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August 31
Absolute vs. invariant
What is the difference between both terms: absolute, invariant?--Email4mobile (talk) 01:55, 31 August 2010 (UTC)- Have you seen these two terms used in some scientific application? If so, it would help us if you describe the scientific application so that we can explain the difference in a way that is meaningful for your application. If not, your question should be re-posted at the Language Reference Desk Wikipedia:RD/L. Dolphin (t) 02:08, 31 August 2010 (UTC)
- When talking about light speed, we almost say it is invariant and it is rarely described in some sites as absolute (for instance: Principle of Invariant Light Speed).--Email4mobile (talk) 03:01, 31 August 2010 (UTC)
- Not sure if this is what you want, but absolute usually refers to a limiting invariant. Thus, 'absolute zero' is the invariable lowest limit of temperature, while other temperatures (such as the boiling point of water at standard pressure) are invariant without being absolute. but without knowing the context of your question, it's hard to be sure if that helps. --Ludwigs2 03:40, 31 August 2010 (UTC)
- One could say that the speed of light is an "absolute maximum" speed, but this is usually taken for granted and is seldom spelled out in those words. "Invariant" just means that it doesn't change, but note that only the speed of light in Free space is invariant. Light "speed" actually depends on the medium through which it is travelling. Dbfirs 08:19, 31 August 2010 (UTC)
- Light only travels in a vacuum, and at only one speed. If it runs into say an atom it gets absorbed and (perhaps) re-emitted -- at light speed, back into the inter-atom vaccum. Wikiscient (talk) 08:38, 31 August 2010 (UTC)
- Well, yes and no. Yes, for the particle description of light. For the wave description, not so much. How can they be true at the same time? Not so easily. You have to swallow one or more of the various weirdnesses of quantum mechanics.
- By the Copenhagen interpretation, I think you would say that the light wave, in matter, is a superposition of various possible world lines where the photons are absorbed and re-emitted, as you say — but there isn't necessarily a fact of the matter as to which of these (mutually incompatible) world lines is the one that "really happened". --Trovatore (talk) 09:25, 31 August 2010 (UTC)
- Yes, thanks for the correction on interpretation. I've put "quotes" round "speed". The word is used informally to mean "speed of propagation", as in the experiment to "stop light". Dbfirs 18:28, 31 August 2010 (UTC)
- Light only travels in a vacuum, and at only one speed. If it runs into say an atom it gets absorbed and (perhaps) re-emitted -- at light speed, back into the inter-atom vaccum. Wikiscient (talk) 08:38, 31 August 2010 (UTC)
- One could say that the speed of light is an "absolute maximum" speed, but this is usually taken for granted and is seldom spelled out in those words. "Invariant" just means that it doesn't change, but note that only the speed of light in Free space is invariant. Light "speed" actually depends on the medium through which it is travelling. Dbfirs 08:19, 31 August 2010 (UTC)
- Not sure if this is what you want, but absolute usually refers to a limiting invariant. Thus, 'absolute zero' is the invariable lowest limit of temperature, while other temperatures (such as the boiling point of water at standard pressure) are invariant without being absolute. but without knowing the context of your question, it's hard to be sure if that helps. --Ludwigs2 03:40, 31 August 2010 (UTC)
- When talking about light speed, we almost say it is invariant and it is rarely described in some sites as absolute (for instance: Principle of Invariant Light Speed).--Email4mobile (talk) 03:01, 31 August 2010 (UTC)
Solar system
When was the last time Jupiter, Saturn and Neptune were in line from Sun, estimated years to next time planets will form straight line from Sun, how does this effect earth's orbit--Golfforgeorge (talk) 04:37, 31 August 2010 (UTC)- It's called an astronomical Syzygy and it's really not that hard to look up past and future planetary alignments, if you're interested, GIYF. And no, the planets are so far apart that there is no appreciable effect on earth's orbit.. Vespine (talk) 06:49, 31 August 2010 (UTC)
- This link, http://www.space.com/scienceastronomy/solarsystem/planets_align_020402-1.html , talks about the alignment in April, 2002 of the Sun, Mercury, Venus, Mars, Earth, and Saturn -- and says that in the next 100 years there will be only three other times when at least five planets are so closely aligned: September 2040, July 2060, and November 2100. (You can also find astronomy software online that will calculate the dates etc. of various planetary configurations for you, if you want.) Wikiscient (talk) 08:02, 31 August 2010 (UTC)
- It should also be noted that such predictions only work on relatively short (centuries or millenia) timeframes. When extrapolated over longer time periods, the system degenerates into an N-body problem, and becomes chaotic. That's because over long time periods, the total of the small gravitational effects of the planets on each other begin to add up, and aren't negligible anymore. --Jayron32 05:43, 1 September 2010 (UTC)
- Vespine - could you please not use that offensive acronym, especially when you fail to do it yourself and find out just how difficult it is to find a list of historical alignments? Most of the results are blogs about 2012, no matter what I search for. The previous suggestion, of downloading a simulator, seems about right - see the post on physicsforums.
- As for the effects of such alignments, I crunched the numbers for you quickly. At closest approach to Earth, each planet exerts their largest gravitational force on us, and during an alignment, all those forces add up. Jupiter's max force on the Earth is 2.2*10^18 N, Saturn's is 0.16*10^18 N, and Uranus and Neptune both exert about 4*10^15 N, giving a total force during alignment of 2.368*10^18 N, which is barely more than what Jupiter exerts normally (about 7% more force). All of this is a counteracting force against that exerted by the Sun on the Earth - 3.5*10^22 N - which is 10,000 times greater than the admittedly-significant force exerted by Jupiter. So how much of a difference do we, as Earthlings, feel in gravity during this largest-planet alignment? The answer is that we feel 0.0005% lighter, which is very insignificant. If you want to change your body weight by this amount, walk a couple steps up a flight of stairs - your distance from the Earth will increase enough to reduce your mass by the amount that this alignment would (source for analogy). SamuelRiv (talk) 17:16, 2 September 2010 (UTC)
- I never thought the acronym was offensive, in fact i thought it was quite purposefully inoffensive, like a backlash to RTFM. As for whether the information the OP seeks could be found by google, well that's just a matter of how much effort you put in, which by the naivete of the question appears to have been NONE up to the point of deciding to post here. I advocate learning for yourself, i gave a lead and i encouraged self discovery, I meant no offense. Your answer is very good, but takes a different approach. I would argue that to anyone who even slightly believes in astrology it will be easily dismissible; magic doesn't require gravity as a medium. Vespine (talk) 23:31, 2 September 2010 (UTC)
- It should also be noted that such predictions only work on relatively short (centuries or millenia) timeframes. When extrapolated over longer time periods, the system degenerates into an N-body problem, and becomes chaotic. That's because over long time periods, the total of the small gravitational effects of the planets on each other begin to add up, and aren't negligible anymore. --Jayron32 05:43, 1 September 2010 (UTC)
- It would be nice if people would answer the questions rather than bicker about irrelevant BS. 1) This conjunction occurs every 179 years with a slight but increasing "drift" in its closeness; as a result, in a few centuries the 179-year cycle will shift to a different "starting point" in the A.D. year-number (i.e., you won't be able to just add 179-year increments to the previous dates). It occurred, for example, in 1345, 1524, 1702, and 1881, but by 1881 the closest the three got was a relatively wide 7 degrees of geocentric longitude. The closest recently was January 20, 1524, when the three got to within 1.3 degrees in longitude and 0.9 degrees in latitude. 2) The next time will be June 2060, when the closest triple conjuntion will be 8 degrees in longitude. Jupiter and Saturn conjoin every 20 years, minus a few months. That increment, added to June 2060 repeatedly, will reveal the next "beginning year" of the 179-year cycle once the "drift" causes the closeness of the conjunction to disappear in the current "...1345/1524/1702..." cycle (which centers on 1524).63.17.54.204 (talk) 03:26, 4 September 2010 (UTC)
The lack of progress in motor vehicles
- It seems to me that this request is asking for opinions. The Science Reference Desk does not provide opinions so it is likely that the OP will not receive satisfying responses. Dolphin (t) 04:45, 31 August 2010 (UTC)
- Hmm... what if I rephrase the question with less whining involved (my fault): Is there any evidence that actual, verifiable work is being made to progress the internal combustion engine into something entirely different and far superior to what it is now by the actual corporations who make them? Students and science contests don't count. – Kerαunoςcopia◁galaxies 05:11, 31 August 2010 (UTC)
- Far superior? I doubt it. See Carnot cycle to get an idea on the thermodynamic limit on efficiency. Dolphin (t) 05:34, 31 August 2010 (UTC)
- Hmm... what if I rephrase the question with less whining involved (my fault): Is there any evidence that actual, verifiable work is being made to progress the internal combustion engine into something entirely different and far superior to what it is now by the actual corporations who make them? Students and science contests don't count. – Kerαunoςcopia◁galaxies 05:11, 31 August 2010 (UTC)
- Thanks for both responses. From what I've heard from owners of hybrids, they're somewhat of a sham. I wouldn't consider them "far superior" by any means. I was hoping someone might know if there are plans in the works to eliminate the internal combustion engine entirely. I just feel like it's 2010 and we're still stuck in the 40s or something. – Kerαunoςcopia◁galaxies 06:53, 31 August 2010 (UTC)
- Battery electric vehicles can be extremely efficient if the batteries are charged by some sustainable source such as solar or wind power. But if the batteries are charged from the mains supply that same efficiency will never be available because at the source is a heat engine of some sort. It depends to a large degree on what you have in mind when looking for improvements. For example, are you looking for improved thermal efficiency and are willing to sacrifice in the area of capital cost? Or are you looking for reduced greenhouse emissions and are willing to contemplate increased nuclear waste? Or are you looking for reduced weight and are willing to sacrifice in the areas of capital cost, thermal efficiency and greenhouse emissions?
- When designers go looking for improvements they need to know the criteria for determining merit. Similarly it would be good to define some criteria for determining merit here. Dolphin (t) 07:29, 31 August 2010 (UTC)
- Battery electric vehicles are just as efficient when the batteries are charged for ANY source. Although coal and petroleum-fired generation plants pollute, they are still much better than having lots of IC-engines since the former are concentrated sources and can thus their pollutants be more easily controlled and contained. -- Sjschen (talk) 14:41, 31 August 2010 (UTC)
- Thanks for both responses. From what I've heard from owners of hybrids, they're somewhat of a sham. I wouldn't consider them "far superior" by any means. I was hoping someone might know if there are plans in the works to eliminate the internal combustion engine entirely. I just feel like it's 2010 and we're still stuck in the 40s or something. – Kerαunoςcopia◁galaxies 06:53, 31 August 2010 (UTC)
- If you compare car engines from 40 years ago, they have improved a lot, especially in the power they can make, and reduction in noxious emissions. Graeme Bartlett (talk) 11:38, 31 August 2010 (UTC)
- Are you asking where you flying car is? -- ToET 14:18, 31 August 2010 (UTC)
Secondly, as others have pointed out, there are hard theoretical limits to the efficiency of heat engines. Also, there aren't many other readily available energy storage systems with the 'energy density' of gasoline. Over the years, people have made all-electric cars, hydrogen cars, pneumatic cars, clockwork cars, propane powered cars, steam-powered (wood/coal/oil fuelled) cars, cars that ran on chemically treated sawdust, etc...but none of them have enough energy density to compete with gasoline. So unless the general public are prepared to live with less range/acceleration/interior-space or less weight (which probably means less safety equipment) - there isn't a whole lot that can displace gasoline until we have laws to force a change - or until it becomes so seriously un-cool to drive a gasoline powered car that nobody will do it anymore.
Thirdly, a lot of the problem is with infrastructure. The technology for hydrogen powered cars already exists. There are many working prototypes of hydrogen powered cars and they work pretty well. But if there is nowhere within 20 miles of my home and/or office that sells hydrogen in the bulk and with the filling convenience that I need, I can't buy a hydrogen car. This produces a chicken and egg situation - there are almost no hydrogen filling stations in the world - so there is no market for hydrogen cars - so there is no incentive to build the filling stations.
Breaking the infrastructure problem is something that can be solved with electric cars - electrical outlets are everywhere! But electric cars don't solve the energy density problems - so you're likely to be stuck with 100 mile(ish) range or (vastly overrated) hybrids until some truly magical battery technology comes along.
Right now, there are ridiculous legal restrictions that prevent some of the technology we do have from being used! I drive a MINI Cooper - and in Europe there is a version that automatically cuts the engine when you stop the car - and then when you pull away again, starts rolling the car forwards using the starter motor rather than immediately restarting the engine. Only when you reach a certain speed (10mph or so) or if the battery starts to run low, does the engine actually start running. This is a ridiculously simple thing to do - it's hardly more than a software change - but it means that in stop/go traffic, you have an electric car. It could be retro-fitted onto most modern cars - and would cost almost nothing to do. However, it's illegal in the USA! So my car is perfectly capable of doing this - but prevented from actually doing it by a software change they had to put in to meet US regulations. Aaaarrrggghhhhh!!!!
SteveBaker (talk) 18:58, 31 August 2010 (UTC)
- (Only partly a reply to Steve.) An article I have read puts an emissions rating of about 100g/km on electical vehicles, based on the way the United Kingdom generates energy. On the development front, Volkswagon's "L1", an internal-conbustion machine, gets 39g/km, or 180 miles per gallon. It's not quite your average car, however, but you can't say they're not trying. On the more achievable side, the article (quoting Richard Parry-Jones) suggests that cars running at about 70g/km should be mainstream by 2025. By comparison, the average UK car (and that includes what Americans would call "SUVs", and cars more common here) gets about 150g/km, it says. I think that's about 30 MPG, but I'm not sure (it would depend on other factors, I would imagine). - Jarry1250 [Humorous? Discuss.] 20:14, 31 August 2010 (UTC)
- (ec - also only a part-way reply to the above): as long as the United States produces most of its electricity using Coal and Natural gas ((see this Department of Energy table for details), switching to Electric cars will actually increase the carbon footprint per each mile traveled. (Coal is a much dirtier fuel than petroleum in many ways). So if the objective is to reduce greenhouse gas consumption, electric cars won't do this - what they will do is break down the dependence on petroleum. There are many reasons to make this transition; but it is not accurate to say that carbon emissions would be lower. Nimur (talk) 20:20, 31 August 2010 (UTC)
- I think you're missing the point though. Cars are fairly long-lived things. Cars that are 10 years old are still on the road. While it's obviously important to get fossil fuel power generation switched over to wind/solar/wave/hydro/nuclear - we shouldn't wait for that to happen before we start to switch the world's fleet of cars & trucks over to electrical power. In fact, it can be argued that the additional profits made available to power generation companies would hasten their ability to invest in new technology. Another argument (which I'm a bit dubious about) is that by centralizing the pollution to one large facility (as opposed to a bazillion separate tiny ones) would make it easier to capture the pollution and fix it. However, that has not historically been the case - cars have cleaned up their emissions considerably over the last few decades - power plants, much less so.
- As for your claim that "Coal is a much dirtier fuel than petroleum in many ways" - well, yes, perhaps in "many" ways - but not in the one very specific way that most concerns us...CO2 production. A 4-stroke steel car engine has a maximum possible theoretical efficiency of 37% - and most cars manage around 18% if 'normally aspirated' and 20% if supercharged or turbocharged. Contrast that with coal fired power stations which actually achieve 33% and natural gas stations which get about 50%. The trouble is that it's not that simple. It costs energy refine oil into gasoline - it takes more energy to haul it to gas stations which are widely and inconveniently scattered. It takes less energy to get raw coal onto a 2 mile long train and haul it to just one destination - which is probably situated conveniently close to the mine.
- But coal is more of a nuisance than just the CO2 - all of the ash piles (which are more radioactive than the vast majority of the waste produced by nuclear power!) - the damage they do to the water table, the sulphur compounds they generate into the air...lots and LOTS of nasty side-effects.
- But for sure, we need to start switching our cars over to electricity in the hope that we'll be ready when clean electricity DOES start appearing.
- SteveBaker (talk) 22:08, 31 August 2010 (UTC)
- Well, the way I see it, even if electric cars initially are fueled by coal, there is the probable eventuality of switching to nuclear energy or geothermal or wind some other source of energy. In other words, electric vehicles have an "exit strategy" from the polluting fossil-fuel base. So, they are advantageous for that reason. But in the short term at least, petroleum is a more efficient fuel - economically, thermodynamically, and so on. I think these issues all elucidate the trouble with the OP's original question: "progress" is very hard to define, because it depends on the timescales involved and the ultimate objective we are aiming at. Nimur (talk) 01:48, 1 September 2010 (UTC)
Vision at the speed of light
This is more fiction than real world science but I'm curious none the less...If it were possible for a person to move at the speed of light (without any other physiological changes than just whatever gave them the ability to do this), how would their vision be affected? After all, we see because light hits our retinas but what if we're moving at that speed. Then would we only see what was directly in front of us since those photons would be going directly into our eyes? Dismas|(talk) 07:56, 31 August 2010 (UTC)
At light speed, Length contraction makes everything have zero length. Any photon you encounter (that would let you see in the first place) would be blue-shifted to infinite energy, or red-shifted to zero energy. Human eyes can detect neither, so you wouldn't see anything. 157.193.175.207 (talk) 08:01, 31 August 2010 (UTC)
- Two photons colliding head-on do so with infinite(x2?) energy...?
- You should start by reading through the Special relativity article, probably, Dismas. Wikiscient (talk) 08:11, 31 August 2010 (UTC)
- The time issue is nasty. The instant you hit lightspeed - the entire universe would be over for you. Whatever ultimate fate befalls the universe is where you are. The incoming energy issue is also fatal - you get hit by an infinite number of photons and each has infinite energy...that'll ruin your entire day right there! The universe would have contracted to zero dimensions along your line of flight - so you'd be everywhere in the universe at once - which would guarantee you'd smack into a star or something...at the speed of light! (Ouch!) Everything you can possibly imagine about this is utterly and instantly fatal. Fortunately, it's impossible, so this is one less thing to worry about! SteveBaker (talk) 18:36, 31 August 2010 (UTC)
- That explanation of neutrino oscillation is incorrect. A particle of zero mass won't oscillate into some other flavor, but neither will a particle of any definite mass. There are three neutrinos with well defined masses that don't oscillate into each other (ν1, ν2, ν3). The three traditional named neutrinos (νe, νμ, ντ) are mixtures of those and do oscillate into each other, which means that the mixtures have no definite mass, which means that ν1, ν2, and ν3 don't all have the same mass. It follows that they don't all have mass zero, but the value zero plays no special role in any of this. -- BenRG (talk) 22:19, 31 August 2010 (UTC)
- Hmm, OK, that's interesting, but just the same, doesn't it independently follow from zero proper time that there can be no oscillation? --Trovatore (talk) 22:29, 31 August 2010 (UTC)
- I don't think the universe is "over for you" when you hit lightspeed, in terms of time dilation. Remember, from your perspective it's the universe moving at lightspeed, and it is not moving forward in time. Of course, that infinitely blueshifted light may mean the universe is over for you in a more mundane way!
- There's a nice simulation video of the changes in angle as you accelerate toward lightspeed... somewhere... eventually all the light compresses toward a point. I didn't find that today. (But while looking I did find the most glorious crank theory of gravity I've ever seen, complete with a comparison of spin-2 graviton theory to Adolf Hitler... [1]) —Preceding unsigned comment added by Wnt (talk • contribs) 18:58, 1 September 2010
- No, you're missing the point. Take any two events along a Lightlike path; what's the interval between them? It's zero. And that's the same as the proper time experienced by an observer along that path. So such an observer does not experience time passing at all.
- The bottom line is that there is no such thing as an inertial frame of reference traveling at lightspeed. You can't set up such a coordinate system at all; you'd have to divide by zero. --Trovatore (talk) 19:11, 1 September 2010 (UTC)
- Hmmm... I did miss some points. An observer "at lightspeed", i.e. in the limit as he approaches lightspeed, should perceive a vast swath of the universe flatten down to a two-dimensional disk moving past him at the speed of light (Lorentz contraction). But time for that seems frozen. The key thing that we're neglecting is that reaching lightspeed involves acceleration, and lots of it. From the perspective of outside observers the acceleration to speed up that last little bit is very small, but the mass is enormous, and so an enormous amount of energy is involved. From the perspective of someone traveling "near" lightspeed, adding another 0.9c involves a tremendous amount of acceleration - and of course, even an object moving relative to him at 0.9c is still slower than light in every frame. So we're talking about just incredible amounts of acceleration, over and over. This is discussed a bit in [[2]], but the formula they give there "t' = t(1 + Φ / c2)", with Φ = gh, confuses me - there's a unitless "1", and it seems like the clock-ticks could go negative for objects behind the accelerating observer.
- I am not well-versed in general relativity, but I think that the gist is that you can't really just reach the speed of light and your life is over. Rather, you can burn your Star Drive at full blast and watch time gradually slip away for as long as you like, never reaching lightspeed. Wnt (talk) 00:56, 2 September 2010 (UTC)
- Hmm, OK, that's interesting, but just the same, doesn't it independently follow from zero proper time that there can be no oscillation? --Trovatore (talk) 22:29, 31 August 2010 (UTC)
Direction of Earth's Revolution
Suppose one were "above" the plane of the solar system, such that, when looking at the Earth, one saw primarily the northern hemisphere. From this perspective, would the Earth appear to revolve clockwise or counterclockwise about the sun? —Preceding unsigned comment added by 203.97.79.114 (talk) 11:17, 31 August 2010 (UTC)- Earth's rotation says counter-clockwise. Dolphin (t) 11:23, 31 August 2010 (UTC)
- (ec)Just imagine if you are looking south from the north, the earth is rotating towards the east, which means it will go anticlockwise. Graeme Bartlett (talk) 11:25, 31 August 2010 (UTC)
- I'm afraid you're not answering the question I asked. You've both told me about the Earth's rotation about its own axis; I'm asking about its revolution about the sun. —Preceding unsigned comment added by 203.97.79.114 (talk) 11:44, 31 August 2010 (UTC)
- Sorry about that. Earth's orbit says counter-clockwise. Dolphin (t) 11:48, 31 August 2010 (UTC)
- Great, thank you. —Preceding unsigned comment added by 203.97.79.114 (talk) 11:49, 31 August 2010 (UTC)
- Interestingly, Earth's rotation does answer it though, in the very first article section, with two diagrams including one from with the questioner's actual perspective. DMacks (talk) 11:50, 31 August 2010 (UTC)
- I would argue that the first diagram doesn't, since there's no way to tell if we're viewing the day side or the night side of the Earth. The second does, though. —Preceding unsigned comment added by 203.97.79.114 (talk) 12:00, 31 August 2010 (UTC)
- Sure enough! The image's own description page has it ("Earth is shown as viewed from the Sun; the orbit direction is counter-clockwise (to the left)") but the caption on the image in the article
doesdid not. Fixed, good catch! DMacks (talk) 12:12, 31 August 2010 (UTC)- Your caption change didn't last. -- ToET 14:08, 31 August 2010 (UTC)
- Sure enough! The image's own description page has it ("Earth is shown as viewed from the Sun; the orbit direction is counter-clockwise (to the left)") but the caption on the image in the article
- I would argue that the first diagram doesn't, since there's no way to tell if we're viewing the day side or the night side of the Earth. The second does, though. —Preceding unsigned comment added by 203.97.79.114 (talk) 12:00, 31 August 2010 (UTC)
- Sorry about that. Earth's orbit says counter-clockwise. Dolphin (t) 11:48, 31 August 2010 (UTC)
- I'm afraid you're not answering the question I asked. You've both told me about the Earth's rotation about its own axis; I'm asking about its revolution about the sun. —Preceding unsigned comment added by 203.97.79.114 (talk) 11:44, 31 August 2010 (UTC)
- (ec)Just imagine if you are looking south from the north, the earth is rotating towards the east, which means it will go anticlockwise. Graeme Bartlett (talk) 11:25, 31 August 2010 (UTC)
- Note also that the Moon rotates and revolves the same way as well (counter clockwise when viewed from well above the earth's north pole). See Orbit of the Moon. -- ToET 14:08, 31 August 2010 (UTC)
- There is of course nothing except our own interpretation that makes north "up" and south "down", it would be just as valid to call the Antarctic "up", it's purely because theres people in the northern hemisphere who sit more on top of the globe then below it. However it's so ingrained on every single map and every globe that even I in Australia struggle to make the switch just in my head. Vespine (talk) 23:56, 31 August 2010 (UTC)
"Reverse osmosis"
Should "Reverse osmosis" really be called "reverse osmosis," as if it's the reverse of osmosis? Osmosis is the movement of water across a semipermeable membrane from an area of high water potential to an area of low water potential. If I've understood reverse osmosis, all they are doing is increasing the pressure on one side of the membrane with the "dirty" water, so that the water moves across to the clean side. But since Water potential is already defined in terms of pressure, among other things, the water is still just moving from an area of high water potential to an area of low watert potential. So it's still just regular ol' osmosis, right? 76.24.222.22 (talk) 11:37, 31 August 2010 (UTC)- Yep, thermodynamically it's just regular ol' osmosis: as you say, the Chemical potential of the water is increased on the "dirty" side of the membrane so that it's higher than the chemical potential on the "clean" side. It's called "reverse" osmosis because most people think of osmosis as water moving the other way, so that solute concentrations on the two sides of the membrane are equal, but that is just a limited conception of osmosis. Physchim62 (talk) 12:48, 31 August 2010 (UTC)
- Alternatively, osmosis is defined as the movement of solvent from the low concentration side to the high concentration, then the opposite is correctly called reverse osmosis. Dbfirs 17:51, 31 August 2010 (UTC)
I have a theory on what the crystal skulls actually are
i would like someone to contact me about the crystal skulls it may be that its a far feched theory but i believe they hold some sort of message could you please contact me asap as i believe i know the key to opening this infomation.. thankyou contact me on (e-mail address removed) —Preceding unsigned comment added by 86.139.245.30 (talk) 12:23, 31 August 2010 (UTC)- Wikipedia has nothing to do with the Crystal skulls. You should read the article to find someone who may be interested. -- kainaw™ 12:28, 31 August 2010 (UTC)
- We don't contact people by e-mail, and you should not post your e-mail address here. I have removed it, to combat spam. --Mr.98 (talk) 13:10, 31 August 2010 (UTC)
- Wikipedia is specifically not interested in ideas you have just dreamed up (see Wikipedia:NOR) - this reference desk is for asking questions and getting answers - not for recruiting people to listen to whatever ideas you've had. If you had a specific question about the Crystal skulls that our article was unable to answer - then it would be appropriate to ask it here. SteveBaker (talk) 18:28, 31 August 2010 (UTC)
- His email address is still available in the history. Aren't these supposed to be permanently removed? I'm just curious. – Kerαunoςcopia◁galaxies 18:57, 31 August 2010 (UTC)
- Please tell me how to find it ! Jon Ascton (talk) 16:17, 1 September 2010 (UTC)
- Permanently removing ANYTHING from Wikipedia is amazingly difficult. Even an admin can't completely eradicate data from the system - it takes yet higher levels of system privilege to do that. Here on the ref.desks we seem to have evolved a system whereby we simply remove the email address from the current version and leave it in the history. IMHO, that's a waste of time - if our OP's wish to leave their email addresses and risk getting spammed - that's their own call. I leave my email address exposed on my User page and I've not noticed any change in the volume of spam I get as a result. Anyway - what really matters is that we're not going to email answers to people - much less get involved in some kind of private debate. SteveBaker (talk) 21:46, 31 August 2010 (UTC)
- His email address is still available in the history. Aren't these supposed to be permanently removed? I'm just curious. – Kerαunoςcopia◁galaxies 18:57, 31 August 2010 (UTC)
Eye Surgery
Strictly speaking how safe is the surgery that gets you rid of spectacles ? Jon Ascton (talk) 14:09, 31 August 2010 (UTC)- See Refractive surgery#Risks -- kainaw™ 14:11, 31 August 2010 (UTC)
- This section doesn't mention that certain measure may be OK only for spherical glass - problem and not for cylindrical
- Also if you want a lot of angry, vocal testimonials from unfortunate people who have had permanent eye damage from the surgery, google lasik disaster or the like. Comet Tuttle (talk) 16:28, 31 August 2010 (UTC)
- Someone deleted this question as a request for "medical advice". However, general discussion of a medical procedure, including its risks, is well within the scientific purview of Wikipedia - it's no different than the question above about whether you can be electrocuted by standing on a 220V plate. As always, be disclaimed that we can't tell you what to do. Wnt (talk) 04:15, 1 September 2010 (UTC)
- Is it a myth or a fact that it works only on cases with spherical lens and not cylindrical lenses ?
- Someone deleted this question as a request for "medical advice". However, general discussion of a medical procedure, including its risks, is well within the scientific purview of Wikipedia - it's no different than the question above about whether you can be electrocuted by standing on a 220V plate. As always, be disclaimed that we can't tell you what to do. Wnt (talk) 04:15, 1 September 2010 (UTC)
At North Pole
If I stand with a magnetic compass exactly on the North Pole, what direction will it point ? Downwards ? Jon Ascton (talk) 14:31, 31 August 2010 (UTC)- If you hold it sideways then yes, it will point straight down. -- kainaw™ 14:35, 31 August 2010 (UTC)
- Wouldn't it just point to the North Magnetic Pole? Deor (talk) 14:38, 31 August 2010 (UTC)
- Well, slightly to that side of vertically down, if by North Pole you mean the point of intersection of the meridians. Incidentally, in scientific terms, the North Magnetic Pole is really a south pole, which is why the "north" of the magnetized needle is attracted to it. At some unknown time in the (arguably fairly near) future, it will probably flip and become a true north pole. Dbfirs 17:45, 31 August 2010 (UTC)
- Actullay if you take a compass that's constructed for use by the equator and use it in for example Sweden, the needle would point a little downwards scraping the compass floor effectively making it less usable. Instead they come with a small counterweight adjusted for the latitude where it's intended to be used, so the needle will stay horizontal. The needle will be attracted more and more downwards as you get clooser to the north pole. Moberg (talk) 14:41, 31 August 2010 (UTC)
- There are "three-dimensional" compasses if that's the right term, they should exactly point downward ?
- Historically, this vertical component of Earth's local magnetic field – with the delightful name Magnetic dip – has been measured by using a separate instrument called a Dip circle or dipping needle. TenOfAllTrades(talk) 15:29, 31 August 2010 (UTC)
- Right - but a dip circle is really just a sideways compass. They take some trouble with the bearings - but aside from that, it's nothing special. If you imagine a "3D compass" (maybe a needle mounted on a ball-and-socket joint or something) then as you'd approach the magnetic north pole, the needle would continue to point towards it - but more and more weakly - and start to dip downwards more and more strongly. Right at the pole, the 'pointing North' force has dropped to zero and the thing would point straight down at your feet. SteveBaker (talk) 18:24, 31 August 2010 (UTC)
- I think the above explains it very well, but it may be worth just mentioning that that there isn't really a single "point" where you are exactly at the north pole. Well there is but you'd be hard pressed to figure out you are there if all you had was a compass. If you look at the diagrams at Earth's magnetic field it becomes easier to see that it's more of a north "zone" rather then a point. It's not like your compass is pointing to your front, then you take a couple of steps and all of a sudden it's pointing backwards, or even worse, spins like a top, like I've seen depicted on more then one occasion. Even with a special compass like Moberg suggests, when you are in the "zone" walking in any direction would not make much noticeable difference. To really work out if you are right on the north pole, I think you'd probably have to plot several points around a fairly substantial area and then derive an average. Vespine (talk) 00:31, 1 September 2010 (UTC)
- Yes, indeed. The amount of force rotating the needle in a horizontal plane drops off dramatically - even at 100 miles from the magnetic pole. You need an increasingly sensitive compass at those latitudes to get any reading whatever. The dip angle is more useful though - but (as you say) it's still not exactly sensitive enough for accurate navigation. There are lots of additional complications - for one, the earth isn't a perfect Dipole and the magnetic poles wander around a lot from year to year. Right now, the magnetic south pole is out in the ocean somewhere - it's nowhere even close to the true pole about which the planet rotates.
- But the ambiguity in our latitude/longitude/heading system at the poles is very real. There is an old puzzle that goes:
- Q: A hunter leaves his tent, walks one mile south, one mile east, shoots a bear and then walks one mile north to arrive back at his tent...what color was the bear?
- A: White.
- Most people think that the North pole is the only place that this story would work - but actually, there are a bunch of places near the South pole where the story would work just as well...except that there are no bears there. It takes a bit of a mental stretch to visualize where those places are though! The easiest ones to imagine are points that are one mile North of the line of longitude that wraps around the south pole and is exactly one mile long - so in walking east for one mile, the man makes a complete lap of the pole and ends up following his own footsteps back for another mile, heading north. However, there is another place that's one mile north of the line of longitude that's a half mile long...then the man makes two laps of the pole as he walks east before returning to his tent. SteveBaker (talk) 04:38, 1 September 2010 (UTC)
- I think the above explains it very well, but it may be worth just mentioning that that there isn't really a single "point" where you are exactly at the north pole. Well there is but you'd be hard pressed to figure out you are there if all you had was a compass. If you look at the diagrams at Earth's magnetic field it becomes easier to see that it's more of a north "zone" rather then a point. It's not like your compass is pointing to your front, then you take a couple of steps and all of a sudden it's pointing backwards, or even worse, spins like a top, like I've seen depicted on more then one occasion. Even with a special compass like Moberg suggests, when you are in the "zone" walking in any direction would not make much noticeable difference. To really work out if you are right on the north pole, I think you'd probably have to plot several points around a fairly substantial area and then derive an average. Vespine (talk) 00:31, 1 September 2010 (UTC)
- Right - but a dip circle is really just a sideways compass. They take some trouble with the bearings - but aside from that, it's nothing special. If you imagine a "3D compass" (maybe a needle mounted on a ball-and-socket joint or something) then as you'd approach the magnetic north pole, the needle would continue to point towards it - but more and more weakly - and start to dip downwards more and more strongly. Right at the pole, the 'pointing North' force has dropped to zero and the thing would point straight down at your feet. SteveBaker (talk) 18:24, 31 August 2010 (UTC)
- Historically, this vertical component of Earth's local magnetic field – with the delightful name Magnetic dip – has been measured by using a separate instrument called a Dip circle or dipping needle. TenOfAllTrades(talk) 15:29, 31 August 2010 (UTC)
- There are "three-dimensional" compasses if that's the right term, they should exactly point downward ?
- Wouldn't it just point to the North Magnetic Pole? Deor (talk) 14:38, 31 August 2010 (UTC)
- In case you asking about the Geographic North Pole, then at that location a compass will point towards the Magnetic North Pole (and also downward). Of course, if you are standing at the geographic pole, then it will be to your South since all directions from there are South by definition. Dragons flight (talk) 05:03, 1 September 2010 (UTC)
- ...which of course would be very odd. Your compass would (weakly) point 'North' - and the magnetic pole would be to your south! SteveBaker (talk) 12:26, 1 September 2010 (UTC)
- "Weakly"? See Geomagnetic field#Field characteristics. And it would point south towards magnetic North from the geographic pole. Wikiscient (talk) 13:36, 1 September 2010 (UTC)
- ...which of course would be very odd. Your compass would (weakly) point 'North' - and the magnetic pole would be to your south! SteveBaker (talk) 12:26, 1 September 2010 (UTC)
DIET PILL OVERDOSE
Hello,Wikipedians I was wondering what happens when a person overdoses on diet pills? Thank You and Have a great day. —Preceding unsigned comment added by 173.56.147.239 (talk) 15:27, 31 August 2010 (UTC)- A warning in advance...we can't give medical advice here. That said, we do have an article on Anti-obesity medication, which covers a big range of drugs. Find the one you're interested in on the list, click its article and see if it has overdose information on the page. You'd have to be more specific with exactly what drug you're interested in to get a more detailed answer. Vimescarrot (talk) 15:56, 31 August 2010 (UTC)
- You should never overdose drugs... that's why they set doses! --Chemicalinterest (talk) 16:21, 31 August 2010 (UTC)
- The hazards of overdosing on individual drugs will vary depending on the drug. Members of a class of drugs such as "diet pill" will not necessarily have the same, or even similar, hazards. -- Ed (Edgar181) 19:44, 31 August 2010 (UTC)
How To Pronounce "Feynman"
Sorry if this question is a bit trivial, but I couldn't find anyone pronouncing his name. Even his online lectures have edited out the start, where he presumably introduces himself. My questionn is, quite simply, after reading Surely You're joking and starting on the Feynman Lectures on Physics (I need to improve my calculus skills), it struck me that I don't know how to pronounce his name, having seen it only in print. I had a look at the article, but couldn't make head 'nor tail of that IPA stuff. Two options presented themselves to me: "fine-man", or "fain-man" (Fain rhyming with vain). In case it matters, I would pronounce it with an english accent, living as I do in England. Thanks very much.--HarmoniousMembrane (talk) 16:01, 31 August 2010 (UTC)- FINE-man (stress on the first syllable). Physchim62 (talk) 16:08, 31 August 2010 (UTC)
- Actually FINE-munn is more like it, I believe. Looie496 (talk) 16:17, 31 August 2010 (UTC)
- You're quite correct. Indeed, carefully listening to this video to see how he pronounces that semi-vowel, I would write it FINE-muhnn (as you might expect from someone from New York). But I'm a native speaker of British English (of the Northern English variety), so pronouncing non-stressed "man" as "munn" is second nature to me ;) Physchim62 (talk) 23:18, 31 August 2010 (UTC)
- Actually FINE-munn is more like it, I believe. Looie496 (talk) 16:17, 31 August 2010 (UTC)
- If you use Firefox, you might consider this Greasemonkey plugin which translates IPA into "B as in Boy": [3]. --Sean 17:34, 31 August 2010 (UTC)
- Thanks for that link Sean, I do indeed use Firefox, and that script is getting installed right now!--HarmoniousMembrane (talk) 21:27, 31 August 2010 (UTC)
- Sadly, I find that script fails to read the 'Feynman' IPA: it doesn't give anything for /a/ and fails to read /aɪ/ as a diphthong :( A shame, since it's a good idea. 86.161.108.172 (talk) 21:53, 31 August 2010 (UTC)
- That is unfortunate. It definitely needs some love as I haven't found it to be useful for non-English IPA at all. Still better than nothing, though, IMO. --Sean 18:26, 1 September 2010 (UTC)
- FYI, I've fixed this bug and reported it to the developer. See here if you want to update your local copy of the script. --Sean 19:15, 1 September 2010 (UTC)
- Yay! Thanks, worked well. 86.161.108.172 (talk) 20:47, 1 September 2010 (UTC)
Number of boobies
Did humans evolve from something with more nipples, or did cats evolve from something with fewer nipples, or did they both evolve nipples independently from a mammal that didn't use nipples, like a platypus? —Preceding unsigned comment added by 174.91.10.238 (talk) 16:40, 31 August 2010 (UTC)- As humans are thought to have descended from a small shrew like critter mammalian line (Epitheria), it is very possible. Even today, some people are born with Supernumerary nipples.--Aspro (talk) 17:20, 31 August 2010 (UTC)
- Humans and cats almost certainly didn't develop nipples independently; they are both Eutherian mammals. However their evolutionary histories split around 100 million years ago (humans belong to Euarchontoglires, cats to Laurasiatheria), so there was a lot of time for differences to develop. Looie496 (talk) 17:40, 31 August 2010 (UTC)
- Re-reading, I think the question has not been clearly answered yet, especially as two different taxonomies have been used which might confuse. So here is some more:
- Fossil records suggest that the platypus, cats and man derived originally from the Eutherian group. A new group diverged away from this when the modified sweat glands (that produced the proto-milk) evolved into clearly defined nipples. Palaeontologist have named this group Epitheria (but perhaps not for this reason alone). Cats and man came from this later group which divided several more times. Fossil evidence further suggests that, the animal from which man evolved from was quite small. Evolution appears to disfavour small litters in small animals and so it is thought likely by some that these animals would have at least one pair of nipples in order to suckle larger litters. However, by the time they had split off again and finaly evolved into primates the number had been reduced to one pair and single births. Fossils do not usually record soft tissue so the actual stage of evolution that this happened can only be guesstimated at. So, it is quite likely that originally several sets of nipples evolved all at once in the common ancestor of 'human and cat' and then reduced down to the one pair in man today.--Aspro (talk) 20:23, 31 August 2010 (UTC)
- So in short, going from little furry thing to big primate means smaller litters, which means you don't need as many nipples. Thanks. --174.91.10.238 (talk) 03:06, 1 September 2010 (UTC)
- That all makes sense except the bit about the platypus, which as a Monotreme doesn't belong with the others. Looie496 (talk) 22:33, 31 August 2010 (UTC)
- You might be right, as I first did this before man first walked upon the surface of the moon, and jeans where something one wore... and my memory is going! Which taxonomy are we taking about? Fossil evidence is dependant on morphology. Looking at the genes and their occurrence in other animals don't over lap exactly with fossil evidence. The two taxonomies don't yet match perfectly (but they could go on to explain horizontal transmigrations and other esoteric theories). The OP asked a simple question and I think we have answered that now. --Aspro (talk) 23:16, 31 August 2010 (UTC)
- The sub section: Fossil-based family tree of placental mammals shows the palaeontological tree. It might come down to tectonics and the geological dates of continental separation. Which group does the platypus not belong to? Molecular phylogenetics however, cannot state, what they state as all 'fact', as they have not a shred of hard evidence (i.e. fossils). Modern mammal (aboriginal man) only arrived 60,000 years ago. --Aspro (talk) 23:57, 31 August 2010 (UTC)
- The one problem with doing it by tectonics is figuring out how the opossum managed to get all the way to the Americas. Unless it was already there before all of the placental mammals showed up. --174.91.10.238 (talk) 03:06, 1 September 2010 (UTC)
- Marsupials are now thought to have developed first in South America, probably after it had split off from Africa (in the breakup of Gondwana) but while it was still connected to Antarctica and Australia. The ones in Antarctica have vanished for obvious reasons. Opossums, and other South American mammals such as armadillos and sloths, did not reach North America until the land bridge opened around 10 million years ago. Looie496 (talk) 04:12, 1 September 2010 (UTC)
- The platypus is not a placental mammal, it lays eggs. Monotremes are generally believed to have branched off at the earliest node that has surviving offshoots, earlier even than the branching between placentals and marsupials. Looie496 (talk) 03:57, 1 September 2010 (UTC)
- The one problem with doing it by tectonics is figuring out how the opossum managed to get all the way to the Americas. Unless it was already there before all of the placental mammals showed up. --174.91.10.238 (talk) 03:06, 1 September 2010 (UTC)
- The sub section: Fossil-based family tree of placental mammals shows the palaeontological tree. It might come down to tectonics and the geological dates of continental separation. Which group does the platypus not belong to? Molecular phylogenetics however, cannot state, what they state as all 'fact', as they have not a shred of hard evidence (i.e. fossils). Modern mammal (aboriginal man) only arrived 60,000 years ago. --Aspro (talk) 23:57, 31 August 2010 (UTC)
- You might be right, as I first did this before man first walked upon the surface of the moon, and jeans where something one wore... and my memory is going! Which taxonomy are we taking about? Fossil evidence is dependant on morphology. Looking at the genes and their occurrence in other animals don't over lap exactly with fossil evidence. The two taxonomies don't yet match perfectly (but they could go on to explain horizontal transmigrations and other esoteric theories). The OP asked a simple question and I think we have answered that now. --Aspro (talk) 23:16, 31 August 2010 (UTC)
- That all makes sense except the bit about the platypus, which as a Monotreme doesn't belong with the others. Looie496 (talk) 22:33, 31 August 2010 (UTC)
- Actually, a question that has always interested me is when breast tissue migrated to the chest. in every non-primate I can think of (including most monkeys) nipples are situated on the belly, and often (as with cows) on the lower parts of the belly - on humans, chimps, and gorillas, though, they are placed over the rib cage. I can see the evolutionary advantage of this (allowing an infant to be fed while held in the arms, which makes it possible to walk and feed a child at the same time), I just don't know where the evolutionary spit for it lies. --Ludwigs2 22:32, 31 August 2010 (UTC)
- The article Nipple claims that humans develop additional nipples that regress during fetal development. Unfortunately it provides no source. I found this paper, which examines tissue from uncertainly dated 14-18 week old fetuses, and finds no evidence of milk line segmentation (barely of the milk line at all). But they are looking too late - mostly, they complain about lack of availability of fetal samples. I'd hoped that other countries wouldn't have this ethical notion that it's OK to abort a fetus but not to look at the tissue afterward (at least, not if it could benefit scientific knowledge or human health...), so I wouldn't rule out that the Wikipedia article really did have some valid source for events around 4-6 weeks development. Wnt (talk) 19:06, 1 September 2010 (UTC)
- I was actually curious about Phylogony, not Ontogeny. --Ludwigs2 01:49, 2 September 2010 (UTC)
- Not really true. Consider a pig (and lots of other animals are similar) - see here for example. The nipples go pretty much right up to just below the front legs, similar to the location in humans. I'd also argue most (all?) primates have nipples up on the chest, not the belly - consider even something relatively distantly related like a lemur, those nipples are right up there. It's also wrong to say they're on the chest to allow "an infant to be fed while held in the arms, which makes it possible to walk and feed a child at the same time" - not many non-human primates could accomplish this, even our close cousins chimps and gorillas are knuckle-walkers, which would make this scenario almost impossible. Most likely the ancestor had multiple nipples, with the extra ones lost and just the upper ones retained. The small number of young raised by primates at any one time - usually one or two at most - would mean no need for the extra nipples and they would be selected against. Retention of the upper nipples would be favoured as it would allow for 'nursing' the young to feed while in dangerous positions like high up in trees. --jjron (talk) 14:28, 2 September 2010 (UTC)
- I was actually curious about Phylogony, not Ontogeny. --Ludwigs2 01:49, 2 September 2010 (UTC)
- The article Nipple claims that humans develop additional nipples that regress during fetal development. Unfortunately it provides no source. I found this paper, which examines tissue from uncertainly dated 14-18 week old fetuses, and finds no evidence of milk line segmentation (barely of the milk line at all). But they are looking too late - mostly, they complain about lack of availability of fetal samples. I'd hoped that other countries wouldn't have this ethical notion that it's OK to abort a fetus but not to look at the tissue afterward (at least, not if it could benefit scientific knowledge or human health...), so I wouldn't rule out that the Wikipedia article really did have some valid source for events around 4-6 weeks development. Wnt (talk) 19:06, 1 September 2010 (UTC)
- So in short, going from little furry thing to big primate means smaller litters, which means you don't need as many nipples. Thanks. --174.91.10.238 (talk) 03:06, 1 September 2010 (UTC)
- Re-reading, I think the question has not been clearly answered yet, especially as two different taxonomies have been used which might confuse. So here is some more:
- Humans and cats almost certainly didn't develop nipples independently; they are both Eutherian mammals. However their evolutionary histories split around 100 million years ago (humans belong to Euarchontoglires, cats to Laurasiatheria), so there was a lot of time for differences to develop. Looie496 (talk) 17:40, 31 August 2010 (UTC)
Sodium bicarbonate deodorant properties
I use Sodium bicarbonate as a deodorant. What makes it work? --Chemicalinterest (talk) 19:05, 31 August 2010 (UTC)- Sodium bicarbonate is a weak base that can react with some odor-causing acids in sweat (such as Butyric acid) to form non-volatile salts. -- Ed (Edgar181) 19:41, 31 August 2010 (UTC)
F5
Has an F5 tornado ever touched down in ireland and is it possible for one too touchdown here. --86.41.136.150 (talk) 20:54, 31 August 2010 (UTC)- Our List of F5 and EF5 tornadoes does not include Ireland; however, our List of European tornadoes and tornado outbreaks notes that Ireland was home to the first recorded European tornado. As such, I expect that it's possible, albeit unlikely, for an EF5 tornado to form in Ireland. — Lomn 21:21, 31 August 2010 (UTC)
- In the US there is a formal process to survey tornado damage and estimate intensity (managed by NOAA, I believe). Unless there is a similar process in Ireland, there may be know way of accurately knowing the intensity of most tornadoes in Ireland. Dragons flight (talk) 21:33, 31 August 2010 (UTC)
- Climatologically speaking there is very, very little chance that this will happen. Violent (F4-F5) tornadoes are rare outside of the United States, and this does not mention that strong tornadoes form that often in the UK or Ireland. Also, if my memory serves me correctly the only locations that have a tendency to suffer strong-violent (F2-F5) (relatively) frequently are the United States, Canada, Australia, Bangladesh, and parts of mainland Europe (don't take this at face value, my memory may be wrong). The list of European tornadoes says that the strongest British tornado is probably the London Tornado of 1091, which should give an idea of what strength Irish tornadoes could have. Ks0stm (T•C•G) 01:14, 1 September 2010 (UTC)
Binoculars - minimum focusing distance
How can the minimum distance for binoculars be calculated? —Preceding unsigned comment added by Kumalo (talk • contribs) 21:40, 31 August 2010 (UTC)- I don't think this can be worked out from a formula because it depends on how the focus mechanics are designed. Theoretically, to focus on something closer you'd just turn the focus knob more, however you'll hit a mechanical limit long before you hit a optical limit to how far you can turn the knob. Vespine (talk) 23:28, 31 August 2010 (UTC)
Cats' senses
hi. I asked this question as a follow up to a different question but nobody responded. How much do the acuity of the senses vary between house cats and wild cats (such as cougars, lions, tigers, etc.) and I read the article but I didn't understand how exactly a cat's vision is inferior to a humans in light. Are they nearsighted, farsighted? Or do they see blurrier? Or what? 76.229.235.27 (talk) 23:22, 31 August 2010 (UTC)- The Cat senses article says: "Testing indicates that a cat's vision is superior at night in comparison to humans, and inferior in daylight."
- "Night vision" in mammals mostly involves "Rod cells" in the Retina; cats have more of these Rod cells in their retina than humans do. But that means they have proportionally fewer Cone cells than humans, which are the cells in the retina that specialize in responding to relatively bright light. These cone cells are also more "tuned" to respond to color, detail, and rapidly changing images. So it is in those ways that cats have "inferior" bright-light vision than humans, because they are relatively specialized for seeing in low-light conditions. Wikiscient (talk) 07:19, 1 September 2010 (UTC)
September 2
Thrust vectoring
Does anyone know of a flat, rather than round, thrust vectoring system that can vector in the yaw besides the X-36? And does anyone have a picture of the X-36's thrust vectoring system? --The High Fin Sperm Whale 03:00, 2 September 2010 (UTC)Shrinking helium
In last Sunday's Ask Marilyn article, Marilyn vos Savant discussed helium escaping from balloons. I understand the microscopic porous nature of the balloon, but I'm skeptical of the following statement: "Helium contracts as the temperature drops, which allows gas to slip through the pores of a balloon more easily."I know that the gas as a whole would contract with decreasing temperature (assuming a constant pressure), but is this true at the atomic level? -- Tom N (tcncv) talk/contrib 04:39, 2 September 2010 (UTC)
- It's a complex process. When a gas contracts because of temperature dropping, the molecular density increases; that is there are more molecules per unit volume of the gas, which may mean more collisions with pores. Of course, as the temperature drops, so does Root mean square speed of the molecules, which may mean less collisions with the pores. Of course, under a first approximation (Ideal gas), these effects should exactly cancel. Since real gases behave slightly differently than ideal gasses, its quite more complex, and one effect may predominate over the other. The relevent discussions could be found in the articles Effusion and Graham's law, though the effusion article seems to lack some. --Jayron32 04:52, 2 September 2010 (UTC)
- Minor nitpick: you're talking about helium atoms; helium doesn't form molecules. --Anon, 04:08 UTC, September 3, 2010.
- Speaking in general terms, its tough to choose a term which readers will recognize, and which is a stand in for "atoms and/or molecules and/or other particles". Chemists use the term "moety" sometimes to mean this, but its not a term in widespread use. When speaking in general terms over the behavior of something like gases in general, given that there are about 7 gases which exist as lone atoms, and about 1 billion that exist as molecules, just using the term molecule is, statistically atleast, close enough. --Jayron32 04:41, 3 September 2010 (UTC)
- I know; in fact I just used "molecule" myself that way in answering another question, below. But on this question we're talking specifically about helium. No big deal. --Anon, 06:42 UTC, September 3, 2010.
- The rubber around the balloon also contracts, and presumably, so do the pores. The walls should actually be slightly thicker as the balloon contracts. Gas transmission rate through the balloon-wall is much more complicated than a simple application of the ideal-gas law. I'd stake my bet on an empirical measurement of gas escape rate as a function of temperature; there are so many relevant factors (gas thermal velocity; pore size; collision rate; rubber material properties, etc) that trying to model them from fundamental physics is unlikely to be accurate. Nimur (talk) 05:35, 2 September 2010 (UTC)
- Also, Helium is about as close to an ideal gas as you can really get, so ideal gas laws are pretty relevant. Googlemeister (talk) 13:05, 2 September 2010 (UTC)
Energy from pressure difference
How do you calculate energy from a pressure difference?For example a hurricane has an eye 100km by 1km high, so a volume of 1.6×10^11 cubic meters, and a pressure of, say, 950 millibars, compared to 1013 millibars for the air around it. How much energy is contained in that pressure difference? Ariel. (talk) 05:40, 2 September 2010 (UTC)
- You need a volume and a pressure to determine energy stored by a gas; and it simplifies if you assume an Isothermal process for the energy release. Nimur (talk) 20:19, 2 September 2010 (UTC)
- There is a discussion at Potential energy#Relation_between_potential_energy.2C_potential_and_force which, while it focuses more on gravity, does deal with the mathematical relationship between forces and potential energy, but not in a simple "Here's a nice equation to use to calculate this." --Jayron32 05:49, 2 September 2010 (UTC)
- Another related idea is Elastic potential energy#Elastic_Internal_Energy_in_Compressible_Gases_and_Liquids. Remember that the Gas constant can be expressed in Volume*Pressure OR as Energy, Joules and pascal*cubic meters are (I think) equivalent units. I think the relevent issue is that the potential energy is proportional to either PdV or VdP; that is under a constant pressure changes in volume represent a change in energy; while under a constant volume, pressure differential would be the relevent relationship to energy. So, I think (and I could be wrong here) that this is as simple as volume of the eye * pressure differental across the eyewall; corrected for units. Since m3*mbar is technically an energy unit, you could leave it as that, or you can do the dimmensional analysis, and change it to joules or kilojoules or whatever. --Jayron32 06:00, 2 September 2010 (UTC)
- Doing that gives me an energy of 1×10^15 joules (about a quarter of a megaton of TNT), which seems low (this says hurricanes release 6×10^14 J/second, and hurricanes can last at least 2 or 3 days on land). But I'm surprised that it doesn't depend on the density of the air. Wouldn't a heavier fluid contain more energy? Moving a given volume of water takes more energy than moving a given volume of air. Maybe not - I guess with a heavier fluid you need to move fewer atoms to produce a given pressure? Ariel. (talk) 06:07, 2 September 2010 (UTC)
- The actual masses of the particles are irrelevent for this particular calculation; pressure and temperature already account for mass in their inherant formulation. The pressure is merely the force acting on a surface; that force doesn't care whether its a smaller particle moving fast or a heavier particle moving slow; its the same force so its effect on the energy should be the same. Also, that potential energy you have is instantaneous potential, that is the energy of the storm right now Besides dissipating energy, a storm also accumulates energy over time; that 1E15 Joules of energy you just calculated is not the total energy availible to the storm, since it will continue to gather energy even over land. On the balance, the storm loses more energy than it gains over land, but that's only because the rate of dissipation is greater than the rate of accumulation; the rate of accumulation is not zero. --Jayron32 06:22, 2 September 2010 (UTC)
- I thought the rate of accumulation over land was zero since the energy source is latent heat of condensation of water. Ariel. (talk) 06:27, 2 September 2010 (UTC)
- Tropical cyclone#Mechanics and Tropical cyclogenesis discuss this in detail. There's even numbers in there. Yes, the primary source of energy is condensing water vapor. However, the process is far too complex to declare that this primary source of energy accounts for 100% of the energy in the storm... --Jayron32 06:34, 2 September 2010 (UTC)
- That page says "When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly." Seems to me that hurricanes must store energy somewhere else besides the pressure gradient, maybe in all the moisture they carry with them. Ariel. (talk) 06:39, 2 September 2010 (UTC)
- Again, that doesn't mean that the energy accumulation over land is zero, only that it is much smaller than the energy accumulation over water. The energy is stored in both the pressure gradient, and in the internal energy of the gasseous water molecules, as compared to the internal energy of liquid water. If you want to know ALL of that energy, you'd also need to know the temperature of the air in the defined volume; that temperature should equal the dew point (the air should be saturated) so you can then compare that to the vapor pressure of water at that temperature, which can then be used to find the partial pressure of the water vapor, which can be used to calculate the total mass (or moles, whatever) of water vapor in the air. You can then use that to calculate the energy differential between the gasseous and liquid water; i.e. the latent heat of vaporization. However, your question only dealt with the energy stored as the pressure gradient. --Jayron32 06:48, 2 September 2010 (UTC)
- Yes it did because I thought that was all of it. I'm going to try calculating the water energy tomorrow (unless someone wants to do it for me :) BTW thank you for the replies. Ariel. (talk) 06:56, 2 September 2010 (UTC)
- Another idea (just popped into my head); a third, probably non-negligible source of energy is Gravitational potential energy. After all, you just raised a HUGE mass of water rather high into the air, this height differential should itself be a possible source of potential energy. --Jayron32 07:00, 2 September 2010 (UTC)
- Indeed it is. This gravitational potential is extremely significant. It is responsible for things like flash-condensation - which you might know as a Lenticular cloud or a Mushroom cloud (things with real wide, flat-bottomed layer structures). As air masses convect and are forced to different altitudes by fluid-dynamics (e.g. by momentum and viscous forces), they are working against an energy gradient, and they must cool rapidly to account for this energy-change. Rapid temperature decreases will lead to a change of state, and vaporous water will condense. That can result in a flat-bottomed cloud - this represents a gravitational equipotential surface (perturbed by local changes in humidity and temperature); but you can often see very sharp, crisp "bottom layers" when this occurs. Nimur (talk) 20:15, 2 September 2010 (UTC)
- Another idea (just popped into my head); a third, probably non-negligible source of energy is Gravitational potential energy. After all, you just raised a HUGE mass of water rather high into the air, this height differential should itself be a possible source of potential energy. --Jayron32 07:00, 2 September 2010 (UTC)
- Yes it did because I thought that was all of it. I'm going to try calculating the water energy tomorrow (unless someone wants to do it for me :) BTW thank you for the replies. Ariel. (talk) 06:56, 2 September 2010 (UTC)
- Again, that doesn't mean that the energy accumulation over land is zero, only that it is much smaller than the energy accumulation over water. The energy is stored in both the pressure gradient, and in the internal energy of the gasseous water molecules, as compared to the internal energy of liquid water. If you want to know ALL of that energy, you'd also need to know the temperature of the air in the defined volume; that temperature should equal the dew point (the air should be saturated) so you can then compare that to the vapor pressure of water at that temperature, which can then be used to find the partial pressure of the water vapor, which can be used to calculate the total mass (or moles, whatever) of water vapor in the air. You can then use that to calculate the energy differential between the gasseous and liquid water; i.e. the latent heat of vaporization. However, your question only dealt with the energy stored as the pressure gradient. --Jayron32 06:48, 2 September 2010 (UTC)
- That page says "When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly." Seems to me that hurricanes must store energy somewhere else besides the pressure gradient, maybe in all the moisture they carry with them. Ariel. (talk) 06:39, 2 September 2010 (UTC)
- Tropical cyclone#Mechanics and Tropical cyclogenesis discuss this in detail. There's even numbers in there. Yes, the primary source of energy is condensing water vapor. However, the process is far too complex to declare that this primary source of energy accounts for 100% of the energy in the storm... --Jayron32 06:34, 2 September 2010 (UTC)
- I thought the rate of accumulation over land was zero since the energy source is latent heat of condensation of water. Ariel. (talk) 06:27, 2 September 2010 (UTC)
- The actual masses of the particles are irrelevent for this particular calculation; pressure and temperature already account for mass in their inherant formulation. The pressure is merely the force acting on a surface; that force doesn't care whether its a smaller particle moving fast or a heavier particle moving slow; its the same force so its effect on the energy should be the same. Also, that potential energy you have is instantaneous potential, that is the energy of the storm right now Besides dissipating energy, a storm also accumulates energy over time; that 1E15 Joules of energy you just calculated is not the total energy availible to the storm, since it will continue to gather energy even over land. On the balance, the storm loses more energy than it gains over land, but that's only because the rate of dissipation is greater than the rate of accumulation; the rate of accumulation is not zero. --Jayron32 06:22, 2 September 2010 (UTC)
- Doing that gives me an energy of 1×10^15 joules (about a quarter of a megaton of TNT), which seems low (this says hurricanes release 6×10^14 J/second, and hurricanes can last at least 2 or 3 days on land). But I'm surprised that it doesn't depend on the density of the air. Wouldn't a heavier fluid contain more energy? Moving a given volume of water takes more energy than moving a given volume of air. Maybe not - I guess with a heavier fluid you need to move fewer atoms to produce a given pressure? Ariel. (talk) 06:07, 2 September 2010 (UTC)
- Another related idea is Elastic potential energy#Elastic_Internal_Energy_in_Compressible_Gases_and_Liquids. Remember that the Gas constant can be expressed in Volume*Pressure OR as Energy, Joules and pascal*cubic meters are (I think) equivalent units. I think the relevent issue is that the potential energy is proportional to either PdV or VdP; that is under a constant pressure changes in volume represent a change in energy; while under a constant volume, pressure differential would be the relevent relationship to energy. So, I think (and I could be wrong here) that this is as simple as volume of the eye * pressure differental across the eyewall; corrected for units. Since m3*mbar is technically an energy unit, you could leave it as that, or you can do the dimmensional analysis, and change it to joules or kilojoules or whatever. --Jayron32 06:00, 2 September 2010 (UTC)
- Pressure-volume work is defined as the integral of
. So, to calculate the work capability of a system with a pressure gradient, you can assume the hurricane is a giant Carnot engine; the pressure gradient defines the limits of pressure in a Thermodynamic cycle; and the volume can be estimated based on geographic scale of the hurricane. If there is net energy influx from Solar radiation (or indirectly via ground or water re-radiation of heat), you can account for this by moving the adiabat. The work done (rather, the energy released by the hurricane), is the difference between two curves (just like any other heat engine). This work done is released as energy; it takes the form of kinetic energy of wind and water; as state-changes as water evaporates and re-precipitates; as changes to the temperature of massive volumes of air, water, and land, and so on. Nimur (talk) 20:06, 2 September 2010 (UTC)
- It's only the first of those two integrals: if V is constant, no work is done because no interface is moving, regardless of the (change in) pressure. --Tardis (talk) 20:30, 2 September 2010 (UTC)
- Well, it's not in a confined area like a piston cylinder; but the volume doesn't have to be fixed. The air-mass could be expanding. But you're right, you can make simplifying assumptions. Trying to model a hurricane from first-principles will require "some approximation." Nimur (talk) 21:26, 2 September 2010 (UTC)
- The
term is simply wrong and should be dropped; my example of constant V was just to prove that. --Tardis (talk) 22:35, 2 September 2010 (UTC)
- Are you saying that the Total derivative
does not equal
? Or that the term
for this case? In either case, I don't understand your reasoning. (The former is a mathematical fact; the latter is because pressure can change in weather systems, and volume is non-zero, so V dP is not negligible). There is additional discussion about path-independent work in our article. Increasing the pressure for a fixed volume requires work; I don't know why you would say "no work is done." Nimur (talk) 23:04, 2 September 2010 (UTC)
- Are you saying that the Total derivative
- The
- Well, it's not in a confined area like a piston cylinder; but the volume doesn't have to be fixed. The air-mass could be expanding. But you're right, you can make simplifying assumptions. Trying to model a hurricane from first-principles will require "some approximation." Nimur (talk) 21:26, 2 September 2010 (UTC)
- It's only the first of those two integrals: if V is constant, no work is done because no interface is moving, regardless of the (change in) pressure. --Tardis (talk) 20:30, 2 September 2010 (UTC)
Falling stick
A straight vertical rod of length l, when pushed, slides for a little while and then topples from the vertical position. What will be the velocity of the upper end when this end hits the ground?My approach was to use the work due to torque (∫τdθ = (1/2)Iω2) about the end touching the ground, but I don't think this is right. If axis I'm using is accelerating (and if there's friction, it should be accelerating), then won't I have to take into account ficticious torques? But that would mean knowing something about the friction, no? 74.15.136.172 (talk) 10:45, 2 September 2010 (UTC)
- To me this looks like a much simpler question. The horizontal component seems to be neglected, what with the "push" and the "sliding" and all. But for the vertical component, you know that the stick starts with the Potential energy g*(l/2)*m (m=its mass, irrelevant) and no kinetic energy (neglecting horizontal). When it hits the ground it has zero potential energy and (neglecting any energy dissipated in friction) Kinetic energy 1/2 m v^2. So v (on average) = sqrt ( 2/m * m/2 * l * g) = sqrt (lg). If one end is stationary, then the other end should be twice that. Unless I forgot something. Wnt (talk) 14:10, 2 September 2010 (UTC)
- Well, I think you forgot about rotational kinetic energy...but anyways, if I were to ignore friction, then what I wrote above would be right, except that I don't think that friction can be ignored; otherwise, why mention that it slides for a little while? 74.15.136.172 (talk) 20:37, 2 September 2010 (UTC)
- I don't believe I have to take rotational versus translational into account, if I simply average up the energy in all the particles of the rod. However, when I said "twice that", I think I needed to consider more carefully just what was twice what, since kinetic energy goes according to the square of the velocity... Wnt (talk) 00:55, 3 September 2010 (UTC)
- OK. To take this your way, the Rotational kinetic energy = 1/2 I ω2. For a rigid rod spinning around its center, I = 1/12 m L2. But here let's look at it spinning around one end, so all the kinetic energy is rotational. Using the integral from that page, I work out that its I = 1/3 m L2. So Lgm/2 = 1/6 m L2 ω2. So ω2=3g/L, and ω=sqrt(3g/L). The top of the rod moves at speed sqrt(3gL) --- note that this differs from the 2 sqrt(gL) I said before because of the error in averaging kinetic energy I mentioned above. Hope I'm right this time... Wnt (talk) 01:24, 3 September 2010 (UTC)
- Both our ways give the same answer, so I guess they're equivalent...but the question seems to suggest that we take friction into account. Any thoughts? 74.15.136.172 (talk) 01:51, 3 September 2010 (UTC)
- I think the implication of "slides for a little while" is that the stick must have been pushed at its base. It stayed vertical until it came to stop. Then it toppled from stationary, meaning that there is no trace momentum of the original push. I think we have to assume the stick is very thin and ignore air friction, although that maeans the base is a point which makes sliding difficult. So we also assume the surface is frictionless. But then the stick would never stop sliding. I am not here and did not think any of this. Cuddlyable3 (talk) 13:16, 3 September 2010 (UTC)
- Both our ways give the same answer, so I guess they're equivalent...but the question seems to suggest that we take friction into account. Any thoughts? 74.15.136.172 (talk) 01:51, 3 September 2010 (UTC)
- Well, I think you forgot about rotational kinetic energy...but anyways, if I were to ignore friction, then what I wrote above would be right, except that I don't think that friction can be ignored; otherwise, why mention that it slides for a little while? 74.15.136.172 (talk) 20:37, 2 September 2010 (UTC)
Mathematical sequence
Hello PPL, whats the best approach for solving mathematical sequences like 1 4 17 54 145 368 945 ___? , the ones that are in IQ tests?Is there any kind of logical one? Or just trying blindly? TY much and sorry for my english.194.138.12.146 (talk) 12:41, 2 September 2010 (UTC)- For integer sequences, taking Forward differences is a good place to start. If you don't see a pattern in the first forward differences, take forward differences again, rinse and repeat. Or, if you get impatient, you can look up the sequence at OEIS. Gandalf61 (talk) 12:55, 2 September 2010 (UTC)
- I didn't see the pattern in the forward differences, even after looking at the entry - maybe I needed to compare something other than adjacent terms? But the ratios tell you something is up that is more complicated than an xn+1=axn+b sort of thing:
- 4 4.25 3.17 2.68 2.53 2.56 ...
- I'm actually surprised that this "Titan test" is so public. And to think the UK newspapers are griefing us over posting the ending to The Mousetrap! Wnt (talk) 14:18, 2 September 2010 (UTC)
- Sounds interesting. Got a link? Vimescarrot (talk) 16:27, 2 September 2010 (UTC)
- Assuming you mean the Mousetrap thing, see User_talk:Jimbo_Wales/Archive_64#Cyclopia.27s_unexpected_promotion_to_.22spokesman.22_for_Wikipedia_by_journalists_of_the_Independent, with lots more links. - Jarry1250 [Humorous? Discuss.] 18:34, 2 September 2010 (UTC)
- Cheers! Vimescarrot (talk) 19:42, 2 September 2010 (UTC)
- Assuming you mean the Mousetrap thing, see User_talk:Jimbo_Wales/Archive_64#Cyclopia.27s_unexpected_promotion_to_.22spokesman.22_for_Wikipedia_by_journalists_of_the_Independent, with lots more links. - Jarry1250 [Humorous? Discuss.] 18:34, 2 September 2010 (UTC)
- Sounds interesting. Got a link? Vimescarrot (talk) 16:27, 2 September 2010 (UTC)
- I didn't see the pattern in the forward differences, even after looking at the entry - maybe I needed to compare something other than adjacent terms? But the ratios tell you something is up that is more complicated than an xn+1=axn+b sort of thing:
- These sorts of sequences can be fit by an infinite number of functions, so there is not one "correct" pattern. Providing several integers and asking to fit "any" function leaves a Null space of infinite size - there is literally no limit to the number of different, unique solutions that can yield those numbers. Typically, there's an implicit "integer-coefficients" assumption; there is usually the assumption that the sequence will be a linear sum of simple terms (like a Polynomial in n), but unless these requirements are formally laid out for the sequence, there is no correct answer. Proper IQ tests do not use "guess the next number in this sequence" questions, because there is no objective way to define "correctness." If you have smarter and smarter participants (especially those who have formal training in mathematics, but not necessarily), they will solve the problem more effectively than the test-provider intended; and the test becomes invalid; so well-structured IQ tests will never ask this kind of question. Nimur (talk) 19:59, 2 September 2010 (UTC)
- While there are indeed an infinite number of functions that'll work, it's generally clear that what is required is the simplest function that'll do the job - and it's usually very clear what that is once you find it.
- Of course some sequences are tougher:
- 0,1,2,5,8,11...is the first N numbers that look the same if viewed upside down on a calculator display.
- 3,3,5,4,4,3,5,5,4,3,6...is the number of letters in the English word for 'N'.
- If someone is using a criterion like that then no amount of messing around with numerical stuff will get you the "correct" answer you really do have to just have the answer pop into your head. But some are completely ambiguous:
- 4,8,12,16,20,24,28,32... has got you thinking 4N - when in fact I was thinking of the years in our calendar that were leap years and you wouldn't have had a hope in hell of realizing that until I said...92,96,104,108,112 and you were forced to figure out why I skipped '100'. Of course if I'd said 2004,2008,2012,2016... then you might have jumped at "Leap year" immediately rather than 2000+4N - but if I'd said 1234,1238,1242,1246,...then again, you might not have thought "leap years" and would have gone back to 1230+4N.
- Even if the answer is "simple" and "numerical", you might never find it other than by luck - but I bet you get: 3,1,4,1,5,9,2,6,5,3,5... which is certainly "simple" and numerical/arithmetic - but trying to fit a function to it would take you forever!
- This clearly isn't about mathematics so much as the very human idea of "simplicity".
- SteveBaker (talk) 06:13, 4 September 2010 (UTC)
Ant?
What is this? It looks like a queen ant from the species Myrmica rubra. Is it the ant flight time of year for this species in the UK? 82.44.55.25 (talk) 15:16, 2 September 2010 (UTC)- It's a bit hard to tell for sure but yes, it looks like a Myrmica rubra queen. AntWeb is your friend in all things ant and Wikipedia's too since they have released all of their images under CC-BY-SA. I guess it's still nuptial flight time in the UK for these guys, yes. Sean.hoyland - talk 16:22, 2 September 2010 (UTC)
- ". . .for these guys"?!! Richard Avery (talk) 19:40, 2 September 2010 (UTC)
- Does "guys" not refer to a group consisting of either/both genders? 82.44.55.25 (talk) 19:55, 2 September 2010 (UTC)
- ". . .for these guys"?!! Richard Avery (talk) 19:40, 2 September 2010 (UTC)
Yes, "guys" as in "Hey guys, let's watch Sex in the City and talk about why the liquids in sanitary napkin adverts are never red". Also, I believe Myrmica rubra males have long campaigned for a move to grammatically genderless semiochemicals. [citation needed] Sean.hoyland - talk 03:20, 3 September 2010 (UTC)
- Microsoft Encarta? Why not Collins or Chambers or Oxford. They support the case, and I stand a little wiser. Up the workers!! Richard Avery (talk) 06:59, 3 September 2010 (UTC)
End organ
In your discussions of cutaneous senses and mechanoreceptors, reference is made to the "end organs" (e.g. Pacinian Corpuscles end organ[s]). What does that mean: "end organ" in terms of these sensory cells? I know cell body, and terminal buttons (at the synapse gap) and dendrites (on the receiving cell). I do not understand what "end organ[s]" is/are. Please explain this to me. (I am studying Neuroscience and have used the text and many web searches. Thank you.97.126.243.41 (talk) 17:07, 2 September 2010 (UTC)- As you stated, Pacinian corpuscles (together with Merkel discs, Ruffini endings, Meissner's corpuscles, end bulbs of Krasue and others) are examples of modified dendrite tips known collectively as special Cutaneous receptors. There are also free nerve endings. DRosenbach (Talk | Contribs) 19:29, 2 September 2010 (UTC)
- (after EC) They call the cutaneous sensory receptors "organs" because they are generally complex arrangements of different types of cells that together serve the purpose of transducing a given sensation to the nerve ending. Take a close look at the pictures in the Pacinian corpuscle, Meissner's corpuscle, Organ of corti, Olfactory bulb, and Taste bud articles -- these structures are complicated collections of nerve fibers, connective tissue cells, blood vessels, etc. and they clearly meet the definition in Organ (anatomy): "a collection of tissues joined in structural unit to serve a common function". The structures you are listing (Cell body, Terminal boutons, and Dendrites) are all integral parts of the Neuron itself, enabling communication of the sensory reception into the nervous system, but the overall process of sensory reception requires the more complex "end organ". Does that help? --- Medical geneticist (talk) 19:38, 2 September 2010 (UTC)
Where find actuarial statistics?
Where could I find data to answer questions like what percentage of woman lived past age 50 circa 1850? RJFJR (talk) 17:07, 2 September 2010 (UTC)- Which country do you want data on? --TammyMoet (talk) 17:57, 2 September 2010 (UTC)
- Try Life table. 92.29.120.223 (talk) 19:37, 2 September 2010 (UTC)
lifting an average passenger train car
I am not sure how heavy the average North American passenger train car is, but I am wondering if one were to want to lift said vehicle off the ground (say even 10 feet) using a helium-style balloon, how big would this balloon need to be? How would this compare to the Hindenberg in size?Related to this, if one were to fill all available space (except where passengers sit, of course)with helium, how significant would this lighten the train car? 142.46.225.77 (talk) 17:54, 2 September 2010 (UTC)
- You're going to need about a cubic meter of helium per kilogram of train car (And per kilogram of balloon!)
- So if you imagine a 75ton train car, you're going to need about 70,000 cubic meters of helium.
- So, Maybe a spherical balloon 110 meters across? Very roughly. APL (talk) 18:05, 2 September 2010 (UTC)
- Our article suggests the Hindenberg had a volume of about 200,000 cubic meters, but then again it did weigh a significant amount in itself. I have no idea how much that is. - Jarry1250 [Humorous? Discuss.] 18:17, 2 September 2010 (UTC)
- Our article also gives a "useful lift" of 10,000 kg, well below that of a rail car. On the other hand, I'm sure that you could build an airship comparable in size to the Hindenburg both much lighter, and that actually had light gas envelopes filling more of the volume. Buddy431 (talk) 18:59, 2 September 2010 (UTC)
- Also, the Hindenburg (famously) used hydrogen rather than helium as its lifting gas - so it would have had a somewhat higher payload than a helium balloon. SteveBaker (talk) 05:40, 4 September 2010 (UTC)
- I also see that a company known as CargoLifter wanted to construct an airship capable of carrying 160 tons, which would have had a volume of 550,000 cubic meters. Perhaps unsurprisingly, the company no longer exists. You can visit their former hanger, though, as the Tropical Islands resort in Germany. Buddy431 (talk) 19:06, 2 September 2010 (UTC)
- Our article also gives a "useful lift" of 10,000 kg, well below that of a rail car. On the other hand, I'm sure that you could build an airship comparable in size to the Hindenburg both much lighter, and that actually had light gas envelopes filling more of the volume. Buddy431 (talk) 18:59, 2 September 2010 (UTC)
- Our article suggests the Hindenberg had a volume of about 200,000 cubic meters, but then again it did weigh a significant amount in itself. I have no idea how much that is. - Jarry1250 [Humorous? Discuss.] 18:17, 2 September 2010 (UTC)
In the book The Golden Age of the Great Passenger Airships: Graf Zeppelin & Hindenburg by Dick and Robinson, details are given of the loading of the Hindenburg for its first transatlantic flight, a year before the disaster. I may as well reproduce the entire table for interest. All weights are in kilograms; divied by 1,000 for metric tons.
2,960 37 passengers 1,840 23 engine personnel 1,680 21 deck crew 800 10 stewards 600 passenger baggage 1,080 crew baggage 3,000 provisions 1,269 freight 84 mail 55,230 fuel oil 4,000 lubricating oil 1,200 reserve parts 1,400 reserve radiator water 1,150 drinking water and liquors 11,300 trim ballast 3,000 emergency ballast 1,120 miscellaneous 2,500 bedding, utensils, etc. 1,000 moisture 1,000 lightness 96,213 SUBTOTAL 118,000 dead weight (approx.) 214,213 TOTAL
Clearly a bunch of these items apply only because we're talking about a passenger airship. And likewise for some of the "dead weight" -- if it wasn't carrying passengers you wouldn't need passenger cabins and all the things that go with feeding the passengers. And you could also go with a lighter structure (a blimp rather than a dirigible) if you were willing to have a less capable airship. So in short I think it's fair to say that while a Hindenburg-size airship wouldn't be quite big enough, it's too small by not all that large a margin.
Of course, the Hindenburg was inflated with hydrogen; with helium you get about 8% less lift, so you need a slightly bigger airship for that reason. (The calculation is (29-4)/(29-2) = 0.926, where 29, 4, and 2 are the respective average molecular weights of air, helium, and hydrogren.)
On the other question, the enclosed volume of a passenger car is something like 70 x 10 x 8 feet, which is 5,600 ft³ or say 160 m³. That is less than 1/1,000 of the gas capacity of the Hindenburg, so you can see that even if you were willing to suffocate the passengers by filling it with helium, you would not get any significant lift.
--Anonymous, 04:45 UTC, September 3, 2010.
Earth's Atmosphere
Coming back to wake you up again! If Earth had no Atmosphere and we were still alive somehow; how can we see things around us look like, including the Sky, Horizon, Sunset, Sunrise, ..etc?--Email4mobile (talk) 21:55, 2 September 2010 (UTC)- The sky looks blue due to Rayleigh scattering - without an atmosphere it'd just be black. It doesn't answer any of your other questions, though. (I don't know whether you'd be able to see the stars during the day, but I doubt it.) Vimescarrot (talk) 21:58, 2 September 2010 (UTC)
- You'd surely be able to see the stars so long as your eyes were dark-adapted at all (which would just involve being in a hole behind a wall). --Tardis (talk) 23:08, 2 September 2010 (UTC)
- There would be no pre-dawn brightening of the sky. It would be completely dark until the sun first appeared over the horizon. Similarly at dusk, the sky would go dark as soon as the sun had set. Rojomoke (talk) 23:36, 2 September 2010 (UTC)
- If it's not obvious, it would be exactly what it is like on the moon. One more thing I would add to the above is that shadows would be much sharper and darker because there would be no light scattering from the atmosphere or clouds. Vespine (talk) 23:49, 2 September 2010 (UTC)
- However, contrary to popular belief, shadows would not be pitch-black. There's still Diffuse interreflection to light things up. --Carnildo (talk) 01:20, 3 September 2010 (UTC)
- While you might be able to see the stars, they wouldn't twinkle as that is caused by turbulence in the atmosphere. Confusing Manifestation(Say hi!) 01:56, 3 September 2010 (UTC)
- No Mirages. No Aurora. No Meteor showers to see until they make craters around you. No Rain, Snow, Wind or Weather at all. During a Lunar eclipse the occluded area of the Moon would be black not dark reddish. Your Barometer pointer is hard against the stop. You might notice that the Tires of your bicycle and car are bulging because they are over-inflated, though I don't know where you got the gas to pump into them. If you had anything held by a Suction cup, well it isn't held. You would see neither the Space Shuttle nor parachutists land more than once (painfully). If you break an ordinary lamp bulb it may still work. Anyway everybody without a space suit would be dead which makes it a horrible idea. Cuddlyable3 (talk) 12:37, 3 September 2010 (UTC)
- If it's not obvious, it would be exactly what it is like on the moon. One more thing I would add to the above is that shadows would be much sharper and darker because there would be no light scattering from the atmosphere or clouds. Vespine (talk) 23:49, 2 September 2010 (UTC)
- We didn't cover sunrises and sunsets. In both cases, the sun would appear as a sharp white circle - there would be no change in the color of sky or sun as it rose or set. Also no rainbows (because no rain). Kinda boring really. SteveBaker (talk) 05:38, 4 September 2010 (UTC)
Theory of Relativity and Time Travel
How does Einstein's theory explain time travel, and more importantly Grandfather's Paradox ? Jon Ascton (talk) 23:46, 2 September 2010 (UTC)- It doesn't, really. There are various interpretations of Special and General Relativity that seem to allow backward time travel from some reference frame (see Time travel#In_physics), but they are pretty speculative and my understanding is that most physicists think they wouldn't have much of a chance of working. Relativity certainly has nothing to say in particular to say about the grandfather paradox. --Mr.98 (talk) 00:08, 3 September 2010 (UTC)
- See however Tachyonic antitelephone. If it were possible to send information faster than light by a frame-independent and direction-independent process, it would also be possible to send information backwards in time. That gets you the grandfather paradox. --Trovatore (talk) 00:15, 3 September 2010 (UTC)
- See Closed timelike curve, especially Tipler cylinder. Wnt (talk) 00:51, 3 September 2010 (UTC)
- See however Tachyonic antitelephone. If it were possible to send information faster than light by a frame-independent and direction-independent process, it would also be possible to send information backwards in time. That gets you the grandfather paradox. --Trovatore (talk) 00:15, 3 September 2010 (UTC)
September 3
Xyliooligo saccharide
Xyliooligo saccharide —Preceding unsigned comment added by 220.136.107.152 (talk) 01:50, 3 September 2010 (UTC)What is protium hydroxide?
Is it the same stuff as dihydrogen monoxide? --81.96.185.94 (talk) 05:37, 3 September 2010 (UTC)- Yes. Someguy1221 (talk) 05:46, 3 September 2010 (UTC)
- (edit conflictTemplate:Safesubst:) Yes. Compare Protium, Hydroxide, Water. It's just water, and someone is trying to be silly. --Jayron32 05:47, 3 September 2010 (UTC)
- Cheers.--81.96.185.94 (talk) 05:49, 3 September 2010 (UTC)
- What happens when you mix diprotium oxide with dideuteriuum oxide? (Heavy water) entropy is increased, but is there any temperature effect? Graeme Bartlett (talk) 11:14, 3 September 2010 (UTC)
- I don't have my tables handy, so I can't tell you which way the temperature would go, but there should be a small change. The protons and deuterons are labile, so there will be a rapid equilibration reaction converting some H2O and D2O into HDO. TenOfAllTrades(talk) 14:10, 3 September 2010 (UTC)
- OK, but for most practical purposes, are they the same? By the way: what's the difference between "protium hydroxide" and "protium oxide"? Was that a typo, or are those the same? (I abandoned chemistry when I was 14.)
- You know, something named "protium oxide" could be a great spoof miracle drink!--81.96.185.94 (talk) 11:06, 3 September 2010 (UTC)
Seen another way, protium oxide is 1H-O-1H, whereas protium hydroxide encompasses three Isotopomers:
- 1H-O-1H, i.e. H2O
- 1H-O-2H, i.e. HDO
- 1H-O-3H, i.e. HTO
- 1H-O-2H (aka semiheavy water, deuterium protium oxide, HDO)
- 2H-O-2H (aka heavy water, deuterium oxide, D2O).
- 1H-O-3H (aka tritium protium oxide, HTO)
- 3H-O-3H (aka super-heavy water, tritium oxide, T2O)
- water, water everywhere, yet not a drop to drink... --Ludwigs2 16:27, 3 September 2010 (UTC)
- You guys put WAY too much effort into analyzing a joke. The person who introduced the OP to the words "protium hydroxide" wasn't expressing a scientific concept, they were using a marginally accurate bit of obfuscation to mask the fact that they are talking about ordinary water. The DHMO joke made its first run through the internet like 15 years ago, this is just another minor variation on it. --Jayron32 02:54, 4 September 2010 (UTC)
- Well, if you know what that person's motivation was, fine. The fact is that "protium" does not mean the same thing as "hydrogen", and it was necessary to say that to answer the question. --Anon, 04:19 UTC, September 4, 2010.
- You guys put WAY too much effort into analyzing a joke. The person who introduced the OP to the words "protium hydroxide" wasn't expressing a scientific concept, they were using a marginally accurate bit of obfuscation to mask the fact that they are talking about ordinary water. The DHMO joke made its first run through the internet like 15 years ago, this is just another minor variation on it. --Jayron32 02:54, 4 September 2010 (UTC)
Quantum mechanics
Niels Bohr said about this theory that those who are not shocked by it don't understand it ! What I want to simply know is that - is there any implication in this theory that says that an electron, proton or photon starts behaving differently when it is under observation Jon Ascton (talk) 06:35, 3 September 2010 (UTC)- The simple answer is no! Particles are not aware when they are under observation. Dolphin (t) 07:33, 3 September 2010 (UTC)
- ... but, of course, the act of observation can change behaviour. Dbfirs 07:43, 3 September 2010 (UTC)
- In quantum mechanics, an observation collapses the particle's Wave function. So, yes, an observation affects a particle's future behaviour, in the sense that it changes the future shape of its wave function and so changes the probability that it will be observed in a given state at some time in the future. For example, in the Double-slit experiment, observing the particle as it passes through the slits affects the interference pattern observed on the screen. Gandalf61 (talk) 09:07, 3 September 2010 (UTC)
- If you're a follower of the Copenhagen interpretation, that is. If, on the other hand, you prefer the Many-worlds interpretation, then a wave function never really collapses, and we just observe one of all possible states. The math's all the same, but there are different ways of viewing the rules of quantum mechanics. Buddy431 (talk) 13:17, 3 September 2010 (UTC)
- I would like to see that example in practice. I have my lamp, slits and screen set up with the expected interference pattern showing. What may I do that will change the pattern on the screen? Cuddlyable3 (talk) 11:40, 3 September 2010 (UTC)
- Block out one of the slits ;) That might seem trivial, but imagine an experiment where the photons are going through one at a time (this can be done practically, although probably not at home). You note where each photon arrives on the screen, and repeat the experiment a few thousand times. When you look at the number distribution of the photons, you have exactly the same pattern (to within experimental error) as you have from a classic Young's slits experiment. So either an individual photon goes through both slits at once or it somehow "knows" that the second slit is there... Physchim62 (talk) 12:41, 3 September 2010 (UTC)
- If you want to see very weird things, look up Wheeler's delayed choice experiment. There are some very odd results that seem to imply some very weird violations of causality, for example. --Mr.98 (talk) 12:54, 3 September 2010 (UTC)
- For Bohr, the heart of quantum mechanics was Complementarity. Give it a read. It is not just about things looking different when you look at them differently. It is about, in Bohr's formulation, the ultimate limits of what meaning means in the physical world. Not all physicists, especially modern ones, do QM in the same way that Bohr did. The best individual experiment that gives an indication of the kinds of "shocking" things Bohr is talking about is Wheeler's delayed choice, linked above, which was dreamed up to specifically show how "shocking" this could be, where very weird things happen that make very little sense using macroscopic (non-quantum) logic.--Mr.98 (talk) 12:54, 3 September 2010 (UTC)
- I think we should really state what "observation" actually means in physics. We actually have an article about quantum observations, but I can summarize briefly. Let's say you want to observe a flower - you look at it, right? But what is "looking" at something? Light is involved - photons from the sun hit the flower and an amount proportional to the size of the flower hit your eye, thus giving it a nice image against everything else in your field of vision. But the key here is that, if there was nothing that actually hits that flower, there'd be no way to see it, feel it, smell it, etc. Something physical must happen to the flower, and in quantum mechanics, this physical interaction is "observation". It doesn't matter if you are a conscious being or not - when a quantum particle interacts with something, it must collapse into a definite space and time to actually make a cause-and-effect billiard-ball interaction. Once it's done interacting, it rapidly becomes the wavy cloudy quantum-uncertainty thing it was beforehand again. All it has to do is hit something - anything - to be observed. SamuelRiv (talk) 20:46, 3 September 2010 (UTC)
- The simple answer is yes. A crucial prediction of quantum mechanics is that any act of observing a particle perturbs it, and there is a limit to how small the perturbation can be. Looie496 (talk) 22:52, 3 September 2010 (UTC)
ISOMERISM
What is D and L designations in organic isomers? and also what is meant by Racemic mixture??Rohit.bastian (talk) 08:25, 3 September 2010 (UTC)- See chirality and Racemic mixture, respectively, and if these don't answer your questions then come back. HTH. --Ouro (blah blah) 08:36, 3 September 2010 (UTC)
mass and charge
what is mass and what is charge? I mean other than trivial attributes attached to different particles, what is it that is actually responsible for them? --91.103.185.230 (talk) 09:57, 3 September 2010 (UTC)- In the Standard Model of particle physics, charge (assuming you mean Electric charge) measures the strength of a particle's interaction with the Electromagnetic field and with its Force carrier, the Photon. There are various theories as to the origins of mass; one that has wide acceptance, although it is not yet experimentally proved, is that mass measures the strength of a particle's interaction with the Higgs field and the (hypothetical) Higgs boson. Gandalf61 (talk) 10:28, 3 September 2010 (UTC)
Hurricane disruption
If a nation were to detonate a 1Mton nuclear device in the eye of a hurricane (for example a cat 3), would the hurricane be weakened, strengthened or not notably affected? Googlemeister (talk) 13:28, 3 September 2010 (UTC)- Our Tropical Cyclone article says
- "Scientists at the US National Center for Atmospheric Research estimate that a tropical cyclone releases heat energy at the rate of 50 to 200 exajoules (1018 J) per day, equivalent to about 1 PW (1015 watt). This rate of energy release is equivalent to 70 times the world energy consumption of humans and 200 times the worldwide electrical generating capacity, or to exploding a 10-megaton nuclear bomb every 20 minutes.
- So an extra 1 Mton is not going to make much difference. Rojomoke (talk) 14:22, 3 September 2010 (UTC)
- That logic doesn't quite work. The energy that the Sun transmits to the surface of the Earth is like exploding god-knows-how-many megatons every few seconds (the Tsar Bomba was only some 1.4% of the power output of the Sun), but the fact that it is dispersed over a great area means that it doesn't, you know, destroy us totally. Raw energy release is meaningless unless you take into account the scale. Nuclear bombs are impressive because they release a lot of raw energy in a very localized area. --Mr.98 (talk) 14:46, 3 September 2010 (UTC)
- NOAA discusses it here. --Sean 14:23, 3 September 2010 (UTC)
- Yeah, it's a really bad idea. Aside from the fact that it probably wouldn't affect the storm (storms are not just a "thing" you can blow up, but a complicated system made up of tiny parts — it's the not the kind of thing a nuke is good against!), you'd spread fallout over a huge area. The worst way to deal with fallout is to have it be taken up by some kind of weather system and rained down on everybody, rather than having it dilute in the upper atmosphere to safe levels. It would be a catastrophic disaster. --Mr.98 (talk) 14:46, 3 September 2010 (UTC)
- A hurricane is a heat engine that feeds on high surface water temperatures and favorable atmospheric circulation to produce a rotating storm system over a scale of hundreds of kilometers. In order to disrupt a hurricane you must disrupt these fundamental conditions. A nuclear weapon, apart from making the storm into an efficient fallout spreader, is but a pinprick. Since a cyclone makes its living by transporting heat into the upper atmosphere from the ocean's surface, you could argue that any large production of heat would actually feed the storm (rather doubtful that enough heat could be generated to make a difference). Acroterion (talk) 15:09, 3 September 2010 (UTC)
- Wouldn't the pressure wave disrupt the eyewall? Googlemeister (talk) 15:28, 3 September 2010 (UTC)
- Not in a meaningful way. It would be of short duration. Also, pressure shock fronts from explosions are "zero-mean" - loosely speaking, this means that an exactly equal amount of wind blows in and then blows back out. So the effect is no net change on the pressure (after the transient pressure shock dies away). For an entity that operates on the size- and time-scales the size of a hurricane, these momentary pressure spikes would be negligible. Nimur (talk) 18:12, 3 September 2010 (UTC)
- Wouldn't the pressure wave disrupt the eyewall? Googlemeister (talk) 15:28, 3 September 2010 (UTC)
- Well, it sounds sort of plausible, but I doubt anyone here really knows. Or more to the point, anyone here who does really know, is probably not allowed to say. --Trovatore (talk) 18:40, 3 September 2010 (UTC)
- Don't despair; User:Rocketshiporion will be around momentarily to simulate it for us... Nimur (talk) 21:05, 3 September 2010 (UTC)
- But don't confuse a Dirty bomb with a Salted bomb... anyway, fallout effects are very hard to predict, even under ideal conditions. I think blowing up a cobalt bomb inside a hurricane would be a pretty good way to contaminate a large area. Whether it would increase the acute causalities much, I don't know. If you want raw casualties, just detonate a hydrogen bomb over a densely populated area. It's hard to beat that for raw numbers. If you were really going for mayhem, what you'd want to do is detonate a very dirty H-bomb over, say, New York, under conditions that would spread the fallout plume along the BosWash corridor. Castle Bravo transposed along the north east. Bleh. --Mr.98 (talk) 02:39, 4 September 2010 (UTC)
- Interesting question. Theoretically, what would happen if a warm bubble were to be placed into the eye of an idealized tropical cyclone? Assuming the bubble is initialized at ~700mb, my intuition is that it would weaken the storm because the updrafts caused by the warm bubble would decrease the natural downdrafts in the cyclone, and thereby reduce the secondary circulation. As others have mentioned above, the effects would likely be very small. -Atmoz (talk) 23:06, 3 September 2010 (UTC)
Novichok agent
According to the article, this nerve agent is a fine powder instead of a gas or vapor. As a weapon, would that be an advantageous trait or a disadvantageous trait? ScienceApe (talk) 15:05, 3 September 2010 (UTC)- According to this, "the nanopowder can bypass most of the chemical weapons detectors commonly used in the modern armies. The nanopowder can, however, firmly attach to the skin and the toxic compound directly penetrates into the body." --jpgordon::==( o ) 15:54, 3 September 2010 (UTC)
What is the Standard reduction potential for Ascorbic acid
I have used ascorbic acid to reduce Iodine to Iodide, Copper(II) oxide to a red powder that could be Copper(I) oxide or Copper, and Chlorine to Chloride. I am curious as to what the reduction potential of ascorbic acid is compared to Stannous ion, for example? --Chemicalinterest (talk) 15:17, 3 September 2010 (UTC)chicken
what is the breed of chicken found hereFile:Industrial-Chicken-Coop.JPG —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 15:56, 3 September 2010 (UTC)
- White leghorn, one of the most popular in the United States. They might also be bantys, based on their combs. See also, Chicken breeds. Nimur (talk) 16:35, 3 September 2010 (UTC)
- They wouldn't be Bantams - Bantam hens are too small to be decent egg layers, except for boutique/niche markets. (i.e. they have small eggs and wouldn't be raised industrially). -- 174.21.233.249 (talk) 02:24, 4 September 2010 (UTC)
Question about being born brain dead
Are there some people who are born brain dead? What happens to them, are they kept alive? Prize Winning Tomato (talk) 18:55, 3 September 2010 (UTC)- Someone who is born brain dead usually does not survive, but not always. What happens to them if they do survive is usually up to the parents. They can be kept alive by machines, but (I believe) more often they let them die (by not providing any medical intervention). See also Anencephaly for a more extreme case. The bottom of that article also discusses the subject of their survival (see Baby K (which BTW does not have a NPOV). Ariel. (talk) 20:13, 3 September 2010 (UTC)
- Ariel, just out of curiosity, what part of the Baby K article did you see as not having NPOV? I just read the article myself and it seems to have a disinterested tone, presenting basically just the facts. Perhaps since I'm reading the article from my own POV, it seems sufficiently neutral, but I would truly be interested to know if there were parts that you found not so neutral. --- Medical geneticist (talk) 00:31, 4 September 2010 (UTC)
- "despite the fact that being born without a brain is not curable or treatable" has kind of a POV tone to it — a snipey sort of thing that doesn't really have anything to do with the argument that the mother made about it. If it were up to me, I'd maybe word it a little more neutrally: "despite there being no medical chance for an improvement in condition" or something like that. --Mr.98 (talk) 00:59, 4 September 2010 (UTC)
- Thanks, I can see how that phrase was a little slanted; it looks like someone has already made some changes to the article! But overall, would you agree that the article handles a touchy subject pretty well? --- Medical geneticist (talk) 10:49, 4 September 2010 (UTC)
- "despite the fact that being born without a brain is not curable or treatable" has kind of a POV tone to it — a snipey sort of thing that doesn't really have anything to do with the argument that the mother made about it. If it were up to me, I'd maybe word it a little more neutrally: "despite there being no medical chance for an improvement in condition" or something like that. --Mr.98 (talk) 00:59, 4 September 2010 (UTC)
- Ariel, just out of curiosity, what part of the Baby K article did you see as not having NPOV? I just read the article myself and it seems to have a disinterested tone, presenting basically just the facts. Perhaps since I'm reading the article from my own POV, it seems sufficiently neutral, but I would truly be interested to know if there were parts that you found not so neutral. --- Medical geneticist (talk) 00:31, 4 September 2010 (UTC)
- (ec)You may be interested in our articles on Anencephaly (note: disturbing images) and Baby K. Matt Deres (talk) 20:19, 3 September 2010 (UTC)
- Brain death is the standard criterion for declaring a person dead, so somebody who is born brain dead is already not alive. Looie496 (talk) 22:45, 3 September 2010 (UTC)
- But note that Brain death has a very restrictive definition. Baby K specifically was apparently not brain dead, because she had a brainstem that controlled autonomic functions. Mere absence of all correlates of cognitive activity is not enough. I suspect that when a fetus experiences brain death, more conventional sort of death follows very quickly, so brain-dead-but-not-all-dead births are probably quite rare. --Trovatore (talk) 22:55, 3 September 2010 (UTC)
- Existence precedes essence Smallman12q (talk) 23:58, 3 September 2010 (UTC)
- But note that Brain death has a very restrictive definition. Baby K specifically was apparently not brain dead, because she had a brainstem that controlled autonomic functions. Mere absence of all correlates of cognitive activity is not enough. I suspect that when a fetus experiences brain death, more conventional sort of death follows very quickly, so brain-dead-but-not-all-dead births are probably quite rare. --Trovatore (talk) 22:55, 3 September 2010 (UTC)
- Brain death is the standard criterion for declaring a person dead, so somebody who is born brain dead is already not alive. Looie496 (talk) 22:45, 3 September 2010 (UTC)
How to calculate the north pole right ascension and declination of Mars
Does anybody know how to calculate the north pole right ascension and declination of Mars using axial tilt, inclination, argument of perihelion, and longitude of ascending node? The north pole right ascension of Mars is 317.681° and declination +52.887°. The axial tilt is 25.19°, inclination to ecliptic 1.850°, argument of perihelion 336.04084°, and longitude of ascending node 49.57854°. I couldn’t figure it how to get that answer. BlueEarth (talk | contribs) 21:56, 3 September 2010 (UTC)Why can we see stars?
I understand that some stars are very large and very bright, but they are also so unimaginably far away that my instinct tells me that they should not be visible to the human eye. Of course, they are visible, so I wonder, is it simply because they are so large and bright, or is there some other "effect" or "phenomenon" that makes them more visible than they would otherwise be. Thanks in advance for any input. Francis78 (talk) 22:21, 3 September 2010 (UTC)- Stars are not all the same distance away. Some very large, very bright stars are so distant that you can't see them. Some small dim stars are near enough to see.
- The further away a star is, the dimmer it is. This fact is used at times to gauge the distance to other galaxies, for example by looking for the spectra of Cepheid variables, which are a class of "standardized" stars with known luminosity.
- The light receptors in your eyes are sensitive to photons hitting them. One or two photons won't register, but above some threshold, you will perceive light. Stars that you can see simply happen to emit enough photons that a sufficient number get into your eye, allowing you to see them. The closest star, our sun, isn't especially big or bright as stars go, but it's so close that you get a huge dose of photons when you look at it, sufficient to burn out your optic receptors.
- You are correct to imagine that stars are so far away that they should not be visible. Starlight is, actually, quite faint. That's why you can't see stars during the daytime, because the light from our own star illuminates our atmosphere to drown out the faint light from other stars. ~Amatulić (talk) 22:30, 3 September 2010 (UTC)
- Light from a star never "wears out", no matter how far away it is, any light that is emitted will keep going. So as long as a couple of the light photons hit your eye you can see the star. The light from the star does spread out, but stars make enough photons, that even when they spread out, enough of them remain next to each other for several of them to enter your eye at the same time. Ariel. (talk) 22:46, 3 September 2010 (UTC)
- (Edit conflict with Ariel) You're quite right that we can't see most stars in the sky. Most stars in our galaxy are Red dwarfs, which are very dim, even when quite close. In fact, the closest star to our solar system, Proxima Centauri is a red dwarf, and has an Apparent magnitude of about 11, well below the threshold that you can see with the naked eye. But even though there are lots of stars that we can't see, there are some that are big enough, bright enough, and close enough to us that we can see them. Some stars that we see are comparable in size to our sun, and are close enough that we can still get enough of their light to see with the naked eye; things like Sirius, Alpha Centauri, Epsilon Eridani, and others. See List of nearest stars. The ones with their apparent magnitude in light blue are bright enough to be seen with the naked eye. Notice that even among the stars closest to us, though, most cannot be seen. When you consider stars further away, it's only the largest and brightest stars that we can see: stars like Canopus, Rigel, and Betelgeuse are really enourmous, atypical stars, but it's only atypical stars that we can see at distances of hundreds of light years. I'm not sure what the farthest individual star that can be seen is, but I bet it's "only" a couple thousand light years away, easily still inside the Milky way galaxy. The Andromeda Galaxy is often cited as the furthest object that can be seen with the naked eye (at 2.5 million light years), and, while not strictly true (people have seen claimed to have seen Messier 83, for example), that's about the limit. And that's literally billion's of stars that can just barely be seen under good conditions. The point is, the vast, vast, vast majority of star's aren't visible from Earth (with the naked eye), but there are just a few (about 6,000 under good viewing conditions) that happen to be big enough, bright enough, and close enough that our eyes can (just barely, in most cases) make them out under very dark conditions. Amatulic also makes a good point: we can only just barely see even the stars that we can; we can't see them during the day, many we can't see when the moon is out, and a good deal of them we can't even see when there's any sort of light pollution at all. Buddy431 (talk) 23:04, 3 September 2010 (UTC)
- So how many photons does it take to trigger our receptors? Clarityfiend (talk) 02:48, 4 September 2010 (UTC)
- It depends on a lot of variables - but under ideal conditions, just one photon is enough to trigger a Rod cell to fire. SteveBaker (talk) 05:29, 4 September 2010 (UTC)
- And not many for it to be treated as signal rather than noise, see Can a Human See a Single Photon? and Optimization of Single-Photon Response Transmission at the Rod-to-Rod Bipolar Synapse. Sean.hoyland - talk 05:42, 4 September 2010 (UTC)
- It depends on a lot of variables - but under ideal conditions, just one photon is enough to trigger a Rod cell to fire. SteveBaker (talk) 05:29, 4 September 2010 (UTC)
- So how many photons does it take to trigger our receptors? Clarityfiend (talk) 02:48, 4 September 2010 (UTC)
Looking at Fundamentals analytically
Can one define a fundamental concept analytically, or will this always lead to a Circular definition?Smallman12q (talk) 23:24, 3 September 2010 (UTC)- I don't understand the question. Do you mean defining the term fundamental concept, or do you mean defining particular fundamental concepts such as energy? And what do you mean by "analytically"? Looie496 (talk) 23:57, 3 September 2010 (UTC)
- I mean fundamental concepts such as though pertaining to Quantum mechanics and Classical mechanics. By analytically, I mean separating into relevant constituent parts.Smallman12q (talk) 00:03, 4 September 2010 (UTC)
- Well, I'm not a philosopher, or a scientist. But it's of note that some of the definitions of fundamental concepts have definitely led to potentially productive circular definitions. I'm thinking of Einstein's basic work in redefining things like "distance" (what a ruler measures) and "time" (what a clock measures). Those are superficially pretty unsatisfying definitions, but the point is to refocus attention less on metaphysical definitions and more on practical definitions, and from there, a very useful theory falls out rather nicely. Anyway, I don't think this resolves your question, but I offer it up as a possible contribution in thinking this through. --Mr.98 (talk) 00:46, 4 September 2010 (UTC)
- Relevent related information to this question would be the idea of the Axiom, that is a concept which is taken as absolutely true but unproven (or unprovable), and Axiomatic system, which are the backbone set of axioms (fundemental concepts) of a system. Also the theorems of Kurt Gödel, which are closer related to mathematics but still germaine to the OP's question, especially Gödel's incompleteness theorems, and the philosophy of Ludwig Wittgenstein, dealing with the relationship between language and reality. --Jayron32 02:45, 4 September 2010 (UTC)
- Yes - Axioms are the key here. Mathematically, one can take a set of arbitary axioms (which may or may not be "true" - in the sense of them being a true representation of the real world) and make some deductions from that - perhaps even prove some interesting theorem or other. But when you do that, you are always saying: "This thing that I've proved is 'true' providing that the axioms that I started with are 'true' - otherwise, all bets are off".
- In the world of science, things are a little different. Rather than taking 'axioms', you'll generally be taking observations of experiments or of nature. You may go through the same process of logic, mathematics, reasoning - and you'll come up with some result. Then you can say "on the basis of this pile of observations - I deduce the following". The observations are kinda like axioms in mathematics in that your conclusion is only valid so long as those observations are correct. What Einstein did was a little different. He noted the results of some experimental observation - things like the Principle of Invariant Light Speed which had been established by the Michelson–Morley experiment and others. But he also picked some axioms (in the mathematical sense). He supposed things like "The Principle of relativity" - which is (roughly) that the laws of nature are the same over all time that they are the same regardless of the person experiencing them. His subsequent deduction of the Theory of Special Relativity is rock solid - but only if the laws of nature are the same everywhere and only if Michelson-Morley (et al) didn't screw up their experiments. But if either of those two things are untrue - then all bets are off. SteveBaker (talk) 04:59, 4 September 2010 (UTC)
Blow hole flap?
Is there an anatomical name for the flap that covers a cetacean's blow hole? - or does it just clench shut? Adambrowne666 (talk) 23:41, 3 September 2010 (UTC)- My understanding is that it doesn't have a cover. It is surrounded by a ridge called the "rostrum" that acts as a splash guard, but it closes by squeezing shut. Looie496 (talk) 00:02, 4 September 2010 (UTC)
- I'm not so sure about that. Sources say 'rostrum' apparently refer to the animals snout! See Rostrum (anatomy), also see the diagram here, which is supposed to be sourced from Seaworld. From the Seaworld website here under HEAD, 2. "In front of the melon, a bottlenose dolphin has a well-defined rostrum (snoutlike projection)." I can't find a specific name for a flap over the blowhole.
• A search on Wikipedai for "blowhole flap" give only one result at Bottlenose dolphin, which is referenced back to the same page on Seaworld as above. "6. A single blowhole, located on the dorsal surface of the head, is covered by a muscular flap. The flap provides a water-tight seal." 220.101 talk\Contribs 11:38, 4 September 2010 (UTC)
- I'm not so sure about that. Sources say 'rostrum' apparently refer to the animals snout! See Rostrum (anatomy), also see the diagram here, which is supposed to be sourced from Seaworld. From the Seaworld website here under HEAD, 2. "In front of the melon, a bottlenose dolphin has a well-defined rostrum (snoutlike projection)." I can't find a specific name for a flap over the blowhole.
Snoring = Collapsed Trachea?
I've often seen in videos of riots or so forth that people who are assaulted and take severe blunt damage to their face/head start to make a very distinct and audible 'snoring' sound when they are down. They appear to be conscious (though sometimes barely) while doing this. I looked at various reasons why people snore and generally found an indication of a difficulty/blockage of the airway. Does anyone know what happened to them to cause this? I assume a collapsed trachea but I'm not particularly adept in anatomy or biology. Robots.by.hand (talk) 01:03, 4 September 2010 (UTC)- A truly collapsed trachea is a very serious event that's likely to lead to death without immediate intervention. I rather think you heard Stridor due to someone being winded, a very unpleasant but hopefully very temporary event frequently caused by one's lungs being used as a dudelsack. -- Finlay McWalter ☻ Talk 01:25, 4 September 2010 (UTC)
- The people I've seen in this condition did not sustain serious blows to their chest/stomach/back. And some of the people were fine after a short while (stood up/walked off after a paramedic/police officer instructed them to breath through in their nose and out through their mouth while they were on the ground for a few minutes in some videos) so it seems it wasn't a collapsed trachea. Robots.by.hand (talk) 01:42, 4 September 2010 (UTC)
- My experience is that it's when I sleep in the wrong posture. Sleeping directly on the back or certain stuff where some flappy body organs do flappy things relaxed and causing the snoring. Are you ready for IPv6? (talk) 07:29, 4 September 2010 (UTC)
World War III and Alein invasion
HOw likely is WWIII and alein invasion? Like is it for certain that WWWIII will never happen ever again and there won't be any more world wars? If it isn't and if WWWIII happens, will there be conscription reinforced in lots of countries where it's abolished? What about the US and selective service?And how about alein invasion? If aleins do invade Earth and exterminate everyone how likely is it? What about meteors? Do people know when the next meteor will hit Earth. Lastly, will humans be extinct by the 25th century? Or sooner? HOw do people predict the Earth will be like in the 25th century.
I've read the above guidelines so don't say please that these questions ask for opinions. I'm not asking for opinions just to be clear. I'm asking for reliable sources or information that gives evidence for any of the above phenomena and past experience that could back up the occurence of the above phenomena.
thanks guys ... —Preceding unsigned comment added by 114.72.206.160 (talk) 08:33, 4 September 2010 (UTC)
- You have asked
fiveseven (by my count) separate questions above; at least one of them requires prediction of unforseeable future events, which the Reference Desks do not (and cannot) undertake. Trying to ask all of them under one heading will lead to confusion and unwieldiness: I suggest you repost your questions one at a time (waiting for each to be dealt with before posing the next one) so that each can be addressed (or not) separately. 87.81.230.195 (talk) 10:52, 4 September 2010 (UTC) - Unfortunately you won't get any reliable sources on the above phenomena. All we can give you are opinions, so here's mine.
- "How likely is WWIII and alien invasion?" - We don't know. No one does, but I'd speculate that the former is more likely than the latter (given we've already have two!).
- "Like is it for certain that WWWIII will never happen ever again and there won't be any more world wars?" - It is by no means certain that there won't be another World War. I'd say it's unlikely unless we get into another severe paranoia, power-bent struggle like the Cold War but we can't predict the future.
- "If it isn't and if WWWIII happens, will there be conscription reinforced in lots of countries where it's abolished? What about the US and selective service?" - I'd say conscription is unlikely in Western countries, at least to the extent it was present back in World War I & II. Most warfare in modern technological countries is carried out almost in proxy with aircraft, ships and bombs. Of course troops are still necessary, but not to the same level as was required by trench warfare.
- "If aleins do invade Earth and exterminate everyone how likely is it?" - If aliens invade Earth and exterminate everyone then obviously it's 100% likely. Sorry, I'll stop joking around, I know what you meant. How likely is it that aliens will invade our planet and kill everyone? Who knows. We're still trying to figure out whether aliens exist, let alone are they violent or peaceful. If they exist, they could be either.
- "What about meteors? Do people know when the next meteor will hit Earth?" - Not for certain. Most meteor impact predictions are just that, predictions based on probabilities! I can't remember the specific examples off my head but there are predicted close-encounters in the near future, but none are predicted to be close enough to cause concern.
- "Lastly, will humans be extinct by the 25th century? Or sooner? HOw do people predict the Earth will be like in the 25th century?" - Again, you're asking us to answer (with reliable sources?! ha!) a question which no one can know the answer to. It depends on too many factors. Do we stop climate change? Do we survive it even if we stopped emitting all ozone depleting gases now? Will a meteor actually hit Earth that we've missed? Will there be a global, nuclear war? It's impossible to predict. As for how people supposedly predict what life will be like in the 25th century: they're guessing. No one knows. We take predictions on technology by extrapolating how we've progressed/how we're progressing, but it's not very reliable in the long term. Regards, --—Cyclonenim | Chat 11:09, 4 September 2010 (UTC)
- Our article on Meteorites says that "an estimated 500 meteorites ranging in size from marbles to basketballs or larger do reach the surface each year" - so there will probably be several meteorite impacts somewhere on Earth in the next 24 hours. NASA has catalogued around 1,000 Potentially Hazardous Objects with diameters of 150m or larger which could potentially impact the Earth at some remote time in the future, but none has ever scored above 4 on the 10-point Torino Scale of impact hazard, and none currently scores above 2. Gandalf61 (talk) 12:41, 4 September 2010 (UTC)
poisoned letter
what is a poisoned letter like that that killedhttp://en.wikipedia.org/wiki/Ibn_Al-Khattab —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 10:48, 4 September 2010 (UTC)
- I don't think any details are available about that or about the many other reported cases of Chechen rebels being a poisoned by the FSB other than that in the more recent cases using food, the poison was slow acting. Sean.hoyland - talk 11:15, 4 September 2010 (UTC)
- Whilst I doubt we can say for certain, it's likely to either be an airborne toxin contained within the envelope, such as anthrax, or a toxin coated on the letter that, when touched, is absorbed through the skin. Regards, --—Cyclonenim | Chat 11:50, 4 September 2010 (UTC)
- Also, you may be interested in Laboratory 12. Sean.hoyland - talk 12:37, 4 September 2010 (UTC)
Where does the ink from whiteboards go when you erase them?
This may sound like a silly question, but what happens to the ink when you clean a whiteboard (like this) with an eraser (like this)? I used to think it went into the eraser, but when I tried to clean mine, which must have been used hundreds of times, with water and soap, I noticed no ink would come out of it.Does it pulverize and go into the air (ready to be inhaled), or does it somehow magically diffuse deeply into the eraser where it can't be washed out? Is it even real ink in those pens, or something else?
Thanks for your ideas, --Sven Eberhardt (talk) 13:00, 4 September 2010 (UTC)
