Wikipedia:Reference desk/Science

Wikipedia:Reference desk/headercfg

October 2

Weighty of charge

I think about charge and current. what is weight of charge and current plese? —Preceding unsigned comment added by 88.109.239.189 (talk) 00:17, 2 October 2007 (UTC)

An electron has a mass of 9.109 382 15(45) × 10^–31 kg, but I'm unsure if charge has mass. Does the negative electrode of a capacitor gain mass when charged? anonymous6494 02:47, 2 October 2007 (UTC)

Along the lines of a capacitor gaining mass, I`ve wondered if a rechargeable battery is just a teeny bit more massive when fully charged compared to when it`s exhausted. I would have to guess yes. Is that correct? I suppose any kind of battery could also apply. Thanks, Dave 64.230.233.209 03:33, 2 October 2007 (UTC)

The electrons may be on the negative electrode, but they have been taken away from the positive electrode, so the net change in mass of a capacitor is nothing. However there will be some relativistic mass (E=mc²) due to the energy stored. The same will apply to the battery. Electrons are just mvoed from one place to another, so the mass of electrons in the battery is the same when it's charged as when it is empty. Graeme Bartlett 04:06, 2 October 2007 (UTC)

Could you not use a static-discharge to transfer electrons to one plate of a capacitor without having electrons drained from the other plate? Something like the active part of an electroscope. I don't think net total charge (i.e., electron count) needs to be conserved in a non-closed system, so how about looking at mass change in only one part of a closed system before/after creating electron imbalance of that part with respect to some other part. DMacks 04:27, 2 October 2007 (UTC)

Static charge capacitors with the other plate at infinity (or earth) have a low capacitance and cannot store much charge. You will be working hard to get a nanofarad of capacitance, and if you combine that with the mass of the electrons involved - you will get very little mass. Graeme Bartlett 00:11, 3 October 2007 (UTC)

Charge itself has no mass. Charge is a fundamental property of a particle, just like rest mass is. Asking what the mass is on charge is as meaningless a concept as asking what the mass of a velocity or the charge of a temperature is. They simply have no such inherent relationship. Someguy1221 04:49, 2 October 2007 (UTC)

According to our electron article, each electron has a mass of 9.109 382 15(45) × 10^–31 kg and a charge of –1.602 176 487(40) × 10^–19 C. This gives us a mass per charge of -5.7 x 10^-12 kg/C or -5.7 x 10^-9 g/C. The negative value means that you will subtract some mass for objects with a positive charge and add some mass for objects with a negative charge. This all assumes that the charge is in the form of ionized atoms, and/or free electrons. Free protons have a positive charge and are much heavier. StuRat 14:24, 2 October 2007 (UTC)

If you took an uncharged capacitor of huge capacitance, say of 1 farad and, and charged it with electricity, the energy stored in it would increase by 1/2*(capacitance)*(voltage)² Joules. The equation for mass and energy says E= mass*c² (where c is the velocity of light, approx 3 x 10⁸m/sec. If it were charged to 100 volts (a very high voltage rating for such a large capacitor), the increase in energy would be 5000 Joules, indicating a mass increase of 5.6 x 10^-14 kilograms, probably not detectable by any existing means, especially considering the mass of such a large capacitor. If it were charged to 1000 volts, the mass increase would be still only 5.6 x 10^-12 kg or a thousandth of a microgram, still unmeasurable in a capacitor probably weighing over a kilogram. (Please check the math, formulas, and analysis). Edison 14:39, 2 October 2007 (UTC)

I don't think that formula is applicable here. That only applies when mass is converted to energy (as in a nuclear reaction) or vice-versa. That doesn't happen in a capacitor. StuRat 14:54, 2 October 2007 (UTC)

It applies to everything. E=mc^2 is right no matter where the energy came from. Someguy1221 16:38, 2 October 2007 (UTC)

In a completely unrelated question, would that mean that a warm cup of coffee has a very slightly higher mass than a cold one? —Preceding unsigned comment added by 66.28.242.74 (talk) 17:40, 2 October 2007 (UTC)

Much higher since the cold one has already lost a lot of steam while it was hot and the hot one is still losing steam :D --froth^t 18:00, 2 October 2007 (UTC)

Yes. Ignoring evaporation, the hot cup of coffee will be very slightly heavier. If you want to think in terms of exactly where the mass is, the particles in the hot coffee will be moving faster, and therefore possess more relativistic mass. Someguy1221 00:23, 3 October 2007 (UTC)

If you wind as alarm clock, it gets heavier (by a tiny undetectable amount). If you accelerate a subatomic particle in a cyclotron, to an appreciable fraction of the speed of light, and fail to allow for the mass increase, your results will not be as anticipated (per old cyclotronists). The meaning of the "weight of current" is harder to interpret. Current into a conductor equals current out, so at first blush current would seem to have no weight. Edison 05:15, 3 October 2007 (UTC)

Another tick question I just thought of...

Is it possible for a tick to transmit HIV from one human to another? --Kurt Shaped Box 00:28, 2 October 2007 (UTC)

theoretically yes, practically no. Each individual tick (or mosquito or other arthropod vector) almost never attacks more than one human. Ticks in particular usually attack an animal host and then a human host. The chances of a particular human being attacked by a tick that had previously attacked a HIV-infected human are vanishingly small. A flea is theoretically more likely, but I have not seen any reports in the literature. -Arch dude 01:42, 2 October 2007 (UTC)

But leeches are another matter. Our article states that blood borne illnesses can be spread through a leech biting an infected person. --S.dedalus 01:45, 2 October 2007 (UTC)

Does water expand when heated?

If a glass of water is heated from 20 Celsius to 80 celsius, does the water expand and become less concentrated? Acceptable 01:28, 2 October 2007 (UTC)

Yes the water will expand a very small amount and become less dense, if that is what you mean by concentrated. See the section on water density. Sifaka ^talk 02:05, 2 October 2007 (UTC)

The table in that article stops at 30°C, but I have here the CRC Handbook, 67th edition. It gives the density at 20°C as 0.99823 g/ml and at 80°C as 0.97183, so the "very small" increase in volume is more than you might think -- a bit over 2.7%. At the boiling point the density is 0.95838, so from room temperature to boiling, water expands by over 4%. This relatively large expansion is why it was possible for some early thermometers to use water as a working fluid; but of course they would not be usable with temperatures close to freezing, where water stops contracting as it gets colder and starts expanding again. --Anonymous, 13:48 UTC, October 2, 2007.

This is also (at the moment) the major contributor to sea level rise, not melting ice, as most people think, although that might become the major factor in the future. DirkvdM 07:42, 2 October 2007 (UTC)

This business of water expanding as it gets close to freezing is an extremely rare thing - there are only a handful of substances that do this. It's also the reason why your water pipes can split if they come close to freezing. The metal of the pipe is contracting with the cold - but the water expands and something has to give! But above those low temperatures water behaves like almost every other substance and expands as it gets warmer. SteveBaker 13:55, 2 October 2007 (UTC)

The water expands when heated alright, look at the overpressure valves dribble on hot water systems; or have a long, hot shower so the hot water system has only cold water in it, wait until the water is fully hot again then open a tap. The pressure is noticeably greater (the water spurts out at higher pressure than usual). This is particularly noticeably where the water pressure is normally fairly low.Polypipe Wrangler 06:50, 6 October 2007 (UTC)

FYI, I think some people may be confused about water expanding as it cools, and also expanding as it is heated. The most dense water (at least at normal atmospheric pressure) is I believe 4 Celsius. Many lakes are permanently 4 C at the bottom because it is heaviest and sinks. —Preceding unsigned comment added by 99.233.83.143 (talk) 16:19, 6 October 2007 (UTC)

I think that's rather the other way around. It's not like 4C molecules sink to the bottom (although there may be some of that too). It's more like the water at the bottom undergoes most pressure and therefore 'tries hardest' to be as compact as possible, so it gives off heat to the water above it. Unless the average temperature is lower than 4C, in which case it will absorb warmth, causing the water at the top to be coldest and freezing first. This is why fish can survive in a frozen lake for a long time - the water at the bottom will remain at 4C. I suppose that if it gets really cold, it might even absorb warmth from the ground underneath to stay as compact as possible. DirkvdM 07:42, 7 October 2007 (UTC)

Atoms

How can one determine the number of neutrons in an isotope. Marlith ^T/C 02:54, 2 October 2007 (UTC)

See mass number. --24.147.86.187 02:57, 2 October 2007 (UTC)

Wow, that page is amazingly verbose for such a simple concept. Let me summarize that page for you: atomic mass = protons + neutrons. DONE. Assuming you know the number of protons and the atomic mass, you should be in good shape. --Ybbor^Talk 03:01, 2 October 2007 (UTC)

Except that's not 100% true, especially for isotopes. Atomic mass is not the same thing as the mass number, which is simply a total of neutrons plus protons; atomic mass also has electrons involved, and the mass of isotopes can be slightly different than the mass number, and can deviate from their mass numbers based on their mass defect. So you have to make sure you are always rounding atomic masses, essentially, before you try to use them to calculate neutrons. --24.147.86.187 12:36, 2 October 2007 (UTC)

Yes - but the error is truly microscopic in all but the most exotic elements. We have:

• 'atomic number' -- the number of protons - which determines what we name the atoms and how many electrons they have when they are electrically neutral - which in turn determines most of their chemical properties).
• 'mass number' -- the number of protons+neutrons - which determines which isotope you have. Two atoms with the same mass number may have a different number of protons, so they may have wildly different chemical properties.
• 'atomic mass' -- the actual mass of an atom. The mass includes protons, neutrons and electrons. Since a proton weighs 1.007276 atomic mass units and a neutron is a little more at 1.008665 units and the electron is 0.000548 units - you can see that roughly, protons and neutrons have masses of almost exactly 1 and the electron weighs almost nothing - so the atomic mass is going to be almost exactly the same as the mass number but with a few extra digits after the decimal point.

So if you have the mass number and that atomic number, subtract them to get the number of neutrons. If you only have the atomic mass and the atomic number, then chop off all of the digits after the decimal point of the atomic mass to get the mass number and then subtract the atomic number. (This rule breaks for the very heaviest atoms - Darmstadtium for example has a mass number is 281 but it's atomic mass is 282 - but I think the rule works OK up to maybe Dubnium - you'll never care about this fact!)

SteveBaker 13:50, 2 October 2007 (UTC)

Also, in reference to the second answer, the mass number changes with each isotope. The atomic mass for any element is an average of all the possible isotopes' masses in relation to their abundance.Mrdeath5493 05:14, 3 October 2007 (UTC)

Foucault Pendulum Animation

I can't seem to wrap my mind around what this animation is trying to do. I think I understand foucault pendulums (it goes back and forth in the same plane relative to the stars, but since the earth is moving, the ground turns under it. Also the whole apperatus is moving around the earth's axis) but this image seems to contradict it. Shouldn't the the pendulum's swing be the same from the star's point of view? The animation is from the star's point of view so why does it spin? The spin would only be accurate if the earth were moving under it and the image was relative to the pendulum. Or is this only valid if the pendulum's on the north pole? Even so the image seems wrong. Aargh, it's hard to visualize things spinning while stuck on the surface of a rotating sphere.. can anyone help? --froth^t 04:33, 2 October 2007 (UTC)

I also wonder about the accuracy of that image. It's sort of hurting my head right now, so I'll think about it some more and report back. Nimur 04:49, 2 October 2007 (UTC)

I'm not going to view the image right now, but it's not correct in general that a Foucault pendulum goes back and forth in the same plane relative to the stars. Its initial plane of motion is determined by three points: the fulcrum F, the center of the Earth E, and the location B where the bob is released. As the Earth rotates, points E and F must remain in the pendulum's plane of motion, but point F is moving and will not (in general) remain in the original plane. The plane of motion thus rotates with respect to the stars as well as with respect to the Earth. --Anonymous, not moving right now with respect to the Earth, 14:00 UTC, October 2, 2007.

*explodes* x_x I see how this is possible and I can look at the animation and imagine it making sense at the north pole where the earth is spinning under it and the fulcrum is stationary, but at an angle when the fulcrum is moving too, it... zomg I see it, it's working hah! thanks --froth^t 17:58, 2 October 2007 (UTC)

The surface of the Earth has intrinsic Gaussian curvature, so parallel transport of a vector around a closed curve may result in a net change in direction. See also Geometric phase#The Foucault Pendulum. —Keenan Pepper 02:45, 3 October 2007 (UTC)

Dimensions in a World

04:47, 2 October 2007 (UTC)210.0.136.138AHow many dimensions exist in the real world? And, how does this really mean to human beings? Can a specific person exist in a separte world of different dimensions, if that exists. Is it true that Eistein has already affirmed this?04:47, 2 October 2007 (UTC)210.0.136.138Allen Chau, from Hong Kong

There are as many dimensions as we define to exist. See degrees of freedom. One might say that the number of dimensions is equal to the rank of the system matrix. Alternatively, one might choose to describe the spatial extent of an object, which would only include three dimensions. One might also choose to represent system space in terms of phase or velocity - so we could easily have six dimensions. These concepts are quite complicated, but in short summary for layman's purposes, there are as many dimensions as we feel like adding to describe the situation at hand. Most systems can be easily described with three spatial dimensions (and often time as an additional dimension). Nimur 04:53, 2 October 2007 (UTC)

I think the OP was referring only to the commonsense meaning of "Dimension" as in space and time dimensions. We can plainly see three dimensions in space, and only three. As Einstein explained, time can be thought of as a fourth, somewhat wierd dimension. This gives our world four dimensions that we can observe. No higher dimensions have ever been observed, ever. Now, if a person were to exist in an "alternate set of dimensions" he'd better damn well be in another universe in the greater multiverse, or one of the many-worlds, because if he isn't, there's pretty much nothing but speculation to explain it (er, those first two were also speculation, but they've been floating around for quite a while). Now, the only remotely close to accepted theory that allows alternate dimensions to exist in our own universe without our observing them is string theory and its variants, but absolutely nothing can occupy these unobservable dimensions (except for strings themselves, which can sort of wiggle around in them). Everything you've seen on Sci-Fi shows about a person entering an "alternate phase" or something like that, and suddenly no one can see him, is entirely bullshit. Someguy1221 05:01, 2 October 2007 (UTC)

Mathematicians and scientists often deal in higher dimensions and calculate things using them. They can be assumed to exist on a theoretical level, in the same way that the square roots of negative numbers are assumed to exist on a theoretical level. These assumptions are useful in such contexts. But whether any human mind can actually visualise or even comprehend what they mean, outside of such theoretical considerations, is a moot point. -- JackofOz 13:05, 2 October 2007 (UTC)

Why do you say that? Have you ever read Flatland? The 2 dimensional people would have had 2 dimensional physics and called time the 3rd, and told their ref desk OPs that it's nonsense to think that you can just poof out into the 3rd dimension.. which of course the sphere does in the story, baffling their scientists --froth^t 18:05, 2 October 2007 (UTC)

Erm, what? Flatland is fiction, by the way. In modern physics, if a spatial dimension exists, there is utterly nothing to prevent any particle from moving through it. And so there would be some quite severe consequences. For example, chirality could not exist in three dimensional objects, which would conflict quite severely with many observations in chemistry. That's just the simplest to imagine example (in my opinion) of where the existence of a fourth spatial dimension would alter the laws of physics (er, chemistry, whatever). Now, string theory does allow wierdness like the existence of extra dimensions that are unobservable to only some observers. For example, every particle on in the universe could be bound to a "three dimensional surface" of a higher dimensional object. Thus, as if flatland were on the surface of a sphere, we would exist in a higher dimensional universe we could not observe. And this does not necessarily prohibit other objects, universes, whatever, from not being bound and limited by this three dimensional surface we are bound to. The problem is that string theory is presently unverifiable. So it is quite correct to say that there is no accepted theory in physics that would allow the existence of unobservable spatial dimensions. Someguy1221 20:08, 2 October 2007 (UTC)

You can define any point in space relative to some fixed coordinate system using three distances. This makes it a three-dimensional world. If you follow Einstein and wish to employ the mathematical convenience of talking about 'space-time' then you need to add one time measurement. This makes three or four dimensions depending on what you are trying to measure. Nimur's degrees of freedom argument is wrong because that's an argument about measuring things other than space itself. You can choose to measure space with things other than three distances - but no matter what, you always need just three numbers...so for example, you can measure every point in space using two angles and one distance ('spherical polar coordinates') or one angle and two distances ('cylindrical polar'). In space/time, you always need four numbers. The exact formulation doesn't matter - the dimensionality of space (or space/time) doesn't change depending on how you measure it.

The extra dimensions that string theory predicts are claimed to be 'very small'. Understanding what this means is tricky - we have do take it in small steps:

• Suppose for a moment that we were observing some two-dimensional creatures - living on the surface of a flat piece of paper. In our present world view, the paper is flat and infinitely large. There is no 'up/down' dimension for them because they are 2D creatures - they only have left/right and forwards/backwards.
• But suppose one of those two spatial dimension (let's pick the left/right dimension) was 'small' - just a 10 miles across say. The universe can't have 'edges' - it has to 'wrap around'. By this, I mean that moving in the left/right dimension for exactly 10 miles would take you all the way around that dimension and back to where you started - for a 2D creature this would be a bit strange - but for us 3D creatures watching them, it would be like they were living on the surface of an infinitely long cylinder of paper that's just one mile in diameter. They could move as far as they wanted along the length of the cylinder - but if they moved a long distance in the other direction, they'd go all around the cylinder and back to the start. Because their 2D light beams are stuck in the 2D surface, if they looked off to the left or right using a pair of decent binoculars, they'd be able to see themselves 10 miles away.
• In a three dimensional universe like ours, if our up/down dimension was only 10 miles across then you'd be able to travel as far as you wanted left/right or forwards/backwards - but if you moved upwards by 10 miles (or downwards by the same amount), you'd be back where you started. Also, if you were out in space and looked up using a pair of binoculars, you'd be able to see your own feet, just 10 miles away. Looking left or right or forwards or backwards - and everything looks kinda normal.
• Now - imagine that third dimension isn't 10 miles across - but just one millimeter across. We would be almost like 2D beings - almost all of our existance would be in two dimensions since nothing in the universe could be more than a millimeter in height - and moving up or down would have almost no effect on your life. That third dimension exists - but it's hardly any use at all. We would have to be almost perfectly flat creatures - it would be ALMOST a 2D world...but not quite.
• Now imagine that instead of the up/down dimension being a millimeter across, it's much MUCH smaller than the diameter of an atom...in that case we'd have no way to know that there even was a third dimension - it would seem exactly like being in a flat, 2D world since any motion at all in the 3rd dimension would have no effect and no object could be as tall as even an atom...atoms themselves would have to be almost exactly 2D objects. We wouldn't even know that the up/down direction existed at all. It the third dimension were that small, we might as well be living in a 2D world for all that it would matter to us.
• OK - so back to a normal 3D world. What would happen if there were a 4th dimension? Well - we can't see it, measure it...it's not in any way detectable...so we might jump to the conclusion that there isn't one. But if the 4th dimension existed but was very small (much less than the diameter of an atom) - then it could very well be there but we'd be totally unaware of it...unable to detect it. It would SEEM like we were living in a 3D world.

The string theorists claim that there are DOZENS of extra dimensions beyond the three we can normally experience - but all but the first three are so small that we can't tell that they are there - even with the most sophisticated equipment we have. I've heard these extra dimensions described as being 'rolled up'. They might very well be correct - but we have no way to know.

SteveBaker 13:16, 2 October 2007 (UTC)

Just to note: dimensions aren't like they appear in cartoons. They aren't alternative worlds somehow layered on top of ours where aliens live (though note that in the many-worlds interpretation of quantum mechanics—something entirely distinct from the idea of "dimensions" in science—there can in fact be multiple layered realities). They aren't ways to conduct psychic or supernatural phenomena. They are different ways in which geometry can be expressed in the world in which we live, basically. The dimension of time can be as mundane as noting that things change — the apple disintegrates on your table as it moves through the time dimension. Dimensions are not all that exciting, from a science fiction point of view.

Einstein's work, via Minkowskii's interpretations of it, basically reduced discussions of time and space to questions of geometry, and emphasized that time has a geometrical, spatial component to it. This is why he is often credited with introducing the idea of time as a fourth dimension, though he was not really the first person to introduce such an idea and in fact most of our understanding of "Einstein's work" in this regard is through the filter of Minkowskii, who "geometricized" Einstein in really wonderful ways. --24.147.86.187 13:50, 2 October 2007 (UTC)

I'm not sure that I'd say that extra dimensions are not exciting in a science-fiction kind of way. If there are more than three spatial dimensions and they are 'small' (per string theory) then, indeed, they aren't much fun. But if there were a fourth dimension - but something about our minds/bodies/physics meant that we somehow couldn't percieve it - then indeed there would be sci-fi possibilities. An ability to move in that fourth dimension would allow you to do some pretty incredible tricks. Escaping from a locked (3-dimensional) room might be as simple as taking a step in the 'other' dimension, walking past the room then taking a step back again into our normal world. It would be like trying to imprison a 3D person in a 2D rectangle - they'd just step out of it using the 3rd dimension. You'd be able to tie knots that would be impossible to untie...all sorts of weird stuff. A lot of people worry about what the 4th dimension would look like - but that doesn't bother me at all - we can use computer graphics to simulate exactly how a 4D world would project onto 2D retinas just as we understand how a 3D world projects onto a 2D retina. The ikkier thing to contemplate is that some of the string theorists want more than one time dimension - and that's really hard to get one's head around. We can guess what 4D space would be like to 3D beings by analogy with how 3D space would seem to 2D beings. But we only percieve 1D time - and we can't use analogies to extrapolate out to 2D time...it's a real head-spinner. SteveBaker 15:19, 2 October 2007 (UTC)

There's a very clever little story along these lines by Heinlein, called ...and He Built a Crooked House. The opening half-page alone is worth the price of the anthology you get the story in. An LA architect builds a house in the shape of a tesseract, but cut open and unfolded into three dimensions, as you might cut a 3-d cube and unfold it into a 2-d shape. Then there's an earthquake....

The story is very carefully constructed to be geometrically accurate and it's an interesting exercise to verify that. A few details, like what happened to certain walls, are sloughed over, but after all it's just a story. --Trovatore 17:34, 2 October 2007 (UTC)

As I linked above, you might too enjoy Flatland. Many people (including myself) report it being much easier to visualize and work in additional spatial dimensions after reading flatland. I disagree with 24.147 and the other guy that extra dimensions aren't like cartoons- stevebaker's got the right idea from a common sense approach, which is what I'm inclined to believe since string theory isn't really demonstrated by anything in our real world -froth^t 18:10, 2 October 2007 (UTC)

Yep - I agree, I'm quite doubtful that String Theory will ever be shown to be correct. It's a shame because it's very elegant - and correct things are usually elegant! But a theory that's unfalsifiable is not acceptable - so unless there is some kind of major new breakthrough, I think we have to put string theory back on the shelf and go back to looking for something else. SteveBaker 18:34, 2 October 2007 (UTC)

Despite all this talk of "rolling up" and string theory, I stand by my original assessment - there are exactly as many dimensions as we choose to model. I have worked physics problems which are not "wacky" (String Theory), but still imply high dimensionality - for example, a triple-pendulum can be described with six or 12 dimensions (perhaps each joint has a displacement, a momentum, and an acceleration; and maybe we want to throw in a nonlinear potential such as a magnetic attraction at each joint to an external magnet). Each one of these dimensions is a physical parameter where motion, displacement, energy, and other physical quantities can "go." We might start calling the dimensions (θ₁, θ₂, ...), (p₁, p₂...) and so forth. Dimensions can interact via the governing equations, derived from fundamental physical laws. We might take care to set up dimensions which are linearly independent and orthogonal, or we might not choose to do so. The system equations would be straightforward, and the dimensions would be quite complex.

I could just as well model the system in three dimensions of an absolute fixed frame, (X, Y, Z) and time (T). These dimensions are very straightforward, but the system equations would become much nastier, since the relationships would become very highly coupled. But, I could never reduce the complexity to fewer than the total number of variables in the system to begin with.

The same can be said of String Theory and any other "magic" theory which introduces a new variable. Decoupling complex interactions into "separate" dimensions is an operation on a mathematical model and does not change the system in any way. Simple transforms are heavily detailed in linear transform. More sophisticated decouplings are the crux of a lot of modern research topics. Nimur 17:34, 2 October 2007 (UTC)

There is a big difference between using multidimensional mathematics to solve a problem and saying that this many dimensions exist in space. It's not at all the same thing. I too have used as many as 14 dimensions to solve work-related problems in computer graphics...but the world still only has 3 dimensions.

Example: Computer graphics hardware really only draws triangles. If you want to draw a quadrilateral, it is usually split into two triangles. If you have two triangles that you think may originally have made up a quadrilateral - but you really wish (for various arcane reasons) that you could have split the quad along the OTHER diagonal, then you need to check that the two triangles lie in the same plane (if they don't then they didn't come from a quad and swapping the diagonal will do weird things to the graphics). This is a simple 3D problem as you might expect. However, if the triangles have (for example) smoothly varying colours that are linearly interpolated between their vertices - then swapping the diagonal can change the look of the final quad (imagine one triangle has three red vertices and the other has two red and one green - as is, the center of the line between the two triangles is red - but if you swap the diagonal, you get an orange colour in the middle - not at all the same thing). To check that it's safe to re-split it, you also need to check for "planarity in colour space" (Red/Green/Blue space) - so now you are doing a six-dimensional check in X/Y/Z/R/G/B space. But there are other parameters of a triangle in a graphics system such as texture coordinates, surface normal, transparency and so on - and to do a proper job, you need to know that ALL of them are 'planar'. I ended up with 14 per-vertex parameters - so I had to check for planarity in 14-dimensional space!

So yeah - it's easy to end up using math in higher dimensions as a convenient way of solving real-world problems - but that doesn't tell you anything about the number of dimensions of 'space'...which is still (seemingly) three. SteveBaker 18:31, 2 October 2007 (UTC)

Note that when I said extra dimensions weren't exciting, all I meant is "the current theories of extra dimensions are not that interesting when compared with the way that the idea of extra dimensions is invoked in popular fiction." You know, dimensional gateways, portals of alien worlds, etc. That's all. Sure, sure, Flatland, but that's not what most people have in mind when they talk about "dimensions". --65.112.10.56 20:41, 2 October 2007 (UTC)

I think we're largely in agreement, SteveBaker. Whether we are doing graphics or physics or string theory, adding new variables to the mathematics does not actually change the real system's dimensionality. It's only our model that changes. Nimur 16:01, 3 October 2007 (UTC)

Yeah - largely. I believe the string theorists claim that all of their extra dimensions are real, actual spatial dimensions - but 'curled up'. So small that we can never detect them. But they need the extra dimensions to give their strings the ability to vibrate in enough different modes to fulfill all of the things that are demanded of them in the theory. Super-strings are very tiny indeed - vastly smaller than an atom - so even the very tiny extra dimensions are large enough to let them vibrate in those directions as well as the usual three. SteveBaker 02:28, 4 October 2007 (UTC)

To Sweep Mercury

If a little mercury poured on ground and scattered, how can we completely remove it(in a normal condition and out of lab)?Flakture 13:20, 2 October 2007 (UTC)

http://www.epa.gov/mercury/spills/index.htm, from the article on, you guessed it, mercury. Lanfear's Bane 13:48, 2 October 2007 (UTC)

If you don't live in the US, you might also want to consult with your local authority or at least check out their website or other documents provided. There may be additional legal requirements or expectations. According to the EPA website, in the US you only have to report a spill of 1 pound/2 tablespoons or more. The minimum could easily be less in other countries and/or could vary depending on where it occurs. You probably should do this for anything more then a thermometer. Also in a lab in particular, there may be additional requirements imposed by whoever owns or is in charge of the lab. You should check with the lab's safety officer if that's not you (if it is you, it is doubly important you make sure you are aware of all legal requirements and check any existing in-lab regulations) Nil Einne 18:07, 2 October 2007 (UTC)

Check page 23 of Princo's mercury barometer guide. It says to NEVER sweep mercury, and not to use a vacuum. In general, use disposable paper, tape, droppers, etc to collect. --Mdwyer 19:50, 2 October 2007 (UTC)

calcium phosphate

what is the molecular formula (empirical would work as well) of the above compound? Our own wikipedia entry is kinda confusing. Am I supposed to combine the molecules it lists? --MKnight9989 14:02, 2 October 2007 (UTC)

The Oxford Concise Science Dictionary OUP, 1984, has the following:- "Calcium phosphate (V) A white insoluble powder, Ca₃(PO₄)₂; r.d. 3.14 It is found naturally in the mineral apatite, Ca₅(PO₄)₃(OH,F,Cl), and as rock phosphate ... The compound was formerly known as calcium orthophosphate." DuncanHill 14:09, 2 October 2007 (UTC)

Thanks mate. --MKnight9989 14:23, 2 October 2007 (UTC)

Which we have as tricalcium phosphate while calcium phosphate refers to a group of related compounds. Rmhermen 14:42, 2 October 2007 (UTC)

Propidium iodide stains only necrotic cells?

According to WP: "Propidium iodide (or PI) ...can be used to differentiate necrotic, apoptotic and normal cells." According to my understanding, PI stains necrotic but not apoptotic and normal cells. Can someone corroborate this? --137.120.3.217 16:46, 2 October 2007 (UTC)

My first Google hit.....there are others. --JWSchmidt 17:01, 2 October 2007 (UTC)

patents::??

hey friends i have thought of a completely new way of ignition in ic engine.i am sure that it would increase the efficiency and would be able to every problem related to spark plugs.but i cant experiment on it since it require quite costly trials,what should i do.how/which company.how to get a patent .please help.

regards Reveal.mystery —Preceding signed but undated comment was added at 17:04, 2 October 2007 (UTC)

Contact a Patent attorney in your area. -- JSBillings 17:26, 2 October 2007 (UTC)

Or, you might just choose to put this detail on your resume and apply for a job in research as a mechanical engineer. If your system is truly innovative, you should have no trouble finding employ as an engineer. You will probably have an easier time funding your idea if you are part of a corporate, academic, or institutional research group. Most importantly, you will gain the insights of expert peers who can examine your system and help you improve it. Science and engineering, especially in the 21st century, is a collaborative effort. Nimur 17:43, 2 October 2007 (UTC)

"Science and engineering, especially in the 21st century, is a collaborative effort." — what planet are you living on? Science and engineering in the 20th century is marked by increasing patents, defensive monopolies, and a total fear of litigation. Universities push researchers to patent anything and to patent broadly. True collaboration and free IP sharing on profitable technologies takes place only in fields heavily influenced by the ideology of the open source movement (basically fields with close connections to computer science) and even then they wring their hands constantly about whether or not they should patent or how they are going to avoid patent wars and the like. Whether you think science and engineering should be collaborative in this economic sense does not have any bearing on whether it really is collaborative in this sense. --65.112.10.56 20:37, 2 October 2007 (UTC)

You can patent it yourself - you don't need a company to do it for you. However, it can be a little tricky to get the language right when you write your patent - it's very easy to not quite patent enough, so that someone can come along with a small variation of your idea and dodge the patent, rendering it useless...or to somehow misword it in some other way that allows a loophole to be exploited. If you are really convinced that this is something special - then certainly you should consult a patent lawyer. I strongly disagree with User:Nimur. Once you have presented your idea in public - without the protection of a patent - they can just take your idea and use it without paying you a cent. So for chrissakes don't put it into a resume or send it to anyone else without having at least applied for a patent. Note that it's enough to have applied for one - it doesn't have to have been granted yet. You can wait YEARS between applying and completing the process. Personally, I would be quite surprised if you could improve on a simple spark gap as an ignition source - and if I were you, I'd DEFINITELY want to do some basic experiments just to prove that it works at all. You ought to be able to do that with something like a small motorbike engine that you could pick up on the cheap. Just to prove that it works - not that it's efficient or better or anything - just to convince yourself that it'll work. If necessary, find someone you trust with the right skills to help you do this. If your idea is truly better/cheaper than spark ignition, you'll make enough millions from it that splitting the rewards with a close collaborator won't be so terrible. The process of patenting something in a bullet-proof manner with lawyers and such isn't cheap - and you wouldn't want to waste that money on an idea that has a fatal flaw. SteveBaker 18:08, 2 October 2007 (UTC)

The premise of course, is that owning a patent provides legal protection. Gauging the cynicism which pervades the above posts, what makes you think a well-worded patent will protect you from large corporations? You must understand that to defend a patent requires a lengthy legal battle with a very high budget. Even if you are completely legally protected by your fully-encompassing patent, a large legal team may still beat you in court or bankrupt you through legal process. Sometimes that may even be part of the strategy - large legal firms do not have to win, they just have to out-live your budget. A patent is among the most exposing ways to demonstrate your technology - you must carefully detail every mechanism of your system, explaining to the whole world how your system works, and hoping that infringers will be prosecutable. Alternatively, by engaging work as a researcher, you can build up a trusted network of colleagues who will support you, and gain the business infrastructure of a larger organization. These people will be on your side, collaborating with you, you make your product more successful.

When I say "collaborative," I do not mean "open-source" at all. I mean that large engineering projects cannot be operated by a single person. You need a team of engineers, a legal team, a finance team - there are so many tasks, one person cannot make it all happen alone. Competition is certainly a key element of the modern technology economy. But when you face the whole world alone, you are competing with everyone. Nimur 16:09, 3 October 2007 (UTC)

The usual trick if a large, rich company infringes on your patent is to let them get away with it until a year before the patent is due to expire - and then sell it to their biggest competitor. Patent law is nasty. SteveBaker 19:15, 3 October 2007 (UTC)

Laches? TenOfAllTrades(talk) 12:27, 5 October 2007 (UTC)

I am doing some reading on patents, so I'll tell you some of what I've learned so far. But if you're not exaggerating about your idea you should indeed consult a patent consultant, because the wording in the patent is very essential to the protection you get. It's a legal thing, so there are loads of loopholes for others to legally steal your idea. This is the reason to patent broadly, as the anon pointed out.

Firstly, laws differ from country to country, but in general they work roughly the same. The most important deviation is (again) the US, where patents are given out more liberally. There, 'anything under the sun made by man' is supposedly patentable. You could go for a national patent (not necessarily in your own country and possibly in several countries) or a PCT patent, which is a wider international patent (there is as yet no such thing as a worldwide patent). In Europe you could also go for a European patent. In that case, the more countries you want to cover, the more it will cost of course. Per country, count on a few thousand euro, more if you want it properly done (researched well and written by an expert). But if in Europe you want a patent in at least 3 or 4 countries, then it is cheaper to get a 'European patent', which is basically a collection of national patents. But the research into patentability only needs to be done once, which saves money.

As I understand it, it makes sense to apply for a patent in one country first to have it researched by the patent bureau. It might turn out to have been thought of before, in which case there is no point in taking it any further. But it may also turn out not to be patentable for various other reasons, such as it following logically from the state of technology; if for an expert in the field, it is a logical solution to a problem then it is not patentable. Then again, if that has been the case for several decades and no-one has patented it yet, then it apparently breaks with some rusty line of thinking and it is patentable again. The loopholes can work both ways, so to say. After you have applied for a patent, it will be kept secret for one year, to give you time to decide on further patents and maybe start setting up your business. Also because any competitors might violate the patent, hoping you won't have the time or money to sue them, as Nimur pointed out. Not uncommon, as I understand it, so even if you have a patent, you're still not in the clear. But that year might give you a decisive head start if you use it wisely.

About getting a job through your idea, keep in mind that if you're hired for the specific purpose of being inventive then your employer gets the patent - all you get is the bone he throws you. Speaking of which ... if you happen to live in the Netherlands, drop me a note. I'm trying to get together some inventive minds with the idea to make money out of patents. Don't worry, I wont' hire you. :) It'll be a joint venture of sorts, something along the lines of what Nimur was talking about (still working on the legal aspects of that - damn, I just want to be an inventor).

But like I and others said already, get professional advise. This is a tricky business (which sort of takes the fun out of inventing if you want to make money out of it). Btw, this is a legal question, so count yourself lucky no-one has bitched about that yet. :) (Damn, now I just did.) DirkvdM 18:45, 3 October 2007 (UTC)

It's certainly no fun being the lone inventor in the face of gigantic multinational corporations and truly pathetic patent offices. You spend a fortune on getting your patent through the process - but yet the patent office probably didn't spend more than a couple of minutes looking at your patent - just barely enough to read through it. So there is no guarantee that your patent is meaningful - or that it'll stand up in court. You won't know that until someone infringes on it and you have to get big expensive law firms on your side to defend it with no real guarantee of winning. SteveBaker 19:15, 3 October 2007 (UTC)

Update on defending the patent before court: for a European patent that only happens in 10% of the cases. The explanation for this is probably that for a European patent an extensive research is required. In the US, a different system is used. Like I said, patents are given out much more liberally. This is possibly the 'declaratory system' (literal translation from Dutch), in which one only needs to apply and pay a sum. The European ('attributive') patenting system gives much more legal certainty. But of course the extra research means it's more expensive. Too bad one doesn't always have a choice between the two. In the Netherlands, one can also apply for a 'small patent', which is cheaper and faster and more appropriate for small inventions that might not be worthwhile for potential competitors to go to court for. This doesn't appear to apply to your invention, so a European or PCT patent (the latter of which leads to an 'International Search Report') might make more sense for you. DirkvdM 11:45, 5 October 2007 (UTC)

Carbonated Water

Is drinking carbonated water (as in, just plain seltzer water) bad for you? The articles on it and soda seem kind of fuzzy on this, and one of my friends claims that the acid they use to carbonate water leeches calcium from bones. 66.28.242.74 17:38, 2 October 2007 (UTC)

Osteoporosis lists the risk factors for calcium loss - it does mention soft drinks as one of the possible causes - but in the context of phosphoric acid - which isn't present in plain carbonated water. Your friend is probably thinking about Carbonic acid - which is certainly present in plain seltzer water because it's formed whenever you dissolve CO₂ in water. However, carbonic acid is floating around in your blood quite naturally - it's the way that CO₂ gets carried from the cells that produce it back to your lungs. Transporting the stuff around is an important blood function - just as carting loads of oxygen around is - so it's hard to imagine it would be a problem. The osteoporosis article also says (in effect) that if you drink lots of soft drinks (with no calcium in them) then maybe you are drinking less of things that provide calcium (milk for example) - but you'd have the same problem if you drank un-carbonated water. It doesn't mention carbonation as being a specific problem though. The article gives some useful links - you should probably read those too. If you are concerned about a health risk - or if you have any symptoms - you should (of course) consult a doctor. SteveBaker 17:56, 2 October 2007 (UTC)

The acidity of carbonated beverages has been implicated in some tooth decay as it may contribute to erosion of tooth enamel. — Scientizzle 19:28, 2 October 2007 (UTC)

The acidity may lower the pH of your blood, eventually leading to metabolic acidosis. In reality, the body's Bicarbonate buffering system is more than sufficient to handle soda water... or lemons... --Mdwyer 19:41, 2 October 2007 (UTC)

Michoud Fault article

http://en.wikipedia.org/wiki/Michoud_fault

I know enough about geology to know that there are not two tectonic plates involved in this fault as it states in the article. I don't know enough to rewrite it. I put a link to a good paper in the external links section. Dansample 18:53, 2 October 2007 (UTC)

You should leave a note on the 'discussion' page relating to that article. List your concerns there. Someone will come along and take note of it. SteveBaker 19:24, 2 October 2007 (UTC)

And you might tag the article as needing expert attention, using {{expert}} . --Anonymous, 21:48 UTC, October 2.

The Michoud fault is a normal fault. DuncanHill 23:36, 2 October 2007 (UTC)

Fungus fungus

Can a fungus get a fungus infection? --Milkbreath 21:49, 2 October 2007 (UTC)

Interesting question. Can whatever 'drug' utilized to treat first infection be considered a fungus on the fungus? Sorry if that`s just stupid. Dave 64.230.233.209 22:11, 2 October 2007 (UTC)

Only if that drug was a fungus which lived on the fungus. I doubt that it was :) 79.65.119.193 22:46, 2 October 2007 (UTC)

Hi again 79.65.119.193. Just as I thought, hence I wrote 'drug' as I did. I didn`t think that answer was very smart. Not my forte. I should stick to high-school-level physics' problems. lol Dave 64.230.233.209 22:58, 2 October 2007 (UTC)

Mushrooms can go mouldy. DuncanHill 23:37, 2 October 2007 (UTC)

Ah. Good. That's what got me wondering in the first place; I don't remember ever seeing that in my fridge, and there's ample reason to suppose I would have. --Milkbreath 00:27, 3 October 2007 (UTC)

Yay, a mycology question, I'm so happy! Absolutely, it happens all the time although the parasitism may be out of sight underground. Most of the species in the genus Hypomyces participate in some form of fungus on fungus action. Hypomyces includes the tasty lobster mushroom (Hypomyces lactifluorum) which basically takes over its host fungus's mushroom and replaces all its tissue with its own. Asterophora lycoperdoides actually grows mushrooms out of other mushrooms, especially the Russulas. (more pictures of this here and here.) The fungal world is full of strange surprises. Sifaka ^talk 01:04, 3 October 2007 (UTC)

Excellent. Thanks. So nobody's safe. Cool links. I'll have to try that microphotography trick. --Milkbreath 01:18, 3 October 2007 (UTC)

This process helps get rid of that fungus among us. Edison 05:08, 3 October 2007 (UTC)

Even better, the fungal fungal infection could be treated with an antifungal medication isolated from a fungus. Most of the antifungal drugs were isolated from bacteria, and others are synthetic, but some, such as griseofulvin, were originally isolated from specific fungal microorganisms (in this case, Penicillium griseofulvum. - Nunh-huh 05:28, 3 October 2007 (UTC)

Do "voices in one's head" ever engage one in normal "small talk"

Are "voices in one's head" seen as negative just becasue a person decided, say, to go around shooting because of them, and the times people hallucinate innocent things don't get attention? Do voices in one's head ever engage in small talk. You know, "Hey, Jim, how are you doing? Nice day, huh? How 'bout that game last night? Our quarterback stunk." I suppose it's possible that such a hallunciation could come from an imaginary friend, but from the article, I don't thikn so, because my understanding of imaginary friends is that they're always internal - i.e.: The person knows they're an imaginary friend, even if it's an adult who has adopted one for some reason, such as Asperger's Syndrome. I could be wrong on that, though. I also am not talking about hypnogogia, as from what I read that usually isn't understandable, it sounds more like mumbling if it's audible. It does seem strange, though, that the only thing one hears about hallucinations is bad stuff, though, never just innocent stuff like, "The voices in my head and I are discussing what we want for lunch." Something which sounds very normal for a young child with an imaginary friend, which as I say, I suppose to be internal, even if the child talks as thought it's external.209.244.187.155 23:24, 2 October 2007 (UTC)

There was a rather long feature article in the New York Times not too long ago about the Hearing Voices Movement, which was basically people arguing that hearing voices is not necessarily something that needs to be medicalized or medicated or something like that. I seem to recall some of the people in the article saying that the voices weren't always abusive or malevolent though I also got the impression that most of the time they were, that something about whatever it is that creates the voices seems to make them focus on the negative. But that was just my impression. Here's the article, in any case, though I last read it last March so my memory of the details might be foggy. --24.147.86.187 02:16, 3 October 2007 (UTC)

(Also, I had never heard of hypnogogia before—how interesting. I've had the "tripping" feeling many times while waking up, and was always shocked by how violent it felt in comparison with other dream-like sensations, but never realized there it was a general phenomena by the name and that it was basically the strange border line between being awake and asleep. How interesting.) --24.147.86.187 02:19, 3 October 2007 (UTC)

It gets better. "Hypnogogia" is specifically the strange border line between being awake and asleep when falling asleep. "Hypnopompia" is specifically the strange border line between being awake and asleep when waking up. - Nunh-huh 05:24, 3 October 2007 (UTC)

Have anyone ever subjected those "voices" to an IQ test? or get the "voices" to write up a scientific paper on Quantum Physics? After all if God is speaking to you, he must know some serious shit. 202.168.50.40 04:21, 3 October 2007 (UTC)

If voices in one's head say innocuous things like "Looks like it might rain today" they probably get little noted nor long remembered. Edison 05:07, 3 October 2007 (UTC)

Thanks, all; especially for the article. I'm trying to do research into a possible novel idea I have, a pitcher with mental challenges who makes the majors, sort of a modern day Rube Waddell but without the alcoholism; so any eccentric behavior is straight mental condition. In a way, one might say it's a cross between Rube Waddell and Harvey (film) —Preceding unsigned comment added by 209.244.187.155 (talk) 12:38, 3 October 2007 (UTC)

Richard Rhodes' fascinating book Why They Kill, while not addressing mental illness as such, spends on a good deal of time on Lonnie Athens' research into violent criminals' "internal community" of voices. --Sean 13:20, 3 October 2007 (UTC)

Another area to research might be Dissociative identity disorder, previously known as "Multiple Personality Disorder." It is a controversial diagnosis, but I am just offering it as another topic that might have some relevance. While fictional, Matt Ruff's excellent novel Set This House In Order contains a protagonist who is a "multiple" and there are depictions of two or more of his "alters" in conversation. Finally, I feel the need to mention that Elwood P. Dowd was a bit of souse, if not an alcoholic himself. --LarryMac | Talk 20:02, 3 October 2007 (UTC)

Thanks.209.244.30.221 13:55, 4 October 2007 (UTC)

October 3

First missile guidance system

After reading the article on missile guidance I started wondering what guidance method the first guided missile had. I have tried searching a bit, but so far I haven't been able to find it. - Dammit 00:23, 3 October 2007 (UTC)

As I recall, and as Anti-ship missile suggests (but does not source!), these first appeared in WW2. I think they were radio guided, as certainly some "plane bombs" were (haven't uncovered the link for that one yet). Someguy1221 00:30, 3 October 2007 (UTC)

Ah, Operation Aphrodite. Someguy1221 00:33, 3 October 2007 (UTC)

Maybe the Henschel Hs 293 radio-controlled anti-ship missle? --Milkbreath 00:37, 3 October 2007 (UTC)

IMO the V1 was the first guided missile. —Preceding unsigned comment added by 88.111.81.231 (talk) 01:02, 3 October 2007 (UTC)

I wouldn't call the V-1 flying bomb "guided." It could only be guided to the extent that the operators could control roughly how far it travelled before it landed, and you can do the same with an artillery shell. Someguy1221 01:55, 3 October 2007 (UTC)

The definition of "guided" in this case is whether the projectile's path can be changed in flight. Which you can't do with an artillery shell. The V-1 could do this in about the bare minimum sense of the word, since its "autopilot" would make adjustments based on the conditions the V-1 encountered. --24.147.86.187 02:31, 3 October 2007 (UTC)

The V1 was more of an unmanned airplane than a missile. It flew at a controlled altitude in a selected direction until the fuel ran out, then it fell and exploded. The V2 was a ballistic missile with a guidance system which operated during the boost phase. —Preceding unsigned comment added by Edison (talk •

contribs) 05:05, 3 October 2007 (UTC)

Come on, the very 1st paragraph of the V1 article contradicts precisely what you are saying. It was NOT simply an unmanned airplane, it was the 1st guided missile as it did have a dedicated albeit rudimentary guidance mechanism. The engine cutting out for lack of fuel was a design flaw and was rectified, the control mechanism caused a powered dive onto the selected target area, it was not simply a "run out of fuel" process. Vespine 05:47, 3 October 2007 (UTC)

My mother was living in London throughout the time of the V1 attacks (and twice came close to being a victim of them). She told me many, many times that her most vivid memory of the V1 (she calls them 'doodlebugs') was that the distinctive sound of their pulse-jet engines going overhead was actually rather comforting because it was only when the engine stopped that the weapon would glide down and explode. She told me this often and explained the terror that everyone felt when the engine sound cut off and there was that awful silence that would end in an explosion - I simply do not believe that they were ever powered into the ground. They may not have run out of fuel - but the engine was definitely not running when the things actually smacked into the ground. SteveBaker 12:50, 3 October 2007 (UTC)

There are details on it in the article. The early ones did not have powered dives but later ones did. And they certainly did not just run out of fuel—they had their distance "programmed" into them and that would make it dive at a steep angle. I mean, we all could just talk about stuff without checking, but it seems so easy to just check, right?)--24.147.86.187 13:10, 3 October 2007 (UTC)

While I also first thought of the V1, as the first one I've found that there already were some before the V1, but I have no idea if one of these is considered the first:

• The US Navy's N-9 Curtis-Sperry Flying Bomb, might not even be considered a missile although NASA states it to be the "Navy's first guided misile effort" (1917)
• The German A3, test rocket with inertial guidance (1937)

As I've said, I've already consulted a few sources, but none that claims to describe the first. - Dammit 10:37, 3 October 2007 (UTC)

If it has to, like, work, I'm pretty sure the Henschel was the first, unless you count the falcon with its biological navigation, acquisition, and terminal homing. --Milkbreath 16:14, 3 October 2007 (UTC)

The dictionary definition of a "missile" is "something that is thrown." A V2 clearly is a missile. It is loose terminology to call any "cruise missile" a missile, when they are sustained in flight by their engine, like the V1. The V1 was a pilotless jet, but it also had a kamikaze style piloted version which the Germans may not have actually deployed. If a WW2 B17 bomber had an autopilot to fly it as an unmanned drone into a populated area of Germany, would that have made it a "guided missile?" I think not. Sure the V1 is a guided missile, like a whale is a fish. Edison 04:24, 4 October 2007 (UTC)

Yeah but a V1 weighs a lot less than whale, doesnt it? —Preceding unsigned comment added by 88.109.121.209 (talk) 20:06, 5 October 2007 (UTC)

"Missile" = "something that is thrown." Hmm... okay, the guidance method for the first guided missile would be tugging on the rope.  :-) 152.16.59.190 08:51, 6 October 2007 (UTC)

joints in the human body

What is a joint in the cranium? —Preceding unsigned comment added by 68.248.145.158 (talk) 01:28, 3 October 2007 (UTC)

From Human skull: "Except for the mandible, all of the bones of the skull are joined together by sutures, synarthrodial (immovable) joints formed by bony ossification, with Sharpey's fibres permitting some flexibility." The term you're probably looking for is suture. --Ybbor^Talk 02:04, 3 October 2007 (UTC)

Household electroplating

I have some small objects that I would like to coat in copper. They are very small, and I believe they are zinc. What would be an effective way to plate them? HYENASTE 02:03, 3 October 2007 (UTC)

Spray the surface with small balls of copper, when the balls hit they heat up and melt forming a thin layer.

In theory, just stick them in a copper sulfate solution. In practice, that will produce a mess of little flakes or feathers, which will be oxidized, so it will be reddish brown and not shiny. If you want a nice and even, permanent, shiny coating, it will take a lot more effort. This classroom lab manual seems reasonable. —Keenan Pepper 03:02, 3 October 2007 (UTC)

Thanks for providing an easy setup. I assume a lantern battery and some wire will work for electrodes. Now, where do I find sulphuric acid, soda lye, and copper (II) sulphate? HYENASTE 01:56, 4 October 2007 (UTC)

Copper sulphate can be found in garden supply stores - it's an old-fashioned herbicide, fungicide and pesticide. I believe tropical fish fanatics use the stuff too - so you could try a pet store if you don't need much of the stuff. If you only need rough-and-ready plating, you can skip the acid and lye. "Soda Lye" is an old-fashioned name for Sodium Hydroxide - it's also called "caustic soda". I've seen it in swimming pool supply stores. You might maybe find it sold as a drain cleaner - but probably it would be mixed with a bunch of other junk. Sulphuric acid used to be easily available for topping up car batteries - but with the advent of sealed-for-life batteries, it may be hard to find. Maybe a car parts store might stock it...I suppose you could get some out of an old car battery - but it's about 30% concentrated in a car battery - so please be VERY careful! Wear gloves, mask, goggles...also, remember - always add acid to water - NEVER add water to acid. SteveBaker 02:19, 4 October 2007 (UTC)

Why so much effort? There's many simpler ways. Here's one that I've personally used. It recommended for home plating enthusiasts by a professional metalworker on finishing.com (an answers forum for the industry).

• Strip the insulation from about 2 feet of copper wire. Clean with toothpaste and a sponge or brush. Coil this up and place in a beaker or bowl. Wear gloves so you don't recontaminate the wire with oil from your fingers.
• Add 100 cc of white vinegar
• Add 1 heaping teaspoon of salt or preferably baking soda. (baking soda is safer, as using salt will produce chlorine gas)
• Add 3-6 cc of ethylene glycol antifreeze, if you have it. It'll still work without.
• Use a spare copper coin or piece of copper wire for a temporary cathode. This is to dissolve enough copper into solution so it can be available for plating. The temporary cathode also keeps you from dirtying the item you want to plate.
• Give the temporary cathode a quick rinse with alcohol and water to remove surface dirt & oil.
• Next, rig a 1.5 volt battery, optionally with a 30 to 200 ohm resistor in series.
• Attach the positive terminal to the anode (your copper wire).
• Attach the negative terminal to the cathode (the temporary copper object).
• If using alligator clips, make sure they grip the very edge. The less space covered, the better.
• Electrolyze the plating solution for 10-15 minutes.
• Replace your original cathode with the item you want to plate. A faint copper color should appear after 60-120 seconds. Occasionally jiggle the cathode a bit during plating.
• Move the clip around the coin a few times while plating to plate the bare spots where the clip was.

Plating brightness, depth and coverage will steadily improve over 20-90 minutes. You can plate pieces for longer periods to get a thicker plate. The color will eventually turn black after plating more than an hour or so. You can wipe this off with a damp cloth, or gently polish to an antique copper finish using toothpaste when you finish. This method of plating will produce a reasonably durable and attractive, but not quite as good as a pro job. Simple as that, and no lye or sulfuric acid needed. Kel - Ex-web.god 02:44, 4 October 2007 (UTC)

Hominin evolution

What is the most recent common ancestor of humans and bonobos? Would it be Australopithecus, or not necessarily?--Sonjaaa 02:30, 3 October 2007 (UTC)

I've only seen the term "Australopithecus" applied to bipedal Hominina. See: Image:Hominintree4.gif. According to Hominini, "both Orrorin and Sahelanthropus existed around the time of the split, and so may be ancestral to both humans and chimpanzees". --JWSchmidt 04:03, 3 October 2007 (UTC)

Building 140 decibel or higher system at 25KHZ (ultrasonic)

I'm wanting to build a 140 decibel or higher system at 25KHZ (ultrasonic). Amazing1.com has something like it, but it's huge. I'm looking for something that'll do it but be really tiny. Anyone have any ideas where I can start? William Ortiz 03:33, 3 October 2007 (UTC)

140dB is a horribly high noise level, which could harm the listener. What is the goal? Deafening mice? Edison 04:50, 3 October 2007 (UTC)

Driving certain animals away. I have something at 130DB and in the most obvious example, birds will still hang out all the time 20 centimeters (less than a foot) away so clearly more decibels are needed. William Ortiz 05:44, 3 October 2007 (UTC)

This seems like a really bad idea - 25kHz isn't much above the level of human hearing (lots of people can hear 20kHz - and young people may hear 22kHz and higher) - and 130dB is quite capable of damaging your ears - 140dB is above the pain threshold! I would certainly not want to be around this thing when it's turned on. If you really need such high amplitudes you should certainly be using a higher frequency to be really sure that humans aren't going to be harmed. Are you even sure that the species of bird you are trying to repel can hear 25kHz? If they could, there is no doubt that 130dB would be enough to scare them off. SteveBaker 12:36, 3 October 2007 (UTC)

Look into hydrophones. These are bidirectional transducers (speakers AND microphones) and are most often used for underwater applications. Next you'll need a signal generator (any standard electronics lab will have a function generator suitable for 25 kHz, or you can build your own oscillator). Finally, you need a power amplifier of a considerable size (unfortunately, there are physical limitations on power densities, and 140 dB is a lot of power). Also, it is more difficult to miniaturize components for such low frequencies (in the electromagnetic spectrum sense). Are you building a sonar or are you trying to make a sonic weapon? Please do not use the reference desk for destructive purposes. Nimur 16:50, 3 October 2007 (UTC)

Reaction to frankincense?

Whenever I smell frankincense resin (in essential oil blends), especially if I am exposed to the scent for a longer period of time, I get a dry, scratchy feeling in the back of my throat. It's like a need to cough that is not satisfied by coughing. It is slightly irritating but doesn't feel like a serious or life-threatening reaction; it never occurred to me before to wonder what it was. I know I can't ask for medical advice here, and I'm sure that my doctor would only tell me to stop exposing myself to frankincense, which I've already figured out. I am really more curious about whether anyone else experiences the same thing, or whether there is a name for that symptom. --Grace 05:31, 3 October 2007 (UTC)

It's possible you are slightly allergic to it, or something else in the oil. Stick go gold and myrrh. Lanfear's Bane 09:42, 3 October 2007 (UTC)

Perhaps you went to too many requiem masses as a kid, and developed a sub-conscious aversion to the stuff?

Atlant 12:05, 3 October 2007 (UTC)

It's the sort of thing that's definitely worth asking a doctor about, as they are going to know about this sort of thing. They might have rather more to tell you than just avoiding frankincense, which may not always be possible; since nobody with medical training will answer this question in this sort of forum, it's really rather hard to tell. On another note, I tend to find many people's throats are irritated by various incenses. —Preceding unsigned comment added by 79.65.119.193 (talk) 22:51, 3 October 2007 (UTC)

Couple of Questions on Acids

pH of HCl, Citric and Acetic Acid

I've read over their articles, but I only have a basic understanding of chemistry so I don't get the kP_a1 things, is someone able to give me the pH and % dissociation of hydrogen molecules of:

• HCl
• Acetic acid (CH₃COOH)
• Citric acid

under standard conditions. Thankyou

Have you taken a look at Acid dissociation constant yet. The first two are monoprotic acids, whereas citric acid is triprotic. Graeme Bartlett 12:55, 3 October 2007 (UTC)

Acidity of Salts

I'm sort of having a little bit of trouble understanding this, so would someone be able to tell me if this is correct:

Some salts are acidic/basic as their ions are derrived from weak bases/acids. They can undergo a hydrolysis reaction with water to reform the original base/acid

For example consider ammonia chloride (NH₄Cl). When it dissolves it dissociates to form NH₄⁺ and Cl^-. The chloride is the conjugate base of a strong acid (HCl), and hence is neutral and will not react with water. The ammonia is the conjugate acid of a weak base (NH₃) and hence will react with water such that NH₄⁺ + H₂O -> NH₃ + H₃⁺. Hence it is an acidic salt derrived from a weak base.

Similarly consider sodium acetate (NaCH₃COO^2-). When it dissolves it dissociates to form Na^- and CH₃COO^-. The sodium ion is derrived from a strong base and hence is neutral and will not react with water. The acetate ion is the conjugate base of a weak acid, and hence will react with water to reform the original acid, such that CH₃COO^- + H₂O -> CH₃COOH + OH^-. Hence it is a basic salt derrived from a weak acid.

On the other hand, consider sodium chloride (NaCl). When it dissolves it dissociates to form Na⁺ and Cl^-. The sodium ion is derrived from a strong base (NaOH), and hence is neutral and won't react with the water. Similarly the chloride ion is derrived from a strong acid (HCl) and hence is neutral and won't react with the water. Therefore it is a neutral salt derrived from a strong base and a strong acid.

That's the pinnacle of my understanding so far, I just have three big biffs with it

• Why don't the ions from strong acids/bases react with water to reform the original acid/base (someone said this was something to do with the conjugate of a strong thing being weak and vice versa but I'm not sure)

The ions such as Cl^- does not react much with water, and the same with Na⁺, so their presence does not alter the pH. You need something that will react with H⁺ or OH^- to change pH. So if you dissolved a salt of a strong acid and a strong base in the water you just get the ions from the salt hydrated in solution. Any H⁺ or OH^- reacts with each other to leave a very small remainder, with the product of their concentrations being about 10^-14. Graeme Bartlett 12:41, 3 October 2007 (UTC)

• What about Fe(OH)₂, it's a weak base but then how does the ionic component of the salt derrived from it act as an acid in water (it has no proton to give up)? This sorta follows for a lot of other weak bases.

The weak acid is actually Fe²⁺ it reacts with water taking away OH^- to form FeOH⁺, and a H⁺ ion in solution. Graeme Bartlett 12:41, 3 October 2007 (UTC)

• Is the reaction between HCl and NH₃ even a proper neutralisation reaction? I thought the formula was acid + base = salt + water, but there's no water involved

Yes - water does not have to be formed. A base can also work by removing H⁺ instead of supplying OH^-. Graeme Bartlett 12:41, 3 October 2007 (UTC)

I have a test on this coming up, and this is the only thing I don't understand. If the question was say, explain the acidic, basic and neutral nature of salts do you think my explanation would be adequate, and if not what can I add in to complete it?

Thankyou very much in advance 124.183.13.48 09:29, 3 October 2007 (UTC)

Balancing equations

--Mostargue 18:05, 3 October 2007 (UTC)

Hi all, thanks in advance.

1. When the question below is balanced correctly, what is the co-efficient for O₂

C₄H₁₀ + O₂→ CO₂ + H₂0

Is the answer:

A: 9

B: 13

C: 18

D: 24

2. Consider the composition of the particle, W, X, Y and Z below.

W: Protons: 11, Neutrons: 12, Electons: 10

X: protons: 12, Neutrons: 12, Electrons: 12

Y: Protons: 12, Neutrons: 13, Electrons: 12

Z: Protons: 13, Neutrons: 14, Electrons: 10

Which two particles are isotopes of the same element.

Once again thanks guys. --Andrew Hadland 2007 07:55, 3 October 2007 (UTC)

1) b - 2C₄H₁₀ + 13O₂→ 8CO₂ + 10H₂0

2) W and Y, they both contain the same number of protons, hence have the same atomic number hence are the same element —Preceding unsigned comment added by 121.217.13.71 (talk) 08:02, 3 October 2007 (UTC)

This looks an awful lot like homework - I don't think we should be answering with exact answers - broad brush explanations please! SteveBaker 12:26, 3 October 2007 (UTC)

And multiple choice, at that! Nimur 16:46, 3 October 2007 (UTC)

For the first problem, put coefficients in front of the CO₂ and H₂0 first, making sure that each side of the equation has the same number of carbon and hydrogen atoms. Once you have the carbon and hydrogen balanced then you move on to the oxygen, count the number of O atoms taking account of the coefficients you already added. For the second question, the article on Isotopes answers your question in the first paragraph. Man It's So Loud In Here 16:43, 3 October 2007 (UTC)

Another way to do the first one is to put coefficients in front of the substances with Hydrogen in them, because on each side there is exactly one substance containing hydrogen.--Mostargue 18:05, 3 October 2007 (UTC)

Electron arrangement

Sorry for the sloppy formatting, the 16 and the eight are supposed to be directly above and underneath each other. What is the electron arrangement of the ion ^16₈O2-. Is it:

A: 2, 6

B: 2, 8

C: 2, 8, 6

D: 2, 8, 8

Thanks --Hadseys 08:42, 3 October 2007 (UTC)

Uh, you've asked for the electron configuration of an ion of oxygen, and then the electron configuration for the diatomic oxygen gas molecule. What I think you're after is the electron configuration of a single oxygen atom which is 2.6 or 1s²2s²2p⁴ (the easy way to see this is that the number of protons in oxygen is 8, and 2+6=8 since the charge is (I think) neutral). So the answer is a UNLESS you are after the electron configuration of the O^2- ion which would be 2,8 which would be b. 124.183.13.48 09:06, 3 October 2007 (UTC) Nevermind, I misread the question (it should be O^2-, not O_2-). In this case the atom has a charge of 2-, so it has two more electrons than protons (10 electrons). The only answer which fits this is b, 2.8 124.183.13.48 09:09, 3 October 2007 (UTC)

HCl vapor from Na2CO3 + H2SO4?!

A friend's sister was working on her upcoming science project, part of which required producing (I think) sodium sulfate by neutralizing sodium carbonate with 97% sulfuric acid. She didn't have any Na2CO3 available, so made some with Arm & Hammer baking soda, which, according to their literature is 99.995% pure. She did this by heating the NaHCO3 at ~200 °C until it (presumably) thoroughly dehydrated into Na2CO3, which she then let cool. However, when she later pipetted H2SO4 onto the Na2CO3, she noticed a bit of white, sharp-smelling fumes being produced which she said smelled "just like HCl fumes". She didn't think this should be possible, so she freaked out and dumped the experiment. She wants to know what this vapor was. She's still too embarrassed about making such a huge mess in the lab that she won't ask her chem teacher. :) My guess was that Arm & Hammer's purity claims aren't as accurate as they'd like to believe, and the product contains small amounts of one or more chloride salts -which would explain HCl vapor. But I could be wrong, and I'm pretty curious myself about what could have caused this. Any ideas? Thanks in advance. Kel - Ex-web.god 08:53, 3 October 2007 (UTC)

Is it possible that she used hydrochloric acid instead of sulphuric? Or that the acid was labeled incorrectly? Lanfear's Bane 09:36, 3 October 2007 (UTC)

Well she would have produced CO₂ gas and some spray consisting of sulphuric acid. A fair bit of heat would be released also. It is quite likely that this would smell like hydrochloric acid. 97% sulphuric acid is pretty nasty, so it is not a good idea to sniff it. One test is to see if it really is sulphuric is if it carbonizes sugar. HCl would not do this. Food products should be quite pure. But I could imagine that NaCl could be a contaminant. Graeme Bartlett 12:30, 3 October 2007 (UTC)

Well, I've seen the lab, and it's definitely reagent-grade sulfuric acid (still in the original dispenser from the supplier). To further clarify, she noticed the fumes from 2-3 feet away, so she didn't exactly stuff her nose into her Erlenmeyer flask. Also, the vapor was wispy and white, just like fuming HCl. It wasn't a spray. Again, I may be wrong, but I'd assume a mist of H2SO4 being released from bubbles of bursting CO2 wouldn't form a visible wispy strand that rises out of the flask. :)

Also, assuming she did somehow accidentally use HCl, (see above, she didn't.) That still doesn't explain the fumes, as if I'm not mistaken: 2HCl + Na2CO3 ---> CO2 +H2O +2NaCl. I also thought there might have been a little carbonic acid that hadn't completely broken down yet, but she says an indicator strip placed at the top of the flask showed a pH of around 1, which that acid wouldn't do. So, any other ideas? Kel - Ex-web.god 21:28, 3 October 2007 (UTC)

• I'm rather nonplussed about her being ashamed to tell her teacher. I think a student with her sort of curiosity about an unexpected result would delight most teachers. As they say, the productive moment in science is not "eureka!", but "that's funny ...". --Sean 21:58, 3 October 2007 (UTC)

I agree, but it's a teenage girl, so what do you expect? :) She apparently made a pretty big mess when she knocked over her entire apparatus. Kel - Ex-web.god 23:50, 3 October 2007 (UTC)

Wonder if she got exothermic and vaporization enough to create substantial H₂SO₄ vapor. Lots of acids smell similarly "sharp" to me, not sure what specific part of "the HCl smell" was noticed. That's a pretty hydroscopic acid, maybe the visible vapor trail was from it absorbing humidity? Or maybe she drove off some SO₃, which would be another sharp/acid-smelling thing, and would maybe also leave a visible vapor trail as it absorbed humidity to become or H₂SO₄ droplets (a la "fuming sulfuric acid"). DMacks 01:56, 4 October 2007 (UTC)

Possibly, but according to her, she had only combined ~100mg of sodium carbonate and 5-6 drops of sulfuric acid when she noticed the fumes. As for the "HCL smell", I can tell a slight difference between HCl and SO₃. Not sure if she can, but that was what seemed the most familiar to her, I guess. Given that she was freaked out about getting an unexpected result, it's possible she was mistaken, hence the question. :) Kel - Ex-web.god 02:49, 4 October 2007 (UTC)

Basically you don't mix 97& sulphuric acid with any base - it is too concentrated and will give out so much it it will volatalise. 10% acid would be safer - usually at school all experiments need to be supervised - for safety - in most places it's the law - however this dosen't seem to have been the case here - this was a dangerous and stupid experiment.87.102.94.194 15:09, 4 October 2007 (UTC)

That answer was incredibly presumptuous and generally unhelpful, not to mention the part about never mixing concentrated acid with any base. I guess the all those college labs that required I do exactly that (on countless occasions) was also stupid? I think not. For the record, the experiment she attempted was taken directly from her textbook, was pre-approved by her teacher, used less than 10 drops of acid, and of course there was an adult supervisor present. She also wore appropriate lab gear. No, stupid are those kids that somehow managed to steal 70% HNO3 and used it to dissolve pennies in the bathroom sink while standing around gloveless in short-sleeve shirts giggling and poking their fingers in that cool cloud of brown smoke. Kel - Ex-web.god 00:59, 5 October 2007 (UTC)

Where exactly does a text book say to mix conc acid with base - maybe america hey - fuck you I cant wait for the next fucking 9/1183.100.250.154 13:14, 5 October 2007 (UTC)

Um, how about any reaction where excess water isn't wanted? Normally, I'd remind you of the minuscule scale of the experiment in an attempt to appeal to your sense of reason, but your last post proves that would be a colossal waste of time. If you can't be helpful, kindly spew your venom elsewhere. Not only does it discourage potentially useful and rational responses, it gives those people with a rational anti-American sentiment a bad name. Kel - Ex-web.god 20:32, 5 October 2007 (UTC)

Marfan Syndrome

How is Marfan Syndrome diagnosed? Is it done solely by physical examination, or is there more to it than that? --MKnight9989 12:09, 3 October 2007 (UTC)

Our article on Marfan syndrome says There are no signs or symptoms that are unique to Marfan syndrome. It is usually a single apparent sign or symptom that leads doctors to look for others and eventually to diagnose the syndrome. So evidently each symptom has to be tested for separately since no single test would be conclusive. From what the article describes, some of the symptoms might require X-ray or MRI exams - there is also an eye test. Since the disease is genetic and the defective gene is dominant, a detailed family history might be a useful aid to diagnosis. SteveBaker 12:23, 3 October 2007 (UTC)

The British Medical Association Complete Family Health Encyclopedia, 2nd ed., 1995, states "There are no specific diagnostic tests for Marfan's syndrome. Echocardiography may be used to investigate heart abnormalities, and an eye exam may be performed." DuncanHill 13:34, 3 October 2007 (UTC)

• I can tell you from experience that many American doctors are eager to diagnose Marfan's when a patient with the usual connective tissue symptoms also has a high palate. In the case of one hapless patient that I know of, though, each of the doctors ultimately found that the diagnosis was non-productive. --M@rēino 17:53, 5 October 2007 (UTC)

Possible to create an aircraft supported by magnetic levitation alone?

Is it possible? 64.236.121.129 15:59, 3 October 2007 (UTC)

Did you read Magnetic levitation? An airplane flies anywhere- magnetic levitation requires that you are directly above the other part of the system. Also, the distances between the objects are typically quite small, whereas an airplane flies pretty high. Friday (talk) 16:02, 3 October 2007 (UTC)

I guess I should have clarified the idea, and yes I did read it obviously, but I don't think you understand what I'm asking. If the aircraft is generating the magnetic field, can it repel the ground with it. 64.236.121.129 16:58, 3 October 2007 (UTC)

In general, the ground is uncharged/unpolarised, and thus won't be affected by a magnetic field. Also, given the relative masses of the Earth and the aircraft, it'd be a tad silly to say that the Earth is being repelled. GeeJo ^(t)⁄_(c) • 17:23, 3 October 2007 (UTC)

The ground is still diamagnetic I believe. I guess this question is directed towards people who are familar with how things can be levitated with diamagnetism. With sufficient energy in the magnetic field generated (by the aircraft), is it possible? Btw, as for your last point, the object of less mass would be the one which is "repelled", in other words, ideally the aircraft would be floating due to it's magnetic repullsion from the ground. 64.236.121.129 17:35, 3 October 2007 (UTC)

Only if the ground was also made of something magnetic. But the problem with using magnetism (Magnetic levitation) is that the force it exerts drops off with the square of the range. So if there was enough force to lift to the aircraft a foot off the ground, it would take a magnet 100 million times more powerful to fly at 10,000 feet. (10,000 squared is 100 million) If you think of the size of magnet you'd need to lift an entire airplane...then imagine one 100,000,000 times bigger! We do use magnetic levitation for trains (Maglev train) - they move on special tracks (unlike a plane - which you'd like to fly everywhere in!) - and they only hover a 15 millimeters above the track! (Remember - the SQUARE of the range!) —Preceding unsigned comment added by SteveBaker (talk • contribs) 17:26, 3 October 2007 (UTC)

Technically you could run a very powerful current through an aircraft, parallel to the Earth's surface and perpendicular to its magnetic field to generate magnetic lift. However, you would need current in one direction to not be going through the aircraft, or else this would generate a counterforce that would exactly cancel out your lift. You could theoretically accomplish this by ionizing a region of air outside the aircraft and sending the current through that (and have the aircraft appropriately insulated so that the current only goes through that. However, needing to constantly ionize the air around the aircraft, as well as needing some rediculous current to levitate on the Earth's oh so weak magnetic field would be quite energy consuming. Disclaimer: This idea I have just described is certifiably rediculous and will probably never work except as an amusement. Someguy1221 17:40, 3 October 2007 (UTC)

Yeah but then you might as well build an Ionocraft - at least those things actually work. SteveBaker 19:19, 3 October 2007 (UTC)

• My magnetic hovercraft is full of electric eels. --M@rēino 17:55, 5 October 2007 (UTC)

• A version of a maglev train could be created with wings, however, to create something similar to a ground effects airplane. This would, though, mean it could only travel a few feet above the ground and only on top of energized tracks. Such a vehicle might be useful for low cost (lower than normal aircraft), high speed transport, along a few busy routes, over flat terrain. StuRat 18:10, 5 October 2007 (UTC)

• The earth's magnetic field is about .06milliTesla. At various locations, the field lines go vertically downward, vertically upward, or parallel to the ground. If our magnetic aeronaut had a magnetic monpole, how powerful would it have to be to support, say, 1000 kilograms at a point where the field lines were vertical? If magnetic monopoles do not exist (no one has ever found one), then aren't there stable configuration of normal magnets or solenoids producing a magnetic field which could in principle hover in a magnetic field with vertical field lines, and with field lines horizontal or at any arbitrary intermediate angle? (Talking theory, not practicality here). Edison 18:32, 5 October 2007 (UTC)

Human Spine

Do all the bones move?

What is the function of the discs?

In which area of the spine do most people get back ache?

This is not for homework, as some of you might think. - 81.158.75.136 16:05, 3 October 2007 (UTC)

Nothing triggers my "homework" RADAR like an assertion that questions are "not homework." In any case, here's some links which will help:

• Vertebral column
• Intervertebral disc
• Back pain

Many of the bones are fused; so these bones do not articulate with respect to each other.

The discs are part of the joint, and serve as a soft cartilaginous material to allow for slight movement.

Of course you can have an ache in any part of your back, depending on the source of the pain. Poor posture may result in lumbar pain. Nervous system problems, such as a pinched nerve, can be very serious. If you are seeking medical advice, see a doctor.

Hope this helps, Nimur 16:43, 3 October 2007 (UTC)

Quantum physics (I think). Confused. Deuterium is a wave?

According to deuterium, deuterium is a boson and according to boson, this makes it a "force carrier" particle like a photon? Does this mean that deuterium is as intangible as light? --Seans Potato Business 16:54, 3 October 2007 (UTC)

Deuterium is a "composite boson" (it's a boson because its spin is an integer: +1), but it acts as a boson only at long distances. In high energy interactions it acts as an assemble of two fermions (a proton and a neutron). Thus it is in a sense as "solid" as any fermion. See under the heading "Composite bosons" in our article boson.--Eriastrum 17:17, 3 October 2007 (UTC)

It's an isotope of hydrogen - one proton, one neutron. In bulk, it's a gas...just like hydrogen - but heavier. SteveBaker 17:18, 3 October 2007 (UTC)

However, at very low temperatures composite bosons can do wierd things, or yet wierder things. Someguy1221 17:34, 3 October 2007 (UTC)

All matter have waves. See matter wave.--Mostargue 17:36, 3 October 2007 (UTC) Oh dear, Wikipedia has no article on that??--Mostargue 17:38, 3 October 2007 (UTC)

There, redirected to de Broglie hypothesis.--Mostargue 17:40, 3 October 2007 (UTC)

Confirm vs define

Mendeleev's_predicted_elements says, in the last paragraph, that hydrogen was confirmed to be the first element. I don't understand what that means. Wouldn't it be better to say that hydrogen was defined to be the first element? How has the definition of "element" changed over time? Of course, the classical elements are no longer considered elements, but I mean from Mendeleev to now.--Mostargue 18:24, 3 October 2007 (UTC)

Mendeleev sorted elements in terms of weight. Therefore, to say that hydrogen is the "first" element is to say that it is the lightest, which can certainly be confirmed. The modern periodic table sorts elements by atomic number, and it can again be confirmed that hydrogen has the lowest atomic number (one), making it first. So, what we are truly saying here is that hydrogen can be scientifically "confirmed" to be the first element, within the confines of a particular definition of "element." Someguy1221 18:30, 3 October 2007 (UTC)

Since Mendeleevs time we have come to understand that the atom is composed of electrons, neutrons and protons, with the number of protons being equal to the number of electrons and corresponding to the ordering of the periodic table. By ionizing hydrogen, one can find that the remaining core has positive charge +1 and it must therefore be the first element. Mendeleev I believe, to say that Hydrogen was the lightest, may have needed the concept of the Avogadro constant. You can't say that element A is heavier than element B just because a litre of A is heavier than a litre of B, you need to know how many atoms goes into a litre of each element. This was easiest with gases, then I believe other regularities in the table allow you to sort the non-gas elements in the right order. EverGreg 20:00, 8 October 2007 (UTC)

Well I've heard of a single Neutron be called the element neutronium, with atomic number zero.--Mostargue 19:02, 3 October 2007 (UTC)

An isotope of which would be neutronium⁰ I suppose? SteveBaker 19:24, 3 October 2007 (UTC)

I've also heard of positronium, which only has an electron and a positron. — Daniel 22:17, 3 October 2007 (UTC)

speed

Does a car speedometer measure speed,velocity or both? —Preceding unsigned comment added by Ekumak (talk • contribs) 19:21, 3 October 2007 (UTC)

Only speed. Velocity is a measure of speed AND direction. So "20mph, heading North" is a velocity, "20mph" by itself is a speed. SteveBaker 19:26, 3 October 2007 (UTC)

Though I wouldn't be surprised if there were a dashboard out there with a built-in compass. GeeJo ^(t)⁄_(c) • 20:40, 3 October 2007 (UTC)

Maybe if it had an inclinometer too... SteveBaker 18:26, 4 October 2007 (UTC)

The surface of a sphere can be treated as a two-dimensional geometry, in which case a compass and speed indicator are enough to give you the velocity. --Carnildo 21:56, 4 October 2007 (UTC)

Well, this "velocity is a vector; speed is a scalar" stuff is convenient for high school physics teachers, but it doesn't necessarily reflect real-world usage. Plenty of times "velocity" is used to mean just the magnitude, and this usage isn't wrong. Similar considerations apply to "weight" and "mass" -- historically, there are lots of contexts in which "weight" means "quantity of matter" rather than "gravitational force". When teaching the subject to students who aren't used to making the distinction, it no doubt helps to have different words, even if you have to be a bit arbitrary about which word to use for which concept. Unfortunately sometimes the students don't realize that the particular semantic assignments made to these terms in a scholastic context don't necessarily apply outside that context. --Trovatore 21:20, 3 October 2007 (UTC)

Well, yes, but the questioner specifically asked about the two as separate terms, so e is clearly aware that there's a difference between the two. It'd be silly to pretend there's another difference between them other than the scalar/vector "stuff" when answering. GeeJo ^(t)⁄_(c) • 22:15, 3 October 2007 (UTC)

My point was precisely that, depending on context, there may not be a difference between the two. Some people have so rigidly internalized what they were taught in freshman physics that they're not aware of that. --Trovatore 22:29, 3 October 2007 (UTC)

Nonsense - there is always a difference between the two words. In some contexts the difference may not matter - but that's not the same thing. A lot of people mis-use these two words - but their meanings are clear and quite distinct. If someone misuses the terms - then please correct them - and if (as in this case) someone asks about the distinction - then we should explain it clearly and without cluttering up the explanation with this kind of misdirection. Some serious errors can be made by people misusing words - so let's not condone it. When we say "The velocity of an object remains constant unless an external force is applied to it" - we mean that neither the speed NOR the direction of motion changed. When we say that "an object cannot exceed the speed of light" - we mean that the direction doesn't matter. It's an exceedingly precise distinction and you make life harder by screwing the terms up. Ditto mass and weight. They are as different as "time" and "thyme". SteveBaker 02:01, 4 October 2007 (UTC)

No, Steve, you're making the mistake I outlined; over-rigidly internalizing a distinction that someone found convenient to make. "Velocity" is simply the Latinate word for "speed" (must be late Latin; I think classical Latin for "fast" is celerus, not velox). Somewhere along the line someone got the bright idea to use the fancier word distinctively for the vector quantity, and that's fine in context, but it's not wrong not to.

For the mass/weight thing, do a "Google Groups" search on Garry Vass's Gene Nygaard's postings on the subject in alt.usage.english; he makes the point quite convincingly. --Trovatore 02:24, 4 October 2007 (UTC)

The word "velocity" has two meanings- a more precise one, used within certain fields (science and engineering) and also a less precise common meaning. When in doubt, consult a dictionary- mine shows both meanings, so I'd say this means they're both considered correct. Yes, unfortunate confusion can happen (the word "theory" is notorious for this), but I don't see that it's terribly bad in this case. If someone uses "velocity" to mean "speed" in physic class, yes they should be corrected, but I don't think it's fair to say the usage is always wrong. Friday (talk) 02:31, 4 October 2007 (UTC)

Exactly -- in physics class, not in physics generally. In class, the assignment speed/scalar, velocity/vector, is observed scrupulously, not at all for linguistic reasons, but as an aid to help students remember that the scalar quantity and the vector quantity are not the same thing (whatever you call them). Once you're past the point where you might confuse the two concepts, there's no longer any great necessity to follow this rather arbitrary naming convention (how would you do a similar thing in Italian, where there's only one word, velocità?). I imagine you wouldn't have to look very hard to find plenty of formal research papers in physics using the word "velocity" for the scalar quantity -- it's hard to imagine a context where this would result in confusion among trained physicists; it will generally be obvious whether the scalar or the vector is intended. --Trovatore 03:09, 4 October 2007 (UTC)

From our Muzzle velocity article: A gun's muzzle velocity is the speed at which the projectile leaves the muzzle ... (emphasis added) - hydnjo talk 03:49, 4 October 2007 (UTC)

But surely that is a vector? The muzzle velocity is the speed in the direction out of the muzzle. The distinction still seems apparent :) I'm not saying people don't use one for the other, just that this is perhaps not an example of it. 79.65.119.193 10:01, 4 October 2007 (UTC)

Maybe the distinction seems apparent because you just happen to know that when a bullet leaves a gun, it travels in the same direction as the muzzle. And, I must say, that would seem pretty obvious to most people, I imagine. I think the purpose of that definition was to talk about the speed/velocity of the bullet without regard to whatever direction it happens to be travelling in relative to the muzzle. Which would explain why the direction isn't referred to. -- JackofOz 10:24, 4 October 2007 (UTC)

Toe Nail

What might make a human toe nail discolor, like to an ugly brown or black? I was assuming that the toe nail was "dead" -- but, on second thought, isn't every toe nail already "dead" (that is, some form of dead skin)? If a toe nail were to become dead/discolored, would it just remain there or would it fall off? And, what type of doctor handles this? Would it be a dermotologist ... or something else? Thanks. (Joseph A. Spadaro 19:41, 3 October 2007 (UTC))

We aren't allowed to offer medical diagnoses. See a doctor...a podiatrist perhaps. SteveBaker 19:48, 3 October 2007 (UTC)

He's asking a question. What makes a toe nail discolor. That's not a medical diagnoses. 64.236.121.129 20:42, 3 October 2007 (UTC)

It can go black when there is blood underneath it. This could happen if a bruise happens to the nail - eg hit with a hammer. If the nail bed is damaged then a new nail may grow out. Eventually the black will disappear. The nail itself is not living cells, but underneath the skin is alive. Graeme Bartlett 21:06, 3 October 2007 (UTC)

I agree. It's a question, not a diagnosis. With that said: The toenail is "dead", but there is a living layer of cells underneath called the nail bed. The most common causes are damage to the nail bed, which can occur from dropping something heavy on your toe or kicking something (or someone!). Also very common are dermatophytic fungal infections of the nail bed. Minor damage from blunt-force trauma will usually heals naturally over a few weeks, however, fungal infections usually persist and may worsen over time. This can result in the nail completely falling off, and even spreading to other toes. Any licensed general/family practice doctor is able to diagnose and treat the problem. If it's a fungal infection, there are prescriptions available (Lamisil). If the problem is due to a less-common problem (skin condition, immunological problem, adverse drug reaction, diabetes, gangrene) or the toe is damaged to the extent that it requires surgery, the family doctor will usually refer the patient out to an appropriate specialist, which may be a dermatologist or even a podiatrist. Kel - Ex-web.god 21:04, 3 October 2007 (UTC)

Apropos of nothing, bruises under nails are subungual hæmatomae GeeJo ^(t)⁄_(c) • 22:00, 3 October 2007 (UTC)

• Another common source of blackened and/or falling-off nails is running marathon distances, as I can currently -- and grotesquely -- attest. --Sean 22:05, 3 October 2007 (UTC)

• Another couple causes of this are frostbite and lead poisoning. StuRat 06:23, 5 October 2007 (UTC)

Tattoos, Moles and Fat

I'm wondering whether moles can have an impact on tattoos. For instance, is it at all possible to tattoo a mole? What happens if you get a tattoo, and some time later you develop a mole where the tattoo is?

And while I'm at it, what happens to a tattoo if you get fatter/more muscular?

Thanks, 81.165.126.252 20:17, 3 October 2007 (UTC)

The Tattoo FAQ on About.com may be of some use. In short: moles, acne, and other skin blemishes while you are getting a tattoo aren't going to make the artist's job any easier, and if the mole(s) are particularly prominent, you'd probably be better off getting them removed. As for weight change, provided it's fairly slow, you should be alright. Pregnancy or other rapid changes to the area the tattoo is covering are less forgiving, though. GeeJo ^(t)⁄_(c) • 20:56, 3 October 2007 (UTC)

No reputable tattooist will tattoo over a mole because occasionally they can develop into skin cancer and a possible warning sign is changes in shape & size of the mole. Covering one with a tattoo would make it harder or impossible to spot changes in the mole. Exxolon 01:05, 4 October 2007 (UTC)

Doppler Effect

If there were two torches, one stationary and one moving towards a stationary observer, the photons from the torch moving towards the observer would have a higher frequency than the other torch. This means that they have a higher energy. Where does this energy come from? (I think I have a basic misunderstanding of the doppler effect, as applied to electromagnetism, but I couldn't decipher most of the article on the Relativistic Doppler effect ). Thanks a lot for your time.86.150.251.208 21:59, 3 October 2007 (UTC)

Before the moving torch is moving fast enough for this effect to be noticeable, the wind will blow out the flame.

But if you had something other than a torch, say a flashlight for example, then to trace where the extra energy was coming from in your frame of reference, you'd have to trace back to the battery, consider time dilation, consider the changes to the electromagnetic fields within the battery, etc. It would be a tricky accounting problem, but all the books balance in the end. Maybe someone else can break it into a manageable number of accounting steps. --Trovatore 22:42, 3 October 2007 (UTC)

A torch can mean a flash light in some parts of the world. --antilived^{T | C | G} 00:57, 4 October 2007 (UTC)

UK IP address generally means UK terms. Torch = electric torch. I hope someone with a better knowledge of relativity than me can answer this question. In my ignorance, I would assume that the energy came from the movement, or something. Hmm, that doesn't really make sense. Skittle 01:00, 4 October 2007 (UTC)

It's ordinary kinetic energy. In the rest frame of the observer, the moving torch has more kinetic energy than the stationary one, and it also loses more due to radiation pressure (it slows down more than the stationary torch accelerates backwards). —Keenan Pepper 01:10, 4 October 2007 (UTC)

Don't say I am spoiling all the fun but since Kinetic energy is half mass times velocity squared, where will you fit this extra energy in the equation? A photon has no mass and it has a specific velocity. Oh, I am falling into my own trap ... --Kushal^{Click me!} write to me 03:18, 4 October 2007 (UTC)

A photon doesn´t have rest mass, but it still has relativistic mass. But does that formula actually work in special relativity? --antilived^{T | C | G} 04:01, 4 October 2007 (UTC)

Of course the kinetic energy of the source (the flashlight, not the photons!) can be non-relativistic. This effectively provides more energy to the photons, even if the total Doppler effect is treated non-relativistically. Nimur 16:22, 4 October 2007 (UTC)

Kinetic energy is the difference between rest mass and relativistic mass. If that formula is applied to photons, the result is that they are pure kinetic energy. — Daniel 23:40, 4 October 2007 (UTC)

OK I am not good at Physics. I always thought the mass of the torch or the apeed of the torch made no impact on the kinetic energy of the <strikethrough>light particles</strikethrough> photons. What am I missing? --Kushal^{Click me!} write to me 02:53, 7 October 2007 (UTC)

normal variation sample #

I've heard more than one stats person say that you need 30 samples to be able to describe a normal variation. Why is this? How do they get 30? I think I once heard 34 too, why would this be? Thanks . —Preceding unsigned comment added by 12.217.195.89 (talk) 22:30, 3 October 2007 (UTC)

Start by reading Sample size and the links within. --Cody Pope 23:47, 3 October 2007 (UTC)

In elementary statistics (professional statisticians look away now !) 30 is traditionally given as a heuristic minimum sample size for applying the central limit theorem - see this Yahoo!Answers link. Gandalf61 08:59, 4 October 2007 (UTC)

October 4

How come cigarrettes don't have nutrition facts?

--Mostargue 01:43, 4 October 2007 (UTC)

Because you're not supposed to eat them? Because they have no nutritional value? Because there is no legislation requiring it? - Nunh-huh 01:46, 4 October 2007 (UTC)

Yeh, I think you have to ingest something for it to have nutritional value? HYENASTE 01:52, 4 October 2007 (UTC)

For the Language Desk I suppose but why does "how come" translate to "why" (or the other way around)? - hydnjo talk 02:01, 4 October 2007 (UTC)

Supposedly, as a locution for "how comes it that..." or "how did it come about that..." The Random House Dictionary gives a list of similar phrases in noted works: ""How comes it then that he is prince of devils?" (Marlowe, Doctor Faustus); "How comes it that they travel?" (Shakespeare, Hamlet); "How comes it thus?" (Milton, Paradise Lost); "How comes any particular thing to be of this or that sort?" (John Locke, An Essay Concerning Human Understanding); "How comes it to be any concern of yours?" (Fielding, Tom Jones); "How comes this about; there must be some mistake" (Jane Austen, Mansfield Park); "How comes it that we whalemen of America now outnumber all the rest of the banded whalemen in the world?" (Melville, Moby-Dick); and "Then if it's so precious how comes it to be cheap?" (Henry James, The Golden Bowl)." -Nunh-huh 02:10, 4 October 2007 (UTC)

Holy cow! Thanks ;-) - hydnjo talk 02:23, 4 October 2007 (UTC)

Thanks ... --Kushal^{Click me!} write to me 03:15, 4 October 2007 (UTC)

What about chewing tobacco then?--Mostargue 05:27, 4 October 2007 (UTC)

The same answer would hold -- not ingested / not required by legislation. — Lomn 12:58, 4 October 2007 (UTC)

It often is ingested; but not normally in quantities that would have any significant effect on your nutrition. You don't usually have nutrition labeling on cayenne pepper, either, and that clearly is ingested by many people. Gene Nygaard 13:10, 4 October 2007 (UTC)

The short answer is, 'because they're not required to'. Depending on your jurisdiction, different products will fall under different legislation and have different labeling requirements. Beer, wine, and liquor; vitamins, over-the-counter medications, and prescription drugs; cigarettes, cigars, and chewing tobacco—these are all things that you put in your mouth, but in most places they tend not to carry nutritional information on their labels. These products all are regulated in one way or another, though, and all will carry some sort of specific information detailed in whatever local laws are appropriate. TenOfAllTrades(talk) 13:25, 4 October 2007 (UTC)

Thanks. Now here's my science question: if Cigarettes DID have a nutrition facts label, what would it list?--Mostargue 14:06, 4 October 2007 (UTC)

According to TheTruth.com there are over 4000 'ingredients' in tobacco smoke. You're going to need a big label if you are going to list the things that come OUT of a cigarette when it's burned. Listing what goes into one is not so useful since you really don't eat them. Mostly, it's leaves and paper...but that's not the problem - it's what happens to those things when you burn them. SteveBaker 15:48, 4 October 2007 (UTC)

That's 4000 chemical compounds that can be found in tobacco smoke, but ingredient labels list actual ingredients, not the chemical constituents of those ingredients, nor the things they become through combustion. The same source suggests that there are about 600 possible ingredients that are used by at least one cigarette manufacturer, with no indication of how many might be in any one particular cigarette. In any case, it's a bit moot. Cigarettes get warning labels, not nutrition facts labels; there's no nutrition involved, so there can be no meaningful answer to the hypothetical. - Nunh-huh 16:01, 4 October 2007 (UTC)

But I've seen stuff like mouthwash, which clearly shouldn't be ingested, have nutrition facts. Certainly tobacco companies are required to list the ingredients of their product? I'm sure they could fit a small folded into the carton listing all the ingredients. If not, is this a result of the tobacco lobby?--Mostargue 16:06, 4 October 2007 (UTC)

I think you are thinking of an ingredient list: certainly mouthwashes have that. I've never seen mouthwash with a nutritional facts label. for, say, a pizza, the ingredients would be Enriched flour, water, mozzarella cheese, pepperoni, tomato puree, asiago cheese, parmesan cheese, yeast, maltodextrin, Salt, Garlic Basil, etc., but the nutritional label would be more like this: . Cigarettes (or mouthwash) don't have the fat, carbohydrate or protein content that would make such a label meaningful or useful. - Nunh-huh 16:25, 4 October 2007 (UTC)

In the USA, alcohol and cigarettes are not managed by the Food and Drug Administration, so both are exempt from the FDA's nutritional information labeling requirements. (Mouthwash usually has an antibacterial agent, so it is regulated as a drug, not as an alcohol... isn't bureaucracy amazing!) We have an entire Bureau of Alcohol, Tobacco, Firearms and Explosives, a federal agency responsible for regulating these items. In addition, individual states may have further requirements regarding distribution (though this probably does not affect labeling and packaging). Nimur 16:24, 4 October 2007 (UTC)

Lungs vs stomach

In response to previous question:

Would it be possible to gain nutrients from an aerosol or powdered spray vitamin? It would be administered like an inhaler. Or are the lungs unsuitable to distribute nutrition to the body? HYENASTE 01:52, 4 October 2007 (UTC)

You can administer certain drugs (such as insulin) through the lungs, but these are drugs, rather than nutritional substances. This in essence is exploiting the highly vascular lung structure as a drug delivery system. A cigarette is a means of getting a drug, nicotine, into the blood stream. You can't eat with your lungs; unlike the G.I. tract, no digestion occurs there. . - Nunh-huh 02:06, 4 October 2007 (UTC)

I understand, but what is the difference between insulin and, for example, vitamin A? And on a tangent, could you create an insulin cigarette? :P HYENASTE 02:40, 4 October 2007 (UTC)

By "cigarette" do you intend a delivery system that "burns" something to deliver useful insulin as a vapor or gas? - hydnjo talk 02:51, 4 October 2007 (UTC)

No, a cigarette is made of tobacco. Inhaled insulin is delivered as a powder. See this page if you are interested in inhaled insulin. - Nunh-huh 04:12, 4 October 2007 (UTC)

There may not be any digestion in the lungs, but digestion is a means to break down food to get the nutrients out, which go into the blood. Lungs are also designed to get stuff into (and out of) the blood (oxygen and carbondioxide, resp). But other substances can also be absorbed, such as several drugs. One could also ask this the other way around; which gases would the lungs not let through? DirkvdM 06:41, 4 October 2007 (UTC)

The lungs let all gasses through (useful in the delivery of anaesthetic gasses, for example), but the drugs so far alluded to are either solid or liquid; the question to be asked in regard to drug delivery is whether enough of the drug can be administered via this route to have the desired effect. - Nunh-huh 15:15, 4 October 2007 (UTC)

For large molecules (sugar, most proteins, etc) you generally need an active cellular pump to move the molecules into and out of the bloodstream. These are present in the digestive system, but not in the lungs. --Carnildo 22:02, 4 October 2007 (UTC)

When do pipes freeze?

How cold does it need to be to freeze pipes. Specifically, at what temperature will pipes freeze where a water faucet that extends from the outside of the house connects to a drip watering system that primarily lays on or just under the ground.

Thanks! —Preceding unsigned comment added by Prplflwr1 (talk • contribs) 02:30, 4 October 2007 (UTC)

Given enough time (this is important) and if the drip is slow enough (also important) and if the water is reasonably free of minerals (again important), slightly below 0ºC should do it. If the ground/soil is colder than 0ºC then things should freeze up faster but remember that the "drip" or flow rate and the temperature of the flowing water and the length of piping etc. could prevent or encourage freezing. So, we need more data to give you even a ballpark estimate. - hydnjo talk 02:59, 4 October 2007 (UTC)

At my place the hose will freeze up easily if temperature is below -1°C and it lies on top of the ground, but the water supply pipe very rearly freezes, it will have to be below -5° for quite a while to go solid. I have never had temperatures below -10° where I live. Graeme Bartlett 06:42, 4 October 2007 (UTC)

Per Hydnjo, there are a lot of factors to consider. Ordinary tap water will freeze at close enough to 0°C so as to make pretty much no difference. While the pressure in the pipe will depress the freezing point very slightly, it's not going to help appreciably—for a single degree drop in freezing point, one would need to elevate the pressure by about 140 atmospheres.

More important is the flow rate in the pipe and its amount of insulation. In order for water to freeze solid, two things must happen. First, it has to get cooled down to 0°C for the freezing process to start. Then you need to remove additional heat – the latent heat of fusion – to actually convert the liquid water into solid ice. It turns out that this second step actually involves quite a bit more energy than the first step. (The specific heat capacity of water is about 4 joules per gram per degree Celsius; to take a gram of cold tap water from 8°C to 0°C one must extract 32 joules of heat. The latent heat of fusion of water is 334 joules per gram—ten times as much.)

So the question becomes, for the flow rate, level of insulation, length of pipe run, and exterior temperature, will a gram of water be able to shed 300 or so joules between the point where it leaves the insulated home and where it exits the pipe? TenOfAllTrades(talk) 13:05, 4 October 2007 (UTC)

Beyond what TenOfAllTrades said, there's also the question of how much heat is getting into the water piping from inside the house. When we had a spate of very, very cold weather, within the house, we deliberately removed some of the thermal insulation that was covering the copper pipe leading to the sill cock/bib cock. This allowed more of the heat from the house to reach the "freezable" part of the pipe, keeping it from freezing. Alternatively, you could wrap the pipe in electric heating tape; these tapes often come with an automatic thermostat so they only switch on as the pipe approaches freezing temperature. All in all, it's a fine dance between wasting energy and frozen pipes!

Atlant 13:23, 4 October 2007 (UTC)

There are way too many variables. In Texas, when the weather gets below freezing, it only ever does it for a couple of days each year. So at the depth below ground of the water main coming into the house, it's still well above freezing - so relatively warm water is feeding the drip and keeping the pipe warm. It's unlikely ever to freeze. However, if you're in a part of the world where there is snow/ice on the ground for many months then the water main itself is only just above freezing (maybe it even runs through permafrost!) - so you are dripping very nearly freezing water - and your outside pipes could very easily freeze. Another variable to consider is where the faucet is plumbed into the house. At our home in England (where it does get cold enough for long enough), we have one outside faucet on the side of the (unheated) garage and another coming out of the wall next to the downstairs bathroom. The former freezes up alarmingly often (and even split once) because the water comes out of the cold ground, through the cold garage and then outside. The outlet next to the bathroom never froze because the air inside the bathroom is nice and toasty - and the pipe T's off of the bathroom plumbing and then heats through the wall to the garden. Only a few inches of pipe are exposed to the cold - so it never freezes even without letting the faucet drip. So it's not enough to say what outside temperature makes things freeze. You need to know the deep underground temperature, the amount of pipe that runs through heated parts of the building, you need to know for how long the outside temperature is that cold...insulation...just too many things. SteveBaker 15:40, 4 October 2007 (UTC)

Is it liquid mercury?

A liquid which produces a convex surface in a graduate cylinder. —Preceding unsigned comment added by Popbet (talk • contribs) 02:46, 4 October 2007 (UTC)

This sounds an awful lot like a homework question. The concavity of a liquid in a graduated cylinder is dependent on the cohesion of the liquid, and its adhesion to the material of the cylinder (with complications that don't matter for your question). From reading those links, you should be able to figure out whether mercury is a candidate. Someguy1221 04:59, 4 October 2007 (UTC)

• (EC) It depends what the cylinder is made of. For glass, mercury will indeed be convex. See meniscus. --Sean 05:01, 4 October 2007 (UTC)

That's what all the books say about mercury, but if you look at a real mercury thermometer, the surface looks flat. Why? Do those not use a glass tube? The article about mercury has an image of a mercury barometer which shows the same. – b_jonas 16:48, 4 October 2007 (UTC)

Thermometers and barometers use very small tubes where the capillary effect is the dominant feature. In other words, the tube is too small for a visible meniscus. Nimur 16:53, 4 October 2007 (UTC)

Ice cubes and the family jewels

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis.

(EC) You should consult a medical professional. If nothing, it will give them a good laugh too. Lanfear's Bane 15:42, 4 October 2007 (UTC)

You know, I'm not sure it's fair to the rest of us Reference Desk Regulars to hide questions like these. We could have at least linked the poor questioner to the Darwin Awards article or made some sort of awful "frozen stiff" joke.

Atlant 13:27, 4 October 2007 (UTC)

That's what edit histories are for :-) SteveBaker 14:35, 4 October 2007 (UTC)

That's pretty lame. Who would look something up if they don't know what it is? And especially if they have to go through that trouble (the history page is of course quite huge here), assuming they know how to do that in the first place. In this case the header might be interesting enough, but that is not normally the case. DirkvdM 18:17, 4 October 2007 (UTC)

Yeah, it wasted 2 minutes of my life to look that up in the history page... --antilived^{T | C | G} 21:05, 4 October 2007 (UTC)

Thank you, Antilived. Personally I can't get up enough enthusiasm to go through all that stuff on the history page.--Eriastrum 22:38, 4 October 2007 (UTC)

LOL that's hilarious --froth^t 23:04, 12 October 2007 (UTC)

Unplugging electronic devices

My router at home doesn't have a power button and, whenever I need a new IP address, I have to unplug it. For some reason I feel suddenly unplugging an electronic device, such as my router, can damage it. On the other hand, there are many computer peripherals which simply don't have a power button, so it mustn't be crucial for the survival of the device. Additionally, what a power button does is to (suddenly) interrupt the flow of electrons into the device, isn't it? So, is it unsafe or not? --Taraborn 13:24, 4 October 2007 (UTC)

Unplug the AC (mains) side of the power brick/wall wart, not the DC connector side. You'll be fine. After all, the router must be designed to survive power failure]s undamaged, right?

Atlant 13:29, 4 October 2007 (UTC)

Could you briefly explain why I should unplug the AC side instead of the DC one, please? Thanks for your answer. --Taraborn 13:51, 4 October 2007 (UTC)

Unplugging the mains side ensures that power goes away monotonically, whereas pulling the DC power connector may lead to a series of brief power interruptions and restorals that might wreak havoc with the electronics of the device. You may even get arcing. Also, if the DC power connector has more than one power rail, who knows what the removal and re-application sequence of the voltages will be? As I said, the device is clearly designed to withstand interruptions of mains power, but it's not nearly so clear that it's designed to withstand (many) cycles of DC power via the DC power connector. But its' your device so you obviously don't have to take my advice ;-).

Atlant 16:34, 4 October 2007 (UTC)

I'd say unplug the DC (almost entirely for convenience' sake, though the paranoid can also take comfort in staying further from mains power). As a practical rule-of-thumb, sudden shutdowns will not break electronic devices. You should avoid sudden shutdowns of data storage devices (USB drives, hard drives, etc) while they're doing stuff to prevent data corruption, but yanking the plug on a router is fine. — Lomn 14:41, 4 October 2007 (UTC)

I can't think of a reason to prefer the AC side. But to answer the original question - with things like this, you only have to worry about unplugging them 'suddenly' if they have data in volatile memory (RAM) that has not been saved out to a more permenant form of storage like a hard disk. For PC's, shutting them down by yanking out the power cord or pushing the OFF switch isn't good for them - but for something like a router that stores things in flash memory, you should be OK to turn it off providing you wait just a few seconds since the last operation. I'm a little concerned that you have to unplug it at all however. Are you doing this so that your computer gets a new IP address when the router comes back up again? Or is it that when you shut down your computer and bring it back up again, the router doesn't give you a new address properly? If it's the latter, then your router is set up incorrectly...which would be a good question for our Computer reference desk. If it's the former...why? SteveBaker 14:41, 4 October 2007 (UTC)

Thanks to all. My reason for needing a new IP address is that one-click hosts impose a download limit for non-premium users. --Taraborn 15:13, 4 October 2007 (UTC)

The flaw in your logic is assuming that the power button does something more than break the power rail circuit. In some sophisticated devices, the power switch may trigger a software or hardware shutdown routine, but most small appliances just power down. In that case, unplugging a cord or pressing a button is technically equivalent. Nimur 16:30, 4 October 2007 (UTC)

I know, I know that my logic isn't the law of gravity, just a general thought for the most common devices. --Taraborn 07:49, 5 October 2007 (UTC)

As a rule, you want to use the power switch if there is one. Among other reasons, any time you make or break a circuit you get an arc. In low-power devices, the arc is a teensy one. Down at the power station, it's a big, nasty, Frankenstein one. A switch is physically and electrically designed to take that. I have to unplug my router once in a while when it gets confused, and I always just yank the DC. But if you're worried about it, put the router on its own little power strip, and use the switch on that. One reason it's better to cut the power at the wall is that the doodads in the pack help soak up whatever spike happens. If you want it more technical, let me know. --Milkbreath 17:50, 4 October 2007 (UTC)

I do not think you should even need to power down your router to get a new IP. There should be a reset button that you can use a paperclip to activate. Alternatively you should also be able to reboot the router or have it release/renew the WAN IP from the router's interface. Try plugging 192.168.1.1 into the adress bar of your web browser (other common router LAN IPs are 192.168.0.1, 192.168.123.254, and 192.168.2.1). If you can access the interface you can get a new IP wothout even getting out of your chair! 161.222.160.8 22:27, 4 October 2007 (UTC)

Pressing the reset button will return the router to factory settings in addition to restarting it, which a lot of people probably don't want to do. Someguy1221 23:28, 4 October 2007 (UTC)

Hmmm... Not for me. I have used it many times. All settings stay the same (ports, DHCP, static vs. dynamic). Come to think of it, on my particualr model I think the only way to restore defaults is through the console. Good point though, reset switch is prob not the best idea unless you know what will happen. 161.222.160.8 00:41, 5 October 2007 (UTC)

I would disagree with Atlant that interrupting the mains by withdrawing the plug would result in a monotonic decay of the output voltage. Any voltage above about 70v a few hundred in air at atmospheric pressure is likely to produce arcing. See Paschen's Law. This will give nothing like a monotonic decease in the output voltage, but a series of surges. I would recommend unplugging at the low voltage or dc section of the power supply.--88.109.121.209 01:36, 5 October 2007 (UTC)

Yeah, but the bulk storage capacitors in the power supply unit will mitigate this; they've already got enough charge in them to ride through at least a half-cycle of the power waveform so introducing small pulses of the (current value of the) power waveform won't affect their charge level much. As I said, one can take my advice or not; it has no impact on me; my networking gear is all powered from a single (common) wall switch so when it needs to be reset (and it does occasionally), I just flip the switch down and back up again.

Atlant 13:27, 5 October 2007 (UTC)

Bear in mind that large electrolytics have quite a high impedance at rf frequencies, so unless there is proper surge protection, these spikes are going to get through your power supply. I surmise that it all depends upon the current one is trying to break, whether there is enough inductance in that circuit to cause arcing, whether that arcing can be supressed by any filtering you have, and whether the residual surges can damage any components. Its not really a simple question. My advice would be; break the circuit at the lowest voltage/current that you can and make sure the switch dosent cause more bouncing than your filters/suppressors can handle.--88.109.121.209 15:12, 5 October 2007 (UTC)

I would love to see this question copied to the Computer reference desk. --Kushal^{Click me!} write to me 02:59, 7 October 2007 (UTC)

Identifying an insect

I don't have a photo, I'm afraid, but it had noticeable orange legs with a browny-orange body, and on the end of the body it had a black patch. It had reasonably long orange antennae and had two points on its 'shoulders' like shoulder blades. Does anyone know what it could be? I'm in the south of England. Thanks. —Preceding unsigned comment added by 84.68.35.79 (talk) 13:28, 4 October 2007 (UTC)

Your description of "shoulder blades" suggests the Shield Bugs, Pentatomoidea. However, I can't after a quick look find one that has orange antennae. Try doing a google image search of these names and see if they are similar. How big was the insect? What was it doing? What kind of environment did you find it? Did it have wings?--Eriastrum 15:47, 4 October 2007 (UTC)

Does it match the pics at shield bug ? StuRat 06:11, 5 October 2007 (UTC)

Peri-synaptic

What does peri-synaptic mean? Lova Falk 14:17, 4 October 2007 (UTC)

Just as "perinatal" means "the time before and after a birth" or "the time around birth", so "perisynaptic" means "the area before and after a synapse" or "the area around a synapse". -- Nunh-huh 15:09, 4 October 2007 (UTC)

Thank you! I didn't know what perinatal meant either. :) Lova Falk 15:31, 4 October 2007 (UTC)

Maybe "periscope" would have been a better explanation...it lets you look all around.....  :) - Nunh-huh 15:53, 4 October 2007 (UTC)

When I think of the meaning of peri-, I always think first of periokoi, but I may be non-typical here. Algebraist 17:20, 4 October 2007 (UTC)

Within this small period of time, several perilous suggestions almost made me perish... Lova Falk 18:31, 4 October 2007 (UTC)

Well then have a look a the Peripatetics walking around. The word gave the now disused french "péripatéticienne" for ... hooker! Keria 21:39, 4 October 2007 (UTC)

You got one out of three. Period does come from Greek peri- "around", but peril comes from Latin periculum "danger", and perish comes from Latin per- "thoroughly, completely", neither of which is related to peri-. —Keenan Pepper 04:47, 5 October 2007 (UTC)

It makes me think of chicken... — Matt Eason ^{(Talk &#149; Contribs)} 23:30, 4 October 2007 (UTC)

about optical microscope

can we start the design of microscope with objective using ZEMAX.If i start like that what happens regarding aberrations.which type of objective i can use to get 100x magnification. —Preceding unsigned comment added by Mahendarkumbham (talk • contribs) 15:13, 4 October 2007 (UTC)

Jack plug

When cutting the wire of a three connector jack plug I can see 3 wires. From the outside it looks like 2 wires running alongside but when i cut them: one in its own plastic insulation and in the second i find a wire wrapped around a smaller third inside a white plastic insulation. Which is left, which right and which is ground? Thank you. Keria 17:34, 4 October 2007 (UTC)

Sorry my mistake it's actually two pairs of wires and the solution is there http://forum.ecoustics.com/bbs/messages/15118/14935.html . Keria 17:48, 4 October 2007 (UTC)

Definition of a Human

What do people think of this definition? An embryo must have both brain and heart cells present (happens three weeks after conception) to be considered a human or must have at least one cell from each organ that a healthy adult cannot live more than a 24 hour period without. I have also heard that a human is composed of three parts: body, soul and spirit. If this is true, is there a way of detecting this and if so would this change the definition of a human to be: have both heart and brain cells present and have a detectable soul/spirit? —Preceding unsigned comment added by Rsdetsch (talk • contribs) 17:38, 4 October 2007 (UTC)

You may define a human however you like for any given argument. Definition of terms is really a matter of choice, not science. As far as detecting a soul, there is no scientific evidence that any detectable item which you might call a soul exists. We do, however, usually have an easily detectable brain. Nimur 17:41, 4 October 2007 (UTC)

One might argue that someone doesn't have a "soul" until well after birth, maybe even back it up with various religious references. As Rsdetsch (actually Nimur) says, there's no empirical evidence of a soul, only religious or non-scientific theories. -- JSBillings 17:46, 4 October 2007 (UTC)

I said that, not Rsdetsch! Nimur 17:48, 4 October 2007 (UTC)

Whoops, sorry. I picked the wrong name out of the earlier wikitext. -- JSBillings 17:51, 4 October 2007 (UTC)

Thanks for your comment(Nimur), but is there an indirect way of detecting a Soul and/or a relational dependence we can associate with its existence. Like a Soul cannot exist without a brain? —Preceding unsigned comment added by Rsdetsch (talk • contribs) 17:49, 4 October 2007 (UTC)

It depends on your definition of Soul. Check out the Science and the soul section, to see some attempts of defining "soul" scientifically. You'll see a later discredited attempt to discover the weight of the soul by measuring the weight of the body before and after death. -- JSBillings 17:55, 4 October 2007 (UTC)

That is an interesting point (JBillings), if one was able to come up with a unique weight of a human soul then one can come up with a necessary (not sufficient) condition of being human e.g. if the embryo weights less than that unique weight it is not a human. —Preceding unsigned comment added by Rsdetsch (talk • contribs) 18:14, 4 October 2007 (UTC)

No - that truly wouldn't help. If you could come up with some bizarro experiment that measured the weight of a soul - I guarantee that you'd be able to do the same experiment on a Chimpanzee - get more or less the same result - then have to fight tooth-and-nail with the religious loonies who claim that "animals don't go to heaven because they don't have souls" - so now you have to label this thing that your experiment showed up with some other name - and now you are no closer to proving the moment of humanity. SteveBaker 18:18, 4 October 2007 (UTC)

Besides, you'd have to prove that souls have constant weight. If not, the weight of a fullgrown one would not help. 69.95.50.15 20:10, 4 October 2007 (UTC)

It doesn't really matter how you make your definition - it's just a word after all. What matters is what you intend to use the definition FOR. If (to take an obvious example) you are talking about the abortion debate - then one bunch of people are going to complain bitterly about your definition because it de-humanises the very young and "permits people to murder them" - and another bunch are going to complain just as much because it implies that the termination of a fetus beyond a certain (fairly early) age is "killing a human" and that would effectively remove "the right to choose". So, by all means, define the word however you like - but don't expect many people to agree with you! There is no "right" definition from a scientific perspective - there is a continuous process from the instant of conception, through birth and into adulthood - and we could pick any one of a bazillion events along the way to label as "the transition to humanity". Personally, I would prefer to use the word 'human' throughout the process - the label says what kind of cells this fetus is made of - as in: "This is a human egg/fetus/baby/child/adult as distinct from a chimpanzee egg/fetus/baby/child/adult." SteveBaker 18:15, 4 October 2007 (UTC)

Well said, SteveBaker. I have to wonder why having a brain, heart or soul matters for the definition of Human. Does having an artificial heart make one less human? What about an artificial brain? One could go as far as defining Human as the common genetic sequences all humans share. I think the OP really was trying to define what makes someone a conscious entity (although the heart is no more important than the lungs when it comes to cognition). -- JSBillings 20:02, 4 October 2007 (UTC)

• Typically these debates focus on "personhood" rather than humanity. My own simple test -- equally unsatisfactory as a universal one, no doubt -- is "if it looks like a person, it is". I could quibble about when that happens, but I'll never be convinced that some "persons" look like this (actual size) ---> • --Sean 20:12, 4 October 2007 (UTC)

Just don't try to use that to advocate abortion. The question isn't about whether or not it's killing something that looks like a person. The question is about whether or not killing a fetus, whether or not it matches any definition of a person, is wrong. — Daniel 23:29, 4 October 2007 (UTC)

I like to look at the implication of a proposed rigorous definition of what is a human. If heart tissue must be present to qualify, then during a heart transplant, the recipient ceases being human for a while once his old hear has been removed and before his new heart in installed. He was human when they began the operation, then he was not human for a while, then he was human again. The notion just doesn't work for me. Edison 02:26, 5 October 2007 (UTC)

We have an article on that effect and several variations (all stem from a continuum fallacy. It's come up on the desk a few times. As I mentioned, you can play whatever games you want with your definitions. Consistency becomes very difficult when you take a large number of scenarios into account. Nimur 03:08, 5 October 2007 (UTC)

The problem is that it's OK (useful, valuable, reasonable) to give a name to some region of a continuum - so to say "This is a fast car" because it can go 200mph is not disputed by anyone and to say "This is a slow car" when it has a top speed of 20mph would not be disputed. The problem comes when you get into the grey area between those two terms. Is a car that can only go 70mph fast or slow? But this doesn't matter so long as you don't use these vague 'partial-continuum' names to force a binary yes/no decision. We don't try to pass laws that say "You aren't allowed to drive fast down this road" - we say "You aren't allowed to drive at more than 40mph down this road".

The same exact problem bedevils the abortion debate. We mostly agree that you shouldn't be allowed to kill a "person" - but almost all of us agree that a single cell is not a "person". If I cut my finger and it bleeds - we don't rush the droplets of blood to the hospital and attempt to keep them alive - yet they are just as 'alive' and 'human' as a newly fertilised human egg cell. So here we have a continuum - yet people are talking about it as if it was not a continuum. This forces some people to have to take an extremist attitude that goes something like "Because we don't argue about whether a two-week premature baby is a person - and we have a continuum from there all the way back to the instant of fertilisation of egg by sperm - then we must declare that one is a full person with all rights that this entails from the moment of fertilisation."...but in reality, that's as dumb as saying "Driving at 200mph is obviously dangerous and should be disallowed - but because there is a continuum between that and 0.001mph, then it follows that all cars must be banned." SteveBaker 14:51, 5 October 2007 (UTC)

I agree the continuum is something a lot of people, particularly religious types tend to miss. Note also that both sperm and (unfertilised) ova are alive before fertilisation. If they weren't alive then fertilisation could not occur. While they may be haploid, they're also human. Also the idea that 'personhood' (whatever that means) begins at fertilisation get's somewhat confused when we consider that with identical twins (or triplets), the same zygote which you say is one person can become two or three people. The reality is trying to define a set beginning to 'life' and 'personhood' just doesn't work IMHO Nil Einne 01:36, 7 October 2007 (UTC)

Yeah there's a continuum, so there's no exact point where it goes from a splattering of cells to a baby, but obviously you can't ignore the change between "I squashed a single cell so what" and 8.9 months later "holy crap that's a baby that happens to be inside a woman".. this is what is struggled over. Just because we can't define exactly when a person acquires said personhood doesn't mean that they don't acquire it.. aborting a fetus 1 day before delivery is essentially identical to birthing it and then killing it, and killing single cells is trivial, but though it make be indeterminate we can't just ignore the space between. My position on abortion is that if people aren't prepared to kill their newborn, but are willing to abort a day before then they're the ones with the nonsensical arbitrary position. Not refuting what you're saying but extending it? --froth^t 03:27, 10 October 2007 (UTC)

In which point this discussion started to be against WP:NOT#FORUM? We can't say, the process was continuum. 200.255.9.38 15:01, 10 October 2007 (UTC)

Moon Rise and Set

I watch the moon quite frequently when out walking my dogs. Although I know there are phases to the moon and how long it takes for that whole cycle to occur. I haven't seen anything that tells how to tell what time the moon will rise and when it will set. Is there a specific way to know that?206.17.145.132 20:32, 4 October 2007 (UTC)beth

Some newspapers print sunrise, sunset, moonrise, and moonset times; otherwise you need to consult an almanac or its equivalent. It obviously depends on your specific location. One that's online is <http://www.skyandtelescope.com/observing/objects/javascript/3305541.html#> - Nunh-huh 21:33, 4 October 2007 (UTC)

A full Moon is opposite the Sun, so it rises when the Sun sets (roughly at the other side of the horizon) and vice versa. A new Moon is at the same side as the Sun, so it rises and sets together with the Sun, at roughly the same spot. You figure out the middle parts. :) (Sorry, a bit tired now, should be going to bed). DirkvdM 18:50, 5 October 2007 (UTC)

Awake again now. See lunar phase. In the first quarter, the Moon is straight overhead at sunset (where it says 6 pm) and then follows the Sun and sets in the west at around midnight (depending on how your timezone differs from solar time). And in the third quarter (when it forms a 'C' in the Northern Hemisphere), it rises at midnight and is overhead when the Sun rises. DirkvdM 08:55, 6 October 2007 (UTC)

Thirst for knowledge and the human condition

Okay, so this is more of a philosophical question than an actual scientific one; but what if one day we reach the limit of miniturisation and computational power and still the technology we have has not unlocked the secrets of the universe and the human condition. What happens next? Are there enough 'clever people' to be able to think our way to the answers we are looking for? Do we simply give up on certain questions? What if locked within our own experience is the inherant inablility to understand even the questions to ask, let alone the answers we find? --russ 22:55, 4 October 2007 (UTC)

You are asking the wrong question. We will never the unlock all the secrets of the universe because we only have 80 years of thinking life. Just look at what it takes to do orignal research nowadays, you need to study for 25 years before you can reach a point where you know the known science.

If we ever reach a point where we need to study 80 years before we can do original research then we have hit our thinking limit and humankind cannot progress further scientificly. 202.168.50.40 23:16, 4 October 2007 (UTC)

Yes, I agree with your perspective, but I meant generally, rather than personally - could one individual not continue another's work until we find the answers we are looking for, much in the same way that that for instance our understanding of 'gravity' continues to develop, even though it takes centuries to build up that knowledge? I am making the assumption that we are able to build upon our understanding, otherwise fields that took Newton and Einsein a lifetime of calculation to grapple with would not have progressed, surely? --russ 23:26, 4 October 2007 (UTC)

John Horgan wrote a book called "The End of Science" and suggested that we are passing out of the golden age of science. My personal view is that there is still a large amount of interesting science to be done, and it seems far to early to put much effort into worrying about "the end of science". --JWSchmidt 02:12, 5 October 2007 (UTC)

It seems to have been a general feature throughout the history of the sciences that as soon as people start making comments about having "discovered nearly everything", "just need to get the constants down to a couple more decimal places and fill in a couple of holes", "solve some minor problems", etc. - that's when someone makes some startling discovery that turns all of our current knowledge on its head. I'd even be willing to guess that we're approaching such a time soon. Confusing Manifestation 04:10, 5 October 2007 (UTC)

What I'm trying to say is that all the easy fruits have already been picked. The fruits of science still left hanging on the tree of knowledge are the really hard ones, ones that needs years of study before you can even begin to try picking them.

But you can't go from this to say that we have picked all the fruits of science. There will always be fruits of science so high up the tree of knowledge that we can never pick them. 202.168.50.40 04:47, 5 October 2007 (UTC)

Science as we know it today is not the right method to unlock the secrets of the universe and the human condition. Lova Falk 09:13, 5 October 2007 (UTC)

People thought we had discovered everything useful in physics in 1905. The only things left were blackbody radiation and the nature of light, but it was thought those things would be solved soon under classical physics. They couldn't be more wrong.--Mostargue 11:20, 5 October 2007 (UTC)

• There's no reason to be sure that we will be *able* to understand everything that we can observe. There's no more evolutionary requirement for us to be able to, say, come up with a grand unification theory than there is for a dog to be able to set the time on a VCR. --Sean 12:34, 5 October 2007 (UTC)

Are we close to knowing everything? The claim that we're close to having learned all that there is to know comes up at least once a century - and every time (so far) it's been proven wrong. To be sure, the rate of new discovery is increasing exponentially - but there are two ways to look at that. One is that at this prodigious rate we'll very soon have discovered everything we're capable of - but the other is that we are opening up lines of new enquiry at an exponential rate too. So I doubt we'll ever know everything - but I'm optimistic that during the last 50 years we've answered a lot of the really big questions to a reasonable degree of accuracy. The very large, the very small and the very old were shut out of our knowledge until quite recently but now we can answer "Where did we come from", "What makes the sun shine", "What is the smallest indivisible object"...many of those things were still completely uncertain even 50 years ago - yet nowadays, even my teenage son has a pretty good shot at giving a good answer.

Are there things that we cannot ever solve? Yes - we know that there are mathematical theorems can be neither proved nor disproved, we know that some measurements are strictly limited in precision, we know that some calculations will take longer than the life of the universe to perform so we cannot calculate an answer, we know that 'sensitive dependence on initial conditions' (chaos theory) puts sharp limits on our ability to do even seemingly easy things like predicting the weather that we once thought we'd have solved within 50 years.

Are there are things we can't ever do because we aren't smart enough?...that's a tough one. Humans have several unique abilities that mitigate the limits of the sizes of our brains. We have computers - it's pretty clear that we can make a computer that's faster than we are and which has a better memory - we're fairly sure that a computer that's generally more intelligent than us is possible (although efforts to actually build one have been frustratingly difficult). But if such a computer existed, it could probably be used to make another computer yet faster and smarter still - and so on to the limits of practical technology. (Let's face it - there is absolutely no way we can design a computer even now without using another computer to do the bulk of the work.) We have writing and speech which lets us communicate ideas so that one person doesn't have to solve a problem alone - we network our brains and our increasing population is making us collectively smarter. We can also spread the work of making a discovery over many generations - breaking problems into sub-problems and sub-sub-problems until we have small enough pieces to be tractable to a single person within their lifetime.

Is there an issue with it taking longer and longer to learn what you need to know to get started on a problem? This is something that we've always solved by specialising. As subjects get too large for one person to fully understand, we split them into specialities. So in the time of Newton, one person could be fairly conversant will all of science and mathematics. Nowadays there are dozens of branches of mathematics and hundreds of sub-specialities within science because even knowing everything there is to know about (say) cosmology is more than one person can handle.

SteveBaker 14:23, 5 October 2007 (UTC)

Dweller's thread of the week. It's an 'out of the box' idea.

Congratulations to all contributing here. This mindbending debate about the depths of our ignorance wins the seventh User:Dweller/Dweller's Ref Desk thread of the week award. Good job. --Dweller 09:17, 8 October 2007 (UTC)

Here's one of those can-of-worms "little details" like blackbody radiation and the nature of light- extraterrestrial life. We tend to ignore it since there's really nothing to be done but wait for technology to advance sufficiently to explore space, but that only sets us up for panic if it actually happens.. think of how much we could learn from the scientific work of a completely different academic universe.. surprising new ideas we would have never considered.. So science is far from reaching its end, but that's assuming that humanity still cares- I tend to see the age of rationalism and science as somewhat of a passing fad :x --froth^t 03:21, 10 October 2007 (UTC)

Please see the five minutes world (fourth quotation of the linked section), brain in a vat, and The Matrix... See also Wikipedia's article on science, which says that science is not supposed to and can not discover any truth. A.Z. 21:15, 12 October 2007 (UTC)

October 5

Level of fossilization in T.Rex Tissue?

I'm reading a paper published in Science magazine two years ago [1]. It documents a famous finding of soft tissue in T.Rex fossil bone. I'm trying to figure out to what extent the tissue recovered from the bone was fossilized, but I'm just a half-educated layman and I get lost easily in all the big words. First, what precisely is the definition of "fossilization" that a scientist would use? To what extent must the remains of the organism be changed (or do they have to be changed at all)? Second, the paper refers to the tissue having to be "demineralized" before analysis. Does this imply that the tissue had been fossilized, or is it something that you would have to do to any bone to get at the tissue? Thanks! 69.218.205.188 00:23, 5 October 2007 (UTC)

FWIW, bone specimens usually are decalcified before attempting DNA extraction, as it greatly increased the yield, even in fresh bone. - Nunh-huh 00:42, 5 October 2007 (UTC)

I was about to say "that's impossible", but then I read this section in our T. Rex article. The term "fossilisation" usually means that the original tissue has been replaced by minerals. So if soft tissue was found inside a fossilised bone then it would be more correct to say it has been "preserved" rather than "fossilised" - indeed the title of the Science paper, which is cited as a reference in our article, is Soft Tissue Vessels and Cellular Preservation in Tyrannosaurus rex. The "demineralisation" process uses weak acid to dissolve the fossilised bone, and so presumably leave the soft tissue remains behind. The researchers claim to have found blood vessels, tissue that is still flexible, and possibly even blood cells. If this find is confirmed by other researchers then it is a truly astonishing discovery. Gandalf61 09:02, 5 October 2007 (UTC)

Macaroni and cheese mystery

Say I pour a packet of cheese powder on my macaroni, then I pour a cup of milk onto the powder. But instead of soaking into the powder, the milk just beads up and rolls right off down to the bottom of the bowl. The powder stays totally dry! What's going on? This has bugged me for years. 154.5.195.217 01:20, 5 October 2007 (UTC)

The cheese is greasy and contains fat that repells water in the way you say. If you can melt the cheese you find that the fat is actually in very small droplets and can disperse in the milk if it is mixed. Graeme Bartlett 01:30, 5 October 2007 (UTC)

I had no idea that cheese came in powdered form. Is it dehydrated? Nimur 02:51, 5 October 2007 (UTC)

Yes, in a little packet that comes in the Kraft Macaroni and Cheese package (or several other brands). You must not be from the US if you don't know about powdered cheese. I don't think the earlier explanation is correct, however, as the cheese packet does not contain much fat. That is supplied by milk and butter which are added to the mix. StuRat 04:17, 5 October 2007 (UTC)

I'm not sure of the cause, but chocolate powder in milk does the same thing. A boundary layer seems to form between the milk and powder which can only be broken up by vigorous stirring. StuRat 04:23, 5 October 2007 (UTC)

The best plan is to add a small amount of milk to the powder in a cup, mix it well into a half-runny paste, add enough more milk to enable it to coat the macaroni, mix it again, pour it onto the macaroni, and pour the remaining milk on top. -- JackofOz 04:59, 5 October 2007 (UTC)

Right, but I think the original poster was looking for an explanation of why the powder won't dissolve more easily. StuRat 06:03, 5 October 2007 (UTC)

Reading between the lines of the question, it seemed apparent that 154.5 wasn't aware there was a way to counteract the problem. Often, when people ask "Why is it so?", they also want to know "How can I make it be different?". -- JackofOz 01:53, 7 October 2007 (UTC)

• It's certainly not due to any fat content, because talcum powder behaves in the exact same way. I think it has to do with wetting and hydrophobicity. Here are the ingredients of the "cheese" packet: Whey, Milkfat, Milk Protein Concentrate, Salt, Calcium Carbonate, Sodium Tripolyphosphate, Contains Less than 2% of: Citric Acid, Sodium Phosphate, Lactic Acid, Milk, Yellow 5, Yellow 6, Enzymes, Cheese Culture. --Sean 12:47, 5 October 2007 (UTC)

General rule: Any product that contains the word "American" and "Cheese" in it should be avoided at all cost. American cheese is bland beyond belief - the only difference between the different kinds is the colour. Somehow they've even found a way to pursuade the French to make stuff that looks just like Brie and even comes in one of those little round wooden boxes - but which tastes of exactly nothing and goes hard as it 'matures' instead of turning into a pungent creamy liquid as should be the case. I don't know how they do this...or why...but it's a fact. I bought some 'Munster' in the supermarket the other day - this is one of the strongest smelliest cheeses you can find in a French supermarket - and this stuff smells and tastes of precisely nothing. As far as I can tell is exactly the same stuff as their "Sharp cheddar" - but without the orange food colouring. "Sharp cheddar" has definitely not been within several thousand miles of Cheddar gorge - and is only sharp in the sense that a marshmallow is. My wife (who is French) found an interesting little cheese shop in Dallas - it turns out that the cheeses they keep are exactly the same as the ones in WalMart except that some have little bits of nuts in them. Hence we may deduce that the strange orange powder that comes with Mac'N'Cheez is some fascinating chemical substance with all sorts of interesting properties...none of which should encourage you to actually eat the stuff. SteveBaker 13:44, 5 October 2007 (UTC)

What you describe is processed cheese. The main ingredient is soybean oil, versus milk/cream for real cheese. Note, though that real cheeses are also made in the US. I do, however, agree that "American cheese" seems to be a keyword for processed cheese. I would expect that if you bought "sharp cheddar" in the US, it would indeed be real cheddar, unless it had some disclaimer on the label like "processed", "cheese food", "cheese product", or "artificial".

Another hint, any cheese that comes sliced in tiny plastic wrappers is also likely to be "processed cheese". (Cheeses sliced with tiny pieces of waxed paper between them tend to be real, however.) Most Americans are rather disgusted by smelly cheeses, however, so you will find a rather small market for limberger, etc.StuRat 17:38, 5 October 2007 (UTC)

It's not cheese if you can't smell it from three counties away! DuncanHill 18:59, 5 October 2007 (UTC)

My wife comes from Lille - and their local cheese ("Vieux Lille") is reputed to be the strongest flavored cheese in the world. She claims that there is a law to prevent one from carrying Vieux Lille in a Parisian Taxi! SteveBaker 17:54, 6 October 2007 (UTC)

My favorite euphemism in this vein is "processed cheese food product". Corvus cornix 01:48, 7 October 2007 (UTC)

digestive tract

05:02, 5 October 2007 (UTC)05:02, 5 October 2007 (UTC)~~m4.239.243.165 05:02, 5 October 2007 (UTC)Is it neccessary to have a bowel movement everyday? And is there a certain number of bowel movements a person should have per day?4.239.243.165 05:02, 5 October 2007 (UTC)

From 3 a day to once every 3 days is the guideline I heard, and that's the latest poop. StuRat 05:51, 5 October 2007 (UTC)

Quite. I once heard that nothing varied so much between humans as much as this statistic. It depends a lot on what you eat. Once every three days was normal for me as a kid, because I was fed hardly any roughage.--Shantavira|^{feed me} 17:37, 5 October 2007 (UTC)

In Western societies, people generally defecate two or three times a day, but it’s an individual matter. All the advice about the importance of regular bowel movements notwithstanding, some people defecate just once a week and are perfectly healthy. Constipation isn’t defined by the frequency of bowel movements, but by whether someone has difficulty when they have one. —Preceding unsigned comment added by 88.109.121.209 (talk) 19:53, 5 October 2007 (UTC)

It's my understanding that keeping feces in the bowel for long periods is associated with higher colon cancer rates. --Sean 14:19, 6 October 2007 (UTC)

I've also heard reports that colon cancer incidence is higher among individuals who feel constipated (eg, [2]). Note that that doesn't suggest anything about causation (not that you're suggesting causation, Sean), just that there's an association. It might be explained by some confounding variable, eg, that some underlying condition predisposes individuals to both colon cancer and constipation, not that longstanding or frequent constipation causes colon cancer. --David Iberri (talk) 15:49, 7 October 2007 (UTC)

Klebsiella Infection

What is the acceptable colony count of Klebsiella per Milligram?

Diya Mukherjee —Preceding unsigned comment added by Diya2710 (talk • contribs) 07:38, 5 October 2007 (UTC)

It's impossible to answer the question for at least two reasons. First, you haven't specifed what is being counted (though I suspect you're talking about urine). Second, colony counts alone are not diagnostic of anything: a colony count has to be considered in light of actual clinical conditions (symptoms of the person, reason for the testing, the presence or absence of instrumentation). As such, a colony count really needs to be evaluated by the treating physician or other medical practitioner. For example, if a patient has an indwelling urinary catheter and a colony count of 10,000, it might be considered a colonization requiring no treatment (in the absence of symptoms), and it might also be considered an infection requiring treatment (in the presence of fever or other symptoms). Similarly, the significance of the presence of Klebsiella in sputum would depend on the clinical setting in order to distinguish between colonization and infection. - Nunh-huh 17:37, 5 October 2007 (UTC)

This sounds like either a homework question or medical advice. The Reference Desk has a policy of not answering either. If homework, look it up yourself (e.g. in your textbook or class material). If medical advice, talk to a licensed medical professional. -- 72.33.121.200 18:58, 5 October 2007 (UTC)

It sounds like neither. A homework question would be more exactly phrased, and medical advice would pertain to a clinical question rather than an abstract one about lab values. - Nunh-huh 20:02, 5 October 2007 (UTC)

What kind of lock / key combination is this?

I need access to this common type of lock to open a panel but I don't know the name of the lock / key I need to get hold of to open it. These things open pretty easily and I have a feeling some thin pliers might do the job, but is there a particular name? Thanks.

http://img515.imageshack.us/img515/862/lockfh6.png

Looks like a meter cabinet - I think (in the UK) you should be able to get one from Screwfix, B&Q, Homebase etc. They are just called "meter cabinet keys". DuncanHill 08:48, 5 October 2007 (UTC)

aids

why aids donot spread by mosquito bite? —Preceding unsigned comment added by 202.177.155.94 (talk) 10:45, 5 October 2007 (UTC)

HIV_and_AIDS_misconceptions#HIV_is_transmitted_by_mosquitoes--Mostargue 11:13, 5 October 2007 (UTC)

unlitateral carotid ligation

What is unlitateral carotid ligation? Does it just mean that the two carotid arteries are connected? What would serve as the conduit? It's used or was used, as part of an animal model for cerebral ischemia. --Seans Potato Business 13:43, 5 October 2007 (UTC)

Here's a partial answer. Unlitateral carotid ligation is the tying off of one of the two carotid arteries, which supply the head and (most importantly) the brain. Normally, this should not cause problems because of the Circle of Willis, which is a circular arterial loop fed by both internal carotid arteries. However, if one of the carotids is partially or completely occluded (e.g. with atherosclerotic plaques), it would be dangerous to ligate the carotid on the other side. -- Flyguy649 ^talk _contribs 15:43, 5 October 2007 (UTC)

(after edit conflict) Unilateral carotid artery ligation is the closure of the carotid artery on one side. The artery is not rerouted or attached anywhere else; it's just closed. It is indeed used in animal cerebral ischemia studies. See for example Guri Bronner, Kendall Mitchell and Frank A Welsh "Cerebrovascular Adaptation After Unilateral Carotid Artery Ligation in the Rat: Preservation of Blood Flow and ATP During Forebrain Ischemia" in the Journal of Cerebral Blood Flow & Metabolism (1998) 18: 118–121 [3].

It turns out that closure of one carotid artery doesn't typically have any serious effects in an otherwise healthy rat's brain. There's sufficient redundancy in the blood vessels of the rat's brain to maintain an adequate supply of blood to the affected hemisphere of the brain. However, combining this closure with other stresses (hypoxia, closure of additional vessels, etc.) will cause damage—there's not as much 'reserve capacity' in the system. Some researchers have looked at the ability of the rat's brain to adapt to closure of one or more major vessels to model chronic disease in humans; the paper I linked above showed that closing one carotid artery results in adaptive vascular changes in as little as three days. (This can happen in humans as well; there are cases of patients with both of their carotid arteries completely closed—their brains get sufficient blood through vertebral arteries that have expanded to take up the slack.) TenOfAllTrades(talk) 15:47, 5 October 2007 (UTC)

Thank you both. I see how "unilateral" was pointing in this direction, and checking that article, I gather "ligation" refers to the closure of the vessel ends created by cutting through it. --Seans Potato Business 18:25, 5 October 2007 (UTC)

"Ligature" refers to closing it by tying (see wiktionary:ligature; compare to ligature strangulation). However, practically , it doesn't matter how one of the carotids is blocked. -- Flyguy649 ^talk _contribs 21:05, 5 October 2007 (UTC)

Petroleum jelly

Is there a silicon based equivalent for Petroleum jelly? 71.100.9.205 17:36, 5 October 2007 (UTC)

For what use? Shoe shine? Lip moistener? Spitball doctoring? Personal lubricant? People use petroleum jelly for many different things, so you'll have to clarify what you want the silicone equivalent for. Note also that silicon is a chemical element, while silicone is the slippery rubbery stuff. --Sean 17:56, 5 October 2007 (UTC)

To compare its physical, mechanical and thermal properties for a school project? —Preceding unsigned comment added by 71.100.9.205 (talk) 18:07, 5 October 2007 (UTC)

Silicone grease probably. You should be able to get some at a car parts store. (Note that's silicone - although it contains silicon). SteveBaker 18:32, 5 October 2007 (UTC)

Is there any real difference between generic silicone O-ring sealing greases and a specialized silicone grease like Dow Molykote 55? Kel - Ex-web.god 20:37, 5 October 2007 (UTC)

Well, Dow chemicals describe this stuff as "Phenyl-methyl" silicone grease - so it obviously has chemicals in it in addition to simple silicone grease - but what these actually do - and whether that makes this stuff actually better than regular silicone grease - is anyones guess. SteveBaker 17:47, 6 October 2007 (UTC)

Modulation techniques book

Can someone give me the name of some good books on modulation techniques for wireless communication systems? I'm particularly interested in information about QAM and the various forms of PSK, which I think are the most used modulation formats and also OFDM. I would appreciate your help, thanks! 217.129.207.58 21:28, 5 October 2007 (UTC)

Look for Signal processing, modulation and noise by J.A.Betts (Dept Electronics Univ of Southampton). Published by Hodder and Stoughton 1970 (reprinted 1975 and maybe later) ISBN N0: 340 09895 3 (paperback) or 0 340 05212 0 (Case bound) —Preceding unsigned comment added by 88.109.121.209 (talk) 22:22, 5 October 2007 (UTC)

Proakis and Manolakis Digital Signal Processing is a good start, and though it's not extremely thorough in the actual modulation architecture, it will provide the processing techniques you need to use, which will assist your understanding. Nimur 22:51, 5 October 2007 (UTC)

Preferential Solubility?

Assume I have two substances of differing solubility in water: A=250mg/mL and B=50mg/mL. Excluding any temperature and pressure variables, what happens when I add 250mg of A and 50mg of B in 1mL of water concurrently? I assume both substances partially dissolve, but in roughly what amount or ratio? Also, what happens when A and B are added to the water consecutively? Last question: what's the name of the rule/law/effect/whatever that governs this effect? Kel - Ex-web.god 23:07, 5 October 2007 (UTC)

I think you are likely looking for the common ion effect. We would need to know more information to tell you specifically what would happen, but this has hints of a homework problem. Someguy1221 00:15, 6 October 2007 (UTC)

Hmm. I never would have guessed my writing style could be confused with that of a 12-year-old. Regardless, were this a homework problem, I'd have asked it a decade ago, when I was still in college. :) This is for my own education. Anyway, what further information do you need that would make any difference? The solubility figures above weren't from any specific substances, but if it makes a difference, I'd say any random hydrochloride (or sulfate) salts. Kel - Ex-web.god 00:39, 6 October 2007 (UTC)

To a first approximation, this turns out not to be the case: the basic rule is that the concentration of one substance in a solution will not affect the solubility of another. This is because the solubility of a substance is not determined by "the amount of dissolved stuff the water can hold", but by a chemical equilibrium at the interface between the solution and the solid substance. Basically, the substance dissolves at a constant rate (per unit area), but also precipitates back at a rate proportional to its concentration (again per unit area). In a saturated solution these two rates will be equal, and no more of the substance can dissolve.

Of course, these rules do have exceptions. One is the "common ion effect" already mentioned above: if the substance split into multiple components when dissolving, the concentrations of all those components will affect the precipitation rate. Another is that, to be precise, the word "concentration" in all of the above really needs to be replaced with chemical activity, a more complicated measure that tends to be proportional to the concentration in dilute solutions but deviates from it in more concentrated ones. The activity can also depend on the general ionic strength of the solution: essentially, as the solution gets concentrated enough, the different dissolved substances start interacting with one another. Our article on the solubility equilibrium lists several more such effects, and also describes the matter in general. —Ilmari Karonen (talk) 15:33, 6 October 2007 (UTC)

Scarlet Macaw

Should his claws cut into and hurt my shoulders like that? I only got him recently and he seems to really dig in and hold on when he sits up there. —Preceding unsigned comment added by 81.79.213.158 (talk) 23:45, 5 October 2007 (UTC)

Excluding the possibility that he really dislikes you, I'd say it's because his claws are designed to grab a branch. Your shoulder is too big, so he needs to squeeze harder to get a good grip. It might help if you wore a strong (for you), yet thin (for him), shirt. And preferably just one (so not a shirt and a t-shirt). DirkvdM 09:01, 6 October 2007 (UTC)

Your avian veterinarian can trim your macaw's talons (and beak, if you wish). We have this done with our sun conure because she really, really likes to cuddle within our clothes, but her sharp little talons can do a number on one's skin when they are "fully sharp". You don't want too much trimmed, though, or your bird won't be able to perch easily.

Atlant 23:39, 6 October 2007 (UTC)

Glucose in benedict's solution

When one puts glucose into a dialysis tubing and into a test tube of Benedict's Solution and heats it in a water bath, the Benedict's solution inside the test tube turns an opaque yellow. But does the glucose inside the dialysis tubing (which is inside the test tube) also turn yellow? I guess in short, will the Benedict's solution diffuse into the dialysis tubing? Thanks. Acceptable 23:46, 5 October 2007 (UTC)

Try Benedict's reagent. --JWSchmidt 15:28, 6 October 2007 (UTC)

October 6

Self sufficient communities

This is a follow up question to Planning for a bleak future on the Miscellaneous reference desk. I have two questions about closed communities:

1. What is the smallest possible genetically self sufficient community? (In other words, how big does an isolated community have to be so it will not die off through inbreeding?) 500? 1,000? 2,000?
2. How many acres of arable land/pasture is necessary to support an adult person year round? (x acres of land divided by x number of people in community). How would this differ between Subtropics, Humid continental and Temperate climates?

Thanks for your help! --S.dedalus 00:28, 6 October 2007 (UTC)

To answer the first question our article on a generation ship says about 500 people. However, there's no citation. And remember you won't necessarily need that many people, just that much genetic material. So a good cryofreezer and a lot of frozen eggs/sperm etc could do the trick with a very small population (assuming the stuff stays fresh for a very long time). Not sure about the second part though. --Cody Pope 01:15, 6 October 2007 (UTC)

For the first question, ask a hillbilly.

For the second question it would matter a lot on how much meat you want, because that takes up a lot more land, it is said. Also, you seem to assume a purely cultivation-based food supply. For the bleak future scenario, it makes more sense to rely on hunting/gathering because that way you won't have much stock that can be stolen. Of course, a combination of the two might be best - under uncertain circumstances, it's always best to put your eggs in as many baskets as possible. And a crossover might also be a good idea - plant the food, but not all in one spot, but spread out over different areas under different conditions, so a failed harvest will be limited and you won't run the risk of being completely out of food.

So there are many variables, but a good indication might be found in mediaeval subsistence farming. Open field system says each villager got 30 strips of 2000 m², so that's 60,000 m² per person, roughly 250 x 250 m (assuming that's really per person, not per family, which I rather expected to find). So a community of 500 would require about 100 km² or 10 km x 10 km. That's about the size of Amsterdam for a small village, which sounds like a lot. But farming was probably much less efficient in those days (as it is likely to be under the survival conditions we're talking about), and there were nowhere near as many people then, so it might still be fairly accurate. I guess most mediaeval villages were about that size and about 10 km apart. Of course, that may also be an explanation. Maybe they used that much space simply because that's what was available. DirkvdM 09:25, 6 October 2007 (UTC)

The Bible says two people are enough. I seem to remember Guns, Germs and Steel giving a figure for how much acreage is needed to support one person's foraging, but I can't recall the number. --Sean 14:00, 6 October 2007 (UTC)

Ian Robert Franklin coined the 50/500 rule (hmm, no articles on either.) It states that, as a rule of thumb, a species needs fifty members for probable short-term survival, and five hundred for long-term survival. A quick search for Franklin "50/500 rule" turns up a number of scholarly articles discussing the topic. GeeJo ^(t)⁄_(c) • 17:33, 6 October 2007 (UTC)

That number will vary wildly depending on whether subsequent breeding is carefully planned to maximise diversity or allowed to happen naturally. SteveBaker 17:40, 6 October 2007 (UTC)

Sean, the bible doesn't say two is enough. I used to think that, but then one day I read that part and it says Kain went out into the wide world, where he met another people ... which leaves the question where the hell they came from. DirkvdM 18:06, 6 October 2007 (UTC)

They came from the Flying Spaghetti Monster of course. Unless they came from the Invisible Pink Unicorn. ;-)

Atlant 23:49, 6 October 2007 (UTC)

That's sacrilage. You aren't supposed to say her name without adding 'bbhhh' or some similar honorific. You probably don't even have pinapple on your pizza. I may have to declare a jehad. SteveBaker 16:50, 7 October 2007 (UTC)

Spider ID

What species am I?

This spider jumps. Seen at Dennis railway station, Melbourne. Can anyone name the species? —Pengo 02:56, 6 October 2007 (UTC)

Well, it's clearly of the family Salticidae (jumping spider), but I'm not sure from that angle it will be easy to distinguish it from many of the very similar looking jumping spiders (many of which are generally brown, have large forward-facing eyes, and make that little sort of face). --24.147.86.187 04:09, 6 October 2007 (UTC)

Another angle.

How about this angle? —Pengo 04:29, 6 October 2007 (UTC)

There are over 5000 jumping spider species. I doubt it would be possible to find the exact species of the spider in your picture. The only way would be if a life specimen crawled through the series of tubes on the Internet for me to perform DNA testing, and then search for the sequence on PubMed. But if you'd be satisfied with just a genus or a family, I'd recommend using this site--Mostargue 12:39, 6 October 2007 (UTC)

There is a "find-a-spider" site for Australian spiders here. I went through all of the pictures for that particular family but didn't see any obvious 100% matches. --24.147.86.187 14:53, 6 October 2007 (UTC)

Better than the previous link, but unfortunately it focuses on Queensland spiders, and that's a far way from Victoria in distance and climate. —Pengo 23:26, 7 October 2007 (UTC)

Killing with sound

Is it possible to generate a sound that can kill a human? Either by the sheer power of it or by creating some kind of harmonic vibration that will shake the body apart? Exxolon 03:30, 6 October 2007 (UTC)

Massive ordnance air blast over-pressures the human with a pressure wave. It might be considered "killing with sound" but it's really more of a supersonic over-pressure. Nimur 04:27, 6 October 2007 (UTC)

See our article on sonic weaponry. General consensus seems to be that lethal sonic weapons are only possible underwater. Gandalf61 08:00, 6 October 2007 (UTC)

Monty Python had a suggestion for this - a joke that is so funny that the enemy will laugh themselves to death. Of course it can't be told by one single person, or they would themselves die. See the episode for solutions. DirkvdM 09:34, 6 October 2007 (UTC)

That would be The Funniest Joke in the World. DuncanHill 12:43, 6 October 2007 (UTC)

On a more serious note, one torturing method (which appears to be used in Guantanamo Bay, or that's where I think I got this from) is to expose people to white noise. Don't know if that could be lethal if used in excessive amounts. Can madness kill? DirkvdM 09:35, 6 October 2007 (UTC)

For a smaller scale version of a similar phenomenon, check out the pistol shrimp. Capuchin 10:28, 6 October 2007 (UTC)

That's more of a blast, a single wave, than a sound, which consists of several waves, or rather, is sustained longer. DirkvdM 18:10, 6 October 2007 (UTC)

In the past, on Sound pressure in the table was information on what dBa's effects on a human body would be. —Preceding unsigned comment added by Mac Davis (talk • contribs) 02:05, 7 October 2007 (UTC)

I checked reference number four on that article, and it states so: 195-190 (P) HUMAN EARDRUMS RUPTURE 50 % OF TIME -REF.2. and 202-198 (P) HUMAN DEATH FROM SOUND (SHOCK) WAVE ALONE. [Mac Δαvιs] ❖ 03:15, 7 October 2007 (UTC)

microbiological test

1. what are the Cleaning procedures in food production site? 2.what are the decision can be taken by quality assurance representative when the products are affected by microbiological problem? —Preceding unsigned comment added by 60.53.109.73 (talk) 04:49, 6 October 2007 (UTC)

These will differ according to site, the food being produced, and the regulations on the industry in the specific jurisdiction. You might want to take a look at this U.S. F.D.A. site which discusses Hazard Analysis and Critical Control Point procedures. - Nunh-huh 05:02, 6 October 2007 (UTC)

Spinal cord, ventral and dorsal tracts

In Kolb & Whishaw, Fundamentals of Human Neuropsychology (2003) is the following sentence: "In the spinal cord itself, the outer part consists of white matter or tracts, arranged so that with a few exceptions the dorsally located tracts are motor and the ventrally located tracts are sensory."
Is this correct? If I compare with pictures, for instance this one: http://faculty.etsu.edu/currie/images/neuro2.jpg, it seems to me that most dorsally located tracts are sensory and most ventrally located tracts are motor. Lova Falk 09:02, 6 October 2007 (UTC)

Spinal cord provides a description of the major tracts. I wonder if "Fundamentals of Human Neuropsychology" just makes that statement in passing or if they have a supporting figure or cited references. Here is another figure similar to those found in many textbooks. --JWSchmidt 15:25, 6 October 2007 (UTC)

That's just what I mean. Would you agree with me that it seems to be a mistake in the book? Lova Falk 09:06, 7 October 2007 (UTC)

I can't imagine a context in which that sentence would be true. From embryology to clinical practice to neurosurgery, it's well understood that the dorsal side is predominantly sensory, while the ventral side is motor. --David Iberri (talk) 15:39, 7 October 2007 (UTC)

Thank you for your very clear answer! I'm quite proud that I discovered this mistake :) Lova Falk 16:35, 7 October 2007 (UTC)

And you should feel proud! I find these sorts of stupid things all the time (I'm feeling a bit like a professional student these days, with all the textbook reading I've been doing lately). It makes me wish there was some universal page for submitting textbook errata. --David Iberri (talk) 00:41, 8 October 2007 (UTC)

Physics???

If we want to become a doctor when we grow up, is it necessary for us to take Physics, Chemistry and Biology in our secondary education?? Or will it be sufficient if we simply take Biology and Chemistry? —Preceding unsigned comment added by 219.74.132.62 (talk) 09:43, 6 October 2007 (UTC)

It varies significatly depending on which institution you choose to seek your degrees from. If you are beginning to plan what colleges you would like to attend, you should look on said colleges' websites for their admission and graduation requirements for their premed programs. My own university's premed program entails what some would consider a surprising amount of physics and mathematics, but I've seen others that require almost none, comparatively. Someguy1221 09:52, 6 October 2007 (UTC)

Basic physics will help you to understand the advanced chemistry and biology which you'll need to be a doctor. Additionally, the way things are approached in physics classes will give you a slightly different set of problem solving skills which may be of use in any profession. Finally, if you are going into certain specialties like orthopedics or radiology, you'll need to have a solid background in physics to understand the principles behind what you are doing. In short, it might not be necessary, but it'll be a good idea. -- 72.33.121.200 16:51, 6 October 2007 (UTC)

It also depends on the country in which you plan to train as a physician. In the US, for example, medical schools require that you take a significant amount of physics during your undergraduate training (usually a full year's worth) in order to be considered for admission. If you already had that physics during secondary school (the equivalent of high school in the US), you'd be in better shape to do well at university and then have a better chance at being accepted into and doing well in medical school. --David Iberri (talk) 18:01, 6 October 2007 (UTC)

RE: helium

as it is a natural resource how many years do we on earth have with the resource of helium, before it is gone? —Preceding unsigned comment added by 12.217.132.163 (talk) 15:02, 6 October 2007 (UTC)

You may find this article of interest. Cheers Geologyguy 15:11, 6 October 2007 (UTC)

Helium is a byproduct of nuclear fusion, so if that ever becomes a major power source, we probably won't run out of it. Assuming it doesn't, as the amount of helium left decreases, it will get more expensive and be used less. Mathematically, it should never run out completely. The same goes for deuterium if nuclear fusion does. — Daniel 15:34, 6 October 2007 (UTC)

Heheh! The amount of helium produced by fusion reactors would be truly microscopic! Think about the amount of energy created by a hydrogen bomb - a massive fusion reaction - but how much hydrogen do you think there is in the bomb? The helium created by reacting the hydrogen will weigh a tiny bit less than the hydrogen did. Worse still, some of the more interesting reactor designs actually consume helium (in the form of He³) - which we'd have to transport from the moon because the stuff is rare here on earth. SteveBaker 17:34, 6 October 2007 (UTC)

The dwindling of this precious natural resource is a direct corrolary of the disproportionate influence Big Balloon has over our government and policies. Enjoy your tiny voices and festive birthday parties while you still can!! 38.112.225.84 20:12, 6 October 2007 (UTC)

Helium comes from natural gas - 7% of natural gas is helium (that's a LOT!). However, just like natural gas, it's not a renewable resource. When we run out of natural gas, we run out of helium. It's reformed (very slowly) from radioactive decay - but (as our article explains) each cubic kilometer of the earth's crust forms just 3 liters of new helium gas per year...that's as close to nothing as you could imagine! So when we run out of natural gas...no more squeaky voices. SteveBaker 15:57, 7 October 2007 (UTC)

And to add a bit - that 7% is by no means across the board in all natural gas -- concentrations of that much are extraordinarily rare, and most of the world's helium comes from just a few natural gas fields (by far the largest in the Texas Panhandle, which produces something like 80% of world helium). Most natural gas fields do not contain helium in proportions to make recovery economic. Cheers Geologyguy 16:25, 7 October 2007 (UTC)

Yup, helium-shortage is all over the general-public news. DMacks 16:28, 7 October 2007 (UTC)

Yes - but right now, the shortage is one of our own making. It's not that the amount of helium underground is close to being exhausted (although that will happen eventually) - it's that the refineries have short term production and maintenance problems. Also, the level at which helium recovery from natural gas is 'economic' depends on the usual laws of supply and demand. As the easy-to-extract stuff becomes rarer, the price will increase and it will become economic to extract it from less right natural gas supplies. However, in the long term, it's a severe problem because whilst we can find alternatives to non-renewable fuel supplies (eg Replacing fossil fuels with nuclear, wind, solar, etc) - there is no alternative to helium in almost all of its applications - and no other economic supply will ever become available. The helium we release into the atmosphere eventually floats off into space and is lost forever. In an idea world, where we manage to stop burning fossil fuels (including natural gas) in order to fix the global warming problem, we'll end up pushing up the price of helium because it will no longer be a convenient by-product of natural gas production - but instead, we'd have to pump out natural gas, extract the valuable helium and somehow dispose of the 'waste product' natural gas without doing something harmful like burning it off. This will make even the 'easy to get at' helium vastly more expensive than it is now. SteveBaker 23:21, 7 October 2007 (UTC)

Harvard Chart Method

This was a method presumably developed at Harvard University which was used to both replace Boolean Algebra and to automate the process of reducing logical equations to minimum form. Yet, I can find no reference to this method either at Harvard or at MIT. It was suggested that the method was developed by Howard Aiken preliminary to development of Aiken's Harvard Mark II. Does anyone have reference to the method or any other information regarding it? Clem 15:31, 6 October 2007 (UTC)

Karnaugh maps probably? Maybe Venn diagrams, Johnston diagrams, Truth tables, Quine–McCluskey algorithm, Logical graphs? I'm not aware of any that are specifically associated with Harvard/MIT - but the methods I linked to here are the common diagrammatic methods I can recall offhand. I'm betting you are thinking about Karnaugh maps - because that's the technique that's probably the most widely used. SteveBaker 17:14, 6 October 2007 (UTC)

Wikipedia once had an article about this and it cited: Hunter, William L. [10-1975]. Chapter 4, "The Laws of Logic, Boolean Equation Simplification - The Harvard Chart". Digital/Logic electronics Handbook(in English), pp.112-113, Blue Ridge summit, PA 17214: Tab Books / No. 774, 1975. ISBN 0-8306-5774-6, ISBN 0-8306-4774-0
--JWSchmidt 17:22, 6 October 2007 (UTC)

Check here.

But beyond references to that book - I can find no references to the technique. That Wikia article is a bit "out there" - claiming that one could prove the existance of God if only you had a big enough computer but that only God is smart enough to run the proof?!?! I don't think we should take it seriously as an article about logic! I don't have access to the book - and the little BASIC program in the article uses a horribly exhaustive approach that'll take vastly too long and vastly too much memory for anything with enough complexity to challenge manual techniques. Whatever this technique does, it's clearly not very useful or it would be in common use thirty some years after it's first description. Check out Karnaugh maps and Quine-McCluskey - those are the ways this stuff is done in practice. SteveBaker 15:31, 7 October 2007 (UTC)

Oddly enough the algorithm seems to work and for multiple states too, which I have never encountered. Have you tried any equations which do not work? Also, it sounds like the author is saying that computers are inferior to the concept of God by definition of God being given the attribute of handling an infinite number of variables whereas a computer can not. Seems like this might be in response to an argument by the North Vietnamese Hanoi Hannah during the Vietnam War that logic and therefore computers and therefore the State were superior to God as the basis for any political, social or economic system. Clem 18:17, 7 October 2007 (UTC)

I'm not saying it doesn't work - I'm just saying that it's an exceedingly brute-force approach and (as the author of the BASIC program admits), the amount or RAM and CPU time it consumes goes up very steeply with the number of variables - to the point where he thought his computer could only handle at most 32 variables (I think the algorithm would have taken an insanely large amount of time in that case though. SteveBaker 23:10, 7 October 2007 (UTC)

I wonder if there might be a more efficient method suitable for distributed processing. If so, a large number of variables might be possible, although of course far less than an infinite number, and what contribution such a program might make toward solving complex logical problems. Clem 23:58, 7 October 2007 (UTC)

beams that reflect from bones

for long i'm looking for some rays or beams that can be transmitted and then sensed back as reflection of the same from bones. may be the rays are not reflecting merely from bones but it gets special deflection after reflecting from bones that can be sensed and hence can be concluded that the object from which the reflection has occured is bone. if some one could help... —Preceding unsigned comment added by Neel shah556 (talk • contribs) 16:09, 6 October 2007 (UTC)

X-rays? All waves will be absorbed/reflected/deflected to some degree by bones - and also by other materials in the body. So you can form images with X-rays, with ultrasound, with really bright light (shine a flashlight through your hand for example). The trick is to find waves that won't harm the person in the process of scanning them. SteveBaker 17:02, 6 October 2007 (UTC)

What are you using this for? That probably makes a big difference in whether you use X-rays, T-rays, Ultrasound etc. — Daniel 15:51, 7 October 2007 (UTC)

Lethal acceleration/jerk

How much acceleration or jerk would kill a human being? --Anakata 16:25, 6 October 2007 (UTC)

Our article on g-force says that an unaided human (say, in a plane) will black out at 50m/s² (5 g) in the vertical direction, but can stand 12-17 g in the horizontal direction. "Any exposure to around 100 g or more, even if momentary, is likely to be lethal, although the record is 179 g." More facts and figures can be found in the article. -- 72.33.121.200 16:44, 6 October 2007 (UTC)

The article is interesting. BTW, if 72's comment is a bit unclear the record of 179 g is the record of an estimated g-force which someone is known to have survived. Nil Einne 01:21, 7 October 2007 (UTC)

I thought jerk was the rate of change of acceleration with time. —Preceding unsigned comment added by 88.109.198.32 (talk) 02:50, 7 October 2007 (UTC)

It might be worth discussing what actually causes the physical harm - is it the force, the acceleration, the change of momentum, the non-rigid-body motion which tears up internal organs? All of these are contributions to physical harm in a collision; to isolate the damage due only to acceleration is difficult in practice. It is commonly said that in any single automobile crash, three collisions cause death, in order of increasing harm: 1)the body of the car quickly decelerates; 2) The human flies forward until snapped back by a seatbelt or dashboard; 3) the human's internal viscera slam forward into the front of the ribcage. Nimur 03:55, 7 October 2007 (UTC)

So a seatbelt that 'gives a little' could be a lifesaver because it spreads out the deceleration and thus reduces the jerk? Or are they indeed somewhat elastic? They don't seem it, but it would have to be elasticity that only sets in under a much stronger stress than a human can exert by simply pulling it. DirkvdM 07:50, 7 October 2007 (UTC)

Seatbelts are a little elastic - but that's not the point. The idea is that there shouldn't be a jerk. If you have a 40mph crash and are not wearing a seatbelt, then as the car crumples and slows down gradually from 40mph to 0mph, your body carries on at 40mph. Only when the car has more or less come to a stop do you smack into the dashboard/steering wheel at more or less 40mph. If you are firmly attached to the car - then as the car slows down gradually - so does your body. The seatbelt allows you to slow down gradually and take advantage of the crumple-zones built into the car body. Some cars have seatbelt pre-tensioners built into the seatbelt receptacle down by the parking brake - these fire off like an airbag and pull the seatbelt tight to try to keep you firmly tied to the seat. Seatbelts are a bit elastic though - and after an accident, they are permenantly stretched. For this reason, it's very important to replace the seatbelts after a significant accident. SteveBaker 15:06, 7 October 2007 (UTC)

Ah yes, of course, I get the first bit now. The second bit, does, however seem to confirm what I was suggesting. There is of course still an added advantage to some elasticity in the seat belt. But how much so they stretch? Might there still be some more room for improvement? For the driver, however, there might be the risk of his head slamming into the steering wheel, I suppose. And some people might wear it too loosely, so one has to compensate for that. Ok, never mind then. :) DirkvdM 18:54, 7 October 2007 (UTC)

Yep - a small amount of elasticity obviously helps to decrease the acceleration still further - but (as you can tell from trying to stretch one) - they are designed to stretch only a tiny amount - and even then only under large forces. If you go to a junk yard and look at wrecked cars, you can see how the seatbelts suffer - it's pretty noticable that they've stretched close to the attachment points. One of the things to look for when you buy a suspiciously cheap used car is the state of the seatbelts. SteveBaker 23:05, 7 October 2007 (UTC)

Hmmm, wouldn't the crumpled front be a dead give away? :)

Btw, I can't remember having ever seen a car junk yard in the Netherlands. Or anywhere else for that matter, except in the US. That's worth a new question. Miscellaneous, I suppose. DirkvdM 06:01, 8 October 2007 (UTC)

Schizophrenia vs. multiple personality disorder

I just wanted to know how schizophrenia has become confused with multiple-personality disorder. I can't think of many similarities between the two. Was this due to a movie or something?--Avant Guard 17:46, 6 October 2007 (UTC)

Schizophrenia vs. Multiple personality disorder.--Mostargue 18:02, 6 October 2007 (UTC)

The incorrect conflation of the two is pretty logical, actually. The distinction between a "split mind" and a "multiple personality" is not intuitively obvious. I was pleased to learn that The first known misuse of the term to mean "split personality" was in an article by the poet T. S. Eliot in 1933.. --jpgordon^∇∆∇∆ 18:16, 6 October 2007 (UTC)

It might help, Avant Guard, to understand that the original concept of the "split" was between three processes of the mind. The understanding of the situation, the emotion felt about the situation and the response to that emotion. I am grossly simplifying the concept. What is really irritating and frankly misleading is the common use by media idiots who use the term 'schizophrenic' as a synonym for having uncertain or opposing views about something, as in "the US government is showing a schizophrenic attitude to the recent reports from Whateverland". Pah! Richard Avery 21:54, 7 October 2007 (UTC)

Finding acid disassociation constants

Is there a website anywhere that lists Acid Disassociation Constants (ka or pKa) values? I'm trying to find the value for the indicator (also a weak acid) Eriochrome Black T but I haven't had any luck searching on the web. I'm finding a whole bunch of MSDS information but that isn't helping. If anyone has a site they can link to me that would be great.--GTPoompt(talk) 18:30, 6 October 2007 (UTC)

this site has a small list, but doesn't seem to contain the particular acid you're looking for. This page seems to be a journal that undertook extensive research, but unless you're already a member, it looks like you've got to pony up $30 to see the results. I'm no expert, so I can't tell you for sure, but the chart on the upper right hand corner of page 6 (page 26729?) of this PDF may give you a general starting point. --Ybbor^Talk 18:41, 6 October 2007 (UTC)

pKa=6.65 @ 25 C from http://ecb.jrc.it/IUCLID-DataSheets/1787617.pdf page 5 - check for yourself for correctness87.102.115.31 13:22, 7 October 2007 (UTC)

positron

what are the possible positions of a positron in an atom along with their justifications?193.251.135.126 19:13, 6 October 2007 (UTC)

The possible positions of a positron are:

1. Not in the atom

That's all (unless you're talking about antimatter). Positrons have positive charge, and so could not be bound in an atom. I have no idea what you mean by 'justifications'. --ColinFine 20:49, 6 October 2007 (UTC)

It could also be in positronium, which you could consider an atom. Someguy1221 20:57, 6 October 2007 (UTC)

And of course there are radioactive atoms that emit positrons, but that doesn't mean they have positrons in them. The positrons are created in the decay event. -- BenRG 11:46, 7 October 2007 (UTC)

Antihydrogen counts as an atom, surely? Algebraist 14:38, 7 October 2007 (UTC)

I said 'unless you're talking about antimatter'! --ColinFine 20:22, 7 October 2007 (UTC)

psychology

What are the relationships between the parasympathetic division and deep breathing?

What are the relationship between the sympathetic division and jogging? —Preceding unsigned comment added by 4.238.183.72 (talk) 21:08, 6 October 2007 (UTC)

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misevaluation, but it is our policy here to not do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn how to solve such problems. Please attempt the problem yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. Thank you. See our articles on sympathetic division, deep breathing and jogging. -- 68.156.149.62 02:04, 7 October 2007 (UTC)

Here you can find a discussion on breathing and the autonomic nervous system. Lova Falk 10:36, 7 October 2007 (UTC)

October 7

exceed the speed of light

if a rod made of unyielding material was attached to a motor perpendicular to its rotation and the speed of the motor could be increased to its maximum for example 10,000 rpm. how long would the rod need to be before the ends would exceed the speed of light? how could it be mesured ? and what would be the effect on the ends of the rod. if a message were attached to one end of the rod and two points along the circumference point A and B were monitered would the message leave A and arrive at B faster than the speed of light? please excuse my spelling and gramer. —Preceding unsigned comment added by 68.253.205.219 (talk) 01:03, 7 October 2007 (UTC)

they wouldnt exceed the speed of light. you cant make anything go faster than the speed of light. —Preceding unsigned comment added by 68.190.122.72 (talk) 03:06, 7 October 2007 (UTC)

• Agreed. Faster-than-light travel may well be possible, but it would involve breakthroughs that would change our fundamental understanding of physics, not something rinky-dink like a motor. Also, for what it's worth, it would also violate known physics to make an "unyielding material. --M@rēino 03:44, 7 October 2007 (UTC)

The flawed assumption is in the "unyielding material." It is not practical to build such a rigid structure. Our theoretical understanding of materials suggests it is not even theoretically possible to have a non-rigidrigid body over such distances. The only way the "other end" moves is when the atoms interact with each other through the material; that interaction can't happen faster than light. Nimur 03:58, 7 October 2007 (UTC)

...of course you mean not even theoretically possible to have a rigid body over such distances, right? —Keenan Pepper 04:35, 7 October 2007 (UTC)

Thanks for correcting my error! Nimur 04:52, 7 October 2007 (UTC)

Be careful with the rote "nothing faster than light" response. Angular velocities can and often do exceed the speed of light. Imagine a pair of scissors and measure the point at which the blades meet. Close the scissors and that point moves from the handle to the tip. It's an angular velocity and can be much faster than light. The key is that no information is gained faster than light. --DHeyward 05:10, 7 October 2007 (UTC)

And since someone usually brings it up whenever "faster than light" questions are asked, it may as well be me: Cerenkov radiation. GeeJo ^(t)⁄_(c) • 10:35, 7 October 2007 (UTC)

Nimur is correct. Any such rod would invariably bend as you attempted to rotate it; perfect rigidity would require a form of matter unknown to our current laws of physics. Someguy1221 05:20, 7 October 2007 (UTC)

Additionally, as the tip of the rod would approach the speed of light (c), its apparent mass would increase, approaching infinity as the speed approaches c, requiring infinite energy for reaching c. Icek 09:57, 7 October 2007 (UTC)

Obviously no real material could withstand such high stress, but nothing in special relativity precludes the existence of a rigidly rotating rod as long as no part of it is moving at c or faster. The formula for the speed at the tip is the same as the Newtonian formula: ω times r. In this case the maximum rod length is 2c / ((10000 rpm) (2π radians/rotation)) = 570 km.

Regarding your second question, the coordinate time for light to travel from one end of the rod to the other should be, in the limit, $\int _{-{\frac {c}{\omega }}}^{\frac {c}{\omega }}{\frac {dr}{\sqrt {c^{2}-\omega ^{2}r^{2}}}}={\frac {\pi }{\omega }}$. This is finite, and the effective time dilation factor at the edges goes to zero in the limit, so in this (totally unrealistic) limiting case, the two ends of the rod will be able to communicate effectively instantaneously from the perspective of their own proper time. This is a good illustration of the fact that the constant-speed-of-light rule only applies to inertial frames. -- BenRG 11:35, 7 October 2007 (UTC)

The key to this is that as far as the engine is concerned, the tip of the rod is moving at relativistic speeds - so the mass of the rod will start to increase as the engine speeds up. The amount of power the engine has to produce to keep the rod spinning increases greatly. Unless the engine is capable of producing an infinite amount of energy, it will never manage to make the rod spin at the speed of light. So there is no weirdness here - nothing gets up to the speed of light. SteveBaker 14:52, 7 October 2007 (UTC)

Only the part of the rod moving exactly the speed of light requires infinite energy. Since this part is infinitely thin, I don't know how that works. Getting anything to exceed the speed of light, however, requires a complex amount of energy. — Daniel 15:25, 7 October 2007 (UTC)

Indeed - it's irrelevent that it's infinitely thin - the fact is that if any part of the rod comes anywhere close to the speed of light, the mass increases spectacularly - as does the power required from the motor. There is absolutely no way to even get as high as the speed of light along any part of the rod - so what happens at the speed of light (or beyond) is irrelevent. You can't get there - so the question simply doesn't arise. SteveBaker 23:00, 7 October 2007 (UTC)

For a rod of uniform density, the average gamma factor at the limiting speed is ${\frac {\omega }{2c}}\int _{-{\frac {c}{\omega }}}^{\frac {c}{\omega }}{\frac {dr}{\sqrt {1-\omega ^{2}r^{2}/c^{2}}}}={\frac {\pi }{2}}$. So indeed it takes only finite energy to spin the rod up to this theoretical maximum: $\left({\frac {\pi }{2}}-1\right)mc^{2}$, or around 14 billion kilowatt hours per kilogram. Could be worse. This ignores the tension in the rod, which also has mass, and it ignores the fact that any real substance would break long before this point. It's also worth pointing out that the rod will not bend, no matter how fast it's spinning, as long as the angular velocity is constant. The ends will lag behind the center as it's being spun up, but once the torque is removed the equilibrium motion is PT invariant, and by symmetry the rod must point radially outward. -- BenRG 19:24, 7 October 2007 (UTC)

Why are you even trying to calculate an average gamma? (Not that your equation is correct - it's not) That's all utterly irrelevent. The energy to get the very tip of the rod up to the speed of light is infinite - the rest of the rod is essentially irrelevent. SteveBaker 23:00, 7 October 2007 (UTC)

Brain damage in new borns

I am trying to find answers on new born brain damage that causes the inability to suck, swallow, cry or know hunger pains. I am doing a paper on this in the name of my son who died from this 4 months after he was born. It is for a psychology report.

Thank you,

darlene Langford —Preceding unsigned comment added by 98.192.21.181 (talk) 01:47, 7 October 2007 (UTC)

• You might want to read The Journal of Obstetrics and Gynecology (the site has a password, but your local research library or university should have a subscription) or Pediatrics. --M@rēino 03:49, 7 October 2007 (UTC)

Hypotonia is a classic cause of the symptoms you describe. Hypotonia is also a sympton/early indicator of other neurological problems.. --DHeyward 05:14, 7 October 2007 (UTC)

Science - Movement Receptors

How do the Movement Receptors receive a sensation of movement when they are well below the surface of the skin —Preceding unsigned comment added by 124.184.77.182 (talk) 04:17, 7 October 2007 (UTC)

That's where movement happens: inside, not on the skin. Proprioception uses proprioceptors within the muscles to give feedback about position and movement. - Nunh-huh 05:19, 7 October 2007 (UTC)

I wonder if the question was really about Semicircular canals. --JWSchmidt 20:49, 7 October 2007 (UTC)

Mosquito bites

Are there any topical creams, chemicals, or other remedies known or claimed to be effective at reducing the severity of a mosquito bite if applied immediately after being bitten? A mild peroxide solution occured to me, but unfortunately I couldn't find much on Wikipedia about this. Someguy1221 06:25, 7 October 2007 (UTC)

I've heard vinegar helps. Why peroxide? DirkvdM 07:56, 7 October 2007 (UTC)

Because ER said it could be used to destroy viruses :-) Oh yes, I know a good source of information when I see one...(not that I think mosquito bites have anything to do with viruses, but the ability to destroy a virus would likely imply the ability to disrupt proteins, blah blah, etc.) Someguy1221 08:07, 7 October 2007 (UTC)

In the United States the FDA recognizes ammonia as effective in reducing the symptoms of insect bites and stings (including mosquito bites): [4]. A number of over-the-counter products contain ammonia. After Bite is probably the largest name; it contains a 3.5% solution of ammonia in a pen-shaped applicator with a sponge tip. The link I provided also has a list of other products that can ease itching and inflammation post-bite. TenOfAllTrades(talk) 15:03, 7 October 2007 (UTC)

Topical steroid cortisone cream (containing 1% hydrocortisone) is very effective in reducing itching. This is readily available over the counter, and because it is applied topically, it does not have the bad side effects of taking steroids internally. I have found it useful in reducing the itching from mosquito bites applied at any time and renewed a few times a day.--Eriastrum 16:55, 7 October 2007 (UTC)

Through the woodchipper

Fatality Assessment and Control Evaluation If you've got a good imagination, these reports can be scarier than any ghost story. Here are three poor people who found themselves inside working woodchippers, and what I am wondering about is why only one of them went all the way through. "The victim's remains were recovered by police forensic detectives and transported from the site." Implies that this poor guy went through, plus the account says the chipper was still running. I imagine an idling woodchipper, a really gruesome mess, and maybe an odor of blood.

Then there's the sad story of a 14 year old "The chipper drum jammed and came to a stop after the victim's torso had been fed into the machine." Meaning this chipper couldn't seem to work him all the way through. The same thing happened to another 28 year old: "When the climber approached the chipper with a load of branches, he noticed the victim’s legs sticking out of the chipper’s feed chute. He ran to the rear of the residence and notified the foreman."(Part of me wonders why anyone needs to be told to shut off the machine in that situation without the forman's say so, the rest of me thinks I don't know what I'd do if I saw that happening to a co-worker)

So I'm wondering if maybe the chipper in the first story was maybe bigger than the latter two? (Because I would have thought a machine which could chip 4-5 inch thick branches wouldn't have that much trouble with tissue and bone, but evidently that's not always so given the second and third cases.) Anynobody 01:59, 8 October 2007 (UTC)

Cerebellum and neural pathways

On this site (in a square to the left) it says: "The cerebellum's anatomical location helps us to better understand its functions. It lies parallel to two main neural pathways: one that carries sensory messages to the part of the brain that analyzes them, and another that emerges from the cortex and descends to the muscles to make them contract." Would anybody know exactly which two neural pathways are meant? Lova Falk 12:32, 7 October 2007 (UTC)

I'm not sure what it means for the cerebellum to "lie parallel" to a neural pathway. But if I had to take a guess: 1) the sensory -> brain pathways are the dorsal column-medial lemniscus system, which is one pathway by which sensory information reaches the brain; 2) the brain -> muscle pathway is the corticospinal tract (and probably the rubrospinal tract), which controls muscle movement indirectly via the spinal cord. The analogous cerebellar pathways are 1) the spinocerebellar tracts and 2) the cerebellocortical tracts. See Cerebellum#Peduncles for more on the input/output tracts of the cerebellum. --David Iberri (talk) 14:04, 7 October 2007 (UTC)

chemicals

which is king of all chemicals? —Preceding unsigned comment added by 61.2.48.232 (talk) 14:51, 7 October 2007 (UTC)

Chemical King? - hydnjo talk 15:14, 7 October 2007 (UTC)

According to Google, it's sulphuric acid. Or maybe mustard gas. Algebraist 16:55, 7 October 2007 (UTC)

Water. SteveBaker 22:52, 7 October 2007 (UTC)

Steven's wrong, you want dihydrogen monoxide. Someguy1221 22:59, 7 October 2007 (UTC)

But then my bottle of says it's "100% pure spring water with no chemicals" :p --antilived^{T | C | G} 03:02, 8 October 2007 (UTC)

Common wildflower ID

I know this is a common wildflower but I can not find an online classification table of flowers that will ask me the value of various characteristics for the purpose of identification. What is the name of this wildflower and is there a way to identify it online by entering the values of its various characteristics? Clem 19:19, 7 October 2007 (UTC)

It looks like Lantana camara, but I doubt it is a "wildflower." Plants can be identified using "keys" that consist of a series of choices that will eventually lead you to the correct identification. However, to use them they require technical botanical knowledge that makes them inaccessible to most people.--Eriastrum 20:31, 7 October 2007 (UTC)

Speeds of Jaguars

What is the average speed of a jaguar, meaning the cat?

I couldn't find a number anywhere online. But they are 'ambush predators' - so they have no need for great speed. I doubt they are particularly fast. SteveBaker 22:49, 7 October 2007 (UTC)

Might you mean cheetahs? The article says they can reach speeds up to 110 km/h. DirkvdM 06:32, 8 October 2007 (UTC)

This page, reports they can run up to 70 miles per hour. I'm not sure about the accuracy of the number, as it doesn't list a source to be checked. Wikipedia now has me checking for Reliable Sources even on non-WP websites. 152.16.59.190 06:36, 8 October 2007 (UTC)

important people in biological sciences

Hello,

I am preparing to take my exams for my Master's in Biology, and need to know if there are any important historical or current scientists that I may have missed while studying. I'm interested in people who have made a very significant contribution to biology- big whigs like Darwin, Gould, etc. Can you help? —Preceding unsigned comment added by 68.90.137.230 (talk) 22:25, 7 October 2007 (UTC)

Oh, but there are so many. If you're up for a good read, try starting at History of biology. Someguy1221 22:32, 7 October 2007 (UTC)

Personality Disorders

Is it possible to have both Borderline Personality Disorder and Histrionic Personality Disorder?

• I've linked the 2 terms for convenience. Exxolon 23:53, 7 October 2007 (UTC)

75.182.70.75 23:50, 7 October 2007 (UTC)

Excess of Speed of Light

I know that man has the idea that the speed of light is the fastest method of traveling, but I'm certain there is a much faster method. The method I'm pondering is traveling at the speed of thought. This method involves almost to time element, and dwafts the speed of light. Is there a method/way to travel at the speed of thought? —Preceding unsigned comment added by Robert Lucero (talk • contribs) 23:55, 7 October 2007 (UTC)

There is no such thing. Thinking is a chemical process of the brain, and has nothing to do with velocity. -- Kesh 00:21, 8 October 2007 (UTC)

The speed of thought, if you mean the speed at which someone thinks, is much, much slower than the speed of light. Consider how long it takes for the brain to process basic physical stimulus—reaction time, or mental chronometry—which is palpable by simple observation (in the millisecond range), unlike the speed of light, which for human purposes along local distances has the apperance of being instantaneous. --00:34, 8 October 2007 (UTC) —Preceding unsigned comment added by 24.147.86.187 (talk)

If some people think they can travel to another planet faster than light, then maybe they are on another planet already. —Preceding unsigned comment added by 88.109.198.32 (talk) 02:58, 8 October 2007 (UTC)

In a science fiction story by E. E. Smith a method is found by which space ships can travel at the "speed of thought" and in the story the "speed of thought" is imagined to be much faster than the speed of light.....a real time saver for plots involving inter-galactic travel!.--JWSchmidt 03:26, 8 October 2007 (UTC)

The entire Dune series uses thought based navigation that is faster than light. They use drugs. Probably the only way to make it work. --DHeyward 07:02, 8 October 2007 (UTC)

October 8

muscular development

if a ten year old child carried a piglet half a mile (or more, how much can a ten year old handle) then would the child be able to continue carrying the pig as it grew into an adult? or would there be a point where the pigs growth outstrips the benefits of the exercise for the child? how would it be after a few years? how about if the kid was a few years older? this has been bugging me for a while, thanks 81.96.164.140 00:20, 8 October 2007 (UTC)

There's too many variables to ever give a reasonable answer here. How big is the child? How big is the piglet? How much development goes on in each? Does the pig wind up as bacon? -- Kesh 00:24, 8 October 2007 (UTC)

ok then: assuming you bought a ten year old boy a normal domestic pig that's one week old for his birthday (his tenth birthday), and then assuming that both he and the pig developed as averagely as possible (aside from the extra development he would gain as a side effect of carrying the pig) would there be a point, say when he's thirteen and the pig is three, that he would be unable to lift the pig? or would he get used to its weight because of the slow speed of its growth and become a freakinishly strong child?

Well, piglet-carrying is like any other form of exercise: it'll build muscles, but only up to a point. Competitive athletes exercise intensively just to stay at their personal limit of muscle strength, but they can't get beyond it -- which is why some of them take drugs to raise the limit. If there are child athletes who at the age of 13 have developed by conventional exercise the strength to carry a 3-year-old pig, then it ought to be possible for the hypothetical piglet-carrier. If there aren't, then probably it's impossible. --Anonymous, 05:03 UTC, October 8, 2007.

silicon life forms

Have any silicon based life forms ever been discovered or is it know whether such life forms are possible by comparison of the properties of silicon versus the properties of carbon? Clem 00:21, 8 October 2007 (UTC)

None have been discovered as of yet. Finding one would be a monumental breakthrough in biological science. As to whether they are possible, that's still being debated. -- Kesh 00:28, 8 October 2007 (UTC)

The origins of life (1964) by George Wald had a discussion of issues such as why carbon is used in living organisms, not silicon. --JWSchmidt 01:56, 8 October 2007 (UTC)

Friction in Trains

Hello all. I'm having some trouble finding information for my school poster. The topic is "Friction in Trains." I tried looking for information here and on google but I couldn't find it. If anyone could help me here it would be greatly appreciated. P.S I'm looking for information relevant to a year 11 level (Upper High School level). Lots of thanks in advance. Cuban Cigar 05:11, 8 October 2007 (UTC)