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December 12

Amount of ohms and stereo speakers

Hello, I'm getting a new stereo and the speakers are 6 ohms (it's 400w, 200 per channel, 6 1/2 inch sub, 3-way bass reflex). A pretty smart guy told me that less ohms means less resistance and better response. I have some pretty small speakers here that are 3.2 ohm, how can they have better response than these high quality 6 ohm ones I'm getting? It seems like bigger speakers have more ohms, then how could my crappy little Audiovox speakers out-respond some top of the line ones with 6 ohms? Is more ohms bad? NIRVANA2764 (talk) 00:40, 12 December 2007 (UTC)

Ohms has no effect on sound or response. The only thing the ohms rating is for is to match the impedance. If you connect your 3.2-ohm speakers to an amplifier that wants 6-ohm speakers, you will probably blow out the amplifier. You can connect speakers with an ohms rating higher than 6 to an amplifier that wants 6 ohms, but the higher the ohms rating of the speakers, the less sound you'll get. This is for amps that don't run on vacuum tubes; that's a horse of a different color. By the way, a good rule of thumb is to get speakers with a power rating double that of the amp. Another good rule is to put most of your money into the speakers, and better speaker simply sound better—compare by ear. --Milkbreath (talk) 01:21, 12 December 2007 (UTC)

According to the impedance matching article, stereo amplifiers actually use impedance bridging (which is news to me). Also, I've used speakers with lower than recommended impedance before (on old equipment, so I wasn't that worried about damaging the equipment), and it worked OK. I don't remember if I've ever used speakers with half of the recommended impedance before, but I may have plugged two speakers into one speaker output at one time, and wouldn't this cut the total impedance in half? It seemed to work, but I wouldn't try it if you're not willing to fry your amplifier.

Also, if I recall correctly, most home audio equipment tends to be 8 ohms. I only remember seeing 6 ohms on smaller "shelf systems". Maybe larger speakers have higher impedance, in general. Philbert^2.71828 02:26, 12 December 2007 (UTC)

Speaker impedance used to matter back in the days of vacuum tube amplifiers, but it's practically meaningless nowadays. Nowadays, impedance only matters in the following two ways:

1. A given amp can drive more power into speakers with a lower impedance than speakers with a higher impedance. But a 200W amp can probably go plenty loud with speakers of any reasonable impedance.
2. There's usually some minimum impedance that a given amp will be happy driving, but it's usually quite, quite low. Go below that impedance and the amp will think that the output is shorted and will current-limit (which you'll hear as clipping). This usually matters the most if you try to drive multiple sets of speakers simultaneously; placed in parallel, the multiple speakers may end up presenting too-low an aggregate impedance to the amplifier.

I haven't worried about speaker impedences for decades.

Atlant (talk) 13:24, 12 December 2007 (UTC)

Benzoylecgonine levels

Is a level of 0.06 mg/l pleural fluid of Benzoylecgonine considered high? 99.251.194.41 (talk) 00:58, 12 December 2007 (UTC)

Do you mean high for a cocaine user or high for a non-user? Rockpocket 01:28, 12 December 2007 (UTC)

I mean high for an occasional user.My son was in an accident (fatal) and his remains showed this level. He told me he never did cocaine. Obviously that was false. I am wondering if he did a lot or this level shows "occasional" use only.Houseman (talk) 22:29, 13 December 2007 (UTC) —Preceding unsigned comment added by 99.251.194.41 (talk) 02:03, December 12, 2007 (UTC)

Based on [1] and related Google results, 0.06 mg/L is a low but significant number. For typical cocaine consumption amounts, it suggests use more than 12 hours prior to death but less than 60 hours. Dragons flight (talk) 02:35, 12 December 2007 (UTC)

Please accept our sympathies for your loss. As Dragons flight notes, assuming typical consumption amounts, the data you provide can some idea as to the last time your son took cocaine prior to the accident. However, with this data alone its not really possible to infer anything meaningful about frequency of use. The best source of this information would probably be your son's friends. Rockpocket 18:02, 12 December 2007 (UTC)

Thank you Rockport, and thank you both for your replies. My sons friends aren't saying anything. They are 5000k from us in north western Canada. (I am on the east coast) Until we get out there and actually talk to them I guess we are in the dark as to what really happened. Houseman (talk) 22:28, 13 December 2007 (UTC) —Preceding unsigned comment added by 99.251.194.41 (talk) 01:52, 13 December 2007 (UTC)

Medicine

Do doctors use a lot of physics? Is it necessary to learn physics in order to get in medical school especially in new zealand? —Preceding unsigned comment added by 118.90.0.137 (talk) 02:35, 12 December 2007 (UTC)

No, and probably. I can't speak for NZ, but the equivalent of two semesters of college physics is required in the US. Dragons flight (talk) 02:38, 12 December 2007 (UTC)

I just remembered, medical school in the US is a post-collegiate program. Outside the US, many medical programs are post-secondary programs. In other words in those countries you enter a 6-8 year medical program instead of going to college, while in the US it is 4 year program beginning after college. Given that fundemental difference, the entry requirements are likely to depend on the structure of NZ medical school programs. Dragons flight (talk) 02:45, 12 December 2007 (UTC)

The amount of physics used, if any, depends heavily on the area of treatment that a doctor specializes in and the specific area of physics you are referring to. Both are extremely wide fields of study with a little overlap. -- kainaw™ 03:26, 12 December 2007 (UTC)

In practice, most doctors would not use much that we would recognize as 'pure physics' in their day-to-day work. Exceptions would include physicians in fields like radiation oncology and radiology, as well as certain branches of sports medicine, kinesiology, and the like. (Often doctors in these fields are supported by medical physicists: individuals with PhD rather than MD degrees who have intensive training in physics.) Some knowledge of physics is important (arguably, essential) to all doctors in order for them to be able to properly understand and interpret a wide range of diagnostic tests and physical maladies. I can't comment on the level of formal physics training required for doctors in Oz. TenOfAllTrades(talk) 04:06, 12 December 2007 (UTC)

Doctors practicing medicine do require an understanding of basic physics up to a certain degree, ie, interpreting CAT scan results or even perhaps reading the heart in some sort of way. —Preceding unsigned comment added by Hey mrs tee (talk • contribs) 04:37, 15 December 2007 (UTC)

I was curious about the system in NZ and had a look. It seems (but definitely don't take my word for it) that both Otago and Auckland have systems with a few different entry level one year courses common for all health sciences, from where you then move on to the actual Medical course. Auckland Uni has a web page[2] with a matrix of entry requirements. It seems physics is not explicitly required except as part of a requirement of having a certain number of credits in sciences. I might have misunderstood things, so I suggest you read through the pages linked from that one. There are contact phone numbers for questions about entry requirements, which might be a very good idea to call if you're about to make career decisions /85.194.44.18 (talk) 18:18, 15 December 2007 (UTC)

Physics is not an explicit entry requirement in Auckland as far as I know. However during your first year (the common health sciences first year) you will do a Physics course, Physics 160 (Physics for the Life Sciences). In my opinion, this paper is very easy, too easy if you have done physics before at secondary level such as at A-level. If you have not, you may find it a bit harder but, and I don't mean to be rude by this, if you find any of the first year papers too hard I'm not sure whether medicine is your calling. Bear in mind that medicine is extremely competitive. There are two entry streams I believe. Either you can make it in in your first year or after your first year. Your GPA or GPE is important in either case so if you don't make it in the first time, you would need to do well in the Physics paper Nil Einne (talk) 20:45, 17 December 2007 (UTC)

Chemistry (gases)

I'm supposed to find out the volume of NH3 (g) produced from 200 L of H2 (g), and the gases are measured at 350C and 400 atm.

I tried the PV/T, and a couple of other methods, but none of my answers still don't match up. Someone please help. --Jeevies (talk) 02:44, 12 December 2007 (UTC)

Chemistry always happens in ratios of moles: find out how many moles of H₂ you have, and then how many moles of NH₃ that makes (write a balanced net ionic equation for the reaction). Then figure out the volume of ammonia that that number of moles is. Are you given the amount of N₂ also (and therefore have to figure out the moles of that, and then the limiting reagent)? DMacks (talk) 02:55, 12 December 2007 (UTC)

How do I get the moles? Apart from that all the info I got was N₂ + 3H₂ -> 2NH₃ --Jeevies (talk) 05:56, 12 December 2007 (UTC)

For a rough answer you do not need to know as each mole of gas takes up the same volume at a given pressure and tempreature. You can see that there is 1 and a half times as many moles of hydrogen as ammonia, so the volume also follows the same ratio. However still you are assuming that there is enough of the nitrogen, and that the reaction goes to completion, this will need to be checked out. Graeme Bartlett (talk) 05:57, 12 December 2007 (UTC)

Oh, thanks a lot! I thought I was going insane for a while there. --Jeevies (talk) 06:36, 12 December 2007 (UTC)

Orange Ice Cream

I was discussing orange ice cream with some friends. This delicious treat sounds like a great idea. But, two questions come to mind.

1. Would the orange's citric acid curdle the milk?
2. Follow-up - what techniques do commercial orange-ice-cream makers use to prevent milk from curdling when adding acidic flavorings?

Thanks! Nimur (talk) 05:08, 12 December 2007 (UTC)

It doesn't seem to be an issue. (Perhaps the other ingredients, like sugar, dilute the acidic effect?). There are lots and lots and lots of recipes for orange ice cream on the web, and they all seem to just mix the ingredients together. - Nunh-huh 05:14, 12 December 2007 (UTC)

I had this idea that the citric acid doesn't affect the milk so much. I've seen it added to yoghurt for example Rfwoolf (talk) 10:05, 12 December 2007 (UTC)

What about having an orange sorbet instead? Lanfear's Bane | t 13:03, 12 December 2007 (UTC)

I've eaten lemon ice cream so it's obviously possible to make citrus-flavoured ice creams.

Atlant (talk) 13:31, 12 December 2007 (UTC)

It would be an easy enough experiment to do. Now, I have some citric acid but I have no milk here to try it with... --BenBurch (talk) 16:42, 12 December 2007 (UTC)

Citrus ice creams may be flavored mostly with zest, oils, or extracts, instead of juice. -- Coneslayer (talk) 16:46, 12 December 2007 (UTC)

Frozen Desserts by Liddell & Weir contains a recipe for orange ice cream, using the zest and juice of 3 oranges. While I will not reproduce the recipe here, the liquids are about 250 ml orange juice, 125 ml milk, and 500 ml heavy cream. -- Coneslayer (talk) 03:00, 13 December 2007 (UTC)

Today's xkcd

In today's xkcd, what's the solution to the problem? My intuition says 0, since $R_{t}^{-1}=R_{1}^{-1}+R_{2}^{-1}...+R_{\infty }^{-1}$, which the right side will be infinite. Since ${\frac {1}{\infty }}=0$, $R_{t}$ must also equal to 0 is well. Am I correct, and is there any formal proof on this problem? --antilived^{T | C | G} 06:07, 12 December 2007 (UTC)

At first I thought it might be zero, but now I think otherwise. Every possible path is in parallel. However, most of these paths are "very long" - so they act as a large resistor in parallel. At a certain path-length, these large resistors in parallel are negligible. The total resistance is dominated by the shortest path(s). Nimur (talk) 06:18, 12 December 2007 (UTC)

I'm going to boldly assert that the answer isn't zero or infinity. Here is a thought experiment: You have a close analogy of this problem if you stick two probes into the ocean about 1cm apart and try to measure the resistance of the sea water between those two points. The oceans of the earth are pretty darned close to being infinite compared to 1cm - and you don't expect to get either zero or infinity as the answer in that case. In fact, I think you'd be surprised if you could measure a different resistance in a bucket of sea water compared to the entire oceans of the world. So we know that the answer doesn't depend significantly on those longer paths. So it's easy to get an approximate answer.

So the real question here is: Why are physicists are only worth two points and mathematicians three? It ought to be the other way around because the physicist can say - "oh about three ohms" and carry on walking. Mathematicians are going to end up worrying about the contribution of an infinite number of paths - each with infinite resistance and wind up with infinity-divided-by-infinity - then FOOOOOMMMM! Maybe they mean theoretical physicists? (You see how you'd find it so hard to score points from a Ref Desk person? We're worth a LOT more than three points!) SteveBaker (talk) 06:42, 12 December 2007 (UTC)

It's definitely less than 3 ohms, since disregarding all the resistor outside the little rectangle drawn up by the two dots, there're 3 paths of 3 ohms resistance so it would be somewhere below 1 ohm IHMO. --antilived^{T | C | G} 07:02, 12 December 2007 (UTC)

F-ing xkcd! 4/pi - 1/2 ≈ 0.77 Dragons flight (talk) 08:16, 12 December 2007 (UTC)

How did you get that? --antilived^{T | C | G} 08:53, 12 December 2007 (UTC)

Q10 on the Google Test answers carries the answer; the paper Application of the lattice Green's function for calculating the resistance of an infinite networks of resistors explains in more detail. Laïka 12:32, 12 December 2007 (UTC)

Backing off a bit, let's consider the inner lattice of 7 resistors between the two points. Is the resistance in that 7-resistor lattice going to be ${\frac {1}{{\frac {1}{2}}+{\frac {1}{3}}}}$ ohms? It's been ages since I've studied physics or electronics so other than simple series/parallel stuff, I'm not necessarily up to snuff. Do I need to consider every possible non-repeating path between the two points in the calculation? Donald Hosek (talk) 17:19, 12 December 2007 (UTC)

For any reasonable answer, you need to consider every path that influences the answer. For example, if I had a 1 ohm resister in parallel with a 1 trillion ohm resistor and asked how many ohms the combined two are to the nearest ohm, it would be 1 ohm. The larger of the two is so large that it doesn't come into play enough to affect the answer. So, you have to consider every path between the two points that changes the answer within the precision you are looking for - which is not an infinite number of paths. -- kainaw™ 17:32, 12 December 2007 (UTC)

So for the seven-resistor lattice, I need to do something along the lines of ${\frac {1}{{\frac {1}{3}}+{\frac {1}{5}}+{\frac {1}{3}}+{\frac {1}{3}}}}$ then (assuming I found all the paths)? Donald Hosek (talk) 17:58, 12 December 2007 (UTC)

Just counting the paths isn't going to work, if those paths overlap... consider, two 2Ω resistors in parallel, vs two 1Ω resistors in parallel with another 1Ω resistor in series. Both have two paths, and all the paths are 2Ω... but the total resistances are 1Ω and 1½Ω, respectively... since, in the latter case, the two paths share a resistor. To solve the small 7-resistor case, you can collapse two pairs of series resistors (the corners that aren't the nodes you're trying to measure), and get 5 resistors arranged like a Wheatstone bridge (except with another resistor in the middle instead of a voltmeter... I only link to that article for the picture). You then need to use the Y-Δ transform on one of the two triangles, and you'll get two resistors in parallel with another two resistors, and a fifth resistor in series with the whole thing... which is solvable with just the series/parallel rules, to get exactly 1.4Ω. Phlip (talk) 22:49, 12 December 2007 (UTC)

We're also discussion that question in the german wikipedia. Thanks for your answer, Dragons flight - I'll post it on the german board. I didn't solve the problem, but was sure, that $0\Omega$ can't be right, since you need at least $0.5\Omega$ because each one of the two points is surrounded by 4 resisters with $1\Omega$ each.--Slartidan (talk) 12:37, 14 December 2007 (UTC)

Geomagnetism

It is taught that the earth has a molten iron core.How does the molten iron core of the earth support permanent magnetism.Molten iron is not usualy permanently magnetic.82.15.53.173 (talk) 10:00, 12 December 2007 (UTC)

It's not a permanent magnet. See geodynamo. It is more analogous to an electromagnet, where the magnetic field is generated by moving charged fluids. Dragons flight (talk) 10:10, 12 December 2007 (UTC)

Also, your initial statement was not completely correct. While the Earth's outer core is molten, the inner core is solid, due to the higher pressure. StuRat (talk) 12:04, 12 December 2007 (UTC)

Dragons flight and StuRat are both correct. The earth's core is theorized to be a solid, mostly iron, crystal that is extremely hot, due in part to the enormous pressure that it is under from the gravitational energy of all the mass of the planet pushing in to the center. However, there are also several other possible reasons that the core of the planet is so hot: 1) leftover heat from the initial accretion phase during which time most of the planet was molten, and 2) heat that is generated from radioactive minerals that are within the earth, 3) the theory that within the earth's inner core there is a fission reactor process known as a Georeactor that produces heat, and 4) heat created through the solidification of the inner core. The reason that the inner core of the earth is not molten, though, is due to the fact that there is just so much pressure that it has been squeezed into a solid mass, instead of a liquid ooze. As one journeys away from the center of the earth, the pressures begin to let up, since there is less mass lying above to push down, and as the pressure is eased, the extremely hot iron no longer is being forced into a solid state, and therefore it becomes liquid, or molten. This is why the outer core and the mantle layers of the earth are molten. Then, of course, the crust of the planet's surface is hard, due to the lack of pressure and also to the cooling effect of being exposed to the thin blanket of ocean and atmosphere before encountering cold space.

Now, as the earth spins on its axis, parts of the interior of the planet spin at slightly different rates from one another. Think of this in terms of when you try to spin a fresh unboiled egg. The egg will very quickly lose its spin. However, if you hard boil the egg, it spins much better because it is solid all the way through. The liquid parts inside a fresh egg want to spin at different velocities from the outer shell, and this is why it doesn't spin so well. With the case of the earth, the inner layers are spinning at different rates from one another - specifically, the inner solid core is spinning at a slightly different rate than the liquid outer core and mantle, which also spin at a slightly different rate from the crust. What this creates is the condition in which iron molecules are passed against one another as these different layers rub against each other due to their different spin rates. Whenever you have such a situation of iron molecules rubbing against other iron molecules, you have created a dynamo (or generator), as Dragons flight described above). What happens as the iron molecules pass one another is that ions are stripped from the molecules and then caught up in the pre-existing magnetic current that makes up the magnetosphere through a process known as Faraday's law of induction. Think of this in terms of a pump pushing water along a closed system. So this is what creates the magnetosphere of the earth, which in turn helps to shield the earth from bombardment of harmful levels of radiation that come from the sun. Most planets that we know of do not have a magnetosphere. We're lucky to have one.

References:

Schneider, David (Oct 1996) A Spinning Crystal Ball, Scientific American

Lehmann, I. (1936) Inner Earth, Bur. Cent. Seismol. Int. 14, 3-31

Herndon, J. Marvin (1996) Substructure of the inner core of the Earth Vol. 93, Issue 2, 646-648, January 23, 1996, PNAS

http://www.nytimes.com/2005/08/25/science/25cnd-core.html

-- Saukkomies 09:27, 12 December, 2007. (UTC)

Sigh. For the second time in two days on this board, the mantle is a solid (specifically a rheid). Dragons flight (talk) 15:16, 12 December 2007 (UTC)

Another small correction to Saukkonies' explanation - pressure by itself does not generate heat, because a stationary force does not transfer energy. Gravitational energy could only be transformed into heat energy if the Earth were contracting, which it is not. Our article on geothermal geology gives a list of the sources of geothermal energy. Gandalf61 (talk) 16:52, 12 December 2007 (UTC)

I stand corrected. Thanks for pointing this out to me, since geology is one of my favorite subjects, and lo! I find I've been under misconceptions in these regards for so many years. ::-- Saukkomies 16:39, 12 December, 2007. (UTC)

sources

wiki pls give two sources of information about water quality in kerala202.88.234.8 (talk) 10:02, 12 December 2007 (UTC)

For these general sorts of questions, google is often a great place to quickly find what you want. See here. Someguy1221 (talk) 10:56, 12 December 2007 (UTC)

Pigeons always pecking the tarmac for invisible food

Does anybody know what the city (and suburban) pigeons are always pecking? They seem to always walk around pecking even when there is clearly no food. I considered that might be pecking small seeds or breadcrumbs but from my observation this doesn't seem to fit - such things aren't scattered so abundantly in the suburbs and city. Maybe they are actually eating small stones, or grains of salt. Rfwoolf (talk) 10:04, 12 December 2007 (UTC)

Some birds' digestive systems rely on having small stones in their digestive tract to help grind food. They're sometimes referred to as "gizzard stones", but are apparently properly known as Gastroliths. EvilCouch (talk) 11:38, 12 December 2007 (UTC)

Thanks! That seems to answer the question. "...Particles as small as sand and stones the size of cobbles or greater have been found" " Domestic fowl, for instance, require access to 'grit', for the purpose of food-grinding." Thanks. Rfwoolf (talk) 11:47, 12 December 2007 (UTC)

why frogs disappear

give me atleast two explanations for why some frogs are disappearing world wide202.88.234.8 (talk) 10:05, 12 December 2007 (UTC)

As in the above, google is a great first place to look. Someguy1221 (talk) 10:57, 12 December 2007 (UTC)

Decline in amphibian populations and Frog#Distribution_and_conservation_status are other good places to look. SteveBaker (talk) 12:48, 12 December 2007 (UTC)

But some are on the increase - see cane toad, particularly about what's happening Down Under. -- JackofOz (talk) 19:44, 12 December 2007 (UTC)

carrying capacity

define human carrying capacity202.88.234.8 (talk) 10:09, 12 December 2007 (UTC)

Carrying capacity is very well defined. Applying the concept to humanity is notoriously debatable, and attempts are discussed in that article. Someguy1221 (talk) 10:54, 12 December 2007 (UTC)

I think we can all agree only on the concept that there is a carrying capacity. Personally, I think we are ultimately limited by arable land unless we can make some real breakthroughs in hydroponics, sea-farming, or completely synthetic foodstuffs. --BenBurch (talk) 16:48, 12 December 2007 (UTC)

It is very well proven that there is a carrying capacity for most species in the wild. This is a dubious concept when applied to the global human population as humanity as a whole has yet to reach a point where further growth is completely unsustainable, as shown by the fact that the human population of the world has yet to cease to grow. While this may be accounted for by the fact that many populations overshoot their carrying capacities, it seems unlikely as humanity seems to be able to increase its available food supply due to advances in agricultural technology and placing more land under cultivation. That being said, there is much histrical evidence to suggest that there were carrying capacities for localized, pre-industrial human populations such as that of France immediately prior to the Black Death. This population reached a plateau immediately before the population crisis of the 14th century, and this plateau is theorized to have been the maximum possible population supportable by the area. Thus, while some human populations have reached a "carrying capacity" in the past, it is a matter of opinion whether this point can be reached in the human population at large, as technological advancements and population isasters are unforseeable in the future, and would cast into doubt any unequivocal statement that there is, in fact, a human carrying capacity.137.186.246.104 (talk) 21:33, 13 December 2007 (UTC)ÊĴÁŶ

No matter how far technology advances, there is a finite carrying capacity for humans.

• Assuming that the entire surface area of the Earth (land and water) is used for photosynthesizing food as efficiently as possible, the carrying capacity is on the order of 10¹⁴ people.
• Assuming that the entire solar output intercepted by the Earth is converted directly to food, the carrying capacity is on the order of 10¹⁵ people.
• Assuming that the entire solar energy output is converted directly to food, the carrying capacity is on the order of 10²³ people.

Of course, at these population levels, the standard of living wouldn't be very good: all available resources are being used for the sole purpose of keeping people alive. --Carnildo (talk) 22:50, 13 December 2007 (UTC)

Gravity

When I worked in a coal mine, I felt that coal was lighter to shovel, than when on the surface.Are things lighter when below the surface considering the mass of the earth that is now above and acting contrary to the normal pull of gravity?Could this effect be percieved by a young miner?Are things perceptively lighter in a submarine as it goes deep under the sea?82.15.53.173 (talk) 10:18, 12 December 2007 (UTC)

If you assume the Earth is uniformly dense, then by Newton's law of universal gravitation the strength gravity inside the earth is directly proportional to your distance from the center of the earth. So even if you're three kilometers beneath the surface of the earth, you're only 0.05% closer than you were at the surface, and so gravity is only 0.05% weaker. While you could certainly measure the difference with a good balance, this would not be perceptible at all. Someguy1221 (talk) 10:51, 12 December 2007 (UTC)

See shell theorem. StuRat (talk) 11:48, 12 December 2007 (UTC)

This is a wild guess, but if the tunnels are on a slight gradient - and I think that it usually the case - you wouldn't normally notice it as you have no frame of reference underground such as a horizon. However, shovelling coal would be easier if you were moving it downhill, even though your brain assumes you are moving it on the level.--Shantavira|^{feed me} 11:15, 12 December 2007 (UTC)

If gravity is 0.5% weaker, a 30-pound shovelful will be 2.4 ounces lighter. As one who has shoveled all day several times in his life, I think I can say that that weight reduction would become noticeable by about 3 in the afternoon. --Milkbreath (talk) 21:28, 12 December 2007 (UTC)

But Someguy1221's calculation is off by a factor of 10 – i. e. 3 km is only 0.05%. Icek (talk) 22:35, 12 December 2007 (UTC)

I have no idea what you're talking about. Someguy1221 (talk) 04:04, 14 December 2007 (UTC)

*LOL*. Correcting a mistake and saying it never happened... Icek (talk) 11:37, 14 December 2007 (UTC)

Maximum/minumum temperature forecasts.

In South Africa the temperature forecast is first the minimum (morning) and then the max (afternoon)[3]; but I've seen British[4] and American[F] forecasts put the max first. Are these minimums the next morning's, or are they just the wrong way round? -- Jeandré, 2007-12-12t13:47z

In US forecasts, the high usually comes first, followed by the "overnight low" that occurs after it. So they give the "Saturday High" that probably occurs Saturday afternoon, then the "Saturday Low" which occurs "Saturday night", but is probably actually early Sunday morning. (It is common here to say "Saturday night" to describe the time between going-to-bed Saturday and waking up on Sunday. This imprecision results in people saying things like, "So Saturday night, the phone rings at 3 in the morning...") -- Coneslayer (talk) 14:06, 12 December 2007 (UTC)

Respiration protocols

Some mammals were treated to three different respiration schemes: group 1: 6.2±0.4 ml/kg VT (PIP 40/0), 30bpm, 95% O2; group 2: 6.2±0.4 ml/kg VT (PIP 40/0), 30 bpm, 95% N2; group 3: PEEP 5cmH2O, 95% O2. I'm trying to figure out what this means. Where it says VT, by the way, T should be subscript.

30 bpm? Beats per minute? I tried searching with google but can't figure it out. I've found out that PIP = positive inspiratory pressure and PEEP = positive end expiratory pressure - does PEEP make it harder to breathe out and therefore generally harder to breathe than PIP? Also what's the 6.2±0.4 ml/kg VT in groups one and two about and the reference to H2O in group three? Thanks for any insight. --Seans Potato Business 16:04, 12 December 2007 (UTC)

I assume that bpm in this context is breaths per minute. 5 cmH₂O is a pressure of five centimeters of water. (A column of water five centimeters tall will exert this much pressure at its base.) One centimeter of water is equivalent to 0.76 mmHg or 98 Pascals: [5]. I wouldn't want to guess at the rest. TenOfAllTrades(talk) 16:19, 12 December 2007 (UTC)

VT = VD + VA. That is... The tidal volume (VT or TV in some textbooks) = the alveolar ventilation (VA) + the dead space (VD). For someone who is not a critical care nurse.... The tidal volume is the amount of air which is normally inhaled and exhaled during breathing.

PIP is the Peak Inspiratory Pressure (the pressure difference between the ventilator and the lungs results in inflation until the peak pressure is attained, and passive exhalation follows)

PEEP is correct = Positive end-expiratory pressure. You will only see the reference to H2O when talking about PEEP. It is the positive resistance that is applied to exhalation. This pressure keeps the small airways open though the entire ventilation cycle.

So. Group #1 had 5.8 to 6.6 mL per kg of 95% oxygen in their tidal volume with a PIP (Peak Inspiratory Pressure) of 40/0 and a rate of 30 BREATHS per minute.

Group #2 was the same ventilator settings but they used Nitrogen as opposed to Oxygen.

Group #3 I suspect was the same as group #1 with the addition of the PEEP to the ventilator settings.

Look here for a crash course: http://www.emedicine.com/emerg/topic788.htm

Hope that helps... ICU RN

Gold that's heavier than pure gold?

I've finally decided to finish the damn Baroque Cycle, having read the first two when they came out and then just put it aside. So I read the second one again (having totally forgotten everything that had happened) and have now just begun with the third book, The System of the World. A major plot point in books two and three is concerning something called "Solomonic Gold", that is, Gold that is heavier than ordinary gold. Newton and others use a lot of alchemical mumbo-jumbo to try and explain this ("It is infused with the Philosophick Mercury!", etc.) , however what is clear is that in this book this is a real metal. Is there such a thing? Can you perhaps make "heavy" gold much like heavy water, by only selecting larger isotopes? Or is it an alloy with some other heavier metal (depleted uranium-gold?) Or did Neal Stephenson just make this up? 83.250.203.75 (talk) 18:43, 12 December 2007 (UTC)

Gold only has one stable isotope (197). The only other nearly stable isotope is 195 with a half-life of 186 days. So, you'd find it very difficult to make heavy gold using heavy isotopes. -- kainaw™ 18:52, 12 December 2007 (UTC)

Gold-Osmium alloy? Osmium is the densest known element. Although, platinum is also more dense than gold and is used in jewelery, too. — Scientizzle 18:56, 12 December 2007 (UTC)

I haven't read the book, but I've spoken to people who have, and I'm reasonably sure the damn stuff is infused with the Philosophick Mercury. Thus Stephenson has decided to make some of alchemy true rather than make up an isotope. Algebraist 21:33, 12 December 2007 (UTC)

He really doesn't explain why the gold is heavier than it should be. A modern reader should probably assume he's talking about an isotope - but (as already explained) that doesn't really work. The point is that the book is written from the point of view of a 17th century alchemical society - and the impact of screwy gold on their currency would indeed be problematic. I suspect (from Stephenson's writing style) that we'll find out more in subsequent books. The business of the same family names carrying on between the Barque Cycle and the Cryptonomicon - and one of the characters in it seeming to be immortal means that the science within those stories cannot be taken as literally true. The mythic compactness of the Qwelgmian language - and a whole lot of other things he talks about - are also impossible. However, the Cryptonomicon is certainly in my top 10 list of best ever works of fiction - the Baroque cycle...is too long to re-read - so I'm not sure! SteveBaker (talk) 00:18, 13 December 2007 (UTC)

• Is it possible he's referring to Growth of High-Density Gold Nanoparticles on an Indium Tin Oxide Surface Prepared Using a "Touch" Seed-Mediated Growth Technique? I've only read Cryptonomicon, so I don't have a complete grasp as to whether Stephenson was attempting to make a real-world reference or creating a fictional substance. --M@rēino 14:34, 13 December 2007 (UTC)

Aliens

What is the probability for the existence of aliens? 64.236.121.129 (talk) 19:19, 12 December 2007 (UTC)

See Drake equation, and consider refining your question. Do you mean aliens we will make contact with in your lifetime? Aliens in our galaxy? Aliens anywhere in the universe? If it's aliens anywhere in the universe (with no requirement that we ever find out about them), then the only realistic answers are 0 (if you believe that we are the unique creations of God, for example), or 1 (if you don't). It would require incredible fine-tuning for life to exist on one and only one planet in the universe. -- Coneslayer (talk) 19:26, 12 December 2007 (UTC)

The probability for aliens to exist somewhere in the universe at some time is so high as to be almost certain. The probability for aliens to exist within the brief (geologically speaking) lifetime of the human race with the ability of physically visiting us on earth is so low as to be almost impossible. There's a lot of wiggle room in between. Personally I take a very pessimistic view of the Drake equation—it makes the idea of any sort of communication (defined as two-way contact, not simply "an alien picks up one of our radio signals someday, long after we're gone") at all seem practically impossible. --24.147.86.187 (talk) 19:48, 12 December 2007 (UTC)

The Drake equation and all speculation on the matter depend on an unknowable variable, what the probability is that life will spontaneously arise given the right conditions, leaving aside mystical ideas about the genesis, no pun intended, of life. Some think the probability is high, or even one. With a tip of the hat to Descartes, it's obviously not zero. The area in between is the very best sort of ground to grow unending pointless debate in, so I'm not going to tell you what I myself think. --Milkbreath (talk) 21:21, 12 December 2007 (UTC)

The problem with the Drake equation is that we have a good idea of the first factor, are working on the second and third, and know nothing whatsoever about the remaining 4. Incidentally, the fact something has happened does not imply its probability was non-zero, at least in the usual mathematical theory of probability. That reminds me: someone ought to point out that questions of the form 'what is the probability of [event in real world]' are fraught with philosophical difficulties. For an extreme example, one could say that the existence of aliens is nonrandom (they either exist currently or they don't) so the answer is 1 or 0 depending on whether they exist or not. Algebraist 21:30, 12 December 2007 (UTC)

If you're interested, there's a recent Damn Interesting article on the odds of aliens and radio communications with them titled "Space Radio: More Static, Less Talk" that includes an interactive Drake equation calculator. You can plug in your own figures and it will give an estimate for the number of communicating civilizations in the Milky Way galaxy. -- HiEv 23:42, 12 December 2007 (UTC)

Technically - there is nothing wrong with the Drake equation - the problem is only with the numbers you plug into it. However, because we know that humans exist, none of the parameters of the equation can possibly be zero. Hence, if the universe is large enough - there will be other lifeforms out there. However, knowing that there are definitely aliens out there is a very different thing from being able to detect them - let alone communicate, meet, cooperate with. The section of the universe that we can ever reach is finite - and that section could be utterly devoid of alien species if the numbers in the equation are small enough. SteveBaker (talk) 23:53, 12 December 2007 (UTC)

Oh - yeah - the other thing about the Drake equation is that it doesn't predict the number of populated alien worlds (which I guess is what the OP is asking) - but the number that have intelligent aliens, that know how to make big radio transmitters and who decide to transmit and who are in roughly the same phase of technology that we are (so they aren't trying to communicate by wormholes or something) and who havn't died out from global warming or nuclear holocaust or something. If you just want to know whether there are primitive alien bacteria out there - then the odds are not only much better - but the answer has a lot fewer unknowns in it. SteveBaker (talk) 00:02, 13 December 2007 (UTC)

SETI doesnt seem to have found any evidence of extraterrestrial intelligence. So draw your own conclusions--TreeSmiler (talk) 02:16, 13 December 2007 (UTC)

I lost what faith I had in SETI when I read somewhere (source forgotten, I fear) that if our present radio emissions had (by the intervention of mischievous time-travelling aliens perhaps) by humanity 50 years ago, then they would have considered it random noise due to the complexity of modern coding. (Hopefully someone here will know if this is a load of marsh gas) Algebraist 02:49, 13 December 2007 (UTC)

That seems quite unlikely. Digital signals are most certainly not natural analog noise. Would the encoding be decipherable? Perhaps not; MP3 isn't really intended as a first-contact codec. It would absolutely be artificial though. — Lomn 04:13, 13 December 2007 (UTC)

Power and duration are also obvious give-aways. Artificial radio signals will always make the detected signal louder than noise, since they add to the noise, and a sudden burst of radio waves that lasts three minutes before suddenly disappearing is definitely conspicuous. The Wow signal is the strongest candidate for an extraterrestrial transmission because it was the most powerful signal Big Ear ever detected, and because it was only received once. --Bowlhover (talk) 06:05, 13 December 2007 (UTC)

That's not entirely true. To make the most possible use of the available spectrum, you need to use data compression techniques. An advanced civilisation still only has the same amount of available spectrum as we do - but they need to send full holographic smell-o-vision movies instead of boring 2D television and such - so they need to resort to techniques like data compression to make the optimum use of it (this is already happening here on earth with analog TV being replaced with digital TV). Our Satellite TV (for example) is both data compressed AND encrypted. The thing about data compression is that it's goal is to remove any semblance of regularity from the signal since regularity can be exploited to further compress the data. The goal of encryption is also to take away any patterns that might be recognisable and to turn them into patternless noise. So compressed and/or encrypted data comes to resemble white noise - a completely irregular, unpredictable stream. It follows then that any civilisation that's even a teeny bit more advanced than we are (say 20 years ahead) - or who simply made better decisions than we did 50 years ago when designing TV transmission standards - would be producing signals that closely resemble white noise. Worse still, we know that 'spread-spectrum' transmission (such as military battlefield communications) and 'frequency hopping' (as in cellphones) makes more sense than the system of descrete bands that we currently use for most of our radio traffic. If the aliens did that, we'd have a heck of a time figuring it out. We'd see white noise, evenly distributed across the parts of the spectrum that their atmosphere transmits comfortably. So the idea that we can use signal-to-noise ratio to detect their routine internal transmissions is a non-starter because no sufficiently sophisticated societies are sending anything with a noticable signal - it's ALL noise to the uninitiated! If we detect a high power white noise source, we're going to assume it's any one of a large number of natural sources - stars put out tons of noise - we would just assume that there was a strong, natural, radio source in that direction. The only signals we're going to be able to figure out are the ones that are sent deliberately towards us - and using a simple enough scheme that any reasonable civilisation would be able to understand it - a prime number sequence - the binary digits of PI - that kind of thing. SteveBaker (talk) 18:28, 14 December 2007 (UTC)

I've always found it interesting that science fiction portrays aliens as being only a little more advanced than us. If there really were intelligent beings who were capable of visiting us, there is a good chance that they would be not just thousands but millions of years ahead of us technologically, and would regard us as we regard animals. Rather than beaming "hi there" messages into space we should be keeping our heads well down.--Shantavira|^{feed me} 09:39, 13 December 2007 (UTC)

Indeed. Think of how we treat chimps, then wonder whether you want advanced aliens noticing us... Skittle (talk) 15:59, 13 December 2007 (UTC)

Absolutely. People slaughter animals that pose no threat to us what so ever, all the time. Indeed, people hunt some of them for fun even. People test experimental drugs on them to see if it will kill them or not. And if it doesn't, they kill them anyway (see animal testing). Hell, people even enslaved other humans because some people thought they were inferior. Why would an alien civilization millions of years ahead of us, treat us like equals? 64.236.121.129 (talk) 15:26, 14 December 2007 (UTC)

• If you'd like an entire book on the subject, I recommend Lonely Planets by David Grinspoon. Or anything by the late Carl Sagan; his theories have held up pretty well over time. --M@rēino 14:36, 13 December 2007 (UTC)

Backcrossing

MyD88-/- mice were generated as described and backcrossed for 9 generations on an H-2d (BALB/c) background. - what's the backcrossing necessary for? --Seans Potato Business 20:15, 12 December 2007 (UTC)

When generating knockout mice, it's generally necessary to mix two different strains of mice. Backcrossing is used to reduce the genetic components of one of the founding strains. — Scientizzle 21:16, 12 December 2007 (UTC)

Here is an ugly graphical representation. After several generations of backcrossing, one can assume that the only non-BALB/c DNA in these mice is from the regions flanking the knocked-out gene — Scientizzle 21:21, 12 December 2007 (UTC)

That's great; thanks. So you only need to perform backcrossing when you have the knockout in a different genetic background than the one you want? Would it not be simpler to have performed the knockout in the genetic background in which you wanted it in the first place? Are some backgrounds in some way easier to use for producing knockouts? --Seans Potato Business 22:07, 13 December 2007 (UTC)

The [[formation of a genetic knockout mouse is moderately complex. A genetically modified embryonic stem cell of strain 1 is placed in the developing blastocyst of strain 2. In order to determine the efficacy of the implantation (and to plan subsequent breeding), it's useful to produce a chimera of strains with different coat colors. There's more information at Knockout mouse. — Scientizzle 22:22, 13 December 2007 (UTC)

But the diagram you link to uses three different strains. One cell type endures the knockout and is put into a blastocyst of another type. They then try to get the transgene in a C57BL/6 background by "backcrossing". If they (the scientists involved) had used C57BL/6 cells in the first place, they could put those cells in the same blastocyst as before, breed with a C57BL/6 mouse, and just like that, all the black offspring are heterozygous for the knockout and fully C57BL/6; no backcrossing necessary. --Seans Potato Business 13:30, 15 December 2007 (UTC)

Ice Cream

I've heard that you can die from eating re-frozen ice-cream, because of salmonella. Is this true? —Preceding unsigned comment added by 89.242.7.45 (talk) 21:23, 12 December 2007 (UTC)

I assume it would depend on how long it was defrosted for. If it was long enough for a significant salmonella colony to develop then yes - you could certainly have active salmonella in the icecream when you eat (and thereby warm it up). But if it only defrosted a little bit on the way home from the store, I can't believe there would be a problem. SteveBaker (talk) 23:30, 12 December 2007 (UTC)

Not to mention salmonellosis isn't typically fatal, although it isn't the most fun experience in life. --Bennybp (talk) 04:58, 13 December 2007 (UTC)

• Some (nice) ice cream is made with a custard that contains lightly-cooked eggs, so the risks are the same as for raw eggs. --Sean 00:01, 14 December 2007 (UTC)

Light perception and evolution

Little background: Sun and moon have been present around earth since quite some time before the evolution started taking place. Specifically, humans have always seen during the whole evolutionary process either sun or moon at any point of time in the whole day. During the day, sun emits light in the whole electromagnetic spectrum, but due to the intense temperature in the sun, its peak wavelength of radiation lies around 550 nm (middle of the spectrum that we actually see). In the night also, moon shines earth by the reflected light of sun that falls on the moon, then again the peak is around the 550 nm. Since light around nature is abundant in this wavelength range, we have actually adapted ourselves to sense the light in this range only.

The question: However, I must say that all bodies on earth (e.g. solid bodies or living organisms etc.) have been emitting infrared radiation also at all points of time ever since humans started evolving. Yet, we can't sense infrared radiation. My question is what could be the reason for this selective evolution. Is it because of the fact that intensity of infrared radiation always tends to be much less than that of the normal visible light that is found in the nature. But then, why did some other creatures develop this infrared sensing feature? And ultraviolet light is generally not present at all in the nature in normal circumstances, yet some creatures develop this sensing also. Why did humans lose? Does it have to be something related to the human intelligence also? DSachan (talk) 22:21, 12 December 2007 (UTC)

You've got a lot of "human exclusivity" in that question ("Why did humans lose?") but keep in mind that homo sapiens may not have gained/lost anything that primates, mammals, etc. had before that. To my knowledge no mammals can see very far into the infrared or into the ultraviolet (as we humans define the visible spectrum), it's not a human-specific thing, you're probably talking about mammal eyes in general. (Some reptiles can see in the infrared, and with bugs and shellfish and etc. there is a whole variety in types of eyes and what they can see.) It probably has nothing to do with humans in particular. --24.147.86.187 (talk) 22:38, 12 December 2007 (UTC)

Given that infrared radiation has also been present all the time in addition to the visible radiation, why did we not evolve to the see this kind of radiation? You did not answer my question. DSachan (talk) 22:45, 12 December 2007 (UTC)

I wasn't trying to answer the question, I was just pointing out that you're probably asking the wrong question. The "right" question (in my mind) is not centered on humans but mammals in general; if mice can't see in the infrared (and as mostly noctural animals you'd think they'd have a lot more to gain from it than humans, who sleep all night and wouldn't benefit much), then humans probably aren't going to have evolved it. --24.147.86.187 (talk) 00:47, 13 December 2007 (UTC)

It would be very hard for an animal that can see in the infrared to get around during the day. Everything would be really bright to them. It would give some advantage when it is really dark but most nocturnal mammals get by without it. Shniken1 (talk) 23:13, 12 December 2007 (UTC)

I don't understand this answer. Why would everything necessarily be "really bright"? Why couldn't they just have a less sensitive retina, or smaller pupils, or something? What part of the spectrum are we talking about here, anyway? —Keenan Pepper 23:19, 12 December 2007 (UTC)

First, let me point out that infrared refers to a much wider range of wavelengths than visible light. "Thermal infrared", emitted by objects around room temperature and with a wavelength about 10 microns, is very different from "near infrared", which is only emitted by very hot objects and has a wavelength around 1 micron.

I think the main reason why animals didn't evolve eyes capable of seeing thermal infrared is because it's fundamentally harder to see those frequencies. It's the same reason why thermographic cameras are in general so much more expensive than visible light cameras. One of the problems that comes up in making thermal infrared cameras is that the inside of the camera should be dark to make good low-noise images. For visible light, this is easy, but for thermal infrared it's quite difficult, because most things glow in the thermal infrared spectrum. That's why good thermal infrared cameras are cryogenically cooled. If an animal had some kind of thermal infrared eyes, it would have to have a way of keeping them cold, which would probably take a lot of metabolic energy that could be used for other things.

That's just the first problem with thermal infrared eyes that comes to mind. I don't think it has anything to do with humans in particular. —Keenan Pepper 23:16, 12 December 2007 (UTC)

The question is not what we COULD evolve (there are owls that can see in the infrared and bees can see in ultraviolet) - it's what is efficient for us to evolve. We would need more sensors in the back of our eyes to be able to see in IR. So either:

• We'd have fewer sensors for colour - but we need daylight colour perception for finding juicy ripe red fruit in the green leaves of a tree - and to distinguish a brown rotten apple from a fresh red one. That failure would be selected against - so IR vision would vanish from the gene pool.
• Or - we'd need bigger eyes...think "Owl". But bigger eyes would require either:
  • A smaller brain. (definitely contrary to what humans needed to survive).
  • A bigger head. But we already are right on the edge of what size head will fit down a womans' birth canal - the death rate from giving birth (without medical assistance and before ceasareans) is already alarmingly large - making it worse would be a problem. Women could perhaps also evolve larger birth canals - but I'm sure there are problems consequent on that change.

So it's impossible to get IR vision without losing something else. Since we sleep at night and gather food in the day - there isn't a VAST benefit to IR vision - but there are significant costs in terms of lost colour vision or smaller brains or larger incidence of birthing problems.

But in any case, evolution doesn't always find the optimum path - it selects the best genes from what shows up from breeding and mutation. If an IR vision mutation never shows up - we'll never evolve it. SteveBaker (talk) 23:21, 12 December 2007 (UTC)

Great answer as usual, Steve! —Keenan Pepper 23:43, 12 December 2007 (UTC)

SteveBaker really should have his own phone-in show! He knows about everything from Mathematics to Computer Programming to Evolution to Red Squirrels !!! Unbelievable! It is sad that someone so smart and helpful is here on the Wikipedia (only as in relation to) while a certain other man, not so smart or helpful is the most powerful person on the planet. That said, hopefully the Wiki will be here forever. I think it is one of the most important projects of our time! So please stay SteveBaker! Saudade7 23:49, 12 December 2007 (UTC)

I have a hard time deciding whether or not I'd like to be Oliver ;-) hydnjo talk 00:52, 13 December 2007 (UTC)

There are animals that can see thermal infrared: the pit vipers. However, they also demonstrate the limitations of being able to see thermal infrared. They can only detect objects that are warmer than the environment (imagine not being able to see plants or any cold-blooded animals) and the resolution is far lower than that of the human eye (imagine not being able to tell the head of an elephant from its rear). --Carnildo (talk) 00:43, 13 December 2007 (UTC)

Hold on. Pit vipers can sense thermal infrared, but they also have functioning eyes - they see plants and cold-blooded animals as well as any other snakes. They also happen to use a niche that's quite different from people and which heavily favours their use of IR sensing. Being a reptile, they don't need to worry so much about 'overloading' their sensor pits since they assume background temperature. They also hunt warm-blooded prey in the cool night-time desert, where IR detection would be very useful and normal sight less so. Matt Deres (talk) 00:31, 15 December 2007 (UTC)

First of all, evolution is not "directed", it's "opportunistic". This means that species usually don't evolve properties that will become useful, but are not currently useful, nor do they have fully-formed complex features spring into place. Instead, minor traits are adapted into complex features if there is an opportunity and a benefit for that to occur, and then evolution continues to refine it if possible. In other words, just because a trait may have advantages, doesn't mean a species will ever get the chance to evolve it.

Second of all, larger animals don't sense infrared with their eyes because IIRC the lens is opaque to infrared. (I couldn't find any good site that says owls see IR, and here is an unscientific test where an owl couldn't see IR.) Precision thermoception is normally done using pits, such as the ones on the heads of snakes or in the noses of some bats, that contain an especially thermo-sensitive membrane. However, as the latter article notes, the accuracy of that sense is rather poor.

Finally, some adaptations have tradeoffs. For example, such a sense organ might be easily damaged by cold or prone to damage and infection. Or, it could be that it also requires "expensive" to produce materials to create such a sensor. Thus, such an adaptation might not be worth the cost. The fact that so few species have thermoception suggests that this might be the case.

So, the answer is that it may not have been worth it for most mammals to evolve thermoception, and even if it is/was, there may have been little or no opportunity to it to evolve. -- HiEv 02:21, 13 December 2007 (UTC)

• "there are owls that can see in the infrared"<-- can you provide some references? --JWSchmidt (talk) 02:52, 13 December 2007 (UTC)

evolution is not "directed", it's "opportunistic". Love this! Excellent quick summary of a lot of ideas. DMacks (talk) 03:03, 13 December 2007 (UTC)

Directed evolution being something else, obviously:) DMacks (talk) 16:10, 13 December 2007 (UTC)

• "We would need more sensors in the back of our eyes to be able to see in IR" <-- why? What kind of sensors are you talking about? --JWSchmidt (talk) 06:06, 14 December 2007 (UTC)

The answers so far are mostly dealing with infrared vision. What about the other end of the spectrum: Ultraviolet? I believe that I have read that common whitetail deer can see in the ultraviolet. Some things that look dull and drab to us, supposedly 'glow' with brilliance to them. And deer, though not primates, are mammals. So, what about ultraviolet vision? Zescanner (talk) 19:45, 13 December 2007 (UTC)zescanner

some animals that see ultrviolet, some reading. --JWSchmidt (talk) 06:06, 14 December 2007 (UTC)

Some people with a damaged or missing lens in their eye(s) can see ultraviolet light too. See the Aphakia article. Of course, without the lens blocking UV light, the retina is more prone to damage by it. Sunburn your skin, you'll recover; sunburn your retina, that's bad. -- HiEv 23:45, 14 December 2007 (UTC)

This was actually a question on the general/introductory chemistry final (hi, Prof. Doll!) I had in college: why we see in the range we do, vs deep (an order of magnitude or so) into IR or UV. DMacks (talk) 06:28, 15 December 2007 (UTC)

While I too am a fan of Steve’s, I DON’T think this is one of his best efforts at all, nor is evolutionary theory a strong suit of his. What he says is that we don’t see in ultraviolet because we would need bigger eyes, ergo bigger heads, ergo the birth canal would not be equipped to deal with it. This is just plain silly. Does that mean marsupials could see in ultra violet? This is treating evolutionary theory as a series of Just So stories. You can always invent ad hoc stories about “how things got that way”. Try this. Humans have purple skin because they don’t have fur, so they need something to camouflage them in the dark. I would guess that most living things can’t see in outside the conventional spectrum because there is very little there that would enhance their survival. In fact, most animals apart from primates, birds, and some sea creatures don’t require much in the way of colour vision at all. Bees can see in the ultraviolet, possibly because some flowers have patterns that can be discerned in that range. In such a scenario, infra and ultra vision can be enhanced by way of symbiotic evolutionary processes. In a way, it is a pity. If humans could see just a little in the infra and ultra ranges, we would see a far more spectacular night sky, more in line with the Hubble Space Telescope images of vast red and purple galaxies. But Nature sure is a no – nonsense boss – we don’t need such tools to survive, so we don’t get them. Myles325a (talk) 00:19, 18 December 2007 (UTC)

December 13

loss of power in optical frequencies

Is there a way to work out the loss of power in a coherent beam of electromagnetic energy in near optical frequencies? My purpose is to work out an effective range for a scifi laser gun working in either IR or x-ray. --203.171.195.34 (talk) 00:48, 13 December 2007 (UTC)

The angle of divergence is very roughly equal to the wavelength divided by the initial diameter of the beam. For details see Angular resolution, Diffraction limited, Airy disc. Icek (talk) 02:32, 13 December 2007 (UTC)

The other thing that's going to have a dramatic effect on range is whether you're firing it through some medium (like air for example) - if it's being used in a vacuum then it's a different matter of course. SteveBaker (talk) 12:54, 13 December 2007 (UTC)

I was particularly thinking about it firing through air at sea level. --203.129.38.192 (talk) 16:53, 13 December 2007 (UTC) (formerly 203.171.195.34)

I thought as much. Check out the graph here: Image:Atmospheric_transmittance_infrared.gif - it shows how well the atmosphere transmits IR - and as you can see - you need to pick a frequency where the air isn't going to block it. 3.5 microns is a good wavelength. SteveBaker (talk) 05:37, 14 December 2007 (UTC)

There's also the problem that lasers aren't truly monochromatic. They transmit over a narrow band of wavelengths, and this causes the beam to become incoherent at some distance. This is largely an engineering issue, however, so for the purpose of scifi you can declare the beam to be coherent as far out as you like. Someguy1221 (talk) 05:41, 14 December 2007 (UTC)

Child pyromaniac

Is child pyromania an actual diagnosed disorder. I asked a Psychologist who is a friend of mine, and they said it was real, but didn't know if it was a diagnosed disorder. This information is for the AFD. Thanks, Malinaccier (talk) 01:33, 13 December 2007 (UTC)

It's in the DSM-IV (see here), so I'd say yes. For more see the "Encyclopedia of Mental Disorders" pyromania entry here. -- HiEv 02:38, 13 December 2007 (UTC)

Though I should have noted that it's not specific to children. -- HiEv —Preceding comment was added at 02:43, 13 December 2007 (UTC)

Rationale behind intraperitoneal injection of immune cells?

What's the rationale behind intraperitoneal injection of immune cells in lab experiments? Is it easier for them to migrate from there than from under the cutis of the skin? If so, any idea why? Do you know of any other options? The journal club presentation I give tomorrow is on a paper that used this mode of injection and it's not likely to be questioned but I'd like to be prepared just in case as well as understand for my own knowledge. --Seans Potato Business 09:10, 13 December 2007 (UTC)

i.p. injections facilitate faster absorption of the injected material as the peritoneum is highly vascularized (draining into the hepatic portal vein). Subcutaneous injections have a slower absorption. Also, i.p. is quite easy to do... — Scientizzle 16:17, 13 December 2007 (UTC)

crystallization

In the early stages of crystallization of a solution the solute molecules begin to come together from the solvent and begin to form clusters.But what is the idea behind the crystallization of water into frost we generally see on a nasty winter morning.Water is a solvent right. —Preceding unsigned comment added by 218.248.2.51 (talk) 09:43, 13 December 2007 (UTC)

Water vapor in the air is a solute. Air is the solvent. Someguy1221 (talk) 10:51, 13 December 2007 (UTC)

Do try this link ..crystallization.--Mike robert (talk) 23:03, 13 December 2007 (UTC)

Flour

Were going to play a practical joke on a friend and want to know whats safe to snort Sugar or flour etc —Preceding unsigned comment added by King Alaric (talk • contribs) 12:40, 13 December 2007 (UTC)

I'm not convinced that any of those things are safe - but I would suggest something that dissolves in water so it won't hang around stuck to nasal passages and lung linings for long. So definitely NOT flour. Salt would probably be safest...especially if you ground it down into a finer powder using a mortar and pestle first. But as I said - I'm not sure any of those things are exactly safe, you should use the smallest amount you can. SteveBaker (talk) 12:50, 13 December 2007 (UTC)

At least in the long run, flour is definitely NOT safe; it causes baker's asthma [6] (no apparent relation to SteveBaker). Confectioner's sugar often has cornstarch or other anti-caking agents added so I'd rule that out too. If "Microfine powdered sugar" is just sucrose, you'd probably survive a small amount of that, but we're verging into medical advice and if your joke goes awry, you may need legal advice too! As one data point, the powder form of Serevent asthma inhalers use lactose powder along with active Salmeterol anti-asthma drug.

Atlant (talk) 13:23, 13 December 2007 (UTC)

Mentioning sugars, how about icing sugar, which is just glucose and a lot finer than normal cane sugar? --antilived^{T | C | G} 00:32, 14 December 2007 (UTC)

• I wouldn't do this myself, but I suppose you could snort dry nasal spray powder (baking soda and salt) to alarm your friend and then later flush it out of your nose with warm water. Anytime you inhale something, though, there's a risk of nosebleeding, so you might want to mention this prank to a nurse or doctor first and get their opinion rather than doing some dumb thing that some guy on Wikipedia suggested. --M@rēino 14:52, 13 December 2007 (UTC)

• I'm surprised that no one has mentioned it, but cocaine is relatively safe to snort in low quantities. Anyway, who's ever heard of snorting flour off a hooker's ass? --Sean 21:25, 13 December 2007 (UTC)

• This begs the question: what do they use in the movies? I doubt they're snorting actual cocaine. And after searching the internet I found that this has been asked on three different versions of Yahoo Answers. The most common answers are baking soda, flour, powdered sugar, powdered milk and vitamin B powder. Both flour and sugar are reported to have nasty side effects. This page lists different substances that are supposedly used as cocaine props depending on whether it is to be shown lying around or snorted. 152.16.16.75 (talk) 01:58, 15 December 2007 (UTC)

I'm having a hard time imagining a "practical joke" involving phony cocaine that isn't a collossally bad idea carrying numerous serious risks of many different types; you might as well go whole hog and use plaster of paris. --Scheinwerfermann (talk) 15:56, 17 December 2007 (UTC)

Cooking Meat

Why is it that humans have to cook most meat to order to avoid becoming sick, while wild animals do not? —Preceding unsigned comment added by 195.188.208.251 (talk) 14:26, 13 December 2007 (UTC)

Humans can eat raw meat without getting sick. However, they risk catching various diseases and parasites that animals commonly catch, such as worms. In addition, the meat you buy from a supermarket is pretty close to carrion :) The animal will have been slaughtered some time ago, this being practical and how we like our meat, which only increases your chances of catching something. So, humans can eat raw meat without getting sick every time. Animals don't always avoid getting sick from eating raw meat. You don't want the life-expectancy of a wild animal. Skittle (talk) 15:46, 13 December 2007 (UTC)

Actually, humans don't require most meat to be cooked in order to avoid sickness. If the meat is from a freshly - slaughtered animal, and hasn't had the chance to have started to become rotten due to decomposition, AND if there are no harmful pathogenic organisms in the meat (such as bacteria or worms or such), then it really is completely fine for humans to eat raw meat. Or, rather, it is completely fine for humans who are not philosophically opposed to eating meat, that is. When people eat steaks that are cooked to be rare they are actually consuming raw uncooked meat in the middle of the steak. The reason this is considered safe enough to eat by many people is that the outside parts of the meat that are exposed to the air is where decomposition happens more quickly than in the center of the meat, which is protected from direct exposure to air.

If a piece of meat has started to "turn" and begins to smell and taste like it's undergoing decomposition, it still may be safely consumed by humans if its thoroughly cooked by being heated to a temperature of at least 170 degrees Fahrenheit (71 degrees Celsius). The heat destroys the harmful bacteria that are living on the meat. However, as the decomposition process continues, the risk factor of picking up something nasty from the decaying meat increases over time. In warmer climates this was historically (before the invention of modern refrigeration) a problem, because warmer conditions speed up the decomposition process. Just as putting a piece of meat in your refrigerator or freezer helps to prolong its shelf life, so too did keeping a piece of meat in cold storage outside of the house in northern latitudes help prolong its shelf life. As a result of this, people who lived in warmer climates tended to eat meat that was more thoroughly cooked than those in colder climates. This also led to the heavier use of hot spices to mask the flavor of turned meat in warmer places around the world.

The idea that wild animals do not get sick from consuming decaying meat is a fallacy. Animals that eat only freshly killed meat have much less chance of picking up parasites and harmful bacteria. Animals that are scavengers, however, often suffer from all kinds of parasitical infestations and problems with digestion of very rotten meat. The longer the life expectancy of a scavenging species of animal, the more likely it is that the individuals of that species will pick up parasites. Bears are a good example of this. In the wild, it is quite common to find bears whose body tissues are riddled with worm infestations. There is a theory that this is why some bears that get older become seemingly insane - due to the fact that they are in constant pain and physical turmoil from all the parasites inside their bodies. At least that was what a Native Alaskan told me once while I was growing up in Alaska. It may be just a folk tale, but there may be some truth to it, as well. At any rate, I've seen when hunters have cut open grizzly bears, and their meat is riddled with so many tiny pellets of worm cysts that it is gritty to the touch. This probably comes from the fact that grizzly bears are notorious for eating turned meat - in fact, after killing an animal, the bear won't eat it right away, but will often dig a hole in the ground, dump the carcass in the hole, urinate on it, cover it with a few scoops of dirt and leaves, and then leave it to rot for a few days. I've seen this in real life - we stumbled on such a hole with a day-old dead elk calf in it - and then promptely got out of there! The rotting process makes the dead carcass softer and easier to chew for the bear (and perhaps makes it easier for the bear's digestive system to break down the proteins). But it also provides an optimum condition for all manner of nasty parasites and bacteria to grow before the bear eats it. You can often tell when a grizzly bear is around because they smell like a walking garbage dump and cesspool combined, and so it is with little difficulty to imagine where the bears pick up all those worm infestations... Saukkomies 16:02, 13 December 2007 (UTC)

Bear in mind that even if you kill all the parasites and bacteria in the meat there is still the possibility toxins produced by said bacteria will remain as these are not usually destroyed by cooking. This is one of the reasons cooking is not always sufficient with significant 'bad' meat Nil Einne (talk) 18:56, 13 December 2007 (UTC)

True, but for these toxins to be in great enough levels to do any real harm, the meat in question would have to be in pretty sad shape. Still, from accounts of people who have had to undergo extreme measures in order to survive, it is quite surprising what the human digestive system can handle. Saukkomies 23:11, 13 December 2007 (UTC)

What's also relevant is the quality of the meat (farming). For example as a sashimi fanatic I was very keen to just walk into my local supermarkey and just buy some raw salmon and take it home with some wasabi, mayonnaise and soya sauce. But no there's a difference between sashimi grade salmon and normal commercial salmon. The commercial salmon is generally meant to be cooked, which kills all parasites. The commercial salmon is also usually farm-produced, where parasites are apparently very common and very easy to get. Sashimi-grade on the other hand is usually freerange caught, must be healthy, and the sashimi-chef is trained to look and detect any parasites. Even then, there are still problems - it's difficult to detect all parasites. Many countries (for whatever reason) now have laws that any fish that is to be sold for raw consumption has to be flash-frozen for a certain amount of hours which kills of the parasites. But critics argue that proper sashimi is never frozen and that freezing hampers the taste.

But eskimos continue to eat raw meat and blubber, and millions of people eat sushi and sashimi every day. There are things like biltong and other forms of cured meats which is raw and slow-dried. So clearly there are some cases where raw meat is okay for humans, provided the animal is free of parasites and types of bacteria (think salmonela with chicken)

What I don't know for sure is why certain animals have a much higher tolerance. My father would sometimes give meat to the dog if it has been left in the fridge too long and didn't quite smell right (it wasn't raw, but I do believe animals do have a higher tolerance) Rfwoolf (talk) 16:30, 13 December 2007 (UTC)

Animals may vey well have a higher tolerance (although bear in mind Sauk said above, just because the animal ate it doesn't mean it didn't give it parasites or cause other problems). One of the common suggestions, although I don't think this is really backed up by any evidence is that we have evolved to have a low 'tolerance' because we have been cooking food for so long so it hasn't been as important Nil Einne (talk) 18:56, 13 December 2007 (UTC)

Animals probably also have a higher tolerance for illness as well, by this I mean, when my dogs eat their own feces, grass, raw fat from whatever I'm cooking or whatever is their dish of the day, they don't come and tell me "jeez, that last meal had me up all night" or have me bring them glasses of water. They just go off and deal with it. My girlfriend is a vetinary nurse and tells me amazing recovery stories of animals on the theatre table one day, running around the next, but I think when your an animal, it doesn't pay to compain - you just get on with it. 81.144.241.244 (talk) 13:48, 18 December 2007 (UTC)

I grew up in Alaska. My father was a search and rescue helicopter pilot, and would sometimes be called out to some Bush community to air-vac someone to a hospital for an emergency. I remember at least three separate instances where there was some Alaska Native who had to be flown in an emergency situation due to some bad meat they had eaten. One of these cases was an old woman who'd left a leg of moose behind her cast iron wood stove for too long. It killed her in the end. So, sure, the Inuit eat raw meat, but that doesn't mean it can't hurt them. Saukkomies 23:17, 13 December 2007 (UTC)

• You might be further horrified to read Carbon monoxide#Role in physiology and food, which notes that the US and other countries permit meat packers to treat their meat with CO, which can keep it looking nicely fresh and red for up to a year (!), even though it's rotting away. Luckily it will still smell bad once you get the package open, though one assumes they're working on that problem as well. --Sean 21:38, 13 December 2007 (UTC)

Curing has long been used to conserve meat. Here nitrite (if nitrate is used it is reduced to nitrite by certain bacteria) protects the meat from bacteria like Clostridium botulinum as well as from discoloration. The drawback is the formation of cancerogenous nitrosamines which may have been responsible for the higher rates of stomach cancer before preservation by freezing was available to most people. Icek (talk) 13:58, 14 December 2007 (UTC)

I love this board. This a really great, helpful answer & discussion.--The Fat Man Who Never Came Back (talk) 14:04, 14 December 2007 (UTC)

Curing meat is also linked to higher rates of deliciousness. --Sean 14:42, 14 December 2007 (UTC)

Average Interstellar Distance

Over at the Wikipedia:Reference desk/Science#Aliens discussion, the Drake Equation came up, which lets you estimate how many communicating civilizations are in the Milky Way at the moment. I've been playing with the interactive version, but now I'm having trouble conceptualizing the totals that I get. Let's say I decide that there are 10, or 42, or 1,000 communicating civilizations. Assuming that they are evenly spaced throughout the galaxy (and likewise assuming that each civlization is confined to its home star, mainly to simplify the math), what is the average distance in light-years between two species? Thanks for any help! --M@rēino 15:28, 13 December 2007 (UTC)

The area of the galactic disk is about 5×10⁹ square light years. To estimate the distance between civilizations, you can divide that up between N societies and take a squart root to get a linear distance. So with 1000 communicating civilizations, the average seperation is ~2200 light years. Dragons flight (talk) 15:55, 13 December 2007 (UTC)

Just in case you start wondering about how close they'd have to be for us to detect them, here is an important fact: If you took our most powerful radio transmitter, put it on a planet orbiting Proxima Centauri (the closest known star - just 4.2 light years away) - then we would not be able to detect it with our most powerful radio telescope. So even if the alien civilisation was our immediate next-door neighbour, we probably wouldn't be able to hear their transmissions. Some people argue that as the civilisation gets more advanced technology, their radio transmitters would get more powerful and we'd be able to pick them up - however, the science of efficient communications says that the most efficient possible means of communication is indistinguishable from white noise. This means that we almost certainly couldn't detect a more advanced civilisation either. Unless the aliens somehow know we're here and are actively aiming a narrow-beam of radio waves (or perhaps a gigantic laser) at us, we stand no chance whatever of finding them. We need vastly more sensitive radio telescopes - perhaps mounted on the far side of the moon where it won't get interference from earthly transmitters. SteveBaker (talk) 05:26, 14 December 2007 (UTC)

Fortunately, such narrow beams already exist. But yes, as you said, the difficulty is knowing where to aim (as that observatory can pretty much only listen/transmit to one teeny piece of the sky at once. Someguy1221 (talk) 05:38, 14 December 2007 (UTC)

"If you took our most powerful radio transmitter, put it on a planet orbiting Proxima Centauri (the closest known star - just 4.2 light years away) - then we would not be able to detect it with our most powerful radio telescope." <-- According to this, the Arecibo message should be detectable by any civilization with an Arecibo -like detector in the Messier 13 cluster, 25,000 light years away. --JWSchmidt (talk) 05:57, 14 December 2007 (UTC)

But the beam is focused - sending at 2380 MHz with a 305 m aperture gives you roughly an angle of divergence (or rather half-angle) of a = c/(2.38*10⁹ Hz) / 305 m, and the fraction of the unit sphere which is illuminated by the beam is approximately b = a²*pi/(4*pi) = 4.26*10^-8. The distance you can reach is, compared to the distance you can reach with an omnidirectional transmitter, b^-1/2 = 5*10³ times as large (it's only a rough estimate, but to show the order of magnitude). Icek (talk) 13:44, 14 December 2007 (UTC)

Yep - but it entails their highly directional transmitter being aimed at our highly directional reciever at precisely the moment we happen to be looking. If they happen to aim at the earth and spend 8 hours transmitting the complete Encyclopedia Galactica at us (as aliens are certain to do! :-) - but they do it when Aracebo is on the opposite side of the planet - or looking at some other star - then we aren't going to know about it. These hypothetical aliens have to know that we are here and broadcast the same signal over and over again using that narrow beam transmitter for centuries at a time. They could reasonably guess we are here from studying earth's transits in front of the sun and plotting the results of our industrial growth in things like our CO2 output. But then they'd need to keep that expensive resource focussed on us from Victorian times (maybe) until we happen to look in their direction. They'd know the odds of this actually working were small - so perhaps they wouldn't bother. For this to work, we either need omnidirectional transmitters or omnidirectional recievers or two civilisations with infinite patience! Our best chance is to study more of these 'exo-planets' (orbiting other stars) and see if we can find one with evidence of civilisation in it's atmosphere - and start broadcasting and listening in it's direction 24/7 for centuries. Somehow, I can't imagine the governments of the world paying for that. SteveBaker (talk) 17:14, 14 December 2007 (UTC)

• Thanks for all the answers! Looks like I'll hold off on sending out the invitations for my "welcome, space aliens" party for a century or so. --M@rēino 16:41, 14 December 2007 (UTC)
  • But you're still inviting us too - right? SteveBaker (talk) 17:14, 14 December 2007 (UTC)

US: Pounds, ounces, and grains

Once again Wikipedia confuses me with US measurements.
I have read Pound (mass) and it fails to express what Americans use in practise for weight. I've heard of things like "he weighed 6 pounds 4 ounces". I've seen American products with liquids measured in oz. (ounces). But I've never ever heard of grains. Please tell me, do Americans actually practically use grains? If you order up something would you ask for "About 2 ounces and 50 grains?". And what about using decimals: can you order 4.32 pounds of something? Or how about 4 pounds and 12.3 ounces of something? Is that the practical implementation of the system? Thanks! Rfwoolf (talk) 15:33, 13 December 2007 (UTC)

Either pounds (including decimals) or pounds and ounces (possibly including decimals on the ounces). Grains are not widely used, except maybe in certain fields (gunpowder?). Of course, in everyday speech, you would probably say "a pound and a half of meat", not "one point five pounds of meat" nor "one pound, eight ounces of meat". -- Coneslayer (talk) 15:49, 13 December 2007 (UTC)

Keep in mind that the fluid ounce is a measure of volume, not weight (or mass), so bringing liquids into the discussion will only confuse things. I thought grain was used in the pharmaceutical industry, but the article only mentions bullets and gunpowder. --LarryMac | Talk 15:59, 13 December 2007 (UTC)

Replying to myself to mention that the grain article does mention a few other applications. Also, the Apothecaries' system (apparently obsolete) used grains. --LarryMac | Talk 16:03, 13 December 2007 (UTC)

The weight measurement term "grain" is only used in gunpowder and not other places is due to two reasons: 1) it is a very minute measurement, so its applicability is not very wide, and 2) it is archaic because it is part of the old English measurement system, so that with industries such as pharmaceuticals, chemicals, and such the more modern use of grams prevails.

Slight correction, from a frequent user of the 'American' system. Grains are used to measure the weight of the bullet, not the powder. You could of course measure the powder in grains if you wanted to, but when you see ammunition specified, the weight in grains is the weight of the actual projectile. --66.195.232.121 (talk) 16:46, 13 December 2007 (UTC)

Grains are very commonly used to measure power, also. But yes, when you buy the box of ammo that says "180 grain JHP" they're referring to the bullet weight. Friday (talk) 20:22, 13 December 2007 (UTC)

As far as using decimals, Coneslayer is correct for most of the time. However, decimals used in weight in regards to pounds or ounces is actually very prevalent in grocery stores in the U.S. This is due to the labels on food items. Canned goods often will use decimals (such as 10.5 ounces), and packaged fresh meat in the butcher section will also use decimals with pounds (so you'd find the label on a packaged pork roast say 5.35 pounds). However, in normal conversation what Coneslayer said was much more common - that people don't talk about pounds in terms of decimals, but rather in terms of fractions, or in conjunction with pounds and ounces combined. So for instance, one would say "a pound and a half", or "one pound eight ounces", which is of course the same thing as 1.5 pounds... Saukkomies 11:22, 13 December, 2007. (UTC)

You'll order a pound and a quarter of meat from the butcher, but what you'll get is 1.25 pounds of meat, because the scale he uses measures using decimals. --Carnildo (talk) 23:10, 13 December 2007 (UTC)

"Grains" were definitely used in pharmaceuticals (and not just weaponry). The standard aspirin tablet in America is the "5 grain" aspirin which is now described as a 325 mg tablet. Take a quarter of that and you get the low-dose aspirin tablet originally used for children and now used for cardiac care. And that is how that aspirin tablet came to have its weird 81 mg dosage; it's really 1.25 grains, 1/4 of a standard 5 grain pill.

Atlant (talk) 17:59, 13 December 2007 (UTC)

In the US you'll rarely hear "grains" used as a form of measure. I'd bet at least half of Americans don't even know that it's a form of measure. However, as far as "pounds" goes, Americans often mean Pound-force, instead of Pound (mass). For example, we in the US often hear phrases like, "If you weigh 120 pounds on Earth, then on the Moon you'd weigh 20 pounds." That's only true if you're talking about pounds as a force, because that is affected by gravity. -- HiEv 00:06, 15 December 2007 (UTC)

Who discovered that Armadillos have identical offspring and how did they do that?

In the article on Armadillos it says they reproduce by Polyembryony in which they typically have 4 babies per litter and they are each genetically identical, like identical twins. I am curious, who made this discovery about armadillos and how was it done? It seems like this is the kind of thing that wouldn't be possible to learn without the use of modern genetic science techniques. I really want to know who and how they discovered this characteristic in armadillos and particularly what got them looking in that direction; what made them even think of looking into that possibility?

Zescanner (talk) 15:52, 13 December 2007 (UTC)zescanner (Jeff in Arkansas)

• This isn't an answer since I am not a historian of armadillology, but this does not seem particularly weird to me. If you've ever seen a litter of puppies, you know that they can be very different individuals right from the start. Presumably anyone caring for captive armadillos (zookeepers, zoologists, etc.) would notice the striking lack of individualism in a given litter. You don't need modern biochemistry to do genetics research, as history of genetics will attest. --Sean 17:50, 13 December 2007 (UTC)

It was discovered by HH Newmann and JT Patterson, reported in a number of papers in the early 20th century, the first being "A case of normal identical quadruplets in the nine-banded armadillo, and its bearing on the problems of identical twins and sex determination" Biol. Bull. Vol. 17 No. 3. This was, obviously, before modern genetic sequencing was available, so how did they discover it? To quote the authors, they "had the good fortune to secure four embryos... from an adult female [and] found four placentae enclosed in one amnion" [7] They went on to secure further gravid females and found that is typical (though on further investigation there is actually four amnia, but all are enclosed in one chorion). I think, as with much science, the discovery was a fortuitous result of their studies into embryology, rather than asking that direct question. It was almost 90 years before the discovery was confirmed genetically (PMID 9025312). Rockpocket 18:32, 13 December 2007 (UTC)

I suppose that the fact that the four offspring are always of the same sex might have been a hint. -Arch dude (talk) 00:16, 14 December 2007 (UTC)

Sherbet and Water

what is the scientific explanation when you mix sherbet with water?195.234.48.50 (talk) 16:15, 13 December 2007 (UTC)

Melting? I'm not really sure what you're getting at—does something unusual happen that you're referring to? -- Coneslayer (talk) 17:49, 13 December 2007 (UTC)

When you add water to sherbet, the citric acid and bicarbonate of soda dissolve. When they're both dry powders, they can't really interact, but when they're both dissolved in the water they can 'get at' each other. So, the citric acid and the bicarbonate of soda react with each other to produce sodium citrate, water and carbon dioxide. The carbon dioxide (being a gas) bubbles out of it, making it fizz. Which is really the point of sherbet: originally sherbet powder was made to be mixed with water to make a fizzy sherbet drink. The carbon dioxide that bubbles out of sherbet to make it fizz is the same stuff that makes a fizzy-drink fizz. Skittle (talk) 18:08, 13 December 2007 (UTC)

Oh, I found this website that might be helpful to you :) Skittle (talk) 18:11, 13 December 2007 (UTC)

Ah, I only know about Sherbet (U.S.), which is not the same as sherbet. That clears things up. -- Coneslayer (talk) 18:21, 13 December 2007 (UTC)

No - the British "sherbet" is not at all the same thing. In the US, sherbet is synonymous with 'sorbet'. In the UK (and possibly Australia and/or NewZealand) it's a kids candy - it's most often seen as a dry white powder that can be mixed in a drink - or (more often) sucked into your mouth through a licorice 'straw' in a thing called a 'sherbet fountain' or stuck onto a lollypop and sucked off in a "sherbet dab"...actually, there are dozens of uses for this stuff in kid's confectionary. It's weird that it doesn't seem to have ever made it into the US market...although 'pixie sticks' may be similar stuff but in vivid colours. SteveBaker (talk) 05:12, 14 December 2007 (UTC)

Origin of Life

Did life begin and go completely extinct more than once on earth?--76.28.67.224 (talk) 19:43, 13 December 2007 (UTC)

There is no evidence for this. Certainly since the Ediacaran life has had a continuous presence. In the Cryogenian period life could have almost disappeared, but there was not much as we know it back then, and something probably survived - eg hydrothermal vent bacteria and blue green algae. On the Creation theology side of things God created the Universe, sea creatures and Humans, everything else was made, but at no point was all this destroyed (yet). Graeme Bartlett (talk) 20:18, 13 December 2007 (UTC)

If you accept the genetic evidence underpinning the last universal common ancestor theory then all currently existing life is related to each other and share a common heritage going back 3.5+ billion years. There is no evidence for life ever having arisen independent of the currently existing group, but we also can't exclude it. Dragons flight (talk) 20:35, 13 December 2007 (UTC)

Paul Davies has recently suggested in the magazine Scientific American that life evolved more than once independently in earths history and such life forms may still survive today even in our own bodies.[8]--Fang 23 (talk) 21:11, 13 December 2007 (UTC)

Did life begin and go completely extinct more than just once on earth?

I must have missed it (in which case nobody reads this stuff anyway)...

Do we have an article on the male equivalent for parthenogenesis ?

Help, I am an endangered species! Cookatoo.ergo.ZooM (talk) 22:05, 13 December 2007 (UTC)

I think the answer to this question is an overwhelming NO. The smaller life is, the higher its population, once the first chemicals could replicate themselves it would be nearly impossible to stop life because it would exist in the oder of billion billion billion billions. The only way to do it would have involved completaly changing the enviroment of the entire planet extremely significantly (a whole orbital change).--Dacium (talk) 00:52, 14 December 2007 (UTC)

Well, a burst of gamma radiation from a nearby supernova might do the trick in wiping out all life on a planet. -- HiEv 00:16, 15 December 2007 (UTC)

Paul Davies suggestion implies that the alternate form of life did not go extinct. For this to exist it would have to be a lifeform not recognised so far. Perhaps a mineral form or nanobe would be in this category, but as I said above there is no evidence of it. Graeme Bartlett (talk) 02:28, 14 December 2007 (UTC)

I don't think we can know this. We don't have fossil evidence going back far enough to see even the first emergence of life. If life appeared, was eradicated, then restarted from scratch, it would have to have happened LONG before we run out of fossil evidence. Actually, I rather suspect life did start more than once...but it depends on your definition of "life". Current theory says that in the early oceans (or perhaps underground), a DNA/RNA-like molecule simply happened out of nothing from random reactions of Amino acids (which we know from countless experiments can appear in early-earth conditions). So here is the question: Did the very first self-reproducing molecule (which we would define as "life") become so spectacularly successful that we are all descended from it? That seems unlikely to me. It seems to me that there must have been some false starts - a molecule that could reproduce made a few hundred copies of itself in the warm summer sun - then when the water cooled in the winter, it fell apart and "died". At that early stage, that would constitute the spontaneous creation of life - followed by it's extinction. I could EASILY imagine this happening many, many times before a molecule that was robust enough to survive an entire year - a decade, a century...would happen to emerge by pure luck. TECHNICALLY - this would fulfill the OP's conditions - life arouse - life went utterly extinct - life reappeared and evolved into us. What I find much harder to believe is the idea that life would emerge - evolve to the state of (say) 6" long fish - and THEN go extinct. That's a tougher sell. But this is all speculation. We'll never know. SteveBaker (talk) 03:39, 14 December 2007 (UTC)

On the other hand, if life did evolve to those 6" long fish, then go completely extinct, then I beleive it would have been cause by one of those armageddon-like catastrophes (you know, giant meteor, lava all over the surface of earth) so it would destroy all traces of those fish and we'd have no way to know about it. – b_jonas 10:49, 14 December 2007 (UTC)

Well, yes - but it doesn't matter - we can't see back that far anyway. Even if they had formed fossils and NOT be catastrophically erased, the oldest fossils we have are not even close to being old enough to show these hypothetical creatures...they've all been eroded away or subducted as a result of plate tectonics or whatever. SteveBaker (talk) 17:03, 14 December 2007 (UTC)

That's not entirely true. There is a large period of time between say 600 Ma and 2.5 Ga where there are still plenty of reasonable rocks and no macroscopic fossils. Maybe you could invent and destroy fish very early in Earth's history without leaving evidence, but for much of the history of the planet we can say with confidence there were no fish. Dragons flight (talk) 17:18, 14 December 2007 (UTC)

werent there small worm fossils from 1 billion years ago?--76.28.67.224 (talk) 14:18, 30 December 2007 (UTC)

Biology

what are bacterial STDs —Preceding unsigned comment added by 147.226.243.137 (talk) 20:50, 13 December 2007 (UTC)

Have you tried Sexually transmitted disease#Bacterial? -- Coneslayer (talk) 21:02, 13 December 2007 (UTC)

Black cats

What breeds of cats would black cats be? —Preceding unsigned comment added by Heegoop (talk • contribs) 21:19, 13 December 2007 (UTC)

Many breeds of domestic cat can be black. Probably the most common in the US is the domestic shorthair. ike9898 (talk) 22:24, 13 December 2007 (UTC)

Actually, our article on domestic shorthair cats says that they are not really a true breed. ike9898 (talk) 22:27, 13 December 2007 (UTC)

There is a relatively new breed called the Bombay that is all black and was developed to look like a miniature black leopard. Our article isn't very good, so check out Bombay cat on google for better information.--Eriastrum (talk) 23:09, 13 December 2007 (UTC)

• "The black cat is a feline whose fur is uniformly black. It is not a particular breed of cat and may be mixed or of a specific breed." Now there is the Bombay (cat) pure breed, which is pretty consistently black, but like most pure breeds, this is a very small proportion of the population -- the breed formation process didn't begin until the 1950s. Among the major breeds there are two big contributors to the black population, AFAIK: (1) many Bicolor cats are overwhelmingly black with small white patches, and (2) Tortoiseshell cats can be primarly black with orange/brown hairs. --M@rēino 16:54, 14 December 2007 (UTC)

Ex Vivo In Vivo?

According to our ex vivo article, ex vivo is usually in vitro. This implies that it's sometimes in vivo. Would an in vivo ex vivo experiment be taking something out and putting it a) back in or b) in another animal? --Seans Potato Business 22:52, 13 December 2007 (UTC)

Not exactly. By saying an ex vivo experiment is usually in vitro, means that sometimes you can have an ex vivo ex vitro experiment. Good examples of this are in silico and, to a lesser extent, in situ. (EhJJ) 23:35, 13 December 2007 (UTC)

I'm not sure one would say that an ex vivo experiment would also be in silico. I would say these are generally considered be mutually exclusive (either an experiment is done on dissected tissue or on a computer, but not both.) In situ experiments are a good example, though. Rockpocket 00:30, 14 December 2007 (UTC)

Symptoms and side effects

A long time ago, I was given a medicated cream to treat a fungial infection. The major symptom of the infection was dry, cracked skin, and the main side effect of the medicine was dry, cracked skin, which made the decision of when to stop treatment a bit exciting. Are there any other situations where the main symptom of the a medical problem and the main side effect of the treatment are the same? --67.185.172.158 (talk) 23:02, 13 December 2007 (UTC)

One example: a major symptom of insomnia is being tired, especially in the morning. The major side effect of taking sleeping pills is feeling tired, especially in the morning. --NorwegianBlue ^talk 23:25, 13 December 2007 (UTC)

I just recently saw someone point out that one of the side effects of aspirin can be pain and headaches.[9] -- HiEv 00:35, 15 December 2007 (UTC)

Global warming and over population

Which is a bigger problem global warming or the amazingly fasting growing population?--Sivad4991 (talk) 23:21, 13 December 2007 (UTC)

Thanks for asking the question. Overpopulation is the direct cause of the changes in climate. I find the trend now to put such great emphasis on climate, and so little emphasis on overpopulation, somewhat depressing. --NorwegianBlue ^talk 23:28, 13 December 2007 (UTC)

This article "Is Anyone Listening?" by Isaac Asimov might interest you. --NorwegianBlue ^talk 23:39, 13 December 2007 (UTC)

They're related but not exactly the same thing at all. Per capita the most populous countries produce far fewer greenhouse gases, etc., than do Western countries of less population but much higher energy consumption. See, for example, per capita carbon dioxide production; China and India don't even make it on the list, even though in terms of raw numbers they rank much higher (but still below the US). To blame all of climate change on overpopulation neglects the fact that there is not a direct correlation between population size and energy usage, it's a bit more complicated than that. If the US population suddenly jumped by 10% it would use a lot more energy than if the population of India jumped by 10%, even though in terms of raw bodies the US jump would be much smaller. --24.147.86.187 (talk) 23:43, 13 December 2007 (UTC)

They are both problems - but there isn't much doubt that global warming is the more urgent. If we don't get serious about it, global warming will become totally disasterous within a couple of generations. Population growth is currently running at 10% per 100 years - and that rate of increase is slowing down. What is encouraging is that the more developed countries have decreasing populations - and the population boom in India and China is levelling off. The massive boom is actually in Africa - which is unfortunate because that country is the most severely lacking in resources to support more people.

Supporting large populations in poorly resourced countries is something you could fix with limitless energy supplies - one hopes that what comes out of solving global warming will be better ways to produce energy cheaply and safely. If you have energy - you can build desalination plants - then you can irrigate fields - then you can use intensive agriculture - and then Africa's population can grow without consequences that are too serious. But the energy problem has to be fixed before that.

But without doubt, if the earth's population was 1% of what it is now, global warming wouldn't be a problem - we could all pollute all we wanted and the planet would hardly notice. But I think it's possible to solve global warming without having to address the population problem - so that should certainly be our priority. There are really no downsides to having a planet with 1% of the present number of humans - the problem is how to get there from here.

SteveBaker (talk) 00:08, 14 December 2007 (UTC)

Asimov wrote how he feared that the problem of going to get there from here will be solved:

“ And as the population increases, as people crowd together more closely, as people find they can only get a smaller and smaller part of a pie that does not increase as the numbers do (but decreases in many ways), there will be increasing alienation, increasing refuge in drugs, increasing crime, increasing chance of war. In short, the world will become ever more violent. Every one of these changes, which come about more or less directly because of the ever-increasing population, will serve to raise the death rate. There will be increasing starvation, and bodies weakened by undernourishment will be more prone to disease. There will be more deaths by violence. In short, the Four Horsemen of the Apocalypse (Famine, Pestilence, War, and Death) will ride the Earth.

This might seem a natural way to make overpopulation self-limiting. It will seem an automatic cure -- but what a horrible cure it will be. Surely, the alternative of a deliberate effort to lower the birthrate is far preferable. But is anyone listening? Does anyone care?

”

--NorwegianBlue ^talk 00:52, 14 December 2007 (UTC)

If that 1% were Americans then it could still easily be an issue in the long run. America only makes up 4% of the current world population and yet out-pollutes in both raw numbers and per capita every other country on the globe. --24.147.86.187 (talk) 00:23, 14 December 2007 (UTC)

(Edit conflict): I would like like to reiterate that IMO the core of the problem is overpopulation, coupled with a very uneven sharing of wealth. The CO2 that contributes to global warming is produced by human activity, and it is a problem because there are so many of us. Sure, much more CO2 is produced per capita in rich countries, which tend to have lower birth rates. In a utopian future society where developing countries had caught up in wealth, their birth rates would probably also have lowered, leading to a stabilization of world population. Their CO2 emissions, of course would have increased dramatically. And world population would stabilize at a level disastrously high, climate being but one of the victims. I read Asimov's essay "The Power of Progression", on which the article I linked to was based, as a youth, and it made a great impact on me. I fully agree that harsh measures must be taken to limit CO2 emissions. I believe that even harsher measures are necessary to control the population explosion. --NorwegianBlue ^talk 00:26, 14 December 2007 (UTC)

Sorry, but you are claiming that population and CO₂ emissions correlate and they don't, which is my point. The problem is not that there are "so many of us" but that "we have become incredibly energy dependent—some far more than others—and we derive this energy from really unpleasant sources." Population size is a variable here but not the primary one—many places with very large populations (Africa) don't have correspondingly high emissions, and many places with relatively small populations (the United States) do have high emissions. Appealing to a "utopian future society" doesn't really convince anyone of anything. I don't mind Asimov but come on, the man isn't gospel. The question of the relationship of population to crime, wealth, emissions, etc. is more complicated than anyone can just gesture at and expect to be compelling. I'm not saying that overpopulation isn't an issue—obviously it is—but claiming it is the only issue of note is hyperbole and not well thought-out, Asimov or no Asimov. Overpopulation is not the driving force of all the world's ills, sorry. The world is more complex than that. (Or put another way: If you want me to be compelled, cite some stronger reasoning/evidence than just repeating what Asimov wrote over a decade ago. People have been writing about overpopulation since the 19th century, the sky hasn't fallen in yet.) --24.147.86.187 (talk) 02:24, 14 December 2007 (UTC)

• I made no statement about correlation in the previous post, I made a statement about causality. If I were to make a statement about correlation, it would be that CO2 emissions correlate with wealth×population.
• I'm well aware that people have been writing about overpopulation since the 19th century. Whether global warming should be classified as "the sky falling in" appears to be a matter of debate. --NorwegianBlue ^talk 09:20, 14 December 2007 (UTC)

Growing population is arguably not a problem now. I believe the UN predictions are for the world population to peak at 12billion at 2050, most growth in 3rd world counteries. Many first world counteries (especially in europe) are already declining population numbers, as first world people tend to have significantly less children. What IS the problem is the polution in general. For example if everyone that were alive today used resources and poluted the way the average americian does, the resources and world would be destroyed very quickly. This is why polution is a concern, because if most of the population 'develops' to match america we will have a huge pollution problem. We already have enough population to cause this problem. Even if the world capped at 7 billion people the pollution problem from devlopment of most of the world would cause huge enviromental problems.--Dacium (talk) 00:41, 14 December 2007 (UTC)

I fully agree with the statement "Even if the world capped at 7 billion people the pollution problem from devlopment of most of the world [to match America] would cause huge enviromental problems." For the very same reason, I find little comfort in predictions of world population stabilizing at 12 billion in 2050. --NorwegianBlue ^talk 01:05, 14 December 2007 (UTC)

If overpopulation was solved thoroughly enough, it would eliminate global warming, in addition to solving the other problems associated with overpopulation. The reverse, however, is not true, in that just solving global warming alone wouldn't help with the other problems associated with overpopulation. So one could argue that overpopulation is the bigger problem, in that if you could ask a magic genie to fix just one problem, it would make more sense to ask for a (deathless, magical) large reduction in the world's population, rather than to ask for greenhouse gas concentrations to return to preindustrial levels.

Another reason that overpopulation could be viewed as the bigger problem is that it's probably harder to solve painlessly than global warming is. Global warming can probably be solved by technological means and political willpower by a small fraction of the world's population working on the problem. Overpopulation could be helped somewhat by improving access to family planning and reproductive health care and information, eliminating incentives to have larger families, public education about the consequences of continued population growth, and improving access of women to education and economic opportunities. But really substantial population reduction in a painless way would involve most people in the world choosing to have fewer than two children. It's easier to get a small fraction of the world's population to work toward a goal than it is to get most people in the world to work toward a goal. Plus, people react a lot more negatively to a suggestion that they consider choosing to have only one child, than they do to a suggestion to replace their lightbulbs and buy a more efficient car. MrRedact (talk) 03:08, 14 December 2007 (UTC)

I disagree. There is evidence (look at the UN estimates below) that populations are stabilising as countries become more affluent. You can see that aside from Asia and Africa, populations sill stabilise and even fall a little by 2150. Asia is levelling out rapidly and only Africa is really growing at alarming rates. It seems likely that - just as with Asia - Africa would self-stabilise eventually. If the UN numbers are to be believed, I think the earth's population will stabilise and then S-L-O-W-L-Y decrease without any drastic measures at all. It's certainly not an urgent panic. The effort to bring populations down would be tremendous - it would require horrible laws that would breach ethical and religious behaviors. It's virtually impossible to get a simple law passed to limit automobile gas consumption in every country around the world...you think you'd get countries to agree to pass laws to halve their birthrate?...I don't thing so! We're going to need to sort out global warming LONG before we can attack the population problem. We need to reduce emissions by 40% over 20 years. You'd have to ban ALL human reproduction for an entire generation to achieve a 40% population reduction - and then how would the smaller population of workers support all of those elderly people? It would be an utter nightmare. On the other hand, switching power stations over to wind, solar and (mostly) nuclear, requiring a very do-able 40mpg average for cars and light trucks, requiring industry to cut emissions by similar amounts...it's hard - but it's very definitely do-able. We have to focus on solving the most urgent - and the most solvable problem first. The evidence is that the population problem may well fix itself. SteveBaker (talk) 03:25, 14 December 2007 (UTC)

Woahhh there. There is something severely wrong with those numbers. Dacium said: "UN predictions are for the world population to peak at 12billion at 2050" - there is simply no way that can be true! There are about 6.6 billion of us now - for the population to DOUBLE in 43 years is virtually impossible! This table is from our "World population" and is referenced as coming from www.un.org:

World historical and predicted populations

Region	1750	1800	1850	1900	1950	1999	2050	2150
World	791	978	1,262	1,650	2,521	5,978	8,909	9,746
Africa	106	107	111	133	221	767	1,766	2,308
Asia	502	635	809	947	1,402	3,634	5,268	5,561
Europe	163	203	276	408	547	729	628	517
Latin America and the Caribbean	16	24	38	74	167	511	809	912
Northern America	2	7	26	82	172	307	392	398
Oceania	2	2	2	6	13	30	46	51

So we'll only hit 8.9 billion by 2050 - and even by 2150 we'll only be at 9.7 billion. SteveBaker (talk) 03:10, 14 December 2007 (UTC)

I fully agree that it is urgently important to develop alternative energy sources, wind, solar and nuclear, and to limit CO2 emission from industry and transportation in whatever ways possible. However, when you write "We're going to need to sort out global warming LONG before we can attack the population problem.", I'm puzzled. In my view, much of what we have been discussing in this thread is whether we should treat the symptoms or the cause of the disease. I think we should do both. However, when I read the previous statement, it translates to "First, let's treat the symptoms and ignore the cause". You also write that "The evidence is that the population problem may well fix itself". I agree, one way or another it will. However, it may do so in very unpleasant ways. Therefore, I believe it is important to increase awareness that global warming and overpopulation are tightly interrelated. --NorwegianBlue ^talk 10:06, 14 December 2007 (UTC)

This is a reference desk, remember? Not a debate forum. --Anonymous, 16:04 UTC, December 14, 2007.

(You might think that but...)

It's not a matter of 'symptoms' and 'causes'. In the end (and I'm being deliberately vague about units and definitions) we have this "thought equation":

   GlobalWarming = PopulationSize x CarbonFootprintPerPerson

If we need to reduce global warming to (say) one quarter of it's present value in the next 20 years, we can either reduce the population to a quarter of it's present value (in 20 years) - or we can reduce the carbon footprint of each person by a factor of four over the same period (or some combination of the two). The problem is that if you attempted to fix global warming by reducing population, you simply couldn't do it fast enough without going out there with machine-guns and taking out 75% of the people out there. That would have to be 75% across-the-board too, you couldn't just take out 100% of the sick and elderly and all of the prison population and 30% of the other adults and leave the children alone. If you did that, the problem would come back again 20 years later when the kids are fully grown.

Even if you somehow prevented all human reproduction for the next 20 years, something like 70% of the people who are alive today would still be living - and you'd only have reduced the population by a third or so...nowhere near enough to prevent a global warming disaster. Cutting population by humane, acceptable means would take several hundred years - and we just don't have that long.

There simply isn't a way to solve global warming by attacking this particular root cause. We have to look at the other factor on the right side of the equation (which is just as much a 'root cause' as population size). We have to cut per-person CO2 production by a factor of four. This is also exceedingly difficult - but it's certainly not impossible. With care we can halve the amount of energy each person uses - better insulate our homes, have 45mpg cars, transport more goods by rail, waste less things that could be recycled, use less packaging, eat local food instead of shipping it, find better industrial processes, build "combined heat and power" schemes in cold parts of the world...you name it. And we can also try to halve the amount of CO2 we produce in generating that energy (carbon sequestration, biomass-fuels, nuclear, wind, solar). That's all do-able...although it's not cheap and requires politicians who are not invertibrates.

But killing 75% of the population just isn't going to happen and even the most draconian birth control measures won't make a dent in the problem in a reasonable time-frame.

SteveBaker (talk) 16:38, 14 December 2007 (UTC)

Taking heed of Anonymous' reminder that this is not a debate forum, it might be appropriate to return to the OP's question: Which problem is bigger, global warming or population growth? Since the two are interrelated, as shown by SteveBaker's equation above, the question needs to be rephrased to get a meaningful answer. --NorwegianBlue ^talk 12:47, 15 December 2007 (UTC)

December 14

Stressful situations

Not sure if this goes in the science section but I guess it could be part of psychology, and behavior.
What are good ways or I guess some could say, good exercises for the brain before an anticipated stressful (on the mind) event. Example, a test, mentally laborious work, etc.
I think I could go for some new tips. My methods are just trying to relax, or getting some light meditation on anything that isn't too heavily related. I try to ease my mind from the harsh reality of solving problems. --Agester (talk) 01:14, 14 December 2007 (UTC)

There are some interesting results from experiments with laboratory animals that suggest physical exercise can be "good exercises for the brain". Starting point in the literature: Neurobiology of Exercise. see also --JWSchmidt (talk) 05:33, 14 December 2007 (UTC)

Disease

I'm looking for the disease that causes victims to fall into an apathetic state. They will fall into a deep slumber, they can be roused to perform tasks, but if allowed to rest they will go back to sleep and eventually die. Some survived for months like this before succumbing. An outbreak that afflicted millions occurred at the same time as the Spanish flu of 1918, it is apparently dormant or gone now. Thanks. 75.175.30.112 (talk) 01:50, 14 December 2007 (UTC)

Read about it in Encephalitis lethargica. Graeme Bartlett (talk) 02:22, 14 December 2007 (UTC)

Numerous Questions About Space

First off, I realize that the information on this subject is limited, but I would greatly appreciate any information. Anyway, to the questions:

Is our solar system unique in that it has 8 planets? Is this considered a high number for a planetary system?

Do most planetary systems have asteroid belts? Do some have have multiple belts?

Sometimes, in video games, you will see that a planetary system has a asteroid "field" as opposed to a "belt." Basically, there is an elliptically shaped area of asteroids in the upper left corner of the map. Is this really possible to have this in a planetary system?

Do all planetray systems have an equivalent of the Kuiper belt?

In sci-fi, spaceships often make a "jump" to some sort of FTL speed. However, in reality, wouldn't they have to be outside of the asteroid and Kuiper belts so as to avoid collisions?

Lastly, is it possible to build a space station in a random spot in the solar system (ie. it wouldn't be orbiting a planet)? Or would it just get pulled into the Sun? What about if it was placed in an asteroid belt? 24.125.31.205 (talk) —Preceding comment was added at 03:01, 14 December 2007 (UTC)

I apologize I can't answer any of those, but to maybe point you in the right direction, wikipedia does have an article on planetary systems (other than ours) as well as links to the various known systems. Also, there is a section Kuiper_belt#Other_Kuiper_belts that states "As of 2006, nine stars other than the Sun are known to be circled by Kuiper belt-like structures. They appear to fall into two categories: wide belts, with radii of over 50 AU, and narrow belts..." Interesting questions though! -- MacAddct  1984 ^{(talk &#149; contribs)} 03:16, 14 December 2007 (UTC)

For your last question, Lagrange points can be a good place to put things. Algebraist 03:39, 14 December 2007 (UTC)

For question three, no. A random blob-like arrangement of asteroids orbiting a sun would pull itself together under its own gravity, or would have to form with sufficient velocity that it would spread out, thus ruining the appearance the video game designers sought. For question five, it depends on what FTL involves. Since there is no known way of traveling faster than light, you can make up whatever rules you want. For question six, Newton's law of universal gravitation necessitates that any body orbiting the sun will have the same orbital speed for a given distance out, regardless of its mass. So a (relatively) light space station would be able to stay in orbit just fine without a planet nearby, although it may still require corrections due to gravity from other objects. Someguy1221 (talk) 03:44, 14 December 2007 (UTC)

The fact is, we still don't have a lot of data on other solar systems than our own. We have found planets orbiting stars, and the number is growing all the time. But these all have to date been massive gas giant planets - not little dinky ones like our own. So, although we do know about other solar systems out there, we simply cannot tell right now how many planets are in any of them. So there's no way to know for sure whether our system is "typical" or not. Saukkomies 04:42, 14 December 2007 (UTC)

Let's take these one at a time:

• Is our solar system unique in that it has 8 planets? Is this considered a high number for a planetary system?

  Our ability to find planets orbiting other stars is not good enough to find small planets - and when there are many planets, the effects of their gravity on the parent star becomes too complicated to decypher - so it becomes hard to count the planets. We know that a large proportion of the stars we have looked at have at least one planet - and we know that some of them have more - but we don't know enough to answer your question yet.

(Just clarifying, here) Let's think about how we find those planets orbiting other stars. Basically, there are several ways to find one. Simplest is to track a star well enough to realize that it's not moving in a straight line. If it's track looks like a wave, then that must be caused by the mass of something orbiting it. Clearly, such an orbital mass has to be big enough to move a star, so that's a pretty big planet, like Jupiter (or larger). Next, we can observe a start long enough with a spectroscope to be pretty sure what it's spectrum is. Then, if we see a dip in either total output or most frequencies, we can assume that something got between us and the star. If it happens periodically, like the star is "normal" most of the time but every 90 days it goes down to another constant level for 30 minutes, we're probably seeing the effects of a planet moving in orbit, causing a partial eclipse. Again, the planet would have to be pretty honkin' big for us to see this.

There are other ways, but mostly they all boil down to "the star is so far away we can only detect huge planets." If we assume that other systems are laid out like ours, and we see something that looks like Jupiter, then it's likely that they also have something like earth/venus/mercury/mars, and also saturn/neptune, but these are assumptions. We can't see the little ones. -SandyJax (talk) 19:49, 14 December 2007 (UTC)

That's a good explanation. Little planets only put very small ripples onto the motion of the star - so they are harder to detect than the bigger ripples caused by huge planets. But also, planets further away from the star cause smaller ripples than those close-by so the outermost planets may cause ripples that are too small to measure. Worse still, if there were as many planets - all large enough and close enough to detect in this way, the star would be pulled back and forth by all of them and it's motion would be quite haphazard. If the interactions are small and you have this much complexity, it can be tough to sort out what planets or what masses are at what distances and what orbital periods are involved. Since it may take many years for a planet to make a complete orbit of the star, you may have to watch the motion of the star for a very long time in order to see enough of the motion to make accurate measurements of all of it's planets. SteveBaker (talk) 13:45, 16 December 2007 (UTC)

• Do most planetary systems have asteroid belts? Do some have have multiple belts?

  Again, we don't know - asteroid belts would be even harder to find than planets.

• Sometimes, in video games, you will see that a planetary system has a asteroid "field" as opposed to a "belt." Basically, there is an elliptically shaped area of asteroids in the upper left corner of the map. Is this really possible to have this in a planetary system?

  If that 'patch' was orbiting the star as a group - then, yes, that could happen if (say) two larger bodies collided while in a similar orbit and produced a bunch of fragments that continued to orbit the star. However, over time, the asteroids mutual gravitation would tend to pull them back together again - so this probably couldn't last for tens of thousands of years without something more complicated going on.

• Do all planetray systems have an equivalent of the Kuiper belt?

  Probably - but again, such things are too hard to measure with the instruments we have. We know SOME of them do.

• In sci-fi, spaceships often make a "jump" to some sort of FTL speed. However, in reality, wouldn't they have to be outside of the asteroid and Kuiper belts so as to avoid collisions?

  There is no such thing as a "jump" and faster-than-light travel is impossible - so there is no "in reality". Some scifi series (eg StarTrek and StarWars) have no problem with you just zipping off to lightspeed once you are in orbit. Others (eg the Isaac Asimov 'Foundation' series) specifically state that you have to fly a long way away from any gravitational sources before you can jump. However, it's all pure fiction...completely and utterly bogus.

  Apart from the fiction of the question, though, the answer is "no" in terms of the asteroid and Kuiper belts. The densities of asteroids, comets, and other hazardous rocks is far too low to make a significant hazard to spacecraft. Consider that any NASA probes going to Jupiter and beyond just sail blithely through the asteroid belt, and that the only collision was purposeful. If, however, you were a fanatic about minimizing risk (and this is not an unreasonable assumption), there's another trivial solution: leave the plane of the ecliptic. — Lomn 13:54, 14 December 2007 (UTC)

  In all of the SciFi I've seen, worm-hole travel is used for FTL travel from one location to another. As such, you do not travel through any obstacles between the origin and destination point. So, asteroids, planets, stars, and all other spacecraft are easily avoided. You only have to worry about someone else using the same wormhole or having something sitting right at the destination point. -- kainaw™ 15:39, 14 December 2007 (UTC)

  You need to read more SciFi! There are many more mechanisms than wormholes. I recall that the book (and less great movie) "Contact" used wormholes. In StarWars, very little is said about how it works (a wise move!). The implication in StarTrek is that space is warped (hence "warp drive") so you are somehow scrunching space up in a region immediately around the ship so you can be moving slower than light - yet still getting from A to B at a speed that keeps the plot humming along. This is claimed to be why they don't use their drives near planets (which don't much like being scrunched up) - and in one episode of The Next Generation, it is revealed that space is somehow weakened by the repeated traversal of fast ships because of all of this scrunching and unscrunching of space. So wormholes are definitely not involved in StarTrek (although they are occasionally used as plot devices). In other books (I'm thinking especially of the god-awful "Lensman" series by E.E.'Doc'Smith), they simply assert that Einstein was wrong...which is unlikely - but no worse than 'bunching up space' I suppose. In a few books, the mechanism is like teleportation - you go from A to B by "folding" the universe so that the points A and B are actually touching (like folding a piece of paper so that two dots - one in each corner - are touching. In others it is claimed that the spacecraft stays still and the universe is moved around it (how does this help?), in even more creative series ("The Hitchhikers guide to the Galaxy") FTL space travel in "The Heart of Gold" works because of quantum improbability - your spacecraft (because of Schrodinger's equation) has a finite probability of being anywhere in the universe - so getting to where you want instantaneously isn't impossible - it's merely highly improbable. You just have to get REALLY lucky - for which they have an infinite improbability generator. It appear that this "saves all of that tedious mucking about in hyperspace". Or in a later radio show in the series a craft exists that takes advantage of the fact that restaurant bills never add up to the same total that each person is supposed to pay. This mathematical property is unique to restaurant bills and can be exploited for hyperspatial travel - so your spacecraft takes on the appearance of a rather cosey little Bistro - and when the check arrives - and doesn't add up - KERPOW! You get where you need to be. Asimov proposes this extra 'hyperspace' - perhaps extra dimensions. The 'jump' takes zero time to occur - but the horribly complex math required to do it limits the distance and frequency at which you can jump. It contains the handy plot device that forces you to take days to weeks to travel conventionally into and out of gravity wells which complicate the horrific math to an unbearable degree. I could go on - there are hundreds of ways this has been written about. SteveBaker (talk) 16:03, 14 December 2007 (UTC)

Edit Conflict: I was about to say the same thing, Kainaw. While hitting a small bit of debris at light speed might do a significant amount of damage, a lot of shows get around many FTL travel-problems by "bending space time", allowing one to fold space and make your current position and destination right next to each other. -- MacAddct  1984 ^{(talk &#149; contribs)} 15:44, 14 December 2007 (UTC)

• But because it is fictional, fictional laws may apply. In Asimov's Foundation universe, the calculations involved in making a FTL jump become impossibly complex when there is any kind of gravity field nearby. So they have to fly at tedious speeds for days or even weeks to get to a point where a jump is possible. Perhaps in those circumstances, even the large distances between asteroids and comets would be too much to make this possible...maybe leaving the plane of the ecliptic turns a 2D calculation into a 3D calculation - thus making it even harder to figure out. It's useless to speculate on the constraints that an entirely fictional device might impose. SteveBaker (talk) 15:41, 14 December 2007 (UTC)

• Lastly, is it possible to build a space station in a random spot in the solar system (ie. it wouldn't be orbiting a planet)? Or would it just get pulled into the Sun? What about if it was placed in an asteroid belt?

  You could theoretically build it in an orbit around the Sun - moving (as a planet does) in a large ellipse around the Sun. But if you were trying to be "stationary" with respect to the Sun, it's gravity would pull your space station to a messy end. It could certainly be build in the asteroid belt too. Asteroids in the asteroid belt are VERY far apart - if you stood on one asteroid, it's very doubtful you'd be able to see any other asteroids around you - even with a good pair of binoculars. So - yeah - you could build a station out there. In general though - you'd want to build where you have plenty of materials for the construction. If you wanted one out in deep space - vastly distant from any moons or planets or whatever - then you'd probably want to build it in orbit around the earth and then use rocket motors to move it to wherever you wanted it to be. Building in the asteroid belt would be a good idea - there are plenty of nickel/iron asteroids that could be melted with a solar powered furnace and refined to make the metal parts of your space station. You could alternatively simply hollow out a regular rocky asteroid to make your space station.

  SteveBaker (talk) 04:59, 14 December 2007 (UTC)

There are some asteroid fields, formed mainly when asteroids enter the Lagrangian point of another planet - the combination of the gravity of the sun and the planet combine to produce a small patch of stable asteroids; the Trojan asteroids near Jupiter are a good example. Laïka 13:39, 14 December 2007 (UTC)

Yes - but the Lagrangian points of the planets aren't stationary - they still orbit the sun. Also, the Lagrange points are exactly that - points - so any object that is not precisely at the lagrange point is going to have some sort of forces causing it to be unstable over the very long term. SteveBaker (talk) 15:41, 14 December 2007 (UTC)

The L4 and L5 Lagrangian points (where Jupiter's Trojans are located) are stable regions, provided the mass of the object at the point is insignificant relative to the masses of the two main bodies. The other Lagrangian points are unstable as you've noted, though orbits about them exist that are more stable -- though probably not stable enough. — Lomn 16:23, 14 December 2007 (UTC)

Addendum: perhaps even the L1-L3 orbits are sufficient -- SOHO has been "at" the Earth-Sun L1 point for over 10 years now, still on its original fuel supply for orbital adjustments, and ACE has been there nearly as long. A space station could presumably be refueled often enough to use this orbit indefinitely. — Lomn 16:28, 14 December 2007 (UTC)

More fuel efficient vs. less air polution (cars)

I know this is some what of an opiniative question but what is more important (for cars) using less gas or giving off less pollutants? Personally I think its more important to give off less pollutants.thanks--Sivad4991 (talk) 03:14, 14 December 2007 (UTC)

Using less gas makes it cheaper to use the car, thus making it more common. In addition, the money saved on gas can be used to buy carbon offsets or, for that matter, it can go to any charity. Of course, the answer depends on how much less gas and how much less pollutants. You wouldn't want to buy a car that uses a million times as much gas and gives off 1% less pollutants, would you? — Daniel 03:58, 14 December 2007 (UTC)

I guess what im asking is should we be trying to find way to decreise our fuel usage of trying to find ways so that our cars give off less pollutants. --Sivad4991 (talk) 04:06, 14 December 2007 (UTC)

The two problems are related. When you burn gasoline perfectly correctly, you end up with carbon dioxide and water. Carbon dioxide is a pollutant - so burning more gasoline produces more of the stuff - burning less produces less. However, it's very tough to do a perfect job of burning the gasoline - and some of it gets combined with oxygen and nitrogen from the air and some of the carbon dioxide to make carbon MONOXIDE (which is pretty poisonous and an even worse greenhouse gas than carbon dioxide) - and also nitric oxide - which is another rather nasty, poisonous pollutant. Worse still, nitric oxide reacts further to form nitric acid - which washed out of the air when it rains in the form of "Acid Rain"...which is yet another major problem! The catalytic convertor in your car removes some of the nitric oxide in the exhaust gasses, turning it back onto plain oxygen and nitrogen - but it doesn't do a perfect job.

So - the less fuel you burn - the less pollutants you emit - as simple as that.

SteveBaker (talk) 04:34, 14 December 2007 (UTC)

Note that diesel fuel is more polluting than unleaded gasoline, but it gets more miles per gallon in almost any equivalent engine. That's why you see a lot of hybrid designs with diesel engines - manufacturers are trying to push that number higher. SamuelRiv (talk) 05:15, 14 December 2007 (UTC)

Plants and carbon

I know that plants take in carbon dioxide and let out oxygen and that they need carbon dioxide to live. But is carbon good for plants just like carbon dioxide is? And if so could it be used in fertalizers? Corect me if im rong but when carbon dioxide is split it becomes sepret carbon and dioxide atoms. Is dioxide a gas and if so is it harmfull to the enviornment. If it dosnt become a dioxide atom then what dost it become and is what it becomes harmfull to the enviornment? thanks --Sivad4991 (talk) 03:27, 14 December 2007 (UTC)

"Dioxide" is just good old oxygen or O₂. Photosynthesis goes like this:

6 CO_2(gas) + 12 H₂O_(liquid) + photons → C₆H₁₂O_6(aqueous) + 6 O_2(gas) + 6 H₂O_(liquid)

So plants aren't left over with just pure carbon. Edit: And the C₆H₁₂O₆ molecule is a sugar molecule that plants uses/stores for energy. --MacAddct  1984 ^{(talk &#149; contribs)} 03:45, 14 December 2007 (UTC)

All of this chemistry happens in the leaves - CO2 comes in through tiny holes in the leaf and water drawn up through the roots meets it there. Sunlight provides the energy to perform the chemistry and Oxygen and Sugar comes out. The oxygen is released from the leaves into the air and the sugar is further transformed into cellulose which is how the plant makes up it's structure. Wood and leaves are mostly cellulose. Plants can't use raw carbon - their biology simply isn't designed for that because there isn't much plain carbon sitting around where plants can take advantage of it. Carbon doesn't dissolve in water - so there would be no easy way for the plants roots to pull the carbon up into the stems and leaves where it would be needed. SteveBaker (talk) 04:24, 14 December 2007 (UTC)

A solution to car pollution (hey that rhymes)

OK for my last question, does any one know of a website where I can offer my ideas and solutions I have for car pollution? thanks for every ones help on my continuoS QUESTIONS! --Sivad4991 (talk) 03:54, 14 December 2007 (UTC)

Since you had no understanding of how cars generate pollution (two questions ago) and didn't know really basic chemistry (that the "dioxide" in "carbon dioxide" is really just oxygen)...(one question ago) - I think it would be EXCEEDINGLY unlikely that anything you have to say on the matter is going to be of much interest to anyone who matters. You need to learn a LOT more before you stand any chance of offering ideas and solutions that are even remotely likely to work and not to have been thought of many times in the past. If you have an interest in helping to solve this major worldwide problem, I strongly suggest you take some chemistry and automotive engineering courses - learn what we already know about this before you try to form your own ideas. If you'd like to explain what you have in mind right here, I'm sure we can tell you whether it's already been thought of - or whether it stands a chance of working. SteveBaker (talk) 04:42, 14 December 2007 (UTC)

How about a little WP:CIVILity here? And who knows? Maybe he or she has an idea unfettered by conventional thinking. Clarityfiend (talk) 09:36, 14 December 2007 (UTC)

You may be interested to read up on the One True Solution.--Shantavira|^{feed me} 12:18, 14 December 2007 (UTC)

I don't see that Steve Baker was at all rude in his comments - he was just being realistic. It's quite common for armchair engineers (with little or no actual engineering knowledge) to think their crazy ideas are somehow better than what the experts come up with. Steve's suggestion was quite good- if you're serious about making contributions to the field, you should first learn what the people before you have already figured out. And, from there, perhaps you can make some real improvements. But approaching the problem without the necessary education is just a waste of time. Friday (talk) 19:30, 14 December 2007 (UTC)

i under stand what you guys are say and i would like to find out what people have alredy thought of but you dont necessarly need to know all about chemistry or automotives to come up with ideas. Maybe all we need to do is change one part on a car. And i did know how cars create exaust.--Sivad4991 (talk) 21:08, 14 December 2007 (UTC)

OK, define what you mean by pollutants? CO₂? Hydrocarbons? FYI the catalytic converter had already reduced a lot of pollution in cars (CO₂ emission isn't really counted as pollution). --antilived^{T | C | G} 21:49, 14 December 2007 (UTC)

• There's a famous quotation about the difficulty of someone from outside of a given field making significant contributions to it. Does anyone know the one I'm talking about? It has of course happened before, like Luis Alvarez and paleontology, and Albert Einstein and eye surgery. --Sean 00:50, 16 December 2007 (UTC)

I know we're straying way off topic here, but what's the story about Einstein and eye surgery? I see you linked to laser eye surgery. Did Einstein make any statements about laser eye surgery that were dismissed by the medical community? --NorwegianBlue ^talk 14:54, 16 December 2007 (UTC)

• • The 'out of field' Einstein story I like the most is the one about how he liked to stroll around the grounds at Princeton and took to chatting with one of the gardeners there. As they pass one particular row of plants, Einstein remarks that they are growing much faster than the others and asks the gardener what kind of plants they are. It seems they are haricots. The gardener was later heard to remark that "Einstein doesn't know beans." SteveBaker (talk) 13:35, 16 December 2007 (UTC)

Carbon at extremely low temperature

Have the properties of carbon, (particularly isotopically pure carbon) been investigated near absolute zero?Thanks, Rich Peterson130.86.14.90 (talk) 06:49, 14 December 2007 (UTC)

From perusing the literature, carbon resistors still function at 1K, but aren't used below this. So presumably it's not terribly affected at the few kelvin area, but I can't find a reason for its lack of use at lower temperatures. This suggests to me that either something funky happens to carbon below 1K, or it's just a technical limitation. Someguy1221 (talk) 08:10, 14 December 2007 (UTC)

One thing I'm wondering about is if at low temperatures, pure diamond or graphite might have interesting electical or heat-conduction properties. Also, what about phonons near 0 K?130.86.14.90 (talk) 01:59, 15 December 2007 (UTC)

Volume of universe compressed

If the entire mass of the universe was compressed to the density of a neutron star, how much volume would it take? MilesAgain (talk) 07:43, 14 December 2007 (UTC)

The mass of the observable universe is estimated at 3x10⁵²kg, and the average density of a neutron star is about 3x10¹⁷kg/m³. So you're looking at a good 10³⁵ cubic meters, which would produce a neutron star 400 million kilometers across (pretending it maintains this same density). This assumes all matter in the universe has the same compresibility as nucleons, which is certainly not true for all mass in the form of neutrinos, EM/gravity waves, or dark matter. But I hope this helps! (and I hope I did my math right) Someguy1221 (talk) 08:07, 14 December 2007 (UTC)

Also, you can't give a figure for the mass of the entire universe, since there is no agreement on the shape of the universe (or evidence to suggest one). For certain possible shapes, the universe could well have infinite extent and infinite mass, and there is no law of physics that would inherently prohibit such universe. Someguy1221 (talk) 08:12, 14 December 2007 (UTC)

Of course, the mass of such a neutron star would certainly be above the Tolman-Oppenheimer-Volkoff limit, so it would collapse into a black hole. —Keenan Pepper 16:56, 14 December 2007 (UTC)

How large would the event horizon be? --Carnildo (talk) 22:55, 14 December 2007 (UTC)

Calculate it yourself. $r_{s}={\frac {2GM}{c^{2}}}$ (Schwarzschild radius). —Keenan Pepper 00:56, 16 December 2007 (UTC)

Plugging in Someguy's mass of the universe into KP's equation gives around 4 * 10²⁵ meters, as compared to around 3000 meters for a black hole with the mass of the Sun (though I'm not sure they can be that small; I know they can't start out that small). --Sean 01:10, 16 December 2007 (UTC)

I think the most interesting thing about that calculation is that the black hole is larger than the equivalent mass neutron star (for which I ignored the possibility of black hole formation). A nice example of how the average density of a black hole surprisingly decreases with mass. Someguy1221 (talk) 04:55, 16 December 2007 (UTC)

But that's hardly a fair comparison. You're recording the diameter of the matter in the neutron star and the diameter of the event horizon for the black hole. To be fair, you have to compare the diameter of the matter in the black hole - and that's zero (well, depending on the position of the observer because the speed at which the material collapses into that singularity becomes relativistic in the final stages). SteveBaker (talk) 13:28, 16 December 2007 (UTC)

Your comment reminded me of the counterintuitive fact that planets above a certain size (e.g., Jupiter), get smaller when you add more stuff to them. --Sean 14:31, 16 December 2007 (UTC)

Interesting. That's the same order of magnitude as the size of the observable universe. --Carnildo (talk) 00:42, 18 December 2007 (UTC)

polar capacitor

is there any symbol of polar capacitor is available in PSPICE schematics version 9.1(student version).193.251.135.125 (talk) 07:43, 14 December 2007 (UTC)

Please, do not crosspost. See WP:RD/C#PSPICE_9.1. ›mysid (☎∆) 12:49, 14 December 2007 (UTC)

How close to a black hole before you are killed?

Lets say you are an astronaut in a space suit. How close can you get to a black hole of stellar mass, lets say 1 or 2 stellar masses, before you are killed? What is the mechanism that kills you? 64.236.121.129 (talk) 15:39, 14 December 2007 (UTC)

The mechanism is extreme tidal forces, otherwise known as spaghettification. Gandalf61 (talk) 15:44, 14 December 2007 (UTC)

How close would you have to be though. 64.236.121.129 (talk) 15:50, 14 December 2007 (UTC)

Estimate the force needed to tear apart a human, and do the math. Gandalf gave you the necessary pointer to tidal forces. -- Coneslayer (talk) 16:06, 14 December 2007 (UTC)

I wouldn't be asking if I already knew how to do that. Haha. Mr. Obvious comes knocking. 64.236.121.129 (talk) 18:16, 14 December 2007 (UTC)

If you really want to be able to figure things out, instead of depending on the Reference Desk for the rest of your life, I would encourage you to get started on basic math and physics. Work your way through algebra, trigonometry, and calculus. Get a good understanding of units of measure. Learn the basic physics. So far, you've been skipping over the basics (Ohm's Law, Newton's law of universal gravitation, gravitational end electric potentials) straight to the complicated phenomena (lightning, black holes). Even if it doesn't seem sexy, you'll be far better off in the long run if you master the basics first. -- Coneslayer (talk) 18:36, 14 December 2007 (UTC)

Naa. 64.236.121.129 (talk) 20:10, 14 December 2007 (UTC)

Isn't the part of the point of this desk that people who are untrained in some area but want to know something about it can ask people who are trained to figure it out for them? I mean, maybe 64.236.121.129 is a horticulturalist...if I had a question on how to grow some plant I wouldn't expect them to say "Go study biology & botany and then learn horticulture and the figure it out yourself." 202.37.62.105 (talk) 04:42, 19 December 2007 (UTC)

See also: event horizon -- MacAddct  1984 ^{(talk &#149; contribs)} 16:10, 14 December 2007 (UTC)

(ec)

This depends heavily on your height, your position relative to the hole, and the mass of the black hole. Using simple Newton's physics (and assuming I didn't screw up my algebra), you end up with: $K={2hGm_{1}m_{2}(r+1)}/{r^{2}(r+h)^{2}}$ where K is the killing force, G is the gravitational constant, m₁ is your mass (negligible and can be ignored), m₂ is the black hole's mass, r is the distance between the black hole and the closest part of your body, and h is the distance between the closest part of your body to the black hole and the furthest part of your body from the black hole. Plug in the values you are interested in and see what the difference in force between your head and toes will be. Then, decide if that is enough to kill you. -- kainaw™ 16:12, 14 December 2007 (UTC)

The only objective way I've heard of this calculation being done is to calculate where the tidal force of the blackhole exceeds that on the surface of the Earth, as this is a very certain lower bound on what will kill you. And I don't think you should be calling a factor negligable when you're multiplying something by it. Someguy1221 (talk) 19:23, 14 December 2007 (UTC)

How long from who's point of view? Your speed as you approach the event horizon will approach the speed of light - so your experience and mine (I'm the one in the nice, comfy space ship a long way off - OK?) will be very different.

Also, isn't it the case that you get cooked by the gamma radiation long before spaghettification sets in?

SteveBaker (talk) 17:20, 14 December 2007 (UTC)

Maybe, if we are assuming there is an accretion disk - but then we could assume a sufficiently shielded space suit too. Gandalf61 (talk) 17:48, 14 December 2007 (UTC)

I think gamma radiation or heat would kill before tidal forces would. 64.236.121.129 (talk) 18:15, 14 December 2007 (UTC)

The larger a black hole is, the weaker its tidal forces are at the event horizon. I'm no GR expert, but if I recall the numbers correctly, it could be hours for a several million solar mass black hole, and days, weeks or even much longer when you get up to the billions of solar masses black holes (time to lethal tidal forces after passing the event horizon). But what Steve said about point of view is very important, but for different reasons. From the faller's perspective, eon's worth of starlight enters the blackhole behind him in mere minutes, tremendously blueshifted. So yes, for a very large black hole, you'll be fried by blueshifted starlight long before the tidal forces get you. Someguy1221 (talk) 19:19, 14 December 2007 (UTC)

I think blue-shifted infalling radiation is only a problem if our astronaut is (somehow) hovering just above the event horizon. However, I was assuming our astronaut is in free-fall. Gandalf61 (talk) 19:51, 14 December 2007 (UTC)

...the light's going to come in behind you no matter how you're falling...Remember that as far as the falling observer is concerned, nothing special happens as he passes the event horizon; everything changes smoothly. He can still see the infalling starlight right up until being squished, getting ever more blueshifted. Someguy1221 (talk) 19:56, 14 December 2007 (UTC)

Surely if the astronaut is in free-fall then infalling starlight coming from behind him should be red-shifted, not blue-shifted. Do you have a source for you blue-shift version ? Gandalf61 (talk) 20:15, 14 December 2007 (UTC)

Yup. (The author is an astrophysicist) Someguy1221 (talk) 20:26, 14 December 2007 (UTC)

Well, my sources say different - you don't see "eon's worth of starlight", and infalling starlight from behind you is redshifted, not blueshifted:

• "Your trip from the event horizon to the singularity is so short that most of the light from faraway distances doesn't have time to reach you so that you can see it." [10]
• "Once inside the horizon, you are doomed to hit the singularity in a finite time, and you witness only a finite (in practice rather short) time pass in the outside Universe. In order to watch the history of the Universe unfold, you would have to remain outside the horizon, the Schwarzschild surface."[11]
• "...there's no way that light from future events far away can get to me. Faraway events in the arbitrarily distant future never end up on my "past light-cone," the surface made of light rays that get to me at a given time."[12]
• "...blueshifts appear in directions transverse to observer motion, while redshifts are always seen in directions towards or away from the black-hole center"[13] Gandalf61 (talk) 21:33, 14 December 2007 (UTC)

• Define short, or just wrong. For truly massive black holes, the distance between you and the black hole can be quite extreme. The black hole at the center of our own galaxy (which is not even that big) has a Schwarzshield radius of about half a light minute.
• "Also time outside would appear to be running much faster, so we would be able to see the evolution of the universe "flash" before our eyes"
• "light from the universe "falls" into the black hole it gains energy. This means that its wavelength gets shorter. Blue light has a shorter wavelength than red light - so very simply things would appear to get bluer" Blueshifting in incoming light has nothing to do with relative velocities, it's entirely thanks to gravitational blueshift
• Regardless of how much time worth of light actually reaches you, you're going to get a very deep tan. Someguy1221 (talk) 01:59, 15 December 2007 (UTC)

• Someguy asked if I could comment on this issue, as I have some experience in the area. The question is rather interesting, but it might take me a while to come up with a complete answer, as most of my references are elsewhere and I'm rather busy this weekend. My guesses are that you probably wouldn't see the evolution of the universe flash before your eyes, and that any possible gravitational blueshifting argument would also have to take into account possible redshifting from the velocities involved. However, the matter is rather complex, and the answers are rather unclear; despite the frequent discussions of the environment inside event horizons, it's not clear to me that a person, or indeed any sentient creature or even any computational device, could survive at all in such a situation, even ignoring tidal forces and radiation. I'm of the opinion that most musings on the subject are probably incorrect, especially when written for a popular audience. --Philosophus ^T 08:34, 15 December 2007 (UTC)

<Response to Someguy1221>Your appeal to gravitational blueshift is incorrect, as the classic analysis of gravitation redshift/blueshift assumes that the source and receiver are stationary with respect to one another. See, for example, Einstein's On the Influence of Gravitation on the Propogation of Light, which says "Let the two material systems S1 and S2, provided with instruments of measurement, be situated on the z-axis of K at the distance h from each other ..." - note that h remains constant throughout the analysis. This analysis would apply to an astronaut who was hovering at a constant distance from the singularity (they would, of course, have to be outside of the event horizon) - I agree that infalling starlight would appear blueshifted to such an observer. However, our astronaut is not stationary with respect to the distant stars - he is accelerating away from them, and towards the singularity. Therefore he observes infalling starlight to be redshifted, not blueshifted. Gandalf61 (talk) 17:56, 15 December 2007 (UTC)

You can't just discount the effect entirely; you now have two competing influences. I suppose then it depends on just how fast can the black hole accelerate you away from the stars, what velocity you approach the event horizon at initially, whether you're fighting or helping the black hole on the way down, and whatever other wierd GR effects would be happening. Someguy1221 (talk) 04:53, 16 December 2007 (UTC)

You know, I think my main difficulty here is that the only GR I know I learned from a somewhat crazy physicist who had a habbit of proposing the construction of space stations inside black holes that would fight gravity to record data as long as possible...Someguy1221 (talk) 04:59, 16 December 2007 (UTC)

What exactly would be the point of that? If the space station is inside the black hole then none of the information it might record would ever reach the rest of the universe! Sure, it finally answers our debate about redshift/blue shift - but the radio transmission (being "light") can't ever escape beyond the event horizon...by definition...so we'd never know what the answer was! SteveBaker (talk) 13:24, 16 December 2007 (UTC)

Remember you'd probably die long before the force is strong enough to tear you apart. For example, it's possible the force may stop the blood from reaching your brain depending on your position meaning you'll blackout and eventually die (as can occur with pilots). g-force may be helpful Nil Einne (talk) 16:40, 16 December 2007 (UTC)

Water + Hot oil

Why does hot oil react the way that it does to water? When I put wet strips of potato into a deep fat fryer, is there a relation to the reaction that occurs when I throw water over a chip pan fire? --Seans Potato Business 16:19, 14 December 2007 (UTC)

When the oil or pan is hot enough, water will very quickly go from liquid to steam. When submerged in oil, it accelerates upward out of the oil - often causing the oil to splatter. When it hits a dry pan, it will bounce as the part that touches the pan will accelerate upward, pushing against the liquid. Both are similar - the water is quickly becoming steam. By the way - that is how I was taught to test the heat for cooking. If the water doesn't jump off the pan or jump out of the oil, it isn't hot enough. -- kainaw™ 16:23, 14 December 2007 (UTC)

I was once told by my wise mother that fat content had something to do with it, as I noticed one time frying onions (I believe) didn't make the oil 'spit'. -- MacAddct  1984 ^{(talk &#149; contribs)} 16:49, 14 December 2007 (UTC)

I was told the same thing when I learned to cook. The thicker the oil, the more it splatters. It makes sense. As the water shoots out, it will carry more oil with it if the oil is thick. -- kainaw™ 16:52, 14 December 2007 (UTC)

That's presumably correlated with an oil's smoke point, right? -- MacAddct  1984 ^{(talk &#149; contribs)} 16:59, 14 December 2007 (UTC)

I don't know, but I doubt it. I cook with multiple oils (all refined). I noticed that all but one have a smoke point of 450F. However, they splatter much differently. -- kainaw™ 17:05, 14 December 2007 (UTC)

I heard that that's not the right method of testing if the oil is hot enough is wrong, because the hot oil could burn your skin. A better method is dropping small crumbs of the breading if you're frying a breaded meat/fish/vegetable, or small crumbs of the breading of something else. If the oil is cold, it just sinks to the bottom. If it's hot, small bubbles will push it around for a while. – b_jonas 16:15, 15 December 2007 (UTC)

I agree dropping water into hot oil is a bit dangerous should be avoided. Your suggestion is a good idea and I believe a cube of bread is also a useful test. How long it takes to brown will vary depending on the the temperature and some recipes/whatever will give this, there's also this general guide which has a fairly small temperature range [14]. Of course, a thermometer suitable for the purpose is probably your best bet for consistent, simple and reliable deep frying Nil Einne (talk) 16:34, 16 December 2007 (UTC)

Aside - this is why you should NEVER use water to try and put out a burning liquid (such as oil) unless you're a trained firefighter and know exactly what you're doing. The water will superheat into steam in a fraction of a second and explode flaming oil everywhere - see [15]. Exxolon (talk) 20:37, 16 December 2007 (UTC)

I feel that it is important to clarify what I meant by testing oil with water. I dip the tip of my finger in water and fling a single drop of water into the oil. I do not take a cup of water and dump it in. A single drop of water pops into steam when it hits the surface of the oil. When testing a hot (dry) pan, it bounces. I hope this explanation keeps someone from trying to pour water into hot oil. -- kainaw™ 00:06, 17 December 2007 (UTC)

Dams

OK so at a normal dam there is water on one side and air on the other. At the bottom of the dam force of the water pressure pushes horizontally is against the dam and here it is at its greatest. So the dam must be thick at the bottom but can be less thick at the top. However, behind the dam there are sometimes mini-dam-things, which can raise the level of the dam further. These don't have to be thick at the bottom because the water pressure from one side cancels out the pressure from the other. But what are these mini-dam-things called? —Preceding unsigned comment added by Swithlander (talk • contribs) 18:06, 14 December 2007 (UTC)

Are you referring to a floodgate? I've always called them flashboards, but apparently that is not the correct term. -- kainaw™ 18:33, 14 December 2007 (UTC)

Flashboards and Stoplogs are mentioned in the article - could use a picture though. The main reason gravity dams are wide at the bottom isn't because the water pressure is greatest at the bottom, it's to give a wide foot space and enough mass to keep the dam from being rolled downstream by the water pressure. --Duk 18:50, 14 December 2007 (UTC)

I don't quite understand what you mean by "raise the level of the dam further" if they have water on both sides. Just to break the log jam, I'll offer cofferdam. Flashboards, meanwhile, at least in New England, are usually big sheets of plywood-like material held vertically at the top dam by metal rods or pipes. The strength of the rod/pipe is engineered so in a (flash) flood, they will bend, allowing the flashboards to wash away and releasing the first four or so feet of water formerly held back by the dam, lowering the risk of a more-serious flood should the dam breach later (and removing from the dam the load of those extra feet of held-back water ).

Atlant (talk) 22:56, 14 December 2007 (UTC)

I don't understand the question either -- does "behind the dam" mean upriver or down? I'd think it means upriver, but if the downriver side is meant, perhaps we're talking about buttresses, as in the photo of The Dalles Dam for example? The buttresses are there, I'm guessing, to allow for a higher and less thick dam -- that is, the water pressure behind the dam is offset by the strength of the buttresses? I have no idea if this is actually the purpose of the buttresses, just another wild guess about what the OP meant; ie, These don't have to be thick at the bottom -- you mean "these kind of dams"? Pfly (talk) 00:27, 16 December 2007 (UTC)

Rising CO2 content in atmosphere: effect on human breathing?

The Keeling Curve shows rapidly increasing carbon dioxide levels in the atmosphere since 1958:

It shows a steady increase in mean atmospheric CO2 concentration from about 315 parts per million by volume (ppmv) in 1958 to over 380 ppmv by the year 2006. This increase in atmospheric CO2 is considered to be largely due to the combustion of fossil fuels, and has been accelerating in recent years.

We know that increasing CO2 levels are affecting Earth's temperatures.

What I want to know is at what point it will affect human breathing. We have gone from 315 parts per million by volume to 380 ppmv in the last 50 years. Since the trend is accelerating, we may at some point in the future have double the amount of CO2 in the atmosphere as we had in 1958.

I'm sure we won't fall over and die suddenly, since the change spans decades or centuries, but won't there be noticeable effects on the efficiency of breathing at some point? What is that point?

Jawed (talk) 19:42, 14 December 2007 (UTC)

I don't know a specific answer, but one factor to consider: What is the normal local variation in CO2 levels already? In other words.. If you, your spouse, and your dog all sleep in the same room, with poor circulation, do you effectively have a higher CO2 level at night? On the other hand, what if you happen to sleep in a room full of plants? Maybe we already deal with local variations that are bigger than the global ones. If they're not a problem, then maybe it's not a significant factor. Friday (talk) 19:46, 14 December 2007 (UTC)

(edit conflict) I could not quickly find the numbers in Wikipedia, but my thinking is that (a) the CO2 concentration of exhaled breath is huge compared to ~400 ppm, and (b) the exchange efficiency of a breath is relatively poor (that is, a good fraction of the air in your lungs is retained each time you breathe). If both of these claims are true, then we should be pretty insensitive to atmospheric CO2, because the CO2 in our lungs is dominated by the effects of our own respiration, not the atmosphere. -- Coneslayer (talk) 19:48, 14 December 2007 (UTC)

The federal government considers concentrations greater than 5000ppm to be unhealthy to adults, although estimates on what constitutes a danger to one's health are as low as 1000ppm [16]. The LD50 of carbon dioxide is 100,000ppm, although prolonged exposure at lower concentrations would also be fatal. Someguy1221 (talk) 19:53, 14 December 2007 (UTC)

I recall reading an old book by Asimov and someone else (nonfiction) about the different kinds of planets we might find and be able to inhabit. I'm not sure how definitive it is, but they put human limits of CO2 at 7 torr... Man, I should've taken better notes. Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 21:45, 14 December 2007 (UTC)

Here is the handy scale of CO₂ concentrations in parts per million (ppm) distilled from our articles on Carbon dioxide, Carbon dioxide in the Earth's atmosphere and other similar places:

• 180 ppm to 280 ppm - historical CO2 levels have oscillated back and forth between these limits from over half a million years ago until about 1940.
• 280 ppm to 380 ppm - rise in CO2 levels from 1940 until today in "clear air" locations.
• 600 ppm - typical present day value in big cities, etc.
• 1,000 ppm - causes discomfort in more than 20% of people.
• 2,000 ppm - majority will feel a significant discomfort, many will develop nausea and headaches.
• 5,000 ppm - maximum safe level for healthy adults over prolonged (8 hour) exposure. Children, elderly & sick people can tolerate 'significantly less'.
• 30,000 ppm - safe for brief exposure.
• 40,000 ppm - immediately dangerous to life and health.
• 45,000 ppm - exhaled breath
• 50,000 ppm - Dangerous when inhaled. Exposure for more than half an hour causes acute hypercapnia
• 70,000 ppm to 100,000 ppm - unconsciousness in only a few minutes.
• 100,000 ppm - Car exhaust (up to 150,000 in California due to laws placing limits on carbon monoxide emissions).

Not a pretty picture - but that's the facts. SteveBaker (talk) 21:55, 14 December 2007 (UTC)

So...you're saying that someone who stands too close to my face while talking could be considered an "immediate [danger] to [my] life and health"? o_O Someguy1221 (talk) 21:59, 14 December 2007 (UTC)

If you were both in a very small, totally enclosed space so that your exhaled breath could not be replenished with fresh air...then yes. But your breath is warm - and warm air rises over cold air - so your breath doesn't leave your nose and just kinda sit there in a big invisible ball ready to be breathed back in again. It floats upwards and outwards and disperses out into the room (watch what happens to the smoke when a smoker exhales - that's a pretty good indication of what's happening to the CO2 in his/her breath). Also, read carefully - 50,000 ppm isn't harmful until you've been breathing it for half an hour - you've got a few minutes even at 100,000 ppm. But if you put a plastic bag over your head, you'll die from rebreathing your own exhalations quite quickly (Hint: Don't try this at home folks!). Of course we're only talking about CO2 levels here. If you don't have adequate amounts of fresh air, you'll also be depleting the oxygen content of the air and running out of oxygen is also fatal. The numbers above are for when there is adequate oxygen but the CO2 levels are becoming poisonous. Recall the events of Apollo 13 (see the movie!) - they had plenty of oxygen for the trip - but the CO2 "scrubbers" were not removing the CO2 from the air - and they are all nervously watching the CO2 meter creep upwards as they construct the famous 'mailbox' gizmo to fit a square box into a round hole and get the CO2 scrubbers working again. That was a case of three guys in a confined space breathing each others exhaled breath. SteveBaker (talk) 13:12, 16 December 2007 (UTC)

Standards seem to have changed since I looked at them: the 8-hour limit I remember was 10,000 parts per million -- higher than any substance. --Carnildo (talk) 23:05, 14 December 2007 (UTC)

We are now at a CO2 level of almost 400 ppm. According to this page on CO2 Health Effects and toxicity levels:

http://www.inspect-ny.com/hazmat/CO2gashaz.htm

Carbon dioxide levels above 1500 to 2000 ppm are likely to be reached only in unusual circumstances (being enclosed in an airtight closet for a long time)

I went to Keeling's website at ucsd.edu:

http://scrippsco2.ucsd.edu/home/ and got their data in Excel format:

http://scrippsco2.ucsd.edu/data/in_situ_co2/monthly_mlo.csv

If you solve for an exponential equation fit, you get:

co2_ppm = 0.1062 * e^(0.0041 * year)

Plugging in 1000 ppm, you get year = 2232. So in the year 2232 everyone on earth will start to feel as if they've been locked into an airtight closet when they breathe?

Jawed (talk) 06:45, 15 December 2007 (UTC)

Yep - that sounds about right. We aren't really likely to have CO2 toxicity problems because if we don't do something to fix global warming in a lot less than 225 years then climate-related problems will get us long before CO2 toxicity does. However, that may well not be true for other plants and animals around the world. The numbers above are for humans...maybe they also apply fairly well to other animals with lungs (maybe) - but we would also need to worry about what they are for pollinating insects and other vital bits of our ecology. SteveBaker (talk) 13:12, 16 December 2007 (UTC)

Absolute Zero Possible?

According to the Wiki article on Absolute zero, the coldest place that has been discovered to date is in the Boomerang Nebula, which the article states is –272.15 degrees Celsius, or about -458 degrees Fahrenheit, or 1 degree Kelvin. Here's an article published in the Sydney Morning Herald that discusses this discovery. The article mentions that this place in the Boomerang Nebula is actually colder than the background cosmic microwave radiation, due to the special influence of the nebula's central star that is acting like a giant refrigerator. It does this by shooting out super cold gas.

So here's my question: if there were more of these type of refrigerator stars in the universe, is it possible that scientists may some day discover one that is able to achieve absolute zero? What I'm asking is - is it actually possible to reach absolute zero, or is this an unattainable goal due to some reason I can't think of right now? -- Saukkomies 20:11, 14 December 2007 (UTC)

Quantum Mechanics says no. Zero point energy? WilyD 20:16, 14 December 2007 (UTC)

No, it doesn't: It only says that there is energy in the system if the temperature is absolute zero. Icek (talk) 02:59, 15 December 2007 (UTC)

See the Third law of thermodynamics. 207.148.157.228 (talk) —Preceding comment was added at 20:49, 14 December 2007 (UTC)

Definitely not. Reaching absolute zero is a bit like reaching the speed of light - you can get close - but you can't quite actually get there. The 3rd law of thermodynamics is a law. SteveBaker (talk) 21:26, 14 December 2007 (UTC)

Isn't that a faulty anology since there actually is something that can travel at the speed of light - light itself?82.182.116.8 (talk) 21:36, 14 December 2007 (UTC)

Change "there" to "past" ;-) Someguy1221 (talk) 21:41, 14 December 2007 (UTC)

Individual particles can obtain a state of minimum energy. This is in fact the normal condition of most particles in a Bose-Einstein condensate. However, the third law of thermodynamics says that no macroscopic process can ever remove all of the thermal energy from an ensemble of particles. In other words, any macroscopic collection of particles will always have an average temperature above absolute zero. Dragons flight (talk) 21:48, 14 December 2007 (UTC)

These are great answers! Thanks. So, do you think it would be a good idea to add something to the Wiki article on Absolute zero that mentions this? I think one of you guys who just replied to my question would be perfect a choice for that (hint hint). -- Saukkomies 16:59, 14 December 2007 (UTC)

It looks to me like the basic parts of it are all stated pretty clearly in the intro of that article, and even the details are there too. The sections on reaching towards absolute zero even mention the Boomerang Nebula. Of course, rewording to make the important parts even more clear especially for non-phyisicist readers would always be welcome! DMacks (talk) 22:28, 14 December 2007 (UTC)

Of course, if you don't mind going below 0K, you can also talk about negative temperatures. Well actually, they're infinitely hotter than 0K, but a lower number. Scientists are weird:) DMacks (talk) 22:24, 14 December 2007 (UTC)

Well you find a better way to designate a temperature that happens to be hotter than infinity :-p Someguy1221 (talk) 01:23, 15 December 2007 (UTC)

Okay, I read most of that article on negative temperature, and now my head hurts. It's well written, but I do think it's a bit foggy for even a somewhat clever non-physicist like myself to fully grasp. It presupposes a certain level of mathematical ability or familiarity with physics on the part of the reader. Of course perhaps I am trying to shortcut the process of mastering these deeper level physics concepts by not reading a physics textbook or taking a physics class, and instead am trying to get it all through the "Cliffs Notes" method of reading Wikipedia articles. Heh. But I do want to understand Negative Temperature. It's completely fascinating to me right now. So is there some book out there written for non-physicists like me that would do a decent job of explaining this stuff? Just to give you an idea of my level of comprehension, I have read Hawking's "A Brief History of Time", and was able to understand most of it. But that wiki article about negative temperatures eludes my grasp. Perhaps because it is sort of isolated on its own - there's not a lot of supportive background other than linking to other Wiki articles and trying to do so in a comprehensible way. Sometimes wikipedia is awesome, but perhaps it has a drawback in instances like this... --Saukkomies 17:40, 14 December 2007 (UTC)

I've never thought of negative temperatures as anything with profound meaning. It's really just a quirk of defining temperature as ${\frac {1}{T}}={\frac {dS}{dE}}$ , where E is energy and S is entropy, if one is given a strict and absolute measure of entropy. For some systems, temperature is simply allowed to have a negative value, and this transition takes place as the graph of dS/dE crosses the energy axis. Someguy1221 (talk) 01:23, 15 December 2007 (UTC)

So actually the claims about absolute zero being "impossible" are not entirely correct, or at least not entirely precise (which is sort of appropriate, because the whole concept of "temperature" is not entirely precise in the first place).

A macroscopic object consists of finitely many atoms, each of which has a discrete spectrum of energy states, and then there are also states describing the interactions among the atoms, which form a discrete spectrum provided the whole system is bound.

So if just by chance the whole thing happens to radiate all its thermal energy away at once and reach its global ground state, do we call that "absolute zero" for the system? Well, I don't know what else "absolute zero" could mean for this system. And it is certainly possible (if extremely improbable -- cf infinite monkey theorem) for this to happen. (By the way, responding to WilyD -- no, the fact that some zero-point vibrational energy remains does not mean the system is not at absolute zero. The zero-point energy is precisely the energy that does remain at absolute zero.)

Now there are a couple of difficult subtleties with this scenario. One is that we could never know that the system was in its global ground state. Another is that temperature is defined as though the spectrum were continuous (it's defined in terms of the derivative of the internal energy with respect to the log of the number of states having that energy, but when we're talking about a discrete spectrum it's not so clear just how you take a derivative). --Trovatore (talk) 23:18, 14 December 2007 (UTC)

Absolute Zero Question, Part B

Okay, after reading the links that were included in the above answers, I became stumped on another related question. Let's say that the theory that states that the Ultimate fate of the universe is a Big Freeze, as opposed to the other possibilities such as the Big Rip, the Big Bounce, the Big Crunch, etc. I noticed in the Wiki article about the Big Freeze that it says that ultimately such an end to the universe would result in everything reaching Absolute Zero. So, assuming this is correct, then I am now puzzled. I was totally grokking what SteveBaker said about comparing Absolute Zero with the Speed of Light. It makes sense to me to think of it as an unreachable condition. But then I read this business about the Big Freeze producing Absolute Zero, and now I'm once again banging my head against the wall trying to get a handle on this. What exactly will happen to "stuff" in the universe if the Big Freeze takes place? Will it all turn into some kind of subatomic quanta? Will everything become nothing? My mind is reeling from trying to figure this one out... Please help! -- Saukkomies 17:26, 14 December 2007 (UTC)

The absolute zero point is only approached asymptotically, so only at infinite time do you get to absolute zero. Of course at any nominated time the temperature is not at absolute zero, so really it is never reached, just approached. The same situation again. Graeme Bartlett (talk) 23:48, 14 December 2007 (UTC)

Okay, I think I've caught the scent of your trail, Graeme. It sounds like there are different kinds of time, is that correct? I mentioned I'd read "Brief History", but it was several years ago since I last peaked into it, and well, that book sort of takes a lot of re-reads to get to the point where I could recall most of it... So - we have different kinds of time, and one of these kinds of time is infinite. Does that mean that infinite time is connected to the Big Rip or Big Freeze theories? Because if I recall, Hawking discusses how if there was a Big Crunch that time would start to go backwards once the universe started to collapse upon itself. I say I remember this, but I don't understand it. I just take his word on it. Am I somewhere in the neighborhood here, or way out on a limb? -- Saukkomies 19:55, 14 December 2007 (UTC)

The going to absolute zero theory heat death only applies if the universe expands for ever. If time stops, the universe contracts, or time goes into reverse, the temperature will not go to zero. If there is a big rip a different thing happens because the macroscopic world is taken apart leaving only widely separated particles. I think that the concept of temperature will not apply in that case. The concept is like in maths $1/t$ where you can get this as small as you like but cannot actually get it to zero, the concept of a limit. Graeme Bartlett (talk) 20:56, 15 December 2007 (UTC)

What it actually means is that for any given temperature above absolute zero, no matter how close, after a certain point in time the temperature stays lower than that. It has absolutely nothing to do with anything infinite. By the way, how can time stop or go in reverse? If t is time, dt/dt will always be one. (In plain english, time always goes forwards at a rate of one second per second. On second in the future is always exactly one second in the future. No more, no less.) It would have to be zero for time to stop, and negative for time to go backwards. It can end, but I don't see how it could stop. —Preceding unsigned comment added by DanielLC (talk • contribs) 17:30, 16 December 2007 (UTC)

Why do Cells divide?

I heard that cells divide to grow, reproduce, renew, and to repair, but what does each of these stages mean? —Preceding unsigned comment added by 68.228.14.91 (talk) 21:29, 14 December 2007 (UTC)

See cell division (or mitosis for how human cells usually divide). But very simply put, for a multicellular organism (like you), cells need to divide to build up your body. The reason you can't just have a handful of ever expanding cells form a multicellular organism is caused by surface area to volume ratio. Basically, cells need to be tiny to work they way they're supposed to, so they need to divide as you grow. For the same reason, cells need to divide to replace any damaged or dead cells in your body, as they can't just expand to fill in the space and function of the dead cell. As for reproduction, it's very simple. If cells never divided, reproduction simply wouldn't happen! You can't make a new organism without splitting it off from something that was already alive. If a single celled organism never divided, there could never be more of it, and when it dies that would be the end of it. For multicellular organisms, if we just lopped off some existing cells to form a new person, we'd eventually run out of cells. Someguy1221 (talk) 21:40, 14 December 2007 (UTC)

That helps(a bit)... 68.228.14.91 (talk) 21:48, 14 December 2007 (UTC)

There are links between cell division and DNA repair. --JWSchmidt (talk) 01:48, 15 December 2007 (UTC)

Speed of light

When the light ray moves, what exactly makes it move at the speed it moves? In other words, when the ray travels (for ex. in vacuum), it has to move at a fixed constant speed, how exactly is it regulated to move exactly at this speed? or, in more other words, how does light know that it has to move at a particular 299,792,458 m/s in vaccum? I understand that this perhaps is because of some kind of weird forces or something of this sort acting on photons which always is equal for all photons no matter how much their energy is, but what is it exactly? Is there something strange happening in the sub-photonic level? - DSachan (talk) 22:58, 14 December 2007 (UTC)

Electromagnetic theory explains this. Basically is due to the wave and field properties of light. The forces are not weird, and are amoungst the best known, they are magnetism and electrostatics. The actual value is down to the permittivity and permeability of a vacuum. Using differential equations it is possible to solve the speed that a change in the fields move at, and it is the speed of light. Graeme Bartlett (talk) 23:57, 14 December 2007 (UTC)

I know where it is derived from but I want more physical picture of the process and if possible intuitive also (which I think is very difficult here). In perfect vaccum (though this is not possible), there is no matter. So, how do I imagine, what is going on with the quantities like magnetic permeability etc. which appear in the wave equation. Also, if I take the particle theory and not consider the wave theory of light, how would I go about dealing with the speed? Photons are also fundamental particles of nature, so what is going on between photons when they move? - DSachan (talk) 13:15, 15 December 2007 (UTC)

Here's a way I have of grasping this idea, which might be completely wrong, and if so I would appreciate being corrected on it. At any rate, as something travels at very fast speeds it begins to get compressed away from the direction of its travel - it becomes foreshortened. However, this is not apparent from the perspective of the object traveling fast. So, for example, if an astronaut was on a spaceship that was traveling at half the speed of light, he, his spaceship, and everything in it would be foreshortened. This would be apparent to an observer standing on a stationary point looking at him and his spaceship through a telescope, but the astronaut himself would not be able to tell that he and his ship were being compressed. Now, as matter approaches the speed of light, it becomes increasingly compressed. Once matter finally crosses the threshold and actually achieves the speed of light, it becomes so compressed that it ceases to be matter anymore and turns into something else: electromagnetic energy, or light. In other words, it has become infinitely compressed. Once it has reached the state of being infinitely compressed, it is impossible for it to get more compressed than it is, for one thing it is no longer even in a state in which compression even can happen. So that is why it can not go faster than the speed of light, because there's no way for it to compress any further. So, does this idea have any basis in reality, or am I way off target? -- Saukkomies 20:05, 14 December 2007 (UTC)

Well, not exactly. First of all, nothing with mass can reach the speed of light. To do so would require an infinite amount of energy, because not only does length decrease as you approach the speed of light, but mass increases. Also, the major factor in relativity is not spatial compression, but time dilation. As you approach the speed of light, time slows down, so light traveling away from your spaceship seems to be moving faster than it does to someone watching you fly past. That way, from both perspectives, the light moving ahead of your spaceship appears to be moving at the speed of light. (see a bit more on it here)

Second of all, the speed of light actually does vary depending on the medium it's traveling through. Light travels through air, water, and glass more slowly than it does through a vacuum. It's even been slowed down to as little as 6 miles per second. So, while the speed of light in a vacuum is a constant, the speed that light can travel is not. As for why the speed of light is that particular number, well, that's one of the great mysteries of science. -- HiEv 01:53, 15 December 2007 (UTC)

I prefer the "modified" relativistic explanation: If you assume the laws of physics are the same in every inertial reference frame, then it is necessarily the case (through some annoying math) that one and only one invariant speed exists (the Mermin article in the reference gives a good derivation, if you have access to it). It can further be shown (through more annoying math present in Mermin's article) that any particle with zero rest mass must travel at the invariant speed, whatever it may be. And then quantum physics can show that photons have zero rest mass, or something. So, this explanation doesn't say why the invariant speed is whatever it is, but it's a very sound proof that light must travel at it. Someguy1221 (talk) 01:39, 15 December 2007 (UTC)

I never thought of that. In mathematics, there are only two fundamental numbers: the additive inverse (zero) and the multiplicative inverse (one.) All other numbers derive from these. In physics, there are only two fundamental speeds with respect to any reference frame: zero, and one times the speed of light. -Arch dude (talk) 02:53, 15 December 2007 (UTC)

You mean identity, not inverse. And there's nothing very fundamental about zero speed in physics, since it's frame-dependent. Algebraist 04:04, 15 December 2007 (UTC)

It's slightly unfortunate that the cosmic speed limit wound up being called "The Speed of Light" - because it makes light sound rather more special than perhaps it ought to be. Photons happen to travel at the cosmic speed limit - other particles happen not to. This has some rather important consequences. Special relativity says that your "rest mass" is multiplied by the "Lorentz factor" ${1 \over {\sqrt {1-v^{2}/c^{2}}}},$ to get your relativistic mass. (where v is the speed that you're moving and c is the cosmic speed limit). So, if your rest mass is some non-zero number - then you can't be moving at 'c' because v² would be equal to c² - and you end up with dividing 1 by the square root of 1-1 - which means dividing one by zero...which means you'd have an infinite mass (or an undefined mass if you are a mathematician), not good! But the reverse problem exists for light. Photons have a small, measurable 'relativistic' mass at the speed of light. So what is their mass if you slowed them down? Well, to calculate rest mass from relativistic mass, you'd have to divide by the Lorentz factor...but that's infinity...and dividing by infinity is another one of those things that mathematicians get all sulky about. So we can't calculate the rest mass of a photon...it doesn't really have a rest mass...and if we can't calculate it's rest mass, we can't use the Lorentz factor to calculate its mass at any speed less than c either! So in a sense, the mathematics is what forces light to travel at the cosmic speed limit. If it somehow managed to go at any other speed, the mathematics that underpins our universe would 'blow up' and produce all sorts of annoying infinities! This argument is somewhat a "tail wagging the dog" thing...but which came first? The behavior of light whose consequences are the Lorentz transform and special relativity? Or perhaps (and I prefer this), relativity is "how the universe works" and light merely travels at that speed because it must. SteveBaker (talk) 16:43, 15 December 2007 (UTC)

December 15

Best armor-penetrating caliber cartirdge?

I understand the .45 has too low velocity, whereas the 9 mm has not enough power... so what's the ideal pistol bullet against standard body armor? —Preceding unsigned comment added by 83.5.250.239 (talk) 01:14, 15 December 2007 (UTC)

See Body_armor#Performance_standards. As a general rule, most decent soft body armor is effective against pistol rounds. Friday (talk) 04:13, 15 December 2007 (UTC)

So-called armor-piercing handgun rounds usually rely on construction, like the teflon bullet and Black Talon, ammunition although their abilities are opften overstated. Rmhermen (talk) 17:40, 17 December 2007 (UTC)

Black Talon is not armor-piercing ammunition, this is an unfortunate fabrication perpetuated by the media. It is essentially normal hollowpoint pistol ammunition, the only difference is that its jacket is scored in such a manner as to create small sharp points when it peels back during impact. It is stopped by all normal pistol-resistant body armor. Black Talon is still sold, both vintage and new, and is not illegal. It was merely renamed Ranger SXT by Winchester to avoid the negative publicity (the joke was SXT stands for Same Xact Thing). As to the original question, for penetrating armor, velocity and diameter are king. Cartridges which combine high velocity and low diameter apply all their kinetic energy to a very small area of armor, allowing them to penetrate. Some cartridges augment this penetration by using hard metal cores, such as steel or tungsten instead of lead. Standard 5.56x45 will penetrate most police body armor, but some military armor will resist 5.56 and 7.62x39 or even 7.62x51. 5.7x28 is a new armor piercing cartridge by FNH, as is 4.6x30-something by H&K.

"Troubleshooting" PCR protocol

If a person is "troubleshooting" a methylation specific PCR protocol with pre-defined primers, what sort of things are they going to be able to vary? I'm told it will be by trial an error. Are there online tools to advise regarding the lengths of time for each stage in each PCR cycle etc? --Seans Potato Business 02:07, 15 December 2007 (UTC)

You can vary annealing temperature, length of annealing or extension time per cycle, magnesium concentration, Mg:dNTP ratio, Mg:salt ratio. You could try hot-start PCR, touch-down PCR or two step PCR. You can, literally, spend weeks playing with PCR variables. There are loads of online tools that will give you every variable known to man that you can use to calculate cycle length, here is one, however the length of time depends very much on which enzyme you are using. Most commercial enzymes synthesize DNA at a rate of around 2kb/min, so if your amplicon is less than that, 1min extension will probably be sufficient with 30 sec of melting and annealing. Rockpocket 02:25, 15 December 2007 (UTC)

It appears that, for methylation specific PCR, there are a few extra things you could play with too, during the bi-sulphite modification step. Rockpocket 02:30, 15 December 2007 (UTC)

Whats special about frequency?

A question thats been bothering me for some time is: why is it not possible to change the frequency of an electrical or optical signal with out going through some non-linear process (like a mixer)? (excluding the Doppler effect which requires relative motion between source and receiver). After all, we can change the wavelength and/or the velocity quite easily. Whats special about frequency?--79.76.208.92 (talk) 03:14, 15 December 2007 (UTC)

How do you mean "changing wavelength quite easily"? Wavelength and frequency are inexorably tied together... Arakunem^Talk 03:28, 15 December 2007 (UTC)

V=f*λ in a certain medium. Change the medium, you change the velocity and the wavelength, but you cant change the frequency! —Preceding unsigned comment added by TreeSmiler (talk • contribs) 03:36, 15 December 2007 (UTC)

Frequency is tied to the energy of a photon, so you're asking how to increase/decrease the energy of a certain photon without absorbing it and re-emitting a new one. I don't know of a physical process that can do that. I'm not sure it's something "special" about frequency though...each parameter is modifiable by a system that interacts with that parameter. Maybe frequency is more intrinsic to the photon itself than to its motion through space, so it's harder to act on it? DMacks (talk) 06:14, 15 December 2007 (UTC)

Not only photons. What about electromagnetic waves? why is frequency invariant there? Does this have to do with energy as well?--TreeSmiler (talk) 12:04, 16 December 2007 (UTC)

A factory at the end of a road is building cars and sending them out on the road with a fixed frequency. As long as all cars are driving at a constand speed, the distance between them (i.e., the wavelength) will be constant as well. If they encounter rough terrain, they might have to slow down (making the wavelength shorter). The frequency with which they pass a roadside observer will not change, however, regardless of the terrain. Think of what would happen if the observer saw a higher frequency than that of the factory. There would be more cars leaving the area between the factory and the observer than entering it. You can't have that (apart from mabye a short while) because soon that area would be empty of cars. Similarily, the crests and troughs of a wave (be it an electromagnetic wave, sound wave, …) don't just disappear or pop up out of nothing. —Bromskloss (talk) 10:57, 15 December 2007 (UTC)

Good point. But if you were to take a fixed number of cars after they left the factory, and sped them all up at the same time, you standing at the end of the road would see an increased frequency (for a short time).The wavelength (distance between cars) would remain the same. The converse is also true.--TreeSmiler (talk) 12:04, 16 December 2007 (UTC)

Frequency is energy is the best statement of this. Because you can't change the speed of a photon, (it MUST go at the speed of light) - the only way to change it's energy is to change it's mass - which isn't an easy thing to do. However, there is a way - which is to set yourself in motion relative to the thing that emitted the light. If you move away from the emitter, the light will be red-shifted and if you move towards it, the light will be blue-shifted - the doppler effect. However, that's pretty inconvenient! I guess you could drag a black hole or something suitably massive nearby - that would bend space and thereby cause a doppler shift...sadly, that's even more inconvenient. SteveBaker (talk) 13:46, 15 December 2007 (UTC)

If by "changing the frequency", you mean producing a time-compressed or time-dilated version of an arbitrary signal, it's not hard to see why it's difficult. Consider a linear blackbox that outputs a time-compressed version of its input, the delay between an input impulse and the corresponding response gets progressively shorter. Eventually the delay will be negative — the system is non-causal! Now consider a linear blackbox that outputs a time-dilated version of its input, the delay between input and output get sprogressively larger. If the system is to exhibit this property on a sustained basis indefinitely, it will need infinite information buffering capacity. --72.78.102.231 (talk) 15:11, 15 December 2007 (UTC)

Good explanation. Thanks. It only needs to be done for a finite time and I have a big buffer. How can it be done?--TreeSmiler (talk) 12:04, 16 December 2007 (UTC)

I don't know what constraints you have, but can't you just sample the input at one rate, store the samples somewhere, and play back the samples at a different rate? --64.236.170.228 (talk) 13:56, 17 December 2007 (UTC)

Energy efficient halogens

hello,

i currently live in a gorgeous, new build appartment. Like most new builds, it has low ceilings, so unlike having one big 'normal' light they have about 9 little halgen spot light things. whilst they're no doubt very trendy, they also burn out really quickly and are SO expensive (£5 for 2). They're also no doubt not very good for the future of the planet. Any one know of any engery efficient alternatives? there don't seem to be any in my supermarket and i'm not really sure i know what the techincal term is to search on the internet. Any ideas? thanks! 81.110.23.77 (talk) 15:22, 15 December 2007 (UTC)

Sorry, but I don't know much about alternatives, but the ones you have aren't supposed to burn out all that quickly. If you will accept a tip, never touch them at all. Put on a pair of those disposable latex gloves before you open the pack, and handle them as little as possible even so. They have to be cleanroom clean. --Milkbreath (talk) 16:03, 15 December 2007 (UTC)

See Halogen lamp for further information on this kind of lamp (you could have found Milkbreath's tip there). As an alternative with greater efficiency I suggest fluorescent lamps. Icek (talk) 16:22, 15 December 2007 (UTC)

You can get led based MR16's [17], [18]. They last longer and are more efficient. Led's have seen remakable improvements lately in efficiency and warm white colors, but halogens still have a better quality of light (IMO). Halogen MR16's put out about 15 lm/W, warm white leds put out about 45 lm/W. The newest white led's are putting out over 100 lm/W. --Duk 17:57, 15 December 2007 (UTC)

LED "bulbs" for general lighting are very exciting and promising for the future, but they currently have the disadvanges of being very expensive, and it tending to be hard to find bulbs that are bright enough. What is currently available at good brightness levels and cost are compact flourescent bulbs. Until recently, it wasn't possible to find compact flourescent spotlights that are small enough to fit into standard fixures (or at least, the spotlight fixtures I have in my kitchen), but that's changed now. They still aren't available yet at stores around where I live anyway, but they are available online.[19] Compact fluorescent bulbs cost a little more than incandescent or halogen bulbs initially, but they more than make up for it with a long lifespan, and more importantly, a large savings in electricity usage. MrRedact (talk) 05:47, 16 December 2007 (UTC)

Fluorescent MR16. --Duk 06:06, 16 December 2007 (UTC)

preventation of Bow legs?

My father has bent legs, mine were ok , until recently, though, they have started to bend. Iam in my late 20s and please tell me, how can I prevent further bending? —Preceding unsigned comment added by 131.220.46.26 (talk) 16:14, 15 December 2007 (UTC)

We are not qualified to offer treatment advice for a medical condition. You should seek medical advice from a professional. -- kainaw™ 16:31, 15 December 2007 (UTC)

I'm aware of the dangers from non-qualified medical advice, including dangers of lawsuite. But, on the other hand, I, personally, didn't see a "medical professional" worth his title the last ten years. I can really feel with people who try to get medical facts on their personal condition from others than the officially so called professionals. 84.160.244.197 (talk) 22:21, 15 December 2007 (UTC)

Nowadays it's relatively easy to search in the literature yourself, using e. g. PubMed. Icek (talk) 01:43, 16 December 2007 (UTC)

Bow legs are generally caused by a pathological condition or they are genetically based. In the former your family doctor can offer an opinion or a referral to a specialist. In the second case there is precious little you can do, except stoically put up with the 'you've got legs like your dad' remarks. Check it out with your doctor he'll be glad of an unusual case among all the coughs and snotty noses at this time of the year. Richard Avery (talk) 10:06, 16 December 2007 (UTC)

It is not correct that "there is precious little you can do". Bow legs can be corrected surgically. Bow legs also predispose for osteoarthritis of the knee, so this is not just a matter of putting up with remarks. Check it out with your doctor. --NorwegianBlue ^talk 15:44, 16 December 2007 (UTC)

I happen to fully agree with you, 84.160, but keep in mind that "professional" just means that you get paid for it :) --Taraborn (talk) 11:03, 16 December 2007 (UTC)

Umm... From the introduction of our article Profession: "Professions are usually regulated by professional bodies that may set examinations of competence, act as a licensing authority for practitioners, and enforce adherence to an ethical code of practice." --NorwegianBlue ^talk 15:50, 16 December 2007 (UTC)

wanna pee . . . but can't . . .

I thought I had already posted this query but I can't find it. So, here goes again.

Reposted question removed. TenOfAllTrades(talk) 19:41, 15 December 2007 (UTC)

We are not qualified to make a medical diagnosis of your problem. See a professional doctor for a diagnosis. -- kainaw™ 17:06, 15 December 2007 (UTC)

Your question was removed from the Miscellaneous desk because we are not allowed to diagnose medical conditions. Please see the instructions at the top of this page – and see a doctor.--Shantavira|^{feed me} 17:56, 15 December 2007 (UTC)

If any medical problem or symptom causes you concern you are encouraged to consult your doctor rather than Wikipedia Reference Desk volunteers who are not allowed to answer such questions. Edison (talk) 02:39, 16 December 2007 (UTC)

Here we can't answer your questions, but there are many resources in the Internet to gather information from (including forums, such as www.wrongdiagnosis.com). --Taraborn (talk) 11:05, 16 December 2007 (UTC)

Termite ranges

The page on termite doesn't specify how widespread they are. I'm wondering how prevalent they are in the US. --BrokenSphere^{Msg me} 18:11, 15 December 2007 (UTC)

Here's a link to start,[20] a bit basic but gives a general indication. Richard Avery (talk) 18:23, 15 December 2007 (UTC)

DNA sequencing

hello i want to know if i had a bacterial culture and i sent it for DNA and Plasmid sequencing the report will show the 2 results and if not how i would know the difference between the 2 (Chromosomal DNA and Plasmid) —Preceding unsigned comment added by 217.53.194.136 (talk) 21:18, 15 December 2007 (UTC)

Homework hint: Plasmid#Plasmid DNA extraction. --JWSchmidt (talk) 03:06, 16 December 2007 (UTC)

The pain of childbirth

Didn't women fear childbirth in the times prior to modern pain relief techniques? I mean, was it a matter of concern while deciding whether to bear children or not? --Taraborn (talk) 21:48, 15 December 2007 (UTC)

I think it would vary from woman to woman. I'd say there would have been many who feared the pain, but just as many who thought of it as the natural way of things. My mother (now aged 82) is in the latter category. She had 4 kids, and has often said she'd much rather go through childbirth than have a tooth cavity filled. They saw it as a matter of lying back, doing what had to be done and getting it over with (that's after having lain back 9 months earlier and ... doing what had to be done and getting it over with). It also varied from culture to culture about whether to express the feelings of pain. In some cultures, the women shriek and scream, in others they remain as quiet as they can. -- JackofOz (talk) 22:07, 15 December 2007 (UTC)

As for "deciding" whether to bear children or not, it's probably worth noting that eras predating modern pain relief also predated modern birth control. — Lomn 22:56, 15 December 2007 (UTC)

Just a side note: According to the latest issue (15th December) of New Scientist, Egyptian doctors prescribed crocodile dung applied as a pessary as a contraceptive more than 3000 years ago. The article suggests that it might have been effective, due to the spermicidal effect of its acidity. It might have been effective for other reasons as well... --NorwegianBlue ^talk 15:11, 16 December 2007 (UTC)

It wasn't just the pain of childbirth that women feared, but the threat of losing their lives. Quoting the Wiki article on Maternal death, it states:

The death rate for women giving birth plummeted in the 20th century. At the beginning of the century, maternal death rates were around their historical level of nearly 1 in 100 for live births. The number today in the United States is 1 in 10,000, a decline by a factor of 100. The decline in maternal deaths has been due largely to improved asepsis, use of caesarean section, fluid management and blood transfusion, and better prenatal care. -- Saukkomies 00:31, 16 December 2007 (UTC)

"in sorrow thou shalt bring forth children" seems to just about cover it. DuncanHill (talk) 00:41, 16 December 2007 (UTC)

Kinda like when they said "all flesh is grass"? That's actually pretty much true for terrestrial life when you consider the various food webs... --Kurt Shaped Box (talk) 01:36, 16 December 2007 (UTC)

Thanks to all. --Taraborn (talk) 11:00, 16 December 2007 (UTC)

December 16

Fertility of male cockatiels?

Asking this question on behalf of a friend. How likely is it that a male cockatiel, aged approximately 20 years will still be physically capable of impregnating a female 'tiel, aged 3 years? He (apparently) still seems to be showing interest in 'girls' but my buddy has doubts over his (the cockatiel's!) potency, being fairly old for his kind... --Kurt Shaped Box (talk) 00:24, 16 December 2007 (UTC)

Picking off a mole

Is this possible, and what are the side effetcs? Will it completely go away? —Preceding unsigned comment added by 75.23.79.10 (talk) 02:52, 16 December 2007 (UTC)

See Melanocytic_nevus#Mole_removal. Moles should only be removed by trained medical professionals, so please consult your dermatologist instead of opting for self-surgery. Further, whether it will come back, or whether it indicates a possible disease can only be determined by a medical professional. Wikipedia prohibits reference desk answerers from providing any prognosis or diagnosis, so we can't answer this question in any more detail. Someguy1221 (talk) 04:42, 16 December 2007 (UTC)

[edit] wanna pee . . . but can't . . . Part 2

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, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

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, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

You really should see a doctor. MrRedact (talk) 05:59, 16 December 2007 (UTC)

Quality of English in scientific publications

Most of the journal articles I read that come from non-native English speakers contain a few errors of various types. The one I'm reading right now is peppered with them (e.g. "hardly to understand" for not understandable (kind of ironic, I suppose)). Don't scientific journals have native-English editors to avoid publishing such mistakes? I think it reflects poorly on the journal. --Seans Potato Business 09:37, 16 December 2007 (UTC)

Most people fail to understand that buying at a grocer's or chit-chatting with a passer-by requires a much lower level of English than writing a scientific article or a literary work. Overconfidence in their own capabilities is probably the cause for those mistakes, so they let them go unrevised. I could have been labeled as "fluent" in English five years ago, and I'm still learning (a lot), mostly thanks to Wikipedia and its Reference Desk. --Taraborn (talk) 11:34, 16 December 2007 (UTC)

It's particularly interesting that it's scientific publications that do this. Science requires above all the ability to think clearly, which goes hand in hand with expressing oneself clearly both orally and in writing. Maybe the editors have a lower standard for writings about scientific work than they do for the work itself. If so, that's a really bad policy, imo. Science would be nothing if the people who do the work couldn't communicate whatever they do to their peers and the general public. But maybe I prejudge. Maybe it's not confined to scientific publications. I'd actually be very surprised if it were. There's a whole new field of work opening up - people are being paid good money to fix the language mistakes others make, mistakes that in former days would not even have been acceptable from a 5th grader, let alone a tertiary trained scientist. Not sure where this is leading, so I'll just trail off now ...... -- JackofOz (talk) 12:47, 16 December 2007 (UTC)

This varies a lot from journal to journal. Many journals copy edit manuscripts extensively before publication, others don't. You usually won't find errors like the one you cited in top-notch journals. You can do great science without being fluent in English, and I wouldn't consider your example as an indication that the author was not thinking clearly. Of course, it can be annoying, especially if the paper ends up "hardly to understand". --NorwegianBlue ^talk 14:20, 16 December 2007 (UTC)

I worked at a historical journal for many years; the heavy-handed editor there would routinely re-write the (very long) articles of non-native speakers (and heck, even a few native speakers—he was heavy-handed!). I only offer that up as an anecdote that some journals have people willing to do that sort of thing, but it is a lot of work, and at times gets so extreme that it blurs the definition of who the "author" of the article is (in the case of the journal I worked at, I once saw the editor re-write every sentence in an article for a non-native speaker—is the original author really the sole author of it, at that point?). --24.147.86.187 (talk) 17:47, 16 December 2007 (UTC)

This is a sort of grammatical trap for native German speakers. In English the suffix "-ly" denotes the adverbial use of the word "hard", whilst "hard" without a suffix is the adjective.

There is NO SUCH DIFFERENCE in German between adjective "schwierig" and adverb "schwierig", thus speakers are seldom aware of the specific function (ie does it define a noun or does it modify a verb). Once they have got the idea, they (well, we actually, as German is my native language) tend do make the odd parsing mistake, thinking "hardly to understand" clearly belongs to the verb "understand", so it must be an adverb, so it must be "hardly" to be correct. Oops, hardly...

I guess it would be comparable to a non-native German speaker using an accusative instead of a dative in conjunction with a specific preposition or mixing up genders of nouns. Maybe it should also be added that scientists generally seem to be non-verbal thinkers, which explains why some of them are "hardly to understand" if all you can see are printed words. --Cookatoo.ergo.ZooM (talk) 18:06, 16 December 2007 (UTC)

In my experience, most scientific journals don't edit for grammar, etc. They simply don't have the budget to be doing that. An article may be kicked back to the authors ~2 times for revisions, but if the grammar doesn't really get fixed, then eventually the journal editor has to decide between rejecting good science because of bad grammar or publishing it anyway. Most journals will generally do the latter and overlook poor English when the science is good. However, I do suspect that papers which are scientifically borderline are more likely to be rejected if they have poor English. Dragons flight (talk) 19:33, 16 December 2007 (UTC)

As a side-note, there is a category of mixed-up English that non-native English speakers come up with, especially in the Far East Asian countries, where it seems that they specialize in this sort of thing, that is known as Engrish. Here's a URL for a web site that celebrates the humorous mangling of the English language in Asia: http://www.engrish.com/ (warning, if you read this site while at a public terminal, people will look at you funny when you start laughing out loud uncontrollably - also, make sure not to have anything in your mouth while reading it, as it may end up spattered all over your monitor) Saukkomies 16:24, 17 December 2007 (UTC)

axon diameter

why does a greater axon diameter denote a higher speed of nerve impulse conduction? isn't it mainly the axon membrane that;s involved? —Preceding unsigned comment added by 116.48.84.133 (talk) 09:42, 16 December 2007 (UTC)

I have no clue about axons and nerve impulse conduction - but wouldn't a larger diameter signify a larger surface area and hence more membrane? SteveBaker (talk) 12:09, 16 December 2007 (UTC)

Action potential#Speed of propagation. --JWSchmidt (talk) 14:28, 16 December 2007 (UTC)

I cannot answer your question, but I can point you to an article that goes into detail about nerve impulse conduction. See Action potential. --NorwegianBlue ^talk 14:26, 16 December 2007 (UTC)

vortex dynamics : decay and impulse

Hello I have asked this before and got no answer so will try to ask it better this time. Vortex's do not suffer diffraction and do not lose impulse as quickly as normal acoustic waves. The pressure that the normal waves produce decays at R4 or four times the pressure when the distance is halved. Vortex's lose impulse as they travel due to the wake that they produce and do to the fluid they entrain as they travel which makes them grow and the pressure becomes less focussed does anyone know the decay rate of a vortices, and how much more force they exert closer to the source? If energy and speed are needed and the answer depends on an equasion and is different for every vortex the how about one of 500 joules traveling at half the speed of sound?

Thank you again

Robin —Preceding unsigned comment added by 80.6.37.199 (talk) 12:25, 16 December 2007 (UTC)

Devonian Sandstone?

Hi, just a quick question. I couldn't find anything on Devonian Sandstone, not that I need anything very detailed, I'm just wondering how porous it is? If so, is it enough to be a factor in how much water a river discharges? Thanks in advance and for any responses. 82.12.214.93 (talk) 13:22, 16 December 2007 (UTC)

There are many different Devonian sandstones worldwide (the most famous being the Old Red Sandstone), and porosity would vary both as to specific types, and within particular formations. Porosity of the underlying rocks does affect river flows, some rivers actually gain volume from a high water table in the rocks over which they flow, others lose water to the rocks, which can lead to dry valleys forming. The good people at the Geology WikiProject are probably better able than me to give a more detailed answer. DuncanHill (talk) 14:26, 16 December 2007 (UTC)

The article Hydrogeology may also be of use to you. DuncanHill (talk) 14:34, 16 December 2007 (UTC)

As may groundwater and Hyporheic zone. DuncanHill (talk) 14:37, 16 December 2007 (UTC)

This Is Not A Homework Question.

I read,this question in a Physics Magazine called PHYSICS WEEKLY.I had to describe the Motion of a penny dropped from THE EMPIRE STATE BUILDING,now THE EMPIRE STATE BUILDING`s height is 381 meters. How long will the penny,take to fall. I also wish to know the acceleration,The time and The Final Velocity.Again,this is not a homework question I tried to figure this out over and over again but couldn`t.PLEASE HELP —Preceding unsigned comment added by 68.161.87.185 (talk) 19:08, 16 December 2007 (UTC)

See this page (or any of the other discussions you can find by searching for "terminal velocity penny Empire State). If it's not clear, you can ask here about the part that's puzzling. - Nunh-huh 19:25, 16 December 2007 (UTC)

You didn't say the magic words "Neglecting Air Resistance". If you wish to recant and utter those magic words then what you need is in Equations_of_motion#Classic_version. However, if you insist on knowing how long it would ACTUALLY take - then as the Mythbusters showed, the terminal velocity of a penny is rather low - so it'll actually take considerably longer than that. I forget what number they came up with - but it was pretty slow. SteveBaker (talk) 19:58, 16 December 2007 (UTC)

The calculations, with and without air resistance, are both on the page I cited. - Nunh-huh 20:06, 16 December 2007 (UTC)

The exact answer will also depend on what orientation the penny was when it was dropped. If it is dropped with its plane parallel to the line of fall, it will take slightly different time than in other cases. Though how long it will take is kind of difficult to calculate, because it will result in complex aerodynamics after it starts to fall. I am assuming that when it was being released off hands, the mechanism was not precise, in a sense inevitably resulting in some initial small fluctuations out of its plane, which will later intensify with the contact of air as the velocity increases. Even if, we make particular care in releasing it, the two sides of the coin which are not same, will be treated differently by the turbulent air wakes, not resulting in same forces, again creating wobbles and will contribute to change the normal time slightly. This also makes assumption that there is no horizontol wind flow. Otherwise the coin will be pushed off its vertical line of fall and the time will change. - DSachan (talk) 20:51, 16 December 2007 (UTC)

To be literal, air resistance and orientation will not be of any use. When I was at the Empire State Building, I connected by camera to a pole and shot pictures over the edge of all the ledges that humans are allowed to access. As can be seen from a side view, the building is a stair-stepped pyramid. No matter where you reach out and drop your penny, it is going to fall one floor and land on the roof of the next floor down. So, the "Empire State Building" can be removed and replaced with a fall of 12-15 feet. -- kainaw™ 21:14, 16 December 2007 (UTC)

Well - I'm not sure I agree with that. When you throw the coin - you can throw it out horizontally - it'll travel horizontally as it's falling vertically. Given that there is a fairly small terminal velocity in the fall, the coin has a LOT of time to move outwards before it starts to encounter ledges. I doubt there is a problem with hitting the ledges in practice. However, if you literally drop the coin - then, yeah - it's gonna end up on a ledge. On the Mythbusters show, they actually talked with one of the staff at the building and she said that the winds around the building are very strong and can even blow upwards. Given that, and the high wind resistance of the coin - I think the coin could wind up a mile away - or could end up back in the observation area...or anywhere in between. SteveBaker (talk) 04:00, 17 December 2007 (UTC)

I should have also pointed out the large quantity of pennies sitting on the roof below the main observation deck. It took me a bit to recognize them as piles of pennies (and many various other things). When I did, I began to wonder about it. Not just one person - many people have tried to toss pennies off the Empire State Building. I'm sure they clean the roofs periodically, so this was many people trying recently. What were they thinking? "Hmm... I wonder if I'll kill someone by tossing a penny off here. Let me try." This is really no different than "Hmm... I wonder if firing a gun into a crowd of people might kill someone. Let me try." Anyway, the winds around the roof do blow upwards with a very strong current. If you attempt to throw a penny horizontally outwards, I expect the winds to blow it back and drop it on top of the piles of pennies already there. -- kainaw™ 13:18, 17 December 2007 (UTC)

Wont the coin orient itself naturally to the position of least air resistance: ie wont it fall edge on if given enough time to stabilize? This seems like common sense, but am I wrong?--TreeSmiler (talk) 02:11, 17 December 2007 (UTC)

The Mythbusters experiment showed very clearly that the coin tumbles all over the place - it doesn't matter how you drop it. See also my previous response about the winds in the area. SteveBaker (talk) 04:00, 17 December 2007 (UTC)

Tasting through my fingers?!

The DMSO article has this to say about my sense of taste: It has a distinctive property of penetrating the skin very readily, allowing the handler to taste it. Its taste has been described as oyster- or garlic-like. - how am I supposed to taste something just from it penetrating my skin? Are traces supposed to make it to my taste buds? --Seans Potato Business 21:45, 16 December 2007 (UTC)

Just in case anyone was doubting, the exerpts alone from a Google Scholar search confirm this is actually true (which surprised me utterly). Someguy1221 (talk) 22:03, 16 December 2007 (UTC)

I was told that it absorbs into the blood stream through the skin so quickly that it ends up hitting your taste buds in sufficient quantities that you can taste it. I was told I could try it, but opted out. -- kainaw™ 00:02, 17 December 2007 (UTC)

I have experienced this and it is unpleasant. A quick search indicates that it comes from the exhaled dimethyl sulfide metabolite. --Joelmills (talk) 00:32, 17 December 2007 (UTC)

I too have experienced this garlic-like taste of DMSO. I also had a rather unpleasant experience, which I swear is true. I was using DMSO on my finger joints to see whether it would help the pain I get in them sometimes when I have to work outdoors on cold days. I'd heard from a folk remedy expert (my wife) that it would help people with arthritis, so I rubbed some on myhands and went outside on an early Spring day to work in the garden. We were putting steer manure on the garden and working it into the soil, when suddenly I began to taste the steer manure in my mouth!! I had definitely NOT put my hands or anything else close enough to my mouth for something to get inside, and the manure was wet, so I couldn't have breathed in some of its dust. The explanation was that the DMSO on my hands had mixed with the manure as I was working it, and then transported this through the skin on my hands and into my bloodstream, eventually reaching my taste buds on my tongue. I was literally full of manure! It was, quite understandably, the last time I used that stuff! Saukkomies 17:02, 17 December 2007 (UTC)

Negative Black Hole

Is it possible that black holes could be made up of compacted negative matter, in some and matter in others. The reason I ask this question is that if there could be in fact be different charged black holes, a theory of the origin of the Big Bang could be made. One could be made through the fact that two different charged black holes meeting and coliding would cause a very big explosion such as a Big Bang. ARedens (talk) 23:31, 16 December 2007 (UTC)

Does the current big bang theory allow for the existence of black holes floating around before its occurrence? --Seans Potato Business 23:38, 16 December 2007 (UTC)

One could be made through the fact that two different charged black holes meeting and coliding would cause a very big explosion such as a Big Bang

How can you call this wild speculation a "fact"? Also, define negative matter. — Kieff | Talk 23:54, 16 December 2007 (UTC)

We have a link - negative matter. DuncanHill (talk) 00:03, 17 December 2007 (UTC)

The Big Bang theory allows for just about anything before its occurrence - the BB is a singularity, so it is just about impossible to say anything about what the universe was like before it - or if there was a universe before it, or even if there was a "before" before it. Confusing Manifestation(Say hi!) 02:25, 17 December 2007 (UTC)

When two ordinary black holes meet - they can coalesce into one black hole without too much drama. This seems to happen all the time in our universe - so it's no big deal. So what you are saying is that somehow because one is made of "negative matter" (or perhaps because it's electrically charged? You don't seem very clear on this point.) that something major and different might happen? It could be perhaps that an 'antimatter' black hole would meet a normal matter hole (note: Antimatter and negative matter and negatively charged matter are all different things) - and the result (if they were 'star sized' or 'supermassive' black holes would be the production of an ungodly amount of energy. But that release is happening inside a region where light (and energy) cannot escape - so it's still not clear that anything very exciting would happen. I don't see why you'd imagine that would somehow create a new universe. The "Big Bang" is a poorly chosen name. It's not just some very big explosion. It's the creation of spacetime itself - and a very large explosion doesn't in any way match the conditions under which the big bang started. SteveBaker (talk) 14:15, 17 December 2007 (UTC)

December 17

cough medecine

Removed obvious vandalism. -- kainaw™ 02:54, 17 December 2007 (UTC)

MRI flying object craziness...

Anyone know if there's a list knocking around (in a similar vein to that famous 'list of rectal foreign bodies') of 'ferromagnetic objects eaten by MRI machines'? I was looking at this tonight and I found it darkly humorous. A friend of mine has actually seen several screwdrivers (at once) being pulled into an MRI at high velocity first hand... --Kurt Shaped Box (talk) 01:07, 17 December 2007 (UTC)

I don't know of any definitive list, but one not included in that list are firearms, and I recall reading a news story some years back about a police officer whose gun was sucked into an MRI magnet and discharged, I believe (apparently in 1999, according to this article which mentions the incident). Apparently it has happened more than once; here is another account of such a thing (with photos), though it must be a different time since it says no one got hurt. --24.147.86.187 (talk) 02:17, 17 December 2007 (UTC)

I remember seeing a video once which I believe is an MRI safety video shown to techs involved. I think most of these were demonstration cases but they did show some examples of real world damage. One of the most common hazards are I believe oxygen tanks and the like which are not removed. Of course, some people also forget about their magnetic cards and while not dangerous it would probably be annoying to have to replace all your magnetic cards when they get wiped Nil Einne (talk) 15:59, 17 December 2007 (UTC)

Did it feature a wrench being released into a magnetic field and allowed to impact with a pile of bricks and a bucket? If so, it's here - found it myself last night. Don't know about you - but my first reaction upon seeing that video was "Cool!" followed by "I want that job!". Maybe it doesn't quite achieve its purpose as a safety video, then... --Kurt Shaped Box (talk) 17:51, 17 December 2007 (UTC)

That's an amazing video. It's an absolute classic of the 'boring commercial training video' genre - interspersed with extremely violent and unlikely things happening with a monkey wrench and a multi-million dollar MRI machine! The section about 4 minutes into the video where they are "lowering" the wrench towards the magnet from about 15 feet away using a 200lb breaking strain nylon rope and a winch is incredible. It's like gravity decided to take a short vacation! SteveBaker (talk) 21:28, 17 December 2007 (UTC)

I wonder how many dudes watched that video and immediately decided to go back to the MRI room and fling paperclips into the magnet's gaping maw for kicks and giggles (and to see who could be first to get one to go all the way through and out the other side)? --Kurt Shaped Box (talk) 22:42, 17 December 2007 (UTC)

Paraphrasing

It is my opinion that Wikipedia should allow paraphrasing in cases where sources are particularly scientific, heavily syntaxed, or in a foreign language. If this is already allowed, please tell me where the guideline for it can be found. Magnonimous (talk) 01:27, 17 December 2007 (UTC)

Uh...what? If we weren't allowed to paraphrase our sources, Wikipedia would consist of nothing but direct quotes. I'm really not sure what you're asking though, but this is really a question for the village pump, as this desk is reserved for questions about science, not about Wikipedia itself. Someguy1221 (talk) 02:54, 17 December 2007 (UTC)

I`ve got a question about a sombero

Hello,I got ANOTHER question and yes it is the SOB who asked about the empire state building.I`ve got another question from PHYSICS WEEKLY.A man with a sombero stands 34th Street,unaware that a physics expierment is in progress. If a penny hits His sombero,will the sombero be knocked off His head. —Preceding unsigned comment added by 71.249.154.50 (talk) 01:56, 17 December 2007 (UTC)

As I stated in answer to your previous question... The penny will not possibly make it to the street level. So, it is impossible for the penny to hit the sombrero unless this man is nearly as tall as the Empire State Building and his sombrero is overlapping one of the upper floors. If so, the answer would still be "no" because the sombrero would likely weigh a few hundred pounds and be unaffected in any way by a little penny. -- kainaw™ 02:57, 17 December 2007 (UTC)

If the penny hit the sombrero (which, as Kainaw points out - is dubious at best) then he'd certainly notice it. When the Mythbusters built a gun to shoot pennies at "from the top of the Empire State Building" speeds, they could shoot it at exposed skin without producing more than a brief stinging - no broken skin, no bruising. Sounds to me (without evidence) that this would probably not be enough to knock off the sombrero - but you'd definitely feel the impact. SteveBaker (talk) 03:50, 17 December 2007 (UTC)

(Pedantry alert!) It is highly unlikely that the penny would knock the sombrero from his head. This question is not necessarily related to the previous one. There are many cities with a "34th Street" and he may be in a city other than New York. The question does not state that the physics experiment in progress involves a penny being dropped from the top of the the Empire State building, nor that the physics experiment involves a penny at all or even that it is anywhere near the man. The mentioned experiment could be someone testing the aerodynamics of paper airplanes during a blizzard in Antartica. The question asked "if a penny hits his sombrero...", not if "a penny dropped from the top of the Empire State building hits his sombrero..." Statistically, if any penny hits his sombrero, that penny is much more likely to have come from a ground level or near ground level source and is unlikely to have the force necessary to knock the sombrero from his head. Hmm... the question doesn't even specify whether or not the man is wearing the sombrero, merely that he has one. He may be holding it in his hand, in which case it would be impossible for it to be knocked from his head. Statistical analysis of the variables would show that the likelihood of a penny hitting his sombrero and knocking it from his head approaches zero. Thus, the answer is "No." 152.16.16.75 (talk) 11:25, 17 December 2007 (UTC)

So the purpose of that utterly useless answer was what? To show us all how clever you are? It didn't work - and it certainly didn't help the OP. You know full well what was being asking: We are told that this was in continuation of an earlier question about dropping pennies from the empire state building - and it was specified that: "If a penny hits His sombero..." - so that a penny hit the sombrero is a "given". Your response was a waste of electrons. Thanks. SteveBaker (talk) 13:56, 17 December 2007 (UTC)

I wish we had a WP:CIVIL template that contained about 30 pages of exceedingly sarcastic filler. I so much want to use a CIVIL template with the obvious intent that you beat me to the uncivil comment. -- kainaw™ 15:53, 17 December 2007 (UTC)

The question doesn't state what size the sombrero is. The physics experiment could be "The Physics of throwing Pennies horizontally at People wearing Small Sombreros." So the answer is possibly, but we don't have enough information. PLAYER ONE please insert FUNDING to continue. Lanfear's Bane | t 19:50, 17 December 2007 (UTC)

Since it's unspecified, I was assuming an ISO-standard sombrero - but if the penny turns out to be a pre-decimalisation British penny - then all bets are off. SteveBaker (talk) 21:24, 17 December 2007 (UTC)

To find an actual answer to this problem (instead of just being a smartass), we first need to find an estimate of the terminal velocity of the penny. This page says it's about 11 m/s, but Mythbusters says it's about 45 MPH[21], which is about 20 m/s. So we'll take the average of the two, and assume the speed of the penny as it strikes the sombrero is about 15 m/s. The mass of a penny is 2.5 g, so the kinetic energy of the penny as it strikes the sombrero is about 0.28 joules. The problem is complicated in that there are a lot of different ways that the penny could land on the sombrero, and there are a lot of different styles and masses of sombreros. But I'll assume that the penny lands such that it has maximum effectiveness in overcoming the gravitational potential energy barrier involved in getting the sombrero off of the head. I don't have data on the average mass of a sombrero, but the average mass of two straw hats I have is about 100 g. .28 joules is enough energy to lift a 100 g hat about 29 cm. So the answer is yes, if the penney hits the sombrero right, it could easily knock the sombrero off his head. MrRedact (talk) 21:31, 17 December 2007 (UTC)

Hmmm - I'd hoped this thread wouldn't come to this! But the penny is moving DOWNWARDS - and to remove a sombrero, you need some kind of upwards force. If the coin hits anywhere in the middle, it's mostly going to simply wedge the hat harder onto the victim's head. The best chance the coin has is to strike the edge of the sombrero - perhaps at the very edge at the back for maximum leverage. Then it has to rotate the hat backwards to a sufficient angle that gravity will do the rest and permit the hat to simply fall to the ground. Thus this is a question of the torque that can be applied to the edge of the sombrero - which has to be enough to overcome the frictional torque of the hat-band against our victims' hair. However, there is a limit to how much force it may apply because the copious brim of the headgear will bend - thereby reducing the amount of downwards force - and applying a force inwards towards the head - which again will tend to force the hat back onto the victims head. So in order to stand any reasonable chance to calculate the consequences, we need to know: The frictional coefficient of hair (or perhaps bald head) against hat brim. The statistical prevalence of baldness amongst sombrero-wearing residents of 34th street (weighted for seasonal factors and a gaussian distribution of hair spray concentrations). The tightness of the brim (and thus the force exerted by the brim normal to the surface of the head). The maximum force that may be applied to the brim of an ISO standard sombrero before it starts to deflect - and subsequently, the rate of resistance to that bend as a function of curvature. This will require a considerable amount of experimentation and measurement and an alarming number of expensive machines that go "beep" occasionally. A cost-conscious researcher who is not under pressure of time might consider it to be more cost-effective to find an undergraduate research assistant at the department of Sartorial Ballistics at NYU and have them stand on 34th street and await the inevitable. A second student should stand three blocks away to act as a control. SteveBaker (talk) 23:10, 17 December 2007 (UTC)

The question explicitly makes the assumption that the sombrero wearer is unaware that a physics experiment is in progress, so a research assistant probably wouldn't be a valid subject. That makes a difference because if the subject isn't a research assistant, he'd be more likely to be a tourist, who'd be more likely to be tilting his head up to admire the famous Empire State Building, or tilting his head down, wondering why there were so many pennies lying on the sidewalk in that area, either of which would make the sombrero easier to knock off. Another complicating factor is that sombreros commonly come with a string that can be tightened under the chin. If the man actually keeps his sombrero string tightened, it'd be really difficult to knock off the sombrero with 0.28 joules, no matter where or in what direction that energy was applied. So we also need to know what fraction of sombrero wearers on 34th street keep their drawstrings tightened. MrRedact (talk) 01:49, 18 December 2007 (UTC)

What does a ray's cheek do?

Yesterday I went to the aquarium and saw a whole bunch of rays. Just behind their eyes they had large holes that led into some kind of internal cavity. The article on stingrays tells me these are called cheeks and are prized for making soups, but doesn't say what they are and what they are for. The gills, nose and mouth are all on the ventrical side so it isn't one of these organs which have migrated. Anyone know anything more? The bellman (talk) 02:39, 17 December 2007 (UTC)

These openings are called spiracles and they connect with the gill chambers as an auxiliary source of sea-water. I guess it makes sense when you think about the ray resting on the sea-bed, the spiracles would supply the gills with sea-water instead of the ray having to suck in sandy debris from under its body. Richard Avery (talk) 11:23, 17 December 2007 (UTC)

Why does dampening darken?

Why is a wet sidewalk darker than a dry one? Why does wetting dry concrete cause it to absorb more light and reflect less light? More generally, why does this happen for other materials (wet towels are darker than dry towels, etc.)? arkuat (talk) 05:42, 17 December 2007 (UTC)

That has to do with the reflective properties of the air-material, air-water and water-material interfaces. See Fresnel equations for details, but in essence the reflected fraction of light on an interface with 2 different refraction coefficients n0 and n1 is

$({\frac {n0-n1}{n0+n1}})^{2}$

Now the refractive index of air is about 1, of water about 4/3 and of asphalt it's a larger number which I don't know exactly. Considering dry asphalt, the reflected fraction is

$r_{air-asph}=({\frac {n_{asphalt}-1}{n_{asphalt}+1}})^{2}$

Considering wet asphalt, it's more complicated: Light can be reflected at the air-water interface, or it can pass the air-water interface and be reflected by the water-asphalt interface. In the latter case it can either pass the air-water interface directly or be again reflected towards the water-aspalt interface etc. Calling the reflection coefficients r_air-w and r_w-asph, this mathematically results in the following infinitely nested expression for the total reflected light:

$r_{total}=r_{air-w}+(1-r_{air-w})\cdot r_{w-asph}\cdot (1-r_{air-w}+r_{air-w}\cdot r_{w-asph}\cdot (1-r_{air-w}+r_{air-w}\cdot r_{w-asph}\cdot (.....))))$

By defining

$X:=1-r_{air-w}+r_{air-w}\cdot r_{w-asph}\cdot (1-r_{air-w}+r_{air-w}\cdot r_{w-asph}\cdot (.....))$

we can use the fact that X is "self-similar":

$X=1-r_{air-w}+r_{air-w}\cdot r_{w-asph}\cdot X$

$X={\frac {1-r_{air-w}}{1-r_{air-w}\cdot r_{w-asph}}}$

The total reflected fraction for the wet asphalt is therefore

$r_{total}=r_{air-w}+(1-r_{air-w})\cdot r_{w-asph}\cdot X=r_{air-w}+r_{w-asph}\cdot {\frac {(1-r_{air-w})^{2}}{1-r_{air-w}\cdot r_{w-asph}}}$

Now we can substitute the known single-interface reflection coefficients (as computed with the formula from the Fresnel equations):

$r_{total}={\frac {16}{49}}+r_{w-asph}\cdot {\frac {({\frac {33}{49}})^{2}}{1-{\frac {16}{49}}\cdot r_{w-asph}}}$

You can do a few more mathematical manipulations to show that high values of n_asphalt result in a lower total reflected fraction in the wet case or - if you are lazy - you can insert a high value (e. g. 20) for n_asphalt.

In reality things are more complicated due to rough surfaces etc.; this is a simple model (and from the fact that the differences in reflectance are rather small in this model, it seems to me that I've overlooked something - please tell me what). Icek (talk) 07:51, 17 December 2007 (UTC)

An answer the the questioner can understand? If that's not being too blunt. Richard Avery (talk) 09:15, 17 December 2007 (UTC)

I don't know whether the questioner or you (Richard Avery) understand the answer, but in short: Reflection from an air-asphalt interface is higher than the combined reflections occurring at the interfaces when water is between air and asphalt, because water has a refractive index lying between the refractive indexes of air and asphalt. Icek (talk) 10:54, 17 December 2007 (UTC)

That was an impressive amount of math - but there is a MUCH simpler way to answer this. Water is shiney - concrete isn't. When something is shiney, most of the incoming light is bounced off in a very narrow angle. If you stand in exactly the right place, you'll see the puddles are REALLY bright because they are reflecting the sun into your eyes. That doesn't happen with concrete - it's rough and reflects the sunlight off in all directions more or less equally. So from MOST angles, the puddles look darker because they aren't reflecting light in your direction - but from that one very special angle, the water acts like a mirror and the water is much, MUCH brighter than the concrete. So on the average, there may not be much of a difference between the two - but from most directions, the water is simply not reflecting any light in your direction but the concrete is sending some light towards you - so the water looks darker. SteveBaker (talk) 12:42, 17 December 2007 (UTC)

Thank you Steve. Not only did I miss what should have been obvious, but my model doesn't even really predict the correct sign of the effect: If the refractive index would be really so high that my model predicts a darkening with water, the dry material should be brighter than it is. At a relatively low refractive index (e. g. 5, the dry reflectance being 4/9 which is brighter than some asphalts I think), my model actually predicts that the reflectance is higher in the wet state. Icek (talk) 15:03, 17 December 2007 (UTC)

But Steve (and what kind of rapping name is Steve anyway), when you drop a drop of water onto concrete it absorbs it, and turns dark, and doesn't reflect most of the light to a specific angle like you've said. Care to explain that? --antilived^{T | C | G} 05:00, 18 December 2007 (UTC)

Turning Carbon Dioxide into useful fuel

Allright Smartguys,

[Here]'s an article from MIT Tech Review describing a solar parabolic mirror that focuses solar rays onto a ferric-oxide ceramic, heating it up 1500 Centigrade, which liberates oxygen from the iron. The ceramic is then brought into vicinity of CO2. The hot iron steals an oxygen atom from the CO2, leaving a CO molecule. This is described as reversed combustion. So, my question is, how is CO then turned into a Hydrocarbon fuel? My guess is that water H2O is somehow used to convert CO into HCHCHC molecules, right? Can anyone state the simple steps in terms of + / - bond energy required for each step? Thanks!

--InverseSubstance (talk) 05:53, 17 December 2007 (UTC)

Well, you can burn carbon monoxide directly in air to get back to carbon dioxide - so there might not be a need to do any more steps to recover the energy at the output. But let's be really clear about this for the benefit of readers who may not fully understand what's going on here: This process isn't using Carbon dioxide as a 'fuel' - no energy is extracted from the CO2. What we have here is a solar power plant whose output energy is in the form of carbon monoxide. It's not going to help global warming any more than a regular solar power plant does because the CO2 it pulls out of the air gets turned back into CO2 when you burn whatever fuel it produces. So whether this is really of much interest depends on the overall efficiency of the plant - and how convenient the fuel it generates is for existing energy consumers. I'll defer to our chemists to answer your question properly. SteveBaker (talk) 12:36, 17 December 2007 (UTC)

As to the use of CO as fuel, you might want to see our articles on Coal gas, Producer gas, Syngas, Water gas, and the links onwards from those articles.

Atlant (talk) 13:23, 17 December 2007 (UTC)

It is plausible that this could be someone's idea of a closed loop system. Use solar power to turn CO2 into CO. Burn the CO to boil water and turn a turbine to create electricity. Capture the CO2 and use solar power to turn the CO2 into CO. However, if the mirror can reach temperatures of 1500C, why not use the mirror to boil the water and take the CO2 and CO out of the equation? I know - it will only work when the sun is out - but it is apparent that CO will burn to CO2 much faster than this can turn CO2 into CO anyway. So there will always be lag time waiting for fuel. -- kainaw™ 13:28, 17 December 2007 (UTC)

Having read the article, I think you must be right. This thing can't just pull CO2 out of the air - it needs pure CO2 to be fed to the hot iron ceramic because any oxygen in the mix would presumably bind to the iron in preference to the oxygen atoms from the CO2 - which would result in major inefficiencies in the system. So they first have to purify their CO2, which would be a costly and energy-intensive process. However, if it's a "closed loop" arrangement then that wouldn't be an issue - the CO2 would simply convert to CO and then back to pure CO2 to go back to the hot iron. But as you say - why they don't just use solar power to produce steam is anyone's guess. SteveBaker (talk) 14:06, 17 December 2007 (UTC)

What's the energy density of CO versus, say, H₂ or Methane? Does it at least make CO a competitive energy storage medium?

Atlant (talk) 16:30, 17 December 2007 (UTC)

The standard enthalpy change of combustion is -283 kJ/mol. If you want to liquify it, you need to cool it to 81 K (compared to about 20 K for hydrogen), the density is (according to the NIST Chemistry Webbook) about 30 mol/l, so you get about 8490 kJ/l. Liquid hydrogen has 0.07 kg/l = 35 mol/l, corresponding to 8464 kJ/l. So the energy density per volume is about the same, with less prohibitive temperature requirements for carbon monoxide. Methane has a higher boiling point of 111 K, a liquid density of 422.62 g/l = 26.3 mol/l, and a standard enthalpy of combustion of -891 kJ/mol, thus it has an energy density of 23,472 kJ/mol, and is clearly the best choice of the 3 gases if volume is the limiting factor and refrigeration is possible. Icek (talk) 18:37, 17 December 2007 (UTC)

(Presumably, that last number was meant to be "23,472 kJ/l".) Thanks for that great analysis!

Atlant (talk) 23:20, 17 December 2007 (UTC)

It's not really what the article advocates, but if I had to guess, I'd think the real goal is to create a "free" process that converts CO2 into more or less anything else. Right now, all of the processes that chemically reduce CO2 require both significant inputs of energy and the consumption of reactants like CaO. This reactor apparently requires only CO2 and an input of heat (currently provided by sunlight) in order to reduce CO2, with no expensive reactants. Since heat and CO2 are two things that power plants have in abundance, this could be a virtually free way to reduce the carbon emissions per unit of energy produced by the plant. Dragons flight (talk) 16:39, 17 December 2007 (UTC)

Methanol would be the next locical step. There is a catalytic pathway to form it catalytical at high tem from CO and Hydrogen.--Stone (talk) 15:49, 17 December 2007 (UTC)

Allright! That article on Methanol helped me understand the process better. Thanks! --InverseSubstance (talk) 17:44, 17 December 2007 (UTC)

Relevance of PCR to northern blotting

For PCR: PCR allows isolation of DNA fragments from genomic DNA by selective amplification of a specific region of DNA. This use of PCR augments many methods, such as Southern and northern blotting and DNA cloning, that require large amounts of DNA, representing a specific DNA region. - but PCR is all about DNA and northern blotting is all about RNA, right? Are they talking about making probes? While I'm on the topic, I wonder why we don't have RNA PCR using an RNA polymerase derived from Taq or wherever? --137.120.3.221 (talk) 09:48, 17 December 2007 (UTC)

If you make cDNA from mRNA you can PCR the RNA sequence too. This is quite common especially if you want to amplify the ORF as seen in the mature RNA. David D. (Talk) 10:00, 17 December 2007 (UTC)

Then perhaps the current northern blotting article is somewhat misleading. What about the RNA polymerase idea? Or is it just not worth it? Seans Potato Business 10:18, 17 December 2007 (UTC)

Why is it misleading, the article does not mention PCR?

The RNA polymerase idea would not work since the template is DNA but the product would be RNA. Thus, the amplification would not be exponential as the original DNA template would be the only one used each time. In PCR, with DNA polymerase, the products are also new templates. David D. (Talk) 12:44, 17 December 2007 (UTC)

Oh yeah, sure. Are there no RNA polymerases out there that use RNA as a template? Some viruses with RNA genomes that don't use reverse transcriptase? Anyway, the northern blotting article is misleading because it says that it uses RNA and in actuality it can use cDNA that has been produced from mRNA. --Seans Potato Business 13:44, 17 December 2007 (UTC)

Northern blots are never done with cDNA, so the article is correct. PCR from an RNA starting material would use cDNA. The RT-PCR link that JWSchmidt mentions below explains the process. David D. (Talk) 16:02, 17 December 2007 (UTC)

• There is a PCR method that is relevant to the goal of northern blotting; see RT-PCR. The quoted statement at the start of this thread might better say something like, "PCR augments other methods, such as Southern and northern blotting that attempt to detect a specific DNA sequence. In general, methods such as Southern and northern blotting require a larger amount of starting nucleic acid than do the related PCR-based methods of target sequence detection." --JWSchmidt (talk) 14:34, 17 December 2007 (UTC)

So you're saying that the article should say that RT-PCR is an alternative to northern blotting? It doesn't really augment northern blotting? I'm pretty sure that the original says that you amplify the DNA for use in northern blotting. Even if you change DNA to nucleic acid, it still isn't right if you can't use PCR to amplify RNA for direct use in a northern blot. --Seans Potato Business 19:57, 17 December 2007 (UTC)

" amplify the DNA for use in northern blotting": this is wrong although I didn't notice that in the northern blotting article. David D. (Talk) 20:26, 17 December 2007 (UTC)

• "PCR augments other methods...." in the sense that it can "supplement" for-, make up for a deficiency in-, or be an alternative to the older methods. Its probably best to not use the word "augment" at all because it gets people thinking that it is used to improve the other methods, which is not generally the case....its usually a matter of providing a more sensitive alternative detection method. --JWSchmidt (talk) 03:23, 18 December 2007 (UTC)

Rationale behind touchdown PCR

According to the touchdown pcr article, the idea is that more specific primer-template annealing occurs at higher temperatures, so that the early phase amplifies the sequence of interest and due to the exponential nature of PCR, the later phases using lower anealling temperatures will amplify mostly the sequence of interest. However, it will also clearly amplify sequences to which the primers bind non-specificially, so where is the incentive? There must be something better about the lower annealing temperature phase to make it worth changing from the more specific one (i.e. if touchdown PCR gives acceptable results, traditional PCR will give even better results - so why bother?) --Seans Potato Business 10:32, 17 December 2007 (UTC)

There are two related issues, efficiency of primer binding and specificity of primer binding. Lower temperature can increase efficiency of binding and increase yield of amplified DNA, but at the risk of having unwanted amplification products dominate the PCR. Higher temperature can increase the specificity but can also decrease the yield. "There must be something better about the lower annealing temperature phase" <-- just to get enough product to work with. --JWSchmidt (talk) 14:20, 17 December 2007 (UTC)

Intracortical networks of connections among subsets of cortical regions

I'm seriously stuck. I've read this phrase over and over again but it doesn't make sense. Does anybody understand what could be meant by: "Intracortical networks of connections among subsets of cortical regions"???
It is supposed to be a solution to the binding problem and a mechanism called reentry (we don't yet have a neuro article about it) is supposed to be part of this solution. Lova Falk (talk) 18:55, 17 December 2007 (UTC)

Articles such as Cerebral cortex, Visual cortex, Broca's area discuss the fact that the cerebral cortex is functionally divided into areas that carry out specialized functions. Watch a falling apple. Although different cortex areas specialize for processing color and motion, we are usually consciously aware of seeing a unified "object" that has both color and motion.....we do not experience the motion and color as independent "reports" of what is in the visual field. What "binds" the activity of multiple cortical areas into a single coherent conscious experience? Many people imagine that there is a homuncular "center of consciousness" that might collect and unify all of the computational results from many distributed cortical areas. However, that does not seem to be the case and many people suspect that our conscious awareness is also distributed and largely co-extensive with the many specialized and distributed cortical areas that include the various specialized areas of visual cortex, such as those for color and motion detection. Conscious unification of what is going on in multiple cortical areas would seem to depend on the continual function of "intracortical networks" that connect "subsets of cortical regions". Some theories propose that cortical brain activity only enters into conscious awareness when there is a special type of feedback in such intracortical networks, allowing a kind of "resonance" in the neurons of linked cortical regions. Of course, connections to other brain regions such as the thalamus are also important, so I doubt if intracortical networks can by themselves account for "binding". --JWSchmidt (talk) 21:00, 17 December 2007 (UTC)

Power Engineering Graduation Project

I am Power Engineering undergraduate student, and I am seeking for a research subject for my graduation project.
Can you suggest a subject please :) Smart_Viral ^(talk) 18:58, 17 December 2007 (UTC)

You can try to find ways to reduce the transmission loss. That is basic and challenging both as an undergraduate. I am very concerned about the huge amount of power that we lose in transmission. Power is one of the most important factors in moving and shaking today's world, and if you think calmly, you can get plenty of decent ideas. By the way, I guess that the duration of your project is one year, right? - DSachan (talk) 19:44, 17 December 2007 (UTC)

Yes two semesters. Thank you. Smart_Viral ^(talk) 21:04, 17 December 2007 (UTC)

Another idea might be to think about, and plan for, how one might address the intermittency problems created by large scale use of solar / wind power. Dragons flight (talk) 21:23, 17 December 2007 (UTC)

"Advanced Strategies to Contain and Minimize System Collapse After a Local Fault" -- Of late, the power grid in North America seems to have lost a lot of its former resilience, and relatively minor, local faults have cascaded into major, region-wide power outages.

Atlant (talk) 23:27, 17 December 2007 (UTC)

One possibility would be to do a further study on whether there is a higher incidence of health risks due to prolonged close exposure to high voltage electric current in power lines or transformers. A number of studies have been laying down what seems to be a pretty convincing case of this, but further research is definitely needed. One paper done in 2000 discusses this here.[22] Another possible angle on this would be to find some way to affordably reduce this potential health risk. That could be a very good seque into becoming very wealthy if it produced something that can be manufactured and marketed. Saukkomies 01:21, 18 December 2007 (UTC)

Gulls and dolphins

Dolphin

Gull

Maybe it's just me - but does anyone else see the similarity in body shape between gulls and dolphins when viewed side-on (if we ignore the wings and flippers)? I don't think that this could technically be described as Convergent evolution, as they are from completely different ecosystems - but is there a term that describes this phenomenon? --Kurt Shaped Box (talk) 19:25, 17 December 2007 (UTC)

Aerodynamic? David D. (Talk) 19:40, 17 December 2007 (UTC)

That makes sense - they both have to 'glide' smoothly through a fluid - convergent evolution is quite likely. A dolphin looks quiet a lot like an upside-down racing yacht too (complete with 'keel')...I'm betting that's no accident either. —Preceding unsigned comment added by SteveBaker (talk • contribs) 21:20, 17 December 2007 (UTC)

That would have to be a case of convergence. Dorsal fins exist to stabilize and help the creature turn, and such keels serve the exact same purposes on a ship. 81.93.102.185 (talk) 22:18, 17 December 2007 (UTC)

Moon pictures to show scale

Have anyone yet put maps of countries onto a spherical model of the moon, in order to give a good impression of the scale of the moon compared to earth? 81.93.102.185 (talk) 19:55, 17 December 2007 (UTC)

You mean putting the countries on the moon at their actual size, showing that not as many fit (since the moon is smaller than the earth)? When I was young, I had a book that showed that the visible surface of the moon was about the right size to hold Australia. But I don't remember the book. -- Coneslayer (talk) 20:23, 17 December 2007 (UTC)

Yes, that would be the exact way. And thanks, that does give a rough sense of scale. :) 81.93.102.185 (talk) 20:24, 17 December 2007 (UTC)

That is an interesting idea. I don't think I've seen maps like that. A quick search turns up the usual comparison graphics showing the whole Earth and the whole Moon globes at scale, like this one at the Wikipedia Commons. I did find a picture showing the United States on Mars. It was apparently made with the free and cool program Celestia, via an add-on created by the person who made that Mars image, available here. So it probably wouldn't be too hard to make a similar image for the Moon. Pfly (talk) 21:10, 17 December 2007 (UTC)

According to moon and Australia, the surface area of the moon is about five times greater. Algebraist 23:57, 17 December 2007 (UTC)

December 18

What happens to weight and pressure at centre of Earth?

This one has had me stumped for years. Imagine being in a very sturdy air-conditioned spherical pod right at the centre of the Earth. Now, you have equal amounts of mass pulling on you from every side, so the gravitational attraction should equal out, and you should be weightless, just floating around in the pod. Could that be right? But if weightlessness rules at the Earth's centre, then how does that affect the enormous pressure that's supposed to be down there. If you are floating around weightless, then there can't be matter pressing in on you, and so there should be no pressure. But that doesn't make sense either. That would mean that you really COULD have a hollow Earth with habitable regions at the middle! And how does this weightlessness tie in with Einstein's General Theory of Relativity, which says that mass curves space, which causes the gravity effect? Does that mean all that mass unwinds the curvature at the centre of massive objects like the Earth. Myles325a (talk) 00:28, 18 December 2007 (UTC)

There is weightlessness, and there is pressure on the outside of the pod due to the weight elsewhere, this is not a contradiction.--Patrick (talk) 00:48, 18 December 2007 (UTC)

I agree with Patrick - you are weightless - but the planet all around you is still being pulled inwards - so the pressure is spectacular. In a previous question, we were asked to explain what would happen if there were some kind of tunnel cut through the center of the earth and lined with some kind of indistructable, heat-proof material. One of the conclusions is that the air pressure at the center of the earth would be enough to liquify the air!

For the second part - imagine the old diagram (which if you watch any science programs at all, you've seen!) of a rubber sheet with a bowling ball rolling around on it - the dimple made by the ball has a flat bottom - corresponding to the lack of gravitation at the very center of the earth. You'll also have seen those pointy, almost conical space-distortion diagrams where there is a black hole...because they have zero size and infinite density. SteveBaker (talk) 01:00, 18 December 2007 (UTC)

values for ATP hydrolysis - enthalpy and entropy

I am looking for the thermodynamic free energy values of ATP hydrolysis to ADP and Pi as a function of the temperature or alternatively the values of the enthalpy and entropy. Thanks, Ron Milo Harvard University —Preceding unsigned comment added by Ron milo (talk • contribs) 01:01, 18 December 2007 (UTC)

Walk over to Widener Library and look up the answer yourself in any biochemistry textbook. Delmlsfan (talk) 02:29, 18 December 2007 (UTC)

Are you looking for standard conditions of physiological conditions? If the latter there is a range depending on the concentrations of ADP, ATP and Pi in the cell at any given time. Have you looked at ATP yet, and it's talk page too? David D. (Talk) 02:36, 18 December 2007 (UTC)

After consulting several textbooks and professors I could not find the values (notice that the text books usually have the free energy (deltaG) at only one temperature). I am looking for either standard conditions or physiological conditions whatever I can find which is reliable. Yes, I did check the wikipedia page. — Preceding unsigned comment added by Ron milo (talk • contribs)

Well standard conditions by definitions will be 25 degrees celcius. Why do you consider the text book values for standard conditions unreliable? (at least that seems to be your implication). What was wrong with the values in the links above. As i mentioned above, if you need a physiological value you will have to deal with a range, not an exact figure, since the physiological conditions will vary in an organism. Try this link that shows two graphs that represent how the free energy of hydrolysis changes with respect to pH and Mg2+ concentrations respectively. Clearly many other factors will change it too. David D. (Talk) 03:45, 18 December 2007 (UTC)

2 cars crash head on

I'm sure this had been asked before, but I couldn't find it. This is a long running fued on alot of sites:

Two identical cars travel at identical speeds in opposide direction crash head on resulting in both coming to a stop. All energy is lost via noise/phsyical deformation.

For a driver, the impact would be identical to driving into a solid immovable stationary wall at either:
-The same speed as was in the head on collision.
-Double the speed as per the head on collision (ie combine the speed of the the vehicles)

I contend the same speed, as in both cases the car goes from the speed to zero and dissipates the same amount of energy, and since the cars are identical, both will dissipate equal and opposite such that the head on collision is effectively as if each ran into a solid wall anyway.

Furthermore I also contend that if one vechile is stronger than the other, the stronger vechicle driver should have the creedence to choose to hit another car head on rather than hit a stationary wall, even if the other car is coming as fast as he is in the opposite direction.--Dacium (talk) 04:11, 18 December 2007 (UTC)

This was asked a few months ago, but I don't feel like hunting it down. The "same speed" scenario is correct. Since the cars are identical, they will symmetrically come to a stop. Therefore, they will each cover exactly half the distance between them, so you can basically just draw yourself in imaginary wall at that meeting point, and neither car will pass through this wall. Then just satisfy yourself that this is the same as each car hitting a very non-imaginary, immovable wall. Someguy1221 (talk) 04:56, 18 December 2007 (UTC)

You could also reason out that going at double speed into a wall would actually involve twice as much energy as the two colliding cars. Indeed, you could think of it entirely in terms of kinetic energy. If each car in the original scenario has energy E, then the total system must dissipate 2E between two cars; each car dissipates E. In the one car, same speed into a wall, the car has to dissipate E as well (you can just say the wall is so heavy and such a good insulator, that it won't help dissipate any energy). For the one car, double speed scenario, it has to dissipate 4E all by itself. Someguy1221 (talk) 04:57, 18 December 2007 (UTC)

Two grounds not matching

Guys I have two digital design boards which use digital ground all perfectly designed PCB. These two boards have two major FPGA chip soldered along with some leds and switches. Now the case is that I use to send data from one to another using one data bus and one clock line.Along with this a ground and a ready signal is provided(4 wires). Problem here is that the leds in the receiver board flickers when I connect as usually.This should not occur,coz that is not how it's programmed.When I provided one more 2nd wire for ground, this problem is solved,program works. 2 ground wires are required to solve the case. I use 5V Dc supply seperatly for these 2 boards. Why isn't the ground shorting with one single wire?. I tried using big wire,fat wire,shielded cable and also measured the resistance between the two boards ground after shorting with 1 wire but it's almost zero.Noise level is under normal level.Please suggest me if there is any way that I can overcome this.It appears so strange and crazy in electronics!. ThanksBalan (talk) 04:34, 18 December 2007 (UTC)