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October 27

Naturally-occurring promethium

I understand that promethium doesn't occur naturally in any place to which we have easy access, but if it did, would we always find it to be radioactive? I understand that all known bits of this metal have been radioactive, but they've always been produced by human-created nuclear reactions, and I know that nuclear reactions can also create radioactive isotopes of elements that aren't normally radioactive, such as carbon. In other words, if we found promethium that hadn't been created by human-started nuclear reactions, would it necessarily be radioactive? Nyttend (talk) 00:50, 27 October 2010 (UTC)[reply]

See Isotopes of promethium. The most stable is ¹⁴⁵Pm with a half-life of 17.7 years. So all of them are radioactive. Note that the more stable the easier it is to find the isotope, so it's not likely there is another more stable isotope out there that we did not find, plus the table seems pretty complete. Ariel. (talk) 01:30, 27 October 2010 (UTC)[reply]

(edit conflict with Ariel) We have an article Isotopes of promethium, which asserts that there are no stable isotopes, but doesn't really give an explanation. However, if we look at Isotopes of technetium, the Liquid drop model, which is pretty good at predicting nucleus binding energies, rules out the possibility of any stable isotope of technetium. I assume that a similar reasoning applies for promethium, and if someone more knowledgable than me wants to, an explanation similar to the one in "Isotopes of technetium" article could be put in the "Isotopes of promethium" article. Buddy431 (talk) 01:34, 27 October 2010 (UTC)[reply]

Note that when a reactor creates radioactive isotopes, it's actually just creating isotopes that happen to be radioactive. To put that (and others' comments) another way, it's an intrinsic property to the isotope, not a result of how it was made. So you'd have to figure out a previously-unknown isotope. And models of the whole general idea here don't seem to find any. DMacks (talk) 01:48, 27 October 2010 (UTC)[reply]

One caveat (which doesn't in any way detract from the general truth of DMacks statements) is the existence of nuclear isomers. Most notable is technetium-99m which has a half life of 6 hours, versus "regular" technetium-99, with a half life of 211,000 years. The two have the same number of protons & neutrons (they are the same isotope, for certain definitions of isotope), but have different half lives. The half life of ^99mTc (or plain ⁹⁹Tc) is an intrinsic property of that state, and doesn't depend on how it's made, but whether you get ⁹⁹Tc or regular ^99mTc depends on how you make it. -- 174.31.221.70 (talk) 02:25, 27 October 2010 (UTC)[reply]

Hmm, DMacks' comment is quite illustrative. I'd never known this before; I'd assumed that these isotopes were radioactive because of the way they were made, not because of their intrinsic natures. For that reason, I had no interest in the isotopes article. So...does promethium not occur naturally in any place to which we have access because it's radioactive? Nyttend (talk) 02:34, 27 October 2010 (UTC)[reply]

Basically if it is only and always radioactive and has very short half lives (which it does), you won't find much of it around. You can still find some of it in very trace quantities because other radioactive elements will convert into it. But if it is very unstable, those won't stick along very long, and the fact that only a few reactions seem to lead to its creation make it pretty rare. If it happened to be created by a more common reaction (e.g. the alpha decade of uranium or thorium or whatever), you'd see more of it, even though it is radioactive. Radon, for example, has no stable isotopes either, but is present in far greater quantities because the reaction that creates it is pretty common by comparison. --Mr.98 (talk) 02:40, 27 October 2010 (UTC)[reply]

The promethium article notes that there is probably about 570 g that exist in the earth's crust at any one time. But given the ~18 year maximum half life, it disappears quickly. Even if the entire earth was made of solid promethium, in just over 100 half lives (2,000 years), you would have less than 1 mg of it left. The only promethium you'll find was made relatively recently. -- 174.31.221.70 (talk) 06:29, 27 October 2010 (UTC)[reply]

Oooh radioactive equilibrium!John Riemann Soong (talk) 03:32, 28 October 2010 (UTC)[reply]

Formation of gold deposits

How do gold and other valuable (and relatively non-chemically-reactive) metals collect and concentrate into very localized deposits, veins, lodes, etc.? I did not get a very good sense of how that is thought to occur from the Gold article; Placer deposits make some sense, but are there other mechanisms? (Would separation-by-density, as in centrifuge enrichment but using gravity and a lot more time, be a possibility?) WikiDao ☯ (talk) 03:09, 27 October 2010 (UTC)[reply]

Have you read Vein (geology) ? Nimur (talk) 03:39, 27 October 2010 (UTC)[reply]

Also see Ore genesis#Gold. Mikenorton (talk) 09:54, 27 October 2010 (UTC)[reply]

Great links, thanks. Interestingly, from Ore genesis#Gold: "A bacterium, Cupriavidus metallidurans plays a vital role in the formation of gold nuggets, by precipitating metallic gold from a solution of gold (III) tetrachloride, a compound highly toxic to most other microorganisms." WikiDao ☯ (talk) 15:16, 27 October 2010 (UTC)[reply]

Also Volcanogenic massive sulfide ore deposit and Seafloor massive sulfide deposits (although the SMS article could do with being updated in light of Nautilus Minerals' Solwara 1 project in PNG). Sean.hoyland - talk 15:31, 27 October 2010 (UTC)[reply]

Why aren't these bacteria commercially used? John Riemann Soong (talk) 03:43, 28 October 2010 (UTC)[reply]

some one will helpme that in which place i should ask my questions

i am a student of electronics engineering and want to ask question about my course and my technology related to be answared by wiki friends so plz some one show me the particuler place where this technology will under discussion thank you —Preceding unsigned comment added by Dawoodian 09 (talk • contribs) 08:01, 27 October 2010 (UTC)[reply]

You've come to the right place! Wikipedia's science reference desk (this web page) is an appropriate place to ask questions about electronics engineering, especially if you haven't been able to find the answer to a question within Wikipedia's articles. We won't do homework problems for you, but we can help you to do it yourself if you get stuck, and help you grasp the concepts that you are learning. Do you have a question currently, and if so, what is your question? Red Act (talk) 08:34, 27 October 2010 (UTC)[reply]

Spelter

Is spelter really an alternative name for zinc? --Chemicalinterest (talk) 11:05, 27 October 2010 (UTC)[reply]

No it's an alloy. Spelter --TammyMoet (talk) 11:12, 27 October 2010 (UTC)[reply]

(EC) Any reason you choose to disbelieve our referenced (admitedly some of them seem dead) article? Spelter Nil Einne (talk) 11:31, 27 October 2010 (UTC)[reply]

See zinc, a FA. --Chemicalinterest (talk) 11:36, 27 October 2010 (UTC)[reply]

Just clarifying: UK usage. Zinc is zinc. Spelter is spelter - at least in the antiques trade! --TammyMoet (talk) 11:43, 27 October 2010 (UTC)[reply]

Is that in contradistinction to American usage? It is conceivable that spelter means zinc in American usage for all I know, but I suspect that most people just don't know the word at all. I certainly didn't. If I'd had to guess, maybe I'd have thought it was someone who trades in spelt. --Trovatore (talk) 21:24, 28 October 2010 (UTC)[reply]

Yes. Another British user raised a complaint about that too. See this. --Chemicalinterest (talk) 12:14, 27 October 2010 (UTC)[reply]

The word "spelter" seems to have been used for alloys of zinc with various other metals (as stated in out article), but Wiktionary has only the plain zinc meaning (until I change it). The OED also has "1912 Trans. R. Geol. Soc. Cornwall XIV. 153 <<In some of the deeper levels..an intimate mixture of chaliopyrite and garnet, which sometimes contains cassiterite also, locally known as ‘spelter’, has been met with in considerable quantities.>>". I first met the word in connection with galvanizing, and there is also a verb "to spelter". Take your choice of meanings. Dbfirs 00:16, 28 October 2010 (UTC)[reply]

Magnetic flux and electricity

Hi, I recently asked a question about electrical current in a conductor placed between 2 repelling magnets. I got some interesting and sensible responses, thanks! I have a few images of what I have in mind, but this site seems too cumbersome to upload images for communication purposes. If someone is at all interested in entertaining an idea of mine, could they kindly beep me e-mail redacted. I know too little about associated electromotive force or magnet technology (despite googling everything I could get my hands on), so any assistance would be very much appreciated!

Thanks —Preceding unsigned comment added by Cordin0792 (talk • contribs) 11:45, 27 October 2010 (UTC) I removed the e-mail address to avoid possible spamming. Answers can be given on this page. Cuddlyable3 (talk) 12:33, 27 October 2010 (UTC)[reply]

Magnetic flux and magnets

...in response to my first question on magnets and electricity generation (let my try and use a few words to paint a thousand pics!):

I am picturing a magnetic bearing designed in a toroidal shape (equilateral triangular in section) which spins around the toroid's central axis. It is supported by repelling magnets on the upper and lower triangular faces and on interfacing surfaces of a spherical holder. A solenoid coil wraps around the toroid, but is attached only to the holder on the inside face, so that the toroid runs inside the solenoid. The bearing therefor is the generator, one and the same. No air inside and no friction, hopefully = no resistence to motion/acceleration(??)

If this ain't gonna work, one could piggyback the generator on the magnetic bearing, but this is plan B...

Any comments? —Preceding unsigned comment added by Cordin0792 (talk • contribs) 11:58, 27 October 2010 (UTC)[reply]

What are your goal? Compact generator, efficient generator, Free energy, eye catching demonstration or what? It is hard to coment on a plan without knowing the goal. How are you going to drive the rotor if it is encapsulated in a toroidal coil? (I do not think it is a solenoid if it is bent to a toroidal shape.) --Gr8xoz (talk) 13:37, 27 October 2010 (UTC)[reply]

I did not fully understand what you describe - in particular upper and lower parts of a triangle?? But anyway, see Earnshaw's theorem, which shows you can not balance the bearing based entirely on magnets, you would need some kind of active control. So even though I did not understand the layout, I can tell you it's not workable - unless you have active control. Ariel. (talk) 18:08, 27 October 2010 (UTC)[reply]

Earnshaw's theorem is only valid for stationary objects not spinning see Levitron. I do not think the device will do anything useful but Earnshaw's theorem is not a valid argument. --Gr8xoz (talk) 19:03, 27 October 2010 (UTC)[reply]

Tillage

Discuss the following tillage equipment under mouldboard plough and Disc plough. -Functions and constructional detail sand components -Principle of operation. -Power requirement. —Preceding unsigned comment added by 80.87.90.71 (talk) 12:39, 27 October 2010 (UTC)[reply]

See the Wikipedia article Plough that has a subsection Plough#Mouldboard plough. Do not ask for a discussion here; you may seek an internet forum instead. Cuddlyable3 (talk) 12:49, 27 October 2010 (UTC)[reply]

chocolate bar

When people offer a chocolate bar to a caveman or an alien they almost always eat it and enjoy it, thus establishing a bond between the human and the creature. Would an alien or a caveman actually enjoy a chocolate bar in real life? —Preceding unsigned comment added by 82.31.238.189 (talk) 13:27, 27 October 2010 (UTC)[reply]

I don't think you're going to have to worry about it, but the "caveman" (i.e. a pre-sapiens hominid) would enjoy the chocolate quite a bit, as many/most primates have a well developed love of sweet things. As soldiers and travelling merchants have found throughout the ages, giving people sweet stuff (and booze) is a great way to make friends. If aliens exist, we have no way of knowing what their metabolism would be like. Maybe they'd like it, maybe they'd drop dead from theobromine poisoning. Matt Deres (talk) 13:36, 27 October 2010 (UTC)[reply]

I think it really depends on whether the alien is anthropomorphic. The caveman, we would know some caveman would like it, and others wouldn't, because they are human, and we are human, and they are human, and they have tastebuds, like a human. But with the aliens we can't be anthropocentric because we have not met aliens. Unless they are already living among us. If they are, then yes, they would enjoy chocolate. Unless they don't. AdbMonkey (talk) 13:59, 27 October 2010 (UTC)[reply]

I thought the most common theme was that of the alien offering the chocolate bar to the native, as with the G.I. giving his Hershey Bar to a local child. -- 124.157.254.112 (talk) 14:42, 27 October 2010 (UTC)[reply]

If the aliens are living among us, what makes them aliens??? :D--Chemicalinterest (talk) 19:02, 27 October 2010 (UTC)[reply]

Their lack of paperwork. Googlemeister (talk) 19:10, 27 October 2010 (UTC)[reply]

Or paperwork of a different kind. -- 119.31.121.84 (talk) 23:01, 27 October 2010 (UTC)[reply]

There are many sources that speak of the toxicity of chocolate to dogs and birds, let alone further diverged life. Note that caffeine and theophylline are methylated analogs of xanthine, a fundamental building block of DNA; thus they are fairly likely to be poisonous to any DNA-based lifeform in the cosmos. (The number of lifeforms, their odds of evolving or being seeded from DNA, and their overall susceptibility to poison being undefined) Wnt (talk) 18:08, 29 October 2010 (UTC)[reply]

The Vitamin B12

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the talk page discussion (if a link has been provided). --TenOfAllTrades(talk) 13:57, 27 October 2010 (UTC)[reply]

Per Kainaw's criterion, the question isn't medical advice. The removal is unwarranted. 82.44.55.25 (talk) 15:51, 27 October 2010 (UTC)[reply]

Is there anything I can ask about this vitamin? Could I rephrase this if it does not apply to humans?

The least we can do is offer a link: Vitamin B12. --TammyMoet (talk) 14:55, 27 October 2010 (UTC)[reply]

I don't see anything wrong in answering this question, so I will. If you disagree, take it up at my talk page, but as far as I'm concerned the OP has made a valid scientific question and has expressed no intent to harm him/herself. Taking vitamin B12 in large amounts has generally been considered safe, and any excess B12 is removed through the lower digestive tract as usual. That said, no study to my knowledge has established a safe upper limit for B12 consumption, so it's clearly best to stick the recommended daily amount unless otherwise instructed by a doctor. If you're considering taking more than the recommended daily allowance, you should discuss this with a physician as B12 can interact with certain drugs, and has been known to cause side effects in rare cases. Unfortunately I can't answer the other half of the question about how long it takes to act. Regards, --—Cyclonenim | Chat 15:22, 27 October 2010 (UTC)[reply]

Hasn't there been recent studies showing B supplements encouraging cancer growth? Imagine Reason (talk) 22:36, 27 October 2010 (UTC)[reply]

Tough one to call, B12 is actually involved in preventing cancer (see Folic acid#DNA and cell division but there is research that it could encourage and support cancer cells. That said, I don't think there's a study saying it causes cancer. Generally, it's still pretty safe for consumption but obviously if you have any side effects, you should consult a doctor. Regards, --—Cyclonenim | Chat 01:14, 28 October 2010 (UTC)[reply]

Vitamin B12 is a Water-Soluble Vitamin, meaning that it is readily excreted from the body. It's much harder to poison yourself with a water soluble vitamin, including B12, than with, say, Vitamin A (what generally happens if you take a lot is you end up producing expensive urine). That's not to say that there aren't possible side effects, and there of course may be long term effects as well that aren't well studied. Buddy431 (talk) 04:18, 28 October 2010 (UTC)[reply]

Vitamin A being fat soluble, just to clarify Buddy's point. Mattopaedia ^{Say G'Day!} 06:08, 29 October 2010 (UTC)[reply]

Cyclonennim, thanks very kindly for answering my question. I would inquire more, but I'm afraid it might teeter on pushing the liability policy of medical advice and risk being deleted . Regardless, thank you so much for answering. I really appreciate it. :) AdbMonkey (talk) 08:09, 28 October 2010 (UTC)[reply]

It should be noted that according to discussion ([1]) this is not a liability or legal issue. Rather, a vocal majority? in control of Refdesk policy believes it would be unethical to allow anyone here to answer your questions. Wnt (talk) 05:39, 29 October 2010 (UTC)[reply]

Yep, I'd question whether or not it was a majority. I'm not one of them...maybe I should write an essay about that one day. God knows I've harped on enough about it here that I'm sick of repeating myself. Then I could have a really cool eponymous term like Kainaw's criterion.Matto paedia ^{Say G'Day!} 06:08, 29 October 2010 (UTC)[reply]

Sorry, I don't understand what that means, but I'll try not to ask out of bounds questys in the future. AdbMonkey (talk) 19:29, 29 October 2010 (UTC)[reply]

mosquito eggs and larva

1.what would be happen to the human when swallow the mosquito eggs and larva?

2.what would be happen to the mosquito eggs and larva inside the human body?

1. probably nothing.

2. the eggs/larva would most likely be digested by stomach acid--Lerdthenerd (talk) 14:21, 27 October 2010 (UTC)[reply]

Well, they'd be digested by enzymes that require stomach acid for activation and unfolding of proteins, but yes. Regards, --—Cyclonenim | Chat 15:15, 27 October 2010 (UTC)[reply]

does puree count as a liquid?

If i was to put a carrot in a blender till it was a soup like consistency, would be considered physically to be a liquid? it would pour like one and fit the shape of the container. also in chemistry solids can't normally be pured or made to fit their container, but salt,sugar and sand can be poured and Play-doh can change its shape.--Lerdthenerd (talk) 14:20, 27 October 2010 (UTC)[reply]

Maybe? A puree is a Suspension (chemistry). If you left it alone for long enough (a week?), the tiny solid carrot particles would sink to the bottom. Salt, sugar, and sand are not liquids because each grain is actually a very small solid. In the case of liquids, each "grain" is a single molecule. The behavior of Play-doh is an example of Plasticity (physics). Anyway, I don't think "being able to fit their container" is a perfect rule for separating liquids from other states of matter, it's just a general rule told to schoolchildren. Indeterminate (talk) 14:52, 27 October 2010 (UTC)[reply]

Oh, snap! Schoolchildren!! You gonna' take that, Lerdthenerd?! 84.153.230.5 (talk) 16:47, 27 October 2010 (UTC)[reply]

Actually, Lies-to-Children (as Terry Pratchett calls them), are an essential part of learning. You need to learn the overly simplistic explanation before more complex concepts can be grasped. For example in math you initially learn only about positive numbers; you need to follow through the permutations of basic arithmetic and so forth before you can understand the concept that numbers can be negative. Liar-to-Children, as pTerry notes, is a position of some respect in all cultures. → ROUX ₪ 16:51, 27 October 2010 (UTC)[reply]

It is certainly a fluid, though though I think not a liquid for the reasons noted above. → ROUX ₪ 15:40, 27 October 2010 (UTC)[reply]

Salts, sands, and so forth are granular material. Individual grains are solid, but the system obeys certain rules of statistical mechanics that can be formulated similarly to fluid mechanics. A few days ago on this reference desk, I posted a link to a very thorough physics and mathemetical review of particle system dynamics. Here it is again: Fundamentals of Particle Technology. No physicist would say that a pile of sand is a "different state of matter," - it is clearly a group of solid particles. But, sand can fill a container as an ensemble. No individual grain of sand is actually changing shape in a significant way; it is the system of particles that behaves in a "fluid-like" way. In the same sense, a pile of sand can have an effective viscosity and mass flow rate and a wall pressure - quantitative metrics that are usually applied to pure liquids. In a sense, it is actually the air between the sand that is a fluid; the sand particles have a "modulating effect" on the fluid parameters. Replacing the air in the pore spaces with some other different fluid, such as water or oil, results in a fluidized granular system. If the pore pressure is sufficiently high, the pore spacing increases, and the result is a suspension. Nimur (talk) 18:35, 27 October 2010 (UTC)[reply]

Simplification. No individual molecule or atom is in a specific physical "state" after all. Phases only make sense if you are talking about groups of atom/molecules. Now because of scale, from our perspective the size of microsystem that composes a phase (say an ice condensation or a gas condensation nucleus) and the actual size of the molecules themselves aren't that all different. John Riemann Soong (talk) 20:39, 27 October 2010 (UTC)[reply]

Well, to some extent at the atomic level the electrons are in a particular quantum state - in the form of a gas, electrons are bound only to one nucleus; in a crystal, the electrons buzz around in a resonance amongst many different nuclei; so in some cases it may be more "clear-cut" whether a particular atom is behaving like a gas or an amorphous solid/crystal/polycrystalline/etc. But the "fringe cases" are much blurrier - so in some sense "phase of matter" really only has meaning as a description of an ensemble. Nimur (talk) 16:54, 28 October 2010 (UTC)[reply]

It depends on your scale. If for your example, your container is an entire city big, and happens to be the soil under say, a city. Now give it a little shake....on the scale of an earthquake, and watch gleefully as all the particles you called "solid" (salt, sugar, sand) undergo liquefaction. =D John Riemann Soong (talk) 20:34, 27 October 2010 (UTC)[reply]

Magnets and electricity...again!

Hi again,

This is a magnet motor design idea. In response, the idea is to try and combine the function of a magnetic bearing with that of a generator (solenoid) - so that you have one set of magnetic array, instead of 2 seperate ones. The coil is fixed to the outer shell on the inside, not fixed to the rotor. The big question still remains: would the repelling flux with the wire between the magnets cause problems instead of electrical induction?

If it does, one needs 2 systems then and the whole thing gets more complicated.

Another consideration: without air or friction bearings, just how fast could this rotor spin (or keep accelerating) before it disintegrates to pieces - centrifugal forces there...?

Thanks all... —Preceding unsigned comment added by Cordin0792 (talk • contribs) 16:25, 27 October 2010 (UTC)[reply]

You will find the Wikipedia articles Magnetic bearing and Electric motor interesting. Cuddlyable3 (talk) 17:09, 27 October 2010 (UTC)[reply]

Is it a motor or a generator? Often the same devise can work as both but not on the same time. Is the generator somhow a part of a motor?

You use very confusing terminology and quite frankly I do not think you understands the terminology. Why are you opening new sections all the time?

Will the devise have any shaft or other mecanical conection to the outside or are it some sort of energystorage flywheel? --Gr8xoz (talk) 19:12, 27 October 2010 (UTC)[reply]

Combining tornadoes

I am wondering about if any tornadoes have any combined. Ever happened? 173.49.140.141 (talk) 17:54, 27 October 2010 (UTC)[reply]

Take a look at this. Regards, --—Cyclonenim | Chat 18:02, 27 October 2010 (UTC)[reply]

This is answered by USA Today's weather expert here. -- Finlay McWalter ☻ Talk 18:03, 27 October 2010 (UTC)[reply]

And here's some sleepily-narrated footage of one such event. WikiDao ☯ (talk) 18:11, 27 October 2010 (UTC)[reply]

Colloidal iron?

I reduced FeCl3 and HCl solution with an excess of ascorbic acid and formed a light reddish-brown solution. Is that colloidal iron? --Chemicalinterest (talk) 20:55, 27 October 2010 (UTC)[reply]

Very unlikely in water. You may have formed an ascorbate complex. Physchim62 (talk) 20:57, 27 October 2010 (UTC)[reply]

Remember that colloidal nanoparticles behave vastly differently from their bulk material counterparts, even if they are both Fe(0). Colloidal particles have a highly activated surface area and non-noble transition colloidal metals are prone to be oxidised by the oxygen in the water or sometimes the water itself. Even noble gold nanoparticles need to be stabilised and "capped", usually with citrate. (Although I don't know if ascorbate works.) John Riemann Soong (talk) 21:23, 27 October 2010 (UTC)[reply]

How would I get FeCl2 crystals? I do not have a good beaker to heat an FeCl2 solution on my stove. Would heating the FeCl2 solution in an aluminium foil dish work, or would 3 FeCl2 + 2 Al → 2 AlCl3 + 3 Fe happen? --Chemicalinterest (talk) 21:20, 27 October 2010 (UTC)[reply]

Remember that aluminum is protected by a passivation layer of aluminum oxide. Otherwise aluminum would reduce your roast chicken. ;-) 01:21, 28 October 2010 (UTC)

What happens when the FeCl2 has excess HCl in it? Definitely it won't last long. Even almost-neutral CuCl2 reacts with aluminium. --Chemicalinterest (talk) 11:14, 28 October 2010 (UTC)[reply]

the aluminium will dissolve in hydrochloric acid. Better to try to exclude oxygen. Graeme Bartlett (talk) 21:09, 28 October 2010 (UTC)[reply]

Are the majority of birds noisy fliers?

I remember the first time I let a budgerigar fly loose in my house, that I was surprised by the noise his wings made in flight (I expected birds to fly silently, for some reason). Later, when the gull chick I was raising was starting to fly around my kitchen, it was much the same whirring, fluttering noise. Ditto for the lovebird I owned, the African grey parrot I babysat for a time, the feral pigeons I've seen around town and the budgies I've owned since. Do the majority of birds produce 'wing noise' when flapping? I know that owls fly pretty silently - and this seems to be something out of the ordinary enough to be commented on... --Kurt Shaped Box (talk) 22:17, 27 October 2010 (UTC)[reply]

Maybe this is for active takeoff, as opposed to gliding. John Riemann Soong (talk) 22:50, 27 October 2010 (UTC)[reply]

I don't have a source, but I'm hazarding a guess this is related to the stiffness or softness of the feathers. Owls, which have soft feathers, are very quiet flyers, the better for suprising small prey on the ground. Exxolon (talk) 23:46, 27 October 2010 (UTC)[reply]

Yes, all of the small birds in my garden are surprisingly noisy in flight (when I am close to them), and game birds such as pheasant and grouse seem to be even noisier. Even predators such as sparrowhawks are very noisy when halting a dive, but have to be silent when gliding, of course. Dbfirs 23:47, 27 October 2010 (UTC)[reply]

Wing sounds can function as alarm signals: here in pigeons [2] and (less surprisingly) hummingbirds [3]. 81.131.40.225 (talk) 04:57, 28 October 2010 (UTC)[reply]

In the English countryside, if you hear a bird taking-off with lots of loud flapping, it's nearly always a Wood pigeon. Now I know why! Game birds make more of a whirring sound. Crows and magpies are very vocal but I don't recall much noise from their wings. Alansplodge (talk) 14:46, 28 October 2010 (UTC)[reply]

Yes, I've never heard wing-noise from a crow, but they do take off very slowly. Dbfirs 07:55, 29 October 2010 (UTC)[reply]

A caged bird never learns to glide. Cuddlyable3 (talk) 20:24, 28 October 2010 (UTC)[reply]

Go (weiqi) - computers vs human brains

I've read the articles about Go and computing, explaining why it is so hard for computers to play Go well. This lead me to a follow-on question, which seems somewhat stupid on its face but for which I'd really appreciate a serious answer - if computers struggle to play Go at even a basic level, how can humans be so good at it? Thank you. The Masked Booby (talk) 22:49, 27 October 2010 (UTC)[reply]

Because humans are not good at building intelligent computers. I think that a typical PC is not powerful enough to simulate the brain of a spider in real time. Count Iblis (talk) 23:06, 27 October 2010 (UTC)[reply]

The article says that good pattern recognition is required. You can show children photographs either of dogs or cats; the child can tell if it is cat or a dog; computers can't. Humans that failed to spot a leopard half-hidden in the trees didn't have children, which gives evolutionary pressure to be better at spotting leopards. Computer chess engines don't use pattern recognition, they use brute force, with early discarding of bad moves (branch pruning). Wei'ci has too many possible move at each turn, and why a move was good might only be obvious 10 or more moves later, so branch-pruning can't be used. CS Miller (talk) 23:10, 27 October 2010 (UTC)[reply]

(Computer Go is presumably the article the original poster is alluding to.) Comet Tuttle (talk) 23:40, 27 October 2010 (UTC)[reply]

Another way to put it is that the human brain is better at some types of tasks than the modern computer is, and vice versa. They don't work the same way at all. --Mr.98 (talk) 02:49, 28 October 2010 (UTC)[reply]

Simply put, we have not developed pattern recognition algorithms that are as good or better than what human brains do. It's even an open question if today's computer architectures (the von neumann architecture is well suited to it. There are many things humans do better than computers, such as analyzing text, recognizing familiar faces and moving around on two legs.

That said, GO and Chess is in a way simpler than e.g. recognizing a face. A chess computer works by thinking several steps ahead, anticipating the possible moves and counter-moves the human may do. Put more computerpower into that job, and it automatically gets better at playing chess. You can't use this strategy when learning to recognize a face.

I wrote GO and Chess, because the best GO-programs, that are able to beat somewhat experienced players, do in fact use this brute-force approach. You could say the computer is playing on its strenghts. EverGreg (talk) 06:44, 28 October 2010 (UTC)[reply]

Cryosurgery to repair torn tissue?

An acquiantance has a detached retina with multiple tears (pronounced "tares", not "teers"); the optic surgeons are planning to use cryosurgery to repair the torn tissue. Reading our article on this procedure, I'm surprised: how can this technique make repairs like this? FYI, I'm not involved in the medical decisions at all — this is a request only for medical information, not for medical advice. Nyttend (talk) 22:56, 27 October 2010 (UTC)[reply]

Unfortunately, the cryosurgery article mostly only describes one therapeutic aspect of the technique — cryoablation. I've added a see also tag to this article in cryotherapy, and if I had more time I'd write some more about other aspects of cryosurgery, but I don't. So maybe someone else can. Anyway, back to your question: Cryosurgical techniques have application in areas other than removal of lumps and bumps. As you have read in the article, the act of freezing obviously kills the tissue involved. This can be used to some advantage in other areas such as retinal surgery because we can use a very small freezing probe in a very controlled fashion to freeze small spots on the retina. By doing this and pushing the retina back onto the internal surface of the globe, the scar that forms from the frozen tissue sticks to the globe and helps to hold it in place. The technique is called cryopexy, and is briefly described in our article on retinal detachment. This technique is usually used in conjunction with addition of a gas bubble into the eye to help maintain pressure on the retina & stick it back into place. Mattopaedia ^{Say G'Day!} 23:25, 27 October 2010 (UTC)[reply]

(ec) I think you'll find more retina-specific info if you search for "cryopexy", e.g. this site is pretty informative. Basically, the freezing creates a small scar that tethers the retina and choroid to the fibrous sclera. -- Scray (talk) 23:30, 27 October 2010 (UTC)[reply]

Quantum Entanglement

I'm learning about quantum physics, but I'm not learning about entanglement this semester. I don't feel like I have much of an understanding without knowing about it. Is quantum entanglement just the Schrödinger equation in three dimensions for each particle involved? For example, would the waveform of a hydrogen atom be six-dimensional, with each point corresponding to the locations of both the proton and the electron, i.e. (1,2,3,4,5,6) would correspond to a proton at (1,2,3) and electron at (4,5,6)? If not, is there anything I can read that explains it mathematically? — DanielLC 23:58, 27 October 2010 (UTC)[reply]

Have you read Quantum entanglement? Also EPR paradox and Bell's theorem. Red Act (talk) 00:13, 28 October 2010 (UTC)[reply]

And no, I can't think of a way that a hydrogen atom would do a good job of illustrating quantum entanglement, because the proton and the electron are too closely bound. To illustrate quantum entanglement, you really need to wind up with particles that are widely spatially separated, after an initial time period during which they interact with each other at a close range, although I imagine there may be exceptions to that that I'm not aware of. Red Act (talk) 00:58, 28 October 2010 (UTC)[reply]

To clarify a bit, if you consider the effect of the electron on the proton in a hydrogen atom in a non-averaged way, then the atom is indeed in an entangled state, so in that regard the six-dimensional wavefunction you mentioned does indeed exhibit quantum entanglement. But the particles are too close together to do a good job of illustrating "nonlocal interaction", a.k.a. "spooky action at a distance", which is a key consequence of quantum entanglement. Red Act (talk) 03:08, 28 October 2010 (UTC)[reply]

I just want to know if the principle is correct. If it is, it's not hard to consider that the universe is just a 3n dimensional wave where n is the number of particles, and every point corresponds to a possible combination of locations of the particles, and the potential energy there refers to the potential energy of the universe. The hydrogen atom thing was more supposed to illustrate that it was still governed by the Schrödinger equation then correlation at a distance. It's also easy to see from that why it's the same to think of it as two orthogonal wave-functions for center of mass and relative position, since that's just a rotation. If this is right, and I guessed it before being taught, I think I can safely say that the idea that quantum physics is too weird for anyone to understand is completely wrong. — DanielLC 15:39, 28 October 2010 (UTC)[reply]

Yes, you've correctly guessed that in elementary quantum mechanics in which spin is ignored, a state with n particles is modeled by a 3n-dimensional wave. That's a simplified picture of reality, though, and in more ways than just ignoring spin. And I can't think of a way of illustrating the weirdness of nonlocal interaction, which is a key interesting aspect of quantum entanglement, in a way that doesn't involve spin, which I'm guessing you haven't studied yet. Come back after you've studied the EPR paradox, and tell me if everything still seems perfectly reasonable and natural to you. Red Act (talk) 18:11, 28 October 2010 (UTC)[reply]

The spin thing looks similar to the angular momentum of an atom, which I have learned about. From what I understand, it looks like "observing" the spin of one particle causes the wave (which represents the universe) to split and move in different directions at astronomical speeds so that they're far enough apart that they have no real effect on each other. That still doesn't seem quite right. Is it possible to control which axis you measure it on? If not, the different possibilities could add up to the axis it was before you measured it, so it would work fine.

I just looked more closely at the Schrödinger equation page, and noticed it said what I was originally asking. I guess I'm glad I missed it, or I wouldn't have been able to work it out on my own. — DanielLC 21:48, 28 October 2010 (UTC)[reply]

Yes, spin is quite similar to orbital angular momentum, except that it's an intrinsic property of the particle that's independent of spatial dimensions (although there may be spin–orbit interaction), and that it takes on half-integral values for fermions like electrons, which is impossible with orbital angular momentum.

You don't seem to be getting the gist of the EPR paradox and Bell's theorem yet. (See also Bell test experiments.) In a nutshell, what's happening is that, in chronological order: 1) A pair of particles A and B are prepared in an entangled superposition state such that the state of the particles is a 50% chance that along some axis, the spin of A is up and the spin of B is down, and a 50% chance that the spin of A is down and the spin of B is up. 2) The two particles are then separated (sometimes by kilometers). 3) The spins of the two particles are then measured.

What happens is that the measured spins are found to be consistent with the state of the particles having been prepared as is described in step 1, and still being in that state until step 3. In particular, it is provably definitely not the case that the apparatus used to prepare the particles in step 1 is such that 50% of the time, the apparatus will prepare the particles such that the spin of A is definitely up and the spin of B is definitely down, and 50% of the time it will prepare the particles such that the spin of A is definitely down and the spin of B is definitely up. It's as if the invisible pink unicorn is tossing a coin to decide what the outcome of the experiment will be, but is waiting until step 3 before tossing the coin. And it's just one coin being tossed, that determines the results of both measurements. But by step 3, the particles, and the devices used to measure them, are completely separated. If the measurement of particle A, for example, is what's causing the metaphysical coin to be tossed, there's no obvious way for particle A to communicate the results of the coin toss to particle B, in order to tell particle B what the result of particle B's measurement needs to be. And yet the measurements are consistent with there having been only one coin toss, that didn't occur until after the particles were separated. Red Act (talk) 06:58, 29 October 2010 (UTC)[reply]

The indentation seems to be getting out of hand, so I'll start back here. First off, how can the particles be separated by distance? Position is the property of a universe, not a particle, right? Also, I'm using the Many Worlds interpretation, which seems to be much simpler. Suppose the eigenvector of the spin is on x=y. It's then measured to become +x, -x, +y, or -y. It's already a linear combination of those, but measuring it means that that universe now has a ton of different particles moving in different directions than they otherwise would have, for instance, if it's written down, the ink stains on the paper will be arranged differently. This means that the universe is rapidly moving to a different place, so that the four wave-forms that combined into the original one are now very, very distant from each other. The other particle that's "kilometers away" is just another component of the position of that universe, so there's no violation of locality. — DanielLC 15:37, 29 October 2010 (UTC)[reply]

I'm afraid I'm not understanding your post, e.g. the phrases "position is the property of a universe, not a particle" and "the universe is rapidly moving to a different place". Perhaps the reason for me not understanding you is due to your viewing things with the many-worlds interpretation, which I'm not into. (Do universes move in the many-worlds interpretation?) I've read a little bit about the many-worlds interpretation, but I fairly quickly decided that it seemed implausible to me, because all that extra information being stored in that vast number of extra universes seemed to me to go against Occam's razor. I realize that some other people view things differently. Red Act (talk) 18:30, 29 October 2010 (UTC)[reply]

October 28

Why do flour and sugar store so well?

In a kitchen you can store in not especially well sealed containers kilos and kilos of raw sugar and flour, and they will last for months without problem. But if you leave out something like bread or cake, it won't last nearly so long. It seems to me that the sugar and flour ought to be delicious to the endless armies of bacteria, and it puzzles me how the flour and sugar remain untouched. What's going on there?

Searching through the Ref desk archives, I see some explanations to the effect that sugar is so hygroscopic that it dessicates and kills any bacteria foolish enough to try to eat it, but is this the whole story, and does it cover flour as well? It seems a little unlikely to me. --Gwern (contribs) 00:26 28 October 2010 (GMT)

Perhaps it is the presence of water that differentiates between the two. Bus stop (talk) 00:55, 28 October 2010 (UTC)[reply]

Actually, this might depend on the location, but if you leave flour unprotected for long periods of time, even though bacteria won't bother it much, it's entirely possible that you'll find squirmy little multi-celled animals in it. As for brown sugar, I'm not sure; I don't ever recall seeing actual larvae in it, but I have seen it take on a sort of stringy character that makes me suspicious something has been there. --Trovatore (talk) 01:03, 28 October 2010 (UTC)[reply]

Isn't that just water absorption? John Riemann Soong (talk) 01:19, 28 October 2010 (UTC)[reply]

Yes, a primary reason bread bacteria and fungi will colonize bread before flour (in similar containers) is moisture. If you want to test this for yourself, add a small amount of water to your flour and see if it is still good in a few weeks. Trovatore has a good point about other contaminants, e.g. Flour_beetles. Also keep in mind that dry flour and sugar are highly processed products that have been designed to store well; they are not naturally occurring food sources, and relatively few species have adapted to utilize them as a primary resource. SemanticMantis (talk) 03:33, 28 October 2010 (UTC)[reply]

Well, good flour (that is, whole-wheat flour) is not so highly processed. But it is still very dry. --Trovatore (talk) 04:31, 28 October 2010 (UTC)[reply]

Honey never goes off "Honey, and objects immersed in honey, have been preserved for decades and even centuries" and is used as an antiseptic. Alansplodge (talk) 08:06, 28 October 2010 (UTC)[reply]

Perhaps it does not go off, but it does irritatingly become semi-solid to the point where you can not squeeze it out of the bottle. Googlemeister (talk) 13:54, 28 October 2010 (UTC)[reply]

Honey ought to be supplied in jars[4], not squeezy bottles. Ah, the wisdom of our forefathers. Alansplodge (talk) 14:20, 28 October 2010 (UTC)[reply]

And honey that has crystallized can easily be made liquid again, by heating in a hot water bath for a few minutes. But we stray far from the original question. Buddy431 (talk) 15:02, 28 October 2010 (UTC)[reply]

But is it the sugar content of honey that makes it an anathma to bacteria? The WP article suggests low Water activity (a property of sugar) as one agent. Alansplodge (talk) 18:19, 28 October 2010 (UTC)[reply]

Yes, honey is highly acidic, but not if you dilute it with water. Imagine Reason (talk) 17:49, 29 October 2010 (UTC)[reply]

force

Is gravity ultimately the most powerful force in the universe? --96.252.213.127 (talk) 02:35, 28 October 2010 (UTC)[reply]

No. Gravity is quite weak. See the table in Fundamental interaction and the discussion of its weakness there. It's responsible for some of the gigantic and interesting effects one gets on the solar system and universe level. But it is many orders of magnitude weaker than the other forces — hence a tiny magnet can resist the force of the entire planet's gravity. Gravity can do some amazing things when you have a lot of mass together (e.g. a black hole, or a quasar), but it's very weak as far as forces go. --Mr.98 (talk) 02:44, 28 October 2010 (UTC)[reply]

However, it often gives the appearance of being the most powerful, because it is the most easily observed since it usually works on a much larger scale than the others. --The High Fin Sperm Whale 03:43, 28 October 2010 (UTC)[reply]

Okay that is why I am asking the question... so let me put it this way... will an infinite amount of mass located in the same place make gravity the most powerful force in the universe? --96.252.213.127 (talk) 03:47, 28 October 2010 (UTC)[reply]

The question is meaningless. An infinite mass does not exist. --Anonymous, 03:56 UTC, October 27, 2010.

(edit conflict) An infinite amount of mass is impossible, and the implications of having an infinite amount of mass in one location creates all sorts of problems in the local physical universe. An abitrarily large mass would be possibly discussable, but this is not the same as an infinite mass. Also, it should be noted that General relativity doesn't treat gravity as a force, rather as a pseudoforce caused by the effect of mass warping spacetime. If you consider the mass-warping effects of General Relativity, objects move in straight lines within warped spacetime, which gives the illusion of a force. Under the standard model, forces require particles to carry them. Gravity has no known force carrier particle, which would mean that it isn't a force. There is a proposed particle (called the Graviton), but it unneccessary under General Relativity, and there has been no evidence of its existence. --Jayron32 03:58, 28 October 2010 (UTC)[reply]

What about an infinitely powerful magnet? Nil Einne (talk) 03:57, 28 October 2010 (UTC)[reply]

Could an infinite amount of mass in the form of energy exist in the same place if only for an instant? --96.252.213.127 (talk) 04:12, 28 October 2010 (UTC)[reply]

No, its is nonsensical to speak of infinite energy or infinite mass. Also, per Special relativity, the distinction is meaningless. It does no good to speak of infinities, since the mathematics of infinity makes no physical sense in the real world. One might as well ask what one would do if one had an imaginary mass or something like that. It makes no physical sense. --Jayron32 04:28, 28 October 2010 (UTC)[reply]

I disagree. The universe may well be infinite in extent, in which case the total amount of mass in the universe is presumably infinite. It's only local infinities that cause serious problems. It is possible that even those exist (for example, leptons and quarks are generally taken to be points, in which case their charge/mass/color charge densities are infinite). --Trovatore (talk) 06:03, 28 October 2010 (UTC)[reply]

Point taken. Infinities are fine, it is local infinities which create contradictions. And only certain types of local infinities. Singularities in black holes are zero volume, which means they contain infinite density. This results from infinite curvature of spacetime, which is sort-of-kind-of like infinite gravity. Except, that since gravity isn't a real force, this doesn't generate the sort of problems one would expect from an infinite force. --Jayron32 06:06, 28 October 2010 (UTC)[reply]

Yet infinite gravity can exist in the form of a Black Hole? --96.252.213.127 (talk) 05:37, 28 October 2010 (UTC)[reply]

Black hole physics is pretty peculiar, and it doesn't depend on the existance of either infinite mass or infinite energy. Black holes don't really have infinite gravity; they just have enough gravity to generate an event horizon; essentially enough gravity to warp spacetime so that the curved path that light appears to follow in the standard three dimensions bends so far that it curves inward towards the black hole. But this is not infinite. --Jayron32 05:46, 28 October 2010 (UTC)[reply]

The force would, however, be infinite at the singularity at the hole's center. --Trovatore (talk) 06:05, 28 October 2010 (UTC)[reply]

No, this would be infinite curvature of spacetime, which would mean that local objects would move as though being attracted by an arbitrarily strong force. However, a real infinite force acting on a finite mass would generate all sorts of contradictions, such as doing an infinite amount of work on the object. Locally infinite energy has all the same sorts of problems as locally infinite mass has. This is, yet again, further evidence that gravity isn't a force in the traditional sense, since no other forces (strong, weak, EM) can operate under these sorts of localized infinities. --Jayron32 06:10, 28 October 2010 (UTC)[reply]

Hmm? What about the bare electron, unshielded by its cloud of virtual electron/positron pairs? The gradient (maybe Jacobian) of the electric field there is infinite. (I shouldn't really have said infinite force — what's infinite at the hole's singularity isn't so much force as the rate of change of force.) --Trovatore (talk) 06:15, 28 October 2010 (UTC)[reply]

Yeah, but this, like the black-hole-singularity, is some pretty esoteric stuff. Under normal circumstances, you cannot have a pile of matter with an infinite mass, you cannot impart an infinite amount of energy onto an object, you cannot submit an object to an infinite force. When we say, for example, that a black hole has "infinite gravity" what we mean is that it would take an infinite force to extract an object from inside of the event horizon to the outside. That doesn't mean that the infinite force actually exists, it is a demonstration of the futility of the exercise. You can generate local infinites in any situation with zero volume because zero volume generates infinite density (for the singularity this is a mass density, for the bare electron, this is a charge density). But this is a derived infinity, caused by the peculiarities of zero volume particles. The physical reality revolves around a local zero, which is perfectly allowable and understandable, rather than a local infinity, which makes little sense. --Jayron32 06:29, 28 October 2010 (UTC)[reply]

I would answer "yes". The reason is that all the other forces are self limiting - the strong force by distance, the electromagnetic by self-repulsion (i.e. there is a limit to how strong you can make it before it bursts), the weak force by distance again. But gravity is not limited - the more mass, the stronger it gets. Ariel. (talk) 06:52, 28 October 2010 (UTC)[reply]

Except that gravity isn't a force. It requires a force to counteract its effects, but it is not a force itself. It is identical in this nature to centrifugal force, or other pseudoforces. It is an effect cause by viewing an object moving in a straight line through a region of spacetime which is itself curved. See General relativity. --Jayron32 07:03, 28 October 2010 (UTC)[reply]

Um, no. Gravity is a force - go read any article on force you like. There are four forces and gravity is one of them. And your explanation fails if you consider an object that is stationary relative to the region of spacetime, yet still experiences a force. A pseudoforces is a force that only exists in certain frames of reference, but not in others, in particular it only exists in moving (non-inertial) frames of reference. But gravity exists in all of them, and the frame does not need to be moving. And BTW the General relativity article does not once mention fictitious of pseudo forces. I think you are confusing using the principles and math of a fictitious force (equivalence principle) with actually being a fictitious force. Ariel. (talk) 08:01, 28 October 2010 (UTC)[reply]

Jayron32 is correct - in the context of general relativity, gravity is a pseudoforce, not a true force, because a point body following a spacetime geodesic does not experience a local gravitational force. First sentence of Gravitation#General relativity says "In general relativity, the effects of gravitation are ascribed to spacetime curvature instead of a force". And Introduction to general relativity says "An observer in an accelerated reference frame must introduce what physicists call fictitious forces to account for the acceleration experienced by himself and objects around him ... Einstein's master insight was that the constant, familiar pull of the Earth's gravitational field is fundamentally the same as these fictitious forces". Gandalf61 (talk) 09:04, 28 October 2010 (UTC)[reply]

Richard Feynman begs to differ: [5]. Gravity can certainly be looked at and calculated as a fictitious force, but it also acts as a regular force, and it most definitely is numbered among the four fundamental forces. And the explanations you posted do not explain why a particle that is not moving still experiences a force. Using a psudoforce was a great mathematical technique, but it doesn't mean it actually is a psudoforce. Ariel. (talk) 19:22, 28 October 2010 (UTC)[reply]

The link you gave doesn't say that Feynman disagreed with the idea of gravity being a pseudoforce -- it merely says that Feynman declined to answer the question of whether it's a pseudoforce, which is very different. Personally, I'm totally with Jayron and Gandalf61 on this one. Gravity only looks like a "force" if you aren't doing general relativity. Red Act (talk) 09:35, 29 October 2010 (UTC)[reply]

Reply to Ariel. :-

Notice that I carefully said "in the context of general relativity". We know that general relativity cannot be the whole story because it is a classical field theory, not a quantum field theory. However, gravity does not really fit into the "fundamental forces" part of the Standard Model either because its hypothetical elementary particle, the graviton, has never been observed. We won't know the true status of gravity until we have a coherent theory of quantum gravity.
You say "a particle that is not moving" - but how do you define "not moving" ? As I said, a point particle following a apacetime geodesic (i.e. in "free fall") does not experience gravity. Geodesic motion is the local equivalent of an inertial frame of reference in GR (although it cannot be extended to a global frame of reference). So, in GR, a point particle that experiences a gravitational force is not following a spacetime geodesic, and is therefore "moving" relative to its local spacetime background. Gandalf61 (talk) 10:20, 29 October 2010 (UTC)[reply]

Sexuality question

Do heterosexual men normally get an erection when:

thinking of a penis?
looking at their own penis in the mirror?

Thank you in advance for any helpful answers,

82.112.147.154 (talk) 04:02, 28 October 2010 (UTC)[reply]

The range of "normal" in terms of human sexual response is VERY wide. What is sexually normal for one person is very different than what is sexually normal for another. Terms like "heterosexual" and "homosexual" are convenient political definitions, but sexuality is rarely a black-and-white issue. What a person finds sexually arousing is highly individual, and subjective to social pressures as well as innate desires. It is highly complex. The seminal (excuse the pun) work in this area is over 40 years old. See Masters and Johnson and Kinsey Reports for the cornerstone works in this area. --Jayron32 04:11, 28 October 2010 (UTC)[reply]

That probably depends on the heterosexual man in question. It probably also depends on their age; the earlier in puberty one is, the more likely one is to be aroused by anything. Some people, no matter their sexual orientation, will become aroused simply by thinking about anything to do with sex. → ROUX ₪ 04:13, 28 October 2010 (UTC)[reply]

I dunno. Do you? But when you are say, 14, you get erections pretty much from random motion of air molecules on your wiener. The curve of a tennis racquet's shape can give you a stiffness problem in about 2 seconds. People often forget about this phase of their lives when they get older, unless they recall some characteristic event or conversation. I recall that, at the age of about 14, I was discussing girls with my (male) pal, and he said that he felt that if he were to be in a girls' changing room and could view fully naked girls, not only would he have an erection, but he would almost certainly have an involuntary orgasm. And I agreed with him. Also, all the boys at our school were checked out medically at one stage, and part of that examination involved the doctor palpating the boy's scrotum to check that development was normal. We knew that this was going to happen, and despite the fact that it would only take a couple of seconds, there were quite a few of us who were concerned that we might get erections from being touched like this, or even thinking about it, and that would mean we were gay. Needless to say, later in life, the fires burn a little less feverishly. Myles325a (talk) 06:03, 28 October 2010 (UTC)[reply]

The answer to the question depends in part by what the question means by "heterosexual". There's a Heterosexual-homosexual continuum, of which two attempts at measuring are the Kinsey scale and the Klein Sexual Orientation Grid. If a man who commonly gets an erection when thinking of penises considers that fact to be a sufficient reason to mark "other sex mostly" instead of "other sex only" in response to the "to whom are you sexually attracted" question on the KSOG, then that man would wind up not being considered 100% heterosexual according to that measure, while still potentially showing up as being mainly heterosexual. One thing Kinsey found is that men tend to be more purely heterosexual or homosexual, with less of a middle ground, than woman are. But there still is a middle ground for men, as well.

And I wouldn't find getting an erection when thinking of a penis to be particularly surprising in an adolescent male, even one that scores as being fairly purely heterosexual. It doesn't take much of a reason for an adolescent male to get an erection. Red Act (talk) 06:16, 28 October 2010 (UTC)[reply]

My theory on why we often can’t run in dreams – is it valid?

Think of that terrible chase dream where you can’t move your legs. A lot of people report dreams like that, but why is it so common? My idea is that it is a consequence of dream time. In dream narratives, the story does not proceed in real-time. If, in a dream, you have to wait for an hour in a doctor’s waiting room, your dream will quickly fill up that time with other events. In other words, dream narrative proceeds much like the narrative of a movie or TV show. What is inessential to the plot is cut out or minimized. In fact dreams are so like stories we tell each other perhaps they are the progenitor of creative story-telling. So dream-time works like story time, roughly lasting as long as it might take for you to tell the story. That means dreams compress time, like narrative usually does. But there are times when this natural order is turned on its head. Sometimes, it takes longer to narrate an event than the event would take to run its course in real time.

Think of those times when you are being pursued by some monster and you feel like you are wading through sticky mud, unable to speed away. Here, the events of what might realistically be a few seconds have crammed into them all sorts of important details each of which might only take a split-second in real time, (how you slipped, what the zombie looked like, where you decided to go etc). In consequence, it takes much longer for the brain to “tell” itself this, than it would to actually just act it out. So in such a case, the action is not speeded up as is usually the case, but slowed down (in order to accommodate all this critical detail). But the “flight to survive” instinct in humans is understandably intense, so the part of your brain that is immersed in the action is screaming: “What the hell’s going on!!??!! Get the HELL out of there!!” And it interprets the slow-down as some catastrophic failure of your body, or the presence of some kind of gooey mud or the like dragging on your feet. (I also have a theory about why so many people dream of being able to fly? Wanna know?)

Do you think I’m onto something? Or just on something? Could I bank on a Nobel Prize? Or is that a dream? Myles325a (talk) 06:28, 28 October 2010 (UTC)[reply]

There's a phenomenon called sleep paralysis that (usually) keeps you from acting out what you do in your dreams. Maybe in the dreams you're talking about, you're actually conscious of that paralysis? --Trovatore (talk) 06:31, 28 October 2010 (UTC)[reply]

Is not being able to run a common theme in most peoples dreams? I've never experienced that, although I have terrible dream recall in general no matter how diligently I attempt to keep a dream journal. I can always walk, run, and hover (not fly though) 82.44.55.25 (talk) 10:45, 28 October 2010 (UTC)[reply]

It's pretty common in my dreams, and a pretty definite result of the aforementioned sleep paralysis; I'm partly awake and my brain is aware that my body is completely unable to move, so it transfers that information into my dream. Eventually I'll wake up, seriously short of breath and almost jumping out of my bed. I see no reason to think it was the more-complicated compressed-time theory put forward.

Also, the Reference Desk isn't here to evaluate your ideas. Vimescarrot (talk) 10:52, 28 October 2010 (UTC)[reply]

I guess my view, as a scientist who has worked on sleep, is that there are already so many ideas about how dreams work that further ideas are not very useful unless they're framed in a testable way. One thing that is completely clear, though, is that physical conditions such as being too warm, breathing bad air, sleeping in a bad posture, needing to urinate, etc, frequently are reflected by the content of dreams. Looie496 (talk) 17:38, 28 October 2010 (UTC)[reply]

Op myles325a back live. From above:

One thing that is completely clear, though, is that physical conditions such as being too warm, breathing bad air, sleeping in a bad posture, needing to urinate, etc, frequently are reflected by the content of dreams.

Someone should have told Freud that. It would have saved him and the rest of us from an enormous red herring. (Like the one that chased me last night and I couldn't move.) No, guys this is not sleep paralysis. I've had that, and you are basically awake when it happens. I'm just talking about nightmares in which time seems to be slowed down. No one has addressed my idea on the inversion of dream narrative time. Looie, it might be difficult to do much in the way of running empirical and falsifiable tests on the content of dreams. The world of Inception is not here yet. There is such a thing as lucid dreaming where the person is aware they are dreaming, and I have often experienced that as well. I invariably shed my clothes and fly off cliff tops. It’s a blast! Myles325a (talk) 23:39, 28 October 2010 (UTC)[reply]

There's something weird about how running is handled by the vertebrate nervous system. Chickens, famously, but also cats^[6] have been observed to run around without control from the motor cortex; as I understand it much is handled not even in the brain but lower in the spine. I don't think the same sort of response has been accomplished in humans - certainly the average quadriplegic takes more than a few prods to start running. I suppose it makes sense, though, since primate locomotion in treetops must be integrated directly with visual maps of the surroundings, which would demand that movements be organized fairly near the visual cortex (for example). Wnt (talk) 04:44, 29 October 2010 (UTC)[reply]

I'll add to the poster's question, without really having done much to answer it, by noting my own peculiar observation from dreams - tripping over an object is the one thing south of the eyes not affected by sleep paralysis for me. So if I dream I trip over an odd terrain I'm immediately awakened by the "compensatory" motion of my legs. Wnt (talk) 04:44, 29 October 2010 (UTC)[reply]

Your dreams might not be sleep paralysis-related. Mine most definitely are. You'd have to find out whose are most common. Vimescarrot (talk) 10:35, 29 October 2010 (UTC)[reply]

Awareness of real physiological states often leaks into dreams; needing to pee is commonly noted to produce corresponding dreams, or if a pet cat jumps on you in your sleep you may dream of being attacked by a monster, and so on. People usually sleep with their legs trapped under blankets. So this is my simple explanation for dreaming of being unable to move your legs: it's because you're unable to move your legs. 81.131.53.127 (talk) 11:40, 29 October 2010 (UTC)[reply]

solar enery storage

Can solar cells be mounted on the top of a car, where the converted electric enrgy is stored in electric cell which can be easily removed and used for domestic purpose? Is there a mechanism by which everyday I can easily remove the charged cells from panel and put discharged cells into panel for solar charging? —Preceding unsigned comment added by 203.199.118.12 (talk) 06:40, 28 October 2010 (UTC)[reply]

Yes, it could be done, but why? If the plan is to use the charged cells to power your car then you will need the charged cells. Putting uncharged cells on your car means your car won't move until the sun has been up for a few hours. If the plan is just to charge cells, why not put them somewhere stationary like a house roof where they can be oriented towards the sun (south if you live in the northern hemisphere, or north if you live in the southern hemisphere.) The roof of your car always points straight up, and that isn't an ideal orientation for a solar panel. Dolphin (t) 06:46, 28 October 2010 (UTC)[reply]

(edit conflict) The problem is that batteries can't really store all that much energy, especially given what a normal house would use in a given day. Plus, batteries have a fairly short lifespan; if you are constantly charging and discharging large storage cells, they need to be replaced frequently enough to make the system too expensive for household usage. A far more efficient system is to use excess solar energy to operate a water pump which fills a retention pond. When demand exceeds supply from the solar system, the water in the pond is sent over a sluiceway to generate hydroelectric power. See Pumped-storage hydroelectricity. --Jayron32 06:47, 28 October 2010 (UTC)[reply]

The amount of energy that could be generated by solar cells on top of a car would be only a very tiny fraction of the energy needed to run the car. It might be sufficient to run a car radio on a sunny day. Solar cells to not store any energy at all, they just generate it. A different type of cell (as in battery) is needed to store the energy generated (or an alternative storage system, as in a hot-water cylinder in a house, or Jayron32's suggestion above). Dbfirs 09:22, 28 October 2010 (UTC)[reply]

Some Priuses have a solar cell on top which is to help ventilate the car when it's parked in the sun so it doesn't get so hot. It was intended to charge the battery (obviously not contributing much) but this was found to cause problems with the radio. (See the article.) There have been addons for cars for a while but these don't work very well [7]. It's been suggested the solar cell may be enough for the AC before (I believe this may have been how the Prius was going to be promoted [8]) but I don't think anyone has done this in practice. Nil Einne (talk) 12:02, 28 October 2010 (UTC)[reply]

Solar cells on top of a car can indeed run the car. See the article Solar car racing which notes recent solar cars crossing Australia at 90 to 100 km/h. Cuddlyable3 (talk) 13:24, 28 October 2010 (UTC)[reply]

Granted, but that is not even close to being the same scenario as bolting a couple of panels to the top of your Taurus. Those cars were designed specifically for that event and are not in wide production. Googlemeister (talk) 14:59, 28 October 2010 (UTC)[reply]

... and they can't cope with hills, or even slight gradients without using their backup battery! Dbfirs 07:49, 29 October 2010 (UTC)[reply]

Is ADD real?

Is it really real? I don't mean to offend anyone by asking this, I just need to know if ADD is as real as a broken bone or a cold. When it shows more red spots in the fMRI images of scanned ADD brains is that due to ADD, or is it do to some other issue that could make it seem like its ADD, but its actually just another correalation? If its real, then why does it not seem to have existed in the past, or even 100 years ago? If anyone knows if it is real, how do they know? And did they get it from an unbiased source that wasn't funded by a pharmaceutical company or had nothing to gain? AdbMonkey (talk) 08:35, 28 October 2010 (UTC)[reply]

I'd say it's definitely real. Whether it's a disorder or not is more a question of interpretation. I'm quite sure it did exist going back as far as you like; it may not have been interpreted in the same way. --Trovatore (talk) 08:41, 28 October 2010 (UTC)[reply]

In extreme cases it certainly is a disorder. APL (talk) 14:25, 28 October 2010 (UTC)[reply]

May I ask what leads you to be certain about it being real? What eveidence leads you to believe it is? What is it that makes you say "Ok, now knowing that, I know it is definitly a real brain thing." AdbMonkey (talk) 08:58, 28 October 2010 (UTC)[reply]

It's essentially defined to be real. Anyone who meets the diagnostic criteria has it, by definition. --Trovatore (talk) 09:04, 28 October 2010 (UTC)[reply]

Here are those diagnostic criteria. It can't really "not be real" as it's basically a description of how some people behave. Some people do indeed behave like that; so it's real. Vimescarrot (talk) 10:47, 28 October 2010 (UTC)[reply]

(edit conflict)Have you read the Attention deficit hyperactivity disorder article and associated articles, like history and controversies? Probably also worth thinking that the world is vastly different from 100 years ago in terms of pollutants, availability of healthcare etc. which may explain part of the increases in diagnoses, although the differences in frequency between the US and UK suggest that pharmaceutical companies may also have something to do with it! Smartse (talk) 10:49, 28 October 2010 (UTC)[reply]

In the past the condition you call ADD was simply characterised as inattention, easy distractibility, disorganization, procrastination, forgetfulness, or lethargy, and teachers and parents would react with negative comments (e.g. "you're irresponsible", "you're lazy", "you don't care/show any effort", "you just aren't trying", etc.). There is nothing new about observing these symptoms (that were certainly seen 100 years ago), the change that has occurred is that they are now classified under particular DSM criteria (see articles here and here) for research and treatment. Cuddlyable3 (talk) 13:14, 28 October 2010 (UTC)[reply]

Ok, well thank you for answering, but I guess this is a hard one to answer. AdbMonkey (talk) 13:35, 28 October 2010 (UTC)[reply]

Let me put it this way. We can define arbitrary parameters and claim it is a condition. So having yellow hair we will call "blonde". It's as real as most anything else, even if there is a spectrum of hair color between yellow and brown or red, and we'd have to argue about where the line should be drawn for someone to be truly "blonde". Now all of that is different than saying that being "blonde" is some kind of disorder, something that should be "treated" (through hair dye) or "cured" or stigmatized or used as an explanation as to why people do certain things (e.g., drive around in red convertibles). Everyone agrees that there is some spectrum of the condition, not everyone agrees it is a disorder, or even a disease, or anything other than the spectrum of normal human behavior, or should be treated with medicine, or what have you. --Mr.98 (talk) 14:06, 28 October 2010 (UTC)[reply]

The study of neurology is still developing. Simply because a problem hadn't been identified doesn't mean it's not real. (Before heart attacks were discovered no one was diagnosed as having one, but people still keeled over mysteriously.)

However, many people claim that ADD is over-diagnosed and/or over-medicated. That's a much more difficult question. APL (talk) 14:25, 28 October 2010 (UTC)[reply]

Maybe what this question is getting at is whether ADD is something identifyably wrong with the brain, for example "too much chemical X in the brain" or "brain region A not talking to brain region B". Given that there are medications that help people with ADD but have different effects on people without it, I would guess that it is a phisical problem in the brain, but I am not a neurologist. —Arctic Gnome (talk • contribs) 15:15, 28 October 2010 (UTC)[reply]

Having an "attention deficit" is probably true of everyone to some extent at least some of the time. But "attention deficit disorder" is not just about having a "short attention span" (although people who have it do have that problem more than is "average"; they also have problems hyper-focusing their attention, ie. have an "attention surplus", at times, too) – the ADD/ADHD subtypes are comprised of clusters of symptoms that seem to tend to appear together in a way that is clinically diagnosable (which is not to say that it is not or cannot be over-diagnosed). I can see how you might question ADD's "reality", OP, if you are just thinking it is a matter of having poor attention and finding someone who will give you speed for that – which is what a lot of people would perhaps like to do, far from all of whom could or should be diagnosed with ADD. Disclosure: I am a case of clinically diagnosed and treated ADD myself. WikiDao ☯ (talk) 17:15, 28 October 2010 (UTC)[reply]

Ok. Yes, I was looking for something that said "Yes, ADD is real, because the brain is different and that difference renders x state." But I guess that person up above is right. It might be more questionable as to how its treated rather, or over diagnosed, rather than whether its real. So my queation now is, the biggest THING about ADD is the ability to pay attention, right? Or you can be so sensory overloaded that you can't decide on something, right? So, but isn't that on a continuious spectrum degree plot thing? So I mean, maybe everyone has this to some degree, but ADDers have it a little more to where its interfering in there lives? Because concentration, or lack thereof affects everyone at some time or another, even if they hardly ever encounter it, right? Its like being forgetful, or being frustrated, or tired, or bored, or talkative, everyone experiences that to some degree, right? So, I'm just trying to figure out... it. Teeny tiny font that everyone can still read: I could have it myself too, but I don't know, I'm trying to understand if my problems arejust me, or my 'ADD'. AdbMonkey (talk) 05:49, 29 October 2010 (UTC)[reply]

You can't answer the small-font question without consulting a doctor, really. Vimescarrot (talk) 10:36, 29 October 2010 (UTC)[reply]

Ok, well, I don't want to consult a doctor, because I have consulted doctorS and they seem to have different opinions. But regardless, I wanted to know what they learn about it. Anyway, wikipedia just seems like its reinforcing what I already know, but thanks. AdbMonkey (talk) 11:15, 29 October 2010 (UTC)[reply]

If you are asking if the pathophysiology is "real" (in the sense that the pathophysiology of say cancer is "real"), well, the Pathophysiology section of the ADHD article says, "The pathophysiology of ADHD is unclear and there are a number of competing theories." (It says a lot more, too, though, which you may want to read;). There have been some brain-imaging studies with, as I recall, some fairly clear results, but which have still not been sufficiently developed to provide a reliable means of diagnosis (as far as I know).

And note that ADD is a "syndrome", which "is most often used to refer to the set of detectable characteristics when the reason that they occur together has not yet been discovered."

On a more personal level, I can definitely recommend the book Driven to Distraction, which was a real revelation to me when I read it (and led me to actually go get treated by one of the co-authors, both of whom have ADD themselves, actually!), though it is perhaps a bit dated now (there have been a few sequels to it, "DtD II" etc...). If you think you may have ADD yourself, AdbMonkey, you should definitely try to be evaluated by an ADD specialist (and I believe lists of them may be given as an appendix to the above book). G.P.'s or your standard-issue psychiatrist are usually not too up on adult ADD (its diagnosis and treatment), I've found. WikiDao ☯ (talk) 13:06, 29 October 2010 (UTC)[reply]

Thank you WikiDao. AdbMonkey (talk) 19:32, 29 October 2010 (UTC)[reply]

np, Adbmonkey! :) (And just btw in case you are interested see also: the Hunter vs. farmer theory ;). WikiDao ☯ (talk) 21:27, 29 October 2010 (UTC)[reply]

O2 effect on metabolism

If a person running in standard atmosphere conditions with a 20% O2 content burned 120 kcals running 1 mile, would the same person performing the same activity under identical conditions save the O2 content was 50% burn more or less kcal from the activity? (I don't think you can get O2 toxicity at 1 atm) Googlemeister (talk) 14:13, 28 October 2010 (UTC)[reply]

You may wish to consider anaerobic metabolism. If this happens then it is relatively inefficient and more calories will be consumed, increased oxygen is likely to reduce that, so more oxygen probably means less calories burnt in a run. Less breathing will be needed too if there is higher oxygen level. Graeme Bartlett (talk) 20:33, 28 October 2010 (UTC)[reply]

Pyrotechnic colorant

I have several questions about this article.

Are sulfates really high-temperature oxidizers? I haven't heard of sulfate explosives yet.
Is carbon monoxide strong enough to reduce magnesium oxide to magnesium?
Sodium bicarbonate reacts with aluminium and magnesium to make hydrogen?
Are barium and strontium chlorides oxidized when heated very hot?

Thanks, Chemicalinterest (talk) 14:26, 28 October 2010 (UTC)[reply]

For 2, you can use an Ellingham diagram to see if this is the case. No, it doesn't look like CO -> CO₂ is able to reduce MgO at any reasonable temperature. However, C -> CO will reduce MgO to Mg above about 2100 C (give or take a few hundred degrees, my diagram's not the most accurate). Buddy431 (talk) 14:56, 28 October 2010 (UTC)[reply]

1,3: yes. 4: depends what you mean by "oxidized" Physchim62 (talk) 18:13, 28 October 2010 (UTC)[reply]

I would assume 2 BaCl₂ + O₂ → 2 BaO + 2 Cl₂ What is the reaction between NaHCO3 and Al? I would assume the bicarbonate has decomposed, maybe even to sodium oxide. --Chemicalinterest (talk) 18:25, 28 October 2010 (UTC)[reply]

Heating the bicarbonate gives off water and CO₂. THe water could react with hot metals to release hydrogen. you may get sodium carbonate formed depending how hot you go. Graeme Bartlett (talk) 20:25, 28 October 2010 (UTC)[reply]

Well, the water would definitely make hydrogen gas. IIRC, the conversion to sodium carbonate happens at a relatively low temperature, somewhere around 200C. The reaction would be 4 NaHCO₃ + Mg → Mg(OH)₂ + H₂ + 2 CO₂ + 2 Na₂CO₃ --Chemicalinterest (talk) 22:24, 28 October 2010 (UTC)[reply]

"Oxidiser" doesn't always mean "explosive". In organic chemistry anyway, we need strong oxidisers to attack or cleave or substitute certain bonds and we definitely don't want explosions. ;-) The issue is that sulfate when reduced either forms sulfur (a solid!) or hydrogen sulfide, a really smelly gas, and sulfur is less electronegative than nitrogen is so it's less likely to form H2S given a certain reducing agent. Nitrate explosives form steam and nitrogen gas when reduced, with much higher explosive velocities. Perhaps sulfates are good oxidising agents but their sulfurous gases make for poor detonation velocities. John Riemann Soong (talk) 06:28, 29 October 2010 (UTC)[reply]

The other issue is that intermediate carbon-nitrogen bonds (single, double, triple) are more likely to form than carbon-sulfur bonds in an explosion. I haven't studied explosive dynamics, but intermediates that give alkenes and ethylene and cause large phase changes will cause some severe shockwaves in pressure. The thing for any sizeable explosion is the generation of pressure and gas -- temperature increases the pressure of an existing gas but you need some good gases in the first place. If there are many pathways to oxidation then many gas products will form, and very quickly. On the other hand, if you use an oxidising agent with only a few routes to oxidation, even if it's strong (the kind of selectivity preferred in industrial, nonexplosive chemistry) then you get "bottlenecks" in gas formation which will result in lower detonation velocities simply because the reaction is slower, despite possibly higher thermodynamic potentials. John Riemann Soong (talk) 06:35, 29 October 2010 (UTC)[reply]

Complement system and antibody-antigen complexes

We recently did experiments regarding these two features of the immune system, but it left me somewhat confused. At one stage we were asked to compare our antibody titre for agglutination of red blood cells, and the titre for complement-mediated lysis. They are different, but I'm unsure as to why. When the amount of antigen outnumbers the antibodies, this serves as a cut off point for agglutination since there are no free antibodies. So why is the titre any higher for complement-mediated lysis? Does complement activate the membrane attack complex and then once the cells are destroyed release the antibody so it can attach to another pathogen, or is it another mechanism? Regards, --—Cyclonenim | Chat 15:03, 28 October 2010 (UTC)[reply]

Two IgG molecules bound to a RBC will not agglutinate; however, they are sufficient to activate the complement cascade (and thus generate a membrane attack complex). -- Scray (talk) 18:32, 28 October 2010 (UTC)[reply]

Tachyons

If a tachyon collided with a normal (not FTL) particle, would it transfer its temporal "momentum" to that particle and thus send it back in time? --J4\/4 <talk> 15:37, 28 October 2010 (UTC)[reply]

No modern, coherent theory exists to explain tachyon interactions with non-tachyons. Here is a paper from 1968 regarding interactions between tachyons: Quantum Field Theory of Interacting Tachyons. Applying the techniques in this paper to an ordinary particle will yield an unphysical result. This is a consistent problem with theories about tachyons. Nimur (talk) 16:57, 28 October 2010 (UTC)[reply]

Another chemistry question

How much beryllium-copper-silver alloy is in a small thermal fuse? --Chemicalinterest (talk) 17:15, 28 October 2010 (UTC)[reply]

The patent Thermal fuse of Kazuhiro Miyazawa gives a example 35mm x 3mm x 0.15mm, so it is not much.--Stone (talk) 19:36, 28 October 2010 (UTC)[reply]

I opened it up and saw nothing more than a spring and some ceramic on the ends. They probably don't want too much toxic beryllium on their hands.--Chemicalinterest (talk) 20:18, 28 October 2010 (UTC)[reply]

I used the material some time ago, but the safety regulations were not that bad. Avoid producing air born particles was the major concern. The small copper spring is the only beryllium containing part in the whole system. The beryllium content is 3% by mass max or 17% by atoms. So there is not much beryllium in that fuse. --Stone (talk) 21:10, 28 October 2010 (UTC)[reply]

I wanted to dissolve the alloy in hydrochloric acid to make the chloride, precipitate the hydroxide, and probably do all that work for a picture for my dear Wikipedia. ;) --Chemicalinterest (talk) 21:30, 28 October 2010 (UTC)[reply]

Geodesic dome garden shed

Would a geodesic dome be a cheap way of creating some storage space in my garden, or would I better using another method? http://sci-toys.com/scitoys/scitoys/mathematics/dome/dome.html What do the critics of geodesic domes in the article suggest as a better alternative? Thanks 92.15.25.142 (talk) 18:59, 28 October 2010 (UTC)[reply]

Probably not, at that scale a ordinary rectangular shed would probably a be a good deal easier to build, and would give you more volume for a given section of ground. APL (talk) 19:28, 28 October 2010 (UTC)[reply]

Our article geodesic dome alludes to their leaking. If you google geodesic dome always leak -wikipedia you'll see plenty of testaments to their propensity to leak, despite the advocates' protests. Comet Tuttle (talk) 19:44, 28 October 2010 (UTC)[reply]

I'm not a critic of geodesic domes (by profession) - but they are complex. As an alternative to a rectangular shed various cylindrical and hemispherical shapes make sense - eg nissan hut/Quonset hut or see http://www.plantmanagers.com/hoop.htm .. using flexible hoops the hemispherical one can be made in wigwam fashion.77.86.42.103 (talk) 12:38, 29 October 2010 (UTC)[reply]

Figuring names out for cells

Before anyone asks, it's for a book. A species that is in the book has a few extra immune cells. These include ones that act like mobile chemical detectors (to trace harmful bacteria and other things in the bloodstream), and then there's what I have termed the otocyte. It cuts harmful cells apart and then the macrophages eat the pieces. I got that from -otomy (to cut) and -cyte. However, since Wikitionary refuses to give those definitions for either of those terms, I've decided to ask here. I'd put it in Humanities, but I figure that cell biologists would be the ones naming things. So, otocyte- good name or psuedoscientific one? Feel free to give one for the chemical-detecting cell too. PS: Might as well just block all school computers preemptively, since every time I try to do something on one without logging in it says that it is blocked for vandalism. PSS: While I'm here, would nickel-neodymium be a sufficient substitute for nickel-iron in the composition of a planet's core? ArchabacteriaNematoda (talk) 20:48, 28 October 2010 (UTC)[reply]

Go to better schools? Nil Einne (talk) 21:35, 28 October 2010 (UTC)[reply]

Even the best schools in the world are home to some of Wikipedia's worst vandals. During my stay at MIT, I often received vandal warnings via the shared-proxy before logging in - User talk:129.55.200.20 records some fascinating vandalism from the Lincoln proxy. MIT Lincoln Laboratory is a federally funded research and development center chartered to apply advanced technology to problems of national security... and to post drinking tips to Wikipedia. Nimur (talk) 22:01, 28 October 2010 (UTC)[reply]

The prefix oto- usually refers to the ear. If you want to refer to cutting, you should call them tomocytes (see tomo-). ---Sluzzelin talk 21:40, 28 October 2010 (UTC)[reply]

I second that. "Otocyte" makes me think of cells that listen for noises inside the body. Which would be interesting, but hard to picture. You'd think cells very roughly 1/1000 the size of the cochlea would detect sounds 1000 times higher in pitch — ultrasonic or higher — and I don't know how far those would carry. I have a fair suspicion cells have some as yet undocumented sense of hearing e.g. in primary cilia, but I won't go so far as to predict a specialized cell type. Wnt (talk) 05:04, 29 October 2010 (UTC)[reply]

There's a reason why it's nickel-iron, although neodymium makes sense among the rare earths. One could in theory assemble a planet out of anything. --Tardis (talk) 22:04, 28 October 2010 (UTC)[reply]

Ah, the nuclear binding energy stuff isn't something I'd considered yet. I thought it was just because it makes a great giant magnetic field. But then again, I'm just a junior in an American high school, I haven't gone into anything that deep. This sort of thing is why the internet is so useful. I often surprise my teachers with random facts that I pull off a page of Wikipedia onto my brain. Thus why I figured I needed Nickel was because it balanced out the magnetic field or some such (seeing as I can't get my neodymium magnets to lift a nickel- although that is more copper than nickle I read). Anyways, thanks for the cell stuff and planetary stuff. ArchabacteriaNematoda (talk) 02:07, 29 October 2010 (UTC)[reply]

I don't see why you "need" some substance in a planetary core, but:

Neodymium is not ferromagnetic. An alloy made from neodymium, boron and iron is.
Ferromagnetism isn't relevant in Earth's core, because the temperature is way too high (see Curie temperature)
Earth's magnetic field is caused by certain convection currents and the effects of the planetary rotation in the molten metal.

Icek (talk) 04:34, 29 October 2010 (UTC)[reply]

The tough part about the neodymium core idea isn't the magnetic field (which is pretty near ornamental anyway) but where does it all come from? I know why Earth has an iron core - because a supergiant star burns down to iron, which is the stablest element toward which all fusion or fission leads. But neodymium is a rare earth - one of many similar elements present as trace components of sands in a now closed mine in the U.S. and a mine in China which recently made the news because its production might be reserved by that country for its own use. Apparently the Japanese are now looking to mine in Vietnam^[9] Anyway, you see why making the core of a planet out of this stuff leads to some pointed questions. Wnt (talk) 05:11, 29 October 2010 (UTC)[reply]

Hey, I should have read that article! Apparently rare earths aren't really that rare, just hard to find in useful ores. Neodymium is actually a little more common than lead. Of course, this is still less common than iron even in the crust, and there's not enough lead to make a core for the planet, but my argument above was still partially defective. See Abundance of elements in Earth's crust. Wnt (talk) 05:16, 29 October 2010 (UTC)[reply]

Possible circuit that shows this particular voltage/current pattern

What kind of circuit will produce this pattern of current ("peaks") for a sinusoidal voltage input? http://i54.tinypic.com/2u61fn9.jpg --Belchman (talk) 21:40, 28 October 2010 (UTC)[reply]

A Zener diode could do something sort of like that. It passes current when the voltage is beyond a threshold (in either positive or negative direction). It looks like there's some hysteresis and some non-ideal behaviors in there as well. Nimur (talk) 21:56, 28 October 2010 (UTC)[reply]

It is very likely a Reservoir capacitor and load behind a full-wave Rectifier. The deformation of the "peaks" and the current between the peeks indicates some circuit between the point of measurement and the Rectifier, probably a transformer or a Line filter.

A transformer would be likely but I do think the current between the peeks should be 90 degree after the voltage, not before as in the picture. Maybe I miss something or the current between the peeks are maybe not the magnetisation current a transformer. Could you describe where you got the measurement?

--Gr8xoz (talk) 23:25, 28 October 2010 (UTC)[reply]

Yes. Sorry for not having said this before. Apparently it was gotten with an oscilloscope and a shunt while measuring the power consumption of a personal computer. The same paper also shows the voltage and current during the analysis of the power consumption of a server. For some reason, the server doesn't show peaks of current; instead it shows two sinusoids (a linear relationship between current and voltage, therefore it can be modelled using a single resistor). I don't know what makes the server so different from the personal computer in its power consumption behavior - maybe some kind of power saving mechanism? --Belchman (talk) 08:29, 29 October 2010 (UTC)[reply]

A personal computer uses a Switched-mode power supply and has no transformer before the first rectifier, the current between the peeks is prbably due to Line filter (EMI-Filter) or measurment errors. It is easy to get disturbances in the measurment when using a shunt.

The server has probably a more expensive Switched-mode power supply using a Power Factor Pre-regulator to minimize the disturbance on the mains see [10]. --Gr8xoz (talk) 09:36, 29 October 2010 (UTC)[reply]

Thanks. Also I have a third picture, where the computer screen of the first personal computer has been turned off. It shows an increase in the amplitude of the current peak and also a delay in said peak - so that the voltage and the current are no longer in phase. What kind of power supply do computer screens (I don't know if it's an LCD or a CRT screen) use? --Belchman (talk) 10:19, 29 October 2010 (UTC)[reply]

Most new displays (typically LCD) would/will have a switched mode power supply. I'm not sure if I've read correctly but if current and voltage are out of phase that would suggest to me that there is an inductor in there - ie it's an old fashioned power supply with the initial component a transformer.77.86.42.103 (talk) 21:11, 29 October 2010 (UTC)[reply]

Thank you!! --Belchman (talk) 16:29, 30 October 2010 (UTC)[reply]

BPA degrade

In this fox "news" article, (citing this article) it states that:

Since BPA degrades in the gut when we consume it, very little gets to our cells.

So does BPA have an effect prior to getting degraded in the gut?Smallman12q (talk) 22:40, 28 October 2010 (UTC)[reply]

I find it a remarkable claim to make that bisphenol A (BPA) is degraded in the gut. Chunky aromatics like that usually go to the liver for degradation, that is they can enter the blood stream. I think the Murdoch media have simply chosen an "expert" who will give them the opinion they want. Physchim62 (talk) 23:24, 28 October 2010 (UTC)[reply]

Why put "news" in quotes? The article referred to was written by John Stossel, and is clearly marked on top as an "Opinion" article-- something that Physchim62's post lacks. Admittedly, "Since BPA degrades in the gut when we consume it, very little gets to our cells" is a paraphrase and not an exact quote, but the claim is completely supported by the linked article in the Sun-- hardly part of the "Murdoch media" conglomerate. Fox News didn't "choose an expert who will give them the opinion they want," as was claimed-- a columnist simply quoted Professor Sharpe as support for an argument. I'm not a shill for either the BPA industry or Fox News (I only get basic cable, which goes up to channel 21...) but the reality is that there is no hard evidence, at least at this point, that BPA is harmful to humans. Why, with no good evidence that I should, would I buy a BPA-free water bottle for $4 when I can buy a regular one for $1?

But, as this is the *Science* desk, the OP was presumably hoping for an answer to his/her question. The linked article says:

Q. What happens if we consume too much BPA?

A. Nothing as far as we can tell.

That seems to be the answer (or at least one answer). If your gut (ha, ha) tells you that this claim is less than completely genuine, perhaps a accurately worded Google search would be a good next step. Kingsfold (Quack quack!) 14:42, 29 October 2010 (UTC)[reply]

"but the claim is completely supported by the linked article in the Sun-- hardly part of the "Murdoch media" conglomerate." Err, The Sun is part of News International - see the News Group Newspapers info at the bottom of the article. Anyway, more importantly, the expert, Richard Sharpe looks as if he should know what he's talking about regarding the effects of BPA, but not necessarily whether it is degraded in the gut. The quote in this section of the article would indicate that it may not be broken down in the gut, as it was found in the urine of 93% of Americans. This paper supports that view, and Physchim62's; rather than being degraded, in monkeys it is linked to glucuronides and excreted in the urine, similar to the way that many drugs are metabolised. (Can't help pointing out the possibility that Dr. Sharpe might not have said it and that The Sun made it up, it wouldn't be the first time.) Because of this I don't think we can really answer your original question, other than to say that a tiny amount will be absorbed into the blood in your mouth. Smartse (talk) 15:38, 29 October 2010 (UTC)[reply]

BPA is correlated with health problems, eg and is found in urine (which means it isn't totally destroyed by the gut), it's also found in other body tissues and fluids.

Richard Sharpe; the source of the claim that BPA does not cause health problems accepts the correlation but suggests that it may be due to people having poor health in general being more likely to drink from BPA containing liquid containers - and the cause of their problems being due to their lifestyle not BPA :

Professor Richard Sharpe, of the University of Edinburgh, said for some people a raised risk of cardiovascular disease and diabetes could simply be down to drinking too many high sugar canned drinks. These people would also be exposed to higher levels of BPA from the lining of drinks cans - but that could be purely incidental. He said more research was needed to tease out the truth before BPA could be labelled as the prime suspect. [11]

At least read Bisphenol_A#Studies_on_humans. The Sun (United Kingdom) by the way is not a reliable source.77.86.42.103 (talk) 15:48, 29 October 2010 (UTC)[reply]

There is absolutely no way for any of the intestinal or salivary enzymes to attack any of the bonds in bisphenol A. Digestive enzymes generally work by hydrolysis of acyl bonds. There is nothing hydrolysable in bisphenol A. John Riemann Soong (talk) 06:59, 31 October 2010 (UTC)[reply]

October 29

Are "spectrum disorders" really just a way of saying "we don't know" ?

The ADD question a bit further up triggered this thought - Autism is a newly-recognized and poorly-understood spectrum disorder, meaning all sorts of different symptoms, to varying degrees of seriousness, can present as "autism". My gut feeling tells me the term spectrum disorder is a bit of a medical cop-out. Where do you draw the line between spectrum and a bunch of unrelated stuff? Are there other valid ailments with more establish medical histories that are classified as spectrum disorder? The Masked Booby (talk) 03:12, 29 October 2010 (UTC)[reply]

This being Wikipedia, we actually have an article that deals with the question: spectrum (psychiatry). Looie496 (talk) 03:30, 29 October 2010 (UTC)[reply]

"Spectrum" just means "it can present itself in varying degrees, from very mild to very extreme." The cut-off line is usually "does it actually negatively impact the patient's life," which is decidedly subjective, of course (and will vary by patient). I don't think it's a cop out so much as a recognition that a lot of what we consider to be "abnormal" human behavior is not often a "has it/doesn't have it" scenario, or at least, doesn't present that way. The bipolar, depressive, and schizophrenic spectrums are all pretty "well established" as far as mental disorders go (in the sense that they've been studied for a very long time). --Mr.98 (talk) 03:43, 29 October 2010 (UTC)[reply]

There's an interesting relationship in the genetics of autism and schizophrenia - in some cases the genetic aberrations are directly opposite one another. So the "spectrum" actually runs from the extremes of the one to the other, with most "normal" people occupying a band near the middle. Of course, any such argument is approximate, and this one is still quite controversial. Wnt (talk) 05:21, 29 October 2010 (UTC)[reply]

The concept of a psychiatric spectrum is an acknowledgement that the mind is a very complicated and tricky thing. For a long time, the sciences were very keen on breaking things down into discrete bits that were useful in formulating ideas. You were male or female, heterosexual or homosexual, left-handed or right-handed. Edge cases were simply disregarded. Concepts such as species are a very clear example of a thing we thought was immutable until it turned out that the clean breaks we thought existed between species don't apply in the real world. Someone above used the concept of blondeness to illustrate the point; it's not an on-off switch, it's a gradual shading that smiles at our attempts to pigeonhole it. As you walk around today, look at the people around you and "diagnose" them - are they blonde enough to be labelled "blonde" or are they "sort of blonde"? Do your categories change when you see new people? Do older blonde people with white hair still get called blonde? How about bald people? When we started, "blonde" seemed like a pretty simple thing to determine, but the longer you look at it, the trickier it gets; the same is true of psychiatric spectra. Some people are very clearly and obviously blonde, some people very clearly and obviously have ADHD, and some people very clearly and obviously have autism, but many cases are not so easy to determine. Matt Deres (talk) 14:52, 29 October 2010 (UTC)[reply]

It seems to me more like variation that can be naturally selected for. 65.88.88.75 (talk) 14:55, 29 October 2010 (UTC)[reply]

It's worth noting that even disorders like hypertension (which can be measured very precisely and quantitatively) are subject to similar concerns. You have to draw lines somewhere, and the place where the line ends up is often somewhat arbitrary. In the case of hypertension, our article gives an American Heart Association definition for normal systolic blood pressure as falling between 90 and 119 mmHg, and prehypertension as between 120 and 139 mmHg. Technically, this means that a patient with a blood pressure of 119/79 is 'normal' but another patient with a blood pressure of 120/80 is 'prehypertensive'; in reality, the distinction between the two of them is virtually meaningless. (Bonus question: why should nature have a particular fondness for round-number blood-pressure thresholds?) In psychology, it gets even murkier, and (as noted above) functional definitions are often important — are the person's symptoms sufficiently severe that they affect their ability to function successfully in society. TenOfAllTrades(talk) 15:59, 29 October 2010 (UTC)[reply]

Well, I have to point out that "ability to function successfully in society" isn't necessarily the best metric either for drawing the line with psychological disorders. I understand what you're saying, and the notion itself is of course valid – obviously, there has to be "a problem" if you are going to consider something to be "a problem". But it's important to point out that one can have a "severe" psychological disorder and still be quite able to "function successfully in society." Take the case of Dr. John Ratey, for example: "severe" (enough) case of ADHD – but a professor at Harvard Medical School, a best-selling author, a highly respected psychiatrist and psychopharmacologist, and (WP:OR) all-around good guy. :) There are many such examples, and it is important to keep that sort of thing in mind when talking about "mental illness" (the stigma of mental illness can in many ways be as "disadvantageous" as the illness itself!), though again I do understand what you mean to say and am in general agreement with it. WikiDao ☯ (talk) 18:46, 29 October 2010 (UTC)[reply]

120W power supply 30W load

Hi, I think that a 120W power supply is no less efficient than a 60W supply when powering a 30W load. Am I right? Presuming both are switch mode and passively cooled to the same temperature. -202.124.75.31 (talk) 03:59, 29 October 2010 (UTC)[reply]

I think it depends on the design, but yes, a switch mode power supply usually draw just slightly more power than is required by the load, not the maximum power at which it is rated, so there will not be much difference in efficiency. The same is true (but to a lesser extent because of higher losses) for an old-fashioned transformer. Dbfirs 07:39, 29 October 2010 (UTC)[reply]

See here for some sample power supplies. Click on some and see the efficiency graph. Obviously yours will be different, but you can get a feel for the approximate change in efficiency as you change how much power you use. Ariel. (talk) 08:37, 29 October 2010 (UTC)[reply]

(reply to original) Yes agree with you for switched mode.. infact the 120W may be slightly more efficient due to a lower internal resistance.. (probably a minor factor assumes internal resitance losses are greater when "on" than when the electronics are in "off" mode).77.86.42.103 (talk) 12:32, 29 October 2010 (UTC)[reply]

... so the 120w power supply will actually draw less current from the mains when running 60w (50%) than a 60w power supply does at full load? The difference seems to be small, but is is correct to say that half-load is optimum efficiency? The 120w unit would not be at its most efficient supplying only 30w. Dbfirs 19:07, 29 October 2010 (UTC)[reply]

Not sure about best efficiency at 50% load - the two numbers are power supply on resistance, and power supply off resistance - I'd be tempted to say that power supply off resistance is so high that the power losses (for off mode) will be negligable - so actually a (trivially) better efficiency is obtained with a heavily overspecced supply. But without the actual numbers I couldn't really be certain.Sf5xeplus (talk) 19:21, 29 October 2010 (UTC)[reply]

On the other hand a SMPS with good Power factor (ie smooth energy demand over the AC cycle) will switch more often than a basic chopper (electronics) circuit with poor Power factor - in which case the switching energy (and time spent inbetween on and off) could become a major factor in energy losses (resistive heating). Sf5xeplus (talk) 19:29, 29 October 2010 (UTC)[reply]

hand waving I'd guess that a simple chopper like SMPS (very slightly) increases in efficiency down to 10% rated power or lower.. Until the time spent actually switching is so small that the supply is drawing power through a 'spike' rather than a semi-square wave - at very low power demands the power supply is drawing much of its energy under switching conditions (ie neither on nor off) - much like a convential resistive or rheostatic voltage controller.Sf5xeplus (talk) 19:36, 29 October 2010 (UTC)[reply]

The reviews I've seen on anandtech.com show efficiency curves that typically peak between 50% and 80% of full load. Based on that, a 60-watt supply powering a 30-watt load (50% of full load) will be more efficient than a 120-watt supply powering the same load (25% of full load). --Carnildo (talk) 01:57, 30 October 2010 (UTC)[reply]

Thanks for the link to AnandTech I didn't know they did efficiency figures on PSUs - 50% does indeed seem to be best in most cases, and typically still good (and not much different) at both 20 and 80% load. By 10% load efficiency is starting to drop off - I was definately over-optimistic in my 'analysis' above.Sf5xeplus (talk) 11:49, 30 October 2010 (UTC)[reply]

OP here, thanks all. Many useful answers! Wanted to know 'cause I'm planning on building a low power computer and getting a power supply with a little margin for incorrect specs and marketing fibs seems to mean a factor of three or more. --203.22.236.14 (talk) 12:26, 30 October 2010 (UTC)[reply]

Phase behavior of pure substances below triple point pressure

Please help me understand what happens with a typical pure substance (say nitrogen) when held at a pressure below triple point pressure.

It seems to me this would be best presented by plotting constant pressure lines on a temperature-internal energy or temperature-enthalpy chart. I have made a thorough search of texts in the library of a local university, searched Wikipedia, and search elsewhere online. Just about all texts only discuss what happens above the triple point pressure - the most they say is that it cannot be liquid. I did find one advanced text that gave theory and no data - unfortunately it's way above my math skill level.

Soem textbooks show the region to the right of the triple point pressure line (ie after it intercepts the vapor sat line) and extendeing well right as "vapour". Surely it is not possible to exist in that region?

I found lots that cover other ways of plotting, eg P-V or P-H axes, but there always seemed to be something missing so I could not see a way of re-plotting with T-H axes.

NIST online thermophysical properties only gives data above triple point pressure.

Alan 05:15, 29 October 2010 (UTC)~ —Preceding unsigned comment added by 121.221.88.214 (talk)

~~You are asking about a temperature below triple point pressure. Presumably you mean a pressure below triple point pressure.~~ Dolphin (t) 07:30, 29 October 2010 (UTC)[reply]

Here's such a thing for water http://www.btinternet.com/~martin.chaplin/phase.html

And a general one http://www.websters-dictionary-online.org/definitions/triple+point?cx=partner-pub-0939450753529744:v0qd01-tdlq&cof=FORID:9&ie=UTF-8&q=triple+point&sa=Search#922

It seems reasonable to state that at pressures below the triple point pressure the substance generally can exist either as a gas or solid (see sublimation) .. though odd exceptions such as Helium exist which has a superfluid state http://ltl.tkk.fi/research/theory/helium.html

(also you seem to have swapped "above" and "below" in pressures - assuming "above" means "more than")77.86.42.103 (talk) 12:29, 29 October 2010 (UTC)[reply]

This depends on the substance. See phase diagram.Smallman12q (talk) 20:05, 29 October 2010 (UTC)[reply]

electricity doesn't weight anything

So instead of heavy battery packs to generate electricity when needed (chemically) why don't electric cars store PURE electricity, which wouldn't weigh anything? 93.186.23.237 (talk) 07:37, 29 October 2010 (UTC)[reply]

How do you propose we store electricity in its "pure" form? Closest I can think of is in a capacitor, but capacitors have mass. --203.202.43.54 (talk) 07:42, 29 October 2010 (UTC)[reply]

Yeah, a capacitor basically stores pure electricity, i.e., it stores a charge simply as an imbalanced distribution of electrons, which indeed do weigh very little). Unfortunately, capacitors are limited by a breakdown voltage, such that they short out internally if you try to store too much electricity in them. The dielectric (a kind of insulator) inside that keeps a capacitor from shorting out is the thing that contributes the most to the weight of a capacitor. The resulting energy density of a capacitor winds up being considerably less than what's available with a battery. Red Act (talk) 08:30, 29 October 2010 (UTC)[reply]

I'm afraid the question asker doesn't really understand what electricity is. Therefore, I suggest you, question asker, have a look at our article electricity. --Belchman (talk) 08:34, 29 October 2010 (UTC)[reply]

We can still answer him. The simplest answer is the electricity repels itself. So you simply can not store a lot of it in one place without it leaking (what Red Act called the breakdown voltage). Instead what you do is store the energy chemically, and convert it to electricity as needed. Ariel. (talk) 08:39, 29 October 2010 (UTC)[reply]

Pure electricity is a lot of balls (see article). Cuddlyable3 (talk) 09:32, 29 October 2010 (UTC)[reply]

The OP might want to take a look at the hydraulic analogy. In this model the closed-circuit flow of water molecules replaces the electrons in an electronic circuit. It's not enough to store the electrons, indeed the number of electrons doesn't change as you consume their energy. There needs to be some way of forcing the water (electrons) around the circuit. Either a large piston with a very strong spring, or a battery. CS Miller (talk) 10:20, 29 October 2010 (UTC)[reply]

Pure electricity wold not be a heap of charged particles but an electromagnetic wave. It can be stored in a cavity but has very low density and is very quickly converted to heat due to losses. --Gr8xoz (talk) 11:26, 29 October 2010 (UTC)[reply]

If I can join in - I sometimes wonder about storing a huge amount of light in an internally mirrored box, and using that as a lightweight power supply. This idea was inspired by an old Noggin the Nog cartoon in which summer sunlight was stored in jars, to be released during the winter months, like jam. In the context of the cartoon this is a ridiculous, hilarious idea, but what's actually wrong with it? 81.131.53.127 (talk) 12:22, 29 October 2010 (UTC)[reply]

The fact that mirrors are not perfectly reflective (even the best ones). Googlemeister (talk) 12:38, 29 October 2010 (UTC)[reply]

A couple things. One, mirrors aren't 100% efficient, nor is the air in the box. Even in a perfect vacuum, a one-meter-cubed box with a 99.999% reflective mirror would have no light remaining after even one second, because there would have been 300 million reflections in that time. Two, light to useful power is not generally efficient, nor is the conversion equipment lightweight. — Lomn 12:39, 29 October 2010 (UTC)[reply]

What are the physical or practical limits on the efficiency of mirrors? 81.131.53.127 (talk) 13:07, 29 October 2010 (UTC)[reply]

The article Solar mirror notes that Alubond Solar Reflector panels are aluminium composites achieving over 93% reflectivity. The article Perfect mirror notes that a simple mirror may reflect 99.9% of the light, and a very complex dielectric mirror can reflect up to 99.999% of the light incident upon it, for a narrow range of wavelengths and angles. Cuddlyable3 (talk) 14:04, 29 October 2010 (UTC)[reply]

The article also notes that total internal reflection is possible; otherwise fiber optic cables wouldn't work for the same reasons. But no material is perfectly transparent... which makes me wish we had a better article on total external reflection (who knew?). But storage of light might be more practically implemented with slow light, though I've not yet heard of someone taking a large chunk of such a material and leaving it out in the sun. Either the energy density should become unreasonable, or something should give.

I should point out to the newcomers that storing light is the most plausible way of storing "pure electricity", as the photon carries electromagnetic energy. If you could bottle pure electrons they'd still have some mass, and the bottle would give way in a great arc (thus capacitors are limited). Light is a bit like an alternating current set free of rest mass. Wnt (talk) 18:21, 29 October 2010 (UTC)[reply]

If you could get pure electrons, perhaps one gram of them and store them in a litre container you would have a lot of energy. However existing technology does not allow this, and repulsive forces would be collossal. Graeme Bartlett (talk) 07:33, 30 October 2010 (UTC)[reply]

Actually you can store a 1 gram electrons in 25 000 Kg standard Electric double-layer capacitor, the energy content depends on the distance to the positive charge. In a Electric double-layer capacitor it is just a few nanometers.

The calculation is: 0.001 kg/9e-31 kg*1.6e-19 C/(6 Wh/kg*3600 s/h /3 V) --82.209.130.40 (talk) 11:13, 30 October 2010 (UTC)[reply]

Fuel Consumption vs CO₂ emmissions

Hi, I've been looking at the specs of two cars - the VW Golf GTD and the Volvo C30 with the 5-cylinder diesel engine. Both manafacturers reports the same overall fuel consumption: 55.4 miles per gallon, which is equal to 46.1 mpg(US) or 5.1 l/100km

However when it comes to CO₂ emmissions, the volvo is listed at 164g/km, and the VW only 134g/km - this has confused me, as the manafacturers' figures claim they both burn the same amount of fuel to cover a kilometer (51ml) so surely they should both put out the same amount of CO₂; I would've thought that burning a certain quantity of fuel will produce the same CO₂ regardless of whether its burnt in a volvo engine, a VW engine, a jet engine, or a paraffin lamp? This assumes that the fuel itself is the same, and complete combustion occurs.

We all know that some figures like these may not be achieved in real life, but I would expect them to be consistent with themselves - especially when the difference in the CO₂ figures of these car would mean the volvo owner paying £60 more each year in Road Tax based on these figures. Shouldn't CO₂ be proportional to the figures for fuel consumption (directly proportional if the fuel consumption is measured in l/100km, or inversely proportional to mpg figures)

The specs I've mentioned are here: Volvo, VW (emmissions), VW (fuel consumption).

Interestingly I found This page listing CO₂ outputs per litre for various types of fuel, and it lists Diesel at 2.68 kg/litre (so 2.68 g/ml). Multiplying this by the 51ml the carmakers claim their vehicles burn to drive 1km, this gives us 137 g/km, very close to VW's figure but miles away from the Volvo's. Is anyone able to explain why the figures that look like they should match don't? Cheers, davidprior ^t/_c 07:47, 29 October 2010 (UTC)[reply]

You are correct. If one of the cars used fuel, but didn't burn it; it would be polluting, but would not release CO2, so its CO2 numbers would be lower than what you would expect from fuel consumption. But I can't think of anything that would make more CO2 than the amount of carbon in the fuel. Is there any possibility they are trying to take into account other things? Oil? Manufacturing? Ariel. (talk) 08:43, 29 October 2010 (UTC)[reply]

Typo second column gives 134g/km as per VW, whereas the third Volvo column gives 164g/km (for the same miles per gallon).Occam's razor meets Murphy's Law 77.86.42.103 (talk) 12:18, 29 October 2010 (UTC)[reply]

Aha! Think you may be right that its an error in the volvo's specs, as I've noticed they're wrong elsewhere too (the engine in the middle column has a description row which says "Four cylinder turbocharged diesel", but the row for number of cyclinders has a 5 in it. So think they must have the CO₂ figures wrong too. Cheers, davidprior ^t/_c 09:55, 30 October 2010 (UTC)[reply]

Firing a ceramic

What happens chemically when a ceramic is fired? Specifically what causes the individual particles to fuse and become hard? Do they melt? Ariel. (talk) 08:49, 29 October 2010 (UTC)[reply]

It looks like the typical firing temperature lies below the melting point. The articles on ceramic engineering (subsection "The sintering process) and on sintering might be of use. ---Sluzzelin talk 11:00, 29 October 2010 (UTC)[reply]

Multiple tasks with both individual hands difficulty

What do you call it when someone can't perform two different tasks one by each hand or one task by a foot and another different task by a hand? There are cases we can manage and many cases we find it difficult if not impossible. Is there also a part of our body (e.g: brain) which has to do with?--Email4mobile (talk) 08:52, 29 October 2010 (UTC)[reply]

I thought it might be ambisinistrous (by analogy with ambidextrous), but that means to be equally clumsy with either hand, which I think is not quite what you're after. -- Jack of Oz ... speak! ... 09:10, 29 October 2010 (UTC)[reply]

There is a special keyboard (that to me looks like an ordinary one sold at an extraordinary price) available for persons unable to type with both hands. Cuddlyable3 (talk) 09:52, 29 October 2010 (UTC)[reply]

I mean to perform multiple tasks at once/synchronously. Example of this is when we try to write the number 6 (added by our hand), while revolving our foot clockwise.--Email4mobile (talk) 10:03, 29 October 2010 (UTC)[reply]

OR: It's easy if I draw the 6 clockwise or difficult anticlockwise. I'm still trying to write 8 without lifting the pen. Cuddlyable3 (talk) 10:44, 29 October 2010 (UTC)[reply]

I don't think there's a particular word for the phenomenon, but it's been discussed previously here. The higher brain can only handle one complex movement at once. However if that movement is repeated, it can be automated to a degree via motor learning, leaving the brain to concentrate on something else. the wub "?!" 10:48, 29 October 2010 (UTC)[reply]

I guess you could call it a task of "inter-limb" motor coordination. Drummers and organ players spend a lot of time "motor learning" for independence of their limbs. (So do cyclists, chauffeurs and cheerleaders and occupiers of many other occupations)---Sluzzelin talk 11:11, 29 October 2010 (UTC)[reply]

Energy Anomaly??

Sir, Einstein's Famous equation E=mc² suggests that energy and mass are just different forms of the same thing.They can be interchanged.Consider a case when infinite amount of energy is converted into mass.An infinite energy would produce matter that is infinitely massive.Or conversely an infinitely massive body should produce infinite energy.Is this phenomenon possible in our universe where energy is a constant?? —Preceding unsigned comment added by Vishnuthelegend (talk • contribs) 09:45, 29 October 2010 (UTC)[reply]

No. Cuddlyable3 (talk) 10:45, 29 October 2010 (UTC)[reply]

By the very definition of "infinite" you can never have it. And BTW it's not so easy to interchange mass and energy (although it is possible of course). Ariel. (talk) 10:52, 29 October 2010 (UTC)[reply]

Mass IS energy but it is rather hard to convert matter to other forms of energy effeciently. All forms of energy has mass. --Gr8xoz (talk) 11:09, 29 October 2010 (UTC)[reply]

Infinite energy and infinite mass mean nothing in our universe. But in an other, hypothetical, universe, yes, an infinite amount of energy could be used and converted into an infinitely large object which would have an infinite mass, but obviously, this would take an infinite amount of time, so you would never ever get there !! --Lgriot (talk) 12:13, 29 October 2010 (UTC)[reply]

As Gr8xoz pointed out, the mass–energy equivalence equation does not just say that mass and energy can be interchanged. It says that they are the same thing. Energy, in all of its forms, has mass; a photon has mass; a compressed spring has slightly more mass than when it is relaxed; a charged battery has slightly more mass than when it is uncharged; a moving object has more mass than when it is at rest. There is no need to "convert" the energy into matter to give it mass. Having said that, the concept of an infinite amount of energy/mass within a finite volume is definitely physcially unrealistic and more or less meaningless. Gandalf61 (talk) 12:46, 29 October 2010 (UTC)[reply]

Any references there Gandalf61? I'm intrigued by the notion that a spring has more mass when compressed than relaxed. I don't disbelieve you, and I see how it's consistent with physical theory, but what is the mechanism? I'm guessing to measure the mass increase due to compression you'd need a very lightweight spring with a very large spring constant and a very accurate scale. Is that right? SemanticMantis (talk) 14:21, 29 October 2010 (UTC)[reply]

The compressed (or stretched) spring is one of several examples in mass-energy equivalence#practical examples. You can use the potential energy stored in a compressed spring to accelerate an object, which increases its relativistic mass. If the mass of the compressed spring were not greater than the mass of the spring when relaxed, then accelerating the object would create mass from nothing, violating the principle of conservation of mass. Of course, the mass involved is tiny - about 10^-17 kilograms per joule - and I doubt there is any feasible way to observe it for "real world" springs. But my whole point is that you don't need a mechanism to turn energy into mass - energy just has mass (and vice versa). Gandalf61 (talk) 15:32, 29 October 2010 (UTC)[reply]

A better (rather, a more practical) example than the "compressed spring" is the mass error measured in atomic nuclei (i.e., two protons stuck together are not

2.{\overline {0}}

times as heavy as a single proton). We call this a mass defect - a change in the mass because of a change in the energy-state of the nuclei. It is a real, measurable effect - we can measure it with a lab scale, or observe it indirectly by observing particle trajectories, and so on. In fact, we can even measure mass defects from non-nuclear binding energies: some inter-atomic binding energies (e.g., chemical reactions) are sufficiently large that we can measure their mass defects. A macroscopic compressed spring also has a mass defect because of a change in internal energy - but there is no lab equipment commonly available that is precise or accurate enough to measure it. To some degree, atomic or nuclear interactions are just a "different kind of spring" - there is a potential energy reservoir due to fundamental interactions; whereas a large metal coil spring has a potential energy reservoir because of billions and billions of fundamental-interactions averaging out. At the end of the day, energy is energy; it always behaves the same way; only, in some cases, it's easier to observe certain properties, like the mass-defect. Atomic physics was therefore a necessary experimental precursor to the modern theories about mass-energy equivalence - we will never build equipment that is accurate enough to observe relativistic effects in "ordinary" Newtonian kinematics scenarios. (Nimur (talk) 17:42, 29 October 2010 (UTC)[reply]

Is the thymus an endocrine gland?

Resolved

Our article Thymus says "It is largely degenerated in elderly adults and is barely identifiable, consisting mostly of fatty tissue, but it continues to function as an endocrine gland..." The caption of the top illustration in Endocrine system declares "Note: the Thymus (labelled 4.) is not an endocrine gland." A definitive answer to the question in the header would be appreciated. Thank you. --Hordaland (talk) 11:49, 29 October 2010 (UTC)[reply]

My impression is that the question can't be answered definitively. It has endocrine activity (it produces thymulin for example), but its most important role is to generate certain types of immune system cells. Looie496 (talk) 17:53, 29 October 2010 (UTC)[reply]

Oh, dear, oh, dear. I can change the sentence in thymus to read something about endocrine activity. But is the note on the illustration correct -- that the thymus "is not an endocrine gland"? That looks dumb and the thymus should be removed from the that illustration, I'd think. What do you think? Hordaland (talk) 18:34, 29 October 2010 (UTC)[reply]

I agree with Looie496, and would add that it appears undue weight is given to thymosins in the lede paragraph of the Thymus article. Secondary sources consistently describe the thymus as a primary lymphoid organ, whereas discussion of its endocrine function are mostly in primary sources. In addition, thymectomy is generally well-tolerated by human adults, with the only prominent phenotype having to do with reduced T cell function. -- Scray (talk) 18:51, 29 October 2010 (UTC)[reply]

There seems to be a fair amount of discussion of thymic endocrine function, including thymulin, thymosin alpha1, thymosin beta4, and thymopoietin, and other more general cytokines (see PMID 19273180). (thymosins can also be produced elsewhere - if cupping has any beneficial effect, I bet they are involved...) The problem is that endocrine organs are a pedagogic construct - probably every cell in the body secretes signalling molecules that have some general effect on the body; it's just that some glands do this disproportionately. It does seem more common to say that the thymus has endocrine function rather than that it is an endocrine gland, and perhaps it's best addressed in this way. Wnt (talk) 19:03, 29 October 2010 (UTC)[reply]

Thanks so much to you all! I am not competent to fix the lede nor to understand much of the rest. But I've changed wording in Thymus to "endocrine function". And in the caption to the top illustration in Endocrine system, I've changed the wording to "[Note: the Thymus (labelled 4.) has endocrine function, though it is not considered to be an endocrine gland.]. Hope it is OK to copy this entire section to the talk page(s). Hordaland (talk) 19:51, 29 October 2010 (UTC)[reply]

Clamped buttress

Resolved

What is a clamped buttress? The article St James' Church, Stretham is passing through a GA review at the moment and I have been asked to clarify the term clamped buttress. Is anyone able to help please? The term is sourced from Pugh (1953) Victoria County History of Cambridgeshire here.

The closest I can get is from here which states "clamp - In architectural construction, a device, usually metal, used to hold together blocks of stone of the same course. Also called a cramp". Also, OED meaning (1) gives "A brace, clasp, or band, usually of iron or other rigid material, used for giving strength and support to flexible or movable objects, or for fastening two or more things securely together. ... e.g. A bar of iron for binding together stones in a building"

--Senra (Talk) 12:10, 29 October 2010 (UTC)[reply]

Looking for "clamp buttress" (compound term, not generic adjective meaning) gives two consistent hits for a description that seems appropriate for this context: [12], [13]. DMacks (talk) 12:28, 29 October 2010 (UTC)[reply]

I suspect that the article text (Clamped buttresses dating from the 12th century are visible in the chancel) is wrong - this image inside the chancel ~~oops~~ [14] shows no buttresses I can see, but isn't clear. This image [15] from outside the chancel shows what I suspect to be "clamped buttresses" they are the thickening of the walls on the corners. Note how they appear to "clamp" the building at the corners, and are also buttresses .. buttresses are more common on the outside.

Also note the source http://www.british-history.ac.uk/report.aspx?compid=21908 - the 12th century parts of the church are show in this diagram http://www.british-history.ac.uk/image.aspx?compid=21908&filename=fig24.gif&pubid=93 also the text "There are clamped buttresses which date from the end of the 12th century" 77.86.42.103 (talk) 12:55, 29 October 2010 (UTC)[reply]

By the way the 'terms' section at the end of my architecture book describes a very similar outside structure as "clasping buttresses". see http://www.prestbury.net/magazine/church_architecture/page05.htm - that's what the chancel of this church has. 77.86.42.103 (talk) 13:19, 29 October 2010 (UTC)[reply]

For another example see [16] St. Peter's Church, Wilburton - the tower is described as "The tower is of three stages and dates from the middle of the 13th century. There are angle buttresses with two set-offs reaching to the top of the first stage, while the second stage has clamped buttresses rising from the string-course." [17] - you can see the (three steps of the) angled buttress in the images, and above that are the clamped (clasped) buttresses slight obscured by trees branches above the first horizontal string (which are just visible). There's a better image here [18]- the clamped buttresses are the buttresses in the middle section on the plain (unwindowed) section of the tower.77.86.42.103 (talk) 13:33, 29 October 2010 (UTC)[reply]

Thank you for the detailed and useful explanation. I have modified the article accordingly by adding a footnote which is sourced to the Pevsner Architectural Guides website --Senra (Talk) 15:38, 29 October 2010 (UTC)[reply]

on utilizing sound energy

can we ever use sound energy as a tool for producing other forms of energy? is there any application that already uses this idea of converting sound to other forms.how much energy do u get when a device produces a sound waves of 40 db —Preceding unsigned comment added by Vijayendra shastri (talk • contribs) 12:48, 29 October 2010 (UTC)[reply]

Imagine a device that turns the energy produced by the sound of your voice into electrical energy. Then, transmits that electrical energy to another device that a friend is holding. Your friend's device converts the electrical energy back into sound energy so your friend can hear your voice from a distance. We could call this something like distance sound, or if want to use Greek to make it cool, it could be telephone. -- kainaw ™ 13:00, 29 October 2010 (UTC)[reply]

A Tin can telephone transports the actual mechanical energy of the speaker's voice but a modern electric telephone uses electric energy from an external supply (central battery) and the actual voice energy just modulates the current sent through the wires. Cuddlyable3 (talk) 13:42, 29 October 2010 (UTC)[reply]

Sound-powered telephones are used on Navy ships and in other places where communication must work even if the electricity goes out. Nimur (talk) 15:26, 29 October 2010 (UTC)[reply]

You could try refrigeration by sound. Rmhermen (talk) 13:20, 29 October 2010 (UTC)[reply]

The OP makes a common mistake of quantifying a sound level in dB (decibels) alone. "40 dB" means a power ratio equal to 10 000. It is a meaningful expression of Sound pressure (see article) only when the 0 dB reference pressure is given. If 0 dB is stated to be 20 µPa RMS, which is about the threshold of human hearing at 1 kHz, 40 dB w.r.t. 20 μPa is typical of normal conversation at 1 m. Cuddlyable3 (talk) 13:22, 29 October 2010 (UTC)[reply]

-40dB ...? (negative means less..)77.86.42.103 (talk) 14:06, 29 October 2010 (UTC)[reply]

Yes, -40dB means 1/10000, the opposite of "40 dB" because the "bel" scale is a logarithmic scale. Dbfirs 18:38, 29 October 2010 (UTC)[reply]

Sonoluminescence is cool! DMacks (talk) 13:31, 29 October 2010 (UTC)[reply]

As an experiment in semi-logical thinking - the blast waves from explosions are sort of like sound energy.. and can be used to liberate minerals such as coal - which is then used as an energy source...77.86.42.103 (talk) 13:36, 29 October 2010 (UTC)[reply]

But only sort of, because to stress rock enough to crack it the blast wave must break the Sound barrier in the rock i.e. stress it beyond its Elastic limit. Cuddlyable3 (talk) 13:48, 29 October 2010 (UTC)[reply]

There is research ongoing in this field: [19]. One possible application mentioned in the article is the use on highways. - Akamad (talk) 13:55, 29 October 2010 (UTC)[reply]

Since sound is vibration, our article on Energy harvesting is relevant. Small autonomous sensors could be powered by vibrations in the material they are embedded in, for instance a sensor tacked onto an engine. That article links to this story: [20] about a piezoelectric device that turns heat into sound which then is turned into electricity.

But "proof of principle" examples are easy to find. If you read the microphone article, you'll find that many microphones work by having a tiny piece of metal vibrate in a magnetic field, creating electricity. This is the principle of Electromagnetic induction which has been a way to produce electricity since the days of Faraday. EverGreg (talk) 14:24, 29 October 2010 (UTC)[reply]

The phonomotor was a device invented by Thomas Edison in 1878 which converted sound energy into rotary motion which could drive a machine such as a small saw or drill. A diaphragm vibrated when the sound waves, as of someone speaking, fell on it. Its back and forth motion operated a pawl on a ratchet wheel with very fine gear teeth, which produced rapid rotary motion of a flywheel and shaft. It was able to operate a small drill and drill a hole in a board, or saw wood.. See [21]. I would expect that the output power was minuscule. It was described as a "scientific toy." Edison (talk) 15:27, 29 October 2010 (UTC)[reply]

Phonomotor. 92.15.12.85 (talk) 14:18, 30 October 2010 (UTC)[reply]

Thanks for pointing to the article I just created. Edison (talk) 20:06, 30 October 2010 (UTC)[reply]

unfunny joke: Please read Wikipedia:Conflict_of_interest#Self-promotion.77.86.42.103 (talk) 00:35, 31 October 2010 (UTC)[reply]

Any loudspeaker is pretty effective at converting sound into electricity (AC). Cacycle (talk) 09:54, 30 October 2010 (UTC)[reply]

Big Cats

Are the big cats viz. Tigers, jaguars, and lions cannibals?

Alwaysshariff (talk) 13:58, 29 October 2010 (UTC)[reply]

Searching for http://www.google.co.uk/search?aq=0&oq=lion+cannib&sourceid=chrome&ie=UTF-8&q=lion+cannibalism etc seems to say yes (under some conditions).77.86.42.103 (talk) 14:03, 29 October 2010 (UTC)[reply]

Aviation Thermobaric Bomb of Increased Power

Our Aviation Thermobaric Bomb of Increased Power article (a.k.a. the "Father of All Bombs" article) says two or three times, basically, that it's more powerful than other bombs "because of nanotechnology". Is this just buzzword nonsense from a Russian PR flack? Comet Tuttle (talk) 16:53, 29 October 2010 (UTC)[reply]

Apparrently just some random crazy guy editing wikipedia.. diff ! (well that never happened before) Sf5xeplus (talk) 17:17, 29 October 2010 (UTC)[reply]

That's a good edit you highlighted, but it didn't touch (or edit) the claims about nanotechnology. Comet Tuttle (talk) 17:49, 29 October 2010 (UTC)[reply]

The ref http://news.bbc.co.uk/1/hi/world/europe/6990815.stm says nanotechnology was used in the development of the explosive - (I thought the nano claim was part of the crazy) - it's possible that nanotechnology could make a better explosive (if it's a mix explosive such as Ammonium Nitrate/Fuel oil - ANFO) (as used in a 'daisy cutter bomb' BLU-82 - though I'm not sure. Can't find the original source. Definately it's true that the finer the fuel mixture the better the bomb. Probably not incorrect.

In russia http://www.youtube.com/watch?v=iCmA7xFPIdU (I think it's some sort of finely divided metal (nano). A russian translation of this might help. Sf5xeplus (talk) 18:13, 29 October 2010 (UTC)[reply]

It's pretty unlikely that the BLU-82's high-explosive mix is "ANFO" or "ANFO-like." Do you have any reference for that claim? The military has access to better technology; while powerful, ANFO is a hallmark of the "improvised from household materials" explosive, not "major Air Force project with access to defense-contract funding and chemical factory." Better high explosive exists, and in most cases, the desirable ingredients are obvious - but access to the prerequisite materials is controlled. Major military powers have a little easier time accessing such materials. Nimur (talk) 18:50, 29 October 2010 (UTC)[reply]

I linked to ANFO as an example.. the old BLU-82 used ammonium nitrate and polystyrene (which is pretty close to ANFO chemically : since both fuel oil and polystyrene are both hydrocarbon sources), plus aluminium powder. (see article or http://science.howstuffworks.com/moab3.htm or http://www.globalsecurity.org/military/systems/munitions/blu-82.htm) - a slurry explosive (see Melvin_A._Cook#Explosives) plus aluminium. when I said as used in the BLU-82 I meant a mix explosive not specifically ANFO. I can see that statement was open to misunderstanding the way it was written.

Nevertheless a BLU-82 does use an ANFO-like explosive plus aluminium improver. Sf5xeplus (talk) 19:10, 29 October 2010 (UTC)[reply]

Our entry links to this article which references a Russian news channel. So it's not the strongest list of sources in my opinion. If there was nanotechnology involved, it probably just means that they have found some way to use very small particle size. The fuel-air bomb article says that the FOAB uses nanoparticles of aluminum (which doesn't sound outrageously implausible to me, but what do I know), but the reference it gives doesn't actually say that. All of the links in that article relating to nanotech either lead to articles that don't say the same thing. --Mr.98 (talk) 18:02, 29 October 2010 (UTC)[reply]

There's something that comfirms that nanoparticles should work http://technologyreview.com/Nanotech/14105/ , but isn't about the russian bomb.Sf5xeplus (talk) 18:33, 29 October 2010 (UTC)[reply]

CFL bulbs afterglow "flashing"

I recently replaced my old "U-tube" compact fluorescent lamp bulb with a new, brighter one of those curly "bee-hive" spiral designs (first two pics in our article). Now CFL bulbs retain an afterglow when they're switched off, but this new one exhibits a stranger behaviour. Not only does it have an afterglow, but also, as if it had some sort of capacitance, it will "flash" brighter for a fraction of second once every 10s or so, before returning to residual afterglow levels. It continues to do this for minutes on end until eventually subsiding. Is this a known phenomenon? What could explain it? Unfortunately my cellphone camera is not sensitive enough to video it (the pic is totally black). Zunaid 17:22, 29 October 2010 (UTC)[reply]

This question has come up before eg http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_January_18#dim_flashes_from_a_Fluorescent_lamp

I think there are other examples but can't find them in the archives - my personal theory is that after the power is switched off the electronic charge pump that produces the tube volatage continues to operate on residual capacitance in the power supply stage of the device - and takes a long time to charge up to discharge voltage due to the low voltage remaining the the capacitors.. this happens a couple of times until the supply side capacitors are totally discharged...Sf5xeplus (talk) 17:32, 29 October 2010 (UTC)[reply]

I have a compact fluorescent lamp that regularly flashes hours after the supply has been switched off. From testing, I know that the cause is the tiny leakage current from old wiring through two-way and crossover switches (called three-way and four-way in the USA). The leakage is sufficient to light the neon on my tester screwdriver, but not sufficient to give an electric shock. I should have my wiring tested and possibly the old switches replaced, and I ought to advise you to do the same because it is possible that this flashing is a warning of a developing dangerous condition. Dbfirs 18:25, 29 October 2010 (UTC)[reply]

I have a new house and wondered about the 8 volts of current in a lamp outlet before I realized that the switch was turned off. --Chemicalinterest (talk) 22:30, 29 October 2010 (UTC)[reply]

"Volts" are units of electric potential, not of electric current whose units are Amps. An AC voltmeter with high impedance will show a small voltage with only a capacitive connection to a 120 or 240 VAC mains supply, which may be what you observed. Cuddlyable3 (talk) 22:57, 29 October 2010 (UTC)[reply]

my project

I wanted to know about George Washington Carver's family life and work.I read your article about him but it is too short because i need to wright 2 pages about him on every part of his biography. Thank you ever so much Yours Sincerely, Mim —Preceding unsigned comment added by 92.29.50.98 (talk) 18:05, 29 October 2010 (UTC)[reply]

You might be better off asking on the Wikipedia:Reference desk/Humanities desk about this.

You can try the links from the article eg George_Washington_Carver#References to get more information, or try Google books http://www.google.co.uk/search?q=George+Washington+Carver&hl=en&tbs=bks:1,bkv:p&source=lnt&sa=X&ei=oBHLTMfGBovoOcul1MkB&ved=0CBEQpwU or a library.Sf5xeplus (talk) 18:26, 29 October 2010 (UTC)[reply]

Toothpaste

Children are advised to use only about a pea-size (1 g??) of toothpaste to prevent accident swallowing. How much toothpaste would it be necessary to "accidentally" swallow to die from poisoning? (this is not medical advice, just curiosity) —Preceding unsigned comment added by 24.92.78.167 (talk) 18:17, 29 October 2010 (UTC)[reply]

To die, quite a lot (and it would depend on the brand of toothpaste). The idea of the advice is to prevent dental fluorosis, especially in areas where the water is already fluoridated. Physchim62 (talk) 18:36, 29 October 2010 (UTC)[reply]

Rough estimates are around over 10 tubes .. http://www.acsh.org/factsfears/newsID.188/news_detail.asp .. See also Fluoride_poisoning#Fluoride_in_toothpaste . In general eating a lot of toothpaste causes stomach pain long before the leathal dose is reached.Sf5xeplus (talk) 18:37, 29 October 2010 (UTC)[reply]

(edit conflict) Hmm, a quick search, not necessarily reliable source [22] reveals that "toothpaste for sensitive teeth" actually is using fluoride to poison the nerves at 0.22 percent (over the counter) to 1.1 percent (prescription). My that sounds like a dubious idea, but let's just use the number for now. A different source says that high-fluoride over the counter toothpastes contain 0.1 to 0.15 percent fluoride.[23] The low concentration there is 0.044/0.05/0.055 percent. (stated as 550 ppm, in case I fouled up) This sort of variation, the likelihood that someone will fail to consider some factor like this, is the reason why some people believe Wikipedia shouldn't give medical advice. I'll bet the medical professional you ask is going to flip an answer in a few seconds without asking what type of toothpaste, but it's their racket.

Now as for toxicity of fluoride, there I'll go by the article, which cites 0.2-0.3 mg/kg for gastrointestinal distress, while lethality begins 15-20x higher (32-64 mg/kg). So a 20 kg child could be uncomfortable eating 4 mg fluoride, which requires 363 mg of volume at 1.1% w/w. (Actually it is probably w/v but we can assume that the toothpaste is very nearly 1 g/ml like water). Now one of our articles 1_E-7_m³ says that the volume of a pea is 200 microliters, which is about half of this. Thus the pea-sized lump sounds relatively safe from gastrointestinal distress, even with toothpaste for sensitive teeth. But bear in mind that every person is a bit different, and most importantly, we haven't spoken of cumulative exposure.

To answer the question accurately, we must discard theory, which is never reliable in biology, and look at experimental data, e.g. PMID 16128790, which finds that 32% of the pea-sized lumps of toothpaste given to 4.5 year old Malaysian children ends up being swallowed. But some British kids apparently swallowed only a third as much (PMID 10365494) - must be a benefit of keeping a stiff upper lip. Another study didn't find that swallowing fluoride toothpaste caused fluorosis, but starting it before age 5 might (PMID 9758424). There's much more data there at PubMed - as usual, looking up the data demands we decide exactly what question we mean to ask. Wnt (talk) 18:47, 29 October 2010 (UTC)[reply]

If it's anything like the proton pump drugs for acid reflux, you don't need to kill the nerve cells to disable them. You just need to provide ions to neutralize the receptors. Whereas disabling acid-producing cells affect digestion in the long run, I don't know what the effects of disabling oral nerve cells are. Imagine Reason (talk) 02:21, 30 October 2010 (UTC)[reply]

Hmmm... I avoided saying anything solid there because I wasn't sure about the mechanism of action of fluoride in sensitive-teeth toothpastes, and the more I read the more confused I get. I've read that it soothes the nerves, that the tin in stannous fluoride blocks the tubules, even that it's actually the calcium and potassium in the toothpaste that has the effect by blocking the tubules (see PMID 20158016). For now I'll offer no opinion about it, beyond my gut feeling that it sounds worrisome.

As an aside, I'll admit I'm prone to suspect as-yet unknown regenerative actions from intact nerves. It's been my subjective impression that after a few days even a small chip at the end of a tooth causes a faint sensation of swollenness within it, and emission of a sweet, salty tasting fluid from the chipped area. I'm suspicious that somehow the nerves might sense damage and coordinate immune responses throughout the bulk of the tooth, but that's purely personal speculation — still, it's the reason behind my gut reaction above. Wnt (talk) 10:26, 30 October 2010 (UTC)[reply]

As an aside, it has nothing to do with children -- a pea-sized amount is recommended for people of all ages. Any more provides no greater efficacy and advertisements to the contrary (a la a full brush head shimmering in the light with a perfectly-arranged tilde of tri-color aquafresh) merely contributes to overuse and subsequent over-purchasing. DRosenbach ^{(Talk | Contribs)} 00:10, 31 October 2010 (UTC)[reply]

Hardness of human teeth

What would be the approximate hardness on the Mohs scale of an adult human incisor in good health? Thank you, DuncanHill (talk) 19:26, 29 October 2010 (UTC)[reply]

Tooth enamel is listed at 5 in our Mohs Scale article that you linked to. Several sources (here, here, and here) corroborate this. --Zerozal (talk) 19:40, 29 October 2010 (UTC)[reply]

Many thanks. DuncanHill (talk) 19:43, 29 October 2010 (UTC)[reply]

Shame on you Duncan ! - even I can remember your question Wikipedia:Reference_desk/Archives/Science/2009_March_2#Hardness_of_teeth and find it doing this [24] ... :) Sf5xeplus (talk) 19:44, 29 October 2010 (UTC)[reply]

How incredibly embarrassing! I wonder if I was watching the same episode of CSI:Miami then as I am now. DuncanHill (talk) 19:48, 29 October 2010 (UTC)[reply]

What looks like peas?

During the first week of October I was in Myrtle Beach, South Carolina and, since they are full grown, these trees must have been there in the past, but for the first time I realized that their fruit (or what I assume is fruit) looks like peas. There is another tree, possibly the same species but I don't think so, where I live in North Carolina. I never noticed this fruit before.Vchimpanzee · talk · contributions · 20:52, 29 October 2010 (UTC)[reply]

It's pretty difficult to say precisely without a better description, but peas are a member of the Fabaceae family of plants which contains 20,000 species, some of which are trees (e.g. Acacia and Gleditsia), and they all have seed pods called legumes which look the same as pea pods. SmartSE (talk) 22:34, 29 October 2010 (UTC)[reply]

I was wondering if you can/could point at a picture of such a tree at http://commons.wikimedia.org/wiki/Category:Myrtle_Beach,_South_Carolina (might remove some guesses from people who haven't been there but are biologists) Sf5xeplus (talk) 22:42, 29 October 2010 (UTC)[reply]

The Indian Bean Tree or Southern Catalpa is my bet. It has seeds in long (8 to 14 inches) pods that look like beans or peas[25]; they stay on the tree all through the winter. It's a native of south-eastern USA but there are some nice ones in Parliament Square in London. Alansplodge (talk) 22:55, 29 October 2010 (UTC)[reply]

We can rule out the Indian Bean Tree because there are no pods.Vchimpanzee · talk · contributions · 17:25, 30 October 2010 (UTC)[reply]

Hang on dude, you said to start with the fruit looks like peas, now you say there are no pods? Did you really mean the fruit is small, round and green, rather than the fruit is contained in things that look like peapods? --TammyMoet (talk) 19:46, 30 October 2010 (UTC)[reply]

October 30

Carbonated drinks and digestive health?

This is a bit speculative here and there might not be a definitive answer:

If it's true that neurotransmitters are reduced in reaction to a receptor being stimulated... So, for instance, capsaicin which normally causes pain and inflammation can also be a treatment for reducing pain and inflammation...

And if there is something like pressure receptors somewhere in the GI tract (mechanoreceptors?? osmoreceptors?? some other name??)...

...Then, in the long-term, couldn't carbonated drinks lead to digestive problems (in the short-term, carbonated drinks can lead to borborygmus, right? In the long-term, couldn't they cause GI pressure to be poorly regulated?) ☯ Zenwhat (talk) 01:24, 30 October 2010 (UTC)[reply]

My anecdotal experience is that excessive CO₂ can lead one to feel a little gassy, but it is usually vented pretty quickly. I'm not sure I see things hanging around enough, or having significant physiological effect, to have long-term effects of the sort you're describing, but I'm no anatomist. --Mr.98 (talk) 02:59, 30 October 2010 (UTC)[reply]

Since the gastrointestinal cavity is not rigid, any accumulation of gas causes bloating, which is not at all difficult to detect, unfortunately. Looie496 (talk) 03:49, 30 October 2010 (UTC)[reply]

uakari fruits

What is the name of the fruit that Bald Uakaris eat in order to produce more babies? —Preceding unsigned comment added by 70.31.22.155 (talk) 01:38, 30 October 2010 (UTC)[reply]

Our Bald Uakari article says: "The overall diet of a uakari consists of 67% seeds, 18% fruit, 6% flowers, 5% animal prey, and buds. They will also eat insects that happen to be cross their path, however they do not specifically pursue this type of food." It also says: "Their powerful lower jaw forms a pseudodental comb, which allows the uakari to open the hard surfaces of unripe fruits and eat the nuts that most other primates would not be able to open," but it doesn't say specifically what they might eat that would affect their reproductive behavior. WikiDao ☯ (talk) 01:59, 30 October 2010 (UTC)[reply]

Time dilation? Time speeding?

Dear friend, I have difficulty understand the beginning of the section {Time dilation and length contraction} in Special Relativity, Could some one tell me what should I say to respond the LAST suggestion from DVdm in the following conversation? Please help.

Regards, John

I see you haven't had any luck so far in getting your question answered. As a suggestion, perhaps you'd have better luck getting an answer if you repost your question as a paragraph that's as brief as possible, while still containing all the information that's essential to understanding what it is that you're asking. A question is a little less daunting to the volunteers if the question can be understood by just reading one brief paragraph, rather than having to read through an entire lengthy conversation to see what's going on. Red Act (talk) 02:29, 31 October 2010 (UTC)[reply]

Time dilation and length contraction

THE BEGINNING OF THIS SECTION IS NOT CLEAR. PLEASE REVIEW WITH THE CAPITAL CHARACTERS.

Stained glass

Resolved

Is there any way of finding out when a particular stained glass window was made and by whom and as a result determine if the artist died more than 70 years ago?

During what has turned out to be a successful GA review of St James' Church, Stretham the reviewer drew my attention to a potential Freedom of Panorama issue with the image I took of the church's stained glass window, File:St James Church Stretham window 06-09-2010.jpg, licensed as {{cc-by-3.0}} i.e. my own work. I raised the issue at the media copyright questions forum here. The church plans website ("Stretham, St James' (1874-76)". Church plans online. Lambeth Palace Library. Retrieved 26 August 2010.) indicates that the church was restored between 1874 and 1876 by architect J. P. St Aubyn. Heavily restored, according to VCH (Pugh, R.B., ed. (1953), The Victoria History of the Counties of England: Cambridge and the isle of Ely, vol. IV, Oxford University Press, pp. 151–159 {{citation}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)). Indeed, VCH records "The chancel has an east window of five lights with modern geometrical tracery, and there is a hood-mould terminating in heads". Does this mean modern in the 1953 (VCH) sense or modern in the not medieval sense? Pevsner is no help either.

The VCH was originally published in the first decade of the 20th Century, so IMHO Victorian would probably be "modern". Alansplodge (talk) 14:33, 30 October 2010 (UTC)[reply]

Short of going down to the Cambridgeshire Archives (hard but not impossible for me) or the Lambeth Palace Library (nearly impossible for me) I am not sure how I can determine who made this stained glass window and when. In any case, would such trips constitute OR? Just for completeness, I have asked the church's team vicar and one of the church wardens; neither can help

--Senra (Talk) 11:17, 30 October 2010 (UTC)[reply]

I've always found Cambridgeshire Archives most helpful by phone, could you try ringing them? --TammyMoet (talk) 11:24, 30 October 2010 (UTC)[reply]

The image you took, second pane from right, bottom - "AD MDCCCLXVIII" = 1868? I would guess that dates the glass though it could refer to an event portrayed in the image - however the image appears to be the Ascension of Christ so I think it's the date - there's also a name "Henricus Herveius Baber" on the second pane from the left - is this the artist (or benefactor)? I would guess the date refers to a commisioning date rather than installation - which would fit with a 1870s restoration. (maybe) Sf5xeplus (talk) 11:40, 30 October 2010 (UTC)[reply]

Ha ha. I'm an idiot. Every artist signs their work don't they? Well then Shylocke (aka Sf5xeplus), I am going to agree with you on the date, thank you. However, Henry Hervey Baber was a vicar of Stretham serving from 1827–1869. Also reading my way through British and Irish stained glass (1811–1918) at the moment too --Senra (Talk) 11:48, 30 October 2010 (UTC)[reply]

Is it concievable that the vicar, Henry Hervey Baber actually designed the window? --Senra (Talk) 11:52, 30 October 2010 (UTC)[reply]

(It's conceivable.. You mean't Sherlock? not Shylock? I haven't lent you any money yet ?! )Sf5xeplus (talk) 11:54, 30 October 2010 (UTC)[reply]

(Concievable was my bad spelling and Shylocke was a freudian slip as I know someone called Shylocke) --Senra (Talk) 12:03, 30 October 2010 (UTC)[reply]

Actually I meant It's conceivable that he designed the window - I didn't even notice the spelling mistake. Sf5xeplus (talk) 12:47, 30 October 2010 (UTC)[reply]

According to our article this Henry Hervey Baber popped his clogs in 1869 - maybe it's a memorial? (or paid for by him as part memorial?)Sf5xeplus (talk) 12:05, 30 October 2010 (UTC)[reply]

Out of curoisity, how did you get such a straight image (no parallax) - special lens, ladder or photoshop ? Sf5xeplus (talk) 12:12, 30 October 2010 (UTC)[reply]

Very careful use of Photoshop CS4's perspective and vertical scale (i.e. corrected the perspective then corrected the resulting foreshortening) though I did not measure it; I relied on the mark one eyeball --Senra (Talk) 12:22, 30 October 2010 (UTC)[reply]

Following your above question and assuming no parallax in this image, I have just measured the two images. The window in this view measures 8.9 x 8.25 whilst the window in this view measures 70 x 68 which is 3.3 mm too short - not bad for mark one eyeball! --Senra (Talk) 12:33, 30 October 2010 (UTC)[reply]

Just some general background on English church stained glass. Surviving medieval stained glass is quite rare, as much of it was destroyed during the English Civil War in the 17th Century. Stained glass depicting religious scenes didn't really re-appear until the second half of the 19th Century, when the Oxford Movement co-incided with the Arts and Crafts Movement. Before that, it would have been considered "popish" except if it showed secular subjects - family crests were common. They became the most popular sort of memorial for parishoners (by late Victorian times, grand memorial tablets were considered a bit vain). The windows would often carry the name and dates of the deceased - "the dedication" - or it might be on a small plaque underneath, usually "To the Glory of God and in Memory of...". I've never seen a church stained glass with the artist's name on it. The east window of my church has the name of a local builders' merchants on it; apparently you could pick one out of a catalogue. I'm certain this would have been a memorial to Henry Hervey Baber commissioned soon after his death. Alansplodge (talk) 13:02, 30 October 2010 (UTC)[reply]

Just a note that although church windows are traditionally not "signed" by the artist, many of them will bear the designer's monogram. You can see one here.--Shantavira|^{feed me} 14:35, 30 October 2010 (UTC)[reply]

I stand corrected. There's rather a good index of makers' marks here[26], mostly quite inconspicuous. This one - Comper, J Ninian - has a strawberry plant as their mark[27]. Thanks Shantavira, I'll look more closely in future. Alansplodge (talk) 16:23, 30 October 2010 (UTC)[reply]

Facinating. Makers marks; memorials; arts and crafts; and all despite my bad spelling!

I have sent an email to Cambridgeshire Archives. In the meantime, I am not certain this window is a memorial to Henry Hervey Baber as he died in 1869 and the date on the glass is 1868. Additionally the restoration was later (1874–1876). I have also carefully examined every inch of the image without finding any marks although the highlights are a little blown making it hard to see a makers mark if it is there. I guess I need to make another visit to the church whilst hoping Cambridgeshire Archives can help too. Thank you to everyone who has taken the time to reply above.

--Senra (Talk) 18:48, 30 October 2010 (UTC)[reply]

Issue resolved by Elen of the Roads (talk · contribs) at Wikipedia:Media copyright questions#Stained glass window .28UK.29 Panoramafreiheit.3F

“

Stained glass windows are considered works of artistic craftsmanship and therefore subject to UK freedom of panorama. Stained glass in a building which is open to the public (which churches have to be in the UK to get exemption from the rates) can be photographed without breach of copyright.

”

--Senra (Talk) 22:30, 30 October 2010 (UTC)[reply]

Is it possible to create an exotic atom with antiprotons instead of electrons?

With the antiprotons in a stable orbital shell around the nucleus. Can this be achieved? ScienceApe (talk) 14:36, 30 October 2010 (UTC)[reply]

"Massive particles in cloud around nucleus" doesn't sound anything like an "atom" at all (would it be possible to condense a bunch of antielectrons into a dense enough core to form a "nucleus" of your thing)? There sure is antimatter, but it's still got the same particle masses in the same "places". DMacks (talk) 14:52, 30 October 2010 (UTC)[reply]

I'm no physicist but it strikes me that if you couldn't do it with regular protons, you couldn't do it with antiprotons. The charge is not what makes them act like protons or electrons in the sense you mean here (which can form nuclei, which form clouds); they have fundamentally different properties and constituent parts separate from their charge. --Mr.98 (talk) 15:13, 30 October 2010 (UTC)[reply]

(ec)Have you read Muonium, and Positronium? It doesn't look like antiprotons are easy to create; so there is little experimental work with even short-lived antiproton species. Nimur (talk) 15:21, 30 October 2010 (UTC)[reply]

I think the proposition was that you'd have a nucleus full of antielectrons surrounded by a cloud of antiprotons — maintaining the charge locations of a standard atom (positive nucleus, negative cloud), but with antiparticles. I don't think that will work — electrons/antielectrons are just not going to work in a nucleus, and protons/antiprotons are not going to behave like an electron cloud. It's not the same thing as nucleus of antiprotons surrounded by a cloud of antielectrons, which is certainly possible (antihydrogen). But I'm no physicist. --Mr.98 (talk) 16:03, 30 October 2010 (UTC)[reply]

Ok what about anti-neutrons instead of neutrons in what would otherwise be a normal atom? Would they annihilate with the normal protons? ScienceApe (talk) 15:19, 30 October 2010 (UTC)[reply]

Yes, the anti-quarks will combine with quarks to form pions which will then decay. But, as far as the original question is concerned, you can actually form a short lived "atom" consisting of a proton and an anti-proton. When a proton and an anti-proton meet they will actually form a bound state at some high lying energy level. Then the system makes transitions to lower lying levels, eventually making the transition to the final state where the proton and anti-proton have annihilated. Count Iblis (talk) 15:56, 30 October 2010 (UTC)[reply]

I see we have articles on antihydrogen, which has been made; antideuterium hasn't been. Antiprotonic helium is an antiprotonic atom for which an article has been started; I suppose you can mix an antiproton into anything. Wnt (talk) 18:53, 30 October 2010 (UTC)[reply]

Isn't what prevents the proton from "annihilating" the electron (to form say, a neutron) is that the electron has much too fast to be absorbed? John Riemann Soong (talk) 23:24, 30 October 2010 (UTC)[reply]

No, Protons don't spontaneously abosorb electrons to form neutrons because neutrons are heavier them the sum of the masses of an electron and a proton so that there is an energy gap that would have to be bridged in order for the reaction to occur. 76.123.74.93 (talk) 03:52, 31 October 2010 (UTC)[reply]

Woodchip bug

Anyone know what species this insect is? It's camouflaged to look like a woodchip=P.Smallman12q (talk) 16:32, 30 October 2010 (UTC)[reply]

Try asking whatsthatbug.com. SmartSE (talk) 23:39, 30 October 2010 (UTC)[reply]

volcanic tropical cyclones

If weather conditions are just right when a volcano erupts and causes an ash cloud to blow over tropical waters is it possible for a tropical cyclone to form. --213.94.238.235 (talk) 18:19, 30 October 2010 (UTC)[reply]

Probably not. Tropical cyclone formation requires evaporation from the sea surface, and the ash would block sunlight from reaching the water. In the Atlantic, there are sometimes surges of dust that blow from the Sahara, and they suppress cyclone formation while the dust is in the air. Looie496 (talk) 19:42, 30 October 2010 (UTC)[reply]

Pure energy

What does pure energy look like? --75.33.217.61 (talk) 18:52, 30 October 2010 (UTC)[reply]

Either "nothing", "it does not exist", or "it depends on its wavelength"--take your pick. DMacks (talk) 19:04, 30 October 2010 (UTC)[reply]

To answer that question, you'd have to define what you mean by "pure" energy. If by "pure energy" you mean a form of energy that has no properties other than energy, then the answer is that we can't see pure energy. The only thing our eyes are capable of seeing is light. And the photons of which light consists not only have energy as one of their properties, but also have nonzero spin, so they wouldn't count as "pure energy" according to the above definition. On the other hand, if you define "pure energy" as massless forms of energy, then light would count as "pure energy", so everything that your eyes are capable of seeing is pure energy, since ultimately, all you can see is light. Red Act (talk) 19:21, 30 October 2010 (UTC)[reply]

By the way, if by "pure energy" you mean a form of energy that has no properties other than energy, then pure energy doesn't even exist. All of the elementary particles that everything in the universe is ultimately made out of have one or more properties other than energy. Red Act (talk) 19:30, 30 October 2010 (UTC)[reply]

And as far as what Pure Energy looks like, the cover art looks rather comic book-y, and the band members themselves consider it to look "dreadful"[28] and "like some 10-year-old's school notebook drawings"[29]. Red Act (talk) 19:43, 30 October 2010 (UTC)[reply]

Choose any picture here. Cuddlyable3 (talk) 22:39, 30 October 2010 (UTC)[reply]

DC Circuits - resistors

O.K., so this is homework, but I'm totally bewildered on a particular point. We've been asked to calculate the current in a branch of a circuit where there is a resistor which has resistance 'approaching zero and infinite ohms'. I'm fine working out the currents / voltages if there are numbers involved - loop rule, junction rule etc, but the infinite bit??? Is it anything to do with moving a charge from infinity, i.e. potential difference? ThanksSophiepuss (talk) 19:35, 30 October 2010 (UTC)[reply]

The exact text of the question would help. Is it two cases "(1)resistance approaching zero; (2) resistance approaching infinity," or is it a single impossible circuit element whose resistance approaches both zero and infinity at the same time? It sounds like if it is two cases, a single pole single throw switch would be the circuit element to consider, since it could be close to zero or close to infinite resistance. Edison (talk) 20:02, 30 October 2010 (UTC)[reply]

(EC) If a resistor has infinite ohms, it's basically the same as if the resistor was completely removed from the circuit. There is zero current flowing through a resistor with infinite ohms. Red Act (talk) 20:07, 30 October 2010 (UTC)[reply]

A zero resistance element will have zero voltage dropped across it, and other resistances as well as the voltages in the circuit will determine the current through it. Edison (talk) 00:53, 31 October 2010 (UTC)[reply]

A teaching/learning note for the OP. Part of the reason for asking this type of question is to take you beyond the "I'm fine working out the currents / voltages if there are numbers involved..." stage. Your formulae may not work with zero/infinity, but they will work with numbers approaching those figures. So do your calculations using 0.1, 0.01, 0.001... and see what happens; this will point you towards what happens as you approach zero, and from that you should be able to extrapolate to what will most likely happen at zero. Then do the same using very large numbers for the case of approaching infinity. (And a slight warning - with some physical situations zero and/or infinity may be special cases with quite unexpected results, but if that's the case questions usually won't be framed in this way unless you've been taught the special cases). --jjron (talk) 04:06, 31 October 2010 (UTC)[reply]

What is the average age of onset of Alzheimer's disease?

Abdbdba (talk) 22:10, 30 October 2010 (UTC)[reply]
Wikipedia has an article on Alzheimer's disease and its section Epidemiology is what we can offer. Note that "onset" of Alzheimer's disease is hard to quantify. The data is for diagnosed cases. Cuddlyable3 (talk) 22:33, 30 October 2010 (UTC)[reply]

I couldn't see an average age of onset in that section. DuncanHill (talk) 22:35, 30 October 2010 (UTC)[reply]

Wikipedia also has an article about Early-onset Alzheimer's disease which notes that the majority of sufferers are in their 50's, or early 60's.Cuddlyable3 (talk) 22:46, 30 October 2010 (UTC)[reply]

SECIS element

The SECIS element causes UGA stop codons to encode selenocysteine instead of stopping translation. But if it occurs in the 3' untranslated region of the mRNA in eukaryots, how does it effect this change in translation? If it binds to the ribosome in some way, couldn't the SECIS element bind to a ribosome while it is translating a totally different mRNA? Icek (talk) 22:40, 30 October 2010 (UTC)[reply]

does citric acid actively mask the taste of ethanol?

It's well-known that citrusy fruit (lime, oranges, etc.) will mask the taste of alcohol, but I see none of our biochemistry articles cover this phenomenon. At what level does the masking occur?

Does it occur at the nervous system level (i.e. citrus reception inhibits ethanol bitterness signals?) or the receptor-chemistry level (citric acid binds competitively to ethanol receptors, or ethanol's affinity for ethanol receptors is downgraded by citric acid?). Is it ionic citrate or the neutral citric acid that does the masking? John Riemann Soong (talk) 22:53, 30 October 2010 (UTC)[reply]

From my perspective, almost anything (except water) added to alcohol masks (changes) its taste. I've never heard (to contrast with your contention that it is "well known") that "citrusy fruit" did a more pronounced job than, say, cola. As for how any soda or fruit juice effects such a change is a question I will leave to the scientists here. Bielle (talk) 23:32, 30 October 2010 (UTC)[reply]

Cola doesn't mask it really well -- it simply dilutes or masks it with the taste of sugar (which isn't that good of a masker). I take it there's a reason that "hard lemonade" and adding lime to drinks are popular practices. John Riemann Soong (talk) 00:20, 31 October 2010 (UTC)[reply]

Taste and smell receptors are limited in variety. It does not seem unlikely that those which are sensitive to one kind of solvent (alcohol) might be limited by another (acid). Ginger Conspiracy (talk) 03:43, 31 October 2010 (UTC)[reply]

I do not know their full diversity, but as I recall, taste receptors have to number several dozen in type, and smell receptors several hundred. (The "five taste" model is vastly oversimplified of course.) John Riemann Soong (talk) 04:53, 31 October 2010 (UTC)[reply]

Difficulty in differentiating actors and actresses from the fictional characters they portray?

Is there a specific term for this? Not necessarily in the creepy, obsessional way (though it could be the same thing) but more along the lines of when fans of long-running dramas and soap operas approach the actors and actresses when they see them in the street and talk to them as though they were the same person as the character they play in the show, refer to them by the character's name, etc. Sometimes when you read interviews with the actors, they tell stories about 'this guy/woman who came up to me this time and...'. Things like people who play doctors being asked for medical advice, or being dragged over to help because someone is having a heart attack/seizure/baby - or actors and actresses being insulted or threatened by members of the public for the actions of their characters (say if the character was a rapist, or murderer, or wife-beater), or being praised for being strong enough to overcome rape/wife-beating/cancer/grievous injury - or actors in sci-fi shows being asked questions as though the fictional universe of the show was real, etc... --Kurt Shaped Box (talk) 23:19, 30 October 2010 (UTC)[reply]

Are you describing an extreme case of typecasting (acting)? -- 119.31.121.89 (talk) 00:29, 31 October 2010 (UTC)[reply]

That is the word, but it's actually less extreme. Just having a few audience members confuse an actor or actress with a character is far better than when casting decision makers start doing it. That could be why casting professionals are often been kept separate by studios from producers and directors. By the way, this question would probably get a better answer on WP:RDH the humanities reference desk, because the theatrical branch of forensics (public speaking) is an art, not a science. Ginger Conspiracy (talk) 03:52, 31 October 2010 (UTC)[reply]

I'm no psychology expert, but it seems to be almost a type of Transference. --jjron (talk) 03:55, 31 October 2010 (UTC)[reply]

Theory?

I can remember seeing a program on teleportation. One (of the many) drawbacks of teleportation was that some theory said it was impossible to know the exact position of every sub-atomic particle all the time. What's the theory called? Albacore (talk) 23:57, 30 October 2010 (UTC)[reply]

The Heisenberg uncertainty principle indicates that we may know the exact position of a subatomic particle, or the speed at which it is moving, not both. (This also applies on the macro level; you can know the location of e.g. a car, or its speed, but cannot discern both at the same time, as speed is dependent on knowing the car's position in at least two places and calculating how fast it got from one to the next.) → ROUX ₪ 00:00, 31 October 2010 (UTC)[reply]

I often find myself driving around in my car and knowing both where I am and how fast I am going both at the same time (and I've noticed that even more since the advent of GPS navigation technology). WikiDao ☯ (talk) 00:08, 31 October 2010 (UTC)[reply]

In that case, it is actually two different observers. Your odometer is observing your speed (and does not know your location), while your GPS knows your location (but not your speed). → ROUX ₪ 00:11, 31 October 2010 (UTC)[reply]

(I'm not often aware of my momentum and my location at the same time, though, it's true). WikiDao ☯ (talk) 00:13, 31 October 2010 (UTC)[reply]

(In practice, your GPS can figure out your speed pretty easily. I think it is probably known on here — but worth stating for such a basic question — that HUP only applies to very small scales, e.g. things smaller than atoms. --Mr.98 (talk) 00:14, 31 October 2010 (UTC))[reply]

There is some uncertainty for an object the size of my car, though, right? It's just that it is indistinguishable from zero because of the value of ħ in

\Delta x\,\Delta p\geq {\frac {\hbar }{2}}

if I recall the explanation for that correctly. Is that right, or what is a better way to understand that? WikiDao ☯ (talk) 01:07, 31 October 2010 (UTC)[reply]

Exactly right:

\Delta x\,\Delta p=\Delta x\,\Delta v\,m\geq {\frac {\hbar }{2}}\approx 10^{-34}\mathrm {J\cdot s} =10^{-17}\mathrm {m} \cdot 10^{-17}\mathrm {m\cdot s^{-1}} \cdot 1\mathrm {kg}

and you are not able to measure the velocity of even a 1 kg particle with an accuracy of 10^-17 m/s nor its position with an accuracy of 10^-17 m. -- 124.157.254.112 (talk) 04:54, 31 October 2010 (UTC)[reply]

Artificial reefs

After reading this article, I still remain with the question as to how long such reefs take to become populated with any life considerable enough to make it a bona fine reef -- I guess that definition as a factor of time can be debated, but assuming a range could be established, the article didn't seem to give one -- so when sinking ships or doing something like this, how long after construction does it take for a reef to appear? DRosenbach ^{(Talk | Contribs)} 00:05, 31 October 2010 (UTC)[reply]

Technically a reef doesn't have to contain any life, so by definition as soon as the artificial reef is put in place it is a bona fide reef. But since you ask about the life, colonisation would begin almost immediately, but the time until you would define that to be a 'bona fide reef' would not be so clear cut as there's probably no hard and fast rules, at least not that I know about, for how much life is required. It would also be highly variable depending on where the reef was being established. For example, put in an artificial reef around the Great Barrier Reef and it will probably be thriving with sea-life within a week, put one up in under the Arctic sea ice and you're probably looking at considerably longer. Coral_reefs#Formation may also be helpful. --jjron (talk) 03:36, 31 October 2010 (UTC)[reply]

If you want to pursue this question further, you may wish to search some fishing message boards which will presumable contain some discussion of fishing conditions at newly created artificial reefs. -- 124.157.254.112 (talk) 04:58, 31 October 2010 (UTC)[reply]

Earthworms

How much of an earthworm is protein? I'd like my oscars and dinosaur bichir to grow at a more rapid rate than they are apparently doing now, and would a diet richer in live earthworms provide me with success? I figure that crickets have too much exoskeleton and wings to give me a good bang for my buck, seeing how earthworms are free from my backyard. Any comments? DRosenbach ^{(Talk | Contribs)} 00:14, 31 October 2010 (UTC)[reply]

Well I really think you could type http://www.google.co.uk/search?sourceid=chrome&ie=UTF-8&q=earthworm+protein+content .. and take my word for it every article on the first page of results is a gem!

Anyway, nagging aside, we are here to serve: http://www.jstor.org/pss/2396435 - by dry weight well over 60% protein, <10% fat, variable carbohydrates

I know that earthworms are considered excellent food for other carnivorves eg salamanders, and are used as bait by fisherman - so I guess you are on to a money saving winner.

Excluding the usual warnings about fish overfeeding, and overloading filter systems with high nitrogen content waste.. which I'm sure you've already read or heard.77.86.42.103 (talk) 00:45, 31 October 2010 (UTC)[reply]

oh hang on . parasites and diseases - I don't recall ever having heard that earthworms are a parasite source, but diseases are a possibility .. I suppose. 77.86.42.103 (talk) 00:55, 31 October 2010 (UTC)[reply]

Optical computing

Why haven't optical computers become widespread? The technology exists and it has many advantages over electronic computing. --75.33.217.61 (talk) 00:26, 31 October 2010 (UTC)[reply]

Have you read Optical computing#Misconceptions, challenges and prospects? The simple answer is that the technology is still in its infancy, and many problems have to be solved first. Clarityfiend (talk) 01:26, 31 October 2010 (UTC)[reply]

why do plants use so much more potassium than animals?

Almost all the biochem taught to me so far has been systemically biased towards animals ... I think my professor is biased in favour of his own race. Anyway...I can't seem to find an explanation. Do they use the potassium to bring water into the cells? Do animals not do this because their cells lack cell walls? I'm really curious why potassium is a micronutrient in animals but a macronutrient in plants. Furthermore, plants usually lack sodium. Do terrestrial rocks have more potassium than sodium? John Riemann Soong (talk) 00:40, 31 October 2010 (UTC)[reply]

First sentence in Potassium in biology: "Potassium is an essential mineral macronutrient and is the main intracellular ion for all types of cells." Furthermore it goes on to say: "Potassium is the major cation (positive ion) inside animal cells, while sodium is the major cation outside animal cells." This would seem to suggest an error in your premise that it's more important in plants than animals. Is this what you're looking for? (And BTW, animals are not a 'race'). --jjron (talk) 03:47, 31 October 2010 (UTC)[reply]

Potassium is a micronutrient, not a macronutrient for animals. Extracellular sodium concentration as I recall >>> cytosolic sodium concentration. Is it potassium a micronutrient because animal cells are usually close to isotonic? John Riemann Soong (talk) 04:51, 31 October 2010 (UTC)[reply]

Contradiction in the solution to a Physics question?

Read Question 10 (c) here: http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/003139/RND01/PH866_paper99.pdf
The solution can be found here: http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/003068/RND01/PH866_report99.pdf
The solution for part i) has the red light going below the blue light, but the solution to part ii) shows it going above the blue light. Can someone explain this apparent contradiction?-220.253.253.75 (talk) 00:48, 31 October 2010 (UTC)[reply]

Simple. Your brain automatically assumes the light came in a straight line. If you project the red and blue rays straight back, it looks like the red one came from a higher point. Clarityfiend (talk) 01:24, 31 October 2010 (UTC)[reply]

Oh OK. However, that still poses a contradiction between that question (Question 10 (c) (i), 1999 paper), and Question 4 (f) (i) from the 1997 paper found here:http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/003429/RND01/PH866_paper97.pdf whose solution can be found here: http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/003378/RND01/PH866_report97.pdf Could someone resolve this contradiction as well?-220.253.253.75 (talk) 03:10, 31 October 2010 (UTC)[reply]

The solutions are AFTER all of the examiner's comments by the way (i.e. scroll down).-220.253.253.75 (talk) 03:18, 31 October 2010 (UTC)[reply]

Seriously, is there anything this person can't do

An IP user recently asked a question which received a very interesting reply, but it was all deleted due to WP:BLP concerns. Rephrased to avoid mention of a specific living individual, the question asked if there was anything that one randomly chosen individual couldn't do which some other human could. In other words, if a person is chosen at random and designated EveryPerson, or E.P. for short, can you state some action that E.P. can't do but which some other human can. Red Act's answer was:

Yes. E.P. is unable to prove the statement "E.P. is unable to prove that this statement is true." If E.P. was able to prove that that statement was true, then the statement would be false, which would be a logical contradiction, so E.P., uniquely, is unable to prove that the statement is true. However, I have just proved that the statement is true, as can anybody else who’s halfway decent at logic or math, so it is provable that there is something that E.P. can't do that other people can.

The above can be made very formal and rigorous, by the way. The proof involved is essentially the same kind of proof used to prove Gödel's first incompleteness theorem, or to prove the undecidability of the halting problem.

I hope that the OP finds this useful. -- 124.157.254.112 (talk) 04:22, 31 October 2010 (UTC)[reply]

October 27

Naturally-occurring promethium

Formation of gold deposits

some one will helpme that in which place i should ask my questions

Spelter

Magnetic flux and electricity

Magnetic flux and magnets

Tillage

chocolate bar

The Vitamin B12

mosquito eggs and larva

does puree count as a liquid?

Magnets and electricity...again!

Combining tornadoes

Colloidal iron?

Are the majority of birds noisy fliers?

Go (weiqi) - computers vs human brains

Cryosurgery to repair torn tissue?

Quantum Entanglement

October 28

Why do flour and sugar store so well?

force

Sexuality question

Related questions

My theory on why we often can’t run in dreams – is it valid?

solar enery storage

Is ADD real?

O2 effect on metabolism

Pyrotechnic colorant

Complement system and antibody-antigen complexes

Tachyons

Another chemistry question

Geodesic dome garden shed

Figuring names out for cells

Possible circuit that shows this particular voltage/current pattern

BPA degrade

October 29

Are "spectrum disorders" really just a way of saying "we don't know" ?

120W power supply 30W load

Phase behavior of pure substances below triple point pressure

electricity doesn't weight anything

Fuel Consumption vs CO2 emmissions

Firing a ceramic

Multiple tasks with both individual hands difficulty

Energy Anomaly??

Is the thymus an endocrine gland?

Clamped buttress

on utilizing sound energy

Big Cats

Aviation Thermobaric Bomb of Increased Power

CFL bulbs afterglow "flashing"

my project

Toothpaste

Hardness of human teeth

What looks like peas?

October 30

Carbonated drinks and digestive health?

uakari fruits

Time dilation? Time speeding?

Time dilation and length contraction

Stained glass

Is it possible to create an exotic atom with antiprotons instead of electrons?

Woodchip bug

volcanic tropical cyclones

Pure energy

DC Circuits - resistors

What is the average age of onset of Alzheimer's disease?

SECIS element

does citric acid actively mask the taste of ethanol?

Difficulty in differentiating actors and actresses from the fictional characters they portray?

Theory?

Artificial reefs

Earthworms

Optical computing

why do plants use so much more potassium than animals?

Contradiction in the solution to a Physics question?

Seriously, is there anything this person can't do

Fuel Consumption vs CO₂ emmissions