Wikipedia:Reference desk/Archives/Science/2007 August 25

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August 25

Mountain height limit

I recall learning about a height at which mountains 'melt' their base, implying a hard limit on the physical height of mountains (on earth, etc). Is this true, and can anyone find details? Thanks :) --Quiddity 00:50, 25 August 2007 (UTC)

Regarding erosion... Angle of repose. —Preceding unsigned comment added by 138.29.51.251 (talk)

There are a few limits you can put on the size of a mountain, depending on exactly what failure mode you're interested in. It turns out that there are different things keeping mountains up: some are effectively floating, some are totally unstable and start to sink as soon as nothing is building them up again... the article at isostasy has some more information. Here's a paper where the author estimates the maximum height of a mountain: How high can a mountain be? by P.A.G. Scheuer, J. Astrophys. Astr. 2, 165 (1982). This primarily considers the failure mode where the mountain simply falls apart. As you make the base wider and wider, it's possible to make the mountain taller and taller. The paper also describes an odd "tower" of blocks that can be arbitrarily tall. There might also be a largest mountain that can be statically compensated, but I'm not sure about that. I don't think that melting as such should be a problem. You have to go all the way to the outer core to get liquid. It's more a matter of overstraining the material until it breaks. --Reuben 06:51, 25 August 2007 (UTC)

To elaborate on Reuben's point, the outer core starts at a depth of several thousand km, whereas mountains grow up to heights of several km or at most tens of km if you measure from the deepest sea trenches instead of the sea surface. However, I imagine there would still be some effect, even if it is not the most decisive. Also, some volcanoes (which are mountains of sorts) arise at hot spots, where the crust is much thinner. DirkvdM 08:28, 25 August 2007 (UTC)

So we know that for most substances, the melting point decreases with increasing pressure - so at what pressure does rock melt at (say) 20 degC ? Once you know that it should be a simple matter to discover the answer to this question. Sadly, I don't know how to find out that first answer. SteveBaker 21:13, 25 August 2007 (UTC)

A minor quibble—the melting point of most substances increases with increasing pressure, not decreases. One of the few materials for which this isn't true is water, resulting in the unusual, negative slope of the solid-liquid boundary on its phase diagram. TenOfAllTrades(talk) 03:07, 29 August 2007 (UTC)

I don't know if "melting" is the right model, but that's the basic reason why Olympus Mons is on Mars, and could never exist on earth with its greater gravity. Gzuckier 15:15, 27 August 2007 (UTC)

Monounsaturated and Polyunsaturated Fats

Hi, I've learnt that mono- and poly- unsaturated fats are beneficial to one's health, yet which is more important or more beneficial? I don't mean totally cutting out the other, but I just wanna know which is better. Thanks

There was a time in living memory when the conventional wisdom was, the more double bonds, the better; polyunsaturated fatty acids were considered to have better properties as regards preventing plaque accumulation in the arteries. I'm not an expert on this, but I believe the mainstream thinking has changed, and nutritionists think that most people would be well advised to increase the proportion of their fat intake that consists of monounsaturated fatty acids such as those found in olive oil and peanut oil (while reducing their total fat intake overall). Supposedly the polyunsaturates are more likely to cleave at the double bonds forming dangerously oxidative free radicals.

But you never know. These guys change their story a lot; five years from now we may be hearing something different. One exception to the "polyunsaturates bad" current conventional wisdom is that people are considered to require a certain intake of omega-3 fatty acids for proper brain function. --Trovatore 06:28, 25 August 2007 (UTC)

regarding heat

I understand that as an electron goes down an energy level it will release a photon or cause the atom or impart more kinetic energy to the atom. Could you please explain how this kinetic energy is imparted?

It still happens by a photon being emitted, but the photon is absorbed by a neighboring atom. Some other effects also come into play. When the photon is sent out it carries some momentum, and the atom moves off in the opposite direction to compensate. The photon is lowered in frequency or energy to compensate. Another way is that energy is shared amongst several atoms. One way to visualize it it to imagine the activated atom to be larger, and it suddenly shrinks or changes shape. If it is attached to other atoms in a chemical bond, it will shake around all the atoms involved disapating the energy. Graeme Bartlett 22:12, 25 August 2007 (UTC)

thanks

bird blood

Hello, if birds have hollow bones how do they synthesise blood ?Boomshanka

I asked the same question a while ago. turns out that bird bones aren't really hollow at all. They have air pockets, but apperently they also have bone marrow the synthesize new blood cells. PvT 17:07, 25 August 2007 (UTC)

Anyone who's sucked the marrow out of a chicken bone has seen it first hand. It's also worth noting that flying birds don't seem to have a lot of blood. I've hit birds with my car windshield, and it was all just feathers and grey guts with little or no blood. --Sean 12:20, 26 August 2007 (UTC)

Toxicity of unrinsed dishes

In the Netherlands (and in the UK, it seems) many people do not rinse the dishes after washing them. Washing-up liquid has a link to a suggestion that that is no problem if the right concentration was used, but I doubt that that happens often (most people use way too much, especially in the US). So is any remaining washing up liquid on the dishes a health risk? Btw, I once heard that swallowing pure washing-up liquid is unhealthy because it makes your intestines stick together, but that's a different thing. DirkvdM 06:22, 25 August 2007 (UTC)

Not in the short term - apart from the taste the small amounts should have no ill effects

In the long term - who knows? Myabe you'll just have a nice clean intenstine!87.102.84.56 12:59, 25 August 2007 (UTC)

It would depend on the composition of the dishwashing detergent used. Since it's not normally intended for human consumption, they may put things in which are somewhat toxic (not highly toxic, mind you). If you consume a substantially larger quantity than they expect, you may suffer from health issues. Of course, my observation is that food contaminated with even tiny quantities of dishwashing detergent is so unpalatable that I can't eat it anyway. This is why you should clean dishes in the organic way (have your dog lick them clean). StuRat 16:58, 25 August 2007 (UTC)

Disclaimer: this is my opinion, and I'm a very opinionated person.. I'll never understand people who don't rinse their dishes. It's like taking a shower and leaving the shampoo in your hair. Rinsing not only removes the detergent leftovers, but it's also an important part of the actual cleaning process. After all, the whole point of detergent is to make the grease come off. The grease will indeed come off the plate and attach itself to the soapy water, but if it isn't rinsed off, then you effectively haven't cleaned the dishes at all. Oh well.Nimlhûg 20:32, 25 August 2007 (UTC)

Exactly, that's what I tell people too. It's the rinse that counts, the soap or whatever is just an aid. I once saw in a hospital how the floor was 'cleaned' by applying a detergent solution (what do you call that?) and then simply sweeping it up again. No rinsing. That's just redistributing (most of) the dirt and adding toxic stuff to it. In a hospital! But a lot of people do that, more than with the dishes.

Anyway, it may be clear that I always rinse, but since a lot of people don't (including my mother) I wondered what the health risks might be, if any. And might washing up liquid be designed with this in mind? DirkvdM 06:13, 26 August 2007 (UTC)

While the thing about the hospital doesn't intuitively sound great, it strikes me as possible that things are not quite as bad as they sound. The "toxic stuff" may well be the point. There are actually two components to washing things -- mechanically removing nasty stuff, and chemically/physically killing it. The balance between the two depends on the context -- those "hand sanitizer" things you see people using a lot these days rely entirely on the second modality. Antibacterial soaps are a separate thorny issue; some people are worried about triclosan getting into the water supply, and about bacteria becoming resistant to it. --Trovatore 16:49, 27 August 2007 (UTC)

It also has to do with how much wash water is left on the dish to evaporate. If your dishes were reasonably hydrophobic and you set them vertically to drain and air-dry, the rinsing step might not make much difference because there might be very little wash-water (and its detergent) left on the dish anyway. By comparison, if the dishes were hydrophilic and/or you set them down horizontally with a puddle of dirty, soapy wash water standing in them to evaporate away, then your results would be quite different. But I'm American, so I'm a rinser.

Atlant 11:47, 27 August 2007 (UTC)

Spherical Magnet?

Why is it impossible to repeat a simple bar magnet onto a sphere at an angle that's perpendicular to the tangent of the surface so that whole of outside have one pole while the whole of the inside have the other pole? --antilived^{T | C | G} 07:15, 25 August 2007 (UTC)

I haven't made the calculation, but perhaps if you added together all their magnetic moments they would sum up to zero? —Bromskloss 10:48, 25 August 2007 (UTC)

I'm not sure that it is impossible - why do you think so (excluding the difficulty gluing the thing together).87.102.84.56 10:56, 25 August 2007 (UTC)

My Physics teacher said so, because of "the field lines would intersect the magnet itself". However is there any other explanation on why is it impossible (or not)? --antilived^{T | C | G} 12:14, 25 August 2007 (UTC)

There's this thing with that the magnetic field should be divergence free ($\nabla \cdot \mathbf {B} =0$), that is, there are no magnetic monopoles. The discussed spherical magnet, however, would have such a monopole in the middle, from which the field lines would originate. —Bromskloss 12:25, 25 August 2007 (UTC)

That would have to be a perfectly made example though - if there were gaps between the magnets there would be no problem.?

(Secondly what if Maxwell is just wrong - does the spin of a neutron not represent a magnetic monopole??)87.102.84.56 12:55, 25 August 2007 (UTC)

If there were gaps, the magnetic field inside would leak out there and cancel the outside field and we would no longer have a magnet. Spin would correspond to a magnetic dipole, I guess. —Bromskloss 16:48, 25 August 2007 (UTC)

Surely if there would be gaps the situation would be just one of having N magnets all arranged about a point - erm - so they would still function as magnets.?

Actually I don't get the original poster's physics teachers response "the field lines would intersect the magnet itself" - say I take a rectangular bar magnet and force (literally) 11 other similar magnets around it (not all N-S alligned) - then the magnetic field lines might be forced inside the magnet - with possible demagnetisation.??

MY ANSWER TO ORIGINAL POSTER I think to be honest your physics teacher has 'dodged the question' - though to be honest I'd like to dodge it also - it's a complicated situation really. And the answer depends on whether there are gaps between the magnets (Ithink) and also has to take into account the possibility of some demagnetisation near the centre due to the concentrated magnetic field.

If you could do it - with specially 'wedge' shaped magnetic peaces then it would be interesting to consider if the thing you would have made is effectively a monopole (from outside). I'm guessing some demagnetisation would stop this happening due to the highly concentrated field lines..87.102.84.56 18:16, 25 August 2007 (UTC)

I remember reading somewhere that mathematically a sphere with uniform density has the same gravitational pull as it would if it was all compressed into a point in the center. Because gravity and magnetism both obey the inverse square law, the same applies to a magnetic monopole. If you had a larger sphere that was a northern monopole, and a smaller one that was a southern one, and you put the smaller inside the larger so they shared the same center (effectively making the magnet you described), from anywhere outside the sphere it would be the same as if they were both in the same point in the center, where they'd counter each other out. In short, the southern magnetic field emanating from the center of the sphere and the northern field emanating from the outside would be the same everywhere outside the sphere and counter each other out. Get it? — Daniel 18:43, 25 August 2007 (UTC)

Yes - thats right - though I'd expect a very weak residual field from the magnets.

I don't know if you'd be able to explain what happens to the 'magnetic field lines' in the case where 'cone/wedge shaped magnets' make up a perfect sphere - (you answered question 1 pretty well - just hoping) - I think they must go through the magnets so there must be some blanking as well?87.102.84.56 18:56, 25 August 2007 (UTC)

Let's just take Maxwell's laws to their natural conclusion. $\nabla \cdot \mathbf {B} =0$. From this, we know that the same number of magnetic field lines enter the sphere as leave it. Further, let's just look at the wedge shaped magnets you'd need to make such a sphere. The same law holds for them, the same number of magnetic field lines entering the north end emanates from the south end. I'd imagine that in a realisticly constructed sphere, you'd have magnetic fields leaving the magnet (in standard magnetostatics, the field lines leave the south end, and enter the north end) through gaps between the wedges, and re-entering across the wedge surfaces. Now, if you could have a flawlessly spherical and uniform magnet, well, let's turn to electrostatics. The laws governing electrostatics and magnetostatics differ only due to the absence of magnetic monopoles. However, if such things existed, magnetic monopoles would interact with one another exactly as electric charges do (except the left-hand right-hand rules get switched somewhere, this has been a while for me!). So, one "monopole" spread over the surface of a sphere, and an equally strong but opposite monopole in the center. From Gauss's law, the monopole on the surface creates a magnetic field outside the sphere identical to one that would be created if it were concentrated at the center of the sphere. Since electromagnetic fields obey superposition quite perfectly, the two poles cancel out completely everwhere outside the sphere, and your long sought after spherical magnet is completely dead. Someguy1221 20:34, 25 August 2007 (UTC)

I think is worth noting (with reference to the later part of your argument) - that the field due to a spherical surface charge is not exactly the same as that of a point charge centred at the sphere centre - there's a (small difference) - which varies with distance... (that difference depends on the nature of the 'field' variation with distance and of course if the field is a vector or scalar quantity matters as well)... 87.102.84.56 21:16, 25 August 2007 (UTC)

Meaning that the spherical magnet is not dead (possibly very weak) but with a <literary effect>unmistakeable feeble pulse</literary effect>...87.102.84.56 21:21, 25 August 2007 (UTC)

That arises from the failure of the assumption that the charge can be uniformly spread over the surface. If it could be, the magnet would, literally, be completely dead on the outside. But since electrons have finite distance between them, this is not the case. Someguy1221 21:35, 25 August 2007 (UTC)

No the effect still arises when the charge is uniformly spread on the surface.87.102.23.4 00:36, 26 August 2007 (UTC)

I'm confused, why? Someguy1221 01:06, 26 August 2007 (UTC)

Consider the gravitational effect from a point mass M

and the gravitational effect from a evenly distributed spherical surface with total mass M (gravity follows the same inverse square law as electrostatics yes?)

The functions of field/force are very similar at great distances

But differ fundamentally - the field is given by a different equation for each case.

You'd need to work out the field due to a distributed mass/charge around a spherical surface as a function of distance - probably you'll end up with a function with two integrals - you don't need to be able to do the integration to show that the function is not the same as the 1/r² that comes from a point mass/charge. (this may be a maths desk problem)

Because the two functions are different - subtracting one from the other results in a non zero field (in fact there is a surface where the field is zero - but everywhere else it is non zero) - in fact the field changes sign. 87.102.23.4 01:16, 26 August 2007 (UTC)

(the gaussian law holds when r (the distance) is greater than R (the radius) r>R but is not 100% correct at finite distances - there is a minute error - which is much more noticable when r approaches R - in fact when r=R the field becomes infinite just as it does when r=0 with a point charge. Gausses law is an approximation - that's why I said that the noticable effect would be 'very feeble' - this is especially true when r>R because the approximation is very good.87.102.23.4 01:25, 26 August 2007 (UTC)

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesph.html#c3 gives the approximations for field according to gauss inside and outside the sphere - note for inside a sphere of radius R the field according to gauss is Qr/4pie₀R³ - not the same as a point charge - I can't find a link to a more detailed analysis right now but can explain if if needed.87.102.23.4 01:33, 26 August 2007 (UTC)

Your own link states, if I may quote: "The electric field outside the sphere (r > R)is seen to be identical to that of a point charge Q at the center of the sphere." Their equations for both inside and outside the sphere are trivial applications of Gauss's law. Someguy1221 01:46, 26 August 2007 (UTC)

I linked just to show that a different equation exists (under guasses approximation) for r<R - there is under gausses approximation - a discontinuity at r=R - this is not the same as being 'identical to a point charge' because for a point charge there is no discontinuity at r=R. How exactly do you explain gausses equation for the field inside the sphere

Qr/4πє₀R³ (inside the sphere) compare Q/4πє₀r² for a point charge?

in terms of a point charge?87.102.44.85 10:54, 26 August 2007 (UTC)

It's actually completely consistent. The example given was that of a sphere whose charge is uniformly distributed through the entire sphere, not just the surface. If you accept that charge distributed across the surface of the sphere creates no electric field within the sphere, then at any point inside the sphere in the example, the charge you are "exposed to," in a sense, is proportional to the cube of your distance from the center. So, as you move out from the center, the apparent point charge increases in magnitude as r³ while the field strength/charge ratio remains proportional to 1/r², yielding the linear relationship Qr/4πє₀R³ (where R is the radius of the sphere, constant). At r = R, the two equations give the same result, there is no discontinuity. Someguy1221 22:24, 26 August 2007 (UTC)

In the example you gave originally "So, one "monopole" spread over the surface of a sphere, and an equally strong but opposite monopole in the center. From Gauss's law, the monopole on the surface" and in the example linked (which isn't connecting unfortunately) the charge was on the surface - I've underlined those parts that refer to the monopole/charge being on the surface. It looks like you don't know this.

You're analysis above is just wrong( the first part). The second part you have just turned into words what was stated in the equation. There is discontinuity in terms of the first and other differentials. If you want to discuss this further can you start a new question because we are getting very far away from the original magnets problem.87.102.45.106 12:01, 27 August 2007 (UTC)

Quoting from your source, again "The electric field of a sphere of uniform charge density and total charge charge Q can be obtained by applying Gauss' law." This is a common problem to be found in any introductory physics text book. Someguy1221 03:31, 29 August 2007 (UTC)

This is all because, from a mathematical perspective, Gauss's law and Coulomb's law are actually identical. The only difference is that Gauss's law does not inherently imply that the electric field of a point charge is radially symmetric, so you must make this assumption (which everyone does). Someguy1221 22:29, 26 August 2007 (UTC)

Note - gauss's law inside the sphere surface is mathematically different from coloumbs. Please be careful when you say things like 'mathematically ... identical'87.102.45.106 12:01, 27 August 2007 (UTC)

Guass's law still produces the same predictions. The electric fields of static charges predicted by Coulomb's law are always always always (i'm not sure I can emphasize this enough) identical to those predicted by Guass's law. The two can actually be derived from one another, provided you asume the obedience of electric fields to the superposition principle and the radial symmetry of the field about a static point charge. Someguy1221 03:31, 29 August 2007 (UTC)

Bacteria in human mouth vs. at the end of the digestion process

I know in some species like the kimono dragon their mouth has so much bacteria that it's what kills people and not their bite, so they may even have worse bacteria in their mouths than at the end of the digestion process (rectum). But what about humans who have bad breath, tooth decay, and that white-yellow film on their tongue from bacteria... how much, how deadly, etc. is that bacteria to the bacteria at the end of the digestion process? mouth (human) is a brief article that says nothing of this. Juanita Hodges 07:18, 25 August 2007 (UTC)

Very little bacteria survives the beginning of chemical digestion in the stomach—the low pH (high acidity) pretty effectively kills most bugs. Intestinal flora are usually quite different from the stuff in your mouth.

Meanwhile, the toxicity of komodo dragon saliva depends partly on the bite; it's not just the saliva by itself. By puncturing your skin, pathogens in the komodo dragon saliva get a free pass into deeper tissues and (potentially) your blood. While your mucous membranes and skin are (somewhat) resistant to many nasty things, most of the rest of your body is more poorly defended against pathogens. (This is one of the reasons why gastrointestinal perforation is so serious—the normally harmless and helpful bacteria in your gut get spilled out into the abdominal cavity, where they cause massive infection.) TenOfAllTrades(talk) 18:33, 25 August 2007 (UTC)

How bad are the human mouth bacteria compared to intestinal bacteria? Juanita Hodges 22:07, 25 August 2007 (UTC)

When placed where they shouldn't be, intestinal bacteria are generally worse. Someguy1221 01:48, 26 August 2007 (UTC)

Can human mouth bacteria be deadly or infectuous in the wrong place? Juanita Hodges 02:26, 26 August 2007 (UTC)

Depends how far along the road to decay the mouth is. If there's an actual infection with bacteria chewing away at the gum tissue, you can correctly imagine that those bacteria will be more than happy to chew away at your arm tissue or foot or whatever as well. This is the basic reason why people with pacemakers for instance have to be careful with dental surgery because those serious bacteria could enter the blood stream and infect the wiring to the pacemaker, etc. Regular tooth-cavity bacteria, not so much. Their big trick is turning sugar into cement, which is not that handy for infecting a puncture wound. Also, scientists currently are beginning to doubt the komodo dragon story, and theorizing that maybe it's a real toxin they secrete. Other reptiles get pretty good mileage out of the poison-bite trick, of course. Gzuckier 15:10, 27 August 2007 (UTC)

Camera emulating the human eye

In a question hereabove, SteveBaker says the human eye uses a combination of colour and brightness detection, a technique also being developed for monitors under the name RGBS or RGBE (note that RGBE is about something different, although related). I had previously thought of making a camera sensor that way. Put a layer in front of the colour sensor that does two things - measure the brightness and darken according to the brightness. Thus, the light passing through it to the colour sensor will be of equal brightness and the colour sensor needs only detect the colour. The idea is that if you split the two functions they can be more precise at what they do - more detail in brightness and shadows and a higher colour depth. Also, performing a more limited task means it can be done in a smaller area, so the pixels can be packed closer together, so the resolution (and with it the pixel count) goes up. Does this make any sense? DirkvdM 07:38, 25 August 2007 (UTC)

After a couple of reads .. yes... You get higher dynamic range (in the overall image) - a pixel seeing bright light can get a good exposure without being overexposed (whiteout) at the same time as a pixel getting low light can also get a good exposure - makes sense..

As for the second part "Also, performing a more limited task...." I'm not sure I agree - wont the pixels just be the same size as normal?87.102.84.56 11:01, 25 August 2007 (UTC)

I seem to remember a vaguely similar system - were there are four sensors - rgb and intensity - the intensity sensor controls the sensitivity of the rgb sensors electronically though - possibly this was in a fuji camera 'ccd' can't remember more though.87.102.84.56 13:39, 25 August 2007 (UTC)

One problem I see is that the time it would take for the first layer to darken wouldn't be enough to block the light from hitting the second layer. With flash photography, perhaps a double flash could be used, where the first flash darkens the first layer and the second flash is used for the second layer. Another problem might be that the first layer would refract light and cause a fuzzy image. The closer the two layers are to each other the less of a problem this would be. StuRat 16:46, 25 August 2007 (UTC)

Someone said something about pixels. This isn't to increase the number of pixels, it's to increase the accuracy of the color in each pixel. Why is it red green blue and brightness instead of hue sat and lum? I know one of those is brightness. — Daniel 17:04, 25 August 2007 (UTC)

It's hard (maybe impossible) to build a 'hue' detector without building it from a set of red, green and blue detectors. Hue is a measure of where on the rainbow spectrum you are - so you'd think it would be a measure of light frequency or something - but then we have 'hues' like Magenta (purple) which is a mixture of red and blue that doesn't ever appear as a single frequency of light. Alternatively, we have the colour humans call 'yellow' which is really one of two totally different physical phenomena. It's either pure light of a frequency somewhere between red and green - or it's a mixture of pure red and pure green. Humans can't tell the difference - but a frequency-measuring-sensor would have to do so in order to produce realistic colours. The concept of 'hue' as we describe it only works for creatures like humans who happen to have red, green and blue sensors. So when you are making a camera, the simplest and most realistic thing to do is to emulate the human eye - producing the exact same artifacts as the human eye does. Hence, our cameras have the exact same problem (that they can't tell the difference between the two kinds of yellow) as we humans do. So RGB is here to stay - adding intensity sensors would perhaps be useful though. SteveBaker 21:25, 25 August 2007 (UTC)

I'm not sure I follow. I'm not suggesting to eliminate the rgb sensor, just present it with a light that is always equally bright, so it can focus more on its own task and thus be better at it. The image at the top of Munsell color system is rather illustrative. I want the first sensor to measure the brightness and 'equalise it' for the second sensor, which then measures hue. Now I wonder how chroma is measured. Or does that go with hue? DirkvdM 07:24, 26 August 2007 (UTC)

The colour system you are talking about is Hue/Saturation/Value (HSV). Hue is best descriibed as 'where on the rainbow you are' - all shades of red through bright red to dark red and including pinks have about the same hue. Saturation is the distinction between red and pink - or blue and 'baby blue' - it's the amount of 'colour' in the colour so to speak. Value is brightness. HSV is a useful way to pick colours if (for example) you are worrying about colours that look good together, concepts of contrasting shades are easier to understand in HSV than in RGB - but there is relatively simple math to convert one into the other and back again. There are many different variations on the HSV theme though. So your idea for the sensor is to normalise the brightness of the incoming signal so that the RGB sensors are operating at higher brightness levels. Essentially, that's what RGBE/RGBS does - it decouples the overall brightness of the signal from the sensitivity of the RGB number range. But whether you can come up with a sensor that physically implements RGBE is a tougher question - as far as I know, all existing high-dynamic-range systems work by taking pictures at a range of different exposures and merging the results. SteveBaker 13:32, 26 August 2007 (UTC)

Ah, that last bit sounds interesting. A disadvantage of that method is that you need to expose several times, which means longer exposure, which becomes a problem at low light and/or a fast moving subject. My system requires only one single exposure with two sensors, the results of which are then combined. Sounds better, doesn't it? If it can be implemented, that is. DirkvdM 18:50, 26 August 2007 (UTC)

Stu, you say the first layer might not react fast enough. But I forgot to mention that the idea is that it takes its measurement-energy from the light. It's sort of like how an analogue film works - the silver halide grains that get hit by light darken and I assume they do that by absorbing the light energy. The idea is that this layer does that too. Since it does this by absorbing the light energy, the reaction is instantaneous. But it also needs to measure the light intensity. Maybe that could be done after the photo is taken, by letting the layer 'leak' its energy and measuring that.

But I just realise this might require wiring in front of the sensor, which is not a good idea. Maybe it could be a mirror that sends the image to the side, where the colour sensor is. There's another thought - why don't we have newtonian cameras? I'll make that a separate question. DirkvdM 07:24, 26 August 2007 (UTC)

Are you sure that reaction is "instantaneous" ? I don't know enough about it to say, but don't many such reactions involve electrons staying in one shell for a fraction of a second, then jumping to another ? StuRat 22:31, 26 August 2007 (UTC)

Maybe the darkening of photographic film is indeed not instantaneous, but in retrospect that might not be a good comparison. What counts is that the energy is taken out of the beam of light. Letting an electron jump to a higher energy state sounds like a good (the only?) way to do that. And maybe the falling back could then be measured somehow. But I now realise that this will probably not let through light of equal distribution. More likely, it will let light through at a fixed percentage of the incoming light. So the brightness is still measured, but the rgb sensor behind it will still have to deal with variable light intensities, and the idea was to be freed from that so the sensor can be made better at colour measurement.

Just in case that last bit needs clarification, think of different scales used for different weights - a very precise scale that weighs to the precision of milligrams will not be able to withstand the weight of, say, a car. A multimeter also has different 'scales' for different inputs, for similar reasons. DirkvdM 07:32, 27 August 2007 (UTC)

WHAT HAPPENS DURING MULTIPLE PERSONALITY DISORDER?

PLEASE LET ME KNOE THE PATHOPHYSIOLOGY OF THIS DISORDER I HAVE CHOSEN THIS TOPIC FOR MY SEMNINAR PRESENTATION AND SO I NEED THE HELP OF ALL THOSE WHO STUDY PSYCHIATRY SPECIALLY PLEASE STRESS ON WHAT HAPPENS TO THE BRAIN

Firstly, using all caps is not a very good idea, as some people may construe your statements as disrespectful. Secondly, Wikipedia is an encyclopedia, have you read our article on multiple personality disorder? Splintercellguy 09:15, 25 August 2007 (UTC)

Yeahhhhhh, using all caps when discussing mental health...? It makes me wonder about the poster's own mental stability. =/ Not a good combonation! --24.249.108.133 20:50, 27 August 2007 (UTC)

WHAT HAPPENS TO THE BRAIN DURING THE DISSOCIATIVE IDENTITY DISORDER?

i AM GOING TO DELIVER A SEMINAR ON THIS AND SO I NEED THE HELP OF ALL PSYCHOLOGISTS NO WEBSITE CLEARLY MENTIONS THE PATHOPHYSIOLOGY OF THE BRAIN AND SO I IMMEDIATELY NEED THE RELATED INFORMATION PLEASE MAIL ME IF POSSIBLE <e-mail removed>

See my response for your other question. Splintercellguy 09:16, 25 August 2007 (UTC)

Oh yeah, it's not a good idea to publicly post your e-mail, it's an invitation for spam. Splintercellguy 09:53, 25 August 2007 (UTC)

21 grams

Does the life force in humans have a discernible weight? - Kittybrewster (talk) 11:01, 25 August 2007 (UTC)

Well there isn't any tangible thing as a "life force" in modern medical science. "Life" itself is defined very differently by many different people, but generally speaking it is often considered to be processes which decrease entropy. These processes can have no independent weight of their own, and indeed are not independent from the functioning of the organism itself. Think of a wind-up toy—would you say the winding of the spring (we'll call it the "mechanical force") has a discernible weight, or was even something physically different from the toy as a whole? --24.147.86.187 12:08, 25 August 2007 (UTC)

Actually ... in 1907 Duncan MacDougall measured the weight of a soul and found it to be 21 grams. However, I think you'll find few people today that believe that the life force in humans has a discernible weight, and there is no scientific rationale to support such a belief. --Ed (Edgar181) 14:28, 25 August 2007 (UTC)

I think you you need to define what a life force is and try to prove it exists. What exacttly was he measuring? --72.202.150.92 18:41, 25 August 2007 (UTC)

Weigh someone just before they die - then again afterwards - the difference (if the experiment is done carefully enough) will certainly be zero. There is simply no such thing as 'life force' in modern science. SteveBaker 21:59, 25 August 2007 (UTC)

The air in your lungs has a weight. If on dying the ribs and diaphragm relax, the chest cavity would collapse slightly and expel some air; probably just over 0.5 litres, which would weigh about a gram, so the mass of the body would decrease slightly. The studies into the mass of the soul were fatally flawed for a number of reasons, though: people dying of terminal diseases tend to be moving quite a bit which can interfere with scales, it is very difficult to work out whether someone is alive or not with late 19th century science (even more so to do it without disturbing the scales), and of course, as the body dies, sweating, breathing and respiration will all decrease the total mass. Laïka 23:42, 25 August 2007 (UTC)

The air in your lungs is at the same pressure as the surrounding air, and therefore has the same density. It contributes to your body's mass, but not to its weight as measured in the normal way with air surrounding it. --Anon, August 26, 2007, 16:23 (UTC).

If you give any credence to the thoughts of naked space vampires, you may want to see Lifeforce (film).

Atlant 11:52, 27 August 2007 (UTC)

Actually, actually, if you wind up a spring or something similar, it does weigh more! Bizarre, huh? --Waldsen 21:59, 31 August 2007 (UTC)

Hooke's law and its integral

If Hooke's Law is $F=-kx\,$, why is its integral $U={1 \over 2}kx^{2}$? Shouldn't it be $U={-1 \over 2}kx^{2}$, although it gives rubbish results? Why does the negative sign suddenly disappears when it's calculating energy instead of force? --antilived^{T | C | G} 12:23, 25 August 2007 (UTC)

I think you should see it as follows. Your $F$ is the force the spring exerts on your hand, which compresses the spring. Your hand, however, exerts the force $-F$ on the spring, and this is the force you should integrate (since this is the force acting on the spring, transferring energy to it). —Bromskloss 12:30, 25 August 2007 (UTC)

So we are not actually integrating Hooke's law to get the energy formula? Shouldn't that be changed in the articles to reflect that? --antilived^{T | C | G} 12:34, 25 August 2007 (UTC)

You're probably right. Of course, it's not a very big thing so a short note would be enough. —Bromskloss 12:38, 25 August 2007 (UTC)

No,no - not right the energy equation is the integral - but the force (opposing) is in the opposite direction to the movement - hence the change of sign - maybe the article needs clarifying.

But the force needed to move the spring is kx not -kx since it is in the opposite direction to the force the spring makes itself - (make sense or not?)87.102.84.56 12:46, 25 August 2007 (UTC)

—Bromskloss has it right.

Work is force x distance. The force exerted by the spring is -kx The force needed to move the spring therefor is kx. Hence the change of sign.87.102.84.56 12:48, 25 August 2007 (UTC)

OK now a new problem comes up. If W = F × D, then isn't W = kx² only? Where does the 1/2 come from? --antilived^{T | C | G} 05:56, 26 August 2007 (UTC)

Work equals the integral of force with respect to distance. Normally this would just be force times the distance co-directional with the force, but for a spring, the force is not constant, but rather is directly proportional to the distance, so you must take the integral of the force this time. The integral of kx with respect to x is kx²/2. Someguy1221 06:16, 26 August 2007 (UTC)

Yea I know that, but I'm wondering WHY is it the integral of force? Why isn't it just a product of manipulating several other formulae like many others? --antilived^{T | C | G} 06:24, 26 August 2007 (UTC)

Well, if you'll accept that the force at a given instant, multiplied by the distance traveled over that instant equals the energy transfered in that instant...This only works for non-infintesimals if you use integrals, as integrals are infinite sums of infintesimals. If I'd remembered my physics better, I could derive for you the relationships from Newton's laws, but that's a few years in the past. The simplest I can put it, short of that, is that simply combining formulae algebraicly doesn't yield every possible physical relationship. Newton created the calculus for the primary purpose of answering physics questions that were beyond contemporary mathematics. Someguy1221 07:43, 26 August 2007 (UTC)

Mains adapter

I just bought a digibox and the mains adapter that came with it was small and surprisingly light, only about 50gm, almost as though there was nothing inside the box, but it works just fine (12v DC from 240v AC). They are usually up to ten times heavier than that. Is this some new technology?--Shantavira|^{feed me} 12:43, 25 August 2007 (UTC)

Digiboxes don't use much power and electronic things are getting more and more energy efficient - so maybe it just has a much smaller transformer than you were expecting?

Alternatively a wholey electronic power supply - (no transformer) could be made - which might be lighter.

I expect the former though - what is the rating of the power supply?87.102.84.56 12:51, 25 August 2007 (UTC)

12w.--Shantavira|^{feed me} 12:55, 25 August 2007 (UTC)

mmmh (I've got one of those too and it is very light) - a web search confirms what I used to think - that a conventional 12va transformer weighs much more about 125g at least...87.102.84.56 13:04, 25 August 2007 (UTC)

It sounds to me like this is a switching power supply and you're thinking of more traditional transformer based power supplies... Switching power supplies are hardly 'new technology' for example they've been used in computers for a long while. However it's perhaps only recently that they've began to become common as replacements for more traditional transformer based 'power brick' type mains adapters. Most mobile phone adapters nowdays are switching ones I presume because of the weight and universal use advantages Nil Einne 13:08, 25 August 2007 (UTC)

Edit: I also noticed this from the above article "In early 2006 even very low power linear regulators became more expensive than SMPS when the cost of copper and iron used in the transformers increased abruptly on world markets." It seems likely that in 10 years time, people will be asking 'why is this old power adapter I found so heavy?' Nil Einne 13:10, 25 August 2007 (UTC)

The article says switching power supplies are more efficient. So they may have been cheaper from the beginning, but alas people usually only look at what something costs now, not in the long run, which is what really matters. If people would wisen up in this area, that might just 'save the world' (climatologically speaking). Or at least it would help. (Of course it becomes totally irrelevant if you occasionally use a car when you don't need to - not to mention gas guzzlers.) DirkvdM 07:44, 26 August 2007 (UTC)

+ & - chargged metals

I am running an inhome experment and would like to use the maximum differencial in possitively and negatively charged metals. Is there an oppisit to isatobe 235, or a less radioactive metal? Is there isatobe 100 and an anti-100? A 50 and anti-50, anything? Can you stear me in the rite direction? Thanks, Gods— World Changer161.51.11.2 13:44, 25 August 2007 (UTC)

Um what? Isatobe 235? You mean Uranium-235 (uranium isotope 235? Um little hint. If you're planning a 'in home' experiment you want to consider elements you can actually obtain easily. Also I don't quite get what your doing. Are you trying to make a Galvanic cell? If so take a look at Standard electrode potential (data page). However personally I would recommend you steer away from anything which produces hydrogen flouride. Nil Einne 13:50, 25 August 2007 (UTC)

Not sure +3 is the usually max charge on a metal as found in Aluminium, maybe you were thinking of electronegativity and electropositivity?87.102.84.56 13:53, 25 August 2007 (UTC) If so gold and lithium would probably be your choices..

There is as far as I know no thing as an 'opposite to isotope 235' or an opposite to an isotope that can be got.87.102.84.56 13:56, 25 August 2007 (UTC)

It would help if you told us more..87.102.84.56 14:09, 25 August 2007 (UTC)

Sacrificial Anode - Aluminium

I have read that aluminium forms an oxide coat that prevents it from oxidising and hence is it quite unreactive. Yet I have been told aluminium could be attached to those drilling stations in the ocean to protect the iron from oxidation. Doesnt the oxide coat prevent this?

What you have been told may or may not be true - I've no idea - but it's a possibility.

The alkaline nature of sea water will tend to dissolve the aluminium oxide - so yes I imagine that aluminium could be used as a sacrificial anode..87.102.84.56 14:04, 25 August 2007 (UTC)

From Galvanic corrosion " Boats and vessels that are in salt water use either zinc alloy or aluminium alloy. If boats are only in fresh water, a magnesium alloy is used. "87.102.84.56 14:07, 25 August 2007 (UTC)

So are you saying the Cl- ions play a factor in this? And why would you use an alloy instead of pure Al? Thx58.107.237.74 15:13, 25 August 2007 (UTC)

The use of an alloy is probably for ease of welding and structural integrity. Nimur 15:44, 25 August 2007 (UTC)

The Cl- ions may help dissolve the Al, but the pH of the sea water is important too.87.102.84.56 16:32, 25 August 2007 (UTC)

I tried rubbing soft aluminium and zinc on different steel structures at the seaside, there was less corrosion compared to an untreated structure. So aluminium does work to some extent.Polypipe Wrangler 00:11, 29 August 2007 (UTC)

Fused NaCl

What does fused mean? (This is at Downs Cell in the diagram) but there is no explanation. Note it says "The electrolyte is sodium chloride that has been fused to a liquid by heating." can someone explain further? Phgao 15:27, 25 August 2007 (UTC)

I think it's a strange usage of the term to mean "melting." I might venture to say "incorrect usage" of the term fusion, which in chemistry and thermodynamics usually means the transition from liquid to solid (latent heat of fusion, for example). In this sense, the molecules "fuse" close together to form a solid phase (not to be confused at all with nuclear fusion, a totally different process). However, Wikipedia is edited by users from many locations, and some regions tend to use dramatically different terminology from the stuff I learned in school in the US. Nimur 15:47, 25 August 2007 (UTC)

It's not incorrect. I admit it's a little con--wait for it--fusing, though. This is one of those words that's its own antonym, like "cleave". I think there's a name for such words, but I forget what it is. --Trovatore 03:31, 27 August 2007 (UTC)

Though 'fused' usually means to us 'set solid' in this case it means melted - it's a standard chemistry term - (search for 'fused salt' if you want to check) Note electrical fuses melt when they fuse..87.102.84.56 16:26, 25 August 2007 (UTC)

Specifically 'to fuse' just means 'to melt' - to be pedantic fused ice is water.87.102.84.56 16:30, 25 August 2007 (UTC)

Just to confuse things 'fused' can also refer to substances that have been melted. Such as fused magnesia.87.102.84.56 18:03, 25 August 2007 (UTC)

Recharging a Lone Ranger atomic bomb ring

Oh boy oh boy. I got a pair of Lone Ranger atomic bomb rings, one of which is in good condition that I won't mess with, one of which is basically just the spinthariscope component and so I don't mind playing with it a bit.

I'd like to "recharge" it. I gather than the original alpha source was polonium-210.

I imagine that "recharging" it basically will come down to figuring out how to open up the isotope chamber, cleaning out the old stuff (now long since decayed into lead), and putting in a new isotope source.

My question is: what sort of radioisotope should I go with? I know that Po-210 was used because it had a high level of activity, and thus would produce more exciting flashes, but its short half-life (138 days) means that to keep it running at a reasonable level I'd have to "recharge" it once a year. Seems like a pain. If I could find something a little less active, but with a better half-life, that might be more ideal. The only site I know of to get radioisotopes seems to only offer Po-210 as its alpha emitter, so I might be stuck with that.

Could I use the Americium-241 sources in a smoke detector? Am I right in thinking that the only way to get a comparable number of alphas as from the original Po-210 source would be to have much more of it? (Obviously I can't get too comparable, as—if I understand half-lives correctly—that means I would need hundreds of times more.) Is it worth trying, since the half-life is a lot longer and the sources are a lot easier to get a hand on?

My next question is: is this even reasonably a good idea? Obviously exotic radioisotopes can be quite toxic though I imagine I am not going to want to be using more than a speck and my understanding of strong alphas is that as long as it doesn't get inside me I should be okay (skin will stop the alphas easily). If I got a needle source of Po-210 from that site, and made sure not to, say, eat it or inhale it, would it be safe to put inside the ring?

If I am totally backwards on any of this please let me know. I'm no physicist and no chemist. --24.147.86.187 15:36, 25 August 2007 (UTC)

I wonder if the interior of the chamber is filled with inert gas (or possibly even vacuum)? If so, opening the case to replace the radiation source would vent the chamber. I suppose, since alpha particles have a mean free path of a few centimeters in air, and this thing is pretty small, that this is a total non-issue. Nimur 15:55, 25 August 2007 (UTC)

Sounds like a bad idea to me. First, even though the skin may stop the radiation, it may do damage to the skin in the process, which might potentially cause skin cancer down the road. Second, handling such material without risking inhalation or ingestion requires specialized equipment and training. In other words, "don't try this at home, kids". StuRat 16:18, 25 August 2007 (UTC)

I agree bad idea - see http://www.hse.gov.uk/laU/lacs/42-6.htm what the article reveals is that "less radiotoxic alternatives have replaced radium in radioactively luminised articles such as tritium (3H) or promethium-147 (147Pm)" - these are beta emitters - I imagine they would still activate a scintillation device?

The major hazard here is inhalation of any dust when cleaning it out, amongst the others - I wouldn't go scraping out a fire sensor or what ever unless I had a device that would keep any dust away from ME. Thinking about glove boxes, breathing filters - note also that the materials used may be harmless when contained in their devices but when exposed can be really bad - this for instance applys to radioluminous watch dials which are consider safe? but if you break the glass it's a case of forget it - and don't even think about touching it - 2mm of glass provides a lot of protection - which out that you could expect 'burns' on your skin.

Specifically all this work needs to be done with tools eg pliers - don't even think of doing it if you would need to manipulate the things with your hands.

I know that there is a lot of 'scare' about radiation - but inhalation of any radioactive dust can be a very serious problem.

See http://www.bhi.co.uk/hints/poison.htm "The hands of the watch or clock should be scraped while immersed in oil and the scraper left submerged in the oil to prevent the particles entering the air being breathed."87.102.84.56 18:34, 25 August 2007 (UTC)

I really wouldn't try this at all.87.102.84.56 18:51, 25 August 2007 (UTC)

Well, obviously I don't want to be handling raw materials here. Am-241 in a smoke detector comes in an insoluable dioxide form inside a gold matrix. I would just be transferring that bit into the ring; I find it unlikely that it would be a significant health hazard, no? Anyway I would not be handling this with my bare fingers in any case.

Cleaning out the existing material is probably the toughest bit. What exactly is the existing material at this point? Po-210 decays to a stable element of lead (Pb-206), which doesn't sound all that dangerous. After 60 years there should only be 1.57 * 10^-48 of the original material left, according to my calculations; I find it hard to believe that this would be a significant amount. I'm also suspicious that the Po-210 was originally in a form that would be prone to be a health hazard if messed with, since it was distributed in children's cereal, but I'm well aware that making assumptions about the safety standards of the past is a losing game!

Anyway, I don't say that to be contrary, but some of the concerns above don't seem to be to be very tailored to this particular situation, and some strike me as being a little uninformed (e.g. replacing it with tritium, for which there is no way in hell I'd be able to get it into such a ring without very sophisticated tools, or the concern about skin cancer from brief contact with a tiny amount of a relatively weak alpha emitter, which is no real threat at all). --24.147.86.187 18:57, 25 August 2007 (UTC)

Yes - it's not 100% applicable - and the Po is in an insoluble form - but what bulk form does that dioxide come in - as a beed or powder - if it was me I'd like to know before opening the gold case.

If it's insoluble you could then make the transfer under water - which does give you additional safety. I deliberately ere on the side of caution here. The radiation (alpha or beta) from an unshielded source can burn you - (unrelated to radiation poisoning as such) - although it would be little more than a 'tiny speck of hot ash' in magnitude.87.102.84.56 19:33, 25 August 2007 (UTC)

The Americium in smoke detectors comes on a little disc, according to this fellow. It'd be nice to know exactly how it is put together, though, because the disc itself is too big to fit in the ring, obviously. The more I think about the cleaning aspect the more I think it is probably a non-issue—there's going to be for all intents and purposes no radioactive material left inside the ring, it is all going to be lead, yes? --24.147.86.187 23:00, 25 August 2007 (UTC)

I read (but can't find the source now) that the Am (don't know if the metal or oxide - think the oxide) is rolled into a very thin gold sheet - i guess that the AmO2 becomes embedded in the gold, as I remember another thin metal sheet is rolled onto this (too thin to stop the alpha particles), there was also a silver? thicker backing and some other metals plates involved - so what you should have is effectively a sandwich of AmO2 between gold - the rolling probably fuses the gold/silver sheets so it shouldn't be separable.. Apparently 0.2mg is the very approximate amount involved, another site says they detected 2000 alphas per second using some sort of counter?87.102.23.4 00:22, 26 August 2007 (UTC)

Here http://www.madehow.com/Volume-2/Smoke-Detector.html

The process begins with the compound AmO2, an oxide of Am-241. This substance is thoroughly mixed with gold, shaped into a briquette, and fused by pressure and heat at over 1470°F (800°C). A backing of silver and a front covering of gold or gold alloy are applied to the briquette and sealed by hot forging. The briquette is then processed through several stages of cold rolling to achieve the desired thickness and levels of radiation emission. The final thickness is about 0.008 inches (0.2 mm), with the gold cover representing about one percent of the thickness. The resulting foil strip, which is about 0.8 inches (20 mm) wide, is cut into sections 39 inches (1 meter) long.

87.102.23.4 00:28, 26 August 2007 (UTC)

http://www.rampac.com/certificates/1030036.PDF shows a structure for a laminate.

87.102.23.4 00:32, 26 August 2007 (UTC)

And the average amount of radiation is 1 microCurie. http://www.epa.gov/radiation/sources/smoke_alarm.htm87.102.23.4 00:34, 26 August 2007 (UTC)

Polonium 210 has been in the news quite a lot over the past year or so since it was used to murder an ex-Russian spy in the UK. What we can learn from that is that Polonium (in very, very small quantities) is insanely toxic if you ingest it or breath it in. But in general, the radiation it produces is stopped by a few centimeters of air or a sheet of paper - so it can be handled safely - with suitable precautions. So once inside the ring, it ought to be pretty safe - but getting it in there safely is going to be tough. The most likely way would be to buy one of those antistatic brushes that photographers use that contains polonium 210 in tiny quantities embedded in a matrix of more inert stuff. Whether the spintharoscope in the ring would be able to detect it - I don't know. At any rate, you ought to go to United Nuclear - those guys will sell you all manner of radioactive samples - and spintharoscopes and whatever else you are likely to need. SteveBaker 21:45, 25 August 2007 (UTC)

It is toxic, yes, but not in the quantities that you can buy on the internet, and not in the forms that you can buy on the internet. Big differences there. Notice that Litvivenko was killed with 50 mCi of Po-210; United Nuclear sells it in 0.1 μCi amounts — a difference of four orders of magnitude! The median lethal dose is still over two thousand times more than you could buy online. So again, I think we're maybe drawing on the wrong associations here, letting our imaginations get a little out of control with all of the scary imagery that surrounds all things nuclear... --24.147.86.187 22:48, 25 August 2007 (UTC)

Sorry - yes, the impression I was trying (and evidently failing) to convey was that the tiny amounts you get in antistatic brushes and from United Nuclear are safe - they wouldn't be sold so freely otherwise. But in much larger quantities, this is nasty stuff. The main point is that the radiation is stopped by your skin before it can do any damage - but if it gets inside your body, it can cause nasty problems (in enough quantity). However, we don't know how much was in the original ring - and we don't know how sensitive the spinthariscope inside the ring was (or indeed still is). It might be that larger quantities are needed to make the ring work - and attempting to make larger quantities (eg by buying a heck of a lot of photographer's brushes and refining the resulting stuff would be a very bad idea indeed. Back in the 1940's, this kind of stuff was not at all well understood and some pretty lethally dangerous products were made before we realised the long term consequences of radioactivity. Note however that Polonium 210 has a pretty short half-life (about 4 months) - so even if our OP sucessfully recharges the ring, it's likely to stop working again after a year or two - and the activity of any "polonium" you do buy may be critically dependent on how old it is - Po₂₁₀ turns gradually into boring old lead and stuff that's a year old has about 1/8th as much active ingredient than 'fresh' Polonium straight from the reactor! But, as I said before, I strongly recommend the United Nuclear web site - they have tons of safety information and will sell you reasonable quantities of several radioactive elements. SteveBaker 13:13, 26 August 2007 (UTC)

Something that concerns me in this whole discussion is the liability of manipulating radioactive materials or telling people to manipulate them to put them in what is clearly a toy, however expensive and collectable a toy it has become. There is a likelihood of such a ring or toy in the future being in the hands (or on the finger) of a child, and of it making its way into said child's mouth. So do not go there. Keep the ring as a collectable. Do not start scraping radioactive material off of something, whether it is the spinthariscope ring, a smoke detector, or an old radium watch dial. It is bad enough when children are harmed by swallowing magnets. Now on to playing with asbestos, mercury, lead, and other 1950's science experiment hazards. Edison 15:07, 27 August 2007 (UTC)

Please - don't go nuts over this. The radioactivity from polonium 210 is blocked by single sheet of paper for chrissakes! You can buy Spintharoscopes with radioactive sources in them in most museum shops and other educational toy outlets - all we're talking about is recreating something like that (although it's far from clear that the original Lone Ranger ring was that safe). [1] for example. SteveBaker 23:58, 27 August 2007 (UTC)

Fields of science

What field of science begins with the letters "Q", "J", "W", and "Y"? Thanks68.78.73.144 16:36, 25 August 2007 (UTC)

Quantum theory Algebraist 17:12, 25 August 2007 (UTC)

Homework question? lol Jonaboff_talk 19:37, 25 August 2007 (UTC)

Yes. please help.

Searching the lists turns up nothing obvious under j,w,y - maybe you'll have to get creative? eg Jungle science - the scientific study of jungles?87.102.84.56 20:02, 25 August 2007 (UTC)

Jupiterean studies, Yttrium chemical science, wastewater science, wetland science, wavelets? (ideas from http://www.dmoz.org/Science/J/)??87.102.84.56 20:06, 25 August 2007 (UTC)

This list might help http://www.daviddarling.info/encyclopedia/alphindexy.html Yeast studies?87.102.84.56 20:08, 25 August 2007 (UTC)

Wet chemistry? Laïka 20:14, 25 August 2007 (UTC)

Jungian Psychiatry? I don't think it's science, but a lot of people do. -Arch dude 01:33, 26 August 2007 (UTC)

See Special Pages (top left) > All Pages (Special:Allpages) and fill in those letters. No, sorry, that hardly narrows it down. DirkvdM 07:53, 26 August 2007 (UTC)

W and Z bosons ? (At least it satisfies the w... Nimur 17:59, 26 August 2007 (UTC)

You could go with Quaternary studies for Q Mac Davis 19:13, 27 August 2007 (UTC)

Elasticity and Strain

The elasticity of a string is its property to resist any deformation when a force is applied. So is it that an elastic string will have a greater strain value than a relatively non-elastic string ... ??? or is it the other way round ???

Please enlighten.

Probably you should read Deformation, Strain (materials science) and Elasticity (physics) - at least the first bits.

The answer is yes - and not the other way round - an 'elastic' string strains/stretches more than a less elastic one for a given weight/force- strain is given by the amount of stretch.87.102.84.56 20:14, 25 August 2007 (UTC)

Animal intelligence testing

Have any intelligence tests been devised that will give meaningful results, on the same scale, for both human and animal subjects? NeonMerlin 20:34, 25 August 2007 (UTC)

The days, at the most technical level, intelligence is usually considered to be a uniquely human concept, but our efforts to investigate the non-human animal equivalent is detailed at Animal cognition. Some of the more simple tests - that we use in testing human children, for example - are also used in animals. You might also see Comparative psychology. Rockpocket 21:42, 25 August 2007 (UTC)

There are plenty of tests - but they tend to be of a qualitative rather than quantitive nature. We have discovered (for example) that Chimpanzees and Dolphins can recognise 'self' - they recognise that the animal they see in a mirror is themself - but that dogs and cats can't do that. Grey parrots can learn the concept of numbers and can count to at least five. Dogs can learn to understand 500 words of English - but have no concept of grammar or word order. But intelligence tests that come up with a distinct number are likely to be impossible. Even IQ testing amongst humans is considered a very dubious science since it's very easy to allow cultural or age biasses to creep in. So I think the answer is a definite "NO!". SteveBaker 21:52, 25 August 2007 (UTC)

But you have to admit, it'd be rather enjoyable if you could confidently say, "My friend, I have quantitative, scientific proof that you are stupider than a hog." --24.147.86.187 23:56, 25 August 2007 (UTC)

Surely animals have intelligence. At least, I define it as the ability to solve problems and learn (the other traits the article mentions, reasoning, planning, abstract thinking, comprehension of ideas and language are all subsets of those two, if you ask me). And all animals can do those two things to some extent. For example, you could put a fence (of finite length) between a dog and a bowl of food. Stupid dogs will run into the fence and start barking in frustration. Intelligent dogs will walk around the fence. I once saw that done with two dogs at the same time. The stupid dog didn't even pick up the smart dog's solution. And that is another intelligence trait. For sheep dogs there are problem-solving contests called sheepdog trials (as shown on BBC), which can qualify as intelligence tests. The dogs are presented with a new situation and have to decide what to do (much the same way in which hunting animals do), possibly under the direction of a shepherd's whistle, which qualifies as language. The herding tests may be fairly standardised, but there are also other tests, where the dog has to follow a course and overcome obstacles they have never seen before. You can actually see them think, standing in doubt about what to do next. A stupid dog wouldn't even understand it was being tested.

However, the question was for a test that can be used for different species, and that would be trickier. Even among humans, there are different tests for different levels of intelligence. So one test for different types of intelligence seems impossible. Of course, it gets even more difficult for the 'lesser species'. Such as plants. Can they be said to have intelligence? DirkvdM 08:08, 26 August 2007 (UTC)

If you choose your own definition of intelligence, then surely they do. Rockpocket 05:08, 27 August 2007 (UTC)

May I politely suggest that sheepdogs are comparatively intelligent but in a limited way. They have a very strong instinct to herd other animals but this ability should not necessarily be assumed to be intelligence. Having watched sheepdog trials on TV it is very clear that the skill of the shepherd in signalling to and guiding his dog or dogs is of paramount importance. When dogs have no contact with the shepherd they frequently herded the sheep in a random way, showing little knowledge of the point of the competition. Richard Avery 09:12, 26 August 2007 (UTC)

I assume that is because they haven't been trained to do that. If they were, an interesting test would be to see how well they would do compared to humans - so dogs without the help of humans and humans without the help of without the dogs. I wouldn't be surprised if dogs would perform better, and that is what I meant with 'different types of intelligence'. Overall humans may be more intelligent (and certainly in tests designed for humans of course), but at specific tasks other animals might perform better. But of course we don't design such tests, as intelligence tests, that is, because we perform worse, so we think that that isn't intelligence. And that is a central problem here. We define intelligence based on what we are good at, so of course other animals are then by definition less intelligent. We've got a bad case of intellectual parochialism. We're human chauvinist pigs. :) DirkvdM 19:17, 26 August 2007 (UTC)

The difficulty and controversy of quantitative intelligence testing of humans has not yet been solved. Our article IQ explains the various criticisms of standardized testing. In my opinion, this boils down to a philosophical question - does "absolute intelligence" exist at all? If so, how can we effectively probe it with standardized testing? If not, what qualities do we generally associate with intelligence? Once these issues are definitively settled in humans, it will be easy to extend the concepts to other creatures, bridging the natural language gaps and so forth. Until then, we will have to use operational definitions with limited scope (such as "time to complete a mouse maze") as a metric for intelligence. Nimur 18:07, 26 August 2007 (UTC)

Yes, nicely put Nimur. I guess without defining what we mean by intelligence (with all its connotations and variations) comparing the intelligence of different species is a problematic excercise. Hey, Dirkvd that's a big tough on the pigs :)) Richard Avery 10:30, 27 August 2007 (UTC)

The root of the problem of intelligence testing is that we don't have a solid definition of what the word means. We originally (I believe) used the term to mean "those intellectual capabilities that man has but animals lack" - we named our own species "Homo Sapiens" (thinking man) as if no other animal has that ability. That definition would mean that all animals would have to score a zero on any true "intelligence test" because if any of them ever managed to score higher, we'd have to admit that the test wasn't testing intelligence at all.

But over the past 50 years or so, we've learned a lot more about animal intellectual capabilities and it's getting harder and harder to draw a line. We have dolphins and chimps who we have proven to have a sense of 'self'. We have all sorts of animals that make and use tools. When I was in high school in the 1970's, we were taught that only Man uses tools - in the 1980's that only Man makes tools - now, we've quietly abandoned the whole tool thing because we've found that even some really small and "stupid" fish make and use tools. In the early 1990's my son was taught that only humans have 'language' - but that's indefensible in the face of things like the lowly cuttlefish's visual 'language' and interpretations of whale 'song' in which personal names seem to make an appearance. Now we have gorillas who can not only learn sign language but also teach it to their children.

We'd probably claim that only humans have written languages - but then we'd be in trouble because plenty of human societies never developed it. Math is similarly problematic. There are human tribes who don't have words for numbers higher than three - yet we have a grey parrot who can clearly understand quantities as high as five.

One by one, things that separate us from the animals are being shown to be quantitative rather than qualitative. We use MORE tools, MORE language and have MORE "intelligence" than the animals. So now, we have to ask ourselves what intelligence is - because it's clearly not "what we have but animals don't have".

Worse still for our definition of 'intelligence' is that a lot of people dislike getting a low score on IQ tests (because it gives them no way to avoid thinking of themselves as "stupid") - so we start insisting that they have "different kinds of intelligence". So I hear that dancers (some of whom might maybe score low on a conventional IQ test) ought to get extra credit for their 'kinesthetic' sense, and that someone with a great memory should score some extra points for that too. That dilutes the meaning of the word - for unhelpful reasons of political correctness rather than as a result of scientific investigation.

We also want a score that allows some kind of absolute measure of intelligence that's irrespective of age or educational level - but it's becoming increasingly obvious that our brains change as a result of learning and that age most definitely is a factor. But without a solid definition - we'll never come up with a scoring system. With the rise of 'political correctness' - it's even less likely that such a measurement can be made without upsetting a lot of people. We dislike anything that discriminates on the basis of the way we were born - so you are in trouble if you try to measure that exact thing with an IQ test.

So it's a bust. The best science can do is to invent a new word and start over with the whole messy business. SteveBaker 17:46, 27 August 2007 (UTC)

I agree with SB et al here. Given that there is no real way to reliably measure the intelligence of humans the issue of animals doesn't really come into the equation. Unless your definition of intelligence is the ability to do IQ tests which nowadays isn't a very popular definition (what's the point of your ability to do a standardised test particularly when that test is supposed to be measuring an inate ability but you can in fact learn to do better on such tests). Somewhat OT but the funniest thing about IQ tests is how people get so worked up about male vs female difference even though the original IQ tests in fact standardised males and females seperately so the average for both should have been 100 Nil Einne 00:32, 28 August 2007 (UTC)

Yeah, that's a good point. I once heard about an IQ test on which women scored higher than men (or the other way around, not sure), which was for that reason rejected. So we don't make a standard and then measure with that. Instead we design the standard to give us the results we want. So we might also design a test on which animals don't score at all. Until we find an animal that does score, upon which we could redesign it again to suit our expectations. So we're not measuring reality, but what we want it to be. DirkvdM 06:20, 28 August 2007 (UTC)

I agree with a lot of what SB wrote above, but with one reservation. It's clear (to me, at least) that there legitimately are different kinds of intelligence and different modes for expressing it. One of the bases of intelligence is the ability to solve problems, but there are many many different kinds of problems to be solved. Solving a Rubik's cube takes a kind of intelligence; composing aesthetic works of art takes a kind of intelligence; discerning which example doesn't fit X pattern takes a kind of intelligence. While you can see that they're all part of the problem solving set, someone good at one of those things may not be any good at the others. It's oddly incongruous that we're willing to label both Mozart and Einstein as geniuses, but only one of them is deemed "intelligent". Matt Deres 20:46, 29 August 2007 (UTC)

Maybe you just pointed out the difference between genius and intelligence. :) DirkvdM 06:38, 30 August 2007 (UTC)

Of some relevance perhaps is this recent study [2] Nil Einne 10:49, 7 September 2007 (UTC)

liquid pressure

Is it possible, as it is with a gas, to cram an ordinary cup of water into a half-cup sealed container with enough pressure? If you dive a mile under the ocean and seal a flask of water, then return to the surface and open it, will it gush out of its container like a geyser? If you go down to the floor of the ocean with 6 sheets of metal and some really strong tape, and you construct a watertight box around yourself, will the water inside still be at high pressure or will the metal take the strain? What if you run a hose from your box up to the surface and keep it clear of water, but the box is still filled? --froth^t 21:57, 25 August 2007 (UTC)

Water's compressibility is very tiny compared to any sort of gas; the sort of question that you're asking is addressed on this external site. Working from those figures, the pressure at six miles depth should be about a thousand atmospheres, giving a decrease in volume of about five percent. In other words, it would be a very short-lived geyser.

If you wanted to keep that pressure inside a metal box, you're going to need something stronger than tape to hold it together. A thousand atmospheres is about fifteen thousand pounds (nearly eight tons) per square inch.

It is possible to increase the density of water by a factor of two, but you need absurdly high pressures to do it. This page has diagrams and details of all the exotic ices that are formed at extremely high pressures; to get water down to half it's normal volume, you'd need pressures closer to a million atmospheres. It also wouldn't be a liquid at that point; it would be an unusual type of ice. TenOfAllTrades(talk) 22:26, 25 August 2007 (UTC)

Here's an interesting bit of trivia. If water weren't compressible, sea level on Earth would be about 40 meters (130 feet) deeper, and the Earth would have about 5% less uncovered land area as a result. TenOfAllTrades(talk) 22:28, 25 August 2007 (UTC)

[EC] For the water flask: No. Fluids are said to be incompressible. If you compress gas the pressure to the walls increases because the density has increased and the particles now hit the wall more often. In a fluid, the particles are so close to each other that you cannot compress them more without forcing them into a crystal. Of course, water is not exactly incompressible, but you need huge pressure to just compress it a very tiny bit. There is no longer proportionality between volume and pressure. For the metal box: Yes, one can construct a metal box that is able to withstand the water pressure from outside and keep atmospheric pressure inside: it's called a submarine. Usually, submarines are filled with air and sailors and torpedoes and all this, but if you insist, you can also fill them with water. (Ok, before someone corrects me: A military submarine is not built to take the pressure at the deep ocean floor, but there are Bathyscaphes). Simon A. 22:32, 25 August 2007 (UTC)

Just a minor nit here: It's liquids that are (almost) incompressible, not fluids. A fluid, technically, is either a liquid or a gas (anything that flows, which is the etymological root of "fluid"). --Trovatore 03:12, 27 August 2007 (UTC)

Wikipedia needs a bit of work on the different forms of ice, and could do with an ice phase diagram. There are no articles on ice II IV V VI VII VIII X XIII or XIV! Graeme Bartlett 22:41, 25 August 2007 (UTC)

Thanks for the answers so far but I think you've missed the main thrust of my question. If you build a metal box around yourself at great depth, will there still be crushing pressure from the water above? Or will the box take the pressure and the water inside have pressure of surface water? Basically I mean like if you seal gas in a container then it retains its pressure, but if you seal high-pressure water in a container so that there's no longer a mile of water on top of it is it still high pressure? Do you see what I'm saying? Let me put it another way.. some guy puts on some super strong diving suit and dive down a mile underwater. He takes off his suit and promptly dies from the crushing pressure. The next guy comes along and has the idea of taking a sheet of metal to hold above his head, hoping that it'll hold up the massive column of water above him. He braces it between some rocks and crawls underneath, then takes off his suit. He's crushed too because the pressure "gets in" from the sides. The next guy decides to totally protect himself from the pressure above by taking down 6 sheets and building a box around himself. Now the gigantic column of water above him is supported by the box, and his body doesn't have to try to push back. Right? That's my question- would it work? Or would it act like gas, and retain its pressure? --froth^t 00:17, 26 August 2007 (UTC)

Your talking about a sealed box that the diver goes down in right (made of super tape that doesn't break) - like a submarine? The answer seems to be yes - because the box he's in isn't crushed or compressed - neither is he?

Or did you mean he builds the box when he's really deep - in which case the box will contain water under pressure when he builds it around him and he'll be crushed.

Or? 87.102.23.4 01:40, 26 August 2007 (UTC)

The original question - build a box/bottle down below and bring it up - as it is raised the pressure from within the box gets greater and greater - if it's opened at the top and it's kept its shape then - yes - water will come out ( a bit) as it expands.

If you build the box at deep pressure the water inside will still be pressureised.

If you take a pipe from sealed box up to the surface - nothing changes - the column of water above the box causing the pressure is the same height.87.102.23.4 01:45, 26 August 2007 (UTC)

I agree with the last guy;

1. if you build a sealed box underwater, the pressure inside when you seal it will be the same as the pressure outside.
2. if you run a hose to the top, as long as the top of the water inside the hose is at the same level as the top of the water outside the hose, the pressure in the box will be at the same pressure as outside. if you pump the water out of the hose until the top of the water is at the top of the box and the rest of the hose is full of air, the pressure in the box will be at atmospheric pressure, plus whatever extra atmospheric pressure you get for being that further down. Odd but true; the height of the water in that hose, even if it's like 1 mm in diameter, governs the pressure in the box. Gzuckier 14:56, 27 August 2007 (UTC)

Accents

This is a strange one, but since it concerns the brain it presumably belongs here. One night several months ago I stayed up all night, drank espresso, and watched episodes of QI. I must have watched every episode. The strangeness began when I went to class in the morning, having just watched the last episode about thirty minutes earlier. Every background voice sounded British or Irish to me. I will explain. Every vocal sound I overheard was analyzed as if it had been spoken by a Briton or Irishman - not at the level of words, but at the level of phonemes. I would be unable to say what was being said. If I listened closer, the effect would vanish. Also, certain phonemes would disrupt the effect, and the American accent would return fleetingly. Also, the effect was less apparent when the overheard voice was one familiar to me. All other background voices appeared to fluctuate between English, Scottish, or Irish. People with non-American accents, such as speakers from India, were no exception. Once I had some sleep, the effect waned, but it was another ten hours or so before it had vanished altogether. It has not happened again. I strongly suspect caffeine and/or lack of sleep was the root cause, but I was just wondering if this effect is known to psychiatry, if it has a special name, etc. Thanks! Bhumiya (said/done) 22:37, 25 August 2007 (UTC)

When I listen to a single voice for too long, my internal voice starts immitating that voice. A.Z. 01:38, 26 August 2007 (UTC)

You say the effect disappeared when you listened more closely. That suggests difficulties in concentration, which could easily have been caused by a lack of sleep. However, that doesn't explain this specific effect. In line with what AZ said, if you expose yourself to something long enough, you will start to expect that in your surroundings and pick up any hints of it and amplify those. So any 'English' traits' in what you heard in the pronunciation of those people would take the overhand. Similar to the effect of walking out of a movie theatre and seeing the world in the perspective of the sort of movie you've just watched. DirkvdM 08:31, 26 August 2007 (UTC)

Perhaps the experience described is akin to what happened to me when I lived for several months in a French-speaking city: if someone spoke English to me when I wasn't expecting it, I sometimes didn't understand it; I only recognized that it made no sense in French. —Tamfang 07:34, 27 August 2007 (UTC)

Haven't heard this one before but the opposite has been seen: "Foreign accent syndrome (FAS) is a rare speech disorder characterized by the appearance of a new accent, different from the speaker's native language and perceived as foreign by the speaker and the listener. In most of the reported cases, FAS follows stroke but has also been found following traumatic brain injury, cerebral haemorrhage and multiple sclerosis.", so it's not altogether surprising that it would go this way as well.

So you're proposing that watching British televison causes brain damage? :) GeeJo ^(t)⁄_(c) • 19:44, 30 August 2007 (UTC)