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July 17

First law of Thermodynamics

Ive tried to calculate and got an answer for a seemingly simple problem yet I don't think it's correct. I have a cylindrical container with a radius of 0.05m which has a vertical frictionless piston of mass 10kg. Air is trapped inside. I want to know what the change in internal energy is when 300J of heat is transferred to the air causing te piston to move upwards by 0.2m. As this is a closed system, I'm assuming there's no mass flow and I'm quite confident that the change in heat energy is 300J so that leaves the change in work done. My initial guess was that this is 10kg x 0.2m but I don't think this is correct. Where an I going wrong? I'm sure that once I have the correct change in work done, I need too add this to the change in heat energy to get the change in internal energy. 82.132.249.136 (talk) 12:25, 17 July 2012 (UTC)

Because the air is doing work on the piston, the resulting change in its internal energy (without the heat) is negative. Meanwhile, check your units: mass times distance isn't energy. --Tardis (talk) 12:42, 17 July 2012 (UTC)

Thanks according to how I've interpreted what you've said, the answer should be -[(10x9.81)x0.1]+ 300. However, I still don't think this is correct. I think it may be to do with pressure but I'm not sure how to apply this. Thanks. 82.132.249.125 (talk) 15:18, 17 July 2012 (UTC)

I don't quite understand the question. Are you asking how much energy you need to add to the system in order to increase the heat energy of the air by 300J (which will be greater than 300J, due to some of the energy going to lifting the piston)? In which case, you were almost there, it's 300J+10kg*9.81m/s*0.2m. --Tango (talk) 20:40, 17 July 2012 (UTC)

Damselfly identification

I photographed a damselfly this morning in Liaoning Province, NE China Imgur Link. If someone can help me identify it, I will gladly add it to Commons and the related article (if one exists). I figure the white leggings should make for easy identification? Those are pretty unusual... The Masked Booby (talk) 15:28, 17 July 2012 (UTC)

There is a White-legged Damselfly (Platycnemis pennipes), already but it doesn't look like your beautiful capture. I think yours is more the Seriously White-legged Damselfly. Sorry I can't be more helpful. Richard Avery (talk) 15:49, 17 July 2012 (UTC)

Wow, based on the description that's definitely it! That article already has a few good photos but they might appreciate a clearer look at the namesake legs... Great job, Richard! The Masked Booby (talk) 21:51, 17 July 2012 (UTC)

I've gone ahead and added it to Commmons. Thanks again. The Masked Booby (talk) 01:11, 18 July 2012 (UTC)

Please check my maths

Hello. I've calculated the amount of energy spent by holding 9 kg in your arms for a minute. I calculated it as follows.

1. 9 kg * 9.8 (g) = 88.2 N.
2. 88.2 N = 88.2 W
3. 88.2 W = 88.2 J/s
4. 88.2 J/s = 5,292 J/min

But the result seems quite low to me. Am I getting it wrong somewhere? If so, where? Thanks. Leptictidium (mt) 15:34, 17 July 2012 (UTC)

You need to check the dimensions of energy. Holding a mass does not expend any energy. If you lifted the mass thru a certain height, you will have then added some potential energy to the mass. If this does not make it clear, imagine youself holding that 9kg for 1 hour. Your arms might then feel sore from having to maintain the force required, but force is not energy, and you'll still be breathing normally. Now, imagine yourself lifting 9 kg weights from the floor to a table top every second for an hour. Bet you can imagine yourself getting puffed out - heck you won't last an hour. That's because your muscles had to release some chemical energy, consuming oxygen to do so, and converting that chemical energy into mechanical energy to transfer as potential energy in the weights. Wickwack58.167.241.156 (talk) 15:47, 17 July 2012 (UTC)

Muscle usage is a strange duck, and analysis of it more rightly belongs with biology than "assume-a-spherical-cow" physics. While you're correct in that there is no additional energy imparted to the 9 kg mass by holding it in a fixed location, (and certainly a table or a mannequin will not expend any energy doing so), you're incorrect that holding something in your flexed arms doesn't expend any energy. If your muscles are in tension, you're expending energy to keep them that way, even if by a rough, entry-level-physics calculation you wouldn't be. The reason for this is that on a microscopic level your muscles have little bits that are constantly grabbing and releasing to maintain that tension, constantly burning chemical energy to do so. (Much like if you start and end with a mass at the same place on a table you don't impart any net energy to the mass, even if you expend much energy raising and lowering the mass repeatedly while the mass is temporarily hidden behind a curtain.) This is why it's often misleading to use muscle-based intuition to judge how much energy or force is required to do something. -- 71.217.5.199 (talk) 16:02, 17 July 2012 (UTC)

Well, yes, my original aim was to find out how many calories you burn by holding 9 kg for 1 minute.Leptictidium (mt) 16:34, 17 July 2012 (UTC)

Clue: the concept in question is isometric exercise. If you Google "isometric exercise calories" then you will find various numbers, but not much information on how they were obtained. I expect they were obtained empirically by measuring CO2 and H2O output from human subjects, since physics won't tell you the answer. As Wickwack said, step 2 is wrong and there's no way to make it right, since the two sides of the equation are related by an unknown function that describes how muscles work. --Heron (talk) 19:03, 17 July 2012 (UTC)

When googling as suggested by Heron, I found that the top sites returned are hardly definitive, but most confirm that isometics burn very little calories. While 71.217.5.199 is certainly correct in what he said, there's the matter of scale. Certainly just holding 9 kg, although making you muscles sore if you hold it long enough, will not alter your breathing rate one iota (try it and see!)- confirming that the additional energy consumed is just about negligible compared to the calories you burn anyway just by being alive, warm, and awake. Wickwack124.178.145.103 (talk) 02:46, 18 July 2012 (UTC)

The way the OP set out his question strongly suggests he's seeking to understand the physics and needs to understand the difference between force, power, and energy - round cow physics if you like, rather than trying to undertstand muscle efficiency and physiology. It's up to Leptictidium to come back to us and let us know which it is - then if he still needs some help, we can tailor it accordingly. Wickwack124.178.145.103 (talk) 02:46, 18 July 2012 (UTC)

Um the OP already came back and said "Well, yes, my original aim was to find out how many calories you burn by holding 9 kg for 1 minute" which suggests he's much more interested in the biological answer (not necessarily how the answer is derived) rather then trying to understand the physics. Nil Einne (talk) 14:31, 18 July 2012 (UTC)

If you say so. It's virtually identical to his original question - no new points in it. I think it neither confirms nor denies he has no understanding of the physics. It neither confirm nor denies he understands that muscles, being an imperfect machine, actually burn calories to exert a force, but those calories are very small in quantity and he wants to estimate them neverthless. Wickwack58.170.181.203 (talk) 15:32, 18 July 2012 (UTC)

What flower is this? (Seen in Chihuly Garden)

The poster of this photo on Flickr wants to know: what flower is it? (I've saved it as a .jpg file but don't know how to paste it here; advice welcome :-) -- Deborahjay (talk) 17:27, 17 July 2012 (UTC)

It looks to be an Eryngium, but not sure which species. Mikenorton (talk) 17:52, 17 July 2012 (UTC)

(edit conflict) It's a false purple thistle also known as "sea hollies", belonging to the genus Eryngium. That's likely to be an amethyst sea holly (Eryngium amethystinum), though like most cultivated ornamental plants that's difficult to tell as it could be a cultivar of another species.-- OBSIDIAN†SOUL 17:54, 17 July 2012 (UTC)

Satellites

In a stable orbit, acceleration remains tangent to velocity

If they are in orbit around Earth and are subject to its gravitational pull, why aren't they continuously accelerating at 9.81m/s²? Is there drag or a terminal velocity for satellites? Ankh.Morpork 21:09, 17 July 2012 (UTC)

Because in a stable orbit, the acceleration is always tangent to the velocity vector, so the magnitude of the velocity does not change. BigNate37_(T) 21:41, 17 July 2012 (UTC)

Great simulation! I forgot that a change in direction counts as an acceleration. Thanks. Ankh.Morpork 21:52, 17 July 2012 (UTC)

In a circular orbit, the acceleration is perpendicular to the velocity. —Tamfang (talk) 04:57, 18 July 2012 (UTC)

Well their velocity changes it's speed does not changeDja1979 (talk) 21:50, 17 July 2012 (UTC)

They accelerate at slightly less than 9.81m/s² because they are further away from the Earth, but they are constantly accelerating towards the Earth. They are moving sideways as well, though, which means they keep missing the Earth (the direction that is towards the Earth changes as they move, so gravity causes them to go in a circle). It's just like when you have a weight on a string and swing it around your head really fast. You're constantly pulling on the string, pulling the weight towards you, but if never hits you (until you stop spinning!). --Tango (talk) 21:51, 17 July 2012 (UTC)

Presumably the larger the diameter of the orbit, the faster a satellite travels if they all have similar orbital periods. Is this the case or can two satellites at different heights travel at the same speed, just the lower one has a quicker time of orbit? Ankh.Morpork 22:06, 17 July 2012 (UTC)

Intuitively, the further a satellite is from the mass it orbits, the weaker the force exerted by gravity. A weaker centrifugal force implies less centrifugal acceleration, so I would assert that velocity must also be lower to maintain the orbit. If I understood Kepler's Third Law better, I would explain the exact relationship between radius and speed of an orbit, but I don't and I can't. BigNate37_(T) 22:22, 17 July 2012 (UTC)

We have Orbital speed. It states low earth orbit satellites travel roughly 7-8km/s, the moon only travels 1km/s. Vespine (talk) 23:43, 17 July 2012 (UTC)

You are correct, objects in higher orbits move slower. Kepler's Third Law says that the square of the period is proportional to the cube of the semi-major axis, ie. $P^{2}\propto a^{3}\,$ where $P$ is the orbital period of the planet and $a$ is the semi-major axis of the orbit (for a circular orbit, that's just the radius). You might find it easier to think of it as $P\propto a^{\frac {3}{2}}\,$. Put another way, if you double the size of the orbit, you multiply the period by $2^{\frac {2}{3}}\approx 2.83$. --Tango (talk) 23:47, 17 July 2012 (UTC)

There's also the Newton's cannonball article, which describes how Issac Newton first determined that orbits are just objects falling in a circle (or eclipse). 62.56.63.195 (talk) 10:32, 19 July 2012 (UTC)

quaternary ammonium compounds

I recently read a study saying that 70% of all hospitals use quaternary ammonium compounds to clean the hospital beds. Personal experience in a hospital by myself has proven this to be correct. They use a dilute bleach solution to clean Most items in the Room except for the bed which they use a quandary ammonium compounds such as Lysol to clean. Why is this? My understanding is that quaternary ammonium compounds do not kill spores, such as Clostridium difficille or ringworm spores. Wouldn't it make sense to clean the bed with a product that kills such spores?--64.38.226.90 (talk) 21:16, 17 July 2012 (UTC)

Many disinfectants can cause skin irritation and are therefore not used when they are likely to come in contact with the patient's skin. Ankh.Morpork 21:32, 17 July 2012 (UTC)

why don't they just use the dilute bleach solution to clean the beds with?--64.38.226.81 (talk) 21:56, 17 July 2012 (UTC)

Bleach can cause metals to corrode, stainless steel can turn rusty with bleach as it contains chloride ion and an oxidiser. Graeme Bartlett (talk) 22:06, 18 July 2012 (UTC)

Is there a list of yeasts that infect Humans?

Is there a list of different types of yeast Human beings can become infected with Besides candida yeast? — Preceding unsigned comment added by 64.38.226.81 (talk) 21:55, 17 July 2012 (UTC)

You could start by reading Candida (fungus) and see where it leads you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:25, 17 July 2012 (UTC)

Or just scroll to the bottom and click on Category:Mycosis-related cutaneous conditions. 75.166.200.250 (talk) 03:24, 18 July 2012 (UTC)

The Candida article is rather incomplete though. I understand that Candida growing inside the eyeball in otherwise healthy people is almost always from "cutting their junk" with lemon juice before injecting. Closet addicts are always shocked when their ophthalmologist diagnoses the condition... --BozMo talk 06:50, 18 July 2012 (UTC)

citation needed --TammyMoet (talk) 08:32, 18 July 2012 (UTC)

The first half dozen turned up by google scholar [1] all look reasonable. "Candida endophthalmitis after intravenous drug abuse" is notable enough to be worth its own article if anyone can take time out from Linux articles to write it. --BozMo talk 17:07, 18 July 2012 (UTC)

July 18

were the apollo missions classified

if not, why not open source all the designs. — Preceding unsigned comment added by 84.3.160.86 (talk) 00:34, 18 July 2012 (UTC)

Seems to me this issue came up some years back at the Moon Hoax page, and some editors there discovered that the designs weren't necessary kept in perpetuity. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:34, 18 July 2012 (UTC)

Certainly some aspects of the Apollo missions were classified, but that's not the only reason why any particular aspect of the missions, like the designs, might not be made available to the public. Another reason might simply be that it isn't in their interet. Why would they make the designs available to the public? Vespine (talk) 01:38, 18 July 2012 (UTC)

Because it's the law?A8875 (talk) 01:51, 18 July 2012 (UTC)

There is an urban legend that the plans for the Saturn V rocket no longer exist. The paper copies were destroyed when they were no longer needed but they still exist on microfilm. As far as the other Apollo hardware, I don't know what happened to the blueprints. They might have been destroyed when they were no longer needed. Bubba73 ^{You talkin' to me?} 01:56, 18 July 2012 (UTC)

"Because it's the law"? The article linked seems to refer to copyright. Even if NASA was covered under this (which is by no means self-evident from the linked article), all it would amount to saying would be that if anyone got hold of the relevant details, it wouldn't be a breach of copyright to publish them - or presumably to use them to build your own Saturn rocket. How would this non-copyright status amount to an obligation to actually provide the details to anyone in the first place - assuming that they still have them? AndyTheGrump (talk) 02:14, 18 July 2012 (UTC)

Works by NASA are in the public domain, but that doesn't mean they need to go out of their way to make everything publicly available on the internet. No one has those kind of resources. -RunningOnBrains^(talk) 15:43, 18 July 2012 (UTC)

I don't know anything about the mechanical aspects, but I do know something about the electronics that have been used in the space program, and if they are typical, then there wouldn't be anything worth open-sourcing. NASA has been so conservative in its engineering that components were generally ten years out of date by the time a mission flew. Given how long it's been since the Saturn V missions, I shudder to think what you would see there. It would be like open-sourcing stone tools from the Neolithic. Looie496 (talk) 02:25, 18 July 2012 (UTC)

And following on from that, much of the hardware might simply no longer be available. Certainly the electronics, but I'd suspect much else besides. I don't think that there is much that is actually 'non-public-domain' in terms of the information you'd need to build a new 'Saturn equivalent' design from scratch - and it would probably be simpler than trying to reproduce the original technology exactly. I suspect that more modern technology would make a better system anyway: lighter/more powerful electronics, composite materials, and all the advances in CAD/CAM manufacturing would surely improve performance a little - though perhaps not a great deal, since basically a Saturn rocket before launch is mostly fuel and oxidiser by mass, and that won't change. AndyTheGrump (talk) 02:43, 18 July 2012 (UTC)

• Not saying directly whether or not the designs are or are not classified, but if they were, one could certainly understand why they would be, and why they would still be, and it has nothing to do with covering up a moon hoax. The Saturn family of rockets were designed for putting people into orbit, but it would take much modification to make them into a perfectly functional ICBM, capable of reaching any place on Earth. The U.S. government has a vested interest in keeping such information on the QT. --Jayron32 03:31, 18 July 2012 (UTC)

Are you saying the Apollo/Saturn plans are not open-sourced? Just my opinion, but I tend to believe if you sought out plans, you could obtain them. Plenty of people have built working replicas of the Apollo CM guidance computer, possibly the most sophisticated piece of equipment on the spacecraft. The computer plans are easily found online. ^{(see here)} The rest of the technology used on the spacecraft is far less advanced, and in the 21st century almost all of it is obsolete.    → Michael J Ⓣ Ⓒ Ⓜ 03:44, 18 July 2012 (UTC)

It was impossible to obtain some specifications of the Saturn V and related guidance systems at the time, and a few of those are probably still classified, but pretty much everything else was out in the open. You can certainly obtain blueprints which are very accurate but omit avionics -- that was one of NASA's most popular FOIA requests for years. You can obtain the Moon landing computer design and program, but not the launch avionics computer programs (digital and analog) for the Saturn V Instrument Unit's computers. The astronauts were often consulted as to how much of their private lives (i.e., medical and duty condition) would be shared with the press, and of course they all wanted pretty much everything out in the open, too. 75.166.200.250 (talk) 04:03, 18 July 2012 (UTC)

You can find source code from the Apollo missions here. -- BenRG (talk) 05:49, 18 July 2012 (UTC)

ITAR will make it complicated to gain access to the technical stuff which is not already available. Every drawing or schematic for hardware used in space is now ITAR restricted. Even giving the name and the type of plug used to connect Mars Science Laboratory parts is only allowed after checking with if it violates ITAR. The WWW is international and therefore putting the drawings onto the net will make you a target for homeland security.--Stone (talk) 10:09, 18 July 2012 (UTC)

The Apollo Guidance Computer is well-documented. Not just the source code listed above, but the whole system. People have built replicas. 209.131.76.183 (talk) 11:41, 18 July 2012 (UTC)

How does ITAR apply to the Apollo program? NASA is a civilian agency, not military.    → Michael J Ⓣ Ⓒ Ⓜ 11:59, 18 July 2012 (UTC)

ITAR is a list of things. Dual use items are on that list too. The classification of all material used in space as significant military equipment is written in the documents. It does not make sense but it is fact. Talk with people from Mars Science Laboratory is very annoying because at that time no TAA (Technical Assistance Agreement) was in place and therefore the only things presented were things already published or general knowledge. The point is different for US Citizens, but the rest of the world is not allowed to get access. --Stone (talk) 12:53, 18 July 2012 (UTC)

[2] is a little story within NASA about ITAR. --Stone (talk) 12:56, 18 July 2012 (UTC)

Was the technology classified? Yes, but not to a very high grade. A brief perusal of NASA Apollo documents shows that many of them have classification stamps on them: a CONFIDENTIAL description of the spacecraft from 1963; CONFIDENTIAL mission description from 1961; CONFIDENTIAL report of some kind from 1961; CONFIDENTIAL mission directive from 1961; CONFIDENTIAL study of moon landing modes from 1962; and so on. I haven't seen anything higher than CONFIDENTIAL, which is the lowest official ranking of classification you can have (it goes CONFIDENTIAL, SECRET, TOP SECRET, more or less; OFFICIAL USE ONLY is a rung below CONFIDENTIAL but is not really a legal classification category).

So that's pretty weak classification for mission-related things. The rocket technology itself was no doubt classified higher than that, because, as others have mentioned, it was (and is) dual-use technology, and because the US was, you know, engaged in a big Space Race with the ol' USSR. Mission details were likely CONFIDENTIAL just to avoid the possibility of sabotage, or giving away programmatic information on the US space effort. The low level of classification is meant to signal that even if they got out, it wouldn't be that big a deal; it also meant that the information could be widely shared within the NASA organization.

As for open-sourcing at the time, the reason you wouldn't do that is because the Cold War US model was "buy all the experts and give them gobs of resources," which gets rid of the need for open-sourcing. (Plus, this is rocket science. It's actually hard. Even when you do the "throw everything at it with the most brilliant people at your disposal" approach, your rockets still blow up on the launch pads half the time.) As to whether you could do it today, sure! In theory. But it takes a lot more to build a moon shot in theory than a bunch of people editing a Wiki. It's a Big Project, much harder in terms of technical accomplishment than, say, designing an atomic bomb or something like that. --Mr.98 (talk) 13:42, 18 July 2012 (UTC)

Pluto / Charon satellites

If one considers Pluto and Charon to be binary planets (rather than Charon being a satellite of Pluto), then how do the satellites Hydra, Nix, P4 and P5 relate to the double system? Do they orbit the same barycenter, or are they satellites of just one or both of the planets, or what? (Yes, I know what the IAU ruled in 2006; I simply disagree.)    → Michael J Ⓣ Ⓒ Ⓜ 07:34, 18 July 2012 (UTC)

They all appear to orbit it's barycenter. I don't think it would be possible to orbit just one or the other, and have it be a stable orbit, unless, perhaps, the orbit was in a Lagrange point (and, even then, it's technically orbiting both). StuRat (talk) 07:38, 18 July 2012 (UTC)

Contrary to popular belief, it is possible to have a stable orbit around just one member of a binary pair: see Binary star#Planets. --Carnildo (talk) 22:38, 18 July 2012 (UTC)

I can't see how this question would be any different for the orbit of all the planets about the Sun. It too is affected by the other planets, and wobbles for each one. The wobbles must all be added up and come to one rather complex wobble. Myles325a (talk) 07:47, 18 July 2012 (UTC)

True, but then every object in the universe could also be said to be wobbling due to in orbit about every other object. The difference is, in the case of Pluto and Charon, it's visually obvious that they are orbiting the barycenter. StuRat (talk) 07:50, 18 July 2012 (UTC)

Are the galaxies orbiting around anything, or are they flying away from wherever the Big Bang supposedly occurred? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:23, 18 July 2012 (UTC)

The Big Bang occurred everywhere. And Stu's statement is not usefully true, but only trivially. So yes, any galaxy is 'in orbit' around any other - but most of the orbits are wildly unstable! AlexTiefling (talk) 11:34, 18 July 2012 (UTC)

This is untrue, unless you consider a hyperbolic orbit to be a true orbit; beyond the Local Group, galaxies are not gravitationally bound. -RunningOnBrains^(talk) 15:40, 18 July 2012 (UTC)

The three body problem is notoriously complicated. To give a simple example, suppose Pluto had the Earth's Moon revolving around it in the opposite direction, and one of those little satellites tried to sneak past five meters from its surface. Would the rock still be orbiting the barycenter? Nope - it'd go ass over teakettle in some odd direction and probably never be heard from again. It can't be modelled simply, except in roughest approximation. Wnt (talk) 17:25, 18 July 2012 (UTC)

Note that Pluto and Charon don't have any close-in satellites orbiting the pair. I suspect this is because any such orbit would be unstable, again with the possible exception of an orbit at a Lagrange point. StuRat (talk) 20:47, 18 July 2012 (UTC)

The Pluto-Charon system doesn't have any stable Lagrange points. L1, L2 and L3 are always unstable and L4 and L5 are stable only when one object is more than about 25 times the mass of the other (see Lagrangian point#Stability). Pluto is only about 9 times the mass of Charon, so L4 and L5 aren't stable. (There might be some quasi-periodic orbits, but they would only be stable in the short-term.) --Tango (talk) 02:20, 19 July 2012 (UTC)

Creationist time line refuted by Neandertal DNA

Scientists figure that the last Neanderthals were about 26000 years ago. Creationists reckon that must have been less than 6000 because the world was created on 4004 BC. And they argue that the presence of Junk DNA in the human chromosome is the result of man's degeneracy over the interim time, as his sinful nature corrupts what was originally a perfect system in the Garden of Eden.

But they DO agree that there are no Neanderthals now, and that they must have died out thousands of years ago. I would thus argue that in that scenario, the DNA of preserved human bodies thousands of years old, Neanderthal or some other variant, should then show much less "corruption" by embedded viruses and so on. If the world is only 6000 years old, and our current DNA has been progressively corrupted over that time, then DNA from even two thousand years ago should show a much smaller degree of such corruption.

But I gather they don't. I am interested to see if there is any difference at all in such junk DNA effects between us and them, and if that difference can lead to a callibration of how different they were to us, and how long ago they died out. Myles325a (talk) 07:42, 18 July 2012 (UTC)

Yes. Please see PMID 21957644 75.166.200.250 (talk) 07:47, 18 July 2012 (UTC)

But radiocarbon dating seems like a much easier and more accurate way to accurately date those fossils. Of course, creationists will ignore that, but they can also ignore DNA evidence and all of geology, astrophysics, and every other branch of science that disproves their world view. StuRat (talk) 07:54, 18 July 2012 (UTC)

It's a simplification to say that all creationists, or even all young-earth creationists, believe the world began in 4004 BC. That's just the Ussher chronology. But StuRat is right: some beliefs can be reinforced by science (such as the intuition that humans and apes have something in common), some are intrinsically unprovable (such as Deism's model of God - which can arguably ignored as irrelevant, but not specifically disproved), and some (like Creationism) are held by their believers directly in the teeth of overwhelming scientific evidence to the contrary. Something as sophisticated as junk DNA analysis isn't on the radar for these people, because they treat rigorous scientific methods as intrinsically suspect. AlexTiefling (talk) 08:07, 18 July 2012 (UTC)

The creationists are not very good at expressing themselves, so they get too little credit. Their typical retort to such things is to say "Were you there?". When we apply the tools of natural science, we assume that the consistent timeline we see in our experiments, which seems consistent with our own, is the only timeline. That if we go back generation after generation, the clock on the wall matches the time people experienced, and the circumstances we live under are those which our examination of historical sites supports. It is, however, definitely true that human experience can misperceive the world, that the timeline as we recall it is not what the facts indicate. Can we rule out, with certainty, that over time there is not some systematic bias - that indeed, our past, as sentient consciousness, is in what we could call one parallel universe, and our future in another? Creationism involves a very deep rejection of the materialistic certainties (faith?) of the secular perspective, and it may not be one that is satisfactorily redressed merely by more facts showing the consistency of the natural science timeline. We can argue to the consistency, clear immediate usefulness, and tremendous beauty of the natural science perspective; but to argue that our perception of the world is truly, absolutely real and not at all a matter of imagination or misperception? That is beyond our kingdom. Wnt (talk) 12:22, 18 July 2012 (UTC)

Wnt's words seem to be a long way of stating that the rate of time could have changed without our knowing it because we don't know everything and cannot be certain there isn't some aspect of physics that we've missed or not yet discovered. As such, it is true in logic, but does not seem very likely, given the weight of evidence in all manner of science fields of study, from geology, study of dinosaurs, radio isotope dating, you name it. I have actually had Christian creationists and Islamic people state this same argument to me. Wickwack124.178.177.30 (talk) 13:30, 18 July 2012 (UTC)

Actually, that's not what I meant. What I mean is more that you could be sitting there, typing away at the computer, and the next moment you look up and out at an audience around some futuristic zoo enclosure neatly labelled: "Day In the Life of an Earthling: Reconstructing the Century of the Anthropocene Extinction". Or many, many other things, some, one can hope, guided by a perfect hand, and possessing a greater level of reality. Wnt (talk) 16:34, 18 July 2012 (UTC)

The logical argument that we cannot know that the world/universe, etc, is real orginated with ancient Greek philosophers, but is it anything more than a perceptive exercise in logic? Wickwack124.178.177.30 (talk) 13:30, 18 July 2012 (UTC)

Although I think creationists are foolish in being such, I don't see that neandertals having a goodly amount of junk DNA proves anything. A Creationist might argue that they were an abombination, extremely degenerate. Further, evidence is coming to light that so called junk DNA is not so much junk after all - recent issues of the magazine Scientific American have elucidated research into this aspect. Wickwack124.178.177.30 (talk) 13:39, 18 July 2012 (UTC)

Even with such evidence, I doubt it will change anything. When faced with the harsh reality that the natural world does not resemble the world described in the Bible, literal creationists will always rather assert that the world is wrong because the Bible is always right. They can not see what is because they're too caught up with what should be. Good luck with making them see that.-- OBSIDIAN†SOUL 17:40, 18 July 2012 (UTC)

Another line I've heard from creationists is that their god deliberately made the world with evidence that seemingly contradicts the Bible simply to test their faith. Once they take that position, no evidence will prove anything to them. HiLo48 (talk) 19:48, 18 July 2012 (UTC)

• I want everyone to memorize this aphorism. Right now. Commit this to memory: "You cannot reason someone out of a position they did not arrive at via reason." Learn it. Know it. Live it. It doesn't matter what evidence you present to the YEC crowd: They evaluate the evidence through the filter of their predetermined conclusion, so there's no sense in trying to talk them out of it. Its a lost cause. --Jayron32 20:07, 18 July 2012 (UTC)

I wonder why you think it's not worth the effort to try. 75.166.200.250 (talk) 22:50, 18 July 2012 (UTC)

Because the evidence is hardly hidden or arcane. If reality punched you in the face every day, and you refused to acknowledge it, what good is one more punch... --Jayron32 23:24, 18 July 2012 (UTC)

From their perspective, it is more hidden and arcane than scripture, because of peer pressure, the promise of life after death for believers, and similar. 75.166.200.250 (talk) 20:40, 19 July 2012 (UTC)

airlifting a diver to hospital

So i was in vanuatu scuba diving the other day, a group of islands only one of which has a hyperbaric chamber to treat sombody with the bends. How might a diver with the bends be moved with haste to the chamber, is airlifting possible since increased altitude would worsen his problem. Can the cabin pressure of conventional planes be maintained at 1 atmosphere, or perhaps airlift by helicopter where the helicopter stays close to sea level? 110.175.191.101 (talk) 12:37, 18 July 2012 (UTC)

For airframe cost reasons, aircraft are presurised to the equivalent of 2000 m (or a little above for older aircraft), ie 80% of sea level pressure (ref http://en.wikipedia.org/wiki/Cabin_pressurization#cite_note-1), this is beacuse it is a good safety margin below the altitude (~2500 - 3000 m) where some pasengers may experience discomfort with certain medical conditions. A helicopter is not necessary for low level flight - all types of powered aircraft are required to be above the same minimum height when not actually landing or taking off - typically 1000 feet, and may be higher in built-up areas. Perhaps pilots undergoing rescue can get authorisation to fly lower, but 1000 Ft /300 m altitude has 95% of sea level pressure and should have negligible additional medical risk. Airfarme structural safety means you will not find an aircraft that can maintain sea level presure. Wickwack124.178.177.30 (talk) 13:15, 18 July 2012 (UTC)

It's more like 98% at 1000 feet. And try flying at 1000 feet in Dubai. Or Shanghai or Manhattan. There's at least 18 things at 1000 feet to fly into in Dubai. Sagittarian Milky Way (talk) 21:47, 18 July 2012 (UTC)

If pressure is an issue for transporting ill passengers, it would be easier to transport a hyperbaric chamber. Ochson (talk) 14:39, 18 July 2012 (UTC)

"Helicopter transport necessitates the pilot maintaining altitude at < 500 feet. Fixed-wing transport should be limited to aircraft that can maintain cabin pressure at surface 1 atm (e.g., Lear Jet,...". -- Finlay McWalterჷTalk 15:14, 18 July 2012 (UTC)

I believe that the helicopters typically used to transport people to a hospital aren't normally pressurized at all. Thus, they can't fly very high. However, I seem to recall hearing about one rigged for mountain rescue, where low air pressure might cause the pilots to pass out, having a pressurized compartment for the crew, and 2 separate rescue nacelles which were independently pressurized, so the patient(s) in them can be slowly returned to sea level pressure. I'd think the same strategy could work, in reverse, for divers. However, this is likely to be cost prohibitive except in areas with lots of divers. Also, one disadvantage to this system is that medical personnel can't tend to the patient during the flight, but, if they are likely to die without it, it's worth that risk. StuRat (talk) 20:22, 18 July 2012 (UTC)

I grew up a short distance from Whipps Cross Hospital in London, which at the time had one of only two hyperbaric chambers in the country. There were fairly regular visits from RAF and RN air-sea rescue helicopters carrying customers for it. I'm fairly sure the Westland Whirlwind didn't have a pressurised cabin. Alansplodge (talk) 22:21, 18 July 2012 (UTC)

Circles, flares around sun in photography.

I'm not sure this is the right section for asking about it

In photography sometimes when the sun is around the corner, strange circles appear in the photography. Something like this you can see the bright behind the tree.

What are those? How are they generated?, (How can I shoot those?) 65.49.68.173 (talk) 14:43, 18 July 2012 (UTC)

Those are lens flares, caused by internal reflections within the camera lens. You can photograph them by taking pictures with very bright objects in or near the frame. That process is easier if you a camera where you look through the lens (such as an SLR camera or, I suppose, any digital camera with a viewscreen on the back) rather than through an independent viewfinder. Various lens filters can further enhance the effect. — Lomn 14:51, 18 July 2012 (UTC)

I'm not 100% sure, but perhaps Bokeh is related to this. Bus stop (talk) 14:59, 18 July 2012 (UTC)

Bokeh is not related to this. Lens flares are internal reflections of light which cause light to appear in front of foreground objects, bokeh is just differences in focal length; foreground objects will not be impacted. -RunningOnBrains^(talk) 15:34, 18 July 2012 (UTC)

Camera on a timer in 1850?

Coaz and the Tscharner brothers on the summit of Piz Bernina during the first ascent, 13 September 1850

I'm writing an article on Johann Coaz and am a little suspicious of a photo I've put in the article. This photo (right) purports to show Coaz and two others on the first ascent of Piz Bernina (according to its description in the Commons). Given that there was no one else around, could this photo have been taken on a timer with the technology available at the time (I'm hoping it could have been), or is it a shot from a different ascent that has been mislabelled? The rockiness of the summit could certainly be Piz Bernina. The source (naturfreunde-maiengruen.ch) is not very helpful at all... Ericoides (talk) 16:02, 18 July 2012 (UTC)

Here's a little history of the camera shutter for some background. This suggests that in 1850 the photographer would not have been using a shutter as we would recognise it, so also wouldn't be able to use a release timer. It seems that they would have come in about 1880. Having said that, I think that if the camera did have a shutter, the technology existed (Clockwork) to enable a delayed shutter release. However, looking at camera technology, this page tells us that Wet plate photography didn't come in until 1851. This photo (if it was taken in 1850) must, therefore, be a Daguerreotype. Here you can see the process involved in taking such a photo, with exposure times from 10 seconds to 30 minutes(!). A reasonably long exposure (maybe over 30 seconds or so) might be enough for the photographer to quickly skip round in front of the camera and arrange himself in an 'I've been here all along' pose. What do you think? - Cucumber Mike (talk) 16:15, 18 July 2012 (UTC)

An ingenious reply, thanks, but would there not be a trace of his movement on the image? Ericoides (talk) 16:31, 18 July 2012 (UTC)

At low sensibility film, there wouldn't be any traces. The sensitive material just register up a certain threshold. If the exposure time is several minutes, then things in the ball park of some seconds won't show up. Apparently, it was not unusual for photographers in the XIX century to portrait themselves: [[3]]. OsmanRF34 (talk) 16:36, 18 July 2012 (UTC)

OK, that sounds sensible, thanks. Two further questions: which one is Coaz, and which one took the photo? My hunch is that Coaz is on the right, looking at the camera, and the fleet-footed photographer is the man standing on the left (who might well also be Coaz). Ericoides (talk) 17:19, 18 July 2012 (UTC)

Looking more closely at the photo, the standing man and the man sitting on our left are holding things that look a little like posing stands. Could it be, therefore, that the man sitting on the right looking directly at the camera is the photographer? Also, you labelled the photo 'Coaz and the Tscharner brothers'; the two men who look most like brothers are the one standing and the one on the right (the potential photographer) - they seem to have similar facial features. If I've got that right, my bet for Coaz would be the man sitting on the left. Admittedly, I'm getting into rather serious guessing now! - Cucumber Mike (talk) 21:37, 18 July 2012 (UTC)

They are holding alpenstocks, the rather long version of the modern ice axe. Ericoides (talk) 05:51, 19 July 2012 (UTC)

Also we seem to be looking down on the summit. When was the helicopter invented? ;-) Alansplodge (talk) 22:16, 18 July 2012 (UTC)

It's an optical illusion. The camera is probably on a standard 5-foot-tall tripod, sitting on a nearly-level ridgeline, aimed slightly downward. --Carnildo (talk) 22:47, 18 July 2012 (UTC)

I have taken pinhole camera photos of myself and others, with exposures of over a minute, and it was quite possible to start the exposure, run to my place in the photo, then run back and stop the exposure. I would not care to run across the ice and rocks evident in the photo. How sure are you there was no 4th person present? If I carried a view camera on a tripod up a mountain, I would not think it much of an additional burden to also bring a remotely operated shutter, even though in those days exposure control was usually by removing the lenscap, counting or timing the exposure with a watch, then replacing the lenscap. A "Bulb" shutter exposure was done by squeezing a rubber bulb attached to a long, thin rubber hose, with a shutter which opened when the bulb was squeezed and closed when it was released. Such bulb-hose-shutter arrangements were in use by 1853: "The Photographic journal: Volume 83, books.google.com Royal Photographic Society of Great Britain, Photographic Society of London - 1853 - Snippet view: "The camera ran on castors, and its height was adjusted by attachment to a pair of tall steel rods, up and down which it slid, and could be fixed at any desired position. Fxposure was made by means of a rubber tube and bulb. The shutter ..."

The adding of a remotely operated shutter would have been a pretty obvious alternative to running back and forth on a slippery mountaintop. The photo as presented is too low res to look for evidence of a remote operated shutter. Photos by 1850 were made on paper negatives, and not just Daguerrotypes. Edison (talk) 19:51, 19 July 2012 (UTC)

I think we can be certain that if this is a photo of 13 September 1850 then no one else was present. All records of Piz Bernina's first ascent say it was by Coaz and the two Tscharner brothers. On such a prestigious first ascent we'd definitely know if there was a fourth person in the party. Ericoides (talk) 07:37, 20 July 2012 (UTC)

I think that the strange quality of the light on the rocks and the completely indistinct background of the sky point toward a very long exposure. Wnt (talk) 11:08, 20 July 2012 (UTC)

Noise reduction

Given a mainstream PC (with a mainstream microphone and mainstream loud speakers/headphones), can a program running on it actively cancel noise? I don't mean any noise reduction filter, that can be applied on a file on the computer, just reducing the environmental noise for the user. OsmanRF34 (talk) 17:48, 18 July 2012 (UTC)

Yes. Start by reading Noise-cancelling headphones. You can get them for a few quid on Amazon these days but the bottom line depends a bit on how white the noise is--BozMo talk 17:53, 18 July 2012 (UTC)

Read carefully: I said with mainstream headphones, not with noise-cancelling headphones. I want to know if a PC (with a mainstream microphone and mainstream loud speakers/headphones) can cancel noise, not if there are noise cancelling headphones at Amazon for a few quid. OsmanRF34 (talk) 18:06, 18 July 2012 (UTC)

Ok/ What software are you proposing to use? It is technically okay if you fix the distance between the microphone and headphones and resign yourself to it only working for wavelengths a lot longer than that (so say two octaves below middle C) but it would be a real faf to program versus the buy a cheap set of phones with a microphone inbuilt which does it better. I think the answer is probably "not with mainstream software". --BozMo talk 18:40, 18 July 2012 (UTC)

Wouldn't latency be a problem (amongst other things)? Even with ASIO, I'm just not sure PCs can achieve the latencies required for such purposes compared to dedicated hardware although I guess with highly predictable noise it may still work slightly. Note that both our article and [4] mention it only really works for low frequencies and placement of the mics are important. Nil Einne (talk) 19:08, 18 July 2012 (UTC)

This depends on the characteristics of the noise and the signal channel. If you are talking about reducing non-speech noise, try running the signal through a vocodec like Speex and see if that makes it more ineligible. If you can characterize the noise spectrally and the channel in more detail, then I can give you a better answer. 75.166.200.250 (talk) 20:22, 18 July 2012 (UTC)

I used to work on Lotus' ANC system for cars. At the time, late 80s, PCs were 286s and the like, and could not process in real time. For real time 6x4 cancellation we used a TMS chip, and could cancel up to about 200 Hz. The chances are you need a higher frequency limit than that but only a single channel system, with the same cancellation signal to each ear. As such I think that current PC probably has the grunt, but getting timely access to the audio circuitry might be tricky in a multitasking environment. If this is a research project, go for it, but my noise cancelling headphones cost about an hours pay, and they are GREAT. Greglocock (talk) 08:47, 19 July 2012 (UTC)

It's a DIY project. So far, maybe it needs a dedicated chip, to deal with the problems cited above, something like an arduino chip. OsmanRF34 (talk) 16:22, 19 July 2012 (UTC)

If there's an Arduino which can do audio DSP, I don't know about it. Think Raspberry Pi. 75.166.200.250 (talk) 06:44, 20 July 2012 (UTC)

Meowing bird sound in western Montana

In western Montana while camping next to the Clark Fork River I heard a bird that made a MRRREEEOOOW MRRREEEOOOW MRRREEEOOOW type sound. Any idea what it was? (It was not a cat. I know this.) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 17:54, 18 July 2012 (UTC)

A Google search for "meowing bird sound" leads immediately to the Gray Catbird. Our article contains a sound sample; you can see if it sounds like what you heard. Looie496 (talk) 18:06, 18 July 2012 (UTC)

...although a mockingbird can also do that. Looie496 (talk) 18:11, 18 July 2012 (UTC)

(edit conflict) They're also in YouTube and quite remarkably cat-like (see [5], [6], [7]). It could also be the related Mockingbirds and other mimids (see [8]).-- OBSIDIAN†SOUL 18:17, 18 July 2012 (UTC)

That's pretty obviously not it. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:03, 19 July 2012 (UTC)

Obviously. Details, man! How'd you know it was a bird? Did you see it? Was the sound angry-cat-like, angry-Ferrari-like, angry-boy-pretending-to-be-an-airplane-like? Fast? Loud? Soft? Repeated how many times? It could be anything from Yellow-headed Blackbirds (sounds like rusty hinges interspersed with plaintive nggrrraooows), any birds-of-prey (which though distinctive, can sound like an angry cat at lower pitches), other mimics like magpies (which like mockingbirds and catbirds can sound like anything they want to sound like), or even squirrels (which do meow like cats apparently, here's an angrier mrrao-ing one).-- OBSIDIAN†SOUL 04:25, 19 July 2012 (UTC)

Radio comedy live audience

I was in the audience of the recording of a BBC radio comedy the other day. Musing about it since I was wondering whether the left channel of audience noise was the audience's left or stage left (actor's left, audience's right)? 10.64.0.169 (talk) 18:55, 18 July 2012 (UTC)

Call the show's producer's office and ask for the sound stage technician. It might not be something they try to keep constant all the time. 75.166.200.250 (talk) 20:24, 18 July 2012 (UTC)

Ideally, since when you view it at home, you "become" the audience, then they should have the left channel be audience left. That way, if an actor looked to the left (or on radio, said "Hey, you on the left in the funny hat...") and asked somebody on the left side of the audience a question, the answer would seem to come from the correct place. However, in shows where there's no interaction with the audience, it wouldn't much matter. StuRat (talk) 20:39, 18 July 2012 (UTC)

The host often introduces people saying where they are seated ("On my left, we have XYZ, and on my right, we have ABC."). I would expect the stereo to be set up in such a way as those directions make sense (with the listener in the audience's position, I agree). --Tango (talk) 03:48, 19 July 2012 (UTC)

London Weather

My friend said she heard on the radio that the UK was doing something to the atmosphere, like sending dry ice up on weather balloons, to force the jet stream to move so there would be "good" weather for the London Olympics. Is this true? 5.48.60.180 (talk) 23:07, 18 July 2012 (UTC)

Dry ice wouldn't move the jet stream, but, what it could do is seed clouds to make it rain. Obviously they don't want rain at the Olympics, therefore they would do this some distance away, so that clouds headed for the Olympic venues would be all "rained out" by the time they arrived. StuRat (talk) 23:10, 18 July 2012 (UTC)

Correct. Please see Weather modification#Storm prevention. 75.166.200.250 (talk) 23:17, 18 July 2012 (UTC)

Is "the UK was doing something to the atmosphere, like sending dry ice up on weather balloons, to force the jet stream to move"? No. As for the link to our weather modification article, the section in question relates to attempts to weaken tropical cyclones - and we don't get many of them in London. AndyTheGrump (talk) 23:21, 18 July 2012 (UTC)

Right. Also, I suspect that these might be military secrets. 75.166.200.250 (talk) 00:14, 19 July 2012 (UTC)

Note that as our article and the source it links to mentions, China claimed to be doing that during the last Olympics. However they have extensive involvement in the field of weather modification, including a Beijing Weather Modification Office and according to various sources something like '$100 million a year and employs 50,000 for rainmaking; 6,781 artillery guns and 4,110 rocket launchers; 30 aircraft'. While they normally try Cloud seeding to encourage rain over areas of drought etc, the method they tried to use during the olympics was fairly similar but as StuRat suggested the attempt was to get it to rain in areas away from the olympics [9] [10]. Our cloud seeding article and the earlier linked source also suggests they tried or were going to try to get it to rain before the olympics to help clear pollution.

As our article implies, whether their effors actually did anything useful is in much debate, as I understand it the field of weather modification is a controversial one with limited science backing up the claims of success (given our current limited ability to predict the weather, you can't know what would have happened if you didn't do anything so the only real way you can test your claims is by randomly choosing when to attempt modification and then carrying out statistical analysis to see if there's any evidence of a change but given how variable the weather is, you really need quite a long term project). Note that in one of the sources, even one of the key players from China said it wouldn't help much with big rain clouds, only small ones.

I somewhat doubt the UK will be attempting the same thing, not just because AFAIK they lack any real infrastructure (I mean they could easily adapt what they have but they'd still need to do more work then a country which already does it a lot), but as I understand it in most developed Western countries weather modification attempts are only generally done for research purposes (although not surprisingly I think a lot of research comes from China although some may question the quality of some of the journals it's published in which I believe includes ones from China) given the perceived lack of any scientific evidence of success (although our article suggests there may be some done for non research purposes in the US and Austria). As our article suggests weather modification attempts are also sometimes carried out in other parts of Asia where they either don't agree with the lack of evidence or don't care so much.

Nil Einne (talk) 05:00, 19 July 2012 (UTC)

July 19

Image artifact of purplish and greenish/yellowish stripes

Take a look at this scan of the actress Shivani Ghai: http://thedressdiscerner.files.wordpress.com/2011/07/asiana-mag-inner.jpg. There are alternating diagonal purplish and greenish/yellowish stripes running across the image. What type of image artifact is this, and what causes it? —SeekingAnswers (reply) 01:41, 19 July 2012 (UTC)

It's a Moiré pattern, and luckily the article somewhat explains the cause, since I can't. Dpreview, who should know, say "If a scene contains areas with repetitive detail which exceeds the resolution of the camera (1), a wavy moiré pattern (2) can appear" and provide onwards links. --Tagishsimon (talk) 01:43, 19 July 2012 (UTC)

For a rigorous mathematical overview of moiré patterns, there are articles on aliasing and Nyquist rate. Nimur (talk) 02:30, 19 July 2012 (UTC)

But for a simple answer, it happens when the image is made of tiny dots, and the dot spacing for the image does not match the dot spacing for the scanner. Looie496 (talk) 17:37, 19 July 2012 (UTC)

To what extent are astronomical observations automated ?

For example, if one of our large telescopes is pointed at some spot in space, and there's a point of light there not in any previous observations, does a human have to spot it, or would it be spotted by software comparing with previous observations ? StuRat (talk) 03:47, 19 July 2012 (UTC)

It depends on what the goal of the observations is. There are projects that look for transient or variable objects (e.g. Supernova Cosmology Project, OGLE), and those apply automatic algorithms to their data to detect variability or "new" objects. In general, survey telescopes such as Large Synoptic Survey Telescope, that revisit the same part of the sky repeatedly, state the search for transient objects as one of their scientific goals and will run those algorithms on their data. On the other hand, data from "visitor telescopes" (like the Very Large Telescope) where astronomers propose observations for a specific scientific purpose are not routinely screened for transient objects (most of the time there will be no other observations of the same field of comparable quality), and it will be luck if an astronomer spots something they haven't looked for. --Wrongfilter (talk) 08:57, 19 July 2012 (UTC)

(ec) Astronomers usually agree to share their observations with the observatory where they make them. Many of the large observatories have standardized processing steps that they perform when they add new observations to their archive libraries. However, a new point of light isn't typically going to flag an image for review unless spectral characteristics are being measured and it doesn't look like something common such as a asteroid or artificial satellite. A missing object or significantly changed brightness in an expected point of light is another matter entirely, and is more likely to flag the observation for review. 75.166.200.250 (talk) 09:03, 19 July 2012 (UTC)

Considering that those new points of light could be a meteor headed for Earth or something else important, it's a shame they can be tracked from 1st discovery. You'd think they could be compared against an artificial satellite database to eliminate that possibility. StuRat (talk) 09:35, 19 July 2012 (UTC)

There are automated, specialized meteor-scanning telescopes plugged into computers. But not every telescope result is checked for meteors — the odds are super low and the number of false-positives would make such a system prohibitive, and many of them are not looking at the sky in ways that would even spot a meteor. I think you are underestimating the amount of astronomical data that is generated, as well. --Mr.98 (talk) 11:49, 19 July 2012 (UTC)

Is the amount of data collected from large telescopes just too large for all our computers to process ? If so, it sounds like we need to build up our computing capacity, maybe in the same way as SETI@home does (using volunteers' home computers). StuRat (talk) 18:34, 19 July 2012 (UTC)

Gluconeogenesis image review

Could someone please check commons:image:Gluconeogenesis_pathway.png please? The final product (top) purports to be glucose (in its pyran form), but is missing the methylol(?) group. This make me question if there are other mistakes in it. One of the previous steps is a furan ring with two methylol groups, so its unlikely the target is a pentose. TIA, CS Miller (talk) 05:39, 19 July 2012 (UTC)

What worries me most about it aren't structural errors, but what's the source of the sequence? 75.166.200.250 (talk) 21:08, 19 July 2012 (UTC)

Galactic wind-up problem

From our Milky Way article:

Another interesting aspect is the so-called "wind-up problem" of the spiral arms. If the inner parts of the arms rotate faster than the outer part, then the galaxy will wind up so much that the spiral structure will be thinned out. But this is not what is observed in spiral galaxies; instead, astronomers propose that the spiral pattern is a density wave emanating from the Galactic Center. This can be likened to a moving traffic jam on a highway—the cars are all moving, but there is always a region of slow-moving cars. This model also agrees with enhanced star formation in or near spiral arms; the compressional waves increase the density of molecular hydrogen and protostars form as a result.

So, how do these density waves manifest themselves ?

1) Do some arms fade away while other arms appear ?

2) Or is it that when they give the variable rotation speed of the inside and outside of the arms, what they really mean is the stars within the arms, but that, as new stars are created and old stars die, the actual location of the arms move relative to the stars, so that the arms really have constant rotation ?

Any clarification would be much appreciated. StuRat (talk) 06:55, 19 July 2012 (UTC)

The stars move at (roughly) constant speed (in km/s), the waves move at constant angular speed; their motion is essentially independent. Individual stars pass through the waves in the same way that water molecules pass through water waves (or the other way round - water molecules oscillate around a fixed position while the wave passes through). Unfortunately, we can only measure the motion of stars and gas clouds in galaxies, not the motion of the arms/density waves. --Wrongfilter (talk) 08:47, 19 July 2012 (UTC)

But the part I don't understand is how the stars and waves can move independently, if the waves are composed of stars. Are the stars inside a "crest" just pushed closer together as the wave passes ? Are the stars brighter while it passes ? StuRat (talk) 09:30, 19 July 2012 (UTC)

That's not specific to stars and galaxies at all, and a partial explanation is contained in Wrongfilter's reference to water waves. Generally speaking, when a wave propagates through a medium, it does not do so by moving all the medium with it, but by vibrating the medium. To take a more obvious example: vibrations move through the strings of a stringed instrument without the entire string moving. If I grab a loose garden hose and waggle one end, the entire hose can adopt a wave-shape without the end running away from me. So with water, the body of water doesn't move as a whole when the waves move - or the tide would come in vastly faster than it does. And with stars - although the forces holding them together are gravitational rather than electrostatic - the same principle applies.

(after ec) So, to answer your question - the stars don't get brighter, they get closer together. AlexTiefling (talk) 09:35, 19 July 2012 (UTC)

So, in that case, the wave must slow the stars at the leading edge and speed up the stars at the trailing edge, to force them closer together ? StuRat (talk) 09:38, 19 July 2012 (UTC)

FOLLOW_UP Q'S:

1) Why aren't pressure waves originating from the galactic core manifested as circular waves moving out from the core ? What gives them their spiral form ?

2) What happens to the pressure waves at the bar in barred-spiral galaxies, like the Milky Way ? StuRat (talk) 09:43, 19 July 2012 (UTC)

I really need to read up on this (it's not trivial), but I just point out that the waves in galactic discs are density waves, not pressure waves. The spiral pattern, i.e. the density pattern arises from the superposition of the stars' orbits, although the gravitational attraction also plays a role. It's a collective phenomenon in a non-collisional self-graviatating system, as is the bar. --Wrongfilter (talk) 10:55, 19 July 2012 (UTC)

Here's my casual explanation, no doubt wrong:

• Galaxies have a core, which contains sites where stars are formed, at least some of which for some reason then travel away from the core.
• They travel at different speeds, causing clusters. The clusters still move away from the core. This is like a series of small, non-stationary traffic jams.
• Galaxies rotate.
• Consider a long straight single-lane north-south road, with clusters of traffic on it. The traffic all emanates from a building in the middle point of the road, half going north, half going south. Rotate the entire road around this building, and the cars will form a spiral pattern (as the slower moving ones, and the ones stuck behind them, are left behind, falling off the rotating road, to form trails).

That analogy became increasing bizarre as I edited and improved it. Oh well. Hope it helped.  Card Zero  (talk) 12:41, 19 July 2012 (UTC)

Yeah, I'm pretty sure that is wrong. Stars orbit the centre - they tend to stay at a roughly constant distance. There will be some stars moving outwards or inwards (mostly due to close interactions with other stars), but I doubt there are enough of those for it to be a significant effect. I'm almost certain it won't be a large enough effect to cause the spiral arms. --Tango (talk) 16:36, 19 July 2012 (UTC)

• Let me give a pointer to density wave theory (already mentioned by Wrongfilter), which contains some animations that may be useful for getting an intuition for the process. Looie496 (talk) 17:34, 19 July 2012 (UTC)

Ooh, so rotated concentric ellipses cause the arms. How nice.  Card Zero  (talk) 17:43, 19 July 2012 (UTC)

Explanation of spiral galaxy arms.

Yes, that makes some sense, but can those spirals create more than 2 arms ? I'd like to create some animations of this illustration and one with multiple arms, if I can figure out how the multiple arms case works in this model. StuRat (talk) 18:29, 19 July 2012 (UTC)

Well, you can get that by superposing two (or more) independent waves. Dauto (talk) 19:06, 19 July 2012 (UTC)

Density wave theory is only a part of the set of theoretical explanations there are about galactic spirals; see Spiral galaxy#Origin of the spiral structure. In general, the dynamics of stars within galaxies is not as well understood as one might expect, with theory at times matching poorly with observation; see Galaxy rotation curve. Red Act (talk) 21:47, 19 July 2012 (UTC)

There is little discrepancy between theory and observations as far as galaxy rotation curve is concerned as long as that theory includes dark matter (which it should). Dauto (talk) 02:46, 20 July 2012 (UTC)

But dark matter fits solidly within the category of "not as well understood as one might expect". Without a clear-cut understanding of what exactly dark matter is, direct (as opposed to gravitational) evidence for its existence, or experimental evidence that would clearly rule out the alternative theories that compete with dark matter, dark matter currently isn't much more than a fudge factor that describes the discrepancy between observation and what the theoretical results would be without dark matter thrown in. That may well change if some good experimental evidence about dark matter starts coming in over the next decades, but at the moment, dark matter isn't a very satisfying explanation. Red Act (talk) 04:21, 20 July 2012 (UTC)

StuRat, perhaps you have figured it out already from the various links, but the density wave is principally a property of the galactic gas. We think of the interstellar medium as empty, but it is filled everywhere with diffuse gas. Though almost empty, waves can propagate through that gas provided that the waves are large enough (in this case on the scale of a whole galaxy). As the wave compresses the gas, that perturbation provides just enough impulse to trigger star formation in gas clouds that were already on the brink of collapsing. This means that the passage of the density wave is marked by a surge of young stars. It is those new stars, many bright and large, that make the spiral arms stand out visually. The stars, once formed, follow elliptical paths and are hardly affected by the density wave at all. However, many of the brightest stars are so big that they live short lives (only ten million years, for example), so they die out quickly compared to the travel time of the density wave. Hence the spaces far from the front of star formation appear darker. So yes, the arm positions (really a front of star formation) is moving relative to the actual stars. Dragons flight (talk) 19:23, 20 July 2012 (UTC)

OK, thanks all, but what actually generates the density waves ? StuRat (talk) 20:26, 20 July 2012 (UTC)

Li-ion current price per kWh

I was wondering how much rechargeable li-ion battery cost per kWh. To grab very rough estimate I gone ebay and searched for different types of li-ion batteries there. To my huge surprise, it seems that 18650 form factor cells are most cost effective... And 10 batteries 3800mAh each 3.7V cost $14.94 with free shipping...

My question, if advertised characteristics reflect real performance, that translates for 140.6 Wh for $14.95, or ~$107 per kWh. My calculations correct? Or have I made a mistake?

And second question, how likely that such lots(not only on ebay, but alibaba etc) reflect the cost of production of 1 kWh rechargeable li-ion battery selling for around $100 and still making profits? Or such batteries are left overs from bigger orders or even flawed cells that haven't passed quality control, and thus price of them do not really reflect cost of kWh...

Example ebay slot 70.49.169.86 (talk) 16:32, 19 July 2012 (UTC)

Um, don't ever trust mAh ratings from eBay. Given the price, you'd probably be lucky if the cells even have half the capacity [11]. I believe the real high end 18650 cells from Panasonic etc tend to be around 3100mAh [12] [13] [14]. From what I've read, cells with Xfire labels can vary from reclaimed battery pack cells to those that didn't make the grade for a battery pack. (You can get okay ones but you need to do a bit of research and ensure it's a supplier you can trust.) In any case, I wouldn't read too much in to the price, but it sounds like you should be more interested in the wholesale price anyway not the price from random eBay sellers who stick random labels on them. P.S. I'm pretty sure your calculation can at best be called simplified since you didn't take in to account the actual discharge curve for your cell which will depend on discharge current and to a smaller extent what voltage you stop at. Nil Einne (talk) 17:48, 19 July 2012 (UTC)

''it sounds like you should be more interested in the wholesale price anyway'' Yes, this is what I'm really interested to figure out. But not GM/Nissan/Ford claimed price of li-ion battery packs, but cheap modern li-ion chemistries produced out there(in China?) and wholesale price per kWh they are selling for... 70.49.169.86 (talk) 18:09, 19 July 2012 (UTC)

My point is the correlation between the price you pay retail for individual cells and the wholesale price is weak at best. Particularly in a case like this where the cheap retail options are of unknown heritage with random labels and the wholesale price will depend greatly on things like what sort of supplier you're willing to trust (given the way things can go wrong with li-ion cells, although of course one cheapish seller may give you total crap which blow up regularly, another selling at the same price may give you decent quality cells most of the time) and capacity (choosing the highest capacity cells is probably not the cheapest option), not to mention the typical stuff like quantity. Your best bet is probably looking at something like Alibaba or one of the other China B2B sites out there for the sort of quantity ranges you're thinking out, but you'd also have to have some idea of what you're looking at which to be honest it sounds like you don't. You can also try asking suppliers since they don't always bother to properly specify. Of course it does depend somewhat on what level you're actually looking at, I would guess at a low level range like 10000 cells a year you may get an okay idea from such sites, but if you're thinking of 100k a month, probably not. It's not that this info is super secret, it's just that it's not out there on some internet site because that's not how people who actually make the decisions are going to look for it. And navigating the China market can be difficult, if you don't much experience, given the variety of problems there is like unreliable suppliers. I don't really get the relevence of GM/Nissan/Ford as I didn't mention them, despite the recent interest in electric cars and the fact some of them now use li-ion cells, I'm pretty sure they still only make up a tiny percentage of the market. Nil Einne (talk) 04:44, 20 July 2012 (UTC)

First of all thank you Nil for pointing out that 3700 mAh was totally unrealistic to expect from 18650 cell. That helped me a lot:) Yes, correlation between retail and wholesale prices is hard to estimate precisely. But it still better then nothing and lowerest retail price would give some idea about wholesale price level... I have mentioned GM/Nissan cuz price of battery packs of Leaf and Volt has been published ($375 and $550 per kWh 'IIRC'). And that theoretically should help estimate wholesale price of batteries... But automotive packs are something different then what I'm looking for(at least the way GM define it). I have got a two question for you, Nil.

1) Wouldn't you think that LiFePO4 chemistry should be cheaper then bunch of 18650 cells with similar capacity?

2) Could you make an educated guess for me about a price of average capacity (2200 mAh?) 18650 cell. What would you consider cheap, but realistic and a good price for ~100k cells? Would you say that $1.50-$1.80 price range per cell is achievable? I know Tesla Motors was using hundred thirty one 18650 cells per kWh in their battery packs. So that translates into 7.6Wh per 18650 cell, should be a good estimate for price effective cell capacity I guess....

Thank you in advance, 70.49.169.86 (talk) 05:59, 20 July 2012 (UTC) PS. I have tried to use Alibaba even before I have asked question here, with very little luck. And really do not feel like approaching companies to get quotes...

energy drink

why we add salt,sugar in water to give energy to a person — Preceding unsigned comment added by 59.177.161.174 (talk) 17:08, 19 July 2012 (UTC)

Such drinks, like Gatorade, have three purposes:

• To provide a quick source of food energy, which comes from the sugar
• To rehydrate someone, due to sweating during exercise, this comes from the water
• Sweating also contains a lot of salt, which needs to be replaced. If you drink too much water and not enough salt, you can get Hyponatremia, so the salt is there to keep the electrolytes in the body at the right concentration.

Does that help? --Jayron32 17:25, 19 July 2012 (UTC)

For why they put salt in energy drinks, see water intoxication. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 17:33, 19 July 2012 (UTC)

Water intoxication and hyponatremia are basically two sides to the same coin. Not exactly, but they are very closely related conditions: if you have too much water, it also means you don't have enough sodium. If the two are in correct relative balance, your kidneys should be working efficiently enough to keep things working well; that is for a properly balanced solution with the right amount of salt, it is hard to over-consume it: you'll just tend to piss a lot more. If you don't get enough salt, you'll experience the symptoms of water intoxication/hyponatremia. Too much salt or not enough water leads to dehydration and Hypernatremia. --Jayron32 17:39, 19 July 2012 (UTC)

That's all correct, but my understanding is that there is also another factor: it is easier for the body to absorb fluids if they are approximately in osmotic balance with the bloodstream -- meaning that they have a comparable level of dissolved molecules, of whatever sort. Looie496 (talk) 18:00, 19 July 2012 (UTC)

The answers above are correct if you're talking about liquids consumed by professional athletes during strenuous training sessions. If you're talking about supermarket "energy drinks" consumed by non-athletes, the sugar and salt are there to make them taste good. -- BenRG (talk) 22:06, 19 July 2012 (UTC)

Yes, the answers above are for sports drinks, rather than energy drinks. Sports drinks are used by amateurs for the same reasons as professionals. Energy drinks are a completely separate market (do they usually contain salt? They're mostly caffeine and sugar, I think). --Tango (talk) 00:37, 20 July 2012 (UTC)

This may be an ultra-dumb question even for me, but one thing about Gatorade is that it tastes a lot better when you've been exercising strenuously than if you just take it like you would soda pop. So, does that have to do with a stressed body "craving" what Gatorade contains? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:08, 20 July 2012 (UTC)

I don't know what is in Gatorade, but I do know you lose the ability to taste salt when severely dehydrated, which makes oral rehydration solution taste a lot better (it tastes like sugar water, rather than sugar and salt water). If Gatorade contains quite a lot of salt, then it could be the same effect. --Tango (talk) 06:04, 20 July 2012 (UTC)

That's exactly it: the salt. But it isn't that severe dehydration makes you unable to taste salt, it's that moderate loss of salt via sweating makes salt taste better than it usually does. Looie496 (talk) 06:39, 20 July 2012 (UTC)

I suspect that the real reason for companies adding anything to water, is so that they can convince people to buy it and thus take your money. Of course other companies manage to extract money from the consumers without even adding anything to the water. Mitch Ames (talk) 03:13, 21 July 2012 (UTC)

Earth and Jupiter

At what point would Earth have to be to Jupiter before it is sucked into its orbit? Reticuli88 (talk) 17:17, 19 July 2012 (UTC)

See Gravitational binding energy. If the kinetic energy of a body exceeds the gravitational energy holding it to another, it will be able to escape. If the kinetic energy of the object is less than the gravitational energy, it will eventually be "sucked in" to the other object. To answer your question meaningfully, which I take it to mean "how close must an Earth-sized object be to a Jupiter-sized object before it will be gravitationally bound to it" the answer is "it depends"; mostly on the relative motion of the two objects. The dynamics are very complex, and can't be answered without more information regarding the specific orientation and relative velocities of all objects involved. However, I wouldn't worry about it happening any day soon. The distance would be a LOT closer than they are now; Jupiter is 5 times as far from the Earth as the sun is at the closest it ever gets to the Earth, and it is only 0.001 times the mass of the Sun. Roughly speaking, that means that Jupiter should exert a gravitational influence over objects only 0.001 times as well as the Sun does, and the Earth falls well outside of that sphere. The earth does experience a tiny effect from Jupiter's gravity, but it isn't going to send us crashing into Jupiter. --Jayron32 17:35, 19 July 2012 (UTC)

Binding energy isn't really the best concept to look at. What you're really interested in is escape velocity. --Tango (talk) 00:39, 20 July 2012 (UTC)

See Hill sphere. manya (talk) 03:52, 20 July 2012 (UTC)

And also see Sphere of influence (astrodynamics). manya (talk) 03:56, 20 July 2012 (UTC)

Sorry, these links are not relevant to answer the question. manya (talk) 04:00, 20 July 2012 (UTC)

Cell Signalling in Development

Hello. Two-cell (comprised of P1 and AB) embryos were incubated either in a translation inhibitor or in a transcription inhibitor. The AB cells were then isolated, washed, and grown in culture. AB cells of embryos treated with the translation inhibitor produced only neurons and skin, while AB cells of embryos treated with the transcription inhibitor also produced muscle–their normal fate. The direction of signalling is from P1 to AB. Why would the signalling interaction at the two-cell stage most likely involve proteins? If proteins are the product of transcription and translation, wouldn't the P1 cells of embryos treated with transcription inhibitor not produce mRNA and, as a result, proteins? This would block the signalling pathway, right? Thanks in advance. --Mayfare (talk) 19:56, 19 July 2012 (UTC)

Because the two cells are adjacent. Low molecular weight hormonal signaling paths are unnecessary under those conditions. Yes to your second and third questions. 75.166.200.250 (talk) 20:46, 19 July 2012 (UTC)

In most organisms, transcription is marginal or completely absent for the first several rounds of cell division after fertilization. In Drosophila melanogaster, for instance, this stage lasts for ~2 hours and 12-14 rounds of cell division. Virtually every mRNA found in very early embryos has actually been produced maternally. And so the transcription inhibitors would have no effect because transcription isn't even on, or is nearly irrelevant if it is. Translation, on the other hand, is quite active, working from the maternally provided mRNA. Someguy1221 (talk) 22:14, 19 July 2012 (UTC)

Equivalent Animal Processing Power of Modern Computers

Out of some recent boredom, I have been reading up on the computer vs. human brain speed dealie. Though I knew that there is no easy way to measure and compare the two, I was interested in some of the (questionable?) methods used to approximate the processing speed of human brains and that they were considered to be vastly superior to current technologies. I was wondering, then: what animal's mental "processing power" is closest to the fastest computer processor available to consumers today? Have we even gotten past ant? Thanks, Sazea (talk) 19:57, 19 July 2012 (UTC)

Well, my opinion is somewhat heretical here, but since I have a Ph.D. in neuroscience I can present myself as enough of an expert to express it: I believe that the computational power of brains is way overstated, and that at a practical level a human brain has capabilities comparable to a powerful modern desktop PC -- except in terms of memory access bandwidth, where the brain really stands out. The thing that really makes brains superior, I believe, is the vast amount of information about the world they take in during the process of development. Looie496 (talk) 20:17, 19 July 2012 (UTC)

Aren't neurons arranged in more than 2 dimensions like computers are?--Canoe1967 (talk) 20:22, 19 July 2012 (UTC)

I'm not sure why you ask that, but there is no doubt that digital computers differ from brains in a variety of important ways. They differ so much that it is hard to find a basis for comparison. In my view, the only proper way to do it is to ask how powerful a computer would be needed to do the same tasks that the human brain can do -- for example, to pass the Total Turing test. I think it is likely that modern PCs, augmented by a few special chips, are powerful enough to do it -- that the real difficulty is in programming them, not in making computers that are strong enough. Looie496 (talk) 20:40, 19 July 2012 (UTC)

I just heard somewhere that they are thinking of biological memory to get some of the advantages of animal brain material and the configuration was one of them. I also remember that if we can make a wire small enough to connect we may try programming animal neuron groups.--Canoe1967 (talk) 21:22, 19 July 2012 (UTC)

Looie, what would be your estimation of the human memory access bandwidth? And yes, hard disks suck. Pitiful bandwidth. Sagittarian Milky Way (talk) 23:34, 19 July 2012 (UTC)

It's been quite some time since I worked through the calculation (calculating the rate at which information in the synaptic weight distribution generates information in the population firing pattern), but my recollection is that I could get a value on the order of 1 terabyte per second without making any assumptions that seemed unreasonable. Looie496 (talk) 03:04, 20 July 2012 (UTC)

Which even ultra high end GPUs are a while away from matching Comparison of AMD graphics processing units, Comparison of Nvidia graphics processing units. Nil Einne (talk) 04:35, 20 July 2012 (UTC)

I dunno, I see 264 GB/s and 2 x 192.256 GB/s for the desktop in those lists. What's the Moore's law for GPU bandwidth? That's only 2.6 times to 1 TB/s (wow, a TB/s, that's fast). Some people put 2 or 3 (4?) graphics cards in the same PC, right? We've already matched it on some PCs. With coolers for each card that can play top games at max settings on a 26, 36 inch or something screen that's like 4 HDTVs worth of pixels. There are supercomputers with 20 TB of RAM, they probably blow away human brains in terabytes/s. Sagittarian Milky Way (talk) 18:07, 20 July 2012 (UTC)

Looie, what are your views on whether brains can even be considered computable. I have read penrose's thoughts on this, but for some reason have completely forgotten the gist of his argument. Perhaps it unsettled me. Egg Centric 17:55, 20 July 2012 (UTC)

I think it was that it's not (fully) computable due to quantum mechanics. I hope that's true, that's where free will comes from. Sagittarian Milky Way (talk) 18:10, 20 July 2012 (UTC)

Well I rather (personally) hope quantum mechanics explains my self-evident consciousness (as I define it) although I can't possibly see how it could. Free will I see no reason to belive in tbh. Egg Centric 21:35, 20 July 2012 (UTC)

Energy requirements for reverse osmosis

How much energy does it take to desalinate 10,000 cubic meters of seawater by reverse osmosis? 75.166.200.250 (talk) 20:38, 19 July 2012 (UTC)

You could try websites that sell them. They may have those specs. I assume the larger the more efficient.--Canoe1967 (talk) 21:24, 19 July 2012 (UTC)

Using numbers from http://urila.tripod.com/desalination.htm/ (for which I do not vouch), and assuming perfect efficiency, it comes to around 1000 kilowatt hours. Looie496 (talk) 21:55, 19 July 2012 (UTC)

You should buy one of these though, which I endorse. http://www.ansl.ca/candesal/article.html --Canoe1967 (talk) 23:40, 19 July 2012 (UTC)

"Mr. De Villiers says if CANDESAL can produce water for less than $1 a cubic metre, the technology has great potential. "If their business plan is right, then they're onto something really big," he says." --Canoe1967 (talk) 23:49, 19 July 2012 (UTC)

You can easily compute this from first principles. It follows from the change in the Gibbs energy. Suppose you have seawater with a concentration of n ions per unit volume in it. You take a volume V from this seawater, which will contain N = V n ions. The Gibbs energy of N ions in a volume V of water is approximately given as g = N k T Log[N/(V Z)] where Z is the single ion partition function. Then the initial state is the water of volume V with ions at concentration n, and the sea which has some huge volume V' with ions at concentration n. The Gibbs energy of the initial state is then

g1 = N k T Log[N/(V Z)] + M k T Log[M/(V'Z)]

We then remove all the ions from the water by dumping into the sea. The limit of N to zero of the first term is zero. The Gibbs energy is thus given by:

g2 = (M + N) k T Log{[M + N]/(V'Z)}

The maximum amount of work that can be extracted from this process is the drop in the Gibbs energy, g1 - g2. This will be negative, so it will require a minimum amount of work of g2 - g1 to get to the final state. We have:

g2 - g1 = (M + N) k T Log{[M + N]/(V'Z)} - N k T Log[N/(V Z)]

      -  M k T Log[M/(V'Z)]

We then want to take the limit of V' and M to infinity such that M/V' = n. We can simplify the first term:

(M + N) k T Log{[M + N]/(V'Z)} =

(M + N) k T Log(n/Z) + (M + N) k T Log(1 + N/M)

The first term of this cancels against the last two terms in the expression for g2-g1, we thus have:

g2 - g1 = (M + N) k T Log(1 + N/M)

For small x we have Log(1+x) = x - x^2/2 + ..., so the limit for M to infinity becomes:

g2 - g1 = N k T

Seawater contains 35 grams per liter of salt. Sodium chloride has a molecular weight of about 58.45 u, so 35 grams of salt contains 3.606*10^23 ions of sodium and 3.606*10^23 ions of chlorine. One liter of seawater thus contains 7.21*10^23 ions, 10^4 cubic metres contains 7.21*10^30 ions. If the temperature of seawater is 15°C, then g2-g1 = 2.87*10^10 Joules. Count Iblis (talk) 03:58, 20 July 2012 (UTC)

That's nearly 8 megawatt hours. I wonder why the discrepancy with the 1 MWh figure above. 75.166.200.250 (talk) 07:02, 20 July 2012 (UTC)

Looie probably forgot a factor of ten somewhere, the source he uses says "0.66 kcal / liter is the minimum energy required to desalination of one liter of seawater, regardless of the technology applied to the process.". If you use this then you get almost the same figure as I obtained (they use 33 g/L for the salt concentration and I took 35 g/L, if you correct for that, then the agreement become even better). Count Iblis (talk) 15:35, 20 July 2012 (UTC)

Neurodynamics of biomusicology

Hi. Recently, I became interested in the concept that some animals other than humans can "understand" music and appropriately respond to it. We all know that humans have a range of musical perception, interest and appreciation, and that other animals use music or music-like sounds as a form of communication. Also, there are videos on Internet of dog and cat dancing to music. Birds, on the other hand, use song that humans interpret as musical. Meanwhile, in the Chinese language there is a proverb that states "playing piano to an ox", suggesting perhaps that oxen do not understand music. In the extreme case, insect buzzing can also be music-like, but their brains are small. Finally, the clade of dinosauria may have used music[citation needed]. Dolphins and other cetaceans use human-understandble music, have the second-largest encephalization quotient in all of Animalia, and some evidence of human-cetacean communication is potentially documented. All of these are examples of anecdotal evidence. However, could there be an overlap between human and non-human music? More specifically:

• What brain structures and patterns allow for the comprehension of music?

Which lead to a more interesting question:

• Is there any corresponding resonance pattern between the types of music that a certain species "understands" and the more subconscious brainwave patterns such as delta, mu and theta?

Furthermore, this leads to an even more interesting question:

• What does this imply from an evolutionary psychology standpoint?

I recently came across the above-linked articles, and they may be relevant in answering the question, as I knew nothing about this topic beforehand. Thanks. ~AH1 ^(discuss!) 22:40, 19 July 2012 (UTC)

Music appreciation is probably a learned social behavior. Please see PMID 22732561 (figures, tables, and supplementary material.) 75.166.200.250 (talk) 22:44, 19 July 2012 (UTC)

Let me just recommend the book Musicophilia by Oliver Sacks, if you want to know more. I haven't actually read it, by everything by Sacks is very readable. Looie496 (talk) 01:37, 20 July 2012 (UTC)

It is largely a collection of case histories, not a theoretical book. But yes, almost everything he writes is excellent, even his account of falling down a mountain. μηδείς (talk) 04:34, 20 July 2012 (UTC)

I was somewhat underwhelmed by it, I must say. I loved some of his early work (Awakenings was by far the best book I read in 1976, probably for the entire second half of the '70s), but Musicophilia didn't do it for me, and it received very mixed reviews. What I would recommend, though, is Robert Jourdain's book Music, the Brain and Ecstasy. -- ♬ Jack of Oz ♬ ^{[your turn]} 11:22, 20 July 2012 (UTC)

"Undertanding" music and enjoying it requires at fundamental level 3 things (1) a sense of timing, (2) a sense of pitch (ie frequency as it is called scientifically), and (3) able to sense and enjoy repetition. The are a number of subtleties, such as what pop music composers have called "ear grabber" notes (notes that are harmonically slightly out of place, or melody lines that sound exciting), but that's what it comes down to. A quite good explanation of music in terms of expliting these 3 aspects was published in a book on how to write pop songs by, of all people, Rolf Harris, about 40 years ago. You may be able to obtain a copy via your local library. Aspect (3) is of course short term memory. Aspect (2) is of general use to animals as it helps to recognise the sounds of prey and predators, and is vital to communication. Aspect (1) is of general use in communication and in understanding the behavior of prey and predators. The brain structures responsible for aspects 2 & 3 have not been pinned down precisely, but a multitude of texts have been published on it. Aspect 1 has until recently been pretty mysterious, however special "clock" neurons have been discovered through the brain. Scientific American and Scientific American Mind has carried articles about it in the last year or so. Given that enjoyment of music is based on such fundamental requirements of intelligence, it should not be a surprise that animals have some sense of music. Having said that, my experience in owning several dogs, from dumb breeds like spaniels, to highly intelligent breeds like german sheherds, is that our music is just noise to them. Wickwack124.178.34.188 (talk) 02:21, 20 July 2012 (UTC)

Medical Term

What is sphincter pharyngoplasty? Does it have anything to do with tonsils? Daonguyen95 (talk) 23:28, 19 July 2012 (UTC)

See Hypernasal speech#Sphincter pharyngoplasty. Red Act (talk) 23:38, 19 July 2012 (UTC)

July 20

Do different languages have different IUPAC names?

Well, sorry for asking this silly question, but I would like to know it. I mean are they comparable to scientific binomial nomenclature of living organisms. Vanischenu m^Talk 16:58, 20 July 2012 (UTC)

The naming rules are universal, however the words themselves are translated depending on the language. Please note this paper, PubMed Tombo7791 (talk) 17:13, 20 July 2012 (UTC)

Thank you so much! That link explained everything. (Did you notice that they thanked WMF in it?:) Vanischenum^Talk 04:10, 21 July 2012 (UTC)

Followup question
There is an Italian article with a different IUPAC name. I do not know why they have omitted the numbers. In our (en) article on it, it was me who put (replaced) the IUPAC name (ref from CHEBI).) So check on it would be helpful. Again thank you.Vanischenum^Talk 04:10, 21 July 2012 (UTC)

It is often omitted when there is no other possible arrangement. 1,1,2,2- is the only choice in this formula. (Unless I am missing something.) Rmhermen (talk) 04:53, 21 July 2012 (UTC)

Freezing a liquid evaporating a part of it

Evaporating a liquid it is absorbing heat, but if you have just one liquid can you use it, evaporating a part of it, at a dissipator and freeze the same type of liquid in another closed chamber? Both parts are at the same temperature. OsmanRF34 (talk) 18:00, 20 July 2012 (UTC)

Yes, at different pressures. 75.166.200.250 (talk) 18:12, 20 July 2012 (UTC)

That's essentially how dry ice is made - they compress the CO2, so it becomes liquid, then release the pressure and some of it evaporates cooling the rest until it freezes (they aren't in separate chambers, though). --Tango (talk) 19:10, 20 July 2012 (UTC)

Yes. The difficulty is that, for most materials, the vapor pressure of the solid is very, very low, and the vapor pressure of the liquid falls quickly as you approach the freezing point. This means that evaporative cooling becomes less effective as you get close to freezing. 75.166 points out that you can get around this by manipulating the pressures in the two reservoirs, and Tango's example of dry ice works well because CO2 has substantial vapor pressure in the solid phase. This online Q&A [15] says that you can also freeze water in a single reservoir with a vacuum pump, and here's a video that does it: [16]. I believe it's not terribly efficient because of the low vapor pressure, but it's interesting to see that it can be done. --Amble (talk) 20:27, 20 July 2012 (UTC)

What would happen if a whale hit a deepwater petroleum pipe?

Maybe this could be figured out with the whale's mass, speed of swimming, tensile properties of the pipe and whale head compressive strength etc.? Generally mechanics and materials science. And what's the biggest species of whale in oil producing regions? (i.e. North Gulf of Mexico, North Sea, Persian Gulf etc.) Sagittarian Milky Way (talk) 18:22, 20 July 2012 (UTC)

A subsea blowout preventer would close the pipe, under ideal conditions. 79.148.233.179 (talk) 18:28, 20 July 2012 (UTC)

If you have access, you can check out this article "Hydrodynamics of a ship/whale collision" [17]. Which covers a lot of the physics involved. "whale collision" returns many hits on google scholar. But none on the first few pages have anything to do with stationary objects. The paper linked above seems to say that ships pose a special challenge for whales, which are normally rather good at avoiding smashing into things. A more realistic risk to pipelines might be large schools of fish, squid, or jellies. SemanticMantis (talk) 18:32, 20 July 2012 (UTC)

Thermoelectric materials

I was wondering what the best thermoelectric materials (not for measuring temperature, but rather for generating electricity) are that one would find in a normal household, or could easily and fairly inexpensively obtain at local stores? I know that there are far better out there, but I am not so optimistic about finding Bismuth chalcogenides laying around in the back room. The only other thing that I am concerned about is that they can be safely handled by an inexperienced experimenter. Thanks! Falconus^{p t c} 19:32, 20 July 2012 (UTC)

Solid state heat pumps are made from semiconductors. They are usually in modern CCD cameras, laser diodes, microprocessors, and the like, but I think you probably want to take the diodes out of something like a USB beverage cooler. 75.166.200.250 (talk) 22:10, 20 July 2012 (UTC)

Assuming you don't mean specifically manufacturered thermoelectric devices, such as the beer cooler mentioned by 75.166.200.250 (you did say materials), I don't think you will find anything much. A good thermolectric material combines a high barrier voltage with very low thermal conductivity. The Russians in the 1940's and 1950' made an extensive search for such a material - the best they could come up with is Bismuth Telluride, and even that isn't very good. Bismuth Telluride is what is used in beer coolers, but not because it is efficient, but because it means no moving parts and convenient to make in a size really too small for a compressor. There are two possibilities I can think of: Copper oxide (once used to make diodes), which you can easily make at home, and Russian "radio lamp" materials. I think copper oxide will be so poor you will only be able to measure temperature with it, and not generate usefull power. I will post the instructions for making a radio-lamp generator later, if & when I find the reference. Wickwack120.145.176.214 (talk) 01:43, 21 July 2012 (UTC)

What components of cigarettes keep weight down ?

First, I suppose I should ask if cigarette smokers weigh less, on average, than nonsmokers. If so, do we know why ? Is it the nicotine or the tar ? And what's the mechanism ? Is it that it retards the sense of smell, and thus the appetite ? StuRat (talk) 20:44, 20 July 2012 (UTC)

Nicotine is an appetite suppressant, probably because it's a stimulant.

thx1138 (talk) 20:46, 20 July 2012 (UTC)

Nicotine thx1138 (talk) 20:47, 20 July 2012 (UTC)

Thanks, is it ever prescribed as such ? Or is the additive nature of nicotine enough to prevent that use ? StuRat (talk) 21:00, 20 July 2012 (UTC)

I doubt it. There are plenty of other appetite suppressants you could use that don't have the same nasty side effects as nicotine. Appetite suppressants aren't usually prescribed at all, though - they just aren't that effective a way of losing weight (and they all have some kind of nasty side effects). I saw something in the news recently about the FDA approving a new appetite suppressant - it was newsworthy because its so rare. --Tango (talk) 21:20, 20 July 2012 (UTC)

What side effects does nicotine have other than addictiveness ? How are they worse than other appetite suppressant side effects ? StuRat (talk) 22:09, 20 July 2012 (UTC)

"First causing a release of glucose from the liver" ... so a cigarette is a way to access stored energy, instead of having a snack.  Card Zero  (talk) 21:16, 20 July 2012 (UTC)

I just wrote a long response full of unsourced speculation, then tried to find some sources and the first google hit was Cigarette smoking for weight loss (WP:WHAAOE!). It mostly contradicts what I had written, so I'll just leave you with the link! --Tango (talk) 21:20, 20 July 2012 (UTC)

Smoking also suppresses the sense of smell and thus the flavor of food. 75.166.200.250 (talk) 22:03, 20 July 2012 (UTC)

Smokers weigh less because they're lighter. Mitch Ames (talk) 03:20, 21 July 2012 (UTC)

July 21

Is is possible to be a sociopath in a narrow area?

we don't offer medical diagnoses, including psychaiatric
The following discussion has been closed. Please do not modify it.
I am certainly not a sociopath in any classical sense, indeed if anything I am fairly sure for various reasons that I have considerably more empathy than most people. However, what I just can't do is get offended by anything. I intellectually understand what offends other people (learned, I think, from trial and error) but have no visceral response at all. What's up with that? Egg Centric 00:41, 21 July 2012 (UTC) Addition: Sometimes I pretend to be offended just cause I have the sense I should be claiming to be, even though I'm not, and I still can't help but think that that is what everyone else is doing. Also sometimes I get angry with twats and express it as being offended, but only cause that seems to be socially acceptable thing to do, not cause I'm actually offended. Egg Centric 00:47, 21 July 2012 (UTC) Can't you get offended by anything, asshole? So, I can crack up a joke about your mommy (that whore) and you would laugh with me? 88.9.110.244 (talk) 00:54, 21 July 2012 (UTC) If it was funny Egg Centric 01:28, 21 July 2012 (UTC) Nah, you're probably just INFP. Some day, someone will cross a line that you didn't know was there, and you'll be surprised by your own reaction. --Amble (talk) 00:59, 21 July 2012 (UTC) Apart possibly from introversion, where I am probably an introvert in terms of intrinsic preference (in that I loves me some nerd time) but an extrovert by usual behaviour, I am basically the opposite on that scale, so I doubt it Egg Centric 01:35, 21 July 2012 (UTC) Interesting. Shows what you get for taking things like MBTI too seriously (bad guesses). --Amble (talk) 01:55, 21 July 2012 (UTC) Three unrelated points: A) As far as psychologists are concerned, there is only "sociopath" and "not a sociopath". While indeed you can fit some of the criteria and not others, there is no defined thing as "sociopath for some things but not others". B) That said, I have only known one other person who so adamantly insisted they never could not be offended. I later realized this insistence was a coping mechanism and they actually took offense quite easily, but hid it well; C) Are you sure that nothing offends you, or are you just talking about insults? Being able to be unbothered by someone's attempts to get a rise out of you makes you more enlightened than the average human being, in my opinion. What if it is something more extreme, like being formally and publicly accused of a wrongdoing you are not guilty of? Or something really extreme, like watching someone kill a baby? Truth be told, even if you could honestly say "not offended" to all of those, I would scream that you're a sociopath. Though if you want a formal diagnosis, you'll need to see a psychologist. Someguy1221 (talk) 01:00, 21 July 2012 (UTC) It may be that we are using different definitions of offended. Of course I would not want to watch someone kill, or even torment a baby. There would certainly be a visceral response. But I couldn't characterise that response as offence, it would be more like horror. I am not unable to be insulted either in principle, but it would just make me angry or irritated. I am talking more about say sexism, racism, or whatever. Egg Centric 01:28, 21 July 2012 (UTC) Still wouldn't call you a sociopath. You just sound like you subscribe to "don't give a fuck"ism, whether you know it or not. Someguy1221 (talk) 01:34, 21 July 2012 (UTC) You are not a sociopath. Sociopaths are narcissists, you are not. Check here: Sociopaths#Cleckley_checklist. Maybe you have reached enlightenment. 88.9.110.244 (talk) 01:52, 21 July 2012 (UTC) We should not be offering diagnoses of people's psyches. μηδείς (talk) 02:46, 21 July 2012 (UTC)

Effect of Electric or magnetic fields on crystallization

So I was thinking if we have a compound whose molecules have polar covalent bonds (imagine it's a simple one, a diatomic molecule) well,the favorable position for them when the compound is crystallized must be something like:

+ - + - + - + - + -

- + - + - + - + - +

But in the presence of an electric field, the favorable position is:

+ + + + + + + + + +

- - - - - - - - - -

(assuming the field is upward) This made me wonder does presence of electric fields or magnetic fields make the crystallization harder (like in this case, although I'm not sure because although the arrangement is unfavorable for crystallization, at least they're aligned in the same... strike?) or easier? Is it done? How effective/practical is it? Does it have any use? What, if so?