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January 26

liquid nitrogen in an electric kettle

I've seen experiments where people throw hot water into liquid nitrogen (I'm not sure how dangerous that is). I wondered what would happen to liquid nitrogen in an electric kettle (switched on)). Would it just break the kettle? Would the element respond differently at low temperature and cause the fuse to blow? --129.215.47.59 (talk) 02:19, 26 January 2012 (UTC)

I am not sure if it helps but you may want to click here and search for "Making better clouds is easy". Von Restorff (talk) 02:33, 26 January 2012 (UTC)

It might break the kettle. Perhaps softer metals, like copper, might hold up a bit better. The electrical element might break, too. If not, then it should work normally. StuRat (talk) 02:46, 26 January 2012 (UTC)

I've stored liquid nitrogen in metal containers. They never broke or became brittle; they're just dangerously cold and inconvenient if uninsulated. But I never did anything foolish, nor tried to heat the nitrogen on a stove. The most important thing to remember when storing liquid nitrogen is to provide a pressure relief - especially if you're going to heat it. Usually, this takes the form of a loose-fitting cap. Here's an OSHA MSDS for cryo nitrogen, and here's a more useful "general safety guide" from the government's Cancer Research Center. For good measure, here's the SLAC/Stanford Environmental Safety and Health manual for liquid nitrogen. Remember: explosions are caused by overpressure, not by combustion (despite what Hollywood has mis-taught everybody). Heating (or even just working with) a cryo liquid, like liquified nitrogen, without providing a safe pressure release is asking for very dangerous, deadly trouble. If you'll be producing large quantities of gas, watch out for asphyxiation hazard. Nitrogen is odorless and tasteless and colorless, and looks an awful lot like regular air, (and mixes well enough to displace room air). You might not have time to notice the lack of oxygen, if you do something stupid. Nimur (talk) 07:23, 26 January 2012 (UTC)

Sometime ago, I saw footage from an experiment with pigs, it was ammusing. There was a food trough inside a fume hood purged with nitrogen, the pig had to stick its head in the fume hood in order to reach the trough. Whenever it did, it fainted and fell over outside of the fume hood, before waking up and trying again. I don't actually remember the point of the experiment. Plasmic Physics (talk) 10:35, 26 January 2012 (UTC)

The Horizon series documentary How To Kill A Human Being featuring Michael Portillo (first broadcast 2008 on BBC Two) examined alternative methods of humane execution, including Nitrogen asphyxiation#As an execution method. The point of the experiment with the pig was to demonstrate that it was not painful, as the pig kept heading back for the food under the fume hood, repeatedly being rendered unconscious. The sequence with the pig appears in the last ten minutes of the programme. Note that the researcher who put on the pig demonstration was Dr. Mohan Raj (not the actor) of University of Bristol, who has researched humane methods of livestock slaughter. -- ToE 14:11, 26 January 2012 (UTC)

From a quick search, it looks like an electric kettle holds 1 to 2 liters; according to liquid nitrogen this volume is multiplied by 700 on evaporation to gas at 20 C. Now 1400 liters is a lot of water, but it's actually only 1400 x (1 decimeter)³ or 1.4 cubic meters of air. A typical room (even a closet) probably averages at least two meters in each dimension, which means that the oxygen would be diluted down by only 17.5%. Of course, that applies only when the gas is well mixed into room air - if you somehow knock yourself out and collapse at the foot of the kettle with the cold vapors down into your throat, or (in the classic oopsie) you want to make a cute visual effect of dry ice or liquid nitrogen in a hot tub you and your friends are bathing in, things can get tragic. Wnt (talk) 14:32, 26 January 2012 (UTC)

Apparently most electric kettles have a heating element made of nichrome; this has a temperature coefficient of resistivity of 0.4 x 10^-3, which is only 1/10 that of silver, copper, aluminum, or tungsten.^[1] Liquid nitrogen, at -196 C = -216 K below room temperature, so by the formula on that page resistance is reduced by a ratio of 0.0004 * 216 = 0.0864 = 8.6%. Unless the kettle is very near the capacity of the breaker indeed, it should not trip it due to the cold. But the first kettle element I found on a Google search mentioned an aluminum element, which being ten times more susceptible might be more likely to trip it. Wnt (talk) 14:58, 26 January 2012 (UTC)

Caution

Placing something extremely cold into something extremely hot might cause the liquid to flash into vapor in an explosive fashion, with liquid getting splattered out of the kettle. If the opening were so small as to confine the vapor expansion, the overpressure might cause the metal to burst (like a small bomb). Some sort of metal fracture due to sudden contraction, or breakage of the heating element seems possible. Edison (talk) 20:11, 26 January 2012 (UTC)

Surely a teakettle isn't designed like a bomb, though! There's a place to pour in the water, which is not designed to resist pressure, and you'd be hard pressed to pour in the nitrogen without having it open. Wnt (talk) 01:52, 27 January 2012 (UTC)

I just think back to childish experiments with explosive substances such as nitrogen tri-iodide, or steam in a confined space, and what might go wrong in a worst-cast incident. With a wide-mouthed kettle and a loose-fitting lid, splatter would be the risk. If a way were devised to try the experiment with a very small opening or a tight lid, explosion potential would increase. Edison (talk) 06:24, 27 January 2012 (UTC)

Liquid nitrogen splatter isn't generally dangerous - it doesn't stick because it's surrounded by gas. You can coddle a drop in your hand if you want. Yes, all kinds of crazy things can happen when kids play with steam and closed containers, but... it's a kettle. It's not supposed to be closed. The other thing to remember is that liquid nitrogen gives off the most gas when the first drops you pour strike the container. You can't get it all in the container, then have it "detonate". Now yes, you can create a pretty dramatic explosion with liquid nitrogen if you try, e.g. by putting a couple of inches at the bottom of a two-liter bottle weighted with a brick, rapidly seal the cap, rapidly dump it into a trash can of water, rapidly cover it with a piece of plywood you would like to send to treetop level, and rapidly retire to a safe distance. But that's a different kettle of fish... Wnt (talk) 16:54, 27 January 2012 (UTC)

WP:BEANS. Von Restorff (talk) 09:48, 29 January 2012 (UTC)

Black umbrella in summer???

Dear frens, i hav a doubt....in summer we are asked not to wear black and dark clothes....but we use black umbrellas....why? -regards — Preceding unsigned comment added by Naviappu (talk • contribs) 15:34, 26 January 2012 (UTC)

At a guess I would say that a) it's "stylish", and b) if you've got your umbrella up then it's generally raining which means it's unlikely there will be much sun to heat up your umbrella up--Jac16888 ^Talk 15:38, 26 January 2012 (UTC)

An umbrella is also not in direct contact with your skin, which means it's not going to heat you up as much as black clothes will. Smurrayinchester 15:46, 26 January 2012 (UTC)

Black and white offer opposite extremes of blackbody radiation, or just the absorption of light, and each have their purposes. And culture varies also. The poor Arabic ladies in chadors wear black in summer; then again, they are more or less supposed to be indoors, where they may be emitting more infrared than they absorb. For an umbrella my guess is that it's more important for it to block the sunlight than for the fabric to stay cool; hopefully the breeze will do that anyway. Wnt (talk) 15:47, 26 January 2012 (UTC)

The rain has a cooling effect on the umbrella (when water evaporates it absorbs heat). --Colapeninsula (talk) 16:04, 26 January 2012 (UTC)

Wow. From the comparison with clothing I just assumed they had to be using a beach umbrella or something. Yeah, in the rain this is just silly and it doesn't matter at all. Wnt (talk) 17:55, 26 January 2012 (UTC)

It rather depends on the desired effct. For these chaps, thermal efficiency is probably not an issue. Alansplodge (talk) 18:03, 26 January 2012 (UTC)

solar storm

dear frens, i went thru topic solar storm in wikipedia...i got information...but i need practical information if anybody can help me...how does solar storm affects us? actually,wen i went thru wikipedia..i was not clear in concept of how earth's magnetic field wud b affected..can anybody pls tell me.... -regards — Preceding unsigned comment added by Naviappu (talk • contribs) 15:36, 26 January 2012 (UTC)

A solar storm can refer to various related phenomena: solar flare, coronal mass ejection, geomagnetic storm; you can read about their effects Solar_flare#Hazards, Coronal_mass_ejection#Impact_on_Earth, Geomagnetic_storm#Geomagnetic_storm_effects. For examples of the effects on earth see March 1989 geomagnetic storm and Solar storm of 1859. Possible effects include radio interference, satellites being temporarily damaged (possibly disabling TV, radio, telephone, GPS satellites), power blackouts, damage to telephone lines (or formerly to telegraph lines), false read-outs on military early warning systems, and damage to pipelines. For people in airplanes or astronauts in space there can be significant radiation exposure. The 1859 storm saw fires started by sparks from power surges, so that's probably a risk as well. --Colapeninsula (talk)

Note that the Earth's magnetic field protects us by redirecting charged particles towards the Earth's poles, where they create the Northern Lights near the north pole and Aurora Australis near the south. StuRat (talk) 18:04, 26 January 2012 (UTC)

Gamma ray lenses?

What material is used to design lenses for gamma ray photography? Germanium seems to be used for infrared. Electron9 (talk) 16:54, 26 January 2012 (UTC)

None. --Aspro (talk) 16:58, 26 January 2012 (UTC)

Compound parabolic refractive lenses have been used for hard x-rays up to ~60 keV, [2]. Mikenorton (talk) 17:11, 26 January 2012 (UTC)

If one wants to gamma ray examine (say) a steel reinforced concrete bridge support, then a gamma point source is placed behind it, and the imagining film the other side, the film just records the shadows, …. no lenses involved. Collimators can be employed for satellite borne instruments but they are not exactly lenses. It would help if the OP indicates what the application is the he is is asking about. Difficult question we can answer immediately; impossible questions and those requiring telepathy take just that little bit longer. --Aspro (talk) 17:46, 26 January 2012 (UTC)

I was thinking about an equivalent to a handheld infrared camera (flir). Translated to this it would be some kind of gamma source and for example an mobile phone that is imaged in detail. Electron9 (talk) 18:10, 26 January 2012 (UTC)

It's "deep" into research territory when you start talking about imaging using gamma rays. When we image with light and infrared and ultraviolet, we use things that generally look "sort of" like glass lenses and mirrors, forming refractive and reflective surfaces. As we get farther out from the visible spectrum, in either direction, "optical" materials start to look stranger. Toward the low frequencies, we get radio telescopes, which still look a lot like a Newtonian reflector, but aren't so "shiny and silvery and reflective" (when viewed by the naked human eye in visible light). On the other side of the spectrum, the optics get really weird really fast, as the wave energy becomes higher (and the wavelengths become shorter). You may find the Chandra X-Ray Observatory enlightening: X-ray optics are pretty weird (they look nothing like optical optics). The key fact to keep in mind is that it's easier to "bounce" than to "bend" a very high energy ray - so the "optical elements" in such imaging systems tend to use oblique incidence (very very shallow angles) on very precisely designed material surfaces to steer the beam toward the imaging element. Consider, Compton Gamma Ray Observatory, too. The angular resolution is very poor - basically, by steering the aperture, you can get some angular resolution; but the images are pretty blurry. There's a schematic at NASA Goddard's Compton Gamma Ray Observatory webpage. I'm sure if you're more interested, we can dig up more technical papers.

The key concepts to keep in mind: if you want an image, you don't need a "lens" or a "mirror." All you really need is coherent scattering. If you generalize this concept, you see that it's possible to image using any type of wave: SONAR and ultrasound uses sound waves; optical light photography uses electromagnetic waves in the visible spectrum; radio astronomy uses radio signals (and sometimes, as in the Very Large Array, usees synthetic aperture imaging; and so on. Nimur (talk) 20:30, 26 January 2012 (UTC)

Thanks!, I thought of gamma photon reflection against heavy metals some minutes after the last post. But considered that they most likely would be absorbed and that the idea was DOA. Seems it I was not completely wrong ;) The links were interesting, but many of the articles lack good illustrations of the actual instruments. Electron9 (talk) 00:03, 27 January 2012 (UTC)

Here's a webpage with a fairly good diagram of the EGRET, the Energetic Gamma-Ray Experiment Telescope on CGRO. As you can see, the instrument doesn't look much as you might expect a conventional visible-light telescope to be designed. And here's a sample image, VP9185, a high-level data product synthesized around 2002 from data collected in early year 2000. As you can see, a gamma ray image isn't really a great "photograph" - but, that's what the object looks like in the gamma spectrum. (In this case, the target was a wide field view of the Milky Way - and it's a loooong exposure photo, around two weeks, with arguably the worlduniverse's worst case of rolling shutter distortion). The target's effectively "at infinity," though, so there's not much visible smearing. Nimur (talk) 02:08, 27 January 2012 (UTC)

Liquid Thorium Reactor

The Liquid Flouride Thorium Reactor sounds like it should be able to solve satisfactorily almost all of the problems associated with current nuclear power, as explained by this presentation at the House of Lords (Youtube). Now anything that solves all of our biggest issues without making new even bigger issues immediately raises my suspicions; is this really stacking up the way that they say it is? Falconus^{p t c} 18:33, 26 January 2012 (UTC)

I know India is very interested in making Thorium breeder reactors since they have abundant thorium reserves. I don't see any major problems. My guess is, shit takes time and money to make. ScienceApe (talk) 18:59, 26 January 2012 (UTC)

The problem is that reactor designs on paper look very straightforward and easy. Reactor designs in reality are full of many different types of engineering difficulties. When designing something as large and complex as a power reactor — and power reactors are quite large, and I heavily recommend touring one if you ever get the chance, to see exactly how big and complicated their whole facilities are — in the end it's often the case that the newer, "next generation" designs don't quite pay off to the degree as they are hyped to. Now, that's not to say that PWRs and BWRs are actually the best options on the table. But in designing a power reactor, one has to go for a very tough-to-reach sweep spot at the intersection of profitability and safety.

Looking at the article itself, I'm not convinced that the design there is really the best out of the possibilities for next-gen reactors. For one thing, reading the "Two versus Single fluid" section seems to imply that the engineering will be quite complicated, and the entire thing uses rather noxious chemicals at many stages (within the reactor, and for reprocessing). It sounds like there's a lot of room for error in the plumbing. It's also riddled with fallacies, e.g. "Burial in rock or clay is reasonable and safe by that time, because we've always lived with uranium in rock." This is true only if one neglects the fact that the natural concentrations of uranium in rock are very low — usually less than 1%, even in mineable ores. (There are a few very rare exceptions where you get concentrations up to 60% or so.) So it's not quite the same thing as uranium in rock, because presumably these wastes would be quite concentrated by comparison. I'm also unclear about the "annual fuel requirements". You can't power a reactor on natural thorium alone — it is fertile, not fissile. So there's some uranium missing from that graphic.

Frankly I find the idea that any nuclear reactor is going to be cheaper than coal a pretty suspicious statement. Coal is pretty damn cheap.

But anyway, it's hard to know. As the article points out, there haven't been many of these types of things built, and the ones that were built were built a long time ago. PWRs and BWRs are the "devil you know." That isn't to say that they're ideal — they're really not. But I would be suspicious of anyone touting the one reactor that's the easy solution to all of nuclear power's difficulties. Most experts who aren't in some way already committed to promoting nuclear power generally don't think there is one easy solution. --Mr.98 (talk) 19:51, 26 January 2012 (UTC)

"You can't power a reactor on natural thorium alone — it is fertile, not fissile. So there's some uranium missing from that graphic." I'm not sure what you are talking about. It's fertile, which means it breeds U233, and apparently according to some designs you can extract energy from the U233 produced in situ so what's the problem? ScienceApe (talk) 21:03, 26 January 2012 (UTC)

You need neutrons before the thorium transmutes into U233, to kick off the process. Where are those initial neutrons coming from? You've got to have some kind of uranium fuel in there to start up each load of thorium, at the very least. --Mr.98 (talk) 22:16, 26 January 2012 (UTC)

Is it possible to use some sort of tabletop (or larger) neutron generator, such as the laser+deuterium setup^[3]? Or do you need a seriously large amount of neutrons from the beginning to get the ball rolling? Wnt (talk) 01:29, 27 January 2012 (UTC)

You need a seriously large amount of neutrons. Remember that to get your chain reaction working, you have to have enough neutrons to keep generating more neutrons. And some number of those neutrons, then, are to breed the U233 (and thus are lost to chain). Now once you have the U233, you can keep the thing going again. But you are going to need a lot of neutrons to begin with (and the transmutation is not instantaneous — it will take a few weeks in most cases). It strikes me that you'd need to be able to keep a chain reaction going from the very beginning. I'm not saying it wouldn't work. It just means that some large number of your rods at any given time probably have to already have U235 or Pu239 or U233 in them. It also means you probably have to swap out the fuel in clever ways to make sure there are always enough there to sustain the reactions you need to breed more U233. But it complicates the very simple idea that you're just plugging in thorium and nothing but. The chemistry of the thing sounds fantastically complicated to me. My main criticism of the idea that this is a panacea is that no panacea actually turn out to exist once you start building them. But there are better and worse designs, to be sure. --Mr.98 (talk) 02:27, 27 January 2012 (UTC)

I don't think the article was claiming that it runs on Thorium alone, obviously it uses U235 as well to kick start the reactor. After that, U233 takes over. ScienceApe (talk) 03:53, 27 January 2012 (UTC)

Okay, thanks. I really hope that it works out the way that they are saying. We shall see though. Falconus^{p t c} 11:55, 27 January 2012 (UTC)

Voltage characteristics of bike dynamo

I want to use my bicycle hub dynamo to drive an LED (using a simple circuit with a rectifier and a capacitor to reduce flicker). The hub is a 2.4W, 6V hub but I'm not sure what this means in practical terms - can it never produce a voltage higher than 6V? What if the circuit is open?

This is the information for the LED I will use, but a simple voltage/current curve is provided here. I can't figure out what will happen... the voltage will be forced to 6V? But then the 2.4W rule would be broken (as well as my LED)? --129.215.47.59 (talk) 19:12, 26 January 2012 (UTC)

Bike generators I own, which are pretty old, produce alternating current, by rotating against the tire rather than being in the hub. The voltage (and frequency) vary with the speed of rotation (low speed, low voltage & low frequency). At a given speed, an AC generator should produce a higher voltage with no load that with a load, since it has impedance. Unless it has some electronic regulation circuit (a real possibility), the voltage should increase above a normal 6 volts as it spins faster than "normal." Powering a resistive load such as an incandescent light bulb, Ohm's law would imply 400 milliamperes at the 6 volts "normal" RMS into a 15 ohm resistive load. A solid state load (nonsinusoidal waveforms) or reactive load will complicate the equations a bit, since there would be vars as well as watts. I would not expect the output to be at all a pure sinusoid in any event. If it has an AC output, you should consider a rectifier circuit such as a full-wave bridge rectifier (available as an integrated circuit, or easily constructed from discrete rectifiers) rather than a single rectifier. Edison (talk) 20:05, 26 January 2012 (UTC)

[4] might be of use to you: it's a chap who's upgrading his old Sturmey Archer dynohub lights to use LEDs. SA hubs kick out about 2W rather than the 2.4W/3W that most dynamos do, but the principles will be the same. FWIW, voltage characteristics are dependent on the hub dynamo: the more expensive ones often have voltage- and current-limiting circuitry in them, but the cheaper ones don't. Some dynamos can hit 20V+ with no load, but most saturate at about 400mA (2.4W dynamos) or 600mA (3W dynamos). See also [5] which has lots of graphs and figures. You can also run a real bodge-job LED lightbulb by getting a 12V MR16 fitting LED lightbulb and a voltage doubler circuit. Very bright, but no standlight and might increase drag slightly - at least for mine. The plus side is that LED lightbulbs tend to have circuitry inside them that cleans up the input so you don't have to. Brammers (talk/c) 21:22, 26 January 2012 (UTC)

You probably should check out forums and other sites where plenty of people have done this, and more, before. E.g. [6] [7] [8]. It sounds like there are a lot of things you haven't considered. For example, unless your dynamo already produces a clean output close to 3.5V, you would want a driver of some sort (probably a constant current buck) which you don't seem to have considered. (Trying to put 6V through the LED is likely to kill it and using resistors or a linear regulator like an AMC7135 if your normal output is 6V is a bit dumb with a dynamo, your efficiency is likely to be something under 65%.) Also have you considered heatsinking? If you're planning to power the LED at 1A for example (perhaps not possible considering your dynamo), you'll easily kill the LED with insufficient heatsinking and at the very least would lose a great amount of efficiency. Air movement on a bike helps considerably but you still need to get the heat away from the LED in the first place. Also why did you choose the XP-G? A XM-L T6 will beat the XP-G S2 or even I expect S3 in efficiency under basically most loads. In your case, this is likely to mean more light output and easier heatsinking. While the XM-L will cost more, the price difference isn't that much (you can buy an XM-L for under US$10 shipped) and considering you're likely to be spending a fair bit more on all the other hardware, shouldn't be an issue. The primary reason I expect to choose an XP-G would be even with good optics, the XP-G would probably give more throw then the XM-L. (Of course a triple XP-G will probably beat a single XM-L in terms of efficiency.) And speaking of optics, have you considered them? P.S. [9] on drivers may be useful although it's not specifically directed at the bicycle market. Nil Einne (talk) 05:40, 27 January 2012 (UTC)

Isn't there something to stop a 2.4W dynamo from producing 1A at 6V? I figured that the voltage would drop because the dynamo couldn't produce enough current to maintain that voltage. If the dynamo produces only 400 mA, then the voltage shouldn't get that high. I bought the LEDs two years ago, and don't recall the reasons for those specifically. I'll worry about optics if I don't like the way the light looks on the road. 129.215.47.59 (talk) 11:15, 27 January 2012 (UTC)

Actually on further consideration you're right, you're not likely to kill the LED with your dynamo (well unless it's not heatsinked properly). However presuming you plan to use a single LED, it's still not going to work very well presuming you want a bright light. From what I read, dynamos are often fairly constant current at speed, so you're liable to be feeding 400mA to the LED. However this IMO isn't that bright even with an XM-L, let alone an XP-G. If your dynamo is capable of producing 6V at 400mA at resonable speed it will make more sense to use appropriate circuitry to either increase the current or alternatively use 2 XP-G or other LEDs in series. Both of these options seem fairly common. P.S. I didn't check the Pilom link earlier but it has a lot of good suggestions, including ways to get good light output at speed while still lighting up at resonably low speed. P.P.S. The XM-L didn't exist 2 years ago. Nil Einne (talk) 15:02, 27 January 2012 (UTC)

Can you make plastic from biofuel?

Topic says it all. ScienceApe (talk) 20:59, 26 January 2012 (UTC)

Read this. Turning plastic into fuel is also possible. Von Restorff (talk) 21:27, 26 January 2012 (UTC)

Wikipedia also has an article on this topic. See Bioplastic. --Jayron32 22:21, 26 January 2012 (UTC)

Another angle is that cellulose can be used to make plastics (celluloid) and biofuels (cellulosic ethanol). SemanticMantis (talk) 00:51, 27 January 2012 (UTC)

January 27

Maximum number of isomers from asymmetric Diels-Alder?

Assuming that I am reacting an non-cyclic asymmetric dienophile with a non-cyclic asymmetric diene, what is the total theoretical maximum number of different isomers that I can get? My textbook says the answer is 8 because you will get two structural isomers each with 2 chiral centers (2^2), so each structural isomer will yield 4 stereoisomers, for a total of 8 stereoisomers between the two structural isomers.

However, I think the answer is 4 because although each structural isomer has 2 chiral centers, the dienophile could only approach the diene either above or below the plane, so only two possible stereoisomers could exist for each structural isomer. In my opinion, what the book is suggesting is that in order to get 4 stereoisomers per structural isomer, the dienophile would have to attack across (sort of like trans) the plane of the diene. Who is correct? Thanks Acceptable (talk) 01:03, 27 January 2012 (UTC)

When you say "from above or below", are you considering each face of each (both endo and exo)? DMacks (talk) 01:13, 27 January 2012 (UTC)

I'm not sure, but are you basically assuming the Diels-Alder#Cis principle? The "theoretical" may not mean products you really see. Wnt (talk) 01:50, 27 January 2012 (UTC)

The cis principle (or not following it) sounds like the concern about adding trans across the plane of the diene. But the diagram at that link is great...it's got 4 possibilities, and then you could also have another set of four where the two stereocenters in that diagram are inverted. DMacks (talk) 02:19, 27 January 2012 (UTC)

alien missionary

IF for example, alien from another galaxy came to earth and preach about christianity (of course not the same history as our bible but the same trinity and all of core beliefs in christianity) does that prove christianity? MahAdik _usap 01:58, 27 January 2012 (UTC)

No. It merely acts as another data point, making the Christianity concept more plausible. In itself it is not a proof. --Tagishsimon (talk) 02:00, 27 January 2012 (UTC)

It would lead to yet another round of re-interpretations of key Biblical passages, making the whole thing even less credible to me. HiLo48 (talk) 02:03, 27 January 2012 (UTC)

It wouldn't necessarily even make it more plausible. Presumably said galaxy-traveling aliens are capable of receiving our radio and television transmissions (either past or present). They could be doing it just to mess with us, for unknown alien reasons. One would have a lot of hypotheses to rule out before one assumed that the example given there was proof of the truth of Christianity. The devil's in the details. If we had records that another civilization, totally disconnected, had been doing the same thing for centuries as well — that would be more interesting. There would still be alternative hypotheses to rule out (perhaps the Christ mythos was delivered to us by aliens! or perhaps convergent evolution applies to cultural matters in ways we don't quite understand.) that would not necessarily be any more bizarre (in the sense of Occam's razor) than Christianity being true. --Mr.98 (talk) 02:10, 27 January 2012 (UTC)

I would say, "the question is ill-posed." "Christianity" is not a fact that can be proven or disproven. It is a complicated set of cultural norms, theological ideas, and social practices, as well as a series of stories and rituals. Within the realm of Christian thought, there are certain tenets - facts - that could be either proven or disproven. For example, it seems plausible that we could collect enough archaeological evidence to prove or disprove whether a person had been crucified. But we could not "prove Christianity." It's not subject to a boolean measure of truth or falseness. Nimur (talk) 02:15, 27 January 2012 (UTC)

I would just note as well that that the trinity is not actually a core belief in all forms of Christianity. Even Christ's resurrection is not. There is no single Christianity — it rather famously has a very large number of sects, some of whom disagree with each other quite sharply on rather core issues. At best one would be getting an alien espousing the beliefs of one or another sect of Christianity. --Mr.98 (talk) 02:24, 27 January 2012 (UTC)

Christianity may not be Boolean, but God is real - unless declared integer. Mitch Ames (talk) 08:49, 27 January 2012 (UTC)

Just out of curiosity, what factual references is the OP seeking? Because this is, after all, the reference desk. This disclaimer at the top states "The reference desk does not answer requests for opinions or predictions about future events." Please post the question at Wikipedia:Discussion forum which has no need for factual answers or references at all. Shit, why is that still a redlink... --Jayron32 02:30, 27 January 2012 (UTC)

I don't think it's an "opinion" to discuss the logic of the thing. Nimur at least has provided a reference on falsifiability; I've provided one on convergent evolution. Seems like there are some ways to provide references to this sort of thing. It's ultimately an epistemological question. --Mr.98 (talk) 02:35, 27 January 2012 (UTC)

Fixed your link Jayron. CambridgeBayWeather (talk) 04:11, 27 January 2012 (UTC)

Burn! Well played, my friend. Well played indeed. --Jayron32 04:48, 27 January 2012 (UTC)

The core beliefs of the Abrahamic religions include the tacit assumption that life exists only on earth (and in heaven). That realm is where everything in those religions occurs. There's no provision for Men from Mars, etc. Very unlikely that an alien species would have independently latched on to Christianity or any other earthly religion as such. However, it would be interesting to know what religion(s) they believe in, if any, to see if there's a cultural parallel. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:13, 27 January 2012 (UTC)

On the other hand, if 10-foot-tall, blue-skinned, sapient humanoids from another planet visit us to tell us to worship a mother goddess called Eywa then it is very likely that James Cameron is a prophet. Until then the sane part of humanity will stick to worshipping the Flying Spaghetti Monster or the invisible pink unicorn because we have proof that they actually exist. Von Restorff (talk) 07:32, 27 January 2012 (UTC)

What would be really interesting is if those aliens had somehow uncovered evidence to definitively prove (or disprove) the elements of standard religious beliefs, such as gods, an afterlife, and so on. Even forgetting the religion question, there is the question of how humans would react to definitive proof that there is life elsewhere. One of the important lessons of 2001: A Space Odyssey that doesn't get much attention is Heywood Floyd's comments about keeping the proof of extraterrestrials a secret until there can be time for "conditioning". For all the talk of E.T.'s, if they actually showed up it could be a highly traumatic experience for the world's human population. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:43, 27 January 2012 (UTC)

Oh, I am sure we would respond in a rational and dignified way. Von Restorff (talk) 08:04, 27 January 2012 (UTC)

"Testing shows the presence, not the absence of Bugs" ;-) [10] AndyTheGrump (talk) 08:55, 27 January 2012 (UTC)

Bugs, I don't think there's anything in the Bible which explicitly rules out extraterrestrials. It doesn't mention them, but it also doesn't really mention dinosaurs or saber-toothed tigers or North America or a lot of other things that believers have been able to more or less assimilate into that worldview. --Mr.98 (talk) 14:17, 27 January 2012 (UTC)

An equivalent of this thought experiment was carried out in the Middle Ages. Although they didn't have any concept of extraterrestrials, what they did consider possible were antichthones - people who lived on the far side of the world, separated from the Northern Hemisphere by impassable deserts and wide oceans. If anyone lived there, there were one of two massive spiritual problems - either these people were all damned, since no-one could teach them about God or, even if they were Christians, this would mean Jesus would have also appeared on the other side of the world (and would also fatally damage the Adam and Eve story). Sadly, the record doesn't appear to show the churches's reactions to finding that the New World was inhabited by people with no concept of Christianity. Smurrayinchester 15:50, 27 January 2012 (UTC)

This is all off topic, but saying it would disprove Adam and Eve sounds like circular logic, and their unfamiliarity with Christianity would be no different than people in Sweden or Namibia for quite some time. As for alien religious beliefs, well... we're assuming a lot there, such as that our thought and their thought are even potentially mutually comprehensible. There's no real substitute for data. Wnt (talk) 17:04, 27 January 2012 (UTC)

The arguments were that: a) Adam and Eve would be damaged because for the antipodes to be inhabited, the immediate descendents of Adam and Eve would have needed to cross the "torrid clime", which was believed impossible. Finding people there, they believed, would have meant two gardens of Eden. b) That people in Sweden weren't converted was thought to be our fault for not getting to them faster. Crossing the equator however was thought impossible, so they could never be evangelised, unless a second Jesus had appeared to them. Smurrayinchester 23:14, 27 January 2012 (UTC)

Well if you believed in one Garden of Eden and a truly impassable "torrid clime", then you'd have to believe the other side was empty, and no one could prove you wrong. It doesn't sound like a great paradox to me. In fact, most scientists would make the same statement any day of the week if you ask them if there are people on Jupiter, Gliese 581d, etc., with very much the same thought process. Wnt (talk) 00:30, 29 January 2012 (UTC)

The question was if there were other people there. And once it was discovered that they were, the paradox became more than just a thought exercise. — The Hand That Feeds You:^Bite 21:44, 31 January 2012 (UTC)

"Cat years" versus "Human years"

Is there a rational way to compare the "age" of a 17 year old house cat to a human? Edison (talk) 06:44, 27 January 2012 (UTC)

Well, it's certainly not a linear relationship. I Googled "cat years human" and got quite a few useful sites. They tend to suggest that a 17 year old cat is equivalent to a human of around 84 years old. HiLo48 (talk) 06:52, 27 January 2012 (UTC)

The tendency to transform age by some obscure formula doesn't make much sense to me. You may as well ask how to convert the weight of an eight-pound cat into human pounds; or the length of a 30 inch cat to human-inches. The units of time, mass, and length are the same for cat and human. The reasonable ranges that we expect to find if we measure a cat are different than those we expect for a human. On average, a healthy housecat should live for ten to twenty years. Our article, cat, and cat health, cite sources for "12 to 14" years as common life expectancies. Seventeen is old, but far from uncommon. There's no rational justification for saying that seventeen cat-years is any way similar to eighty-four years. They've orbited the sun seventeen times, not eighty-four; and they've been around for the same number of minutes and seconds as a seventeen-year-old human, horse, or block of cheese. You might say, "it's unusual for a cat or block of cheese to last 17 years," but I still don't see why that makes them "84" in "cat years" or "cheese years." Clearly whoever came up with this conventional wisdom for conversion had no concern for precision of timekeeping or proper dimensional analysis, and they had no qualms taking liberty with the definitions of common units of measure. Nimur (talk) 07:27, 27 January 2012 (UTC)

I was going to point out that 84 is double 42, then thought better of it, but now I think it's important to highlight that significant fact. HiLo48 (talk) 07:44, 27 January 2012 (UTC)

Hoping Nimur's answer is a least a little tongue in cheek - though this question is on the science desk so fair enough! I always assumed the idea of these 'conversions' is to help people put a pets age into context and help people understand what age their pet is in terms of expected lifespan. Remember that prior to the mass of knowledge that is the internet this information was not so readily available...I.e. in the old days saying '1 year for a dog is equivalent to 7 for a human' provides a handy ratio for people to use. ny156uk (talk) 08:11, 27 January 2012 (UTC)

If you're going to remember that 1:7 ratio, you might as well remember that a dog's average lifespan is 12 years. Unless you're a 3-year-old who needs to count fingers to remember numbers, I see no reason why 7 would be easier to remember than 12. Furthermore, human life expectancy has increased by more than a factor of two over the past two hundred years (although most of it is due to decreased infant mortality rate). 1/7 of 35 years is very different from 1/7 of 82 years. --140.180.15.97 (talk) 10:34, 27 January 2012 (UTC)

It seems unlikely that the human:dog years ratio would be based on a detailed knowledge of mortality rates; it is more likely to derive from a perception of what counts as old age or a good lifespan. In humans you can get this knowledge either from observation or from traditional sources such as the Biblical "three score years and ten"; in dogs, people who own animals can typically differentiate premature death from old age. These figures have not changed greatly through history. --Colapeninsula (talk) 10:52, 27 January 2012 (UTC)

From a scientific point of view, it may make no sense (unless trying to compare stages of life and trends in ageing between the two... not that I'm sure that that would be feasible); however from a pet-owner point of view, it makes quite a bit of sense. I think some people would feel much better thinking that their cat lived 12 years, which is like 84, a decent life, rather than thinking "poor cat, it only had twelve years". Falconus^{p t c} 12:00, 27 January 2012 (UTC)

The biggest problem is that, as HiLo mentions, it's not linear (ie. there isn't a constant number you can just multiply by). 7 humans years=1 cat year works reasonable well for total lifespan, but if you work in terms of sexual maturity, say, you get a completely different answer (cats reach sexual maturity at about 6 months, humans at about 15 years, which suggests the factor to multiply by is 30, rather than 7 - a very big difference). That means the idea of converting human years to cat years is never going to work. --Tango (talk) 12:38, 27 January 2012 (UTC)

Well, physically, humans reach sexual maturity faster than that, so the difference is not quite so much. And with human-grade health care they might live longer on average. Meanwhile, a cat's heart beats at only twice the human rate, a little less, 110-140, so they get fewer heartbeats. I once was compiling a table of lifespans, heartbeat rates, and calls for many species (mostly I was impressed by a chimney swift's impossibly rapid and expressive communications, which to me suggested a genuinely faster "subjective time"), and it seemed like there was a fairly general scaling law, but lost it all to a disk crash before I could get to the bottom of it. Certainly any result has to be an approximation of the zeroeth order. Wnt (talk) 17:19, 27 January 2012 (UTC)

I meant physical maturity - other measures of maturity (emotional, economic, social, educational, etc.) tend to take a lot longer. Even physical maturity can take longer than that, particularly for boys. --Tango (talk) 19:13, 28 January 2012 (UTC)

Count telomere size and the associated hayflick limit ..? Electron9 (talk) 12:48, 27 January 2012 (UTC)

Dr. vs. Ph.D.

From a legal point of view, if a person receives the grade "Dr." in a European county (e.g., in Germany), can this person then state in English publications (e.g., in his CV) that he has received a "Ph.D." or does he need to use the German title ("He received his Dr. degree at the University of ...")? In other words, is "Ph.D." the English translation of "Dr." or would "Ph.D." misleadingly signal that he has received a degree in a country where "Ph.D." is the typical name for that type of degree, i.e., not in Germany? 130.149.229.180 (talk) 14:41, 27 January 2012 (UTC)

Sorry, but we can't answer that 'from a legal point of view'.

The reference desk will not answer (and will usually remove) questions that require medical diagnosis or request medical opinions, or seek guidance on legal matters. Such questions should be directed to an appropriate professional, or brought to an internet site dedicated to medical or legal questions.

- Cucumber Mike (talk) 15:36, 27 January 2012 (UTC)

The Wikipedia reference desk is unable to offer legal advice; in any event, the question of 'legality' is going to depend on the jurisdiction (rules will almost certainly vary from country to country) and the purpose for which the title is used. Legal questions aside, if you're applying for a job (particularly for an academic job) it's definitely not a good idea to appear to claim a degree which you don't hold (even if the degree is functionally a close equivalent).

The German Dr. degree often has requirements similar to those required to attain a Ph.D. in English-speaking countries, but it doesn't mean that you can make the substitution willy-nilly. (Consider—two universities might offer similar programs in mathematics; one school offers a B.Math. degree, while the other calls it a B.Sc.. Even though the course of study is equivalent, the graduate with a B.Sc. would be torn to shreds if he claimed to have a B.Math., or vice versa.)

In situations where a translation is likely to be helpful, some guidelines might be:

• Include the original degree name, so there's no ambiguity about what was awarded;
• Translate terms to preserve their sense and literal meaning as much as possible—for example, a Dr. sc. nat. should be translated as Doctor of natural sciences and not as Ph.D. in natural sciences; and
• If possible, use the same terminology the university uses in its own English-language documents, press releases, promotional materials, or websites, or find widely-accepted translations for the degree name (Wikipedia can be helpful).

Hope that helps. TenOfAllTrades(talk) 16:08, 27 January 2012 (UTC)

And how do people in the US refer to PhDs: as Dr. so-and-so or Mr. so-and-so? — Preceding unsigned comment added by 88.26.74.157 (talk) 15:41, 28 January 2012 (UTC)

Dr. so-and-so, at least professionally. See Doctor (title)#United States. --Tango (talk) 17:47, 28 January 2012 (UTC)

By the way, in the U.S. at least, don't double-up and refer to yourself as "Dr. Jack Harkness, Ph.D." unless you want to look like a quackpot. SamuelRiv (talk)

What health hazard does sand or glass particle which are used in sand blasting causes?

In sand blasting machine sand particls or glass particls are used which is normally inheled by the surrounding peoples. Which kind of dieses or health hazard does it cause? — Preceding unsigned comment added by 220.225.96.217 (talk) 16:29, 27 January 2012 (UTC)

See silicosis. Wnt (talk) 17:06, 27 January 2012 (UTC)

Also, sand-blasting is incredibly loud, so hearing damage is likely, if proper protection is not used. StuRat (talk) 18:28, 27 January 2012 (UTC)

permanent cure of stye.

We delete these questions for a good reason. Please start a discussion at WT:RD seeking to change the rule rather that trying to circumvent them every time
The following discussion has been closed. Please do not modify it.
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 talk page discussion (if a link has been provided). --Jayron32 18:01, 27 January 2012 (UTC) As I said - recognizing that we can neither diagnose nor treat the condition - I think it does no harm to point the OP to our article on styes, nor to point out that old or contaminated cosmetics can carry the bacteria. That is neither diagnosis nor treatment, which the OP's doctor already did three times, but just common sense. The Refdesk prohibition has been explained as a matter of "ethics", and what sort of ethics could require us not to repeat such a basic and widely publicized piece of advice? Wnt (talk) 20:23, 27 January 2012 (UTC) The guy's doctor can't fix it and he's coming to us for advice? That's funny. Sort of. There's nothing we can do for him except tell him to find another doctor. ←Baseball Bugs What's up, Doc? carrots→ 22:40, 27 January 2012 (UTC) Doctors are always in a rush, and don't take the time to give you instructions you should have read on the Internet. Or to follow instructions they should have read on the Internet. Not two months ago I had a doctor trying her level best to intimidate me into taking ciprofloxacin, threatening to "discharge" me as a patient otherwise, for a simple ingrown toenail, telling me that podiatrists have limited knowledge, when I'd just had an unbearably sore Achilles tendon from gout five days before, and two other risk factors for getting sudden tendon snaps from that crazy substance. Even when I pointed out the problem she made out as if that crippling side effect was nothing to worry about. Well, to the podiatrist it was a run-of-the-mill case, and the X-ray showed none of the bone infection she claimed I "probably" had despite my strong impression otherwise. I say, if your ethics allow you, you can try trusting a bookie or a drug dealer and you might get away with it, but never trust a doctor. Wnt (talk) 00:21, 28 January 2012 (UTC) "Trust but verify." Did you take your problem to a bookie or a drug dealer? No, you took it to another doctor. QED. :) ←Baseball Bugs What's up, Doc? carrots→ —Preceding undated comment added 00:27, 28 January 2012 (UTC).

Energy density of algae produced biodiesel and biogasoline

Is the energy density of the aforementioned fuels the same as their petroleum counterparts? ScienceApe (talk) 20:12, 27 January 2012 (UTC)

I do not have sources but I guess the answer is no, because that would be highly unlikely. It is hard to find two different materials with the exact same energy density. Von Restorff (talk) 01:39, 28 January 2012 (UTC)

Are they different? Petroleum is just biomass (mostly algae) that has been subject to intense heat and pressure over a long time. ScienceApe (talk) 01:59, 28 January 2012 (UTC)

Common biofuels are often a little lower in energy density than the conventional fuels they are intended to replace (e.g. 5-10% lower), but it can vary based on the feedstocks and processes used. I don't have any specific details for algae-based fuels, but as a first guess it wouldn't be surprising if they are a little lower on average. Of course petroleum also varies considerably in energy density, but we defined standards for fuels and require refiners to adjust the final product to match. I would assume that before biofuel really takes off there would be similar standards adopted for its expected energy content. Dragons flight (talk) 06:17, 28 January 2012 (UTC)

Farsi Island

Is there any source mentioning the area of Farsi Island? Or maybe a naval map with large scale? Thanks --тнояsтеn ⇔ 22:28, 27 January 2012 (UTC)

It's pretty small. My CM93 charts represent is as a 9-vertex polygon about 0.46 nm long (WNW to ESE) and 0.22 nm at its widest (SSW to NNW), with an average width of about 0.15 nm, suggesting an area of about 0.237 km ². It also shows a smaller island 85 m off the south coast of main island (in an area of coral) which is represented as a 5-vertex polygon, roughly a 123 m x 103 m rectangle with its NW corner lopped off, yielding an area of about 0.011 km². The combined land area is about one quarter of a square kilometer. My chart doesn't actually call them as "Farsi Island", instead labeling them as "Al Farisiyah" and reports a radar transponder beacon, tower, and light (28.0 m, flashing twice every 15 seconds, visible for 16 nm) at 027.9925N 050.1729E. On this chart, the coordinates given in the article (27.98N 50.18E) are of a point 0.85 nm SSE of the light in open water about 40 m deep. I don't know the original source of the data here, and can't give you an RS. Sorry. -- ToE 22:36, 28 January 2012 (UTC)

Spanish Wikipedia mentiones a much larger dimension of the island (es:Isla Farsi) and so do other Wikipedias. Aerial images show a quite small island, that is why I asked. So your numbers make much more sense. Thank you! --тнояsтеn ⇔ 22:51, 28 January 2012 (UTC)

What aerial imagery have you seen? With Google Maps satellite view, I can't make out any land either there or at the spot 12.5 nm south where the Saudi island Al Arabiyah is supposed to be. The nearest land I can make out is Jazirat Karan 25 nm to the SW. -- ToE 02:51, 29 January 2012 (UTC)

Bing Maps ([11]). --тнояsтеn ⇔ 13:21, 29 January 2012 (UTC)

Size of the Universe at the Big Bang.

Can anyone tell me what the size, that is volume, of the universe was at the moment of the Big Bang, or at least as close to it as we can get. When I say universe, I mean the entire universe, not only the parts we can see. I've been getting contradictory answers to this question, (either it was a point or already infinite), and I look to you for some clarification. 23:42, 27 January 2012 (UTC) — Preceding unsigned comment added by 68.6.88.47 (talk)

I suppose it depends on how you define the universe. If all the matter is in one geometric point, and then you have infinite space around it, does that make the universe the point or infinite ? Note that there could also be other big bangs, in which case some coin the term "multiverse" to encompass all of them, and perhaps the vast empty spaces between them, too. StuRat (talk) 23:50, 27 January 2012 (UTC)

A single point of matter within an infinite space is an incorrect picture of the Big Bang. Near the Big Bang, the whole universe was in a hot, dense state. There was no space around it. Spacetime itself rapidly expanded from the singularity.

It isn't known for sure whether the universe was nearly a single point or infinite near the Big Bang, because it isn't known for sure whether the universe is finite or infinite, although according to Shape of the universe#Open or closed, the universe is considered to be without boundaries in the standard FLRW model of cosmology. Red Act (talk) 00:33, 28 January 2012 (UTC)

If the ruler with which one measures the universe is within the universe, I'm guessing the size would be infinite. As for being outside and measuring it.... (my mind is threatening to explode) HiLo48 (talk) 00:34, 28 January 2012 (UTC)

Why would you say that? A flatlander living on an S² manifold (say, the surface of a sphere) could do experiments to measure the size of its universe, even though its ruler is contained within its universe. -- ToE 18:53, 28 January 2012 (UTC)

Lets assume the matter was in a gravitational singularity before the Big Bang, and there was no space around it. Von Restorff (talk) 00:38, 28 January 2012 (UTC)

We're assuming Big Bang cosmology, which doesn't say that matter was a gravitational singularity before the Big Bang. I don't think that really makes sense. -- BenRG (talk) 05:49, 28 January 2012 (UTC)

Traditional big bang cosmology predicts a gravitational singularity before this time, but this theory is based on general relativity and is expected to break down due to quantum effects. Von Restorff (talk) 11:35, 28 January 2012 (UTC)

That's correct; what it says is that traditional big bang cosmology, which suggests there is a gravitational singularity, is expected to break down (i.e. to be wrong) in the era where it predicts the singularity. That's as contrasted with modern-day big bang cosmology, which doesn't have the singularity. -- BenRG (talk) 02:00, 29 January 2012 (UTC)

There wasn't actually a "moment of the Big Bang". All we know is that the universe has been expanding and cooling from a very hot, dense, and amazingly homogeneous state for about 13-14 billion years. We don't know how large the homogeneous region was or where it came from. If you believe inflationary cosmology then it was very large, much larger than the part we can see now, but beyond that it's hard to say anything. -- BenRG (talk) 05:49, 28 January 2012 (UTC)

It is not known if something existed before the singularity that appeared at the moment of the Big Bang, nor if time is linear, since the expansion estimated by Hubble's law assumed a linear expansion, and later work indicates there may have been variations. Von Restorff (talk) 14:18, 28 January 2012 (UTC)

That's gibberish added by a well-meaning layperson almost a year ago. I'll delete it. -- BenRG (talk) 02:00, 29 January 2012 (UTC)

I think that the meaning of a measure of time defined in terms of oscillations of a cesium atom, at a time when a cesium atom was larger than the universe, is rather mysterious. A tremendous amount of stuff happened in those first few "instants" of the universe, which had impact on future eras. To imply that that was all "nearly instantaneous" rather abuses the concept. Really the Big Bang reflects the inability of our standard of time, the laws of physics of our conventional forms of room temperature matter, to be relevant to higher energy regimes. I get the impression that, in the same way, when protons and electrons decay, when the universe is a vast cold dark wasteland perhaps populated by "neutrino nuggets" (see Wikipedia:Reference_desk/Archives/Science/2011_September_15#Neutrino_chemistry), a vastly longer scale of time and space might make its doings again seem exciting to its residents. Wnt (talk) 16:19, 29 January 2012 (UTC)

January 28

structure of hair

complete the description of hair by filling in the gaps.the missing words are provided below. the hair that shows above the skin's surface is ........... it is composed mainly of ............ the same protein hat makes up the ........... and .............. a hair is made up of 3 layers, the cuticle,the cortex,the medulla. the ........... is the tough,outer protective layer of the hair.the cells are ............... . they allow colour from beneath to show through.they form ............., which overlap towards the hair............... the .............. is the main part of the hair , which contains the colour pigments ...............(brown/black) and ............(yellow/red). the cells in the ...........contain bundels of ............... The ................,thickness and ......... of the hair is determined by the way in which the ............ and ............ are held together. ................is formed in this layer. the ............... is the middle ............. of the hair . it is not always present and does not have a significant function.

cells keratin fibres core dead cortex tip cuticle pheomelanin scales medulla elasticity translucent keratin nails melanin fibres skin strength cortex — Preceding unsigned comment added by Payojana (talk • contribs) 00:42, 28 January 2012 (UTC)

It is probably better if you do your own homework. Von Restorff (talk) 00:46, 28 January 2012 (UTC)

It might get a bit hairy, but try looking at cells, keratin, core, dead, cortex, tip, cuticle, pheomelanin, scales, medulla, elasticity, translucent, keratin, nails, melanin, fibres, skin, strength, cortex. StuRat (talk) 01:11, 28 January 2012 (UTC)

Clearly hair is the place to start. To be technical, one thing in this exercise is not strictly correct - keratin is not a single protein, but a large family of proteins, and there are slightly different varieties present in each structure - indeed, in each layer of the skin the mix differs. An example of a specific keratin is keratin 14. Note also that type I keratins and type II keratins typically work together in each structure, with one of each type working together as a heterodimer. But it is true that there is a fundamental relationship between all the keratins, tracking back to some single precursor long ago in single celled organisms which evolved into many different specialized forms by duplication and divergence.^[12] Also, I would personally prefer to say eumelanin rather than melanin at one point there - to me, pheomelanin is a form of melanin, rather than an alternative to it, and the article we have is written that way also. Wnt (talk) 00:22, 29 January 2012 (UTC)

Folding spacetime

We all know what happens when spacetime bends. What happens when it folds instead? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:07, 28 January 2012 (UTC)

Wormholes ? StuRat (talk) 01:12, 28 January 2012 (UTC)

This is not a perfect answer but it is well worth reading. Von Restorff (talk) 01:14, 28 January 2012 (UTC)

I'm afraid that answer is almost totally wrong... -- BenRG (talk) 05:56, 28 January 2012 (UTC)

I meant, folds as in suddenly changes direction all at once, like the knife-edge folds at the edge of a paper airplane. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:17, 28 January 2012 (UTC)

General Relativity gives no way for that to happen. It's sort of like asking how a guitar would sound if its strings had folds, or how waves would propagate if the surface of a lake had folds. It really doesn't make sense. Looie496 (talk) 02:34, 28 January 2012 (UTC)

All that matters to general relativity is the "intrinsic curvature" of spacetime, which affects things like the ratio of a circle's circumference to its diameter. Folding spacetime, in the sense of folding a piece of paper in two, doesn't change the intrinsic curvature, so it's a no-op as far as general relativity is concerned. Pointy bits in the intrinsic curvature are possible, though, and are better known as gravitational singularities. -- BenRG (talk) 05:56, 28 January 2012 (UTC)

Looie496: In your analogy, wouldn't a fold just act as a node? Or if you compare the lake to a particle in a box model with a step in it? Plasmic Physics (talk) 23:12, 28 January 2012 (UTC)

There are gravity waves, at least in theory. Could you have a "gravity shockwave", or is the term meaningless? If you could, would that be a fold of some sort? Wnt (talk) 00:08, 29 January 2012 (UTC)

Yes, you can. A massless particle travelling at the speed of light is a source of a gravity shockwave. It is a rather curious construction, and you could say that it is a fold. As a very rough mental analogy, imagine a paper cylinder and think about an edge between the side and the top. The top and the side are flat everywhere (in the strict geometrical sense - they have zero intrinsic curvatures), the edge is unexceptional and there are no singularities, but the whole construct has unusual topology.--Itinerant1 (talk) 01:33, 29 January 2012 (UTC)

If "Solubility in Water" is 58.2% at 20 °C, what does that mean in practical terms?

Hi there.

I have Potassium Sorbate granules and I need it in liquid form as concentrated as posible.
According to Potassium_sorbate, its "Solubility in Water" is 58.2% at 20°C,
but I'm not sure what that means in practical terms?
(In other words, if I take 100g of Potassium Sorbate, what is the minimum amount of water I will need to dissolve it, and, therefore what strength Potassium Sorbate would that solution be?)

Thanks in advance
14.200.130.252 (talk) 12:38, 28 January 2012 (UTC)

my guess is that it is g/100ml that is meant by the %. To make a saturated solution, why dont you just add a little water to some of the powder, warm, mix and let it stand. The liquid above it will b as satuarted as it can go after a few days of standing.Staticd (talk) 13:31, 28 January 2012 (UTC)

Mass concentration (chemistry)#Usage in biology would suggest your guess is correct. --Tango (talk) 17:42, 28 January 2012 (UTC)

Japanese bird name mix-up

On a website about unusual Linnaean names I visited a few years back, there was a mention of two Japanese birds of the same genus whose common names in Japanese were mixed up when they were given scientific names. Something like the bird called yosenabe in Japanese was given the scientific name Nipponavis akamichi and the bird called akamichi in Japanese was given the scientific name Nipponavis yosenabe. I can no longer find this page, and searching for "japanese birds" and "mix up" has left me empty-handed. Does anyone know the names of the two bird species who got their names mixed up? Wiwaxia (talk) 17:17, 28 January 2012 (UTC)

Could this be it (search for "Erithacus" on the page)? Deor (talk) 21:56, 28 January 2012 (UTC)

See Ryukyu Robin and Japanese Robin. Alansplodge (talk) 01:43, 29 January 2012 (UTC)

This is it! Thank you! Wiwaxia (talk) 09:35, 29 January 2012 (UTC)

Reminds me of Siebenrockiella leytensis from Palawan, which got mixed up with the more common Cyclemys dentata from Leyte en route from their respective collection sites. This caused the turtle to be classified as Critically Endangered and possibly extinct for years as the zoologists assessing its conservation status were looking for it in the wrong island.

Anyway, where did you get the names Nipponavis akamichi and Nipponavis yosenabe? Did you make those up? Should have put gen. nov., sp. nov. there to avoid them being red herrings. LOL -- Obsidi♠n Soul 22:41, 28 January 2012 (UTC)

Yes, I made up Nipponavis (Japan bird), since I didn't remember the real genus name. akamichi and yosenabe were trying to recall the Japanese names (and I got the aka- part right). I admit I got yosenabe from this Japanese soup. Wiwaxia (talk) 09:35, 29 January 2012 (UTC)

January 29

Terminology question

Suppose you have a measurable quantity of some kind, such as 123 MWh of energy. This is the same as 123 thousand kWh. The "MWh" and "kWh" bits are called units, but what are the "123" and "123 thousand" bits called? JIP | Talk 00:27, 29 January 2012 (UTC)

Quantity? --Mr.98 (talk) 00:59, 29 January 2012 (UTC)

But isn't the whole thing called a quantity? I am asking specifically about the bit with the numbers. Changing that bit without also changing the unit would change the overall amount of energy. JIP | Talk 01:02, 29 January 2012 (UTC)

Numerical value. From WP: "the value of a physical quantity q is expressed as the product of a numerical value Nq and a unit of measurement uq" 88.26.74.157 (talk) 01:08, 29 January 2012 (UTC)

88.26 is quoting from Physical quantity#Definition of a physical quantity. -- ToE 02:56, 29 January 2012 (UTC)

Artificial melatonin

How can melatonin be synthesized artificially? I wanted to know both chemically and extracting it from plants. 88.26.74.157 (talk) 01:04, 29 January 2012 (UTC)

Note that if it's extracted from plants, it's natural, not artificial. StuRat (talk) 01:13, 29 January 2012 (UTC)

OK, I meant, not naturally produced in humans (the melatonin from pills). 88.26.74.157 (talk) 01:15, 29 January 2012 (UTC)

Three processes of chemical synthesis are shown here. Hmmm ... Firefox is telling me the site is untrusted, so proceed at your own risk. Clarityfiend (talk) 02:03, 29 January 2012 (UTC)

So chemistry sites are unsafe ? Good thing I limit my web browsing to Eastern European porn sites. :-) StuRat (talk) 03:34, 29 January 2012 (UTC)

That's it, time for a spanking! Whoop whoop pull up ^{Bitching Betty | Averted crashes} 05:22, 29 January 2012 (UTC)

That would be a case of "whoop whoop pull down." :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:19, 29 January 2012 (UTC)

Whoop whoop pull up ^{Bitching Betty | Averted crashes} 06:32, 29 January 2012 (UTC)

Horses in roller skates

Would it be possible to fit specially shaped roller skates onto a horse's feet to allow it to move faster? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 05:18, 29 January 2012 (UTC)

Fitting them would be no problem, but training a horse to roller skate would be difficult, perhaps impossible. You might be able to do it, if you put them on the horse from birth (putting on larger ones as needed).StuRat (talk) 05:35, 29 January 2012 (UTC)

According to Inline speed skating, rollerblading a "metric mile" is about 50 percent faster than running it would be. Here's the problem, though: rollerblades complement the way humans run, which is on two feet combined with arm-swinging. Horses don't have arms to swing and help them keep their balance. The side-to-side thing would be totally unnatural for a horse. It might be interesting to try, though. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:33, 29 January 2012 (UTC)

I googled [horse on roller skates], and a number of things came up, including this somewhat nondescript picture,[13] but I suggest you do some googling and see what you can find. The point being, it's been done. Whether it's faster than running, I couldn't say. But obviously it would have to be done on a paved surface. Roller blades don't usually do well on turf or earth. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:37, 29 January 2012 (UTC)

LIFE magazine ends the magazine with a "Miscellanny" picture. The first "Miscellanny" picture was a horse on rollerskates, Jimmy, he appeared in the May 19, 1952 issue. But no-one cares about Jimmy anymore, because now we have Tarra. Even parrots try to imitate Tarra. After a lot of training some cockatoo's can rollerskate pretty quickly. Abused monkeys rollerskate too. If you torture a bear long enough he can skate on ice. I don't think fish rollerskate, they usually prefer skateboarding, just like dogs. Dogs like surfing too. This planet is pretty weird. Did you see this ass called Pinky? Search for "Pinky" on this page, maybe you can find video. Here are the newspaper 1 and newspaper 2. extra info. Pinky was probably painted pink. Von Restorff (talk) 07:22, 29 January 2012 (UTC)

My chief concern with trying that would be the risk of the horse breaking legs, which usually ends in the death of the horse. Falconus^{p t c} 15:04, 29 January 2012 (UTC)

Jimmy! That rolls back memories. Here you can see him horsing around on skates -so to speak. It start just after 6 minutes in. I've Got A Secret - Easter Parade (2/3). It's not the horse but the panel of celebrities that appear to be worried about breaking a leg - their own.--Aspro (talk) 17:01, 29 January 2012 (UTC)

Anecdotes...

OK, I can't ignore this, too many bad memories...

• Much like today's problems involving a spherical cow, when I was in high school Physics, it was guaranteed that on every Mechanics exam, there was one question which began, A horse on frictionless roller skates is moving at [N] m/s..."
• It also seems that this piece of "Bumper sticker wisdom" applies: Never try to teach a pig to sing. It wastes your time, and annoys the pig.

--DaHorsesMouth (talk) 22:20, 29 January 2012 (UTC)

diabete melitus

is diabetes mellittus a x-linked character? if not on which chromosome is its character present? — Preceding unsigned comment added by 123.201.155.125 (talk) 11:50, 29 January 2012 (UTC)

See Diabetes mellitus type 1#Genetics and Genetic causes of diabetes mellitus type 2. Red Act (talk) 12:03, 29 January 2012 (UTC)

If everything is heavier than the air we breathe why do clouds and fog ( which are water droplets) apparently FLOAT ?

Floating clouds and fog- how are they supported. ? — Preceding unsigned comment added by Swavcrewson8 (talk • contribs) 13:35, 29 January 2012 (UTC)

Not everything is heavier than air; e.g. helium. Read this article. Von Restorff (talk) 13:47, 29 January 2012 (UTC)

Same reason why ships float and don't sink? Lynch7 13:48, 29 January 2012 (UTC)

Nope. Read Displacement (ship). Von Restorff (talk) 13:52, 29 January 2012 (UTC)

My chemistry lab instructor would always point out that we shouldn't leave a beaker upside down in a rack to dry as water vapor (H₂O at 2(1) + 16 = 18 g/mol) is lighter than air (roughly 80% N₂ + 20% O₂ at 0.80 (2) 14 + 0.2 (2) 16 = 0.8 * 28 + 0.2 * 32 = 28.8 g/mol). I always figured that there must be an optimum time to leave the beaker upside down so that as much liquid water as possible will drain out before inverting it to air dry the rest of the way; I doubt that such a time would be much more than a minute. The OP may also be interested in reading Density of air#Water vapor which explains why humid air is actually lighter than dryer air, a fact counterintuitive to many who feel hot, heavy air "weighing down on them", but an important fact for pilots as planes have less lift in less dense air and thus need longer takeoff rolls when it is hot, humid, or low pressure (either from weather or, more importantly, altitude). -- ToE 14:50, 29 January 2012 (UTC)

That's a very good point, and explains why the layer of humid air containing the clouds will float. Of course, individual droplets of water that we see (i.e. clouds) are heavier than air, but they fall so slowly due to air resistance that they can't get to the ground - until they join up to be big enough, at which point the rain most assuredly comes down. Wnt (talk) 16:12, 29 January 2012 (UTC)

That reason for not inverting beakers seems a bit silly, as the natural tendency of water vapor to diffuse will greatly outweigh any density differences, at that scale. I would invert them, both to let water drain out, and to keep dust from settling inside. This is particularly important if they are to be used for biology cultures, as that dust will inevitably contain bacteria. (Of course, the beakers really should be sterilized better than that, and not be allowed to air dry at all, but in a school lab they may not have the expensive equipment to do it properly.) StuRat (talk) 18:18, 29 January 2012 (UTC)

The chemical term is suspension. (Or, if the water droplets are small enough, an aerosol.) Firstly, due to square-cube effects, as you decrease the size of the droplet, air resistance becomes proportionally much larger when compared to the force of gravity, meaning that small droplets fall slower than larger droplets. Cloud droplets are very small, and thus take much longer to settle out than rain droplets. Also, below a certain size, the random drift of the droplets due to brownian motion is larger in size than the slow settling due to gravity, effectively keeping them "permanently" suspended in still air. But again, air is rarely still, and clouds typically form when warm, moist air rises as a mass, and then cools enough to for the water to condense. This bulk rising also can serve to keep clouds afloat, or even cause them to rise further. -- 67.40.215.173 (talk) 20:08, 29 January 2012 (UTC)

Sleep deprivation

Why is it that, after missing a full eight hours of sleep, a nap of only three hours or so plus sunlight and a meal is enough to leave me perfectly revivified? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 17:57, 29 January 2012 (UTC)

It won't, actually -- if you tried to do that every day, you would find yourself suffering in the long run. But generally speaking, the relationship between sleep, time of day, light, and alertness is quite complex and far from completely understood. Our article on circadian rhythms contains some useful information, but I won't pretend that it fully answers the question. Looie496 (talk) 18:08, 29 January 2012 (UTC)

Agreed. Our bodies are designed to operate on limited hours of sleep, on occasion, but not full time. StuRat (talk) 18:11, 29 January 2012 (UTC)

Hopefully it leaves you "revived", not "revivified". StuRat (talk) 18:09, 29 January 2012 (UTC)

Yeah, I meant "revived", Stewed Rat. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 18:15, 29 January 2012 (UTC)

I knew a guy who stayed awake 7 days straight, and was fine after 8 hours of sleep. by constrast, I feel cruddy after sleeping a few hours each of several consecutive nights. Heck froze over (talk) 18:46, 29 January 2012 (UTC)

Note that they may have only appear to be fine, the long-term consequences of sleep deprivation are fairly well documented. StuRat (talk) 19:23, 29 January 2012 (UTC)

Feeling awake doesn't mean that you are indeed equally able to perform any task. Self-assessment of your cognitive abilities is tricky, since you are employing your own cognitive abilities, which could be impaired. Do not try to drive under such conditions, since your body could ask you for some microsleep. 88.26.74.157 (talk) 20:01, 29 January 2012 (UTC)

• I work in a 24 hour a day business, and I can tell you that I have most certainly seen the negative effects of long term sleep deprivation with my own eyes. New night shift workers will often try to stay up during the day as well, either to hang out with friends or even to do another job. I've honestly seen people lose their minds doing this, they become extremely irritable and irrational and stop paying attention to details. I even had one guy come up to me several months after I fired him for such behavior and thank me for letting him go because he believed he was on the verge of psychosis caused by sleep deprivation. Beeblebrox (talk) 20:17, 29 January 2012 (UTC)
  • As noted in Fatal familial insomnia, which is the absolute worst form of sleep deprivation, namely that you can't sleep at all, sleep deprivation can ultimately lead to dementia and death. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:50, 29 January 2012 (UTC)

If you work out vigorously almost every day, like running fast for half an hour or longer, you will feel the difference between getting a proper amount of sleep at night or just napping for a few hours, already after a few times. Count Iblis (talk) 00:34, 30 January 2012 (UTC)

Incandescent light bulb self limiting current?

In the Incandescent light bulb one of the references says "Edison's research team was aware of the large negative temperature coefficient of resistance of possible lamp filament materials and worked extensively during the period 1878–1879 on devising an automatic regulator or ballast to stabilize current. It wasn't until 1879 that it was realized a self-limiting lamp could be built.". So how come the lamp is self-limiting?, and would the lamp life be extended if the lamp were current controlled? Electron9 (talk) 17:59, 29 January 2012 (UTC)

As the 'newer' bulb's 'tungsten' filament gets hotter so the resistance goes up (positive coefficient), with say silicon (transistors, glass bottles etc.) and carbon it goes down. This is a poor example on youtube but it was all I could find quickly. [14]. Early Wirelesses often used a bulb to regulate the current because the poor power regulation of mains electricity. Uranium is another element used to regulate current as its resistance go up when too much juice goes through it. The early carbon filaments had a negative coefficient -thus the need to regulate the current.--Aspro (talk) 18:31, 29 January 2012 (UTC)

This clip demonstrates the negative coefficient of glass which at room temperature is normally a pretty good insulator but heat it up and its resistance goes way down and so starts to absorb microwaves very well . [15]

Hey thanks! An instance of melted Pyrex in the microwave was one of the Great Mysteries - and this provides the explanation. Wnt (talk) 01:35, 30 January 2012 (UTC)

Ships flying out of water

Can a large explosion really lift a large destroyer completely out of the water? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 18:01, 29 January 2012 (UTC)

“completely' is maybe a bit of a euphemism. This clip is of a torpedo stick and the ship certainly rises some what.[16] A magazine explosion would be worse. Merchant ships carrying munitions have been reported to come out of the water when their cargo explodes but of the footage I can recall, the blast obliterates the ship making it impossible to tell. I would suggest that the bow and stern would blow fore and aft without leaving the water completely. The energy however, would be sufficient to raise it several miles if it was all applied evenly from beneath the keel.--Aspro (talk) 19:14, 29 January 2012 (UTC)

A Type 45 destroyer has a mass of about 8000 tonnes. Ignoring buoyancy and using the formula E=mgh, we find that it would take 78 Megajoules to lift it one metre. A tonne of TNT releases 4.2 Gigajoules, so could (if all the energy could somehow be used to lift it) lift the destroyer 54 metres. The Father of All Bombs, which is apparently the largest non-nuclear bomb, is equivalent to 44 tonnes of TNT. If you could get all of that energy to lift the ship, it would go 2.4 km (1.5 miles) into the air. Of course, you couldn't actually get all that energy to lift the ship, a lot of it would go down and sideways and a lot of it would go into destroying the ship rather than lifting it. If you really wanted to, you could probably get it to lift a metre of two clear of the water with a perfectly placed explosion. --Tango (talk) 22:52, 29 January 2012 (UTC)

Nukeproof armor

Is there any known or hypothetical material which can shield a person from an atomic bomb detonating right next to them? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 18:13, 29 January 2012 (UTC)

Depends on the size of the nuke and how close. A Hiroshima-sized nuke could be defended against with little more than a conventional bomb shelter, even at ground zero (directly below the air burst). If you were sitting atop the Tsar Bomba when it was detonated, though, you should kiss your ass goodbye. StuRat (talk) 19:17, 29 January 2012 (UTC)

I am not sure that a conventional bomb shelter would defend you against being directly below a nuclear detonation. Even if the structure was not crushed by the overpressures (which is not impossible, depending on the construction), the heat and radiation would be extreme. You'd roast. Put another way: a suitable rugged structure, like the Hiroshima Genbaku Dome, might survive such a blast (that building benefited by being directly under the explosion, because the forces on it were primarily vertical, which preserved many of the walls). But nobody inside it would likely survive. You'd need really much more than your conventional bomb shelter to take a direct hit with an atomic bomb of almost any militarily significant size. Even direct hits from conventional bombs can destroy conventional bomb shelters. Fallout shelters were not about surviving direct hits — they were about surviving misses or the effects of bombs some distances off, or avoiding residual radiation. They were meant to save some lucky lives, not all lives. Many of them would have just served as kettles for their occupants, as was the case of shelters used in the firebombings of Dresden. --Mr.98 (talk) 22:23, 29 January 2012 (UTC)

You don't need to be far underground to be protected from heat and radiation. Air is another problem, though, as you wouldn't be able to get breathable air from above for some time. So, oxygen tanks would be needed, and water. You could likely be rescued before a lack of food would kill you. StuRat (talk) 03:48, 30 January 2012 (UTC)

It is not that theoretically hard when considering small tactical weapons. As Project Orion discovered, only a few millimetres of a strong shield gets to be eroded by the heat. Next problem: one needs sufficient 'mass' to resist the force to stop the occupants inside from being bounced around to a pulp. Nuclear bunkers are provided with very thick walls of hard zinc cement (like what your dentist uses – if you can afford visit one) reinforced with tungsten rods – all of which weighs many thousands of tons. On the inside, on the upper floors and ceilings, they often apply an epoxy composite layer, of about a foot in thickness. This both stops the concrete spalling off and hitting people, as well as absorbing any neutron radiation that gets through (and prevents some Bremsstrahlung being created as well perhaps). Of course, a poor man's equivalent, is to just use the closest Kelvinator or equivalent - as demonstrated in this clip by Mr. Jones. [17] Don't try this at home kiddies- they don't open from the inside. Hope this helps and are you asking because you’ve heard something on Fox news that we haven't?--Aspro (talk) 20:06, 29 January 2012 (UTC)

Most modern refrigerators do open from the inside, in that they are only held shut with a magnet, and can be pushed open from the inside easily. It's the old ones with latches that killed kids. StuRat (talk) 20:20, 29 January 2012 (UTC)

A lot of those fridges are still around in the world (they never brake down) and how is your magnet going to keep the door shut. It wouldn't even happen in the movies ;-) --Aspro (talk) 20:48, 29 January 2012 (UTC)

They are also angled so gravity holds the door shut, and the magnet doesn't have to do much, just keeps it from bouncing back open when closed (I've had some fridges with weak magnets that do bounce back open). Also, I'd put the brakes on that spelling of "break". :-) StuRat (talk) 22:02, 29 January 2012 (UTC)

There are three main effects from the atomic bomb: pressure, heat, and radiation. It's a lot of radiation we're talking about "right next" to the exploding bomb, so a few inches of lead ain't gonna do it. The heat is going to be extreme — millions of degrees celsius. The pressure is quite a lot. So one could imagine being in some sort of container that is going to be blasted into the distance — that's probably your best bet. But you'd still probably die from one thing or another. I think many of the posters above underestimate the amount of energy were talking about here. It's orders of magnitude more than what human beings are used to dealing with. Project Orion is paradoxically misleading on this front. If by "material" you mean, "an elaborately constructed giant spaceship that is designed to translate that energy into thrust," then sure. But that isn't "nuke-proof armor." It's a spaceship. The answer is more or less "no." You can imagine some setups where you could make some sort of container that might help with survival in that it would blast you out of the area once the bomb hit, but that would be pretty dang contrived, and require you to know a lot about the size and location of said bomb ahead of time to have any confidence in it working. In my opinion, the best nukeproof armor you could have would be the live children of whomever has the nukes! --Mr.98 (talk) 22:26, 29 January 2012 (UTC)

According to our Atomic bombings of Hiroshima and Nagasaki article; "Eizo Nomura (野村 英三, Nomura Eizō?) was the closest known survivor, who was in the basement of a reinforced concrete building (it remained as the Rest House after the war) only 170 m (560 ft) from ground zero (the hypocenter) at the time of the attack" (Hiroshima). He was in a concrete box though, rather than a suit of armour. Also nuclear weapons make a much bigger bang these days. Alansplodge (talk) 00:38, 30 January 2012 (UTC)

And 170m is a long way from "right next to you". --Tango (talk) 00:41, 30 January 2012 (UTC)

And he was ridiculously lucky. Don't let the fact of a special exception distract you from the general rule. --Mr.98 (talk) 00:55, 30 January 2012 (UTC)

I agree, your best bet is to not try and resist the explosion but to let it throw you clear. You need a sealed sturdy container with something inside to cushion you (some springs, maybe?). --Tango (talk) 00:41, 30 January 2012 (UTC)

Suppose Tsar Bomba (50 Mton) etc.. is unlikely to be used. But if an B90 nuclear bomb with rating of 200 kton (836.8 TJ) would be used. What level of radioactive exposure in [Sv] (J/kg) will occour?, this essential to calculate any shield. And how much heat energy per area [J/m²] is radiated in order to calculate condensation energy for any wall?, pressure level?, let's assume the distance is 10 meters. Regarding an "blast driven shelter" one still needs to keep the body exposed to less than 50 G in order to not get crushed even with soft cushion. Electron9 (talk) 03:16, 30 January 2012 (UTC)

It would have help if the OP had given a specific measurable distance and yield. For instance, folks in Washington USA who say they where right next to Mount St. Helens when it blew, really mean they where living 30 miles away, a distance which in little o' Europe is often somewhere in another country where everyone speaks a different language. Yet, let's go though it in more detail. Heat: yes millions of degrees but what does that do ? Just flakes of a little of the outer surface. Its not the temperature that's important. People think that the tower of the Trinity test got vaporised – myth. The Project Orion team scoured the area and found most of it, their just wasn't enough calorific energy in the fireball to vaporize it! Pressure: A direct hit means about 30 psi of over-pressure at ground level. Enough to destroy most structures -which is why the high of burst is chosen to give this figure. It would be a piss poor bunker that could not withstand this and they are often designed to withstand a 1000 psi and more. OK that's air burst. What about ground bust. Well, with an air-burst, one has the advantage, that the shock wave hitting the ground gets reflected back and more or less doubles the over-pressure. With a ground bust however this effect (known as the Mach reflection region -speed of sound relative to temp , density, blah, blah) is much reduced. So you need a at the very lest a contact burst. Also, the concrete is exceedingly resilient. Much the same stuff was used for the WW2 military defences in Europe, they could withstand explosive shells (the pressure of which I forget get but it is something like 25 to 35 bar). Which is why one can still see so many structures in Europe – how can you blow them up without ripping all the roof tiles off the neighbouring houses and shattering the windows in the hamlets round about. Radiation: Just 2.4 inches of concrete halves the transmission of radiation. The thickness of bunker-walls gives nigh on complete protection over 3 months of occupation. Children: This requires attributing the same rationality into the minds of the enemy warlords as on might poses oneself. Did Magda Goebbels accept the offer to have her children passed over to the safety of the Red Cross? History is littered with the children of leaders being less important that the 'great plan'. Just in the last half century there are numerous example of despots refusing to accept the inevitable without regard to their kin.--Aspro (talk) 01:30, 30 January 2012 (UTC)

In my opinion, one's best bet is to, first of all, attempt not to be close to a nuclear device when it detonates. --Ouro (blah blah) 07:27, 30 January 2012 (UTC)

The only genuinely effective "nukeproof armor" available with current technology is several billion tons of rock - for example Cheyenne Mountain. Roger (talk) 09:23, 30 January 2012 (UTC)

Bacteria ID₅₀

What is the average minimum number of bacteria of any one type that has to be present in the human body to cause an infection? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 18:27, 29 January 2012 (UTC)

Okay, that makes two silly questions in a row plus one unanswerable question. Please try to restrain yourself. Looie496 (talk) 19:05, 29 January 2012 (UTC)

Per the guidelines at the top of the page, the reference desk is not a forum for general discussion. Wikipedia is not a discussion forum. Please try to stay on the task of creating an encyclopedia. Do you need help locating a general discussion forum? Nimur (talk) 19:46, 29 January 2012 (UTC)

42. Von Restorff (talk) 21:04, 29 January 2012 (UTC)

1. Count Iblis (talk) 00:24, 30 January 2012 (UTC)

0, infections are not always caused by bacteria. But 42 is much funnier. Von Restorff (talk) 05:46, 30 January 2012 (UTC)

Benefits of eating meals ?

...as opposed to snacking continuously all day long (and assuming the same food is consumed either way, in the same quantities). And does the blood sugar spike after a meal actually have a purpose, like the blood pressure spikes during a heartbeat, or is it just a negative consequence of eating meals ? StuRat (talk) 20:15, 29 January 2012 (UTC)

[18] — Preceding unsigned comment added by 92.28.79.174 (talk) 21:15, 29 January 2012 (UTC)

That doesn't answer my Q. StuRat (talk) 21:23, 29 January 2012 (UTC)

Part of the reason would be social. For most of the time humans have eaten meals at "fixed" times, it's been with other people. It would be a time for doing many of those things that humans do when they gather in groups, especially involving talking to each other. HiLo48 (talk) 21:38, 29 January 2012 (UTC)

I've read that in young children, continuous snacking can inhibit the onset of socialism (it is typically hard to learn to socialise with a breadstick in one's mouth), increase the likelihood of choking (because a toddler who is playing might forget that he's also eating), and increase the likelihood of tooth decay (because the toddler has food continuously in her/his mouth for a longer period of time), but I have no information about effects of continuous snacking in anyone else. :S Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:44, 29 January 2012 (UTC)

I think you meant "socialization" rather than "socialism", unless you were being funny. :) But I think the answers given here are correct - that a few meals a day, as opposed to a "continuous meal", fits better with agrarian and industrial societies, as compared with hunter-gatherer societies. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:46, 29 January 2012 (UTC)

The main benefit from eating fixed meals is that is works well with a sedentary agricultural lifestyle. I'm not sure there's much more supporting it than that (other than habit and culture at this point). Before agriculture — at least, this is my understanding — humans fed more or less continuously through the day. Agriculture and division of labor means you can't do that as easily. --Mr.98 (talk) 22:33, 29 January 2012 (UTC)

Primates including primitive peoples often eat as they come across food. The only reasons that springs to my mind for three-square-meals-a-day is that it is more convenient for a diet of cooked food, it also allows time to work on other activities, as found in non nomadic societies. The blood sugar spike -if its too high- is not good, but this is less pronounced on say a Paleolithic diet. The spike just means that that sugar is being absorbed by the guts faster that the body can convert it. It serves no purpose, other that to provide pharmaceutical companies with a steady supply new patients to buy their type 2 diabetes treatment products.--Aspro (talk) 22:40, 29 January 2012 (UTC)

I was fascinated by this research; "In a first-of-its-kind study, Harvard researchers have shown that cooked meat provides more energy than raw meat, a finding that challenges the current food labeling system and suggests humans are evolutionarily adapted to take advantage of the benefits of cooking." The researchers present a hypothesis suggesting that the extra calories provided by cooked food may have allowed developmental changes to early humans 1.9 million years ago. Obviously, if you have to cook food on a fire, it makes sense to do a whole lot together and then sit down with your family and eat it (ie "a meal"). Anyone who has tried cooking food from scratch on a campfire will know that it's a lengthy process. The ability to open a packet of pre-prepared food and bung it in the microwave is a recent luxury. Alansplodge (talk) 00:26, 30 January 2012 (UTC)

But cooked food doesn't have to be eaten immediately. Heck, if you make jerky out of it, you can eat it months later. StuRat (talk) 03:42, 30 January 2012 (UTC)

It's a lot less effort to eat it as soon as it's cooked isn't it? Alansplodge (talk) 09:08, 30 January 2012 (UTC)

That claim depends on two big and very shaky assumptions: one, that people ate meat in significant quantities 1.9 million years ago; two, that they had enough control over fire to cook that meat. Both of these would, I think, be considered extreme fringe theories in anthropology. There is no evidence of cooking beyond 300 or 400 thousand years before present. There's very little evidence of systematic big-game hunting, and essentially no evidence of serious hunting weapons like bows or throwing spears, before ~100 thousand years BP. By 100 kya, humans had modern-size brains and were in many ways similar to us (there are tribes in Africa whose ancestors split from the rest of the human phylogenetic tree 140 kya ago).

Hunting and cooking certainly played an important role in colonization of Northern Europe and Siberia, but they haven't been with us as long as the authors of that article claim.--Itinerant1 (talk) 07:09, 30 January 2012 (UTC)

What do they know in Harvard? Alansplodge (talk) 09:08, 30 January 2012 (UTC)

Being a Harvard student does not keep you from getting involved with fringe theories.--Itinerant1 (talk) 09:53, 30 January 2012 (UTC)

January 30

Mustard seed

Is Mustard seed the smallest seed in the world? roscoe_x (talk) 09:15, 30 January 2012 (UTC)

No, of course not. The bible is full of claims that are not true, because the people who wrote and rewrote and edited and censored and translated the bible were often incorrect. Read this. Von Restorff (talk) 09:24, 30 January 2012 (UTC)

After reading your userpage: read this... Did you know God prefers atheists? Von Restorff (talk) 09:32, 30 January 2012 (UTC)

Is it really necessary to turn a simple scientific question into a religious issue? Roger (talk) 11:01, 30 January 2012 (UTC)

I assume you were probably not aware that this is a religious issue and not a simple scientific question but it is. I wish it wasn't, and I assume you do too. It is 2012, people should've stopped believing this kind of nonsense a long time ago. Von Restorff (talk) 11:10, 30 January 2012 (UTC)

No, the smallest seeds are found with certain orchids [19] The mustard seed is about 15 times bigger than the smallest orchid seeds. EverGreg (talk) 11:31, 30 January 2012 (UTC)

Colder on high mountains

why is it colder on high mountains — Preceding unsigned comment added by Toshad Salwekar (talk • contribs) 10:48, 30 January 2012 (UTC)

Please see Lapse rate. -- ToE 10:58, 30 January 2012 (UTC)