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November 16

Miscellaneous questions about work and energy

1) If work is done on a system, then W = ΔE. But how can we calculate the work done by the system on its surroundings? Intuitively, I would think the answer is -ΔE, but I can't prove it :(. When I try, I run into contradictions (two planets at rest, gravitationally attracted to each other; if one planet is considered as the system, then its energy will increase. W_ext = -ΔE, then the other planet shouldn't speed up, but it does).

2) The work article says that the total work done in an isolated system is independent of the frame of reference. What's the significant/implications of this? 76.68.247.201 (talk) 02:07, 16 November 2010 (UTC)

1. Yes, work is antisymmetric like that: if I do work on you, you're doing negative work on me. However, your planets are each doing work on the other, but they also are losing potential energy in the process, so their actual $\Delta E=0$. A heavy piston sliding down into a cylinder of gas (perhaps because the gas is cooling, so its pressure is dropping) does work on the gas even if it's moving at constant speed; the negative work done on it by the gas annihilates its potential energy.
2. It means that changing your frame of reference doesn't change, say, the laws of chemistry. If I fire a gun while on a train, the work done by the expanding gas on me and on the bullet is the same, which means that the energy of the chemical reaction is the same. --Tardis (talk) 15:53, 18 November 2010 (UTC)

It depends entirely on what conventions you are using. All that matters is that changing the direction of the work switches the sign of ΔE. Under some systems, we take the perspective of the system (chemical thermodynamics takes this perspective, thus exothermic reactions have a ΔE < 0 ). Under other systems, we take the perspective of the observer (who is part of the surroundings), thus the sign convention would be opposite. However, your intuition is correct. All other things being equal, the only difference between the direction of the work is the sign of ΔE. It becomes obvious if you place two objects on a number line. If object A pushes object B in the positive direction, then object A did +ΔE, if object B pushes object A with the same force over the same distance, then object A did -ΔE. As long as you keep the perspective on "work done on/by object A" you will always get opposite signs for those two situations. The implication of the independence of work from the frame of reference is the Law of conservation of energy. If you could vary the amount of work merely by changing the frame of reference, then total energy would not be conserved. --Jayron32 04:17, 16 November 2010 (UTC)

What you said for part 1 makes sense. For part two, why does it imply the conservation of energy? 76.68.247.201 (talk) 04:54, 16 November 2010 (UTC)

If I could change the amount of work done in an isolated system just by altering my frame of reference, that would imply that if I was in motion past an isolated system, and observed the work done in the system, that value would be different than if I was stationary relative to that system. That would imply that there were differing amounts of energy exchanged in the two situations; where would the extra energy come from or go to? --Jayron32 05:00, 16 November 2010 (UTC)

In the original example, both planets gain positive kinetic energy and the system (the two planets together) loses gravitational potential energy. Dbfirs 08:41, 16 November 2010 (UTC)

Yes, I had just realized that I forgot about PE after I posted. Thanks for the clarification! 76.68.247.201 (talk) 12:10, 16 November 2010 (UTC)

Wireless v fibre internet

Is it true that wireless internet will never attain the speeds of (optical) fibre internet due to the laws of physics? We're having a debate about an National Broadband Network in Australia at the moment and I hear this statement a lot. I'm wondering if it is theoretically true. 124.149.24.85 (talk) 10:35, 16 November 2010 (UTC)

I believe that the theorietical maximum is based on the frequency of the carrier, and light has a much higher frequency than radio. However I don't think that radio or fibre are near this maximum (though I could be wrong), so possibly tomorrow's wireless will exceed the maximum speed of today's fibre -- Q Chris (talk) 11:32, 16 November 2010 (UTC)

'Speed' can be a bit of nebulous term. It's more an issue of bandwidth. The argument goes that due to the finite range of frequencies available for wireless transmission it can only handle so much bandwidth, whereas for fibre, if you're running out of bandwidth you can just lay another optical fibre cable down and increase it. Wireless is often proposed as a solution in low population density areas for two main reasons - the wide spread of the few people makes laying the cable uneconomical, and secondly with only a small number of people accessing the wireless network each can have a bigger share of the limited bandwidth and thus achieve higher speeds than would be possible in high population density areas (but not as high as they'd get with fibre). As the saying goes, never say never, but with current technology and knowledge these limits apply. --jjron (talk) 12:13, 16 November 2010 (UTC)

Thanks. Do you know the name of the physical principle that limits the bandwidth in wireless communication?124.149.25.247 (talk) 01:25, 17 November 2010 (UTC)

You'll want to read the articles Bandwidth (signal processing) and most importantly Spectral efficiency. --Jayron32 01:35, 17 November 2010 (UTC)

It is hard to find true theoretical limits without very well defined conditions but for reasonable conditions in the next 30 years or so fibre seams to have a big advantage if you are concerned with bandwidth while wireless can theoretically have a small advantage in Round-trip delay time due to higher speed of electromagnetic waves in air than glass(300 000 km/s and approx. 200 000 km/s).

I define wireless internet as communication in the radio and microwave frequencies. (Ruling out Free-space optical communication and other high frequency devices that has very different properties than current wireless internet such as WIMAX, WLAN, 3G and 4G) The fastest wireless link I found was on 6 Gbit/s, see [1], it uses a frequency band at 85 GHz, it achieves 2.4bits/s/Hz over a distance of 250 m. Depending on definition the microwave band is up to 300 GHz wide. Depending on the signal to noise ratio the number of bits per second and Hz vary, se Spectral efficiency and Shannon–Hartley theorem. With very low noise the best modulations give about 15 bits/s/Hz, this would give a theoretical maximum capacity of 4.5 Tb/s and antenna. With MIMO several antennas (independent channels) can be combined to higher capacity, the number of antennas is theoretically unlimited but due to limits in device size, signal-processing and the need for path diversification the number of effective independent channels are probably limited to less than 10.

This gives a upper limit on the capacity of microwave communication to less than 50 Tb/s for each cell. (A device anywhere near this capacity will probably not be mobile and very directional so it has probably no place in a cellular network)

The physical bandwidth in a conventional fibre are about 150 THz (1000 nm to 2000 nm).

The fastest fibre optical link that has been demonstrated uses 10.8 THz and was able to achive 69.1 Tb/s over 240 km. So a single optical fibre can already get higher capacity than the "theoretical" upper limit for microwave communication.(http://www.ntt.co.jp/news2010/1003e/100325a.html) If they where able to use all the physical bandwidth they would get a capacity about 1 000 Tb/s. This can then be multiplied by an almost unlimited number of fibres. The fastest commercial links to date can archive 1.6 Tb/s, see Wavelength-division multiplexing.

--Gr8xoz (talk) 01:42, 17 November 2010 (UTC)

Thanks for your reply. My understanding is that the Shannon-Hartley theorem defines the maximum error free data transfer under a noisy channel. So, my guess is that the physics that puts an upper limit on wireless communication is the existence of Additive white Gaussian noise, which from my understanding models background radiation and other universal physical phenomena. Given that, I might rephrase my original question: is Shannon-Hartley theorem a fundamental physical law? Is there no way to theoretically circumvent the principle? 124.149.25.223 (talk) 02:52, 17 November 2010 (UTC)

After searching a bit, I think I have already found an answer to my own question. It's all about entropy. Thanks again to all who answered. 124.149.25.223 (talk) 03:23, 17 November 2010 (UTC)

Species identifcation for File:Rama rama.jpg

The image in question

In order to expand on the image description, so the image can be moved to Commons, Is anyone on the Science Reference desk able to provide a more specific species identification?

Image is used on Fauna of Borneo if you need some indication of geographical location.

Sfan00 IMG (talk) 12:46, 16 November 2010 (UTC)

Just so you don't waste time looking it up rama rama is apparently just Malay for 'butterfly', Google yields nothing. —Preceding unsigned comment added by 86.4.183.90 (talk) 14:08, 16 November 2010 (UTC)

I can confirm that. I'll provide some more suggestions on Sfan's talk page (out of respect for the uploaders privacy). Nil Einne (talk) 18:28, 16 November 2010 (UTC)

Red v. grey squirrels

If grey squirrels had not been introduced into the UK, would red squirrels still be in such decline as they are now? In other words, have the grey squirrels merely taken up the space left by the red squirrels, or have they ousted them by direct competition or disease etc? Thanks 92.28.252.5 (talk) 13:26, 16 November 2010 (UTC)

There are various theories as to why grey squirrels have generally supplanted red squirrels - here - but the consensus does seem to be that the red squirrel has declined due to competition, rather than any other reason. Ghmyrtle (talk) 13:36, 16 November 2010 (UTC)

If you read that page carefully, you can see that in pine forests, there are about the same number of both kinds of juvenile squirrels. The reds' shorter lifespan, weaker constitutions, and less aggressive foraging behavior could easily be responsible for their decreased prevalence. Ginger Conspiracy (talk) 00:27, 17 November 2010 (UTC)

Seeing the space station

If I were to buy a medium range consumer available telescope and look at the international space station with it from earth, would I be able to see the station clearly and in detail? —Preceding unsigned comment added by 93.84.7.186 (talk) 14:11, 16 November 2010 (UTC)

The International Space Station's orbit never brings it lower than 278 km (173 miles) above ground. I'm not certain what is considered a typical "medium range consumer telescope" today, but I doubt it would have useful magnification much above 300 power. Even at 500 power, at the very best the station would look as though it was about 1/5 km (1/3 mile) away -- and usually farther, depending on where it was in its orbit and where on the ground you were. Not what you would call seeing it "clearly and in detail". --Anonymous, 14:31 UTC, November 16, 2010.

The ISS moves very fast, so any telescope would have difficulty keeping up with it.--Shantavira|^{feed me} 15:04, 16 November 2010 (UTC)

Starting about halfway down this page, there are several images (including some video) of the ISS transiting (passing in front of) the Sun and the Moon. Note that to observe a solar transit you need to have an appropriate telescope with suitable filters, and to get anything that would look space-station-like you need to have a big aperture telescope (several inches). Here's another solar transit, captured using a 160 mm (roughly 6-inch) telescope. Meanwhile, it is also possible to catch the ISS by itself — this image used a 100 mm – 3 inch – refractor.

However, what you aren't going to see when you look through the scope is the ISS hanging there in space. It's in low Earth orbit, moving at more than seventeen thousand miles an hour, and it's going to be rushing across the sky at about 1.25 degrees per second. It's very bright (when illuminated by the Sun) but very, very quick. Chasing it with your telescope is going to be difficult; you'll be lucky to see it slide briskly across your field of view. (The last link I provided above describes the challenge.) Ralf Vandebergh is an old hand at this stuff, however; he's coupled a video camera to his 10-inch Newtonian, and then stacks video frames together to get sharper, lower-noise images. With lots of time, effort, and practice, he's able to generate processed images that look like this or this. This remarkable frame may have captured an astronaut on a spacewalk. TenOfAllTrades(talk) 15:08, 16 November 2010 (UTC)

You can see the International Space Station with the naked eye; and you can photograph it directly, if you're careful. But it sounds like you want to produce an image of more than a bright dot. So let's clarify: a "medium range consumer scope" will probably not provide enough angular resolution, even in perfect weather and overflight-trajectory conditions, to image small details of the spacecraft. You will need a pretty good sized scope - we could say, eight-inch aperture as an absolute minimum, and a larger scope for better imaging. There are two optical "hard limits of physics" you need to worry about: angular resolution, and field of view. Our article angular resolution describes the physical limitations of angular resolution - it depends on your telescope aperture, so you can calculate a minimum observable feature size for any give down-range distance. The ISS is going to overflying me at about 750 km downrange for the next three weeks, so my eight-inch will allow me to resolve 2.0 meter features. (That's pretty darned good!) Now here's the really hard part: the other limiting factor, field of view, which depends on your telescope focal length. You can think of this as "magnification power." The more you magnify, the smaller the area of sky you can look at. So you're going to need a really accurate computer prediction of the ISS trajectory (which you can find from NASA's website or the various enthusiast tools linked above - I use kstars on Linux). And you're going to need a really carefully aligned telescope (I'm usually pretty darned sloppy, but you should find true astronomical north with a polar scope, weight down your scope with a really good tripod and mount, and very precisely position your sights on the expected overflight path. You'll have one spot of sky - you can't move your scope fast enough to track ISS. (Military-grade fast-tracking scopes that can pan the sky as fast as an orbit-track as an "exercise to the reader"). Now, you've got to wait - depending on how perfectly aligned your clock is to the ISS (in theory, both you and NASA are synchronizing to the GPS clocks). The ISS should enter your field of view exactly on schedule, and you'll have ... about two seconds, if you're lucky. So you'll want your imaging system to capture as many photos as possible (burst mode, or video mode). And you'll want to make sure your imagers are well coupled, optically, to your tube, so that you aren't losing resolution at the film or digital imager. Finally, be certain to run some numbers for your optical system, camera's shutter speed, ISO settings, and set your exposure settings properly - you won't be very happy if you return a photo of a black sky or a washed-out dot! If you're lucky, you'll have captured ten or so photographs of the ISS overflight. With a good deal of image post-processing (to first order, an image stack to denoise, and maybe a superresolution algorithm), and you should be able to produce fine-quality photographs of ISS. As I mentioned, my 2-meter feature resolving capability means I could (theoretically) produce a decent photo of the solar panels and individual modules; but I recognize the inherent challenges in this endeavor. So far I have not been able to capture ISS - but the orbit's approaching my latitude/longitude in end of November! Nimur (talk) 18:14, 16 November 2010 (UTC)

I've been able to catch the ISS in my telescope, but low power is preferable for this task and the view only lasts for a fraction of a second! Capturing an image would be much easier by mounting the camera "piggyback" to the telescope and shooting a long exposure photograph that captures the space station's trail. ~AH1^(TCU) 03:29, 18 November 2010 (UTC)

Differences between clone and original

What physical differences could be between human clone and its original "prototype"? —Preceding unsigned comment added by 89.77.156.31 (talk) 18:27, 16 November 2010 (UTC)

Age? Current cloning techniques can't instantly create an exact copy, just an embryo which, in time, will grow up to be a "copy". --131.188.3.20 (talk) 18:39, 16 November 2010 (UTC)

Fingerprints and obvious stuff like height, weight and various other things. Identical twins should give you a clue although given that the clone would likely be raised in a rather different environment some differences are likely to be more pronounced. (Clones and identical twins also have a relatively different genetic history.) Nil Einne (talk) 18:47, 16 November 2010 (UTC)

New somatic mutations, epigenetic differences, telomere length, chance differences during embryogenesis, differences in neuronal connections and experience-dependent synaptic plasticity. Just to name a few. --- Medical geneticist (talk) 19:17, 16 November 2010 (UTC)

Further to Nil's post, you might find Twin study interesting. Although as it states in the article, twin studies are mostly about behavioral not physical differences. Vespine (talk) 23:02, 16 November 2010 (UTC)

Absolutely, any difference you expect between identical twins you would also expect in clones. Freckles, birthmarks, that sort of thing visually. Ginger Conspiracy (talk) 06:21, 17 November 2010 (UTC)

Monozygotic twins might be even more identical than clones, because the in utero environment for twins would be very similar, whereas the environmental experience of the clone would be quite different from the original. -- Scray (talk) 19:44, 17 November 2010 (UTC)

It's also not yet possible to clone humans, so one of the differences is that the original can exist. Paul (Stansifer) 03:28, 17 November 2010 (UTC)

Schrödinger's cat

It seems to me that this is a very bad example. Who could believe the cat could be both dead and alive? AdbMonkey (talk) 22:31, 16 November 2010 (UTC)

Much of quantum mechanics is classically non-intuitive; that does not make representative examples (such as Schrödinger's cat) "bad". Note that our article describes the cat as a reductio ad absurdum intended to critique an interpretation of quantum mechanics. Note also that by the time you get to interpretations you're really into the philosophy aspects of the science: the math is the same, but the explanation for "how" varies. — Lomn 22:40, 16 November 2010 (UTC)

I thought that was sort of "the point". Vespine (talk) 23:07, 16 November 2010 (UTC)

It isn't "both dead and alive" -- the cat's wave function is comprised of two juxtaposed but completely different states, only one of which is, has been, or will ever be real. Just because there are two disjoint juxtaposed states doesn't mean that they are both as real as the other. Ginger Conspiracy (talk) 23:55, 16 November 2010 (UTC)

What do you mean when you say that only one state is real? Are you suggesting a hidden variable theory? Rckrone (talk) 02:30, 17 November 2010 (UTC)

No, only that the wave function collapses deterministically, so only the one state which eventually prevails was ever real in the first place. Ginger Conspiracy (talk) 06:09, 17 November 2010 (UTC)

Doesn't work. Not even consistent with the two-slit experiment. If there's a real answer to which slit each photon went through, you don't get an interference pattern. --Trovatore (talk) 09:43, 17 November 2010 (UTC)

The case where the wavefunction collapses into a density function representing both of its disjoint states is distinct from the case where it can't. Ginger Conspiracy (talk) 17:33, 17 November 2010 (UTC)

"Anyone who is not shocked by quantum theory has not understood it." — Niels Bohr. --Mr.98 (talk) 02:08, 17 November 2010 (UTC)

Wouldn't the cat observe itself, thereby collapsing the juxtapostion of states. Plasmic Physics (talk) 06:25, 17 November 2010 (UTC)

Certainly, but for the purposes of the thought experiment, traditionally the cat isn't considered to observe itself. When this comes up in class, often the cat is removed from the box which then contains only the radioisotope, Geiger counter, relay, solenoid, and poison capsule, which everyone has an easier time believing can't observe itself. Ginger Conspiracy (talk) 08:20, 17 November 2010 (UTC)

It's not actually a problem that the cat observes itself. The cat is in a superposition of two states: one where it is dead, and one where it has observed itself, and to itself the wave function appears to have collapsed to the state where it's alive. Rckrone (talk) 08:48, 17 November 2010 (UTC)

Personally, I agree. The difference between classical and quantum mechanics is quite specific and can be illustrated with a number of simple thought-experiments. Schrödinger's cat is not one of those experiments. There is nothing really quantum about Schrödinger's cat; the quantum prediction for anything you might measure in this situation is the same as the classical prediction (unless you believe that there's no such thing as classical randomness—but quantum mechanics is not just classical mechanics with randomness). I think it became popular because of the vivid imagery of killing an innocent cat with poison gas, not because of any pedagogical merit. -- BenRG (talk) 08:20, 17 November 2010 (UTC)

What is obervation defined as? Does it have to involve a conscious entity? In my opinion, any interaction at all counts as some degree of observation. I think that whether an observation of this definition causes a wavefunction collapse is determined by how far information of the states propagates before being smeared by quantum mechanics; and by some sort of relationship to entropy and time. Thus, I propose a scenario: two equivalent closed cells containing one rod of atoms each. One rod is a micrometer long, the other is a centimeter long rod, both are initially in a juxtaposition of states. If both cells remain closed, there is a probability that both wavefunctions will have collapsed, there should be a larger probability for the longer rod have collapsed. This is my theory. I have never studied quantum mechanics, I just read the occational popular science journal like New Scientist, so I might be completely wrong, but seriously, what is obervation defined as? Plasmic Physics (talk) 09:20, 17 November 2010 (UTC)

Observation most definitely does not have to do with consciousness. It has somewhat to do with interaction, but more to do with information. If information is transfered from the system it was "observed". You can interact with it (for example a mirror), without transferring information and then it's not "observed". I don't follow your example with the rods. Ariel. (talk) 10:35, 17 November 2010 (UTC)

I'll explain: The mere presence of the rods within the box counts as an observation, because the electromagetic fields of the constituent atoms that make up the rods themselves transfers information to the cell walls. There is no way to completely isolate the rods, information is always transfered, so there cannot exist a juxtaposition. This is conclussion is clearly not true. As such, the degree of observation must be proportional to the probability of wavefunction collapse. This is different from the norm, where observation is a true or false property. I suggest that it is impossible to describe with perfect certainty whether a juxtaposition of states has collapsed or not without actively observing as in the Schrödinger's cat thought experiment.

Back to the example. The implications of this theory are, there is a non-zero probability that the juxtaposition of states will have collapsed for both of the cells, without having opened them. The propability is, among other things, dependent on the number of quantumn particles in a juxtaposition. The probability of the longer rod having a collapsed wavefunction in a closed cell is larger than that of the shorter rod. Plasmic Physics (talk) 11:22, 17 November 2010 (UTC)

People keep missing the one of the most important aspects of the Schrodinger's Cat paradox. Science requires an uninvolved observer, in order for results to be reproducable, which is a cornerstone part of science, we need to assume that our observations of phenomena indicate that the phenomena would go on even if we weren't there. When we say that a black hole behaves some way, we assume that the black hole behaves that way even when we aren't looking. When a biologist wants to observe the behavior of a lion in the wild, he has to do so without interacting with the lion, lest his presence alter the lion's behavior. Someone analyzing the effect of some substance on living cells wears gloves to avoid contaminating the sample with oils from their skin. Science works to try to isolate the phenomenon from the observer, so we can make universal statements about the phenomenon, and so we can assume that our results are reproducable independent of the observer. Here's the kicker with quantum mechanics: Independent observation is impossible. This is not a function of technology (lacking the proper instruments), it is a function of the nature of quantum mechanics itself. We cannot observe a quantum mechanical phenomenon without interacting with the phenomenon itself. Passive observation is impossible. Thus, when we want to say "How is this electron behaving when we aren't looking", it is actually impossible to predict with accuracy, since ANY test we would do to look at the electron involves bouncing a photon off of it, which alters the nature of the electron. We actually can't say what the electron was doing before we bounced the photon off of it. It is indeterminate. This is why quantum mechanics, as unsettling as it is to most people, is actually MORE unsettling to people of a scientific worldview, since QM violates one of the fundemental principles of science itself. --Jayron32 16:17, 17 November 2010 (UTC)

Quantum zeno effect. ~AH1^(TCU) 03:26, 18 November 2010 (UTC)

Never mind the cat — has anyone created a box? Some way to hold a bit of information that is removed from the original source, which doesn't allow a collapse of states until it is looked into? For example, a way to look at which slit a photon passes through in a double slit experiment, and store the result in a quantum computer, and then you look at the interference pattern, and only after that you decide whether to look at the quantum computer and see which slits each photon went through (retroactively erasing the interference pattern and your memory of having looked at it and seen it) or alternatively you just erase the bits unread and the interference pattern stands. Does something like that exist? Wnt (talk) 09:19, 18 November 2010 (UTC)

http://www.newscientist.com/article/dn18669-first-quantum-effects-seen-in-visible-object.html

See delayed choice quantum eraser. --Tardis (talk) 15:46, 18 November 2010 (UTC)

There's no retroactive memory erasure, or retroactive anything, in quantum mechanics. The delayed choice quantum eraser experiment is relevant here, but there is no retroactive disappearance of interference patterns in that experiment. Don't pay much attention to the name, which was chosen more for audience appeal than accuracy, as names so often are. -- BenRG (talk) 21:04, 18 November 2010 (UTC)

I'm happy to agree that there's no concept of passive measurement in quantum mechanics, though there can be passive measurements in special cases. The quantum Zeno effect illustrates that well. I don't see how Schrödinger's cat illustrates it. In fact, opening the box is a passive measurement, since the internal state has long since collapsed to a mixed state. Schrödinger can be forgiven for not knowing that, but modern presentations can't. -- BenRG (talk) 21:04, 18 November 2010 (UTC)

Ok so it has nothing to do with the torture of a cat in a box. It has to do with the fact that physicists think they may be getting accurate results but they are not taking into consideration that their presence has probably altered the result. And this is on a micro level. It actually has nothing to do with killing a cat with radiation. And even if it did, it would be wrong, because a cat cannot both be dead and alive at the same time. The cat is really an atom, or isotope or something physics- like. AdbMonkey (talk) 20:35, 18 November 2010 (UTC)

In Schrödinger's original paper the fact that the cat was a macroscopic living being was important. One could try to recycle the same thought-experiment for a different purpose, but I see no reason to do that except that one likes fictional cat-killing as a way to engage one's students. And I think that Schrödinger's original purpose has been rendered obsolete by the modern understanding of measurement in quantum mechanics.

(And physicists most certainly do take the quantum measurement process into account. It is metaphysically troublesome that the description of isolated systems looks different from the description of systems under observation, but in practice it's known how to correctly model both cases.) -- BenRG (talk) 21:04, 18 November 2010 (UTC)

Ok, I'm just a tad confused and I'm sorry to ask this, but what key concepts should you walk away from this thought-experiment knowing? AdbMonkey (talk) 21:17, 18 November 2010 (UTC)

In practice, the cat is in one state (or, in the many worlds interpretation, we are entangled with it long before we physically open the box), because real boxes interfere with only the most simpleminded of measurements. (Consider checking for the body heat of the cat, or listening for its breathing, or x-raying the box, etc.) If one could build a sufficiently well-sealed (and insulated, and electromagnetically sealed, etc.) box, then the point of the thought experiment is that (with such a fantastic box) we really could have a cat in a mixed state, and the world really is that weird! --Tardis (talk) 06:24, 20 November 2010 (UTC)

Oh, you need a complete vacuum inside the box, and the cat can't touch the sides, because of its size the cat must be impossibly black or as close to a black body radiator as possible, and the temperature must be as close to absolute zero as possible; the matter comprising the box must be least aware of the presence of the cat - inanimate objects can observe and collapse the mixed state through field interactions. The more observing particles being directly influenced by a mixed state, the higher the chances of its collapse. As a result, this concept only works for systems small in physical size. The more particles participating in the mixed state, the harder it becomes to isolate it from observers, be they boxes, scientists, or cats. Plasmic Physics (talk) 13:06, 20 November 2010 (UTC)

Anacoustic

There seems to be something like Anacoustic, but neither google nor google books nor google scholar gives me at a first glance a good explanation. (The barium sulfate article contains the word and I have no clue what the application in Anacoustic faom could be.) --Stone (talk) 22:44, 16 November 2010 (UTC)

I'm thinking it's something like this. DMacks (talk) 22:50, 16 November 2010 (UTC)

Most likely yes!--Stone (talk) 07:17, 17 November 2010 (UTC)

It's probably anechoic, aka sound-proofing. CS Miller (talk) 22:53, 16 November 2010 (UTC)

The anacoustic zone is the atmosphere above 100 miles or so where there are still enough gas molecules to produce substantial drag, but they aren't close enough to transmit sound because the probability of molecular collisions is so low. Ginger Conspiracy (talk) 00:00, 17 November 2010 (UTC)

November 17

Please, help me decide whether to drink my tea.

I dispensed hot water into my plastic CamelBak water bottle so that the tea-bag can do a better job than it would in cold water. Now I remembered my mother telling me about pouring hot beverages in a plastic container causing cancer. However, no one else said this.

Does a hot beverage leech plastic chemicals into the drink, thereby causing one to develop cancer? If not, what ill effects could it cause?

Also, would anyone please post sources backing this up? Thanks. --98.190.13.3 (talk) 04:22, 17 November 2010 (UTC)

Our Reuse of water bottles article has some info. I don't know what kind of plastic a CamelBak is made from, so I don't know any specifics of what may be leached out, etc. DMacks (talk) 04:25, 17 November 2010 (UTC)

Some (but NOT all) plastics contain Bisphenol A which has been shown to be linked to a number of health issues. Hotter water tends to dissolve more Bisphenol A than cold water (this is a nearly universal property; hot water tends to dissolve more of anything than cold water). There are also a host of other chemicals which may (or may not) be linked to health issues depending on the specific type of plastic. Again, you would have to know the specific type of plastic in your water bottle before you could decide if you just killed yourself. --Jayron32 04:29, 17 November 2010 (UTC)

Your mother may have heard about microwaving plastic. The Mayo Clinic says microwave-safe containers are okay, but notes that the FDA warns that non-safe plastics that melt when you nuke 'em may potentially leak chemicals. So, as long as you don't want your tea really really hot, you should be fine. Clarityfiend (talk) 04:39, 17 November 2010 (UTC)

The CamelBak article says that their water bottles don't contain Bisphenol A (BPA). Red Act (talk) 04:44, 17 November 2010 (UTC)

Almost all of the chemicals which can leach out of plastic food containers are not toxic at all (chemists don't want to get sued!) but some of them can taste pretty bad. Even bisphenol A is only a serious threat to fetuses and possibly infants. Ginger Conspiracy (talk) 06:15, 17 November 2010 (UTC)

You need a teapot. The spherical ceramic kind are best. 92.28.250.11 (talk) 10:20, 17 November 2010 (UTC)

@Ginger: They're relatively nontoxic. Companies are willing to put up with a small (non-zero) number of lawsuits over their products, if the difference in cost between a product and its alternative (safer) product is GREATER than the money that could be saved by the lower number of lawsuits, companies would then choose to use the less safe, but cheaper, product since the outgoing cash on the lawsuits on it is still small enough to make it worth it. When actuarial science meets economics, that's what you get. The only reason that companies took Bisphenol A out of baby bottles wasn't because some new science indicated they should, it was that the likely cost of keeping it in the bottles grew exponentially such that the more safe, but more expensive, plastic became cheaper when factoring in the likely lawsuits. --Jayron32 16:08, 17 November 2010 (UTC)

chemistry

if the hydrogen gas is flammable and it burns with pop up sound oxygen is also necessary for burning the combination of these two [water] is used to extinguish fire —Preceding unsigned comment added by Bharat.293 (talk • contribs) 04:30, 17 November 2010 (UTC)

I am guessing that you are asking for an explanation of the relationship between hydrogen, oxygen, water, and burning. Lets see if I can give you the short-short version.

• Elemental hydrogen and elemental oxygen are both relatively unstable. Both hydrogen and oxygen would be more stable if they were part of a chemical compound rather than as pure elements (nearly ALL elements, with the notable exceptions of the noble gases, are like this). The reason for this is that both elements have the wrong number of electrons for their most stable state. Hydrogen has too many electrons (it would rather have a positive charge than neutral) and oxygen has too few electrons (it would rather have a negative charge than neutral). When we chemically react hydrogen and oxygen, what happens is hydrogen and oxygen rearrange their electrons such that oxygen gets extra electrons and hydrogen gets to give up some of its electrons. This makes BOTH of them more stable. In chemistry, stability is related to potential energy; the more potential energy stored up in something, the less stable it is. When it releases that potential energy, usually as heat, the new substance that forms is more stable than the substances that formed it. In this case, the new substance is water, which is composed of atoms of hydrogen and oxygen, but in this case arranged such that BOTH have the number of electrons that makes them most stable. This is why water is not very chemically reactive; it already has its electrons in a relatively stable arrangement, so it will no longer burn. Burning is just the outward sign of the chemcial reaction between the fuel (in this case hydrogen) and oxygen.
• To sum up, the process of burning involves a rearrangement of the electrons between hydrogen gas and oxygen gas to form a new substance (H₂O) which is more stable than the starting state. Because this new state is more stable, it isn't going to react further, so it will now put out flames rather than burn itself. --Jayron32 04:46, 17 November 2010 (UTC)

Bharat, are you remarking on the oddity that the combustion of hydrogen and oxygen produces water, yet water is what we commonly put fires out with? —Steve Summit (talk) 06:14, 17 November 2010 (UTC)

That has to be it. So the answer is "Yes, that's right" I'd say. Ginger Conspiracy (talk) 06:17, 17 November 2010 (UTC)

Water can be used to put out SOME fires. This is because it typically acts either to reduce the 'heat' of the combustion reaction. Other forms of (non-water) extinguisher target other parts of the fuel triangle, like for example a C02 extinquisher works by denying the fire access to oxygen.. Sfan00 IMG (talk) 20:40, 17 November 2010 (UTC)

We have a fire triangle article. DMacks (talk) 21:01, 17 November 2010 (UTC)

Although the water itself does not put out the flame, the instant reaction of hydrogen and oxygen produces a flame that immediately extinguishes itself. Water does not put out all fires, as a grease fire will continue burning as its heat fuel source is removed only briefly, and water can often start electrical fires though even hot water will cool a red-hot iron nail as liquid water cannot be hotter than 100°C under normal circumstances. ~AH1^(TCU) 03:23, 18 November 2010 (UTC)

It's really quite simple: wood will burn, but the ash that's left over will not burn again. Hydrogen and oxygen burn, and the ash is water. Sand is the ash of silicon and oxygen. Since fire needs oxygen, if you cover a fire, it goes out. Of course, the fire may ignite the thing you cover it with, and then you just have a new uncovered fire. If the cover won't burn, then the fire does go out. You can thus put out many fires by covering them with ashes, sand, or water. --Tardis (talk) 15:42, 18 November 2010 (UTC)

Catfish

I just watched an episdode of River Monsters, and the host would take very large catfish, such as the Piraíba or Jaú, out of water. They made strange grunting and moaning sounds, which he said were because of air moving over the gills, rather than water. This set me wondering: can they breathe in air? Thanks, --The High Fin Sperm Whale 06:20, 17 November 2010 (UTC)

Some can for a while, see airbreathing catfish. Sean.hoyland - talk 06:40, 17 November 2010 (UTC)

Yes, I am familiar with airbreathing catfish. My question was whether or not a large one, such as those I mentioned earlier can. --The High Fin Sperm Whale 18:42, 17 November 2010 (UTC)

Yet another mistake in the solutions?

Read Question 4 (b) (iii) (inelastic) here: http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/006039/RND01/PH866_paper02.pdf to which the solutions are here (scroll down to the second last page): http://www.tqa.tas.gov.au/4DCGI/_WWW_doc/006121/RND01/PH866_report_02.pdf . Where did he get 10.6 eV from?? If he got it by subtracting the gap between n=2 and n=3 (which would be 1.9 eV) from the 12.5 eV that the electrons originally had, that's wrong, isn't it? Since the hydrogen atom is in the ground state, there are no electrons to excite in n=2, correct? 220.253.217.130 (talk) 08:42, 17 November 2010 (UTC)

My guess is the person writing the answer key should misread the n=1 level for the n=2. Assuming the collision is involving the ground state hydrogen atom, you should be able to use the energy bled off of the colliding electron in an inelastic collision to do the n=1 -> n=2 transition and the n=1 -> n=3 transition. The n=1 -> n=4 transition won't happen because you would need excess energy in the colliding electron. So the only two answers should be 0.4 eV (1->3) and 2.3 eV (1->2). --Jayron32 15:59, 17 November 2010 (UTC)

Lambert's cosine law

In Lambert's cosine law it describes how if the sun were a perfect black body radiator it would appear to us as a circle the same brightness all over, yet it darkens towards the rim. The full moon on the other hand should darken towards the rim, but it seems almost as bright at the rim as at the centre. There is an explanation about the sun at Limb darkening, but why does the full moon seem brighter at the edge than one might expect thanks? Dmcq (talk) 10:10, 17 November 2010 (UTC)

Is the moon really brighter at the edge? I've never noticed that. Perhaps it's obvious, but the moon is not a black body radiator, it's a reflector. But I'm not sure if that makes a difference. It probably depends on how directional the reflection from moon rocks is. In a black body the light is emitted evenly in all directions, but in a reflector it may have a preferred direction. Ariel. (talk) 10:30, 17 November 2010 (UTC)

It should also bear stating that a blackbody is an unrealistic ideal, something like an ideal gas or perfect vacuum. We can do mathematical calculations which show how a blackbody should behave, and some real objects aproximate these calculations, but no real object acts like a blackbody. --Jayron32 15:30, 17 November 2010 (UTC)

The Moon's maria on the Earth-facing side make it brighter towards the center in total but also brighter on most of its rim. Ginger Conspiracy (talk) 17:49, 17 November 2010 (UTC)

I got my wording a bit confused, the lambert law should apply to the moon, just the article mentioned the sun. I don't think the maria quite explain the effect, they don't say why the edge shouldn't be fairly dark. I was wondering perhaps the moon isn't as dark as it should be towards the edge because it has lots of craters and what we see at the edge are the reflections from the sides of the craters, does that sound like it might be possible? Dmcq (talk) 10:48, 18 November 2010 (UTC)

The article isn't talking about the edge of the moon as viewed from here, but rather as viewed from the sun: the edge of the lit part of the moon. Of course, those are the same when it is full; the article goes on to say that the lack of darkening indicates that the moon isn't Lambertian. If it were, we would expect its limb to be bright (which it is), but more terminator darkening than we see. --Tardis (talk) 17:44, 19 November 2010 (UTC)

You're mistaken. The article is talking about the edge of the moon as viewed from Earth.--Srleffler (talk) 18:58, 21 November 2010 (UTC)

Please help me clear up this hogwash about adjusting braces at the SAME orthodontist.

Hi, when I saw that getting braces in India was only going to be as low as $225 to as high as $1800 USD, I then had a desire to travel to India to get the deeply-discounted orthodontic work.

Then someone told me that I'd have to fly back to the same orthodontist to get them readjusted every so often. I thought that was a bunch of hooey, because get THIS logic:

TRUE OR FALSE: A driver who buys his Ford in Texas and moves to Maine, must drive his car all the way back to that same Ford dealer in Texas to realign his axles (and perform other substantial maintenance.)

See the fallacy here? He only has to drive it to the nearest Ford dealer from his house in Maine. Or if an independent mechanic is closer, he can simply drive it to them and they can do all the maintenance needed just so long as they have the right equipment.

Now the orthodontists' equipment is state-of-the-art back Stateside, so they'll undoubtedly have all they'll need to readjust Indian braces.

So since the logic of having to travel back to the same orthodontist to readjust braces falls under the same level of fallacy as the car maintenance analogy, I didn't buy what they said.

(Also, think of military families whose family must move with the active duty serviceperson, and sometimes on short notice. If their child got braces in Fort Hood, and they move to the base in Landstuhl, their child would hate to fly all the way back to Fort Hood for a mere readjustment. Some kind of accommodation would need to be made. That would be to just get it done at a local orthodontist.)

So can someone clear this up? I still hope to get braces at the cheapest possible place, but get them readjusted wherever I happen to be. Thanks. --70.179.178.5 (talk) 10:33, 17 November 2010 (UTC)

I'm confused as to what sort of answer you expect since apparently the last one wasn't good enough. Wikipedia:Reference desk/Archives/Science/2010 September 5#Why can't I just get a local orthodontist to readjust braces installed in India?. Ultimately even though as I said last time, it seems unlikely that you won't be able to find some other orthodontist to deal with your braces, no one here can guarentee your local orthodontist will be able to handle your braces. Your best bet if it concerns you is to ask your local orthodontist yourself. Nil Einne (talk) 10:45, 17 November 2010 (UTC)

Cool, N.E., that IP user must've been on a similar mental plane as me. Seems like we have a lot in common; I'll have to study his editing history now. --70.179.178.5 (talk) 11:13, 17 November 2010 (UTC)

You do indeed have a lot in common as it seems you both use the same ISP and appear to live in the same area in or near Manhattan. Nil Einne (talk) 14:07, 17 November 2010 (UTC)

One thing they don't share is time. The old IP address made edits through mid-September. Then, they stopped. Once the old IP address stopped making edits, this IP address began making very similar edits (similar topics, similar grammar, similar misspellings...). -- kainaw™ 15:29, 17 November 2010 (UTC)

... but they do share a blog at "bigyesbomb"! Dbfirs 01:45, 18 November 2010 (UTC)

(ec)As much as possible you need to stick with one person when adjusting, this is because you make a plan for the adjustments, when to do what, which tooth, etc. If you go to a different person each time you'll get a mix. The solution to this is very good records, and presumably the military does that, but I doubt a regular orthodontist is going to carefully read and follow the documented plan. You'll be lucky to even get a written detailed plan. That said, you can probably get them installed in India or wherever, then stick with the same new local person for all the future adjustments. But you better hope that he has tools or equipment to service the exact type of braces you are getting, I believe there is a wide variety of types, and a variety of ways of attaching them. Ariel. (talk) 10:49, 17 November 2010 (UTC)

"Someone told you"... Did you ever ask an orthodontist if they would be willing to manage the periodic readjustments of braces installed elsewhere? There could be many reasons why an orthodontist would prefer to have the braces be his or her own handiwork, but people move all the time and they don't generally have this problem. I suspect that you won't get an answer that satisfies you here on the RefDesk and would be better suited simply asking the orthodontist that you hope to be followed by. --- Medical geneticist (talk) 16:45, 17 November 2010 (UTC)

Periodontal resident here -- orthodontics is a field in which comprehensive care can and often does exceed the length of a treating resident's residency -- for example, if the average ortho case takes 18 months to complete, any case began within 18 months of graduating needs to be completed by another resident. That being said, ortho residencies are highly regulated and organized by their administrators and professors, and the case will likely go though a thorough hand-off review. But outside, in the real world, I can certainly see an orthodontist refusing to pick up a case. Excepting death of the original practitioner (and perhaps even not excluding it) there has to be a really good reason to switch mid-therapy, because, as you can probably figure out, there are multiple ways to accomplish most any goal in dentistry, and mixing a case up between clinicians is like having two contractors building your house -- you might have to have good luck to make sure pipe A is able to meet up with pipe B when they're done. There are many orthodontic systems, many possible treatment planning options, many types of appliances, many different springs, hooks, wires, brackets and they can probably be used in different ways depending on the level of training, experience and personal preference. And this is assuming that the Indian orthodontist practices on a level congruent with American standards. Eastern European/Russian root canal therapy is a really strange thing to look at from a United States-trained dentist's perspective, and so is Central/South American restorative work (crown and bridge). Foreign dentistry may be inexpensive because there's no Manhattan premium, but it may also be inexpensive because it's shoddy. DRosenbach ^{(Talk | Contribs)} 19:40, 17 November 2010 (UTC)

Thank you for responding, Dr. Rosenbach. Not having straight teeth could give me dim job prospects because in this kind of economy, employers are looking for any slightest excuse to throw out an applicant, when they have so many resumes/applications for so few job openings, that they may even throw me out just because my teeth aren't straight enough. I would have to walk on so many eggshells just to have the slightest glimmer of hope for a job offer, that having to pay so much just to make it in the world defeats the whole deal. If there was a charity/schooling orthodontist office anywhere close to 66502, please let me know where the nearest location is and I'll consider that. Otherwise, this daunting catch-22 is one more reason why I must move overseas for good. --70.179.178.5 (talk) 08:40, 18 November 2010 (UTC)

Unfortunately, it appears as though the closest reliable discount for orthodontics might be UMKC in 64108, just over 2 hours away. DRosenbach ^{(Talk | Contribs)} 05:27, 21 November 2010 (UTC)

All cars of the same model (and production run) are (or should be) identical, so any garage with suitably experienced staff is usually happy to carry out your repairs and adjustments. Only identical twins have identical teeth (and even then, not always), so there is an element of creative art in the work of an orthodontist. It's rather like asking an interior designer to make small adjustments to your bodged DIY decorating, or an architect to improve the look of your self-built home. They might do it for you, but they will not necessarily be delighted to be asked. Dbfirs 01:17, 18 November 2010 (UTC)

Why does the sex drive far exceed what is biologically needed for reproduction?

Just wanted to know.--X sprainpraxisL (talk) 10:56, 17 November 2010 (UTC)

Define "needed".

For males, at least, and in species that are not 100% monogamous, it's evolutionarily advantageous to have as many offspring as possible. It's just another example of how rank selfishness, much as we'd like to define it as a social ill, is a biological imperative. —Steve Summit (talk) 12:29, 17 November 2010 (UTC)

(e/c)This is rather open ended. What species are you talking about, or just in general? Are you referring to humans? If so, whose sex drive...? Let's assume you're referring to an 'average' human, though I guess you could generalise and substitute in other species. In a historical and evolutionary sense, the simple answer to your question is that it doesn't. Let's say in basic terms the sex drive spurs the activity that results in reproduction. For the sex drive to "exceed what is biologically needed for reproduction" that would mean the reproduction rate would result in more children born than needed to replace their parents and an ongoing population boom. Historically this is not the case - populations in general remain fairly stable, unless or until something upsets the equilibrium. Now it is true that nature generally does produce more offspring than needed for replacement, and evolution will favour population growth if it can (greater spread of genes, etc), as well as needing to 'hedge its bets' for the bad times; indeed the excess individuals are the fodder for natural selection, but in normal conditions these excess offspring are removed from the population through conflict, starvation, etc and the overall population numbers remain relatively constant. When something does upset the natural balance we can see population booms like the recent one in human populations. As I said at the start, sex drives vary greatly both between and within species, but a generalisation would be that the average sex drive of a species is that which has been favoured by natural selection to maximise that species' long term survival - different species use different strategies (fewer offspring and greater parental care, more offspring and less parental care...) to try to achieve that best balance between producing enough offspring for the species to survive and prosper, and expending too much energy on reproduction. That's all pretty general; really you could do an entire thesis on this. --jjron (talk) 12:39, 17 November 2010 (UTC)

A relatively higher sex drive will tend to be selected for as long as it isn't detracting from survival or child rearing. Ginger Conspiracy (talk) 17:53, 17 November 2010 (UTC)

For humans who engage in media and other forms of entertainment, suggestive shows, films and commercials likely help promote the drive. DRosenbach ^{(Talk | Contribs)} 19:30, 17 November 2010 (UTC)

Unlikely to be the case. People have been randy long before there was television. In fact, my understanding is that various studies have shown that people's sex drives decrease as a function of how much television they watch. I don't have references handy, though. --Mr.98 (talk) 01:21, 18 November 2010 (UTC)

Keep in mind that before the invention of modern medicine, a significant fraction of human babies died in childbirth. thx1138 (talk) 19:33, 17 November 2010 (UTC)

None of that answered his question. You are talking about how many babies are born, but he asked why humans want to have sex far more often then is needed to get pregnant. The answer is twofold: Humans are the only species with Hidden estrus, so the male does not know when to have sex, so the males will try as often as possible. The the second reason is that sex reinforces pair bonding, so the male is motivated to stay with the female and help raise the babies. In an animal instinct can do this, but in humans a greater incentive is used. Note that contrary to impressions, and sitcoms, married men have sex far more often than single men. Ariel. (talk) 20:36, 17 November 2010 (UTC)

See libido. Also this article from LiveScience. ~AH1^(TCU) 03:19, 18 November 2010 (UTC)

Only? Are you sure? The article you linked to doesn't think so. It links to a ref on the occurance in vervet monkeys which mentions the occurance in other primates. It doesn't really mention any others per se from what I saw although it does mention others with prolonged sexual receptivity although that's more complicated then concealed ovulation per se (for example it mentions orangutans where it says it's often due to forced encounters). I believe some dolphins may also show concealed ovulation/hidden estrus although I couldn't find a decent ref. Nil Einne (talk) 18:06, 18 November 2010 (UTC)

See Also: Red Queen's Hypothesis Hcobb (talk) 18:17, 18 November 2010 (UTC)

What kind of moss covered bug is this?

I was walking around Norfolk, Virginia this weekend and I saw this piece of moss walking along a concrete pillar. I got a few photographs and videos of it. I feel like I've seen the bug before (without the moss). Such an interesting defense mechanism, I someone out there can help identify it. The insect does look familiar.

Here is a photo of the moss. On the right side you can see what I think are mandibles.

Here is a photograph of the creature upside-down.

Here Is a (handheld, sorry) video of it walking around.

Here Is a youtube video of it righting itself.

I went out again, and upon closer inspection, I this is the same bug, without the moss covering. The mandibles look the same, the size is similar, the legs look the same (from the upside-down shot), and the movement was similar.

Keegstr (talk) 15:06, 17 November 2010 (UTC)

It may not be moss at all, but may instead be Mimicry. Some bugs like planthoppers and walking sticks have amazingly complex ways to mimic their environment. I do not recognize this exact bug you have found, but I would assume that the stuff you are calling moss is actually an integral part of the bug itself. --Jayron32 15:23, 17 November 2010 (UTC)

It's a brown lacewing larva.[2] Very helpful in the garden for keeping aphids under control. Ginger Conspiracy (talk) 18:13, 17 November 2010 (UTC)

Thanks for the ID. Any idea what the deal with the moss is? Is it defense / camouflage? Keegstr (talk) 19:03, 17 November 2010 (UTC)

Sometimes known as 'trash bugs' apparently [3] and your assumption seem to be correct [4]. Mikenorton (talk) 10:52, 18 November 2010 (UTC)

Reaction products of opianic acid with strong acid

Is this image likely to be right? Reaction with strong hydrochloric or hydriodic acid. Possibly isomeric phenols are formed?
--Wickey-nl (talk) 17:25, 17 November 2010 (UTC)

Looks OK to me. You shouldn't get any isomerization whith hydrochloric or hydriodic acid, simply the hydrolysis of the two ester groups. I wouldn't like to guarantee that they get hydrolysed in the order that shown, but that's a fairly minor point. Physchim62 (talk) 17:58, 17 November 2010 (UTC)

nit: s/ester/ether/ DMacks (talk) 18:04, 17 November 2010 (UTC)

(ec)It's a plausible reaction, probably S_N2-like. Methyl ethers are stable to just about everything except strong acid. My protecting-groups table for "phenols, methyl ether" says the only suitable deprotection conditions are aqueous pH<1 and AlCl₃ (but only slowly unless warmed). I don't see an easy mechanism for isomerization. DMacks (talk) 17:59, 17 November 2010 (UTC)

FWIW, there is a known aqeous-acid-catalyzed isomerization of a different part of the structure in opianic acid and related compounds: the 1,2 acid-aldehyde portion can form cyclic ester-hemiacetal. (see doi:10.1007/BF00568016 and refs therein). DMacks (talk) 18:14, 17 November 2010 (UTC)

Cold-weather urination

Why does being in the cold make people urinate more? The core body temperature where the kidneys are must be either the same or nearly the same as in warm surroundings. 92.15.28.182 (talk) 18:09, 17 November 2010 (UTC)

I'm not sure it does, in general. Maybe because people drink more hot diuretic coffee? Ginger Conspiracy (talk) 18:14, 17 November 2010 (UTC)

People generally sweat less in cold weather but I don't think that's the whole explanation. A quick search for 'urinate more cold weather' comes up with some results, the most promosing looks to be [5]. That links to [6] for rats. From that same search, it seems in humans there's also greater urgency [7], in other words it may not simply be that you have more urine but that you feel a greater urge to urinate. Nil Einne (talk) 19:07, 17 November 2010 (UTC)

The phenomenon is called "cold-induced diuresis". Exposure to cold temperatures causes your body to respond with vasoconstriction in the extremities, which helps your body retain heat. The vasoconstriction causes blood pressure to become elevated, to which the kidneys respond by removing fluid from the blood stream in order to lower the blood pressure. The kidneys pass that removed fluid through the ureters into your bladder, which makes you need to urinate.[8] Red Act (talk) 19:37, 17 November 2010 (UTC)

The phenomenon is apparently sometimes also called "cold diuresis", as that's what the polyuria and hypothermia articles refers to it as. Cold diuresis is unfortunately a rather useless redirect. Cold-induced diuresis is part of the cause of immersion diuresis, as is explained a little bit in that article. Red Act (talk) 20:00, 17 November 2010 (UTC)

Frog dissection

Is there a common species of frog that would usually be dissected in a lab class to measure the contraction of its gastrocnemius muscle? 149.169.142.37 (talk) 22:05, 17 November 2010 (UTC)

Rana pipiens. --- Medical geneticist (talk) 01:25, 18 November 2010 (UTC)

When I was at Uni, we used the Cane Toad (Bufo marinus) in a lot of pracs. --jjron (talk) 12:31, 18 November 2010 (UTC)

Direction of apparent weight

Is apparent weight a directionless quantity? Or is it a vector equal to the normal force in both magnitude and direction (for instance, in an accelerating lift, in which case the direction would be up). -- 220.253.217.130 (talk) 22:21, 17 November 2010 (UTC)

There may be more than one way to define "apparent weight" but I would describe it as a force vector equal to the normal reaction with the lift floor, but in the opposite direction. Dbfirs 22:59, 17 November 2010 (UTC)

So in general, apparent weight is equal to the vector difference Fnet – Fg, but in the opposite direction (including for arbitrary direction for Fnet)? 220.253.217.130 (talk) 23:20, 17 November 2010 (UTC)

Or equivalently, apparent weight is equal to Fg – Fnet ? 220.253.217.130 (talk) 23:22, 17 November 2010 (UTC)

Well I would define real weight as a downwards force of magnitude mg (I assume that this is your Fg). If the lift is accelerating upwards with acceleration a, the normal reaction will be mg + ma upwards (assuming that the person or object is not moving relative to the lift floor), so by my definition, the apparent weight will mg + ma downwards. I'm not sure what your Fnet denotes. I think the safest way to deal with the situation is to consider only real forces and apply Newton's second law (Resultant force = mass times acceleration). Dbfirs 23:40, 17 November 2010 (UTC)

Fnet is the net force, that is the vector sum of the force due to gravity and the normal force, and is equal to ma, where a is the acceleration of the lift and m is the mass of the person. 220.253.217.130 (talk) 23:53, 17 November 2010 (UTC)

Sorry, yes, I should have realised that you meant the same as my "resultant force". (It's after midnight here.) Dbfirs 00:12, 18 November 2010 (UTC)

So does that make Fg – Fnet a correct formula for the apparent weight? 115.178.29.142 (talk) 00:32, 18 November 2010 (UTC)

Only when the lift is accelerating downwards (and a ≤ g), or if you allow Fnet to be negative when the lift is accelerating upwards. The safest method to avoid confusion is always to draw a diagram showing the directions of real forces, then apply Newton's second law. Dbfirs 01:03, 18 November 2010 (UTC)

-See also Weight#Vector_or_scalar, Apparent weight.Smallman12q (talk) 21:41, 18 November 2010 (UTC)

Glycerol

How stable is glycerol stored in a clear glass bottle? I see that it's hygroscopic, but would that just make it gradually dilute itself over time, rather than reacting with the water? Also, not much water is going to get in anyway. Does it decompose into anything given time and a small amount of normal air, in the top of te bottle? Does is decompose into anything in sunlight? I'm just wondering, because it seems such a bland thing, and yet I know it's used in various reactions, including making explosives. Would a bottle of the stuff still be just glycerin after a few years? 86.163.213.68 (talk) 23:45, 17 November 2010 (UTC)

Glycerol is pretty stable, especially if the bottle is kept closed. It can oxidize to compounds such as glyceraldehyde and glyceric acid, but this is very slow in the absence of a catalyst. Physchim62 (talk) 23:53, 17 November 2010 (UTC)

In my personal experience, glycerol is stable when stored at room temperature and out of direct sunlight for years. Proctor and Gamble have verified that room-temperature storage doesn't appreciably degrade glycerin over a the length of a two-year monitoring and testing program: [9]. I don't have (and was unable to find) specific information about the photostability of glycerol exposed to sunlight over extended periods, though I wouldn't be surprised if the sunlight affected the plastic bottle it's shipped in more than the glycerol itself. TenOfAllTrades(talk) 01:25, 18 November 2010 (UTC)

Thanks, these are both good answers. 86.163.213.68 (talk) 15:42, 18 November 2010 (UTC)

November 18

Inconstant red

I've noticed that certain rare reds, such as a certain flower that grows along the banks of the Lehigh, seem to be red beyond comprehension, so as to seem to flicker or shimmer continually. It is not so for plain #FF0000 or any other red shade on a computer. Has this effect been observed and named? Wnt (talk) 09:31, 18 November 2010 (UTC)

I guess you are describing iridescence, which is a form of structural color. 88.112.56.9 (talk) 10:57, 18 November 2010 (UTC)

You might also be noticing a red that is outside the gamut of the RGB color space. Selective yellow is another color that is not representable by RGB. —Bkell (talk) 11:36, 18 November 2010 (UTC)

I thought about iridescence, but the shimmering seems to be a function of the color, not the angle; and I do think it is outside the RGB gamut. Wnt (talk) 01:51, 19 November 2010 (UTC)

Kicking a ball

There are four fundamental forces in nature. Which of them acts on a ball when I kick it forward? To me, the force exerted by me upon the ball does not seem to match the description of any of these forces. --13XIII (talk) 11:15, 18 November 2010 (UTC)

If you'd got to the second paragraph of the fundamental interaction article you linked you would have read: "The four known fundamental interactions, all of which are non-contact forces...". Kicking a ball is clearly a contact force. Having said which, to quote again "Strictly speaking, contact forces are only a useful simplification for introductory physics classes and other applications of classical mechanics. Everyday objects on Earth do not actually touch each other; rather contact forces are the result of the interactions of the electrons at or near the surfaces of the objects.". --jjron (talk) 12:26, 18 November 2010 (UTC)

Well, we can rule out the strong and weak nuclear forces straight away, as there are no nuclear reactions taking place - although the strong force "acts" on the ball in the sense that it explains why there is a ball in the first place, rather than a rapidly expanding cloud of quarks and electrons. The ball experiences a gravitational force, but that is essentially the same before, during and after the kick. So that just leaves the electromagnetic force ... Gandalf61 (talk) 12:37, 18 November 2010 (UTC)

So basically, the ball is kicked because my atoms electronically repel the ball's atoms?--13XIII (talk) 14:46, 18 November 2010 (UTC)

That's correct. Red Act (talk) 15:12, 18 November 2010 (UTC)

You'd generally say the atoms electrically repel the ball, not electronically, even though it's the electrons doing the repelling. Sad, but true. --Sean 15:47, 18 November 2010 (UTC)

It is chemical energy, as per the sliding filament model that makes your muscles contract. Chemical energy is mediated by the electromagnetic force. The electromagnetic force also holds your ligaments et c together and transfers the force from your foot to the ball, rather than your foot piercing the ball. CS Miller (talk) 19:20, 18 November 2010 (UTC)

Since there aren't any chemical interactions between your shoe and the ball, the transfer of inertia is mediated by the Pauli exclusion principle between electrons in molecular orbitals causing elastic collisions. That is more of a quantum electrodynamical effect than an electromagnetic effect, but the force from your foot certainly originates in the electromagnetic chemical energy in your muscles. Ginger Conspiracy (talk) 20:20, 18 November 2010 (UTC)

Chances of getting cancer and age

If you compare the age groups 5-6 years and 59-60 years, which one has a higher incidence of cancer? The former group goes through more cell divisions, could that increase the risk of getting some DNA copied in the wrong way? However, could the later be affected by other factors, like some tendency of old cell to produce faulty DNA copies?Mr.K. (talk) 11:51, 18 November 2010 (UTC)

Adults have a higher cancer incidence by far. I don't have the data for the specific age ranges you are asking about, but according to the American Cancer Society: in the USA the incidence from birth to age 39 is 1 in 70 for males and 1 in 48 for females; the incidence from 40 - 59 is 1 in 12 for males and 1 in 11 for females; the incidence from 60 - 69 is 1 in 6 for men and 1 in 10 for women. As for why this might be the case, the older you are, the more total cell divisions your body has gone through (and hence the more chances for a somatic mutation), and the longer you have been exposed to carcinogens in the environment. This increased occurrence of cancer in older age groups is consistent with the "two-hit" hypothesis of carcinogenesis. --- Medical geneticist (talk) 12:10, 18 November 2010 (UTC)

The age groups were just an example. The older you are = the higher your chance of getting cancer is clear to me. What is not clear is the older you are = the higher your chance of cancer onset. Cancer takes several years to manifest itself, so if a 20 year old is having lots of cell division (more than a 30 years old), his chances of cancer onset could be higher, but this cancer would only manifest itself when he turns 30 (increasing the statistics of this age group). Right? Quest09 (talk) 12:57, 18 November 2010 (UTC)

I think you are over-thinking the situation. There isn't a difference between "your chance of getting cancer" and "your chance of cancer onset". It's the same thing: incidence of cancer. Sure, it's true that some cancers are found serendipitously (the person is asymptomatic and cancer is discovered by accident), other cancers are found at an early stage through screening programs before they manifest significant symptoms, others aren't discovered until widely metastatic. Is this what you mean by "cancer onset?" Certainly the biology of tumors is different, and some childhood cancers are particularly aggressive and progress rapidly while some adult cancers are indolent and progress slowly. But the opposite can also be true. There is no way for us to know when the first cancerous cell arose in any given person's body, so cancer incidence numbers simply measure the age at which a cancer was diagnosed. --- Medical geneticist (talk) 14:00, 18 November 2010 (UTC)

Accumulation of bad copies overwhelming copeing mechanisms that are supposed to kill them? Bad copies of cells that is. Like making a hundred photocopies of a document, each successive one copied from the previous copy? Plasmic Physics (talk) 12:46, 20 November 2010 (UTC)

information technology

How and where can information technology be used? What are the qualities of a good media programme? What are the materials used for information technology e.g generator,contr —Preceding unsigned comment added by Perooy (talk • contribs) 12:57, 18 November 2010 (UTC)

While I don't wish to cast aspersions, this reads very like a series of homework questions. Wikipedia will not do your homework. Instead, you may want to look at Information technology and its associated articles at Category:Information technology which may be of use. If you are having problems with a specific concept, feel free to come back here (or to the Computing reference desk) and ask specific questions. --Kateshortforbob _talk 13:04, 18 November 2010 (UTC)

American winter climate compared with Scotland

Which parts of the US have a winter climate that is about as cold as that of Scotland? Thanks 92.24.187.23 (talk) 13:32, 18 November 2010 (UTC)

Scotland's weather is maritime, which means the temperature (and the rainfall) is heavily influenced by the sea, and (as with the rest of Britain and Ireland) by the gulf stream. The nearest comparison to Glasgow would be the Pacific Northwest, maybe Portland or Seattle (in that it rains a lot, but doesn't really get that cold and doesn't snow massive amounts). Parts of Georgia or Virginia might be roughly temperature comparable (in the winter), but it's different weather and overall a different climate. -- Finlay McWalter ☻ Talk 13:42, 18 November 2010 (UTC)

It seems like Dutch Harbor, Alaska corresponds fairly well to Aberdeen, at least for this time of year. Googlemeister (talk) 15:19, 18 November 2010 (UTC)

Aberdeen is on the east coast, which is colder and dryer than the west. I've seen large patches of snow in June in the Cairngorm mountains. Alansplodge (talk) 15:25, 18 November 2010 (UTC)

Aberdeen, Scotland and Portland, OR is a pretty good comparison. Having lived in both cities the winters were quite similar in terms of temp, number of times falling over of the ice, some but not much snow in the city etc. Sean.hoyland - talk 15:49, 18 November 2010 (UTC)

Thanks. Never mind the precipitation, what states away from the coast would be about as cold as Scotland in the winter? 92.15.5.101 (talk) 17:43, 18 November 2010 (UTC)

You can't ignore the precipitation; it's the presence of water that moderates the temperature. Away from the coasts a continental climate holds, where it's very hot in summer and very cold in winter. For example, right now Glasgow and Omaha are about the same temperature, but compare the climate of the two (Glasgow, Omaha). The average low for Feb in Glasgow is 0C, for Omaha its -10C; they're about the same in November. The only places in North America that are roughly the same temperature as Scotland over the entirety of the winter are the coastal pacific northwest, from Seattle into Alaska. Any given inland place will be roughly the same as Scotland only for a few weeks or so. -- Finlay McWalter ☻ Talk 18:47, 18 November 2010 (UTC)

I'm just wondering where a hypothetical curvy line across the US would be where the mid-winter (early January?) temperature is similar to what you get in Scotland. In the early or late winter it would be warmer. 92.15.13.70 (talk) 20:28, 18 November 2010 (UTC)

Very roughly, you could draw a line connecting Norfolk, Virginia, Memphis Tennessee and Tulsa, Oklahoma and get average daily highs and lows within a couple of degrees C of Aberdeen, but because of the continental vs maritime climate difference between the USA and the UK, the record highs and lows will be a greater span for the US cities. Googlemeister (talk) 21:23, 18 November 2010 (UTC)

Frozen LCD TV

Can LCD TV's be stored in cold tempatures? Can LCD TV's freeze (at what temp.) and will freezing damage the TV? —Preceding unsigned comment added by DB61955 (talk • contribs) 16:05, 18 November 2010 (UTC)

I'm not sure there is a one-size-fits-all answer. Googling for LCD storage temperature suggests some LCD panels may survive freezing. However, a TV will contain other components, such as electrolytic capacitors, whose liquids may not take well to being frozen. For a specific make and model of a TV, consult its user manual for storage and operating temperatures. When bringing electronic devices in from the cold, be sure to allow them plenty of time before switching them on, to allow for condensed moisture to evaporate - here, too, the user's manual is your friend. 88.112.56.9 (talk) 18:02, 18 November 2010 (UTC)

One way that electronic devices fail when stored at very low (or very high) temperatures, or when the ambient temp is cycled up and down a lot, is the breakage of connections, either the microscopic connections inside semiconductor chips, or solder joints where devices are attached to the circuit board.Different materials have different thermal expansion coefficients. Edison (talk) 20:09, 18 November 2010 (UTC)

To illustrate the difficulty of getting an answer to your question, a poster here has been waiting since October 2009 with a question about the operating AND storage temperature limits of a Samsung LCD TV, with no reply yet. Cuddlyable3 (talk) 01:38, 19 November 2010 (UTC)

Maybe the problem is people are waiting for answers after posting in random irrelevant (not associated with manufacturer) blogs nearly one year after that blog entry was posted? A simple search for 'samsung lcd temperature' comes up with [10] which says they recommend 10°C as a minimum operating temperature. (Specifically "When it is used at low temperature of 10°C or lower, response time and brightness are affected in such a way that the proper display may not be obtained.")

If you want more detailed specs, from experience the manual of most products commonly have such storage and operating conditions in their manuals. The blog entry was about the Samsung LN52A580 in particular. Since the blog and TV appears to be directed to the US, a look on their US (but not UK or Malaysian) site finds [11] which has the manuals for the LN52A580P6F. Sure enough from the user manual we find:

Environmental Considerations

Operating Temperature 50°F to 104°F (10°C to 40°C)

Storage Temperature -4°F to 113°F (-20°C to 45°C)

Of course simply asking the manufacturer of the TV your interested in is also likely to be a better bet then a random blog post in a random blog.

Each manufacturer may choose to rate their products differently. For example I earlier looked at some random Sony LCD TV (KDL-40HX701). The manual I got appears to be one of those limited/user friendly ones and it only has 24 pages. I couldn't find a more detailed one for that model on Sony's site but didn't look very hard. Anyway as you may expect it did lack detailed storage and operating conditions but it did at least say "Avoid operating the TV at temperatures below 41°F (5°C)".

In other words it isn't hard. You just have to look or ask in the right place. (In other words help yourself and use a little common sense.)

From these statements, I'll take a punt that as the temperature goes down, the performance changes I guess because the liquid in the LCD changes. Above freezing but presuming no condensation or other such problems I would guess your TV isn't going to blow up but it may not perform as you would expect. But for that reason, manufacturers generally recommend 5-10°C. Actual performance at such low temperatures is likely to vary depending on several factors and is not something you'd expect there to be any real guarantee for cheap consumer TVs.

In terms of storage, from what I've seen most electronics can be stored below freezing. I would guess if they can't this would require greater care to be taken during transport and storage so is something usually avoided. So it's not really surprising that LCD TVs can (at least the Samsung one mentioned above).

In terms of at precisely what temperature the LCD will begin to be irreversible damaged, I suspect that will vary. Finding an answer is probably going to be difficult since manufacturers may not bother to test such details instead just setting minimum temperatures they are sure will be tolerated.

Nil Einne (talk) 18:26, 19 November 2010 (UTC)

trans former

what is trans former? —Preceding unsigned comment added by Pritamcool199 (talk • contribs) 16:41, 18 November 2010 (UTC) (Question reformatted. Richard Avery (talk) 16:56, 18 November 2010 (UTC))

Do you mean Transformer or Transformers or something listed at Transformer (disambiguation)? --Jayron32 16:59, 18 November 2010 (UTC)

Transpired solar collector for sale

I have not been able to find any transpired solar collector for sale.I have sent many emails and have had not one reply.Would you be able to tell me where I could purchase 200 sq ft to see if it will work in my sisuation ? Thanks you, George Jackson 208.127.199.228 (talk) 17:19, 18 November 2010 (UTC)

What do you mean by transpired? Ginger Conspiracy (talk) 19:57, 18 November 2010 (UTC)

A "transpired" solar collector is an unglazed collector that draws a thin layer of air through a perforated absorber; see Solar thermal energy#Heating, cooling, and ventilation. Red Act (talk) 20:23, 18 November 2010 (UTC)

Have you tried just phoning the companies that make transpired solar collectors? They all appear to have phone numbers listed on their web sites, and that way you don't need to worry about things like an overzealous spam filter or something causing e-mail messages to get lost. Red Act (talk) 03:37, 19 November 2010 (UTC)

Type of ruler used to show size of objects

Hi There, What is the name of the type of ruler/measuring device that you see in science pictures where there are squares of alternating color, 1 inch or centimeter or whatever, to make the scale easy to see? Thanks! —Preceding unsigned comment added by 148.66.156.170 (talk) 18:29, 18 November 2010 (UTC)

There doesn't appear to be a standard name for a ruler with a feature like that. There is no mention of such a type of ruler at Ruler#Types, and rulers I can find on the web with that feature are variously described as "[featuring] alternately colored bars"[12], "divided into ... segments by color"[13] or "marked in blocks ... in alternating ... segments"[14]. Red Act (talk) 19:24, 18 November 2010 (UTC)

Maybe a Linear scale? DMacks (talk) 22:04, 18 November 2010 (UTC)

Or a colorful Scale ruler? WikiDao ☯ (talk) 22:16, 18 November 2010 (UTC)

Despite its name a scale ruler is used in making drawings to scale, not for giving the scale in a photograph. I would call the ruler a scale bar, which is what most people (1.6 million hits on google) use for the thing described in linear scale. Mikenorton (talk) 22:32, 18 November 2010 (UTC)

How realistic are the species, descriptions, evolutions, geologics, and so on given at www.metazoica.com?

Per above. Especially, I want to know about the possibility of the listed mammal species/genera/whatever. --Eu-151 (talk) 18:33, 18 November 2010 (UTC)

As per the introduction at the top of this page, "the reference desk does not answer requests for opinions or predictions about future events". Any discussion of Speculative evolution#Future Evolution would require purely speculative predictions about future events. Red Act (talk) 19:40, 18 November 2010 (UTC)

Actually this is a question about a present website rather than a future event. I think it's quite clear that the website involves a rather arbitrary imagination rather than any observed trend. Also, even if an evolutionary trend is observed, it can't be relied upon in a post-human world. For example, under ordinary circumstances new species often diversify from a small, generalist ancestor that is good at dispersing itself; but in a post-human society many exotic animals like lions and pythons and housecats and chickens will be dispersed all over the world to start with. The site seems to postulate both wide radiations e.g. from an elephant shrew and diversifications of highly specialized species like the edentates. It is an open question in biology to what degree wide radiations of species depend on catastrophism, especially where the diversification of mammals prior to the K-T event are concerned, but well known stories like the cichlids in more recent times depend on significant geologic change. It would probably take a rather specific scenario to allow both sorts of events to occur at the same time. Wnt (talk) 02:16, 19 November 2010 (UTC)

thanks, especially pay attention to one Species name in the genus "Procyon" (raccoons)!. But Why or how should carnivorous deer and antelope evolve (see Deinognathids), and is it a external link worthy of inclusion in Speculative Evolution? —Preceding unsigned comment added by Eu-151 (talk • contribs) 11:45, 19 November 2010 (UTC)

nicotine

Why do nicotine patches induce vivid dreams?. My dad was trying to quit smoking many years ago and we bought him patches, and he forgot to take it off when going to bed one night. He said he had the scariest most vivid dreams of his life. I've searched online and found similar accounts from many people, but no scientific reason for it. 92.158.144.48 (talk) 19:35, 18 November 2010 (UTC)

Any substantial metabolic perturbation during dreaming--including indigestion--can produce disturbing dreams, in my experience. Ginger Conspiracy (talk) 19:54, 18 November 2010 (UTC)

You didn't find [15] in your searches? It was the second result for me for 'nicotine dreaming'. Some of the related cites also look relevant. Nil Einne (talk) 19:54, 18 November 2010 (UTC)

What happens if you touch anti-matter?

Will your hand be hurt? AdbMonkey (talk) 20:22, 18 November 2010 (UTC)

How much antimatter? A single positron annihilating with an electron in your body would produce about 1 MeV of energy in the form of photons, which is only about 1.6 x 10^-13 joules, which is negligible. But if you tried to hold an entire gram of antimatter in your hand, you would not survive the experience, to say the least. Red Act (talk) 20:42, 18 November 2010 (UTC)

If you touched one gram of it, the blast would be about equivalent to a 40 kilotons explosion. (The bomb dropped on Hiroshima was 15 kilotons.)

However, modern science doesn't have the capability to create anywhere NEAR that much antimatter. APL (talk) 20:53, 18 November 2010 (UTC)

PET scans generate antimatter inside your skull, so it's not magical annihilation dust. It all depends on how much there is, as Red Act mentioned. --Sean 20:50, 18 November 2010 (UTC)

Pet scans do certainly use positrons, but not anywhere near enough to be called "dust". APL (talk) 20:57, 18 November 2010 (UTC)

So how did the scientists in Switzerland contain it? And how will they study it without it evaporating? Or exploding. AdbMonkey (talk) 21:20, 18 November 2010 (UTC)

Difficult to say without knowing what scientists you are referring to. But the article on antimatter Red Act linked to above has general info in the #Preservation section. Nil Einne (talk) 21:41, 18 November 2010 (UTC)

If you're referring to "the ALPHA collaboration announced that they had so trapped 38 antihydrogen atoms for about a sixth of a second.[24] This was the first time that neutral antimatter had been trapped" it may be helpful if after reading the article Red Act linked to in particular the the parts before my quote, you ask while explaining what still confuses you about how they trapped the antihydrogen. The Nature article the collaboration published that our article uses as a ref may be the best source if you can understand it and have access. But as I expect it's too technical, reading some of the writeups in more general sources may help like [16] [17] [18]. Nil Einne (talk) 21:47, 18 November 2010 (UTC)

Or are you talking about the antimatter from the book and movie Angels and Demons? CERN has a rather well written FAQ about that. -- BenRG (talk) 22:00, 18 November 2010 (UTC)

The short, non-technical explanation is "they used magnets in a vacuum." Magnets are a nice way of containing charged particles without having them touch anything. The same kind of technique is used for trying to contain fusion reactions as well. --Mr.98 (talk) 01:56, 19 November 2010 (UTC)

Magnets without metal?

Is it possible to generate magnetic fields without metal? Googlemeister (talk) 21:13, 18 November 2010 (UTC)

See Plastic magnet. Mikenorton (talk) 21:27, 18 November 2010 (UTC)

Very cool. Googlemeister (talk) 21:51, 18 November 2010 (UTC)

Wind a Solenoid using a Carbon fiber conductor and energize it by an Electric eel. Cuddlyable3 (talk) 01:18, 19 November 2010 (UTC)

If you also use a paperclip you earn the right to be called MacGyver. Rimush (talk) 10:23, 19 November 2010 (UTC)

I would suggest a rubber band since non-metallic paperclips are tough to find. Googlemeister (talk) 15:00, 19 November 2010 (UTC)

1 in 80 million death

There's an AP Release which reads:

The FDA has estimated that the risk of fatal cancer from the maximum allowable dose would be 1 in 80 million per backscatter screening. And doses from a single scan are considerably lower than the maximum, Kassiday said.

The source for this reads:

General-use systems operating in accordance with this standard produce a maximum reference effective dose of 0.25 μSv (25 μrem) per screening. Therefore, an individual may be screened up to 1,000 times each year without exceeding the annual 0.25 mSv (25 mrem) limit. The associated incremental risk of death is 1 in 80,000,000 per screening.

Is this supposed to be interpreted as for every 80 million screenings, 1 lucky soul will receive a dose of radiation resulting in fatal cancer?Smallman12q (talk) 21:35, 18 November 2010 (UTC)

No. Rather, as noted both in the summary and in the details, a screening at maximum allowable radiation dosage results in such a risk. The summary notes that the scanners do not operate at that maximum (though offhand I see no details as to what dosage they dole out), and so the risk should be further lessened. I'll note as a matter of personal opinion that I'd be more concerned with the possibility that the dosage could be inadvertently increased to catastrophic levels via software than the risk of long-term low-dose accumulation. — Lomn 21:59, 18 November 2010 (UTC)

Just as an aside, the amount of radiation you are exposed to from natural sources while on the airplane is significantly higher than the maximum dose per scan. --Mr.98 (talk) 01:40, 19 November 2010 (UTC)

It would be more correct to say that "1 additional person will develop cancer and die for every 80 million screened", than "1 lucky soul will receive a dose of radiation resulting in fatal cancer". It would be impossible to look at any given cancer case and say that it was the result of getting an x-ray at the airport. However, we can look at a large number of cancer deaths, and see that populations that receive more radiation get cancer at higher incidence than those who receive lower doses. We can even come up with some sort of "marginal deaths per mrem", which appears to be the case here. It's obvious that no one has studied the effects of getting just one extra 25 mrem dose; it would be impossible to draw any Statistically significant conclusions from such a study, even if you could control other exposures to ionizing radiation that accurately over a person's lifetime. It will be interesting to see if (assuming this backscattering thing catches on) research starts coming in 30 years from now looking at cancer rates among frequent fliers who have had lots of these scans, vs. people who hadn't. I suspect that even then, it will be hard to draw significant conclusions; as Mr. 98 pointed out, the act of flying itself contributes a non-zero extra dose of ionizing radiation. Buddy431 (talk) 02:10, 19 November 2010 (UTC)

The TSA and Backscatter X-ray articles are useful in sketching out some of the controversies, for example in skin vs. whole-body exposure. Regrettably the articles on rem and Sievert are woefully incomplete, and some of the most confusing that I've seen on Wikipedia. I will say though that I am suspicious of the idea that the absorbed energy of radiation in joules is the only factor in determining cancer risk, especially when you contrast cosmic rays striking an airplane with a machine deliberately designed to produce (I assume) a larger number of much lower energy gamma ray particles. But I don't know the specifics about this.

Another specific to nail down is how many people are to be subjected to this treatment. I've seen a number of very unreliable looking estimates of how many passengers fly yearly; one claimed over 1 billion. That figure should be nailed down, since it establishes just how many people we propose to sacrifice to the Minotaur yearly; a rough guess of 120 around the world would apply from this data. It would also be nice to have more data about terror attacks; this seems approximately equal to the number killed by terrorists. This is, to my mind, in keeping with an equipartition theorem-based First Law of Natural Disasters, which is that a catastrophic event and its government response are equally dangerous.

It seems like discussion of terahertz scanners seems to have quietly dropped out of sight, and I suspect there's a reason... Wnt (talk) 02:55, 19 November 2010 (UTC)

Looking at the number of terrorist related deaths involving airplanes is useful, but what's really more important is how many terrorist related deaths will these things stop? That's even harder to figure out, especially now when this technology is being introduced. Presumably this technology would have caught the underwear bomber, but he didn't cause any deaths anyway, so we couldn't credit these machines with saving lives in that case. If the List of aircraft hijackings is to be believed, since 2000, there have been only three hijacking incidents that resulted in fatalities, the well known September 11 attacks (almost 3000 deaths)(which fine, was four seperate hijackings) and the lesser known incidents in November 2000 and March 2001 in which 1 (the hijacker) and 3 (one of the hijackers, a passenger, and a stewerdess) were killed. The airport bomb in the 2005 Songkhla bombings (2 killed) presumably could have prevented something like this, although it sounds like any sort of baggage screening could have prevented it (the bomb wasn't on a person, I don't think, but rather in a bag). The 2004_Russian_aircraft_bombings could have probably been stopped by screening; they killed 89. That's all of the fatalities that I could find related to people intentionally trying to cause deaths on commercial aircraft since 2000 (looking at things like List of aircraft hijackings, List of terrorist incidents, and List of accidents and incidents involving commercial aircraft). The 9/11 attacks skew things considerably, but if you put your finger over them, these backscattering x-ray scanners seem awfully expensive for the number of fatalities that they're going to reduce (in financial terms, as well as possible health effects, as well as the goodwill of the public in having TSA guys see them naked). Buddy431 (talk) 03:45, 19 November 2010 (UTC)

Well all the above assumes that these scanners will simply be implemented alongside all existing technologies and procedures, but my guess is that they will replace some current technologies and procedures. The benefit might not be "deaths prevented" but instead it might simply make screening easier, less labor intensive, less technical or prone to error, etc. Vespine (talk) 05:46, 19 November 2010 (UTC)

Yes, but Buddy431 consider that the scanners make excellent Security theater. Indeed, the very fact that they are controversial makes them very well suited as security theater, since such controversy raises the consciousness of them, and thus improves their profile in our minds. --Jayron32 08:09, 19 November 2010 (UTC)

Here's an interview with Bruce Schneier in which he says the new TSA measures "won't catch anybody" compared to the old measures. Schneier has stated that the only two important differences between 2001 and now are (a) maybe the reinforced cockpit doors, and (b) definitely that the passengers have now learned to attack anyone who is a threat. The success of the underwear bomber incident was because in order to get through the old security measures he had to resort to an ignition contraption involving a syringe and 90 minutes in the bathroom; and because the passengers attacked as soon as it was apparent something was awry. (b) also stopped the shoe bomber. Comet Tuttle (talk) 17:57, 19 November 2010 (UTC)

Here's a humorous take on the matter from XKCD. Buddy431 (talk) 17:32, 19 November 2010 (UTC)

How evolution explains the division into autonomic nervous system and somatic nervous system

I know why we are unable to control such things as heart rate for example, but how evolution explains the division of nervous system into somatic and autonomic one (and thus determining what we can control and what not)? Thanx.

Wikipedia has articles about the Autonomic nervous system and the Somatic nervous system. Primitive living things have only autonomic responses. Evolution of consciousness is accompanied by introduction of conscious control of parts of the body. The tradeoff is that conscious control increases the precision and adaptability of the controlled function, at the cost of making it slower. Modern humans have evolved towards an unprecedented level of conscious control and therefore see most animals as relatively quick and stupid. Cuddlyable3 (talk) 01:11, 19 November 2010 (UTC)

At the same time conscious thought is energy intensive - the human brain consumes about 20% of the body's energy already (far higher than in less intelligent animals). The body does not want to waste energy 'thinking' about functions that can be performed automatically, thus evolution would favour continuing to perform functions that can be performed automatically to remain that way, and thus the retention of the autonomic nervous system. --jjron (talk) 13:14, 19 November 2010 (UTC)

In environments that are relatively stable (stable "unchanging" food sources, predation pattern, temperature, rainfall), autonomic responses are all one needs since there are no immediate significant advantages to select for generalists that perform well in quickly changing or unstable environments. A specialist could survive and prosper by being less complicated and having doing the same task better. It's the same idea as with tools, for instance if all you will be doing is either drinking soup or skewering solid foods, you really only need a spoon or a fork (specialists) and something like a spork (generalist) would be less ideal since it does neither task very well. The evolution of more non-autonomic controlled "generalized" creatures such as humans are shown in geological records to have evolved in fluctuating or variable environments where creatures need to quickly adapt and be able to do a bit of everything (although perhaps less well). In the case of heart rate control in the heart's environment (the body), the change of pulse is either (1) detrimental to the survival of the heart and the body or (2) simply does not require complex interpretation of numerous body parameters, which is maybe why it is not selected for somatic response. -- Sjschen (talk) 19:45, 19 November 2010 (UTC)

animals natural disasters

How come animals seem to sense natural disasters before they even happen and Humans don't sense natural disasters naturally. —Preceding unsigned comment added by 83.71.80.54 (talk) 23:45, 18 November 2010 (UTC)

Our article on earthquake prediction has a bit about this here. Matt Deres (talk) 00:10, 19 November 2010 (UTC)

They typically don't, actually. It's mostly human power of suggestion. (After the earthquake people say "Hmm! No wonder kitty was acting funny!" never mind that cats tend to have mood swings every couple of days anyway.)

Here's an article that discusses the question as regards to earth quakes.

On the other hand, storms can often be predicted by sudden changes in air pressure, (up or down), even some humans can do that unaided. (Arthritis patients mostly.) APL (talk) 00:15, 19 November 2010 (UTC)

Are earthquakes preceded by low frequency sounds that somehow would not show up as a seismograph signal? Because many people act as if oblivious to very loud low frequency sound. Wnt (talk) 03:00, 19 November 2010 (UTC)

There's probably some of that, but it is far more likely that such an explanation is still more after-the-fact justification for what APL mentions; pets cannot predict earthquakes, but we believe they did, so we come up with justifications to explain how they did it. I am not aware of any actual controlled experiments which show that our pets can predict earthquakes, just a lot of unverified beliefs that they can. I am, of course, willing to be shown wrong, but I haven't seen anything yet. --Jayron32 05:00, 19 November 2010 (UTC)

I'm pretty sure, based on my own personal observations that gulls know when there's a big storm coming. Probably the same way that I can feel/smell it in the air as the skies begin to darken. They mass on the surface of the sea (or fly out seawards in their tens), emitting short, low-pitched, repetitive barking calls - quite different from the standard gull vocalizations that you normally hear. --Kurt Shaped Box (talk) 05:17, 19 November 2010 (UTC)

I'm not sure I would necessarily agree with a statement as strong as "They typically don't, actually. It's mostly human power of suggestion". It's reasonable to expect evolution to have found many different ways for animals to avoid death from natural disasters. It's probably unreasonable to assume that we know anything much about them yet especially when it comes to something very complex like earthquake precursors. At least it's clear is that we're still pretty terrible at earthquake prediction. As for other things, one species of ant in my part of the world is exceptionally good at predicting heavy rain hours before it starts. Thousands of workers, multiple queens and males, thousands of eggs and larvae all carefully arranged into staging groups metres off the ground on vertical surfaces. Very impressive. Anyway, perhaps the IP will find this paper interesting "Earthquake prediction by animals: evolution and sensory perception". Sean.hoyland - talk 07:18, 19 November 2010 (UTC)

I don't think Earthquakes are frequent enough that natural selection would have have worked and shaped behaviour in that manner. Also in the wild, most natural disasters don't kill you except flooding and fire. Earthquakes, for example, only kills you if you have a roof over your head. --85.119.25.27 (talk) 08:48, 19 November 2010 (UTC)

The paper I linked to tries to address those questions. Also, tens of thousands of land animal species have a roof over their heads. Sean.hoyland - talk 09:04, 19 November 2010 (UTC)

Hmm, so for example rats and rabbits could have evolved an escape behaviour (so that not to be burried alive), as well as birds nesting on the coast (to avoid a tsunami). Interesting.

But, like humans, dogs and cats wouldn't have evolved it, because of their lifestyle in the open, an earthquake in the wild would not kill them unless they are very very unluky and a tree fals onto their head. --Lgriot (talk) 13:23, 19 November 2010 (UTC)

Regarding weather, big storms are typically preceded by a drop in atmospheric pressure -- in the days before weather satellites, a barometer was the best tool for predicting storms. Some people with rheumatism can feel a drop in air pressure in their joints. Since birds have hollow bones, there is a decent chance that they can feel a drop in air pressure literally in their bones. Looie496 (talk) 18:12, 19 November 2010 (UTC)

Would it not be possible from evolution that the animals in there enviroment and habitat somehow learned of warning signs like for instance animals know to move up to higher ground if a tsunami triggered by an earthquake is approaching. --213.94.232.102 (talk) 21:26, 19 November 2010 (UTC)

On a related note (some of the items relate to natural disasters like fire), see this CRACKED.com article about "super powers" that some animals have. (Warning: Cracked.com will waste years of your life, only proceed if your boss doesn't value your job outputs anyway.) Zunaid 08:14, 20 November 2010 (UTC)

November 19

Time Dilation? Time speeding?

I think the following section in Special Relativity has a wrong conclusion, “This phenomenon is called time dilation.”, △t’=γ△t should mean time speeding, isn’t it? Please help. Thanks.

Time dilation and length contraction

Writing the Lorentz transformation and its inverse in terms of coordinate differences, where for instance one event has coordinates (x1,t1) and (x'1,t'1), another event has coordinates (x2,t2) and (x'2,t'2), and the differences are defined as Δx = x2 − x1, Δt = t2 − t1, Δx' = x'2 − x'1, Δt' = t'2 − t'1 , we get △t’=γ(△t-(v△x/c^2))， △x’=γ(△x-v△t)， and △t=γ(△t’+(v△x’/c^2)), △x=γ(△x’+v△t’)， Suppose we have a clock at rest in the unprimed system S. Two consecutive ticks of this clock are then characterized by Δx = 0. If we want to know the relation between the times between these ticks as measured in both systems, we can use the first equation and find: △t’=γ△t (for events satisfying Δx = 0) This shows that the time Δt' between the two ticks as seen in the 'moving' frame S' is larger than the time Δt between these ticks as measured in the rest frame of the clock. This phenomenon is called time dilation. Jh17710 (talk) 05:09, 19 November 2010 (UTC)

I am having a bit of deja vu. Oh, yeah, that's because this question has been asked, by you, before, and answered already. To save everyone the trouble of answering it again, here are the responses from the first time it was answered. If there is something you need clarified from those responses, please feel free to ask that. --Jayron32 05:19, 19 November 2010 (UTC)

Jayron, Thanks for you link. There were 3 responses and only the 2nd one responded to my explanation, however, there is no name to that 2nd response.

This time, I did not put my explanation and just ask question. If △t’=γ△t and △t'=△t/γ are both for the same moving frame S' and rest frame S, even thay are for different events, △t’ is for the moving clock and △t is for the rest clock. My question is so simple, if we call △t'=△t/γ "time dilation" or "moving clock runs slow" then, we should not call △t’=γ△t the same names, right?

I will respond to your comment and the comment from RedAct when I have time to study it. What I hope is that someone else could help me to understand my simple question.Jh17710 (talk) 06:22, 19 November 2010 (UTC)

Actually, since neither clock has a privileged frame of reference, when each observer views the other person's clock, he sees it as running slower than his own. There is no time speeding because no observer will ever view another clock as running faster than his own; every observer takes their own frame of reference to be at rest. This is covered at Time_dilation#Relative_velocity_time_dilation. --Jayron32 06:57, 19 November 2010 (UTC)

You're still making the same conceptual error I pointed out last time, by considering there to be "the moving clock" and "the rest clock". Each observer uses a system of synchronized clocks that are at rest according to that observer, not just one clock. In the example in the article, the clock being examined is a clock in the unprimed system. That clock is "moving", from the perspective of the primed observer. For the two events in the example, △t' is measured with two different clocks in the primed system, so there isn't a clock in the primed system that appears to be running fast according to the unprimed observer. △t' appears "too large" to the unprimed observer, not because there's a clock in the primed system that appears to be running fast, but because the unprimed observer considers the primed system's clocks to not be synchronized properly. Red Act (talk) 12:28, 19 November 2010 (UTC)

Δt is the elapsed time, not the rate of the clock. These are reciprocals of each other. (The elapsed time might be measured in seconds, the clock rate in Hertz.) Δt' = γΔt means that Δt' is larger (since γ > 1), so the clock is running slower, in some sense, in the primed frame. Does that help? -- BenRG (talk) 00:24, 20 November 2010 (UTC)

Jayron32, you clearly explained "moving clock runs slow". You aslo mentioned about one of the key point "If ... each is in communication with the other, ..." and according to Red Act, because the speed of light is finite there having to be a delay for light to travel the distance between the event and the clock, I think the delay is also true for your way of communication. However, my question is for the difference of two "equations".

Red Act, let's have two systems of clocks, not just two clocks with two observers. When you said "...from the perspective of the primed observer." did you mean the primed system is considered the rest system? In that situation Δt' = γΔt is Δt = Δt'/γ , that is the same as Δt' = Δt/γ when S' is considered moving. Then, in your analysis, △t' is measured with two different clocks in the primed system, S'; since all clocks in the S' are synchronized, △t' is the actual time period of two ticks measured by the system of clocks in the S', so that "a" clock in the system of clocks should have same speed as the system of clocks. Finally, your main point is that the unprimed observer considers the primed system's clocks to not be synchronized; I think that could be one way to explain the difference between two systems of clocks if you can explain it in detail. That is why the observer in S considers clocks in S are synchronized and clocks in S' are not synchronized.

Of course there isn't really any such thing as a "rest system" or a "moving system"; all inertial frames of reference can equally validly be said to be "at rest". However, for the purposes of illustrating the principle that "moving clocks run slow", in this particular example it's the unprimed system that needs to be considered to be "moving", and the primed system that needs to be considered to be "at rest". That's because the clock in question isn't moving (is at rest) according to the unprimed system, but it is moving according to the primed system. Unfortunately, the article referred to S' as the "moving" system, which is the opposite of the perspective needed to make the article's analysis mesh with the phrase "moving clocks run slow". I just this morning dropped the word "moving" from the article, because "moving" is basically meaningless when talking about a reference frame, and because it suggests adopting the opposite perspective of what's more appropriate for thinking about time dilation and length contraction. I also changed the article to point out that it's a clock in the unprimed frame that's running slow, as perceived from the primed frame (as opposed to a clock in the primed frame that's running fast).

You said "Δt' = γΔt is Δt = Δt'/γ , that is the same as Δt' = Δt/γ when S' is considered moving". However, it's important to be mindful that Δt' = Δt/γ applies to a different set of circumstances than Δt = Δt'/γ does. It’s not just a matter of a choice as to which system is considered to be moving; the two equations apply to different pairs of events. (In the following, I'm presuming no motion in the y or z directions.) Δt = Δt'/γ only applies to pairs of events such that Δx=0, which is the case in the article's example. Δt' = Δt/γ would only apply to a pair of events such that Δx'=0, which is not the case in the article's example. The only way Δx=0 and Δx'=0 would both be true for a pair of events would be if S and S' were at rest with respect to each other, which gives the trivial case of γ=1, in which case there’s no contradiction between Δt = Δt'/γ and Δt' = Δt/γ.

It isn't possible to explain the differences between the systems of clocks purely in terms of synchronization issues (which is formally known as relativity of simultaneity). Synchronization issues and time dilation both exist, and are distinct. Consider the equation from the article $\Delta t'=\gamma \left(\Delta t-{\frac {v\,\Delta x}{c^{2}}}\right)$ . Basically the phrase "time dilation" is referring to the γ factor not being 1, whereas the phrase "relativity of simultaneity" is referring to the $-{\frac {v\,\Delta x}{c^{2}}}$ term not being zero.

You are correct in your observation that all clocks in the primed system run at the same speed. Both observers will agree that all clocks in the primed system all run at the same speed (although they will disagree about how fast it is that they are running). However, it still matters which specific clocks in the primed system you use, because according to the unprimed observer, the primed clocks do not all show the same time. "Showing the same time" means to look at all of the clocks simultaneously, and note that at that instant, the clocks have the same value. For example, if you look at all the clocks simultaneously, and they all say "noon", then the clocks all "show the same time". The problem is that the two observers do not agree on what "simultaneous" is. For more information, see relativity of simultaneity. Red Act (talk) 13:13, 20 November 2010 (UTC)

BenRG, thanks a lot. Your response is the one touched my question. Could you review the mathematics in "Δt' is larger (since γ > 1), so the clock is running slower,.." once again? Normally, Δt'=t'2-t'1, so that, when Δt' is larger, the clock should run faster so that we can count more units between time t'1 and t'2, isn't it? For the same event, Δt' = γΔt means the event is recorded as Δt' of S' units in S' and Δt of S units in S. If Δt' is larger, the clock in S' is quicker. That is why I said, the author of that section should use the clock in S' as the reference clock, same as what Einstein did in year 1905.Jh17710 (talk) 05:43, 20 November 2010 (UTC)

Δt and Δt' are the time interval between the same two events, just measured with respect to different frames. They are talking about the same clock, not two different clocks. E.g., suppose you're stationary with respect to S, moving uniformly with respect to S'. You note down the times shown on nearby clocks of S and S' (event 1), then time 60 seconds with your stopwatch, then note down the times now shown on the clocks (event 2). Subtracting the unprimed and primed readings gives you Δt and Δt'. "Time dilation" refers to the fact that Δt' > 60 seconds. (Δt = 60 seconds.) The "dilated" clock is your stopwatch, not one of the clocks used to define the systems—although, since you're stationary with respect to S, you could use the nearest clock belonging to S as your stopwatch instead.

The only way to measure the "speed of a clock" is using another clock, so could you say instead that the clocks of S' are running fast? Not exactly, because the two readings you subtracted to get Δt' were taken from two different clocks (you always take the reading from the clock that's nearest at the time of the reading). Thus the difference depends not only on the "speed of the clocks" but also on how they were synchronized. You can't exactly say that any clock is going fast, because which clock would that be? You never looked at any of them more than once. -- BenRG (talk) 08:11, 20 November 2010 (UTC)

Wheatstone bridge

I'm supposed to find the change in voltage across the central voltmeter as Rx is moved away from equilibrium, assuming the first three resistors have a common resistance R.

However, I am obstructed by several conceptual problems.

Theoretically the voltmeter should have an infinite resistance, right? Yet it permits a finite current. Even for an ideal circuit? I have the relation ΔV / I_v = resistance of the voltmeter = ΔRx + R(I1/I_v - 2). John Riemann Soong (talk) 06:07, 19 November 2010 (UTC)

The current through an ideal voltmeter is zero. So an ideal voltmeter doesn't affect the circuit it's in at all. You basically analyze the voltages and currents in the circuit as if the voltmeter wasn't there. The voltage measured by the voltmeter is then the difference between the voltages of the two points in the circuit that the voltmeter is connected to. Red Act (talk) 12:51, 19 November 2010 (UTC)

The galvanometer used in a Wheatstone bridge is not an ideal voltmeter: it has a finite resistance. When the bridge is unbalanced, a current flows through the galvo and deflects it. You then adjust one of the resistors to balance the bridge so that the galvo does not deflect. Once the bridge is balanced, the resistance of the galvo doesn't matter since there is no voltage across it. --Heron (talk) 18:35, 19 November 2010 (UTC)

I'm presuming the current through the galvanometer is to be neglected in this problem, or else the galvanometer's resistance would have to have been specified as part of the problem. Red Act (talk) 19:33, 19 November 2010 (UTC)

Yes, I see what you mean. In which case we need to know where John gets his term I_v from, because that implies a non-ideal voltmeter. If I_v is non-zero then of course the equation in our article doesn't apply. --Heron (talk) 19:51, 19 November 2010 (UTC)

JRS gets a non-zero I_v because he doesn't understand the problem. The problem is completely soluble if I_v is taken to be zero, trivial even, the solution is given in the article. Physchim62 (talk) 20:00, 19 November 2010 (UTC)

From the article: "The direction of the current indicates whether R2 is too high or too low. Detecting zero current can be done to extremely high accuracy (see galvanometer)." 128.143.181.23 (talk) 20:41, 19 November 2010 (UTC)

The article is slightly confusing on this point. I've tried to clarify it. --Heron (talk) 11:52, 20 November 2010 (UTC)

why isn't adenosine monophosphate used in alcoholic beverages?

I imagine that as an anti-bitterant it would mask the taste of alcohol really well -- or does it not? John Riemann Soong (talk) 10:14, 19 November 2010 (UTC)

Why would you want to mask the taste of alcohol? Some people actually enjoy the flavor of their drinks, indeed that is generally the idea. If you really wanted to, you could use a much less expensive alternatives, like fruit juices, simple syrup, colas, etc. A properly trained bartender can mix a drink to suit anyones taste without exotic chemicals. --Jayron32 16:16, 19 November 2010 (UTC)

Wikipedia:Reference desk/Archives/Science/2010 October 30#does citric acid actively mask the taste of ethanol? Nil Einne (talk) 18:52, 19 November 2010 (UTC)

I tweaked the wikilink to fix typo in anchor. Hope you don't mind the third-party mod, Nil! DMacks (talk) 19:13, 19 November 2010 (UTC)

Thanks! Nil Einne (talk) 06:15, 20 November 2010 (UTC)

I'm not sure I see the logic of using an anti-bitterant to mask the taste of something that most people don't describe as bitter and that is chemically unlike general bitter things or the more specific molecules noted as blocked by AMP. DMacks (talk) 19:08, 19 November 2010 (UTC)

Indeed. People are more likely to *add* bitter ingredients to drinks (e.g. tonic water of a gin and tonic, or even bitters themselves). -- 140.142.20.229 (talk) —Preceding undated comment added 19:50, 19 November 2010 (UTC).

The thing is, AMP is apparently a bitter reception antagonist. It's not a mere masker. I would describe the fire of vodka for example, as just really intense bitter. 128.143.181.23 (talk) 20:37, 19 November 2010 (UTC)

To me, ethanol just tastes like bitter like apple seeds, I find it repulsive. This is the reason for why I dislike strong liquors like spirits. I don't choose my liquors for the taste of the ethanol, ethanol is not the major contributor to the taste of the beverage. Ethanol is not meant to be anything other than a mind altering stimulant. Plasmic Physics (talk) 00:21, 20 November 2010 (UTC)

You don't like apple seeds? I quite enjoy them. They're a lot of work (you have to take off the endocarp I think it's called) but they have a very nice delicate flavor, reminiscent of almond delight. They're poisonous if you eat a lot of them (cyanogenic glucosides I think), but I only ever eat one or two at a time. --Trovatore (talk) 09:30, 20 November 2010 (UTC)

See also Apple seed oil. The key safety concern looks like amygdalin according to our apple article. DMacks (talk) 09:34, 20 November 2010 (UTC)

That is of course, a personal preference. I personally enjoy the taste of ethanol itself, good vodka is basically just water and ethanol. Ethanol is meant to be enjoyed, and for myself I find the flavor effects of ethanol to be more important than the mind altering effects. I actually find those somewhat of an anoyance, as getting drunk severly limits my ability to drink more ethanol. --Jayron32 01:42, 20 November 2010 (UTC)

OR here but I don't like the taste of most alcoholic drinks. However on those occasions when I've tried them, alcopops have seemed fine, no real different from a random soft drink (hence why I don't drink them a lot). I guess there are some people like JRS who still find alcopops bitter but I suspect they aren't that common and most people who just want to get intoxicated (which I presume is the case if you're trying to completely mask the taste of ethanol) and do find even alcopops bitter probably don't want to spend a lot of money. For those who don't mind alcopops, the fact that it's just masking the bitterness seems irrelevant unless perhaps your diabetic. Nil Einne (talk) 06:29, 20 November 2010 (UTC)

I would agree that ethanol doesn't seem bitter. But see PMID 12090789 - AMP simply isn't stable at room temperature, even in a pure solution. The organic phosphate bond is just too high in energy and too easily hydrolyzed especially in non-neutral pH. (I assume in the cell it spends most of its time bound to something or other that helps stabilize it, but I'm not recalling just what that might be at the moment) Wnt (talk) 13:17, 20 November 2010 (UTC)

Species identifcation for File:Sagittaria.jpg

The image in question

In order to expand on the image description, so the image can be moved to Commons, Is anyone on the Science Reference desk able to provide a more specific species identification?

It appears when the is uploaded, there was some discussion, it may have been mis-identifed.. Sfan00 IMG (talk) 12:46, 16 November 2010 (UTC)

Sagittaria sagittifolia

It looks very much like Sagittaria to me. There are lots of species though. Looie496 (talk) 17:58, 19 November 2010 (UTC)

shemales

Do shemales really exist? —Preceding unsigned comment added by 59.95.48.140 (talk) 13:28, 19 November 2010 (UTC)

Yes. See shemale, trans woman and transsexualism. Red Act (talk) 13:38, 19 November 2010 (UTC)

There are also people born with both genders, see hermaphrodite. --Jayron32 16:14, 19 November 2010 (UTC)

Also see intersex. Red Act (talk) 18:25, 19 November 2010 (UTC)

Definitive deletion of a phobia (classical conditioning)

By considering absence of the Renewal effect and the Spontaneous recovery a proof of a definitive deletion of a phobia, can one expect a definitive deletion of a phobia after sufficiently repeated extinctions?--Kooz (talk) 19:27, 19 November 2010 (UTC)

It's all a matter of probability, not certainty and proof. Any variety of phobias can be conquered, but in some people that means complete extinction and in others it means simply reduction of the response under an acceptable threshold. Time can make things better or worse, depending on the subject and the circumstances. Ideally a therapist will be able to help a patient come up with some exercises the patient can perform by themselves should the problem return. There's nothing exact in psychiatry. Ginger Conspiracy (talk) 04:03, 20 November 2010 (UTC)

Orgasmic sensation during pull-ups

When doing pull-ups or chin-ups, what is causing the tingling, sexual sensation in the groin area? This question is not looking for medical diagnoses or opinions. Thanks Reflectionsinglass (talk) 20:49, 19 November 2010 (UTC)

Orgasm#Spontaneous_orgasms covers some of this; it is entirely possible to experience orgasm, or orgasm-like sensations, without any direct stimulation of the genitals. --Jayron32 21:08, 19 November 2010 (UTC)

Chinups tend to be a very intense physical activity - it's possible that performing them gives you some type of endorphin rush, and combined with the increased peripheral blood flow that results from exercise, your body may be interpreting this as a sign of sexual release. There are suggestions that exercise in general helps to stimulate the libido, so this could be related. It would be interesting to attempt other strenuous exercises to see if it produces similar effects. --jjron (talk) 02:38, 20 November 2010 (UTC)

Are we allowed to talk about our own experiences in detail? If not, someone can delete this response, but consider this as simply my own experiment. I've been able to reach orgasm by lifting myself and holding myself up, since childhood, four or five years old (no emission, of course). Several years ago, much older and with other means of release, I'd suddenly remembered about this and I thought I would experiment. I used a chin-up bar, held myself up, and was able to experience full orgasm, including emission. It was extremely quick to achieve climax. I doubt I could do it again, I can barely hold myself up for 20 seconds these days. Thanks for the link to spontaneous orgasms. It was too brief a section, unfortunately. I may have to continue looking online. Reflectionsinglass (talk) 07:11, 20 November 2010 (UTC)

I tell you what, reflections and jjron, if there is anything in what you say, we've beaten the obesity epidemic right here. For my own case, I went to my doctor once and told him that in all my adult life, I felt strong orgasmic sensations when I sneezed. He said "Half your luck...". Myles325a (talk)

November 20

Entropy gun?

Would it be possible to make a weapon that shoots pure entropy? If so, why hasn't it been done? Blobs of entropy would be able to go through any type of protective shielding by scrambling the particles in the matter when it hit. --75.33.217.61 (talk) 00:13, 20 November 2010 (UTC)

Entropy isn't a substance. It's similarly not possible to make a gun that shoots pure inertia, or viscosity, or prettiness. Paul (Stansifer) 00:16, 20 November 2010 (UTC)

But would it still be possible to make a weapon that generates large amounts of entropy, even if it isn't pure? The second law of thermodynamics should make that easy. --75.33.217.61 (talk) 00:23, 20 November 2010 (UTC)

All explosives, in effect, increase the local entropy wherever they go off. That's why it is easier to blow things up than it is to put them together. --Mr.98 (talk) 00:25, 20 November 2010 (UTC)

Entropy is a measure of disorder. The more disordered something is the larger is its entropy. What you're suggesting is like designing a gun that shoots kilometers (or miles, if you're that way inclined), it simply makes no sense. Plasmic Physics (talk) 00:27, 20 November 2010 (UTC)

A gun that shoots pure entropy would be like a gun that shoots pure temperature, or pure color, or pure beauty. Abstract concepts can't be shot from a gun. Looie496 (talk) 00:46, 20 November 2010 (UTC)

I dare say you haven't had much practice. --Trovatore (talk) 11:12, 20 November 2010 (UTC)

If you say it that way, it actually sounds comical, like something you would find in Hitchiker's Guide to the Galaxy. An abstract concept gun compoared to the point of view gun. Plasmic Physics (talk) 01:10, 20 November 2010 (UTC)

But again, in all seriousness, all weapons (I've been trying to think of an exception) serve to increase entropy at the local level in their targets. The entire goal of a weapon is to disrupt all of that important and necessary order that is necessary for living organisms or buildings or technologies to keep functioning. Humans need entropy to be pretty low in order to survive — move their stomach a few inches in the wrong direction, or push down on their neck with a few pounds of force in a small enough time span, and their bodies quickly become disordered, jumbled, rotting, etc. The force of the weapon's ability to increase entropy is usually limited by the ability to keep entropy low — through, say, having a rigid target, or by having a target that will too readily become disordered and dissipate the energy of the entropy-raising projectile (e.g. earthworks or the ceramics used in bullet-proof vests). Entropy change can certainly be a seen as a way to look at how weapons work, but it's a secondary characteristic. --Mr.98 (talk) 14:15, 20 November 2010 (UTC)

Parts of the body where cancer *can't* happen?

Are there any human organs or tissues that haven't been associated with any known cases of cancer? NeonMerlin 00:48, 20 November 2010 (UTC)

Hair, fingernails and toenails. Maybe teeth? HiLo48 (talk) 01:33, 20 November 2010 (UTC)

To explain HiLo48's answer, cancer is a disease of cell division; any part of the body where cells can divide (and all living cells can divide) could experience cancer. Hair and fingernails have no living tissue, so they cannot have cancer. --Jayron32 01:38, 20 November 2010 (UTC)

The name of intermolecular forces acting between alkanes

What is the name of intermolecular forces acting between alkanes, especially large alkanes such as decane? I think they are a special case of van der Waals forces, but van der Waals forces also include H-bonding and dipole-dipole attraction which are not present in alkanes. 220.253.217.130 (talk) 01:22, 20 November 2010 (UTC)

London dispersion forces. --Jayron32 01:34, 20 November 2010 (UTC)

Note that our van der Waals force article lists the three major subtypes, including London. DMacks (talk) 06:27, 20 November 2010 (UTC)

White Dwarf

How close does a white dwarf have to be to another star to "steal" hydrogen? —Preceding unsigned comment added by 76.161.251.228 (talk) 14:26, 18 November 2010 (UTC)

I don't know what answer to give you, but I can tell you that there is no real cutoff value for the distance. Gravity is responsible for this phenomenon, and it decreases exponentially with radial distance from the white dwarf. You should specify the rate at which mass is gained or lost, and the mass of the white dwarf. Using both these variable, someone can calculate an answer. Plasmic Physics (talk) 03:12, 20 November 2010 (UTC)

Harrumph. Gravity doesn't decrease exponentially with distance. It decreases as the inverse square of the distance. That is, it varies as 1/r², not 1/a^r. --Anonymous, 06:25 UTC, November 20/10.

Sorry, bad mistake, but the rest of what I said still holds. Plasmic Physics (talk) 06:32, 20 November 2010 (UTC)

That would be the Roche limit. It depends on the masses and radii of the white dwarf and the star. I would try the formula given in the subsection about a fluid satellite. --Wrongfilter (talk) 11:18, 20 November 2010 (UTC)

Hmmm ... but the huge difference in densities between the white dwarf and the secondary probably means that the Roche limit is less than the radius of the secondary star, so the stars will collide before the Roche limit is reached. We can get a ballpark upper limit by looking at the period of the cataclysmic variable binaries listed in the Catalog and Atlas of Cataclysmic Variables. Most of these periods are less than 1 day. If the main star has a mass comparable to the Sun, then an orbital period of 1 day means an orbital radius of around 3 million km, or about 4 to 5 times the radius of the Sun. So a ballpark figure is "within 5 solar radii". The exact answer for a given binary will depend on the masses and temperatures of the stars involved, and probably on a lot of more complex factors such as their magnetic fields. Gandalf61 (talk) 11:38, 20 November 2010 (UTC)

Trapping antihydrogen

The antihydrogen was created back in 1995, as the article says, so why to claim that its atoms are now trapped? It's akin to saying that I baked a bread some time ago and now captured its crumbs. —Preceding unsigned comment added by 89.77.156.31 (talk) 09:09, 20 November 2010 (UTC)

Antihydrogen is as stable as hydrogen, but it's hard to keep around because it annihilates on contact with ordinary matter. Thus there's a difference between merely producing it and preventing it from annihilating afterwards. -- BenRG (talk) 09:17, 20 November 2010 (UTC)

I think you have misunderstood the intended meaning of "since 1995" in the antihydrogen article. Each individual atom of antihydrogen only exists for a fraction of second before it is annihilated by contact with "ordinary" matter. The recent breakthrough was to trap atoms of antihydrogen with relatively low energies ("cold" antihydrogen) usaing magnetic fields - but even these atoms could only be kept for one sixth of a second. Antihydrogen atoms are created fresh for each experiment by bombarding a target in a particle accelerator - the antihydrogen atoms that were created back in 1995 are long gone. Gandalf61 (talk) 10:46, 20 November 2010 (UTC)

Initially, only antihydrogen-nuclei could be studied. Without positrons electrons, the nuclei are negatively charged, allowing them to be captured and contained indefinitely within a Penning trap. The trick was to create neutral atoms, a Penning trap is useless at containing neutral atoms. It is this proble that was recently overcame. Plasmic Physics (talk) 12:30, 20 November 2010 (UTC)

Space marines/soldiers?

I remember reading a while back about a Navy or Air Force veteran who wanted to start a U.S. Space Marines or something. He planned to send these five guys into space and said they should practice Tai Chi and Meditation techniques to keep them at peak psychological stamina. Anyone know about this?--Editor510 ^{drop us a line, mate} 12:53, 20 November 2010 (UTC)

I find it unlikely that one would send soldiers to space for any sort of benefit. They could practice Tai Chi and meditation on Earth in quiet rooms if they so desired at much less cost. On top of this, low/zero-gravity is known to affect muscular fitness and with enough time wastage can occur. I don't think it'd be beneficial for soldiers to go to space. Regards, --—Cyclonenim | Chat  15:10, 20 November 2010 (UTC)

Yea, astronauts who spend more than a week or so in space usually can't even walk when they land. They would hardly strike fear into our nations enemies. APL (talk) 21:10, 20 November 2010 (UTC)

You mean like Orbital Drop Shock Troopers? Cool. :] WikiDao ☯ (talk) 15:54, 20 November 2010 (UTC)

Or these space marines? SmartSE (talk) 21:05, 20 November 2010 (UTC)

Very, very expensive on top of everything else, and they'd have to rely on a certain foreign power of uncertain disposition to get them there and back, now that the Space Shuttle is being retired (unless Virgin Galactic expanded its reach considerably). Clarityfiend (talk) 20:28, 20 November 2010 (UTC)

Check out Blue Gemini. It was to be a military version of the space program that would have run parallel to the Nasa Gemini program and served as a build-up to a military run space station. It was canceled because it wasn't cost effective to have two space agencies.

Nowadays, of course, by this time next year USA will have no launch vehicles. We couldn't put soldiers up there if we wanted to! APL (talk) 21:10, 20 November 2010 (UTC)

Understanding inflammation

If inflammation is "part of the complex biological response of vascular tissues to harmful stimuli" and, therefore, as I understand it, a positive state during which the body is attempting to heal tissue damage; why are anti-inflammatories, ice, etc. (with hopes of reducing inflammation) prescribed? By consciously reducing inflammation, aren't we really hampering the body's effort to heal the damage? Or is that we are not really attacking the inflammatory process itself but we're actually speeding it up - and therefore, it goes back to a non-inflammatory state faster, "reducing" the inflammation? --Belchman (talk) 13:56, 20 November 2010 (UTC)

Surprise: Scientists discover that inflammation helps to heal wounds. So I think this all means that: if you want to 'recover' fast from say a marathon, then a 'cool' but not cold bath gets you back to normal fast, but for training perposes, let nature take it's course. --Aspro (talk) 16:06, 20 November 2010 (UTC)

Thanks to anyone that helps me with this question, but I'm particularly interested in a physician's opinion if possible - I hope that non-physicians understand this. --Belchman (talk) 17:06, 20 November 2010 (UTC)

Formal classification of fallacies

What are all the formal fallacies the second respondent at <a href="http://theboard.byu.edu/questions/60673/">this</a> site (the one who tries to reverse the Galilean experience into a defense of religion) commits? I was looking at List of fallacies and "appeal to authority" seems to fit the way he's able to determine for himself that "if I feel good after doing X, X must be a good thing." which itself fits under "correlation does not imply causation." Any other/better analyses? Thanks. 76.27.175.80 (talk) 14:04, 20 November 2010 (UTC)

That's sort of a long post at that link. Can you help narrow down your question by quoting from it exactly where you see the fallacy you are asking about being applied? WikiDao ☯ (talk) 14:46, 20 November 2010 (UTC)

When he or she says "truth is truth" (which I take as the "Galilean" section — Earth and sun and etc.) it's just tautology. The general argument is axiomatic with a tiny bit of "it makes me happy" thrown into it. But I don't think he or she is committing a strict logical fallacy here. It's just an appeal to faith. He or she is pretty self-consciously aware that this does not constitute scientific evidence and would not be compelling to skeptics. --Mr.98 (talk) 15:03, 20 November 2010 (UTC)

The "if I feel good after doing X, X must be a good thing" line of reasoning sounds like an argumentum ad consequentiam.

The poster's invocation (at the link given in the OQ) of "I plant the seed and take care of it and it grows" as applying to LDS Church (ie. that it exists as a "major" religion these days; therefore, it must be divinely favored; therefore, God exists and the LDS Church is good and true...) involves Retrospective determinism (and, historically, also involved a certain degree of argumentum ad baculum from what I understand). There are many more fallacies of reasoning in that post. I'd say Wishful thinking may well pertain, too. WikiDao ☯ (talk) 17:48, 20 November 2010 (UTC)

Mental disorders

Is bipolar disorder a real disorder or are some people just moody? Is ADD a real disorder or are some people just easily distracted? Is narcissistic personality disorder a real disorder or are some people just full of themselves? --124.254.77.148 (talk) 14:16, 20 November 2010 (UTC)

Yes. just change all your or's to and's and you're right:) WikiDao ☯ (talk) 14:27, 20 November 2010 (UTC)

I've known many people who were classic bipolar, and it goes far, far beyond "moody." They swing between completely manic and completely paralyzed depressed. It's clearly some kind of major chemical imbalance and it often completely inhibits their ability to be effective people. I can be "moody" in the sense that sometimes I'm more effective or elevated and sometimes I'm grumpy or sad. But that's not what bipolar is. Now every spectrum disorder (like bipolar, or ADD) has some shades of being similar, at its mildest levels, with what we define as "normal" variation. But when it crosses into the extremes it is pretty apparently the sort of thing which conflicts with how people function and is largely out of their control. That's usually when we class those kinds of extremes as being "disorders". --Mr.98 (talk) 15:07, 20 November 2010 (UTC)

Vehicle identification

Hello fellows!

Does anybody know who is the manufucturer of these two vehicles and which type is it.

• File:CU-Juggernaut crane on a flatbed railroad car.JPEG
• File:Wheeled bulldozer in 1973.JPEG

Thanks for helping. Cheers, High Contrast (talk) 16:41, 20 November 2010 (UTC)

You've also asked at the Miscellaneous desk where I think this question is more appropriate. I suggest the answers should go there. Franamax (talk) 17:03, 20 November 2010 (UTC)

For the first, the clue is in the name - I searched for "juggernaut tracked vehicle" and found this site, number 32 is a similar vehicle which is a Thiokol juggernaut. Then I searched for "thiokol jugernaut", found this which has a link to this which shows it is a Thiokol Juggernaut 6T that has been adapted with a drill rig. The bulldozer is a lot more difficult though, I'll have a hunt, but if nobody here can help this forum might be the place to ask. SmartSE (talk) 20:49, 20 November 2010 (UTC)

I've surprised myself, but I think it is a Caterpillar 830M, based on this listing on craigs list and this book which says they were made for the military, which obviously fits with the source and the timing. Here's a better picture of one in another book as well. SmartSE (talk) 21:02, 20 November 2010 (UTC)

Is bobbing your head to music an instinctual act or a learned one?

Thanks--72.178.134.134 (talk) 17:22, 20 November 2010 (UTC)

Definitely learnt. People in the tropics obviously got the idea from watching their parrots. [19] --Aspro (talk) 17:40, 20 November 2010 (UTC)

Composting cooked vegetable matter

I've often seen it said that cooked veg shouldn't be added to compost heaps. Why is this? Thanks. DuncanHill (talk) 17:32, 20 November 2010 (UTC)

It might be as simple as: cooked veg is sterilised veg and has most of its low temperature enzymes (those that would cause natural lysis) get inactivated. Thus, it would be an ideal culture medium for anaerobic bacteria. Its the thermophilic anaerobics what course smelly drains etc., and there is plenty of heat in a good compost heap. The solution is not to have the heap directly outside kitchen window, but in the traditional place at bottom of the garden. Bones and things in my experience don't cause any problem either. Spread out each layer, rather than dump it on, so that the air can get to it. Any vermin issues gets more than offset by having to buy less cat food.--Aspro (talk) 17:54, 20 November 2010 (UTC)

Thanks, that makes sense. I suspect that mixed with sufficient raw trimmings, peelings and garden waste it should be fine. DuncanHill (talk) 20:11, 20 November 2010 (UTC)

Looking at the sites that give this advice not to use cook food, they appear to be for these piddling little green composting drums. They also don't advise wood ash. Thinking back to when I kept two large compost heaps on the go (about 2 foot square a piece), I would put anything organic on them, even chicken heads and their eviscerate, dead rats, pizza shaped roadkill etc., by putting down first, a layer of dirt and then a bit of wood ash over the top of the carcass and offal. The lyle or potassium hydroxide in it, helped I guess, to brake down the tissue in an alkali environment and the soil bacteria stopped any smells arising. Certainly don't remember any smells. If it was organic it when on. What I had left after sieving into the wheel barrow (bones, woody bits and so on), went back on to the new heap for a second pass. Garden waste has plenty of bulk but if one is just using kitchen scraps, then that might need more careful layering as you say. --Aspro (talk) 21:01, 20 November 2010 (UTC)

Excimer lamp

Hello, what is the overall luminous efficacy (lm/W) of an excimer lamp?, ideal black-body radiator at 7000 K has 49 lm/w, so 180 lm/w like some stupid friend of mine pretends that a self invented excimer lamp should produce would be total trashtalk (his 5w selfinvented excimer lamp produces 900 lm)?TY DST —Preceding unsigned comment added by 86.127.164.33 (talk) 19:10, 20 November 2010 (UTC)

Scott toilet tissue ad touts no inner tube.

But can't that cardboard be recycled? Less waste is good, I suppose, but I'm still curious. Thanks. Imagine Reason (talk) 20:09, 20 November 2010 (UTC)

So what is the question? Yes a cardboard inner tube can (but may not) be recycled. However a cardboard tube costs money for the producer - a direct overhead. If they have a way of winding paper without the core then once they've the right machines it should cost them less AND they can advertise the cost saving to them as an environmental benefit (and perhaps charge more for it). -- SGBailey (talk) 21:28, 20 November 2010 (UTC)

A company engaged in greenwashing? No wai! DMacks (talk) 21:34, 20 November 2010 (UTC)

Anti matter

Why is antimatter important? I understand trying to understand and produce antimatter is part of understanding what makes up the universe and how it works, but do some people think it would be useful for a new class of weapons, or energy production, or could it affect how we travel or build things. Would it fundamentally change our view of how the universe is structured? Laura —Preceding unsigned comment added by 41.225.41.4 (talk) 21:13, 20 November 2010 (UTC)

None of the above, which does not mean it doesn't have any uses. For instance, anti-matter is produced inside our bodies in a pet scan machine in order to create a image for medical purposes. 76.123.74.93 (talk) 21:48, 20 November 2010 (UTC)

Rootstocks

Anyone know for sure if "semi vigorous" is more or less vigorous than "moderate vigour". I am comparing Montclaire with St Julien rootstocks and the catalogues are not consistent about which will grow a bigger tree. --BozMo talk 21:43, 20 November 2010 (UTC)