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March 23

"Forces of Potential"?

Is there a special name for forces that arise from potential energy, such as spring forces, electric forces, or gravitational forces? My coined phrase is "forces of potential," but is there a real scientific term for these types of forces? Yakeyglee (talk) 00:19, 23 March 2010 (UTC)

All forces, in fact, arise from some form of potential but it's not always possible to describe the force in terms of a potential from a macroscopic point of view. For instance, there is no macroscopic description of the friction force in terms of a potential but from the microscopic point of view the friction force arises due to electromagnetic interactions which arise due to a potential. Said that, the word you are looking for is probabily "conservative force". Dauto (talk) 00:29, 23 March 2010 (UTC)

It is generally regarded as impossible to construct a potential field for the strong nuclear force or the weak nuclear force. Depending on your school of thought (and your quantum physics professor), a macroscopic approximation can be used, e.g. Yukawa potential or some variant thereof. In quantum theory and in particular in the Standard Model, the idea of a potential field is replaced by the more general exchange of virtual particles; it is preferable to think in terms of "interactions", rather than "potential fields". Nimur (talk) 01:26, 23 March 2010 (UTC)

Nimur, I have a PhD in particle physics. you don't have to tell me about weak interaction. But your description, while actually quite accurate, is not really helping the OP. Dauto (talk) 01:48, 23 March 2010 (UTC)

The OP may be several years out from their first QM class, but it never hurts to give them a heads-up to the different ways that physicists think about energy and forces. I'm glad that my description is "quite accurate" as interpreted by a particle physics Ph.D.! Nimur (talk) 14:10, 23 March 2010 (UTC)

Coriolis Force

Okay, if we write the acceleration of a point in planar coordinates, we get a = (r' - rθ')r + (rθ' ' + 2r'θ')θ, where r and θ are unit vectors, and ' denotes a derivative. the 2r'θ'θ is supposed to represent the Coriolis term. But I thought the Coriolis force is always perpendicular to the velocity, not just to the radius. Help? 173.179.59.66 (talk) 02:03, 23 March 2010 (UTC)

The Coriolis acceleration (and hence the Coriolis force) only exists when using polar co-ordinates. It is one of the two components in the θ direction. If the motion of the point is analysed using co-ordinates based on the direction normal to the velocity vector and tangential to the velocity vector there is no 2r'θ' term and so no need to resort to a Coriolis acceleration.

If an artillery shell is fired over a great distance, an observer in a fixed position and orientation on the Earth's surface sees the impact of the shell occur to the right of the aim point in the northern hemisphere, or the left in the southern hemisphere. He attributes the deviation of the shell's trajectory to a Coriolis force (or the absence of the Coriolis force necessary to achieve a direct hit.) However, if the observer is orbiting the Earth in a satellite and is able to observe the rotation of the Earth, he will see the shell achieve a direct hit at the point where the aim point was at the instant the shell was fired; he will also observe the Earth rotating and will understand why observers on the Earth's surface imagine the shell deviated from the desired path.

The observer in a fixed position and orientation on the Earth's surface is, without realizing it, seeing things using rθ co-ordinates, and the observer in the satellite is able to see things using nt co-ordinates. Dolphin51 (talk) 03:02, 23 March 2010 (UTC)

The formula you are using assumes that the motion is radial from the point of view of the rotating reference frame. BTW The correct expression is a = (r' ' - rθ' ²)r + (rθ' ' + 2r'θ')θ. Dauto (talk) 03:18, 23 March 2010 (UTC)

I'm sorry, I don't see how. ${\boldsymbol {r}}=r{\boldsymbol {\hat {r}}}$ can represent any arbitrary vector, and so ${\frac {d}{dt}}{\boldsymbol {r}}={\boldsymbol {v}}={\frac {d}{dt}}(r){\boldsymbol {\hat {r}}}+r\omega {\boldsymbol {\hat {\theta }}}=v_{r}{\boldsymbol {\hat {r}}}+v_{\theta }{\boldsymbol {\hat {\theta }}}$ should represent any arbitrary velocity, as the equation seems to imply, right? I trust that I'm wrong, but I don't see where. 173.179.59.66 (talk) 04:31, 23 March 2010 (UTC)

Yes, the motion is arbitrary, but you need two separate independent arbitrary motions. One for the motion of the particle and one for the rotation of coordinate system. As it is the formula is using the same $\omega \,$ for both the motion of the particle and the rotation of the system which means that from the point of view of the rotating system the motion of the particle is radial and the coriolis force will be perpendicular to the radius. Dauto (talk) 12:56, 23 March 2010 (UTC)

Gotcha, thanks. 173.179.59.66 (talk) 14:30, 23 March 2010 (UTC)

Air pollution UK

I heard on BBC Radio Four yesterday morning that air pollution in some parts of London, for example, is well above EU limits and takes eight or more years off people's lives. Yet it is difficult to get maps of how average air pollution varies within the UK.

Are any more detailed versions of the maps in section 5 "How air pollution varies across the UK" of this pdf http://www.airquality.co.uk/reports/cat05/0408161000_Defra_AQ_Brochure_2004_s.pdf available anywhere please?

I've read the air pollution article. Some of the links are broken. I did find some links to what were called "maps" but were just CSV files of raw data, not graphical. Thanks 92.24.91.12 (talk) 02:23, 23 March 2010 (UTC)

http://www.airquality.co.uk/ itself has more detail. Example: click on London, select the monitoring sites, check out the Last Hour's Data and the Weekly Graphs. You simply do not get much more granular than 16 or so monitoring stations in London. --Tagishsimon (talk) 02:29, 23 March 2010 (UTC)

Those links do not provide any maps, just graphs over time unfortunately. Am I being paranoid or is it a sinister cover-up that this death information is not being made available, except in obscure ways that you need a PhD to appreciate? 78.149.198.14 (talk) 00:44, 27 March 2010 (UTC)

Question about blackbodies and emissivity.

I recently asked a question about light particles and how they react with ionization. I have a new question, however, apropos emissivity and prisms.

Imagine a cubic box —approximately 15 cm X 15 cm X 15 cm— closed on 5 sides and open on the remaining side. The inside surface of the "bottom" of the box (the surface opposite the open side) is covered with a large number of microscopic prisms. Each of said prisms is oriented so that the "flat" end faces the open side of the box, and the other two ends lie at a 45-degree angle to the "bottom" of the box.

Also, each of those ends (but NOT the flat end of each prism facing the open end of the box) is coated with "Super Black" or some other ultra-low-emissivity substance.

My question is, would somebody looking inside the box see nothing but total darkness? To wit, would virtually all light entering the box fail to reflect back outside the box? Would the light refracted by the prisms be absorbed or "bounced around" to the point where it would become nothing but low-grade heat?

Also, could such a setup be engineered —with extant equipment and scientific methods— which could minimize both reflection of the right from the "flat ends" of the prisms and ensure that enough photons are either absorbed or "exhausted" (for lack of a more scientific term) that no visible light would exist in the box —regardless of how powerful the external light source?

Thank you for reading this! Pine (talk) 05:52, 23 March 2010 (UTC)

what the main focus of this artical or the purpose of the work?? —Preceding unsigned comment added by 58.165.81.107 (talk) 06:01, 23 March 2010 (UTC)

Sort of. At first you can absorb light, however over time the box will get hotter, and will start to emit blackbody radiation. You can make a box to absorb light, but not as you described. If you coat the outside of a prism, the inside can still bounce light. So your prism will actually bounce the light right back at you, and will ignore the coating on the outside (but see frustrated total internal reflection). Also the flat face of the prism will bounce light. It's not possible to make a surface that will "redirect" the light inward forever, at best you can absorb the light with carbon black and the like. See Anechoic chamber for the basic design, but be aware that it works only because the light source is 'inside' the room. You can't make an open room like that. The pyramids cause the light/sound to be bounced many many times, each time absorbing more of the energy - but it's not forever, eventually it bounces to the bottom of the pyramid and then starts bouncing back out, and then it goes to the other wall and starts again. You can make it bounce so many times that it absorbs a lot, but not everything. Ariel. (talk) 07:33, 23 March 2010 (UTC)

Yep - I agree. From a 'thought experiment' point of view, your box sits in a perfect insulating vacuum and no light or heat can escape. Light is energy - so if you shine light into the box and doesn't come out again, then you're adding energy into the box. Eventually, it's going to heat up - and then in the real world would likely start emitting infrared radiation until the IR energy emitted by the box equalled the energy of the light going in. If you imagined your "super-black" material to be SO black that it didn't emit anything then the box would continue to heat up until it started getting red-hot and glowing that way. If you somehow prevent that (or re-absorb the red light) then it'll get hotter and hotter until it starts emitting in some yet higher energy waveband - and if you prevent that, it'll melt! The point is that the energy has to go SOMEWHERE. The laws of thermodynamics don't allow energy to be destroyed. Maybe you could make your box turn energy into matter so that it could just get slowly heavier! SteveBaker (talk) 17:02, 23 March 2010 (UTC)

It's not clear to me what is the purpose of the prisms in this setup. Dauto (talk) 20:19, 23 March 2010 (UTC)

Wow, thanks for the prompt replies!

Let me first say that I'm finding this conversation to be extremely eye-opening! I'd just like to clarify a couple of points, if I may:

"[I]n the real world would likely start emitting infrared radiation until the IR energy emitted by the box equalled the energy of the light going in."

Obviously, the energy (as per the Law of Conservation) must go SOMEWHERE. At first, I figured it would all —or nearly all— be lost as low-grade heat. I realize now that I was very mistaken about that.

As for the "output", however, could such be engineered so that all (or virtually all) light emitted back out of the "box" would be in the IR spectrum —or some other wavelength invisible to the naked eye? If so, then (1) how would somebody engineer such a setup? And (2) if practically all of the light were emitted outside of the ROYGBIV frequencies, would an external observer see total darkness or some other visual effect?

"It's not clear to me what is the purpose of the prisms in this setup."

That likely was a stupid idea on my part. Perhaps I ought to more closely model this after the Anechoic chamber concept.

--Again, thank you! Pine (talk) 21:09, 23 March 2010 (UTC)

Here is an anecdote from the early days of television when the Test card was an actual printed card at which a camera was pointed. It was difficult to print a true black swatch at the dark end of the grey scale. The solution was to cut through the card a hole that lead to a tiny chamber built behind the card and lined with black velvet. Cuddlyable3 (talk) 22:43, 24 March 2010 (UTC)

aircrafts

is it possible to make a propeller of airplanes to fly using superconductors on the basis of magnetic levitation principle...... —Preceding unsigned comment added by Ravi3s31 (talk • contribs) 06:11, 23 March 2010 (UTC)

The propeller? Do you mean a Magnetic bearing maybe? Or do you mean the airplane itself? If you mean the airplane, it's probably far too high for a magnet to be possible. (It would have said practical, but there is a limit to how strong a magnet you can make using superconductors, so above a certain height it's impossible.) Ariel. (talk) 07:16, 23 March 2010 (UTC)

You might want to read our article on Maglev. These (not hugely successful) craft fly at a height of about 15 millimeters.--Shantavira|^{feed me} 08:53, 23 March 2010 (UTC)

Perhaps like the old propeller-driven monorail proposals: [1][2]. You would just replace the maglev's linear induction motor with a propeller but would still need an magnetic track so I don't know that you would gain any advantage. 75.41.110.200 (talk) 14:18, 23 March 2010 (UTC)

I seem to interpret this Q differently than the rest of you. I think they are asking if the friction in the bearings for a plane propeller in a prop plane can be reduced or eliminated using superconductivity. I would guess that it's possible, but that the additional weight needed to provide coolant to maintain the low temps needed would make the cost far more than any benefit. So, possible ? Yes. Practical ? No. StuRat (talk) 16:18, 23 March 2010 (UTC)

You can do Magnetic levitation without superconductors though - it's just that you need to control the magnetic fields more carefully. Check out Magnetic bearing for example. This requires some power - but nothing like what you'd need to maintain a superconducting setup. SteveBaker (talk) 16:52, 23 March 2010 (UTC)

Pressure in a liquid

Part One

So suppose we have a liquid, say water. Now, at a certain depth, the upwards force acting on a small point (say a molecule of water) will be equal to the weight of the water above it. That I understand: the water molecule must be at equilibrium, and the force above it will be the weight of the water compressing it. Now, when an object (for simplicity, say a cube) is placed submerged in the water, what is the force acting on the bottom side of the cube? I would have thought, by the same logic as above, that the water below the cube would be pushing up with a force equal to the weight of the water above it plus the weight of the cube, but apparently that's not correct? 173.179.59.66 (talk) 02:18, 23 March 2010 (UTC)

The pressure acting on the bottom side of the cube is the pressure acting everywhere at the depth of the bottom side of the cube. Pascal's law is relevant. The weight of the cube is irrelevant for the following reason. If the density of the cube is greater than the density of water there must be a force supporting part of the weight of the cube - for example, that force might be the tension in a string supporting the cube. Alternatively, if the density of the cube is less than the density of water there must be a force holding the cube under the water - for example, that force might be the compression in a rod holding the cube under the water.Dolphin51 (talk) 02:31, 23 March 2010 (UTC)

So, to finish that thought, if the cube is in equilibrium (neither rising nor sinking) the pressure on the bottom of the cube equals the pressure due to the weight of the water above the cube plus the weight of the cube, just as you said. This also equals the pressure due to the weight of water above that surface, if the cube wasn't there. In other words, since the density of the cube is the same as water, it acts just like there was water in it's place. StuRat (talk) 02:44, 23 March 2010 (UTC)

Oh, I didn't say the cube was in equilibrium. It could be less or more dense than water. I know that the cube will rise or fall, due to Archimedes' principle. If my question is unclear, let me know. 173.179.59.66 (talk) 04:57, 23 March 2010 (UTC)

Your question is perfectly clear. Is our answer clear? Dolphin51 (talk) 05:24, 23 March 2010 (UTC)

Apparently not. You said that "if the density of the cube is greater than the density of water there must be a force supporting part of the weight of the cube". Why? 173.179.59.66 (talk) 05:33, 23 March 2010 (UTC)

Pressure depends on depth. For any real object the pressure pushing down on the top is slightly less than the pressure pushing up on the bottom. Since we know that a volume of water having the same shape as the object would be stationary, we must conclude that net force pushing on a submerged object is equal the weight of a packet of water occupying the same volume (this in the principle behind buoyancy). Hence the net force of the water is always upward and equal to the weight of the water displaced. Whether this is enough to counteract the pull of gravity will depend on the density of the object in question. Dragons flight (talk) 07:27, 23 March 2010 (UTC)

Well, see, that logic is circular. This assumes that the net pressure on any given region doesn't depend on what's inside of it (ie it's the same if it was water or lead), which is what I'm trying to understand. Normally, I would have thought that pressure exerted by a point would equal the total weight above it, and so would depend on what's above, but that appears not to be the case. 173.179.59.66 (talk) 14:36, 23 March 2010 (UTC)

I presume that it makes a difference if the cube is falling, and the force adds to the pressure immediately below the cube, like you said. I'm not an expert though, I'm just butting in because you didn't get any more replies. (Seems pretty clear that if the cube is held in place by strings then its weight is irrelevant, but that's not what you're considering, is it. Oh, and I suppose the falling cube would also lower the pressure on its upper side?) 81.131.36.119 (talk) 20:09, 23 March 2010 (UTC)

Your initial question was based on a cube is placed submerged in the water. This creates an image in the mind of a cube, stationary at the nominated depth in still water. All the answers that have been provided have been based on fluid statics, and they are correct for zero relative velocity between the cube and the water. If we now consider the cube falling through the water so that there is a non-zero relative velocity, we need to consider fluid dynamics and the situation becomes more complex. For example, the pressure on the underside of the cube would be the stagnation pressure and that depends on the relative velocity - how fast is the cube falling? Dolphin51 (talk) 05:27, 24 March 2010 (UTC)

Part two

I've been looking up on pressure in a liquid, and I've noticed a recurring trend: equations and rules are generally stated without proof or justification, with the exception of heuristic arguments that convince you that the results are plausible. For instance, the hydrostatic pressure of a liquid is given as P = ρgh, although I don't see why that would be true in general, or why it would take the same value regardless of direction. Same thing for Pascal's principle. [I did, however, find a delightfully clever proof for Archimedes' principle.] Any insight would be helpful. Thanks! 173.179.59.66 (talk) 06:48, 23 March 2010 (UTC)

In case what I said was confusing, allow me to clarify my question. 1) If you would consider a column of water, the pressure at the bottom of the column (or at any height) would be P = F/A = mg/A = ρAhg/A = pgh. But why is this equation valid in general. And say we were considering a point (in the same column) at some height h, and that this point is touching the container. Then apparently P = ρgh is still true, but I can't see why. Finally, why is Pascal's principle true? I saw a little clip that explained it for a U-bend with different areas (courtesy of http://www.youtube.com/watch?v=lWDtFHDVqqk&feature=SeriesPlayList&p=AD5B880806EBE0A4), but it's validity in general remains a mystery to me. 173.179.59.66 (talk) 07:05, 23 March 2010 (UTC)

Consider an infinitesimal cube of fluid with dimensions dx, dy, dz, and density ρ. Assuming a static equilibrium, that packet of fluid must be at rest. Which means that the net force on the packet must be zero. Consider the force on the cube. The available forces are the pressures pushing on all six sides, and the downward force of gravity. Specifically:

$(P(x,y,z)dydz){\hat {x}}+(P(x+dx,y,z)dydz)(-{\hat {x}})+$

$(P(x,y,z)dxdz){\hat {y}}+(P(x,y+dy,z)dxdz)(-{\hat {y}})+$

$(P(x,y,z)dxdy){\hat {z}}+(P(x,y,z+dz)dxdy)(-{\hat {z}})-(g\rho dxdydz){\hat {z}}=0$

It follows immediately that $P(x,y,z)=P(x+dx,y,z)=P(x,y+dy,z)=P(z)$, i.e. that the pressure doesn't change as one moves horizontally. While the last term implies:

$P(z)-P(z+dz)=\rho gdz$

$\Rightarrow {\partial P(z) \over \partial z}=\rho g$

$\Rightarrow P(z)=\rho gz+C$

Dragons flight (talk) 07:50, 23 March 2010 (UTC)

Dragons flight explanation is correct but is unlikely to dispel the OP's confusion since the OP seems to be asking why the pressure used for the vertical force is also the same pressure used for the horizontal force. I think he wants an explanation for hydrostatic pressure. Dauto (talk) 13:13, 23 March 2010 (UTC)

A couple of comments which, I hope, complement the answers above:

You asked "For instance, the hydrostatic pressure of a liquid is given as P = ρgh, although I don't see why that would be true in general,". It isn't true in general, only in the specific case of an incompressible fluid.

Then you said, "or why it would take the same value regardless of direction. Same thing for Pascal's principle" . I think both of these state the same question. But it seems to me that neither are things to be proved or derived. The first is an observation (which you could test by putting a manometer under water, and putting the nozzle at any orientation you like, though I never have.) The second, Pascal's law, seems to be a postulate of mathematical physics, that can only be verified because it is able to predict experimental results, a little like Newton's law of universal gravitation. I may be wrong, but Pascal's law looks like a definition of an ideal static fluid. However, unlike gravitation, we know that it is caused by fluid molecules, so I guess that somewhere in the literature, there is an explanation or derivation hydrostatic pressure starting from jiggling marbles or statistical mechanics, perhaps. If so, it would be interesting to see it, and perhaps to add it to the article.

These are actually laws for ideal situations, where fluids are uniform and highly symmetrical. In real life, some fluids won't obey this law: in particular some fluids that are in between a liquid and a solid. As a fluid starts to crystallise, it may transmit stress preferentially in some directions over others. I suspect there will also be problems with moving fluids, such as in viscous flow, or in boundary layers, but I don't recall any examples, though we know, for example, that Bernoulli's equation doesn't work for some non-ideal fluids.

--Hroðulf (or Hrothulf) (Talk) 14:19, 23 March 2010 (UTC)

The OP might also like to read our article on continuum mechanics. The various examples presented are generalizations of the Newtonian mechanics formulations to fluids, taking into account that mass, position, acceleration, and so forth, all must be rewritten in terms of infinitesimal fluid elements. Rigorous derivation of the laws of fluid mechanics is sometimes ugly and requires a lot of calculus. As for "proof", Newtonian mechanics has been demonstrated countless times; and so physical principles that reduce to the Newtonian case by mathematical manipulation are generally accepted as valid. Nimur (talk) 14:26, 23 March 2010 (UTC)

OP here. First off, thanks, you've made this stuff much clearer. However, a few more questions: I understand ${\partial P(z) \over \partial z}=\rho g$, but to go from that to :$P(z)=\rho gz+C$, doesn't that assume that ρg is constant? If there were something other than water above the infinitessimal cube (say a rock), would the result change? 173.179.59.66 (talk) 14:52, 23 March 2010 (UTC)

If there was a dense rock above the cube, it would sink towards our pressure sensor, so we don't have the equilibrium we wanted.

But, we could fix the rock in place, for example we could glue it to the wall of our container. A naive integration over $z$ with $x$ and $y$ constant wouldn't work. When we reach the rock we get to a discontinuity where $p(z)$ doesn't apply. However, Pascal's principle allows us to move horizontally at will, and experience the same pressure. With a horizontal movement or two, we can find a way to the surface, so we might as well integrate over $z$ after all. (The container is not symmetrical, but all that fluid mechanics requires is local symmetry: each infinitesimal element of fluid is symmetrical.)

What does the $\P$ symbol mean here?

By the way, I suggested looking into statistical mechanics, and I just noticed that in hydrostatic pressure, Wikipedia says that $\ p(h)=p(0)e^{-Mgh/kT}$ can be derived from the assumptions of statistical mechanics. I guess if we consult any statistical mechanics textbook, we can add the derivation to the article, which would help answer your question (for the gas case, not a liquid). For small $h$ this is equivalent to $P=\rho gh$.

--Hroðulf (or Hrothulf) (Talk) 15:32, 23 March 2010 (UTC)

It occurred to me that it might help you get to grips with this if you turn the thought experiment about the dense rock on its head. The rock is fixed to the sides of the container, so you can use P = ρgh above and below the rock to predict the forces on the rock. In other words, you can calculate how much upward force the container has to exert on the rock to support it, which will be its weight less its buoyancy. The rock doesn't interfere with the calculation of pressure, and if you use a balance or a strain gauge to measure the rock's buoyancy, you can use it to demonstrate that P = ρgh holds true. --Hroðulf (or Hrothulf) (Talk) 16:39, 23 March 2010 (UTC)

Everything makes sense now, much thanks. 173.179.59.66 (talk) 22:50, 23 March 2010 (UTC)

Damage due to loss of circulation in extremities

This question is inspired by the question further up the page asking about organ failure, but I'm curious about the other extreme. If one loses circulation in a non-vital region, say a finger or toe, or perhaps an arm or a leg, then how long does it take for permanent damage to occur? Similarly what tends to be first permanent consequences of such loss of circulation (e.g. what is first to be damaged)? I would assume, though I don't really know, that the extremities can be sustained longer without circulation than the internal organs generally can. Dragons flight (talk) 08:10, 23 March 2010 (UTC)

They can go quite a long time. See Reperfusion injury for a non obvious injury. Ariel. (talk) 08:19, 23 March 2010 (UTC)

I assume that you (the OP) are talking about an acute injury such as an arterial blockage due to an embolism (cholesterol embolism, fat embolism, etc.). The bottom line is that the timing of damage is going to depend on the metabolic rate of the organ involved, the degree of collateral circulation, and the amount of tissue that experiences ischemia. A finger/toe, which is mostly skin, connective tissue, tendons, nerve endings, etc., may tolerate temporary cessation of blood flow better than an arm/leg, which contains significant amounts of muscle, not to mention a great deal more tissue. The tourniquet article discusses some consequences of sudden loss of circulation to distal tissues but doesn't give any specific duration that I can see. Acute mesenteric ischemia can cause bowel infarction, and the article says that "prognosis depends on prompt diagnosis (less than 12-24 hours and before gangrene)" suggesting that for the gut, at least, permanent damage happens after about 12-24 hours, probably varying a great deal depending on the size of the infarcted area. You might also want to consider chronic peripheral circulatory problems such as those seen in diabetes or peripheral vascular disease, which can lead to necrosis over long time periods. Take a look at the gangrene article for some nice photos of the process (unless you happen to be queasy about that sort of thing). --- Medical geneticist (talk) 18:48, 23 March 2010 (UTC)

I'm not a medic, but my info is that a limb can survive for up to 2 hours with blood flow completely cut off before gangrene sets in. FWiW 24.23.197.43 (talk) 23:23, 23 March 2010 (UTC)

You may also be interested in frostbite and reflex cold urticaria. ~AH1^(TCU) 01:59, 24 March 2010 (UTC)

What is the quantum model for refraction of light?

Could I ask you to recommend a website or text book that would introduce to me a quantum mechanical model for the transmission of light (photons) through a dielectric like glass or water?

I wish to explore the verbal description in this article more deeply: http://www.physlink.com/education/askexperts/ae217.cfm (Why does light slow down when entering a prism but speed up when it exits?)

So I read Refractive index#Speed of light.

However I am confused by the claim that though the phase velocity (wavelength divided by frequency period) decreases, the speed of the individual photons is said to be unchanged. If I understand the implications of the classical model correctly, the vibration of the electrons predicted by Maxwell's equations shortens the wavelength, similar to the way a sound wave has its wavelength shortened and refracted when it moves from a stiff solid to a less stiff one. In my mind, the classical model predicts that the actual velocity of the light will change, which seems to correspond to Fizeau's experimental results on the speed of light through a tube of water. Therefore, to help fight my way through the forest, I wanted to see a mathematical description of quantum light transmission through matter, if it can be boiled down to a small set of consistent equations.

Is there a single accepted quantum model for this effect?

Is it covered in Feynman's QED: The Strange Theory of Light and Matter? (If so I will seek out a copy or watch the lectures online)?

--Hroðulf (or Hrothulf) (Talk) 12:16, 23 March 2010 (UTC)

You are correct. The speed of individual photons decreases due to interactions with the dielectric. Dauto (talk) 12:33, 23 March 2010 (UTC)

Thanks, Dauto! I suspect that the two descriptions (1) of a photon slowing, and (2) a photon being absorbed, and then an identical one emitted at speed $c$ with a time delay and phase shift, though they appear contradictory, are actually two different, correct, viewpoints of exactly the same phenomenon.

I will be interested to discover if, when a photon wavefunction overlaps the wavefunction of an electron, the mathematics produces the same outcome as when a light wave oscillates a classical point charge. I ordered Feynman's QED from the library.

--Hroðulf (or Hrothulf) (Talk) 14:57, 24 March 2010 (UTC)

You are in for a treat. Feynman's QED is a delight to read. I don't remember seen the answer for that specific question in there but it's been quite some time since I last read it. Either way, it's a book worth reading. Dauto (talk) 20:24, 24 March 2010 (UTC)

National Medal of Science

Did Bush forget to award 2008 and 2009 National Medals of Science? Why does our article only go to 2007? Why does http://www.nationalmedals.org/medals/laureates.php only go to 2006? Does the sad shape of these medals' records have anything to do with the censorship at the White House office of Science Policy? 99.56.137.254 (talk) 12:23, 23 March 2010 (UTC)

According to the NFS website, there were none in 2008 and nine in 2009. Someone should update our article with last year's winners. Speculation about political intrigue is out of scope for this ref-desk. DMacks (talk) 13:41, 23 March 2010 (UTC)

It seems unlikely that the lack of any winners would have to do with top-level politics. There is no shortage of scientists who do good work on topics with no political relevance, or relevance primarily on things that even Republicans like to take credit for (George Bush was as happy as any to talk about how great renewable energy research was). --Mr.98 (talk) 14:44, 23 March 2010 (UTC)

Well, there could be a scenario where the obvious winner is someone they don't want to award, like a global warming scientist. So, then the choices would be to hold the award ceremony, and snub that scientist, getting all sorts of negative press, or just cancel it altogether for some believable reason, hopefully garnering less negative press. I have no idea if this actually happened, just offering one possible scenario. And, looking at the list, it seems that there were many years when no medal was awarded, so I'd tend not to look for conspiracy theories. StuRat (talk) 16:09, 23 March 2010 (UTC)

I'm not sure if there is any difference between a medal recipient and a "notable laureate". I left a question at Talk:National_Medal_of_Science#2009_recipients.3F. --Enric Naval (talk) 16:59, 23 March 2010 (UTC)

I think the database is wrong, there are no 2009 recepients yet and won't be until later this year. The ones listed under 2009 are actually the ones for 2008, whoever manages the database probably screwed up, I've emailed them. Check out the article talk page for more details. Incidentally as noted in the article the 2005 & 2006 medals were awarded together, in 2007, I don't know why. Perhaps there was too much campaigning going on in 2006. Maybe they wanted to save money so decided to only have one ceremony for two years. You may be able to find out if you search around. Nil Einne (talk) 23:08, 23 March 2010 (UTC)

Thiomersal/Thimerosal

Why the two names? Is it a brand name thing, or just English variants (à l'aluminium/aliminum)? Our article doesn't seem to say. AlmostReadytoFly (talk) 14:47, 23 March 2010 (UTC)

I believe it's just a spelling variant. This MSDS lists a couple of other names for the same, including some trade names. SDY (talk) 14:53, 23 March 2010 (UTC)

Thiomersal is the International Nonproprietary Name designated by the World Health Organization. Thimerosal appears primarily in North American usage; I don't have access to a suitable database at the moment, but I suspect that is probably a United States Adopted Name. (Both are considered 'generic' names in their respective jurisdictions; manufacturers will have their own unique trade names for the product.) As to the 'why' — it comes down to different standards in jurisdictions with different governing bodies. Why is parecetamol sold as acetaminophen in the United States? ("Why can't you carry acetaminophen in the jungle?" "Because paracetamol!") TenOfAllTrades(talk) 15:11, 23 March 2010 (UTC)

Scrambled eggs

When scrambling eggs, if you give them a vigorous stir after they begin to set, they will return to a liquid state. What chemical & physical processes are going on? DuncanHill (talk) 14:54, 23 March 2010 (UTC)

Denaturation (biochemistry) has a nice photograph at top of the article. It is probably a special type of Maillard reaction (which is normally discussed in the context of cooking meat). We also have a great article on Molecular gastronomy - again, there's a really nice egg photo at the top of that article too. Nimur (talk) 15:42, 23 March 2010 (UTC)

Towards the perfect soft boiled egg discusses several quantitative models for egg cooking chemistry. And Cooking for Eggheads says: "when an egg cooks, its proteins first unwind and then link to form a rigidifying mesh. But not all its proteins solidify at the same temperature. Ovotransferrin, the first of the egg-white proteins to uncoil, begins to set at around 61 degrees Celsius, or 142°F. Ovalbumin, the most abundant egg-white protein, coagulates at 184°F. Yolk proteins generally fall in between, with most starting to solidify when they approach 158°F. Thus, cooking an egg at 158°F or so should achieve both a firmed-up yolk and still-tender whites, since at that low temperature only some of the egg-white proteins will have coagulated." When you stir scrambled eggs, you're probably rehomogenizing the mixture, which has started to fractionally solidify. Nimur (talk) 15:48, 23 March 2010 (UTC)

Thermal Radiation

What's the difference between the average surface temperature and effective temperature when treating Earth as a Black body? I can find the new article has the following formula:

$T_{E}=T_{S}{\sqrt {\frac {R_{S}{\sqrt {\frac {1-\alpha }{\overline {\epsilon }}}}}{2D}}}$

But I remember I've read this article before (an old revision of the Black body article), with the following equation:

$T_{E}=T_{S}{\sqrt {\frac {R_{S}}{2D}}}$

Applying first equation gives about -18.8 °C and is called effective temperature, whereas the 2nd one gives about +14.5 °C.

Was that a correction or what?. Thanks in advance.--Email4mobile (talk) 16:33, 23 March 2010 (UTC)

It's an improvement that takes into account that the earth doesn't emit or absorb radiation as effectivelly as ablack body but you would know that had you acctually read the article. Dauto (talk) 18:41, 23 March 2010 (UTC)

Thank you very much, Dauto. I've another question indeed regarding the maximum theoretical Temperature T_E. If we assume a perfect black body but with a shape different from a sphere, let's say a sheet or disk in the space with one side exposed to the radiation and the other not. Can we estimate the maximum possible temperature in this case and can we say that it won't exceed $T_{S}{\sqrt {\frac {R_{S}}{D}}}$?--Email4mobile (talk) 21:10, 24 March 2010 (UTC)

Trailing off...

Is there a name for a speech impediment where the person starts out talking strongly, but then the volume drops off until eventually they aren't speaking at all ? For example:

"I NEED TO GO to the store to get ...".  

Do we have an article on this ? StuRat (talk) 16:42, 23 March 2010 (UTC)

Blue for murmur and Prosody_(linguistics). Red for muttering and mumbling. The most common term for that I've heard is "trailing off". A reverse dictionary didn't find anything. There is a stub for enunciation. I'm almost sure this isn't what you are looking for but Sotto voce. If you want to be poetic about it you could use a musical equivalent and say someone is speaking "al niente", "calando", "decrescendo", "diminuendo", "perdendo", "perdendosi", "morendo", or "smorzando". I'm no music buff so I couldn't tell you which one of those would best fit the bill. 152.16.15.144 (talk) 17:37, 23 March 2010 (UTC)

Edit. Probably not aposiopesis. List of voice disorders? 152.16.15.144 (talk) 17:39, 23 March 2010 (UTC)

Doesn't so much sound like a speech impediment as it does a memory problem. I'd expect this sort of behavior in someone with either an physical injury to the brain, on some sort of drug or with some sort of memory based disease (either degenerative or attention based). Sorry I can't link you to anything in particular. Regards, --—Cyclonenim | Chat  21:46, 23 March 2010 (UTC)

Maybe the loss of one's train of thought, or a tip of the tongue phenomenon? ~AH1^(TCU) 01:57, 24 March 2010 (UTC)

My first thought was ADHD. Second thought was Absent-mindedness. Third thought.. was.. ...was... Pfly (talk) 09:52, 24 March 2010 (UTC)

Is this a known symptom of ADHD ? StuRat (talk) 15:17, 24 March 2010 (UTC)

Well I meant to link to ADD, but it redirects to ADHD predominantly inattentive, which is apparently what ADD is called now. I piped it to say ADHD, for reasons that made sense in the moment but don't now. Anywa, the page actually linked to says "it is characterized primarily by inattention, easy distractibility, disorganization, procrastination, forgetfulness.." So, well, ..um, oh look, cows. Pfly (talk) 09:23, 25 March 2010 (UTC)

I don't think ADHD presents like this. I know I said an attention based disorder above, but I wasn't suggesting ADHD. In fact, I'd expect a person with ADHD to blurt stuff out rather than trail off. My best guess for this case would be traumatic brain injury which has affected either the person's Broca's region (responsible for producing speech, though I'm sure not sure why they'd trail off, usually one would just stop speaking completely) or perhaps one of the areas responsible for memory such as a part of the hippocampus. Regards, --—Cyclonenim | Chat  18:59, 25 March 2010 (UTC)

Yes, sorry, I was just saying what my first thoughts were, and perhaps trying to say that the question was a bit vague. For something more related to neurology, perhaps some kind of expressive aphasia? That term is broad and includes all kinds of things, but it appears that there are a number of things that might cause a trailing off of speech type symptom. Pfly (talk) 20:46, 25 March 2010 (UTC)

Including stroke ? StuRat (talk) 23:59, 25 March 2010 (UTC)

Strokes tend to create incoherent speech rather than trail off well produced speech, but it could be a post-stroke symptom if damage was severe enough to memory regions. Regards, --—Cyclonenim | Chat  12:02, 26 March 2010 (UTC)

UH-60L data busses ....

I have a need to know what data busses are employed by the UH-60L copter. For instance, what bus does the Honeywell H764 navigator use? My guess: 1553. But I can't confirm that. Is there a site I can look at or publication that I can determine what data busses are used on the various subsystems?

Thanks, Whatsamatteru (talk) 17:47, 23 March 2010 (UTC)

This Honeywell Document says that the Honeywell H-764 features both MIL-STD-1553 and RS-422 busses. -- Finlay McWalter • Talk 18:21, 23 March 2010 (UTC)

And this and this both say that the M version of the Blackhawk use 1553-based glass cockpits. I can't immediately find comparable info for the L version. -- Finlay McWalter • Talk 18:26, 23 March 2010 (UTC)

Yeah. I'm trying to find a technical document that details the data busses like the doc I have that details the electrical busses. Difficult to find. But thanks for checking into it for me, Finlay.

Whatsamatteru (talk) 19:06, 23 March 2010 (UTC)

Such technical documents are probably ITAR-controlled. Nimur (talk) 09:16, 24 March 2010 (UTC)

Rh disease and James Harrison

Is this real? And if it is, how come I can't find a thing about it? Nor any details of what exactly they do with his blood? And what they plan to do after he dies? Except for a paragraph someone plopped at the bottom of Rh disease I couldn't find anything on wikipedia.

After some more searching I found this. So apparently this is an Australian thing only? i.e. it's only in Anti-D, but not RhoGAM? Kinda confused, maybe someone know more. Ariel. (talk) 21:47, 23 March 2010 (UTC)

I don't think it's Australia only. Our article says "Rho(D) Immune Globulin is a derivative of human plasma". According to the second article, there are about 200-300 donors in Australia producing the required antibodies which are sufficient for the Australian requirement, the idea that this single person is supplying antibodies for the whole of Australia is I presume wrong (hardly surprising, Daily Mail isn't particularly notable for the accuracy of their science articles and it is a feelgood story) although he was one of the earliest suppliers. I presume most other countries have similar setups. I also don't think these are the only special plasma components collected from a small subset of donors, e.g. this discusses the issue when it comes to people selling their blood plasma [3] and there are also rare blood types e.g. [4] which similarly come from a small number of donors Nil Einne (talk) 22:39, 23 March 2010 (UTC)

(post Edit conflict) Basically the treatment of Rhesus disease consists of injecting the Rh- mothers with an antibody Rho(D) immune globulin (why is it written immune globulin instead of immunoglobulin?) which binds to and will lead to the destruction of fetal Rh positive blood cells which have crossed the placenta. I think the idea behind it is to keep the mother's immune system from becoming sensitized to Rh antigens. The sensitization and subsequent reaction storm can lead to the mother's antibodies crossing the placenta and attacking the fetus's blood. If they are using this guy's plasma for its antibodies, then this guy probably has Rho(D) immunoglobulin and thus is Rh- and sensitized to the antigens. The blood types article noted that "It is common for D-negative individuals not to have any anti-D IgG or IgM antibodies, because anti-D antibodies are not usually produced by sensitization against environmental substances." That's one reason the guy's blood may be uncommon then. Rho(D) immune globulin is made from human plasma, so I'm guessing this guy's plasma is used to make this stuff. His blood might also have other useful attributes, like being AB type, which means the plasma lacks the IgG anti-A or IgG anti-B antibodies and can be donated to A, B, and O types safely. This is all a guess so hopefully this helps... 152.16.15.144 (talk) 22:44, 23 March 2010 (UTC)

Avalanches

Hello everyone, I think I might have asked a similar question some time earlier, but I'll ask it anyway: What is the latest in the spring that a major avalanche had been recorded in the Rockies of central Alberta (in the area around Jasper, or thereabouts)? By "major", I mean an avalanche big enough to destroy/badly damage one or more buildings or kill/bury multiple victims. If someone could point me to where I can find this information, I'll be very thankful. Thanks in advance! 24.23.197.43 (talk) 23:33, 23 March 2010 (UTC)

OK, looks like nobody here knows the answer. Looks like I got to look it up on my own. Oh, well... 24.23.197.43 (talk) 03:20, 27 March 2010 (UTC)

March 24

Bone marrow donations

Now that I'm 18, in the UK I'm eligible to sign up the bone marrow donation register next time I go in to donate blood. I've heard there are two separate methods of donation: bone marrow harvest directly from your pelvic bone, or stem cell donation after a few days of injections (by normal blood extraction methods).

My question is what are the advantages of bone marrow harvest over stem cell donation, and vice versa? Presumably there are advantages to both methods, or the bone marrow harvest would not be performed (as it's done under general anaesthetic and therefore inherently carries more of a risk). Thanks. Regards, --—Cyclonenim | Chat  00:57, 24 March 2010 (UTC)

A little terminology nit-pick: "bone marrow donation" clearly is extraction of bone marrow. But the goal is usually to get stem cells from it, so that's why extraction from blood is an alternative. Bone marrow transplant#Risks to Donor following Peripheral Harvesting of Stem Cells looks like it has some info. Also, "after a few days of injections" could have effects other than boosting the amount of harvestable cells (as well, having an elevating effect might itself have side-effects...not sure). DMacks (talk) 01:44, 24 March 2010 (UTC)

Thanks, interesting link. If anyone has any information on the advantages of using bone marrow harvesting specifically, that'd be great. Regards, --—Cyclonenim | Chat  08:57, 24 March 2010 (UTC)

We're not supposed to answer medical questions. I suggest asking the people where you go to donate blood. They probably know more about it than we do. — DanielLC 05:03, 24 March 2010 (UTC)

We're not supposed to answer medical advice. You're allowed to answer questions by which no harm could come from answering. Me asking the advantages of bone marrow donation over stem cell donation is not something that could harm me. Regards, --—Cyclonenim | Chat  08:54, 24 March 2010 (UTC)

(ec)Actually we are supposed to answer medical questions as long as they don't require medical advice. Kainaw's criterion is a good rule to follow. AlmostReadytoFly (talk) 08:58, 24 March 2010 (UTC)

I expect that if you are ever found to be a donor match to someone that your doctor will talk you through the various options for donation. By then a different method may be used. 137.73.4.211 (talk) 13:36, 24 March 2010 (UTC)

From the Cochrane database: "Bone marrow harvest versus peripheral stem cell collection for haemopoietic stem cell donation in healthy donors". It's quite a long document. Of note:-

• Pain prior to the donation procedure was experienced by peripheral blood donors only.
• More bone marrow donors experienced pain at donation site in comparison to peripheral blood donors.
• Pain subsequent to donation was experienced by both groups of donors. Bone marrow donors experienced more back pain and peripheral blood donors experienced more skeletal pain.
• Bone marrow donors are more likely to develop haemorrhage, anaemia and hypotension in comparison to peripheral blood donors.
• Bone marrow donors tended to experience more days of restricted activity, had more mean discomfort and a greater number were still experiencing restricted activity 14 days post-bone marrow harvest. Peripheral blood donors experienced greater difficulty in functioning within the first seven days.
• Bone marrow donors are more likely to require hospitalisation than peripheral blood donors.
• Both bone marrow and peripheral blood donors experienced psychological morbidity. Both groups had increased fatigue and reduced energy and anxiety following the procedure.
• The number of donors reporting any adverse events, was greater in the bone marrow group in comparison to the peripheral blood group.
• No life threatening adverse events were reported.

Axl ¤ [Talk] 18:36, 24 March 2010 (UTC)

Thanks, great summary of the disadvantages of both marrow donation, but are there any advantages? I haven't found any, and if that's the case, why is it still used commonly (though not as commonly as peripheral blood donation)? Regards, --—Cyclonenim | Chat  19:22, 24 March 2010 (UTC)

About coefficient of mastication

Could you please through some light on the term " Coefficient of Mastication " Kasiraoj (talk) 05:53, 24 March 2010 (UTC)

I think it means how thoroughly you chew your food when eating. FWIW 24.23.197.43 (talk) 07:01, 24 March 2010 (UTC)

Sounds like a term of art in the fletcherizing sciences. --Sean 12:43, 24 March 2010 (UTC)

An article about A model for comparison of masticatory effectiveness in primates includes a coefficient of masticatory effectiveness (E) the value of which increases with effectiveness of exposing new food surface area with each chew. Cuddlyable3 (talk) 22:25, 24 March 2010 (UTC)

Question on Scientists

Is it true that Watson and Crick, may have discovered the double helix on acid(LSD)? —Preceding unsigned comment added by Hmrnkng901 (talk • contribs) 06:05, 24 March 2010 (UTC)

FYI, LSD does not have a double helix structure -- that would be DNA. I think you might have confused the two acids. FWIW 24.23.197.43 (talk) 06:59, 24 March 2010 (UTC)

No, Hmrnkng means "is it true that they may have been taking LSD when they discovered the structure of DNA?" This discussion thread from 2007 at snopes.com discusses the claim without reaching a clear conclusion. It seems as though the claim originates from this article from the British tabloid The Mail on Sunday. It asserts that Crick told someone he was on LSD (and then this claim is treated as truth for headline purposes), but when asked about it by the reporter, Crick denied it. --Anonymous, 08:30 UTC, March 24, 2010.

I'd be pretty sure they weren't - it took a lot of work and thinking, it wasn't just an afternoon's "eureka moment". Aaadddaaammm (talk) 09:25, 24 March 2010 (UTC)

is there any reliable evidence/a good citation that either of them had EVER used LSD? 82.113.106.90 (talk) 10:01, 24 March 2010 (UTC)

Of course they were on LSD - at that time it was the acronym for the Sterling money system of pounds, shillings and pence! --TammyMoet (talk) 11:39, 24 March 2010 (UTC)

LSD really didn't become a recreational or even common drug until the 1960s. Watson and Crick discovered the double helix in 1953. Their work was built up of incremental steps and careful reasoning, not one "OH, DUDE" moment. I would say, "signs point to no," or at least, "a second-hand account in a British tabloid is not very convincing to me." As for whether either of them ever did LSD later—it's entirely possible, of course. Both lived long lives! --Mr.98 (talk) 13:17, 24 March 2010 (UTC)

James Watson would probably want it pointed out that he is still living a long life! – ClockworkSoul 23:06, 28 March 2010 (UTC)

Editing Wikipedia

I am new to editing Wikipedia, though I have been using it for several months now I did my first edit a few weeks back. I have a few questions: Our organisation has over 40 thousand computers connected on Internet in different locations in the city and I dont use one particular computer. I could use several computers in a period of one month.

But when I saw recently a messsage it said some entries that were made were removed and so on. My question is I never made these entires but someone using the same internet network could have done so. Is there a way I can make my own comments/ edits and retain my uniqueness without Wiki mistaking me for someone else? —Preceding unsigned comment added by 213.130.123.30 (talk) 06:55, 24 March 2010 (UTC)

Questions about Wikipedia itself should generally go to the Help Desk, rather than here at the Reference Desk. That said, basically the solution to your issue is to create a user account and login. [5] It's free, provides a variety of benefits, and requires no personal information (not even an email address). As long as you are logged in, the edits will be uniquely associated to that account regardless of what computer you use. Dragons flight (talk) 07:27, 24 March 2010 (UTC)

Create a user account. You see over at the top-right of your browser window where it says "Log in / create account"? Click on that - then on "Don't have an account? Create one." - click on that - then follow the instructions. Now, when you log in, your contributions are credited to your account - and not to a bunch of nameless IP addresses that change when you move from place to place or (possibly) whenever you reboot your computer. Doing this has other benefits - it lets you hook up your email address so other Wikipedians can email you - and it also makes it possible to create new articles and do a bunch of other things that are forbidden to 'anonymous' users. Ironically, having a user account actually makes you MORE anonymous because Wikipedia hides your IP address. Right now - I can tell (because your IP address is 213.130.123.30) that you're posting via Qatar Telecom - so you probably live in or around Doha. If we look at Dragons flight - the only things we know are what he or she decides to put on his/her user page. You get to control what you reveal. In my case, I chose to reveal my real name (Or did I? You'll never know!) SteveBaker (talk) 13:13, 24 March 2010 (UTC)

But somehow I suspect there may be more than just the one Steve Baker in the world. StuRat (talk) 13:21, 24 March 2010 (UTC)

There is a way to make it one less (video at 1:04). Cuddlyable3 (talk) 22:12, 24 March 2010 (UTC)

This video contains content from MyVideoRights (Mr Bean), who has blocked it in your country on copyright grounds. Vimescarrot (talk) 10:01, 25 March 2010 (UTC)

The video plays in my country.Cuddlyable3 (talk) 13:16, 26 March 2010 (UTC)

I agree with Dragons flight and SteveBaker. There is also another benefit in creating your own account - as well as a User page (on which you might choose to post a little information about yourself) you also get a User Talk page. Other Users can send you a message on your User Talk page, and that message will usually be about edits you have made to an article. Other Users can make suggestions or ask you questions. That is always a better alternative than merely deleting something another User has written. (To see a User's Talk page, simply click on the blue word (talk) following immediately after the User's name.) Dolphin51 (talk) 22:36, 24 March 2010 (UTC)

thanks everyone for the replies... i would log in and create my user name and do it the proper way henceforth. appreciate all the reply. thanks Steve for given a detailed reply though you called one of my earlier questions nonsense ( which in my assessment was a very valid and scientific q) neways thanks everyone and I liked cuddlyables comment too ;))213.130.123.12 (talk) 10:26, 25 March 2010 (UTC) done that. Thanks again everyoneFragrantforever 10:37, 25 March 2010 (UTC) —Preceding unsigned comment added by Fragrantforever (talk • contribs)

DC supply in tripping circuits

Why Dc circuits are used in Tripping of Circuit breakers instead of AC circuits? —Preceding unsigned comment added by 109.82.139.192 (talk) 08:57, 24 March 2010 (UTC)

I think you are mistaken. Some circuit breakers may have a digital control system which runs on a DC power supply, but the overwhelming majority of circuit breaker elements are totally passive, and trip mechanically when overcurrent is detected. See Circuit breaker#Types of circuit breaker for more information. Nimur (talk) 09:13, 24 March 2010 (UTC)

In electrical generating stations and substations, there are large batteries which supply direct current for tripping and closing circuit breakers and other switching devices. Sophisticated and sometimes computerized relay systems, perhaps with communication from relays at the other end of the line, determine when a breaker should trip, and operate backup breakers if it fails to trip. In a home , the electrical panel has circuit breakers with magnetic elements (coils or solenoids) which can trip instantaneously for an extremely high fault current, and thermal elements which allow a smaller overload to persist for a short time, as when a motor is starting. No DC supply is really needed for their operation. DC for tripping of such small breakers would require expensive batteries and chargers, with additional possible failure modes from old or overcharged batteries, and additional maintenance. It is also possible to keep a capacitor charged from a rectifier to provide DC for tripping a breaker. I'm not sure what the benefit is. Some large utility breakers used a tank of compressed air to provide energy for tripping. Some 12 kv breakers use a spring for tripping energy. DC is typically used to trigger the stored energy mechanism. Edison (talk) 20:01, 24 March 2010 (UTC)

Screw Compressor

Why screw compressor make more noise as compared to reciprocating compressor?203.199.205.25 (talk) 10:03, 24 March 2010 (UTC)

Who says they do? This page says just the opposite. At any rate, according to this document and many others it's not the case. A huge factor is going to be whether it's an oil-flooded screw compressor where the oil itself will dampen the sound. Another important distinction is what "more noise" means; screw compressors run faster so have a higher pitch, but that's more readily muffled than higher-output low pitch sounds. --Sean 13:38, 24 March 2010 (UTC)

testicles

Can a human being created without testicles. If he does can he able to bear (give birth) to a child. A man with very small size of testicles can give birth to a child? —Preceding unsigned comment added by 196.200.103.5 (talk) 11:05, 24 March 2010 (UTC)

For your first question, it happens all the time. For your second question, a woman with a properly developed reproductive system and of appropriate age will usually be able to bear a child, but most will object to being refered to as 'he'. For your last question unless the man has a female reproductive system (in particular the parts essential for carrying and giving birth to a child like a fully developed uterus and vagina) it is obviously impossible for them to bear and give birth to a child. In some cases a person may have ovotestis but I don't know if there's ever been a case where someone with ovotestis (let alone testes) has had a fully developed uterus and vagina however if such cases do occur while the person is likely to be naturally infertile it may be possible for them to bear and give birth to a child using IVF with donated eggs (and a partner or someone else's sperm) or embryos and likely appropriate hormone treatment. However they may not identify as being 'a man' and it would be inaccurate (and probably offensive) to simply say they have 'small size testicles' Nil Einne (talk) 11:12, 24 March 2010 (UTC)

A boy can be born without testes. This is called Anorchia. Men do not bear (give birth to) children, but can normally father them. AlmostReadytoFly (talk) 12:47, 24 March 2010 (UTC)

All women and a very few men are born without testicles. However, there is a lot more to bearing a child than not having testicles - you need a womb and ovaries and a bunch of other stuff that men don't have. Hence a man isn't going to be able to bear a child no matter what's happening in the testicles department. SteveBaker (talk) 13:03, 24 March 2010 (UTC)

I think the OP wanted to ask "Can a male be born without testicles? If so, would they be able to father a child? What if the testicles were very small rather than absent - would they be able to father a child?"--Frumpo (talk) 14:58, 24 March 2010 (UTC)

Just a wild guess, but perhaps our questioner is from a culture that does not consider females as human beings...? alteripse (talk) 00:45, 25 March 2010 (UTC)

I think a more generous guess is that the questioner, being in Eritrea, doesn't speak English fluently and is confused by the distinction between 'man' (relating to mankind and replaceable with 'human') and 'man' (meaning male). AlmostReadytoFly (talk) 09:10, 25 March 2010 (UTC)

Rarely, women have had babies delivered alive from ectopic pregnancies attached to the abdomen outside the uterus or fallopian tubes. Could such an abdominal ectopic pregnancy be successfully transplanted to a man, particularly if he did not have male hormones circulating? Edison (talk) 20:06, 24 March 2010 (UTC)

The Wikipedia article Male pregnancy answers definitely maybe perhaps. It's harder if you want baby and dad to survive. Cuddlyable3 (talk) 21:57, 24 March 2010 (UTC)

Sorry, let me ammend may question. Can a man without a testicle or with a small size of testicle be fertile (become a father). —Preceding unsigned comment added by 196.200.103.9 (talk) 10:43, 26 March 2010 (UTC)

1) (without testicle) No, 2) (small testicles) Probably, and in either case it's fun trying. Cuddlyable3 (talk) 13:11, 26 March 2010 (UTC)

Apart from the "fun trying" answer, the others are probabilities, as not all men with normal sized testicles have normal sperm. The infertility rate in apparently normal adult men is a few percent I think. In contrast the infertility rate in men with small testicles is higher because there are a number of conditions in which the testicles do not develop right and do not make sperm. Examples are Klinefelter syndrome, Kallman syndrome, gonadal dysgenesis, and hypopituitarism. The actual probability for our non-medical-advice-seeking questioner varies by "how small". For a twenty year old man with testes 4cc or less, the expectation of infertility would be well over 75%. alteripse (talk) 19:51, 26 March 2010 (UTC)

has anything impossible ever happened for sure, well verified, with scientific consensus (there will be a followup question)

My first question is whether anything considered, then and today, scientifically impossible for the time, ever nonetheless for sure happened, in a way that is well verified, and for which there is scientific consensus that it happened in that impossible way. It doesn't have to be effects that depend on the power of the mind, or something paranormal, the only criterion I'm looking for is that it must be scientifically impossible, yet nonetheless have happened, and that the scientific community should be in agreement on both these points. ie I'm talking about something "supernatural" or "miraculous", but with consensus both on the fact that it's impossible ("a miracle") and also on the fact that it must have happened in that impossible way. Then I will have a followup question. Thank you. 84.153.234.218 (talk) 12:03, 24 March 2010 (UTC)

Are you meaning things that were once considered 'scientifically impossible' but are now considered possible? Or are you meaning things that were (and still are) considered 'scientifically impossible'? 194.221.133.226 (talk) 12:07, 24 March 2010 (UTC)

As I tried to say with my words "considered, then and today, scientifically impossible for the time", I mean that not only whenever it occurred, it should have been considered impossible then for it to have occurred, but also today it should still be considered impossible for it to have occurred then the way that it did. Nevertheless, my crucial second point is that there there should be full, well verified scientific consensus that it in fact did in fact occur in the way that is impossible. 84.153.234.218 (talk) 12:11, 24 March 2010 (UTC)

I think the question is flawed. If the scientific community agrees that a certain thing actually happened, then there's no way they would also agree that it was impossible. The very fact of it having happened proves that it is possible. If the thing in question had previously been in the category of "miracles" (by definition beyond scientific explanation), then it would be removed from that category quick smart. Such corrections have often occurred throughout science. -- Jack of Oz ... speak! ... 12:13, 24 March 2010 (UTC)

American Revolutionary War patriot and hero Ethan Allen wrote "In those parts of the world where learning and science have prevailed, miracles have ceased; but in those parts of it as are barbarous and ignorant, miracles are still in vogue." Wikipedia offers an article Miracle. Cuddlyable3 (talk) 12:21, 24 March 2010 (UTC)

first of all I disagree completely with your saying that the question is "flawed". That is akin to saying it is a "flawed" question to ask "are there any even primes greater than a million?" That question is not flawed in the least. 84.153.234.218 (talk) 12:26, 24 March 2010 (UTC)

(edit conflict) It's more like asking if there's a number that's known to be prime, but has multiple prime factors. -- Coneslayer (talk) 12:32, 24 March 2010 (UTC)

Fine. That question is not flawed in the least either, it is perfectly sensible and meaningful and has a well-defined answer. Viz, I'll post it now. Note: despite the fact that it is not flawed in the least, and an infinite AI intelligence would answer "no", not meaningless or flawed or undecidable question or division by zero or anything else, it is possible the math reference desk will sputter out an answer more like this latter. If so, that will be a flaw in their contributors, not in the question, as the question is very easy to answer, though AI that can do so is still fifty years away. 84.153.234.218 (talk) 12:38, 24 March 2010 (UTC)

Ok, the question isn't flawed, the answer is just so obviously "no" that you are wasting everyone's time asking it. --Tango (talk) 12:42, 24 March 2010 (UTC)

Thank you, I know it might seem like I'm wasting people's time (I've removed the math reference desk question now) but that is why I stated right in the original question that there will be a followup question. It simply depends on this question. 84.153.234.218 (talk) 12:48, 24 March 2010 (UTC)

By the way, it is trivial for existing "AI" software to answer your question. Any worthwhile software proof assistant will be able to detect bare contradictions such as "prime number with prime divisors" and say that such a number does not exist. Staecker (talk) 12:57, 24 March 2010 (UTC)

The reason I said 50 years is the exact phrasing "asking if there's a number that's known to be". For the simpler question "do any numbers satisfy the condition: x" where x is the above (or, more simply "number is both 7 and the number is 8), can you link me to AI that will answer questions of this form? (ie of the form "are there any numbers that" but which will answer "no" for obvious answers such as "are both negative and positive" and so forth.) This question is important enough for me that I've asked it on the computing reference desk.84.153.234.218 (talk) —Preceding undated comment added 14:27, 24 March 2010 (UTC).

As Staekcer said, any proof assistant will be able to spot that there is a contradiction and thus no solutions. --Tango (talk) 17:42, 24 March 2010 (UTC)

Okay, it seems from the two responses given so far that the only two possible answers modern, Western science has to an observed miracle, ie an observation of something impossible are: "It did not happen as observed" or else "It happened as observed but what was observed is therefore not now considered impossible". In other words, is what you're both saying that there is no third option: "It happened as observed, and what was observed was and is now impossible." Is it correct to say that this third italicized option is simply not one that Science has? 84.153.234.218 (talk) 12:31, 24 March 2010 (UTC)

That statement is not one that anyone can make (consistently), because it contradicts itself. If something happens, it is not impossible. Tinfoilcat (talk) 12:37, 24 March 2010 (UTC)

Yes, that third option doesn't exist. You only need to look up "impossible" in a dictionary to verify that. --Tango (talk) 12:39, 24 March 2010 (UTC)

It sounds like you're using some nonstandard definition of the word "impossible". Maybe you mean "unexplainable"? or "unexpected"? (These latter are words typically used of "miracles". People who believe in miracles shouldn't call them "impossible"-- if you believe in miracles then you believe they are possible.) Staecker (talk) 12:45, 24 March 2010 (UTC)

While his/her wording may be technically incorrect, I think I understand exactly what his/her intent is. The trouble is that if something is "scientifically impossible" but actually happened (i.e. God circumvents the laws of physics), scientists would be so busy trying to retroactively come up with new laws that they would never realize it. Near Death Experience is something that certainly is recognized by mainstream scientists, but there are many people (including some scientists) that feel that there is no (and never will be) scientific explanation. The mere fact that every person in the country hasn't taken it as a sign to embrace a faith shows that they are far from "proving" this to be unexplainable. Also, in science, nothing has ever been proven, only strongly supported. Falconus^{p t c} 12:48, 24 March 2010 (UTC)

Do you have a source for the claim that there are scientists who feel that there will never be an explanation for near-death experiences? Zain Ebrahim (talk) 14:13, 24 March 2010 (UTC)

Near death experience#Spiritual viewpoints names a scientist that believes that conciousness survives after death. To be fair, it doesn't say that he says there is no scientific explanation. Also, I never said that anybody says that there will never be an explanation; I was referring to scientific explanations. Falconus^{p t c} 14:58, 24 March 2010 (UTC)

Yes, I'm also only referring to scientific (or "natural") explanations. You claimed above that there are people (including scientists) who believe that there will never be a scientific explanation. I'd like to see a source for that. Zain Ebrahim (talk) 15:11, 24 March 2010 (UTC)

Perhaps I was wrong, I haven't been able to verify my statement. I'm smiting it. Falconus^{p t c} 22:05, 24 March 2010 (UTC)

The problem here is that scientists do their work based on evidence. If there is solid evidence (observations) that something is happening that does not fit our current understanding of the laws of physics (or whatever) then we don't say "Something definitely impossible just definitely happened!" - we say "Huh! I guess our laws must be broken someplace." - and we rush off with great excitement to try to figure out what's wrong with those laws so we can fix them. So when the Michelson–Morley experiment showed us that the speed of light is a universal constant - we didn't say "Newton's laws of motion forbid this - so it's impossible" - we said "Something is wrong with our understanding of the universe". Eventually, we discovered that "Newtons laws of motion are wrong" and "Einsteins' theory of relativity is right".

Because we think that way - the hypothetical situation your question supposes couldn't happen. That's not because we know everything that it's possible to know and that our laws are perfect and therefore nothing "impossible" can ever happen - it's because once something happens that clearly contravenes those laws, we immediately say "One or more of those laws must be wrong". Things that violate known laws are sought out eagerly because it's only by 'breaking' a law that we find out that there is something wrong with those laws. Scientists get very excited when that happens because that's always really interesting - and it's the way you make a name for yourself and earn a Nobel prize!

SteveBaker (talk) 12:56, 24 March 2010 (UTC)

What about the discovery that the speed of the light is always the same? According to newtonian physics (the one which was universally accepted at the time) this was impossible.--Pokipsy76 (talk) 13:04, 24 March 2010 (UTC)

The OP has said, and clarified, that they are looking for things that are still considered impossible. --Tango (talk) 13:09, 24 March 2010 (UTC)

Continuing along Falconus's line of reasoning, if the entire world were just a virtual machine (The Matrix) and someone figured out how to exploit a buffer overflow in the rendering of physical objects, and by precisely crafting a certain physical object (on an atomic scale) were able to achieve so far just one single effect, which is to make that physical object disappear as an exception is thrown. So all the person can do so far, after years of trying to program something better, is to make a certain arbitrary physical object disappear upon being produced (we're talking about something on the scale of a processor, where the pattern is very small also). So they are frustrated and want more money so they can hire some engineers to help them, they want to rule the world. They approach the James Randi company with their claim: They are not going to tell you the pattern until an agreement on the test methodology, but the claim is that they can make a solid physical object by steps, that will be an existing, actual, physical CPU-like, physical object, and by adding one little bit more to it it will disappear, the supernatural claim. Now this is a very supernatural claim, that you can just make a large physical object disappear from the universe, but my problem is that what's to stop the James Randi company from agreeing, and then, once the preliminary test had been done, stating: "You know what, actually we cheated. We had so many scientists looking at this preliminary step that this object-disappearing thing is now known to be physically possible. I bet you could do it in a repeatable way a million times over. In fact, so could anyone else - we even photographed the pattern you used, and we're trying to reproduce it again." So they don't agree to a final test. Moreover, why would they ever agree to the final test, once the preliminary test has been shown to be physically possible? Isn't the moment you do something, even if it is by means of hacking the physical world on a supernatural level, doesn't the moment you share that with the world means the physics jumps to encompass the metaworld as well? In short, I think for this reason that the James Randi proposition is inherently fraudulent, it does not appear to me to be made in good faith. If it is made in good faith, can someone explain to me how someone with the object-disappearing insight I have conjectured above could use it to get $1,000,000 from the Randi corporation? Thank you. 84.153.234.218 (talk) 13:58, 24 March 2010 (UTC)

I think Randi's offer is clearly regarding things that are deemed supernatural now. That science will try (and probably succeed eventually) to explain it shouldn't be a factor it determining whether something qualifies. --Tango (talk) 14:25, 24 March 2010 (UTC)

As a mathematician of course I think the answer is "no, by definition" and indeed Polkinghorne often says that even the Resurrection is not impossible or miraculous to Christians, but "inevitable" when you have the most complete and consistent way of looking at the universe. --BozMo talk 14:39, 24 March 2010 (UTC)

Time to tell us your follow up question, even though you didn't get the answer you wanted... Dauto (talk) 14:28, 24 March 2010 (UTC)

Agree, whats the follow on? --BozMo talk 14:39, 24 March 2010 (UTC)

Among the learned, meteorites were considered "impossible" until the 19th Century. 63.17.46.33 (talk) 04:26, 25 March 2010 (UTC)

the followup question

it seems we have established it is the scientific consensus that whatever happens, ipso facto was possible when it happened. But if the latter word, possible, means anything at all in a physical sense, it must mean that other things were not possible.

Let me reiterate "in a physical sense." I don't mean, in terms of how people thought, or in terms of what was expected, or had been experienced previously, or was predicted in someone's equation. I mean, what was possible in terms of reality; of physical truth; of the actual way things are (as opposed to are understood), the facts of the situation, the physical nature of reality.

In this latter sense, what is possibility? —Preceding unsigned comment added by 84.153.234.218 (talk) 15:04, 24 March 2010 (UTC)

First of all, have you read possibility? It links to several sub-definitions, from a philosophical and logical point of view. The closest we can come for a definition in a scientific context is probably from "logical possibility" - something to the effect of "A logically possible proposition is one that can be asserted without implying a logical contradiction." It is up to the scientist to define the relevant axioms which might be contradicted. Typically, scientists axiomatically assume that there is some degree of consistency in the laws of physics, and that our observations of the universe reveal facts about our surroundings. These are pretty basic axioms; all the rest of science is built on those two ideas through the scientific method.

SteveBaker, Tango, and the others have stated this very well above. Anything at all is certainly possible. Scientists use the recorded body of observed evidence to evaluate how likely something is (assuming, of course, that the universe has some level of consistency and predictability). If you spend a good amount of time reading proper scientific literature (textbooks, peer-reviewed publications, and so forth), you'll see that any well-respected, disciplined scientist is very careful about how they use terminology when describing the hypothetical. I don't think I ever read a textbook that said, for example, that a violation of physical law is impossible. Sometimes, there will be conditional possibility; "antigravity boots are impossible unless our understanding of conservation of energy is flawed," for example, is a logical deduction that forces a scientist to weight a claim against a well-tested and widely-understood idea. This uses scientific analysis of consequences in order to tease out the inherent implications of certain possibilities. Ultimately, these careful and detailed explanations point out that modern science is based on generalizing ideas about the things which we have already observed, and not excluding the things which we have not. At the same time, an intelligent scientist has reservations and skepticisms, which are necessary to keep an open mind well-disciplined. Nimur (talk) 15:31, 24 March 2010 (UTC)

The OP's promise of follow-up questioning suggests they seek a debate about the place of supernatural miracles in modern Western science. This Ref. Desk is not the place for such debates that tend to founder on strawman claims like Science has failed to prove that my God doesn't exist. Below is a taxonomy of scientific interpretations of observations. It seems the OP will argue from classical premises that there can be supernatural causation. Post-classical science including quantum mechanics never claims to have eliminated the supernatural but neither does it invalidate the stance of atheism.

SCIENCE EVOLUTION     | CATEGORIES OF OBSERVATION             XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
==============================================================XXXXXXXXXXXXXXXXXXXXXXX/           \XXXXXXXXXXXXXXXXXXXXXXXXXXXX
Pre-intellectual      | Visible or          | Unknown cause   XXXXXXXXXXXXXXXXXXXXXXX SUPERNATURE XXXXXXXXXXXXXXXXXXXXXXXXXXXX
                      | remembered cause    |                 XXXXXXXXXXXXXXXXXXXXXXX\           /XXXXXXXXXXXXXXXXXXXXXXXXXXXX
----------------------|---------------------|-----------------XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Primitive             | Known cause         | Unknown cause   XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
----------------------|---------------------|-----------------------------------------------------XXXXXXXXXXXXXXXXXXXXXXXXXXXX
Enlightened classical¹| Known cause         | Knowable cause  |	Unknown	    | Unknown unknowns XXXXXXXXXXXXXXXXXXXXXXXXXXXX
----------------------|---------------------|-----------------|----------------|----------------------------------------XXXXXX
Post-classical        | Known cause         | Analyzable cause| Fundamentally  | Unknown unknowns | Unknowable unknowns XXXXXX
                      |                     |                 | indeterminate² |                  |                     XXXXXX
------------------------------------------------------------------------------------------------------------------------------

¹Unknown unknown - Donald Rumsfeld 1932 -

²Uncertainty principle - Werner Heisenberg 1901 - 1976

Cuddlyable3 (talk) 15:47, 24 March 2010 (UTC)

I fixed your ASCII art, it was broken. Nimur (talk) 16:48, 24 March 2010 (UTC) Thank you. Cuddlyable3 (talk) 21:39, 24 March 2010 (UTC)

One fine point we should make is that when the seemingly impossible happens, it hasn't changed what is actually possible, just our (formerly incorrect) view of what is possible. Therefore, nothing really impossible has, or can, happen. StuRat (talk) 15:54, 24 March 2010 (UTC)

See also Kiri-kin-tha's First Law of Metaphysics. -- Coneslayer (talk) 16:53, 24 March 2010 (UTC)

no, I had absolutely no inkling of an intention to start any debate. On the contrary, I expect all of the answers to my mundane physical questions to be quite uncontroversial. It is only for my personal edification, being as how I lack the funds for a first-rate education through the college and maybe masters (in philosophy of course) level. 84.153.234.218 (talk) 18:02, 24 March 2010 (UTC)

Magicians make a living demonstrating things that are impossible according to known laws of science. I have seen a close up magician sitting at a table with several observers make an ordinary baseball appear in an ordinary teacup which was clearly empty before the trick was done, a clear violation of the laws of physics. I expect he used slight of hand. Stage magicians have made elephants appear on stage, and have travelled through solid walls, or have levitated themselves or volunteers. Again, I expect this is done through machinery and misdirection. That would be the common answer to other seeming violations of the laws of physics: it was a trick. When a scientist announces he has demonstrated cold fusion, or an inventor announces his motor/generator produces more electricity than the batteries put into it, it is attributed to errors in measuring the energy input and output (or to simple chicanery). When someone announces he has discovered a way to do something thought impossible, modern science calls for him to writeup the method, and for others to be able to replicate the work in their own labs. Edison (talk) 20:17, 24 March 2010 (UTC)

I agree with the above by Cuddlyable3 but I think for completeness you should consider the question about whether people exist, in the sense of whether the appearence that we are conscious and able to decide or act is a delusion. I think you will only really get a handle on what is and isn't supernatural or "God" or anything once you have reconciled your view of what people are with the fact people are also incapable of doing anything "impossible". --BozMo talk 22:17, 24 March 2010 (UTC)

The answer is no. Impossible things do not happen, by definition. There are things that have happened (and still do happen) which science has no explanation for, there may be things that happen for which science will never have an explanation, but if science says something cannot happen, and it does happen, then scientists change their theories to fit the observed evidence. Science isn't some magical claims about ontological truths; science is an ongoing effort to understand the world through careful, reasoned observation. --Ludwigs2 23:02, 24 March 2010 (UTC)

I feel the urgent need to mumble something about the multiverse in reply to the question "what is possibility". Things which are not possible in our universe may be possible in a variation of it. However, logical contradictions remain impossible, since their meaning is undefined. The laws of physics in the multiverse could perhaps resolve to the set of everything logically possible (as Nimur said), which removes the problem of the set of possible things being arbitrary. 81.131.4.31 (talk) 16:01, 25 March 2010 (UTC)

Someone may have written this before, cannot be bothered to read all above, but the Catholic church requires impossible things - ie a miracle - to happen when it creates a new saint, such as this man http://online.wsj.com/article/SB10001424052748704896104575139691810314722.html?mod=WSJ_hp_editorsPicks as an aethiest I think its silly. When an impossible thing happens, it becomes possible, and is no longer an impossible thing. So heavier-than-air flight was once an impossible thing, but now it is not. Edit: someone must have deleted the 'signature' information, making it seem that the below paragraph was written by me. I've added the 'signature' again here: 78.144.250.185 (talk) 16:08, 28 March 2010 (UTC)

The fact that something has happened doesn't mean that it is "possible" existentially. Right now the earth is in a certain spacial relationship to every other body in the solar system, including asteroids, comets, and everything in the Kuiper belt; this relationship "has happened." However, it is impossible that it will ever happen again. Yes, it was "possible," but it no longer is -- and something that is impossible in the future is impossible, existentially. The past doesn't exist anymore and will never exist again. 63.17.79.42 (talk) 04:10, 28 March 2010 (UTC)

How much of the Sun's energy is used for light and how much is used for heat?

I just read in "Living in the environment" by G. Tyler Miller Jr. that only 5% of the electrical energy that comes into a light bulb is used to get light, while 95% is becoming heat energy. What is the equal relationship for the sun? //moralist 12:25, 24 March 2010 (UTC)

According to Luminous_efficacy, the sun comes in at about 12%...however, that article says that a 110volt incandescent lamp has an efficiency of between 0.7% and 2.6% (depending on the wattage) and that only photographic and projector lamps get up to 5%. Compact florescent lamps make 8 to 11% efficiency and LED lamps can reach 12% - so you can do better. Anyway there are some nice tables at the end of that article that summarize this stuff very nicely. SteveBaker (talk) 12:41, 24 March 2010 (UTC)

The sun is very nearly a black body with a temperature of 5800 K. It emits a mostly continuous spectrum with a maximum at around 500 nm. Light bulbs are also approximately black bodies, but radiate at between 2000 and 3300 K, meaning that their maximum emission is around 800 nm or longer, already outside the visible spectrum. This is further complicated because the eye does not perceive all visible wavelengths equally. If you look at Luminous efficacy, you can see that light bulbs have a luminous efficiency between 0.7% and 5.1%, the sun has an efficiency of 12%, and sunlight has an efficiency of 14% (the difference is that sunlight is filtered through the atmosphere, which removes mostly frequencies outside the visible range, improving the nominal efficiency, see File:Solar_Spectrum.png). --Stephan Schulz (talk) 12:50, 24 March 2010 (UTC)

Okay, thank you for your excellent answers! What about the heat energy, thought? The heat is also very important both in light bulbs and especially the sun, so how much of the sun's energy becomes heat? Is it the rest? And in comparison with for example radiators, how much of the energy used to radiators is used to heat up? //moralist 13:07, 24 March 2010 (UTC)

The image I linked (File:Solar_Spectrum.png) has the visible part of the spectrum marked. The majority of non-visible radiation is in the infrared and longer for the sun, but a significant part is ultraviolet (that's why we get sunburns ;-). For light bulbs, very little of the energy is in the ultraviolet. If you are not afraid of formulas, check out Planck's law for the gory details. --Stephan Schulz (talk) 13:23, 24 March 2010 (UTC)

Pretty much all energy ends up as heat eventually. Whenever electromagnetic radiation, of whatever frequency, is absorbed it heats up whatever it is absorbed by. Even the visible light will end up as heat once it is absorbed. So, any heater will be 100% efficient. The heat may not go where you want it, but it will definitely heat something up. --Tango (talk) 13:24, 24 March 2010 (UTC)

I want to point out that Luminous efficacy includes a factor related to the human eye's sensitivity which seems foreign to the quation asked. Most of the sun's energy is acctually in the form of visible light. Also worth pointing out that "heat" in this context is electromagnetic radiation and therefore division between light and heat is also dependent on the human eye'e inability to see those longer wavelengths. Dauto (talk) 13:42, 24 March 2010 (UTC)

This correlates with another question I thought of before, so I continue: The heat death of the universe is a known thing, but what happens with all the other kind of waves (those you talk about above) in the heat death? I mean, will all the lightwaves become entropy (some sort of disorded light or something) too, or will they eventually become heat? And what about sound waves, will the heat death of the universe have a constant disorded noise-sound? //moralist 18:44, 24 March 2010 (UTC)

Entropy isn't a thing, it's a property of a system. If the universe goes into a heat death (which isn't certain, but it does seem the most likely fate) then there will be electromagnetic radiation just flying around very rarely interacting with anything (which is a high entropy state). If the radiation is absorbed by something and heats it up then it will emit more radiation (as thermal radiation) anyway, so the radiation will never disappear. The expansion of the universe will result in the radiation gradually getting longer and longer wavelengths (that is, corresponding to cooler and cooler thermal radiation). Sound is pressure waves, so it needs a medium to travel through. There is no such medium in space, so there is no sound ("In space, nobody can hear you scream."). --Tango (talk) 18:50, 24 March 2010 (UTC)

standing on one leg with eyes closed

I can stand on 1 leg for more than 30 seconds easily. But, if I close my eyes, I can only do it for 10 seconds max. Why is this so? Obviously I understand that vision has an important part in helping us see where we are going when moving but I assumed it was of limited use in keeping our balance when standing up, after all we don't have to look at our feet to maintain balance when standing. Any suggestions would be great, thanks. RichYPE (talk) 13:19, 24 March 2010 (UTC)

Eyesight is actually a very important part of balance. You have a sense of balance from your inner ear and you have proprioception (the sense of where your various body parts are from the feedback from your muscles), but eyesight is more precise than either of those and will override them. That is why it is difficult to walk when what you can see around you is moving in a way that makes your brain think it is you that is moving (science museums sometimes have demonstrations of this). If you close your eyes, you can walk fine, since your brain relies on balance and proprioception, but with your eyes open it assumes your vision is right and your balance/proprioception wrong, and you fall over. --Tango (talk) 13:30, 24 March 2010 (UTC)

WOW!! I was going to test it and expected to reply that maybe the OP just has some personal neurological issue or something. I stood on one leg with my eyes open, and started timing with my mobile phone, then surfed the web a bit and so on, until I got bored. It was easy, well over a minute etc. Then I switched legs, started the timer, and closed my eyes. It very quickly got very very hard, and by second 12 I had lost my balance (that's when I opened my eyes and looked). WOW.

The most amazing thing about this is that while standing on one leg it was no effort, it was 100% stable, not like walking a tightrope. But with the eyes closed it was like walking a tightrope.

The answer is that there is a totally subconscious feedback mechanism with the eyes. You THINK that you aren't looking at the background when standing on one leg and looking at the mobile phone, but in fact your subconscious is doing feedbakc on the BACKGROUND you see. While doing the same with the eyes closed, the information disappears, and only your uh ear balance sensory organ thing shows you which way you're facing, and the feedback becomes like tightrope walking. AMAZING. 84.153.234.218 (talk) —Preceding undated comment added 13:31, 24 March 2010 (UTC).

I've often wondered how it is that birds are so much better at balancing on one leg than humans are. Not only can they stand on one leg for hours at a time - but they can actually sleep whilst standing on one leg, *with their heads turned through 180degrees*. Believe it or not, if they do this, it's an indication that they're relaxed, healthy and getting a nice, deep sleep! Any ideas how they manage this, folks? --Kurt Shaped Box (talk) 14:10, 24 March 2010 (UTC)

That's an easy one. They have a lower center of gravity. It's the same way that it's easy to balance 10 matches on the head of a match - you just arrange them so that the center of gravity is real low. My hypothesis is that it's much easier to crouch on one leg while closing your eyes. Let me test it... 84.153.234.218 (talk) 14:41, 24 March 2010 (UTC)

I was under the belief that birds could lock their legs and feet so that they could effortlessly perch in position, but I'm having trouble coming up with anything in Bird anatomy or reliable sources to support this belief. -- Coneslayer (talk) 15:01, 24 March 2010 (UTC)

Yes, I've read that (somewhere) too. When a bird sleeps, the muscles/tendons in its feet 'lock' so that it doesn't fall off its perch. It's a slightly different issue from being able to maintain balance on one leg though... --Kurt Shaped Box (talk) 15:27, 24 March 2010 (UTC)

Only some birds can perch on branches like that. Not all of them have locking feel. By the way, did you ever see a goose perched in a tree? --Cheminterest (talk) 21:10, 26 March 2010 (UTC)

I found something similar recently, its very easy to walk along a balance beam, using both feet, but the moment I closed my eyes it became incredibly difficult--Jac16888^Talk 14:55, 24 March 2010 (UTC)

This is the principle behind Romberg's test. Axl ¤ [Talk] 18:40, 24 March 2010 (UTC)

Another experiment which I've tried before: try balancing a broomstick upside-down on the open palm of your hand. It's easy enough if you keep your eyes fixed at the top (bottom) of the broom. The minute you close your eyes or look away, e.g. look down at the palm of your hand, you are unable to balance it properly. Zunaid 22:04, 24 March 2010 (UTC)

I was able to maintain my balance for much longer, but with significantly more wobbling than with my eyes open. 67.243.7.245 (talk) 22:27, 24 March 2010 (UTC)

Another one that always bothered me is that I can fill a glass 90% full of water - and walk around at full speed without spilling a drop - all without looking at the glass. Turn the lights out and you can't take three steps without spilling it. SteveBaker (talk) 00:19, 25 March 2010 (UTC)

I've long suspected that the ability to do this is unconsciously practised by carrying beer in the brim-full measure beer glasses customary in the UK. I wonder if a study comparing this ability's levels in the UK to those in countries (such as Germany) where beer glasses are customarily not filled to the brim would reveal significant differences. I'd like to offer my availability as one of the test subjects. 87.81.230.195 (talk) 09:49, 25 March 2010 (UTC)

I bet it's because when your eyes are open you know the exact direction "up" (due to the doors etc), and that this benefit would disappear in a special room that was all monitors showing all different skewed directions - you could only not spill the water then if you were looking at it directly. It would be interesting to verify somehow. 84.153.234.218 (talk) 10:02, 25 March 2010 (UTC)

You could verify it by carrying a glass through a room with flat floor but everything that should be vertical tilted a few degrees. I believe such experiments have been done and it does make it difficult to balance. --Tango (talk) 12:31, 25 March 2010 (UTC)

A wonderful example of this is a carnival trick where you walk through a rotating tunnel. You're walking on a perfectly stable raised platform, but everything around you is spinning around the axis of the direction you're trying to walk. With your eyes open it is extremely difficult to walk straight and upright because your eyes are telling you that you're falling over. (They've got one of these at the Ripply's Believe It Or Not museum in Orlando. It's probably the most Authentic thing in the place.) APL (talk) 02:13, 26 March 2010 (UTC)

How long does it take to see changes in blood cholesterol levels?

When a person switches from a very high cholesterol diet to a very low one, is the change immediately visible on blood tests? If someone is told they need to fix their cholesterol intake, then does so, how long should they wait before getting re-tested? 202.10.89.185 (talk) 14:54, 24 March 2010 (UTC)

The medical professional that told them they needed to get their cholesterol levels down would be the best person to ask. It won't necessarily be the same for everyone. --Tango (talk) 18:51, 24 March 2010 (UTC)

Hardly a reliable source or a good study, but a TV program in the UK took a healthy man with a good diet, and an overweight man who had a terrible diet, and switched their diets. Within, I think, two weeks - the healthy man's cholesterol was worse than that of the overweight man. Should I Worry About...? was the program. Here is a description of the episode. Anyway, I just thought this might give you a rough idea of the timeframe involved. Vimescarrot (talk) 09:52, 25 March 2010 (UTC)

Another vacuum cleaner drive belt bites the dust

Vacuum cleaners with rotating brushes at the carpet-vacuum interface commonly use a rubber "drive belt" to transfer rotary motion from the motor spindle to the brush. When the brush is prevented from rotating due to, for example, a shoelace becoming ensnared and wrapped around the brush, the motor spindle continues to turn while the drive belt slips. The drive belt is heated until it fails and breaks, disconnecting the brush from the motor. Are there no alternatives that do not require the replacement of belts but use a mechanism which slips when unable to turn? ----Seans Potato Business 14:59, 24 March 2010 (UTC)

It depends on whether you live in a Communist or a Capitalist country. In a Communist country linear programming is used to allocate resources such that a thermal or torque cut-off switch would probably be included to make the system operate more soap bubble/wire frame like. In a Capitalist system you want belts to burn out fast as possible so you make the contact surfaces extra rough and small radius. 71.100.11.118 (talk) 15:06, 24 March 2010 (UTC)

Your rant is off-topic, but I'm curious: is there any evidence that communist countries produce longer lasting products? I understand the logic, but it doesn't seem to happen in practice. --Tango (talk) 19:05, 24 March 2010 (UTC)

@Tango evidence Exhibit AK-47: In service 1949-present. Number built: 100 million. Exhibit M14 In service 1957-present. Number built: ~1.5 million. Cuddlyable3 (talk) 21:30, 24 March 2010 (UTC)

@Cuddlyable3 evidence Exhibit Big Rigs: Over the Road Racing: Without a shadow of doubt, the worst computer game ever written by far - developed by a team in the Ukraine. Just amazingly, spectacularly inept. Actually - the disks last for an unrivalled number of years...but only because nobody is stupid enough to play them. SteveBaker (talk) 00:15, 25 March 2010 (UTC)

My favorite part is the complete lack of collision detection except for the start/finish line, where half the time you win when you cross the line to start. Horribly made but incredibly entertaining! -Pete5x5 (talk) 03:40, 25 March 2010 (UTC)

The claims on the back of the box and the screen-shots of things that completely don't exist in the game are quite impressive - they claim you'll be evading the police and smashing through roadblocks...but there are no police or roadblocks anywhere in the game! I also like the way the programmers limited the speed of your truck to 100mph or so - but forgot to check for large negative speeds. Hence you can accelerate in reverse to literally unlimited speeds! SteveBaker (talk) 02:02, 26 March 2010 (UTC)

Tetris vs Boulder dash. --Polysylabic Pseudonym (talk) 10:07, 25 March 2010 (UTC)

Soviet vacuum cleaners suck blow but this hardware trumps any software so now All your base are belong to us. Cuddlyable3 (talk) 18:41, 25 March 2010 (UTC)

Off-topic-y: It's definitely the case that the Soviet design ethos worked better in some cases than others. With regards to weaponry, the Soviets were pretty good. Their rifles, tanks, planes, etc. were usually not as high-performing at US models, but were cheaper to develop and produce, and could generally be serviced by people with far less training than high-performance Western models. The Soviet ethos was to make things that could be serviced in the field by someone with about as much training as an auto-mechanic, and would last forever. That comes with some performance cost, but allows you to make up for it in volume and overall lower investment cost. There are lots of academic papers on this in regards to things like jet development, firearm, rockets, etc. --Mr.98 (talk) 13:06, 26 March 2010 (UTC)

A mechanical carpet sweeper uses a drive wheel (driven by the user moving the thing back and forward) to run a belt or gears which rotates its brushes. People still swish their vacuum cleaners around as if they worked this way, so you could always put this mechanism back into powered cleaners. -- Finlay McWalter • Talk 18:30, 24 March 2010 (UTC)

71.100.11.118 offered an informative answer wrapped in an entertaining joke (though I didn't get every aspect of it. Joke aside, I can't see evidence cleaner manufacturers are motivated to sell large quantities of replacement drive belts.)

Many motors in industry do not burn out their transmissions in the event of a jam. If the motor drove the brush directly, or through a gearbox, I think the motor could usefully be fitted with a power cut off. A clutch could usefully slip (though that would eventually burn out too), this is essentially a role that the drive belt plays. A magnetic drive would have a maximum torque before slipping (though would still generate some heat.) However, I suspect that my ideas are more expensive than occasionally replacing a drive belt - it is a cheap alternative to wrecking a bearing or the motor windings.

I think Finlay McWalter's idea is more cost effective.

--Hroðulf (or Hrothulf) (Talk) 19:13, 24 March 2010 (UTC)

Compare the Trabant with the Reliant Robin. You get an extra wheel under Communism. 78.149.198.14 (talk) 00:49, 27 March 2010 (UTC)

household voltage and frequency

If the world (or a new [artificial] planet) had it to do over again what would be the most efficient voltage and frequency (with all other things considered like interference and danger) for household consumption? 71.100.11.118 (talk) 15:01, 24 March 2010 (UTC)

60 Hz @ 240volts. This frequency produces low saturation of transformers (as opposed to 50 Hz) and so reduces power loss, and so can be made smaller. This makes cabling cheaper for carrying same amount of power. 240v needs smaller conductor cross section for the same amount of power (the resistance gets proportionaly smalller as you increase the volatge). Voltages higher than this increase electrocution risks to unacceptably higher levels (assuming the 240 volt tolerance is no more than + 6 % or 254v which is what it is likely to be at the sub-station).--Aspro (talk) 15:35, 24 March 2010 (UTC)

400 Hz @ 230 volts r.m.s. The higher frequency as used in avionics allows size and cost savings on transformers and filters. For starting anew, the electric power net will carry Internet data and accurate time and frequency reference signals. Cuddlyable3 (talk) 16:52, 24 March 2010 (UTC)

I though 400 hz was already in use with avionics but was declining due to skin and proximity effect resulting in the need for special (hollow stranded or thicker) conductors to reduce resistivity. 71.100.5.192 (talk) 20:36, 24 March 2010 (UTC)

Going from 60 to 400 Hz the skin depth reduces to 39%, e.g. in copper it is 8.5mm@60Hz and 3.3mm@400Hz. That means thicker cables for long-distance transmission but not more expensive copper because the resistivity of the cable core is largely immaterial. See Aluminium Conductor Steel Reinforced. Cuddlyable3 (talk) 21:25, 24 March 2010 (UTC)

High tension at 400 Hz?!!
The current carried by the corona is determined by integrating the current density over the surface of the conductor. You'd be limited to lower voltages in high tension cables. The voltages are at their maximum for the newer 50 and 60 Hz grids.--Aspro (talk) 23:45, 24 March 2010 (UTC)

Power transmission lines are dimensioned to carry a desired voltage and there is no maximum limit if one is building afresh. Why should corona loss increase on going from 60 to 400 Hz at the same peak voltage? Increasing the radius of a cable reduces the corona current. Cuddlyable3 (talk) 18:22, 25 March 2010 (UTC)

I don't disagree with any of the above answers. I think an important consideration is that there is no best solution to the problem. Lowering the voltage has safety benefits and lowers the cost of insulation but it requires higher currents and that, in turn, requires more copper and hence more weight and more cost for the copper. Alternatively, raising the voltage causes lower currents and requires less copper and hence less weight and less cost. However, raising the voltage requires more weight and cost for insulation, and progressively there is reduced safety. That explains why there is a proliferation of voltages and frequencies around the world. There are even situations where direct current is preferred over alternating current, but for household consumption I believe alternating current is better because of the ability to transform voltages from high voltage for long-distance transmission to low voltage at the point of consumption. Dolphin51 (talk) 22:20, 24 March 2010 (UTC)

History explains best why there is a proliferation of voltages and frequencies around the world. They were based on the best compromises that technology provided and economics allowed at the time that each system was originally founded. The trade off's and compromises are well understood. The next grids (as economics allow) will be DC. As for local distribution around the house, who knows, as 400 Hz does then have advantages ( but the main circuit frequency will still remain at 60 Hz or 50Hz for the reason I have previously given). Well have to wait until China is ready to tell us what the new standards will be. The service life of capital equipment is 25 to 50 years, so I don't think there is a terrific urgency --Aspro (talk) 00:09, 25 March 2010 (UTC)

population stratification in a normal sample of the general population

This question relates to genetic research. I am looking for a scholarly reference (or several) that discusses the issue of 'population stratification' in a 'normal sample'. I have searched the library databases for these and related terms (like 'population substructure'). I am not interested in a discussion of the issue in a case-control design or in a family-based study and have attempted to remove these terms with a Boolean search command. I found one PowerPoint presentation by someone at the Centers of Disease Control that said that population stratification was less of an issue in a normal sample but there was no citation for that particular bullet point and no name on the file. I assume there are statistical reasons why population stratification might be less of an issue when people vary on a continuous phenotype but that stratification is still an issue if there are different ethnic groups (or any genetic substructure) in the sample tested.

Citations (partial or complete) and explanations of the reasoning behind this issue are especially welcome. Thanks!Becstudent (talk) 15:25, 24 March 2010 (UTC)

Dentists identifying need for fillings by x-ray

(not after medical advice just wondering). I was at the dentist today and my dentist checked my teeth in the usual way (sharp metal stick, mouth open, little mirror) and said 'they all look ok' then they said they'd wait for the x-rays back. They get the x-ray back and within seconds i'm now at the dentist for 3 treatments - 3 fillings! My assumption is that the x-ray is finding 'hidden' decay that is perhaps covered by an existing filling or is between teeth or whatever. Anyhoo my questons...Is this quite new a new technique? (in my 27 years of dentisting i've never had a check-up like it)...Is my assumption in the right ball-park? Cheers 15:36, 24 March 2010 (UTC) —Preceding unsigned comment added by 194.221.133.226 (talk)

In my experience (in the USA), no, this is pretty common. The x-rays can find things that are not large enough to be easily seen, and they can identify "problem areas" that have not yet matured into full cavities yet. My anecdotal experience is that some dentists are more enthusiastic about dealing with minor cavities or problem areas than others. --Mr.98 (talk) 15:43, 24 March 2010 (UTC)

To elaborate, both common and not particularly recent (for the US). I've had x-rays at routine dental visits for at least 25 years, though I seem to recall that as a child they weren't a feature of every visit (perhaps every second or third), I assume to reduce radiation exposure. These days I get them snapped at every 6-month check, and the "film" is instead some x-ray-reactive USB dongle that immediately uploads to a PC monitor beside the table. Pretty slick. — Lomn 15:53, 24 March 2010 (UTC)

See also Dental radiography. TenOfAllTrades(talk) 16:28, 24 March 2010 (UTC)

Well I don't know where you are, OP, but I've been having dental X-rays since 1980 in the UK... --TammyMoet (talk) 09:16, 25 March 2010 (UTC)

Dentist here -- certain lesions (areas of demineralization that are commonly referred to as cavities) are evident only clinically (that is, by physically looking at the teeth in the mouth) and others are evident only radiographically (that is, they can be seen on an x-ray film) and others are evident both clinically and radiographically. Generally, occlusal caries (decay on the biting surface of teeth) can be seen clinically, but if such decay is small-to-moderate, it might very well not be detectable radiographically -- this is because the buccal-lingual dimension of the tooth in question (that is, the thickness of the tooth in the cheek/lip-to-tongue dimension) is too much to detect small changes in the mineralization of the tooth structure. Such decay is usually detected either visually or with an explorer (and there is certainly a bulk of literature debating the specificity and sensitivity of such a "sticky catch" method of detecting such decay). Another type of region of decay is interproximal decay that exists on the surface of a tooth that is adjacent to another tooth. Such an area, as you can probably see for yourself in the mirror, is hardly visualized in a clinical exam and especially for posterior teeth (premolars and molars), radiographic detection is really the only way to visualize such demineralization. I have frequently checked a patient's mouth and told him or her that they appeared all clear only to find 3, 5 or even 10 "cavities." This photo montage is a great example of what appears to be very slight clinical decay (a mere dot in the central fossa of a maxillary molar) but what is really a ridiculously large interproximal lesion that was actually contiguous with the surface of the root (see C in the montage) after I removed tooth structure only from the top of the tooth (i.e. the side hole was already there). Such a situation occurred because this case was from a location at which I worked in which practitioners would routinely not take radiographs and treat patients on a clinical basis only. The little black dot didn't seem too bad and so it had gone untreated for probably over a year (decay is very slow). The tooth was extracted because the patient could not afford the cost of restoring the tooth with crown lengthening, root canal therapy, post and core and crown. DRosenbach ^{(Talk | Contribs)} 20:09, 26 March 2010 (UTC)

What's in a can of tuna?

While eating a can of tuna for luch, I was curious and decided to look at the ingredients, and what I found confused me. According to the Percent Daily Values label, one serving is 56g of drained meat, but the figures add up to a lot less than 56g — it's 1g fat, less than 1g of carbohydrates, less than 1g of fiber, and 11g of protein, and the only other figures (cholesterol, sodium, and potassium) add up to 300mg. What could the other 40g+ of substance be? Is it all water? Nyttend (talk) 16:15, 24 March 2010 (UTC)

Calories/Energy? 194.221.133.226 (talk) 16:23, 24 March 2010 (UTC)

Yep, it's water. This site gives the water content of canned tuna as 73%, give or take. TenOfAllTrades(talk) 16:25, 24 March 2010 (UTC)

Water will be present in drained tuna as Ten states. And 194, calories/energy are recorded as fat, carbohydrates, proteins and alchohol (which I presume tuna will not actually contain). Googlemeister (talk) 18:35, 24 March 2010 (UTC)

Most forms of animal life are 60-75% water. So virtually all meat that hasn't been cured or dried in some way will have a similar discrepancy between the tally of caloric content and the per serving weight. —ShadowRanger ^(talk|stalk) 20:52, 25 March 2010 (UTC)

Not all substances in foods contain calories. Cellulose, for example, is not metabolized, so it does not contain calories.--Cheminterest (talk) 21:04, 26 March 2010 (UTC)

supermarket salt + vinegar

Using this combination quite often to make marinading brines, I wonder how much a hazard sodium ferrocyanide in consumer salt is? John Riemann Soong (talk) 17:57, 24 March 2010 (UTC)

I see that Morton salt sells a no-additive "canning and pickling salt" so there may actually be an issue or at least a perception that there is an issue. Rmhermen (talk) 18:59, 24 March 2010 (UTC)

I think the no additive is because it does something to the pickle, not because of the hazard. It's not very hazardous. There is little of it in there, and cyanide in general is not super hazardous in low quantities. Some poisons have cumulative damage (arsenic or lead for example), but cyanide doesn't since the body can metabolize it. So as long as it doesn't kill you it's not damaging. Ariel. (talk) 19:34, 24 March 2010 (UTC)

Morton says the canning salt is due to the anti-caking agent settling at the bottom of your jars of pickles. Recipes I've read that call for it say the same thing. --Sean 19:58, 24 March 2010 (UTC)

The WP article actual provides a link to a toxicology report. [6] As Ariel points out: Cyanides are metabolised. It also occurs widely in nature including in the foods we eat. [7]. So I can not see an issue. Mind you... why should it be in brine? Manufactures buy what ever salt is the cheapest and don't need to specify anti-caking salt.--Aspro (talk) 23:24, 24 March 2010 (UTC)

I interpreted this as being about making your own pickles, not store-bought ones. Rmhermen (talk) 00:17, 25 March 2010 (UTC)

Ferrocyanides and ferricyanides aren't very toxic, unlike cyanides, because the iron is bound strongly to the cyanide, preventing its release.--Cheminterest (talk) 21:03, 26 March 2010 (UTC)

Unusual rock

Several years ago, I found an unusual rock in Riley County, Kansas on the shores of Tuttle Creek Lake. I'll do my best to describe it.

It's about the size of my hand. It's dark and very porous (like those lava rocks that people use in landscaping) and it has all kinds of different smaller rocks stuck in it. One side of it is more porous than the other side which is rougher and less porous. I broke it in half and you can clearly see how the layers have different porosity. I've never seen a rock like this in Northeast Kansas since most of the rocks here are light colored limestone.

I'm no geologist, but it almost seems like a volcanic rock to me. I was under the impression that there weren't any igneous rocks in Kansas. Could it have been something carried here by glaciers during the ice age? Is it a meteorite?

I took several pictures of it, but the lighting is bad and they're out of focus. I did the best I could.

http://img232.imageshack.us/img232/5144/dscn0190j.jpg http://img413.imageshack.us/img413/8402/dscn0193t.jpg http://img689.imageshack.us/img689/5870/dscn0194j.jpg http://img715.imageshack.us/img715/2195/dscn0200.jpg http://img291.imageshack.us/img291/9512/dscn0201z.jpg http://img339.imageshack.us/img339/7301/dscn0202.jpg http://img708.imageshack.us/img708/7194/dscn0208e.jpg http://img718.imageshack.us/img718/8140/dscn0216b.jpg http://img689.imageshack.us/img689/2358/dscn0217y.jpg —Preceding unsigned comment added by 63.245.168.34 (talk) 23:32, 24 March 2010 (UTC)

It looks volcanic to me (though I'm not an expert). Kansas doesn't have any active volcanoes, and hasn't for tens of millions of years. It's possible the rock you found is in fact very old (dating to an age with local volcanism), but it is more likely that is was transplanted there. Kansas and much of the American Midwest is downwind of the Yellowstone supervolcano. Geologically recent eruptions at Yellowstone (i.e. during the last 10 Myr), created multi-meter thick ash deposits in parts of the Midwest. Most of that ash would be very fine material, but larger rocks thrown great distances would occur too. In fact, the fertility of the soil in the region has actually been enhanced by those ancient ash falls. So you certainly can find igneous rocks in Kansas, though relatively large rocks would be rather uncommon. Dragons flight (talk) 00:48, 25 March 2010 (UTC)

If its a bit of furnace slag there will probably be more bits near by. However, a couple meteor types are called “slag” due to their similarity. It does look promising. [8]. Suggest you would be better off doing a little study and then contacting meteor experts. Remember, they not only have a scientific value but a monetary one as well. You should at least be able to get a auto-focus camera out of it and a descent lens. --Aspro (talk) 00:51, 25 March 2010 (UTC)

Er, sorry but I think you've misread that page. It says slag is commonly MISTAKEN as a meteor. Vespine (talk) 21:51, 25 March 2010 (UTC)

Gosh! You right. I must get that lens prescription filled! Well, suppose we can safely discount furnace slag then.--Aspro (talk) 18:28, 26 March 2010 (UTC)

If it's volcanic, it's not from Kansas. I've done some research on Kansas geology and the only igneous rocks in Kansas are miles beneath the ground. The surface rocks where I live are from the Permian era and they're all sedimentary. There are ash deposits out west (and I even own some Yellowstone ejecta I found there), but there's no ash in Riley County. As for the meteorite thing, I highly doubt it. I found a smaller piece of similar material in almost the exact same spot several years before I found this one and the chunks of softer material embedded in it doesn't seem to fit with a meteorite. I suppose it's important to note that I found it on a rocky beach on Tuttle Creek Lake. It may have been washed there. Being so porous, I wouldn't be surprised if it floats (I've seen lava rocks that float).

Also, since I wrote my first post, I've noticed that some of the smaller objects stuck in it appear to be limestone, but I could be wrong about that. There's still other chunks stuck in it that are so hard that I can't even scratch it with my pocketknife. —Preceding unsigned comment added by 63.245.168.34 (talk) 01:09, 25 March 2010 (UTC)

It seems like a composite rock, to me. It may have started out as igneous rock, then spent some time at the bottom of a body of water next to pebbles, and was cemented to them via sedimentation. StuRat (talk) 01:23, 25 March 2010 (UTC)

My sediments exactly. Edison (talk) 14:46, 26 March 2010 (UTC)

OP here again. I found something very interesting. Read this article:

http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_kansas.html

Apparently I was wrong that there are no native volcanic rocks at the surface in Kansas. I was surprised to find out that there's a few Kimberlite formations in Riley County! Kimberlite is the rock that diamonds are found in, and it's notable because it's formed in the earths Mantle.

It would seem to fit with what I found since kimberlite is known for collecting many xenoliths as it plows through the layers of rock on its journey to the surface. That would explain the wide variation in the xenoliths too (some of them are so hard I can't scratch them with a pocketknife, while others are soft and powdery).

Could the rock I found be a chunk of kimberlite? Could I be holding here in my hands a piece of the Earths mantle? —Preceding unsigned comment added by 63.245.168.34 (talk) 20:40, 26 March 2010 (UTC)

If you really think you might have diamonds in there, try scratching a piece of glass with them (obviously not any glass you care about). If it won't scratch glass, then it's not diamond. If it does, then more testing would be required to prove they are diamonds. Note that most diamonds are ugly and discolored, not like the pretty ones you see in a jewelry store. StuRat (talk) 20:49, 26 March 2010 (UTC)

No, you misunderstand. I don't think I've found any diamonds in it, and the resources I've found on the Kimberlites here say that they don't contain diamonds. I just want to know if what I found is a piece of Kimberlite. —Preceding unsigned comment added by 63.245.168.34 (talk) 21:11, 26 March 2010 (UTC)

Finding amount of chloride in a solution using ion-selective electrode

I want to use an ion-selective electrode to find the amount of chloride in an unknown solution. I will obviously need to use the chloride-ion selective electrode, but where can I find the method and procedures for such an experiment? —Preceding unsigned comment added by 142.58.43.153 (talk) 23:39, 24 March 2010 (UTC)

March 25

Currency manipulator

Question moved to the Humanities desk. Comet Tuttle (talk) 04:41, 25 March 2010 (UTC)

Questions about casting resin

Is the type of clear casting resin sold in craft stores suitable for making lenses for science experiments at home? If so, how do you make precision mold(s) that would give the lens produced the right shape? How do you give cast resin a smooth finish? What is the easiest method of replicating an object using resin casting? Thanks. —Preceding unsigned comment added by 173.49.9.9 (talk) 03:26, 25 March 2010 (UTC)

I don't think it's possibly to get as smooth of a surface from casting as from grinding. However, having an extremely smooth, nonstick surface on the mold would help. You might also want to let it set while the lens is standing on it's side (I'm assuming a two-piece mold here). That way, any bubbles will hopefully migrate to the top, which won't be a critical area of the lens. StuRat (talk) 12:58, 25 March 2010 (UTC)

I just did an evening class on resin casting. The stuff you are after sounds like the stuff I was interested in. Solid cast 606. clear doming epoxy. That's a product specific to the place I went but if you look at the data sheet you'll probably find something similar wherever you are. Resin copies the surface of your mould with surprising fidelity. If you have a very smooth surface on the mould the resin will also be very smooth, if you have a frosted surface the result will be frosted. If you have an existing lens you want to copy, you can get silicone casting rubber which you use to make a 2 piece mould. The easiest way to do that is using klean klay to make the 1st half of the mould, then make the other half off the 1st. If you don't have a starting lens, that will make it a lot harder I think. Let me know if you want me to clarify anything. Vespine (talk) 21:43, 25 March 2010 (UTC)

Thanks, Vespine, for putting everything into focus for us. I'm sure your answers will all resonate with the Original Poster. StuRat (talk) 23:23, 25 March 2010 (UTC)

Thanks for the answers. A few futher questions: Vespine, how do you use the 1st half of a mold to make the second half? Are you assuming some kind of symmetry here? How do you make a cast resin sculpture from scratch? Do you need to make a positive mold first using some easily sculptable material, then make a negative mold from it using silicone rubber? What kind of material would be good for making the positive mold? How do you make the final product smooth and crystal clear? Can you polish it somehow? Thanks. --173.49.9.9 (talk) 23:42, 26 March 2010 (UTC)

cosmology

Does faster than light expansion of universe during inflation violate the special relativity? Don't we need to take the movement of time backward to unify gravity physics with the non-gravity physics? —Preceding unsigned comment added by 115.186.130.253 (talk) 06:23, 25 March 2010 (UTC)

No, not according to cosmologists who claim to understand it. Though I haven't read it myself, this article by Davis and Lineweaver may be helpful: http://arxiv.org/PS_cache/astro-ph/pdf/0310/0310808v2.pdf

--Hroðulf (or Hrothulf) (Talk) 07:35, 25 March 2010 (UTC)

Also, we need to establish faster than light relative to what? It is possible for two objects to move away from each other at faster than the speed of light relative to each other. If they do so, they effectively lose contact, since they will be traveling outside of each other's light cone. So there is nothing wrong with assuming that the "leading edge" of one side of the universe is moving away from the other "leading edge" at faster than the speed of light, relative to each other. --Jayron32 16:04, 25 March 2010 (UTC)

Jayron, your last two sentences don't make sense to me. I don't think inflation requires parts of the universe to lose contact, though it does say that there is much more to the "cosmos" that was never in touch with our universe. If things move away from us at near light speeds, (special) relativity merely says they move away from each other at near light speed. Am I oversimplifying inflation or Hubble expansion? --Hroðulf (or Hrothulf) (Talk) 16:51, 25 March 2010 (UTC)

You may find the articles cosmic inflation and metric expansion of space interesting. As I understand it, the rapid expansion during cosmic inflation is what disconnected parts of the universe. In other words, the universe was able to transmit information throughout itself right at the beginning of time, but cosmic inflation rapidly separated areas of it enough so the distances between points were large enough so light was (and is) not able to move between them fast enough to transmit information. We also got our large-scale structure of the universe from the quantum fluctuations present during cosmic inflation.

I believe you're right about relativity saying two objects can only be moving away from each other at up to the speed of light. Implicitly, a third reference frame is used when measuring the velocities of each object, which is not allowed. However, it is possible for two objects to be moving away from each other due to Hubble expansion. Imagine a photon sent from Earth toward Proxima Centauri, 4.2 light-years away. You would expect the photon to reach Proxima Centauri in 4.2 years, right? Well, say Proxima Centauri and Earth were not gravitationally bound in the Milky Way. Space between Earth and the star would be expanding as the photon traveled, so it would have to travel through this new space as well. It might take 4.21 light years to get there (again, if the two objects were not gravitationally bound, as most galaxies aren't). Now, say you send out a photon toward the most distant galaxies we see. Eventually, more space will be created between the photon and its destination than it can travel. Given enough distance, over one light-year of distance will be created that the photon will have to pass through, so it will never reach its destination. This is why our observable universe is shrinking with time. Hope this helps. —Pie4all88 ^{T C} 18:45, 25 March 2010 (UTC)

what, in a physical sense, is an impossibility?

I have received a definitive answer above that for anything that has ever existed, or will exist, or anything that has happened, or will happen, it is a given that the thing was/will be possible at the time that it existed/happened/will exist/will happen.

So if any thing is always possible, then what is a physical (not conceptual) impossibility?

I got some answers above, but they aren't really clear enough for me. I would like a simple answer to what, physically impossibility would be. As far as I can see, it seems to be a non property, like centrifugal force: it is not a force itself, it just seems to be. Impossibility then isn't a real aspect of the physical Universe; it just seems to be. Is this understanding correct, or is there a physical meaning of impossibility, and if so, what is it? 84.153.202.26 (talk) 10:25, 25 March 2010 (UTC)

Impossibilility can never be a property of any object or process which exists, because if it exists it cannot be impossible. Therefore, on initial examination I would say that your conclusion is correct. However, you are within the realms of philosophy here, and I claim no expertise in that field. You might be interested in Physics of the impossible, where Michio Kaku expounds a sort of heirarchy of impossibilities; or in "Impossibility: the limits of science and the science of limits" by the Cosmologist John D. Barrow (preview available on google books here [9]). Oh and here is the obligatory XKCD link for centrifugal force [10]. Equisetum (talk) 11:02, 25 March 2010 (UTC)

Mathematical/logical impossibility and physical impossibility are different. Physical impossibility, like physical proof, is based on scientific theories. Such theories, while often very well supported, are strictly preliminary, and open to modification or even replacement if conflicting evidence turns up. It is physically impossible for a cannonball at rest to spontaneously and without the application of a force lift itself one meter into the air (based on both Newtonian and relativistic laws of motion). It is physically impossible for a well-mixed container of lukewarm water in a environment at normal room temperature to turn into half ice and half steam (based on classical thermodynamics). In these cases, the "impossible" phenomenon is well within the set of situations covered by the respective theories, hence we drop the quotes and call those events simply impossible without the caveats. However, both events are possible, if extremely unlikely (as in "will not happen even once in 10^bignum lifetimes of the universe") under quantum theory. --Stephan Schulz (talk) 12:30, 25 March 2010 (UTC)

Isn't one of the fundamental truths that something can not "be" AND "not be" at the same time? Could you say that's an impossibility? Vespine (talk) 21:17, 25 March 2010 (UTC)

That depends on the definition of "to be" ;-). But yes, a straight contradiction describes something that is logically impossible. However, very many things that are logically possible are physically impossible. There is nothing logically wrong with ESP, or superluminal travel, or Microsoft making an OS that does not suck. --Stephan Schulz (talk) 22:23, 25 March 2010 (UTC)+

In case nobody has mentioned it, there's a parallel universes theory whereby there are an infinite number of universes, some of which may even have different laws of physics than our own. Therefore, all things may be possible ... somewhere. StuRat (talk) 23:03, 25 March 2010 (UTC)

"The difficult we can do immediately, but the impossible may take a bit longer." StuRat (talk) 23:03, 25 March 2010 (UTC)

You want an example of something that is physically impossible

• A planet made up of only electrons and held together by it's own gravitational field
• A rocket ship capable of escaping from inside the event horizon of a black hole using only chemical propulsion

122.107.207.98 (talk) 08:54, 26 March 2010 (UTC)

Pretty much anything that breaks any physical law is what we'd currently call "an impossibility" so long as it's a hypothetical event. I can say that it's impossible to build a perpetual motion machine or to travel faster than the speed of light - but if such a thing ever actually happened, it would no longer be considered to be impossible - and previous statements to the effect that this thing was impossible would have to be re-visited and corrected. Consider a real example: when the Alchemists sought to turn lead into gold and failed, we invented chemistry and wrote laws that said that you couldn't turn lead into gold. Transmutation would have been considered possible (but incredibly difficult) in the 1600's, impossible in the 1800's after Lavoisier and Dalton claimed it was impossible - and possible again in the 1900's when Glenn Seaborg actually succeeded in doing it using Nuclear transmutation. SteveBaker (talk) 23:39, 26 March 2010 (UTC)

this question's for you SteveBaker - is this demo rigged?

[11] Is that demo rigged? Especially the final part, where they get sky and ground from nothing, and it looks exactly like it needs to. Is there any way to tell if they didn't REALLY start with the whole image (what seems to be the "product") and then remove parts of it, and the "tool" in the rigged demo doesn't calculate those parts at all, but puts them back from the original image?

If the demo is NOT rigged, how on EARTH can in POSSIBLY work like that?? 84.153.202.26 (talk) 10:46, 25 March 2010 (UTC)

Content-aware fill looks like an extension of content-aware scaling, which Photoshop CS4 featured. This is an explanatory video made by the two researchers who invented it - one of them subsequently moved to Adobe to drive the introduction of this technology into CS4. -- Finlay McWalter • Talk 10:55, 25 March 2010 (UTC)

For our article on the topic, see Seam carving. -- Coneslayer (talk) 11:54, 25 March 2010 (UTC)

I think it is genuine. It is really really clever, but not impossible. Basically, it's extrapolation. You look at what is all around the deleted area and make the interior look the same. That is, of course, easier said that done! The bit I'm really impressed by is the right-hand side of the final image. I was going to say that it looks like they've run an edge-finder on it (a tool that has existed for years, albeit with increasing quality), extrapolated the edges and then filled in the various regions. However, if you look at the foreground hill on the right, at the point where the original image ends the hill is going upwards. If it were extrapolating the edge in the obvious way you would expect it to keep going up at the same angle (which is what it does on the left-hand side, give or take), but it doesn't. It goes up for a tiny amount and then goes down. Somehow, the tool has realised that if it continued going up it would be out of proportion with the rest of the hills. They must have looked at the entire edge, done some statistics on the way it goes up and down and come up with an extrapolation that fits it. That is mindbogglingly clever! --Tango (talk) 11:47, 25 March 2010 (UTC)

@Tango, note that the profile of the extrapolated hill at the right is obtained by reflection about the edge of the original image and that edge (dotted line at 4:45) is not vertical. BTW it's better to view the demo here where it can be shown full-screen. Cuddlyable3 (talk) 17:43, 25 March 2010 (UTC)

It's clever. Will it work in all cases as well as you want? Probably not. The Magic Eraser is a similarly cool feature in CS4 that can remove spots and errors pretty instantly and works pretty well in most cases. Sometimes it goes way wrong and sometimes even when it works right, it is obvious when you zoom in that something hinky has been going on. I imagine that this will be somewhat similar... good for a quick fix at low res but probably not what you're going to want to use for something at high res. But who knows! We will wait and see. --Mr.98 (talk) 13:29, 25 March 2010 (UTC)

There's no reason to think it's rigged as in "the software didn't really do that", but it's extremely common in software demos to 1) do a bunch of them and present the best one, and 2) have the demo presenter walk a very specific path that is known to perform well. Finally, there's LG's refrigerator, which is programmed to detect that it's in a demo and goes into super-power-saving mode. :D --Sean 14:44, 25 March 2010 (UTC)

@Sean please don't introduce issues that have nothing to do with graphics. Cuddlyable3 (talk) 17:43, 25 March 2010 (UTC)

I was addressing the broader practice of demonstrations not necessarily representing real-life usage. --Sean 17:59, 25 March 2010 (UTC)

There are several tools out there that are even more impressive than that - there have been papers in SigGraph proceedings for at least 5 years describing these kinds of trick - so it's nothing new. One technique is to look at the pixels around the object you're trying to remove - then look elsewhere in the image for other places where very similar groups of pixels exist. Then you copy the scene near to those pixels into the space occupied by the thing you're trying to remove. You can repeat this process over and over to gradually 'erode' the object you want to get rid of. With minor variations on this basic idea, it works amazingly well. SteveBaker (talk) 01:43, 26 March 2010 (UTC)

How might a person be exposed to (x number of) rems?

Hi guys.

I need to know just what kind of environment might expose someone to certain levels of radiation:

• 5-20 rem
• 20-100 rem
• 100-200 rem

It's been relatively easy to research higher levels of exposure, and to find out the effects of such levels. But it's just how someone might be exposed in this way which I'm finding harder to ascertain. If anyone can provide any answers, sourced preferably, it will be greatly appreciated! Thanks. 83.104.127.226 (talk) 11:09, 25 March 2010 (UTC)

See Ionizing_radiation#Ionizing_radiation_level_examples. It is all in sieverts, but they are easily converted into rems - 1 rem=0.01 Sv, so your ranges are 0.05-0.2 Sv, 0.2-1 Sv and 1-2 Sv. (WP:WHAAOE strikes again!) --Tango (talk) 11:53, 25 March 2010 (UTC)

Correction - it's all in milisieverts, so your ranges are 50-200 mSv, 200-1000 mSv and 1000-2000 mSv. --Tango (talk) 11:57, 25 March 2010 (UTC)

Natural background radiation can produce expsoures in the range 5-20 rem per year - Ramsar in Iran has the highest level of natural background radiation in the world, and inhabitants can be exposed to up to 26 rem (260 mSv) per year. So someone living in an area with high levels of background radiation for, say, 10 years or more could have a cumulative exposure of over 100 rem. However, because the exposure is spread over time, giving the body's cells time to repair themselves, there may be no ill-effects from this exposure, whereas the same level of exposure over a time-span of minutes or hours would likely result in radiation poisoning. Gandalf61 (talk) 12:08, 25 March 2010 (UTC)

Thanks guys, this is exactly the kind of stuff I was looking for. It was interesting to read about Ramsar, and especially the seemingly counter-intuitive radioresistance of the inhabitants. Bonus points. 83.104.127.226 (talk) 12:37, 25 March 2010 (UTC)

By the way, I put a fact-tag and a dubious-tag on those claims. The article should cite a reliable medical study to support these very dubious claims. Comet Tuttle (talk) 16:37, 25 March 2010 (UTC)

I don't think the dubious tag is warranted. The article Radiation hormesis contains some citations that could also be attached to the Ramsar article. The article states "It has also been claimed that residents have healthier and longer lives". That is not dubious at all. Claims like that have been in fact made by many studies (Just read the linked article). Whether those claims turn out to be true or not is, of course, is still controversial but the Ramsar article doesn't take sides on that controversy simply stating the true fact that claims of radiation hormesis have been made. You should remove the tag. BTW I happen to believe that there is likely some truth to those claims. Dauto (talk) 13:58, 26 March 2010 (UTC)

Political spectrum

The article says,

"For almost a century, social scientists have considered the problem of how best to describe political variation; a sample of their results is given below." [edit] Early research In 1950, Leonard W. Ferguson carried out an analysis of political values using ten scales measuring attitudes toward:

• Birth control
• Capital punishment
• Censorship
• Communism
• Evolution
• Law
• Patriotism
• Theism
• Treatment of criminals
• War

Is there a comparison anywhere of values in terms of vehicle or highway construction, i.e. a road built according to Republican values, for instance, would have no speed limit signs and vehicles would have no speedometers? 71.100.5.192 (talk) 12:54, 25 March 2010 (UTC)

Confused, what do you mean? Nyttend (talk) 13:07, 25 March 2010 (UTC)

Do not tell anyone else this if you are a politician. 71.100.5.192 (talk) 00:00, 26 March 2010 (UTC)

I'm not aware of a comparison, but you could look at how the Autostrada and Autobahn networks were massively expanded by the Fascist governments of the 1930s, and perhaps use speed limits in the United States to compare limits in Democrat- or Republican-majority states. But I'm not sure that there's a clear correlation - the National Maximum Speed Law was brought in by Nixon. Warofdreams talk 13:36, 25 March 2010 (UTC)

One problem with comparing speed limits and the dominant party for different states is the population density of different states — as far as I know, speed limits are generally higher in Republican-dominated states, but a more likely explanation for that fact is that Democratic-dominated states are more densely populated. Nyttend (talk) 21:15, 25 March 2010 (UTC)

I'm assuming this is about US politics. I think no speed limits would be more of a Libertarian value, as Republicans are typically for strict law-and-order. So, what differences could we expect between Democrats and Republicans ? I would expect that Republicans would want more local funding, which would result in better roads in wealthy areas and crap roads, or none at all, in poor areas. Democrats, on the other hand, would want national funding and be in favor of borrowing whatever money it takes to provide first class roads everywhere, no matter what the effect on the national debt. StuRat (talk) 13:53, 25 March 2010 (UTC)

StuRat, your bias is oozing all over the place. 169.139.217.79 (talk) 14:08, 25 March 2010 (UTC)

If I'm equally biased against everyone, doesn't that make me balanced (while simultaneously unbalanced)? :-) StuRat (talk) 14:15, 25 March 2010 (UTC)

Democrats, socialists and communists drive on the left; conservatives, aristocrats and rogues drive on the right. Cuddlyable3 (talk) 14:00, 25 March 2010 (UTC)

What you need to watch out for then is the centrists, because they crash into everyone. Googlemeister (talk) 14:22, 25 March 2010 (UTC)

It isn't so easy to lump all US Republicans and Democrats under one label. See Conservatism in the United States#Types and Liberalism in the United States#Varieties of liberalism. 152.16.15.144 (talk) 17:50, 25 March 2010 (UTC)

I took the Liberty (*ahem*) of linking "centrist". ~AH1^(TCU) 00:55, 26 March 2010 (UTC)

Space colonisation

1) Would it be possible to grow crops on Mars?

2) How large an area would be needed to supply a manned base there?

3) I notice the Martian atmosphere is almost entirely CO2, which might be good for plants, and could be changed to oxygen by them as well, though I doubt an atmosphere of mostly oxygen and CO2 would be much better. Would it be possible to create a breathable atmosphere on Mars at all?

4) How long would it take for the fastest spacecraft yet built/designed to reach the moon Titan?

5) Is there anywhere I can find reasonable estimates on when different missions may be launched, those listed on here seem only to go up until around 2030?

6) Has anyone yet considered sending some sort of probe to this Gliese581?

7) Are there any other questions I've forgotten?

148.197.114.158 (talk) 13:47, 25 March 2010 (UTC)

I've numbered your Q's so we can reference each in our responses:

1) Yes, probably using hydroponics and water from the polar caps.

2) I don't understand. Do you mean how large of an area on Mars ? This doesn't seem very important, since nobody is using any part of Mars now.

3) Maybe, after thousands of years, via terraforming.

5) Realize that any missions planned for over 20 years from now are little more than wild speculation, as changes in technology, economics, and politics would make them extremely unlikely to happen as planned.

7) How about artificial satellites used for space colonization ? StuRat (talk) 14:00, 25 March 2010 (UTC)

6) Gliese 581 is a star 20.3 light years away. Voyager 1 has taken 32 years to travel 16.8 billion km away. A light year is 10 trillion kilometers. How long do you want to wait for some sort of probe data?

7) You left out little stuff like how to breathe, eat and keep warm on Mars, and who pays for all this. Cuddlyable3 (talk) 14:19, 25 March 2010 (UTC)

One interesting thing about the atmosphere of Mars is that if you added O2 and N2 in sufficient quantities to bring the pressure up to that which we have on Earth, the CO2 level will be about 30x higher then we have on Earth. This is right at the lower end of CO2 toxicity, so you would, in addition to needing to add O2 and an inert gas like N2, you would also need to figure out how to remove a large amount of the CO2. Maybe not all the way down to earth levels (375ppm or so), but probably a good chunk of it, so to answer question 3, You would probably need a heck of a lot of plants to pull this off, and to keep the plants, you a heck of a lot of water. Googlemeister (talk) 14:20, 25 March 2010 (UTC)

(edit conflict x2)

4) New Horizons took about 2.5 years to reach Saturn's orbit from Earth, while Voyager 1 and 2 took 3 and 4 years, respectively. Presumably, the time could be cut down somewhat if you were willing to be less efficient with your fuel.

6) Interstellar travel is currently non-existent (and unlikely to exist for some years), so if someone has thought of sending a probe to Gliese 581, it was either idle speculation or wishful thinking. In any case, we would surely send a probe to one of our closer neighbors first. Buddy431 (talk) 14:22, 25 March 2010 (UTC)

2) Heavily dependent on how well you terraform and what techniques you use. Hydroponics are probably the most space-efficient.

4) Cassini–Huygens took 7 years to reach Titan. Orbital mechanics and practical engineering dictate that that's about the best you can do with present tech. However, throwing out those considerations, New Horizons (the fastest launch from Earth) could get there in 854 days, and Voyager I (the currently fastest man-made object) could get there in 814 days. Again, those two numbers have no physical significance.

5) 2030 is probably a good outer limit for "reasonable" estimates. I personally wouldn't consider it "reasonable" past 2020, as many factors can't be accounted for.

6) Considered? Probably. But interstellar probes aren't reasonable with present tech. It would take Voyager nearly 400000 years to return data from a target 20 light years away. Sure, we could improve that by orders of magnitude if we really wanted to dump the money on it, but orders of magnitude still means waiting for centuries if not millennia. — Lomn 14:22, 25 March 2010 (UTC)

Cassini only took so long because they used two gravitational assists from Venus and one from Earth. If you're willing to burn much more fuel, you can do it faster. I'll grant that getting a trajectory that allows you to enter orbit may take longer than New Horizons or Voyager, but I'm sure you can do it much faster than the 7 years Cassini took (for example, it flew by Earth in 1999, for only a five year journey). And strictly speaking, 148. didn't require the spacecraft to orbit Titan or Saturn, so I think New Horizons and Voyager qualify. Buddy431 (talk) 18:05, 25 March 2010 (UTC)

Good point on Cassini. On the other hand, my NH/V1 numbers assume Earth at aphelion and Saturn at perihelion plus a straight-line trajectory between them. That's still not realistic (particularly the trajectory), as far as I know. But bump it 30% or so and call it 3 years and that's probably a good ballpark. — Lomn 20:04, 25 March 2010 (UTC)

In addition to the obvious political problems of launching something that's going to take centuries or millenia to achieve results, there's also the issue of any mission potentially being overtaken by a future faster mission. IIRC, some space sim (can't remember which) had this as a minor? plot element where some colonists were sent on a sleeper ship but found when they arrived other colonists had already arrive, having left sometime after them but on faster ships (not surprisingly they weren't happy about this). For example if you can design a probe nowadays and expect results for the 10001 millenium celebration the celebration is gonna be somewhat muted if you already have results from the team who made their probe 1000 years later and got their results in time for the 8888 celebrations. (Even more muted if the results were a message from some alien civilisation warning you that if you ever attacked their system again, be prepared for war.) Of course even if your probe can travel at close to light speed and accelerate/decelerate at 3G it's still going to take you around 45+ years to achieve results (not very good at relativisitic calculations so didn't try but 25 years earth time to reach the destination may be a resonable estimation under the described conditions, plus 20 years for the signal to reach earth). And as others have state, were very, very far from being able to do something like that. Nil Einne (talk) 21:24, 25 March 2010 (UTC)

Glise 581 has a negative radial velocity. So in the future, it may actually be closer to Earth than it is now. ~AH1^(TCU) 00:53, 26 March 2010 (UTC)

The sad - but very, very realistic problem with projects that take thousands of years to come to completion (interstellar probes, terraforming mars, etc) is that they cost a ton of money and NO politician or industrialist will ever vote for something that doesn't offer at least some prospect of return within a human lifespan. We can't solve something as serious as global warming for chrissakes! So if we can't do it in (let's say) 40 to 50 years - we can't do it at all.

The fastest interstellar-capable craft that comes within the laws of physics and the limits of technology would be Project Daedalus or the 1960's Project Orion (not to be confused with the recent proposals of the same name). They could credibly reach 10% of the speed of light and therefore make it to the nearest star in 40 to 50 years...which just about fits the maximum project span that humanity will ever attempt. These craft would have to be gigantic - with space for thousands of people on board - because they would powered by the exploding of atom bombs...and would cost about 10% of the US GDP for a year to build. You couldn't make a reasonable 'probe' with that technology. However, you could set up a 'biosphere' and comfortable living space for 1000 people (sufficient for a viable colony) and shoot it to the nearest star.

The problem with that is that the nearest star doesn't seem to be very habitable. Gliese-876 (not as famous as -581, but closer!) is 15 lightyears away - but that's a 150 to 200 year trip - meaning that this would be a 'generational' ship. And we're back with the funding issue.

The only way I can see humanity managing this is if enough rich enthusiasts could somehow fund the construction in order to live in utter luxury and safety for the rest of their lives. They might be interested in setting such a gargantuan machine in a solar orbit far from bothersome Earth. For such a hypothetical community, they might have enough helium-3 on board to power their society and not care whether they orbit the sun or shoot off into deep space - and I suppose they might spring for the costs of the bombs to head off out of the solar system. Then - several generations later, humans arrive at the other star. Because (we hypothesize) they are pretty much self-sufficient, they don't really NEED a habitable world at the other end - but they're going to need to refuel their fusion reactors.

But that's a hell of a stretch. I think humans are going to be stuck in the solar system for a very long time.

SteveBaker (talk) 01:25, 26 March 2010 (UTC)

The Mars Society (founded by aerospace engineer Robert Zubrin) has sponsored and collected a wide portfolio of mission, colonization and terraforming options that answer questions 1,2,3 and 5, and probably some of the questions you forgot to ask. If I recall correctly, Zubrin's own book The Case for Mars (ISBN 9780684827575, OCLC 34906203) summarizes a terraforming proposal that would produce a useful atmosphere and biosphere in two or three centuries, as well as describing Mars Direct.

Regarding the objection to missions that take many human lifetimes, it is worth noting that princes and popes in late medieval Europe and Asia planned many generations ahead, for example with the construction of cathedrals, universities and madrasah. I suspect that they didn't have to wait lifetimes for a payoff: the projects created employment, a sense of power and permanence, and a communal ambition. All of these could motivate modern politicians and universities to probe space, though it would be a bonus if an interstellar probe would be able to send back useful science data from the outer reaches of the solar system in a few decades, as Voyager does.

--Hroðulf (or Hrothulf) (Talk) 12:00, 26 March 2010 (UTC)

Most Cathedrals were not built with the intention of them taking hundreds of years, they were built with the expectation of taking 20-30 years and funding or construction or warfare stopped construction, or forced part of the building to be rebuilt. Googlemeister (talk) 13:18, 26 March 2010 (UTC)

That's true - but the people who paid for them believed that they'd get their reward "in heaven" - so it's not true to say that they set the work in motion with no hope of a return on their investment. I suppose if you could convince some religious nuts that god wanted them to terraform Mars or fly to the nearest star - maybe you'd get some funding. SteveBaker (talk) 23:18, 26 March 2010 (UTC)

JASSA

Hello! Can anybody get something for me out of the British Library. It is from the JASSA : Journal of applied sciences in Southern Africa.

• A. J. Masuka: Dynamics of mushroom (Boletus edulis) production in pine plantations in Zimbabwe. In: JASSA, Journal of Applied Science in Southern Africa. 2(2). 1996. pp. 69–76

It should be available at the British Library, maybe as printed or electronic edition. Thank You very much for Your help, Doc Taxon (talk) 13:53, 25 March 2010 (UTC)

Here is a link for people who have access to AJOL. The article costs $18, but maybe somebody can help you. Indeterminate (talk) 14:11, 25 March 2010 (UTC)

British Library shelfmark is 4663.148900 (Lending Collection). Thanx again for any help ... Doc Taxon (talk) 14:28, 25 March 2010 (UTC)

If you belong to a British Public lending library, they should be able to get it for you via the Library interloans service. It’s worked for me. --Aspro (talk) 18:06, 25 March 2010 (UTC)

Sorry, but I am from Germany. Can You get this article and forward to me, please? Doc Taxon (talk) 19:18, 25 March 2010 (UTC)

Wouldn't it violate copyright to send someone a printout of an article the copyright holder demands ripoff high prices for? One workaround used to be to write to the principal author and say "I would greatly appreciate a copy of your article "XXXX." I collected hundreds of such reprints back in the day. Edison (talk) 19:50, 25 March 2010 (UTC)

If this magazine was at a German library, I can get a copy from the library too. Isn't it a copyright violation, too? If this copy is for own use only, it's okay for the library. It is a violation to publish a copyrighted article in books or internet without the confirmation of the principal author. Doc Taxon (talk) 09:01, 26 March 2010 (UTC)

Without getting into the legalities of copyright, I'd suggest asking at your local library. UK libraries can request material from the continent - admittedly the overdue fees are exorbitant and there's a week or so's wait, but I'd give this option a shot and see if German libraries can do it too rather than ask someone to break the law. Brammers (talk) 10:22, 26 March 2010 (UTC)

meat products

In some places in Eastern Europe, they make meat jelly. Though the stuff sounds quite vile, it got me to thinking, is it possible to make meat based alcoholic beverages that are not toxic? Googlemeister (talk) 14:30, 25 March 2010 (UTC)

I don't know about alcoholic meat, but along the lines of meat jelly, look at Spam and Yorkshire pudding. StuRat (talk) 14:38, 25 March 2010 (UTC)

No meat in Yorkshire pudding. Perhaps you meant black pudding. Gandalf61 (talk) 16:07, 25 March 2010 (UTC)

Classic Yorkshire pudding is made from fat drippings from roasting meat. StuRat (talk) 16:32, 25 March 2010 (UTC)

Sorry, but not so. Yorkshire pudding is made from batter. The ingredients are very similar to a plain pancake. Two hundred years ago it would have been fried in fat taken from the dripping pan, but in modern times it is baked in the oven. Gandalf61 (talk) 16:41, 25 March 2010 (UTC)

It looks like classic Yorkshire pudding was made from batter and fat drippings from meat, but the modern pudding skips the drippings, and gets the fat or oil from another source. StuRat (talk) 17:02, 25 March 2010 (UTC)

Bovril with a tot of brandy in it. As for meat jelly - not a particularly Eastern European thing. Brawn is good English food. DuncanHill (talk) 14:44, 25 March 2010 (UTC)

Take a look at aspic too. I don't get what Yorkshire puddings have to do with meat jelly. DuncanHill (talk) 14:50, 25 March 2010 (UTC)

Jell-O is meat jelly, for the record. --Sean 14:49, 25 March 2010 (UTC)

I do not mean adding other alcoholic beverages to meat, I mean fermenting, or distilling or whatever, the meat to make alcohol. Googlemeister (talk) 15:06, 25 March 2010 (UTC)

Generally, to make alcoholic beverages, you want to start with something that has a lot of sugar (like fruit juice), or starches that can be easily converted to sugar (as in potato or grain vodkas). Meat doesn't have a lot of sugar or starch. -- Coneslayer (talk) 15:22, 25 March 2010 (UTC)

Not meat per se, but Alcohol can be made from milk- see Kumis from Central Asia, Blaand from Scotland, and probably others (though I don't recommend them). Staecker (talk) 16:09, 25 March 2010 (UTC)

Meat does ferment, but it does not produce appreciable amounts of ethanol when it does. When carbohydrates ferment, they produce two major products: usually ethanol or acetic acid, hence wine/beer and vinegar. Meat is mostly protein, and protein contains a sizable amount of nitrogen in it. As a result, when meat ferments it produces lots of nitrogen compounds, like ammonia and amines, some of which have lovely names like Putrescine and Cadaverine, which smell about as lovely as it sounds. Amines are generally toxic, which is why rotten (fermented) meat is generally a bad thing to eat. We have fermented grain and fruit products (booze), and fermented dairy products (cheese, yoghurt), but fermented meat is pretty nasty stuff. --Jayron32 16:12, 25 March 2010 (UTC)

Our article fermentation (food) has sections Fermentation_(food)#Meat-based and Fermentation_(food)#Fish-based. Neither list any alcoholic beverages. Staecker (talk) 16:15, 25 March 2010 (UTC)

Well I guess if Icelandic cuisine does not have a meat alcohol, it probably does not exist in a safe form regardless of palateability. Googlemeister (talk) 16:25, 25 March 2010 (UTC)

@Googlemeister (indenting of above threads seems screwed up so not replying there to avoid confusion):I think Sean's point is that most fruit flavoured deserts we call 'jellies' in Commonwealth countries or Jell-O in the US are made with gelatine which is derived from animal sources, usually pig or cow, occasionally seafood. From a vegetarian standpoint, all these may indeed be considered meat jellies (although most of the stuff use to make gelatine wouldn't generally be called meat). If you have an agar agar desert without any animals products then that definitely wouldn't be a meat jelly Nil Einne (talk) 19:45, 25 March 2010 (UTC)

Imagine being stranded in an agar agar desert. Staecker (talk) 20:03, 25 March 2010 (UTC)

Probably better then being stranded in a real desert. At least you shouldn't die of thirst and may be not even starvation although you will likely get malnourished eventually unless it's some super nutritionally complete agar designed as a growth media or something Nil Einne (talk) 21:35, 25 March 2010 (UTC)

"Meat jelly" also often refers to frozen gravy. ~AH1^(TCU) 00:49, 26 March 2010 (UTC)

Are ad hominen reasons sometimes reasonable?

If some scientist is well-known for faking data, could we discard his theories on the base of that? It seems like the common practice for me, but couldn't such a scientist also produce something of value? ProteanEd (talk) 17:44, 25 March 2010 (UTC)

Scientists would usually maintain some scepticism about results until they have been independently corroborated, regardless of whose results they are, so I guess it isn't too much of a problem anyway. Reputation is certainly important in science, though, and it can result in a "The Boy Who Cried Wolf" scenario. Ad hominen attacks are a logical fallacy, but science isn't based solely on logic. It is based on evidence. You shouldn't dispute somebody's conclusions drawn from the evidence based on who they are, but you can dispute the accuracy of the evidence presented (and if the evidence isn't credible, the conclusions drawn from it aren't either). --Tango (talk) 17:58, 25 March 2010 (UTC)

That's nice, in theory, but, in reality, it takes times and money to verify or disprove another person's claims. In this case, people tend not to waste time and money on the claims of obvious cranks. StuRat (talk) 18:05, 25 March 2010 (UTC)

I was not thinking about an "obvious crank" who may try to prove that the world will explode in 100 days. I had in mind scientists like Jan_Hendrik_Schön, who have been discovered manipulating data, but who might have done some valid honest and valuable research before that.--ProteanEd (talk) 18:20, 25 March 2010 (UTC)

Well, then, the same idea would apply, but to a lesser extent. That is, a scientist choosing to try to duplicate the work of another might prefer to choose one with a better track record. But, if the "discovery" by the one with the poor track record seems feasible and important enough, maybe they would overlook his past. StuRat (talk) 18:26, 25 March 2010 (UTC)

If some scientist is well-known for faking data, could we discard his theories on the base of that? Yes one could but who will be looking stupider if the scientist happens to be right? ..couldn't such a scientist also produce something of value? Yes. Jan_Hendrik_Schön...discovered manipulating data...might have done some valid honest and valuable research before that Yes, or he might in the future as he is only 40 and wiser now. Cuddlyable3 (talk) 18:59, 25 March 2010 (UTC)

Post EC: A situation similar to the one you describe occured in the case of Hwang Woo-Suk. He claimed to have succeeded in generating human embryonic stem cells via cloning. This result was discovered to be fabricated, but a later review of his data suggested he managed to extract generate cells from parthenogenetic human eggs which would make his group the first to do so. [12] Ultimately, ad hominem based dismissals of a theory still aren't "valid" because someone's choices and bad data have no bearing on the validity of their testable arguments. Scientific misconduct can set a legitimate theory back for years to decades AFTER it is exposed because scientists with legit data are afraid of being associated with it or are unfairly ignored because the dishonesty has tainted that field. This was the case when the Piltdown Man fraud effectively "supressed" real Australopithecine fossil finds. 152.16.15.144 (talk) 19:09, 25 March 2010 (UTC)

I think the scientific rejection of researchers who "fake" is less about them making a strictly logical argument as it is a community/social reaction to those who violate community norms. Additionally peer review is not really set up to catch willing fakers—it is meant to catch honest error. An argument could be made that expelling known fakers from the process is probably more expedient than treating all scientists like potential fakers. --Mr.98 (talk) 21:25, 25 March 2010 (UTC)

In a sense, yes. In theory, if someone makes a scientific hypothesis that seems basically reasonable, writes it up properly and gets it published in a reputable journal - and especially if they present some experimental evidence and a viable means for reproducing the experiment - or otherwise testing that claim - then in theory, other scientists will attempt to reproduce those results and either verify it or explain why it's wrong. Thus the hypothesis becomes a 'theory'.

However, in practice, scientists are limited in number and have limited time and budget - so it may be that some claims won't be tested. Now - the tricky part is the decision as to who you trust enough to make it worth-while to spend the time to check their results - and who you think so little of that you find something more useful to do with your time. In a sense, that's ad-hominem because you're using the person's prior reputation to determine whether you're even going to try to replicate his entirely new hypothesis.

Imagine in a case like Uri Geller - who claimed to be able to bend spoons with the power of his mind. The claim was tested - found to be not just bogus - but flat out fraudulant. Geller's reputation is totally in the toilet and so, if Mr Geller were now to make a much more reasonable claim...maybe to have found some clever chemistry that would make a somewhat more efficient battery for electric cars...then he'd probably be totally ignored. On the other hand, if Stephen Hawkins were to state a fairly radical hypothesis about how galaxies are formed - then even though his theory on information loss inside black holes has been effectively disproved - and even though his new galaxy-formation hypothesis seems a bit far fetched, people would certainly be prepared to spend the time needed to check out his findings. The only difference being the reputation of the person making the claim...which, is essentially what 'ad hominem' is all about.

The point though is that we don't "discard" the bad person's hypothesis - we simply fail to push it towards possibly becoming a proper theory. Scientists are unlikely to say that Uri Geller's hypothetical car battery idea is false - merely that nobody can be bothered to test it because they have better things to do. Hence the hypothesis remains unproven.

SteveBaker (talk) 00:26, 26 March 2010 (UTC)

Wikipedia has an article on Genetic fallacy which is the mistake of judging a claim not on its merit but instead by what one's opinion about its originator. Cuddlyable3 (talk) 12:43, 26 March 2010 (UTC)

Nicotine and the kappa-opioid receptor

Does nicotine or tobacco affect the kappa-opioid receptor in the brain in any way? If so, is it an agonist or antagonist? I understand the kappa-opioid receptor helps modulate addiction; I am more interested in if it is involved with the stimulatory affects. Several Google searches have failed me. Thanks for the help! —Pie4all88 ^{T C} 18:13, 25 March 2010 (UTC)

Well, a search on Google Scholar finds PMID 15979169, if nothing else. Looie496 (talk) 18:30, 25 March 2010 (UTC)

This is how I see it:

If you look at Reward system you will see that psychotropic drugs release dopamine in a certain part of the brain. However, neither nicotine or alcohol nor probably several other drugs have a (direct) effect on the kappa Opioid receptors. To compliment the link above see also: Kappa-opioid receptor modulation of accumbal dopamine concentration during operant ethanol self-administration.But by stimulating these receptors (with a suitable agonist) it modifies (and in this case reduces) the amount of dopamine released further down the neural ‘reward system.’ There is bound to be more to this than meets the eye because, for in the case of heroin addicts ( with the exception of those who’s addictions were iatrogenic) they all appear to be heavy smokers as well. The two addictions go hand-in-hand. Also, another interesting point, there is one country that escapes me for now (Burma?) that uses (very) high doses nicotine to ‘cure’ (so they say) opiate addicts.--Aspro (talk) 19:06, 25 March 2010 (UTC)

As I implicitly suggested above, it is perhaps possible that nicotine may ‘indirectly’ effect these receptors (there is so much about addiction that is still unknown) by way of repeated doses of nicotine reducing the bodies natural output of Endogenous_opioids. So they may end up getting less stimulation, leading to graving for more of the drug responsible. For the purposes of your question though, I would ignore this, as I only put it in to give a broader picture. --Aspro (talk) 19:20, 25 March 2010 (UTC)

Excellent—thanks for everyone's help! —Pie4all88 ^{T C} 16:52, 26 March 2010 (UTC)

Terminology for planetary orbits

I was watching a documentary about secret government atuff and the replicators sent s satellite to attack Atlantis. Down in the control room they said "It's taken up geosynchronous orbit above the city". However Atlantis is at about 45° north latitude. It would be possible to set up a geosynchronous orbit so that the satellite returned to that point once per planetary rotation but in this case the satellite stayed in the same location above the city, so it should probably have been called a geostationary orbit. My first question though is whether it would be correct to term the satellite as being "in orbit" at all? It's not revolving around a common centre of mass, so I'm thinking it would need a continuous expenditure of energy to maintain its position. Would that correctly be called "station-keeping" (but not orbital station-keeping)?

I'm not looking for comments about dramatic license in fiction or inaccuracy in SF TV shows, just about the correct way to describe an object maintaining position over a fixed point not on the equator of a planet. Bonus question would be, what direction of thrust vector would be required to maintain that position? Thanks! Franamax (talk) 19:30, 25 March 2010 (UTC)

Well, there is the Tundra orbit. While not fully geosynchronous, it is an approximation for areas further away from the equator where the satellite spends most of the time above the point of interest by doing lop sided figure eights. Googlemeister (talk) 20:11, 25 March 2010 (UTC)

I don't think a term exists since, as you say, it isn't really an orbit and the thrust required would be impractical. We have a force towards the centre of the planet of ${\frac {GMm}{r^{2}}}$ and we want a force towards the centre of the circle at 45 degrees north of $mr\omega ^{2}$. Those forces differ in angle by 45 degrees. Let's say we have a thrust force F at an angle $\theta$ to the gravitational force and we resolve forces parallel and perpendicular to the desired force. We get the following simultaneous equations:

${\frac {GMm}{r^{2}}}\cos(45^{\circ })+F\cos(\theta -45^{\circ })=mr\omega ^{2}$

${\frac {GMm}{r^{2}}}\sin(45^{\circ })-F\sin(\theta -45^{\circ })=0$

We then need to substitute in all the values and solve. I'll come back to that in a minute! --Tango (talk) 20:22, 25 March 2010 (UTC)

Ok, let's solve them. The first term of each are actually equal, so we can cancel them and get that $F(\cos(\theta -45^{\circ })+\sin(\theta -45^{\circ }))=mr\omega ^{2}$. The minimum thrust will be obtained when $\cos(\theta -45^{\circ })+\sin(\theta -45^{\circ })$ is maximised, which is when $\theta =90^{\circ }$, ie. we're thrusting perpendicular to the line joining the craft and the centre of the planet. We end up with a thrust required of $F={\frac {mr\omega ^{2}}{\sqrt {2}}}$. I'm not going to substitute in values because I think I've made a mistake somewhere (for one thing, I've used r for two different radii, but one cancelled out so that's not a problem - the r in the final equation is the radius of the actual circle travelled, not the distance to the centre of the planet). Common sense tells me that it should be easier to do at the right altitude for a geosynchronous orbit, but my equation says it is easier the closer you are to the planet... Can anyone help me? --Tango (talk) 21:29, 25 March 2010 (UTC)

Geosynchronous orbit requires you to be really high above the earth - 36,000km in fact - this diagram (right) is about to scale and gives you a reasonable feel for the geometry of the situation. So even at a latitude of 45 degrees, a craft in a geostationary orbit vertically above the equator and at the same longitude as the city would be fairly high up in the sky and would still appear to be stationary from the point of view of the city. Certainly it wouldn't be vertically overhead - but it would be well above the horizon. So, everything depends on your strict definition of the word "above". Certainly a satellite in that position could do surveillance and conveniently launch an attack on the city. I'll admit that it's somewhat loose language - but I don't think it seriously impacts whatever plot point they were trying to make and it's not unreasonable that an experienced space-faring bunch of people wouldn't immediately understand what was meant by that phrase. From the perspective of the screen-writers, saying that the satellite was "in a geosynchronous equatorial orbit at the same longitude as the city" would leave 99% of their audience having no clue as to what this meant and the other 1% having to lose track of the action while they thought through the tortured implications. SteveBaker (talk) 00:05, 26 March 2010 (UTC)

Does the height of the orbit make any difference to the position in the sky? I can't see why it would. --Tango (talk) 22:56, 26 March 2010 (UTC)

Sure it does. If the craft was infinitely far away, and positioned vertically above the equator, then it would be 45 degrees above the horizon at 45 degrees latitude. If the craft was resting on the ground on the equator, then it would be 45 degrees below the horizon at 45 degrees latitude. The higher the orbit it gets, the closer it gets to being 45 degrees above the horizon. SteveBaker (talk) 23:13, 26 March 2010 (UTC)

I have encountered the term "forced orbit" for an orbital path that can only be maintained by continuous thrust, but that was in science fiction; I don't know if the author invented the term. In the story it was used for an orbit with a shorter period than would otherwise be possible at that altitude, which was maintained by thrusting continuously downward; but the example in the original question seems to qualify as well.

The direction of thrust for a spacecraft maintaining a forced "geostationary" orbit above a position at altitude 45°N would have to contain a northward component and a vertical component. At low altitude the vertical component would be upward and large (basically it's just be hovering), at higher altitudes less; at some altitude similar to the one for a normal geostationary orbit the vertical thrust requirement would go away, and at a higher altitude you'd have to thrust downward (see previous paragraph). I think. --Anonymous, 00:25 UTC, latitude 43.7°N, March 26, 2010.

I don't see a problem and remind the OP that Stargate Atlantis is fiction and not a Documentary film. Therefore the writers at a stroke of a pen can adjust the Center of mass of the planet to latitude 45 degrees. Furthermore the word Orbit used in astronomy can be traced back to 1526 in the Ptolemaic system and therefore need not imply a Keplerean/Newtonian gravitational orbit. Cuddlyable3 (talk) 12:37, 26 March 2010 (UTC)

Sorry for interrupting, but I understood that a geostationary orbit has been already defined to be a type of geosynchronous orbit that is directly above the Earth's equator (0° latitude), with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. So, I expect that Atlantis won't follow this definition. I think that Tango's equation can be valid, relating orbital rotation parallel to equatorial plane (i.e.: $F_{Thrust}=mr_{e}\omega ^{2}sin(latitude)\,$, r_e is the Earth's radius). This is of course provided that the equation is solved for $r=[({\frac {GM}{\omega ^{2}}})^{2/3}-(r_{e}sin(latitude))^{2}]^{1/2}$. However, if Tango means that orbit with radius r must also have the relation r/R=cos(latitude), where R is the distance between the two masses m, M; then the previous equation must become $F_{Thrust}=mr\omega ^{2}tan(latitude)\,$ for $r=({\frac {GM}{\omega ^{2}}})^{1/3}cos(latitude)$.

I might be misunderstanding or lack for further knowledge (My English is also weak).Email4mobile (talk) 14:23, 26 March 2010 (UTC)

What is the source of the OP's latitude for Atlantis? Plato's dialogues Timaeus and Critias say only that the island continent was located[13] at such a latitude on the planet to allow it to have a mild Mediterranean climate for most of the year, and it produced bountiful harvests of fruits and vegetables. Wikipedia has an article about the abundent Location hypotheses of Atlantis. Cuddlyable3 (talk) 21:38, 26 March 2010 (UTC)

The OP is talking about the alien city in Stargate: Atlantis, not the mythological island. --Tango (talk) 22:56, 26 March 2010 (UTC)

Converting from eV to cm^-1

I have vertical excitation energy levels between the S0 and S1 states in Salicylic acid in eV and a paper that gives the energies in cm^-1 and I want to compare them. As far as I can tell the paper gives a barrier for fluorescence quenching of 1100cm^-1 which i'm guessing is the energy difference between the ground and S1 level. I know that I can convert the eV into a photon wavelength, so for a 3.9eV separation I get 317nm which sounds about right but I can't work out how to get this into cm^-1 so I can compare. —Preceding unsigned comment added by Orthas (talk • contribs) 20:24, 25 March 2010 (UTC)

Just convert 317 nm to 0.0000317 cm, then take the inverse (1/0.0000317 cm) to get 31545 cm-1 24.150.18.30 (talk) 01:14, 26 March 2010 (UTC)

Isn't that a very strange way of specifying energy? Why would they do that? Ariel. (talk) 07:45, 26 March 2010 (UTC)

Certain processes, like Raman spectroscopy, measure an energy difference by detecting a wavelength shift. When doing that cm^-1 is a natural framework. Dragons flight (talk) 11:25, 26 March 2010 (UTC)

And the inverse wavelength is sometimes called wavenumber. -- Coneslayer (talk) 11:42, 26 March 2010 (UTC)

From Planck's equation $E=h\nu \,$ we see that energy is proportional to the frequency $\nu \,$, and from the indentity $\nu \lambda =c\,$ we see that frequency is inversily proportional to the wavelength so it is actually quite natural to think of energy as the inverse wavelength of a photon. That's kind of the standard unit for people that work with spectroscopy. Dauto (talk) 13:29, 26 March 2010 (UTC)

Taxonomic promotion

How is it decided that a branch of the evolutionary tree should be "promoted" to a more fundimental branch? For example, mammals and lizards have their own orders, they aren't classified as a type of fish even though they came from fish. Birds, on the other hand, seem to be a subtype of the superclass of dinosaurs. Will birds get their own superclass in a hundred million years, or will we just keep making lower and lower categories as they evolve, so they'll have many layers of subclasses with dinosaur still at the top? On a smaller scale, panda bears have their own genus, whereas polar bears have to share a genus with grizzly bears. As grizzlies and polars evolve to be more different from each other, will one get its own genus, or will they have to diverge by going down the classification and getting their own sub-sub-sub-species? --Arctic Gnome (talk • contribs) 23:25, 25 March 2010 (UTC)

In the millions of years it would take for those type of changes to evolve, people may go extinct or at least develop an entirely different method of classification. StuRat (talk) 23:49, 25 March 2010 (UTC)

Clearly we won't see the bear example actually pan out. I was asking how the system is suppose to work. --Arctic Gnome (talk • contribs) 00:08, 26 March 2010 (UTC)

I doubt if they ever considered how to address new developments in evolution, for the reasons I listed. StuRat (talk) 01:48, 26 March 2010 (UTC)

Okay, then I'll simply ask why are birds a subclass of their ancestors the dinosaurs but mammals get their own class and not a subclass of one of their proto-mammal ancestors like Morganucodon or Docodonta. --Arctic Gnome (talk • contribs) 02:26, 26 March 2010 (UTC)

Birds have distinct features that make them very different from the majority of the dinosaurs so they need their own sub-class. Mammals are relatively quite similar to the proto-mammals. SteveBaker (talk) 11:01, 26 March 2010 (UTC)

Cladistics and Linnaean taxonomy do not match seamlessly. Cladistics arranges the "tree of life" according to the common ancestry, but this (in cases of divergent evolution, for example) groups together fairly dissimilar critters. Taxonomy, on the other hand, works by grouping animals together by anatomical and physiological similarity, which leads to many groups being polyphyletic; this makes them incompatible with cladistic systematics (in which all groups must by monophyletic). Hope this helps. Please read the articles I linked here. Do not hesitate to ask again if something is still unclear after you've read them. --Dr Dima (talk) 08:53, 26 March 2010 (UTC)

Regarding birds and mammals, it is indeed a good example, although somewhat complicated. Mammals evolved from synapsid craniates. Synapsids, last time I checked, are no longer considered reptiles. Birds, on the other hand, evolved from diapsid craniates, and are therefore cladistically true reptiles. Taxonomy, however, puts birds (Aves) in a group of their own, outside Reptilia. This contradiction is of the kind I pointed out above, and is probably irreconcilable. Indeed, of the animals that evolved from the basal diapsids, only few still have two temporal fenestra in their skull; which is the defining feature of Diapsida to begin with. --Dr Dima (talk) 09:16, 26 March 2010 (UTC)

March 26

Biology (Incompatible bloods?)

a father has negative blood and a mother has positive blood, what is some problemsDeanna574839 (talk) 01:10, 26 March 2010 (UTC)

I assume we are talking about Rh factor ? If so, then the only potential problem is when the mother and baby don't match (which can happen if the parents don't match). See Rh_blood_group_system#Hemolytic_disease_of_the_newborn. StuRat (talk) 01:13, 26 March 2010 (UTC)

It's not when the mother and baby don't match, it's when the mother is Rh negative, has been previously sensitized to the Rh antigen, and the baby is Rh positive. The reverse situation (mother Rh positive, baby Rh negative) is not a problem. Or, simplifying and applying it to the original question: when the mother is Rh positive, no problems are anticipated, regardless of the Rh status of the father or the baby. - Nunh-huh 01:41, 26 March 2010 (UTC)

That's why I said "potential" problem and directed them to the article for details. StuRat (talk) 01:46, 26 March 2010 (UTC)

Well, yes, that's my point, and why I felt compelled to clarify your answer. In the question asked, there are no "potential" problems. An answer that suggests that there are is potentially misinformative. - Nunh-huh 02:32, 26 March 2010 (UTC)

If a disease condition cannot be predicted with certainty then StuRat is right to characterise it as potential. There are a wide variety of potential causes of the hemolytic disease problem. The OP can refer to the article Rh blood group system which clarifies the concepts Rh positive and Rh negative, and links to the article about potential problems with newborn that are commonest when the mother has D negative blood. I changed the question title for easier reference.Cuddlyable3 (talk) 12:03, 26 March 2010 (UTC)

There's no uncertainty at all that Rh incompatibility does not result when the mother is Rh positive - which is the question asked. - Nunh-huh 14:31, 26 March 2010 (UTC)

Ok, I (and probably Cuddlyable3) didn't understood what you were trying to say, until just now. Thanks, for the clarification. StuRat (talk) 17:05, 26 March 2010 (UTC)

I agree that your title is better, but I also tried to keep the original title, in case it's used as a search term by the Original Poster to find their Q.StuRat (talk) 12:31, 26 March 2010 (UTC)

Cityscape and skyline

What is the difference between a cityscape and a skyline? --Extra999 (Contact ^me + _contribs) 06:44, 26 March 2010 (UTC)

A cityscape is the profile of a city skyline, a skyline can be the view of any notable horizon, e.g. buildings, mountains or whatever. —Preceding unsigned comment added by 86.4.186.107 (talk) 07:02, 26 March 2010 (UTC)

See cityscape and skyline.--Shantavira|^{feed me} 07:48, 26 March 2010 (UTC)

Don't confuse a city's skyline with a Nissan Skyline. ~AH1^(TCU) 00:17, 27 March 2010 (UTC)

G-23 paxilon hydrochlorate (PAX)

My inner geekdom asks: hypothetically if "paxilon" here refers to a synonym for the herbicide methazole (C₉H₆C_l2N₂O₃), is "PAX" a plausible chemical and what might be its formula based on the name "paxilon hydrochlorate"? How would "G-23" be a realistic part of its nomenclature?

If you wonder where this comes from, check out Serenity. --Kvasir (talk) 16:40, 26 March 2010 (UTC)

Do you think the novelist thought about it that deeply?

Remember the number 42

Douglas Adams was asked many times during his career why he chose the number 42. Many theories were proposed,[7] but he rejected them all. On November 3, 1993, he gave an answer[8] on alt.fan.douglas-adams:

“The answer to this is very simple. It was a joke. It had to be a number, an ordinary, smallish number, and I chose that one. Binary representations, base thirteen, Tibetan monks are all complete nonsense. I sat at my desk, stared into the garden and thought '42 will do.' I typed it out. End of story. --Aspro (talk) 18:16, 26 March 2010 (UTC)

Of course not, I just thought it would be interesting to "reverse-engineer" this chemical from the mere name, but first we need to know what might the formula. --Kvasir (talk) 18:37, 26 March 2010 (UTC)

Moon crashes into the Earth

The Moon currently orbits the Earth and so it doesn't crash into the Earth (at least, in our lifetime). For this thought experiment, assume that the Flying Spaghetti Monster suddenly sticks out his noodly appendage and brakes the moon to a halt (we'll use the Earth as our reference frame just for convenience - from the point of view of an observer on Earth, the Moon is now at "absolute rest"). Now, instead of an orbiting moon, we have a moon that is in free fall and on a collision course with the nearest large body (aka Earth). My question is, how long will it take for the moon to collide with the surface of the earth? Assume that the only bodies that have significant gravity are the moon and the earth, the gravitational constant G is 6.67 x 10⁻¹¹ kg⁻¹ m³ s⁻², the mass of the earth is 5.9742 x 10²⁴ kg, the mass of the moon (maybe not important, but here just for reference) is 7.349 x 10²² kg, initial distance between earth and moon (center to center) is 384403000 m, and the radii of earth and moon are 6378100 and 1737400 m, respectively.

It looks to me as though solving the problem involves a differential equation, which I don't know how to use. So instead I approximated a solution using Excel. According to my estimate, it would take 4.85 days for the two objects to collide. Is this close to the correct answer? 66.178.138.144 (talk) 18:02, 26 March 2010 (UTC)

Also please assume that gravity is the only force (no friction/aerodynamic drag) and the rotation of the earth is insignificant for this problem. 66.178.138.144 (talk) 18:05, 26 March 2010 (UTC)

Well, even without full diff-eq (which I'm not an expert at; I'm more of a number theory guy), an iterative solution should get you fairly close. Just use Newton's law of universal gravitation with your initial conditions to find the instantaneous acceleration involved. Then assume that acceleration applies for, say, an hour, and use basic calc to find the distance traveled.. Then recalculate the acceleration for the reduced distance. Repeat until the distance from the center of the Earth to the center of the Moon is less than their combined radii. It will actually happen a little more quickly than that (since it spends most of each hour accelerating more rapidly than it did at the very beginning), but it should be close enough. —ShadowRanger ^(talk|stalk) 18:09, 26 March 2010 (UTC)

The Moon was in free fall even before the noodly FSM meddled with it. Hopefully he/she/it will allow the "textbook" equation for vertical motion of a falling object ignoring air resistance to give an approximate answer. Taking the OPs figures:

Distance to fall y = 384 403 000 - 6 378 100 - 1 737 400
                   = 375 287 500 m
Free fall acceleration g = 9.81 m/s²

                                0.5
Then time to fall t = (2 y / g )

                    = 8747 s
                    ~ 2 hours 26 min

Cuddlyable3 (talk) 18:41, 26 March 2010 (UTC)

Sorry, but wrong. That 9.81 m/s² equation is for objects of relatively negligible mass relatively close to sea level on Earth. You need to use Newton's law of universal gravitation to calculate the acceleration when dealing with two objects, both of non-trivial mass, at a significant distance. —ShadowRanger ^(talk|stalk) 18:47, 26 March 2010 (UTC)

Also, while in normal gravitational calculations on Earth (where the object attracted to the Earth has trivial mass), the force exerted by the object on the Earth can be ignored. In this case, the mutual gravitational attraction between the Earth and the Moon would rapidly become non-trivial, so you'd need to keep track of the acceleration of the Earth as well, assuming you want a really precise answer. —ShadowRanger ^(talk|stalk) 18:50, 26 March 2010 (UTC)

In other words, the gravitational attraction from the Earth is far less than 9.81 m/s^2 at the distance of the Moon (which would make it take longer) and the Earth falling toward the Moon must also be considered (which would make it shorter). I believe the former has more effect than the latter, so it ends up longer. StuRat (talk) 18:52, 26 March 2010 (UTC)

Nice summation, and I agree with your intuition. I do wish I'd done some diff-eq though. Now *I* want to know the precise answer! —ShadowRanger ^(talk|stalk) 18:56, 26 March 2010 (UTC)

Mr. Scots-Irish Jewish atheist it is you who must show the superiority of your method while I am content to put my faith in the Holy IPU. Cuddlyable3 (talk) 19:03, 26 March 2010 (UTC)

I'm aware it's a weird ethnic background. My dad was Eastern European Ashkenazi, my mother was a mix of Irish and Scots-Irish who converted. I was raised Jewish, but only the cultural aspects took. That said, I'm fairly sure neither the Invisible Pink Unicorn nor the Flying Spaghetti Monster nor the Abrahamic God is likely to post on this reference desk and give us the answer. :-) —ShadowRanger ^(talk|stalk) 19:10, 26 March 2010 (UTC)

My kids will be even more confusing if someone tries to categorize them, as I'm engaged to an ethnically Chinese woman, born in Indonesia, but raised in the States. They'll get to check *at least* half the boxes on the Census form! —ShadowRanger ^(talk|stalk) 19:16, 26 March 2010 (UTC)

If we make a boundary for 9.8>g>0.163 m/s², then one can verify at least that the time must be between 2.5 and 19 hours. I don't think it will take days when solving the differential equations (neglect air friction).--Email4mobile (talk) 20:44, 26 March 2010 (UTC)

Oops, that's my mistake, 9.8> g > 0.0266 m/s² will lead to 6 > t > 0.1 days.--Email4mobile (talk) 21:16, 26 March 2010 (UTC)

Like all gravitational problems, your falling moon will obey Kepler's Laws so:

${\text{Time}}\approx {1 \over 4}2\pi {\sqrt {({\text{orbit distance}})^{3} \over {G(M_{Earth}+M_{Moon})}}}$

Which gives 6.82 days. Dragons flight (talk) 22:50, 26 March 2010 (UTC)

Hi, OP here. Are you sure that this is the correct equation, Dragons flight? 6.82 days would be an average acceleration of 0.00221 m/s, which is smaller than the initial acceleration of 0.00270 m/s! I would expect acceleration to increase in magnitude as the moon and earth get closer together.

Thanks everyone for the answers you've given so far; they've been helpful. I was assuming that the mass of the moon was negligible (as implied by my original question) but I tried my Excel "iterative solution" again with the mass of the moon factored in and it didn't make a significant difference. This is understandable - the moon is two orders of magnitude less massive than the earth. If someone knows how to do the diff-eq, I would appreciate them chiming in. :) Oh yes, I found this: [14] archived version of [15] which is currently down. They say it takes "about five days" so that tells me I'm in the right ballpark according to them. I'd still appreciate more confirmation. 66.178.138.206 (talk) 23:15, 26 March 2010 (UTC)

Dragons flight's formula is almost right. The correct one is

${\text{Time}}\approx {\frac {2\pi }{4{\sqrt {2}}}}{\sqrt {({\text{orbit distance}})^{3} \over {G(M_{Earth}+M_{Moon})}}}$

The extra square root of two that was missing changes the final answer to 4.82 days which is pretty close to the answer from the spread sheet. Dauto (talk) 02:05, 27 March 2010 (UTC)

black and white

Has anyone produced a black and white only digital slr? The sensors aren't wavelength-sensitive, so in order for them to differentiate wavelength, they need a filter in front of them of the right colour. However, if you remove the filters, you could squeeze in more pixels per square inch of the sensor, but they'd only sense light and dark. I would imageine it would have a highly specialist use in high iso, high shutter speed, low light photography. But has anyone built one? —Preceding unsigned comment added by 81.147.56.162 (talk) 18:23, 26 March 2010 (UTC)

The digital output of the camera doesn't "know" about the colour filters so the full pixel resolution is there already (before jpeg compression). Removing the filters would gain some sensitivity. Since they are added last to the CCD chip it might be possible to bleach them out. Cuddlyable3 (talk) 18:49, 26 March 2010 (UTC)

If nobody has done this, it sounds like a good idea to me. It would be good for pics of color subjects where black and white is used for artistic reasons, and also for subjects which lack color. StuRat (talk) 19:01, 26 March 2010 (UTC)

For subjects that lack colour the individual pixels are immediately available in the BMP image format and only need relative weighting of Red/Green/Blue. Cuddlyable3 (talk) 19:39, 26 March 2010 (UTC)

It's not a new idea (not necessarily in a DSLR; possibly a digital back for medium or large format cameras, or a rangefinder). I don't think any such camera has gone into production, though, presumably because of the relatively small market. -- Coneslayer (talk) 19:52, 26 March 2010 (UTC)

I know that some microscope cameras are monochrome only. Over the past couple of months I have been using a Leica fluorescence stereomicroscope as part of a research project (if you are particularly interested I was using this one [16]) in conjunction with a digital camera (this one [17]). It doesn't need to be full colour since it is being used for fluorescence microscopy - so the only colour it will see is the fluorescence emission wavelength coming through the emission filter of the selected filter set. If I needed multiple fluoresence channels I took individual images with different filter sets, false coloured them and overlayed them in photoshop. Sensitivity is very important here, which is another reason to use monochrome. It's also interesting to note that the camera was only 2 megapixels, since minimising noise is far more important in this application than maximising resoultion (If you need to enlarge something you use a higher magnification lens, whereas if there is too much noise to precisely interpret/measure fine details in the image you're stuck). Equisetum (talk) 19:53, 26 March 2010 (UTC)

Sorry, I should really take more time to read the question - I missed the "SLR" bit Equisetum (talk) 21:05, 26 March 2010 (UTC)

Yes. Several models in the Kodak/Nikon Pro DCS line were available in three chip styles, Color, Infra-Red, and Black And White. I see that it's not mentioned in our article, but see here.

I'd be surprised if there weren't more modern pro cameras offered with similar options. APL (talk) 21:25, 26 March 2010 (UTC)

All astronomical CCD's are monochrome (see http://en.wikipedia.org/wiki/Charge-coupled_device#Usage_in_astronomy) in the sense that they don't have any filters. However, to collect any useful data, 1 filter, allowing in a certain range of wavelengths, must be put in front of the CCD. —Preceding unsigned comment added by 216.16.224.186 (talk) 21:42, 26 March 2010 (UTC)

The deal is that a color digital camera has groups of (typically) four sensors grouped into a single "pixel" - one red, two green and one blue. But a slightly different part of the image lands on the red, green and blue sensors. Hence, if you can get the "RAW" image (not JPEG or whatever) and if you know the physical layout of those four sensors, then with the right software you can get a good monochrome image at somewhat higher resolution than you'd get a color image from the exact same camera. Since monochrome digital cameras are not in high demand, they'd be costly specialist items. So you'd be better off using a color camera that saves "RAW" format images - and use some really good image processing software to make your final monochrome image. SteveBaker (talk) 23:06, 26 March 2010 (UTC)

From some more searching, it looks like the Kodak DCS cameras mentioned above may have been some of the last SLR cameras to offer monochrome chips as a standard option. (In certain forums they seem to be fondly remembered for this reason.) It looks like a monochrome conversion may be possible. (ie: They remove the colored filters from the chips.) Check it out [18].

Whatever they were in the 90s, now it looks like Steve is right : They're specialty items. APL (talk) 03:06, 27 March 2010 (UTC)

Ethanol

Within the context of talking about food safety, would it be correct to call ethyl alcohol a "toxin"? Our article does not say so, and neither do the other articles I've looked at it, but it would seem to (loosely) meet the definition. Created by a living thing, harmful if swallowed, etc. Our articles treat it within the context of it being a "drug", which it certainly also is, but I wonder if the term "toxin" would also make sense. Matt Deres (talk) 18:37, 26 March 2010 (UTC)

It has a Median lethal dose (LD50) so yes, I suppose it is very much a toxin that is dependant on the dose.--Aspro (talk) 18:45, 26 March 2010 (UTC)

More importantly, it has an LD50 that can be achieved without exceeding the ability of the human in question to consume it. There are toxins with theoretical LD50s that, practically speaking, are never hit, because they must be consumed and the amount required to kill you is so great that it can't all fit into a normal human before the excretion processes end up removing it. —ShadowRanger ^(talk|stalk) 18:55, 26 March 2010 (UTC)

But there must be all sorts of things that we could use to kill ourselves by eating too much, does that make them all toxins ? StuRat (talk) 18:57, 26 March 2010 (UTC)

Yeah, I'm not real sure on that definition. Water can kill you by drinking too much of it (no need to drown), though usually only if you are drinking truly absurd amounts and not peeing or sweating out an appreciable amount, and/or you keep it up long enough that you manage to disrupt the electrolyte balance in your body. That said, alcohol is clearly a toxin; it can kill you by the direct metabolic effects of the alcohol, not just by displacing or disrupting the balance of various chemicals in your body. —ShadowRanger ^(talk|stalk) 19:02, 26 March 2010 (UTC)

Perhaps the word 'acute' should have gone before 'dose' and 'low' before 'median'. And of course, semantics can make these things confusing. This may account for the habit of clinicians to say 'poisoning' for when it is life threatening.--Aspro (talk) 19:31, 26 March 2010 (UTC)

No, ethanol is not a toxin. Toxins and poisons are two different things. Ethanol can be a poison in some doses but is never a toxin. alteripse (talk) 19:43, 26 March 2010 (UTC)

Can you explain why? Our article says that "a toxin is a poisonous substance produced by living cells or organisms". Ethanol can be produced by fermentation with yeast. This would seem to fit that definition - why doesn't it? 94.168.184.16 (talk) 20:06, 26 March 2010 (UTC)

I just wrote you a long answer that was completely lost when Stu answered the next question. Here are 6 more definitions of toxin: [19]. If you define toxin so broadly that it refers to any substance produced by an organism that can cause harm, then you must consider water, oxygen, carbon dioxide, chalk, and glucose to be toxins because they are all substances produced by organisms that can cause harm in sufficient quantities, rendering that usage pretty meaningless. alteripse (talk) 20:26, 26 March 2010 (UTC)

Where did it disappear to? When you get an Wikipedia:Edit_conflict, just save your text (e.g., to the clipboard), cancel out, then try again.--Aspro (talk) 21:16, 26 March 2010 (UTC)

Yea, with any modern web-browser you should be able to simply hit the [BACK] button and retrieve what you have written. Admittedly, this isn't immediately obvious. APL (talk) 21:27, 26 March 2010 (UTC)

“rendering that usage pretty meaningless”

To whom? Without identifying a cohort that statement may apply to, don't you think that statement is, err . . . pretty meaningless. Are not clinicians in The Royal Navy, oil recovery industries etc. familiar with Oxygen toxicity?. Maybe I should have said "And of course, some people use semantics to make these things confusing"--Aspro (talk) 23:48, 26 March 2010 (UTC)

Ethanol is considered toxic because even consuming it in small amounts kills some brain cells, starts some cirrhosis, etc. Other substances, like water or glucose, are necessary for life and are not toxic in normal amounts.--Cheminterest (talk) 20:59, 26 March 2010 (UTC)

There's a lack of evidence that alcohol kills brain cells. Vimescarrot (talk) 21:42, 26 March 2010 (UTC)

Rusted hammer

Someone borrowed my hammer and now the head is all rusted. It's got a fiberglass handle (no wood) so I was wondering if there's anything I can do (soak it in something, perhaps) that will de-rust it? DRosenbach ^{(Talk | Contribs)} 20:11, 26 March 2010 (UTC)

WD40 and 0000 steel wool, or superfine wet-and-dry paper. DuncanHill (talk) 20:17, 26 March 2010 (UTC)

If it's a Craftsman (Sears) hammer, you can return it for a replacement, they are quite generous with their terms. Otherwise, I'd just sand off the rusted spots. But beware if the head is now loose in the jacket, as it could fly out during use. And you could always tell whoever borrowed it that they owe you a new hammer; I would. StuRat (talk) 20:21, 26 March 2010 (UTC)

There are chemicals used to remove rust, but they might cost as much as a new hammer, so that's why just sanding it off might be best. And be sure to keep the metal portions of this hammer oiled from now on, as obviously it has a tendency to rust. StuRat (talk) 20:23, 26 March 2010 (UTC)

I would second the suggestion for WD40 and steel wool. You can also paint it with a rust converter, which will turn it black, but protect it from future rust (it converts iron oxide to iron tannate). Ariel. (talk) 20:33, 26 March 2010 (UTC)

That will teach you to lend your tools to somebody else!
Three rules for tools:

1. Buy the best tools you can afford.
2. Learn to use them safely and thoroughly.
3. Never lend them out for any reason.

--Aspro (talk) 20:47, 26 March 2010 (UTC)

I'd have to disagree with 1 and 3. Number 1 because there are times when you only need a tool for a single use, and buying the premium model would be a waste, and number 3 because that will result in your friends not lending you any tools either. If you and a buddy each lend the other tools and treat them with respect, you can double the number of tools each of you have at your disposal. StuRat (talk) 21:00, 26 March 2010 (UTC)

Rule 3 depends on the tool - you may borrow my pots and pans as much as you like but you may NOT, not ever, borrow my shiny new Santoku. Equisetum (talk) 21:11, 26 March 2010 (UTC)

Wow! OK, I am envious. I'm left handed and thus find their sharpened on the wrong side, can they by ground the other way?--Aspro (talk) 21:38, 26 March 2010 (UTC)

Do you mean THEY'RE sharpened? Cuddlyable3 (talk) 21:54, 26 March 2010 (UTC)

I'm left handed too, and my santoku is actually sharpened on both sides, and isn't Japanese, which I guess means it isn't a proper santoku. If you're interested the knife is [20] and it only costs $20, I have several of that series of knives, recommended by my uncle who takes his cooking quite seriously. Neither of us has any idea how Kuhn Rikon makes such good knives so cheaply - my only concern is that at that price I don't know how long they'll last, but for $20 it's worth taking a chance. The reason I won't lend it is mainly that it's a very thin blade and if you tried to cut inappropriate things with it (like bones) it would get damaged. Equisetum (talk) 22:39, 26 March 2010 (UTC)

A dip in hydrochloric (muriatic) acid to dissolve the iron III oxide followed by a dip in phosphoric acid may remove and prevent rust. --Cheminterest (talk) 20:55, 26 March 2010 (UTC)

If you are exceptionally proficient with a tool, even if that proficiency is largely a self-held opinion, you would not want to loan such tools to anyone. The other person will always be using that tool in a less desirable way. And most tools are not indestructible. Bus stop (talk) 21:48, 26 March 2010 (UTC)

For those that now find themselves in the mood for some real hard Engineering porn, here is the Snap on online catalogue - enjoy!--Aspro (talk) 22:31, 26 March 2010 (UTC)

Wow, 751 different kinds of screwdrivers — this is great. Thanks. Bus stop (talk) 22:39, 26 March 2010 (UTC)

It's worth periodically squirting a little WD40 onto a shop cloth and wiping down all of the metal parts of your tools once in a while - especially those used to cut wood such as saws and chisels. That thin film of water-displacing oil keeps them shiney for months. I usually use a Dremel with a wire-brush head for removing superficial rust from old car parts and such like...but once something has gotten rusty, any surface coating it may once have had is gone and it'll rust again, soon after you've cleaned it - so using some kind of water-repelling oil on the surface is a good idea. (Bonus Fun fact: WD-40 is so called because it was Norm Larsens 40th attempt at creating a Water Displacing oil! You've gotta admire Norm's determination - even if you're less than impressed by his product naming skills!) SteveBaker (talk) 22:53, 26 March 2010 (UTC)

Molasses - I remember reading more than once that you can put rusty things in them and after some days (as far as I recall) they come out shiny new. 78.149.198.14 (talk) 01:09, 27 March 2010 (UTC)

Pyrophoric qualities of Ni-MH cells

What substances would spontaneously ignite in a nickel-metal hydride cell? I took one apart, and some particles from one electrode contacted particles from another electrode. After a couple of minutes, both the electrolyte paper and the cathode material were up in flames. All of the black corrosion on the cathode was burnt away, and the paper was charred. I quenched the fire by putting a heavy piece of metal on top of the materials. It immediately extinguished it. There also seems to be a strong oxidizer in the anode, because it produced large quantities of chlorine gas when reacted with hydrochloric acid. --Cheminterest (talk) 20:53, 26 March 2010 (UTC)

Diet defined by required and forbidden foods

I have found a table of foods which distinguish carnivore from vegan diets and Kosher from Hindu diets. Is there a list of required or forbidden foods that can be added to the table to distinguish Muslim (or Islamic) diets and Christian diets from the rest? 71.100.5.192 (talk) 21:46, 26 March 2010 (UTC)

I think Halal refers to a diet in keeping with Islam. Bus stop (talk) 22:02, 26 March 2010 (UTC)

I don't think there is a "Christian diet" for mainstream Christian churches. At some time in the early first millennium what was to become the orthodox church decided to interpret Matthew 15:11 as abolishing Jewish food laws and allow Christians to eat everything, even Big Macs. But see Pentabarf. --Stephan Schulz (talk) 22:18, 26 March 2010 (UTC)

The LDS Church has the Word of Wisdom, though no foods are specifically forbidden in it (some other things are, though). ···日本穣^? · 投稿 · Talk to Nihonjoe 22:29, 26 March 2010 (UTC)

What comes to mind are Friday Fast and Lent in food-related practices in Christianity, other than that there is no specific blanket forbidden food. Well except for cannibalism of course. --Kvasir (talk) 22:35, 26 March 2010 (UTC)

That's pretty funny! Matthew 15:11 says: "Not that which goeth into the mouth defileth a man; but that which cometh out of the mouth, this defileth a man.". So an off-hand comment that's clearly intended to mean that you shouldn't talk nonsense is taken to overturn an entire raft of detailed rules about diet?! It's just as well nobody actually reads the Bible isn't it? Anyway - there is at least one dietary law for many christians - where does the Catholic "Fish on Friday" rule come from? SteveBaker (talk) 22:42, 26 March 2010 (UTC)

That's a very interesting point, Steve (if I may call you by your first name). Hospital dietitians of today normally recommend a 30% fat, 60% carbohydrate and 10% protein diet with exceptions made for particular aliments on doctors orders. I found a table more or less for meals based on various combinations of foods but I do not know where in the Wikipedia to find or simulate this. 71.100.14.194 (talk) 23:16, 26 March 2010 (UTC)

Not all catholics follow that rule. Many do it only on good friday. Dauto (talk) 22:54, 26 March 2010 (UTC)

Re Matthew: Well, I suspect that the conflict between Christianity as a Jewish sect, with all the inconveniences of food restrictions and Sabbath and Circumcision, and Paul's more radical "it's a new religion. Eat pork and keep your bits" had more to do it than the actual (pre-)text. If you are looking for a justification for anything in the bible, you're likely to find a suitable passage. And Paul won... --Stephan Schulz (talk) 23:31, 26 March 2010 (UTC)

I thought the no-meat-on-Friday thing was obsolete? I thought it was now acceptable for a catholic to substitute some other penance? Even a penance that was not food-related. APL (talk) 02:51, 27 March 2010 (UTC)

Shouldn't this discussion be moved to the humanities reference desk? --The High Fin Sperm Whale 23:17, 26 March 2010 (UTC)

I suppose it all depends upon whether the diet plans are based on religious belief or have a health or scientific basis. For instance, not eating pork may have a religious basis but prior to that the basis appears to be health. 71.100.14.194 (talk) 23:34, 26 March 2010 (UTC)

That table probably shouldn't be there - it's redundant to the one directly above, with the only difference being that it is much less attractive. Intelligentsium 23:36, 26 March 2010 (UTC)

The new Wikipedia is about being attractive? What ever happened to the idea of presenting content in a usable and meaningful way. You can always add color and take care of the attractive end but I find it completely atypical of a lack of anything better to do than for administrator to remove content for such a stupid rational. 71.100.5.167 (talk) 00:52, 27 March 2010 (UTC)

Chile

I heard that in plate tectonics, Chile is being slowly pulled away and separated from South America and will one day move away as an island (can't find this on wikipedia)- is this true? Thanks, --AlexSuricata (talk) 23:33, 26 March 2010 (UTC)

No. The Nazca Plate is being subducted underneath the South American Plate. Chile is part of the South American Plate. As the Nazca Plate is forced under the South American Plate, it causes the South American Plate to kink, forming the Andes. --The High Fin Sperm Whale 23:37, 26 March 2010 (UTC)

(ec)You're probably thinking of California. From what I can see on the article on the nearby Nazca Plate, the Nazca Plate is perpetually moving towards and underneath the South America Plate. That wouldn't cause Chile to split, just to become ever more mountainous. —ShadowRanger ^(talk|stalk) 23:39, 26 March 2010 (UTC)

March 27

Do topical vitamins still work if dietary intake is sufficient?

I know that a number of studies show topical vitamin A fights acne, and C and E rehydrate dry skin. Has it been studied whether these effects vary with dietary intake or bloodstream levels of these vitamins? That is, how do we know the topical vitamins aren't simply replacing missing dietary vitamins? NeonMerlin 00:39, 27 March 2010 (UTC)

Interference (wave propagation)

In that article, the description of the image to the right says: "As time progresses, the wave fronts would move outwards from the two centers, but the dark regions (destructive interference) stay fixed."

Is that true? 1) If the dark regions stay fixed, then how could the light regions move? 2) The animation further down the page does not have any stationary dark regions. Thanks 78.149.198.14 (talk) 01:19, 27 March 2010 (UTC)

The "dark regions" in the picture would be the cyan parts. There's several unmoving cyan lines radiating outward. There are also cyan regions moving along with the other-colored regions, but that's not what it's referring to. 67.172.112.226 (talk) 01:43, 27 March 2010 (UTC)

gravity

Although of higher local intensity or density throughout the universe is gravity the equivalent or substitute for atheists what God is represents for theists? 71.100.6.104 (talk) 03:09, 27 March 2010 (UTC)