Wikipedia:Reference desk/Archives/Science/2013 February 9

= February 9 =

Organs Questions
I've got three questions about organs and whatnot?


 * 1. If someone old dies and then an organ/body part of his/hers gets put into another body, does this organ/body part still function based on its actual age or does being put in a new body makes it function as if it were of a younger age?
 * 2. What is the age limit for donating blood, bone marrow, and various organs? Can a 100 year old's donated organ(s) or blood work successfully/well in another person's body?
 * 3. Does any country maintain a list of the blood types and organ donation status of all or most of its population? I'm tempted to think No and that it would be considered a violation of privacy to do something like this, but I am still interested in finding this out for sure.

Thank you very much. Futurist110 (talk) 00:24, 9 February 2013 (UTC)


 * 1. Yes to the former, age is not a state of mind, it is a biological fact, you can't rejuvenate organs in that way. Plasmic Physics (talk) 00:33, 9 February 2013 (UTC)


 * Thank you very much. Here's another question--do the various human organs age and decline in the same way that humans do? For instance, a healthy human who takes care of himself/herself would probably reach age 85 or 90, but afterwards it becomes a very uphill climb, with very few people who reach age 90 reaching age 100 and very few people who reach age 100 reaching age 110. Do most human organs (if put in a functioning body) also stop functioning when they (meaning the organs) are 85-110 years old? Futurist110 (talk) 00:42, 9 February 2013 (UTC)


 * I'm not an expert in this this field, but I would say yes, which is why younger transplants are prefered - they have a longer useful lifetime. Plasmic Physics (talk) 00:51, 9 February 2013 (UTC)


 * Thank you. I'm interested in this because I saw this article from 2008 about a 123-year-old living cornea (here is that article--http://www.reuters.com/article/2008/10/23/us-norway-eye-idUSTRE49M6BL20081023). Futurist110 (talk) 01:38, 9 February 2013 (UTC)


 * That's believable, because I know for certain that different organs age at a different rate. Take a car for example, the tires get worn out faster than the transmission (usually). Plasmic Physics (talk) 01:47, 9 February 2013 (UTC)


 * But this contradicts your previous statement of appearing to agree with me that human organs probably age as fast as human themselves do. That said, theoretically it might be possible for a human male to reach age 123, but this hasn't happened before since by that point it would be extremely rare for all of a human male's organs to still be working/alive. Futurist110 (talk) 02:10, 9 February 2013 (UTC)


 * I never stated that they age at the same rate, only that they age. Otherwise, please name the time stamp of my comment which is contrary. Plasmic Physics (talk) 05:59, 10 February 2013 (UTC)


 * In the UK the age limit for blood donation used to be 70, but they scrapped that (ref), and it's now based on the donor's health. Crucially, certain medications for chronic conditions (medications that are very commonly taken by people as they age) disqualify people as donors, so in practice the number of donors older than 70 is pretty low. -- Finlay McWalterჷTalk 00:38, 9 February 2013 (UTC)


 * So in the U.K. someone aged 100 or above but in good health can (sometimes) donate his/her blood? What about organ donations and bone marrow donations? Futurist110 (talk) 00:42, 9 February 2013 (UTC)


 * 83 year old kidney donor. 146.90.50.59 (talk) 01:49, 9 February 2013 (UTC)


 * Thank you. Futurist110 (talk) 02:10, 9 February 2013 (UTC)


 * As I thought I had remembered, and it's confirmed in Red blood cell, blood is constantly being created and recycled, so it might be that any donation age limits are concerns about the general well-being of the donor, rather than any concerns about "old" blood. ←Baseball Bugs What's up, Doc? carrots→ 06:13, 9 February 2013 (UTC)
 * When DFDBA (demineralized freeze-dried bone allograft) is procured from cadavers, a molecule known as BMP (bone morphogenetic protein) acts to trigger greater osteblastic potential in the recipient site, theoretically leading to greater bone growth following grafting. The BMPs are even able to trigger de novo bone growth even in the absence of osteblasts by stimulating regular fibroblasts to transform, and studies have shown ossicle formation in murine muscle pouches (in the absence of bone tissue).  Anyway, it was shown by Schwartz in 1996 (J Perio) that the age of the cadaver donor correlated with the osteoinductive potential of the bone graft because of the relative potency of the BMPs.  He studied the results of DFDBA from both genders and various ages and determined that the dentist (or other clinician) will not know the effects because he or she won't be able to pick the age of the donor.  DRosenbach  ( Talk 15:11, 10 February 2013 (UTC)

Particle-wave duality
In an atom, it is said that the electron has a probability of being located at a position. Is that technically, or heuristically, correct - is the electron truely whizzing about the atom in a random way, or is it everywhere around the atom at once? I just find it hard to imagine that the electron retains its particle identity. I consider an unbound electron to be like an icy small solar system body, and a bound electron to be like the same SSSB vaporised and converted to the atmosphere of a planet. So, does the probability indicate how often the electron is expected to be encountered at that location, or how much of the electron is to be encountered at that location? Plasmic Physics (talk) 00:30, 9 February 2013 (UTC)


 * It's dangerous to think in those "normal" terms. It's not particularly meaningful to ask where the electron "is" or how much of it is where - because it's really only a probability field - and it (in a sense) "teleports" between locations within the probability cloud.  For example, there is an effect called "Quantum tunnelling" (which is what makes the flash memory in your phone/tablet/memory-stick work - so we know it's true!).  In very simple terms, the flash memory cell has a barrier between two locations that (classically) the electron cannot cross - but it can teleport between those two locations if properly coerced because there is always a finite probability of it being on the other side of the uncrossable barrier!  So this is a very real effect - large, real-world things like telephones rely utterly on this weird quantum behavior.  But it's quite hard to reconcile with day to day life...and that's the core problem with understanding quantum theory.  At those levels of existence, things are very, very weird - and trying to get your head around a physical understanding of it is impossible.  The only real way to get a handle on it is via the math. SteveBaker (talk) 01:02, 9 February 2013 (UTC)


 * So, a bound electron has a precise location that changes with time? I know about quantum teleportation, I just never reconcilled it with the behaviour of bound electrons. They never discussed electron motion within atoms in the lectures. Plasmic Physics (talk) 01:42, 9 February 2013 (UTC)
 * Quick aside &mdash; what's being discussed is quantum tunneling, not quantum teleportation, which I think is some information-theoretic abstraction rather than an electron actually showing up in a different place.


 * I figured. Plasmic Physics (talk) 03:48, 9 February 2013 (UTC)


 * Whether an electron has a precise location is a subtle question that gets into interpretations of quantum mechanics. I think most physicists generally prefer to avoid the question altogether ("shut up and calculate" says the shade of Feynman) and leave it to the philosophers. --Trovatore (talk) 03:22, 9 February 2013 (UTC)


 * Is there a way of testing either alternative? Plasmic Physics (talk) 03:48, 9 February 2013 (UTC)
 * There are more than two alternatives. As far as I know, no experiments have been devised that would distinguish among any of them.  Strict positivists probably consider it a meaningless question for that reason, but for people with a more realistic view this is hard to swallow.  But it's hard to get realism to play nice with QM under any conditions. --Trovatore (talk) 04:03, 9 February 2013 (UTC)
 * I should say, though, that your notion of a sort of "electron vapor", spread out over space, is not really one of the alternatives. Or at least I don't think it is.  The electron itself is very tiny &mdash; as far as anyone knows, pointlike.  The probability distribution tells you how likely it is that the electron will be found at a given location, but it is not the electron itself. --Trovatore (talk) 05:12, 9 February 2013 (UTC)


 * The thing is, the "wave" vs. "particle" thing is a false dichotomy. There are not "alternatives" and these are not the two.  Electrons always behave like electrons.  The problem is that the way they behave simply does not have analogues you can experience with your 5 senses.  That is, there is nothing in anything you have experienced, and thus nothing you can "visualize" which fully captures what an electron is.  The best we can say is that, in some applications it is helpful to visualize the electron as a particle (but only for those applications) and for other applications, it is helpful to visualize the electron as a wave.  Those are still human-created models, however.  The electron doesn't change its behavior, it doesn't swap "modes" or jump between "alternatives": it just goes on being an electron doing what electrons always do.  It's our problem to come up with models to explain it.  And it's been about a century since physicists stopped trying to create a "picture" of what an electron is.  That's the whole spirit of the "shut up and calculate" exhortation is above.  Electrons are best modeled by mathematical equations that describe and predict what they do: that there is no single nice visualization you can make which captures the full nature of "electronness" is ultimately not the electron's problem.  -- Jayron  32  05:22, 10 February 2013 (UTC)


 * The picture of the electron in a hydrogen atom as a stationary wave and the picture of it as a particle randomly moving around are about equally valid. They can't be tested against each other—they're just two different ways of looking at the same physics.


 * Quantum mechanics actually has two different classical limits. If you take ħ → 0 while keeping the E in E=hf constant (so that f → ∞) you get the classical particle limit: each particle still carries energy E, but the infinite wavelength means you can never observe any wave interference behavior. If you take ħ → 0 while keeping the f in E=hf constant (so that E → 0) you get the classical wave limit: there are infinitely many particles each carrying infinitesimal energy that smoothly cover everything so you never see shot noise. Quite a lot of behavior that's often described as "purely quantum" is really behavior that vanishes in the particle limit but survives in the wave limit. Tunneling is one example of that: in the classical context it's called Evanescent-wave coupling. Of course there are other things that vanish in the wave limit but survive in the particle limit, like shot noise. Quantum mechanics sort of sits halfway between these two types of classical theories, so it's helpful to keep both pictures in mind. -- BenRG (talk) 05:15, 9 February 2013 (UTC)
 * I'm worried that this answer sounds overly compatible with the "electron vapor" idea. A stationary wave is not the same as a spread-out electron, any more than a radio wave is a spread-out photon.  --Trovatore (talk) 05:26, 9 February 2013 (UTC)
 * A radio wave containing one quantum of energy is a spread out photon. A radio wave containing many times that much energy is a bunch of spread out photons. Photons are not localized in a coherent wave.
 * I'm not sure exactly what you mean by the electron vapor idea but I think there's nothing especially wrong with that idea. Feynman famously said that the single most informative statement about the world is "all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another". That's a picture of atoms as somewhat sticky, somewhat rubbery balls. Sure they're quantum objects but that doesn't mean these aren't useful classical analogues for various aspects of their behavior. -- BenRG (talk) 06:56, 9 February 2013 (UTC)
 * Well, no, come on, I know you're a physicist and I'm not, but a radio wave is not a spread-out photon. A radio wave is electric and magnetic fields.  An electron "wave" is an area of probability density.  It's not a particle spread out.  That's a cheap way of restoring realism that doesn't work.
 * You can restore realism with the many-worlds interpretation, by letting the real thing be the entire collection of worlds rather than just ours. Maybe you can restore it by the transactional interpretation; I've never understood it well enough to be sure.  But not with the image of a "spread-out particle".  It's just the wrong image; it doesn't lead to intuitions that correspond with theory or experiment. --Trovatore (talk) 09:12, 9 February 2013 (UTC)
 * I'm not a physicist, I just studied it in college. First, as I mentioned in another thread, the Standard Model is a quantized classical field theory. The wave nature of the electromagnetic and electron fields (the latter has no good name) is already there at the classical level. Quantization adds particle-like behavior, but the wavelike behavior doesn't disappear. You can and should think of a photon as the dimmest possible electromagnetic field. It's a misleading name for it, but it's too late to change that. If you want to talk about the pointlike behavior of light (i.e., shot noise), it would probably be better to talk about the "darkenon", which is one quantum of energy transferred from the electromagnetic field to a single silver halide crystal. (I just made that word up.)
 * Quantization is always the same. You probably wouldn't say that phonons are points and the bulk vibration of the crystal is just an indication of the probability of finding one in a particular place, but it's just as true for them as it is for electrons or photons. Or quantum vortices, which don't seem to have a commonly used name ending in -on but are particles nonetheless. -- BenRG (talk) 18:32, 9 February 2013 (UTC)
 * A radio wave totally is just a spread-out photon (or, more commonly, for normal amplitudes, it is a superposition of many photons). It's rarely useful to analyze this way; and we rarely have a wave at RF frequencies whose amplitude is so low as to be a single quantum emission; but this is still definitionally true and is easier to build a single RF photon emitter, in practice, than a single-photon-emitter at optical frequencies.  Any electromagnetic wave can be viewed as a wave or as a particle.  Considering a macroscopic wavelength as a "particle" can be very instructive in developing intuition about wave-particle duality.  BenRG's comments about phonons are spot-on.  Nimur (talk) 20:51, 9 February 2013 (UTC)
 * I disagree. It's a bad guide to intuition.  It avoids confronting the failure of local realism.  It sounds as though there's all this real "stuff" that's spread out over space, and that just isn't true.  Also it completely clouds (ha!) the issue when you try to extend it to non-pointlike particles, like the proton &mdash; the learner can be forgiven for saying, wait a minute, here you're telling me about the proton "radius" (as distinct from the electron radius of, presumably, zero), but at the same time you have a picture of the proton as spread out over space, are these the same thing or not?
 * Particles are ipso facto localized, but the place they're localized to is, depending on interpretation, uncertain, different in different "worlds", or something else. --Trovatore (talk) 21:00, 9 February 2013 (UTC)
 * Well, I mean, the world is as real as it ever was, and failing to acknowledge that seems like an error to me. Of course there's stuff out there; it's what we've been trying to understand with all this physics nonsense. Saying that we've discovered by studying it that it isn't real, aside from being philosophically silly, doesn't tell you anything. It's wakalixes. What Feynman said about atoms does tell you things. The stickiness of macroscopic objects derives from the stickiness of atoms. Solids tend not to be sticky because they have rough surfaces and there's very little atom-to-atom contact when you press them together. Liquids stick to solids because they flow into the gaps. Gas molecules don't stick to each other because they're moving too fast, but if they slow down enough they do stick together, and that's why gases liquefy when you cool them down. And so on. Atoms are solid objects. Macroscopic solids are made of atoms and derive their solidity from the solidity of atoms (which is due to the Pauli exclusion principle). It's ridiculous to deny all of this or to imply that there's some kind of connection to many-worlds or what have you. We've actually learned some things about the everyday world in the last hundred years.
 * It's true that protons have an intrinsic (interaction) radius and also are spread out and that those things are independent. Saying that you shouldn't tell people about that because it's confusing isn't a very good argument. Mathematically the interaction radius shows up in the interaction part of the Lagrangian as a coupling of field values at different points in space. The photon-electron interaction in QED is a product of field values separately at each space(time) point, integrated over all the points, and that's the sense in which they are pointlike. A free field/particle is not pointlike in any way. That's why I said above that it's probably better to treat the interactions as pointlike rather than the particles themselves.
 * In many ways Standard Model particles/fields behave like classical particles. But saying that the particle picture is more fundamental, and the wave picture secondary, is completely wrong. -- BenRG (talk) 22:17, 9 February 2013 (UTC)
 * Wait a minute, I didn't say there wasn't real stuff out there. I said a delocalized pointlike particle is not "real stuff spread out".  I stand by that.  A point particle is a point, no matter how spread out its probability density function is. --Trovatore (talk) 22:27, 9 February 2013 (UTC)
 * Okay, look. What you seem to be saying is that fundamental particles don't occupy space—which means that the term "occupying space" is useless, since nothing does it—but that they do something, presumably involving the Pauli exclusion principle, that creates the impression of occupying space. I suggest calling that thing that they do "occupying space". I don't see what other meaning the term can have.
 * As far as I can tell, you haven't explained why you think the particles are just points even in the face of all the arguments to the contrary that I've presented. If it's because you think the wave function is a probability density, I think you're forgetting that it's a probability distribution over classical field configurations, not classical particle coordinates, since the Standard Model is a quantized field theory. If it's because of Feynman diagrams, I'll explain the reasons why Feynman diagrams are unlikely to be fundamental. -- BenRG (talk) 00:04, 10 February 2013 (UTC)
 * Well yeah, the path integral formulation makes a lot of sense to me. Why do you see that as non-fundamental?
 * But you know, anyway, your point about a probability distriubtion over field configurations &mdash; that's just a different basis for the vector space. Surely the appropriate basis when you're calling them particles, specifically, is the one where the position distribution is a delta function.  That's kind of what "particle" means. --Trovatore (talk) 01:36, 10 February 2013 (UTC)
 * To particle physicists "particle" and "field" are nearly synonymous. You're taking the terminology too literally. Atoms aren't indivisible, protons aren't fundamental and particles aren't points. Also, the wave function has an independent value at all field configurations, not just a set of basis states. There's no basis for the quantum Hilbert space that limits you to delta functions in physical space.
 * Individual Feynman diagrams break gauge symmetry and in some cases involve fictitious particles. The symmetry is restored and the fake particles disappear in the sum, but it's not very plausible that the universe is really adding a bunch of asymmetric diagrams with extra particles and ending up with a perfect symmetry. It's similar to treating the expansion $$\gamma mc^2 = mc^2 + \tfrac12 mv^2 + \cdots$$ as fundamental. Very similar, in fact, because Feynman diagrams label terms in a series expansion of the path integral. The basic idea is easy to understand. Start with $$\partial\psi/\partial t = -iH\psi$$. If H is not a function of time, the solutions are $$\psi(t) = e^{-iHt} \psi_0$$. You can expand that as $$\psi(t) = \psi_0 + (-iHt) \psi_0 + \tfrac12 (-iHt)^2 \psi_0 + \cdots$$, i.e., as a sum of ψ0, ψ0 acted on once by −iHt, ψ0 acted on twice by −iHt, .... If H = H1 + H2 then the sum includes ψ0 acted on once by −iH1t, once by −iH2t, twice by −iH1t, once by each, etc. This is very sloppy since I should be using the Lagrangian and I should separate the interacting and noninteracting portions, but I hope you see that in a series expansion you quite naturally get a sum of all finite combinations of discrete interaction terms. That's not to say that the boson-exchange picture suggested by the simplest diagrams is wrong. At least in QED scattering it's correct inasmuch as it's a good approximation, but it's not The Truth any more than E = ½mv².
 * Another problem is that there are phenomena in the Standard Model that don't have an expansion in Feynman diagrams, such as the Higgs mechanism. (Which is not the same as the Higgs particle, but I think the detection of a particle so similar to the predicted one proves the correctness of the Higgs mechanism beyond a reasonable doubt.)
 * Another thing is that you can do classical wave mechanics with Feynman diagrams, but there is no particle-like behavior in those theories. -- BenRG (talk) 02:46, 10 February 2013 (UTC)


 * 'Electron vapour' is exactly the name I would give it - a bound electron completely evaporates, from a particle into a vapour, surrounding the nucleus where the cloud density is equal to the 'probability'. Plasmic Physics (talk) 09:18, 9 February 2013 (UTC)
 * But that's exactly the wrong image. If you use that image, your intuition will lead you to incorrect conclusions.  The electron has (as far as anyone knows) zero volume &mdash; it's just a point.  That's true whether it's bound or free.
 * The "cloud" is a quantum superposition of places the electron might be. But each of those places is just a point (again, as far as anyone knows). --Trovatore (talk) 09:24, 9 February 2013 (UTC)


 * Yes, that's wrong—the electron's nature doesn't change just because it's part of an atom. If it's a cloud in that situation, it's a cloud the rest of the time too. If it's a point particle the rest of the time, it's a point particle when part of an atom. -- BenRG (talk) 18:32, 9 February 2013 (UTC)


 * There are several mistakes here. You're forgetting the solid-illusion, nothing is truely solid, especially electrons. Electrons consists of various fields that are concentrated in a very small space without definite boundaries. The 'radius' which comes in at a maximum of 10-22 m, is completely arbitrary, and was chosen to represent a distance from the centre of the fields to where the electric field decayed sufficiently. Ergo, the electron itself is a tiny version of the 'electron vapour'. The only difference between the bound and unbound electron would be the diffusivity gradient and shape depending on which orbital was occupied.
 * P.S. From the article, 'point particle' is just a heuristic to describe the relative dimensions of a partcile. Plasmic Physics (talk) 19:36, 9 February 2013 (UTC)

Concluding remarks? Plasmic Physics (talk) 02:49, 11 February 2013 (UTC)
 * lemme toss the uncertainty principle into the mix; the uncertainty referred to is split between the position and momentum of the electron (in this instance). So, if you know the position of the electron to a high degree of accuracy, you have no idea what the momentum might be (i.e., is it moving or not?); alternately, if you know the velocity of the electron, you can't know what the position is, i.e. is the position changing. So, "is the electron truely whizzing about the atom in a random way, or is it everywhere around the atom at once"? You're asking for both position and momentum simultaneously, which makes this a question which cannot be answered, or more accurately, a question which is basically meaningless at this scale. Gzuckier (talk) 04:59, 11 February 2013 (UTC)

Covering bare floorboards
Okay, so basically today I put the wrong kind of soap in the dishwasher (liquid instead of powder : and apparently the dishwasher didn't like that. I found this out as an hour after I started the load, I got up to check it, and found the kitchen floor F**KING FLOODED IN LATHER AND SUDS! Needless to say, i put away the dishes and cleaned up the mess, and the kitchen floor was so clean afterwards I could see my reflection in it. It was then I decided that as long as I was working around the bottom of the dishwasher, I might as well nail down the curled up linoleum around the edges of the floor. So I got out a box of 1&1/4" nails and a hammer and started pounding away. However, some portions of the floor around the dishwasher and sink were so curled, distorted, and cracked that I couldn't nail them down, I had to cut off and throw away the ends before doing so. This led to a small, but long area of bare floorboard under the sink and dishwasher. This is a problem because: So anyway, my problem is I can't decide which substance would be best for a sort of footstop under the counter. What I want to do is take one of those inclined thresholds like the sort under a front door to a house and nail it down there. I need a footstop which can prevent water damage and accidental kicking of the baseboards, hold the linoleum down indefinitely without cracking it, and last for up to five years. My options are: So, which would be best? (PS I filed this under science because I thought this was an engineering topic) -- Free   Wales Now!   what did I screw up?   00:56, 9 February 2013 (UTC)
 * The floor is particle board, so can cause splinters in the feet if stepped on wrong.
 * In addition to the water damage that the floor has doubtless suffered through the years already, it is now completely bare and any liquid spilled on the floor in that area could damage it.
 * Metal
 * Rubber
 * Plastic
 * Treated Wood
 * More linoleum flooring
 * Tile


 * Free Wales now? Is Jimbo in jail? Oh, wait... :)
 * Will a high dam sill do what you want to do? They come in long versions for use with garage doors. --Guy Macon (talk) 02:30, 9 February 2013 (UTC)
 * A bare margin with some sort of sill is not going to do you well if you have another flood. You're probably better of with a new floor that sits flush against the counter although I am sure you don't want to hear that.  I won't laugh at your situation having gone through it myself and had a friend go through it last month. μηδείς (talk) 02:49, 9 February 2013 (UTC)
 * Thank you, that high dam sill thing does sound exactly what i'm looking for. Since my dishwasher seems to have flooded from under the door rather than the baseplate, needing a new floor shouldn't be a problem. Pretty much all I needed was a durable "ramp" to allow water to drain out onto the rest of the floor and off the baseboards while looking decent. Heading to Home Depot tomorrow... -- Free   Wales Now!   what did I screw up?   03:41, 9 February 2013 (UTC)


 * It is altogether possible that some hose behind will develop a small leak at some time and what you are doing would hide the damage and make a pool to soak into the floor. Just fix the floor properly and cover the edge between the wall and the floor behind to stop any small leak into the crack. Dmcq (talk) 11:38, 9 February 2013 (UTC)


 * Note that the Refdesk does not give advice, accepts no liability if black mold spreads throughout your house causing serious and permanent illness that can be palliated only by expensive visits with a mind-body therapist, and we are not licensed interior designers and therefore are not allowed to give interior design advice in Florida. Except in residences.  Or is it Virginia now?  Heck, it's a racket every bit as legitimate as the "medical advice" thing they're always on about here. Wnt (talk) 17:35, 9 February 2013 (UTC)

why was rutherford model of an atom discarded ?
Rutherford model was discarded because according to that model electrons will radiate energy as they move around the nucleus. In Bohr model, electrons revolve around the nucleus without radiating any energy. How is this possible ? The case (radiating energy), which was applicable for Rutherford model, was not applicable for Bohr model, why. --Concepts of Physics (talk) 03:05, 9 February 2013 (UTC)


 * For convenience, see Rutherford model and Bohr model. Basically, the Bohr model was just more specific than the Rutherford model. Rather than predicting the electrons existed in a cloud, possibly orbiting the nucleus, Bohr predicted very specific orbits. His model never explained how stably orbiting electrons fail to radiate energy, which was part of why physicists knew there was still a deficit in their understanding of the electron. Someguy1221 (talk) 03:18, 9 February 2013 (UTC)


 * An easy way to think of the historical chronology of these models is this:
 * Thomson: "atoms are not indivisible, but are made up of negative subatomic particles in complicated orbits, all within a diffuse positive field"
 * Rutherford: "actually, atoms are a dense positive nucleus around which tiny negatively subatomic electrons orbit in a classical way, but I don't know why they don't lose energy"
 * Bohr: "ah, they don't lose energy because they're quantum, not classical, and in fact the way they gain/lose energy has to do with discrete stable states. But I don't know why that is other than to say that the quantum world is strange."
 * De Broglie: "ah, the reason they are distinct stable states is because there are only so many stable wave functions, and the electrons are basically waves"
 * It's not so much that Rutherford was "discarded" so much as "built-upon." Ditto with Bohr's, which wasn't the last step there either. (Nor was de Broglie's, of course.) Obviously I'm simplifying the technical stuff here but such is how it goes with simplifications! --Mr.98 (talk) 18:05, 9 February 2013 (UTC)
 * In fact, the "plum pudding" model works pretty well for many applications in classical mechanics. You only need to worry about the breakdown of this model when you perform experiments with resolution better than the scale length of the atom.  That means you're sending down photons of particular wavelengths (so you need the mechanics of Compton scattering; or you're analyzing emission spectra of atoms with high resolution.  If you apply classical theory to the plum pudding model, and your scale length is always sufficiently larger than the atom, you will never find any conundrums!  In formulations of quantum mechanics, this is an important and often-underemphasized empirical fact.  Mathematically, this corresponds to a boundary condition, or a limit case, of any equation proposed to describe a quantum mechanical system: when extrapolated to large numbers, or large sizes, the formulation must remain consistent with what we observe!  It is my opinion that most of the "conundrums" people encounter when they try to study quantum mechanics would be straightforwardly resolved if people would review the mathematical conceptual leap in the limit formulation of these problems.  Nimur (talk) 20:01, 9 February 2013 (UTC)
 * See this is related to your question. Sunny Singh 09:03, 10 February 2013 (UTC) — Preceding unsigned comment added by Sunnysinghthebaba (talk • contribs)


 * Quantum theory revolutionized physics at the beginning of the 20th century, when Max Planck and Albert Einstein postulated that light energy is emitted or absorbed in discrete amounts known as quanta (singular, quantum). In 1913, Niels Bohr incorporated this idea into his Bohr model of the atom, in which an electron could only orbit the nucleus in particular circular orbits with fixed angular momentum and energy, its distance from the nucleus (i.e., their radii) being proportional to its energy. Under this model an electron could not spiral into the nucleus because it could not lose energy in a continuous manner; instead, it could only make instantaneous "quantum leaps" between the fixed energy levels. When this occurred, light was emitted or absorbed at a frequency proportional to the change in energy (hence the absorption and emission of light in discrete spectra).


 * Bohr's model was not perfect. It could only predict the spectral lines of hydrogen; it couldn't predict those of multielectron atoms. Worse still, as spectrographic technology improved, additional spectral lines in hydrogen were observed which Bohr's model couldn't explain. In 1916, Arnold Sommerfeld added elliptical orbits to the Bohr model to explain the extra emission lines, but this made the model very difficult to use, and it still couldn't explain more complex atoms. Want to be Einstein (talk) 10:09, 10 February 2013 (UTC)
 * This reminds me of my favorite piece of dumb management/marketing speak, where something or other is described as a "quantum leap" in blahblahblah. Someday I'll stick up my hand and say "You mean it's the smallest possible change?" Gzuckier (talk) 05:05, 11 February 2013 (UTC)

Why is the GAU-8 effective?
Why is the GAU-8 Avenger effective at destroying tanks when its caliber is only 30 mm and modern MBTs are designed to reliably withstand hits from 120 mm guns? Whoop whoop pull up Bitching Betty 05:30, 9 February 2013 (UTC)
 * Diameter is not a determinant for destructiveness against armor; note that sabot anti-tank rounds have a "shoe" (fr. sabot) that separates from the round to release a kinetic energy projectile which is smaller than the diameter of the barrel from which it is fired.  From the article:   For reasons why a smaller diameter projectile can be desirable, see external ballistics and terminal ballistics.   ~E:74.60.29.141 (talk) 06:02, 9 February 2013 (UTC)


 * It probably wouldn't be sufficiently effective against a modern MBT. This 1980 report about an attack by A-10s on Korean War era M47 Pattons says the 140 hits, only 17 penetrated the Patton's armour. A Patton has 100mm of steel armour; the later M1 Abrams variants have advanced reactive Chobham composite armour which give a protection equivalent to 600-1000mm of steel armour. That's why the A-10 carried higher performance weapons like AGM-65 Maverick as well, specifically for hard targets that the GAU-8 wouldn't kill. The GAU-8 is still useful against a wide variety of battlefield targets like AFVs, APCs, trucks, tankers, jeeps, artillery pieces, tractors, and self-propelled guns, and against unfortified structures. -- Finlay McWalterჷTalk 16:33, 9 February 2013 (UTC)


 * That said, it's not totally useless against an MBT; given the GAU's weight of fire, it's quite possible it would be able to detrack an MBT, rendering it ineffective and vulnerable. -- Finlay McWalterჷTalk 16:36, 9 February 2013 (UTC)


 * The M829's KE penetrator is only 20 mm in diameter. However the A-10's cannon is ineffective at killing modern MBTs. It can handle out of date T-62s and the likes, but not a post-1980 MBT. It can several damage them, destroying their tracks, vision equipment, even weapons and engine (weakly armored grille). A machine gun can be completely destroyed by a hit and I don't think a crew would risk firing a big gun that has been damaged by an autocannon, the shell might explode before leaving the barrel. All of this is repeairable though, for an assured detruction it must used its missiles. You must remember though that MBTs are only a small percentage of the vehicles in an army. Lightly armoured and soft skinned vehicles are the bulk, and the cannon can effectively destroy these without wasting a missile.--Whichwayto (talk) 17:11, 9 February 2013 (UTC)


 * For a kinetic kill system like a DU anti-armour round, the crucial factor is the projectile's kinetic energy. If I'm doing the maths right, the KE (at the muzzle) for a GAU-8 round is about 0.2 MJ; for an M829A3 from an Abrams its about 12 MJ. -- Finlay McWalterჷTalk 17:27, 9 February 2013 (UTC)


 * Actually, in the case of the Hog's GAU-8, the most crucial factor is hitting the top armor rather than the frontal armor -- a tank's armor is weakest on top. 24.23.196.85 (talk) 20:22, 9 February 2013 (UTC)
 * ineffective at killing modern MBTs is incompatible with what follows that claim. A blind, motionless, gunless MTB might as well be dead. It's certainly a mission-kill, and it's an easy target for infantry with any kind of anti-armour. --Stephan Schulz (talk) 21:18, 9 February 2013 (UTC)
 * But, as he said, almost all of that damage is repairable by the tank crew. Just bolt on the spare machine guns, realign the main gun, fix the tracks, and you're ready to go.  Even if some of it isn't repairable, the tank can still be useful; for instance, if the periscope is wrecked, the commander can still effectively direct fire by standing up in the cupola (good tank commanders do this anyways), and even if the tank is rendered completely motionless, it is still quite useful as a fully traversable, armored artillery piece. Whoop whoop pull up Bitching Betty 17:16, 10 February 2013 (UTC)
 * Although modern armies are very efficient at recovering and repairing damaged tanks, as long as you're advancing and not retreating. Another point is that modern armies have a great many more armoured vehicles that are NOT main battle tanks; armoured personnel carriers, armoured reconnaissance vehicles, self propelled guns, armoured command vehicles, and so on; it is these that the "Avenger" is really intended to counter. Alansplodge (talk) 13:07, 10 February 2013 (UTC)

do we know what Mars sounds like?
did Curiosity or any other mars probe have a few grams to spare out of their multiton payload on a microphone, so we could hear what Mars sounds like? 178.48.114.143 (talk) 06:46, 9 February 2013 (UTC)
 * One noise emanating from this phenomenon sounded something like "Illudium Q-36 Explosive Space Modulator." ←Baseball Bugs What's up, Doc? carrots→ 07:01, 9 February 2013 (UTC)

http://www.youtube.com/watch?v=DJ3A4XOWSFE

http://curiositywatch.com/sounds-from-mars-why-curiosity-has-no-microphone/


 * Considering the rover is two tons, the mic would have added precisely two grams and a single analog input, and was not mission-critical, would not need to be pointed anywhere and can literally be in any crevice, does not need to even be automatically collected or read or affect any other mission requirements, can break or fail to function without consequences, yet if it happened to still work, would bring huge outsider interest in mars, I hope you will agree that I am simply smarter than NASA. That video, until the rickroll, was absolutely FASCINATING.  I was like, wow, wow, wow.  Two grams.  Fuck you, stilted engineers.  You didn't even try! 178.48.114.143 (talk) 09:01, 9 February 2013 (UTC)


 * I'm sorry to disappoint your hope, but I don't agree. I suspect that the predominant sounds would be those of the motion of the rover. Are those of interest?  I'd be surprised if a Mars microphone picked up any interesting sounds. ( dinosaurs? little green men chatting? )    D b f i r s   09:30, 9 February 2013 (UTC)
 * It's impossible to predict what scientific discoveries will be made in advance, or else they wouldn't be discoveries. For example, the LHC was predicted to discover the Higgs boson, a particle that's been part of the Standard Model for decades, and that nobody seriously doubted the existence of.  If that's all it discovers, the LHC is a huge waste of money, but physicists are hoping for something unexpected that will revolutionize physics.  What will that be?  Well, if anybody knew, it wouldn't be a discovery.  --140.180.247.198 (talk) 17:41, 9 February 2013 (UTC)
 *  Mars... I can't believe I'm back on Mars. Three times before, this place almost killed me. I swore I'd never give it another chance to finish the job. Humns got no business being here. No business at all. &mdash; Michael Garibaldi.  How different is that from Saigon...shit? --Trovatore (talk) 09:36, 9 February 2013 (UTC)


 * Yes, the sounds of the motion of the rover would have been very interesting. Out of curiosity, why do you think we wouldn't have heard wind, as in the video?  Or explosions in the distance from volcanos nearby, which the rover cannot see visually?  Acoustics is so so cheap.  If nothing else, the sound of the gravel/sand/whatever under the rover's feet... This article says it is "probably still volcanically active today": http://en.wikipedia.org/wiki/Volcanology_of_Mars  - so, out of curiosity, if the rover happened land within earshot of a volcano, you don't think having a mic onboard would be something anyone would be interested in hearing?  No mic is simply irresponsible.  It's not like I'm asking you to include speakers, so we can blast some music and hear its echoes if we are near a wall.  I'm asking for a two gram mic.  There is no excuse.  Aren't there dust storms, too?  You don't want to know what they sound like?  No imagination around here.  178.48.114.143 (talk) 10:14, 9 February 2013 (UTC)
 * “Curiouser and curiouser!” Cried Alice: I find usage of the cliché out of curiosity curious interesting in a thread discussing NASA's Curiosity rover -- Senra (talk) 22:14, 9 February 2013 (UTC)
 * If we prorate the ENTIRE budget of $2.5 billion just into the 2000 pound payload - which is a huge overstatement, imagine if a scenario where the actual final payload is just 100 grams. Making it 101 grams by adding a gram to what we consider, wouldn't have cost a further marginal $25 million or increased the budget by a full percentage point!  Most of the budget is in developing the rover, delivery system, etc.  So this is a huge, huge, huge, huge, HUGE overestimation.  Still, by this HUGE overestimation, another 2 grams added to the payload would have increased the size of the payload by 1/500000th, or the prorated budget from $2.5 billion by another $5,000.  A handful of people, hell, a single individual, would have gladly paid that amount to hear Mars.  If the only place a single recording ever appeared was youtube, the advertising revenue would be more than $5,000 from it.  Think about it!!!  There is just no excuse, except ignorance and lack of creativity.  178.48.114.143 (talk) 10:30, 9 February 2013 (UTC)


 * "ignorance and lack of creativity", eh? And yet ironically they're the ones driving a robot on Mars and you're the one wasting your time ranting on an internet forum which isn't actually a forum at all.Dncsky (talk) 13:36, 9 February 2013 (UTC)
 * I wouldn't be so quick to discount the OP's opinions, though some of them could have been expressed in a more rational fashion. I, for one, wouldn't mind listening to dust storm or similar event taking place on Mars (imagine all the relaxation CDs off-brand record labels could sell in five-and-dime shops!), and I'm certain the cost would have been neglibible compared to the other components of the rover. Let's also not forget that technical know-how does not necessarily correlate with creativity or a propensity for brilliant ideas (for example, this is a product that smart people allow to exist). Evanh2008 (talk&#124;contribs) 13:58, 9 February 2013 (UTC)


 * This question has been asked before, here. Here's one of the responses:
 * "Plenty of people have pushed for including a microphone on a Mars mission, most notably the Planetary Society, whose microphone actually flew on the failed Mars Polar Lander. The Phoenix lander also included a microphone, but only because its descent imager (MARDI) happened to have a microphone on its circuit board. MARDI was turned off because it had a risk of interfering with IMU measurements during landing, which could have been fatal to the spacecraft. According to an interview I heard with a Planetary Society member (Emily Lakdawalla), the Society lobbied to have their microphone included on Curiosity, but it was rejected because the rover was already complex enough (she didn't elaborate on this, and I haven't been able to find a more detailed explanation). Personally I think that's a strange reason, because a microphone is one of the smallest and simplest electronic devices possible (just look at your cellphone to see how small it could be). Having one would be great for PR, and NASA only gets funding if the public is excited and inspired by its missions."
 * Here's an answer from the Curiosity team themselves: . The second part is interesting:
 * "Here's a little more info on the Phoenix microphone. It was essentially a hitch-hiker. It was built into another instrument taken off the shelf for the the lander, but it was never intended for the mission. There was no science team or budget connected to it. Since it was not intended for use it was never tested before launch and never entered into the power budget for the lander. Only after Phoenix successfully completed it's mission, 5 months after landing in the polar region, was the mission somewhat willing to test it. They couldn't do it earlier because they couldn't risk the prime goals of the mission if anything went wrong. The project manager was fairly certain it wouldn't work and was against trying it because he didn't want to raise expectations. His mind changed when we got a tweet to the @MarsPhoenix account from a man who said he was blind and how much he wished he could hear Mars because he couldn't see the pictures. A couple days later, they sent the signal to Phoenix to turn it on but we got.. well.. nothing. Empty files. If we had received anything, it would have been released. The team figured the mic was frozen solid and decided to give it a second try by leaving it on longer to warm up. Unfortunately, the Phoenix mission lost its last bit of power (as expected) before it got the second instruction." --140.180.247.198 (talk) 17:41, 9 February 2013 (UTC)


 * Let's rephrase the answer another way. Spaceship engineers are not stupid.  They know what their instruments measure.  Now, let's review this carefully, because it is not clear whether the OP knows what a microphone measures.
 * "Sound, obviously!" says the enthusiastic OP! "I want to record sounds!  Put a microphone on the spaceship!"
 * Now, as the reference desk regulars who follow Science know, we've had a recent spate of questions asking about minimum densities that sound can propagate in. And, as we have repeatedly answered, there is no well-defined answer to that question.  So, "is there sound on the Moon?  Is there sound on Mars?"  While our knee-jerk response is "of course not, these places are nearly total vacuums, and sound cannot propagate!" ... if we stop to really really carefully answer the question, we find that we must refine this to say, "...well, actually, the amplitude of acoustic waves in very-very-sparse atomspheres are very tiny, and the frequencies are very low."
 * This brings us back to my first point: spaceship engineers are very smart. So while you think "a microphone measures sound" and cuss out the engineers, let me defend their line of reasoning.  A microphone doesn't measure sound at all.  Most modern "2-gram" microphones are piezoelectric crystal attached to high gain differential amplifiers, and then digitally sampled.  They measure a voltage, proportional to the mechanical stress on a piezoelectric crystal.  When a sound is audible to a human, that sound corresponds to a pressure wave propagating in air, which will exert a mechanical stress on a collector plate and deform the piezo, inducing a voltage.  That voltage will be amplified and sampled.
 * We can calculate exactly what voltage will be produced for any given deflection.
 * We know the density of the Mars atmosphere, and we know its pressure, and we know how much force a molecule can exert on a piezoacoustic coupling... and we know the electronic noise floor of the finest differential amplifier circuit this side of the Jovian moons... and we know the realistic sampling rate and quantization error for digitizers, because we studied elementary digital design theory... and the net result is: the signal will be all zeros.
 * If we know (from other experiments, and from application of the laws of fundamental physics, that it is not physically possible to measure signal, given the sparse atmosphere of Mars, we don't waste time putting a microphone on the spaceship.
 * Instead, we go back to basics: what are we trying to measure? Vibrations?  Particle flux?  We have instruments on Mars Science Laboratory to do that.  MEDLI, RAD, and others.
 * So, the real point here is, the OP is making an unreasonable demand to place an instrument known not to work on a billion-dollar spacecraft. When the OP finances, engineers, and executes his/her own billion dollar spacecraft, they may place any instrument they like onboard ...and if that is your objective, start by reading my post on engineering tradeoffs in spaceship design, with links to a complete lecture-series... : but until then, accept at face-value this simple fact: somebody very smart thought about your idea and dismissed it for very good reasons, long before you even knew they were planning a Mars rover.  Nimur (talk) 20:25, 9 February 2013 (UTC)


 * OMG, did you read anything that other people wrote before harping, falsely, about how it's impossible to record sound on Mars? NASA's Mars Polar Lander had a microphone, by design, for the purpose of recording sound.  Phoenix carried a microphone by "accident", and though it heard nothing, the team thought that was because it got frozen and gave it a second try.  The Planetary Society has built a Mars microphone for inclusion on a spacecraft, and it flew on the Polar Lander.  Your claim that it's physically impossible to hear sound on Mars is simply wrong.  --140.180.247.198 (talk) 00:40, 10 February 2013 (UTC)
 * I agree. Unusually for Nimur, he was wrong in detail (eg most modern cheap microphones are electret, not piezo - piezo has been obsolete for 30 years) and wrong in overall thrust.  While the low altitude atmosphere density on Mars is only about 1/50th of that on on Earth, this is still quite sufficient to carry sound - you'll just need a much bigger microphone diaphram area to get equivalent sensitivity, as was explained in another recent question on Ref Desk. Detectable frequencies can easily cover a good bit of the audio range.  However I also agree that nothing much is lost by not having the microphone.  What do you expect to hear?  I should think nothing other than the mechanical noises of the spacecraft, and a bit of wind noise.  We know what wind noise sounds like.  It's not as though we seriously expect the sounds of alien construction work or something.  A transducer to measure wind velocity would be MUCH more cost effective.  Wickwack 121.215.84.193 (talk) 03:08, 10 February 2013 (UTC)
 * I harp about many things, and so I am occasionally wrong. In this instance, I regret that my post did not cover all possible types of acoustic transducers; and that I did not formally reference or calculate the exact data that we would record for a particular sound pressure level at Mars' surface.  My hope is that the interested reader could follow my line of reasoning and trivially estimate these parameters themselves, using their favorite type of transducer, amplifier, sampler, compression algorithm, and so forth.  Perhaps this was an instance where the exercise should not have been left to the reader.  As a result of this omission, I did not personally calculate the expected signal level, and so I may have overemphasized my position.  In review, I concur that it is not "physically impossible" to record acoustic signals on Mars; but I stand by my position: recording acoustic signals on Mars is "still not an effective use of engineering time or science budget."  I apologize that my overemphatic post may have inadvertantly conveyed an incorrect conclusion.
 * But, regarding electrets and piezos: it is a fair point that most new computers use condenser microphones; but piezos are not obsolete; my electric guitar was built in 2004 and uses piezo devices similar to this, and they sound quite nice. I have strong reason to believe that they are linear to many hundred octaves above the human ear's capability to hear sound (and far beyond the ordinary frequency range of a condenser microphone).  And, in other work, I've used piezo couples for lots of reasons, particularly when I need to put my microphone in a vacuum, or on a rocket, or in a radiation-hazard enviroment, or any other place I need to doubt the integrity of a condenser microphone.  Nimur (talk) 06:21, 10 February 2013 (UTC)
 * We are off-topic now, but you'll find if you check, those mikes in laptop computers are electret, not condenser. However the operating principle in both is the same (charge pumping by varying the distance between electrodes), and some people are sloppy with their terminology. In any case neither electret nor condensor are piezo.  For electric guitars, magnetic pickups are used almost exclusively.  Only in acoustic guitars with non-steel strings are piezo pickups (such as the Palathetic )used, as obviously magnetic pickups will not work without steel strings.  For studio work, a conventional mike will give a better sound for acoustic guitars, though of course just what the sound is, is a matter of choice between the musician and the producer. Your link returns a 404 error.  The design of condenser mikes is a compromise (a rather good compromise compared to other types of mike, but still a compromise), explained extremely well in Harry F Olson's, Acoustical Engineering - a venerable but still excellent standard text on the subject. Condensor mikes are certainly NOT good for hundreds of octaves above human capability - that would be greater than 15 kHz x 2100 ie ~2 x 1033 Hz, well and truely beyond the range of theoretical physics! Visible light is only around 6 x 1014 Hz!  You are being ridiculous. Condenser mikes, by the nature of how they operate, are not inherently linear but typically are good covering just the frequency and amplitude range of human hearing.  Wickwack 120.145.68.197 (talk) 09:37, 10 February 2013 (UTC)
 * It would violate the law of physics, i.e. "in space nothing can hear you scream". Gzuckier (talk) 05:13, 11 February 2013 (UTC)

Why is my charger emitting high pitched sound?
I think it has something to do with the transformer, but I don't know why. — Preceding unsigned comment added by Inspector (talk • contribs) 07:04, 9 February 2013 (UTC)


 * It uses a Switched-mode power supply, and is probably a "cheapy" ~15 kHz - which is within normal human hearing range. ~E:74.60.29.141 (talk) 07:33, 9 February 2013 (UTC)


 * And I am guessing that the person who asked the question is either under 40 years old (if male) or under 60 years old (if female). Otherwise he/she would not be able to hear it. --Guy Macon (talk) 11:19, 9 February 2013 (UTC)


 * I guess the sound frequency is much lower. There is still one other strange thing when I studied further: when I connect it to my cell phone, the continuous buzzing stopped and changed to intermittent buzzing like heartbeat buzzing in the hospital.--Inspector (talk) 11:45, 9 February 2013 (UTC)


 * As far as I know this is an indication that it's either broken or or does not conform to the usual specifications required in industrialised countries (conformance is often claimed fraudulently). And that it's an incendiary risk. If it's expensive to replace, the device you are charging is not very valuable, and there is no reason to trust that a new charger will be better, then I personally would just continue to use it but would be careful never to keep it plugged in when I leave the house. Also, I would always think of it first when there are any problems with radio or tv reception, wlan etc. Hans Adler 11:52, 9 February 2013 (UTC)


 * Hans, I wouldn't go that far... it sounds like you're spreading a little FUD about a common, harmless annoyance. It's far more likely that the power-supply is functioning correctly, but its designers did not go through the painstaking analysis to guarantee that it never emits audible noise under any condition.  If the device has a marking from UL - Underwriters Laboratory - or from the FCC, then its safety and emissions have been tested and verified, even if it makes an annoying noise.  Outside the U.S., other agencies and industry groups are responsible for similar testing.  This should not be construed to mean that any UL-tested product is always safe under any condition - you need to apply common sense and be aware of defects and damage.  But, I am not aware of any requirement that audible noise in a switching power supply must be suppressed, and I don't understand why you think audible noise has any correlation to fire-hazard.  Audible noise might be caused by any number of conditions, and most are not hazardous.  In many scenarios, noise might indicate that the power supply is not operating at peak efficiency or that it's exerting unnecessary mechanical stress on some component, reducing its usable lifetime.  But ... risk of fire?  Surely if audible noise indicated fire-hazard, then every speaker cabinet would be a fire hazard during normal use?  Nimur (talk) 19:46, 9 February 2013 (UTC)


 * A high-pitched buzzing noise might indicate sparking, but this is improbable. More likely this is the result of some transistor-induced harmonics causing the transformer core to intermittently vibrate and emit audible noise. 24.23.196.85 (talk) 20:27, 9 February 2013 (UTC)


 * I think Hans Adler is suggested that any device which emits noise must be a poorly made device which fails to comply with proper safety standards as present in most developed countries and any such markings suggesting otherwise are fraudulent so that the device must be a fire risk; not that noise itself indicates a fire risk. I agree this is going way too far. It may be slightly more likely a improperly designed or made power supply which violates safety standards makes audible noise, but there are a large number of perfectly safe devices which comply with whatever local standards which also make noise. And there will be plenty of unsafe devices which don't have noise.Nil Einne (talk) 21:18, 9 February 2013 (UTC)


 * Modern chargers are almost certainly switched-mode power supplies (SMPS). Our own article suggests such supplies emit acoustic noise (almost a tautology?) suggesting that such noise is "[u]sually inaudible to most humans, unless they ... are malfunctioning, ...". I think that means unless the SMPS is malfunctioning, not the human. Also "[t]he operating frequency of an unloaded SMPS is sometimes in the audible human range, and may sound subjectively quite loud for people who have hyperacusis in the relevant frequency range". QED? -- Senra (talk) 21:55, 9 February 2013 (UTC)


 * Sincere apologies to who mentioned SMPS above. Didn't see that. Sorry. -- Senra (talk) 22:02, 9 February 2013 (UTC)


 * I don't think I am alarmist, just a bit careful after I have read several reports like this one. Hans Adler 22:20, 9 February 2013 (UTC)


 * I have a bit of experience in this area, having designed everything from components for NASA manned space flight to toys for Mattel. Warnings are good, but they have to be accurate. Otherwise you are chicken little or the boy who cried wolf. The fact of the matter is that there is no known correlation between SPS acoustic noise and safety. You are warning people about the wrong things. --Guy Macon (talk) 23:26, 9 February 2013 (UTC)


 * I would also note that the example you gave (the counterfeit power supply with no components that fed the 12V straight through instead of the proper 5v) is completely silent and very unlikely to malfunction any more than it is already doing... --Guy Macon (talk) 00:56, 11 February 2013 (UTC)


 * It could be a phasor on overload, so toss it down the nearest disposal chute right away ! :-) StuRat (talk) 23:29, 9 February 2013 (UTC)
 * What! The resulting explosion might kill the princess! -- Senra (talk) 17:22, 10 February 2013 (UTC)
 * Back to the topic, is it functioning right for the charger to change to periodical beeping when connected?--Inspector (talk) 02:02, 10 February 2013 (UTC)
 * It depends what you mean by beeping. If it is charging something that has charge control circuitry, the load might be switching on and off, but I wouldn't expect this to be a fast "beep".  A slow cycling with the high frequency periodically going on and off might just be caused by the noise disappearing when current is drawn.  This could well be normal operation because it is not unusual for the high frequency switching to induce a tiny vibration in laminations of the core, especially under no-current conditions.  Technically, this would be regarded as a "fault" because energy is being wasted, but it is a very minor fault.  If the charger is getting very hot, then there might be a more serious fault, but just warm is normal.    D b f i r s   12:56, 10 February 2013 (UTC)
 * You have not told us the age and model of your cell-phone, nor whether the charger is the original or a low-cost replacement. If I had this problem, I would be searching the manufacturers forum to determine if others had reported similar problems. In your case, I would also eliminate other potential explanations. For example, responders above mention age and I noted hyperacusis as a possible cause. Have you asked non family members (in case hyperacusis is hereditary) if they can hear it too? -- Senra (talk) 17:22, 10 February 2013 (UTC)


 * Are you sure this is not what you are actually hearing? μηδείς (talk) 21:33, 10 February 2013 (UTC)

i think i've heard that Leptin inhibits Gerlin. is that true?
thanks. 79.179.134.180 (talk) 16:32, 9 February 2013 (UTC)


 * If you only think you've heard something, it is unlikely to be true. Anyway, what is gerlin? Is it like trollin?--Shantavira|feed me 16:35, 9 February 2013 (UTC)


 * They are somewhat antagonistic, but it's not simple - our articles (note spelling) cover this pretty well: leptin and ghrelin. -- Scray (talk) 16:55, 9 February 2013 (UTC)


 * In a quick scan of our articles I didn't see any discussion of that question. There is some evidence that leptin inhibits ghrelin, for example, but the data seem to be limited. Looie496 (talk) 16:59, 9 February 2013 (UTC)
 * ...which is why I said what I said. -- Scray (talk) 02:55, 10 February 2013 (UTC)

in simple words
how do i culculate my bmi index?, please give me a verbal explanation. thanks 79.179.134.180 (talk) 16:32, 9 February 2013 (UTC)


 * Please see Body mass index or http://simple.wikipedia.org/wiki/Body_mass_index --Shantavira|feed me 16:38, 9 February 2013 (UTC)


 * Or go to http://nhlbisupport.com/bmi/ and the US Department of Health will calculate it for you. --Guy Macon (talk) 16:46, 9 February 2013 (UTC)


 * Measure your height (in meters) and your weight (in kilograms), and plug them into this formula:


 * $$\mathrm{BMI} = \frac{\text{weight}}{\left(\text{height}\right)^2}$$.


 * That's all there is to it. Looie496 (talk) 16:48, 9 February 2013 (UTC)


 * Weigh yourself, in kilograms. Measure your height, in metres. Square your height (that is, multiply your height by itself). So, if you are 1.5m tall, you do 1.5 times 1.5 (1.5 x 1.5). Make a note of your answer. Take your weight, and divide it by your previous answer. This number is your BMI. 86.163.209.18 (talk) 12:34, 10 February 2013 (UTC)


 * Or if you prefer pounds and inches, use
 * $$\mathrm{BMI}= \frac{\text{weight}(\text{lb})}{\left(\text{height}(\text{in})\right)^2}\times 703$$. Duoduoduo (talk) 13:28, 10 February 2013 (UTC)

Graphite
I think I have found a new way of synthesising graphite. In order to be certain that it is graphite, I need to know whether the route of production is a possibility.

Crystallisation of graphite from solution. I added organic material to 38% sulfuric acid, and boiled until the material was fully carbonised. The resulting product was a highly acidic, opaque, black sol (colloid)(?). Upon, cooling and standing for several hours, large, insoluble, opaque, black crystals have formed. I could send photos of the mystery crystals. Plasmic Physics (talk) 22:28, 9 February 2013 (UTC)


 * I suggest you try writing on paper with it, then using an eraser on it. If it acts just like graphite in both respects, it probably is graphite (lead behaves similarly, but I can't see how you could have produced lead without having put lead in).  Of course, graphite is quite cheap, so you probably aren't going to make it any cheaper than the current methods. StuRat (talk) 22:31, 9 February 2013 (UTC)


 * It quite possibly is graphite. Adding oleum to sugar will produce a ball of carbon, that is larger that the reactants you started with. CS Miller (talk) 22:58, 9 February 2013 (UTC)


 * (edit conflict) The black stuff you made is the product of the dehydration reaction between the sulfuric acid and the organic material (a typical reaction for sulfuric acid, I should add), and as such, is essentially pure carbon. However, I should caution you that it might still contain free acid, which would tend to damage the paper. 24.23.196.85 (talk) 23:01, 9 February 2013 (UTC)


 * I'll wash it several times in water. Plasmic Physics (talk) 23:14, 9 February 2013 (UTC)


 * Considering that the sulfuric acid predominantly acts as a catalyst, and the reactant is essentially free, I fail to see how it would not be cheaper? Plasmic Physics (talk) 23:14, 9 February 2013 (UTC)


 * Well, the energy needed to boil it until carbonized isn't free. StuRat (talk) 23:31, 9 February 2013 (UTC)


 * Put it in perspective with the cost of mining, or generating thousands of degree temperatures for synthesis. Plasmic Physics (talk) 00:00, 10 February 2013 (UTC)


 * Should we ask the name of your unfortunate victim which you describe merely as "organic material" ? :-) StuRat (talk) 23:34, 9 February 2013 (UTC)
 * Don't ask, Stu. We do not out people here (unless it is public knowledge anyway) -- Senra (talk) 23:52, 9 February 2013 (UTC)


 * I call him Cooking Oil. Plasmic Physics (talk) 00:00, 10 February 2013 (UTC)


 * Or perhaps "Cooking Earl" ? StuRat (talk) 03:56, 10 February 2013 (UTC)


 * Is your organic material free? (don't forget transportation costs!) Is the energy used to boil the acid free? Is the amortized cost of the equipment free? Is the hazardous waste disposal that your washing step requires free? Labor? Renting a building? Remember, you are competing with people who are digging graphite out of the ground in China. --Guy Macon (talk) 23:39, 9 February 2013 (UTC)
 * According to the charcoal article, creating charcoal by the dehydration of sugar by sulfuric acid will produce the purest charcoal. CS Miller (talk) 23:45, 9 February 2013 (UTC)


 * Pond scum should work, 'organic material' is a pretty wide menu. As for waste desposal, such a plant could be adjacent to a sulfuric acid plant/phosphate fertilizer pant. The hardous waste could be recyled thus. Plasmic Physics (talk) 00:00, 10 February 2013 (UTC)


 * I've known people who work in the industry, so I feel safe saying that sulfuric acid production is nasty business. It produces gobs of really nasty waste which is a bitch to take care of, and we're not likely to be able to produce it in volumes necessary to produce enough fuel given that it is already, by far, the most produced chemical in the world.  In order to make a viable source of carbon as a fuel to replace mined coal, you'd need more sulfuric acid than is availible.  In 2011, the world produced 7,695.4 million tonnes of coal.  That's 7,695,400,000,000 kilograms of coal.  To produce a similar amount of carbon from random carbon sources, you'd need at least a 1:1 stoichiometric amount of sulfuric acid; probably a lot more.  That'd be 7,695,400,000,000 *98/12 = 62,846,000,000,000 kilograms of sulfuric acid.  The world produces about 180,000,000,000 kilograms per year, so even if you converted the entire world production of sulfuric acid over to your plan, you'd create enough pure carbon to replace 0.2% of the world's coal output.  So, you're "cost of mining" issue is irrelevent.  You couldn't possibly make enough carbon to make a difference in mining operations.  -- Jayron  32  04:57, 10 February 2013 (UTC)


 * Just a note: this subdiscussion is about synthetic graphite, not coal. Plasmic Physics (talk) 05:47, 10 February 2013 (UTC)


 * You brought up the coal mining, not me. To what end are you proposing to use the graphite?  Is there a shortage of graphite or is the economics of the current graphite market in sore need of you scaling up a middle-school classroom demonstration into an industrial process?  -- Jayron  32  06:03, 10 February 2013 (UTC)


 * That was the first time I "coal" escaped my mouth, in a manner of speaking. Well, I think so. Plasmic Physics (talk) 08:46, 10 February 2013 (UTC)
 * Well, even if you were wanting to replace coal, it's not entirely out of the question. Firstly, you don't need to replace all coal, coking coal is the most valuable coal commodity, so extra costs of production are more easily absorbed there. Also, if you use a renewable source of organic material, then your material is carbon neutral (ignoring the energy input required which may or may nor be fossil fuel based), which gives it an advantage in a market with carbon trading or carbon taxes. Also, Jayron, who is clearly a very good physicist, is no economist. If there was a massive extra demand for sulfuric acid, there would be a massive incentive to increase supply. Unless we've already allocated every applicable resource to producing sulfuric acid, there's always more production possible. 202.155.85.18 (talk) 01:41, 11 February 2013 (UTC)
 * Unless we're already at or near capacity for producing sulfuric acid, then all we're likely to do is drive up the price or divert supplies away from other uses. -- Jayron  32  03:00, 11 February 2013 (UTC)
 * The price will be driven up by the increased demand. That is a given. You can only divert from other uses by offering a higher price. If we're at capacity for H2SO4 production, then we can only divert from other uses. 202.155.85.18 (talk) 03:42, 11 February 2013 (UTC)
 * (edit conflict) And what of the capital investment required for new sulfuric acid plants, which would run into the hundreds of megabucks? (Not to mention the other barriers to entry, like environmental regulations.)  Also, graphite CANNOT replace coking coal -- coke must be not only chemically pure, but hard as well (because it must not crumble to dust when dropped a hundred feet or more down a blast furnace along with a tonload of iron ore and limestone), whereas graphite (no matter whether it's natural graphite, Acheson graphite or Plasmic graphite) is soft and easily abraded. 24.23.196.85 (talk) 03:06, 11 February 2013 (UTC)
 * Plasmic's exact phrase was "cost of mining" -- so he said "mining", not "coal". Graphite is a different material than coal, with different applications, but it's found naturally and mined in a similar manner to coal.  It can also be produced synthetically by carbonization of coal tar pitch, which is more economical than Plasmic's method of dehydrating sugar or cooking oil with sulfuric acid (coal tar pitch being a major industrial waste from the steelmaking industry, and the raw materials for the Plasmic Process being more expensive, along with the prohibitive cost of hazardous waste disposal in the latter process). 24.23.196.85 (talk) 01:49, 11 February 2013 (UTC)


 * Raw material, as I've said, includes most organic material, even waste. Using cooking oil, or sugar would not be wise choices in this regard. Oil was merely used as a proof of concept. And sulfuric acid is not a main reactant, but a catalyst, it is ordinairily only slowly consumed. Plasmic Physics (talk) 02:47, 11 February 2013 (UTC)


 * It is gradually diluted and contaminated, and eventually must be disposed of as hazardous waste, every drop of it. Also, when the graphite is washed to remove the free acid (which would otherwise corrode anything that comes into contact with Plasmic graphite), the wastewater also has to be disposed of as hazardous waste.  Sorry, the Acheson process is still much more economical than what you propose, even with the high energy costs these days. 24.23.196.85 (talk) 02:53, 11 February 2013 (UTC)
 * What are all of these supposed toxic byproducts? The sulpfuric acid itself ig gradually diluted with water, so you have dilute sulphuric acid which is great for making...concentrated sulfuric acid. Even if you did want to dispose of it, just add lime to balance the pH and discharge. 202.155.85.18 (talk) 03:39, 11 February 2013 (UTC)
 * This "dilute sulfuric acid" is actually UNFIT for making concentrated sulfuric acid, due to extensive contamination with organics and metals and whatnot. Purifying it before reconcentrating would be even MORE expensive than its disposal. 24.23.196.85 (talk) 04:15, 11 February 2013 (UTC)
 * It's not going to have "extensive contamination with organics". How do you remove organics from things? You percolate it through finely divided carbon. What was just in the acid? Oh yeah, finely divided carbon. And disposing of it is not expensive anyway. And there's no real need for the conc H2SO4 to be ultra pure anyway. The whole "recycling sulfuric acid" is not up for debate since it's a stable of industry, as in sulfuric acid recovery plants. 202.155.85.18 (talk) 04:35, 11 February 2013 (UTC)


 * I think you're thinking of activated carbon, not finely divided carbon. Plasmic Physics (talk) 18:04, 11 February 2013 (UTC)


 * Evaporate the liquid, purify and recycle the sulfurous oxides back into sulfuric acid. Using various separation techniques, the only waste should be in the form of a solid residue (metal oxides and sulfates). Plasmic Physics (talk) 03:41, 11 February 2013 (UTC)
 * And the energy needed for the purification and evaporation would cost how much? 24.23.196.85 (talk) 04:16, 11 February 2013 (UTC)
 * Without reviewing the chemistry, I think this sounds like a plausible notion to get coal out of biodiesel, but don't people actually want liquid fuels out of coal? Wnt (talk) 16:08, 11 February 2013 (UTC)
 * Not coal, but graphite. Plasmic Physics (talk) 18:04, 11 February 2013 (UTC)

I used piranha solution today. Heating it is a bad idea, unless you want a steaming hot acid volcano. Plasmic Physics (talk) 01:16, 12 February 2013 (UTC)


 * (un-indent) Plasmic and 202 IP, you know your chemistry very well, but it's clear you're no engineers. I recommend you look in the Kirk-Othmer Encyclopedia of Chemical Technology and see for yourselves just how involved and energy-intensive the process for re-concentrating waste sulfuric acid is in real life. 24.23.196.85 (talk) 03:11, 13 February 2013 (UTC)