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January 31

take a solution of enantiomerically pure lactic acid in water ... pH 4-5

The lactic acid will start racemising slowly, right, until an equilibrium is reached between the two isomers? How long will this take? Racemisation of chiral sugars seems pretty rapid -- so why does the optical purity of your lactic acid matter?

Or is it harder to racemise a carboxylic acid versus an aldehyde/ketone? The enol form seems stabilised by the alpha-hydroxy group though. I could imagine the hydroxy group becoming a carbonyl and carboxylic acid carbon bearing two hydroxy groups (as one of the tautomers). John Riemann Soong (talk) 00:00, 31 January 2010 (UTC)

Thinking about other things and performance in minesweeper while tired

I have noticed that, while tired, I get better times in 16x30 99 mines minesweeper when I'm thinking about other things. I would get 1:50 or a few seconds over two minutes most of the time, but when thoughts start to wander I hit 1:30 - 1:40, about the same as when in a state of full awareness. What's happening and could you name something similar? Are the events both effects or this there causality? Wild speculation is wished. --194.197.235.240 (talk) 02:21, 31 January 2010 (UTC)

Are you writing down the times for every single game you play? Otherwise it could be Confirmation bias or Illusory correlation. Ariel. (talk) 02:29, 31 January 2010 (UTC)

This is purely WP:OR but personally I find that my limiting factor at most points during a given game is my click speed rather than the rate I can process the information. My times are around where yours are (typically 85-110s). My level of concentration doesn't seem to make much difference (although I don't have any data to back that up). However when I try really hard to achieve fast click speed I tend to make more mistakes and it ends up slowing me down compared to when I'm "loose", including when I'm not paying attention. Many times that I've gotten a high score have been when I wasn't expecting it. As for tiredness, I do have data for time of day versus completion time, and I seem to do worst in the few hours after I wake up and then fairly steady for the rest of the day with a slight improvement late at night. Rckrone (talk) 03:56, 31 January 2010 (UTC)

(OR) I have noticed a similar effect when solving Sudoku puzzles and I attribute it to subconscious Pattern recognition (psychology). Cuddlyable3 (talk) 16:41, 31 January 2010 (UTC)

Yes, and I've noticed this effect in Minesweeper specifically. For example, if I have uncovered a "1" and one adjacent mine has already been marked, I can either consciously think that this means the other 7 squares must not have mines, or my subconscious can do that for me. Apparently, the subconscious is significantly faster at such tasks, and seems to take over more when the conscious mind is either fatigued or busy. I believe this is because the conscious only works on a single thought at a time, while the subconscious is capable of multiprocessing. As I write this, it's probably thinking about scratching that itch on my leg and several other things, all at once.

So, then, if the subconscious is actually faster at certain "no-brainer" tasks, perhaps we should think about how to use it more for such things. I've noticed that most of car driving seems to operate on a subconscious level, which is normally good, but can be bad when you mysteriously arrive at the wrong destination. Getting just the right mix of conscious and subconscious brain activity involved in every task is quite important, it seems to me, and significant research should be devoted to this topic. Thus, your seemingly trivial Q may give us a very important insight into an much bigger and more important Q. StuRat (talk) 18:08, 31 January 2010 (UTC)

It seems to me that the ability of the 'sweet spot' of human awareness to really focus on a task at hand is generally limited. There are other parts of our awareness that are paying better attention than us. This is evident to me when I can't find something that I set somewhere. As long as I consciously look and look for it, it's impossible to find. But then when I stop seeking it myself and let that part of me that knows right where it is show me where it is, all of a sudden I will realise I am looking right at it. --Neptunerover (talk) 20:26, 31 January 2010 (UTC)

I would even compare a human to the Starship Enterprise, where, while we might be the captain, we cannot keep track of everything going on around us. And so we have a crew too who monitor the sensors and alert us if there's need. The onboard computer keeps track of everything, and tapes can all be reviewed (memory). --Neptunerover (talk) 23:38, 31 January 2010 (UTC)

Sleep and creativity may be of interest. ~AH1 02:34, 1 February 2010 (UTC)

I asked a similar question last month, please see this discussion and the VERY useful external links provided therein:Misplaced Pages:Reference desk/Archives/Science/2009 December 18#Autonomous behaviour on Guitar Hero. Regards. Zunaid 12:54, 1 February 2010 (UTC)

No matter how much I eat, I don't gain weight.

Request for medical advice (and some highly irresponsible advice) removed. If you wish to debate this removal, please start a thread on the talk page - not here. SteveBaker (talk) 16:24, 31 January 2010 (UTC)

Polyethylene foam bed vs Urethane

breathing? —Preceding unsigned comment added by 67.246.254.35 (talk) 05:55, 31 January 2010 (UTC)

Breathing? --Neptunerover (talk) 09:09, 31 January 2010 (UTC)

BREATHING? --124.157.247.221 (talk) 09:40, 31 January 2010 (UTC)

Both of these polymers are watertight and impervious to air, you cannot breath through them. Whether they will suffocate you will depend on the structure, whether there are holes that connect. However a firm foam is likely to be closed cell. Graeme Bartlett (talk) 10:52, 31 January 2010 (UTC)

So then, Polyethylene foam bed vs Urethane: Not for breathing, no. --Neptunerover (talk) 11:06, 31 January 2010 (UTC)

i mean which will breathe better so i dont sweat —Preceding unsigned comment added by 67.246.254.35 (talk) 15:26, 31 January 2010 (UTC)

They could only stop you from sweating by keeping you cool...so the question becomes one of how to get the heat out. Maybe less bedclothes? SteveBaker (talk) 16:20, 31 January 2010 (UTC)

no —Preceding unsigned comment added by 67.246.254.35 (talk) 16:24, 31 January 2010 (UTC)

For breathing (porosity to air), try a feather bed, but if you want air to circulate below you, then perhaps just a wire mesh would be best, though not most comfortable. As Steve said, if you want to avoid sweating, just reduce the thermal insulation above you. Dbfirs 17:34, 31 January 2010 (UTC)

While keeping the body cool will limit the moisture released from the skin, it will not eliminate it. Thus, the circulation of air and/or absorption of moisture by the bedding material is important. Note, however, that the "bedding material" also includes the sheets and perhaps a "feather top", etc. Thus, the mattress itself may be completely impervious to water, so long as enough absorbent material is between it and the occupant. This might be a good way to do things, as a mattress may be ruined if someone has an "accident", while other bedding may be more washable. I myself use a comforter as a "bottom sheet" (although I haven't had an accident in several decades now :-) ). StuRat (talk) 17:48, 31 January 2010 (UTC)

We do not provide medical advice. However materials such as those mentioned and even nylon can cause overheating (this is how a sleeping bag works). Cotton does not restrict heat flow as much and therefore may have better air flow. ~AH1 00:57, 1 February 2010 (UTC)

Horrible Insects

Inspired by Red imported fire ant, what prevents an insect species from evolving that would prey on mammals, entering by the ears, feeding on the brain and using the scull as protection? 95.115.151.113 (talk) 15:05, 31 January 2010 (UTC)

Evolution is a slow, incremental process. You'd first have to imagine an insect that would be interested in clambering around inside a mammalian ear without somehow getting through the skull and into the brain - and then imagine incremental benefits to each step. Expect this change to take maybe a million years to happen. Bear in mind that the mammals in question will also be evolving ways to keep these pesky insects out of their ears in the meantime. It's not a simple matter. SteveBaker (talk) 16:19, 31 January 2010 (UTC)

The eggs of parasites are microscopic and can be passed sexually, through shaking hands, walking barefoot, from a pet, eating or drinking from someone else's glass, bottle, can, fork etc., swimming in polluted lakes, rivers or streams, going to the beach, etc. Entamoeba Histolytica can get into the liver, the lungs and the brain. Cuddlyable3 (talk) 16:34, 31 January 2010 (UTC)

This would be catastrophic for whatever insect species decided to try to prey on mammals. We are thinking, feeling, revenging creatures that would, upon discovery of this new predation, seek out and destroy every nearby colony! Vranak (talk) 16:51, 31 January 2010 (UTC)

Um, no. Plenty of insects prey on living mammals—mosquitos and fleas being two obvious ones, not to mention all of the parasitic worms and larvae that would love to get inside us and burrow around. Even us mighty revenging, thinking human beings have been shown to have limited capacity to deter such activities (it has taken until the 20th century to even start to get a handle on the worst of such pests in the most developed parts of the world). And of course if we get beyond the mistake that "mammals" and "humans" are identical, there are even bug-sized creatures that eat small mammals, birds, and fish (army ants, certain large spiders). The issue, here, is that insects don't seem to outright hunt and kill large animals. The reason for this is probably both ecological (it would be a tremendous waste of biomass, and such an insect would probably deplete its food supply rather quickly) and evolutionary (it is evolutionary easier to feed on carrion than it is to try and hunt a big animal, when you are that small). --Mr.98 (talk) 19:24, 31 January 2010 (UTC)

Mmm, as I read the initial question, I inferred a sort of nightmarish glint about, well, horrible insects actively going after healthy individuals. Everything you point out is true of course, but these infestations are inevitability spawned out of disease. The prime mover is a lack of health, not hungry little insects. Vranak (talk) 22:10, 31 January 2010 (UTC)

Not true for botflies, an article I fond after posing the question. Guessing from the answers raising up every god and reason (like that a dog could make its paw scratch behind the ear-hole already inside the scull) to make believe this cannot happen, I must have hit some severe archetypical nightmare. 95.112.190.236 (talk) 17:43, 1 February 2010 (UTC)

I disagree that evolution has to be slow and incremental. When the barrier to selection is low, evolution is very, very, very rapid, like tossing water into a solution of acid chloride. A selection barrier is a bit like activation energy -- when high enough, it will prevent selection in a certain direction even though that direction may be favourable to the species and thus selection in that direction will be slow. John Riemann Soong (talk) 16:56, 31 January 2010 (UTC)

It wouldn't work. The inner ears are extremely sensitive, and if a bug gets in there (which happens occasionally), people will do whatever it takes to get it out, even if it means pushing sticks in and damaging sensitive tissues. There was an African explorer (Stanley?) who lost hearing in one ear due to an episode of that sort. Looie496 (talk) 17:02, 31 January 2010 (UTC)

What could a cow, a dog, a cat do to get such a bug out of the ear or at least kill it? 95.115.151.113 (talk) 17:24, 31 January 2010 (UTC)

A dog or cat could maybe get a claw in there and do some damage. As for cows, there are birds, like oxpeckers, which specialize in removing parasites from them. Also, animals would be under evolutionary pressure to develop a defense, like a thick, poisonous earwax. StuRat (talk) 17:38, 31 January 2010 (UTC)

The dog or cat would probably do more damage to themselves than the bug. They have limited ability to remove pests from themselves, even if they are bothered by them. Ear mites drive dogs crazy but there isn't much they can do other than shake and scratch ineffectively. The thing is, it is better for the mite to not be fatal—the affected dog then can spread more mites to other dogs, and so on, and the mite has plenty of food as it is (what would a mite do with a whole dog?). --Mr.98 (talk) 19:24, 31 January 2010 (UTC)

What provides the bugs/mites/critters with such wisdom? Imagine a mutant putting (nearly) all available resources into reproduction. A brain even as small as from a cat can provide large amounts of nutrients (yummy fat and proteins). Having more offspring is a primary trait in natural selection. As insects have far more generations than mammals do have in the same timespan, the mammals would not have enough time to adapt. Such a mutant would spread explosively, killing off their pray nearly entirely in a short time, than die out or establish an equilibrium with the more hardy and resistant specimens of their pray. Is there any evidence/hint that this ever happened in the history of live? 95.112.190.236 (talk) 17:09, 1 February 2010 (UTC)

There's some sort of cat disease that a large proportion of people are said to be infected with and includes cysts in your brain. 92.24.73.102 (talk) 21:43, 31 January 2010 (UTC)

Toxoplasmosis? --Dr Dima (talk) 22:48, 31 January 2010 (UTC)

There's also Baylisascaris sp., and Taenia solium. Note that these three are very different critters: Toxoplasma gondii is a protozoan, Baylisascaris is a roundworm (class Nematoda), and Taenia is a tapeworm (class Cestoda). None of them is an insect, though :) . The only insects I can think of that live in the relative safety of the mammalian skull are the fly larvae that live in the sinuses of the sheep. Their Latin name will come back to me in a moment. --Dr Dima (talk) 22:56, 31 January 2010 (UTC)

The sheep nasal bot-fly is Oestrus ovis. Nasty, nasty critter. We don't have an article on it, much to my surprise. --Dr Dima (talk) 23:07, 31 January 2010 (UTC)

However, we do have an article on the gnat in the Titus' brain (which Titus entirely deserved for what he did). Mysterious are the ways of the Editors. --Dr Dima (talk) 23:14, 31 January 2010 (UTC)

I saw a doco recently which would have been great to post here. It was of a herd of African cattle of some sort, they were all peacefully grazing, relatively still, except for their ears which were wildly gyrating, no doubt because of the insects, it actually made me laugh it looked a bit ridiculous. Even Darwin in Origin of Species recognised that insects play a not insignificant role in the success or failure of larger mammal species. He said even the small tail of the giraffe may seem superficially quite ridiculous and pointless to evolve but even if it provides a little relief as a swatter from the constant harassment of insects, it makes the animal more fit, not just less likely to be killed by insects, but being so worn down by them as to succumb to diseases or even other predators. Vespine (talk) 23:43, 31 January 2010 (UTC)

And of course immediately relavant to this topic is myiasis, I thought someone would have mentioned it already. Vespine (talk) 23:46, 31 January 2010 (UTC)

The tsetse fly's bite causes African trypanosomiasis, where the infection spreads to the brain. Naegleria fowleri is a form of "brain-eating amoeba". Also, under certain circumstances microorgaisms and species in smaller niches can evolve rather quickly, and the effects of global warming on most of those species are currently not known. ~AH1 00:53, 1 February 2010 (UTC)

Earwig. 124.157.247.221 (talk) 01:35, 1 February 2010 (UTC)

This has been recorded, although through the nose, not ear, and I'm not certain we'd regard it as a scientifically rigorous report, as the objectivity of the source is somewhat in doubt. --Dweller (talk) 12:06, 1 February 2010 (UTC)

Depth and temperature

Why is it very cold six miles underwater, but very hot six miles underground? 213.122.14.252 (talk) 18:38, 31 January 2010 (UTC)

Water is a liquid. Hot water tends to be less dense than cold so will float on top if it. Hence water will colder as you go deeper. Rock OTOH is a solid plus the source of heat is radioactivity in the rock itself plus primordial heat. The earth is slowly cooling down, but is doing it from the outside in, so the surface is cooler than the core. Theresa Knott | token threats 18:55, 31 January 2010 (UTC)

Why then does ice form at the top of lakes? 213.122.14.252 (talk) 19:16, 31 January 2010 (UTC)

Because it's lighter than the water, see water: The maximum density of water occurs at 3.98 °C (39.16 °F). Water becomes even less dense upon freezing, expanding 9%. This results in an unusual phenomenon: water's solid form, ice, floats upon water... --Ayacop (talk) 19:23, 31 January 2010 (UTC)

OK. Why isn't the deep ocean heated up by pressure? 213.122.14.252 (talk) 19:26, 31 January 2010 (UTC)

It probably is, but again, hotter water is less dense, so any water heated by pressurization will tend to rise. --Ludwigs2 20:04, 31 January 2010 (UTC)

1. Is it naive of me to think of thermal energy as molecules jiggling around?
2. When a fluid expands, do the molecules jiggle around less, and if so, why?
3. Alternatively, does the fluid get colder simply because the molecules are further apart, meaning less jiggling per unit of volume, in which case how is the fluid any more able to absorb heat from its surroundings than it was before? 213.122.14.252 (talk) 20:28, 31 January 2010 (UTC)

1) No, that's precisely what thermal energy is (well, molecules and atoms jiggling around). I'll let somebody else tackle 2 and 3. --Tango (talk) 20:41, 31 January 2010 (UTC)

For 2, the answer is yes, if the expansion does work. When you let compressed air out of a bottle, the air does work against the atmosphere, and the nozzle gets cold. Similarily, water expanding against the weight of the ocean would also do work (of course, the expansion would come from an input of thermal energy, so the actual temperature of the water would rise. But the rise in temp would be less than expected from the amount of thermal energy put in). If, on the other hand, you let a gas expand into a vaccuum (some 17th or 18th century science guy did this, but I'm not sure who or why. Perhaps it was to test the phlogiston theory?), the temperature doesn't change. For point 3, the temperature article has some good stuff, though it's quite dense. Short answer is: temperature is not equal to thermal energy. Additionally, heat capacity (how much the temperature changes when thermal energy is added) is measured on a per mass or per mole basis, not a per volume basis. Buddy431 (talk) 21:26, 31 January 2010 (UTC)

Have I got this right? I have some gas in an expandable container, like bellows (yes, with the nozzle sealed). I forcibly expand the container: the gas stays the same temperature, because I did the work. If I instead I was forcibly holding the container compressed, and let go, letting it work to expand against atmospheric pressure, the gas cools down. If I let go of it in a vacuum, and we imagine the container expands until it stops expanding without offering any resistance along the way, the gas doesn't cool down. 213.122.14.252 (talk) 21:57, 31 January 2010 (UTC)

When you pull open the bellows, you're only doing some of the work; the air inside's doing some of the work, and the temperature will decrease. If you don't believe that the air is doing some work, try to immagine pulling apart a bellows with nothing in it (that is, a vaccuum) verses one that has some air in it. Buddy431 (talk) 22:55, 31 January 2010 (UTC)

OK, that works. :) Bit surprising. 213.122.48.165 (talk) 23:03, 31 January 2010 (UTC)

Having some trouble visualizing this. So far I'm at: water on the bottom of the ocean is heated by the pressure. It expands from the heat. It does work against the pressure as a result of expanding, so it doesn't heat up all that much. So water on the bottom of the ocean basically expands and rises. That doesn't sound right... is it constantly convecting, or does it just find its level, which I suppose would be the at bottom despite the heating? What if it's a system with a really compressible fluid and a lot of pressure, like the atmosphere of Jupiter - would the gas at the bottom of the atmosphere be heated up massively and become, er, much less dense, and rush to the top? Is there a bit of a delay between heating and expanding, which would cause constant frantic convection just because of pressure, or am I making up a lot of nonsense? 213.122.14.252 (talk) 22:09, 31 January 2010 (UTC)

Trouble is, pressure doesn't heat up the water. Pressure plus a decrease in volume heats up the water. Water at the bottom of the ocean is already compressed (what little amount it does), so the pressure doesn't affect its temperature. If water was heated up by a different means (like a hydrothermal vent) then convection currents would be set up, though probably not all the way up to the surface. Buddy431 (talk) 22:50, 31 January 2010 (UTC)

What happens to some ice-cold (OK, nearly ice-cold) water added at the surface? Does it sink to the bottom? Does it then compress and heat up and rise again? 213.122.48.165 (talk) 23:11, 31 January 2010 (UTC)

It will sink, and as it does, the increasing pressure will compress it a tiny amount, heating it up a tiny amount. So it's not like the liquid sinks to the bottom, then compresses and heats up; it's doing that all the way down, until it reaches a layer of water that's the same density (and same temperature), where it will stay (barring currents, etc.). Buddy431 (talk) 00:05, 1 February 2010 (UTC)

It is compressed as it sinks, which makes it heat up, which makes it expand again, canceling out the compression, canceling out the heating, leaving it no denser than it was at the surface. It can only reach the level where the water is the same density as very cold water at the surface. It won't end up any denser (or hotter, or colder). Is that right? (Edit: I've concluded that it would in fact end up both denser and hotter, as Buddy said. The "hot water rises" remarks from earlier threw me off.) 213.122.48.165 (talk) 00:59, 1 February 2010 (UTC)

I think this must be a mistake ("hotter water is less dense, so any water heated by pressurization will tend to rise"). If it's heated by being compressed, it's not expanding. I think this contradiction has been confusing me for a while now, and the answer is that it just gets slightly hotter and doesn't rise because it doesn't get less dense. In fact it should get more dense and sink. Pressurization means getting more dense, right? 213.122.17.58 (talk) 01:39, 3 February 2010 (UTC)

No, both your scenarios are essentially the same thing. In the 1st scenario you decrease the pressure and the temperature will drop. In the second scenario you first inscrease the pressure which will raise the temperature, but then presumably you wait for the increased temperature to dissipate which means when you release it again the temperature will drop. What you have described of course is the simplest kind of heat pump. Water is NOT being heated by the pressure, you have to be careful: pressure is NOT Work (physics), it's an easy mistake to make, for the same reason you can't just get energy out of a magnet, a magnet can make pressure. Vespine (talk) 22:18, 31 January 2010 (UTC)

Excuse me but what is this first scenario where I decrease the pressure? Can't relate this to what I wrote, sorry. 213.122.14.252 (talk) 22:27, 31 January 2010 (UTC)

I was referring to your previous comment, when you forcibly expand the bellows (I presume with the nozzle sealed) you decrease the pressure and the temperature will decrease. Vespine (talk) 22:36, 31 January 2010 (UTC)

Oh, OK. I was confused by your answering down here with random indentation and by the word "both" when there are three scenarios. In the third one, the gas is essentially expanding in a vacuum so I take it you agree with Buddy431 that it doesn't heat up. Why is the first one different - my muscles do the work of decreasing the pressure in the gas, the gas doesn't do the work, so why should the gas lose energy? (Am I right in thinking that Buddy431's stipulation about doing work is because the work provides somewhere for the heat energy to go? It's a little confusing since many things, such as muscles, heat up when they do work.) 213.122.48.165 (talk) 22:55, 31 January 2010 (UTC)

Read the comment I made under your scenerios. When you pull open the bellows, the air does do some work; it's not all you. When you let it expand in a vacuum, with no resistance, it does no work. Buddy431 (talk) 22:59, 31 January 2010 (UTC)

Sorry it starts getting confusing when you are talking about so many related topics, by the time I replied there were already 2 other posts in between. Work is energy transferred by a force through a distance, your muscles provide the force, the gas provides the distance. Does that clear it up a bit? Part of the confusion might be that you think heating something up takes "work" so the opposite: cooling something down takes the opposite of work: (lack of work?) but what you are actually doing is not heating something up or cooling something down, it's heat transfer, all that is changing is the direction of that transfer, either case takes work. Vespine (talk) 23:18, 31 January 2010 (UTC)

Er, I thought the gas provides some of the force, by resisting less than a vacuum would. I get the heat transfer bit alright (the heat is transferred to the atmosphere, which you wouldn't notice since the atmosphere is very large). 213.122.48.165 (talk) 23:32, 31 January 2010 (UTC)

You're right 213. Vespine doesn't know what he's talking about. (Although "resisting less than a vacuum would" probably isn't the best way to put it. Better would be: "helping out more than a vacuum would"). Buddy431 (talk) 23:53, 31 January 2010 (UTC)

And just for the record, when I said the gas provides the "distance" I did actually mean "and the associated resistance across that distance." I was just simplifying. Of course opening bellows with the end closed takes more work then flapping your arms. Vespine (talk) 00:36, 1 February 2010 (UTC)

And importantly, the gas does NOT lose energy when you expand it, it loses temperature but increases volume, the energy remains the same!Vespine (talk) 23:20, 31 January 2010 (UTC)

NO. Gas can lose energy in expansion, and usually does. For an ideal gas, the volume has no effect at all on the internal energy. I think you mean that the total energy doesn't change (energy of gas + energy of everything else, including what the gas transferred energy to when it did work), which is just the First law of thermodynamics. And No to the post above your last one too. When pulling open the bellows with air in them, your muscles apply a force, and the gas does too. If you pulled apart a bellows with a vaccuum inside, the same amount of work would be done (same total force, same distance), but you would do all of the work. Buddy431 (talk) 23:50, 31 January 2010 (UTC)

So am I alright with "the work provides somewhere for the heat energy to go"? 213.122.48.165 (talk) 23:56, 31 January 2010 (UTC)

Well come on Buddy, that's not playing nice. I don't think you are correct either, where is the expanded gas losing energy to? Won't it GAIN energy? Such that if you release the force you used to expand the bellows the gas will be warmer than when it started? Also, if you really had a vacuum in the bellows, you wouldn't be able to expand it no matter how great a force you apply! That's how those glass holding suction cups work that can lift tons of weight. Unless you are also in a vacuum of course, which is a bit of a big detail to leave out. ;) Vespine (talk) 00:11, 1 February 2010 (UTC)

The gas is losing energy to whatever it's doing work on. For the case of a gas expanding against the atmosphere, it's transferring energy to the atmosphere (which will just heat up the atmosphere a tiny bit). And you certainly can pull against a vacuum, it's just hard when you're pulling against atmosphere. Atmospheric pressure is 14 lb/sq inch, so a suction cup even 7 inches square (a 3 inch diameter) could lift 100 lb. But in a barometer, just 30 inches of mercury can pull against a vacuum. Buddy431 (talk) 01:35, 1 February 2010 (UTC)

The Thermohaline circulation shows how complex the convection and advection currents in the ocean are. ~AH1 00:25, 1 February 2010 (UTC)

In reply to 165's last comment, the work doesn't really PROVIDE the place for the heat to go, the place was there all along, I would instead say the work provides a temperature gradient for the heat transfer to occur across. Vespine (talk) 01:08, 1 February 2010 (UTC)

I was thinking about a fridge. The refrigerant is compressed at the back of the fridge, it goes through a radiator, then it is squirted through a narrow gap into pipes inside the fridge. It expands a lot in these pipes. Presumably the particles in the refrigerant are jiggling less at this point than before it was squirted in. Why is that? I was thinking along the lines of "the particles are jiggling less because they've done some work", though it doesn't seem like they've done very much work. (I'm leaving out the phase change, I hope I can get away with that.) 213.122.48.165 (talk) 01:25, 1 February 2010 (UTC)

I think I've worked out where my confusion stems from, I was taking atmospheric equilibrium as the reference point, where as you guys are all talking about vacuum being the reference point which I admit is more correct, however in thought experiments I think it is easier to sometimes use the atmosphere as the reference point. Case in point the fridge example above: The refrigerant is compressed, as the volume decreases the temperature and pressure increases but the ENERGY effectively remains the same. What changes the energy is that the radiator takes the heat away and the energy of the refrigerant decreases at that point. Now you have compressed refrigerant at the same temp as the ambient atmosphere. Then when the refrigerant is squirted back into the pipes inside the fridge and expands the volume increases and the temperature decreases but the energy is STILL the same. At this point the "heat" in the fridge can transfer into the refrigerant until both are equal. Then the refrigenrant with more energy is taken out of the fridge and the cycle is repeated. The real work that is done here is done by the compressor, all the other work by the gas expanding and all that only confuses the issue IMHO. Vespine (talk) 01:47, 1 February 2010 (UTC)

(ec)It is mostly the phase change of the refrigerent that's pulling heat out of the frige, so you can't ignore it. See vapor-compression refrigeration for how the whole process works. Vespine's right, in that it's the compressor doing work, and when it does, the vapor comes out at a higher temperature, and higher internal energy, than when it came in. It then loses that energy from the compressor, plus the energy from cooling the frige, in the condenser. It's squirted into the coils in the frige, where it evaporates, which requires energy, which comes from the air inside the fridge (which is why it cools down inside). Buddy431 (talk) 02:03, 1 February 2010 (UTC)

Yep, I read that article a while back. I'm trying to comprehend how the energy in the fridge can transfer into the refrigerant. I find it necessary to go into detail, because I figure the heating of the refrigerant by the air inside the fridge consists of the evening-out of the jiggling of particles. Therefore I want to know what it was about expansion of the refrigerant that caused the particles in it to jiggle less. I could just say "the same energy occupies more volume, and therefore it can now accept some energy from inside the fridge," but if I imagine the individual particles, this explanation doesn't work, because the spreading out of the particles doesn't explain why each particle has less energy. 213.122.48.165 (talk) 02:13, 1 February 2010 (UTC)

Each particle doesn't have less energy. Pressure and temperature are two different things but are correlated, you can't change one without changing the other. The temp is like the "jiggling" and the pressure is more like "jostling against each other". When you decrease the pressure, the particles spread out and jostle against each other less but they still jiggle with the same energy they had before, it is the decrease of "jostling against each other" that accounts for the drop in temperature, not the individual particles losing any energy. Now that the particles aren't "jostling against each other" so much, they need more jiggle to bring them up to the same temperature they were before the pressure was decreased. Vespine (talk) 03:28, 1 February 2010 (UTC)

Yes you can reduce pressure without affecting temperature: release a gas into a vacuum (like I said, there was some guy who did just that to prove something or other). And in a gas anyway, temperature is related to the kinetic energy of the particles (the "jiggling", I think), NOT to how often they collide (the "jostling"). A gas with particles moving at the same average speed is a given temperature, regardless of what the pressure is. When a gas cools down while expanding, it is because the particles have lost energy in doing work, and they are moving at slower speeds. See the Kinetic theory article, especially the pressure and temperature sections. Buddy431 (talk) 04:18, 1 February 2010 (UTC)

Would the fridge not work without the phase change? (Something like a backwards stirling engine?) Would evaporation in a vacuum cause cooling? 81.131.48.166 (talk) 05:17, 1 February 2010 (UTC)

For your second question, yes, evaporating in a vacuum would cause cooling. A phase change from liquid to gas absorbs energy: see enthalpy of vaporization. I'm not sure about a compression fridge without a phase change, but I think it certainly wouldn't be as effective at cooling as the ones typically used. Buddy431 (talk) 17:01, 1 February 2010 (UTC)

I'm still uncertain about the original question. Let's try this: suppose we collect a lot of water and put it on a bare planet to make an ocean. Imagine it's insulated above and below. It was all originally the same temperature, and now suddenly it's an ocean, and subject to gravity. So the bottom of this new ocean is getting compressed. There is no heat input from anywhere. When everything has settled down, is the ocean the same temperature throughout, or cold at the bottom, or hot at the bottom? Does everything ever settle down? 213.122.17.58 (talk) 01:27, 3 February 2010 (UTC)

These "planet" scale questions I think are going to have different issues affecting them. You can't just say "bare planet" because I think for liquid water you have to have at least an atmosphere of some sort, otherwise it would freeze or evaporate away, I think. So as far as I know, planets including the earth, form as molten balls due to the forces of accretion but once that is settled down and new material isn't being added, they gradually cool. After that point the pressure of gravity does not "add" any more heat to this process, the planet slowly cools until it geologically "dies", which means there is no heat left in the core. You could call that "settled down". For example it is believed that Mars is geologically inactive. So if you added water to that, even if there was enough pressure to heat something up, the heat would dissipate and that too would eventually settle down. The pressure down there is not what creates the heat, the only reason the earth has heat deep down inside is because it is still cooling. Once it has cooled down you could drill all the way to the core and it would be the same temp as the crust, the "pressure" is not adding extra heat.Vespine (talk) 00:46, 4 February 2010 (UTC)

This is archived now, but I'm pissy enough to observe here that you ignored my "imagine it's insulated above and below" sentence. Just straight out ignored it. 81.131.60.13 (talk) 19:17, 7 February 2010 (UTC)

What gas is green?

What gas is green in nature, without electrical charges or other tricks to make it glow? I remember in science class in high school talking about one specific gas that naturally occurs green. Maybe there's more than one.

People might not know the answer offhand, so can you recommend a good way to search? Or an article topic or category or something I could use? Thanks 24.20.200.67 (talk) 19:52, 31 January 2010 (UTC)

Chlorine gas is said to be green, looks more greeny/olive/brown to me. Nanonic (talk) 19:56, 31 January 2010 (UTC)

Fluorine too. But neither of these gases occur in nature. Buddy431 (talk) 20:20, 31 January 2010 (UTC)

I think its Fluorine I was thinking of. Thanks wikipedia!! 24.20.200.67 (talk) 21:31, 31 January 2010 (UTC)

As far as I know, the dihalogen gases (eg. Cl2, and F2 mentioned) are not coloured as a diatomic molecule. The colour that is observed is due to tiny amounts of radicals formed from the dissociation of the diatomic (Cl_2 -> 2 .Cl). The diatomic and radical species are in an equilibrium (the diatomic side is heavily favoured over the radical side). —Preceding unsigned comment added by 24.150.18.30 (talk) 02:42, 2 February 2010 (UTC)

Order of reaction Mg + HCl

How does the rate of the reaction Mg(s)+HCl(aq) depend on the concentration of HCl? Is it first order or second order? My class did an experiment in which both my group's data, and the averaged data of the entire class, clearly show that it is first order. However, the teacher claims this was wrong and gave us "real" data which showed the reaction to be second-order. I searched on the Internet and found some sources claiming it's first-order and some claiming it's second-order.

Which one is right? --99.237.234.104 (talk) 19:58, 31 January 2010 (UTC)

What is the balanced chemical equation for this reaction? What is the coefficient of the HCl (or the ionic part of it that is really reacting)? Often the coefficients are Order of reaction of each reactant. DMacks (talk) 21:18, 31 January 2010 (UTC)

This and this suggest that the mechanisms not really known, and that different concentrations and different types of acid can give different rate dependences, and that different people have gotten results that can't be reproduced. That sure inspires confidence. They cite an article claiming that it's second order though. You can download the article, and it becomes clear that even real scientists with lots of experience are getting different results based on how exactly the experiment is set up. I think the conclusion is that this probably isn't the best experiment to be teaching high school chemistry students about rate laws. Buddy431 (talk) 04:04, 1 February 2010 (UTC)

One thing this does illustrate is the importance of careful experimental procedures (and documentation of them) to make sure all variables are controlled. The results don't sound random/non-reproducible, but rather are just highly affected by experimental details. DMacks (talk) 06:51, 1 February 2010 (UTC)

Reactions don't have to be one or another. For example, the substitution reactions of secondary alkyl halides can proceed through SN1 or SN2 pathways depending on the solvent and other experimental conditions (like say, the presence of nucleophilic catalysts). Whether the HCl was added as a gas or was added dilute or added in concentrated form or maybe added as a solution in ether (as opposed to water) would all affect the mechanism. Reactions aren't often only first order or second order -- sometimes they can go through both types of pathways (to give the same product). John Riemann Soong (talk) 23:02, 1 February 2010 (UTC)

There are all sort of side reactions that can take place because the reaction actually occurs by multiple steps and multiple mechanisms. You have an aqueous solution and solvent effects are very important. Is the magnesium effectively protonated, forming a polar covalent Mg+-H bond, or does magnesium reduce protons to free hydride ions? The latter would be a first order reaction -- hydrides are so reactive that they will pull off other protons right away, forming hydrogen gas.

But if Mg+-H is formed instead, then protonation would be a "fast step" and the Mg+-H species is vulnerable to nucleophilic attack by water or chloride. It could be protonated again to yield hydrogen and Mg2+, but this may be "slow" because it is difficult to protonate an already protonated species (think of the equilibrium between HMg+ and H3O+ and Mg2+ and HOH). Water is actually a better nucleophile than chloride so it competes and bind to HMg+ as a ligand; this relieves positive charge on the Mg (magnesium-bound water becomes a little more acidic) and then H3O+ finds it more easy to react with the magnesium hydride. (This step produces H2). But now you have HOH-Mg2+ <---> H+ , OH-Mg+ which might react with chloride or bind with water and you have to turn this into MgCl2. Which is actually thermodynamically favourable but chloride will find it difficult to displace hydroxide by a direct substitution so it will actually have to go through a roundabout pathway first.

But if you use a solvent that might not bind magnesium as well, then a different mechanism might occur.

Some metals also like to react by single electron transfer and the metal could release an electron first, releasing a solvated electron. This means sometimes radical mechanisms are involved, especially in redox reactions. There are multiple pathways to be pursued and some pathways have two rate-limiting steps, thus complicating the calculation of the rate laws for the reaction. John Riemann Soong (talk) 16:45, 2 February 2010 (UTC)

Chemical formula of cellulose

Should the chemical formula of cellulose be (C
₆H
₁₀O
₅)
_n·H
₂O? --84.61.165.65 (talk) 20:44, 31 January 2010 (UTC)

No, the use of a dot in the formula suggests it is specifically a monohydrate (contains a single actual molecule of water bound in the structure). Are you perhaps thinking about the ends of the polymer chain, one of which has an H and one an OH? Those are a total of H
₂O but they are not "together as a water molecule". This is a general concern for the chemical formula of any polymer. WP:Chem would be the place to see if there is a need to adjust the infoboxes...I spot-checked a few polymer articles and none of them include end-groups in their chemical formula. DMacks (talk) 21:13, 31 January 2010 (UTC)

Energy from reversing desalination

The desalination article says that desalination requires large amounts of energy. Why then, if I pour some salt into a glass of fresh water, do I not get any energy back? 92.24.73.102 (talk) 21:40, 31 January 2010 (UTC)

Actually, dissolving table-salt in water absorbs energy (it has a positive Heat of solution). The desalination process does not result in overall addition of energy into the water (i.e., the products having more energy, which could be recovered by remixing). For example, distillation consumes lots of energy to boil the salt-water, but then that energy is released when the water-vapor condenses and the salt and water cool back to room temperature--the cooling water winds up containing the energy that was transiently in the pure water vapor, and is then discarded into the environment. Problem is that it's difficult to recover that energy efficiently--the products do not have a higher energy content, just a lot of energy was wasted (in a net sense) to get them separated. Is reverse osmosis energy-efficient (other than perhaps having to pump the water)? DMacks (talk) 21:53, 31 January 2010 (UTC)

The large amounts of energy required are either to evaporate the water (in distillation, including multi-stage flash distillation) or to force it through a semipermeable membrane (in reverse osmosis). In the first instance, energy is released when the steam condenses, but as DMacks pointed out, it's hard to recover this. In the second instance, you (in theory) could get back some of this energy by allowing normal osmosis to occur and capturing energy from the water movement created across the membrane. Needless to say, it's not worth wasting using fresh water like this to generate electricity. Buddy431 (talk) 22:06, 31 January 2010 (UTC)

There have actually been suggestions on capturing the energy of freshwater/saltwater mixing. See, for example "Energy Recovery from Controlled Mixing Salt and Fresh Water with a Reverse Electrodialysis System" Environ. Sci. Technol., 2008, 42 (15), pp 5785–5790, or "Extracting Renewable Energy from a Salinity Difference Using a Capacitor" Physical Review Letters 103, 058501 (2009). or any number of the news articles from last year, e.g . The thought is that the generation plants would be located at the mouth of rivers, where there already is substantial mixing of salt and fresh water. -- 174.21.224.109 (talk) 22:45, 31 January 2010 (UTC)

The first "salination" power plant in the world (or so the owners argue) opened last year~in Norway, see this page Jørgen (talk) 13:40, 1 February 2010 (UTC)

Perpetrual-reality

understanding the theroy of perpetual reality and its consept in to continues energy? —Preceding unsigned comment added by Angeldell (talk • contribs) 23:13, 31 January 2010 (UTC)

Sorry, I don't understand. Could you define "perpetual reality"? Are you perhaps referring to perpetual motion machines? Comet Tuttle (talk) 23:22, 31 January 2010 (UTC)

I refer to if reality as we know it! is continues and by understanding the way it works can we creat a machine based on it's machnics? —Preceding unsigned comment added by Angeldell (talk • contribs) 23:30, 31 January 2010 (UTC)

I think you're asking whether a machine might be made that does some useful work based on the simple fact that time advances. I'd suggest that this is unlikely, because entropy always increases (see Second law of thermodynamics). Comet Tuttle (talk) 23:48, 31 January 2010 (UTC)

If you are correct, then it sounds like, yes. You might look at the mathematical links under mobius for a model of something which could be considered continuous. I'm not sure Science has anything beyond possible speculation in the area of reality, and creating such a machine could prove the existence of reality having a continuous shape, which would be an interesting discovery for science. --Neptunerover (talk) 23:54, 31 January 2010 (UTC)

This response from NeptuneRover is a clear breach of the WP:NOR rule. It is not true - I advise our OP to ignore it. SteveBaker (talk) 02:42, 1 February 2010 (UTC)

I have this idea in mind for years that an active formal that is not yet seen that might prove that such a machine might be created. --Angeldell (talk) 00:00, 1 February 2010 (UTC)

Sorry, the phrase "active formal" doesn't mean anything in English — could you try a rephrasing? Comet Tuttle (talk) 00:08, 1 February 2010 (UTC)

(edit conflict x2)Are quantum mechanics, chaos theory and illusion partially relavent? ~AH1 00:06, 1 February 2010 (UTC)

Maybe he's wondering if it's possible to create a machine to simulate the entire universe. It's very hard to understand the question.

Angeldell: try posting the question in your native language. There are many editors here, maybe someone will know your language. Ariel. (talk) 01:00, 1 February 2010 (UTC)

possibly he's wondering if he can keep us guessing what he's after for the rest of eternity... --Ludwigs2 02:01, 1 February 2010 (UTC)

More suggestions: end of the Universe, vacuum energy, expansion of the universe, supercomputer, reality, perception of time, spacetime, Special Relativity, out of body experience, Eschatology, Large Hadron Collider, The Quantum Prophecy, Kali Yuga, Infinity, hypercube, information, self-reference. ~AH1 02:23, 1 February 2010 (UTC)

We need a clearer statement of this question before we can attempt to answer it. It is pointless to guess at what our original poster is asking and the answers presented so far are as likely to mislead as they are to inform. We should cease to comment until/unless the questioner can expand a little on what we're being asked. SteveBaker (talk) 02:44, 1 February 2010 (UTC)

If you don't even know what the question is, Steve, how can you decide which answer might be wrong? --Neptunerover (talk) 03:12, 1 February 2010 (UTC)

Steve's ". . . as likely to mislead as . . . to inform" is not equal to "wrong" in my understanding of English. The very point is that we can't decide right or wrong based on what is here. Bielle (talk) 03:24, 1 February 2010 (UTC)

I understood what the question was though. Steve doesn't. I gave the guy an answer fitting his question. --Neptunerover (talk) 04:58, 1 February 2010 (UTC)

If Steve doesn't understand the question, then he cannot judge how my answer relates to it. --Neptunerover (talk) 05:03, 1 February 2010 (UTC)

"I'm not sure Science has anything beyond possible speculation in the area of reality, and creating such a machine could prove the existence of reality having a continuous shape"? This is nonsense from beginning to end. Comet Tuttle (talk) 05:37, 1 February 2010 (UTC)

I see what you misunderstand, but you are misunderstanding what that statement says. Did you read the OP's question? It was a question mentioning perpetual reality as if it were a fact. I pointed out that science is not aware of such being a fact. As the OP mentioned a machine based on perpetual reality, I informed him that if there were to be such a machine, that would be quite a discovery for science. I didn't tell him to run build a machine! I didn't even tell him any such thing was possible. All I said was yes, if the OP was correct in all the statements he said about reality being perpetual and continuous, then yes, a perpetual reality-based machine would be a yes, or at least it sounds like it, for how would I know? --Neptunerover (talk) 06:06, 1 February 2010 (UTC)

Guys, let it go. the question was confused, and there's no need to go over whether the answers are confused as well. I think what we all need to do is go home, take some heavy-duty mind expanding drugs, and reconsider the issue from an altered state of perception. sound like a plan? --Ludwigs2 06:14, 1 February 2010 (UTC)

No. Mind-expanding drugs are not even the only way to acheive an altered state of mind.

It was an accident. ~AH1 04:00, 3 February 2010 (UTC)

February 1

Earth gear

When I was younger I said to my mom that we could create a good energy source using the earth's rotation. All I need was a gear which the earth could spin using its rotation much like the gears in clock work. This spinning gear would then be used to generate electricity. My mom said it was impossible. Why?--121.54.2.188 (talk) 02:09, 1 February 2010 (UTC)

The difficulty of finding something to mount this gear to, such that the earth will spin it. --Tagishsimon (talk) 02:11, 1 February 2010 (UTC)

You could probably find a way to extract energy from a foucault pendulum. It's unlikely that you'd be able to extract much. Essentially, you'd be tapping off the reservoir of angular momentum (or rather, rotational kinetic energy, and slowing the earth's rotation. Nimur (talk) 02:36, 1 February 2010 (UTC)

You can only do that once. After that the pendulum is spinning at the same rate as the earth, and you can no longer extract any energy. It would be a violation of conservation of angular momentum if you could constantly extract energy from the rotation of the earth by slowing it down. Ariel. (talk) 08:31, 1 February 2010 (UTC)

I guess tidal energy is sort of that. 213.122.48.165 (talk) 02:39, 1 February 2010 (UTC)

Perhaps a gyroscope in a vacuum cylinder spinning on frictionless magnetic bearings at one of the earth poles would stay still as the Earth turned, allowing the difference in rotation to turn gears to speed up the rotation and turn a dynamo?Trevor Loughlin (talk) 03:33, 1 February 2010 (UTC)

See what I wrote above. You can only do that once, because you need to conserve angular momentum. Ariel. (talk) 08:31, 1 February 2010 (UTC)

If I understand you correctly, the maximum energy you'd get out of that would be somewhat less than you had to put in to it to get the gyroscope spinning in the first place. --Tagishsimon (talk) 03:40, 1 February 2010 (UTC)

Well, I'm not quite clear on Trevor Loughlin's idea. But, it's possible to harness energy that's stored in the form of Earth's rotation - actually netting more energy than you expend to collect it. You aren't creating any energy - you're just harnessing kinetic energy of Earth's rotation. Presumably, that energy is left over from the formation of the solar system (and by extension, from the Big Bang and cosmogenesis... whether the energy was created or has always been there is irrelevant for this discussion). Presently, that energy takes the form of rotational kinetic energy in the planetary rotation of the Earth. If you could actually build a device that could be spun by the Earth, you would be ever-so-slightly slowing down the enormous planetary-sized flywheel; and you could extract energy from it. It's not perpetual motion - there's a finite (but really, really huge) amount of energy to extract. However, the impracticality of building such a device makes it less attractive than harnessing other natural energy reservoirs (tidal motions have already been brought up). Nimur (talk) 03:58, 1 February 2010 (UTC)

No, i's not impractical. It's impossible unless you can transfer the momentum somewhere. With tides the momentum goes to the moon. Ariel. (talk) 08:31, 1 February 2010 (UTC)

The gyro would not be spinning horizontally like a top, it would be at right angles to the Earth-dynamo axis. Would this make a difference?Trevor Loughlin (talk) 03:58, 1 February 2010 (UTC)

No. How does this differ from spinning a bike wheel then putting the bike down? --Tagishsimon (talk) 03:59, 1 February 2010 (UTC)

Oh come on! It's easy! Buy a simple electrical generator with a large wheel welded to it's input shaft. Take it to the South Pole and bolt it firmly though the ice and into the bedrock beneath with the input shaft pointing straight up and the wheel laying horizontally. Tie a long rope to one side of the wheel. Tie the other end of the rope to a nice strong nail hammered into the south pole of the moon. As the earth spins, so the generator turns at roughly one revolution per day (actually, not quite that because the moon orbits the earth once a month). You'll keep generating power until the earth eventually stops spinning - an event that would be very slightly hastened by doing this. (Actually, since the moon does set below the horizon even at the south pole, you might need to erect a very tall tower and mount your generator on top of that to ensure you have a continual path for the rope.) There are of course some trivial engineering issues to deal with! SteveBaker (talk) 08:09, 1 February 2010 (UTC)

Now this could work. It would do rather interesting things to the orbit of the moon. Especially if you don't lengthen the rope. (But you could never actually make the earth stop spinning, the best you could do would be to have it spin at the same rate as the orbit of the moon. But I think you could get that to any desired slowness you want (very far away moon), just not zero.) Ariel. (talk) 08:31, 1 February 2010 (UTC)

I think it would be hard to get the rope really tight enough that the elliptical orbit of the moon would be a problem, and the rope doesn't need to be tight for this to work. But to assuage your concerns, I'd be prepared to spend the extra to buy bungee cord. (In truth - if you could do this at all, you might be better off to forget the generator and use a conductive wire instead of rope - generating electricity directly from the motion of the wire through the magnetic field. You'd need two wires - one from the north pole and one from the south with a wire running across the lunar surface to complete the circuit.) SteveBaker (talk) 19:19, 1 February 2010 (UTC)

SteveBaker, you've solved the energy problems of the earth. Except that people who like eclipses and use a lunar calendar would object since as you transfer momentum to the moon it will get farther and farther away. (You are lucky the moon and earth rotate in the same direction, otherwise you might just bring the moon crashing down on us.) Ariel. (talk) 19:28, 1 February 2010 (UTC)

That won't be a problem because, sadly, eclipse-lovers and anyone who even knows where to find a lunar calendar will have died during the three centuries of enforced labor required to hand-make half a million kilometers of bungee cord and an antarctic generator tower several hundred miles tall. The lunar antipodeal nail could be purchased at Home Depot for approximately 50 cents and I was planning to repurpose the spare generator out of my 1963 Mini Cooper - so relatively little loss of life would be entailed in those phases of the construction project. Rewiring the major world-wide power grids to run off 12 volts with a positive ground will have to be someone else's problem because I have to talk NASA into lending me one of those million dollar space-hammers. :-)

Steve, have you taken into account the tensile strength of the bungee cord involved? 146.74.230.105 (talk) 01:00, 3 February 2010 (UTC)

A vaguely related topic is the use of Gravity assist to "steal" energy from other planets orbital momentum, rather than their rotational energy. The energy is not free - it causes the planet's orbit to slow. Mitch Ames (talk) 12:13, 1 February 2010 (UTC)

The Foucault pendulum suggestion was correct, the objection to it was wrong. The only problem is that to get a significant amount of energy the pendulum would have to be miles high. The winds in winter storms, it might be worth noting, are powered by the same mechanism -- that is, they draw their energy mainly from the Earth's rotation. Looie496 (talk) 17:11, 1 February 2010 (UTC)

You object to conservation of angular momentum? The winds are not powered by the rotation of the earth, they are powered by the sun. The rotation just effects what direction they will go in. Ariel. (talk) 19:24, 1 February 2010 (UTC)

Hmmm - so we could build a vast, elliptical train track - with the major axis of the ellipse running north-south. The train would be loaded with bowling balls which we'd release from the side of the train on the southern leg of the journey - picking them up again on the northern leg after the coriolis effect had moved them across the width of the track. Recovering the kinetic energy from the bowling balls and using this to power the train itself is a mere engineering detail that will be left as an exercise for the reader. SteveBaker (talk) 19:19, 1 February 2010 (UTC)

I assume this is a joke in reply to Looie496 :) (Since this will not work.) Ariel. (talk) 19:24, 1 February 2010 (UTC)

Why not? SteveBaker (talk) 19:46, 1 February 2010 (UTC)

Because to move the balls north on the return trip you would have to spend energy in the train to speed them up against the (reverse) coriolis effect. And conservation of angular momentum also says no, since you have nowhere to transfer the momentum of the rotating earth. Ariel. (talk) 20:06, 1 February 2010 (UTC)

Oh, yeah - conservation of angular momentum...duh. SteveBaker (talk) 20:21, 1 February 2010 (UTC)

All joking aside, I don't see any reason a gyroscope running perpendicular to the earth's axis wouldn't feel some force from the earth's turn. The force would be incredibly weak, so actually constructing a device so frictionless that it would turn is probably impossible, but I don't think there are any theoretical problems with the idea. APL (talk) 19:41, 1 February 2010 (UTC)

It would feel a force. But you can only collect the energy once, after that the force would move (accelerate) the gyroscope, and there would no longer be a force. The only reason a foucault pendulum turns is that they work really hard to make sure there is no force at the joint (frictionless). Ariel. (talk) 20:06, 1 February 2010 (UTC)

Angular momentum would be conserved. The object you accelerated would now have angular momentum. Earth would have less angular momentum. Energy and momentum are both conserved, but the process of the transfer can be used to do productive work (accelerating something you want accelerated, like a turbine). Why can you transfer angular momentum to the moon, but not to a bowling ball or a turbine? Ariel's objection doesn't seem valid. Again, the engineering details of how to couple a turbine to Earth's rotation are left to the reader; but I think it's definitely feasible. Nimur (talk) 21:58, 1 February 2010 (UTC)

You can do it once. The reason you can transfer to the moon is that it's in orbit around the earth, not on the earth. I guess technically you are also transferring just once to the moon, but you can collect almost all the rotational momentum of the earth, by giving the moon a huge orbit with lots of momentum. With a gyroscope or pendulum you can't give that much - they are not able to hold that much momentum. Ariel. (talk) 22:24, 1 February 2010 (UTC)

If you used the moon as an anchor you would of course decelerate the moon and consequently lower the orbit, and probably also slow the earth's rotation, which is something we probably don't want to do. You might be able to get an arbitrarily large amount of energy before we had cataclysmic side effects but ultimately you would crash the moon into the earth. Vespine (talk) 03:17, 2 February 2010 (UTC)

That's true in theory - but if you are really concerned about it as a practical matter then you should be out there protesting tidal power stations because those are having the exact same effect. For an identical amount of power generated, my "generator + rope + nail" approach would cause exactly the same amount of slowing of spin and lunar orbit degradation as tidal power stations are actually doing in practice TODAY! (Trust me: the effect of extracting power this way would be negligable.) SteveBaker (talk) 14:30, 2 February 2010 (UTC)

You would actually accelerate the moon, not decelerate it. The earth and the moon both rotate/orbit in the same direction. So if you slow one down, you must speed the other up. So you would raise the orbit of the moon. This is why eclipse lovers are so mad at SteveBaker, with the moon farther away you don't have a good eclipse. Ariel. (talk) 20:54, 2 February 2010 (UTC)

I don't know if I agree with that Steve. Aren't you extracting power that is there either way, except that when you don't harvest it, the waves just crash and dissipate as "heat" and noise and what not. I can't see how it would effect the moon. I would think it would be similar to saying that collecting solar energy has some sort of effect of depleting the sun, the energy is already there either way, either you collect it and use it or you don't and it just goes to waste. As for your second point, I thought that if you go to the trouble of attaching a gear to the earth you'd want to get a little more then megawatts.

As for ariel's point, that's extremely counter intuitive, I'm really struggling to model in my head how that would work, it's like a plane taking off on a conveyor belt:) If you are "extracting" energy, how can you be accelerating the moon? I get that the earth is rotating a lot faster then the moon is orbiting, but isn't the whole point "not" to accelerate anything but instead extract that force as "energy"? Vespine (talk) 03:55, 4 February 2010 (UTC)

Ok, I think I got it, it's much easier to visualize if you place yourself on the moon and if the initial condition is that the moon starts as a stationary object. ignoring the gravity that would cause it to crash into the earth of course. But that makes it easy to see why the moon will be accelerating. Vespine (talk) 04:22, 4 February 2010 (UTC)

linear permanent magnet bearing?

I have heard about rotational magnetic bearings. But has anyone invented an (unpowered) linear magnetic bearing, which could do away with wheels without the costs of electromagnetic levitation? And don't cheat by using high temperature superconductors floating above liquid nitrogen-this has its costs-I'm talking about ordinary magnets. Is it theoretically possible? There is no violation of thermodynamics or conservation of energy laws to make it impossible(?)Trevor Loughlin (talk) 03:52, 1 February 2010 (UTC)

See Earnshaw's theorem. It's not possible. Rotational ones don't work either. Ariel. (talk) 06:55, 1 February 2010 (UTC)

See . Misplaced Pages has a short article on the Barnett effect. Cuddlyable3 (talk) 11:45, 1 February 2010 (UTC)

It seems it could be done with Diamegnetic Levetation, or at least our WP article would have you believe so. CoolMike (talk) 01:34, 4 February 2010 (UTC)

Thermal Gravimetric Analysis

Is it possible to determine the composition of a mixture of CaC2O4 and CaCO3 using Thermal Gravimetric Analysis? If so, how? —Preceding unsigned comment added by 70.68.120.162 (talk) 04:04, 1 February 2010 (UTC)

Thermogravimetric analysis, for those interested. --Tagishsimon (talk) 04:07, 1 February 2010 (UTC)

Welcome to the Misplaced Pages Reference Desk. Your question appears to be a homework question. I apologize if this is a misevaluation, but it is our policy here to not do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn how to solve such problems. Please attempt to solve the problem yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. TenOfAllTrades(talk) 04:17, 1 February 2010 (UTC)

Contracting diseases via intercourse with cells?

If an individual has sexual intercourse with a cancerous cell (e.g. a mutated cell cluster or cancerous tissue as detected in a biopsy), will they contract cancer? Does it matter if the disease that the cell carries is a sexually transmitted disease (e.g. gonorrhea); that is, is it more viable or likely that the person will become infected as a result of intercourse? Further, why or why not would this happen? As much as this may seem like a facetious question, I am genuinely curious and would appreciate any insight that can be offered, whether it is theoretical or concrete. Thank you, Arcendet (talk) 06:00, 1 February 2010 (UTC)

You will not 'catch cancer' by having sex with someone who has cancer. If the cancer was generated by an underlying sexually transmitted disease (e.g. gonorrhea or HPV) you might catch that particular disease, and that disease might (eventually) induce cancer in you as well, but there is no necessary, direct, or causal relationship implied there. relax, you're relatively safe. next time use a condom. --Ludwigs2 06:18, 1 February 2010 (UTC)

Actually we don't know that. See Devil facial tumour disease which is a transmissible cancer (we actually have a page on that). There is no reason to assume it could not happen to humans too - and in fact the page lists one case where it happened. Especially if the lag/incubation period is very long it would be very hard to figure out the correlation. Ariel. (talk) 07:01, 1 February 2010 (UTC)

Uh... those refer to dogs and tasmanian devils... and (excuse me) apparently to Syrian hamsters as well. There is no known pattern of a transmissible cancers in humans, or even in primates. assuming that the OP is not a tasmanian devil, canid, or Syrian hamster (and has not been using Syrian hamsters in some fairly perverted way) I see no reason to alarm him/her over the risk of transmissible cancers. --Ludwigs2 07:20, 1 February 2010 (UTC)

And a human too, did you miss that part? It's not just theoretically possible, it's actually happened. I never said it was common, I said we don't know. He did ask for even theoretical information. Ariel. (talk) 07:43, 1 February 2010 (UTC)

I missed any mention of Devil facial tumour disease being transmissible to humans and I would think the amount of research that has been done on it is a reason to assume that would have been noticed if it were possible. However research into dog to human STD's is as yet only in its infancy puppyhood. Cuddlyable3 (talk) 11:33, 1 February 2010 (UTC)

I don't think Ariel is referring to Devil facial tumour disease being transmissible to humans. Rather some surgeons have had tumours that have been transmitted via accidential implantation on an injury site with the article linking to this specific reference . This clearly is very uncommon and requires a specific set of circumstances (i.e. isn't something that occurs in the 'wild' if that has any meaning for humans) and tumour types and isn't associated with sexual intercourse nor blood transmission but Ariel never said it was. Transplanted organs can of course also effectively transmit cancer although I don't know if you'd call that a transmittable cancer. Nil Einne (talk) 14:16, 1 February 2010 (UTC)

It would have to be a mighty big cell to have sexual intercourse with it! As for human transmissible cancers, see HPV which is responsible for transmitting cervical cancer. However, as I assume the questioner is a man, he won't actually catch cervical cancer (not having a cervix), but apparently can get cancer of the penis. You're at most risk of catching an STD if you don't use a condom. It's possible cervical cancer could be classified as an STD. --TammyMoet (talk) 09:09, 1 February 2010 (UTC)

As an aside, HPV infection is also associated with oropharyngeal cancers – cancers of the mouth and throat – which again are of concern to both women and men. TenOfAllTrades(talk) 14:28, 1 February 2010 (UTC)

File:Cases of HPV cancers graph.png is perhaps of interest here.

However as explained by Ludwings, this isn't really a transmittable cancer at least by the definition used in both of the earlier linked articles. Rather the virus is transmittable which when it infects a human can eventually (along with a whole host of other changes) lead to cancer in a small number of people. This compares to a transmittable cancer where the cancerous cells themselves infect the other host. A more complicated case which perhaps illustrates the complexity is HIV which usually compromises the immune system can also greatly increase the risk of cancers . This includes for example Kaposi's sarcoma itself caused by Kaposi's sarcoma-associated herpesvirus

Nil Einne (talk) 14:43, 1 February 2010 (UTC)

Scientific Film Association

The Scientific Film Association was constituted on 20 November 1943 to promote the use of the scientific film in order to achieve the widest possible understanding and appreciation of scientific method and outlook. Active members included eminent film makers such as Sir Arthur Elton and Edgar Anstey. Several standing committees were set up and the Medical Committee became a leading authority on medical films in the UK and published several catalogues of appraisals of films on specialist medical topics. The SFA, together with the French Institut de Cinematographie Scientifique, established the International Scientific Film Association in October 1947.

There is no mention of the SFA in Misplaced Pages but one note of an Italian who was an ISFA member. Do you think that I should prepare a possible entry? Michaelsthgate (talk) 10:35, 1 February 2010 (UTC)

First look at WP:N. Have you citations that verify the SFA is a leading authority? Cuddlyable3 (talk) 11:19, 1 February 2010 (UTC)

Leading or not, if it existed and produced lasting artefacts like catalogues, then I would go ahead and include it. But, as Cuddlyable said, you must provide citations for every claim. --Heron (talk) 12:43, 1 February 2010 (UTC)

Googling the name produces articles about the association in Nature and several other significant references. I don't think you'd have a hard time establishing notability. So yeah - I think Misplaced Pages needs an article about this. As others have pointed out - you need to be sure that there are a good number of references for the article in general - and in particular that all potentially controversial statements are individually tagged with a specific reference. I look forward to reading it! SteveBaker (talk) 18:59, 1 February 2010 (UTC)

ELECTRIC WIRE

IS THERE ANY INFORMATION ON ZERO HALOGEN FLAME RETARDANT CABLES? —Preceding unsigned comment added by 118.94.161.137 (talk) 13:15, 1 February 2010 (UTC)

You can find references to them in our articles on Trirated cables and Low smoke zero halogen. Does that help? Gonzonoir (talk) 14:21, 1 February 2010 (UTC)

Do wires carrying DC get corroded more or less easily than those carrying AC?

Do wires carrying DC get corroded more or less easily than those carrying AC, or are they the same? --173.49.13.59 (talk) 13:32, 1 February 2010 (UTC)

Yes where dissimilar metals are in contact e.g. aluminium cable to brass or copper connectors. This reports "5% of total corrosion costs in USA, from electrified DC transit system operations". Cuddlyable3 (talk) 14:40, 1 February 2010 (UTC)

Otherwise, there should be NO difference between AC and DC that I know of. See Electrolysis and Electrolytic cell for relevant info. See the related Sacrificial anode for corrosion prevention. Also Galvanic corrosion--220.101.28.25 (talk) 15:29, 1 February 2010 (UTC)

Wires get corroded by heating-up. They heat-up since they have a typical resistance per unit length (depending on the material), so when current flows through them, it disspates power in them given by P=I²•R (where I is the current). Note that AC current must have a larger amplitude than the DC current, to generate the same power. The result of integrating the square of the current over time, to find the mean of the power-contribution, is called (or RMS). So an ac current of the same RMS as a dc current will dissipate the same amount of power along thw wire, and will generate the same amount of heating-up. The result of the RMS integral is dependant upon the waveform of the ac current. For sine (cosine) waves, the RMS value is sqrt(2)/2 (=~0.7071...) of the amplitude. For example, in incandescent light-bulbs, you need an ac amplitude of current, which is larger (times the inverse RMS amount) than a constant dc current, to produce the same amount of heat (and light). --Shimon Yanowitz (talk) 16:39, 1 February 2010 (UTC)

I would expect more electrolytic effects from wires carrying DC than AC, unless the insulation is perfect. With AC, the metal removed in one half cycle might be returned in the other half cycle, but with DC there should be a continuous deposition of metal, provided there is leakage current, as when wires are underground and there are small cracks in the insulation. There is also electrolytic action causing ferrous metal underground to lose metal when copper is nearby, but that should not depend on AC versus DC current in the copper, as long as the circuit has a return path and is not just unipolar. Edison (talk) 20:43, 1 February 2010 (UTC)

Advice on modelling a flood

For a creative project I'm imagining a scenario in which unprecedented rainfall causes disastrous flooding in (inter alia) Cambridge, UK. The premise is unrealistic, but I want what follows from it to be as plausible as possible. So I'm seeking tips on how I could model what flooding would look like in this town: I'd like to be able to produce a map showing which parts of the city are still above the flood level.

I guess I would need to find values for variables, including:

1. rate of precipitation (how much rainfall per time period)
2. topography of the area
3. effect of rainfall upstream
4. ?season (drains clogged with leaves in autumn? Water table higher at certain times of year?)

Can anyone give me pointers on how I could realistically model the flooding of the town, if I had set values for these variables? If I wanted to say "it has rained solidly for x days at a rate of y centimetres per day", how can I figure out what effect that would have on the ground? I'd be very grateful for tips on ways to get started, or on factors I'm missing from my list. Gonzonoir (talk) 13:44, 1 February 2010 (UTC)

You will want a relief map of the area such as the maps with contour lines published for the U.K. by the Ordnance Survey. Without effective measures of Flood control, floodwaters will settle within a given elevation contour line. Cuddlyable3 (talk) 14:27, 1 February 2010 (UTC)

Further, you'd need to estimate flood points and try to work out a flow pattern. rising water does not create floods; floods are created when water passes the lowest point on the river bank, and how it flows from there will determine damage patterns (damage will be more extensive, for instance, where water can pick up momentum or build up pressure). You'l also want to consider whether you're talking about natural flooding (where water passes a bank and more or less gradually fills the surrounding region) or catastrophic flooding (where the failure of a natural or man-made containment wall releases huge quantities of water rapidly). --Ludwigs2 15:46, 1 February 2010 (UTC)

Historical information about previous floods in the city may be helpful (perhaps to confirm whether your model has validity). A google search throws up links to photographs of previous floods. You may be able to estimate how high the water was at the stated locations but I didn't find an aerial photograph. Museums and pubs often seem to have photos of floods :-) --Frumpo (talk) 16:33, 1 February 2010 (UTC)

Another variable you need is the percolation/drainage capability of any area - and that's complex since drainage capabilities of any area will be affcted by the drainage capability of another area (e.g. if both discharge into a common and limited drainage channel). --Tagishsimon (talk) 17:37, 1 February 2010 (UTC)

Many thanks all - this is exactly the sort of thing I was after. Some follow-up questions:

1. The OS 1:25 000-scale map for the city has contour intervals of 5 metres. Cambridge is as rugged and mountainous as a pancake, so there ain't that many of them. Does anyone know of a resource showing contours at a finer level of detail?
2. The point about percolation is well taken. Can I make the blanket assumption that the broader the scale of the storm (i.e., the greater the size of the area that's getting rained on), the worse drainage at any one point will be?
3. Ludwigs2, just to clarify, by "flood point" you mean the spot(s) at which the river breaks its banks? That seems like an area where Frumpo's suggestion of gathering data on earlier floods would be helpful. Gonzonoir (talk) 20:15, 1 February 2010 (UTC)

The Environment Agency has maps of areas likely to flood. AndrewWTaylor (talk) 14:00, 2 February 2010 (UTC)

Cheers AndrewWTaylor. Gonzonoir (talk) 09:19, 3 February 2010 (UTC)

Speed of heat transfer

Can we say that heat is transferred at the speed of electromagnetic waves throughout a medium? I understood it is transferred by conduction, for instance at the speed of sound, but isn't there a radiation contributing factor through this medium?--Email4mobile (talk) 16:53, 1 February 2010 (UTC)

There are three important ways heat is transferred: radiation, which goes at the speed of light; diffusion, which does not have a definite speed; and convection, which depends on bulk movements of the medium. In many situations radiation does not play a significant role and diffusion is the main factor. "Conduction" is the same thing as diffusion here, and it does not go at the speed of sound -- its speed drops off with distance. Looie496 (talk) 17:01, 1 February 2010 (UTC)

I'm afraid I couldn't get it. Let me rephrase the question: What is the time required to cause an infinitesimal or tiny change in temperature provided that a significant change has taken place at a given distance of known medium (with its characteristics involving heat transfer)?--Email4mobile (talk) 17:21, 1 February 2010 (UTC)

It depends on what your medium is. If it is transparent to infra-red radiation then a solid object immersed in the medium will be heated most rapidly by electromagnetic radiation (although the medium itself is not heated this way becqause it does not absorb the e.m. radiation). If the medium is opaque to infra-red radiation then a thin layer near its surface is heated rapidly by e.m. radiation but the bulk of the medium has to be heated more slowly by convection in a liquid or gas or by conduction in a solid. Gandalf61 (talk) 17:37, 1 February 2010 (UTC)

Then at what (slowly) speed will the heat transfer by conduction and convection occur? This question will help me save the time asking another question about a maximum theoretical possible speed for sound if it will be the same, thanks in advance.--Email4mobile (talk) 18:04, 1 February 2010 (UTC)

The question you phrased is probably not the question you want to be answered. As any (as far as I know) medium is transparent to some kind of electromagnetic radiation, and as any material will radiate on any frequency (albeit and notably not at the same intensity) any change in temperature will reach any other body at the speed of light. The energy exchanged in this way will in most cases be negligible compared to the energy flow by slower convection and conduction. 95.112.190.236 (talk) 18:28, 1 February 2010 (UTC)

Let's try to break this down a bit.

• Radiation: If you had a hot body and a thermometer separated by some distance in a hard vacuum - then such heat as would be transferred from one to the other would happen via infrared radiation (mostly) and that travels at the speed of light (because it is light).
• Conduction: If you had a steel bar and heated up one end with the same thermometer at the other end, then because steel is opaque to infrared light, the heat would have to travel from one end to the other by conduction...a much slower process in which the jiggling of a hot atom at one end knocks into another atom next door and sets that jiggling too - and atom-by-atom, the jiggling spreads from the heat source to the thermometer. The speed at which that happens varies dramatically from one material to another. At one extreme, metals like steel conduct heat fairly quickly (although nothing like as fast as the speed of light). At the other extreme, materials such as aerogel or the stuff they make space-shuttle heat tiles out of conduct heat incredibly slowly. Everything depends on the structure and constituents of the material. The speed of conduction is nothing like the speed of sound. Sound travels through steel bar at hundreds of miles per hour - but when you stick a metal teaspoon into a near-boiling cup of coffee - it might take several seconds for the heat from one end of a six foot chunk of steel to be noticable at the other end.
• Convection: If you put a hot body into a room that's full of air - and put one thermometer six feet to the left of it and a second thermometer six feet above it - then the first thermometer will take a lot longer to register the temperature rise than the second one. That's because as the air around your heat source warms up, it expands. It's density gets lower...the air becomes "lighter". This lighter, warmer air tries to float on top of the denser air - just like a piece of wood floats on water. As the air rises upwards, it reaches the thermometer above the heat source quite soon - but that warm air has to be replaced by cool air from around the sides - so the conduction of heat through the air is messed up by that air flow and the thermometer off to the side may never show a temperature increase at all! This convection effect relies on the materials being free to move around - so you don't see convection in a steel bar - but you do see it in water, mercury, air, etc. Even within liquids, the runnier the liquid, the faster the convection currents can move. The amount of convection in (say) treacle is far less than (say) in water. I suppose that the rate of convection might be limited by the speed of sound...but I don't think so. At any rate, it's not usually that fast.

So the answer to your question is fairly complex. In many situations, the transfer of heat from one place to another depends on all three of these mechanisms. If you light a fire in your fireplace, you are immediately warmed by the thermal radiation - but as the hot air produced by the fire goes up the chimney, you feel a cool draft from the colder air in the rest of the room. However, heat from the fire is also warming up the walls and floor of your house by conduction - and you get some warmth that way too. Figuring out the results of those three things complicates the answer to the point where we can't give you any kind of measure of speed without knowing precisely what materials and distances are involved. SteveBaker (talk) 18:44, 1 February 2010 (UTC)

Just to add to Steve's reply, in a thin column of air (or other fluids), the descending cool air can't move to the side of the ascending warm air, and thus inhibits free convection. This is one of the methods in double-glazing. CS Miller (talk) 20:26, 1 February 2010 (UTC)

Steve, your description of the conduction microphysics is incomplete. Thermal conduction in most solids is mediated by phonon diffusion. Phonons do travel at the speed of sound in the material, but most materials are opaque to thermal phonons. As a result the thermal diffusivity in most solids can be estimated as the speed of sound in the material (typically a few km/s) times the phonon mean free path (typically several angstroms). I assume the original poster knew something about this or else he wouldn't have mentioned the speed of sound. So, in principle the information about a new thermal contact could transfer as fast as the phonons do, i.e. at the speed of sound, but in practice most materials are limited by the internal scattering of phonons and measurable diffusion takes much longer. The other issue with your discussion was the choice to use a steel bar. Heat conduction in steel, like all metals, is totally dominated by the propagation of conduction band electrons. So the idea of atoms bumping into each other, though an appropriate image for phonons in insulators, is not the right image to use for metals at all where essentially all the work is done by electrons bumping into each other. This difference is also why thermal conductivity of metals is so much higher than for insulators. Dragons flight (talk) 23:15, 1 February 2010 (UTC)

Europa (moon)

When Europa warms up I thouhgt this is possible Europa can end up back to watery globe. The surface is made of white ice which is thick layers of oxygen. If scinetist think Europa is once cover with oceans when gravity is too low how can they keep a substantial atmosphere? Isn't Europa even smaller than Pluto so outgassing should be even likely--209.129.85.4 (talk) 17:29, 1 February 2010 (UTC)

I don't know about "when" Europa warms up - that seems unlikely to happen before the sun turns into a red giant...and even then, not for long. Anyway - what prevents all of the oceans from boiling off into space is precisely because there is all of that ice there. If the planet warmed up enough for the ice to melt, it would start to boil. On a larger body, the water vapor would form an atmosphere, the pressure of which would gradually increase until there was an equilibrium between liquid water and water vapor. But Europa has insufficient gravity to keep that water vapor as an atmosphere - so rather than the pressure building up to maintain that equilibrium, the oceans would keep on boiling until they were all gone. If there are liquid oceans there - they are locked below a thick layer of ice which (being a solid) is only sublimating away very slowly. Outgassing (of a sort) is one of two proposed mechanisms to explain the cracked appearance - yet super-smooth surface of the moon. It is thought that the surface ice may occasionally crack due to tidal forces from nearby Jupiter. The pressure in the oceans beneath the ice would force geyser's of water to be forced up through the crack - only to freeze as soon as it reached the surface. This mechanism would continually force water from the liquid oceans, up through cracks - across the surface. Because warm water from the ocean is likely to slowly melt the underside of the ice - undermining it and causing more cracks - there would be a slow recycling of water through the ice sheets. This seems to be the most likely explanation for the observations of Europa - but there is another plausible theory that there is no liquid water - but merely slowly flowing ice beneath a brittle surface layer. SteveBaker (talk) 18:28, 1 February 2010 (UTC)

Hang on. Europa was once thought to have watery surface in the history billion of years ago . It must be said somewhere in our article if somebody could find it. That's what solarview website said.--209.129.85.4 (talk) 20:40, 2 February 2010 (UTC)

See oceans of Europa. Also, the end of the Sun would cause many parts of the solar system to be destroyed, including (according to one documentary) all of the gases of Jupiter, leaving only its core, which it erroneously claims will be smaller than Europa (which is not possible, given the size of Jupiter's core). The shedding of the sun's outer layers would be sufficient to disrupt the ice if the expansion does not do it first, but it's possible that its entire orbit around Jupiter would be disrupted, sending it into the planet or being swept out to space–we don't know. ~AH1 02:53, 2 February 2010 (UTC)

is melvin manhoef okay?

? —Preceding unsigned comment added by 67.246.254.35 (talk) 17:53, 1 February 2010 (UTC)

Does this question has any scientific aspect? (Mind you, you're asking this on the Science Reference desk, not on a news desk.) 95.112.190.236 (talk) 18:08, 1 February 2010 (UTC)

Our Melvin Manhoef page doesn't list any current injuries, and I went to Google News and typed "Melvin Manhoef", and 25 stories were found about this weekend's fight. I only read one of them, which didn't mention any lasting injuries. For future reference, 95 is correct, this would probably belong better on the Entertainment desk; and also for future reference I do recommend a news site like Google News for "what happened yesterday" questions like this; it's faster than coming here to Misplaced Pages, asking, and then waiting several hours for someone like me to go Google it for you. Comet Tuttle (talk) 18:27, 1 February 2010 (UTC)

Ah, this is our world today and I don't have much capacity to complain about but, please all of you think twice, is the state of health or injury of any human being really a matter of entertainment? I think, yes, in the world as it is, it is, but it should not. 95.112.190.236 (talk) 18:39, 1 February 2010 (UTC) (And sorry if this violates Misplaced Pages:NPOV and current political correctness.)

Good one! I suggested the Entertainment desk not because injuries are hilarious, but because Melvin is the Light Heavyweight World Champion of Cage Rage, which is a form of entertainment. Questions about injured boxers or wrestlers belong there too, unless, I suppose the questioner is asking about the details of the fighter's subdural hematomas. Comet Tuttle (talk) 19:18, 1 February 2010 (UTC)

So isn't it illegal to inflict such injuries to anyone, or to promote or endorse such doings? Why aren't all those rubbernecks paying attention and money to see such incidents simply going to prison? 95.112.190.236 (talk) 19:55, 1 February 2010 (UTC)

Presumably these actions are between consenting adults? Googlemeister (talk) 21:03, 1 February 2010 (UTC)

If so, why then is there any fuss about any injuries consented? (And if in any countries with national health care, is there any compensation for the non-consent-forced-contributors?) 95.112.190.236 (talk) 21:53, 1 February 2010 (UTC)

This is not really the place to soapbox about the morality or moral hazard of boxing. Please do it elsewhere. Rckrone (talk) 22:57, 1 February 2010 (UTC)

I'm surprised that there is no boxing license article. 124.157.247.221 (talk) 21:40, 1 February 2010 (UTC)

Can I eat my father's popcorn?

For the longest time I didn't know it was there. It was in the back of a cabinet. I've never bought popcorn, so it must be his.

My father moved out 11 years ago.Vchimpanzee · talk · contributions · 18:48, 1 February 2010 (UTC)

Are you asking if it has gone bad? Popcorn will basically not go bad IF it has not been exposed to moisture or bugs. But you should be able to tell by looking at it if it has gone bad—with over a decade of time, it has either probably gone reeeeeaallly bad (it will be able to carry out a conversation with you), or it is just fine to eat. Note that this may vary depending on any flavoring or coating on the popcorn—if it has all sorts of synthetic butter stuff on it, I don't know whether that stuff goes bad, stale, whatever. I would be a bit wary of that stuff. --Mr.98 (talk) 18:58, 1 February 2010 (UTC)

I found a bunch of other stuff too. Sugar, cocoa, pancake syrup ...Vchimpanzee · talk · contributions · 19:07, 1 February 2010 (UTC)

Assuming this is a commercial product, it probably has a relatively long shelf life. at any rate, or popcorn to go bad it needs to absorb moisture, and if it absorbs any significant amount of moisture is won't pop.

That being said, popcorn costs a dollar or two (US currency) per pound. Unless you're talking about a huge quantity (e.g., your father stockpiled shelves of the stuff), it's probably wiser just to toss it and buy a new package. --Ludwigs2 19:08, 1 February 2010 (UTC)

It's a very small amount. That's why I never saw it. Vchimpanzee · talk · contributions · 19:11, 1 February 2010 (UTC)

(after ec) Answering quite formally, we are not to give legal (that stuff is owned by your father, ain't it?) nor medical advice (no one would like to be liable if you get stomach cramps or worse) I have to tell you that we cannot answer your question. But I can tell you what I did in a similar situation (which is not even original research, I did not research, I just did it). I used the sugar, threw away the cocoa (it tastes bitter when rotten, but it also tastes bitter when fresh), and I had a taste on the syrup before deciding it didn't taste of and was sticky enough that it would have not enough free water for any bacteria to live in it. If you are not in really dire need of food, throw away whatever you're in doubt of being harmful. 95.112.190.236 (talk) 19:23, 1 February 2010 (UTC)

This is why we have "use before..." dates - are there any of those on these products? I would be surprised if any of the things you mentioned would be a problem - providing no moisture got into them - and no rodent chewing/droppings are evident. SteveBaker (talk) 19:30, 1 February 2010 (UTC)

"Best before" dates are set very restrictive, to protect the selling company from lawsuit. It's not a Median lethal dose test. (Which is well, that is is not.) 95.112.190.236 (talk) 19:38, 1 February 2010 (UTC)

The popcorn is not in its original container. Neither is the sugar. I could check the cocoa.Vchimpanzee · talk · contributions · 20:24, 1 February 2010 (UTC)

Old popcorn loses the internal moisture needed to explode into steam and make it pop, so the size of the popped kernals should decrease and the number of unpopped kernals should increase in very old popcorn. We cannot predict other harmful effects such as fungus or insect infestation. Edison (talk) 20:36, 1 February 2010 (UTC)

I missed one the responses. As executor of my father's estate and the only one who inherited from him after his wife agreed to a certain amount, the food is mine.Vchimpanzee · talk · contributions · 20:39, 1 February 2010 (UTC)

So I assume it has some kind of personal, memorable value. I encountered this from personal experience, in a time when Germans socialists where on top and I didn't know if I'll ever get a job again, thus valuing any left food twice as high (not wanting to be in need to beg the apparatchniki for sustenance). My personal advice is: throw away what is clearly rotten, use what can safely be eaten, and await a time where the rest of it clears out to be on one or the other side. 95.112.190.236 (talk) 21:15, 1 February 2010 (UTC)

None of the things you mentioned will spoil, but you might have bugs in them, and the taste might be bad. But from a safety point of view, I would be comfortable eating them. The popcorn will almost certainly not pop, and the cocoa might taste bad. The sugar and corn syrup will be fine. But please check for bugs (look for webs). It's a rare airborne fungus that would be harmful to eat (as opposed to breathe). And bacteria can not live in those things (too dry). Ariel. (talk) 21:11, 1 February 2010 (UTC)

Good advice from Ariel and Mr.98 (among others). As an aside to 95.112.190.236 re " 'Best before' dates are set very restrictive". The meaning of these terms may be different between jurisdictions, meaning countries. In Australia 'Use by' means it should be used by and NOT eaten after. 'Best before' is a much more rubbery figure. Many foods are perfectly good to eat well after that date, ie. Fruit cake comes to mind, but probably not (depending on food and storage) 11 years (I have some cake 5 months past best before, still very yummy). Shelf life covers both terms. --220.101.28.25 (talk) 22:58, 1 February 2010 (UTC)

Some dangerous microbes also live in anaerobic environments. That's why canned foods can be dangerous. 67.243.7.245 (talk) 02:18, 2 February 2010 (UTC)

to get to orbit, is the weight of the rocket fuel you need linear with the weight of the payload you get up?

if a trillionaire was inspired by a successful government rocket launch and decided, I wanna get a payload that's ten thousand times heavier up into orbit, would they need a rocket system that is ten thousand times as massive? (ie a linear relationship). Or would it be more/less?

In general, how massive a rocket system (rocket system including fuel) do you need to get x pounds of weight up into orbit? (ie what is the formula).

neitehr is homework question, thanks. 84.153.232.162 (talk) 19:13, 1 February 2010 (UTC)

• Depending on the distance you want to go and the time you have (if a trillonnaire, plenty or none ?), fuel may put you off terrestrial gravity and then you just have to let solar winds or ionic propulsion take the relay with very much less load costs. --82.227.17.30 (talk) 19:25, 1 February 2010 (UTC)

No. See Rocket equation. The reason is that you need to lift (part of) the fuel, too. 95.112.190.236 (talk) 19:30, 1 February 2010 (UTC)

You are wrong. It IS linear with the amount of stuff you want to lift. Here is a thought experiment: Imagine you have a launch vehicle that can get 1 ton up to the required orbit with a certain amount of fuel. Now you want to launch a 1000 ton object. Well, you could cut it up into 1000 one ton pieces and launch each piece using a 1 ton launcher and the cost in fuel and motors would be exactly 1000 times as much as for launching 1 ton. Then, because all of the 1000 rockets are identical and with identical payloads - they would go up at the same speed/acceleration. That means that you could launch them all simultaneously and they would stay together. So you can bolt them all together and pretend that they were just one large rocket - and now you don't have to cut your payload into bits. In reality, there would be some parts such as control circuitry and many redundant systems that would not need to be duplicated 1000 times - so in practice, it's a little better than linear. SteveBaker (talk) 19:58, 1 February 2010 (UTC)

You are right, it is linear from the equation. I got it wrong in memory and was too convinced to read the article I've linked for a check. It probably is not linear with very small weights as the hull weight is not linear (so I think). 95.112.190.236 (talk) 20:23, 1 February 2010 (UTC)

No doubt that below the size of an effective present-day launch vehicle, things might get unlinearly worse - but above the present size shouldn't be a problem in principle. Of course, the practical issues are a problem. If you have 1000 rockets, the probability of them all working perfectly is close to zero - so you need lots of redundancy. A one in one hundred chance of a 1 ton launch vehicle getting off the ground would translate into a near certainty of failure for a 1000 ton launcher made up of 1000 one ton launchers. Hence you need more thrust to take account of that expected failure rate. But in theory, it's a linear thing. SteveBaker (talk) 14:25, 2 February 2010 (UTC)

Agreed. If my math is correct, if your rockets were 99.93% reliable, you would have just under a 50/50 shot at success. Googlemeister (talk) 17:35, 2 February 2010 (UTC)

But I would like to hitch-hike the question and add my own: how small (weight and dimensions) can a rocket be to enter near earth orbit from earth? 95.112.190.236 (talk) 19:30, 1 February 2010 (UTC)

Well, our comparison of heavy lift launch systems provides a good starting point. Considering low earth orbit only, here's some common systems and their efficiency (payload over launch mass):

• Atlas V: 5.4%
• Titan IV: 2.3%
• Delta IV: 3.5%
• Ariane 5: 2.7%

Now, of those, the Titan (the least efficient) is also the largest. The Atlas (most efficient) is also the smallest. It's also got a large payload range specified, so I'm more suspicious of that estimate being high. Anyway, we can finally consider the Saturn V, with 3.9% efficiency to LEO, and it's many times larger than any of the above. So basically, economy of scale doesn't apply from a size standpoint. As such, you're probably not going to make one ten-thousand class launcher; instead, you'll launch ten thousand generic ones (or one thousand ten-class launchers, or something else that really will let you use economies of scale). — Lomn 19:32, 1 February 2010 (UTC)

Addressing the rider question: Given the above, you could expect to launch a 1 kg payload to LEO with about 50 kg of rocket, if everything scaled well. 500 kg of rocket should work out fine as a theoretical minimum launch vehicle. Poking through our comparison of small lift launch systems, the British Black Arrow was the smallest actual launch vehicle I saw at 18000kg and 13 m tall. — Lomn 19:40, 1 February 2010 (UTC)

So if you wanted to send something really high, best to use a ballon. Beach drifter (talk) 19:44, 1 February 2010 (UTC)

No - a balloon won't get you above the top of the atmosphere - and it won't get you the orbital speed you need so even if you could get up to the right altitude, the payload would just fall back to earth again. So you still need a rocket or something similar to get you up to orbit. However, a balloon is a great way to get really high without orbiting. SteveBaker (talk) 20:03, 1 February 2010 (UTC)

Er, well, thats why I said really high, and said nothing about orbit. Beach drifter (talk) 20:18, 1 February 2010 (UTC)

Uh me bad for original thinking! I imagine a pipe of glass carbon (what, no article on that? Did I get the spelling wrong?) filled with oxidizing rocket fuel and using the flopping effcet (what, no article???) to throw off burnt parts of the pipe as to emulate multiple stages of a rocket thrown off. And, of course, set off in a high altitude reached using a hydrogen balloon. 95.112.190.236 (talk) 20:07, 1 February 2010 (UTC)

Rockets that use the airframe as part of the fuel do exist. They usually explode on impact, too. (Not commonly a design goal for orbital launchers and certainly not for manned rockets!) Generally, if you want to guarantee safety of the payload, it's considered a bad idea to burn through your structural elements. I've never heard of "glass carbon", at least not in the context of a rocket fuel. It's worth noting that graphite is used in nozzles because it's reluctant to combust and/or ablate, even in the presence of extraordinarily strong oxidizers and extreme heat. As for the OP, you can cut down on your mass ratio in a lot of ways. The easiest way is to cut down on your safety factor. This is rarely desirable. Ultimately, as has been pointed out, you want to see rocket equation - and remember that "inert mass" includes all kinds of structural things like pipes, tubes, aerodynamic control surfaces, and more "connective tissue" than you probably expect. (Every part of the rocket has to be held in place). Extremely small rockets can't ammortize this overhead mass very well. Extremely large rockets suffer from an excessive requirement for structural support. The result is a "sweet spot" in terms of total rocket size, as evidenced above. This is more about engineering details than pure physics - but there's a theoretical limit too. Even an infinitely staged rocket can't beat certain physics, based on the efficiency of your rocket motor's combustion (in particular, the energy-per-mass of propellant, which is related by the effective exhaust velocity). Nimur (talk) 22:10, 1 February 2010 (UTC)

I have to admit that I am a bit startled that I can't find neither the (an??) article about glass carbon nor on flopping. From my memory, glass carbon is a from of carbon (supposedly) based on fullerenes that is "glassy" (none-crystalline), gaining its optimal strength at somewhat over 3000°C. Flopping is a mostly undesirable effect of uncontentious burning of rocket fuel leading to yet undesirable pressure fluctuations that could (warning: original thinking!) be used to throw off burnt stages of the rocket. 95.112.190.236 (talk) 22:36, 1 February 2010 (UTC)

Combustion instability goes by many names. I've never heard it called "flopping" but I've heard "chugging", "luffing", "chuffing", "burn instability," "oscillation", and "parametric decay instability." I don't think anybody wants this to happen, it's generally an undesirable effect that can lead to poor performance and even damage. Nimur (talk) 02:20, 2 February 2010 (UTC)

Yes, it's Combustion instability and I can't find "flopping" any more but it's what I remember as name for it when I first heard of that effect. The other thing is spelled glassy carbon. 95.112.189.37 (talk) 21:22, 3 February 2010 (UTC)

Your trillionaire would be better thinking outside the box and coming up with an innovative launch method that does deliver economies of scale - such as Project Orion or a space elevator. Gandalf61 (talk) 14:46, 2 February 2010 (UTC)

Space elevators have got a few mentions recently, so this may be of interest to help deskers. 220.101.28.25 (talk) 11:17, 3 February 2010 (UTC)

mRNA and secondary structure...

What causes mRNA secondary structure? What impact did the presence of secondary structure in the mRNA have on the scanning and initiation steps of translation? —Preceding unsigned comment added by 137.141.248.112 (talk) 21:12, 1 February 2010 (UTC)

RNA structure and mRNA might be a good start. Rckrone (talk) 23:40, 1 February 2010 (UTC)

Black Arrow awakened

Is there any reason why, if the engineering plans and other details survive, that a Black Arrow could not simply be built, giving a working launch vehicle with zero development costs? Obviously a launch site would be needed too. 92.29.34.140 (talk) 21:33, 1 February 2010 (UTC)

Are you counting the cost of the engineers needed to build it? Rocket scientists aren't cheap. Nimur (talk) 22:18, 1 February 2010 (UTC)

That program had 2 successful launches and 2 failures, according to the infobox. It would be possible to take the plans and go and make one and launch it, yes; but there would be the cost of building whatever ground control facilities are necessary to communicate with the thing. You might consider that a development cost. Upon launch, if there is a launch failure, you're going to want to fix the problem on future rockets, so there will be development costs there for incremental improvements. There will also be the inevitable engineer's burning desire to improve this 40-year-old design, with all the improvements in materials science and rocket engineering that have transpired. If I know engineers, they're going to say "start from scratch" when this is proposed. Comet Tuttle (talk) 22:18, 1 February 2010 (UTC)

I think the OP is underestimating the difficulty of looking at a rocket schematic, and actually building a rocket. It's not exactly like a Lego set. Material costs are high. Rockets are built from weird stuff (exotic metal alloys, dangerous chemicals, toxic fuels and oxidizers). Many of the things you need to acquire to build one, including the metals, chemicals, electronics, and software, are controlled by the government (ITAR). A huge amount of hassle and red tape goes into this to make sure you aren't building anti-aircraft systems or weapons. (Let me clarify - the cost of this red-tape comes out of your budget!) The actual costs of design are much lower than the total project cost. Testing is often dangerous and/or destructive. (If you had a re-usable rocket, you'd be in great shape!) But a huge number of elements - even things you wouldn't expect - are "consumable". This means you need one item per test, (not even counting catastrophic failures!) Even if you have a perfect schematic, what about assembly? You need dozens, if not hundreds, of skilled engineers, technicians, machinists, and a huge variety of hard-to-find, specialized skill-sets. Hiring those people, either full-time or contractually, is not free. Are these enough reasons why a Black Arrow, or indeed any rocket, can't be built with "zero development cost"? Nimur (talk) 22:25, 1 February 2010 (UTC)

It's 1960's technology. Can't be that difficult. 78.144.201.75 (talk) 00:38, 2 February 2010 (UTC)

Well, there was a bunch of stuff commonly manufactured fifty years ago which is not manufactured now. And if your rockets happens to need any of that stuff - which is fairly likely - then you do have to rediscover how to make it. And I agree that all things being equal, that is well possible. But it is a damned site harder than simply being able to put in an order at your nearest supplier. And that is one of the reasons that "can't be that difficult" is not very well observed. --Tagishsimon (talk) 00:45, 2 February 2010 (UTC)

I'm sure if "1960's technology" equated with "trivial to acquire", then classic car enthusiasts would be a lot richer. "Classic aerospace engineering" is a little more expensive than repairing an original Mini-Cooper! You could start with that, and once you've totally mastered it, start working your way up the ladder of vehicle complexity. Nimur (talk) 02:23, 2 February 2010 (UTC)

It's incredibly difficult to take someone else's plans and turn it into a workable thing. There will always be ambiguities - and situations where you really need to ask the designer "why did you do it like that?" - and in this case (as User:Comet Tuttle points out) the rocket only had a 50% success rate - so you already know that there's going to have to be a certain amount of redesign. But without being able to talk with the original designers, it would be an uphill struggle to turn these things to a solid launch vehicle. SteveBaker (talk) 03:00, 2 February 2010 (UTC)

See ths story about another program having trouble following some blueprints. To refurb some not so very old nuclear warheads: "The component, known by the code word "fogbank," is thought to be made of an exotic material and is crucial...When it came time to make new batches of fogbank for the refurbishment program, the current workforce was unable to duplicate the characteristics of the batches made in the 1970s and 1980s, according to a March report by the Government Accountability Office. 'I don't know how this happened that we forgot how to make fogbank,' Coyle said. 'It should not have happened, but it did.'" Rockets have similar national security and technical issues. 75.41.110.200 (talk) 06:31, 2 February 2010 (UTC)

Nice story! And we have an article on this: FOGBANK. Comet Tuttle (talk) 18:29, 2 February 2010 (UTC)

The unused latest rocket is in a museum somewhere for inspection - pity it wasnt/isnt filled up with juice and fired off. 89.242.39.49 (talk) 12:33, 2 February 2010 (UTC)

horse distance

How far can a horse travel in one day over flat terrain such as the American Midwest without wearing it out (it must be able to travel roughly the same distance for many days in a row) presuming it has 300 lbs or rider and equipment? I am sure that various breeds would have different results, so am just looking for a ballpark estimate. Googlemeister (talk) 22:11, 1 February 2010 (UTC)

You're talking about draft horse work. I googled on the phrase "typical speed of a draft horse" and there was exactly one hit, which said that at one time many cities set their speed limit to 6 mph because that was the typical speed of a draft horse. I don't know how many hours a day a horse could walk under the specific conditions you're talking about, but I imagine it would be most of the daylight hours, so 60 miles (100 km) would be my ballpark estimate.

At Oregon Trail it says wagon trains took 4-6 months to cover 2,000 miles, and that's only 11 to 17 miles a day; but the wagons were heavy enough that they used slower animals than horses. Plus the logistics of operating a wagon train must have been more difficult than a single animal. --Anonymous, 00:00:00:00:00:00:00:00... :-) UTC, February 2, 2010.

Anonymous, why did you link to a movie in your signature? ~AH1 02:35, 2 February 2010 (UTC)

As a hint explaining the joke just before that. --Anon, 11:20 UTC, February 2, 2010.

It is Groundhog Day today, so I guess it's appropriate. (I'm not the original Anonymous, BTW.) 66.178.144.217 (talk) 03:45, 2 February 2010 (UTC)

I think 60/day is pretty generous -- 6 mph is a trotting pace, not sustainable indefinitely, plus the horse will need several hours each day to graze. I would guess 30-50/day is a more reasonable range. Looie496 (talk) 00:21, 2 February 2010 (UTC)

I was under the impression that the Roman Legions could easily march 20 miles along the Roman roads in a day, so I would imagine a rider on horseback could manage much further, even without the benefit of a road. Astronaut (talk) 06:22, 2 February 2010 (UTC)

You might find Horses in the Middle Ages#Transportation useful (it provides some typical daily distances). Astronaut (talk) 06:31, 2 February 2010 (UTC)

As a tangent, to this day the fastest army in history, over long distances, is likely still the all-cavalry Mongol armies of Genghis Khan. They pretty much pushed the horse to its limit, and by some calculations they still covered more ground per day than even a modern mechanized army can. Mongol military tactics and organization notes that they covered up to 100 miles per day. --Jayron32 02:14, 2 February 2010 (UTC)

Why not look at Endurance riding, not draft horse (speed not power): 300 lbs, 100 miles, rough terrain in one day. 75.41.110.200 (talk) 06:18, 2 February 2010 (UTC)

Looks like a good ballpark guess then would be between 20 and 40 miles a day. Not sure if it can be done for 10+ days in a row, but it seems like this might be one of the areas of human knowledge that has been reduced in the last 100+ years. Googlemeister (talk) 15:03, 2 February 2010 (UTC)

See Yahoo Answers: which says 8 mph, 100 miles per day. Another says that a horse might go 100 miles in a day in a grueling endurance ride, but would need rest and care afterward.That writer says he did a distance ride and let the horse set the pace and decide when to stop for the night. The load was 190 pounds on an 1100 pound horse, and he covered 24 miles per day for 58 days out of a 5.5 month period. After a 40 mile day, he rested for two days. Another answer was 10-15 miles carrying 200 pounds. They say the load must not be more than 20% of the horse's weight. How much did you say your horse weighs that has to carry 300 pounds? Other answers there say 25 miles per day over several days. Other accounts I have read say the horse will break down or go lame after a few days at such a pace. In wartime, a messenger might ride a horse literally to death to get a message through, so extreme values of milage covered might not be sustainable. Keeping the weight carried to a minimum would be important, and a 150 pound rider with 50 pounds of tack and cargo would be more successful than your 300 pound load. See also the Long Distance Riders' Guild website. Its "Hall of Shame" exposes many lies about speed and distance, and cases of horse abuse. Edison (talk) 16:48, 2 February 2010 (UTC)

The hundred-miles-per-day number for the Mongol armies was actually due to their wise use of their horses. They would often have 3-4 horses per rider, so each rider could change rides multiple times in the journey; an individual horse may ride 100 miles with a rider on one day, and then the horse may have spent a day resting, and a few days catching up without a rider, and at a more leisurely pace. Besides being good riders and horsemen, the Mongols were also master logisticians, able to get the most out of their horses without ruining them. --Jayron32 17:45, 2 February 2010 (UTC)

The same was true of the Comanche, also known for their expert horsemanship. Comanche war parties would have several times as many horses as people. Pfly (talk) 05:54, 4 February 2010 (UTC)

Drug expiration dates

Inspired by the "best by XXX date" discussion above: I've been told the US military purchases prescription and/or over-the-counter drugs in bulk that have expired, because the prices are at rock bottom (believable) and because the Army's doctor-accountants have a table of dates and drugs telling them the real expiration dates — or, at least, the dates past which soldiers will start to keel over if they take the drugs. (Less believable.) The theory is that the drug companies are incentivized to label drugs with the nearest possible palatable expiration date not for product effectiveness reasons or liability reasons, but because consumers and pharmacies will throw out the old Tylenol to go buy more Tylenol. (I'm pretty sure the expiration date is not something consumers really look at when comparing Tylenol v. Advil.) True about the Army? False? Lunacy? Comet Tuttle (talk) 23:21, 1 February 2010 (UTC)

There has been some research done by a number of organizations into extending the permissible shelf life of some pharmaceuticals. This paper offers a summary of some recent work in the area.

The Shelf Life Extension Program (still a redlink, unfortunately) is a joint program of the U.S. Department of Defense and the Food and Drug Administration (FDA); it may be the basis for the rumors you heard. Here's the website: . Here's a detailed program description (Word .doc file): . Briefly, the DoD maintains large stockpiles of certain drugs (particularly antidotes for chemical or biological weapons) which have limited peacetime use. As it would be extremely costly to replace these drugs upon their nominal expiry dates, SLEP was established to determine if properly-stored drugs might be safely and effectively retained for longer periods. From the outline document:

It is important to note that products tested under this program are maintained under tightly managed, controlled conditions at a limited number of locations. Extrapolation of these data to drugs stored by others would be inappropriate. Storage conditions may vary widely across the population and SLEP data are not generalizable unless storage conditions are identical and verifiable. Even within the SLEP, products known to have been stored under adverse conditions (i.e., high temperature or low temperatures) by SLEP Participates are excluded from the program, unless they are marked and tested separately from “normal” stocks."

In other words, the information that the DOD has collected may not be applicable to pharmaceuticals stored and handled outside the military. There's also no program for purchase of expired drugs, as the military cannot rely on outside organizations to have stored and handled the drugs properly. TenOfAllTrades(talk) 23:57, 1 February 2010 (UTC)

It's also worth noting that an "emergency stockpile" needs to satisfy a different set of practical conditions than a normal supply - whether it's food, medication, or anything else. In the event of cataclysmic chemical warfare, I think most people would be willing to make exceptions about antidote potency, side-effect hazard, and other potential pitfalls of extended shelf-life. During non-emergency situations, the level of concern for those issues is much higher. Nimur (talk) 16:37, 2 February 2010 (UTC)

February 2

Ob. XKCD question.

This looks plausible (forget the last few panels):

   http://xkcd.com/620/

...it looks like it would be a heck of a lot of fun too. I wonder why there aren't people doing it for real? You'd think there would be people like base-jumpers doing it...maybe even have these rigs in theme parks. Any ideas? SteveBaker (talk) 05:07, 2 February 2010 (UTC)

There was some dude who did this, or something very like it, off of a bridge in the Tampa Bay area. I am researching it now. --Jayron32 05:19, 2 February 2010 (UTC)

See Sunshine Skyway Bridge, under "Bridge Suicides". A group of daredevils tried a pendulum swing from the bridge, and failed to take into account the additional stresses on the cable when it was actually swinging. The cable broke and several people were injured. --Jayron32 05:24, 2 February 2010 (UTC)

Doing it old-style usually doesn't work. Astronaut (talk) 05:35, 2 February 2010 (UTC)

It would be an engineering nightmare. You'd need some sort of automatic belaying system that could apply a constant tension to someone who's squirming around and flapping wings. It would need to be accurately tuned to each different person who went on it. It would quickly be tiring for the person on the cable; even if if most of the weight is taken off by the cable, you still have 60 kg of mass to pull around. You'd basically be stuck going up or down, because any deviation to the side and the cable would act as a pendulum and apply a restoring force to the middle. And I wouldn't have any clue how to flap my wings to apply force in a particular direction, and would just end up flailing around. Maybe an effective flapping technique could be developed with practice (and trial and error), but human arms aren't exactly built for flapping. In any case, the experience needed would rule out any sort of carnival ride. I invite someone to try building something like this; I'd like to see how it turns out (videos would be appreciated) And of course, neither me nor Misplaced Pages assume any liability for anyone crazy brave enough to try it. Buddy431 (talk) 06:01, 2 February 2010 (UTC)

Certainly the cable would act as a restoring force to keep you vertically below the attachment point - but if the cable is long enough, the deflection angle could be kept fairly small - perhaps enough to allow a modest amount of lateral flight. Having some restoring force to keep the flier within some reasonable boundaries would be a useful thing. Seems like you could build some kind of computerized winch to keep the tension in the rope constant - and also perhaps to limit the rate of descent if the person looks to be in danger of smacking into the ground at high speed. We can weigh the participant in advance to understand the amount of tension that would be needed. But it seems like the ability to experience what it would be like to literally fly like a bird would be worth the effort. SteveBaker (talk) 14:17, 2 February 2010 (UTC)

With some tracking cameras and some clever software, you could put the winch on a pair of tracks, and keep it directly over the user at all times. Compensating for the pendulum effect. APL (talk) 15:33, 2 February 2010 (UTC)

Peter Pan does it (video). Cuddlyable3 (talk) 11:37, 2 February 2010 (UTC)

Although I have not seen peeople doing this with a cable attached, there is a Base Jumper version of this already. In fact, we have an article on Wingsuit flying, which describes the practice. --Avicennasis 17:47, 2 February 2010 (UTC)

Wingsuits are really only gliders - what I'm thinking of is something where you actually flap to generate thrust...powered flight. Think "Bat", not "Flying Squirrel". SteveBaker (talk) 20:38, 2 February 2010 (UTC)

Flapping-wing suits in low gravity are a time honored trope in written science fiction. I'd love to know how much upward thrust a normal human could reasonably generate with a well designed pair of wings without exhausting himself. APL (talk) 02:01, 3 February 2010 (UTC)

This trope is sometimes portrayed as happening in a hyperbaric flying stadium at 1/6 g on the moon, implying that the authors felt that thicker air was needed to generate sufficient lift even in such reduced gravity. 124.157.247.221 (talk) 02:23, 3 February 2010 (UTC)

If the XKCD cartoon is to be believed (and that guy is pretty good at getting science facts right), then it requires the 0.09g gravity of titan and 50% denser atmosphere...so at 1/6th g, the air density would have to be pretty high. Of course you can easily "fly" at 1.0g in a fluid as dense as water...it's just that we call it "swimming". That's mostly because the bouyancy of the water cancels the gravitational force on a typical human body so you don't need much thrust in order to change altitude. SteveBaker (talk) 16:29, 3 February 2010 (UTC)

Death

How long after brain death occurs does it take for absolutely all nerve impulses in the body to stop? —Preceding unsigned comment added by 114.75.61.49 (talk) 12:45, 2 February 2010 (UTC)

This article at HowStuffWorks confirms that even after brain death the heart may still beat without assistance and some spinal reflexes may be present. So, if a patient is on a ventilator and is receiving fluid and nutrients, then I think the interval between brain death and cessation of absolutely all nerve impulses in the body could be a very long time indeed. Gandalf61 (talk) 13:01, 2 February 2010 (UTC)

I was thinking more about without any sort of life support, but thanks for the article. —Preceding unsigned comment added by 114.75.61.49 (talk) 13:50, 2 February 2010 (UTC)

Mike the Headless Chicken lived 18 months without a brain. Cuddlyable3 (talk) 20:37, 2 February 2010 (UTC)

He still had most of his brain stem, which is what controls the heart and lungs. Buddy431 (talk) 22:53, 2 February 2010 (UTC)

GLUT transporters

Hi guys, I'm currently reading about carbohydrate metabolism and I came across GLUT in the different organs. It is stated that GLUT2 transporters in eg pancreatic beta-cells are low-affinity transporters while GLUT3 transporters in brain are high affinity transporters. Can anyone explain clearly what low affinity vs high affinity transporter means and the significance of it, with respect to the organ which the transporter it is found in?

Thanks a million!! :) —Preceding unsigned comment added by 121.6.60.209 (talk) 14:16, 2 February 2010 (UTC)

Basically a transporter has to grab hold of a molecule before it can transport it, and then hang on to it during the transport process. The affinity is basically the "grip strength" -- a high affinity transporter is more likely to get hold of a molecule that is passing by, and tends to keep hold of it longer once it has gripped it. All else being equal, a high-affinity transporter can be expected to be more efficient. Looie496 (talk) 15:40, 2 February 2010 (UTC)

Hi, just to clarify, do you mean that since a high-affinity transporter has a low michaelis constant, so it's more efficient as Vmax is reached at a lower concentration of glucose? Thanks in advance :) —Preceding unsigned comment added by 121.6.60.209 (talk) 15:55, 2 February 2010 (UTC)

Yes, low K_M = high affinity. --Mark PEA (talk) 20:22, 2 February 2010 (UTC)

ohms law and current

In ohms law current is designated as I why not A for amps or C for current —Preceding unsigned comment added by 69.129.88.122 (talk) 14:22, 2 February 2010 (UTC)

This suggests that it might be I for Integral (of current density), but I don't know whether that was the original reason for choosing the letter I. Dbfirs 15:17, 2 February 2010 (UTC)

While I does happen to be equal to the (surface) integral of the current density J, I would be rather surprised if that were the origin of the notation. It should be noted that the link above simply provides the formulae and their definitions; it doesn't explicitly address the question of how the symbols were chosen. TenOfAllTrades(talk) 15:24, 2 February 2010 (UTC)

(ec) There are at least two competing stories out there (both referenced in this discussion). One is that the I came from the French intensité (literally, intensity), a synonym for current. Another version of the story is that the I came from impetus, yet another historical synonym.

Some sources note that if C were used for 'current' it could lead to confusion with the also-important-in-physics constant c, the speed of light. While such confusion would indeed be problematic, the widespread use of c for the speed of light didn't really occur until around the beginning of the twentieth century: . (Einstein himself didn't make the switch from V to c until 1907.) A (for amps or ampere) wasn't used because a lot of the equations involved were developed by Ampère himself — and he wasn't so boastful that he was going to name an important variable after himself. TenOfAllTrades(talk) 15:24, 2 February 2010 (UTC)

I agree that the integral is just coincidental. TenOfAllTrades beat me to the real reason(s), but all I could find was opinion. Dbfirs 15:41, 2 February 2010 (UTC)

Back in 1860 a scientific handbook(p281) discussing Ohm's Law might have used E for the electromotive force, R for the sum of resistances, and F for the "force of the current." Then see Ferguson "Electricity" from 1873 which says "The quantity of the electricity passing in a current, or the strength of the current (Fr. Intensité, Ger. Stromstärke), is estimated by the power of the current to deflect the magnetic needle, by the chemical decomposition it effects, or by the temperature to which it raises a wire of a given thickness and material." An 1872 journal calls it "intensite de courant." An 1875 journal notes the standardization of previously vague and conflicting terms for electrical quantities, in which "intensity" sometimes meant current strength and sometimes meant electromotive potential. It notes that "intensité" was universally used by French writers for current. Some writers in 1875 still used "i" for "intensity of the electrostatic field" or "electrical force at a point" and "C" for current strength (p 65)." The "Ampere" was apparently not adopted as the international unit of current until 1881. Edison (talk) 16:24, 2 February 2010 (UTC)

My raw nuts are green - have they gone to seed?

Sorry for the bad pun. Normally I eat roasted mixed nuts, but because I heard that raw/unroasted nuts are healthier, I bought some. When I opened the package this morning, though, some of the nuts had a green colour...is this mould, or just their natural, uncooked colour? I'd heard somewhere that peanuts can often have fungus, and even if the mould isn't harmful, I don't find the idea of eating it very appetizing.... Thanks in advance! Quietmarc (talk) 15:19, 2 February 2010 (UTC)

What kind of nuts exactly are in the package? Photo please? Comet Tuttle (talk) 15:31, 2 February 2010 (UTC)

Stupid me, left the package at home, and I'm at work. I'll take and upload a picture as soon as I'm home. A similar (but not identical) product from the same store has cashews, almond, pecans, filberts, and brazil nuts listed as ingredients, but there may be some variation in the product I actually got. I've texted my roommate to see if he can take a picture sooner....Quietmarc (talk) 15:54, 2 February 2010 (UTC)

Pistachios are often naturally green when eaten, so it may be likely, if your mix contained pistachios, that it would be perfectly normal. Some distributors used to dye their pistachios a bright red color because the green bothered some people, but I see less and less of this than I used to. --Jayron32 17:39, 2 February 2010 (UTC)

Funny, my first thought at the idea of red nuts was betelnut. Nyttend (talk) 13:55, 3 February 2010 (UTC)

Okay, false alarm. I double-checked and it looks like it was just green pistachios. I swear when I looked at them yesterdcay morning (at 5am, far too early for me to be up) that several kinds of nuts had the greenish colour, but yesterday it was clearly just them. Thanks guys.Quietmarc (talk) 14:20, 3 February 2010 (UTC)

counterfeit stamps

There are a great number of security devices on US banknotes to prevent things like photocopies and such, do stamps have similar security features? Googlemeister (talk) 17:00, 2 February 2010 (UTC)

Per this 2007 news story, "the investigation into counterfeit stamps was triggered after postal inspectors discovered that hundreds of letters were being rejected for delivery because the stamps lacked the required phosphor tagging." So yes, there are security devices. — Lomn 17:05, 2 February 2010 (UTC)

Here is another article on the security features. (Google "postage stamp security"). Unsurprisingly, the higher value stamps have more intricate features. --Mr.98 (talk) 17:31, 2 February 2010 (UTC)

In the UK, a phosphor stripe is used by the machinery to distinguish between first and second class letters. I'm surprised phosphor tagging is not mentioned in the postage stamp design article, but I'm not sure how widespread it is.--Shantavira| 09:21, 3 February 2010 (UTC)

Not sure about third-world countries, but it's common in the developed world to use tagging. Virtually all US stamps have been tagged since the 1970s (or 1980s? I can't remember for sure), with untagged stamps being either (1) the occasional error, or (2) older ones. There's not really a ton of need for security in stamps; unlike in the nineteenth century, people don't produce postal forgeries (conterfeits to deceive the post office) very often, as it doesn't pay very well. Ironically, most forgeries today are made to deceive collectors, and the stamps typically counterfeited are nineteenth-century stamps (such as the one pictured) that were made with security devices similar to traditional US banknotes. Nyttend (talk) 14:01, 3 February 2010 (UTC)

Hmm, now that I read the article from Linn's, I should note — while bank tellers are trained to know counterfeit money (they handle enough of the real stuff, after all), most stamps aren't handled by many people. After all, if you produce postal forgeries and use them, you're going to be the only one handling most of them; unless you get caught, the large majority will stay on the envelope all the way into the trash can. While some of the features mentioned in the article have been used on US stamps in the past — especially the watermarking, which is sometimes obscure and makes it hard for those of us who collect early twentieth-century US stamps — they're not as common, and ideas such as the sycopated perforations and the holograms (unless I'm remembering badly) have never been used on US postage. Nyttend (talk) 14:10, 3 February 2010 (UTC)

Interestingly, the U.S. government experimented with blurring the line between stamps and currency during the civil war: postal currency. TenOfAllTrades(talk) 15:40, 3 February 2010 (UTC)

Recipe for production of hydrogen by electrolysis

I would appreciate a basic recipe for efficient production of a liter of hydrogen ( and a half liter of oxygen) by electrolysis of water. Our article on Electrolysis of water does not go into specifics, since Misplaced Pages avoids being a "how-to" guide. I expect to use a DC power supply set at whatever voltage is optimal, with carbon electrodes (from old drycell batteries) submerged in water with some acid added. I want to do it on the cheap with materials available in my workshop, including sulfuric acid (battery acid, specific gravity 1.265) added to tapwater (would added to distilled be better?). I could use hydrochloric acid, salt, or baking soda if there were some advantage). I would collect the gas by displacement of water in a 1 liter bottle over the electrodes. It has been many years since I took chemistry, but I am aware of basic safety precautions such as adding acid to water rather than the converse. Is carbon (old battery carbons) inert enough for the process, since I don't have platinum electrodes? Would stainless steel be better in some way? How much of the sulfuric acid per liter of water is optimal? What is the ideal voltage (like 1.5 volts? 6 volts?)? Is there some problem or issue of diminishing returns with more than the minimum voltage? Is there some problem of diminishing returns with more than a minimal acid concentration? What volume of gas would then be expected per ampere hour? Is use of dilute sulfuric acid better in quantity or purity of hydrogen and oxygen produced some way than dilute hydrochloric acid or sodium chloride solution? Thanks. Edison (talk) 17:52, 2 February 2010 (UTC)

You don't want to use a chloride ion, because you'll get a significant amount of chlorine gas instead of oxygen. I think sulfuric acid is best, though of course it's nasty stuff and you need to be careful. Here's one setup: it's probably a bit smaller scale than you're looking for, but it's a good starting point. They use 0.1 M sulfuric acid, and say carbon electrodes are fine. They also use a variable voltage power supply, and use it to control the current. That seems like a good idea to me, rather than use a battery at a fixed voltage. Buddy431 (talk) 22:48, 2 February 2010 (UTC)

If the formula weight of sulfuric acid is about 98, the 1.265 specific gravity of my stock solution would indicate 2.70 molar, wouldn't it? (I never did chemistry for a living, many years since I took a course). Would a 27 parts water to 1 part stock solution volume dilution be about right to get from my stock solution of sulfuric acid down to the 0.1 molar solution (not sure if the volume would be greater or lesser than the sum of the parts)? Edison (talk) 06:00, 4 February 2010 (UTC)

This says that acid with a specific gravity of 1.2609 (close to yours) is 34.63% acid (by weight, I assume). That's a molarity of about 4.45 mole/L. To dilute to 0.1 M, add about one part acid to 45 parts water. The volume might change a little, but not enough to worry about. Buddy431 (talk) 06:35, 4 February 2010 (UTC)

Percent loss

If you want to find percent loss of water,

(mass of water lost / initial total mass of water) x 100?

I keep getting this is wrong. What's the real formula? —Preceding unsigned comment added by 142.58.156.63 (talk) 18:15, 2 February 2010 (UTC)

That formula looks correct. -- Flyguy649 18:29, 2 February 2010 (UTC)

Yes, percentage loss and gain are always expressed as percentages of the original amount unless there are special circumstances that dictate otherwise (such as retail profit where profit was traditionally expressed as a percentage of takings which were a known quantity). Dbfirs 19:17, 2 February 2010 (UTC)

I would disagree with the "x 100", since 0.7 (say) actually is 70%. I'd replace it with "x 100%", but this is a particularly minor detail. Grandiose (me, talk, contribs) 19:41, 2 February 2010 (UTC)

Dental Cavities

I scanned the article on dental caries already, but I found no information about why dental caries cause a color change in tooth enamel. What happens chemically to cause the whitish enamel to cause a dark stain when there is a cavity?130.127.52.67 (talk) 19:33, 2 February 2010 (UTC)

The destruction section of the Tooth enamel article seems to give a lot of details. Beach drifter (talk) 20:51, 2 February 2010 (UTC)

Indeed it does, but none of them refer to colour changes. Richard Avery (talk) 07:11, 3 February 2010 (UTC)

Color change in enamel and dentin occurs because bacterial products and debris become stuck in the hollow areas at which sound tooth structure used to be present. DRosenbach 04:52, 4 February 2010 (UTC)

vision acuity between 20/80 and 20/100 or 20/200

If the vision is between 20/100 and 20/200 is value identify? Do 20/140 or 20/170 exist? Is 20/300 or 20/90 exist? I never seen any doctors calling 20/90 or 20/130 or 20/250. I seem to hear either black or whites on 20/x00s I only hear is either 20/100 or 20/200 or 20/400 nothing between--209.129.85.4 (talk) 21:19, 2 February 2010 (UTC)

Yes. See our Visual acuity article; the article is pretty heavy going, but if you scroll down halfway there's a chart and an accompanying discussion about what is meant by measurements like 20/30. Comet Tuttle (talk) 21:27, 2 February 2010 (UTC)

This system is easy to understand. What it (roughly) means is that what this person can distinguish at the first distance, a 'normal' person would be able to distinguish at the second distance. So 20/20 vision means that this person can see at 20 feet what normal people can see at 20 feet - in other words, normal vision. 20/100 means that what this person can see at 20 feet - normal people could see at 100 feet. 20/10 would mean that this person can see at 20 feet what most people would have to get 10 feet away from to see...that's pretty good eyesight! So, sure, someone's vision could be 20/140 or 20/170 or 20/300 or 20/90. Probably the reason they round to a set of standard numbers is that with a simple eye chart, they only have letters printed at particular sizes - and it's not such an exact science since you're relying on what the viewer is telling the doctor - which could be inexact. But in principle, your vision could be 20/123.456789 if someone could measure it that accurately. The use of 20 as the first number is simply because that's as far back as you can get from the eyechart in most doctor's offices. SteveBaker (talk) 02:08, 3 February 2010 (UTC)

hydrogen ion concentration

I think I've managed to determine the hydrogen ion concentration and the pH when 2.16 g of hydrobromic acid is dissolved in water; if the molar mass is 80.9 mol, then 2.16 g divided by 80.9 mol equals 0.027, and -log(0.027) = 1.6. A pH of 1.6 seems reasonable for hydrobromic acid, though a little on the high side, I was expecting negative pH. First, I guess the appropriate question is, have I got that part of it right? But that's assuming /mol dm, and I want to know what the hydrogen ion concentration and pH will be if the final solution is 0.05 dm. Suffice to say I don't really understand this, but my first guesses are getting me to take 0.027, multiply by 0.05 to get 1.35 x 10, and then -log(1.35 x 10) gives me 2.87. I don't think that answer is right but I can't see what I'm doing wrong. Sorry for the formatting I don't know how to get math stuff here. Differentially (talk) 21:26, 2 February 2010 (UTC)

Your mistake is that you do not say how much water the acid is disolved in. In your first set of calculations, you take the -log of the number of moles of HBr which is dissolved. This is where you went wrong, since the pH is based on the concentration which is measured as the number of moles per liter. So you would need to divide the .027 by the volume of the solution in liters, and then take the -log of THAT number. --Jayron32 21:59, 2 February 2010 (UTC)

Hmm, I kind of tried that; my volume of final solution is 0.05 dm, and 0.027 divided by 0.05 gives me 0.54; but the -log of 0.54 is 0.268. Correct me if I'm wrong, but does a pH of 0.27 make any sense at all? That's why I had discarded it as one of my options. Differentially (talk) 22:11, 2 February 2010 (UTC)

That's right, I think. A pH of 0.27 is certainly pretty acidic, but you have a lot of acid in only 50 mL of water. Buddy431 (talk) 22:32, 2 February 2010 (UTC)

I think he may be close to surpassing the solubility of HBr water there. You can only assume complete dissociation before there is too little water to solvate all the HBr and the HBr starts boiling out of solution. John Riemann Soong (talk) 01:42, 3 February 2010 (UTC)

As with hydrogen chloride (which dissolves to form hydrochloric acid), hydrogen bromide is extremely soluble in water. Our article gives a figure of 193(!) grams HBr per 100 mL of water. Though that sounds high, that's about the same solubility on a mole-for-mole basis as HCl. TenOfAllTrades(talk) 02:05, 3 February 2010 (UTC)

Yup, HBr as a 48% aqueous solution is a standard commercial chemical. On the other hand, "pH == -log (H concentration) and HBr fully dissociates" are each not really correct at extremely high concentrations. The so-called strong acids are not infinitely dissociative, only "really high, essentially 100% at moderate concentrations"--the pKa is merely measurably a little negative. And the activity coefficient can also alter the actual pH even if the proton concentration is known...diverges more as concentration gets large. On the other-other hand, all of that is not usually considered for simple school-work calculations. DMacks (talk) 03:25, 3 February 2010 (UTC)

To answer the OP's question on whether a pH of 0.27 is OK. Its perfectly fine. pH is somewhat eroneously assumed to run from 1-14 because the "median value", 7, falls nicely in the middle. However, a pH of seven isn't really a median value. Its merely a result of the autoionization of water, and pH has no hypothetical upper or lower bounds. pH can be a negative number, and it can be higher than 14. A pH of 0.27 is very reasonable for a strong, highly soluble acid like HBr. --Jayron32 03:35, 3 February 2010 (UTC)

Differentially says he expected a negative value, so why he thinks 0.27 "doesn't make sense" is a bit hard to reconstruct. --Trovatore (talk) 03:41, 3 February 2010 (UTC)

Heh, it had been a very long day. I'd first got 0.27 (and discarded it) before I'd researched HBr and determined that a negative pH was likely. Differentially (talk) 09:10, 3 February 2010 (UTC)

Thank you for the help. Differentially (talk) 09:11, 3 February 2010 (UTC)

cuts on penis

Most recent common ancestor for humans and dogs, or How closely related am I to my two dogs?

Given that all life on Earth evolved from a single common ancestor, I'm curious as to how closely related I am to my two dogs. Has last common ancestor between humans and dogs been identified or know long ago it lived? A Quest For Knowledge (talk) 23:52, 2 February 2010 (UTC)

This tree of life suggests about 60 million years ago, while this indicates closer to 80 mya. You can also check out Evolution of mammals, which indicates that there's some disagreement about when and where certain types of mammals developed, but it's sort of ambiguous when the branching is though to have occured. As both dogs and humans are placental mammals, an upper bound is about 125 mya, as this is when the first placentals emerged. Buddy431 (talk) 00:27, 3 February 2010 (UTC)

Interesting -- the divergence happened before the Jurassic period? John Riemann Soong (talk) 01:39, 3 February 2010 (UTC)

The Jurassic period ranged from 200 mya to 145 mya. The Cretaceous period ranged from 145 mya to 65 mya. 124.157.247.221 (talk) 02:15, 3 February 2010 (UTC)

I take it "mya" is "million years ago"? Would that be 200 million years before today, or 200 million years before 1 January 1950, as in Before Present? --Trovatore (talk) 03:38, 3 February 2010 (UTC)

I suppose that's a joke (you can use one of these :) guys to indicate that it is - it's hard to pick up tone from a short post like this). If it's not, consider that when we throw out a nice round number like 200 mya or 145 mya (both clearly rounded to the nearest five million years), it doesn't really matter if there are a few dozon, or even a few dozen thousand years of ambiguity. Even so, it would be nice to have a standard. We have a small mya (unit) article, but it doesn't clear things up. Buddy431 (talk) 04:04, 3 February 2010 (UTC)

Man visiting museum: "How old is that dinosaur?" Guard:"65 million and 7 years old" Man:"How can you be so accurate?" Guard:"Well when I started here they told me it was 65 million years old, and that was 7 years ago." --Frumpo (talk) 11:55, 3 February 2010 (UTC)

To avoid confusion, I put my jokes in small text, a smiley face, and an edit summary saying that it's a joke. Since I started doing that, no one's taken my jokes seriously. A Quest For Knowledge (talk) 04:39, 3 February 2010 (UTC)

Thanks, AQFK, a useful cautionary tale. --Trovatore (talk) 04:42, 3 February 2010 (UTC)

Indeed, a difference of 0.000060 million years isn't relevant to the ages of the Jurassic, which Misplaced Pages gives as 199.6± 0.6 mya to 145.5± 4 mya, but it would be interesting to know if the formal definition resolves it. (Precise definition may even vary by usage.) Before Present#Usage of "BP" addresses some dispute over whether the term "BP" should be reserved for radiocarbon estimations. I would assume that a common baseline would be useful where stratification and radiocarbon dating methods overlap, but it would be good to hear from a geologist. 124.157.247.221 (talk) 04:42, 3 February 2010 (UTC)

Mya isn't really a formally defined, and tends to be discouraged in the professional literature in favor of BP and annum (though you still see mya a lot in popular science writing). Everyone professional, in my experience, bases BP at 1950 regardless of whether they mean radiocarbon years or calendar years. I've also seen the less common B2K (before 2000) crop up occasionally in recent years. I know the BP article talks about whether "BP" should always mean radiocarbon, but I've yet to meet a geologist who is actually in favor of that. Only people who live and die by radiocarbon seem to like that idea. Dragons flight (talk) 18:48, 3 February 2010 (UTC)

February 3

Stopping nuclear reactions with a jamming field

In the anime Gundam Seed, they have this device called a neutron jammer which stops fission reactions from taking place by jamming the flow of neutrons and preventing them from striking the nucleus of a fissionable atom. Is there anything like this in real life, and/or is it possible to make one? 192.12.88.10 (talk) 05:02, 3 February 2010 (UTC)

1. Almost certainly NO, and
   
2. Almost certainly NO--220.101.28.25 (talk) 05:35, 3 February 2010 (UTC)

You'd be better off trying to slow down the speed of neutrons (though sometimes this backfires as slow neutrons are vulnerable to neutron capture). John Riemann Soong (talk) 05:51, 3 February 2010 (UTC)

See Misplaced Pages Articles Slow neutron, Fission reactions and Physics.
ps. The answer is most likely a resounding NO to both questions, but I am not a Nuclear Physicist. Don't despair, a Physicist (or a close facsimile of one) will most likely be along to answer this question in some detail. It may be a bit late in the US, but our English volunteers will likely be up and about in a few hours. --220.101.28.25 (talk) 06:44, 3 February 2010 (UTC)

Anybody here recall a science fiction short story about psychics who were able to prevent nuclear weapons from detonating, and who were used when the USSR attempted to blackmail the US by threatening to detonate a couple of dozen bombs they had smuggled into various cities? (The psychics were able to sense the presence of the bombs and control them without initially knowing their precise location.) I seem to recall it as being by Heinlein, but it doesn't sound quite like his style. 124.157.247.221 (talk) 10:37, 3 February 2010 (UTC)

Indeed by Heinlein: "Project Nightmare" (1953). Deor (talk) 13:56, 3 February 2010 (UTC)

The conceit was also used by Larry Niven, in Protector (truly excellent story, by the way). Phthsspok's alliance discovers a way to suppress the fission trigger in fusion bombs and is able to make a good life for its breeders for a while. Then the rival alliance finds a way to set off a fusion bomb without fission, and kills all Phthsspok's descendants. That makes him a childless protector, which is where our story really starts. --Trovatore (talk) 21:24, 3 February 2010 (UTC)

I recall a story called (maybe) "Christmas Present" about psychic children who deactivate the "sparkly stuff" in ICBMs because it "makes grownups unhappy" and are discovered when they innocently teleport into an army base. Does someone remember more? Cuddlyable3 (talk) 14:06, 3 February 2010 (UTC)

The closest you get is that in the 1940s, one of the ways that was investigated as a means for preventing attacks by atomic bombs was to FIRE lots of neutrons at an incoming plane. The idea was that you could get the bomb to predetonate (fizzle), which isn't great but is better than a full explosion. The idea was abandoned pretty early on, though, because it's not that easy to shoot out a beam of neutrons like that, and it would be pretty trivial to shield the bomb from outside neutrons (and, in fact, the cores usually are pretty shielded anyway), and even then, the defense isn't much better than just trying to shoot down the plane normally. (And once you have rockets, that rules this out pretty completely.)

Did they try Tesla's "Teleforce Death Ray? Worked for Flash Gordon. Edison (talk) 14:59, 3 February 2010 (UTC)

But other than that... no. There's no way to stop a nuclear detonation from going off other than dispersing the core (e.g. blowing up the bomb before it really fires). Certainly no way to jam the neutrons before they hit the uranium/plutonium atoms. Inside the core of a bomb you have LOTS of plutonium/uranium atoms that suddenly are confronted by a HUGE burst of neutrons from the initiator. Even if there were some way to somehow manipulate the neutrons from a distance, the idea that you could somehow block enough of those to not start a chain reaction seems pretty impossible. --Mr.98 (talk) 13:39, 3 February 2010 (UTC)

Superman throws an atomic bomb into the Sun where it goes "Mummph" (Video). Cuddlyable3 (talk) 14:23, 3 February 2010 (UTC)

Well I'll guess you could inhibit an ongoing fission reaction by beaming in a super-dense flash of protons. But that would unavoidably destroy anything else remotely in this direction. 95.112.189.37 (talk) 21:14, 3 February 2010 (UTC)

I was just assuming that Duck and cover would be good enough. SteveBaker (talk) 17:12, 3 February 2010 (UTC)

Or 'kiss your ass goodbye'. Where are our resident Physicists? As said above I know its unlikely, but I'm very intererested in the why. --220.101.28.25 (talk) 20:25, 3 February 2010 (UTC)

I'm not sure you have a mechanism for inhibiting/slowing neutrons at a distance anyway (they are fairly non-reactive—anything you do that is going to interfere with neutrons is also going to do a lot more than just that), and, as noted, slow neutrons are worse in some ways that fast ones—they increase the U-235/Pu-239 cross-section (which seems counter-intuitive until you consider how the DeBroglie relation works with neutrons), which should be even worse for the first generation of fissions. I also think one easily underestimates how many neutrons we're talking about in a chain reaction... it's a lot, on the order of 2. Naturally you don't have to inhibit/block all of those with your magic neutron-blocker gun, but it isn't like you have your work cut out for you. I'm not a physicist, though. --Mr.98 (talk) 20:56, 3 February 2010 (UTC)

superacids that aren't corrosove?

"The carborane superacid H(CHB11Cl11), which is one million times stronger than sulfuric acid, is entirely non-corrosive" (from superacid). This makes me curious -- why should this be? Is it because carborate is a non-coordinating anion and not very soluble in water whereas chloride is weakly coordinating (e.g. it can form halohydrins) and water-soluble? John Riemann Soong (talk) 05:10, 3 February 2010 (UTC)

HCl is also noncoroding. However, H₂SO₄ contains a highly oxidized form of sulfur (S), and so will tend to be a good oxidizing agent, and thus oxidize (corode) metals. Being a strong acid, or even a super acid, has nothing to do with corrosiveness, the H+ ion will itself not protonate metals (what are you going to do, create metal anions? Possible, but not very likely with most metals). Any acid can catalyze a corrosion reaction in the presence of other oxidizers, but by itself acid has zero effect on metals. --Jayron32 15:54, 3 February 2010 (UTC)

That's totally bogus. Acids can corrode certain more reactive metals because the hydrogen is reduced from the H ion to H₂ gas. See for example the question about Magnesium and Hydrochloric acid a couple of days ago. I agree that that isn't enough for certain metals (like gold), in which case it doesn't matter how strong the acid is. However, I'm not sure where Mr. Soong is finding that the carborane superacid is non-corroding. I looked in both the carborane and Superacid article, and I didn't see that it ever said it's not corrosive. Buddy431 (talk) 16:24, 3 February 2010 (UTC)

Well, I'm not sure you'd call Mg + HCl a "corroding" reaction. Yeah, its chemically identical in that it involves the oxidation of a metal to its ionic form. But calling that reaction "corrosion" would be akin to calling the formation of rust: Fe + O₂ --> Fe₂O₃ a "combustion" reaction. Yeah, technically it is a combustion because it involves a reaction with oxygen. But if you made someone watch iron rust, and asked them if it were "combusting", they'd say "no way". The strength of the acid will affect the rate of corrosion reaction, but any metal that will not oxidize in the presence of H will not do so regardless of the source of the H. Take copper, for example. It is unreactive with acids, except for nitric acid, which it will readily dissolve in, but not because of the H (or rather, not because of the H alone). In this case, its the nitrate anion which acts as the oxidizing agent. In superacids like carborane, there's nothing present that will oxidize any metals that themselves would not already be oxidized by any acid. With the most of the so-called "strong acids", like sulfuric acid, nitric acid, and perchloric acid, the anion itself is a fairly strong oxidizing agent. So, if you want a strong acid which will not cause any oxidation because of its anion, you are limited to hydrochloric acid and or superacids like carborane. The issue is not that no acid ever oxidizes anything, its in finding acids where the non-acid-bit will not oxidize stuff. --Jayron32 18:53, 3 February 2010 (UTC)

If this is some technical chemical meaning of non-corrosive, that should probably be explained in the article. To me "totally non-corrosive" means "you can stick your hand in it, and it won't destroy your skin (though of course it could still poison you systemically)". --Trovatore (talk) 22:15, 3 February 2010 (UTC)

Wouldn't it be nice is we had a free source of information, like an encyclopedia, where terms were explained. Oh yeah, you're soaking in it. From the article corrosion, and I quote: "Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen.". You are bathed in oxygen right now, it makes up 20% of the atmosphere, and your skin is fine. And yet that oxygen is busy corroding all sorts of the world around you. The definition is right there as the first sentance of the Misplaced Pages, just in case you didn't know what corrosive meant. It has nothing to do with what it does to your skin. Lots of stuff is corrosive and harmless to living tissue, likewise lots of stuff is harmful to living tissue and noncorrosive. And then theirs some stuff thats both. And some stuff that is neither. --Jayron32 02:53, 4 February 2010 (UTC)

Fine, that's the chemist's meaning of the word corrosive. Ordinary usage is different, and the reader is not warned about it. Now granted, most people who don't understand chemistry are unlikely to have access to carborane superacid, but supposing they did (literally) get their hands on it, the outcome could be unhappy, no? As I say, this should probably be explained in the article. --Trovatore (talk) 07:24, 4 February 2010 (UTC)

No - it's NOT just the chemist's meaning. Is warm salty water corrosive? Well, our bodies are mostly made of the stuff - and swimming in it doesn't seem to harm us noticably. But immerse your car in warm salty water and you'll soon discover that it's corrosive as all hell to bodywork. Warm salty water is (by any reasonable definition) "corrosive". That's a pretty close fit to the definition given in our article and quoted by Jayron...and it's definitely the "day-to-day" meaning of the word. You just need to be aware of the context in which you are using it. Arguably, our article on this acid should be specific on how dangerous the stuff is to human skin just to be sure - but context matters. SteveBaker (talk) 12:04, 4 February 2010 (UTC)

Sorry, it's actually in the strong acid article. John Riemann Soong (talk) 18:30, 3 February 2010 (UTC)

Wal-Mart Orange Early Rise Drink Mix

I buy Wal-Mart's... ahem... Crystal Light knock-off "Orange Early Rise". I like it because it doesn't have any carbonation or caffeine, and only or has 5 calories per serving. I usually mix it in a jug (shaken, not stirred), put it in the freezer and then a few hours later, shake it into a slush. (Yum.)

Sometimes I forget to put it in the fridge before I leave work, and by the next morning, a white cloudy substance settles to the bottom. I'm just curious what it might be. I'm confident that it's not harmful, but I'm not sure I care to drink it, whatever it is. I e-mailed Wal-Mart Customer Service a few months ago, but never heard back. (However, I'm pretty sure they don't actually *make* the stuff. I think they just package it and sell it.) Ingredients and nutrition information are found within the link above.

Also, I think they've slightly modified the recipe in months past, because the "white stuff" used to be more granular and less soluble, and I used to mix it with hot water in a clear plastic mug, let the white stuff settle, and pour the concentrate off the top until I could simply rinse the "sediment" down the drain. Now it must be more ground up, though, because I don't even notice it unless it sits at room temperature for a few hours. It's rather "unsettling." Ha. Thanks much! Kingsfold (talk) 13:49, 3 February 2010 (UTC)

The ingredients list is at , and also probably on the side of the container. Among the ingedients are the following generally insoluble stuff: calcium carbonate, calcium phosphate, magnesium oxide, cellulose. The white stuff is probably a slurry of the above. Those substances are probably a very small percentage of the overall ingredients, but its probably enough to create a noticable precipitate at the bottom of the drink. Its all pretty harmless; I would be much more worried about substances like aspartame, which is used to sweeten the drink and is known to have some adverse effects in some people (see Phenylketonuria). --Jayron32 15:49, 3 February 2010 (UTC)

Err, though if you have PKU you probably already know that. It is tested for at birth these days. --Mr.98 (talk) 00:50, 4 February 2010 (UTC)

How long have they tested on newborns? If this is something they started in 1990, that advice would not apply to those of the age of 20 for example. Googlemeister (talk) 13:58, 4 February 2010 (UTC)

Different species named "E. coli"

When I first began biology several years ago, I thought that "E. coli" was an amoeba species. What similarity is there between this species and Escherichia coli, that they have the same species name? I understand that they're not somehow related; I just don't understand why both were given the name "coli". Nyttend (talk) 13:51, 3 February 2010 (UTC)

I would assume it's because both are found in the colon (genitive coli means "of the colon" in Latin). Deor (talk) 14:25, 3 February 2010 (UTC)

I'll add that lots of particular words are used as specific names for a variety of organisms. Consider sativa/sativus ("cultivated") in Medicago sativa, Lactuca sativa, Cannabis sativa, Pastinaca sativa, Crocus sativus, and many more. Deor (talk) 15:12, 3 February 2010 (UTC)

I should add that 99 times out of 100, the abbreviation E. Coli is used to refer to the bacterial Escherichia coli, and not the ameobic species. E. Coli is one of the more studied strains of bacteria in history. It's used as a "protein factory" in all sorts of recombinant DNA technology, the K12 variety is the "model bacterium" for just about any bacterial study in the past 50 years. Entamoeba coli is an endemic amoebic parasite, but far less interesting, since its main purpose, according to our article, is to be confused with more harmful Entamoeba strains. --Jayron32 15:29, 3 February 2010 (UTC)

My understanding of Binomial nomenclature is that every species is uniquely identified by its genus name and its specific name. Species of different genera may share a specific name, so confusion that may result from abbreviation of the genus name must be resolved by context. 124.157.247.221 (talk) 07:11, 4 February 2010 (UTC)

At what percentage alcohol does beer dehydrate rather than rehydrate?

I've read the articles about small beer and alcohol and seen related questions in the reference desk archive but didn't find what I was looking for.
At low levels of alcohol, the overall effect of beer is rehydrating (e.g. small beer) . At higher levels of alcohol the overall effect is dehydrating (I have researched this extensively but don't think it's OR and my results are unreliable).
Is it possible to say at what percentage-alcohol this boundary occurs?--Frumpo (talk) 15:24, 3 February 2010 (UTC)

I'm not sure its the percentage of alcohol in the drink as much as it is the Blood alcohol content. Broadly speaking, alcohol is a Diuretic in that it increases the rate at which the kidneys eliminate water from your body. That's why drinking tends to "dehydrate" you; the higher your BAC, the more your kidneys work to eliminate the excess alcohol, and in the process, also remove lots of water from your blood stream, which is what dehydrates you. If you consumer higher-alcohol containing beers at a slower pace, maintaining a low BAC all the time, the net effect would probably be hydrating. If you were to slam a whole bunch of lower-alcohol containing beers really fast, raising your BAC to a high level, you may end up with a net dehydrating effect.

Historically, in lots of cultures, alcoholic beverages (beer and/or wine) are often the predominant means to actually get hydrated, as the only other common options were milk (and many adults are Lactose intolerant) and water (which in the past, often contained nasty stuff like Cholera and Dysentery). So people drank either beer or wine or some other alcoholic beverage since the alcohol preserved both the caloric content (the grain and/or fruit) AND the water. And they weren't drunk all the time, they drank an appropriate amount. For many cultures, drinking till you got drunk is like eating until you puke; yeah its possible, but why? --Jayron32 15:40, 3 February 2010 (UTC)

I never really understood the sanitation aspect. Even hard liquor has a problem killing germs, so I can't really believe that beer and wine help clean the water at all. —Preceding unsigned comment added by 67.243.7.245 (talk) 16:11, 3 February 2010 (UTC)

Beer is boiled as part of the brewing process, I don't know about the rest. Nanonic (talk) 16:21, 3 February 2010 (UTC)

(ec) It's not just the alcohol content that's important. Remember that in brewing beer, the wort is boiled for an extended period of time — the beer can't go bad if it doesn't have any living pathogens in the bottle or cask. Similarly, distilled spirits are obviously raised to high temperature during their manufacture, and they have a high enough alcohol content to kill (or at least inhibit the growth of) nearly all human pathogens. Wine, meanwhile, has a higher alcohol content that beer and so is at least somewhat inhibitory to the growth of pathogens; the fermentation process also consumes many of the sugars which pathogens could use as a food source. The tannins (particularly in red wines, but present in all barrel-aged wine) are naturally antimicrobial as well. Nevertheless, spoilage remains a potential problem in winemaking, and in recent decades preservatives such as sulfur dioxide and potassium sorbate are often employed. TenOfAllTrades(talk) 16:33, 3 February 2010 (UTC)

I don't think there is a clear answer to this question. According to this article, "roughly every extra 10 grams of alcohol results in an extra 100 cc urine excretion". With ethanol's density of 0.789 g/ml, this would be equivalent to 7.89% alcohol. However ethanol undergoes zero order kinetics. The duration of action of the ethanol is highly dependent on the quantity consumed, more so than the concentration. More original research is required. Axl ¤ 10:12, 4 February 2010 (UTC)

Where do I sign up? 87.81.230.195 (talk) 11:30, 4 February 2010 (UTC)

Thanks everyone. That's very interesting. --Frumpo (talk) 18:14, 4 February 2010 (UTC)

Putting a very small satellite into orbit in space

1) If you wanted to put a small ball-bearing that weighed 1g into LEO, how big would the rocket have to be? 2) If you wanted to fire a bullet into LEO, how big or long would the gun have to be? 3) Is it correct that that some modern artillery shells have electronics in them? 4) Why cannot satellites be minaturised down to the size of a matchbox? 84.13.53.3 (talk) 16:37, 3 February 2010 (UTC)

I don't know about (1) or (2) but Saddam Hussein tried to build a Space gun capable of putting a payload into orbit. Our article covers some of the details. Some artillery shells can steer themselves in mid-flight to correct for the wind, etc - others have fancy fuzes - both require some electronics. Satellites can be made fairly small - if they don't have to do anything. But if you want to use the satellite for communications or photography or something useful like that then you're going to need solar panels, batteries, antennae and other bits and pieces - and the size soon adds up. But you could launch a really small object if you had a reason to. You should read Miniaturized satellite for more information about some really tiny satellites that have actually been launched. Occasionally, schools and universities have managed to get this kind of microsatellite launched for free alongside a commercial launch of some kind. Those launchers sometimes carry ballast to even out the weight of an unevenly balanced payload - and sometimes, they'd be just as happy to launch your science project as they'd be to send up a lump of lead. SteveBaker (talk) 17:10, 3 February 2010 (UTC)

(edit conflict) 1) and 2) see Gerald Bull and related articles 3) yes: M712 Copperhead among others 4) you might find cubesat interesting -- Finlay McWalter • Talk 17:20, 3 February 2010 (UTC)

I was typing this while others were replying so may cover same areas.
Re question #2, Project HARP may provide some answers.
#3 Yes, some 'modern' artillery shells definitely have electronics in them, in fact since WW2, so early 1940's or over 65 years. See Proximity fuse as an example. In fact these early electronics used Vacuum tubes!
#4. Perhaps the largest part of most satellites is the solar panels used to power them, about which there are size limitations. They have to be a certain minimum size to power the electronics. Some other parts, such as RF waveguides and dishes, have a certain minimum size by virtue of the laws of physics they operate with. Getting rid of heatThermal management can be a factor so heat sinks and radiators also place limits on minimum size. Any optical instruments ie telescopes have some similar constraints, thought they have certainly got better & smaller with technological improvements. Possibly the most important reason is many satellites require attitude control systems (ie rocket motors) for orientation and 'station keeping' ie, geostationary orbit. That is to keep it pointing where it needs to (for ground comms/control etc), and to keep it in orbit. Satellite life is AFAIK largely determined by the life of its 'thrusters', which relies on the amount of fuel carried. For a single use satellite, it could be made very small, but a literal matchbox size would seem to be too small to be of any use. Question 1 I can't answer--220.101.28.25 (talk) 18:29, 3 February 2010 (UTC)

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