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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]