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December 9

Is the refrigeration technique advanced enough to preserve ice in July in Hittin during the 12th century?

In the article Battle of Hattin there is a sentence:"The exhausted captives were brought to Saladin's tent, where Guy was given a goblet of iced water as a sign of Saladin's generosity." I checked Tiberias#Geography and climate where was near the location of battle, and found that only in extreme occasions did the temperature there reach zero. Those articles about refrigeration such as Refrigeration, Timeline of low-temperature technology are alomst devoid of information about that time (There are some remnants of earlier Ice house in China and Rome, but I am not sure if it helps to this question). So was ice ever possible at that time and that location?--Inspector (talk) 08:01, 9 December 2012 (UTC)

Our article on Evaporative cooler doesn't mention the production of ice, but I believe it's possible at night in a dry atmosphere. In my student days when I couldn't afford a refrigerator, I kept milk cool by this method, but the humidity was too high to make ice. In some areas of desert, it is possible to produce ice at night purely by radiative cooling, using an ice pit insulated from the surrounding warm sand with straw, and the technique was developed in ancient times, with the resulting ice being stored in ice houses. Dbfirs 08:36, 9 December 2012 (UTC)

I don't know if radiative cooling is really a feasible way of producing ice. The linked article has some doubts about it. OsmanRF34 (talk) 13:51, 9 December 2012 (UTC)

I think it's possible, but only in certain conditions, especially including a clear dry atmosphere above the ice pit. The discussion seems to conclude that it doesn't violate any laws. Dbfirs 20:10, 9 December 2012 (UTC)

It's also possible that they used salt to lower the temperature. 24.23.196.85 (talk) 00:07, 10 December 2012 (UTC)

A couple of sources[1][2] state he had ice brought from the mountains. Clarityfiend (talk) 08:40, 9 December 2012 (UTC)

• Ice can be both be brought frozen over the mountains from pits dug for the purpose or brought from the mountains. μηδείς (talk) 04:26, 10 December 2012 (UTC)

Subconscious phrases in mind

Sometimes, but not often, I experience short phrases that pop in while I rest or sleep. It's not like I hear them, they just flare up in mind spontaneously, without my intent. The phrases are like "Want to take a photo?", "No, thanks" etc. They appear before I fall asleep or so when I'm not dreaming. I think it's related to brain rest, but not sure. Is there a name for such phenomenon?--93.174.25.12 (talk) 10:42, 9 December 2012 (UTC)

In the Sleep article, it mentions a "non-REM stage 1", which might be what you're experiencing. When you're not quite awake and not quite asleep, things can seem "real" which aren't real. I've had this happen from time to time... as have many others, as this is presented as an explanation for some folks who think their bedroom is "haunted", as they feel as if they're being stifled by some spook... but that only happens when they're in that in-between stage, and it feels "real". Seems to me there's a more specific term than "non-REM stage 1", but it's not popping right now. P.S. If this is bothersome to you, as opposed to merely interesting, you should consider seeing a professional. (If nothing else, they could probably give you better terminology.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:43, 9 December 2012 (UTC)

Bugs, I think it's part of sleep paralysis. --TammyMoet (talk) 13:58, 9 December 2012 (UTC)

No, this is known as "hypnagogic imagery" -- see Hypnagogia#Sounds. "Hypnagogia" is the formal term for the process of falling asleep. Looie496 (talk) 15:54, 9 December 2012 (UTC)

Very good. I don't know if either terms are what I saw on TV, but sleep paralysis explains the spooky stuff, and hypnagogic imagery explains my experience perfectly... and it sounds like it would explain the OP's as well. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:13, 9 December 2012 (UTC)

I believe I saw that as well, many years ago, on one of those "unsolved mysteries"-type shows. I don't recall the details of the show, but it led me to a book called The Terror That Comes in the Night, which was quite interesting, though it looked at the phenomenon through the paradigm of folklore study. By coincidence, a few years later my young daughter began experiencing night terrors, which is a closely related phenomenon; she never saw any hags though. Matt Deres (talk) 20:55, 9 December 2012 (UTC)

As someone whose workplace was destroyed on 9/11, and who has been treated for night terrors, with good reason, I can assure you that mere vocalizations as one falls asleep do not count as night terrors. 04:24, 10 December 2012 (UTC)

It's not a contest; night terrors often have no trigger in the way that nightmares (for example) often do; the experience itself is the terror as the half-asleep brain attempts to interpret the paralysis it suddenly "finds" itself in. Night terrors are not necessarily worse or easier to live with than nightmares; they're something else entirely. Matt Deres (talk) 01:42, 11 December 2012 (UTC)

Humidifiers and temperature

The manual of my (ultrasonic) humidifier states that increasing the humidity with it will increase the felt air temperature and effectively reduce heating costs. Two questions: 1) Does higher humidity always mean higher felt air temperature or does it depend on temperature as well? At least to me, for sub-zero (Celsius) temperatures, a dry climate is much more pleasant than a wet one. 2) All costs included, can a humidifier really lower total expenses? bamse (talk) 19:53, 9 December 2012 (UTC)

Higher humidity will slow evaporation from your skin; and it increases the heat capacity of the air, which can make you feel warmer in hot temperatures and cooler in cold temperatures, also depending on the air flow, and other factors. See heat index for the combined effect of heat and humidity. μηδείς (talk) 20:05, 9 December 2012 (UTC)

Thanks. Any ideas on the second question? bamse (talk) 19:14, 10 December 2012 (UTC)

There are many factors that go into the second calculation:

1) What type of humidifier is it ?

a) You said yours is ultrasonic. Now, the energy usage for that should be low, however, you need to use distilled water, since it will otherwise vaporize all the minerals in the water and coat the area with dust. So, the question comes up as to how much you pay for your distilled water. If you buy it, that will get expensive fast. If you distill it yourself, then the energy to do that must be considered. If you just use tap water and ignore the dust, the cost will be lowest.

b) An electric evaporation humidifier will cost a lot, too, because electricity is expensive. Tap water can be used, but will create mineral deposits in the humidifier (which is much better than on your walls).

c) A natural gas humidifier will be less expensive. I essentially do this by having a huge stock pot on the stove with a tiny flame always under it. This has the advantage that moisture is also an exhaust product from combustion, so you get moisture from two sources. As above, tap water mineral deposits go into the pot, so don't plan on using it for food again. Use a huge pot so you can leave it on overnight or while at work without danger of it running dry (mine lasts about 2 days). Another approach is always having a big pot of stew of the stove in winter.

d) An integrated humidifier which works with the furnace, using air already heated there, is probably best of all. This also has the advantage of distributing it throughout the house. (With any single source of humidity, you will see higher humidity in that room, possibly with condensation at the windows leading to mold, and lower humidity elsewhere.)

2) What type of heat does your home have ?

a) Natural gas heating is the least expensive (unless you count heat pumps, in the temperature range where they work). However, the water vapor generated by combustion goes up the chimney, along with some of the heat.

b) Electrical is the most expensive, except that some forms can be set up for zone heating, so you only heat the areas you want.

3) How well insulated is your home for heat and humidity ? A poorly insulated house will lose heat and humidity through the walls, and water will also condense on the windows, and maybe walls, causing mold.

So, it's probably impossible for us to judge which is cheaper, in your home. However, humidity should be kept up for other reasons, like avoiding dry skin, callouses, chapped lips, cracked wooden furniture, etc. StuRat (talk) 19:40, 10 December 2012 (UTC)

entropy in information science and thermodynamics

what, if anything, is the relationship between the word "entropy" used in information science (e.g. 2 bits of entropy per english letter, etc) and entropy in thermodynamics? if nothing, why is it the same word - historical coincidence? or is there nevertheless something in common. thanks. 178.48.114.143 (talk) 20:45, 9 December 2012 (UTC)

Compare the formula for entropy from Entropy (statistical thermodynamics): $S=-k_{B}\,\sum _{i}p_{i}\ln \,p_{i}$ with the formula from Entropy (information theory): $H(X)=-\sum _{i=1}^{n}{P(x_{i})\log _{b}P(x_{i})},$. Dauto (talk) 21:20, 9 December 2012 (UTC)

Can you be a little more vague or general, please? I understand that your answer is very precise but I am neither a mathematician or physicist. I understand the latter because it's "obvious" to me or intuitive, but not the thermodynamic version. Why is it not the same formula? Could you 'dumb it down a tad' for me? more importantly, can you explain the relationship between the concepts. thanks. 178.48.114.143 (talk) 21:24, 9 December 2012 (UTC)

The difference between the formulae is just cosmetic. Both formulae define entropy as the negative of a sum each term of which is given by a probability times its logarithm. Dauto (talk) 22:59, 9 December 2012 (UTC)

This doesn't help me at all. Are the units the same? Is the concept the same? What are we talking about and what does heat have to do with winzip (for example ; i.e. higher-entropy files will be larger when zipped). I get the latter concept and would like to know what, if anything, this has to do with thermodynamics. Thanks. 178.48.114.143 (talk) 23:15, 9 December 2012 (UTC)

It is not a coincidence. Thermodynamic entropy came first, but the same concept was later applied to information. See Entropy in thermodynamics and information theory, which handles them both and describes the ways they do or don't overlap. One early and interesting example of the interrelation of thermodynamic and information principles is Leo Szilard's informational interpretation of Maxwell's demon and its implications for the second law of thermodynamics. --Mr.98 (talk) 23:43, 9 December 2012 (UTC)

Guys, you're asking me to read these articles (I'd found the one you just linked already) and I'm saying it's too hard. Can you help? Thanks. 178.48.114.143 (talk) 23:52, 9 December 2012 (UTC)

(I didn't mean to annoy you by posting a relevant link — we lack the ability to know what you have and have not read, if you do not tell us, and figured that if you had looked at the article, even uncomprehendingly, you'd have understood that the shared language was not one of historical coincidence — the very fact that there is an article seems to indicate that, I thought.) --Mr.98 (talk) 01:46, 10 December 2012 (UTC)

In both cases, entropy is a precise way to compute something that corresponds to the "randomness" of the system. Randomness is sort of vague and poorly defined. In information-theory contexts, we might hand-wavingly say that random information content is less structured, or has less redundant/repeated information. In statistical physics or thermodynamics, we might say that random arrangements of molecules have more atoms flying around in more different directions. All of these hand-wavey imprecise statements leave a lot to be desired, because we can't compute values for such vague concepts. So, we define entropy, which is a convenient and precise way to express this sort of concept. And, as it happens, our equation definition is useful because we can relate it to other computed quantites. We have equations to relate entropy and temperature, in the case of thermodynamics. In information theory, we have equations to relate entropy and algorithm efficiency, or entropy to expected data loss rate, and so forth. Nimur (talk) 00:01, 10 December 2012 (UTC)

This is very helpful. Are we saying that the entropy is LITERALLY the same concept, or an analogous concept? By literally the same concept, I mean, "air molecules on one side vacuum on the other take less bits to describe than in a highly mixed state" just like a file that is five million ones and then five million zeros takes very few bits to describe - it has little entropy. To me, entropy isn't "counter-intuitive" at all because I always equate it with the size if you try to compress or describe it (e.g. winzip). So is it literally the same concept - if you had a "replicator" and sent across a description of the system to be replicated perfectly, then you don't need very much information (it "zips" well) if it's all air molecules on one side and vacuum on the other (e.g. low-temperature) but if you wanted to replicate it perfectly at a higher temperature or better-mixed then you need more information? Is this LITERALLY the same concept (not just an analogy)? Or am I now going too far? 178.48.114.143 (talk) 00:45, 10 December 2012 (UTC)

Ok, you asked for it -- here's a very hand-wavy discussion that is not rigorous or precise, but I think captures the general similarities. The Shannon notion of information (Information_theory#Entropy) equates information with randomness. The idea is that there is more "information" in a specific random string, than a specific string with a lot of structure. For instance, Let X be the string with 50 ones and 50 zeros. This has low information, because it can be described much more succinctly, and we could transmit or store that shorter expression, rather than the whole string. On the other hand, let Y be a "random" string of 100 ones and zeros, say Y=10101110000101000011110100101010100101001...1

Y carries more information than X because we'd basically have to record every digit to faithfully transmit that string. Though I'm speaking qualitatively, we could work out specific quantities of entropy for X and Y by computing the formulae that are (tersely) quoted above. This discussion also matches up with the "entropy is a measurement of disorder" analogy in physics. In that case, X is similar to a box with air on one side and vacuum on the other, and Y is similar to a box of air at uniform pressure. So, the mathematical form of "structure vs. order" in physics is also useful for describing "high vs. low information". Counter-intuitively, the "structured" case, X, corresponds to the low information example. Another application of this same idea is to measuring biodiversity, see Shannon index.

In short, we use the same word because they are mathematically the same thing. The differences are in the way that we interpret the math, in hopes of that interpretation being useful for solving a certain problem or discussing a certain field of science. SemanticMantis (talk) 00:02, 10 December 2012 (UTC)

This is very helpful. See my question imm. above at same indent level as this. 178.48.114.143 (talk) 00:45, 10 December 2012 (UTC)

Let me give you a very explicit answer this time. Yes, the two concepts are LITERALLY the same concept, but applied to different situations, and that's why the mathematical formulae are identical. Dauto (talk) 14:29, 10 December 2012 (UTC)

Is my replicator analogy also 100.00% correct? Imagine you have a supernatural replicator that can make anything as described (that comes over its communications link). Is it the case that to perfectly replicate a hot drink, you need more bits (more coming over the line) than to perfectly replicate a cold drink? I mean, imagine that you describe an x by x by x cold vacuum, and it replicates that for you. That takes almost no bits, it's like zipping an empty file. Then as you are replicating more and more complicated things, it takes larger and larger space to get all that to the replciator, even compressed. Now here is the question: IS THE THERMODYNAMIC ENTROPY IN AN OBJECT LITERALLY EQUIVALENT TO HOW MUCH ENTROPY ITS DESCRIPTION TO THE REPLICATOR CONTAIN? Please bear in mind that the questino this time is hether this description is NOT hand-wavey but 100% perfectly rigorous. Is what I've just said, technically, perfectly, rigorously true in a mathematical and physical sense? Thank you. 178.48.114.143 (talk) 19:09, 10 December 2012 (UTC)

note also that by introducing the supernatural replicator I have stopped having to talk about "concepts" and reduced the question to a yes-or-no truth value about how many bits must get to the replicator given a certain object given optimal compression, and whether this is literally the same "number" as its thermodynamic entropy. There is no longer any question of "concepts" but instead, teh truth-value in a thought experiment. THank you. 178.48.114.143 (talk) 19:12, 10 December 2012 (UTC)

Yes, yes. The two concepts of entropy really are identical. The only difference is choice of units. Information entropy is usually measured in bits or nats while the thermodynamic entropy is measured in Joules/Kelvin. That's why the formula for the thermodynamic entropy is multiplied by Boltzmann constant which is nothing more than a conversion factor between those choices of units. Dauto (talk) 20:45, 10 December 2012 (UTC)

Achievement unlocked! Thank you, Dauto, and others, for your answers. In fact I now feel (if it really is this simple :) ) that I have understood it very well. Forgive me if I seemed incredulous - the relationship seemed a lot more complicatd than before I asked this question :). Thanks for all your help! 178.48.114.143 (talk) 21:30, 10 December 2012 (UTC)

You might find Entropy in thermodynamics and information theory interesting. Dauto (talk) 18:40, 12 December 2012 (UTC)

Chloromethane on mars

The SAM instrument on Curiosity is a pyrolysis GC-MS with a relative slow heating ramp of less than 50°C / minute. They found chlorinated methane [3] in a sand dune on mars (they choose it because it would be the point with only minimal organics). (Viking found the same stuff in a sand dune in the 1970s) It is a very small amount. The other results make it relative obvious that perchlorate is present. Perchlorate decomposes to oxygen and chlorine. The source of carbon might be earth organics traveling with the rover to mars, mars organics, or inorganic carbon from carbonates.

Is it possible to get chloromethane from carbonates and perchlorate? Carbonates decompose and give off carbon dioxide which decomposes at temperatures above 800°C forming carbon and carbon monoxide Boudouard reaction. I can come up with no good rection forming that compounds from carbonates. --Stone (talk) 23:34, 9 December 2012 (UTC)

Neither can I, and I'm very familiar with these types of reactions. 24.23.196.85 (talk) 00:05, 10 December 2012 (UTC)

I can't answer the question directly but, chloromethane is known to be produced by several species of phytoplankton here on Earth. It's also seemingly becoming clear that liquid water once existed on mars, and as per [4], it's looking more certain than ever that life once existed on Mars, it's possible the chloromethane they found could be organic in origin. douts (talk) 22:14, 11 December 2012 (UTC)

Fixed link. Evanh2008 ^{(talk|contribs)} 22:39, 11 December 2012 (UTC)

December 10

Does Quantum entanglement apply to the entire visible universe?

Are we in a state of Quantum entanglement with those distant proto-galaxies at the edge of Hubble's fuzzy vision? Did we have time to mingle into a single cosmic scale wave function before Inflation (cosmology) went off like a bang? Just how far out of the box is the reach of the undead cat? Hcobb (talk) 00:46, 10 December 2012 (UTC)

No. Nonclassical entanglement isn't a normal state of affairs; it's very easily destroyed by environmental interactions. That's one reason building quantum computers is so hard. -- BenRG (talk) 02:54, 10 December 2012 (UTC)

But isn't the entire universe ruled by a single wave function and decoherence simply an mirage caused by our inability to fill in all the blanks? Coherence is said to be lost once one of the particles interacts with some "random element" from the outside, but that simply means that whatever is being interacted with is itself part of a larger coherence? Hcobb (talk) 03:23, 10 December 2012 (UTC)

Well, operationally speaking, there isn't any nonclassical result like Bell's theorem that applies to different galaxies. Philosophically speaking, in the many-worlds/relative-state picture (which is what you're probably thinking of), measurements entangle the measuring device with the system being measured, and this entanglement at the scale of the whole universe is responsible for the fact that the world appears as it does. I'm not sure it's right to call this entanglement, though. It's just plain old classical correlation, which is another name for entanglement that doesn't violate Bell's theorem. -- BenRG (talk) 05:21, 10 December 2012 (UTC)

What's to keep a distant galaxy from sending single photons at us followed by their observations to play Bell's theorem across the breadth of the Universe? Also wouldn't we use Entanglement-assisted classical capacity to chat with interstellar probes simply because of power considerations? There is no range limit on the wave function. Hcobb (talk) 16:55, 10 December 2012 (UTC)

Yes, in principle you can send one half of some Bell pairs toward another galaxy, wait until they've traveled far enough that they can be treated as part of that galaxy instead of this one, and then there's a small amount of nonclassical entanglement between the galaxies. This is an artificial situation maintained by careful isolation of the entangled particles. You could use those Bell pairs for superdense coding, but the amount of nonclassical entanglement would decrease as the Bell pairs were consumed. It's very hard for me to believe that this could ever be the most power-efficient option. For starters, the Bell pairs would presumably need active containment for the entire trip. -- BenRG (talk) 17:25, 11 December 2012 (UTC)

A typical particle is entangled with many particles far outside our horizon Count Iblis (talk) 23:42, 11 December 2012 (UTC)

That's the kind of entanglement that I called "plain old classical correlation". A world without correlation wouldn't make any sense. For life to exist there has to be a correlation between genotype and phenotype and between phenotype and reproductive fitness and between objects in the world and images on your retina and on and on for absolutely every aspect of the world. This is obvious and has nothing to do with quantum mechanics as such. All they're saying is that the universe is extremely uniform and the uniformity resulted from a common origin, not coincidence. -- BenRG (talk) 05:26, 12 December 2012 (UTC)

Lack of carb in meat

According to Chicken (food), it contains zero carb. Just curious, where does the muscle glycogen go? --PlanetEditor (talk) 05:11, 10 December 2012 (UTC)

It breaks down into glucose, which is quickly consumed by the cells' mitochondria. 24.23.196.85 (talk) 05:16, 10 December 2012 (UTC)

But why the stored glycogen is broken down? And how can a dead cell's mitochondria be active? --PlanetEditor (talk) 11:31, 10 December 2012 (UTC)

There may be trace amounts of glycogen or glucose in the meat, but a very small amount. Labeling laws allows rounding (usually to the nearest whole number, sometimes to the nearest 5, depending), so small amounts get rounded down to zero. --Jayron32 13:01, 10 December 2012 (UTC)

The mitochondria consume the glucose before they die - cell death is not an instantaneous process. Roger (talk) 15:25, 10 December 2012 (UTC)

Curie temperature of welding steel

I understand that stray drops of molten steel from a welding operation will not be deflected by a magnet because the steel is above its Curie temperature 700 deg C. However the drop cools as it falls and will become magnetic. Does its magnetism recover instantly or does it increase gradually over a number of degrees aabout the Curie point? Will the falling drop aquire a cooler magnetic shell around a paramagnetic interior? Is there a formula for the cooling of a molten drop falling in air? SkylonS (talk) 09:32, 10 December 2012 (UTC)

See Curie's Law. The long and short of it: Below the Curie temperature, magnetization is inversely proportional to the temperature, whereas above it, the steel does not magnetize and its magnetic susceptibility is inversely proportional to the difference between the steel's actual temperature and its Curie temperature. The steel also exhibits critical behavior at its Curie temperature -- which means that it changes abruptly from paramagnetic to ferromagnetic as it cools down past its Curie point. 24.23.196.85 (talk) 00:57, 11 December 2012 (UTC)

The drops will also be affected by the current induced by moving past a magnet, the effect would be to repel the drops. Dmcq (talk) 19:03, 11 December 2012 (UTC)

When toilets flush

What determines whether a toilet's flush will be more... forceful? Stronger? Basically, what makes it so that some toilets barely trickle the water and waste out while others make you think that the whole of reality will be sucked down the pipes? Is it a difference in altitude over where the sewer/septic system is? Or a combination of other factors? Dismas|^(talk) 11:58, 10 December 2012 (UTC)

It may depend on local water pressure in pipes and on toilet's construction, as well as on the amount of water in toilet cistern. Brandmeister^talk 14:39, 10 December 2012 (UTC)

Yes, the amount of water discharged from the cistern, the rate at which it is discharged, the height of the cistern above the toilet, and the dynamics of the flow, are all significant, but the pressure in the pipes is a factor only in the time it takes to refill the cistern. Dbfirs 16:24, 10 December 2012 (UTC)

Toilet#Water usage may be helpful. Duoduoduo (talk) 15:09, 10 December 2012 (UTC)

Height above the sewer line is not a factor, except in the rare cases where the sewer backs up all the way to the toilet. The size of the discharge hole in the bottom is also important, and any clog will reduce that. The infamous low flow toilets, which may require several flushes instead of one, are one cause of poor flushing. StuRat (talk) 18:30, 10 December 2012 (UTC)

Why is solid carbon at room temperature much denser than minus 300 degree oxygen solid?

Carbon atoms are lighter and larger. 96.246.63.155 (talk) 13:42, 10 December 2012 (UTC)

What form of solid carbon do you mean ? Graphite, diamond, carbon nanotubes ? StuRat (talk) 18:27, 10 December 2012 (UTC)

Only answer I can come up with without actually doing the work of researching it: carbon forms four bonds, allowing for packed crystal lattices, while oxygen almost exclusively forms O₂ molecules, which do not pack well at all. i kan reed (talk) 21:59, 10 December 2012 (UTC)

But the OP asked about it at "minus 300 degree oygen solid", which does not make any sense temperature wise or in the english language, but presumably is meant to mean "at 300 K below room temperature, where oxygen is solid". Which it will be. Oxygen is not O₂ molecules when solid, it is a continuous crystal structure. The OP is trying to compare room temperature carbon (a solid) to near zero K oxygen, which is a crystaline solid. Darned if I know why. Perhaps he meant the diamond form but forgot to say so. The OP needs to clarify what he wants. Wickwack 120.145.0.81 (talk) 00:39, 11 December 2012 (UTC)

He probably means -300°C. Yes, absolute zero is at −273.15°C, but they were just rounding imprecisely. StuRat (talk) 00:51, 11 December 2012 (UTC)

(ec) That would be below absolute zero, so in the everyday sense, there is no such temperature. There is a sense in which such a temperature could exist (see negative temperature) but it's "hotter than infinite temperature", so it doesn't fit with solid O2.

I would guess instead that the intent is −300 degrees Fahrenheit, but then it's incorrect, as O2 does not solidify until you get down to −362 F, if I remember correctly what I just looked up. --Trovatore (talk) 00:57, 11 December 2012 (UTC)

Solid oxygen is a crystal lattice of O₂ molecules. "Molecular" and "lattice" are not mutually exclusive terms. It's simply bound O₂ molecules connected in a lattice by van der Waals forces.[5] Someguy1221 (talk) 00:50, 11 December 2012 (UTC)

Only at very high pressures, I think. Wickwack 60.228.248.5 (talk) 01:56, 11 December 2012 (UTC)

No, it is true down to vacuum. At very high pressures, you can get O₈ molecules in a van der Waals lattice, but you never get a covalent lattice as with carbon. Someguy1221 (talk) 02:01, 11 December 2012 (UTC)

One would think people would take the time to make sure their questions make sense, that way we could spend our time debating the best answer instead of debating the meaning of the question. Just saying it... Dauto (talk) 15:46, 11 December 2012 (UTC)

No, that's ok. We should recognise that not everybody has english as their first or even second language. What annoys me is that, like in this case, when the OP is asked to clarify what he wants, he doesn't post again - that tells me we've all wasted our time - the OP has not come back to read what's posted. Wickwack 120.145.197.96 (talk) 00:51, 12 December 2012 (UTC)

I don't think English as a second language was the problem. The English is OK. The problem is that the question doesn't make sense. Dauto (talk) 04:23, 12 December 2012 (UTC)

AIDS

I just got done watching a documentary about AIDS in Africa, and it got me thinking, do black people have some genetic predisposition towards getting HIV? Their continent has AIDS as an epidemic and while some people may blame lack of education, There are many other poor, uneducated areas of the world where HIV is not epidemic, although it is still high, such as South America, and the more rural areas of South East Asia.--Wrk678 (talk) 13:59, 10 December 2012 (UTC)

AIDS is only an epidemic in southern Africa. I don't know are they too poor to afford (enough) condoms? Then that's the reason. You can't really end humping now can you? Sagittarian Milky Way (talk) 14:20, 10 December 2012 (UTC)

HIV originated in Africa, as such this continent still takes the brunt of the epidemic. Brandmeister^talk 14:33, 10 December 2012 (UTC)

Didn't it spread worldwide really quickly the first time a world traveler got it though? I believe Congo is the source but that isn't the place the hardest hit. Maybe places like Botswana with the ridiculous amount of AIDS are poor even by third world standards. It's hard to get poorer than sub-Saharan Africa (South Africa and a few others like maybe the Ghana with the hydroelectricity excepted). Sagittarian Milky Way (talk) 15:17, 10 December 2012 (UTC)

Actually Botswana is one of the wealthiest countries in Africa on a per capita basis, however with a high Gini coefficient the wealth distribution is very skewed. South Africa has the highest Gini coefficient in the whole world. Roger (talk) 15:32, 10 December 2012 (UTC)

Come on, people, we keep a copy of the world's largest free encyclopedia right behind the Ref Desk. Use it!

• Epidemiology of HIV/AIDS#Sub-Saharan Africa
• HIV/AIDS in Africa

Getting back to the original poster's question, it is true that some populations have a greater innate resistance to HIV infection. Carriers of one copy of the CCR5-Δ32 mutant form of the CCR5 gene have some resistance to HIV infection; individuals with two copies of the CCR5-Δ32 mutation are strongly resistant to HIV. It is estimated that roughly 10% of northern Europeans carry at least one copy of CCR5-Δ32, and perhaps 1% have two copies. CCR5-Δ32 is essentially unheard-of anywhere else in the world. By itself, however, this improved resistance in a small fraction of the population has a negligible effect on HIV infection rates in Europe (or elsewhere) versus those in Africa; the social, political, and economic factors contributing to the high levels of HIV infection and AIDS in sub-Saharan Africa are far more important. TenOfAllTrades(talk) 15:46, 10 December 2012 (UTC)

Right, ignore anything I said, those articles are very good. Basically, it's complicated. Wow, that is one crappy place to live. Sagittarian Milky Way (talk) 15:53, 10 December 2012 (UTC)

No small part of the African AIDS epidemic has been due to religion. The Catholic Church has consistently made empirically false claims about the effectiveness of condoms, and generally opposed contraception at every step. Since contraception is by far cheaper than education or treatment, this has greatly hindered attempts to tackle the epidemic. See Catholic Church and AIDS.

Also, I challenge the OP's comparison between sub-Saharan Africa and South America or Southeast Asia. Look at the 2011 UN Human Development Index. Almost every country in South America has a decent quality of life; Chile and Argentina have a Western-level HDI. Southeast Asia is indeed poor, but almost all of it has a "medium" HDI, whereas almost all of sub-Saharan Africa is "low". There's just no comparison between the poverty and loss of social order in this part of Africa and that in any other part of the world. There's a reason that most charity TV ads you see are about Africa rather than Haiti, China, the Philippines, or Papua New Guinea--because it really is much worse. --140.180.249.194 (talk) 18:19, 10 December 2012 (UTC)

I have to agree with IP 140. You'd be surprised how many negroes Benedict has had buttsex with. (Whoops, no refs? Who cares! They are Catholics!) μηδείς (talk) 21:41, 10 December 2012 (UTC)

Was that supposed to be a sourced and helpful contribution, or are you just PMSing like you always do? --140.180.249.194 (talk) 22:09, 10 December 2012 (UTC)

Medeis, you would do well to read John Scalzi's brief commentary on The failure mode of clever.... TenOfAllTrades(talk) 03:00, 11 December 2012 (UTC)

Nice one Ten --Lgriot (talk) 08:25, 11 December 2012 (UTC)

John Scalzi is very wise... --Jayron32 13:02, 11 December 2012 (UTC)

The factors involving the HIV epidemics in Africa are complicated and, frankly, not yet fully understood even by experts. There are many things going on there, and any single-variable, pat answer is going to be inadequate. (I don't claim to be an expert on this, but I've been surprised as at how much question there still is on some of the basic questions, like to what degree needles versus sexual activity are responsible for the cases.) That being said, I don't think anybody who has studied the issue thinks that genetic predisposition has anything significant to do with the rate of exposure there. "Dire poverty" is obviously the context for the answer(s) but it's not the answer itself. --Mr.98 (talk) 02:38, 11 December 2012 (UTC)

Dilated eyes

Last time I had my dilated eye exam I drove home after dark and all bright lights had a starburst effect around them. What causes the starburst? (I thought maybe it had to do with the pupil not being a perfect circle but I don't know if that would explain it.) RJFJR (talk) 17:15, 10 December 2012 (UTC)

Star-bursts or halos? Have you had any laser work done? Do you have astigmatism – if so at which angles (for both peepers)?--Aspro (talk) 17:50, 10 December 2012 (UTC)

Was it in your eyes or in the windshield - moisture, soap residue, construction of the glass... 88.112.41.6 (talk) 18:19, 10 December 2012 (UTC)

'star-bursts' (rays around bright lights). I didn't think it was the windshield but I suppose it could have been the windshield and I noticed the effect much more due to the dilated. RJFJR (talk) 22:31, 10 December 2012 (UTC)

I too have noticed the star burst effect after dilated eye exams, bad enough to make using a PC difficult, but I'm sure it didn't happen when I was young. Perhaps it is due to imperfections in the cornea and/or lens, and isn't noticed normally because the aperture is small enough to avoid most of the imperfections. Wickwack 120.145.0.81 (talk) 00:48, 11 December 2012 (UTC)

This is unscientific, but I suspect it has more to do with the fact that your iris dilator muscle as well as your ciliary muscle both are affected by the norepinephrine in the drops they give you, and that makes it more difficult to focus, leading to that effect. However, that's mostly just an educated guess. I did find one medical text that referred to halos after certain eye surgeries apparently due to an optical phenomenon with larger pupils, which may be of some interest, but I don't have the technical background to know if that answers your question. ISBN 0865777594, page 358. Shadowjams (talk) 17:17, 11 December 2012 (UTC)

Let's be clear here that we're not able to give advice about anything medical, and besides, the eyes were just diagnosed. But a factors such as corneal neovascularization from contact lens use, or any other kind of opacity/haze anywhere in the anterior part of the eye, could lead to less perfectly clear areas near the edge of the cornea having an effect when the iris is kept fully open. Wnt (talk) 03:27, 12 December 2012 (UTC)

I can't see how it could be due to lack of focus - this is about a starburst effect, not bluring. In any case, my main eye defect is a complete loss of the ability to focus, combined with abnormally long eyeballs - the combined effect is that instead of my natural relaxed focus being to infinite distance like a normal person, combined with the ability to focus thru eyes muscle effort down to 200 mm or so, my eyes are permanently stuck on being focussed to 350 mm - which is just fine for using a PC or reading a book. I notice the starbursts on things in focus, not things out of focus. Wickwack 124.178.149.151 (talk) 07:26, 12 December 2012 (UTC)

Spherical aberration occurs due to light passing through the peripheral portion of the crystalline lens. [6] Location (talk) 06:12, 13 December 2012 (UTC)

So? What has this to do with eyes? Spherical aberation arises with manmade lenses because it is easy to accurately grind a spherical surface, and hard (meaning expensive) to grind an optically correct surface. This does not apply to the eye. In any case spherical aberation causes blurring, not starburst effect. Wickwack 121.221.33.51 (talk) 03:10, 15 December 2012 (UTC)

You don't know what you're talking about. The reference I supplied confirms that spherical aberration occurs in dilated eyes exactly as I explained above, and your understanding that it manifests only as blur is incorrect. Starburst, glare, and halos can occur on things otherwise "in focus" because most of the light (i.e. that which is passing through the crystalline lens closest to the optical axis) is indeed focused on the retina. Location (talk) 05:43, 15 December 2012 (UTC)

Spontaneous generation vs. abiogenesis

What is the difference between spontaneous generation and abiogenesis? I think spontaneous generation can be summed up by "maggots come from flesh", where as abiogenesis can be summed up by "first population of cells comes from a population of organic molecules in the primordial soup in the early earth. It seems to me that both are trying to suggest that life comes from non-life. 75.185.79.52 (talk) 19:27, 10 December 2012 (UTC)

Convenience links: Spontaneous generation, Abiogenesis. hydnjo (talk) 21:27, 10 December 2012 (UTC)

Yes, both of them are life coming from non-life, though the two ideas are very different they do have that fact in common. Dauto (talk) 20:34, 10 December 2012 (UTC)

The difference is that one says it happens all the time, and the other that it's an extremely rare event that only occurs once over billions of years and, perhaps, billions of planets, or even an infinite number of universes. Also, spontaneous generation is supposed to produce far more complex organisms, initially. StuRat (talk) 20:37, 10 December 2012 (UTC)

The (long-ago-dismissed) idea of spontaneous generation really applied to large organisms. If you left a bunch of cheese lying around the house, soon afterwards you have an infestation of mice...so mice are made from mouldy cheese(!)...that kind of thing. It was a stupid idea that was widely dismissed pretty much as soon as it had been suggested. We knew how mice reproduce(!) and cheese isn't involved.

Abiogenesis is a much more subtle idea - which is by far the most widely accepted scientific explanation for the beginning of life. It suggests that life arose as just one tiny step - from molecules that cannot not make copies of themselves to molecules that can - and once a single self-reproducing molecule had formed and copied itself, evolution would kick in and everything else would follow from that. But abiogenesis isn't about large scale organisms...it talks about things like individual RNA molecules. You wouldn't exactly say that an RNA molecule was "alive" but the steps from that to the most primitive bacterial cell are never especially large ones. Evolution drives those steps once a basic self-reproducing molecule had come into being more or less by chance. The threshold at which we'd consider something to be "alive" is a fuzzy one - not everyone agrees on a single definition. So the point at which "non-life" turns into "life" becomes a matter of semantics rather than science. I would define abiogenesis as that point where the primordial soup became susceptible to evolution. It's a cleaner definition than "non-life" to "life". SteveBaker (talk) 20:07, 11 December 2012 (UTC)

I agree with everything except your first statements. Spontaneous generation wasn't a "stupid idea" that "was widely dismissed pretty much as soon as it had been suggested." It persisted well into the 19th century and existed for centuries prior to that. It was eminently empirical — maggots and tiny flies do seem to come pretty much out of nowhere if you aren't controlling for enough variables. It seems "stupid" to us today because it is totally incompatible with our thinking on what life is and how it works, but it fits very much within the Romantic manner of thinking about life of the early 19th century, much less earlier periods. --Mr.98 (talk) 00:03, 12 December 2012 (UTC)

Transportation gunpowder ingredients world war I era

Research for historical novel. Need to know how munitions raw materials such as camphor, pyrite and saltpeter were packaged for bulk transportation in 1914. I've tried many web searches to find information from this period, with no success so far. 98.125.189.95 (talk) 19:40, 10 December 2012 (UTC)

By the time of WWI, gunpowder (often referred to as "black powder") was rather obsolete as an explosive. Modern high explosives, mostly TNT, were in use for the bursting charges of artillery shells, aircraft bombs and those huge mines that they set off in tunnels under the enemy trenches. Low explosives, such as cordite, were used as propellants, to fire shells and bullets out of guns and mortars. I believe that gunpowder was still in use for artillery fuzes. There is some information about British munition plants in Filling Factories in the United Kingdom which says that "The Filling Factory's raw materials, such as TNT, RDX, or propellants, such as cordite, were manufactured in National Explosives Factories (World War I) or Explosive ROFs (World War II) and transported, by railway trains, to the Filling Factories for filling into munitions, produced at other plants." Not much to go on, but it might give you some useful search terms. Alansplodge (talk) 22:04, 10 December 2012 (UTC)

I wonder whether you'd get some useful information by reading about some of the failures of such bulk storage. The resulting explosions were large and prominent events - so lots has been written about them - and I'd imagine that you'd find information about storage and transportation in those accounts. Check out List_of_the_largest_artificial_non-nuclear_explosions#World_War_I_era and start following the references. SteveBaker (talk) 20:35, 11 December 2012 (UTC)

Gays and noses

Women have more sensitive noses, they can smell more things then men. (so I heard).

If its true, does gays (men) have a similar ability? does they have a better noses then straight men?

Maybe some scientist already did experiments about it? Yes, this sounds like a really dumb question to investigate, but I'm sure I'm not the first one in the world who think about it :)

UPD: Sorry if my question sounds arrogant or insulting, its because bad wording (I'm not a native English speaker). Also, you can make fun from my bad English (if you think its funny) --Ewigekrieg (talk) 21:03, 10 December 2012 (UTC)

You might be the second. I also did no know that gays are all men or that there were none left. I guess you learn something new...165.212.189.187 (talk) 21:08, 10 December 2012 (UTC)

No offence. I didn't say gays are women or something. One of my friends is a gay and he is a definitely a man (and a good guy) --Ewigekrieg (talk) 21:16, 10 December 2012 (UTC)

The issue is that some gay people are women, gay refers to a person of either sex. You were also using the passed tense: "did gays have a similar ability" which implies that homosexuals have vanished. Obviously you didn't mean any of this and intended to refer to gay men in the present tense, but this is a reference desk on the internet so a degree of pedantry and perhaps snark is to be expected. --Daniel(talk) 21:25, 10 December 2012 (UTC)

Speaking of which, if you're going to correct others, you have to be squeakily correct yourself. The term is past tense, not "passed tense". Also, he made it clear he was asking about male gays; he wasn't saying that all gays are male. -- Jack of Oz ^[Talk] 11:49, 11 December 2012 (UTC)

There's a reference desk guideline that would seemingly frown on a snarky response to an obvious verb conjugation mistake in a non-native English speaker's question. Red Act (talk) 04:13, 11 December 2012 (UTC)

He added the "(men)" after, Jack. And The question came across extremely ignorant and snarky in its own right, regardless of improper verb conjugation. is there a ref desk guideline for that, Red?165.212.189.187 (talk) 13:49, 11 December 2012 (UTC)

Whether 'gay' includes men and women or just men is a matter of contention (I am not sure by whom) which leads to the rather ponderous LGBTVXYZ terminology. I occasionally typeset essays discussing the matter. I can't remember a word anyone said. μηδείς (talk) 02:18, 12 December 2012 (UTC)

Gay men do have a greater olfactory sensitivity to some pheromones than do straight men[7], and the activation of neural circuitry in response to pheromones is different than in straight men; see Neuroscience and sexual orientation#Response to pheromones. But I'm having a harder time finding information about olfactory sensitivity in gay men in general. Red Act (talk) 21:45, 10 December 2012 (UTC)

As a bisexual I can tell you that I have seemed to have a much higher sensitivity to the sexual smells of both men and women, in comparison even to heterosexuals for the smell of the opposite sex. That's OR, of course; not that there's anything wrong with that. μηδείς (talk) 00:22, 13 December 2012 (UTC)

"Gays" do not form a well-defined biological group. But I smell great. μηδείς (talk) 21:38, 10 December 2012 (UTC)

You seem to smell like anyone else on the internet Medeis. OsmanRF34 (talk) 22:17, 10 December 2012 (UTC)

And next time you tickle my chocha with your nariz, I'll admit that fact, Os. μηδείς (talk) 22:33, 10 December 2012 (UTC)

The olfactory has given way to the information age. Bus stop (talk) 11:59, 11 December 2012 (UTC)

Some of us can read Portuguese. Dauto (talk) 15:39, 11 December 2012 (UTC)

And most everybody else can read inuendoese.165.212.189.187 (talk) 19:45, 11 December 2012 (UTC)

In you end, oh! --Jayron32 00:57, 12 December 2012 (UTC)

It could be that a nosegay is needed. Bus stop (talk) 13:49, 12 December 2012 (UTC)

If this meme gets legs any longer it'll be on the next episode of The Simpsons. μηδείς (talk) 00:18, 13 December 2012 (UTC)

It's innuendo, not inuendoese. Now what's wrong with being an Inuit already? - ¡Ouch! (^{hurt me} / _{more pain}) 09:54, 13 December 2012 (UTC)

Maybe the OP is confused by the term Nosegay. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:41, 13 December 2012 (UTC)

"Gays" ("gay people" being the more polite term) are defined as a group by identifying as gay, in much the same way as, say, women or French people or Christians are. Biology and sexual orientation discusses some of what is known about the connections between biology and sexual orientation, and there is evidence of correlations between aspects of physiology and sexuality, so what the OP is suggesting doesn't seem impossible. Our article olfaction says "In women, the sense of olfaction is strongest around the time of ovulation, significantly stronger than during other phases of the menstrual cycle and also stronger than the sense in males". It doesn't say anything about sexuality. 130.88.99.231 (talk) 15:46, 13 December 2012 (UTC)

Leaving the Solar System

Let's say I build a spaceship to travel to the stars. To accelerate the ship to the highest possible velocity, I aim it at multiple planets and make use of gravity assist. Assuming I don't really care in which direction my ship leaves the Solar System, what is the maximum velocity I can achieve? Can I also use the sun as a slingshot? Hemoroid Agastordoff (talk) 21:47, 10 December 2012 (UTC)

I think the question leaves way too many open variables to even hazard a guess. What is power source, your fuel supply, starting position(earth surface, leo, the moon), the frame of reference from which you are comparing your velocity? With "near future" sci-fi like p-b11 fusion ion drives, starting in L3, using the SUN, and unlimited resources to design your rocket, you'd get multiple orders of magnitude more momentum than a fairly typical liquid-solid multi-stage rocket launched from cape Canaveral. To make it out of the solar system, you'd need a (sun's frame of reference) velocity of 10 km/s. We've only ever launched two rockets with the intent of passing the edge of the solar system: Voyager probes 1 & 2. Voyager 1's current relative velocity to the Sun is 17,043 m/s. Voyager 2's is closer to 40 km/s. Sort of answer your question? i kan reed (talk) 22:09, 10 December 2012 (UTC)

Voyager 2 is 15, 16 km/s or something. Pioneer 10 and 11 have messages to aliens (sounds intentional to me) and New Horizons is also leaving. Sagittarian Milky Way (talk) 22:32, 10 December 2012 (UTC)

I think the total speed you could reach is limited only by the drag experienced by encountering particles in the solar system (if this limit didn't exist, you'd eventually run into the speed of light limit). You could use the Sun, too, but the solar wind would decrease your speed as you approached (and then increase your speed as you leave, but to a lesser degree, since you are going faster then, thus exposed to it for less time, and also because your velocity relative to the solar wind is less, then). StuRat (talk) 22:18, 10 December 2012 (UTC)

You should get it all taken back though, and would require a bunch of time too (multiple inner planet assists, or maybe going all the way out to Jupiter just to get close to the Sun). Well you do go faster for awhile, don't know if it's quicker to just start outwards in the first place. Unless you have a reallly long timeframe and are talking about altering the probe's galactic orbit. Sagittarian Milky Way (talk) 22:32, 10 December 2012 (UTC)

See gravity assist, unpowered assists only add (non-transient) speed because of the planet's motion. Sagittarian Milky Way (talk) 02:45, 11 December 2012 (UTC)

Our article says, with each pass, the initial velocity V (relative to the sun) can be increased to V + twice the planet's velocity (relative to the Sun). However, if we're talking about speeds relative to the galaxy, then V (relative to the galaxy) can be increased to V plus twice the Sun's velocity (relative to the galaxy). StuRat (talk) 02:53, 11 December 2012 (UTC)

The sun cannot be used as an assist because it is the dominating body. However, its gravity can prove useful to approach a planet which can be used.

Once you get past the escape velocity of the solar system, you are not coming back, so then, you would not make many other passes. There can be slight exceptions if Mercury pushes you above the limit, and you happen to pass Jupiter on the way out, but that approach comes with its own limits. One, it's not possible to get back to planets "behind" you (Mercury in that example) once ypou're well beyond the planetary (Jupiter's) escape velocity, because you won't be close enough for long enough time to make the turn. At least not turns like the "simplified" one shown in the Gravity assist article.

Basically, gravity assist is a great method if you're limited to chemical propellants and/or low thrust ratings, because the kick you get is virtually "free", compared to the cost of more delta v. Once you have a continuous-beam plasma thruster with a cheap power source, you can just "floor it" without caring too much about assists.

Things would change again if you had a binary Black Hole to work with; these do crazy things to mass, light, and spacetime itself. You could go from near-zero to 42% c in one pass (or so I've read). - ¡Ouch! (^{hurt me} / _{more pain}) 11:38, 11 December 2012 (UTC)

Ouch: don't take everything you read about physics from Stanislaw Lem at face value. That use of a black hole is a literary device to make the story more interesting. – b_jonas 19:00, 11 December 2012 (UTC)

I've read it in a magazine, not in Fiasco, nor The Forever War or Neutron Star. It was non-fiction and scientific in tone, and although I can't give the ref (it was in the 2nd millennium), it did mention the 42% c.

On top of that, I'd doubt that one Black Hole can do the trick. Unless it's moving fast or rotating near the theoretical limit. The Penrose process could be useful, tho. It should rival annihilation in terms of delta v, with a rotating Hole that's known to exist. - ¡Ouch! (^{hurt me} / _{more pain}) 09:56, 13 December 2012 (UTC)

December 11

Medical degrees

Is it possible to do MS (surgery) or MD without MBBS? With MCAT score and without MBBS is it possible to do MD or MS (surgery)? — Preceding unsigned comment added by 199.224.149.10 (talk) 08:21, 11 December 2012 (UTC)

Is a masters in pediatrics course without MBBS considered a specialization in that field? after completing masters in diagnostics radiology without MBBS, is it possible to be considered as a professional radiologist? — Preceding unsigned comment added by 199.224.149.10 (talk) 08:22, 11 December 2012 (UTC)

In which country or countries? --Dweller (talk) 11:37, 11 December 2012 (UTC)

The OP's IP geolocates to Hyderabad, in case that helps. Marnanel (talk) 13:52, 11 December 2012 (UTC)

Rocks

How this type of rock (on the foreground) is called? Thanks.--93.174.25.12 (talk) 18:41, 11 December 2012 (UTC)

I think that's just a series of sedimentary layers that are very radically tilted. Looie496 (talk) 19:19, 11 December 2012 (UTC)

It bears some resemblance to Devils Tower. Bus stop (talk) 19:28, 11 December 2012 (UTC)

The Devil's Tower is an example of columnar jointing in an igneous rock, but Looie496 is right, these are layers of sedimentary rock tilted to nearly vertical. They look like alternating thin layers of sandstone and shale, with the sandstone layers possibly being turbidites, deposited from turbidity currents, as part of a flysch sequence. Mikenorton (talk) 21:20, 11 December 2012 (UTC)

Flow rate

I should be able to find the formula for this...but I can't seem to find the right one...argh!

I have a small vessel that's pressurized to around 20psi with nitrogen gas from a large cylinder with a regulator valve. The gas is flowing out to atmosphere through a 5mm diameter circular hole. Everything is at room temperature. I'm trying to find out roughly how long an 80 cu.ft cylinder will be able to maintain that pressure before I run out of gas.

Thanks in advance. SteveBaker (talk) 18:59, 11 December 2012 (UTC)

This can be solved approximately by a multi step process:-

1. Assume the flow out the orifice will be turbulent

2. Use standard fluid dymanics tables to convert the orifice to an equivalent pipe or 5 mm diameter. If the hole has abrupt edges (no chamfering) the equivalent length is roughly 10 x diameter

3. Add a length equal to the thickness of the material the hole is in

4. Add an equivalent length to represent the abrupt interface on the inside of the pressurised vessel

5. Apply the Fanning-Darcy equation to the total equivalent pipe length.

6. With the flow rate calculated in step 5, calculate the Reynolds Number

7. Use the Reyolds Number to verify that the flow is indeed turbulent.

If the flow is not turbulent, do Step 5 again using teh laminar flow version of the Fanning Darcy equation.

Fanning Dracy for turbulent flow is F = 0.718 Π [ ΔP/L x D¹⁹/(μρ³) ]^1/7

where F is flow rate m³/s; ΔP is pressure drop; L is equiv pipe length, m; D is pipe diameter, m; μ is viscosity of air, mPa.s; ρ is density of air, kg/m³.

Ratbone 124.178.135.56 (talk) 02:00, 12 December 2012 (UTC)

Depending on what assumptions you're making, this problem can more easily be solved by one of the Bernoulli equations. I would try the one for adiabatic compressible flow even though the adiabatic assumption may not jive with your request of Everything being at room temperature. Dauto (talk) 04:09, 12 December 2012 (UTC)

Neither of the above seems to notice that you have asked for the impossible, as soon as you let some gas out the pressure will drop below 20 psi and according to your question that's the end of that. Flow through orifices is well known at an engineering level, I can't say that Bernouilli or t'other stuff would actually even enter into my approach, once you have decided what you want. Incidentally is the tank insulated? (clue). Incidentally you are aprroaching and probably over the pressure ratio for Mach choked flow (second clue). Greglocock (talk) 23:42, 12 December 2012 (UTC)

Not correct. While a 5 mm orifice is quite significant, providing the pressurised chamber is large enough so that the percentage of gas released in the time frame of interest is low, a steady state pressure can be assumed. And if the throttling between the gas cylinder and the chamber is such that the gas cylinder can replace the gas let out of the chamber, steady state is maintained in the chamber until the cylinder drops to 20 psig. There must be a regulator between the cylinder and the chamber, in order to set the pressure to 20 psig. The OP didn't specify the time required to drain the cylinder - that's what he wants to calculate. Ratbone 124.178.41.96 (talk) 23:58, 12 December 2012 (UTC)

Sorry, yes you are right. oh well, he needs to specify the amount of gas in the supply tank as well, obviously. http://lss.fnal.gov/archive/d0-en/fermilab-d0-en-173.pdf is relevant. Greglocock (talk) 00:25, 13 December 2012 (UTC)

He did - it's an 80 cu ft cylinder. Ratbone 121.215.68.145 (talk) 01:31, 13 December 2012 (UTC)

how much power does humanity consume with respect to the amount of solar power it receives?

I read from Dyson sphere that the Sun would provide only an order of a trillion times more energy than the power consumption of humanity. This makes humanity's power consumption seem quite large, as I would have expected it to be on the order of 10^15 or more. This means that humanity doesn't seem to have a lot of space to expand even within the solar system, energy-wise. 71.207.151.227 (talk) 23:02, 11 December 2012 (UTC)

Incoming solar power is 174PW [8]. World average power use is 15TW [9]. 15TW/174PW = 0.0086%. Sun's total output is 380YW[10], which is 2.5*10^13 times mankind's current energy usage. I doubt anyone can even make educated guesses on what the energy consumption of a civilization capable of building a dyson sphere would be like. Dncsky (talk) 23:35, 11 December 2012 (UTC)

We can't of course use all the solar power the Earth recieves. We need to leave much land and sea clear. A more practical view is this: The peak insolation at the Earth's surface is about 1 kW/m². over the 24 hour cyle it is approximately a half sine curve, integrating and allowing for weather and conversion efficiency (PV panels about 20%, other metthods about the same), you can generally extract an average of about 100 W or so. Taking the average roof plan area of a house as 400 m², Solar power is good for about 4kW, barely enough for an advanced western lifestyle. And it is far far too expensive. Floda 120.145.197.96 (talk) 01:30, 12 December 2012 (UTC)

Astronaut Lifestyle

Are (male) astronauts allowed to masturbate while in zero gravity? If not, due to, well, basically the mess it could create, would the prohibition have an impact upon their mental health? 86.13.97.144 (talk) 23:54, 11 December 2012 (UTC)

One of the Apollo 12 astronauts did that very act, and was gently critisized for it by the flight surgeon for using up too much oxygen, but not seriously reprimanded. See the Flight Journal at 092:07:53. Tevildo (talk) 00:47, 12 December 2012 (UTC)

It should be noted that they were provided (as a bit of a joke) material for that exact purpose, as noted in the Apollo 12 article you linked. --Jayron32 00:55, 12 December 2012 (UTC)

Indeed. :) And, incidentally, when it comes to creating a mess, going to the lavatory in zero gravity is far more of a problem, and something that no amount of self-control can prevent. Apollo 8 had particular issues in this area. Tevildo (talk) 00:58, 12 December 2012 (UTC)

At the risk of feeding a troll OP, I think the transcipt has been misinterpreted. While the bit about eels is clearly a reference to masturbation, it is a joke reference. It is extremely unlikely that Pete Conrad would have, he was 39 and had been married since 1953; Richard Gordon was 40; Alan Bean 38 and married. At that age they were well and truely past the the teenage urge stage, and even if not married, were quite unlikely to be virgins. From personal experience, I know that when I had my first girl it was so far and away better than any tug, there was thereupon absolutely no interest in tugging ever again. Floda 120.145.197.96 (talk) 01:20, 12 December 2012 (UTC)

Happily married men don't masturbate?. --Jayron32 01:22, 12 December 2012 (UTC)

I can't speak for you, Jayron. However, from personal experience, normal men who have sexual access to a female, whether maried or not, happy or not, have something so superior to tugging, its like eating cheap hamburgers with bad meat, only more so, - if that's all you have, those hamburgers taste fine, but if you get regular perfectly cooked meals made from fresh ingredients, you won't ever bother with those smelly burgers. And folk in their middle ages, as the astronauts were, don't have the urges of teenagers. Floda 120.145.197.96 (talk) 01:38, 12 December 2012 (UTC)

I think what you mean to say there is that you stopped masturbating. It is important to remember not to generalize from singular experiences. --Jayron32 04:04, 13 December 2012 (UTC)

I'm glad you said "singular" and not "one-off". I wonder if NASA had any contingency plans if the Apollo capsule were involved in a high-jacking. DMacks (talk) 04:39, 13 December 2012 (UTC)

Approximately 70% of married people masturbate at least occasionally.[11] The reference I cited doesn't say so, but my presumption is that the percentage for married men alone would be higher than the 70%, since more men than women masturbate in general (92% vs. 62% according to our article). Red Act (talk) 02:10, 12 December 2012 (UTC)

In a study cited by the Kinsey Institute web site[12], 85% of men who were living with a sexual partner reported masturbating within the past year. Red Act (talk) 02:19, 12 December 2012 (UTC)

This is the first time I've ever heard it called feeding the troll. μηδείς (talk) 02:13, 12 December 2012 (UTC)

"Feeding the troll" means posting in response to a post made by a troll - that is, someone who posts a question to see what we all do about it, rather than because they need an answer. Ref Desk is unfortunately infested with trolls. The OP question ij this case could be a troll question. Floda 120.145.163.32 (talk) 02:24, 12 December 2012 (UTC)

The concept even has its own semi-nifty illustration, which you can see in Wikipedia:Deny recognition. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:25, 12 December 2012 (UTC)

Am I the only one who took Medeis' (Medeis's?) comment as a joke? Evanh2008 ^{(talk|contribs)} 04:30, 12 December 2012 (UTC)

Oops, you're very likely right. I'm slow (as is the IP just below, perhaps). But I still insist that the illustration is semi-nifty. I would call it flat-out nifty except it took me about a year to figure out what was going on in that illustration. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:13, 12 December 2012 (UTC)

Like always, Ref desk volunteers are not open-minded enough to assume good faith, and denounce every question which they themselves aren't mature enough to legitimately ask as "trolling". --140.180.249.194 (talk) 06:46, 12 December 2012 (UTC)

This is not actually a troll question - it demonstrates the conflict between astronauts as an exercise in public symbolism and conventional morality versus the scientific question of whether free-fall has any effect on this process. I would be prone to think that the sensation of constant falling might have some far-reaching instinctive effects (actually, it amazes me that astronauts can adjust to the point of being able to sleep) but I don't know. Looking up briefly, I don't know if anyone has actually gotten mice to breed in space for example [13] - actually, the things they are described in breeding in that article are all things that can be done more or less "in vitro" with sperm and eggs. Until I see actual evidence that an astronaut can ejaculate in free fall I don't know it will happen. Wnt (talk) 03:43, 12 December 2012 (UTC)

I'm bemused by this whole conversation... particularly the notion that anyone over 20 and married ceases to masturbate, especially when at least part of that notion's based on the fact that they have wives... which is of course very relevant when one is in outer space for weeks on end. Shadowjams (talk) 03:53, 12 December 2012 (UTC)

A related question is someone is certain to brag about being the first to be conceived in space, and someone is going to be able to brag about being the first to be born in space. Both a certainty. Apteva (talk) 04:22, 12 December 2012 (UTC)

Apollo astronauts were not in space for weeks on end - they were only in space for a few days. The reference to eels in the transcript came at 3.8 days into the flight and refered to an oxygen anomaly that happened some hours before. Not that the flight time would matter much. Floda 121.215.48.204 (talk) 07:08, 12 December 2012 (UTC)

I guess it is a good thing I am not an astronaut cause it appears I am not normal! lol I am 50, have been happily married for many years, have an amazing sex life yet still manage to masturbate at least once ot twice a week! 99.250.103.117 (talk) 04:29, 12 December 2012 (UTC)

Indeed. It seems that men who never masturbate, or claim never to do so, regardless of marital status or ready access to sexual partners, are the ones who are way outside what is statistically "normal". But I rather think that Floda didn't mean "normal" in that sense. -- Jack of Oz ^[Talk] 21:48, 12 December 2012 (UTC)

My buddy used to tell me about the times he would date "Rosy Palm and her Five Sisters". Seriously, the Apollo Command Modules were not much bigger than your typical subcompact car on the inside; with two crewmates sharing the space with you, getting a little time alone was impossible. Hemoroid Agastordoff (talk) 17:30, 12 December 2012 (UTC)

Nowadays, probably few boys graduate from high school still a virgin, but back in the 1960's (in my country at any rate) that was not the case. Back then, drinking alchohol was illegal until you were 21, illicit sex was a lot less culturally acceptable, and folk left high school at 16 instead of 18 now.

When young 16 year olds started employment back then, the old guys at work would often try a few tricks and pranks to put the younguns in their place, or to try them out. A not uncommon initation workplace exchange was something like this:-

Old tradesman: "Are you a wanker?"

Young apprentice: "Of course not." - spoken with an indignant expression.

Old tradesman: "Are you married?"

Young apprentice: "No."

Old tradesman: "Do you live with a girl, then?"

Young apprentice: "No."

Old trademan: "Well, you must be a wanker!"

At that point, the young guy was usually red in the face and speechless. That pretty much sums the matter up. Floda 124.178.41.96 (talk) 00:34, 13 December 2012 (UTC)

That is a fantastic story, that I didn't actually read. And I think is long overdue to close up this retarded question. Shadowjams (talk) 03:56, 13 December 2012 (UTC)

Resolved

December 12

how did the discoverer of prussic acid / hydrogen cyanide not get like majorly killed or hurt

From hydrogen cyanide: "In 1752 the French chemist Pierre J. Macquer made the important step of showing the Prussian blue could be reduced to a salt of iron and a new acid, which could be used to reconstitute the dye. The new acid, hydrogen cyanide, first isolated from Prussian blue in pure form and characterized about 1783 by the Swedish chemist Carl Wilhelm Scheele, was eventually given the name Blausäure (literally "Blue acid") because of its derivation from Prussian blue, and in English became known popularly as Prussic acid."

Okay, so at the time the lethality wasn't noted? How do you isolate hydrogen cyanide without getting killed, if you wouldn't even have anticipated a gas? I mean, chemists regularly tasted their compounds (at the time) and it's not like they would conduct every experiment with gas masks. 137.54.1.116 (talk) 03:31, 12 December 2012 (UTC)

Perhaps other (earlier) discoverers did taste/breathe it? The implications are left as an exercise for the reader... -- Scray (talk) 04:39, 12 December 2012 (UTC)

Did their 18th century grad students get killed while they claimed the credit? 137.54.1.116 (talk) 04:42, 12 December 2012 (UTC)

You know, cyanide deserves its reputation for lethality, but that doesn't mean it's impossible to overestimate it. Our article says that around 300 ppm "will kill a human within about 10 minutes". Now, 300 ppm isn't a lot, but it's not the merest trace either. If you generate 10 mL of HCN gas in a test tube, and it spreads out over a cubic meter, that's only 10 ppm, if I've done my arithmetic right (please don't count on it!). Without more details on the experiment, it's hard to know whether Macquer was in danger. --Trovatore (talk) 9:22 pm, Today (UTC−8)

Presumably they were smart enough to only taste a tiny amount of anything new, and thus received a non-fatal dosage. StuRat (talk) 05:07, 12 December 2012 (UTC)

My understanding is that the effects occur very rapidly and are pretty obvious -- a person exposed to cyanide feels like he is suffocating. If the person recognizes that something bad is happening and gets out of there, his state won't get any worse -- he'll feel like he is suffocating for a while, and then gradually recover. So if it takes 10 minutes to get a fatal dose, a person is likely to realize that something is badly wrong long before that. Looie496 (talk) 07:34, 12 December 2012 (UTC)

It is possible to ingest small amounts of cyanide without being affected at the time, but the build up over a period of time would kill. (I remembered reading that Napoleon Bonaparte died in such a manner, and googled "cyanide death of Napoleon". The results tell me that he died of arsenic poisoning. Does arsenic equate cyanide, metabolise to cyanide, or have I missed something here?) --TammyMoet (talk) 10:31, 12 December 2012 (UTC)

No, cyanide and arsenic are unrelated.

I do not think that cyanide "builds up". The body has mechanisms for detoxifying small amounts of cyanide (it has to, because cyanide is a ubiquitous molecule). So it does not make sense to me that it would "build up". What may be true is that the continued presence of cyanide causes cumulative damage that is not repaired. See for example konzo. --Trovatore (talk) 10:53, 12 December 2012 (UTC)

I apologize if I've asked this before, but I don't recall. In The Princess Bride, the pirate builds up an immunity to the fictional poison "iocaine" over a five year period. Is it possible to build up an immunity to cyanide? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:09, 12 December 2012 (UTC)

Our article on mithridatism specifically says that this is not possible for cyanide. It does not give a citation for this, however. So I don't really know. But the konzo experience argues against trying it, unless you really really have to. --Trovatore (talk) 11:13, 12 December 2012 (UTC)

pKa of hydrogen

I'm trying to find the pKa of hydrogen as it is the conjugate acid of sodium hydride. However, I can't find a reliable source (searching for "pKa of hydrogen" infuriatingly reveals all sorts of irrelevant results, like the pKa of hydrogen sufide, hydrogen fluoride, basically every Bronsted acid). I want to add it to both the article for sodium hydride and this article. Can someone help me? Also, why is Google's search algorithm so terrible? 137.54.1.116 (talk) 03:45, 12 December 2012 (UTC)

I would suggest looking in here. It's the most comprehensive list of pKa that I'm aware of. Is it right to call hydrogen gas the conjugate acid of sodium hydride rather than the hydride ion itself? It's been a while since I took chemistry, but I feel like hydride ion is the conjugate acid. In water, this ion will subsequently react with water to form hydrogen gas an a hydroxide ion. Someguy1221 (talk) 04:10, 12 December 2012 (UTC)

Actually, I think the IP is right. The hydride ion is a Bronsted-Lowry base, being a highly good proton acceptor - hydrogen gas can be thought of as its protonated form, and thus its conjugate acid. All I know about the original question is that pKa is very very high - it's barely acidic at all.--Jasper Deng (talk) 05:22, 12 December 2012 (UTC)

I've seen values listed around 42 (no, seriously). But I've also seen in essence "it's not really a measurable value because there's not a useful solvent in which both MH and H₂ are sufficiently soluble" (need to measure the equilibrium). DMacks (talk) 19:52, 12 December 2012 (UTC)

That seems about right. I seem to remember that butyllithium reagents have conjugate pKa values somewhere in the 50s (i.e. the pKa of the alkyl hydrogen), which would seem to be about right for hydride to fall in the 40s. I think you can derive pK values thermodynamically (i.e. ΔG=-RTlnK), so it should be technically possible to get the values via Hess's law, i.e. from the thermodynamics of a series of equations rather than via direct equilibrium measurment, that is you can get the pKa value by looking at how it reacts with other substances rather than by direct equilibrium with its conjugate. --Jayron32 05:05, 13 December 2012 (UTC)

in what types of cells, except Haploid reproduction cells, does meiosis occur?

thanks. — Preceding unsigned comment added by 109.64.147.124 (talk) 06:21, 12 December 2012 (UTC)

None -- all other cells undergo mitosis. 24.23.196.85 (talk) 06:33, 12 December 2012 (UTC)

Well, to be a bit pedantic, it can occur in polyploid reproductive cells too. Looie496 (talk) 07:29, 12 December 2012 (UTC)

Not quite night terrors

What is it called when someone gets frightened by some imagined or dimly-seen object in the dark (as a one-time or occasional occurrence only), even though that person is not normally afraid of the dark? It's not the same as night terrors, because night terrors are when you're half-asleep and you start seeing scary things, and it's not nyctophobia, because that is when you're always afraid of the dark. So what is it? 24.23.196.85 (talk) 06:29, 12 December 2012 (UTC)

I would call it a standard response from a visually oriented creature to dealing with low-light conditions. Humans, like apes and most, but not all, other primates, are primarily diurnal animals which use their eyesight far more than, say, their hearing or sense of smell to interpret their environment. As such, we easily get freaked out by things in low light conditions. Your cat, for example, would never have that same response to a shadowy object. Matt Deres (talk) 15:22, 12 December 2012 (UTC)

Wasn't hypnogogia recently mentioned here? Having suffered both phenomena, I can assure you they are quite different, and night terrors much scarier to one's boy-or girl-friend or family or spouse or children. μηδείς (talk) 00:16, 13 December 2012 (UTC)

Thanks, Medeis and Matt! You see, I'm researching for several books all at the same time, and one of them will be about a young boy who suffers from multiple interrelated phobias -- and early on, although he is not normally afrais of the dark, he suffers from precisely this condition (a pattern of shadows in the darkened bedroom causing him to imagine things that freak him out), which gives his babysitter a good idea of precisely what he fears, and why (I don't want to give too much away, but while screaming he mentions "six-armed giants", which she guesses correctly are transmission towers). 24.23.196.85 (talk) 01:48, 13 December 2012 (UTC)

Question regarding the orbital period of the Earth around the Sun

In the article "List of gravitationally rounded objects of the solar system":

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

the orbital period of the earth is listed in the "Planets" table as 1.000174 years. Footnote [g] indicates that these are sidereal years, but the word "years" links to the article "Julian year (astronomy)":

http://en.wikipedia.org/wiki/Julian_year_%28astronomy%29

Which is correct? In either case, how is 1.000174 derived?

Thank you for your help 50.137.168.64 (talk) 08:59, 12 December 2012 (UTC)

I don't see any discrepancy here. The "sidereal" in the footnote means it's the sidereal period. The unit of said period is Julian years.Dncsky (talk) 10:30, 12 December 2012 (UTC)

In other words, 1 sidereal year = 1.000174 Julian years. The sidereal year is measured - as opposed to derived. Dauto (talk) 15:01, 12 December 2012 (UTC)

And the way it is measured is by taking precise measurement of many astronomical objects. The actual method is briefly explained at this webpage, Greenwich apparent sidereal time, provided by the United States Naval Observatory. The measurement depends on the very careful calculation of the equation of the equinoxes, and is something that astronomers spend a lot of effort to refine and work out the messy details. As our machinery gets better and more accurate, we have to compensate for more non-ideal observations - things like the non-perfect shape of the planet, and its orbit, and the change in actual and apparent positions of even very distant astronomical objects during the span of just one year, not to mention practical problems with earth-based telescopes and optics, and imprecisions in even the best clocks we know how to build, and so forth. Nimur (talk) 22:41, 12 December 2012 (UTC)

Blue sky?

Randall Munroe makes a decent point: [14]...why isn't the sky violet? I never thought about it til I saw that comic. Ks0stm ^{(T•C•G•E)} 10:17, 12 December 2012 (UTC)

The short answer is, as the cartoon suggests, Rayleigh scattering. I don't know enough big words to give you the long answer. Evanh2008 ^{(talk|contribs)} 10:20, 12 December 2012 (UTC)

So why isn't the sky violet?Dncsky (talk) 10:21, 12 December 2012 (UTC)

There are dozens of very good answers here[15].Dncsky (talk) 10:22, 12 December 2012 (UTC)

Yeah, I realized the trick in the question (violet being shorter in wavelength than blue) just after posting. My first guess is, as one of those posters suggested, that the sun emits more radiation in the form of blue light than violet. I am reading Diffuse sky radiation at the moment. Good question, BTW. Evanh2008 ^{(talk|contribs)} 10:29, 12 December 2012 (UTC)

"The traditional way that people teach this subject is that sunlight is scattered — more so for shorter wavelengths than for longer ones," says Glenn Smith, an engineering professor at Georgia Tech. "The other half of the explanation is usually left out: how your eye perceives this spectrum." Evanh2008 ^{(talk|contribs)} 10:41, 12 December 2012 (UTC)

The spectrum of a typical sky on Earth

.

For context, here's the spectrum of the sun - and additional details from National Renewable Energy Laboratory.

We can eschew the complications of human visual perception by looking at the spectrum of diffuse sky light using a spectrometer (or even a simple prism). This spectrum should be compared to, e.g., the solar spectrum, to see what effect Rayleigh scattering actually has. Nimur (talk) 16:12, 12 December 2012 (UTC)

There are no violet sensors in the eye, just three cone types all sensitive to a wide range of the visual spectrum. If you're looking at light that peaks in the green-blue-violet part of the spectrum, you're going to see what amounts to a weighted average of those spectral colors, which will be a color somewhere in the middle, not all the way at one end. That doesn't prove the sky is blue, but it does show the error in the naive argument that it ought to be violet. -- BenRG (talk) 05:00, 13 December 2012 (UTC)

Burning oil at low rate using catalyst for "greenhouse".

I'm wondering about how I can heat my mother's planters to protect the plants after I've put a PVC cover over them. They're fairly small planters and I don't think they need a lot of heat. I was wondering about those catalyst hand warmers made by Zippo etc. The handwarmers only last up to 24 hours (a week or more would be better) Do you think I could use such a catalyst to burn, say, vegetable oil without a flame, at a low rate? — Preceding unsigned comment added by 78.150.23.29 (talk) 12:42, 12 December 2012 (UTC)

I'm not sure what you mean. I don't think the chemical type would combust veggie oil, nor do I think that veggie oil would burn properly in the zippo models, which call for lighter fluid. You didn't ask for gardening advice, but depending on the location and plants, insulation and passive radiant heat are often enough to over-winter plants successfully. SemanticMantis (talk) 15:15, 12 December 2012 (UTC)

Don't know if I'm following this right, so I'll start at the beginning. An elephant has a grater ratio of mass to surface area. Therefore, a mouse loses more body heat then an elephant. If one was to get (say) Bubble wrap and with it, construct a rude green house, then a single candle will protect all the planters placed within it - from frost. Are you wanting to protect from frost? If however, your propagating orchids, pineapples, bananas etc., please ignore this. --Aspro (talk) 19:56, 12 December 2012 (UTC)

I think a candle might generate too much heat, too fast and damage the plants/PVC tarp, as well as needing to be frequently replaced. I'd like something that burns slowly and cleanly. — Preceding unsigned comment added by 129.215.47.59 (talk) 22:46, 12 December 2012 (UTC)

These things are for use with lighter-fluid filled hand-warmers. Lighter fluid is relatively expensive. Do you suppose they will also work with regular unleaded petrol/gasoline? I could then rig something up using a glass jar full of petrol and, if necessary, wadding. Perhaps this converter would just float on the gasoline and not need any wadding.

Also, those catalysts are only meant to last 90 times as 12 hours per time. What do you suppose the catalyst is made of and what happens to it to limit it's life span? Could it be restored to full function after use? — Preceding unsigned comment added by 129.215.47.59 (talk) 23:04, 12 December 2012 (UTC)

An alternative way to heat small volumes is with an incandescent light bulb. Just snake an extension cord over there, and use a plug-in socket you buy at a hardware store (you could even use an incandescent night light, if the heating needs are modest enough). This is an old technique for heating doghouses in winter, and far less likely to cause a fire. StuRat (talk) 03:07, 13 December 2012 (UTC)

Candle and Carbon Monoxide

Hi, a friend asked me how long would a single candle need to burn in an airtight room before it would set off a carbon monoxide detector? I'm not really sure how to find an answer, so was wondering if anyone here could be of help. For my own curiosity, what if we assume that the room has only a small crack under the door that connects it to another in door room? Note: please don't take this as a medical question, or some such, if you're trapped in an airtight room, candles would be the least of your issues:-)Thanks:-)Phoenixia1177 (talk) 13:02, 12 December 2012 (UTC)

It would depend quite a lot on the size of the room, the size of the candle and where the detector was placed. More detail usually gets a better answer. Richard Avery (talk) 14:39, 12 December 2012 (UTC)

There are several points to be understood here:-

1. A burning candle, which is essentialy a means of slowly burning a hydrocarbon wax, will produce very very little carbon monoxide, unless the oxygen level is so low you'd already be dead - most of the combustion product is water vapour and carbon dioxide, as for conbustion of any hydrocarbon.

2. A truely airtight room is quite difficult to achieve. A "small crack under the door" is likely to provide enough diffusion of oxygen in and carbon dioxide and water vapour out to overwhelm the output of a typical candle.

3. The presence of any human in the room will also consume oxygen and replace it with carbon dioxide.

4. There are various sorts of carbon monoxide detectors sold, and the common ones don't just react to carbon monoxide. For instance the "Cricos" detectors one of my old employers uses to detect carbon monoxide in confined spaces is routinely tested by breathing out into its' air input - by holding your breath a moment first, you can reliably trigger the alarm.

Floda 120.145.143.148 (talk) 14:44, 12 December 2012 (UTC)

Neither the UK Fire Service nor the US Environmental Protection Agency list candles as a source of carbon monoxide. The US National Candle Association has an interesting page on the THE SCIENCE OF CANDLES, which says that "The heat of the flame vaporizes the liquid wax (turns it into a hot gas), and starts to break down the hydrocarbons into molecules of hydrogen and carbon. These vaporized molecules are drawn up into the flame, where they react with oxygen from the air to create heat, light, water vapor (H2O) and carbon dioxide (CO2)." It quotes the 2007 Okometric Wax and Emissions Study, which says that candles "exhibit clean-burning behaviour" and "pose no discernible risk to human health or air quality". It also quotes M. Matthäi and N. Petereit: THE QUALITY CANDLE which says; "When burning candles, as in every case when burning hydrocarbons, water and carbon dioxide are produced. In addition, other combustion products can be formed in traces such as carbon monoxide, nitric oxide, organic hydrocarbons and soot." but it continues "In the case of high quality candles, which do not visibly emit soot, measurements taken have confirmed that combustion products produced are harmless" Alansplodge (talk) 14:48, 12 December 2012 (UTC)

I agree with the above. To summarize, it won't set off the alarm, ever. StuRat (talk) 03:11, 13 December 2012 (UTC)

Critical Illness cover

Questionable whether this is a science desk question, but I regarded it as so. I work for an insurance company and recently got critical illness insurance for a little over 1 GBP a month, with a payout of £25,000 on diagnosis of a specified list of critical illnesses (the usual you would expect - cancer, heart attack etc). My question is, how is this so cheap? This would imply that the amount of people my age (25) getting a critical illness is 1/25,000 of the population every month? This seems very low but cannot find any statistics for people this young, only 65+ (Where 1GBP a month would be a bargain - so presumably is much more expensive for the over 65s). Thanks for any help! 80.254.147.164 (talk) 13:20, 12 December 2012 (UTC)

A combination of factors; which applies specifically to you depends on your circumstances: 1) you've got an employee discount 2) there's a deductable 3) 25K is the max payout, one they only pay for the worst cases (compare to the disfigurement and body-part loss numbers for cheap travel insurance - losing a finger only gets you £400 and a leg only £3000) 4) check their delineation between critical and chronic illness - if you get Hepatitis-B or Malaria (which are going to affect you for the rest of your life), the probably won't pay for anything beyond the initial episode 5) they think they can recover some of their costs from other insurers (e.g. your travel insurance, or the liability insurance of involved parties) 6)they only insure you for out-of-pocket expenses; in the UK the NHS pays up the lion's share of the healthcare costs 7) if the insurance covers you for lost wages, they're relying on people your age being fairly low earners, and on employers having to pay statutory sick pay. For someone your age, who doesn't already have a history of chronic illness, that 1/25000 is probably about right. -- Finlay McWalterჷTalk 13:47, 12 December 2012 (UTC)

Read the limitations and exclusions. Probably non-terminal cancer is not covered, and due to advances in medicine most cancers aren't terminal. Heart failure might kill you right away. HIV might be excluded, unless accidentally infected, and this is rare. And insuring 25 year olds for Alzheimer, heart valve replacement and Parkinson is a joke. If you are part of the NHS, I don't know if you need this kind of lump sum insurance, although you could cover the basics (health, disability, death, property) with some extra insurance. OsmanRF34 (talk) 22:18, 12 December 2012 (UTC)

A quick scan says that in the UK the rate of cancer diagnoses per month for 25 year old males is about 1 in 500,000; for heart disease around 1 in 100,000. Those are probably the two most common critical illnesses in this age group, so there is plenty of room for the insurance to be profitable. Note that we have an article on critical illness insurance. Looie496 (talk) 01:41, 13 December 2012 (UTC)

word for a type of visual disturbance

I am curious if there is a term for a type of visual disturbance where the items one is looking at (letters on a page, for example) seem to swim about a bit, maintaing their relative position, and being perfectly legible, but seeming to shift a bit side to side and up and down like dead leaves floating on the surface of a pool. Searches have led me to blurred vision and floaters, neither of which is at all what I mean. Thanks. μηδείς (talk) 18:04, 12 December 2012 (UTC)

Sounds a bit like one form of dyslexia. According to our article: "... dyslexic readers ... move letters around when reading – this only occurs in a very small population of dyslexic readers". StuRat (talk) 18:20, 12 December 2012 (UTC)

You say that they "seem" to exhibit the visual quality that you go on to describe. What is instrumental in bringing about the "visual disturbance" that you describe? Can you link to an example of this? Bus stop (talk) 18:28, 12 December 2012 (UTC)

Sorry, I can't help provide a name, but I will at least clear up that it is in no way similar to dyslexia. What Medeis is describing (and which I've also been curious about) is the visual trick where letters or some other pattern is printed in bright, saturated colours against a background of a dissimilar bright, saturated colour. I most often notice it with bright red printing against a bright blue background, such as what might be on the cover of a children's colouring book. As you move your head, the letters or patters seem to "shudder" slightly, as if they're not attached to the page. Matt Deres (talk) 18:44, 12 December 2012 (UTC)

After some casting about on Wikipedia, I'm thinking it's a form of "active" afterimage, where the high contrast and sharp borders allow you to experience the afterimage almost directly on top of the original image. Matt Deres (talk) 18:53, 12 December 2012 (UTC)

Hallucination suggests this could be considered a type of pseudohallucination, since you are are that your perceptions are "not real". I suspect you are looking for a more specific term, but I'm not sure there would be a rigorous scientific classification of something so subjective. If you are ok with folksonomy, you'd probably get some good answers at the fora of erowid. If you are interested in WP:OR and guesses, then I also think I have perceived what you and Matt are talking about, for me I assumed it had something to do with eye fatigue, different focal points for each eye, and maybe eye wetness. SemanticMantis (talk) 18:47, 12 December 2012 (UTC)

• I did find Scotopic sensitivity syndrome, which is a controversial "syndrome" and not apparently recognized widely, but which mentions "Text that appears to move (rise, fall, swirl, shake, etc.)" as a symptom. I have no idea if that particular symptom is unique to the syndrome or not. There may be others at Category:Visual disturbances and blindness. --Jayron32 18:52, 12 December 2012 (UTC)

Complementary colors are said to "clash". A Google search for complementary colors clash might reveal some relevant links. For instance: "A pair of complementary colors printed side by side can sometimes cause visual vibration (clash) making them a less than desirable combination."[16] Bus stop (talk) 18:54, 12 December 2012 (UTC)

Like this ? I was going to suggest that it might be caused by sneezing on the screen or reading in the rain which would have been foolish. Luckily, I didn't. Sean.hoyland - talk 19:00, 12 December 2012 (UTC)

(ec) It hearkens back to my once taking ololiuqui in the 1980's and the visual effects. The initial experience was quite extreme, but for the following month or so I had "flashbacks" where items in my field of vision, especially letters on a page, dots in paint on a wall, or the tiles on the floor would seem gently to shift side to side, very reminiscent of, say, looking down from above on boats crowded together on the surface of a body of water, not exchanging places or being indistinct or confusing blurry, and not at all illegible in the case of letters, just not maintaing equal distance. I have seen similar effects on cartoons or depictions of people tripping, although that's usually a lot more disturbed than what I am describing. Having just picked up Oliver Sacks's latest, hallucinations, brought the idea back to me and made me want took it up on line. Unfortunately searches for things like "swimming letters" get hits on letters of permission or commendation for swimming events, and most of the rest I am getting has to do with floaters in the eye cavity, which is not what I am looking for. μηδείς (talk) 19:28, 12 December 2012 (UTC)

Some of this effect is due to dispersion in the eye, so that different colours require a different focus from the lens. Where they abut each other it is hard to focus on both edges at the same time. Graeme Bartlett (talk) 20:20, 12 December 2012 (UTC)

Okay, I have just read through the very interesting responses above in full. None has quite hit it on the head. It's definitely not dyslexia, which I have never had under any circumstances. It's not an after image, since there was only one clear image--simply that items which I knew were fixed seemed to be swaying slowly relative to each other, but my field of vision was clear and I could read (when I was reading) without a problem. Bus Stops' link to complementary colors leads to a different phenomenon with which I am familiar--but the author in that case seems to be using the word vibrate metaphorically. Sean's image is actually very helpful, since, if you ignore the color differences and assume they instead indicate a slow swaying motion of black on white text (and word-by word, rather than letter by letter) you will get a good idea of what I am talking about. The scotopic sensitivity syndrome Jayron mentions matches in only that one aspect; the "text that appears to move (rise, fall, swirl, shake, etc.)" but is otherwise unconnected.

SemanticMantis is correct that this would have to be described colloquially as a pseudohallucination, since it occurred in my experience when I ate morning glory seeds in the 80's and tripped very strongly while aware I was hallucinating, along with "flashbacks" which of the phenomenon I am trying to name, and yet again around the turn of the century when I was hospitalized and had to have several major abdominal surgeries. In the later circumstance I went for three days or so without sleeping, and had the same visualizations; that words on text or spots on paint or abstract patterns on the wall were "crawling" or rows of tiles on the bathroom floor were not quite keeping parallel. (Just now I am reminded of Star Trek's "distorted space".) They went away when they made sure I got a good night's sleep.

I think if we had a list of visual hallucinations or list of visual disturbances I might possibly come acrost a term that matches what I am looking for. If anyone's got any suggestions as to such categories here or on other sites it would be very helpful. μηδείς (talk) 21:35, 12 December 2012 (UTC)

PS, Graeme, can you give an example of what you're talking about? I don't think it's the exact phenomenon, but I am curious. μηδείς (talk) 21:54, 12 December 2012 (UTC)

This seems most likely to be nystagmus. The morning glory seed effect is definitely due to nystagmus -- that mechanism is well understood. (Ironically, this question could be interpreted by a pedantic person as a request for medical advice, since various neurological issues could cause this to happen.) Looie496 (talk) 22:35, 12 December 2012 (UTC)

No, I am not seeking medical advice, unless there is some way to prevent symptoms that last occurred well over a decade ago, and the memory of which one does not need to be rid of. I simply want to read the literature on the phenomenon. Nystagmus sounds relevant and interesting, but the article is about a diagnosis or a physical act, not an experience as such. I am more looking for what the psychological experience might be called, than rather than what its cause might be. 00:06, 13 December 2012 (UTC)

Our article does not explain it very well. What happens physiologically in nystagmus is that the eyes move slightly when you try to keep them pointed at something; the experience is that the thing you are pointing them toward seems to move. Looie496 (talk) 00:23, 13 December 2012 (UTC)

Could it be related to an ocular migraine? The wp article isn't too good as it doesn't make it clear that they are often painless, but this explains it better. I know the symptoms are different, but perhaps it could be an atypical form. Richerman (talk) 00:28, 13 December 2012 (UTC)

wrist-mounted mini rocket launcher?

As sometimes seen in video games, anime, etc.. A weapon worn on the outer wrist that can fire out a rapid-fire volley of small, but high-explosive rockets at a given target.

Does (or did?) any such weapon exist in real life, even if it was only a prototype? I suspect that in real life, the high likelihood of setting one's own arm on fire would probably make it a largely unworkable concept... --Kurt Shaped Box (talk) 22:41, 12 December 2012 (UTC)

Well, "only a prototype" virtually ensures that the answer is "yes". Youtube shows people making wrist-mounted launchers. They're frequently pneumatic and fire darts and other non-lethals, but it's no stretch to replace "pneumatic" with "rocket" (model rocket engines are of reasonable scale) and "Nerf" with "C4". That said, I feel reasonably confident saying that no such device has yet been seriously considered for fielding by any modern military. In addition to the heat problem you note, rockets of that scale confer neither an accuracy nor a firepower advantage over a conventional rifle, grenade launcher, or likely even a hand-thrown grenade. — Lomn 23:04, 12 December 2012 (UTC)

On the plus side, the efflux from the rocket motor would remove all those unsightly hairs on your arm, although it might remove your skin in the process. Alansplodge (talk) 01:01, 13 December 2012 (UTC)

Wouldn't such a rocket launcher be useful as a concealable weapon? 24.23.196.85 (talk) 01:53, 13 December 2012 (UTC)

You may be interested in Gyrojet, which was a family of firearms including pistols that fired very small rockets. Why isn't every army using these, you ask? Because they suck nuts. Army testers reported that the guns jammed easily, rockets failed to ignite at least 1% of the time, and they had poor accuracy. In all fairness, they were designed in the 1960s, so perhaps modern technology could produce a more reliable minirocket, but this experiment probably killed the Army's enthusiasm for the idea for a long time. On the plus side, the guns are very light and have low recoil. Someguy1221 (talk) 01:43, 13 December 2012 (UTC)

Now let me make some suggestions to get such a device to work:

1) Launch it several meters by means other than the rocket, such as explosives, just like in a bullet, then ignite, once it is far enough from the person to avoid burning them.

2) Add a guidance system, such as a heat seeking missile, so you can actually hit the target. StuRat (talk) 03:17, 13 December 2012 (UTC)

It's not necessary you chime in on every topic you know some tangential amount about stu. Shadowjams (talk) 04:00, 13 December 2012 (UTC)

Can amounts be tangential? 182.5.158.187 (talk) 04:47, 13 December 2012 (UTC)

December 13

Gold complex solubility

I'm trying to find a reference for the solubilities of sodium aurocyanate and potassium aurocyanate in water, but I'm not having much luck. Can anyone give me a hand? 182.5.158.187 (talk) 04:37, 13 December 2012 (UTC)

aurocyanate or aurocyanide? This paper [17] has the data for both sodium and potassium aurocyanide. I don't find much of anything on aurocyanates. --Jayron32 04:44, 13 December 2012 (UTC)

Sorry, aurocyanide is what I'm after. My iPhone's autocorrect seems to know only aurocyanate. 182.5.158.187 (talk) 04:49, 13 December 2012 (UTC)

Animal extract for industrial use as an emulsifying agent (cattle semen & neem oil)

I run a weekly podcast 1 and a listener emailed our show this question for our "ask us anything segment" where we try to find answers to the most upvoted question. This week, we have to find an answer to the following listener-submitted question:

As you know, in the cattle industry, ranchers purchase "sexed semen" (which will yield only male calves) and it is a highly expensive process. At least 50% of the semen is wasted and I have a business venture where I'd like to market the excess semen from the industrial sex-selection process and use it as an emulsifying agent for organic pesticide/fungicide. My question is if semen could be used as an emulsifier between water & oil? (in this case neem oil).

Now the only thing I know about emulsification is from the food network, where you have to use dijon mustard as an emulsifier so that the oil & vinegar will come together in a salad dressing. A little more background on neem oil is that it is very good at keeping away aphids, fungus problems, and bacterial/viral diseases from agricultural crops such as tomatoes, peppers, cabbages, etc. 71.52.194.57 (talk) 05:45, 13 December 2012 (UTC)