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January 15

Why don't mountain climbers' eyeballs freeze?

I've seen documentaries on TV about how cold some mountain climbs are. Exposed flesh will get frostbite in a matter of seconds. Why then don't eyeballs freeze? I would expect the very least that the moisture on the surface of the eye would either evaporate quickly or freeze. --71.158.216.23 (talk) 00:39, 15 January 2009 (UTC)

Exposed extremities freeze pretty quickly because they have a large surface area and are a long way from the warmth of the body's core. That doesn't really apply to eyeballs. People get frostbitten ears and noses, but the rest of the head is probably pretty difficult to freeze because it is basically one big sphere, which has the lowest surface area to volume ratio possible. For the eyeball to freeze, the rest of the head would have to get pretty cold, and blindness would be the least of the climber's worries. --Tango (talk) 01:10, 15 January 2009 (UTC)

In addition, vasoconstriction often reduces perfusion of the extremities, but would not cut off circulation to the head (and the brain therein). --Scray (talk) 01:59, 15 January 2009 (UTC)

Frostbite of exposed cheeks is fairly common, so these explanations don't seem to work. Algebraist 02:06, 15 January 2009 (UTC)

Just speculating here, but it could be due to their being sunken within the head. I know when it's cold and a wind is biting at my face I squint my eyes, and it seems to keep them warmer.-RunningOnBrains 02:14, 15 January 2009 (UTC)

Cheeks, or cheek bones? The cheek bones stick out quite a bit. --Tango (talk) 02:30, 15 January 2009 (UTC)

They wear mountain climbing goggles: [1]. StuRat (talk) 04:15, 15 January 2009 (UTC)

That's more to protect against wind, snow and bright light. I've seen photos of people on top of Everest that have taken their goggles off for the photo, their eyes didn't seem to be in any great discomfort. --Tango (talk) 05:43, 15 January 2009 (UTC)

The wind, snow, and dry air (causing evaporative cooling) will chill the eyes quickly, perhaps quickly enough for frostbite. On the other hand, on a clear, wind-free day, the goggles can probably be removed long enough to take a few pics safely. StuRat (talk) 06:20, 15 January 2009 (UTC)

(after ec) : People can, and do, get cornea frostbite (freezing keratitis). We have it mentioned in Doug Swingley article. Goggles, indeed, protect your corneas from both frostbite and UV exposure, see snow blindness --Dr Dima (talk) 05:47, 15 January 2009 (UTC)

Is it possible Swingley got this frostbite because he was travelling very quickly in his sled and his goggles slipped? With massive wind chill, I wouldn't be surprised if any part of the body could get frostbitten within seconds. --Tango (talk) 05:56, 15 January 2009 (UTC)

I would think it's because there's a lot of blood vessels in your eyes (as shown when they go bloodshot) and they probably have a relatively large amount of blood flowing through them. This would definitely keep them above freezing, but I'm not at all sure this is correct. Just a theory. -Pete5x5 (talk) 06:15, 15 January 2009 (UTC)

That's true of the white parts of your eyes - but the corneas have special issues because they have to remain transparent. Since you can't have all of that red stuff pumping across your field of view, there are no blood vessels in the cornea. So if it really was "cornea frostbite" rather than the entire eyeball - then blood flow is not relevent. SteveBaker (talk) 13:41, 15 January 2009 (UTC)

As long as the blood goes reasonably near by (which it does), the thermal conductivity of the various tissues would probably be enough to keep the cornea warm under most conditions. --Tango (talk) 17:45, 15 January 2009 (UTC)

work and momentum

Okay,so let's say I want to open a door 90 degrees as quickly as possible. Naturally, my first inclination is apply a force as far away from the axis of rotation as possible, as this will increase the distance I apply the force for the 90 degree angular displacement, thereby increasing the angular acceleration. Clearly this is the best solution. If I were to apply the force closer to the axis of rotation, I would be applying the force for a longer period of time, right(hence is beneficial not to push close to the axis of rotation). But since Im appplying the force for longer, would the momentum of the door be greater if I were to push closer to the axis of rotation? I know this can't be, because that would mean it would be better to push closer to the axis of rotation, but I can't see a reason why it wouldn't be true. And also, if you bring up the difference bewteen angular momentum and linear momentum, well angular momentum is really just a bunch of different linear momenta with a centripetal force to change it's direction... —Preceding unsigned comment added by 65.92.7.221 (talk) 06:34, 15 January 2009 (UTC)

I assume you mean that you have a constant maximum force that you can apply no matter where you push on the door or how fast that point is already moving while you are pushing on it. (In many real machines, the force available becomes less as the speed increses, because they are limited by power, which equals work over time, which is force times distance over time, which is force times speed.)

In that case, for any particular place where you push, the angular acceleration will be constant. The greater the angular acceleration, the greater the final angular velocity and therefore the greater the final angular momentum. So pushing with the same constant force at the point farthest from the hinge will give the greatest angular momentum. (Which makes sense because that situation involes the greatest power.)

--Anonymous, 12:50 UTC, January 15, 2009.

The problem with that answer is that it neglects the biomechanical limitations of the human body. Sure it may require more force/work/energy to open the door by pushing on it's center point than it does at the outer edge - but there are other limitations at work here. For example - no matter how little the load is, you can't physically move your hand faster than (let's say) the speed of a baseball pitcher's pitch (100mph?) - even with close to zero load. So to get maximum angular velocity on the door - you might have to push further in than the outside edge of the door simply in order to have enough speed - even though it requires more effort to do so. I don't know whether that's truly the case that it's better - but this consideration certainly has to be examined before coming to a conclusion. SteveBaker (talk) 13:36, 15 January 2009 (UTC)

• If the question is meant as I interpreted it, that's a problem with the question, not the answer... as I said, in effect. --Anonymous, 20:41 UTC, January 15, 2009.

It would require more force to open the door from the center point than the outer edge, but the work and energy will remain constant no matter where you push it from. All assuming speed, door size, etc. remain constant, of course. — DanielLC 17:37, 15 January 2009 (UTC)

With some common basic assumptions (i.e. friction is independent of velocity) it is clear that it recquires the same amount of energy to open the door; wherever you push it for a given final velocity. This is because work done is ʃFdx not ʃFdt as was implied by the question. This means that however long you apply a force for is irrelevant, and only how far you push it determines your energy cossumption. —Preceding unsigned comment added by 129.67.39.140 (talk) 21:36, 15 January 2009 (UTC)

Fate of feral pigeons, feral gulls and feral starlings if humans became extinct?

Would they all die off, or would some of them manage to learn to survive in the 'real wild'? Supposing that the event that precipitated human extinction left the ecosystem mostly as it is now, I mean. --90.240.126.109 (talk) 08:47, 15 January 2009 (UTC)

Humans as a race has still quite a good survivability, so an extinction should have been caused by very drastic events. Or, I suppose, you were asking about the hypothetical situation where all humans suddenly and magically disappear? --131.188.3.20 (talk) 09:20, 15 January 2009 (UTC)

In the very unlikely event of humans suddenly disappearing from the earth the animals (in its widest sense) that have become partially or wholly dependent on us would have two alternatives, in survival terms. They would have to adapt to the new environment and find new sources of food and/or breeding environments or they become extinct. A certain Charles Darwin proposed a similar idea very much earlier, he thought that those that were more adaptable would stand a better chance of surviving. I won't bore you further with the details but you might find the Theory of Evolution interesting. Richard Avery (talk) 10:47, 15 January 2009 (UTC)

I think the questioner knows that. That's why he asked. All you've done is restate his question. The questioner wants to know which of the animals he mentioned are irrevocably dependent on humans and which are not. APL (talk) 17:14, 15 January 2009 (UTC)

Hmm, if the OP thinks seriously that any of the birds he names are dependant on humans then he may need a wider view on the subject. Richard Avery (talk) 23:09, 15 January 2009 (UTC)

The more domestic of the domesticated animals, like domesticated turkeys, would perish. The more feral, like wild turkeys, would survive. Some dogs and cats are much wilder, smarter, and better able to survive without human assistance than others. I have even seen a few feral chickens which would fly from the chicken yard to a tall tree in the woods at night. If all humans disappeared and all domestic animals were set free, the 1% or .001% with the best survival skills would be the genesis of the next generation, after the great starvation and the great devastation by predators. I expect that starlings and gulls would get along fine without humans, and that some small number of pigeons would have the appropriate survival skills/instincts and be near enough a niche environment in which they could find shelter (like a cliff edge) and naturally occuring/wild food. Some pigeons could adapt to the habitat of their wild ancestors, rather than waddling around on the sidewalk eating stale bread someone throws to them. The extinction of humans would not necessarily remove all the cornices pigeons presently use for nesting away from rats/cats/snakes. Edison (talk) 20:01, 15 January 2009 (UTC)

So what exactly is a feral gull and a feral starling. My understanding is that both these species are wild birds which have very little reliance on humans for their existence. They both may casually feed in urban areas but that does not define them as feral. The possibly feral pigeons that exist in cities would certainly continue to forage in urban gardens or leave for the more rural parts. I think the OP needs to brush up on his biology a bit. —Preceding unsigned comment added by 86.4.182.202 (talk) 22:56, 15 January 2009 (UTC)

I saw a doco recently called life after people which explored just that question. It basically said most domestic animals would be the 1st to die off, cats would fare better then dogs, (unless they were locked inside) but many dogs would also survive, the toy and exotic breeds not doing as well as the more "traditional" dog. Rodent populations would explode over a short term, things like supermarket cereal isles and houses would provide a heaven for them, eventually tho those resources would run out and the populations would dramatically decrease again. Similarly with birds, junkyards and stuff which have sustained massive populations of birds would eventually "dry up" and with no one to feed the pigeons in the town square, those populations would also see a decline, sometimes dramatic, but the majority of those populations are nested in a niche which reaches further then total reliance on human waste, so they would survive.. Vespine (talk) 23:52, 15 January 2009 (UTC)

Was that the one that mentioned that the descendants of domestic cats might eventually evolve the ability to glide from skyscraper to skyscraper in the urban wastes, a-la flying squirrels? That was an interesting premise. IIRC, it also said that gulls would (eventually) thrive in a human-free world - due to the seas recovering to their pre-human state after a few hundred years and flourishing with edibles again. --Kurt Shaped Box (talk) 00:37, 16 January 2009 (UTC)

For cats to evolve wings, it would need many thousands of years at least. Skyscrapers won't last that long without maintenance. --131.188.3.20 (talk) 20:26, 24 January 2009 (UTC)

For the record, Life After People. You could try thinking about life after Maccas. Terry Irwin in the short term suggests they'll adapt much as humans would if fast food chains started closing down. She left the conclusion open. Not betting either way, Julia Rossi (talk) 03:04, 16 January 2009 (UTC)

The Macca's analogy is a good one. Remember also that the feral population would have less competition from us as well- while the pelicans might not have us to feed them, they wouldn't have to compete with fishermen so much either. The grass seed eating pigeons might not have us to feed them, but they'd have less competition from lawnmowers and combine harvesters. WotherspoonSmith (talk) 06:06, 16 January 2009 (UTC)

Well perhaps here in Sydney, a vast number of seagulls might get their first view of the sea, as opposed to the malls outside of Maccas outlets 20 miles inland, where they live on discarded French Fries. I've read accounts that suggest that deserted cities would, even many hundreds of years later, contain rich though remnant populations of flora and fauna previously cultivated in gardens, homes and zoos. The film I Am legend has evocative sequences of lions and deer running through a post-apocalyptic New York, and the original Planet of the Apes featured places where such remnants could be housed in almost perfect museum conditions: in the vast underground rail tunnels beneath the city. Once again, it was NYC. (Doesn't anything happen anywhere else? I've just seen Klaatu plunk himself down in Central Park - from The Day the Earth Stood Still (2008)). Myles325a (talk) 05:57, 17 January 2009 (UTC)

Neutron star with event horizon

My question is, is it possible to exist a neutron star with radius less than its Schwarzschild radius i.e. is there a neutron star covered by an event horizon. It is clear that if the Pauli exclusion cannot stop the collapse, then the star becomes a black hole, I mean at the and its state satisfies the Schwarzschild vacuum-solution. But is it possible to exist a singularity at r_s without the singularity at r=0. Thanks! Mozó (talk) 09:48, 15 January 2009 (UTC)

Standard physics has it that if something is compressed beyond its Schwarzschild radius, it will collapse or has collapsed to a black hole. Two arguments can be raised for this. First, that time and space switches place inside the black hole, so that anything right under the horizon must fall in to the singularity as surely as it must move forward in time. Secondly, what's "really" beyond the horizon is regarded by some as an immaterial question, it's a black hole for all intents and purposes. EverGreg (talk) 11:44, 15 January 2009 (UTC)

Thanks a lot EverGreg! So can we say that, we do not have (or probably don't have) stabile solution concerning a body compressed beyond its Schwarzschild radius? Regards Mozó (talk) 16:44, 15 January 2009 (UTC)

Correct. Anything inside the event horizon of a black hole must inevitably reach the point r=0 within finite (proper) time (this is due to what EverGreg was saying about time and space being reversed, although that's a rather confusing way to put it - technically speaking, the radial direction of space becomes "timelike" and time becomes "spacelike", but all that really means is that some minus and plus signs have been swapped around in the equations). Once an object collapses beneath its Schwarzchild radius it is a black hole and it indistinguishable (from the outside) from any other black hole with the same mass, charge and angular momentum. --Tango (talk) 17:55, 15 January 2009 (UTC)

Hold on - is that right? We can distinguish a rotating from a non-rotating black hole - right? As our neutron star shrinks - won't it start spinning faster and faster? So even if it started off rotating infinitesimally slowly - when it reaches a singularity, even that most minute rotation becomes infinitely fast...right? Wouldn't that allow us to tell what the fate of the collapsing star was? (Probably not - I just like to understand why not!) SteveBaker (talk) 01:37, 16 January 2009 (UTC)

The key thing isn't rate of rotation, but angular momentum. While rate of rotation increases as the star collapses (to infinity, which is your first clue that something isn't right), the angular momentum remains constant. Remember, a black hole (after sufficient time has passed) is just a singularity, there is nothing actually there to rotate. We call it angular momentum, but really it's just a constant of integration that appears when you solve the differential equations and happens to behave like angular momentum (the same way the spin of an electron behaves like angular momentum despite it being either a point particle or a probability wavefunction, depending on how you look at it, neither of which have a meaningful definition of rotation). I don't honestly know how astronomers measure the angular momentum of a black hole, but it's not by picking a point on the surface and seeing how long it takes to come back round. --Tango (talk) 02:44, 16 January 2009 (UTC)

As an apropos, the Kerr metric predicts that a flattening of the black hole as well as a frame dragging effect will be indications of a rotating black hole. But i guess astronomers will only see indirect hints, like a high angular momentum of gas going into the black hole, which must then absorb this momentum and "rotate". EverGreg (talk) 10:28, 16 January 2009 (UTC)

Indeed, but the frame dragging is going to depend on angular momentum, not rate of rotation. --Tango (talk) 23:32, 16 January 2009 (UTC)

Thanks Tango, you explain the argument in a mathematician-wise way which is close to me :) Mozó (talk) 08:36, 16 January 2009 (UTC)

Actually, in a black hole, there are only three laws of physics that aren't nessecarily broken: the law of gravitation, electromagnetism, and rotation. So, time probably will not follow its usual mechanism in a black hole, as time would be bent along with space. There's even the concept, as partially suggested by João Magueijo, that nothing can ever enter a black hole because time stops. As for neutron stars, a marshmellow dropped onto its surface would release energy equivalent to roughly 50 Hiroshima bombs, so they too have very strong gravitation. ~AH1^(TCU) 23:49, 16 January 2009 (UTC)

Is there a center of the universe?

I was reading this thread here [2] where it was stated that there is no center of the universe. Couldn't the location of the big bang be considered the center of the universe? Everything is moving out in a 360 degree sphere from this point, correct? A Quest For Knowledge (talk) 13:30, 15 January 2009 (UTC)

I'll take a shot at this one: in brief, there is no point where the big bang took place, because everything was "there". If the material that makes up Alpha Centauri, and the material that makes up my pocketwatch, were both in the same place at one time, we can't really say that one or the other is moving away from the center of the universe. Be careful not to think of the big bang as a concentration of material in empty space -- it IS that space; there was, at the time, no universe outside of that big bang. jeffjon (talk) 13:47, 15 January 2009 (UTC)

We've answered this one before - and it comes about because of our inability as humans to properly visualise the expansion of space. It's tempting to think of the big bang as if there were this vast, utterly empty universe - with a tiny dot someplace - which then explodes, scattering stuff out into the inky void. But that's WRONG. The big bang produced the space itself. So at the instant of the big bang, space was infinitely scrunched up - and space itself expanded, along with the matter within it...as it continues to do today. So even though it was an infinitesimal 'dot' at the outset, that dot completely filled the infinitesimal "space" that comprised all of existence. So we have to go back to the balloon analogy. The surface of a deflated balloon is space. Dots drawn onto that balloon are "matter" (galaxies maybe). You have to imagine the balloon deflated down to a dot (not a wobbly lump of rubber like a real deflated balloon!).

Balloon analogy	Real universe
The deflated balloon is very tiny.	The universe at the time of the big bang is infinitesimal.
The dots drawn on the balloon are so close together, they almost touch.	The matter in the universe is scrunched together into a 'dot'.
As the balloon is blown up...	As the big bang explodes...
the surface area of the balloon grows rapidly.	the volume of space itself expands rapidly.
Yet there is no 'edge' to the surface of the balloon.	Yet there is no edge to the universe.
As the balloon inflates...	As space expands...
so the dots on the balloon move further apart.	so the stars and galaxies move furhter apart.
No point on the surface of the balloon could be called "the center".	No point within all of space could be called "the center".

SteveBaker (talk) 14:51, 15 January 2009 (UTC)

I think it's important to clarify - you are describing a "closed" (ie. finite) universe. If the universe is open (and infinite) now, then it was infinite to start with (although the observable universe was infinitesimal). Don't try and visualise the expansion of already infinite space, you'll just give yourself a headache! (Now, where did I put that aspirin...) --Tango (talk) 18:02, 15 January 2009 (UTC)

To make sure I understand the analogy, the universe is the surface of the balloon and not the air inside the balloon? A Quest For Knowledge (talk) 19:06, 15 January 2009 (UTC)

Yes, except there is no balloon. —Preceding unsigned comment added by 82.124.85.178 (talk) 19:13, 15 January 2009 (UTC)

Yes, it's a 2D analogy of our 3D universe, the rubber of the balloon represents "the fabric of spacetime" (just be careful with the inverse tachyon emitter!). --Tango (talk) 19:53, 15 January 2009 (UTC)

To do the best justice to the balloon analogy - try to forget that the balloon is round - look at one small, nearly flat patch of the balloon. Then, the balloon can be considered to be a two-dimensional analog of the universe...except that the rubber of the balloon is 'space-time'...but it's still stretchy! Now that we're looking at a flattish local patch of the balloon - we can cautiously extend our analogy to imagine that it has other 'shapes' - maybe it's infinite and flat...maybe it does curve back on itself - maybe it's "saddle-shaped"...but it still expanded from an infinitesimal 'dot'. But as Tango says - just don't let your poor overtaxed brain try to envisage an infinite universe that's scrunched into zero volume...yet is still infinite. Because...OW! (Tango - could you just pass me over some of those Asprin?) SteveBaker (talk) 01:34, 16 January 2009 (UTC)

I never did find them... Perhaps if I make your head hurt enough it will just go numb: The infinite universe isn't scrunched into zero volume, it's still perfectly infinite, it just also has infinite density. Now try and imagine how much matter/energy that is! --Tango (talk) 02:52, 16 January 2009 (UTC)

This is a very complex concept. If there was a "starting point" for the Universe, would that "point" be in the same location in spacetime now as it was when it was created? No. Even at the "center" of the universe, if it still exists, space is expanding at the same rate as the rest of the universe, and there would be no redshift anomaly if an observer was looking at the "origin". The Universe is considered "flat", meaning it is of infinite size, and the "surface" of the universe's exterior, which doesn't exist, would be "flat", and not "round". There's the concept that a spaceship launched fron Earth would arrive back at Earth googols of years later. This probably doesn't work in an infinite universe, and besides the "location" of Earth in the present universe would have moved "away" by then. Also with the balloon analogy, if you pop the ballon, the "universe" explodes. This probably doesn't work in real life, but there is the Big Rip scenario hypothesis. ~AH1^(TCU) 23:38, 16 January 2009 (UTC)

Power adapter

I am searching a power adapter for a laptop and found one with an output of 15/16/18/19/20V (3,5 A) or 24V (3A). However, the original adapter had an output of 19V (3.42A). Does this adapter fit the laptop? Should I use 18V instead of 19V to compensate for the extra 0.08A? Can this adapter burn the laptop? --Mr.K. (talk) 15:06, 15 January 2009 (UTC)

Short answer: yes, if the polarity is right and the plug fits; no; and no. Longer answer: When you look at a power supply, think of the amps figure as a maximum capacity; in other words, the adapter you found can provide any amount of current up to 3.5 A before the rated voltage starts to fall off (or the magic smoke is released). Your laptop draws no more than 3.42 A—very little in hibernate mode, more when a drive fires up, but always less than 3.42—so you're fine as far as that goes with 3.5. (The adapter could be rated at 3.5 million amps, and that would be fine, too.) As for the voltage, a volt or two either way often doesn't make any difference to an electrical device, but to be absolutely safe set it to the voltage of the original adapter. --Milkbreath (talk) 16:31, 15 January 2009 (UTC)

Set it to 19V. Think of voltage as flow and current (amps) as capacity; the new adapter has a bit more capacity. --—— Gadget850 (Ed) ^talk - 20:43, 15 January 2009 (UTC)

It's essential to get the voltage right - you could easily damage the laptop by giving it the wrong voltage. The current is merely a capability of the power supply. We assume from the old powersupply that the laptop never pulls as much as 3.42Amps - probably quite a bit less. The new supply (at 19volts) should be able to supply the most the laptop will ever demand - with a bit to spare. It's a good idea to have plenty to spare because power supplies get hot when they are operating near to their limits - and that prolonged heating shortens the life of the power supply. The plug shape actually tells you almost nothing. Sadly there are at least a dozen very similar connectors and little or no control over which ones relate to which voltages and currents. But you do need to get the polarity right...again, there is a risk of damaging the laptop if you get it wrong. SteveBaker (talk) 01:26, 16 January 2009 (UTC)

The universal adapter for laptops had no way of changing the polarity. I suppose that all laptops have the same combination. Anyway, it has worked fine, but what would have happened if the polarity was wrong?

Well, the laptop MIGHT have internal protection against that - in which case it would simply not work. Failing that, you'd fry some chips - and it would almost certainly kill the laptop. I havn't yet done that to a laptop - but I messed up my music synthesiser that way - but I got lucky and replacing the power transistor (which was the first thing I tried) fixed it perfectly. SteveBaker (talk) 00:05, 17 January 2009 (UTC)

No sleep

Respected

Well i would kindly request you to give approximate numbers on how much a 22 year old should sleep for a healthy life. the next doubt is what and the problems that one will face in present or in future for spending sleepless nights.

THANK YOU —Preceding unsigned comment added by 220.227.68.5 (talk) 15:17, 15 January 2009 (UTC)

The Ref Desk cannot and will not provide specific medical advice for you. However, I can point out that our sleep article addresses the idea of optimal sleep for humans. To summarize what's there, it varies both by how long you sleep and when you sleep. A quick overview of the studies we reference suggests that something in the 6-8 hour range during nighttime is common. — Lomn 15:51, 15 January 2009 (UTC)

You might also want to read out article on insomnia. We cannot give you medical advice, but there are many on-line tips for falling asleep if you have insomnia. ~AH1^(TCU) 23:26, 16 January 2009 (UTC)

menstrual cycles

so girls who spend a lot of time together menstruate all at once.

my question is could the evolutionary reason for this be that it means they will also be their friskiest and most promiscuous (ovulating) all at once... setting up the perfect storm for dorm orgies, banging sisters or best friends, hell the whole cheerleading squad why not, it happens???!!

Because if it is the reason, that is just sweet. —Preceding unsigned comment added by 82.124.85.178 (talk) 16:27, 15 January 2009 (UTC)

Evolution doesn't have reason. Its entirely random. If you make up your own reason, it will be just as good as any that someone here could give you. --Jayron32.talk.contribs 16:53, 15 January 2009 (UTC)

God does not play dice! —Preceding unsigned comment added by 82.124.85.178 (talk) 18:03, 15 January 2009 (UTC)

W-e-e-l-l-l-l... Evolution doesn't have an "ultimate" reason or a target it's working toward, but adaptations surely have a reason - they allowed the relevant population to differentially outbreed populations with different adaptations. I don't have any idea why women tend to synchronize their cycles, but I'm sure there have been theories put forward. I would bet (were I a betting man) that there is some kind of tie-in to the "hidden" ovulation humans have. Many/most mammals come into "heat" or oestrus, where people and a few others don't. It would be interesting to see if those other hidden ovulators also get synchronized menstrual cycles. Matt Deres (talk) 17:54, 15 January 2009 (UTC)

A bit of elaboration. Humans are strange, reproductively speaking, in two ways. First, they have hidden ovulations: neither the woman nor her partner know exactly when she’s capable of being fertilized. Second, they have sex much more frequently than other mammals. Most mammals only mate when there is a chance of the female to get pregnant. Researchers such as Jared Diamond (among others) have theorized that there is a connection between these two strange adaptations. The theory goes something like this: human children are a huge time and resource investment to parents, which leads to a problem: men aren’t going to want to invest their time/energy is raising a child that’s not theirs while women have a huge incentive to make sure some man – any man – helps her raise the child (she is, after all, sure of maternity). Women who obscured their ovulation would have an adaptive advantage because her potential partners would have no idea when the best time would be to mate, making it advantageous for them to stick around long term, so they can be sure to mate with her at the right time. He "knows" the child is his while she gets help bringing up baby. Everyone wins, at least according to this theory.

The reason I suggested the synchronized ovulation might be tied to this is that a population of women who ovulated at the same time would have an easier time tying down a specific partner. While he might be tempted to stray, he runs into two problems: first, he’s not sure who is ovulating, so he’s not sure who to try to mate with. Second, with everyone ovulating at the same time, he probably doesn’t want to be away chasing "the other woman" at the very time his partner is also ovulating. That’s just asking for some other philanderer to sneak in while he’s away. Matt Deres (talk) 19:00, 15 January 2009 (UTC)

We have an article McClintock effect. In particular, note that it's by no means established that this effect occurs at all. Algebraist 18:00, 15 January 2009 (UTC)

Cecil Adams covers it here, with some speculative reasons. Short answer: nobody even knows if it really happens, much less why. Whenever you hear someone explain some trait of humanity with "well, in prehistoric times ..." your bullshit detector should start tingling immediately. --Sean 18:24, 15 January 2009 (UTC)

It doesn't particularly sound like the OP is thinking of prehistoric times Nil Einne (talk) 19:32, 15 January 2009 (UTC)

You mean they didn't have cheerleaders or dorm orgies in prehistoric times? :) A Quest For Knowledge (talk) 19:43, 15 January 2009 (UTC)

They didn't have them in the 1990's when I was in college, or atleast I never got invited to those kinds of parties. Not sure if that qualifies as "Prehistoric". --Jayron32.talk.contribs 00:39, 16 January 2009 (UTC)

I have another theory: Not only would the women ovulate together - but they'd also enter that god-awful bitchy, naggy, grumpy phase of the month simultaneously. If the all did this at different times - the man who's suffering this particular day may well go look for fun with other women in the tribe. But if they all do it at once - the men simply have to leave the cave for a few days and go do "guy stuff" - hunting mastodons for example. SteveBaker (talk) 01:16, 16 January 2009 (UTC)

Synchrony of estrus is a common theme in mammalian reproduction, though its best studied in mice. There are two major and contrasting factors the modulate estrus. Firstly there is the Whitten effect: contact with adult males, or their pheromones, cause the acceleration of estrus. This makes a lot of evolutionary sense from the male perspective, as it is to his reproductive advantage to have fertile females around. A version of this is also called the Vandenbergh effect, which is when exposure to male pheromones causes the acceleration of puberty of young female mice (the advantage of that for the male is obvious too). In contrast to that is the Lee-Boot effect: when female mice are housed together they suppress each other's estrus cycles, and their pheromones delay puberty in young females. The dual effect of these conflicting pressures tend to result in synchrony.

The best argument for the existence of human pheromones lies with the McClintock effect. Though its by no means been proven, and the statistical validity of the data has been questioned, it does seem to fit with what we see in other mammals. The major problem with it is the organ the detects these pheromones in other animals is not present and/or functioning in humans. In an excellent textbook on pheromone communication (Wyatt, Tristram D. (2003). Pheromones and Animal Behaviour: Communication by Smell and Taste. Cambridge: Cambridge University Press. ISBN 0-521-48526-6.) the evolutionary aspect of esrus synchrony in social animals is discussed on p285. The major hypotheses are:

• It helps regulate seasonal breeding (and all the advantages that has for survival)
• It helps combat predation pressure (a troop with many young will move slowly, but a lone mother may get left behind)
• It helps to equalize the operational sex ratio, bringing it closer to 1:1, which increases paternal investment by creating a situation that favors pair mating.
• It promotes communual rearing (which benefits the mothers and the young).

The relevance of these to modern humans is questionable, but its entirely possible that the McClintock effect (if it actually happens) is an evolutionary relic from our primate ancestors. As an aside, a student in my lab is currently working on identifying the specific molecule that drives the Whitten and Vandenbergh effects. Once she characterizes it, we may have more evidence for (or against) the same effect in humans. Rockpocket 01:21, 16 January 2009 (UTC)

Meniscus Lens Ray Diagrams

Hello. How do I draw a ray diagram for a positive meniscus, thin lens since there are two focal points on the "concave" side? Thanks in advance. --Mayfare (talk) 20:53, 15 January 2009 (UTC)

January 16

Saving money by freezing water

Every couple months, I buy raw chicken for my dogs for their daily meals. As time goes by, the freezer empties. To save money on electricity, I've started adding plastic bottles of water to the freezer to make up for the space that opens up as the dogs eat. I'd like to reuse these bottles, they're empty juice bottles, so how much should I fill them to keep the ice from breaking the plastic open as the water expands upon freezing? I thought about squeezing the bottle slightly before putting the cap on, thinking that the ice formation would push the sides out as far as it needed. Is this a good strategy? Thanks, Dismas|^(talk) 01:29, 16 January 2009 (UTC)

Why are you filling the bottles with water at all ? Air has a much lower thermal capacity, meaning it will take far less energy for the freezer to bring air-filled bottles down to freezer temps than water-filled bottles. As for how full, you'd need it less than 90% full of water to prevent overflowing, if the water flows evenly and no expansion or contraction of the bottle is allowed. Unfortunately, neither assumption is valid. For example, ice might very well form across the surface of the water, preventing it from expanding upwards (depending on the bottle geometry), and split the bottle open, even if only half full. StuRat (talk) 02:27, 16 January 2009 (UTC)

Why do you need bottles at all? I'm really not getting this... what's wrong with leaving your freezer half empty? --Tango (talk) 02:37, 16 January 2009 (UTC)

Yeah, since water takes more energy to cool than air does, why add room temperature water to the freezer at all? It seems that that would be a waste of energy and resources... --Jayron32.talk.contribs 02:46, 16 January 2009 (UTC)

The problem with a half-empty freezer is that whenever you open it warm air enters, and has to be cooled, wasting energy. As StuRat points out, this can be averted by filling the space with empty bottles or such. Algebraist 02:49, 16 January 2009 (UTC)

I strongly suspect that the energy required to cool the air is far, far less than the energy needed to cool and freeze the water occupying the equivalent space, by orders of magnitude. Unless you need jugs of frozen water, do not place jugs of water in the freezer to occupy the space previously occupied by frozen food. If you open the freezer "daily" just leave the space empty until you buy more dog food.How many times would one have to cool air from room temp (20 Celsius?) to freezer temp (fifteen below zero Celsius?) to make up for the energy required to cool water from over the same range? Look at the specific heat of air versus the specific heat of water as well as the heat of fusion of water. Water appears to have about 1000 times the density of air and a specific heat of 4.1813 kiloJoules per kilogram per degree Celsius, about 4 times the specific heat of air (1.0035 kilojoules per degree celsius per kilogram). Once it freezes, it has about twice the specific heat of air of the same mass, 2.050 kiloJoules per kilogram per degree Celsius). In addition, for the phase change from water to ice, add 333 kiloJoules per kilogram. It looks like the freezer would have to be opened an unrealistic number of times to make the freezing of water of the equivalent volume more economical than cooling the warm air which entered. (But, then, I am not a chemist). Edison (talk) 03:49, 16 January 2009 (UTC)

Ah, that makes sense. Yes, air-filled bottles could save some energy, water-filled bottles most likely won't (and certainly not as much as air-filled ones). --Tango (talk) 04:01, 16 January 2009 (UTC)

Except for Edison's answer, which went over my head, it sounds like the rest of you are saying that I should just put in empty bottles. I was filling them with water because I thought that the ice blocks would keep the condenser from having to run as often to maintain the temperature. That they would aid in keeping everything cold for longer than the same volume of air. Dismas|^(talk) 04:35, 16 January 2009 (UTC)

Yes, that's what we're saying. While water-filled bottles will store more coldness (don't look at me like that!), which would help maintain the temperature, that effect is outweighed by the energy required to freeze the water in the first place. --Tango (talk) 04:43, 16 January 2009 (UTC)

Thanks for dumbing it down for me. Neither of my degrees are in engineering or anything of the sort. Dismas|^(talk) 04:54, 16 January 2009 (UTC)

I wasn't intentionally dumbing it down, I was thinking about it in terms of storing coldness myself, so that's how I wrote it. (Yes, I cancel dx's too, so sue me!) --Tango (talk) 05:06, 16 January 2009 (UTC)

Please contact my lawyer immediately - he'd like to discuss what date you could make it into court! (Thermodynamics - it's not just a good idea - it's the LAW!)

There are two effects going on here:

1. Preventing volumes of cold air from spilling out and being replaced by warm air when you open the freezer door. Cold air is denser than warm air - so if you have a "chest" freezer - there is little problem - but for freezer's with doors that hinge open at the front, all of the cold air will "fall" out of the bottom in just a few seconds. To stop that, it's only necessary to prevent the air in the unused parts of the freezer compartment from moving - and a few three liter coke bottles will do that just fine.
2. The idea of 'thermal inertial' - that something like water/ice would slow down the rate of change of temperature. That's a more dubious thing. Certainly, if the thermal inertia is high then when you open the door, the temperature won't fall by so much before you shut it again. That SOUNDS good - except that the high thermal inertia ensures that having fallen a bit - it takes so much longer for the freezer to get back to the right temperature again. So from a point of view of saving energy - there isn't any benefit to using high-thermal inertia materials inside those bottles. It's only use is to prevent the temperature from rising to the point where the food might spoil - but for that, you'd need to leave the door open for a considerable amount of time even without anything like bottles of water in there.

So the conclusion is that any kind of system for stopping the air in the empty parts of the freezer from moving when you open the door is probably about as good as any other. Balloons, empty cardboard boxes, coke bottles, dead aarvarks...it doesn't matter. But if you have a "chest freezer" it's hardly worth bothering with since the cold air will pretty much stay put. So if you're going to do this - you might as well use bottles full of air because (a) the initial cost of chilling them is much less and (b) there is no chance of them rupturing. SteveBaker (talk) 15:36, 16 January 2009 (UTC)

Dead aardvarks are mostly water. Dessicated aardvarks, on the other hand, ... Saintrain (talk) 18:22, 17 January 2009 (UTC)

Cecil Adams covers this question here. --Sean 13:50, 16 January 2009 (UTC)

There is one advantage to having lots of frozen water in the freezer, it will keep the food frozen longer in the event of a power failure. You can also use freezer gel packs that will hold even more "coolth", but then again, those cost money and you can't drink the melting water on a hot day in summer. StuRat (talk) 15:24, 16 January 2009 (UTC)

How about freezing the bottles outdoors when it's cold out? Since your user page indicates that you live in Vermont, I recommend doing it today! That will give you the benefits mentioned above, without the energy cost. -- Coneslayer (talk) 15:57, 16 January 2009 (UTC)

That's an excellent idea. Even better, fill those bottles with cold maple syrup. :-) StuRat (talk) 06:57, 17 January 2009 (UTC)

I do something similar with large leftover items I want to freeze, like a ham or turkey. I have an enclosed, but unheated, porch, so I put food out there to cool down before I put it in the freezer. Of course, if I just left those items outside, I would find dogs and racoons fighting over them in my yard. StuRat (talk) 14:00, 22 January 2009 (UTC)

An additional point about not freezing water; when the frozen bottles are removed to make space for food, the energy used to freeze the water just melts away :-) Saintrain (talk) 18:22, 17 January 2009 (UTC)

Stone use

Is the British unit of weight the stone used for anything other than human body weight, commonly or otherwise? --Milkbreath (talk) 01:41, 16 January 2009 (UTC)

The only other usage I have ever encountered was by me, expressing the mass of meat in my family's Christmas dinner in stones and pounds to emphasize its size. Algebraist 01:48, 16 January 2009 (UTC)

I believe it is (or at least was) used for the weight of horses, as well. StuRat (talk) 02:21, 16 January 2009 (UTC)

Back in the 1950's it was used for weighing coal for domestic delivery. But generally, no - it's going the way of the Dodo. SteveBaker (talk) 03:06, 16 January 2009 (UTC)

I remember it being used by people buying potatoes (usually as "half a stone"), but I haven't heard that for many years. AndrewWTaylor (talk) 10:13, 16 January 2009 (UTC)

I suspect it's not even used for bodymass any more, except perhaps colloquially. I'd be very surprised if you went to a doctor's surgery or hospital and they measured your mass in anything other than Kilogrammes. Alun (talk) 13:14, 16 January 2009 (UTC)

I met Brits a few years ago who could readily state their weight in stone,(like "I weigh 12 and a half stone") but had to do mental calculations to come up with the pound or kg equivalent. When did Brit scales for home or medical use switch from "stone" to pounds or kilograms, if ever? "Stone" still shows up in Brit press along with pounds and kg for the weight of fish [3] adults [4] and babies [5] . Stone still shows up in "ideal weight" charts [6]. Edison (talk) 14:57, 16 January 2009 (UTC)

That switch has yet to occur. Every Briton I know states their weight in stones, or in stones and pounds. Scales for weighing oneself normally have a scale of stones and pounds and a scale of kilograms. Algebraist 15:01, 16 January 2009 (UTC)

Hi! <wave> It's me! The Brit who has no clue how much a 'stone' is and only knows his weight in kilo's (but who can do a rough conversion into pounds if required). :-) SteveBaker (talk) 15:21, 16 January 2009 (UTC)

Sounds like Brits vary considerably in how they note their weight. Edison (talk) 18:02, 16 January 2009 (UTC)

Steve, you live in Texas now. You don't count as a Brit. ;-) Axl ¤ [Talk] 18:18, 16 January 2009 (UTC)

Well, he certainly doesn't count as a Texan if he thinks about his weight in kilos. Dragons flight (talk) 18:28, 16 January 2009 (UTC)

I'm a Brit (that actually lives in Britain) that measures his weight in stone (well, when he weighs himself at all...). Doctors certainly use kilograms, but I don't think anyone else does (those that do, we exile to the other side of the pond ;)). --Tango (talk) 23:39, 16 January 2009 (UTC)

Don't send them to the US, as we measure our weight in pounds, except for doctors, again, always using those silly kilograms. StuRat (talk) 23:34, 18 January 2009 (UTC)

When you guys eventually get with the program and start using kilograms and kilometres (oh, alright, kilometers if you must), you'll all wonder "Why didn't we make this very sensible change two centuries ago?". -- JackofOz (talk) 04:16, 19 January 2009 (UTC)

Kilograms are too big, so you must resort to fractions or decimals to give your daily weight. StuRat (talk) 15:27, 19 January 2009 (UTC)

I'm a Englishman who lives in England, measures his weight in kilograms, but knows others who still use stones and pounds. None use pounds on their own. I also measure my height in metres but know others who quote feet and inches. I buy my bottled English beer in half-litre quantities but it's always a pint (or several) in the pub. Milk from the supermarket comes in 3.4 litre plastic containers, but from the corner shop in 1 litre packs. I fill my VW up with 55 litres of diesel and get 45 miles for every gallon. It is one of the nicer things about living here that we are able to mix everything up this way and yet still know what we want to know at the end of it. Bazza (talk) 15:02, 19 January 2009 (UTC)

Question about waves

Hi - I was at the lake yesterday afternoon - a shallow, broad artificial lake; it was a bit blowy, and I saw two types of waves - a low chop moving across the water, and other, more sinuous waves that were neither rising or falling, but remaining in place. From the article on waves, these aren't standing waves, as I understand them, because according to the animation they rise and fall, albeit in the same spot - whereas these crests remained fixed and unmoving. Is there a name for this phenomenon?

Thanks Adambrowne666 (talk) 01:44, 16 January 2009 (UTC)

In rivers you often get a bulge in the water right after it passes over a rock, so perhaps something similar is happening here. StuRat (talk) 02:19, 16 January 2009 (UTC)

Thanks for the answer, but it didn't look like that, because the crests were regularly spaced, and the water wasn't flowing - there was no movement, only apparent movement, an effect of the ripples blowing across the surface. Adambrowne666 (talk)

Could there have been a shape at the bottom of the artificial lake that resembles the shape of the waves above ? And how can you tell there was no motion of the water ? It seems to me that the chopiness would tend to disguise this. I'd dip the end of a stick in and see if you get a wake. StuRat (talk) 15:05, 16 January 2009 (UTC)

It's possible the water was moving - but is it likely in a shallow artificial lake with no inlets? - maybe, I dunno - the ducks etc were bobbing in the same spot, so it seemed not to be moving. You may be right - though I was thinking of something along the lines of the wind setting up waves that were reflected back from the shore causing interference patterns on the surface; is that possible too? - I'm totally guessing here... If it was that, would they be defined as standing waves? Adambrowne666 (talk) 11:16, 18 January 2009 (UTC)

The wind could blow the surface water one way, and it might need to flow the other way underneath, to maintain equilibrium. With wind waves being reflected back from the edge, you could get standing waves, but they would go up and down at any given point, not "stay up", as you noted earlier. StuRat (talk) 23:30, 18 January 2009 (UTC)

Yeah, makes sense - well, maybe it was flowing - next time I see it, I'm definitely going to check - my curiosity's piqued - thanks for the answers, Stu.

You're welcome. I'm curious, too, so be sure to let me know what you find out. StuRat (talk) 22:18, 19 January 2009 (UTC)

solid objects behavior under stress

we all know that any materials in solid state will respond by change in its dimension (strain)when be subjected to aforce . but will there be any change between the volume before and after applying of the force? —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 02:39, 16 January 2009 (UTC)

We probably shouldn't be answering your homework questions, but you may want to read the articles titled Compressibility and Condensed matter physics, which contain information for you to answer the question yourself. As an alternate idea, your teacher may have issued you a text book, if our articles are more detailed than you need to answer your question, the information may likely be found there, or possibly in the lecture notes from class when you learned this. --Jayron32.talk.contribs 02:44, 16 January 2009 (UTC)

How about we assume good faith, huh? While that's certainly the kind of question that may be set for homework (although I wouldn't set it if I were the teacher, since it just tests if you were awake in class and doesn't touch on any actual understanding), it's also the kind of question that a naturally curious person may come up with by themselves. If it was homework, at least the OP went to the effort of writing it in their own words. --Tango (talk) 02:48, 16 January 2009 (UTC)

Yeah - I don't think this is in any way obviously a homework question. Certainly any material could be compressed into neutron-star-material ("neutronium") and even black-hole-material - so the answer is yes - for absolutely all normal or abnormal matter. But what about for 'ordinary' kinds of forces? Well, consider diamond - it's formed by applying huge compression forces to 'normal' carbon. The density of diamond is about 150% that of graphite - certainly that is an example of a material which can be compressed to a smaller volume...and which will remain at that volume when you withdraw the pressure. SteveBaker (talk) 03:04, 16 January 2009 (UTC)

You can try this yourself and observe the result. First, squeeze a dry sponge or a stuffed animal. Does the volume change? Now, fill a ballon or a plastic milk jug with water, with no air. squeeze it: Does the volume change? If you cannot tell by direct observation, do this experiment under water in a tub and observe the displacement. Now, explain any differences. Note: when I do this, I can dramatically reduce the volume of the stuffed animal, but I cannot reduce the volume of the water balloon. -Arch dude (talk) 22:25, 18 January 2009 (UTC)

Bogus answer based on bogus experiment: The stuffed animal is mostly air. When you compress it - you (probably) aren't compressing the solid material at all - you are either compressing or (more likely) expelling the air. The issue of whether the solid material that makes up the individual fibres is compressible is the question at issue here - and your experiment doesn't show that. SteveBaker (talk) 01:25, 19 January 2009 (UTC)

fibrinogen

a friend of mine is having a fibrinogen count that is below the reference level. the blood test report states that the fibrinogen level is 120mg/dl while the reference range is 175-350mg/dl. what will be the effect of such a shortage?what is the function of fibrinogen? i am not able to understand the wikipedia article. —Preceding unsigned comment added by 117.193.225.118 (talk) 08:38, 16 January 2009 (UTC)

The Fibrin article certainly could be made more reader-friendly. Basically, fibrinogen is a major building block for blood clots. Under conditions that trigger clot formation, a fibrin polymer can be created. This protein mesh forms the backbone of a clot. Circulating fibrinogen (an inactive form) is the principal source of fibrin, is converted to it's functional state when it is cleaved by the clotting enzyme thrombin. Information about any possible medical implications for your friend would represent medical advice, which should not come from the RefDesk. --Scray (talk) 13:05, 16 January 2009 (UTC)

Of itself, a slightly low fibrinogen level doesn't have any clinical significance. However the clotting abnormality disseminated intravascular coagulation can cause a low fibrinogen level. Axl ¤ [Talk] 18:23, 16 January 2009 (UTC)

Tests are always interpreted within a clinical situation. The fibrinogen level was presumably ordered for a specific purpose: to assess abnormal bleeding or abnormal blood tests like PT/PTT; to assess the progression of liver disease which might interfere with protein synthesis, or to assess the risk of developing cardiovascular disease. A low fibrinogen level would have different significance depending on the clinical setting in which it was ordered, so really your friend has to discuss this with his physician. - Nunh-huh 18:31, 16 January 2009 (UTC)

More likely the fibrinogen level was a default test in the coagulation screen. If the PT and APTT are normal, the fibrinogen level isn't very helpful. Axl ¤ [Talk] 07:48, 17 January 2009 (UTC)

In the context of the OP, this is beginning to look a lot like medical advice. --Scray (talk) 18:44, 17 January 2009 (UTC)

fifth dimension

what is the fifth dimension? light is said to be the vibration of the fifth dimension in the book "HYPERSPACE" by michio kaku. but in the same book, it is said that the universe was earlier made up of 10 dimensions and six broke off. ours is the remaining four. also, the remaining six dimensions have shrunk to the size of the fraction of the size of a proton. so how doesit fill our universe so that light would travel? —Preceding unsigned comment added by 117.193.225.118 (talk) 08:49, 16 January 2009 (UTC)

This sounds like fiction, not science - which fits the source you cite. We do have science-based articles on the fourth and fifth dimensions that might interest you. --Scray (talk) 12:54, 16 January 2009 (UTC)

A book called Hyperspace is unlikely to be a reliable source. Light is not a vibration of the fifth dimension, but rather an electromagnetic phenomenon that can be adequately if unsatisfyingly described in the usual 3 (special) plus 1 (time) dimensions. In science fiction, the fifth dimension is often assumed to be an extra spatial dimension that allows for faster-than-light travel via some handwaving pseudophysics, and hyperspace is the medium that allows this. In string theory, a fairly advanced and controversial area of higher nonsensetheoretical physics, more-dimensional are models considered, and they often have the property that many of the extra dimensions are somehow compacted so that we only perceive the normal ones. See String_theory#Extra_dimensions, and take an aspirin or two in advance ;-). --Stephan Schulz (talk) 13:08, 16 January 2009 (UTC)

According to the article Hyperspace (book) it is a real science book. And Michio Kaku is an expert in string theory, apparently. So I don't think the reliability of the source can be in doubt. I don't know anything about theoretical physics though. Alun (talk) 13:21, 16 January 2009 (UTC)

Thanks for pointing that out. I agree that the person who wrote the book sounds reliable, but I retain the impression that it sounds like (well-informed) speculation. --Scray (talk) 13:27, 16 January 2009 (UTC)

Ha, it just occurred to me, upon reading what you wrote that all scientific theories are well-informed speculation!! Alun (talk) 13:47, 16 January 2009 (UTC)

Why are the spatial dimensions special? Zain Ebrahim (talk) 13:28, 16 January 2009 (UTC)

For me, I can travel more easily to the kitchen than to yesterday... --Stephan Schulz ([[User talk:

A fifth dimension wouldn't fill any particular place in the universe - it would be everywhere but curled up. The usual comparison is to a telephone line, far away it looks like a line but close by for an ant it is two dimensional with one dimension curled up an circular. A string can just go straight along the line or wind around it an these two paths would be different so one can get different effects. In our three spatial dimensions there could be another tiny dimension curled up everywhere just like the curve round the wire is all along it. An alternative is tha there could be an extra huge dimension but we can't look in that direction, for instance if our universe is like a layer of an onion and light only travels along a layer of the onion, the fifth dimension would be between layers. I'm sure this is the sort of Michio Kaku would be writing anyway, perhaps you could be more specific? Dmcq (talk) 13:53, 16 January 2009 (UTC)

Michio Kaku is considered a joke by his fellow physicists and I would recommend ignoring anything he says. In this case, though, when he talks about light as a vibration in a fifth dimension he's probably talking about Kaluza-Klein theory, and when he talk about six extra dimensions he's talking about Calabi-Yau compactification in string theory. The six extra dimensions in string theory have, as far as I know, nothing to do with the one extra dimension of Kaluza and Klein's theory. There's no standard "fifth dimension" that everyone agrees on. -- BenRG (talk) 14:21, 16 January 2009 (UTC)

I have personally seen and heard the Fifth Dimension. Edison (talk) 14:47, 16 January 2009 (UTC)

Michio Kaku is the 'physicist' who is trotted out on every Science Channel and Discovery Channel show to say impressive, dramatic, surprising (and often VERY wrong) sciencey things on every subject under the sun. If you watch any of those shows - check out the photo (at right) and I'm sure you'll recognise him. He was once a leading string theorists - but I certainly would take anything he wrote in the last 5 to 10 years or so with a huge pinch of salt. His latest book is about "the technologies of invisibility, teleportation, precognition, star ships, antimatter engines, time travel and more"...which is a measure of how much he's "sold out" to the media business. He clearly hasn't been a hard-working grass-roots scientist for many years because he must be spending close to 100% of his time with film crews, in makeup tents and writing trash about precognition and teleportation with the flimsiest of scientific pretext. I find this very sad. SteveBaker (talk) 15:18, 16 January 2009 (UTC)

You know, as much as love the Science Channel and the Discovery Channel (and the History Channel too), I am distressed by all the shows on Nostradamus, the Bermuda Triangle, Roswell, etc.. Now I find out that the guy on the legitimate science shows on astronomy and physics isn't exactly reliable either? Ugh. Where's a lay scientist supposed to turn? A Quest For Knowledge (talk) 16:28, 16 January 2009 (UTC)

From my experience, most popular scien-tists (as in scientists heavily active in the popular science field not as in scientists who are popular) tend to be somewhat disconnected from real science Nil Einne (talk) 18:33, 16 January 2009 (UTC)

How about Carl Sagan? A Quest For Knowledge (talk) 19:03, 16 January 2009 (UTC)

I said most, not all Nil Einne (talk) 19:08, 16 January 2009 (UTC)

The Wikipedia Ref Desk, of course! --Tango (talk) 23:45, 16 January 2009 (UTC)

Hey, I know that book (his latest Steve mentioned, not the one under discussion here). It's riddled with factual errors. Algebraist 18:36, 16 January 2009 (UTC)

Branes? ~AH1^(TCU) 23:08, 16 January 2009 (UTC)

unified theory

have scientists arrived at an equation that can explain all the laws and features of nature? what is the equation? —Preceding unsigned comment added by 117.193.225.118 (talk) 08:50, 16 January 2009 (UTC)

Not yet. Algebraist 12:43, 16 January 2009 (UTC)

No; see Grand unification theory for the most famous attempt. Even there, it's a long way from understanding particle physics to understanding why blue-footed boobies behave the way they do. Nature isn't just big; it's everything! --Sean 13:57, 16 January 2009 (UTC)

... but it is known that 42 is the answer to life, the universe and everything. 98.220.251.111 (talk) 14:03, 16 January 2009 (UTC)

We haven't - but what we do know is that there are hard limits to what we CAN explain. We have several sources of fundamental unknowability to contend with: The Heisenberg uncertainty principle and associated quantum weirdness limits what we can know at the nano-scale. Chaos theory and Catastrophy theory limits what we can predict - even at the macro-scale. Hawking radiation has been argued as a source of cosmic-scale randomness. Godel's theorem limits what we can prove mathematically. The Halting problem (and it's greater consequences) limit what we can compute with software. So I guess what we DO know is that even if we do find "the equation of everything" - it's not going to help us to understand or predict everything. We do not have a mechanical universe (how is that a red link?!?) - and Einstein notwithstanding: "God" does indeed play dice...or possibly roulette...in fact it often seems that it's the only game (s)he knows! SteveBaker (talk) 15:04, 16 January 2009 (UTC)

What do economists know, really?

With the economy seeming to fall into a quagmire, I can't help but wonder why more economists didn't see this coming? (I suspect some did, at various points along the way, but all along the way down there has also been no shortage of people to suggest things will get better soon.)

I'm generally interested in analysis of the accuracy of forward looking economic predictions. Presumably someone tries to figure out how accurate analysts have been, right? I'm not sure what the right data sets to look at are though. Any ideas? Dragons flight (talk) 08:52, 16 January 2009 (UTC)

Economics is a science in flux. Rules change. Sometimes this is the point. For example FDIC was created in 1933 to prevent future runs on the bank, no one knew what it a run on the bank would look like with this new insurance in place. Could one still happen? No one knew because there wasn't any data for something that had never been tried before.

A lot of economists study cause and effect rather than getting good at predictions. To draw another example, suppose I asked an economist why people speed less on the freeway in a recession. They would tell you that it could be because people can't afford a ticket or that they are trying to get better gas mileage. If I ask them why they speed MORE they will say because they can't afford to be late for work or they are burning off frustration. But if I ask whether people speed more or less in a recession they would have no idea unless they went out and collected data. So they are not effective at predicting something they haven't seen. Once they have data on this though, they'll be able to predict it for a while in the future unless traffic laws change significantly, in which case they could make predictions based on old predictions but ultimately they just have to collect more data.

These mortgage backed securities are like new traffic laws. No one really knew what would happen if they started bottoming out. Sure there were some that viewed it overly optimistically, and some that viewed it overly pessimistically (turns out these ones were right).

Now that being said there are some incredibly bright economists out there that probably see true most of the time. The problem is that firms don't necessarily have the incentive to listen to these economists. Seems stupid? Its not. Companies are rewarded for taking risks. Companies are also rewarded for making short term (one-quarter) quick profits that can be put into their prediction for their next quarterly release. Unlike Japanese firms which always keep long term in mind and take very few risks, American firms jump boldly into new cash making endeavors. This generally gives American firms better growth but sucks in times like these.

In fact often companies do things that are not in their own interest. The Game Theory that is created by open markets sometimes make Prisoner's dilemmas. For example when the banks stopped leading to each other, it sucked for all of them. They would've been better off if they had all kept lending, but individually they all thought, "Well it'd be great if everyone BUT me kept lending, so that I don't have to expose myself to that risk." This creates a scenario of no lending for the Nash equilibrium.

As far as predicting stock prices or market movements anyone who doesn't have insider information is no better at predicting than a monkey throwing at a dart board. Shows like Mad Money actually predict stock movement at slightly worse than random rates. Managed Mutual funds (meaning having an active "expert" playing the market buying/selling everyday to try and maximize profits) have historically done worse than indexed funds (just a list of stocks that never changes or infrequently change) in just about any economic climate. No one can predict the market.

Anyway probably a bit wordy there, hopefully you got something interesting out of it. Anythingapplied (talk) 09:23, 16 January 2009 (UTC)

to say frankly, the world economy is controlled by the gulf countries. they provide the world with nearly 80% of crude oil and so, they can control the price of petroleum by increasing or decreasing production. a decrease in production will cause an increase in petrol prices. this increase already is causing turmoils in India. the government did not increase the petrol price significantly when oil prices rose to $140 a barrel. this results in accumulated loss for all companies. But when the price fell to $40, the gov. will not reduce the price since there was no increase. the stock market situation is similar to that of the uncertainty principle at the quantum level. you cant just find for sure anything. u can just find the probability. the same applies for weather reports and stock markets. Harnithish (talk) 09:41, 16 January 2009 (UTC)

Unfortunately in the short term doing stupid things can seem right so the more silly politicians and economists get the limelight. It annoys me at work too that people who plan properly, bring in a profit and don't have a crisis get little reward compared to people who are always rushing around patching up the trouble they've caused. But on the original question I can't answer better than the old joke of what's the difference between an exam in philosophy and in economics? ---- One asks a different question every year and expects the same answer, and the other asks the same question every year and expects a different answer. Dmcq (talk) 10:32, 16 January 2009 (UTC)

Economics isn't really a science. We should stop calling it that. You can't do experiments with economies - not proper, controlled double-blind experiments. If you could then the major opposing camps (The Marxians and the Keynsians) would long ago have figured out which of those two theories was "correct" and we wouldn't have one bunch of highly paid, trained, professional economists claiming that lowering taxes on the rich would cause them to invest more money and cause a 'trickle-down' effect from which everyone benefits - while another group of equally highly paid, respected economists claim that we should raise taxes on the rich so we can lower them for the poor and have those consumers spend more and thereby raise the economy from the bottom up. We literally don't know the answer to something as fundamental as that. Sure, we can change some policy and a year later it SEEMS like things either got better or they got worse - but without a "control group" you have no clue whether it was what you did that caused that - or some other factor like the weather or the discovery of a new source of energy or a terrorist flying a plane into a building.

The scariest thing about economists is their propensity for having graphs with no numbers on their axes! Ask them about their most well-known theory: 'Supply and demand' and 100% of the time, they'll trot out this pretty graph with one curve swooping down dramatically from one side and another curve swooping down from the other - and right there at the point of intersection there will be a big red arrow. OK - so this tells us that supply and demand should be equal and the price of the goods will change until that happens - fair enough. So, you ask - what are the numbers? At what price should we sell this item? Surely we can look at the curves and read off the answer? No? Well, at least we have the equations for price-versus-supply and price-versus-demand curves then? Well, sadly, no. Because economists have no clue how (mathematically - numerically) supply and demand change as a function of price because THERE ARE NO NUMBERS ON THE FREAKING AXES!! Proper scientific theories have to produce PREDICTIONS that can be tested. So, nobody was prepared to sign off on Einstein's theories of relativity until some poor sap had hauled a bunch of telescopes through the middle of a war zone and later out into the back of beyond and measured how a star is displaced during a solar eclipse! Where is the seminal experimental evidence for those supply and demand curves?

So what use is this wonderful 'supply and demand' theory? All it tells you is the most blindingly obvious thing - that if something gets cheaper, more people will buy it (and vice-versa) and if it gets more costly, more people will want to make it. Yeah - great job guys! If I'm a manufacturer and I make widgets in small quantities for discerning customers - so the supply is short and the prices are high...should I invest in another factory and sell twice as many widgets (albeit at a modestly reduced price) or will the price drop so steeply when I do that that I will drive the price down so far that I'll actually make less profit than I do now? Maybe instead, I should cut back on production and let the price rise? I should be able to toss the numbers into a spreadsheet using the equations provided in the Economics 101 "big book of equations" and PREDICT (within the limits of experimental error) whether I should open the new factory or not. In truth - nobody knows - ask N economists and you'll get 2x(N-1) answers! This is one of their most fundamental principles - and certainly the one they teach first in Economics 101 - and we don't have even the basic math to tell us how it works. This stuff isn't just a lack of scientific rigor - it's an actual practical matter for which there is no known answer...just look at the way governments work to try to artificially limit supply (eg by buying agricultural 'setasides' where they pay people NOT to increase the supply) - or the way that they try to increase supply by offering subsidies. These are direct tinkerings with that supply/demand curve - but in the absence of any science - there are these huge debates about whether to institute these kinds of practices. If it were a science, you'd plug the numbers into your spreadsheet - people would look at your numbers and everyone would nod sagely and "do the right thing".

That's not to say that economists are a waste of space (let's reserve that for the philosophers!) - but what they are doing isn't science - and they shouldn't call it that. Obviously there are very good reasons why they can't do these kinds of experiments - which is an excellent excuse for the state of economic theory...but we should please just not call it 'science'.

SteveBaker (talk) 14:50, 16 January 2009 (UTC)

I would rate philosophers above economists. Mistakes by economists are disastrous; mistakes by philosophers merely ridiculous. Matt Deres (talk) 16:44, 16 January 2009 (UTC)

A problem which virtually precludes the success of economics is that economists publish their findings, and the economic actors have access to these publications. They then try to gain an advantage from the insight and change their behaviour and therefore the economy which is being studied by the economists. There may not be that many people who actually read the papers of economists, but a few smart individuals should be enough (if they run successful businesses then others will be interested in their business models and copy it). In general, economists are not smarter than economic actors. Icek (talk) 22:57, 16 January 2009 (UTC)

Evidence

Apparently I hit a nerve. However, the verbose responses given above largely missed the point of the question. Rather than offering opinions about how good/terrible economics is at making predicitons, I would like to see actual evidence of what comes from those predictions. User:Anythingapplied alluded to what could be good evidence saying: "Shows like Mad Money actually predict stock movement at slightly worse than random rates. Managed Mutual funds (meaning having an active 'expert' playing the market buying/selling everyday to try and maximize profits) have historically done worse than indexed funds", but didn't give any references to back up his assertions.

In response to SteveBaker's assertion that economics is not "science" and shouldn't be treated as such, well that's what I would like to investigate. So what if there is only one economy? That doesn't preclude making predictions and verifying whether the results are statistically better than random guessing. By analogy, cosmologists have only one universe and climatologists have only one planet, and yet neither field should be accused of being incapable of scientific analysis. Some economists, such as stock analysts and money managers, are routinely making predictions about the future of the economy. Either they turn out to be right or wrong, but that's what I would like to know. Before we condemn all economists, I'd like to see some data about their actual performance. Dragons flight (talk) 16:32, 17 January 2009 (UTC)

You miss the point of my post. What makes something a science or not has nothing to do with how often it's right. It's to do with methodology. Science has a long and (mostly) successful history of applying "The Scientific Method" - where you have some idea for a theory - you test it with an experiment - the experiment either confirms your theory or rejects it. Economics doesn't (and indeed, cannot) work like that. Furthermore, it wraps itself in the trappings of science - graphs and charts - but misses out on the aspects of measurement and testing. So it may be 100% successful or worse than chance - it doesn't matter - it's not science because it doesn't apply scientific methodology. So if your goal is to claim (as I do) that economics is not a science - then you don't need evidence of how economic predictions turn out. You merely have to ask how economists make those predictions...and they'll readily admit that they can't do proper experiments because that's in the nature of their field.

Cosmologists certainly do perform experiments - a good example is that they hypothesised that the big bang was the origin of the universe. They reasoned that if that really happened then the cosmic microwave background radiation should have a certain set of properties. Finally, they launched a spacecraft with microwave detectors and they measured that radiation experimentally. The result fitted their prediction and debunked the older theories - so now we have a new cosmological finding and we regard the Big Bang as "A True Theory".

I agree that climatologists can't experiment on the entire planet - but they can take results and equations from other fields of science and apply those to the systems they study. Weather (not climate) prediction (for example) is a notoriously inaccurate field of study. We all know that weather forecasts are unreliable. But they DO use scientific principles - they have a computer with a 'model' of the atmosphere which includes things like the gas laws and the laws of thermodynamics - and they run that data against current data. They test that model (which is a kind of 'theory') against historical weather data - and that is a kind of experiment. When the model fails, they figure out why - and hopefully fix it...that is (in a sense) their scientific "law". It's not perfect and the results aren't particularly reliable because of Chaos theory...but they know why it doesn't work - and they know the accuracy of their forecasts falls of as a function of time. When the next hurricane heads towards Florida - they will predict it's track and various teams of meteorologists will largely agree on the results. Hence it's a scientific method. Economists rarely agree - if they were following a set of laws that had been scientifically derived and proved by experiment - they wouldn't disagree so violently. Stock market prediction is also unreliable - but it's not done with a scientific model - it's just statistics and the best gut feel that various stock market 'experts' can come up with.

Cosmology and climatology can build on the results of physics and chemistry. Economists have nasty unfathomables like the behavior of humans under stress, the weather, the random-seeming discovery of new raw material deposits, massive fraud in ENRON, one guy becoming President rather than another as a result of 'dangling chads' - they simply can't build their results on the back of other scientific results - and they can't come up with scientific laws of their own. It's not their FAULT that it's not a science - but none-the-less, it's not.

But none of that changes whether they are right or wrong when making predictions. Weather forcasting has a TON of science thrown at it - but Chaos theory dooms us to forecasts that are no better than chance beyond a week or so - and short term forcasts that do better than chance - but not much better than following the rule "Today's weather will be the same as yesterday"...which is remarkably effective! Some economic theories work really rather well in practice (certainly better than weather forecasting) - but they aren't based on science.

SteveBaker (talk) 18:36, 17 January 2009 (UTC)

Actually, you miss my point. I don't care what you think of their methodology. I don't care whether what they do qualifies as science. I want to see evidence evaluating their reliability.

Look at this way. Athletics is not generally considered a science. On any given day, an athlete may have a good performance or a poor one. Nonetheless, what they are capable of doing is often interesting and great athletes are consistent enough to build legendary careers.

Maybe economists indulge in superstition and fantasy, but regardless, I am still interested in whether there exist economists who are right often enough that they are able have useful insights about the future of our economy. I consider all this discussion about whether the methodology is scientific to be largely irrelevant to the question of whether economics, as a field of human endeavor, can be empirically demonstrated to be useful. Dragons flight (talk) 06:38, 20 January 2009 (UTC)

Dragons flight, there are some very successfull investors like George Soros, but I don't know their methods ;-)

I strongly disagree with SteveBaker's reasoning. Cosmologists certainly don't perform experiments! A hypothesis is not an experiment. Economists hypothesise as well, and the hypotheses can be falsified.

As I already said, the largest problem is not the inherent complexity but the lack of separation between the theory and the economic actors who shall be described by the theory.

-Icek (talk) 11:48, 23 January 2009 (UTC)

Using frogs to keep milk cold

My father told me once that when he was young (around year 1920) they used a frog to keep milk cold. They put the frog into the milk container and by having the frog there, the milk would stay cold. I wonder if this possibly could be true? --Kr-val (talk) 09:26, 16 January 2009 (UTC)

Short answer: No. Longer answer: once people found out there's a frog in the milk, my guess is that they would leave it alone, and it would stay colder because it's not being handled. I don't think that's the intended effect, though. --Scray (talk) 10:07, 16 January 2009 (UTC)

The closest thing I have heard to this mistaken lore is my dad saying they would put a jug of milk in the spring to cool it. Frogs do spring sometimes. Wasn't there a Three Stooges episode where one of them put a frog in the beer they were trying to make, saying the recipe included "hops?" Edison (talk) 14:44, 16 January 2009 (UTC)

Your dad's story is corroborated by this NY Times article from 1854. Presumably it was not unusual to find a frog in your spring-cooled milk, and some people mistakenly guessed that it was the frog that was doing the cooling. --Heron (talk) 14:35, 17 January 2009 (UTC)

moment of inertia

I looked all over for a logical defintion for moment of inertia .

i dont need a mathmatical defintion , i need atext answer without numbers...thank you...? —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 09:39, 16 January 2009 (UTC)

Google has a special function for bringing up definitions. Search by writing "define:moment of inertia" [7] The article Moment of inertia may also help, but I guess you've read it already. EverGreg (talk) 10:32, 16 January 2009 (UTC)

It is the resistance to turning you might notice when starting a wheel rotating. It' bigger for heavier wheels. I'm sorry but maths is the language of science. One can put words in instead of the symbols but it would still be maths. Dmcq (talk) 10:44, 16 January 2009 (UTC)

It's not necessarily true that heavier wheels have a higher moment of inertia. It depends on how the weight is distributed...a point on which I elaborate in my explanation below. SteveBaker (talk) 13:48, 16 January 2009 (UTC)

The canonical 'gut feel' thing is the ice-skater spinning on tip-toe. As she starts off, her arms are outstretched - when she pulls them in she immediately spins much faster. The amount of angular momentum she has stays the same even though she's spinning faster - and that's because she changed her moment of inertia by becoming more "compact". So I guess the loosest definition would be 'state of compactness'.

Hence (to pick a practical example that I was discussing with fellow car club members a few days ago): if you have 10" radius wheels on your car with 3" deep tyres (tires) mounted - for a total radius of 13" - and you decide to switch them out for sexier 12" wheels with 1" 'skinny' tyres - you are putting more heavy metal out towards the edge of the wheel and removing some the lighter weight rubber. So even though your new wheel/tyre combo may not weigh any more than the old ones - and even though you didn't change the overall circumpherence - you may be shocked to discover that it added half a second to your 0-60 time! That's because the moment of inertia of the wheel got bigger - the denser parts moved outwards - it became less "compact". This increased moment of inertia requires more torque to accelerate them up to speed - which in turn makes your car's acceleration (and braking) noticably worse....although it does LOOK pretty cool!

SteveBaker (talk) 13:46, 16 January 2009 (UTC)

Informally you can think of moment of inertia as a measure of rotational inertia, i.e. the tendency of an object to maintain its state of rotational motion. To accelerate a stationary (non-rotating) object to a given speed of rotation, you need to give it a certain amount of angular impulse. Say you applied a torque (turning force) $\tau$ for duration $t$. You can get the same result by using half the turning force (i.e. $\tau /2$) but you have to apply it for twice as long (i.e. $2t$). Or you can use double the turning force ($2\tau$) and apply it for half as long ($t/2$). There are many ways you can accelerate the object to the same speed of rotation, but the product of (turning force)×(time) remains the same. So the product of (turning force)×(time) provides a measure of the amount of “effort” expended in changing the rotational speed of an object. You can understand an object of large moment of inertia as one whose speed of rotation cannot be changed easily — you have to either apply a large turning force, or apply a turning force for a long time, or do both, to change its rotational speed. --98.114.146.183 (talk) 18:40, 17 January 2009 (UTC)

Which part of "I don't need a mathematical definition" didn't you understand?! SteveBaker (talk) 01:20, 19 January 2009 (UTC)

Blood spurts

To kill one of my chickens for dinner, I hang it upside down, hold its head, and make deep cuts (down to the bone) on both sides of its neck, just below the skull. I know I've done it right when I see rhythmic spurts of blood shoot out. In the butchering books I've read, they say this method cuts the jugular vein, which I happily accepted due to the phrase "go for the jugular", but it occurs to me that usually arteries, not veins, should do more spurting. The cuts are so deep that I'm certainly also cutting the carotid artery. Which vessel is likely to be the important one that drains the blood out? Thanks. --Sean 14:08, 16 January 2009 (UTC)

A tree stump and a sharp hatchet also gets the job done, severing all arteries and vessels, although the chicken is likely to run around flapping its wings for a minute or less. Your method seems to offer the possibility of greater suffering for the animal if done hesitantly or incompletely, but might drain the blood more completely. Edison (talk) 14:40, 16 January 2009 (UTC)

I've done it both ways, and much prefer the way I described. I always use an exquisitely sharp knife, and I've noticed in other contexts that being cut by a very sharp blade is not particularly painful. Wacking heads off is much more likely to go awry, in my experience. --Sean 15:11, 16 January 2009 (UTC)

I realize that this still does not answer your question, but by taking a thin blade and poking it through the chickens beak (as if it were being swallowed) angled up towards the brain is the way I've done it in the past. What I was told is that if you stick the knife into the brain, it's instant death for the bird and the least painful. Then you can cut the throat and have the blood run out like you have been doing. You'll still get the death rattle effect, so watch out for blood splashing about. Dismas|^(talk) 16:35, 16 January 2009 (UTC)

I do indeed do that, but I didn't want to cloud the discussion further. --Sean 18:07, 16 January 2009 (UTC)

I argue that it would be extremely painful to have a knife thrust through the roof of the mouth into the brain. Ever had sinus surgery or dental surgery? Edison (talk) 19:46, 16 January 2009 (UTC)

According to a report by Compassion in World Farming Trust, [8] " the time taken by a chicken to die varies enormously, depending on which blood vessels in the neck are cut... Research, however, shows that of all the neck cutting methods, the severing of both carotid arteries (these are the major blood supply to the brain) is the quickest method of inducing death (Gregory & Wotton, 1986). Cutting both carotid arteries (and both jugular veins) is vital if a rapid bleed out and quick death are to be achieved. Failure to cut both carotids can add two minutes to the time taken to reach brain failure (MRI, 1984)" Rockpocket 19:28, 17 January 2009 (UTC)

Thanks for the informative reply. Carotids, then! --Sean 13:23, 19 January 2009 (UTC)

Short tongue and snipping

Medical advice question removed.

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, 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 Reference Desk's talk page.

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 Reference Desk's talk page. --~~~~

Milkbreath, StuRat (talk) 16:39, 16 January 2009 (UTC)

My tongue is very short and from the looks of it, it seems there is a sort of attachment that is preventing it from stretching out too far from my mouth. I don't know what it's called but I know that some children have this snipped in order to help with speech. However, my adult friend also had the same problem, and when he went to get his tongue pierced, the tattoo shop gladly snipped it for him. He said there was a lot of blood but now he has healed and he can stick his tongue far out. What is this surgery called and are there any health benefits for adults to have this "snipped"?--Emyn ned (talk) 14:19, 16 January 2009 (UTC)

---

It sounds as though you are talking about a frenulum. Children with ankyloglossia have a frenulum that is too short and causes problems with speech (sometimes called being "tongue tied"). The procedure you are referring to is a lingual frenectomy but the reference desk is not meant for giving medical advice. The tongue is highly vascularized and is known to bleed profusely; if the person at the tattoo shop who "snipped" your friend's frenulum also "snipped" one of those juicy arteries, that would explain the bleeding. Please ask your doctor about it. --- Medical geneticist (talk) 14:35, 16 January 2009 (UTC)

I, personally, am not asking for medical advice. I am asking what are the benefits, if any, for adult lingual frenectomy? --Emyn ned (talk) 14:46, 16 January 2009 (UTC)

you mean besides the obvious one, right? —Preceding unsigned comment added by 82.124.85.178 (talk) 15:10, 16 January 2009 (UTC)

Please let me ask a few questions of Emyn ned. You're not personally asking for medical advice? How are you asking for it, then? Whose tongue are we talking about here, yours that you described in detail in your question, or no? Are we supposed to believe that it is mere coincidence that you suffer from the very medical condition whose surgical remedy you are only asking impersonally about? Are you considering having that surgery, and would what you discover here on the Wikipedia reference desk help you decide whether to have it or not? --Milkbreath (talk) 17:19, 16 January 2009 (UTC)

Ok, pretend I asked "what is the medical benefit of adults having their stomach stapled?" And pretend I didn't mentioned anything about having a obesity issue. Would you then be able to provide me with this info? I am looking for the general medical benefits of adults have such surgery, not for me. I tried searching the internet for any reputable sites stating the need for such. --Emyn ned (talk) 18:50, 16 January 2009 (UTC)

Thanks for the reply. Yes, such a question would be kosher. Nobody's trying to hurt anybody here. The rules here are for everybody's protection. You can read all about it here. Will you please answer my other questions, and, if you don't mind my asking, what prompted you to ask this question? --Milkbreath (talk) 19:07, 16 January 2009 (UTC)

Curiosity. Why else would anyone ask any question. I am asking what are the benefits, if any, for adult lingual frenectomy? Is this a normal procedure or is it done just for children? If it is done on adults, what would some of the reasons why MD would recommend this for an adult? Next time I ask a question, I'll be sure to remove any personal experiences. --Emyn ned (talk) 19:51, 16 January 2009 (UTC)

How many possible genetic variations or combinations from one couple ?

If you have a couple and each time they have a child it's a single, not a twin or triplet etc, how many children could they theortically have before they start haveing children with the same DNA as those already born ?

Sorry if this has been asked some where else

Scotius (talk) 15:33, 16 January 2009 (UTC)

The probability of this happening is so small that it would essentially never happen in the reproductive lifetime of a couple. I don't have time to crunch the math, but I doubt that such a thing is likely to have happened in the history of humanity (surely someone will challenge this!). Each time an egg or sperm is made, the chromosomes are shuffled and randomly segregated. Nearly infinite combinations are possible. See meiosis. --- Medical geneticist (talk) 15:41, 16 January 2009 (UTC)

According to Human genome, there are about 20,000-25,000 different genes (assuming we're only interested in the actual protein-coding ones). That means the probability of two siblings having the same genes from the same parent (assuming perfect Chromosomal crossover, which isn't quite the case, and taking the 20,000 figure) is $\left({\frac {1}{2}}\right)^{2\cdot 20000}\approx 10^{-12041}$, so that would require an infeasible number of children to get the probability up to anything that isn't essentially zero. The fact that the crossover isn't perfect may increase the chances, and if you don't distinguish between different copies of the same gene it will increase the probability quite a lot (a large portion of the genome is the same in everyone, I believe), but it will still be far below anything that could happen in one lifetime. Random mutations will decrease the probability even more, as well. --Tango (talk) 15:52, 16 January 2009 (UTC)

Strictly speaking you are overcounting. In a substantial number of cases, a parent will have the same alleles on both chromosomes so it doesn't matter which one the child receives. Also, a single genotype might be arrived at in more than one way from the parents. Removing redundancies will move your stupendously improbable number to a slightly larger, stupendously improbable number. Doesn't change the conclusion, though. Dragons flight (talk) 18:39, 16 January 2009 (UTC)

Also, both parents may in many cases have the same genes. Hence, to make a calculation possible, the similarity of the parents' genes would need to be known (I suppose inbreeding would increase the chance although I still suppose it's negligible). If a more general answer is expected, distributions are instead needed. —Preceding unsigned comment added by TERdON (talk • contribs) 02:15, 18 January 2009 (UTC)

I have read somewhere that each time a sperm or egg is made the process used, meiosis, means that there will ever be two sperm or two egg with the same DNA. I just liked to know, for knowing sake. I read somewhere that a human shares something 90 odd percent of their DNA with most (non related) humans. I'm not sure if I am remembering right or getting mixed up with that one with chimps, but I'm sure it's a high percentage thats shared. —Preceding unsigned comment added by Scotius (talk • contribs) 16:01, 16 January 2009 (UTC) Scotius (talk) 15:54, 16 January 2009 (UTC)

What do you mean by "the same DNA"? It's a confusing way to express it. DNA is just a molecule. Do you mean something more like like genetically identical? Really the question depends upon the probability of recombination at the same regions and segregation to the same gamete. Tyhen you need this to happen in both parents and for these two specific gametes to come together twice. So it'a w ahole series of improbable events, it's not just about producing identical gametes twice.

On the other hand, people produce genetically identical siblings all the time. They are called identical twins. Alun (talk) 16:08, 16 January 2009 (UTC)

All siblings share at least some of the same DNA. Sibs have a coeficient of reletedness of 0.5 don't they? So about half of their DNA is always the same. In fact the question makes no sense. The couple would only need to have two children, and those two would share (on average) as much DNA with each other as each does with either parent. If the question is "how many before they produce identical sibs", then I think the question is one of probability isn't it? I would imagine that even though recombination is not completely random, it would be close to impossible except from a theoretical point of view, depending upon how strict you want to be. I mean do you want "genomically identical" sibs, or "phenotypically identical" sibs? Most of our DNA doesn't code for any genes remember. But I think this is just a different way to express the Infinite monkey theorem. Alun (talk) 15:58, 16 January 2009 (UTC)

On average, half the DNA of siblings is the same, that's what the coefficient of relatedness tells us. We have an article, Human genetic variation, which people may want to read. Basically, two unrelated people are expected to share about 99.9% of their genes (well, actually I think that's base pairs, genes is going to be a little different). I think siblings would be expected to share about 99.95% of their base pairs. --Tango (talk) 16:14, 16 January 2009 (UTC)

Yes, it's a confusing question. The question was "how many children could they theortically have before they start haveing children with the same DNA?". My answer was two, because you only need two sibs for them to share the same DNA. Obviously they are not genetically identical, but they still share the same DNA. That's because all humans share the same DNA, as you point out about ~99.9% of SNPs are shared between all humans. Alun (talk) 16:26, 16 January 2009 (UTC)

To have two children with exactly identical DNA (every base pair is identical) would be almost impossible due to random mutations and the sheer number of pairs. However, I think that have two phenotypically identical children (exactly the same traits) that are not twins is possible, but still incredibly unlikely. There's still too much information for it to really happen. Plus I don't think current technology would be able to test either scenario (because even though it looks like they have all the same phenotypes, you'd have to check every one) so I guess we'll never know. Which raises the question 'how do we know that identical twins are really identical?' Maybe the traits we can't see are different. -Pete5x5 (talk) 19:12, 16 January 2009 (UTC)

I think the question is asking for this: the genes in a human cell are grouped into 46 chromosomes in 23 pairs. The mother's egg cells (ova) and the father's sperm cells each receive one chromosome randomly from each pair. The cells that unite to ultimately form the child represent 46 of these random two-way "choices" and therefore there are 2^46 = 70,368,744,177,664 possible combinations -- much greater than the total number of people who have ever lived.

However, this is a simplified picture! First, a mutation is always possible. Second, during meiosis when the sperm and egg cells are formed, sometimes a chromosomal crossover occurs. Say that in the mother, chromosome pair #1 includes versions A and B. Then usually her egg cells will include either A or B. But in case of a crossover, an egg cell might be formed with the first 3/8 of A and the last 5/8 of B. Since there are many points on each chromosome where a crossover or mutation might occur without the result being fatal to the child, the true answer is many, many times higher than 2^46.

--Anonymous, 21:02 UTC, January 16, 2009.

As Anonymous notes, even given the astromonical number one can calculate based on the assortment of alleles from each parents, each person has the own set of unique de novo mutations that occur in the germ line. Its not known for sure, on average, how many novel mutations each individuals has, but to keep things simple lets just say there are 10. Therefore, on top of the number above (is that 70 trillion?): what are the chances that the same 10 base pairs would be mutated in two people, out of 3 billion? My maths isn't good enough to represent that number. Rockpocket 19:07, 17 January 2009 (UTC)

Storage capacity of the human brain ?

Does the human brain have a limit on how much can be stored and how many 'operations per second' like with computers ?

Sorry if this has been asked and answered somewhere else

Scotius (talk) 15:49, 16 January 2009 (UTC)

There will be a limit, but no-one really knows what it is. Physics puts an upper bound on it (you can't store more information than there are atoms, for example), but that's about it. It's probably meaningless to talk about operations per second for the brain, it just doesn't work like that (I'm not sure how it does work, though, and I doubt anyone else is!). This has been discussed on this ref desk before - try searching in the box at the top. --Tango (talk) 15:55, 16 January 2009 (UTC)

Strictly speaking, the physical limit is more like the number of possible arrangements of the atoms, which is a much larger number than the number of atoms. Though I suspect one can make practical arguments that the real answer is no where near that large. Dragons flight (talk) 18:31, 16 January 2009 (UTC)

Okaydoke, thanks Scotius (talk) 16:04, 16 January 2009 (UTC)

There are many articles on the subject on the internet, as revealed by this Google search. However, it's up to you to sift through the crap and find a well referenced, peer-reviewed article. I'm not even sure they'll be one beyond speculation. —Cyclonenim (talk · contribs · email) 17:40, 16 January 2009 (UTC)

Sifting through the crap isn't hard, just use Google Scholar. Now you just have to find something there that actually deals with this question. Algebraist 17:58, 16 January 2009 (UTC)

The brain is not a digital computer, although in the 1960's cognitive psychologists published thousands of papers comparing it to one. The comparison might be like asking noting that both a camera and Johannes Vermeer created images based on scenes, then asking what the artist's film speed, shutter speed, lens opening and focal length were. Edison (talk) 17:56, 16 January 2009 (UTC)

The brains' capacity could certainly be estimated - but it's going to come out to be a much smaller number than we might expect. The tricky part is that when we think of computers, we have a system that stores data PRECISELY - no matter how old the data is - a movie you stored will be precise down to the pixel. With the brain, the data is simplified - reduced to it's essentials. You may remember seeing a friend over the weekend - and you MIGHT even recall what they were wearing - you certainly don't remember every exact wrinkle in the clothing at the instant the person stepped into your front door. You have the impression that you remember the event like it was a movie - but you don't. Furthermore, in a month from now, you MIGHT recall that your friend showed up - but you'll probably have no memory about what they wore. In ten years time you'll have a general feeling that your friend would occasionally show up some weekends. In fifty years you'll remember you had that friend and their name escapes you. The core memory is there - it's just getting fuzzier and less exact. With a computer, it's all or nothing. It would be possible to have a computer memorize things like people do - automatically blurring the data when more memory is needed...but one of the reasons we like computers it that very precision that we lack. Wikipedia works precisely BECAUSE it doesn't work like a brain does - and that's what makes it so helpful. SteveBaker (talk) 23:52, 16 January 2009 (UTC)

"Operations per second" depends on what you're measuring. If it's conscious math (eg. "What do you get when you multiply six by nine?"), the human brain can normally do one or two operations per second. If it's applied math (eg. catching a thrown ball), the brain is better modeled as an analog computer, which can't be measured in those terms. --Carnildo (talk) 00:57, 17 January 2009 (UTC)

It's a common myth that information theory can't be applied to analog systems - but that's really not true. Any real-world analog system has finite bandwidth and there must be limits to the size of signal it can handle - and some degree of imprecision or noise in the analog 'signal' as it passes between parts of the system. That, ultimately, necessarily limits the amount of "information" that even an utterly analog system can process or store - when you know how much that is - you can convert that number to bits and produce an entirely valid comparison between the capabilities of an analog and a digital system. It's a little tougher to crunch the math because most analog systems have worse signal precision at higher frequencies - but you can do it. Once you know how many bits that is - you can build a digital system with the same capacities and if it's done right, it'll be (theoretically) capable of the same performance. I don't know enough biology to say what that number is for the human brain - but it most certainly CAN be computed. SteveBaker (talk) 04:09, 17 January 2009 (UTC)

The number of operations per second is certainly not larger than the number of synapses (between 10¹⁴ and 10¹⁵) times the maximal firing frequency of neurons in Hz (maybe 250, see refractory period (physiology)). The memory (in bits) is certainly no larger than the upper limit for the number of synapses times the base-2 logarithm of a reasonable number of relevant synapse states (one million? I don't know). Icek (talk) 01:11, 17 January 2009 (UTC)

These parameters are pretty irrelevant to the number of "operations per second." In tests, simple reaction time is around 100 msec and choice reaction time is around 300 msec. So perhaps 10 operations per second is an upper and generous bound. Short term memory can hold 7 or fewer items. Long term memory is vast. Edison (talk) 04:56, 17 January 2009 (UTC)

Reaction time is an input-to-output process. There is no reason to think that it necessarily bears of the number of operations being performed in the brain. It is also a rather poorly defined concept. Computer processors have well-defined elementary operations. One can sensible ask how many elementary operations are required for a computer to display a sentence on a screen (hint: it is much greater than 1 even though it is a single output event). But one would have a much harder time asking how many operations the brain performs when it constructs and speaks a sentence. Given the difficulty of constructing natural language software, I strongly believe that if one did try to map the brains activity in holding a conversation onto a set of elementary computer operations, the number of operations per second would be enormous. Dragons flight (talk) 05:13, 17 January 2009 (UTC)

What complicates this is that the brain is a massively parallel machine - where most computers are not. Those 10¹⁴ synapses can (in principle) all fire or not fire in parallel. Even if they can only fire 250 times a second - that's 2.5x10¹⁶ operations per second. Compared to a typical high end PC (quad core, 3.8GHz) - which can do four things in parallel in each clock tick - you only have 1.6x10¹⁰ operations per second. So on that VERY rough estimation, the brain has an edge over a state-of-the-art machine - but only by a factor or around 10,000! There are computers (such as the 'Roadrunner' at LosAlamos) capable of over a petaflop/sec (a 'flop' is a floating point operation). So 'Roadrunner' is capable of 10¹⁵ non-trivial operations per second - so maybe 5% of a single human brain!

SteveBaker (talk) 05:36, 17 January 2009 (UTC)

This hardly seems a sensible comparison. A "floating point operation" means something like a 64x64 bit multiplication computed with an accuracy of 0.5 ulp, that is, an error of less than one part in 10¹⁵. It takes a lot of transistors to make that happen, and it would take a lot of neurons too if we could do it at all, which of course we can't, except using our ridiculously slow and linear general reasoning capabilities. The brain is massively parallel at the synapse level but pretty linear at a higher level. Microprocessors are massively parallel at the transistor level too, and with more than 10⁸ transistors switching more than 10⁹ times per second, they would seem to beat out the human brain in raw switching ability. Not that that's a sensible comparison either. Also, a minor point, but the cores in your quad-core CPU are superscalar. They don't execute one instruction per cycle. -- BenRG (talk) 12:57, 17 January 2009 (UTC)

Also keep in mind that it seems that our brains are much "better" at certain tasks than a general computer. Just like a single inexpensive embedded video chip can decode a high-def movie that would churn a microprocessor, our brains are "hard wired" to very efficiently recognize faces (our brains are phenomenally good at pattern recognition), synthesize coherent speech from general ideas, and coordinate muscles. I don't know a whole lot about brain neurology but IIRC the whole brain is an "embedded system", with every neuron dedicated to a particular task. We have sensory processing neurons that are tied to consciousness-loop-neurons which are tied to a web of linked symbol-groups of neurons. Yes, it's possible for all the amazing things that we can do to be a product of a simple but large neural network. It's also clear that it's possible for consciousness to arise from an artificial processing construct, and it's particularly self-evident that consciousness as we know it identifies closely with the associative nature of the neural net. Also just because we can't do 64 bit floating point operations in our head doesn't make us stupid; our brains aren't good at that kind of thing because we haven't needed to do that kind of thing.. and now that we do, we can abstract it out and invent a machine to do it for us! While the particular algorithms used by machines and AIs are powerful and exact, abstract and stochastic thinking is actually far more powerful in that it allows high level phenomena like creativity and innovation. While a computer may be able to draw a high-resolution photorealistic landscape out of 3D vector graphics resources and update it 150 times a second, no computer today could invent itself. Not that we could invent ourselves σ_ο .froth. (talk) 18:06, 23 January 2009 (UTC)

Perception of one colour being "brighter" / "darker" than another

I'm colour deficient / colour-blind, but to me certain colours obviously appear "brighter" to me than others, but I worry that this is not the case for other people.

Yellow for example is one of the most bright colours, but not as bright as white.

Orange is darker than Yellow but brighter than red.

Red is about as dark as blue or green.

Has this been quantified in any way? Perhaps we have an article of colours organised by perceptual brightness?

As a side-note, in some software I wrote I used these colours to show priority of jobs, and I'm hoping that the colours had as much meaning to me as they did to the users!!

Rfwoolf (talk) 17:07, 16 January 2009 (UTC)

Just before hunting for more, I do know that some colours are indeed brighter than others and yellow is the brightest, although not as bright as white. Steve is the guy to wax forth on the subject, but I'll see if I can dig up some links while you wait... 79.66.46.92 (talk) 17:10, 16 January 2009 (UTC)

Eeeeee! Check this out! Luminosity function! !! And as a little background, you might want to read the colour vision article, or at least study the second picture in it. 79.66.46.92 (talk) 17:15, 16 January 2009 (UTC)

You may want to specifically look at luminance and chromaticity articles. In brief, for the people with full color vision, under not-too-dim light conditions, there is a percept of "brightness" (luminance) and an independent "two-dimensional" percept of "color" (chromaticity: think of one dimension as red vs. green and the other one as blue vs. yellow, although that is not strictly correct). Human retina, thalamus, and visual cortex are wired in such a way that our luminance percept is dominated by the responses of long-wavelength and medium-wavelength cone receptors, but not short-wavelength cone receptors; thus blue is inherently perceived as a "darker" color than red or yellow. However, you can make a brighter blue and a darker yellow to look equally bright. if you look up any two-dimensional isoluminant color chart, all colors on the chart (blue, yellow, red, green, and everything in between, including gray) should look to a human with normal color vision as having the same luminance ("brightness"). Not so for the people lacking one or two types of cone receptors in the retina: for those people different parts of an isoluminant color chart may look as having different brightness AFAIK. Hope this helps. --Dr Dima (talk) 21:12, 16 January 2009 (UTC)

The order of brightnesses that you describe are pretty much the same for people with normal color vision. What's bothersome is that the explanations for why that is revolve around being able to see color! Yellow is a mixture of red and green - so it stimulates two sets of color receptors ("cone cells") as well as the "rod cells" that see only intensity. Red, on the other hand, stimulates only the red receptors and the rod cells. So less cells are stimulated - and red looks darker than yellow. Since the red and geen receptors are each more sensitive than the blue receptors - it makes sense that yellow looks brighter than cyan or magenta. But if your cone cells don't work - I don't understand why yellow would seem brighter. That's weird. Which of the (many) varieties of color blindness do you have? SteveBaker (talk) 23:33, 16 January 2009 (UTC)

• It is not correct that "yellow is a mixture of red and green". What you mean is that the human eye cannot distinguish yellow from a mixture of red and green, because either one stimulates the cone cells the same way. --Anonymous, 05:24 UTC, January 20/09.

Another article you may want to take a look at is Munsell color system. It's been quite a while since I've studied these matters, but I think that your (along with non-color-deficient folks') perceptions of the brightness and darkness of colors involve a combination of Munsell's "value" and "chroma." Look, for example, under "Hue," at the table of different hues ("colors") at the same value and chroma. Do they all seem pretty much equally bright to you? They do to me. Deor (talk) 02:29, 17 January 2009 (UTC)

Steve: Not sure exactly, but I've done the online and offline tests where they show a serious of images where a number can be conceived in a circle of dots - after a few images I can no longer see the numbers. On a roulette table I often confuse the green chips with the orange chips. With coloured pencils at school, light green would look yellow unless I could see yellow next to it. Brown and red were sometimes confused but that hasn't really happened for a long time.

Dr Duma: Indeed those colours do seem "equally bright" to me. Rfwoolf (talk) 01:00, 18 January 2009 (UTC)

The point is this: Most forms of color blindness (such as, for example, the kind my son has) only affect one of the color receptors - and much of the time they only weaken that receptor. The form of color blindness in which no color is seen AT ALL is quite rare. There being three color receptors, Red, Green and Blue, you might have:

• Weak red
• Weak green
• Weak blue
• No red at all
• No green at all
• No blue at all
• Weak red AND weak green
• Weak red AND weak blue

...and so on...

• No red AND No green AND No blue (ie totally color blind).

The tests you took with the circles containing colored dots are quite enough to tell you which of the MANY combinations you have. But if it turns out that (like my son) you have just one weak sensor - then your color vision may be pretty good - except that you can't pass the colorblindness test because that's specifically designed to ferret out that precise situation. What you're describing sounds like your blue sensor is working OK but that either red or green (or both) aren't working correctly. The difference between green and yellow or green and orange is the amount of red - and the difference between brown and red is the amount of green but also the amount of orange - so I'd tentatively suggest your problem is with the red sensor. But this is straying dangerously from "explaining what's going on" into the realm of "Diagnosing a medical condition" - which we're not allowed to do here on Wikipedia reference desks. Our articles on color blindness DO explain this stuff in quite a bit of detail. I strongly recommend re-doing the tests (online or with a professional) - and this time pay careful attention to the precise diagnosis. This (combined with our article) will tell you precisely which sensor or sensors are misbehaving - and that should be useful to you in the future - both in ensuring you know your limitations - but also that you can be confident where there are NO limitations. My son only found out he had a problem (he is "weak green") because he couldn't tell the color of the LED on the front of his Wii game machine which is red when the thing is turned off and orange when it's in standby. He was always leaving it in standby instead of turning it off - when I'd nagged him about this several dozen times - we figured it out. But he can actually see ALL colors differently - but the difference between red and orange (which is just a small amount of green) isn't enough for him to tell the difference. He also has trouble with shades of pale blue/greens - but that's a common matter with men in general - so no big deal there. We found that a small piece of green-tinted plastic held over the LED on the Wii was enough to enable him to tell the difference - and he sometimes uses a piece of green plastic to distinguish other colors he's not sure of. Something like that could possibly help you too.

However - in DIRECT answer to your original question, the fact that you can see differences in brightness that match what "normally sighted" people can see suggests that you ARE seeing some colors correctly - and that explains my surprise in my earlier response. SteveBaker (talk) 01:17, 19 January 2009 (UTC)

Organ barter

Donating in life a kidney to a loved one is a no-brainer for me. I suppose many other people are in the same situation. On the other hand, I won't consider donating my kidney in life to a unknown person. In the case I am not compatible with my loved one, could I perhaps exchange my kidney with other people that could donate to a family member of mine? What if, a more complex scenario exits? Like A donates to B that donates to C that donates to A? --80.58.205.37 (talk) 18:32, 16 January 2009 (UTC)

See Organ transplant#Paired-exchange. Such transactions are uncommon, but not unheard of. Dragons flight (talk) 18:44, 16 January 2009 (UTC)

(edit conflict)Sure you could, if you just agreed on it with the other people involved. Under those circumstances -- where both you and the other potential donors were willing to donate organs to a loved one, but were incompatible -- they'd probably be happy to agree to an exchange. After all, the end result is pretty much the same: they go under the knife, and their loved one gets what they need. Where's the problem? There would be nothing illegal about that; anyone can donate a kidney to anyone they like, even a complete stranger. That's certainly happened before, though it's not exactly common. (Selling organs is a different story, though -- that's illegal in most countries. Technically, this would be a trade, of course, but I doubt anyone would have a problem with that, since clearly no one is trying to profit from the exchange.)

Of course, the practicalities involved could well be overwhelming: it probably wouldn't so much be a question of willingness, but rather one of timing and circumstances. There are some organizations that might be of help in a situation like this, though. -- Captain Disdain (talk) 18:51, 16 January 2009 (UTC)

The OP's example of a kidney transplant is a good one - getting a new kidney often isn't as urgent as other transplants since people can survive for years on dialysis in many cases, so you can wait for a suitable sharing arrangement to become available. --Tango (talk) 21:21, 16 January 2009 (UTC)

Private health care in the US

Why is private health care in the US much more expensive than in other developed countries? --Mr.K. (talk) 18:48, 16 January 2009 (UTC)

maybe the fact that the United States is the greatest country on Earth (as even Noam Chomsky admits) has something to do with it... 82.124.85.178 (talk) 19:00, 16 January 2009 (UTC)

That's an extremely poor explaination Nil Einne (talk) 19:01, 16 January 2009 (UTC)

I also have an explanation involving "what the market wants", if you'd prefer it. —Preceding unsigned comment added by 82.124.85.178 (talk • contribs)

Most payers for health care in the U.S. do not pay the "list price" which appears on doctor and hospital bills. The government only pays much lower rates, and insurance companies also knock the price down to half or less in many cases. It is only the person who lacks insurance but does not qualify for the government to pay who is stuck with the full price. Edison (talk) 19:42, 16 January 2009 (UTC)

It's because the United States is the only developed country in the world that doesn't have a universal health care system. See Health care in the United States. ~AH1^(TCU) 22:57, 16 January 2009 (UTC)

... but does have heavy subsidies and other political distortions of the market. —Tamfang (talk) 07:16, 18 January 2009 (UTC)

Neither of those explainations really explain why in any satisfactory way. If you say it's because the US is the greatest country, then why does the greatest country have a much more expensive cost of health care. If you say it's because it's what the market wants, why does the market want a high cost in the US but not elsewhere? You could apply those answers to many situations and they would be equally unsatisfactory. For example, why is the US one of the only developed countries that tortures people suspect of a crime? Because it's the greatest country. Why has the US economy collapsed? Because it's what the market wants. Nil Einne (talk) 08:11, 17 January 2009 (UTC)

If people don't have to pay the full cost of their health-care, they'll tend to get more expensive care than they need. I've read that HMOs were started to combat this. — DanielLC 00:13, 17 January 2009 (UTC)

Yes, darned those people who want to get cured of their illnesses. If they only just accepted their fates, and didn't demand to actually get better, we wouldn't have to have such expensive care... --Jayron32.talk.contribs 00:34, 17 January 2009 (UTC)

It's not as if there's a certain amount of necessary health care. You can, for example, do an arbitrary number of expensive tests for diseases that the patient is arbitrarily unlikely to have. That head-ache they've been having could be cancer, and they could get a cat-scan to check. The doctor, who gets payed for medical procedures, and not for the patient's health, has every reason to try to convince them to take expensive tests, and the patient has no reason to disagree with the doctor. — DanielLC 17:07, 17 January 2009 (UTC)

There are many reasons why health care is so expensive in the US. Here are a few:

1) Doctors are paid more than most other countries. Nurses and others are too, but to a lesser extent.

2) Lack of preventative care. Frequently only emergency care is available to those without health insurance, meaning they wait until the condition is far more expensive to fix, and, in the case of infectious diseases, until after they've spread them to many others.

3) Pharmaceutical companies are able to control Congress through lobbyists to prevent imports of cheaper alternative meds.

4) Lack of central planning means that you may have two hospitals next to each other with the same equipment, while neither has some other item of equipment and people must drive many miles for that. This inefficiency costs money.

5) Administrative costs are very high, due to all the competing private and government insurance programs. Hospitals need many employees to sort out all the associated paperwork. StuRat (talk) 06:45, 17 January 2009 (UTC)

You missed one that doctors cite as a major cause: The cost of malpractice insurance. Because the US legal system is prepared to award truly crazy amounts of money for things that are simple accidents or even bad luck (neither of which are "malpractice" per-se) - doctors have a need to purchase insurance against those kinds of claims. Both doctors and hospitals have to carry this insurance on behalf of Nurses and other ancilliary staff - so nobody is left 'exposed'. That insurance is horrifyingly expensive. SteveBaker (talk) 17:37, 17 January 2009 (UTC)

why does gas burn blue?

why does gas (from a stove etc) burn blue? when something spills on it and it burns orange briefly is it because its temperature is now lower or because it's not burning the same way/as purely/etc

(already tried asking google)

82.124.85.178 (talk) 18:53, 16 January 2009 (UTC)

Incomplete oxidation leaves unused hydrocarbons, resulting in orange flame. A well-regulated gas flame should be blue. - Nunh-huh 18:58, 16 January 2009 (UTC)

yes, but WHY blue? is it because the temperature natural gas burns at is a "blue" temperature (so that if you heated a rock to the same temperature, it would glow blue-hot)? 82.124.85.178 (talk) 19:02, 16 January 2009 (UTC)

I believe this [9] (from [10]) is mostly correct Nil Einne (talk) 19:05, 16 January 2009 (UTC)

The flame color section of our article on flame also addresses this. -- Captain Disdain (talk) 19:07, 16 January 2009 (UTC)

I'm sorry, could you dumb it down for me? Is it temperature, or the biproduct of a particular chemical reaction, such as a bang might be a byproduct, or what —Preceding unsigned comment added by 82.124.85.178 (talk) 23:27, 16 January 2009 (UTC)

In simple terms, when you burn anything, along with the heat energy and other forms, you get a lot of light given off. Depending on what is burning, you get different wavelengths of light given off, which are responsible for different colours. —Cyclonenim (talk · contribs · email) 23:41, 16 January 2009 (UTC)

I think the OP knows that, the question is what causes the different colours. Is it due to different temperatures (ie. black body radiation) or different chemical reactions? I think the answer is a bit of both. --Tango (talk) 23:49, 16 January 2009 (UTC)

That's right, I'm where you put me. 82.124.85.178 (talk) 00:40, 17 January 2009 (UTC)

It's simple blackbody radiation. Incomplete combustion produces a low-temperature orange flame; complete combustion produces a high-temperature blue flame. --Carnildo (talk) 01:02, 17 January 2009 (UTC)

so if the blue flame were rising through an even hotter something (being heated further as it rose, by convection-not chemically), it would turn from blue-hot to white-hot? Conversely, if it were rising through something very cold (after burning) it would go from blue-hot to mere red (or orange)-hot? Thanks! —Preceding unsigned comment added by 82.124.85.178 (talk) 01:08, 17 January 2009 (UTC)

Isn't blue-hot is hotter than white-hot? The even hotter something would already be glowing whatever colour it is, and brighter than the flame, so you probably wouldn't see the flame. Also, not being hotter than the surrounding air, it wouldn't rise, so the flame probably couldn't even form. The other way round (the flame cooling) could work, though, I think. Usually the hot particles dissipate before they can cool down that much, but in a really cold environment the tip of the flame might end up a different colour, I'm not sure... (it would have to really cold, possibly cold enough that the oxygen would condense and the flame couldn't form). --Tango (talk) 01:16, 17 January 2009 (UTC)

I think you're not using your imagination if you think that you couldn't see the flame because it was being heated by something hotter, which would itself glow too brightly. I mean just imagine a lot of holes to see the flame through, and between you and the material a mask that only shows the holes. —Preceding unsigned comment added by 82.124.85.178 (talk) 12:59, 17 January 2009 (UTC)

Are you sure about that? Our article seems to suggest you're wrong "on the right a lean fully oxygen premixed flame produces no soot and the flame color is produced by molecular radicals, especially CH and C2 band emission." Admitedly this is butane not LPG but I would presume the same reasons likely apply. Also wouldn't blue be something like 6000K? Does a stove flame realy become that hot (n.b. the image File:Wiens law.svg is highly misleading, the colours shown don't correspond with the wavelengths, I haven't yet corrected the articles hoping someone will fix it) Nil Einne (talk) 12:13, 17 January 2009 (UTC)

I think you have point there - if you hold a piece of metal (insulated, of course) in the flame of a bunsen burner (with a blue flame), it glows red hot, not blue hot. --Tango (talk) 16:29, 17 January 2009 (UTC)

Another factor, besides flame temperature, is the spectral line phenomenon. Each atom absorbs and emits certain frequencies of light, which in turn have certain colors associated with them. This has to do with the electron shells. Any time an electron jumps between shells it absorbs or gives off a specific frequency of light, due to the energy level change. The total of all of these possible jumps gives a characteristic color for each chemical element. StuRat (talk) 06:34, 17 January 2009 (UTC)

Yes, and this property of elements is used in the flame test. --Bowlhover (talk) 03:01, 18 January 2009 (UTC)

Correct me if I'm wrong, but I don't think blackbody radiation can make something "blue hot". First it heats to where it emits red light, and it appears red, then it heats to where it emits red and green light, and it appears yellow, then it heats to where it emits red green and blue light, and it appears white. — DanielLC 21:21, 18 January 2009 (UTC)

Well, yes, but then it gets hotter than that and the peak of its radiation is somewhere at or past ultraviolet, which means that the part of its spectrum in the visible range is much higher in blue wavelengths than anything else. Hence blue giant stars. Confusing Manifestation(Say hi!) 22:18, 18 January 2009 (UTC)

January 17

Will Uranus and Jupiter eventually lose it's rings?

Will Uranus and Jupiter eventually lose it's rings, since Jupiter and Urnaus rigns is made of charcoal, and it's even too dark to be seen by spacecraft (almost black). Saturn's rings has also been slowly eroding and getting browner, and eventually Saturn's rings will disappear.--69.111.37.66 (talk) 01:35, 17 January 2009 (UTC)

If the rings are unable to be seen by spacecraft, how do we know they are there? And I don't know of any significant observed colour change or erosion of Saturn's rings. I think you need to check the reliability of wherever you got this information. As for the stability of ring systems - according to Planetary ring#Overview: "Most rings are thought to be unstable and to dissipate over the course of tens or hundreds of millions of years, but it appears that Saturn's rings might be quite old, dating to the early days of the Solar system." --Tango (talk) 02:03, 17 January 2009 (UTC)

Wouldn't the rings eventually get pulled into the planet? 96.242.34.226 (talk) 02:05, 17 January 2009 (UTC)

They're just as likely to be perturbed away from the planet, or get pulled into one of the shepherd moons. It's a little unclear why Saturn's rings are so stable, but it presumably has something to do with the shepherd moons. --Tango (talk) 02:39, 17 January 2009 (UTC)

The rings are not easily seen - but they were detected by the fact that they occluded the planet's own disk in some kind of characteristic manner. I believe Voyager observed Uranus's rings by observing the occlusion of a distant star by the ring system. SteveBaker (talk) 03:54, 17 January 2009 (UTC)

When spacecrafts take pictures they use black-and-white images with purple, orange, and brown lights on the back. To you, when you orbit around Jupiter and Uranus' rings, they look nearly black, but that have nothing to do with this OP. My question is would Uranus and Jupiter eventually lose it's rings? THe article Tango linked me said most planet's rings will deprecate over time, and Earth could have rings a loong time ago. It is not only because planet eats it, meteorites comes any time, and wipe fragments out.--69.111.37.66 (talk) 04:00, 17 January 2009 (UTC)

Well Rings of Jupiter says that the material from the Jovian ring system is continually falling into the planet - and is replenished by meteor impacts onto various moons and moonlets. I suppose that means that they are going away - eventually the moons will be eroded to nothing - then no more source of dust and sometime later, no more ring system. Rings of Uranus says that Uranus's rings are relatively recent - and it also remarks that their formation mechanism is similar to the Jovian rings - so one presumes they'll suffer the same fate. The article says that without replenishment, the rings might only last 100 to 1000 years! Also, it mentions that if there we have not detected any 'shepherd moons' adjacent to some of the rings - and that they would be expected to dissipate for that reason if no such moons are there. I don't think the color of the rings matters in this regard...although in the case of Saturns rings (which are made of ice - not dust) - I suppose a darkening of them might cause them to absorb more sunlight and get a little warmer - which I suppose might in turn cause some evaporation from the ice...but that's a long shot. I strongly recommend that you read the two articles I've linked to because there is a lot of information in there - too much to convey conveniently in a Ref Desk post. SteveBaker (talk) 05:15, 17 January 2009 (UTC)

Steve, the part where you said the moons may erode to nothing may very well take far longer than the projected life of the solar system. Since we are maybe halfway through that life now, waiting for the Sun to go nova die, I'd expect the moons to last until then. StuRat (talk) 06:24, 17 January 2009 (UTC)

Our sun will not "go nova". For a start, you probably mean supernova, not nova, and secondly, the sun is nowhere near big enough. It will turn into a red giant and then collapse into a white dwarf, nothing particularly dramatic - it certainly won't do anything to the moons of outer planets. --Tango (talk) 16:07, 17 January 2009 (UTC)

Why would I mean "supernova" ? That requires even more mass. StuRat (talk) 17:12, 17 January 2009 (UTC)

Because a nova can only happen in a binary system, and we don't live in a binary system. A supernova is not just a big nova, it's a completely different thing (well, 3 completely different things, actually) - read the articles. --Tango (talk) 17:20, 17 January 2009 (UTC)

OK, but does this mean that the outer planets (and their moons) will last forever ? Or will they end up sucked into the giant black hole in the center of the galaxy or be destroyed in some other way ? StuRat (talk) 05:32, 20 January 2009 (UTC)

If you wait long enough, something will happen to them, although it's not clear what. They could very slowly spiral into and crash into the white dwarf that is left of the Sun due to the radiation of gravity waves, they could be perturbed out of their orbits by a passing star, their protons could decay, they could be ripped apart by the ever accelerating expansion of the universe, they could end up falling into a passing black hole, etc., etc. See Ultimate fate of the universe and the pages linked to from there for details of the possibilities. --Tango (talk) 16:27, 20 January 2009 (UTC)

Do we lack an article for the Ultimate fate of our solar system ? StuRat (talk) 20:51, 20 January 2009 (UTC)

Not a single article, but Red giant discusses the death of the Sun, and the various fate of the universe articles give an idea of what might happen after that. --Tango (talk) 22:25, 20 January 2009 (UTC)

There's a huge amount of time between the two, though, especially if we are talking about proton decay as the end of the universe. Won't something else destroy the solar system on that time scale ? What about our Milky Way galaxy, won't it eventually be destroyed prior to the death of the universe, due to collisions with other galaxies and/or the black hole at the center, and won't that take our solar system with it ? StuRat (talk) 14:58, 21 January 2009 (UTC)

Collisions between galaxies rarely have any effect on individual stars - galaxies are mostly empty space, they pass straight through each other (gravity and tidal forces distort them and slow them down so they eventually merge, but the individual stars just carry on as they were). Apart from radiating gravity waves (which is an extremely slow process) there is nothing to cause stars orbiting a black hole at a safe distance to fall into it. Once the Sun dies, the solar system will just sit here slowly cooling down for billions of years undisturbed (passing stars may perturb a few comets out of the Oort cloud towards the inner solar system every now and again and we may get irradiated by nearby supernovae, but that's about it). Wait long enough and random interactions and perturbations and whatever else will eventually result in everything ending up in black holes, but you're talking trillions of years for that, I think... we have a timeline somewhere... Here it is: Future of an expanding universe#Timeline --Tango (talk) 23:19, 21 January 2009 (UTC)

Thanks for the answer, but I disagree that collisions of galaxies rarely have an effect on individual stars. The stars are pulled out of their orbits by gravity and strewn all about, as shown on this page: [11]. I'm not sure what would happen to the planets associated with such stars, they might be thrown out of their stellar orbits, too. StuRat (talk) 04:08, 22 January 2009 (UTC)

Sure, the arrangement of stars is affected, but nothing happens to the star itself. Planets are very tightly bound to their stars, another star would have to pass very close to cause any significant change in planetary orbits (which will happen if you wait long enough, but you're talking on the scale of quadrillions (1000s of trillions) of years according to the timeline I linked to). --Tango (talk) 15:54, 22 January 2009 (UTC)

The Earth is believed to have had a ring formed of debris from a massive collision which coalesced into the moon over the course of a few hundred or thousand years. See giant impact hypothesis. --Tango (talk) 16:07, 17 January 2009 (UTC)

Darvocet (Propoxyphene) Overdose Dosage

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. --Jayron32.talk.contribs 01:52, 17 January 2009 (UTC)

--Jayron32.talk.contribs 01:52, 17 January 2009 (UTC)

Jayron, I have not asked for a prognosis. I have asked for a fact. Propoxyphene has a toxic dosage, and I have asked what that dosage is based on weight and gender. I am not asking for advice or counsel. I need not a qualified professional to answer a simple question.

The fact you asked for can only be given by a qualified medical professional. If you have a question about the correct dosage of a drug to take, consult a doctor, not random strangers on teh intertubez... --Jayron32.talk.contribs 02:09, 17 January 2009 (UTC)

Considering the nature of my question, consulting a doctor would be... undesirable. Once again, Wikipedia proves itself to be full of cancer. If I thought it was important enough to find a doctor to talk about this, I would have done just that. I'm asking for a simple answer to a simple question. I could be mistaken, but I believe general toxicity dosages are available for other substances. Whatever, though. I'm not going to piss around with this with you. Hopefully it won't matter tomorrow. 71.115.157.126 (talk) 02:30, 17 January 2009 (UTC)

{{Suicide response}}

Well, if asking a doctor becomes undesirable, then that implies that the drug has not been duly prescribed by a doctor. This is quickly becoming a legal issue. We don't give that sort of advice either. --Jayron32.talk.contribs 02:36, 17 January 2009 (UTC)

If you believe someone may have taken an overdose, they need to see a doctor. They can do so completely confidentially, they don't even have to give a name, but they do need to seek medical advice immeadiately even if there's only a small chance they have overdosed. The toxicity dosages you can find online won't help you since they won't take into account the patient's medical history and any other medication they may be on, only a doctor can give you accurate numbers. --Tango (talk) 02:44, 17 January 2009 (UTC)

• Since it was deleted I'm not sure how exactly the question was phrased, but it sounds like people are getting paranoid again. Not every question is a medical or legal advice. If someone wanted to take an overdose, all they'd have to do is take too much. This person asked for the exact documented dose which simply means digging in the literature and finding an LD50 value. - Mgm|^(talk) 11:53, 17 January 2009 (UTC)

Although I think suicide prevention would be an important thing. While we can't give medical advice, we have gone above and beyond on things like dating advice,a and I think it's important to mention that there are many positive thigns that life has to offer. the person may need to make a total change of his or her life, but it can be done. As a lot resort, I will add this, as odd and out of place as it may seem. But, Jesus Christ loves you, and has made grat changes in my life. he can in yours too, 71.115. Please choose to live.209.244.30.221 (talk) 14:00, 17 January 2009 (UTC)

My first thought was that it sounded like a request for advice on suicide, but the "Hopefully it won't matter tomorrow." comment suggested the dose had already been taken and the OP was wondering if whoever took it needed medical help or not and was too afraid to go to a doctor unless it was absolutely necessary. --Tango (talk) 16:16, 17 January 2009 (UTC)

Tidal lock with the sun

Let's imagine that the Earth had a tidal lock with the Sun. Obviously the half that was facing the Sun all the time would be roasty-toasty to a degree intolerable for life, and the half always facing away would be too frozen over for life. But what about the border region, right on the line? How big of a line would that be, what temperature would it be? Obviously I'm not asking you to work out the specifics but I'm just curious what would happen generally speaking. Would it be a strict sun/not sun divide, or would there be any sort of overlap? Assuming the planet still had an atmosphere, would that lead to all sorts of crazy weather phenomena at the interface line? Just a strange idea I had today, thought I would ask on here... --98.217.8.46 (talk) 02:45, 17 January 2009 (UTC)

The ring around the middle would get sunlight in the same way we get it during sunset or sunrise. What affect that would have on the planet, I don't know, although extrasolar planets like that have been discovered, I think (although they are gas giants, not Earth-like). I do seem to remember such a planet appearing in a scifi book, but I don't recall the details. --Tango (talk) 02:48, 17 January 2009 (UTC)

There are, I believe, many such sf stories, with the earliest being set on Mercury when it was still believed to be locked. I can't remember any titles though (might have a look tomorrow). Algebraist 02:51, 17 January 2009 (UTC)

Weather wise your biggest issue is likely to be wind due to the atmosphere on one side of the planet being rather warmer than the other side.Geni 05:40, 17 January 2009 (UTC)

The condition of the earth would depend on the temperatures of the lighted and dark sides. If the dark side is cold enough to freeze solid the oxygen and nitrogen of the atmosphere, and the temperature on the warm side keeps them a gas, the atmosphere on the warm side would have flowed into the vacuum produced by the freezing, and all the atmosphere would be a frozen mass on the dark side.

At first, libration would alternately freeze and unfreeze some of it in the libration zone, but the gas released would have flowed into the dark side, be frozen there, and will stay there permanently. Some of the released gas will stay on the warm side, but its pressure will gradually force all of it to the cold side. Eventually, no frozen atmosphere will be left in the libration zone. There would be a liquid phase between the solid and gas states in the libration zone.

Various other conditions could exist if the temperature on the cold side is a bit higher. Oxygen liquifies at about 54 K and solidifies at about 90 K. Nitrogen liquifies at about 63 K and solidifies at about 77 K. I started to write up the various conditions for the two substances on the two sides of the planet, but it got too lengthy to include here. Briefly, one gas could be liquid and the other solid, or both gases could be liquid, or both solid. Also, the various minor gases in the atmosphere are a complicating factor.

If the temperature on the cold side is above 54 K, the atmosphere will be a gas all around the earth. But atmospheric pressure will be less on the warm side, causing a complex wind pattern, probably with wind in opposite directions at different altitudes. Libration will introduce further wind complication. I can't predict what the winds would be, but neither can professional meteorologists reliably predict winds on present-day earth, so I don't feel too dumb about that. – GlowWorm. —Preceding unsigned comment added by 174.130.253.174 (talk) 06:04, 17 January 2009 (UTC)

Surely they condense at a higher temperature than they freeze? And the condensing point will presumably depend on pressure, so it's all rather complicated. --Tango (talk) 16:22, 17 January 2009 (UTC)

The oceans on the dark side would eventually freeze solid, and water from the light side would evaporate and the water vapor would cross to the dark side and fall as snow. So, eventually, all the water would find it's way to the dark side as ice. The dark side temps might drop to those which would allow for dry ice. If so, the carbon dioxide in the air would all freeze out when it circulated to the dark side. I don't think we'd get temps anywhere near as low as is needed to liquify, much less solidify, oxygen and nitrogen. The cold side would still be heated by tidal forces from the Moon, reflected sunlight from the Moon, radioactivity, volcanism, and heat transfer from the lighted side, after all. StuRat (talk) 06:15, 17 January 2009 (UTC)

Because of the large tidal influence of the Moon, I believe it would be impossible for the Moon to still exist at the same time that the Earth was tide locked to the Sun. The tendancy to tide lock on the Moon would dominate. Dragons flight (talk) 16:12, 17 January 2009 (UTC)

I agree, you might be able to get some system with the moon at L4 or L5, but with it in orbit around the Earth, you're not going to get a tidal lock to the sun. --Tango (talk) 16:22, 17 January 2009 (UTC)

StuRat suggests that if the oceans on the dark side freeze solid, water vapor in air moving to the dark side will freeze and be deposited there. The end result would be that all water on earth will accumulate as ice on the dark side. I wonder why that doesn't happen now in the Arctic and Antarctic regions. I suppose melting around the edges of those areas, including iceberg melt and ice-pack melt, keeps liquid water on the rest of the earth's surface. I wonder what the relative humidity of air in the polar regions is in present conditions. It will be low but it won't be zero - so why isn't it zero (even in nonpolar regions) when the air temperature is below freezing?. – GlowWorm. —Preceding unsigned comment added by 174.130.253.174 (talk) 18:44, 17 January 2009 (UTC)

I asked why the relative humidity of the atmosphere is not necessarily zero when the air temperature is below freezing. Perhaps the reason is that water molecules are kept aloft by air turbulence. I think that if the air is in a container and left long enough for turbulence to vanish, all grouped water molecules would become ice and fall out. I said "grouped water molecules" because a single water atom cannot freeze - for freezing to occur, a number of water molecules must be involved. I don't think Brownian motion would keep grouped water-ice molecules aloft because of the relatively heaviness of the grouped water ice molecules. Individual water molecules might remain in the air, keeping relative humidity above zero, unless their weight took them below the gaseous components of the air. – GlowWorm. —Preceding unsigned comment added by 174.130.253.174 (talk) 19:38, 17 January 2009 (UTC)

For the first question, "why doesn't all water end up frozen at the poles", you essentially got it right, the moisture in the air that falls as snow forms glaciers that eventually flow to the sea, break off, and melt. The summer season, when sunlight occurs 24 hours a day in polar regions, is critical to this process, however, and I wouldn't expect this to happen in the absence of sunlight. As for why the humidity isn't zero in the air above the polar regions, there is a continuous supply of moisture from warmer areas, and some water vapor can sublimate (evaporate from ice). The colder the temps, though, the less water will sublimate. StuRat (talk) 02:15, 18 January 2009 (UTC)

What's a good resource for algae?

I'd like to see a list of algae species (most common ones, I guess, or atypically interesting ones) that includes things like preferred temperature, nutrient requirements, light requirements, oil content, colour, etc. Anyone know of anything? My Google searches have been fruitless. Thanks! --Kickstart70TC 03:52, 17 January 2009 (UTC)

Um you can try reading our article Algae. It may give you an idea of why your question is way too open ended to be answerable. For example "algae are national foods of many nations: China consumes more than 70 species". It's rather likely most of these species are resonably common otherwise they wouldn't be consumed. Look at the number of groups there. Care to take a guess of how many species there are? After you have take a look at the section on numbers and see "The Algal Collection of the U.S. National Herbarium (located in the National Museum of Natural History) consists of approximately 320500 dried specimens, which, although not exhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of the number of algal species" (although we have no idea how many of these are unique species, I would expect the ratio is higher then 1/1000). If you just want a list of some algae, just pick some at random from the article and try researching them. However it appears to me you're in Algae fuel. If so rather then randomly looking at algae, it may be better to nail down what charestics you want and look for those that fulfill them. You can also take a loon at the ones currently of interest in that field (e.g. Category:High lipid content microalgae and SERI microalgae culture collection) and perhaps others that have been cultivated to some degree. In the end, your list will be extremely far from complete, which isn't surprising. Many scientists are likely looking into this at the very moment because there is no simple list they can consult to give them the answer. Nil Einne (talk) 16:01, 17 January 2009 (UTC)

For use as a source for making fuel (or for any other large-scale industrial application), it might be better off to breed your own algal strain that would meet the criteria more exactly. I guess they have a pretty short generation time - you could presumably devise some means to apply evolutionary pressure to produce the characteristics you need. SteveBaker (talk) 17:29, 17 January 2009 (UTC)

Wikipedia articles are unlikely to contain the specific information you are looking for over such a wide range of algae species, but you may be able to find the information you're looking for by following the links found at List of algal culture collections. 152.16.16.75 (talk) 02:21, 18 January 2009 (UTC)

mass of photon

what is the rest mass of photon? is it zero? if the rest mass is zero, then according to the formula of SR formula that states that the mass of an object that moves will have a relative mass that can be found by dividing the rest mass by the square root of 1-v²/c²(sorry! i don't know to type the formula here). so the relative moving mass must also be 0. then its momentum is 0. so how will NASA use solar sails [12] to construct a space ship? --Harnithish (talk) 14:20, 17 January 2009 (UTC)

In general, real (as in, non-virtual) particles compy to the energy-momentum relation $E^{2}=c^{2}p^{2}+m^{2}c^{4}$, where $m$ is the rest mass of the particle. For photons (and in general, massless particles), the momentum is thus equal to the energy, which, for photons, is $h\nu$. baszoetekouw (talk) 14:28, 17 January 2009 (UTC)

For completeness, the concept of relativistic mass that you seem to be referring to is obsolete and no longer commonly used in modern physics. For the case of massless particles, it is also ill-defined as it implies a division of zero rest mass by a zero factor ${\sqrt {1-v^{2}/c^{2}}}$ with $v=c$ baszoetekouw (talk) 14:34, 17 January 2009 (UTC)

All photons move at the speed of light, so it's meaningless to talk about the rest mass of a photon. A moving photon (which is the only type that exists) has momentum due to its energy, you can calculate a mass from that, but it's a pretty meaningless number, it's momentum that matters. --Tango (talk) 16:25, 17 January 2009 (UTC)

Certainly you can't stop a photon - so it's meaningless to talk about a "rest mass". Indeed, if it had a non-zero rest mass then its mass at the speed of light would be infinite. This doesn't affect solar sails because they are mirrors that take the momentum of the photon coming towards the spacecraft and turn it around into a photon moving away from the craft. That reverses the sign of the photon's momentum - and conservation of momentum requires that the spacecraft accelerate. A black solar sail that would simply absorb the photon would also work - but it would heat up and have to radiate that heat away as infrared which would reduce its efficiency. SteveBaker (talk) 17:20, 17 January 2009 (UTC)

it doesn't HAVE to radiate any of the new energy away. you could glue on one-sided black holes for example (so that the black hole doesn't suck the spacecraft in the other side) —Preceding unsigned comment added by 82.124.85.178 (talk) 18:30, 17 January 2009 (UTC)

Yeah - that's a REALLY practical solution! "Your answer is wrong because you could use 'one-sided-black-holes'."...very helpful. Thanks for the correction. SteveBaker (talk) 18:44, 17 January 2009 (UTC)

It wouldn't help anyway - it would still (probably) radiate Hawking radiation, which isn't significantly different to thermal radiation for these purposes. --Tango (talk) 18:50, 17 January 2009 (UTC)

More to the point - if such an impossible thing as a 'one-sided' black hole existed - you could simply aim your one-sided holes at the nearest massive object and let them pull you towards it! But 'one-sided' gravity is a craziness - if gravity is a distortion in space-time, how could you possibly have a distortion only in one direction?! 82's answer is equivalent to saying "Steve you're wrong because Harry Potter can just wave his magic wand and make the spaceship fly". SteveBaker (talk) 20:50, 17 January 2009 (UTC)

Of course, but I decided to ignore the obvious criticisms of the idea and pick a more obscure one - it's more fun that way! --Tango (talk) 00:01, 18 January 2009 (UTC)

hey, you said that photons can't be stopped but in this article[13] it is given that some scientists actually stopped light. so they must have stopped photons. Anyway i understood the solar sail thing. thank you.Harnithish (talk) 15:22, 18 January 2009 (UTC)

They stopped the light as a whole, they didn't stop any individual photons. It's complicated and not something I've read up on, so I'll leave someone else to explain the details. --Tango (talk) 16:49, 18 January 2009 (UTC)

The explanation is complicated - and it also relates to the speed of light in air, glass, etc being slower than light in a vacuum...when it's not possible to slow down photons AT ALL. The answer is to do with 'group frequency'. But suffice to say that slowing down (and even 'stopping') light isn't the same thing as slowing down or stopping photons - which is flat out impossible. Because an object's mass at the speed of light is infinitely larger than its mass at (say) 99.99999% of the speed of light - a photon's mass has to be zero if it were slowed down even by the smallest amount. Because E=mc² - the photon would have to give up ALL of it's energy in order to drop in speed AT ALL - it can't slow down without ceasing to exist. Which must essentially be what happens when a photon is absorbed by (for example) an atom. SteveBaker (talk) 17:06, 18 January 2009 (UTC)

Vitamin D and Tanning

I was wondering how tanning (specifically artificial tanning) is related to production of vitamin D? After browsing through Vitamin D, Ultraviolet, Tanning Bed, and many other related articles, I have determined that the output of the ‘good’ kind of UV, UVB, in tanning lamps is typically very little (5-6.5%) while the ‘make you darker then give you cancer’ type of UV, UVA, is very high. However, wouldn’t it be healthier for the ratio to be more like 50-50, possibly even more towards the UVB side? This would increase vitamin D and decrease cancer potential, wouldn’t it? Since we can control the % of different UV light output this is probably easily done, and it would probably get a lot of people to go tanning once they knew it was safer. Since this hasn’t been done yet there must be a flaw in my theory. Maybe UVB isn’t as great as I think it is? -Pete5x5 (talk) 17:37, 17 January 2009 (UTC)

Q: Who uses tanning beds? A: Those people who appear to think orange coloured skin is a good look. Therefore reducing the tanning efficiency of a bed is entirely defeating the point of using one for most users. The whole vitamin D theory of tanning is a bit misleading. For a vast majority of the world's population, incidental exposure to sunlight provides more than enough vitamin D. Moreover, the more tanned you are, the more UVB you need to synthesize the same amount of vitamin D. Therefore tanning is completely counterproductive for this goal. Its also important to realize that there is no "safe" level of tanning. The very process of of one's skin darkening is a physiological response to UV damage. Rockpocket 18:42, 17 January 2009 (UTC)

So then in order for it to be used as a 'vitamin D supplement' of sorts the UVA/UVB ratings would basically have to be switched. Then you wouldn't get darker, but you also wouldn't get Rickets! -Pete5x5 (talk) 00:09, 18 January 2009 (UTC)

Sure, but there are far easier ways to avoid rickets. Just eating a good diet can be enough, you don't need any sunlight (consider people imprisoned in basements for years on end, eg. the recent incest case in Austria). --Tango (talk) 00:19, 18 January 2009 (UTC)

In what world is UVB the "good" UV? UVB causes direct DNA damage by photo-dissociating base pairs in DNA. UVA, which has somewhat greater penetrating power, causes indirect DNA damage through the creation of free radicals. Yes, melanoma seems to be caused 9 times out of 10 by the action of indirect damage, but it is rather big leap to conclude therefore that direct damage is "good". Dragons flight (talk) 06:26, 18 January 2009 (UTC)

It helps the production of Vitamin D, which is good. But I agree, it does more harm than it's worth in any large quantities - just go for a nice walk outside every now and again and you'll be fine. --Tango (talk) 16:50, 18 January 2009 (UTC)

And that's exactly why we don't offer medical advice, because that may very well be true for you but it is far from being the case for everyone. Scotland and Canada, for example, are places where it is quite possible to not get enough vitamin D simply by going 'for a nice walk outside every now and again'. There are a lot of factors, and blanket statements that apply in California and Australia do not apply everywhere. 79.66.92.148 (talk) 21:42, 18 January 2009 (UTC)

Perhaps, but the treatment for them isn't more exposure to UV, it's a better diet or vitamin supplements. The article on Scotland seems to be saying (I haven't read it fully) that the problem is people not going out in the sun enough or wearing too much sunscreen when they do - in that case, my advice is entirely appropriate. I've only read the abstract of that Canadian study, and it doesn't give any explanation for the deficiency, just that it exists, it could be poor diet rather than lack of sun (although, obviously, going for a walk in the sun doesn't work during an Arctic winter - as with any advice, mine needs to be interpreted with a little common sense). --Tango (talk) 21:53, 18 January 2009 (UTC)

PS On second thoughts, me being right isn't really an excuse for giving medical advice... the rule exists because we can never be 100% sure we are right. The issue I should have responded to is whether or not my comments constitute medical advice, and I think it's borderline. It was a general comment and was not aimed at any specific person with any specific medical problems, which would suggest it's not medical advice, just a comment about medicine. So, I think I'm just the right side of the border. --Tango (talk) 22:21, 18 January 2009 (UTC)

Yeah, it was the 'you' in your last statement that really made me comment... 79.66.92.148 (talk) 23:13, 18 January 2009 (UTC)

That's just sloppy English, I meant "one". --Tango (talk) 23:43, 18 January 2009 (UTC)

(e/c) Note, though, that the Scottish study samples those "... who were overweight; or Asian; or housebound in some way resulting in little expose to sunlight." Those people very likely lead a sedentary lifestyle which results in minimal amounts of incidental UV exposure, or their skin tone means the require more exposure in such northern latitudes. For most people, who have even a moderately active lifestyle and a moderately varied diet, incidental exposure is sufficient even countries with little sunshine. Thats said, when deficiencies do occur in high risk groups, health professionals typically recommend they should be addressed by diet or supplement, not by tanning. Rockpocket 22:16, 18 January 2009 (UTC)

Just to clarify I'm definitely not looking for medical advice. I have no desire to artificially tan/take vitamin D supplements, I was just wondering if something generally viewed as unhealthy could theoretically be used to increase someone's health instead. Also, even though this clearly isn't the place to bring it up, I've noticed that like 10% of all the questions on the science RefDesk have this rule brought up in the answer. Although I see why it exists, too many questions are being viewed as medical instead of curiosity in my opinion. Turns out that a lot of people want to know about things that relate to the human body, but hardly any of them want medical advice. It's a good rule, it just bothers me slightly. -Pete5x5 (talk) 23:22, 18 January 2009 (UTC)

sun collapsing

i heared that at some point the moon will be pulled by the sun ... and abig explosion will be the product of that impact...is that true....? —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 20:01, 17 January 2009 (UTC)

No. In order for the Moon to collide with the Sun it would need to lose almost all its orbital velocity and seeing as it is moving at around 30km/s (that's Earth's orbital speed, the Moon's will vary a bit from that depending on where it is in its orbit around the Earth) and has a mass of 7x10²²kg, that would take an enormous amount of energy. It is highly possible, however, that when the Sun turns into a red giant (in about 5 billion years) it will engulf the Earth and Moon, but that's about it. --Tango (talk) 20:27, 17 January 2009 (UTC)

1) The Moon and Earth form a system orbiting the sun, if the moon was to be "pulled" (as in brought closer and closer) by the Sun, so would the Earth.

2) The Sun does in fact "pull" the Earth constantly due to gravity, the happy consequence of which is that the Earth doesn't wander off in the darkness and coldness of interstellar space, instead the Sun keeps the Earth (and Moon) at a safe and cozy (for us) distance in a stable orbit. Equendil Talk 20:41, 17 January 2009 (UTC)

Collisions with the sun(four related questions)

1. If an asteroid collided with the sun, would it produce any effects that could be detected from Earth?
2. Would a comet colliding with the sun be detectable?
3. If a larger object(say, the size of a planet) hit the sun, how large would it have to be to make a detectable impact?
4. Could any such collisions possibly endanger life on Earth by, for instance, disrupting the sun's output? 69.224.37.48 (talk) 20:29, 17 January 2009 (UTC)

Asteroids (and comets) are, more or less by definition, small (compared to a planet or the Sun that is), a collision with the Sun would be detected from Earth if the asteroid/comet itself was large enough to be detected. The "effects" of such a collision would be short lived and confined to a tiny region of the Sun, it would be a mere astronomic curiosity as was the collision between Comet Shoemaker-Levy 9 and Jupiter a decade ago. The largest asteroids are grains of dust compared to the Sun and couldn't possibly disrupt it in any significant way let alone endanger life on Earth. Equendil Talk 20:49, 17 January 2009 (UTC)

I think at worst such a collision could cause some kind of solar flare or similar solar activity, but they happen all the time and we survive just fine. Asteroids, and even small planets, are so small relative to the Sun that I can't see them causing anything beyond a local disturbance. --Tango (talk) 22:45, 17 January 2009 (UTC)

There's certainly no chance of a collision "disrupting" the sun's output. If any effect were to be observed, it would be an increase in output rather than a decrease, due to an increase in available fusible material. A super-Jupiter (or Sub-brown dwarf) may contain enough hydrogen to significantly increase the luminosity of the sun, possibly rendering Earth uninhabitable, but it's a long shot. Anything larger than that and you're talking about smashing two stars together, and, well, that's never good.-RunningOnBrains 23:57, 17 January 2009 (UTC)

Like the Earth, the surface of the Sun is relatively cool, so any object which temporarily displaced a noticeable portion of the surface would expose the much hotter interior, which might create a temporary bright spot. StuRat (talk) 02:07, 18 January 2009 (UTC)

Indeed, that's the kind of thing I was thinking might cause flares - especially if the asteroid if ferrous-heavy and can mess (locally) with the Sun's magnetic field. --Tango (talk) 02:13, 18 January 2009 (UTC)

See Kreutz Sungrazers and there is also video at http://sohowww.nascom.nasa.gov/bestofsoho/Movies/movies2.html#comets "A popular misconception is that sungrazing comets cause solar flares and CMEs (coronal mass ejections). While it is true that we have observed bright comets approach the Sun immediately before CME's/flares, there is absolutely no connection between the two events. The sungrazer comets -- in fact all comets -- are completely insignificant in size compared the Sun." [14] So, the Sun would just absorb a comet or asteroid. Also, the temperature of the photosphere is about 10,000 F. --mikeu ^talk 03:48, 18 January 2009 (UTC)

Which is far cooler than the Sun's interior. StuRat (talk) 11:09, 18 January 2009 (UTC)

Tachycardia

Does anyone know the fastest recorded heart rate for a survivor of tachycardia? Just curious :) Fastest I heard of was my dad's and that was 220, so I suspect it's a lot higher than that. —Cyclonenim (talk · contribs · email) 20:32, 17 January 2009 (UTC)

This question may require refinement for an accurate answer. For example, I would guess you mean ventricular rate; if not then some extremely high atrial rates have been survived, even tolerated with few symptoms. If we focus on ventricular tachycardia (VT), it is not always clear in the clinical setting when VT gives over to ventricular fibrillation (VF), for which some very high rates can be observed e.g.: which is shown on the VF page and appears to display a rate around 375 (I did not pull out my calipers). I've seen VF rates like this in a number of people whom I treated and survived, and I'm sure we could find reports of same.

If we focus on classical ventricular tachycardia (VT), and my guess is that this was your original intent, then 220 is very high, but it might not be clear whether your father was in VT or VF. My guess is that such comparisons are not very meaningful. --Scray (talk) 22:39, 17 January 2009 (UTC)

Not at all, that is quite helpful thank you. To clarify a bit further, I was referring to supraventricular tachycardia as that was what my father had. I was just curious to see what the highest recorded rate was. —Cyclonenim (talk · contribs · email) 00:23, 18 January 2009 (UTC)

This article mentions successful treatment of a 300 beats per minute tachycardia, atrial flutter w/ 1:1 conduction due to Wolff-Parkinson-White syndrome.—eric 03:47, 18 January 2009 (UTC)

Here's atrial fibrillation + WPW, i don't see how this guy could have had a pulse.—eric 04:32, 18 January 2009 (UTC)

Am I right in thinking that when atrial flutters are that fast, there's little, inefficient contractions rather than stronger contractions present at more normal heart rates? Or is it that there is still a full contraction happening, but requiring a lot more energy to do so? —Cyclonenim (talk · contribs · email) 09:59, 18 January 2009 (UTC)

If the ventricles are contracting at such a high rate, they have little time to fill with blood. The end-diastolic volume would be very low, leading to a very low stroke volume. The EDV also partially determines the strength (intropy) and energy (ATP burned and oxygen consumed) by each contraction. A larger EDV means a greater preload and more forceful contraction and greater oxygen demand.

In the above two cases, even though each individual contraction might be weak, i would think there would be a huge oxygen demand because of the high rate, along with almost no cardiac output. Maybe one of the docs around here could explain how these people lived long enough for someone to get a 12-lead on 'em. (it took me so long to write this response that one showed up before i could hit the save button.)

Usually with atrial flutter or afib, conduction is blocked in the AV node, the ventricles will be contracting at a much lower rate.[15][16] The contractions are less efficient because the atria do not contribute to the ventricular preload, but it's not nearly such a dangerous arrhythmia as those above where the AV node was bypassed by a high velocity conduction pathway.—eric 18:54, 18 January 2009 (UTC)

The maximum (ventricular) rate is about 300/min. Rates above this tend to provoke VF. A discussion of VF isn't really meaningful because different parts of the ventricles are all contracting at different times. With a fast atrial rate (as might be seen in atrial fibrillation or atrial flutter), the ventricles are usually limited to about 160/min because the atrio-ventricular node is refractory to conduction. In Wolff-Parkinson-White syndrome, the accessory pathway allows transmission at higher rates, hence the reports noted above. These high ventricular rates lead to impaired diastolic filling of the ventricles. This significantly reduces the stroke volume and causes hypotension and dizziness. Pulse rates cannot be maintained at this level because the reduced cardiac output leads to cardiac arrest. Axl ¤ [Talk] 18:17, 18 January 2009 (UTC)

Limit of Cold

Is there a limit at which point a human can no longer tell that it's any colder?

Say it's 20 below (fahrenheit) and then the next day it's 30 below, i'd say BRRRR it's COLDER!!!

Is there a point where'd I'd cease to notice the increase in cold?

What about on the other end of the scale?192.136.22.5 (talk) 20:35, 17 January 2009 (UTC)

This question brings up an interesting, related question: does human perception of temperature work on a logarithmic scale? Several aspects of human perception seem to be log-based, but I've never heard whether or not temperature perception works on a similar basis. 152.16.16.75 (talk) 02:34, 18 January 2009 (UTC)

The elapsed time between exposures would confound the comparison, mightily. hydnjo talk 02:59, 18 January 2009 (UTC)

Id say that you could no longer tell its colder when you are unconscious (or dead).--GreenSpigot (talk) 03:51, 18 January 2009 (UTC)

They do say that just before you die you start to feel pleasantly warm (although how this was discovered is not clear).--GreenSpigot (talk) 04:16, 18 January 2009 (UTC)

It is worth noting that humans don't feel temperature; they feel temperature differences. If your arm (for example) becomes chilled to the same temperature as the ambient environment then your arm will no longer feel cold. In general, good blood circulation should prevent that from happening, but with very harsh conditions one can start to lose the sensation of cold as your extremities become chilled. From personal experience at the National Ice Core Lab, I can tell you that -35 C (-31 F) still feels a lot colder than -25 C (-13 F), so if there is a lower limit it must be less than that. Dragons flight (talk) 05:19, 18 January 2009 (UTC)

AFAIK, significant local cooling may result in either pain or loss of sensation; it depends which way and how fast you cool. Either way, there is certainly a limit beyond which you can't tell whether the skin temperature is decreasing further or not. Suggestion that human perception works rather generally on a logarithmic scale is called Weber–Fechner law. I don't know if it works for perception of temperature. There is a paper published 68 years ago: Herget, Granath, Hardy, Am J Physiol 134: 645-655, 1941; which suggests that the law does apply, but in a rather limited range. It certainly does not apply at the extremes. Note also that they tested for "hotter" and not for "colder", presumably because that's easier. All the best, --Dr Dima (talk) 05:43, 18 January 2009 (UTC)

Temperature perception is very tricky. For example, if you touch a piece of plastic and a piece of metal that are at the exact same temperature - you'll judge the metal to be cooler because it conducts heat away from your skin faster than the plastic does...unless both are above body temperature - in which case the opposite will happen. SteveBaker (talk) 06:23, 18 January 2009 (UTC)

January 18

Can I buy cyanide being 16 year old

It's to separate a rock from gold. Hope you understand me, I am not English-Native. --190.49.126.240 (talk) 03:16, 18 January 2009 (UTC)

In what jurisdiction? Algebraist 03:23, 18 January 2009 (UTC)

You could extract it from apple seeds. Our article on cyanide gives a cursory overview of the process. Still, there are likely easier methods of extracting gold from ore than attempting a home Au/CN complex reaction... --Jayron32.talk.contribs 03:40, 18 January 2009 (UTC)

Sigma-Aldrich sells cyanide, though you would probably need a credit card to buy it and you would have to check with local laws. Here is the link to Sigma Argentina. Rockpocket 03:44, 18 January 2009 (UTC)

I AM IN ARGENTINA. --190.49.126.240 (talk) 03:47, 18 January 2009 (UTC) JAYRON, and what can I do if it's not with cyanide, does the article of Wikipedia explain it? --190.49.126.240 (talk) 03:48, 18 January 2009 (UTC)

Thank you Rockpocket. Thank you everyone. And if I can't buy cyanide, does a hammer work? —Preceding unsigned comment added by 190.49.126.240 (talk) 03:50, 18 January 2009 (UTC)

Yes, the hammer sure works. We have lots of information on various methods of gold mining and gold extraction. By the way, the latter article suggests that thiosulfate may be used to extract gold. If sodium thiosulfate indeed works, then you can just go to a photography supplies store and buy as much of it as you want. They probably sell it as hyposulphite of soda, or simply hyposulphite. And, most important, just enjoy the scenery as you travel; you may or may not get rich, but Argentina is the most beautiful country I've ever been to, and I've been to many. --Dr Dima (talk) 06:13, 18 January 2009 (UTC)

It goes without saying that cyanide is not the most environmentally friendly thing to mess with! Gold is relatively easy to extract because it doesn't chemically react with the rock - so you only have to physically separate it - not do any messing around with chemicals. If you can merely crush the rock small enough (and on a small scale, a hammer should be fine for doing that) then you can use the 'panning' technique to separate out the heavier stuff - which will be mostly fairly pure gold. Our article Placer mining has some fairly concise instructions on that - and other physical separation techniques. SteveBaker (talk) 07:05, 18 January 2009 (UTC)

Agreed. Cyanide poisons the water and kill animals (and maybe people). If it isn't illegal, it should be. StuRat (talk) 11:03, 18 January 2009 (UTC)

Even without cyanide, large scale gold extraction is a disaster for the ecology of the area because of the large amounts of water required - and the 'tailings' (left-over crushed rock) getting washed downstream and eventually silting up something that wasn't silted up before. But an individual with a hammer and a gold pan hunting for nuggets in a stream won't do significant damage. SteveBaker (talk) 16:59, 18 January 2009 (UTC)

Can I buy cyanide, being much older than 16? Seriously, can any adult just buy cyanide from a chemical supplier without special licensing and whatnot? As a well known poison, I would have thought that it's distribution would be regulated, even for adults. Dragons flight (talk) 01:29, 19 January 2009 (UTC)

Yes, but considering how many other poisons are readily available, like antifreeze and wood alcohol, it would be difficult to ban all poisons. StuRat (talk) 01:34, 19 January 2009 (UTC)

I don't think that is a fair comparison. Many people use and need antifreeze. How many people outside specialized industries need cyanide? Not to mention that it is relatively easy to make the poisonous gas hydrogen cyanide from most cyanide salts. How many poisons do you use that readily form poisonous gases? Dragons flight (talk) 01:45, 19 January 2009 (UTC)

Bleach? APL (talk) 02:34, 19 January 2009 (UTC)

Yes, I believe chlorine bleach and ammonia mix to produce deadly chlorine gas. StuRat (talk) 15:21, 19 January 2009 (UTC)

Both of the items I mentioned have relatively safe alternatives. There's non-toxic automotive anti-freeze, and ethanol can be used for cleansing wounds just as methanol can. Ironically, it's not legal to sell ethanol for such purposes, as the government is afraid people will drink it and the gov will lose their alcohol tax income. So, we get a poisonous alcohol to use instead. (But, of course, the amount absorbed through the skin isn't enough to be toxic.) StuRat (talk) 15:13, 19 January 2009 (UTC)

I don't think I've every seen methanol used to clean a wound, though isopropyl alcohol is used pretty commonly in my experience. Where do you find methanol being used to clean wounds? --Scray (talk) 17:31, 19 January 2009 (UTC)

In my experience, it's not easy to buy isopropyl alcohol in the UK. I got asked questions about what I needed it for when I last tried to purchase some - and I had to try four different places before I found one that would accept "to soak my print head in overnight" as a legitimate reason. I'm still not entirely sure why. --Kurt Shaped Box (talk) 17:41, 19 January 2009 (UTC)

They didn't accept your first try when you said "to poison my mother-in-law's drinks" ?  :-) It's completely unregulated in the US. StuRat (talk) 20:30, 19 January 2009 (UTC)

Depends on the country. Cyanide in Australia is governed by the Poisons Act 1964. A licence or permit is required for the purchase, sale and use of cyanide from the Department of Health. But in the US, it seems its perfectly legal to by cyanide, as long as you have a legal reason for doing so. See this article about a man who bought a pound of cyanide, telling the company that sold it to him that "he needed it to clean jewelery". Rockpocket 03:05, 19 January 2009 (UTC)

Cyanide shouldn't be handled by just anyone. A person should be fully trained and understand the very significant dangers there are when handling it. I would advise a 16 year old to avoid it regardless of the legalities. It's just not something to be casual about. 89.159.158.241 (talk) 03:51, 19 January 2009 (UTC)

Chest pain

I'm looking for medical conditions that can be mistaken for a heart attack other than heartburn. (Everybody knows that when a fictional character has sudden, severe chest pain, it's either a heart attack or acid reflux. I want something different.) --Carnildo (talk) 06:08, 18 January 2009 (UTC)

What's the fictional purpose? If you want it to be a "false alarm" you could choose costochondritis. If you want it to have consequences, it could be an old fishbone that was accidentally swallowed two weeks ago and has now caused esophageal rupture. Anyway, you'll find ideas by googling "chest pain differential diagnosis", and you can pick what you like. Echinococcus granulosus anyone? - Nunh-huh 06:17, 18 January 2009 (UTC)

Pleurodynia seems like it might fit the bill. --Scray (talk) 06:44, 18 January 2009 (UTC)

Our article on Chest pain lists a couple dozen causes. 152.16.16.75 (talk) 11:35, 18 January 2009 (UTC)

A heart attack can appear as a sore shoulder or a sore jaw. Lifting something heavy could cause a sore shoulder. Chewing something tough could cause a sore jaw muscle. Hope this helps. Edison (talk) 22:41, 18 January 2009 (UTC)

related to physics

Hi, I would feel extremely happy if I could get details about the structure and characteristics (like no.of atoms per unit cell.co-ordination number,atomic radius, packing factor, density) for the following crystals:NaCl, ZnS, graphite, diamond along with the diagrams. Thanks

Have you looked in our articles sodium chloride, zinc sulphide, carbon, graphite and diamond? SpinningSpark 15:36, 18 January 2009 (UTC)

knowledge key

Iam asmart person,i got that wish to have deep understanding for evry thing , i tried so mush , and with the time i found out that its impossible ,because evry question will lead you to anther question , at the end iam willing to focus on my title , iam acivil engineer , i'd like to understand the basics of structural analysis step by step , some thing so detailed ... thank you ...??? —Preceding unsigned comment added by 94.249.18.171 (talk) 14:37, 18 January 2009 (UTC)

You could start off with our structural analysis article and then read all the articles in the navigation box. There is also a Wikibook on strength of materials. You might also be interested in Business English as you will need to write reports now and then in Civil Engineering. SpinningSpark 15:22, 18 January 2009 (UTC)

dim flashes from a Fluorescent lamp

My room has a circular Fluorescent lamp installed. When I turn it off, the room is totally dark save from a few electronic lights from various devices. I know that these type of lamps emit phosphorescence for a while after it is switched off. However, I sometimes see some part of the circular lamp momentarily flash more brightly than the others. One time, it flashed and dimly lighted my room before turning off again. My question is, what would that flash be? --Lenticel ^(talk) 15:18, 18 January 2009 (UTC)

This is only a guess but. . .discharge from the ballast choke? SpinningSpark 15:51, 18 January 2009 (UTC)

I have seen fluorescent lights continue to flash dimly when the wiring is incorrect, such that the neutral is being switched rather than the hot wire, or when there is a "sneak circuit" backfeeding the lamp from some other source. I would check for this if the lamp continued glowing dimly or flashing occasionally long after it was turned off. If it is just one flash right after turnoff it could be as stated above. Edison (talk) 19:53, 19 January 2009 (UTC)

I think the sneak circuit scenario might be plausible since it does glow for a little while from time to time. The lamp dangles from a wire tethered to the roof rather than fixed in a ceiling, (my room sorts of "leans" on the main house, its roof only has a layer of insulation rather than a ceiling).--Lenticel ^(talk) 05:29, 20 January 2009 (UTC)

pi calculation formula

${\frac {1}{\pi }}={\frac {2{\sqrt {2}}}{9801}}\sum _{k=0}^{\infty }{\frac {(4k)!(1103+26390k)}{(k!)^{4}396^{4k}}}\!$ i am a nineth grade student who is a bit ambitious. can some explain me this formula part by part?Harnithish (talk) 15:26, 18 January 2009 (UTC)

You may do better if you asked this question at the math desk. --Jayron32.talk.contribs 15:35, 18 January 2009 (UTC)

This formula was discovered by Srinivasa Ramanujan. I'm assuming you just want to know what the expression on the right hand side means rather than how the identity is proved (which is a much, much more difficult question !). Well, the $\sum _{k=0}^{\infty }$ part means "sum over the integer values of k starting at 0". Of course, we can't actually write down all the terms of this infinite sum, but we can write down as many as we have patience or time for. The $(4k)!$ means the factorial of 4k - the product of all the positive integers from 1 to 4k. And $(k)!^{4}$ is the fourth power of the factorial of k.

So the first term of the infinite sum, with k=0, is:

${\frac {(0)!\,(1103)}{(0!)^{4}\,396^{0}}}=1103$

because, by convention, 0! = 1. The second term, with k=1, is:

${\frac {(4)!\,(1103+26390)}{(1!)^{4}\,396^{4}}}={\frac {24\times 27493}{(396)^{4}}}$

and if we just stop with these two terms we have:

${\frac {2{\sqrt {2}}}{9801}}\,\left(1103+{\frac {24\times 27493}{(396)^{4}}}\right)=0.3183098862\cdots$

According to my calculator this is within 2x10^-11 of 1/π, so even with just two terms this is a very good approximation. Gandalf61 (talk) 17:21, 18 January 2009 (UTC)

A little algebra shows that the ratio of successive terms is asymptotically ${\frac {1}{99^{4}}}\left(1+O(k^{-1})\right)^{4}$, which I'm pretty sure means that every extra term you add gives you approximately 8 more decimal places of accuracy. Which is just further proof that Ramanujan had an amazing talent for generating formulas that seem to make no sense (and involve somewhat arbitrary-looking values) but do quite extraordinary things. Confusing Manifestation(Say hi!) 22:47, 18 January 2009 (UTC)

How was this formula derived? Genius notwithstanding, it seems unlikely that Ramanujan came up with the obscure and large numeric constants needed to make it work by "sheer insight." Was there a geometric or algebraic procedure that he used to convert some other pi identity form into this rapidly-converging form? Nimur (talk) 03:07, 20 January 2009 (UTC)

(Apparently so..., although I'm still not totally satisfied. More credit to Ramanujan's abilities, I suppose... Nimur (talk) 03:14, 20 January 2009 (UTC)

Certainly, if it hadn't come from Ramanujan, I'd have said it had to be bogus - but that guy certainly came out with a lot of very bizarre identities of this kind and I'm DEFINITELY not going to be the person who says he was wrong! SteveBaker (talk) 03:24, 20 January 2009 (UTC)

Long-term storage of lithium ion battery

I've read Lithium_ion_battery#Shelf_life, and it seems to suggest that I should store such batteries at refrigerator temps at a 40-60% charge. However, they won't stay at that charge, requiring me to periodically remove and recharge them (which will also heat them up). Is that better than just allowing them to fully discharge in the fridge ? These are backup batteries for cell phones, in case the primary batteries fail. Thus, I may not need them for several years. StuRat (talk) 17:10, 18 January 2009 (UTC)

Lithium-ion batteries should hold their charge for a long time. Self-discharge times are usually measured in years. If yours are not doing this then they are probably past their best. Here is a manufacturers' data sheet. Does not specifically say anything about periodically charging batteries in storage but I would say don't do it; each charge cycle shortens the batteries useful life and Li-ion batteries do not have the same problems that Ni-Cd and Pb-acid have with being left fully discharged. SpinningSpark 20:37, 18 January 2009 (UTC)

Muscle Tone and Protein Intake

Hello! I've heard that after strength-training exercises, it is important to eat something with a lot of protein immediately to foster muscle growth. Is there any truth to this? Does potential muscle growth significantly suffer if there is no immediate protein intake after a workout? If it is true, what qualifies as "immediate"? 30 minutes? 1 hour? 2 hours? There seems to be a lot of pseudoscience in the fitness community, so I was just wondering if this was a part of it. Thanks!--el Aprel (^facta-_facienda) 20:25, 18 January 2009 (UTC)

Well, yes and no. Eating protein doesn't automatically give you increased muscle tone: you need exercise for that. However, muscle is made of protein (among other things), so it only makes sense that in order to develop muscle tissue you'll need the raw materials to do it. You don't need to eat tons of protein for that though: a healthy, balanced diet will provide plenty of protein for that. The only rationale for an otherwise healthy person to eat much more protein (that I can think of off hand, at least) is if you also want to lose weight by eating fewer carbohydrates and proportionally increasing your protein intake. In summary: you need some protein to build muscle, but not tons of it, and not in the absence of exercise. – ClockworkSoul 22:43, 18 January 2009 (UTC)

These references are helpful: Dietary protein intake ... after endurance exercise and Postexercise protein intake. It is useful to eat protein immediately after exercise. I'm not aware of a study that examines the exact timing of the protein intake. Given that it will take a little time for the protein to be digested and absorbed, I guess that it would be best to eat the protein meal immediately after exercising. Axl ¤ [Talk] 23:06, 18 January 2009 (UTC)

Definitely yes. The post-workout meal is THE most important one, I read ("...except breakfast of course" it continue). Those who ate protein IMMEDIATELY post-workout got 33% more results, as I recall, than those just at regular mealtimes not near the exercise. Dont have time to google it maybe later I'll find the study. (I have no vested interest in protein shakes etc direct or indirect in case youre wondering)

Negritos, Indigenous Australians, Pacific Islanders, and Thai people...

File:Migration map4.png

Out of Africa

Why is it that all of these people in my opinion have something about them which is similar to black Africans? It says that there's no definitive knowledge about the origin of Negritos but they are considered negroid, Indigenous Australians share many characteristics with negroes but some other things are different (noticably hair texture) and they also look a bit more mongoloid than pure African, and Pacific Islanders and people from Thailand do not look negroid yet they look more negroid than other obvious mongoloids (such as the Chinese, Koreans or Japanese) in my opinion.

Basically, is there any scientific evidence of a migration out of Africa for these population groups? It seems strange that they would develop similar traits independently.--Spring and Port Wine (talk) 21:39, 18 January 2009 (UTC)

In a sense, we all migrated out of Africa. However, I don't think that there are any closer connection than that between dark-skinned Africans and the other dark-skinned ethnic groups you list beyond the coincidence of dark skin. Also, don't read much into how people "look" as a test of genetic "closeness". Outward appearences mean little with regard to actual relatedness, and the outdated categories of "caucasoid" , "negroid" and "mongoloid" have little presence in modern science. --Jayron32.talk.contribs 22:05, 18 January 2009 (UTC)

Quite right. I live in the US and when the opportunity strikes, I like to say "We're all African Americans. Think about it.". ;) A Quest For Knowledge (talk) 15:07, 19 January 2009 (UTC)

If you accept the Recent African origin of modern humans, its unlikely they developed similar traits independently, rather their similar traits betray the shared origin of all humans. Rockpocket 22:25, 18 January 2009 (UTC)

I think the OP is asking whether the inhabitants of those regions migrated there without settling for a while at some other locale. In short, yes, genetic evidence suggests that the ethnicities you named may be part of a human migration that extended from Africa, along the coast to Southeastern Asia, and onward to Australia and the Pacific Islands. Take a look at early human migrations and prehistory of Australia for a bit more info. – ClockworkSoul 22:30, 18 January 2009 (UTC)

Indeed, see also Coastal Migration. Rockpocket 22:43, 18 January 2009 (UTC)

That map is way incomplete. What about cavemen who migrated from costal Europe to Newfoundland in North America 17,000 BP? ~AH1^(TCU) 01:27, 19 January 2009 (UTC)

I'm fairly certain that map is just meant to illustrate the inferences based on the haplotypes of the long-term inhabitants of various regions, and isn't actually supposed to describe every single migration event in the past 30,000 (give or take a few millenia) years. You might, however, be interested in models of migration to the New World. Note that it doesn't at any point make use the word "caveman". – ClockworkSoul 03:57, 19 January 2009 (UTC)

I don't have much experience with Thai people but from what little I've seen, Thai's aren't that dissimilar from other South East Asians like Malays for example, so I'm not particularly sure why you single them out... If anything, I would say they look more similar to Chinese, Koreans and Japanese. Nil Einne (talk) 19:31, 22 January 2009 (UTC)

A question and a few "if so..."s

Has the HIV genome been mapped? If so, has DNA microarray been performed to determine which transcripts are present at high levels in different stages? If so, is the information available online? 90.206.220.158 (talk) 21:58, 18 January 2009 (UTC)

And some answers...

• Has the HIV genome been mapped? Oh, yes. Here are three links to the complete reference genomes for:
  1. HIV1 (and 1286 more
  2. HIV2 (and 27 more)
  3. Simian-Human immunodeficiency virus (and 7 more)
• If so, has DNA microarray been performed to determine which transcripts are present at high levels in different stages? A search for "HIV microarray" over at PubMed [17] gives 194 hits, some of which are actually relevant. Here is an abstract of a very recent example of the application of microarrays to HIV infection.

Hope that's what you're looking for. – ClockworkSoul 22:11, 18 January 2009 (UTC)

wet vs. cold

does wet really feel different from cold, or is it an illusion? (we feel it's wet because we SEE that it is). —Preceding unsigned comment added by 82.120.227.136 (talk) 23:42, 18 January 2009 (UTC)

Well, considering that it's quite possible to be wet but not cold (warm or hot water, for instance) I'd say that they are indeed separate. Further, even when blindfolded I suspect you can reliably tell the difference between "cold" and "wet". This is science that is easy enough to test on your own (well, with someone else's help): blindfold the participant, then apply either a cold washrag from the freezer or a wet washrag to their hand and see if they can reliably determine which is which. -- 74.137.108.115 (talk) 00:02, 19 January 2009 (UTC)

In some cases, yes, you can certain tell. However, when bringing laundry in after its been hanging outside, I often find it difficult to tell if it's still wet or just cold. --Tango (talk) 00:15, 19 January 2009 (UTC)

Damp yes--but consider that a damp article of clothing probably behaves as if it were only cold. That is, the moisture is trapped in the material, so it will not "wet" a surface (or a hand testing its "wetness") but it will absorb heat (probably somewhat more effectively than the material alone). Even in this case, though, you are comparing "cold" to "wet and cold", not "cold" to "wet". -- 74.137.108.115 (talk) 00:46, 19 January 2009 (UTC)

The trouble is that both wet and cold things lower the temperature of your skin while it's in contact with it. The water in wet cloth conducts body heat away better than a dry cloth does - so in a very real sense, it IS cold as far as your skin is concerned. Worse still - dry-but-cold cloth could well become wet due to condensation of water out of the warm air surrounding your body...hence what was originally merely cold could become superficially moist to the touch. Obviously the degree of wetness and the degree of coldness of the cloth makes a difference to the feel - but whether you could judge that difference would depend on the exact conductivity and/or wetness of the cloth. However, because dry cloth will generally have a pretty low thermal conductivity - holding a piece of cold-but-dry cloth should warm it up to skin temperature pretty quickly...where you're unlikely to be able to dry out a piece of wet cloth very quickly by just holding it. So I think the trick should be to hold the cloth tightly in one hand for a few seconds and then see if it STILL feels cold to the touch with the other hand. This is only a theory - so do the experiment and let's see if we can do some new science. I want half of the Nobel prize money - but you can go to Stockholm to collect it. :-) SteveBaker (talk) 00:50, 19 January 2009 (UTC)

What Steve should have said is that its only a hypothesis, and you should do the experiment to test it. A theory being something entirely different than what he describes above. OK. I'm done being a pedantic asshole for the day. Back to your regularly scheduled discussion. --Jayron32.talk.contribs 01:44, 19 January 2009 (UTC)

Indeed - Steve should know better... shame on you! ;) --Tango (talk) 02:11, 19 January 2009 (UTC)

Yeah! If anyone should get the Nobel prize it is you two (in Literature) for your valuable refutation of Steve's word choice. —Preceding unsigned comment added by 82.120.227.136 (talk) 12:00, 19 January 2009 (UTC)

Damn! Obviously you're going to make me turn in my magic decoder ring - but do I get to keep the lab coat? SteveBaker (talk) 15:53, 19 January 2009 (UTC)

Well, we'll let you stay in the scientist club for now, but there will be a demerit on your permanent record! --Jayron32.talk.contribs 18:48, 19 January 2009 (UTC)

I'm not sure Steve's experiment would work very well anyway. I often get puzzled with whether my drying is still damp or merely chilly and the squeeze test doesn't work well for me. Cloth is typically a good insulator, so it really doesn't warm up in a significant way. What I typically do is examine the rest of the load. Since it's unlikely to dry in a uniform way, a load that's damp will probably have a wet piece in there somewhere (rolled sock, folded cuff, etc). In fact, a rolled sock or other lump can be useful from the outset; being more insulated, it stays damp the longest, but also takes longer to chill down to ambient temperature. Matt Deres (talk) 19:06, 19 January 2009 (UTC)

I good insulator should warm up quicker, since you only have to warm up the part in immeadiate contact

My thoughthypothesis exactly. If it's just cold then the thermal mass of (say) the first millimeter of depth of the cloth is tiny and should warm up quickly (while your hand senses it as cold). The heat won't be conducted away into the body of the cloth because it's such a good insulator - so the surface of the cloth will get warm. To contrast, wet cloth will conduct the heat from your hand away without getting significantly warmer - and it'll continue to do that until it finally dries out. Hence, if you warm it up with one hand - then switch to the other hand to measure the resulting temperature, you should get a feeling which is actually the opposite of the truth: If your 'measurement' hand still feels that the cloth is cold - then it's wet (it might be cold AND wet), but if your 'measurement' hand says that the cloth now feels warmer than it did before - then the cloth was definitely not wet - but merely cold. That's the hypothesis - now we need to proceed to the experiment - after which we may publish the results in the well known peer-reviewed "Wash-day journal of thermodynamics and biosensing". If others can repeat the experiment successfully then it will become a Theory (big 'T') and the Nobel prize will surely follow. SteveBaker (talk) 13:58, 20 January 2009 (UTC)

(ahem) Getting back to the original question, I was wondering how the sense of touch works when it comes to non-solid objects. Is it only because of the substance's behavior and our feeling its movement that we know it is "wet", or is there some intrinsic property of our sense of touch which determines the "wetness" or "dampness" of a subject? So I guess I haven't answered anything, but instead added a new question.-RunningOnBrains 18:57, 19 January 2009 (UTC)

I believe surface tension has something to do with it, a liquid with very high surface tension (mercury, say) won't feel as wet as something with a lower surface tension (water or oil, say). I haven't spent much time handling mercury, though, so I'm not entirely sure that's right. --Tango (talk) 19:07, 19 January 2009 (UTC)

My recollection of handling mercury (and that was 35 years ago) was that it doesn't feel wet...but to be honest, your senses are too busy saying "This is unreasonably heavy for a liquid" for you to notice much else. It's a good conductor of heat - so it ought to feel cold - but it also doesn't "wet" the surface of your hand - so even as you move it around, you don't have a wet hand. It's really weird stuff when you actually get to play with it. SteveBaker (talk) 20:40, 19 January 2009 (UTC)

That fits with my understanding of the theory. We should probably point out at this point that mercury is toxic and it is unwise to play with it in the manner described by Steve. --Tango (talk) 20:53, 19 January 2009 (UTC)

I can't remember exactly where I heard/read about it, but I recall a science program/article that discussed the issue. According to the program, it seems that we do not have "wet" touch receptors. The sensation of "wet" is actually caused by the joint triggering of "cold" and "pressure" receptors in our skin. This was then demonstrated by the host being blindfolded, and having the skin pressed lightly by a cold object. The blindfolded host remarked that the object felt "wet". Just pressure or just cold isn't enough to get the "wet" feeling - it's a combination of cold and pressure which does it. -- 128.104.112.113 (talk) 22:51, 19 January 2009 (UTC)

Which returns us to the question of warm and hot liquids--do they not feel "wet" then? And why would mercury, which possesses (and presumably excels in) those two criteria be "less wet" than water?

I suspect that some part of the determination rests on friction--if the "unknown material" slides easily across the skin then "wet" would be indicated. If the material applies signficant friction or resists movement across the skin than "wet" would be counterindicated. This is, however, only speculation. -- 74.137.108.115 (talk) 04:08, 20 January 2009 (UTC)

After somewhat extensive review in Cognitive psychology, Perception, Somatosensory system, and Mechanoreceptor I believe I better understand how the brain determines the sensation "wet". The simplistic introductory explanation that touch consists of hot, cold, pain and pressure neglects the further subdivision of the "pressure" receptors. From Mechanoreceptor, they are:

Ruffini's end organ detects sustained pressure.
Meissner's corpuscle detects changes in texture (vibrations around 50 Hz); adapts rapidly.
Pacinian corpuscle detects deep pressure and rapid vibrations (about 200-300 Hz).
Merkel's disc detects sustained touch and pressure.
Mechanorecepting Free nerve endings ((touch, pressure, stretch)
Hair follicle receptors are located in hair follicles and sense the position of hairs.

This gives us many combinations of "pressure" sensory input, some of which are most likely identified as "wet" by our brain. Several possibile indicators are:

• "wet" substances distribute pressure more evenly
• "wet" substances don't cause significant friction (stretching of the skin)
• "wet" substances have internal fluid flows that can be detected (through vibration, texture or motion of hair follicles)
• "wet" substances expand predictably on the skin (wetting the surface)
• "wet" substances do not force uniform motion

Undoubtedly there are other inputs that may suggest "wet" (temperature and temperature differential, sight, sound, etc.) but the exclusion of those inputs does not seem to eliminate the ability to perceive "wet" (though accuracy may be reduced). It's amazing the amount of complexity that goes into a simple evaluation of "wetness". -- 74.137.108.115 (talk) 06:20, 20 January 2009 (UTC)

Fascinating information! Thanks!

So now we know that there isn't some kind of special 'wetness' sensor (I didn't think there could be because the sensing organs themselves have to be under the layer of skin cells - so they would be out of contact with the water anyway).

But everyday experience says that we have an incredibly hard time telling the difference between "cold" and "wet" - anyone who put laundry out to dry outdoors on a chilly day will attest to that. You go out to grab your clothes and you simply can't tell whether they are dry-yet-cold or still wet. The theoryhypothesis that various forms of pressure/friction/stretch are giving you wetness cues seems to be busted by that simple, familiar, experiment. The alternate hypothesis (that the 'cold' receptor predicts wetness by estimating thermal conductivity) is entirely born out by that experience. It's possible that some of these other mechanisms provide backup information - but the sensation of cold clearly overrides anything that's saying "No! It must be dry because it's not slippery enough". We feel "cold" and our brain says "wet". QED.

SteveBaker (talk) 20:42, 20 January 2009 (UTC)

Which, again, completely ignores that something can be "wet" without being "cold". I'm not saying that "cold" doesn't play an important role in determining wetness (or, more appropriately for your example, dampness); but it cannot be a uniquely-determining factor. Also consider that "damp" but not "wet" laundry probably does not exhibit the potential indicators of wetness as described above (the cloth having a greater affinty for the water than skin would), so in that case you would be relying on primarily "cold" information. The next time you have an ambiguously cold/"damp" cloth, try putting it under running water for a few moments and then see if you can tell a difference between "damp" and "wet" (and "cold"). From my personal experience, every "cold" object does not feel "wet" or "damp". Perhaps in your laundry example your brain expects to feel "damp" and ends up misinterpreting "cold". -- 74.137.108.115 (talk) 21:41, 20 January 2009 (UTC)

I don't know whether this anecdone will help. I used to live in Malaysia. There it's usually relatively easy to tell if your clothes are damp or not. Here in NZ particularly in winter, I find it rather difficult to tell whether my clothes are damp, or simply cold. As SB says, there are definitely other sensations that come into play, including the sensation related to friction and stuff of wet objects and likely including visual, but I do think cold is a very big factor in determing wetness. Bear in mind it's unlikely to be simply cold per se, but in precisely how it feels cold, i.e. that it quickly conducts heat away from your body so feels cold rather quickly Nil Einne (talk) 19:41, 22 January 2009 (UTC)

leaded brass

Is it safe to handle leaded brass? I made a paperweight out of machine shop brass. Do I need to wash my hands if I handle it? --VectorField (talk) 23:56, 18 January 2009 (UTC)

Lead isn't so toxic that just handling it is harmful, you would generally have to eat it, drink it, or inhale it. And only a small portion of leaded brass is lead. The other main ingredients are copper and zinc, neither of which is dangerous to handle. I suppose you might as well wash your hands, though, why not ? The only likely danger I could see is inhaling fumes when you first made it. StuRat (talk) 00:39, 19 January 2009 (UTC)

I also wonder whether the lead is forming an amalgam with the zinc and copper - in which case it ought to be OK. For the longest time, dentists have been filling teeth with an amalgam of silver and the oh-so-very-toxic mercury - so long as it remains as an amalgam it's pretty safe. SteveBaker (talk) 00:52, 19 January 2009 (UTC)

It might be wise to wash your hands before you eat if you've been handling it, but unless you suck your thumb, that's the only way you're likely to get much lead into your system from touching it. Even then, it will be minute amounts. --Tango (talk) 01:15, 19 January 2009 (UTC)

As noted, its probably entirely safe to handle it, but its probably not a good idea to eat or drink off of it. As long as you are not regularly ingesting things which are in contact with it, you are likely fine. Most of the problems with lead comes from lead-containing compounds, such as tetraethyl lead and lead paint, which are soluble in body tissues and much easier to ingest into the body. Metallic lead, or lead-containing alloys are much less of a threat; you can get lead poising my directly ingesting lead or inhaling powdered metallic lead, but the threat is MUCH less than from lead-based compounds. See Lead poisoning for more info. --Jayron32.talk.contribs 01:42, 19 January 2009 (UTC)

Always wash your hands before putting them in your (or anyone else's) mouth or handling food.--GreenSpigot (talk) 02:03, 19 January 2009 (UTC)

Despite statements above of what lead use is safe, U.S. standards for lead in consumer products are being sharply cut starting February 2009 by the Consumer Product Safety Improvement Act. The exposure level for surface coatings on a wide array of products, especially those intended for children, drops to 600 ppm 10 February 2009, then down to 300 ppm on 14 August 2009, then down to 100 ppm 14 August 2011, with certificates of testing by certified labs which do not exist yet in sufficient numbers. This is partly because of toys made in China with lead paint, and also because a metal charm on a shoe was lead and may have killed the child who swallowed it. In general, lead-containing objects should be kept out of the reach of children. No more toy lead soldiers. Edison (talk) 19:50, 19 January 2009 (UTC)

I believe we did say that the danger from lead comes from ingesting it, not touching it. I have a hard time imagining a child swallowing a paper-weight, unless it's far smaller than I'm thinking. I suppose they might lick it, though, so keep it away from small children. As for tightening up the lead requirements, that seems to rather miss the mark, as toys from China which don't adhere to our current standards are the real problem. StuRat (talk) 20:18, 19 January 2009 (UTC)

How so? According to Edison and the article, the new standards impose new testing and documentation requirements. Also are you sure all those toys from China don't adhere to the current standards? Some of them may it's just that the manufacturers realised sellng toys with any appreciable quantity of lead is not good business sense. Nil Einne (talk) 20:05, 22 January 2009 (UTC)

If "new testing and documentation requirements" means they will actually enforce the current standards, then that's good. I found a source which says that 54 toys were found which exceed the 600 PPM standard: [18]. The American Academy of Pediatricians recommends a level of only 40 PPM, so I've changed my opinion, they need to lower the amount allowed in toys even more AND they need to enforce the law. StuRat (talk) 20:52, 22 January 2009 (UTC)

Most lead soldiers were actually made of a lead/tin alloy and painted or enameled - so the amount of lead getting out to the children was much less than some people think. Early pure-lead soldiers were so fragile that intact examples are now exceedingly rare collectors items. Of course in those early days, the 'lead' in pencils was really lead... SteveBaker (talk) 20:01, 19 January 2009 (UTC)

Except that ignores how lovely it was to bite the soft lead toys... My grandparents held on to some old toys for us to play with when we visited; none of the lead farm-people in the farm animal box had feet, some were missing heads. There were little toothmarks on the ends. 79.66.92.148 (talk) 21:48, 19 January 2009 (UTC)

The classic British guardsmen that I have (given to me by my father from when he was a kid) had all lost their heads. When I got them the heads were held on by plasticine stuffed into head and body with a matchstick pushed through both. I didn't see any tooth-marks though. I was able to clean them up and flow some solder into the lead to fix them up like new. This probably destroyed any antique value they may ever have had - but they look nice. SteveBaker (talk) 23:18, 19 January 2009 (UTC)

Perhaps you could make everyone happy by shining up your paperweight one last time, then giving it a light coat of spray sealant (polyurethane, etc). --DaHorsesMouth (talk) 03:06, 20 January 2009 (UTC)

What? How old are these lead soldiers? It's questionable if real lead was ever used in pencils. According to our article on pencil, a pure deposit of graphite was discovered sometime in the 1500s (even if it was thought to be lead) which had to be covered by something (often sheep skin or string) because it was too soft to simply hold. Eventually the Italians thought of using wood. The Germans and later the French, Austrians and potentially Americans managed to use powdered graphite (the French had to since the English had/have the only source of naturally occuring known suitably pure graphite in the world and they were at war). While lead was used in styluses by the ancient Egyptians, it's questionable IMHO if these can be called pencils sine they share virtually none of the characteristics. Nil Einne (talk) 20:00, 22 January 2009 (UTC)

January 19

What kind of audio processing is this?

In signal processing terms, what kind of processing gives the opening refrain of the song Body II Body its distinctive quality? —Preceding unsigned comment added by 173.49.15.243 (talk) 02:20, 19 January 2009 (UTC)

Is this the song you're talking about? [19] I don't notice anything special about the first few seconds, except that the voice has an unusual impulse response i.e. there's perhaps some reverb and definitely some kind of band-pass filter which is reducing the apparent bandwidth of the signal by attenuating high and/or low frequency signals. There might be a hint of distortion too. This makes the audio sound like a low-quality, narrow-band audio system (like a telephone or cheap walkie-talkie). 4.242.147.97 (talk) 04:51, 19 January 2009 (UTC)

Yes, that's the song I was talking about; I was just using it as an example. The voice sounds bandwidth-limited, but that doesn't seem to be the only thing done to it. I'm trying to find out exactly what's done to it to give it the kind of quality that it has. --173.49.15.243 (talk) 05:20, 19 January 2009 (UTC)

Don't know what processing you'd use, but a similar distortion could be achieved using s.th like this [20] - --76.97.245.5 (talk) 01:05, 20 January 2009 (UTC)

Sounds to me like they took the bass out of (only) the voice-track to make it sound "tinny." This is a fairly common technique in many pop-music (and other genre) songs. Nimur (talk) 03:19, 20 January 2009 (UTC)

Is the areola/nipple of the breast (any breast, but a female breast I'm thinking of) a mucous membrane?

I mean, the holes that the milk comes out of must count for something... so could sucking a woman's nipple theoretically be a way in which AIDS could transfer? This is a serious question. It's not medical advice and nor is it a joke - it's just something I would like to know the answer to.--Terminal left (talk) 05:16, 19 January 2009 (UTC)

Theoretically it could if a fluid containing some HIV virons was transferred through the nipple of the suckee, and into a cut in the mouth of the sucker. That means if the nipple is expressing milk, is infected in some way, or is pierced and not fully healed. A healthy nipple from a non-lactating female has no real potential to transfer HIV. [21] Rockpocket 07:48, 19 January 2009 (UTC)

A quick googling brings up conflicting information. Apparently HIV has been detected in the milk and breastfeeding is listed as one of the ways a mother may transmit the virus to her child, but there's also claims that breast-feeding reduces the risk of transmitting the virus. EverGreg (talk) 09:54, 19 January 2009 (UTC)

Is that because the colostrum will contain antibodies against HIV, so the infant gets a head start in fighting it? --Tango (talk) 11:14, 19 January 2009 (UTC)

The study (The Lancet, March 2007) was only a statistical study, but the researchers hypothesis was that the mucous membrane within the intestines might act as a barrier to HIV infection, with the breast milk reinforcing the lining.. I've never heard of this effect from breast feeding, but it's not my field either. EverGreg (talk) 11:20, 19 January 2009 (UTC)

So just saying 'this is not medical advice' is the easy way to get medical questions answered? Especially if it is a sexually orientated question!

It depends whether we believe you, or not. In this case, I'm not sure I would have believed the OP... --Tango (talk) 16:36, 19 January 2009 (UTC)

Its not medical advice because it doesn't diagnose, address or advise about a treatment for medical condition. Its a question about the transmission of a virus, and can be answered based on knowledge of how the virus functions. If the OP chooses to utilize that newfound knowledge for medical or prophylactic purposes that is entirely his choice, but no-one has provided an answer recommending any course of medical action. Rockpocket 20:57, 19 January 2009 (UTC)

Dodging the question here, but looking up milk banks and donated milk gives the info that other viruses are transferable via breast milk. Polypipe Wrangler (talk) 22:55, 19 January 2009 (UTC)

Apparent violation of the Second law of thermodynamics at quantum level?

I was wondering weather the spontaneous creation of a particle-antiparticle pair out of nothing could decrease entropy in a closed system.

(1) For example, if in an isolated container were nothing but just vacuum, wouldn't the appearance of a particle create information?

(2) Or if the container had one single radioactive particle (or just a small number of them, not allowing us to use statistics), the decay of it seems to be without an external cause.

(3) On macroscopic scale it's nearly impossible to occur, but looking at the (nearly zero, but not equal to zero) possibility of a chunk of matter spontaneously rearranging into another chunk of matter with, let's say, higher potential energy, wouldn't it violate the second law of thermodynamics? --131.188.3.20 (talk) 10:20, 19 January 2009 (UTC)

This involves some nuances of entropy and information. It's possible for entropy to decrease purely by chance, since the law of nondecreasing entropy is a statistical law. If you invoke a system with few components, notions like entropy, gas pressure, temperature and such break down. A violation of the conservation of energy, which you'r also invoking here, is a wholly different matter. EverGreg (talk) 11:07, 19 January 2009 (UTC)

The second law is really an emergent property of statistical mechanics, which tells us that the average behavior of a thermally interacting collection of N particles tends towards a maximum in entropy and spontaneous deviations from that maximum have a probability proportional to $1 \over {\sqrt {N}}$. At macroscopic scales N is typically huge and the probability of measurable deviations from the second law is vanishingly small. However, whenever one starts talking about small number of particles it is entirely possible that an instantaneous state will show a large variation from the average, entropy-maximizing state. Dragons flight (talk) 11:15, 19 January 2009 (UTC)

Agreed. The second law of thermodynamics doesn't exactly forbid a decrease in entropy in a closed system, it just says that this is very unlikely - and as you add more particles, degrees of freedom and microstates, a violation of the second law becomes exponentially more unlikely. Virtual particle/anti-particle pairs exist for such a short time that any theoretical decrease in entropy is unobservable because of the Heisenberg uncertainty principle. Even if one of the pair of particles is captured by a black hole, and the other escapes, then this causes an increase in the black hole entropy which is greater than the decrease in entropy outside of the black hole. Gandalf61 (talk) 11:25, 19 January 2009 (UTC)

The issue seems to be that you have artificially constrained your system so as to give the appearence of a "closed system" or otherwise an violation of the Second Law without actually doing so. In any real world scenario, the second law holds perfectly so long as you don't purposefully ignore some bit of information which would cause it to appear to be violated. Once you consider that in reality, the only closed system is the entire universe, then any real situation obeys the laws of thermodynamics just fine... --Jayron32.talk.contribs 12:33, 19 January 2009 (UTC)

MANUFACTURING PROCESS

how close tolerance(that is gap) can we get if we swage stainless steel and Zr-4,can anyone get 0.1 microns?203.199.205.25 (talk) 10:55, 19 January 2009 (UTC) i mean if two tubes are swaged. —Preceding unsigned comment added by 203.199.205.25 (talk) 03:29, 20 January 2009 (UTC)

Fresnel drag

Is "Fresnel drag" the same concept described at Aether drag hypothesis? The reason I'm asking it that Sagnac effect has a redlink to Fresnel drag and I want to make sure I don't link to something completely off-base. I'm not familiar enough with these concepts to be sure I've got the right target page, although from context I think I may. Thank you. 152.16.51.125 (talk) 11:28, 19 January 2009 (UTC)

Yeah, I think you have found the right place. Fresnel drag is covered in that article and this confirms you have the rigt concept. SpinningSpark 19:25, 19 January 2009 (UTC)

Is there any solvent in the world has ph below 1.5 but without bubbles when spraying?

Is there any solvent in the world has ph below 1.5 but without when spraying? —Preceding unsigned comment added by Chlim (talk • contribs) 14:44, 19 January 2009 (UTC)

Creating a solution of pH < 1.5 is fairly easy. Concentrated strong acids such as Hydrochloric acid and Sulfuric acid are fairly easy to come by, and as far as I know, they aren't all that prone to frothing or bubbling. --Jayron32.talk.contribs 18:46, 19 January 2009 (UTC)

I just want to point out how important it is to dilute those particular acids, since they're really, really strong. With pKa's of -8 and -3, respectively, the pH's of the pure stuff is a lot lower than 1.5. Even if you don't consider their ridiculously strong acidity, their pure forms really need to be worked with in a fume hood, and I can also tell you from experience that it's a particularly unpleasant experience to inhale their fumes, so if you do use one of them in their concentrated forms, be sure that you know how to dilute the stuff properly, and have access to a fume hood or respirator. – ClockworkSoul 21:26, 19 January 2009 (UTC)

All absolutely true. However, most weaker acids are difficult to get in solutions of a pH that low. You can, of course, purchase stock solutions of HCl or H2SO4 already diluted to, say, 1 normal concentration (pH 0) which is much less problematic to handle than the concentrated stuff. --Jayron32.talk.contribs 22:39, 19 January 2009 (UTC)

tensing head/neck muscles

Is it possible to damage the brain from constant tensing of the neck and head muscles? (constant meaning it happens more or less consistently for more than 12 straight hours) —Preceding unsigned comment added by 75.23.83.54 (talk) 15:09, 19 January 2009 (UTC)

We can't give medical advice, I'm afraid. If you are concerned, see a doctor. --Tango (talk) 15:25, 19 January 2009 (UTC)

I am not asking for medical advice, I am just curious. It seems like it could but at the same time the notion seems impossible. —Preceding unsigned comment added by 75.23.83.54 (talk) 16:24, 19 January 2009 (UTC)

With the usual warnings of not considering this to be in any way correct or comprehensive: unlikely, vice versa on the other hand it's rather well documented for many conditions. Neck muscle tension is one if the items checked in a neurological evaluation. You might find the following pages helpful for drawing your own conclusions: Internal carotid artery, Head and neck anatomy, Cerebral hypoxia, Encephalopathy, Hypertonia, Headache. Good hunting.--76.97.245.5 (talk) 00:14, 20 January 2009 (UTC)

Thank you very much :) —Preceding unsigned comment added by 75.23.83.54 (talk) 00:50, 20 January 2009 (UTC)

stimulated emission

in a laser, a higher energy electron emits a photon and jumps to a lower energy level. How does another photon stimulate this electron to emit another photon? in a laser, how do the photons have the same phase and frequency?--Harnithish (talk) 15:26, 19 January 2009 (UTC)

We have an article on Lasers. Actually we have MANY articles on Lasers. If you read the main article, and follow the links from there, you can answer your own question. They are quite detailed and fairly accessable (compared to many Science articles at Wikipedia). --Jayron32.talk.contribs 18:43, 19 January 2009 (UTC)

Is there a chance that Mars will be swallowed up/?

Is there a chance mars will be swallowed up by the time sun becomes a white dwarf? Some sources had said there is a chance Mars will be swallowed up before sun becomes a white dwarf, just less likely than that of Earth.--69.226.46.118 (talk) 18:28, 19 January 2009 (UTC)

If you read Red giant#The Sun as a red giant, it describes the situation quite well. It seems that Mercury and Venus are definately toast, and the earth is likely a goner too, while its about even money on whether or not Mars in some form will survive. --Jayron32.talk.contribs 18:34, 19 January 2009 (UTC)

• What you mean by its about even money on whether or not Mars in some form will survive.--69.226.46.118 (talk) 18:38, 19 January 2009 (UTC)

I believe he means that scientists cannot say with any certainty given our current knowledge of stellar evolution.-RunningOnBrains 18:51, 19 January 2009 (UTC)

"Even money" means about a 50/50 chance, that is, it's as likely to happen as it is not to happen. --Tango (talk) 18:55, 19 January 2009 (UTC)

• Uh, is the calculation even right? The academic paper said sun's maximum extent suppose to be 1.15 AU, sun's lost of mass could push Venus and Earth's orbits to 1.24 AU and 1.71 AU, that's enough to keep those planets from being engulfed. What they said about Earth been dragged into sun is only news, doesn't mean it's right. Who said sun's expansion can hit Mars' orbit?--69.226.46.118 (talk) 18:56, 19 January 2009 (UTC)

I don't think it's likely Mars will be engulfed, I haven't seen any reliable sources suggest it. It will certainly be scorched, though. --Tango (talk) 19:09, 19 January 2009 (UTC)

I always thought Mars is engulfed by 0% chance, Venus by 90%, and Earth by 60% chance, or is it Mars is engulfed by 30% chance, Earth by 65%, and Venus by 99%.--69.226.46.118 (talk) 19:39, 19 January 2009 (UTC)

At any rate - it's worth pointing out that the disruption in solar output - the short, sharp high-energy bursts as the sun goes through this trauma - the orbital disruptions and all else - means that the earth and mars might "survive" in a technical sense - but without atmospheres or oceans, possibly with their surfaces reduced to molten lava flows and their axes tilted to make areas or perpetual (red!) sunlight and other areas of perpetual night. It's not a matter that lifeforms on earth could possibly care about because there won't be any! SteveBaker (talk) 19:56, 19 January 2009 (UTC)

• Steve, We have source said Venus might survive, I thought if Venus survives, it will just be black and hot with no life AT ALL, just land uniform surface as molten lava, just like Earth. 1.15 AU sun could push Venus' orbit to 1.24 AU. --69.226.46.118 (talk) 20:13, 19 January 2009 (UTC)
  • Why, 69.226, are you arguing? You asked a question which implied you didn't know and wanted more information, and when you are presented with links to that information, you start to argue about it? If you already had your opinion, why ask the question in the first place?!? --Jayron32.talk.contribs 20:58, 19 January 2009 (UTC)

  Why do you emphasise "at all"? Venus doesn't have any life at all now, as far as we are aware... --Tango (talk) 21:28, 19 January 2009 (UTC)

Are you impugning the first-hand findings of Professor Abbott and Dr. Costello? Or this noted trio of scientists? Clarityfiend (talk) 22:24, 19 January 2009 (UTC)

This said Venus could survive.--69.226.46.118 (talk) 22:51, 19 January 2009 (UTC)

And this too.--69.226.46.118 (talk) 23:00, 19 January 2009 (UTC)

Bob the alien's website said there is a chance that mars could be swallowed up as well. I question about updated and trustworthy of those sources.--69.226.46.118 (talk) 23:08, 19 January 2009 (UTC)

When they say "survive" - they mean as a burned out cinder with no atmosphere, etc. It's just possible for venus to "survive" within the limits of that meaning. The precise dynamics of what happens when a star does this aren't perfectly understood - and whether there would be enough force involved to push the existing planets outwards or whether they'd be pulled inwards to certain doom depends on too many variables for it to be calculated as a certainty. The probability of "surviving" obviously depends on the distance from the sun - so mercury is regarded as certain to go - venus is very likely to go too (but there is a chance) - out here where the earth is, it looks like it's a 50/50 chance and for mars the odds are evidently better than 50/50, Jupiter and everything further out is "safe" (although it's hard to imagine that it would be unaffected!). Trying to pin things down more accurately than that is impossible - even the experts can't agree. So - you get a statistical answer with large error bars. SteveBaker (talk) 23:11, 19 January 2009 (UTC)

• Can you restate and for mars the odds are evidently better than 50/50, I'm sorry I don't understand.--69.226.46.118 (talk) 23:27, 19 January 2009 (UTC)

Well, if the odds for the Earth are 50/50 (which certainly seems to be the consensus opinion) - and Mars is further away than the Earth which means it's odds of survival are definitely better - so we can reasonably say that Mars has a better than 50% chance of survival. SteveBaker (talk) 03:20, 20 January 2009 (UTC)

Original use of copper wire, before electric use

When early experimenters like Humphry Davy , Michael Faraday , and Joseph Henry started doing electrical experiments, they were able to buy considerable lengths of copper wire. They did not have to have it custom made. Why was it manufactured in large amounts, before it was useful as an electric conductor? It is more expensive than iron wire and far weaker, although malleable and flexible. What was its original use in the early 19th century? Edison (talk) 19:41, 19 January 2009 (UTC)

It has the advantage of not rusting. Copper wire will turn green, but won't fall apart like a rusty iron wire will. So, I imagine any outdoor use for wire, like in building fences, would tend to have used copper, or a copper blend, like brass or bronze, at least until stainless steel was invented. Copper wire is also more malleable, meaning it can be bent more without breaking, which would make it as good choice for things we would now use plastic zip-ties to do. StuRat (talk) 20:11, 19 January 2009 (UTC)

Take a look here. -hydnjo talk 22:25, 19 January 2009 (UTC)

Copper wire, especially the very fine wires used in early electrical experiments, is also used in making jewelry. --Carnildo (talk) 01:03, 20 January 2009 (UTC)

Joseph Henry (1797-1878), an American scientist, did some significant early work in electromagnetism, including invention of the relay. He could not find insulated copper wire for his experiments, so his wife ripped her silk wedding gown into strips and wrapped them around copper wire for him to use. She probably used some sort of glue or paste, or maybe shellac, to hold the cloth in place. - GlowWorm. —Preceding unsigned comment added by 174.130.253.174 (talk) 01:59, 20 January 2009 (UTC)

Another book on this subject is Copper Wire and Electrical Conductors: The Shaping of a Technology, by Blake-Coleman. Amazon has it, but the price is pretty hefty. – GlowWorm. —Preceding unsigned comment added by 174.130.253.174 (talk) 02:17, 20 January 2009 (UTC)

Carding wool.—eric 07:57, 20 January 2009 (UTC)

I checked Google Books for 18th century mentions of copper wire, and found that it was often used, along with brass or iron, to connect bell pulls throughout a house with signal bells in servant's quarters or the kitchen. When I had seen the term "bell wire" I thought it referred to its modern use for connecting doorbell pushbuttons to the transformer and bell or buzzer. That may have been the common usage which kept it available in quantity in the eaarly 19th century. Edison (talk) 22:34, 21 January 2009 (UTC)

I would have thought that copper wire would stretch too much for such usage.--GreenSpigot (talk) 02:26, 22 January 2009 (UTC)

Longevity of woman

What is the leading scientific theory on the reason of this disparity in average lifetime? My speculative opinion is that it is more sociological than biological. Waiting to hear from you folks.Bastard Soap (talk) 22:30, 19 January 2009 (UTC)

Well, this isn't really a place to discuss unsupported opinions, but we do have the following section from one of our articles: Life expectancy#Gender differences in life expectancy which has some links to some outside sources, as well as giving a short overview of some potential sources of the differences. --Jayron32.talk.contribs 22:34, 19 January 2009 (UTC)

The generally accepted theory is that it is stressed levels. As women have been more and more likely to enter the work force in recent decades the longevity disparity has shrunken. So you would be correct that it is more sociological than biological. I google search for "Why do women live longer than men" gave me several useful articles that talk about many of the more specific reasons also talking about the actual causes of deaths relating to each gender. Here is a short TIME article [22] and here is an article from WebMD [23]. Anythingapplied (talk) 06:15, 20 January 2009 (UTC)

I think that the macho bullshit also has something to do with it, women are generally more tollerated for ridiculous emotional release while men almost universally frown upon for any emotions of the not wanting to fuck or kill types. Is this a reasonable factor in the jumble? Bastard Soap (talk) 11:33, 20 January 2009 (UTC)

As it's a big topic you might enjoy this search for "gender differences in emotional expression"[24]. Wikip also has the article emotional expression – it's very small, but the links at "see also" look better. Julia Rossi (talk) 17:52, 20 January 2009 (UTC)

That reminds me of a joke my grandfather used to tell: why do men die before women? Because they want to. My grandmother out lived him by 16 years, by the way. – ClockworkSoul 20:56, 20 January 2009 (UTC)

I've heard it to be because men die at a young age in war; that a number of counterbalancing women die at a young age in childbirth is no longer so true. - Nunh-huh 21:46, 20 January 2009 (UTC)

While it may have an effect, I don't think it's enough to explain the difference. I'm pretty sure if you look at the life expectancy at 50 or 30 or something you'd find that there is still a resonable age gap which would imply it's not simply because men died young in wars. While you could argue the wars killed a lot of the men who would have lived the longest, it doesn't seem that likely to be such a big factor to me. Besides that many countries which have not had a significant number of people dying in wars still have the difference I believe. Nil Einne (talk) 20:41, 21 January 2009 (UTC)

Monks and nuns life nealy to the same age so the monastery and the stile of living there must have an influence.--23:26, 21 January 2009 (UTC)

Types Of Cells Containing Nuclear Pores

Just a quick question, are Nuclear Pores found in both plant and animal cells?

Thanks

Our article nuclear pore suggests that they are present in all cell nuclei. Plants and animals are all eukaryotes, so they all have nuclei and hence pores. Algebraist 00:28, 20 January 2009 (UTC)

That's correct. The nuclear pore is vital, allowing selective transport into and out of the nucleus. – ClockworkSoul 03:13, 20 January 2009 (UTC)

abbreviation for the word molecules that is different from mol or moles

I am looking for an abbreviation for the word molecules, that is not similar to words like "mol" or "mole" (as in a mole of substance, 6e23 things) —Preceding unsigned comment added by Cinnamon colbert (talk • contribs) 22:58, 19 January 2009 (UTC)

Do I read your question correctly: You are looking for an abbreviation for the word molecule that can not be mistaken for the SI unit mole or the corresponding sign mol? Not sure there is such a thing. [25] The dot could be used to tell one from the other, but that leaves a lot to be desired. 76.97.245.5 (talk) 00:40, 20 January 2009 (UTC)

The trouble is that there really isn't a synonym for the word 'molecule' - so any abbreviation is more or less going to have to be something like 'mol'. So I think you're kinda stuck. SteveBaker (talk) 03:15, 20 January 2009 (UTC)

Actually, the abbreviation for molecule is mole, which makes sense because that's what a mole is: lots and lots of molecules. Since you seem to want to smaller version of it, we can just work some SI magic: since 1 mole = 6.02x10²³ molecules, 1 molecule would be about 60 yoctomoles (ymol), and 60,200 zeptomoles (zmol). Will that do? – ClockworkSoul 08:21, 20 January 2009 (UTC)

Are you sure about that? I get 1 molecule = 1.66 yoctomol... Someone42 (talk) 09:36, 20 January 2009 (UTC)

Hmm... I was wrong, but it's not 1.66 ymol either: (6.02e23 molecules/mole)(1 mole/1e24 ymol) = (6.02e23 molecules/1e24 ymol) = .602 molecules/ymol (and 602 molecules/zmol). I really should remember not to try to do simple arithmetic so late at night. – ClockworkSoul 18:03, 20 January 2009 (UTC)

Yes, there are .602 molecules in a yoctomol, so 1 molecule is 1.66 ymol, as Someone42 said. Algebraist 18:12, 20 January 2009 (UTC)

Doh, thanks. Here's a query for the ref desk: what's wrong with me today? – ClockworkSoul 20:52, 20 January 2009 (UTC)

Have you been spending too much time in Australia lately? --Tango (talk) 22:22, 20 January 2009 (UTC)

That took me a second. Brilliant, Tango! – ClockworkSoul 00:36, 21 January 2009 (UTC)

How about 'cule? — DanielLC 18:18, 21 January 2009 (UTC)

January 20

A pore excuse for a question...

Do we have the same pores on our skin all our lives, or do some close up and others develop ? How about those at the nipple which deliver milk in nursing females, do they develop in pregnancy and close up after nursing ? StuRat (talk) 00:48, 20 January 2009 (UTC)

We can't give medical advice, I'm afraid. (You forgot the requisite 'this is not medical advice' disclaimer.) If you are concerned about your pores, please consult a doctor.  :-) 74.137.108.115 (talk) 04:46, 20 January 2009 (UTC)

The pores around the tip of the female nipple are called lactiferous ducts. They grow and proliferate quite significantly during pregnancy, but are present also in non-lactating females. Apocrine sweat glands become functional at puberty, eccrine sweat glands much earlier. A lot of sweat glands are associated with hair follicle, and together they form a functional "pore". The ducts and follicles themselves remain relatively static, but after the sweat duct passes through the dermis it essentially stops, and the sweat drains through clefts between prickle cells, through the stratum corneum on to the surface. This sweat-channel changes all the time as the cornified cells of the epithelium slough off. Rockpocket 05:27, 20 January 2009 (UTC)

Come on, this is clearly an anatomy question. As you'll see if you follow the link from the subject line, pores in the skin are associates with sweat glands. According to my copy of Gray's Anatomy (the 1958 edition, but I don't imagine this has changed), sweat (sudoriferous) glands are formed in the fetus during the 4th month of pregnancy. The breast is in effect "a greatly modified collection of sudoriferous glands" and its structures are also formed before birth. So the answer is yes, you keep the same pores. --Anonymous, 05:20 UTC, January 20/09.

Rockpocket says the "female nipple" has lactiferous ducts. How about the male nipple? Wouldn't it be similar to the nipple of an immature female, and capable of producing milk in such conditions as Gynecomastia or prolactin secreting pituitary tumors? Edison (talk) 19:50, 21 January 2009 (UTC)

Apparently so. Lactiferous ducts develop before the differentiating effects of testosterone, so male nipples have them too. Rockpocket 20:17, 21 January 2009 (UTC)

True color image vs. false color images

is there any difference between true color and false color images? Isn't it right what we see in space is always very different from what we see through satellite iamges. Ex. blue stars in space looks way too blue from what it actually looks, our sun is not as yellow from what it look from space. Mars is not as rust color as it is if we are orbiting around it. Mercury, Venus, and Mars is perfect enough to see clearly orbiting around it, but is Mercury brown or silver, all spacecraft's images is unfortunately wrong, even Mars and jupiter, although color vision is enough for humans, is it pink, orange in space which is shouwn by true color image-spacecraft-it's wrong,wrong,wrong, am I rght. I thought, the amount of light on Saturn is essentially dim,what you expect 100 times dimmer than Earth, Titan will not look pretty tangerine-yellow, they only look like a dim, almost gray sphere when you fly a rocket around it. Europa, is it brown or white, nothing is right, I thught Europa is dark eough to only have little color vision. Whatever SteveBaker, said, I count on him. He's a better scienctist than I am--69.226.46.118 (talk) 01:53, 20 January 2009 (UTC)

I think what you are trying to get at is, "is there any really 'true' color?" In which one can reply: what 'true' and 'false' mean can vary from situation to situation. In one case it can mean, as you indicate, "as if we were not viewing it through Earth's atmosphere", but in another it can mean, "we've represented infrared signals as part of the visible spectrum". --98.217.8.46 (talk) 02:20, 20 January 2009 (UTC)

The diff is that a true color image attempts to match the colors as closely as possible, while a false color image does not. They may decide to color a map based on elevations, for example, instead of the actual colors, in a false color image. StuRat (talk) 02:59, 20 January 2009 (UTC)

I think there are actually three kinds of image out there.

• False color images are nothing like 'reality' - the colors are used to deliberately distort some property of the science data to allow our eyes to see it. So you might be looking at rainbow colors representing (say) temperatures or altitudes or radio emissions. Things which are quite meaningless to our eyes without some false coloring.
• Enhanced images are an effort to give us an idea what the object could look like - perhaps if it were better illuminated or illuminated with more 'normal' colored light. The images we get back from the Mars rovers are kinda like that. The rovers have little color swatches on their bodies whose colors in normal earth lighting are well known. By adjusting the output of the rover cameras to make those color swatches look like they do here on earth, the colors on mars can be related to our normal experience...but those images are still not what our eyes might see if we were really on mars.
• Color approximated images. Very often, the nature of the science that a particular craft needs to do precludes them from taking proper Red/Green/Blue images that we can understand. So it might be that the spacecraft took an image in infra-red, another in ultra-violet and another in (say) sodium-yellow. None of those colors are things that our eyes can see directly - but it's possible to use the data in the other bands to make an estimate for the red/green/blue colors we might really see.

It's debatable what 'should' be shown in these cases - certainly false color can be downright misleading to the untrained eye. Enhanced color is often necessary because we simply can't see anything in many of these cases...and Color-approximated images are a lot more interesting and (arguably) useful than a monochrome image. But as we've discussed before - in many such cases, our eyes would 'really' see almost nothing - it would perhaps be just too dark to see anything.

Should NASA show us black images for far distant moons? That would be the most "realistic" thing - but it's just not useful. The one think I wish is that they would be more clear about exactly what processing they DID do on these images...even if it's just for "the general public". SteveBaker (talk) 03:09, 20 January 2009 (UTC)

Does Saturn count as far distant planet? Uh, it's 100 times dimmer. if you rocket around Saturn, it would look close to black, perhaps just dim gray sphere. humans can barely see Saturn with their own eyes. All spacecraft do is use black-and-white cameras, NASAs just use spectrums/chemicals to fix the image, so it will look better, all those iamges are hopelessly wrong.--69.226.46.118 (talk) 03:25, 20 January 2009 (UTC)

I'm not sure 69.226.46.118 is correct in calling these devices "black-and-white" cameras. Some of them use a variety of techniques for hyperspectral imaging, including a "monochromatic" imaging sensor, with a set of filters for different bands... but isn't that how all cameras / eyes work, anyway? On some level, every color imager is simply a multi-channel intensity imager. Nimur (talk) 03:36, 20 January 2009 (UTC)

The cameras vary - some are indeed a wide-spectrum monochrome camera with various color filters that can be placed in front to select some range of frequencies to be captured. That's not how our eyes work - we genuinely do have four different kinds of sensors - each of which is responsive to the light in a different way. One sees only monochrome - the other three each see one band of frequencies (one each for red, green and blue light). So you're right about many spacecraft cameras - you're wrong about eyes. SteveBaker (talk) 13:36, 20 January 2009 (UTC)

Here are some samples all from NASA. The greens and yellows in the false color image just feel wrong to me. The "true color" image is definitely better, but still noticeably more vibrant than the actual photo. Also, one might note that in both composite images the day/night shading is artificial, and the image was stitched together from many smaller images covering less than a whole globe and taken over several days. Dragons flight (talk) 03:38, 20 January 2009 (UTC)

• 
  False color satellite composite
• 
  "True color" satellite composite
• 
  Astronaut photograph from Apollo 17

• i've watched the news about Mars on January 1, 2009. When spacecraft went on Mars, they took it with black-and-white image from spacecraft, the NASA team review it and revise the color with pink, salmon, orange and brown color. That's not what it will look like if we actually were hanging out on Mars. Spectrum for example use yellow color for sulfur. 3 peoples have been on Moon in 1969, when they went on moon, out in space is black, and they have no light. is the planet brown or gray, nobody can answer it.--69.226.46.118 (talk) 05:54, 20 January 2009 (UTC)
  • The sun provides plenty of light to the Moon; it is gray. You can see this from Earth if you simply look at the Moon. Dragons flight (talk) 06:01, 20 January 2009 (UTC)

(after edit conflict) There is definitely light in space, on the moon, and on other planets. The intensity may vary for a large number of reasons (distance from sun, dust / atmospheric absorption and refraction, insolation angle, etc). But there is definitely light on the moon and elsewhere in the solar system. You might also want to read about Color constancy. And from color, "The color of an object depends on both the physics of the object in its environment and the characteristics of the perceiving eye and brain." However, there is an absolute, quantitative answer about an object's color - you can parameterize its reflection and absorption spectrum. Nimur (talk) 03:22, 21 January 2009 (UTC)

You can certainly scientifically, qualitatively talk about the 'color' of any object by plotting it's spectrum - this is an exact matter with precise and undeniable results. HOWEVER, that doesn't help much in describing "how it would really look" because our eyes don't work by measuring a spectrum and our brains do an unbelievable amount of "image processing" on the data that our eyes produce. What might technically be a source producing such-and-such number of lumens of light in the such-and-such nanometer waveband of the yellow region of the spectrum can still look anything from white to yellow to orange to brown to black to us humans. Worse still, our perception of 'hue' shifts depending on the brightness. Objects look much more blue-ish in dim light than they do in bright light. As our dark-adaptations kick in, the color of a single, unchanging object will shift. How our brains interpret a color depends dramatically on the nature of the colors of objects close-by in our field of view - and the longer we look at an environment that's all of one color, the more we percieve that as "normal" and start to skew that color towards white. If we spent all of our lives living on a reddish planet like Mars, the more we'd start to see 'red' as a neutral color and note the colors of everything else by contrast to red. The last astronauts on the moon (who'd spent days looking at a more or less monochrome world) were blown away by what they said were intensely bright orange rocks at the end of their last moon-walk. They were so blown away by this sudden (and to them) INTENSE color that they came close to running out of suit oxygen while collecting them. In reality, the rocks are pretty subtly tinted - but to color-starved eyes, they looked incredibly intense. So: What some particular image would "really" look like is an incredibly complicated question. Making a set of photographs "look real" is an essentially hopeless task - and you can't rely on your eyes to tell you the "truth" when it comes to color anyway. SteveBaker (talk) 13:36, 20 January 2009 (UTC)

I agree with everything you are saying, but I think it is nonetheless important to keep in mind that some reconstructions are reasonable approximations to photographic images, and other imagery does not achieve (or even want) to do that. As much as psychology and ambient conditions impact perception it is still true that there are right and wrong answers when the goal is to develop something that approximates what humans could see. The things we call "true color" images often want to be approximately photographic, while "false color" images may have many other goals entirely. Dragons flight (talk) 16:05, 20 January 2009 (UTC)

Regarding the false-color earth pictures above, the most amazing thing to me is the "terrain" emphasis. There's a lot of visibility for the terrain of mountain ranges, visually depicted as a shadowing effect, on both the false-color composites; while the Apollo photograph does not really indicate any shadowy terrain. There's an example of a false-color application which may distort the interpretation of the image. Nimur (talk) 06:06, 20 January 2009 (UTC)

"Distort" is a loaded term. Without understanding what you're seeing, yes, you may get a false impression - but if you set up that false color for a very particular reason (like you're looking for subtle undulations in a relatively 'flat' world) - then juicing up the image so that the subtle shadowing becomes more prominent - is a perfectly valid way to extract more useful information from an image. Remember - we don't take these pictures as art for the masses - they are taken to allow scientists and trained image analysis experts to discover new scientific fact about the subjects of these photos. So one man's "distortion" is another mans "enhancement". SteveBaker (talk) 13:36, 20 January 2009 (UTC)

The light from the sun would illuminate Saturn at about the same level as a good office I believe, see lux. Much better than a sitting room at home. So it wouldn't seem dim at all if we were close. Our eyes can accommodate an enormously wide variation in brightness. Dmcq (talk) 18:23, 20 January 2009 (UTC)

Here's a good guide to the brightness of outer planets: According to Apparent magnitude, the full moon has an apparent magnitude of −12.6. I think we would all agree that we can see fairly well under a full moon, when given a few minutes for our eyes to adjust. The same list puts the brightness of the sun when viewed from Neptune as −20. This means that the sun's brightness at Neptune's distance is around 700 times as bright as a full moon on Earth. Given these facts, I'd say that Neptune, and thus any other planet, would be quite bright enough to see comfortably from a spacecraft.-RunningOnBrains 18:52, 20 January 2009 (UTC)

That's an odd way to calculate it...and I'm not even sure it's right because the apparent magnitude of an object is independent of it's area - but the amount of light it casts is not...or is it? Well, it doesn't matter because here is the direct way to calculate it: The Earth is 150 million kilometers from the sun - Neptune is 4550 million kilometers from the sun - because brightness decreases with the inverse square of the distance, the amount of light available on Neptune is 920 times less than on Earth. That's a lot - but (as you say) the eye is pretty sensitive. Our eyes can adjust between brightest and darkest by a factor of about 100:1 - meaning that if you are in a brightly sunlit area and then in an area that has 100x less light, you can see just as well in both cases - and after a few minutes of adaptation, you can't even tell the difference between the two. But Neptune is 920x darker - so it would definitely seem nine times darker than here on earth - even after your eyes had adjusted. However, we can see brightness differences down to around 1/1,000,000th of bright daylight - so we'd certainly be able to see something in the gloom. Furthermore (and more germane to this question) - even if we accept User:Runningonbrains's result - you can see by the light of a full moon - BUT YOU CAN'T SEE COLOR. Everything looks blueish. That's because your 'cone cells' (which are responsible for color perception) don't work in light that dim - they simply shut down - and leave you with only the 'rod cells' which detect brightness across the entire spectrum but without giving any perception of color. So, sure - you'd be able to see on Neptune - but not in color. So this leads us back to the original point: When you see a color photo of Neptune, is that "what it really looks like"? Well, no - because if you were really there - you wouldn't be able to see any color. But it is this very complexity of explanation that reinforces the impossibility of answering this question cleanly. SteveBaker (talk) 20:25, 20 January 2009 (UTC)

Defining magnitude for non-point sources is of only limited use - see Surface brightness. One major correction to your calculations - it wouldn't seem 9 times dimmer, since we perceive light logarithmically, the difference between 1:100 and 1:1000 is 2/3 as bright (or 1.5 times dimmer). --Tango (talk) 22:21, 20 January 2009 (UTC)

Actually - it's not logarithmic - it's a power law - but in any case, we adapt for the difference of a factor 100 - the REMAINING factor of 9 after we run out of adaptation is what we're discussing here. SteveBaker (talk) 01:03, 21 January 2009 (UTC)

If it's not logarithmic, why is the magnitude scale logarithmic? --Tango (talk) 01:11, 21 January 2009 (UTC)

Weber–Fechner law#The case of vision says it's logarithmic... Could you provide a reference for it being a power law? --Tango (talk) 01:13, 21 January 2009 (UTC)

"Misconceptions About Astronomical Magnitudes," E. Schulman and C. V. Cox, American Journal of Physics, Vol. 65, pg. 1003 (1997).

...or you could believe our article Apparent magnitude: "A common misconception is that the logarithmic nature of the scale is because the human eye itself has a logarithmic response. In Pogson's time this was thought to be true (see Weber-Fechner law), but it is now believed that the response is a power law (see Stevens' power law)." - which actually cites that paper. But I have indepenent (WP:OR) verification of that in my studies of dim-light vision as relating to the simulation of night vision using computer graphics. The whole area of dim light perception is very messy...it almost seems like the human body doesn't like people fitting mathematical relations to it! But for sure the astronomical 'magnitude' thing is an ugly mess brought on and perpetuated by poor science and an appalling inattention to appropriate ways to set standards for use into the future. In an age of amazingly precise instruments and computers, astronomers are still talking in terms of brightness scales devised using naked eye astronomy in 300BC! SteveBaker (talk) 14:38, 21 January 2009 (UTC)

So our article on the Weber-Fechner law is incorrect? Could you fix it (and save me having to actually read the paper!)? We have introduced fractional magnitudes since the system was first invented, and have defined in all rather more precisely. If we measured brightness in watts it would all be written in scientific notation and people would only look at the exponent anyway, so why not just use a logarithmic scale? --Tango (talk) 15:47, 21 January 2009 (UTC)

I don't think the rods detect brightness across the entire (cone) spectrum, at least not according to diagrams like this. -- BenRG (talk) 20:32, 21 January 2009 (UTC)

Can you restate If we spent all of our lives living on a reddish planet like Mars, the more we'd start to see 'red' as a neutral color and note the colors of everything else by contrast to red this again? I don't fully understand it Steve. What you said about neptune is same thing about Saturn. i said Saturn is 100 times dimmer, 10 times farther away from sun than Earth. You can still see Saturn the planet but not the color.--69.226.46.118 (talk) 22:33, 20 January 2009 (UTC)

Let me point out an experiment you can do right now that'll illustrate it better than I can explain it. Click on the weird colored US flag to the right here. Open it up so it more or less fills the screen - grab a sheet of white paper. Now, stare at the center of the flag for at least 30 seconds...then hold the white paper up in front of the screen so you're suddenly staring at a white "screen". What happens is that you suddenly see the flag in it's correct colors (red, white and blue). That's because in just 30 seconds your eyes started to 'adapt' to the colors in the weirdly-colored flag - when you suddenly look away, what is white now looks colored. Similarly - if you spent your time staring at red ground and reddish sky on mars - then when you set eyes on a pure white object, it would look pale blue (cyan) because the red receptors in your eyes are sick of seeing red - and the green and blue sensors are struggling hard to see anything at all in that reddish world. When you look at something white, the red receptors are still 'dialled down' and the green and blue receptors are hyper-sensitive - so you see the color 'cyan' (pale greenish-blue). Once again, should photos taken by the Mars rovers show white objects as "true" white - or should it show them as our adapted eyes would see them in "realistic" shades of baby-blue? See Afterimage for a better explanation. SteveBaker (talk) 00:49, 21 January 2009 (UTC)

• I know sky color vs. what the true color of planet in my own eyes are not relevent. The sky on Neptune ro Saturn will not be black until we go right inside the planet's mantle. Above the cloud-tops, the sky wouldn't be black yet, they still scatter some light waves, so the color should be moderate. Between the clouds, the light scatter is different-the sky would be shallow-moderate level there.--69.226.46.118 (talk) 22:46, 20 January 2009 (UTC)

• • What?? I stare at grass everyday, the color is green all the time. i stare at the wooden tables all the time-it is always brown? So what will be the world like, if I stand on Mercury and Venus, especially Venus a world over thick layer of greenhouse heat?--69.226.46.118 (talk) 03:08, 21 January 2009 (UTC)

Because the grass is green and the sky is cyan (blue/green), red objects seem very VERY 'visible' to us - red is a bright color. That's no accident - we're evolved from creatures who looked for ripe fruit in the branches of trees - so being able to spot something red in a sea of green had a huge evolutionary benefit. If you were on mars, you'd hardly notice a red object because the red receptors in your eyes would be exhausted! Dunno about Venus - we don't have enough data from the couple of old Russian probes that landed there (and were promptly destroyed by the atmosphere) decades ago. Mercury has almost no atmosphere. On the dark side the ground would be profoundly black because the only illumination would be the stars (and perhaps venus if it's the right time of the year). It would be like looking out into space from anywhere else in the vacuum of the solar system. On the bright side - well, mercury is 3x closer to the sun than use - so it would be 9x brighter than the sunniest day on earth...well - more even than that because there is no atmosphere to scatter and attenuate the light...so it would be far too bright to see anything at all with the naked eye - so you'd have dark glasses on and now all bets are off because it depends on the nature of the glasses. SteveBaker (talk) 14:38, 21 January 2009 (UTC)

This general subject has been discussed before on the Ref Desk—see Venus and Jupiter's true color for one. This page is interesting. -- BenRG (talk) 20:49, 21 January 2009 (UTC)

Rechargable batteries - the 'S' terminal?

I've noticed that most batteries in mobile phones have three terminals, +ve, -ve, and 'S'. Anyone know what this 'S' terminal is for or how these cells work? I've searched around and tried the Wiki article Rechargable_battery but can't find any mention of this third terminal? —Preceding unsigned comment added by 194.63.116.72 (talk) 10:20, 20 January 2009 (UTC)

It's a guess - but laptop batteries have a pin that enables the charger to sense (hence 'S') the temperature of the battery so that it can be recharged at the maximum rate without destroying it. Presumably there is a thermistor wired between the -ve and 'S' pins. I'm guessing that cellphones have now reached that same level of sophistication. But I don't know for sure...someone else may know better. SteveBaker (talk) 13:14, 20 January 2009 (UTC)

My phone has a T pin (which may concur with SB's suggestion) Nil Einne (talk) 20:25, 21 January 2009 (UTC)

First movie projector for more than one person?

Who invented the first movie projector that could project an image for an audience? Lumiere brothers are sometimes quoted, other sources tell they weren't the first, but fail to mention another name. 82.181.93.226 (talk) 12:09, 20 January 2009 (UTC)

The History of film article mentions Robert W. Paul and Birt Acres as contenders for the title, in addition to Auguste and Louis Lumière. The three projectors were created pretty much the same time. Who exactly ran a first successful test of a projector in his laboratory may be lost in history; Acres appears to have a good claim for the first scheduled demonstration. 88.114.222.252 (talk) 14:16, 20 January 2009 (UTC)

Homo genus

I've been reading about the Homo_(genus) and about the fossil records that have been used to try and establish the history of this Genus, as there is only one presently living species in the genus. My question is how do paleontologists know based of features of a fossil that two specimens actually should fall under different species (which means they are making assumptions about their ability to mate). I understand there is plenty of controversy to which specimens fall under what species and how many species there are, but what is to say that any give one can't mate with any other given one? What establishes that line? What is the scientific reason that two closely related species can't mate? Anythingapplied (talk) 14:43, 20 January 2009 (UTC)

It's definitely a gray area. Obviously species that are very different couldn't mate to produce fertile offspring, but for those which are fairly similar, scientists must use other methods to determine if this was possible. If the two species existed in the same time and place, and they could interbreed, you'd expect to find some fossils of half-breeds. If they were separated by space and/or time, then this method doesn't apply. Assumptions can be made based on how long the two have been apart, as genetic drift tends to happen at a somewhat predictable rate, meaning that a certain amount of time is required to create a distinct species. Another option, if the fossils are recent enough to contain DNA, is to do a genetic analysis. Species with different numbers of chromosomes, for example, are less likely to be able to mate to produce fertile offspring. StuRat (talk) 15:48, 20 January 2009 (UTC)

Paleontologists don't care about mating. Really they don't. When dealing with extinct taxa, these decisions really are all about fossil morphology and whether one group of fossils arising in a particular time and place has quantifiably different characteristics than another group found at a different time and/or place. How big the differences have to be are a matter of debate (see lumpers and splitters), but it is really all about form and seldom ever about mating compatibility. Dragons flight (talk) 15:56, 20 January 2009 (UTC)

"Species with different numbers of chromosomes, for example, are less likely to be able to mate to produce fertile offspring". I thought only plants could mate with something that didn't have the exact number of chromosomes? Is this what you meant? or are there other exceptions?

When you (or I) say "species can't mate", what does that mean and why is that scientifically? Suppose I put Hare DNA (46 chromosomes) into my sperm to fertilize an egg. Shouldn't it fertilize just fine? I'm guessing something would start to grow too... it probably just wouldn't live very long, right? Die before birth. Is that what is meant when you say creatures can't mate? I suppose a lot of times it is also physically impossible or the male/female delivery systems are different enough that it wouldn't even get to the fertilization point, but those two obsticles shouldn't apply to closely related species. Anythingapplied (talk) 20:41, 20 January 2009 (UTC)

I didn't say "species can't mate", I said that, if they can't mate to produce fertile offspring, they aren't the same species. It certainly seems unlikely that species with a different number of chromosomes are likely to pass this test, but I'm not willing to say it's completely impossible. Here's a case where a pregnancy occurs, but isn't viable, for sheep-goat hybrids, due to a differing number of chromosomes: [26]. Also, this doesn't mean that all species with the same number of chromosomes can interbreed. You may get a pregnancy that's not viable, like your hare-human example. As for closely related species always being able to mate, that isn't always even true of the large dog/small dog example of the same species, given below. If they do somehow manage to mate, I would expect the combo of a small male and large female would be viable, but the small female/large male combo would not be, as the uterus of the small female would be too small for the litter of medium-sized offspring. Perhaps aborting all but one of the puppies early on and then delivering the surviving puppy by C-section could work, though. You could also do in-vitro fertilization and implant the embryos in a female dog large enough to carry them. StuRat (talk) 14:34, 21 January 2009 (UTC)

(This is in reference to your initial question). Palaeontologists largely don't know when to classify something as being a single species. They can make an educated guess, obviously, but the sheer scarcity of fossils versus the richness of nature makes it a very difficult decision. All the classic dinosaur names people know (triceratops, diplodocus, stegosaurus, etc.) are simply the genus names. If a dinosaur is only known from ten fossils found over thousands of square kilometers, how could you ever know whether they represented different species, different genuses, different ages, different sexes, or even just good ol' natural variation? And even if two skeletons look anatomically identical, what does a term like species even mean if the actual animals lives a hundred thousand years from each other? Think of the dozens (hundreds?) or warbler species extant today. If you laid out the skeletons for each one, perfectly preserved and all in one place for ease of comparison, not even a ornithologist could separate them all out; they'd call them perhaps a half dozen species of one genus and probably still louse it up by conflating a female skeleton or three as being a distinct species. Birds are dinosaurs, so imagine trying to do the same thing, except the skeletons are millions of years old, broken into dozens of pieces, and scattered around the globe. Oh, and each bone is bigger than you can even lift. Matt Deres (talk) 21:28, 20 January 2009 (UTC)

We've discussed this a few times before - it's clear that the quasi-formal definition of "a species" involves the issue of whether a cross-breeding produces viable, fertile offspring that breed true...not just 'offspring'. So a mule is not a species and although crossing a horse and a donkey will reliably produce a living mule - the mule cannot itself breed more mules because it's infertile. Hence horses and donkeys are not the same species. Similar arguments apply to lions and tigers and their crosses the 'ligar' and 'tigon' (yes - we really do have separate articles!). Whether you get a tigon or a ligar depends on whether it was the momma who was the lion or the daddy - but you can't breed tigons or ligars (at least, not reliably). So the issue of whether the egg will be fertilised and become viable or the foetus or the birth or living more than a few weeks...it's all moot. If the offspring doesn't survive and breed true - it's not a species and the two parent species are different too. Contrast that with (say) dogs - a Labrador and a Poodle can be crossed to make a Labradoodle - and if you take two labradoodles and breed them, you get (probably) more labradoodles - but for sure you get live, healthy, fully functional dogs. Hence Labradors and Poodles and Labradoodles are not separate species, they are all the same.

Having said that - there are an enormous number of grey areas - species A can breed with B which can breed with C which can breed with D...but D can't breed with A. Are A,B,C,D all the same species? Tough. I doubt that crossing a Chiuahua with an Irish Wolfhound would produce viable puppies - so which one of them isn't considered to be a dog? So it's all very vague and fuzzy and nasty.

The one CRUCIAL thing you should take away from this is that words like "species" are merely convenient shorthand - they don't represent any "real world" thing - they are just handy words for biologists to toss around. Everyone agrees on what's going on - the underlying mechanisms that make Tigons, Mules and Labradoodles is pretty well understood - we just can't make up our minds what to call the resulting groups of animals. Just as the decision as to whether Pluto is a Planet or not was completely arbitary - so the decision as to whether the Chimpanzee should be renamed "Homo-Pan" or remain "Pan Trogolodytes" is more a matter of religion than of science. (I'm all for the change - mostly because it'll piss off the fundies and the other nutjobs - and I have a mischievious nature!)

SteveBaker (talk) 22:21, 20 January 2009 (UTC)

Naively, you would expect a litter of labradoodle-labradoodle pups to contain 25% Labradors, 25% poodles and 50% labradoodles. In practice, it will be more complicated than that, but you would almost certainly get a litter ranging from predominantly Labrador to predominantly poodle, with most somewhere inbetween. --Tango (talk) 01:20, 21 January 2009 (UTC)

Those ratios would only apply if there was a single gene which determined which breed you get, while there are actually many genes, on different chromosomes. StuRat (talk) 14:09, 21 January 2009 (UTC)

Hence "naively", and the more accurate but less precise "in practice" sentence. --Tango (talk) 14:37, 21 January 2009 (UTC)

von brun's nest

what is von brun's nestDreamoftrust (talk) 15:21, 20 January 2009 (UTC)

Not sure. Could possibly be refering to Von Braun (crater), a crater on the moon. See also Von Braun which shows several other articles which may contain this info... --Jayron32.talk.contribs 15:52, 20 January 2009 (UTC)

It's probably (von) Brunn's nest: [27], given the genre of the question below. Fribbler (talk) 15:58, 20 January 2009 (UTC)

nissle's substance

what is nissle's substanceDreamoftrust (talk) 15:23, 20 January 2009 (UTC)

It's another word for Nissl body. Fribbler (talk) 15:45, 20 January 2009 (UTC)

Is this a lichen or an animal colony?

I couldn't find another way to ask (submit?) for information about the enclosed colony. I couldn't find anything similar in your terrific database. This colony? is on a granite boulder in Truckee, CA at about 6400' elevation. The photos are magnified for better viewing....actual size of the group is about 1 cm across. How can I find out what this is and more information about it? (I can't figure out how to include the images with this query.) Many thanks!76.197.15.28 (talk) 16:03, 20 January 2009 (UTC)

do you have a link? Julia Rossi (talk) 17:40, 20 January 2009 (UTC)

How's this for going out on a reference-desk limb? Without a photo or any specific information at all, I'm guessing slime mold. Deor (talk) 13:08, 21 January 2009 (UTC)

I hope that's with a net! You Daring Deor you. Richard Avery (talk) 14:02, 21 January 2009 (UTC)

MAG 29

What does the MAG stand for in the name of this carbon star? 196.2.124.248 (talk) 19:18, 20 January 2009 (UTC)

Well, the MAG 29 link does no good, as that article is about something completely different. It's just a guess, but could it mean they are in the vicinity of the Magellanic Clouds ? StuRat (talk) 19:38, 20 January 2009 (UTC)

Presumably you are referring to the MAG 29 of this week's Science (journal) article entitled Dust Formation in a Galaxy with Primitive Abundances. For those who do not have access to the full text, here is the abstract. The article cites "...studies with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) and the Fornax Dwarf Spheroidal", and goes on to mention MAG29 in detail, "a carbon star in the direction of the Sculptor Dwarf Spheroidal galaxy with the IRS on Spitzer. The Sculptor Dwarf is a satellite of the Milky Way, with a metallicity only 0.04 that of the Sun. A study of carbon stars in the Galactic Halo detected a candidate, MAG 29, in the field of the Sculptor Dwarf."

It would appear that MAG 29, while not actually located in the Magellanic Cloud, appears in the same region of the sky, and was thus named "MAG 29" incorrectly. However, I'm not particularly familiar with my Dwarf Spheroidals and it's possible that Fornax is on the outskirts of the Magellanic clouds.

This of course brings up the interesting problem of naming a deep sky object, because it takes a fair amount of scientific study to accurately position the object in "3-D", but to do thorough study, you need to locate it in the "2-D" field of view of earth's sky. So a name may be assigned prematurely, as it seems was the case here. Nimur (talk) 03:34, 21 January 2009 (UTC)

In fact, further research (N. Mauron et al.: Halo carbon stars, Astron. Astrophys. 418, 77 (2004), PDF) (I'm deep diving here, bear with me), indicates that the actual location of MAG 29 is not well known (even though it has been observed since at least 1985!) "No radial velocity could be determined by us for #29, and its membership to Sculptor needs further observations to be proven." It makes me a happy scientist when an astrophysicist has enough confidence and integrity to state the degree of uncertainty without embarrassment. It's really really hard to know where things actually are, when they're some 300,000 light years away. Nimur (talk) 03:50, 21 January 2009 (UTC)

Lest the user get the impression that astrophysics is a rough science when it comes to positioning, it might help to point out that the celestial latitude and longitude are always known with great accuracy and it is only the radial distance which chronically is a problem. (see Cosmic distance ladder). Rotational (talk) 05:48, 21 January 2009 (UTC)

Seems to me (and SIMBAD) that the identifier has nothing to do with the Magellanic Clouds (it should be LMC or SMC in that case) but is formed from the initial letters of the names of the first three authors of the discovery paper by Mauron, Azzopardi, Gigoyan & Kendall (2004, linked above). It may have been more polite to include the fourth author as well... --Wrongfilter (talk) 12:21, 22 January 2009 (UTC)

Temperature of a lit cigarette

What temperature does the lit end of a cigarette reach during inhalation? I have a vague memory of hearing that it can be as hot as a blast furnace, but have no idea if this is true, or just something I heard in the pub. DuncanHill (talk) 20:15, 20 January 2009 (UTC)

I guess the parts that glow reddish-orange are closer to 1000 K, and the parts that glow brighter yellowish-orange would be closer to 2000 K temperature or even a bit higher. You may look at the chart here for a rough estimate. --Dr Dima (talk) 20:39, 20 January 2009 (UTC)

So yes, it is definitely in the same ballpark as a typical blast furnace temperature (which is around 2000 K, see e.g. here). --Dr Dima (talk) 20:45, 20 January 2009 (UTC)

Many thanks. DuncanHill (talk) 20:51, 20 January 2009 (UTC)

It glows the same colour as a blast furnace, so it's the same temperature - the colour of thermal radiation is a function of temperature. (There are exceptions, as with any rule, of course - but this isn't one of them!) --Tango (talk) 22:15, 20 January 2009 (UTC)

It is important to note the difference between temperature and thermal energy. A small quantity of mass at high temperature does not have the same total thermal energy as a blast furnace, even if it is at the same temperature. Nimur (talk) 03:38, 21 January 2009 (UTC)

Color of a blackbody object at a certain temperature in the mired scale. Mired number = 1,000,000/temperature in Kelvin

I think I fixed the formatting this time. 152.16.15.23 (talk) 04:05, 21 January 2009 (UTC)

rice in a silo exploding

I heard from somebody that you have to dry out rice before you put it into a silo. I asked why, and they said it was because gravity would make them explode or something like that. They didn't give any more explanation, so I'm coming here. Is this a myth or would that actually happen? flaminglawyer^c 22:06, 20 January 2009 (UTC)

I can't see them being wet with water making them explode... certain oils maybe. Rice in a silo could probably explode, given the right conditions - the surface area is enormous so if it caught fire it would burn extremely quickly, we call burning very quickly "exploding". I would have thought dry rice would burn better. Wet rice may well go rotten and mouldy - not very dramatic, but still undesirable. I can't see what gravity would have to do with any of it, though. --Tango (talk) 22:13, 20 January 2009 (UTC)

Spontaneous combustion hints that dampness might help bacteria in hay to heat up and cause a fire. I suppose it might happen also to rice. The article doesn't say that, though, so I can't say. APL (talk) 22:18, 20 January 2009 (UTC)

Perhaps the drying process removes any part of the grain that would end up as dust in the silo, so has nothing to do with wetness at all. 161.222.160.8 (talk) 23:25, 20 January 2009 (UTC)

Fine dust can and does cause explosions in silos, but wouldn't moistness keep the dust levels down? Apparently "dust removers" (presumably filters of some sort) are used to cut down on the level of fine airborne particles.152.16.15.23 (talk) 01:39, 21 January 2009 (UTC)

Are they really talking about a large scale explosion? At first sight, I'd take this to mean that with a bazillion tons of rice pushing down on the grains at the bottom - they simply wouldn't be structurally strong enough - so they's split and 'pop'. Dried rice is much harder - and therefore more able to resist that pressure without splatting. But I don't really know. Dust explosions are a serious matter - but dry rice has got to be more prone to that than wet stuff. SteveBaker (talk) 00:26, 21 January 2009 (UTC)

Also, dry rice may become wet and expand in the silo. If packed tight enough, this could generate enough pressure to cause a spectacular failure of the silo without heat and/or flames at all. A 40-foot tall structure splitting open violently and spraying chunks of rice across the landscape may cause one to call the event an "explosion" even if there was no fire or no heat. --Jayron32.talk.contribs 00:31, 21 January 2009 (UTC)

What's all this I hear about dust? Is dust easily explodable or something? Why does dust matter? flaminglawyer^c 01:19, 21 January 2009 (UTC)

Dust is highly explosive - flour mills are very dangerous places. It's because of the enormous surface area to volume ratio (which increases reaction rates) - surface area is proportional to the square of diameter, volume to the cube, and the square of a very small number is much bigger than the cube of a very small number. As always, we have an article: Dust explosion. --Tango (talk) 01:28, 21 January 2009 (UTC)

Dust explosions are very dangerous. To put Tango's post into layman's terms - imagine taking a treetrunk and trying to set light to it with a match...you wouldn't succeed. With some effort you could set light to twigs from the exact same tree though. Take a piece of wood the size of a matchstick and it burns pretty easily. Take wood-shavings and they burn quickly and vigorously. Take fine sawdust and it burns so fast that it's an EXPLOSION. The finer the dust the more easily it burns...and as Tango says - it's because the surface area is so large compared to the volume. SteveBaker (talk) 02:04, 21 January 2009 (UTC)

This PDF discuses many causes of silo failure. One thing they note is that moisture can migrate between static particles (the rice in this case) if the moisture is not evenly distributed. Moisture causes the rice to expand. If no rice is being withdrawn for a period of time, upwards expansion is greatly restrained so the pressure is instead focused on the walls of the silo. Failure of the steel hoops which hold the silo together will cause the silo to burst open: sort of like an explosion. A case involving moist corn not being removed over a period of a couple days resulted in five times the normal pressure on the walls of the silo. Additionally, drying the rice will put less stress on the silo walls by reducing the weight. Rice and other grains can be thought of as a fluid of sorts. Hypothetically, moist rice may flow differently than dry rice. Improper or unexpected flow of the grains can cause a silo failure by placing unexpected stress on the silo's structure. 152.16.15.23 (talk) 01:39, 21 January 2009 (UTC)

Wow. You mean I was right?!? That NEVER happens! --Jayron32.talk.contribs 03:13, 21 January 2009 (UTC)

Now that reminds me of a Hornblower story. Hornblower is sailing a prize ship with a cargo of rice. During the action in which the prize is captured, it was holed below the waterline. The sailors patch the holes and man the pumps. Strangely, the pumps are dry. Unknown to Hornblower and his shipmates, the rice is absorbing all the water leaking into the ship. Eventually - the ship starts to break up, and they have to abandon her. Which just goes to shew that I should have been able to answer this question! DuncanHill (talk) 14:56, 21 January 2009 (UTC)

For the record, that's Mr Midshipman Hornblower#Hornblower and the Cargo of Rice. Algebraist 15:35, 21 January 2009 (UTC)

Thanks - and what a sensible title for a story about Hornblower and a cargo of rice it is! I must re-read it. DuncanHill (talk) 15:49, 21 January 2009 (UTC)

I had asked a similar question a while back when Car Talk's weekly puzzler involved the dangerous transportation of rice by ships.

And as for dust explosions, search YouTube for "sawdust cannon" and "non-dairy creamer cannon". Mythbusters did a pretty impressive experiment about it. -- MacAddct1984 ^{(talk &#149; contribs)} 18:03, 21 January 2009 (UTC)

Lycopodium powder (the spores of some clubmoss or other) is an amazingly fine (and therefore highly explosive) powder. It's sometimes used in fireworks because a first charge can disperse the powder outwards and a second can set it off to make a large 'blossom' of (IIRC) yellow flame that appears all at once rather than seeming to spread outwards. Anyway - that and (as the Mythbusters showed) non-dairy creamer are the substances of choice for making large explosions without using anything obviously explosive. SteveBaker (talk) 21:03, 21 January 2009 (UTC)

Aah, but did they try custard powder? I recall an explosion in a custard factory in the 1980's. DuncanHill (talk) 02:32, 22 January 2009 (UTC)

Golden Ratio

I"m confused as to why there's such a fuss made about this...

What's so "aesthetically pleasing" about these various shapes constructed with these ratios?

are the buildings built using the ratio any better? stronger?

are these pieces of music containing little ratio nuggets any more passionate or moving?

I'm not trying to start a fight, i just was wondering if someone could explain to me the point

(by the way Steve Baker--you rock)192.136.22.6 (talk) 23:49, 20 January 2009 (UTC)

You may want to read Golden ratio; additionally this question may be better suited at The mathematics desk. --Jayron32.talk.contribs 23:53, 20 January 2009 (UTC)

The math desk will tell you that it's the "most irrational number" and turns up in a lot of surprising ways, but is not better suited to answer any of these questions. —Tamfang (talk) 06:23, 21 January 2009 (UTC)

There's no evidence that people find it esthetically pleasing and no evidence that it's ever been used in the design of buildings or any other form of art. There are people who see it in everything just like there are people who see Jesus in everything. It has some nice mathematical properties, but no more than many other numbers. I think it does appear in nature, though not in the conch shell, which is the most commonly cited "example". Possibly it appears in Romanesco broccoli (better image here), but don't quote me on that. See "Misconceptions about the Golden Ratio" by George Markowsky. -- BenRG (talk) 12:08, 21 January 2009 (UTC)

It is true that coincidental close approximations to the golden ratio can be found in the ratios of almost any sufficiently numerous set of measurements, and there is no direct evidence to support claims that the golden ratio was used in the design of ancient buildings such as Stonehenge and the Pyramids. However, some architects in modern times have explicitly and deliberately used the golden ratio in their designs and their theories of aesthetics - for example, Le Corbusier used it in the Modulor. Gandalf61 (talk) 12:33, 21 January 2009 (UTC)

I've run into several people who thought that the golden ratio is in every equiangular spiral! Argh. —Tamfang (talk) 06:51, 22 January 2009 (UTC)

There is also a relationship between the golden ratio (technically the golden angle) and the seeds of a sunflower. The spacing of seeds occurs in Fibonacci numbers because (as I understand it) this is a very efficient way of packing the seeds together. -- MacAddct1984 ^{(talk &#149; contribs)} 17:51, 21 January 2009 (UTC)

This has decent coverage about the sunflower. —Tamfang (talk) 06:51, 22 January 2009 (UTC)

"I"m confused as to why there's such a fuss made about this..." Well, the fuss is mostly because it was heavily mentioned in a recent best selling book and, I assume, the movie based on the book. (The Da Vinci Code) APL (talk) 01:23, 22 January 2009 (UTC)

— And because people keep asking about it. B00P (talk) 16:28, 22 January 2009 (UTC)

Nutrition of a Egg whites

The wikipedia article has a nicely broken down nutritional makeup of a whole egg (including the yolks.) However, any such diagram is sadly absent from the wikipedia article regarding egg whites. I was wondering if anybody could obtain the nutritional value of Egg white (therefore a whole egg minus the yolk.) The USDA nutrient database also didn't yield many results, and a google search yielded conflicting reports. Thank you in advance.

http://en.wikipedia.org/wiki/Egg_(food)

(The diagram under nutritional value is perfect, and if one along those lines could be found for egg whites I would greatly appreciate it.) 216.165.25.53 (talk) 23:58, 20 January 2009 (UTC)

Now you have to do some work here because I can't give you a direct link... (USDA Nerds...) Anyway... Begin Here.Next step, type "Egg, white, raw, fresh" into the search field, then ensure "All Food Groups" is selected. Now click submit and then select the radio button next to the search result. Tadaaa! Wish granted! Have a great Wiki-Day! Operator873 (talk) 09:31, 21 January 2009 (UTC)

Here's a direct link to the "raw egg white" page on www.nutritiondata.com: [28]. StuRat (talk) 13:53, 21 January 2009 (UTC)

January 21

Surface roughness

if two tubes one of steel and other of Zr-4 is coswaged is it possible to get 0.1 microns gap cosidering there suface roughness also?203.199.205.25 (talk) 03:52, 21 January 2009 (UTC)

I don't know what Zr-4 is (do you mean Zircaloy-4 (Zry-4)?) or exactly how you plan to swage the two, but this link may help you. It discusses the surface roughness height for steel produced by different methods. [29] Since 4 microinches is about .1 micron you are going to need to get a very very very smooth set of tubing. If you are talking about Zircaloy-4 when you mean ZR-4, I stumbled across some micrographs from an electrode corrosion test. In the tests, it was found that Zircaloy-4 is susceptible to forming corrosion films which have surface irregularities which eyeballing the pictures appear to be on the order of a micron or so in height. That could be a problem depending on what exactly you are using the tubing for. From experience, stainless steel hypodermic tubing with a net diameter difference of 25.4 microns threads cleanly and slides easily but definitely not frictionlessly. I am going to guess that on the level of .1 micron the surface irregularities are going to be significant. I am no expert on this so I would suggest asking someone who has done this sort of thing or simply trying it out if it isn't difficult and you have materials and methods on hand. 152.16.15.23 (talk) 05:31, 21 January 2009 (UTC)

BATTERY

BATTERY THAT CAN BE CHARGED WITHIN 30 SECONDS FOR 2 HOURS WITH 5000V OR MORE VOLTAGE SUPPLY. —Preceding unsigned comment added by 117.99.4.227 (talk) 05:29, 21 January 2009 (UTC)

Apparently that battery is MAKING YOU SHOUT. Now, do you have a question, or did you merely want to scream at us about your battery? --Jayron32.talk.contribs 05:36, 21 January 2009 (UTC)

I would suggest you start with Rechargeable battery and Battery charger. I am not sure what your question is because you seem to have omitted the first word. If your question is, "Can a battery be charged within 30 seconds for 2 hours with 5000V or more?" the answer is no. Attempting to recharge many types of rechargeable batteries with a voltage of that magnitude is likely to irreparably damage the battery via excessive heating. Additionally, the battery could also explode. According to rechargeable battery, Duracell and Rayovac now sell chargers that can charge AA- and AAA-size NiMH batteries in just 15 minutes. It is good online etiquette to not use all-capital letters when writing because it is interpreted as yelling. 152.16.15.23 (talk) 05:58, 21 January 2009 (UTC)

(following EC) ::Sounds like an awful lot of juice and a very short time. Couldn't you charge a capacitor first and then design your circuit to take your merry time to charge the battery?? I'm also not quite sure If I understand your question correctly: You are trying to find out whether there's a rechargeable battery that will supply in excess of 5kV for 2 hrs. That would most likely be a (huge) battery array, but with that many you are likely to run in to all sorts of strange effects because of internal resistance. Electrolysis of water and Fuel cell might help. 76.97.245.5 (talk) 06:15, 21 January 2009 (UTC)

You don't say how much current you need this thing to source or at what voltage...that's a crucial question! It certainly sounds like you need a supercapacitor rather than a battery. If you need to source a lot of current then putting that much energy in one place so quickly means that any inefficiency within the battery/capacitor is going to get turned into heat. So if the charging process is even a tiny bit inefficient (say it's 80% efficient - so 20% of the energy gets turned into heat) - then the battery is going to get insanely hot - and presumably destroy itself. When you charge more slowly, the battery has time to radiate that heat naturally and it's not much of a problem...but even batteries that recharge over hours do get noticably hot during the process. If you shorten that time to 30 seconds then all of that heat is still created - but all at the same time! This will get the thing so hot that it'll literally melt (that's if the liquids inside don't boil or otherwise explode). So you need to find a supremely efficient solution that'll keep the heat down - or you'll need to consider some kind of active cooling approach. You could also consider other means to store the energy. For example, you would wind up a spring in a clockwork motor or pump water to the top of a tower and let it flow back through a turbine. My long-case clock can be wound up in 30 seconds and runs the clock for a month - that (technically) meets your requirements - but without knowing how much current & voltage it has to generate, there is no way to know whether that would work for you. More information needed please! SteveBaker (talk) 14:12, 21 January 2009 (UTC)

Any device which stores large amounts of energy is inherently dangerous. Things fall, explode, react chemically, cause electrocution, etc. High voltages are easy to get from batteres, by connecting lots of cells in series. Humphry Davy built a primary (non-rechargeable) battery of 2000 cells of zinc and copper way back in 1808, which likely produced 2000 volts or so and could supply it for an extended time if the current draw was small. It could supply about 3 kilowatts[30]. Lead-acid batteries provide about 2.1 volts per cell, so 2500 cells would suffice. It would be pretty dangerous and there would be a great danger of death or injury from electric shock. The 30 second recharge demand is unrealistic. You could use other forms of energy storage, such as putting current into a Superconducting magnetic energy storage, charging a capacitor, spinning up a flywheel, winding a spring, compressing air, lifting a weight, heating up a thermal storage mass, or adding chemical fuel to a device. Edison (talk) 19:30, 21 January 2009 (UTC)

Plastic In Bandy Balls

What kind of plastic makes up Bandy balls? Are they hollow? Please look at the description here:

To the rightmost a modern, plastic bandy ball.

96.53.149.117 (talk) 05:47, 21 January 2009 (UTC)

Some more info from our Swedish page: The thing is 60 mm in diameter and weighs 60g. Maybe OP could find s.o. who speaks Russian and see what the Russian page / googling in Russian will give him. If you trust this article [31] new balls in Sweden are 2.4 mm thick, it doesn't say whether that's just a coating or whether they're hollow. That's barely a tenth of an inch. They're also a tad bigger at 62.4 mm76.97.245.5 (talk) 06:25, 21 January 2009 (UTC)

Bandy balls are not hollow, the inside is cork. Usually, I should add, since the official rules only require that the ball shall be made of an "approved material". Here is an article, in Swedish but with pictures, about bandy balls being made in Sweden out of cork and PVC plastic. --Rallette (talk) 07:51, 21 January 2009 (UTC)

And as to that Aftonbladet article, it is actually about a dispute in the Swedish bandy league over the size of the ball. The ball used to be 60 mm in diameter, but this was increased in 2001 to 62,4 mm for better audience and television visibility. One team refused to use the new ball, but the bigger size is now official. So the 2.4 mm is just that increase in diameter, not the thickness of the plastic.--Rallette (talk) 08:03, 21 January 2009 (UTC)

We had this question just the other day - but I'll repeat the answer (and repost the photo at right showing the stages of construction): They are made of cork, covered with a "knitted" material that looks like some sort of knotted rope and then painted with a thick coat of red paint. As far as I can tell from our article - they are not made of plastic at all - although there may be unofficial practice balls or something that aren't made "properly". SteveBaker (talk) 14:01, 21 January 2009 (UTC)

The description on that picture's page says the ball on the far right is a modern, plastic bandy ball. -- Mad031683 (talk) 17:25, 21 January 2009 (UTC)

It may well be they're made or have been made in a number of different ways; my answer was mainly based on that newspaper article about the major Swedish manufacturer (Jofa), who make them by spraying a shell of PVC onto the cork core. This also squares with my personal experience with bandy balls: the ones I've seen and handled (and even played with, this all brings back some awkward schoolday memories) have been of the plastic coated kind. I imagine the process described by SteveBaker is the original or old-fashioned way, and the knobbly surface of today's balls is an imitation of the result.--Rallette (talk) 09:16, 22 January 2009 (UTC)

penicillin test

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, 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 Reference Desk's talk page.

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 Reference Desk's talk page. --~~~~

--Milkbreath (talk) 20:17, 21 January 2009 (UTC)

Whether this is a medical advice request is being debated here: [32]. StuRat (talk) 13:38, 22 January 2009 (UTC)

747-400 seat cushion dimensions

What is the depth of a Thai Airways Boeing 747-400 ecomony class aircraft cushion? I need the measurement from the front of the seatback to the front of the seat cushion, NOT the pitch.Sarahonthemove (talk) 08:03, 21 January 2009 (UTC)

There are different seat dimensions for different airlines, unfortunatley. Each airline has the 747-400 constructed to their specs. American Airlinesloves to boast of their extra leg room in economy class. I, personally, have struggled to locate these mysterious few extra inches. :-) Operator873 (talk) 09:00, 21 January 2009 (UTC)

Depleted uranium

Is ever used for the core of bowling balls? Thankyou. --90.240.55.65 (talk) 10:08, 21 January 2009 (UTC)

I personally doubt it. Bowling balls simply don't require the density. Even making the ball's core from mostly iron would be enough Nil Einne (talk) 11:22, 21 January 2009 (UTC)

(EC)For example Bowling ball says they're 21.6cm. Even assuming the inner core is only 16cm that would give a volume of 4/3 pi 8 cm^3 i.e. 2.14466058 liters. Taking the density of iron at RT from our article that is, 7.874 g/cubic centimetre we end up with nearly 17 kg. That is already a lot heavier then "Regulation ten-pin bowling balls must weigh no more than 16 pounds (7.2 kg)". While I appreciate some are constructed in somewhat different fashion then just having a solid core of weight, clearly you don't need the density given by depleted uranium. Nil Einne (talk) 11:41, 21 January 2009 (UTC)

Ok I know what he was thinking, cuz I was thinking it too... no way right? Then I got to looking and searching... And then I nearly puked. Are You Kidding Me? (Click Here). Yes, Virginia, there is a Santa Clause... and an "Enriched Uranium Bowling Ball" with a core made of U235. Wow... I'm left speechless by this... Upon further mental reasoning... U235 Uranium core has got to be a marketing gimic. U235 is radioactive with a halflife of 700 million years. Nevermind, I feel better now. Operator873 (talk) 11:25, 21 January 2009 (UTC)

I beg forgiveness from all Wikipedians out there. I don't know what to say to explain my lack of mathmatical and realistic reasoning. In a famous word, "oooopsieee." Operator873 (talk) 11:44, 21 January 2009 (UTC)

The benefit to using depleted uranium (or any other denser material) would be a reduction in the moment of inertia of the ball whilst remaining in the legal range of ball weights. As Nil Einne points out, you can easily reach the maximum allowed weight with very conventional materials - but if you used something with greater density, you could concentrate that mass in the center of the ball rather than distributing it through a larger part of the volume of the ball. The result would be a ball that ought to be much more responsive to spin - it would change direction more easily as friction 'grabs' it and it would be easier to impart more spin onto the ball when you start it rolling. So I can definitely see an advantage for better players to have a denser center even if the ball remains at the legal maximum.

Sadly, our article on bowling balls doesn't say what their centers are currently made from. If they are already using (say) lead - then the benefits of switching to depleted uranium would perhaps be quite significant in allowing more spin to be applied. If you are riding the competitive edge, it might make the difference. Lead has a density of 11gcm^-3 and uranium is up at 19gcm^-3 (about the same as gold)...we should probably calculate how much that would help the "spinability" of a 16lb ball...but I'm not going to because I'm feeling lazy today! Osmium would be the most dense "practical" choice - at 22gcm^-3 it's even denser than gold...sadly, if you buy Osmium from these guys it's going to cost you $880,000 to get 16lbs of Osmium oxide...which you'd have to refine...so you might want to stick with the Uranium! The ultimate would be a Hassium-centered ball. Hassium is more than twice as dense as uranium or gold...of course it's not going to be cheap since it has to be made atom by atom in a nuclear reactor...and it's radioactive as all hell...and it's going to turn back into lead within an hour or two...unless 16lbs is more than it's critical mass - in which case what you have is more of an atom bomb than a bowling ball(!)...but for that championship game where the slightest edge matters, nothing else can beat it.

SteveBaker (talk) 13:54, 21 January 2009 (UTC)

Does blowing up the bowling alley (and most of the surrounding city) count as a strike? --Tango (talk) 14:00, 21 January 2009 (UTC)

Yes. You're certainly unlikely to risk a 7-10 split - but sadly it risks a counter-strike. SteveBaker (talk) 20:53, 21 January 2009 (UTC)

Years of researching this matter by watching the Loony Toons has taught me that no matter how badly the bowling ally is demolished, in the middle of the rubble, at least one pin will still be standing. It may be badly scorched. It may be wobbling. But it will not fall. APL (talk) 14:29, 21 January 2009 (UTC)

I see you're familiar with my bowling style! SteveBaker (talk) 20:53, 21 January 2009 (UTC)

Natural Polymers

I need a conclusion on the topic Natural Polymers. —Preceding unsigned comment added by 59.93.15.143 (talk) 12:40, 21 January 2009 (UTC)

Without seeing your essay it's impossible to give a conclusion 78.146.113.20 (talk) —Preceding undated comment was added at 13:02, 21 January 2009 (UTC).

We don't have an article on natural polymers - but if you do a search on the term, you'll find that there is a lot of material on the topic scattered throughout the encyclopedia.

Natural rubber might be a good place to start, but perhaps not the best place to conclude. StuRat (talk) 13:42, 21 January 2009 (UTC)

There's also the ubiquitous carbohydrate and protein, the two types of polymers used by organisms to fill structural (and a myriad of other) roles. If you're not just looking for structural functions, I would be remiss if I neglected to mention the nucleic acid polymers, RNA and DNA. – ClockworkSoul 18:14, 21 January 2009 (UTC)

I just noticed these, which may be helpful: biopolymer and bioplastic. They need some love, but you may find them helpful. – ClockworkSoul 18:18, 21 January 2009 (UTC)

I have almost completed my project on Natural Polymers, I just need a conclusion. The sub-topics were Nucleic acids, natural rubber, protein, cellulose and chitin. It mainly contains structure, characteristics and their uses. All I need is a conclusion. Any ideas?59.93.1.19 (talk) 14:28, 22 January 2009 (UTC)

Iris Depigmentation

Is there a disease or condition in which the iris in the eye will slowly depigmentate (years), especially in teens or young adults? I am aware of what glaucoma can do to the elderly..... --Emyn ned (talk) 14:09, 21 January 2009 (UTC)

Perhaps a nutritional deficiency could also cause this. Also, glaucoma doesn't always just affect the elderly. StuRat (talk) 15:31, 21 January 2009 (UTC)

--Emyn ned (talk) 17:45, 21 January 2009 (UTC)

Lingual Frenectomy in Adults?

I have asked this question recently but was never answered. I am asking what are the medical benefits, if any, for adult lingual frenectomy? Are there any sound medical reasons an adult would need this, not want this? --Emyn ned (talk) 14:11, 21 January 2009 (UTC)

Have you read Lingual frenectomy? --Tango (talk) 14:39, 21 January 2009 (UTC)

Better question, have you? --Emyn ned (talk) 14:40, 21 January 2009 (UTC)

The one benefit they listed which might apply to adults is to "help improve speech". However, this, and any other benefits, would only apply if there's some abnormality to begin with. StuRat (talk) 15:27, 21 January 2009 (UTC)

I thought the article in Wiki only refers to children or infants. Did I misread it? It is possible...--Emyn ned (talk) 15:29, 21 January 2009 (UTC)

It doesn't specify that the speech improvement only applies to children. --Tango (talk) 15:40, 21 January 2009 (UTC)

The article in Wiki says:

This is used to treat a tongue tied patient. Immediately after this minor oral surgery, the tongue can often dramatically extend out of the mouth which it could not do before. This can help reduce breastfeeding complications, help improve speech and promote proper tooth arch development.

The last sentence implies that everything else stated was referring to infants. I realize that adults can be tongue tied, but the article does not imply that at all. If the Ref Desk doesn't know the answer to my question, that's all right. No need to conjecture. It is possible that adult Lingual Frenectomy is only done for aesthetic reasons. --Emyn ned (talk) 15:50, 21 January 2009 (UTC)

While breastfeeding complications and tooth arch development would seem to refer to children, that doesn't mean the speech improvement does (although, in most cases it will do - why wait until adulthood to fix a speech impediment?). --Tango (talk) 17:01, 21 January 2009 (UTC)

I am only referring to reading comprehension here. The article clearly implies children only despite your opinion that the article references adult speech impediment. All in all, the article ONLY refers this procedure as performed on children. Please let's not fight about what you think the article should state. Besides Tango, do you have a direct answer to my original direct question? Do you have any knowledge or expertise in oral surgery in general? --Emyn ned (talk) 17:45, 21 January 2009 (UTC)

BTW Tango, don't confuse my bluntness for rudeness. I do actually want to know if you have any knowledge or expertise in oral surgery in general. I would like to know which volunteer takes the most medical/biological questions on this board. --Emyn ned (talk) 21:48, 21 January 2009 (UTC)

Woah - slow down here. We're all just volunteers - we're not REQUIRED to answer your question. If you need an answer from an expert in oral surgery then this is a question of a medical nature that we are emphatically NOT allowed to answer. If it's just general curiosity then please listen to the volunteers because they are amongst the smartest people you'll ever meet AND they have this incredible encyclopedia at their fingertips which they know how to use effectively. There is also an element of common sense here. So chill out - stop arguing with the very people you're asking to help - listen to what they have to say and take away whatever nuggets of truth you wish. If you don't want to do that - then please feel free to head over to Yahoo Answers] and seek the truth there. Thanks. SteveBaker (talk) 20:48, 21 January 2009 (UTC)

SteveBaker, in that case, Tango and the rest of the Ref Desk volunteers should state "we're not REQUIRED to answer your question". I can't listen to the volunteers because they are not speaking. However, I can READ their responses. And in response to your comment "they are amongst the smartest people you'll ever meet AND they have this incredible encyclopedia at their fingertips which they know how to use effectively", why does my original question remain unanswered? Any reason will suffice. BTW - I was already chilled. I wanted to point out to Tango that reading comprehension should be required when responding to questions.

In the meantime, do you have an answer to my question or did you just want to bite OP's? --Emyn ned (talk) 21:37, 21 January 2009 (UTC

I couldn't find any relevant Pubmed or Google references for this in adults. Axl ¤ [Talk] 21:54, 21 January 2009 (UTC)

The reason for the focus on treatment of children in the phrase you quoted might be because that's the most common application of the procedure. Medicine is compartmentalized into pediatrics, geriatrics and the like to allow practitioners and researchers to focus on the most relevant factors. The medical professions try to prevent or counteract an impairment as close to it's onset as possible. The more is known about a condition and the longer treatments have been around the closer to early intervention you get. That means that if the known onset is in childhood or prenatal there are fewer adult sufferers who remained untreated and treatment and new developments are going to be focused on young patients and treatment in the womb. Information on such conditions will reflect that. An article on Alzheimer's disease on the other hand will rarely contain information on treatment in children. OR When the Allergy wave hit I used to be frustrated by having to wade through tons of information on treatment of children and babies. So I sympathize if you find the sentence you quoted frustrating. Information on application of the procedure in adults may be hard to come by. If you do find something you could add a paragraph to the article. If it is indeed rarely done, be sure to identify that by adding something line "In rare cases..." 76.97.245.5 (talk) 23:01, 21 January 2009 (UTC)

Emyn ned, my impression is that you don't realize that some of your responses are very off-putting. Not sure whether this is helpful, but please realize that folks on the RefDesk are well-intentioned and well-informed as a rule. This is not a medical advice forum, it is a Reference Desk for Science questions. People have tried to be helpful within the guidelines we have, so if you're not satisfied with the answer please don't criticize. Please assume good faith. --Scray (talk) 02:14, 22 January 2009 (UTC)

Emyn ned another thing you don't seem to appreciate is that the RD isn't like some single entity. It's possible someone could give a better answer but hasn't yet seen your question, or perhaps has but can't be bothered replying after seeing the way you responded. If you really need an answer so desperately, I believe there are one or two doctors around, I don't know if there are any whose expertise is in this area but if you offer to pay them I'm sure they could research the matter better. For that matter, even no experts could as well. Nil Einne (talk) 11:45, 22 January 2009 (UTC)

P.S. This article [33] while not a reliable source, suggests speech improvement is actually a common reason for adults seeking the surgery, contrary to your beliefs to the contrary. The good thing is, again despite your claims to the contrary, nothing in our article suggests it is the speech thing is for adult only. It also gives other reasons. Having said that, there's no evidence any of the reasons, even in children are really a case of need. Actually that applies to a lot of surgeries we're it comes down to a balance of the advantages and potential complications. If the advantages are overwhelming (e.g. a significant improvement of the quality of life) and the complications/disadvantages few for most people the choice is clear but unless your going to die without the surgery, it's difficult to say you need the surgery. Perhaps you're thinking of the definitions used, particularly by government funded health services and I guess insurance companies for elective surgery but even these are rather complicated Nil Einne (talk) 11:49, 22 January 2009 (UTC)

The history of Medicine is littered with cases where surgeons have jumped in to "correct" things in children that seem abnormal - only to later discover that they weren't abnormal at all - or that fixing them wasn't necessary because the child would "grow out of it" later - or that the risk of the procedure exceeds the actual benefits. Hence (no doubt) there is extreme caution involved in leaping into something like this. This may explain why the procedure isn't common in kids. I would assume (without evidence) that the issue of whether to perform this surgery on kids or not would hinge on whether there were collateral developmental issues with not treating it early. Does a child with this condition actually fail to learn intelligable speech such that when treated for it as an adult, the impairment continues after surgery corrects the anatomical problem? If so then you'd expect there to be more research into treating children. If the surgery is effective even when delayed into adulthood - then probably doctors will advise a 'wait and see' approach simply because adults survive surgery at better rates than little kids do.

Examples that I can think of are with cross-eyed babies...about 15 to 20 years ago, it was discovered that if that's not corrected within just a few months of birth, the child will never form the brain "circuitry" to perform adequate depth-perception - and even if the eyes straighten themselves out by (say) two years of age as they typically do. Just three or four years ago, the impairment was considered permenant and untreatable. Hence, early correction of cross-eyes in tiny babies is currently seen to be essential. However, in just the last couple of years there have been a few cases of successful adult treatment - where certain exercises can allow someone with no effective depth perception to see in perfect 3D - research into brain plasticity tends to back this up. It should now be expected that early intervention for cross-eyed babies would be regarded as a bad idea - it being better to let them un-cross naturally and to treat the resulting brain underdevelopment later. In that case, we're right on the nexus of "OMFG! They treated all of those poor babies unnecessarily!"...having only recently gone through "OMFG! We didn't treat this baby and now it's permenantly impaired!"...it's a tough business!

So - expect caution, and a firm adherence to the "First, Do No Harm" oath that doctors are (mythically, I think) supposed to swear to. SteveBaker (talk) 15:19, 22 January 2009 (UTC)

While not your fault given the way the discussion has progressed, I think you may have gotten confused. As far as I'm aware, the claim made by the OP, semi supported by the refs that the surgery is usually performed on children and the OP was demanding to know if there was any reason why an adult would need the surgery and if there was, why our article didn't say there was (even though our article didn't really comment on the age the surgery is performed). I don't know if I got this through or not but my point was the 1) It appears the surgery is performed on adults for at least one of the same reasons it is performed in children 2) Whether you can say they 'need' the surgery as opposed to 'want' the surgery is an extremely complicated issue since it's a continuum, there's no line between need and want and depends on how you classify each. On your point, from my brief look through the refs and wikipedia articles, it looks like there is some controversy of how often this surgery should be performed (and although I never saw any, I'm guessing there is also some discussion over whether it should be delayed to adulthood) which while an interesting ethical issue, not really one for the RD and AFAIK is not what the OP was asking. Nil Einne (talk) 16:34, 22 January 2009 (UTC)

All, found more info at this article ankyloglossia. Pretty much mirrors what Nil Einne wrote. Can we now end this discussion. I am tired of discussing and wasting space on how Steve Baker's feelings were so hurt. If you bite OP's, expect, once in a while, someone might bite back. --Emyn ned (talk) 17:05, 22 January 2009 (UTC)

This snipping of the membrane under the tongue, if done badly, can result in a tongue which can be thrust out of the mouth to an unseemly extent, as in the case of a relative who comes to mind. Edison (talk) 05:35, 23 January 2009 (UTC)

Total size of all Wikipedia articles

Please see Wikipedia:Reference desk/Computing#Total_size of all Wikipedia articles for duplicate question. Cycle~ (talk) 14:49, 21 January 2009 (UTC)

This page seems to imply there are only 4330 people with >100 total edits? This seems really low to me, am I reading it right? Thanks Anythingapplied (talk) 21:34, 22 January 2009 (UTC)

That page, which is 2+ years out of date, is referring to >100 edits per month in the column you are reading. Dragons flight (talk) 21:41, 22 January 2009 (UTC)

Submarine motion

hai i am doing aeronautical engineering i suppose to do a working model of submarine is it possible to get the up and down motion of the submarine by using a elevator as in a aircraft? —Preceding unsigned comment added by Veeraraghavan.D (talk • contribs) 15:00, 21 January 2009 (UTC)

(I added a header for your question.) I don't understand what you mean. Is it possible to have an elevator inside a submarine? Sure it is. But the "up and down motion" part is confusing -- an elevator isn't going to make the submarine rise or descend. (It doesn't do that in an aircraft, either.) -- Captain Disdain (talk) 15:09, 21 January 2009 (UTC)

Are you talking about a passenger elevator ? I'm sure they meant elevator (aircraft). StuRat (talk) 15:15, 21 January 2009 (UTC)

Oh... yeah. Never mind. Ahem. (Geez, it's not often that my English vocabulary fails me, but what the hell, here's something to file away for future reference...) -- Captain Disdain (talk) 15:48, 21 January 2009 (UTC)

Consider yourself lucky, you managed to improve your vocab today. We should all strive for that every day. :-) StuRat (talk) 03:47, 22 January 2009 (UTC)

Ironically, if there was a passenger elevator on a sub, which lacked a counterbalance but relied exclusively on motors to raise it, moving it up and down would slightly change the depth of the sub, based on "every action causes an equal and opposite reaction". StuRat (talk) 03:54, 22 January 2009 (UTC)

Are you sure? I think it would push you one way when the elevator accelerated and then push you the other when the elevator stopped- zero net force. You'd need a mile high elevator that you could keep going and going so you can stay deep for awhile and then you stop the elevator to go back to where you were. 72.236.192.238 (talk) 18:43, 22 January 2009 (UTC)

You're correct that there would be no net, long term change in the depth of the submarine, but it would cause small, temporary changes in depth, that's all I'm saying. StuRat (talk) 18:52, 22 January 2009 (UTC)

(I improved the header.) In the short term, yes, but to maintain a certain depth you will need to alter the buoyancy of the submarine. This is typically done by filling and emptying ballast tanks. You might wonder why this is different from aircraft. Well, (heavier-than-air) aircraft must always be moving forward to stay aloft, and you can therefore use an elevator to adjust the altitude, but submarines are often still, or moving too slowly for the elevator to be used in this way. StuRat (talk) 15:13, 21 January 2009 (UTC)

I have definitely seen pictures of Personal submarines that use control surfaces exclusively to control their depth. The obvious problem of this is that you need constant forward motion to fight the craft's normal buoyancy. (Compare to an airplane.)

This isn't practical for large navel submarines need to be able to control their depth independently of their forward speed. APL (talk) 15:25, 21 January 2009 (UTC)

The best depth control makes use of a ballast tank which can be variably filled with water or gas (usually from a compressed gas tank). There are other submarine depth control techniques such as elevators (which are used on large navy submarines in conjunction with ballast tanks). ROVs are often designed to be neutrally buoyant (a difficult challenge, sensitive to tiny variations), the idea being that the ROV will float at whatever depth it is currently at - and then a vertical motor or propulsion system is used to set that depth. You can fight buoyancy with such a method but it will impact your energy budget, controllability, and reliability. Nimur (talk) 15:37, 21 January 2009 (UTC)

(ec) You're probably looking for our article on dive planes. A surfaced submarine with its ballast tanks 'blown' (empty) has a substantial amount of positive buoyancy; it would be difficult or impossible to force it beneath the surface using its dive planes alone, and the submarine would have to be under constant thrust.

A large military submarine beneath the surface and with ballast tanks 'trimmed' (adjusted) to neutral buoyancy will tend to hold a constant depth — the average density of the submarine matches the surrounding water. Since both submarine and surrounding water are poorly compressible – and consequently, have nearly constant density even through large changes in depth – it is very difficult to select a depth using ballast adjustments alone. (It would also take a long time for the submarine to change depth, as very small changes in buoyancy would be used.)

Instead, a very small amount of forward thrust combined with elevation changes of the dive planes allows a submarine commander to change depths without requiring further adjustment of ballast tanks. Unlike elevators on aircraft, submarines fit dive planes in up to three locations: bow, stern, and sail/conning tower (these last are sometimes called 'fairwater planes'). Since water is much, much, much denser than air, the control surfaces on a submarine are smaller and work at much lower speeds than comparable equipment on an aircraft. TenOfAllTrades(talk) 15:46, 21 January 2009 (UTC)

A very detailed guide to building a model submarine with an electric motor and a ballast tank which has a compresssed air supply to make it resurface after it dives is found in "The boy's book of submarines" by A. Frederick Collins, pages 21-48. Although the book was written in 1917, you could alter the shape to match that of modern submarines. Although Collins discussed diving planes elsewhere in the book, his model omitted them. Edison (talk) 18:54, 21 January 2009 (UTC)

It's possible to get downthrust with an 'elevator' - and indeed, real submarines do have such things for subtle depth and attitude adjustment (those are the "Bow planes"). However, they only work when you're moving through the water - and only when the elevator is submerged...both of which might be a problem. Real submarines sink because they pump water into and out of ballast tanks - compressing the air inside...but that's a pain to deal with in a model. The model submarine we have at home for messing around in our swimming pool uses a propeller encased in a vertical tube as a 'down-thruster' to drive it underwater - and before you play with the submarine, you have to adjust the bouyancy with little metal disks to get the submarine to very slowly rise by itself when the motor shuts off. That's for the vital reason that you want to be able to get the submarine back when it goes too deep for the radio signal to reach it anymore - or if the batteries die on you. With ALMOST neutral bouyancy, the thruster controls both up and down motion while the propeller and rudder deal with turning and forward or reverse motion. If you drive the submarine too deep and the radio stops working, the electronics inside simply stop all of the motors so the submarine can gently rise until radio contact is re-established. This works amazingly well - much better than I thought it would. When you drive the submarine too deep, all you really notice is that it refuses to go any deeper - but if you look closely, you see that it's actally drifting up and down over a period of a half second or so as the vertical thruster motor cuts in and out - but that gives you enough control that you can still steer at maximum depth. The trouble with an 'elevator/bow-planes' is that once the submarine goes too deep for you to control, you really want it to come back up automatically. Theoretically, turning off the thrust motor will stop the boat from moving forwards - then the bow planes can't drive it down anymore - so it'll float back up into radio range. That's a difficult approach because even when you shut off the thrust motor, the sub will still slide through the water for quite a distance before water resistance slows it down enough for the bow planes to stop working. For all of that time, you have no radio control because the sub is still too deep. So now you need to alter the bow plane angle to push the sub upwards when it loses radio contact. Ikky. That's why I like the vertical thruster concept. SteveBaker (talk) 20:33, 21 January 2009 (UTC)

Wouldn't a balloon work for a model? You put a balloon inside the hull, with the hull open to the water. You then attach a tube to the neck of the balloon (making sure it's airtight) and take the tube up to the surface. You then blow the balloon up to make the submarine surface and let the air out to make it sink (after adding the appropriate amount of weights, anyway). --Tango (talk) 20:59, 21 January 2009 (UTC)

steel

what is the weight of 10mm mild steel plate per square meter as per indian standards —Preceding unsigned comment added by 122.167.114.29 (talk) 16:58, 21 January 2009 (UTC)

You can find the density of mild steel in our article. For Indian standards, you would need to check the website of a steel service centre in India to see what actual thickness they roll "10mm" steel to. Franamax (talk) 17:07, 21 January 2009 (UTC)

According to our article, the density of mild steel is: 7,861.093 kg/m³. If it truly is 10mm thick then the weight is 78.611kg/m² regardless of where you happen to be! However, (as Franamax alludes) some materials are quoted a being some thickness "before polishing" or they might include some kind of protective coating or whatever. So I suppose it's possible that 10mm steel plate isn't exactly 10mm thick in India. (Just like a '2x4' piece of timber is really only 1+1⁄2" × 3+1⁄2" in reality because the 2"x4" refers to the dimensions before planing). SteveBaker (talk) 19:22, 21 January 2009 (UTC)

concrete specimen

when we subject aconcrete cube 15*15*15 cm to acompressive strength , the regular result will start from 150 kg\cm2 to 500 kg\cm2 in ordinary structures , and as we know cement is the material which provide cohesive bond between concrete components , so why is that the compressive strength of a cement cube will be much less than aconcrete one , since that the essintisl bond is been provided by cement... the answer must have scientific base.., thank you...? —Preceding unsigned comment added by 79.173.224.133 (talk) 20:28, 21 January 2009 (UTC)

The little rocks and other 'aggregate' carry most of the compressive loads in concrete. Cement lacks that. SteveBaker (talk) 20:35, 21 January 2009 (UTC)

You may be interested in our articles on Cement and Concrete. Your engineereing teacher likely also talked about this in class, so if you re-read your notes from that day, teh information is likely there. Also, if your teacher gave you a textbook, it is likely in there as well. --Jayron32.talk.contribs 20:49, 21 January 2009 (UTC)

Let's assume good faith, shall we? While the OP may have been learning about this in class recently, the question could well be something they've thought of for themselves rather than homework. --Tango (talk) 20:53, 21 January 2009 (UTC)

I assumed no bad faith at all. The reference desk is designed to help people find answers to questions. Lecture notes from ones own classes and textbooks given out in those classes are likely going to contain lots of good information for answering this question. If you have a place better than his own textbook to look this information up in, please feel free to add it. But please, the assumption of the assumption of bad faith is an assumption of bad faith in itself. --Jayron32.talk.contribs 22:20, 21 January 2009 (UTC)

i had reed about it ... the explanation presented that alot of cement will release alot of heat from the reaction and so ... larg volume changs will occure producing dangrous hairy cracks within the mass of concrete which cause the low compressive strength ... but if we manage to avoide the heat effect could the compressive strength come larger or it will remain the same...? --Mjaafreh2008 (talk) 09:49, 22 January 2009 (UTC)

Well, it would seem to me that the methods of avoiding the heat effects all involve adding something to the cement in some way. I suppose you could add a network of pipes through the cement through which we could pump water to keep the cement cool; however in order to have enough pipes to be effective, you'd have created what would essentially be reinforced concrete; the pipes would act like rebar and would at that point be serving exactly as the aggregate stone does in concrete. I'm not sure we have any reliable method of cooling the drying cement in a manner that does not end up creating what would functionally be concrete anyway. Plus, I am pretty sure that the aggregate itself provides considerable strength, even assuming that the cement could be cooled and dried under ideal conditions. --Jayron32.talk.contribs 13:08, 22 January 2009 (UTC)

Obviously concrete with no cracks is stronger than concrete with cracks! It is indeed a standard practice to try to abate the heat when that's an issue. See Hoover Dam#Concrete_pouring for an example. --Sean 14:10, 22 January 2009 (UTC)

Except the question was not about "cracked concrete" vs. "uncracked concrete". The question was about "cement" vs. "cement with stuff in it" (otherwise known by the name "concrete"). The question was about why concrete was stronger than an otherwise idenitcal amount of pure cement. The OP then noted that in his reading, he came accross the explanation that the aggregate (the stuff in the cement that makes it concrete) had a dampening effect on heat generation, and that was what resulted in a stronger product. He then asked about other ways to dissipate the heat in such a way as to retain the purity of the cement; however I noted that I doubted that any system which could be used to dissipate the heat of the drying cement would not in itself produce a product which was essentially concrete. In other words, it would be impossible to actually effectively cool a block of pure cement without in some way introducing foreign materials or objects; which would then make it concrete. --Jayron32.talk.contribs 18:14, 22 January 2009 (UTC)

The ways they have to control heat build up when making large concrete structures (like dams for example) is to pour in thin layers - let each layer cool - then pour another layer. But I saw a Discovery channel thing about making large concrete structures in the middle east where they mixed ice and in some cases even dry ice into the cement along with the aggregate. So there certainly are ways to do that without pipes and such. SteveBaker (talk) 21:18, 22 January 2009 (UTC)

Regarding sight

Why do objects farther away appear smaller? And is there a way to mathematically find the relationship bewteen apparent size and distance (i.e. inverse relationship)? —Preceding unsigned comment added by 65.92.7.221 (talk) 21:58, 21 January 2009 (UTC)

Articles such as Perspective (visual) and Visual angle may be of use to you. --Jayron32.talk.contribs 22:17, 21 January 2009 (UTC)

(EC)See Perspective (visual). For a mathematical calculation of image size versus distance, see Visual angle. For an excruciatingly mathematical treatment of the subject, see "Teaching Leonardo" by Rick Faloon. You might also find Vanishing point useful. Edison (talk) 22:20, 21 January 2009 (UTC)

I poked around and couldn't find a reference in Wikipedia, but it's a simple ratio. An object one meter away will look ten times bigger than the same object ten meters away. This is for apparent size in inches or centimeters, not degrees or radians. --Milkbreath (talk) 22:31, 21 January 2009 (UTC)

What does "apparent size in inches/centimeters" mean? Axl ¤ [Talk] 23:15, 21 January 2009 (UTC)

I was afraid somebody would ask that. Say you're on the International Space Station, and the Space Shuttle is approaching head-on. If you know the Shuttle's wingspan, you can determine how far away it is by holding a meter stick out and noting its apparent wingspan on the stick. If you then measure from your eyes to the stick, you can calculate the distance by the ratio eye-to-stick/eye-to-shuttle = apparent wingspan/true wingspan. --Milkbreath (talk) 23:43, 21 January 2009 (UTC)

Imagine you are looking through a window that's 'Z_W' meters in front of your eyes. Some object is X_O meters across and Z_O meters from your eyes. The size of the object as it appears to be on the glass of your window is: X_W = X_O x Z_W / Z_O Hence, when the object is twice as far away, it's appears to be half the size. The reason is a matter of similar triangles. If you draw a line that's the same size and distance as the object and then form a triangle from the ends of that line back to your eyes...then draw another triangle using the width and distance of the image of the object that you see on your window - then the ANGLES inside those triangles has to be the same...right? Geometry 101 says that two triangles with the same interior angles are SIMILAR and the ratio of their sides is the same. Hence, the ratio X_W / X_O equals Z_W/Z_O -- which you can rearrange into my equation above. That is also the "why" of why things get smaller as they get further away. If the angles stay the same (which is also implied by the object retaining the same general shape) as it gets further away - then in order to keep that true - the size has to change in the same exact proportion. SteveBaker (talk) 00:04, 22 January 2009 (UTC)

Titan vs. Europa over 5-7 billion year sun

Isn't it possible when sun swells up in 5 to 6 billion years, Europa's ice can melt into oceans, and Titan I thouhgt will keep some atmosphere. It is ultraviolet light and solar winds which kill atmopshere. Europa's surface is made of frozen oxygen and methane, when sun heats up I thouht it will sublime into atmosphere. This all deepnds on sun's expansion. Maybe for a certain amount of time, Europa can harbor life, eventually Titan will drain probably about 90% of atmosphere, but it will keep some at least, I thought.--69.226.46.118 (talk) 23:40, 21 January 2009 (UTC)

Both those moons are very small, so if they heated up the Earth-like temperatures (and they could well end up much hotter or much colder, it would be a pretty big coincidence if they were just right) they would lose (most of) their atmospheres very quickly. It would probably take some effort to make them breathable anyway, so it would probably be better just to build domes or similar on them and just worry about a little bit of atmosphere. However, the Sun will only remain a red giant for a very short period of time on astronomic scales (millions of years, maybe). If the human race survives the next 5 billion years, I hope it is thinking more long term than the next few million (especially since Earth will be uninhabitable in about 1 billion years, so they'll have already had 4 billion years of living with a dead planet, so they ought to be prepared to live with a dead star!). --Tango (talk) 23:56, 21 January 2009 (UTC)

Europa may harbor life now. The oceans on Europa are among the best candidates for harboring life in our solar system outside the Earth. Dragons flight (talk) 00:02, 22 January 2009 (UTC)

• What about Mars. The academic paper said when the sun heats up in aobut one billion year, frozen carbon dioxiode and wapour can gradually sublimes, creating a greenhouse effect and more substantial atmosphere, may make Mars blue again. Anyways, I saw one source said the sun's expansion could be up too 400 R (up to 1.6 AU or so), will it expand enough to penetrate Mars' orbit. Mars may be swallow up as well, but unlikely-but no guarentee to survinve. Europa's ice layers is made up of oxygen and methane, it is possible that it may create an atmosphere for short time. Do Tango mean if they create an atmopshere for short of tme, it will go away quickly. The thing is ultraviolet, and solar winds wipes out atmospheres. —Preceding unsigned comment added by 69.226.46.118 (talk) 00:12, 22 January 2009 (UTC)

No, no, no! We have to put an end to this "after the sun turns into a red giant" crap. Step 1: The sun's intensity grows by 10% per billion years - this is quite enough to boil away our oceans long before the sun does the red giant thing. Step 2: Before it blows up - it first collapses and becomes (for a while) 1,000 to 10,000 times brighter. That's quite enough to boil all of the oceans on Europa and sterilise life there. Step 3: There is a "Helium pulse" - for a very brief time, the sun gets 100,000,000 times brighter. This ensures that all hope of anything at all surviving or having an atmosphere is gone. Step 4: It gently expands and swallows some of the toasted wrecks of molten lava that might be close enough - tearing more apart due to bizarre tidal effects.

So - no life left ANYWHERE within a few lightyears. Game over. SteveBaker (talk) 00:15, 22 January 2009 (UTC)

Incidentally, if it is only ~1000 then Triton and Pluto would see flux like the modern day Earth and could be quite livable for a while. Dragons flight (talk) 01:57, 22 January 2009 (UTC)

Yea right, Triton have been slowly diminishing it's orbit, and somewhere between 1.4 and 3.6 billion years, Triton will most likely get torn apart by tidal force, most likely form a ring. Few billion years, Neptune's rings like Saturn's now will go away too. About pluto, why you think pluto will get benefit, it's so faraway from sun.--69.226.46.118 (talk) 02:46, 22 January 2009 (UTC)

Was I unclear? At ~1600 times modern luminosity, Pluto would get the same amount of light as the Earth does now. Hence, when the sun is a red giant, Pluto would be expected to have roughly the same temperature as the Earth does now. Pluto is not so far away that one can ignore it when you start throwing around factors of 1000. Dragons flight (talk) 03:31, 22 January 2009 (UTC)

Life couldn't survive the helium pulse even at that distance. And once the sun actually reaches the red giant stage - the energy it pushes out to a lower level than it does now. So Pluto's fate as the Sun ages is that it slowly gets nice and warm and for a short time (well, assuming it's orbit doesn't expand too much due to the reduction in mass of the sun) life could even survive there - then it's bombarded by the planetary nebula - then it's irradiated to hell, sterilizing anything that might have survived - then it's back to being an even colder ice-ball than it is now. It's hard to imagine any kind of life that would survive that kind of mistreatment...and that's what it takes to still be there when the sun becomes a red giant. SteveBaker (talk) 03:56, 22 January 2009 (UTC)

• • First, does planetary nebula even swallow and destroy planets. I originally thought Pluto's orbit might almost double by then.--69.226.46.118 (talk) 04:16, 22 January 2009 (UTC)

That's after sun's giant stage, when sun forms a planetary nebulae and disintegrates it's outer laers. Between sun's maximum extent and white dwarf stage, there is something call "planetary nebulae". Planetary nebulae big enough (trillions of mile across), it glows white but don't swallow planets. At step two Titan is further from sun, it's atmosphere might just be half gone. At that time, Titan probably heats up to Mars' surface temperature, then when Titan heats up to around Earth's temperature, then the atmosphere is probably down to 0.02.--69.226.46.118 (talk) 00:31, 22 January 2009 (UTC)

Atmospheres bleed away over time even without UV and solar wind (although, there will be plenty of both anyway), warm air molecules move around a lot, at any given time a certain proportion will be moving around enough to escape and will do so. I guess it's possible that Mars will become close to habitable for a short period as the Sun brightens, before it gets bright enough to scorch the planet (probably only a span of a few million, or tens of million years), but it would probably be some time after the Earth was rendered dead, so the human race would have to survive elsewhere for a few million years anyway... --Tango (talk) 00:44, 22 January 2009 (UTC)

Aerated autoclaved concrete

Does anyone know how to make Aerated autoclaved concrete? —Preceding unsigned comment added by Elatanatari (talk • contribs) 05:24, 22 January 2009 (UTC)

The "Raw materials" section of its article explains it. DMacks (talk) 06:03, 22 January 2009 (UTC)

How to have a nightmare

Is there any way I can arrange to have a nightmare shortly before I need to get up in the morning, sufficiently intense that I'll rapidly become wide awake and fully alert, won't have to drag myself out of bed, and will be relieved to have returned to the real world, rather than disappointed as after a pleasant dream? NeonMerlin 06:01, 22 January 2009 (UTC)

I suppose a cassette player on an appliance timer, set to go off an hour before you wake up, with sufficiently spooky sounds on it, might work. StuRat (talk) 06:08, 22 January 2009 (UTC)

That's not really going to be reliable, because even if the tape could trigger nightmares, which is dubious, you've still got to synchronize it to your REM sleep cycles. If I recall correctly, REM sleep is the minority of your actual sleeping time. So that would very rarely work, if at all. APL (talk) 06:14, 22 January 2009 (UTC)

Our article on lucid dreaming may be of interest. --Jayron32.talk.contribs 06:18, 22 January 2009 (UTC)

(lyrics of Lucid Dreams by Franz Ferdinand removed) --Scray (talk) 12:22, 22 January 2009 (UTC)

When I was very young I convinced myself, in that way of children, that if I crossed my hands over my chest like a mummy while I slept then I'd have nightmares. And you know what? It worked very well—I had fantastical, nightmarish dreams whenever I set upon doing it. Later I tried to figure out why that might be, as it was obvious that any connections with mummies were only in my head, but that, of course, is quite a lot. I think the act of convincing myself that what I did would produce nightmares did, in fact, produce nightmares in some strange and subliminal way. I haven't tried it again for a long time, but it seemed to work even when I knew that it was just in my head—maybe something about the contrivance of it? I don't know. But hey, it's worth a shot—no harm if it doesn't work. --98.217.14.211 (talk) 15:42, 22 January 2009 (UTC)

Self-hypnosis it is, then. Julia Rossi (talk) 20:52, 22 January 2009 (UTC)

If you want to wake up at the best possible time then there are a few options available:

• http://www.happywakeup.com/en/index.htm
• http://www.sleeptracker.de/
• http://www.axbo.com
• http://www.reuters.com/article/technologyNews/idUSL0878172320070829

Isaac Asimov years ago noted the amazing ability of the brain to wake one up shortly before an alarm is to go off. He speculated that maybe (mechanical) alarm clocks made some small sound, or there was some alteration in their ticking shortly befre the alarm sounded. Without ruling out that hypothesis, I note that I have many times woken up a minute before a purely electronic alarm sounded at odd hours of the night, when I had to get up for some reason or other. I assert that it is possible to program the brain to wake you up at a particular time when there is something to be done. Edison (talk) 05:32, 23 January 2009 (UTC)

There is a much better modern explanation for Asimov's observation - which is that our conscious mind doesn't operate in "realtime" as we think it does. We are consciously registering events at least seconds (and possibly more) behind "realtime" and we're getting a highly edited version of events because the conscious brain simply doesn't have the bandwidth to handle all of that data. Our subconscious mind is doing ALL of the work and making our consciousness merely think that it's in charge. The subconscious edits the timeline to make all of this seem self-consistant and that means that since subconsciously we are collecting data BEFORE the alarm goes off - and long before the conscious mind needs to know about it - there is no problem with collecting some of the memory of events just beforehand and inserting those into the stream of events going to the conscious part. Like so many things in our world - the mind doesn't work the way common sense says it does and life is MUCH weirder than you'd think. SteveBaker (talk) 14:42, 23 January 2009 (UTC)

Creation of unfeasably large nuclei through the quantum zeno effect

A question arose in freenode ##physics, where a fellow wondered if it would be possible to create through nucleosynthesis elements heavier than would normally be possible due to high decay frequency by forestalling decay with the quantum zeno effect: sampling (measuring) the state of the nucleus at a frequency high enough that the probability of decay is vanishing.

A precursory search reveals nothing relating to the application of the quantum zeno effect to heavy atomic nuclei. Theoretically, one would suppose, there is a limit for frequency of measurement at some function of the planck time, and thus at some point the probability of a quantum vacuum fluctuation somewhere within the nucleus occuring between measurements will break even. However, I am not mathematically-conversant enough to be able to calculate even roughly this limit.

Any thoughts? 86.157.24.150 (talk) 12:45, 22 January 2009 (UTC)

Except that functionally, rapid "sampling" is functionally equivalent to bombarding the nucleus with particles; there is no such thing as "passive observation" in the quantum world, which is why observation always effects the properties of what you are looking at; you can only observe BY altering the properties of the subject. So while you may think that you are delaying decay by simply watching the particle to make sure it doesn't decay, what you are really doing is delaying decay by adding lots of energy to the system in such a way as to cause the decay to take longer. Paradoxes in the quantum world only appear to be paradoxes if you make incorrect assumptions about the ability to make passive observations. Once you realize that ALL observation occurs only by changing the target subject, then the apparent paradoxes disappear. SteveBaker is much more conversant in these matters than I, so I am sure he will be able to direct you to a more quantitative explanation. --Jayron32.talk.contribs 18:05, 22 January 2009 (UTC)

A few comments. First, to 86.157: if it was a simple quantum tunneling (think Gamow model) then, yes, a measurement that localizes the tunneling particle to the volume inside the potential well (rather than outside) reduces the amplitudes of the continuum (outgoing wave) components of the wavefunction and thus hinders tunneling for a short while. That is the essence of the quantum Zeno effect. However, for superheavy nuclei there are many decay modes to be expected, and I don't think it is even remotely possible, with present-day technology, to measure the location of all the possible "fragments" of the superheavy nucleus. And you need to do this more than once, and without destroying the nucleus in the process... So, in brief, it does not look like a feasible experiment to me at present, although it may, in principle, become feasible at some point in future. And a side note: our article on quantum tunneling is quite incomplete, and does not nearly give a proper insight in terms of scattering theory or energy spectra. I won't have time to fix it anytime soon, but I probably will fix it eventually. Now, to Jayron: I'm not sure what you mean by "passive observation", but a concept of "null measurement" is well established in quantum mechanics. Think of lack-of-interaction as a measurement: a photon passed through the system without scattering; nothing happened to the system, but some information about it has been gained. --Dr Dima (talk) 19:45, 22 January 2009 (UTC)

That;s true, however such null measurements do not actually cause "spooky action at a distance", or quantum paradox, or the "quantum zeno effect" that the OP is refering to. After-the-fact information gathering is NOT the same as live sampling, which is what the OP is asking about. Think to the classic double slit experiment. Measuring the location at which the electrons hit the target is a "null measurement" and does not effect the behavior of the electrons as they pass through the slit; knowing where the last electron hit does not effect where the next one will hit (it is still random) any more than not knowing would. However, live sampling of the slits themselves, where you "watch" which slit the electrons go through DOES effect the electrons flight path, and thus affects the outcome of the experiment. What the OP is asking about is whether some sort of rapidly repeated sampling could some how affect the decay rate of the particles. If you only count the particles after they have decayed, then no it won't. If you set up a device to observe the particles as they decay, then yes it very likely CAN effect the decay rate; however its not the fact that information is obtained that matters. You could set up your obeservation equipment and then not collect the data; and the decay rate would be effected by the same as if you tabulated the data. Its not information collection that matters; its observation in this case. --Jayron32.talk.contribs 02:54, 23 January 2009 (UTC)

Your understanding of the term "null measurement" is incorrect. A null measurement is a measurement (i.e. something causing the measurement effect) that isn't associated with any (ordinary causal) interaction between the system of interest and your lab equipment. Measuring the location at which the electrons hit the target is not a null measurement, since the electrons do interact with the target. The classification has nothing to do with the time at which the measurement takes place. That really has no relevance in quantum mechanics. All that matters is what you learn about the system. The reason measuring the electrons at the target shows an interference pattern in the double-slit experiment is because that particular measurement doesn't tell you which slit the electrons went through. It's pointedly not because the measurement takes place after the electrons have already gone through the slits. There's no theoretical reason why a null (i.e. interaction-free) measurement can't cause the quantum Zeno effect just like any other measurement. -- BenRG (talk) 14:15, 23 January 2009 (UTC)

Effect of Sildenafil (Viagra)

I read the subject published on Wikipedia concerning Sildenafil,but I have a quistion which is: we know that Sildenafil is not recommended for the patient with cardiac problems, althought sometimes it's given as antihypertensive drug? Can you give me a simple explanation on how it can be use for this case.

Thank you —Preceding unsigned comment added by Ghost whispers (talk • contribs) 16:36, 22 January 2009 (UTC)

Sildenafil is well-known to reduce blood pressure. However Pfizer noticed an unusual side-effect when their male volunteers took the drug. ;-) Hence it subsequently became marketed for erectile dysfunction. Sildenafil is also used to treat pulmonary arterial hypertension. Axl ¤ [Talk] 17:38, 22 January 2009 (UTC)

Expanding universe

If the expanding universe is stretching space and, I presume time, and we and our measuring instruments are an inevitable part of this expansion, then how do we determine that it is expanding and the rate at which it expands? 196.2.124.251 (talk) 17:19, 22 January 2009 (UTC)

The size of a ruler (and other material objects) is not affected by the expansion of space. Dragons flight (talk) 17:29, 22 January 2009 (UTC)

Why are rulers not part of the expansion? 196.2.124.251 (talk) 17:36, 22 January 2009 (UTC)

Because the chemical bonds holding them together are stronger than the expansion. --Tango (talk) 17:44, 22 January 2009 (UTC)

That's not quite right. The expansion of the universe is not a force. When you think of something like a balloon expanding, the force (pressure) causes it to happen, and that force puts a strain on the chemical bonds holding the balloon together, actually altering the properties (like size and shape of the balloon). The expansion of the universe is a different sort of event entirely; what is expanding is the actual space between objects. Its not that the objects are being pushed away from each other by some unknown force; its that the space between the objects is actually ITSELF getting bigger. This expansion does not affect other forces except where those forces are themselves dependant on distance (i.e. inverse square law forces like gravity. For example, the force of gravity between two objects will decrease due to the increasing distance between them, but it is not counteracted by any applied "force"; if it were, you would see decreasing gravity effects to be GREATER than the increasing distance due to cosmological expansion, and you do not. --Jayron32.talk.contribs 17:57, 22 January 2009 (UTC)

While the expansion is not a force, it does require a force to overcome it. If that force isn't strong enough, the objects get further apart, if it is strong enough, they don't. --Tango (talk) 18:50, 22 January 2009 (UTC)

If the actual space between objects increases, then surely that would include the space between molecules and the space between atoms? Would the dimensions of the nucleus itself not also be affected? 196.2.124.251 (talk) 18:02, 22 January 2009 (UTC)

The size of objects is determined by chemical bonding. These bonds have a characteristic length and resist efforts to stretch or compress them. You can't use your hands to appreciably stretch a ruler, and for the same reason the expansion of the universe doesn't change the length of a ruler. The bonds simply return to their natural size after being perturbed. Dragons flight (talk) 18:11, 22 January 2009 (UTC)

(EC) No. As Jayron32 says, the expansion does not constitute a force, hence it does not enter into the equations governing stable structures held together by electromagnetic or gravitational forces. These forces keep the physical distances (that's the distances that enter e.g. Newton's and Coulomb's laws) between, say, the nucleus and the electron in a hydrogen atom or between the Sun and Earth, constant (I'm using simplified pictures of these things, of course). To describe the situation, you could say that these forces cause Earth to move through an expanding space, that motion balancing the expansion. Or you could say, equally appropriately and much simpler, that the space in the solar system or the hydrogen atom is, in fact, not expanding at all. What it boils down to is that the phrase "Space is expanding" is an imperfect rendition in plain language of what the mathematical equations of general relativity imply (in pretty much the same way as the expanding balloon is an imperfect model for the universe), and is indeed to some extent a coordinate-dependent concept. --Wrongfilter (talk) 18:18, 22 January 2009 (UTC)

Going back to the trusty balloon model, if the universe is like the surface of an expanding balloon, does that mean that objects on the surface, like a ladybug, will also expand when the balloon is blown up ? No. StuRat (talk) 18:46, 22 January 2009 (UTC)

The idea of only select portions of space being affected by expansion sits rather awkwardly. If the space between atoms, and in fact the dimensions of atoms themselves, had to change in step with universal expansion, then surely the changes would not be detectable by any measurement one could carry out? 196.2.124.251 (talk) 20:49, 22 January 2009 (UTC)

Yes, you are correct. If absolutely everything changes then it would be indistinguishable from a situation in which absolutely nothing changed. Please note though that changing "everything" would also requiring changing the force laws that depend on distance by a comparable amount. The idea that physical matter stays the same size is comparable to saying that the strength of the forces holding matter together are unaffected by the expansion. Dragons flight (talk) 20:57, 22 January 2009 (UTC)

Things changing by just the right amount so that everything still appears the same, is a notion that happened once before, isn't it? Michelson and Morley. 196.2.124.251 (talk) 21:28, 22 January 2009 (UTC)

More specifically, Lorentz's interpretation of Michelson and Morley (and the source of the Lorentz contraction that we still use today). --98.217.14.211 (talk) 23:25, 22 January 2009 (UTC)

The expansion of the universe is sort of like gravity—it is very weak over short distances, powerful over long distances. Compare that with, say, electromagnetism. You can observe that a tiny, tiny magnet easily contains more strength over a short distance than the gravity of the entire Earth. However the strength of the magnetic force quickly diminishes as you get away from the source. The expansion of the universe isn't going to affect things at scales that are governed by chemical bonds, electromagnetism, etc. But it'll affect things at big, big scales—entire galaxies moving apart from one another, staying internally ordered by the powerful shorter range forces. --98.217.14.211 (talk) 23:25, 22 January 2009 (UTC)

The idea of an expanding universe selectively affecting the spaces that make up its structure, doesn't fly well. The "internal ordering" at chemical, and for that matter quantum scales, is simply another way of saying that things don't seem to change at that scale, and what I'm saying is that is to be expected if everything changed proportionately, when we wouldn't be able to tell if there were a change, would we? 196.2.124.251 (talk) 04:50, 23 January 2009 (UTC)

See, that's the thing. The expansion of the universe is a measureable effect, so any conclusion that would lead us to not notice it (if, for example, our "rulers" were growing at the same rate as the expansion) is a faulty conclusion at the a priori level. It must be a bad understanding because it does not explain observation. So we need to come up with conclusions about what is happening that fit the observations... --Jayron32.talk.contribs 04:57, 23 January 2009 (UTC)

Well, strictly speaking, what has been measured is redshift, the rest is surmise 196.2.124.251 (talk) 05:15, 23 January 2009 (UTC)

"selectively affecting the spaces that make up its structure, doesn't fly well"—why not? All of the forces have limited ranges on which they act. I don't see why the expansion of space would be different. The expansion force (though I am aware it is not technically a "force") is so small and so slight on the micro level that it can't compete with the strong localized forces like the nuclear force or the electromagnetic force. Think about how powerful expansion of space would have to be to have any affect on the nuclear force—it just isn't going to happen. One way to think about it is as particles in a giant grid. Let's say the grid spaces double slowly and weakly over time. On the whole of the grid, the grid space increases. But localized groups of particles, tightly bound to each other, are going to stay together. The net result is that the spaces between the clumps of particles will change but the particles themselves will stay internally ordered, not because the doubling is "selective" but because it is far too weak to affect the powerful forces that maintain their internal organization. You don't have to postulate any selective or intelligent force here—just one that is weak on small scales. Again, consider the example of gravity and electromagnetism. A tiny magnet easily defies the entire gravitational force of the earth. But as a whole, on the aggregate, gravity is powerful enough to organize the entire solar system. Different scales do get affects by forces differently. --98.217.14.211 (talk) 11:27, 23 January 2009 (UTC)

The expansion is not just "not technically a force" it is quite simply not a force. Therefore it is not a small effect on small scales, it is no effect. --Wrongfilter (talk) 11:46, 23 January 2009 (UTC)

Quite so! The assumption that in some way forces (or some of them) would be immune to such an expansion, is bizarre. In dimensional analysis a force would be (mass x length)/(time x time). At its most basic level time could be measured by the orbital period of an electron around a proton. If the mass and the scale of an atom's components were to change as a result of universal expansion, then the forces in such a system - be they gravitational, electromagnetic or nuclear - would all seem to remain constant. Since we and our instruments are of the very same stuff we are examining, it is impossible to gain an outside perspective. 196.2.124.251 (talk) 12:23, 23 January 2009 (UTC)

But our instruments do detect the expansion. Your theory doesn't match observation, so it must be wrong. --Tango (talk) 12:30, 23 January 2009 (UTC)

It has an effect, that effect is just easily compensated for by other effects (due to actual forces). --Tango (talk) 12:18, 23 January 2009 (UTC)

Let's try again. Why does the Universe expand? We do not know. It expands because we observe it to expand. Peacock ("Cosmological Physics") expresses it as follows: "The Universe expands today because it expanded yesterday." When we solve Einstein's field equation to build a model of the Universe, we put the expansion in as an initial condition. The field equation admits solutions that are not expanding, solutions that are for instance contracting. But that doesn't conform to our initial conditions, hence we throw these solutions out and only keep those that are expanding at the present time. Expansion is not a dynamical effect, it is not part of the dynamical equations, and there is no necessity for space to expand everywhere and at all times. Whatever caused the Universe to expand initially is not known, and it is not relevant for this discussion. Now, consider for example a cluster of galaxies (whose structure is unaffected by anything except gravity): At some point in the past, the region occupied by the galaxies that now belong to the cluster was expanding, the distances between the galaxies increased, and the whole thing was well described by a Robertson-Walker metric. But because the matter density in that region was higher than the average, the expansion was reversed, so the region collapsed. As the local density increases due to the collapse, the Robertson-Walker approximation to the true local metric breaks down, and in fact the cluster virializes. Today, the metric in a cluster is anything but Robertson-Walker. Clusters form stable objects and space in clusters has forgotten that it once expanded a long time ago. --Wrongfilter (talk) 13:04, 23 January 2009 (UTC)

OK Let me try again too. Does the Universe expand? We do not know. Why do we think it expands? Basically because of our interpretation of redshift. Do we get redshift if and only if it is caused by recession? No, there are a number of redshift causes we know and doubtless many that we as yet don't know. Then why does the mainstream of astrophysicists and cosmogonists believe in an interpretation based on expansion? Largely because it is the flavour of the month and because of something called Cosmic Microwave Background Radiation which is considered the best argument ever in favour of a Big Bang and a consequent expansion. Does this mean there are dissenting opinions on expansion? Certainly! There are some great minds in the fields of cosmogony and theoretical physics who are not at all convinced by the circumstantial evidence supposedly supporting the Big Bang. Does this mean the jury is still out in this case? It most certainly does! 196.2.124.251 (talk) 13:40, 23 January 2009 (UTC)

There are many more phenomena than just redshift that are consistently described by relativistic cosmology (and the big bang, incidentally, is not part of the theory). Alternative models are welcome if they're sufficiently sensible. --Wrongfilter (talk) 13:55, 23 January 2009 (UTC)

Alright, name 4 great minds in physics or scientific cosmogony that don't believe in the expansion of the universe? Some people argue about the details, or dark energy, but I can't think of any that dispute the entire idea of expansion. Dragons flight (talk) 14:15, 23 January 2009 (UTC)

I've said it before and I'll say it again: the expansion of the universe is just objects moving apart. Forget general relativity and spacetime curvature, it's just plain old Galilean inertia. There's nothing mysterious about "the space between objects increasing". That's what happens when things move apart. There's nothing mysterious about the expansion applying to some things and not others. Just because some things are moving away from each other doesn't mean others can't be moving towards each other or maintaining a constant distance. There's nothing deep here except for the Galilean principle that objects don't need to be pushed to keep moving, and the cosmic inflation (or whatever) that gave them the initial separating velocity. When Peacock says "the Universe expands today because it expanded yesterday", he's expressing Galileo's principle.

The only exception to the above is a cosmological constant (if it's real, which isn't clear yet). It does behave like a force: like a centrifugal (not centripetal) force, in fact, but directed in all three dimensions instead of only in a plane perpendicular to a rotational axis. But this force is utterly negligible in ordinary situations compared to another force that people routinely neglect: the self-gravitation of your lab equipment. For a meterstick weighing one kg, the ΛCDM cosmological constant is trying to pull the ends apart with a relative acceleration of about 10⁻³⁵ m/s², while self-gravitation (Gm/r²) is trying to push the ends together with a relative acceleration of about 10⁻⁹ m/s². We don't have the technology to measure the self-gravitation of a meterstick to one part in 10²⁶. The cosmological constant is noticeable at large scales only because the overall density of matter in the universe is so low, about 10²⁷ times smaller than the density of air. -- BenRG (talk) 13:19, 23 January 2009 (UTC)

Viewing it as just standard Galilean inertia (incidentally, wasn't it Newton that talked about inertia? At least he's the one the law is named after, although that doesn't usually mean much.) only works for an infinite universe. If the universe is finite (a 3-sphere, say), it would be impossible for everything (on a large enough scale) to move away from everything else, there would have to be things moving together on a large scale, but we don't see that (we see Hubble's law instead). Now, it could just be our bit of the universe (ie. the 46 billion light year radius ball around Earth, or whatever the number is) where everything is moving outwards, but that would violate the Copernican principle. If what you're saying was the mainstream understanding, then people wouldn't still be wondering what shape the universe is (well, there are still plenty of options, but it narrows it down a lot). --Tango (talk) 14:29, 23 January 2009 (UTC)

Foucault pendulum in Lost

I guess he was trying to find out where in the world he is with a foucault pendulum. Longitude is impossible to determine with it of course, but it got me thinking about latitude. The article says that the pendulum appears to take different amounts of time to return to its original floor-relative position depending on your latitude, so by measuring that time you can determine your latitude. But this is very confusing to me. Isn't the whole idea of a Foucault pendulum that the ball swings back and forth with no external forces except the top of the string getting pulled along with the rotation of the Earth (and gravity of course)? Doesn't that mean that when the rotation of the Earth brings it round 360 degrees back to its starting point that the swing of the pendulum should be the same as when it started? In other words, shouldn't the pendulum take the same amount of time on every latitude: 360 degrees in 1 day? 72.236.192.238 (talk) 18:37, 22 January 2009 (UTC)

Do yourself a favor, as I did: Stop trying to make scientific interpretations of events in LOST. It's all Hurley's dream anyhow :-D -RunningOnBrains 19:52, 22 January 2009 (UTC)

Yes yes lost is a bit out there (There are rules! Principally that time travel is impossible; second, that you can't change the past.. unless you say "please let this work" 3 times.) but I'm mostly asking about the pendulum. Hours of swinging my cell phone back and forth around my fist have only made me more confused. I really think that the pendulum should be "back where it started" relative to the ground at the end of the day, regardless of latitude, although I admit it must move at the poles and not move at the equator and don't understand what happens in between. It can't possibly have anything to do with Solar time can it? 72.236.192.238 (talk) 20:12, 22 January 2009 (UTC)

Latitude is easy to measure though. What's wrong with measuring the angle to which either Polaris or the Sun or any of the planets rises above the horizon? All of those things lie in the plane of the ecliptic - so you know the angle of your local horizon to that. You need to take account of the tilt in the earth's axis - and I suppose if you don't know what time of year it is, you might need to take both a daytime and a nighttime reading to get that. But that's WAY simpler than messing around with the pendulum. (And I agree that I don't see how it actually works) The trick is in figuring out longitude...but I don't see how the pendulum helps there. Unless you've got a pretty well detailed almanac or a perfectly synchronised clock - you're basically doomed. SteveBaker (talk) 19:54, 22 January 2009 (UTC)

It works because the precession of the plane of the pendulum in 24 hours is not 360 degrees, it is $360\cdot \sin \phi$, with $\phi \,\!$ being the latitude. The calculation is in the article, but to accept this result consider that the plane does not rotate at all at the equator, and there must be a smooth transition between that value and the 360° at the poles. Geometrically, if you're familiar with vectors, the rotation about the vertical that we're looking at here, is only a part of the angular velocity vector of the Earth (of magnitude 360°/24\,h), a projection of the latter onto the local vertical, which of course has a smaller magnitude, implying a slower rotation. And yes, I also find it difficult to actually picture what's going on here. --Wrongfilter (talk) 20:08, 22 January 2009 (UTC)

Hmmmm with your velocity vector analogy I just thought of sort of a way to picture it:

Forget the rotating frame of reference and the markings on the floor, and think of the pendulum as being fixed in space above the earth as the earth rotates below it. On the equator the pendulum just swings back and forth like the article says; the earth rotates below it but it doesn't affect the pendulum. But once you move north of the equator and become slightly more aligned with the axis of rotation, you can imagine the pendulum experiencing torque and starting to turn slowly. As you get to the pole, the pendulum's spin catches up with the speed of the earth until when the axis of rotation and the pendulum are perfectly aligned they're in sync. Now that's very easy to picture, and the jump to the torque being a fictitious force is almost as easy to accept, though not really to picture. 72.236.192.238 (talk) 20:31, 22 January 2009 (UTC)

Another thing just occurred to me to explain why the pendulum doesn't turn over the equator. Imagine a low pressure zone in the northern hemisphere, and air is rushing north to fill it. It moves in a straight line but the earth rotates under it, seeming to a ground-based observer that it's deflected it to the right. No matter which way you approach from it will deflect clockwise. But if there's a low pressure zone right on the equator, the earth isn't rotating under it! There's no coriolis effect at all because it's completely orthogonal to the only axis of rotation. 72.236.192.238 (talk) 20:54, 22 January 2009 (UTC)

I don't think that was a foucault pendulum on the show, since the pendulum wasn't on the island it was in Los Angeles I don't see the point of using it when GPS is available. That was some instrument they used to find the island so they could go back. Unless I missed some other pendulum on the show... -- Mad031683 (talk) 21:49, 22 January 2009 (UTC)

That it doesn't rotate at the equator can perhaps be seen best from that it will rotate in opposite directions at the two poles. Dmcq (talk) 23:25, 22 January 2009 (UTC)

Two quick points. Wrongfilter is right that a Foucault pendulum will tell you your latitude, but Steve is right that observing the sky is a much easier way to do it. As for what was shown on the show, I have no comment.

And one slower point. We usually think of the Coriolis effect as a fictitious force that appears to deflect an object's motion sideways on the Earth's surface. That's true as far as it goes, but there is also a vertical component. Because the effect is generated by the Earth's rotation, the "force" is necessarily felt in a plane parallel to the equator. There is a Coriolis effect at the equator -- but it's entirely vertical. (Imagine moving rapidly east along the equator so that your speed was added to the Earth's rotational speed. You would get slightly lighter. That is an upward Coriolis effect.) As your latitude increases, the Earth's surface comes nearer to being parallel to the plane of the equator. Therefore the horizontal component of the Coriolis effect increases and the vertical component decreases, becoming zero at the poles. This is also why the Foucault pendulum reveals your latitude: as seen from the Earth's rotating surface, it is the Coriolis force pushing it sideways with each swing the causes its plane to rotate, and at higher latitudes, the (horizontal part of the) force is greater. The vertical part, of course, has no effect on its plane.

--Anonymous, 05:47 UTC, January 23, 2009.

:: in gene notation

What does the notation something::something mean in regards to genes? E.g. spt10::KanMX6 ? ----Seans Potato Business 20:24, 22 January 2009 (UTC)

Googling for Template:Websearch tells me that A::B designates a particular insertion of the B transposon within the gene A. --Sean's Utter Lack of a Potato Business 20:49, 22 January 2009 (UTC)

Its perhaps more typical in today's usage, that the double colon is used to denote a fusion gene has been engineered by inserting a sequence in frame behind, or in front of, a coding gene. So MC1R::GFP would indicate that you have a gene construct that has the Melanocortin 1 receptor gene sequence followed by the sequence for green fluorescent protein. The result, when the construct is expressed is a fusion protein. Rockpocket 06:44, 23 January 2009 (UTC)

air compressor

I want to know that what is two-stage air copressor? and how i done it's intercooling and thermal analysis? —Preceding unsigned comment added by Munish malik (talk • contribs) 00:24, 23 January 2009 (UTC)

See our article titled Gas compressor, expecially the section with the name Staged compression. Cheers! --Jayron32.talk.contribs 02:42, 23 January 2009 (UTC)

how do explosions destroy things

will ... i looked about the meaning of explosions , and it was a rapid chang in volume , but i need to understand whats the mechanisem of destruction effect ... how did it destroy objects within the range . —Preceding unsigned comment added by Mjaafreh2008 (talk • contribs) 01:28, 23 January 2009 (UTC)

Shock wave? Also, even a simple "rapid change in volume" means there's a lot of force pushing out in all directions...push against "something" hard enough and it will break. DMacks (talk) 01:48, 23 January 2009 (UTC)

Overpressure says that (for example) C4 explosive produces 10 psi (pounds per square inch) of "overpressure" (although it doesn't say how much C4 or in how much volume?!?) - but let's run with that number. Suppose you have a brick wall that's 20' long by 10' high. That's around 30,000 square inches - and at 10psi of pressure, the explosion would exert a third of a million pounds of pressure onto the wall! It's really not hard to imagine why that would destroy the wall! SteveBaker (talk) 03:03, 23 January 2009 (UTC)

Another way to look at it: The forces exerted by the explosion are not applied equally for all parts of the exposed object – typically having the greatest effect on the near exposed surface of the object. That causes internal stresses (compression, tensile, sheer, or torque) within the object which may exceed its strength. The result is that the object distorts or breaks up. Those same forces may then accelerate different parts to different velocities resulting in a scattering of the remains.

In contrast, if the forces were applied equally to the entire object, down to the atomic level inside and out, the object would remain intact because there would be no internal stresses. Theoretically, the object could survive near-infinite acceleration in such cases. Examples would include gravitational and possibly electrical and magnetically induced acceleration. For example, the earth's gravity exerts an enormous amount of force on the ISS, but the station remains intact because the force is applied uniformly. If an equal force were applied using a thruster pack connected to one module of the station, the resulting stresses would likely cause structural failure. -- Tcncv (talk) 05:15, 23 January 2009 (UTC)

And note that if it is easier for the object in question to maintain its structure and to just move, it'll do that rather than be destroyed, even if the explosive force is huge. (See, for example, Project Orion (nuclear propulsion)) --98.217.14.211 (talk) 11:18, 23 January 2009 (UTC)

Viewing memories from a cat's brain?

Did I dream this? I remember reading, a few years ago, an article about a scientific study that was able to somehow find images from the memory of the cat, somehow encoded into its brain cells. It was accompanied by a few blurry pictures of a man that were said to be from the cat's brain. Knowing what I know now about how memory works, this seems somewhat unlikely, but I'd like to find the article again. Does anyone know about it? Was it a hoax? 99.245.92.47 (talk) 01:52, 23 January 2009 (UTC)

This is the closest I could find on a quick search. I'm pretty sure it's not the article you were after, but will (purr-haps) jog your memory? Cycle~ (talk) 02:36, 23 January 2009 (UTC)

That's by measuring the neural activity in realtime - that can only work at the instant the cat sees the image. There is no way we know enough to extract a memory of an image - that would require decoding the entire storage mechanism - and we are a tremendous way away from being able to do that. It was either a hoax or you are remembering the research on seeing the images in realtime. SteveBaker (talk) 02:55, 23 January 2009 (UTC)

I would not be surprised if something like this were possible far in the future, but it seems beyond the capabilities of today's technology. I note that there was a recent report of a brain scan technique which could brain imaging to accurately detect which letter of the alphabet a person was looking at, and iirc they hypothesized that the technique might also allow determining which letter the subject was thinking of. Edison (talk) 05:25, 23 January 2009 (UTC)

Yes - but that's still "What you are thinking about right now" - and that's a VERY different matter than "Extracting images from memories". It's pretty clear that our memories of scenes from the past do not consist of a bunch of pixels stored away like a photo in your computer. Instead we have a bunch of associations. We have a picture on the wall at home that I "remember" - there is a river with some canal boats and a pub in the background. I can "picture" that painting clearly in my mind - but I can't tell you the colors of the boats or the number of windows on the front of the pub. That's because I'm only remembering the concept of "classic village pub", "river" and "canal boats" - I don't have anywhere in my brain the actual image stored. Hence, in order to reconstruct that image, the computer would have to be able to extract from my memory not just the memory of the painting - but also my general concept of what a village pub typically looks like. That would require decoding more or less the whole of the brain function - and THEN being able to reconstruct the pathways by which we remember things. Worse still - if the person remembering that photo was an expert on 18th century architecture - he wouldn't be remembering a "village pub" - he'd be remembering a particular style of architecture and construction. An expert on canal boats would be remember a particular boat manufacturer and a specific model number they produced. A horticulturalist might remember the species of tree off to the left of the pub. Someone who's been there will also remember the flavor of the beer they serve there and details of the pub interior that aren't even IN the painting. No two people will remember that picture in the same way. We know that memories are stored in a diffuse 'holistic' manner so nothing short of scanning the connections between every neuron in the brain would enable us to do this. So this is AMAZINGLY beyond our current understanding - let alone the technology to measure what we'd need. Worse still - the number of neural connections in even a cat's brain are vastly too great to store in the available RAM + disk space of even a pretty large super-computer. So even if we knew what to do - we don't have the storage space to process it. It's going to be 30 to 40 years of "Moores law" improvements before we have a computer that has the power to do this - I'm betting a hundred years before we know enough about brain organisation to do it. This is science-fiction technology. So our OP is DEFINITELY mistaken. The only question is how/why. SteveBaker (talk) 14:21, 23 January 2009 (UTC)

It was more recent than 1999, and definitely talked about memories, but thanks. 99.245.92.47 (talk) 05:51, 23 January 2009 (UTC)

Your are either mistaken - or you've been hoaxed. It's not remotely possible with todays technology. SteveBaker (talk) 14:21, 23 January 2009 (UTC)

They did a study on cats dreaming where they removed the block that keeps cats (and us) from moving their muscles in response to the dreamed reality. They found cats dream about hunting and stalking. But that's not memories either, they might have mentioned those in the report, though. 76.97.245.5 (talk) 09:18, 23 January 2009 (UTC)

Hmmm - if they'd used dogs they could have saved themselves a lot of trouble! I've owned many dogs over the years and you can EASILY tell that this is what they are dreaming about because that suppression of muscle action during REM sleep isn't as complete as it is with humans (and perhaps cats). Dogs sleep a lot - so you have plenty of chance to watch! When you see their eyes start to move under their eyelids - you know they are entering REM sleep. Then within seconds you can see the tips of their paws twitching as they walk in their dreams - you see the feet first twitch in a 1-2-3-4 pattern like they are walking - then you see them start to twitch in pairs like they are running - you can see their bodies heaving like they are breathing fast (but they really aren't) - then you will see the jaws moving and the cheeks puffing slightly in and out and you may even hear very soft barking (more like little 'yip' sounds). On some occasions, I've seen the dog's running pattern stop and chewing actions happen in the jaw. It's totally compelling - my dog dreams of running and chasing things - sometimes of catching and eating them. No question about it. Cats on the other hand...who knows? SteveBaker (talk) 14:18, 23 January 2009 (UTC)

Do female athletes and sportswomen, especially in 'masculine' sports, have more testosterone than average women?

I would expect so but is there any good scientific work on the subject? Just seeing today's featured article made me think about it.--Ib.nib op.cit. (talk) 06:31, 23 January 2009 (UTC)

Because they say (citation needed) that oestrogen is produced by fat, and that testosterno is produced by muscle. Is this true?--Ib.nib op.cit. (talk) 06:34, 23 January 2009 (UTC)

Here is a nice review of the scientific literature: Athletes’ Testosterone Levels by Sports Team: An Exploratory Analysis. Note also that during the Cold War, East Germany decided to administer about 60 times the natural level of testosterone per day to their female athletes (under the direction of Manfred Ewald). The result was striking. Although a relatively small country, the GDR excelled in the Olympic medal tables during the late 70s and 80s. Their female athletes and swimmers did particularly well. Rockpocket 07:09, 23 January 2009 (UTC)

It's important to distinguish between the questions, "do women who have more testosterone tend to end up in 'masculine' sports?", and "do women in masculine sports tend to end up with more testosterone?". --Sean 12:46, 23 January 2009 (UTC)

One of the problems that the sports officials have had is determining whether some of their "female" competitors are truly female (See: Santhi Soundarajan)- to that end they have defined limits to the amount of testosterone that they consider normally "female" and a few women have been outraged to discover that they are excluded from female sports because the officials consider them to be "men" by virtue of their body chemistry [34]. So I think the answer is likely to be a cautious "yes". Cautious because of the definition of a "masculine" sport...weight lifting? shot putt?...yeah - sure. Is rifle shooting "masculine"?...if so then I need to change my answer and say "no". SteveBaker (talk) 13:48, 23 January 2009 (UTC)

Neanderthal cranial size

What is the current consensus concerning the cranial capacity of H. neanderthalensis? Was it smaller, about the same, or larger than H. s. sapiens? Viriditas (talk) 09:27, 23 January 2009 (UTC)

Human on the left - Neanderthal on the right

We have an article: Cranial capacity which contains a table of cranial capacities:

• Orangutans: 275–500 cc
• Chimpanzees: 275–500 cc
• Gorillas: 340–752 cc
• Humans: 1100–1700 cc
• Neanderthals: 1200–1700 cc

So more or less the same. Of course we have FAR more human skulls to measure - so we know where the outliers are in the data set (ie we've seen incredibly small and incredibly large skulls) - but the relatively limited number of Neanderthal skulls that we've found could easily mean that we simply have not yet found any of the larger or smaller-brained individuals yet. That suggests to me that the 1200 to 1700 range is probably narrower than it really was. That's why I'd tend to say "larger".

We should be careful about what we take away from those numbers though. Larger skull capacity doesn't necessarily equate to greater intelligence. Neanderthals also had much larger nasal cavities than modern humans - so they may have had a very acute sense of smell - that being the case, they may have devoted more of their brain to processing, analysing and remembering olfactory sensations. So even with a larger brain than us - they may not have been as smart. Also, while Neanderthals were typically shorter than modern humans - they would have been taller than the humans that were when Neanderthals were common - and their body's were generally chunkier. (Our Neanderthal article somewhat scathingly compares them to modern Americans & Canadians!) But our Brain to body mass ratio and Encephalization articles point out that a rough measure of intelligence can be obtained by comparing the ratio of body mass to brain size between species. So even with slightly bigger brains, if their bodies were significantly larger than the humans of their era then perhaps we have to assume that they were not quite so smart. (Did I just imply that Americans and Canadians are stupid?)

But whatever the difference - it would probably be fairly small and there would certainly have been some Neanderthals who were smarter than some Humans - and vice-versa.

SteveBaker (talk) 13:39, 23 January 2009 (UTC)

spiral bevel gears

Can the teeth of spiral bevl gears can be forged directly without any machining? —Preceding unsigned comment added by 203.90.64.100 (talk) 10:57, 23 January 2009 (UTC)

Electronics

I'm having trouble trying to understand something to do with electricity/electronics. In a circuit current is said to take the path of least resistance. So what I don't understand is why parallel circuits work: wouldn't the current just flow through the path which has the least resistance? --212.120.247.244 (talk) 14:07, 23 January 2009 (UTC)

Everything that moves is said to take that path. The "resistance" in "path of least resistance" is the general word meaning opposition to movement. The "resistance" in electronics is a special case of the word, borrowed rather than make up a new one, a well-defined term meaning something like "opposition to the gross movement of electrons in non-reactive media". There is another, more specific term, "impedance", that actually applies more accurately to electronics and is the word best thought of when thinking about these things. Bottom line, electrons do not take the path of least resistance, they take all paths available in inverse proportion to the impedance of those paths. --Milkbreath (talk) 14:42, 23 January 2009 (UTC)

microbiology

what i meant by streptolysin test,where is it applied and which is the procedure of carrying it out? —Preceding unsigned comment added by 196.202.206.37 (talk) 14:48, 23 January 2009 (UTC)

microbiology

what is meant by streptolysin test,where is it applied and which is the procedure of carrying it out?