Wikipedia:Reference desk/Archives/Science/2011 May 3

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May 3

When did the stratosphere form?

I've read that there wasn't much ozone in the atmosphere until quite recently in Earth's geological history, I think in the period before about 500 million years ago. The stratosphere is the layer of the Earth's atmosphere above the troposphere where there is no convection, because the heat released when atomic oxygen combines with oxygen to form ozone, leads to temperature inversion.

It seems to me that without this formation of ozone, you can't have a stratosphere. So did the stratosphere form only half a billion years ago and where weather patterns before that time a lot different than they are now as a result? Count Iblis (talk) 01:47, 3 May 2011 (UTC)

I suspect that most models of the paleoatmosphere are insufficiently detailed to account for turbulence. As such, they model the entire atmospheric column as the stratosphere (obviously, a model which is only somewhat valid). It would be incredibly difficult to divine any sort of evidence about atmospheric stratification throughout geological history; at best, modern geology and geochemistry can make moderately accurate predictions about the chemical makeup of the ancient earth atmosphere. Such models implicitly assume "uniformity;" no serious geochemist would say that this is correct, but only that the available data can not provide any further detail. Here's some reading material: The photochemistry of the paleoatmosphere, which discusses ozone, and The prebiological paleoatmosphere: Stability and composition. I think I have a textbook back home that goes into more detail on atmospheric evolution, if you're interested; I want to say it's the Lissauer planetary science book, I can get the exact title. Nimur (talk) 01:57, 3 May 2011 (UTC)

See geological history of oxygen. The ozone layer probably formed, in part, as soon as oxygen levels became non-trivial, e.g. ~1.5 billion years ago, though the initial ozone layer was probably proportionally less substantial than today. There is little evidence of ancient weather patterns, and essentially no evidence for or against stratification of the early atmosphere. However, one can argue from basic physics that if you remove the inversion layer, then convection would be expected to reach much greater altitudes, and as a result weather would undoubtedly be different. Exactly how it would be different is difficult to say. The effects would probably matter most for tropical regions and midlatitude thunderstorms, which are the places where we see deep convection limited by the tropopause today. Dragons flight (talk) 02:09, 3 May 2011 (UTC)

A good answer by Dragons flight. The formation (and destruction) of the ozone layer is extraordinarily complicated, but at its heart lies the Chapman model, which is a self-sustaining reaction whereby the sun's UV light breaks up molecular oxygen, which then recombines into ozone. Therefore, as soon as you have oxygen in the atmosphere in decent quantities (about 2 billion years ago, according to this figure), you have an ozone layer, and the heat from these reactions forms an inversion: voila! a stratosphere. It's possible that the stratospheric inversion was less intense up until 800 million years or so ago when oxygen REALLY got going, but it was almost certainly there.

However, now my interest is piqued: I can't see any reason that speculative modelling would be impossible (or even especially difficult, given today's inexpensive computing), and I'd like to see what happens if you remove the stratospheric inversion. Certainly jet stream structures would be different, probably similar to what I see in my Mars modeling work where the jet stream is much higher and much stronger. In addition, convection and thunderstorms would be different, at the very least in appearance (lacking that anvil top that all us weather weenies love to see), and possibly in strength; but exactly how different is really speculation coming from me.-RunningOnBrains^(talk) 13:33, 3 May 2011 (UTC)

Do you really do mars atmospheric modeling? If so, and if your interest is really piqued, then you are the right person to run some modeling and at least partially answer that question. If you do, please post your results on this page because my interest is also piqued (I promise not to complain about OR). Dauto (talk) 14:10, 3 May 2011 (UTC)

Unfortunately, I am a mere grad student (in the middle of writing my thesis, so OBVIOUSLY wikipedia is the best use of my time :P), and don't really have a good idea about the construction of atmospheric models, I mostly work with the output. I will say though, dynamically and on large scales, the mid-levels of the Martian atmosphere could easily be confused with the terrestrial atmosphere, but looking at a cross-section would show that the jet stream is much thicker vertically, as well as much faster (west-to-east wind speeds are up to 200 m/s in the strongest part of the jet). Any convective processes of course would look completely different (if they existed in my model, which they really don't due to low resolution [side note: convection isn't even dynamically resolved in most Earth models, they are handled by statistical parameterization]) due to Mars' lack of substantial water vapor. And, of course, all this should be taken with a grain of salt because this is purely based on a computer model, not observations.-RunningOnBrains^(talk) 17:31, 5 May 2011 (UTC)

Yes, this looks quite interesting. I had the feeling that something non-trivial would go on, particularly with the jet stream which would then influence the weather, but I'm not an expert in atmospheric physics. Count Iblis (talk) 22:20, 3 May 2011 (UTC)

Quantum of space

What is the quantum of space? The Planck length seems far too "big" for this... Leptictidium (mt) 05:29, 3 May 2011 (UTC)

I'm not sure that space is even quantized. There are physical limits to measurement (the Plank length article discusses this a bit), which are based on laws of physics, and not technological limitations; however that doesn't mean that space is strictly quantized. For one thing, quantized properties have quantum numbers, there is no "space" quantum number. --Jayron32 05:39, 3 May 2011 (UTC)

I'm an almost total ignoramus on the subject, but I'll always remember a friend saying that the paradox of Achilles and the tortoise suggests that space isn't infinitely divisible - if there were an infinite number of points between the competitors, Achilles would never catch up - so implying that space is quantized... As for the size of the quanta, there was a lay article last year suggesting that spacetime is actually grainier than the Planck length, which added support to the holographic theory of the universe...Adambrowne666 (talk) 07:40, 3 May 2011 (UTC)

Okay, suppose we play an Achilles and the Tortoise board game. You're the Tortoise, so you get twenty squares of advantage. We take turns simultanously, and each turn, I move my Achilles marker two squares, whereas you move your marker one square forward. I can't catch you, because by the time my marker would reach your marker, your marker has moved half as much, right? Well no, I will catch you in twenty turns and overtake you the turn after that, even though the game board is quantized. – b_jonas 08:24, 3 May 2011 (UTC)

Real numbers are not quantized. However an abstract number has no instrinsic dimension and may have more Significant figures that any real-world application can support. I'm not sure what happens if such numbers are expressed in prayers. Cuddlyable3 (talk) 10:50, 3 May 2011 (UTC)

I think you're both thinking about this wrong: Zeno's paradox is a false paradox, and ignores the existence of finite limits to an infinite series, which are a fundamental part of calculus.-RunningOnBrains^(talk) 13:48, 3 May 2011 (UTC)

...which says nothing about quantization of space. Cuddlyable3 (talk) 16:17, 3 May 2011 (UTC)

May I ask why you think the Planck length is far too big? Dauto (talk) 13:39, 3 May 2011 (UTC)

Second the above question. Indeed, if the current theories of the universe are even remotely correct, the Planck length is the absolute smallest quantum of space that even makes physical sense. Talking about smaller distances than the Planck length is like talking about speeds faster than the speed of light (not an exact analogy, but bear with me, I'm pre-coffee). -RunningOnBrains^(talk) 13:48, 3 May 2011 (UTC)

If the Planck length represents a "distance" than wouldn't the quantum of space be something that represents a "volume"? —Preceding unsigned comment added by 165.212.189.187 (talk) 17:41, 3 May 2011 (UTC)

Yes, it seems funny to me to say that the Planck length is too 'big'. The ratio of the Planck length to the size of an atom is comparable to the ratio of an atom to the size of the solar system (give or take a couple of orders of magnitude). How small would you like it to be? Looie496 (talk) 21:16, 3 May 2011 (UTC)

I think you're under the impression that, according to quantum mechanics, everything is made up of tiny discrete pieces in something like the way that a solid is made of atoms. That's not correct. A quantized perturbation of spacetime is called a graviton, but spacetime is not made of gravitons (at least, not in anything like the way that a solid is made of atoms), and the existence of gravitons doesn't imply that spacetime has any sort of discrete structure. Nor does the existence of a "Planck length" (obtained by dimensional analysis) imply anything about physics at that length scale, except that it's likely to be different in some way from large-scale physics. -- BenRG (talk) 21:49, 3 May 2011 (UTC)

You can also ask how much information you can store in a volume, see here. This depends on the energy in the volume, but that energy is limited because if you make that too much, you get a black hole. Then, what you see is that the maximum amount if information you can store in a volume is not proportional to the volume (if that were the case, you could use that to define a smallest length), rather you are led to the Holographic principle. Count Iblis (talk) 22:39, 3 May 2011 (UTC)

However the Planck mass or Planck energy is too big to be a quantum limit. Graeme Bartlett (talk) 02:16, 4 May 2011 (UTC)

I suggested the Planck length is too big because it is equivalent to the distance travelled by light in one Planck time. Surely the distance my guinea pig travels in one Planck time is even smaller than this. Leptictidium (mt) 12:19, 4 May 2011 (UTC)

May be the Planck time is too small... Dauto (talk) 15:07, 4 May 2011 (UTC)

Suppose you try to determine the position of the center of mass of a macroscopic object of mass m to an accuracy of r Planck lengths. Then, the uncertainty relation implies that the minimum uncertainty in momentum equals 1/(2 r) in Planck units (put hbar = c = G = 1, so that all physical quantities are dimensionless). So, the uncertainty in the kinetic energy of the object is (delta p)^2/(2M) = 1/(8 r^2 M).

To get back to conventional units, we can simply replace M by M/(planck mass) and multiply the result by the Planck energy. As long as hbar = c = G = 1, these quantities are equal to 1 anyway, so we're not changing anything. But since the resulting formula is then also dimensionally correct in SI units, we can insert the SI values for these quantities and get the correct result in conventional units.

The minimum possible uncertainty in energy in conventional units can then be written as E_planck^2/(8 m r^2 c^2) = 5.3 Joule/r^2 Kg/M. So, you get a huge macroscopic quantum uncertainty in the kinetic energy of the object if r is of order 1. In reality this is impossible, because due to interactions wit the environment, the quantum uncertainty of the energy of an object is always extremely small. Count Iblis (talk) 15:11, 4 May 2011 (UTC)

But any small distance could replace the Planck distance there. The Planck distance is only special in quantum gravity, and you haven't used any property of quantum gravity to derive your result.

Leptictidium's guinea pig objection is valid. Lorentz invariance implies that distances other than multiples of a base length must exist. Even simple rotational invariance implies that. So why not break Lorentz symmetry? Because there are insanely many different ways to do it and no experimental data to guide the choice. And because there's no reason (at the moment) to believe that it's necessary. -- BenRG (talk) 21:43, 4 May 2011 (UTC)

chemistry

why ethanol cannot be tested in the solid state —Preceding unsigned comment added by Babyreadbook (talk • contribs) 10:52, 3 May 2011 (UTC)

It can.

Maybe if you read your textbook and think about the chemical and question being asked, you will figure something out in the context of your class. DMacks (talk) 11:06, 3 May 2011 (UTC)

For fans of solid enthanol you may be interested in this: File:Ethanol-xtal-1976-3D-balls.png or the crystal form:monoclinic system. Or take a look at Ethanol in particular the infobox. Perhpas we need an article on solid ethanol and ethanol hydrate. Graeme Bartlett (talk) 02:13, 4 May 2011 (UTC)

chemistry

name the group of substances that conducted in the solid and liquid state. what are the mobile charges in these substances? name the type of substances which conducted in liquid and in solution but not in the solid state. what are the mobile charges present in this type of substances. could these substances also have charged particles in the solid state? If so, why are they not conducting? Is the meliting point you have named high or low and why is this so? what 2 types of substances contained no mobile charges, whether solid or liquid? what did you notice about their melting point and what does this say about the nature ( weak or strong ) of their intermolecular bonding? —Preceding unsigned comment added by Babyreadbook (talk • contribs) 11:00, 3 May 2011 (UTC)

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to 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 nearly as much as doing it yourself. Please attempt to solve the problem or answer the question 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. DMacks (talk) 11:02, 3 May 2011 (UTC)

Take a read of Electrical conductor, Electric current, Conductivity (electrolytic) and Ionic liquid. Graeme Bartlett (talk) 01:52, 4 May 2011 (UTC)

Something in a dog's ear

I just found this picture: [1] What happened to this poor dog? Slijk (talk) 14:18, 3 May 2011 (UTC)

Blech. It seems to be an open wound with numerous ticks and other parasites on it. If you Google Image search "dog ear tick" (not pleasant) you can find many similar images. --Mr.98 (talk) 14:28, 3 May 2011 (UTC)

Yes, ticks. Poor dog indeed; dogs can get Lyme disease just like humans. Acroterion (talk) 14:31, 3 May 2011 (UTC)

Water testing in New York City

I live in an apartment. Is it worth getting my drinking water tested? How much roughly would it cost? Should I spend the money on nutritious foods instead? 66.108.223.179 (talk) 17:20, 3 May 2011 (UTC)

You can get home drinking water testing kits for $30 or so. If you're worried about the water quality, the $30 is probably better spent there than on "nutritious foods," of which it will buy not that much. --Mr.98 (talk) 18:40, 3 May 2011 (UTC)

Do you have reason to believe there is a problem with your water? The water company will be required by law to do all sorts of testing. --Tango (talk) 20:42, 3 May 2011 (UTC)

You could also buy a simple pitcher-type water filter system for around the same $30. StuRat (talk) 23:59, 3 May 2011 (UTC)

As for water testing, you would likely have some indication of a problem, such as a bad taste or smell, yellow color, cloudiness, or floaters in the water, if there was a problem. Yes, there are invisible poisons, like arsenic, but those aren't likely to be in the municipal water supply. StuRat (talk) 00:02, 4 May 2011 (UTC)

Yes, I've got non-white water. I got the idea because Consumer Reports said that water should be tested every year (overkill I guess?) and that it'd help in choosing the kind of filter I buy. I've tried a $25 testing kit before but either it didn't test for many useful things, and I wasn't sure I did it correctly anyway. 66.108.223.179 (talk) 03:58, 4 May 2011 (UTC)

I assume you mean non-clear water. White water would also be a concern, unless it was from bubbles and quickly dissipated. StuRat (talk) 00:56, 7 May 2011 (UTC)

earth rotation question

Suppose some James Bond supervillan built a super-mega-ultra rocket that could produce an extremely high amount of thrust, like 10^20 N or something. This rocket was attached to the earth in such a manner that it would not move when fired (yeah I know not realistic at all) at the equator flat on the ground pointing straight west. If he fired the thing, would it speed up the rotation of the earth itself, or just cause the atmosphere of the earth to rotate faster since it's just propelling a massive amount of super fast exhaust gasses? Googlemeister (talk) 19:02, 3 May 2011 (UTC)

That depends on whether you mean point the rocket streight West or point the exaust streight West.190.56.112.203 (talk) 19:22, 3 May 2011 (UTC)

For purposes of argument, the nose would face west. Googlemeister (talk) 19:34, 3 May 2011 (UTC)

In that case, unless Ive become completely befuddled, then you couldn't possibly speed up earth's rotation Because you're heading in the wrong direction. The very best you might do is to slow it down, but that,I think, is a math problem that other people on Wiki might be able to help you with.190.56.17.111 (talk) 20:20, 3 May 2011 (UTC)

I don't think there would be a net effect. Ultimately, the particles coming out the back end of the would effect the earth just as much as the bolted-down rocket would. APL (talk) 20:48, 3 May 2011 (UTC)

If we bear in mind that the the bulk of force is acheived not by the exhaust particle acceleration but by the unequalised forces in the combustion chamber ( the thing about equal and opposite force) then it might be possible to have an effect on the earth's rotation if the rocket was powerful enough and if it were fixed far enough above the ground. Once again it comes down to math. I wish I could help.17.111Phalcor (talk) 21:12, 3 May 2011 (UTC)

Those forces should be identical. Forward pressure on the combustion chamber is the action, exhaust going backwards is the equal but opposite reaction.

Or maybe the exhaust is the action and the rocket is the reaction. Whichever. It's semantics. In most cases you can think about it either way and get the exact same answer. APL (talk) 01:15, 4 May 2011 (UTC)

Consider the angular momentum of the Earth and the atmosphere, the sum of the two is conserved. Count Iblis (talk) 21:40, 3 May 2011 (UTC)

It depends on whether the exhaust (and the angular momentum it carries) escapes from earth's gravity field or whether it's all just dissipated in the atmosphere. Even in the latter case, when no angular momentum is shed, you would get the earth spinning faster in one direction and the atmosphere in the other direction, at least for a while until friction puts everything back to its initial state. Essentially, you've built a large version of Heron's aeolipile. --Wrongfilter (talk) 22:07, 3 May 2011 (UTC)

One interesting thing to consider is that the rocket would just be attached to a single plate on the crust, so that plate would be moved relative to the rest of the Earth, pushing up against the next plate and also opening a gap behind it. So, you'd get volcanoes and earthquakes and mountain building. Perhaps next you'd get all the plates moving, by pushing one another. Then, eventually, friction with the molten portions of the mantle and core would cause them to start to turn, too, and, lastly, the solid inner core. StuRat (talk) 00:12, 4 May 2011 (UTC)

The typical geological force is on the scale of a few TeraNewtons per lineal meter. The force would not just be experienced at the plate edge, but would cause rupture of nearby faults and folding and thrusting lower down. Graeme Bartlett (talk) 01:40, 4 May 2011 (UTC)

shrimp genetics

after watching clips of deep ocean shrimps and other creatures living around the hydrothermal vents in the deep ocean, I couldn't help wondering how closely related they may be to their shallow water cousins. Studies of evolution make it clear that just because two species look similar doesn't mean that they are neccessarily closely related genetically. If their relative positions on the evolutionary ladder can be established, then that might be a pointer as to whether life first evolved in the deep cold/hot ocean or in the warm shallow waters. I imagine that since the origin of life has been a scientific preocupation for a long time now that some body is working on this. However I can't find anything on the net about it. Maybe I just didn't put the correct magic words together. does anybody know anything about that.190.149.154.185 (talk) 20:07, 3 May 2011 (UTC)

How would that knowledge help find out where life first evolved? Dauto (talk) 21:00, 3 May 2011 (UTC)

The basic logic behind the question is reasonable, but it would only make sense to apply it to single-celled life forms such as Archaea, not to shrimps, which are certainly arthropods. Looie496 (talk) 21:07, 3 May 2011 (UTC)

(ECs) It's an interesting idea leading to a wide range of topics, but as a first pass I'd suggest that since, according to what evidence we have, life seems to have originated at least 3,800 million years ago (see Abiogenesis), but the earliest known arthropods (of which shrimps are evolved descendents) date back only to around 570mya (see also Timeline of evolution), the roots of shrimp genetics are unlikely to have much relevance to how and where the origin of life played out some 3,000 million years earlier.

While convergent evolution can indeed cause superficially deceptive resemblances, and hence mistaken estimates of close relatedness, between actually more distantly related organisms, I'm pretty sure that by now biologists would have realised if hydrothermal vent "shrimps" were not shrimps nor even arthropods at all, but something completely different that have only come to closely resemble them after aeons of separate development, which is what this scenario would require.

Incidentally, the notion of currently-existing species being on "different rungs of the evolutionary ladder" doesn't really accord with modern evolutionary theory: the "ladder" is a persistance of an early and unhelpful analogy that was discarded decades ago, just as the concept of "missing links" is a holdover from the even-longer superceded "great chain of being" concept.

If you have a few spare weeks, you might like to pursue the overall subject through the Evolutionary biology Portal (of which you may already have been aware). {The poster formerly known as 87.81.230.195} 90.201.110.208 (talk) 21:20, 3 May 2011 (UTC)

OP.154.185. I'm not suggesting that it would produce a diffinitive answer, but information comes in small increments, so it seems logical that if for example the arthropod of the deep ocean (definitely an arthropod as defined by it's body structure) could be linked with the shallow water cousins but happened to be an earlier form, then that would at least indicate migration from the depths to sunlit seas, or it might indicate the reverse. Just a small directional pointer.Phalcor (talk) 21:55, 3 May 2011 (UTC)

I would appreciate it anon 230.195--110.208 if you did not talk down to me citing archaic belief simply because I did not explain my concept in a way that you could understand.Phalcor (talk) 23:30, 3 May 2011 (UTC)

I apologise if I unintentionally came across as condescending, Phalcor. I was not trying to suggest that you actually subscribed to archaic beliefs; I was merely trying to flag up the fact that a term you used can be unhelpful when thinking about the complex topic of evolution, and to give related background which might have been of interest to yourself and/or others reading the Desk: being a former science textbook editor, I am perhaps too eager to counter apparent misconceptions before they take root. I was also led by your spelling and inconsistent capitalisation into a careless and doubtless mistaken assumption about your age and hence likely grasp of the history of evolutionary thought. Unfortunately my own default writing style tends towards the formal and archaic, and I fear may sometimes give a misleading impression. {The poster formerly known as 87.81.230.195} 90.201.110.208 (talk) 00:15, 4 May 2011 (UTC)

Nope doesn't mislead me one bit.Phalcor (talk) 04:20, 4 May 2011 (UTC)

This article, and the links and introduction therein, might put you on the track to the info you're searching for. It uses phylogenetics to look at the relationships of different deep water vent shrimps, not between normal shrimp and vent shrimp. [2] Aaadddaaammm (talk) 13:28, 4 May 2011 (UTC)

pressure vs temperature of water in a closed system

It is my understanding that for water in a closed system, pressure will rise in linear proportion to a rise in temperature. 1. I would like a scientific reference formula or law stating this and the name of the law. All I have found previously are gas laws. eg> P1/T1 = P2/T2 at constant Volume for liquids

2. I would like a statement, formula or law clearing showing that the volume of the closed system of water does not affect the outcome. eg> In a 100 gallon system of water at 50 psi and 70F, if water were heated to 210F (3x temp increase) then the water pressure in the closed system would be (3 x 50 psi)= 150 psi? V = 100 gallon; P1 = 50psi; T1 = 70F; T2 = 210F therefore P2 = 50 psi x 210F / 70F = 150 psi.

Then, if another system were V = 500 gallon of water, and the same P1, T1, T2 then P2 would also calculate to 150 psi ?

Do I need to use absolute temperatures when working with these equations for liquids?

Thanks a lot.207.34.120.71 (talk) 21:09, 3 May 2011 (UTC)

Why are you using gas laws for water in a liquid state. In general that won't work at all. How are you applying the pressure and where are you measuring? To lowest order, the pressure in a water column is proportional to the amount of liquid above it (plus any externally applied pressure), and is independent of temperature except near the boiling point. Even then, provided you give the water room to expand (roughly 4% at 100 C), the water will still be water under atmospheric pressure until you reach temperatures high enough to boil it away. If you use a truly closed system, and give the water no room to expand at all (e.g. no compensating air space), then you'll find the heated water exerts 100s of atmospheres of pressure on the system, and consequently will rupture most rigid vessels. Dragons flight (talk) 21:38, 3 May 2011 (UTC)

Although, if you tried that in the real world, there would be some air in the container (or at least some space that would fill with water vapour) and that would expand far far more than the water and the cause a pressure increase. The expansion of the water would be insignificant. --Tango (talk) 23:38, 3 May 2011 (UTC)

Actually I doubt that. Since water is almost incompressible, the volume of the air would remain constant if the water didn't expand, so the pressure would go up only by the proportion that the absolute temperature went up. The water wanting to expand, when it can't, should cause a much larger pressure increase than that (again, because of the near-incompressibility of liquid water). --Trovatore (talk) 23:48, 3 May 2011 (UTC)

I realize this is a gas law, however one of my questions was if there were a specific associated law for liquids. It seems it should also apply in this scenario however I am looking for a clear reference. The scenario is a 100 gallon closed tank (vessel) of water with a pressure gauge reading at the top of the tank vs a 500 gallon vessel with a pressure gauge reading also at the top of the tank. Water columns above the tanks are not applicable, and neither system is open to atmospheric pressure. There is negligable air in the system - just incompressable water. The pressure being applied is through the increase in temperature such as from an immersion heater sealed in the tanks. —Preceding unsigned comment added by 207.34.120.71 (talk) 00:48, 5 May 2011 (UTC)

There is no general law. It depends on the compressibility and density of the liquid as a function of temperature and pressure, which varies from liquid to liquid. To lowest order, you can estimate the pressure change of a rigidly constrained fluid as:

$\Delta P\approx {1 \over \beta (T_{final})}{\Delta V \over V}\approx {1 \over \beta (T_{final})}({\rho (T_{initial}) \over {\rho (T_{final})}}-1)$

Where $\beta$ is the compressibility and ρ is the density.

Given the properties of water, e.g. 4.3% expansion from 0C to 100 C and compressibility at 100 C of ~49 / Mbar, the constraining pressure would need to be ~850 atmospheres (13000 psi). Unless your vessels are really overengineered, they won't be that rigid. They will bulge and/or rupture as you heat them. More typically though, people would rarely ever do this. If you devote 10% of the volume of your vessel to air, then the water can easily expand while heated, and you'll find the increase in pressure for temperatures just below 100 C is only about 1 atmosphere (16 psi). Heating (or freezing) water in a confined volume with no mechanisms to compensate for the associated changes in density is generally stupid and will often destroy your container unless it is specifically designed for that. Dragons flight (talk) 02:22, 5 May 2011 (UTC)

Noiseless helicopters

Some media report that the men how were sent to kill Osama came with a noiseless helicopter. Do such helicopters really exist and if so, why isn't that technology used on all helicopters? 77.3.163.234 (talk) 21:19, 3 May 2011 (UTC)

Nutshell answer: pure fiction. Note the many stories about the guy who liveblogged the raid, largely due to obvious helicopter noise. There are means of making helicopters less noisy (usually by reducing the turbulence between the main and tail rotors), and they either have performance or complexity trade-offs. — Lomn 21:33, 3 May 2011 (UTC)

I agree with Lomn. There are ways of reducing the noise emitted by a helicopter rotor and the helicopter engines, but these ways incur a reduction in the performance of the helicopter - weight-carrying capability, hovering altitude, speed and acceleration. In a combat application, performance is the most important consideration. Reducing noise to zero in flight is not possible. Dolphin (t) 23:47, 3 May 2011 (UTC)

I would modify that to say that "Reducing noise to zero in flight is not possible in fast aircraft/helicopters". You could make a slow enough plane, such as a glider, virtually silent. Helicopters have an additional noise problem, though, that they can't really make the blades move slowly enough to be silent, unless you're talking about a tiny, unmanned device. StuRat (talk) 06:49, 6 May 2011 (UTC)

We had several blackhawks flying around Melbourne for several days after the airshow, just a few months ago. They're actually not THAT loud, I mean they are loud but not loud like a jet. A jet is LOUD even if it is kilometers away, we used to hear them from inside our house about 5km away when they'd buzz the Albert Park Grand Prix, but you could hardly hear the blackhawks, especially if they were up wind, from barely a kilometer away. If they were coming in low and hot, which they no doubt would have been, and they came from upwind, who ever was in the compound would have had a couple of minutes at best between realizing what was happening and the SEALS coming down the ropes. EDITL: Cruising speed of 173 mph / 278 km/h, just btw, so maybe not even a couple of minutes.. Vespine (talk) 01:04, 4 May 2011 (UTC)

In a populated urban environment, hearing one or more large helicopters approaching doesn't mean those helicopters are coming to visit your house! It is likely that in this case the residents didn't know they had visitors until they became aware the helicopters were hovering overhead and people were fast-roping down to the ground. Dolphin (t) 03:30, 4 May 2011 (UTC)

And the proximity to the Pakistani military academy probably meant that helicopters were landing there on a regular basis. StuRat (talk) 06:43, 6 May 2011 (UTC)

Is 3-bromopyruvate toxic in humans? What is the status of human clinical trials?

[3] says that Bromopyruvic acid is toxic in rabbits, but [4] says it's nontoxic (in mice?) (1) Does anyone know whether it is toxic in humans? and (2) What is the status of human clinical trials for this chemotherapy? There is more information at [5] and [6]. Thank you. 171.66.146.107 (talk) 23:27, 3 May 2011 (UTC)

Anything used for chemotherapy is going to be toxic. The claim for bromopyruvic acid is that there is a dosage level where it is much more toxic to some types of tumor cells than to healthy cells. As far as I can tell there have not yet been any clinical trials. Looie496 (talk) 00:39, 4 May 2011 (UTC)

(1) Maybe. (2) Apparently less toxic and/or more patentable is "a new glycolytic inhibitor 3-bromo-2-oxopropionate-1-propyl ester (3-BrOP) ... a cell permeable ester of 3-bromopyruvate ... readily hydrolyzed by cellular esterase to release 3-BrPA, which is known to potently inhibit glycolysis"[7] and it is in clinical trials.[8] 99.39.5.103 (talk) 16:22, 4 May 2011 (UTC)