Wikipedia:Reference desk/Science

July 14

A wire from head to toe moving through earth's magnetic field

When wiring moves through a magnetic field it generates electricity. Would it be practical to use this to generate a small amount of electrical energy by having a wire or loop running from ones head to ones toes, as this would pass through the earth's magnetic field as you walk about?

Could (or is) the earth's magnetic field be used in any other way to generate 'free' electrical power? I recall that radio aerials on moving ships, for example, can spontaneously get a high voltage. Thanks. 80.2.220.179 00:08, 14 July 2007 (UTC)

I'm not sure how much power you could generate that way, as the Earth's magnetic field is very weak. But in any case it would not be free: the wire would resist your movement, requiring you to expend extra energy equal to the amount of electricity generated. Of course, if you're walking for exercise then you might not mind that. --Anonymous, July 14, 2007, 00:25 (UTC).

Not only is the Earth's magnetic field very weak (30-60 microtesla), it's the change in magnetic field which induces current (as seen through Faraday's law of induction). For a rough calculation, assume you're walking north, with the horizontal component of Earth's magnetic field decreasing from 50mT to 0mT from the magnetic equator to the magnetic pole, over $10000km=1.0\times 10^{7}m$. Assume you walk at $1{\frac {m}{s}}$, and have $100$ loops of $2m^{2}$ wire. That will generate ${\mathcal {E}}=-N{d\Phi _{B} \over dt}=-100\times {\frac {dB}{dt}}\times 2m^{2}=-200m^{2}\times {\frac {dB}{dx}}{\frac {dx}{dt}}=-200m^{2}\times {\frac {5.0\times 10^{-2}T}{10^{7}m}}{\frac {1m}{1s}}=1.0\times 10^{-6}V$
In short, this would be a horrifically ineffective means of generating electricity. However, if you're patient enough, you could mount enormous loops of wire on the surface of the Earth and wait for the magnetic poles to drift, thus extracting energy from this motion (again, this would be extremely impractical). Borbrav 01:49, 14 July 2007 (UTC)

The problem with this is that you can't mount this gadget on the surface of the earth. As the earth spins, the magnetic field lines spin with it - and you spin with that. Your wire loop doesn't cross any field lines - so no electricity is generated. The idea is to put this gadget into orbit - (NOT a geosynchronous orbit) so it's crossing lots of field lines - and for it to be many kilometers long. However, I'm not convinced that there is a net gain anyway - doesn't it require some effort to push the wire loop through the field - so the craft would gradually slow down and drop out of orbit? I don't think there is a 'free lunch' here. SteveBaker 14:02, 14 July 2007 (UTC)

It is another matter if you are moving very fast, because you are the [[Space Shuttle} in orbit and have deployed a long wire (an electrodynamic tether) which stretches away from the space shuttle for a full 20 kilometres. Then, you may get a quite useful energy source. Unfortunately, the tether ripped when they tried it [1]. But I understand that NASA wants to try again. User:sanders_muc 85.127.180.47 07:58, 14 July 2007 (UTC)

If you made a magically strong wire that wouldn't break and placed it in non-geostationary orbit, it would generate electricity as a result of the Earth's magnetic field moving relative to it. It would also produce mechanical drag from the coupling and heat from the resistance. The Earth will slow down imperceptibly. Your wire will be yanked out of orbit and burn up. 76.185.61.24 (talk) 06:02, 20 October 2009 (UTC)

Does the magnetic field strength have to change? I thought it was just moving through a constant field that did it. And what about if you had wire windings attached to the soles of your feet? They move faster - twice the distance in the same time I think - than your body and are orientated differently so maybe more electricity. I was thinking of enough to generate some electricity for an electronic device of some sort rather than an electric heater. 80.0.106.3 13:48, 14 July 2007 (UTC)

It is not necessary for the magnetic field to change, or lots of generators would quit working. The wire will generate electricity proportional to the lines of flux it cuts. If it moves parallel to the lines of flux, no electricity. If it moves across the lines of flux, maximum voltage is generated. Experimenters looked into this kind of phenomena back in the era of Michael Faraday and Joseph Henry. At any location on the Earth, a compass points toward magnetic north (more correctly the North-seeking magnetic end of the compass needle points toward the Earth's South magnetic pole, which is at about 70 degrees north latitude, near the east coast of Greenland) and a Dipping needle shows the angle the lines of magnetic flux make with the horizontal. At that spot near Greenland, the flux enters the earth and the angle is vertical, so a wire connected between your feet would move perpendicular to the flux and produce a bit of electricity. At the equator the flux lines and dipping needle are about horizontal. In the northern United States, it is about 75 degrees. A wire moving transverse to this magnetic flux would thus have a potential created in it. A stationary or moving wire with a current flowing through it would experience a force, and as said previously, if current flowed from induced current, it would resist the movement. The Earth's magnetic field is about .00006 Tesla. A wire 2 meters long (assume the guy is tall) carrying one Ampere perpendicular to the Earth's magnetic field would produce a force of (1 Ampere)*(2 meters)*(.00006 Tesla)= .00012 Newtons or .00043 ounces force, which no one would notice. If you hooked a voltmeter to 2 strips of metal 2 meters apart and perpendicular to the earth's magnetic field, and arranged for your vertical wire attached to the runner to slide along them like trolley wires while he moved perpendicular to the field (perhaps moving in an east-west direction near the equator), then you could generate electricity as proposed. The induced emf would be B*l*v where B is the magnetic field, say .00006 Tesla, l is the length of the moving wire, and v is the velocity. If he moved at brisk walk, 4 miles per hour (1.8 meter/second), he would generate (.00006 Tesla)*(2 meters)*(1.8 meter/sec)=.00021 volts. If he ran at the world's record 100 meter speed of 9.77 seconds for 100 meters, or 10.23 meters/second (22.9 miles/hour), he would generate (.00006 Tesla)*(2 meters)*(10.23 meters/second)=.0012 volts. (I'm not fond of math, so feel free to check it). The amount of current and power which could be produced would depend on the resistance of the wire and connections, but would be too small to run even most small electronic devices. Now work out the details if an ice skater were doing his/her fastest spin [2] (say 308 revolutions/minute) in the same magnetic field while attached to a vertical 2 meter coil of wire. Each turn in the coil would generate the same voltage, which is what(ignoring that the coil would slow them down)? Edison 17:18, 14 July 2007 (UTC)

Rafting ants... why?

Ants rafting in a pool

Why on earth are all these ants "rafting" in a pool? Is this "normal" behavior and they purposely sought out water to raft in en masse, or is it unintentional, like a large number of ants blew into the pool and are simply clinging to one another or anything they can to stay afloat? Sifaka ^talk 06:02, 14 July 2007 (UTC)

I'd assume a serious lack of chlorine... --L^augh! 09:01, 14 July 2007 (UTC)

It's a natural behavior for river crossing - but it seems doubtful that they "decided" to cross your pool that way. An ant colony works by the sum of thousands of tiny (almost mindless) behaviors. If an ant falls into water, it probably has some kind of instinct to paddle to another ant and cling onto it. If a significant number of ants end up in the water - they'll just 'naturally' form a raft to cross that water. Sadly, these kinds of behaviors don't always work - especially in an unnatural environment like a swimming pool. SteveBaker 13:56, 14 July 2007 (UTC)

What's the name of this space telescope?

I remember reading or seeing on TV, a space telescope that is a cluster of satelite telescopes, joined using interferometry. It's supposed to have jawdropping resolution compared to existing telescopes. I have no idea if it was a definite plan or a theoretical one, but I'm fairly certain it had a name. Does anyone here know what that telescope was called?

Apparently, it will be called the Space Interferometry Mission. Clarityfiend 08:22, 14 July 2007 (UTC)

Might also have been the Terrestrial Planet Finder. Both programs have been just about axed, unfortunately. But there's always the very low-cost alternative New Worlds Imager program. — RJH (talk) 18:05, 15 July 2007 (UTC)

Satellite dish

Why is the satellite antenna shaped like a dish?

The "dish" part isn't actually the antenna; the antenna part is the little part that hangs in front of the dish. The "dish" part is a (typically) parabolic reflector. It acts like a mirror to take an incoming signal that's the size of the dish, and reflect it an focus the whole thing down to a small spot that's the size of the (small) antenna part. You may recall old-style home-TV satellite dishes that were 6-8' across, with a little "tube" held in the middle. They would grab 6-8' worth of incoming radio-waves (which travel in a line from the satellite much like invisible "light"), and reflect and focus it onto that little 2-3" tube, which was the actual antenna part. In this way, a relatively weak signal could be magnified, in much the same way that you magnify (or "focus") energy when you use a (say, 6") magnifying glass to focus 6" worth of light into a tiny little dot.

You know how the dot seems really hot? That's because you've put 6" worth of sunlight into 1/4" of space, compressing it greatly. The higher quality the magnifying glass, the more "dark space" you'll see around your dot, because it focuses ALL of the light that hits the lens, with little "slop." In this way, "regular-old weak" sunlight can be made to seem "very powerful", by the focusing.

Same thing with the satellite signal. A relatively "weak" signal can be made to seem "more powerful" by focusing it. The dish is like the magnifying glass, except it's turned the other way because it's also a mirror.

Trick you can do with a flexible mirror (i.e., a strip of that mirrored plexiglass stuff): face the Sun and reflect a mirror sized spot on the ground. Now flex the plexi-mirror so that rather than a mirror-shaped patch of sunlight, you make a teeny-tiny little line (or dot, depending on how you deform the plexi.) The curvature you make when the line/dot is near-perfect in its small&round-ness is the shape of a satellite dish.

Hope that helps! 4.246.42.103 07:37, 14 July 2007 (UTC)

Satellite dishes are actually shaped like a paraboloid, which is generated by rotating a parabola around its axis of symmetry. A parabola is a geometric figure you can create mathematically (for example, by graphing the function y=x^2). The special characteristic of the paraboloid is that all light rays that travel parallel to the axis of symmetry are reflected to the same point. This allows us to focus a large amount of electromagnetic waves to a small detector, mounted at the specific point where the reflected waves converge. --Waldsen 19:56, 14 July 2007 (UTC)

You can just about see the 'squarial' on the wall of this house

It doesn't actually have to be dish-shaped. The BSB system in the UK used a flat, square plate called a 'Squarial'. SteveBaker 01:02, 15 July 2007 (UTC)

Need details about heat-transfer for simplified weather-sim

The first answer given below satisfies the initial question. The text is left as background for the followup question, below.

Short: I'm looking to find details on how energy (heat) is absorbed and released by various materials to do a simplified weather simulation.

Details: I've checked several articles -- for example, <http://en.wikipedia.org/wiki/Specific_heat_capacity> gives a lot of information that is "close" to what I need. The part I'm missing is how to put all the various numbers and coeficients together.

I'm trying to code a simple wx-sim for a game. It does not need to be "exact" like a full-Earth sim, but I'm trying to understand what bits WOULD need to go into a full-Earth sim, so that I can understand how to simplify it and get my "close enough for the game" sim. I'm trying to avoid "pre-programmed" weather, and end up with some realistic-seeming emergent behaviours.

I've got heat coefficients for various materials, latent-heat-of-fusion numbers (i.e., ~80kC/L for water), Solar energy (i.e., 1500-2500kWhr/M^3/yr), etc. So now the part that I'm stuck on is:

If I have a brick (let's say) that's 1cubic-meter, and it's at 20°C (let's say), and I apply 100kW of energy to it for an hour (total energy applied = 100kWhr) -- how does its temperature change over time?

Follow up: now that my brick (or tub of water, or block of salt or whatever) is warmed-up, if I turn off the energy input, and just leave it in a 20°C (dark) room, how does it cool back down, over time?

What are the factors that go into that, and how does the "changes over time" part work?

More fun example (from an apocraphal anecdote which might be familiar): If I have a 5lb roast at 65°F and I want to get it to a uniform 140°F how much energy to I have to put into it? <G> (Assume that roast is mostly-water.)

I think I sort-of get the bit about <substance> + <energy> = rise-in-temp, but I don't get the "temp changes throughout the volume of the substance, over time" part. I guess "conductivity" is in there, somewhere (let's assume that my brick/roast/tub-of-water has no circulation, for the time being. I'll deal with circulation, later.)

Thanks 4.246.42.103 07:26, 14 July 2007 (UTC)

Newton's law of cooling is an excellent first-order equation describing simple heat transfer (so it's suitable for quick programming and fast run-time!). It may be suitable for a "somewhat realistic" simulation, but it will not take into account things like convection, air mass motion, and non-ideal behavior. Nimur 15:30, 14 July 2007 (UTC)

Follow-up question.

Yes, that link (and ones from it) gave me exactly what I was looking for, thank you! I now have a tangential follow-up.

Short: What's the name of the property of a material which relates to how it radiates-out heat? (And where can I find a list of said property for common materials?)

Detail: In this question, we completely ignore both conductivity and circulation -- I'm asking ONLY about radiation. Suppose I have a substance -- say an asteroid in space. It is being radiated by a source, say sunlight. To simplify, let's call the incoming radiation constant and the rock made of homogenous material. At first, my rock heats up with the incoming radiation. After a while, though, it stabalizes, and radiates-out exactly as much energy as is radiated into it. What is that property called? That is: I want to read-up on that property for various substances, so that my Wx-Sim (see above) can properly account for "soaked-up as much radiation as it can, will now begin radiating-out" of water, bricks, etc. So what's the thing I want to read about called?

Color? Nimur 19:32, 14 July 2007 (UTC)

No, color is more related to an object's albedo. I'm talking more about something's "radiation temperature" or some-such. I guess it's related to "color", except that the color can fall way out of the visible light spectrum and is not the every-day use of the word. I'm looking for "how much energy does a brick heated to 150°C radiate?", and color is more like "what wavelengths of white light does a brick reflect?" Except that I'm looking for "how can I calculate the radiated-out energy for a variety of common substances at a variety of Earthly temperatures?" I suspect that, once I find the answer it will be of the form:

* There is some forumla x=yz^k (or whatever) where x=kWatts, y=time and z=size of object.

* The value for constant k for water is 1, brick is 3.2, air is 0.5, wood is 1.1, etc.

"Or something like that." Btw, you (Nimur) seem to know this stuff pretty well, is there a way I can contact you off-wiki? I guess email-posting is discouraged due to spamming -- is there another mechanism? (I suppose I need to create a new account -- I forgot my old password and have no email on file.) Thanks! 67.72.98.25 19:55, 14 July 2007 (UTC)

There's really no reason; use my talk page, (I can respond there faster than I can respond to email anyway). Nimur 17:52, 15 July 2007 (UTC)

Ok, I'm getting closer. I think the thing I'm asking about is Black_body#Equations_governing_black_bodies. I haven't yet found different values for different substances, but maybe I'm about to learn that it's the same for every substance, and the difference is how it absorbs/conducts heat such that the volume changes temperature. Thanks again! (Oh, and I figured out my account :)) Oliepedia 20:17, 14 July 2007 (UTC)

The black-body approximation is the idealization that is independent of materials. (Hence, "black body"). Other materials have non-black-body radiation patterns, but as a first-pass approximation, you can assume that it is a perfect absorber and perfect radiator. The color of an object determines how well it absorbs / reflects at a given set of frequencies (namely the visible spectrum). An abstract generalization of color would be the frequency absorption for any arbitrary frequency of radiant energy. Nimur 00:06, 15 July 2007 (UTC)

The exact quantity you are looking for is emissivity. It's not really analogous to color, because emissivity applies to conditions of thermal equilibrium, but color doesn't. Objects which are strongly colored at room temperature can look quite different when heated - they become "red hot" or even "white hot". Unfortunately, emissivity is itself a function of wavelength, depending on the material, and also the surface shape and texture. Tungsten has an emissivity which is somewhat less than one, which is why a tungsten filament bulb has a color temperature which is different to its real temperature. --Prophys 08:59, 15 July 2007 (UTC)

Levers

If a load 40g that is 6cm away from the fulcrum is balanced by another load 8g that is (a)cm away from the fulcrum, what is (a)cm?

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It's quite easily solved knowing the moment arm formula. Someguy1221 09:47, 14 July 2007 (UTC)

Faster than light travel

iam just an artist.i believe it is possible that a human can travel faster than the speed of light. Simply by thinking of their arrival, at the destination, before the time it takes light to arrive there?Vonvilhelm 08:31, 14 July 2007 (UTC)

Nope, can't travel faster than light. Someguy1221 09:47, 14 July 2007 (UTC)

It's fine to imagine that - but unless you have some actual proof that you can do it - it's just that...imagination. It would great if that were true - teleportation by power of thought at infinite speed would be about the most liberating thing imaginable (insanely dangerous too! Accidentally thinking of arriving on the moon would result in immediate, explosive decompression...not good!). But this kind of wishful thinking is a cause of a lot of pseudo-science and it's crucial to separate out things that you wish were true from things that actually are true because madness (of the Time Cube variety) lies in the other direction. But sadly - it's conclusively, (mathematically) proven that nothing can go faster than "the speed of light in vacuum" - it's not just that we don't know of a way to go faster than light - it's that we've shown that such a way cannot possibly exist. For those of us who would dearly love for humanity to spread through the galaxy - colonise the stars, this is a desperately disappointing fact. Typically when something is proven as convincingly as relativity, scientists accept it and move on - but this restriction is SO frustrating that enormous scientific efforts have gone into trying to find a loophole in that law - but despite the best efforts of many great minds - as yet nothing convincing has been found. SteveBaker 13:43, 14 July 2007 (UTC)

To put one more nail in the coffin, numerous tests of general relativity verify experimentally that the mathematics is pretty solid. In simple terms, First, they thought about faster-than-light travel, and couldn't think of a way it could possibly work. Then, they tested it, and it didn't work. This sequence of steps is pretty much what makes science different from art. Scientists must check their work with verifiable, repeatable experiment. Nimur 15:34, 14 July 2007 (UTC)

That said, the remaining semi-plausible method for very long-distance travel is (as far as I understand) wormholes, although whether these exist or could be made viable for travel is not known by any means. These get round the problem of faster-than-light travel by taking a "short-cut" that does not go through space: imagine going from one side of an apple to the other; if you could cut through it you would seem to be going very fast to those who could only go around the side. Daniel (‽) 16:24, 14 July 2007 (UTC)

Well yes. I can bounce a laser beam off the moon to a spot one meter away from the laser source. I have 2.4 seconds to move that one meter to beat the laser there. I can move faster than light! :D. Capuchin 16:29, 14 July 2007 (UTC)

At best, it's hypothetical. My assessment is that wormholes are a clever science-fiction workaround to the problem of interstellar travel. Nimur 16:27, 14 July 2007 (UTC)

Yes - I agree. Science says that IF a wormhole existed THEN you could use it as a shortcut. It wouldn't let you travel faster than light (because that's STILL impossible) - it just gives you a shortcut that lets you travel a shorter distance. But the only way anyone can envisage a wormhole existing is by mucking about with black holes...this is all very well - but to 'cross' the wormhole would entail flying into the event horizon of a spinning (and possibly electrically charged) black hole - with all of the annoying gamma/Xray irradiation problems, the oh-so-painful spaghettification and that annoying relativity thing that would make everyone else think you're taking an infinite amount of time to reach the wormhole. Not all that practical...and probably impossible. SteveBaker 00:24, 15 July 2007 (UTC)

"...pretty much what makes science different from art..." What a condescending statement about art, and an idealistic statement about science (and a statement which speaks volumes of someone's ignorance about the ways in which science and art have been intertwined for centuries). If I recall much of what is hot in theoretical physics today is totally unverifiable by experiment, and in fact in the history of theoretical physics a great deal of it was done without the slightest collaboration with experimentalists.

To answer it is non-condescending terms: the current model of how the universe works does not seem to allow for faster than light travel. This is not an arbitrary speed-limit set, but is reflective of the fact that space and time are linked in a very deep way, and the speed of light happens to be something reflective of the barrier between them (moving through space faster than light ends up with wonky time problems — events ending before they start, etc.). Our current equations for how things move at sub-light speeds basically preclude any possibility of going faster than light — if you substitute a speed faster than light into a Lorentz contraction, for example, you end up with a nonsensical equation (you end up having to take a square root of a negative number, which ends up with an imaginary number). In addition to this, the equations also tell us that attempting to get to the speed of light requires using an infinite amount of energy — which doesn't exist, and we can't get even close to that amount.

So basically the universe as we know it is divided, speed-wise, into light, things going slower than light, and hypothetical entities which are faster than light, but cannot ever slow down. The equations have so far behaved extremely well experimentally and make a lot of logical sense as well, when you start to take them apart (they are based in relatively common-sense reasoning about the nature of space and time — Einstein's axiomatic approach is generally quite clear and quite straightforward).

All of that being said — could the equations be wrong? Sure. Nothing is more assured in science than the eventual destruction of old understandings (generally known as "progress"). Would any new understandings allow for faster than light travel by humans? Probably not — any new replacement theory would not likely change the way these things operate on scales that we could appreciate much less exploit for practical purposes. (But who knows. The idea of splitting something as massive as a uranium nucleus with something as paltry as a neutron seemed nonsensical even to those who originally proposed it. How quickly we forget how amazing some ideas once were.) --24.147.86.187 17:41, 14 July 2007 (UTC)

Firstly, it's OK to be condescending about some things - all of the politically correct bullshit about having to "respect the ideas of others" is not something I care to deal with - respect has to be earned. The 'intertwining' of art and science is WAY overrated. However, having said that, I do have a lot of respect for art and artists - just so long as they don't start trying to claim that what they have thought up out of thin air and without any evidence is somehow "real". I'm a huge SciFi book fan - they force you to stretch your mind and make you think out of the box. In my imagination - faster then light travel is not only possible - but routine. But a scientist can separate out what is imagination from what is proven. So by all means imagine what it would be like to be able to travel faster than light just by thinking about it - feel free to write great fiction, paint pictures, make sculpture - but please don't start believing it has applicability to the real world. At that point you cross the line between art and reality - and reality demands science and science is just unbelievably tedious and boring about the whole faster-than-light thing. I hate that as much as anyone - it completely sucks - but I hope I'm mature enough to accept it and relegate faster-than-light travel to the unlimited realms of my imagination. This particular imaginative leap had that kind of artistic value. It got me thinking...if it were true - what would it be like? Would I have to be very careful not to look up at the moon and wonder what it's like up there in order to avoid being teleported there and dying a horrible death? Would using this trick to get to work quickly require me to take into account the motion of the earth around the sun in order to avoid arriving where my office was a fraction of a second before and ending up underground? Would my clothes somehow 'know' to come with me when I travelled? What about my stomach contents? If I can travel faster than light then time travel is also real...what does THAT mean?!? So many mind-twisting things to think about...but that doesn't make it real...interesting...but never real. SteveBaker 00:24, 15 July 2007 (UTC)

Could Einsteins equations be wrong? Yes - of course. But they are amongst the best tested of anything we have in science - we've measured time-dilation directly using atomic clocks put on board planes. We've seen the subtle shift in frequency of radio waves coming from deep space probes - we've got photographs of gravitational lensing - the observations of the transit of Venus...utterly concinging. Everything we try at every extreme we can manage works 100% as Einstein said. If there is something wrong with those equations - it's very, very subtle indeed (and it's probably only at the level of Quantum theory that won't help us big, chunky humans much). SteveBaker 00:24, 15 July 2007 (UTC)

I stand by my assertion that art is not bound by the constraints of experimental verifiability. I don't see this as condescending. It's a statement about the different realms in which science and art operate. Artists are rarely asked to "prove" that their art is worthy. This opens up entire avenues for art to explore. Scientists must regularly prove their work has experimental verifiability. Even the "theoreticians" must be held accountable to experimental evidence eventually, or else they are categorically labeled mathematicians, philosophers, or at worst, crank scientists. Nimur 17:54, 14 July 2007 (UTC)

SteveBaker said But sadly - it's conclusively, (mathematically) proven that nothing can go faster than "the speed of light in vacuum" - it's not just that we don't know of a way to go faster than light - it's that we've shown that such a way cannot possibly exist. Actually, I believe that what we've shown isn't possible is for anything to travel AT the speed of light (results in the equivalent of a divide-by-zero in the Lorentz transformation.) Indeed, the big mystery of tachyons is that they appear to travel faster than light and to move backward in time. 67.72.98.25 19:33, 14 July 2007 (UTC)

You say that in a way that makes it sound like tachyons actually exist - for which there is zero evidence - and a very strong reason why they might not. The divide-by-zero problem in the Lorentz transforms doesn't prevent things from travelling at the speed of light (because the photons in a beam of light do exactly that...duh!) - it prevents things that travel at that speed from having non-zero rest-mass or length...which photons do not. Mathematics doesn't disallow dividing by zero - it merely says that the result is undefined. Dividing by zero happens all the time - and it's OK so long as the result is then multiplied by zero so that the undefinedness doesn't show up in the result. Hence zero rest mass and zero lenght for photons.

However, when you plug in v²>c² into the Lorentz transform, you have to take the square root of a negative number - and that results in an imaginary number - which is a big problem. Imaginary numbers are often handy mathematical tricks for getting around notational difficulties - but they never, ever show up in the results of correct calculations. They always get squared again at some later point in the calculations so they disappear again in the results. There is not one single case in all of math and physics where an imaginary number popped out into the "real" world. However, for a tachyon to exist, something imaginary (in the mathematical sense) would have to actually exist in the real world - and that seems impossible. If it were true then imaginary numbers would start popping up all over the place and we'd surely have noticed that in some way.

Scientists use the term tachyon as a convenient hypothetical when discussing theories (we use the term 'tardyon' for all particles that travel slower than light) - but theories that require the existance of these peculiar beasts are generally severely wounded in their credibility because of that. It's like "Oh oh...your theory of quark-meson-wibbloscity implies the existance of a tachyon"..."Oh - crap, you're right. Maybe I'd better try something else.". But even if tachyons did exist, they don't help our questioner. Just as regular tardyon matter can't be accellerated up to the speed of light without using an infinite amount of energy - so a hypothetical tachyon would require infinite energy to be slowed down to the speed of light and it's imaginary mass & length would make it impossible for it to travel slower than light. So it's not possible for tachyone to become tardyons and vice versa. So even if tachyons did exist - they would be of no help whatever to a human wishing to travel faster than light. We can't somehow magically transform ourselves into tachyons - travel to our destination - then change back again because tachyons can't slow down enough.

I blame Star Trek for the popular idea that tachyons are real - they use the word all the time when they need something to shoot at an 'interstellar anomaly' (a wibbly-wobbly green thing that's up there in the forward view screen). SteveBaker 23:55, 14 July 2007 (UTC)

I just want to step on your "Mathematics doesn't disallow dividing by zero - it merely says that the result is undefined. Dividing by zero happens all the time - and it's OK so long as the result is then multiplied by zero so that the undefinedness doesn't show up in the result." An undefined number, multiplied by zero, remains undefined. The rigorous way to absolve this issue is to create an expression for the final, desirable value (mass, length, whathaveyou) such that the limit as the speed approaches the speed of light does not display any undefinedness (if that's a word), if i recall my math correctly. Someguy1221 00:15, 15 July 2007 (UTC)

I disagree. The slope of a ladder is conveniently represented by the height it reaches up the wall divided by the distance from the bottom of the ladder to the base of the wall. If I push the ladder parallel to the wall, the slope is the length of the ladder divided by zero...damn! However, if I wish to use the slope to calculate the frictional forces required to stop the ladder from slipping - the horizontal component of that force ends up being proportional to zero multiplied by the slope of the ladder - which is undefined. Fortunately anything times zero is zero - so we're good to go with a zero as the result...which is correct. Sadly, this is not true for the vertical component of the force where the top of the ladder meets the wall because we have something non-zero multiplied by an undefined number - but that's OK - with the top of the ladder only just barely touching the wall, the vertical friction is indeed a meaningless concept. Math works - often despite the mathematicians. SteveBaker 00:37, 15 July 2007 (UTC)

And as far as my own purposes go, I do agree with you. But given my plentiful interaction with one or more mathematicians, do expect one to slap you if you suggest that zero multiplied by an undefined number is always zero. Even though ultra-strict mathematical formalism is often unnecessary in physics. Someguy1221 01:36, 15 July 2007 (UTC)

SteveBaker's assertions are pretty valid. Indeed, complex numbers are useful abstractions, but observable physical quantities (conveniently called "reality", but also very well-defined in theoretical physics) do not have imaginary components. Nimur 00:23, 15 July 2007 (UTC)

In no particular order: (1) There are useful contexts in which it is meaningful to divide by zero -- see Riemann sphere. (2) Whether it's well-defined to multiply an ill-defined quantity by zero, again, depends. Usually not. But there are situations where you get away with it, and Steve may well have identified one. (3) The claim that it has been "mathematically proven" that nothing can go faster than light is completely wrong. That is not the sort of thing even subject to mathematical proof. --Trovatore 08:41, 16 July 2007 (UTC)

But here's a thought experiment. Imaginary numbers are often used to express frequency domain phenomena to time-domain creatures as ourselves. But wouldn't photon be more of a frequency domain creature and see our world as imaginary anomaly? Also, the energy barrier to exceeding the speed of light is infinite as we know it. But my own feeling is that nature abhors the infinite and that the physical model will break down before that at some point and another theory will be needed. Just a guess but like the elegant laws of Newton, so to will elegant laws of the theory of relativity, need to enhanced. --Tbeatty 05:46, 17 July 2007 (UTC)

Alternative To Evolution

Are there any alternatives to evolution by natural selection that are supported by scientific evidence? The article on evolution says that it is "completely uncontested in the scientific literature" and i was wondering wether this is strictly true Fountainmon

No - that's truly the only theory that's accepted to any degree whatever. There are small variations on the details - for exmple, whether evolution is a continual process of gradual change or whether species stay stable for long periods then evolve relatively quickly as a result of a sudden change - but there is no significant argument about the core principles. Historically, Lysenkoism was an alternative theory - it held that (for example) Giraffes were originally a lot like horses - but as they had to reach up into trees to get food, the necks of living animals would be slightly stretched by doing that activity (just as you can getter at lifting weights by doing that exercise) - and that the offspring of that animal would inherit that slight neck stretch. Hence - kindof like evolution - giraffes would get longer and longer necks as generations passed. As an idea, it's not bad - and it's a lot like evolution - the only problem is that we have no mechanism to explain the inheritance of an aquired-by-exercise ability. We can look at the genes of an animal at birth and again when it reproduces and there are no changes. So that theory was heavily pushed and taught in Russia. But the idea has been conclusively disproved. SteveBaker 13:28, 14 July 2007 (UTC)

You seem to be confusing Lysenko and Lamarck. Eran of Arcadia 16:36, 19 July 2007 (UTC)

Well, in addition to "evolution by natural selection" there's "evolution by sexual selection", but that's not so much an alternative as an additional mechanism. "Completely uncontested in the scientific literature" seems quite proper. - Nunh-huh 14:34, 14 July 2007 (UTC)

Maybe you need a concise definition of natural selection - this will help you see that it is self-evident. Things that die off more often don't stay around for long. Organisms that can live better tend to stick around more often. They have been "selected" naturally. How could it possibly work any other way? Unless... there were an intelligent designer who is super-naturally selecting unfit species who would normally die without some kind of interference? Nimur 15:38, 14 July 2007 (UTC)

Well, the non-self-evident part is that selective pressures are enough to constitute species change. The question never was whether there was truly a "survival of the fittest," just whether that actually accounted for evolution. (And evidence as to how non-self-evident that is can be found in the fact that even after Darwin proposed it, most scientists didn't think natural selection could actually account for evolution until the 1930s!!) --24.147.86.187 16:10, 14 July 2007 (UTC)

You are probably confusing evolution and speciation - related but different concepts. In any case, scientific consensus is that natural selection and genetic variation are sufficient to cause speciation. The speciation article contains many references including this list of observed instances of speciation. Nimur

Well, I'm not confusing them, but that is almost certainly what the poster meant when they said "evolution", and it is what most non-biologists mean. The modern synthesis definition of "evolution" is practically tautological and is not at all what people (including Darwin) meant by "evolution". In any case I am not arguing against natural selection in any way; I am just arguing that it is all as "self-evident" as you'd make it out to be. It's not — which is why it took a long, long time to get to the current theory of it, and why a lot of very smart and very capable people were long opposed to natural selection as the force behind evolution. --24.147.86.187 17:25, 14 July 2007 (UTC)

There are a few scientists who disagreed that natural selection could cause speciation in the long term. Another detail I guess, but already mentioned above. See punctuated equilibrium. Someguy1221 19:10, 14 July 2007 (UTC)

Somethign that I couldnt find with a quick google.

You hear often hear that the tap water you drink has passed through half a dozen (or more/less) people before you. I have no problems believing that but i'd love a scientific source if you can find one? Does it differ for different countries? Capuchin 16:14, 14 July 2007 (UTC)

Half a dozen? Try hundreds. Think about it- you drink five glasses of water. You urinate most of that back out, be it into a toilet, where it is taken to a waste treatment plant, or behind a bush, where it filters through the earth, and eventually joins an underground water source, where it flows out to ponds/oceans where it becomes rain, which falls to earth, etc. Given the Water cycle, it's entirely possible that the water you drink used to be Napoleon's bath water, or part of a soup from some obscure village eons ago. --L^augh! 16:56, 14 July 2007 (UTC)

And of course, the water ends up being thoroughly mixed in the pipes and lakes, so it's not just one bit of water but a great mixture; I remember going to a chemistry lecture where the speaker stated that in a cup of water, every person on the planet, alive and historical, had drunk and passed at least a few of the molecules in the glass (1 tablespoon of water contains about 6 hundred thousand million million million water molecules, so it's not surprising really!). Laïka 17:17, 14 July 2007 (UTC)

Well, the second law of thermodynamics basically implies that you'll never get much of any given bit of water that anybody has previously drunk or used, and the oceans are incredibly vast. So I don't think you can at all say with certainty that a molecule of Napoleon's bathwater is in any given small amount of water. The odds of getting any individual molecule of water are incomparably small, though the odds of getting some molecule of water that was used in the long past are quite high. --24.147.86.187 17:21, 14 July 2007 (UTC)

I seem to recall the lecture addressing this by saying that the oceans contained approximately the same number of litres of water as the bottle contained water molecules, so if you took a one litre sample of water, there should be on average one water molecule in the litre sample for every litre of the original water product; a bathtub contains maybe 100 litres, Napoleon must have had hundreds of baths over his lifetime, so the bottle might contain up to 10000 water molecules from Napolean's bathtub - not much, but still... Laïka 17:29, 14 July 2007 (UTC)

A very similar calculation to the famous "odds of breathing in a molecule of air from Julius Caesar's Et tu Brutus" problem. Conclusion: you don't want to think about how many people your water has passed through. — Laura Scudder ☎ 17:45, 14 July 2007 (UTC)

There is a fallacy in assuming a totally random redistribution of all water-molecules. It would be ridiculously complicated to try to track a single molecule through multiple iterations of the water cycle, but it would be worthwhile to estimate the statistical time-distance propagation constant (i.e. a molecule travels X miles in one week through evaporation, rain, ocean currents... etc). I bet it's fairly localized; if ocean waves are anything to compare, the net propagation of energy does not require mass movement of individual fluid components... but current and wave motion are not identical. (Rivers are a good counter-example, of course). Nimur 17:50, 14 July 2007 (UTC)

Oceanic mixing time is long (i.e. ~2000 years), but atmospheric mixing is rapid (e.g. months). A gentle breeze (e.g. 10 miles per hour) can carry molecules 1700 miles in a week. Dragons flight 17:57, 14 July 2007 (UTC)

Yes of course, by direct multiplication... but does a single molecule travel all 1700 miles? Brownian motion, convection, and other considerations might yield a very complicated and statistical answer. Nimur 18:33, 14 July 2007 (UTC)

Wind is direct mass transfer, so yes the statistical average particle in a 10 mph breeze is advancing at 10 mph. Dragons flight 20:01, 14 July 2007 (UTC)

I would like to add that we can see it happen with large volcanic eruptions as the ash and sulphates disperse globally over a period of months. Dragons flight 20:02, 14 July 2007 (UTC)

In truth, we can't know whether a particular volume of water does or does not contain water that was drunk/bathed in/whatever by someone else in the past. So any definite statement is going to be false a lot of the time and true other times. It is safe to say that if you go far enough into the past (eg Julius Ceasar's bathwater) then it's more likely to be true than for (say) President Nixon's pee-pee! If mixing were essentially perfect then it's true that every day you'd definitely be drinking a few molecules of everyone who ever lived. If mixing is imperfect then it's likely that the water you are drinking has never passed through any other human in history. If you dug down a few thousand feet under the Antarctic ice, grabbed a cupfull of the stuff - melted it and drank it - then I think it's safe to say that no other humans drank it before. If you took a cupful of water from the municipal water supply of a large city - then it's certain that many other humans will have processed much of that water through their bodies before. The truth lies between those extremes - but it's impossible to say where. The adage has value in that it rams home the point that there are a truly insane number of molecules in a glass of water! SteveBaker 23:27, 14 July 2007 (UTC)

Is it worth pointing out that there is no distinguishable difference between one molecule of pristine Antarctic ice meltwater, and one molecule of undiluted Napoleon pee water? --Prophys 09:11, 15 July 2007 (UTC)

Of course that's true - but does it matter? We are interested in the history of those molecules - not whether they are different in any way. SteveBaker 18:49, 15 July 2007 (UTC)

By certain definitions they are the same molecule if they are exactly the same in every way except location. Also, photosynthesis involves breaking up water molecules and reforming them. I don't know how big the effect is, but it could make it improbable that all the atoms in any molecule in your volume of water were in one of Napoleon's water, and it would be even more improbable that they were still in the same molecule. Electrons exchange atoms even more than atoms exchange molecules. — Daniel 03:02, 16 July 2007 (UTC)

Ants

Ants have queens. Do they ever have coups?

There's more to being queen ant than just leading the nest and getting lots of food; queens are made at birth by being fed special food, allowing the queen to develop wings and lay eggs. Normal ants are not given this food, and as a result, they can never lay eggs. If a nest of ants ever managed to get rid of their queen, they'd be stuck - no new ants could be born and the colony would die out. Laïka 18:19, 14 July 2007 (UTC)

Queen ant says that there can be more than one queen in a colony, depending on the species. It doesn't say if they all breed or only one does and the rest are spares. Clarityfiend 20:12, 14 July 2007 (UTC)

Make sure you don't take the political metaphor too seriously... it is a metaphor only, and as such only certain parts of the source domain apply to the destination domain (they don't wear little crowns either, or get their portraits done by Annie Leibowitz). --24.147.86.187 21:50, 14 July 2007 (UTC)

Maybe not in ants, but in stingless bees there are upstarts called dwarf queens. Bendž|Ť 22:59, 15 July 2007 (UTC)

240 V 50/60 Hz

On reading Domestic AC power plugs and sockets, I see that some parts of the world use 240 volts at 50 Hz, while others use 240 volts at 60 Hz. What would happen if you supplied something expecting a different frequency (e.g. 60 Hz on something that wants 50 Hz)? Nothing? Boom? --Tim1988 ^talk 18:23, 14 July 2007 (UTC)

Probably very little; most systems with sensitive electronics use a power supply and convert the AC to DC. Those converters often use a filling (or holding) capacitor, and since 50 and 60 Hz are fairly close anyway, the capacitor will effectively convert to DC. A few AC items such as motors might possibly be sensitive to the frequency deviation, so you should check tolerances for particular devices. Nimur 18:31, 14 July 2007 (UTC)

Nimur is right "in general" however, you probably don't want to risk your electric devices by plugging them into the wrong source. Basically, you'll run into an inefficiency which can lead to heat which can either ruin the device or, in extreme cases, lead to a fire. While technically possible, it's highly unlikely that anything would "explode" ("boom") unless you happen to be on the set of a Hollywood movie ;)

Imagine that there is a vending machine with a candybar behind a door, and the door opens and closes 60x/minute. You have a mechanical arm that you can extend on the 50ths of a second (up to 50x/sec). You want to grab the candy bar. You can see how, while it can be done, you'd be "fighting against your tools", right? Now imagine that, instead of a whole candy bar, there was a teeny-tiny crumb of a bar that, once you had all 10,000 of them, you could assemble them into a whole bar & eat. Door opens & closes 60x/sec, your grabber-arm is on the 50ths, you need to do this 10,000 times.

Very-abstractly, that's what it's like when you plug your 60hz electric razor into a 50hz outlet. It's not so much that you'll "break everything", as that you're putting undue stress on it, making it over heat, aging it beyond its years, etc. So a razor that might normally last 3 yrs might wear out after 3 months or weeks.

(Lost my password, and no email on file. I guess I just create a new account...?) 67.72.98.25 18:48, 14 July 2007 (UTC)

Always check your electrical devices or their power adapters, or their manuals thereof, for their tolerances for electrical input before plugging into a foreign outlet. Someguy1221 19:16, 14 July 2007 (UTC)

Incidently a friend of mine plugged his 50 hz alarm clock into a 60 hz system and the time was screwed up. That might only depend on how this specific clock determined time. As well, our building has elevator motors that are wound for a 50 hz system, but are used at 60 hz, and they apparently produce more heat than designed for because of that - this is according to the elevator tech. Flyguy649 ^talk _contribs 21:28, 14 July 2007 (UTC)

Yes, many alarm clocks use the frequency of the AC as signal to determine time. Because of this power providers are actually required to maintain 60 Hz to a rather high tolerance over the long term. During times of peak demand, the generators may slow down a little due to high load, so you might get 58 Hz for a while, but if this happens the operators are required to spin them up to 62 Hz (etc.) to catch up later in the day so that clocks run right. Dragons flight 21:35, 14 July 2007 (UTC)

I would like to award User:67.72.98.25 the Official Wikipedia platinum plated platic spork award for the most confusing and useless answer in the history of the help desk! WHAT?!?! Most (but not all) 60Hz devices work perfectly at 50Hz (and vice-versa) because the manufacturers want to sell them in markets where they other frequency is standard without having to redesign them. However, you can't rely on this and some products won't work, others will get outrageously hot, and yet others will burn out or catch fire. There is really no way to tell which are which. Being a Brit (240V, 50Hz) who lives in the USA (120V, 60Hz), I have a bunch of gizmos that purport to convert one into the other - but as far as I can tell, they all convert the voltage without changing the frequency. My UK CamCorder charger works fine when plugged into one of these things - my Laptop charger has a 110/220v switch - but not a Hz conversion - and it works just fine. An antique table lamp works - no problems. But the UK charger for my son's R/C car overheated to the point where it burned my finger when I touched it here in the USA on 60Hz/220V and our US cellphone charger didn't charge the cellphone battery at all on 50Hz/110V in the UK. So "your milage may vary". Good luck with that! SteveBaker 23:14, 14 July 2007 (UTC)

Okay, here's how I'd divide things:

• Most purely-electronic things that work on 50 Hz (and don't use the line frequency for timing as many clocks do) will work fine on 60 Hz but the reverse isn't necessarily true.
• Transformers designed for 50 Hz will work fine on 60 Hz, but a transformer designed solely for 60 Hz will may over-heat when operated on 50 Hz.
• In power supply units, bulk-storage capacitors designed for 50 Hz will work fine on 60 Hz, but capacitors sized solely for 60 Hz will be sized too small when operated on 50 Hz and the power supply unit will have too much ripple in its output.
• AC induction and synchronous electric motors operated on the wrong frequency will turn at the wrong speed. 60 Hz motors operated on 50 Hz may overheat.
• AC universal motors will work fine.
• DC motors will work fine if their power supply units work okay.

Nowadays, because manufacturers usually like to be able to ship world-wide, many things are truly universal (100-240 VAC, 50-60 Hz), but the ratings on the manufacturer's nameplate is the best final arbiter of what will work and what will cause the release of the magic smoke.

Atlant 00:38, 15 July 2007 (UTC)

Very good! No platinum-plated spork for you then! One VERY minor quibble. A 60Hz transformer running on 50Hz will certainly get hotter than it would on 50Hz - but whether that is over-heating is not so certain. It may be able to dissipate that heat without problems - in which case it may merely get warm. SteveBaker 00:53, 15 July 2007 (UTC)

Once the core of your transformer becomes magnetically saturated, it stops being a transformer and starts being a short circuit. If your transformer is sized for 60Hz, then 50Hz won't be changing fast enough to prevent this. --Carnildo 22:59, 16 July 2007 (UTC)

Yes in reply to atlant there is a lower frequency limit on a transformer, going below which will release the magic smoke! It occurs when the magnetising current (due to insufficient reactance) increases to such an extent that the pri winding overheats/melts/ bursts into flames! Zero frequency is therefore good to avoid. Tuggy

Shape of raindrops - teardrop shape or spherical?

Has real rain been studied, for example by high-speed photography, and the typical shape of raindrops been found empirically? Is it teardrop or sphere? 80.0.96.159 18:39, 14 July 2007 (UTC)

According to raindrop (which please see for more details), "Small raindrops are nearly spherical. Larger ones become increasingly flattened on the bottom, like hamburger buns; very large ones are shaped like parachutes."--Shantavira|^{feed me} 18:54, 14 July 2007 (UTC)

To be more precise regarding the "very large" raindrops (>4.5 mm or so), they go unstable, become increasingly concave and briefly look like a thick-edged parachute, and then break up into smaller droplets [3]. This instability is because the dynamic pressure of the air in front of the drop (which increases with drop size, partly because the terminal velocity does) becomes larger than the drop's internal hydrostatic pressure caused by surface tension (which decreases with size). --mglg_(talk) 21:19, 14 July 2007 (UTC)

The origin of the teardrop shape is the shape of upside-down accumulated water getting heavier than what the surface tension can stand. The water drop, just before dripping, stretches away of the surface in a teardrop shape, until the surface tension breaks and the water drop stars falling. From there on, the shape should be roughly spherical, as explained. — Kieff | Talk 00:37, 15 July 2007 (UTC)

Even if you don't ever see the raindrops themselves, every time you see a rainbow, it is due to the fact that raindrops are spherical. You wouldn't see the distinct colors if the raindrops were nonspherical. -- JSBillings 02:11, 15 July 2007 (UTC)

I suspect that's not precisely true. The raindrops need only have internally-reflective surfaces and be generally similar in shape. An oblate raindrop will still refract (and internally reflect) light. But the difference is probably negligible if the distortion is minor. — RJH (talk) 17:59, 15 July 2007 (UTC)

And in any case - just as the raindrops aren't spherical - so the rainbow isn't 100% perfect - they are fuzzy, blurry things. Take a look at the spectrum you get out of a glass prism - it's much crisper and richer in colour than natural rainbows. You are seeing the result of reflections and refractions from the AVERAGE of an awful lot of raindrops. SteveBaker 18:46, 15 July 2007 (UTC)

Time Zones

I am curious. What time zone is Wikipedia based on ... and why? I guess I am looking for an answer such as "Wikipedia is on USA Pacific Time because their headquarters are in Los Angeles." --- or whatever. Thanks. (JosephASpadaro 19:03, 14 July 2007 (UTC))

Wikipedia time is Coordinated Universal Time, that UTC next to your sig. I don't know what the specific reasoning for this was, though. Someguy1221 19:13, 14 July 2007 (UTC)

UTC is a pretty standard default time zone. It has the advantage of being theoretically culturally neutral. Donald Hosek 20:33, 14 July 2007 (UTC)

Incidently, both the Wikipedia servers and the Wikimedia Foundation are based in St. Petersburg, Florida, so if they did use local time, it would be UTC-5 (UTC-4 in the summer). Laïka 21:11, 14 July 2007 (UTC)

Culturally neutral? I'd think that would be more like UTC-2 or -11, so one can grab large swaths of ocean where no one lives.  ;-) By contrast, I think the English would be annoyed to know you think they have no culture. Dragons flight 21:26, 14 July 2007 (UTC)

And indeed, the determination of Greenwich as being "universal" was highly controversial! The French wanted it centered on Paris, but the British controlled the shipping... in any case, I'm pretty sure it can be adjusted in one's settings. --24.147.86.187 21:48, 14 July 2007 (UTC)

You have to pick somewhere - and wherever you pick will upset someone. We Brits happened to get the technology that made it matter first - so we win! SteveBaker 23:03, 14 July 2007 (UTC)

How's that again, Mr. CDT? :-) —Steve Summit (talk) 12:00, 15 July 2007 (UTC)

Speaking as a Brit, I just want to point out we are currently on UTC +1. Algebraist 23:34, 14 July 2007 (UTC)

Indeed. If you make the casual assumption that GMT == "British time", you're not alone, but it's quite wrong, and the distinction is more than merely theoretical. There was a minor scandal a couple of years back when it was discovered that in some version of Microsoft Windows or another, the folks in Redmond (in PST/PDT) had made this same assumption, but it meant that you couldn't set the clock forward for summer time in Britain without screwing up GMT, or vice versa. (That is, the relevant timezone dropdown box had only one choice, "GMT", rather than the necessary two, "GMT" and "British time", distinctly separate.) —Steve Summit (talk) 00:02, 15 July 2007 (UTC)

Yes - just because we have arbitarily chosen the little town of Greenwich (specifically center of the brass line that travels through the middle of the old royal observatory there) as 'zero' doesn't in anyway imply that British people use GMT+0 for wall-clock time. We have daylight savings time just like many other countries (except we call it "British Summer Time"). So during the winter, we use GMT+0 and in the Summer, GMT+1 - but there is no particular connection between the time we use and where the meridian happens to be, There have been some fairly serious proposals to switch to GMT+1 in the winter and GMT+2 in the summer. SteveBaker 00:49, 15 July 2007 (UTC)

A follow-up. When it is exactly 0:00:00 in UTC ... it is exactly midnight where? In Greenwich, England? Thanks. (JosephASpadaro 00:58, 15 July 2007 (UTC))

According to this site, a couple of them are Casablanca and Reykjavik. But this would change depending on day-light savings. That's why currently, Greenwich is not at UTC+0 time (as stated by Algebraist above). - Akamad 06:14, 15 July 2007 (UTC)

Not so sure about "no particular connection between the time we use and where the meridian happens to be", Steve. It would be a little odd if the UK was on GMT+7, say. I'm not saying they can't do this, but would they, realistically? -- JackofOz 06:21, 15 July 2007 (UTC)

Well, "no particular connection" might have been a little strong, but it's certainly the case that there are several areas where the time zones depart rather significantly from the nice, regular, 15-degree-centered stripes you might expect. See this excellent map. —Other Steve (talk) 23:52, 15 July 2007 (UTC)

Two small points. First, the Greenwich meridian was chosen as the prime meridian not because of who "controlled the shipping", but because of what existing mapmakers were doing. Not only maps made in Great Britain, but also in the US, the Netherlands, Italy, and Japan, among others, all used the Greenwich meridian. According to figures presented by Sandford Fleming at the International Meridian Conference, 65% of the world's ships (representing 72% of the world's shipping tonnage) used maps based on Greenwich. And the maps used by the other 35% (28%) were divided between many other prime meridians; the Paris meridian was the second most popular, and it had just 10% of ships (8% of tonnage). See Greenwich Time and the Longitude by Derek Howse (1997 edition ISBN 0-85667-468-0).

Second, the prime meridian is no longer actually defined by the old Greenwich Observatory, and in fact is now computed in a way that makes it about 100 m (330 feet) off the old position at Greenwich. See Prime Meridian and World Geodetic System.

--Anonymous, July 15, 08:43 (UTC).

Ah, thank you, Mr. Whoever-you-are, that point needed making. But there's one more point: the whole point of zone time is that it doesn't change the answer. When it's exactly 00:00:00 in UTC (or GMT), and unless summer time is in effect, it is exactly midnight in Greenwich. That is, the arguments in this earlier thread do not apply, and the time in Greenwich is not 100 ÷ 1000 ÷ 40032 × 24 × 60 × 60 = 0.2 seconds earlier, or anything. It's also exactly midnight, of course, in London, Edinburgh, Milton Keynes, Barrow-on-Trent, Weston-super-Mare, and Ashby-de-la-Zouch. And Casablanca and Reykjavik, as Akamad said. And Dublin, Lisbon, Laâyoune, Nouakchott, Bamako, Dakar, Conakry, Abidjan, Monrovia, Freetown, Ouagadougou, Lomé, and Accra. —Steve Summit (talk) 4:57, 15 July 2007 (PDT)

When you talk about 'exactly midnight' it makes me think of solar midnight, which isn't the case for the aforementioned cities. -- JSBillings 14:06, 15 July 2007 (UTC)

If JosephASpadaro was in fact asking about "solar midnight" (which sounds kind of like an amusing oxymoron!), then my answer is incorrect, and it actually ends up being a rather interesting question. I don't know (and our UTC article doesn't say) what the relationship is between UTC midnight and the WGS84 geoid upon which most lat/long measurements are based. So I don't know whether UTC midnight is supposed to correspond to local solar midnight at Greenwich, or at the WGS84 0° longitude (which as our anonymous informant has reminded us is about 100 m off of Greenwich), or somewhere else. In practice, of course, the exact geographical location of UTC midnight wanders around somewhat, due to leap seconds, somewhat as shown here. —Steve Summit (talk) 23:52, 15 July 2007 (UTC)

July 15

Harnessing rotational energy into stored energy

Strange question, but i am curious if i were to place my bike on a frame, suspending me while i pedal, how would i be able to harness and save this energy, and what equipment exists (if any) that someone knows of that i could to use to convert my mechanical energy into a useful energy source (battery) Thanks if anyone is willing to tackle this.

If I'm correct in understanding your description, you are talking about a standard electrical generator. Have a look at this site to see how they work. - Akamad 01:21, 15 July 2007 (UTC)

Our hub dynamo article specifically answers your question. StuRat 06:09, 15 July 2007 (UTC)

Yes, this will definitely work - although the voltage you get out from a bicycle dynamo might be a bit feeble for doing much other than lighting a couple of flashlight bulbs. With more efficient use of gearing and a better generator, you could do better. According to Human-powered transport The average "in-shape" cyclist can produce about 3 watts/kg for more than an hour (e.g., around 200 watts for a 70 kg rider), with top amateurs producing 5 watts/kg and elite athletes achieving 6 watts/kg for similar lengths of time.. According to Electrical generator bicycle generators are only 40% to 60% efficient - and a car alternator would be a better bet at 90% efficiency. So with optimal gearing and the best available generator, at 180 Watts, you could keep three 60 Watt lightbulbs burning - for "more than an hour" (assuming that you could keep up that rate of exercise). Alternatively, if you tried to power your PC with it - you'd have to pedal pretty hard to keep it running - you'd have to be a "top amateur" cyclist to run a PC for an hour before getting tired out. According to Orders of magnitude (power), two square meters of solar panels would produce more energy - assuming you get an hour of sunlight per day. SteveBaker 18:40, 15 July 2007 (UTC)

I think the best application is providing power for a bicycle to turn on lights for night driving. (It should also have rechargeable batteries so the lights don't go off when you stop.) StuRat 01:23, 16 July 2007 (UTC)

Search using "Flywheel Energy Storage" also .Polypipe Wrangler 07:52, 17 July 2007 (UTC)

Weight

I have noticed an odd phenomenon, and I would like some input. I weigh myself every day -- at roughly the same time of day, wearing the same outfit each day (i.e., my birthday suit). I understand that one's weight will always have minor variations from day to day (say, water retained for example) and even from hour to hour. Due to many factors, and the degree of accuracy on a bathroom scale, one's weight fluctuates constantly, plus or minus a few pounds (I imagine). So, here is my question. I have consistently noticed that when I place the scale on Spot A on the floor in the bathroom, it will always give me a lower weight than when I place the scale on Spot B on the floor in the bathroom. This is very consistent and the difference is sometimes as much as 3, 4, 5 pounds. What on earth could cause this? Spot A and Spot B are barely a foot apart, perhaps 1/2 a foot. The only thing I can think of is that the bathroom floor has some minor inconsistency in not being perfectly level. (But I don't even know if that would contribute to the weight gain/loss recorded.) Nonetheless, it is a "normal" flat bathroom floor -- meaning, there certainly are no glaring inclines/declines. Even if there were a minor difference in how level the floor is, that certainly cannot account for 3, 4, 5 pounds? Does anyone have any ideas? Thanks. (JosephASpadaro 01:09, 15 July 2007 (UTC))

Probably your scale reports a different weight depending on the weight distribution on top of it. Maybe it's a different angle, or maybe you stand on it differently when it is in a different spot. Why don't you try experimenting with standing on different parts of the scale when you weigh yourself? -- JSBillings 01:56, 15 July 2007 (UTC)

No, I make a point to stand on it exactly the same each time. (JosephASpadaro 04:02, 15 July 2007 (UTC))

Maybe you could do a more controlled experiment by placing a couple of books on the scale. At least with books you don't have to worry about the weight distribution -- as long as you make sure the books don't move. If the scale insists that the books are heavier in one place than in another, then the floor might have some defect, as suggested by JSBillings. Beyond that, we could speculate forever and not arrive to an answer. Might as well apply the scientific method. Good luck! --Waldsen 04:29, 15 July 2007 (UTC)

A standard bathroom scale is just a spring scale, and those a notoriously poor. If you intentionally stand on one corner of the scale, you can likely get a 50 pound variation. Thus, a 3-5 pound variation can happen just as a result of imperceptible changes in the weight distribution. This may be because the floor bows a bit, or because you are closer to a wall in one position and naturally lean away from it a bit. StuRat 06:03, 15 July 2007 (UTC)

Good input -- thanks. (JosephASpadaro 17:34, 15 July 2007 (UTC))

Another variation happens when you put the scales on carpet, and the scales are supported all over the base, rather than 4 feet as they were designed. When I first saw this I didn't beleive it - that gravity could change between carpet and tiles! But as StuRat says, its just the design with a spring, and the distortion in the metal case is taken into account with the measurement. GB 21:47, 15 July 2007 (UTC)

Legless Lizards

I'm watching 'Man vs. Wild' and the guy picks up and shows what looks like a snake. He said it was a legless Lizard. I went to the Wiki article, and the intro has '4 legs' in the description. Are there legless lizards? Why aren't they snakes? Thanks! Bmedley Sutler 02:13, 15 July 2007 (UTC)

According to the Pygopodidae (Legless Lizard family), they differ from snakes by having external ear holes and non-forked tongues. -- JSBillings 02:15, 15 July 2007 (UTC)

I think one answer to the question, "why aren't they snakes?" is that they evolved separately, so if we called them "snakes" then "snakes" would be a polyphyletic group, and that's considered bad naming practice. --Allen 14:35, 15 July 2007 (UTC)

Yes, it's important to note that the definition of snakes isn't simply "reptiles that have no legs". It's more complicated than that, as we have to consider other physical and genetic attributes to call something a snake.128.163.171.68 17:51, 15 July 2007 (UTC)

Properties of mercury

Below is the original question and my question is in bold at the end. Thanks NA --75.75.13.217 03:45, 15 July 2007 (UTC)

Mercury is the only metal element that is liquid at room temeratures. Why?

It's melting point is -37.9 °F (= -38.83°C), and its boiling point is 674.11 °F. What is it about this element's atoms, and/or electron layers, that makes it different in this respect from other metails?

The answer has partly to do with the electron configuration of Mercury, and also relativistic effects. The electron configuration of mercury is [Kr] 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s². The last shell labeled 6s is completely full, and is noticibly closer to the nucleus than what would be expected if relativistic effects were not taken into account. The combination of these two factors results in rather tightly bound outer shell of electrons for mercury. Hence, mercury cannot form particularly strong metal-metal bonds. The result is an element which is liquid at room temperature. Contrast this with gold and thallium which are right beside mercury on the periodic table, but are solids. Let the reference desk know if you'd like a more detailed explanation, I hope this answers your question! --HappyCamper 1 July 2005 00:03 (UTC)

Thanks HappyCamper for explaining more clearly than I usually manage! "Relativistic effects" occur in atoms of a high atomic number: the positive charge of the nucleus is so high that some of the electrons in the atoms are moving very fast—fast enough that special relativity has to be taken into account in predicting their movement. This causes a number of changes in the chemistry of the elements concerned, of which the fact that mercury is liquid at room temperature is perhaps the most striking. Physchim62 4 July 2005 08:46 (UTC)

You're welcome, Physchim62 :-) You do great edits on Wikipedia too! --HappyCamper 7 July 2005 04:25 (UTC)

One small quibble, if I may: "electrons moving fast". Well, yes the electrons whether acting particle-like or wave-like do have velocity and momentum data associated with them. But while in an orbital (a standing wave) "moving fast" is a poor way to describe a charge that is not doing what charged particles do when they move fast (in a circle - i.e. accelerating). Visualizing a charged particle zipping about the nucleus like a planet around a sun at a relativistic speed is terribly misleading. (Even if expert chemists who don't care about the physics of charged particle movement DO use that heuristic.) 4.250.168.127 23:04, 25 July 2005 (UTC)

I took the liberty to take the result of this discussion to Group 12 element, thanks all! V8rik 23:08, 25 November 2006 (UTC)

Hello, I am not sure I understand but maybe you can point me to a good source. Zn ([Ar] 3d10 4s2) and Cd ([Kr] 4d10 5s2) also have full s and d outer shell. So what gives for Hg. Hg from what I have read here can make amalgams with gold and zinc but I am not sure what kind of bonds these are. Also please give a little bit more about how special relativity comes into play here?

Current rate of extinction

hey all, i would like a source that states the current world extinction rate. i have heard in a several different places that there are currently 200 species going extinct a day but never (to my knowledge) with a source. --74.97.142.249 04:30, 15 July 2007 (UTC)

Somewhere between 0.5 and 50 extinctions per day (Stuart L. Pimm; Gareth J. Russell; John L. Gittleman; Thomas M. Brooks (1995). "The Future of Biodiversity". Science. 269: 347–350. {{cite journal}}: Unknown parameter |last-author-amp= ignored (|name-list-style= suggested) (help)). The large uncertainty comes from the assumption that the vast majority of extinctions occur without being noticed. Only 748 extinctions have been documented since 1500 AD. Dragons flight 04:51, 15 July 2007 (UTC)

Do those figures include bacteria ? Viruses ? StuRat 05:55, 15 July 2007 (UTC)

Macroscopic animals and plants. Dragons flight 05:58, 15 July 2007 (UTC)

This brings up the question of where one draws the line between macroscopic and microscopic. Perhaps single-celled organisms versus multicellular organisms would be a good dividing line, but you definitely need a microscope to see some multicellular organisms. StuRat 13:59, 15 July 2007 (UTC)

Well..from what I know, macro means big, while micro means small..is that correct? --Zacharycrimsonwolf 13:03, 16 July 2007 (UTC)

That's true - but they are both relative terms. Relative to a virus, an amoeba is 'big'. Relative to a Californian redwood, an ant is 'small' - but an ant is big compared to an amoeba...so where do you draw the line for the purposes of answering this question? SteveBaker 17:37, 16 July 2007 (UTC)

I believe that as practical matter, "macro" means unaided human eyesight. The stuff we can't see is even less well understood, so we start with those things where we have half a clue. Dragons flight 00:56, 17 July 2007 (UTC)

Even that is a widely variable scale, as some people can see much smaller things than others. There is a species of tiny orange spiders that some people can see and others can't, for example. StuRat 13:39, 17 July 2007 (UTC)

The concept of "species" is rather weak for non-sexually-reproducing individuals, which in turn makes the concept of "extinct" a fuzzy one. --Carnildo 23:09, 16 July 2007 (UTC)

Otto Wilhelm Thomé

I can find no biographical data to go with this article - no date or place of birth or death, no parents, no education...... Any suggestions? Googlesearch doesn't turn up the right answers - perhaps I'm asking the wrong questions Raasgat 06:34, 15 July 2007 (UTC)

At the bottom of this page I found the information he apparently lived 1840-1925. He also published a book entitled Lehrbuch der Zoologie für Gymnasien, Realgymnasien. Not a lot of information I must admit.

/ Mats Halldin (talk) 12:32, 15 July 2007 (UTC)

Thanks Mats - More information than I could come up with! I'm sure there's a full biography around somewhere - I'll keep searching. Raasgat 19:16, 15 July 2007 (UTC)

You could try contacting Kurt Stüber, his page gives you his address. ---Sluzzelin talk 13:23, 16 July 2007 (UTC)

HONEY

WHY doesn't honey go bad(decay) and always stay good?

165.146.39.29 13:38, 15 July 2007 (UTC)Lucy

I believe it is the same reason why table sugar (sucrose) doesn't go bad: They are both hygroscopic. Any germs that land on it quickly dry out. --Mdwyer 15:43, 15 July 2007 (UTC)

Honey is also somewhat acidic and has some antibacterial components. (Although you still shouldn't feed a baby honey because it can still contain nasty bacteria like Clostridium botulinum) -- JSBillings 22:10, 15 July 2007 (UTC)

Firstly, there is no therapeutic antibacterial component in honey. Still, no bacteria can survive in honey because of its high concentration of sugar (in water). Honey is a syrup and is a sugar-in-water solution; however, there is more sugar (by weight and by volume) than there is water. Bacterial cell membranes are Semipermeable. When a bacterium is submerged in honey, the concentration of sucrose (the main sugar in honey) is much much higher in the honey than within the bacterium. This concentration difference will equilibrate via diffusion. Since the cell membranes of bacteria are semipermeable, the sugar in the honey is too big to move from the honey into the bacterium. Water is not. So, water moves from the bacterium into the honey, literally crushing and killing the bacteria cells. So, honey never "goes bad" because the bacteria can never live long enough to reproduce and spoil it. This goes for Clostridium botulinum as well. This is not to say that honey is safe for infants though. When bacteria experience harsh conditions in the environment, they can form endospores. Endospores can survive a range of harsh conditions that a regular bacterium could not. Clostiridium botulinum endospores are contained in a significant portion of commercial honey. This is because they are picked up by the bees from vegetation. Such endospores would be eliminated by our immune systems in children and adults, but not by infants. So in infants, the endospores make it all the way to the small intestine and reactivate there feeding on whatever is inside and cause infant botulism. Mrdeath5493 20:51, 16 July 2007 (UTC)

Organic Adult Diapers

OK, this subject requires some actual maturity, so anyone subject to replying with "Ewww, gross", please leave now. My elderly father has entered the stage in life where he needs to wear adult diapers. Unfortunately, most of those contain nasty chemicals (like chlorine) for "odor control". The effect of these is to destroy good bacteria and promote fungal infections. I have no problem finding organic baby diapers without those nasty chemicals, but haven't been able to find organic adult diapers. I either need a brick and mortar store in the Detroit area, or a site which sells online and delivers to the US. Any suggestions as to where I should look ? StuRat 14:10, 15 July 2007 (UTC)

Uh, might be slightly insulting, but have you tried looking at websites that sell BDSM type stuff? They might have something. --L^augh! 14:20, 15 July 2007 (UTC)

Have you asked a medical doctor or health professional? An adult health care center would probably be familiar with this issue and could direct you to a manufacturer or provide an alternative solution altogether. Nimur 15:51, 15 July 2007 (UTC)

Why can't an adult wear baby diapers? Is it simply a matter of size (i.e., a large adult cannot "fit into" a small baby diaper)? If so, can't you manipulate baby diapers in some way (i.e., tape two together) ... or so? (JosephASpadaro 17:38, 15 July 2007 (UTC))

Is it not possible to use towelling (non disposable diapers) instead? You can then control the cleaning/material environment of the product. I know that's probably not the ideal solution but may be an alternative if you struggle to locate your first choice. ny156uk 18:00, 15 July 2007 (UTC)

Hmm, even cloth ones seem to be anti-bacterial. Skittle 12:00, 16 July 2007 (UTC)

That's internally though, surely it won't affect the skin much? Nil Einne 12:58, 16 July 2007 (UTC)

I believe liquids are able to transport the anti-bacterial agents to the skin. StuRat 13:29, 17 July 2007 (UTC)

If these are meant to be reusable, might the anti-bacterial thing be something that doesn't wash away? I'd probably ask them if it was me. Skittle 19:33, 17 July 2007 (UTC)

industrial use of insecticides

What types of insecticides and pesticides are use industrially, specifically in transport containers coming from the eastern countries

Molecular orbital formation

How exactly can two atoms[say,two oxygen atoms] combine to form two molecular orbitals[anti bonding and bonding] when there are only two orbitals combining?

The atomic orbitals don't combine in the simple "overlap or merge" physical sense, but rather recombine in various proportions to form molecular orbitals. This recombination can be constructive or destructive: the atomic orbitals could reinforce each other or cancel each other out. So there's the answer: two AO, two ways to combine them, now you have two MO. There's more detail and several examples on the molecular orbital page. DMacks 01:39, 16 July 2007 (UTC)

There are in this case two ways the O orbitals can combine giving two types of resultant orbital, if say the atomic orbitals cn each hold one electron, then each resultant molecular orbital can hold 2 electrons.

Each atomic orbital can hold two electrons, just like each molecular orbital. That's another sign that two atomics become two moleculars: gotta have a place to put all the electrons (start with "space" for four, wind up with space for four). DMacks 03:11, 18 July 2007 (UTC)

Unusual bird behavior

Hi all! There's a bird outside my kitchen window, I believe it's a goldfinch, that keeps on trying to fly through the (closed, unopenable) kitchen window. Someone else told me that it's been doing this for over a week. It keeps on making attempts to enter the house on a very regular, rapid basis. There are some bird feeders in the area, but strangely, this bird is mostly hanging from a hummingbird feeder. What's causing this odd behavior, and is there anyway I can effectively get this bird to stop? - RedWordSmith 17:25, 15 July 2007 (UTC)

It's possible that the bird can see its reflection in the glass and is trying to attack the perceived intruder it in order to defend its territory. Is it by any chance the breeding season for this type of bird where you live? Is it a cock bird? Quite a lot of male songbirds get 'antsy' and 'hormonal' at that time of the year. --Kurt Shaped Box 17:32, 15 July 2007 (UTC)

If it's attacking a reflection in the window, then you could try putting a picture of a predator on the wall. Bart133 ^{(t) (c)} 17:34, 15 July 2007 (UTC)

Editing conflict. I agree with our sea gull expert Kurt. The best thing to do is to cover the window so that the image is not visible. --Eriastrum 17:37, 15 July 2007 (UTC)

When I was a kid, my bedroom window had a *very* reflective anti-glare coating (it was pretty much a two-way mirror on the outside). While it did get the odd small songbird crashing into it, most interesting was the way the mapgies would perch on the windowsill at dawn and hammer on the glass with their beaks. Sometimes there were ten birds lined up and tapping away. I didn't need an alarm clock. :) After a few months, the coating was chipped away in several places and the glass was beginning to spiderweb. I'm still not 100% sure what they were doing - it didn't look like aggressive, territorial behaviour. More like fun. --Kurt Shaped Box 17:50, 15 July 2007 (UTC)

(Edit conflict me too). You could also try tacking a piece of chicken wire or other similar mesh over the window on the outside, in order to break up the reflection. Many songbirds die every year after flying head-first into windows in pursuit of themselves. --Kurt Shaped Box 17:41, 15 July 2007 (UTC)

I thought this kind of thing only happened in movies and comic books. Kittens tend to play with the cat in the mirror, for a while Nil Einne 19:53, 15 July 2007 (UTC)

Anyone that's ever owned a parrot or parakeet will know that birds can become totally obsessed with their own reflections. They don't even need a proper mirror - anything shiny that they can see a little glint of themselves in becomes an object of fascination. They'll try to fight their reflection, feed it, snuggle up to it, or sometimes even try to mate with it. Most birds seem to be unable to grasp the concept that the bird in the mirror is actually itself. --Kurt Shaped Box 20:07, 15 July 2007 (UTC)

I'd be impressed by any that did. Elephants and apes are the only animals recorded to recognise their own reflections, as I recall. Bendž|Ť 22:46, 15 July 2007 (UTC)

I believe mirrors are used to judge the intelligence of animals. The lowest level is animals that always see an enemy and attack it, and never learn. This sounds like what we are dealing with here. The next level is animals that learn it's them in the mirror, then have no more interest in it (no introspection), like cats and dogs. The highest level is animals that become fascinated with their own reflection and use it to look at themselves constantly, such as happens with some primates (including humans). Incidentally, I've also seen a bird do the same thing, trying to get into a glass-walled cafeteria. It kept trying until the glass door was opened by a customer and it got in, at which point it started doing the same thing, only flying at the glass from the inside this time. StuRat 01:13, 16 July 2007 (UTC)

I'm pretty sure that I read somewhere that African greys and some of the larger macaws and cockatoos were capable of recognising their own reflections. Sorry, I can't remember where now - I do read a lot of stuff-stroke-crap. --Kurt Shaped Box 07:29, 16 July 2007 (UTC)

The study is mentioned here [4] and elsewhere (Google). So far, the only animals showns to have this sort of reflection self awareness are dolphins, (Asian) elephants and various primates at least according to the source. Do note though that it's easily possible other animals may possess it, it simply hasn't been demonstrated yet. Also, while obviously related to intelligence, it's important to remember it's only one factor. I.E. Just because a cat is capable of learning that attacking its reflection is pointless doesn't mean it's more intelligent than a bird which isn't (also see bird intelligence too). While there is probably no directly evolved component, it is possible there is some influence and I presume a bird which is usually flying has less need to learn about reflections then an animal like a cat on the ground. Nil Einne 12:08, 16 July 2007 (UTC)

I wonder if seabirds are aware of their own reflections? Thinking about it, they must see themselves reflected in the water reasonably often - and crash-landing in the sea every five minutes in an attempt to fight themselves would be pretty counter-productive. Thinking about 'my' gulls (i.e. the ones I feed every day, I have never had one attacking my windows - and they do come very close. Sometimes they've even been right up to the glass to peer in at me and squawk for my attention. Is a gull technically a 'seabird' anyway? As I understand it (aside from the very strange little Kittiwakes), they never actually go 'out to sea', as such. --Kurt Shaped Box 23:27, 16 July 2007 (UTC)

I didn't think seabirds were terratorial (at least not while at sea!) - so why would they be attacking others of the same breed in the first place? SteveBaker 02:15, 17 July 2007 (UTC)

Have you ever watched the seagulls, man? They look for any excuse to have a fight. If one just looks at another the wrong way or walks a bit too close they end up flapping, screeching, pecking and bickering. Would they really hold back on that because they were over the water? --62.136.231.228 13:56, 17 July 2007 (UTC)

Okay, I figured something like that might be responsible. Covering up the whole window doesn't seem like an option at this point (it's very large!), but I've covered up the bird's favorite spot to perch in front of and attack with a page from a catalog (do songbirds like tea?). We'll see how it works. Thanks for your help so far. - RedWordSmith 20:19, 15 July 2007 (UTC)

I've definitely seen video footage of a chimpanzee recognising itself. The way they test the theory is to aneathetise the animal and while it's unconscious they put a smudge of coloured makeup on it's forehead (imagine a big red dot of lipstick or something). When it wakes up, the chimp is totally unaware that the smudge is there. When it looks into a mirror, it sees "another" chimpanzee with a smudge of colour on it's forehead. If the chimp rubs it's own forehead to get rid of the smudge - then it clearly recognised that the thing it's seeing is a reflection of itself - and not some other animal. I've seen that done with chimps and the result is really conclusive. The problem with doing the experiment with dogs (and maybe cats too) is that dogs live in a sensory environment that's totally dominated by smell. A mirror doesn't easily fool them because it doesn't smell like another dog. So if they care at all about the reflection - it's not because "they think it's another dog". If they care at all (and my dogs never did) then it's just because there is something moving back there that doesn't smell...which is weird to them. I'd imagine dolphins would get a similar cue because their echolocation isn't showing the distinctive sonar image of another dolphin, this is certainly helpful in distinguishing that the mirror isn't just a window onto another world with another dolphin in it. SteveBaker 17:34, 16 July 2007 (UTC)

If researchers have started putting lipstick on chimps I'd say they've been locked up in the laboratory a bit too long. :-) StuRat 13:47, 17 July 2007 (UTC)

On a serious note, since smell only works up close, dogs do use sight at a distance, so just do the test with the dogs 10 meters away from the mirror. StuRat 13:47, 17 July 2007 (UTC)

Dogs have a sense of smell that is (allegedly) 1,000,000 times more sensitive than ours. 10 meters is simultaneously not far enough to disable the sense of smell - and too far to allow their (relatively poor) eyesight to operate. SteveBaker 13:57, 17 July 2007 (UTC)

And both dogs and dolphins would have a hard time rubbing a spot off of their foreheads? Capuchin 12:06, 17 July 2007 (UTC)

Yes - but there was a variation of the experiment that was performed with dolphins, see: Cetacean_intelligence#Self-awareness for details. SteveBaker 13:55, 17 July 2007 (UTC)

Need help with evaporation rate.

I've looked around a few placees, specifically the pages on Evaporation, Absolute Humidity and Relative Humidity, and see a couple of formulas, but am not quite sure how to apply them.

My question is: Say I have a pool of water with surface area A and temp T, with air temp T', relative humidity R and pressure P (assume no-wind, closed system, no external energy sources, ideal conditions.) I want to calculate how much water I expect to evaporate over a given time M.

I'm doing this for a grossly simplified wx-sim for a game, so wild approximations are ok, although I'd like to have at least some understanding of the "real" physics behind it, so that I can make intelligent adjustments and choices about what factors to include/exclude.

By way of example, my sim will be doing things like: "over this kM^2 of ocean, temp T, air-temp T', pressure=1atm, X-amount of water evaporated (contributing to the RH of that block of air) over the past hour." We'll be ignoring things like wind, extra-evaporation from unsmooth ocean surface, etc. So, you can see, there are lots & lots of shortcuts being taken. The goal is to create something "realistic-seeming it its effects", not necessarily "100% true to life."

Thanks! Oliepedia 18:20, 15 July 2007 (UTC)

Go for a formula like $rate=cARe^{T}$ GB 22:01, 15 July 2007 (UTC)

Term meanings? (I got A & T, and maybe P. Is e "e"? c?) Can you point me at a reference to read more?

Thanks! Oliepedia 04:01, 16 July 2007 (UTC)

I'm pretty sure he just wanted to spell carpet. But e would be e and c would be c. Capuchin 06:40, 16 July 2007 (UTC)

Sorry I had to stop work on the question abruptly! ok its not carpet - its caret, e is the mathematical constant, c is a constant - not the speed of light, but a figure that might give about cm of evaperation per day at about 40°C. However are there extreme conditions involved? It the temperature wildly different to the earth surface? If you get a big difference between water and air temperature you will get fog - are you interested in that? The Pressure (P) of the air will make little difference in the rate, so I should not have put it in. GB 10:24, 16 July 2007 (UTC)

Uh... ok. Can you help me out with the application? (Is there a standard way, on these pages, to abbreviate "I'm pretty smart, and understand math and more physics than the average Joe, but I don't do this every day, and it's certainly not fresh in my head!"?) My sim/game-planet is Earth-like, so temp extremes in that general range.

Ok, let's try this...

Pool area = $1m^{2}$

Pool Temp = 20°C

Air temp = 25°C

You said to ignore pressure, then replaced with "R" -- what's that? RH%? Let's say 60%

So now I have

rate=c*1*R*(2.71828^20)

Or is T the temp differential (5)? And if R is, indeed, RH%, then I have:

rate = c*1*.60*(2.71828^20)

or

rate ~= c * 291,099,117

So, if I knew what R was, I could work out a c that gave me ...uh... what? "1" (cc per day)? Is "rate" in "cc per day"? Do I have the other terms right? My answer looks big, like it would need nano-units to come out.

Thanks! Oliepedia 02:45, 17 July 2007 (UTC)

FWIW, I found some really good info in this Hydrology Textbook and surrounding pages. 63.201.144.200 21:15, 23 July 2007 (UTC)Oliepedia (forgot my password, again!)

July 16

psi for knockdown

How much PSI [pressure per square inch] would it take to send a man flying backwards about two foot if the force was only applied to around 11.8 square inches of the mans body, he is 5.11 feet tall and weighs 155 pounds, can anyone calculate this? Thank you

This sounds suspiciously like homework. In any case, we'd still probably need to know the coefficient of friction between his shoes and the ground. --Ybbor^Talk 00:44, 16 July 2007 (UTC)

I don't think the coefficient of friction means much here - there is enough of a moment between frictional force and center of pressure of the body to rotate the guy backwards and then the friction in the feet will essentially go away. So neglecting the friction of his shoes...Well, how fast to we have to accellerate him to get him to "fly" backwards for two feet? Actually, if he just fell backwards, he'd end up with his center of gravity two feet from where his feet were so the answer might strictly be zero. But let's suppose you actually wanted his feet to move back two feet in the time it took him to fall flat on his back. That would mean moving his center of gravity (CofG) maybe 4 feet backwards in the time it takes his CofG to fall maybe 2 feet. That's going to need an accelleration of about 2 g's - so a force equal to maybe twice his weight? If he weighed 115lbs - then we need 230lbs of force spread over 11.8 sq inches - so the pressure is 230/11.8 or about 20psi. That's a LOT! SteveBaker 02:21, 16 July 2007 (UTC)

Is there a way of converting between wind speed and the effective pressure one would feel (average) if standing directly in the path of the wind? Someguy1221 03:07, 16 July 2007 (UTC)

Look up Drag (physics). Mathematically, it's the same weather the body is moving and the fluid is at rest or if the fluid is moving and the body is at rest. — Daniel 03:51, 16 July 2007 (UTC)

Why can the sky be blue or red, but not green?

If the red sky during sunrise and sunset is due to refraction, why aren't there times when the angle is such that a different wavelength, such as green light, hits where you're standing and causes the sky to turn that color? — Daniel 00:08, 16 July 2007 (UTC)

It's not. See: Rayleigh scattering and diffuse sky radiation. The sky away from the sun looks blue because blue light is more easily scattered back towards you. If you look towards the sun at sunrise or sunset, then there is so much atmosphere in the way that all the blue is scattered off and what you see is the leftover reds. Dragons flight 00:17, 16 July 2007 (UTC)

Green Flash? --L^augh! 00:26, 16 July 2007 (UTC)

How come there isn't a time between a blue sky and red sky when there is enough atmosphere to filter out most of the blue light but not most of the green light, and more green light gets scattered towards you then red light? Also, why is the green flash only green, or occasionally blue? From what I read of the article, it seems like it should have a rainbow look. How come the effect I mentioned doesn't happen to the moon during a lunar eclipse? It's red in the middle of the shadow, and blue at the edges, but it's purple in between, rather than a rainbow containing every color but purple. — Daniel 00:51, 16 July 2007 (UTC)

I think some of the green flash types are a full rainbow, as seen in the pics, but the "normal" colors just aren't worth mentioning, as they're so common. Also, I've seen pale green skies as a result of severe thunderstorms (and, I imagine, hurricanes), perhaps due to some matter that has been drawn into the air, like droplets of sea water. StuRat 00:57, 16 July 2007 (UTC)

Green flash has this covered. The deal is that the human eye doesn't see the pure frequency of a colour - it sees the amount of pure red, pure green and pure blue - and anything between those three primary colours seems to us to look like a mixture of the two. We can't tell the difference between 'yellow' and a mixture of 'green' and 'red'. In physical terms, those are different things - but not to our eyese. The sky isn't ever truly "blue" (the intense blue our retinas respond to) - it's more of a 'cyan' - which is about a 50/50 mixture of blue and green. Similarly, the 'red sky' of a sunset is more often yellowish/orange - which is a mixture of red and green. So if there is never a period in which there is neither red nor blue light in the sky - but instead it's always a mixture of colours - then all you'd see would be a muddy transition from yellow to cyan - without there ever being a 'pure' green. SteveBaker 02:28, 16 July 2007 (UTC)

Technically, you can't even see pure green, because green light excites red and blue receptors, though less then green ones. I'd expect you'd at least see a distinctly greenish gray. — Daniel 03:06, 16 July 2007 (UTC)

To amplify Daniel's point here, it is not correct that the eye "sees the amount of pure red, pure green and pure blue". There are three kinds of color receptors and it sees the amount of light each one detects, but each responds to a range of frequencies. The three primary colors are only relevant to technology that wants to trick the eye into thinking it is seeing a full range of colors without actually producing them all -- i.e. printing, photography, and video. And I don't believe Steve is correct to suggest that the details of human color vision are relevant to the main question. The question can be recast as, how come it doesn't seem to ever happen that of the range of frequencies in sky light, the dominant one is green?" And I suggest that the answer is just that there are only so many ways that color gets into the sky, and it happens that none of them enhances the ratio of green light to other frequencies. --Anonymous, July 16, 2007, 07:52 (UTC).

Anonymous makes an important point here. The frequency responses of the various pigments in the human eye don't correspond very well to blue-red-green and IMHO this is not that relevant to the question anyway. See Colour vision. However several points which need to be clarified from anonymous... There is a large variety of possible primary colours. Red-green-blue (RGB) is the most common additive combination by far and is therefore relevant in monitors, cameras, scanners etc. CMY (cyan, magenta, yellow) is the most common subtractive combination and is therefore relevant to printers, paiting etc. Nil Einne

This is not about printers or technology or TV or anything like that. Allow me to explain in more detail - I'll split the explanation into little bite-sized chunks:

• Each type of receptor in the eye has a roughly gaussian response curve centered on whichever frequency it is responsive to - these being the colours we label as 'red', 'green' and 'blue' - the precise 'center' frequency isn't particularly important here - so let's just label those three center frequencies 'red', 'green' and 'blue' for the purposes of these discussions.
• In order for our eye/brain to see 'green', there must be very little red or blue light present. If there is green light AND red light entering the eye - we see yellow or orange because we are totally unable to distinguish a mixture of red light and green light from (say) a true orange light from a sodium lamp - even though there is a very, very clear physical difference between the two.
• Since the light from the sun is pretty much evenly spread over all of the visible spectrum, if the sky at sunset were to filter out (refract away/absorb/whatever) all of the light within the range of frequencies close to the center of our blue response - then we'd see the sky as being a yellowish orange even though the light is actually a mixture of all of the frequencies from red through green. That's because when both red and green sensors are being adequately stimulated - we can't tell the difference.
• Similarly - if the sky is getting rid of all of the red light (as during most of the day) then we get a mixture of all of the frequencies from green through to blue - and we see the colour that computer graphics folks call 'cyan' (a paler, baby-blue..."sky blue" to use a common name for it).
• If the frequencies that are filtered out by the sky never include both red and blue simultaneously - then we'll never percieve the resulting light as 'green' even though there is tons of green light present, the addition of either red or blue in sufficient quantities will result in us seeing yellow or cyan respectively.
• So - if the sky filters out red light ("all of the frequencies close to red") during the middle of the day - and blue light ("all of the frequencies close to blue") at dawn and dusk - leaving green light always present - then it can be (and actually *is*) the case that green light may never be present by itself.

What all of that long explanation means is that you'll only ever see the sky transition from cyan (blue+green) to yellow/orange (red+green). Halfway between the two, you are seeing red+blue+green = white or grey. If you actually watch a sunset sometime, you'll see that between the blue sky and the orange sunset there is indeed a band of grey right where our questioner expected there to be a pretty green rainbow-effect. The 'green flash' phenomenon is something else. SteveBaker 17:17, 16 July 2007 (UTC)

Green dominates this image.

I say again, all the details of the eye's color perception are irrelevant. The only important issue is in order to see the sky as green, the dominant color of the light would have to be green, and for the reasons explained, that doesn't happen. --Anon, July 18, 02:52 (UTC).

<sigh> Well, you can say it all you want - but this (====>) image proves you are wrong. The cyan and yellow swatches (because they are being displayed on a computer monitor) are not 'true' monochromatic colours - light of wavelength ~480nm (cyan) and ~580nm (yellow) are not present in the light from your monitor. I deliberately painted those swatches so that they have more green than either red or blue. In your terms "green is the dominant colour" in both colour swatches. Yet they don't look green - they look sky-blue and yellow...just the kinds of colour you'd see around sunset. This is all the more surprising because our eyes are more sensitive to green light than to red or blue. A spectrometer reading (or a super-human being with perfect colour vision) would immediately reveal that these are mixtures of green/blue and green/red - and not cyan and yellow at all. Such a being/instrument would be able to tell you that there is lots of green there just as there is lots of green light in the sky at sunset. We poor humans can't see that because our eyes just can't do that. So details of human perception are entirely relevent to this explanation. SteveBaker 23:42, 18 July 2007 (UTC)

I said "in order to see the sky as green, the dominant color of the light would have to be green", not the converse. And anyway, we are talking about natural light, which does not consist of a mixture of just two or three widely separated frequencies like light from a monitor. --Anon, July 18, 02:44 (UTC).

Not to take sides (because you both lost me a ways back), but I just came across this little piece of doggerel last night, which seems somehow apposite:

Cold-hearted orb that rules the night

Removes the colours from our sight

Red is gray, and yellow white

But we decide which is right

And which is a quantization error.

—after The Moody Blues ("Nights in White Satin"), as found on the NetPBM man page for ppmtopgm

—Steve Summit (talk) 15:45, 22 July 2007 (UTC)

(unindent)

The OP asked why there is no green in the sky around sunset. We agree that sunlight contains (more or less) all light frequencies. Your statement is of course true - the sky won't look green unless there is green light in there somewhere - but we're not being asking why the sky looks green. The OP asked why it DOESN'T look green - which makes your statement useless (although it's undoubtedly true). My point is that there are two possible (and very different) interpretations of the observation no part of the sky looks green in a typical sunset sequence:

1) There is no green light present around dusk because it's somehow being filtered out.

...or...

2) There is plenty of green light present - and it might even be the dominant frequency band - but because sunlight contains an almost complete spectrum, the presence of blue or red light in the mix will trick our eyes into seeing cyan or yellow/orange and make the perception of a green band a virtual impossibility.

My explanation for the reason for not seeing green in the sky is NOT (1) - it's (2). I happen to know for sure it's true because I've studied the sky in order to render it in computer graphics for flight simulation. There is in fact plenty of green light in the sky throughout sunrise and sunset - and frequencies close to green might even dominate the frequencies in some parts of the sky (between the orange sunset and the cyan zenith) - but we can't see that as an obvious green band because there is still enough blue and red present in the sky to fool our eyes. The fact that our eyes can be fooled into not seeing green even though it's dominant is elegantly demonstrated by the colour swatches (above). That statement is only explained if our eyes work the way they do - which is why my discussion of how human vision works is entirely relevent to the discussion. A hypothetical creature with better colour perception than humans (a goldfish or certain species of freshwater shrimp) would be perfectly able to see a green band in the sky. SteveBaker 12:07, 19 July 2007 (UTC)

You say the colour picture is supposed to be sky blue? You must have a very weird sky then, because it looks distinctly turquoise to me.

Actually, it does on my LCD monitor here at work too - but not on my CRT at home...well, whatever. It's not green. SteveBaker 19:04, 19 July 2007 (UTC)

plant leaves turning bright red

I noticed a few species of plants are already turning bright red. I wonder why. (It's a normal summer here in Iowa.) Is some evolutionary advantage conferred by this early shutdown of photosynthesis? --Halcatalyst 03:59, 16 July 2007 (UTC)

Are you referring to leaves which have started senescencing earlier then normal or plants which always undergo leaf senescence fairly early on? If it's the former, there are a variety of reasons why this may happen. Check out [5] and [6] for some discussion but I'm sure I've read better discussions somewhere, perhaps it was on here even. If it's the later, the first thing to consider is what plants are you talking about. Are they natives? If not, they may very well be adapted to a different environment and there is no evolutionary advantage to them to start leaf senescence so early, indeed if they survive naturally in their current environment in the next say 50 generations their leaf senescence may be likely to evolve to a later period. Of course, if the plants have a wide range, then they may always exhibit a fairly early senescence in certain areas. Late senescence is I presume far worse then early senescense and the competiting pressures over the range means it will always be a balance of both... Nil Einne 12:26, 16 July 2007 (UTC)

• Thanks for your response. Leaf senescence is a concept new to me. I poked around a little on the web to find out more, but the articles I found were beyond my competence, or at least beyond my time availability. ;-)
• Not knowing much about botany, I can't answer your questions very well. I assume they're native plants; I found them in the wild; I don't know how to identify the species. What struck me was the bright red, brighter than any maple I've seen. The red would be produced by one of the substances remaining in the leaf when photosynthesis ends. Are there classes of plants that produce especially bright red leaves early in the season? --Halcatalyst 14:34, 16 July 2007 (UTC)

We don't have an article on leaf senescence but we do have a (rather poor) article on plant senescence. You don't really need to understand leaf senescence (I briefly studied it once but have now mostly forgotten what I learnt) but it's important I think to appreciate, and I think you already did that the leaves of decidious plants turn red and eventually fall off during autumn by a tightly regulated process (which we're only just beginning to understand). Also, perhaps I was a little too technical in my answer. What I was trying to say is, are you referring to a case where the leaves turned red earlier then would normally be expected or plants whose's leaves always turn red very early on? From your later responses, it's appears you may not be sure. Nil Einne 23:12, 17 July 2007 (UTC)

A cold snap can cause leaves to turn colors earlier than usual (senescence), basically by making the plants think fall is here. Have you had a cold period there ? StuRat 14:18, 16 July 2007 (UTC)

• Hi StuRat. We had some unusual cold earlier this year, but it's been a month or two. There was a hot period, and it's been fairly dry, so that could have stressed the plants. But the rest of the plants in the particular place where I noticed the red leaves seem to be thriving as usual. --Halcatalyst 14:37, 16 July 2007 (UTC)

The principle is pretty straightforward - the plant needs to use some energy to keep the leaves alive - once those leaves produce less energy than they are consuming - the tree is better off without them - so it dumps them and shuts down until spring. It's not about heat - it's about incident sunlight. As the days get shorter and the angle of the sun lower to the horizon, the amount of energy produced by the leaves gets less and less. So even if there are periods during the day when the sun is bright and the weather is hot, the leaves may still be producing less energy than they consume as an average over each 24 hour period. SteveBaker 15:39, 16 July 2007 (UTC)

• Here's what I'm really interested in knowing: Are there classes of plants that produce especially bright red leaves early in the season? If so, what might be the evolutionary advantage? Thanks, Halcatalyst 18:24, 16 July 2007 (UTC)

Evolutionary advantage, I wouldn't know. But if you're in chaparral country in the American West, there is one particular plant that notoriously tends to turn red early. Don't count on it being red, though -- there could still be green bushes of it quite late into the summer (maybe even fall). --Trovatore 18:43, 16 July 2007 (UTC)

Red leaves tend to indicate a state of stress, to much heat or lower leaves not receiving enough light will cause the plant to shut down leaves, people like red leaves so they put selective pressure on plants with red colored leaves - in the 'wild' they (red leaves) would be at a disadvantage. Hardyplants 09:39, 17 July 2007 (UTC)

• Thanks all for your responses. I conclude from what you say that the red color has no particular evolutionary consequence. --Halcatalyst 13:55, 18 July 2007 (UTC)

research for a sermon concerning flames

how far can a single flame be seen by the naked eye in the dark? miles? feet?

please email me at (deleted).

The custom is that questions asked here are answered here, not by email.

At this page is a table showing how far away a typical candle flame can be seen with different optical instruments. With the naked eye it says 1.4 km, which is just under a mile. Similarly, if you look at the Galileo Galilei page, it talks about experiments he invented in an attempt to measure the speed of light, which were conducted using lanterns about a mile apart. Presumably a greater distance would have been used if the lantern could have been seen. So it seems the answer for a small flame is about a mile. --Anonymous, July 16, 2007, 08:10 (UTC).

Obviously it depends somewhat on what you mean by a single flame. A burning tree could probably be seen for far greater then a mile, even though it's arguably a single flame. Nil Einne 12:56, 16 July 2007 (UTC)

Agreed. Oil well fires can even be seen from space, like these in Kuwait after the 1991 Gulf War: [7]. StuRat 14:14, 16 July 2007 (UTC)

Though it's much easier to see smoke than flame in a large fire. A smoke plume can rise thousands of feet in minutes, while a flame rarely gets anywhere close to that altitude. Nimur 15:20, 16 July 2007 (UTC)

The original questioner may also want to see Visibility, which has precise definitions of the atmospheric condition. Nimur 15:27, 16 July 2007 (UTC)

Remember we're talking about the dark here. Presuming we mean no other light at all, then won't see any smoke if you can't see any light from the flame. Nil Einne 22:58, 17 July 2007 (UTC)

There are lots of variables here. Firstly, are the viewer's eyes dark-adapted by being in darkness for at least 30 minutes beforehand? Secondly how much other light is there? You can see incredibly dim things with dark-adapted eyes in total darkness - but in full sunshine it would be hard to see a candle flame at 100 feet. I believe I've heard the distance of about a mile for a candle flame on a dark (ie moonless) night, far from any cities with dark-adapted eyes. But this is for a sermon? You might as well make up a number - everything else is unlikely to be scientifically correct anyway. SteveBaker 15:32, 16 July 2007 (UTC)

WP:Don't bite the newbies, SteveBaker... we have no way to know what the contents of the sermon are, and the effort that is being made towards scientific fact should be encouraged. Nimur 02:17, 17 July 2007 (UTC)

See Candela. The candela is a modern unit of luminous intensity, light emitted by a point source in a given solid angle [8] carefully set to equal the brightness of the 19th century unit the "candle" which was defined in terms of the composition and the grams burned per hour. "The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×10¹² hertz and that has a radiant intensity in that direction of 1/683 watt per steradian." Now relate that to the threshold sensitivity of human vision and you have your answer. Certainly I would assume full scotopic vision after a half hour or more of dark adaptation. In lab experiments the brightness of a distant candle could be simulated for test purposes with a point source of light closer to the observer. I would not assume it was foggy, or that there was dust in the air, or that it was broad daylight or any other assumption that diminished the distance, as the goal seems to be to state the maximum distance. I seem to recall that under ideal conditions and lab conditions the threshold was just a few photons. The observer would not see a bright flash, but would see a slight change in a small area of the random visual noise generated by the retina and nervous system. This absolute threshold would only show up in a forced-choice psychophysics experiment, and an observer would typically want intensity to be several deciBels above it to confidently say he "sees" the light. The Theory of signal detectability provides a theoretical framework for measuring the detection of signal in noise, which is always the case near threshold. The range of stimulus intensity for human vision is large. The most intense light that can be viewed without pain is 10¹⁶ more intense than the weakest light that can be seen, which is a range of 160 deciBels. 10^-10 lambert has been stated as the visual threshold.(P. Lindsay and D. Norman, Human information Processing, Academic Press, New York, 1973, p153). Per Graham and Veniar, 1949, [9] "photons=(10/π)* (pupil area in square millimeters)*(brightness in millilamberts). Per Pupil the dark adapted human pupil has a 8mm diameter when dark adapted, or an area of 50.3mm. This means the stated threshold would equal .00016 photon, which is pretty surprising! Perhaps others can work from the one candela, the 8mm pupil, and find another statement of brightness threshold to yield a max distance. Hecht in the 1940's developed a night vision adaptation testing device which flashed a light repeatedly 4 degrees from the center of fixation, where night vision is most sensitive. [10] reprints his data graph showing the threshold to be about 3.2 log micromicro lamberts, which should equal 16 *10^-10 Lambert. This was apparently not a forced choice modern psychophysics experiment, so it would have yielded a higher threshold. Still have to work this back to distance. Edison 16:10, 16 July 2007 (UTC)

I find luminance questions tedious to calculate because of the numerous different bases, and this at least makes me more sympathetic to people who can't grasp the various electrical units and measurements. At leastI found an apparently authoritative answer to the original question. A source at Electro Optical Industries [11] says "At the threshold of vision the dark adapted observer can see a flash if it contains on average 90 photons at the cornea or 9 at the retina. This is equivalent to a candle at 30 miles on a clear night." The difference between this answer and the previous 1.4 kilometer answer is a factor of 67.6, and assuming an inverse square law for the brightness decrease, the light at 1.4 km would be 4573 brighter than the same light at 30 miles. Perhaps the greater distance would be during careful forced choice psychphisics experiments in a lab, and the 1.4 km figure would be for seeing it as a strong clear unmistakable signal, but the difference is 36 decibels, and I would expect only about 5 decibels of signal strength above a TSD threshold would make it pretty clear to an observer. Such a tiny, faint light would work in a sermon as an analog of the "still small voice" in 1 Kings 19:11-13 (King James Version). Edison 15:45, 17 July 2007 (UTC)

There is something seriously wrong with that answer. How long is the flash? It doesn't say. A candle that's 1000 miles away will EVENTUALLY produce 90 photons that hit your eye - and yet a candle that's only exposed for a few picoseconds at a distance of a meter might not happen to shoot 90 into your eye. Relating candelas to number of photons makes no sense - you can only translate it into photons per second. Worse still, what can your eye see? 90 photons - one entering your eye each night over three months? No! Of course not. 90 photons per picosecond? Yes - that would be a bright light - much brighter than (say) 90 photons spread over a second. Without stating the duration of the flash and the period within which the eye must get hit with those photons just stinks of oversimplification of the problem. Furthermore, the size of a candle flame at 30 miles means that it would subtend such a tiny angle at your eye that there is a fair chance that none of the incoming photons would actually hit a light receptor - your eye doesn't have infinite spatial resolution - it's not just a matter of brightness. SteveBaker 19:09, 17 July 2007 (UTC)

The source said "flash" which would be a defined brief period such that there is time intensity reciprocity. Even more than the reciprocity failure in photographic film, the eye only integrates perfectly for a small fraction of a second. The small angular subtense of a distant candle is no problem at all, any more than the small angular subtense of the disc of a star. It can be treated as a point source, which will produce a blur circle, and there is no danger its light would fall in between rods in the retina. I expect that 90 photons in a millisecond, would look remarkably like 90 photons in 1/30 second, but nothing like 90 photons in 1 minute or even in 1 second, because the the natural limits on temporal resolution in the human eye, which make 50 or 60 Hz AC lighting look like it is on continuously. See Persistence of vision and Flicker fusion threshold for related topics. Absolute visual threshold measurements use brief flashes. They also use an artificial pupil to remove pupil diameter effects. I could not satisfy myself with my calculations trying to calculate the distance from a 1 candela source to an 8mm pupil (7mm might be more realistic) of a fully dark adapted eye, with the claimed thresholds of 1 *10^-10 to 16*10^-10 Lambert. Edison 20:55, 17 July 2007 (UTC)

Edison's reply is sound, and I think the various estimates can be reconciled. A source with a luminous intensity of I = 1 candela at a distance of r = 50 km (converting to SI units for sanity's sake) produces an illuminance of E = I/r² = 4*10^-10 lux (or lumen/m²). Over the area of the eye pupil, which is A = 5*10^-5 m², this translates to a total luminous power of P = EA = 2*10^-14 lumen. How many photons per second is this? The most "efficient" candle would be one which emits all its photons at the peak of the eye's response, 555 nm or 540*10¹² Hz frequency. At this frequency, one watt corresponds to 683 lumen, so in terms of radiometric units the threshold is about 3*10^-17 watt. One photon at this frequency carries an energy of 3.6*10^-19 joule (multiplying frequency by Planck's constant). Therefore the number of photons per second at the cornea is about 80. Now the average luminous efficacy (lumen/watt) will be less than 683 lumen/watt, but also a flash of duration of less than one second should be visible, so the minimum photon number of 90 looks to be reasonable.

The problem with the threshold figure of 1*10^-10 lambert (= 3.2*10^-7 cd/m²) is that the lambert is a measure of luminance L, which is power per unit area and solid angle, and as such it can only be applied sensibly to an extended source, rather than the point source that the candle presents at a distance of 50 km. We have to assume a limiting solid angle of resolution for the eye, corresponding to the minimum area of the retina that the photons need to fall within to register. There are various figures for this solid angle, depending on the duration of the flash, the brightness level, saccadic motions of the eye, etc, but the Laser Safety standard uses a figure of between 1.7 milliradians and 24 milliradians angular diameter to draw the line between a point source and an extended source. Taking an angle of 20 milliradians gives a solid angle of W = 1.3*10^-3 steradian. The corresponding illuminance is then E = LW = 4*10^-10 lux, which agrees nicely with the first calculation.

So, 30 miles sounds like a good estimate. The obvious application is to Susan B. Warner's hymn. --Prophys 14:11, 18 July 2007 (UTC)

A couple of engineering handbooks said that if the light source was less than one second of arc in diameter it could be treated as a point source. Another said of it was ten times the diameter away it could be treated as a point source (rather more tolerant). Further research shows that per Bloch's Law there is time intensity reciprocity in the human eye up to 100 msec (the shortest time found was 87 msec for threshold level illumination). The most sensitive wavelength is closer to 510 nanometers in scotopic (night time) vision rather than the 555 nanometer figure for photopic vision, per the Purkinje shift. See also the gospel song "This little light of mine, I'm gonna let it shine" [12]. ps: I found a number of sites [13] which state the "30 miles on a clear night" claim for candle visibility threshold, but others state that a certain kind of distress flare or even a lighthouse has that range. The candle, the viewer, or both would have to be at an elevated viewing point or the curvature of the earth would prevent seeing it. For an authoritative published source, there is [14] at Google books, see "Contemporary Color" By Steven Bleicher, Published 2004, Thomson Delmar Learning, ISBN 1401837409, which says on page 4 "...the minimum amount of light required to produce a visual entity is a candle flame at 30 miles on a clear night." Edison 01:35, 19 July 2007 (UTC)

Dead ants on the shore of Topsail Island

About several ago, I spent a weeks vacation at Topsail Island in North Carolina. And every afternoon, the creepiest thing would happen. thousands of large black ants would wash up on the shore of the beach and would lay there to die. When the sun set, crabs would come out and eat the ants. They'd all be gone by morning, but the same thing would happen the next afternoon.

Does anyone know how and why so many ants washed into the ocean ended up there? Is it some kind of natural cycle that happens all the time, or a freak accident? I have a phobia of ants (especially huge ones) so put a huge damper on my beach vacation, but I'm still curious about the phenomena. I haven't found any information on it, which is why I'm asking you.

There are some pictures of the ants here from someone who had a similar experience (they may have been there the same week as me): http://www.coasttocoastam.com/gen/page2030.html?theme=light

Please shed some light on this mystery! Thanks ^_^

--76.50.80.171 05:20, 16 July 2007 (UTC)

User:Dyanega, who apparently has a PhD in entomology, says:

... those are dead ants from mating flights. The winged reproductive ants normally emerge by the millions, in synchrony, in many different ant species. They mate if they can, and most die. The only unusual thing here is that they should be concentrated in one small area, perhaps because of the wind or water currents. Otherwise, nothing odd or newsworthy about it. It happens all the time.

--TotoBaggins 17:35, 16 July 2007 (UTC)

Flank bell?

What does it mean when a military naval ship or submarine performs a "flank bell"? 75.35.111.26 06:50, 16 July 2007 (UTC)

A "flank bell" refers to the position on the Engine Order Telegraph. It's position the bell, "AAIII", means "all ahead flank speed" and is essentially a signal to set the engines to the fastest speed the sub will go in the forward direction. [15] Rockpocket 07:14, 16 July 2007 (UTC)

electrical and electronics project

I am an enginnering student and I need to do a project as part of my academics. My branch is electrical and electronics engineering. can anyone suggest me a good topic. i would be very grateful to u. i have been searching for weeks but i have never hit upon a suitable one. thank u for ur help.

What sort of thing are you interested in? And what kind of level are you studying? Suggestions:

1. something to do with mobile phones - can you make a readable LCD display that does not need lighting?
2. Greenhouse gas reduction - can you design something to be much more energy efficient?
3. build a terahertz radiation detecter and imager to see if someone is carrying a hidden gun
4. Make a cheap quadrapole nuclear magnetic spectroscopic detector to detect smuggled substances - like alcohol for customs.
5. Make a USB decoration different to anything else.
6. make a television out of plasticine - that works.

GB 10:37, 16 July 2007 (UTC)

Anything which solves world hunger or creates world peace is a good start. On a more serious note, why don't you try asking your course coordinator/lectures/academic advisors and friends/course-mates? Nil Einne 12:11, 16 July 2007 (UTC)

How about a system to turn window fans on and off automatically when the temp outside is lower than the temp inside ? I imagine two temperature probes on the end of wires, one hanging inside the house and one outside. For a bonus, also consider humidity. If you really feel ambitious, you could have one master control send an RF signal to turn all fans in the house on or off at the appropriate times. See [16] for a description of how window fans can be used as an alternative or supplement to A/C. StuRat 14:00, 16 July 2007 (UTC)

Microwave death ray.

Oh, here's something I found in a "they oughta make" column in a (no kidding) 1944 Mechanix illustrated or popular mechanix or whatever: a bathtub that turns the water off when it's full. I'd enlarge the concept to include sinks. You could build something into the overflow hole. Sheesh, these days when you can spend $500 on a faucet, you'd think it would be an obvious option. They've had 60 years to think about it since that guy mailed it in to the magazine. Gzuckier 15:06, 16 July 2007 (UTC)

A television for hamsters? Powered by their excercise wheel? Capuchin 22:22, 16 July 2007 (UTC)

Ooh ooh even better! A little hamster camera that is wired up to their hamster TV so they can see themselves working out! Awesome! I wish I was your hamster! Capuchin 10:03, 17 July 2007 (UTC)

Freshwater and the Himalayas

In this article [17], it says: "The glacial retreat presents a double peril for those who live in the Himalayas and the populations of India and China, where the water flowing from the mountains accounts for 40 per cent of the world's fresh water." Is it really 40%?? (that figure seemed high and I was wondering if anyone could confirm it, I can´t find this info. on wikisites freshwater and Himalayas). Thank you. --AlexSuricata 11:40, 16 July 2007 (UTC)

I'm thinking they mean 40% of the fresh water which is used by people. Since the water from the Himalayas would flow into populous nations like China and India, as well as Southeast Asia, it is likely that a large portion of it is used, versus melt-water from Greenland, Northern Canada, Siberia, or Antarctic glaciers, which likely pours into the oceans unused. StuRat 13:48, 16 July 2007 (UTC)

"Water flowing from the mountains" would include rain that falls on the mountains, and especially in a place with India's climate, there's going to be a lot more of that than the amount of glacial meltwater, right? --Anon, July 17, 2007, 05:35 (UTC).

Equilibrim data of CO2 in MEA solution (10%)

I'm chemical engineering undergraduate and designing a stripping column for my project.

The Column have to separate CO2 gas absorbed into 10% aqueous MEA (mono ethanol amine) solution with the use of steam stripping. So i need vapor liquid equilibrium data on Steam-CO2-MEA(10%) system.

Is there is any method to calculate column/packed bed height without using equilibrium data?

What are to recommended references for steam stripping column design (web sites/Books) ?

Thank you Malinda

Well, maybe you could ask your lecturer? I'm not up to that standard yet. Cheers!!! --Zacharycrimsonwolf 13:35, 16 July 2007 (UTC)

Some clarification questions:

1. Are you dealing with 10% MEA in water?

2. Do you have to give a quantitative answer as to the amount of CO2 that was absorb in the sample?

Mrdeath5493 20:00, 16 July 2007 (UTC)

Can I hazard a speculation that the steam only adds heat and the presence of water vapour does not alter the partial pressure of carbon dioxide in the gas phase. Water only absorbs a small amount of carbon dioxide and you can see the figures on carbon dioxide (data page). So you could expect CO₂ in the liquid phase to be proportional to the monoethanolamine MEA concentration. Next you will have to work out the equilibrium with bicarbonate ions and the weak base. One shortcut may be to measure the pH of your solution, or find the Ka for MEA. GB 21:45, 16 July 2007 (UTC)

Rheum

I'm saddened by the lack of article on rheum. What is this stuff? Mainly minerals from tear evaporation? Has anybody ever collected a large amount of it (Gypsies?)? How much? Are there any conditions where rheum does not form or forms too much? I remember as a child occasionally having my eyes welded shut when I woke up, was this due to rheum? What caused a large enough production of rheum to weld my eyes shut? These are the kind of world-changing questions that science should be answering. Capuchin 14:42, 16 July 2007 (UTC)

I'd guess it's got some mucus in it. What does it have to do with rheumatoid arthritis, is what I'd like to know. Gzuckier 15:10, 16 July 2007 (UTC)

The only time I've come across eyes welded shut like that is with conjunctivitis. Skittle 17:31, 16 July 2007 (UTC)

Definately didnt have conjunctivitus. It has maybe happened to me 5 times in my life. I remember my father having the same thing one morning too, with no particularly obvious illness going on. Capuchin 22:20, 16 July 2007 (UTC)

To answer yor question Gzuckier, from wiktionary definition of rheumatism: "First attested 1601, from Latin rheumatismus, "rheum", from Greek rheumatismos, from rheumatizesthai, "to suffer from rheum (which was thought to cause pain)", from Greek rheuma "a stream, flow," from rhein "to flow," from PIE *sreu-, "to flow". This shows the link between the two. Etymology is ridiculously interesting. Capuchin 09:56, 17 July 2007 (UTC)

Thanks. (every time I see the word rheum, I think of Inspector Clouseau). Gzuckier 14:34, 17 July 2007 (UTC)

I always think of Shylock -

Signior Antonio, many a time and oft

In the Rialto you have rated me

About my moneys and my usances:

Still have I borne it with a patient shrug,

For sufferance is the badge of all our tribe.

You call me misbeliever, cut-throat dog,

And spit upon my Jewish gaberdine,

And all for use of that which is mine own.

Well then, it now appears you need my help:

Go to, then; you come to me, and you say

'Shylock, we would have moneys:' you say so;

You, that did void your rheum upon my beard

And foot me as you spurn a stranger cur

Over your threshold: moneys is your suit

What should I say to you? Should I not say

'Hath a dog money? is it possible

A cur can lend three thousand ducats?' Or

Shall I bend low and in a bondman's key,

With bated breath and whispering humbleness, Say this;

'Fair sir, you spit on me on Wednesday last;

You spurn'd me such a day; another time

You call'd me dog; and for these courtesies

I'll lend you thus much moneys'?

JackofOz 04:27, 19 July 2007 (UTC)

1800-1850 Medicine

What were the common practicing medical beliefs during the first half of the 19th century?

You may need to be a bit more specific in your question. Our articles on medicine and the history of medicine may be helpful, as might our timeline of medicine and medical technology. The history of biology might also come in handy. TenOfAllTrades(talk) 19:38, 16 July 2007 (UTC)

You might also read Madame Bovary, which contains a presumably plausible, but quite grim account of medicine in that period, as performed by a mediocre/bad doctor. --TotoBaggins 19:12, 17 July 2007 (UTC)

Popularity of home birth

Where can I find information about how many women in United States bear their children at home? I.e. with the help of a doctor or a midwife, but at home and not in the hospital. In percents to the total number of births. If you have any reliable data about other countries, please post it too. Thanks in advance! 83.237.160.59 19:29, 16 July 2007 (UTC)

The CDC keeps statistics on this. Go to this page and look for the term 'final data'. Download the PDF and go to 'Medical Services Utilization, Attendant at birth and place of delivery'. Statistics are available on that page from 2004 back to 1999.

In 2004 (PDF link),

• 91.5% of births were delivered by physicians in hospitals.
• 7.9% of all births were attended by midwives.
• About 1% of all births took place outside of a hospital; a third of those were in a freestanding birthing center, most of the remainder were in residences. About two-thirds of the non-hospital births were attended by midwives.

Hope that helps. TenOfAllTrades(talk) 20:09, 16 July 2007 (UTC)

One more: this site provides links to Office of National Statistics for Britain and the UK, broken down by region. The UK average is 2.4% for 2005. TenOfAllTrades(talk) 20:15, 16 July 2007 (UTC)

tungsten

How can I lower the melting point of tungsten?

Tungsten is an element. You cannot lower its melting point without changing the elemental composition to something other than tungsten. --Anonymous 20:45, 16 July 2007 (UTC)

If you wish to change the elemental composition of your sample to something other than tungsten (an alloy, for example), see freezing-point depression (note that freezing point is the same as melting point). --Anonymous 20:52, 16 July 2007 (UTC)

Hmm, well, speculating a little here -- the melting point might go down very slightly as you lower the ambient pressure. I wouldn't expect it to be lower by any significant amount, though. --Trovatore 20:54, 16 July 2007 (UTC)

In the melting point article, it mentions this phenomenon, but notes that "Unlike the boiling point, the melting point is relatively insensitive to pressure". --Anonymous 20:58, 16 July 2007 (UTC)

Interestingly, the graph there shows the melting point decreasing, rather than increasing, with increasing pressure. This had me confused for a moment, until I realized that that particular graph is for water, which (somewhat anomalously) expands when it freezes -- by Le Chatelier's principle, it therefore makes perfect sense that its melting point would decrease with increasing pressure. --Trovatore 21:16, 16 July 2007 (UTC)

High pressure physics gets no love, just because temperature is so much more accessible. Neat recentish result - negative melting curve in Na. For reference on their units, a million atmospheres is 100 GPa. -Eldereft 04:31, 18 July 2007 (UTC)

Texture of testicle

Medical question closed.
The following discussion has been closed. Please do not modify it.
Hi there My girlfriend seems to be concerned by my one testicle, because it seems to have a veiny mass attached to it, whereas the other testicle is perfectly smooth with nothing attached. Can someone possibly provide me with a reputable source to prove to her that my testicle is not abnormal? Thanks a lot 41.241.100.11 20:49, 16 July 2007 (UTC)

We cannot provide medical advice here on Wikipedia. Your best bet would be to seek the professional advice of a physician. TenOfAllTrades(talk) 20:57, 16 July 2007 (UTC)

I would add that testicular cancer is the most common form of cancer among young adult males, so if there is significant concern I would strongly encourage you to speak to such a medical professional. Dragons flight 21:04, 16 July 2007 (UTC)

Ok, in that case, let me rephrase. In terms of the anatomy of the human testicle, is it normal for one of these testicles to have somekind of chord/mass attached to it?

One's testicles should not be remarkably different in shape, texture, or configuration. If there is actually a difference, it should be checked by a physician (who, in any case, may be able to teach you what you're feeling, which may or may not be the epididymis or the vas differens). And you should learn to examine your own testicles: girlfriends may come and go, but your testicles are - hopefully - forever. - Nunh-huh 21:07, 16 July 2007 (UTC)

There is a helpful article at Testicular self-examination, but I would strongly re-state the advice above that you Consult your medical practitioner if you have any concerns about your testicles, or any other body-part. DuncanHill 00:24, 17 July 2007 (UTC)

July 17

Albatross

Why is it considered bad luck to kill an Albatross? --81.79.246.87 01:25, 17 July 2007 (UTC)

The Rime of the Ancient Mariner is relevant, there is also some information in the article Albatross. My understanding has always been that albatrosses are the souls of drowned sailors. DuncanHill 01:29, 17 July 2007 (UTC)

How to apply heat-conduction formulas? (Hopefully my last Wx-sim question!)

(My apologies for the barrage of wx-sim related questions -- in trying to do my own research, I've run up against a seemlingly endless stream of helpful formulae which leave-out the units or the application!)

Pre-question: Would it be helpful if, once I get these things all figured out (search this page for "weather-sim"), I added some examples to the relevant wiki-pages? There are lots of helpful pages with formulae and coefficients, but which lack examples & units for the laymen.

The real Question (short): I'm not quite sure how to apply the heat transfer equations for heat conduction; could someone please provide an example?

More detail: (EDIT: (I forgot to mention in the original) this is for a grossly simplified weather-sim for a game. I'm willing to take lots of shortcuts & approximations, the goal is more to give "realistic appearances" rather than "true to life" actual physics.)

For example, let's say I have a sandstone "rod", $1m^{2}$ in area, 3m long. It's 40°C at one end and 20°C at the other end, in a smooth gradient. I want to apply conduction equasions, so we'll ignore radiation & convection. To idealize the situation, we'll also ignore any heat conducted into space, and just say that the rod conduction is "pure." (I know, I know...) Let's say an hour passes; what is the temperature at both ends of the rod?

Heat conduction tells me that the basic formua is

${\frac {\Delta Q}{\Delta t}}=-kA{\frac {\Delta T}{\Delta x}}$

where

Q is the amount of heat transferred,

t is the time taken,

k is the material's conductivity.,

A is the cross-sectional surface area,

$\Delta T$ is the temperature difference between the ends,

$\Delta x$ is the distance between the ends.

Checking the links in the question, and several related sites, applying to our example, I get

${\frac {\Delta Q}{\Delta t}}=-2.4*1{\frac {20}{3}}$

or

${\frac {\Delta Q}{\Delta t}}=-2.4*6.667$

Follow up: What to do with numbers so far?

So now my questions are:

• What is the units for Q?
• What is the units for t?

Assuming seconds, I get

${\frac {\Delta Q}{3600}}=-2.4*6.667$

or

$\Delta Q=-2.4*6.667*3600=-57,600$

but, um... what do I do with that number in order to determine the ending temps of both ends of the rod?

Might Q be in watts? So, I subtract 57.6kW from one end and add it to the other? (I thought I had a formula for how to do that, but could someone help me convert that to °C, just for example?)

Btw: Hats off to you guys who know all this stuff. I know it's not magic, but it's pretty darned close!

Thanks! Oliepedia 03:21, 17 July 2007 (UTC)

You've picked a real tough problem here. Digging through my heat transfer book, I can't find any simple relationships for the situation you have, which is one-dimensional conduction with adiabatic boundary conditions at both ends (no heat transfer in or out of either end). Unless someone finds a way I've overlooked, it looks like you'll have to apply Fourier's Law. You're on the right track with what you have, but you've made an incorrect assumption to arrive at the equation you give (and which is given in the article). Namely, there must be heat flux through the ends of the rod. If you're willing to make that assumption, then you're on the right track. If the ends of the rod must be adiabatic, we have to start with the general form (for Cartesian coordinates)

File:Anonymous6494eq-1.png

Since this is one dimensional, the above boils down to

where $\rho$ is the material density, cp is the specific heat, and k is the thermal conductivity. This is a partial differential equation, which is best solved numerically. I'll leave that up to you. Sorry about the format of the equations, if someone wants to put them in Tex, please do.--anonymous6494 04:21, 17 July 2007 (UTC)

I'm happy to have heat-flux through the rod-ends (uh... what does that mean?!) if it makes the math simpler. See edit, above. Oh, heck, I'll repeat it, here: (I forgot to mention in the original) this is for a grossly simplified weather-sim for a game. I'm willing to take lots of shortcuts & approximations, the goal is more to give "realistic appearances" rather than "true to life" actual physics.

Also, I dropped from pre-calc. So, while I get the general concepts, I can't always read all the equations (plus, it's been 30+ years, so details like units escape me.) That's why I was looking for an example walk-through with numbers. I'm hoping to come out of this with something like "So, as you can see, after an hour, the rod will have a smooth temperature gradient, ranging from 35.78°C to 23.9826°C" (numbers made-up for example only.)

Thanks! Oliepedia 04:47, 17 July 2007 (UTC)

Q is in Joules, its a unit of energy. What happens next depends on where that energy is going. Depending on what the "rod" is anchored to (if anything) it will flow from the stuff at one end to the stuff other. Or in the case of a free floating rod, you can imagine the energy going from the hot "half" of the rod to the cold "half". But anyway, the piece of the puzzle you are missing is $\Delta Q=Mc\Delta T$, where M is the mass of stuff the energy is moving in to (or coming out of), c is the specific heat which is simply a constant that varies by material, and $\Delta T$ is the resulting change in temperature. Dragons flight 05:58, 17 July 2007 (UTC)

PS. Please note that the $\Delta T$ I just used, is the change in local temperature for a given amount of energy transfer and is different than the $\Delta T$ you used above to describe the difference in temperature across the two ends. Dragons flight 06:05, 17 July 2007 (UTC)

Since you are going to run it as a weather sim, don't bother trying to solve this analytically; you'll have to convert it to a numerical solution anyways. Since this is a partial differential equation, I would advise using the Crank-Nicolson numerical method to solve the BVP. First discretize with respect to $\Delta x$ with a second-order centered finite difference, then with the algebraic mean of the forward Euler method and backward Euler method for $\Delta t$. It also allows you to declare adiabatic/insulated/fixed-temperature boundary conditions with minor modifications to the code. Titoxd^{(?!? - cool stuff)} 06:12, 17 July 2007 (UTC)

Follow up: Attempt to apply formulae

Leaving off with $\Delta Q=-2.4*6.667*3600=-57,600$ (above), and tossing in Dragons Flight's $\Delta Q=Mc\Delta T$, which I'll switch around to

$\Delta T={\frac {\Delta Q}{Mc}}$

(since I'm trying to solve for $\Delta T$), and since I know the density of my sandstone (2.323) gives me M=6,969,000g (for 3m^3), and a c of 0.92 for sandstone, I now get:

$\Delta T=0.008983885156$

(Hmm, well, I guess it WAS a 3m rod, and only a 20°C differential for an hour...) So, ~0.009°C temp change at both ends -- does that seemreasonable to everyone? (Later, I'll do it with a shallower pool of water, something with which I'm more familiar and better able to speculate the correctness of the answer.)

Just to make sure I've got it, though (and, remember, we're doing gross simplifications & uber-idealization, here -- eliminating all the complicating factors like radiation, conduction, external objects, etc.) -- since 57.6kj "left" one end of the rod (in order to heat the other), then the "hot half" is going to cool-down by the same amount that the "cool half" warms up, and that amount will be my $\Delta T$, in °C, right?

A big thank you to everyone for your patience in getting me through all this. I'll need to read-up on wiki standards and then see if I can't back-fill some of these examples into the relevant pages. Oliepedia 15:16, 17 July 2007 (UTC)

canebreak or timber rattlesnake / range to desert West Texas?

I ran across a rattlesnake last weekend, and based on Wikipedia articles and photos, decided it looked like an excellent example of a timber or canebreak rattlesnake. Problem is, the wikipedia article and other sources describe it's range as the Eastern US, possibly including eastern Texas. I ran across my snake about as far west in Texas as possible -- in the Franklin Mountains above El Paso, Texas. (that's about as far west as Denver, Albuquerque, etc.)

Is the article wrong? If so, I don't really feel qualified to edit it. Anyone want to look at my photos or video? I'm wondering if anyone specializing in rattlesnakes would be interested in knowing about timber rattlers living in the desert southwest. My father, who's been in El Paso for 86 years says he's never seen one like that before (we usually see diamondbacks.)

One photo can be seen at: http://web.mac.com/xlyon/iWeb/Site/hothike_files/IMG_1747.jpg

I have more, as well as some .avi video files (not as high res as the stills.)

UPDATE: nevermind, he's positively a Banded Rock Rattlesnake. I found a good description and photo that identifies him as such, a known resident of the Franklin mountains.

Blyon3 03:22, 17 July 2007 (UTC)blyon3

Proof (if ever it were needed) of the wiseness of Wikipedias' WP:NOR policy. Even if you had found a canebreak snake in the Franklin mountains, you should not have changed the article since your finding of the snake would count as "original research" - which Wikipedia does not allow. What you would have had to do would be to find a book (ideally) or a reputable web site that stated that canebreak snakes were found in that region. SteveBaker 10:59, 17 July 2007 (UTC)

oxygen enriched v. anti-oxidant

To whom it may concern:

I attended an event where a promoter was handing out bottles of oxygenated water. I've also read about oxygen bars and the indulgent few who sleep in hyper-baric oxygen chambers.

On the flip side many food and nutritional products boast of their anti-oxidant properties.

Obviously, oxygen is essential resource for much of life on earth and yet I also know that it is an essential part of the fire triangle - fuel, oxygen, heat.

Is there a different value to the way that oxygen is consumed – breathed v. infused in water v. part of the molecular structure of the food/water itself?

Should there be an RDA for oxygen?

David — Preceding unsigned comment added by Carbon333 (talk • contribs)

On the one hand, you need enough O2 to perform your metabolic conversions. RDA is "that much" (depends on your weight, metabolism, physical activity, etc.) On the other hand, anti-oxidants are things which slow the oxidation process, and are reputed by some to be a preventative against cancer [citation needed]. Since cancer is basically cell-replication-gone-haywire, perhaps the idea is that anti-oxidents "slow down the fire" to a "safe and sane" level. I'm not 100% sure on that part, but it sort of follows reason.

At any rate, you need O2. Also, Oxygen at pressure (i.e., breathing compressed O2 under water) can be toxic to the point of fatality. Breathing oxygen enhanced air even at surface pressures certainly accelerates metabolic processes. You can debate whether that's benefitial (gives you a lift) or harmful (over-works your system.) Oliepedia 04:54, 17 July 2007 (UTC)

Okay, there's a lot of confusion here. First of all, an antioxidant is not something that fights or inhibits oxygen in particular. An antioxidant is something that prevents oxidation. Oxidation is the removal of electrons from a chemical. Elemental oxygen is a familiar oxidizing agent, but certainly not the only one. The similar sound of the words oxygen and oxidize is a historical accident, so try not to let it confuse you.

Second of all, you need to breathe oxygen in order to live. Your lungs are your only organs capable of getting oxygen to the bloodstream anywhere near efficiently enough. Drinking water with oxygen dissolved in it will not do you any good if you are asphyxiating. In fact I'll go ahead and say that it probably won't do you any good under any circumstances. It's a scam. —Keenan Pepper 07:28, 17 July 2007 (UTC)

As for bottled oxygenated water (stub required), it's highly recommended if you happen to be a fish. Otherwise, scam is probably the most appropriate term.--Shantavira|^{feed me} 07:41, 17 July 2007 (UTC)

If you aren't getting enough oxygen, your body will make you breathe faster. Simple as that. You don't need to "supplement" the oxygen that you are breathing. It doesn't work that way. Inhalation is by far and away the most efficient way of getting the oxygen you need. As other have said, oxygen infused water sounds like complete bunk. Capuchin 07:48, 17 July 2007 (UTC)

The urge to breathe is actually due to a build up in Carbon Dioxide. If there is a lack of oxygen in the air, you probably wouldn't notice and you would either faint or die, depending on the circumstances. Most Water is already oxygenated in a way anyway, see Dissolved Oxygen for more info.--GTPoompt(talk) 12:42, 17 July 2007 (UTC)

Under normal conditions, the solubility of oxygen in fresh water tops out at 14.6 mg/L. (That's under regular atmospheric pressure; at 4°C and three atmospheres – the pressure inside a soda can[18] – that limit increases to about 35 mg/L[19]. Meanwhile, the density of oxygen is about 1.4 grams per liter (1400 mg/L) at room temperature. The air around us is about 20% oxygen, giving a concentration of about 280 mg/L. Draw what conclusions you like. TenOfAllTrades(talk) 12:53, 17 July 2007 (UTC)

As I recall, the above numbers are one of the primary reasons why humans can't breathe water (another major one is the unsuitability of the lungs to circulate something as dense as water), as contrasted with being simply unable to process the water at all. You may be interested in reading liquid breathing. — Lomn 13:18, 17 July 2007 (UTC)

Also remember to compare how much air you breathe compared to how much water you drink. Capuchin 10:58, 18 July 2007 (UTC)

The oxygenated water is just a gimmick. might taste better. Certainly, water with all the gas removed from it tastes kinda flat. As to the folks who are consuming more oxygen for their health, unless they have severe lung problems this is also dumb. On the other hand, as you note, evidence is that free radicals and their oxidative properties are part of the aging process. Oxygen is, after all, a corrosive gas, which was toxic to the lifeforms existing when algae first started pumping it into the air; some of them still remain, Clostridium for instance (as in, botuslism, which can only survive in the absence of oxygen, as in canned food). The rest of us made our peace with it and even learned to use it under controlled circumstances, but the concept that sleeping under a hyperbaric tent is good for you is akin to all the other bright ideas Michael Jackson has. On the other other hand, nobody sleeps under a low-oxygen tent to reduce free radical formation, because you'd need somebody monitoring your brain waves and blood O2 level continually to make sure you weren't nosediving into a coma. Gzuckier 14:32, 17 July 2007 (UTC)

I have seen oxygen bars advertising that they mitigate the effects of altitude sickness in the Colorado mountains. Whether this is true or not I don't know, but it makes sense because part of altitude sickness is caused by the lower partial pressure of oxygen. Sifaka ^talk 05:57, 18 July 2007 (UTC)

I thought athletes sleep in hypobaric chambers to increase their amount of red blood cells so they can carry more oxygen quickly and have better stamina. It will increase the chance of getting a stroke or (myocardial)infarction though because the blood is thicker. Hyperbaric chambers are used to relieve altitude sickness. --antilived^{T | C | G} 06:01, 18 July 2007 (UTC)

Coconut Husks and Water Absoprtion

My question on 11 July, should I say, as a whole fruit, the skin of the coconut is water-proof (does not absorb water), and the fact that the inner part of it contains husks, shell, flesh, coconut juice and some amount of air - to explain why it is float from island to island as a form of dispersal. Should I say too that coconut husks absorb water while the coir fibres that are found between the skin and the husks is relatively water-proof but still absorb water to certain extend ( if you soak the coir fibres in the water, it will swell and soften - to explain the absorption ). (Teng)

Yes, I stated all these points. You can follow the experimental procedure that I suggested to obtain an idea of absorption. It'll be fun for your son! Capuchin 07:49, 17 July 2007 (UTC)

Water Stain Removal on Standard Steel SUS430

Pls help. Whats the best cleaning solution for the water stain on standard steel? I use Nitric Acid still can't remove. HFI a bit strong...

203.120.44.158 09:13, 17 July 2007 (UTC)

Is this rust? Better to use a file, wire brush, or steel wool in that case. What sort of item is it?--Shantavira|^{feed me} 12:54, 17 July 2007 (UTC)

Follow-Up: Its not realy a rust, more of water spot which scattered all over the surface of HDD Cover. Can't use file ot steel wool as it will leave scratches on the surface.

203.120.44.158 04:33, 18 July 2007 (UTC)

You can purchase stainless steel polish for cleaning saucepans and cutlery. It probably has somehting like toothpaste in it. GB 07:13, 18 July 2007 (UTC)

One thing I would do would be to repeat the stain all over the cover - eg wipe with a damp wet cloth - then your cover would be a different shade of steel (greyer) but at least it would look uniform. I'm guessing that the surface is 'burnished' in someway to give a 'rough industrial' effect rather than being highly polished.. If it's just a water stain the staining might by due to salts (water hardness) - I'd try something alcoholic (but pure) - you could use isopropyl alcohol if you can get it.. or even vodka. Be careful on any plastic parts with the solvents - especially lacqueered bits. By the way did the nitric do nothing - I'd imagine it making the stain worse.. ps how did it happen ? are you sure it's water - not grease?87.102.23.249 18:16, 18 July 2007 (UTC)

Cottage Grove seismic zone in Southern Illinois

I have been searching for information on fault locations and seismic history for this area. I have been able to ascertain it is a series of strike/slip faults on the eastern edge of the New Madrid system near the start of the Wabash Valley system and that some of its features interfere with coal mining in the region, but little to nothing on its seismic history and potential hazards. We are particularly interested in information pertaining to the area within a 50-mile radius of the Harrisburg (IL) quadrangle.208.0.30.32 13:58, 17 July 2007 (UTC)goldcatt

This PDF may provide some guidance. So far as I could determine in a quick search, it is not particularly active sesimically. The Illinois Geological Survey would be your best source of authoritative information. Cheers Geologyguy 17:45, 17 July 2007 (UTC)

The Skimmer - how does it avoid injury whilst feeding?

After watching the videos linked from the Skimmer article, it made me wonder how on earth these birds avoid accidents whilst feeding. Flying rapidly along, just above the surface of the water with the lower mandible trailing in the drink seems like a recipe for disaster. What if there was tangled plant matter, or even worse - a rock (hello broken jaw!) just under the surface? Has anyone seen Skimmers feeding in real life? Do they often injure themselves whilst going about their business? --Kurt Shaped Box 15:12, 17 July 2007 (UTC)

Because the article says they are in the same family as gulls, I have to assume they have similar eyesight. Gulls can easily see fish (and other objects) in the water. So, the skimmer must be able to see the fish it is "skimming". -- Kainaw^(what?) 15:18, 17 July 2007 (UTC)

I have occasionally watched Black Skimmers feeding at Morro Bay in California, and as I recall when they hit something and/or catch something (hard to tell which) their head and lower mandible moves very quickly backwards (as if they were tucking their head underneath their body and trying to touch their underside--hard to describe). So I assume that if their lower mandible did hit some solid object their head and bill would simply move backwards out of danger. Also their lower mandible doesn't extend very deep into the water, so the chance of their hitting something solid that they could not see would be pretty small. On the other hand when they are feeding they seem to be moving very, very fast! Please note this is purely on the basis of my own observations and I could be completely wrong.--Eriastrum 16:38, 17 July 2007 (UTC)

Your observations make sense when you consider the mechanics of the situation. Sorry, I'm not a physics student, so I don't know the correct terminology here - but striking and underwater object 'stiff' (i.e. without using its flexible neck to absorb some of the force of impact) would cause the bird to either 'break' or be flipped forwards, like a human going through a car windscreen, wouldn't it? --Kurt Shaped Box 22:34, 17 July 2007 (UTC)

Yes, the head would experience increased drag and thus deceleration, but the body would continue moving at the same speed. Capuchin 06:48, 19 July 2007 (UTC)

Kerala Fever and Blood Platelet count

Hi,

My mother is very sick and she is hospitalized. The doctor says it is only a viral fever. The platelet count is very low. She had the same issue about 2 years ago. Then it became very dangerous and she had to receive the platelet component from a donor. Sine we are aware that for last few years it is repeating at Kerala during the monsoon season, we had taken enough care to maintain hygienic and healthy environment at our house. But still, she got it again; she is only around 60 years old.

We all have got viral fever in the past; but never happend the issue of platelet count. The doctor’s explanations are not convincing enough. As our politicians are stonehearted creatures who are getting ready to face the disaster by preparing mass condolence messages, we desperately hope whether Wikipedia could immediately mobilize the work of some experts on the issue.

I would like to know

1. Under what circumstances (diseases) the platelet count can go down.

2. Is the level of seriousness of the issue (lower count of platelets) is different under different root causes?

3. What is the relation between ordinary viral fever and platelet count? Why not all people have the issue of platelet count go get affected by viral fever?

4. At Kerala, this issue has become so wider spread only since last few years. About a few years ago, there was a strange phenomenon of ‘coloured rain’ at different parts of Kerala. There were news paper reports saying that analysis showed the rainwater contain unknown life forms that might have come from some asteroids. a. The Kerala fever and this ‘coloured rain’ has any connection?

b. What really caused the coloured rain?

c. Could it be the hand work of some inhuman research organizations experimenting with ‘rain cloud engineering’?

5. How serious is the ‘Kerala Fever’?

6. Why it is repeating each year?

7. How can people escape from it?

For medical advice you should consult a doctor. For extraterrestrial advice you should consult a scientologist. Lanfear's Bane

To find out more about platelets, you can read about platelets. The red rain in Kerala was caused by colored algae spores, which possibly looked extraterrestrial to someone who has no idea what algae spores look like. If you don't trust your doctor, find another one. 151.152.101.44 17:43, 17 July 2007 (UTC)

1. See thrombocytopenia.
2. Yes.
3. It depends; see your doctor.
4. a) The Kerala Fever you're referring to is probably Chikungunya. It is caused by a virus transmitted via mosquitoes. b) The red rain in Kerala was (most likely) caused by algal spores. c) See weather control, and no.
5. See Chikungunya.
6. There's no vaccine, and it's hard to get rid of mosquitoes.
7. Avoid mosquitoes.

Please speak to a physician to discuss specific personal health issues. TenOfAllTrades(talk) 17:47, 17 July 2007 (UTC)

Is this real?

Ballard score, uncategorized for ages, unlinked to, I don't know anything about. It's way out of my field, but... I can't tell if it should stay or go and unfortunately I don't know what Wiki-Projects to notify about it... 68.39.174.238 17:02, 17 July 2007 (UTC)

It should be under Ballard Maturational Assessment. And, it is used to assess gestational age. -- Kainaw^(what?) 17:28, 17 July 2007 (UTC)

 Done Moved it to that title--VectorPotential^Talk 17:35, 17 July 2007 (UTC)

Just thought to add a link to a BMA form, http://www.medcalc.com/ballard.html -- Kainaw^(what?) 17:28, 17 July 2007 (UTC)

Just need some links to it from the relevant articels and it'll be fine, thanx. 68.39.174.238 14:58, 18 July 2007 (UTC)

shielding angle and protective margin

What do you mean by shielding angle of a transmission line and what are its recommended values? What is protective margin and what are its recommended values> Thank you for your reply. — Preceding unsigned comment added by 59.89.20.20 (talk • contribs)

Never heard of the term shielding angle. What sort of transmission line are you asking about?--Tugjob 01:18, 18 July 2007 (UTC)

gapless surge divertor

I have two questions. What are the advantages of gapless surge diverters? What are the differences between a surge diverter and a surge absorber? — Preceding unsigned comment added by 59.89.20.20 (talk • contribs)

I would say that an absorber totally dissipates the energy of the surge, whereas a diverter reflects it.--Tugjob 01:15, 18 July 2007 (UTC)

Power Systems

What are the differences between the two types of lightning strokes: A stroke and B stroke on transmission lines? — Preceding unsigned comment added by 59.89.20.20 (talk • contribs)

three questions in power systems

What is an isolator? What is a back flashover? What are the types of lightning strokes that can cause such back flashovers of line insulators? What is surge impedance of a transmission line and what are its significances? — Preceding unsigned comment added by 59.89.20.20 (talk • contribs)

I suggest you re read your lecture notes!--Tugjob 01:20, 18 July 2007 (UTC)

gapless surge diverter

can someone briefly describe the working and construction of a gapless surge diverter? Thanks for ur help. — Preceding unsigned comment added by 59.89.20.20 (talk • contribs)

See transient suppressor--Tugjob 01:11, 18 July 2007 (UTC)

Uncertainty in various fields

(This question was originally asked at the Mathematics Reference Desk but editors there suggested the Science desk was more appropriate.)

When giving error limits, there is almost always an uncertainty associated with the limits. For example, the August 2007 edition of Scientific American contains a graph on page 67 that shows various causes of radiative forcing which are thought to be driving global warming, and for each forcing an error bar is shown, which represent a 90 percent liklihood that the value lies within the error bar. Similarly, page 66 contains the statement "the updated trend over 1906 to 2005 is now 0.6 ± 0.2 degree C." There must be some unstated uncertainty associated with this tolerance; perhaps the phrase realy means there is a 90 percent probability that the trend lies between 0.4 and 0.8 degree C.

What I would like to know is whether there is/are document(s) that state what level of uncertainty is usually used in various fields when there isn't enough information to rigorously choose an uncertainty level? If this had been a biology article instead of a climate article, would the uncertainty level have been 95 percent rather than 90 percent?

I understand that on rare occasions, the economic consequences of the measurement falling outside the error bounds is known, and the budget available to deal with the outliers is known, so an appropriate error bound can be rigorously calculated, but this seldom is the case. --Gerry Ashton 22:03, 16 July 2007 (UTC)

A rigorous, peer-reviewed scientific journal will always explain the meaning of an error bar or interval in a figure, and explain how it is derived. Unfortunately, publications meant for popular consumption usually omit the details of these derivations. (Scientific American – well-written and generally high-quality though it may be – is no exception.) In order to get the information about how these values are derived, you need to go back to the primary sources. I'm going to assume that the Scientific American figure you're referring to is similar to the one in our Image:Radiative-forcings.svg, which in turn is based on the IPCC's Fourth Assessment Report; you'll have to look through that document to see how they arrived at those particular confidence intervals.

Different fields of study will tend to have different standards for evidence and reporting, and even within a field (and indeed even between papers in a single journal) there are apt to be differences depending on circumstances. To get an idea of acceptable standards of evidence and statistical significance, you might be well-advised to pull a few journals from the relevant field and look at the statistical tests used. TenOfAllTrades(talk) 21:04, 17 July 2007 (UTC)

In general, a point on graph represents a measurement of some sort. It may represent a single datum, or it may represent the mean (or other statistic) of a set of data. If it represents a single measurement, (for example, a reading from a voltmeter) then the uncertainty of the measurement is based on the precision of the instrument and the experimental setup, as calibrated during other experimental runs. The calibration is done using statistical methods. In either case, we are now in the realm of statistics. The "error bounds" given in any particular case represent a crude representation of the underlying statistical methodology. Basically, you are getting three points (the datum, the lower bound, and the upper bound) of what is actually a continuous statistical curve. You must go back to the original report to discover which particular curve these three points represent. If for some reason you disagree with the statistical model used by the author, you must go all the way back to the original data. In many cases, the author assumes a gaussian distribution. In this case the author can use the mean and the standard deviation as the three points. If the underlying distribution is not gaussian, the result is misleading. -Arch dude 03:15, 18 July 2007 (UTC)

As far as I know, and certainly in physics, the plus/minus errors on a number represent one standard deviation. That is a 68% probability. People will also tend to prove things up to a certain confidence limit, 95% is a standard choice. Somehow being used to more precise fields of physics 90% doesn't seem that convincing, but I suppose it is quite high really. Cyta 07:19, 18 July 2007 (UTC)

I think you may be confusing a p-value with a confidence interval. The former is a way of evaluating whether or not there is a statistically significant difference between two values. The latter is a way of expressing the uncertainty in a measured or calculated value.

In other words, the apples-to-apples comparison you should be making is between standard deviations and confidence intervals as ways of expressing uncertainty. For a normally distributed variable, a 95% CI is going to be 2 SD, a 90% CI a bit less (but still much larger than 1 SD error bars). CI's have the advantage of not necessarily implying a normal distribution, of course. As you've probably noticed, if certain conditions are met it is entirely possible to have two values with partially-overlapping distributions still be statistically significantly different. TenOfAllTrades(talk) 13:16, 18 July 2007 (UTC)

Chemistry and Childbirth

How does chemistry relate to childbirth? 71.54.53.133 21:01, 17 July 2007 (UTC)

That's a bit broad. Narrowing your question would help us answer it. For instance, are you interested in the chemicals (hormones, etc.) that dominate during pregnancy, labor-inducing drugs, contraceptives, etc? Help us help you. --David Iberri (talk) 02:24, 18 July 2007 (UTC)

thermoconduction

im looking for the best available thermoconductor to extract heat from hot air, i need to find the most efficient way of doing it , colud anyone help me with this please

Best depends on many things - are you after the cheapest, the longest lasting, the least maintenance, what sort of temperature range does it have to work over (sub freezing, or over boiling point of water?). and by efficient do you mean to cool the air as fast as possible, or as cold as possible, or using the least energy possible? Water in a copper pipe is a way to do it, but if you have a narrow range of temperature, a liquid that boils at your temperature can extract heat quickly. Have a look at how airconditioners work! GB 22:22, 17 July 2007 (UTC)

sorry, i think i didnt mean thermoconduction here , i forgot to mention that i need to extract heat form hot air and turn it to electrical current , in the most cost efficient way possible ,this would be used at the same time to generate electricity and prevent the system from overheating , im planing on using a lot of these conductors in a tube and passing the air contained in the system trough the tube and back in the system to be heated again , the only thing is i dont know what kind of conductors to use.

Have you considered using something other than air for your heat exchange? -- JSBillings 13:24, 18 July 2007 (UTC)

not really since im pretty sure it would increase the cost a lot and i coudnt have fluids go inside the main chamber where all of the heat if generated and needs to come out quickly to keep from over heating , the unit would be sealed tough so i could use an other gas than but i dont know anything about gas thermoconductivity , i could surround the main chamber in fluid filled pipes but im not sure if that would be enough

why is it

that generally men have darker skin than women? — Preceding unsigned comment added by Jolly hockey sticks what (talk • contribs) 22:10, 17 July 2007 (UTC)

Do they? Never noticed. Where do you live? Simon A. 22:21, 17 July 2007 (UTC)

Men often spend more time outdoors in the sun, therefore get a tan and are less likely to use daycream. GB 22:25, 17 July 2007 (UTC)

Oh, that really depends on where you live/work. The dynamic could be easily reversed (except that daycream part). Someguy1221 23:55, 17 July 2007 (UTC)

In some cultures it's considered more attractive for females to be lighter skinned, while not necessarily for males. --antilived^{T | C | G} 05:53, 18 July 2007 (UTC)

So, just how does a gull's eyesight compare to that of your average human's?

(Question in relation to the Skimmer thread above - not just another self-indulgent seagull query, hehehe).

I've seen it stated that birds generally have better eyesight than humans - but what about the gull family in particular? How do they measure up to us in terms of colour vision, depth/motion perception and general sharpness of sight? --Kurt Shaped Box 22:54, 17 July 2007 (UTC)

Gulls are evidentally UV sensitive [20] Nil Einne 23:22, 17 July 2007 (UTC)

Cool. Do you have a non-blog-related source for that? I'd really like to add this info to the Herring Gull article... --Kurt Shaped Box 23:36, 17 July 2007 (UTC)

Don't know if birder's world counts as a reliable source, but [21] says "Besides hummingbirds and songbirds, parrots and gulls are known to see UV light". Hope you don't mind, I corrected your borken link Capuchin 07:45, 18 July 2007 (UTC)

My understanding is that essentially all birds have much better vision than humans -- and humans (and other primates) have generally better vision than other mammals. While I am not sure about gulls in particular, I think all or nearly all birds have four color receptors rather than the normal two receptors found in mammals. Humans have three (red, green, blue if I'm not mistaken), but one of them is a bit of a kludge and not as good as any of the four that birds have. Also, most or all birds have a variety of other vision-enhancing things, like "oil droplets" in or near the eye lens, to help focus, and better foveas. Some birds even have more than one fovea per eye. My quick search indicated that birds of prey tend to have multiple fovea. While gulls are not birds of prey, they are scanvangers (at least where I live!), which, as I understand it, requires sophisticated vision and flying skills beyond what people commonly think. A google search turned up all kinds of info on bird vision, but it would take more time to find something specific to gulls. I found a few clues while googling, but didn't spend that much time on it. A more determined search would probably turn up gull-specific vision info. Finally.. for some reason I always enjoy pointing out how birds are far superior to humans in both vision and vocalization. We literally cannot conceive of what it would be like to see things the ways birds do. Pfly 08:40, 19 July 2007 (UTC)

AFAIK, birds also have much more efficient respiration and metabolism than humans. They're incredibly well-'designed' for what they do. I'm not too sure about their senses of smell, taste and hearing - I've heard conflicting information. --Kurt Shaped Box 22:53, 19 July 2007 (UTC)

Well, most birds have a really poor sense of smell but there are some really notable exceptions (kiwis, albatrosses, vultures, etc). It doesn't take long to figure out why - a keen nose would require some keen olfactory-sensing brainpower and weight is precious to flying birds; they'd need a really good reason to have a good sniffer. Albatrosses and vultures need it because they scavenge for a good portion of their calories. Kiwis obviously don't have the same weight-worries. On the other side, smell would be of little use in finding seeds, worms, bugs, fish, and live meat - or rather, it would not be as useful as good eyesight, which the bird needs anyway to fly.

I've no idea about the taste sensation in birds. The hearing is probably pretty good (especially in owls) since they need to recognize some pretty complicated songs and oftentimes repeat them back. Matt Deres 20:30, 20 July 2007 (UTC)

How do you control and eliminate the aquatic plant Wolffia (aka Watermeal/Mealweed)?

Location is central South Carolina; the Wolffia grows extensively in a large pond that has catfish and bream in it that is caught for human consumption. I would like to know what chemical and biological treatments are available and their effectiveness as well as duration of time needed for the treatments. What side effects are there to these treatments? It would also be helpful to know what options are available in preventing its spread in coming years. BotanistWannabe 23:41, 17 July 2007 (UTC)

wolfia is difficult to get rid of - one possible method is to remove all of the plant - but that would be difficult - one possible method would be to use a rolling filtration system similar to that used to harvest algae (it's a bit like an up escalator - with mesh for steps).

alternatively plant competing plants (reeds, bullrush etc) after skimming the wolffia - that should compete for nutrients and limit it's grow back.

http://ohioline.osu.edu/a-fact/0014.html (http://ohioline.osu.edu/a-fact/pdf/0014.pdf same thing as pdf) gives lots of answers - note the use of carp and water fowl to eat it - ducks are tasty -why not add those!87.102.23.249 12:46, 18 July 2007 (UTC)

the above also lists chemical treatments - note that limited amounts of duckweed will proved shelter and food for fish fry.87.102.23.249 12:48, 18 July 2007 (UTC)

July 18

Relationship between electron affinity and ionization energy levels

Is the ionization energy of an atom related to it's electron affinity? For example, chlorine has an electron affinity of 349 and a first ionization energy of 1251 (in kJ/mol). But would the first ionization energy of Cl+ be equal to 349 kJ/mol? Likewise, would the electron affinity of Cl- be related to that first ionization energy of Cl neutral? Thanks! Delta 02:44, 18 July 2007 (UTC)

You are correct in that there is a relationship, but I think you got the specifics wrong. The electron affinity of Cl would be equal to the first ionization energy of Cl-. Why? Because the reaction for the electron affinity of Cl is as follows: Cl + e- --> Cl- (-349 kJ/mol), while the exact reverse of that reaction is the first ionization energy of Cl-: Cl- --> Cl + e- (energy is therefore the opposite, or +349 kJ/mol). ugen64 06:19, 18 July 2007 (UTC)

Frequent Urination

Since yesterday, i have been urinating a lot. I don't have diabetes and I've been cutting down on my fluids, but I'm still going a lot. Any ideas why? BTW, my urine is clear if it makes a difference.71.218.37.80 04:22, 18 July 2007 (UTC)

We have an article on this at polyuria. However, Wikipedia cannot offer a medical diagnosis, so if you are concerned about the frequency of your urinations, please consult a doctor. Someguy1221 04:44, 18 July 2007 (UTC)

Any pharmacy (chemist) sells little test strips for detecting sugar in urine. Just saying. Edison 01:26, 19 July 2007 (UTC)

Diabetes mellitus says that Type 2 diabetes can go undetected for years, with intermittent symptoms. Unless you have seen your doctor since the onset of the abnormally frequent urination, you probably are not justified in stating that you do not have the condition. Edison 18:07, 19 July 2007 (UTC)

Waterdrops- Perfume spray

Always when I was spraying the perfume (aerosol metallic tin) I was noticing some thing unusual.. after spraying some drops are being accumulated around the nozzle even though I wiped it away it was appearing for second time..why this was happening? Temuzion 06:56, 18 July 2007 (UTC)

It could be due to the depressurising gas in the aerosol being very cold due to adiabatic expansion. This will chill the nozzle, which will get condensation from humidity in the air. GB 07:17, 18 July 2007 (UTC)

Yes the expansion of the gas will take lot of heat from the can therefore making it cold and encourages condensation. Don't do this on someone (they can get frostbite from it) but if you tip the can upside down the gas bypasses the heatsink of the can and gives out very cold aerosol, which will create a mist-like stream coming out of the nozzle. --antilived^{T | C | G} 07:34, 18 July 2007 (UTC)

A more noticeable effect can be demonstrated by letting air out of a car tire. Since the air is under pressure and it expands after being let out, according to the Ideal gas law there should be a corresponding drop in temperature. You can feel the nozzle drop in temperature as you let out the air. (Just don't let anyone catch you giving them a flat tire.) -- JSBillings 13:18, 18 July 2007 (UTC)

Excess drinking of water!

Since one week I was drinking high amounts of water..even though I'm not thristy I was forcing myself to pour in some litres of water every day..when ever I remember water I was drinking minimum 1&half litres of water..in that way I was intaking some 6-8 lts of water daily..& similarly i was urinating very frequently.. which kind of effect will be shown on my body by this new habit? I hope it'll be definitely +ve..! Temuzion 07:03, 18 July 2007 (UTC)

A) Wikipedia cannot give medical advice. B) Water intoxication is a potentially fatal condition brought on by drinking too much water too quickly. Dragons flight 07:11, 18 July 2007 (UTC)

The font of all medical knowledge, House, showed that this can mess you up real bad. All I remember is that the guy had crippling muscle cramps - It doesn't say much about this, but the episode was House_vs._God, I think. Aaadddaaammm 07:57, 18 July 2007 (UTC)

In the end it turned out he had herpes; he was drinking the excess water in an attempt to 'cleanse' himself of his guilt and the virus, nothing to do with water intoxication. Lanfear's Bane

Except that his symptoms are that of the water intoxication, so it has everything to do with water intoxication. Capuchin 09:00, 18 July 2007 (UTC)

See Jennifer Strange. Not a nice way to die. --S.dedalus 22:00, 18 July 2007 (UTC)

See the Q & A about "Frequent urination" above. Edison 18:08, 19 July 2007 (UTC)

Number of Perpetual Motion Machine Patents?

Hello,

Is there anywhere it is possible to find out the number of patents for perpetual motion machines that are filed in a given year?

--91.104.48.234 07:24, 18 July 2007 (UTC)

I'd guess so. The WIPO maintains the International Patent Classification (IPC) which it used by patent offices around the world to classify patents. The purpose is, of course, to help in searching: you can quickly look up what patents have been filed or granted in a certain subfield. A quick look at the IPC's index ("catchwords" in their lingo) shows you that there are four keys for "perpetua mobile, alledged". Now, you just have to find out how to search for all patents with a given ICP classification key on one of the public web sites offering access to patent databases (on the USPTO, for example, or with Google Patents) and count. There is only one catch: If you search in a database for granted patents, you won't find much, because in most jurisdictions patent offices may refuse to deal with perpetua mobile and reject them by default. So, you have to find a way to search through the database of filed applications, not of granted patents. This information is public, too, but maybe not as readily accessible. Have fun and tell us what you found. Simon A. 07:47, 18 July 2007 (UTC)

Yes, you cannot be granted a patent for something which defies the known laws of physics. Capuchin 07:50, 18 July 2007 (UTC)

I am not arguing for the perpetual machine here (I know it can not be built), but out of curiosity: How can they not grant patent for something just because they don't understand what it is or how it works, just because it does not conform to the known laws of physics? It is always possible for someone to come up with something which defies all known laws. Take the example of the idea of matter waves or the theory that sun is at the center of the solar system. Till these were proposed, people had different ideas. What is the rationale behind refusing patents? -- WikiCheng | Talk 09:57, 18 July 2007 (UTC)

This is exactly the problem that steorn is facing. They have had to patent each part of their device seperately, as they cannot patent the device as a whole. They claim that it creates energy, but have yet to form an explanation of how it works. I must admit, this is the only example that I have knowledge of patenting free energy machines from. (They have yet to demonstrate it in public, and i'm fully expecting for the source of the energy to be found, if it does indeed work). I would be happy to be proved wrong. Capuchin 10:21, 18 July 2007 (UTC)

A patent is essentially a trade between the inventor and the government: the government grants a temporary monopoly, and in return, the inventor teaches the public how the invention works, or more precisely, provides a description that allows a person skilled in the art to practice the invention. Ordinarily patent offices take the inventor's word that the invention will work, but in exceptional cases, can demand working prototypes. So you can't invent a perpetual motion machine and at the same time keep secret how to build one that works. Also, inventions must be useful. A perpetual motion machine that merely moves, but does not allow one to extract any energy from it, might not be considered useful. --Gerry Ashton 13:26, 18 July 2007 (UTC)

It's actually a tough thing about patent offices and always has been — on the one hand, they are expecting the devices to be on the cutting edge and thus not necessarily conforming to standard understandings; on the other hand, they are also on the lookout for tricksters, hucksters, and frauds, all of whom could exploit a poorly granted patent for their personal and economic gain, at the expense of others. That's why the patent office has its own experts who are trained to examine patents to see if they would work, to see if they have obvious fallacies in them, to see if they are just preposterous or not. Patents are supposed to be written in a way which means that anyone skilled in the art can understand how they work, and the patent examiner is presumably skilled in the art. Does it always work? Of course not — there are a lot of factors going into whether a patent is granted (according to these guys, the US patent system today grants patents far too easily because the examiners are overburdened and only get punished if they don't grant enough patents, not if they grant too many bad ones), but that's the general idea. --24.147.86.187 13:51, 18 July 2007 (UTC)

The biggest problem in finding such things is that since the USPTO explicitly says it won't grant patents on perpetual motion machines, no patentee with half a brain would make it clear that this is what they were trying to patent. They will try as hard as possible to make them look like standard electrical/mechanical devices, and to cloud the fact that they apparently violate the first law of thermodynamics (conservation of energy: it's not just a good idea, it's the law!). So you're basically looking at something which will be, rationally speaking, deliberate obfuscated. Which isn't impossible — but it's not easy! --24.147.86.187 13:57, 18 July 2007 (UTC)

Our article on Motionless Electromagnetic Generator gives a link to one such patent. So I count 1. Capuchin 14:09, 18 July 2007 (UTC)

"Yes, you cannot be granted a patent for something which defies the known laws of physics." - actually, as described in our article, with the specific exception of prepetual motion machines, you can: With the exception of cases involving perpetual motion, a model is not ordinarily required by the Office to demonstrate the operability of a device. If operability of a device is questioned, the applicant must establish it to the satisfaction of the examiner, but he or she may choose his or her own way of so doing. - http://www.uspto.gov/web/offices/pac/mpep/documents/0600_608_03.htm I can't remember where I read it, but a non-trivial percentage (something like a quarter) are for things that do not work. Raul654 14:09, 18 July 2007 (UTC)

Great, thank you for correcting me! Capuchin 14:10, 18 July 2007 (UTC)

Raul654, thanks for taken over the job of clarifying this mess. A few additions: A Raul correctly points out, the patent office's job is only to check whether the invention is new, i.e. that there is no prior art and that it is sufficiently non-obvious. There is no need at all to check, whether it would work, and there is no point to checking that. After all, if the state grants the inventor a monopoly in exploiting a useless invention in exchange for the inventor's paying patent fees to the state, this is no loss for the society and only the inventor's problem. Given that most patents are filed as soon as the idea is there, before it has been worked out sufficiently in details to even think of making a prototype, it would also be hard to show conclusively that it works. Now, the fact that most countries' patent laws explicitly exclude perpetua mobiles from patenting is, of course, an exemption to the rule that checking the soundness of an invention is not the patent office's business. The reason for this exception is, I think, just a courtesy to the poor patent examiners for whom the amusement value of having to deal with cranks might wear off pretty quickly. Furthermore, it is rather hard to judge whether one pertuum mobile is an invention that goes beyond another pertuum mobile invention in a non-obvious way, if the person having ordinary skill in the art would find both inventions equally stupid, and asking courts to check such jedgement would be quite a waste of time. So, the original poster was quite right in asking not how many patents on pertua mobile are granted but how many are filed. Given that all filed patent applications are made public already before they are examined by the patent office, it should be possible to count all the declined perpetuum mobile claims. Simon A. 17:00, 18 July 2007 (UTC)

Kent Couch - Lawn Chair Balloons - did he really go up to 13,000+ feet?

I saw Kent Couch, on a nightly talk show explaining his journey over Oregon and he said he got to altitudes of 15,000 feet. However, several articles I read online stated he got up to 13,000. I do not doubt that he made this trip in his lawn chair, but I am hightly skeptical of the altitude. He claims he used no supplumental oxygen at all. Some of the articles also stated that despite being so high he could even hear cows mooing. So, was he really that high? Would he be able to breath fine and not be sick during an 8 or 9 hour trip up in the air? Also, isn't it quite cold up at that altitude? I'd appreciate any references or further information. Thanks.

Have you looked at our article on Kent Couch? It gives his altitude as 3 miles (15840 ft). A lot of the information that is useful to you can be found in the outer space article. This has a list of the important point in the atmosphere. It gives 15,100ft as the point in the atmosphere where the FAA requires supplemental oxygen. It's not until 26,200 ft that you reach the death zone. Altitude sickness can occur at 6,500ft. I don't know if he was affected.

This page shows that it would be about 3 degrees celcius, so not too cold (that's not exactly a reliable source, but I couldnt be bothered to find a better one). I think it's certainly plausible. There's even more information and lots of sources on Larry Walters, who also went up to 16,000 ft in a lawnchair. Capuchin 08:19, 18 July 2007 (UTC)

Speaking from personal experience, I've been to the summit of Mauna Kea in Hawaii as part of a tour ([22]) a number of years ago. The summit is at just shy of 14,000 feet (4200 m), and most people have no trouble with it. (The tour operators reject visitors with heart or lung conditions, pregnant women, the morbidly obese, and children under 13—though the last group may just be because kids would get bored on the long drive up the mountain.) So yes—it's certainly quite possible and reasonable to breathe comfortably at that altitude.

Of course, as Capuchin notes it's apt to be cold. In Hawaii, in August, we were all glad to have warm fluffy coats when we were at the summit. It was above freezing, but not by much. TenOfAllTrades(talk) 13:31, 18 July 2007 (UTC)

Also note that international badass Reinhold Messner climbed Mount Everest (29,000 feet) with no oxygen, and presumably you need a lot more oxygen to climb a mountain than to sit in a lawn chair. --TotoBaggins 15:17, 18 July 2007 (UTC)

15,000 feet isn't too high - there are several towns in the world up at this altitude (Le Riconada, Peru is at 16,700 feet). Mt.Everest is 29,000 feet - so you're a long way from that kind of problem. He's not exactly exerting himself - so oxygen ought not to be a problem. It would be pretty cold though. The rule-of-thumb is that you get a temp drop of 6.5 degC per 1000m of altitude. So he was looking at a temperature drop of maybe 30 degrees C - it would be freezing - but he'd be OK if he was properly dressed for it. SteveBaker 18:36, 18 July 2007 (UTC)

Arctic Fox

My daughter needs to do a project on hibernation and the Arctic Fox was presented by her teacher as one example of an animal that hibernates. I don't find a sigle reference to the hibernation of the Arctic Fox and infact, found an article indicating that the Artic Fox does not hibernate - can you kindly clarify. Thanks.

You are correct, the Arctic Fox does not hibernate. In fact the article has pictures of its different seasonal coats. Lanfear's Bane

I'm pretty sure that only the hibernating animal in the arctic is the Arctic Ground Squirrel. Some say that pregnant female polar bears hibernate, but it is debatable whether this is hibernation in the true sense. --GTPoompt(talk) 12:59, 18 July 2007 (UTC)

Perhaps you could tell your daughter's teacher that she/he made a mistake. Hibernation is a form of defense against cold, harsh weather; the Artic Fox is suited for cold weather, so it would never hibernate. Cheers!!! --Zacharycrimsonwolf 13:39, 18 July 2007 (UTC)

Why would an animal that hibernates change its coat color to match the snow? Gzuckier 19:02, 18 July 2007 (UTC)

This page says:

black and brown bears are just two of the seven mammals that curl up in dens or burrows or otherwise slumber through Alaska’s cold, dark season. The others are Alaska marmots, hoary marmots, woodchucks, arctic ground squirrels and brown bats, according to Loren Buck, a professor of biology at the University of Alaska Anchorage.

, but I don't know which of those critters occur in Alaska's sliver of Arctic.

Separately, a note of caution: I have encountered both in my own education and in my daughter's some teachers who do not appreciate being corrected on any subject. It's unfortunate, but true, so I would advise tact and discretion on your daughter's part. --TotoBaggins 15:26, 18 July 2007 (UTC)

Yeah - I can definitely agree with that whilst you have a responsibility to get to the truth, it's going to be painful. We've had long and hard arguments with teachers - extending up to principals when my son has given the correct answer and the teacher (and very often the textbooks) are wrong. It's not so bad when the teacher is wrong and the textbook is right - or vice-versa - but when both teacher and textbook are wrong, you're in for a hard time! (eg: Here are a whole bunch of triangles, list which triangles are isocelese, list which triangles are equilateral. My kid listed the equilateral triangle in both the equilateral list AND the isosceles list. The teacher said "No" that's an equilateral triangle - it's not isoscelese. The teacher's answerbook agreed with her. It took a month, three letters (one backed up by a college math professor!) one meeting with the teacher and one more with the principle to get them to agree and to change his grade. Then we had "Which is the odd word out: Orange, Apple, Pear, Tomato" - the official answer was "Tomato"...because "it's a vegetable"...well, I'm sorry but a Tomato is a fruit just like the others. My son not only knew this but chose "Orange" as the answer because "All of the others have rhymes - but nothing rhymes with orange". When told he was wrong he offered "Apple" because it's the only word that doesn't have an even number of letters and the only one with two successive identical letters - but conceded that perhaps "Pear" might be correct because it's the only word whose first letter is not symmetrical - and the only one that doesn't end in a vowel and the only one with two consecutive vowels. When he said it was an ambiguous question he got kicked out of class for being disruptive. (The question was "Which word" was the odd one out - so arguably the question wasn't about fruit anyway.) SteveBaker 18:32, 18 July 2007 (UTC)

Hahaha, I had that happen before. A teacher that insisted Mexico was part of South America, amongst other things I don't remember. I've had stupid teachers, but they weren't totally wrong that often. What your kid did though, Steve, is just plain awesome :D --L^augh! 18:38, 18 July 2007 (UTC)

Funny, and fun, and perfectly correct, but you might also want to inform him that "how to jump through the correct hoops" is also a valuable life skill. A teacher could be forgiven for finding a child's assertion that the object at right is called a "rectangle" to be deliberately obtuse, especially when multiplied by 20 kids in the class or whatever. --TotoBaggins 18:57, 18 July 2007 (UTC)

I remember my eighth grade science teacher informing us that ultraviolet light was yellow in color. Even in eighth grade I figured, WTF? Gzuckier 19:08, 18 July 2007 (UTC)

That's an unfortunate fact of life; "bright" kids, i.e. intelligent and/or original, can see a bunch of patterns, not just one. It would be vastly different if the question had some kind of point to it; i.e., "Which is the odd word out: Orange, Apple, Pear, Tomato, if you were writing a poem?" Just visited a classroom in a pretty good public school, but compared to a pretty good local private school, you can still tell the difference. Teacher in the public school classroom: "We're going to decorate these now. What's a nice shape to decorate with?" Happy, eager kindergartener: "Snowflakes!" Teacher: "But we don't see snowflakes in the summer. How about something else?" Gzuckier 19:08, 18 July 2007 (UTC)

I particularly enjoyed the textbook in year 6 which is now correct, sort of. The book, my teacher and everyone else on my table insisted that Mercury was the smallest planet. How I gloated, months later, when we got new books in secondary school that backed me up. If the book had just missed Pluto out altogether you could use it today :/ And in Britain at least, it's not a private/state thing I think. On the other hand, I knew someone at a private school who got their teacher in serious trouble through a reverse of this; the teacher kept marking their work as correct without checking, so they started making things up to see what would happen. What happened was terribly embarrasing. Skittle 21:42, 18 July 2007 (UTC)

On that last point, see this news story. --Anonymous, July 19, 02:54 (UTC)>

It is the duty of the student

Without question to be prudent.

If smarter than the teacher, tact

Demands that he conceal the fact.

-- Hilaire Belloc [I think --scs 17:18, 20 July 2007 (UTC)]

I had to face the wrath of my math teacher in 8th standard for arguing that the diagonals of a square cross at right angles. She had mentioned that rhombus is the only quadrilateral with this property. She did not seem to be in a mood to appreciate the fact that square is a rhombus, exactly because of this property. Needless to say, I didn't get a chance to prove what I said -- WikiCheng | Talk 06:29, 19 July 2007 (UTC)

Her original statement was wrong. A "kite-shape" (any quadrilateral composed of two isosceles triangles sharing a base) has perpendicular diagonals. Any rhombus is a "kite-shape", and any square is a rhombus. -Arch dude 12:48, 19 July 2007 (UTC)

Isn't even "kite-shape" is an incomplete answer? Stop restricting yourself to where either of the two diagonals bisects the other and you have...an irregular mess. Could be a quadrilateral with no pairs of congruent or parallel sides and no right angles or pairs of congruent angles. DMacks 13:24, 19 July 2007 (UTC)

That's true - I suspect she meant to stipulate that the diagonals had to bisect each other at their midpoints and at right angles. That's what gets you a rhombus - but she's still in trouble for not knowing that a square is merely a special case of a rhombus. That business of special cases not being allowed to take the name of the more general object was my kid's problem with isoscelese triangles and equilateral triangles. The trouble is that once you accept that, nearly all of the class must now be told they got it wrong even though the textbook says they are right. Teachers must just hate smart kids! (Erm...and we've strayed a bit off-topic here haven't we!) SteveBaker 21:48, 19 July 2007 (UTC)

night in the northern hemisphere

Is it possible for the whole of northern hemisphere to have night at the same time ? -- Myth (Talk) 13:25, 18 July 2007 (UTC)

no. the south pole would have to be pointing towards the sun. that will not happen unless something HUGE happens to change the way the Earth rotates. Capuchin 13:33, 18 July 2007 (UTC)

I suppose if you could tilt the whole earth so the north pole points away from the sun ... -- JSBillings 13:35, 18 July 2007 (UTC)

Actually, I suppose a comet or asteroid of sufficient mass could strike the earth at an oblique angle and send it spinning off in to space, so at one point it could have it's north pole facing away from the sun. It might even end up in a stable orbit, and have a tilt like Uranus.

And in that case, we won't be here to care :) Capuchin 14:06, 18 July 2007 (UTC)

(Edit conflict) Yes, but it probably won't be pretty for us on Earth when that happens. The comet would compress the Earth, and all the pent-up gas in the Earth's crust will be released, causing a huge blaze, and practically roasting everything on the Earth's surface. The shockwaves would also pretty much change the entire face of the planet. In fact, Earth might not even make it. And even if she did, it would take thousands to millions of years of years for the ecosystems on Earth to form again, and another million years for primapes to evolve into humans (or our equivalent). --Zacharycrimsonwolf 14:07, 18 July 2007 (UTC)

The Earth would not fall apart because of a mere comet. It would take something with much more mass to do that. Clarityfiend 17:15, 18 July 2007 (UTC)

Indeed - but a 'mere comet' couldn't flip the earth's axis to a noticable degree either (unless it was moving insanely fast!). But something big enough to change the earth's axis would certainly be enough to wipe out all life on the planet in the process. No - to address the OP's question: The answer is a categorical "No". SteveBaker 18:09, 18 July 2007 (UTC)

And any impactor with sufficent mass to significantly change the angular momentum of the earth would likely liquify the earth's surface in the process, making it an interesting fluid dynamics problem with no one around to solve it :) Unless of course, we can find a way to move to our similarly-created neighbor-RunningOnBrains 22:59, 18 July 2007 (UTC)

I think it's unfair to say the answer is "No". It is possible for it to happen, even if it kills every living thing on the planet, and in fact, it has happened to another, much larger planet in our own solar system. -- JSBillings 11:22, 19 July 2007 (UTC)

Actually, even if the south pole were aimed 100% accurately at the center of the sun - you still wouldn't get night over the entire northern hemisphere because (a) the sun is a lot bigger than the earth so it shines over more than half of the planet no matter how it's turned and (b) refraction through the atmosphere makes the sun appear higher in the sky than it really is - so even after the sun has mathematically 'set', it's still not dark - so you wouldn't get a full hemisphere of darkness - it would be a lot less. Still - if we're allowed to postulate catastrophies of earth-twisting proportions, let's just relocate the earth close to a neutron star and blow away all of the atmosphere - or maybe just move it so far from any star that it's "night" all the time, everywhere. Well - that's all well and good - but the "fair" answer is "No" - so let's not confuse the OP by saying otherwise. SteveBaker 21:37, 19 July 2007 (UTC)

Alternately, we could just redefine "Northern Hemisphere" to mean what "Eastern hemisphere" means now . . . Eran of Arcadia 17:21, 19 July 2007 (UTC)

How does that help? SteveBaker 21:37, 19 July 2007 (UTC)

Well, I don't reaslly have a reply, but I wanna ask, what does OP stand for? — Preceding unsigned comment added by Zachary crimsonwolf (talk • contribs) 11:37, 20 July 2007 (UTC)

See here. —Steve Summit (talk) 12:41, 20 July 2007 (UTC)

Is it possible...

...that the sun never sets on Russia? If their furthest west point is that little land-island that use to be Prussia (I think), and the furthest East is Diomede... has this been gone over before? 68.39.174.238 15:01, 18 July 2007 (UTC)

The sun never sets "on" any location on Earth. It is too far away to make physical contact. -- Kainaw^(what?) 15:12, 18 July 2007 (UTC)

Don't give stupid responses to straightforward questions.--138.29.51.251 15:14, 18 July 2007 (UTC)

It is not a stupid response. The question is not straightforward. A straightforward question would be "Is it possible that the sun is always visible from somewhere in Russia throughout the day?" Instead, the question is "It is possible that the sun never sets on Russia?" That question is vague. There are sunsets visible all over Russia every day. By simply using some intelligence in asking a question, it is easier to get an intelligent response. -- Kainaw^(what?) 15:46, 18 July 2007 (UTC)

Kainaw, the OP is no doubt referring to the concepts in The empire on which the sun never sets, or perhaps the British Empire, about which was said "the sun never sets on the British Empire". The idea is that a country and all its colonial possessions could encompass a sufficient number of widely-spaced territories on the Earth that the sun would always be above the horizon in at least one of them. Please don't assume that the OP is asking about the sun physically setting down on some piece of land—it's not polite to assume that degree of cluelessness without good cause. TenOfAllTrades(talk) 16:28, 18 July 2007 (UTC)

Thank you. 68.39.174.238 19:20, 18 July 2007 (UTC)

Our Russia article says the Russian Federation spans 11 time zones, which implies (roughly) that it covers not quite half of the span of longitudes, so clearly at some point (in the winter) the Sun is on the opposite side of the earth. You can see in this map that, even counting Kaliningrad, Russia does not span the more than the 180 degrees that would be necessary to have the sun never set.

I see... thanx. 68.39.174.238 19:22, 18 July 2007 (UTC)

You can play with [http:// www.daylightmap.com/ one of Google's toys] to see what is day vs night on a map. DMacks 15:53, 18 July 2007 (UTC)

Kainaw is perhaps not familiar with the old saying "The sun never sets on the British Empire," which was an observation of vast imperial geographic footprint, rather than a trivial astronomical fact. Edison 16:16, 18 July 2007 (UTC)

...which was also noted in can't-remember-what-humor-book with the explanation something like "this is because Britain is in the east, and the sun sets in the west". DMacks 16:54, 18 July 2007 (UTC)

Anguished English ? 68.39.174.238 19:22, 18 July 2007 (UTC)

Because the sun isn't a dot - it actually covers some angular extent, and refraction through the air means that that you can see the sun when it's technically below the horizon. According to Sunrise equation you get an extra 0.83 degrees at sunrise and sunset. Hence you don't quite need to cover 180 degrees of the earth's surface to get this result - but 178.4 degrees (OK - that's still not enough!). Also, our article on Antarctica says that Russia "reserves the right" to claim a part of that continent as it's terratory. Since it also owns parts of the earth very close to the north pole too - is it possible that between those two places that the sun never sets? It's a bit of a stretch though. The answer has to be "very nearly never sets". SteveBaker 18:06, 18 July 2007 (UTC)

Simply having Antarctic territory, without getting land somewhere in the 200° longitude not covered by Russia, would be insufficient. In the time frame around the equinoxes you can basically ignore the midnight sun effects of the polar regions, and you're left with the "not enough longitude" problem. For that matter, I don't think even some Antarctic land in the uncovered longitude is sufficient. My gut suggests that land sufficiently south (say, below 83°S or so) could still be under 24-hour night before the northernmost reaches of Russia (81°52') get 24-hour day. This, however, is a fairly fuzzy assertion. I'm quite confident that the problem would be simpler if we could talk territory outside the Antarctic Circle, and I'm pretty sure it would work out if Antarctic territory at the appropriate longitude were no further south than their antipodes were north. — Lomn 18:37, 18 July 2007 (UTC)

Further pedantry: 1) Kamchatka is both very easterly, and has a volcano 16,000 feet tall, so that might make the sun rise a bit earlier there. 2) According to this page, Russian modules on the International Space Station may be considered Russian territory for certain purposes, so that might affect the outcome, depending on its orbit (seems doubtful, though). Atmospheric lensing and the oblateness of the Earth should also not be ignored! --TotoBaggins 19:15, 18 July 2007 (UTC)

As a large portion of northern Russia is within the Arctic Circle, I thought of an interesting follow-up question: How long of a span during the summer does at least some part of Russia receive sunlight? Just a few days in June? Most of spring and summer? I don't have the right equations to do the calculations, just curious. -RunningOnBrains 22:51, 18 July 2007 (UTC)

Well, Extreme points of Russia says the northernmost point of Russian land is Cape Fligely. Plugging its coordinates into this web page along with various dates in 2007, I find... hmm, an anomaly. It shows sunrise and sunset on April 8, but neither sunrise nor sunset on April 9. Anyway, clearly the midnight sun starts about then. Then sunset will be on September 4, so that's about 149 days of daylight. --Anonymous, July 19, 2007, 03:18 (UTC).

Ah, this companion page shows sunrise at 20:22 UTC on April 8. I bet the other page just didn't look fr enough back into the preceding day. --Anon, July 19, 03:57 (UTC).

Mould and Toxins

I'm writing a dissertation on coffee, and back when I started it I had access to a paper that said something along the lines of 'moulds undergoing temperature fluctuations produce more toxin than if they had been kept at a steady temperature' (specifically Ochratoxin A). Now that I have nearly finished, I find I cannot locate either the name or the address of this paper. While it appears to be common knowledge in the right areas that not only do fluctuating temperatures increase moisture levels, they stress mould into producing toxins, I cannot find a paper to use as a reference. Help!

I'm really hoping someone knows of, or can find, a decent thing I can use as a reference. I have access to a library, but I'm not subscribed to any places that offer papers. If it mentions it in the abstract (which I can view), that would be nice, or in a book, or anything that looks properly referencable. I'm having real trouble finding anything other than Geocities sites that actually mentions what I need to say I read D: Getting a bit desperate....

Thanks for any help. Skittle 16:04, 18 July 2007 (UTC)

• Production of Penicillic Acid and Ochratoxin A on Poultry Feed by Aspergillus ochraceus: Temperature and Moisture Requirements C. W. Bacon, J. G. Sweeney, J. D. Robbins and D. Burdick Appl Environ Microbiol. 1973 August; 26(2): 155-160
• Journal of Applied Microbiology Volume 97 Issue 2 Page 429-438, August 2004 Modelling the effect of temperature and water activity on growth of Aspergillus niger strains and applications for food spoilage moulds R. Parra and N. Magan

And many others.--Stone 16:42, 18 July 2007 (UTC)

And here's another:

"Under alternating temperatures OTA production was higher than at constant temperature, and alternating temperatures indirectly favoured OTA production due to condensation and a subsequent rapid increase in moisture content and water activity of the coffee beans." The production of ochratoxin A by Aspergillus ochraceus in raw coffee at different equilibrium relative humidity and under alternating temperatures (Palacios-Cabrera, et al. Food Control. Volume 15, Issue 7, October 2004, Pages 531-535) link

-- MarcoTolo 16:46, 18 July 2007 (UTC)

Thank you sooooo much! My saviours! :D Skittle 16:54, 18 July 2007 (UTC) In fact, I think Marco's one is the very one I initially had, right back at the beginning. Hooray! Skittle 17:00, 18 July 2007 (UTC)

greying eyes

I have dark brown eyes and they are actually changing to a greyish blue from the outter rim inwards and i am still young so I called my doctor and he told me that it was normal, then i was talking to my friend the other day and she said it's a loss of pigments and it happened to her brother (freaky!) so what exactly is the cause of losing pigments then?

There is discussion of this in Eye color. SteveBaker 16:55, 18 July 2007 (UTC)

Remove Scratches in Leather

Not sure if this belongs in Science Help Desk, but it's as good a bet as any. Does any one know how to get a fine scratch out of leather? It is a top quality leather sofa and the scratch is very fine (as if gently scraping your fingernail against the leather) -- yet noticable. The scratch is perhaps 1-2 inches long. Any suggestions on whether or not it can be "removed" or doctored up to be less visible? Thanks. (JosephASpadaro 20:05, 18 July 2007 (UTC))

http://www.google.co.uk/search?hl=en&q=leather+remove+scratch&meta= - apparently there are repair kits for these sort of small scratches commercially available. My first thought was a little shoe polish of a similar colour, but you might wish to try shop bought product first. Lanfear's Bane

Thanks. (JosephASpadaro 21:31, 19 July 2007 (UTC))

Wholemeal v. wholegrain in the UK

Is there any difference between the two in the UK please? The article treats them as both the same, but I seem to rember reading about a difference at least in the UK. Thanks. 80.2.221.87 23:18, 18 July 2007 (UTC)

Wholemeal is meal (flour) made from whole grains of wheat, wholegrain is the whole grains of wheat etc. DuncanHill

How come you get wholegrain bread then? 80.2.192.45 11:02, 20 July 2007 (UTC)

Wholegrain bread has whole grains in it. DuncanHill 11:07, 20 July 2007 (UTC)

Harmone receptor question

What is Harmone receptor positive and Harmone receptive negative?72.76.142.100 23:37, 18 July 2007 (UTC)

I think you may mean Hormone receptor. There is some information in that article, but it is written in quite technical language. DuncanHill 23:41, 18 July 2007 (UTC)

I'm guessing you may be referring to how oncologists classify types of breast cancer. Patients with estrogen receptor (a type of hormone receptor) positive tumors will typically receive a hormone therapy treatment such as Tamoxifen. These treatments are ineffectual in hormone receptor negative tumors. Rockpocket 04:52, 19 July 2007 (UTC)

Parrot/Conure ID needed

I very nearly bought a parrot (poss. conure?) on a complete and utter whim today. This is a story that'll sound familiar to many pet owners - I saw it sat alone in a cage at the pet shop, looking very bored and it came up to me and let me stroke it when I tapped on the bars and made kissing noises. Very cute little bird - though I have no idea what species it was/is (never seen one like it before). Very, very tempted to take it home with me, though in the end I saw sense and decided to think it over.

It was a similar size to a cockatiel, though slightly 'wider', mostly olive green with some grey/brown on the head/neck and red feathers on the belly, a long darkish tail, black beak and white skin around the eyes and nostrils. It was completely silent the whole time I was there.

Anyone have any suggestions what kind of bird this is? The kid at the counter was only a part timer and she didn't know. --Kurt Shaped Box 23:45, 18 July 2007 (UTC)

Kurt, oh fellow bird lover. Don't do it! It sounds like a Sunday Conure, but there are several similar species. Parrots, especially Conures can be incredibly rewarding pets, but they take a great deal of commitment and time. After all they can live for 40-50 years or more! That said, go ahead and do some research and if you are ready to make the leap and are well prepared, then go for it! I highly recommend subscribing to the magazine Bird Talk (it is however, an American magazine and you may not be able to get it in Great Britian).--Eriastrum 00:24, 19 July 2007 (UTC)

I've owned/looked after a few different types of parrots before, so I do know what I'd be getting myself into - which at the moment is something I don't want to be doing. :) I have a few budgies at present (some in an aviary, one lone 'indoor budgie') - but they don't need a huge amount of one-to-one attention if you have several. Even the little guy seems to prefer to be left to his own devices (and his toys/beloved mirror!) most of the time. It's just so tempting when you see them in the shop, isn't it? I made that mistake once, with a lovebird when I was a kid - and the little thing ran me ragged for most of my teenage years (even though she was great)... --Kurt Shaped Box 01:07, 19 July 2007 (UTC)

July 19

Save energy by texting instead of eMailing?!?

Women’s Health magazine published a bunch of simple things we can do everyday to protect the environment (based on the new book, The Green Book: The Everyday Guide to Saving the Planet, One Simple Step at a Time). One of the tips is:

Text Him (or Her) Up

Instead of emailing to ask when he wants to meet at the restaurant, text him. It uses about 30 times less energy per message.

This seems like a pretty dubious claim to me - what do you guys think? SteveBaker 00:47, 19 July 2007 (UTC)

The sum total of saved energy would not be enough to remove the air from the brain of the person who thought this idea up.

Well technically, you probably are spending less energy to light the cellphone's screen than power a computer- but since your computer is probably on anyway, leaving it on while you use your cellphone spends more time and wastes energy on your cellphone. To be brutally honest though, that idea will save about as much energy as shaving your pencils with a swiss knife. --L^augh! 00:59, 19 July 2007 (UTC)

I think that the idea with that suggestion was that a cellphone has a small battery, while a computer is probably spending a lot of electricity to run. However, since your computer is probably already on, it's actually wasting energy. Bart133 ^{(t) (c)} 03:52, 19 July 2007 (UTC)

In my opinion, this is a gimmick by the service providers to get more people to start using text messages. They get paid for every text message (At least they do, in India). I have seen many such suggestions in general magazines, mainly because the writer of the article is not qualified enough to understand that what he / she reads / hears somewhere else may not be correct. The claim would be true only if one needs to power on the computer just to send a mail. But this fact is very obvious -- WikiCheng | Talk 06:54, 19 July 2007 (UTC)

Worthy of a Dilbert cartoon - almost as good as "smaller fonts take up less disk space". Gandalf61 10:33, 19 July 2007 (UTC)

Yeah, this is pretty stupid. Even though the computer uses more power, it most likely is on already. Also, you could probably type you message in and email it about 5x faster since you can generally type much faster on a keyboard then you can on a cellphone.--GTPoompt(talk) 20:24, 19 July 2007 (UTC)

(Saving Wikipedia disk space as instructed) That's pretty much what I've been thinking too - but then I wonder whether the cumulative load of trillions of emails has resulted in a ton of extra Internet infrastructure that could have been smaller/simpler otherwise - but then whether the cellphone network would be simpler if there were no text messaging. Seems like it's an incredibly difficult assessment to make - I can't imagine where you'd start gathering the data for such a claim. SteveBaker 21:04, 19 July 2007 (UTC)

And yet clearly someone did gather the data, because they didn't just claim that texting used less energy than email, they quantified it! I mean, that "30 times" figure has to mean something, right? --Steve Summit (talk) 21:44, 19 July 2007 (UTC) (Saving disk space on the confession that, yes, I'm being sarcastic.)

Oh - undoubtedly. If they'd said that emailing took 31.457 times more energy than texting then we'd know for sure that it was a totally bogus figure! "30 times" is right on the borderline of being oddly exact! SteveBaker 01:50, 20 July 2007 (UTC)

Game without rules

It seems that every game has rules and that if something has rules that it is (or is treated as) a game. Are there any games that do not have rules and is there anything that has rules that is not a game? (Including any system such as law as being a rule and therefore the legal system a game.) 71.100.170.92 23:59, 18 July 2007 (UTC)

Calvinball --Trovatore 00:00, 19 July 2007 (UTC)

Unfortunately its only rule disqualifies it as being ruleless. 71.100.170.92 00:20, 19 July 2007 (UTC)

Actually - Calvinball does have one rule - you may never use the same rules twice. SteveBaker 00:46, 19 July 2007 (UTC)

Something that had no rules at whatever would not be an identifiable game - in as much as all games of that kind would (of necessity) be utterly identical. So: Here is a game called "Blank" which has no rules whatever:      -Let us know how much fun it is! There are lots of games with very few rules (eg Go), or rules that can be changed by the players (eg Nomic) - or where rules change as a part of how the game is played (eg Lemma [23])- or which have rules you make up as you go along (eg Calvinball)- or which simply don't exist at all (eg Mornington Crescent (game)). Here is a game I played with friends in college: Take a chess set - set it up the usual way - but make the rule that no piece is allowed to move at all. Each turn, you may either redefine how a type of piece moves (eg pawns can only move if they start on a black square and they do so by moving three spaces diagonally in any direction) or you can move a piece according to whatever set of rules exists. If you lose your king, you lose - and if you are 'in check', you can't redefine the movement pattern of any of the pieces that have you in check. SteveBaker 00:35, 19 July 2007 (UTC)

Mao (game) has rules that are kept secret from new players. List of games with unspecified rules is of relevence. SteveBaker 01:06, 19 July 2007 (UTC)

And the second part of the question - things with rules that are not a game are everywhere. Our legal system - computer programming - electronics design - life itself! SteveBaker 00:39, 19 July 2007 (UTC)

Steve, please read WP:NPOV --L^augh! 00:57, 19 July 2007 (UTC)

Sorry, this is Wikipedia - we make up the rules as we go along. SteveBaker 01:06, 19 July 2007 (UTC)

Would you like to play the game of questions from Rosencrantz & Guildenstern are Dead? --Trovatore 01:18, 19 July 2007 (UTC)

"Oh! You mean....you pretend to be him, and I ask you questions!" -- MarcoTolo 02:07, 19 July 2007 (UTC)

Statement. One-love. Whose serve? --Trovatore 02:08, 19 July 2007 (UTC)

Since this is science desk, Science and Mathematics in particular have rules that are not a game. --Tbeatty 04:32, 19 July 2007 (UTC)

Well, anyone could always consider it a game if they chose, although I'm still waiting for a physicist to shout "PWNED" while receiving a Nobel Prize. Someguy1221 04:46, 19 July 2007 (UTC)

zOMG LAG. Capuchin 06:40, 19 July 2007 (UTC)

Yes, I would say so. After all, game theory, the mathematics to reason about strategy in games, is not used to reason about children's games but about real live, and a key point is that rules may emerge because it would be disadvantegeous not to follow them. Capitalism in its most extreme form is a game without rules. International politics may be an even better example: as there is no world police, there is no way to enforce compliance with international treaties -- except for the fact that you may be punished by other players for cheating one player. These other players enforce the rules not because they are rules but because the enforcement is a game move of advantage. (See altruistic punishment.) A very extreme example is the classic application of game theory: nuclear strategy. There are no rules in nuclear warfare, just the goal to get not too many of your own people killed. ("Mr. President, I'm not saying we wouldn't get our hair mussed. But I do say no more than ten to twenty million killed, tops. Uh, depending on the breaks." --General Turgidson in Dr. Strangelove). And, finally, the largest game ever, with no rules at all: Evolution. Pity that our article on Evolutionary game theory is just a stub. Simon A. 08:53, 19 July 2007 (UTC)

My understanding of evolution is that it most certainly does have rules. Anyways, it seems that anything people are involved in that is competitive, which often seems like damn near everything, will be understood or framed by some as a "game" regardless if it has any clearly defined rules or how serious it might appear to be (ex. "The Great Game"). In some games winning is all that counts; Love and War are often seen as games and if it's true that "all is fair" in them, then I suppose they have no rules. -- Azi Like a Fox 12:14, 19 July 2007 (UTC)

The laws of physics (biology/chemistry/math/whatever) are a set of 'default' rules that are inherent in every game we play. If we count them as "rules" in the context of this question then there can be no games that have no rules because the laws of nature are irrefutable and immutable. If we say "No - those aren't really 'rules' in this context" - then evolution has no rules. I just basically dislike equating an arbitary 'process' with a 'game' and laws of nature as 'rules'. Rules should be arbitary things that humans have imposed in order to restrict arbitary behavior to some subset that we call 'the game'.

Actually - it's not just humans. My dog has a clear set of rules for the 'pull rope and fetch' game.

1. Human and dog grab opposite ends of the rope - nobody pulls until everyone has a good grip.
2. If dog pulls rope from humans hand then dog holds the rope 6 inches from human hands - and moves it just out of reach if human tries to grab it - until human succeeds in grabbing it.
3. If human pulls rope from dog then human throws rope far away and dog has to run and bring it back at which point human grabs it or (optionally) dog may choose to invoke rule 2.
4. Game is over when either party drops rope without a fight.
5. (and this is the rule I'm least clear on) Scoring has something to do with the amount of growling involved - if you can employ ventriloquism in order to bark without causing rule 3 to be invoked, that's extra points?!?

But these are a clear set of rules - that were not thought up by a human. SteveBaker 19:59, 19 July 2007 (UTC)

TEGWAR. Corvus cornix 17:41, 19 July 2007 (UTC)

Basis of distinction

In reference to SteveBaker POV (as in Perspective (cognitive), which is highly valuable, relevant to the question and sought after here within the context of this discussion) How does one distinguish (i.e., what rule might one use to distinguish) between something that has rules and is a game and something that has rules and is not a game? Julie Dancer 08:46, 19 July 2007 (UTC)

A game is an event which has a goal and/or a winner. Even our academics (passing from one grade to another) can be viewed as a game. Bidding for a project can also be viewed as a game. Planning and executing a theft is a game too :-) -- WikiCheng | Talk 12:20, 19 July 2007 (UTC)

In that context then, in absence of a rule to make the distinction, is there anything which has rules that can not be played as a game? Julie Dancer 12:33, 19 July 2007 (UTC)

I would say no, there would be nothing preventing someone from playing whatever as a game given cheng's definition. Can think of things that should not be played as a game and also things that in most cases would not be (for example anything involving going to the DMV- there might be rules to follow and a goal, but you would have to be fairly masochistic to view the experience as a game). 38.112.225.84 12:56, 19 July 2007 (UTC)

Yes, but what about a rule that makes such a distinction? Julie Dancer 14:49, 19 July 2007 (UTC)

It's really all in the mind. Take the classic Prisoners Dilemma "game". If you are an actual prisoner facing a life or death situation - then this is a situation with arbitary rules that is most definitely not a game! If you are a mathematician studying the prisoners' dilemma as a part of game theory - then (ironically), it's still not a game. If you play Prisoners Dilemma with a good friend in a pub over a couple of beers - then it's a game. The group who were testing the theory of altruism using an iterated version of the prisoners dilemma were doing serious research (using 'tit-for-tat' strategies within it) - but the people they asked to contribute computer programs to play it were treating it as a game - in that case, this thing was simultaneously a game and not a game. This is true of many things. Just think of the number of competitions there are for things like good cooking skills - which is a game when they say it's a game - and a chore to do if you don't feel like being the one whose turn it is to cook tonight. SteveBaker 19:43, 19 July 2007 (UTC)

So are you saying that the distinction is that in the presence of rules something is a game if you choose to play (or participate as a player) and not a game if you choose not to play (or to participate as a player)? If so then what about those situations where you are required to participate whether you like it of not in order to exist or to not be terminated? Is this the rule that you would use to determine whether or not the presence of rules did or did not entail the presence of a game?

For instance. Suppose I am a bus driver and I am told (given a rule) that if I see a knife or a gun then the passenger can not come on board or if on board must be told to leave but if same passenger hides the gun or knife so that it can not be seen by me then the passenger can come on board or remain on board unless I have already seen the knife or gun then the passenger must leave.

To me these rules amount to playing the game of deceiving the driver as official policy of the bus line and I choose to decline to play this game. If I decline then I cannot be a bus driver. I either play this game or I loose my job. Julie Dancer 21:05, 19 July 2007 (UTC)

No - not at all. I'm saying it's a game if you treat it as such - no more, no less. If winning isn't all that critical to you - then maybe it's a game. If playing it is life-and-death or losing your job or whatever - then it's not a game anymore - even though the rules are the same and the players are the same. To quote the Wiktionary: Game - A pursuit or activity with rules performed either alone or with others, for the purpose of entertainment. - that last bit says it all 'for the purpose of entertainment' - as soon as it's not entertainment anymore - it's no longer a game. Those same set of arbitary rules (which evidently aren't a game to the bus driver) might make perfectly good rules for children playing "bus driver and urban terrorist" in the schoolyard. My point is that it's not what the rules are that make it a game or not - it's purely the context in which those rules are being obeyed and the mindset of the participants.

This may not be entertainment for the driver but what about for the administration? If the administration finds it entertaining then it would seem to still be a game.

Take the Roman Colosseum. For whom was the death at the mercy of the Gladiator or the wild beast a game whereas for the Emperor, no doubt it was all merely entertainment.

In our own legal system, many including prosecutors, judges, clerks and defense attorneys in addition to the accused him or her self may see the entire process as a game to be played at someone else's expense. Nonetheless I agree that entertainment is probably the best rule for determining whether or not something that has rules is or is not a game. Julie Dancer 08:08, 20 July 2007 (UTC)

Is One Button a game? Nimur 06:58, 20 July 2007 (UTC)

And if it is, when does the game begin? According to some, everybody is already playing One Button, they just haven't won it yet. Nimur 07:00, 20 July 2007 (UTC)

To me, it seems that Julie and Steve use the word "game" in pretty much opposite meanings. Steve uses the everyday definition of "game", namely something that you do for fun. Julie uses the definition from game theory: everything where a set of rules is either set explicitely or can be abstracted from the circumstances that detemine who is wins and who loses. To me, the game theorists have a point, albeit one for a slightly cynical realist: A gambler plays a game, and a daytrader seems to do the same, and it's clearly not just for fun. Looking at maps and military strategy plans one can't help noticing that from generals' point of view, war looks like a game. And that it, in fact, is one is the great tragedy of all history. Simon A. 14:46, 20 July 2007 (UTC)

Then are you saying that the rule which distinguishes a set of rules as being or not being a game is the consequence of playing the game for the individual player or for the follower of the rules? Julie Dancer 16:40, 20 July 2007 (UTC)

Re:Magnets

I know that magnets' opposite poles attract each other (north attracts south), but why does a magnet's north pole points to the Earth's North pole? Shouldn't it be going the other way instead? --Zacharycrimsonwolf 12:16, 19 July 2007 (UTC)

Well, we call the pole towards which a magnet's north pole points as the north pole. As you mentioned, it is the earth's south (magnetic) pole which attracts the magnet's north pole. To put it in simple words, if you imagine earth to be a big magnet, the south pole of the earth magnet is near the geographic north pole and vice versa. See Magnetic_North_Pole. It states that 'the Earth's North Magnetic Pole is therefore physically a magnetic south pole' -- WikiCheng | Talk 12:30, 19 July 2007 (UTC)

The choice of the magnet's names of the poles comes from the direction they point when used as a compass. They were named before people realized that the earth acts as a giant magnet. -- JSBillings 12:57, 19 July 2007 (UTC)

Okay. That would mean the Earth's south magnetic pole is named the North Pole? Thanks. Cheers, Zacharycrimsonwolf 11:32, 20 July 2007 (UTC)

project

can someone explain to me where to search for the abstract and implementation of any electrical project? i need to do an electrical project for my final year in college and i have already searched countless webpages in vain. i did not find a suitable project. can someone say where to search for a good electrical project (projects as advanced as the projects one can find in IEEE magazines). — Preceding unsigned comment added by 59.89.20.202 (talk • contribs)

Why not take one of those existing projects and add a clock to it? :) Or do some other novel adaptation that contributes something to the field, and catches your interest? MAKE magazine frequently has spiffy electrical projects, but they may be too simple for what you're looking for, but perhaps you'll find some inspiration there. --TotoBaggins 17:01, 19 July 2007 (UTC)

Solar powered garden light that turns on when it hears footsteps instead of turning on only when it is dark.Polypipe Wrangler 01:48, 20 July 2007 (UTC)

To expand on that last idea, also consider the use of passive infrared sensors rather than acoustic detection.

Atlant 12:03, 20 July 2007 (UTC)

Causes of losing a wheel

I'm interested in knowing more about the technical aspects of the holding capacity of lug nuts on Wheel studs.

I've found a fascinating article at [24] explaining how bolts work, but I have two questions which I hope someone could answer in terms which are not too technical.

1. Apart from not being adequately tightened, what other factors, or conditions, might cause a nut on a car's wheels to loosen and eventually come off?
2. If a wheel stud does not completely penetrate and pass through to the other side of an open lug nut, will this reduce the holding force of the nut, and, if so, how might one calculate the reduction of holding power related to the depth of penetration of the stud? --JAXHERE | ^Talk 17:05, 19 July 2007 (UTC)

Lots of things can reduce the grip of the nut on the bolt:

• If you somehow got oil or grease onto the threads - that would do it.
• If they are over or under-tightened.
• If they were overtightened sometime in the past.
• If a nut with the wrong kind of thread were put onto the bolt - either now or in the past or if it somehow became cross-threaded either now or in the past (this was the case when I took delivery of my 1963 Mini which had seven cross-threaded wheel nuts on it - three of which were on one wheel!!).
• Some old/large vehicles have threads that tighten up in the anticlockwise direction on one side of the vehicle to allow for the fact that the direction of rotation of the wheel can cause wheel nuts to loosen - so I suppose the nuts on that side of a 'normal' car would be more prone to this than those on the opposite side.
• I suppose that if you've swapped wheels an insane number of times then the threads might start to wear out...seems unlikely though.
• Corrosion of the threads is a problem because the rust doesn't have the strength of the metal - and even if the rust has been removed, the resulting loss of metal will reduce the quality of the contact between nut-thread and bolt-thread.
• Certainly if the entire depth of the nut is not fully threaded onto the bolt. The actual math of a nut that's only partially threaded onto the bolt is going to be complicated. It's tempting to say that if the bolt only goes X% of the way through the nut then the nut must have only X% of the usual 'holding power' - but the thing about wheel nuts is the damage that happens to the threads on the bolt. When you over-tighten them (for example), you can actually distort the metal of the threads on the bolt so that the nut doesn't grip as well. Even after you correct the tension on the fitting - that distortion remains - weakening the grip of the nut on the bolt forever more after that. Similarly (I suppose), having the nut correctly torqued up - but with only half of the thread engaged is putting double the usual force on every centimeter of the thread - and that's like you over-torqued it. So you might find that you damage the bolt so the holding force of the nut is halved because there is half as much thread providing the necessary friction - but ALSO, you now have a damaged or weakened thread on the half that is engaged - so that could easily reduce the amount of grip even further.
• You can use a commercial 'thread lock' compound ("Loctite" is the most popular brand) to improve the adhesion of nut to bolt.

Bottom line is whichever of those things you think you screwed up: "Don't Do That!" ...and if you did, consider getting a new set of wheel bolts. The ones I bought for my Mini only cost a couple of bucks each and they were pretty easy to replace. I would also recommend buying a torque wrench and tossing that into the toolkit in the back of your car so you can get the tension right even if you are putting on a spare tyre at the side of the road. SteveBaker 19:27, 19 July 2007 (UTC)

I'll bet more wheels fall off as a result of wheel bearing failure than lug nut failure. That is, someone botches the assembly of the wheel bearing, its castellated nut, the cotter pin, or what-have-you and the bearing falls apart on the road. Or the bearing freezes as a result of faulty lubrication and overheats, eventually causing something mechanical (like the stub axle) to break.

Atlant 12:10, 20 July 2007 (UTC)

Supporting principles

• Thanks for the responses, everything seems to make sense, to me. Now the really tough part: Can you direct me to on-line authorative explanations of these concepts? The link I gave at the beginning is a part, but I'd hope I can find more, but the searches I've done so far hasn't uncovered enough. --JAXHERE | ^Talk 15:07, 20 July 2007 (UTC)

Reusing Nomenclature

Okay, so I know that if any given organism (living or extinct) is given two names, then the one published first is used; but what happens to the old name? In other words, if we discover the direct ancestor of Hyracotherium, can it be called Eohippus? If they definitely identify the oldest ancestor of humans that is not an ancestor of chimpanzees (assuming we haven't already) can it be called Eoanthropus? These are just examples; I guess they could call an insect Eohippus as well. Eran of Arcadia 19:30, 19 July 2007 (UTC)

I don't know about previously used names, but there are examples where the same name appears in two widely seperated family trees, i.e. there might exist a Sillius group of rodents and a Sillius group of insects. As long as they are sufficiently distinct organisms there is little chance of confusion. Often this occurs when the name itself is not very inventive, such as naming a group after the country in which they were first found. Sorry, I don't recall any specific examples. Dragons flight 01:58, 20 July 2007 (UTC)

What do you mean by "group" in that case? Can a genus name appear twice, or only higher levels? Eran of Arcadia 02:51, 20 July 2007 (UTC)

I don't have the time to go slogging through the primary source material at the moment, but Nomenclature Codes has links to the widely-accepted codes governing the naming of organisms. There are separate codes for animals (ICZN), plants and fungi (ICBN), and bacteria (ICNB). I would expect (or at least hope) that the Codes would contain the rules on re-use of names. TenOfAllTrades(talk) 02:46, 20 July 2007 (UTC)

Strictly speaking, only specific names may be shared among several species (in different genera, but all other ranks must be unique. There are so many rules that some violations are overlooked if they're benign, simply because scientist have better things to do. The Vianna code] is coming online soon. I suspect old invalid names may be reused, but only with fairly unrelated organisms to avoid confusion. Bendž|Ť 21:05, 20 July 2007 (UTC)

Need help with particle reactions

can anyone give me the net energy changes, or a method of working them out, and also the required conditions for the following events.

1. ${\nu }_{e}+{\hbox{n}}\to e^{-}+{\hbox{p}}$
2. ${\bar {\nu }}_{e}+{\hbox{p}}\to e^{+}+{\hbox{n}}$
3. ${\hbox{n}}\to {\bar {\nu }}_{e}+e^{-}+{\hbox{p}}$

Cheers. Philc 19:36, 19 July 2007 (UTC)

You can get an idea by using E=mc², along with the mass of the neutron, proton, and electron. Your neutrino or antineutrino are approximately massless, though that is a hypothesis. The positron is the same mass as the electron. Your last reaction is the spontaneous decay of the neutron. GB 21:21, 19 July 2007 (UTC)

That only takes into account the mass changes, I want to also consider the kinetic energy of the particles on either side of events. Because also I don't know how much energy is required to initiate the reactions, and how much is released as KE. Philc 23:29, 19 July 2007 (UTC)

To Graeme, I don't think ignoring the neutrino mass is a hypothesis, it's more of an approximation (a very good one). As for knowing the KE of all the particles, that is tricky. The neutrino is not repelled in anyway, so there's not really a 'coulomb barrier' style activation energy. The neutrino I think can have any energy. Certainly in the three body decay (the third equation), you cannot tell how the energies will split. This was in fact some of the early evidence for a neutrino, had the neutron simply gone to e and p their energies would have been well defined, but the existence of the neutrino means they aren't. Sorry if that's not so helpful. Cyta 07:47, 20 July 2007 (UTC)

Number 3 is the spontaneous decay of a neutron - no initial kinetic energy is required, but all the mass difference goes into the kinetic energy or the products. You can work this out. For part 1 of the homework this is the neutron decay accelerated by neutrinos. The crosssection will be very low, but it may vary with the energy of the neutrino. Number 2 is your inverse neutron decay, you will have to supply enough energy to create the extra mass. You cna't know the kinetic energy of all the particles as Cyta says, instead tehre is a range of possible values as the energy is split between particles. see beta decay. I was saying that the idea the the neutrino is massless is a hypothesis. GB 07:57, 20 July 2007 (UTC)

I thought that with the observation of neutrino oscillation, the idea that the neutrino is massless is simply wrong? Algebraist 10:49, 20 July 2007 (UTC)

It's a shame you had to imply this is homework. It's Late July, I don't know of any schools that aren't on holidays, and I certainly am, I was purely wondering out of interest in a larger picture, I can explain to you if you want. I was looking at the possibility (purely playing with ideas in my head) of using the ${\bar {\nu }}_{e}$ and fast ${\hbox{n}}$ generated during nuclear fission. Using the equations I listed:

1. ${\nu }_{e}+{\hbox{n}}\to e^{-}+{\hbox{p}}$
2. ${\bar {\nu }}_{e}+{\hbox{p}}\to e^{+}+{\hbox{n}}$
3. ${\hbox{n}}\to {\bar {\nu }}_{e}+e^{-}+{\hbox{p}}$

by adding (1) and (2) you get;

${\bar {\nu }}_{e}+{\nu }_{e}+{\hbox{n}}\to e^{-}+e^{+}+{\hbox{n}}$

if you add this to (3) you get;

${\bar {\nu }}_{e}+{\nu }_{e}+{\hbox{n}}\to e^{-}+e^{+}+{\bar {\nu }}_{e}+e^{-}+{\hbox{p}}$

${\bar {\nu }}_{e}+{\nu }_{e}+{\hbox{n}}\to 2e^{-}+e^{+}+{\bar {\nu }}_{e}+{\hbox{p}}$

if you add this to (2) you get

${\bar {\nu }}_{e}+{\nu }_{e}+{\hbox{n}}\to 2e^{-}+2e^{+}+{\hbox{n}}$

The electron and positron could then be tapped off using magnetic fields as they would move in opposite directions, therefore preventing instant annihilation.

What I was basically wondering is how much kinetic energy this chain of events would require to initiate, and pass through to the end, and how comparable that would be with the KE of ${\bar {\nu }}_{e}$ and fast ${\hbox{n}}$ from fission, and the billions of ${\nu }_{e}\,$ flying in from the sun every second. Philc 11:25, 20 July 2007 (UTC)

Sorry about upsetting you with the homework suggestion. The minimum egergy required will be that required to form the two electrons and two antielectrons, which I think is 4*511keV or 2.022 MeV. However the reaction you describe would have an incredibly low cross-section. It is hard enough for one neutrino to hit a neutron, let alone two at the same time. You can see how slowly the detectors find neutrinos from the sun to get an idea of the low chance that a reaction occurs. Extrememly high energy neutrinos with energies in the EeV range have a much bigger chance of impacting matter. GB 11:59, 20 July 2007 (UTC)

Because of the nature of the reaction stages as opposed to all at once, it wouldn't require the neutrinos to impact simultaneously, but point taken on the non-likelihood of the reaction taking place. Do you have any idea where I can find out the kinetic energy of neutrons and antineutrinos from nuclear fission. I was assuming it was quite high, given that they are known as fast neutrons, and have to be mediated with boron. But since they were called fast neutrons simply to differentiate from slow neutrons, purely in the context of propagating fission reactions, I can't really assume that it is comparable to the energies required for particle reactions. Philc 13:25, 20 July 2007 (UTC)

Electronics: Can something that requires 100mA run off of 500mA?

Hello, I play guitar and in the world of electric guitar there are foot pedals that you can switch on and off to use a desired effect, and I prefer powering them with an adapter. In this case, my Electro-Harmonix Small Clone chorus pedal says it requires 100mA of current. I went to 3 separate stores and they didn't have the exact adapter that the company would like you to have, but one store did have an Electro-Harmonix adapter that provides 500mA instead of the required 100. My question is, is this going to fry my pedal? Or does the pedal limit the current draw? I'm pretty sure it is limited and should be fine, but I don't want to take a chance cause this pedal was almost $90. Thanks! NIRVANA2764 20:34, 19 July 2007 (UTC)

It's no problem - the pedal will only pull the amount of current it needs. You need to be sure that:

• The voltage is set correctly for the pedal.
• That the power socket has the correct tip/ring polarity. There is usually a picture on the pedal that shows which is positive - most 'generic' power supplies have a way to get the wrong!
• That you have ENOUGH amps avaliable on the power supply (which you do!)
• If you plug it all in and it doesn't immediately work - unplug it REALLY QUICKLY and double check everything - with any luck you'll avoid damaging it.

Personally, I wouldn't buy an adaptor for another pedal - I'd go to WalMart or RadioShack (or whatever your local equivalent is) and buy one of those switchable power supplies that comes with a bazillion different connectors and can be switched to any voltage. Those are cheaper - have a range of connectors and are generally more flexible in terms of tip/ring polarity. My son has several effects pedals - and they all run off of these switchable power supplies. SteveBaker 20:53, 19 July 2007 (UTC)

Thanks a lot for your help. A lot of people are recommending universal adapters to me, and it seems like a good idea (they are cheaper than regular ones...don't know why though) but I have fried 2 of them to date, and I don't know why. Perhaps my pedal required more current than the pedal could supply. I would use them fine for a few months, then one morning, find them to be not providing any current to my pedal. The sticker on them would be warped, leading me to believe that they got overheated and just died out. I've asked many people and nobody can explain it. So now my philosophy is that I will buy only the adapter that the manufacturer suggests, because I'm tired of frying adapters. NIRVANA2764 20:58, 19 July 2007 (UTC)

Certainly you need to ensure that the adaptor can provide the current the pedal demands - and with some of them you have to read the fine-print on the packaging because some of them can deliver less amperage at higher voltages. Ideally, you want the adaptor to be able to produce roughly twice the amperage of the device it's driving in order that it should run fairly cool. If the adaptor is putting out close to it's maximum then it'll get hot and probably, it's lifetime will be shorter too. My son uses four 'COBY' 500mA supplies to drive four guitar effects pedals from various different manufacturers - and so far, none of them have died over more than a year of fairly frequent use. I'm running my laptop from a universal adaptor too - but it's running fairly close to its' maximum capacity for over a month now. It's hot and the label has warped and fallen off...so I don't expect it to last for very long. But the original supply for my laptop died and HP wanted $80 for a replacement. The no-name variable supply cost $20 - so I figure I'll still be ahead of the game when I'm on my fourth one! But buy universal adaptors with plenty of spare capacity for the pedal you have and they'll run cooler and last MUCH longer. SteveBaker 01:32, 20 July 2007 (UTC)

Questions about voltage and current are surprisingly frequent here on the Reference Desks. Here is a handy way to think about and remember the difference. It is traditional to use fluids in these analogies.

Suppose you have a recipe for Cherries jubilee that calls for one cup of 80 proof Kirschwasser. Suppose you are low on funds (and have a tin tongue to boot) and you try to use Budweiser instead of Kirschwasser. But when you try to ignite the flambé, it ain't gonna burn, because beer just doesn't contain a high enough concentration of alcohol for that.

Suppose that, stung by this demoralizing failure, you resolve to save your pennies until you have enough to head down to your friendly neighborhood liquor store to buy some of the real stuff. But they won't sell you a cup of it -- the smallest bottle of Kirschwasser they have is 500 ml, or a little over 2 cups. The burning question is: will the 500 ml bottle do? And the answer is, of course it will (assuming you can afford it). You can almost certainly find something to do with the extra 1.113 cups of liqueur when you're done with (or perhaps even as you're enjoying) that dessert.

Amps are like cups. Volts are like proof. It doesn't matter if your supply has too many cups; it only matters if it has too few, or if the proof is too low, or too high. Prost! —Steve Summit (toast) 02:38, 20 July 2007 (UTC)

[P.S. Stay tuned for our next exciting episode, in which we learn that watts are like hangovers.]

Wot?

Atlant 12:20, 20 July 2007 (UTC)

Another comparison: Watts are like beer, while Volt-amperes reactive are like the foam on the beer. Edison 20:55, 20 July 2007 (UTC)

I'm going to make a platinum plated spork - I mean that! SteveBaker 01:12, 21 July 2007 (UTC)

What is the difference between sociopath and psychopath?

Right now, sociopath redirects to psychopath, and the psychopath article says that they are the same thing, just different terms. But the sociopath page has sort of an edit war with some users redirecting it to antisocial personality disorder and others changing back to psychopath. Which is correct?--64.149.176.55 21:25, 19 July 2007 (UTC)

Yes, those editors are demonstrating an approximately correct usage of the terms, sounds like. --Steve Summit (talk) 22:36, 19 July 2007 (UTC)

If memory serves, psychopath is an antiquated term, which has been replaced with sociopath. They might have slightly different shades of meaning, but I think that that's the gist of it. Raul654 21:30, 19 July 2007 (UTC)

"Psychopath" and "sociopath" are terms used in common parlance but the APA would say that these refer to persons with antisocial personality disorder (cf DSM IV). Donald Hosek 22:13, 19 July 2007 (UTC)

I think both Raul & Donald above are on the right lines, it might also be useful to compare dictionary definitions, these from Chambers Dictionary 1983 edition. " Psychopath - one who shows a pathological degree of specific emotional instability without specific mental disorder: one suffering from a behavioural disorder resulting in inability to form personal relationships and in indifference to or ignorance of his obligations to society, often manifested by anti-social behaviour, as acts of violence, sexual perversion, etc." " Sociopath - sociopathy - any of several personality disorders, resulting in asocial or antisocial behaviour. " DuncanHill 22:38, 19 July 2007 (UTC)

For what it's worth, DSM IV doesn't use either term, as Donald says, it does have antisocial personality disorder. DuncanHill 22:48, 19 July 2007 (UTC)

David T. Lykken illustrated the difference with the classic nature and nurture division: psychopathy is a psychological condition caused by natural conditions such as brain damage or atypical neural development, while sociopathy is a sociological condition caused by nurtural (is that a word?) conditions childhood abuse, poverty, extremely high/low intelligence (although of course most people would have a combination of the two, brought about by a combination of nature and nurture). Laïka 00:13, 20 July 2007 (UTC)

Relativity

Suppose there are two beams of light alongside each other, Beam A and Beam B. According to the special theory of relativity, the speed of light is the same from any ppoint of reference. Would Beam B be traveling at the speed of light from Beam A's point of reference? ¿SFGiДnts! ^{¿Complain! ¿Analyze! ¿Review!} 21:35, 19 July 2007 (UTC)

By talking about "beams of light", do you really mean, "the point of view of a photon inside a beam of light"? As it is you make it sound like you think of the beams as static entities, but they aren't. But in any case — yes, assuming they could be observers in a traditional sense, from their frames of reference they will measure one another as going the speed of light (assuming they are both in a vacuum). --24.147.86.187 22:47, 19 July 2007 (UTC)

Short answer, yes. Long answer, the question is ill-posed. Time would appear to stand still for a hypothetical observer moving at the speed of light and hence he would be unable to measure the speed of the second beam of light. So, technically it is not possible for any measurements to be made from the point of view of a beam of light. However for reference frames arbitrarily close to the speed of light you can still make the measurement and you will always find that light moves at light speed.  ;-) Dragons flight 22:55, 19 July 2007 (UTC)

(edit conflict x2) Things get funny in special relativity if you pick a lightlike reference frame, since you end up with infinite time dilation. Essentially, for an observer moving at the speed of light, no time passes, and so questions like "how fast is something else moving relative to me?" become rather meaningless. —Ilmari Karonen (talk) 22:55, 19 July 2007 (UTC)

The main problem with the question is the misunderstanding of the special theory of relativity. The question uses the phrase "from any point of reference". That is not what the special theory of relativity states. It only applies to inertial frames of reference. A photon traveling at the speed of light is not an inertial frame. As the article the OP linked states: "Relativity theory depends on "reference frames". A reference frame is an observational perspective in space at rest, or in uniform motion, from which a position can be measured along 3 spatial axes. In addition, a reference frame has the ability to determine measurements of the time of events using a 'clock' (any reference device with uniform periodicity)." It is hard for a photon to measure time when time is standing still. -- Kainaw^(what?) 23:06, 19 July 2007 (UTC)

I knew I should have paid better attention in middles school science. :) ¿SFGiДnts! ^{¿Complain! ¿Analyze! ¿Review!} 00:09, 20 July 2007 (UTC)

July 20

Tabby Markings in Lions

Why do lion cubs (possibly also adult lions) have the "M" tabby marking on their forehead, just as house cats do? See http://www.dailymail.co.uk/pages/live/articles/news/worldnews.html?in_article_id=469379&in_page_id=1811, see images 5 and 7. - MSTCrow 03:16, 20 July 2007 (UTC)

I've never noticed that before. I guess it's conserved patterns of gene expression for fur mottling. here's a great shot. Bendž|Ť 21:16, 20 July 2007 (UTC)

Mechanical engineering

WHAT IS THE CURRENT CHALLENGES IN MECHANICAL OR MANUFACTURING ENGINEERING?

Mechanical engineering#Frontiers of research in mechanical engineering and the main articles listed therein. Someguy1221 06:09, 20 July 2007 (UTC)

The question I posted below is a perfect example of a current challenge of mechanical engineering... unfortunately. Nimur 06:20, 20 July 2007 (UTC)

The maintenance of old steam pipes?

Atlant 12:23, 20 July 2007 (UTC)

How to unstick all of those CAPS LOCK keys by the look of it. SteveBaker 01:10, 21 July 2007 (UTC)

Generator Problem

Greetings Science Reference Deskers! One of our field teams is deploying a remote site in Alaska as we speak. They have purchased the Troy-bilt 5550 Watt Generator and have an interesting "show-stopper" of a problem. The generator has a pull-cord to start its engine, and apparently this cord "is stuck" and "will not pull." Our home-office version does not have this problem, and the generator seems to work fine here in the lab. What in the world could be causing this issue? The engine has been properly fueled and oiled and is brand-new. Unfortunately, the team is in too remote a site to easily "buy a new one" and we are furiously trying to get it working. Any small-engine experts know what we should do? Nimur 06:08, 20 July 2007 (UTC)

Ice? —Bromskloss 07:21, 20 July 2007 (UTC)

It's about 60 degrees Fahrenheit now, though. Nimur 07:24, 20 July 2007 (UTC)

Perhaps the cord is tangled and looped over itself. Or perhaps some extraneous matter has got into the clutch or something. You might have to take off the cover to see what is happening! Did the generator get transported with oil in it? If it was placed on its side, oil could have gummed up the spark plugs and stop it starting - though it should still turn over. TO fix this problem take out the spark plugs and clean them. GB 07:46, 20 July 2007 (UTC)

I'm no small-engine expert, but I agree with GB's suggestion about the cord. I think there's probably an easily-removeable cover over the pull-cord mechanism; your field team should remove that and see if anything's amiss. If there's nothing obviously wrong with the cord, they should then figure out some way of gripping the pulley (the one around which the pullcord is wound) very tightly and securely, and trying to turn it, slowly, by a small amount. It's at least somewhat likely that something in the engine has gotten stuck or seized, and that a larger force (larger than can be applied using the pullord, smaller than it would take to break anything) will unstick the engine, after which the pullcord can again be used to turn it over, after which (cross your fingers!) it will start. —Steve Summit (talk) 11:50, 20 July 2007 (UTC)

[But if the pullcord won't pull and the engine won't turn over at all, the spark plugs are definitely not the problem.]

Liquid lock might be a problem, especially if the generator set was tipped to some bizarre angle during shipment so oil or gasoline filled the cylinder(s). Remove the spark plug(s) and see if the engine can be cranked using the pull-cord.

Atlant 12:32, 20 July 2007 (UTC)

It's a smaller engine, but I have known my lawnmower pull start to jam. I have gotten it loose by repeated jerking and releasing the cord. Cussing it in the process seemed to help. Not sure exactly what the mechanism of it getting stuck was. Edison 20:51, 20 July 2007 (UTC)

Principle of the hand pump

WHAT IS THE PRINCIPLE OF HAND PUMP?

Firstly, let me be the first to commend you for your eloquent and polite question. As for your actual question, there's some very sketchy information at hand pump - but maybe some of the types of hand pump may help you find specific information about how these work. Google is your friend. Good luck. Aaadddaaammm 09:52, 20 July 2007 (UTC)

Pump#Positive displacement pumps seems to be the right place to look.

Atlant 12:34, 20 July 2007 (UTC)

Are humans the most successful creatures on earth?

In terms of numbers of individuals, or in terms of total biomass, where are humans in the success stakes compared with other species?

And I'm always surprised to learn that there are more for example cows in my country than humans - do they have secret underground cities? 80.2.192.45 11:10, 20 July 2007 (UTC)

Insects would be far more populous than humans or cows. Ants for instance are pretty kick ass when it comes to huge numbers. The most 'sucessful' 'creatures' however could possible be considered bateria (5×10³⁰ in the world according to the article) or viruses although it all depends which criteria you choose to use to measure success. Lanfear's Bane

Although, neither insects, viruses nor bacteria are a species. But there could well be one species from within these groups that fits the required criteria. It always grates with me when people say things like 'humans have only been around so long, dinosaurs ruled the earth for millions of years'. Well that's hardly a fair comparison! Yes defining success is difficult, there are more cows because humans grow them for food, who's the more successful there? Anyway to quote from our Biomass (ecology) article: 'The most successful animal, in terms of biomass, is the Antarctic krill, Euphausia superba, with a biomass of probably over 500 million tons, roughly twice the total biomass of humans.' Cyta 11:37, 20 July 2007 (UTC)

That very last figure sounds a tad dubious; although they don't state whether they mean wet or dry mass, the fact that the overall source seems to be about krill as food suggests that they mean wet mass. Assuming an average body mass of 70 kg (slightly less than highly developed countries, slightly more than less economically developed countries), * 6.5 billion people gives an approximate biomass of 455 million tonnes; virtually the same as the krill. Laïka 17:49, 20 July 2007 (UTC)

You're forgetting that a large fraction of humanity (as represented by that 6.5bn figure) are children - some a light as a couple of kilos. It wouldn't surprise me to find that the average human weighed in at 35kg on that basis. So I can believe Krill have out out-massed 2:1. SteveBaker 01:08, 21 July 2007 (UTC)

Reflection

Hi, I was reading the Wikipedia article on 'Reflection' and came across this phrase which I don't really comprehend - 'the photon absorbed by the molecule may match energetic levels of the molecule. I would be very grateful if anyone could explain what it means. Thanks!

Full context:

As the photon absorbed by the molecule may match energetic levels of the molecule (kinetic, rotational, electronic or vibrational), the photon may not be reemitted or alternatively may lose some of its energy in the process. The emitted photon will have a slightly different level of energy.

When the photon hits the molecule, it gets completely absorbed, adding some form of energy to the molecule. Depending on the original state of the molecule and the amount of energy in the photon, the new state may be stable or unstable. If it's stable, the molecule will not emit a photon, in which case the photon has not been reflected. If it's unstable, the molecule will emit a photon, but not necessarily one with the same amount of energy.

Say that some property of the molecule has stable points at 3, 5, and 12 units of energy. If it's sitting at 3 and a photon with 7 units of energy hits it, it will jump up to 10. 10 is unstable, so the molecule emits enough energy to drop down to 5, the closest stable point. That means that the reflected photon will have only 5 units of energy.

Now imagine that another photon with 7 units of energy hits it. This time, it goes up to 12. 12 is stable, so no photon is emitted, and the photon has been (in the classic sense) absorbed.

Hope that helps! -FunnyMan 11:57, 20 July 2007 (UTC)

The simple fact that is lost in all this physics is the following: If the atoms absorb the photon and immediatly re-emit them in a coherent manner, this is reflection. "Coherent" means that it fits into the phase (the "rhythm" of oscillation) which ensures that the light goes in the right direction. If the photon is absorbed and not re-emitted at all as visible light, then this colour is not reflected. Silver, for example reflects all colours, while copper canot reflect the blue part of the spectrum, and this is why everything refelected off copper (and hence copper itself) has a redish hue. Simon A. 14:58, 20 July 2007 (UTC)

Sharlel Mary Talo Palsy?

My girlfriend's brother has a type of palsy called sharlel mary talo palsy, but I am not sure hoe to spell it so I can't find any information on the subject. If anyone knows the correct spelling of this condition, please advise! Thanx in advance! Steve (removed email signature) — Preceding unsigned comment added by 209.206.132.56 (talk • contribs)

Never heard of that particular name of a palsy, but are you referring to Charcot-Marie-Tooth disease? -- JSBillings 13:44, 20 July 2007 (UTC)

an indelicate question

I noticed when cleaning my bottom in the shower after a bowel movement that there are insoluble, fine sand-like particles from the feces. What kind of substance(s) would these be? --Halcatalyst 14:35, 20 July 2007 (UTC)

For medical advice you should consult your doctor. It could however simply be sand. Have you been to the beach recently? Lanfear's Bane

I'm not looking for medical advice, since I'm not experiencing any illness, and no, I haven't been to the beach in a long time. Rather, I take this to be a normal occurrence which I've noticed for a long time, and I'm looking for information related to intestinal processing, presumably with respect to normal diet. --Halcatalyst 15:50, 20 July 2007 (UTC)

Do you eat a lot of bread made from stone-ground flour? DuncanHill 20:14, 20 July 2007 (UTC)

No. I'm wondering if these particles might be accumulations of minerals in the diet. (I'm pretty sure it isn't just me. I've noticed it because my shower drain is flat and in a couple of spots the water (and particulate debris) doesn't flow away. It helps that the floor is white.) --Halcatalyst 21:04, 20 July 2007 (UTC)

Psychopathy vs suicide rate

I have been reading the Wikipedia article on psychopathy, and it is said that Hervey Cleckley asserts that psychopaths are not likely to commit suicide as they score high on both of the PCL-R factors. Yet it is said that Factor 1 is not related (istead of negatively related) to suicide and factor 2 strongly correlated to suicide, shouldn't that mean that psychopaths should also be very susceptible to suicide? Thanks! — Preceding unsigned comment added by 58.153.96.35 (talk • contribs)

Pollination of sacred fig (peepul tree, bo tree)

Britannica says: "Each fig species are pollinated by species-specific wasps." (Under Ficus) Is this true? Sacred fig (aka as peepul or bo tree) has very tiny fruit. Does pollination occur with the help of fig wasp in bo tree? Thanks in advance for your valuable instruction. — Preceding unsigned comment added by 58.216.233.166 (talk • contribs)

lazar radar operated by police

help. is there any way to beat the lazar radar used by police. the make is atlantis.

thanks,

u.k.nown — Preceding unsigned comment added by 204.138.85.6 (talk • contribs)

We have an encyclopedia article about LIDAR if you care to read it. Friday (talk) 18:07, 20 July 2007 (UTC)

Laser ranging is particularly sensitive; far more so than plain radar, so it is very difficult (read impossible) to beat, even if you were to coat your car with matt black paint which would normally beat a light-operated device (laser ranging is so powerful that it can even pick up reflections of thin clouds of water vapour). There is only one surefire method: slow down. Of course, this is only good for a laser radar; the easiest way to beat a lazar radar is to take a mixture of rifampicin, dapsone and clofazimine once a day for the leprosy... Laïka 18:17, 20 July 2007 (UTC)

When my father was trained on the laser radar gun, he was told to aim for the headlights because they provide a much better reflective surface. So, if you are paining your car flat black, ensure you either remove or paint over the headlights also - and don't drive at night. -- Kainaw^(what?) 19:12, 20 July 2007 (UTC)

Hypothetically moving a mountain

If one were to move a mountain or the weight equivalent to one, what would be the most scientifically sound way to do so. Even though impossible, what would be the closest way?

A bunch of dump trucks. Clem 19:05, 20 July 2007 (UTC)

Correct - divide and conquer. -- Kainaw^(what?) 19:10, 20 July 2007 (UTC)

Don't take my word for it, but I'd consider the following. First of all, we don't want to lift the mountain at all, because the work necessary to lift a mountain even a small amount would be enormous. I can imagine slowing cutting the base of the mountain, replacing the stone removed by two thick layers of solid steel (that could support the wieght of the mountain); the bottom one attached to the ground and the rop one attached to the base of the mountain. If you place a thin layer of teflon on the contact surfaces and a very thin layer of lubricating liquid, you could get the friction down quite a lot. Also, to further reduce the friction, you could use maglev technology to reduce the normal force produced at the contact surface (we probably couldn't get the mountain to levitate, but the repulsion would have an effect equivalent to further reducing the fiction coefficient). Once all that was done, maybe you could slowly slide the mountain to one side. --Waldsen 19:11, 20 July 2007 (UTC)

p.s. My way is nice to imagine, but in practice it would be an engineering nightmare (practically impossible). --Waldsen 19:16, 20 July 2007 (UTC)

You would have an extremely long chute that could remove the material from the top as far away as possible, so the rock would initially be distributed in a circle around the mountain. As the mountain got lower you'd use a shorter chute(s). The mountain would be moved as you said. You didnt say anything about keeping it the same shape. 80.0.105.59 19:21, 20 July 2007 (UTC)

I think it said in a documentary I saw that they pretty much fully demolished a mountain during the construction of KIX in order to build the artificial island. Philc 19:41, 20 July 2007 (UTC)

How large is the cross section of the mountain in the plane where it is to be cut, and what is its mass? Large buildings clearly are orders of magnitude less massive than a typical mountain, but they have been separated from their foundation and placed on springs for earthquake protection. Large buildings, even lighthouses, have been jacked up and moved by house movers.Cleopatra's Needle is the name given to several stone obelisks which were move between countries in ancient times and more recently. Our ancestors 5000 years could move large stones with rollers or skids and muscle power. Saturn V moon rockets and the Space Shuttle are routinely driven to the launch pad by a gargantuan lowboy. So in principle, I would prepare a roadbed which could support the weight, perhaps using multiple parallel rails and wheeled assemblies on either side similar to but vastly scaled up from railroad wheels and axles. Perhaps multiple wheels, rails, and bearings in an assembly on each side. Hydraulic jacks would take up the strain to support it after supporting beams were inserted in holes drilled through it, and below those holes the cut would be made completely through it. Roll it along the roadbed to the new site where a foundation has been prepared, lower it into place, remove the beams, cement up the holes, which would be below the finished grad, and voila. Rather than assuming it is impossible, it would be a good exercise for a mechanical engineer to calculate the upper limit of early 21st century technology to move a mountain. Assuming cost was no object, like the Pyramids, Space Program, or the present global war budget, then it could be cut into the largest hunks that today's technology can move, moved, and reassembled at the destination. (Number the pieces to keep track and avoid a jigsaw puzzle). The Abu Simbel temple, carved out of solid stone, was moved in this way from 1964 to 1968 at a cost of $80,000,000 to save the World Heritage feature from being submerged by a lake. I don't know the total mass of stone moved or the max weight of each block.Edison 20:41, 20 July 2007 (UTC)

Edward Teller used to quip, "If your mountain is not in the right place, just drop us a card." --24.147.86.187 21:36, 20 July 2007 (UTC)

Well, you have not specified whet the mountain must be intact after its move. In Seattle the city did actually “move” a mountain at one time. They just aimed a bunch of fire hoses at it for a while and washed in into the Puget Sound, I believe. It probably killed of a lot of the salmon. These days that would never be allowed. --S.dedalus 22:28, 20 July 2007 (UTC)

Heh I was going to mention the Denny Regrade myself. Then there is Mountaintop removal mining, which essentially moves mountains. The question is, do you want the mountain to be in the same shape after you move it, or is it ok to just be a thick flat layer of debris? Pfly 01:12, 21 July 2007 (UTC)

batteries constructed on chip same as transistors on ICs

Is there a battery or electricity storage device that is constructed on a chip such that the chemical/physical components of the capacitor or electrochemical cell (LiFePo4) have been implemented at the nanoscopic level? If so has such technology been stacked and used to provide power for larger battery powered devices in place of a conventional battery? Clem 19:04, 20 July 2007 (UTC)

I remember reading somewhere on the Internet recently about a little device that gets electrical energy from vibrations and thus powers things without batteries. 80.0.105.59 19:14, 20 July 2007 (UTC)

The article Micropower would be a good place for covering the new device which gets power from vibrations or the battery on a chip , but those have apparently not been added yet. A battery built into a chip sounds like a very high expense item, if the implication is that both the battery and the device it powers is on the chip. Then when the battery gets low, you have to replace the device as well? At the present time, PCs have a backup battery with a shelf life odf several years to keep configuration info memory powered, and it is fairly easy to replace the battery. A backup battery may not have to furnish appreciable current as long as the device has power, and the drain can be extremely snall even without power. I suppose there is no reason a microscopic battery could not be built, and be capable of furnishing several volts, but the amp-hours would have to be correspondingly minute. Edison 20:21, 20 July 2007 (UTC)

Well I would assume any battery design committed to a chip would also be rechargeable especially if charged from vibrations. But what I am getting at is more like a conventional battery that has been reproduced at the microscopic level not to power an included circuit but rather as one of a trillion basic cells that would all be wired together as an alternative to say using airgell to maximize the surface interface between say lead and sulphuric acid. Clem 23:57, 20 July 2007 (UTC)

fates worse than nature

this is with reference to the question asked a few days back. i was thinking about these parasitoids and their amazing ability to control the minds of the hapless bugs. is it possible for them to evolve to something that could possibly target humans? for instance, like that ant which was made to wait on the grass to be eaten by the cow - i would be quite upset(to say the least!) if i were made to, say, enter a river full of crocs just to complete the life cycle of a parasitoid! 59.180.95.229 21:45, 20 July 2007 (UTC)RSP

See toxoplasmosis#Behavioral changes for a possible example of a known parasite that may impact human behaviour. Dragons flight 22:01, 20 July 2007 (UTC)

July 21

Cough cough

Can any animal cough in its sleep? —Pengo 00:35, 21 July 2007 (UTC)

Yes - my dogs do. SteveBaker 01:01, 21 July 2007 (UTC)