The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
My fairly small garden pond loses considerable volumes of water to evaporation in summer, but using a watering can to refill it disturbs the sediment and plant roots in an unsatisfactory way. Ideally the water would flow in very gently, perhaps even drip by drip, but I don't want to be standing holding a watering can for a couple of hours to achieve this. One solution I am thinking about, involves having a second container that can be topped up with water manually - perhaps a bucket or barrel sitting by the side of the pond, with a lid that can be closed after refilling to prevent clogging up with dead leaves or other garden detritus. The idea would be for the water to then flow through a pipe connected near the bottom of the container, and drip into the pond. So I'm talking about something gravity-driven, and in terms of scale of water-flow, imagine a dripping tap. This raises several practical questions:
How thin should the internal diameter of the pipe be to ensure there is a flow, but to minimise the volumetric flow rate? Japanese water features seem to produce a surprising flow even through a tube of bamboo. But if we get down to the couple-of-millimetres scale, there must be considerable risk of the tube clogging, and presumably at some point it just stops flowing at all.
What's the trick to getting the water to drip out (or just barely trickle out), rather than flow out? I'm guessing the idea is to have some sort of narrower cap fitting over the end of the tube?
Bearing in mind this is a gravity-fed contraption, are there restrictions on e.g. the length of the pipe, or the angle it need to run at? I suspect that a longer thinner pipe may need to be put at a steeper angle to ensure flow. The length of pipe I am thinking about is in the 10 to 30 cm region. It's Question Time (talk) 00:37, 9 June 2011 (UTC)[reply]
Since this is all quite empirical, I'm thinking you're best off with a stopcock or plug valve or an adjustable clamp on a piece of rubber tubing. To prevent annoying clogs, I think your tube should generally be wide open except for one key point. Wnt (talk) 00:52, 9 June 2011 (UTC)[reply]
An adjustable set-up makes sense - if it's set to produce nothing more than drips, does that have any impact on the length of tube that can be sustained, or the angle it needs to lie at? (It seems intuitive that a continuous flow can "push" further/harder.) It's Question Time (talk) 01:03, 9 June 2011 (UTC)[reply]
Wouldn't a simple soaker hose do the trick ? (That's a flat garden hose with many small holes in it and a cap at the end [1].) Curl the soaker hose around the perimeter of the pond, and adjust the water pressure at the tap down to a level where it drips out of the many holes slowly. Having so many tiny holes makes it unlikely they will all get clogged. StuRat (talk) 01:08, 9 June 2011 (UTC)[reply]
Also, a caution, having standing water on your property, like you described, can allow mosquitos to breed there, unless chemicals are added to prevent that. StuRat (talk) 01:14, 9 June 2011 (UTC)[reply]
The water container would have a lid on it, and should drain near-enough completely within a couple of hours at most, so it shouldn't act like a water-trough. Mosquitos already come to the pond to breed, although most of the larvae just get predated! The flat soaker is an alternative; would it work if connected to a standing water source? (The solutions on sale seem to be several metres long which is excessive for my needs, although the site you linked to has the interesting review snapshot "Cons: Inefficient (3), Leaks (3)" which suggests not everyone gets the point! I wonder if it's possible to rig one up from other materials) It's Question Time (talk) 01:25, 9 June 2011 (UTC)[reply]
I would just use a short length of old hose pipe and drill many tiny holes with the smallest drill bit I could find (and stop the free end). The hose could be fixed above the bottom of the pond to avoid disturbing the sediment, and fed by gravity from your container a foot or two above pond level. If the container empties after an hour or so, then there will be no problem with insects breeding there. The rate of flow will be roughly proportional to the difference in height between the surface of the water in the container and the surface of the water in the pond. Dbfirs07:08, 9 June 2011 (UTC)[reply]
Once the container is nearly empty, there will very little pressure in the tube. Does that mean there's a minimum size of hole that water would be able to drip through? I'm imagining there will be surface forces that would make the water cling to the hole, so that some pressure is needed to force the water through (the same reason, I presume, that flat soakers nneed to be connected to a faucet with at least a little pressure) and that intuitively a smaller hole produces a greater contact force per volume of water. It's Question Time (talk) 12:38, 9 June 2011 (UTC)[reply]
I think StuRat/Dbfirs may be on to something with the soaker hose, which is more fault tolerant than a pipe with a single pinch point.
For another point of view, consider why it is that you want to spend resources to keep the pond full all summer. What is your goal? Have you ever seen what happens when no water is added? Depending on where you live and how the pond was formed, it may just be a natural Ephemeral pool, which will attract a unique blend of flora and fauna. You also may be able to decrease evaporation by installing shading trees, or even water lilies. SemanticMantis (talk) 14:14, 9 June 2011 (UTC)[reply]
The pond is artificial (and indeed is already shaded). But the point is a good one! Unfortunately without topping up the surface level drops very rapidly into the pre-formed shell, and it gets more difficult e.g. for frogs to to get in and out. It's also less aesthetically attractive that way. It's Question Time (talk) 18:32, 9 June 2011 (UTC)[reply]
Although they said using a small drill bit ;) Will that make a difference? It strikes me that when the container has nearly drained) the difference between water surfaces will be < 10 cm then the pressure will be very low and I wonder if pin-holes will actually hold the water in. It's Question Time (talk) 21:57, 10 June 2011 (UTC)[reply]
Pinholes will quickly become blocked with bacteria and algae, so I recommend drilling holes of at least a millimetre (larger would be OK because the flow will be slow for many holes and low header). If all the holes are under the surface of the pond, and the header container is designed to drain completely, then there will be no water above pond level for most of the time, and the container and upper hose will dry out, mainly preventing growth of clogging agents. Using an opaque hose rather than a transparent one will also reduce growth of any "nasties". Dbfirs09:42, 11 June 2011 (UTC)[reply]
You could have a large vertical cylinder pushed into the bottom of the pond. Fill it up with water, it will eventually reach the same level as the pond. It could have many holes in its sides - for example it could be made of a metal gauze (as a flour sifter is). Or have an open sack in the pond. Or you could make a cylinder out of twigs or chicken-wire. 92.24.181.38 (talk) 00:12, 12 June 2011 (UTC)[reply]
I'm late on this one but no one suggested the 1st thing to come to my mind.. Get a big plastic bottle and fill it with water and put it in your pond so that it sits on top of the water sticking out upside down with the mouth just at the level at which you want the pond to be filled. Now work out some sort of bracket so the bottle will stay there but so that you can also take it out and fill it, when needed. When the water level drops below the mouth of the bottle, some water will fall out of the bottle until the pond is level again.. Simple. And if you don't want an ugly bottle sticking out of your pond, cover it with bamboo or reeds or something.. Vespine (talk) 01:39, 14 June 2011 (UTC)[reply]
Gauss's Law for Electric Fields
Brushing up on my E&M, I just realized the one of Maxwell's equations, Gauss's law for electric fields has the permittivity of free space. My questions is that is this law true in any kind of a medium or only in a vacuum? If I want to use this law in some other medium like water for example, do I need to change the constant? Thanks!-Looking for Wisdom and Insight! (talk) 02:40, 9 June 2011 (UTC)[reply]
So the law is still valid in any medium as long as the value of the constant is appropriately changed? Another question I have, for magnetic fields there are diamagnets (which lower the strength of an externally applied magnetic field) and paramagnets (which increase the strength of an externally applied magnetic field). Comparing that with electric fields, I only know of dielectrics which weaken an externally applied electric field. Is there a paramagnetic analogue for electric fields? Have any experiments/research been done on this? What about gravitational fields? Any such matter which will strength or weaken an externally applied gravitational field?-Looking for Wisdom and Insight! (talk) 01:21, 10 June 2011 (UTC)[reply]
I am M.J.Varghese, the chief commender of LOVE (Liberation Organisation of Virtual Energy). LOVE is for doing charitable works in the name LOVE of Charity. Our supream commander is father God, who create, exist and controlling this nature. 2000 years ago, Jesus said that love each other because God is love. After 2000 years, I am saying that love everybody, then you get love because love is God.
Dear sir, I am contacting you to clear one of my doubts that is: there is BC that is before Christ, it means before the birth of Christ; and AD (after Christ), it means after the death of Christ. If so, the life time of Jesus is not accounted - 2000 AD is 2000 years after his death. If he come back by birth, he should born approximateky 33 years before 2000 AD, becasue then 2000 years after his birth is completed.
None of the incarnations or the prophets comes directly from heaven, and all of them born in between us. Hence, the second coming Jesus may be in between us, am I right?
Thanking you. With regards, M.J.V, C.C, LOVE.
I am exposing three ideas, want urgent research, I have no facility for research.
First one is: tender-coconut is the remedy to HIV, because HIV attacks our w.b.c., tender-coconut-water increases our w.b.c. rapidly, and the increased w.b.c. overlaps HIV. Hence, HIV cannot split up and attacks out w.b.c - thus, AIDS cannot forms. HIV happens like the seed thrown in to the cactus (the parable said by Jesus).
The second one is: water is a good fuel because it consist hydrogen and oxygen - by electrolysis, we can split water in to hydrogen and oxygen. This hydrogen burns in an engine chamber, we will get power to run a motor engine.
The third one is: the definition, location, and stages of mind. The modern medicine cannot define, locate, say about the stages of mind, but here I am saying about it. Mind consist of three main parts like a computer:
A.D. doesn't stand for "after death". It stands for Anno Domini, which is a Latin phrase meaning "in the year of our lord". There is no 33-year gap between the B.C. years and the A.D. years; indeed, there isn't even a year 0. 1 A.D. is the year immediately following 1 B.C. Red Act (talk) 05:04, 9 June 2011 (UTC)[reply]
Water isn't a fuel. Sure, you can electrolyze water into hydrogen and oxygen, and then burn the hydrogen. But the electrolysis requires energy in the form of electrical energy, that's actually somewhat more than the energy gained by burning the hydrogen, due to some heat loss in the process. So electrolyzing water and then burning the hydrogen results in a net loss of usable energy. Red Act (talk) 05:16, 9 June 2011 (UTC)[reply]
It isn't possible to do research into your idea that there are seven "stages for the mind", because that isn't a falsifiable hypothesis. I.e., without so much as a definition of what exactly a "stage of the mind" consists of, there is no experiment which can determine whether the number of "stages" the mind has is 7 or 42 or 666. Red Act (talk) 05:35, 9 June 2011 (UTC)[reply]
(edit conflict)If you can prove that "tender-coconut is the remedy to HIV", then you deserve a Nobel Prize and you will probably become very rich. Unfortunately, others have not been able to find a remedy. Jesus never mentioned a cactus, by the way. In your "stages for the mind", why restrict yourself to three dimensions. The human mind is much more complex, with many more "axes". Dbfirs06:57, 9 June 2011 (UTC)[reply]
Looie, I think you have something there! The axes of "extraversion" and "conscientiousness" would seem to fall pretty close to the energy/depression and good/evil stages he describes. I don't see from the article which of the Big Five axes is given credit for, shall we say, "Weiner games", but surely one of them must be.
It seemed like the tender coconut thing was too original for this person to have devised, and it is so - there's stuff about tender coconut water or coconut oil curing HIV all over Google. Looking back to see where the fire started I get PMID11365012 "interviews and anecdotal reports": "The third interview reveals a patient's success at dropping HIV viral load and increasing CD4 counts using Naltrexone and NK911 and supplementing with coconut oil, garlic, and raw goat's milk." (1998, Posit Health News) Another article PMID11366549 from that source talks about "transfer factor" as a prophylaxis for hepatitis, which somehow tied into coconut oil. Then PMID12349090 (1999, Reprowatch) is an abstract about a trial that was going to be started in the Philippines about coconut milk and "monolaurin, a coconut oil byproduct". Then nothing, at least in NCBI. Another 2007 article PMID20161889 talks about coconut being used in African traditional medicine for HIV. My guess is that there was some kind of flash in the pan about HIV and coconuts around the time of that Philippines trial, but it must not have come to anything.
I should say that I do hold traditional and herbal medicine in fairly high regard; I believe that likely half, or at least a third, of the treatments described by Dioscorides or extant in Chinese traditional medicine are somewhat effective, and of those only about half have been studied scientifically to this day. But traditional medicine for a new disease is a dicey business, and traditional medicine was never much good with diseases that take a long time to worsen or get better - things like lead and Aristolochia were used in traditional medicine on several continents, because only the short-term effect was apparent. With HIV, the alternative medicine is unfortunately all a matter of hoping for luck despite a lack of published success, whereas conventional treatments have with much difficulty evolved to the point of saving lives. Wnt (talk) 07:35, 9 June 2011 (UTC)[reply]
The OP posted the same message here. The organisation of which the OP is chief commender(?) is unknown to Google. The OP should not be using the Ref. Desk as a soapbox for a bizarre collection of claims. Cuddlyable3 (talk) 21:05, 9 June 2011 (UTC)[reply]
Can you explain what w.b.c. is supposed to mean? Also, many small electrical devices run on water, for example a water-activated battery, this thing, this thing, some other recent inventions worldwide], and another program I've encountered discussing a German company powering about a volt of energy from just a drop of water. For the Latin phrase you discussed, see Deus Caritas Est. ~AH1(discuss!)15:31, 11 June 2011 (UTC)[reply]
So why did they need a complete drop for *that*? And what was the effective energy output? I can make 2000 volts with a silk tie. 5BYv8cUJ (talk) 20:24, 11 June 2011 (UTC)[reply]
Water-activated batteries don't use water as their source of energy, even if some ill-informed reporter calls them "water powered". Water-activated batteries always have at least one other substance like sodium borohydride or something that's consumed in the process, that's actually the source of the chemical energy that gets turned into electrical energy. Once the chemical reaction involved has consumed all of that other substance, you can't get more energy out of the battery just by adding more water. Instead you need more of that other substance, which invariably is far less plentiful and far more expensive than water. I.e., it's really that other substance involved that gets consumed that reasonably should be called the fuel, not the water.
[citation needed] on the German company using the drop of water as an energy source, as well as on the phrase "some other recent inventions worldwide".
The Yi Cui thing looks like garbage to me, for multiple reasons. First, if he's really made some big breakthrough, why hasn't he published anything about it in a peer-reviewed journal? Google scholar turns up nothing about this from him. Second, sea water has a fairly low resistivity. If the electrodes have direct contact with the sea water (and it sounds like they do), why doesn't the sea water just short out any charge that's stored on the electrodes? Third, although it's hard to tell from a vague, rather nontechnical article in the popular press, it sounds like the basic principle that he's using is the fact that if you replace the dielectric in a capacitor with a different dielectric with a lower dielectric constant (sea water has a lower dielectric constant than pure water[2]) without changing the charge on the capacitor, the energy stored on the capacitor will increase. However, what he's neglecting to mention, and perhaps isn't even aware of, is that it requires as much mechanical energy to replace the dielectric in a situation like that as the increase in energy stored on the capacitor. It actually requires even more mechanical energy than that, due to the energy lost as heat. Where is that mechanical energy coming from? If he's neglecting that mechanical energy required, then that's a serious flaw in the idea, and he's got yet another flawed idea for a perpetual motion machine. Or if that mechanical energy is coming from the flow of the river, then all he's basically got is a different mechanism for producing hydroelectricity. Hydroelectricity doesn't use water as a fuel, i.e., it doesn't convert chemical energy in the water into a more useful form of energy. Instead, the output energy comes from stored gravitational potential energy. The fact that it happens to be water instead of some other substance that's the source of the gravitational potential energy isn't really important. Red Act (talk) 21:39, 11 June 2011 (UTC)[reply]
The coconut cure should be easy enough to test, so why not set up your own trials and see how many people with AIDS it cures ? As for using water as fuel, while it does require more energy to split it than you get back when you burn it, this still might make sense if you have a large source of electricity and want to produce oxygen and hydrogen gas as more portable sources of energy, such as for a car. There might be more efficient means of producing hydrogen alone, though (a car normally just uses atmospheric oxygen). Therefore, splitting water only makes sense if you have some use for the excess oxygen produced. StuRat (talk) 18:44, 11 June 2011 (UTC)[reply]
I looked back for that coconut oil study. What I found was http://www.coconut-info.com/aids.htm (a commercial site) which serves up the "full results" of the study (which say that it has "miraculous healing power" but that results "are not completed yet" and its effect is "mostly on the quality of life". Further digging reveals the study had 14 patients.[3] Now mind you, I do respect the Ayurvedic traditional medicine as representing centuries if not millennia of experience of trial and error experience regarding what is helpful against disease, and a very important source of future medical advances, but I don't respect people who sell "Ayurvedic medicine" against diseases that were not known more than a few decades ago. Wnt (talk) 22:21, 11 June 2011 (UTC)[reply]
Or are signals from both possibilities generally tracked and chosen from after a sufficient number of samples to discern between have been observed? Can some kind of bit parity, start or stop bits make that easy? 76.254.22.47 (talk) 22:54, 9 June 2011 (UTC)[reply]
After reading this, I've come to the conclusion that infinity cannot exist in the physical universe, that it's just a mathematical construct. Is that true? --Leptictidium (mt) 10:23, 9 June 2011 (UTC)[reply]
There are those who think that, but I think they're wrong, at least depending on what you mean by "cannot". For example it is consistent with all known observations that the physical universe itself is infinite (contains infinite volume, infinitely many particles).
A superconductor, according to theory as I understand it, has infinite conductivity, which simply means that a current passing through it does not dissipate any energy whatsoever to resistance (it can still lose energy by interaction with external electromagnetic fields). Whether that constitutes an infinite measurable quantity seems to be a question of definition. --Trovatore (talk) 10:35, 9 June 2011 (UTC)[reply]
Does that mean the universe has always been infinite? If so, how does that fit in with claims that the universe was infinitely dense just before the Big Bang? Thanks for your answers. --Leptictidium (mt) 10:45, 9 June 2011 (UTC)[reply]
My understanding is that, if the universe is infinite, then it always has been. But there are subtleties I've never completely come to terms with. You should ask User:BenRG, who seems to know about these things. --Trovatore (talk) 10:50, 9 June 2011 (UTC)[reply]
However that is not what a physicist means by "the conductivity of a superconductor is infinite". According to theory, the conductivity of a superconductor is literally infinite. --Trovatore (talk) 11:07, 9 June 2011 (UTC)[reply]
Well, yes, according to theory. But to what extent can this prediction be experimentally verified ? How can you experimentally tell the difference between exactly zero resistivity and a very, very small resistivity ? Sometime when a physicist says "zero", they mean "smaller than I can measure". Gandalf61 (talk) 12:32, 9 June 2011 (UTC)[reply]
If we assume the theory to be correct (because it is based on quantum mechanics and the approximations made are not relevant for this issue, otherwise the theory would not have been accepted as the explanation for superconductivity), then you can see that zero resistance arises in the limit of zero frequency. As long as the current has finite frequency components, the resistance is not exactly zero.
If you take a non-superconducting loop, and then move a magnet near it, there will then be a nonzero magnetic flux through the loop. If you then cool the loop so that it becomes superconducting, then you get a current if you move the magnet away from the loop. This is because the superconductor will keep the flux through the loop the same. This persistent current through the loop is then very stable, but according to the theory, it will slowly decay. The system is clearly not in the ground state and it can make transitions to lower energy eigenstates. But the time scales involved here are astronomical. Count Iblis (talk) 14:57, 9 June 2011 (UTC)[reply]
I am not completely up-to-date on this, but I don't really think your remarks about frequency are correct. I think what you mean is that the impedance is nonzero when there are finite frequency components. But impedance is not resistance. It does allow there to be a potential difference across the ends of the superconductor, but it does not allow any energy to be lost to thermal processes, which is the definition of resistance. --Trovatore (talk) 19:34, 9 June 2011 (UTC)[reply]
The real part of the impedance of any object at finite frequencies will be strictly larger than zero. If you have non-steady currents, you get all sorts of dissipative processes e.g. due to changing magnetic fields inducing currents elsewhere. So, if you have an LC-circuit and the current oscillates at some frequency, the current will die down on quite small time scales, nothing like the astronomically large time scales for superconducting rings carrying DC currents. I think that at a frequency of 1 kHz, the best superconducting coils have a quality factor of just 10^6 or so. The current will thus dissipate on a time scale of a few hours at that frequency. Count Iblis (talk) 02:15, 10 June 2011 (UTC)[reply]
Hmm, is it fair to attribute dissipation due to currents in nearby objects to resistance in the superconductor? It's a bookkeeping question, maybe, more than a physics one strictly speaking. --Trovatore (talk) 03:40, 10 June 2011 (UTC)[reply]
I think there are also other processes involving only the superconducting object. I think that the dominant source of the losses are due to processes in the surface layer of a superconductor. Electromagnetic fields penetrate a small distance into the superconductor, the perfect screening only happens some finite distance into the superconductor. An oscillating supercurrent will give rise to an oscillating electric field in the surface layer. There, the supercurrents are not effective in screening this out 100%, so this leaves room for charges there to oscillate with that electric field, causing dissipation. Count Iblis (talk) 15:13, 10 June 2011 (UTC)[reply]
Ah, but aren't you then saying that the surface layer is not in fact superconducting? So there is resistance, but it's not in the superconducting part of the object. Or no? I'm certainly no expert on superconductivity. --Trovatore (talk) 20:30, 10 June 2011 (UTC)[reply]
Yes, you could say that. I studied this quite a long time ago, so I don't know all the details. But it should be clear that in any material there are always degrees of freedom that are able to dissipate energy. What happens in a superconductor that carries a DC current is that all these processes are 100% frustrated. The supercurrent nullifies any potential difference, so there is nothing left for the dissipative processes to do. You can also say that putting a resistance of zero parallel to a resistance of R > 0 makes the net resistance zero. When you have a non-steady current, things are completely different. You can now excite all sorts of processes that were perfectly frozen in the DC case. Count Iblis (talk) 16:30, 11 June 2011 (UTC)[reply]
The statement that conductivity is infinite simply means that resistance is zero. No actual positive infinity is implied, or could be. μηδείς (talk) 20:40, 9 June 2011 (UTC)[reply]
Not sure what you mean by that. The conductivity is by definition the reciprocal of the resistivity; if the resistivity is zero, then the conductivity is infinite (in the Riemann sphere sense, say, although the more relevant structure is really the interval [0,+∞]). Your second sentence has the feel of an ideological rejection of infinity. --Trovatore (talk) 21:14, 9 June 2011 (UTC)[reply]
I think the statement that conductivity is infinite means that the resistance is theoretically zero, and is in practice too small to measure. No-one has yet provided experimental evidence that the resistance of an actual superconductor is exactly zero, and the theroetical models seem to make various simplifying assumptions (see spherical cow). Gandalf61 (talk) 06:10, 10 June 2011 (UTC)[reply]
Conductivity is a potential, and is not the same as what is actually conducted. Any actual current will be finite, but it may meet zero resistance. Again, no actual infinity is involved. Of course conductivity is defined as the reciprocal of resistance. We might arbitrarily define the term "applelessness" as the reciprocal of the number of apples one has in one's lunch bag. But it would be absurd to pretend that saying someone with no apples in his bag has infinite applessness proves the existence of real infinities. Actual concrete existents are always finite because they are what they are, and no more (or no less), while infinities are not concrete entities, but are relative abstractions. μηδείς (talk) 15:46, 10 June 2011 (UTC)[reply]
Do you imagine that the numbers used to quantify, say, current, are less abstract than infinities? Take a current of 2 Amperes, and point out to me the 2 in that.
The somewhat valid point that you have here is that conductivity is defined as a ratio of things that we find intuitively more basic. It has that in common with intensive properties generally (although conductivity is an intensive property itself, that isn't really the issue here, because its intensiveness comes from the fact that it has area in the denominator, and we're not concerned with zero area). For example, density is an intensive property, and point particles may have infinite density (if they're truly point particles, that is).
However there may also exist concrete extensive infinities, as I alluded to above; the physical universe itself may well be infinite, and contain, for example, infinitely many baryons. --Trovatore (talk) 20:10, 10 June 2011 (UTC)[reply]
Both integers and the various concepts of infinity are abstractions, but the concept of infinity exists at a higher level of abstraction than do the counting numbers. Numbers are abstractionss and infinity is an abstraction form abstractions. Concrete realities, however, are not abstractions. Any real act of conduction or any real entity or charge or substance is a real existent. Any concepts we use such as the reciprocal of zero which deal in infinities are based on abstracted concepts of relationships. If, for example, we were to talk about the conductivity of water through a hose we could imagine that none of the pressure of the water entering the hose was converted into heat and that the water exiting the hose did so with zero loss of pressure. Only from those concrete relative terms could we manipulate the math and speak in terms of the infinite conductivity of the hose, but that would be like the infinite applelessness of the empty lunch bag, a derived formal infinity, not a real concrete infinity.
As for infinite baryons, the notion is not coherent. It would amount to saying that there is no actual number of baryons in the Universe, because whatever the actual number of baryons were, there would have to be even more. If the unioverse were infinite we couldn't even make a mathematical statement about it in any relation to any known object since the equation would be undefined, like dividing by zero. The standard theory of the universe is a finite closed but unbounded system having existed for some finite duartion, apparently a hyper(^x)sphere some 13,500+ million years in radius. There is no physical evidence of an infinite universe. Any such notion is incomplete or incoherent or at some point undefined. All very mysterious, but not infinite. μηδείς (talk) 02:00, 11 June 2011 (UTC)[reply]
If the curvature of the universe is negative, then the most natural simple model is not a finite 3-sphere, but rather a pseudosphere I think it's called, which would have infinite volume, and therefore (assuming constant density) infinitely many baryons. That's a very simple-minded analysis and as I say there are some subtleties I'm not extremely solid on; for more details ask User:BenRG.
There is nothing incoherent about the notion of infinitely many baryons (please, not "infinite baryons"; no one is suggesting that any individual baryon is infinite). Your remarks on that meaning that there would "not be any particular number of them" seem to come from a pre-Georg Cantor understanding of mathematics. --Trovatore (talk) 02:09, 11 June 2011 (UTC)[reply]
I hope I didn't say finite three sphere, did I? The negative curvature of spacetime is usually taken to mean that it is not gravitationally closed in the future, not that currently existing space is infinite, of which there is no evidence. And yes, I am familiar with the formal notion of commensurable and non-commensurable infinities, but there is no evidence of the actual existence of a concrete infinity of baryons, hence nothing to refute. μηδείς (talk) 17:55, 11 June 2011 (UTC)[reply]
No, I believe your second sentence is not true. If the curvature is negative (I think we're talking about the curvature of space, not spacetime, but I'm a little fuzzy on that point) then the most natural models do in fact have infinite extent in space. If that is the case, then the principle of uniformity would suggest that the number of baryons is infinite, and that would in fact constitute evidence (albeit somewhat indirect) that a concrete infinity of baryons exists. --Trovatore (talk) 19:43, 11 June 2011 (UTC)[reply]
No, the measurable negative curvature of spacetime is in the time dimension. It was originally assumed for aesthetic reasons that gravity would stop the expansion of space over time. Present observation shows that this is false, and that the expansion is speeding up over time. Look at this image, with time in the Y axis and space in the x axis: [5]. The closed cigar shape to the left shows a universe in which time is positively curved and space and time are finite and the universe ends in a big crunch. The image like an expanding horn on the right shows a universe with negative curvature in time, and no finite end, no boundary in the upward time dimension. But note that the cross section in the x axis representing space is finite at any point, although it does keep growing over time. (Note that even this universe does come to an end with local heat death, rather than a big crunch.)
If space were negatively curved, deep space would appear to be much more crowded with stars than local space because the volume of space would increase at a higher rate per distance along a radius. That has not been observed. μηδείς (talk) 18:16, 12 June 2011 (UTC)[reply]
I believe that is incorrect. The observations are consistent with (very small) negative spatial curvature, or with (very small) positive curvature, but seem most to resemble asymptotic flatness. Note that the simplest model for flat space is also infinite. --Trovatore (talk) 18:56, 12 June 2011 (UTC)[reply]
Also there is no indication, in the image you linked, that the cross-section shown represents the entire universe. It may be, say, just the observable universe, or just some collection of stars. That's a bit subtle of a point to get across in a simple graphic. Also I think astrophysicists, when popularizing, tend not to try to explain what it means for an infinite universe to be "expanding", not a particularly problematic notion but not as easy to convey to the public as the "inflating balloon" one. --Trovatore (talk) 19:12, 12 June 2011 (UTC)[reply]
Yes, I am familiar with the limitations of a two dimensional depiction of an object in five or more dimensions. But clearly you understand my point of the difference between the curvature of the space versus the time dimension, and you do not contest the fact that there is observational evidence for the negative curvature the universe in time, but not for the negative curvature of space, no? μηδείς (talk) 19:28, 12 June 2011 (UTC)[reply]
I never said there was evidence for the negative curvature of space. What I said, or at least what I meant, is that negatively-curved space is consistent with all known observations. The error bars all include the value zero. It couldn't be much negative curvature, but it doesn't take much; even asymptotically flat space is, in the simplest model, infinite.
To be clear, I am not saying that space is infinite. I am saying we don't know. There is no clear evidence one way or the other. (Such evidence could exist, in the form of a confidence interval for the curvature that does not include zero; that would constitute evidence for a finite universe if it were on the positive side, or an infinite universe if it were on the negative side. Even that would not be conclusive, as there are various loopholes, but it would certainly be evidence.)
You, on the other hand, seem to think that we do know. I haven't yet seen why you think that. The reasons you've offered sound naive; your later remarks seem to contradict that impression, so I have to assume your earlier ones were rushed or oversimplified. --Trovatore (talk) 20:08, 12 June 2011 (UTC)[reply]
Well, let me draw an analogy, and please take it as offered in a friendly manner, even if it sounds absurd. If we were to assume that time travel is possible, I could certainly form the (baseless) notion that you committed the Jack the Ripper murders. Of course, I have both no evidence for this and no coherent way of explaining in real terms how time travel would be possible. But I could hold that both arbitrary and incoherent idea. Yet I don't, because I prefer to stick to dealing with ideas which can be coherently expressed and for which there is actual evidence. Real human knowledge is both coherent and foundational. And so I don't expect you to have to disprove the possibility that you committed those murders before I will refrain from accusing you of them.
In effect, I am certainly not claiming to "know" in some positive sense that the universe is not infinite, just as I don't know in any positive sense that the Flying Spaghetti Monster didn't create the Rolling Stones. I simply have no evidence, and do not find that I can express the hypothesis in any way that ties in with the concrete reality I do know. The burden is upon him who makes the claim to express himself coherently and to provide the evidence.
It appears to me that you have asserted affirmatively that the universe is not infinite. It is not clear why you think lack of evidence should militate more towards a finite universe than an infinite one, or why the idea of an infinite universe is more "arbitrary and baseless" than a finite one.
As for coherent expressibility, what exactly are you looking for? We have detailed mathematical models of what the universe may look like, if it is infinite. If those are not "coherent", does it mean that you think they are self-contradictory?
Finally, let us suppose that when the error bounds on spatial curvature are sufficiently tightened by observation, they fall on the negative side of the line. How would you respond to such an observation? I don't get the impression that your distaste for the infinite-universe idea has much to do with such observations; certainly, it doesn't affect your earlier remarks about not being able to "make a mathematical statement about it in any relation to any known object since the equation would be undefined, like dividing by zero." --Trovatore (talk) 21:43, 12 June 2011 (UTC)[reply]
I believe in the burden of evidence. If you make the claim, please both provide the evidence and express it coherently. Vaguely asserted possibilities are cot testable evidential hypotheses. μηδείς (talk) 21:53, 12 June 2011 (UTC)[reply]
I think you're being rather selective. You made the claim that the notion of an infinite universe was "incoherent". You have not explained (ahem) coherently just what you mean by its alleged incoherency, nor supplied evidence for it.
You seem to be under the mistaken impression that I am arguing with you and the words you are typing. I am interested in the verifiable concrete sensory evidence. You don't seem to understand that a word is meaningless if not related to concrete facts. Claims of an infinite universe, when such a term is not defined in relation to concrete facts, are as empty as claims to a callifragilistic universe, when callifragilistic is not defined in relation to concrete existence. Your entire point is that if there were evidence that the universe is XYZ there would be evidence that the universe is XYZ. That is tautology, not observation. But do let me know when you get some infinite observational evidence. μηδείς (talk) 22:28, 12 June 2011 (UTC)[reply]
I have outlined a concrete and not-implausible scenario under which there would be observational evidence, of a specific sort that I have specified, that the universe is infinite. Are you going to answer on the question of how you would respond to such a scenario? Also acceptable would be arguing that it's an implausible scenario, but I don't see how you're going to do that. If you default on both of these, then it appears to me that you have made a claim that you're unable or unwilling to justify. --Trovatore (talk) 22:34, 12 June 2011 (UTC)[reply]
That there would be evidence if there were evidence is not in itself evidence. μηδείς (talk) 00:55, 13 June 2011 (UTC) Next you will tell me O.J. was framed because someone says he might have been framed. μηδείς (talk) 00:55, 13 June 2011 (UTC)[reply]
OK, let's go back and see what the discussion was actually about. You asserted that "actual concrete existents are always finite". That is an affirmative assertion, for which the burden of proof is on you. I gave an example of something that may be a counterexample to your claim, depending on contingent facts as yet unknown, but possibly in principle knowable. You have not defended your original assertion against this claim. --Trovatore (talk) 02:28, 13 June 2011 (UTC)[reply]
I am not interested in arguing my point. I understand my position, and know I am right. I don't see any point in starting the disagreement over, assuming no one says that I have been unclear. Are you actually asking me to explain myself? If so, explain to me in your own words (a good faith effort) what you think I mean by a "concrete existent", and we can proceed from there. μηδείς (talk) 02:43, 13 June 2011 (UTC)[reply]
Coulomb's Law
I can show that Coulomb's Law + superposition implies and . I want to go the other way and derive Coulomb's law and superposition from the vector identities. I know from Gauss' Law that Gauss' Law implies Coulomb's law if we assume that the electric field is radial. Can the assumption be justified from ? And how does superposition emerge? Nevermind, that's easy to show. Thanks. 65.92.5.252 (talk) 07:36, 9 June 2011 (UTC)[reply]
Well and if you take the limit as V is small you will get the point charge used in Coulomb's Law. I think you are ontrack with Gauss's law which would apply when .
Gauss' Law should apply whether or not the electric field is curl-free. My trouble is that I can't use curl E = 0 to show that E is radial and symmetric, which would be enough to prove Coulomb's Law. 65.92.5.252 (talk) 21:54, 9 June 2011 (UTC)[reply]
Well the next step is to use in spherical coordinates.
This can then be simplified by assuming no variation with theta or phi, leaving
, which ends up with r-1. The force will be proportional to derivative of E over r, yielding a r-2 proportionality. Graeme Bartlett (talk) 13:16, 10 June 2011 (UTC)[reply]
Adrenaline sensing anti-perspirant/deodorant
Advertisers are such liars but they shouldn't go completely off the reservation in claims. I just acquired a stick of Degree "Adrenaline series" anti-perspirant/deodorant, which claims on its label that it "is designed to respond to increases in adrenaline..." Sounds like total bullshit to me. Is this possible?--Fuhghettaboutit (talk) 13:31, 9 June 2011 (UTC)[reply]
I would assume that it "responds" to increased moisture. The antiperspirant ingredients (generally aluminum compounds) can be encapsulated or otherwise designed to have low availability until wetted. Adrenalin (epinephrine) in the blood triggers increased secretion from sweat glands, so by a somewhat indirect route, they're not flat-out lying to say that their product responses to adrenaline. On the other hand, it's definitely not an adrenaline-specific response, and I'm not sure that the basic mechanism of action (sweating dissolves more antiperspirant ingredients, increasing their effect) is particularly novel or unique to this product. TenOfAllTrades(talk) 14:00, 9 June 2011 (UTC)[reply]
Just saying they designed it to do X doesn't mean they are competent designers. For example, would you deny that tinfoil hat creators have designed the hats to block mental transmissions? Of course they have. That doesn't mean such things exist or work, though. 20:37, 9 June 2011 (UTC)
The question is about technology and science, i think it's pretty safe to say that so far we are the only species to employ science, and methodologically only fairly recently. I think this sounds like a homework question. Vespine (talk) 04:25, 10 June 2011 (UTC)[reply]
Earmarking Human Infants at Birth
I asked my mom about this Earmarking of mine, had it ever since I can remember. She told me I was born that way. I don't buy it. By the laws of science I tell you. I like to imagine I was a Genetically Modified Baby, created in joint-venture of the U.S. Government and IBM Labratories in Silicon Valley. Project: OLD NAZI FILE. The Project was scrapped and all test subjects terminated. I was the one that got away. I'm in Hollywood now, watching too many movies. I figure the reality of this marking probably not as cool as all that. Note, if thought leads towards marking a twin, I was born by C-section at 11 lbs, rules out the twin possiblity, unless my moms an elephant. She's not. I did much online research on this, found nothing. Anything known in the Wikiworld? For conversation, possibilities. Cheers, --i am the kwisatz haderach (talk) 16:08, 9 June 2011 (UTC)[reply]
Sorry but do you actually have a question for the reference desk? This isn't the place for medical advice, to have a conversation or for rambling ideas on your birth. (But hint: the Nazi's were before the role of DNA in carrying hereditary information was even clear; it's difficult to be sure but from the photo it looks like you were born before Flavr Savr; when what your suggesting is wackier then an episode of Fringe (TV series) you've perhaps gone too far; and if you're really the only one that got away posting on a highly public forum about it probably isn't a good idea) Nil Einne (talk) 17:12, 9 June 2011 (UTC)[reply]
Instead of the non-serious tone I took to bastardize Hollywood productions, maybe amend question for OBJECTIVE Science. Click on image, where face meets top of ear, little hole. Fact: It is a Piercing. Question: Possible reasons on piercing an infant? --i am the kwisatz haderach (talk) 19:48, 9 June 2011 (UTC)[reply]
It certainly does not look like a congenital condition. Maybe mommy did something at some point, but doesn't want to confess? μηδείς (talk) 20:31, 9 June 2011 (UTC) I mistook you to be speaking about what looks like a mark from a stapler across your lobe--that would wscare me more than your vestigial extra gill hole.μηδείς (talk) 15:52, 10 June 2011 (UTC)[reply]
It looks like a freckle in that pic. But from your description, that could be the result of a routine medical test. I have something like that from the tine test administered on my shoulder (although it's 6 indentations, in my case). StuRat (talk) 20:37, 9 June 2011 (UTC)[reply]
My son was born with a similar tiny hole on his ear and the doctor referred to it as a "preauricular dimple". Try googling that term or "preauricular pit" and see if the descriptions that you find match what you have. — Preceding unsigned comment added by 148.177.1.210 (talk) 21:04, 9 June 2011 (UTC)[reply]
(ec)Are you saying that hole goes all the way through? (Have you tried an earring in it?) Otherwise, to me it looks like a very small thing indeed, something like a dimple at most. (You should also examine the photo carefully in dimples of Venus for purely academic interest) Now your ear lobe looks unfamiliar to me - I expect them to be smoother - and somewhat reminds me of various paranoia about ear lobe creases and risk of heart disease.[6] But, yours doesn't look like the ones I saw in the pictures, which were more diagonal and seemed less cartilage-y, so probably not. None of this should be taken in any way remotely as medical advice, as it is all purely speculation about natural physical diversity.
Odd, there are actually nine different genes on OMIM in which both "preauricular" and "pectus excavatum" are mentioned.[7] You might find it interesting to go through the list and see if any have other effects that are familiar to you. (Remember, for every extreme case in which people have diagnosable genetic diseases, there are many others in which people simply tend a little in that direction as part of the healthy natural diversity of the human species). Wnt (talk) 21:39, 9 June 2011 (UTC)[reply]
We are definitely straying way too far into the field of medical diagnosis here, let's rein it in and call this question answered. If the "kwisatz" is concerned about a genetic disorder, he or she should see a doctor. --- Medical geneticist (talk) 22:22, 9 June 2011 (UTC)[reply]
As I said, we are dealing with normal, natural variation. This person is not sick; therefore this is not medicine. Wnt (talk) 22:37, 9 June 2011 (UTC)[reply]
To address the conspiracy question expressed by the OP (not even that unusual - from the forums it sounds like there are a lot of people with strange explanations about these pits; in any case I would wonder if some environmental factor influenced development), and because some people with them notice a smelly keratin-containing fluid coming out on a routine basis, I went hunting for "ear" in Dioscorides' Materia Medica (Osbaldeston's translation). There are very many sections describing ear treatments for purulence or sores, but his section on myrrh said that "rubbed on the ear externally it alleviates long-enduring discharges". Since this is the only section specifying externally I wonder if indeed this is a description of such pits from ancient times, but alas, it's just too vague to tell. There doesn't seem to be much sign that current herbalists do this, so I can't even argue by tradition. I feel like there ought to be some way to wring a clear mention of this out of ancient literature, but I haven't hit on it yet. Wnt (talk) 23:12, 9 June 2011 (UTC)[reply]
Now that's a weird story. "Strength" is inherited, but coat color results from parents mating in front of willow branches with stripes?[8]Wnt (talk) 00:04, 10 June 2011 (UTC)[reply]
I guess the only way I would believe is if like 148.177, I actually saw a baby coming out of a womb with this Preauricular Dimple. Seems more like an Earmarking, a Branding when the Nurses/Doctors take the baby to the side tray to clean and wrap before handing back to the mother. Because its close to the Sinus there are complications with infections later. This seems like better logic. I'm not a geneticist, so I could be wrong (more than likely). If the theme of my questioning is earmarking a baby then it isn't about diagnosable genetic diseases. For hard science, best answered by 148.177/Wnt/Medical geneticist. A co-worker brought up Satanists like in Roman Polanski's horror 'Rosemary's Baby'. I like that answer, but also far fetched. --i am the kwisatz haderach (talk) 23:41, 9 June 2011 (UTC)[reply]
It sounds like you're actually looking for imaginative explanations. On the Medhelp forum[9] I read people who thought they'd been poked with the amniocentesis needle, or the holes were from being grasped with obstetrical forceps during delivery, or their parents had pierced their ears as a baby, or that they were "ghost holes"/"spirit holes" with some kind of psychic significance. Wnt (talk) 23:52, 9 June 2011 (UTC)[reply]
I still would like to see a birth and check for it being genetic (odds not in favor), maybe talk to an OB that's seen one right out the womb. In regards to marked humans, I've seen foreigners with the Smallpox Vaccination scar on upper arm. Leaves a pretty big mark in comparison to my marking. That could be from the actual vaccine. I am looking for both scientific and imaginative explanations. The more the merrier. Thanks much y'all. This is a lot to work with from just googling EARMARKING HUMAN INFANTS. --i am the kwisatz haderach (talk) 20:11, 10 June 2011 (UTC)[reply]
Safety on stairs
Running downstairs or only using every second stair is clearly more dangerous than walking and using every stair. But if someone is doing this dangerous thing, how much safer is the activity IF they grip the handrail? (Let's say a hypothetical "average person".)
My hunch is that using the handrail does not make it very much safer because a) a person can't maintain a good grip on the handrail when they have to "regrip" quickly due to running and b) most people are not strong enough to maintain a grip on it if their feet go out from under them (or they lose their balance in some other way.) Thanks, CBHA (talk) 18:45, 9 June 2011 (UTC)[reply]
Ask yourself what it would even mean to say "using the handrail is 12% safer". Now imagine what kind of data it would take to support that claim. I'll be surprised if anyone can give us a quantified answer, but who knows what kinds of data e.g. OSHA might have... SemanticMantis (talk) 19:45, 9 June 2011 (UTC)[reply]
Thank you. I understand that pinning this down to "X percent safer" would be very difficult or impossible. I was just thinking of three or four levels. For example, "trying to use a handrail while running downstairs"
- a) "makes it considerably safer",
- b) "makes it a bit safer",
- c) "does not make it safer" or
- d) "makes it more dangerous because it takes the runner's attention off the stairs".
Given the varied backgrounds of Reference Desk editors, I look forward to hearing from some with experience in running downstairs. ;o) Perhaps there are some movie stuntpeople answering questions here.
Well, as somebody who at a younger age frequently used to run down stairs or take them two or three at a time, my opinion is that using a handrail is safer because it makes it easier to get your feet to land where you want them too. Also it steadies you on the landing. I don't think it has much value for saving yourself once you start to fall. Looie496 (talk) 00:19, 10 June 2011 (UTC)[reply]
Unrelated fun fact : In college I discovered that by jumping forwards, catching the handrails like they were parallel bars, and sort of flinging myself downwards, I could go down entire flights of stairs without touching a single step except the landings. In this manner I could go down 15 floors much faster than the elevators. I guess you need long arms to do this. Great for making up lost time when I was late for class. However, I can't make any claims as to how safe this was. Probably not very. APL (talk) 07:04, 10 June 2011 (UTC)[reply]
"most people are not strong enough to maintain a grip on it if their feet go out from under them". Is this really the case? I know there was a recent news story about most children not being able to hang from the monkey bars any more, but have our arms and hands really withered this much? I don't think of myself as especially strong (I couldn't go hand-over-hand on the monkey bars anymore), but I'm also someone who used to fall down the stairs a lot, and still have occasional 'incidents'. I find it is much safer to hold the handrail because a) it steadies you if you start to fall b) you can hold tightly and stop yourself pitching down the whole flight c) even if your grip is not strong enough to hold you there, it jerks you back so that you fall backwards and slide down the stairs, which still hurts but less severely than going head first or tumbling d) if you slip, you don't tend to slide as far if you have even an imperfect grip on the banister. 86.161.212.100 (talk) 14:16, 10 June 2011 (UTC)[reply]
I agree with the post above. Having a hand on the rail (not necessarily a grip) means that you can quickly grip the rail if you start to fall. It's pretty common to start to fall on stairs and to grab the rail and either prevent the fall or improve how you land.--Srleffler (talk) 17:05, 10 June 2011 (UTC)[reply]
There's been a few projects that attempt to genetically modify cotton so that the seeds can be used as human food. Ordinary cotton seeds have a substance on the seed coat that prevents them from being a useful food source. Here is a relevant link, which was the first google hit for /cotton seed food/ [10]. SemanticMantis (talk) 19:41, 9 June 2011 (UTC)[reply]
Jokes aside, cotton seeds contain gossypol, which is poisonous. Though presumably, if you somehow remove all traces of it, you might then use the detoxified cotton seeds for food. 67.169.177.176 (talk) 23:35, 10 June 2011 (UTC)[reply]
Because there are two types of particles, fermions and bosons where the values of the spin are either 1/2 integer (fermions) or whole integer (bosons). Furthermore, they have unique properties regarding how each class of particles obeys certain physical laws, such as the Pauli exclusion principle. The mathematics of 1/2 integer and whole integer spins are covered by such topics as Fermi–Dirac statistics and Bose–Einstein statistics. But basically, the answer is that 1/2 spin particles like electrons have a spin which is half of the magnitude of whole integer spin particles, like photons or the Higgs particle. --Jayron3220:45, 9 June 2011 (UTC)[reply]
I think the way to look at it is that Planck's constant relates the energy of light to its frequency. The "reduced Planck's constant" (h/2pi) is the "fundamental unit of angular momentum". Note this 2pi is the difference between radians and full cycles. Now if an electron wants to go from +1/2 to -1/2, it changes by emitting or absorbing a photon, and the reduced Planck's constant is the angular momentum of that photon. There is no particle that changes from 0 to +1/2 or +1/2 to 1 (unless I'm terribly wrong about something). That's because there are no half photons with half angular momentum. So there's no call to create a unit h/4pi and present that as a fundamental unit so leptons are odd and bosons are even - it would just make a sometimes confusing system much worse. Wnt (talk) 21:00, 9 June 2011 (UTC)[reply]
Not sure about changing, but it is possible for fermionic matter to form bosonic matter. mesons are bosons composed of two quarks, which are fermions. Likewise the Bose–Einstein condensate has bosonic properties (it violates the Pauli principle, for example) despite being otherwised composed of normal atoms (composed of fermionic protons, neutrons, and electrons). I do not, however, know of any process whereby fermionic matter can be created by multiple bosons. In other words, you can additively create whole integer spins out of even numbers of half-integer particles, but there is no way to get a half integer spin with nothing but whole integer spin particles. --Jayron3200:49, 10 June 2011 (UTC)[reply]
Still, the OP raises the question if there is anything more intuitive about the current scheme of assigning integer and half integer spins to bosons and fermions respectively versus assigning them even and odd spins, or is it just a historical accident such as the choice of positive and negative charges? -- 110.49.241.141 (talk) 21:25, 10 June 2011 (UTC)[reply]
I'm pretty sure that is completely arbitrary; you could do all the math with odd/even spin numbers, and just do the math with spin/2 and get all the same results. It's probably one of those things where the standard is abitrary, but has to exist as a standard, i.e. someone had to pick SOME standard, so they chose halves and wholes instead of odds and evens, for no reason in particular other than preference. --Jayron3200:36, 11 June 2011 (UTC)[reply]
The spin quantum number, s, is related to the physical angular momentum via . That is generally introduced first from the energy relationships in quantum mechanics, but is also ubiquitous in momentum problems as well. You can't really change either L or (aside from redefining the units on both) without screwing up lots of relationships between classical and quantum mechanics. What one could do is define , such that , and other similar relationships. I don't see anything wrong with that other than that it adds an arbitrary 1/2 or 2 everywhere. Personally, I suspect that equations of the form , with s taking integer or half-integer values was simply preferred due to an economy of notation, i.e. it felt more "natural". Dragons flight (talk) 01:23, 11 June 2011 (UTC)[reply]
If you rotate a particle with spin 1/2 about its axis, you have to rotate it 720° to get back to the initial state. Rotating only 360° leaves the wavefunction with the wrong phase. Particles with integer multiples of spin always return to their initial state when rotated through 360°. This is mentioned in passing (phrased differently) at Spin (physics)#Spin and rotations.--Srleffler (talk) 17:47, 13 June 2011 (UTC)[reply]
color perception different in each eye
I've always had a slight difference in color perception between my eyes. I know this is not uncommon, but I only have anecdotal evidence - other people confirming they too have the same experience. I would like to find something written by a medical authority (journal article, book, something!) that confirms this, and might provide some explanation. Thanks, Kingturtle = (talk) 20:43, 9 June 2011 (UTC)[reply]
In the extreme case, there are reports of unilateral colorblindness: PNAS article (PDF). The subject of that paper had normal color vision in one eye, and deuteranopia in the other.
The previous Ref Desk discussion touched on a much more likely explanation for most cases of differential perception of color: transient changes in sensory adaptation, blood flow, and pigment bleaching. TenOfAllTrades(talk) 23:09, 9 June 2011 (UTC)[reply]
Amongst astronomers, particularly amateurs today and professionals in former times when visual as opposed to photographic & digital observations are/were more common (and describing the exact visually perceived colours of stars was thought interesting and/or useful - see Stellar classification), it was a commonplace that most observers' two eyes differed detectably, and sometimes obviously, in their colour perceptions, just as they usually do in various other parameters of focus and abberation.
One factor affecting this is that as the eyes' lenses age, they absorb relatively more at the blue end of the spectrum, and an individual's two eyes sometimes show the effects of age differentially (resulting partly from differential light exposure if he/she has favoured one over the other at the eyepiece). This becomes very obvious if he/she develops cataracts and has one lens removed or replaced (with compensation provided by an external spectacle or internal plastic lens) before the other (as is usual for obvious reasons) - the contrast between the gradually changed eye and the suddenly restored one is very noticeable, as was once described to me by the eminent amateur astronomer Commander Henry Hatfield following such an operation.
My vision seems tinted blue in my left eye and orange in my right. I wonder if this has a benefit for distinguishing similar shades? When I took the standard vision plate test as part of a lab experiment in Biology 102 I (the only one out of some 30 students) received a perfect score, which the proctor complained was statistically impossible. I always wondered if it was my eyes or if I guessed well.μηδείς (talk) 18:02, 11 June 2011 (UTC)[reply]
Well, I din't mean to imply my vision was exceptional, only that I had hypothesized that my perfect result using the full test might be due at least in part to the difference between the eyes. Here is the relevant article: Ishihara color test. I note thta the most dificult plate with the number "2" does appear noticeably different to each eye. μηδείς (talk) 19:01, 12 June 2011 (UTC)[reply]
When people talk about "good cholesterol" and "bad cholesterol", they usually are referring to HDL and LDL, respectively. These actually aren't different cholesterols (all cholesterol is the same chemical compound), but rather different cholesterol-carrying complexes in your bloodstream. Because HDL and LDL are really only found in blood, it doesn't make sense to talk about food having "good cholesterol" or "bad cholesterol". (Animal derived foods/fats do have cholesterol in them, but not as HDL or LDL.) Different foods, however, will have different effects on your HDL vs. LDL levels. High-density lipoprotein#Diet and lifestyle mentions eating omega-3 fatty acids and soluble fiber, and avoiding trans fatty acids as some dietary ways of increasing your HDL levels. Other places have other recommendations - if you are specifically concerned about your HDL levels, your best bet is to talk to a dietitian or doctor. -- 174.31.219.218 (talk) 23:04, 9 June 2011 (UTC)[reply]
Another thing to keep in mind is that there is a plenty of ongoing controversy regarding the interpretation of the studies which gave rise to the terms you are asking about. As far as I can tell, you're much better off replacing fatty foods with fruits and vegetables, lowering your caloric intake, avoiding red meats in favor of vegetable protein sources, fish or poultry, and getting more exercise than spending any time thinking about cholesterol types, unless a doctor reviewing your test results tells to do something specific about them. 76.254.22.47 (talk) 20:18, 13 June 2011 (UTC)[reply]
June 10
Avian body odour?
Is it a noted fact that birds tend to have little or no body odour? Just something that occurred to me today while my friend's really stinky dog was running around the room in front of me - while accumulations of bird poop do smell bad, I'm yet to encounter a bird that in itself, has an obvious scent. --Kurt Shaped Box (talk) 00:47, 10 June 2011 (UTC)[reply]
Feathers don't work very well if they get dirty so birds spend a lot of time preening and keeping themselves clean. Conversly, some dogs seem to take pleasure from rolling around in the foulest substance that can be found. Vespine (talk) 01:10, 10 June 2011 (UTC)[reply]
Could the fact that birds lack sweat glands be a significant/more significant factor? I mean, odour-producing bacteria grows in sweat, doesn't it? I know that it's also said that (IIRC) most birds have a poor sense of smell too, so odour-for-the-purposes-of-identification/scent marking would seem to me to be a rather unnecessary. --Kurt Shaped Box (talk) 01:17, 10 June 2011 (UTC)[reply]
Dogs don't sweat? Hmmm. Never owned a dog, but I could swear that I've known other people's dogs that've been all sweaty after going for a run (might be wrong). --Kurt Shaped Box (talk) 10:52, 10 June 2011 (UTC)[reply]
Overheated dogs have been known to jump into puddles or other water, so a hot, wet dog might be mistaken for a sweaty one. StuRat (talk) 17:35, 11 June 2011 (UTC)[reply]
Knowing nothing about this topic, I did a Google search for "odorous birds", and the top hit is a National Geographic article titled BO Attracting Predators to Birds, whose first sentence is "New Zealand's native-bird BO is so pungent, it's alerting predators to the birds' presence, ongoing research shows". The remainder of the article contains some useful information about bird body odor as well. Looie496 (talk) 02:33, 10 June 2011 (UTC)[reply]
Doing a casual google also suggests that some birds have fairly highly developed sense of smell, but most do not. So it's not a class wide feature (or more specifically 'lack of' in this case). Vespine (talk) 04:15, 10 June 2011 (UTC)[reply]
From what I've smelled of the parrots I've been close to (not that I've been deliberately going around sniffing parrots, mind), they do have a very faint, oily scent. I'd actually theorized that this may be the smell of the preen oil/wax. FWIW, Caiques are supposed to have a distinctive scent, as mentioned in the article. --Kurt Shaped Box (talk) 10:52, 10 June 2011 (UTC)[reply]
Penguins have a terrible odour. I couldn't stand being near to them for a long time. But then again those are not "normal" birds. --helohe(talk)22:30, 10 June 2011 (UTC)[reply]
Well, those that live in Antarctica do have the problem of all their waste simply freezing and accumulating, rather than decaying. While frozen it's probably not bad, but on the few days warm enough for it to thaw, I imagine there's a horrid stench. One would hope that zoos would clean up after them, but, it they are used to being able to lie on a pile of crap after it freezes in an hour, perhaps they still do that when in a warmer zoo, not realizing that those rules no longer apply there. StuRat (talk) 00:15, 12 June 2011 (UTC)[reply]
The mother of a friend of mine raised a few score parrots of various species for commercial sale in her basement. The house smelled a bit dusty, but no more so in the basement than the rest of the house. μηδείς (talk) 01:46, 13 June 2011 (UTC)[reply]
Hollowed asteroid generation ships are a common science fiction theme; see for example Greg Bear's Eon. Hollow comets are little bit harder to come by (there seems to be a certain psychological reluctance to use ice as a building material, even though it would stay quite comfortably frozen on the long journey between the stars). Nevertheless, David Brin offers us Heart of the Comet. Those examples are novels; I strongly suspect that you'll find quite a few examples if you delve into the world of short fiction. (Isaac Asimov's novella The Martian Way introduced the use of chunks of ice from Saturn's rings as cubic-mile-scale spacecraft (but didn't broach the subject of generation ships). TenOfAllTrades(talk) 03:32, 10 June 2011 (UTC)[reply]
With out current technology it wouldn't make much sense, as it would take more energy to move that extra mass around, and to catch up to a comet and land on it in the first place, without any corresponding benefit. However, my fave design for an interstellar ship is a massive linear accelerator/nuclear reactor combo (or maybe anti-matter reactor) that clamps onto an asteroid, and hollows it out for material to fling out at the speed of light, while using the asteroid as a shield in the front. StuRat (talk) 03:37, 10 June 2011 (UTC)[reply]
Let's not forget that many comets follow a hyperbolic trajectory that takes them out of the Solar System on their own.[11] While it is unlikely indeed, it is possible to imagine spotting a comet on its way into the Solar System, plotting out a trajectory that comes close to Earth, and seeing that it will go near a planet you want to colonize in a bazillion years or less. So you round up a bunch of idiots astronauts and convince them to take a few tiny, fast ships with just a few basic essentials, confident that they can live off the water and carbon dioxide and other goodies locked away in the cold, dark core of the comet for countless generations before sallying out to claim some barren rock a few parsecs over. (Better bring a lot of mirror foil to concentrate that starlight...) Wnt (talk) 17:12, 10 June 2011 (UTC)[reply]
It's obviously still unrealistic, but the only realistic proposals so far in space travel are to extremely local things like the moon or the inner planets, so that it's not immediately feasible isn't surprising. Regardless, my original question was answered. SDY (talk) 17:50, 10 June 2011 (UTC)[reply]
Do pigs have orgasms that last for thirty minutes?
Somebody told me that pigs have orgasms that last for thirty minutes, but I can't find any evidence supporting it. I've already checked the pages about pigs, orgasms, and animal sexual behavior. Additionally, if this is true, is it true for both sexes? — Preceding unsigned comment added by Undercooked (talk • contribs) 04:03, 10 June 2011 (UTC)[reply]
Sounds like nonsense to me, and there is an awful lot of nonsense out there. I suggest you ask them to support their claim. Why would you prefer to believe something that someone told you than trust your own researches?--Shantavira|feed me07:19, 10 June 2011 (UTC)[reply]
(edit conflict) The simple answer is yes, assuming that (1) by "weight" you mean "mass"; (2) the substance you are calling "water" has a density more than 3 times that of ordinary water; (3) we can neglect any small changes in mass due to release or absorbtion of dissolved gases etc; (4) we can neglect the really really small changes in mass due loss of thermal energy. Basically, mass stays the same, but volume and density will change. Gandalf61 (talk) 09:20, 10 June 2011 (UTC)[reply]
I'd have to disagree with the first two posters, just on an everyday level, as ice has a lot "heavier" feel to it, from being solid. --188.29.60.182 (talk) 09:35, 10 June 2011 (UTC)[reply]
This means: "If you take ice and water of same volume, ice would feel heavier". This is not right for the reason: 1) Unlike other solids, ice is less dense than its liquid state (water). (See Properties of water#Density of water and ice). I have to note that this statement is unrelated to freezing a piece of water in isolated environment and having its mass save due to the law of conservation of mass, which the question is about. :) --Gryllida09:41, 10 June 2011 (UTC)[reply]
"Feels solid" (maybe mentally related to things that are hard and therefore large and/or massive?) and "feels heavier" are separate issues. If you are trying to compare "how heavy" (the question), take a bucket-full of each. Gandalf61 makes an interesting point #2 I'd like to emphasize: though the poster might just be making up numbers for this example, 300 mL of water would actually weigh approximately 300 g and 1 kg of water would be approximately 1000 mL at normal earth conditions. DMacks (talk) 09:53, 10 June 2011 (UTC)[reply]
To make things clear: I'll rephrase the question. It can be interpreted in two different manners (I used the first one). --Gryllida10:04, 10 June 2011 (UTC)[reply]
2. "Is a solid of given volume heavier than liquid?" --The answer is "yes" for everythingalmost everything [updated per reply -Gryllida 13:27, 10 June 2011 (UTC)] other than water (see here). --Gryllida10:04, 10 June 2011 (UTC)[reply]
The change in volume is an important point to consider, given the distinction between weight and mass. The ice and the liquid water would have essentially the same mass; the state change doesn't affect the amount or type of matter present, and the relativistic effects (associated with different amounts of internal energy) are negligibly small for any reasonable purpose I could imagine.
Whether or not they are the same weight depends on one's definitions, however. If one defines 'weight' to be solely the attractive gravitational force between the ice/water and the earth, then they will have the same weight. If one defines 'weight' as the net apparent force between the water/ice and the earth, then under sensitive measurement conditions the two states will actually show slightly different weights. This latter 'operational' definition represents how most balances and scales tend to work in real life. To consider an extreme example, think about what happens if you tie a helium-filled party balloon to the pan of a balance. Even though we all know the balloon has real mass, it will show up as having a negative weight. The net force exerted by the balloon on the scale is upwards, because the balloon displaces more than its own mass in air: buoyancy.
While this effect is usually only obvious when weighing objects that are comparable in density to (or lighter than) air, it actually comes into play for all objects being weighed in atmosphere. In round numbers, the density of air at sea level is on the order of 1 gram per liter, so 1 kg of liquid water will displace about 1 gram of air. The density of ordinary ice is about ten percent less than that of liquid water; a kilogram of frozen water will displaces about ten percent more air (an extra 0.1 g). This extra volume means extra buoyancy, which means that the measured, apparent weight will be reduced by about one part in ten thousand. That doesn't sound like a lot – it's too small a shift to pick up on a bathroom or kitchen scale, for instance – but it's readily detectable using a good analytical balance (of the sort you'd find in any reasonably-equipped chemical laboratory). That said, buoyancy due to air is something that only has to be explicitly accounted for when making extremely precise measurements of weight. TenOfAllTrades(talk) 14:35, 10 June 2011 (UTC)[reply]
Hence the ice would have the same mass as the water, but would weigh slightly less, right? If you take two equal-weight buckets, each containing 300ml of water, as well as plenty of room at the top to expand, you could freeze one of them, and although the one containing ice would weigh measurably less, merely carrying them they should "feel" the same weight. Right? ←Baseball BugsWhat's up, Doc?carrots→ 14:42, 10 June 2011 (UTC)[reply]
Because the heat of fusion of water is 337 kJ/kg, and the weight of a joule is 11.1 femtograms, a 1 kg block of ice should be 37.2 nanograms lighter than the corresponding amount of water at the same temperature. Additionally, if we suppose that the 1000 cc of water begins as a 1 decimeter cube, and if we constrain the sides and force it to go only upward when freezing, then because ice is 0.9167 the density of water, the center of gravity of the ice will be 4.54% (0.454 cm) higher than that of the water. Since the Earth is 6371 km in radius, at sea level this increases the distance to the center of the Earth by a ratio of 7.13 x 10-11 - which should decrease the weight by twice as much (i.e. (1 + that) squared), or 142.6 nanograms. In total then (for that shape and manner of freezing) that's 0.18 micrograms - almost a weighable difference! B) Wnt (talk) 16:54, 10 June 2011 (UTC)[reply]
You need the change in internal energy here, not the enthalpy; the latent heat is the heat needed to melt ice, which is less than the internal energy change in this case, because you get some energy "free of charge" due to the volume decreasing and the atmosphere performing work on the water. Count Iblis (talk) 18:29, 10 June 2011 (UTC)[reply]
If 300ml of water weighed 1 kg then it wouldn't be water on planet Earth. Here the heaviest water we know about is only 10.6% denser than ordinary water. If you freeze heavy water you get heavy ice that actually sinks in ordinary water. I suppose one could make an alloy of ordinary and heavy ice that has exactly the same density as ordinary water (and I think they could coexist at slightly above 0 deg. C.). Cuddlyable3 (talk) 22:34, 10 June 2011 (UTC)[reply]
There seems to be a general confusion in several posts here (including the original poster) between mass and weight. 300ml of water has a mass of approximately 300g anywhere in the universe; on Earth it has a weight of approximately 3 Newtons. Gandalf61 (talk) 02:42, 11 June 2011 (UTC)[reply]
Following Wnt, if 300 g (or 1000 g) of water gave up energy and froze, consider the mass equivalent of the energy lost, by the formula E=MC2 Would this energy loss make the ice have less mass than the water? Granted, no practical measuring device could measure the difference. But theoretically is the ice less massive than the water? I've heard that a car accelerated from zero to 100 km/hr gains a tiny amount of mass, and that a wound up clock gains a tiny amount of mass. Does this energy-mass equivalence extend to freezing/thawing? Edison (talk) 04:10, 11 June 2011 (UTC)[reply]
Yes, and there is a very simple way to see this. The center of mass of an object at rest on which no external forces act, cannot change. If you assume that this is always true, then considering a situation where a pulse of light is exchanged between two parts of the object, leads to the conclusion that the transfer of energy was accompanied by a transfer of mass. If there were to exist another hypothetical process in which energy is transferred without a change of mass, the relation E = M c^2 would not be valid; you would be able to transfer arbitrary large amounts of mass from an object of mass M without affecting its internal energy, you could make that mass negative while makig the mass of another object arbitrary large. Count Iblis (talk) 15:46, 11 June 2011 (UTC)[reply]
Electric signal
Hi i need what will be output waves form if the input signal were standard test signals(sine, step, square, ramp, triangle,) to the passive components resistor, capacitor and inductor separately and two combined in series and parallel then three combined in series and parallel
actually what happens when these combinations are energized with these signals and how they respond (pictures preferred) — Preceding unsigned comment added by Kanniyappan (talk • contribs) 14:45, 10 June 2011 (UTC)[reply]
This appears to be homework, but it is hard to tell what level. At the most basic level, a resistor reduces the amplitude of any wave in the direction of 0V (a big enough resistor and you'll pretty much have just 0V). A capacitor allows AC signals to pass, but inhibits DC signals. An inductor allows DC signals to pass, but inhibits AC signals. I know, the idea of a DC "signal" is silly. But, if you are in a higher level, you will be discussing how current and voltage relate to one another as they go through a capacitor/inductor. I was taught "ELI the ICE man" in the Marines. E (voltage) in an L (inductor) precedes I (current). I (current) in a C (capacitor) precedes E (voltage). -- kainaw™15:02, 10 June 2011 (UTC)[reply]
Your list of test signals starts with a sinewave, which has a single frequency. The other signals are actually just sets of sinewaves added together. See the article Fourier series. A Resistor is not frequency-sensitive and it passes a current according to Ohm's law. To tackle your circuit questions you need some AC theory. In fact your question looks much like the syllabus of an AC electronics course. This article gives a general introduction: Network analysis (electrical circuits). Cuddlyable3 (talk) 22:12, 10 June 2011 (UTC)[reply]
thnx for ur reply these are known by myself what makes me confusion is using resistor and capacitor in parallel when voltage taken across resistor it both act as filter and spike signal generator so that how this is possible — Preceding unsigned comment added by Kanniyappan (talk • contribs) 03:32, 11 June 2011 (UTC)[reply]
Hello. I am a costumer who has been given a very specific request by a client, and I wanted to verify that the client's idea is going to work before I go to the trouble of making the thing.
The client wants a large prism on her costume that will throw rainbows all over the stage. Client's idea is to mount the prism (like a precious stone) on her costume with a mirror backing, on the assumption that light will pass into the prism, bounce off the mirror, and come back out of the prism as rainbows. I was unsure whether rainbows would be created and thrown about the stage without the light being able to pass all the way through the prism and out the other side. So I thought that I'd better try to find a physicist to explain whether this will work or not before I build the thing.
Light has to pass through a prism in order to bend the light. If it is reflected back by a mirror, any bending will be unbent on the reverse trip. Light would have to pass through the prism and then hit a mirror on the side and not come back through to cause a rainbow. And this will cause just one rainbow per prism, not throw them all over the place. Unless your client is actually wearing little lamps on her body, any such effect is going to be minor and overwhelmed by the amount of white light stage illumination she will need. She'd be better of with a reflective costume of some sort and an experienced lightman with colored lights. μηδείς (talk) 16:07, 10 June 2011 (UTC)[reply]
Anyone who has tinkered with a prism knows that getting good rainbows can be problematic. Though with a mirror-backed prism it seemed easier to me. I wonder if you could do better using a diffraction grating, perhaps concealed as the "mirror" in the prism. But still you're up against the solid wall that the light coming out of the prism is no more than what goes in, so if you have a spotlight on her and one little jewel reflecting, it's going to be washed out. If you had the sophistication to use a video camera and image recognition to lock onto the prism and send a 1-inch wide beam straight at it all the time no matter how fetchingly it jigged and danced ... (which I think really could be done with off the shelf technology, but maybe not your shelf or mine!) ... then you'd have something. Wnt (talk) 17:00, 10 June 2011 (UTC)[reply]
In my opinion, it would be cheaper and easier to use a color-changing LED kit. I've seen color changing LED keychains for around $5. With those, you can get a lot of colors glowing. Keep in mind that with a prism or LED (or anything similar), you will not a rainbow arcing through the air. You will get an array of colors on the floor of the stage, which the audience most likely will not be able to see. You can use smoke to keep the color around the performer but that won't work well. The smoke will appear to glow and make it very difficult to see the performer. -- kainaw™17:54, 10 June 2011 (UTC)[reply]
I can only see this working if she wears the prism on the top of her head and has a strong spotlight shining at it from behind? Exxolon (talk) 18:02, 10 June 2011 (UTC)[reply]
On second thought, she could wear a costume that has some kind of small glass prisms (such as rhinestones, etc.) sewn in; their shape could cause them to act as Porro prisms and redirect the light back toward the audience by total internal reflection at the same time as refracting/dispersing it. Her original idea (with the mirror backing) simply will not work. -- An American ultranationalist 67.169.177.176 (talk) 03:23, 11 June 2011 (UTC)[reply]
Suggestion: To stick with the prism idea, how about it she has several prisms on her head, with a vertical light between them, and a mirror on the top, like the 3 prisms show here (top view, with mirror removed):
/\
/ \
/ \
/\ /\
/ \ °/ \
/ \/ \
If an electric cord wouldn't work, then a battery pack would be needed to power the light. This light could be either fluorescent or incandescent. The latter requires more energy and creates more heat, but might also make better rainbows. No other light source should be used on stage, as that would wash out the rainbows created. Unless, that is, you want to create additional rainbow light sources to supplement the prisms. StuRat (talk) 08:56, 11 June 2011 (UTC)[reply]
I think you mean refraction, not diffraction? Although it's common to do x-ray diffraction of diamonds, and there does exist a new technique for cutting diffraction gratings into diamonds that work at visible wavelengths,[13] the wavelength of visible light is normally several orders of magnitude too large to be diffracted by diamonds. The wavelength of visible light is about 400nm or longer, which is much larger than the feature size of the crystal structure of diamond (the carbon-carbon bond length in diamond is 154 pm), so you wouldn't normally get a noticeable diffraction pattern by shining visible light on a diamond. Red Act (talk) 00:18, 12 June 2011 (UTC)[reply]
It would not work. For one thing, you are suggesting that more light comes out of the prism than goes in. If you recall what "slides" were - used to be called the "magic lantern" by the Victorians - then you would need several very powerful slide projectors powered by electricity that project the slide of a rainbow. Unfortunately it could not be made to work in any practical way. Perhaps you could suggest instead having lots of light-bulbs in her costume, like Christmas decorations, although this may be dangerous. A better option would be having her costume covered in small plastic mirrors. 92.24.181.38 (talk) 23:33, 11 June 2011 (UTC)[reply]
Or small diffraction gratings, if available -- the diffraction would serve to enhance the rainbow effect. I don't know if those are avialable in small enough sizes, though -- the only diffraction gratings I've ever seen are the ones used in spectrometers, which are typically several inches across. 67.169.177.176 (talk) 01:22, 12 June 2011 (UTC)[reply]
I recall reading a Scientific American article long ago where a piece of a CD was used as a diffraction grating. So use pieces of old CDs instead of mirrors, and cover her costume with them. The costume may look irridescent, under powerful focused spotlights you might get possibly get small rainbows. 2.101.1.42 (talk) 11:25, 12 June 2011 (UTC)[reply]
It's probably easier to fake it by having a prism on the costume that does nothing, and having a followspot equipped with diffraction gratings to produce rainbows, which follows the actor around the stage.--Srleffler (talk) 17:52, 13 June 2011 (UTC)[reply]
Re; Electro Mechanical Spectrum
I have a question: Isn’t it about time the geniuses (et al) call the electromagnetic spectrum what it really is; the ENERGY SPECTRUM?
J Hoelz, P.E. Ret (c/q thermo) — Preceding unsigned comment added by 173.69.175.253 (talk) 19:27, 10 June 2011 (UTC)[reply]
The place on a spectrum doesn't tell you the energy of light. You'd need both a measure of intensity and frequency to determine the overall level of energy in a beam of light. Your idea seems half baked. i kan reed (talk) 20:33, 10 June 2011 (UTC)[reply]
The only reason the geniusses of the World haven't done this already is that we can't deduce whether you mean electromechanical or electromagnetic. Cuddlyable3 (talk) 21:43, 10 June 2011 (UTC)[reply]
The only thing correlating energy and frequency is the fact that photons of shorter wavelengths, higher frequencies generally have greater energy and vice versa. However this breaks down when you start discussing non-photon non-spectrum particles such as beta particles and some cosmic rays. ~AH1(discuss!)14:59, 11 June 2011 (UTC)[reply]
Isotopes
Is there any difference between atoms with the same number of protons and neutrons in the nuclei but with those nucleons arranged differently in the nucleus? --75.40.204.106 (talk) 19:50, 10 June 2011 (UTC)[reply]
Yes. See, nuclear isomers. While alternate nuclear configurations are possible, the atom will seeks out the lowest energy nuclear configuration and typically reach it within a nanosecond. As a result such configuration differences only occur very briefly and only under very specific circumstances. They won't generally be observed in everyday experience. Dragons flight (talk) 20:21, 10 June 2011 (UTC)[reply]
Maybe not everyday experience, but there are a few important meta-stable nuclear isomers 180m 73Ta being the most notable) that are of interest to nuclear physicists and those that would like to use them as high-density energy storage (of course far from being practical with today's technology). The idea is that these isomers, when they return to their ground state, will release an enormous amount of energy, and it may be possible to induce this release by stimulated emission, similar to the way a laser works but on a much more energetic scale.-RunningOnBrains(talk)18:26, 12 June 2011 (UTC)[reply]
So if a single electron is diffracted into two (or more) parts, what are the resulting parts? Are they both electrons? Doesn't that violate conservation of mass? --75.40.204.106 (talk) 22:04, 10 June 2011 (UTC)[reply]
The two blobs are the probability of finding the single electron in either spot. Every atom heavier than Beryllium has split blobs. Hcobb (talk) 22:08, 10 June 2011 (UTC)[reply]
It is one electron that goes through both slits. At the receiving screen you will find that each electron arrives at a single unique position, but the distribution of the arrival positions over many electrons is not uniform, and has peaks and valleys caused by the wave-like properties of the electron interfering with itself. Quantum mechanics isn't known for being very intuitive. Dragons flight (talk) 22:54, 10 June 2011 (UTC)[reply]
(EC) You can try reading the later parts of Double-slit experiment (look for discussions of single photon or one by one or one photon) and if you're really interested Englert–Greenberger duality relation. These are primarily about photons (although the first article does mention when the first one electron at a time experiment was performed) but I'm pretty sure it's the same for electrons. Nil Einne (talk) 23:01, 10 June 2011 (UTC)[reply]
Electron diffraction occurs in the dual-slit experiment (interference pattern) even when electrons are fired and arrive at the detector one-at-a-time. You can model this pattern as a probability distribution of finding any arbitrary individual electron at any point in the diffraction pattern; the deal with wave-particle duality is that the particles, in bulk, obey statistics that give the same results as the wave properties would. Thus, its not that an individual particle behaves as a wave, its that in bulk particles behave as waves, and they do so whether emited in bulk or emitted individually. If you look at discussions at articles like Wave function you see it is full of statistical language, that's because the core of wave-partile duality is probability... --Jayron3200:27, 11 June 2011 (UTC)[reply]
I'm not sure it's quite right to say that an individual particle doesn't behave like a wave. In this experiment the electron is only in a single particular location at the end because we measure it then, which makes the wavefunction collapse. Rckrone (talk) 06:41, 12 June 2011 (UTC)[reply]
An individual electron, unobserved, has indeterminate status vis-a-vis wavelike properties. If I fire one electron at the double-slit set up, I get a dot on the detector. I fire another electron. I get another dot. Insofar as no measurement is made of the electron in transit, whether it is behaving like a wave as it passes through the slit, or it behaves like a particle as it passes through the slits, is not only unknown, it is probably unknowable. The explanation of the end results; that of a statistical spread of individual particle hits, OR of an interference pattern created by wavefronts interacting with each other, is entirely moot. Whichever explanation works better for your purposes, you use. But they both work entirely well, and so there's no reason to say definitively that one is right, or one is wrong. The electron is the electron, it does electronish things, and it always does them. That we can't wrap our head around it without forcing it into the "wave" box or the "particle" box isn't really the electron's problem. Its better to think that we can set up some experiments and can interpret the results to mean that it has wavelike properties, and we can use different experiments and different interpretations and say that it has particlelike properties. The whole point is we don't have to actually decide, its neither, but we pick the model for which our application needs it... --Jayron3203:13, 13 June 2011 (UTC)[reply]
Echolocation in cats?
If you have a housecat or watch them stalk birds, then you're probably familiar with the teeth chattering behavior they engage in when they spot a bird. Looking at the popular literature to find out why they do this, I found this site which summarizes the concept.[14] Chattering in cats is considered a "frustrated hunter reflex", usually seen when a cat can't get to a bird and/or the cats way of preparing to bite the bird. Has anyone ruled out animal echolocation as an alternative explanation? Viriditas (talk) 22:19, 10 June 2011 (UTC)[reply]
An interesting idea, but a little implausible, I'd think. Cats are basically ground-level hunters, and picking up the echo of prey against the background clutter would be difficult. I'm sure they use their excellent directional hearing to hunt, but passively. Any noise loud enough to produce an echo may alert the prey. For bats, this isn't really a problem, as an insect in free flight has nowhere to hide, but a cat stalking a bird isn't going to have much success. There may be technical difficulties as well, to do with the relative size of the prey and the signal wavelength - but I'll leave that to someone else to clarify... AndyTheGrump (talk) 03:08, 11 June 2011 (UTC)[reply]
Apparently, echolocation is used by smaller ground mammals. The last two times my cat has done this, he has had a view of the bird above or below him. Indoors, he was looking down at it from about four meters; outdoors, the bird was about the same distance above him on a small hill. Intuitively I got the sense he was trying to measure the distance to the bird before he could pounce, but that's just my own idea; I have no such evidence. I'm also curious how my cat was generating the chattering and clicking sound, and I wonder if there is a way to record and analyze it. Viriditas (talk) 07:44, 11 June 2011 (UTC)[reply]
The only terrestrial mammals our article mentions are shrews and tenrects Animal echolocation#Shrews and tenrecs. For shrews according to both that article and Shrews#Echolocation they only use it to "investigate their habitat rather than additionally to pinpoint food". The article includes a quote:
Except for large and thus strongly reflecting objects, such as a big stone or tree trunk, they will probably not be able to disentangle echo scenes, but rather derive information on habitat type from the overall call reverberations. This might be comparable to human hearing whether one calls into a beech forest or into a reverberant wine cellar.[9]
In other words, it's only used to give broad based info and doesn't give precise location and distance information of small objects.
Echolocation in tenrecs isn't described but as they have poor eyesight it seems likely it's similar to shrews. In other words, echolocation in these animals doesn't seem particularly relevant to the suggested ability of cats to use it to locate or sense the distance of prey. If there are other small mammals with a comparative sense of echolocation to what you suggest in cats, this isn't described. The closest thing is perhaps the learnt human skill Human echolocation.
Partially based on [15], some non RS suggest domestic cat chattering is actually a form of mimicry [16]. Of course demonstrating why an animal shows a behaviour is usually fairly difficult. Purring seems to be better studied but is still poorly understood. About how the sound is produced, I believe it may be a combination of vocal chords, lips and teeth, see [17] for example. Nil Einne (talk) 14:03, 11 June 2011 (UTC)[reply]
I think they want to "shout" because they see something exciting, but know they can't or will give away their position, and this results in partially suppressed sounds. Compare this to when they dream, but the partial paralysis of sleep makes them move just a little bit. Evolutionarily, I suppose that the suppression in both cases continued to grow stronger as long as doing so increased their chances of survival. However, once it became "good enough", such that further suppression wouldn't increase their survival chances, no further strengthening of this suppression response occurred. StuRat (talk) 08:29, 11 June 2011 (UTC)[reply]
My cat only chatters at insects out of reach. While he occasionally views the birds outside, he never enters any kind of hunting mode (he's an indoor cat). Based on my lifelong experience with cats, it's always seemed to me a frustration behaviour - they don't do it when they're hunting, only when they're after something that's out of reach. Kind of like a cartoonish "gnashing of the teeth in frustration". Regarding the echolocation hypothesis - it seems quite doubtful. Animals that use echolocation almost always do so due to poor visibility, either due to poor eyesight or atmospheric conditions. You don't need to watch too many cats in the hunt to realize they're primarily reliant on eyesight; hearing gives them a direction for stuff in the underbrush and echolocation wouldn't help with that. Matt Deres (talk) 15:42, 12 June 2011 (UTC)[reply]
Given that felines have superb hearing abilities, I would think that an evolved ability to echo-locate is a reasonable hypothesis, and that echolocation would not need to be utilized frequently in their hunting forays for it to have evolved and be useful. It could be advantageous in judging distances wherever there is little or no nearby ground clutter during their nocturnal hunts and other situations where it might serve as a reference system that reveals the ambient acoustic conditions in which any prey, or foe, are generating sound, helping to better locate them. As far as the observed chatter being too noisy, cats certainly have discretion to the extent of its use, so I don't think that would always be a problem, and it wouldn't surprise me if they reserve their loudest echo-locating chatter, should they use it for that purpose, to deliberately startle their prey. There are at least a couple of reasons such a prey flushing technique would be useful. For instance, prey that is moving is easier for a cat to visually see, so a cat may just be attempting to get a better view of a possible bug/bird or whatever. Also, during a hunt, spooking the prey can initiate the prey's escape movements so that a cat can then rapidly plot an intercepting charge upon the animal's intended flight or escape route and thereby improving its chance of capture. .Thus, the chatter may serve any of several different purposes, but I'm unconvinced that the frustration hypothesis or the mimicry hypothesis can adequately explain the cats' chatter. Cats prey on all sorts of critters with different appetites, so I don't think mimicry of a potential meal (which the chatter does not seem to mimic in any case) can explain this particular vocalization. Their chatter also has a very regular quality about it; but should it be produced due to frustration, then I'd expect more irregularity in both its quality and frequency, such as also occurring when the cat is distracted. Instead, these cats are exhibiting their hunting and stalking instincts when they stare at the bird or bug with their ears rotated forward (something that people cannot do) to listen intently (something people should do) while simultaneously chattering. They also can be seen to be literally laidback during their focused chatter, so they seem to be simply exercising one of their innate abilities to target potential prey. Thus, I think their chatter does merit investigation into whether echo-location (and/or the flushing of prey) is occurring. Modocc (talk) 00:34, 14 June 2011 (UTC)[reply]
So I'm having surgery in two months on my eyes. The surgery is to correct a rather villainous Strabismus that has become noticeable lately (both for myself, damn double vision, and those around me). Apparently my doctor is going to basically detach and reattach muscles attached near the front of the eye that control the ability to see inward. I'm curious, what muscle or muscles are those exactly? Sir William Matthew Flinders Petrie | Say Shalom!01:26, 11 June 2011 (UTC)[reply]
I'm thinking of an object similar to this made of glass or metal, but more elongated, turn it upside-down, and putting holes or tabs on any of the surfaces so that they could be directly fingered or remotely adjusted (think trumpet valves), and using the entire device similar to a saxophone or like a pan flute. What's the timbre? ~AH1(discuss!)14:45, 11 June 2011 (UTC)[reply]
Hi. What would a klein bottle sound like as a musical instrument, considering that a mouthpiece is attached to the open end, while holes on any part of the surface that can be fingered either directly or using valves adjust its pitch? Thanks. ~AH1(discuss!)02:16, 11 June 2011 (UTC)[reply]
I don't see how you could use a klein bottle as a horn or similar instrument. There's nowhere for the air to go once you blow into it. I suppose you could use it like a jug though. In which case, it would depend on the interior dimensions of the bottle. More space = deeper tone. Dismas|(talk)02:40, 11 June 2011 (UTC)[reply]
A Klein bottle is a topological entity. The musical characteristics of a container depend on its resonances, which are essentially independent of its topology. So, the question doesn't really have an answer. (Also it's impossible to embed a genuine Klein bottle in 3D Euclidean space, but that's another issue.) Looie496 (talk) 02:53, 11 June 2011 (UTC)[reply]
Can someone please direct me to an article that discusses how a space craft is navigated between planets, and between galaxies? I can find a number of Wikipedia entries on space travel, orbital dynamics, etc, but nothing that explains how a space craft can recognise where it is in relation to (say) Earth, what direction it is travelling, and what course corrections it needs to make in order to arrive at where it's destination will be when it gets there, be it another planet or another galaxy.58.174.69.136 (talk) 06:31, 11 June 2011 (UTC)[reply]
Dawn sun tracker is the pink rectangle on top, seven others are on each other corner
All space crafts I know of use a Star tracker and a sun tracker. A light sensor looks for the sun which is very easy, for example the Dawn (spacecraft) has a sensor at every corner. The Camera system makes an image of the stars and compares the image with stored maps. With this information it is clear where you are and the where you go is easy to know, because you always go on a straight line (plus gravity) if you do nothing, which is the case most of the time. --Stone (talk) 11:10, 11 June 2011 (UTC)[reply]
Just for clarity - no human-built space probe built to date has ever needed a guidance system for interstellar travel. So far, only a couple of our space probes have ever left the vicinity of our Sun; and it's fair to say that they are unguided spacecraft at this time. For example, Voyager II is widely regarded to have transmitted the solar magnetopause and is by some definition now "interstellar" - but the craft has not made an orbital trajectory correction in something like a decade or two. Currently, we here on Earth know where Voyager II is because we track it from Earth using powerful, specialized RADAR (Deep Space Network) - but up there, Voyager II probably doesn't know exactly where it is. It's guidance systems aren't designed for this phase of its lifetime. Its limited computer programs and guidance were intended to control its planetary flyby stages, not post-heliopause navigation. All that the spacecraft is currently aware of are a few readings from a few still-functional scientific instruments. It may still have attitude awareness, but probably has essentially no positional awareness. Nimur (talk) 17:42, 11 June 2011 (UTC)[reply]
Note, everything mentioned so far is for working out what direction the spacecraft is pointing in. You also need to know where you are, but that isn't too difficult. You can just see what direction the radio signals from the spacecraft are coming from and how long they take to get to the Earth (or a relay craft if one is being used). --Tango (talk) 17:36, 11 June 2011 (UTC)[reply]
Your question is entirely hypothetical because an infinite mass does not exist, and an infinite force also does not exist. Science does not concern itself with things that are known not to exist.
It is often claimed that the universe has an infinite amount of mass. Hence, according to these claims, the mass of the universe is infinite.--Leptictidium (mt) 07:43, 11 June 2011 (UTC)[reply]
The universe may have infinite mass, but it's hardly a rigid object. Supposing you had a way of applying infinite force, where exactly would you hook it up to? --Trovatore (talk) 08:04, 11 June 2011 (UTC)[reply]
I was actually thinking of the Big Bang. If the universe indeed had an infinite mass, it would've taken an infinite force to initiate its expansion, wouldn't it?--Leptictidium (mt) 08:10, 11 June 2011 (UTC)[reply]
So I have to admit I don't understand the Big Bang in detail, but I don't think you can apply notions like "force" to it in exactly the same way you do in the current era. Those things get confusing when you start talking about things on the scale of universal expansion. At the time of the Big Bang, everything is on the scale of universal expansion. So for example I have only the vaguest notion of what might have caused inflation (cosmology); maybe there's more information at that article. --Trovatore (talk) 08:47, 11 June 2011 (UTC)[reply]
You say it is often claimed that the universe has an infinite amount of mass but you haven't commented on who makes that claim. It isn't a scientist or a mathematician. The mass of the universe is extremely large - so large that we have no way of assigning a number to it, or knowing exactly how large it is, but this does not make it infinite. Most of the universe is empty space and if the mass of the universe was to be infinite all that empty space, all of it, would have to be filled with mass and both the empty space and the mass would have to be increasing continuously. Clearly that isn't the situation so it is incorrect to apply the mathematical concept of infinite to the universe. Dolphin(t)08:14, 11 June 2011 (UTC)[reply]
Hmm? No, that's not so. If the universe has infinite volume, then it can have arbitrarily small positive density and still have infinite mass. --Trovatore (talk) 08:36, 11 June 2011 (UTC)[reply]
Thanks for your answer, Dolphin. I actually knew everything you're telling me, but forum members at Physics Forums made me doubt by saying that the volume of the universe is simply more infinite than its mass. From what you're telling me, the forum members' claim is plain gibberish. Leptictidium (mt) 08:20, 11 June 2011 (UTC)[reply]
Physics Forums works by arguments from authority, don't trust a word they are saying on face value. I'm not saying that they are wrong, but they still managed to ban me indefinitely last year, simply because they could not stand that I would very, very occasionally contradict what the "mentors" were saying. What they do is very effective at keeping cranks out, but over time the forum has become similar to Libya under Gaddafi's rule. Count Iblis (talk) 16:51, 11 June 2011 (UTC)[reply]
Hmm, I think that article could use work. For example, we learn from it that [i]f there exists an irresistible force, it follows logically that there cannot be any such thing as an immovable object, and vice versa. But is that really so? Why can't there exist both an irresistible force and an immovable object, but for some reason the force cannot be applied to the object? For example, maybe the force is attached to an unstoppable object that happens to be moving away from the immovable object. The article doesn't seem to be well-sourced; I'm sure someone willing to put in the work could find a more in-depth analysis somewhere. --Trovatore (talk) 09:31, 11 June 2011 (UTC)[reply]
Better sources are always appreciated, but I believe the issue is one of definitions. What do you mean by "immovable object"? Usually you mean "an object that nothing (if it tried) could move". What do you mean by "irresistible force"? Usually "a force which will move anything (if it were applied to it)". So if the "irresistible force" is applied to the "immovable object", and the latter moves, it really wasn't an "immovable object". Conversely, if it *doesn't* move, then it really wasn't an "irresistible force". The only way around that is to alter the definitions (e.g. by dropping the implication of the parenthetical elements). But then you're talking about something different, and would need to be clear what exactly you meant by "irresistible" and "immovable". ("I once knew a dog which danced professional ballet" is surprising until you're told by "a dog", the person means their ex-boyfriend.)
Likewise, the original poster's question hinges on how they come by (the definition of) their infinities. In physics, "what happens when I combine two infinities" is usually referred to a "renormalization", which can yield sensible results, but which depends on where the infinities are from and how they're combined. For example, with a = F/m, we could have and , which would give one answer (no acceleration), or we could have and , which would give another (a finite, non-zero acceleration). -- 174.31.219.218 (talk) 16:03, 11 June 2011 (UTC)[reply]
Slight correction, the mass of the Observable universe is not infinite. The entire universe seems to be much larger and so could easily have an infinite extent, infinite mass and an infinite number of flame wars. Hcobb (talk) 16:59, 11 June 2011 (UTC)[reply]
Statements that we simply don't know the extent of the universe, and we don't know whether it is infinite or not, and therefore we should disregard the fact that the observable universe is not infinite, look to me to be a bit like saying We don't know whether Newton's Laws of Motion hold true at the farthest extremes of the universe and therefore we should not be claiming that Newton's Laws of Motion are true. Dolphin(t)05:49, 12 June 2011 (UTC)[reply]
The theory of universal expansion predicts that the observable universe must be finite, whether the full universe is finite or infinite. Therefore the finiteness of the observable universe gives us no information about whether the full universe is finite or infinite.
On the other hand, if the curvature of space were reliably measured to be negative (it has not been, thus far; all accepted confidence intervals for the curvature include the value zero), then your very uniformitarian argument would be a point in favor of an infinite universe, for why should the curvature turn positive only far from us, to allow space to wrap back on itself?
I should note that negative curvature does not require an infinite universe; there has been some interesting research into what might be the topology of a compact universe with negative curvature. To my naive eyes, though, these seem rather forced, kind of epicycle-ish. --Trovatore (talk) 07:40, 12 June 2011 (UTC)[reply]
Well, no, we actually do have evidence of the existence of a very large finite mass in the universe, while there is neither any evidence for an infinite mass nor any way even of coherently connecting that idea to any real known observational truth. We simply don't take such ideas seriously, or try to refute them, any more that you would be expected to have to prove that you are not a murderer in response to someone who asserted the mere theoretical possibility of the accusation without bothering to specify who youd had killed or when you had killed them. μηδείς (talk) 21:46, 12 June 2011 (UTC)[reply]
For the first point, there is a very large finite mass for which we have direct evidence; that is not the same as direct evidence that it is finite.
As for "real known observational truth": what is known is subject to change. The error bars on the curvature of space currently include zero. Someday they may be tightened to the point that they do not, and they may lie on the negative side of the line. In that case, the simplest models of spacetime would coherently connect that idea to an infinite universe. Are you suggesting that we should not try to refute that idea by tightening the error bars? --Trovatore (talk) 22:04, 12 June 2011 (UTC)[reply]
So you yourself say that "there is a very large finite mass for which we have direct evidence" yet ask me for "direct evidence that it is finite." That reminds me of an Aristotle quote, something about the fool asking for the proof of the prior by means of the consequent. I will have to post that on the humanities board and get back to you. μηδείς (talk) 02:52, 13 June 2011 (UTC)[reply]
Perhaps my wording was not ideal. The referent of the last it is "all the mass in the universe". That is, we have direct evidence for the existence of a very large finite mass, for example all the mass in the observable universe. We do not have direct evidence, as yet, that the mass in the whole universe is finite.
I can see on rereading that it is possible to interpret the it as referring to the "very large finite mass", and that would indeed give a very strange pair of propositions to assert simultaneously, but that is not what I meant. --Trovatore (talk) 04:35, 13 June 2011 (UTC)[reply]
What nature is, then, and the meaning of the terms 'by nature' and 'according to nature', has been stated. That nature exists, it would be absurd to try to prove; for it is obvious that there are many things of this kind, and to prove what is obvious by what is not is the mark of a man who is unable to distinguish what is self-evident from what is not. (This state of mind is clearly possible. A man blind from birth might reason about colours.) Presumably therefore such persons must be talking about words without any thought to correspond.
I'm studying physics on a very basic level with a book and without a teacher, and now there is a line of reasoning in my book that I don't understand. The book says, summarized:
"A projectile thrown horizontally will in the first second fall a vertical distance of 5 meters below the straight-line path it would have taken without gravity. The curvature of the Earth is such that its surface drops a vertical distance of nearly 5 meters for every 8000 meters tangent to its surface. Thus, a stone thrown fast enough to go a horizontal distance of 8000 meters during the 1 second it takes to fall 5 meters, will orbit Earth. So we see that the orbital speed for close orbit about Earth is 8000 m/s."
Now, I understand how this would work during the first second. But what happens with the acceleration of gravity??? Because during the 2nd second a projectile thrown horizontally will fall 15 meter. How come the projectile keeps orbiting and doesn't crash during the 2nd second??? Lova Falktalk08:21, 11 June 2011 (UTC)[reply]
I'm too lazy to do the numbers, but from the principle, in the second second, the 8000m line segment has a slight angle with respect to the first. With respect to the second, the first one goes "upward" and the and gravity bends it down for the next segment to be tangential again. Note that in this picture the circular orbit is approximated by straight line segments. To get good results, the approximation would use ever more but shorter segments. 5BYv8cUJ (talk) 09:49, 11 June 2011 (UTC)[reply]
I did a quick sketch (at right, click to zoom) of the situation. The black curve is a segment of a circle and represents the surface of the earth. The gray line is a horizontal tangent at height equal to zero units. What one finds is that the surface of the circle locally approximates a parabolic curve; at time t=1 it has bent away from the horizontal tangent by 1 unit of vertical height; at time t=2 there is a separation of 4 units of height, at t=3 the distance between the tangent and the circle is roughly 9 units. In other words, the rate at which the surface of the earth moves away from the horizontal tangent increases with o distance from the starting point.
What this sketch doesn't account for is the fact that the direction of gravitational acceleration changes as our hypothetical orbiting object changes with time. (Having a constant direction for 'down' is fine when one deals with objects travelling well below orbital speed – a ball tossed in the air really does follow a parabolic path from start to finish – but it doesn't work at all for paths that approach the size of the planet.) From the sketch, it's plain to see that at later time points the gravitational force being exerted won't be straight towards the bottom of the picture. At each point in time, there is a new 'down'; this is what bends the path of the orbiting object into a circle instead of a parabola. TenOfAllTrades(talk) 14:22, 11 June 2011 (UTC)[reply]
(edit conflict) Picture the projectile being far above the Earth's surface, travelling fast enough to maintain a roughly circular orbit, rather than either crashing toward the Earth or flying off into space. At this velocity, the object will experience centripetalacceleration, such that the orbit will follow the curvature of Earth, where every 8 km of forward motion experiences 5 metres of motion toward the Earth's core. Assume also that a hypothetical straight-line velocity, ie. one tangential to a circular orbit with a given radius distance from Earth's core from the object's position, will experience no accelerational "tugging" effect toward the Earth. Conversely, such an object with no forward motion will fall toward the Earth in full gravitational acceleration (9.8 m/s2), given negligeable air resistance. Thus, in low earth orbit, the Earth's acceleration is largely applied unto the object's forward motion, keeping its trajectory the same distance to the Earth's core, which in fact does not accelerate the object, but keeps it at constant velocity. In other words, there are vector components of acceleration (down and forward), but along the projectile's velocity there is no +/- acceleration. Hope this helps. ~AH1(discuss!)14:37, 11 June 2011 (UTC)[reply]
The key point here is that acceleration is a change in velocity, not just a change in speed. Velocity, and thus by extension acceleration, is a vector, not a scalar, so it has a direction as well as a magnitude. In a constant orbit, even though you're not experiencing a change in speed, you *are* experiencing a change in velocity, as the direction of movement changes. Gravity, acting as a centripetal force, causes an acceleration which rotates the velocity vector, but doesn't change its magnitude. -- 174.31.219.218 (talk) 15:21, 11 June 2011 (UTC)[reply]
Another way to explain this problem: the book is trying to explain a change in height for each second. But, as you intuitively know, the projectile isn't falling all that distance during one single instant - it's falling continously. To really describe the height, and velocity, of the projectile as it flies it's trajectory, we must use a little bit more sophisticated physics - that is, the mathematics must handle the height and velocity as continuous functions of time. Ultimately, this is the the most basic and fundamental application of simple calculus - and it is this problem that forced Isaac Newton to formulate the kinematics of falling objects using calculus. Basically, the book is describing a Riemann sum to approximate height at the end of each second, while in fact height changes continuously during each second. When we treat the function continuously, the math is actually easier to compute (even though a more complex process is being conceptually described). So we simply write that velocity is the first derivative of height, and (here is the most important contribution that Newton made to simple kinematics) ... Acceleration is the second derivative of height ... and acceleration is due to gravity only. You know this when we phrase it as "F = m a" but we are now going to write it as "the height at any time is equal to the integral of velocity, and the velocity is equal to the integral of the acceleration of gravity.". Now, because we're near Earth's surface, gravity is almost constant, so the height is a simple parabola. But in your more sophisticated "orbital cannon" case, the problem becomes more complicated - force due to gravity is changing with position - so we have to compute a more challenging integral! Saving you the complexity of that slightly more difficult Calculus problem, you can accept that the solution to that math problem is a conic section - it can be a parabola, a hyperbola, or an ellipse. If the trajectory intersects with the surface of the planet, the object falls back and hits the Earth. If not, the object becomes orbital, and either stays bound to the Earth or reaches escape velocity and never returns. Our article on orbit illustrates each of those cases. If you want to solve this math for yourself, you can - the simple two-body problem walks you through a standard solution. As you add more complicated effects, like perturbations in the gravity field due to the Moon, Sun, Jupiter, or the imperfect/not-quite-spherical Earth, you must solve a very difficult orbital dynamics math problem, usually with the help of a powerful computer. Nimur (talk) 17:27, 11 June 2011 (UTC)[reply]
Some unscrupulous food producers in Taiwan have been adding plasticisers to food. Some of the plasticisers include Di-isodecyl phthalate, DIDP; Di-(2-ethylhexyl) phthalate, DEHP; Di-n-octyl phthalate, DNOP; Di-isononyl phthalate, DINP; Di-n-butyl phthalate, DBP; Butyl benzyl phthalate, BBP. The government responds by burning al the contaminated products in incinerators.[18] Is this a good way to destroy the products? Would the plasticisers escape in the air and pollute the environment? F (talk) 09:50, 11 June 2011 (UTC)[reply]
That depends on the temperature. But I think the main purpose is destroying the food, so no one will eat it. I don't think that low quantities of such stuff are dangerous unless you eat it. From the names they look like organic molecules (in the sense of organic chemistry) and will be decomposed by nature (UV-radiation, weathering, micro-organisms), just as the many toxins produced by a large number of poisonous plants. 5BYv8cUJ (talk) 10:37, 11 June 2011 (UTC)[reply]
Generally, temperatures high enough to incinerate the food would also be high enough to destroy most other organic substances, including phthalates. -- An American ultranationalist 67.169.177.176 (talk) 01:25, 12 June 2011 (UTC)[reply]
Plasticizers are organic compounds (in the chemical sense), just like plastics and most food components. They'll burn like all the rest, if subjected to sufficient temperature. The one concern is if they volatilize and escape before combustion. But typical garbage incineration not only handles such compounds regularly, but actually creates a large number of hazardous chemicals during the combustion process. All modern waste incinerators will be fitted with emission control systems and scrubbers which will ensure that what goes up the smokestack contains only a minimal amount fo dangerous compounds, if any. -- 174.31.219.218 (talk) 18:25, 12 June 2011 (UTC)[reply]
Principles of Quantum Mechanics
Wikipedia says ( Postulates of quantum mechanics) the Ket-Vectors were elements of some Hilbert space, wheras Dirac (The Principles of Quantum Mechanics, 4th edition, page 40) says "The space of bra and ket vectors when the vectors are restricted to be of finite length and to have finite scalar products is called by mathematicians a Hilbert space. The bra and ket vectors that we now use form a more general space than a Hilbert space."
To resolve that contradiction I assume that some later development has put all of Diracs intuitive integration and the need for infinity as a number (with all its ensuing troubles and inconsistencies) into a solidly defined mathematical framework that turned out to really be a proper Hilbert space. The question is now: where can I find this solid definition? 5BYv8cUJ (talk) 10:26, 11 June 2011 (UTC)[reply]
Not infinity as a number per se, but the theory of distributions had yet to be set up. One could then use that re-define the Hilbert space you need in quantum mechanics when you want to work in an infinite volume. You then get the Rigged Hilbert space. Note that you don't actually need to know about this to do computations in quantum mechanics. Count Iblis (talk) 15:12, 11 June 2011 (UTC)[reply]
I remember a talk long ago when someone stated that students of mathematics can't do computation. For example, they cannot compute the inverse of a matrix, whereas students of physics can. Someone answered, yes, that's true. But, on the other hand, students of physics can compute the inverse for any matrix.
Having told this anecdote I hope you understand what I have in mind if the following looks like nitpicking or trolling. Dirac thinks he needs vector lengths and scalar products to be allowed to be infinite, and vector lengths and scalar products should result to give numbers (elements of a commutative field), because otherwise all the theorems for vector spaces (and basic computation, too) would have to be prooven again. Every try to do computations with infinity leads to a hell of trouble, the least of which is me proving that zero equals one, using only the contradicting assumptions. Now your link to the rigged Hilbert space doesn't give me the mental breakthrough. Just for any one simple example from quantum mechanics, how exactly would that H and that really be defined? 5BYv8cUJ (talk) 16:15, 11 June 2011 (UTC)[reply]
While I have studied functional analysis, I don't know much about rigged Hilbet spaces. It is actually pretty useless in theoretical physics. You can avoid using this and still be rigorous, by putting systems in finite volumes (take the limit of V to infinity at the end of computations), avoid working in the ill-defined position basis (even if you can define it using rigged Hilbert spaces, physically it is not well-defined). Count Iblis (talk) 15:18, 12 June 2011 (UTC)[reply]
I have been rereading the book (up to page 40 where I throw a "NotANumberException"). I thought of a Schwartz space to fix it, which is not exactly what you are proposing but runs in the same lines. But I don't see how or even if either of those would cure the problem. For what I have seen, the only reason those infinity-values are needed is to fix problems that arise when he does what he calls "superposition" in the introduction and needs to do it on more than countably many kets, which in turn he believes to be necessary to represent any ket from the "complete sets" of eigenvectors of an observable. I am sure modern maths can give those intentions a solid base somehow, but I get crazy because I can't find such a thing anywhere. 5BYv8cUJ (talk) 15:51, 12 June 2011 (UTC)[reply]
You should look at the proof of completeness of bases of eigenfunctions in functional analysis textbooks. The case of discrete spectrum is rather simple, the case of the continuous spectrum is more complicated. But then, if you limit yourself to systems in a finite volume, you only have to deal with the discrete case. Also, physically, an infinite volume is in practice always a finite volume which is very large, so this is understood as the limit of V to infinity. Count Iblis (talk) 16:08, 12 June 2011 (UTC)[reply]
I have recovered that book yesterday and was shocked how much I have forgotten. I'll have a look at spectral theory and see if this gives me the hint I'm lacking now. 5BYv8cUJ (talk) 16:39, 12 June 2011 (UTC)[reply]
I am in orbit round a planet and am a few hundred meters behind my command module at the same altitude. I need to dock with the command module. What combinstion of forward and reverse thrust should I use? (Not home work-- just interested).--78.150.233.171 (talk) 19:45, 11 June 2011 (UTC)[reply]
To quote Larry Niven, "Forward takes you out, out takes you back, back takes you in, and in takes you forward."[19] I don't know how literally true this is, but it seems to make sense... ;) Wnt (talk) 22:25, 11 June 2011 (UTC)[reply]
If you think about it, it would have to be a combination of first thrust TA (say) in direction DA (say) to introduce relative movement that decreases the distance between your module and the command module, followed by no thrust as the relative velocity between continues to decrease the distance, followed by reverse thrust TB (say) in directon DB (say) to bring the relative velocity back to zero. Hopefully exactly at the time the two are docking together. I would suspect that thrust TA = TB, and direction DA = - DB. I can't prove it though.--InverseSubstance (talk) 23:37, 11 June 2011 (UTC)[reply]
InverseSubstance is correct -- you need to use forward thrust to speed up and close the distance, followed by an equal amount of reverse thrust to bring the speed back down to the same level as before. You also need to apply a small amount of downward thrust (toward the planet) at the same time as the forward thrust, and upward thrust at the same time as the reverse thrust, in order to compensate for the small change in orbital radius that is caused by the change in speed. Or alternatively, you could use downward thrust alone to speed up and the upward thrust alone to slow down, which is essentially equivalent to doing a low yo-yo in a fighter plane to catch up to your target without overshooting it (though the latter admittedly looks a lot more dramatic). 67.169.177.176 (talk) 01:47, 12 June 2011 (UTC)[reply]
Using forward thrust won't work. It has the paradoxical effect of slowing you down because it will bring you to a higher orbit and for every unit of energy provided by the thrust, two units of energy get "stolen" by gravitational potential energy effectively removing one unit of energy from your kinetic energy and slowing you down. What you need to to is break! That will get the low yo-yo maneuver you described started. Dauto (talk) 05:33, 12 June 2011 (UTC)[reply]
"Flying a spacecraft is very different than flying a plane. There is no true up or down and the dynamics of orbital flight make maneuvering to dock, or rendezvous, two spaceships very complex. I focused my research on solving the problems of speed and centrifugal energy which lead to an ‘orbital paradox’ – a situation in which a pilot who speeds up to catch another craft in a higher orbit will end up in an even higher orbit, traveling at a slower speed and watching the second craft fly off into the distance. The solution to this paradox is counter intuitive, and required new orbital mechanics and procedures. Later, after joining the NASA astronaut corps, I spent time translating complex orbital mechanics into relatively simple flight plans for my colleagues – they thanked me (with a mixture of respect and sarcasm) with the nickname Dr. Rendezvous." Buzz Aldrin.
That is a very interesting aspect. What if the acceleration is done by gravitation? OK, you might not want to wait for this in a space ship, but I'm thinking about Theia_(planet). 5BYv8cUJ (talk) 06:54, 12 June 2011 (UTC)[reply]
Those kind of collisions happen by random chance. If you have hundreds of planetoids in similar orbits then, over millions of years, some of them are inevitably going to intersect. --Tango (talk) 13:00, 12 June 2011 (UTC)[reply]
I was thinking about if it was predictable that Theia hit earth from a slightly increased orbit thus accelerating earth's rotation instead of de-accelerating or reversing it. 5BYv8cUJ (talk) 16:33, 12 June 2011 (UTC)[reply]
(un-indent) The space shuttle faces this exact same problem when docking with the ISS. For the final part of the shuttle docking profile the shuttle starts a couple hundred meters ahead of the ISS at the same altitude, and the same velocity. To move towards the station the pilot maneuvers the shuttle radial out, that is away from the Earth. This temporarily moves the shuttle to a higher altitude where it has a slower velocity than the ISS, thus closing the distance between the two. The effect is that the final approach profile is a series of hops, as you can kind of see in this photo. In your situation the active vehicle is behind the passive vehicle, so you will need to move radial-in (towards the Earth), dropping into a lower, faster orbit to close the distance with the passive vehicle. anonymous649414:37, 13 June 2011 (UTC)[reply]
Yes, thank you Dauto and Anonymous, you are correct. I was thinking more as an airplane pilot (which I am) rather than an astronaut (which I'm not) when I first answered the question. So my first answer (forward thrust) was wrong, while the second one (the "low yo-yo") was indeed correct. I also assumed, from the way the OP phrased the question, that the spacecraft has provision for thrust straight up and straight down (I meant radial out and radial in -- see what I mean when I say that I can't stop thinking like an airplane pilot?) as well as forward/reverse. 67.169.177.176 (talk) 21:42, 13 June 2011 (UTC)[reply]
Is the Pythagorean scale universally pleasing?
Pythagoras said that musical strings of lengths in simple ratios (1 through 4) will produce "pleasing" sounds. Are only people in Western cultures (beginning with the Greeks) pleased by such sounds, or do all people people find the sounds pleasing? 82.31.133.165 (talk) 20:29, 11 June 2011 (UTC)[reply]
I don't know about what people find pleasing, but Musical scale#Non-Western scales will tell you a bit about what different cultures use in their music. It sounds like most do use harmonic scales (which is Pythagoras was talking about), but apparently Indonesia doesn't. It doesn't go into any detail, though. --Tango (talk) 23:59, 11 June 2011 (UTC)[reply]
From personal experience I would say the human ear / brain combination, adopts with time to new scales, as with languages. Newly heard music in an previously unknown scale or system may sound strange at the beginning, but eventually one finds it very pleasing. Take for example the music of Arnold Schoenberg or Free Jazz which are both in western scales, but may sound strange at first. Or Persian Music or Arabic Music or Greek Music which use different scales. Also note that the "western" scales (equal temperament) that we use today are quite different from the scales used a few hundred years ago, like the well temperament, kirnberger or werckmeister temperament. --helohe(talk)00:07, 12 June 2011 (UTC)[reply]
Also note that not everyone likes Schoenberg or free jazz -- in fact, there are a lot of people who absolutely hate it. This has to do with personal and cultural preferences more than anything else. 67.169.177.176 (talk) 01:35, 12 June 2011 (UTC)[reply]
Note that Schoenberg and free jazz (and other modern western composers inserting smaller dissonaces in their work) are intentionally trying to be jarring to their listeners by not using the "well-tempered" notes that everybody used in earlier works. 75.41.110.200 (talk) 14:33, 12 June 2011 (UTC)[reply]
Oh, please. Simple pleasant harmonies not only appeal to humans but to most animals as proof of health. Dislike of dissonances compared to consonance has nothing to do with learning. Human preference for simple harmony, especially the octave, is universal. Helmholtz. μηδείς (talk) 22:46, 12 June 2011 (UTC)[reply]
How does the virtual particle exchange work for attraction? For example electromagnetic attraction between a proton and an electron. I mean, the virtual particle would need to have negative mass, or be emitted in the opposite direction (away from the centre of both particles). I couldn't find a good explanation anywhere. --helohe(talk)23:09, 11 June 2011 (UTC)[reply]
Are you talking about gauge boson theory ? Yes, it's extremely non-intuitive, but then so is most of quantum dynamics. Even worse than what you mentioned is that a nearly infinite number of virtual particles would be required, especially in the case of gravitons, where a continuous stream of gravitons is needed from every atom to every other in the universe. That's a lot of gravitons. Myself, I think it might be a useful model, in some cases, but don't think it's literally correct (something like how the Dalton model of the atom was useful, but later needed many refinements). StuRat (talk) 23:46, 11 June 2011 (UTC)[reply]
Yes I meant gauge boson theory. I'm also wondering how the virtual particles "detect" the presence and the position of the involved particles. I would find it much more intuitive to understand if all virtual particles would be replaced with fields (or space-time "curvature" like in general relativity). --helohe(talk)00:00, 12 June 2011 (UTC)[reply]
I think the idea is that there's so darned many virtual particles that those given off by each particle are bound to hit every other particle in the universe. Yes, this seems silly to me, too, and a field or wave does seem like a better approach. However, due to wave-particle duality, perhaps the bosons are sometimes particles and sometimes waves. StuRat (talk) 00:08, 12 June 2011 (UTC)[reply]
Virtual particles can have negative mass. Physicists refer to that by stating that virtual particles are not constrained to their mass shell. But note that any attempt to understand QM in terms of classical concepts is bound to fail at some point. Dauto (talk) 00:09, 12 June 2011 (UTC)[reply]
Compare with tunneling. In quantum mechanics an intitial state can evolve to some final state that classically would be impossible, because the system would have to evolve via an intermediary state which would have an inconsistent energy and momentum. In this case, the charged particles couple to photons, and the "forbidden" intermediary state is the virtual photon, which thus carries energy and momentum in a way that is unphysical. Count Iblis (talk) 15:29, 12 June 2011 (UTC)[reply]
The momentum is off-shell and unphysical whether the force is attractive or repulsive, so I don't think that was the question. Also, the off-shell momentum transfer is the same in classical electromagnetism, and loop-free Feynman diagrams can be used to describe classical electromagnetism, so I don't think there's anything essentially quantum about the question. -- BenRG (talk) 18:53, 12 June 2011 (UTC)[reply]
Not a spacetime diagram.Quantum field theory is a theory of fields, as the name suggests. Virtual particles show up in Feynman diagrams, which are a useful way of doing some calculations in quantum field theory, but don't work at all for others. I don't think it's very helpful to say that fields (like the electromagnetic field) are caused by virtual particles, because, for one thing, that picture doesn't even work in general.
Feynman diagrams look like spacetime diagrams, but they aren't. They are actually just graphs, that is, vertices connected by edges. The position of the vertices, and the orientation and length of the edges, don't mean anything. In a spacetime diagram, the momentum of a particle is always tangent/parallel to its worldline, but in a Feynman diagram you can assign any momentum to any edge as long as momentum is conserved at each vertex. So attractive forces don't present any difficulty. It's hard to explain why like charges repel and unlike charges attract, but it's easy to explain how Feynman diagrams can accommodate the attractive case: it's the same as the repulsive case because directions are meaningless. -- BenRG (talk) 18:53, 12 June 2011 (UTC)[reply]
I agree with every thing you said except that Feynman diagrams can be seen as abstract space-time diagrams. For instance, in that penguin picture to the right time is usually taken to flow to the right, in the sense that the lines on the left represent incoming particles while the lines on the right represent out-going particles, even though the intermediary vertices may happen at any point in time or space (even if that requires fast than light travel). Dauto (talk) 22:19, 12 June 2011 (UTC)[reply]
I think you are asking if it takes more energy to get a temperature change started than to keep it going in the same direction. In that case, the answer is "no, the first degree of temperature change takes about the same energy as the next". An exception would be if the first degree requires a phase change. StuRat (talk) 23:44, 11 June 2011 (UTC)[reply]
What about the time required to initiate the heating, assuming constant energy input into the fluid? Or is any "inertial" effect caused by the starting time required of the heating device itself? ~AH1(discuss!)23:50, 11 June 2011 (UTC)[reply]
Yes, the heating time of the device itself, or whatever is in-between. In the case of a pot on an electric stove, for instance, first the burner must heat up, then it must radiate that heat to the bottom of the pot, then that heat must conduct to the inside of the pot. Only then will the liquid in the pot start to heat up. With a thick, cast-iron pot, that could take a while. With a thin, copper pot on a high flame, the heat should make it to the liquid quite quickly. A glass of liquid in a microwave should start to heat essentially instantaneously. StuRat (talk) 23:58, 11 June 2011 (UTC)[reply]
In the case of the microwave, this also has to do with the fact that the liquid is being heated directly by absorbing electromagnetic radiation, rather than by conduction. So essentially, you can think of it as the case where there's nothing in between at all. 67.169.177.176 (talk) 01:30, 12 June 2011 (UTC)[reply]
What biotech company is doing the study that replicates ccr4 immunity for people with hiv?
A few months ago I read a news article that a biotech company in South San Francisco or San Bruno is in the middle of human trials for a therapy where people with HIV are infused with t-cells that are adapted to not allow hiv to enter them similar to the ones that people with natural immunity have and that it was promising research because these t cells were replicating themselves in most people in the trial on their own. I want to find this article as some people I told don't believe me or want to know more and I want to look into the company, I also want to expand the article on the HIV timeline and Hiv treatment articles.Thisbites (talk) 00:32, 12 June 2011 (UTC)[reply]
I think this is [21]Irvin S. Y. Chen, head of the UCLA AIDS Institute. "He is currently engaged in a start-up company for HIV-1 genetic therapy involving collaborations with UCLA, Salk Institute, and Cal-Tech." Also [22], [23]. [24] says he formed the company with David Baltimore, former president of Caltech. There are various bits of flotsam [25] floating around that link Chen and Baltimore with Calimmune, a California company headquartered in Tucson, Arizona? - it isn't clear to me that this is the company. Wnt (talk) 02:40, 12 June 2011 (UTC)[reply]
Well, [26] ($20 million) makes it sound like Calimmune is doing just the right kind of study to match your criteria: "methods to transduce autologous hematopoietic progenitor stem cells (HPSC) with a viral vector delivering a specific interfering short hairpin RNA (shRNA) designed to block production of CCR5. In addition, since combination treatment strategies are often more effective than monotherapy, the applicant proposes to add a second inhibitory component to the vector, a gene encoding an inhibitor of virus-cell fusion." I should note however that there are considerable obstacles that come to mind right off. First, all sorts of gene therapy have been under the cloud of potential cancers when DNA goes into the wrong spot in the genome, and these immune cells will be undergoing rapid turnover in people prone to AIDS lymphoma already. Next, RNA interference isn't 100%. They say the cells may be protected anyway since the virus is less likely to bind, but is there really an excess of virus? If not, then the virus can just drift past a hundred missing receptors and bind the one that is there, without any delay. Finally, there's the matter of whether the gene therapy can be "rejected". Every once in a blue moon I've read the strangest claims about DNA being rejected by the immune system, or antibodies somehow getting into the cytosol of the cell. More recent publications include [27] and [28], a less radical claim that viruses bring antibodies into the cell with them that trigger special interfering factors inside the cell. But the point is this: we don't know how the body will respond to long term gene therapy. I can picture for example that the hairpin RNAs found together with the antibody-tagged HIV virus will be tagged somehow as foreign RNA, diced up, and the inserted genes end up being tagged as "spam" by methylation or chromatin changes. Wnt (talk) 18:23, 12 June 2011 (UTC)[reply]
Also that those links are for bone marrow/stem cell style treatments. What I read was not a bone marrow transplant. It was modified blood of the patients themselves to alter their t-cells so that they do not have ccr4 receptors. Furthermore there was mention that it was believed to cost 90-120 thousand dollars for the one-time treatment and that that was considered good since hiv medicines can cost upwards of 18k a month.Thisbites (talk) 05:09, 12 June 2011 (UTC)[reply]
I think you mean CCR5-Δ32. I heard some stories about a "healing" (remission below detectable levels) taking place after a bone-marrow transplantation of a donor with the CCR5-Δ32 mutation. Which makes sense as it replaces the T-cells with cells having some receptors missing. I also know of companies which offer genetic testing for the CCR5-Δ32 mutation. There is evidence that people with CCR5-Δ32 mutation are less likely to develop aids, and respond better to treatment. It may also be possible that people with CCR5-Δ32 are less likely to get infected, but this has not been researched properly at the moment and might be wrong. Introducing a CCR5-Δ32 mutation into someone's blood might be possible, but I guess a bone-marrow transplantation is a much easier, and already feasible way (even though much more risky). I don't know about recent research though --helohe(talk)08:22, 12 June 2011 (UTC)[reply]
Also note that this treatment, even if successful, would make the person more susceptible to the West Nile virus. On the other hand, it would also give him/her better immunity against smallpox (and possibly black plague as well). -- An American ultranationalist 67.169.177.176 (talk) 02:21, 13 June 2011 (UTC)[reply]
Vulcan hearing
It is well known in the Trek universe that Vulcan's have superior hearing. For the most part, it seems people associate this with the shape of their ears. I know that animals can physically move their ears to hone in on a sound (e.g. deer listening for predetors). Since Vulcans cannot move their ears (like an animal, anyway), what affect (if any) does the shape of their ears have on their ability to hear? 99.250.117.26 (talk) 01:54, 12 June 2011 (UTC)[reply]
I'm not a Star Trek fan, so I can't tell you for sure, but generally larger ears (such as those of the elephant or the fennec fox) are better at capturing and focussing sound waves, which translates to better hearing. 67.169.177.176 (talk) 02:09, 12 June 2011 (UTC)[reply]
There are stores that sell "Vulcan ear" costumes to those Trekkies... they don't work as hearing aids. I think external ears in animals that enhance acuity are distinguished more by a concave shape, which allows them to concentrate sound to a single point. Wnt (talk) 02:14, 12 June 2011 (UTC)[reply]
I can't see the shape of their ears making any difference. I don't think it's ever been said on the show that they do (that they have superior hearing is stated, but not the cause). Vulcan's also have superior strength and longevity. I think they are made to be so superior physically so that it's all the more impressive when the emotional humans always better them. --Tango (talk) 13:13, 12 June 2011 (UTC)[reply]
This is, of course, what is called fiction, but do keep in mind that the Vulcan (Star Trek planet) atmosphere is less dense, and hence carries less sound energy. Presumably Vulcans have to have more sensitive hearing to have hearing as good as other species which live in thicker atmospheres. μηδείς (talk)
The shape of the ear does have an effect on hearing. Sound pressure levels at the human eardrum are typically 7-18dB higher in the 1 kHz to 6 kHz frequency range (essential for good speech reception) than they would be without the pinna. Table 1 on this page gives a breakdown of this. Si1965 (talk) 12:11, 13 June 2011 (UTC)[reply]
I asked this question in the "Entertainment" section of the Reference Desk as well, but I feel that it pertains to both categories.
Hey everybody. I've been wondering something about some of the special effects in the newly-released movie Super 8, which came out in theaters on June 10th, 2011. In it, there is a horrible train crash that involves a mid-sized pickup truck (think mid-90's F-150) driving head-on at full speed into a diesel freight train travelling at well over 50 mph. The collision immediately results in an explosion and the locomotive grinds to a halt. But the filled freight cars behind it continue to shoot forward under their own momentum an end up flying everywhere. This continues to occur as the rear of the train continues moving forward. What makes me think that this is unlikely is the immense speed at which the rear of the train continues to move. I mean, of course the effects of inertia would cause the cars to continue moving, but would they really move at such speed? If you have not already seen the movie, here is a link to that particular scene on the Internet Movie Database: Clip 1, and here is another that is longer, but shows a more complete view of the crash: Clip 2. If anybody could help explain or describe this better to me, it would be much appreciated. Basically, all I want to know is, is this scene probable, or is it simply "movie magic" that looks realistic, but defies the laws of physics. Thanks! Stripey the crab (talk) 02:49, 12 June 2011 (UTC)[reply]
Perhaps you should have responded to and thought about my response on Wikipedia:Reference desk/Entertainment before posting here. The film is science fiction, not science. Putting the same question on two ref desks means that responses are dispersed. Not a good move. HiLo48 (talk) 03:00, 12 June 2011 (UTC)[reply]
Red Act, thanks, I forgot about that. :P And User:HiLo48, sorry about that. I posted it here, then went back to check at the Entertainment section. And despite the responses being dispersed, it's not that hard to navigate back and forth between two web pages, or easier still, two tabs. As for being a bad move, on the contrary - you expose the question to more people. I usually spend my time strictly on the Science section. I hadn't even visited the Entertainment section before today, and I'm sure I'm not the only one out there who behaves similarly. But thank you for your response, and for your time. It is much appreciated! :) Stripey the crab (talk) 03:12, 12 June 2011 (UTC)[reply]
It's clearly a CGI train, so of course it's not going to precisely do what a real train would do. However, I don't see anything in either clip that super obviously defies the laws of physics. Train crashes can indeed be immensely destructive, as a Google image search readily shows.[29]Red Act (talk) 04:05, 12 June 2011 (UTC)[reply]
What was less credible to me was that the truck's driver was still alive, the kids weren't harmed, and their camera and car survived. But it was sill a great movie. HiLo48 (talk) 04:47, 12 June 2011 (UTC)[reply]
IIRC, one of the wagons of the train was labeled "explosives". so I guess "theoretically" is is possible. but its unlikely, I have seen a few traincrashes/de-railings and usually I guess it just turns the wagons over squeezes them together etc (similar to what would happen if you do the same in a model-train at high speed)...
Also I don't think a pick up truck would be enough to do much to a train. There have been accidents where some car was in the middle of a crossing, when the train struck, and I guess it just "catapults" the car away, with minor damage to the train. --helohe(talk)08:13, 12 June 2011 (UTC)[reply]
If a pickup truck crashes headon into a locomotive pulling a long freight train, the locomotive itself is so more massive than the pickup that the collision could not possibly bring the locomotive to a halt. The loco and the freight cars would continue at about the initial speed until the application of the train brakes brought the train to a halt. Train brakes are air operated and designed to bring the locomotive and cars to a smooth and safe stop, without the freight cars running over the magically stopped locomotive. The whole scenario sounds bogus. Standard Hollywood garbage, its physics about on a par with Roadrunner cartoons. If the lead locomotive somehow derailed, or it it hit a massive gravel truck or truck load of rolls of steel, the scene would be more plausible. It is still a great scene, cinematically, and I will make it a point to see the movie. Edison (talk) 00:50, 13 June 2011 (UTC)[reply]
Edison is exactly correct, the locomotive would not come to a dead stop given it outmassed the truck but the cars behind would have continued at the same speed they were being pulled by the locomotive. What really effs up a movie is when a falling object falls faster than gravity because Catwoman (film) jumped downward. μηδείς (talk) 01:20, 13 June 2011 (UTC)[reply]
The truck wouldn't need to itself bring the locomotive to a stop. If the locomotive is derailed by hitting the truck (which is conceivable) it's going to slow down pretty fast which could cause the subsequent cars to pile up. If the train happens to be packed full of explosives (which I have to assume it is by the way everything starts exploding) I guess it could be pretty catastrophic. Rckrone (talk) 04:35, 13 June 2011 (UTC)[reply]
I still don't buy it -- even if the engine is derailed and the other cars pile up behind it (pretty unlikely given the small size of the truck), modern high explosives are very stable and will not detonate simply from being jostled in this manner. In order to explode in this manner, the train would have to be carrying either some kind of high explosives with extremely high sensitivity to impact, such as nitroglycerin (implausible, since these types of explosives are no longer used as such, nor transported), or else live munitions with detonators fitted (TOTALLY implausible -- munitions are ALWAYS transported with detonators removed, precisely to avoid a disaster of this type). Or else the train would first have to catch on fire and the flames spread to the explosives (which is possible, but would take a while). But then again, most people don't know what REALLY happens when a train hits a pickup truck, much less what happens when a train derails. And all those peddlers of cheap thrills capitalize on this scientific ignorance to make big bucks... 67.169.177.176 (talk) 07:05, 13 June 2011 (UTC)[reply]
Cold fusion applicability
Reading cold fusion confuses me — I understand somewhat of what the proponents claim is happening, but I fail to see the applicability. Let's say that tomorrow someone shocks the scientific community and conclusively proves to everybody's satisfaction that cold fusion really is possible. What possible applications are there for it, aside from reducing the prices for manufacturers of helium balloons? As far as I know, all our uses for fusion rely on the significant amounts of energy that result, whether using the explosion as a powerful weapon, or (if we can figure it out) using a slower process to generate electricity with the very non-cold temperatures that result. Nyttend (talk) 12:17, 12 June 2011 (UTC)[reply]
The most common idea that I've seen is that you scale it up to the level of "personal reactors" that would power your household, heat your water, power your car, whatever. It's meant to be small-scale, personal, clean power. (This is part of the alleged conspiracy theory — it would destroy the need for centralized utility companies, oil companies, and so forth. So they've rallied against it, blah blah blah.) Obviously the prototypes don't really intend to do that, any more than Hahn and Meitner's experiments weren't a fission reactor (or bomb). If we could use hot fusion on that scale, we would, but hot fusion requires starting temperatures on the order of millions of degrees Fahrenheit, so getting back what you put into it requires liberating a huge amount of energy. --Mr.98 (talk) 12:49, 12 June 2011 (UTC)[reply]
Yes, you are right. Cold fusion would be useful as a source of energy. That's it. That is a extremely important applicability which makes me wonder why you say you fail to see the applicability. Dauto (talk) 18:42, 12 June 2011 (UTC)[reply]
I think the question is: if it is cold, then it doesn't generate energy that we can transform into electricity. So is the word cold in cold fusion misused? Or can we generate elecricity without heat or explosions? --Lgriot (talk) 10:25, 13 June 2011 (UTC)[reply]
To put it in perspective, the temperature inside of a conventional coal based electric power plant is of the order of 1000 K while the temperature required for hot fusion is of the order of 100 000 000 K. There is plenty of space in between that would be hot enough to produce electric power but too cold to generate conventional fusion. If fusion is achieved in that range it would be considered cold fusion. Dauto (talk) 16:48, 13 June 2011 (UTC)[reply]
Would it be an effective diet just to be outside our thermal comfort zone? This way our body would have to burn calories to keep us cool or warm. Which way would be more effective - hotter or colder? Quest09 (talk) 12:32, 12 June 2011 (UTC)[reply]
Cold. You don't really use energy to cool down, that would be counter-productive since using energy almost always converts it into heat (energy is never created or destroyed, remember). You cool down by sweating and redirecting blood to the skin. That doesn't really take energy. When you're cold, though, you need to use energy to generate heat (for example, by shivering). I don't think it would be a particularly good way to burn calories, though - you would need to be dangerously cold for it to have a significant effect. You would be better off going for a nice jog. --Tango (talk) 13:22, 12 June 2011 (UTC)[reply]
But, if you need 1Cal to heat one Kg of yourself 1 °C, and you put the A/C 3 °C below the comfort zone, you'll end up spending a lot of Calories each day (provided you don't get hungry in the cold), won't you? Quest09 (talk) 13:40, 12 June 2011 (UTC)[reply]
He got it right. One food Calorie is one kg (1000 grams) of water for 1 °C. Thermodynamic calories are one gram of water for 1 °C. Hence by saying kilogram he already included the factor of 1000. Dragons flight (talk) 18:56, 13 June 2011 (UTC)[reply]
You'll gain weight when you attempt to change the energy balance like this, without drastically cutting back on your energy intake. This is because the body attempts to maintain a stable body weight on the long term. So, unless you go outside the range where the feedback mechanisms the body uses break down, you won't lose weight. Instead, the feedback mechanisms will lead to the opposite result, a modest weight gain, because it will take measures against a perceived threat to its long term energy reserves.
Incidentally, the article Mike Stroud (physician) says that Antarctic explorers can use over 10,000 calories a day (which I've seen described by a simple calorie count of the food consumed from some much earlier expedition). Wnt (talk) 17:59, 12 June 2011 (UTC)[reply]
Recent research has pointed to something else you can do to lose weight without dieting: Sleeping for longer. This is because during sleep the metabolic rate is slower. Naively, you may think that you'll gain weight if you sleeep better and longer. But what really happens is that the metabolic rate during sleep is regulated as part of all the feedback mechanisms to maintain a stable weight. Then, because the body will regulate the amount of energy reserves such that it can do without food for some given amount of time, a longer sleeping period means that you need less fat. You could say that the time you sleep counts as virtual fat, and the more virtual fat you have, the less real fat you'll have. The body apparently keeps track of how much you sleep on you get on the long term and uses that to regulate to what degree the fat cells are filled. Count Iblis (talk) 15:12, 12 June 2011 (UTC)[reply]
I personally find that it is much easier to lose weight when it is hot. Not because the heat is burning calories, but the heat makes me not feel like eating. Googlemeister (talk) 17:31, 13 June 2011 (UTC)[reply]
Electronic compass
I've just bought a GPS unit that includes an electronic compass, i.e. it supposedly doesn't rely on GPS data and functions when stationary, unlike cheaper GPS units which can only determine direction when moving. I was curious to know how the electronic compass worked, but there isn't a Wikipedia article, and the compass article refers readers to fibre optic gyrocompass, so I created a redirect to that article from electronic compass. However, reading the article on fibre optic gyroscope (to which fibre optic gyrocompass refers me) I am not sure I have done the right thing. Does my Oregon 450 GPS unit really contain a laser and lots of fibre optic cable? If not, how does the "electronic compass" work?--Shantavira|feed me13:27, 12 June 2011 (UTC)[reply]
Reading the question above, I wondered how the first magnet / compas needle was created. The only way I can think of to create a magnet is using an electromagnetic field applied to some iron or similar which would require electricity. then again to create electricity (besides using a chemical process like a battery) one needs a magnet to induce an changing electric field in a coil. --helohe(talk)16:47, 12 June 2011 (UTC)[reply]
The English scientist William Gilberd (1544 – 1603) was the first person to study magnetism in any scientific way. He found out how to manufacture magnets as Finlay describes - only natural lodestones were used previously. He also disproved the widely held belief that compasses could be demagnetised by contact with garlic! He was the first to suggest that the earth had magnetic poles - it had previously been thought that there was a big magnetic island in the Arctic that all compasses pointed to. He is credited with coining the word "electricity". He deserves to be better known, but few have heard of him outside of his home town of Colchester. Alansplodge (talk) 17:37, 12 June 2011 (UTC)[reply]
The Baghdad Battery is a likely hoax. Lodestones may have been created by lightning strikes in soil containing iron ore. Edison (talk) 00:43, 13 June 2011 (UTC)[reply]
I have a Sandisk Sansa Clip+ which is charged over USB (mini-B) and doesn't come with a wall charger, and I have a Motorola mini-USB cell phone wall charger, model FMP5185B, input 100–240V, 50/60Hz, output 5.0V, 550mA. Can I safely charge the one with the other? This thread is full of people saying it's okay, but this thread makes me worry. If there's any doubt, I'd rather not do it. -- BenRG (talk) 19:02, 12 June 2011 (UTC)[reply]
I'm not an expert but those wall chargers just emulate a normal usb cable from a computer so they should be using the same specification. The USB article lists normal usb power as "500–900 mA @ 5 V" which is the same as yours AvrillirvA (talk) 22:41, 12 June 2011 (UTC)[reply]
As I remarked recently on the RDC, all wall AC/DC adapters for mobile phones or heck nearly everything I've seen in the past 4+ years or so have been SMPSs. There may be some traditional linear transformer only wall AC/DC adapters with fullsize/mini/micro USB sockets or plugs but I doubt they we were ever common. Definitely all image search results for the motorola razr v3 adapter I find seem to be SMPSs. Of course since you actually have the adapter you can probably tell by the size and weight. However since the specs for your device say it supports 100–240V, it obviously has some regulation and is almost definitely a SMPS.
Also if you overcharge li-ion batteries they may explode fairly violently. Since manufacturers find this undesirable, they tend to design devices to avoid this. If you supply too high a voltage you may kill the device or charging circuitry. You're far less likely to overcharge the batteries. (Li-ion batteries also should generally be charged with a CC-CV charging profile. And the CV stage should generally be 4.2V regulated to with +/- 0.05V or better [30], there are specialised chips for this which may be what most manufacturers use but in any case this isn't something you handle by simply dropping the voltage of a 5V USB supply where +/- 5% is within regulation.)
Finally if you're drawing a higher current then the AC adapter can supply and there's no safety or fuse, you risk damaging the adapter, perhaps even causing a fire. Alternatively the voltage may drop too low (as the poster sugggested) and the device and charging circuitry won't be able to function correctly. There's a slight chance this may result in an incomplete charge, more likely you're just get random problems or the device/charging won't work at all.
In other words, nearly all the claims of the person in the second link are questionable.
Identifying small trilobites in Ordovician-age rock
Hi. I have some samples of Ordovician fossiliferous limestone. Some of those samples may contain fragments of trilobites, and I would like to identify them using specific features if possible. How do I identify the body fragments and distinguish them from other fossils, a partial list being bryozoans, gastropods, porifera, crinoids, brachiopods, and possibly others such as cephalopods and ostracods? Thanks. ~AH1(discuss!)20:17, 12 June 2011 (UTC)[reply]
Take a course in invertebrate zoology. Look for a continuos closed chitinous exoskeleton. Contact Robert Loveland of Rutgers University. Look for a segmented body and jointed limbs. Publish any pictures yo have and ask for comments if you are not sure. μηδείς (talk) 22:35, 12 June 2011 (UTC)[reply]
Pain & C-Fibers
I'm having a hard time tracking down an answer for what I was assuming was a straightforward empirical question: People argue that pain is possible even without c-fiber stimulation. But are there cases on record of normal, psychologically healthy adults who complain of pains that cannot be correlated with any kind of c-fiber activity? I.e., cases where an otherwise normal (I say that to sort of weakly rule "hypochondriacs" or, generally, people we have reason to doubt make veracious claims about their physiological states) adults sought medical help for pains which subsequently could not be grounded to any neurological goings-on.
I think phantom pain, and neuropathic pain of the "central" type, are pretty clear examples. C-fibers contribute to phantom pain in some instances, but some of the worst pain comes in people for whom all the relevant C-fibers appear to have degenerated. Looie496 (talk) 00:31, 13 June 2011 (UTC)[reply]
Really? In all my life I never have. Heck, when I had the gout I would sometimes avoid moving my legs for up to an hour after waking, simply to keep the sleep paralysis going so I wouldn't feel the pain. Wnt (talk) 05:14, 13 June 2011 (UTC)[reply]
It is actually a quite remarkable fact that people are not able to experience pain in dreams. You can dream that your legs are blown off by an explosion, but you will not feel any pain when it happens. Other forms of distress are common, such as a feeling of suffocation or overheating, or a need to urinate. Looie496 (talk) 06:38, 13 June 2011 (UTC)[reply]
That is wrong. I've felt pain in dreams, and I can't find any sources stating it's impossible to feel pain a dream. I understand that sometimes something which would cause pain in real life doesn't in a dream or the perception of pain is different in dreams, but that is very different from never being able to experience pain in dreams 82.43.90.27 (talk) 21:04, 13 June 2011 (UTC)[reply]
I speak from personal experience, I had my hand chewed on and I can tell you: it wasn't as painful as you'd think, but still very much (like a painfully firm handshake). Coincidentally, I realised that I was infact dreaming. As soon as I did, I managed to rationalise the pain away. You know what, dreaming is so much more fun when you know you are dreaming. The annoying thing is that as soon as you know that you are dreaming, one of two things can happen: either, your brain sabotages you and you wake up, or your state of mind lets you forget very easily that you are dreaming. Plasmic Physics (talk) 08:02, 13 June 2011 (UTC)[reply]
I don't know about others but I can occassionally feel pain in dreams. I once went to sleep with a headache, and was aware of the headache in my dream. I then took some asprin in my dream and the headache went away. And it stayed away until I woke up whereupone the headache returned. This has also convinced me personally that the placebo effect is a real thing. Googlemeister (talk) 17:27, 13 June 2011 (UTC)[reply]
That's not true. You get fat if you eat more calories than you burn in exercise, whether those calories come from carbohydrates or from fat. The moral is: eat, but don't eat too much. Simple, but not always simple to follow.Itsmejudith (talk) 21:26, 12 June 2011 (UTC)[reply]
(ec) Because the body also uses fat as a source of energy. (See Citric acid cycle for extensive details. Well, it's a bit complicated on the biochemistry level.) Fat is only synthesized from carbohydrates because fat has a higher energy density and thus can be stored more easily. 5BYv8cUJ (talk) 21:36, 12 June 2011 (UTC)[reply]
June 13
what are the health effects of chronic *low* blood sugar? (if there is such a thing)
Please note that nothing in this question is a request for medical advice, anyone who requires medical advice should seek the advice of a qualified doctor, rather than anonymous unqualified respondents from an online reference desk, who are liable to be completely mistaken in their understanding and assume no responsibility for anyone who kills or injures themselves or others by mistaking anything here as medical advice or relating to it in any way.
This is not a request for medical advice -- indeed, it does not relate to me or anyone I know -- but I was wondering what, if anything, the health effects of chronic *low* blood sugar are? For example if a diabetic using insulin were to be mistaken in the amounts of insulin given, but not to the point of an acute hypoglycemic attack, but, instead, consistently low (rather than high) blood sugars, so that it remains chronically below that of a healthy person by a significant amount, but not enough to cause an acute hypoglycemic ris... then is what are the health effects? thanks.
to give you an idea of my impression, it seems that unlike moderately high blood sugar, moderately low blood sugar is not something with chronic health effects - it can be an acute episode, but nothing chronic. This is my impression, since I'm having trouble digging anything up -- that's why I've come to the ref desk :)
Note: this is a question about blood sugar not blood pressure, which is a different question.
(EC)An answer more responsive to the question would cite the article Hypoglycemia, which says that low blood sugar produces the symptoms of shakiness, anxiety, nervousness, palpitations, tachycardia, sweating, pallor, coldness, numbness, hunger, nausea, vomiting, abdominal discomfort, headache, abnormal mentation, impaired judgment, fatigue, confusion, and a host of other symptoms. It can also be fatal, per the article. Edison (talk) 01:31, 13 June 2011 (UTC)[reply]
Note the (EC). The preceding response by Medeis was the one I considered less than ideally responsive to the question. You and I cited both cited Hypoglycemia. Chronic low blood sugar would not be much fun, with the symptoms listed in the article cited, as well as anger and depression listed as symptoms in some of the "alternative medicine" books about the claimed widespread hypoglycemia. Chronically reduced mental efficiency might be a problem. For a diabetic on insulin or oral sugar lowering meds, there would be the constant fear that it is about to drop from a low 70 mg/dL to a disastrous 40 mg/dL. It is rare for blood sugar to be really stable in a diabetic. There would be little margin for error between "low" and "so low as to cause convulsions and unconsciousness." "Chronic hypoglycemia" was a popular pseudodisease or fad disease of the 1970's and 1980's, [31] among gluconormal nondiabetic hypochondriacs, with popular books, [32] written about how to treat it. There are many true believers in chronic hypoglycemia as a cause of a variety of ailments not widely supported by the medical establishment, who claim that 10 to 25% of the general population suffers from hypoglycemia. Drugstores sell inexpensive glucose meters which can readily tell whether blood sugar is normal, low or high. Edison (talk) 03:12, 13 June 2011 (UTC)[reply]
Let's hear from the poster, who did, I believe, use the word chronic. There certainly was no question of the acute effects which you referred to, while extreme caloric restriction, which I referred to, is posited as a method of life extension. Or did I get that wrong too? μηδείς (talk) 03:38, 13 June 2011 (UTC)[reply]
Chronic hypoglycemia actually causes someone (well, at least some rat) to increase the amount of sugar transport past the blood-brain barrier. Thus some of the effects of acute hypoglycemia don't apply as the person's system adapts. Likewise, glucose transport decreases in diabetes, perhaps a bad thing for diabetics when insulin dose is too high.[33]Wnt (talk) 03:30, 13 June 2011 (UTC)[reply]
you guys don't really get the question. (op here). I mean, if you read about "diabetes complications" you can see that if someone has a blood sugar of 8 for 20 years (instead of the normal 5.5), or on the other scale 144 instead of the normal 100, then they can get complications. That is just slightly above normal. So, what about consistently slightly below normal? Like 4 (72 on the other scale) consistently day in day out for years? Are there complications that develop over time from chronic slightly below average blood sugar? (Note: all you guys have said about headache and vomiting and passing out etc are an acute attack of way lower blood sugar. Not my question). Thanks, and sorry I might not have been the clearest possible in originally asking. Nothing here relates to medical advice in any way, this is just more of a science quesiton. --188.28.126.160 (talk) 12:20, 13 June 2011 (UTC)[reply]
The article Hypoglycemia does "get the question, and answers it. Chronically low blood sugar has a host of possible symptoms that range widely both from person to person, and for any given person. Here, for example, from the linked article (boldface mine):
Determining the presence of both parts of this definition is not always straightforward, as hypoglycemic symptoms and effects are vague and can be produced by other conditions; people with recurrently low glucose levels can lose their threshold symptoms so that severe neuroglycopenic impairment can occur without much warning, and many measurement methods (especially glucose meters) are imprecise at low levels.
Reading the article will help you understand why a simple list of chronic symptoms is not going to be very accurate, although the list of possible symptoms and consequent damage is there. Bielle (talk) 17:09, 13 June 2011 (UTC)[reply]
Bed Bugs
I don't understand why people freak out about bed bugs. They are much more benign than other blood sucking insects, such as mosquitoes and ticks (for instance, they have not been proven to transmit diseases, and only a small percentage of people actually have a noticeable skin reaction to their bites. Most aren't even aware of it.). We get bitten by other insects all the time. So why all the fuss about bed bugs? Thanks. Quinn❀ BEAUTIFUL DAY03:30, 13 June 2011 (UTC)[reply]
People are generally unpleased to be eaten by things, even if they are only being eaten in small bits at a time. There's a general revulsion against this, which is a Good Thing, since many other blood-sucking insects and other such parasites are known to transmit real disease. That bed bugs are comparatively less disease carrying isn't necessarily a factor in the level of revulsion people feel viscerally to being eaten. It's not an intellectual response. Furthermore, while bed bugs are pretty low on the "disease carrying vermin" ladder, the presence of any vermin is usually an indication of general uncleanliness; apartment buildings with bed bugs infestations can also have other pests (fleas, rats, etc.) which are not always so benign. Even if not true in every case, the presence of vermin of any sort is generally met with revulsion, for reasons described above. --Jayron3205:22, 13 June 2011 (UTC)[reply]
Unlike mosquitoes or ticks, bed bugs infest homes, and particularly mattresses. Bed bug infestations are easily spread, and can be difficult to eradicate. Rckrone (talk) 05:30, 13 June 2011 (UTC)[reply]
I appreciate the answers, but I would point out that bed bugs have absolutely nothing to do with "un-cleanliness:". Bed bugs are generally brought in by the last person you allowed to sleep in your bed. Whether in luggage or other such transmitter.Quinn❀ BEAUTIFUL DAY06:27, 13 June 2011 (UTC)[reply]
Inviting unclean people to sleep in your bed isn't itself a risky behavior? How is this different from inviting someone with fleas from sleeping in your bed? --Jayron3217:49, 13 June 2011 (UTC)[reply]
Not terribly dangerous but they can be very irritating [34] on a whole lot of levels. I'm not sure people are paranoid about them; I think they are anxious which is rather different. Richard Avery (talk) 06:27, 13 June 2011 (UTC)[reply]
There is also what might be called the tautological response — people are disgusted by bedbugs because other people are disgusted by bedbugs. That is, it doesn't matter what I think, if all my friends will find me disgusting. Or, more to the point, if my property values are going to be affected, and so on. --Mr.98 (talk) 10:10, 13 June 2011 (UTC)[reply]
A sterile home were there are none of the insects that you find outdoors in Nature is a paradise for specialized bugs adapted to live in the home environment. Count Iblis (talk) 18:03, 13 June 2011 (UTC)[reply]
Need help identifying this ladybird-lookalike
Hi,
Was in my garden two days ago and noticed this colorful critter crawling around on an asparagus plant.
Colors and spots look like a ladybird. I am mostly familiar with the common seven-spotted ladybird, but I know there are other species of ladybirds. But this isn't a ladybird, is it? It is a bug trying to look like one, isn't it? The shape of the body just does not fit well with a ladybird. Any help on the id would be appreciated. Thanks,
With the recent icelandic eruptions and now the chilean eruption pushing vast amounts of ash into the atmosphere, would this effect global temp or would this be an insignificant event? What scale of eruption at various points on the planet would significantly effect global temp? which could by all tense and purposes reverse global warming? — Preceding unsigned comment added by 109.224.25.11 (talk) 05:43, 13 June 2011 (UTC)[reply]
Pinatubo in 1991 had a significant effect, but it was on the same scale as natural variations on top of the warming trend
These are both fairly insignificant events on the global scale. In order to see significant global cooling you need to inject a vast amount of ash and sulfates into the stratosphere, which requires an extremely energetic eruption. The current eruptions of Puyehue in Chile and Grímsvötn in Iceland are 3 and 4 on the Volcanic Explosivity Index (VEI) respectively. To give you a sense of the scales involved: Mount Pinatubo's 1991 eruption had the effect of lowering the global temperature by about 0.4 °C; this about the same as the amount of warming seen in the past 20 years (see image). However, Pinatubo's eruption was a 6 on the VEI (i.e. about 100 times more material erupted than Grímsvötn and about 1000 times more material erupted than ), had an ash column up to 21 kilometres (13 mi) high, and occurred near the equator which facilitated the spread of cooling stratospheric aerosols across the entire globe. Even with this extreme event, its cooling effect only lasted about 2 years. The current eruptions have only had ash clouds up to 10 and 12 km respectively, which is just barely into the stratosphere (if it is at all; the height of the stratosphere actually changes from day to day with the weather).
Also, your idea that a volcanic eruption could somehow "reverse" global warming is quite unlikely; the residence times of sulfates and ash in the atmosphere are on the order of a few years, while CO2 has a residence time of about 400 years. Volcanoes also emit large amounts of carbon dioxide in addition to ash and sulfates, so I imagine in the long run the overall effect of a large volcanic eruption would be a net warming.-RunningOnBrains(talk)06:25, 13 June 2011 (UTC)[reply]
I realize upon re-reading that I was unclear on a few things. Volcanic aerosols (mainly volcanic ash and sulfur dioxide) suspended in the atmosphere reflect sunlight back into space, thus if you inject a large amount of volcanic aerosols into the stratosphere you can lower the amount of sunlight that reaches the earth by several percent, leading to cooler temperatures. The reason you need the eruption to reach into the stratosphere is that there is very little in the way of weather-related processes such as rain which quickly remove volcanic aerosols from the atmosphere. Ash and sulfates in the troposphere will likely be washed out on the order of weeks; not nearly long enough to cause significant cooling.-RunningOnBrains(talk)06:31, 13 June 2011 (UTC)[reply]
Note that the Mount Pinatubo eruption began in the early summer, while the Chilean eruption is occurring in early winter. μηδείς (talk) 18:56, 13 June 2011 (UTC)[reply]
why are triplet carbenes normally sp2 hybridised but become sp hybridised when bonded to oxygen ,nitrogen ,sulphur or halides ? Raky rough (talk) 12:05, 13 June 2011 (UTC)[reply]
why is it that if you unplug a fridge for a while, even if you clean it fastidiously, it will smell really musky. no matter how long you air it out. but lo, when you plug it back in again, as soon as it finishes cooling again, that smell is gone! why does cold desmellify in this mysterious manner. thanks for any scientific insight you might have on this question. --188.28.126.160 (talk) 12:50, 13 June 2011 (UTC)[reply]
I've tracked down the musty smell in my refrigerator to the condenser and drain pan. So, cleaning the inside of the fridge won't help with that. A long time ago, when I lived in an apartment, my fridge really stank. That is how I learned about the drain pan because I tracked it down and found that the drain pan in that fridge was full of blood. -- kainaw™13:08, 13 June 2011 (UTC)[reply]
(edit conflict)Possibly, because there exists bacteria on the inside surface of your fridge that isn't removed by anything short of bleach. Low temperatures negatively impacts cellular metabolic rates, explaining why you only detect a smell when the fridge is above normal operating temperature. Bacteria give off gases as a waste product of metabolism, the lower the temperature, the lower the concentration in the air. Plasmic Physics (talk) 13:16, 13 June 2011 (UTC)[reply]
And that should be testable by storing said unplugged refrigerator in consistently cold conditions, say outside in locations where temperatures stay around freezing for several months at a time. Surely someone around here's done this? --jjron (talk) 14:28, 13 June 2011 (UTC)[reply]
It's not just a metabolic effect. The vapor pressure of the smelly compounds that produce the odor you're detecting also varies with temperature. Higher temperatures mean that the maximum concentration of stinky stuff in the air is also higher; higher temperatures will also tend to drive faster evaporation of these nasties. Your nose can detect some odiferous compounds at concentrations of parts per billion or even less, so it takes a very small reservoir of these compounds in the fridge (tucked into crevices, hidden in door seals, even just adsorbed on the plastic surfaces) to continue to release odor for a very long time. TenOfAllTrades(talk) 15:10, 13 June 2011 (UTC)[reply]
Depending on your social environment, there are taboos in some societies about masturbation, so you could suffer socially. There are lots of different cultures in the world, each with their own opinions on these things, and depending on which culture you find yourself in, you may experience various levels of social consequences from masturbation. --Jayron3217:46, 13 June 2011 (UTC)[reply]
WebMD has some funny stuff up, that frequent masturbation is correlated with an increased risk of prostate cancer in men in their 20s and 30s, but a decreased risk in men in their 50s.[35]Wnt (talk) 18:23, 13 June 2011 (UTC)[reply]
Yes, but in that article the researchers say that the frequency only indicates the sex drive, which in turn is a function of the level of hormones. A man's prostate can't tell whether orgasms come from masturbation or intercourse - probably, how would it? Itsmejudith (talk) 21:23, 13 June 2011 (UTC)[reply]
Portnoy's Complaint _does_ highlight one disadvantage - the real thing is rather disappointing and difficult in comparison. I recall a story on Fark[36] some years ago (not the most reliable of sources, of course) about Japanese men who suffer from this problem, although I'm sure it's applicable across the world. Tevildo (talk) 20:20, 13 June 2011 (UTC)[reply]
Normalizing Associated Legendre Polynomials to get Spherical Harmonics
Hi all. I've been working on this problem for like weeks, and I can't seem to figure it out. I'm trying to normalize Associated Legendre polynomials to turn them into Spherical harmonics. The integral comes out to:
I have a styrofoam cooler that I use all the time, just for ice and soda so it really doesn't get funky because no foodstuffs are in it ever. Anyway, after a lot of use, the inside is a bit yellowed and has a slightly musty odor, so I thought I'd put some water in it with some bleach (about one-half cup bleach to a half-gallon of water is what I usually use for such applications, I guess that's a 1:16 mixture). This works great for mildew and the like. However, my friend told me that bleach and styrofoam are a bad mix, that they give off deadly fumes. Of course, I am now terrified to do this, especially indoors. Is there validity to this? I guess I should be very precise: My household bleach doesn't say what's in it but does say that it
"CAUTION, CORROSIVE! contains sodium hydrochlorite". The styrofoam does not say exactly what it is but it is marked with a triangular recycle symbol with a 5 inside, and says just below that, "PS"--maybe PolyStyrene? Note that there's nothing on the bleach label's caution list to single out styrofoam, but of course it can't list every stupid thing anyone might try, so I'm not putting any store by that. Oh, and if anyone knows of an alternative method that works well with styrofoam, of course I'm all ears.--108.54.17.250 (talk) 23:03, 13 June 2011 (UTC)[reply]
![[5]](http://www.users.muohio.edu/lazzarma/astronomy/images/universe_expansion.gif){kind=link}
