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September 20

birth control

If the failure rate of mirena is 0.2, how come i saw a study saying that it's higher? [1] 24.207.79.50 (talk) 00:05, 20 September 2014 (UTC)[reply]

One obvious flaw in most of the birth control statistics is that they assume they are used properly. When you factor in human error, especially when people may be somewhat distracted, the failure rate is a lot higher. However, since Mirena is an IUD, and those are inserted well in advance, this isn't an issue. Thus our article lists both "Perfect use" and "Typical use" failure rates of 0.2%. StuRat (talk) 02:08, 20 September 2014 (UTC)[reply]

The 0.2% comes from a study of 1169 Swedish and Finnish women age 18-35 that was conducted as part of the clinical trials to establish the efficacy of the implant. Specifically, the 0.2% refers to the chance of becoming pregnant during the first year after implantation. As is typically the case, results established during approval trials become the "approved" facts for discussing a new treatment. In some cases, subsequent evidence suggests that the initial conclusions about efficacy should be revised, but getting such revisions into the official drug literature is difficult due to the extensive regulations surrounding prescription meds. Looking at this particular trial, some points stick out. For one, Swedish and Finnish women are likely to be for the most part racially and culturally homogeneous, so it is possible that women from other ethnic groups or with different lifestyles might have a somewhat different responses to the treatment. Secondly, 0.2% of 1169 women is a fancy way of saying that exactly 2 women in the trial became pregnant during the first year. When you are talking about single digit numbers of events, there is some inherent uncertainty. If I repeated the trial with another 1200 women, I might get 2 again, or I might get 6, or 0, or some other small number. That randomness associated with rare events will make this result a bit uncertain. I could well be that the drug companies got lucky with that initial study and the true failure rate is a bit higher. On the other hand, even if the true failure rate were ten times higher (2%), it would still be very effective compared to most typical use contraceptives. Dragons flight (talk) 04:34, 20 September 2014 (UTC)[reply]

Yea, that should be about a 3% margin of error, so they should say it has a 0.2% failure rate ±3.0%, although a -2.8% failure rate makes no sense (unless it terminates that many existing pregnancies ?), so a 0-3% failure rate is probably the best way to put it. StuRat (talk) 22:42, 20 September 2014 (UTC)[reply]

Or maybe it's because the study was done over 8 years instead of just one year.They only seemed to mention the percentage of people who got pregnant over the entire period of time instead of the percentage for each single year. Do you think that would be correct?24.207.79.50 (talk) 00:24, 21 September 2014 (UTC)[reply]

I guess no one has come to answer my question further. Perhaps that means i'm going too off topic, or simply end of discussion? — Preceding unsigned comment added by 199.119.235.184 (talk) 06:21, 21 September 2014 (UTC)[reply]

Not necessarily. The Wikipedia Reference desk is manned by volunteers, if nobody has any useful information to contribute, you may not get a complete or meaningful answer. In this case, you may just be asking us to guess what was in the minds of the authors of the study - and we can't do that. A better bet might be for you to locate one of the study authors and ask them the question directly. SteveBaker (talk) 20:16, 23 September 2014 (UTC)[reply]

Eunuchs, Estrogen, and Erections

I read somewhere that estrogen (or something along those lines) can boost a eunuch's sex drive and allow him to have more frequent erections. Is this true? And Yes, this is a completely serious question. Futurist110 (talk) 07:35, 20 September 2014 (UTC)[reply]

These may be of use [2], [3]. The degree appears to be variable. Phoenixia1177 (talk) 10:16, 20 September 2014 (UTC)[reply]

Thank you very much for these links. Do you and/or anyone else here have any additional links which address this question of mine? Futurist110 (talk) 02:54, 21 September 2014 (UTC)[reply]

Simple mechanical system that satisfies Newton's laws but is not Hamiltonian

Does anyone have such an example? I need it for a presentation. Thanks!--Leon (talk) 18:08, 20 September 2014 (UTC)[reply]

Any mechanical system with dissipation (friction). Ruslik_Zero 19:16, 20 September 2014 (UTC)[reply]

IUPAC nomenclature of an organic compound with one double bond at one end and one triple bond at the other end?

What is it called? Is it an alkene or alkyne? 71.79.234.132 (talk) 18:45, 20 September 2014 (UTC)[reply]

It "is" a molecule with both:) This is one advantage of the "new" rules for ene/yne, using infix numbers (as a simple case, "but-1-ene") rather than giving greater emphasis of it as the parent chain itself (old name "1-butene"). Your case is just some carbon-chain that happens to have two functional groups. So vinylacetylene lists in its infobox "but-1-en-3-yne" with the two modifiers ordered by normal ordering rules (alphabetical/numerical precedence). But using synonym in the infobox using older naming pattern is "3-butene-1-yne", which is confusing as hell regarding precedence and parent+modification patterns. DMacks (talk) 19:19, 20 September 2014 (UTC)[reply]

Found the authoritative answer: IUPAC nomenclature of organic chemistry 1993 recommendations rule "R-3.1.1 Suffixes denoting multiple bonds" says in part:

The presence of both double and triple bonds is similarly denoted by endings such as "-enyne", "-adienyne", "-enediyne", etc. Numbers as low as possible are given to double and triple bonds as a set, even though this may at times give "-yne" a lower number than "-ene". If a choice remains, preference for low locants is given to the double bonds.

which matches the patterns used in the example I noted earlier. DMacks (talk) 19:38, 20 September 2014 (UTC)[reply]

Nocturnal animals

Kind of a silly question, but: how do nocturnal animals sleep through the noise made by diurnal ones? I have been out birdwatching at a local park around sunrise, and I often see a Black-crowned Night Heron trying to settle down to sleep on a tree branch, while all around it the other birds are singing and squawking and generally making a racket. Not to mention all the noises generated by humans. 75.4.18.101 (talk) 19:46, 20 September 2014 (UTC)[reply]

How do humans sleep through traffic noise? Our brains filter out known harmless background noise when we're asleep, and only wake up if an unexpected noise occurs. I expect it is the same for most animals. CS Miller (talk) 20:38, 20 September 2014 (UTC)[reply]

Yes, that's accustomization. Country folk can't sleep in the city, because of all the noise from traffic and the subway, while city folk can't sleep in the country because of those crickets, bullfrogs, owls, etc. But after a while they will get used to it and be able to sleep again. In the case of nocturnal animals, they may have even evolved a permanent way to ignore certain sounds. (Probably not closable ears, as it's far simpler to suppress the sound in the brain than there.) StuRat (talk) 21:27, 20 September 2014 (UTC)[reply]

In the early 18th century, people who came to New York City couldn't sleep because of the frogs. It was much smaller then. (even 1810s City Hall was further than a large pond) Sagittarian Milky Way (talk) 02:46, 23 September 2014 (UTC)[reply]

(OP here, my IP may have changed.) Thanks for the responses. I wonder if there are local variations in what sounds nocturnal animals can sleep through, or individual ones (my sister sleeps through earthquakes, I am woken up by a raccoon on the roof). 75.4.18.101 (talk) 00:18, 21 September 2014 (UTC)[reply]

So there's this guy who lives in a house in the country. Every night the Midnight Special goes by on a distant railroad track and blows its horn, but the guy always sleeps through it. One night the Midnight Special doesn't blow its horn. The guy wakes up and says, "What was that?" ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:39, 21 September 2014 (UTC)[reply]

The accustomization would be pretty specific for an animal that depends on hearing things while it's asleep to make sure it doesn't become some diurnal critter's lunch. They would likely take cues from the various noises even a familiar non-threatening critter might make, i.e. they'd subconsciously distinguish between a bird's mating call and its alarm call. I myself work nights and have 5 dogs. I often sleep through them barking at people walking down the road in front of my house (from what my wife informs me of) but will wake up if they are barking at someone coming up the drive. Dismas|^(talk) 01:09, 21 September 2014 (UTC)[reply]

(OP, maybe I should make an account:) On the other hand (in my particular case), there don't seem to be any predators here that could kill a Night Heron. Even Buteo hawks probably couldn't take one down, or easily maneuver through the trees where they doze. So maybe these birds can afford to "tune out" better than some. 75.4.18.101 (talk) 01:49, 21 September 2014 (UTC)[reply]

Yes, by all means make an account. It is easy and free.--Srleffler (talk) 18:19, 21 September 2014 (UTC)[reply]

It's also not required. There are advantages, though. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:46, 22 September 2014 (UTC)[reply]

I spent sixth moths in the hospital on an IV that had to be changed every 8 hours, with nurses chatting outside my door, with a patient in the bed next to me. After about the third night I could sleep through anything but the IV needle re-insertion. Animals get used to sleeping, and I even saw my sister train my nephew to sleep on a regular schedule rather than cry when he was a newborn. It's like feeding a spoiled dog hard kibble. They might refuse the first night, but they'll get hungry enough to eat anything, eventually. μηδείς (talk) 17:27, 21 September 2014 (UTC)[reply]

Another factor here may be that since nocturnal animals have evolved to sleep during the day, their brains may be configured to get more alert when there is little noise while a lot of background noise will help to fall asleep. Count Iblis (talk) 17:45, 21 September 2014 (UTC)[reply]

bug ID

Hello, could someone please tell me what bug this is. Specifically if it's a parasite, like a louse or a flea. Here is another pic taken using a scanner (warning, nasty.) If it helps, I'm in western Central Europe Asmrulz (talk) 20:45, 20 September 2014 (UTC)[reply]

Looks like a louse to me. But there's many hundreds of species, and only a few are known to infest humans. Being a louse doesn't mean it's a problem, per se. --Jayron32 20:49, 20 September 2014 (UTC)[reply]

F*** :( What do I do now? Asmrulz (talk) 21:05, 20 September 2014 (UTC)[reply]

Depends. Based on the odds, there's a 0.1% chance it's one of the species that infest humans (3000 species of louse; only 3 are problems for people). So, you could do nothing. --Jayron32 21:18, 20 September 2014 (UTC)[reply]

However, since it looks like he found it in his bathroom, not on the back of a Sumatran tiger, that rather changes the odds, don't you think ? It looks like it's belly is full of blood too, so it just fed on either a human or pet in the house. I'd have everyone check for bug bites and watch any pets (except fish) for signs of scratching. There are methods for killing lice on either humans or pets, but first you have to figure out which it is. StuRat (talk) 21:34, 20 September 2014 (UTC)[reply]

Maybe he has a tiger as a pet. It's been known to happen. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:12, 21 September 2014 (UTC)[reply]

not just known to happen. Happens too much. There are more tigers kept as pets in the United States alone than there are tigers in the wild. See [4] --Jayron32 19:23, 22 September 2014 (UTC)[reply]

Judging by what looks like blood in its digestive tract, it is probably a parasite. In any case, Diatomaceous earth is a possible non-toxic solution for that sort of critter. —71.20.250.51 (talk) 01:21, 21 September 2014 (UTC) —I hate to nit-pick, but head lice might require a different solution, and of course, Wikipedia has an article on that: Treatment of human head lice[reply]

This critter is so hard to see it may as well be a cricket for all I can tell, but if it is a louse they are very easy to deal with, your pharmacists will provide an over-the-counter shampoo/lotion and further instructions. μηδείς (talk) 17:20, 21 September 2014 (UTC)[reply]

Thank you very much to all who replied. This is indeed from the bathroom. I don't think I have anything in my scalp, but I'll be checking once every few days. I find these often on books and stuff. This would indicate booklice, but the thing is, they don't suck blood whereas in the photo it clearly has, as StuRat has noted, blood in its intestine. Could be I have those AND those... :(( Asmrulz (talk) 21:10, 22 September 2014 (UTC)[reply]

Chest of drawers: noise

How can a person build (or retrofit) a chest of drawers so as to minimize the noise caused by the drawers being slid in and out?
—Wavelength (talk) 20:55, 20 September 2014 (UTC)[reply]

WD-40. --Jayron32 21:00, 20 September 2014 (UTC)[reply]

Well, some drawers have little wheels under the drawers on which they slide in and out on. In that case, some lubricant at the axles of those wheels might indeed help. Others just slide directly on the surface. In this case, reducing the friction of those surfaces is in order, and, if both the drawer and cabinet are wood, perhaps furniture wax might be the best option. Talc (baby powder) could also work, but expect some of it to get on things in the drawer and nearby. You could also retrofit the drawers with wheels, but that's a major project, and may require reducing the height of the drawers to make room. Also, if a wheel is off the track, that may cause noise, too, so check for that.

The first step is to pull a drawer all the way out, look at what's on the bottom, then look in the hole to see where the wear patterns are. If you see sawdust, that's a clue that something is rubbing directly against the wood. It's also possible the sides or top of the drawer are rubbing, but the drawer would probably be hard to open then. In that case, you'd need to sand down the drawer so it fits properly. StuRat (talk) 21:44, 20 September 2014 (UTC)[reply]

Rub pencil lead (graphite) on the runners. Oldie but a goldie. DuncanHill (talk) 21:59, 20 September 2014 (UTC)[reply]

Soap, or candle-wax, can also be used. DuncanHill (talk) 22:04, 20 September 2014 (UTC)[reply]

French chalk (which redirects to "Talc", but it's not the same thing as talcum powder) is the traditional substance. Tevildo (talk) 22:12, 20 September 2014 (UTC)[reply]

Traditional where? I'm with Duncan. My old Scottish woodwork teacher taught me about candle wax 50 years ago. No mess. Long lasting. HiLo48 (talk) 22:18, 20 September 2014 (UTC)[reply]

Well, it's what my grandfather used to use. And see this site (other suppliers of such materials are available), where "Fix Sticky Drawers" ooer missus! is listed as one of its uses. But wax will also work, I agree. Tevildo (talk) 22:41, 20 September 2014 (UTC)[reply]

Thank you all for your answers. Instead of a lubricant, I am looking for a solution in the actual design of the chest of drawers, either by the shapes of its components or by its material(s), which might include metal or plastic (even if only as coverings on contact surfaces). The choice of wood(s) is also of interest.
—Wavelength (talk) 23:33, 20 September 2014 (UTC)[reply]

Drawer slides come in a variety of types and quality. A ball-bearing suspension drawer slide is smooth and quiet. There are even smooth-close types, etc. I don't want to endorse a particular brand, but this site is quite informative (videos, etc.), no matter which brand you choose: [5] — I noticed there is something called 'Sliding Compound', "for wood or metal". —71.20.250.51 (talk) 01:46, 21 September 2014 (UTC)[reply]

Since searching for "slider compound" will give you results about "sliding compound miter saw", I guess I need to provide the trade-name: Slipit^© Sliding Compound. —71.20.250.51 (talk) 01:56, 21 September 2014 (UTC)[reply]

Thank you for this information about prefabricated drawers.

—Wavelength (talk) 22:21, 21 September 2014 (UTC)[reply]

Perhaps you misunderstood. Drawer slides not only relate to prefab drawers, they are hardware that can be purchased separately and applied to DIY projects. 71.20.250.51 (talk) 01:14, 22 September 2014 (UTC)[reply]

Thank you for this clarification.

—Wavelength (talk) 01:19, 22 September 2014 (UTC)[reply]

If you're considering changing the design of an old wood-sliding-on-wood drawer to make it move more easily, then I'd suggest buying some PTFE tape and sticking that onto one of the surfaces. PTFE is really slippery and avoids having wax or talc from an upper drawer falling down into the drawer below. SteveBaker (talk) 15:54, 22 September 2014 (UTC)[reply]

September 21

Paper and water

Why is ordinary paper damaged so significantly by getting even a little bit wet? It's not simply the fact that water causes damage, but paper exposed to very tiny quantities of water can be impossible to restore to anything like its original condition. Peter Grey (talk) 03:54, 21 September 2014 (UTC)[reply]

I think you'll find that paper based from pulp wood is much more easily damaged by water than is high-quality rag-bond paper. Dunk a dollar bill in water and I think you'll find that it recovers quite nicely. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:08, 21 September 2014 (UTC)[reply]

If you read the papermaking article it says "In paper-making, a dilute suspension of fibres in water is drained through a screen, so that a mat of randomly interwoven fibres is laid down. Water is removed from this mat of fibres by pressing and drying to make paper". If you add water back to the paper you are reversing the process and turning back into paper pulp. This causes the randomly aligned fibres to expand in different directions, which causes the flat sheet of paper to buckle. To get it back to a flat piece of paper you would have to repeat the original process by drying it and rolling it out again. In practice this would be impossible to do whilst preserving the integrity of anything printed on the surface. Richerman (talk) 08:56, 21 September 2014 (UTC)[reply]

Thermite torch

There's this clip of MacGyver on YouTube which shows him creating a "termite torch" by mixing magnesium shavings with rust in a pipe and then igniting it with a road flare. Is this possible? I know there's something called a thermal lance, but that seems to be slightly different. It's using iron rods packed into an iron rod and then injects the rod with oxygen while this device that MacGyver uses seems to just be ignited thermite in a tube. ScienceApe (talk) 06:49, 21 September 2014 (UTC)[reply]

A Sparkler mixes ingredients like this for fireworks. Not sure what rust would do except color (temperature control?) --DHeyward (talk) 07:13, 21 September 2014 (UTC)[reply]

The rust provides the oxygen. Rust is not s single material (water and oxygen can combine differently with iron to make rust), but one possible reaction is 2Fe₂O₃+6Mg -> 6MgO+4Fe. Magnesium yields its electrons easier than Iron, so that should be an exothermic reaction. Of course, I don't know if many road bikes are really made from magnesium (aluminium seems to be a lot more common), and the MacGyver version is, as always, a bit cinematic. But I seem to remember that Pashtun gunsmiths in Afghanistan used a mixture of rusty scrap metal and magnesium in a crucible to produce molten steel for casting gun parts. --Stephan Schulz (talk) 09:21, 21 September 2014 (UTC)[reply]

There's one or two errors in the film clip. Thermite is normally created using aluminium and rust. Magnesium is possible but less common. Bicycles are very rarely made from magnesium, and those that are are cast. They are now commonly made from aluminium. The one shown was steel. You can't put out a thermite reaction by touching the torch on the ground. It supplies its own oxygen and so taking away the oxygen like that would have no effect. Aprart from that, it's all quite feasible.--Phil Holmes (talk) 12:56, 21 September 2014 (UTC)[reply]

Pretty amazing, a thermite reaction inside a metal pipe that doesn't melt the pipe itself... Ssscienccce (talk) 19:48, 21 September 2014 (UTC)[reply]

Bioluminescent Dinoflagellates

Do you think it is possible to farm bioluminescent dinoflagellates at home? What equipment could such farming require? 85.141.226.92 (talk) 15:50, 21 September 2014 (UTC)[reply]

So, you want glowing plankton that kills people? μηδείς (talk) 17:16, 21 September 2014 (UTC)[reply]

The question is hypothetical. Also I as far as I know not all dinoflagellates are toxic, aren't they? And shouldn't they be eaten first to harm the human body? 83.237.120.61 (talk) 18:06, 21 September 2014 (UTC)[reply]

I swam in a bioluminescent bay in Vieques, Puerto Rico, on an organized excursion, and was exposed to these little dinoflagellates as are thousands of tourists a year. They were said to be harmless. When a fish swam through them, they would leave a light streak to mark the passage. If you moved in the water, they lit up. Visitors doubtless consumed some of them while in the water. Their colony was said to be very fragile, and the guides (who were licensed/authorized/accredited) said that in a different bioluminescent bay, misguided attempts to improve their habitat had exterminated them. Guides said that they were worried about proposed resort construction, since the critters seem to expire when there is a lot of artificial light. In sum, I doubt it would be easy to farm them, but research about what conditions allow their survival would be of value. Edison (talk) 21:30, 21 September 2014 (UTC)[reply]

Unknown Insect

I found this insect tonight. It behaves like a fly but it seems unusually large and colourful for urban England. Any ideas what it is?

File:An insect I found 1.jpg
File:An insect I found 2.jpg
File:An insect I found 3.jpg
File:An insect I found 4.jpg
And for size comparison

And for size comparison

Matt's talk 22:01, 21 September 2014 (UTC)[reply]

I've fixed the formatting on your links. No idea about the insect, I'm afraid. Tevildo (talk) 22:27, 21 September 2014 (UTC)[reply]

Thank you. I tried using the new snazzy markup tool but it wasn't a success. Matt's talk 22:47, 21 September 2014 (UTC)[reply]

Looks like a Horsefly to me, but I have no idea on the specific species. --Jayron32 22:31, 21 September 2014 (UTC)[reply]

Definitely a true fly, i.e. a member of the diptera ('two wings') - while most insects have four wings, flies have two wings and two little stubs called halteres. If you look closely in the photos, I think you can see the halteres. Other key features are the large eyes and sucking mouthparts. SemanticMantis (talk) 13:54, 22 September 2014 (UTC)[reply]

Agree with horsefly. See Horse flies, clegs & deer flies. They bite like a mosquito only bigger, their only saving grace is that they're a bit slower to fly away than a midge or mossie and so they're easier to swat. Alansplodge (talk) 12:18, 23 September 2014 (UTC)[reply]

binding profile quetiapine

Dear ladies and gentlemen,

at the following URL-Adress, there is something wrong.

Quetiapine On your website, there ia a table with the binding-affinity to some receptors.

When I look at the canadian database - http://www.drugbank.ca/drugs/DB01224 there I can see, that in your table are missing following receptors:
Alpha adrenergic 2B,
5HT1B,
5HT1C,
5HT1E;

Maybe you can give me the information, where I can get a better table. By - www.drugbank.ca/drugs/DB01224, there a only the receptor-type, but no binding-affinity (Ki-value)

And maybe you can look too for a save and better Ki-Table for Halperidol, Olanzapine, Risperidon.

And sorry, one more question. This metabolit norquetiapine - the value in the table - is this an antagonsit too? Can I add the first value from quetiapine with the second value from norquetiapine to get the atagonism together for this receptor? for example:
5-HT2A Quetiapine: 118nM Norquetiapine: 48nM --> together: 166nM Antagonist ?

And maybe you can answer this question:
This is in the table on your side
NET Quetiapine: >10000nM Norquetiapine: 12nM
When I say, I only look for this value 12nM, then I have a big effekt to the NET-/NAT-transporter.

How large is thus the opposite effect to antagonism of adrenergic receptors.

For example - the average Ki-value of all adrenoreceptors is 36nM. The opposite effect by blocking norepinephrine reuptake is accomplished by 12nM on the NET-transporter. Is there a way these two opposite effects to count against each other? Are there any estimates how to do this?

thank you very much for your help.

Dai Dirtd Germany — Preceding unsigned comment added by Dirtdai (talk • contribs) 22:12, 21 September 2014 (UTC)[reply]

September 22

Why do we sleep

I recently read this. I don't understand why is it still a mystery to science. It even states in the article that "sleep is the time when our bodies repair tissues and perform other maintenance activities..." That's 'the reason' why we sleep, simply as that. What more evidences do they want? What is really the mystery behind sleep that we can't explain with science right now? Thanks! 146.151.82.248 (talk) 01:02, 22 September 2014 (UTC)[reply]

Part of the reason is that we do not have a good scientific theory of sleep. Theories are explanations (or more properly explanatory frameworks) that have evidence to support how or why something happens. There is a hypothetical theory that proposes that sleep's purpose is to allow maintenance, or to allow neural connections to strengthen, or any number of explanations. The problem is not the lack of explanations, it's the lack of experimental verification of the explanations. A good theory has lots of evidence. The current set of theories are still hypothetical theories because, while logical, there isn't a lot of good evidence that indicates their validity. They may actually be correct. But compared to other theories which we use all the time in science (like evolution, or atomic theory, or general relativity) there isn't a lot of good solid evidence one way or the other to explain why we need sleep. We do know we need it, there's lots of pathologies that result from lack of sleep, but beyond the simple relationship of "no sleep = unhealthy in specific ways" we don't have much to explain why functions that seem to occur during sleep couldn't occur while we are awake. --Jayron32 01:14, 22 September 2014 (UTC)[reply]

I found it hard to believe that we can't prove what is going on in our brain during sleep. I believe it has been proven that our brains do in fact in maintenance during sleep. As i can see we have a pretty good theory so far about it. With that theory, i can say that we need sleep because we need our bodies to be repaired before it's broken. 146.151.85.154 (talk) 08:05, 22 September 2014 (UTC)[reply]

You misunderstand. We can establish what is happening. We don't have a good explanation for why it happens during sleep (as opposed to simply all the time while we are awake). --Jayron32 10:51, 22 September 2014 (UTC)[reply]

We do know that sleep is pretty much universal in the animal kingdom; this universality then suggests that it has nothing to do with biology, it is a consequence of mathematics. If you and I have a system that can only function at a certain level for that to be sustainable, and I operate it at that sustainable level then you can easily outcompete me by operating your system at a higher level, and then letting it take a rest during which the focus is on self maintainance. Also, by tweaking the system you can let the self-maintaince be performed more efficiently during the downtime which then allows the system at the active phase to perform even better. This is a universal feature of almost any system from biological to simple machines like your pc. Count Iblis (talk) 02:01, 22 September 2014 (UTC)[reply]

So is this your theory of why we sleep?146.151.85.154 (talk) 08:05, 22 September 2014 (UTC)[reply]

Yes, but note that many universal phenomena require mathematical explanations that go beyond the particular subject matter. They tend to be mysteries for a long time because people seek an explanation in terms of the concepts of the subject matter which often isn't appropriate. E.g. Von Neumann made an important discovery about the way DNA works, long before the structure of DNA was discovered by Watson and Crick, see here: "Von Neumann's crucial insight is that part of the replicator has a double use; being both an active component of the construction mechanism, and being the target of a passive copying process. This part is played by the tape of instructions in Von Neumann's combination of universal constructor plus instruction tape.

The combination of a universal constructor and a tape of instructions would i) allow self-replication, and also ii) guarantee that the open-ended complexity growth observed in biological organisms was possible.[3] The image below illustrates this possibility. This insight is all the more remarkable because it preceded the discovery of the structure of the DNA molecule by Watson and Crick, though it followed the Avery-MacLeod-McCarty experiment which identified DNA as the molecular carrier of genetic information in living organisms.[5]" Count Iblis (talk) 18:38, 22 September 2014 (UTC)[reply]

My PC doesn't self-maintain when it is switched off. AndyTheGrump (talk) 05:07, 22 September 2014 (UTC)[reply]

My PC spends an annoyingly large portion of its processor time on self-maintenance when I want it to be doing useful work, but I accept that this is just a disadvantage of "Windoze". (It's time I replaced it!) Dbfirs 07:41, 22 September 2014 (UTC)[reply]

I don't know anything about this, but surely the mystery is why we have to be unconscious for a significant fraction of our lives. It would seem to be a huge adaptive disadvantage in almost any situation. At the very least you'd expect it to be healthy but optional, skippable if you really need to stay alert. But you can't stay alert for long without sleep. What happens in the brain during sleep that's so important that it counterbalances those disadvantages? Also, some animals can sleep one brain hemisphere at a time; why don't all animals at least have that option, given that it could probably save their lives in some situations? -- BenRG (talk) 06:51, 22 September 2014 (UTC)[reply]

Probably because evolution selects the animals who sleep and able to repair and perform better than those who don't. The fact that most animals need sleep prove that sleep-animals outperform no-sleep-animals. No-sleep-animals probably died off ages ago because of evolution.146.151.85.154 (talk) 08:05, 22 September 2014 (UTC)[reply]

Related to that hypothesis, it's useful to observe the effects on those who cannot sleep, as in Fatal familial insomnia. The end result is typically dementia and death. It's clear that the brain requires some down time. BenRG asks why we have to be unconscious. Keep in mind that our (un)consciousness level during sleep rises and falls, it's not a steady level. If you've ever taken a "cat nap" while watching TV or whatever, sometimes you just barely slip into unconsciousness. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:49, 22 September 2014 (UTC)[reply]

I could have asked any question about biological systems and you could have said "the fact that evolution selected for it proves that it's better". That's a wakalixes answer. It's not wrong, just devoid of useful information. What is the advantage of being mostly unaware of your surroundings while healing, versus keeping an eye on your surroundings while healing, that led to the former being preferred by evolution? (I think the correct answer is that there is no advantage, and sleep is not actually about healing, as SteveBaker said below.) -- BenRG (talk) 19:09, 22 September 2014 (UTC)[reply]

I heard a scientist on RadioLab say that sleep patterns were related to Predation risk. It does seem that the option to forego sleep for much longer than is currently possible would have survival value regardless of predation risk, though. OldTimeNESter (talk) 15:41, 22 September 2014 (UTC)[reply]

It's true that we really don't know for sure - and certainly we don't have all of the details down. But it seems that it's something like this:

First, consider that animals like Dolphins which would drown if they ever fell completely asleep. They often sleep with one hemisphere of their brains at a time, so they always have enough brain power to do things like swim and breathe. That's also true of sharks - which have to keep water flowing over their gill-slits. Some perching birds have an interesting behavior where a group of birds will perch together on a branch and the birds at each end of the row sleep with just the hemisphere of their brains that allows one eye to keep watching for attack from their exposed side - while the birds in the middle of the row can fully sleep with both hemispheres.

These examples indicate that sleep isn't so that our bodies can perform repairs - at least not muscles and bones and other major organs. If that were the case then continually swimming sharks and dolphins would never have time for those repairs - yet their bodies do just fine. So this is best thought of as "brain maintenance" - and that starts to make a lot of sense. But even so, our brains are obviously still active as we sleep...we have dreams - and MRI studies show that there is plenty of activity. If you play music to a sleeping person, the areas of their brains that light up when they listen to music while awake also light up while they're asleep. So if it's "brain maintenance" then it's not that the brain is turning off so that physical structures can be maintained. It's more like the "software" of the brain undergoing some kind of special maintenance.

Consider this: We continually take in and record sounds, images, text and other stuff which we sometimes remember. Yesterday was my granddaughter's 3rd birthday party - and even though it was flushed out of my short-term memory after 20 minutes or so, I recall most of what happened. But when I think back to her 2nd birthday, I only recall a few highlights. Looking back 10 years, I no longer have any memory about my son's 12th birthday - beyond that we went to some kind of indoor rock climbing thing. My memories of these events have slowly faded. But this fading is highly selective. There are things like my son's birth, where every detail is still fairly sharp. So fading memories isn't a kind of dumb, automatic thing like the decay of a banana...it requires selectivity. We lose the memories we don't "need".

There are many, highly divergent, estimates for the capacity of the human brain for memory - but a typical estimate (eg [6]) is that the number is a couple of petabytes - which, in computer terms is about 1000 modern 1 terabyte hard drives. That's a VERY small amount considering that we have decades of video and audio stashed away in there. A low resolution video of the events of that birthday party would be many, many gigabytes. So clearly, this business of selectively (and gradually) 'softening' memories, making them more and more blurry is essential to keeping our brains working.

The best guess for what sleeping brains do while we sleep is that we're dealing with memory reorganization. It seems likely that dreams happen because of this. When a memory needs to be simplified in order to take up less space, we are (perhaps) pulling it into short-term memory, then saving it back out into long-term memory in a simplified way. Consider the analogy of running out of space for photos of some long-ago holiday on your PC. You might pull each photo in turn into Photoshop, reduce the resolution of the image and increase the JPEG compression level - then save it back out again. When we wake up in the middle of a dream, we have all sorts of little snippets of memory from who-knows-where sitting in our short-term memories, seeming like it all just happened. We rapidly turn that into some kind of bizarre story and then (mostly) completely forget it again. All of this makes perfect sense in computing terms.

Of course we know that memories aren't saved as pictures and videos - but as collections of interlinked concepts - but at that higher level of abstraction, we're still editing our memories down to save space.

Further evidence of this is that people's memories get bad if they don't get enough sleep...makes sense if there is insufficient time for the brain to do the necessary housekeeping...and in the extreme case of Fatal familial insomnia when people don't sleep at all for weeks or even months - the consequences of being unable to perform brain maintenance is clear. Memory fails, we run out of space to store things - and the results are predictably disasterous.

The best computer analogy is probably 'defragging' a hard drive - something that users of older versions of Windows are probably familiar with. This is the process of having the system reorganize the files ("memories") on the hard drive ("brain") for more efficient access. The computer shuffles files into and out of RAM memory and puts them back onto the hard drive in a more logical order. If it were possible to have software that uses those files be running while this rearrangement was going on, the results would be a chaotic mess, not unlike dreaming. It's not true in practice, but naively, you could be editing a WORD document, and while you were editing it, bits of other documents could be dumped into that place on the disk drive and the resulting documents would be a weird mix of bits of old documents, stuck together in a strange order. Sounds just like a typical dream - right?

So we don't allow that - other programs should not be running while you're doing a defrag. In the human brain, that option is "sleep" - and we also do things like shutting off muscle control in order that we don't try to act out our dream states...and failures of that mechanism are things like sleep-walking or talking in your sleep. It's fascinating that dogs seem to has a more limited version of that shut-off control and almost always act out their dreams with little twitches of their feet and jaws and small, quiet, barks and growls.

SteveBaker (talk) 15:45, 22 September 2014 (UTC)[reply]

WP:TLDR

The human "brain" consists of well over a dozen organs, such as the various lobes of the cerebrum and their subsections, such as Broca's and Wernicke's lobes, the rest of the sensory and motor cerebrum, the cerebellum, the thalamus, hypothalamus, amygdala, pineal gland and its various parts and so on and so forth.

The brain has two major modes, wakefulness, modulated by serotonin, and sleep, especially REM sleep, modulated by acetylcholine. There is also D sleep.

During serotonin mediated wakefulness we are conscious and our working memories are at full capacity.

During ACh mediated REM sleep we dream and our brains lay down permanent memories as mediated by acetylcholine.

The neurons that have fired due to serotonin during the day (and norepinephrine, AKA adrenaline) during the day connect at night during the ACh phase.

Sleep is a state of the various organs of the brain which allows the retention of emotional, verbal, and kinetic memories to be laid down as permanent memories, rather than daily experiences. Refs avail on request. μηδείς (talk) 03:00, 23 September 2014 (UTC)[reply]

does the moon's pull affect river

Does the moon's pull affect river currents and river waves? — Preceding unsigned comment added by 199.7.159.41 (talk) 03:50, 22 September 2014 (UTC)[reply]

If you mean the tidal force resulting from the Moon's gravitation, yes it affects them - in as much as it affects everything on Earth (though the force involved is very small - the lunar tidal acceleration at the Earth's surface along the Moon-Earth axis is about 1.1 × 10−7 g, where g is the gravitational acceleration at the Earth's surface). In terms of being able to actually measure the direct effects of the tidal force, I don't think this would be possible except in 'tidal' portions of rivers, where the rise and fall is the result of tides out to sea causing the outward flow to stop and reverse. Such effects can be very pronounced, however - see for instance the Severn bore, where the shape of the estuary causes a dramatic upstream-moving wave under the right conditions. AndyTheGrump (talk) 04:59, 22 September 2014 (UTC)[reply]

Get your exponents right. It's 1.1 × 10⁻⁷ g.

But yes, the tidal effects on rivers are negligibly small. Not only is the force quite small; it affects two points of the same river to a similar extent, and most things we could observe rely on the difference between forces acting on separate points, not the forces themselves. For example, the Moon even attracts the terrain surrounding the river, another effect which is often overlooked.

The strong tides of the Severn bore are almost purely secondary effects: it's the tides of the ocean which get channeled upstream into a narrower basin, where the reduction in width translates into more height (Kudos to Andy for that example). - ¡Ouch! (^{hurt me} / _{more pain}) 07:58, 22 September 2014 (UTC)[reply]

Another well-known example is the "Reversing Falls" of New Brunswick. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:37, 22 September 2014 (UTC)[reply]

I'd like to explain why tides are so much smaller on rivers, since the tidal force exerted on a river is the same as on the ocean. It has to do with the depth of the body of water. You can think of water like a coil spring, which compresses a tiny amount when more force is applied, and extends a bit when less force is applied. The tides are caused by the addition and subtraction of the Moon's (and to a lesser extent, the Sun's) gravity to the Earth's. Since the Earth is so much closer to the water, it's gravity is far greater. Now the deeper the water (the longer the spring) the more the water (spring) moves up and down at the top. Rivers just aren't deep enough to have much of an effect, except, as noted previously, where the tides from a much deeper body of water spill over into them. Lakes are in-between, and deep lakes might have a noticeable tide, but still less than oceans. And, again, note that the lake doesn't need to be deep right where the tide is measured, since the water will spill over from where it rises in the deep area.

Sturat. Are you suggesting by "You can think of water like a coil spring, which compresses a tiny amount when more force is applied, and extends a bit when less force is applied" that tides are the result of the volume of water varying locally due to gravity induced compression? Could we have a reference for that? This is a long from my understanding. 2A01:E34:EF5E:4640:C5F3:58BA:E680:C3A2 (talk) 18:05, 22 September 2014 (UTC)[reply]

Another factor that affects tides is the shore geometry. If the shore is absolutely flat and at low tide level, then the water that spills over will move far inland, but not raise much in height, since the water is spread out over such a large area. StuRat (talk) 13:27, 22 September 2014 (UTC)[reply]

How large is the "tide" on the world's largest (somewhat) isolated bodies of water, such as the Great Lakes? Edison (talk) 12:35, 22 September 2014 (UTC)[reply]

According to NOAA, the tides on the Great Lakes are only a couple of inches, and local weather has a much greater impact on lake levels than tides do. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:40, 22 September 2014 (UTC)[reply]

Tides affect everything including the land, buildings, and your body, although in small solid objects, the stretching is microscopic and only noticed in suche cases as approaching neutron stars and blackholes (spaghettification). The tide does affect the land and crust, but Spain doesn't "fow" into Portugal or New Jersey into Pennsylvania because these are solids. Liquids flow freely, however, and ocean tides in effect have a greater fetch over which to build up, meaning a more dramatic effect. The westward pull of the moon doesn't cause the North-South running Nile and Delaware rivers to flow up dramatically onto their western banks the way a very small part of the very large Atlantic ocean does. The tidal effect on the Delaware, which is felt as far north as Trenton, is due to ocean water pushing up the delaware bay, not due to any direct effect on the river water itself, which again would be microscopic were the river a canal with a closed southern end. μηδείς (talk) 17:31, 22 September 2014 (UTC)[reply]

But there are people that claim that if there's no measurable tide the stream high tide (besides the full moon, hour, season and weather) still makes it better to fish, even if it's New Moon. Sure fish are sensitive but is there any possible way they could feel a river tide? Or maybe they just claim the moonlit tide, if night is low predator but they often can only use their other senses (water would only transmit moonlight well a few hours a night), the fish might gain lunar day (24.8 hour) sleep patterns and bite best near full moon when it's high in the sky. And maybe it's optimal for fish to eat a second time a day and they minimize hunger and/or digest slowly? Ed:thus explaining the non-moonlit high tide eating peak, if that was indeed what was claimed Sagittarian Milky Way (talk) 01:21, 23 September 2014 (UTC)[reply]

I'll just assume you are trolling us with bullshit as usual, but no, of course fish in small bodies with tides that affected their bodies to the same amount as the water itself would not be able to detect the few nanometers stretch that affected them or the water they were in, unless you believe in psychic fish? In which case, why are you asking here? We deal with facts and you obviously have too many. μηδείς (talk) 02:44, 23 September 2014 (UTC)[reply]

Remember to be civil, medeis199.119.235.162 (talk) 03:10, 23 September 2014 (UTC)[reply]

(edit conflict) I hadn't done the math, and didn't think of how water-like a fish's body must be for very tiny stretches. (Fish can detect very small water pressure changes on their body, and I subconsciously misremembered the ounce lunar pull on a man at the Lagrangian point as at Earth, giving me the wrong idea). Of course I don't believe in psychic fish, but building their circadian rhythm around feeding when moon angles with low water albedo appear could be a means which doesn't require nanometer precision. Anglers who claimed this thought inland tides would not lag the Moon like sea tides (probably true?), making this more likely. Sagittarian Milky Way (talk) 04:50, 23 September 2014 (UTC)[reply]

IIRC, fish detect minute pressure changes using their Lateral line. --Jayron32 16:45, 23 September 2014 (UTC)[reply]

Polarity of Electret Microphone?

[[7]]

i want to know which is the Ground (GND) terminal of Electret Mic? one of its two terminals carries mark beside it--- is it GND or +VE ? pls help... thnk u. — Preceding unsigned comment added by 101.210.20.198 (talk) 11:34, 22 September 2014 (UTC)[reply]

If the microphone has a metal case, that will almost certainly be grounded. So you could use a multimeter to measure resistance between each pin and the case - if either of them is a dead short, then that's the ground pin. The photo at the top of our article shows that one of the two pins is obviously connected to the case...but your actual device may be different. SteveBaker (talk) 14:57, 22 September 2014 (UTC)[reply]

Falling on your eye

When people fall on their eye, is the natural instinct to close the eye or try to dodge? Or stick their hands out like a regular fall, or try to block it with their hand? What I mean is if they slip and their eye is headed toward something pointy in the wall that looks like this:

What if it's a nail or a screw, putting the protect the nose instinct against the protect the eye instinct? (though unless you've got a bad nail protrusion length to nose length ratio, I think the danger to your eye is illusory. Sagittarian Milky Way (talk) 00:27, 23 September 2014 (UTC)[reply]

Obvious BS with no referenceable answer. μηδείς (talk) 02:39, 23 September 2014 (UTC)[reply]
- How is it obvious BS? There could possibly be cases. I'd like to know what they did, even if selection effects prevent a referenceable answer as there'd be a strong bias to reporting when the subject did not in fact manage to prevent major harm of their eyeball. Sagittarian Milky Way (talk) 05:13, 23 September 2014 (UTC)[reply]

- I hadn't been aware that assholes punching their partners and saying they fell is the major cause of such claims, or even of any claims. (Okay, now I think I have heard that before.) Anyway I was thinking of long protrusions smaller than the your eye socket, as that would be the scarier than a black eye. Sagittarian Milky Way (talk) 05:47, 23 September 2014 (UTC)[reply]

September 23

Salk polio vaccine tested in Russia?

The article Jonas Salk does not seem to mention testing of the polio vaccine in the Soviet Union, but I recall a tv documentary which said that there was testing of it in a large city in the USSR, and being surprised that the soviets would have allowed it. 1)Was there such Soviet testing before the announcement in the mid 1950's that it was safe and effective? 2) Did they followup initial administration of the Salk injected vaccine in the US with the Sabine oral vaccine, to the same children a year or so later, or did they stick to a Salk booster injection the next year for children who had the initial Salk injection? Edison (talk) 02:17, 23 September 2014 (UTC)[reply]

Here's a few freely accessible scientific articles on the topic. At a quick scan, these all seem to give dates 1958-1960 for studies in the USSR. Also, it seems that the tests done in USSR were for the live attenuated vaccine developed by Albert Sabin, not the Salk inactivated 'killed' vaccine. [8] [9] [10]. Here are a few documentaries on the topic if you want to follow up on that angle [11] [12]. The second link, from the Smithsonian, seems to indicate that Salk's trials started in 1954 in the US, while Sabin's were in Europe. SemanticMantis (talk) 16:41, 23 September 2014 (UTC)[reply]

Compensation of cost losses in the economy (Write-off of cost losses)

off topic for this board

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Obviously, that the expensive capitals are always more expensive than the cheap capitals in to its nominal value, so that, should the bourgeois capitalist economy do to equalize the costs of capitals?--Alex Sazonov (talk) 08:03, 23 September 2014 (UTC)[reply]

This is the Science Ref Desk. Only a madman would call economics a science. HiLo48 (talk) 08:40, 23 September 2014 (UTC)[reply]

Thanks. I suppose that economics is be a science! Should the bourgeois capitalist economy do to compensate the costs of the lost (unfulfilled) labor - work?--Alex Sazonov (talk) 08:45, 23 September 2014 (UTC)[reply]

All this questions are always be equal to the same. Should in the bourgeois capitalist economy a profitability of capitals be the equal, that is so, should in the bourgeois capitalist economy a rates of calculation (accrual) of profits on capital are be the equal?--Alex Sazonov (talk) 10:51, 23 September 2014 (UTC)[reply]

You mean "Write-off of cost losses" as lowering taxes tru Depreciation? Any number of n economists are usually blamed for having n+1 different opinions so "economics" indeed always has some difficulties with its claim to be science. Anyway this is a question of economic policy aka politics and this makes it an not fitting question here. --Kharon (talk) 11:04, 23 September 2014 (UTC)[reply]

Of course, the collapse (disintegration) of the Soviet Union (USSR) had objective reasons!--Alex Sazonov (talk) 11:41, 23 September 2014 (UTC)[reply]

If you look at Wikipedia:Reference_desk you see economics falls under the Wikipedia:Reference_desk/Humanities. Post there as you are unlikely to get a sensible answer on this desk.--Salix alba (talk): 11:07, 23 September 2014 (UTC)[reply]

Very much thanks, I don’t know about it. So I been suppose, that is been obviously, that the profitability of economies as also economic actors could not be the equal, otherwise, at the expense of someone will had to cover the losses. Thanks a lot for all.--Alex Sazonov (talk) 11:24, 23 September 2014 (UTC)[reply]

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Nose shaping

There have been spate of so called "nose shaping" devices flooding the market like Nasofix. Nose Magic, Nose Up etc... They claim that the cartilage in nose which gives it's shape is actually malleable if pressed for a period of time everyday and that too at a particular temperature. How true is it ?? — Preceding unsigned comment added by 119.235.54.187 (talk) 11:07, 23 September 2014 (UTC)[reply]

i'm not sure about the products but i don't think "malleable" is the right word to describe cartilage; iirc it's displaced during a nose job, not moulded? ~Helicopter Llama~ 11:54, 23 September 2014 (UTC)[reply]

Is the speed of the electrons is not been enough?

Is it right to consider that the speed of electron (the speed of flow of electrons) is insufficient by compared to the speed of light, although all nuclear physics just is been based on the speed of the electrons (on the speeds of flow of electrons)?--Alex Sazonov (talk) 13:04, 23 September 2014 (UTC)[reply]

Who says so? ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:41, 23 September 2014 (UTC)[reply]

However, I suppose, that the division of nuclei and atoms (nuclear decay) always had been a high-speed output of flow of electrons instead of light energy output.--Alex Sazonov (talk) 14:50, 23 September 2014 (UTC)[reply]

Our article on beta particles says that their speed is typically greater than 0.75c. Gandalf61 (talk) 15:07, 23 September 2014 (UTC)[reply]

Thank you Gandalf61. The intensity of the electromagnetic fields is always been determines the speed of the electrons (the speeds of flow of electrons).--Alex Sazonov (talk) 15:15, 23 September 2014 (UTC)[reply]

It also depends on what you mean by speed. The speed of a single electron in isolation is rarely a useful thing to know when modeling the behavior of matter. What you want is the Root-mean-square speed of electrons in a given environment. --Jayron32 16:19, 23 September 2014 (UTC)[reply]

Under the speed of electron, I been mean the permissible speed acceleration of electron.--Alex Sazonov (talk) 17:16, 23 September 2014 (UTC)[reply]

This is explained by bremsstrahlung: "The total power radiated in the two limiting cases is proportional to

\gamma ^{4}

(

a\perp v

) or

\gamma ^{6}

(

a\parallel v

). Since

E=\gamma mc^{2}

, we see that the total radiated power goes as

m^{-4}

or

m^{-6}

, which accounts for why electrons lose energy to bremsstrahlung radiation much more rapidly than heavier charged particles" Count Iblis (talk) 18:40, 23 September 2014 (UTC)[reply]

Also relevant to Iblis's link is Larmor formula. --Jayron32 18:55, 23 September 2014 (UTC)[reply]

As far as I know the resonances of the electric current and dynamics of the electric current in the gases are always had been not so great dynamics as in the metal alloys. Therefore, gases are not been the environment on which we can speak.--Alex Sazonov (talk) 19:22, 23 September 2014 (UTC)[reply]

Still, the natural environment of all electrons are always been metals!--Alex Sazonov (talk) 03:14, 24 September 2014 (UTC)[reply]

Question about iud study

Question moved from "Question about iud study" on the Miscellaneous desk. -- Eron^Talk 16:52, 23 September 2014 (UTC) [reply]

In one study about iud on the internet, it said that 1.8 percent of teenagers became pregnant while using mirena iud. Do they mean that the first year failure rate for teens using it is 1.8, or do they mean that 1.8 percent of teens became pregnant over the course of the study? It said they used descriptive statistics to determine the failure rate within first year of use.199.7.159.41 (talk) 03:41, 22 September 2014 (UTC)[reply]

Complications and Continuation of Intrauterine Device Use Among Commercially Insured Teenagers

Table 2 has the the percentage you listed, and the text associated says

“

The frequency of complications within the first year of use was low among users of both types of IUDs in all age groups (Table 2)

”

-- looks like a first year ~~failure~~ rate of normal pregnancy to me (edit: there are other failure modes and complications that are also listed in the table, so, overall complications/"failures" due to any cause would be higher). SemanticMantis (talk) 14:27, 22 September 2014 (UTC)[reply]

But it says that out of 1528 teenagers, 28 became pregnant, which is close to 1.8 percent of 1528. If you look at table 1, you will see that the number of teens applying for a hormonal iud every two year period, adds up to 1528. My question is, how did they come up with 1.8 percent as the first year failure rate?24.207.79.50 (talk) 17:46, 22 September 2014 (UTC)[reply]

By the way, I'm the same person who posted the first question24.207.79.50 (talk) 17:47, 22 September 2014 (UTC)[reply]

Table 2 shows the frequency of various outcomes in the first year of use. Of 1528 subjects aged 15 to 19 years old at time of insertion, 28 became pregnant within one year. So the first year failure rate for this cohort was 1.8%. The key is that 28 did not become pregnant during the full study; 28 became pregnant within one year of having an IUD inserted. - Eron^Talk 18:08, 22 September 2014 (UTC)[reply]

I think i understand. what you are basically saying is that there were 28 teenagers who reported pregnancy after one year. Which means there could have been possibly more pregnancies during the entire period, but because they were after one year of use, they weren't mentioned, since the study was not looking for the total number of pregnancies during the entire period, but instead for the number of teens who reported pregnancy after their first year. — Preceding unsigned comment added by 24.207.79.50 (talk) 18:49, 22 September 2014 (UTC)[reply]

Yes. This is explicitly stated in the abstract: "A retrospective cohort study was conducted... to estimate the odds of experiencing complications, method failure, or early discontinuation within 12 months of insertion by age group and type of IUD inserted." - Eron^Talk 19:04, 22 September 2014 (UTC)[reply]

Anyway, my last question before i make myself look more foolish is, does that mean that the total number of pregnancies during the full study could have been even greater than the number of pregnancies reported after one year of use? Also, maybe this study should be cited in wikipedia — Preceding unsigned comment added by 24.207.79.50 (talk) 19:17, 22 September 2014 (UTC)[reply]

Yes, the total rate of pregnancies would be greater than the rate in the first year. - Eron^Talk 20:21, 22 September 2014 (UTC)[reply]

Anyways, thanks a lot for your answers. They really helpde, because for some reason, i was confused about the study, but i realized that it was because I didn't look at the study carefully enough. I still have some doubts about your answers,and i also still wonder why the percentage would be so high, but thank you24.207.79.50 (talk) 21:17, 22 September 2014 (UTC)[reply]

Also, would it be correct that out of each of the four numbers shown in table 1, 1.8 percent of them each became pregnant? or would it be correct if i divided 28 people or 1.8 percent by 8? According to table 1, 53 people applied from 2002-2003. When you add them all up it comes out as 1528, which is the total number of people in the study.24.207.79.50 (talk) 22:33, 22 September 2014 (UTC)[reply]

It wouldn't be correct to say that for each of the cohorts shown in table 1 exactly 1.8 percent of them became pregnant. That is the average value across all four cohorts. It may have been 1 from 2002-03, 2 from 2004-05, 7 from 2006-07 and 18 from 2008-09; but it could just as easily been 2, 3, 6, and 17, or 0, 1, 8, and 19, or other combinations that add up to 28.

That said, the farther the numbers for each cohort get from the 1.8% mean, the less statistically likely they are to be correct. It would be highly unlikely for there to have been be 0 pregnancies in three of the years and 28 in the fourth. So for that reason you would not want to divide 28 by four and say there were 7 pregnancies for each two-year period, as that would mean the percentage failure rates would have been 13%, 6%, 1.8%, and .7% respectively - this is not statistically likely. - Eron^Talk 00:25, 23 September 2014 (UTC)[reply]

Well, when i divided 1.832460732984293 percent (28/1528) by 8, the result was 0.2290575916230366. When i calculated the failure rate using the pearl index, the result came out the same. And besides isn't that close to what the mirena iud failure is normally said to be?24.207.79.50 (talk) 00:56, 23 September 2014 (UTC)[reply]

The Pearl Index is ( (Number of pregnancies x 12) / (Number of women x Number of months) ) x 100. For this study, the number of pregnancies is 28, the number of women is 1528, and the number of months is 12. Remember, the study only reported pregnancies in the first 12 months after IUD insertion. Plug those numbers in and you get ( (28 x 12) / (1528 x 12) ) x 100 = 1.8. Don't be confused by the fact that there are data covering eight years. The reported pregnancy rate is only for the 12 months after insertion for each individual woman, not the rate over the full eight years. Regardless of what the Mirena failure rate is reported as, the rate reported in this study is 1.8%. - Eron^Talk 01:29, 23 September 2014 (UTC)[reply]

I wonder why the first year failure rate is so high according to the study then. Anyways, iforgot, yes 28 people got pregnant after one year, not during the full study.24.207.79.50 (talk) 01:51, 23 September 2014 (UTC)[reply]

The authors wondered that as well and they refer to these findings in the discussion section:

"It is possible that some pregnancies in our study were the result of luteal phase placements or spontaneous expulsions that were not coded. Additionally, our observation of elevated odds of pregnancy in younger women (15–19 year olds) compared with those 25 years and older may be the result of differences in fertility between the younger and older groups, leading to the observed differences.

"We used claims codes that indicated pregnancy for the outcome “normal pregnancy” but could not confirm the pregnancy in many cases. In addition, it was not always possible to determine whether pregnancy occurred as a result of spontaneous expulsion, because a claim may not have been made."

- Eron^Talk 03:15, 23 September 2014 (UTC)[reply]

Maybe i'll ask more tomorrow. Or perhaps move the qusetion to the science desk. How do i do that?199.119.235.162 (talk) 03:50, 23 September 2014 (UTC)[reply]

Don't move the question; you can just post a new one on the Science desk. - Eron^Talk 04:54, 23 September 2014 (UTC)[reply]

Is it ok to copy the answers from here to the new question?199.119.235.162 (talk) 14:21, 23 September 2014 (UTC)[reply]

Yes - in fact moving the question is OK too, I've just done that. - Eron^Talk 16:52, 23 September 2014 (UTC)[reply]

OP, what is your current question? It seems to me that Eron has sufficiently answered all the followups you've asked. Anyway, the quote above speculates a bit on why there is a higher rate of pregnancies for young women. It seems high compared to to other figures because many other sources will just report one figure for all ages, and given the data in table 2, that would be true for this study as well. SemanticMantis (talk) 17:17, 23 September 2014 (UTC)[reply]

Well, okay, here is thing. When i added up the number of pregnancies across the three age groups, the sum was 630, which is close to 0.9 percent of the sum of people using mirena from all the three age groups. That is still way above the yearly failure rate normally reported for mirena.199.7.159.55 (talk) 18:11, 23 September 2014 (UTC)[reply]

Yes it is. The authors asked the same question. They don't have an answer but suggested some possibilities, i.e. the IUD may have been placed during the luteal phase or the IUD may have been spontaneously expelled. The clinical trials that showed a 0.2% failure rate included 3330 women. We don't know the ages or other information of those women. We can surmise that as a clinical trial the results were probably carefully screened to eliminate pregnancies resulting from luteal phase placement or spontaneous expulsion. I would also expect the clinical trial did not include 15 to 19 year olds, the group that had the largest incidence of pregnancy in the study you originally referenced. - Eron^Talk 18:36, 23 September 2014 (UTC)[reply]

I agree. OP should keep in mind the difference between a retrospective study like the one cited, and studies based on clinical trials. The former simply cannot control as many variables as the latter. The data from a retrospective does not have the same quality control and quality assurance as a the data resulting from a controlled trial. Also, I'll point out that calculating a first year pregnancy rate is not the purpose of the cited study. Rather, the cited study has a goal of assessing safety of IUD for young women. The other stuff about pregnancy is just ancillary icing on the cake. Unless you are a specialist in the field, I would suggest trusting results from studies that were designed to find those results, over results that fall out of related studies. SemanticMantis (talk) 19:31, 23 September 2014 (UTC)[reply]

And as a response to eron, the pregnancy failure rate for those aged 25-44 was 0.8 percent, which is also still a far cry. But, anyways, yes, i understand, the main purpose of this study was to assess safety for teens, not to determine the yearly failure rate.24.207.79.50 (talk) 20:45, 23 September 2014 (UTC)[reply]

I wonder then if there are other studies on the effectiveness of iud in teens24.207.79.50 (talk) 02:31, 24 September 2014 (UTC)[reply]

Probably the expulsion rate would be higher among teens due to their cervix?24.207.79.50 (talk) 02:45, 24 September 2014 (UTC)[reply]

Take a look at this: Adolescents and Long Acting Reversible Contraception. It is not a study, more of a medical guideline, but it references several studies. There is a good section on IUDs and adolescents and lots of references (not all are freely accessible, however.) Regarding expulsion, it notes "Intrauterine device expulsion rates range from 3% to 5% for all IUD users and from 5% to 22% in adolescents.". - Eron^Talk 04:18, 24 September 2014 (UTC)[reply]

Explaining the speed of light travelling through matter. Clarification sought.

In the case of well made glass, or even clean air, light can travel very well without much scatter and giving every appearance of near perfection. I think for instance of using good quality binoculars to observe a star set in a quarter second through 400 odd km of varying atmosphere across a marine horizon at 15km. If one thinks of the passage through the air and then the binoculars and then the lens of the eye, such that a very clear and faithful message is seen by the brain; I am drawn to conclude that the speed of light in the three media (air, glass and human lens) is utterly systematic. The atoms in the three media are changing the speed of transmission in an extremely uniform way. Now the optics and the explanation for the refractions are all very well explained, but my impression is that explaining the physics of why light slows near matter is not explained at all. We have been thinking this normal for so long now, that it just normal, but not explained. Can I be corrected on this assumption of no explanation?

By no explanation, I mean that I am very happy with explanations for how light amplifiers work and the action of phonons, it all seems very logical. Are we missing a mystery here? Biezanek (talk) 20:32, 23 September 2014 (UTC)[reply]

Our article on refractive index has a description in the section Refractive_index#Microscopic_explanation. As light travels through a medium, electrons within the material respond to the changing electric and magnetic fields. This means that the wave that travels is not just "bare" light, but a coherent, coordinated combination of an elecromagnetic wave with a wave propagating in the electrons in the material. (In some cases, sound waves in the material also participate.) You can think of this in terms of classical electromagnetic waves and a population of electrons that can be pushed around by the EM field. You can also describe it in terms of Feynman diagrams in which the photon gets absorbed and re-emitted many times as it travels through the material. Both pictures are describing the same thing. --Amble (talk) 21:50, 23 September 2014 (UTC)[reply]

September 24

Colour in electron microscopy

Asking from a lay point of view - I understand that everything is splattered in gold, so a true-colour image would be pretty much monochrome anyway - but don't electron beams have wavelengths as photon beams do? - if so, why don't they translate to different colours on the monitor?

Thanks Adambrowne666 (talk) 00:27, 24 September 2014 (UTC)[reply]

...Because such an image is not generally useful, scientists rarely build or use a machine that would create such an image.

If you're willing to stretch your definition of "imaging," you can find machines that do actually distinguish different type of electrons: electron spectroscopy. For example, a long time ago, I studied results from the electron spectrometer on the DEMETER spacecraft. The signals we processed were not images - we processed the data into spectrograms. If you wanted to build an imager in the sense of an electron microscope, you'd have to do one of several things: you'd need to turn your electron microscope's imager into a spectrometer, either by adding a filter pattern (analogous to a color filter array on a digital camera); or you'd need to combine multiple exposures with different settings (e.g., hyperspectral imaging). Alternately, you'd need to take an existing spectrometer and turn it into an imager, by adding directionality and some kind of focusing plane. Or you could come up with something else new and creative that hasn't been invented yet! (Again, most scientists haven't invented such a device because it'd be really hard to make, and probably wouldn't provide much new useful information). But if it did work, it would provide an image based on the electron's energy - not its "color." As you already know, the perceptual relationship between color- and wavelength- is only relevant for photons in the visible spectrum!

Our article on SEM covers the use of false-color, and also describes some extant techniques used to collect multiple-data-values per pixel, which can be rendered in post-processing into colorful images.

Nimur (talk) 01:58, 24 September 2014 (UTC)[reply]

Excellent answer, thanks, Nimur. Adambrowne666 (talk) 02:27, 24 September 2014 (UTC)[reply]

Whether it's coated in gold depends on the sample. That's only done for non-conductive samples. It's unnecessary for conductive samples and it can be avoided in other situations by using a low accelerating voltage and/or low vacuum.

And the interaction between the electrons and the sample isn't reflection like with photons. Most of what is used to form the image in the SEM is secondary electrons produced by inelastic scattering events. They fall into a fairly small, low energy range and aren't very dependent on things like atomic number, so even if you could distinguish between electrons of different energy (wavelenth), I'm not sure it would give you any useful contrast. But the process used to collect them would make it basically impossible anyway. The electrons can be emitted in any direction, so the detector works by using a positively biased grid to accelerate them toward the detector, which means any of the original energy information would be lost.

The other main imaging mode uses backscattered electrons formed by elastic interactions with the nucleus. The energy is high enough and the angular distribution small enough that they're generally measured directly. But since the electrons can undergo multiple scattering events I don't know that the energy value would really be that useful.

There is a similar, but much less common technique that does use the energy of the electrons to form the image called scanning Auger microscopy, based on Auger electron spectroscopy. [13] has some example images. Because Auger electrons are emitted from the top few nanometers of the sample, the preparation requirements are much more stringent. Obviously coating would be impossible and even small amounts of surface contamination could make imaging impossible. Systems all have to use ultra-high vacuum. But like the more common SEM technique of energy-dispersive X-ray spectroscopy, which can generate similar images, the colors are assigned arbitrarily. Mr.Z-man 03:31, 24 September 2014 (UTC)[reply]

Thanks, even more interesting. On another topic, from my reading of the WP article, I see no suggestion that samples might be altered or explode from within in the necessary vacuum. Also, where do I get hold of a goldbug after it's been used? Adambrowne666 (talk) 03:56, 24 September 2014 (UTC)[reply]

Moon in collision course with Earth

As shown in the TV miniseries Impact, is it possible that the moon might ever be on a collision course with Earth? If not, please explain the scientific reason behind it. Thanks. --EditorMakingEdits (talk) 01:55, 24 September 2014 (UTC)[reply]

Inertia is a real thing that exists! If the moon were on a collision course with Earth, ... we'd see it coming from two hundred thousand miles away! Perhaps you'd like to read about orbit or conservation of angular momentum: the moon won't just magically start coming towards us. Something immensely energetic would have to take place that could transfer energy and momentum to move the moon off its existing course, which is a very stable, nearly circular orbit around our planet. Objects like the Moon are quite large and massive: they do not change their motion with great vitesse. Nimur (talk) 02:00, 24 September 2014 (UTC)[reply]

(edit conflict) No. The moon is drifting away from earth. See Orbit of the Moon#Tidal evolution. The article Tidal acceleration explains why. --Jayron32 02:01, 24 September 2014 (UTC)[reply]

Right, but that's an incredibly slow change! Nimur (talk) 02:02, 24 September 2014 (UTC)[reply]

So an asteroid impact may send the moon on a collision course with Earth? (as trasfer of energy and momentum takes place) --EditorMakingEdits (talk) 02:07, 24 September 2014 (UTC)[reply]

It must be a very very big asteroid indeed! (or traveling very fast) 202.177.218.59 (talk) 03:13, 24 September 2014 (UTC)[reply]

It would have to be a stupendously huge asteroid. Unimaginably large. Here is a Quora response to exactly this question. Basically, it would take something a bit smaller than 4 Vesta. Huge. Mingmingla (talk) 03:18, 24 September 2014 (UTC)[reply]

Hmmmm, given the mass of the Moon and its orbital speed which you want to reduce to zero realtive to Earth in the collision, Vesta won't be enough. You would need approximately 4 times the mass of Vesta coming in at a relative speed of 60 km/s. Count Iblis (talk) 03:36, 24 September 2014 (UTC)[reply]

Thanks for the explanations. --EditorMakingEdits (talk) 05:07, 24 September 2014 (UTC)[reply]

Wikipedia:Reference desk/Science