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December 21

Does an Alpha emitter also emit Beta?

Does an Alpha emitter also by necessity emit Beta radiation? Because over time the source will become highly charged and it seems to me it has to release some electrons (although possibly at low energy). I'm thinking especially of an RTG in a spacecraft (i.e. vacuum). Ariel. (talk) 00:51, 21 December 2010 (UTC)

Not really. Beta emission is a different process than just losing electrons from the electron cloud. Excess electrons in the electron cloud after alpha emission will just drift off; while beta decay is basically just an electron, IT involves formation of that electron from the conversion of a neutron into a proton. Different processes. --Jayron32 01:25, 21 December 2010 (UTC)

I know the process is different - I was wondering about the end result. (I guess it's not called beta emission if the process is different.). My question is: Would an alpha emitter spark occasionally? I can only imagine the ionization of air would allow it to neutralize, and in a vacuum I assume they ground the RTG? Or, does the alpha particle grab an electron on the way out? Ariel. (talk) 02:00, 21 December 2010 (UTC)

At the bulk level, it is hard to track individual electrons with any meaning. Alpha particles end up, eventually, as neutral helium. Whether they grab an electron "on the way out" from the parent atom, or whether they grab electrons from some other bit of matter, and then that bit grabs from something else, down the line, is probably undeterminable. Uranium-238 decays into Thorium-234 and Helium. The electrons just all kinda work out. --Jayron32 02:51, 21 December 2010 (UTC)

Yep, air ionization is definitely one way of balancing charges. Odds are the smoke detector in your home contains a very tiny piece of americium-241, which is used to continuously ionize a small amount of air inside the detector. A small amount of current flows between electrodes on opposite sides of the ionized region; the presence of smoke particles reduces the ionization of air, triggering an alarm when the corresponding reduction in current is detected.

On the other hand, this effect is only important for very small pieces (or least, very thin pieces) of radioisotope. While alphas emitted from the surface atoms may travel a few inches in air, the mean free path of 1 MeV alpha particles in most solid matter is down between 20 and 50 microns [1]. In other words, the vast bulk of alpha particles generated within a fuel rod (for example) come to rest less than a millimeter from where they were created. If this occurs in a metallic alloy, then there are plenty of electrons sloshing about to sort out any local accumulations of charge.

Note that you can get some pretty interesting effects if you work in nonconducting systems. While I'm not aware of anyone using alpha particles this way, one can spray intense beta rays (high-energy electrons) at a block of plastic; at reasonable energies (a few MeV to a few tens of MeV) electrons will penetrate a few centimeters. Charges build up inside the plastic until an edge of the block is grounded. This triggers breakdown of the plastic's resistance, and all the accumulated charge drains out at once. This abrupt current damages the plastic, leaving a Lichtenberg figure. TenOfAllTrades(talk) 04:00, 21 December 2010 (UTC)

In space, (i.e., an RTG on a spacecraft), there will be an interaction called the Debye sheath or plasma sheath. Because space is not a complete vacuum, but is actually a very sparse plasma, the buildup of charge will cause an electrostatic response in the surrounding plasma. The characteristic scale-length and the magnitude of this response is determined by the amount of charge and the parameters of the (not-totally-empty) region of space. The average distance between particles, the percentage of ionized to neutral particles, and the energy of the ions, all determine the "thickness" of this sheath region, where bulk electrostatic effects are detectable. This will include accumulation of electrons to form a layer around the positively-charged object. Beyond the edge of the sheath, (the far field, so to speak), the alpha-emitter appears totally neutral, because charge has been conserved and has shielded any electrostatic interactions. Nimur (talk) 17:34, 21 December 2010 (UTC)

Poison mushroom

I've been a long time collector and eater of wild mushrooms. I definitely know how to identify the small variety of edible mushrooms I eat (Chanterelles and Porcini mostly) as well as a large number of poisonous or just undesirable varieties. So here is the question, why would mushrooms evolve toxicity? Some mushrooms have strong bitter taste/peppery or a foul smell despite being nominally edible, this I can understand as it definitely keeps me away The most deadly species like Amanita phalloides take many hours even days before causing symptoms so I don't imagine this would be an effective deterrent against being eaten, at least by large animals. Some mushrooms like the Fly Agaric are brightly colored and attractive like fruit but are also poisonous or at least unpleasantly hallucinogenic, why evolve this combo? The only things I can come up with are that these toxins are not evolved as a deterrent but are the byproduct of some other process or that they evolved as they culled the populations of animals who eat them and thus left only the phenotype who avoids their variety. --Leivick (talk) 09:13, 21 December 2010 (UTC)

The bright red Fly Agaric may be an example of warning coloration. Bright colors can serve to attract, as in flowers, or to repel, as in poison dart frogs. There is something to be said for the `by product' theory. For example, defensive compounds in mushrooms may be selected for because they decrease invertebrate predation (a large source of selective pressure). Mammals may not exert much selective pressure on a given species, but still experience deleterious effects from ingestion. SemanticMantis (talk) 15:08, 21 December 2010 (UTC)

The mushrooms an animal eats are just the "tip of the iceberg" and eating them does not normally kill the whole organism. Killing you in a few days is a completely adequate way of keeping you from being too much of a nuisance to the organism, and is an excellent way of stopping you from passing on any "ooh that looks tasty" genes to descendants. --Sean 15:19, 21 December 2010 (UTC)

It may also be worth bearing in mind that the toxic quality of any given fungus (or plant) may be coincidental. Not everything about fungi, plants and animals has evolved for protection. Richard Avery (talk) 16:02, 21 December 2010 (UTC)

The effective inhibition of RNA polymerase is something that will kill just about any living organism. Is it possible that these mushrooms (like Amanita) secreting amatoxins are actually doing so primarily as a means to compete with other fungi for their cool, damp, dark ecological niche? Remember that another genus of fungus – Penicillium – secretes antibiotics to ward off competition from bacteria. Does anyone know if the amatoxins are broadly toxic to other fungi (Amanita has presumably evolved to be resistant to its own toxins, but what about other mushrooms?) or to prokaryotes? If that's the case, then the effect on vertebrates (or even on invertebrate animals) may be a minor, almost coincidental one. TenOfAllTrades(talk) 16:04, 21 December 2010 (UTC)

This is OR. The distinctive colour and texture of the fly agaric is broadly similar to carnivorous plants that purposefully attract insects for the purpose of devouring them. Given the reason for its name, I wonder if the poison was developed in part to draw flies in, kill them, and so enrich the soil the mushroom was growing in. Just a guess on my part, so take that with a grain of salt. Despite being a featured article, our article doesn't seem to touch upon any theories regarding why these mushrooms are so toxic. Our article on mushroom poisoning also doesn't seem to touch on why mushrooms have evolved this defense, though it does say that relatively few mushrooms are poisonous, let alone deadly (though when they are...) Matt Deres (talk) 00:58, 23 December 2010 (UTC)

wet dreams

Are nocturnal emissions the male body's way of getting rid of stale sperm? If that isn't the case then how come women get wet during sexy dreams? —Preceding unsigned comment added by 188.186.237.190 (talk) 10:33, 21 December 2010 (UTC)

Wikipedia has an article about Nocturnal emissions. Their reported incidence is not often enough to match the continual production of sperm and so they cannot be called the male body's only way of disposal. Human sperm has a finite lifecycle estimated[2] as 42 days and if not ejaculated they are absorbed into the body at the vas deferens. After a vasectomy, the testes still produce sperm which are blocked and die in the vas deferens but this site warns that sperm beyond the blockage may survive up to seven months. The logic of the 2nd question is unclear because a women's vulva when sexually stimulated is lubricated by secretions from the Bartholin's glands, which has nothing to do with sperm production. Cuddlyable3 (talk) 15:14, 21 December 2010 (UTC)

Bear in mind that sperm constitute only a small proportion of semen, which is what is actually expelled; the bulk of the seminal fluids is produced outside the testes, primarily in the prostate gland (25-30%) and seminal vesicles (60%). Since the production of these fluids is independent of the testicles and does not turn on and off like a tap according to how much is already "loaded in the chamber", so to speak, periodic flushing of any excess unused by procreative or autostimulatory activities occurs in the form of nocturnal emissions, and I am fairly sure (though cannot find an immediate Wikipedia reference) that seminal fluid production and nocturnal emissions continue following the cessation of the sperm supply through vasectomy or even testicular castration.

Although women do not, obviously, produce seminal fluid, they do produce homologous fluids for lubricatory and perhaps other reasons, and the article on nocturnal emissions explicitly states, "women are also capable of having them." Similar considerations of excess production disposal presumably apply.

It is widely assumed (he weaselled) that during nocturnal emissions, it is the sensation of ejaculation/secretion that give rise to the "sexy dreams" rather than the reverse. 87.81.230.195 (talk) 01:15, 22 December 2010 (UTC)

It can also be widely assumed on the basis of diligent and exhaustingive empirical bio-studies employing the relevant gender-specific appendage activated manually in a turgid modality that the referred emission is obtainable with comparatively equal facility throughout the diurnal cycle and is therefore not necessarily correlated exclusively with the crepuscule or nocturnal phase of solar illumination absence so I have heard. Cuddlyable3 (talk) 10:35, 22 December 2010 (UTC)

You don't say. Do go on. -- Jack of Oz [your turn] 08:19, 23 December 2010 (UTC)

Straight back, diaphragm

If I sit with my back straight, does it make the diaphragm to be less restrained? It is a common explanation in meditation lessons, and it also makes intuitively sense (however, laying on the side also seems to be good for unrestrained breathing). Quest09 (talk) 14:32, 21 December 2010 (UTC)

Yes. When sitting straight up, gravity acts on the contents of the abdomen to pull them downwards. This makes the work of the diaphragm easier. When lying down on the back (supine), the abdominal contents press against the diaphragm, so the diaphragm needs to work harder. The diagnosis of "diaphragmatic paralysis" can be shown by measuring the spirometry ("lung capacity") when sitting up and lying down. In people with diaphragmatic paralysis, there is a big difference. Here is a report that remarks on this: "Paralysis of the diaphragm may be suspected in a patient ... in whom the vital capacity falls appreciably in the supine position." Axl ¤ [Talk] 10:44, 23 December 2010 (UTC)

c

Is it true that most oncologists (about 80%) when polled said they would not use chemo on their families or themselves? — Preceding unsigned comment added by Kj650 (talk • contribs) 16:23, 21 December 2010 (UTC)

I have not heard of it before but it seams reasonable given that most of them does not need it be curse they do not have cancer. --Gr8xoz (talk) 16:54, 21 December 2010 (UTC)

Presumably the OP means "as a treatment for cancer," durrr. --Mr.98 (talk) 17:11, 21 December 2010 (UTC)

I assume this is the origin of whatever statistic you are thinking of. The sample sizes are not huge, and the specifics of what kind of cancer are rather specific, and even then the number is not nearly as large as 80%. Additionally, the original "very high" (~75%) poll was over 20 years ago; even this one, which is well over 10 years ago, 64% said they would use chemo. I don't know what it would be today — medicine of this sort changes rather rapidly, and 10 years can make a big difference. --Mr.98 (talk) 17:14, 21 December 2010 (UTC)

It sounds like the typical position of some doctors like Matthias_Rath (a real doctor in Germany) who advocate to treat many diseases (including AIDS, diabetes, cancer) with vitamin supplements (that can be bought from them for a reasonable fee) rather than with the 'poisonous' mainstream treatment. Quest09 (talk) 17:31, 21 December 2010 (UTC)

I think that's a little extreme. There are significant numbers of oncologists who think that chemo is not the best treatment. That doesn't make them all quacks who believe in the miraculous powers of vitamin supplements. Chemo is an intense and possible detrimental form of treatment, and not the only one, and not necessarily the best one. Just because you aren't in favor of it doesn't mean you're in favor of quackery. Just because you're skeptical of a supposedly mainstream response doesn't mean you're necessarily in favor of the fringe response. --Mr.98 (talk) 19:43, 21 December 2010 (UTC)

I expressed myself wrongly. I don't mean that oncologist against chemotherapy are quacks. Chemotherapy might not be the best choice for some treatments. I wanted to say that quacks use phony statistics (like 80% of oncologist are against chemo), taken out of context to bash chemotherapy, and to offer you an 'alternative' like a high dosage of a vitamin supplement (which you have to buy from them, overpriced). Quest09 (talk) 20:30, 21 December 2010 (UTC)

It is important to recall that 'cancer' isn't one disease but many, and 'chemotherapy' isn't one particular treatment but a regimen tailored to the given patient and disease. It's extremely misleading to talk about 'chemo' as a single monolithic process or treatment. Different chemotherapeutic agents have very different side effects and different (often disease-specific) efficacies. Different patients will respond in different ways, and may find antinauseants and other supportive treatments more or less effective.

I would be very surprised if you were to find a practicing oncologist anywhere in an industrialized, first-world country who would flatly refuse chemotherapy for themselves or family members. Instead, what I am certain of is that you will find are oncologists who under some circumstances – of disease progression, life expectancy, and predicted marginal benefit – would opt not to undergo chemotherapy themselves, while still offering their patients a choice in similar circumstances. Consider a hypothetical (and grossly oversimplified) case involving a patient with advanced metastatic disease and a median expected survival time of one year. Suppose that an aggressive chemotherapeutic regimen will probably make the patient miserable for a month; the statistics say that on average his expected survival will be extended by two months and his chance at five-year survival will increase by some trifling amount. Good tradeoff, or not? There isn't a 'right' answer in some situations. TenOfAllTrades(talk) 01:38, 22 December 2010 (UTC)

I did a little bit of research into this a while ago and I think the critical statistic which is left out of the opponents of chemo therapy is "quality of life". Yes the pure "survivability" statistics for a lot of cancers treated with chemo seem far from stellar, and the chemo does make you feel miserable for a few months, but after that you might have a few years of relatively decent life. Without the chemo or radio therapy, the cancer will just grow unchecked and the pain and suffering it causes to those who didn't opt for therapy is what's NOT discussed by people who oppose chemo. Vespine (talk) 02:17, 22 December 2010 (UTC)

Chemotherapy has had some really amazing strides in the past few years. I'm going to go out on a limb and say if the hominid toxicity of 3-BrPA is anything like its toxicity in other mammals, the retiring baby boomers might not end up a net health care negative. Ginger Conspiracy (talk) 06:55, 22 December 2010 (UTC)

The colour of this morning's lunar eclipse

Hi. Compare the two images, one from the latest eclipse (right) and the other taken during the eclipse of February 2008 (left). Both have a reddish hue, but the most recent one is darker. Is this due to the recent volcanic activity? Thanks. ~AH1^(TCU) 17:25, 21 December 2010 (UTC)

Before anyone jumps to conclusions, note that the February 2008 image is a digital composite of 1180 frames captured over a three-hour period. The amount of digital postprocessing required to synthesize and perform superresolution from more than 1,000 images is huge - so use caution before jumping to any conclusions about any characteristic of these images. (I was tipped off that something was a little "weird" when that image appeared to resolve lunar features that even I have a hard time shooting through my 200mm Newtonian reflector). The color and light intensity should be considered false color, and unless you have detailed information about the compositing method, avoid making inferences about true light intensity from it. Nimur (talk) 17:43, 21 December 2010 (UTC)

It's not totally unreasonable to say volcanic ash might affect how the moon looks from earth, but i don't see why you would only notice the effect during a lunar eclipse. Also, i don't think the rate of volcano eruptions is any different then in 2008 except maybe for maybe Eyjafjallajökull, that article shows the spread of the ash cloud so you should be able to tell if it's at least plausible that's what caused it. Hint: if you are in america: no; if you are Europe: maybe. Also relevant from the Volcanic ash article it states Volcanic ash particles have a maximum residence time in the troposphere of a few weeks. The finest tephra particles remain in the stratosphere for only a few months, they have only minor climatic effects, and they can be spread around the world by high-altitude winds. This suspended material contributes to spectacular sunsets. This confirms it's possible for the view of the moon to be affected for months after an eruption, but again I don't see why you'd only notice it during a lunar eclipse. Vespine (talk) 02:08, 22 December 2010 (UTC)

I have to say I don't know the answer, but I want to clarify some things. First, it's true that the recent eclipse is darker. Sky and Telescope gives a Danjon estimate of 2.5-3 for the 2008 eclipse and 2 for the 2010 eclipse (see http://www.skyandtelescope.com/community/skyblog/observingblog/15838502.html and http://www.skyandtelescope.com/observing/home/112248339.html), although these numbers are early estimates, and it's frustratingly difficult to find accurate brightness data on past eclipses.

Second, to answer Vespine, notice how the Moon appears red during totality, even though it's completely inside Earth's umbra. The only light that reaches the Moon during totality has to refract around the Earth, which means it has to travel thousands of kilometers through Earth's atmosphere. This light is red for the same reason sunrises/sunsets are red, and it's heavily affected by volcanic dust for the same reason volcanic eruptions cause brilliant sunrises/sunsets. Another way of looking at it is that some light from every sunrise and sunset on Earth is leaving the atmosphere, hitting the Moon, and reflecting back. So if you watched the recent eclipse from North America, part of the light that reached the Moon during totality would have passed through European skies, because the Sun was rising in Europe around that time. --99.237.234.245 (talk) 03:40, 22 December 2010 (UTC)

I admit I actually didn't consider the light passing through the atmosphere on the way to the moon, only passing from the moon back to earth. I thought since the atmosphere is only a tiny part of the diameter of the earth it would only have a very small impact on the light behind the earth, but refraction around the earth makes perfect sense when you explain it like that. Thanks. Vespine (talk) 05:38, 22 December 2010 (UTC)

I was not referring to the Icelandic eruption, but rather the more recent volcanic eruptions such as those at Mount Merapi, Mount Bromo and Mount Bulusan. ~AH1^(TCU) 17:26, 22 December 2010 (UTC)

Does sleep deprivation do permanent damage to the brain?

In the Wikipedia article it is mentioned that sleep deprivation has temporary effects. However, it is not mentioned if prolonged lack of sleep has any permanent effects on the brain.
So does it have permanent effects on the brain, or are they limited to them time spent under sleep deprivation? --87.68.248.194 (talk) 17:40, 21 December 2010 (UTC)

It might be difficult to study this, since clinical studies would be unethical, leaving us with only apocryphal cases. An even if a case is verified, would it be clear whether sleep deprivation caused the brain damage or the brain damage led to insomnia, and hence sleep deprivation ? StuRat (talk) 21:29, 21 December 2010 (UTC)

When you say prolonged lack of sleep do you mean staying awake for multiple days straight? Or do you mean not enough sleep each night? Ariel. (talk) 21:34, 21 December 2010 (UTC)

Sorry for not making it clear. When I say "lack of sleep" I mean staying awake for multiple days, not having little sleep at night. I would also like to know after what period of time the damage starts.--The Dimak (talk) 16:25, 22 December 2010 (UTC)

What about Stress (biology), which may accompany the sleep deprivation, causing effects on the organism which indirectly affect the brain. If the subject is under extreme internal or external pressure to finish writing some work, to finish a construction project, is in combat, is fleeing a menace, or is deliberately being kept awake by a captor, researcher or interrogator, would the prolonged release of cortisol or adrenalin directly affect the brain? The stress article mentions "ulcers, depression, diabetes, trouble with the digestive system or even cardiovascular problems, along with other mental illnesses." Some heart rhythm disturbances can cause blood clot formation leading to stroke. Digestive disturbances or diabetes can affect the blood chemistry, thus affecting the brain. Edison (talk) 17:20, 22 December 2010 (UTC)

The complete absence of sleep will eventually cause death. Brain damage could occur somewhere in this range. ~AH1^(TCU) 17:21, 22 December 2010 (UTC)

See: Fatal familial insomnia. Count Iblis (talk) 22:38, 22 December 2010 (UTC)

That's not exactly what the OP is asking. FFI is very rare prion disease in which the brainstem is damaged first, followed by a host of autonomic problems including insomnia, followed by death. It is a pretty horrific disease, to be sure, but the OP wants to know if physically staying awake for multiple days at a time could cause brain damage. --- Medical geneticist (talk) 12:58, 23 December 2010 (UTC)

As noted, heart disease or stroke resulting from the concomitant stress could permanently damage the brain, as could the severe hypoglycemia resulting from diabetes caused by the stress. People rarely stay up for days on end just because it is fun to do so, without some powerful and likely stressful motivator. Edison (talk) 05:29, 24 December 2010 (UTC)

radio-metry and its uses in optical instrumentation

what is radiometry and its types uses in optical instrumentation — Preceding unsigned comment added by Mahi09 (talk • contribs) 17:58, 21 December 2010 (UTC)

Have you read our article on radiometry? Photometry_(optics) and Photometry_(astronomy) may be of interest, they refer to similar fields of study, but restricted to visible light. SemanticMantis (talk) 18:45, 21 December 2010 (UTC)

why does skin on your face get wrinkled and how does cream help?

why does skin on your face get wrinkled and how does cream help? 82.234.207.120 (talk) 20:44, 21 December 2010 (UTC)

The Wrinkle page might help explain why skin wrinkles. Most skin creams are just emulsions of oil and water and just provide a temporary moisturizing effect, making your skin appear less wrinkled. Most of the other compounds advertised in skin creams (Like vitamin A, E or other antioxidants) are not proven to do anything at the level of the amounts in the cream. -- JSBillings 21:12, 21 December 2010 (UTC)

The main effect is from ultraviolet exposure from sunlight. That's why you hardly ever see a wrinkled vampire. :-) StuRat (talk) 21:24, 21 December 2010 (UTC)

(...nor any other kind of vampire.) Botulinum toxin type A is BION an approved cosmetic for temporarily fixing skin wrinkles, see Botox#Cosmetic. Cuddlyable3 (talk) 21:44, 21 December 2010 (UTC)

Wrinkle cream helps those who sell it to make money through the vanity of others. HiLo48 (talk) 22:12, 21 December 2010 (UTC)

Basement temperatures

If an unheated basement or pit ten feet deep had a well-insulated roof, what sort of temperature would it have during the year in northern europe? I have been unable to find this kind of information. Thanks 92.15.15.127 (talk) 22:53, 21 December 2010 (UTC)

There are too many variables to give a definitive answer. Temperatures vary considerably throughout northern Europe. Deep pits tend to remain at a fairly constant temperature if there is no strong airflow to the atmosphere and there is good insulation, but there would still be some variation according to air temperature. The temperature would tend to follow that of the ground at a similar level if the walls and floor are uninsulated. There may be some areas where the pit would be below the freezing-point of water all winter, and others where it would become uncomfortably hot in summer. Dbfirs 23:29, 21 December 2010 (UTC)

My grandparents had a basement used as a pantry, just dug into the ground under their house, in a small town north of Warsaw in Poland. It's not northern Europe but I believe this was not uncommon practice all around Europe. The fact it had a house on it that was kept warm in winter would have played a big part in it never freezing. I don't think insulation, no matter how "good" without any source of heat would do something similar. Insulation just makes the escape of heat slower, but without a source, the heat would eventually escape. Earth it self is a very good insulator, in seasonally frozen ground I believe you wouldn't expect the ground to freeze more then a few to several feet deep so insulation might work, (it would probably help if was black to capture as much sunlight as possible, however in places of permanent frost like areas of Siberia and Alaska the ground can be frozen to hundreds of feet where I doubt any insulation would do very much. Vespine (talk) 01:51, 22 December 2010 (UTC)

Yes, it does very. For instance, at Cheddar Gorge, the caves stay at a steady 52°F -which is just right for maturing traditional cheddar.[3] The article about the Geothermal gradient explains more.--Aspro (talk) 10:36, 22 December 2010 (UTC)

It depends very strongly on how deep you are. Near the surface (like a basement) it's going to vary winter/summer - but once you go deeper it starts to vary less and less, basically the earth both insulates it and acts as a heat sink/source. Ariel. (talk) 11:22, 22 December 2010 (UTC)

A basic pit with a sealed roof will act like a "fruit cellar" and stay substantially above the outside temp in the northern winter. The dimensions and insulation level of the roof would be important factors in the actual air temperature. In the Northern US winter temps drop to perhaps -30F (-34C) and the frost line drops fairly deep. The basement footings or house foundation must be below this frost line to prevent "heaving" or movement due to soil freezing below the footings. This may be 5 feet (1.52 meters) in Minnesota. In northern Canada or Alaska there is permafrost. The pitwall would approximate the soil temperature, with the deeper portion at a more constant temperature, but in Minnesota, the soil down to 5 feet would be below freezing. Convection currents inside would circulate warmer air from the bottom up along the walls, so the soil or wall temp would be a bit warmer near the surface than in undisturbed soil of the same depth. In an abandoned house, especially if it is not sealed against air circulation and infiltration, and without the benefits of heating or the retention of solar heating, it is common for the frozen ground to break the basement walls and force them inward, near the ground. I have also seen basement wall broken where rainwater of snowmelt from the roof is allowed to dump next to the foundation, so pooled water next to the cellar wall freezes and expands and causes it the wall to break and tilt inward. I have seen the air temp in an unheated shallow basement of a heated house in the northern US stay near freezing for days when the outside temp is many degrees below freezing. A cave completely below ground might have air temperature at about the average yearly temperature for the area, although as the depth went far below ground, like a gold mine, the temperature would rise significantly. Edison (talk) 17:04, 22 December 2010 (UTC)

December 22

glowing embers on the road

For the past few months, whenever I drive home on the highway during the evening, I see the same strange thing on that little bit of road between the median and the fast lane: There, on the ground, is a small pile of what appears to be glowing coal embers - a pile of about ten roundish egg-sized things (in a small cluster the size of a bird's nest) emanating orange light. The first time I saw them, I thought they were actually coal embers. But because I've seen them in the same spot night after night, that can't be the case. Anybody have any idea? --Vectorflux (talk) 02:19, 22 December 2010 (UTC)

Where in the world? HiLo48 (talk) 02:49, 22 December 2010 (UTC)

Simplest explanation is a broken orange corner reflector. An idea: Make a careful note of where it is, then drive it during the day with a passenger with a camera. Have them try to take a high speed picture of the spot (make sure to set the exposure very low/fast to avoid blurriness, and physically pan the camera as well). Ariel. (talk) 05:29, 22 December 2010 (UTC)

Edit: Even more likely: Cat's eye reflector. Maybe a construction crew dumped some they didn't need? Or lost them? Ariel. (talk) 05:34, 22 December 2010 (UTC)

Due to the location on the road I suspect the objects are something that fell from a vehicle. The article Automotive lighting provides candidates such as turn indicators, brake lamps, sidemarker lights or reflectors, emergency lights and others. Someone might have lost their Christmas lights or possibly fluorerscent strip lights that served the 90's fad for under-car lighting. But could not the OP just go back and look? Cuddlyable3 (talk) 10:11, 22 December 2010 (UTC)

I, too, would venture to say it's a cat's eye reflector. There are varying designs; some are just one chunk of mirror whilst others have several small, circular reflectors and that sounds like what the OP saw. The best way to tell is to go back in daytime. Regards, --—Cyclonenim | Chat  18:36, 22 December 2010 (UTC)

Normal human body surface area = 1.73 m^2

How was 1.73 m^2 chosen as the "normal" human body surface area? If women typically have a BSA of 1.6 m^2 and men 1.9 m^2, 1.75 m^2 would seem a more likely choice unless there was a reason for choosing a less "round" number. Note that this normal BSA enters into the choice of units for renal function where the BSA corrected glomerular filtration rate (GFR) is given in mL/min/1.73 m^2. -- 119.31.126.66 (talk) 03:03, 22 December 2010 (UTC)

The origin of the 1·73-m² body surface area normalization: problems and implications by James G. Heaf in Clinical Physiology and Functional Imaging, Volume 27, Issue 3, pages 135–137, May 2007, sounds like it would tell me what I want to know. Now if only I can get access somewhere. -- 119.31.126.66 (talk) 03:27, 22 December 2010 (UTC)

Here's a relevant excerpt from Heaf: "In these evidence-based times, it is perhaps surprising to read how little documentation was required for the derivation of this figure, which first appeared in a study by McIntosh et al. (1928) (Fig. 2). On the basis of clearance studies of eight children and seven adults, the paper states: ‘Our experience confirms that of Addis and his colleagues. More constant normal values are obtained if one substitutes A (= surface area) in place of W (= weight) in the clearance formulae. We have found it convenient to use as a unit the surface area 1·73 square meters which is the mean of the areas of men and women of 25, estimated from the adjusted medico-actuarial tables of Baldwin and Wood published by Fiske and Crawford’. The Du Bois formula was used. The tables described young US citizens applying for life insurance. They were not referenced directly, but an adjusted version was published by Fisk & Crawford (1927). While these individuals had been examined fully clothed, every effort was made to reach as accurate an estimate as possible: the figures for men were ‘adjusted from the Medico-Actuarial Tables by subtracting 1 inch from height in shoes, and 5 pounds from weight in clothes’, and for women by subtracting 1·5 inches and 4 pounds, respectively, thereby giving us an insight into American clothing standards in the 1920s. There seems to be a minor error in the calculation: the correct figure is 1·72 m2."

References are McIntosh: PMID 16693840; Fisk: Fisk EL, Crawford JR. How to Make the Periodic Health Examination (1927) p. 345. Macmillan, New York.; Dubois: Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med (1916); 17: 863–871.

Interestingly, here's a description (from Heaf) of the method of Dubois: "The most commonly used formula for determining BSA is the Du Bois formula from 1916 (Du Bois & Du Bois, 1916). BSA was determined by tightly covering the patients with manila paper moulds. The moulds were then removed, opened and placed flat on photographic film. The film was subsequently exposed to light. Finally, the unexposed film was cut out and weighed. The BSA was derived from the weight by dividing by the average density of the photographic area." Hope this helps. -- Scray (talk) 05:09, 22 December 2010 (UTC)

Thank you! I am surprised that the original figure was actually expressed in square meters as opposed to square feet or square inches since the tables mentioned were apparently of US citizens described in pounds and inches. I had not realized that the medical / physiological community in the US had adopted the metric system so early. -- 119.31.121.84 (talk) 05:32, 22 December 2010 (UTC)

Based on the description of the gross approximations in the determination, it is hard to justify more than 2 significant figures. Edison (talk) 16:49, 22 December 2010 (UTC)

Arsenite color

Are they colorless? --Chemicalinterest (talk) 16:30, 22 December 2010 (UTC)

Yes, as long as the cation isn't coloured. So sodium arsenite is colourless, while copper arsenite is a well-known green pigment. The colour isn't the normal blue colour of copper(II), but the principle is the same. Physchim62 (talk) 16:34, 22 December 2010 (UTC)

Thanks. I needed the information for my work. --Chemicalinterest (talk) 17:24, 22 December 2010 (UTC)

Arsenite solubility

Are arsenites soluble? Sodium and potassium vs. copper arsenite. --Chemicalinterest (talk) 17:26, 22 December 2010 (UTC)Never mind. --Chemicalinterest (talk) 19:23, 22 December 2010 (UTC)

hear sine wave vs square wave

Is there an easy way that I can hear the difference in a sine wave and a square wave? For instance, is there a website or sound files that demonstrate the two, so I can listen to them? Bubba73 ^{You talkin' to me?} 16:41, 22 December 2010 (UTC)

A sine, square, and sawtooth wave at 440 Hz

Our article on waveforms actually has an example sound file; I've copied the link here. The addition of harmonics to the square wave gives it a much 'harsher' sound that the pure, single-frequency sine wave tone. TenOfAllTrades(talk) 16:54, 22 December 2010 (UTC)

Thank you, that was pretty much what I was looking for. It is a bit short and the square wave starts while the sine wave is still going on. Bubba73 ^{You talkin' to me?} 18:19, 22 December 2010 (UTC)

Puts on professor hat The square and the sawtooth waves are made by adding harmonics to the sine wave, which means the sine wave is actually present through the entire sequence. If one filters away their harmonics, the square and sawtooth waves turn into sine waves. ("Harmonics" means other sinewaves with frequencies that are whole multiples of the fundamental sinewave.) A proper mathematical sinewave keeps on going forever so any demonstration has to be cut short to be practical. Cuddlyable3 (talk) 21:34, 22 December 2010 (UTC)

For a more mathematically rigorous take on the matter, you can read the article Fourier series. It turns out that any periodic function can be treated as a superposition of multiple (perhaps infinite) sine and cosine functions. Buddy431 (talk) 21:50, 22 December 2010 (UTC)

OK, I understand that. To me, though, it sounds like two things - the sine plus something else, rather than one tone. Bubba73 ^{You talkin' to me?} 21:54, 22 December 2010 (UTC)

A square wave is $y=\sin x+{\frac {\sin 3x}{3}}+{\frac {\sin 5x}{5}}+{\frac {\sin 7x}{7}}+\cdots$

Power-of-2 harmonics step up the octaves and thus sound pleasant. Other harmonics can sound, well, unharmonic. Wolfram-Alpha square wave graph. CS Miller (talk) 23:07, 22 December 2010 (UTC)

And the triangular wave is $y=\sin x-{\frac {\sin 3x}{3^{2}}}+{\frac {\sin 5x}{5^{2}}}\cdots$    CS Miller (talk) 23:21, 22 December 2010 (UTC)

I guess it is those non-power-of-2 harmonics that makes it sound like two things. Musical instruments have a lot of harmonics, but not like the square wave. Musical instruments still sound like one thing whereas the square wave sounds like two. Bubba73 ^{You talkin' to me?} 00:41, 23 December 2010 (UTC)

Try this (lets you do sine and square at the same time) and this from [4] Ariel. (talk) 00:46, 23 December 2010 (UTC)

That is even more interesting. I started wondering about this because of my memory of the sound on my old Apple II. I thought it was probably a square wave. My memory is that it sounded like these square waves. Bubba73 ^{You talkin' to me?} 01:12, 23 December 2010 (UTC)

The cochlea has a profoundly different frequency response to waveforms with infinite first derivatives. Ginger Conspiracy (talk) 03:32, 23 December 2010 (UTC)

I imported the sound file of 1 second of sine, 1 second of square, and 1 second of sawtooth into a sound editor - and it is what it says (although there are some squiggles on the square wave). Bubba73 ^{You talkin' to me?} 04:12, 23 December 2010 (UTC)

The "squiggles" might be due to the Gibbs phenomenon. —Bkell (talk) 05:10, 23 December 2010 (UTC)

Looks like they are. Bubba73 ^{You talkin' to me?} 06:26, 23 December 2010 (UTC)

Space between particles

Considering the amount of space between subatomic and all other particles, what percent of the human body is empty space? — Preceding unsigned comment added by Daselter (talk • contribs) 19:30, 22 December 2010 (UTC)

If you only consider the gaps between atoms as empty space, you will get one figure, if you add the gaps between the nuclei and electrons, you will get a much higher percentage of empty space, and if you add in the space between quarks, you will get a higher figure still. It may well be that the answer is 100%, as no fundamental particle exists which is completely solid. (I don't believe the strings in string theory have a volume, although they do have a length.) StuRat (talk) 19:47, 22 December 2010 (UTC)

It should come up to 100% empty space. This is fundamentally the same as measuring infinite distance along a shoreline by using a smaller and smaller unit of measurement. -- kainaw™ 19:52, 22 December 2010 (UTC)

Or if you consider everywhere that a molecular orbital has non-zero probability as "occupied", then you get approximately 0% empty space (not counting the actual open spaces in the lungs and bowel, etc.). The question hinges as much on the semantic meaning of "empty space" as it does on the physical properties of the body. Dragons flight (talk) 20:07, 22 December 2010 (UTC)

Alas, we mortals live from Cantor dust to Cantor dust, the peculiar states of being nowhere dense. Cuddlyable3 (talk) 21:39, 22 December 2010 (UTC)

Let me explain why we can be 100% empty space, and yet still physically interact. When you touch an object with your finger, the atoms of your finger don't actually touch the atoms in the object. Instead the electromagnetic force of the atoms in your finger repels the corresponding electromagnetic force of the atoms in the object. It's just like two magnets that repel, and yet have empty space in between them. This is true when two atoms interact, it's true for an electron around a nucleus (it's all empty space, yet they interact), it's true for the nucleons in the atoms (except they also use the strong force), and it's true for the quarks inside each nucleon (but they use a different force). As far as anyone can tell electrons and quarks have no physical size (although they do have a wavelength). So where do you want to stop the line? If you draw a box around an atom it certainly has a size - and you can talk about the space between atoms. You can instead draw your box around the nucleons, or you can go larger and draw your box around molecules (like Dragons flight suggested). Ariel. (talk) 21:55, 22 December 2010 (UTC)

Isn't it something like 99.999999%? I forget how many nines. 100% is absurdly wrong, but very close. Ginger Conspiracy (talk) 23:05, 22 December 2010 (UTC)

From Point-like particle: "There is no experimental evidence for any of the elementary particles having spatial extent, and so they are usually considered to be point particles in the more general sense too...." Ariel. (talk) 00:35, 23 December 2010 (UTC)

That seems inconsistent with Planck length and the general idea of surface area corresponding to the force activity regions involved. Ginger Conspiracy (talk) 01:20, 23 December 2010 (UTC)

We don't have the ability to experimentally probe down to the planck length, and that sentence specifies experimental. One day we may find that electrons have internal structure (maybe by probing with neutrinos?) But, right now as far as we know they are point-like. I don't understand the second part of what you wrote. Ariel. (talk) 02:50, 23 December 2010 (UTC)

One analogy I've read, I'm not sure how accurate it is, if the nucleus of an atom was the size of a pea and you put it in the middle of a football field, the electrons would be orbiting around the boundary of the field. But as the above states, even the nucleus isn't really a solid. Vespine (talk) 23:26, 22 December 2010 (UTC)

I agree with Ariel that 100% "empty space" is a valid answer. There is no "solid matter" even at deepest level. It is all "energy". Of course, various other answers are possible, depending (as others have said), on where you draw the "boxes". Dbfirs 00:03, 23 December 2010 (UTC)

It will depend on our definition of solid. We have a variable volume dependent on pressure. In Human experience it means that the material resists human force. In that respect the human body is solid enough, but if the force becomes extreme enough you can make degenerate matter or neutron star matter. If pressure is reduced, then the body will evaporate and fill a much larger volume with water vapour and carbon dioxide! Graeme Bartlett (talk) 00:37, 23 December 2010 (UTC)

This was asked recently. The answer depends 100% on what you mean by "empty space". This term has no definition in modern physics, unless you define it as the absence of any field, in which case 0% of your body is empty space. It's not true that the fundamental particles are Planck-sized. Planck units are obtained by dimensional analysis and their physical significance, if any, isn't clear. -- BenRG (talk) 07:39, 23 December 2010 (UTC)

The "empty space" inside each atom is perhaps 99.9999999999% or more of the "volume" of the atom (based on the atomic radius being at least 10,000 times the nuclear radius), but the space can hardly be described as "empty" because other atoms cannot normally enter it, and only certain particles can normally gain access. This analysis is not at all scientific, and has little basis in "reality", because each constituent particle in the atom has a calculable probability of being found at any point in this "empty space". In fact, each electron has a probability of about 1/3 of being found somewhere "inside" the Bohr radius. Dbfirs 12:53, 23 December 2010 (UTC)

They aren't particles, they're more like waves. There's some amplitude everywhere. As resuch, it's 100%. I think pretty much any particle has a chance of being anywhere in the universe. — DanielLC 22:37, 25 December 2010 (UTC)

Has anyone told electrons that they are not particles? Perhaps they need to change their behaviour? If all particles are waves and exist everywhere with a finite probability, then you meant 0% empty space, as discussed above. (I wasn't actually disagreeing with the statistical analysis, just trying to answer the question from the point of view of the Bohr model which seemed to be what the questioner wanted.) Dbfirs 08:34, 26 December 2010 (UTC)

Arsenic trisulfide's NFPA health rating

Why does arsenic trisulfide, one of the less toxic arsenic compounds, have "4" for its NFPA health rating while arsenic trioxide, an extremely toxic arsenic compound, has "3"? --Chemicalinterest (talk) 21:40, 22 December 2010 (UTC)

This may be a MSDS error. Thank you for bringing it to our attention. Please forgive the research delay necessary to answer. Ginger Conspiracy (talk) 23:10, 22 December 2010 (UTC)

One of my purposes here is to find and report errors in chemistry articles. I hope you all don't get annoyed at my often posting here. In the course of my work at Simple English Wikipedia (using this Wikipedia as a source) I come across errors that I fix or ask clarification. --Chemicalinterest (talk) 23:50, 22 December 2010 (UTC)

One of the difficulties of the NFPA system appears to be that for many compounds the classification is left up to individual suppliers or users, and may vary somewhat depending on quantities in use or other application-specific conditions.

• Stanford synchrotron: Health: 3, Fire: 1, Reactivity: 0
• Temarry Recycling of Mexico: Health: 2, Fire: 0, Reactivity: 0
• HazMat data: for first response, transportation, storage, and security by R.P. Pohanish: Health: 3, Fire: 0, Reactivity: 0
• NOAA Cameo Chemicals database: Health: 3, Fire: 0, Reactivity: 0
• Fisher Scientific: Health: 3, Fire: 1, Reactivity: 0
• our own article (needs citation?): Health: 4, Fire: 0, Reactivity: 2

I suspect that our article is overstating the hazard. Ideally, someone should check the relevant NFPA guideline (NFPA 704) and report back to us. TenOfAllTrades(talk) 01:24, 23 December 2010 (UTC)

If there is a conflict in reliable sources, my opinion is that wikipedia should list the most stringent (and link to it), but also include links to sources with lower numbers, perhaps with a footnote mentioning the discrepancy. Deciding on a number ourself is reasonable to avoid sources that are probably errors, but would otherwise be a violation of wikipedia policy. We should only do that if we can't find any good sources. Ariel. (talk) 02:55, 23 December 2010 (UTC)

I think it should list the one that makes sense, not necessarily the one that is most stringent. You can always rely on these people to make up something really scary-sounding. --Chemicalinterest (talk) 13:46, 24 December 2010 (UTC)

3-0-0 is a reasonable mid-point of the values listed above. 4-0-2 is ridiculous for this compound, and is clearly an outlier when compared with other sources. Physchim62 (talk) 09:51, 23 December 2010 (UTC)

If I may have an opinion, 3-1-0 would seem right as it is poisonous when left in air, burns when heated to around 300C, and does not explode or make other substances ignite. --Chemicalinterest (talk) 12:11, 23 December 2010 (UTC)

Does it actually burn? You can certainly roast it in air, but I can't find any reference to a self-sustaining reaction: in other words, as far as I can tell, if you take the heat away, the reaction stops. That would be a zero for flammability. Physchim62 (talk) 18:46, 23 December 2010 (UTC)

December 23

ASB THE POLYMATH- opc question

What is the chemical composition of OPC drum coating solution i.e. CTL liquid? what can I use to coat OPC drums at home? —Preceding unsigned comment added by 117.242.112.81 (talk) 09:28, 23 December 2010 (UTC)

It would help if you could explain what those abbreviations mean. StuRat (talk) 15:52, 23 December 2010 (UTC)

OPC seems to mean Organic PhotoConductor and CLP should be Charge Transport Layer. --Cookatoo.ergo.ZooM (talk) 21:09, 24 December 2010 (UTC)

I expect the OP is asking about how to make a Xerox copier. Cuddlyable3 (talk) 15:54, 25 December 2010 (UTC)

Two questions about lightning

1. Several years ago, I was in my apartment sitting in front of my computer. To my left was my stereo and to my right was my electric guitar and amp. Everything was plugged in. There was a sort of thunderstorm outside, nothing too heavy, but suddenly, there was a massive explosion of sound, but I never saw any light. As I sat there, time seemed to slow down, and in an extremely slow fashion, my entire body felt like it was expanding. I later described it to people as if every cell in my body had become a balloon and was being filled with a bit of air. I didn't move, either because I couldn't or because I wouldn't, and I honestly thought I was going to explode. But there was absolutely no pain. Just that uncomfortable feeling that lasted a few moments, and then my body "deflated" just as slowly. By the time I realized the situation was over, my computer was shut off. Everything was dead, and only the electric guitar still worked (half of the amp was destroyed, but it still worked on one insert). I've looked at the articles on positive lightning and lightning EMPs, and I've since done some research on Google, but I haven't been able to find any human recounts of physically witnessing an EMP. So my question is, was what I went through a lightning EMP of sorts? What was it doing to my body?
2. Back in the early 90s, I was backpacking through the US southwest during a storm. On the horizon, a strange bolt of lightning appeared. I cannot find an image of what it looked like (I've looked online for years), but imagine a straight bolt of lightning from sky to ground, but every few yards (massive estimation), the bolt expanded into a huge ball. There were three or four balls of light, like Christmas lights on a string, or popcorn on a necklace, within this bolt (or on this bolt), thus: ---O---O---O---O---. I keep running into ball lightning, but this wasn't a single ball of light moving around strangely. This was merely a bolt with a few glowing globs built in. The bolt acted like any bolt would: it appeared quickly, then faded quickly.

Any ideas on what it could be? Thanks for any help on this! Reflectionsinglass (talk) 09:28, 23 December 2010 (UTC)

Something like this: Transcranial magnetic stimulation may be related to what happened to you. This is interesting too: Ball lightning#Transcranial magnetic stimulation (and a nice synchrony with your next question). Regarding #2 the first thought that came to mind was birds :( - the bolt may have traveled from bird to bird before hitting the ground, and each bird burst into flame (I hope they died quickly :( Was the storm very sudden? I assume birds normally take cover during a storm. Another idea: Cosmic rays are hypothesized to stimulate lightning[5] strikes, maybe it was a meteor? It's possible that could do it too (but I've never actually heard or read anything to suggest that, so it's speculation only). Ariel. (talk) 09:47, 23 December 2010 (UTC)

For #2, perhaps it was Bead Lightning? Or perhaps it was more an optical effect, due to over-saturation of your retina? -- JSBillings 14:13, 23 December 2010 (UTC)

For 1), I wonder if it wasn't so much the effects of an EMP on your physiology that you experienced as it was a startle response that you experienced when you heard the massive explosion of sound. Was that thunder, or did it come from your amp and speakers before they blew? WikiDao ☯ (talk) 20:02, 23 December 2010 (UTC)

Simpler causes than EMP for the subjective effects the OP reports might be tentatively confirmed or eliminated by taking an EEG test. In the hospital procedure, strobe light may be used to stimulate a possible abnormal (epilepsiform) response. Cuddlyable3 (talk) 15:51, 25 December 2010 (UTC)

Light

Does light can be used disturb the moving particle be any metal or nonmetal (car, fish, ball,etc) because of its dual character in nature (as particle cum wave)? Please provide me is it possible? isn't it. (or) How it can be possible? (else) Any other suggestions regarding it. Kanniyappan (talk) 10:52, 23 December 2010 (UTC)

Light can move an object because light has momentum like anything else. But it's not because of the dual character of light. Just like if you throw grains of sand at something you can move it, you can do the same with light - but light does not weigh very much, so it barely moves the object. But light does move single atoms quite well, since atoms weigh so little. How well do you read English? I can link to some articles about this, the main ones would be solar sail and Radiation pressure, the others would be Momentum of photon and laser tweezer, but those are harder to read. Maybe this version is easier? simple:Radiation pressure. Ariel. (talk) 11:07, 23 December 2010 (UTC)

One clarification, a photon has no rest mass, so it's not like sand in that way. It does, however, have the equivalent to mass due to it's speed (the speed of light, of course). This is a result of relativity, which is difficult to explain (perhaps someone else will try). And, of course, both waves and particles can do work, so either model of light can explain why it can move objects. StuRat (talk) 15:47, 23 December 2010 (UTC)

(ec) In fact, light weighs exactly zero - its mass is exactly zero. A photon can have momentum, because in the relativistic treatment, momentum is not exactly equal to (mass × velocity) as it is in Newtonian mechanics. In fact, we have an article/section on relativistic momentum which explains this well. In mathematical terms, relativistic momentum is defined by a Lorentz transform; in "laymans' terms", you can simply understand that even a massless particle (such as light) can carry momentum and cause another massive particle to "move" after a collision. The simplest worked example is called Compton scattering, in which incident light hits matter and exchanges momentum and energy with an electron. The equations that define Compton Scattering are explained in our article; depending on the energy of the incident light, it can cause total ionization of an electron. More sophisticated light/matter interactions are described in detail by other processes; the photoelectric effect is one of the more practical uses of light impinging on matter. Nimur (talk) 15:53, 23 December 2010 (UTC)

You said: "in "laymans' terms", you can simply understand that even a massless particle (such as light) can carry momentum and cause another massive particle to "move" after a collision". That doesn't seem intuitively obvious, to me. In fact, I would assume the opposite, based on lighter objects causing proportionally less movement. StuRat (talk) 21:22, 23 December 2010 (UTC)

I make no assertions that any of that is intuitive or obvious - but it is correct and is the way that light interacts with matter in this universe. If you want to get an intuitive feel for relativistic light/matter interaction, all I can suggest is to spend a lot of time working with experimental setups that exhibit this momentum property of photons, and after you see the experimental results turn up the same way a whole lot, they will seem perfectly "normal" and intuitive to you. Or, if you are not the type who wants to independently verify such things, you can accept this fact on faith and trust myself and the many physics textbooks that attest to its veracity. Nimur (talk) 21:46, 23 December 2010 (UTC)

I'm not doubting that it's true. After all, I said as much in my first post. I'm just saying it's not intuitive. StuRat (talk) 00:06, 24 December 2010 (UTC)

BTW there is a reason I did not mention the massless nature of light, and that's because while it obviously has zero rest mass, while it's traveling it does have mass, inertia, momentum and everything else a massy particle has. And except for its refusal to change speed it acts exactly like something with mass. And even the zero rest mass thing is just another way of saying that when it doesn't exist it doesn't have mass. Remember that when light stops the mass doesn't disappear (zero rest-mass) the mass gets deposited onto whatever stopped the photon and the photon is converted into something else. Pretty much the only implication of zero rest-mass is that it travels exclusively at the speed of light, and the implications of that are beyond the scope of the original question. Ariel. (talk) 22:18, 23 December 2010 (UTC)

Thermoelectric

Can u please give me the emf induced and current flowed when thermoelectric couples of zinc and copper wires kept with 5°C of change in junction temperatures between hotter and colder junction kept at a distance of one meter? Please give also any other thermocouples gives more emf or current for the same standards mention above.Kanniyappan (talk) 11:04, 23 December 2010 (UTC)

The Seebeck coefficient of a metal isn't quite constant, but in the 0-100°C range, it's about 3.4μV/K for zinc, and about -1.8μV/K for copper.[6] So from the second equation in the article section Thermoelectric effect#Seebeck effect, a zinc/copper thermocouple with a temperature difference of 5°C will produce an EMF of about 26μV (with no load).

The current produced would depend on the load, as per Ohm's law. For very low-resistance loads, the non-zero resistance of the wires would need to be taken into account, and for that, you'd need to specify the cross-sectional area of the wires used, so that the resistance of the wires can be computed from the resistivity of zinc (59.0nΩm) and copper (16.78nΩm).

For materials that exhibit the thermoelectric effect more strongly, see Thermoelectric materials. Red Act (talk) 17:54, 24 December 2010 (UTC)

Dragon's breath

It's been very cold here in Blighty lately and this has had me wondering. Is there a specific temperature at which dragon's breath appears? (when you can see your breath when you exhale on a cold day). --TrogWoolley (talk) 14:28, 23 December 2010 (UTC)

The short answer is 'it depends'.

The longer answer is, it depends on the current relative humidity, ambient temperature, and local wind. The air that you exhale is going to be fairly close in temperature to your core body temperature (it just came straight from your lungs, after all) and at close to 100% relative humidity at that temperature. What that means is that the dew point for that air – the temperature at which the exhaled air is supersaturated with moisture and capable of precipitating out liquid water droplets as fog or dew – is just a few degrees below your body temperature. So, if that's true, why is it that you don't see a cloud of fog all the time?

First, when air saturated with moisture is chilled, droplets don't form instantaneously; the process takes some time to occur, and often relies on the presence of nucleation sites (little bits of dust and whatnot) in the air to kick the process off. Nucleation and droplet formation are faster when the temperature is further below the dew point and the air is more supersaturated, so visible fog formation is more likely in chillier air.

Second, fog is forestalled if the supersaturated air is diluted rapidly to a non-saturated state. If there is rapid, turbulent airflow (blustery wind!) in front of your face, then the exhaled supersaturated air is mixed quickly with very unsaturated ambient air and no droplets form. Finally, the effectiveness of this dilution is going to depend on how much water there is the air around you. If the ambient air is nearly saturated with water, then you need to mix a much greater volume of it with your breath to dilute the resulting blend down to an unsaturated state — if the ambient relative humidity is high, you'll be able to see your breath much more readily than under conditions of low humidity. (Under low-humidity conditions, any droplets that do form will also evaporate and disappear much more rapidly.) TenOfAllTrades(talk) 15:30, 23 December 2010 (UTC)

Good answer. One other thing I would add is that lighting conditions matter. The ideal lighting condition would be darkness with a sunbeam right on your breath, so that the lighted water droplets stand out against the darkness. On the other hand, if the sunbeam is in your eyes, and not on your breath, you may not see your breath. StuRat (talk) 15:42, 23 December 2010 (UTC)

I wondered the same thing and actually tried to work it out myself. To give a "rough" answer, where I live in Melbourne Australia, under the conditions that were present when i conducted my experiments, I found the temperature to be around 11 or 12 degrees (EDIT: Celsius) when I could begin to see my exhaled breath. I however have no idea how much that could vary depending on the other conditions mentioned above, such as humidity. Vespine (talk) 01:12, 24 December 2010 (UTC)

Resolved

- thanks guys! --TrogWoolley (talk) 11:15, 24 December 2010 (UTC)

is flow of holes called current flow?

flow of electrons is called as the current flow, but whereas the holes are also moving from the p region to the n region. Then why can't we say that the flow of holes is called as the current flow? —Preceding unsigned comment added by 117.197.186.12 (talk) 17:41, 23 December 2010 (UTC)

Hole flow and electron flow are just two ways to look at the same thing. If a hole flows one way, it means that an electron went the opposite way. Some people find it easier to think in terms of hole flow. Some find it easier to think in terms of electron flow. -- kainaw™ 17:46, 23 December 2010 (UTC)

Perhaps see conventional current (which redirects to the conventions section of current but seems to say it nicely). RJFJR (talk) 18:04, 23 December 2010 (UTC)

Climate change and biodiversity

People keep on warning about the "devastating" effects global warming could have on biodiversity, yet the geological past and present of our planet points to the contrary. We should take into account three main things:

• In periods such as the Eocene, global temperatures were much higher than today, just like biodiversity. Biodiversity has been declining ever since the world started to cool in the Miocene. Therefore, warmer climates are more conducive to a high biodiversity.
• Biodiversity hotspots in all the world are concentrated in warm areas, whereas polar areas are much poorer. It's better to lose a small percentage of species to global warming than a large percentage to global cooling.
• It is naive to believe that, if we don't alter the climate, it will stay the same forever. If the climate doesn't warm up, we're headed straight for a new glacial period which really won't do much good to biodiversity.

Why do people continue to consider climate change bad? Are there any factors I haven't thought of (not counting hippyish, kumbayah-irrational arguments). --79.89.248.148 (talk) 19:08, 23 December 2010 (UTC)

I think the problem are the speed of change. I think fast climate change in any direction is one cause for mass extinction events. Diverse ecosystems move very slowly and many will be extinct be cause of the climate change. It is possible that the biodiversity would be greater after some millions of year with higher temperature but most predictions relating to AGW take a shorter time scale of millennias or less. Of course will the climate continue to change what ever we do but the AGW are faster than most natural changes. --Gr8xoz (talk) 19:41, 23 December 2010 (UTC)

In addition to the speed of the change, it's a matter of changing the climate to something we aren't used to, or prepared for. Sure, many plants and animals will thrive, but our coastal cities will all be flooded by rising sea level, and Europe will lose the Gulf Stream and become as cold as it really should be, at that latitude. Much more severe hurricanes will make living near the US Gulf or Atlantic coasts a bad idea, and tornadoes will do the same for the Central Plains states of the US (and soon Canada). So, if we all are willing to move north and inland, then we can survive. But considering the portion of humanity that lives in warm areas or near the sea, that's a tall order. Also, some species, like polar bears and certain penguins, may become extinct, because the climate to which they have evolved will no longer exist. StuRat (talk) 20:29, 23 December 2010 (UTC)

I encounter conceptual problems with Biodiversity#definitions and Biodiversity#Human_benefits. Are we trying to save and promote the diversity of the megafauna (i.e. pandas, which are largely decorative), the microfauna (which we depend on), or the humans? These lead to different notions of "diversity" - for instance, does "diversity" include the diversity of diseases hostile to humans and injurious to our food supply? Do we score the pandas higher than worms because they're bigger, or lower than worms because they're useless (not even doing much good for their own ecosystem), or equal because they're a species? Is preserving an animal in a zoo, or a seed in a seedbank, a valid way of preserving biodiversity, or does the biodiversity have to be active in an ecosystem, and if so, for what reason? So you end up with political and philosophical questions about what sort of world is a good world, and how we view ourselves. Are we concerned about biodiversity because a lack of genetic variation might spoil our plans to turn the world into a massive farm, or because it might spoil our plans to turn the world into a massive garden, or just because we like genes for their own sake? Like Gr8xoz says, are we worrying about the next thousands of years, or the next billions of years? Different agendas produce different definitions of "harmful". 213.122.23.52 (talk) 07:52, 24 December 2010 (UTC)

Why exactly do you say 'we'? What use are you to me? I'm more interested in pandas than I am in you. Dmcq (talk) 10:24, 25 December 2010 (UTC)

drug

are there any stimulant drugs that are not also vasoconstrictors — Preceding unsigned comment added by Kj650 (talk • contribs) 19:43, 23 December 2010 (UTC)

Modafinil, and most of the racetams. Vasoconstriction is a peripheral side-effect of adrenergic drugs, therefore the more readily the drug crosses the blood-brain barrier, the less likely it is to cause vasoconstriction. There are also drugs which act independently of the adrenergic system, such as dopamine reuptake inhibitors, dopamine agonists, certain nicotinic agonists, histamine agonists (or H3 receptor inverse agonists/antagonists) and drugs which stimulate orexin receptors/release. --Mark PEA (talk) 20:12, 23 December 2010 (UTC)

isint cocaine a dopamine reuptake inhibitor and a vasoconstrictor — Preceding unsigned comment added by Kj650 (talk • contribs) 21:03, 23 December 2010 (UTC)

Yes but it's also a noradrenaline reuptake inhibitor, which is probably responsible for this effect. (It also inhibits serotonin reuptake, and these drugs are normally referred to as triple reuptake inhibitors). --Mark PEA (talk) 18:16, 24 December 2010 (UTC)

Beer pong

In beer pong, if the ping pong is spinning along the sides of the cup, blowing will cause the pong to rise out of the cup. Why? And if I take a glass half-way filled with juice and turn it over, with a piece of cardboard covering the top, the liquid won't fall...what's the reason for this? Thanks. 65.92.7.244 (talk) 23:49, 23 December 2010 (UTC)

I think first is bernoulli effect. See the experiments here: [7]. The second is because the piece of cardboard would have to move downward, decreasing the pressure in the glass, and that causes the higher pressure under the cardboard to push it back up. StuRat (talk) 00:05, 24 December 2010 (UTC)

Place a sheet of paper or a playing card on a flat smooth table and blow lightly along the table - you can make the paper float. It's the same principle and it's called Bernoulli's principle and is quite similar to the venturi effect. Ariel. (talk) 00:38, 24 December 2010 (UTC)

I'm still having trouble seeing it. Bernoulli says that the pressure created by fast moving fluid is less than that of slow moving fluid. But where is the fluid traveling faster? If the ball goes up, then it should travel faster above the ball, but why would it? 65.92.7.244 (talk) 02:06, 24 December 2010 (UTC)

Because when you are blowing above the ball, the air is now moving faster above the ball, so the pressure drops above the ball. --Jayron32 03:22, 24 December 2010 (UTC)

But isn't it also moving faster under the ball? And if not, why does blowing air underneath a ping pong ball keep it up? 65.92.7.244 (talk) 04:31, 24 December 2010 (UTC)

You are confusing two slightly different things. Air moving directly at the ball will move it; air is matter, and matter in motion has momentum, and it can transfer that momentum to the ball. Hence, blowing directly under the ball will cause it to move up. However, blowing past the ball, as in not directly at the center of the ball, but such that the air moves past the ball, will cause the pressure to drop. There is an INCREASE of pressure in the direction of airflow, that is in front of the puff of air, and an equivalent DECREASE of pressure perpendicular to the air flow. The trick is to blow NEXT to the ball (i.e. very close to it) but not AT it, so that the air moves past the ball, but not at it. --Jayron32 04:36, 24 December 2010 (UTC)

What!? air pressure, bernoulli's principal!? Try this: take a cup and hold it a couple inches from your mouth, now blow in it. What do you feel? Your own breath blowing back in your face! The air has no where to go but out. if you are still confused put some salt in the cup and do it again. Why didn't the salt stay in the cup?????? —Preceding unsigned comment added by 165.212.189.187 (talk) 14:56, 24 December 2010 (UTC)

December 24

When two metal panels with different work functions approach, what happens?

When two metal with different work functions approach but still is seperate finally, will their surface produce opposite charge (+, and -) when at equilibrium? and will their Fermi levels line up finally?

Another similar case, when a thin oxide is sanwiched by a metal and a semiconductor, if the metal and the semiconductor with different Fermi levels, do their Fermi levels equalize when at equilibrium? --Wkfan (talk) 03:18, 24 December 2010 (UTC)

Why do superstrings "vibrate"?

What causes them to vibrate? Have they always been eternally "vibrating" or does something initially "pluck" the string to get it going? Can they ever stop vibrating? and if so what would happen then? In layman's terms please. (I'm a layman so if these questions doesn't make much sense it's probably because I'm misunderstanding some aspect of the theory :) -- œ^™ 05:17, 24 December 2010 (UTC)

It is better to think of superstring theory as a model used to represent physical reality. Like all models, it is an explanation of reality, and not reality itself. That is, these "strings" are not strings in the literal sense, which need to be plucked in order to vibrate. Rather, the attempt is to represent matter by vibrating strings, insofar as the mathematics of resonance seems to apply to the way in which fundemental particles interact. Using "standing waves" as a model for fundemental particles actually predates superstring theory by some time, for example the Schroedinger equations and wave functions are a much older model used to explain the behavior of the electron cloud in an atom. Superstring theory is in some ways expanding upon these earlier models to a more fundemental level. --Jayron32 05:24, 24 December 2010 (UTC)

A string in a frictionless environment would continue to vibrate forever. They likely existed (and vibrated) since the Big Bang, but all bets are off for what existed before that. StuRat (talk) 06:43, 24 December 2010 (UTC)

Vibration, also known as harmonic oscillation, shows up everywhere in physics. In quantum theories, because of the uncertainty principle, the vibration can never stop completely, so everything vibrates (though this "vibration" is a bit different from what you might think of as vibration in a non-quantum world). String theory is a quantum theory, and because it's possible, geometrically, for string-shaped objects to vibrate, they always do. That property of universal vibration isn't new to string theory, nor is it a particularly important aspect of string theory. The reason it's emphasized in popularizations is that they don't know what else to talk about. Explaining what string theory is really about would be too confusing, so they fall back on showing vibrating violin strings, even though those could just as well illustrate any physical theory from the last few hundred years. -- BenRG (talk) 23:13, 24 December 2010 (UTC)

makeshift loudspeaker

I'm a little confused by this: http://www.youtube.com/watch?v=oGrlz6t28XE

If the sound is being caused by the bottle vibrating, then why is it still making sound when: 1) he is holding it, and 2) when he holds it near the magnet, but not on the table? Thanks. 65.92.7.244 (talk) 08:08, 24 December 2010 (UTC)

At normal frequencies the sound is not from the bottle knocking on the table. The sound is from the bottle directly shaking the air, which causes sound waves that you can hear. Earlier, he ran it at a very low frequency of 5 hz (times per second), which is far too low for you to hear. So what he did is make the bottle knock into the table and you heard a knocking sound each time. Notice how at 5 hz you hear a series of tick, tick, tick, rather than a pure "tone". But at higher frequencies you are actually hearing those tones. Excellent question BTW. Ariel. (talk) 09:52, 24 December 2010 (UTC)

See the Wikipedia article Voice coil.

1. The source of the sound vibration is the wire that is attached to the bottle neck. The vibrations travel through the bottle material at the speed of sound in the plastic. Holding part of the bottle does not prevent other parts of the bottle vibrating.
2. The wire must be close to the magnet to be within its magnetic field for the motor effect to work. The resulting music sound is weaker but less distorted when the bottle is suspended slightly above the magnet so the downward swings of the sound vibration won't cause the bottle to hit the metal plate. Cuddlyable3 (talk) 15:15, 25 December 2010 (UTC)

Heavy luggage in small, light car

Where would the best place be to put heavy luggage (huge bags of books in this case) in a small, light car (Hyundai Atos). I put it in the trunk but it seemed to put tremendous strain on the rear suspension so I was hoping someone with the knowledge on this could help me out. I don't want to break my car but I also want to have the best fuel economy. Would the position of the heavy luggage have an effect on the fuel economy whatsoever? I'm just a student and I need to travel far so that's why I'm so curious as to where to put the bags in order to save money! :O 196.210.239.252 (talk) 11:22, 24 December 2010 (UTC)

For fuel economy I don't think the position will matter much. You use extra fuel because you have to work harder to accelerate the extra weight. But for handing purposes try to balance it evenly front to back, too much weight in the back can severely hurt handling and breaking power, too much in the front is not as bad, but still bad. Also, you will need to add extra air to the tires - besides needing to do it to keep from damaging the tires, this will also help you save money. As for how much air, I can't check the numbers for you right now, but find out how much your car weighs, and how much pressure you normally need, then divide to find pressure/weight, and then calculate that for the extra weight. Ariel. (talk) 11:35, 24 December 2010 (UTC)

Anywhere between the wheels is good. You should avoid putting heavy weights beyond the wheels, as that will cause it to handle poorly. StuRat (talk) 18:08, 24 December 2010 (UTC)

Unladen weight of the Hyundai Atos is quoted as 847 kg. It is a 4-seat car so should be within its limits carrying the equivalent weight of 4 heavy adults. Recommended tyre pressures are 30 PSI front and rear. Do check the car handbook. Cuddlyable3 (talk) 14:46, 25 December 2010 (UTC)

meningiomas (a.k.a. brain tumor;angle tumor)

Periodically I search the internet for any mention of connection between meningiomas (a.k.a. brain tumor;angle tumor)and either estrogen or progesterone receptors. I was surgically treated for such a tumor in 1991. In 1998 I was told of 'recurrence'(that word is significant in my opinion,based on research). I went to Mass Genl for radiation treatment.In making usual/customary rounds for various physical exams, it was the endocrine/ob-gyn doctor who inadvertently and casually mentioned that said tumor in my case had progesterone receptors. She didn't seem to notice my shock when I said 'what?'. "yeah, she said, they see these types of tumors all the time during autopsies, they're very common. They become problematic when they grow too large and progesterone can make one with progesterone receptors grow."

I was prescribed and took progesterone (the so-called "bioidentical good kind from Women's International Pharmacy in Denver, Co.) It was prescribed for reasons not at all 'cosmetic' or superficial. I began taking it in the mid 1980's and contimued taking it after meningioma surgery in 1991. I stopped taking it after I left the informing doctor's office that same day.

While surgeon told me he removed it all, his written record stated that it was "unlikely due to the very vascular nature of the tumor". Ir follows, with some logic I would say, that continuing to take progesterone would cause further growth, hence future problem (these tumors are slow growing). In the late 1990's *Mifeprestone (a.k.a. RU486, the abortion pill;a.k.a. "anti-progesterone") was used in clinical trials to treat meningiomas. I may have misspelled *it. While it met with significant success, there were other strange blocks(of the political and/or greedy types and tones) to making it available to those in need (many with much more frightening alternative choices,if any choice at all). My most recent search (12/23/10 revealed a brief reference to mifeprestone as treatment modality, but required much digging to get to that partial one line reference.

To this day, I cannot find anywhere by anyone any straigtforward, clear mention of this connection as I have described it. I tell every female with whom I cross paths-they 'hear' me with considerable attentiveness; I've written everyone I deem 'should know and disclose'-I know of no response or interest. I have mentioned it to every doctor/healthcare provider with whom I come into contact (most of whom not even visibly moved enough to shrug a shoulder). The kind of empty eyed void or twilight zone experience I have come to call the 'Is it just me? Am I crazy?-game. Or, why isn't 'logic' a required course?

After telling this to my dentist's assistant, she responded by telling me that during a conversation between her mother and Assurant Health Insurance Company, the rep told her mother that she was considered 'disposable'.

Can someone broaden my understanding of this?11:35, 24 December 2010 (UTC)Wastetime4info (talk)

We have a very small article on it Hormone receptor positive tumor. Nothing in the article limits it to breast, but all of the references mention that. Mifepristone may help, but nothing in there mentions cancer. This article seems to match what you wrote - it mentions meningiomas (but I did not read it), maybe it will help you. You can continue searching for articles using this search. Adding meningiomas to the search comes up with lots of stuff. You will not have access to read many of the articles, but your local public or university library probably will have a subscription, so you want to search from there. Ariel. (talk) 12:19, 24 December 2010 (UTC)

Edit: In the article meningiomas I found "Antiprogestin agents have been used, but with variable results." So it could be they did think of it - but it didn't help much. Ariel. (talk) 12:24, 24 December 2010 (UTC)

..and the source used in that article, which you may have already seen says "About 70% of meningiomas express progesterone receptors, while fewer than 31% express estrogen receptors. These observations suggest that progesterone influences tumor growth. A progesterone antagonist such as mifepristone therefore may inhibit tumor growth." This study has something to say about hormonal exposures and risk so it may be of interest if you haven't seen it before. Sean.hoyland - talk 12:47, 24 December 2010 (UTC)

To the OP: background information/observations combined with logic are the first two steps to developing a good hypothesis. However, the field of medicine generally requires more than a good hypothesis to justify treatment decisions (hence, the 'logic' course you mention is not part of the regular medical curriculum). The next step is to generate data that supports or refutes that hypothesis. There seems to have been a reasonable amount of research into whether or not hormone exposures are truly a risk factor for meningioma (see [8], [9], [10], [11], [12], and a meta-analysis of different studies here). The overall result of those studies seems to be that hormone exposure plays a minimal role in the development of meningiomas, if at all.

The next thing you are interested in is whether (based on the progesterone receptor expression in meningiomas) a treatment based on progesterone blockade, using mifepristone (RU-486) would be a good treatment. This is another excellent hypothesis, but one for which there is again no strong evidence. The best I could see was a recent study (here) that looked at long-term effects of mifepristone. The main outcome measures were tolerability and side effects, and I don't think the study was specifically designed to look at treatment outcomes. However, they did mention "minor responses" in a subset of patients (8 out of 28 treated). Altogether, it seems as though (despite the good hypothesis) progesterone blockade hasn't proven to be an effective treatment for meningioma. --- Medical geneticist (talk) 13:44, 24 December 2010 (UTC)

Testosterone levels

Does the Testosterone level in a male human body change after ejaculation? --119.155.10.188 (talk) 11:56, 24 December 2010 (UTC)

Usually, although the extent likely depends on mental health. See PMID 16871136. Ginger Conspiracy (talk) 23:22, 24 December 2010 (UTC)

The PMID reference is about treatment of sexual dysfunction in patients with epilepsy and depression but it does not seem to address the OP's question about change in hormone level after ejaculation. Cuddlyable3 (talk) 21:12, 25 December 2010 (UTC)

So normally would the level increase or decrease in an average human? --119.155.18.241 (talk) 14:50, 25 December 2010 (UTC)

Mercury's mineral status

Is native mercury a mineral? I have a cite [13] to back up my claim that it is a mineral, but nonmineral "uncitedly" states otherwise. Is it a mineral? --Chemicalinterest (talk) 17:28, 24 December 2010 (UTC)

Your reference does not exactly address the question of what is, and is not, a true mineral. According to the mercury article mercury is rarely found as a native metal. I notice your source also lists iron, which afaik, is never found as a native metal. SpinningSpark 18:16, 24 December 2010 (UTC)

I don't know how it is classified, but it is possible to find natural deposits of metallic iron (typically as micron to millimeter sized grains). It can form when iron bearing minerals are heated to high temperatures in the presence of abundant carbon and with very low levels of oxygen. A typical example is when a coal seam is set on fire by lightning or magma intrusion. Not exactly a common scenario, but such things do happen. Dragons flight (talk) 19:11, 24 December 2010 (UTC)

Chemicalinterest wasn't asking whether or not it commonly forms naturally; he was asking whether or not it would be a mineral. According to our article, "A mineral is a naturally occurring solid chemical substance that is formed through geological processes and that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties". So the answer is yes. --T H F S W (T · C · E) 21:06, 24 December 2010 (UTC)

Sorry for being so dense! "A mineral is a naturally occurring solid chemical substance". So I geuss no, if you stick to the rules. However, native copper of gold would be a mineral. --T H F S W (T · C · E) 21:20, 24 December 2010 (UTC)

Where's your citation for the "fact" that a mineral is solid? --Chemicalinterest (talk) 22:21, 24 December 2010 (UTC)

Here. --T H F S W (T · C · E) 22:31, 24 December 2010 (UTC)

THFSW, your reference explicitely states "Mercury, however, is recognized as a mineral even though it does not occur in a crystalline state on Earth". And maybe it does occur in a crystalline state sometimes: Temperatures at higher latitudes are sufficiently low - at least in the winter. Icek (talk) 23:44, 24 December 2010 (UTC)

Your source supports my source. It proves that mercury is a liquid mineral. --Chemicalinterest (talk) 00:40, 25 December 2010 (UTC)

Well, from whatever I posted on simple talk, if correct, that's not the case. native mercury = mineral. Liquid mercury = not a mineral. wiooiw (talk) 07:43, 25 December 2010 (UTC)

Native mercury is liquid mercury. Mercury does not exist in a crystalline state on Earth. Look! What needs to be found out is whether mercury (its status of liquid is given) is a mineral. --Chemicalinterest (talk) 13:07, 25 December 2010 (UTC)

Could we agree that mercury is a mineraloid, and a mineral when it is very cold? Dbfirs 20:40, 25 December 2010 (UTC)

As far as Britannica is considered, Native Mercury is a mineral, but liquid mercury does not fit the definition of a mineral, but a mineraloid. wiooiw (talk) 22:25, 25 December 2010 (UTC)

Huh, I found this and this to be quite useful. It reviews older definitions of "mineral". It appears that Brittcanica uses and older version of the definition, thus really is not a valid source to use. So, liquid mercury is now a mineral? wiooiw (talk) 23:46, 25 December 2010 (UTC)

Well, let's look at the official CNMNC guidelines (my italics):

A mineral substance is a naturally occurring solid that has been formed by geological processes, either on earth or in extraterrestrial bodies (Nickel 1995a). A mineral species is a mineral substance with well-defined chemical composition and crystallographic properties, and which merits a unique name. General criteria for defining mineral species are given below. In practice, most mineral species conform to these criteria, but exceptions and borderline cases inevitably arise, and ultimately each proposal to introduce a new mineral species or to change mineral nomenclature must be considered on its own merits.

Now looking at the official IMA-CNMNC List of Mineral Names, we see that native mercury is "grandfathered", that is its "original description preceded the establishment of the CNMNC in 1959, and [it is] generally regarded as a valid species". The only conclusion that one can draw is that the IMA considers native mercury to be an exception to the normal rule that mineral species should be solid. Physchim62 (talk) 00:08, 26 December 2010 (UTC)

Yes. THFSW's reference stated the same thing, but gave native mercury (a liquid) as an exception to the rule. --Chemicalinterest (talk) 12:21, 26 December 2010 (UTC)

December 25

Astronomy question

Approximately what day of the year would the earth cross an imaginary line connecting the sun and the center of the Milky Way galaxy? 76.27.175.80 (talk) 00:33, 25 December 2010 (UTC)

Our Galactic Center article says that it lies in the direction of Sagittarius A*, which is on the border of the constellations Scorpius and Sagittarius. According to our Zodiac article, the Sun enters that region with respect to Earth in the early weeks of December. The Earth would therefore be on the opposite side of the Sun, ie. between the Sun and the Galactic center, half-a-year from then, or in early June. WikiDao ☯ (talk) 04:28, 25 December 2010 (UTC)

White copper peroxide

Is it true that a white and highly explosive copper peroxide can form on copper if it is exposed to air too long? --Chemicalinterest (talk) 01:46, 25 December 2010 (UTC)

Logically, that can't be true, because lots of copper is exposed to air, and it doesn't turn white or become explosive, it acquires a green patina. So, copper + air alone doesn't do it. StuRat (talk) 02:03, 25 December 2010 (UTC)

Here is a description of how to make copper peroxide: [14]. It seems to be reddish orange, not white, and there's no mention of it being explosive. StuRat (talk) 02:07, 25 December 2010 (UTC)

Hrumph. Section 10: Stability. This as well. There are some others. --Chemicalinterest (talk) 12:57, 25 December 2010 (UTC)

I don't understand. Since copper metal stands outside on roofs and such for long times, why don't they all explode, then ? StuRat (talk) 04:10, 26 December 2010 (UTC)

Maybe the rain dissolves the peroxide to make oxygen and copper oxide. But how did they get this into all their MSDS's? --Chemicalinterest (talk) 21:42, 26 December 2010 (UTC)

Species names by C. Linnaeus

How many names are unchanged since C. Linnaeus: Homo sapiens, Lemur catta, Hippopotamus amphibius, what else? Can we include that somehow in 10th edition of Systema Naturae or it's subarticles? --Eu-151 (talk) 13:05, 25 December 2010 (UTC)

Because of the Principle of Priority, many plants and animals retain the binomial names given by Linnaeus. If you look at the "What links here" page for his article (especially the links to the disambiguation page "Linnaeus"), you will find quite a few such plants and animals among the entries, as you can see by looking at their articles' infoboxes. Deor (talk) 14:11, 25 December 2010 (UTC)

Arun S Bagh question about opc drum

The original post attempted to include an image but failed to upload properly; I have removed the broken wikisyntax. Arun, please see the instructions for uploading an image, and retry posting your picture/question. Nimur (talk) 16:08, 26 December 2010 (UTC)

Are are you trying to post an image using the local file path instead of an image hosting service? That's not going to work. 81.131.30.210 (talk) 13:54, 25 December 2010 (UTC)

Here are many pictures of opc drums in case the drum type you ask about is already posted there. Cuddlyable3 (talk) 14:18, 25 December 2010 (UTC)

earth flip

I heard that the earth flips its axes where the north pole becomes the south pole. My questions are, 1. would this be notice able or will the earth do it slowly. 2. will this cause earthquakes to happen. 3. what would the climate of europe be like particularly around Ireland and britain. 4. Will it cause climate change. —Preceding unsigned comment added by 213.94.236.7 (talk) 19:44, 25 December 2010 (UTC)

I think you have some misconceptions about the switch you're thinking of. I suggest you start off at Geomagnetic reversal (which has a short Geomagnetic reversal#Effects on biosphere and human society) and come back with any questions. Nil Einne (talk) 19:50, 25 December 2010 (UTC)

Yes, the OP is surely thinking of the Earth's magnetic not geographic poles. Geomagnetic reversal#Effects on biosphere and human society notes a few speculations but we can't predict answers to questions 1 to 4. Cuddlyable3 (talk) 20:39, 25 December 2010 (UTC)

To clarify: the Earth doesn't move. The Earth's magnetic field moves. --Tango (talk) 21:16, 25 December 2010 (UTC)

There is also a fringe theory that the Earth's axis itself moves significantly: see Cataclysmic pole shift hypothesis. I don't know of any serious geologist who believes that the pole shifts a significant amount. There is, however, True polar wander: the Earth's axis of rotation wanders about on the surface of the Earth, at apparently no more than 1 degree every million years, or so. Insignificant on human timescales, but important on stellar time scales (it's thought, evidently, that Europa (moon)'s pole has shifted about 80 degrees). There is also Precession and Nutation, where the location of Earth's pole on the ground doesn't change, but the axis shifts relative to the stars. Buddy431 (talk) 23:01, 25 December 2010 (UTC)

No, it's a real worry that it's going to hit us in "about 1.5 billion years" Axial tilt#Long period variations Hcobb (talk) 05:07, 26 December 2010 (UTC)

Oh, well that saves me worrying about the sun becoming a red giant and consuming the earth, because that won't happen for five billion years! Dbfirs 17:09, 26 December 2010 (UTC)

Ungulate reptile/(amphibian/bird/...)

I (by chance) met Stegosaurus ungulatus on the Stegosaurus page. Although it is a nomen dubium and usually united with S. stenops? (or armatus?), it shouldn't have it's specific epithet with no reason. And I read about a "blunt hoof" on Stegosaurine feet. Now my question: 1. Were any reptiles, especially any Dinosauria (improbable: amphibians, birds, synapsids,...), truly hooved? What about genera like Giraffatitan, Paralititan, Argentinosaurus and how the giants are called some had horns (Ceratopsia), but were there any hooved ones? Would hooves preserve in fossils? If they exist, can we cover hooved dinosaurs and their being hooved in a matter to Ungulate? Why are no dinosaurs (except for the one nomen dubium S. ungulatus) namend after being hooved? — Preceding unsigned comment added by Eu-151 (talk • contribs) 21:36, 25 December 2010 (UTC)

A proper hoof is basically a modified toenail; I don't think that any animal group besides the true ungulates walk on hoofs. --Jayron32 22:00, 25 December 2010 (UTC)

Magnet

I got a 250 pound lifting capacity magnet for Christmas. What can I do with it? I noticed that when I get close to my computer with it, the magnet changes the computer's screen color. Why? Also, I noticed that I can screw up AM radio with it. Why? Will this do any damage to the computer? Albacore (talk) 22:23, 25 December 2010 (UTC)

I'm assuming your computer has a CRT monitor? This gives a very detailed explanation for why magnets effect CRT screens. Also take a look at the Degaussing article which is related. Yes, it can sometimes permanently damage the screen. —Preceding unsigned comment added by 82.44.55.25 (talk) 22:57, 25 December 2010 (UTC)

One wonders why you got a magnet that can lift 250 lbs for Christmas if you didn't have any use for it...206.116.252.164 (talk) 01:31, 26 December 2010 (UTC)

A powerful magnet too close to your computer can also destroy your computer's hard drive; see Degaussing#Irreversible damage to some media types. Red Act (talk) 02:24, 26 December 2010 (UTC)

Agreed. Also, any magnetic media, like diskettes or tapes, could be damaged. StuRat (talk) 04:04, 26 December 2010 (UTC)

I'd be mighty careful with that. You may want to store it well away from all of your electronic devices. My dad used to wipe data off of media devices in the course of his work. I recall him saying he used magnets to do so. I'm sure that the magnets in question were nowhere near that strong. Falconus^{p t c} 05:35, 26 December 2010 (UTC)

To answer the "what can I do with it" question, here are some fun things you can do with magnets. Red Act (talk) 06:57, 26 December 2010 (UTC)

250 pound lifting force? Hang on! Doesn't that mean you would have to use more then 250 pounds of force to pry something off that thing? I smell a fish. I would be way too scared to play with such a magnet, imagine getting your hand (or worse) caught between a magnet like that and something attracted to it. Vespine (talk) 13:10, 26 December 2010 (UTC)

It would have to be in direct contact with a large, 100% iron object to apply the full force. Even a small offset, like that due to having your hand in between, would significantly reduce the force. StuRat (talk) 14:49, 26 December 2010 (UTC)

Permanent magnet (I assume the OP is not talking about electromagnets) lifting magnets usually have a mechanism for releasing the load when required. Example advert for the kind of size being discussed. See this video of how permanent magnet switching works. SpinningSpark 16:50, 26 December 2010 (UTC)

If you aren't careful, you can wind up pinching your fingers, causing blood blisters.[15]

December 26

Fog

What would happen if you boiled fog machine liquid? Would it make a load of fog? 82.44.55.25 (talk) 00:23, 26 December 2010 (UTC)

I know of two types of fog machines, one basically does boil water, so nothing would change. The other uses dry ice (frozen carbon dioxide), which goes directly from a solid to a gas, with no liquid in between (it sublimates). It's not possible to boil carbon dioxide at normal atmospheric pressure. If you pressurized it and heated it, you might get a liquid, and if you suddenly released the pressure, you might get a lot of "fog". StuRat (talk) 04:02, 26 December 2010 (UTC)

I am confused when you say "nothing would change". Do you mean nothing would change with the fog liquid if I boiled it and it would just sit there in the pot, or do you mean there's no difference between whatever a fog machine does to the liquid and just boiling it, so it would make fog? And I'm specificlly talking fog machine liquid, not dry ice. 82.44.55.25 (talk) 10:45, 26 December 2010 (UTC)

From fog machines Typically, fog is created by vapourizing proprietary water and glycol-based or glycerine-based fluids or through the atomization of mineral oil. I don't think boiling would vapourize it particularly effectively, I don't think you'd get a LOT of fog. Vespine (talk) 13:05, 26 December 2010 (UTC)

What is the scientific term for levels of activity by time of day?

An organism is diurnal if it is active during the day, nocturnal if active during the night, etc, but what is the formal term for nocturnality and diurnality themselves? Is there a scientific word meaning "the level of activity of an organism by time of day" that includes diurnality, nocturnality, crepuscularity and all other variants on the concept? I've been wondering this for a long time but haven't been able to find this term despite a hard search. Circadian rhythm seems to be the most closely related concept that I've found, but it seems to be a bit broader than just activity levels. Abyssal (talk) 04:11, 26 December 2010 (UTC)

Chronotype? Clarityfiend (talk) 04:34, 26 December 2010 (UTC)

I don't think that's exactly what I'm looking for. That concept seems to be behavioral, like if a person (a diurnal animal) is a "night owl" (ie chooses to adopt different behavior). I'm more interested in activity levels innate to a species. Abyssal (talk) 07:24, 26 December 2010 (UTC)

Circadian? SpinningSpark 16:22, 26 December 2010 (UTC)

"The time during which an organism is normally active is referred to as the subjective day" - from Pace-Schott & Hobson (2002). NRN. 3, 591–605. Is this what you are referring to? --Mark PEA (talk) 21:39, 26 December 2010 (UTC)

Solar sails

Why aren't solar sails used to propel all spacecrafts? Since they don't require any energy other than to deploy and retract the sails, wouldn't they free up space that would've been used to carry fuel? --75.28.52.27 (talk) 20:31, 26 December 2010 (UTC)

They are difficult to make and deploy, take a long time to build up speed 82.44.55.25 (talk) 20:38, 26 December 2010 (UTC)

"Minimize total energy consumption" is only one objective during spacecraft engineering. While it is true that a solar sail will reduce the energy consumption, and consequently the mass of chemical propellant, a solar sail may incur other costs. Those costs compete against other design objectives - such as "minimize total flight-time"; "minimize flight-mass;" "minimize flight volume;" "minimize risk of failure;" "minimize monetary cost of spacecraft;" and "test specific scientific or engineering design." (With some imagination, you can expand that list ad nauseum). The point is, when you think of spacecraft design, you always have to keep yourself in the mindset of engineering tradeoffs and cost-benefit analysis. With present technology, even though solar sails might reduce the total mass of the propulsion system, they may significantly increase the flight-time - which is usually a tradeoff that the space-flight program cannot afford (because it affects the science objectives, the spacecraft design, and the dollar-budget). They may also introduce signficant risk - because they are both less-tested and less-controllable than a chemical rocket propulsion system. The chance that the propulsion system could underperform (or fail altogether) is altogether unacceptable, and generally outweighs any cost, mass, or other benefit that a solar-sail might provide. You might be interested in reading through the Lecture Notes for AA 222 - Multidisciplinary Design Optimization (a graduate course in spacecraft design from Stanford); you can learn how an aerospace engineer will formally specify the design requirements, evaluate various technologies, and plan the spacecraft. We also have the less-technical spacecraft design article, which mostly just links to articles about related subfields of engineering. Nimur (talk) 20:54, 26 December 2010 (UTC)

To date, Solar sails (skim the article, it's informative) are a basically untested technology. There has been a grand total of one spacecraft to successfully deploy a solar sail and use it for acceleration: IKAROS (Here's a news article about IKAROS, showing the sail). And it's only been up for about 6 months. If it successfully reaches Venus, and there are no major problems with the sail, other solar sail-equipped spacecraft may begin to appear; it's claimed in the IKAROS article that Jupiter is the planned next destination for a JAXA solar sail if this one works out. It's hard to find what exactly IKAROS is carrying (unfortunately, the IKAROS official website is woefully incomplete), but it appears that it's not accelerated solely by the sail: it also accelerates using an Ion thruster. I think it's safe to say that solar sails have a few years to go before becoming common on spacecraft.

It's interesting to note that ion thrusters, now pretty common on interplanetary spacecraft, were not really used in spacecraft propulsion until Deep Space 1, launched in 1998 (ignoring the SERT-1 probe, where one ion engine only ran half an hour, and the other one failed). If solar sails improve at a pace similar to ion thrusters, we may be seeing solar sails used fairly frequently in 20 years. Buddy431 (talk) 22:28, 26 December 2010 (UTC)

has any famous scientist ever expressed doubts about the moon landing authenticity?

bertrand russell, a very famous mathematician and philosopher, expressed doubts about the official jfk assassination story. did any famous scientists (like feynman, etc) ever express doubts about the authenticity of the moon landings? 87.91.6.33 (talk) 22:34, 26 December 2010 (UTC)