due to the enhanced near-field coupling. However, very small particles suffer from large ohmic losses.
<ref>{{cite journal|last=Atwater|first=Harry|coauthors=A. Polman|title=Plasmonics for improved photovoltaic devices|journal=Nature materials|date=19 February 2010|volume=9|pages=205–13|bibcode=2010NatMa...9..205A|doi=10.1038/nmat2629|issue=3|pmid=20168344}}</ref>

=== Metal Film ===
As light is incident upon the surface of the metal film, it excites surface plasmons. The surface plasmon frequency is specific for the material, but through the use of [[grating]]s on the surface of the film, different frequencies can be obtained. The surface plasmons are also preserved through the use of waveguides as they make the surface plasmons easier to travel on the surface and the losses due to resistance and radiation are minimized. The electric field generated by the surface plasmons influences the electrons to travel toward the collecting substrate.
<ref name=Huag>{{cite journal | doi = 10.1063/1.2981194 | title = Plasmonic absorption in textured silver back reflectors of thin film solar cells | year = 2008 | last1 = Haug | first1 = F.-J. | last2 = SöDerström | first2 = T. | last3 = Cubero | first3 = O. | last4 = Terrazzoni-Daudrix | first4 = V. | last5 = Ballif | first5 = C. | journal = Journal of Applied Physics | volume = 104 | issue = 6 | pages = 064509 |bibcode = 2008JAP...104f4509H }}</ref>

== Materials<ref name=Conibeer/><ref>http://www1.eere.energy.gov/solar/solar_cell_materials.html</ref> ==
{| class="wikitable" border="1"
|-
! First Generation
! Second Generation
! Third Generation
|-
| Single-crystal silicon
| CuInSe2
| Gallium Indium Phosphide
|-
| Multicrystalline silicon
| amorphous silicon
| Gallium Indium Arsenide
|-
| Polycrystalline silicon
| thin film crystalline Si
| Germanium
|}

== Applications ==
The applications for plasmonic solar cells are endless. The need for cheaper and more efficient solar cells is huge. In order for solar cells to be considered cost effective, they need to provide energy for a smaller price than that of traditional power sources such as [[coal]] and [[gasoline]]. The movement toward a more green world has helped to spark research in the area of plasmonic solar cells. Currently, solar cells cannot exceed efficiencies of about 30% (First Generation). With new technologies (Third Generation), efficiencies of up to 40-60% can be expected. With a reduction of materials through the use of thin film technology (Second Generation), prices can be driven lower.

=== Space ===

Certain applications for plasmonic solar cells would be for [[space exploration]] vehicles. A main contribution for this would be the reduced weight of the solar cells. An external fuel source would also not be needed if enough power could be generated from the solar cells. This would drastically help to reduce the weight as well.

=== Rural ===

Solar cells have a great potential to help rural [[electrification]]. An estimated two million villages near the equator have limited access to electricity and fossil fuels and that approximately 25%<ref>http://www.globalissues.org/article/26/poverty-facts-and-stats</ref> of people in the world do not have access to electricity. When the cost of extending [[power grid]]s, running rural electricity and using diesel generators is compared with the cost of solar cells, many times the solar cells win. If the efficiency and cost of the current solar cell technology is decreased even further, then many rural communities and villages around the world could obtain electricity when current methods are out of the question. Specific applications for rural communities would be water pumping systems, residential electric supply and street lights. A particularly interesting application would be for health systems in countries where motorized vehicles are not overly abundant. Solar cells could be used to provide the power to refrigerate [[medication]]s in coolers during transport.

Solar cells could also provide power to [[lighthouse]]s, [[buoy]]s, or even [[battleship]]s out in the ocean. Industrial companies could use them to power [[telecommunications]] systems or monitoring and control systems along pipelines or other system.<ref name=web/>

=== High Power ===

If the solar cells could be produced on a large scale and be cost effective then entire [[power station]]s could be built in order to provide power to the electrical grids. With a reduction in size, they could be implemented on both commercial and residential buildings with a much smaller footprint. They might not even seem like an [[eyesore]].
<ref name=web>http://www.soton.ac.uk/~solar/intro/appso.htm</ref>

Other areas are in hybrid systems. The solar cells could help to power high consumption devices such as [[automobile]]s in order to reduce the amount of fossil fuels used and to help improve the environmental conditions of the earth.

=== Low Power ===

One application which has not been mentioned is consumer electronics. Essentially, solar cells could be used to replace batteries for low power electronics. This would save everyone a lot of money and it would also help to reduce the amount of waste going into [[landfill]]s.<ref>http://blog.coolerplanet.com/2009/01/23/the-4-basic-types-of-solar-cell-applications/</ref>

== Recent Advancements ==

=== Choice of plasmonic metal nanoparticles ===

Proper choice of plasmatic metal nanoparticles is crucial for the maximum light absorption in the active layer. Front surface located nanoparticles Ag and Au are the most widely used materials due to their surface plasmon resonances located in the visible range and therefore interact more strongly with the peak solar intensity. However, such noble metal nanoparticles always introduce reduced light coupling into Si at the short wavelengths below the surface plasmon resonance due to the detrimental Fano effect, i.e. the destructive interference between the scattered and unscattered light. Moreover, the noble metal nanoparticles are impractical to implement for large-scale solar cell manufacture due to their high cost and scarcity in earth crest. Recently, Zhang et al. have demonstrated the low cost and earth abundant materials Al nanoparticles to be able to outperform the widely used Ag and Au nanoparticles. Al nanoparticles, with their surface plasmon resonances located in the UV region below the desired solar spectrum edge at 300 nm, can avoid the reduction and introduce extra enhancement in the shorter wavelength range.<ref>{{cite journal| title=Low cost and high performance Al nanoparticles for broadband light trapping in Si wafer solar cells| year=2012 | last1=Yinan | first1=Zhang et al| journal=Applied Physics Letters | volume=100 | issue=12 | pages=151101 |bibcode = 2012ApPhL.100b1101N |doi = 10.1063/1.3675451 }}</ref><ref>{{cite journal| title=Improved multicrystalline Si solar cells by light trapping from Al nanoparticle enhanced antireflection coating| year=2013 | last1=Yinan | first1=Zhang et al| journal=Opt. Mater. Express| volume=3 | issue=4 | pages=489 }}</ref>

=== Light Trapping ===

As discussed earlier, being able to concentrate and scatter light across the surface of the plasmonic solar cell will help to increase efficiencies. Recently, research at [[Sandia National Laboratories]] has discovered a photonic waveguide which collects light at a certain wavelength and traps it within the structure. This new structure can contain 95% of the light that enters it compared to 30% for other traditional waveguides. It can also direct the light within one wavelength which is ten times greater than traditional waveguides. The wavelength this device captures can be selected by changing the structure of the lattice which comprises the structure. If this structure is used to trap light and keep it in the structure until the solar cell can absorb it, the efficiency of the solar cell could be increased dramatically.<ref>http://www.sandia.gov/media/photonic.htm</ref>

=== Absorption ===

Another recent advancement in plasmonic solar cells is using other methods to aid in the absorption of light. One way being researched is the use of metal wires on top of the substrate to scatter the light. This would help by utilizing a larger area of the surface of the solar cell for light scattering and absorption. The danger in using lines instead of dots would be creating a reflective layer which would reject light from the system. This is very undesirable for solar cells. This would be very similar to the thin metal film approach, but it also utilizes the scattering effect of the nanoparticles.
<ref>{{cite journal | doi = 10.1002/adma.200900331 | title = Design of Plasmonic Thin-Film Solar Cells with Broadband Absorption Enhancements | year = 2009 | last1 = Pala | first1 = Ragip A. | last2 = White | first2 = Justin | last3 = Barnard | first3 = Edward | last4 = Liu | first4 = John | last5 = Brongersma | first5 = Mark L. | journal = Advanced Materials | volume = 21 | issue = 34 | pages = 3504 }}</ref>

=== Third Generation Solar Cells<ref name=Conibeer/> ===

The goal of third generation solar cells is to increase the efficiency using second generation solar cells (thin film) and using materials that are found abundantly on earth. This has also been a goal of the thin film solar cells. With the use of common and safe materials, third generation solar cells should be able to be manufactured in mass quantities further reducing the costs. The initial costs would be high in order to produce the manufacturing processes, but after that they should be cheap. The way third generation solar cells will be able to improve efficiency is to absorb a wider range of frequencies. The current thin film technology has been limited to one frequency due to the use of single band gap devices.

==== Multiple Energy Levels ====

The idea for multiple energy level solar cells is to basically stack thin film solar cells on top of each other. Each thin film solar cell would have a different band gap which means that if part of the solar spectrum was not absorbed by the first cell then the one just below would be able to absorb part of the spectrum. These can be stacked and an optimal band gap can be used for each cell in order to produce the maximum amount of power. Options for how each cell is connected are available, such as serial or parallel. The serial connection is desired because the output of the solar cell would just be two leads.

The lattice structure in each of the thin film cells needs to be the same. If it is not then there will be losses. The processes used for depositing the layers are complex. They include Molecular Beam Epitaxy and Metal Organic Vapour Phase Epitaxy. The current efficiency record is made with this process but doesn't have exact matching lattice constants. The losses due to this are not as effective because the differences in lattices allows for more optimal band gap material for the first two cells. This type of cell is expected to be able to be 50% efficient.

Lower quality materials that use cheaper deposition processes are being researched as well. These devices are not as efficient, but the price, size and power combined allow them to be just as cost effective. Since the processes are simpler and the materials are more readily available, the mass production of these devices is more economical.

==== Hot Carrier Cells ====

A problem with solar cells is that the high energy photons that hit the surface are converted to heat. This is a loss for the cell because the incoming photons are not converted into usable energy. The idea behind the hot carrier cell is to utilize some of that incoming energy which is converted to heat. If the electrons and holes can be collected while hot, a higher voltage can be obtained from the cell. The problem with doing this is that the contacts which collect the electrons and holes will cool the material. Thus far, keeping the contacts from cooling the cell has been theoretical. Another way of improving the efficiency of the solar cell using the heat generated is to have a cell which allows lower energy photons to excite electron and hole pairs. This requires a small bandgap. Using a selective contact, the lower energy electrons and holes can be collected while allowing the higher energy ones to continue moving through the cell. The selective contacts are made using a double barrier resonant tunneling structure. The carriers are cooled which they scatter with phonons. If a material with a large bandgap of phonons then the carriers will carry more of the heat to the contact and it won't be lost in the lattice structure. One material which has a large bandgap of phonons is indium nitride. The hot carrier cells are in their infancy but are beginning to move toward the experimental stage.

== References ==
{{Portal|Renewable energy|Energy}}
{{Reflist|2}}

{{Photovoltaics}}

{{DEFAULTSORT:Plasmonic Solar Cell}}
[[Category:Solar cells]]

Puget-Sound-Verwerfungen

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{{anchor|PLmap}}[[File:Puget Sound faults.png|right|thumb|upright=1.34|The principal [[Puget Sound]] faults (approximate location of known extents) and other selected peripheral and minor faults. Southern tip of Vancouver Island and San Juan Islands at top left (faults not shown), Olympic Mountains at center left, Mount Rainier at lower right (near WRZ). Faults north to south: [[#DMF|Devils Mountain]], [[#UPF|Utsalady Point]], [[#SPF|Strawberry Point]], [[#RB|Mount Vernon Fault]], [[#LRF|Little River]], [[#SQF|Sequim]], [[#SWIF|Southern Whidbey Island Fault]], [[#CCFZ|Cherry Creek]], [[#TCF|Tokul Creek]], [[#RMFZ|Rattlesnake Mountain Fault Zone]], [[#LF|Lofall]], [[#CR|Canyon River]], [[#FC|Frigid Creek]], [[#SMF|Saddle Mountain faults]], [[#HCF|Hood Canal]], [[#SF|Seattle Fault Zone]], [[#Tahuya Fault|Tahuya Fault]], [[#TFZ|Tacoma Fault Zone]], [[#EPZ|East Passage]], [[#WRF|White River]] (extends east), [[#OS|Olympia Structure]], [[#ScCF|Scammon Creek]], [[#DF|Doty]] (extends west), [[#WRZ|Western Rainier Zone]], [[#SHZ|Saint Helens Zone]] (extends south). Also shown: part of the [[Olympic-Wallowa Lineament]].]]
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The '''Puget Sound faults''' under the heavily populated Puget Sound region (Puget Lowland) of Washington state form a regional complex of interrelated seismogenic (earthquake-causing) geologic faults. These include (from north to south, see map) the:

* [[#DMF|Devils Mountain Fault]]
* [[#UPF|Strawberry Point and Utsalady Point faults]]
* [[#SWIF|Southern Whidbey Island Fault]] (SWIF)
* [[#SF|Seattle Fault]]
* [[#TF|Tacoma Fault]]
* [[#HCF|Hood Canal Fault]]
* [[#SMF|Saddle Mountain Faults]]
* [[#OS|Olympia structure]] (suspected fault)
* [[#DF|Doty Fault]]
* [[#SHZ|Saint Helens Zone and Western Rainier Zone]]

==General background==

=== Earthquake sources and hazard ===
The [[Puget Sound region]] (Puget Lowland<ref>"The Puget Lowland is a north-south-trending structural basin that is flanked by Mesozoic and Tertiary rocks of the Cascade Range on the east and by Eocene rocks of the Olympic Mountains on the west." {{Harvnb|Barnett|Haugerud|Sherrod|Weaver|2010|p=2}}, and see Figure 1. The [[Georgia Basin]] to the north is structurally related, but topographically demarcated by the [[Chuckanut Mountains]] near [[Bellingham, Washington|Bellingham]].</ref>) of western [[Washington (State)|Washington]] contains the bulk of the population and economic assets of the state, and carries seven percent of the international trade of the United States.<ref>{{Harvnb|Ballantyne|Pierepiekarz|Chang|2002|p=2}}.</ref> All this is at risk of earthquakes from three sources:<ref>{{Harvnb|Bucknam|Hemphill-Haley|Leopold|1992|p=1611}}; {{Harvnb|Fisher|Hyndman|Johnson|Brocher|2005|p=8}}; {{Harvnb|Karlin|Abella|1996|p=6138}}.</ref>

* A great subduction earthquake, such as the [[Richter magnitude scale|magnitude]] M 9 [[1700 Cascadia earthquake]], caused by slippage of the entire [[Cascadia subduction zone]], from approximately [[Cape Mendocino]] in northern California to [[Vancouver Island]] in British Columbia.

* Intraslab ([[Benioff zone]]) earthquakes, such as the M 6.7 [[2001 Nisqually earthquake]], caused by slippage or fracturing on a small part of the subducting plate at a depth of around {{convert|50|km|0|abbr=in}}.

* Relatively shallow crustal earthquakes, generally less than {{convert|25|km|0|abbr=in}} deep, caused by stresses and faulting in the near-surface crustal structures. The energy released depends on the length of the fault; the faults here are believed capable of generating earthquakes as great as M 6 or 7.

[[File:OFR 99-311 fig48.gif|thumbnail|upright=1.2|Concentration of mid-crustal (10–20 km deep) seismicity in the Puget Lowland. ([http://pubs.usgs.gov/of/1999/ofr-99-0311/seismaps.htm Fig. 48] from [[#{{Harvid|Stanley|Villaseñor|Benz|1999}}|USGS OFR 99-311]])]]
While the great subduction events are large and release much energy (around magnitude 9), that energy is spread over a large area, and largely centered near the coast. The energy of the somewhat smaller Benioff earthquakes is likewise diluted over a relatively large area. The largest intra-crustal earthquakes have about the same total energy (which is about one-hundredth of a subduction event), but in being closer to the surface will have more powerful shaking, and therefore more damage.

One study of seismic vulnerability of bridges in the Seattle – Tacoma area<ref>{{Harvnb|Ballantyne|Pierepiekarz|Chang|2002|p=11}}</ref> estimated that an M 7 earthquake on the Seattle or Tacoma faults would cause nearly as much damage as a M 9 subduction earthquake. Because the Seattle and Tacoma faults run directly under the biggest concentration of population and development in the region, more damage would be expected, but all of the faults reviewed here may be capable of causing severe damage locally, and disrupting the regional transportation infrastructure, including highways, railways, and pipelines. (Links with more information on various hazards can be found at [[Seattle Fault#External links|Seattle Fault]].)

The Puget Sound region is not just potentially seismic, it is actively seismic. Mapping from the Pacific Northwest Seismic Network shows that the bulk of the earthquakes in western Washington are concentrated in four places: in two narrow zones under Mt. Saint Helens and Mt. Rainier, along the DDMFZ, and under Puget Sound between Olympia and approximately the Southern Whidbey Island Fault.<ref>{{Harvnb|Stanley|Villaseñor|Benz|1999|loc=figures 46—50}}. [http://pubs.usgs.gov/of/1999/ofr-99-0311/seismaps.htm See the maps].</ref> The southern limit nearly matches the southern limit of the glaciation; possibly the seismicity reflects rebound of the upper crust after being stressed by the weight of the glacial ice.

===Discovery===
Thick glacial and other deposits, heavy vegetation, urban development, and a topography of sharp relief and rapid erosion obscures the surface expression of faults in this region, and has hindered their discovery.<ref>{{Harvnb|Harding|Berghoff|2000|p=2}}.</ref> The first definite indications of most of these faults came from gravitational mapping in 1965,<ref>{{Harvnb|Daneš|Bonno|Brau|Gilham|1965}}.</ref> and their likely existence noted on mapping in 1980 and 1985.<ref>{{Harvnb|Gower|1980}}; {{Harvnb|Gower|Yount|Crosson|1985}}.</ref> As of 1985 only the Saddle Mountain Faults had been shown to have [[Holocene]] activity (since the last ice age, about 12,000 years ago).<ref>{{Harvnb|Barnett|Haugerud|Sherrod|Weaver|2010}}, p. 1</ref> Not until 1992 was the first of the lowland faults, the [[Seattle Fault]], confirmed to be an actual fault with Holocene activity, and the barest minimum of its history established.<ref>{{Harvnb|Adams|1992}}.</ref>

Discovery of faults has been greatly facilitated with the development of [[LIDAR]], a technique that can generally penetrate forest canopy and vegetation to image the actual ground surface with an unprecedented accuracy of approximately one foot (30 cm). An informal [http://pugetsoundlidar.ess.washington.edu/ consortium] of regional agencies has coordinated LIDAR mapping of much of the central Puget Lowland, which has led to discovery of numerous fault scarps which are then investigated by trenching ([[paleoseismology]]).<ref>{{Harvnb|Haugerud|Harding|Johnson|Harless|2003}}; {{Harvnb|Harding|Berghoff|2000}}; {{Harvnb|Nelson|Johnson|Kelsey|Wells|2003|p=1369}}; {{Harvnb|Sherrod|Brocher|Weaver|Bucknam|2004}}; {{Harvnb|Johnson|Nelson|Personius|Wells|2004b|p=2299}}.</ref> Marine [[seismic reflection]] surveys on Puget Sound where it cuts across the various faults have provided cross-sectional views of the structure of some of these faults, and an intense, wide-area combined on-shore/off-shore study in 1998 (Seismic Hazards Investigation in Puget Sound, or SHIPS)<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001}}.</ref> resulted in a three-dimensional model of much of the subsurface geometry. Aeromagnetic surveys,<ref>{{Harvnb|Blakely|Wells|Weaver1999}}; {{Harvnb|Blakely|Wells|Weaver|Johnson|2002}}.</ref> seismic tomography,<ref>{{Harvnb|Calvert|Fisher|2001}}.</ref> and other studies have also contributed to locating and understanding these faults.

===Geological setting===
[[File:Tectonic forces in Cascadia.png|upright=1.2|thumb|Simplified view of tectonic forces affecting Washington. The Olympic Mountains (the lobe of grey "accretionary complex" rock sliding past the south end of Vancouver Island), having failed to subduct, are being pressed against the basement rock ("fixed block") of the North Cascades, which has been accreted on to the North American craton. This is blocking a stream of [[terranes]] that have been flowing northward in the trough above the subduction zone. As a result Washington is crumpling in a series of folds (dotted lines show [[syncline]]s and [[anticline]]s) and faults, and Oregon is rotating in a manner similar to a jack-knifing trailer. Folding has exposed patches of Crescent Formation (Siletz) basalt ("mafic crust", black). (USGS<ref>{{Harvnb|Parsons|Wells|Fisher|Flueh|1999|loc=figure 5a}}.</ref>)]]

The ultimate driver of the stresses that cause earthquakes are the motions of the [[plate tectonics|tectonic plates]]: material from the Earth's [[Mantle (geology)|mantle]] rises at [[Mid-ocean ridge|spreading centers]], and moves out as plates of [[oceanic crust]] which eventually are subducted under the more buoyant plates of [[continental crust]]. Western Washington lies over the [[Cascadia subduction zone]], where the [[Juan de Fuca Plate]] is subducting towards the east (see diagram, right). This is being obliquely overridden by the [[North American plate]] coming out of the northeast, which has formed a bend in the subducting plate and in the [[forearc]] basin above it. This bend has distorted the subducting slab into an arch that has lifted the [[Olympic Mountains]] and prevented them from subducting.<ref>{{Harvnb|Brandon|Calderwood|1990}}.</ref> For the past 50 million years or so (since the early [[Eocene]] epoch) these have been thrust by subduction up against the [[North Cascades]] ("fixed block" in the diagram), which sit on the North American Plate. This forms a pocket or trough – what one local geologist calls the "big hole between the mountains"<ref>Troost, [http://earthweb.ess.washington.edu/jparsons/OCEAN310/Troost_origin_of_Puget_Sound.pdf '''The Origin of Puget Sound'''].</ref> – between the [[Cascade Range|Cascades]] on the east and the [[Olympic Mountains]] and [[Willapa Hills]] on the west. This pocket is catching a stream of [[terranes]] (crustal blocks about 20 to 30 km thick<ref>{{Harvnb|Pratt|Johnson|Potter|Stephenson|1997|p=27,471}}.</ref>) which the [[Pacific plate]] is pushing up the western edge of North America, and in the process imparting a bit of clockwise rotation to southwestern Washington and most of Oregon; the result has been characterized as a train wreck.<ref>{{Harvnb|Stanley|Villaseñor|Benz|1999|p=43}}.</ref> These terranes were covered by the [[basalts]] of the Crescent Formation (part of the [[Siletz River Volcanics]]). Folding and faulting has exposed these basalts in some places (black areas in diagram); the intervening basins have been filled by various sedimentary formations, some of which have been subsequently uplifted. Glacially deposited and shaped fill covers most of the lower elevations of [[Puget Sound]]. This is the Puget Lowland. The principal effects of this complex interplay of forces on the near-surface crust underlying the Puget Lowland are:

* The [[basement]] rock of the Crescent Formation is being forced up on the southern, eastern, and northern flanks of the Olympic Mountains, and at various folds (wrinkles).
* Some of the upper-crustal formations (such as the Western and Eastern Melange Belts, see [[#SCFmap|map]]) have been pushed onto the older (pre-[[Tertiary]]) basement of the North Cascades.
* There is a general north or northeast directed compression within the Lowland causing folds, which eventually break to become [[dip-slip faults|dip-slip]] (vertical movement) [[thrust fault|thrust]] or [[reverse fault|reverse]] faults.
* Some [[strike-slip]] (horizontal) movement is expected along the peripheral faults (such as Southern Whidbey Island and Saddle Mountain faults).
Further complicating this is a feature of unknown structure and origin, the [[Olympic-Wallowa Lineament]] (OWL). This is a seemingly accidental alignment of topographic features that runs roughly east-southeast from the north side of the Olympic Peninsula to the [[Wallowa Mountains]] in northeastern Oregon. It aligns with the West Coast fault and Queen Charlotte Fault system of [[strike-slip]] fault zones (similar to the [[San Andreas Fault]] in California) on the west side of [[Vancouver Island]], but does not itself show any significant or through-going strike-slip movement. It is of interest here because the various strands of the Seattle Fault change orientation where they appear to cross the OWL,<ref>{{Harvnb|Blakely|Wells|Weaver|Johnson|2002}}</ref> and various other features, such as the [[#TF|Rosedale monocline]] and Olympia structure, and a great many local topographical features, have parallel alignments. It may also be the original location of the Darrington—Devils Mountain Fault (the bowed fault seen [[#DMF|here]]).<ref>{{Harvnb|Tabor|1994|pp=217, 230}}.</ref> The OWL appears to be a deep-seated structure over which the shallower crust of the Puget Lowland is being pushed, but this remains speculative.

===Uplift and basin pattern {{anchor|pattern}}===
[[File:Puget Lowland basins and faults.png|right|thumb|upright=1.2|[[gravity anomaly|Bouguer gravity anomaly]] map of the Puget Sound region showing basins and uplifts, and principal faults and folds, over outline of Puget Sound, Hood Canal, and east end of Strait of Juan de Fuca. Blue and green generally indicate basins (with lower density sedimentary rock), red is generally uplifted basalt of the Crescent Formation. Unlabeled lines northwest of Everet Basin = Strawberry Point & Utsalady Point faults; E-F = Seattle Fault zone; C-D = Tacoma Fault zone; A = Olympia Fault; Doty Fault is east-west dashed line just north of Chehalis Basin; curved dashed line = Hood Canal Fault; Saddle Mountain Faults are due west of "D"; Tahuya Fault between D & C. (Modified from {{Harvnb|Pratt|Johnson|Potter|Stephenson|1997|loc=plate 1}}.)]]
Most of these "faults" are actually zones of complex faulting at the boundaries between sedimentary basins and crustal uplifts. There is a general pattern where most of these faults partition a series of basins and uplifts, each about 20 km wide. From the north these are (see the map at right):

* '''Devils Mountain Fault zone''' (including Strawberry Point and Utsalady Point faults)
** Everett Basin
* '''Southern Whidbey Island Fault''' (SWIF)
** "Uplift of unknown origin" (Port Ludlow)
* '''Kingston arch''' (Lofall Fault<ref>Because of the geometry of the SWIF and the Kingston arch, the "uplift of unknown origin" between them is smaller, and the fault separating the uplift from the arch (the Lofall Fault, discovered relatively recently by {{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|p=13,557}}) is shorter; it is not notably seismogenic.</ref>)
** Seattle Basin
* '''Seattle Fault zone''' (line E)
** Seattle Uplift
* '''Tacoma Fault Zone''' (line D)
** Tacoma Basin
* '''Olympia fault''' (line A)
** Black Hills Uplift
* '''Doty Fault / Scammon Creek Fault''' (dashed lines)<ref>Strictly speaking the southern edge of the Black Hills Uplift would be the southeast striking Scammon Creek Fault that converges with the east striking Doty Fault at Chehalis. In the angle between these is located the minor Lincoln Creek uplift, the Doty Hills, and, further west, an impressive chunk of Crescent basalt. If the pattern is continued to the southwest, along cross-section A-A' in Pratt's figure 11 (and missing the mapped trace of the Doty Fault), then the next basin is at Grays Harbor (not shown here). The Doty Fault/Chehalis Basin sequence follows the cross-section X-X' shown on the [[#PLmap|map]].</ref>
** Chehalis Basin

The Hood Canal Fault (and its possible extensions) and Saddle Mountain faults to the west are believed to form the western boundary to all this. On the east, the Devils Mountain Fault connects with the south striking Darrington Fault (not shown) which runs to the OWL, and the Southern Whidbey Island Fault extends via the Rattlesnake Mountain Fault Zone (dashed line) to the OWL. South of the OWL a definite eastern boundary has not been found, with some indications it is indefinite. (E.g., the Olympia Fault is aligned with and appears to be the northernmost member of a set of faults between Olympia and Chehalis that may extend to the Columbia River, and there has been a suggestion that the Tacoma Fault may connect with the White River—Naches River fault on the east side of the Cascades.<ref>{{Harvnb|Blakely|Sherrod|Weaver|Wells|2009b}}; {{Harvnb|Blakely|Sherrod|Weaver|Wells|2011|loc=§5.2.1}}.</ref>)

The uplift and basin pattern is continued to the west and southwest by the Grays Harbor Basin, Willapa Hills Uplift, and Astoria Basin,<ref>See {{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, figure 2.</ref> but it is not known if these are bounded by faults in the same manner as in the Puget Sound region.

===Structural models===

==== Thrust sheet hypothesis ====
It is believed that all of these faults, folds, basins, and uplifts are related. According to the preeminent model, the "Puget Lowland thrust sheet hypothesis",<ref>{{Harvnb|Pratt|Johnson|Potter|Stephenson|1997}}.</ref> these faults, etc., occur within a sheet of crust about 14 to 20 km deep that has separated from and is being thrust over deeper crustal blocks. Most of this thrust sheet consists of the Crescent Formation (corresponding to the Siletz River volcanics in Oregon and Metchosin Formation on Vancouver Island), a vast outpouring of volcanic [[basalt]] from the [[Eocene]] epoch (about 50 million years ago), with an origin variously attributed to a seamount chain, or continental margin rifting.<ref>{{Harvnb|Babcock|Burmester|Engebretsen|Warnock|1992|p=6799}}.</ref> This "basement" rock is covered with sedimentary deposits similar to the [[Chuckanut Formation]], and more recent (typically [[Miocene]]) volcanic deposits. The Seattle uplift, and possibly the Black Hills uplift, consist of Crescent Formation basalt that was exposed when it was forced up a ramp of some kind. This ramp could be either in the lower crustal blocks, or where the thrust sheet has split and one part is being forced over the next.<ref>{{Harvnb|Pratt|Johnson|Potter|Stephenson|1997}}, see figure 2; {{Harvnb|Johnson|Blakely|Stephenson|Dadisman|2004a}}, see figure 17.</ref> Faults and folds may develop where the thrust sheet is being bent, or where the leading edge is thrust over softer, weaker sedimentary deposits, and breaks off and slumps.

If, as this model suggests, the various faults are interconnected within the thrust sheet, there is a possibility that one earthquake could trigger others.<ref>{{Harvnb|Pratt|Johnson|Potter|Stephenson|1997|p=27,486}}.</ref> This prospect is especially intriguing as a possible explanation of a cluster of seismic events around 1100 years ago.<ref>{{Harvnb|Logan|Schuster|Pringle|Walsh|1998}}.</ref>

====Seismotectonic modeling====
The previous model studied seismicity, surface geology, and geophysical data to examine the fault structuring of the upper crust. Another model (of {{Harvnb|Stanley|Villaseñor|Benz|1999}}, USGS Open-File Report 99-0311) – not so much in competition with the first as complementing it – used seismic and other data to create a 3-D tectonic model of the whole crust; this was then analyzed using [[finite element]] methods to determine regional geodynamic characteristics.

A principal finding is that "[c]rustal seismicity in the southern Puget Sound region appears to be controlled by a key block of Crescent Formation occurring just south of the Seattle fault."<ref>{{Harvnb|Stanley|Villaseñor|Benz|1999|p=46}}, and see figure 64.</ref> More particularly, the concentration of seismicity under Puget Sound south of the Seattle Fault is attributed to that area riding on single block (terrane), bounded approximately by the Seattle Fault, the Olympia structure (fault?), Hood Canal (Saddle Mountain Faults?), and vaguely east of Seattle/Tacoma. And it is suggested that the [[Seattle Fault#Notable earthquake|Great Seattle Quake]] of approximately 1,100 years ago, and other coseismic events in southern Puget Sound around that time, were a single event that affected this entire block, with a magnitude of around 8, possibly triggered by an earthquake deeper in the crust.<ref>{{Harvnb|Stanley|Villaseñor|Benz|1999|pp=45, 46}}.</ref>

Very little is known about the structure of the deep crust (below about {{convert|30|km|abbr=in|disp=or}}), though this and other seismic tomography studies (such as {{Harvnb|Ramachandran|2001}}) provide tantalizing glimpses.

----
For the following reviews the primary source of information is the U.S. Geological Survey's [http://gldims.cr.usgs.gov/webapps/cfusion/Sites/qfault/index.cfm Quaternary fault and fold database (QFFDB)], which includes details of discovery, a technical description, and bibliography for each fault; a specific link is provided (where available) at the end of each section.

==Devils Mountain Fault {{anchor|DMF}} ==
{{anchor|SCFmap}}
[[File:Straight Creek Fault.gif|right|thumb|upright=1.2| Puget Lowland and other areas divided from the "North Cascade Crystalline Core" by the Straight Creek Fault. The green colored area on the left has been pushed north, the purple area ("HH Melange") on the Darrington—Devils Mountain Fault originally being at or southwest of the Olympic Wallowa Lineament. (Fig. 1 from [[#{{Harvid|Tabor|Frizzell|Booth|Waitt|2000}}| USGS I-2538]], modified.)]]

The Devils Mountain Fault (DMF) runs about 125 km (75 miles) from the town of [[Darrington, Washington|Darrington]] in the Cascade foothills due west to the northern tip of [[Whidbey Island]], and on towards [[Victoria, British Columbia]], where the DMF is believed to join the Leech River fault system at the southern end of [[Vancouver Island]]. At Darrington it is seen to connect with the Darrington Fault, which runs nearly south 110 km to converge with the [[Straight Creek Fault]] (SCF), and then to turn near [[Easton, Washington|Easton]] to align with the [[Olympic-Wallowa Lineament]]; together these are known as the Darrington—Devils Mountain Fault Zone (DDMFZ).

The Devils Mountain Fault separates two similar but distinctive ensembles of [[Mesozoic]] (pre-[[Tertiary]], before the dinosaurs died) or older rock. On the north is the Helena—Haystack mélange (HH mélange, purple in the diagram at right), on the south the Western and Eastern mélange belts (WEMB, blue). There are some interesting relationships here. E.g., HH mélange rock has been found in Manastash Ridge, 110 km to the south (look for the small sliver of purple near the bottom of the diagram). Also, the sedimentary [[Chuckanut Formation]] (part of the NWCS, green) north of the DMF correlates to the Suak and Roslyn Formations just north of Manastash Ridge. All this is explained by right-lateral [[strike-slip]] motion on the [[Straight Creek Fault]], which initiated about 50 to 48 [[Mya (unit)|Ma]] (millions of years ago). This is just after the terrane carrying the Olympic Mountains came into contact with the North American continent. These mélanges may have been off-shore islands or seamounts that were caught between the Olympic terrane and the North American continent, and were pushed up ([[obduction|obducted]]) onto the latter. Other similar rock has been found at the Rimrock Lake Inlier (bottom of diagram), in the San Juan Islands, and in the Pacific Coast Complex along the West Coast Fault on the west side of Vancouver Island. It appears the entire DDMFZ and Leech River fault system was pushed onto the early continental margin from an original alignment along the OWL. This is an important observation because the Strawberry Point, Utsalady Point, Southern Whidbey Island, and various other unnamed faults lying between the DDMFZ and the OWL – all of which converge at the western end of the DDMFZ – seem to be intermediate versions of the DDMFZ.<ref>{{Harvnb|Tabor|1994}}.</ref>

Movement on the southern segment of the DDMFZ that converges with the SCF – the Darrington Fault – was, as on the SCF itself, right-lateral. And like the SCF, strike-slip motion died out between 44 and 41 MA (due to plutonic intrusions). But the western segment – the Devils Mountain Fault – has ''left''-lateral movement. This is because the Olympic terrane is moving (relative to North America) northeast; its continued clockwise rotation is akin to a giant wheel rolling up the western side of the North Cascade crystalline core. The geology also suggests that the DMF is moving obliquely up a ramp that rises to the east,<ref>{{Harvnb|Hayward|Nedimović|Cleary|Calvert|2006}} possibly an ancient coastal shore.</ref>

The Devils Mountain Fault is seismically active, and there is evidence of [[Holocene]] offsets. If the entire 125 km length ruptured in a single event the resulting earthquake could be as large as magnitude 7.5. However, there are indications that the fault is segmented, which might limit rupturing and earthquake magnitude.<ref>Geologic Map {{Harvnb|GM-61}} (McMurray).</ref>
* [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1344&ims_cf_cd=cf&disp_cd=C USGS QFFDB Fault #574, Devils Mountain Fault]

==Strawberry Point and Utsalady Point faults {{anchor|UPF}}{{anchor|SPF}}==
Strands of the east-striking Devils Mountain Fault cross the northern tip of [[Whidbey Island]] at Dugualla Bay and north side of Ault Field (Whidbey Island Naval Air Station). Just four miles (6 km) south the city of [[Oak Harbor, Washington|Oak Harbor]] straddles several stands of the Utsalady Point Fault (UPF) as they head roughly east-southeast towards Utsalady Point at the north end of Camano Island. And in between these two the Strawberry Point Fault (SPF) skirts the south side of Ault Field, splits into various strands that bracket Strawberry Point, and then disappear (possibly ending) under the delta of the Skagit River. Both the SPF and UPF are said to be oblique-slip transpressional; that is, the faults show both horizontal and vertical slip as the crustal blocks are pressed together. These faults also form the north and south boundaries of uplifted pre-[[Tertiary]] rock, suggesting that the faults come together at a lower level, much like one model of the Seattle and Tacoma faults, but at a smaller scale. Marine seismic reflection surveys on either side of Whidbey Island extend the known length of these faults to at least 26 and 28 km (about 15 miles). The true length of the UPF is likely twice as long, as it forms the southern margin of an aeromagnetic high that extends another 25 km to the southeast.<ref>{{Harvnb|QFFDB Fault 573}}.</ref> Trenching on the UPF (at a scarp identified by LIDAR) shows at least one and probably two Holocene earthquakes of magnitude 6.7 or more, the most recent one between AD 1550 to 1850, and possibly triggered by the [[1700 Cascadia earthquake]].<ref>{{Harvnb|Johnson|Nelson|Personius|Wells|2004b}}, p.2313.</ref> These earthquakes probably caused tsunamis, and several nearby locations have evidence of tsunamis not correlated with other known quakes.

While there is a bit of uplifted pre-Tertiary rock between the SPF and UPF, this does not truly fit the [[#pattern|uplift and basin pattern]] described above because of the small scale (2 km wide rather than around 20), and because the uplift here is entirely like a wedge being popped out between two nearly vertical faults, rather than being forced over a ramp such as is involved with the Seattle and Tacoma faults. Nor does this uplift delineate any significant basin between it and the Devils Mountain Fault.<ref>Geologic Map {{Harvnb|GM-59}} (Oak Harbor and Crescent Harbor).</ref> On the basis of marine seismic reflection surveying in the Strait of Juan de Fuca it has been suggested that the DMF, SPF, and UPF are structurally connected (at least in the segment crossing Whidbey Island).<ref>{{Harvnb|Hayward|Nedimović|Cleary|Calvert|2006}}, p.444.</ref>
* [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1341&ims_cf_cd=cf&disp_cd=C USGS QFFDB Fault #571, Strawberry Point Fault]
* [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1343&ims_cf_cd=cf&disp_cd=C USGS QFFDB Fault #573, Utsalady Point Fault]

== Rogers Belt {{anchor|RB}}==

In the northeast corner of the Puget Lowland, running from approximately [[Monroe, Washington|Monroe]] to a point on the Devils Mountain Fault (DMF) just short of [[Mount Vernon, Washington|Mount Vernon]], is a belt about 15 miles wide of strikingly parallel drainages, indicating a strong albeit subdued pattern of topographical folding.<ref>Interstate 5 runs nearly due north from Everett to Mount Vernon, except for a stretch southeast of Conway that parallels one of these low-amplitude folds. In some places, such as along the South Fork of the Stillaguamish River between Arlington and Granite Falls, there are also contrasting geological contacts. Geologic Map {{Harvnb|GM-50}}.</ref> Observing this, some parallel gravity gradients, and a "very active zone of minor seismicity", William Rogers inferred a "fault or other major structural feature".<ref>{{Harvnb|Rogers|1970|p=55}}.</ref>

{{Harvtxt|Cheney|1987}} subsequently argued for a ''Mount Vernon Fault'' (MVF; originally the ''Bellingham Bay—Chaplain fault zone'') from Lake Chaplain (northeast of Monroe) along a distinct lineament running past Lake McMurray (near where the DMF has a slight bend), Mount Vernon, and eventually [[Lummi Island, Washington|Lummi Island]].<ref>The lineament and general context is readily seen on GM-50, though the MVF itself is not marked. Lummi Island can be seen at top edge of the [[#PLmap|map]].</ref> This interpretation was not accepted, likely because it was also argued that the MVF had offset the DMF 47 km. to the north (past Lummi Island), contrary to the prevailing consensus that the DMF is ''not'' offset.<ref>{{Harvnb|Dragovich|Norman|Grisamer|Logan|1998}} (OFR 98-5, Bow and Alger) p. 44.</ref>

Mapping in 2006 revealed the right-lateral ''McMurray Fault Zone'' (MFZ) near Lake McMurray, aligned with the Lake Chaplain—Mount Vernon lineament, and suspected of being a major bounding fault that may correlate with the MVF.<ref>{{Harvnb|GM-61|p=10}}.</ref> The implications of this for the rest of the Rogers belt have yet to be assessed. The interaction of the MFZ and adjacent ''Mount Washington Fault Zone'' with the [[#DMF|DMF]] (part of the Darrington—Devils Mountain Fault Zone, a major regional structural boundary) is complex, with hints of northward extensions; the geological structure to the north has yet to be adequately mapped. The southern end of the Rogers belt runs into an area of complex faulting and active seismicity between Monroe and North Bend which is associated with the Southern Whidbey Island Fault and Rattlesnake Mountain Fault Zone; this will be discussed below.

==Southern Whidbey Island Fault {{anchor|SWIF}}==
[[File:Southern Whidbey Island fault-1.png|right|thumb|Location and known extent (prior to 2004) of Southern Whidbey Island Fault (SWIF). Also shown: Devils Mountain, Strawbery Point, and Utsalady Point faults (crossing northern Whidbey Island), Seattle Fault zone, southern part of Rattlesnake Mountain Fault Zone, Tokul Creek Fault (striking NNE from RMFZ). This map is approximately one-quarter the scale of the map below. (USGS<ref>{{Harvnb|Blakely|Sherrod|2006}}.</ref>)]]

The ''Southern Whidbey Island Fault'' (SWIF) is a significant terrane boundary manifested as an approximately four mile wide zone of complex [[transpression]]al faulting with at least three strands.<ref>{{Harvnb|QFFDB Fault 572}}; {{Harvnb|Johnson|Potter|Armentrout|Miller|1996}}.</ref> Marine seismic reflection surveys show it striking northwest across the eastern end of the Strait of Juan de Fuca.<ref>{{Harvnb|Johnson|Potter|Armentrout|Miller|1996}}.</ref> Just south of [[Victoria, British Columbia]] it intersects the west-striking Devils Mountain Fault (reviewed above), and either merges with it,<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|loc=§5.10}}.</ref> or crosses (and possibly truncates) it to connect with the Leech River Fault.<ref>{{Harvnb|Clowes|Brandon|Green|Yorath|1987}}; {{Harvnb|Johnson|Potter|Armentrout|Miller|1996|p=336}}.</ref> The Leech River Fault has been identified as the northern edge of the Crescent Formation (aka Metchosin Formation, part of the [[Siletzia]] terrane that underlies much of western Washington and Oregon).<ref>{{Harvnb|Clowes|Brandon|Green|Yorath|1987}}.</ref> Seismic tomography studies show that this portion of the SWIF marks a strong contrast of seismic velocities, such as is expected of Crescent Formation basalts in contact with the metamorphic basement rocks of the Cascades geologic province to the east.<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|loc= §5.10}}. This contact is the Coast Range Boundary Fault, discussed below.</ref>

To the southeast the SWIF passes through Admiralty Inlet (past [[Port Townsend, Washington|Port Townsend]]) and across the southern part of [[Whidbey Island]], crossing to the mainland between [[Mukilteo, Washington|Mukilteo]] and [[Edmonds, Washington|Edmonds]]. This section of the SWIF forms the southwestern side of the Everett Basin<ref>{{Harvnb|Johnson|Potter|Armentrout|Miller|1996|loc=Fig. 1}}; {{Harvnb|Barnett|Haugerud|Sherrod|Weaver|2010|loc=Map 5}}, [http://pubs.usgs.gov/of/2010/1149/of2010-1149_map05.pdf on-line].</ref> (see [[#pattern|map]]), which is notably aseismic in that essentially no shallow (less than 12 km deep) earthquakes have occurred there, or on the section of the SWIF adjoining it, in the first 38 years of instrumental recording.<ref>{{Harvnb|Sherrod|Blakely|Weaver|kelsey|2008}}, paragraph 11.</ref> Yet it is also notable that "most seismicity in the northern Puget Sound occurs along and southwest of the southern Whidbey Island fault at typical depths of 15–27 km within the lower part of the Crescent Formation."<ref>{{Harvnb|Johnson|Potter|Armentrout|Miller|1996|p=351}}.</ref>

The contrast of seismic velocities seen to the northwest is lacking in this section, suggesting that it is not the Coast Range—Cascade contact.<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|loc=§5.10}}.</ref> The significance of this — whether the edge of the Crescent Formation (and implicitly of the Siletz terrane) turns southward (discussed [[#CRBF|below]]), or the metamorphic basement is supplanted here by other volcanic rock — is not known. It has been suggested that a corresponding change in the character of the SWIF may reflect a change in the direction of regional crustal strain.<ref>{{Harvnb|Sherrod|Blakely|Weaver|Kelsey|2008| loc=par. 71}}.</ref>
Prior to 2000 prominent aeromagnetic anomalies strongly suggested that the fault zone continued southeast, perhaps as far as the town of [[Duvall, Washington|Duvall]], but this was uncertain as the SWIF is largely concealed, and the faint surface traces generally obliterated by urban development. Since 2000 studies of LIDAR and high-resolution aeromagnetic data have identified scarps near [[Woodinville, Washington|Woodinville]] which trenching has confirmed to be tectonically derived and geologically recent.<ref>{{Harvnb|Blakely|Sherrod|Wells|Weaver|2004}} (USGS OFR 04-1204); {{Harvnb|Sherrod|Blakely|Weaver|Kelsey|2005}} (USGS OFR 05-1136); {{Harvnb|Sherrod|Blakely|Weaver|Kelsey|2008}}; {{Harvnb|Liberty|Pape|2008}}.</ref>

Subsequent mapping shows the SWIF wrapping around the eastern end of the [[#pattern|Seattle Basin]] to merge with the Rattlesnake Mountain Fault Zone (RMFZ); the RMFZ, despite the approximately 15° bend and different context, is now believed to be the southern extension of the SWIF.<ref>{{Harvnb|GM-67|pp=11, 12}} (Fall City); {{Harvnb|GM-73}} (North Bend); {{Harvnb|Dragovich|Littke|Anderson|Wessel|2010}} (Carnation).</ref> Reckoned between Victoria and approximately [[Fall City, Washington|Fall City]] the length of the SWIF is around 150 km (90 miles).<ref>{{Harvnb|Sherrod|Blakely|Weaver|Kelsey|2008}}, paragraphs 75, 78, & 84; Geologic Map {{Harvnb|GM-67}}.</ref>

It has been suggested that the SWIF might extend past its intersection with the RMFZ (with only peripheral strands turning to join the RMFZ) to cross the Cascades and eventually merge with or cross the [[Olympic-Wallowa Lineament]];<ref>{{Harvnb|Sherrod|Blakely|Weaver|Kelsey|2008|loc=§6.3, par. 78}}.</ref> a study of regional features suggests such a pattern.<ref>{{Harvnb|Blakely|Sherrod|Weaver|Wells|2011}}. Their preferred interpretation is that the SWIF is right-offset along the RMFZ (par. 71). See fig. 22.</ref> But detailed mapping just past the intersection shows only a complex and confused pattern of faulting, with no indication that there is, or is not, through-going faulting.<ref>{{Harvnb|Dragovich|Anderson|Mahan|MacDonald|2012}} (Lake Joy).</ref> Mapping of areas further east that might clarify the pattern is not currently planned.<ref>The long-range mapping plan area and current status of planned mapping can be seen at [http://www.dnr.wa.gov/Publications/ger_24k_mapping_status.pdf Washington State DNR].</ref>

Paleoseismological studies of the SWIF are scant. One study compared the relative elevation of two marshes on opposite sides of Whidbey Island, and determined that approximately 3,000 years ago an earthquake of M 6.5—7.0 caused 1 to 2 meters of uplift.<ref>{{Harvnb|Kelsey|Sherrod|2001|p=2}}.</ref> Another study identified an unusually broad band of scarps passing between [[Bothell, Washington|Bothell]] and [[Snohomish, Washington|Snohomish]], with several scarps in the vicinity of King County's controversial [[Brightwater sewage treatment plant|Brightwater regional sewage treatment plant]] showing a least four and possibly nine events on the SWIF in the last 16,400 years.<ref>{{Harvnb|Sherrod|Blakely|Weaver|Kelsey|2005|pp=15, 2}}.</ref> Such seismic hazards were a major issue in the siting of the plant, as it is tucked between two active strands, and the influent and effluent pipelines cross multipe zones of disturbed ground.<ref>For the County's interpretation of the geological hazard and anticipated impacts of a major earthquake, see the [http://www.kingcounty.gov/environment/wtd/Construction/North/Brightwater/Background/Env-Review.aspx Environmental Impact Statements].</ref>
* [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1342&ims_cf_cd=cf&disp_cd=C USGS QFFDB Fault #572, Southern Whidbey Island Fault]

== Rattlesnake Mountain Fault Zone {{anchor|RMFZ}} ==
{{anchor|SVfmap}}
[[File:Snoqualmie Valley faults.png|right|thumb|Simplified geologic map of the Snoqualmie Valley (east of Seattle) from North Bend to Duvall, showing various strands of the Rattlesnake Mountain Fault (RMF), and the Snoqualmie Valley (SVF), Griffin Creek (GCF), and Tokul Creek (TCF) faults. The stream NNE of Carnation lies in the Cherry Creek Fault Zone. Southeastern limit of Southern Whidbey Island Fault at Duvall ('''3'''), other faults south of I-90 not shown. Tiger Mountain is the uplifted "Evc" formations southeast of Issaquah, between I-90 and Hwy. 18. (Figure 2 from DGER Geological Map {{Harvnb|GM-73}})]]

Rattlesnake Mountain is a prominent NNW trending ridge just west of [[North Bend, Washington|North Bend]] (about 25 miles east of Seattle). It is coincident with, and possibly a result of uplift on, the ''Rattlesnake Mountain Fault Zone'' (RMFZ), a band of at least eleven faults that show both dip-slip (vertical) and right-lateral strike-slip motion.<ref>{{Harvnb|GM-73}} (North Bend).</ref> (See the adjacent map. In the map above these are represented by the pair of dotted lines at the lower right. A different mountain and fault zone of the same name are located near [[Pasco, Washington|Pasco]]; see [http://geohazards.usgs.gov/cfusion/qfault/qf_web_disp.cfm?qfault_or=1333&ims_cf_cd=cf&disp_cd=B QFFDB Fault #565])

The southern end of Rattlesnake Mountain is truncated at the [[Olympic-Wallowa Lineament]] (OWL), and the faults turn easterly to merge with the OWL.<ref>Geologic Map {{Harvnb|GM-73|pp=29–30}}.</ref> The northern end of the mountain falls off where it crosses the eastern end of the [[#SF|Seattle Fault]], which in turn terminates at the RMFZ; Rattlesnake Mountain forms the eastern edge of the [[#pattern|Seattle Uplift]].<ref>Geologic Maps {{Harvnb|GM-67}} (Fall City) and {{Harvnb|GM-73|p=31}}.</ref>

The RMFZ continues NNW past Fall City and Carnation, where strands of the RMFZ have been mapped making a gentle turn of 15 to 20° west to meet the Southern Whidbey Island Fault zone (SWIF, discussed above); the RMFZ is therefore considered to be an extension of the SWIF.<ref>{{Harvnb|Dragovich|Littke|Anderson|Wessel|2010}} (Carnation), p. 2; {{Harvnb|Dragovich|Anderson|Mahan|Koger|2011}} (Monroe), p. 2.</ref> The relationship between these two fault zones is not entirely clear. Slippage along the SWIF would be expected to continue east-southeast until it merged with the OWL, but instead appears to be taking a shortcut ("right step") along the RMFZ.<ref>{{Harvnb|Blakely|Sherrod|Weaver|Wells|2011|loc=par. 71}}.</ref> This is where the SWIF encounters the edge of the Western and Eastern Melange Belts (remnants of a mid-[[Cretaceous]] subduction zone<ref>Geological Map {{Harvnb|GM-52|pp=5, 6}}.</ref>); the RMFZ is where the Seattle Uplift is being forced against the Western Melange belt<ref>{{Harvnb|GM-73|loc=Figures 3B and 3C}}, and throughout. Whether RMFZ is also the Crescent-Cascade contact, and thereby the Coast Range Boundary Fault, depends on whether the Crescent Formation reaches this far. Gravity studies {{Harv|Finn|1990|p=19,538}} suggest not, or at least not near the surface. The situation at depth at depth is not known. There is a suggestion of a décollement about 18 km down, {{Harv|GM-73|p=31}}, but at a similar décollement further south (under the [[#SWCC|SWCC]]) the underlying basement is believed to be pre-Tertiary.</ref>

To the north the Melange Belt is manifested as the [[#RB|Rogers Belt]], a zone of low-amplitude folding stretching from [[Monroe, Washington|Monroe]] to [[Mount Vernon, Washington|Mount Vernon]]; the apparent western edge of this zone is on-strike with the RMFZ. South of Monroe the folds of the Rogers Belt are obscured by subsequent volcanic formations, but other faults parallel to the RMFZ (e.g., the Snoqualmie Valley and Johnson's Swamp fault zones) extend the general trend of NNW faulting as far as Monroe<ref>{{Harvnb|Dragovich|Anderson|Mahan|Koger|2011}}. Detailed mapping north of Monroe has not yet been done.</ref>

{{anchor|TCF}} East of the RMFZ faulting is complex and not yet understood. Two faults stand out. The Tokul Creek Fault (TCF) strikes NNE from Snoqualmie, aligned with a possible offset of the Western Melange Belt<ref>{{Harvnb|GM-52|loc=Fig. 1}}.</ref> and with a valley that cuts through to the Skykomish River; it is now believed to be of regional significance.<ref>{{Harvnb|Dragovich|Anderson|Mahan|MacDonald|2012}} (Lake Joy), Appendix H.</ref>

{{anchor|CCFZ}} The Cherry Creek Fault Zone, a few miles north of the TCF and parallel, is the location of a notable concentration of low-level seismic activity, and the 1965 Duvall earthquake.<ref>However, according to {{Harvtxt|Stanley|Villaseñor|Benz|1999|p=34}} the Duvall earthquake was on a fault striking 350°. This suggests the quake was actually on the cross-cutting Cherry Valley fault, the northern most member of the RMFZ, and possibly an extension of the Griffin Creek fault. {{Harvnb|Dragovich|Littke|Anderson|Wessel|2010|p=2}}; {{Harvnb|Dragovich|Anderson|Mahan|MacDonald|2012|loc=plate 2}}.</ref> The Cherry Creek Fault Zone follows a NNE trending topographical feature that extends to [[Rockport, Washington|Rockport]] on Highway 20; it may coincide with a tectonic contact of formations of the Western Melange Belt.<ref>Geological Map {{Harvnb|GM-52}}.</ref>

{{space|3}} (Rattlesnake Mountain Fault Zone not included in QFFDB.)

=== Coast Range Boundary Fault {{anchor|CRBF}}===
West of Puget Sound the tectonic basement of the Coast Range geologic province is the approximately 50 million year (Ma) old marine basalts of the Crescent Formation, part of the [[Siletzia]] terrane that underlies western Washington and Oregon. East of Puget Sound the basement of the Cascades province is various pre-[[Tertiary]] (older than 65 Ma) metamorphic rock. The contact between these geological provinces is expected somewhere between Puget Sound and the Cascades foothills.<ref>{{Harvnb|Johnson|Potter|Armentrout|Miller|1996| p=340}}: "must occur".</ref> As the juxtaposition of various disparate tectonic structures in northwest Washington requires significant strike-slip movement, it is further expected that this contact will be a major fault, which has been named the ''Coast Range Boundary Fault'' (CRBF).<ref>{{Harvnb|Johnson|Potter|Armentrout|Miller|1996|p=336}}.</ref>

The northern end of the Crescent Formation (aka Metchosin Formation) has been identified as the east-west trending Leech River fault on the southern tip of Vancouver Island.<ref>{{Harvnb|Johnson|Potter|Armentrout|Miller|1996|p=336}}, and see fig. 1.</ref> This turns and runs just south of Victoria, nearly in-line with the SWIF. Seismic tomography studes show a change in seismic velocities across the northern end of the SWIF, suggesting that this is also part of the Coast Range—Cascade contact. It therefore seems reasonable that the rest of the SWIF (and its apparent extension, the RMFZ) follows the Coast Range—Cascade contact, and (these faults being active) constitutes the CRBF.

One problem with this is that the on-shore parts of the SWIF do not show the velocity contrasts that would indicate contrasting rock types.<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|loc=§5.10}}.</ref> Another problem with the SWIF/RMFZ as CRBF is that a large westward step is required to connect from the RMFZ to the [[#SHZ|Saint Helens Zone]] (SHZ; see [[#SWCC|map]]), whereas the RMFZ turns easterly to align with the OWL.<ref>{{Harvnb|GM-73|p=30}} and map. There is some evidence for a décollement (horizontal separation) at about 18 km depth, and it is possible that the surface patterns of faulting do not reflect faulting or structure below the décollement. See {{Harvnb|GM-73|p=31}} and preceeding figures.</ref> This last problem is partly solved because there is a locus of seismicity, and presumably faulting, extending from the northern end of the SHZ to the northern end of the [[#WRZ|Western Rainier Zone]] (see [[#fig48|Fig. 48]]), along the edge of a formation known as the ''[[#SWCC|Southern Washington Cascades Conductor]]''.<ref>The SWCC appears to be Tertiary marine sediments, not the pre-Tertiary metamorphic rock of the Cascades province; this would seem to make it part of the Coast Range province, with the Coast Range—Cascade contact further east. However, the SWCC is relatively shallow (no more than 15 km deep), and likely is draped over pre-Tertiary bedrock. (See {{Harvnb|Stanley|Johnson|Qamar|Weaver|1996| loc=Fig. 5}}.) The Crescent Formation is expected to be in contact with the pre-Tertiary rock along the SHZ at depth.</ref>

However, gravity data constrains the eastern edge of the Crescent Formation to be near Seattle.<ref>{{Harvnb|Finn|1990|p=19,538}}. This constraint might not apply at depth.</ref> This has led to a suggestion that the CRBF lies below Seattle, and runs south-southeast to the WRZ.<ref>{{Harvnb|Johnson|Potter|Armentrout|1994}}; {{Harvnb|Johnson|Potter|Armentrout|Miller|1996}}.</ref> Other seismic tomography has tantalizingly suggested three north-striking strands under Seattle, and a fourth just east of Lake Washington.<ref>{{Harvnb|Snelson|Brocher|Miller|Pratt|2007|loc=Figures 6 & 7}}.</ref> Although there is no direct evidence for any major north-striking faults under Seattle, this prospect appears to be endorsed by the geological community.<ref>As indicated in {{Harvnb|GM-50}} and the location maps of {{Harvnb|Brocher|Parsons|Blakely|Christensen|2001}}, {{Harvnb|Van Wagoner|Crosson|Creager|Medema|2002}}, {{Harvnb|Johnson|Blakely|Stephenson|Dadisman|2004a}}, {{Harvnb|Snelson|Brocher|Miller|Pratt|2007}}, and {{Harvnb|Ramachandran|2012}}.</ref>

How the CRBF might run north of Seattle (specifically, north of the OWL, which Seattle straddles) is unknown, and even questioned, as there is no direct evidence of such a fault.<ref>There is a preliminary report of aeromagnetic and gravity mapping placing the eastern edge of the Siletz terrane under Lake Washington. See {{Harvnb|Anderson|Blakely|Wells|Dragovich|2011}} (abstract).</ref> There is an intriguing view from {{Harvtxt|Stanley|Villaseñor|Benz|1999}} (see Fig. 64, [http://pubs.usgs.gov/of/1999/ofr-99-0311/radiocarbon.htm on-line]) that the edge of the Crescent Formation offsets west along the Seattle Fault, with the Seattle Basin resulting from a gap between the main part of Siletiza and a northern block that has broken away.

==Seattle Fault {{anchor|SF}}==
{{Main|Seattle Fault}}

The Seattle Fault is a zone of complex [[thrust fault|thrust]] and [[reverse fault|reverse]] faults – between lines E and F on the [[#pattern|map]] – up to 7 km wide and over 70 km long that delineates the north edge of the Seattle Uplift. It stands out in regard of its east-west orientation, depth to bedrock, and hazard to an urban population center.<ref>{{Harvnb|Liberty|2009|p=3}}.</ref> It is the most studied fault in the region; it will be treated in somewhat greater detail.

[[File:Seattle Fault location.png|right|thumb|upright=1.2|Approximate location of the Seattle Fault, showing eastern junction with SWIF and RMFZ. Western extension uncertain past Blue Hills uplift (marked "OP"). (Excerpt from DGER Geological Map {{Harvnb|GM-52}}.)]] 
The Seattle Fault was first identified in 1965<ref>{{Harvnb|Daneš|Bonno|Brau|Gilham|1965|pp=5576–5577}}, and figure 5.</ref> but not documented as an active fault until 1992 with a set of five articles establishing that about 1100 years ago (AD 900—930) an earthquake of magnitude 7+ uplifted Restoration Point and Alki Point, dropped West Point (the three white triangles in the Seattle Basin on the [[#pattern|map]]), caused rockslides in the Olympics, landslides into Lake Washington, and a tsunami on Puget Sound.<ref>See {{Harvnb|Adams|1992}}, and additional references at [[Seattle Fault]].</ref> It extends as far east as (and probably terminates at) the Rattlesnake Mountain Fault Zone (RMFZ; the southern extension of the SWIF) near [[Fall City, Washington|Fall City]]. This seems geologically reasonable, as both the SWIF and RMFZ appear to be the contact between [[Tertiary]] Crescent Formation basement of Puget Sound on the west and the older [[Mesozoic]] (pre-Tertiary) mélange belt basement rocks under the Cascades on the east.<ref>Geologic Map {{Harvnb|GM-67}} (Fall City), p. 11; Geologic Map {{Harvnb|GM-73}} (North Bend), pp. 9, 12.</ref>

===Question of western termination===
Determination of the western terminus of the Seattle Fault has been problematic, and has implications for the entire west side of the Puget Lowland. Initially it was not specified, and rather vaguely indicated to be west of Restoration Point (i.e., west of Puget Sound).<ref>{{Harvnb|Bucknam|Hemphill-Haley|Leopold|1992}}, see figure 1.</ref> In 1994 it was stated (without support) that "the Seattle Fault "appears to be truncated by the Hood Canal fault ... and does not extend into the Olympic Mountains".<ref>{{Harvnb|Johnson|Potter|Armentrout|1994|p=74}}.</ref> This seems reasonable enough, as Hood Canal is a prominent physiographic boundary between the Olympic Mountains and Puget Lowlands, and believed to be the location of a major fault.<ref>{{Harvnb|Daneš|Bonno|Brau|Gilham|1965|pp=5577–5579}}.</ref> Subsequent authors were confident enough to trace the fault west of Bremerton to just north of Green Mountain (the northwestern corner of the Blue Hills uplift – see "E" on the [[#pattern|map]] – a topographically prominent exposure of uplifted basalt) and just short of Hood Canal;<ref>{{Harvnb|Johnson|Dadisman|Childs|Stanley|1999|loc=figure 6}}; {{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|loc=figure 1}}; {{Harvnb|Blakely|Wells|Weaver|Johnson|2002|loc=figures 1, 2, and 3}}. Curiously, {{Harvtxt|Johnson|Dadisman|Childs|Stanley|1999}}, having failed to find any definite indications of a fault zone in seismic-reflection profiles in Hood Canal, claimed (p. 1048) that "the Seattle fault does ''not'' extend west as far as Hood Canal" (emphasis added).</ref> but reluctant to map the fault further west as the distinctive aeromagnetic lineament used to locate the Seattle Fault dies out just west of Bremerton.<ref>{{Harvnb|Blakely|Wells|Weaver|Johnson|2002|loc=figures 2 and 3}}; {{Harvnb|Liberty|2009|p=6}}.</ref>

An extension of some 10 km west of Hood Canal into the Olympic Mountains has been suggested on evidence that the Saddle Mountain Fault (discussed [[#SMF|below]]), to the ''west'' of Hood Canal, might extend as far north as the Seattle Fault, and might be even be kinematically linked.<ref>{{Harvnb|Blakely|Sherrod|Hughes|Anderson|2009a|p=15}}.</ref>
Other studies<ref>{{Harvnb|Haeussler|Clark|2000}} (Wildcat Lake map); {{Harvnb|Liberty|2009|p=2}}, and see Figures 3 and 10; {{Harvnb|Contreras|Weeks|Stanton|Stanton|2012|p=2}}.</ref> show the Seattle Fault wrapping around Green Mountain to strike southwest towards Hood Canal, and likely joining the Saddle Mountain Fault.

{{anchor|Tahuya Fault}}Another complication is an unusually strong north-south striking geophysical anomaly (appearing in gravitational, aeromagnetic, and seismic tomography data) that bounds the west side of the Seattle uplift (vertical black line below "D" on the [[#PLmap|map]]), separating it from the Dewatto Basin to the west.<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|loc=§5.4}}, p. 13,553, and various plates. Also observed by {{Harvnb|Daneš|Bonno|Brau|Gilham|1965}}, {{Harvnb|Pratt|Johnson|Potter|Stephenson|1997}} (from which the [[#PLmap|map]] above is taken), and others.</ref> This appears to be a deep fault, possibly with significant vertical and horizontal offsets, which has recently (2009) been named the ''Tahuya Fault''.<ref>{{Harvnb|Lamb|Liberty|Blakely|Van Wijk|2009}}. Although it has been suggested {{Harv|Polenz|Czajkowski|Legorreta Paulin|Contreras|2010b|p=17}} that there is no fault.</ref> To the south it appears to terminate at the Tacoma Fault; the nature of its junction with the Seattle Fault is undetermined. It is suggestively aligned with Dabob Bay, where the Hood Canal Fault is believed to strike north, but any possible connection is as yet pure speculation.

===Structure===
[[File:Seattle uplift 17D.png|right|thumb|upright=1.2|Cross-section of one model of the Seattle uplift. Models differ on the nature of the ramp and details of the faults. (From {{Harvnb|Johnson|Blakely|Stephenson|Dadisman|2004a|loc=figure 17D}}.)]] 
The Seattle Fault is the most studied of the regional faults, which has led to several models of its structure, which may also be relevant to other faults. In the ''wedge'' model of {{Harvtxt|Pratt|Johnson|Potter|Stephenson|1997}} a slab of rock – mainly basalts of the Crescent Formation – about 20 km thick is being pushed up a "master ramp" of deeper material; this forms the Seattle Uplift. The Seattle fault zone is where the forward edge of the slab, coming to the top of the ramp, breaks and slips into the Seattle Basin. In this model the Tacoma fault zone is primarily the result of local adjustments as the slab bends upward at the bottom of the ramp.

The ''passive roof duplex'' model of {{Harvtxt|Brocher|Parsons|Blakely|Christensen|2001}},<ref>And further amplified by {{Harvnb|Brocher|Blakely|Wells|2004}} and {{Harvnb|Johnson|Blakely|Stephenson|Dadisman|2004a}}.</ref> relying on seismic tomography data from the "Seismic Hazards Investigation in Puget Sound" (SHIPS) experiment, retains the thrusting slab and master ramp concepts, but interprets the Tacoma fault as a reverse fault (or back thrust) that dips north towards the south dipping Seattle fault (see diagram); as a result the Seattle Uplift is being popped up like a [[horst (geology)|horst]].

While these models vary in some details, both indicate that the Seattle Fault itself is capable of a magnitude 7.5 earthquake.<ref>{{Harvnb|ten Brink|Song|Bucknam|2006|p=588}}.</ref> But if the Seattle Fault should break in conjunction with other faults (discussed [[#Seismotectonic modeling|above]]), considerably more energy would be released, on the order of ~M 8.<ref>{{Harvnb|Stanley|Villaseñor|Benz|1999|p=46}}.</ref>
* [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1340&ims_cf_cd=cf&disp_cd=C USGS QFFDB Fault #570, Seattle Fault]

==Tacoma Fault Zone {{anchor|TF}}{{anchor|TFZ}}{{anchor|Tacoma Fault}}==
[[File:Tacoma fault zone.png|right|thumb|Tacoma fault zone, with multiple southeast-striking strands, and part of the Olympia fault.(USGS<ref>{{Harvnb|Nelson|Personius|Sherrod|Buck|2008}} (SIM 3060)</ref>)]]
{{Main|Tacoma Fault}}

The Tacoma Fault (at right, and also between lines C and D on the [[#pattern|Uplift and basin map, above]]) just north of the city of [[Tacoma, Washington]] has been described as "one of the most striking geophysical anomalies in the Puget Lowland".<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|loc=§6.1}}.</ref> The western part is an active east–west striking north dipping reverse fault that separates the Seattle Uplift and the Tacoma Basin, with approximately 30 miles (50 km) of identified surface rupture. It is believed capable of generating earthquakes of at least magnitude 7, and there is evidence of such a quake approximately 1,000 years ago, possibly the same earthquake documented on the [[#SF|Seattle Fault]] 24 miles (38 km) to the north.<ref>{{Harvnb|Sherrod|Brocher|Weaver|Bucknam|2004|p=11}}.</ref> This is likely not coincidental, as it appears that the Tacoma and Seattle faults converge at depth (see [[#Structure|diagram]] above) in a way that north-south compression tends to force the Seattle Uplift up, resulting in [[dip-slip fault|dip-slip]] movement on both fault zones.<ref>{{Harvnb|Johnson|Blakely|Stephenson|Dadisman|2004a}}, §5 and figure 17.</ref>

The Tacoma Fault was first identified by {{Harvtxt|Gower|Yount|Crosson|1985}} as a gravitational anomaly ("structure K") running east across the northern tip of Case and Carr Inlets, then southeast under Commencement Bay and towards the town of [[Puyallup, Washington|Puyallup]]. Not until 2001 was it identified as a fault zone,<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001}}.</ref> and only in 2004 did trenching reveal [[Holocene]] activity.<ref>{{Harvnb|Sherrod|Brocher|Weaver|Bucknam|2004}}. See also {{Harvnb|Brocher|Parsons|Blakely|Christensen|2001}}, §6.1 (p. 13,558).</ref>

Interpretation of the eastern part of the Tacoma Fault is not entirely settled.<ref>The QFFDB, citing lack of consensus, ignores the eastern part.</ref> Most authors align it with the strong gravitational anomaly (which typically reflects where faulting has juxtaposed rock of different density) and topographical lineament down Commencement Bay. This follows the front of the Rosedale monocline, a gently southwest-tilting formation that forms the bluffs on which Tacoma is built.

{{anchor|EPZ}}On the other hand, the contrasting character of the east-striking and southeast-striking segments is unsettling, and the change of direction somewhat difficult to reconcile with the observed fault traces. Especially as seismic reflection data<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001}}; {{Harvnb|Johnson|Blakely|Stephenson|Dadisman|2004a}}, see figure 4, and compare the differences in cross-sections A-A' (west) and B-B' (east) in figure 17.</ref> shows some faulting continuing east across Vashon Island and the East Passage of Puget Sound (the ''East Passage Zone'', EPZ) towards [[Federal Way, Washington|Federal Way]] and an east-striking anticline. Whether the faulting continues eastward is not yet determined. The EPZ is active, being the locale of the 1995 M 5 Point Robinson earthquake.<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|loc=§6.3}}.</ref>

There is evidence that the Tacoma Fault connects with the ''White River River Fault'' (WRF) via the EPZ and [[Federal Way, Washington|Federal Way]], under the Muckleshoot Basin (see [[#PLmap|map]]),<ref>{{Harvnb|Blakely|Sherrod|Hughes|Anderson|2009b}} (abstract); {{Harvnb|Carley|Liberty|Pratt|2007}} (abstract); {{Harvnb|Liberty|2007|loc=figure 3}}; {{Harvnb|Blakely|Sherrod|Weaver|Wells|2011|loc=§5.2.1}}, and see Fig. 22. Alternately, the Tacoma Fault may be only a splay, with the main part of the WRF fault continuing WNW past Kent and Bremerton (Washington Narrows).</ref> and thence to the ''Naches River Fault''. If so, this would be a major fault system (over 185 km long), connecting the Puget Lowland with the Yakima Fold Belt on the other side of the Cascades, with possible implications for both the Olympic—Wallowa Lineament (which it parallels) and geological structure south of the OWL.

The western end of the Tacoma Fault is curious, as near the small town of Allyn (near the extreme tip of Hood Canal) it appears to make a sharp turn to the north, and follows a strong geophysical lineament<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|loc=§5.4}}.</ref> which has recently (2009) been named the [[#Tahuya Fault|Tahuya Fault]].<ref>{{Harvnb|Lamb|Liberty|Blakely|Van Wijk|2009}}.</ref> This appears to be the western termination of the Seattle Uplift. The gap between this and Hood Canal is the Dewatto Basin, which thus forms an appendage to the northwestern corner of the Tacoma Basin. One hypothesis as to how this formed is based on the regional compressive force coming not from the south, but southwest (normal to the Rosedale monocline); this raises the prospect of left-lateral strike-slip motion on the east-west oriented parts of the Tacoma and Seattle faults.<ref>{{Harvnb|Johnson|Blakely|Stephenson|Dadisman|2004a|loc=figure 18}}.</ref>
* [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1352&ims_cf_cd=cf&disp_cd=C USGS QFFDB Fault #581, Tacoma Fault]

==Hood Canal Fault {{anchor|HCF}}==
[[Hood Canal]] marks an abrupt change in physiography between the Puget Lowland and the [[Olympic Mountains]] to the west. Gravitational anomalies and seismic reflection data suggest that there is a major fault zone from the south end of Hood Canal to Dabob Bay,<ref>{{Harvnb|Daneš|Bonno|Brau|Gilham|1965}}, p. 5579.</ref> and continuing north on land. It is inferred that if this fault is a terrane boundary between the Olympics and the Puget Lowland (but read about the Saddle Mountain Faults, below), then it must connect with various faults in the [[Strait of Juan de Fuca]]. But whether this is via the Discovery Bay Fault, or further east (passing close to Port Townsend) remains speculative due to lack of definite scarps and paleoseismological investigation.

This fault is "largely inferred"<ref>{{Harvnb|QFFDB Fault 552}}.</ref> due to a paucity of evidence. Possible Holocene movement is likewise inferred from a possible connection with the Seattle Fault, but even that connection is doubted (discussed [[#Question of western termination|above]]). Evidence is accumulating that the Saddle Mountain Faults (discussed next), which show recent activity, are the structural boundary of the Puget Lowland. It is possible that there is no fault under Hood Canal. A 2001 study<ref>{{Harvnb|Van Wagoner|Crosson|Creager|Medema|2002|loc=§4.1.9}}.</ref> questioned its existence on the basis of high-resolution seismic tomography, though a recent study<ref>{{Harvnb|Ramachandran|2012|loc=3.5}}.</ref> interprets a different variety of tomographic data as showing a major, active fault zone. Recent mapping (2010, 2012) "found no convincing evidence for the existence of this fault".<ref>{{Harvnb|Contreras|Legorreta Paulin|Czajkowski|Polenz|2010}} (OFR 2010-4, Lilliwaup), p. 4; {{Harvnb|Contreras|Weeks|Stanton|Stanton|2012}} (OFR 2011-3, Hoodsport) p. 3.</ref>
* [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=2522&ims_cf_cd=cf&disp_cd=C USGS QFFDB Fault #552, Hood Canal Fault]

==Saddle Mountain Faults {{anchor|SMF}}{{anchor|FC}}{{anchor|CR}}==
[[File:Saddle Mountain faults.png|left|thumb|upright=1.2|In red: Saddle Mountain faults (west and east) extension to the southwest inferred from aeromagnetic and LIDAR evidence, Dow Mountain fault (offset by SM east), and Frigid Creek fault.]]
The Saddle Mountain Fault'''s''' ("East" and "West", and not to be confused with a different Saddle Mountain'''s''' Fault in Adams county, eastern Washington<ref>See QFFDB [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1327&ims_cf_cd=cf&disp_cd=B Fault 562a] and [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1328&ims_cf_cd=cf&disp_cd=B Fault 562b]</ref>), are a set of northeast trending reverse faults on the south-east flank of the Olympic Mountains near Lake Cushman first described in 1973 and 1975.<ref>{{Harvnb|Carson|1973}}; {{Harvnb|Carson|Wilson|1974}}.</ref> Vertical movement on these faults has created prominent scarps that have dammed Price Lake and (just north of Saddle Mountain) Lilliwaup Swamp. The mapped surface traces are only 5 km long, but LIDAR-derived imagery shows longer lineaments, with the traces cutting Holocene alluvial traces. A recent (2009) analysis of aeromagnetic data<ref>{{Harvnb|Blakely|Sherrod|Hughes|Anderson|2009a|p=1}}.</ref> suggests that it extends at least 35 km, from the latitude of the Seattle Fault (the Hamma Hamma River) to about 6 km south of Lake Cushman. Other faults to the south and southeast – the ''Frigid Creek Fault'' and (to the west) ''Canyon River Fault'' – suggest an extended zone of faulting at least 45 km long. Although the southwest striking Canyon River Fault is not seen to directly connect with the Saddle Mountain faults, they are in general alignment, and both occur in a similar context of Miocene faulting (where Crescent Formation strata has been uplifted by the Olympics) and a linear aeromagnetic anomaly.<ref>{{Harvnb|Blakely|Sherrod|Hughes|Anderson|2009a|pp=13–15}}, and figure 4.</ref> The Canyon River Fault is a major fault in itself, associated with a 40 km long lineament and distinct late Holocene scarps of up to 3 meters.<ref>{{Harvnb|Walsh|Logan|2007}} (OFR 2007-1).</ref>

Although these faults are west of the Hood Canal Fault (previously presumed to be the western boundary of the Puget Lowland), they appear to be kinematically related to the Seattle Fault: trench studies indicate major earthquakes (in the range of M 6. to 7.8) on the Saddle Mountain faults <ref>{{Harvnb|Witter|Givler|2005}}, p. 16; {{Harvnb|Blakely|Sherrod|Hughes|Anderson|2009a|pp=1, 15}}.</ref> at nearly the same time (give or take a century) as the great quake on the [[#SF|Seattle Fault]] about 1100 years ago (900—930 AD).<ref>[http://pubs.usgs.gov/of/1999/ofr-99-0311/radiocarbon.htm Figure 64] of {{Harvnb|Stanley|Villaseñor|Benz|1999}} (USGS OFR 99-0311) shows additional dates of various co-seismic events. See also {{Harvnb|Logan|Schuster|Pringle|Walsh|1998}}.</ref> Such quakes pose a serious threat to the City of Tacoma's dams at Lake Cushman,<ref>See [[Cushman Dam No. 1]] and [[Cushman Dam No. 2]].</ref> located in the fault zone,<ref>{{Harvnb|Witter|Givler|2005}}, p. 1, and see Figure 2.</ref> and to everyone downstream on the [[Skokomish River]]. The Canyon River Fault is believed to have caused a similar-sized earthquake less than 2,000 years ago;<ref>{{Harvnb|Walsh|Logan|2007}}.</ref> this is a particular hazard to the [[Wynoochee Dam]] (to the west). The history and capabilities of the Frigid Creek Fault are not known.
* [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1345&ims_cf_cd=cf&disp_cd=C USGS QFFDB Fault #575, Saddle Mountain Faults]

==Olympia Structure {{anchor|OS}}==
The Olympia structure – also known as the ''Legislature fault''<ref>{{Harvnb|Sherrod|1998}}, pp. 99, 131, and figure 4-19.</ref> – is an 80 km long gravitational and aeromagnetic anomaly that separates the sedimentary deposits of the Tacoma Basin from the basalt of the Black Hills Uplift (between lines A and B on the [[#pattern|map]]). It is not known to be seismic – indeed, there is very little seismicity south of the Tacoma Basin as far as Chehalis<ref>{{Harvnb|Stanley|Villaseñor|Benz|1999}} (OFR 99-311), figures 46—50. See [http://pubs.usgs.gov/of/1999/ofr-99-0311/seismaps.htm seismic maps].</ref> – and not even conclusively established to be a fault.

This structure is shown in the gravitational mapping of 1965, but without comment.<ref>{{Harvnb|Daneš|Bonno|Brau|Gilham|1965}}, figures 3 and 4.</ref> {{Harvtxt|Gower|Yount|Crosson|1985}}, labelling it "structure L", mapped it from [[Shelton, Washington|Shelton]] (near the Olympic foothills) southeast to [[Olympia, Washington|Olympia]] (pretty nearly right under the state Legislature), directly under the town of [[Rainier, Washington|Rainier]], to a point due east of the [[#DF|Doty Fault]], and apparently marking the northeastern limit of a band of southeast striking faults in the Centralia-Chehalis area. They interpreted it as "simple folds in Eocene bedrock", though {{Harvtxt|Sherrod|1998}} saw sufficient similarity with the Seattle Fault to speculate that this is a thrust fault. {{Harvtxt|Pratt|Johnson|Potter|Stephenson|1997}}, while observing the "remarkable straight boundaries that we interpret as evidence of structural control",<ref>{{Harvnb|Pratt|Johnson|Potter|Stephenson|1997}}, p.27,472.</ref> refrained from calling this structure a fault. (Their model of the Black Hills Uplift is analogous with their "wedge" model of the Seattle Uplift, discussed [[#Structure|above]], but in the opposite direction. If entirely analogous, then "roof duplex" might also apply, and the Olympia Fault would be a reverse fault similar to the Tacoma Fault.)

Aeromagnetic mapping in 1999 showed a very prominent anomaly<ref>{{Harvnb|Blakely|Wells|Weaver|1999}} (OFR 99-514). [http://pubs.usgs.gov/of/1999/of99-514/maps/shelton.pdf.gz Download the map] and see the aeromagnetic anomaly. Additional aeromagnetic and gravitational imagery of the Olympia and other structures available on the [http://www.dnr.wa.gov/Publications/ger_ofr2004-10_geol_map_summitlake_24k.pdf Summit Lake geological map].</ref> (such as typically indicates a contrast of rock type); that, along with paleoseismological evidence of a major Holocene earthquake, has led to a suggestion that this structure "may be associated with faulting".<ref>{{Harvnb|Sherrod|2001}}, p. 1308.</ref> One reason for caution is that a detailed gravity survey was unable to resolve whether the Olympia structure is, or is not, a fault.<ref>{{Harvnb|Magsino|Sanger|Walsh|Palmer|2003}}.</ref> Although no surface traces of faulting have been found in either the Holocene glacial sediments or the basalts of the Black Hills,<ref>E.g., {{Harvnb|Logan|Walsh|2004}} (Summit Lake map). More recently it has been suspected that a natural berm across the delta of the [[Skokomish River]] may be due to faulting, which could implicate the OS as an active fault. But the researchers are not yet ready to assert that. {{Harvnb|Polenz|Czajkowski|Legorreta Paulin|Contreras|2010a}}; {{Harvnb|Polenz|Czajkowski|Legorreta Paulin|Contreras|2010b}}.</ref> on the basis of well-drilling logs a fault has been mapped striking southeast from Offut Lake (just west of Rainier); it appears to be in line with the easternmost fault mapped in the Centralia—Chehalis area.<ref>Geologic Map {{Harvnb|GM-56}} (East Olympia).</ref>

A marine seismic reflection study<ref>{{Harvnb|Clement|2004}}; {{Harvnb|Clement|Pratt|Holmes|Sherrod|2010}}.</ref> found evidence of faulting at the mouth of Budd Inlet, just north of the Olympia structure, and aligning with faint lineaments seen in the lidar imagery. These faults are not quite aligned with the Olympia structure, striking N75W (285°) rather than N45W (315°). It is uncertain how these faults relate to the structure, and whether they are deep-seated faults, or fractures due to bending of the shallow crust.

It has been speculated that the OS might connect with the seismically active Saint Helens Zone (discussed [[#SHZ|below]]), which would imply that the OS is both locked and being stressed, raising the possibility of a major earthquake.<ref>{{Harvnb|Weaver|Smith|1983}}, pp. 10,376, 10,380.</ref> Alternately, the OS appears to coincide with a gravitational boundary in the upper crust that has been mapped striking southeast to [[The Dalles]] on the Columbia River,<ref>{{Harvnb|Blakely|Jachens|1990}}, plate 2.</ref> where there is a swarm of similarly striking faults.<ref>See QFFDB 580, "[http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1351&ims_cf_cd=cf&disp_cd=C Faults near The Dalles]".</ref>

That Olympia and the south Sound are at risk of major earthquakes is shown by evidence of subsidence at several locations in southern Puget Sound some 1100 years ago.<ref>{{Harvnb|Sherrod|1998}}; {{Harvnb|Sherrod|2001}}, p. 1308 and generally.</ref> What is unknown is whether this was due to a great subduction earthquake, to the noted earthquake on the [[Seattle Fault]] about that time, or to an earthquake on a local fault (e.g., the Olympia structure); there is some evidence that there were two earthquakes over a short time period. Subsidence dated to between AD 1445 and 1655 has been reported in Mud Bay (just west of Olympia).<ref>{{Harvnb|Logan|Walsh|2004}} (Summit Lake map).</ref>

{{space|3}}(Not included in QFFDB.)

==Doty Fault {{anchor|DF}}==
[[File:Centralia-Chehalis District faults GM-34.jpg|thumb|upright=1.2|Excerpt from Geologic Map {{Harvnb|GM-34}}, showing faults in the Centralia—Chehalis Coal District, Lewis County, Washington. Doty—Salzer Creek Fault runs east-west between Centralia and Chehalis (black squares). Map available [http://www.dnr.wa.gov/Publications/ger_gm34_geol_map_sw_wa_250k.pdf on-line]. Click on image for enlargement.]]

The Doty Fault – the southernmost of the uplift-and-basin dividing faults reviewed here, and located just north of the Chehalis Basin – is one of nearly a dozen faults mapped in the Centralia—Chehalis coal district in 1958.<ref>{{Harvnb|Snavely|Brown|Rau|1958}}.</ref> While the towns of [[Centralia, Washington|Centralia]] and [[Chehalis, Washington|Chehalis]] in rural Lewis County may seem distant (about 25 miles) from Puget Sound, this is still part of the Puget Lowland, and these faults, the local geology, and the underlying tectonic basement seem to be connected with that immediately adjacent to Puget Sound. And though the faults in this area are not notably seismogenic, the southeast striking faults seem to be en echelon with the Olympia structure (fault?), and headed for the definitely active Saint Helens Zone; this appears to be a large-scale structure. The Doty fault particularly seems to have gained prominence with geologists since it was associated with an aeromagnetic anomaly,<ref>{{Harvnb|Finn|Stanley|1997}}, p. 4; {{Harvnb|Finn|1999}}, p. 330.</ref> and a report in 2000 credited it capable of a magnitude 6.7 to 7.2 earthquake.<ref>{{Harvnb|Wong|Silva|Bott|Wright|2000}}, Table 1, p. 7.</ref> The prospect of a major earthquake on the Doty Fault poses a serious hazard to the entire Puget Sound region as it threatens vital economic lifelines: At Chehalis there is but a single freeway (Interstate 5) and a single rail line connecting the Puget Sound region with the rest of the west coast; the only alternate routes are very lengthy.<ref>See [http://wadot.wa.gov/NR/rdonlyres/77F51020-4607-44D2-A4F2-B1866B183B25/0/WSDOT_I5_90ClosuresFinalReport.pdf report] from the Washington State Department of Transportation for the economic costs when flooding closed the freeway for just several days.</ref>

The Doty fault has been mapped from the north side of the Chehalis airport due west to the old logging town of [[Doty, Washington|Doty]] (due north of Pe Ell), paralleled most of that distance by its twin, the ''Salzer Creek Fault'', about half a mile to the north. Both of these are [[dip-slip fault|dip-slip]] (vertical) faults; the block between them has been popped up by compressive forces. The Doty Fault appears to terminate against, or possibly merge with, the Salzer Creek Fault at Chehalis; the Salzer Creek Fault is traced another seven miles east of Chehalis. The length of the Doty Fault is problematical: the report in 2000 gave it as 65 km (40 miles), but without comment or citation.<ref>{{Harvnb|Wong|Silva|Bott|Wright|2000}}, Table 1, p. 7. 40 miles would include the combined Doty—Salzer Creek fault plus a 15 mile extension west to [[South Bend, Washington|South Bend]], on Willapa Bay. {{Harvtxt|Finn|1990}}, without identifying it, associated the Doty Fault with notable gravity and aeromagnetic anomalies (Plates 1 and 2) that extend towards Willapa Bay.</ref> Such a length would be comparable to the length of the Seattle or Tacoma faults, and capable of an earthquake of M 6.7. But it does not appear that there have been studies of the deeper structure of these faults, or whether there has been any recent activity.

{{anchor|ScCF}}
The Doty—Salzar Creek Fault does not fully fit the regional pattern of basins and uplifts bounded by faults described [[#pattern|above]]. It does bound the north side of the Chehalis basin, but the south boundary of the Black Hills Uplift is more properly the southeast striking ''Scammon Creek Fault'' that converges with the Doty—Salzar Creek Fault just north of Chehalis.<ref>{{Harvnb|Pratt|Johnson|Potter|Stephenson|1997}}, Plate 1.</ref> In the acute angle between these is located the minor Lincoln Creek uplift, the Doty Hills, and an impressive chunk of uplifted Crescent basalt (reddish area at west edge of the map). The SE striking Scammon Creek Fault seems to be terminated by the Salzer Creek Fault (the exact relationship is not clear), with the latter continuing east for another seven miles. Yet the former is only the first of at least six more parallel southeast striking faults, which do cross the Salzer Creek Fault. These faults are: the ''Kopiah Fault'' (note the curious curve), ''Newaukum Fault'', ''Coal Creek Fault'', and three other unnamed faults. Just past them is the parallel Olympia Structure, which as a geophysical lineament has been traced to a point due east of Chehalis;<ref>{{Harvnb|Gower|Yount|Crosson|1985}} (Map I-1613).</ref> these would seem to be related somehow, but the nature of that relationship is not yet known.

Though these faults have been traced for only a little ways, the southeast striking [[anticline]]s they are associated with continue as far as Riffe Lake, near [[Mossy Rock, Washington|Mossy Rock]]. They are also on-strike with a swarm of faults on the Columbia River, bracketing [[The Dalles]]. As all of these are [[thrust fault|thrust]] and [[reverse fault|reverse]] faults, they probably result from northeast directed regional compression.<ref>Geologic Map {{Harvnb|GM-34}} (Southwest Quadrant).</ref> These faults also cross the Saint Helens Zone (SHZ), a deep, north-northwest trending zone of seismicity that appears to be the contact between different crustal blocks.<ref>{{Harvnb|Weaver|Grant|Shemata|1987}}.</ref> How they might be connected is unknown.

What makes the Doty—Salzer Fault (and the short ''Chehalis Fault'' striking due east from Chehalis)
stand out from the many other faults south of Tacoma is its east-west strike; the significance of this is not known.

{{space|3}}(Not included in QFFDB. See {{Harvnb|Snavely|Brown|Rau|1958}} and Geologic Map {{Harvnb|GM-34}} for details.)

==Saint Helens Zone, Western Rainier Zone{{anchor|SHZ}}{{anchor|WRZ}}==
{{anchor|fig48}}[[File:OFR 99-311 fig48.gif|thumbnail|upright=1.2|Mid-crustal (10–20 km deep) seismicity in western Washington.
(Fig. 48 from [[#{{Harvid|Stanley|Villaseñor|Benz|1999}}|USGS OFR 99-311]]) ]]
The most striking concentrations of mid-crustal seismicity in western Washington outside of Puget Sound are the ''Saint Helens Zone'' (SHZ) and ''Western Rainier Zone'' (WRZ) at the southern edge of the Puget Lowland (see seismicity map, right).<ref>{{Harvnb|Stanley|Villaseñor|Benz|1999}}, figures 46—49; {{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, p. 5.</ref> Indeed, it is mainly by their seismicity that these faults are known and have been located, neither showing any surface faulting.<ref>{{Harvnb|Weaver|Smith|1983}}; {{Harvnb|Stanley|Finn|Plesha|1987}}, p. 10,179; {{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, pp. 6—7.</ref> The SHZ and WRZ lie just outside the topographical basin that constitutes the Puget Lowland (see [[#PLmap|image]]), do not participate in the [[#pattern|uplift and basin pattern]], and unlike the rest of the faults in the Puget Lowland (which are reverse or thrust faults reflecting mostly compressive forces) they appear to be [[strike-slip]] faults; they reflect a geological context distinctly different from the rest of the Puget Lowland. In particular, to the southeast of Mount St. Helens and Mount Rainier they reflect a regional pattern of NNW oriented faulting, including the Entiat Fault in the North Cascades and the Portland Hills and related faults around [[Portland, Oregon|Portland]] (see QFFDB [http://earthquake.usgs.gov/hazards/qfaults/or/van.html fault map]). Yet the SHZ and WRZ may be integral to the regional geology of Puget Sound, possibly revealing some deep and significant facets, and may also present significant seismic hazard.

[[File:Southern Washington Cascades conductor.png|upright=1.25|thumbnail|The Southern Washington Cascades Conductor (SWCC, yellow) located at depth approximately between [[Mount St. Helens]] (MSH), [[Mount Adams (Washington)|Mount Adams]] (MA), [[Goat Rocks]] (GR), [[Mount Rainier]] (MR), and Riffe Lake, with a lobe extending towards Tiger Mountain (TM). Also shown: Entiat Fault, [[Straight Creek Fault]] (inactive, southern continuation unknown), Southern Whidbey Island Fault, Rattlesnake Mountain Fault Zone, [[Olympic-Wallowa Lineament]], White River/Naches River fault, Rimrock Lake Inlier (outlined in green), surface outcrops of the Crescent Formation (outlined in brown), Olympia Structure, Portland Hills fault zone.]]
{{anchor|SWCC}}The WRZ and SHZ are associated with the ''southern Washington Cascades conductor'' (SWCC), a formation of enhanced electrical conductivity<ref>Several possible explanations of the enhanced conductivity have been considered; Eocene marine sediments containing brine are most likely {{Harv|Stanley|Finn|Plesha|1987|pp=10,183—10,186}}. {{Harvtxt|Egbert|Booker|1993}} discuss evidence that the conductivity anomaly may be broader than shown here, and suggest it is a remnant of an "early Cenozoic subduction zone which is analogous to the present-day Olympic Peninsula." (p. 15,967)</ref> lying roughly between Riffe Lake and Mounts St. Helens, Adams, and Rainier, with a lobe extending north (outlined in yellow, right). This formation, up to 15 km thick, is largely buried (from one to ten kilometers deep), and known mainly by [[magnetotellurics]] and other geophysical methods.<ref>{{Harvnb|Stanley|Finn|Plesha|1987}}; {{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, pp. 6—7.</ref> The southwestern boundary of the SWCC, where it is believed to be in near vertical contact with the Eocene basalts of the Crescent Formation, forms a good part of the 90 km (56 mile) long SHZ. On the eastern side, where the SWCC is believed to be in contact with pre-Tertiary terranes accreted to the North American [[craton]], matters are different. While there is a short zone (not shown) of fainter seismicity near [[Goat Rocks]] (an old [[Pliocene]] volcano<ref>{{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, p. 6.</ref>) that may be associated with the contact, the substantially stronger seismicity of the WRZ is associated with the major Carbon River—Skate Mountain anticline.<ref>{{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, p. 4</ref> This [[anticline]], or uplifted fold, and the narrower width of the northern part of the SWCC, reflects an episode of compression of this formation. Of great interest here is that both the northern lobe of the SWCC and the Carbon River anticline are aligned towards [[Tiger Mountain]] (an uplifted block of the Puget Group of sedimentary and volcanic deposits typical of the Puget Lowland) and the adjacent Raging River anticline (see [[#RMFZ|map]]). The lowest exposed strata of Tiger Mountain, the mid-Eocene marine sediments of the Raging River formation, may be correlative with the SWCC.<ref>{{Harvnb|Vine|1962|pp=7–8}}; {{Harvnb|Stanley|Johnson|1993}}, p. 3; {{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, figure 13, pp. 15—16. If the Carbon River and Raging River anticlines are related, and the SWCC and Raging River formations correlative, the [[#RMFZ|RMFZ]] would be the eastern edge of the SWCC. That the fault strands of the RMFZ turn easterly, and seismicity jumps from a fault contact to an anticline, suggests there is more to learn about the OWL/WR-NR zone.</ref>

Does the SHZ extend north? Though the [[#OS|Olympia Structure]] (a suspected fault) runs towards the SHZ, and delineates the northern edge of an exposed section of the Crescent Formation, it appears to be an ''upper'' crustal fold, part of a pattern of folding that extends southeast to cross the Columbia River near [[The Dalles]], and unrelated to the mid and lower crustal SHZ.<ref>Geologic Map {{Harvnb|GM-53}}, (Washington State).</ref> It has been speculated that the SHZ might extend under the Kitsap Peninsula (central Puget Sound), possibly involved with a section of the subducting Juan de Fuca plate that is suspected of being stuck. The implications of this are not only "the possibility of a moderate to large crustal earthquake along the SHZ", but that the tectonics under Puget Sound are more complicated than yet understood, and may involve differences in the regional stress patterns not reflected in current earthquake hazard assessments.<ref>{{Harvnb|Weaver|Smith|1983}}, pp. 10,383, and 10,371. See also p. 10,376, and figure 8.</ref>

==Deeper structure==
Mount St. Helens and Mount Rainier are located where their associated fault zones make a bend (see map, above).<ref>{{Harvnb|Weaver|Grant|Shemata|1987}}, pp. 10,170, 10,176; {{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, p. 16.</ref>(Mt. Rainier is offset because the faults are deep and the conduits do not rise quite vertically.) These bends are located where they intercept a "subtle geological structure"<ref>{{Harvnb|Weaver|Grant|Shemata|1987}}, p. 10,175.</ref> of "possible fundamental importance",<ref>{{Harvnb|Evarts|Ashley|Smith|1987}}, p. 10,166.</ref> a NNE striking zone (line "A" on the map) of various faults (including the Tokul Creek Fault NNE of Snoqualmie) and early-Miocene (about 24 Ma) volcanic vents and intrusive bodies ([[pluton]]s and [[batholith]]s) extending from [[Portland, Oregon|Portland]] to [[Glacier Peak]];<ref>{{Harvtxt|Tabor|Crowder|1969|loc=p. 60, and see figure 60}} (possibly relying on an earliar writer) reported a "zone of basaltic dikes and cinder cones that trends north-northeast" (NNE), including Mount Rainier and Mount St. Helens "to the southwest". {{Harvtxt|Evarts|Ashley|Smith|1987|p=10,166}} state that "Mount Rainier and Glacier Peak are aligned along the projection of this trend," described as NNE, or "roughly N25E". While MR does bear nearly N25E from MSH, [http://www.movable-type.co.uk/scripts/latlong.html calculation] from latitude and longitude shows the MSH—GP bearing to be more accurately N21E; lining up all three volcanoes would require a slight bowing of the lineament. However, features near MSH (such as Yale Lake and Spirit Lake) bear N20E, not aligned with MR. It is more likely that MR, in rising to the surface, has "drifted" off of the underlying lineament. This NNE striking lineament should not be confused with other lineaments striking N50°E. See {{Harvnb|Evarts|Ashley|Smith|1987}}, p. 10,166, {{Harvnb|Weaver|Grant|Shemata|1987}}, p. 10,175, and {{Harvnb|Hughes|Stoiber|Carr|1980}}, figure 1.</ref> it also marks the change in regional fault orientation noted above. This MSH-MR-GP lineament is believed to reflect a "long-lived deep-seated lithospheric flaw that has exerted major control on transfer of magma to the upper crust of southern Washington for approximately the last 25 [million years]";<ref>{{Harvnb|Evarts|Ashley|Smith|1987}}, p.10,166.</ref> it has been attributed to the geometry of the subducting [[Juan de Fuca plate]].<ref>{{Harvnb|Hughes|Stoiber|Carr|1980|p=16}}; {{Harvnb|Guffanti|Weaver|1988|p=6523}}.</ref>

A parallel line ("B") about 15 miles (25 kilometers) to the west corresponds to the ''western'' limit of a zone of seismicity stretching from the WRZ to southwest of Portland. Curiously, the extension of line "B" north of the OWL is approximately the ''eastern'' limit of Puget Sound seismicity, the rest of southwestern Washington and the North Cascades being relatively aseismic (see the seismicity map, above).<ref>{{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, p. 5; {{Harvnb|Stanley|Villaseñor|Benz|1999}}, "Seismicity Patterns", and figures 46—49. The location and orientation of line "B" as shown here is approximate.</ref> This line may also mark the northwestern boundary of the SWCC.<ref>The apparent gap north of Riffe Lake is possibly due to obscuration by volcanic deposits of the Northcraft Formation. {{Harvnb|Stanley|Johnson|Qamar|Weaver|1996}}, p. 4 and figure 3.</ref> North of the RMFZ it follows a topographical lineament that can be traced to Rockport (on Hwy. 20);<ref>Along part of the [[Sultan River]] and the west end of Blue Mountain, the east sides of [[Mount Pilchuck]], Three Fingers, and Whitehorse Mountain, and (north of [[Darrington, Washington|Darrington]] and the DDMF) the west side of North Mountain and part of the North Fork of the Stillaguamish River. North of Hwy 20 it is paralleled by [[Lake Shannon]].</ref> it includes the Cherry Creek Fault Zone NNE of Carnation, location of the 1965 Duvall earthquake.<ref>However, according to {{Harvtxt|Stanley|Villaseñor|Benz|1999|p=34}} the Duvall earthquake was on a fault striking 350°. This suggests the quake was actually on the cross-cutting Cherry Valley fault, the northern most member of the RMFZ, and possibly an extension of the Griffin Creek fault. {{Harvnb|Dragovich|Littke|Anderson|Wessel|2010|p=2}}.</ref> Between the Cherry Creek and parallel Tokul Creek faults is a contact between formations of the Western Melange Belt.<ref>Geological map {{Harvnb|GM-52}} (Tectonic elements).</ref> The zone between these two lines, reflecting changes in regional structure, seismicity, fault orientation, and possibly the underlying lithospheric structure, appears to be a major structural boundary in the Puget Lowland.

Also intersecting at Mount St. Helens is a NE (045°) trending line (red) of [[Pleistocene]] (about 4 Ma) plug domes and a topographic lineament (followed in part by Highway 12).<ref>{{Harvnb|Evarts|Ashley|Smith|1987}}, p. 10,166.</ref> This line is the southernmost of a band of NE trending faults and topographical lineaments that extend from the Oregon coast into the North Cascades. A similar line aligns with the termination of the WRZ, SHZ, and [http://earthquake.usgs.gov/hazards/qfaults/or/van.html Gales Creek Fault Zone] (northwest of Portland), with faulting along the upper [[Nehalem River]] on the Oregon coast,<ref>{{Harvnb|Olbinski|1983}}, pp. 149—151.</ref> and a topographical contrast at the coast (between [[Neahkahnie Mountain]] and the lower Nehalem River valley) distinct enough to be seen on the seismicity map above (due west of Portland). Other similar lineaments (such as from [[Astoria, Oregon|Astoria]] to Glacier Peak) align with various topographical features and changes in fault orientation. These lineaments have been associated with possible zones of faulting in the crust and subducting plate.<ref>{{Harvnb|Hughes|Stoiber|Carr|1980}}, p. 15.</ref>

These features suggest that the southern Puget Lowland is influenced by the deep crust and even the subducting Juan de Fuca plate, but the details and implications are not yet known.

==Other faults==

=== Actual ===
Each of the faults reviewed here is more typically a zone of related faults, or strands. There are numerous other seismogenic faults (or fault zones) in the Puget Lowland, sketchily studied and largely unnamed. These are usually fairly short, and not believed to be significantly seismogenic, though the ''Snoqualmie Valley Fault'', ''Griffin Creek Fault'', and ''Tokul Creek Fault'' (see [[#SVfmap|map]]) are in an area of active seismicity.<ref>Geologic Map {{Harvnb|GM-75}} (Snoqualmie).</ref> The newly discovered (2010) ''Cherry Creek Fault Zone''<ref>{{Harvnb|Dragovich|Littke|Anderson|Wessel|2010}}.</ref> north of [[Carnation, Washington|Carnation]] (north end of the RMFZ, [[#SVfmap|map]]) may be the source of a 1996 M 5.3 earthquake just east of Duvall.

The ''San Juan Island'' and ''Leach River'' faults crossing the southern end of [[Vancouver Island]] are significant and undoubtably connected with the Darrington—Devils Mountain and Southern Whidbey Island faults, and certainly of particular interest to the residents of [[Victoria, B.C.]]. But their significance to the Puget Sound area is unknown.

{{anchor|LRF}}{{anchor|SQF}}
The ''Little River Fault'' (see the [http://gldims.cr.usgs.gov/webapps/cfusion/sites/qfault/qf_web_disp.cfm?qfault_or=1315&ims_cf_cd=cf&disp_cd=C QFFDB, Fault 556]) is representative of an extensive zone of faults along the north side of the Olympic Peninsula and in the Strait of Juan de Fuca (likely connected with the fault systems at the south end of Vancouver Island, see [http://earthquake.usgs.gov/hazards/qfaults/wa/vic.html fault database map]), but these lie west of the crustal blocks that underlie the Puget Lowland, and again their possible impact on the Puget Sound region is unknown. One of these faults, the ''Sequim Fault Zone'' (striking east from the town of [[Sequim, Washington|Sequim]]), crosses Discovery Bay (and various possible extensions of the [[#HCF|Hood Canal Fault]]) and bounds the Port Ludlow Uplift ("uplift of unknown origin" on the [[#pattern|map]]); it appears to extend to the Southern Whidbey Island Fault.<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001|p=13,557}}.</ref>

An ''Everett Fault'', running east-northeast along the bluffs between [[Mukilteo, Washington|Mukilteo]] and [[Everett, Washington|Everett]] – that is, east of the SWIF and at the southern edge of the Everett Basin – has been claimed, but this does not appear to have been corroborated.<ref>{{Harvnb|Molinari|Burk|2003}} (abstract).</ref>

{{anchor|LF}}A ''Lofall Fault'' has been reported on the basis of marine seismic reflection surveying,<ref>{{Harvnb|Brocher|Parsons|Blakely|Christensen|2001}}, p. 13,557.</ref> but has not been confirmed by trenching. This fault seems to be associated with the Kingston arch anticline, and part of the [[#pattern|uplift and basin pattern]], but shortened because of the geometry of the SWIF. It is not notably seismogenic.

{{anchor|WRF}}Although the largely unstudied ''White River Fault'' (WRF) appears to lie just outside of the Puget Lowland, it may actually connect under the Muckleshoot Basin to the East Passage Zone and the [[#TF|Tacoma Fault]] ([[#PLmap|map]]).<ref>{{Harvnb|Blakely|Sherrod|Weaver|Wells|2009b}} (abstract); {{Harvnb|Carley|Liberty|Pratt|2007}} (abstract); {{Harvnb|Blakely|Sherrod|Weaver|Wells|2011|loc=§5.2.1}}, and see Fig. 22. Or it might continue WNW in association with a topographical lineament extending from Lake Meridian (Kent) past Southworth, the Washington Narrows (entrance to Dyes Inlet), the western end of the Seattle Fault, and the southern tip of the Toandos Peninsula.</ref> This would pose significantly greater seismic hazard than currently recognized, especially as the White River Fault is believed to connect with the ''Naches River Fault'' that extends along Highway 410 on the east side of the Cascades towards Yakima.

The [[Straight Creek Fault]] is a major structure in the [[North Cascades]], but has not been active for over 30 million years.<ref>{{Harvnb|Vance|Miller|1994}}.</ref> Various other faults in the North Cascades are older (being offset by the Straight Creek Fault) and are unrelated to the faults in Puget Sound.

===Conjectured===
A ''Puget Sound Fault'' running down the center of Puget Sound (and [[Vashon Island]]) was once proposed,<ref>{{Harvnb|Johnson|1984}}; {{Harvnb|Johnson|Dadisman|Childs|Stanley|1999}}.</ref> but seems to have not been accepted by the geological community. A ''Coast Range Boundary Fault'' (CRBF, discussed [[#CRBF|above]]) was inferred on the basis of differences in the basement rock to the west and east of Puget Sound (the Crescent Formation—Cascadia core contact), and arbitrarily mapped at various locations including Lake Washington; north of the OWL this is now generally identified, with the Southern Whidbey Island Fault.<ref>{{Harvnb|Johnson|Potter|Armentrout|Miller|1996}}, pp. 336, 341, 348; Geologic Map {{Harvnb|GM-67}} (Fall City).</ref> Where it might run south of Seattle is not known; an argument has been made that it runs beneath Seattle<ref>{{Harvnb|Snelson|Brocher|Miller|Pratt|2007}}, p. 1442.</ref> but this is still conjectural.

Study of surface deformation suggests possible unmapped faults near Federal Way, running between Sumner and Steilacoom, and south of Renton.<ref>{{Harvnb|Finnegan|Pritchard|Lohman|Lundgren|2008}}.</ref>

Each of the principal Puget Lowland faults discussed here is notable largely for demonstrated or suspected seismic activity, usually a geologically recent ([[Holocene]]) major earthquake. However, significant movements on these faults (such as the Great Seattle Quake of ~930 AD) are rare, and most seismic activity is not associated with any known fault.<ref>{{Harvtxt|Rogers|2002|p=145}}: "... there is little evidence of fault planes aligning with spatial trends of epicentres. Instead, most crustal seismicity seems to be occurring on random faults, all responding to the same regional stress."</ref> Seismicity sometimes occurs in zones, such as has been observed under Mercer Island, or from downtown Seattle towards Kirkland<ref>{{Harvnb|Yelin|1982}}. See also [http://www.pnsn.org/USGS_GOTER_MAP/goter.gif Map view of quakes in western Washington] at PNSN.</ref> but whether particular zones reflect undiscovered faults, or might be the source of damaging earthquakes, is generally unknown.

==See also==
*[[Geology of the Pacific Northwest]]

==Notes==
{{Reflist|30em}}

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|bibcode = 2002JGRB..107.2381V }}.
*{{Citation
|year= 1994
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|journal= Geological Society of America 1994 Annual Meeting, Abstracts with Programs
|volume= 24 |pages= 88
}}.
*{{Citation
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|year = 1962
|title= Stratigraphy of Eocene rocks in a part of King County, Washington
|journal= Report of Investigations No. 21
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|url= http://www.dnr.wa.gov/Publications/ger_ri21_strat_eocene_king_co.pdf
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*{{Citation
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|year= 1987
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|first5= H. W. |last5= Schasse
|title= Geologic map of Washington – Southwest Quadrant
|journal= Washington Division of Geology and Earth Resources
|volume= Geologic Map GM–34
|at = 2 sheets, scale 1:250,000, 28 p. text
|url= http://www.dnr.wa.gov/Publications/ger_gm34_geol_map_sw_wa_250k.pdf
}}.
*{{Citation
|ref = CITEREFGM-56
|first1= T. J. |last1= Walsh
|first2= R. L. |last2= Logan
|date = June 2005
|title= Geologic Map of the East Olympia 7.5-minute Quadrangle, Thurston County, Washington
|journal= Washington Division of Geology and Earth Resources
|volume= Geological Map GM–56
|at = 1 sheet, scale 1:24,000, with text
|url= http://www.dnr.wa.gov/Publications/ger_gm56_geol_map_eastolympia_24k.pdf
}}.
*{{Citation
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|first2= R. L. |last2= Logan
|year= 2007
|title= Field data for a trench on the Canyon River fault, southeast Olympic Mountains, Washington
|journal= Department of Geology and Earth Resources
|volume= Open File Report 2007-1
|at = poster, with text
|url= http://www.dnr.wa.gov/Publications/ger_ofr2007-1_canyon_river_fault_trench.pdf
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*{{Citation
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|first2= W. C. |last2= Grant
|first3= J. E. |last3= Shemata
|date = September 10, 1987
|title= Crustal Extension at Mount St. Helens, Washington
|journal= Journal of Geophysical Research
|volume= 92 |issue= B10 |pages= 10,170–10,178
|doi= 10.1029/JB092iB10p10170
|bibcode=1987JGR....9210170W
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*{{Citation
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|first2= S. W. |last2= Smith
|date = December 10, 1983
|title= Regional Tectonic and Earthquake Hazard Implications of a Crustal Fault Zone in Southwestern Washington
|journal= Journal of Geophysical Research
|volume= 92 |issue= B12 |pages= 10,371–10,383
|doi= 10.1029/JB088iB12p10371
|bibcode=1983JGR....8810371W
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*{{Citation
|first1= R. C. |last1= Witter
|first2= R. W. |last2= Givler
|year= 2005
|title= Final Technical Report: Two Post-Glavial Earthquakes on the Saddle Mountain West Fault, southeastern Olympic Peninsula, Washington
|journal= U.S. Geological Survey
|volume= NEHRP
|at = Program Award 05HQGR0089
|url= http://earthquake.usgs.gov/research/external/reports/05HQGR0089.pdf
}}.
*{{Citation
|year= 2000
|first1= I. |last1= Wong
|first2= W. |last2= Silva
|first3= J. |last3= Bott
|first4= D. |last4= Wright
|first5= P. |last5= Thomas
|first6= N. |last6= Gregor
|first7= S. |last7= Li
|first8= M. |last8= Mabey
|coauthors= Sojourner, A.; Wang, Y.
|title= Earthquake scenario and probabilistic ground shaking maps for the Portland, Oregon, metropolitan area
|journal= Oregon Department of Geology and Mineral Industries
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|url= http://www.oregongeology.org/sub/publications/IMS/ims-016/Text/Ims-16text.pdf
}}.
*{{Citation
|year= 1982
|first1= T. S. |last1= Yelin
|title= The Seattle earthquake swarms and Puget Basin focal mechanisms and their tectonic implications [Masters thesis]
|publisher= Univ. of Washington
}}.

==External links==
*[http://pubs.usgs.gov/of/2010/1149/ Preliminary Atlas of Active Shallow Tectonic Deformation in the Puget Lowland, Washington (USGS Open-File Report 2010-1149)] Maps of the region's faults, with an overview.
*[http://earthquakes.usgs.gov/regional/qfaults USGS Quaternary fault and fold database] Technical descriptions and bibliographies.
*[http://www.pnsn.org/ The Pacific Northwest Seismic Network] All about earthquakes and geologic hazards of the Pacific Northwest.
*[http://earthweb.ess.washington.edu/jparsons/OCEAN310/Troost_origin_of_Puget_Sound.pdf The Origin of Puget Sound] Short, but good.
*[http://pubs.usgs.gov/of/1999/ofr-99-0311/seismaps.htm Earthquake locations.]
*[http://www.dnr.wa.gov/Publications/ger_gm50_geol_map_nw_wa_250k.pdf Geologic map of northwestern Washington (GM-50).]
*[http://www.dnr.wa.gov/Publications/ger_gm34_geol_map_sw_wa_250k.pdf Geologic map of southwestern Washington (GM-34).]
*[http://www.dnr.wa.gov/ResearchScience/Pages/PubMaps.aspx Various maps from Washington DGER.]
*[http://pubs.usgs.gov/of/1999/of99-514/maps Aeromagnetic anomaly maps (USGS OFR 99-514).]

{{Faults}}

{{DEFAULTSORT:Puget Sound Faults}}
[[Category:Geology of Washington (state)]]
[[Category:Seismic faults of the United States]]

Plasmonische Solarzelle

2013-09-11T13:40:42Z

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'''Plasmonic solar cells''' (PSC) are a class of [[photovoltaic device]]s that convert light into electricity by using [[plasmon]]s. PSCs are a type of [[Thin film solar cell|thin-film SC]] which are typically 1-2μm thick. They can use [[Substrate (materials science)|substrates]] which are cheaper than [[silicon]], such as [[glass]], [[plastic]] or [[steel]]. The biggest problem for thin film solar cells is that they don’t absorb as much light as the current solar cells. Methods for trapping light on the surface, or in the SC are crucial in order to make thin film SCs viable. One method which has been explored over the past few years is to scatter light using metal [[nanoparticle]]s excited at their [[surface plasmon resonance]].
<ref name=Catchpole>K. R. Catchpole and A. Polman, "Plasmonic solar cells," Opt. Express 16, 21793-21800 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-26-21793</ref>
This allows light to be absorbed more directly without the relatively thick additional layer required in other types of thin-film solar cells.

== History ==
=== People ===

There have been quite a few pioneers working with plasmonic solar cells.<ref name=Catchpole/> One of the main focuses has been on improving the thin film SC through the use of metal nanoparticles distributed on the surface. It has been found that the [[Raman scattering]] can be increased by [[order of magnitude]] when using metal nanoparticles. The increased Raman scattering provides more [[photon]]s to become available to excite [[surface plasmon]]s which cause [[electron]]s to be excited and travel through the thin film SC to create a [[Current (electricity)|current]]. The list below shows a few of research which has been done to improve PSCs.

*Stuart and Hall: Photocurrent enhancement by 18x with 165 nm SOI [[photodetector]] with wavelength of 800 nm using silver nanoparticles used for scattering and absorption of light.<ref>{{cite journal | bibcode=1998ApPhL..73.3815S | doi = 10.1063/1.122903 | title=Island size effects in nanoparticle-enhanced photodetectors | year=1998 | last1=Stuart | first1=Howard R. | last2=Hall | first2=Dennis G. | journal=Applied Physics Letters | volume=73 | issue=26 | pages=3815 }}</ref>

*Schaadt: Gold nanoparticles used for scattering and absorption of light on doped silicon obtaining 80% enhancements with 500 nm wavelength.<ref>{{cite journal | doi = 10.1063/1.1855423 | title = Enhanced semiconductor optical absorption via surface plasmon excitation in metal nanoparticles | year = 2005 | last1 = Schaadt | first1 = D. M. | last2 = Feng | first2 = B. | last3 = Yu | first3 = E. T. | journal = Applied Physics Letters | volume = 86 | issue = 6 | pages = 063106 |bibcode = 2005ApPhL..86f3106S }}</ref>

*Derkacs: Gold nanoparticles on [[thin-film silicon]] gaining 8% on [[conversion efficiency]].<ref>{{cite journal | doi = 10.1063/1.2336629 | title = Improved performance of amorphous silicon solar cells via scattering from surface plasmon polaritons in nearby metallic nanoparticles | year = 2006 | last1 = Derkacs | first1 = D. | last2 = Lim | first2 = S. H. | last3 = Matheu | first3 = P. | last4 = Mar | first4 = W. | last5 = Yu | first5 = E. T. | journal = Applied Physics Letters | volume = 89 | issue = 9 | pages = 093103 |bibcode = 2006ApPhL..89i3103D }}</ref>

*Pillai: Silver particles on SOI obtaining 33% photocurrent increase.<ref>{{cite journal | doi = 10.1063/1.2734885 | bibcode= 2007JAP...101i3105P | title = Surface plasmon enhanced silicon solar cells | year = 2007 | last1 = Pillai | first1 = S. | last2 = Catchpole | first2 = K. R. | last3 = Trupke | first3 = T. | last4 = Green | first4 = M. A. | journal = Journal of Applied Physics | volume = 101 | issue = 9 | pages = 093105 }}</ref><ref>{{cite journal | doi = 10.1063/1.2195695 | title = Enhanced emission from Si-based light-emitting diodes using surface plasmons | year = 2006 | last1 = Pillai | first1 = S. | last2 = Catchpole | first2 = K. R. | last3 = Trupke | first3 = T. | last4 = Zhang | first4 = G. | last5 = Zhao | first5 = J. | last6 = Green | first6 = M. A. | journal = Applied Physics Letters | volume = 88 | issue = 16 | pages = 161102 |bibcode = 2006ApPhL..88p1102P }}</ref>

*Stenzel: Enhancements in photocurrent by a factor of 2.7 for ITO-copper [[phthalocyanine]]-[[indium]] structures.

*Westphalen: Enhancement for silver clusters incorporated into ITO and [[zinc]] phthalocyanine solar cells.<ref>{{cite journal | doi = 10.1016/S0927-0248(99)00100-2 | title = Metal cluster enhanced organic solar cells | year = 2000 | last1 = Westphalen | first1 = M | last2 = Kreibig | first2 = U | last3 = Rostalski | first3 = J | last4 = Lüth | first4 = H | last5 = Meissner | first5 = D | journal = Solar Energy Materials and Solar Cells | volume = 61 | pages = 97}}</ref>

*Rand: Enhanced efficiencies for ultra thin film organic solar cells due to 5 nm diameter silver nanoparticles.<ref>{{cite journal | doi = 10.1063/1.1812589|bibcode=2004JAP....96.7519R | title = Long-range absorption enhancement in organic tandem thin-film solar cells containing silver nanoclusters | year = 2004 | last1 = Rand | first1 = Barry P. | last2 = Peumans | first2 = Peter | last3 = Forrest | first3 = Stephen R. | journal = Journal of Applied Physics | volume = 96 | issue = 12 | pages = 7519 }}</ref> <ref>http://www.prima-ict.eu</ref>

*Brown: Enhanced photocurrent and efficiencies in dye-sensitized solar cells incorporating metal-insulator core-shell nanoparticle geometries. <ref>{{cite journal | doi = 10.1021/nl1031106 | title = Plasmonic Dye-Sensitized Solar Cells Using Core−Shell Metal−Insulator Nanoparticles | year = 2010 | last1= Brown | first1 = M. D. | last2 = Suteewong | first2 = T. | last3 = Kumar | first3 = R.S.S. | last4 = D'Innocenzo | first4 = V | last5 = Petrozza | first5 = A | last6 = Lee | first6 = M | last7 = Wiesner | first7 = U. | last8 = Snaith | first8 = H | journal = Nano Letters | volume = 11 | issue = 2 | pages = 438–445|bibcode = 2011NanoL..11..438B }}</ref>

=== Devices ===

There are currently three different generations of SCs. The first generation (those in the market today) are made with crystalline [[semiconductor wafer]]s, typically silicon. These are the SCs everybody thinks of when they hear "Solar Cell".

Current SCs trap light by creating [[pyramid]]s on the surface which have dimensions bigger than most thin film SCs. Making the surface of the substrate rough (typically by growing SnO2 or ZnO on surface) with dimensions on the order of the incoming [[wavelength]]s and depositing the SC on top has been explored. This method increases the [[photocurrent]], but the thin film SC would then have poor material quality.
<ref name=Muller>{{cite journal | doi = 10.1016/j.solener.2004.03.015 | title = TCO and light trapping in silicon thin film solar cells | year = 2004 | last1 = Müller | first1 = Joachim | last2 = Rech | first2 = Bernd | last3 = Springer | first3 = Jiri | last4 = Vanecek | first4 = Milan | journal = Solar Energy | volume = 77 | issue = 6 | pages = 917 }}</ref>

The second generation SCs are based on [[thin film]] technologies such as those presented here. These SCs focus on lowering the amount of material used as well as increasing the energy production. Third generation SCs are currently being researched. They focus on reducing the cost of the second generation SCs.
<ref name=Conibeer>Gavin Conibeer, Third generation photovoltaics, Proc. SPIE Vol. 7411, 74110D (Aug. 20, 2009)</ref>
The third generation SCs are discussed in more detail under recent advancement.

== Design ==
The design for a PSC varies depending on the method being used to trap and scatter light across the surface and through the material.

=== Metal Nanoparticle Plasmonic Solar Cell ===
[[Image:PSC using Metal Nanoparticles.png|thumb|alt=A plasmonic solar cell utilizing metal nanoparticles to distribute light and enhance absorption.|PSC using metal nanoparticles.]]
A common design is to deposit metal nanoparticles on the top surface of the thin film SC. When light hits these metal nanoparticles at their surface plasmon resonance, the light is scattered in many different directions. This allows light to travel along the SC and bounce between the substrate and the nanoparticles enabling the SC to absorb more light.
<ref name=Tanabe>{{cite journal | last1 = Tanabe | first1 = K. | year = 2009 | title = A Review of Ultrahigh Efficiency III-V Semiconductor Compound Solar Cells: Multijunction Tandem, Lower Dimensional, Photonic Up/Down Conversion and Plasmonic Nanometallic Structures | url = | journal = Energies | volume = 2 | issue = 3| pages = 504–530 | doi = 10.3390/en20300504 }}</ref>

=== Metal Film Plasmonic Solar Cell ===

Other methods utilizing surface plasmons for harvesting solar energy are available. One other type of structure is to have a thin film of silicon and a thin layer of metal deposited on the lower surface. The light will travel through the silicon and generate surface plasmons on the interface of the silicon and metal. This generates electric fields inside of the silicon since electric fields do not travel very far into metals. If the [[electric field]] is strong enough, electrons can be moved and collected to produce a photocurrent. The thin film of metal in this design must have nanometer sized grooves which act as [[waveguide]]s for the incoming light in order to excite as many photons in the silicon thin film as possible.
<ref name=Ferry>{{cite journal | doi = 10.1021/nl8022548 | pages= 4391–4397 | title = Plasmonic Nanostructure Design for Efficient Light Coupling into Solar Cells | year = 2008 | last1 = Ferry | first1 = Vivian E. | last2 = Sweatlock | first2 = Luke A. | last3 = Pacifici | first3 = Domenico | last4 = Atwater | first4 = Harry A. | journal = Nano Letters | volume = 8 | issue = 12 | pmid = 19367883 |bibcode = 2008NanoL...8.4391F }}</ref>

== Basic Principles ==
=== General ===
[[Image:Thin vs Thick SC.png|thumb|alt=Light effects on thin and thick solar cells.|Thin film SC (left) and Typical SC (right).]]
When a photon is excited in the substrate of a SC, an electron and hole are separated. Once the electrons and holes are separated, they will want to recombine since they are of opposite charge. If the electrons can be collected prior to this happening then the SC is pretty efficient. The way to collect the electrons quickly would be to make the conducting material very thin. If the surface is made very thin, there will be less light absorbed by the device. A thick device absorbs more light.
<ref name=Tanabe/>

=== Metal Nanoparticles<ref name=Catchpole/> ===
==== Scattering and Absorption ====
The basic principles for the functioning of plasmonic solar cells include scattering and absorption of light due to the deposition of metal nanoparticles. Silicon does not absorb light very well. For this reason, more light needs to be scattered across the surface in order to increase the absorption. It has been found that metal nanoparticles help to scatter the incoming light across the surface of the silicon substrate. The equations that govern the scattering and absorption of light can be shown as:
*<math>C_{scat}=\frac{1}{6\pi}\left(\frac{2\pi}{\lambda}\right)^4|\alpha|^2</math>
This shows the scattering of light for particles which have diameters below the wavelength of light.
*<math>C_{abs}=\frac{2\pi}{\lambda}Im[\alpha]</math>
This shows the absorption for a point dipole model.
*<math>\alpha=3V\left[\frac{\epsilon_p/\epsilon_m-1}{\epsilon_p/\epsilon_m+2}\right]</math>
This is the polarizability of the particle. V is the particle volume. <math>\epsilon_p</math> is the dielectric function of the particle. <math>\epsilon_m</math> is the [[dielectric function]] of the embedding medium. When <math>\epsilon_p=-2\epsilon_m</math> the [[polarizability]] of the particle becomes large. This polarizability value is known as the surface plasmon resonance. The dielectric function for metals with low absorption can be defined as:
*<math>\epsilon=1-\frac{\omega_p^2}{\omega^2+i\gamma\omega}</math>
In the previous equation, <math>\omega_p</math> is the bulk plasma frequency. This is defined as:
*<math>\omega_p^2=Ne^2/m\epsilon_0</math>
N is the density of free electrons, e is the [[Electrical resistivity and conductivity|electronic charge]] and m is the [[Effective mass (solid-state physics)|effective mass]] of an electron. <math>\epsilon_0</math> is the dielectric constant of free space. The equation for the surface plasmon resonance in free space can therefore be represented by:
*<math>\alpha=3V\frac{\omega_p^2}{\omega_p^2-3\omega^2-i\gamma\omega}</math>
Many of the plasmonic solar cells use nanoparticles to enhance the scattering of light. These nanoparticles take the shape of spheres, and therefore the surface plasmon resonance frequency for spheres is desirable. By solving the previous [[equation]]s, the surface plasmon resonance frequency for a sphere in free space can be shown as:
*<math>\omega_{sp}=\sqrt{3}\omega_p</math>

As an example, at the surface plasmon resonance for a silver nanoparticle, the scattering cross-section is about 10x the cross-section of the nanoparticle. The goal of the nanoparticles is to trap light on the surface of the SC. The absorption of light is not important for the nanoparticle, rather, it is important for the SC. One would think that if the nanoparticle is increased in size, then the scattering cross-section becomes larger. This is true, however, when compared with the size of the nanoparticle, the ratio (<math>\frac{CS_{scat}}{CS_{particle}}</math>) is reduced. Particles with a large scattering cross section tend to have a broader plasmon resonance range.

==== Wavelength Dependence ====
Surface plasmon resonance mainly depends on the density of free electrons in the particle. The order of densities of electrons for different metals is shown below along with the type of light which corresponds to the resonance.
*[[Aluminum]] - Ultra-violet
*[[Silver]] - Ultra-violet
*[[Gold]] - Visible
*[[Copper]] - Visible

If the dielectric constant for the embedding medium is varied, the [[resonant frequency]] can be shifted. Higher indexes of refraction will lead to a longer wavelength frequency.

==== Light Trapping ====
The metal nanoparticles are deposited at a distance from the substrate in order to trap the light between the substrate and the particles. The particles are embedded in a material on top of the substrate. The material is typically a [[dielectric]], such as silicon or [[silicon nitride]]. When performing experiment and simulations on the amount of light scattered into the substrate due to the distance between the particle and substrate, air is used as the embedding material as a reference. It has been found that the amount of light radiated into the substrate decreases with distance from the substrate. This means that nanoparticles on the surface are desirable for radiating light into the substrate, but if there is no distance between the particle and substrate, then the light is not trapped and more light escapes.

The surface plasmons are the excitations of the conduction electrons at the interface of metal and the dielectric. Metallic nanoparticles can be used to couple and trap freely propagating plane waves into the semiconductor thin film layer. Light can be folded into the absorbing layer to increase the absorption. The localized surface plasmons in metal nanoparticles and the surface plasmon polaritons at the interface of metal and semiconductor are of interest in the current research. In recent reported papers, the shape and size of the metal nanoparticles are key factors to determine the incoupling efficiency. The smaller particles have larger incoupling efficiency due to the enhanced near-field coupling. However, very small particles suffer from large ohmic losses.
<ref>{{cite journal|last=Atwater|first=Harry|coauthors=A. Polman|title=Plasmonics for improved photovoltaic devices|journal=Nature materials|date=19|year=2010|month=February|volume=9|pages=205–13|bibcode=2010NatMa...9..205A|doi=10.1038/nmat2629|issue=3|pmid=20168344}}</ref>

=== Metal Film ===
As light is incident upon the surface of the metal film, it excites surface plasmons. The surface plasmon frequency is specific for the material, but through the use of [[grating]]s on the surface of the film, different frequencies can be obtained. The surface plasmons are also preserved through the use of waveguides as they make the surface plasmons easier to travel on the surface and the losses due to resistance and radiation are minimized. The electric field generated by the surface plasmons influences the electrons to travel toward the collecting substrate.
<ref name=Huag>{{cite journal | doi = 10.1063/1.2981194 | title = Plasmonic absorption in textured silver back reflectors of thin film solar cells | year = 2008 | last1 = Haug | first1 = F.-J. | last2 = SöDerström | first2 = T. | last3 = Cubero | first3 = O. | last4 = Terrazzoni-Daudrix | first4 = V. | last5 = Ballif | first5 = C. | journal = Journal of Applied Physics | volume = 104 | issue = 6 | pages = 064509 |bibcode = 2008JAP...104f4509H }}</ref>

== Materials<ref name=Conibeer/><ref>http://www1.eere.energy.gov/solar/solar_cell_materials.html</ref> ==
{| class="wikitable" border="1"
|-
! First Generation
! Second Generation
! Third Generation
|-
| Single-crystal silicon
| CuInSe2
| Gallium Indium Phosphide
|-
| Multicrystalline silicon
| amorphous silicon
| Gallium Indium Arsenide
|-
| Polycrystalline silicon
| thin film crystalline Si
| Germanium
|}

== Applications ==
The applications for plasmonic solar cells are endless. The need for cheaper and more efficient solar cells is huge. In order for solar cells to be considered cost effective, they need to provide energy for a smaller price than that of traditional power sources such as [[coal]] and [[gasoline]]. The movement toward a more green world has helped to spark research in the area of plasmonic solar cells. Currently, solar cells cannot exceed efficiencies of about 30% (First Generation). With new technologies (Third Generation), efficiencies of up to 40-60% can be expected. With a reduction of materials through the use of thin film technology (Second Generation), prices can be driven lower.

=== Space ===

Certain applications for plasmonic solar cells would be for [[space exploration]] vehicles. A main contribution for this would be the reduced weight of the solar cells. An external fuel source would also not be needed if enough power could be generated from the solar cells. This would drastically help to reduce the weight as well.

=== Rural ===

Solar cells have a great potential to help rural [[electrification]]. An estimated two million villages near the equator have limited access to electricity and fossil fuels and that approximately 25%<ref>http://www.globalissues.org/article/26/poverty-facts-and-stats</ref> of people in the world do not have access to electricity. When the cost of extending [[power grid]]s, running rural electricity and using diesel generators is compared with the cost of solar cells, many times the solar cells win. If the efficiency and cost of the current solar cell technology is decreased even further, then many rural communities and villages around the world could obtain electricity when current methods are out of the question. Specific applications for rural communities would be water pumping systems, residential electric supply and street lights. A particularly interesting application would be for health systems in countries where motorized vehicles are not overly abundant. Solar cells could be used to provide the power to refrigerate [[medication]]s in coolers during transport.

Solar cells could also provide power to [[lighthouse]]s, [[buoy]]s, or even [[battleship]]s out in the ocean. Industrial companies could use them to power [[telecommunications]] systems or monitoring and control systems along pipelines or other system.<ref name=web/>

=== High Power ===

If the solar cells could be produced on a large scale and be cost effective then entire [[power station]]s could be built in order to provide power to the electrical grids. With a reduction in size, they could be implemented on both commercial and residential buildings with a much smaller footprint. They might not even seem like an [[eyesore]].
<ref name=web>http://www.soton.ac.uk/~solar/intro/appso.htm</ref>

Other areas are in hybrid systems. The solar cells could help to power high consumption devices such as [[automobile]]s in order to reduce the amount of fossil fuels used and to help improve the environmental conditions of the earth.

=== Low Power ===

One application which has not been mentioned is consumer electronics. Essentially, solar cells could be used to replace batteries for low power electronics. This would save everyone a lot of money and it would also help to reduce the amount of waste going into [[landfill]]s.<ref>http://blog.coolerplanet.com/2009/01/23/the-4-basic-types-of-solar-cell-applications/</ref>

== Recent Advancements ==
=== Choice of plasmonic metal nanoparticles ===

Proper choice of plasmatic metal nanoparticles is crucial for the maximum light absorption in the active layer. Front surface located nanoparticles Ag and Au are the most widely used materials due to their surface plasmon resonances located in the visible range and therefore interact more strongly with the peak solar intensity. However, such noble metal nanoparticles always introduce reduced light coupling into Si at the short wavelengths below the surface plasmon resonance due to the detrimental Fano effect, i.e. the destructive interference between the scattered and unscattered light. Moreover, the noble metal nanoparticles are impractical to implement for large-scale solar cell manufacture due to their high cost and scarcity in earth crest. Recently, Zhang et al have demonstrated the low cost and earth abundant materials Al nanoparticles to be able to outperform the widely used Ag and Au nanoparticles. Al nanoparticles, with their surface plasmon resonances located in the UV region below the desired solar spectrum edge at 300 nm, can avoid the reduction and introduce extra enhancement in the shorter wavelength range.<ref>{{cite journal| title=Low cost and high performance Al nanoparticles for broadband light trapping in Si wafer solar cells| year=2012 | last1=Yinan | first1=Zhang et al| journal=Applied Physics Letters | volume=100 | issue=12 | pages=151101 |bibcode = 2012ApPhL.100b1101N |doi = 10.1063/1.3675451 }}</ref> <ref>{{cite journal| title=Improved multicrystalline Si solar cells by light trapping from Al nanoparticle enhanced antireflection coating| year=2013 | last1=Yinan | first1=Zhang et al| journal=Opt. Mater. Express| volume=3 | issue=4 | pages=489 }}</ref>

=== Light Trapping ===

As discussed earlier, being able to concentrate and scatter light across the surface of the plasmonic solar cell will help to increase efficiencies. Recently, research at [[Sandia National Laboratories]] has discovered a photonic waveguide which collects light at a certain wavelength and traps it within the structure. This new structure can contain 95% of the light that enters it compared to 30% for other traditional waveguides. It can also direct the light within one wavelength which is ten times greater than traditional waveguides. The wavelength this device captures can be selected by changing the structure of the lattice which comprises the structure. If this structure is used to trap light and keep it in the structure until the solar cell can absorb it, the efficiency of the solar cell could be increased dramatically.<ref>http://www.sandia.gov/media/photonic.htm</ref>

=== Absorption ===

Another recent advancement in plasmonic solar cells is using other methods to aid in the absorption of light. One way being researched is the use of metal wires on top of the substrate to scatter the light. This would help by utilizing a larger area of the surface of the solar cell for light scattering and absorption. The danger in using lines instead of dots would be creating a reflective layer which would reject light from the system. This is very undesirable for solar cells. This would be very similar to the thin metal film approach, but it also utilizes the scattering effect of the nanoparticles.
<ref>{{cite journal | doi = 10.1002/adma.200900331 | title = Design of Plasmonic Thin-Film Solar Cells with Broadband Absorption Enhancements | year = 2009 | last1 = Pala | first1 = Ragip A. | last2 = White | first2 = Justin | last3 = Barnard | first3 = Edward | last4 = Liu | first4 = John | last5 = Brongersma | first5 = Mark L. | journal = Advanced Materials | volume = 21 | issue = 34 | pages = 3504 }}</ref>

=== Third Generation Solar Cells<ref name=Conibeer/> ===

The goal of third generation solar cells is to increase the efficiency using second generation solar cells (thin film) and using materials that are found abundantly on earth. This has also been a goal of the thin film solar cells. With the use of common and safe materials, third generation solar cells should be able to be manufactured in mass quantities further reducing the costs. The initial costs would be high in order to produce the manufacturing processes, but after that they should be cheap. The way third generation solar cells will be able to improve efficiency is to absorb a wider range of frequencies. The current thin film technology has been limited to one frequency due to the use of single band gap devices.

==== Multiple Energy Levels ====

The idea for multiple energy level solar cells is to basically stack thin film solar cells on top of each other. Each thin film solar cell would have a different band gap which means that if part of the solar spectrum was not absorbed by the first cell then the one just below would be able to absorb part of the spectrum. These can be stacked and an optimal band gap can be used for each cell in order to produce the maximum amount of power. Options for how each cell is connected are available, such as serial or parallel. The serial connection is desired because the output of the solar cell would just be two leads.

The lattice structure in each of the thin film cells needs to be the same. If it is not then there will be losses. The processes used for depositing the layers are complex. They include Molecular Beam Epitaxy and Metal Organic Vapour Phase Epitaxy. The current efficiency record is made with this process but doesn't have exact matching lattice constants. The losses due to this are not as effective because the differences in lattices allows for more optimal band gap material for the first two cells. This type of cell is expected to be able to be 50% efficient.

Lower quality materials that use cheaper deposition processes are being researched as well. These devices are not as efficient, but the price, size and power combined allow them to be just as cost effective. Since the processes are simpler and the materials are more readily available, the mass production of these devices is more economical.

==== Hot Carrier Cells ====

A problem with solar cells is that the high energy photons that hit the surface are converted to heat. This is a loss for the cell because the incoming photons are not converted into usable energy. The idea behind the hot carrier cell is to utilize some of that incoming energy which is converted to heat. If the electrons and holes can be collected while hot, a higher voltage can be obtained from the cell. The problem with doing this is that the contacts which collect the electrons and holes will cool the material. Thus far, keeping the contacts from cooling the cell has been theoretical. Another way of improving the efficiency of the solar cell using the heat generated is to have a cell which allows lower energy photons to excite electron and hole pairs. This requires a small bandgap. Using a selective contact, the lower energy electrons and holes can be collected while allowing the higher energy ones to continue moving through the cell. The selective contacts are made using a double barrier resonant tunneling structure. The carriers are cooled which they scatter with phonons. If a material with a large bandgap of phonons then the carriers will carry more of the heat to the contact and it won't be lost in the lattice structure. One material which has a large bandgap of phonons is indium nitride. The hot carrier cells are in their infancy but are beginning to move toward the experimental stage.

== References ==
{{Portal box|Renewable energy|Energy}}
{{Reflist|2}}

{{Photovoltaics}}

{{DEFAULTSORT:Plasmonic Solar Cell}}
[[Category:Solar cells]]

Enterobakteriophage PhiX174

2013-09-11T12:20:11Z

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[[File:phiX174.jpg|thumb|right|180 px| Structure of phage phi X 174 capsid]]
{{Taxobox
| virus_group = ii
| familia = ''[[Microviridae]]''
| genus = ''[[Microvirus]]''
| species = '''''ΦX174 phage'''''
}}
The '''phi X 174''' (or '''ΦX174''') [[bacteriophage]] was the first DNA-based [[genome]] to be sequenced. This work was completed by [[Fred Sanger]] and his team in 1977.<ref>{{cite journal |doi=10.1038/265687a0 |title=Nucleotide sequence of bacteriophage φX174 DNA |year=1977 |last1=Sanger |first1=F. |last2=Air |first2=G. M. |last3=Barrell |first3=B. G. |last4=Brown |first4=N. L. |last5=Coulson |first5=A. R. |last6=Fiddes |first6=J. C. |last7=Hutchison |first7=C. A. |last8=Slocombe |first8=P. M. |last9=Smith |first9=M. |journal=Nature |volume=265 |issue=5596 |pages=687–95 |pmid=870828|bibcode = 1977Natur.265..687S }}</ref> In 1962, [[Walter Fiers]] and Robert Sinsheimer had already demonstrated the physical, covalently closed circularity of phi X 174 DNA.<ref>{{cite journal |doi=10.1016/S0022-2836(62)80031-X |title=The structure of the DNA of bacteriophage φX174 |year=1962 |last1=Fiers |first1=Walter |last2=Sinsheimer |first2=Robert L. |journal=Journal of Molecular Biology |volume=5 |issue=4 |pages=424}}</ref> Nobel prize winner [[Arthur Kornberg]] used phi X 174 as a model to first prove that DNA synthesized in a test tube by purified enzymes could produce all the features of a natural virus, ushering in the age of synthetic biology<ref>National Library of Medicine Profiles in Science. The Arthur Kornberg Papers. "Creating Life in the Test Tube," 1959-1970. [http://profiles.nlm.nih.gov/ps/retrieve/Narrative/WH/p-nid/209/p-docs/true link]{{psc|date=February 2013}}</ref><ref>{{cite journal |first1=Mehran |last1=Goulian |first2=Arthur |last2=Kornberg |first3=Robert L. |last3=Sinsheimer |title=Enzymatic Synthesis of DNA, XXIV. Synthesis of Infectious Phage φ X174 DNA |doi=10.1073/pnas.58.6.2321 |jstor=58720 |bibcode=1967PNAS...58.2321G |pmc=223838 |year=1967 |journal=Proceedings of the National Academy of Sciences |volume=58 |issue=6 |pages=2321–2328}}</ref> In 2003, it was reported by [[Craig Venter|Craig Venter's]] group that the genome of ΦX174 was the first to be completely assembled ''in vitro'' from synthesized oligonucleotides.<ref>{{cite journal |first1=Hamilton O. |last1=Smith |first2=Clyde A. |last2=Hutchison |first3=Cynthia |last3=Pfannkoch |first4=J. Craig |last4=Venter |doi=10.1073/pnas.2237126100 |title=Generating a Synthetic Genome by Whole Genome Assembly: ϕX174 Bacteriophage from Synthetic Oligonucleotides |year=2003 |journal=Proceedings of the National Academy of Sciences |volume=100 |issue=26 |pages=15440–5 |bibcode=2003PNAS..10015440S |jstor=3149024 |pmc=307586 |pmid=14657399}}</ref> The ΦX174 virus particle has also been successfully assembled ''in vitro''.<ref>{{cite journal |doi=10.1016/j.jmb.2011.07.070 |title=In Vitro Assembly of the øX174 Procapsid from External Scaffolding Protein Oligomers and Early Pentameric Assembly Intermediates |year=2011 |last1=Cherwa |first1=James E. |last2=Organtini |first2=Lindsey J. |last3=Ashley |first3=Robert E. |last4=Hafenstein |first4=Susan L. |last5=Fane |first5=Bentley A. |journal=Journal of Molecular Biology |volume=412 |issue=3 |pages=387–96 |pmid=21840317}}</ref> Recently, it was shown how its highly overlapping genome can be fully decompressed and still remain functional.<ref>{{cite journal |doi=10.1016/j.virol.2012.09.020 |title=A fully decompressed synthetic bacteriophage øX174 genome assembled and archived in yeast |year=2012 |last1=Jaschke |first1=Paul R. |last2=Lieberman |first2=Erica K. |last3=Rodriguez |first3=Jon |last4=Sierra |first4=Adrian |last5=Endy |first5=Drew |journal=Virology |volume=434 |issue=2 |pages=278–84 |pmid=23079106}}</ref>

==Virology==

This [[bacteriophage]] has a [+] circular single-stranded [[DNA]] genome of 5386 [[nucleotide]]s encoding 11 [[protein]]s. Of these 11 genes, only 8 are essential to viral morphogenesis. The [[GC-content]] is 44% and 95% of nucleotides belong to coding genes.

{| class="wikitable"
|-
! Protein !! Function
|-
| A || Stage II and stage III DNA replication
|-
| A* || An unessential protein for viral propagation. It may play a role in the inhibition of host cell DNA replication and superinfection exclusion
|-
| B || Internal scaffolding protein, required for capsid morphogenesis and the assembly of early morphogenetic intermediates. Sixty copies present in the procapsid
|-
| C || Facilitates the switch from stage II to stage III DNA replication. Required for stage III DNA synthesis
|-
| D || External scaffolding protein, required for procapsid morphogenesis. Two hundred and forty copies present in the procapsid.
|-
| E || Host cell lysis
|-
| F || Major coat protein. Sixty copies present in the virion and procapsid
|-
| G || Major spike protein. Sixty copies present in the virion and procapsid
|-
| H || DNA pilot protein need for DNA injection, also called the minor spike protein. Twelve copies in the procapsid and virion
|-
| J || DNA binding protein, needed for DNA packaging. Sixty copies present in the virion
|-
| K || An unessential protein for viral propagation. It may play a role optimizing burst sizes in various Hosts
|-
|}

Table from ΦX174 et al. the ''Microviridae'' by B.A. Fane et al.

Infection begins when G protein binds to lipopolysaccharides on the bacterial host cell surface. H protein (or the DNA Pilot Protein) pilots the viral genome through the bacterial membrane of ''E.coli'' bacteria (Jazwinski et al. 1975) most likely via a predicted N-terminal transmembrane domain helix (Tusnady and Simon, 2001). However, it has become apparent that H protein is a multifunctional protein (Cherwa, Young and Fane, 2011). This is the only viral capsid protein of ΦX174 to lack a crystal structure for a couple of reasons. It has low aromatic content and high glycine content, making the protein structure very flexible and in addition, individual hydrogen atoms (the R group for glycines) are difficult to detect in protein crystallography. Additionally, H protein induces [[lysis]] of the bacterial host at high concentrations as the predicted N-terminal transmembrane helix easily pokes holes through the bacterial wall. By bioinformatics, this protein contains four predicted coiled-coil domains which has a significant homology to known transcription factors. Additionally, it was determined by Ruboyianes et al. (2009) that ''de novo'' H protein was required for optimal synthesis of other viral proteins. Interestingly, mutations in H protein that prevent viral incorporation, can be overcome when excess amounts of Protein B, the internal scaffolding protein, are supplied.

The DNA is ejected through a hydrophilic channel at the 5-fold vertex (McKenna et al. 1992). It is understood that H protein resides in this area but experimental evidence has not verified its exact location. Once inside the host bacterium, replication of the [+] ssDNA genome proceeds via negative sense DNA intermediate. This is done as the phage genome supercoils and the secondary structure formed by such supercoiling attracts a primosome protein complex. This translocates once around the genome and synthesises a [-]ssDNA from the positive original genome. [+]ssDNA genomes to package into viruses are created from this by a rolling circle mechanism. This is the mechanism by which the double stranded supercoiled genome is nicked on the negative strand by a virus-encoded A protein, also attracting a bacterial DNA Polymerase to the site of cleavage. DNAP will use the negative strand as a template to make positive sense DNA. As it translocates around the genome it displaces the outer strand of already-synthesised DNA, which is immediately coated by ssBP proteins. The A protein will cleave the complete genome every time it recognises the origin sequence.

As D protein is the most abundant gene transcript, it is the most protein in the viral procaspid. Similarly, gene transcripts for F, J, and G are more abundant than for H as the stoichiometry for these structures proteins is 5:5:5:1.

==Notes==

Phi X is regularly used as a [[Scientific_control#Positive_and_negative_control|positive control]] in [[DNA sequencing]] due to its relatively small genome size in comparison to other organisms and the extensive work that has been done on it.

==See also==
* [[Bacteriophage MS2]]

==References==
{{Reflist|2}}


==External links==

* [http://www.ncbi.nlm.nih.gov/nuccore/NC_001422 Complete genome]
* {{cite web |url=http://www.rcsb.org/pdb/101/motm.do?momID=2 |title=Bacteriophage phiX174 |month=February |year=2000 |work=Molecule of the Month |first=David |last=Goodsell |publisher=RCSB-PDB}}

[[Category:Microviridae]]

Olympic-Wallowa-Lineament

2013-09-11T00:52:59Z

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[[File:OWL-location.png|right|frame|Location of the Olympic-Wallowa Lineament.]]
[[File:OWL-shadedrelief.png|right|frame|Is the OWL an optical illusion?]]
The '''Olympic-Wallowa lineament''' (OWL) – first reported by cartographer [[Erwin Raisz]] in 1945 <ref>{{Harvnb|Raisz|1945}}. Now available on-line; see citation.</ref> on a relief map of the continental United States – is a physiographic feature of unknown origin in the state of Washington (northwestern U.S.) running approximately from the town of [[Port Angeles, Washington|Port Angeles]], on the Olympic Peninsula to the [[Wallowa Mountains]] of eastern Oregon.

{{bots|deny=Citation bot}}

==Location==
Raisz located the OWL particularly from [[Cape Flattery (Washington)|Cape Flattery]] (the northwest corner of the Olympic Peninsula) and along the north shore of Lake Crescent, thence the Little River (south of [[Port Angeles, Washington|Port Angeles]]), Liberty Bay (Poulsbo), Elliott Bay (setting the orientation of the streets in downtown Seattle), the north shore of Mercer Island, the Cedar River (Chester Morse Reservoir), Stampede Pass (Cascade crest), the south side of the Kittitas Valley (I-90), [[Manastash Ridge]], the [[Wallula Gap]] (on the Columbia River where it approaches the Oregon state line), and then the South Fork of the Walla Walla River into the northeastern corner of Oregon. After crossing the [[Blue Mountains (Oregon)|Blue Mountains]] Riasz associated the OWL with a dramatic scarp on the north side of the [[Wallowa Mountains]]. Riasz observed that the OWL tends to have basins on the north side (Seattle Basin, Kittitas Valley, Pasco Basin, Walla Walla Basin) and mountains on the southern side (the Olympics, Manastash and Umtanum ridges, Rattlesnake Mountain, the Horseheaven Hills, the Wallowa Mountains), and noted parallel alignments at various points, generally about four miles north or south of the main line. The alignment of these particular features is somewhat irregular; modern maps with much more detail show a broad zone of more regular alignments. Subsequent geological investigations have suggested various refinements and adjustments.

==Introduction to a puzzle==
[[File:Kanizsa triangle.svg|thumb|What triangle?]]
Most geological features are initially identified or characterized from a local expression of that feature. The OWL was first identified as a perceptual effect, a pattern perceived by the human visual system in a broad field of many seemingly random elements. But is it real? Or just an [[optical illusion]], such as the [[Kanizsa triangle]] (see image), where we "see" a triangle that does not really exist?

Raisz considered whether the OWL might be just a chance alignment of random elements, and geologists since have not been able to find any common unitary feature, nor identify any connection between the various local elements. {{Harvtxt|Davis|1977}} called it a "fictional structural element". Yet it has been found to be coincide with many faults and fault zones, and to delineate significant differences of geology.<ref>
Such as the older "crystalline" plutonic rock of the North Cascades from the younger basaltic rocks of the South Cascades.{{Harv|McKee|1972|p=83}} There are also more subtle differences, such as in the [[Columbia Plateau]] where the OWL marks a difference in structural expression, with strike-slip faulting and
rotation predominate to the southwest but subordinate to the northeast {{Harv|Hooper|Camp|1981}}. See also {{Harvnb|Hooper|Conrey|1989}}, pp. 297–300.</ref> These are much too correlated to be dismissed as random alignments. But for all of its prominence, there is as yet no understanding of what the OWL is or how it came to be; it looms just beyond the horizon of current human knowledge.

The OWL piques the interest of geologically minded persons in part because its characteristic NW-SE angle of orientation – approximately 50 to 60 degrees west of north (a little short of northwest)<ref>Estimating the northing and westing from a map and applying the usual trigonometric methods gives an angle of 59 degrees west of north (N59W, azimuth 301°) from Wallula Gap to Cape Flattery. There is a bit of a bend east of Port Angeles – the shore line between Pillar Point to Slip Point has a more westerly angle of 65 degrees – but that section is so short that the angle from Wallula Gap to Port Angeles is still 57 degrees. A line run from the strong relief at Gold Creek to the mouth of Liberty Bay and beyond – a line that runs along several seeming OWL features – has an angle of 52 deg. In Seattle the angle of the Ship Canal (which is a reasonably close proxy for the natural feature it lies in) has an angle of 55 degrees...

It is possible that whatever causes the OWL is straight, but at depth, and its expression towards the surface is deflected by other structures. E.g., the Olympic Mountain batholith might be pushing Gold Creek out of alignment. And perhaps the Blue Mountains cause a similar bend. But this is entirely speculative.</ref> – is shared by many other seeming local features across a broad swath of geography. Around Seattle these include strikingly parallel alignments at the south end of Lake Washington, the north side of Elliott Bay, the valley of the Ship Canal, the bluff along Interlaken Blvd. (aligned with the Ship Canal, but offset slightly to the north), the alignment of Ravenna Creek (draining Green Lake southeast into Union Bay) and Carkeek Creek (northwest into Puget Sound), various stream drainages around Lake Forest Park (north end of Lake Washington), and (on the Eastside) the Northrup Valley (Hwy. 520 from Yarrow Bay to the Overlake area), and various smaller details too numerous to mention. All of these are carved into "recent" (less than 18,000 years old) glacial deposits, and it is difficult to conceive of how these could be controlled by anything other than a recent glacial process.

Yet the same orientation shows up in the Brothers, Euguene-Denio, and McLoughlin fault zones in Oregon (see [[#regional-map|map]], below), which are geological features tens of millions of years old, and the [[Walker Lane]] lineament in Nevada.

Likewise to the east, where both the OWL and the Brothers Fault Zone become less distinct in Idaho where they hit the old North American continental craton and the track of [[Yellowstone hotspot]]. But some 50 miles to the north is the parallel Trans-Idaho Discontinuity, and further north, the Osburn fault (Lewis and Clark line) running roughly from Missoula to Spokane. And [[aeromagnetic survey|aeromagnetic]]<ref>{{Harvnb|Zietz|others|1971}}; {{Harvnb|Sims|Lund|Anderson|2005}}.</ref> and [[Bouguer anomaly|gravitational anomaly]] <ref>{{Harvnb|Simpson|others|1986}}, see figure 9.</ref> surveys suggest extension into the interior of the continent.

All of these alignments seem too strong to be random, but as yet it is quite a puzzle of how features millions of years old are linked with features only thousands of years young, and across hundreds of miles of diverse geology. Geology has not yet sorted this out. So this article will examine what the puzzle looks like before the pieces are assembled, touching on what may – or may not – be parts of the answers, and showing that shadowy zone at the edge of knowledge. Because geologists do not yet know even which pieces are relevant, a wide and even speculative view must be taken. This is what science looks like at the edge, before it is tamed and neatly trimmed.

==Structural relationships with other features==
{{anchor|regional-map}}

A problem in evaluating any hypothesis regarding the OWL is a dearth of evidence.
Raisz suggested that the OWL might be a "transcurrent fault" (long strike-slip faults at what are now known to be plate boundaries), but lacked both data and competence to assess it. One of the first speculations that the OWL might be a major geological structure {{Harv|Wise|1963}} – written when the theory of [[plate tectonics]] was still new and not entirely accepted<ref>As late as 1976 {{Harvtxt|Thomas|1976}} referred to the "presently
popular plate tectonics theory".</ref> – was called by the author "an outrageous hypothesis". Modern investigation is still largely balked by the immense span of geography involved and lack of continuous structures, the lack of clearly cross-cutting features, and a confusing expression in both rock millions of years old and glacial sediments only 16,000 years old.

[[Image:Geofeatures-PacificNW.png|right|frame|'''Major geological structures in Washington and Oregon:''' 
SCF – Straight Creek fault;
SB – Snoqualmie batholith (dotted area to the left);
OWL – Olympic-Wallowa lineament;
L&C – Lewis and Clark line (gravity anomaly);
HF – Hite fault;
KBML – Klamath-Blue Mountains lineament (slightly misplaced);
NC – Newberry caldera;
BFZ – Brothers Fault zone;
EDFZ –Eugene-Denio fault zone;
MFZ – McLoughlin fault zone; 
WSRP – western Snake River Plain;
NR –  Nevada Rift zone;
OIG – Oregon-Idaho graben;
CE – Clearwater Embayment;
(From {{Harvnb|Martin|others|2005}}, Fig. 1, courtesy of [http://www.pnl.gov/notices.asp PNNL])]]
Geological investigation of a feature begins with determining its structure, composition, age, and relationship with other features. The OWL does not cooperate. It is expressed as an orientation in many elements of diverse structure and compositions, and even as a boundary between areas of differing structure and composition; there is yet no understanding of what kind of feature or process – the "ur-OWL" – could control this. Nor are there particular "OWL" rocks which can be examined and radiometrically dated. We are left with determining its age by looking at its relationship with other features, such as which features overlap or cross-cut other (presumably older) features. In the following sections we will look at several features which might be expected to have some kind of structural relationship with the OWL, and consider what they might tell us about the OWL.

===Cascade Range===
The most notable geological feature crossing the OWL is the [[Cascade Range]], raised up in the [[Pliocene]] (two to five million years ago) as a result of the [[Cascadia subduction zone]]. These mountains are distinctly different on either side of the OWL, the material of the South Cascades being [[Cenozoic]] (<66 [[annum|Ma]]) volcanic and sedimentary rock, and the North Cascades being much older [[Paleozoic]] (hundreds of millions of years) metamorphic and plutonic rocks.<ref>{{Harvnb|McKee|1972}}, p.83. See also {{Harvnb|Mitchell|Montgomery|2006}}.</ref> It is unknown whether this difference is in any way linked with the OWL, or is simply a coincidental regional difference.

Raisz judged the Cascades on the north side of the OWL to be offset about six miles to the west, and similarly for the Blue Mountains, but this is questionable, and similar offsets are not apparent in the older – up to 17 Ma ([[annum|millions of years]]) old – [[Columbia River Basalt Group|Columbia River basalt flows]]. In general, there are no clear indications of structures offset by the OWL, but neither are there any distinct features crossing the OWL (and older than 17 Ma) that positively demonstrate a lack of offsetting.

===Straight Creek Fault===
[[File:SCF-terminus.png|frame|Geological topography where the SCF meets the OWL, showing general curvature to the southeast around Lakes Keechelus, Kachess, and Cle Elum. Red line is Interstate 90, Snoqualmie Pass is at upper left corner, [[Easton, Washington|Easton]] is near center. The White River—Naches Fault Zone, at the bottom of the red area, appears to be the southern edge of the OWL. Excerpted from {{Harvnb|Haugerud|Tabor|2009}}.]]

The [[Straight Creek Fault]] (SCF) – just east of Snoqualmie Pass and running nearly due north into Canada – is a major fault notable for considerable identified dextral strike-slip offset (opposite side moving laterally to the right) of at least {{convert|90|km|mi|abbr=on}}.<ref>{{Harvnb|Vance|Miller|1994}}; {{Harvnb|Umhoefer|Miller|1996}}. Estimates of offset vary; this is the minimum.</ref> Its intersection with the OWL (near [[Kachess Lake]]) is the geological equivalent of an atom smasher, and the results should be informative. For example, that the OWL is not offset suggests that it must be younger than the last strike-slip motion on the SCF,<ref>Alternately, could the OWL be a reflection of some kind of structure – perhaps in the [[lithosphere]] – that is not affected by the SCF?</ref> anywhere from around 44 to about 41 million years ago<ref>{{Harvnb|Tabor|others|1984}}; {{Harvnb|Vance|Miller|1994}}; {{Harvnb|Tabor|1994}}, pp 224, 230.</ref> (i.e., during the middle-[[Eocene]] epoch). And if the OWL is a strike-slip fault or megashear, as many have speculated,<ref>{{Harvnb|Raisz|1945}}; {{Harvnb|Wise|1963}}; {{Harvnb|Hooper|Conrey|1989}}.</ref> then it should offset the SCF, and whether the OWL offsets the SCF, or not, becomes an important test of just what the OWL is.

So does the OWL offset the SCF, or not? It is hard to say, as no trace whatsoever has been found of the SCF anywhere south of the OWL. While some geologists have speculated that it does continue directly south, albeit hidden under younger deposits,<ref>{{Harvnb|Davis|1977}}; {{Harvnb|Wyld|others|2006}}, p. 282.</ref> not a trace has been found.

If the SCF fault does not continue directly southward<ref>{{Harvnb|Tabor|others|1984}}, p.30; {{Harvnb|Campbell|1989}}, p.216.</ref> – and the utter lack of evidence that it does makes a case for evidence of lack – then where else might it be? {{Harvtxt|Heller|others|1987}} suggest some possibilities: it may curve to the east, it may curve to the west, or it may just end.

Tabor mapped the SCF turning and merging with the Taneum fault (coincident with the OWL) south of Kachess Lake.<ref>{{Harvnb|Tabor|others|1984}}, p. 27; {{Harvnb|Tabor|others|2000}}, p. 1.</ref> This conforms with the general pattern seen in Lakes Keechelus, Kachess, and Cle Elum, and associated geological units and faults (see image, right): each is aligned north—south at the north end, but turns to the southeast where it approaches the OWL.<ref>Downloadable maps available; see {{Harvnb|Haugerud|Tabor|2009}}, {{Harvnb|Tabor|others|1984}}, and {{Harvnb|Tabor|others|2000}}.</ref> This is suggestive of the OWL being a ''left'' lateral (sinistral) strike-slip fault that has distorted and offset the SCF. But that is inconsistent with the SCF itself and most other strike-slip faults associated with the OWL being ''right'' lateral (dextral), and incompatible with the geology to the southeast. Particularly, studies of the region to the southeast (in connection with Department of Energy activities at the [[Hanford Reservation]]) show no indication of any fault or other structure comparable to the SCF.<ref>E.g., {{Harvnb|Caggiano|Duncan|1983}}, generally, and {{Harvnb|Reidel|Campbell|1989}}.</ref>

[[File:Straight Creek Fault.gif|Figure 1 from USGS Map I-2538 {{Harv|Tabor|others|2000}}.|left]]
On the other hand, {{Harvtxt|Cheney|1999}} maps the SCF as proceeding southerly (without addressing the situation south of the OWL). (He has subsequently speculated<ref>{{Harvnb|Cheney|2003}}, {{Harvnb|Cheney|Hayman|2007}}.</ref> that the missing part of the SCF may have been dextrally offset to become a southerly trending fault in the Puget Lowland. But same problem: later deposits cover any traces.) The seeming southeasterly curvature is possibly explained as a geometrical effect of foreshortening: it occurs in a belt of intense folding (much resembling a rug which has slid against a wall) which, if unfolded, could restore some of the "curves" to a linear position along the southerly extension of the SCF.<ref>See the maps of {{Harvnb|Cheney|1999}} (DGER OFR 99-4) and {{Harvnb|Tabor|others|2000}} (USGS Map I-2538); see also {{Harvnb|Haugerud|Tabor|2009}} (USGS Map I-2940).</ref>

There seem to be no indications that the SCF ''turns'' to the west. Although such indications would mostly be buried, the general sense of the topography suggests no such turn. Displacement, to either the west or the east, seems unlikely in that certain effects that would be expected are not found.<ref>E.g., displacement of the Olympic Mountains is not observed, so the block moving away from the Olympics should leave a gap, and likely [[graben]]s. There is a basin – the Seattle Basin – just immediately north of the [[Seattle Fault]], but it appears no one has attributed it to movement on the OWL.
</ref>

Could the SCF just end? This is difficult to comprehend. If there is displacement along this fault, where did it come from? To quote Wyld et al.<ref>{{Harvnb|Wyld|others|2006}}, p. 282.</ref> (albeit in the context of a different fault): "it cannot just end". Although the SCF has had substantial strike-slip displacement, {{Harvtxt|Vance|Miller|1994}} claim that final major movement on the SCF (about 40 Ma ago) was dominantly dip-slip (vertical displacement). So perhaps the displacement came from the depths, and, as it was extruded, was eroded and redistributed as sediments. But this has not been established.

Another possibility is that the missing southern segment of the SCF is on a [[crustal block]] that rotated away from the OWL. There is evidence that around 45 million years ago much of Oregon and southwestern
Washington rotated some 60° or more about a pivot somewhere in the Olympic Peninsula (see [[#Oregon rotation|Oregon rotation]], below). This would have left a large gap south of the OWL, which could explain why Tertiary rocks are not found immediately south of the OWL. This suggests that a continuation of the SCF, if any, and the missing Tertiary rock, might be somewhere southwest of [[Mount Saint Helens]], but this has not been observed.

===Darrington–Devils Mountain Fault Zone===
The interaction of the Straight Creek Fault with the OWL has yielded practically no intelligible information, and remains as enigmatic as the OWL itself. More informative is the closely related Darrington—Devils Mountain Fault Zone (DDMFZ). It runs east from a complex of faults on the southern end of [[Vancouver Island]] to the town of Darrington, where it turns south to converge with the SCF (see map, above).<ref>{{Harvnb|Dragovich|Stanton|2007}}.</ref>

North of the DDMFZ (and west of the SCF) is the [[Chuckanut Formation]] (part of the "Northwest Cascade System" of rocks shown in green on the map), an [[Eocene]] sedimentary formation which formed adjacent to the Swauk, Roslyn and other formations (also in green) south of [[Mount Stuart]]; their wide separation is attributed to right-lateral strike-slip movement along the SCF.<ref>{{Harvnb|Johnson|1984}}, p. 102.</ref> That the northern part of the DDMFZ shows ''left''-lateral strike-slip movement<ref>{{Harvnb|Dragovich|others|2003}}.</ref> is not the inconsistency it may initially seem – think of the motion on either side of an arrowhead.

It appears that what is now the DDMFZ was originally aligned on the OWL. Then about 50 Ma ago North America crashed into what is now the Olympic Peninsula along an axis nearly perpendicular to the OWL, pushing the rock of the Mesozoic (pre-Tertiary) Western and Eastern Melange Belts (WEMB, blue on the map) across the OWL, bowing the DDMFZ, and initiating the SCF and thereby splitting the Chuckanut Formation. On the north side of the DDMFZ, and wrapping around a bit to the east side, is a suite of distinctive rocks – the Helena—Haystack mélange ("HH Melange" on the map) – which was collapsed into vertical folds. Similarly distinctive rock is found in [[Manastash Ridge]] (shown on the map, but almost too small to see) still lying on the OWL, just ''east'' of the SCF.<ref>{{Harvnb|Tabor|1994}}.</ref>

This can explain an early puzzle<ref>See {{Harvnb|Davis|1977}}, p. C-33 and Figure C-10.</ref> as to why the Mesozic rocks just south of the DDMFZ – the Western and Eastern Melange Belts – have no counterpart on the east side of the OWL and offset to the south: they were not faulted by the SCF, but were pushed against it from the southwest.

Then it gets curiouser. Rock very similar to the WEMB (including a type called [[blueschist]]) is also found in the San Juan Islands, and along the West Coast fault on the west side of Vancouver Island. This suggests that the OWL was once a strike-slip fault, possibly a continental margin, along which terranes moved from the southeast. But similar rock also occurs in the Rimrock Lake Inlier, about 75 km south of the OWL and just west of the projected trace of the SCF, and also in the Klamath Mountains of southwestern Oregon.<ref>{{Harvnb|Tabor|1994}}; {{Harvnb|Brandon|1985}}; {{Harvnb|Miller|1989}}.</ref> To account for the wide dispersal of this rock is difficult; many geologists see no alternative to transport along an extended SCF. But that upsets some of the "solutions" described above, and there is yet no consensus on this.

===CLEW and Columbia Plateau===
Further east is the "CLEW", the segment of the OWL from approximately the town of Cle Elum (marking the western limit of the Columbia River basalts) to the [[Wallula Gap]] (a narrow gap on the Columbia River just north of the Oregon border). This segment, and the associated Yakima fold belts, do include many northeast-trending faults crossing the
OWL. However, these are largely [[Dip-slip faults#Dip-slip_faults|dip-slip]] (vertical) faults, associated with compressional folding of the overlying basalt. As there is typically 3 km of sedimentary deposits separating the basalts
(also about 3 km thick) from the basement rock,<ref>{{Harvnb|Rohay|Davis|1983}}.
</ref> these faults are somewhat isolated from the deeper structure. The geological consensus is that any strike-slip activity on the OWL predates the 17 Ma old [[Columbia River Basalt Group]].<ref>{{Harvnb|Caggiano|Duncan|1983}}.</ref>

There is some evidence that some of the northwest-trending ridges may have some continuity with the basement structure, but the nature and details of the deeper structure is not known.<ref>{{Harvnb|Caggiano|Duncan|1983}}.</ref>
A 260 km long [[seismic refraction]] profile<ref>
{{Harvnb|Catchings|Mooney|1988}}.
</ref>
showed a rise in the crustal basement beneath the OWL, but was unable to determine if that rise was aligned with the OWL, or just coincidentally crossed the OWL at the same location as the profile; gravity data suggested the latter. The seismic data showed a uniformity of rock type and thickness across the OWL that discounts the possibility of it being a boundary between continental and oceanic crust. The results were interpreted as suggesting [[continental rifting]] during the Eocene, perhaps a failed [[rift basin]],<ref>
But questioned by others. See {{Harvnb|Reidel|others|1993}}, p. 9, and also {{Harvnb|Saltus|1993}}.</ref> possibly connected with the rotation of the Klamath Mountain block away from the Idaho Batholith (see [[#Oregon rotation|Oregon rotation]], below).

There is a curious change of character of the OWL in the center of the CLEW where it crosses the roughly north-trending Hog Ranch—Naneum Anticline. West of there the OWL seems to follow a ridge in the basement structure, to the east it follows a gravity gradient, much like the Klamath–Blue Mountain LIneament (see [[#Columbia Embayment and KBML|below]]) does.<ref>{{Harvnb|Saltus|1993}}, p. 1258.</ref>
The significance of all this is not known.

===Hite Fault System===
Past the Wallula Gap the OWL is identified with the Wallula Fault Zone, which heads towards the [[Blue Mountains (Oregon)|Blue Mountains]]. The Wallula Fault Zone is active, but whether that can be attributed to the OWL is unknown: it may be that, like the Yakima Fold Belt, it is a result of regional stresses, and is expressed only in the superficial basalt, quite independently of what ever is happening in the basement rock.

At the western edge of the Blue Mountains the Wallula Fault zone intersects the northeast-striking Hite Fault System (HFS). This system is complex and has been variously interpreted.<ref>
{{Harvnb|Kuehn|1995}}, p. 9.</ref>
Although seismically active it appears to be offset by, and thus should be older than, the Wallula fault.<ref>
{{Harvnb|Caggiano|Duncan|1983}}; {{Harvnb|Kuehn|1995}}, p. 97. But see also {{Harvnb|Kuehn|1995}}, p. 90.
</ref>
On the other hand, a later study found "no obvious displacement" of either the OWL or HFS–related faults.<ref>{{Harvtxt|Hooper|Conrey|1989}}, p. 297.</ref> Reidel et al.<ref>{{Harvnb|Reidel|others|1993}}, see figure 3 (p. 5), and p. 9.</ref> suggested that the HFS reflects the ''eastern'' margin of a piece of old continental craton (centered around the "HF" – Hite Fault – on the [[#Cascade Range|map]]) that has slipped south; Kuehn<ref>{{Harvnb|Kuehn|1995}}, p. 95.</ref> attributed 80 to 100 kilometers of left-lateral displacement along the HFS (and significant vertical displacements).

The interaction of the Wallula and Hite Fault systems is not yet understood. Past the Hite Fault System the OWL enters a region of geological complexity and confusion, where even the trace of the OWL is less clear, even to the point where it has been suggested that both the topographic feature and the Wallula fault are terminated by the Hite fault.<ref>{{Harvnb|Caggiano|Duncan|1983}}, p. 2-17.</ref>
The original topographic lineament as described by Raisz is along the scarp on the northeast side of the Wallowa Mountains. However, there is a sense that the trend of the faulting in that area turns more to the south; it has been suggested the faulting associated with the OWL takes a large step south to the Vale Fault Zone,<ref>
{{Harvnb|Kuehn|1995}}.</ref> which connects with the Snake River Fault Zone in Idaho.<ref>
{{Harvnb|Sims|Lund|Anderson|2005}}.
</ref>
Both of these lines introduce a bend into the OWL. The Imnaha Fault (striking towards [[Riggins, Idaho]]) is more nearly in line with the rest of the OWL, and in line with the previously mentioned gravitational anomalies that run into the continent.<ref>{{Harvnb|Simpson|others|1986}}.</ref>
Which ever way is deemed correct, it is notable that the OWL seems to change character after it crosses the Hite Fault System. What this says about the nature of the OWL is unclear, although Kuehn concluded that, in northeastern Oregon or western Idaho, it is not a tectonically significant structure.

===Wallowa terrane===
{{anchor|Kuehn-map}}
As described above, the trace of the OWL becomes faint and somewhat confused between the Blue Mountains and the margin of the North American [[craton]] (the thick orange line on the [[#regional-map|map]], just beyond the Oregon—Idaho border; the dashed line on the diagram below). This is the Wallowa terrane, a piece of crust that drifted in from somewhere else and got jammed between the Columbia Embayment to the west and the North American continent to the east and north. A notable feature is the anomalously elevated [[Wallowa Mountains]], to the east is [[Hells Canyon]] (Snake River) on the Oregon—Idaho border. Northeast of the OWL (Wallowa Mountains) is the Clearwater Embayment ("CE" on the [[#regional-map|map]]), delineated by ancient rock of the craton. Southwest of this section of the OWL is a region of [[graben]]s (where large blocks of crust have dropped) extending about {{convert|60|mi|km}} south to the nearly parallel Vale Fault Zone (see diagram, below).

[[File:Kuehn95-fig46a.png|right|frame|Wallula-Vale Transfer Zone and environs.
WFZ – Wallula Fault Zone;
IF – Imnaha Fault;
WF – Wallowa Fault;
LG – La Grande Graben;
BG – Baker Graben
PG – Pine Valley Graben.

Map courtesy of [http://www.ualberta.ca/~skuehn/msthesis/Kuehn_1995_MS.pdf S. C. Kuehn.] ]]
[[Graben]]s form where the crust is being stretched or extended. Several explanations have been offered as to why this is happening here. {{Harvtxt|Kuehn|1995}} theorized that right-lateral slip on the Wallula Fault is being transferred to more southerly faults such as the Vale Fault, wherefore he labelled this region the Wallula–Vale Transfer Zone. {{Harvtxt|Essman|2003}} suggested that crustal deformation in this region is a continuation of the [[Basin and Range Province|Basin and Range]] region immediately to the south, with any connection to the OWL deemed circumstantial. Another explanation is that clock-wise rotation of part of Oregon (discussed below) about a point near the Wallula Gap has pulled the Blue Mountains away from the OWL;<ref>
{{Harvnb|McCaffrey|others|2000}}; {{Harvnb|Pezzopane|Weldon|1993}}; {{Harvnb|Dickinson|2004}}.
</ref> this might also explain why the OWL seems to be bending here.

These theories may all have some truth to them, but what they might imply regarding the genesis and structure of the OWL has not been worked out.

[[Hells Canyon]] – North America's deepest river gorge – is so deep because the terrain it cuts through is so high. This is generally attributed to thinning of the crust, which allows the hotter, and therefore lighter and more buoyant, [[mantle (geology)|mantle]] material to rise higher. This is believed by many to be involved with the [[Yellowstone hotspot]] and [[Columbia River Basalt Group|Columbia River Basalts]]; the nature of such involvement, if any, is hotly debated.<ref>
See {{Harvtxt|Christiansen|others|2002}},
[http://www.mantleplumes.org/Coffin.html "The plume coffin?"], [http://www.semp.us/publications/biot_reader.php?BiotID=218 "The Great Mantle Plume Debate"], and [ftp://rock.geosociety.org/pub/GSAToday/gt0012.pdf "Beneath Yellowstone"] ({{Harvnb|Humphreys|others|2000}}). See {{Harvtxt|Xue|Allen|2006|p=316}} for additional references.
</ref>
While the Yellowstone hotspot and Columbia River Basalts do not seem to directly interact with the OWL, clarification of their origin and context might explain some of the OWL's context, and even constrain possible models. Likewise, clarification of the nature and history of the Wallowa terrane, and particularly of the nature and causes of the apparent bending and multiple alignments of the OWL in this region, would be a major step in understanding the OWL.

===Columbia Embayment and KBML===
The bedrock of Washington and Oregon, like most of the continent, is nearly all pre-Cenozoic (or pre-Tertiary<ref>
The [[Cenozoic]] ''era'' is everything since the dinosaurs died out; the [[Tertiary]] ''period'' is all of the Cenozoic except the last 1.6 million years. For present purposes these are interchangeable.</ref>) rock, older than 66 million years. The exception is southwestern Washington and Oregon, which has virtually no pre-Cenozoic strata. This is the Columbia Embayment, a large indentation into the North American continent characterized by oceanic crust covered by thick sedimentary deposits.<ref>{{Harvnb|McKee|1972}}, p. 154; {{Harvnb|Riddihough|others|1986}}.</ref> ("Embayment" is perhaps a misleading term, in that it suggests a bowing of a coast line, which only seems so in the context of the modern coast. In the geological past, the coast of North America was in Idaho and Nevada, as will be described later.)

The Columbia Embayment is of interest here because its northern margin is approximately delineated by the OWL. The variations are mainly in the region of the [[#CLEW and Columbia Plateau|CLEW]], where sediments are buried under the basalts of the [[Columbia Basin]], and in Puget Sound, where the Cenozoic geology extends as far north as Vancouver Island.<ref>The contact between oceanic and continental crust seems to be the [[#Southern Whidbey Island Fault and RMFZ|Southern Whidbey Island Fault]], discussed below. Whether this contact extends south of the OWL is not yet known.</ref> Whether the OWL might reflect a deeper crustal boundary has been
questioned by geophysical studies which may – or may not – see the characteristics expected of such a boundary.<ref>
E.g., {{Harvtxt|Cantwell|others|1965}} sees some kind of boundary, {{Harvtxt|Catchings|Mooney|1988}} do not.</ref>

The southern edge of the Columbia Embayment is along a line from the Klamath Mountains on the Oregon coast to a point in the Blue Mountains just east of the Wallula Gap. Unlike the OWL, this line has little topographical expression,<ref>The lack of topographical relief may be due to in-filling by the Grande Ronde and Picture Gorge basalt flows (related to the Columbia River Basalts).
{{Harvnb|Hooper|Conrey|1989}}, p. 297.</ref> and aside from the Hite Fault System is not associated with any major fault systems. But mapping of gravitational anomalies shows a definite lineament, some 700 km (about 400 miles) long, called the [[Klamath-Blue Mountain Lineament]] (KBML).<ref>{{Harvnb|Riddihough|others|1986}}.</ref> This lineament is of interest here because of the possibility it was formerly conjugate with OWL, discussed in the next section.

===Oregon rotation===
Then the situation gets very interesting. Measurements of [[paleomagnetism]] (the record of the direction the rock was pointed when it cooled) from a variety of sites in the Coast Range – from the Klamath Mountains to the Olympic Peninsula – consistently measure clockwise rotations of 50 to 70 degrees.<ref>
{{Harvnb|Simpson|Cox|1977 }};
{{Harvnb|Hammond|1979 }};
{{Harvnb|Magill|Cox|1981 }};
{{Harvnb|Wells|others|1998 }};
{{Harvnb|McCaffrey|others|2000 }};
{{Harvnb|Wells|Simpson|2001 }}.
Geologists are often disturbed by the results from [[geophysical]] methods, which they attribute to various kinds of errors. Geophysicists claim their results have a consistency that precludes such errors.</ref> (See map, below.)

One interpretation of this is that western Oregon and southwestern Washington have swung as a rigid block about a pivot point at the northern end, near the Olympic Peninsula.<ref>
{{Harvnb|Simpson|Cox|1977 }};
{{Harvnb|Hammond|1979 }};
</ref>

[[File:Oregon rotation.png|right|frame|Rotation of Coast Range (light green) and Blue Mountains shown by red lines. (Authorities differ on amount and location of poles; see text.) Dashed red line is OWL; dashed blue line is KBML; intersection is approximate location of Wallula Gap.

Original map courtesy of William R. Dickinson.<ref>See {{Harvnb|Dickinson|2004}}, Fig. 8, p. 30, for an earliar version.</ref>
]]
The interesting thing is: backing out this rotation restores the Coast Range to an earlier position nearly juxtaposed against the OWL. {{Harvtxt|Hammond|1979}} argues that the Coast Range (believed to be seamounts that had previously accreted to the continent) were rifted away from the continent starting about 50 Ma ago (mid-[[Eocene]]). This interpretation implies a "[[back arc]]" of magmatism, probably fed by a subduction zone, and possibly implicated with the intrusion of various plutons in the North Cascades around 50 Ma. Curiously, this is just when the Kula–Farallon [[spreading ridge]] passed under the OWL (discussed [[#Kula|below]]). {{Harvtxt|Magill|Cox|1981}} found a spurt of rapid rotation around 45 Ma ago. This may be when this block was impinged by the Sierra Nevada block of California; {{Harvtxt|Simpson|Cox|1977}} note that around 40 Ma ago there was a change in the direction of the Pacific Plate (possibly due to collision with another plate). (The cause and nature of the rifting does not seem to have been worked out yet. Certain complications in the subduction of the Kula and Farallon plates may have been involved.)

During this rotation of the Coast Range the block of continental crust that is now the Blue Mountains (on the eastern side of the KBML) was also rifted away from the Idaho batholith, and also rotated about 50 degrees, but about a point near the Wallula Gap (or perhaps further east).<ref>{{Harvnb|Simpson|Cox|1977 }}; {{Harvnb|Dickinson|2004}}. In a later work {{Harvtxt|Dickinson|2009}} [?] leans towards a more eastern location of the hinge point, as indicated on the map.
</ref>
In the resulting gap the crust was stretched and thinned; the buoyancy of the hotter mantle have contributed to the subsequent rise of the Wallowa and Seven Devils Mountains, and perhaps also with the irruption of the [[Columbia River Basalt Group|Columbia River basalts]] and other basalt flows.

While the rigid-block rotation model has much appeal, many geologists prefer another interpretation that minimizes whole–block rotation, and instead of rifting invokes "dextral shear" (resulting from the relative motion of the Pacific plate past the North American plate, or possibly from the extension of the [[Basin and Range province]]) as the primary driving force. The large values of paleomagnetic rotation are explained by a "ball bearing" model:<ref>
{{Harvnb|Beck|1976}}.
</ref> the entire Oregon block (western Oregon including the Cascades and southwestern Washington) are deemed to be composed of many smaller blocks (on the scale of tens of kilometers), each of which rotates independently on its own axis.
Evidence of such small blocks (at least in southwestern Washington) has been claimed.<ref>
{{Harvnb|Wells|Coe|1985}}.
</ref>
Later work has attempted to work out how much of the paleomagnetic rotation reflects actual block rotation;<ref>
{{Harvnb|Wells|Heller|1988}}.
</ref>
although the amount of rotation has been reduced (to perhaps only 28°), it seems it will not entirely go away. How this affects the postulated rifting does not seem to have been addressed. A more recent work based on analysis of GPS measurements concluded that "most of the Pacific Northwest can be described by a few large, rotating, elastic crustal blocks",<ref>{{Harvnb|McCaffrey|others|2007}}, p.1338.</ref> but noted that in a zone about 50 km wide on the Oregon coast the apparent rotation rate seems to double; this suggests that multiple models may be applicable.

Modern measurements show that the central Oregon is still rotating, with the calculated rotation poles bracketing the Wallula Gap.,<ref>{{Harvnb|Wells|others|1998}}; {{Harvnb|McCaffrey|others|2000}}; {{Harvnb|Wells|Simpson|2001}}.</ref> which is approximately the intersection of the OWL and KBML. It is intriguing to consider whether the KBML has participated in this rotation, but this is unclear; that it is unbent where it crosses the OWL suggests it is not. The OWL seems to be the northern edge of the rotating block,<ref>{{Harvnb|McCaffrey|others|2000}}, p.3120, Conclusions.</ref> and the paucity of paleomagnetic data to the southeast of the KBML suggests it might be the southern edge. But the details of all this remain murky.

===Puget Sound===
[[File:Puget Sound offset.png|thumb|The west side of central Puget Sound, Holmes Harbor, and Saratoga Passage forms a lineament (between blue bars) that is offset at Port Madison (red bar).]]
Another notable feature that crosses the OWL is [[Puget Sound]], and it is curious to consider the possible implications of a Puget Sound Fault. (Such a fault was once proposed<ref>{{Harvnb|Johnson|others|1999}}.</ref> on the basis of certain marine seismic data, but the proposal was stiffly rejected, and now seems to have been abandoned.) Combined terrestrial and bathymetric topography shows a distinct lineament along the west side of Puget Sound from Vashon Island (just north of Tacoma) north to the west side of Holmes Harbor and Saratoga Passage on [[Whidbey Island]] (see image). But at [[Port Madison]] (at the red bar in the image) it is split by a distinct offset of several miles.

Curiously, the southern section lies in the approximate zone of the OWL. (Note OWL–associated lineaments running parallel to the red line.) This suggests dextral offset along a strike-slip fault. But if that is the case then there should be a major fault in the vicinity of Port Madison and crossing to Seattle (perhaps at the Ship Canal, aligned with the red line) – but for this there is even less evidence then there was for the Puget Sound fault.<ref>The southern segment of this lineament is where {{Harvtxt|Brandon|1989}} located the boundary of the Cascade orogen (the "Cenozoic Truncation Scar" in his Fig. 1). But this boundary is now known to be the South Whidbey Island Fault, which crosses Whidbey Island near Holmes Harbor and strikes southeast.
</ref>
The significance of this lineament and its offset is entirely unknown. That it seems to be expressed in Ice Age (16 Ka) deposits implies a very recent but entirely unknown event; but perhaps these recent deposits are only draped over a much older topography. A recent offset might explain the apparent offsetting of north–south glacial [[drumlins]] bisected by the Ship Canal, but is not evident in more eastern segments.

Alternately – and this would seem very pertinent in regard of the OWL – perhaps some mechanism other than strike-slip faulting creates these lineaments.

===Seattle Fault===
{{Main|Seattle Fault}}
A locally notable feature that crosses the zone of the OWL is the west-east [[Seattle Fault]]. This is not a strike-slip fault, but a [[thrust fault]], where a relatively shallow slab of rock from the south is being pushed against and over the northern part. (And over the OWL.) One model has the slab of rock being forced up by some structure about 8 km deep. Another model has the base of the slab (again, about 8 km deep) catching on something, which causes the leading edge to roll.<ref>{{Harvnb|Kelsey|others|2008}}. See {{Harvnb|Johnson|others|2004}} Fig. 17 for cross-sections of several models.</ref> The nature of the underlying structure is not known; geophysical data does not indicate a major fault nor any kind of crustal boundary along the front of the Seattle Fault, nor along the OWL, but this could be due to the limited reach of geophysical methods. Recent geological mapping at the eastern side of the Seattle Fault<ref>DGER Geological Map {{Harvnb|GM73|p. 24+}}.</ref> suggests a [[decollement]] (horizontal plane) about 18 km deep.

These models were developed in study of the western segment of the Seattle Fault. In the center segment, where it crosses surface exposures of Eocene rock associated with the OWL, the various strands of the fault – elsewhere fairly orderly – meander. The significance of this and the nature of the interaction with the Eocene rock are also not known.<ref>{{Harvnb|Blakely|others|2002}}.</ref>

Examination of the various strands of the Seattle Fault, particularly in the central section, is similarly suggestive of ripples in a flow that is obliquely crossing some deeper sill. This is an intriguing idea that could explain how local and seemingly independent features could be organized from depth, and even across a large scale, but it does not seem to have been considered. This is likely due, in part, to a paucity of information on the nature and structure of the lower crust where such a sill would exist.

===Southern Whidbey Island Fault and RMFZ ===
The Southern Whidbey Island Fault (SWIF), running nearly parallel to the OWL from Victoria, B.C., southeast to the Cascade foothills to a point northeast of Seattle, is notable as the contact between the Coast Range block of oceanic crust to the west and the Cascades block of pre-Tertiary continental crust to the east.<ref>{{Harvnb|Johnson|others|1996}}.</ref>
It appears to connect with the more southerly oriented right-lateral Rattlesnake Mountain Fault Zone (RMFZ) straddling Rattlesnake Mountain (near North Bend), which shows a similar deep-seated contact between different kinds of basement rock.<ref>DGER Geological Map {{Harvnb|GM67}}.</ref> At the southern end of Rattlesnake Mountain – exactly where the first lineament of the OWL is encountered – at least one strand of the RMFZ (the others are hidden) turns to run by Cedar Falls and up the Cedar River. Other faults to the south also show a similar turn,<ref>DGER Geological Map {{Harvnb|GM50}}. Recent mapping (DGER Geological Map {{Harvnb|GM73}}) shows a multiplicity of fault strands; it is possible that these seemingly arcuate faults may be artefacts of slightly confused mapping.</ref> suggesting a general turning or bending across the OWL, yet such a bend is not apparent in the pattern of physiographic features that express the OWL. With awareness that the Seattle Fault and the RMFZ are the edges of a large sheet of material which is moving north, there is a distinct impression that these faults, and even some of the topographical features, are flowing around the corner of the Snoqualmie Valley. If it seems odd that a mountain should "float" around a valley: bear in mind that while the surface relief is about three-quarters of a kilometer (half a mile) in height, the material flowing could be as much as eighteen kilometers deep.<ref>DGER Geological Map {{Harvnb|GM73|p=13}}.</ref> (The analogy of icebergs moving around a submerged sandbar is quite apt.) It is worth noting that [http://www.scn.org/cedar_butte Cedar Butte] – a minor prominence just east of Cedar Falls – is the southwestern-most exposure in the region of some very old Cretaceaous (pre-Tertiary) metamorphic rock.<ref>DGER Geological Map {{Harvnb|GM50}}.</ref> It seems quite plausible that there is some well-founded and obdurate obstruction at depth, around which the shallower and younger sedimentary formations are flowing. In such a context the observed arcuate fault bends would be very natural.

==Broader context==
It is generally assumed that the pattern of the OWL is a manifestation of some deeper physical structure or process (the "ur-OWL"), which might be elucidated by studying the effects it has on other structures. As has been shown, study of features that should interact with OWL has yielded very little: a tentative age range (between 45 and 17 million years), suggestions that the ur-OWL arises from deep in the crust, and evidence that the OWL is not (contrary to expectations) itself a boundary between oceanic and continental crust.

The lack of results so far suggests that the broader context of the OWL should be considered. Following are some elements of that broader context, which may – or may not – relate in some way to the OWL.


===Plate tectonics===
{{Main|Plate tectonics}}
The broadest and fullest context of the OWL is the global system of [[plate tectonics]], driven by convective flows in the Earth's mantle. The primary story on the western margin of North America is the accretion, subduction, obduction, and translation of plates,
micro-plates, terranes, and crustal blocks between the converging Pacific and North American plates. (For an excellent geological history of Washington, including plate tectonics, see the [http://www.washington.edu/burkemuseum/geo_history_wa Burke Museum web site].)

The principal tectonic plate in this region (Washington, Oregon, Idaho) is the [[North American plate]], consisting of a [[craton]] of ancient, relatively stable [[continental crust]] and various additional parts that have been accreted; this is essentially the whole of the North American continent. The interaction of the North American plate with various other plates, terranes, etc., along its western margin is the primary engine of geology in this region.

Since the breakup of the [[Pangaea]] supercontinent in the [[Jurassic]] (about 250 million years ago) the main tectonic story here has been the North American Plate's subduction of the [[Farallon Plate]] (see below) and its remaining fragments (such as the [[Kula Plate|Kula]], [[Juan de Fuca Plate|Juan de Fuca]], [[Gorda Plate|Gorda]], and [[Explorer Plate|Explorer]] plates). As the North American plate overrides the last of each remnant it comes into contact with the Pacific Plate, generally forming a [[transform fault]], such as the [[Queen Charlotte Fault]] running north of [[Vancouver Island]], and the [[San Andreas Fault]] on the coast of California. Between these is the [[Cascadia subduction zone]], the last portion of a subduction zone that once stretched from Central America to Alaska.

This has not been a steady process. 50 Ma (million years) ago<ref>{{Harvnb|Sharp|Clague|2006}}.</ref> there was a change in the direction of motion of the Pacific plate (as recorded in the bend in the [[Hawaiian-Emperor seamount chain]]). This had repercussions on all the adjoining plates, and may have had something to do with initiation of the Straight Creek Fault,<ref>{{Harvnb|Vance|Miller|1994}}.</ref> and the end of the [[Laramide orogeny]] (the uplift of the [[Geology of the Rocky Mountains|Rocky Mountains]]). This event may have set the stage for the OWL, as much of the crust in which it is expressed was formed around that epoch (the early [[Eocene]]); this may be when the story of the OWL starts. Other evidence suggests a similar plate reorganization around 80 Ma,<ref>{{Harvnb|Umhoefer|Miller|1996}}, p.561.</ref> possibly connected with the start of the Laramide orogeny. {{Harvtxt|Ward|1995}} claimed at least five "major chaotic tectonic events since the Triassic". Each of these events is a possible candidate for creating some condition or structure that affected the OWL or ur-OWL, but knowledge of what these events were or their effects is itself still chaotic.

Complicating the geology is a stream of [[terranes]] – crustal blocks – that have been streaming north along the continental margin<ref>{{Harvnb|Jones|others|1977}};{{Harvnb|Jones|others|1982}}; {{Harvnb|Cowan|1982}}.</ref> for over 120 Ma<ref>{{Harvnb|McClelland|Oldow|2007}} [?].</ref> (and probably much, much earlier), what has recently been called the ''North Pacific Rim orgenic Stream'' (NPRS).<ref>{{Harvnb|Redfield|others|2007}}.</ref> However, these terranes may be incidental to the OWL, as there are suggestions that local tectonic structures may be substantially affected by deeper and much older (e.g., [[Precambrian]]) basement rock, and even lithospheric mantle structures.<ref>{{Harvnb|Sims|Lund|Anderson|2005}}; {{Harvnb|Karlstrom|Humphreys|1998}}.</ref>

===Subduction of the Farallon and Kula Plates===

{{anchor|Kula}}
Roughly 205 million years ago (during the [[Jurassic]] period) the [[Pangaea]] supercontinent began to break up as a [[rift]] separated the [[North American Plate]] from what is now Europe, and pushed it west against the [[Farallon Plate]]. During the subsequent [[Cretaceous Period]] (144 to 66 Ma ago) the entire Pacific coast of North America, from Alaska to Central America, was a [[subduction zone]]. The Farallon plate is notable for having been very large, and for subducting nearly horizontally under much of the United States and Mexico; it is likely connected with the [[Laramide Orogeny]].<ref>
{{Harvnb|Riddihough|1982}};
[http://www.washington.edu/burkemuseum/geo_history_wa/ Burke Museum].
</ref> About 85 Ma ago the part of the Farallon plate from approximately California to the Gulf of Alaska separated to form the [[Kula Plate]].<ref>
{{Harvnb|Stock|Molnar|1988}};
{{Harvnb|Woods|Davies|1982}};
{{Harvnb|Haeussler|others|2003}};
{{Harvnb|Norton|2006}};
{{Harvnb|Wyld|others|2006}}.
</ref>

The period 48–50 Ma (mid-Eocene) is especially interesting as this is when the subducted Kula—Farallon [[spreading ridge]] passed below what is now the OWL.<ref>{{Harvnb|Breitsprecher|others|2003}}. A slightly variant view is that this piece of the Kula plate had broken off to form the Resurrection Plate {{Harv|Haeussler|others|2003}}, so this was actually the ''Resurrection''—Farallon spreading ridge.</ref> (The Burke Museum has some [http://www.washington.edu/burkemuseum/geo_history_wa/The%20Challis%20Episode.htm nice diagrams] of this.) This also marks the onset of the [[#Oregon rotation|Oregon rotation]], possibly with rifting along the OWL,<ref>{{Harvnb|Simpson||Cox|1977}}; {{Harvnb|Hammond|1979}}.</ref> and the initiation of the Queen Charlotte and Straight Creek Faults.<ref>{{Harvnb|Vance|Miller|1994}}.</ref> The timing seems significant, but how all of these might be connected is unknown.

Around 30 Ma ago part of the spreading center between the Farallon Plate and [[Pacific Plate]] was subducted under California, putting the Pacific plate into direct contact with the North American plate and creating the [[San Andreas Fault]]. The remainder of the Farallon Plate split, with the part to the north becoming the [[Juan de Fuca Plate]]; parts of this subsequently broke off to form the [[Gorda Plate]] and [[Explorer Plate]]. By this time the last of the [[Kula Plate]] had been subducted, initiating the [[Queen Charlotte Fault|Queen Charlotte]] transform fault on the coast of British Columbia; coastal subduction has been reduced to just the [[Cascadia Subduction Zone]] under Oregon and Washington.<ref>{{Harvnb|Riddihough|1982}}; {{Harvnb|Wyld|others|2006}};
[http://www.washington.edu/burkemuseum/geo_history_wa/ Burke Museum].</ref>

===Newberry Hotspot Track – Brothers Fault Zone===
[[File:Newberry-Yellowstone tracks.png|thumbnail|350px|Age progressive rhyolitic lavas (light blue) from the McDermitt Caldera (MC) to the Yellowstone Caldera (YC) track the movement of the North American plate over the Yellowstone Hotspot. Similar age progressive lavas across the High Lava Plains (HLP) towards the Newberry Caldera (NC) have been termed the Newberry Hotspot Track, but this goes the wrong direction to be attributed to movement of the plate over a hotspot. Numbers are ages in millions of years. VF = Vale Fault, SMF = Steens Mountain Fault, NNR = North Nevada Rift.]]
The Newberry Hotspot Track – a series of volcanic domes and lava flows closely coincident with the [[Brothers Fault Zone]] (BFZ) – is of interest because it is parallel to the OWL. Unlike anything on the OWL, these lava flows can be dated, and they show a westward age progression from an origin at the McDermitt Caldera on the Oregon-Nevada border to the [[Newberry Volcano]]. Curiously, the [[Yellowstone hotspot]] also appears to have originated in the vicinity of the McDermitt Caldera, and is generally considered to be closely associated with the Newberry magmatism.<ref>{{Harvnb|Xue|Allen|2006}}; {{Harvnb|Christiansen|others|2002}}; {{Harvnb|Shervais|Hanan|2008}}.</ref>
But while the track of the Yellowstone hotspot across the Snake River Plain conforms to what is expected from the motion of the [[North American Plate]] across some sort of "hotspot" fixed in the underlying mantle, the Newberry "hotspot" track is oblique to the motion of the North American Plate; this is inconsistent with the [[hotspot (geology)|hotspot model]].

Alternative models include:<ref>{{Harvnb|Xue|Allen|2006}}.</ref> 1) flow of material from the top layer of the mantle (asthenosphere) around the edge of the Juan de Fuca Plate (a.k.a. "Vancouver slab", 2) flows reflecting lithospheric topography (such as the edge of the craton), 3) faulting in the [[lithosphere]], or 4) extension of the [[Basin and Range province]] (which in turn may be due to interactions between the North American, Pacific, and Farallon Plates, and possibly with the subduction of the [[triple point]] where the three plates came together), but none is yet fully accepted.<ref>E.g., {{Harvtxt|Xue|Allen|2006}} concluded that the Newberry track is the product of a lithosphere-controlled process (such as lithospheric faulting or Basin and Range extension); {{Harvtxt|Zandt|Humphreys|2008}} disagree, arguing for mantle flow around the sinking Gorda—Juan de Fuca slab.</ref>
These models generally attempt to account only for the source of the Newberry magmatism, attributing the "track" to pre-existing weakness in the crust. No model yet accounts for the particular orientation of the BFZ, or the parallel Eugene-Denio or Mendocino Fault Zones (see [[#regional-map|map]]).

===Bermuda Hotspot Track?===
It was noted as early as 1963<ref>{{Harvnb|Wise|1963}}, see figure 2.</ref> that the OWL seems to align with the [[Kodiak-Bowie Seamount chain]]. A 1983 paper by Morgan<ref>{{Harvnb|Morgan|1983}}, recapitulated by {{Harvtxt|Vink|Morgan|Vogt|1985}} in a popular article in ''Scientific American''.</ref> suggested that this seamount—OWL alignment marks the passage some 150 Ma ago of the [[Bermuda hotspot]]. (This same passage has also been invoked to explain the [[Mississippi Embayment]].<ref>{{Harvnb|Cox|Van Arsdale|2002}}.</ref>) However, substantial doubt has been raised as to whether Bermuda is truly a "hotspot",<ref>{{Harvnb|Vogt|Jung|2007a}}.</ref> and lacking any supporting evidence this putative hotspot track is entirely speculative.

The 1983 paper also suggested that passage of a hot spot weakens the continental crust, leaving it vulnerable to rifting. But might the relation might actually run the other way: do some of these "hotspots" accumulate in zones where the crust is already weakened (by means as yet unknown)? The supposed Newberry hotspot track may exemplify this (see Megashears, below), but application of this concept more generally is not yet accepted. Application to the OWL would require resolving some other questions, such as how traces of a ca. 150 Ma event resisted being swept north into Alaska to influence a structure believed to be no older than 41 Ma (see [[#Straight Creek Fault|Straight Creek Fault]]). Possibly there is some explanation, but geology has not yet found it.

===Orofino Shear Zone===
The OWL gets faint, perhaps even terminates, just east of the Oregon—Idaho border where it hits the north-trending ''Western Idaho Shear Zone'' (WISZ),<ref>Also known as the western Idaho ''suture'' zone, or the Salmon River suture zone, depending on what portion of its long history is being addressed. {{Harvnb|Fleck|Criss|2004}}, pp. 2—3; {{Harvnb|Giorgis|others|2008}}, pp. 1119—1120.</ref> a nearly vertical tectonic boundary between the accreted oceanic terranes to the west and the plutonic and metamorphic rock of the North American [[craton]] (the ancient continental core) to the east. From the [[Mesozoic]] till about 90 Ma (mid-[[Cretaceous]]) this was the western margin of the North American continent, into which various off-shore terranes were crashing into and then sliding to the north.

Near the town of Orofino (just east of Lewiston, Idaho) something curious happens: the craton margin makes a sharp right-angle bend to the west. What actually happens is the truncation of the WISZ by the WNW-trending ''Orofino Shear Zone'' (OSZ), which can be traced west roughly parallel with the OWL until it disappears below the Columbia River Basalts, and southeast across Idaho and possibly beyond. The truncation occurred between 90 to 70 Ma ago, possibly due to the docking of the [[Insular Belt|Insular super-terrane]] (now the coast of British Columbia).<ref>{{Harvnb|McClelland|Oldow|2007}}; {{Harvnb|Giorgis|others|2008}}, pp. 1119, 1129, 1131.</ref> This was a major left-lateral transform fault, with the northern continuation of the WISZ believed to be one of the faults in the North Cascades. A similar offset is seen between the Canadian Rocky Mountains in British Columbia and the American Rocky Mountains in southern Idaho and western Wyoming.<ref>{{Harvnb|Wise|1963}}, p. 357, and figure 1. See also figure 1 of {{Harvnb|O'Neil|others|2007}} and figure 1 of {{Harvnb|Hildebrand|2009}}.</ref>

Then another curious thing happens: before the west-trending craton margin turns north, it seems to loop south towards Walla Walla (near the Oregon border) and the Wallula Gap (see [[#regional-map|orange-line here]], or [[#Kuehn-map|dashed-line here]]). (Although southeastern Washington is pretty thoroughly covered by the Columbia River Basalts, a borehole in this loop recovered rock characteristic of the craton.<ref>{{Harvnb|Reidel|others|1993}}, p.9, and see figure 3 (p. 5).</ref>) It seems that the OSZ may have been offset, perhaps by the [[#Hite Fault System|Hite Fault]], but, contrary to the regional trend, headed south. If this is a cross-cutting offset it would have to be younger than the OFZ (less than 70 Ma), and older than the OWL, which it does not offset. That the OWL and the OFZ are parallel (along with many other structures) suggests something in common, perhaps a connection at a deeper level. But this offsetting relationship indicates that they were created separately.

===Megashears===
The OFZ (also called the Trans-Idaho Discontinuity) is a local segment of a larger structure that has only recently been recognized, the ''Great Divide Megashear''.<ref>{{Harvnb|O'Neil|others|2007}}.</ref> East of the WISZ this turns to the southeast (much as the OWL may be doing past the Wallula Gap) to follow the Clearwater fault zone down the continental divide near the Idaho—Montana border to the northwestern corner of Wyoming. From there it seems to connect with the Snake River—Wichita fault zone, which passes through Colorado, and Oklahoma.,<ref>{{Harvnb|Sims|others|2001}}; {{Harvnb|Sims|Lund|Anderson|2005}}. A few sources have described this general trend the Olympic—''Wichita'' Lineament (e.g., see {{Harvnb|Vanden Berg|2005}}, or the
[http://www.colorado.edu/GeolSci/Resources/WUSTectonics/AncestralRockies/transtension.html Transtension in the West] article). This is inaccurate. The Great Divide Megashear, even if it existed past the Cascades, would be well north of the Olympic Peninsula, while the OWL, if it is presumed to connect with the Snake Fault zone (via the Vale zone) misses the Great Divide Megashear, and likely Wichita as well. This lineament is said to dextrally offset the ''Colorado Lineament'', said to run from the Grand Canyon to Lake Superior.{{Harv|Vanden Berg|2005}}.</ref> and possibly further.<ref>A "Montana—Florida Lineament" and even a "Mackenzie—Missouri Lineament" (from the Mackenzie River valley in the Yukon to Florida) have been claimed by Carey (see [http://web.archive.org/web/20091026204116/http://www.geocities.com/CapeCanaveral/Launchpad/8098/2.htm excerpts from his book]), but are not generally recognized. For an interesting trip outside of main-stream science read about the [[Expanding Earth]] theory.
</ref>
There is a significant age discrepancy here. Whereas the OFZ is a mere 90 to 70 Ma old, this megashear is ancient, having been dated to the [[Mesoproterozoic]] – about a billion years ago. The Snake River—Wichita fault zone is of a similar age. What appears to be happening is exploitation of ancient weaknesses in the crust. This could explain the Newberry "hotspot track": parallel weaknesses in the crust open as the Brothers, Eugene—Denio, and Mendocino Fault Zones in response to development of the [[Basin and Range Province]]; magma from the event that initiated the Yellowstone hotspot (and possibly the Columbia River and other basalt flows) simply exploits the faults of the Brothers Fault Zone. The other faults do not develop as "hotspot tracks" simply because there is no magma source nearby. Similarly, it may be that the OWL reflects a similar zone of weakness, but does not develop as a major fault zone because it is too far from the stresses of the Basin and Range Province.

This could also explain why the OWL seems possibly aligned with the [[Kodiak-Bowie Seamount chain]] in the Gulf of Alaska, especially as the apparent motion is the wrong direction for the OWL to be a mark of their past passage. They are also on the other side of the spreading centers, though that does suggest a pure speculation that these postulated zones of weakness could be related to transform faults from the spreading center.

===Precambrian basement===
Following the Great Divide Megashear into the mid-continent reveals something interesting: a widespread pattern of similarly trending (roughly NW-SE) fault zones, rifts, and aeromagnetic and gravitational anomalies.<ref>Especially dramatic is the 2005 "Precambrian Crystalline Basement Map of Idaho" {{Harv|Sims|Lund|Anderson|2005}}. See also {{Harvnb|Marshak|Paulsen|1996}}, {{Harvnb|Sims|others|2001}}, {{Harvnb|Vanden Berg|2005}}, and numerous others.
</ref> Although some of the faults are recent, the NW trending zones themselves have been attributed to continental-scale transcurrent shearing at about 1.5 [[annum|Ga]] – that's ''billions'' of years ago – during the assembly of [[Laurentia]] (the North American continent).<ref>{{Harvnb|Sims|Lund|Anderson|2005}}; {{Harvnb|Sims|Saltus|Anderson|2005}}.</ref>

Curiously, there is another widespread pattern of parallel fault zones, etc., of various ages trending roughly NE-SW, including the [[Midcontinent Rift System]], the [[Reelfoot Rift]] (in the [[New Madrid Seismic Zone]]), and others.<ref>The [[#Columbia Embayment and KBML|KBML]] and other less well known trends in Oregon and Washington have a similar orientation, but
the context is so different that they are generally excluded from studies of midcontinental geology.</ref> These fault zones and rifts occur on tectonic boundaries that date to the [[Proterozoic]] – that is, 1.8 to 1.6 billions of years old.<ref>{{Harvnb|Karlstrom|Humphreys|1998}}, p. 161.</ref> They are also roughly parallel to the [[Ouachita orogeny|Ouachita]]— [[Alleghenian orogeny|Appalachian mountains]], raised when [[Laurentia]] merged with the other continents to form the [[Pangaea]] supercontinent some 350 million years ago. It is now believed that these two predominant patterns reflect ancient weaknesses in the underlying [[Precambrian]] [[basement (geology)|basement]] rock,<ref>{{Harvnb|Sims|Saltus|Anderson|2005}}.</ref> which can be reactivated to control the orientation of features formed much later.<ref>{{Harvnb|Holdsworth|others|1997}}.</ref>

Such linkage of older and younger features seems very relevant to the OWL's troubling age relationships. The possible involvement of the deep Precambrian basement does suggest that what we see as the OWL might be just the expression in shallower and transitory terranes and surface processes of a deeper and persistent ur-OWL, just as ripples in a stream may reflect a submerged rock, and suggests that surficial expression of the OWL may need to be distinguished from a deepr ur-OWL. But neither the applicability of this to the OWL nor any details have been worked out.

==Puzzle pieces==
How any of the broader context relates to the OWL is unknown, as nothing is known of the nature of the ur-OWL. When the story is finally known it may be that the significance of some of these elements is in their non-significance.<ref>
Like in Arthur Conan Doyle's story "[[White Blaze]]", where Sherlock Holmes refers to "the curious incident of the dog in the night-time." "The dog did nothing in the night-time", says Inspector Gregory. "That was the curious incident."
</ref>

In attempting to solve puzzles it is often the case that pieces seem impossible to fit – until we discover we have been holding them the wrong way. It is often the same way with scientific puzzles. In an article titled "The value of outrageous geological hypotheses", {{Harvtxt|Davis|1926}} mentioned "the Wegener outrage of wandering continents". It is instructive to note that the similarity of the western and eastern shores of the Atlantic Ocean – obvious even to a schoolchild – was long a puzzle. It seemed to require choosing between obvious impossibilities: either some kind of control of shore-line building processes over thousands of miles apart, or "wandering continents". Either of these seemed outrageous. Wegener's [[theory of continental drift]], first published in 1912, was rejected on the basis of impossibility until the theory of [[plate tectonics]] explained ''how'' continents could 'wander'. Such reinterpretation of concepts and evidence seems characteristic of the resolution of puzzles; it is intriguing to consider what modifications and extensions will result when the puzzle of the OWL is finally solved.

Retrospectively the solution may seem "obvious", with future generations wondering why we could not sort it out. Perhaps it will be obvious – once we get all the pieces turned around the right way up.

==Summary: What we know about the OWL==
* First reported by Erwin Raisz in 1945.
* Seems to have more depressions and basins on the north side.
* Associated with many right-lateral strike-slip fault zones.
* Seems to be expressed in Quaternary (recent) glacial deposits.
* Does not offset Columbia River Basalts, so older than 17 million years.
* Not offset by the Straight Creek Fault, so probably younger than 41 million years. (Maybe.)
* Approximately separates oceanic-continental provinces.
* Not an oceanic-continental crustal boundary. (Maybe.)
* Not a hotspot track. (Maybe.)
* Seems to be aligned with lithospheric flow from the Juan de Fuca Ridge.
* Seems to be faint and confused in Oregon.

==See also==
*[[Geology of the Pacific Northwest]]

==Notes==
{{reflist|2}}

==References==
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OSTI: DOE's [http://www.osti.gov/bridge Office of Scientific and Technical Information].
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==External links==
*[http://www.washington.edu/burkemuseum/geo_history_wa Burke Museum web site] Geologic history of Washington.
*[http://www.northwestgeology.com Evolution of the Pacific Northwest] Good text on the geology of Cascadia.

[[Category:Geology of Oregon]]
[[Category:Geology of Washington (state)]]

Biosignatur

2013-09-01T21:21:58Z

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{{other uses2|Biomarker}}
A '''biosignature''' is any substance – such as an element, [[isotope]], [[molecule]], or [[phenomenon]] – that provides [[scientific evidence]] of past or present [[life]].<ref name=SSG >{{Cite book| first=Beaty | last=Steele| coauthors=''et al.''| contribution=Final report of the MEPAG Astrobiology Field Laboratory Science Steering Group (AFL-SSG)| title=The Astrobiology Field Laboratory | publisher=the Mars Exploration Program Analysis Group (MEPAG) - NASA| place=U.S.A.| pages=72| date=September 26, 2006| id= | contribution-url=http://mepag.jpl.nasa.gov/reports/AFL_SSG_WHITE_PAPER_v3.doc| format=.doc| accessdate=2009-07-22| postscript=. }}</ref><ref>{{cite web | url = http://www.science-dictionary.com/definition/biosignature.html | title = Biosignature - definition | accessdate = 2011-01-12 | year = 2011 | work = Science Dictionary}}</ref><ref name='Biosignatures 2011'> {{cite journal | title = Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group | journal = The Astrobiology Journal | date = 23 February 2011 | first = Roger E. | last = Summons | coauthors = Jan P. Amend, David Bish, Roger Buick, George D. Cody, David J. Des Marais | volume = 11 | issue = 2 | doi = 10.1089/ast.2010.0506 | url = http://eaps.mit.edu/geobiology/recent%20pubs/AST-2010-0506-Summons_Mars%20Taphonomy.pdf | accessdate = 2013-06-22|bibcode = 2011AsBio..11..157S }}</ref> Measurable attributes of life include its complex physical and chemical structures and also its utilization of [[Thermodynamic free energy|free energy]] and the production of [[biomass]] and [[Cellular waste product|wastes]]. Due to its unique characteristics, a biosignature can be interpreted as having been produced by living [[organisms]]; however, it is important that they not be considered definitive because there is no way of knowing in advance which ones are universal to life and which ones are unique to the peculiar circumstances of life on Earth.<ref>{{cite web | url = http://astrobiology.nasa.gov/nai/library-of-resources/annual-reports/2003/cub/projects/philosophical-issues-in-astrobiology/ | title = Philosophical Issues in Astrobiology | accessdate = 2011-04-15 | last = Carol Cleland | first = | coauthors = Gamelyn Dykstra, Ben Pageler | year = 2003 | publisher = NASA Astrobiology Institute}}</ref>

==In geomicrobiology==
[[File:Calcidiscus leptoporus 05.jpg|thumb|Electron micrograph of microfossils from a sediment core obtained by the [[Deep Sea Drilling Program]] ]]
The ancient record on Earth provides an opportunity to see what geochemical signatures are produced by microbial life and how these signatures are preserved over geologic time. Some related disciplines such as [[geochemistry]], [[geobiology]], and [[geomicrobiology]] often use biosignatures to determine if living [[organism]]s are or were present in a sample. These possible biosignatures include: (a) [[microfossils]] and [[stromatolites]]; (b) molecular structures ([[biomarkers]]) and [[Isotope|isotopic compositions]] of carbon, nitrogen and hydrogen in [[organic matter]]; (c) multiple sulfur and oxygen isotope ratios of minerals; and (d) abundance relationships and isotopic compositions of redox sensitive metals (e.g., Fe, Mo, Cr, and rare earth elements).<ref name='PSARC'>{{cite web | url = http://php.scripts.psu.edu/dept/psarc/index.php?page=executive-summary | title = SIGNATURES OF LIFE FROM EARTH AND BEYOND | accessdate = 2011-01-14 | year = 2009 | work = Penn State Astrobiology Research Center (PSARC) | publisher = Penn State}}</ref><ref>{{cite web | url = http://astrobiology.nasa.gov/articles/reading-archaean-biosignatures/ | title = Reading Archaean Biosignatures | accessdate = 2011-01-14 | first = David Tenenbaum | date = July 30, 2008 | publisher = NASA}}</ref>

For example, the particular [[fatty acids]] measured in a sample can indicate which types of [[bacterium|bacteria]] and [[archaea]] live in that environment. Another example are the long-chain [[fatty alcohol]]s with more than 23 atoms that are produced by [[plankton]]ic [[bacteria]].<ref>[http://www.cyberlipid.org/simple/simp0003.htm Fatty alcohols]</ref> When used in this sense, geochemists often prefer the term [[biomarker]]. An other example is the presence of straight-chain [[lipids]] in the form of [[alkanes]], [[alcohols]] an [[fatty acids]] with 20-36 [[carbon]] atoms in soils or sediments. [[Peat]] deposits are an indication of originating from the [[epicuticular wax]] of higher [[plant]]s.

Life processes may produce a range of biosignatures such as [[nucleic acids]], [[lipid]]s, [[protein]]s, [[amino acid]]s, [[kerogen]]-like material and various morphological features that are detectable in rocks and sediments.<ref name=Beegle >{{cite journal|title=A Concept for NASA's Mars 2016 Astrobiology Field Laboratory |journal=Astrobiology|date=August 2007|first=Luther W.|last=Beegle|coauthors=et al |volume=7 |issue=4|pages=545–577|id= |url=http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0153?cookieSet=1|format=|accessdate=2009-07-20|doi=10.1089/ast.2007.0153|postscript=. |pmid=17723090 |bibcode=2007AsBio...7..545B}}</ref>
[[Microbes]] often interact with geochemical processes, leaving features in the rock record indicative of biosignatures. For example, bacterial micrometer-sized pores in [[carbonate rock]]s resemble inclusions under transmitted light, but have distinct size, shapes and patterns (swirling or dendritic) and are distributed differently from common fluid inclusions.<ref>{{cite journal | title = Micrometer-scale porosity as a biosignature in carbonate crusts | last1 = Bosak | journal = Geology | date = May 18, 2004 | first = Tanja Bosak | coauthors = Virginia Souza-Egipsy, Frank A. Corsetti and Dianne K. Newman | volume = 32 | issue = 9 | pages = 781–784 | doi = 10.1130/G20681.1 | url = http://geology.gsapubs.org/content/32/9/781.abstract | accessdate = 2011-01-14 | bibcode=2004Geo....32..781B}}</ref> A potential biosignature is a phenomenon that ''may'' have been produced by life, but for which alternate [[Abiotic component|abiotic]] origins may also be possible.

==In astrobiology==
[[File:ALH84001 structures.jpg|thumb|right|Some researchers suggested that these microscopic structures on the Martian [[ALH84001]] meteorite could be fossilized bacteria.<ref name=disbelief>{{cite web | title=After 10 years, few believe life on Mars | url=http://www.usatoday.com/tech/science/space/2006-08-06-mars-life_x.htm | last=Crenson | first=Matt | publisher=[[Associated Press]] (on [http://www.usatoday.com/ usatoday.com]) | date=2006-08-06 | accessdate=2009-12-06}}</ref><ref name="life">{{cite journal |last=McKay |first=David S. |authorlink= |coauthors=''et al.'' |year=1996 |month= |title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 |journal=Science |pmid=8688069 |volume=273 |issue=5277 |pages=924–930 |doi=10.1126/science.273.5277.924 |url= |accessdate= |quote= |bibcode=1996Sci...273..924M}}</ref>]]
[[Astrobiology|Astrobiological exploration]] is founded upon the premise that biosignatures encountered in space will be recognizable as [[extraterrestrial life]]. The usefulness of a biosignature is determined, not only by the probability of life creating it, but also by the improbability of nonbiological (abiotic) processes producing it.<ref name=astrobiology >{{cite web|url=http://astrobiology.arc.nasa.gov/roadmap/g5.html |title=Understand the evolutionary mechanisms and environmental limits of life |accessdate=2009-07-13 |last=Rothschild |first=Lynn |date=September, 2003 |publisher=NASA }}</ref> An example of such a biosignature might be complex [[Organic compound|organic molecules]] and/or structures whose formation is virtually unachievable in the absence of life. For example, some categories of biosignatures can include the following: cellular and extracellular morphologies, [[biogenic substance]] in rocks, bio-organic molecular structures, [[chirality]], [[Biogenic silica|biogenic minerals]], biogenic stable isotope patterns in minerals and organic compounds, atmospheric gases, and remotely detectable features on planetary surfaces, such as [[photosynthetic pigment]]s, etc.<ref name=astrobiology />

Biosignatures need not be chemical, however, and can also be suggested by a distinctive [[magnetic]] biosignature.<ref name="Wall-20111213">{{cite web |last=Wall |first=Mike |title=Mars Life Hunt Could Look for Magnetic Clues |url=http://www.space.com/13911-mars-life-search-magnetic-signatures.html |date=13 December 2011 |publisher=[[Space.com]] |accessdate=2011-12-15 }}</ref> Another possible biosignature might be [[Morphology (biology)|morphology]] since the shape and size of certain objects may potentially indicate the presence of past or present life. For example, microscopic [[magnetite]] crystals in the Martian [[meteorite]] [[ALH84001]] were the longest-debated of several potential biosignatures in that specimen because it was believed until recently that only bacteria could create crystals of their specific shape. However, anomalous features discovered that are "possible biosignatures" for life forms would be investigated as well. Such features constitute a working [[hypothesis]], not a confirmation of detection of life. Concluding that evidence of an extraterrestrial life form (past or present) has been discovered, requires proving that a possible biosignature was produced by the activities or remains of life.<ref name=SSG /> For example, the possible [[Biomineralisation|biomineral]] studied in the Martian [[ALH84001|ALH84001 meteorite]] includes putative microbial [[fossils]], tiny rock-like structures whose shape was a potential biosignature because it resembled known bacteria. Most scientists ultimately concluded that these were far too small to be fossilized [[cell (biology)|cell]]s. A consensus that has emerged from these discussions, and is now seen as a critical requirement, is the demand for further lines of evidence in addition to any morphological data that supports such extraordinary claims.<ref name=SSG />

Scientific observations include the possible identification of biosignatures through indirect observation. For example, [[Electromagnetic radiation|electromagnetic]] information through infrared radiation telescopes, radio-telescopes, space telescopes, etc.<ref name='Gardner'>{{cite web | url = http://www.kurzweilai.net/the-physical-constants-as-biosignature-an-anthropic-retrodiction-of-the-selfish-biocosm-hypothesis | title = The Physical Constants as Biosignature: An anthropic retrodiction of the Selfish Biocosm Hypothesis | accessdate = 2011-01-14 | last = Gardner | first = James N. | date = February 28, 2006 | publisher = Kurzweil}}</ref><ref name=BC>{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | accessdate = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet}}</ref> From this discipline, the hypothetical electromagnetic radio signatures that [[SETI]] scans for would be a biosignature, since a message from intelligent aliens would certainly demonstrate the existence of extraterrestrial life.

On [[Mars]], surface oxidants and UV radiation will have altered or destroyed organic molecules at or near the surface.<ref name='Biosignatures 2011'/> One issue that may add ambiguity in such a search is the fact that, throughout Martian history, abiogenic organic-rich [[Chondrite|chondritic meteorite]]s have undoubtedly rained upon the Martian surface. At the same time, strong [[Oxidizing agent|oxidants]] in [[Martian soil]] along with exposure to [[ionizing radiation]] might alter or destroy molecular signatures from meteorites or organisms.<ref name='Biosignatures 2011'/> An alternative approach would be to seek concentrations of buried crystalline minerals, such as [[clay]]s and [[evaporite]]s, which may protect organic matter from the destructive effects of [[ionizing radiation]] and strong oxidants.<ref name='Biosignatures 2011'/> The search for Martian biosignatures has become
more promising due to the discovery that surface and near-surface aqueous environments existed on Mars at the same time when biological organic matter was being preserved in ancient aqueous sediments on Earth.<ref name='Biosignatures 2011'/>
[[File:PIA16461-MarsMethane-20121102.jpg|thumb|left|300px|[[Atmosphere of Mars#Methane|Methane]] (CH4)on Mars - potential sources and sinks (November 2, 2012).]]
;Atmosphere
Over billions of years, the processes of life on a planet would result in a mixture of chemicals unlike anything that could form in an ordinary chemical equilibrium.<ref>{{cite web | url = https://www.technologyreview.com/blog/arxiv/26247/ | title = Artificial Life Shares Biosignature With Terrestrial Cousins | accessdate = 2011-01-14 | date = 10 January 2011 | work = The Physics arXiv Blog | publisher = MIT}}</ref> For example, large amounts of [[oxygen]] and small amounts of [[methane]] are generated by life on Earth. The presence of methane in the atmosphere of [[Mars]] indicates that there must be an active source on the planet, as it is an unstable [[gas]]. Furthermore, current photochemical models cannot explain the presence of methane in the atmosphere of Mars and its reported rapid variations in space and time. Neither its fast appearance nor disappearance can be explained yet.<ref>[http://mepag.jpl.nasa.gov/decadal/TGM_Mars_Panel-cleared-9-4-09.ppt Mars Trace Gas Mission] (September 10, 2009)</ref> To rule out a biogenic origin for the methane, a future probe or lander hosting a [[mass spectrometer]] will be needed, as the isotopic proportions of [[carbon-12]] to [[carbon-14]] in methane could distinguish between a biogenic and non-biogenic origin.<ref name="nasa">[http://rst.gsfc.nasa.gov/Sect19/Sect19_13a.html Remote Sensing Tutorial, Section 19-13a] - Missions to Mars during the Third Millennium, Nicholas M. Short, Sr., et al., NASA</ref> In June, 2012, scientists reported that measuring the ratio of [[hydrogen]] and [[methane]] levels on Mars may help determine the likelihood of [[life on Mars (planet)|life on Mars]].<ref name="PNAS-20120607">{{cite journal |last1=Oze |first1=Christopher |last2=Jones |first2=Camille |last3=Goldsmith |first3=Jonas I. |last4=Rosenbauer |first4=Robert J. |title=Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces |url=http://www.pnas.org/content/109/25/9750.abstract |date=June 7, 2012 |journal=[[PNAS]] |volume=109| issue = 25 |pages=9750–9754 |doi=10.1073/pnas.1205223109 |accessdate=June 27, 2012 |bibcode = 2012PNAS..109.9750O }}</ref><ref name="Space-20120625">{{cite web|author=Staff |title=Mars Life Could Leave Traces in Red Planet's Air: Study |url=http://www.space.com/16284-mars-life-atmosphere-hydrogen-methane.html |date=June 25, 2012 |publisher=[[Space.com]] |accessdate=June 27, 2012 }}</ref> According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."<ref name="PNAS-20120607" /> Other scientists have recently reported methods of detecting hydrogen and methane in [[extraterrestrial atmospheres]].<ref name="Nature-20120627">{{cite journal |last1=Brogi |first1=Matteo |last2=Snellen |first2=Ignas A. G. |last3=de Krok |first3=Remco J. |last4=Albrecht |first4=Simon |last5=Birkby |first5=Jayne |last6=de Mooij |first6=Ernest J. W. |title=The signature of orbital motion from the dayside of the planet t Boötis b |url=http://www.nature.com/nature/journal/v486/n7404/full/nature11161.html?WT.ec_id=NATURE-20120628 |date=June 28, 2012 |journal=[[Nature (journal)|Nature]] |volume=486 |pages=502–504 |doi=10.1038/nature11161 |accessdate=June 28, 2012 |arxiv = 1206.6109 |bibcode = 2012Natur.486..502B }}</ref><ref name="Wired-20120627">{{cite web |last=Mann |first=Adam |title=New View of Exoplanets Will Aid Search for E.T. |url=http://www.wired.com/wiredscience/2012/06/tau-bootis-b/ |date=June 27, 2012 |publisher=[[Wired (magazine)]] |accessdate=June 28, 2012 }}</ref> The planned [[ExoMars Trace Gas Orbiter]] to be launched in 2016 to Mars, will study [[Atmosphere of Mars|atmospheric trace gases]] and will attempt to characterize potential biochemical and geochemical processes at work.<ref name='June 2011'>{{citation | first = Mark Allen | coauthors = Olivier Witasse | contribution = 2016 ESA/NASA ExoMars Trace Gas Orbiter | title = MEPAG June 2011 | publisher = Jet Propulsion Laboratory | date = June 16, 2011| id = | contribution-url = http://mepag.jpl.nasa.gov/meeting/jun-11/13-EMTGO_MEPAG_June2011_presentation-rev2.pdf | accessdate = 2011-06-29}} (PDF)</ref>

===The Viking missions to Mars===
{{Main|Viking biological experiments}}
[[File:Sagan Viking.jpg|thumb|[[Carl Sagan]] with a model of the Viking lander]]
The [[Viking Lander|Viking missions]] to [[Mars]] in the 1970s conducted the first experiments which were explicitly designed to look for biosignatures on another planet. Each of the two [[Viking landers]] carried three [[Viking Biological Experiments|life-detection experiments]] which looked for signs of [[metabolism]]; however, the results were declared 'inconclusive'.<ref name=Beegle >{{cite journal|title=A Concept for NASA's Mars 2016 Astrobiology Field Laboratory |journal=Astrobiology|date=August 2007|first=LUTHER W.|last=BEEGLE |coauthors=et al |volume=7 | issue = 4|pmid=17723090 |pages=545–577|id= | url=http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2007.0153?cookieSet=1 |format= |accessdate=2009-07-20| doi=10.1089/ast.2007.0153 | bibcode=2007AsBio...7..545B}}</ref><ref>Levin, G and P. Straaf. 1976. Viking Labeled Release Biology Experiment: Interim Results. Science: vol: 194. pp: 1322-1329.</ref><ref name="Chambers">{{Cite book| first = Paul | last = Chambers| title = Life on Mars; The Complete Story|place = London| publisher = Blandford| year = 1999 |isbn = 0-7137-2747-0}}</ref><ref>{{cite journal | title = The Viking Biological Investigation: Preliminary Results |journal = Science|date = 1976-10-01 |first = Harold P. | last = Klein| coauthors = Levin, Gilbert V. | volume = 194 | issue = 4260 | pages = 99–105 | doi = 10.1126/science.194.4260.99 | url = http://www.sciencemag.org/cgi/content/abstract/194/4260/99 | accessdate = 2008-08-15
| pmid = 17793090 | bibcode=1976Sci...194...99K}}</ref><ref name=ExoMars>[http://www.esa.int/SPECIALS/ExoMars/SEMK39JJX7F_0.html ExoMars rover]</ref>

===Mars Science Laboratory===

The ''Curiosity'' rover from the [[Mars Science Laboratory]] mission, is currently assessing the potential past and present [[planetary habitability|habitability]] of the Martian environment and is attempting to detect biosignatures on the surface of Mars.<ref name='Biosignatures 2011'/> Considering the MSL instrument payload package, the following classes of biosignatures are within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.<ref name='Biosignatures 2011'/> The ''Curiosity'' rover targets [[outcrop]]s to maximize the probability of detecting 'fossilized’ [[organic matter]] preserved in sedimentary deposits.

===ExoMars===
The 2016 [[Trace Gas Orbiter]] (TGO) will be a Mars telecommunications orbiter and atmospheric gas analyzer mission. It will deliver the ExoMars EDM lander and then proceed to map the sources of [[Atmosphere of Mars#Methane|methane on Mars]] and other gases, and in doing so, help select the landing site for the ExoMars [[Rover (space exploration)|rover]] to be launched on 2018.<ref>{{cite news | first = Boris Pavlishchev | title = ExoMars program gathers strength | date = Jul 15, 2012 | url = http://english.ruvr.ru/2012_07_15/ExoMars-program-gathers-strength/ | work = The Voice of Russia | accessdate = 2012-07-15}}</ref> The primary objective of the 2018 [[ExoMars]] rover mission is the search for biosignatures on the surface and subsurface by using a drill able to collect samples down to a depth of {{convert|2|m|ft}}. <ref name=ExoMars/><ref name="MSL-main_page">{{cite web|title=Mars Science Laboratory: Mission |url= http://marsprogram.jpl.nasa.gov/msl/mission/ |publisher=NASA/JPL |accessdate=2010-03-12 }}</ref>

==See also==
*[[Bioindicator]]
*[[Biomarker]]
*[[Planetary habitability]]
*[[Taphonomy]]

== References ==
{{reflist}}

{{Extraterrestrial life}}

[[Category:Astrobiology]]
[[Category:Bioindicators]]
[[Category:Biology terminology]]
[[Category:Astrochemistry]]