Wikipedia:Reference desk/Archives/Science/2008 July 3

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July 3

House water pressure from flow rate?

Can I determine the pressure of my water lines just from the flow rate and the physical dimensions of the tubing? Thanks.

I measured 2.1 GPM through a 1/2" copper tube.

--jcmaco (talk) 01:35, 3 July 2008 (UTC)

You may be able to get an approximation (e.g. water will flow through a hole at a rate determined by pressure based on its pressure coefficient) but in the case of water lines, you don't have any way to account for friction or restrictions upstream. When the water isn't flowing, your water pressure is independent of restrictions or friction that would affect the flow.

I recently measured my pressure after installing a reverse osmosis water filter in my kitchen. The manufacturer provided a table showing how much water would be drainable out of the storage tank for various water pressures. I drained 1.8 gallons out of a 4 gallon tank (meaning that my water pressure was sufficient to push 1.8 gallons into the tank), which equated to a fairly low pressure of 40 psi. =Axlq 05:43, 3 July 2008 (UTC)

Not unless you could work out the resistance of the pipes to water flow. A much easier way to get your pressure would be to use a manometer.if you cant get hold of a mercury manometer, one could be made with a long length of garden hose with a transparent bit at the open end. Having connected the other end to your tap, you climb up a ladder holding the transparent end. When the water stops flowing out the end, the pressures are equal and you measure the height of the tube above the ground. Since pressure is height times density, you know the pressure on your system. —Preceding unsigned comment added by 79.76.137.118 (talk) 02:45, 6 July 2008 (UTC)

Tell diffrence

If man and woman are berried in same grave how can u tell the diffrence after 1000 years/ —Preceding unsigned comment added by 79.76.174.168 (talk) 01:51, 3 July 2008 (UTC)

Human skeleton#Sex-based differences. PrimeHunter (talk) 02:02, 3 July 2008 (UTC)

I'd expect the boys to be blue-berried. :-) StuRat (talk) 03:38, 3 July 2008 (UTC)

But blueberries are "false berries". Should that be taken into account? The questioner really should have specified which kinds of berries are to be used. I feel that strawberries would do nothing more than stain the bones a little red. Red currants are highly acidic. Use enough of them and you might make skeletal identification difficult. -- kainaw™ 05:13, 6 July 2008 (UTC)

Skin color of ancient Egyptians

So I've come across the debate of whether ancient Egyptians were black, white or something in-between. It seems that neither side has conclusive proof. My question is whether there are any accounts by travelers about the skin color of the country they had visited? If there are, then why is the debate still going on? —Preceding unsigned comment added by 24.7.54.224 (talk) 02:50, 3 July 2008 (UTC)

Mostly "white", or what essentially is the ethnic group we now call Arabs, I believe. Ancient Egypt consisted of Lower Egypt, in the North, and Upper Egypt, in the South, which were later united. South of that was Nubia and the kingdom of Kush, which, I believe were populated, then, as now, by "blacks". Since there was some interchange of populations, I'd expect some "blacks" to have been in ancient Egypt, especially Upper Egypt, as well. StuRat (talk) 03:27, 3 July 2008 (UTC)

As for evidence, there were many surviving color paintings in Egyptian tombs, so there's no need to resort to 2nd or third-hand accounts. Here's one that shows a nice racial blend: [1]. Forgive me if I break into a round of Ebony and Ivory while viewing it. :-) StuRat (talk) 03:31, 3 July 2008 (UTC)

Some people get confused about this because Cleopatra was white, but she had only four great-grandparents and all of them were of European descent. In general, you'd expect the skin shade of ancient Egyptian people to be about the same as that of peoples from around the world at the same latitudes, which would probably count as "somewhere in-between" on OP's proposed scale. --arkuat (talk) 03:44, 3 July 2008 (UTC)

It boggles my mind how anyone can have only four great-grandparents. Having eight should be more typical, no? Thank you for your replies, StuRat and Arkuat, but if what you said is correct, I don't understand why the debate still goes on. —Preceding unsigned comment added by 24.7.54.224 (talk) 05:02, 3 July 2008 (UTC)

Why the debate still goes on is perhaps a question better taken to the Humanities desk, but I think it has to do with the intellectual history of the African diaspora. Personally, I feel that it is important to recognize that people from all over Africa contributed to ancient Egyptian civilization, mostly for the simple reason that this is true.

As for having only four great-grandparents, that comes easy if your family culture encourages first-cousin marriage, or aunts marrying nephews, or uncles marrying nieces, or, as was expected of Egyptian royal families off and on since time immemorial, sisters marrying brothers. --arkuat (talk) 05:39, 3 July 2008 (UTC)

See pedigree collapse. Rmhermen (talk) 13:54, 3 July 2008 (UTC)

Pedigree of Don Carlos, illustrating pedigree collapse: grandparents (4) in yellow, great-grandparents (4) in blue

You may also be interested in Serious inbreeding among European Royals, which features several with four great-grandparents. - Nunh-huh 03:08, 4 July 2008 (UTC)

Good thing they didn't have Christmas then, talk about getting ripped off for presents! Franamax (talk) 19:55, 3 July 2008 (UTC)

We have an article on this debate: Race of ancient Egyptians. Rmhermen (talk) 13:54, 3 July 2008 (UTC)

"How" is quite simple: her grandparents on her father's side were siblings, and her grandfather on her mother's side was the brother of her paternal grandparents. The family tree at Cleopatra#Ancestry shows a remarkable degree of inbreeding. --Carnildo (talk) 22:02, 3 July 2008 (UTC)

The current majority in Egypt are arabs I believe, but they weren't the original inhabitants of Egypt when talking about ancient Egypt. I believe the copts are survivors of the original inhabitants of ancient Egypt. ScienceApe (talk) 17:26, 3 July 2008 (UTC)

That's true. At that time the Arabs were still mostly on the peninsula. The simplest way to think about it in todays terms is imagine Egypt and Sudan as one, sometimes two, kingdoms that keep taking eachother over. Depending on which group is dominating when, sometimes the pharaoh looks roughly like a black Sudanese and sometimes he looks like a Coptic Egyptian. There's obviously been a lot of intermixing with the Arabs but if you go back that's always been common by the sea, what with the Helens and Philistines and whatnot. -LambaJan (talk) 16:55, 6 July 2008 (UTC)

The Arab expansion has been mostly cultural, not genetic. It brought a new religion and often a new class of rulers, but not a massive population shift. The vast majority of Egyptian population remained of ancient stock, and has by now thoroughly absorbed many population groups, including Greeks, Jews, Romans, Arabs and Turks. One point of confusion may be that for most mediterranean people, skin colour is very much influenced by lifestyle. If they stay indoors, they remain pasty white. If they spend a lot of time in the sun, they get a very dark tan. I'm not officially mediterranean (well, who knows what exactly my ancestors did for fun ;-), but I have a set of passport photos taken 4 weeks apart. On the one I look like an unhealthy Englishman, on the other like a Southern Indian. The difference is two weeks of beach volleyball in June in Greece. --Stephan Schulz (talk) 17:52, 6 July 2008 (UTC)

hypoglycemia vs hypertriglycerides

what is the relationship of sugar to triglycerides? is it normal to have hypoglycemia with high triglycerides? —Preceding unsigned comment added by Docbenjie (talk • contribs) 05:54, 3 July 2008 (UTC)

Well, firstly hypoglycaemia is not normal. Secondly, hypoglycaemia (lack of glucose) is not affected by the level of triglycerides (which are fats). It's true that fat can be used as an energy source when glucose has been used up but that does not affect hypoglycaemia itself. That's just my knowledge though, if this affects you medically you should see a doctor. — CycloneNimrod ^talk?_contribs? 11:53, 3 July 2008 (UTC)

Hyperglycaemia (high sugar), seen in poor diabetic control, is associated with higher triglyceride levels. Not sure direct link, rather via common factor of hyperinsulinaemia (raised insulin levels in those who are insulin resistant due to obesity)... for a quick synopsis, see the PubMed abstract of: Reaven GM, Javorski WC, Reaven E (1975). "Diabetic hypertriglyceridemia". Am. J. Med. Sci. 269 (3): 382–9. PMID 168773.{{cite journal}}: CS1 maint: multiple names: authors list (link)David Ruben ^Talk 13:28, 3 July 2008 (UTC)

Cyclone: Hypoglycemia is not normal, but it's also not really abnormal, if that makes sense. Your body is constantly operating to maintain homeostasis, but sometimes one parameter or other shifts too much and your blood sugar drops. It's abnormal the same way dehydration is abnormal: it's an abnormal state of the body that can occur transiently to otherwise healthy people. Sometimes folks who exercise to hard without carb loading or people who eat an especailly carb heavy meal end up experiencing attacks of hypoglycemia. See Hypoglycemia#Causes and Reactive hypoglycemia --Shaggorama (talk) 07:13, 4 July 2008 (UTC)

Why don't spaceships turn into blackholes

According to Einstein, as a spaceship goes faster and faster towards the speed of light, the mass of the spaceship gets larger and larger while the lenght of the spaceship gets shorter and shorter.

So why don't spaceships turn into blackholes? 122.107.135.140 (talk) 12:17, 3 July 2008 (UTC)

Interesting question... I've never thought about it. I think it's just a matter of perspective, though - the spaceship gets denser from the point of view of a "stationary" observer, but it's density remains constant from its own point of view, and that's the reference frame you need to work in to tell if it's going to collapse into a black hole. --Tango (talk) 12:23, 3 July 2008 (UTC)

The question assumes you could accelerate the spaceship to a meaningful fraction of the spead of light, but as its mass increases, so does the force needed to accelerate further. Using the Lorentz transformation a ship at 99% the spead of light has a Mass 7 times that before and a length one seventh. Tango is correct that onboard every seems as normal, but to an outside observer indeed the density (M/V) would seem to be 7 / (1/7) = 49 times as great, which for any reasonable size ship is not going to have any real gravitational effect. 99.99% of c gets us to outside observer measured denisty x5000 and 99.9999%c to 500,000 density; so still not even in our thought experiments getting anywhere close to a density that might cause us problems. Schwarzschild radius indicates one would need to compress the Earth's 6,371km radius into just 9mm radius to become a black hole; that's a compression of over 700million !

See also Gravitational singularity#Curvature, about our assumptions about measurments of weight and distance need to be rethought.

Finally see Micro black hole#Creation of micro black holes for the effort to smash just a few atoms together (accelerator of 1000 light years) so I think we're safe from any fast spaceship ! David Ruben ^Talk 13:19, 3 July 2008 (UTC)

There is no physical limit on how close to the speed of light you can get. It may not be physically possible even under the most extreme assumptions to do it, but we can still discuss what would happen (as you can probably tell, I'm a mathematician, not a physicist!). So, if I got in a spaceship and travelled past the Earth at such an enormous that I observed the Earth's mass and dimensions to be such that it ought to collapse into a black hole, what would I see? The Earth obviously doesn't actually collapse, from the point of view of someone on Earth, but what would I see? I've been thinking about this, and I just don't know. --Tango (talk) 13:40, 4 July 2008 (UTC)

What, you think you might see the Earth collapse, even though it doesn't? No, that's not going to happen. Relativity isn't that relative. Gravitation is controlled by the stress-energy tensor, which is a frame-invariant quantity.

That's not to say that velocity is never relevant at all. The invariant mass of a complex system involving multiple bodies that are not at rest with respect to one another does depend on their relative velocities. I can imagine something like, say, a system of two sets of rods approaching each other very fast, both in checkerboard patterns so that they slide past each other. The invariant mass of this system would depend on the speed at which that happened, and maybe if you made that speed high enough you could get the system to undergo gravitational collapse in principle. --Trovatore (talk) 17:32, 5 July 2008 (UTC)

Oh, or here's another way of putting it: Suppose you fly your ship fast enough, and close enough to the Earth, that the Schwarzchild radius for the invariant mass of the combined system (Earth+spaceship) envelops both the Earth and your ship. Then, perhaps, the combined system collapses, both you and the Earth, and both you and observers on Earth agree this happens, though they may not agree on why. There are some possible gotchas here, not sure whether the Schwarzchild solution is still a solution for a system this asymmetrical, but it's at least sort of plausible. But note that the rest mass of your ship is a key ingredient. If your ship is just a massless, energyless, metaphysical point of view flying past, there is no speed at all that would cause the Earth to collapse, either as it observes it or as you do. --Trovatore (talk) 18:05, 5 July 2008 (UTC)

The rest mass doesn't change. Only the relative mass changes. The matter that makes up the ship doesn't increase, nor does it become more dense. In order for a black hole to form, you need to mash a large mass into a very dense form. Like collapsing Mount Everest into something smaller than a human cell. ScienceApe (talk) 17:20, 3 July 2008 (UTC)

Also, the situation described sounds an awful lot like a situation where you'd need quantum gravity. -RunningOnBrains 22:59, 3 July 2008 (UTC)

Our article on mass in general relativity answers this question. It says "Can an object move so fast that it turns into a black hole? No. An object that is not a black hole in its rest frame will not be a black hole in any other frame ...". There is also a link to this page in the Usenet Physics FAQ. Gandalf61 (talk) 14:55, 4 July 2008 (UTC)

Thanks Gandalf61 for pointing to that answer. I also not the later Q&A re heated atoms possibly having more mass because thay have kinetic energy when heated. David Ruben ^Talk 20:53, 4 July 2008 (UTC)

Wheat allergies

Hi. I'm curious about wheat allergies as someone I know has one. Could it be that such a person would have a worse reaction from eating a "whole wheat" product (say pasta) than a regular one? --Dweller (talk) 13:42, 3 July 2008 (UTC)

Wikipedia cannot, does not, and will not provide medical advice. That said, you may want to read our Wheat allergy article, a more medical website, or consult a physician. Plasticup ^T/C 13:57, 3 July 2008 (UTC)

I'm not looking for medical advice, nor do I need to consult a physician as there's nothing wrong with me. I'm just curious. But thanks for the articles - I'll read them. --Dweller (talk) 14:24, 3 July 2008 (UTC)

The first of those articles does mention whole wheat, but the reference comes in an incomprehensible paragraph. The second article does not mention whole wheat. --Dweller (talk) 14:29, 3 July 2008 (UTC)

Everything I look at merely lists foods to be avoided, with refined wheat and whole-wheat considered to be the same. It could be that the difference in allergic reaction, if any, is not significant enough to be mentioned. Fribbler (talk) 14:37, 3 July 2008 (UTC)

Thanks. --Dweller (talk) 14:47, 3 July 2008 (UTC)

Based on reading the wheat allergy article, it looks to me like, because there are many allergenic components in wheat, you get all of those components with whole wheat and less of them with processed wheat. The processing may remove some of the minor allergens (but seems to preserve the main one, gluten). A hypersensitive person could conceivably have a worse reaction if more allergens are present. ~Amatulić (talk) 17:43, 3 July 2008 (UTC)

Also, remember that allergies are funny things. People with a severe allergy can have a bad reaction to tiny amounts of allergen and past reactions are not necessarily indicative of future reactions. So the distinction between whole wheat and refined wheat products may be entirely irrelevant. 86.141.89.124 (talk) 23:39, 4 July 2008 (UTC)

botanical name

What is the botanical name of the tree that is supposed to go to sleep when the sun sets and rise up again with the sun? Its leaves droop down in the night and freshen up in the morning.

Shyam59.92.72.54 (talk) 14:47, 3 July 2008 (UTC)shyam

With heliotropism, flowers and leaves track the sun as it moves through the sky. At night they either default back to facing east or just some random orientation. -- MacAddct  1984 ^{(talk • contribs)} 16:31, 3 July 2008 (UTC)

There are several types of trees that do this. Albizia julibrissin is the one that came to mind first.--Eriastrum (talk) 23:19, 3 July 2008 (UTC)

I like the ones you touch and they fold, like Mimosa pudica. Then there's one with a folding name: Prayer plant. But they're not trees. Julia Rossi (talk) 09:56, 4 July 2008 (UTC)

Species with long luteal phase

I am interested in which species have a long luteal phase of the estrus cycle. So far I only know that dogs and elephants fall in that category. Any other species? Thanks in advance. Arisa. —Preceding unsigned comment added by 131.211.166.194 (talk) 15:05, 3 July 2008 (UTC)

After googling a bit, I gotta admit this information is difficult to find. I did confirm that elephants have the longest cycle. I thought maybe other large mammals like whales may also qualify, but I couldn't confirm that. ~Amatulić (talk) 21:59, 3 July 2008 (UTC)

Material acting like Maxwell's demon?

Hi all,

Is there anything theoretically impossible about a material, say some kind of not-yet-invented cloth made out of nanotubes, which only lets fast-moving molecules through? How about a material which only lets molecules through in one direction? I can't see anything wrong with the idea except that it may never be invented. But wouldn't such a material essentially act as Maxwell's demon and break the Second Law of Thermodynamics (allowing us to create order out of disorder)?

All the arguments against the demon seem to involve the energy that he must exert separating the molecules, or the energy that he adds observing them, or the lack of infinite memory to know where they all are (I've never really understood that one). This material, however, wouldn't need to "know" which molecules are fast any more than a coffee filter "knows" that water can pass through and larger particles can't. And likewise, like a filter, it wouldn't need to do any work to let the fast molecules through.

So is there anything theoretically wrong with this idea?

Thanks! Sam 16:51, 3 July 2008 (UTC)

I don't really see anything theoretically wrong, per se, with a membrane that would only allow things moving quickly to pass through. As I think about it more, theres plenty of those in existence...pretty much everything fits the criteria. Its just a matter of how you define fast. The penetration of cosmic rays through buildings and such is a good example. Unidirectional motion is also possible, but usually in cases like veins where you've got some kind of pressure being exerted and valves used to control flow.

A common error made when people look at the Second Law of Thermodynamics is they forget the caveat to that rule. You cannot create order out of disorder without adding energy. There is energy in the membrane. If it stops slow moving particles, then it is doing some kind of work from some energy source (mechanical, chemical or otherwise) to stop them. If we were to use a piece of paper as the membrane, its still doing that same work on a fast moving particle, but the fast moving particle has so much energy that it keeps going anyway and breaks the bonds or whatever. This seems a little convoluted, but I hope it helps. Lemme know if I should try again...EagleFalconn (talk) 17:14, 3 July 2008 (UTC)

This is an interesting question. Although I am certainly not the scientist that Maxwell was, nor do I claim to be anything close, I will give it a try. First, this is a thought experiment for a reason. We have several ideal parts of this system: the box, the particles, the wall, the evil-looking green demon, and an ideal separation from the rest of the universe. It is hard to imagine anything close to this level of ideality in a real world system. With that said, the second law of thermodynamics is built to work for ideal systems, too.

One comparison you draw is the difference between a coffee filter and a fast-molecule filter. This is a broken simile I think. A coffee filter distinguishes water from grounds based on size. Energy is a totally different beast. One of the facets of the uncertainty principle is that momentum and position cannot be measured simultaneously. This is because in the act of measuring, the particle is perturbed, changing the other property. In the same way, if a barrier were created such that only particles of a certain energy could pass through, it would strip the particles of that energy as it passed through the barrier, eliminating any gain in entropy. I say this carefully though, because if the particles being discussed were electrons, by using a tunnel barrier you could take advantage of the quantum tunnelling effect and allow particles of certain energy to pass through without such a loss in energy. The risk here is that tunnelling is itself a probabilistic process. ANY electron could conceivably tunnel without losing energy. Higher energy ones just have a larger probability of making the leap so to speak.

What all of these theories lack, however, is an impetus for separation. In your coffee filter example, water and beans are on the same side of the filter and gravity pushes the water through. Now imagine trying to operate the same system in a zero-g environment. That wouldn't really work. Sure all the grounds would stay on one side, but the water would be everywhere. In the same way, unless some gradient were created to move the particles in the right direction, equilibrium would still exist. If you started with all particles on one side and allowed them to move to the other via any of the previously mentioned methods without field, the particles could just as easily move back again, given a high energy. What you are talking about is some sort of thermodynamic diode or valve that requires no potential.

My last comment is this: great thinking. Diodes exist, spin valves exist, many things for separating particles of different properties exist. All need energy. Minimizing that energy is key. It is possible that Maxwell's demon may never exist, but something close to it (operating on the energy of room temperature, for example) would not violate the second law, and may well be very useful. Gjmulhol (talk) 17:18, 3 July 2008 (UTC)

Thanks for the two comments. In response to the argument about the "impetus for separation," I'm not sure that this is needed. (1) If we have a zero-g box with coffee and water on one side of a coffee filter, eventually there will be a mix on one side and pure water on the other, so some separation has occurred (even if not all the way), and (2) If it is a one-way filter (like I mentioned above), eventually each water molecule will have randomly gone to the other side and not been able to get back, thus completing the separation.

I think you're both probably right about the fact that it may be impossible to separate fast- and slow-moving molecules without slowing down the fast-moving ones -- making them rip through the filter, for instance. (I don't think, however, that a barrier has to do work on a slow-moving molecule to make it bounce off -- the molecule's energy would be maintained).

Does the energy that it seems that a molecule loses as it goes through the barrier have to be so much that the fast molecules that pass through it a turned into "slow" molecules? By which I mean, would it be theoretically possible for a barrier to stop all molecules with V < x, and when fast molecules (V > x) break through, their speed is still greater than x? If so, we're still creating a potential difference between the two sides of our box that could be used to generate work, right?

Thanks, Sam 17:45, 3 July 2008 (UTC)

Well, I think we need to distinguish between molecules and electrons here. I am not an expert in physical chemistry. I do have some training in solid state physics. When an electron impinges on a surface, it can do one of 3 things:

• bounce back
• tunnel through
• go over

By go over, I mean have enough energy that it is able to go through the barrier. If the barrier is an energetic one, which I think is what we are talking about here, it will sacrifice the energy used to overcome that barrier and fall to the lowest state available. If you were to erect a barrier of a specific height x (to use you example from before), then the only reason that the particle can pass is that it has enough energy to give. It is like buying a ticket, if you don't have the money, you don't get in. If you do have the money, you get it, but you leave the money.

I still stick with my p-n junction argument that I posted a few minutes ago farther down. I think that is the closest thing of a separating barrier. A solar cell is based on the exact principle described here, but you need that pesky addition of sun to provide some nominal amount of energy to cause current flow.

I honestly have no idea whether there is some corollary to molecular movement as I have described electron movement. Gjmulhol (talk) 23:28, 3 July 2008 (UTC)

Slightly different question, brought to mind from the comments above: Is a one-way filter alone theoretically plausible? If so, would this be a great way to produce usable energy out of un-ordered states? Say I strap a one-way filter to one side of a box, so that air can only go in. The pressure in the box can only increase. If I punch a hole in the other side and add a turbine, my one-way filter will create a stream of air, which could be used to generate electricity, right? Any theoretical objections to that one? Thanks again! — Sam 17:51, 3 July 2008 (UTC)

Well, other than being a perpetual motion machine... (The act of ordering states from unordered states requires energy. Pure and simple. Any instance when you find yourself suddenly getting lots of energy out without putting any energy in is a sure sign that something has gone wrong in your calculations.) --98.217.8.46 (talk) 18:26, 3 July 2008 (UTC)

The input energy in his example is from the random movement of particles in the air. I don't see any immediate flaws. Oh, and I like to think of your theoretical material as fish trap. Plasticup ^T/C 19:26, 3 July 2008 (UTC)

Probably the best example of something that seems to violate the second law is an optical isolator. But even a hypothetical perfect optical isolator doesn't do it, not that I really understand the explanation [2] Someguy1221 (talk) 19:37, 3 July 2008 (UTC)

One example of something similar is a solar cell. Although it does absorb energy, based on the p-n junction's built in potential, electrons flow one way and holes the other. This creates a current. It is a one-way system. Even when no light is on it, there is some small generated 'dark' current from heat effects. Like I said though, it is not a closed system and does require some sort of energy. Gjmulhol (talk) 23:16, 3 July 2008 (UTC)

(ec)Scale matters for this question. Newer research points out that the Second Law of Thermodynamics does not apply to nanoscale systems.[3] I read a few weeks ago that one of the most promising future ideas in nanotech is harnesing Brownian motion to power molecular machinery.-RunningOnBrains 23:18, 3 July 2008 (UTC)

I would be very interested to see the full text of that article. Much of the BBC coverage seems simplistic for a such bold claims. Do you have the DOI, author name, or date of the article? I know from personal experience that forces at the nanoscale level are much different than at even the micro level. For example, capillary action and surface tension are the dominant forces in any system with nanoscale features. I would guess (and remember I haven't yet read the article, so I don't know the details) that the Second Law of Thermodynamics is not being violated. There must be energy coming from somewhere (the shaking of the canister? heat from the room? potential energy of the charge on the bead? again, I don't even know what they measured). Do the researchers make such claims of violating the second law explicitly? If so, this paper really should have been in Nature or Science rather than PRL ;).

Much Brownian motion comes from heat. Motion cannot exist without energy. By harvesting the energy from Brownian motion, we will simply be absorbing heat. This could be done from phonons or diffusion current. Gjmulhol (talk) 23:36, 3 July 2008 (UTC)

The second law of thermodynamics has been put through every thought experiment anyone can think of. Have some faith in these scientists. Don't ask if your idea will work; ask why it won't. As for why it won't:

I don't see how a material that only lets fast-moving particles through can be used to break the second law of thermodynamics. Maxwell's demon requires it to only allow fast particles one way and only allow slow the other. I don't know if it's possible.

The one-way filter is impossible. In addition to breaking the second law, it wouldn't be time reversible. After writing the next part, I noticed it could be time reversible.

I don't know much about the optical isolator, but I'm going to guess that it either can't be made reflective (so entropy is gained from light turning to heat). It's time-reversible because switching the direction time runs would switch the direction of the magnetic field, causing the isolator to face the other direction, and if it can absorb light, it can also spontaneously emit it.

This part's not really related, but it's a pet peve of mine: Gjmulhol, the uncertainty principle is because of inaccuracies in measuring. It's possible to make multiple particles with the same quantum properties, and to measure different properties in different ones, thus bypassing the observer effect.

98.217.8.46 and Plasticup, this isn't about creating energy; it's about destroying entropy.

RunningOnBrains, they don't go into much detail so I'm going to say that it's A: talking about the fact that at a small scale, entropy has some chance of decreasing, but won't consistently, or B: wrong. Also, take a look at the Brownian ratchet, which is based on building up small scale chance decreases in entropy, and still doesn't work. — DanielLC 22:46, 4 July 2008 (UTC)

Shooting down the barrel of a tank

Kinda inspired by a previous question. Lets say you have a high caliber machine gun, and you shoot down the barrel of the main gun of a tank with full automatic fire. What would happen? Would the cannon be damaged? Could it still fire as if nothing happened? Would the bullets cause a "clog" eventually? ScienceApe (talk) 17:16, 3 July 2008 (UTC)

That depends on a couple of things: (a) your aim, and (b) the cannon bore size. You could probably fairly easily shoot a 50-caliber machine gun down the barrel of a 155mm howitzer cannon, without the bullets touching the cannon barrel.

Even if the bullets did touch the side of the barrel, they impact at a grazing angle and will likely not cause any more damage than a cannon projectile being shot through it.

If a cannon barrel is clogged, you wouldn't want to fire the cannon, or you risk rupturing the barrel. ~Amatulić (talk) 17:30, 3 July 2008 (UTC)

Well basically what I'm asking is if you took a 50 cal and fired down the barrel of the cannon of a tank. Would it damage it, and/or would it clog it? ScienceApe (talk) 18:48, 3 July 2008 (UTC)

If there was a shell loaded, you might be able to detonate the shell (cover your face if you're looking down the barrel). Otherwise, the bullets would strike the breech - likely they wouldn't damage it all that much, unless you hit the firing mechanism, but you could stick enough lead onto the breech to make it unusable to seat the shell. And yes, if you keep firing an infinite number of bullets, eventually you'll clog the barrel with hot lead. Franamax (talk) 19:39, 3 July 2008 (UTC)

Ah... I assumed your original question was about firing a gun through a tank barrel from the inside of the tank. You're asking about firing a gun into the muzzle? That could damage the breech if the cannon isn't loaded, not only in the way Franamax describes, but also in that some cannons use a laser to detonate the propellant, and you could damage the laser window. If the gun is loaded, you might hit the fuzing mechanism of the round, or even clog the barrel, which would get cleared out when the cannon is fired, possible with damage to the barrel. However, I doubt you would do serious damage to the barrel by firing into it due to the grazing angle the bullets make with the inner wall of the barrel. ~Amatulić (talk) 21:53, 3 July 2008 (UTC)

If you simply roll a rock down the barrel or pack some mud in it and induce the tank crew to fire through the barrel, that should cause the gun to explode , possibly killing the crew. This recommendation is from a friend who says this was a tactic used against German tanks in WW2 when it was infantry against armor with no antitank weapons. A tank without infantry support is not all that secure against infantry attack. Edison (talk) 14:11, 4 July 2008 (UTC)

Imagine that - Sarge hands you a rock and says "go fight that tank" :) Franamax (talk) 23:05, 5 July 2008 (UTC)

Strange skull

Hi guys, I was wondering if somebody could identify the animal this skull belongs (belonged :p) to:
It was found on the beach somewhere in northern Crete. It is around 5-6 cm in length.
http://img20.imageshack.us/img20/2782/scull1ad2.jpg
http://img20.imageshack.us/img20/4995/scull2gc4.jpg
http://img503.imageshack.us/img503/6638/scull3ft8.jpg
Thanx a lot!
PervyPirate (talk) 17:25, 3 July 2008 (UTC)

At first I thought it might be some sort of bird, but it looks like there are teeth in the front. A big rat, maybe? It doesn't look like what I'd expect for a fish. Great pictures, though. If someone can identify it, and Wikipedia has an article on it, please put that picture in the article. ~Amatulić (talk) 17:35, 3 July 2008 (UTC)

Was I the only person who saw those and immediately thought 'dragon'? :) At a guess, I'd say some sort of predatory eel... --Kurt Shaped Box (talk) 17:46, 3 July 2008 (UTC)

That was my first guess as well, since moray eels are quite common in that part of Greece, but a quick google image search proved me wrong... PervyPirate (talk) 17:54, 3 July 2008 (UTC)

Are you sure it's a skull? It looks to me like a pelvic bone. Compare the third image above with this of a seagulls pelvis: [4]. Fribbler (talk) 17:57, 3 July 2008 (UTC)

Wow! I would never have guessed! Thank you Fribbler (and everybody else)! However, since it's not a skull after all, I doubt the pics will be of any use in an article. PervyPirate (talk) 18:06, 3 July 2008 (UTC)

Why not? Bird anatomy in the skeletal section, or pelvis (currently an overly human-centric article) could benefit from one of those nice, clear pics! Fribbler (talk) 18:11, 3 July 2008 (UTC)

Fair enough. I will ask permission from the friend who made the pictures, upload them properly, and update the talk pages of the articles you mentioned. PervyPirate (talk) 22:12, 3 July 2008 (UTC)

Pelvis? Whoa. How utterly unexpected. Shades of three blind men and an elephant? ;) --Kurt Shaped Box (talk) 18:37, 3 July 2008 (UTC)

Or at least a few men who haven't spent much time around comparative anatomy courses... skulls are pretty distinctive, and even though I arrived to this question pretty late in the game it was clear that those pictures weren't of a skull. --98.217.8.46 (talk) 19:18, 5 July 2008 (UTC)

Great pictures by the way, you've got some skill, like that as a desktop background...(got any more?)87.102.86.73 (talk) 19:49, 3 July 2008 (UTC)

To be honest, these are not really my pics. But I'll pass the good words to the friend who made them. Cheers! PervyPirate (talk) 22:12, 3 July 2008 (UTC)

basic difference between stroke and depression?

Okay, first, let me assure you I'm not looking for a diagnosis. Rather, I have a question more about the basic differences in these two.

It seems in depression, some of the basic themes apply as to those in strokes. A person may have difficulty speaking, moving, etc.; becuase strokes apparently don't have to affect only one side of the body. And, that in severe enough depression, close to a nervous breakdown, such things can, in fact, stop, just like in a stroke.

Is it common for people to mistake the two? Or, to miss a stroke in a person who has severe depression? Becasue, if the person can't bring themselves to move, and suddenly can't move, how do you know the difference?

Also, has anyone ever tried stroke recovery methods for combatting depression? My guess is it wouldn't work, but a lot of those symptoms are seeming the same right now.

I'm sure things that confuse the common person (like myself) are very clear to someone who has spent 4 years in medical school, another 4 in residency :-)209.244.187.155 (talk) 18:25, 3 July 2008 (UTC)

They are totally different. Tennis elbow and amputation might both leave you with a sore arm, but they are not related in any way. A stroke is a physical disease and depression is a psychological one. Plasticup ^T/C 18:47, 3 July 2008 (UTC)

Depression does not cause paralysis! Jdrewitt (talk) 19:50, 3 July 2008 (UTC)

Perhaps you're confusing depression with a total nervous breakdown? They can prevent the body from functioning, but only because the central nervous system is so ovreloaded. It's not a clinical term per se, but a pshycological condition, in general, is a function of chemical imbalance, I believe, not like a stroke, where it is somply a blood clot blocking something. Also, during a nervous breakdown, cells don't die. (I'm putting it in very simple terms, but seening as you could be confused between physical and psychological conditions themselves, so I felt that might be helpful.)

I'm not sure that stroke therapy could help with a nervous breakdown, becasue the object of stroke therapy is to teach the brain to function again. (Again, making it very simple.) My guess is that it could help to some small degree, if the person views him or herself incapable of simple tasks (for instance, they had stopped speaking), and they need to be encouraged to do them...but that would only be part of the treatment.

I know this kind of goes off the OT, but...I'm struggling to understand the nature of the question, and I felt I had to try *something*. Somebody or his brother (talk) 01:08, 4 July 2008 (UTC)

One general way to think of it is that a stroke is neurological -- lack of oxygen to the brain -- whereas depression is psychological (very broad generalization that I realize treats chemical imbalances too lightly). As they are so different in nature, the treatment of one doesn't really apply to the other. One important difference between the two is that a stroke (also reffered to as a brain attack) is an emergency condition. If chronic depression is left untreated, over time the person may lose control of their lives and potentially kill themselves. If a stroke is left untreated for a matter of hours, the individual may suffer permanent nerve damage and die within days. --Shaggorama (talk) 06:59, 4 July 2008 (UTC)

There are several reasons why these two conditions should not be confused by a competent medical professional. Firstly the onset of the two conditions will be different. In the case of a stroke caused by a thrombus (as opposed to a cerebral bleed) there will be a fairly quick onset, varying from instantaneous to tens of minutes. Immobility caused by depression is likely to take weeks or months to develop, a gradual process that should be apparent to the person's family or friends. The presentation of the two conditions are quite different. Following a stroke the person will have variable paralysis and impairment of conciousness depending on the severity of the thrombus. There will be specific neurological signs present in a person who has suffered a stroke that will be absent in a person who has impaired movements caused by deep depression. In a person with incapacitating depression all their concious mental and physical bodily processes are inhibited but in a person who has suffered a stroke there will be some variability in the movements of the body, and their thought processes (those still working) will react at normal speed. The main difference will however show itself in the onset of the condition. It is very unlikely that 'stroke therapy' will assist someone suffering from a deep depression - or vice versa. Richard Avery (talk) 07:07, 4 July 2008 (UTC)

While trying to avoid giving actual medical advice, let me also add that a person who has suffered a stroke can lapse into depression - i.e.: person who suffers is too weak to get out of bed easily, or paralyzed for a short time with a transient ischemic attack, winds up becoming depressed about this and may begin to get more depressed, but the depression does not relate directly from the death of brain cells, but rather from the notion that said person is not able to function at their previous level. (So, to the untrained eye, it may *look* like they're related in that instance, when they're not. I shan't delve too much further, though, because it is possible that there is a medical concern on the Op'ers part, and that this is where the confusion lay.Somebody or his brother (talk) 22:02, 5 July 2008 (UTC)

Gnat ID

I'm trying to identify a Gnat that has a black abdomen which is clearly separated from the thorax (although this could be an illusion produced by a black intrail or its contents and a clear thorax) like that of an ant and extremely large red eyes and relatively short wings which is about a mm long.

The remarkable thing about this Gnat is its ability to hover and to precisely adjust its location to maintain a distance of about 3 to 6 inches from any object which comes close and to relocate itself to its original position when the object moves away in sync with the objects motion.

What species might this Gnat be? -- adaptron (talk) 19:57, 3 July 2008 (UTC)

Could be a fruitfly. Take a look at this [5].--Eriastrum (talk) 23:14, 3 July 2008 (UTC)

Yes, very close for the eyes, thorax also is orange but only a transparent tint. The legs are also clear. Wings, however, are much shorter. The hovering behavior is so controlled and precise its scary - as if being operated remotely in real time by a much bigger brain. :-) -- adaptron (talk) 23:31, 3 July 2008 (UTC)

...as a matter of fact here it is... Drosophila melanogaster. -- adaptron (talk) 23:33, 3 July 2008 (UTC)