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October 12

Missing reference/article

Where/How do I find "the more complicated exact equation" is "derived without using any approximations" enticingly alluded to in the last paragraph of

http://en.wikipedia.org/wiki/Doppler_effect#Analysis

At LEAST a computer accessible reference NEEDS to be provided !!

What does the "gadget at the end of the URL mean ? I would like to contact the author of this URL to be sure to get the complete derivation. RARE —Preceding unsigned comment added by 83.226.97.246 (talk) 03:10, 12 October 2010 (UTC)

I don't usually do this, but I've fixed the question. The link was mistyped, and I figured I might as well clean up the other mess while I was at it. Looie496 (talk) 03:14, 12 October 2010 (UTC)

Do you mean the #Analysis part of the link? If so, it's an URL anchor. This makes your browser scroll to the 'Analysis' section of the web-page when you follow the link. CS Miller (talk) 10:16, 12 October 2010 (UTC)

The more complicated exact equation appears to be the second last equation in that section. It is then simplified to the last equation presented. The derivation shown appears to be uncomplicated math, so doesn't necessarily need a source. The Lord Raleigh book is mentioned and likely should be properly referred in the "Further reading" section. It is computer accessible - use your computer to look up the address of your local library. If by "gadget" you mean the little box-on-box thingy right after the link, that is automatically put in by the software for any link that starts with http:, as these links usually lead off the Wikipedia site. Franamax (talk) 15:58, 12 October 2010 (UTC)

Nuclear isomers for chemical transmutation of gold i.e. alchemy?

I wish I understood this figure. But I think it means that in order to chemically drive a nucleus into an excited isomer, you might need to hit it with several photons or electron transitions of exactly the right energy?

I think that for purposes of sci-fi, there are very few things so splendidly versatile as nuclear isomers. Even so, this application is likely a bridge too far. Yet...

• Many nuclear isomers are known, which have slightly different masses than other isotopes with the exact same number of protons and neutrons.

• Nuclear isomers can have very different stability - for example, 106 days for 177mLu versus 6 days for 177Lu by beta decay.

• Nuclear isomers may be increased or decreased in energy by absorption of photons of the right frequency, or internal transitions with electron potential differences of the right frequency.

• Nuclear isomers can have a half-life more than comparable to the age of the universe, e.g. 10¹⁵ years for ^180mTa.

Now what all this means is that, while it is by no means certain, it is possible that exposing a compound of lead to just the right excitation in a flame, for example, might cause the nucleus to jump to a slightly higher metastable state. Or perhaps lead as we know it is in a metastable state and it can be decreased in energy to some as yet unrecognized "stable" state? And if the effect is to increase the chance of alpha-decay, maybe it wanders over to be mercury... and maybe (perhaps with more excitations) it can emit a positron and then an alpha and end up as gold?

It's all very unlikely sounding, and yet, based on what I've read of these nuclear isomers, it seems like modern science can't preclude the conceivability of chemical alchemy, i.e. the possibility of rare but meaningful effects of chemical ionizations and other electron transitions on the breakdown of the nucleus. Can you prove me wrong? Wnt (talk) 06:22, 12 October 2010 (UTC)

Science cannot prove you wrong, that's not what scientific evidence does. It can show zero support for your ideas, but it cannot prove you wrong. Proof is an illusion, all we have is the existance or nonexistance of evidence. --Jayron32 06:25, 12 October 2010 (UTC)

Granted... yet before I thought of this just recently I'd have said that "alchemy is impossible" like anyone else. Now I look at a figure like the one above and I wonder, can you go below "7/2+"? If you can, why don't we see Lu or Hf with the lower energy that should correspond to that - does it spontaneously decay into something else? (I forgot to mention above that usually the higher energy isomer is more stable than the lower, though I don't know how consistent this is) And if such a transition should be triggered, it looks like it should take well under 100 keV (though admittedly, this is actually well over the ionization energy - I don't know why internal transition is so important for nuclear isomer decays...) So I feel like I've gone from thinking "how" to "how not?" quite abruptly. Wnt (talk) 06:44, 12 October 2010 (UTC)

I have to say I must completely disagree with Jayron. Science is better at showing something must be false than it is as showing that something must be true. I don't know enough about isomers to say anything useful, but if this were a question about nuclear reactions or about conservation of energy or whatever, I am very confident that people would be happy to pipe up to say "that is wrong and here is why." Science can definitely say that some ideas are wrong according to all current theories, no problem. One just has to know a bit about the subject at hand. On the subject of isomers, I've got no idea, personally, but surely others do. --Mr.98 (talk) 18:20, 12 October 2010 (UTC)

The main problem here may be one of definitions. You say you want "chemical" transmutation, but when exactly does something stop being "chemistry" and start being "nuclear technology"? I cannot imagine how you would excite a nucleus to the tune of even a single keV (~ about 10 million kelvin!), by methods that anyone would reognize as "chemical". –Henning Makholm (talk) 19:18, 12 October 2010 (UTC)

Agreed. This is a matter of definition. "Chemistry" deals with that domain of atomic interactions related to the electron cloud; while nuclear physics deals with that set of interactions related to the atomic nucleus. A series of famous papers was published during the 1930s and especially during the buildup to Manhattan Project, as the science of nuclear transmutation shifted from alchemical nonsense to scientific reality. Among these were infamous nuclear transmutations of lead to gold; but these "nuclear chemistry" tricks turned out to be among the least useful applications of nuclear science. In any case, the historical papers do make for interesting reading; and the processes to convert heavy elements into noble metals are well-known (just not very practical). You won't be inducing nuclear reactions with an ordinary candle-flame. Nimur (talk) 19:43, 12 October 2010 (UTC)

In chemistry there are all sorts of catalysts that will overcome absurdly high kinetic barriers. Isn't it possible perhaps to have some sort of "strange matter" catalyst that will use a bunch of stabilising interactions to lower the kinetic barrier, in a sort of nuclear version of an enzyme or Zeolite? John Riemann Soong (talk) 19:50, 12 October 2010 (UTC)

That really has been the domain of cold fusion research, and it has largely been unsuccessful at convincing the scientific community that any such "catalyst" does exist (or even that it theoretically could exist). Modern "cold fusion" research is often published with the key-phrase "low energy nuclear reaction" - you can evaluate the status for yourself; so far, no "useful" reactions with low activation-energy have been found under any conditions, including the presence of catalysts. Conventional theories of nuclear interaction (and by "conventional" I also include "relativistic quantum mechanical theories") require huge activation energies to overcome the electrostatic repulsion of the nucleus; or uncharged, fast neutron triggers in the form of a nuclear chain reaction. Nimur (talk) 20:27, 12 October 2010 (UTC)

If a transmutation is inherently exergonic, wouldn't you be able to supply an investment of activation energy that would be recouped later, in a controlled fashion? What about very strong electric or magnetic fields? John Riemann Soong (talk) 22:09, 12 October 2010 (UTC)

Yes, but it gets hot, because it's a lot of energy: nuclear fission. The process yields a net release of energy, in great quantities, even though the "activation energy" is high. Nimur (talk) 23:30, 12 October 2010 (UTC)

Ha, why gold? Gold is easy to procure. I need a process that will give me rhodium or osmium. I'm really glad that no chemical process can cause transmutation though -- if that were so, biological life would be very much under threat. John Riemann Soong (talk) 19:37, 12 October 2010 (UTC)

Part of my confusion is that there are low energy nuclear isomers like ^229mTh with a transition of 4.5-2.5 eV with a "nuclear gamma emission in the optical range".[1][2] (Does anyone have access to this one [3]? They didn't trigger it with a laser, did they??) I didn't realize till I'd gone on a bit that this other example I gave involved many KeVs, but I'm still not sure it's irrelevant, because I don't know if by causing an optical-range shift in nuclear energy, you might make an isotope go on to emit a multi KeV gamma ray. It is true that for such an improbable process as lead to gold you'd at least hope to be allowed to juxtapose various isotopes and transmit these gammas back and forth directly rather than relying on purely chemical reactions - I suppose I was counting it as "chemical alchemy" if it merely looks like you're doing a chemical reaction, from some 18th-century point of view, without an obvious nuclear reactor or particle accelerator being used. Wnt (talk) 20:24, 12 October 2010 (UTC)

Oh, here's where I got into hundreds of KeV by "chemistry" - [4]. Another paper I can't access, but it describes getting up to 150 KeV by creating "autoionization states" in which two or more electrons are promoted from holes in deep inner electron shells. From this I suppose that ionizing an ion takes a whole lot of energy. Admittedly though, reversing this process is not exactly what I'd call "chemistry" in the normal sense of the word... isn't quite exactly nuclear physics either though. Wnt (talk) 20:36, 12 October 2010 (UTC)

Your IOP article says

`Nuclear light', or the gamma radiation emitted by an atomic nucleus in the optical range, will probably be discovered experimentally in one or two years.

so they didn't do it (but that was in 2002). In order to use an optical-to-keV "amplifier", you'd have to have an excited isomer already (as your second SpringerLink article says), in which case you're not using true "base metal"; moreover, the lower energy states should be less likely to then conveniently emit alphas. As for ionization, it's just that the core electrons have much higher ionization energies than the valence electrons, as well as that each successive ionization energy is (typically, at least) higher. But you'll have to use un-alchemical processes like lasers or ion beams to preferentially excite/remove the inner electrons; normal chemistry will always go after the outermost ones. --Tardis (talk) 14:25, 13 October 2010 (UTC)

You're probably right. Even so, I wonder if some of the "ground states" we know and love are actually higher-energy nuclear isomers with half-life >> 10¹⁵ years. And if they can be triggered to drop to a lower energy ground state that is not so stable.

Also, I wonder if you can mix just the right combination of nuclear isomers so that the emissions from one are tuned perfectly to trigger a transition in the next. For example, to break up nuclear gammas down into bits of usable chemical energy, or in this case, to drive an alchemical transition. Wnt (talk) 20:04, 13 October 2010 (UTC)

I suggest taking a look at island of stability, Bismuth, neutrino theory of light, deuterium, double beta decay, proton decay, delta decay and Radium. ~AH1^(TCU) 02:19, 15 October 2010 (UTC)

Calculate the heat supplied

This example problem in my class XI chemistry book proceeds as follows : A swimmer coming out from a pool is covered with a film of water weighing about 18g. how much heat must be supplied to evaporate this water, if it is at 298K? given, enthalpy of vapourisation of water at 373K = 40.66kJ/mol Solution : 18g is equivalent to 1 mole. heat supplied is equal to 40.66kJ/mol * 1mol = 40.66kJ

I feel that this solution to the problem is wrong, as the water on his body is not at 373K, but only at 298K. So, to raise the temperature of the water from 298K to 373K, 18*(373-298)*4.19 = 3771J = 3.771kJ of heat must also be supplied. So the final answer would be 40.66 + 3.771 = 44.431kJ. Am I right?? This is not a homework problem, I'm just asking out of doubt.. Can the enthalpy of vapourisation of a liquid be used at any temperature, or only at its boiling point? How can we assume that the enthalpy of vapourisation of water is same at both 373K and 298K?? Thank You. harish (talk) 10:57, 12 October 2010 (UTC)

Are you confusing evaporation with boiling? I evaporate solutions at 288K, so it doesn't have to be boiling. Also, boiling water would make the swimmer very uncomfortable. Finally, how does the water get hot enough to boil? Evaporation is AFAIK only a random escaping of high-energy liquid molecules at the surface of a liquid. --Chemicalinterest (talk) 11:13, 12 October 2010 (UTC)

Does the book problem really say about 18g ? Cuddlyable3 (talk) 11:35, 12 October 2010 (UTC)

What you need is the heat of evaporation at 298 K. If the only figure you have is for 373 K, you can adjust for the temperature difference using conservation of energy: It should take the same energy to evaporate the water at 298 K and then heat the vapor to 373 K as it should to heat the water to 373 K and evaporate it there. At the precision you're working at here, you can probably get away with assuming that the specific heat of liquid water (resp. water vapor) is not temperature dependent. –Henning Makholm (talk) 12:32, 12 October 2010 (UTC)

Boiling is always a kinetic phenomenon, because that's when vapor pressure of the liquid equals vapor pressure of the atmosphere, allowing bubbles to form within the water -- below this temperature, nucleation is simply unfavourable because bubbles cause surface energy. Evaporation is a thermodynamic phenomenon. The heat of vaporisation should be nearly constant (it probably changes dramatically when you have really large differences, but within the range of 0-100C I suspect it's rather the same). Notice that you cool down when your sweat evaporates! Your body has to supply heat for it to evaporate -- evaporation and boiling are inherently, endothermic processes. John Riemann Soong (talk) 15:53, 12 October 2010 (UTC)

The first figure at Enthalpy of vaporization shows a thermal dependency that appears to give about a 10% difference over that interval. I wouldn't call that "rather the same". –Henning Makholm (talk) 16:25, 12 October 2010 (UTC)

is it a contradiction to know something about something we can't know anything about?

Is it a contradiction if you prove, physically/mathematically, that we cannot know ANYTHING about a given "other Universe", and go on to prove, physically/mathematically, something that must be logically true in any "other Universe" -- I'm talking pure logic there, so that if a mathematician in that other Universe were to explore the property of the natural numbers in that Universe... -- , implying that you DO know something about it?? Thank you. 84.153.253.103 (talk) 13:18, 12 October 2010 (UTC)

We don't know anything about the potential other universe, we know something about maths and logic (namely, that they are universal in a sense that our "universe" possibly is not). From an information theory point of view, there is not information gain (if you hear that a guaranteed event has happened, you gain no new knowledge). If we prove or disprove a mathematical result, we do not gain any new information - we just make previously available information explicit. --Stephan Schulz (talk) 13:50, 12 October 2010 (UTC)

It is tempting to say that the truths of mathematics are synthetic truths analytic truths i.e. true by virtue of the definitions of the terms involved. Thus the truth of 1+1=2 is implicit in the definitions of "1", "+", "=" and "2" - it can only be false in a context in which at least one of these definitions is changed. And therefore an analytic truth, such as 1+1=2, must be true in all possible universes. However, there is a philosophical objection to this stance. To determine whether a proposition such as 1+1=2 is a synthetic an analytic truth, you have to use the laws of logic. But then you need to establish that the laws of logic are themselves synthetic analytic truths ... and you run into an infinite regress. Whether or not there are any analytic truths, true in all possible universes, is vigorously debated among philosophers. Gandalf61 (talk) 14:49, 12 October 2010 (UTC)

I think you've got your terminology a little mixed up. "True by virtue of its meaning" is "analytic", not "synthetic". Synthetic truths are true because they correspond to the state of things. "True in all possible worlds", on the other hand, sounds more like "a priori". --Trovatore (talk) 18:39, 12 October 2010 (UTC)

Yikes, I got that post really scrambled. Fixed now, I think. Gandalf61 (talk) 09:49, 13 October 2010 (UTC)

Um, thank you for your feedback guys but neither of you is answering my question, which includes the hypothetical that we do prove something necessarily true (and not by definition) that must be true in another Universe. This part of my question is not really what I wanted feedback on. I want you to assume that we can know, for sure, that if there is a being in another Universe who explores his universe somehow, then he will find something true (and not because he must define it the same way we do). If we do make that assumption: is this state now inconsistent with the fact that, in point of fact, we know nothing about the other Universe? That is, is there a contradiction or paradox here? (I am not asking if my assumptions are correct in your opinion: in both of your opinions Gandalf and Stephan, they are not; rather, I am asking if my assumptions lead to a contradiction/paradox in any sense). 84.153.253.103 (talk) 16:44, 12 October 2010 (UTC)

The answer is obviously yes, it's a contradiction to prove both that we can't know anything and that we know something. Why do you even need to ask? But the contradiction is meaningless, because the statement that we can't know anything at all about a different universe will never be true. Looie496 (talk) 17:11, 12 October 2010 (UTC)

And for me (OP again), it is just as obvious that 'we can't know anything at all' is in some sense true: we have no channel of information. The other Universe could be any way at all (it has perfect informational entropy in Shannon's sense -- we have perfect uncertainty about it), and we have no informational channel; yet, even though it could be "any way at all", and without our having any channel to learn anything about it, what would happen if we presumed to know something about that Universe anyway? You say this could be a paradox: can you make the paradox more explicit for me, like mathematical? Thank you. 85.181.51.248 (talk) 18:51, 12 October 2010 (UTC)

If you know that you "can't know anything about a given other Universe" then you know that much about it already. Can you imagine a universe with slightly different values of universal constants? With that assumption, you can derive likely properties of that other Universe. But that also assumes that there would be any physical laws at all in other universes, whatever they might be. And it would seem likely that every universe must have laws, but that is again an assumption being made just by employing the concept of "universe" itself: something as distinct from nothing, or from "pure chaos" which would amount to the same. I think the answer is yes, the paradox arises from your assumptions. WikiDao ☯ (talk) 12:15, 13 October 2010 (UTC)

I belive your apparent paradox arises because you postulate a separate universe which we can't know anything about, but by then you have already stated one property of it, that it exists. (As opposed to bigfoot and the loch ness monster.) If you drop this assumption, saying that the universe may or may not exist, it follows that you can't make any a-priori true statement. EverGreg (talk) 08:25, 15 October 2010 (UTC)

Yikes! Spooky overlapping of Non-overlapping magisteria: this is somewhat close to the ontological argument for the existence of god! --ColinFine (talk) 09:34, 16 October 2010 (UTC)

Electrode potentials at red heat

Why do electrode potentials change at high temperatures? For example, charcoal can reduce sodium carbonate to sodium at a high temperature. Oxide can reduce protons to hydrogen at high temperatures, decomposing water. Iron(III) chloride releases chlorine when heated. Why do oxidizing agents and reducing agents get so much stronger at high temperatures? --Chemicalinterest (talk) 14:10, 12 October 2010 (UTC)

Electrode potentials measure the equilibrium point of the chemical reaction that takes place at the electrode. Such an equilibrium changes with temperature because it is in principle just an expression of the Boltzmann distribution as applied to different binding states. –Henning Makholm (talk) 15:04, 12 October 2010 (UTC)

Thanks. A more specific question: Why is carbon such a strong reducing agent at high temperatures? --Chemicalinterest (talk) 15:42, 12 October 2010 (UTC)

See Gibbs free energy. Unfavourable reactions can sometimes become more favourable at high temperatures, because of entropy. Notice in all these reactions you release a gas that also escapes at that high temperature! John Riemann Soong (talk) 15:47, 12 October 2010 (UTC)

Also, it isn't just the "T" in the G=H-TS equation that makes the Gibbs Free Energy temperature dependant. In general chemistry, they teach you to "assume" that H and S are temperature independant. This is not strictly true; at the small ranges of temperature near room temperature, say from 1-100 degrees celcius, H and S show only small variances with temperature, enough to be ignored. At very high temperatures, however, H and S show measurable temperature variation. --Jayron32 20:09, 13 October 2010 (UTC)

Chile mine rescue

How much did the rescue operation for the 33 Chile miners cost to date? I realize it is ongoing, but is there an estimate for a final cost? Googlemeister (talk) 15:30, 12 October 2010 (UTC)

Codelco is a nationalized corporation, so it will be hard to differentiate between public- and private-sector expenses. Any labor or equipment that was needed for the rescue could be diverted from another mine at "no market cost." (Read Chilean nationalization of copper for historical background on revolutionary Chileanized Copper politics). As another example, the paramedic to be sent down is a member of the Chilean Navy - are his expenses to be counted? He'd have to receive his training and salary whether he were on a rescue mission or not. Probably the most clear-cut expenses are the purchases (or leases) of three large, advanced drills which otherwise would not have been needed (a 27-inch diameter bore drill (Schramm TX130) is pretty expensive - but it is both a rescue expense and a capital investment for the mining company - and our article notes that the American skilled-labor to operate it was "all volunteer"). Keep in mind of course, you can't walk into any old store in Chile and buy a TX130 - only one authorized dealer exists, and it's priced on a case-by-case basis... (like most large, special-purpose industrial equipment - and in this case, there is exactly one buyer, exactly one seller - "market economic price" does not apply). Finally, don't forget to factor in monetary losses - the opportunity cost of suspended mining operations while the rescue effort diverted labor-force (and presumably, the actual cave-in interfered with normal operations as well, both to re-evaluate safety and simply because the cave-in disrupted normal operation of the mine). In summary, this rescue operation is large and it is nigh-impossible to clearly account for every attributable expense that it incurred, especially the intangibles like labor costs and loss-of-productivity. I would recommend an approach similar to estimating the cost of a space-shuttle launch - where you evaluate the total project-size, number of man-hours consumed, and the fixed- and variable costs (see this economic evaluation of Space Shuttle). This way you can end up with two numbers, loosely translated as: "amount spent" and "amount we would have spent anyway." Similarly, consider reading Codelco's financial reports for 2010 and comparing originally projected- (pre-accident) versus actual- (post-accident) earnings for 2010. The difference, after you account for other market factors, should give you a good approximation of losses due to the mining accident. Ironically, the reduced production of copper will drive the price of copper up - economics is a complicated topic. Nimur (talk) 16:57, 12 October 2010 (UTC)

Don't forget that there are also gains from the rescue operation that go beyond the lives of the 33 miners. In the short term, all the rescue workers, families and journalists have to be fed and lodged, which must be a boom for the general economy of the area (although local miners who weren't traped have lost wages). In the long term, the whole operation is great publicity for Chile as a whole: it will be hard to quantify the effect of that publicity, but if you imagine that winning the World Cup in soccer is said to be worth a gain in 0.5% of the winning country's GDP, you can imagine that the economic benefits of the mine rescue will be very substantial indeed. Physchim62 (talk) 17:52, 12 October 2010 (UTC)

Publicity cuts both ways. One of the "messages" attached to this story is that Chile's industry operate using unsafe and archaic conditions, which could discourage investment in Chile. Obviously that is a gross generalization that may or may not be connected with the larger reality beyond this one company. However, in general I would expect that industrial disasters are not good for a country's image. Rescuing the men does help, but it isn't obvious to me that this story is a net positive. Dragons flight (talk) 22:54, 12 October 2010 (UTC)

I personally wonder what the miner's next paycheques are going to look like, considering they haven't yet punched the timeclock on the way out the gate after their shift ends. There's going to be an awful big number in the "overtime hours" column. ;) Franamax (talk) 20:00, 12 October 2010 (UTC)

Well supposedly their company is bankrupt anyways so they might not get a paycheck. Of course, they are stuck in a gold mine, so maybe there are some nuggets lying around for payment. Googlemeister (talk) 20:20, 12 October 2010 (UTC)

What's more, they can't have been awake 24/7 while trapped; surely they've been sleeping on the job for several hours every day. Nyttend (talk) 01:30, 13 October 2010 (UTC)

When the two miners were rescued from Australia's Beaconsfield Mine collapse after two weeks trapped underground four years ago, they made a deliberate and conspicuous act in front of the TV cameras of placing their time cards back into their relevant places. Don't know if they got paid any overtime for it. Both did subsequently do OK from media appearances. HiLo48 (talk) 06:13, 13 October 2010 (UTC)

Did the miners have a union contract? If their contract was anything like a union contract at a US company where I once had to work "around the clock" for days, you get straight time for the first 8 hours, then time and a half for the following 8 hours, then double time for the next 8 hours, which brings you to the start of the regular work day, and then the overtime pay stops because you are in an 8 hour "rest period" at regular straight time, even if still at the jobsite. After the 8 hour "rest period," (at straight time) you are back on a cycle of 8 hours time and a half, followed by 8 hours of double time, and then the cycle repeats. By that plan, it would be 60 days times the equivalent of 36 hours pay per day, or 2160 hours pay. A year's pay for two months in hell. Their contract might have additional benefits for missed days off, or having to work Sundays and holidays. Edison (talk) 16:26, 13 October 2010 (UTC)

Or, given the unique conditions and hazards of their work, they may have specific contractual line-items that specify payment-terms for emergency events such as these. While this particular cave-in was extraordinary, accidents of lesser severity happen often enough that a "shelter" was built inside the mine; it seems probable that the labor contract would include provisions for dealing with such conditions. Nimur (talk) 17:43, 13 October 2010 (UTC)

Back to the original question, the Santiago Times has estimated the cost of the rescue at US$20 million, mostly in the hire of equipment. Physchim62 (talk) 07:55, 14 October 2010 (UTC)

Unitary operator

Much like |±z> and |±x>, imagine we have two orthonormal set of eigenvectors given by |αi> and |βi> with i = 1, ..., n. They could be thought of as eigenvectors of two operators A and B respectively. Using these two set of eigenvectors, assume that I construct an operator U such that it has the following matrix elements: (U)_ij = <αi|βi>. Show that U is unitary.

This was my homework question, but I've done a pretty good job of convincing myself that U is not unitary. I figure that (U^†U)_ij = Σ<βi|αk><αk|βj>, which, if U is unitary, is supposed to equal δ_ij. But I don't see why it should. Did I do something wrong? 74.15.136.172 (talk) 18:48, 12 October 2010 (UTC)

Use the completeness relation : Σ|αk><αk|=1 and then use the orthogonality relation : <βi|βj> = δ_ij. 169.139.219.254 (talk) 19:25, 12 October 2010 (UTC)

But, if we said |α1> = |+x>, |α2> = |-x>, |β1> = |+z>, and |β2> = |-z>, then we get... oh wait, I forgot about the sum, nevermind! 74.15.136.172 (talk) 23:49, 12 October 2010 (UTC)

Emulsion paint - why not water-soluble when dry?

Emulsion paint goes hard after drying but does not soften when it gets wet. Why? What would make it soften - what solvents? Emulsion paint is used in the UK for painting interior walls and ceilings and may have a different customary name in other countries. Thanks 92.15.31.184 (talk) 20:59, 12 October 2010 (UTC)

Emulsion polymerization is a good place to start. Acroterion _(talk) 21:31, 12 October 2010 (UTC)

I'm very doubtful that applies to humble emulsion paint, despite having one word in common, as emulsion polymerisation appears to involve a lot of heat. Whereas emulsion paint just dries off at room temperature. 92.15.31.184 (talk) 21:57, 12 October 2010 (UTC)

From the lead section: "In other cases the dispersion itself is the end product. A dispersion resulting from emulsion polymerization is often called a latex (especially if derived from a synthetic rubber) or an emulsion (even though "emulsion" strictly speaking refers to a dispersion of an immiscible liquid in water). These emulsions find applications in adhesives, paints, paper coating and textile coatings." How the dispersion then acts is unclear to me. Acroterion _(talk) 01:04, 13 October 2010 (UTC)

You may find a useful start in acrylic paint, which is the term I'm familiar with. That article doesn't have much on the process, but following the links in that article, particularly to acrylic resin and emulsion provides a little more information. Basically it seems the acrylic resin suspended in the water based solution undergoes polymerisation as the water evaporates, creating an insoluble product. The polymerisation probably is mildly exothermic, but becuse its such a thin layer it may be hard to perceive (just me speculating). The article doesn't say what solvents would dissolve it, but acrylic resin goes on to talk about Poly(methyl_methacrylate) as another acrylic resin and I know that can be dissolved with xylene (and probably other similar organic solvents). Mattopaedia ^{Say G'Day!} 05:03, 13 October 2010 (UTC)

Yes, polymerisation can be somewhat favourable, in terms of energy. however an excess of water makes polymerisation unfavourable. Drive off water -- drive polymerisation forward. John Riemann Soong (talk) 08:13, 14 October 2010 (UTC)

... and, from my experience of cheap emulsion paint in the UK, it does remain partially soluble, especially if it is applied in an area where it fails to dry out fully. I haven't found a solvent for fully dried paint. Dbfirs 07:43, 13 October 2010 (UTC)

White spirit or turpentine are used for cleaning paint brushes, so perhaps they would be a solvent. 92.15.20.132 (talk) 15:46, 17 October 2010 (UTC)

No, these are solvents only for oil-based paint. They cannot be used for emulsion paint (or at least they are less effective than water). Dbfirs 16:57, 17 October 2010 (UTC)

why wrinkles around mouth

why do we get wrinkles around the mouth (like a cartoon beard)? I'm in my late twenties and it is one of the first places I'm getting wrinkles. I can't think of particular facial gestures / expressions I make that stress that part of the skin, unless it is from brushing my teeth... Is there something I can avoid doing so as not to exacerbate that... Thank you. 85.181.51.248 (talk) 22:14, 12 October 2010 (UTC)

There is no way to avoid wrinkles, but if you smile more often than you frown then you will have pretier wrinkles. 169.139.219.254 (talk) 22:25, 12 October 2010 (UTC)

Injections of Botox are used for cosmetic reduction of wrinkles, typically by celebrities. See Botulinum toxin#Cosmetic. Cuddlyable3 (talk) 08:49, 13 October 2010 (UTC)

See transverse muscle of the chin. ~AH1^(TCU) 02:10, 15 October 2010 (UTC)

natural sciences v. finance

How feasible is it to transition from the natural sciences to finance? A lot of the skills seem similar. Because I haven't taken an econometrics class, I am curious when people complain about all-nighters in finance or accounting (this is at the McIntire School of Commerce) whether their complaints are really legit, compared to all-nighters in the study of something also intensively quantitative like ecology or physical chemistry for example.

I guess I want to ask is -- what do undergrad students of finance and accounting study? Is it really hardcore? Looking at some appropriate articles, I see things like stochastic models and fractals -- so I wonder if I'm missing out. John Riemann Soong (talk) 22:30, 12 October 2010 (UTC)

Around the science buildings at Stanford are many job-postings for banks, insurance companies, and brokerage agencies seeking to recruit "quants" - the industry buzz-word for "quantitative thinker." There are more postings for financial industry careers than for jobs in engineering and science. In the computer science building, the posters advertise with the catch-phrase "Hack Wall Street." The operational wisdom in the finance industry seems to be that anybody who can get (part-way) through a science or engineering curriculum has already well-satisfied the mathematical and cognitive requirements for a career in the financial industry. I imagine that if you sought a degree transfer you would have no trouble with the material. Undergraduates Graduate students in finance at Stanford study the Financial Math curriculum, (which is more rigorous than a Finance curriculum); their mathematical training includes elementary statistics and probability, some calculus, a differential equations class, and at least one economics course. Comparatively, undergraduates in the physical sciences are required to fulfill more rigorous mathematical training: advanced calculus and differential equations, advanced statistics, probability, and at least one economics class. Nimur (talk) 22:37, 12 October 2010 (UTC)

Haha I don't want to transfer degrees. I just want to know that if grad school / med school / TFA doesn't pan out or whatever, how difficult would a transition be after graduation. (Also I happened to sign into an honors physics track despite being a biochemistry major -- for the sole reason that the honors track was more interesting. So in the face of uncertainty I wonder if I will be punished careerwise instead of rewarded for my risk-taking.) John Riemann Soong (talk) 22:45, 12 October 2010 (UTC)

As Richard Feynman pointed out on numerous occasions, as long as there are wars, there will be demand for physicists:

“ After the war, physicists were often asked to go to Washington and give advice to various sections of the government, especially the military. What happened, I suppose, is that since the scientists had made these bombs that were so important, the military felt we were useful for something. ” — Richard Feynman

This is still true in the 21st century. Nimur (talk) 22:52, 12 October 2010 (UTC)

If you do any kind of math based natural science at a well-known university, you will be actively courted for consulting and financial jobs. --Mr.98 (talk) 13:04, 13 October 2010 (UTC)

What's the usual GPA cutoff for a tier 1 school? John Riemann Soong (talk) 21:15, 13 October 2010 (UTC)

expansion of the universe

Does the correlation of greater speed at which bodies travel away from us and the greater distance just mean that the greater the distance away from us not only the older the body is but the faster that time is ticking? --96.252.213.127 (talk) 22:53, 12 October 2010 (UTC) In other words does a second near a Quasars or other distant object that is moving away at faster speed than closer objects, ticking faster than a second here? --96.252.213.127 (talk) 04:19, 13 October 2010 (UTC)

You will perceive that any object with a GR redshift (from motion or gravity or the expansion of the universe) has a "slower clock" than yours, by definition. Let's take a very common clock, which is light itself. Red light "vibrates" slower than blue light does. So any light that has been red shifted will vibrate less quickly than its source would otherwise indicate. Hence the events encoded in that red shifted light will take the same number of "light vibrations" as usual, only those vibrations will be spread over a longer period of time from the observer's point of view. Hcobb (talk) 04:39, 13 October 2010 (UTC)

Okay then that seems to confirm that whatever is going on now where the object is, is occurring at a faster rate than we can observe. In other words explosions that occur at greater distances will appear to take longer to complete. Can we use percent redshift to determine how much slower our observation tiem frame is for these events versus the time they actually take to complete? --96.252.213.127 (talk) 05:37, 13 October 2010 (UTC)

The universe (as far as we can see) is roughly homogeneous; that means that nothing else is going faster or slower in any absolute sense, since that would make it different from us. That said, yes, we see cosmological events slowed down by the same ratio that their light frequencies are lowered. This is possible because the object emitting the light is moving away from us; see Doppler effect for some pictures. For example, type Ia supernovas all look similar to one another, and the redshifted ones also happen slower by just the right ratio. This is an important piece of evidence that the cosmological redshift really is a Doppler shift and not, say, a light scattering effect like the one that makes the sun appear red near the horizon. -- BenRG (talk) 07:15, 13 October 2010 (UTC)

... and don't forget (as Ben implied above) that any observer on the far side of the observable universe would see events here slowed down by the same amount. The whole effect is thought to be caused by the metric expansion of the space in between. There is no "real" difference in the speed of events (or the speed of objects) here and at the extreme, just a symmetric difference in our observations. Dbfirs 07:35, 13 October 2010 (UTC)

"...just a symmetric difference in our observations." okay that is the terminology and understanding I was looking for. In other words a second is a second here and a second is a second there but an even that takes a second to happen there that is observed from here only appears to take longer than a second when observed from here. --96.252.213.127 (talk) 13:11, 13 October 2010 (UTC)

I suppose we should exclude regions near to large black holes or similar super-massive objects, because a large gravitational field will upset the symmetry. Dbfirs 15:36, 13 October 2010 (UTC)

Would gravitational microlensing in this case bend not only space, as viewed from a faraway observer, but also distort the apparent speed of time relative to the observer? ~AH1^(TCU) 02:06, 15 October 2010 (UTC)

I'm not sure about that (we await an expert in GR), but my intuition is that it wouldn't if the large mass was well away from the two observers. Dbfirs 13:05, 15 October 2010 (UTC)

October 13

Water being included as a test subject

Why would water be included as a test subject in a Benedicts test or biuret reagent test? Isnt it already confirmed that water is neither a protein nor a reducing sugar? (the experiment was done using many other solutions- each solution was tested seperately) —Preceding unsigned comment added by 24.86.167.133 (talk) 03:44, 13 October 2010 (UTC)

Is it? You sure that label is correct? Sure that no one dropped a little sugar into the water bottle when they were carrying the weighing paper back to their work bench? In the case of something like a high school biology assigment, it's probably just to show you what a negative result looks like. In real world applications, it's important to confirm that the chemicals you use to prepare or dilute a sample have not themsleves been contaminated with the very chemical you're testing for. Someguy1221 (talk) 04:50, 13 October 2010 (UTC)

The OP can read more about this in our article on scientific control. Someguy's point is that the water is being used as a "negative control." --- Medical geneticist (talk) 15:52, 13 October 2010 (UTC)

While it may seem absurd to do an experiment on water, which you made up the reagent in to begin with, for the colorimetric tests the rationale should actually be quite apparent: you literally want to see what a negative reaction looks like. It's not enough to say that a test should be purple rather than blue: you want to see how purple. If you're doing a reasonably elaborate test, you might take the water-only tube and measure it in a spectrophotometer, then measure with various quantities of protein (a standard curve), and plot out all the numbers on a sheet of graph paper. (ehhm, I mean a spreadsheet. I suppose graph paper just doesn't get used much nowadays ;) ) The water gives you a direct measurement of the point where the concentration crosses zero. This extra data point at the end will help you do a better linear regression to make the best fit of not entirely accurate data, if you come to that. Wnt (talk) 06:21, 14 October 2010 (UTC)

Sanpaku

Does anyone have any information on the incidence of sanpaku? Is it at all genetic? Both Kennedys apparently had it, but I seem to be the only one in my family who has it. Google hasn't turned up anything useful. 74.15.136.172 (talk) 04:02, 13 October 2010 (UTC)

See Culture-bound syndrome for some possibly-relevant context. 109.155.37.180 (talk) 16:58, 13 October 2010 (UTC)

Is it a fungus?

I'm afraid my descriptions on File:Nikaufungus1.jpg and File:Nikaufungus2.jpg are dismally vague, as I have no idea what was actually going on there. This cluster of sickly nikau and silver ferns were in the middle of a perfectly healthy nikau grove. Does anyone have any idea what the black stuff is? Sorry about the poor photographs, I was curious and thought someone here might know. sonia♫ 09:57, 13 October 2010 (UTC)

Possibly a secondary fungus known as 'sooty mould' related to an infestation by something like mealy bugs. Mikenorton (talk) 10:15, 13 October 2010 (UTC)

Incinerating raw sewage using liquid oxygen?

Could raw sewage mixed with LOX and ignited be instantly reduced to its harmless elemental constituents using such a method, with some of the energy released used to create more liquid oxygen to continue the process? The ultimate "chemical" toilet for the Glastonbury festival perhaps? —Preceding unsigned comment added by 80.1.88.10 (talk) 10:57, 13 October 2010 (UTC)

The Wikipedia article on Sewage treatment mentions incineration as possible but uncommon because of air emission concerns and the amount of fuel needed to burn the low calorific value sludge and vaporize residual water. The article Glastonbury Festival notes that Network Recycling manage refuse on the site, and in 2004 recycled 300 tonnes and composted 110 tonnes of waste from the site. Cuddlyable3 (talk) 12:29, 13 October 2010 (UTC)

Oxygen by itself is not flammable, and liquid oxygen requires very low temperatures or tremendously high pressures to be maintained. ~AH1^(TCU) 02:01, 15 October 2010 (UTC)

Of course oxygen is not flammible, but can make something of low calorific value burn completely. For example a calorimeter completely oxidises food-this is what gave me the idea. The advantage would be instant disposal of the waste with no unpleasant gas as in the case of organic and chemical methods. —Preceding unsigned comment added by 80.1.80.7 (talk) 06:32, 15 October 2010 (UTC)

Gas can be easily absorbed. I would just add concentrated hydrogen peroxide. It kind of works like liquid oxygen, especially at 98% concentration (30% is already strong). John Riemann Soong (talk) 08:07, 15 October 2010 (UTC)

The "new" method of treatment is to use the nitrogen, potassium and phosphorous in the sewage and co2 from power plant emissions to grow ethanol and oxygen producing algae. In this way many goals are served. A usable fuel is produced without killing the algae and The nitrogen, phosphorous and potassium and co2 do not harm the environment while oxygen is released into the atmosphere or compressed and bottled as well as the ethanol gas. A win-win-win-win-win-win scenario.

speed and distance of expansion

What is the formula that relates the increase in speed of expansion of the universe with distance space away from Earth? for instance is it percent redshift times something or another or what? --96.252.213.127 (talk) 12:59, 13 October 2010 (UTC)

Hubble constant -- Finlay McWalter ☻ Talk 13:06, 13 October 2010 (UTC)

"pass through" versus "bounce"

When some stars collapse depending on the amount of matter evolved either form a Black Hole or explode of "bounce". If you view this graphically as a cone with the narrowest point being the point of greatest density and the cone extending through this point to form another cone as in a classical conic section representation diagram for a hyperbola then isn't it possible that instead of a "bounce" the collapse could result in simply a "pass through", meaning that the momentum of the collapse transfers through the point of greatest density rather than "bounce" back off of it? --96.252.213.127 (talk) 13:35, 13 October 2010 (UTC)

You are describing a Type II supernova. Our article notes that the gravitational collapse is stopped by degeneracy pressure (among other forces). There's no plausible reason to expect that matter passes through this extremely dense core rather than rebounding. — Lomn 13:43, 13 October 2010 (UTC)

Naturally I realize to observe such a phenomenon with sufficient precision to denote the difference between "bounce" and "pass through" does not offer at this time a plausible reason. However, if you think mathematically in terms of a Gravity well with infinite density at the bottom then emergence on the other side has certain advantages in regard to the law of conservation of momentum for a collapse than does a "bounce". --96.252.213.127 (talk) 20:00, 13 October 2010 (UTC)

(Fixed your confusing repeated spelling error.) --Anon, 06:03 UTC, October 14, 2010.

As Lomn says, the core of stars are much too dense for anything to pass through. The material in the core is an ultra-high viscosity fluid (closer to a solid than a gas really). Each particle will collide with others about a quadrillion times per second. Those collisions ensure nothing could pass through. Dragons flight (talk) 10:29, 14 October 2010 (UTC)

When particles of a collapsing supernova approach the core, the density of the material as well as the force pushing inward increase exponentially, so it becomes much harder for particles to simply pass through the core as doing so would mean neutrons passing through each other. The core during its collapse also becomes denser very rapidly, so any matter attempting to pass through would have a much harder time doing so, as iron atom nuclei are produced at this point. In supernovae that from black holes, the imploding matter hits a gravitational singularity and is shrunk to an infinitely small point, but is not swallowed by the new singularity quickly enough to prevent rebounding of the star's collapsing core and outer layers. ~AH1^(TCU) 01:59, 15 October 2010 (UTC)

Not only did you find my spelling too confusing but to correctly conceive what I am speaking of. (If you like you can change "speaking" to "saying" or to "writing.") The idea of "pass threw" and "bounce" are not applied here to matter but to energy or more precisely to force and momentum and reference the space-time grid diagram of a gravity well where as you correctly say that infinite gravity is not reached within the time and space constraints which will allow a black hole to form or stay formed. The concept of "bounce" is that this depression in the grid is like a depression in a net into which a ball is dropped that reverses rather than being stretched to an infinite point and "locking" or staying there. The concept of "pass threw" or "pass through" as your preference refers to the side view of the hyperbola and the perpendicular edges of the conic and hyperbolic sections of the gravity well to show that indeed a singularity was achieved but that due to the time and space constraints represented by the diagram were not able to "lock" or to stay singular but rather "pass threw" or "pass through" to the other side of the point of infinite intensity as represented by the grid diagram of the gravity well. --96.252.213.127 (talk) 00:27, 17 October 2010 (UTC)

In other words, it might help to think of the place of infinite gravity as the bottom of the well but the well not being at the bottom of the diagram but in the middle of the diagram such that the top and bottom represent least gravitational intensity - two universes if you will in the space-time continuum. --96.252.213.127 (talk) 01:15, 17 October 2010 (UTC) i.e. criteria for a worm hole. --96.252.213.127 (talk) 08:29, 17 October 2010 (UTC)

Conductive Napalm

I was looking at railgun and it got me thinking that it may be possible to fire napalm using a railgun if the gel was conductive. Is it possible to do this? ScienceApe (talk) 14:56, 13 October 2010 (UTC)

Thinking about anything is possible. But napalm in the form of jellied gasoline does not have the high conductivity needed to carry the extremely high current required in a railgun and there is nothing to stop it breaking into an aerosol. Cuddlyable3 (talk) 15:37, 13 October 2010 (UTC)

It would also be a questionable weapon, pragmatically speaking. napalm could already be dispersed by fairly standard flame throwers; the only advantage to a rail gun would be speed and distance, but speed is irrelevant (it's a continuous stream that's not particularly aerodynamic, so any initial velocity differences will quickly be neutralized), and how far does one want to be shooting a stream of napalm? remember, everything in the range and general direction of the weapon would be subject to accidental splashes from wind gusts and such; a weapon like that would be almost as dangerous to nearby troops as to the enemy. --Ludwigs2 17:10, 13 October 2010 (UTC)

I'm just asking if it's possible to make a conductive napalm. Perhaps by adding electrolytes or something. ScienceApe (talk) 19:09, 13 October 2010 (UTC)

I think the intention is not practicality, but to be as cool a thing as a railgun that squirts napalm. ScienceApe brought up electrolytes. What would strong acids, like HCl, which dissassociate in solution do to this mixture? Mac Davis (talk) 19:11, 13 October 2010 (UTC)

You probably want a polar but lipophilic but flammable solvent. Acetamide or acetonitrile, maybe? John Riemann Soong (talk) 21:39, 13 October 2010 (UTC)

Humans in North America

Moved from Talk:Human --Cybercobra (talk) 15:15, 13 October 2010 (UTC)

If the human race originated from Africa, how come the Red Indians were there in North America. As we are aware of the fact that America was discovered by Columbus and the Red Indians were found to be original habitats of the continent. If the human race originated from Africa, how come they reached to America before Columbus did. —Preceding unsigned comment added by 202.79.203.51 (talk) 13:10, 13 October 2010 (UTC)

Columbus didn't discover the Americas; the Indians came there first, a few thousand years ago. (And after that, the Vikings also got there before Columbus.) Ucucha 15:24, 13 October 2010 (UTC)

Exactly when the first group of people migrated into the Americas is the subject of much debate. Asian nomads are thought to have entered the Americas via the Bering Land Bridge (Beringia), now the Bering Strait and possibly along the Northwest coast. see the articles Pre-Columbian era and Settlement of the Americas. Cuddlyable3 (talk) 15:27, 13 October 2010 (UTC)

Humans originated in Africa between 400,000 and 250,000 years ago. That means that Native Americans had at least 249,598 years to move through Asia and arrive in America on time to greet Columbus. The earliest Archeological remains in the American continent date to around 14,000 years ago, and even those archeologists who argue for an early entry of humans in to the Americas do not believe that they could have arrived earlier than 40,000 - 30,000 years ago. That would mean that there is a timespan of 210,000 years between the rise of humans in Africa and the first possible date of arrival of humans in the Ameircas. Do you understand now?·Maunus·ƛ· 15:41, 13 October 2010 (UTC)

I believe that the problem with understanding this comes from a religious belief that the entire human population is only about 3,000 years old. Then, there simply hasn't been time for populations to move from Africa to Asia and then to completely populate the Americas before Columbus showed up. Science doesn't necessarily obey religious beliefs. So, when confronted with an argument based on a religious belief, I use the "God did it" variant of "a wizard did it". People originated in Eden in Africa. Then, God picked up a bunch of them and put them in North and South America. He is all powerful, so you can't argue that it is impossible for God to simply redistribute human populations as he sees fit. -- kainaw™ 15:43, 13 October 2010 (UTC)

Well the Bible doesnt say anything about him doing that though.·Maunus·ƛ· 15:45, 13 October 2010 (UTC)

There may have been some sarcasm in Kainaw's answer. The OP should have a look at our article on Recent_African_origin_of_modern_humans, which explains the current theory of when and how different global populations were established. --- Medical geneticist (talk) 15:48, 13 October 2010 (UTC)

And surely, pre-Columbian translators of the holy texts did not know the ancient Hebrew, Syriac, Aramaic, or old Greek word for "Bering Sea" or "Meso-America"; obviously, they mistranslated any section of the representative texts that explained that part. Any pure biblical literalist should insist on proper name/glyph reassignment to help the "original" text coincide with established fact. I'm pretty sure that Bible scholars have historically had no problems with such scholarly "literal" reinterpretation. Nimur (talk) 16:15, 13 October 2010 (UTC)

Genesis 11:8... God scattered the people all over the Earth, which probably includes the Americas since God certainly knew he created them. -- kainaw™ 15:49, 13 October 2010 (UTC)

There are other possible settlement routes than the Bering Land Bridge. While that was certainly one method, there are of course variances in ideas on when people crossed the land bridge into the Americas, whether it was one event, multiple events, or a continuous migration back and forth over many millenia. Dealing with the OP's other misconceptions, there is also evidence of other pre-Columbian contacts between the Americas and other parts of the world. Of course, there were the Viking contacts, see Norse colonization of the Americas, esp. Vinland and L'Anse aux Meadows, which occured c. 1000 AD. From the other direction, there were also clear evidences of Polynesian contacts with the Americas, see Polynesian_navigation#Pre-Columbian_contact_with_the_Americas and Pre-Columbian_trans-oceanic_contact#Polynesians, which occured even earlier than the Vikings, there were South American sweet potatoes in the Cook Islands as early as 1000 AD, which means they had to have gotten there much earlier. There are also things like pre-Columbian Chickens (native to S.E. Asia) and boat construction techniques known to the Chumash people of the Pacific coast of N. America which show polynesian influences. Besides these two confirmed cases of pre-Columbian contacts, there have also been some less certain ones. Brendan of Clonfort allegedly visited the Americas, and some mysterious sites in Connecticut have been attributed to him. The Olmec heads have been speculated to indicate African contact with Mesoamerican peoples, and certain people have speculated that the Quetzelcoatl myth shows European influences. --Jayron32 16:07, 13 October 2010 (UTC)

I think "Clear evidence" of Polynesian contact is overstating the case. It would be safer to say there is some evidence suggesting Polynesian contact. thx1138 (talk) 23:21, 13 October 2010 (UTC)

Sweet potatoes don't swim... --Jayron32 02:06, 14 October 2010 (UTC)

Coconuts swim. Are you sure no sweet potato could have viably endured such a journey without assistance? WikiDao ☯ (talk) 02:39, 14 October 2010 (UTC)

Sweet potatoes don't have large air pockets which make them bouyant. --Jayron32 02:47, 14 October 2010 (UTC)

Okay, I now see that the article says (uncited): "The theory that the plant could spread by floating seeds across the ocean is not supported by evidence." I will, therefore, yield the point (and because for another thing I do not have a sweet potato exemplar on hand, nor ocean water to float (or not) it in.) Sorry for the distraction from your overall and well-stated point, Jayron32, with which I fully agree. :) WikiDao ☯ (talk) 02:59, 14 October 2010 (UTC)

The deal with the evidence for Polynesian contact is that it is approaching the level where Occam's razor begins to take hold. Yes, it is possible that the sweet potato could have migrated ONLY to polynesia over 3000 miles by nothing but ocean currents, and somehow not anywhere else. It is possible that, likewise, a bird native to South East Asia (the Chicken) could have made the opposite journey equally as well, again, with no evidence that it ever made this journey to any other part of the world. Or, an oceangoing civilization, known to range widely through every other part of the Pacific Ocean, carried the potatoes one way and the chickens the other. You decide which is the more likely explanation. Admitedly, the potatoes and the chickens could have been carried by Native American peoples instead, but this seems less likely than the Polynesians, because only one of these two groups of people are known to have an entire civilization built on boat travel... --Jayron32 03:15, 14 October 2010 (UTC)

I'm not sure if maybe already mentioned elsewhere, but are there gene studies showing higher "Polynesian" allele frequency among native South Americans than among, say, native North Americans? (I realize that the potential yam-acquisition-event easily might not also have led to any sexual congress between members of the two groups.) WikiDao ☯ (talk) 03:30, 14 October 2010 (UTC)

You know, I am not sure about that. It's a valid question, and a very good one. I just don't have the answer yet. The article Polynesian_navigation#Pre-Columbian_contact_with_the_Americas has noted a genetic study done on the pre-Columbian South American chickens, indicating that they did come Polynesia, and not from say Europe or Africa. But I am not sure of any similar studies on humans. This evidence has been disputed by some. --Jayron32 03:35, 14 October 2010 (UTC)

The final out-of-Africa dispersion of modern humans is thought to have happened about 100,000 years ago. Their spread across Europe and Asia can be traced: they reached Australia by 50,000 years ago and northeast Asia by around 40,000 years ago. There is no convincing evidence that they made it into North America (via Alaska) until about 14,000 years ago; but then they spread very rapidly down along the Pacific coast and reach the tip of South America in less than 2000 years. Looie496 (talk) 17:06, 13 October 2010 (UTC)

Archaeologists always underestimate the capabilities of human ancestors, because they're nervous to hypothesize things that haven't been found in the record. But I'd bet that there were very impressive watercraft a very long time ago, and that humans could have gotten around the Bering bridge on water, hunting sea mammals, if they were so minded. But they were also awesome survivors in Arctic environments and surely could have bulled through on foot if that was their preference. P.S. Jayron — thanks for some really interesting information! Wnt (talk) 19:57, 13 October 2010 (UTC)

There is also evidence of Solutrean contact with Eastern North America several thousand years ago. No matter how you cut it though, Columbus certainly did not discover the New World. Columbus also did not discover that the world was round. That was well known by pretty much anyone with any kind of education before he set sail. Falconus^{p t c} 21:41, 14 October 2010 (UTC)

Blood tranfusion

Why is blood always taken out from veins and not from arteries? Since the veins carry blood lacking oxygen. —Preceding unsigned comment added by 113.199.183.255 (talk) 15:32, 13 October 2010 (UTC)

When donating blood the oxygen isn't important since the recipient's lungs will oxidise it again. Regards, --—Cyclonenim | Chat  15:41, 13 October 2010 (UTC)

(after EC, same answer) It is easier, safer, and less painful to perform venipuncture than taking blood from an artery. While it is true that venous blood is less oxygenated than arterial blood, it is not completely devoid of oxgyen (see Oxygen-hemoglobin_dissociation_curve), and this doesn't really matter to the recipient of a blood transfusion since their lungs will happily oxygenate the newly received blood just as they will all the other blood in the recipient's body. --- Medical geneticist (talk) 15:43, 13 October 2010 (UTC)

The pressure inside an artery is much higher than in a vein, so it is very difficult to puncture an artery without creating a mess. Also artery are generally placed deep inside the body where they are more protected, so they are quite a bit harder to access than veins. Looie496 (talk) 17:00, 13 October 2010 (UTC)

In addition to various practical matters as discussed above, I can tell you, from having had artery-level blood drawn a couple of times, it hurts like hell and you practically have to put a tourniquet on it. So it's to be avoided unless absolutely necessary. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:56, 13 October 2010 (UTC)

Perhaps a more direct answer is that transfused blood does not pass through any capillaries before reaching the lungs, where it gets fully oxygenated in one pass (if the lungs are normal). It may not be intuitively obvious that blood does not need to be oxygenated except when it passes through capillaries in tissues that need oxygen, and that does not happen immediately with transfused blood. Blood passing through peripheral veins, where it is harvested for donation, is already de-oxygenated and on its way toward the heart. That's also where blood is given to the recipient during transfusion (sometimes it's delivered to a central vein, but the effect is pretty much the same). Oh and by the way, Bugs, Radial artery puncture is not always very painful - it depends on many factors including the skill of the person holding the needle. -- Scray (talk) 01:10, 14 October 2010 (UTC)

If it's not in UniProt, does it still exist?

If I can't find 'small glutamine-rich tetratricopeptide repeat (TPR)-containing protein' on UniProt for Gallus gallus, does that mean it's safe to say that it is not known to exist in chicken? ----Seans Potato Business 18:27, 13 October 2010 (UTC)

Not necessarily. It depends a little on which UniProt database you were using, but my experience with UniProt is that it tends to be somewhat more conservative about the genes/proteins included. I like the National Center for Biotechnology Information (NCBI) a little better. When I searched Entrez Gene for "small glutamine-rich tetratricopeptide repeat (TPR)-containing protein" I came up with SGTA and SGTB. Is that what you're looking for? --- Medical geneticist (talk) 19:24, 13 October 2010 (UTC)

That and PubMed are great ways to do this. Though in truth, I think it's always best to sniff around for sequence homologies yourself, in case there's something better that was missed before. It's not uncommon for a gene to be annotated as if it were an orthologue but it's not an ortholog, it just dates back to a time when only one of the type was known from a species. (I'm not saying that's true here though)

The chicken genome coverage is 6X, which isn't perfect.[5] I'm sure there's a very simple statistical rule to relate that to a percentage of missing clones, which, alas, I don't recollect - if you cover 1X in little bits, how much is left uncovered? I don't remember the number and had a little trouble finding it, but I think it was something like 36% - to use that as a crude guess, 6X would mean you miss 0.2% of all the genes. But that's under optimal conditions - a genome can be mis-assembled based on repetitions (about 25% of the chicken sequence). On the other hand, someone might have helpfully sequenced through problem spots and connected the gaps in the random assembly. You'd have to look up the exact methods for the sequencing project to estimate such things (see [6]).

But it's more likely that the gene is just not annotated, or not annotated under that name. What protein has less than three names? What database ever lists them all? And your request is no ordinary catalytic domain, but simply a motif defined by four alpha helices which can be rather extensively substituted. Nonetheless, there are some truly awesome bioinformatic tools on the task, most notably the combination of EBI and PFAM: see e.g. [7] [8] [9] [10] [11]

Now at the end this trails out in many directions because I can't know exactly what you're looking for, but I think you might find what you want. Wnt (talk) 19:51, 13 October 2010 (UTC)

Identify device

What is the device featured in this clip? Note, VERY non-safe for work link

Erotic electrostimulation electrodes. Red Act (talk) 20:31, 13 October 2010 (UTC)

So the next time the OP's babe tells him he needs to "jump start it", there's an actual way to do that. Ya learn something new every day. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:54, 13 October 2010 (UTC)

What happened to my apple juice?

It fizzed and tasted like vinegar.

I was gone for three days and didn't open the bottle during that time. It is true I refilled the bottle several times. But I figure it was empty when I poured new juice into the same bottle. Right now I'm using a bottle I just opened which is harder to hold.Vchimpanzee · talk · contributions · 19:27, 13 October 2010 (UTC)

Sounds like you made it from apple juice→cider→cider vinegar, impressive in three days. Mikenorton (talk) 19:31, 13 October 2010 (UTC)

It wasn't true vinegar. It just had a strange taste. I did finish it.Vchimpanzee · talk · contributions · 19:35, 13 October 2010 (UTC)

As Mikenorton implied, it fermented, which is not harmful unless you have zero tolerance for alcohol. The longer something ferments, the more sour it gets, but it's very unlikely it would reach the vinegar stage in three days even if you left it in a warm room. Apple juice ferments pretty readily, though. Looie496 (talk) 19:40, 13 October 2010 (UTC)

Apple cider vinegar might be a useful page, although it is about cider really turned into vinegar. Apple cider has more info about the process. Unfortunately, the terms "apple cider" vs "apple juice" have more to do with filtering rather than pasteurizing, if I understand right. The page does say about unpasteurized apple cider: "Within a week or two refrigerated it will begin to become slightly carbonated and eventually become so-called "hard cider" as the fermentation process turns sugar into alcohol." Assuming you had "cider" and not what I would call "juice", and that it wasn't refrigerated, three days would probably be enough to significantly alter the taste in the direction of "vinegar". In the village where I grew up, in western New York state, there was an old village mill that made real unpasteurized apple cider every autumn. It tasted so much better than apple "juice". At least, I remember it tasting better. Perhaps the mill people just knew their craft very well, and it wasn't about pasteurization. But yes, the stuff did turn "hard" quite readily. Once "hard", some people put the gallon containers in the freezer. It wouldn't freeze due to the alcohol. Where I live now, near Seattle, real cider like this is not so easy to come by, even though Washington is a major apple growing region. Stores around here sell so-called "apple cider", especially in the autumn. But it is just unfiltered pasteurized apple juice. If you have access to unpasteurized cider, count yourself lucky! It's not just that it turns hard, it tastes better...or so my experience tells me. But remember how quickly the stuff goes hard. If what you had was in fact pasteurized, the ignore me. I have no idea. Pfly (talk) 08:20, 14 October 2010 (UTC)

The reason I asked the question was that it is the normal apple juice one buys in the stores and has to refrigerate after opening. It wasn't old, though the bottle had been around a while. I was reusing it. I will say the juice, after those three days of being out of town, looked like the glass on the left in the top photo in the apple cider article.Vchimpanzee · talk · contributions · 18:49, 15 October 2010 (UTC)

October 14

difference between quantum state and wavefunction?

Hi, what is the difference between a quantum state and a wavefunction? Can you change one without changing the other? Does every particle or system have both a quantum state and a wavefunction, even, say, completely static ones like ground state electrons?? Thanks in advance, It's been emotional (talk) 00:08, 14 October 2010 (UTC)

The quantum state is the set of quantum numbers that completely define a unique quantum system, for example, a single electron energy state, with spin state, in an atom. The wave function is the function which describes the probability space where a particle can be found. In other words, the wave function describes the shape and density of the volume of space where an particle (like an electron) is likely to be found. The three-dimensional plot of a wave function of an electron, for example, describes the shape of the orbital that contains that electron. Depending on your perspective, you can think of a wave function as either 1) a "scatter plot" graph which describes the location of an electron in the space around an atom as measured over an arbitrary length of time or 2) as a mathematical description of the shape of a standing wave centered on the nucleus. Perspective 1) relates to the "particle half" of an electron's nature, while perspective 2) relates to the "wave half" of an electron's nature. Quantum physicists don't make a distinction between these two perspectives, because electrons don't either, but you can think of either definition as being what a "wave function" is. So, here is how quantum state and wave function are related. The wave function is the mathematical equation itself which describes this space, while the quantum numbers are the variables in that mathematical equation. The distinction between the two is kinda like the distinction between a mathematical equation (x² + y² = r²) which will graph a circle, and the english definition of a circle as "the sum of all points equidistant from a fixed point". They both describe a circle, but they are not identical definitions. --Jayron32 01:48, 14 October 2010 (UTC)

Thanks very much for that answer. It clarifies things a lot. I have one further question, though: you seem at the beginning of your answer to be suggesting the wavefunction only represents the point in space where an electron is located. Does the wavefunction also represent the electron's spin quantum number? In other words, should I go more by your final point that a wavefunction and a quantum state describe the same information in different ways (as in the mathematical and the English descriptions of a circle), or is there any exception to this summary? It's been emotional (talk) 17:33, 14 October 2010 (UTC)

No, the wavefunction also contains the spin quantum number as a variable, I am pretty sure the wavefunctions of two electrons which differ only by their spin quantum number occupy the same space, but are orthogonal in some manner; this is why two electrons can occupy the same orbital but with opposite spins; their wavefunctions are perfectly orthogonal so that they don't interact with one another in any way (either constructively or destructively). Admitedly, my quantum chemistry is about 12-13 years sketchy at this point, so I forget exactly how they are orthogonal, but it's probably "orthogonal" in the same way that electrons have "spin", i.e. electrons don't have actual spin; but the property of particle spin behaves mathematically like angular momentum. In the same manner, the wavefunctions of the spin-opposite particles would be orthogonal, not in the sense that they are at physical right angles to each other, but in the sense that orthogonal waves do not interact. I wish I could explain that better, but as I said I am a bit rusty. Someone who remembers more than me will be along shortly to set it straight. --Jayron32 22:32, 14 October 2010 (UTC)

They're orthogonal in the math sense. That is, their inner product is zero. When discussing the standard inner product on vectors in 3D, the inner product being zero is equivalent to the vectors being at right angles (assuming they're non-zero) which is why this property it called "orthogonality". However wavefunctions don't live in Euclidean 3 space but some abstract infinite dimensional Hilbert space of all possible states. Rckrone (talk) 22:57, 14 October 2010 (UTC)

Great answer, thanks to you both. Glad I pursued it. It's been emotional (talk) 23:17, 14 October 2010 (UTC)

Contact lens solutions don't drip out of bottles when inverted.

Ok, they do, but the flows always stop. Is that atmospheric pressure at work? 67.243.7.240 (talk) 00:12, 14 October 2010 (UTC)

Yes, atmospheric pressure plays a large part. Initially, (with an open aperture at the tip of the bottle) the pressures inside and outside the bottle would be equal, and liquid will simply respond to gravity by flowing downward; however, if the bottle is un-vented (which would be true in this case) then this downward movement of the liquid lowers the pressure in the bottle, such that the greater atmospheric pressure (compared to the pressure in the bottle) exerts a force greater than gravity. If not for surface tension, the drops might still flow downward, replaced with upward (into the bottle) flow of air, but the small aperture plus surface tension are enough to keep the drops from leaking out. -- Scray (talk) 01:20, 14 October 2010 (UTC)

More drops will drip from a flexible plastic bottle than a rigid glass or metal one. Cuddlyable3 (talk) 12:55, 14 October 2010 (UTC)

Space telescope naming question--Edwin Hubble got one, how about Henrietta Leavitt?

Hi, does anyone know how the names for various NASA et al telescopes are decided on? Has Leavitt's name been bandied about? Thanks, Rich Peterson199.33.32.40 (talk) 00:39, 14 October 2010 (UTC)

I would expect the method varies a lot depending on the particular case. For one example Fermi Gamma-ray Space Telescope#GLAST renamed FGST. There's almost definitely a lot of politics involved. Nil Einne (talk) 04:34, 14 October 2010 (UTC)

When visiting Houston a couple of years ago some staff told me that there is a lot of politics involved in deciding on names, i.e. no formal process. HiLo48 (talk) 06:39, 14 October 2010 (UTC)

I see. Thanks to you both. Rich (talk) 06:47, 14 October 2010 (UTC)

Some space probes are named by contest. The Mars Exploration Rovers were named by a essay contest, as was The earlier Mars rover (Interestingly, pathfinder was named the "Carl Sagan Memorial Station" after the mission ended, in what I assume was an internal decision). In both cases there's still obviously a bit of subjectivity and politics that occurs in choosing the winner, but at least they're getting input from the public. The Mars Science Laboratory's name "Curiosity" was chosen by an online poll.

Some of the names have pretty whimsical sources. The telescope and UV spetrograph on the New Horizons probe are named, respectively, Ralph and Alice. Alice is named for the earlier instrument on the Rosetta (spacecraft), while Ralph is named for Alice's husband in The Honeymooners. It's unclear how Rosetta's UV spectrograph came to be known as Alice. Rosetta itself appears to be named after the Rosetta Stone [12](I guess this will help people understand comets the same way the Rosetta stone helped people understand Egyptian Hieroglyphics), and the landing probe is appropriately named the Philae lander, after a place where an inscription was found that helped refine our understanding of Hieroglyphics. It would be interesting to know the process by which those two names were chosen, but I don't see anything off hand.

Unsurprisingly, many names of satellites and instruments are acronyms. Sometimes, though, an acronym is forced to get a word that's somehow related to the mission; STEREO is a pretty good example of this. Buddy431 (talk) 14:42, 14 October 2010 (UTC)

See also Acronym and initialism#Contrived acronyms. Here are a few other suspects: AGILE, APEX, CHIPS, INTEGRAL, QUIET, WISE. PrimeHunter (talk) 23:05, 15 October 2010 (UTC)

Synthesis of 3-Carbethoxycoumarin

What is the synthesis mechanism for 3-Carbethoxycoumarin? Your article on Salicylaldehyde doesn't provide any detail. —Preceding unsigned comment added by Milt50 (talk • contribs) 01:40, 14 October 2010 (UTC)

I added a key detail to the item in salicylaldehyde. DMacks (talk) 04:40, 14 October 2010 (UTC)

magnitude of contact forces

two boxes, one on top of the other in an elevator. The bottom block weighs 30 N, the top weighs 20 N. The combined weight feels like 70 N. What is the magnitude of the contact force between the two boxes?

So I've solved that the total mass is 5.10 kg (3.06 kg for the bottom box and 2.04 for the top box). The acceleration of the elevator must be 3.92 m/s^2 upward to account for the difference in weight. I'm completely confused on the magnitude of the contact force though--i know that the force between the boxes should be equal in magnitude but point in opposite directions. Help!24.63.107.0 (talk) 05:12, 14 October 2010 (UTC)

Use Newton's 2nd law to find the net force acting on the top box. That net force must be the difference between the contact force and the weight of the top box. 174.58.107.143 (talk) 06:02, 14 October 2010 (UTC)

(edit conflict) Well you've done the hard bit! Now just forget about the lower box: imagine that the top surface of the 3 kg box is actually the "floor", and calculate the apparent weight of the 2 kg box. That is the contact force between the two boxes. Physchim62 (talk) 06:05, 14 October 2010 (UTC)

You have been told the contact force between the bottom box and the floor of the elevator is 70N. You only have to determine the contact force between the top box and the bottom box. Dolphin (t) 06:15, 14 October 2010 (UTC)

OP here, If I understand Physchim correctly, then I merely multiply 2.04 kg by the 13.72 (force of gravity + acceleration of elevator) to get a contact force of 28 N? Sweet!24.63.107.0 (talk) 06:20, 14 October 2010 (UTC)

Yup! Except it's even easier than that... For a bonus point, can you see a way to resolve this problem without solving for the mass of the boxes? Physchim62 (talk) 09:01, 14 October 2010 (UTC)

Weight x WeightAmplification = 20 x 70/(30 + 20) = 28 N Quod erat demonstrandum. Cuddlyable3 (talk) 12:51, 14 October 2010 (UTC)

What Cuddlyable3 is calling WeightAmplification is also known as load factor. Dolphin (t) 21:46, 14 October 2010 (UTC)

Yes, it gets a bit confusing to talk about different weights, but that's the terminology that the OP used. Cuddlyable's got the method, though. Another way to look at it is to consider the opposing contact force, the one in the upwards direction. There has to be one component of this force to counterbalance the weight of the box (due to gravity) and another component to accelerate the box upwards. We're told that the total contact force at the floor of the elevator is 70 N, and that the weight of the boxes due to gravity is 50 N. Hence there is a 20 N force accelerating the boxes upwards (with the rest of the elevator, obviously), so the acceleration must be 2⁄5 g. Physchim62 (talk) 02:20, 15 October 2010 (UTC)

Walking or Cycling?

As a form of exercise, which is more efficient, walking or cycling, in terms of energy expended against distance covered? Thanks asyndeton talk 08:38, 14 October 2010 (UTC)

Interesting phrasing. Walking burns more energy per mile, so I suppose in that sense it's "more efficient" as a form of exercise, assuming that for some reason you wish to cover as few miles as possible. --Trovatore (talk) 08:42, 14 October 2010 (UTC)

Of course a lot depends on how vigorously each exercise is performed, a 1km cycle sprint would expend more energy than a leisurely 1km stroll. -- Q Chris (talk) 08:49, 14 October 2010 (UTC)

(ec) Actually, I doubt that. A lot more per unit time, sure. But it would take maybe 10% to 20% of the time. It gets complicated if you start trying to figure in increased metabolic rate after the exercise, especially since how much that happens depends a lot on how much exercise you do regularly. --Trovatore (talk) 08:57, 14 October 2010 (UTC)

From a physics viewpoint, walking the 1 km should expend more energy since walking is less efficient (physics definition) than cycling, but Q Chris is probably correct from a physiological viewpoint because the sudden burst of vigorous effort resets the metabolic rate. "Efficiency" is a confusing concept in this context. I would suggest that sprinting the 1 km would burn more energy in total than either walking or cycling because it requires a vigorous effort and is intermediate in (physics) efficiency between walking and cycling. I'm not sure where jogging comes in the efficiency scale. Dbfirs 08:56, 14 October 2010 (UTC)

I'm somewhat with Trovatore on this one in being unsure. Definitely if you compare cycle sprinting vs leasurely strolling for the same amount of time, the cycle sprint will expend more energy. In this case I think it's far less clear cut and likely to depend on other factors. Nil Einne (talk) 10:41, 14 October 2010 (UTC)

Are not people confusing energy with power? Cycling 1km will require less energy than walking 1km, but if you sprint-cycle then you would use more power than walking, but the duration would be much less, hence the total energy should be less. The answer to the original question is, cycling would be more efficient as a form of transport. Cycling requires less energy than walking to travel the same distance. I understand that this is because when walking you use energy to stay upright, and much of this is saved when sitting down on a bicycle. In terms of being an "efficient" means of exercise, than whatever gets your heart beating faster works: running or fast-cycling. 92.15.2.211 (talk) 14:00, 14 October 2010 (UTC)

Yes, I agree fully, except that walking involves moving the body's centre of mass up and down, and this is the main reason (or one of the reasons) that it uses more energy for a given distance. Some people might interpret "exercise efficiency" as using more energy, not less, so there is vast scope for confusion here. Dbfirs 14:12, 14 October 2010 (UTC)

(EC) I don't think people are confusing energy and power. People are simply referring to the fact that human energy usage is complicated. Nil Einne (talk) 14:17, 14 October 2010 (UTC)

As a somewhat OT example of what we're talking about, this study [13] described here [14] found walking 1.6km requires less energy then running that distance. Nil Einne (talk) 14:45, 14 October 2010 (UTC)

In terms of energy expenditure, cycling lies between walking and running -- where it lies depends on how fast you are riding. On a good road bike, cycling at 12 mph on flat ground, with no wind, is hardly more effort than walking at a brisk pace; cycling at 18 mph is equivalent to running at a modest pace; cycling at 20 mph is equivalent to a pretty fast run. Looie496 (talk) 16:32, 14 October 2010 (UTC)

True, but cycling requires least energy for a given distance. This article might be of interest for the comparison between walking and running from a mechanical viewpoint. It supports my claim that walking is the least efficient activity, but that is from the physics of the actions. Physiological factors will probably change the balance, and might vary depending on the fitness and running style of the individual. Dbfirs 16:42, 14 October 2010 (UTC)

Cycling usually allows more distance to be covered and therefore more total energy expenditure, while running would generally use more energy than either walking or cycling. Cycling uphill on a wet muddy gravelly road would use up far more energy than cruising down a steep hill that has a smooth paved surface on a bike for the same distance. ~AH1^(TCU) 01:42, 15 October 2010 (UTC)

N-Acetylglucosamine as a protein ligand

These are pretty common ligands for a lot of proteins listed in PDB, especially membrane receptors. Is N-acetylglucosamine used to help induce crystallisation? John Riemann Soong (talk) 11:06, 14 October 2010 (UTC)

N-acetylglucosamine is a common component of eukaryotic glycosylation, both for N-linked glycosylation an O-linked glycosylation. Cell surface proteins, particularly receptors, tend to be heavily glycosylated. Have you checked if the proteins you thinking of have N-acetylglucosamine as a ligand (non-covalently bound) rather than as a covalent modification? (Most covalent modifications of proteins show up as "ligands" in the PDB files, due to limits of the PDB format.) -- 140.142.20.229 (talk) 23:33, 14 October 2010 (UTC)

Magnesium flame test

Do magnesium compounds really produce a white flame when it is heated? I heated magnesium oxide, magnesium hydroxide, and magnesium sulfate and none of them made a white flame. They made no flame and didn't even glow red-hot. --Chemicalinterest (talk) 13:53, 14 October 2010 (UTC)

No. Magnesium metal burns with a bright white flame, but the oxide is just too stable for the compounds to give the same flame colour. Physchim62 (talk) 14:48, 14 October 2010 (UTC)

Everlasting interest in flame tests

The magnesium oxide you used is also sold as pressed thin sticks to hold them into a flame for flame spectroscopy. This material is a good choice, because it gives no colour when heated and is extremely temperature stable. Platinum is the better alternative, but it is more expensive and for most test magnesia is good enough. --Stone (talk) 18:16, 14 October 2010 (UTC)

Would carbon work well in a flame test? I recall that it only makes a small flame, similar to copper, and it is unreactive. --Chemicalinterest (talk) 19:11, 14 October 2010 (UTC)

Pure carbon is to extent already much oxidised; plus it's polyaromatic, making it already quite stable. (It's a powerful testament to the carbocation as a Lewis acid...) When you burn hydrocarbons most of the released energy comes from formation of H2O...the stability of CO2 simply compensates for the loss of C-H bonds. John Riemann Soong (talk) 19:54, 14 October 2010 (UTC)

Pure carbon oxidized? Isn't it just rows and layers of graphene, carbon? --Chemicalinterest (talk) 00:26, 15 October 2010 (UTC)

My point of reference was hydrocarbons, sorry! It's C-H bonds that supply most of the energy in a combustion reaction. Carbon dioxide, because of its very electropositive carbon, as you know is a decent Lewis acid -- compare the enthalpies of formation of methane + carbon dioxide (-18 kJ/mol + -393 kJ/mol) versus acetic acid (-490+ kJ/mol). Clearly it's more thermodynamically stable for the carbon dioxide to be reduced to carboxylate by methane (methane gets oxidised by creation of a C-C bond and loss of a C-H bond). To an extent, the second oxygen already has trouble getting electron density out of that carbon, which is why the bond is polar covalent and not say, ionic. John Riemann Soong (talk) 00:50, 15 October 2010 (UTC)

This brings up an interesting question. How vulnerable would magnesium metal-frame buildings be to fire and corrosion by rain water? What if piping surrounded the building and natural gas filled the pipes? ~AH1^(TCU) 01:37, 15 October 2010 (UTC)

This probably isn't a worry as long as magnesium oxide coating survives (though in a fire this might be an issue). John Riemann Soong (talk) 04:51, 15 October 2010 (UTC)

Chilean miners' dental problems

I understand why skin problems and lung problems have been prevalent during the miners' months underground in 30 degrees (C) temperatures and high humidity, but many reports have mentioned dental problems, too. Two of the miners required immediate dental surgery for abcesses upon rescue. I/we could speculate on everything from poor dental health from the start, through poor nutrition during the ordeal, through poor hygiene (before and during). Can anyone locate hard information on the source being any of the above list or, like the skin and lung problems, a consequence of the underground air and temperature? Thanks from User:Bielle writing from the lobby of a hotel in Ottawa. 207.219.128.198 (talk) 14:57, 14 October 2010 (UTC)

Professor Francis Hughes (a Professor of Periodontology from Kings College, London) speaking right now on the BBC's PM programme says this is a well-known condition: severe gingivitis known as "trench mouth" (because it was seen in WWI), and ascribes it to poor dental hygene (they couldn't brush for a long time), malnutritition (there was a long time before food could be sent to them), vitamin D deficiency (because of so long without sunlight) and stress (which he said was a major and well-recognised factor for oral abscesses in circumstances like these). -- Finlay McWalter ☻ Talk 16:20, 14 October 2010 (UTC)

The relevant article appears to be Acute necrotizing ulcerative gingivitis, but I'm eating so I'm too squeamish to read it (lest there be scary photos). -- Finlay McWalter ☻ Talk 16:31, 14 October 2010 (UTC)

It's safe to look - no photos! AndrewWTaylor (talk) 17:04, 14 October 2010 (UTC)

If it's so common I wonder why they didn't send down toothbrushes and UV flashlights. --Sean 16:57, 14 October 2010 (UTC)

I remember reading about toothbrushes when they lowered the first pail lowered down the little borehole, and I'm pretty sure they sent vitamins also. I've seen discussion about whether the form of vitamin D in multivitamins is satisfactory to replace for sunlight or good food, but never came to a conclusion about it. Though I have no evidence at all, I wouldn't rule out that there could be some other photochemical reaction in the skin that is not yet known to science... Oh, and also, melatonin has an effect on the immune system; though the article describes it as positive, sometimes the effects of inflammation are regarded as damaging, and also there tend to be trade-offs in the immune system where stimulating one response may hinder another. Wnt (talk) 17:54, 14 October 2010 (UTC)

I speculate that there may also be damage arising out of a 70 day coating of abrasive dust, combined with the miners grinding their teeth due to the stress. --Tagishsimon (talk) 18:00, 14 October 2010 (UTC)

I would suspect stress as they did have access to dental hygiene and their diet was maintained at 2,000 kcal/day. PЄTЄRS J VЄСRUМВА ►TALK 18:12, 14 October 2010 (UTC)

After the first 17 days that is. Before that, they had like 3 cans of tuna for all 33 of them. Googlemeister (talk)

The first dental problems were beng mentioned in early September, so my speculation is that they were an aggravation of pre-existing conditions rather than something completely new. So some of the miners had less-than-perfect teeth to start with, and these problems got worse (for the reasons described above) to the point of being really troublesome. Physchim62 (talk) 01:46, 15 October 2010 (UTC)

While I don't wish to shut down any other explanations or references, I do want to thank those who have already replied. I have learned a lot. 207.219.128.198 (talk) 19:18, 15 October 2010 (UTC)

Semi-terrestrial octopuses/octopi/octopodes...

Just been reading the Pacific Northwest tree octopus (which is a hoax) article and it brought to mind video footage I've seen of octopi (or whatever) actually moving reasonable distances across land, say to escape from an isolated pool in which they have become trapped when the water receded. Which species in particular have this ability? --Kurt Shaped Box (talk) 18:14, 14 October 2010 (UTC)

This thread on the topic mentions several species. --Sean 18:25, 14 October 2010 (UTC)

Also look at tidal pool. ~AH1^(TCU) 01:32, 15 October 2010 (UTC)

How does this levitation magnet system's feedback system likely work?

This one: http://www.crealev.com/wp-content/uploads/A4_CLM_2.pdf Thanks 20.137.18.50 (talk) 18:43, 14 October 2010 (UTC)

The literature notes optical sensors; I guess these feed positional information to a controller which varies the strength (or duration) of each one of a set of electromagnets in the base unit. --Tagishsimon (talk) 21:22, 14 October 2010 (UTC)

A single electromagnet could suffice if its core is shaped to give a suitable shape of external field. The reference does not specify the stability of the levitation height so it is worth noting that one could obtain a similar levitation without feedback, or even without electric power if permanent magnets are used. The levitation height would then decrease with load. Cuddlyable3 (talk) 09:57, 15 October 2010 (UTC)

No it can not be done with permanent magnets only see Earnshaw's theorem and Magnetic levitation. --Gr8xoz (talk) 11:16, 15 October 2010 (UTC)

There are several exceptions to Earnshaw's theorem that allow magnetic levitation, such as when the levitated material is diamagnetic. (The system in the reference may not be rotationally stable.) Cuddlyable3 (talk) 13:12, 15 October 2010 (UTC)

If diamagnetic materials are used then the levitation is not done with permanent magnets only. Diamagnetic effects are very small except for cryogenic superconducting materials so it is very unlikely that it would be able to lift 10 kg with permanent magnets and diamagnetic effects. Of curse it need to be 'rotationally' stable, in order to levitate it can not tip over so it need to be stable around two axes. The rotation around the vertical axis need to either have zero moment at all angles (It is on the stability limit) or it need to have both positive and negative moments over a turn in order to conserve the energy, and in that case there must be an angle of rotation that gives rotational stability. --Gr8xoz (talk) 14:17, 15 October 2010 (UTC)

Horse Chestnuts, leaf miner and bleeding canker

I have just seen a BBC nature program implying (contrary to what I have previously read) that the leaf miner affecting most British horse chestnuts is responsible for materially weakening the tree leading to infection with the fatal "bleeding canker". Is there any more authoritative source on this link? It matters because I have a number of red-flowered horse chestnuts which appear immune to the leaf miner and I need to guess whether that species is vulnerable to the bleeding canker or not; to decide whether to plant them as a replacement for the white flowered horse chestnuts which are dying. None of the reds have any sign of canker or a single leaf mined. --BozMo talk 21:28, 14 October 2010 (UTC)

We have an article on the Horse-chestnut leaf miner. You may be able to find some information there. --Jayron32 22:23, 14 October 2010 (UTC)

Personal research, but I am not convinced these trees are dying. The problem is in the leaves and infestation does not start until the leaves are mature. The browning occurs from midsummer and worsens into autumn thus giving the tree a significant amount of time to 'thrive' before the leaves are affected. The leaves then drop off and the horse chestnut miner with them. The trees I have examined do not not have any sign of 'canker' and the size of the 'conkers' do not indicate a problem in the plants ability to produce seed. This problem does not bear any comparison with the Dutch Elm disease of decades ago. Essex County council are not too concerned at present[15]My opinion is the BBC Autumnwatch were being a bit over the top about the fate (or success) of the horse chestnut trees. Richard Avery (talk) 07:28, 15 October 2010 (UTC)

There was a discussion on this a few weeks ago. Alansplodge (talk) 08:43, 15 October 2010 (UTC)

Odds of discovery of Pioneer plaque by an ET

Of the two 'messages to ET' sent out, the Pioneer plaque and Voyager Golden Record (were there others?) what are the odds that either one of these would be discovered by an extra-terrestrial intelligence? And what is the most likely way it would be discovered? ie. is it most likely that the probe would by chance crash into a planet? or is it more likely that it would it be found floating in space by a space ship? or will it just continue 'voyaging' for millions of years never hitting another another cosmic object? -- œ^™ 21:39, 14 October 2010 (UTC)

Voyagers are now in their "interstellar" mission phase. "In about 40,000 years, Voyager 1 will drift within 1.6 light years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis. In some 296,000 years, Voyager 2 will pass 4.3 light years (25 trillion miles) from Sirius, the brightest star in the sky." You can read about SETI and the Drake Equation to inform your speculations about the probabilities of encountering intelligent life in the universe: "unlikely" sounds like a reasonable prediction for a "face-to-face" or orbital-rendezvous encounter between Voyager and some life-form. For perspective, imagine if a small extra-terrestrial craft passed 1.6 light-years from Earth - its RADAR and optical cross-section would be essentially zero; its presence would be transient; and if it happened to pass in, and then out, of range even just 300 years (or heck, even one second) too early, intelligent species who were actively looking for it might not be operating the technology for a deep sky survey to find it. So, it's most probable that Voyagers and Pioneers will drift indefinitely, probably for millions or billions of years, before their materials degrade beyond recognition as a "technological object". Nimur (talk) 22:12, 14 October 2010 (UTC)

Or the Americans go collect them in a couple of hundred years and put them on public display in the National Air and Space Museum. --Kurt Shaped Box (talk) 22:26, 14 October 2010 (UTC)

Have you estimated the date of launching a US salvage mission and the accelerations necessary to achieve that collection. Would this be a manned vehicle? Cuddlyable3 (talk) 09:43, 15 October 2010 (UTC)

(after edit conflict.)

Tough to say. For all we know we might recover Voyager and Pioneer some day and put them in a museum. If space travel that is even remotely cheap is invented, all those old probes will probably be tracked down by treasure hunters. While still a bit far fetched, to me that seems far more likely than an ET recovering them. Sure they're moving away from us, but at least we know where to look for them.

Active SETI projects have beamed messages to (potential) aliens. They probably have a higher chance of being noticed, but still quite low. APL (talk) 22:35, 14 October 2010 (UTC)

Not factored into the above estimates are the probability that some kind of space faring alien civilization has advanced means of differentiating between space junk over long distances. "Say there, Rhsdfndfpop, the super-duper-long-range-asteroid-tracker (SUDULORAST) has found something that looks extraterrestrial in origin out there near Sirius. Send our probe out there at warp 400 and pick it up." Could happen. Impossible to really say how likely it is — we simply lack sufficient data to make a very good "likely" judgment. I think we could say that an alien with current Earth knowledge, or even Earth knowledge extrapolated for 100 years or so, has essentially zero chance of finding it. But if we allow for not-totally-prohibited-by-physics possibilities, it might be more feasible, if there is some kind of "search and find" possibility. I say this though as someone who reads the Drake equation very pessimistically when it comes to the possibility of human-ET contact. --Mr.98 (talk) 22:41, 14 October 2010 (UTC)

Unless they have some new kind of physics for detection, we can actually say that can't happen. The diffraction limit pretty much rules out any possibility of this, unless they have planet sized detectors, but worse is that within a hundred years or so the probes will not be radiating anything, and they will be basically invisible. Ariel. (talk) 23:59, 14 October 2010 (UTC)

There are still the unknown possibilities that they have cleverly thought of a way to use physics as we understand it to build a SUDULORAST, or that physics as we understand it is merely approximation of reality and the difference allows the possibility of a SUDULORAST.

The first is pretty unlikely, but we can't rule out the possibility that alien ways of thinking and alien ways of doing things make certain solutions far more likely to be discovered than our human way of thinking does.

The second is even more complicated. Physics as we know it almost certainly is an approximation for something else, but what? There's simply no way to guess without actually discovering it. Two hundred years ago no one could have sat around pondering the probability that one day special relativity would be discovered by an alien race. APL (talk) 00:51, 15 October 2010 (UTC)

Who is ruling out planet-sized detectors? These guys are aliens! Maybe they're into that kind of thing. Maybe they got clobbered once with an asteroid a long time ago and decided that they'd take the nearest rock planet and coat it with nanobots who could magically terraform the whole thing using only solar power and naturally occurring methane and self-organize into a planet-sized detector. --Mr.98 (talk) 01:28, 15 October 2010 (UTC)

Nobody is ruling them out. In fact reputable peer-reviewed journals have published papers suggesting that we should keep an active watch for astrophysical evidence of planetary-sized and solar-system-sized construction activity by advanced civilizations: Search for Artificial Stellar Sources of Infrared Radiation was published in the journal Science, and Communications from Superior Galactic Communities was published in Nature. Nimur (talk) 02:44, 15 October 2010 (UTC)

I guess the least unlikely scenario is that ET monitors Earth and discovers from us that we sent them. Maybe they are already in ET's Earth museum or on the way and we are only receiving fake signals from ET's replacement. PrimeHunter (talk) 05:01, 15 October 2010 (UTC)

Based on NASA tracking data to the point the signal is finally lost, the trajectory through interstellar space might be well defined enough that alien civilizations monitoring our computer networks now or in the future might send out a craft to retrieve Earth's first two interstellar probes and return them to us after they reveal their existence. Or maybe they monitored the launch and tracked it with their superior systems. When a baby drops his rattle, an adult may similarly say "Uh oh, dwopped it!" and hand it back to the baby. Edison (talk) 05:23, 15 October 2010 (UTC)

The Arecibo message was a putative message to aliens transmitted in 1974. Nobody is holding their breath expecting a reply soon. Cuddlyable3 (talk) 09:47, 15 October 2010 (UTC)

First, we assess the probability that there are extraterrestrial civilizations in the vicinity. If we believe that our civilization has a good chance to survive and grow, so should we assume that a significant proportion of the extraterrestrial civilizations do too. With the current increase in our energy consumption, 3% per year, we will use much of the sun's total output in 1000 years. (Not just the part that hits the earth but the whole power of 3.846 × 10 ^ 26 W) The long-wave infrared radiation which we will emit will make us easy to detect.

In order to continue to grow as a civilization, we must either increase the solar power or colonize other stars. It is reasonable to assume that it takes less than 100 milijoner years to colonize most of the galaxy. (Travel by about 0.1% of the speed of light) Long before this the civilization should be very easy to detect. Civilizations like ours has been able to evolve in at least the past 2 billion years. Given that we have still not seen any signs of extraterrestrial civilizations in either the Milky Way or in other galaxies this suggests that they are very rare. I would guess on between one civilization in the observable universe to a few small isolated civilizations in each galaxy.

Pioneer plaque and Voyager Golden Record will with very high probability continue their journey in millions of years unless we retrieve them before then, the question is what will happen to them for billions of years. It seems unlikely that they will be detected over interstellar or intergalactic distances, although it is difficult to predict the detection ability of extraterrestrial civilizations. They will only go near (<100 AU, 0.00158 light yers), a few stars (less than one star per billion years.). The probability that these have civilizations is very low. A civilization must be much more advanced than ours to detect that they are artificial at interplanetary distances. The probability that they fall down on an inhabited planet must be close to zero. The greatest likelihood that they will be found by extraterrestrial civilizations is probably that they get information from us about where to look by radio or otherwise.

A civilization that colonizes a large part of the galaxy would have a reasonable chance of finding them but because we do not see such civilisations in other galaxies, it seems unlikely that any other civilizations than our will colonize the Milky Way. It is very unlikley that the probes will be found by planetary civilizations like ours whithout information of where to look. I would put odsen higher than one to 100 billion. With extraterrestrial civilizations, I mean civilizations that arose independently of life on Earth. Relevant articles are Fermi paradox, the Drake equation and Dyson swarm. --Gr8xoz (talk) 13:53, 15 October 2010 (UTC)

Not to be rude, but just because our civilization is currently expanding our energy usage by 3% a year does not make it statistically significant. You have a sample size of 1. Googlemeister (talk) 18:57, 15 October 2010 (UTC)

For the relevant discussion of this energy-growth, see our article on the Kardashev scale. Any discussion of SETI is limited by our "sample size", but we also know some things about basic mechanics and energy. It has been brought up in many SETI contexts that our definitions for "life" and "intelligence" are just subsets of generalized energy transfer/transformation processes. If our Voyager probe were to encounter a dense hydrogen cloud, some billion years in the future, in an unlikely region of space, could we safely say it has encountered a "natural phenomenon" as opposed to some intelligent natural process? Exactly how sophisticated does a dense accumulation of atoms need to be before we consider some portion of it "intelligent"? It is fair to say that in our conventional wisdom, some portion of those atoms need to be undergoing stellar fusion, and some other portion of those atoms need to be harnessing the energy that stellar fusion converted into electromagnetic radiation, and repackaging it as complex chemicals; and some other portion of those atoms need to be eating those chemicals so that they can re-invent stellar fusion without obliterating themselves. (We call the last group of atoms intelligent until they obliterate themselves). If those criteria are sufficient for intelligent life, any sufficiently dense blob of hydrogen might qualify as intelligent life, depending on conditions. Nimur (talk) 19:37, 15 October 2010 (UTC)

Thank you all for the excellent answers, I am satisfied. I'm left fascinated with the thought of these spacecraft, if not recovered by us sometime in the future, continuing on travelling indefinately through space, not encountering any other object because of the vast distances between the stars. Yet knowing this scientists still held out enough hope to place these ET messages on them. I can only hope this optimism grows with time. -- œ^™ 02:49, 16 October 2010 (UTC)

October 15

how do you define time ?

time is something which is going on is what I understand......... then

• 1)what happened at time = minus infinity ?( I cannot imagine time running to minus infinity)
• 2)or there is a starting point to time ?
• which theory help me to understand about time ?????????? —Preceding unsigned comment added by Sridhargunnam (talk • contribs) 04:28, 15 October 2010 (UTC)

Time is NOT an easy thing to think about, and it gets harder to think about the more you know about it. The fictional work Einstein's Dreams is actually a pretty good lay-person's primer to the problem of time. A Wikipedia articles you may want to read would be Arrow of time. The starting point of time is the Big Bang. The concept of time running backwards, as a serious discussion in modern physics, is discussed at T-symmetry, and on physical concepts which display both time symmetry (i.e. they are equally valid if experienced bot forward and backwards in time) and time asymmetry (i.e. they only work in a world where time moves forward). One common definition of time (alluded to in the Arrow of Time article cited above) is the idea of the relationship between time and the Second law of thermodynamics, aka Entropy. --Jayron32 05:06, 15 October 2010 (UTC)

Wikipedia has an article about Time. It has been joked that "time is only there to stop everything happening at once". Historical time measurements are based on astronomical observations e.g. 1 year = time for Earth to complete an orbit of the Sun. Apart from the unproven hypothesis of a Big Bang or creation event, we have no access to an absolute time reference, so "negative" time is meaningful only when understood relative to a reference event. (An estimated birth date of Jesus is conventionally used as a zero time reference between negative years BC (Before Christ) and positive years AD (Anno Domine - "year of the Lord"). For example, this year is AD 2010. Modern precise time measurements are based on Rubidium or Caesium atomic standards. There is no infinite time, see Ultimate fate of the universe, although in mathematics a Periodic function of time e.g. y = sin(t) where t=time implicitly extends from t = minus infinity to plus infinity. Cuddlyable3 (talk) 09:36, 15 October 2010 (UTC)

There isn't a shred of evidence that "time" exists at all. The known laws of physics can be reformulated in a manifest timeless way. Julian Barbour shows here how to do this for classical physics. Count Iblis (talk) 14:54, 15 October 2010 (UTC)

I think it's worth noting that Barbour's approach is pretty controversial and certainly not commonly held. --Mr.98 (talk) 21:32, 15 October 2010 (UTC)

Time at the exact instant of the Big Bang would be zero, so to use "negative time" in this context makes assumptions about what (or who?) actually created the Big Bang. We are getting into multiverses, or possibly brane theory, but another theory is that the big crunch of a different universe created this one (and the events in that universe are in negative time). See also fourth dimension and retrocausality. ~AH1^(TCU) 00:58, 16 October 2010 (UTC)

memory storage devices

we heard of TTL and CMOS memory in electronics.......... taking full charge on capacitor ......as high n zero charge as low, can we have capacitor memory ? if not what are the drawbacks ????? —Preceding unsigned comment added by Sridhargunnam (talk • contribs) 04:44, 15 October 2010 (UTC)

Yes, certainly. The main drawback is that capacitors can't be made as small as transistors, as I understand it. Looie496 (talk) 05:19, 15 October 2010 (UTC)

Yes indeed. This is how DRAM memory chips work. It is likely that you have several of them in a PC that you are using. The disadvantages of DRAM are that their content must be periodically refreshed by reading and re-writing, and that their content is lost when power is turned off. Accepting that DRAM is "volatile" memeory, they are one of the cheapest memory types in terms of cost per storage bit. The capacitive storage elements in DRAM take less space than the transistors in SRAM non-volatile memory, which makes it possible to build chips with higher density. The cited article gives the interesting history of DRAM development. Cuddlyable3 (talk) 09:02, 15 October 2010 (UTC)

how to explain the oxidation of ethers to esters with calcium hypochlorite? (and a question about activated C-H bonds)

A C-H bond would never show up as red on an electron density diagram would it? I've been trying to come up with a mechanism for this reaction -- obviously hemiacetals can be easily oxidised to esters but it seems to me that maybe the ethoxy oxygen has to react with some sort of electrophilic catalyst first.

(In one reaction, this was done in a mixture of 3:2 acetic acid and acetonitrile, resulting in 58% yield for the ester.)

C-H bonds almost never attack nucleophilically correct (that is, with a strong polar character)? They usually have to undergo some sort of fluid hydride shift. I'm thinking the hypochlorous acid displaces an ethoxy oxygen (which may be bound to calcium or acetonitrile or something) via SN2, allowing a hydride shift to occur. The ethoxy oxygen is eventually released from its catalyst and reforms the previous C-O bond. (This works better with cylic ethers). John Riemann Soong (talk) 04:57, 15 October 2010 (UTC)

Upper limit on speeds

say two objects are initialy at rest with respect to each other. I accelerate one of them(object1) towards the other to 50% the speed of light. would it now take infinite energy to accelerate object2 to 50% the speed of light towards object1?

If so why wouldn't it take infinite energy to accelerate object1 to 50% of light speed when object2 was at rest? --Diwakark86 (talk) 11:33, 15 October 2010 (UTC)

No, it wouldn't. You seem to be under the impression that if A is moving to the right at 50% of the speed of light, and B is moving to the left at 50% of the speed of light (both measured in some external frame) then the speed of B relative to A will be 100% of the speed of light. This is not the case. Algebraist 11:58, 15 October 2010 (UTC)

Or simply put another way, when you add velocities relativistically (that accounts for special relativity), you use a different formula than you do when you add them non-relativistically (Galilean velocities). If you use the relativistic formulae you only get up to .799c with your example, not 1c. You can bump your objects up to 99% the speed of light and you still won't get a relative velocity that is 1c or above. --Mr.98 (talk) 12:23, 15 October 2010 (UTC)

Why give the approximation 0.799c as opposed to the exact value 0.8c? -- 119.31.121.84 (talk) 23:38, 15 October 2010 (UTC)

When two objects are moving at each other under the speed of light, the energy required to move either one is not infinite and neither is the combined energy required. Photons and other particles (some having mass) already move at light speed but do not require nor contain infinite energy. ~AH1^(TCU) 00:47, 16 October 2010 (UTC)

Which particles with non-zero rest mass can move at the speed of light? I thought that only luxons were capable of light-speed. Dbfirs 07:48, 16 October 2010 (UTC)

I think only objects with zero rest mass can move at the speed of light. But of curse photons and other "mass-less" particles has a relativistic mass due to its energy. At the speed of light the relativistic mass is infinity times rest mass but infinity times zero are undefined so this does not tell us the mass of a photon. --Gr8xoz (talk) 10:05, 16 October 2010 (UTC)

Yes, that's my understanding, too, but I wondered if AstroHurricane had discovered some new particle. Of course, particles with mass are being accelerated to within a hundredth of one percent of the speed of light in accelerators. Dbfirs 22:05, 16 October 2010 (UTC)

reversible oxidation of a USB plug?

I have an iHome HM60 -- a portable speaker, and there's a mini-USB cable between the 3.5 mm auxiliary jack and the speaker (there's also a regular USB cable for charging). Yesterday I played it in the rain -- with no problems -- it just kept on playing. I let it dry, studied for a few hours, started up the speaker again -- no issue.

Then hours later it ceased to work -- then I noticed the mini-USB plug was grey'ish and somewhat rough and it look corroded. It wouldn't work for hours. And it was basically charged.

So I don't know what I did -- I just let it charge for a few hours (but the charge lasts for 40 hours so I know it isn't that), and then hours later, it worked again. (Sound is crystal clear.) I wonder if it's possible for water to cause reversible oxidation of a USB plug when consuming energy, which is reversed upon charging? John Riemann Soong (talk) 12:14, 15 October 2010 (UTC)

Here is a description of the iHM60 speaker and of various mini-USB connectors. If the connector is corroded I would expect this to show as a crackling sound when you wiggle the connector while playing music. If that is the case then there are electric contact cleaners such as Electrolube or Servisol that might help, but your best action may be to buy a new speaker and keep it out of the rain. It will sound just the same wrapped in a polythene bag. Cuddlyable3 (talk) 12:50, 15 October 2010 (UTC)

No crackling...I'm guessing it's not oxidation? I mean, it's gold-plated I think. But before the rain this never happened. I did keep it in my coat -- but the raindrops seeped in cuz I wanted a tiny aperture. John Riemann Soong (talk) 14:31, 15 October 2010 (UTC)

Link crashes

The first two English links in

http://en.wikipedia.org/wiki/John_Strutt,_3rd_Baron_Rayleigh#Bibliography

crash. (I don't spikka da frang, which further more is mysteriously organized)

83.226.97.246 (talk) 12:41, 15 October 2010 (UTC)

They seem to work ok for me.....?

you are talking these links, aren't you (?)

• The Theory of Sound vol. I (London : Macmillan, 1877, 1894) (alternative link: Bibliothèque Nationale de France
• The Theory of Sound vol.II (London : Macmillan, 1878, 1896) (alternative link: Bibliothèque Nationale de France)

Darigan (talk) 12:54, 15 October 2010 (UTC)

(ec)Assuming you mean the links to The Theory of Sound vols. I & II, they worked ok for me. The alternative French library links are to copies of the same book in English which should give you no difficulty. Cuddlyable3 (talk) 12:58, 15 October 2010 (UTC)

The links were called with Netscape 7.02 over MacOS 9.2.2. Is that the reason ? —Preceding unsigned comment added by Rolf.Evren (talk • contribs) 02:51, 16 October 2010 (UTC)

Sodium tellurate

Sodium tellurate

Does it exist? I was about to create an article on simple and found out that en didn't have an article on it! Thank you. --Chemicalinterest (talk) 13:13, 15 October 2010 (UTC)

It does appear to be a real compound, if that's what you mean by "exist":) 10101-83-4 (that takes you to a meta-search, whose specific entries seem to find some refs). Now whether it's notable enough to merit an en.wp article...dunno. DMacks (talk) 14:23, 15 October 2010 (UTC)

Sodium is one of the simplest (in terms of economy/pragmatics) counterions there is. How can you have an article on the generic tellurate ion and not on sodium tellurate? John Riemann Soong (talk) 14:32, 15 October 2010 (UTC)

Yes, I would think it is notable. Any binary chemical compound should be notable enough. --Chemicalinterest (talk) 14:33, 15 October 2010 (UTC)

At least if one of the counterions is cheap! I realise that "silver tellurate" or "gold(III) tellurate" may not be hot or whatever. John Riemann Soong (talk) 14:52, 15 October 2010 (UTC)

Yes, we should have an article on it. I'll run one up later unless someone beats me to it. Physchim62 (talk) 14:55, 15 October 2010 (UTC)

Cost doesn't matter. What matters is the presence of reliable sources discussing the topic. So a certain anion may be generally of scientific interest and literature publications, and/or one certain compound of it may be, and/or another certain compound, etc. If there's something scientifically special about the silver one, then it could have an article. If nobody cares to study the potassium one more than just stating it exists and reporting its physical/chemical properties, then maybe that one doesn't get an article. As years of deletion-discussions have said, "notability is not inherited" (the parts can be notable but the combination not, or vice versa). DMacks (talk) 16:32, 15 October 2010 (UTC)

User:Chemicalinterest/Sodium_tellurate. --Chemicalinterest (talk) 19:04, 15 October 2010 (UTC)

methane + CO2 --> acetic acid

By bond enthalpy at least, this reaction seems favourable (what is the loss of entropy due to two gas phases converting into a single liquid?) This seems a convenient way to tackle two greenhouse gases at the same time to give a useful feedstock...and methane seems fairly abundant. Are there any theoretical catalysts that could be worked on? I know there's a "catalyst" being worked on at my school that can convert methane to methanol...however there are issues with the catalyst (yield, turnover, recovery, etc.) that currently make it economically infeasible. John Riemann Soong (talk) 14:42, 15 October 2010 (UTC)

Google: methane CO2 "acetic acid": "about 650,000 results". About a quarter of the hits of the first few pages are about this reaction (theoretical and practical studies, journal articles and patents). DMacks (talk) 16:35, 15 October 2010 (UTC)

Why doesn't our article on acetic acid cover this route? John Riemann Soong (talk) 20:06, 15 October 2010 (UTC)

Because it's utterly irrelevant, inconsequential compared to the real-life routes of making acetic acid. Wikipedia prefers to deal in real chemistry, not pipe dreams and undergrad speculation. Physchim62 (talk) 20:11, 15 October 2010 (UTC)

Such a synthesis remains largely pedagogic, the reaction is not thermodynamically favored without a catalyst. There are relevant patents such as US 5659077 . Hope this helps.Smallman12q (talk) 21:09, 15 October 2010 (UTC)

Catalysts do not change the thermodynamics of a reaction, only its rate. This reaction is not thermodynamically favourable, either going to the liquid or the gas. The idea is irrelevant nonsense. Physchim62 (talk) 23:06, 15 October 2010 (UTC)

However, please do look at this previous question, discussing the decomposition properties of acetic acid. ~AH1^(TCU) 00:32, 16 October 2010 (UTC)

Thermodynamics question

1. Since, as I understand it, two litres of water at 50 degrees cannot be separated into one litre at 90 degrees and one litre at 10 degrees without some expenditure of energy, is there a sense in which the latter intrinsically contains more energy than the former? If so, how is this quantified?

2. If, in a sealed system, a liquid is allowed to evaporate, then have the hotter molecules spontaneously separated from the cooler molecules in apparent violation of the principle in (1)? If so, how is this explained? —Preceding unsigned comment added by 86.183.171.204 (talk) 17:49, 15 October 2010 (UTC)

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our policy here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

...perhaps you could take a shot at this first, state where you got stuck? Have you read about Entropy and Thermodynamic systems? -- Scray (talk) 18:19, 15 October 2010 (UTC)

This is not a homework question. The last time I did homework was approximately forty years ago. 86.183.171.204 (talk) 19:01, 15 October 2010 (UTC).

Question 1. Why does your air conditioner need electricity? It is separating an 80-degree intake into a 50-degree output and a 110-degree output which is vented outside. Molecules tend to have a uniform concentration of energy unless energy is added from an external source. I think this is the opposite of entropy, which is the decay of a structure. Separating the water would require the expenditure of energy to decrease entropy. Please correct me if I am wrong. --Chemicalinterest (talk) 19:07, 15 October 2010 (UTC)

Question one is a fundamental point in thermodynamics: the two systems contain the same amount of internal energy, but the system at 50 degrees has a greater entropy than the latter system. To lower the entropy of a system, you have to expend energy, but it goes into the surroundings, not the system itself. Physchim62 (talk) 19:22, 15 October 2010 (UTC)

(1) is true. The article on Carnot engine should even give you a precise value for the amount of energy which can be extracted from the 90 and 10 degree reservoirs, and the (larger) amount of energy that it would take to reverse the process.

(2) I assume you mean a liquid evaporating in vacuum, rather than in air (which you can see is a simple mixture, increasing entropy). Spontaneous phase separation (harrumph, there's an article in need...) is an interesting case, isn't it? But there's nothing about entropy that says that the chaos has to be homogenous - if there's not enough energy to keep all the molecules as a gas flying around free of noncovalent interactions, then some have to clump somehow. So as many molecules evaporate as the available energy allows, leaving energy randomly distributed between particles flying around as vapor and particles jiggling in a liquid, such that further random interactions tend to go either way as often as the other. Wnt (talk) 19:26, 15 October 2010 (UTC)

(1) I think Exergy could be interesting to you.--Gr8xoz (talk) 22:37, 15 October 2010 (UTC)

Should my neighbor's cat drink old milk?

Several years ago ...

(at this point one should fear for the cat's life)

... a jug of milk fell off my kitchen table and I didn't see it for several days. I was afraid of what it would smell like so I just put it outside, and for months I was afraid of what the smell would be like, so I never dumped it. I did notice the liquid changed color and got dark and clearer. But I never dumped it. Then the jug got broken and I caught my neighbor's cat drinking out of it. At that point I dumped it though I don't remember where. The cat is fine.Vchimpanzee · talk · contributions · 18:52, 15 October 2010 (UTC)

It's all a matter of what bacteria get into it. Good bacteria, you get cheese or yogurt. Bad bacteria, you get poison. But bad bacteria usually make it smell bad, and if it smells bad a cat won't touch it (unless starving). Looie496 (talk) 19:52, 15 October 2010 (UTC)

I'm curious as to what the liquid consisted of by this time. It wasn't white, but dark and sort of clear.Vchimpanzee · talk · contributions · 20:02, 15 October 2010 (UTC)

Perhaps a form of whey? See also Little Miss Muffet :-) . 87.81.230.195 (talk) 20:48, 15 October 2010 (UTC)

Take a look at curd. ~AH1^(TCU) 00:26, 16 October 2010 (UTC)

The weird thing is I never saw any curds. And the photo of whey was a different color entirely. Maybe it was a photo of a specific process but this was dark and almost clear.Vchimpanzee · talk · contributions · 15:43, 16 October 2010 (UTC)

Next Day Soup.

I don't know if the Science Desk is the best place to ask this but here goes. I am an Englishman living in Scotland these past 35 years and have always known that the Scots take their soup-making skills extremely seriously - and with some real justification. But I can't figure out why it is that the best soups made today always taste better tomorrow. I have just made a throw-everything-in-except-the-cat soup that tastes, well, you know, quite sharp/raw/bitter/rough, but I have every confidence that tomorrow, it will be hearty, tasty, zingy, zesty, warming, nourishing, moreish, and oh so smooth in the mouth-feel department. So exactly what is it that happens overnight to effect that transformation? Are there soup-fairies in Scotland or what? 92.30.9.83 (talk) 19:25, 15 October 2010 (UTC)

I would vote for very long time-constants for the substances in the solid ingredients to dissolve. So after a long time, you have saturated the broth with flavorful compounds from the meats, vegetables, and spices in the soup. See rate equation for quantitative analysis. Nimur (talk) 19:34, 15 October 2010 (UTC)

(EC) I am well familiar with the phenomenon you describe. I attribute it to diffusion. Take an example of potatoes in broth. After cooking, a certain amount of the flavorful compounds have permeated the potatoes, but the center will have less than the edges. After sitting for ~24 hours or more, the centers will have the same concentration as the edges, making them tastier. Note that you can't just boil the potatoes longer to get this effect, because that would break them down into mush. There are certainly other factors as well, but I think this is the main reason soup is better on the second day. What Nimur says above also makes sense.--SemanticMantis (talk) 19:39, 15 October 2010 (UTC)

I think oxidation also matters to some degree. When it cools a sits for a few hours, oxygen dissolves in it and reacts with some of the reactive chemicals that give it a sharp and bitter taste. Looie496 (talk) 19:54, 15 October 2010 (UTC)

Curry tastes better the next day too. Itsmejudith (talk) 23:21, 15 October 2010 (UTC)

It depends on what type of curry but I generally find that they mature over about a week, then last for about another three. Fish curries are less robust but a Rogan Josh or similar matures to it's best by about the ten day point, in the fridge.

ALR (talk) 16:06, 16 October 2010 (UTC)

It has a lot to do with gelatin. Gelatin is formed from collagen, a protein common in animal tissue. It has almost no flavor on its own, but it has a very pleasing mouthfeel, and its presence completely changes the eating experience. The reaction which turns insoluble collagen into soluble gelatin takes a very very long time. This is why grilled meat tastes so different than barbecued meat. If you have ever had a grilled pork chop, and also had good, slow-cooked pork barbecue, ostensibly the same meat, that soft, unctuous taste that barbecue has that a pork chop doesn't is due mostly to gelatin. It's why good barbecue takes upward of 10-12 hours to cook, while you can grill a porkchop in 15 minutes. It's the same deal with soup. When you cook soup, the cooking process extracts gelatin from the meats. However, this gelatin needs to partially polymerize (the smaller gelatin molecules need to aggregate and crosslink) in order to provide the "gelatin" effect. This only happens over time, so that freshly cooked soup doesn't taste as good as the soup overnight, which has had the time to form proper gelatin. --Jayron32 03:30, 16 October 2010 (UTC)

In my experience (WP:OR!) this happens with vegetarian chili, too. The texture pretty much stays the same, I think, but the taste is much ... uh, deliciouser after a night or two in the fridge. Paul (Stansifer) 04:59, 16 October 2010 (UTC)

While, strictly speaking, gelatin has to come from animal sources, there are plant analogs, especially in stuff like beans and okra, known as mucilage. Additionally, there is Starch gelatinization. If left overnight, you can get Retrogradation (starch), which is why starch soups and sauces "set up" overnight (i.e. form into a pudding-like texture). --Jayron32 05:05, 16 October 2010 (UTC)

is there such a thing as "mild chlorine poisoning"?

Normally when bleach is sprayed on say, a decaying pot full of maggots and organic acids, how much chlorine is released (order of magnitude)?

Not a request for medical advice -- take the most general case. John Riemann Soong (talk) 23:12, 15 October 2010 (UTC)

There was an earlier debate over whether the acids produced chlorine and in my experience they do not in any amount more than bleach reverses its production reaction NaClO + NaCl + H₂O → NaOH + Cl₂ although this reaction is encouraged with acids. If it is producing too much chlorine, cover it with ascorbic acid crystals--they seem to reduce the chlorine to chloride and hence get rid of the odor. --Chemicalinterest (talk) 10:07, 16 October 2010 (UTC)

I think you've missed the point. By the time you realised it's 'producing too much chlorine'. It may be too late. Also covering it with ascorbic acid crystals seems an exceptional bad idea. Far better to ventilate the area and stay well away until the reaction has died down. Nil Einne (talk) 10:40, 16 October 2010 (UTC)

I would like to ask why, other than the expense, covering the mixture of foods with ascorbic acid is a bad idea?

And yes, keep it ventilated. Chlorine can collect in low places. Ascorbic acid will neutralize some of the chlorine that comes into contact with it, provided there is some water available for the reaction to occur in. BTW, mild chlorine poisoning may be a horrible smell in your nose that makes you a little bit sick. --Chemicalinterest (talk) 13:25, 16 October 2010 (UTC)

The first thing you do when confronted with an uncontrolled release of toxic gas in a confined area is get out! You don't stand around trying to control the release, unless you happen to be wearing self-contained breathing apparatus at the time. Or, rather, natural selection means that there are very few chemists who stand around trying to control the release, and they don't do it a second time. Physchim62 (talk) 13:54, 16 October 2010 (UTC)

That green air looks pretty! --Chemicalinterest (talk) 15:54, 16 October 2010 (UTC)

Mmm--almonds! But wait, did someone just spread hay around here? DMacks (talk) 17:28, 16 October 2010 (UTC)

Hehe! You laugh, but I've had to deal with the situation of a student in an undergrad class who calls me over to say "I don't feel very well, and I've just been doing the experiment with cyanide..."! She was fine – she had very mild gastroenteritis, not mild cyanide poisoning – but I'll be perfectly happy if I never have to face that again in my career! Physchim62 (talk) 19:57, 16 October 2010 (UTC)

How does matter fall into a black hole?

My very basic understanding about black holes is this: Anything falling into a black hole takes an infinite time to pass the event horizon to an external observer. If that's the case how do supermassive black holes form? i.e. how can we have supermassive black holes when it takes an infinite amount of time for them to form? I'm sure there's already an answer on wiki or google somewhere but I must be using the wrong search terms. I found this but it made no sense to me. Tx in advance Spoonfulsofsheep (talk) 23:59, 15 October 2010 (UTC)

According to the article, light from a distance just outside the black hole's event horizon reaches the external observer very slowly, taking perhaps millions of years because the light takes that long to fight against the gravity of the event horizon. Past the event horizon, light cannot escape. Similarly, the outside observer sees the initial collapsing matter go into making a black hole, but only when it is outside the event horizon. When the material passes the event horizon, light from that area takes infinitely long to reach the observer. Therefore, from the observer's vantage point, the initial formation of the black hole takes very long for the matter just outside the event horizon but takes an infinite amount of time for the actual black hole to "form" according to the observer. Matter far from the event horizon takes a near-normal amount of time to reach the observer, but the light takes longer to reach you the closer to the event horizon it is. There are also theories such as Varying speed of light that make this even more complicated, and according to the VSL theory matter at the event horizon never escapes the black hole but never enters it. ~AH1^(TCU) 00:21, 16 October 2010 (UTC)

Thanks for the comprehensive answer but now my head hurts! I still don't really understand after reading your reply many times, I'll read the article again and see if that helps :-) Spoonfulsofsheep (talk) 00:51, 16 October 2010 (UTC)

You're welcome! ~AH1^(TCU) 02:13, 16 October 2010 (UTC)

Think of it in terms of reference frames. from the perspective of a far-away observer, it appears that it takes something a very, very long time to fall into a black hole. from the perspective of something falling into a black hole, it would appear to happen very, very fast indeed. It's hard to conceptualize, but with extremely strong gravitational fields the passage of time itself changes - someone falling into a black hole would experience an ordinary-seeming finite passage of time, but on Earth thousands or millions of years might pass while we watch the person fall. So, a black hole could accumulate a large amount of material very quickly from its reference frame; it's only from our reference frame that it seems impossibly slow.

It's a bit like going to an amusement park, actually. while you're standing on the ground waiting in line, the roller-coasters don't seem all that thrillingly fast. when you're sitting in one, the ride is over before you know it. Now just imagine that while you're on that 30-second ride, 4 hours pass in the rest of the park. --Ludwigs2 03:09, 16 October 2010 (UTC)

October 16

Wedge Constant:- newton laws of motion

please tell what is wedge constant and where and how to use it? —Preceding unsigned comment added by Alche stalwart (talk • contribs) 04:57, 16 October 2010 (UTC)

In what context did you find the wedge constant? I have not heard of it and a search on google mostly returns this question and your questions at answers.com and /www.physicsforums.com. I also found something called so in telescopes but no references to newton laws of motion. --Gr8xoz (talk) 09:48, 16 October 2010 (UTC)

Do you by any chance mean the wedge product (also known as an exterior product)? The wedge product does have applications in Newtonian mechanics. For example, see Geometric algebra#Torque for a presentation of torque in terms of a wedge product. However, in Newtonian mechanics, things are more commonly instead expressed in terms of the cross product, which is closely related to the wedge product. A cross product is the Hodge dual of the bivector formed by a wedge product; see Cross product#Cross product as an exterior product. Red Act (talk) 14:05, 16 October 2010 (UTC)

EDTA reaction

I did the following reaction in a lab with magnesium sulfate.

Is MgSO₄ + EDTA^4- → MgEDTA^2- a redox reaction?

Why does EDTA lose 4 electrons before the start of the reaction?--72.145.140.75 (talk) 16:15, 16 October 2010 (UTC)

I used 10 mL of a solution that my teacher called "EDTA buffer." What exactly is EDTA buffer? I used Calmagite for endpoint detection.--72.145.140.75 (talk) 16:17, 16 October 2010 (UTC)

The "EDTA solution" link in your web-link says that "EDTA has four protons", which is in agreement with our EDTA article's discsussion of it having four acidic groups. Your page gives a recipe for a buffer with pH 10, and our page talks about how "EDTA^4-" is the four-way-deprotonated form--that's all consistent with an alkaline solution containing EDTA in which the acids have been deprotonated. See the "Nomenclature" section of our article for the variations in these naming patterns. Note that if EDTA had lost 4 electrons it would be +4 not -4. DMacks (talk) 17:24, 16 October 2010 (UTC)

The page that I have linked to prescribes Eriochrome Black T to be used as pH indicator. I actually used Calmagite in the lab. Nobody told me what "EDTA buffer" was made up of. Is it possible that I used something other than ammonia buffer?--72.145.140.75 (talk) 17:30, 16 October 2010 (UTC)

It doesn't actually matter what else is in the "EDTA buffer", as long as there is EDTA and probably that it's got an alkaline pH in order to make sure the ETDA is in the highly deprotonated form. As you noted in the reaction, only the EDTA^4- actually participates in the titration (not the ammonia, or whatever else buffering agent was added)--one of the neat things about chemistry is that only a few details matter, and other variables might just be facts that do not alter the results you need (analogy: it doesn't matter what color coat you're wearing, they will all keep you warm the same way, and the presence of shoelaces vs velcro straps doesn't affect your coat at all). Likewise, it doesn't matter exactly what indicator you use, as long as it indicates the situation you need indicated in a noticeable way. Comparing our Eriochrome Black T and Calmagite pages, you can see they are both indicators of the same type of thing--changing color when complexed to certain types of ions. DMacks (talk) 17:57, 16 October 2010 (UTC)

aging and sensory capacity

It is commonly known that aging reduces one's visual and auditory capabilities. Is the same also true for other senses? For example, balance (part of the vestibular system)? That is, is there a general decline in sensory capacity with aging? --Halcatalyst (talk) 16:34, 16 October 2010 (UTC)

Hearing definitely declines with age, particularly with respect to higher pitches becoming harder and harder to hear. As for visual senses, I don't think acuity is affected more than it is earlier on when you get glasses etc. but I can be proved wrong on that! You are more prone to getting things like cataracts, though. I'm not aware of any growing defecit in other senses like taste, smell or touch but again I welcome suggestions. Regards, --—Cyclonenim | Chat  20:28, 16 October 2010 (UTC)

(OR warning) From my observations, I would conclude that other senses do deteriorate, but the effect often is less obvious. There is also an enormous variability in the deterioration. In some people it begins in "middle-age", whereas some 90-year-olds have sight and hearing that is still good. Perhaps someone can find some research on other senses? Dbfirs 21:57, 16 October 2010 (UTC)

Elliptical Orbit vs Circular Orbit problem

A satellite has an elliptical orbit at altitudes ranging from 230 km to 890 km. At the high point it's moving at 7.23 km/s.

I'm supposed to find the radius of a circular orbit in which the total orbital energy of the satellite is the same as for the elliptical orbit above.

I know that the total energy of a circular orbit is given as E=-GMm/2r and that the total energy of an elliptical orbit is given by E=GMm((1/r1)-(1/r2))

When I set those two equal, the GMm should cancel and leave me with r1-r2/-2=r r=330 km. That answer doesn't match the answer that I'm given, what am I doing wrong?199.94.68.201 (talk) 17:46, 16 October 2010 (UTC)

Are you sure that equation for an elliptical orbit is right? If you treat a circular orbit as a special case of an elliptical one, you get E=GMm((1/r)-(1/r)), which can't be right, surely. Our Specific orbital energy article gives the energy for an elliptical orbit to be -G(M+m)/2a where a is the semi-major axis. (Please note I know nothing about orbital mechanics) Rojomoke (talk) 18:48, 16 October 2010 (UTC)

I am also skeptical to the formula E=GMm((1/r1)-(1/r2)) for the same reason. I also note that you have done a alegebraic misstake,

GMm((1/r1)-(1/r2))=-GMm/(2*r) => 1/r1-1/r2=-1/2*1/r => r= -(1/2)/(1/r1-1/r2) => r=-(1/2)*r1*r2/(r2-r1) = 155 km.

This value satisfy the first equation.--Gr8xoz (talk) 19:43, 16 October 2010 (UTC)

-G(M+m)/(2a) gives the specific orbital energy, the orbital energy will be E=-G(M+m)*m/(2a) if the satelite has much less mass than the planet then you can use E=-GMm/(2a) and for a circular orbit a=r you get E=-GMm/(2r) --Gr8xoz (talk) 20:37, 16 October 2010 (UTC)

Train tracks and leaves

I saw a poster on the train today about when it's Autumn and the leaves fall, there's an effect where the high pressure between the rail and wheel creates a very slippery substance that means the trains have to travel slower and brake earlier in badly affected areas. Is there a name for this effect, and do we have an article on it? Regards, --—Cyclonenim | Chat  17:53, 16 October 2010 (UTC)

Slippery rail. -- Finlay McWalter ☻ Talk 17:54, 16 October 2010 (UTC)

Thanks, very quick! Regards, --—Cyclonenim | Chat  17:55, 16 October 2010 (UTC)

Shouldn't that be British Rail?92.30.154.94 (talk) 18:10, 16 October 2010 (UTC)

You're showing your age! Alansplodge (talk) 20:29, 16 October 2010 (UTC)

tunnel diode

what is tunnel diode —Preceding unsigned comment added by Omveer Singh Gurjar (talk • contribs) 19:51, 16 October 2010 (UTC)

Tunnel diode--Gr8xoz (talk) 20:21, 16 October 2010 (UTC)

Sapience

Is sapience something that all humans are innately born with, or is it something which must be achieved with the help of others? Can sapience be achieved by other species with enough effort and teaching? I'm thinking here of Alex the parrot. --95.148.105.245 (talk) 22:27, 16 October 2010 (UTC)

Nuclear Physics

"The advent of high energy ion colliders in Europe and North America caused a remarkable advance in Nuclear theory. New and surprising experimental results and exciting new theoretical insights and predictions are continuously being published while large number of puzzles still remain to be investigated. This is an exciting time to be a theoretical physicist."

Any truth to this? 74.15.136.172 (talk) 22:43, 16 October 2010 (UTC)