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Think that the moment of air from the poles to the equator (and the coriaceous effect) would mess up the calculations. On top of that, one should not fly due north/south because of the earth's rotation of about a thousand miles per hour and to ignore that, it would also mess up one's sums... one would have to fly at an angle to get a truer figure. Gravity at the poles is also less and the troposphere gets lower, thus the aircraft would require less fuel to stay in the air as it goes north, which is another factor to consider. Sorry, if I'm not answering your question.--] (]) 00:36, 23 January 2012 (UTC) | Think that the moment of air from the poles to the equator (and the coriaceous effect) would mess up the calculations. On top of that, one should not fly due north/south because of the earth's rotation of about a thousand miles per hour and to ignore that, it would also mess up one's sums... one would have to fly at an angle to get a truer figure. Gravity at the poles is also less and the troposphere gets lower, thus the aircraft would require less fuel to stay in the air as it goes north, which is another factor to consider. Sorry, if I'm not answering your question.--] (]) 00:36, 23 January 2012 (UTC) | ||
:The OP has asked a very sound question. The fuel required when traveling towards the poles is less than when traveling towards the equator. I imagine that for a wide-body passenger jet, the difference would amount to many hundreds of kilograms; possibly even a tonne. | |||
:Routine operations by airlines rely on standard tables to determine the amount of fuel to be carried at the time of take-off, so the flight crews don't need to concern themselves with this consideration. However, when an engine or aircraft manufacturer is carrying out fuel consumption tests, particularly tests to determine what guarantees of specific fuel consumption to offer, or to determine whether compensation should be paid to a customer, it is desirable to determine exactly where all the fuel went during a flight. For these tests, the engine or aircraft manufacturer will account for the amount of fuel consumed in going from the latitude of take-off to the latitude of the destination. ] ''(])'' 01:40, 23 January 2012 (UTC) | |||
== How "wrong" is string theory == | == How "wrong" is string theory == |
Revision as of 01:41, 23 January 2012
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January 16
Ice fossils
Can fossils be formed in ice? Whoop whoop pull up 02:29, 16 January 2012 (UTC)
- I don't think so, if by "fossils" you mean where the bone is replaced by minerals. That requires that the minerals be transported in by a liquid. Of course, an animal can be frozen as long as the ice remains, so that's even better than a fossil, but not likely to be as old. StuRat (talk) 02:36, 16 January 2012 (UTC)
- I meant ice as the minerals, not the medium. Whoop whoop pull up 18:28, 16 January 2012 (UTC)
- I don't understand. How can ice be minerals ? StuRat (talk) 22:53, 16 January 2012 (UTC)
- Maybe minerals embedded in the ice. Though I would think they are too diluted to do anything. ←Baseball Bugs carrots→ 00:51, 17 January 2012 (UTC)
- I think that water serves as the solvent for minerals that replace the structural details of a once-living organism in the process of fossilization. I would think that pure ice would not be able to contain the detail of fossils as normally understood. I think it may be theoretically possible to have impure water containing any type of contaminant participating in a variation on fossilization in which contaminants serve to record detail, and which would have to be maintained at a temperature that will keep it in its solid state. But that makes me consider yet another difficulty—how would molecules of water move into place in a fossilization process if they were frozen? Bus stop (talk) 01:16, 17 January 2012 (UTC)
- Maybe minerals embedded in the ice. Though I would think they are too diluted to do anything. ←Baseball Bugs carrots→ 00:51, 17 January 2012 (UTC)
- I don't understand. How can ice be minerals ? StuRat (talk) 22:53, 16 January 2012 (UTC)
- You mean permineralization, but with ice crystals instead of minerals filling in the spaces between tissue? In a way. Freezing is pretty much the same process as permineralization. The water is trapped within the tissues that then solidify. These can form casts. But they're quite useless aren't they? as the original tissue still exists anyway.
- Ice (and water) is too plastic and ephemeral. Global temperatures fluctuate too much. By the time the organic tissues begin to disappear for the ice cast to be of any value, the ice itself will have long rearranged themselves again or have gone.
- While you can technically have more macroscopic trace fossils preserved in ice (like a footprint), I doubt it would also last for more than a few years. You cant exactly overlay it with another "stratum" of ice and still expect it to be recognizable either.-- Obsidi♠n Soul 01:31, 17 January 2012 (UTC)
- Well, they can identify individual yearly layers in the ice, and count them to tell how old a given sample is. So, theoretically, they could also make out a footprint, but the problem is they wouldn't know to look for it. Perhaps if there was something that would reflect a signal between the layers, like a thin layer of ash from a volcano, the footprint might be a bit more visible. Also, in places where interesting footprints are expected, like by a cave entrance, the scientists might make the effort to search for them. StuRat (talk) 05:43, 17 January 2012 (UTC)
- True, but then you'd have to rely on more serendipitous factors as well. Like the ice having to maintain constant temperature - unlikely when talking in geochronological terms. They can't be buried too far or compacted - pressure = heat. While stratigraphic sequence is still preserved even after that, the trace fossil is not. They most likely wouldn't survive in interglacials as well. Not to mention collection problems. The only places where I can reasonably expect these criteria to be met is in space. If ever exopaleontology/exoarcheology become valid sciences, ice fossils would probably be common. On the other hand, if the ash falls on the footprint and then solidifies, that can theoretically make a perfectly recognizable trace fossil - a mold. Again with the stipulation that the ash wasn't warm in the first place.-- Obsidi♠n Soul 06:14, 17 January 2012 (UTC)
Information transfer Faster Than Light - DIY
Not a physicist, so maybe this is an old question, but I didn't find a good saerch query response.
There is an insanely simple method for communicating faster than light, and I wonder whether it violates some obscure physics rule or equation.
It's this: run a string that cannot stretch or break (hypothetical material) out a REALLY LONG WAY, like a billion miles, or maybe Earth to the Moon. Put a person on each end. Send signals in real time, with zero delay, along the string by a series of tugs, like Morse Code, only by pulling on the string. That's it. If it really can't stretch, then the far end will feel the tug from the near end at precisely the moment it is pulled. There will be no delay for signal transmission regardless of the distance between the two points.
I know - it is technically ridiculous. But, purely from an idea standpoint, wouldn't it in fact constitute sending information faster than light?
If not: why not?
Dave — Preceding unsigned comment added by 24.113.99.57 (talk) 02:38, 16 January 2012 (UTC)
- Nope, those type of waves don't move faster than the speed of light, they may be more like the speed of sound. Any real-world string will have some elasticity, so it will stretch when you pull on it, until eventually the far end catches up. StuRat (talk) 02:44, 16 January 2012 (UTC)
- A similar thing has occurred to me too in the past, except I envisaged pushing and pulling a long rigid rod. I concluded, as you say, that far from being instantaneous, the transmission of information would be at the speed of sound in the material, just like if you whack an iron girder then the vibrations would travel along it at the speed of sound. But what about some hypothetical absolutely rigid material, with no little atomic "springs" inside it? Does the restriction about speed of information preclude such a material from existing (independently of other objections)? 86.181.172.222 (talk) 03:02, 16 January 2012 (UTC)
- You have to consider carefully what 'rigid' means. The forces that bind atoms together in a solid material are electromagnetic in nature, and therefore mediated by photons—and so limited by the speed of light. In other words, if I wiggle an atom at one end of the rod, the next atom down the line has no way of 'knowing' what I did to the first atom until my wiggle is transmitted – no faster than the speed of light – through electromagnetic interactions. Your hypothetical 'absolutely rigid' material is an impossibility. TenOfAllTrades(talk) 03:10, 16 January 2012 (UTC)
- Sorry, but you're ignoring my provision "independently of other objections" which I expressly put in to ward off this kind of answer. Say there was some other novel type of matter that was not composed of atoms but of some completely rigid stuff. Can we say that this substance can't exist solely because it would violate faster-than-light transfer of information? 86.181.172.222 (talk) 03:16, 16 January 2012 (UTC)
- Restating your question as "If superluminal communication were possible, would superluminal communication be possible?", the answer would be yes—but not terribly informative. Once one starts invoking non-physical imaginary materials, we're out of science and into science fiction. In the real universe, forces are mediated by force carriers limited by the speed of light. TenOfAllTrades(talk) 03:24, 16 January 2012 (UTC)
- Yeah, I guess .... but I was hoping there might be a more interesting answer! 86.181.172.222 (talk) 03:40, 16 January 2012 (UTC)
- I think the answer is quite interesting! Prior to twentieth century understanding of physics, who could have predicted that material properties like tensile-strength and elasticity would have hard upper limits? And... that these limits would be governed by properties of electricity and magnetism? It's a fair bet that Archimedes' lever gedankenexperiment never took account of this limitation - even though he probably knew a lot about electrostatics! The really interesting part of the answer you received is that we now understand this connection. Nimur (talk) 05:20, 16 January 2012 (UTC)
- Science Fiction has suggested other forms of "matter" (sometimes from an alternative "super-dense" universe) with "magic" properties, but such inventions really don't belong in the universe as we know it. We know about Supersolids and Bose–Einstein condensates, where atoms don't behave conventionally, but "super-rigidity" has never been found or postulated by experts. The nearest anyone has found to super-rigidity" is possibly on the surface of a cool Neutron star, and light certainly behaves strangely there, but this is because of the high gravity, not because shock waves are transmitted instantaneously. The only other forms of instantaneous communication that I've heard suggested are quantum entanglement (where the "effects due to entanglement travel at least thousands of times faster than the speed of light", but it doesn't actually work, even in theory, as faster-than-light communication), and telepathy (believe whatever you wish about that). Dbfirs 09:10, 16 January 2012 (UTC)
- I think the answer is quite interesting! Prior to twentieth century understanding of physics, who could have predicted that material properties like tensile-strength and elasticity would have hard upper limits? And... that these limits would be governed by properties of electricity and magnetism? It's a fair bet that Archimedes' lever gedankenexperiment never took account of this limitation - even though he probably knew a lot about electrostatics! The really interesting part of the answer you received is that we now understand this connection. Nimur (talk) 05:20, 16 January 2012 (UTC)
- Yeah, I guess .... but I was hoping there might be a more interesting answer! 86.181.172.222 (talk) 03:40, 16 January 2012 (UTC)
- Restating your question as "If superluminal communication were possible, would superluminal communication be possible?", the answer would be yes—but not terribly informative. Once one starts invoking non-physical imaginary materials, we're out of science and into science fiction. In the real universe, forces are mediated by force carriers limited by the speed of light. TenOfAllTrades(talk) 03:24, 16 January 2012 (UTC)
- Sorry, but you're ignoring my provision "independently of other objections" which I expressly put in to ward off this kind of answer. Say there was some other novel type of matter that was not composed of atoms but of some completely rigid stuff. Can we say that this substance can't exist solely because it would violate faster-than-light transfer of information? 86.181.172.222 (talk) 03:16, 16 January 2012 (UTC)
- You have to consider carefully what 'rigid' means. The forces that bind atoms together in a solid material are electromagnetic in nature, and therefore mediated by photons—and so limited by the speed of light. In other words, if I wiggle an atom at one end of the rod, the next atom down the line has no way of 'knowing' what I did to the first atom until my wiggle is transmitted – no faster than the speed of light – through electromagnetic interactions. Your hypothetical 'absolutely rigid' material is an impossibility. TenOfAllTrades(talk) 03:10, 16 January 2012 (UTC)
- It seems others have already provided an answer, but allow me to link to the same question in the Physics FAQ which gives the same answer, hoping you or other readers will find the FAQ useful. – b_jonas 12:11, 16 January 2012 (UTC)
- I will just note that when people say "real world substance," they don't mean, "oh, this is just an engineering problem." They mean, "any substance that acted in such a way would violate the rules of physics." It violates non-even obscure physics rules and equations for the reasons given above. It does so by deliberately ignoring what rigidity means on a physical level. --Mr.98 (talk) 14:26, 16 January 2012 (UTC)
Another answer is based on the relativity of simultaneity. If a force were to be able to act instanteneously accross a finite distance, then in your frame momentum would be consererved, because the change in momentum of one object would be the opposite of the change in momentum of the other object, and his would happen at the same time. However, in the frame of someone moving relative to you, the two mometum changes will happen at different times, so momentum would not be conserved. The only way to conserve momentum in all frames, is to have momentum conserved locally, at each point in space-time. Count Iblis (talk) 13:44, 16 January 2012 (UTC)
- From Quantum entanglement, "Quantum entanglement is a form of quantum superposition. When a measurement is made and it causes one member of such a pair to take on a definite value (e.g., clockwise spin), the other member of this entangled pair will at any subsequent time be found to have taken the appropriately correlated value (e.g., counterclockwise spin). Thus, there is a correlation between the results of measurements performed on entangled pairs, and this correlation is observed even though the entangled pair may have been separated by arbitrarily large distances." so if you did the following experiment: 1) Entangle two pairs of atoms, pair #1 and pair #2, 2) Carry one atom from pair #1 and one atom from pair #2 on a spaceship out 10 light minutes away from the laboratory on Earth where the other atoms from pair #1 and pair #2 are 3) Out at the remote location on the spaceship, flip a coin in your floating spaceship and slap it against the wall. If it comes up heads, cause the spin of your pair #1 atom with you to change and shine a red light back to Earth. If it comes up tails, cause the spin of your pair #2 atom with you to change and shine a blue light back to Earth. 4) Back on Earth, where the atoms are being watched and a telescope is pointed in the direction of the spaceship, the observers on Earth will know the result of the coin flip by way of the atom, practically 10 minutes before they get the message by way of the light, no? 69.243.220.115 (talk) 16:54, 16 January 2012 (UTC)
- This idea has been bandied about since Bell's early work, but I don't think it works out. The problem, as I understand it, is that you can't arbitrarily decide what state to collapse it into, nor can you know if the other person has already collapsed the state. So you can't send a signal this way; you can't even send an "empty" signal (you can't say, "when I collapse the state, then you'll know the deed has been done" — because you can't detect if the state has already been collapsed, or if your measurement collapsed it). You can compare the states and find they are the same — but that requires slower-than-light communication. But I'm not a physicist, so someone surely can elaborate more on this, or correct me... --Mr.98 (talk) 17:44, 16 January 2012 (UTC)
- I'd say you pretty much covered it. Truthforitsownsake (talk) 18:19, 16 January 2012 (UTC)
- Is the FTL nature of quantum entanglement not confirmed experimentally? If so, then that (set up the test the way they did that does work to confirm it). If not, why is it believed by scientists to be true? I haven't carefully read the entire article and am not highly trained in physics, and so might not even be able to understand it all. 69.243.220.115 (talk) 19:20, 16 January 2012 (UTC)
- From the article, "Experimental results have demonstrated that effects due to entanglement travel at least thousands of times faster than the speed of light," with a ref to this article in Nature, which seems pretty unambiguous about it. But again, I'm not a physicist... --Mr.98 (talk) 19:42, 16 January 2012 (UTC)
- So if the effect is experimentally confirmable, use the same method they used to confirm it to send information FTL. 69.243.220.115 (talk) 19:47, 16 January 2012 (UTC)
- It doesn't work that way, for the same reason I explained. The experiment looks roughly like this: we separate entangled particles. We both agree to check it at the same exact time. We check them. Then we telephone each other and confirm that the states are the same. That is, it takes slower-than-light communication to know what the states are (we can't set them), and it takes slower-than-light communication (the telephone call) to know that we did it at exactly the same time, and using our very precise time measurements regarding when we checked the state to calculate the speed. There's no FTL information passing there. If I screwed it up and checked it a week earlier, the person on the other end would have no way to know that unless I told them... via something slower than the speed of light (e.g. the telephone). We cannot arbitrarily set the state, we can only read it. There's no information traveling FTL here. The key distinction you have to make here is whether information is being exchanged FTL, not whether there is FTL phenomena. The latter is not necessarily prohibited by SR, but the former is, and there isn't currently a way to do it within the current laws of physics.--Mr.98 (talk) 19:51, 16 January 2012 (UTC)
- So you on Earth and the guys out 10 light minutes away have really good clocks synchronized and agree to look at your atoms at a specific time. You look at the appointed time and see that yours is "up" or whatever state your equipment can measure, and that "information" leads you to believe that at that point in time, the state of the atom 10 light minutes away is also "up" and then 10 minutes later you get the confirmatory color of light beam, but you knew that 10 minutes earlier than the light beam told you because you looked at your entangled atom. True, it didn't involve any setting by the guys in the spaceship. They couldn't tell you anything they wanted, but it still seems like a kind of information, you knowing what the state of an atom 10 light minutes away was before any slower-than-light means could tell you. 69.243.220.115 (talk) 20:13, 16 January 2012 (UTC)
- There's no information communicated FTL; that's the key part of SR. Zero communication. Case in point: if a meteor destroyed the other station, you'd have no way of knowing unless some STL communication took place as well. Another way to think about this, is how your situation above is any different than if instead of entangled particles, you simply have duplicate photographs in sealed envelopes. You can both open the envelopes and say, "oh, look, it's a photo of a dog," and you can say, "well, according to our system, he has a photo of a dog, too." But neither of you get to choose what the photos are (nobody does, technically), and there's no way to use them to pass any information between the two of you. The photo is itself a "piece of information," as it is, but you can't pass information this way. If all you're saying, at this point, is, "isn't it cool that particles are entangled?," then I agree, but trying to find a convoluted way to argue that this allows FTL communication is just not going to pan out, sorry. This stuff has been hashed over at length by more clever people than you or I, including folks who had strong vested interests in trying to come up with FTL communication schemes. :-) --Mr.98 (talk) 20:25, 16 January 2012 (UTC)
- I see now. Your envelope analogy is very good. 99% of the time, I remember to just not bother trying to think of ideas that work and that someone else will always have thought of it first if it is a good idea :) 69.243.220.115 (talk) 20:58, 16 January 2012 (UTC)
- There's no information communicated FTL; that's the key part of SR. Zero communication. Case in point: if a meteor destroyed the other station, you'd have no way of knowing unless some STL communication took place as well. Another way to think about this, is how your situation above is any different than if instead of entangled particles, you simply have duplicate photographs in sealed envelopes. You can both open the envelopes and say, "oh, look, it's a photo of a dog," and you can say, "well, according to our system, he has a photo of a dog, too." But neither of you get to choose what the photos are (nobody does, technically), and there's no way to use them to pass any information between the two of you. The photo is itself a "piece of information," as it is, but you can't pass information this way. If all you're saying, at this point, is, "isn't it cool that particles are entangled?," then I agree, but trying to find a convoluted way to argue that this allows FTL communication is just not going to pan out, sorry. This stuff has been hashed over at length by more clever people than you or I, including folks who had strong vested interests in trying to come up with FTL communication schemes. :-) --Mr.98 (talk) 20:25, 16 January 2012 (UTC)
- So you on Earth and the guys out 10 light minutes away have really good clocks synchronized and agree to look at your atoms at a specific time. You look at the appointed time and see that yours is "up" or whatever state your equipment can measure, and that "information" leads you to believe that at that point in time, the state of the atom 10 light minutes away is also "up" and then 10 minutes later you get the confirmatory color of light beam, but you knew that 10 minutes earlier than the light beam told you because you looked at your entangled atom. True, it didn't involve any setting by the guys in the spaceship. They couldn't tell you anything they wanted, but it still seems like a kind of information, you knowing what the state of an atom 10 light minutes away was before any slower-than-light means could tell you. 69.243.220.115 (talk) 20:13, 16 January 2012 (UTC)
- It doesn't work that way, for the same reason I explained. The experiment looks roughly like this: we separate entangled particles. We both agree to check it at the same exact time. We check them. Then we telephone each other and confirm that the states are the same. That is, it takes slower-than-light communication to know what the states are (we can't set them), and it takes slower-than-light communication (the telephone call) to know that we did it at exactly the same time, and using our very precise time measurements regarding when we checked the state to calculate the speed. There's no FTL information passing there. If I screwed it up and checked it a week earlier, the person on the other end would have no way to know that unless I told them... via something slower than the speed of light (e.g. the telephone). We cannot arbitrarily set the state, we can only read it. There's no information traveling FTL here. The key distinction you have to make here is whether information is being exchanged FTL, not whether there is FTL phenomena. The latter is not necessarily prohibited by SR, but the former is, and there isn't currently a way to do it within the current laws of physics.--Mr.98 (talk) 19:51, 16 January 2012 (UTC)
- So if the effect is experimentally confirmable, use the same method they used to confirm it to send information FTL. 69.243.220.115 (talk) 19:47, 16 January 2012 (UTC)
- From the article, "Experimental results have demonstrated that effects due to entanglement travel at least thousands of times faster than the speed of light," with a ref to this article in Nature, which seems pretty unambiguous about it. But again, I'm not a physicist... --Mr.98 (talk) 19:42, 16 January 2012 (UTC)
- Is the FTL nature of quantum entanglement not confirmed experimentally? If so, then that (set up the test the way they did that does work to confirm it). If not, why is it believed by scientists to be true? I haven't carefully read the entire article and am not highly trained in physics, and so might not even be able to understand it all. 69.243.220.115 (talk) 19:20, 16 January 2012 (UTC)
- I'd say you pretty much covered it. Truthforitsownsake (talk) 18:19, 16 January 2012 (UTC)
- This idea has been bandied about since Bell's early work, but I don't think it works out. The problem, as I understand it, is that you can't arbitrarily decide what state to collapse it into, nor can you know if the other person has already collapsed the state. So you can't send a signal this way; you can't even send an "empty" signal (you can't say, "when I collapse the state, then you'll know the deed has been done" — because you can't detect if the state has already been collapsed, or if your measurement collapsed it). You can compare the states and find they are the same — but that requires slower-than-light communication. But I'm not a physicist, so someone surely can elaborate more on this, or correct me... --Mr.98 (talk) 17:44, 16 January 2012 (UTC)
- I was interested above to read "the effects due to entanglement travel at least thousands of times faster than the speed of light". Although my understanding of this is very hazy to say the least, I'd always imagined that these effects did not actually entail anything "travelling" anywhere, and that they were therefore instantaneous. The Misplaced Pages article says that the "thousands of times faster" is experimentally confirmed. Is it still an open question whether the effects are instantaneous? But, while writing this, another thing has occurred to me, which is that there is not actually any such thing as simultaneity, right? So how do we determine this question anyway? Now my head hurts. 86.181.206.2 (talk) 12:49, 17 January 2012 (UTC)
- My reading of that statement is that there are limits to the precision of our ability to measure simultaneity. Simultaneity is when we say two events occur at the same time. It's a non-trivial thing to measure precisely, and there are technical (and theoretical, but I don't think those experiments approach those) limits to our ability to measure precise times. (Relatedly, see relativity of simultaneity.) Saying it propagates at least 1000 times faster than the speed of light is highly encouraging to the idea that it propagates instantly. The deeper question is whether the property (e.g. spin) was the same all along — e.g. is it like an envelope, which has a photo in it even if you haven't opened it. This is a deeper quantum question about the nature of the uncollapsed wave function. Too deep for me, but my understanding of the Bell test experiments is that it has been more or less confirmed that the properties are not there until you look for them (there are no "local hidden variables" — the particles don't just secretly have the information with them). But there are still multiple interpretations of that data available. This is exactly where the analogy with the envelope breaks down — in the quantum case, there isn't a fixed photograph inside the envelope until somebody looks. Then both envelopes have the same photographs inside of them. This is what Einstein thought was "spooky." It doesn't make a lot of sense in a macroscopic world, but that's true of most of quantum mechanics. Being spooked by it is a sign that you actually are taking it seriously, I think. --Mr.98 (talk) 13:13, 17 January 2012 (UTC)
- Thanks! The "relativity of simultaneity" thing is puzzling me still. If there are events A and B, then according to the article you linked (and according to what I previously understood), some observers may see A before B, some may see B before A, and, presumably, some special-case observers will see them both happen at precisely the same time. So in the case that A and B happen to be quantum-entangled events, how does the question of whether they are simultaneous even make sense? 86.181.206.2 (talk) 14:05, 17 January 2012 (UTC)
- The relativity of simultaneity should not come into effect unless the two observers are in different inertial frames. Given that they are both on Earth and their labs are presumably "still" I don't think it really comes into play. If one of them was in a very fast traveling rocket then you'd have a much harder time saying which even happened before the other. Generally these sorts of SR effects don't come into effect unless one of the frames is moving at a significant fraction of the speed of light. But they are interesting to think about, nonetheless. What the relativity of simultaneity emphasizes (and the only reason I linked to it here as food for thought) is that the definition of simultaneity is based on two events happening at the same time. The problem is, according to relativity, what time it is varies according to your inertial frame. In a Newtonian view, saying something happened "at the same time" implies that there is one universal time somewhere out there, but that isn't the case. There are local times, and they can vary from other local times. In the case of this experiment, though, this probably doesn't matter too much except maybe in a few decimal places far at the end of the time measurement. But I'm not 100% sure of this; knowing where you are and when something happened very precisely can be very tricky in physics. --Mr.98 (talk) 14:22, 17 January 2012 (UTC)
- Do you mean to imply that there is some theoertically sound and exact way of establishing simulaneity by ensuring that everything is "still" (in some appropriate sense), and this obviates all the relativistic objections that simultaneity is actually not well defined? On a more practical level, though I can't do the maths, I would have thought that even the slow speeds of normal experience might be relevant when distinguishing between something travelling, over a short distance, thousands of times faster than light, and something instantaneous. The difference must be only some vanishingly small fraction of a second. But I am speculating because really this is well beyond my knowledge. 86.181.206.2 (talk) 14:38, 17 January 2012 (UTC)
- Well, my knowledge of SR and inertial frames isn't perfect, so I could be pretty off on that. This also strikes me as a not-totally-normal use of SR since even if the two observers are not in the same reference frame, they are not "communicating" in the same way you would in a typical SR situation. But the more I ponder over it, the less confident I am that you could, even theoretically, distinguish between absolute simultaneity and very-very-very-very close simultaneity. Even if you could measure time to arbitrarily low values (which you can't, not even theoretically), being able to distinguish between entanglement acting instantly or ridiculously fast is probably not possible. Even if you had one experimentalist on the other side of the universe from the other, you probably couldn't distinguish it from being many billions times the speed of light and being actually instant. (Before one rushes off to make that experiment, keep in mind it would take billions of years for the results to be received from each station.) --Mr.98 (talk) 18:53, 17 January 2012 (UTC)
- As far as I know, simultaneity is perfectly well-defined within a single reference frame. As long as you both have good clocks you can synchronise them by relying on the speed of light being constant. Just send a pulse of light from A to B, where it hits a mirror and goes back to A. A times how long it takes the light to get there. Halve that and you have the time it takes light to travel from A to B (1 minute, say). B then says to A "According to my clock, it's 12:00am". When A receives that message it knows that, according to B's clock, it is now 12:01am so A can set its clock to 12:01am too and then you have an easy way of knowing when events are simultaneous. (Note, you have to do it like that rather than just having A and B starting off in the same place, setting their clocks, and then walking away from each other because as soon as they start moving they aren't in the same reference frame and all bets are off .) --Tango (talk) 00:05, 18 January 2012 (UTC)
- "simultaneity is perfectly well-defined within a single reference frame". So, for example, if I have two alarm clocks not moving relative to each other, then will all observers also not moving relative to the clocks agree that the alarms go off at the same time? Does that not mean that the two events really are simultaneous, in some absolute sense, and anyone disagreeing because they are moving is just looking at things from "a distorted perspective"? Like I could say two lines really are parallel, but you might not see them that way. 86.181.206.2 (talk) 00:28, 18 January 2012 (UTC)
- Do you mean to imply that there is some theoertically sound and exact way of establishing simulaneity by ensuring that everything is "still" (in some appropriate sense), and this obviates all the relativistic objections that simultaneity is actually not well defined? On a more practical level, though I can't do the maths, I would have thought that even the slow speeds of normal experience might be relevant when distinguishing between something travelling, over a short distance, thousands of times faster than light, and something instantaneous. The difference must be only some vanishingly small fraction of a second. But I am speculating because really this is well beyond my knowledge. 86.181.206.2 (talk) 14:38, 17 January 2012 (UTC)
- The relativity of simultaneity should not come into effect unless the two observers are in different inertial frames. Given that they are both on Earth and their labs are presumably "still" I don't think it really comes into play. If one of them was in a very fast traveling rocket then you'd have a much harder time saying which even happened before the other. Generally these sorts of SR effects don't come into effect unless one of the frames is moving at a significant fraction of the speed of light. But they are interesting to think about, nonetheless. What the relativity of simultaneity emphasizes (and the only reason I linked to it here as food for thought) is that the definition of simultaneity is based on two events happening at the same time. The problem is, according to relativity, what time it is varies according to your inertial frame. In a Newtonian view, saying something happened "at the same time" implies that there is one universal time somewhere out there, but that isn't the case. There are local times, and they can vary from other local times. In the case of this experiment, though, this probably doesn't matter too much except maybe in a few decimal places far at the end of the time measurement. But I'm not 100% sure of this; knowing where you are and when something happened very precisely can be very tricky in physics. --Mr.98 (talk) 14:22, 17 January 2012 (UTC)
- Thanks! The "relativity of simultaneity" thing is puzzling me still. If there are events A and B, then according to the article you linked (and according to what I previously understood), some observers may see A before B, some may see B before A, and, presumably, some special-case observers will see them both happen at precisely the same time. So in the case that A and B happen to be quantum-entangled events, how does the question of whether they are simultaneous even make sense? 86.181.206.2 (talk) 14:05, 17 January 2012 (UTC)
- My reading of that statement is that there are limits to the precision of our ability to measure simultaneity. Simultaneity is when we say two events occur at the same time. It's a non-trivial thing to measure precisely, and there are technical (and theoretical, but I don't think those experiments approach those) limits to our ability to measure precise times. (Relatedly, see relativity of simultaneity.) Saying it propagates at least 1000 times faster than the speed of light is highly encouraging to the idea that it propagates instantly. The deeper question is whether the property (e.g. spin) was the same all along — e.g. is it like an envelope, which has a photo in it even if you haven't opened it. This is a deeper quantum question about the nature of the uncollapsed wave function. Too deep for me, but my understanding of the Bell test experiments is that it has been more or less confirmed that the properties are not there until you look for them (there are no "local hidden variables" — the particles don't just secretly have the information with them). But there are still multiple interpretations of that data available. This is exactly where the analogy with the envelope breaks down — in the quantum case, there isn't a fixed photograph inside the envelope until somebody looks. Then both envelopes have the same photographs inside of them. This is what Einstein thought was "spooky." It doesn't make a lot of sense in a macroscopic world, but that's true of most of quantum mechanics. Being spooked by it is a sign that you actually are taking it seriously, I think. --Mr.98 (talk) 13:13, 17 January 2012 (UTC)
Persistent BO
I have some cotton T-shirts that are getting a few years old now but still in pretty good condition so still wearable. The problem is that within only a couple of hours of putting them on they can start smelling of BO from the armpits, usually as soon as they get the slightest bit of sweat in them. It doesn't matter how they're washed or how often they're washed it still happens. I don't have bad BO in general and other T-shirts I wear don't have this problem even older ones. What would cause this and why are only some T-shirts affected? Any suggestions about how it could be fixed? Dob in a Nerd (talk) 03:19, 16 January 2012 (UTC)
- Is it possible it's tighter than the other T-shirts you wear ? I find having good air flow to the pits is essential to them keeping dry. If they stay wet, then they start to stink. StuRat (talk) 04:33, 16 January 2012 (UTC)
- Interesting. Well I would say that they are probably fairly tight ones and I don't think I have this problem in any looser fitting ones, however I do have as old or older ones just as tight that don't smell either so it can't be just that. Dob in a Nerd (talk) 04:47, 16 January 2012 (UTC)
- I've also noticed that certain fabrics tend to cause BO more than others. Cotton usually isn't bad (presumably because it wicks away moisture), but nylon and other artificial fabrics are. Are you sure there's no nylon in it ? Also, I suggest you wash them with bleach, as plain detergent will probably remove most of the stink, but leave enough bacteria to "seed" your pits and start them stinking quickly. StuRat (talk) 04:54, 16 January 2012 (UTC)
- Yes agree that the synthetics tend to smell more quickly in general. But these are definitely cotton, just checked two of them. Can't use bleach cos they're colours and specifically say not to bleach but I have tried those stain removal sprays with little effect but will try again. Dob in a Nerd (talk) 05:06, 16 January 2012 (UTC)
- There is "color-safe bleach", although perhaps "oxidizer" is a better name than "bleach". You could also pour alcohol directly on the pits, but be sure they are rinsed thoroughly before drying, or they could catch fire. StuRat (talk) 05:14, 16 January 2012 (UTC)
- OK thanks for your suggestions I might give it a try. If anyone else has got any ideas still happy to hear them. Dob in a Nerd (talk) 06:55, 16 January 2012 (UTC)
- It might be that there is odorous material trapped in the fabric, and when it heats up (as a result of your body heat) the smell comes out. So it's not you that smells, but the t-shirt. Soaking in vinegar is sometimes suggested to remove smells from fabrics. --Colapeninsula (talk) 11:06, 16 January 2012 (UTC)
- Changing to a biological washing powder should solve the problem for you. You may need to make a solution of the powder first and paste it onto the affected areas, let it soak for a while (not dry out though) and then wash. Using washing powder that has enzymes in it (biological washing powder) will prevent this problem happening. --TammyMoet (talk) 12:06, 16 January 2012 (UTC)
- I do use an "enzyme powered" detergent possibly the dearest one on the supermarket shelf that usually tops comparative independent tests of washing powders in this country so it's not that and that's not preventing it, however I haven't tried making the concentrated paste thing first and letting that soak in so I will give that a try thanks. Dob in a Nerd (talk) 03:25, 17 January 2012 (UTC)
Time is stopped
What is the time? That is a big question.The matter move from a place to another place,but time never change.The change just a feel people thought,because you are you in this situation.Time like space and place .We just a geust in the situation of time.So giving up the concept of thime.You will be liberated by the new opinion.That is my view about time. — Preceding unsigned comment added by 123.138.31.86 (talk) 04:15, 16 January 2012 (UTC)
- What's your question? We do have an article called Time, if that would help. ←Baseball Bugs carrots→ 04:32, 16 January 2012 (UTC)
- We also have an article on the human perception of time, which is probably less well-understood than the actual physics-descriptions of time. In physics, definitions of time as a dimension or as a variable in an equation tend to be axiomatic, so there's really not much to explain. Nimur (talk) 05:25, 16 January 2012 (UTC)
- The nature of time can also be a very interesting, complicated and challenging topic in physics. See List of unsolved problems in physics#Arrow of time and Arrow of time. Red Act (talk) 05:58, 16 January 2012 (UTC)
- We also have an article on the human perception of time, which is probably less well-understood than the actual physics-descriptions of time. In physics, definitions of time as a dimension or as a variable in an equation tend to be axiomatic, so there's really not much to explain. Nimur (talk) 05:25, 16 January 2012 (UTC)
Hyperbolic lines around radio towers
While walking through the National World War II Museum today, I saw a map in one of the exhibits. The caption said something about planes finding their way to France for the D-Day bombings and such. The map, besides having an outline of the coasts of England and France, had various radio navigation towers on it with hyperbolic lines drawn around them. The caption didn't mention them or explain in any detail how the pilots used them. So what were these lines and why would they be hyperbolic and not circular? Thanks, Dismas| 05:37, 16 January 2012 (UTC)
- See Decca Navigator System. AndyTheGrump (talk) 05:45, 16 January 2012 (UTC)
- G was the World War II phase navigation system used by the RAF, that later evolved into Decca (post-war)... but I don't know what the actual chart you saw was, so all this is a little speculative.
- I don't think that Decca was ever used in the United States (at least, non-experimentally). 1940s-vintage American aeuronautical NAVAIDs were usually nondirectional beacons, LORAN, and eventually VOR. I presume in Occupied Europe, the navaids were German, not British; but the physics is the same for all Hyperbolic navigation navaids. (NDBs would have circular radiation patterns, so iso lines aren't drawn on sectional charts). RAF and American AAF pilots probably used British or American equipment dialed to German stations. One of the most important post-War technology development thrusts was spurned by the realization that enemy bombers could use our own NAVAIDs, resulting in the technology that we now call the Emergency Broadcast System. (The beeping noise on television was just for testing. In an actual bomber-air-raid emergency, the TV station would be spoofing as a radar tower or malformed NDB in the wrong state). Nimur (talk) 06:13, 16 January 2012 (UTC)
- Would that spoofing actually be a part of the Emergency Broadcast System, or just something else that was also implemented (or considered)? I can't find anything about it in the EBS article, but it would be neat to cover if it we had reliable sources for the design, testing, or implementation of such a system. TenOfAllTrades(talk) 23:18, 16 January 2012 (UTC)
- Some more information at CONELRAD. I'll see if I can dig up a more authoritative reference. Nimur (talk) 23:38, 16 January 2012 (UTC)
- Official handbook for station-operators (2007): AM & FM Emergency Alert System Procedures. Steps 5 through 9, for participating stations, to enable your tower to transmit data from the National Activation system. The FCC and FEMA will jointly decide, under direction of the White House, what signals to transmit out of your tower. Additional information, Emergency Communications, from the FCC.
- And, Special Temporary Authority, for ad-hoc, emergency use of radio towers. Nimur (talk) 23:57, 16 January 2012 (UTC)
- Would that spoofing actually be a part of the Emergency Broadcast System, or just something else that was also implemented (or considered)? I can't find anything about it in the EBS article, but it would be neat to cover if it we had reliable sources for the design, testing, or implementation of such a system. TenOfAllTrades(talk) 23:18, 16 January 2012 (UTC)
Tau-catalysed fusion
Wouldn't tau-catalysed fusion be even more efficient than muon-catalysed fusion, because taus are over fifteen times more massive than muons and would therefore bring two deuterium or tritium atoms over fifteen times closer to each other than muons do? Whoop whoop pull up 19:15, 16 January 2012 (UTC)
- I don't know, but it's worth noting that a tau's lifetime is seven orders of magnitude shorter than a muon. So that's lowering the threshold of usefulness substantially, no? --Mr.98 (talk) 19:49, 16 January 2012 (UTC)
- The tau appears to have a 17.39% chance of decaying into a muon anyway when it finally does decay though. The alpha sticking problem seems to be more of a critical issue with muon-catalysed fusion, not sure if taus will stick to alpha particles as often as muons do. If they don't, then it would make more sense to produces taus. I guess it all depends on which can produced more efficiently, muons or taus. ScienceApe (talk) 11:02, 17 January 2012 (UTC)
- If taus are 15 times more massive than muons, presumably that means they take 15 times more energy to make. If muon-catalysed fusion uses more energy than it produces, then tau-catalysed fusion would be even worse. --Tango (talk) 12:18, 17 January 2012 (UTC)
- Is there anything that decays and produces taus? ScienceApe (talk) 12:57, 17 January 2012 (UTC)
- Yes, of course. Anything that is heavy enough to produce a tau particle in its decays will occasionally produce them. But other things like protons and neutrons are much more likely to be produced. Dauto (talk) 19:47, 17 January 2012 (UTC)
- To clarify Dauto's "of course": it is a general principle in particle physics that any way of decaying that doesn't violate any conservation laws will sometimes happen (it may happen with an incredibly low probability, but it will happen sometimes). It's worth noting that a tau is about twice the mass of a proton, though, so there aren't many particles heavy enough to decay into a tau on their own (but you can certainly make them by colliding particles together so that the kinetic energy contributes as well). --Tango (talk) 21:27, 17 January 2012 (UTC)
- Is there anything that decays and produces taus? ScienceApe (talk) 12:57, 17 January 2012 (UTC)
- Didn't realize Taus were actually bigger than Protons. Curious, could anti-protons work? ScienceApe (talk) 03:20, 20 January 2012 (UTC)
- I can't find any mention of a particle made up of a proton and an anti-proton, which makes me think it would be incredibly unstable. I would expect the proton and anti-proton to annihilate each other before either of them could fuse with anything. --Tango (talk) 16:03, 21 January 2012 (UTC)
- If you are capable of producing antiprotons efficiently enough to make them useful for fusion, you may as well just use antimatter annihilation as your energy source. It's way more efficient. Law of Entropy (talk) 01:47, 22 January 2012 (UTC)
- No it's not. Producing antiprotons will never be an energy source since it will always take much more energy to produce antiprotons than you will get out of proton-antiproton annihilation. ScienceApe (talk) 02:00, 23 January 2012 (UTC)
- Note: "If you are capable of producing antiprotons efficiently enough..." Point being, instead of getting the comparatively tiny energy from a catalyzed nuclear reaction, just completely consume the antiproton, if you are generating them efficiently. If making the antiproton is inefficient, then you shouldn't be using it to catalyze fusion in the first place.Law of Entropy (talk) 09:15, 24 January 2012 (UTC)
- The tau requires more energy to produce, has a much shorter lifetime and suffers from a more serious alpha-sticking problem (Being heavier it moves more slowly making it easier for the alpha particles to capture it). Dauto (talk) 19:47, 17 January 2012 (UTC)
climate data
Anyone know where on the internet I can get climate data for Hampshire, England, preferable Petersfield. I need temperatures, rainfall and wind direction averages for each month, and within the next few hours if at all possible. The internet only gives me tomorrow's weather and climate change stuff.
148.197.81.179 (talk) 22:19, 16 January 2012 (UTC)
- Have you tried searching pubmed? Might be your best bet. Nformation 22:23, 16 January 2012 (UTC)
That's a collection of biomedical journal references, apparently. i can't see the connection myself. 148.197.81.179 (talk) 22:42, 16 January 2012 (UTC)
- Derp, I meant google scholar. Sometimes I forget that science exists outside of biology :). Nformation 22:43, 16 January 2012 (UTC)
- This site gives temperatures, rainfall, sunshine hours but no wind speeds I'm afraid. Mikenorton (talk) 22:57, 16 January 2012 (UTC)
I've just found the temperature and rain data, half an hour of searching on the Met Office site. Now all I need is the wind data. 148.197.81.179 (talk) 23:01, 16 January 2012 (UTC)
6 hours left to find it... 148.197.81.179 (talk) 01:57, 17 January 2012 (UTC)
January 17
Order of chemical reaction
It is said by many references (e.g., http://en.wikipedia.org/Reaction_order) that the rate at which a chemical reaction of reactants A and B to give products X, Y, ... occurs is given (approximately) by: r = ^n ^m k where r = reaction rate, & are the reaction concentrations, n & m are "reactant" orders, and k = the arrhenious factor, modified arrhenius factor, or eyring factor to taste. The sum of n amd m is known as the reaction order and is generally 2 or 3. I gather that depending on the actual reactants, n & m may or may not be equal, and are usually but not always are equal to 1 or 2 (may be fractional vaules]. Chemical databases often seem to give only the reation order, and not the individual n & m values. What I would like to know is this: Q(a) how do you apportion the order between ? Q(b) The Wikipaedia at http://en.wikipedia.org/Reaction_order implies that if the reaction is elementary, the reaction order is related to the stoichiometry. What is the relation? Some simple reactions I have checked e.g., O+C>CO (monatomic O & C) are order 3 if there is one product, and order 2 if there 2 products (eg O2>O+O or O2+C>CO+O) - is this the rule? None of this makes much sense to me - one would think that doubling the concentration of of either reactant would double the rate of particle collisions & therefore the probability of a molecular change. So for O2>O+O (which would actually be O2+O2>O+O+O+O i.e., two oxygen molecules colliding) and ought to be proprtional to the square of the O2 concentration, ie order 2 - but this is apparently wrong! Why? — Preceding unsigned comment added by 124.182.32.40 (talk) 03:05, 17 January 2012 (UTC)
- Can you give an example of a chemical database that only gives the overall order? Often times, a reaction will be described as "2 order in "A", or something of that nature, meaning that has an exponent of 2. As for why a reaction is a particular order, it has to do with the reaction mechanism. You cannot simply look at the overall reaction and predict the order (i.e. your "rules" for one or two products will not hold up in general). This is not a subject that is easily learned from an encyclopedia such as Misplaced Pages - it is best to learn from a competent teacher, or at least a textbook. Even many chemists do not really fully learn about why reaction orders are the way they are (though many do - it depends on the person and the sub-field) Buddy431 (talk) 03:34, 17 January 2012 (UTC)
- One major flaw in your (IP 124.) thinking is the "therefore..." of "doubling the concentration of of either reactant would double the rate of particle collisions & therefore the probability of a molecular change". The actual change from reactants to products might involve several discrete steps (the "reaction mechanism" Buddy431 mentions), not just a single unified change as suggested by the equation. One key is to look at the rate limiting step and the identities and numbers of molecules involved in it, definitely not the collisions of reactant molecules for the net reaction. DMacks (talk) 03:45, 17 January 2012 (UTC)
Buddy431 may be correct, but weren't the examples given elementary (single hump) reactions? The database at http://kinetics.nist.gov/kinetics/index.jsp is an exapmple that gives the overall order only. So unless there is a way of working out how to allocate the reaction order, this database would seem to be near useless. Surely, if it is not just a matter of particle collision rates, the additional factor(s) can be at least named, if not described? I have some chemistry textbooks of undergraduate & graduate level, and the most intelligent thing they say on the matter is "the order can be determined by experiment". Is this because the subject is outside the syllabus, or because it is too complex, or because it is not understood by even experts? I would suspect the first. Meanwhile, I obtained data for all the reactions involving monatomic and molecular C & O and H & O, and the Inquirer's "rule" holds up in every case. Keit124.178.159.199 (talk) 04:25, 17 January 2012 (UTC)
- In an elementary reaction, with no intermediates, the reactant order for liquids and gases is generally the same as the stoichiometry. For example n A + m B -> C is generally governed by a reaction rate like , where the exponents are the same as the reduced stoichiometric coefficients. There are lots of exceptions however. For example, reaction involving solids (or solid catalysts) are generally zeroth order. In addition, many reaction rates are controlled by non-obvious intermediate phases that may have unexpected reaction orders. So in general one usually has to look up the reaction rate (or at least the reaction mechanism) to know for sure what the rate is. Dragons flight (talk) 06:02, 17 January 2012 (UTC)
- So, taking C+O>CO as an example, DragonsFlight's n and m are both 1 and thus the reaction order is 2. Isn't there no intermediate phase? But this reaction is listed (http://kinetics.nist.gov/kinetics/index.jsp ) as Order 3, not 2. Why? Keit124.178.159.199 (talk) 07:34, 17 January 2012 (UTC)
- Monoatomic oxygen isn't stable. 2 C + O2 -> 2 CO is a third order reaction that would seem more natural. The intermediate in this case would then be 2 O -> O2 via fast reaction. Dragons flight (talk) 07:42, 17 January 2012 (UTC)
- Yup, again there is an assumption that the given net equation is actual reaction (atomic/molecular species as written, single mechanistic step, no other catalytic components, etc.). The reaction proposed in the ref given in the database is:
- C + O + M → CO + M
- all taking taking place in the gas phase as part of a rapid high-energy sequence of reactions (so single-atom oxygen is correct--actually they studied the dissociation of CO and extracted this reverse-reaction as part of a complex series of reactions under steady-state or equilibrium conditions). But notice "M"--an unidentified "collision partner" involved in the reaction! If I understand the details correctly, it could just be a sink for excess energy or balance the electronic states or something like that. So its chemical identity is not changed or specifically identified, so a "net equation" analysis might ignore it on both sides. But there it is, now that the actual reaction is given for the specific mechanistic details, rather than the net chemical one--a third chemical entity to correlate with it being third-order. DMacks (talk) 08:05, 17 January 2012 (UTC)
- Yep, that's a correct interpretation for "M"; it's an energy sink. You'll quite often see something similar whenever you have two monatomic species coming together to form a diatomic product in the gas phase. (Consider what happens when, for example, the independent C and O atoms meet. They start out as free atoms, then when they get together, they form a chemical bond...which releases energy...which has to go somewhere...and the only place that energy can go is back into the kinetic energy of the two atoms, which just pulls the bond apart again. The only way that the bond can be stable is if a third atom or molecule is present right when the C and O get together; one or both atoms can then collisionally transfer some energy to the third party, leaving the newly formed CO without enough internal energy to break itself apart again.) TenOfAllTrades(talk) 15:33, 17 January 2012 (UTC)
- Yup, again there is an assumption that the given net equation is actual reaction (atomic/molecular species as written, single mechanistic step, no other catalytic components, etc.). The reaction proposed in the ref given in the database is:
- Monoatomic oxygen isn't stable. 2 C + O2 -> 2 CO is a third order reaction that would seem more natural. The intermediate in this case would then be 2 O -> O2 via fast reaction. Dragons flight (talk) 07:42, 17 January 2012 (UTC)
- Heterogeneous catalyst anyone? Gas-phase reactions involving three reactants with no intermediates don't really happen in real life. "2 C" would simply be part of a solid carbon substrate, oh hey like they form syngas.
- and the only place that energy can go is back into the kinetic energy of the two atoms, which just pulls the bond apart again.
- Not necessarily. See rabi frequency. I wonder if it is possible to do stimulated emission with photochemical reactions; it would be so cool. 137.54.17.9 (talk) 20:23, 17 January 2012 (UTC)
- It's not clear they are proposing exactly "no intermediates" for the C+O→ CO (with M involved), just that the concentrations of all three are involved in the rate-limiting part of the pathway. However, they do propose and then argue against:
- C + O → CO*
- followed later by a discrete reaction of decay of that excited state via collision with M using data from their experiment. DMacks (talk) 20:38, 17 January 2012 (UTC)
I had thought that when two particles collide, then there is a probability of forming a new complex, depending on whether their kinetic energy and their orientation (steric factor) permits it. The new complex then spontaneously decays back into new particles,which may or may not be the same molecules as what collided (and they could be of the same molecular formula but different atoms paired/joined up. In the case of two atoms such as C & O coliding (as distinct from two molecules colliding) there are no bonds to break, but the resulting CO holds less (bond) energy - this just means that the CO complex will form at lower kinetic energies than otherwise. In other words, TenOfAllTrades is incorrect - the resulting CO molecule will carry on with kinetic energy greater than the summed kinetic energy of the reactant C & O - hey - this means a temperture rise, just what we get! Is this wrong? I read the[REDACTED] article on rabi frequency - I'm none the wiser for it. Keit
Incidentally, I think this is Misplaced Pages Reference Desk at it's best. Right or wrong in theory, each contributor, and my own effort in explaining it, has improved my undertsanding better than hours of pooring over textbooks. Please keep it up! Keit121.221.234.228 (talk) 02:51, 18 January 2012 (UTC)
Energy density greater than diesel petrol
Are there any liquids that have an energy density that is greater than diesel petrol? ScienceApe (talk) 10:41, 17 January 2012 (UTC)
- I think some thicker fuel oils are higher energy density than diesel. This slightly dubious chart claims that #6 oil has significantly more energy than diesel. (However, #6 fuel oil is not something you would put in your car.) APL (talk) 11:35, 17 January 2012 (UTC)
- Would #6 fuel oil be useful as a napalm ingredient? ScienceApe (talk) 12:38, 19 January 2012 (UTC)
The list cited by APL gives energy density per volume. The energy in a liquid fuel comes from the hydrogen and carbon atoms. It follows that liquids with a higher density (mass per unit volume) have proportionally higher energy value, and meassured on a energy per unit mass basis, all hydrocarbon fuels have the same energy value, within an insignificant variation range. But measured on a volume basis, the energy content can vary a little bit, as carbon is a heavier atom than hydrogen, so an increased carbon conent leads to greater mass per volume. Keit124.178.159.199 (talk) 12:23, 17 January 2012 (UTC)
- Doesn't the energy come from the hydrogen and carbon bonds? (Also, what is "diesel petrol"? "diesel" and "petrol" are two different things.) 86.181.206.2 (talk) 12:51, 17 January 2012 (UTC)
- According to diesel fuel diesel is any fuel that can be used in a diesel engine. Diesel petrol is just a way to be more specific about the petroleum derived substance. ScienceApe (talk) 12:59, 17 January 2012 (UTC)
- Perhaps this is a regional thing. Are you American? In the UK, "diesel" and "petrol" are two different types of fuel. What we call "petrol" over here is called "gasoline" in the US, so perhaps "diesel petrol" would not sound so odd there. 86.181.206.2 (talk) 13:55, 17 January 2012 (UTC)
- No, it still sounds pretty odd. We mostly don't use the word petrol at all; most people probably recognize it, as the British way of saying "gasoline". To the best of my recollection I have never heard anyone refer to diesel petrol. --Trovatore (talk) 17:08, 17 January 2012 (UTC)
- That's because no one does. I got the name wrong. According to the article, it should be called petrodiesel. ScienceApe (talk) 19:43, 17 January 2012 (UTC)
- Oh, I see — sounds like a back-formation, like snow skiing, motivated by the advent of "biodiesel". --Trovatore (talk) 20:44, 17 January 2012 (UTC)
- That's because no one does. I got the name wrong. According to the article, it should be called petrodiesel. ScienceApe (talk) 19:43, 17 January 2012 (UTC)
- In USA, it's relatively common to hear people refer to "diesel gas", even though that's technically incorrect. (I guess on the idea that anything you get at a gas station and then put in your car must be a type of gas.) I assumed that the commonwealth speakers did the same with their words. APL (talk) 21:20, 17 January 2012 (UTC)
- No, it still sounds pretty odd. We mostly don't use the word petrol at all; most people probably recognize it, as the British way of saying "gasoline". To the best of my recollection I have never heard anyone refer to diesel petrol. --Trovatore (talk) 17:08, 17 January 2012 (UTC)
- Perhaps this is a regional thing. Are you American? In the UK, "diesel" and "petrol" are two different types of fuel. What we call "petrol" over here is called "gasoline" in the US, so perhaps "diesel petrol" would not sound so odd there. 86.181.206.2 (talk) 13:55, 17 January 2012 (UTC)
- The chart in the Energy density article is very relevant. It visualizes the distinction that Keit above emphasize. From the chart you can see that diesel beats liquid hydrogen on density per volume, while it beats aluminium and anthracite on density per mass. Considering fuel for transportation, it's appaling to see how bad lithium ion batteries are doing. The chart also seem to indicate that laptops (where volume is key) would not run significantly longer if they were fuelled by hydrogen fuel cells. EverGreg (talk) 12:56, 17 January 2012 (UTC)
- Could I burn "aluminium" in an aluminum engine block? What does it cost per gallon? Edison (talk) 14:42, 17 January 2012 (UTC)
- A mixture of water and molten aluminium is highly explosive and has been theorized to have played a part in the WTC collapse . Aluminium powder can be used as Thermite, which produces extremely high temperatures. So the energy is there, but nobody has built an engine that runs on it. Yet.. EverGreg (talk) 14:58, 17 January 2012 (UTC)
- One of the early internal combustion engines could run on coal dust. It burns at a significantly lower temperature than aluminum, though.
- Actually, Space Shuttle Solid Rocket Boosters ran on aluminum. It's a pretty standard material for solid rockets. --Itinerant1 (talk) 20:30, 17 January 2012 (UTC)
- A mixture of water and molten aluminium is highly explosive and has been theorized to have played a part in the WTC collapse . Aluminium powder can be used as Thermite, which produces extremely high temperatures. So the energy is there, but nobody has built an engine that runs on it. Yet.. EverGreg (talk) 14:58, 17 January 2012 (UTC)
- Could I burn "aluminium" in an aluminum engine block? What does it cost per gallon? Edison (talk) 14:42, 17 January 2012 (UTC)
How does constructive/destructive interference work in a chorus?
Hi all. When a single voice is singing in a chorus, from a given distance back you hear it at a given volume. When another voice joins in, singing at the same volume, you the listener hear it grow louder. As more voices join in, it becomes louder still. I assume that this is because of interference — the different waves are contributing to make bigger waves. But why is this always the case? Shouldn't the additional waves be just as likely to cause destructive interference? Shouldn't the net effect of a dozen voices cancel each other out? Why does adding another voice (and note, they could be singing something completely different) always make it louder? Thanks! — Sam 63.138.152.219 (talk) 14:53, 17 January 2012 (UTC)
- Great question! I'll give it a first try. :-) Each singer produces a lot of different frequencies, so some will cancel destructively and some constructively with other frequencies from other singers. This also depends on where you and the singers are standing. It can be constructive in one place and destructive in another. But your issue remains. This should even out, so that two singers sound as loud as one on average.
- That is, if the amplitude of one singer is 2, you get constructive interference with 2+2 = 4 or you get 2-2=0, with the average (4+0)/2 = 2 or one singer. So what's wrong here? Judging from the decibel article, the power is proportional to the square of the amplitude. So an amplitude of 2 results in a volume from the singer of 2*2 = 4. While the amplitude of two singers in constructive interference gives a volume of 4*4 = 16. If you then average constructive and destructive interference you get (16+0)/2 = 8. Then we're back with our initial intuition: Two singers produce a volume twice as high as one.
- But since decibles involve a logarithm, this isn't quite right, nor is our intuition. The relevant formula, with a handy calculator, can be found here: EverGreg (talk) 15:28, 17 January 2012 (UTC)
- Very interesting. So is this saying that, while the average amplitude of the waves that hit our ears will still be the same ("2", in your example), the average power will be greater? That's pretty surprising. — Sam 63.138.152.219 (talk) 16:09, 17 January 2012 (UTC)
- No—the amplitude does vary from 0 to 4, but the average isn't 2 because it isn't symmetrically distributed. For incoherent superposition the average works out to 8/π ≈ 2.5, but I don't think this is physically meaningful. The square of the amplitude is proportional to the energy of the vibration and simply adds, as you'd expect. -- BenRG (talk) 01:20, 18 January 2012 (UTC)
- Yes, but on top of that, a doubling in energy does not double the perceived volume, because our ear (and the decibel scale) has a logarithmic relationship between sound energy and volume. EverGreg (talk) 14:21, 19 January 2012 (UTC)
- Interference only happens when waves are coherent. Sound from two different singers is never coherent, therefore neither destructive nor constructive interference occurs. The intensity of the waves adds linearly: two singers produce twice the intensity of one. In theory, if two singers sang exactly the same frequency to much better precision than the human ear can distinguish, their voices could interfere. This isn't going to happen in practice, though. --Srleffler (talk) 17:48, 17 January 2012 (UTC)
- That doesn't sound like a correct explanation. Humans can most certainly perceive interference that occurs between two humanly distinguishable pitches. Humans can hear pitch differences down to about 6 cents, which for example for a 440 Hz pitch (A above middle C) is 2.6 Hz, well below the roughly 15 Hz cutoff below which audible beats can be perceived. For a pitch difference of considerably more cents (and/or between higher pitches), the interference can instead be perceived as a difference tone, but it's audible interference occurring between distinguishable pitches either way. Red Act (talk) 19:03, 17 January 2012 (UTC)
Relatedly
I don't want to hijack the above question (please feel free to reply to the section above!) but I had a related question that came to mind. When I was a child (well before puberty), I could at will make a kind of high pitched ringing voice in the back of my throat. It was quite loud. I can't quite describe how I did it — it wasn't just screaming or shrieking, but sort of interior whistle. It wasn't just me that could do it, there were a few other boys who could as well. Anyway, if two of us did it at the same time, it would produce a very strange sound, almost electrical sounding in nature (like the sound a rippling electrical transformer would make in movies), or something somewhat similar to what a cicada sounds like. (I'm having trouble describing this, like most qualia.) My real question is what caused this very strange and really quite distinct sound. My guess is that the frequencies being emitted by me and the other boys were more or less fairly close to being pure tones of some sort, and the differences between them were somehow creating some kind of dynamic interference. Does that make any sense? (Is there a name for this kind of sound that young children can produce?) --Mr.98 (talk) 19:23, 17 January 2012 (UTC)
- If the frequencies were close enough, probably they could produce beats. Have you tried it out as an adult? :P Lynch7 19:31, 17 January 2012 (UTC)
- Agreed that beating of two similar frequencies is a key player. Note that the beats will drift dynamically. I had a very similar experience to Mr.98 as a child, with the exception that my high-pitched sound was not especially different than a normally-voiced falsetto. The phenomenon does sound rather different than say, listening to someone else tune a flute to a tuning fork. I think this is because, if you are producing one of the two voices, then, in addition to the beats in the sound waves carried by the air, your skull is beating too :) SemanticMantis (talk) 20:09, 17 January 2012 (UTC)
- Good point. Your voice will be sorta interfering with the beats as well, so all in all, quite a weird sound. Lynch7 20:39, 17 January 2012 (UTC)
- Agreed that beating of two similar frequencies is a key player. Note that the beats will drift dynamically. I had a very similar experience to Mr.98 as a child, with the exception that my high-pitched sound was not especially different than a normally-voiced falsetto. The phenomenon does sound rather different than say, listening to someone else tune a flute to a tuning fork. I think this is because, if you are producing one of the two voices, then, in addition to the beats in the sound waves carried by the air, your skull is beating too :) SemanticMantis (talk) 20:09, 17 January 2012 (UTC)
- Re: "Is there a name for this kind of sound . . .", Overtone singing and its links may be of relevance/interest. {The poster formerly known as 87.81.230.195} 90.197.66.192 (talk) 09:22, 19 January 2012 (UTC)
Gravitational time problem.
On earth I am attracted by a force = G * m1m2/r^2
However what happens if there is say a globular cluster 100 light years away. I did not exist 100 yrs ago so It cannot be the above formula there must be a time element. — Preceding unsigned comment added by 92.30.204.80 (talk) 17:25, 17 January 2012 (UTC)
- The formula you gave applies only for two masses at a single instant in time. If there is another mass (your cluster) or a mass which is changing over time (you?) or relative movement of the various objects, then things get more complicated. Basically a time element will appear because m1, m2, and r will not be constants but each will be a function of t. Staecker (talk) 17:38, 17 January 2012 (UTC)
- You're quite correct, there is a time element to gravity. Gravity is most accurately modeled with general relativity, which does take speed-of-light considerations into account. The simple Newtonian gravity model expressed by the equation above can be viewed as an approximation to general relativity, that only works well under a certain set of circumstances. Red Act (talk) 17:51, 17 January 2012 (UTC)
- You are correct that the formula you give is not appropriate for that situation. You need general relativity to deal with gravitational forces between very distant objects. --Srleffler (talk) 17:52, 17 January 2012 (UTC)
- If you don't like Einstein tensors, it's possible to use a formulation analogous to the relativistically-correct Liénard–Wiechert potential for electromagnetism. You simply replace time with retarded time in all the relevant places in your equations, and presto - a general, relativistically-correct formulation of gravity. (Not to be confused with a general-relativistic correct formulation of gravity). There's no shortage of research on the applicability of this approach: Google found almost 2,000 research papers; and I'm pretty sure I saw this worked out to completion in a physics course-note some time ago. The moral is, you don't need general relativity, unless you need it. Nimur (talk) 19:41, 17 January 2012 (UTC)
- In addition to the Newtonian model, there are dozens of other alternatives to general relativity, some of which are consistent with special relativity, and some of which avoid the use of tensors. One historical example that uses retarded potentials is Whitehead's theory of gravitation (although that one does use tensors). Like the Newtonian model, the other alternatives all work well in some circumstances, and give wrong answers in other circumstances. Only general relativity always gives the right answer (although it has problems dealing with quantum mechanics, and it has awkward singularities). Red Act (talk) 01:34, 18 January 2012 (UTC)
- If you don't like Einstein tensors, it's possible to use a formulation analogous to the relativistically-correct Liénard–Wiechert potential for electromagnetism. You simply replace time with retarded time in all the relevant places in your equations, and presto - a general, relativistically-correct formulation of gravity. (Not to be confused with a general-relativistic correct formulation of gravity). There's no shortage of research on the applicability of this approach: Google found almost 2,000 research papers; and I'm pretty sure I saw this worked out to completion in a physics course-note some time ago. The moral is, you don't need general relativity, unless you need it. Nimur (talk) 19:41, 17 January 2012 (UTC)
- I'm not sure if everyone's got what the OP is on about. I think the question is really about how the gravity formula can even make sense, given that there is an attraction between two things that are so far apart, the concept of their simultaneous existence is mucked up. In fact, if I've understood rightly, it's not that complicated. Whatever general relativity involves, it reduces to Newtonian physics in most cases (I don't know how big the corrections are for a distant star). So the gravity that you feel is from the star as it was 100 years ago, and in simple calculations, you don't need to know anything more. If it got destroyed about 50 years ago, that will have no effect on the current gravitational pull. Same for your gravitational pull on the star, ie. at the moment, it doesn't sense any pull from you, since your existence is outside its light cone. IBE (talk) 20:11, 17 January 2012 (UTC)
- When I was in school ca. the early 2000s, our astronomy professor taught us that it wasn't entirely clear how fast gravitational force propagated. That is, if the Sun blinked out of existence right now, how long until we felt the gravitational effects on Earth? At the time I recall some science writer (Brian Greene?) suggesting it would be instantaneous, while my professor (a serious astronomer) said that this was wrong, that it would propagate at c. I see we have an article on speed of gravity which more or less agrees with my professor. --Mr.98 (talk) 20:33, 17 January 2012 (UTC)
- School in the 2000s? Then you must be fairly young, and I don't know where (or rather when) you cram this knowledge in. I doubt it was Brian Greene, since The Fabric of the Cosmos explains quite carefully the speed of gravity is exactly c (p72, 2004 ed). IBE (talk) 20:50, 17 January 2012 (UTC)
- By the early 2000s, I think it was pretty well established that gravity didn't act instantaneously. Reference 17 of the article you link to is dated 2001 and describes experimental evidence for gravity travelling at approximately the speed of light. --Tango (talk) 21:10, 17 January 2012 (UTC)
- It was probably in 2000 or 2001, so that probably would have been pretty fresh stuff at the time. (It was right around when all the evidence for inflation came out — the professor in question had some small role in one of the experiments involved in detecting that.) I think it must have been Greene's Elegant Universe. The preview pages I can see online don't have the right pages in them (I think it is 73 or 74? He talks about time and GR there.) so I can't recall who was right and who was wrong — the positions might have become switched in my mind. (And I've long since given away my copy at a yard sale.) But I remember it being a subject of contention. --Mr.98 (talk) 01:21, 18 January 2012 (UTC)
- It was controversial once, but I thought it was settled by the observations of PSR B1913+16 in the 1970s. I feel obliged to point out that general relativity requires energy conservation, so you can't extract any prediction about what would happen if the sun blinked out of existence. It has to go somewhere, and whatever causes its sudden departure has to come from somewhere, and whatever that is, it gravitates too, because everything gravitates. That's why the whole thing was controversial: in contrast to the electromagnetic case, you can't reach in with an uncharged manipulator arm and push your charged particles around. Gravity "knows" about everything, and that made it plausible that there might be no need for gravitational waves to correct the long-distance field when the gravitating object's state of motion changed. The other problem was/is figuring out what it even means for a gravitational wave to propagate at c, given that a gravitational wave is a distortion of the spacetime geometry that gives meaning to the speed c in the first place. -- BenRG (talk) 02:27, 18 January 2012 (UTC)
- It was probably in 2000 or 2001, so that probably would have been pretty fresh stuff at the time. (It was right around when all the evidence for inflation came out — the professor in question had some small role in one of the experiments involved in detecting that.) I think it must have been Greene's Elegant Universe. The preview pages I can see online don't have the right pages in them (I think it is 73 or 74? He talks about time and GR there.) so I can't recall who was right and who was wrong — the positions might have become switched in my mind. (And I've long since given away my copy at a yard sale.) But I remember it being a subject of contention. --Mr.98 (talk) 01:21, 18 January 2012 (UTC)
'Blue' Veins in the Heart, elsewhere?
So I understand that blood in the human body is never blue. However, veins do look blue from the skin. The[REDACTED] article claims that this is a side effect of light absorption through the skin. However why does the human heart have visible blue veins? See this photo for an example. --188.220.46.47 (talk) 19:38, 17 January 2012 (UTC)
- Veins are not blood, veins are vessels that carry blood. If I have a green hose, it does not make the water inside the hose green. --Jayron32 16:44, 19 January 2012 (UTC)
lens as spatial filters
A focusing lens focuses light focused at infinity into some image 100 cm away.
Does it matter if a diffraction filter is placed before, or after the lens? I mean, a lens is an inverse fourier transform right? And a diffraction screen forms a fourier transform? Do the operations commute, so long as the diffraction screen is placed well before the image plane? 137.54.17.9 (talk) 19:49, 17 January 2012 (UTC)
- A lens is a lens; it's not a fourier transform. The operation that a lens performs can be modeled by a fourier transform.
- As far as commutation of optical elements: to first order, some optical elements commute; but you should be aware of the real-world effects that countermand that. All (passive) optical elements attenuate the light somewhat. Imperfections in the optics are usually unpredictable and therefore irreversible in practice. Changing the optical path changes the scale sizes you need. (For example, if you magnify an image, your next optical element needs a larger aperture; in other words, aperture is non-commutative if you have magnifying optics).
- I don't know how you would place a diffraction grating in the optical path. How would the light go through it? Nimur (talk) 20:18, 17 January 2012 (UTC)
- Wouldn't the collimated beam get diffracted and then get focused later? 137.54.17.9 (talk) 20:52, 17 January 2012 (UTC)
Most classical theory considers infinitely thin apertures. What happens when the spacings have thickness, as in real life? Do you get a 3D fourier transform? Do you get optical aberrations because now different orders of light are diffracted and focused differently? 137.54.17.9 (talk) 20:32, 17 January 2012 (UTC)
- What you get is "a thing that can't be accurately modeled with the thin lens equation." For this reason, we have optical ray tracing and full wave equation modeling. Such mathematical models take into account the way that waves interact with sophisticated material properties and complicated geometries. Nimur (talk) 22:45, 17 January 2012 (UTC)
Searching for medical term (not advice)
From personal experience, when I go to the doctor for a regular check-up, one of the first things they do is check my blood pressure. It is invariably always a little higher when they check it at the office, as opposed to when I check it at home. I attribute this to just being nervous- or a little high strung- about the whole doctor's office experience. Is there a specific medical term for this? Note: I am looking for a specific medical term (if it exists). I realize that "false-positive" or "placeabo effect" might loosely apply...but I imagine there is an actual term found in medical texts. Anyone know? Quinn 21:00, 17 January 2012 (UTC)
- Excellent, thank you. The converse term Masked hypertension (found in the article) is also very useful info for my project. Cheers! Quinn 21:10, 17 January 2012 (UTC)
- My own doctor has told me that blood pressure can vary quite a bit during any given day. What they're looking for is trends. There are various tests your doctor can schedule for you if your blood pressure is consistently elevated or high. ←Baseball Bugs carrots→ 00:06, 18 January 2012 (UTC)
- Well, no matter how many BP tests are scheduled at the doctor's office, if every one makes you nervous, then that approach is no good. Perhaps you might get used to them over time. If not, home testing would seem to be the only alternative. No doubt the docs are worried those aren't accurate enough, though. Some way to do highly accurate home tests is apparently needed for these patients. StuRat (talk) 00:27, 18 January 2012 (UTC)
- That isn't necessarily true. As our article notes and should be obvious, most trials regarding the risks of high blood pressure are based on blood pressures recorded in clinical settings. So most of the values we have for risks are based on the value recorded in clinical settings, not any lower values you may record at home. Furthermore, if you're having your blood pressure recorded regularly, your still likely to detect changes (they may be slightly masked, although that's unclear to me from the article).
- Of course since the effect varies between individual, it's likely best (as our article also hints at), for further studies to be done on the risks associated with blood pressure based on values not recorded in a clinical setting. But even this doesn't mean the clinical value is useless once we have such information, and it would only make sense to consider non-clinical values. In fact our article appears to suggest it may provide additional useful information about risks, which isn't that surprising.
- Nil Einne (talk) 05:46, 19 January 2012 (UTC)
- Also, the blood pressure meter you are using at home could be faulty in a way that it consistently measures lower than real pressure. – b_jonas 16:35, 21 January 2012 (UTC)
Deepest drilling
Apologies for the multiple questions (I'm trying to get through some of my to-ask list before the big black banner at the top of the page reaches the Zero hour), but both this one and the above are actually related to a project I'm working on...I'll spare you the boring details. So, the question is, what is the deepest anyone has drilled into the Earth? To clarify, I am looking for "closest to the core" as opposed to "from sea level". And, if possible, I'd like to know what, if any, technical limitation prohibit someone from drilling deeper. Is it just because there has been no reason to go deeper...or is it temperature...pressure...or perhaps the drill itself become too weak after a certain point? Anyway, any links to articles or outside resources about this are appreciated. Quinn 21:17, 17 January 2012 (UTC)
- The Mohorovičić discontinuity article lists several attempts (each in turn with their own articles linked) to drill down that deep. -- Finlay McWalterჷTalk 21:20, 17 January 2012 (UTC)
- Take a look at the articles that are linked to in the Mohorovičić discontinuity article as well. Project Mohole, Kola Superdeep Borehole and Sakhalin I. However, the Sakhalin I wells are "extended reach boreholes" which means the well path turns underground and goes horizontal. So, the Sakhalin depth of 12,345 meters (40,502 ft) is actually only about 1000m deep.
- As for the problems, everything you mentioned above, is part of the reason. The conventional procedure to drill a well uses a motor on surface to turn the drill bit. The drill bit is connected to the surface by drill pipe, which comes in about 10m/30ft joints, which can be combined into 30m/90ft stands. As the bit drills through the earth, fluids called drilling mud are pumped though the drill pipe and come out drill bit. The mud cools the bit and helps wash cuttings (ground up rock) up hole. You have to remove the cuttings to keep drilling. Mud also helps to prevent blowouts, which happen if the pressure of the fluids in the rocks exceed the pressure in the borehole. Blow outs are bad. Once you've drilled 30m/90ft, you have to stop drilling for a minute and connect another stand of drill pipe, using the derrick and another motor to lift and move the stand. Each stand is heavy. Drill pipe can weigh over 100lb/ft (130kg/m) so a stand can easily weigh as much a couple cars. So, the deeper you go, the more powerful your drilling motor and derrick motor have to be and the stronger your derrick has to be. So the first reason is every bit of depth you drill adds a lot of more weight.
- While you drill the bit will start to wear out. It wears out faster at higher temperatures. While mud can help with this, there are problems with mud at very deep depths as well. Once the bit wears out, you have to pull out the drill bit and replace it. A good crew can pull a stand (move the drill string up by 90ft) about every 5 minutes. So at 40,502 ft, it takes at least 37hours to pull the bit and 37 hours to run back in. So if it takes 3 or more days every time you have to change the bit, and you have to change it pretty often that deep (due to temperature and other factors) that really adds up and costs a lot of money. A deep water drilling rig may cost $2-3 US per second to operate. So the second reason, bits wear out faster due to temperature and take longer to replace and cost a lot of money.
- Finally, the mud system gets more complex. You have design muds that won't boil at temperatures over 400F and will be viscous enough at those temperatures to bring up cuttings, but not be too viscous at surface temperature. Exotic muds are very expensive. Then you get to the point where it's impossible to get the properties you need with conventional fluids, so you have to go to experimental fluids, which cost even more. Eventually you get to the point where you can't get a fluid that does everything you need, and have to design much more complex systems. You also need a lot of fluid moving very fast to cool the bit, so you have to have larger and more powerful mud pumps to get flow rate necessary to cool the bit. Which adds more cost. The third reason is the cost and complexity of the drilling mud.
- Even with an infinite amount of money, conventional drilling eventually hits a point where it becomes technologically impossible to go any deeper due to the temperature, ie steel or titanium melt, fluids break down from temperature and pressure, derricks and motors can't be made any stronger.
- the ;tl:dr version. The deeper you go the hotter it is, the longer it takes and the more it costs until the equipment just can't do it. And the cost and time don't increase linearly, but maybe exponentially. Tobyc75 (talk) 22:01, 17 January 2012 (UTC)
- What a nice and clear explanation. Thank you. --Mr.98 (talk) 12:58, 19 January 2012 (UTC)
- I concur. Just got back after the black out, and was pleasantly surprised to find this very informative and detailed answer. Thank you for the time you spent on this! Quinn 16:53, 19 January 2012 (UTC)
- Thanks, for the kind feedback. Tobyc75 (talk) 22:41, 19 January 2012 (UTC)
- I concur. Just got back after the black out, and was pleasantly surprised to find this very informative and detailed answer. Thank you for the time you spent on this! Quinn 16:53, 19 January 2012 (UTC)
- What a nice and clear explanation. Thank you. --Mr.98 (talk) 12:58, 19 January 2012 (UTC)
- the ;tl:dr version. The deeper you go the hotter it is, the longer it takes and the more it costs until the equipment just can't do it. And the cost and time don't increase linearly, but maybe exponentially. Tobyc75 (talk) 22:01, 17 January 2012 (UTC)
- If you launch unmanned probes in space, you get to show nice close-up photos of Jupiter moons to show to the public. But how would you convince a senator to approve money for a project to drill down deeper than ever? According to Irregular Webcomic strip 2835, geology has always been the abandoned foster child of science. – b_jonas 16:34, 21 January 2012 (UTC)
January 19
What was "opening medicine"?
I heard an Australian author on the radio today talking about her books, based around the life of her convict ancestor, William Wiseman. She asked the audience if anyone knew what 'opening medicine' was. There were groans and laughs from the audience and she asked those in the know to explain, on the quiet and if they felt they could, to the others. In her book it is a treament for worms in children. Could you find this out please? — Preceding unsigned comment added by 137.92.97.212 (talk) 03:18, 18 January 2012 (UTC)
- A medical book from the 1840's used "opening medicine" to describe laxatives. (The editor formerly known as Edison). BnBH (talk) 05:13, 19 January 2012 (UTC)
- In other words, "that opens the bowels" (OED).--Shantavira| 11:45, 19 January 2012 (UTC)
superconducters
what is the value of resistance offered by superconducters connected in parallel? (0/0,1/0,0) — Preceding unsigned comment added by Sanoy samuel (talk • contribs) 05:51, 19 January 2012 (UTC)
- It will be very small, approaching zero for ideal superconductors. You can solve this analytically by applying L'Hôpital's rule to the parallel resistor equation, with R1 and R2 each approaching zero for ideal superconductors. Nimur (talk) 06:15, 19 January 2012 (UTC)
Blot (biology)
Was the term 'blot' in use for laboratory techniques before the invention of the Southern blot method? --NorwegianBlue 08:52, 19 January 2012 (UTC)
- The OED seems to imply that the use of "blot" as a means of recording proteins onto film doesn't show up until Southern blot. Browsing around results in JSTOR for "blot" in biological journals doesn't seem to bring up any consistent technical usage of the term prior to Southern blot. The place to really look is where the term "Southern blot" comes from. (I know the inventor's name is Southern, but did he call it a "blot" or did others coin the term?) It's not in the original paper by Southern linked to in the article; the only use of "blot" is the sentence: "After the appropriate period, strips are removed from the solution or paraffin oil, blotted between sheets of filter paper and washed, with stirring, for 20 to 30 min in a large volume of the hybridization solvent at the hybridization temperature." The usage of blotting paper seems responsible for the term. I can't help but wonder if it was influenced by the Rorschach inkblot. This isn't meant to be a conclusive answer, just what I was able to come up with. There doesn't seem to be much out there on the history of the Southern blot, unfortunately. It would make for an interesting historical study in the proliferation of laboratory techniques. --Mr.98 (talk) 19:27, 19 January 2012 (UTC)
- Nice answer. I'll only add that, publishing his work in 1975, Southern was likely fairly familiar with blotting paper, so that "oil, blotted between sheets" wouldn't need any additional referents. SemanticMantis (talk) 20:05, 19 January 2012 (UTC)
- Also, blotter paper is used in thin layer chromatography, which was developed in the 1940s, according to History_of_chromatography#Thin_layer_chromatography. So, if biologists were using TLC in the 1960s, they may well have been using "blot" in a similar context before the Southern blot technique was invented. SemanticMantis (talk) 20:13, 19 January 2012 (UTC)
- Thanks a lot, both! I've just received the 1975 paper from my library, which confirms that Edwin Southern didn't use the word 'blot' as a noun at all, only as a verb, and only in the sentence that Mr.98 quotes. I really liked the reference to the Rorschach blot, which predates the Southern blot by half a century! Blotting paper indeed must be the origin of the term. Although blotting paper is used in chromatography, I've never heard the term 'blot' being used to describe a chromatogram. I think the reason is that in Southern/Northern/Western/etc blots, the action occurs somewhere else (gel electrophoresis), and the separated mixture of biological substances in transferred -- blotted --- onto blotting paper. In chromatograpy, however, the separation occurs in the filter paper itself, and there is no blotting step. --NorwegianBlue 21:45, 19 January 2012 (UTC)
- Nice answer. I'll only add that, publishing his work in 1975, Southern was likely fairly familiar with blotting paper, so that "oil, blotted between sheets" wouldn't need any additional referents. SemanticMantis (talk) 20:05, 19 January 2012 (UTC)
Evolution again...
Well, this time I want to ask about two things I can't relate about genes and evolution.I can't relate the "all or none" nature of genes and how they work, and the smooth, gradual nature of evolution(or even smooth differences between individuals, which can be explained easier by considering the large number of genes...or can it?).I mean in cases like evolutionary arms race for example, it's often said that for example, lions become faster as the zebras become faster.What does this "getting faster" mean in genetic terms.I mean genes don't get "amplified".Does each little level of getting faster require a different genetic change?
Also is this right to say that when the environment doesn't change in a long time, some traits in species tend to be exaggerated?(please don't sacrifice any of my questions for the other, this is the last level for me to get a satisfying picture of how evolution works, or maybe one of the last ones!)
Last question: is it true that chromosomes only form during cell division?--Irrational number (talk) 15:56, 19 January 2012 (UTC)
- For question 1) it isn't exactly clear that genes (DNA) are the ONLY thing which affects evolution, there are also epigenetic factors, research in this field is somewhat nascent, but there is considerable evidence that some heritable characteristics can be passed outside of nucleic acids. Also, there is not universal agreement among the scientific community that evolution is constant and gradual. There are two competing theories on the rate of evolution (and, as always, reality probably lies somewhere between them). The kind of evolution you are talking about is called phyletic gradualism, while the competing theory, which says that evolution occurs in fits and starts, is called punctuated equilibrium. Both ideas are probably at work in evolution. The reason lions and zebras both get faster has to do with natural selection: in a very broad sense lions that are too slow to eat zebras starve to death and thus don't get to have slow babies to pass their slow genes onto, while zebras that are too slow to avoid lions don't get to have slow babies to pass their slow genes onto. For your last question, yes, the actual "chromosome" structure you recognize in the pictures only forms during certain phases in the cells lifetime. At many times, the individual chromosomes aren't visually identifiable, see Chromatin which has some nice descriptions on the various forms it takes. The chromasome structure most people will recognize seems to happen during the metaphase part of the cell's life cycle. --Jayron32 16:40, 19 January 2012 (UTC)
- On the very first part of your question regarding the 'all-or-nothing' 'present-or-not' nature of genes, you may want to have a look at our article on gene expression. Getting from a particular DNA sequence to a visible trait is a multistep process that can be tweaked all the way along by a pretty huge number of factors. There are some very complex mechanisms that regulate the effects of single genes. (If you think about it, your own body is a powerful demonstration of this. Trillions of cells with the same DNA, yet some of those cells are germ-hunting macrophages that can engulf and eat bacteria; some are two-meter-long neurons that can electrically link your brain to your toes with a single cell; some are hair-making trichocytes that spin out nothing but fibers all day long. If you were to separate out all these different cell types and look at them in a petri dish, you'd have no idea they all came from the same organism—yet their genes are identical.) TenOfAllTrades(talk) 16:59, 19 January 2012 (UTC)
- hm... I had the very question that "why are the cells in my body different when they are genetically identical" here in refdesk...--Irrational number (talk) 17:12, 19 January 2012 (UTC)
- (edit conflict)x2 Well we obviously can't enumerate which genes (and proteins, etc.) specifically make modern lions and zebras faster than their ancestors, but the overall genetic change meant they are phenotypically expressed to make the animals faster. It doesn't necessarily mean it has to be the same gene again and again, as genes aren't usually that discrete (e.g. there is no "fast gene"), but sometimes it does.
- The evolutionary arms race is best explained by the Red Queen's Hypothesis. The name comes from Red Queen's race in Lewis Carroll's Through the Looking-Glass, from a conversation between Alice and the Red Queen:
- "Well, in our country," said Alice, still panting a little, "you'd generally get to somewhere else — if you run very fast for a long time, as we've been doing."
- "A slow sort of country!" said the Queen. "Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!"
- Imagine that species (or even different sexes in a species) are constantly in a coevolutionary arms race to outwit the other. As soon as one overtakes the other in weapons/skill/reproductive potential, the other must adapt or die. A classic example would be the extreme toxicity of the rough-skinned newt (Taricha granulosa). Why is it so poisonous when only a tenth of its poison could already kill a full-grown man? The answer lies in its predator - the common garter snake (Thamnophis sirtalis). The snakes continuously adapt to the toxins of the newts so they can eat them. In turn, newts continue to become more poisonous so they can avoid being eaten. Snakes who have lesser resistance to tetrodotoxin die and thus only the snakes with the strongest resistances pass their genes to the next generation. Newts with less lethal poison get eaten, so only the more poisonous pass on their genes to the next generation. Each drives the other's adaptations, and in turn, evolution, until you end up with newts with extreme amounts of poison and snakes with extraordinary resistance to that poison due to the positive feedback. To an outsider species not part of the coevolution, the adaptations of the two seem too much; but to both species, they are simply maintaining the status quo. The number of newts getting eaten and the number of snakes dying is probably the same as when the two first began their predator-prey relationship (hence "running to stay in the same place").
- And yes, the rate of evolution is still unclear but it may be both gradual and slow over long periods of time, or rapid in short bursts.
- As for the second question, not necessarily. Isolation can induce allopatric speciation usually through genetic drift, and different environments induce different evolutionary pressures. The longer an organism is in a certain environment, the degree into which it has evolved to fit that environment is usually greater. Not always though, some environments can exert enough different evolutionary pressure to keep organisms always "on their toes" so to speak, so it could readily adapt to new environments. Some have limited effect such that the organisms begin to "forget" their former "malleability". Instead, their evolution is focused on exploiting the environment they are in as best as they possibly can; with the disadvantage that if the environment were to abruptly change or if they find themselves in another environment, they would be more vulnerable (e.g. whales have adapted so much to life on the sea that beaching them will mean death).
- And your last question is a bit vague. If you meant the formation of genetic material, see mitosis and meiosis. Chromosomes are DNA. They divide and reorganize during these phases, but they do not form out of nothing. If you meant the visible clumped chromosomes (chromatin), refer to Jayron's answer above.-- Obsidi♠n Soul 17:40, 19 January 2012 (UTC)
- Getting faster is a goal, not a means; it has no one implementation in genetic terms. Some aspects are trade-offs, for example fast twitch muscle fibers versus slow twitch depend on whether your wildebeest has to run away from a sprinting predator or one which can sustain speed for a longer period. I think that the attachment of tendons to the bone should have something to do with it; they can be designed to apply better leverage to improve strength, at the cost of slowing the speed at which the joint actually moves, just like different gears on a car transmission. Wnt (talk) 08:29, 22 January 2012 (UTC)
- Your question touches on something I've wondered about: to what degree is the existence of a prey species dependent on the predator? We all know the story of the dodo - without predators to keep it in shape, it was just waiting for the first thing to come along and wipe it out. I wonder whether evolution, acting on large populations over a long time scale, might punish populations of zebras that become too fast for the lions to catch just as effectively as it punishes individuals that fail to keep up. Wnt (talk) 08:32, 22 January 2012 (UTC)
Genetically engineering healthy foods
So far genetic engineering has been done to benefit farmers, but not consumers (except perhaps by lowering price). For example, crops have been engineered to be either disease or parasite resistant, or to better tolerate pesticides. Now my questions:
1) Is anyone working on genetically engineering foods to actually be healthier (or perhaps to make healthy foods more palatable) ?
2) For a specific example, could chicken eggs be engineered to have more good cholesterol and less bad cholesterol ? StuRat (talk) 18:27, 19 January 2012 (UTC)
- 1) See golden rice. Also, I would not say that GMO crops that increase yield "benefit farmers, but not consumers". Independent of price, genetic engineering, as well as "traditional" techniques of hybrid crops and artificial selection, have dramatically increased worldwide food production over the past ~50 years, effectively increasing the carrying capacity of Earth. SemanticMantis (talk) 19:20, 19 January 2012 (UTC)
- The infamous Flavr Savr was clearly intended to be appealing to consumers even if it failed. In addition to what SM has said, note that disease and parasite resistance, and in some cases even better tolerance of pesticides may benefit consumers in ways besides yield. For example by reducing the amount of pesticides that have to be used, or allowing the use of potentially less dangerous pesticides (in the case of pesticide tolerance). (In a more roundabout fashion, they may in some cases reduce environmental damage which is likely to be a benefit to consumers living near the farmers and perhaps even some further away. And remember with the carrying capacity/yield thing, it not only means you can support more people at a lower price, but for a given number of people use less land.) I expect the controversy of GMOs means that there's less incentive for more obvious benefits to consumers. If your product is healthier or more palatable, you're likely going to need to label it as such. And when you label it, some people will start to ask why and will quickly find out it's from a GMO. Nil Einne (talk) 05:07, 20 January 2012 (UTC)
- But the problem is people's perceptions of GMO foods. If there was something demonstrably healthier, like the egg I mentioned, perhaps this would overcome people's reluctance to embrace the "unknown". Specifically, something "improved" that actually shows up on the nutrition label. StuRat (talk) 05:14, 20 January 2012 (UTC)
- That's a nice theory. When you're spending millions of dollars developing, marketing etc a GMO however, you have to live in the real world where your theory could easily fall flat on its face, particularly in Europe. Nil Einne (talk) 15:54, 20 January 2012 (UTC)
- That's my point exactly, GMO foods without any obvious consumer benefit have fallen flat in Europe, so it's time they try something else. StuRat (talk) 16:02, 20 January 2012 (UTC)
- 2) From the looks of it, egg cholesterol can be modified simply with drugs or diet, which is probably cheaper. The fact we haven't been able to breed low-cholesterol chickens also implies that so far we have no way knowing which genes are responible for egg cholesterol levels. It does seem at least theoretically possible - chickens produce more cholesterol than their embryoes need, so GM chickens would still be able to breed. Smurrayinchester 09:54, 20 January 2012 (UTC)
- Benefit to farmers, but not consumers? Norman Borlaug is often credited with saving over a billion people worldwide from starvation (he used multiple techniques, not just GE food). Von Restorff (talk) 12:32, 20 January 2012 (UTC)
- To clarify, I mean obvious benefits to those consumers who can freely choose between GMO and non-GMO foods. This doesn't apply to those in third world nations, who will eat any food they can get, even if it glows. To some extent, it doesn't apply in the US, where GMO foods are not labelled as such. However, some consumers will still find out which brands use GMOs and avoid them. Europe is probably the biggest market where consumer perception of the value of GMOs is critical. StuRat (talk) 16:06, 20 January 2012 (UTC)
- Point of clarification / mincing words: GMO crops are often designed to be herbicide resistant, e.g. Roundup Ready soybeans, or to be pest resistant, e.g. Bt corn. Pest resistant crops may allow for lower or less use of pesticides. In contrast, pesticide tolerance is not a normal goal of GMO crop design. Commonly used pesticides, even the most noxious (e.g. Sevin), don't harm the conventional crops they are applied to. SemanticMantis (talk) 15:35, 20 January 2012 (UTC)
- See pesticide. Herbicides are a class of pesticides. You're correct herbicides are by and large the only pesticides for which tolerance is engineered in plants (for obvious reasons). Nil Einne (talk) 15:44, 20 January 2012 (UTC)
- Duly noted, thanks. Now I'll start correcting my weed science associates when the get sloppy with terminology ;) SemanticMantis (talk) 16:16, 20 January 2012 (UTC)
- See pesticide. Herbicides are a class of pesticides. You're correct herbicides are by and large the only pesticides for which tolerance is engineered in plants (for obvious reasons). Nil Einne (talk) 15:44, 20 January 2012 (UTC)
- Genetically_modified_tomato#Improved_nutrition lists a couple of examples. SmartSE (talk) 17:23, 20 January 2012 (UTC)
- Note that LDL and HDL are defined by the human protein constituents that interact with the cholesterol and other lipid materials during the period when they pass through the bloodstream. A chicken egg contains neither, and can't control what the body will do with ingested cholesterol unless it acts more or less like a drug (say, if you added statins to them...). Reducing the cholesterol content of an egg would be complicated, because the egg by its nature needs to produce a whole chick's worth of cell membranes quite rapidly. Of course, as biology is flexible, I'm sure you could reduce it by some significant amount. In the extreme instance I suppose you could design an egg to respond to some external stimulus by destroying its stored cholesterol, which would not be provided to eggs for breeding. Wnt (talk) 08:23, 22 January 2012 (UTC)
Why is it easier to make an electric car than it is to make an electric airplane?
^Topic ScienceApe (talk) 20:28, 19 January 2012 (UTC)
- Weight of the batteries. AndyTheGrump (talk) 20:32, 19 January 2012 (UTC)
- ... Rather, energy density of the batteries. Avgas contains some 100x more energy per kilogram than a lithium ion battery. Nimur (talk) 20:40, 19 January 2012 (UTC)
- Yup, strictly speaking, you're right. Plus, using Avgas, the plane gets lighter as you use it up - so you need less power, which makes it even more efficient. AndyTheGrump (talk) 21:28, 19 January 2012 (UTC)
- Note that it's not being electric that's a problem for airplanes, it's storing the electricity. Solar-powered electric motor airplanes do have some potential, in the form of an unmanned, light-weight, observation platform. StuRat (talk) 04:16, 20 January 2012 (UTC)
- Induced gamma emission may be of tangential interest: among the potential applications is powering electrical airplanes. 157.193.175.207 (talk) 09:11, 20 January 2012 (UTC)
- And to state the obvious, but that completes the answer to the questions: The car has all 4 wheels continuously touching the ground which supports it, so the weight is less of an issue (although it is still a bit of an issue).--Lgriot (talk) 09:13, 20 January 2012 (UTC)
- There are a couple of battery electric aircraft in development, such as the Sonex ESA and an electric version of the Pipistrel Panthera. The problems encountered are a very short range and aircraft endurance (by modern standards). With a normal engine (and a typical fuel system) these aircraft would far outpace themselves in terms of performance. The electric Panthera is intended to have a range of 215nm (400km), per the company website, and sacrifices two of the four seats to accommodate the batteries. The all gasoline version is intended to do 1,000nm for comparison. I personally think that battery powered aircraft technology will creep into the market and become somewhat popular, if for no other reason than with prices often at $5 a gallon or more for AvGas in the United States (and therefore probably much more elsewhere), many of us simply cannot afford to fly a lot of the gasoline powered aircraft very much anymore. For local sport-type flying, I suspect that the electric aircraft would cut down on the costs tremendously (after initial purchase). Falconus 20:04, 20 January 2012 (UTC)
- You seem to be saying that the cost per mile is less in a battery-powered airplane. I'm rather skeptical. Battery powered cars are more expensive per mile, when you prorate the much higher cost over the life of the vehicle (or life of the batteries). It would be even worse for airplanes, because of the inefficiency in carrying all that extra weight around (and fewer passengers, in your example). I'd say fuel prices would have to go up far more for batteries to be cheaper, and, even then, alternatives like ethanol or compressed hydrogen would probably replace fossil fuels. StuRat (talk) 08:39, 21 January 2012 (UTC)
- If I put 100,000 miles on a Nissan Leaf, by my rough calculations (figuring 34,000Kw for 100,000mi), which is when the warranty runs out, I would spend $3,060 on electricity, assuming 9¢ per kW. In the same number of miles, for a vehicle that gets 30mpg, I would burn 3,333.33 gallons of gas. At $3.50 per gallon, that's
$11,6667$11,667. In the US, it is more cost effective to get a standard car, as new batteries currently cost Nissan $18,000 a pop. However, in England, where fuel costs €1.58/L, or €5.98/gal ($7.75/gal). There, the fuel costs for that same distance would be $25,833.33. Assuming electric costs of 15p per kW, that would be £5,100, or $7,942.23. That means that in effect, in England (if my calculations are correct), you would only spend $118 more per 100,000mi assuming a battery life of 100,000 miles. With improvements in technology, rising gas prices, less maintenance (if I am not mistaken, motors are more reliable, are they not?), and the fact that the battery life is probably quite a bit more than the 100,000 guaranteed miles (a car company would be insane to put that guarantee on it while predicting that it will die at 101,000), I think it probably would in fact be be cheaper (if not significantly so) in places such as England, at least without including the initial purchase costs. Maybe I am missing some factors, however. Airplanes are a different beast, and I do not have the numbers, nor time to research them at the moment. You may be correct that at the moment the new technology would be much more expensive, even after the initial purchase. I assumed it was far cheaper, but the car demonstrates that even that doesn't break even yet in the US. Does my math look right there? Falconus 14:17, 21 January 2012 (UTC)
- If I put 100,000 miles on a Nissan Leaf, by my rough calculations (figuring 34,000Kw for 100,000mi), which is when the warranty runs out, I would spend $3,060 on electricity, assuming 9¢ per kW. In the same number of miles, for a vehicle that gets 30mpg, I would burn 3,333.33 gallons of gas. At $3.50 per gallon, that's
- Looks roughly right, with a few caveats:
- 1) Your "$11,6667" seems to have acquired an extra digit, but I don't think you carried that through to the subsequent calcs.
- 2) Many batteries are able to hold progressively less charge as they get old. Not sure if this applies to electric car batteries or not. However, if so, they might very well only replace "bad batteries" when they no longer hold any charge at all, or an absurdly low charge, so one needs to read the fine print to determine what this 100,000 mile warranty actually covers.
- 3) Batteries also lose charge when sitting still, so some accounting for that is needed.
- 4) The higher costs of gasoline/petrol in England is due to some rather stiff taxes, and there may also be subsidies in the cost of the electric vehicle. Whether those should be figured in is debatable. If we're trying to determine which is generically the most efficient technology, then perhaps taxes and subsidies should be removed from the calcs. If we are including them, then we need to also consider future changes. While taxes on gasoline and subsidies for electric vehicles may make sense when trying to encourage a new industry (and discourage the old one), that picture would change if the majority switched to electric vehicles. In particular, the gasoline taxes may no longer be sufficient for road maintenance, etc., when gasoline sales start to drop off, and governments may no longer be able to afford to subsidize electric vehicles once sales reach tens of millions. So, inevitably taxes will be shifted from gasoline to electric vehicles at some point. Is this likely to happen within the 100K mile test period ? Hard to say. Then there's the cost of disposing of the batteries once they fail. Who will pay for this ?
- 5) The gasoline-electric hybrid seems to be a better bet, as it doesn't need to have so much battery capacity to have a reasonable range. Maybe our calcs should include those.
- 6) You said "...I think it probably would in fact be be cheaper (if not significantly so) in places such as England, at least without including the initial purchase costs". However, I see no justification for excluding the initial purchase price. StuRat (talk) 18:40, 21 January 2012 (UTC)
Captain Obvious to the rescue: cars in general are easier to make than airplanes, and we have much more experience researching, developing and building cars. @StuRat: Gasoline-electric hybrid airplanes may be a good idea, but hybrid cars suck. Von Restorff (talk) 19:06, 21 January 2012 (UTC)
- Just to update on the UK situation, your price for electricity was a little on the high side. Average cost for a 'unit' is about 13p (1 unit = 1kWh), although this can be reduced to 4.5p/unit if you have an Economy 7 tariff and charge your car at night. Also, a grant of 25% of the purchase price of an electric car (up to a maximum grant of £5000) is given by the government. See here. I realise this doesn't help to answer the original question, but I hope it helps in the accuracy of the comparison. - Cucumber Mike (talk) 19:23, 21 January 2012 (UTC)
- Okay, thanks; that should then drastically decrease the electricity costs for England to £1,530, or $2,382.67 at the 4.5p/kW rate, giving a difference of $23,450.66. That would be $5450.66 left over after the $18,000 battery. I also found this. Nissan is saying that once the battery capacity dips below 80%, people should start replacing individual cells, not the whole pack. Granted, at some point by default you will have replaced the whole battery, one cell at a time, so I'm not sure if/how that helps in the long run (unless the cost of the unit itself, without the actual cells, is significant), but that kind of relates to question number two. As for the hybrid aircraft, there will also be the hybrid Pipistrel Panthera, with performance figures between the electric and the gasoline versions. The thing to be seen is how the technology develops in the future; how much the prices will come down, and what the eventual disposal costs will be, as StuRat said. Although, apparently some people are looking into reusing the batteries in other applications that don't require the 80% charge capacity to be useful, thus extending the battery life (and meaning that the battery/cells would still have some value when it's time to switch them). Falconus 20:07, 21 January 2012 (UTC)
- My reading on that link is that they won't do anything about weak batteries until they drop below 80%, and then will just replace enough cells to bring it back up to 80%. So, you should probably figure on 80% of the stated range as the real range, further limiting it's usefulness. StuRat (talk) 04:29, 23 January 2012 (UTC)
Photosynthesis Poster
Hello. Where can I buy a poster of photosynthesis appropriate for university? I prefer a supplier that can deliver to Canada. Thanks in advance. --Mayfare (talk) 20:55, 19 January 2012 (UTC)
- My first reaction was Fisher Scientific, fishersci.com - where I found this photosynthesis poster. You'll have to decide if it's appropriately detailed; there are a few other items - lab kits, CD ROMs, and so on. Nimur (talk) 21:07, 19 January 2012 (UTC)
- As a supplement, there are nice graphics in our article on Photosynthesis as well (more in Commons:Category:Photosynthesis). You can print them freely (and even sell them), with the only requirement being that you provide attribution to the artist(s).-- Obsidi♠n Soul 21:38, 19 January 2012 (UTC)
- Several of those charts are not in English. If you need assistance translating or modifying them, you can post a request for translation here on the reference desk, or on WP:TRANSLATE. Nimur (talk) 01:36, 20 January 2012 (UTC)
Forging a ring from fountain pens
I'm into forging a ring from iridium-platinum (or iridium-osmium) tips of fountain pens (according to some sites, 30-40 tips for one ring is sufficient). The idea is to melt those tips in a form and then cool the alloy down. Is there a relatively simple and cheap device to create the appropriate melting temperature? I'm also concerned about the proper way of cooling, thanks. --46.204.99.30 (talk) 22:46, 19 January 2012 (UTC)
- Not being funny but I think you'd be better off finding some other to do. The time taken to achieves this, would make it more economical to use other sources of platinum. The pen tips have only enough plating to ensure that one has a non corrosive tip which will allow ink to flow smoothly to the paper. Your sources may be misleading you. --Aspro (talk) 23:14, 19 January 2012 (UTC)
- Iridium, platinum, and osmium all melt quite a bit hotter than any steel you've ever worked. Are you a skilled metallurgist? Do you have a furnace? High temperature crucible? Oxy torch? No, there is no way to do this on the cheap-and-easy. This article seems to be a pretty good overview. Nimur (talk) 03:26, 20 January 2012 (UTC)
In which U.S. states are capybaras legal?
In which U.S. states are capybaras legal as pets? I'm hoping for a link that will show all states instead of having to go to each state individually. Thanks, 72Dino (talk) 23:53, 19 January 2012 (UTC)
- In urban areas of the Southern U.S. (like Houston and New Orleans especially) you can find nutria living in drainage ditches and sewers and the like. Nutria are very similar to capybara, so perhaps if you hang out with some of the homeless in New Orleans, one will just come along and decide to be your pet. No need to import yet another invasive giant rodent into the U.S. One is enough, thanks. --Jayron32 01:50, 20 January 2012 (UTC)
- However I'm guessing if you're Catholic, you can't eat your pet nutria during lent if the urge ever arises. Nil Einne (talk) 05:13, 20 January 2012 (UTC)
- This page has a summary on laws about exotic animals in each state. None of them specifically mention capybaras.
- Many states ban or place severe restrictions on "inherently dangerous animals" (Virginia), "potentially dangerous animals" (Connecticut), etc, laws which are sufficiently flexible that they might apply to capybaras. However, many of these laws have grandfathering provisions, so if you had a capybara for long enough you could keep it.
- Realistically if an animal is sufficiently unusual, a state may never have considered if it should be allowed. Most states have a State Veterinarian who will answer questions on this sort of thing. --Colapeninsula (talk) 12:43, 20 January 2012 (UTC)
crazy
No medical advice. See talk page. |
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The following discussion has been closed. Please do not modify it. |
how do i know that im not crazy? I cant remember where i learned it but i know crazy people doesnt know their condition, so what assurance do i have that everything i see and does is normal? — Preceding unsigned comment added by Arah18 (talk • contribs) 23:57, 19 January 2012 (UTC)
If I show you a proof that you are not crazy, would it help? How could you know that you are judging the validity of the proof correctly? Looie496 (talk) 00:54, 20 January 2012 (UTC)
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- If you are interested in pursuing this question from a purely philosophical viewpoint, feel free to repost it on the Humanities desk and make it clear that you are referring to something abstract, not any actual diagnosis of mental illness. If you are actually wondering if you are suffering from mental illness, please consult a professional: we cannot give medical advice on the Reference Desk. --Mr.98 (talk) 22:13, 20 January 2012 (UTC)
January 20
odd rabbit behavior
Where I live on the Kenai Peninsula we have snowshoe hares running around. As is indicated on the article, they undergo population spikes every so often, and one has been ongoing here for the last two years. Something I have observed is that at this time of year they are quite often found on the edges of roads, and they have this annoying/.stupid habit of running out in front of moving cars in the dark. I have seen them sit on snow berms on the side of the road and wait until a car got close, so that it's lights were illuminating the area right in front of the hare, and then they run out. So my question is, why would they wait like that? It seems completely counter-intuitive that theirt instinct would tell tham to wait until a threat was close before running directly in front of it. — Preceding unsigned comment added by Beeblebrox (talk • contribs) 00:58, 20 January 2012 (UTC)
- Our Spotlighting article (while a pretty crappy one) describes some of this behaviour, telling us that "...many animals (e.g. foxes and rabbits) often remain to continually stare at the light and do not appear to see the light as a threat as they normally would view a human". HiLo48 (talk) 02:03, 20 January 2012 (UTC)
- Interesting question, and I don't think there's a definitive answer. A few possibilities to consider:
- Your observations may have some bias, i.e. you aren't as likely to notice if the rabbits run away from the road when the car approaches.
- Fight or flight type instincts don't have to be perfect to be beneficial on average. For example, if the rabbits bolt in a random direction when threatened, this still may save more lives on average, compared to doing nothing. So it's not that surprising that the behavior stays around, even when it sometimes ends up killing the rabbit.
- As for the timing: the classic natural predator of the hare is the lynx. Footage such as this shows how the hare gets away by being better at cornering, not by being faster in a straight run. In this case, the hare is better off not bolting until the last second.
- In many modern environments, cars may well kill more hares than lynxes. This could be providing selective pressure, and perhaps future generations will be slightly better at avoiding cars.
- Lastly, peak population density puts all kinds of pressures on the critters, they are competing intensely for good forage sites, etc. This is bound to make them act a little funny. SemanticMantis (talk) 02:21, 20 January 2012 (UTC)
- The rabbits are probably thinking the car is a predator, and applying their evasion method for those predators. Since those predators aren't as fast as cars, the rabbits can dart across their path, get the predator to turn sharply and tumble over, and thus get away. Obviously, this doesn't work well with cars (although some idiot will occasionally crash their car swerving to avoid them). StuRat (talk) 04:05, 20 January 2012 (UTC)
There is a theory here in Australia that Kangaroos, Deer, Water Buffalo, etc run out in front of vehicles at night because they are trying to escape from a scary/confusing situation, so they run into the only areas they can see clearly in, ie the area lit up by your headlights! I've certainly found that if I turn my headlights off they don't run out in front of me. — Preceding unsigned comment added by 124.191.177.248 (talk) 08:01, 20 January 2012 (UTC)
- And of course one more thing to add is that hares have been selected to avoid lynx for millions of years, by lynx killing those who didn't behave in a logical lynx avoidance pattern, whereas cars have only been around in any significant number for 60 years. Evolution doesn't work that fast! A new hare behaviour may occur at some point cause by selective pressure, but by the time it occurs, we may already be in the process of replacing cars with another transport mechanism, which may or may not kill hare in a different manner. --Lgriot (talk) 09:32, 20 January 2012 (UTC)
- Arctic Hare do the same thing. Curious though. Do snowshoes sometimes sit very still if you are walking? The Arctic hare will often let you walk past them without moving. I assume they don't see you as a threat and/or figure you can't see them. CambridgeBayWeather (talk) 23:55, 20 January 2012 (UTC)
- Sitting perfectly still is actually a great defense mechanism in this case. Von Restorff (talk) 00:01, 21 January 2012 (UTC)
- The one near my house was using the shadow created by the power/phone/street light pole. Now that I think about it the sitting still is a defence against the Snowy Owl. I watched an owl trying to catch a hare one day and as long the hare kept still the owl would too. When the hare made a break for it the owl would attack. At one point the owl was sitting on a sign and the hare right below it. CambridgeBayWeather (talk) 01:25, 21 January 2012 (UTC)
- Sitting perfectly still is actually a great defense mechanism in this case. Von Restorff (talk) 00:01, 21 January 2012 (UTC)
- Arctic Hare do the same thing. Curious though. Do snowshoes sometimes sit very still if you are walking? The Arctic hare will often let you walk past them without moving. I assume they don't see you as a threat and/or figure you can't see them. CambridgeBayWeather (talk) 23:55, 20 January 2012 (UTC)
- And of course one more thing to add is that hares have been selected to avoid lynx for millions of years, by lynx killing those who didn't behave in a logical lynx avoidance pattern, whereas cars have only been around in any significant number for 60 years. Evolution doesn't work that fast! A new hare behaviour may occur at some point cause by selective pressure, but by the time it occurs, we may already be in the process of replacing cars with another transport mechanism, which may or may not kill hare in a different manner. --Lgriot (talk) 09:32, 20 January 2012 (UTC)
A common hypothesis is that the moving shadows are perceived as a danger, and run from onto the road. Polypipe Wrangler (talk) 20:12, 21 January 2012 (UTC)
Blood dye
A few nights ago, I had a dream in which it became fashionable to dye one's blood green. This gave the skin a greenish tinge. Trendy people carried around syringes of green food coloring which they administered to themselves like insulin shots. I awoke with many questions. In principle, would it do harm to inject food coloring into the blood? Or is it inert and harmless? How much would it take to dye all the blood in one's body? Would a pocket-sized syringe be sufficient? Assuming you're pale in complexion, would your outward appearance be dramatically greener? How green could the blood get? (In my dream it acquired a lurid, absinthe-like appearance.) How long before the effect wore off? LANTZY 04:01, 20 January 2012 (UTC)
- Not sure if it's harmful or not when injected, so don't try it. You probably could change blood color dramatically, but green would be difficult, being the opposite of red. I suspect green coloring would make the blood closer to black. You could probably manage a color closer to red, like orange or purple, provided you could find a safe dye. And yes, changing your blood color would dramatically change your apparent skin color, if you are pale to begin with. StuRat (talk) 04:10, 20 January 2012 (UTC)
- If you want to change your skin colouration, overenthusiastic consumption of carrots (or other carotene containing vegetables) can turn you distinctly orange. Not recommended though, as there can be side effects. As for other colours, gold salts are apparently quite effective in turning people shades of grey. Irreversably.... AndyTheGrump (talk) 04:21, 20 January 2012 (UTC)
- Read Argyria if you want to be blue-ish gray. Can someone find a picture for Stan Jones (politician)? Why green blood, and not blue? Von Restorff (talk) 12:05, 20 January 2012 (UTC)
- If you want to change your skin colouration, overenthusiastic consumption of carrots (or other carotene containing vegetables) can turn you distinctly orange. Not recommended though, as there can be side effects. As for other colours, gold salts are apparently quite effective in turning people shades of grey. Irreversably.... AndyTheGrump (talk) 04:21, 20 January 2012 (UTC)
- Insulin shots are administered under the skin into fatty tissue, not into veins or arteries. Edison (talk) 05:45, 20 January 2012 (UTC)
Eating beetroot turns your urine pink (well it does with me), so presumably the red colouring must be in your blood to get to your kidneys. I wonder if it makes the blood look redder? No side effects apart from bright red faeces! — Preceding unsigned comment added by 124.191.177.248 (talk) 08:06, 20 January 2012 (UTC)
- If you want to change the colour of your faeces, I recommend several pints of Guinness for a noticeable darkening, or spinach for a greenish tint. Then again if such things matter to you, I'd recommend expounding your interests elsewhere... AndyTheGrump (talk) 08:19, 20 January 2012 (UTC)
- Methemoglobinemia results in blue or brown blood, and can visibly affect people's appearance: see the section on "Carriers" (sadly it doesn't have photos, but there's one here if you scroll down past the X-Men character). --Colapeninsula (talk) 12:52, 20 January 2012 (UTC)
- That photo is of Paul Karason. He used to look like this, but later he looked like this. His girlfriend didn't seem to mind. Von Restorff (talk) 13:01, 20 January 2012 (UTC)
- He isn't that way because of his genes. He's that way because he has Argyria — he essentially overdosed on collodial silver because he believed quack stories about its antibacterial powers. Totally different causes — the blog is wrong to list him that way. That blog in general is not what I would call a reliable source. --Mr.98 (talk) 13:54, 20 January 2012 (UTC)
- I would assume that Karasons' hair is very light because of his age (58 then) but I am wondering if the silver had any effect? - 220 of 06:08, 22 January 2012 (UTC)
- He isn't that way because of his genes. He's that way because he has Argyria — he essentially overdosed on collodial silver because he believed quack stories about its antibacterial powers. Totally different causes — the blog is wrong to list him that way. That blog in general is not what I would call a reliable source. --Mr.98 (talk) 13:54, 20 January 2012 (UTC)
- That photo is of Paul Karason. He used to look like this, but later he looked like this. His girlfriend didn't seem to mind. Von Restorff (talk) 13:01, 20 January 2012 (UTC)
- A guy a few years ago surprised surgeons by spurting dark green blood all over the operating table: have a look at the links in sulfhemoglobinemia. Brammers (talk/c) 13:59, 22 January 2012 (UTC)
Farming fish
Are there any fish that are bred and harvested specifically for consumption? My understanding is that fish are mostly just caught in the wild, and they are left to replenish their numbers on their own without external forces to ensure their numbers are high. Is this correct? ScienceApe (talk) 11:44, 20 January 2012 (UTC)
- Some fish are bred and harvested specifically for consumption (e.g. salmon, trout, sea bass, carp, tilapia, and catfish). See fish farming. Today more than 40% of the fish consumed is farm raised. Von Restorff (talk) 11:46, 20 January 2012 (UTC)
- Farmed fish is a very big industry, especially within salmon production. In fact, almost all salmon that is offered to consumers is farmed. See the article on Fish farming. DI (talk) 11:52, 20 January 2012 (UTC)
- Huge industry - also including shrimp, sturgeon, and many other fish. Lovely exhibit at EPCOT if you ever get there. Alligators do count as seafood? Collect (talk) 13:16, 20 January 2012 (UTC)
- In the United States, most fish markets have signs which say which ones are wild and farmed near the price markers. My recollection is that most of them I've seen are farmed. The proportions no doubt vary by country, but "aquaculture has been growing rapidly worldwide, and in 2009, farmed fish and shellfish surpassed wild-caught stocks as the major source of seafood worldwide." So I'd say your understanding of this is probably not correct. --Mr.98 (talk) 13:18, 20 January 2012 (UTC)
- It should also be noted that many farmed fish are better in terms of environment and sustainability. The top wild-caught fishes, especially cod and tuna, are apex predators in their environment, and so have a very low "convertability", i.e. they need a lot of food and territory to survive. These large commercial fish are essentially the lions of the fish world, so are impractical to farm; they also take a long time to grow to economical size for catching, so they take some time to rebound from overfishing. The reason you don't raise lions for food is that lions eat grass eaters. So, you have to first farm a whole lot of grass eaters (like, say, cows and goats) and then feed the grass eaters to the lions. It is much more economical and sustainable to just eat the grass eaters yourself. It's the same with fish: the wild fish we catch and eat themselves eat the small-to-medium sized fish similar to what we now farm. Now, fish farms are not perfect, and some have their own environmental problems, but aquaculture is likely the best route we have for sustainable fish consumption. I've seen shows that make the case that tilapia is one of the best options, even better than salmon, in terms of sustainability. --Jayron32 17:07, 20 January 2012 (UTC)
- But there is some tuna farming. See Tuna#Aquaculture. 75.41.110.200 (talk) 22:06, 20 January 2012 (UTC)
solar panel construction
How do I wire (solder) my solar cells together to build a solar panel??? Please do not direct me to the buy a plan site I got ripped off already so I am broke.... I have 300 6 by 6 inch crystaline or monocrystaline cells but I dont know how to put them in a panel and wire connect them correctly.......Thanks Joe Green in Beaumont Texas.... — Preceding unsigned comment added by 24.242.111.205 (talk) 13:14, 20 January 2012 (UTC)
- If you type "build a solar panel" into the search box at the website www.google.com and select the first result, it is this website which has the plans to build a solar panel from 6-inch monocrystaline cells. Those plans calls for 36 cells per panel, so you should be able to construct several. --Jayron32 15:23, 20 January 2012 (UTC)
- Do the solar cells already have wire leads? That makes things much simpler. I have rarely been successful soldering leads to the tinned area on a solar cell. Edison (talk) 16:11, 20 January 2012 (UTC)
- What do you plan to power with the final unit? It will make a difference - whether you want to connect them in parallel or in series; whether you need load balance circuitry or active power control circuitry, and so forth. Nimur (talk) 19:53, 20 January 2012 (UTC)
- Do the solar cells already have wire leads? That makes things much simpler. I have rarely been successful soldering leads to the tinned area on a solar cell. Edison (talk) 16:11, 20 January 2012 (UTC)
drug test
does tramadol show up the same as hydrocodine/oxycodine in a drug test — Preceding unsigned comment added by 71.51.57.30 (talk) 15:54, 20 January 2012 (UTC)
- We cannot tell you, we cannot give medical advice. Von Restorff (talk) 16:53, 20 January 2012 (UTC)
- But we can refer you to our tramadol article, and in particular the Detection in biological fluids section, which may help. (Or it might not, but it can't hurt to read it.) Mitch Ames (talk) 02:49, 21 January 2012 (UTC)
- I can't quite figure why this question is deemed to be seeking medical advice. The OP does not refer to him/herself, there is no mention of personal action, there is no reference to illness or pathological condition. It could be regarded as a perfectly simple haematological enquiry. Perhaps if the OP had put in some disclaimer that this was a scientific question and did not apply to any person specifically then it would have been OK? Richard Avery (talk) 08:38, 21 January 2012 (UTC)
Efficiency Test for Evolutionary Algorithms
I was working on evolutionary algorithms, particularly a variation of DE that we have developed. As with most updates, it gives better results but with higher computing time, so i want to find out how good it really is quantitatively, like with some measures. For example the likes of Amdahl's Law or those in the wiki page on Algorithmic Efficiency that deal with cases were one or more of the desired characteristics are getting better at the expense of others. Basically i need some kind of measure depending on the final error and the computing time. Any suggestions?--tathagata 19:11, 20 January 2012 (UTC) — Preceding unsigned comment added by Nonstop funstop (talk • contribs)
Polyneuropathy and GABA
This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the talk page discussion (if a link has been provided). --Jayron32 20:47, 20 January 2012 (UTC)
Atomic explosion in your hands
You have 2 half-spheres of pure plutonium-239 in your hands. Each half-sphere has a sub-critical mass - 9 kg. You join the half-spheres. Now you have a sphere of pure plutonium-239 with a super-critical mass (18 kg, almost two critical masses).
Should it explode?
Can you create a scenario where bringing together subcritical fissile masses results in a small explosion?
--Zhitelew (talk) 21:18, 20 January 2012 (UTC)
- No. Read the second paragraph for your answer. KägeTorä - (影虎) (TALK) 21:24, 20 January 2012 (UTC)
- They have a mass just above critical (in this case nuclear reaction becomes subcritical again within a few seconds). How about a half-spheres with sub-critical masses (each)? --Zhitelew (talk) 21:34, 20 January 2012 (UTC)
- No, they were subcritical. Read the 'Incidents' section of that article to see. KägeTorä - (影虎) (TALK) 21:38, 20 January 2012 (UTC)
- I mean joining the half-spheres:) Something like Gun-type fission weapon (but with the low speed). Also, small explosion is ok, I don't require a full explosion of the mass --Zhitelew (talk) 21:47, 20 January 2012 (UTC)
- No, they were subcritical. Read the 'Incidents' section of that article to see. KägeTorä - (影虎) (TALK) 21:38, 20 January 2012 (UTC)
- They have a mass just above critical (in this case nuclear reaction becomes subcritical again within a few seconds). How about a half-spheres with sub-critical masses (each)? --Zhitelew (talk) 21:34, 20 January 2012 (UTC)
- At the *very* best, you'll get a fizzle. But really you'll just die of radiation sickness. You simply can't whack the spheres together fast enough to get a decent explosion. Not even Thin Man was fast enough, which is why they abandoned it. See Predetonation. --Sean 21:49, 20 January 2012 (UTC)
- Well, the OP did specify pure Pu-239. It's possible you could use pure Pu-239 in a gun-type device and get a substantial yield. But pure Pu-239 is hard to manufacture. The plutonium they had during WWII was not pure; it had lots of Pu-240 in it, which is why they couldn't use it in the Thin Man. --Mr.98 (talk) 21:56, 20 January 2012 (UTC)
- If it's just a critical mass, you probably see nothing, but the rate of reaction rate is increasing. Eventually the thing will heat up and melt. If it's supercritical, the bits may have a small explosion and separate. But not a full nuclear explosion. Your hands are not adequate for holding together an exploding core enough for the reaction to build to that level. The cores in nuclear weapons need to be held together for a small amount of time for the reaction to really propagate like they do in a nuclear weapon.
- Even rather simple nuclear weapons need a little more "help" than what you're describing to get even kiloton ranges of explosives: confinement, a tamper, a neutron initiator, etc. What you're describing is essentially an unshielded fast-neutron reactor, not a bomb. --Mr.98 (talk) 21:56, 20 January 2012 (UTC)
- Can it works with another fissile material (in theory)? With something like californium-252. According to Critical mass article, you need only 3kg of californium-252, and the sphere is pretty small, so neutrons don't need to fly long --Zhitelew (talk) 22:14, 20 January 2012 (UTC)
- Define "work"? Can you create a scenario where bringing together subcritical fissile masses results in a small explosion? Then almost certainly yes. Even the force of a single stick of TNT could presumably kill the person handling it before the equally lethal radiation. Figuring out where the transition from major criticality accident to minor nuclear fizzle occurs is likely to be very difficult though. If you want a nuclear detonation that is actually impressive however, then you probably need substantially more than your hands to manipulate the pieces regardless of the material being used. Dragons flight (talk) 22:33, 20 January 2012 (UTC)
- I think irregardless you'll need something more than your hands. It'll heat up and expand and separate. A little explosion if any. But I'm just basing this on an intuitive notion of it, not actual calculations. The reaction process in a bomb is an exponential process, and almost all of the energy released is in the last couple of fission generations. But there are explosively significant generations before that. If there isn't something holding them together when they go through the "just a dab of TNT" generation of energy release, it won't ever get to the "really impressive amounts of energy" stage. --Mr.98 (talk) 23:58, 20 January 2012 (UTC)
- I remember seeing a film with a guy doing exactly doing that in front of a group of people. A blue flash and and a loud boom and most of the people died of radiation sickness and inhalation of plutonium although the both spheres looked nearly intact.--Stone (talk) 14:50, 21 January 2012 (UTC)
- I suspect the film you have in mind was Fat Man and Little Boy, which features a fictionalization of the Louis Slotin/Harry Daghlian cases. --Mr.98 (talk) 14:56, 21 January 2012 (UTC)
- Joe Don Baker's character does that in the TV series Edge of Darkness (with rods of Pu); I've not seen the film remake but the description there suggests that scene isn't recreated. -- Finlay McWalterჷTalk 15:00, 21 January 2012 (UTC)
Escape velocity of major star
Could there exist a star with about 10 × 10 kg in mass, therefore having an escape velocity of about 300,000 km/s (more than the speed of light?) If it could exist, would that mean that light could not escape that star? And hypothetically, what would that star look like? 64.229.180.189 (talk) 22:05, 20 January 2012 (UTC)
- A stellar mass Black hole is precisely such an object. {The poster formerly known as 87.81.230.195} 90.197.66.242 (talk) 22:08, 20 January 2012 (UTC)
- Note, though, that escape velocity is not strictly a function of mass; rather, it's a function of mass and distance. It is entirely possible to have a mass far greater than 10 kg that has a lower escape velocity (such as a galaxy); it's conceptually possible (though not experimentally determined) to have a mass far less that has that escape velocity (see primordial black hole). Instead skewing the distance, it is entirely possible to escape the gravitational pull of a black hole if you start at sufficient distance (see the supermassive black hole at the center of the Milky Way, which the solar system is in no danger of falling into) so long as you don't get near the event horizon. — Lomn 22:55, 20 January 2012 (UTC)
- If you bring in galaxies, I think it's even more complicated than that — galaxies are not closely approximated by spheres, so the escape velocity depends on the direction you're trying to escape in. At least I think it does. Let's say you're near the edge of the galaxy, a little above its plane. If you try to escape going "up" (normal to the plane of the galaxy), then the far limb of the galaxy is not receding as fast as if you try to go "out", so you should need more speed to overcome it.
- Of course your total energy is the same at the same speed, so let's say you go "up" at the speed that would let you escape going "out" — maybe you fall back in, follow some complicated orbit, and eventually escape going "out", even without further rocket boost. Whether that counts as "escape velocity" I'm not sure — depends on what you're trying to capture by the notion, I suppose. --Trovatore (talk) 23:02, 20 January 2012 (UTC)
- You are mistaken. Escape velocity depends only on gravitational potential energy, and does not depend on direction. Provided the gravitational field you are escaping from isn't itself changing, and you avoid colliding with any obstacles in your way, then the energy required to escape doesn't depend at all on the path you take. However, it is true that some paths will require a longer travel time to get "out", but not more energy. As a more practical side comment, when talking about the gravitational field of extended body, it is often possible to exploit changes in the gravitational field caused by the relative motions of its constituent parts in order to extract energy (e.g. gravitational slingshot). So for a truly static field, the escape velocity is the same regardless of the path you take, but for the practical deep space traveler, you would often want to exploit changes in the field to get you were you want to go while avoiding having to fire rockets as much as possible. Dragons flight (talk) 23:35, 20 January 2012 (UTC)
- But if you're dealing with speeds near c, which is specifically what the OP is asking about, then the Newtonian model of gravity works poorly, including the Newtonian concept of gravitational potential energy. And with general relativity, direction does matter, even in a static, spherically symmetrical situation. For example, the photons in a photon sphere around a nonrotating black hole don't escape from being near the black hole, even though the photon sphere is outside the event horizon (namely, the photon sphere is at 1.5 times the Schwarzschild radius). But photons that start at a photon sphere, but travel straight outward (or actually anywhere within an exit cone instead of on its boundary), do escape the black hole. Red Act (talk) 04:18, 21 January 2012 (UTC)
- You are mistaken. Escape velocity depends only on gravitational potential energy, and does not depend on direction. Provided the gravitational field you are escaping from isn't itself changing, and you avoid colliding with any obstacles in your way, then the energy required to escape doesn't depend at all on the path you take. However, it is true that some paths will require a longer travel time to get "out", but not more energy. As a more practical side comment, when talking about the gravitational field of extended body, it is often possible to exploit changes in the gravitational field caused by the relative motions of its constituent parts in order to extract energy (e.g. gravitational slingshot). So for a truly static field, the escape velocity is the same regardless of the path you take, but for the practical deep space traveler, you would often want to exploit changes in the field to get you were you want to go while avoiding having to fire rockets as much as possible. Dragons flight (talk) 23:35, 20 January 2012 (UTC)
- Two things. First, 10 × 10 kg = 10 kg. Is that what you meant, or did you intend 10 kg? That is either 500 or 50 solar masses. While 50 solar mass massive stars do exist (see List of most massive stars), 500 solar masses is probably above the upper limit for stars (see Star#Mass and Eddington limit). The most massive star know is R136a1 at 265 solar masses (birth mass of probably 320 solar masses) and radius 35 solar radii.
- Next, you mentioned an escape velocity of 300,000 km/s = c (the speed of light). As explained above, the escape velocity is dependent on the distance from the massive object. A common quoted figure is the escape velocity at the surface of a planet or star. The surface escape velocity for the earth is 11.186 km/s, for the sun is 617.7 km/s, and for R136a1 is about 1700 km/s (2.75 times that of the sun).
- Our article defines the Schwarzschild radius as "the distance from the center of an object such that, if all the mass of the object were compressed within that sphere, the escape speed from the surface would equal the speed of light." Derived from Einstein's field equations, the formula, is exactly what you get by naively substituting ve = c and solving for r in the escape velocity equation. I assume that you came up with your 10 kg or 10 kg figure by solving for m with a given r. For m = 10 kg, r = 1,485 km; and for m = 10 kg, r = 148.5 km. That mantissa looks suspiciously familiar; 1 astronomical unit is 149.60×10 km. Is that just a coincidence, or were you trying to determine the mass of a star which would have a Schwarzschild radius of 1 AU, and accidentally applied the conversion between km and m backwards, inducing an error of (10)? If the latter, some supermassive black holes will meet your criteria, but you'll have to look beyond our galaxy, as Sagittarius A* doesn't quite fit the bill. -- ToE 01:48, 22 January 2012 (UTC)
January 21
Resource Monitor, Maximum Frequency
I am using Windows 7 with a Sandy Bridge i7 quad-core processor that has Intel TurboBoost on. When I am running a fairly CPU intensive task, I went into the Resource Monitor from the Task Manager and it shows that my total CPU usage hovering around 50% and my maximum frequency at 115%. What does the maximum frequency mean? Is it referring to the clockrate? If so, does it mean that TurboBoost is activated if the number is above 100%? If not, how can I check when my processor is using TurboBoost without using a Windows Desktop Gadget? Thanks. Acceptable (talk) 00:13, 21 January 2012 (UTC)
- Your chances of getting a useful answer might be better on the Computing ref desk. Looie496 (talk) 00:15, 21 January 2012 (UTC)
- TurboBoost is not what you expect it to be. The CPU in a laptop with TurboBoost is not used to its full potential 24/7, because that would consume too much power and produce too much heat, if you run a CPU intensive task TurboBoost allows the CPU to use a bit more of its potential. Read Intel Turbo Boost. Download Intel® Turbo Boost Technology Monitor. Von Restorff (talk) 01:08, 21 January 2012 (UTC)
Formula from normal magnitude to apparent magnitude
As topic. By the way, the magnitude i'm talking about is the astronomy related one.Pendragon5 (talk) 00:47, 21 January 2012 (UTC)
- And plus not sure if i ask the correct question. I know apparent magnitude is consider the brightness of any stars without our atmosphere. So in other word what is the formula to find apparent magnitude? And like do i have to know the normal magnitude first? Like the magnitude also consider with our atmosphere. Pendragon5 (talk) 00:51, 21 January 2012 (UTC)
- And also please explain what all the letters in the formula stands for.Pendragon5 (talk) 00:54, 21 January 2012 (UTC)
- By normal magnitude, did you mean absolute magnitude, which is equal to the apparent magnitude at a distance of 10 parsecs (~32.6 light years)? Essentially, it is a logarithmic scale, where an increase in 5 magnitudes corresponds to a brightness decrease of 100 times. For a change in magnitude of 1, the corresponding change in brightness is a factor of approximately 2.51188643. Remember that brightness changes with the square of distance. As for negative atmospheric effects, the three main ones are atmospheric transparency (or lack thereof, including cloud cover), atmospheric seeing and atmospheric extinction. ~AH1 02:51, 21 January 2012 (UTC)
- Well no i didn't mean absolute magnitude. I didn't know what i'm talking about. Ok let ask the question again. Let say i was given a random star. What is the formula to get the apparent magnitude? Like what information i need to have to find out the apparent magnitude and how to use them?Pendragon5 (talk) 05:05, 21 January 2012 (UTC)
- All you need is its intensity - that is, energy per unit time per area. We know, from stellar physics, that this number is strongly determined by the star's age, mass, composition, and temperature - in fact, all of these parameters fall in to a fairly predictable pattern, called the main sequence. There are some outliers, so we use an HR diagram and some extra observation - radio and other measurements of the invisible light from a star - to help us be more precise. Nimur (talk) 05:15, 21 January 2012 (UTC)
There is no formula. The apparent magnitude is how bright an object looks to an observer on the Earth. (Isn't apparent magnitude wrong when it states that it is "adjusted to the value it would have in the absence of the atmosphere"?)Clarityfiend (talk) 05:19, 21 January 2012 (UTC)- In fact, my explanation was a little bit backward: early astronomers knew nothing except the apparent magnitude. As our observations became better, astronomers also measured the color, too - and eventually, the spectrum, and the minor spectral perturbations that we now understand as cosmic redshift, and eventually, we had a well-developed theory of stellar evolution, in large part based on our understanding of nuclear fusion. These theories are very advanced and well-understood, allowing us to work backwards from observations like apparent magnitude to properly estimate things like stellar mass, which are impractical to measure directly. Nimur (talk) 05:22, 21 January 2012 (UTC)
- And to answer ClarityFiend - I have always seen Apparent Magnitude used as described - calibrated "as if there were no atmosphere." This was useful in the days of paper almanacs - the apparent magnitude was published, and never changed, whether you consulted the almanac on a clear night at high elevation or on a humid evening at sea level. Compare to photographic magnitude or "observed" magnitude. Nimur (talk) 05:27, 21 January 2012 (UTC)
- Well no i didn't mean absolute magnitude. I didn't know what i'm talking about. Ok let ask the question again. Let say i was given a random star. What is the formula to get the apparent magnitude? Like what information i need to have to find out the apparent magnitude and how to use them?Pendragon5 (talk) 05:05, 21 January 2012 (UTC)
- Possibly the OP means
- where - things fairly close by on astronomical scales. The fact that this relies on the stated approximation is not common taught at lower levels. D is distance, in parsecs; M absolute is magnitude and m is apparent magnitude. Grandiose (me, talk, contribs) 21:20, 21 January 2012 (UTC)
Optimism bias toward one's own profession
From http://abundancethebook.com/qa-2/ :
- Human beings are designed to be local optimists and global pessimists and this is a big problem for abundance. By necessity, any organism struggling for survival is a control fiend. And we are significantly more optimistic about things we believe we can control.
During my undergraduate studies, I noticed that students majoring in the humanities tended to be very pessimistic about the impact of new or esoteric technology on social problems, and very optimistic (at least compared to me) about the ability activism and public debate to solve them. Furthermore, the few technologies they were optimistic -- mobile communications, social media, public transit -- were those that students of all majors tended to be the most familiar with. Students majoring in the sciences, on the other hand, seemed to overlap pretty heavily with the pro-nuclear minority. I've also noticed that scientists, engineers and technical professionals seem to be overrepresented in the Singularitarian/Transhumanist communities, and tend to be pessimistic about politics.
The above quote suggests that this is part of a general trend: the closer a discipline is to the one you're trained in, the more optimistic you'll be about it. This seems like a subtype of both golden hammer and collective narcissism. Is there a more specific term for it? NeonMerlin 06:15, 21 January 2012 (UTC)
- Er... I don't think that's true at all. There are some things that many people are afraid of in gross disproportion to the actual danger, and education can help dispel those fears. And there are other things that seem to inspire irrational optimism, and education can help dispel that too. Education doesn't inspire optimism as a rule. I'm not optimistic about the things I understand best. -- BenRG (talk) 08:56, 21 January 2012 (UTC)
- I don't know if this is really about optimism and pessimism. Your observation that people that are knowledgeable about science tend to be more in favour of nuclear power can probably be explain in terms of fear of the unknown. Scientists know that nuclear power is actually very safe (even Fukuishima, which was the worst nuclear disaster since Chernobyl, didn't directly kill anyone - there may be a fairly large number of "statistical deaths" from increased risk of cancer due to radiation exposure, but even those are trivial in number compared to the other deaths caused by the earthquake and tsunami). Since scientists know that, they aren't afraid of it. Non-scientists don't know that (they've been told, obviously, but they have to just take the experts' word for it, which isn't as convincing as knowing it for yourself) so are afraid. (Obviously, those are generalisations.) It can work the other way around, though. Scientists tend to be more concerned about global warming because they know it is happening and how much damage it will do if we don't stop it. Non-scientists are often not particularly concerned because they don't know enough to be convinced that it is happening or that it will do much damage (and, they would rather not believe it because taking action against it could harm their standard of living). (Again, lots of generalisations.) So, I would say that experts tend to fear things that are actually dangerous and don't fear things that aren't. Non-experts tend to be less accurate in what they do and do not fear. --Tango (talk) 16:16, 21 January 2012 (UTC)
- I would say that the quote is better reflected in economics statistics: far more people are positive about their own households' financial position in the coming year and the country's here in the UK. (I could reference that, but I can't recall exactly.) Grandiose (me, talk, contribs) 23:25, 21 January 2012 (UTC)
Please identify the animals
- What bird is it?
- What is this lizard?
- Are these monkeys Rhesus macaque or Stump-tailed macaque
- What are these crabs? --SupernovaExplosion (talk) 06:21, 21 January 2012 (UTC)
- I think these monkeys are rhesus macaques. Von Restorff (talk) 06:37, 21 January 2012 (UTC)
- The crabs are probably red fiddler crabs. They can have many colors. Von Restorff (talk) 07:03, 21 January 2012 (UTC)
- That bird looks like a juv oriental turtle dove Streptopelia orientalis. Von Restorff (talk) 07:07, 21 January 2012 (UTC)
- Sorry, I do not know what kind of lizard that is. Von Restorff (talk) 07:09, 21 January 2012 (UTC)
- Thanks a lot. But I have confusion whether the bird is Oriental Turtle Dove or Spotted Dove. --SupernovaExplosion (talk) 07:26, 21 January 2012 (UTC)
- YVW. I am totally not an expert, hopefully an expert comes along for a definitive answer, but that bird looks more like a Dusky Turtle Dove than a Spotted Dove to me. My first guess would probably be the Dusky Turtle Dove, and my second guess the Oriental Turtle Dove. Von Restorff (talk) 07:35, 21 January 2012 (UTC)
- Thanks a lot. But I have confusion whether the bird is Oriental Turtle Dove or Spotted Dove. --SupernovaExplosion (talk) 07:26, 21 January 2012 (UTC)
- 1) Difficult to identify because of the ruffled feathers. It's definitely a columbid though (doves and pigeons). Most likely a juvenile
StreptopeliaSpilopelia chinensis (compare) or Streptopelia lugens (compare) - 2) The lizard is an agamid of the genus Calotes, which are difficult to identify as they can change color. Possibly the common Calotes versicolor.
- 3) Both seem to be Macaca mulatta (medium length tails, light faces on both adults and juveniles)
- 4) Both photos are of the painted ghost crab Ocypode gaudichaudii
- -- Obsidi♠n Soul 08:02, 21 January 2012 (UTC)
- Those spotted doves are hard to identify because they do not acquire the neck spots until they are mature. Von Restorff (talk) 09:01, 21 January 2012 (UTC)
- Yep. -- Obsidi♠n Soul 10:06, 21 January 2012 (UTC)
- Scroll down to the bottom of this page to see a Dusky Turtle Dove with ruffled feathers. Von Restorff (talk) 19:13, 21 January 2012 (UTC)
- Notice the very prominent brilliant orange edges of the covert feathers in Streptopelia lugens though. Same with the photo I posted earlier. In contrast, that of Spilopelia chinensis are pale gray or a light tan, like in the OP's picture. The same thing is also evident in adults (S. lugens: , , ; S. chinensis:, , ). Also birdwatching identification guides for the former here, and for the latter here. It really is more likely to be a Spotted Dove juvenile.-- Obsidi♠n Soul 19:59, 21 January 2012 (UTC)
- You are probably right but with some barbecue sauce they all taste the same. Von Restorff (talk) 21:13, 21 January 2012 (UTC)
- Yep. They all taste like kittunz.-- Obsidi♠n Soul 06:14, 22 January 2012 (UTC)
- You are probably right but with some barbecue sauce they all taste the same. Von Restorff (talk) 21:13, 21 January 2012 (UTC)
- Notice the very prominent brilliant orange edges of the covert feathers in Streptopelia lugens though. Same with the photo I posted earlier. In contrast, that of Spilopelia chinensis are pale gray or a light tan, like in the OP's picture. The same thing is also evident in adults (S. lugens: , , ; S. chinensis:, , ). Also birdwatching identification guides for the former here, and for the latter here. It really is more likely to be a Spotted Dove juvenile.-- Obsidi♠n Soul 19:59, 21 January 2012 (UTC)
- Scroll down to the bottom of this page to see a Dusky Turtle Dove with ruffled feathers. Von Restorff (talk) 19:13, 21 January 2012 (UTC)
- Yep. -- Obsidi♠n Soul 10:06, 21 January 2012 (UTC)
- So, female dogs are not the only kind of animal you like? Von Restorff (talk) 08:19, 21 January 2012 (UTC)
- Of course not. I adore kittunz. It's what I had for breakfast. ;) -- Obsidi♠n Soul 08:39, 21 January 2012 (UTC)
- You eat those? I give em to mr. Vibber who puts them in computercases for storage and kills them once in a while. Von Restorff (talk) 09:11, 21 January 2012 (UTC)
- Ah, the evil Mr. Vibber. I suppose WikiLove were the ones who managed to escape. I propose we black out Misplaced Pages to save the kitties.-- Obsidi♠n Soul 10:06, 21 January 2012 (UTC)
- You eat those? I give em to mr. Vibber who puts them in computercases for storage and kills them once in a while. Von Restorff (talk) 09:11, 21 January 2012 (UTC)
- Of course not. I adore kittunz. It's what I had for breakfast. ;) -- Obsidi♠n Soul 08:39, 21 January 2012 (UTC)
- Those spotted doves are hard to identify because they do not acquire the neck spots until they are mature. Von Restorff (talk) 09:01, 21 January 2012 (UTC)
- 1) Difficult to identify because of the ruffled feathers. It's definitely a columbid though (doves and pigeons). Most likely a juvenile
Any evidence?
This is a research question and not a request for advice in any form. Also this is not a trolling question, I am genuinely interested in any web links on the subject. so i post my Q for the 3rd time. Please do not delete it. Is there any evidence in the literature that ear wax production increases during or after a person gets a head cold?--89.243.132.82 (talk) 22:39, 20 January 2012 (UTC)
- Stress, loud noises, trauma, and using a hearing aid can cause increased production. But I can't find anything about having a cold causing increased ear wax (and no evidence of increased production with an ear infection, which is a common side-effect of a head cold). --Colapeninsula (talk) 18:37, 21 January 2012 (UTC)
Could the Rosenhan Experiment happen today?
In 1973 the Rosenhan Experiment made the mental illness system in America (and by extension much of the world which uses similar systems) look like a farce. Is there anything to suggest that the experiment couldn't be replicated today, and that the problems have been fixed? Prokhorovka (talk) 13:25, 21 January 2012 (UTC)
- Including a link would really help get your question answered - Rosenhan experiment. Roger (talk) 14:35, 21 January 2012 (UTC)
- See also Rosenhan_experiment#Related_experiments. I would point out that the psychiatric hospital (like a prison) is something of a closed system of belief: once one is inside it, one's actions are interpreted through a very specific framework. The trick in the Rosenhan experiment was lying to get into the hospital in the first place, to get into the closed system. Once inside, getting out is no easy thing. I don't personally think that's the same thing as a "farce". It means that a little bit of deception can go a long way. I'm not defending the practice of mental health, but I do have sympathy for the folks who are dealing with actually sick patients out there (and don't have a lot of sympathy for the idea that none of the patients are actually sick — you don't have to meet too many people actually suffering from mental illness to think that such is not an argument based in experience). --Mr.98 (talk) 15:11, 21 January 2012 (UTC)
- Interestingly, the "How Mad Are You?" BBC 2008 programme has demonstrated how difficult it is to successfully diagnose such things; ergo, it might not be the system failing but the difficulty of the task. Grandiose (me, talk, contribs) 15:14, 21 January 2012 (UTC)
- You may like to examine the views of Thomas Szasz and his book "The Myth of Mental Illness", and the work of R D Laing, and also anti-psychiatry. --TammyMoet (talk) 17:34, 21 January 2012 (UTC)
- For an entertaining, brief exploration of these issues, I can recommend the book The Psychopath Test by Jon Ronson. We also have to be careful not to assume, as often happens in these discussions, that problems defining edge cases and involving institutional bias and overdiagnosis somehow mean that mental illness doesn't exist at all: that is incredibly dismissive of the reality of many people's lives. Be alert to the extremes. 86.164.75.123 (talk) 18:41, 21 January 2012 (UTC)
I'm not suggesting that mental illness doesn't exist, just that the experiment seemed to suggest we aren't really in a position to deal with it given that people who aren't mentally ill can be considered it for 2 months based on one very weak lie, and 40 people who apparently were mentally ill can be considered fine due to another lie (other experiments also suggested that people will diagnose mental illness listening to a normal person who they've been told is mentally ill, despite no symptoms!). Surely, given the system hasn't qualitatively changed since the experiment was done, we still would be better off basically not trying until we've gained a better understanding of the problem? Prokhorovka (talk) 11:32, 22 January 2012 (UTC)
Distribution of individually wrapped chocolates within a box
For Christmas I was given a box of Cadbury Roses, and very nice they are too. However, I have noticed that they are not uniformly distributed through the box. My evidence seems to suggest that the cream- or caramel-filled ones are found mainly at the top of the box, whilst more solid and chewy toffees and fudges are found more towards the bottom. Interestingly, the solid Dairy Milk one has turned up at the top more than anything else, and the hazelnut-and-caramel-filled one (somewhat of a hybrid between the other two types) only a little less. So, I have two questions. Firstly, what is causing this effect? (I vaguely recall that someone did some studies that found that the nuts in muesli will similarly rise to the top - are there any conclusions to be drawn from that?) And secondly, how many more boxes of Roses do I need to consume in order to get a decent sample size? Always happy to do my bit for science! Nom nom! - Cucumber Mike (talk) 15:39, 21 January 2012 (UTC)
- Are you sure that they were placed into the box with a random distribution in the first place? Maybe the toffees go in first, and the dairy milk last? AndyTheGrump (talk) 16:00, 21 January 2012 (UTC)
- The food industry sometimes induces unnecessary randomness into its products, because customers report the perfection of machine-generated foodstuffs is unsettling and makes the food product feel unnatural. Chicken McNuggets are pressed into four predetermined shapes ("bone", "ball", "boot" and "bell") all of which are irregular - if McDonalds wanted, they could as easily be spherical. Similarly when Pringles were first made, they were thicker than they are now, and shipped in cardboard tubes with thicker walls. When customers opened them they found all the crisps identical and unbroken, and when surveyed found this uncanny. So Pringles made their crisps thinner and the tubes slightly weaker, so a proportion of crisps would be broken. Likewise for the Cadbury's Roses - they could easy have one filler-funnel for each of the N species, and the customer would find the product layered, a bit like a trifle (neglecting in-transit shifting, like granular convection). But that would be an undesirable outcome, so they surely put the different types together (presumably on a moving belt) in a way to ensure a roughly equal distribution of each throughout the whole pack. -- Finlay McWalterჷTalk 16:15, 21 January 2012 (UTC)
- (e/c) Granular convection - also known as the Brazil nut effect - suggests that when shaken, larger items such as nuts in muesli will gradually migrate to the top. However from my memory of Roses (I haven't had a box in years, always getting Celebrations for Christmas now) the difference in size isn't all that significant. the wub "?!" 16:01, 21 January 2012 (UTC)
- Does granular convection work on similar sized but differing density "granules"? Roger (talk) 18:36, 21 January 2012 (UTC)
- I've often suspected Cadbury and the like intentionally seed their boxes with the yummy cream ones and the like at the top, and the typically less popular ones lower down, so that when you look through the little plastic window you think you're getting a box unintentionally oversupplied with the yummy creams and buy it, only to be later disappointed when you find they were just at the top. :) --jjron (talk) 04:11, 22 January 2012 (UTC)
- Why wouldn't they just make more of the ones people like? Rckrone (talk) 19:10, 22 January 2012 (UTC)
- I've often suspected Cadbury and the like intentionally seed their boxes with the yummy cream ones and the like at the top, and the typically less popular ones lower down, so that when you look through the little plastic window you think you're getting a box unintentionally oversupplied with the yummy creams and buy it, only to be later disappointed when you find they were just at the top. :) --jjron (talk) 04:11, 22 January 2012 (UTC)
- I don't know if the different flavors vary in density, but denser ones will tend to settle to the bottom. Rckrone (talk) 19:10, 22 January 2012 (UTC)
Offroad vehicle
Hello!
Does anybody know which vehicle is shown on the photograph (right)? --High Contrast (talk) 18:04, 21 January 2012 (UTC)
- Looks like a WW2 era Jeep, to me: . StuRat (talk) 18:11, 21 January 2012 (UTC)
- It definitely isn't the standard Willys MB Jeep. I think it might be an eastern-bloc variation. AndyTheGrump (talk) 18:32, 21 January 2012 (UTC)
- The File page mentions Germany in a redlink category, so it may very well be Eastern European. Roger (talk) 18:38, 21 January 2012 (UTC)
- For what little it helps with the location: the tractor next to it is a German make – Allgaier, and the mobile facility behind that seems to have German signage (at the limits of full legibility). The beer bottle behind the vehicle looks similar to the German (though internationally marketed) Beck's brand, although it's not an exact match to other pictures I can find. {The poster formerly known as 87.81.230.195} 90.197.66.42 (talk) 21:40, 21 January 2012 (UTC)
- That mobile facility is a mobile Sanitätswache. Von Restorff (talk) 22:17, 21 January 2012 (UTC)
- For what little it helps with the location: the tractor next to it is a German make – Allgaier, and the mobile facility behind that seems to have German signage (at the limits of full legibility). The beer bottle behind the vehicle looks similar to the German (though internationally marketed) Beck's brand, although it's not an exact match to other pictures I can find. {The poster formerly known as 87.81.230.195} 90.197.66.42 (talk) 21:40, 21 January 2012 (UTC)
- The File page mentions Germany in a redlink category, so it may very well be Eastern European. Roger (talk) 18:38, 21 January 2012 (UTC)
Well, the poster is not some IP like "87.81.230.195" (as 90.197.66.42 suggested) but me. The image was photographed in Bavaria that is definately not connected with eastern Europe. --High Contrast (talk) 00:24, 22 January 2012 (UTC)
- I was not suggesting you were that IP – it's my own identity, my former fixed IP which I continue to "sign" all my posts with since I had to change over to a dynamic IP (after Sky took over my old ISP). {The poster formerly known as 87.81.230.195} 90.197.66.42 (talk) 01:02, 22 January 2012 (UTC)
- OK, now I see. Thanks for helping with this image. Do you know this automobile on the image? --High Contrast (talk) 01:39, 22 January 2012 (UTC)
- If I did, or had any further clue that might help, I would have mentioned it above. I was struck that the vehicle had absolutely no visible marque identifiers, which in my (not extensive) experience of civilian and military vintage vehicles in the UK is highly unusual, but I don't know if this in itself might provide any clue to its origin for someone familiar with such vehicles from the Continent. {The poster formerly known as 87.81.230.195} 90.193.78.23 (talk) 14:35, 22 January 2012 (UTC)
- OK, now I see. Thanks for helping with this image. Do you know this automobile on the image? --High Contrast (talk) 01:39, 22 January 2012 (UTC)
- It's a bit of a puzzle isn't it. The closest I could find was the Willys Quad but it's not the same. It's quite different from the Soviet GAZ-64 and GAZ-67 that was used all over Eastern Europe. I'll try again tomorrow. Alansplodge (talk) 02:31, 22 January 2012 (UTC)
- The Willys MA is also rather similar, but not the same either. Alansplodge (talk) 02:39, 22 January 2012 (UTC)
- It's a bit of a puzzle isn't it. The closest I could find was the Willys Quad but it's not the same. It's quite different from the Soviet GAZ-64 and GAZ-67 that was used all over Eastern Europe. I'll try again tomorrow. Alansplodge (talk) 02:31, 22 January 2012 (UTC)
- The more I look at it, the less convinced I am that it a 'Jeep' variant (or ripoff) at all. Instead, I think it may possibly be a smallish Tractor unit for an articulated vehicle - possibly converted to an 'off-roader' or utility vehicle. AndyTheGrump (talk) 04:10, 22 January 2012 (UTC)
- Ask over at the German Misplaced Pages. I don't believe the beer is a Beck's, the label doesn't bear all that much resemblance, and this label style is quite popular. --Ouro (blah blah) 07:14, 22 January 2012 (UTC)
- The beer is a Hacklberger beer, not Beck's. But we should focus on the vehicle. I think it is a Jeep but visually modified. --High Contrast (talk) 11:15, 22 January 2012 (UTC)
- Good spot, High Contrast (that one's not in any of my illustrated international beer encyclopaedias), but I agree the beer is a red herring – I had not initially realised that the OP had himself taken the photo so no location clues were required. {The poster formerly known as 87.81.230.195} 90.193.78.23 (talk) 14:45, 22 January 2012 (UTC)
- Agreed - maybe a Jeep chasis with locally built (or home made) body panels. Alansplodge (talk) 12:57, 22 January 2012 (UTC)
- The beer is a Hacklberger beer, not Beck's. But we should focus on the vehicle. I think it is a Jeep but visually modified. --High Contrast (talk) 11:15, 22 January 2012 (UTC)
- Ask over at the German Misplaced Pages. I don't believe the beer is a Beck's, the label doesn't bear all that much resemblance, and this label style is quite popular. --Ouro (blah blah) 07:14, 22 January 2012 (UTC)
- The more I look at it, the less convinced I am that it a 'Jeep' variant (or ripoff) at all. Instead, I think it may possibly be a smallish Tractor unit for an articulated vehicle - possibly converted to an 'off-roader' or utility vehicle. AndyTheGrump (talk) 04:10, 22 January 2012 (UTC)
Gender & emotions
Is there scientific reason behind why males tend to show emotion less than females or is it simply cultural/ life experiences? 2.121.172.172 (talk) 21:26, 21 January 2012 (UTC)
- There may be some sort of evolutionary advantage, but I am speculating here. Von Restorff (talk) 21:35, 21 January 2012 (UTC)
- The "standard explanation" seems to be that relationships were more important to early women, both to convince other women to care for their children when they were away and to convince men to give them food, when they returned from the hunt. Showing emotions seems to be important to developing such relationships. StuRat (talk) 21:50, 21 January 2012 (UTC)
- (edit conflict) We actually have an article on Sex and Psychology with an emotion section. That may relate to what you are looking for. The short answer to your question seems to be "yes," based on that article. There seem to be potential scientific factors, as well as "cultural/life experience" factors. Falconus 21:54, 21 January 2012 (UTC)
- Anyone who has noticed the variation in these norms between cultures would be wary of evolutionary psychology explanations that posit the cultural norm for modern western scientists (or, indeed, American scientists in the 1950s) is hardwired in to all humans. The book Delusions of Gender is very interesting if only for the way it looks at how these sorts of things are researched and tested, and how they are reported. 86.164.75.123 (talk) 02:14, 22 January 2012 (UTC)
What road-legal production vehicle model line has had the fewest traffic fatalities thus far?
Moreover, how is that line of vehicles safer than the rest? Would I be able to easily obtain it? (Just to be sure that you won't list the NASA shuttlecrawler, it needs to be legal to be driven on everyday streets, roads and highways in the US, Canada, Australia, and/or New Zealand- the places I may move to after college. Thanks.) --70.179.174.101 (talk) 22:16, 21 January 2012 (UTC)
- Read criticism of sport utility vehicles and automobile safety. Buy a new car with side-airbags and put a rollbar in (a heavy car with a good ground clearance), you will be pretty safe. Buy a emergency hammer. Do not distract yourself by using a phone or listening to music. Use this site. Von Restorff (talk) 22:20, 21 January 2012 (UTC)
- Just to clarify, you don't actually mean the smallest number of fatalities, do you ? If so, the answer is sure to be a car with very few sales. A more reasonable standard of safety is the rate of fatalities, say as a percentage of the vehicles on the road. StuRat (talk) 22:35, 21 January 2012 (UTC)
- Is cost a factor? HiLo48 (talk) 22:39, 21 January 2012 (UTC)
- If cost was not a factor it wouldn't matter if the vehicle was streetlegal or not. Trains are not cheap but they are pretty safe. Von Restorff (talk) 22:46, 21 January 2012 (UTC)
- Is cost a factor? HiLo48 (talk) 22:39, 21 January 2012 (UTC)
- Building off StuRat's excellent point above, you'll probably want to normalize for many factors. Take, for instance, high-performance sports cars. I'll guess they're proportionally high on crash numbers. Is that inherently because of the car or because of the way people tend to drive them? You might also consider the value of crashes per number of cars vs crashes per miles driven. Or whether "per passenger" should also factor in. Anyway, US-only numbers at the NHTSA crash database may be useful for getting a feel for such things. For instance, cars and light trucks were involved in the same number of fatal accidents in 2009 despite there only being about 70% as many registered light trucks in the US as registered cars. Thus, we can conclude that light trucks are generally riskier, and reduce our search area to cars, and so forth. — Lomn 00:05, 22 January 2012 (UTC)
- Guessing at general trends for the "why/how" bit: the safest mass-produced passenger vehicle is probably a modern high-end full-size sedan. Modern and high-end means it'll have things like anti-lock brakes, stability control, and multiple airbags (plus maybe early-warning driver alert systems). Full-size gives your car more mass, which means you'll have more momentum on your side in a multi-car collision (less important for single-vehicle accidents). A sedan has a low center-of-gravity, so it's less susceptible to rollovers, which are propotionally a huge number of of fatal accidents. Probably the single biggest safety factor, though, is wearing your seat belt. Only 15% of people in the US aren't wearing a seat belt as of 2010, but they account for 27% of fatalities in accidents. That means they're about 3 times more likely to die on a per-wreck basis than those properly restrained. I doubt any other single factor approaches that degree of safety improvement. — Lomn 00:13, 22 January 2012 (UTC)
- The only reasonable way to test for car safety is to remove the non-mechanical factor; since different kinds of drivers tend to drive different types of cars, and different places in the world tend to have a preponderance of different car types, and different cars are driven for different purposes, etc etc (i.e. movie stars in Beverly Hills drive different cars than farmers in Peoria and they both drive different cars than bankers in NYC or factory workers in Nashville). The raw numbers of fatalities for each model is a nearly useless statistic when trying to decide safety, and the average number of fatilities normalized per car is only marginally less useless. The best measure would be to see how the car performs isolated from all non-mechanical factors, so the only thing we are testing is the safety of the car (and not the safety of the driver or the road it is on or any of a number of other unrelated issues). Thus, you'll want to see how cars perfom in crash tests and other similar normalized tests. That article lists agencies that are respected for their crash test data, you'll want to go to those agencies to find out what cars get the best ratings. --Jayron32 01:15, 22 January 2012 (UTC)
- But there's also an issue with crash tests not representing "real world accidents" accurately. They revise the test occasionally, but can never quite keep up. A recent revision was to account for cars being struck by SUVs. StuRat (talk) 01:47, 22 January 2012 (UTC)
- Vaguely touched on by others, but one of the key criteria in car safety is the driver - the old "nut behind the wheel" argument. Get properly trained, ensure you know the road rules, avoid risky situations, drive to the conditions (slow down in the wet or poor visibility, etc), don't do stupid things like using your mobile phone, drink driving, not wearing a seat belt, or driving when you should be sleeping, and you'll reduce your risk of accidents far more than spending your time and money buying the 'safest car'. I'm not underplaying all the great safety features in modern vehicles, but the best possible safety feature is to avoid the accident to start with. Ironically I find a lot of people that seek out cars for their safety features are the same people who don't follow those commonsense driving rules, and consequently are a danger to everyone on the roads. --jjron (talk) 04:03, 22 January 2012 (UTC)
- The illusion of safety may cause you to take greater risks. I have a bike, and not being at the "top of the foodchain" means I am a lot more careful than some people who are protected by hundreds of kilo's of armor. Von Restorff (talk) 04:11, 22 January 2012 (UTC)
- Risk compensation is a helpful article on this theory Jebus989 16:45, 22 January 2012 (UTC)
- The illusion of safety may cause you to take greater risks. I have a bike, and not being at the "top of the foodchain" means I am a lot more careful than some people who are protected by hundreds of kilo's of armor. Von Restorff (talk) 04:11, 22 January 2012 (UTC)
- Vaguely touched on by others, but one of the key criteria in car safety is the driver - the old "nut behind the wheel" argument. Get properly trained, ensure you know the road rules, avoid risky situations, drive to the conditions (slow down in the wet or poor visibility, etc), don't do stupid things like using your mobile phone, drink driving, not wearing a seat belt, or driving when you should be sleeping, and you'll reduce your risk of accidents far more than spending your time and money buying the 'safest car'. I'm not underplaying all the great safety features in modern vehicles, but the best possible safety feature is to avoid the accident to start with. Ironically I find a lot of people that seek out cars for their safety features are the same people who don't follow those commonsense driving rules, and consequently are a danger to everyone on the roads. --jjron (talk) 04:03, 22 January 2012 (UTC)
January 22
Spraying water with alcohol to evaporate faster
Suppose I spill some water on my floor in my house at around STP (25C, 1 atm). If I spray the puddle of water with some alcohol, say isopropyl alcohol, will it help the puddle evaporate faster? Since isopropyl alcohol has a higher vapor pressure than water and since the total vapor pressure will be the sum of the two liquids, the total vapor pressure will be closer to the atmospheric pressure. Acceptable (talk) 00:46, 22 January 2012 (UTC)
- Just mop it or wipe it up. Von Restorff (talk) 00:58, 22 January 2012 (UTC)
- Section 3 of Vapor Pressure may be of interest. {The poster formerly known as 87.81.230.195} 90.197.66.42 (talk) 01:08, 22 January 2012 (UTC)
- I would expect the alcohol component to evaporate at close to the rate alcohol normally evaporates, and the water component to continue to evaporate as slowly as ever. In other words, the percentage of alcohol will quickly reduce down to near zero. (Not quite zero, though, as having all that water in the way will prevent some of the alcohol from evaporating first.) StuRat (talk) 01:26, 22 January 2012 (UTC)
- Just adding alcohol won't help water evaporating faster. However, in theory, if you add much more alcohol than you have water spilled, the you can mop up most of the puddle, and (due to alcohol and water mixing well), the residue that you can't clean by mopping will be alcohol in more part than water, and thus evaporates faster than if you had as much water as the residue. You would of course have to use alcohol without additives (water doesn't count), because additives would leave a stain residue on the floor that you would have a harder time removing than what you'd save with the whole alcohol thing. Also, I wouldn't recommend the whole messing with alcohol in practice, because the alcohol could catch fire.
- If you want to spend money on drying your floor faster, you'd better buy disposable paper towels (instead of alcohol), as these suck up the water easily. If you live in a geographical area where the air is very humid (but only in that case), then air conditioning in the room can help dry the air and thus make the puddle dry faster.
- Here's a reference that mentions drying glass bottles with alcohol in practice. Note that in this case the bottles have a very small mouth so air can't get in easily, which is why the inside of the bottle dries very slowly under normal condidions. This is not the case in the floor, where there's plenty of air available. – b_jonas 22:23, 22 January 2012 (UTC)
Men: shaved or with beard
Are men with beard more attractive than shaved men? From an evolutionary perspective it makes sense to suppose that women would prefer real men with a grown beard, but almost all men that I see shave their beard. — Preceding unsigned comment added by 88.14.192.250 (talk) 01:21, 22 January 2012 (UTC)
- Nope. Attractive to who? Attractiveness is extremely subjective. What is a real man? Shaving is not a sex-change operation. Women generally prefer men who care about their appearance; so being well-shaven or having a well-trimmed beard is better than looking like this. Look at People_(magazine)#Sexiest_Man_Alive. Von Restorff (talk) 01:24, 22 January 2012 (UTC)
- I suppose by that logic women with hairy armpits should be attractive to men. Both of these may have been the case almost universally, at some point, but once shaving became possible, being clean-shaven could be taken as being "well groomed", and this indicates a fit individual. StuRat (talk) 01:30, 22 January 2012 (UTC)
- If you could grow money in your beard that would probably attract a lot of females. Is this a real man with a grown beard, or did he just forget to shave for three days? Von Restorff (talk) 01:36, 22 January 2012 (UTC)
- I don't believe that Attractiveness is extremely subjective. It's mainly biology, even if you don't experience it like that and live in the illusion that your will is free. Anyway, the case of women is different: if they shave their armpit and legs and whatever, they look younger, but why could a man would like to look like a boy? A beard sends the information: this man is an adult. 88.14.192.250 (talk) 01:40, 22 January 2012 (UTC)
- Heterosexual males and heterosexual females seem to disagree on which features make someone attractive. To make it even more complicated, think about the fact some people are attracted to animals or hairy heavy-set men or objects or certain situations. I think that if attractiveness was not so subjective it wouldn't change much over time. Have you ever seen 80's porn? Read Physical_attractiveness#Hairiness. Everyone seems to like symmetrical faces for some reason. But to me certain goodlooking women are unattractive because they are stupid or they have a weird voice or weird laugh. You probably do not have free will, but I do. Are you a robot or a puppet or a religious person or a lazy philosopher who believes in fate? Do you think everything is predestined? If so I will not debate about that, that would be a waste of time since I am predestined to win that debate. Sean Connery was rated as a very attractive male and he has a fullgrown beard, but the "clean-shaven"- and "forgot to shave for 3 days"-groups are the majority. Von Restorff (talk) 01:51, 22 January 2012 (UTC)
- yeah, you clearly live under the illusion that your will is free. BTW, that's the standard religious or lazy philosophy position. The biological alternative explanation is the more elaborate one. Note also that your examples do not constitute the mainstream sexuality of society. Humans survive being what they are due to what most of us do, the minorities are not so relevant here.88.9.209.157 (talk) 19:32, 22 January 2012 (UTC)
- Heterosexual males and heterosexual females seem to disagree on which features make someone attractive. To make it even more complicated, think about the fact some people are attracted to animals or hairy heavy-set men or objects or certain situations. I think that if attractiveness was not so subjective it wouldn't change much over time. Have you ever seen 80's porn? Read Physical_attractiveness#Hairiness. Everyone seems to like symmetrical faces for some reason. But to me certain goodlooking women are unattractive because they are stupid or they have a weird voice or weird laugh. You probably do not have free will, but I do. Are you a robot or a puppet or a religious person or a lazy philosopher who believes in fate? Do you think everything is predestined? If so I will not debate about that, that would be a waste of time since I am predestined to win that debate. Sean Connery was rated as a very attractive male and he has a fullgrown beard, but the "clean-shaven"- and "forgot to shave for 3 days"-groups are the majority. Von Restorff (talk) 01:51, 22 January 2012 (UTC)
- I don't believe that Attractiveness is extremely subjective. It's mainly biology, even if you don't experience it like that and live in the illusion that your will is free. Anyway, the case of women is different: if they shave their armpit and legs and whatever, they look younger, but why could a man would like to look like a boy? A beard sends the information: this man is an adult. 88.14.192.250 (talk) 01:40, 22 January 2012 (UTC)
- The OPs original 'evolutionary argument' could also be turned on its head. Over the last 5 million years or so humans have evolved significantly less body hair; compare us to our closest cousins the chimps. Now while this could possibly be more a consequence of neoteny through the selection of other traits more vital to survival, rather than the selection of hairlessness itself, it is nonetheless clearly a pattern in our evolution, and our remaining body hair largely mirrors that where it first appears in the development of apes. It could therefore be argued that from an evolutionary perspective we should all be more attracted to mates with less hair on all parts of the body. And as a male starting to show some traces of male pattern baldness, that suits me much better. ;) --jjron (talk) 03:48, 22 January 2012 (UTC)
- It's not clear to me why you believe being an 'adult' matters. If you want to talk 'biology' one simplistic common modern POV is that for a human female, when it comes to choosing a male to be the biological father to her children (during her period of greatest fertility), they want a 'masculine' man (with signs of more testosterone exposure during development). Facial hair may play a small part in this, but other things like the shape of the face and muscle are often seen as bigger signs. (They may also value other things like facial symmetry and MHC variance.) This is to ensure the best genes for her offspring. Outside that window, they may care less about physical attractiveness and prefer a man who is somewhat more feminine and who is considered more likely to stick around. With the fairly widespread use of birth control in a number of countries which may reduce the effect of any fertility window, it may very well make sense to be someone who is perceived as likely to stick around and help look after the children, who coincidentally may not be his children, and just remember to do a DNA test for each of your children (if you have any). However while this theory may make some sense (but also seems to have some possible flaws), and there may be some evidence backing most parts of it up, it's just one of many theories many of which have their own evidence and also may make implicit sense. (And sometimes the evidence may be disputed, e.g. Sexy son hypothesis mentions this.) Our article Physical attractiveness which mentions body hair but not facial hair in men also makes clear in a number of areas things are far from clear cut and there does seem to be some variance across people. Perhaps these are really simply arising from differening spread of genes amongst different people as you seem to believe, or perhaps physical attractiveness really does have a cultural factor. Nil Einne (talk) 12:32, 22 January 2012 (UTC)
- As very briefly mentioned in Facial hair, there are ethnic differences in the amount of facial hair developed. Now bear in mind that races, such as Native Americans or East Asians, date back only a very brief evolutionary interval, to sometime near the end of the last Ice Age. I would presume that in previous eras there were other races, likewise prone to have or omit facial hair pretty much at random, and the sexual desires built into the human race have never really made its presence or absence much of a hindrance to perpetuating the species. Wnt (talk) 07:57, 22 January 2012 (UTC)
Machine
what are the latest technology in mechanical field?
give a list of machines and tools used in mechanical engineering ? — Preceding unsigned comment added by Krsrv (talk • contribs) 02:52, 22 January 2012 (UTC)
c is fastest but what is slowest speed possible?
Get two atoms, a clock and a ruler. Now if one atom (or smaller particle) is moving towards another, then is there any speed so slow that it cannot be any slower? And if so, what is it? Myles325a (talk) 04:44, 22 January 2012 (UTC)
- The Heisenberg uncertainty principle makes it impossible to know any particle's momentum, and hence its velocity, precisely, unless it's completely unknowable where the particle is located. So at speeds too low, it becomes impossible to know whether the particle is moving at that low speed, or isn't moving at all. What speed that occurs at depends on how tightly the particle's location is constrained, and on the particle's mass. Red Act (talk) 05:14, 22 January 2012 (UTC)
Dyson sphere/swarm surrounding planet rather than star
Does a Dyson sphere or Dyson swarm go by a different name if it's inside-out and surrounds a planet rather than a star (e.g. as a transitional solution for reaching Kardashev type I)? I think I've seen a space-based solar power proposal that amounted to a Dyson-like swarm of satellites a few inches wide, but I can't remember where. NeonMerlin 09:24, 22 January 2012 (UTC)
Time of sunrise and sunset as viewed from the Moon
Are there any online sunrise/sunset calculators that will give a table of sunrises and sunsets for user-supplied selenographic coordinates? —Mathew5000 (talk) 09:40, 22 January 2012 (UTC)
Equinoxes on the moon
Defining a lunar equinox as the moment the Sun passes directly over the Moon's equator, how frequently does it occur? Twice a year like equinoxes on Earth? Or would it be approximately twice a month because the Moon is tidally locked to the Earth? And is there a table accessible online of the times of the lunar equinoxes and lunar solstices? —Mathew5000 (talk) 09:48, 22 January 2012 (UTC)
- Some terminology: You're looking for the selenographic latitude of the subsolar point, in particular the times when that latitude is 0°. Here is a bit of information, though not exactly on your question. Given that the moon's rotational axis and its equatorial plane are fixed in space (like earth's axis and equator), the moon has to move around the sun for the latitude of the subsolar point to change. Hence, the equinoxes should occur twice a year. --Wrongfilter (talk) 14:31, 22 January 2012 (UTC)
- Thank you, Wrongfilter. Do you have a source for the statement that the Moon's rotational axis is fixed in space? The article Moon doesn't specifically state that. I guess that is one cause of libration. Also, as the rotational axis of the Earth and that of the Moon each retains its orientation (relative to the stars) throughout the year, do they have the same orientation? I know the Earth's axial tilt is much greater, but what I mean is, if you consider the plane that is perpendicular to the ecliptic and contains the Earth's axis, as well as the plane that is perpendicular to the ecliptic and contains the Moon's axis, are those two planes parallel? —Mathew5000 (talk) 23:53, 22 January 2012 (UTC)
How can we join the definitions of entropy?
Exactly how does one prove that, for any process, ? I've looked through the statistical thermodynamics article, and couldn't understand all the new symbols (I'm used to classical thermodynamics, and I only know a bit of statistical).
I was able to prove that the two definitions of change in entropy are equivalent for an isothermal process carried out on a gas (by quantizing space and then limiting the quantization to infinity), but my proof makes the absolute entropy of the gas infinite. If the process is not infinite, the particle's velocities come into the picture and I don't know how to deal with that. I tried making various assumptions (quantizing time, etc), but it didn't work. I know that once I prove it for another process, it will be proven for any process carried out on ideal gases(as I can write any process as the combination of isothermal and another process).
Could anyone please point me to the proof? Thanks, ManishEarth 10:09, 22 January 2012 (UTC)
Helium hydride ions
Wouldn't it be possible to prepare condensed helium hydride ions in a solution of pure helium, since the product of protonation by the helium hydride ions would merely be more helium hydride ions? Whoop whoop pull up 17:15, 22 January 2012 (UTC)
- What counter-anion would you be able to use that wouldn't wind up re-combining with it? DMacks (talk) 17:25, 22 January 2012 (UTC)
- What are you talking about? Whoop whoop pull up 18:17, 22 January 2012 (UTC)
- That is, you are correct that:
- HHe + He ⇌ He + HHe
- is obviously a wash, so the HHe persists. If this is the strongest acid known, then any base, no matter how weak, would be protonatable and when you prepare an actual solution of X, you get a balanced amount (in terms of charge) of Y. Even if it's formed by beta decay, the expelled electron has to go somewhere...not sure how much overall positive charge you could form in a flask (via escape of the electrons) before coulombic repulsion makes it explode, and the beta particles of H decay are fairly low-energy anyway. Are there any such anions that are less protonatable than? Otherwise:
- HHe + Y ⇌ He + HY
- would shift to the right. DMacks (talk) 18:23, 22 January 2012 (UTC)
- Keep in mind that even if there wasn't any counter ion in solution, the walls of the container would also likely act as such a base, so you'd have the adsorption of the proton onto the glass/metal as soon as ion gets close. I don't have any clue as to the rate of diffusion through a solution of liquid helium is, but the coulombic repulsion of multiple helium hydride ions and/or the coulombic attraction with (induced) charges on the walls of the container will likely mean you'd get faster than diffusion transfer to the container walls. -- 67.40.215.173 (talk) 19:41, 22 January 2012 (UTC)
- How about a) a noncoordinating anion such as SbF6 and a container made of solid helium? Whoop whoop pull up 20:50, 22 January 2012 (UTC)
- You would only be able to hold small groups of HHe ions in solution using this method, due to the repulsion problem, but how about b) matrix isolation at a temperature of < 10K in solid helium? Whoop whoop pull up 21:03, 22 January 2012 (UTC)
- See the cited comments in the fluoroantimonic acid about the structure of this chemical. But regardless of the perceived "coordinating" property, check the pKa values for the standard way of deciding where the H+ is more likely to go in an equilibrium. DMacks (talk) 21:06, 22 January 2012 (UTC)
- OK, there goes a), but how about b)? Whoop whoop pull up 21:10, 22 January 2012 (UTC)
- A helium matrix would be 0.95 K at 2.5 MPa of pressure (freezing point of helium). That's probably hard to achieve and maintain for long enough and stable enough to perform chemistry in it (for example, waiting for enough embedded tritium to decay to get a detectable presence of HHe). Solid helium is also not particularly rigid in terms of crystal structure, and defects are fairly mobile (per cite in helium). That means your inclusions of HHe aren't really fixed in position--the whole reason you would be wanting to use a matrix. DMacks (talk) 21:26, 22 January 2012 (UTC)
- Ah. How about a huge, planet-sized ball of an extremely dilute solution of HHe in pure liquid helium, large enough for its own gravity to hold it together? Whoop whoop pull up 21:45, 22 January 2012 (UTC)
- How about a) a noncoordinating anion such as SbF6 and a container made of solid helium? Whoop whoop pull up 20:50, 22 January 2012 (UTC)
- Keep in mind that even if there wasn't any counter ion in solution, the walls of the container would also likely act as such a base, so you'd have the adsorption of the proton onto the glass/metal as soon as ion gets close. I don't have any clue as to the rate of diffusion through a solution of liquid helium is, but the coulombic repulsion of multiple helium hydride ions and/or the coulombic attraction with (induced) charges on the walls of the container will likely mean you'd get faster than diffusion transfer to the container walls. -- 67.40.215.173 (talk) 19:41, 22 January 2012 (UTC)
Hydraulic Pressure
As per Bernaulli's equation, P.E.+K.E.+Pot.E.=constant in a pipe flow. So, if water flows from larger pipe to smaller pipe, then Potential Energy remains the same(assume), kinetic energy increases, therefore, pressure energy decreases. Then, why smaller pipe will burst for the same flow. It means, if pressure energy is more in larger pipe, then larger should burst instead of smaller pipe. — Preceding unsigned comment added by Pkbansal22 (talk • contribs) 18:07, 22 January 2012 (UTC)
Not necessarily. Since the smaller pipe is smaller in diameter, and hence, smaller in internal surface area, the critical radial stress is lower (P=F/A) (assuming same thickness of pipe). It hence requires lower pressure to rupture, a pressure which could be supplied even by the reduced pressures of the flow. Lynch7 19:18, 22 January 2012 (UTC)Just figured out that radial stress is not proportional to surface area. Lynch7 19:28, 22 January 2012 (UTC)- Feeling quite stupid now. I guess the larger pipe should burst, given that the entrance to the smaller pipes are filleted out properly. Lynch7 19:42, 22 January 2012 (UTC)
- Of course, all this is true if you assume that the flow is steady, and there are no obstructions. Lynch7 19:51, 22 January 2012 (UTC)
Resting Membrane Potential
Hello. When measuring the membrane potential of muscle fibres at different concentrations of extracellular KCl with glass micropipettes, why is KCl a better electrode solution than NaCl? Thanks in advance. --Mayfare (talk) 18:12, 22 January 2012 (UTC)
- Because normally the concentration of K ions inside a cell is much higher than the concentration of Na ions. If you use NaCl, the sodium will diffuse from the pipette into the cell and depolarize the muscle fiber. Looie496 (talk) 18:57, 22 January 2012 (UTC)
- From what I've learned, K and Cl have similar ionic sizes, and hence, similar ionic mobilities, and hence are used to measure membrane potentials. Feel free to disregard this explanation, its been quite a while since I went towards chemistry. Lynch7 19:02, 22 January 2012 (UTC)
On the same note, how does the pipette measure membrane potential if the electrode solution (3 M) is of a concentration different from the bath? (This is a dissected muscle fibre submerged in KCl on the scale of mM.) The membrane potential does change with the concentration of extracellular KCl. The pipette does make a tight seal with the cell membrane. --Mayfare (talk) 21:44, 22 January 2012 (UTC)
- Think there is something missing here in the question, as the question didn't seem to make 'complete' sense. If the extracellular medium is potassium rich (equal to the intracellular concentration) it will neutralize the potential. E.g. Inject enough potassium salt into the blood stream and the hart will stop. Can the OP expanded on the purpose this experiment. The potential is dependant ( I think) on the relative concentrations between these two ion on each side of the cellular wall. As Looie alludes to, the intracellular medium is normally potassium rich in In vivo but the OP is talking in vitro. However, to measure the potential 'change' one needs to refer to the potential difference from within the cell which is normally -in vivo- potassium rich. So again, to measure a change in potential from the 'normal' in vivo condition one still needs to use a potassium electrolyte, as sodium would alter the very potential that one is attempting to measure. Also for the pump to continue to function (and maintain any potential), one would also need some glucose; which one would imagine is not included in this experiment. --Aspro (talk) 23:52, 22 January 2012 (UTC)
Chunks of ions
What would a chunk of pure sodium ions or chloride ions look like? Whoop whoop pull up 18:19, 22 January 2012 (UTC)
- It would be extremely difficult to try to create a "chunk" of any single kind of ion, since the ions would strongly repel each other. How would you hold a chunk of pure anions, or a chunk of pure cations, together? Red Act (talk) 18:28, 22 January 2012 (UTC)
- One thing that could be done would be to use Inertial electrostatic confinement to contained a charged plasma consisting of purely sodium ions or chloride ions. The density of such a plasma would have to be very low, to be able to contain it successfully. I'll leave it up to you as to whether that counts as a "chunk", since "chunk" is a nontechnical term that could either mean "a thick solid piece" or "a considerable amount". The plasma wouldn't fit the former definition, but it could arguably fit the second definition. Different states of matter for the same substance can appear quite different, and my previous answer assumed you were asking about a solid state, since I interpreted "chunk" using the first definition. And you just can't form a true solid out of all the same kind of ion.
- I'm not sure, but it might also be possible to form some other nonclassical state(s) of matter out of pure anions or pure cations, in addition to a plasma. Red Act (talk) 21:45, 22 January 2012 (UTC)
- Wouldn't you be able to form a solid of ions if you compressed them enough to overcome the electrostatic repulsion and force them to form a solid? Whoop whoop pull up 21:53, 22 January 2012 (UTC)
Rain vs. snow
Common experience has shown those of us in snowy areas that when the temperature is above freezing, rain will cause the snow to melt much faster than if it were not raining. Have there been attempts to quantify this effect? Comet Tuttle (talk) 19:01, 22 January 2012 (UTC)
- I think you're just talking about thermal conductivity; liquid water is about 25 times better than air at transferring heat (alternately phrased, air is about 25 times as good a thermal insulator). Thus, direct contact with cold water will melt things much faster than contact with even hot air. — Lomn 20:34, 22 January 2012 (UTC)
- Thanks for that link; I was also interested in the effect of the kinetic energy of the raindrops adding some heat to the snow. Comet Tuttle (talk) 23:43, 22 January 2012 (UTC)
regarding to communicatio
sir, why mobile no. is 10 digit.? how to communicate with two mobile no.????? — Preceding unsigned comment added by Kaim1008 (talk • contribs) 19:05, 22 January 2012 (UTC)
- Telephone numbering plans vary worldwide and generally exist via long-term gradual evolution rather than a one-time design statement. E.164 is the present international recommendation but it doesn't mandate a single length for phone numbers.
- I'm not sure what you're asking by your second question, though in my experience, mobile phones call each other via the same functional mechanism as calls between any other phones. Or are you asking about three-way calling? — Lomn 20:39, 22 January 2012 (UTC)
Fusor weapon
Would it be possible to use a fusor in neutron-production mode as an modulated neutron initiator in a nuclear weapon? Whoop whoop pull up 22:03, 22 January 2012 (UTC)
- To be useful in a nuclear weapon, a neutron source must be able to be activated nearly instantly, and provide a sharp pulse of fast neutrons. Now I don't know much about the fusors but the videos I've seen of them on YouTube show them taking at least a few seconds to go from zero to bright balls of gas. That isn't fast enough. --Mr.98 (talk) 22:56, 22 January 2012 (UTC)
- How about if you activated the fusor first, and then the explosives, giving the fusor a few seconds to warm up before the explosives fire, so it emits it's neutrons at exactly the right time for it to do so? Whoop whoop pull up 23:16, 22 January 2012 (UTC)
- It probably depends on the specifics of the neutron flux. What you want is a sudden, precisely timed burst. Too many neutrons too soon and you run the risk of predetonation. Too late and, well, they're too late to be useful. I don't know much about fusors. I doubt they fit the requirements for this. There are various Rube Goldberg ideas one could use to try and do something like this (e.g. keep the fusor in a shielding, and then explosively remove the shielding at the instant you need the neutrons), but I don't know why you'd bother with all that. --Mr.98 (talk) 01:01, 23 January 2012 (UTC)
Dyeing one's brain
I had a dream where at a fair there was a booth where people could pay to have their brain dyed a different color via immersion in dye solution. My question is, would this be possible, and would it have any side effects? Whoop whoop pull up 22:13, 22 January 2012 (UTC)
- Nothing said here should be taken as medical advice. First, as to the pointlessness of the practice, If your brain were dyed some color, how would you know, unless the skull was opened to see the brain? Second, when there is to be a "brain scan," a contrast medium, or dye, is sometimes introduced into the cerebrovascular fluid via a lumbar puncture. The dye is not so much to color the brain as to be radio-opaque to aid in radioimaging, but it can discolor the urine for the next day. Some patients do have side effects from the contrast dye or the procedure. See "Illustrated manual of nursing practice" (2002) pp 452-453 "Clinical neurology," (2002) page 24, and "Comprehensive medical terminology",(2010) page 289. Edison (talk) 22:37, 22 January 2012 (UTC)
- Is this a reaction to the question on dying your blood (link valid later) from a few days earlier? – b_jonas 22:27, 22 January 2012 (UTC)
- Well they could certainly have their brain dyed by immersion but whether they'd be able to get it back inside their skull again is a question I'm not qualified to answer - me not being a brain surgeon and all. How the brain would be dyed by simple immersion of the body, total or part thereof remains an zero improbability for me, given the impermeability of the skin and the difficulty of knowing whether the brain has been dyed. You had the dream, how did the folks know their brains were green or black or whatever colour? Side efects? well when someone comes up with a theory about how to dye the brain by immersion I will disclose the likely side effects. I'm not holding my breath! Richard Avery (talk) 23:15, 22 January 2012 (UTC)
- In the dream, this was done by removing the skull caps. No idea as to whether this would work in reality. Whoop whoop pull up 23:18, 22 January 2012 (UTC)
- Well they could certainly have their brain dyed by immersion but whether they'd be able to get it back inside their skull again is a question I'm not qualified to answer - me not being a brain surgeon and all. How the brain would be dyed by simple immersion of the body, total or part thereof remains an zero improbability for me, given the impermeability of the skin and the difficulty of knowing whether the brain has been dyed. You had the dream, how did the folks know their brains were green or black or whatever colour? Side efects? well when someone comes up with a theory about how to dye the brain by immersion I will disclose the likely side effects. I'm not holding my breath! Richard Avery (talk) 23:15, 22 January 2012 (UTC)
Lettuce
How long has Lactula sativa (Lettuce) been around as a species? i.e., approximately when did it first appear? 69.243.220.115 (talk) 22:20, 22 January 2012 (UTC)
- If mean the date the species was established taxonomically - it was one of the first plants ever classified, by Linnaeus of course, in Species Plantarum (1753).
- If you meant the oldest known cultivation date - the oldest identifiable depiction of L. sativa (believed to be L. sativa var. longifolia) is from Egyptian tomb paintings from around 4500 BC.
- If you meant the date when it became a distinct species - it probably didn't (at least not yet). There are no reproductive barriers between L. sativa and its wild ancestor Lactuca serriola and they can undergo normal meiosis when crossed and produce perfectly fertile "hybrids" with each other. They are better treated as ecotypes rather than species. In addition, two other species are also probably ecotypes of L. serriola : Lactuca dregeana and Lactuca altaica.-- Obsidi♠n Soul 23:09, 22 January 2012 (UTC)
- I was pretty much getting at the third thing you mentioned. Were heads of whatever you would classify in the same group as lettuce around in the Cretaceous, Jurassic, Carboniferous, or what? 69.243.220.115 (talk) 23:32, 22 January 2012 (UTC)
- Heh, they're flowering plants, so definitely not Jurassic nor Carboniferous. But neither even Cretaceous. I can't find any sources for the fossil record of Lactuca, but the family it belongs to (Asteraceae) first diversified around 42 to 36 million years ago in the Lutetian to Priabonian Ages of the Eocene Epoch, Paleogene (or Lower Tertiary) Period; with the stem group diverging 49 million years ago in the Ypresian Age.-- Obsidi♠n Soul 23:45, 22 January 2012 (UTC)
Poisonous contrails?
This doesn't go in the direction of the chemtrail conspiracy theory, but if some aircrafts use chlorosulfuric acid to avoid leaving a contrail, wouldn't that contaminate, at least a little, the area below its trail? 88.9.209.157 (talk) 23:25, 22 January 2012 (UTC)
- Technically it'll contaminate something, but whether that's the area below the contrail, or somewhere miles (dozens? hundreds? thousands?) away due to wind, or whether it remains in measurable quantities, or even if its byproducts remain in measurable quantities.... Sure. It got used, so it's in the environment. Whether that rises to anything remotely resembling "contamination" is another matter. — Lomn 23:38, 22 January 2012 (UTC)
- OK, "below" is the wrong word. It would be better to say "some area in the ground." — Preceding unsigned comment added by 88.9.209.157 (talk) 00:04, 23 January 2012 (UTC)
- I think "contaminate" might also be the wrong word. What Lomn is saying — and I don't know if this is correct — is that the release of that amount of chemicals into the atmosphere is going to dilute it to immeasurable quantities by the time it gets anywhere near the surface. If that's the case then it is probably not much of a contaminant. Presumably this has been studied to some degree before it was introduced into use. --Mr.98 (talk) 00:58, 23 January 2012 (UTC)
Nerveagentase
Would it be possible to create artificial enzymes which would deactivate nerve agents by replacing their leaving groups with inactive alkyl groups? Whoop whoop pull up 23:43, 22 January 2012 (UTC)
- Enzymes already deactivate nerve agent that block other enzymes – its just that they don't do it fast enough to prevent the grim reaper -if the dose is too high. Gardeners don't drop dead from normal spaying (with lesser versions) but rub the same stuff undiluted (agricultural grade) all over your skin and you too, will be soon pushing up the daises. And just what destruction do you think these artificial enzyme would do to you're other metabolic processes. If it was humanly possible to avoid deathly side effects, they already would be under development. The best defense from these WMD's is not boffin concocted enzymes but the same that holds true for nuclear weapons – just be on another continent when they go off. --Aspro (talk) 00:10, 23 January 2012 (UTC)
January 23
Difference in airplane fuel needs going to/from equator
We all know it takes more energy to walk from the center of a merry go round to the edge than vice versa because, well, however I explain it some pedant will correct me because I haven't taken a physics class in a few years. But imagine this: when you are at 20 degrees latitude, you are closer to the Earth's axis of rotation than you are when you're at the equator. In case 1, you take off from an airport at longitude X, latitude 20 degrees North (for instance), and fly due south to longitude X, right on the equator, and you note how much fuel you used. Then you take the exact same plane with the exact same conditions as far as the weather and your plane's weight (say, a 747), efficiency, etc. and fly back to your starting point. Given the energy content of jet fuel, would the difference in fuel used due to the difference in energy needed to get further away from the Earth's axis of rotation compared to the energy needed to get closer to it be, in terms of jet fuel, a few grams, a few kilograms, or what? If it's significant, airlines must have already thought of this and fueled the jets differently whether they're going from Rio to New York or from New York to Rio, for instance. 69.243.220.115 (talk) 00:12, 23 January 2012 (UTC)
Think that the moment of air from the poles to the equator (and the coriaceous effect) would mess up the calculations. On top of that, one should not fly due north/south because of the earth's rotation of about a thousand miles per hour and to ignore that, it would also mess up one's sums... one would have to fly at an angle to get a truer figure. Gravity at the poles is also less and the troposphere gets lower, thus the aircraft would require less fuel to stay in the air as it goes north, which is another factor to consider. Sorry, if I'm not answering your question.--Aspro (talk) 00:36, 23 January 2012 (UTC)
- The OP has asked a very sound question. The fuel required when traveling towards the poles is less than when traveling towards the equator. I imagine that for a wide-body passenger jet, the difference would amount to many hundreds of kilograms; possibly even a tonne.
- Routine operations by airlines rely on standard tables to determine the amount of fuel to be carried at the time of take-off, so the flight crews don't need to concern themselves with this consideration. However, when an engine or aircraft manufacturer is carrying out fuel consumption tests, particularly tests to determine what guarantees of specific fuel consumption to offer, or to determine whether compensation should be paid to a customer, it is desirable to determine exactly where all the fuel went during a flight. For these tests, the engine or aircraft manufacturer will account for the amount of fuel consumed in going from the latitude of take-off to the latitude of the destination. Dolphin (t) 01:40, 23 January 2012 (UTC)
How "wrong" is string theory
I read the article, and I saw that the main issue seems to be it's testability, but I see many people (well honestly, on youtube, not scientific community!) that hold strong views about it and say it's somehow like religion, which I think is a dubious comparison.To what extent is it unacceptable?--Irrational number (talk) 00:27, 23 January 2012 (UTC)
- XKCD explained the problem with string theory very well. Some people have used "string theory" as a term to describe some semi-religious pseudoscientific ideas they had. This does not necessarily discredit string theory itself of course. Von Restorff (talk) 00:48, 23 January 2012 (UTC)
- I would not say its unacceptable, as it is just like any other of many other theories. The math is great when applied to attempts to answer certain questions. What I personal don't like about it is that it doesn’t scale up to the observable (dare I say it) real world. Way toooo complicated. --Aspro (talk) 00:49, 23 January 2012 (UTC)
- Good one Restorff. As they say: a picture is worth a thousand words.--Aspro (talk) 00:59, 23 January 2012 (UTC)
- The serious critics (e.g. Peter Woit, Lee Smolin) are unhappy because basically all theorists and especially young theorists are spending their time on it, and we are spending a lot of money researching it, when it isn't clear that it actually does resolve the problems in the previous theories or even explain the stuff that is already known. It's an issue with putting all of the scientific eggs in one apparently untestable basket. The quote in the Woit article sums it up well. It's about the fact that the scientific community is more or less pursuing this as its only option, even though there is not much evidence for it and it is not entirely clear even what it is. As for what is acceptable, it depends on who you ask. Smart people disagree on the matter. --Mr.98 (talk) 01:06, 23 January 2012 (UTC)
- That was not very kind. Some of my best friends are fizzy-cysts. Yet, then again... maybe I should I ask for some of my tax dollars back? Oh, and I like your last quip - smart people disagree on the matter - does that apply to the dark stuff too ;-)--Aspro (talk) 01:22, 23 January 2012 (UTC)