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November 9

Antimatter meteor/comet

What would happen if an antimatter meteor or comet hit the Earth? --168.7.238.36 (talk) 06:22, 9 November 2012 (UTC)

A large one would pretty much destroy the planet, while a small one might just destroy all life on Earth. However, if it hit at a shallow angle, the initial explosions when it first contacted the atmosphere might blast it back into space before it did much damage. Fortunately, there don't actually seem to be any. Within our solar system, I suspect that even the sparse gas here would cause sufficient explosions on it's surface to break it up. StuRat (talk) 07:27, 9 November 2012 (UTC)

Incidentally, are you aware that one theory is that the Tunguska event was a tiny antimatter meteor which struck Russia ? StuRat (talk) 17:42, 9 November 2012 (UTC)

See antimatter comet. StuRat (talk) 17:44, 9 November 2012 (UTC)

You should read the short story "Flatlander" in the collection Neutron Star by Larry Niven. We have an article on it, but the article is basically one big spolier, so just get the book Neutron Star at the library, or buy it used for a penny at Amazon. μηδείς (talk) 15:49, 10 November 2012 (UTC)

I once (1993? 1984?) heard Robert L. Forward say that if you put an anti-iron cannonball on the ground it would probably sizzle, not explode. Whether this implies anything for an anti-body crashing at escape velocity, I don't know. —Tamfang (talk) 16:21, 10 November 2012 (UTC)

It would surely do a lot of radiation damage even if it sizzled / bounced off the atmosphere. The solar winds would make the object highly visible, too, so you could probably defeat it by crashing a kill vehicle into it at the right angle (OR). The annihilation would do good enough to make any explosive warhead utterly redundant. - ¡Ouch! (^{hurt me} / _{more pain}) 17:31, 10 November 2012 (UTC)

The minimum diameter for an incoming antimater asteroid travelling at 30 km/s to reach the surface is about 50 km. If you approximate the problem as an ideal photon rocket, then the change in velocity w.r.t. to the initial rest frame of the asteroid is:

$v=c{\frac {m_{1}^{2}-m_{2}^{2}}{m_{1}^{2}+m_{2}^{2}}}$

where m1 is the initial asteroid mass and m2 the final asteroid mass. Then we put m2 = m1 - delta m and expand to lowest order in delta m. We then put delta m = pi r^2 rho_at L where rho_at is the density of the atmosphere and L the effective lengtht it travels through the atmosphere, as this is the amount of mass it scoops up in the atmopshere and this will be annihilated. The initial mass is 4/3 pi r^3 rho_as, where rho_as is the density of the asteroid. You then find:

$r={\frac {3\rho _{\text{at}}Lc}{4\rho _{\text{as}}v}}$

which gives the minimum radius of the asteroid needed to reach the surface. For an incoming asteroid at speed 30 km/s the change in velocity is v = (30 + 11.2) km/s. In reality the radius it can be a bit less than this because the ideal photon rocket model overestimates the propulsion from annihilation. Count Iblis (talk) 18:08, 10 November 2012 (UTC)

Whether it reaches the surface seems rather besides the point. The energy released by the annihilation of a 49 km diameter antimatter asteroid will vaporize the Earth's crust, in any case. StuRat (talk) 23:14, 10 November 2012 (UTC)

As for a really tiny antimatter meteor, that might fry anyone in a direct line-on-sight, and the blast wave might kill people hundreds or thousands of miles beyond that. People 90 degrees from it (or a bit past 90) might have the best chance at survival, since the blast would be most diluted, there. At the opposite side of the Earth, the blast wave again builds up to a deadly level. StuRat (talk) 23:21, 10 November 2012 (UTC)

Lead poisoning

I have an extension PCB(a pci card of some sort) that is not compliant with ROHS That is built with lead-solder, DOES handling it pose a threat to health or something of that nature, like getting poisoned if you are to have contact with the solder joints on it? Should you always wash your hands thoroughly after handling it? — Preceding unsigned comment added by 77.35.32.100 (talk) 09:38, 9 November 2012 (UTC)

There is nothing to be concerned about. No need to wash hands beyond the usual requirements. Electric and electronic devices have been made with tin-lead solder for around 100 years without any problems whatsoever from handling. If there was any problem, it would have occured with the factory people doing the soldering - and for the first 70 years or so it was mostly done by hand. No problems have been reported. Same with electronics hobbyist and radio hams - who have always, and still do, assembled their devices with tin-lead solder. Problems are unknown. I have an electronics background myself. Employers generally banned the consumption of food at the workbench, and recommended washing hands before eating. But this was more about keeping the workplace clean and avoiding the transmision of microbes (thereby keeping teh workers healthy and not off sick) than about lead. Later I worked in a diesel engine facility, and they had the exact same rules, and zero use of lead.

In circuit boards of at least reasonable quality, after soldering, the solder side of the board is coated with a type of varnish. This varnish is very thin and generally is not visible.

You need to understand the reason for the use of lead free solder in recent years. It has been determined that very small amounts of lead affect intelligence, and most people have medically significant lead in their bodies. First, various countries banned lead in gasoline. That had little effect, except in the USA, where the number of gasoline engined cars and trucks per unit area is much greater than in other countries (and even in the USA, significant lead levels in humans still occur). So the Europeans decided to ban the use of lead altogether (an exemption has been made for lead-acid batteries). However, lead is still ubiqitous in the environment. One of the major causes of lead in our bodies is the use of lead-based paint in houses. In most advanced countries it was banned decades ago, but every house gets sanded back and repainted once in a while, releasing the lead as dust into the air. There are lots of other reasons for lead in the environment that far swamp out any nanoscopic source in electronic cards.

Keit 120.145.147.142 (talk) 10:35, 9 November 2012 (UTC)

I should add that one problem with lead in landfills, or any stable element, is that it doesn't decay. So, while something like feces ceases to be a problem after it's been buried a few years, this isn't the same with lead. It's permanent. As new layers of soil are deposited on top, the lead will eventually be buried so deeply that we will be unlikely to have much contact with it, but this will take thousands of years. StuRat (talk) 17:24, 9 November 2012 (UTC)

The lead in the solder would be released back into the environment if it is discarded into the earth and the lead gradually corrodes over the years. As others have mentioned there is no hazard by handling it. But don't eat it or grind it to dust. Graeme Bartlett (talk) 11:01, 9 November 2012 (UTC)

Yeah, like everybody says, the major health risks of lead-based solder are water pipes, where it's been banned for a long time, and for the solderers who are inhaling the vapors over a lifetime. Although, I would definiely recommend against eating a lot of it. Gzuckier (talk) 19:11, 9 November 2012 (UTC)

Ive heard that by getting lead solder inhaled or in your blood your gonna get deaf partly blind and and have no sexdrive plus seizures and have problems with fertility im gonna def check all of my home appliances on whether they meet up with the rohs standards and requirements — Preceding unsigned comment added by 77.35.33.248 (talk) 10:29, 10 November 2012 (UTC)

Yes, so don't grind lead up to a powder and snort it. Otherwise, you should be fine. StuRat (talk) 07:08, 12 November 2012 (UTC)

What was the purpose of the Galileo thermoscope

I try to understand what were the purposes of Galileo galilei when he made the thermoscope? It seems that the him purpose was not been to make a scale of the heat, but he meant to see or prove something... Do you know what was it? מוטיבציה (talk) 14:00, 9 November 2012 (UTC)

Why do you discount the idea of making a scale of the heat? This was a non-trivial scientific and instrument-based question in the 17th century, and there was considerable debate at the time what temperature really was (e.g. was it a substance or was it something else? We now know that it is identical with movement on a very small scale, but they didn't know that then). --Mr.98 (talk) 14:29, 9 November 2012 (UTC)

First off, let's point out to those that aren't aware that Galileo's thermoscope was completely different from a Galileo thermometer, which wasn't even invented by Galileo. With that out of the way, even if you don't have an absolute scale on the device, you can have a rough relative scale - if I use this hot object, the column is visibly greater than if I use this cold object. By playing around with it, you can find out interesting things, like a piece of metal which feels much colder than a piece of wool actually doesn't register any different with the thermoscope. (It's different because how warm/cold something feels is due to the rate of heat transfer, rather than absolute temperature - I don't know if Galileo did such an experiment, but it something he could have done.) [1] quotes a contemporaneous source saying he used it to "examining the degrees of heat and cold" - which at a time when the concept of heat was still fuzzy is no small thing. [2] says that experimenting with his thermoscope lead Galileo to formulate a hypothesis about the nature of heat. That's a lot of what the early scientists did. There was very little existing knowledge, so they played around with toys and other scientific instruments, coming up with theories of why things behave as they do. It was less hypothesis testing and more "hmm.... that's funny"[3]. It's probably worth pointing out that prior to constructing a thermoscope, it was probably a question if one *could* construct an absolute scale for measuring temperature. Note that once it was constructed, [4] and the previous references indicate that researchers very quickly applied various reference points to the thermoscope, which with intermediate graduations became a thermometer. -- 205.175.124.30 (talk) 03:32, 10 November 2012 (UTC)

Thank you for this information. I asked this question because I read once, that Galileo wanted to prove something about the atmosphera... I don't know what it is. (maybe that the crowding in the buttel\vessel depends in changes of atmosphera). I believe that Galileo approach to this experiment in order to looking for something. Is there any Information about in him writing or him pupils writing? (except of 33 origin) מוטיבציה (talk) 16:20, 10 November 2012 (UTC)

Converting candela per square metre to "photon density"

Greetings!

Given the luminance (in candela per square metre) and wavelength of a light source, I'd like to obtain its "photon density" (a measure that's new to me but used to describe stimuli in some vision research papers; its units are given as photons/cm²/s). One paper specifies that a red light source has a wavelength of 635 nm, a luminance of 34 cd/m², and a photon density of 1×10¹⁴ photons/cm²/s (I include these values as they can - presumably - be used to check that a computation using the first two values correctly results in the third).

The candela is defined as a measure of "luminous flux per unit solid angle"; if it could be converted to an energy measure, the conversion should simply be a matter of computing the energy per photon of the light source using $E=h\nu =h{\frac {c}{\lambda }}$, dividing the overall energy by the per-photon energy, and then accounting for the change from m² to cm². Based on the fact that 1 candela = 1 lumen⋅steradian and 1 lumen = 1/683 Watts, 1 candela should be 1/683 Watt⋅steradian. There are 4π steradians in a sphere, so for a light source emitting light equally in all directions 1 candela should be equivalent to 0.0184 Watts.

Coming back to the values given in the aforementioned paper, 34 cd/m² becomes 0.63 W/m² and the energy per photon for a 635 nm wavelength light source is 3.13×10^-19 W⋅s (1 Joule = 1 Watt⋅second). Dividing the first value by the second (to obtain the number of photons) results in 2×10¹⁸ photons/m²/s ("photons" is a unitless quantity here in the same way that "cycles" is for frequency (cycles/s), so the units are technically s/m²); finally, dividing by 100² to convert from s/m² to s/cm² results in 2×10¹⁴ photons/cm²/s.

As this result doesn't match the value given in the paper, something is evidently amiss. The only thing I can see that might be incorrect is the assumption that the source emits light equally in all directions, but I would appreciate any suggestions or corrections. Hiram J. Hackenbacker (talk) 18:05, 9 November 2012 (UTC)

If I'm reading it right, the basic problem I see is that the candela is a measure of light emitted from a source, while the the photon density is a measure of the light received at the target. So, in astronomy terms, one is absolute magnitude and the other is apparent magnitude. The apparent magnitude varies not only with the absolute magnitude, but also the intervening distance and particles. So, there is no direct conversion between the two, and a conversion can only be done when you know what lies in between. StuRat (talk) 19:10, 9 November 2012 (UTC)

The candela is indeed a measure of the intensity of the source (and not directly comparable to luminance measures), but the stimulus in the paper is characterized by its luminance given as candela per square metre, which should be comparable to other per-unit-area measures (the paper used a Ganzfeld-type stimulus, which is basically a surface illuminated such that it has uniform luminance, which is why the surface is characterized by a luminance measure rather than one of luminous intensity). I converted candela to Watts via an assumption about the effective point source illuminating the Ganzfeld surface (which may or may not be valid) but this was just for the purpose of converting the given candela per square metre value to one expressed in more useful units, so the luminance of the surface is still a per-unit-area measure after the conversion and should remain comparable (and convertible, hopefully) to photon density. Hiram J. Hackenbacker (talk) 19:34, 9 November 2012 (UTC)

You may enjoy reading Labsphere's introductory guide to integrating photometry. This guide is not overtly commercialized: it actually provides a lot of solid physics and mathematics that is useful for people who are interested in quantitative measurement of light. A large quantity of educational literature is available on the company's website in the science section.

Particularly note their list of various units (page 2); it provides a handy breakdown between flux, flux-per-area, flux-per-solid-angle, and flux-per-area-solid-angle. Each of these quantities represents a different useful parameter in photometry and radiometry. The candela is a measure of photometric photons per solid angle - approximating a standardized human perception of light - so you can't directly convert it to total number of photons. This critical distinction is elaborated in the guide, and is covered in our article on spectrophotometry. Nimur (talk) 20:00, 9 November 2012 (UTC)

Thanks for the suggestion, Nimur; I'll take a look at the resources you've linked to. I'm beginning to suspect that, rather than performing a conversion of some sort to obtain the photon density, the various papers I've seen that use it actually directly measured it with an appropriate instrument (it'd be nice if that was mentioned in the papers, though). Hiram J. Hackenbacker (talk) 14:37, 11 November 2012 (UTC)

Many instrument vendors use the CIE standard to convert between radiometric and spectroradiometric photons; but others use (name-brand equipment-maker)-proprietary-standard-number-(whatever), which you have to obtain by calling up their sales team and hoping you can make sense of whatever half-truths they tell you about the equipment. (This tends to be impossible, especially if you're a low-volume customer). In theory, you can use these data to convert to absolute photon-count. In practice... you can't. For that reason, it's much more useful in practice to know how the measurements were acquired - what instrument make and model, and how the lab bench was setup - instead of trusting the vendor to follow any "standard" that has "colorspace" or "perceptual curve" in its name. Always compare measurements under conditions that are as identical as practical. Nimur (talk) 19:50, 11 November 2012 (UTC)

Deer

Why do mother deer run off their young bucks?--Wrk678 (talk) 23:12, 9 November 2012 (UTC)

To prevent inbreeding is the evolutionary answer. Psychologically it will most likely have to do with smell, which is one reason humans don't often commit incest--relatives don't smell good. Curious whether there's a ref for this. μηδείς (talk) 23:17, 9 November 2012 (UTC)

Human relatives don't smell good? Clarityfiend (talk) 23:28, 9 November 2012 (UTC)

You never heard siblings tell each other "you stink"? —Tamfang (talk) 16:15, 10 November 2012 (UTC)

But if our natural smell is covered by artificial scents, wouldn't that mean that we start to get sexually interested in our relatives? Comploose (talk) 17:44, 10 November 2012 (UTC)

See Body odor and subconscious human sexual attraction, where it says "The increased attraction between people of dissimilar MHCs is also hypothesized to prevent incest and its possibility of producing birth defects." And it has TWO cites. --Jayron32 23:46, 9 November 2012 (UTC)

I'd say it a bit differently: The mother deer runs him off so he will go spread his genes, which are half hers, as widely as possible, thus ensuring that they are passed down. StuRat (talk) 02:03, 10 November 2012 (UTC)

Recent but little-known paleontogy studies show that ancient deer discovered DNA eons before Watson and Crick came along. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:46, 10 November 2012 (UTC)

"Has the deer a little doe?" "Yeah, two bucks." -The Three Stooges. Gzuckier (talk) 04:35, 13 November 2012 (UTC)

Dull drama Wnt (talk) 04:02, 12 November 2012 (UTC)

And I get threatened with eternal damnation for awarding people RD-best stars? What a fucking crock. μηδείς (talk) 23:11, 10 November 2012 (UTC) Not eternal, just purgatory. I found Stu's comment "The mother deer runs him off so he will go spread his genes..." to be pretty funny, as if a deer would know anything about spreading genes. That might be the practical effect, but that doesn't mean the mother reasoned that out. ←Baseball Bugs What's up, Doc? carrots→ 08:12, 11 November 2012 (UTC) Please see Strawman. You did not upset people for congratulating them for good answers. We should do that. You upset people when you placed stars after their answers with no context which implied some sort of official standing in such an award. You should tell people that they give good answers. You shouldn't try to establish a system of semi-official looking awards that implies that it is endorsed by the ref desk as a whole. Your actions in awarding those stars should unambiguously represent you singularly, and not the entire reference desk. Also, when people object to something you do, please don't invent something they didn't object to, as though your invented reason were the actual reason they were upset. Instead, pay attention to words people use, and the exact reasons why they object to your actions. --Jayron32 23:17, 10 November 2012 (UTC) I would also point out that despite suggestions to the contrary when μηδείς was blocked, when the issue of the stars first came up there was clear consensus it was inappropriate to add them without signing, even if we accept (I'm not saying I do) there wasn't consensus against adding the stars. Just to be sure I rechecked the original discussion Wikipedia talk:Reference desk/Archive 93#Are we grading responses now? and I can't see anyone suggesting adding them without signatures was okay. In fact nearly everyone who didn't just say don't do it specificially mentioned the need for signatures. Most also mentioned the need to do it on a new line and otherwise make it clear it wasn't part of the original response beyond just adding signatures. The flaw with the hidden 'signature' method was raised by at least 2 people (me and 203), with no response that I saw, so it was resonable to assume it was accepted. In any case, anyone who mentioned the need for signatures can be taken to be suggesting the need for something compliant with Wikipedia:Signatures unless they said otherwise. And a hidden 'signature' clearly does not comply. Note that while neither WP:TPO or WP:SIG seems to have been specifically linked to in the original discussion on the stars, it's resonable to assume a regular is familiar with these guidelines. And in any case, the basic requirements were discussed as relevent to the specific example. Nil Einne (talk) 13:35, 11 November 2012 (UTC)

Inbreeding is pretty common in nature so I dont think thats the reason--Wrk678 (talk) 01:45, 11 November 2012 (UTC)

Actually no. Outcrossing is the norm in the wild, given that inbreeding is almost always genetically undesirable and deleterious to the population (see inbreeding depression). Almost all species have mechanisms that minimize the possibility of inbreeding as much as possible, while at the same time maximizing the possibility of outbreeding. Some examples:

• The formation of harems, with a dominant male maintaining control of a number of females. Male offspring in such groups are forced to leave as soon as they attain sexual maturity. Lions exhibit this. Deer exhibit this briefly during the mating season.
• The formation of sex-specific social groupings and sex-biased dispersal. Elephants, for example, have highly social females that form matriarchal herds. Young male elephants will stay with the female herds but will depart at maturity to join bachelor herds of young male elephants. Fully mature bull elephants are usually loners. Cats, as well, have social females, but itinerant males. In some species of ants, alate queens take flight first, followed by the drones. Deer exhibit this throughout much of the year.
• Communal breeding, usually involving mass migration to mating grounds during the mating season. This ensures that normally scattered populations will mingle with each other and exchange genetic information. Examples include penguins, flamingos, and whales.
• Sequential hermaphroditism, where all individuals are a certain sex at a certain age, but change into another sex once they reach a certain age. This is common among fish like groupers and other serranids. It ensures that all offspring hatching from the same clutch of eggs (and thus be of the same age) will be of one sex at the same time, making it impossible for them to mate, though in certain special circumstances, one of them may assume the opposite sex if absent.
• Dichogamy in plants, where flowers produce pollen when the stigmas are nonreceptive or vice versa, therefore avoiding self-pollination. This is sometimes timed (synchronous dichogamy), e.g. in avocados, when the flowers first open they are functionally female. They then close. On the following day, they again reopen, but this time as functionally male flowers. This is coupled with the fact that avocados exhibit two morphs, and in a larger system known as heterodichogamy, one avocado morph open their flowers in the morning, while another open theirs in the evening. The result is an overlap in the flowering times, and at any given time an avocado tree possessing flowers that are functionally one sex will always have other trees that have flowers of another for cross-pollination.
• Negative assortative mating. A form of nonrandom mating where individuals will mate more frequently or mate exclusively with individuals of a different phenotype/genotype. In simpler words: opposites attract.
• Extreme sexual dimorphism. E.g. in scale insects, velvet ants, and cockroaches, males are winged, while females are not.
• Highly motile juvenile stages, like planktonic larvae in marine animals. This ensures that offspring will be scattered far and wide before they even reach sexual maturity, making it unlikely that they will mate with a sibling or a close kin.
• Kin recognition. Aside from identifying recipients of nepotistic behavior, kinship recognition is also used to avoid mating between individuals recognized as close kin. What μηδείς pointed out earlier is an example of this. The use of pheromones is a common method of kinship recognition and inbreeding avoidance. This includes humans, reinforced by physical recognition and social mechanisms like incest taboos.

Etc. There are others of course. Some of them so elaborate, it's a wonder they even find mates at all. -- OBSIDIAN†SOUL 09:07, 11 November 2012 (UTC)

November 10

where do new layers of earth come from

hello, one sometimes reads that paleontologists found some fossils so and so many meters deep, or archaeologists excavated some city or something, I wonder where has the earth that buried historical artifacts underneath it, come from? Do the upper strata just get reshuffled so that that which was down goes up and vice versa (we have been naught... lol), or are these cosmic matter (in which case that would mean that the earth becomes bigger, wouldn't it?) Thanks in advance Asmrulz (talk) 13:10, 10 November 2012 (UTC)

A number of factors contribute. The action of plants and animals builds up a layer of soil. In many cases rain and wind driven erosion moves sand from one place to another. Over time, in the absence of geologic activity, mountains tend to get lower in height and low level areas tend to get higher. A recent article in Scientific American magazine decribed how wind lifts sand off the Sahara into the upper atmosphere and transports it to overseas countries. Where the sand is dropped, which is an extremely slow process, plants and animals convert it into nutrient laden soil. In some areas, particularly coastal and island, bird droppings has added hundreds of metres. Wickwack 124.178.149.139 (talk) 13:18, 10 November 2012 (UTC)

(ec)The atmosphere is fixated by abiotic sedimentation and biological fixation. Bodies with no atmosphere (like the Moon) don't fix new regolith. This process, and the loss of atmosphere to space, would leave the Earth without an atmosphere, and so this process would stop here too - but Earth is tectonically active, which means volcanoes are spewing forth new atmosphere, keeping the process going. Magma is produced from very deep material, so it doesn't disturb the geological layers except right where the volcano erupts. For human settlements (where the timeframe is just a few thousand or tens of thousands of years) many are quite literally buried with trash. And when archaeologists are looking at say a Roman villa, they're mostly looking at the foundations and a few layers of stones, and all the junk that got dropped down the cloaca or buried in the garden - the whole of centuries of life compressed down to a few inches. -- Finlay McWalterჷTalk 13:23, 10 November 2012 (UTC)

See also Erosion and Deposition (geology). Ghmyrtle (talk) 13:24, 10 November 2012 (UTC)

Indeed. There is also an large element of survivor bias here - most buildings (especially wooden ones) leave no trace behind, and most animals are not fossilised, so we only ever find the exceptional cases. Gandalf61 (talk) 13:33, 10 November 2012 (UTC)

Didn't Charles Darwin write up an estimate of the rate at which earthworms churn the soil? —Tamfang (talk) 16:14, 10 November 2012 (UTC)

Yes he did. His final book, reprinted many times as was much of his output, was "The formation of Vegetable Mould through the Actions of Worms." In it he described how earthworms effectively raise the level of the soil by a quarter of an inch per year. This obviously buries things after a while. HiLo48 (talk) 04:02, 11 November 2012 (UTC)

Exposed face of a peak in the French Alps

"Reshuffling", though oversimplistic, is basically correct. If you're asking about the "short term" origin of new rock layers, then the answer is as above. Fossils and artifacts are found in only one type of rock - sedimentary rocks. And it is subject to a somewhat semi-cyclical process of weathering, erosion, deposition, and lithification. In most cases, the sediments that constitute a certain stratum come from rocks exposed during that time period. The sources are often rocks set higher or at more exposed places that are then eroded into lower places (e.g. sediment from mountains eroding into lakes or basins which results in characteristic lentification). See also Stratigraphy, Stratum, and Stratigraphy (archaeology).

If you're asking about the "long term" origin of new rock layers, then the answer lies in the rock cycle. Remember that we are basically living on very thin floating islands of solid rock on top of a very deep "ocean" of "boiling" magma. All rocks on the crust (aside from those originating from celestial objects like remnants of comet impacts), ultimately derive from magma. But again, by long term, I mean very long term. Large parts of the crust haven't been to the mantle for a very long time, and are basically just being "recycled" as you implied earlier. Though conversely, some parts of the crust have long since disappeared forever back into the mantle, like the Farallon Plate which slid under the west side of the North American plate, leaving only bits and pieces and the Rocky Mountains as a testament to its demise. Plate tectonics itself play a part by deforming the rock layers (orogeny) as the plates move around. The movement of the crust can thrust layers of rocks up, down, or fold them around like taffy, exposing old layers to erosion and burying others. -- OBSIDIAN†SOUL 16:31, 10 November 2012 (UTC)

When it comes to archeology I think much of the layers are human made derbies and maybe soil from decomposing plants.Gr8xoz (talk) 20:35, 10 November 2012 (UTC)

Twin follicles in horses

From my understanding twin follicles are follicles produced at the same time and of roughly the same size and that they will produce twins. But I'm not sure why this produces twins and why it's a sign of pregnancy in the first place. Thanks. 138.253.210.27 (talk) 17:25, 10 November 2012 (UTC)

It basically has to do with the production of eggs (ova) in the estrous cycle. Aside from differences in timing and the way the uterine lining is disposed of if fertilization is unsuccessful, it is largely similar to human menstrual cycles.

Like humans, horses have ovaries which contain primordial follicles. In regular intervals coinciding with each estrous cycle (after puberty, of course), a number of these primordial follicles start to develop in a process called folliculogenesis. Note that more than one primordial follicle is being grown per cycle. They are essentially being grown in batches.

Once they reach a certain stage of growth where they are known as antral follicles, they enter the next stage known as the follicular phase. In this phase, the different follicles start to compete with each other until only one dominant follicle is selected. It is this swollen ovulatory follicle (around 35-50 mm in diameter) that is detected in the mare during estrus. This is not a sign of pregnancy. The presence of ovulatory follicles of the proper size only means the mare is ready for mating. That dominant follicle that emerges from the follicular phase will then proceed to ovulation, releasing a single egg into the uterus in the final phases of the estrus. If the horse has mated, then the egg will have a chance of being fertilized.

But in rare cases, two follicles will emerge as dominant after the follicular phase (in very very rare cases, more than two). This means two eggs will be released during ovulation (double ovulation, one per ovulatory follicle). This does not necessarily mean that the mare will bear twins though. Indeed multiple follicles have the advantage of increasing the chances of successful fertilization. But yeah, since there are more than one egg now in the equation, this introduces the possibility of both eggs being fertilized. If this happens, then yeah, you'll get twins (although note that these are fraternal twins, not identical, since they developed from different eggs).-- OBSIDIAN†SOUL 18:47, 10 November 2012 (UTC)

Cycling drugs

Users of recreational drugs normally 'cycle' them to be sensitive to them again, but users of legal psychoactive drugs seem to take them regularly during the whole treatment or even for an indefinite time. Do the potheads know stuff that the doctors do not? Are the potheads wrong? Or are both groups doing what works better for each one? Comploose (talk) 17:52, 10 November 2012 (UTC)

I question the second part. I think doctors often do cycle through various meds for their long-term patients. However, this isn't just to prevent loss of effectiveness of one med. Some other reasons:

A) A new med comes out and they want to try it, to see if it will be more effective or have fewer side effects.

B) Some meds require the patient to periodically take a break.

C) Rather than proactively, doctors will change meds after the fact, if they cease to become effective.

D) Switching doctors often means switching meds, too.

E) Some meds are already a mix of meds, like the AIDS cocktail.

F) Some meds have their content changed on a regular basis, like flu vaccines. StuRat (talk) 18:01, 10 November 2012 (UTC)

Drug tolerance is common in both recreational and normal use of drugs (corticosteroids for example need a rest phase). Since people who are hooked on a substance will use it frequently, it might be pretty common among this group of people to build tolerance. On the other hand, people who are just treating an illness will just stop using the substance once the treatment is successful. In some cases, it's the bacteria that are getting resistant to the drug, and not the patient, but in this case too, it's wise not to abuse antibiotics. 19:05, 10 November 2012 (UTC) — Preceding unsigned comment added by OsmanRF34 (talk • contribs)

Recreational antibiotics? Alternated with what? Ground glass capsules? Please do . μηδείς (talk) 23:08, 10 November 2012 (UTC)

Your vision must be better than mine; somehow you can see the phrase "recreational antibiotics" where none exists. Antibiotic abuse occurs when antibiotics are given when they're not required, as for a viral infection. You can read more about that here. My parents, for two, were terrible for that: bugging the hell out of our GP for antibiotics every time my sister and I got colds. Matt Deres (talk) 23:19, 10 November 2012 (UTC)

Thanks Matt, you got the point. Medeis is out of tone again. OsmanRF34 (talk) 00:02, 11 November 2012 (UTC)

Google at it again. It pointed me to this section when I was looking for this. Epic Google fail. - ¡Ouch! (^{hurt me} / _{more pain}) 08:51, 12 November 2012 (UTC)

How would {100} monocrystalline semiconductor grade silicon be made using common materials and no specialized machinery?

This video starts by casually saying they have such material. It seems safe to suspect that this is a person without access to million-dollar (or even multi-thousand-dollar) machines from Intel or any research lab. Yet they don't explain where they got or how they made the {100} semiconductor grade monocrystalline silicon. How could one individual make this then? Peter Michner (talk) 19:17, 10 November 2012 (UTC)

I do not see any statement that it is homemade, I would assume the boring answer is that they bought it some where.Gr8xoz (talk) 20:30, 10 November 2012 (UTC)

Third section down, second to last in section: Cz (made with Czochralski process ) <100> (orientation) 25.4mm diameter Undoped 1.5" thick 45 grams $360.00. With prices like that, it's probably not something easily makeable in the kitchen or the garage. 67.163.109.173 (talk) 23:17, 10 November 2012 (UTC)

Radiation from wifi

Does the radiation emitted from a laptop's wifi depend on what is being done (upload/download/idle)? Also, does it depend on the direction? (I'd be mostly interested in potential health issues, so perhaps in the radiated power!?) bamse (talk) 21:49, 10 November 2012 (UTC)

The radiation from Wifi is not functionally different than the radiation from other radio sources such as cordless phones, walkie-talkies, CB radios, etc. It is at the high-energy end of the Radio spectrum, but that doesn't necessarily mean much: visible light is higher energy radiation than WiFi and you're happily bathed in it every day with no ill effects. --Jayron32 22:07, 10 November 2012 (UTC)

Reading Wireless electronic devices and health or Electromagnetic radiation and health or Mobile phone radiation and health it is not as clear as you want to make it. I am not claiming there is an effect on health, but my question is: If there was an effect on health, would it depend on whether one is uploading/downloading or just having an idle wifi link? bamse (talk) 23:52, 10 November 2012 (UTC)

Yes, more energy is being radiated if the link is in use than if it is idle. Uploading will radiate more energy than downloading (reception of information isn't significant, but a downloading laptop is still continuously replying "yeah, I got that piece"). Downloading will radiate more energy than sitting idle ("yeah, I got that piece" in addition to the always-happening occasional "here I am" in all modes). Given that battery tests generally show a significant difference in lifetime-with-wifi and lifetime-without-wifi, I also suspect that wifi energy is a significant fraction of the overall radiated energy of the laptop. — Lomn 23:57, 10 November 2012 (UTC)

Thank you. bamse (talk) 16:18, 11 November 2012 (UTC)

(Not directly related to the topic, but...)

Shouldn't the articles Wireless electronic devices and health , Electromagnetic radiation and health , Mobile phone radiation and health be named Health effects of ... or Effects of ... on the human body? I can remember, though very vaguely, that article names like "ABC and XYZ" are to be avoided, is that a policy? - ¡Ouch! (^{hurt me} / _{more pain}) 08:50, 12 November 2012 (UTC)

Abiogenesis

Have humans ever successfully synthesized the most simple form of cell which is "Prokaryote" from inorganic matter? If we didn't then what are some recent attempts of doing it? 174.20.101.190 (talk) 22:27, 10 November 2012 (UTC)

Craig Venter claims that he has already synthesize bacteria. OsmanRF34 (talk) 22:37, 10 November 2012 (UTC)

It would help if you'd give a link to that, Osman. I find the claim dubious in the extreme. μηδείς (talk) 23:05, 10 November 2012 (UTC)

Well I have read the Craig Venter article and Synthetic biology article. In the Synthetic biology article, Craig Venter clearly said "we do not consider this to be creating life from scratch but rather we are creating new life out of already existing life using synthetic DNA." And according to the processes in which he used to create the cell are not entirely from inorganic matters. So that's not what I'm looking for.174.20.101.190 (talk) 23:12, 10 November 2012 (UTC)

Craig Venter's work is the closest thing so far. It's only a matter of time, though. Looie496 (talk) 00:15, 11 November 2012 (UTC)

Well I think we are capable of doing it right NOW but unfortunately there is no motivation to do so. In other word, no one is willing to put a big amount of money to do it. Pure interest is not a strong reason for any private funding or the government funding to jump in the case. Compare to the feat of getting to the moon, this is "a piece of cake". Let just look at Venter's work, it costs him 40 millions and he already got very close to a complete synthesized cell. Got man to the Moon cost billions of dollars back in 1960's and by today standard it must have cost a lot more. But the thing is the only reason that we, humans, got to the Moon is thanks to the "space race" between the US and Soviet Union. It wasn't done just for the sake of science to explore the universe. It is funny how everything has a good side. I think we just have to wait for a great cause as a catalyst for ultimate goal of completely synthesized cell. That is a very significant step forward something big! We used to think God is the only one who can create life out of scratch, it turned out not so much... Humans are not too bad compare to God!174.20.101.190 (talk) 07:10, 11 November 2012 (UTC)

To Osman: the popular press sold to their audience that Venter had created life. I do not know if Venter is happy with the way they depicted his development. Comploose (talk) 01:38, 11 November 2012 (UTC)

Genetics question

How accurate are the following statements? "The basic form of life is female. The first male specimens were evolved from females." A8875 (talk) 23:30, 10 November 2012 (UTC)

If one defines female as "An individual that physically produces an offspring" it is self-evidently true. Life cannot propagate if offspring are not produced. Males don't gestate or grow or give physical shape to offspring directly, excepting for a tiny few atoms that contain their genetic code. Functionally close to 100% of an offspring is created by the female body. Males contribute only information to creating offspring. It's a bit flawed to assign sex or gender to species that undergo asexual reproduction, but I see where that statement is going. It would be better to say that before sexual reproduction, there were no sexes at all, and that sexual reproduction created two genders: the Female that produces the egg and the Male that produces the sperm. Of course, many forms of female life don't actually give much more physical material to the offspring than males do. So it's not a great statement, but it's not completely wrong either. Just trite. --Jayron32 23:39, 10 November 2012 (UTC)

• It might be useful to look at our article on isogamy, which was probably the first type of sexual reproduction. In isogamy, individuals cannot be classified as either male or female. Looie496 (talk) 00:07, 11 November 2012 (UTC)

Right. Then the "first male specimens" question can be interpreted as a question on the evolution of anisogamy. SemanticMantis (talk) 05:19, 11 November 2012 (UTC)

Not quite what you're after probably, but it's worth noting that in mammals (at least in rodents and humans, don't quote me on the rest) the developing embryo is female as default, unless it's turned male by amongst other things the expression of anti-Müllerian hormone Fgf10 (talk) 08:04, 12 November 2012 (UTC)

November 11

Could you collect all the CO2 that a vehicle emits?

How much volume would that have? Can you transform it into a solid form? Comploose (talk) 00:48, 11 November 2012 (UTC)

Yes, it could be transformed into a solid, but the question is whether that would be cost-effective (one method would be to lower the temperature to where it forms dry ice). It could also be stored as a compressed gas. If left as an uncompressed gas, it would take up too much space. Also consider that carbon dioxide tanks pose a risk, as leaking ones could knock the driver out and cause an accident, and you can't smell or see it. StuRat (talk) 00:59, 11 November 2012 (UTC)

But, if you remove the 02 and keep the C, the amount won't be bigger than the gasoline. Comploose (talk) 01:35, 11 November 2012 (UTC)

The amount of energy that would take would be prohibitive. StuRat (talk) 01:38, 11 November 2012 (UTC)

((edit conflict) and network timeouts) Removing the O₂ from CO₂ takes a huge amount of energy--you would have to burn probably several times the amount of gas in order to drive that process as well as the car itself. Both of your proposed products are reasonably high-energy (coal is a good fuel and oxygen strong oxidizer) and your proposed starting material is low energy (already-burned), so it takes even more energy to undo that reaction than you get by burning it. Essentially you are proposing an overall process of that gets economically viable energy from "gas + oxygen to coal + water" conversion. It is thermodynamically correct if I understand the numbers correctly, so at least you would not be violating the laws of nature, but not by a lot, so your overall car efficiency (miles per gallon) will suffer greatly. Coal still has a lot of energy, so you are only getting a small amount of the energy density of the gasoline. Energy density is one of the major problems in various alt-energy vehicles. DMacks (talk) 01:56, 11 November 2012 (UTC)

Hypothetically, you could sequester the CO2 from car emissions chemically, that's what Carbon dioxide scrubbers do on an industrial scale. There are several ways to sequester CO2 in this way, most commonly as carbonates. The problem is how to do that efficiently on car exhaust; the chemistry however is simple and used in other applications for exactly this purpose. --Jayron32 02:23, 11 November 2012 (UTC)

Yes: Top Gear (2002 TV series) has demonstrated this. See http://youtube.com/watch?v=nz-Q-4RUd28. The bit about the Range Rover and the greenhouse is complete hogwash, but from about 2m30s there is some actual science. They show that you can use chemicals to sequester the CO2, like Jayron mentioned. They say that they're using Lime crystals; I'm not sure how accurate that is, but it seems to work. See also Carbon dioxide scrubber. - Cucumber Mike (talk) 12:28, 11 November 2012 (UTC)

If something "increases dopamine receptor sensitivity", is that good or bad?

From a fast research, I could find that morphine, fasting (sexual and food-wise), hypothyroidism, and Electroconvulsive shock do that. But is that a desirable effect or a harm done? Is it reversible? Comploose (talk) 00:55, 11 November 2012 (UTC)

I think it all depends on the context. Consider an analogy with increasing light sensitivity in your eyes. That's good in the dark, but not when it's bright out. StuRat (talk) 00:57, 11 November 2012 (UTC)

There are several dopamine receptors with subtly different effects. It also depends on how and where in the brain you are altering dopamine receptor activity. Looking at some real classes of drugs, MAOIs enhance increase the levels of dopamine at certain synapses, which may treat symptoms of depression. Antipsychotics, on the other hand, inhibit dopamine receptor activity, which may treat symptoms of schizophrenia. So the answer to your question is that whether it is desirable, whether harm is done, and how easily it is reversed is entirely contextual. Someguy1221 (talk) 01:05, 11 November 2012 (UTC)

OK, I see that people can have too sensitive dopamine receptors, in the case of schizophrenia, or not sensitive enough dopamine receptors, in some mood disorders. What happens to two normal cases where one mentally healthy person has more sensitive dopamine receptors than the other? The sensitivity of dopamine receptors is also inversely related to the BMI. Could you say that the brain of thin people works differently than the brain of fat people? If yes, how would a brain with more sensitive dopamine receptors differ? Comploose (talk) 01:21, 11 November 2012 (UTC)

As far as I know, none of those manipulations actually increases dopamine receptor sensitivity. They enhance the effects of dopamine, but that isn't quite the same thing. There are drugs that increase the sensitivity of receptors -- for example, benzodiazepine tranquilizers increase the sensitivity of GABA receptors. But I'm not aware of any such effect occurring at dopamine receptors. Looie496 (talk) 02:54, 11 November 2012 (UTC)

There's a general rule in evolutionary biology (Fisher's geometric model) that very small mutations have a 50% chance of being beneficial. The idea is that biological pathways aren't absolutely perfectly tuned, so if you jiggle them just a little, your odds are 50-50 of jiggling them the right way. However, larger mutations are more commonly bad, and extremely large mutations almost invariably so. The same should usually apply to chemical perturbations (provided that they are strictly regulatory rather than say nutritional in nature). I think. So these various drugs, taken in very low doses, should be very slightly good 50% of the time. Combined with even a vague knowledge of when such a modification is a good thing, the effect of many drugs chosen in this way intermingled, at low doses, should on the average be beneficial quite often. Come to think of it, I would speculate (though I've never seen it expressed this way) that this might be the basis of traditional herbal medicine, at least in cases where there is less specific indication for one particular herb. Wnt (talk) 07:53, 12 November 2012 (UTC)

Liquifying francium

I know that francium has a huge heat of decay. However, I'm wondering that if we could prepare a macroscopic sample, keep it renewed by constant synthesis of new atoms, and have a cooling system powerful enough to ensure that the atoms remain liquid, i.e. conducting away all the heat from radioactivity.--Jasper Deng (talk) 02:07, 11 November 2012 (UTC)

There's information on speculative states of matter of Francium at the Wikipedia article titled Francium. Otherwise, I'm not sure the reference desk's mission would be such as to allow us to sit around and invent things out of whole cloth to speculate about what liquid Francium would look like or behave like if we could collect enough of a sample, which we have not yet. --Jayron32 02:18, 11 November 2012 (UTC)

I don't know how to answer this, but it's answerable. Our article shows an image of 300,000 francium atoms in a magneto-optical trap, as a gas. I think it's possible to cool atoms in traps like this, but I don't know how quickly. I assume it's not easy or we'd have a picture of liquid francium there too. Wnt (talk) 16:15, 11 November 2012 (UTC)

It's worth bearing in mind that 300,000 atoms is not a lot—collected into a droplet, you would have a sphere about 80 atoms (probably around 15 nanometers) across. Under visible light, you're not going to see much of anything, and I'm not sure if a particle that size would even be properly 'macroscopic' in its behavior (you get weird things like melting-point depression happening at these sizes, for instance). TenOfAllTrades(talk) 21:41, 11 November 2012 (UTC)

Now there's a general science question I never thought of. What's the smallest possible quantity of a liquid? (or of a solid?) The article doesn't really say, and melting point depression per se shouldn't prevent you from having one. Wnt (talk) 03:53, 12 November 2012 (UTC)

My question is purely theoretical; what if we got at least nanogram quantities (at least ~2.7 billion atoms) and were able to maintain such a sample? The central question is not what the liquid would look like, but whether we would be able to cool such a sample to keep it liquid.--Jasper Deng (talk) 02:56, 12 November 2012 (UTC)

In that case, it is unanswerable by the reference desk. We provide references here so you can know what people already know about things. This isn't the place for people to speculate about unknowns. --Jayron32 00:06, 13 November 2012 (UTC)

Would dogfighting spacecraft need to bank when turning?

Someone told me recently re: "soft science epic Star Wars, that the space craft bank when they make sudden turns (as in dogfights), and they would not need to do this in a gravity-free vaccuum. It made me wonder tho, coz banking would mean the inertial force was felt by the pilot as one pushing him down on his seat, rather than to the left or right.

So where you need to turn suddenly left and right a number of times in quick succession, a banking pilot would feel each of these as a force in the same direction, not as ones zapping him suddenly now to the right, and then to the left. And the force downwards is one very famiiliar to all terrestial beings experiencing gravity, whereas chiral-specific forces are not.

Perhaps banking in extreme turns would also be less stressful on the craft's structure. Myles325a (talk) 07:24, 11 November 2012 (UTC)

Yes, inertia still exists without gravity, so banking would help the pilot. In fact, you'd want to bank more, a full 90 degrees, while on Earth you want somewhat less than 90, because gravity is also pulling you down. As for stresses on the ship, that would all depend on how it was designed. Of course, if they figure it will bank in turns to protect the pilot, then they will design with that in mind. StuRat (talk) 07:32, 11 November 2012 (UTC)

Of course, a ship that does zero to lightspeed in five seconds might need inertial dampeners, in which case it probably wouldn't matter. (Given that maybe the inertial dampeners aren't 100%, the ship might not "really" accelerate to go up and beyond lightspeed, etc.) Wnt (talk) 16:12, 11 November 2012 (UTC)

As far as human tolerances go, in the absence of aerodynamic considerations it would make more sense in a turn to yaw than to roll; humans can tolerate much higher g-forces perpendicular to the spine than along it.

That said, the whole thing is a little bit silly. Standard dogfighting tactics and doctrine (heck, even movie dogfighting tactics and doctrine) have to be rethought once you're working in no air and no gravity. There are an awful lot of what-if and why-didn't-they games one can play (why are there no missiles in the Star Wars universe? why do such otherwise-advanced craft have to rely on manually-aimed guns? etc. etc.) but I'll leave off with a brief nod to the recent Battlestar Galactica remake. In the new BSG series, pilots facing a bad guy 'on their six' didn't panic; they just flipped end-over-end with their manoeuvring thrusters so they could bring their guns to bear while coasting 'backwards'. TenOfAllTrades(talk) 16:42, 11 November 2012 (UTC)

If you would like to read about why aircraft bank during turns (and they don't always!) - I recommend the vintage Aerodynamics for Navy Aviators (1965), available for free online from the FAA. Combining a bank and a yaw maneuver is called a coordinated turn, and helps keep the aircraft stable. During a dogfight, stable flight is not always desirable, especially with very high-performance aircraft. However, in modern air doctrine, dogfighting is totally nonexistant: a combat pilot should never be anywhere near his opponent. Direct air-to-air engagement is risky, ineffective, and expensive, compared to alternatives. This would be even more prominent if current technology were projected forward to guide military doctrine in space: risking manned vehicles in remote areas for minimal strategic benefit would be hard to justify. Nimur (talk) 19:12, 11 November 2012 (UTC)

However, in modern air doctrine, dogfighting is totally nonexistant: a combat pilot should never be anywhere near his opponent. Direct air-to-air engagement is risky, ineffective, and expensive, compared to alternatives. What are you talking about? How else is a pilot supposed to kill his opponent? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:32, 11 November 2012 (UTC)

I think Nimur is talking about using long-range AA missiles. A8875 (talk) 22:12, 11 November 2012 (UTC)

Which are easily avoidable/distractable/interceptable etc. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:43, 11 November 2012 (UTC)

I assume it must depend on your point of view. If one military is telling its pilots not to engage, surely the other must be saying "Get as close as you can, and engage those Star Destroyers at point-blank range." Wnt (talk) 03:47, 12 November 2012 (UTC)

"However, in modern air doctrine, dogfighting is totally nonexistant: a combat pilot should never be anywhere near his opponent. Direct air-to-air engagement is risky, ineffective, and expensive, compared to alternatives." -- Wasn't this doctrine discredited during the Vietnam War? 24.23.196.85 (talk) 05:40, 12 November 2012 (UTC)

It's a cost benefit analysis. A modern American fighter costs about $100 million. A modern medium-range (20 km) anti-air missile has a cost of only about $100,000. Against older planes, missiles have demonstrated a kill rate over 50% (Falklands War). Against modern aircraft the kill rate is expected to be much lower (e.g. 10-20%), but it is still perceived as more cost effective to launch 5, 10, or even 20 missiles at a target than risk a much more expensive fighter. Of course, there will be tactical situations where your aircraft runs out of missiles and is far from any surface-to-air support, and needs to be able to dogfight, but modern American tactics encourage fighters to avoid those situations whenever possible. Better to have the expensive fighter run away, and wait for cruise missiles or other weapons to destroy the enemy's airbase. Of course it helps that America has recently focused on opponents that generally have much older technology, which makes them easier to kill and easier to avoid. Dragons flight (talk) 20:39, 12 November 2012 (UTC)

Playing the vintage arcade game Asteroids will give you a very accurate intuitive grasp for the mechanics of dogfighting in space. μηδείς (talk) 17:09, 11 November 2012 (UTC)

The most damage resistant configuration would be to have the main engines fixed in place with several fixed reaction jets for turning. (Think Apollo Command/Service Module.) The pilots would be strapped down to resist the push of the main engines, and wouldn't worry about any other forces. Hcobb (talk) 17:26, 11 November 2012 (UTC)

Great swooping turns in space to face an enemy rather than just rotating with thrusters or reaction wheels would would be be very wasteful of fuel. Lots of sci-fi writers either don't know this or don't care, and maker of space-opera like Star Wars just want pretty dogfight scenes like in World War 1, where biplanes made Immelmann turns and other aerobatic maneuvers, which are pointless in the absence of air. If one is worried about stress on the pilot, he could be in a sphere in the center of the craft which rotates independently of the warcraft, to keep him stable while it spins, and in an optimal attitude for translations. Edison (talk) 21:14, 11 November 2012 (UTC)

Dogfighting in space? Surely if the enemy ship was close enough for it to register on your ship's sensors, it would be close enough to hit with a computer-targeted laser beam? Considering that it's a vacuum, I'd guess that you could probably shoot him from the other side of the solar system if your machine could correctly predict his trajectory, provided that there was nothing in the way. As he could also do to you. --Kurt Shaped Box (talk) 23:56, 11 November 2012 (UTC)

When you come right down to it, there's no reason the pilot has to be actually in the craft; without the extra mass required for life support, a drone space fighter would have a lot better performance, and no worries about the pilot's reaction to inertial loads. Gzuckier (talk) 01:50, 12 November 2012 (UTC)

It may help to have a human nearby, to make decisions with short communication lag. But of course space battles, if any, are more likely to be fought by computers. It's absurd (but dramatic) that the Enterprise waits for the Captain's order to fire ... Now!. —Tamfang (talk) 03:09, 12 November 2012 (UTC)

Particularly when the captain is James Kirk who has this tendency to................. pause............... randomly. Gzuckier (talk) 04:00, 12 November 2012 (UTC)

"[Long-range AA missiles] are easily avoidable/distractable/interceptable etc.": In space at very long ranges, there would probably be some dedicated interceptor missiles which would only have one purpose: to slam head-on into incoming anti-ship missiles or any "fighter" foolish enough to get close. There would be dedicated anti-missile guns, both ship-mounted and in drone spacecraft (which would not be crippled as easily as ship-mounted defenses, should one torpedo actually strike home, and thus have a better chance to ward off follow-up strikes) orbiting the capital vessels. And then, there would be some smaller long-range missiles, not intended to destroy, but to fool and to saturate enemy point defense.

This is not just speculation on my part: many of these exist today in the wet navies of the world: Phalanx / Kashtan CIWS , and manned interceptors guard the capital vessels against both air and surface attack.

"If one is worried about stress on the pilot, he could be in a sphere in the center of the craft which rotates independently of the warcraft": just what I would think but for different reasons. If there is only one fixed "main" thruster, that thruster can be more powerful than a vectoring thruster or different thrusters for different directions. Turning before firing the main thruster could save a lot of mass (and thus, fuel).

"a drone space fighter would have a lot better performance" but from time to time, it has to receive new orders. If the enemy manages to jam the communication, its performance goes out the window. Humans on-board may be more like today's AWACS crews rather than "pilots" as depicted in the movies, but they safeguard against both, runaway AI and obsolete programming.

"Considering that it's a vacuum, I'd guess that you could probably shoot him from the other side of the solar system if your machine could correctly predict his trajectory" which is a big IF. One light-second is ~300,000km, an AU is 500 times that, and that's still a fraction of the solar system. Of course, there are only two options: maneuver from time to time erratically but give your position away each time you do so, or put Newton in control (drift) and remain stealthy but predictable if the enemy did spot you before. Stealth will probably play a very important role in space. Huge vessels are not even close to the optimum in that case.

I liked the Honorverse novels the most. They have some plot devices, including inertial dampeners and gravitic drives, but they are few and far in-between. Weapons include lasers, gamma ray amplifiers(basicaly a more badass kind of laser), and anti-ship missiles carrying disposable X-ray lasers. Defensively, they use small point-defense weapons , ECM and banking maneuvers (they "roll ship" to expose the well-protected top and bottom rather than the more vulnerable sides). And I'm not sure if a Honor Harrington movie could not be as epic as another Trek or Wars movie. - ¡Ouch! (^{hurt me} / _{more pain}) 14:27, 12 November 2012 (UTC)

Weber, of course, devised the technologies of the Honorverse so that his ship-to-ship battles would recapitulate the sense and style of ship-to-ship combat of the Napoleonic era. (Honor Harrington's universe owes a great deal to the world of Horatio Hornblower—right down to her initials.) Weber invented a shielding system that protected his spaceships from attacks coming from above and below, because seagoing ships of the early nineteenth century essentially could not be attacked from these directions by the technology of the day. Weber's fictional spaceships lack shielding fore and aft, to mimic the vulnerability of ships of the line to raking fire and emphasize the strategic value of Crossing the T. Weber's 'ships of the wall' were named after, and deployed in a manner akin to, the ships of the line. His more recent work in the Honorverse has moved into the development of carrier warfare and tactics. While it's all fun, and shiny, and exciting, underneath the scifi gloss it's the Battle of Trafalgar. TenOfAllTrades(talk) 21:15, 12 November 2012 (UTC)

Bicycle wheel question

Hi. A spoke from my rear bike wheel broke the other day and I had to buy a new wheel because the rim had cracked. I was chatting to the guy in my LBS and he suggested that the problem arose because I use a single pannier bag, always on the left. My bag weighs 4kg or so. I smell BS, but what do you guys think? Robinh (talk) 09:05, 11 November 2012 (UTC)

I carry a single bag only on the right for about 4900 km per year (I have two on for the remaining 100 ;-). I do sometimes have broken spokes, but very rarely. I've never had a cracked rim. Normally, spokes break because the wheel is not well-build. I had one wheel where the rim was unsuitable for the angle of the spokes caused by the hub, with spokes literally breaking at the the rim. But the most frequent problem is spokes breaking at the knee due to metal fatigue if there is to little tension on the spokes so that they go through a load-unload cycle on each rotation. So yes, I agree with your suspicion. --Stephan Schulz (talk) 09:14, 11 November 2012 (UTC)

If this guy is in your local bicycle shop why not push him a bit further with his explanation. I won't ask why you didn't ask for a specific explanation at the time ;-). Stephan seems as close to any expert we'll see on here. Richard Avery (talk) 14:20, 11 November 2012 (UTC)

We would also need to know how many miles you put on these wheels. It might be completely normal after all. OsmanRF34 (talk) 18:55, 11 November 2012 (UTC)

(OP) rough figures, 20km per working day for about 2 years, thus about 5000km, comparable with Stephan. Follow-on question, the *new* wheel has developed three very very loose spokes (which seem to be in compression) and I've taken it back to the LBS. The guy said that sometimes new-built wheels take some time to "settle out" (I think that was his phrase) and need retensioning after a few weeks. Is this also BS? Hey, I appreciate your advice here guys, Robinh (talk) 20:11, 11 November 2012 (UTC)

With standard wheels, for a standard city-bike, things should be working much better than that. Unless you are going through a rough terrain with a mountain bike, I would expect less incidents and less strange explanations. OsmanRF34 (talk) 00:25, 12 November 2012 (UTC)

Your LBS chap is bullshitting in all respects. I also have biked to work & shops and back every day, about 15 to 18 km every day for years, mostly carrying laptop, personal stuff, shopping, etc often in unbalanced loads. My rims are aluminium alloy and the bike is a fairly heavy general use bike (ie not racing or mountain). I usually did in about one spoke per one to 2 years. New built wheels never showed any problem. I agree with Stephan that the cause of broken spokes appears to be metal fatigue as early failures don't generally occur. Riding over potholes and curb-jumping increases the probability of spokes failing. If you have broken spokes soon after a wheel rebuild/adjustment, I suggest that you LBS chap is not doing the job right. I take it you do sensible weekly checks on your bike, and immediately after shop servicing? As well as checking brake travel, bearing slop, gearchange action, etc, while you have your bike upside down, give each wheel a spin, and watch the rim pass a frame member. There should be NO visible side-to-side movement in the rim. If there is, spokes have either failed or are just about to, or have been incorrectly fitted. Also, at the shop, while the bike is upside down, or just held off the ground, give each wheel a spin and hold your thumbnail so it lightly hits the spokes. They should all make the same "ping" sound. If they don't, they need attention. I bet if you do this when you go to pick up your bike at the shop, the guy will do one of 4 things: a) Say, "sorry I need to give your bike more attention" (ok), or get his more skilled mate to fix it (ok), get bad tempered (find another shop), or tell you more bullshit, such as "the rim needs replacement" (which may or may not be true, but if it is, why did he not say before?). Wickwack 121.215.11.232 (talk) 00:37, 12 November 2012 (UTC)

In this case I disagree with the "in all respects". Newly build wheels, especially if machine-build (which most wheels are nowadays) will indeed tend to "settle", and will need re-tensioning after a reasonable amount of use (2-4 weeks, if you ride as much or as little as you or I ;-). After that, or if build a master wheel builder to begin with, it should be good for a year or three before it needs attention again. I've changed my back rim after 6 years (~30000km/~20000miles) all-weather riding, but it was not strictly necessary. I just like to have everything about my bike shipshape, and the spokes needed replacement anyways. --Stephan Schulz (talk) 08:36, 12 November 2012 (UTC)

(OP) thanks for this. My daily route is all road/cyclepath, no rough ground at all. Just to be clear, the old wheel's rim cracked after two years' use. The new wheel has not suffered any broken spokes, it was perfectly true when bought a couple of weeks ago (ie no side-to-side motion, I checked when I adjusted the brakes). Wickwack, you say you break a spoke every two years or so, but you don't need to replace the rims as often? Stephan's rims last indefinitely, I think. I guess the old wheel's rim was a lemon (lasting only two years), and the new wheel had poorly tensioned spokes(lasting only two weeks before needing retensioning). How long should a rim last? How often should I retension my spokes? Robinh (talk) 01:06, 12 November 2012 (UTC)

I don't know how long a rim should last. I purchased my bike about 20 years ago. The rims have never been replaced, and they are still perfect. However, I only rode it every day to work for about 10 years staring about 12 years ago, due to changing work address. I still use it for shopping. When a wheel has had service attention, use the thumbnail trick to make sure it's perfect. However, after some use you will get some variation in spoke ping. Repalce/retension spokes if there is visible side-to-side movement of the rims, which in my experience will ocurr roughly once a year or two as I said above. If there is no visible side-to-side movement, nothing needs to be done. That's the rule I've followed anyway. Check each week, but do nothing unless it needs it. Wickwack 121.215.11.232 (talk) 01:54, 12 November 2012 (UTC)

I can't prove it mathematically, but off-center loading, particularly 4 kg at the short distance from the center a pannier is at, seems very unlikely to bust a spoke and crack a rim. Particularly since you are one of probably millions doing this, and no epidemic has surfaced. Thinking as I write, I'd say, cracked rim is likely to be result of rim flexing and metal fatigue. From too much tension in spokes? Too little? Can't decide right this second. Somebody probably will know. How did it crack; parallel to the radius, I presume, as if flexing in and out towards the center in the plane of the rim? Note (of course) that the rear wheel is asymmetrical, the right side spokes being shallower and under higher tension, trigonometry being what it is. If it cracked from flexing side to side, that's another thing entirely. There are various kluges around to construct wheels where the rim is less asymmetric, but I can't think of them right now. Yeah, sometimes new wheels need retruing after like 50 miles or something on that order, but various practices like relaxing twist in the spoke nipple after adjustment, etc. reduce that. Also, of course, one can build a metastable wheel which has the spokes all out of whack but is kept in true by the rim for a little while. Oh yeah, another item, are the spokes 3 cross, 4 cross, or something odd? 36 spokes? My current ride has radial spokes in the front, and radial on the left side of the rear. Which is just me screwing around, since I've never really broken a spoke or rim before or since, other than catastrophically with a pothole or automobile or such. Anyway, this is like the Bible of wheelbuilding. Gzuckier (talk) 02:15, 12 November 2012 (UTC)

• If the weight load on your bike is asymmetrical, in order to balance you will have to have your wheel at an angle to the ground, which is not good. But I doubt that 4kg is enough to matter. Looie496 (talk) 03:27, 12 November 2012 (UTC)

Timeline of chemical elements discoveries

Why it took so long to confirm elements 113, 115, 117, 118? 3 of them has been discovered since 2002 and 2003. God, that is like 10 years! Some scientists (especially if they're old) may be dead after 10 years and never know if their discovery has been confirmed. When I think about this, it just doesn't make sense! Did they already confirm it and the article simply is out of date or is it actually not confirmed? Seriously 10 years is a long long time to me. And if it hasn't been confirmed then how come the article Joint Institute for Nuclear Research, it says "2010 – successful synthesis of element 117"? How could it be a successful synthesis if it wasn't being confirmed?174.20.101.190 (talk) 09:21, 11 November 2012 (UTC)

I think its because almost no one have an equipment to repeat the experiment. Only a few big labs have it. --Ewigekrieg (talk) 11:43, 11 November 2012 (UTC)

Some of the elements have been created in one place and nobody ever tried the confirm it. Why should I spent millions worth of equipment time to verify a experiment? You can not publish such a result, because it is nothing new. If you have the equipment everybody would aim for 119 a leave confirmation of 118 to others. After 10 or 20 years the equimpent becomes better and you can do what the others had to do for the discovery of an element for calibration of your machinery in a few days, weeks or months. --Stone (talk) 12:59, 11 November 2012 (UTC)

Put another way, there is "not a lot of interest" in the scientific confirmation of Element 113, 115, and so on; in this case, I have arbitrarily defined "a lot of interest" to mean "enough interest to justify funding immediate confirmation." These elements have no currently-known practical use; their discovery did not refute any well-established theory of nuclear physics, or enlighten us about subtleties that we did not already know. The production of these very heavy transuranic elements can be described as a sort of incremental advance to the knowledge of nuclear physics. Compare this with the history of the semiconductor, or even the discovery of uranium fission; for many decades, the cutting-edge of pure research into the physics of these materials immediately translated into commercialization and productization. Nimur (talk) 20:02, 11 November 2012 (UTC)

I guess Stone brought a good point. People are naturally thirsty for fame and famous but being the first one to confirm it is something right? It is much harder to try to create a "new element" than to try to repeated an early successful experiment to confirm it. I guess the one who discovered it will gain more fame but being the first one who confirmed it is not too bad either. At least your name will be somewhere in science's history or physic's history for being the first one to confirm it, maybe it is just a brief mention of your name if it is there! Eventually someone got stand up to confirm it.

@Nimur: it can said that that while those discoveries of new elements have no significant impact on science but look at it this way, I'm sure somewhere along the line it will become a crucial tool for us, humans, to understand the universe and perhaps dark matter. It may take until element 119 or 125 or even 150 so on... Great discovery doesn't come easy but we're building up to it. I believe the discovery of any new element now will be another step closer to something BIG, but unfortunately we don't know what it is yet! And yes this is comparable to getting man to the Moon. What is it really benefiting us about getting man to the Moon really? That's mostly the result of the "arm race" between Soviet and US and the pride it gives for being the first to get man on the Moon. I'm sure the cost of getting man to the Moon is significant higher. I wish there is something like "element race" between all the countries in the world to find like the ultimate element. If that happened, I think within the next 10 or 20 years, plenty of new elements will be discover. It is sad that people are losing interest in science compare to the 1940's to 1960's (look at all the feats we have accomplished). That being said in the 1940's and 1960's science discoveries are mainly for war purpose and not for the sake of science. 174.20.101.190 (talk) 20:42, 11 November 2012 (UTC)

And one of question above didn't receive any answer, can anyone answer it? how come the article Joint Institute for Nuclear Research, it says "2010 – successful synthesis of element 117"? How could it be a successful synthesis if it wasn't being confirmed??174.20.101.190 (talk) 20:42, 11 November 2012 (UTC)

Maybe it means that they believe they successfully synthesised it, but it hasn't been confirmed yet. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:28, 11 November 2012 (UTC)

I believe there is something wrong with that assumption. They can't just assume that they actually synthesized it without confirmation. If it is considered as successful then there is no reason to be confirm. What if they were wrong? Who knows? To me that is a false statement.174.20.101.190 (talk) 06:01, 12 November 2012 (UTC)

No, that makes sense. As far as their evidence is concerned, they've synthesised it, but there has been no independent conformation by a different lab. Also remember that with these elements it's not like you get a nugget of them, we're talking a few atoms here, requiring careful analysis of data and statistics to find them. Fgf10 (talk) 07:59, 12 November 2012 (UTC)

Good physics simulation sandbox?

Could you recommend me a good physics simulation educational software? Something powerful enough to recreate most of school physics experiments? --Ewigekrieg (talk) 11:56, 11 November 2012 (UTC)

Garry's Mod is a very good physics sandbox based on the Half-Life engine. You might also be interested in Learning physics with the Unreal Tournament engine. - Cucumber Mike (talk) 13:18, 11 November 2012 (UTC)

Visual Python makes it very easy to quickly write a 3D visualization for simple mechanics and electrodynamics equations, like simulating an orbiting planet-sun system, in just a few lines of code. Visual Python is free and open source software; you can find installation instructions at the VPython.org website, including some demo videos. Here is a video demonstrating a for-loop and elementary kinematics. If you want to learn physics and learn simulation programming, a little bit more "structured" format will be very helpful. Here is a (not-free) introductory physics textbook, Chabay & Sherwood's Matter & Interactions (available from the publisher), which is used at many universities to guide the freshman-level university physics course with programming examples. Owners of the textbook have access to online versions of the source-code. Nimur (talk) 18:44, 11 November 2012 (UTC)

Always glad to see free publicity for the family! —Tamfang (talk) 03:02, 12 November 2012 (UTC)

Psychology

What's the difference between social anxiety disorder and avoidant personality disorder? --168.7.231.4 (talk) 18:47, 11 November 2012 (UTC)

social anxiety disorder and avoidant personality disorder has the answer. More specifically in Avoidant_personality_disorder#Differential_diagnosis OsmanRF34 (talk) 18:58, 11 November 2012 (UTC)

Self-help books

What research have psychologists done into the effectiveness of self-help books? 65.92.7.202 (talk) 20:44, 11 November 2012 (UTC)

[[5]] OsmanRF34 (talk) 21:29, 11 November 2012 (UTC)

Richard Wiseman, a psychologist, has written a self help book about self help books called 59 Seconds. I'm a big fan of his. Vespine (talk) 21:43, 11 November 2012 (UTC)

Dogbert would say they are highly effective - provided they sell enough copies. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:06, 11 November 2012 (UTC)

Behavior while drunk/under the influence

To what extent does results expectancy affect one's behavior while under the influence of a substance? e.g Are the impairing effects of alcohol naturally induced, or do they occur as a result of our expectations? Same goes for the reduction in inhibitions associated with particular substances. Ankh.Morpork 22:18, 11 November 2012 (UTC)

That's as broad a question as the Milky Way. Can you specify at least a specific drug? μηδείς (talk) 22:25, 11 November 2012 (UTC)

Alcohol. I live on a desert island and eat some fermenting fruit, having never watched Geordie Shore, what happens next? Ankh.Morpork 22:32, 11 November 2012 (UTC)

(ec) To start with alcohol: Testa et al. (2006) "Understanding Alcohol Expectancy Effects: Revisiting the Placebo Condition" Alcohol Clin Exp Res. 30(2):339–348. As Medeis says, this is a very broad and complex question, even if you limit it to one well-studied compound like alcohol; that article provides a lot of references to get you started. See also Short-term effects of alcohol. TenOfAllTrades(talk) 22:36, 11 November 2012 (UTC)

Given you live on an island with no people, don't worry, none of your symptoms will be socially constructed. Enjoy. μηδείς (talk) 23:31, 11 November 2012 (UTC)

Didn't some philosopher once wonder how many people would fall in love if they hadn't been made familiar with the concept via society? Gzuckier (talk) 02:18, 12 November 2012 (UTC)

Related question... The effect of alcohol placebos is very interesting, though I wonder if it is definitely known to be placebo as opposed to some other (unknown) mechanism of contact high. I remember that there have been instances, falling in with people who were drunk for 15 minutes or more, when I've not merely felt intoxicated and felt less socially constrained, but literally felt unsteady on my feet and observed apparent motion of stationary lights when turning my head due to poor tracking, just as with actual alcohol use. I've wondered if there is some natural transition between internal social/mental states of sobriety and drunkenness that preexisted before alcohol was discovered, and if alcohol is only the most common means by which it is forced. Wnt (talk) 19:44, 12 November 2012 (UTC)

Colour black

Hello, is it true, that colour black does not exist in nature? And what about white? Bennielove (talk) 22:20, 11 November 2012 (UTC)Bennie

Are you suggesting those colors are supernatural? Can you clarify your question? μηδείς (talk) 22:22, 11 November 2012 (UTC)

I wouldn't say supernatural. You can not find colour black in nature; I've heard sth like that, but now I'm not sure anymore ... Bennie — Preceding unsigned comment added by Bennielove (talk • contribs) 22:37, 11 November 2012 (UTC)

Black is actually when light is not being reflected, so, it doesn't exist in the sense that it's the absence of light being reflected. OsmanRF34 (talk) 22:43, 11 November 2012 (UTC)

So how is black different to colourless? Ankh.Morpork 22:50, 11 November 2012 (UTC)

There are many caves where, if you go down a certain way, no light penetrates. Is not what we see pure blackness? Also, many animals are black - some species of panther, for example; and cats, dogs, cattle, snakes, you name it. As for white, pick from thousands of different white flowers. -- Jack of Oz ^[Talk] 22:59, 11 November 2012 (UTC)

Those animals still reflect some light, so they are not pure black. StuRat (talk) 07:00, 12 November 2012 (UTC)

Re how black differs from colorless: Wiktionary says only that colorless means lacking color, and one of the definitions it gives for color is Hue as opposed to achromatic colours (black, white and greys). [For example] 'He referred to the white flag as one "drained of all colour".' In line with this, in my experience when people say colorless they mean lacking any hue -- that is, being only white, gray, or black. Duoduoduo (talk) 23:13, 11 November 2012 (UTC)

When my black cat is strongly backlit, I can see that his coat is really dark brown. —Tamfang (talk) 03:01, 12 November 2012 (UTC)

Black and color are both psychological terms. They have to do with human perception, not nature in and of itself. Black is what one perceives when there is no even semi-saturated hue. This is so basic as to be childish. Please read hue and color. μηδείς (talk) 23:29, 11 November 2012 (UTC)

However, "a colourless liquid or gas" is transparent, and lacks all hue. Bielle (talk) 23:31, 11 November 2012 (UTC)

The word black is ambiguous, in that it can either mean the absence of light, or the complete absorption of light. But even within those two definitions, the word light is also ambiguous, in that it can either mean electromagnetic radiation of any frequency, or merely electromagnetic radiation in the visible spectrum. There are no substances, whether found in nature or not, that absorb light perfectly; the blackest material yet created has a total reflective index of 0.045%, which is small but nonzero.[6] Using the "absence of light" meaning of "black", the example of the inside of a deep cave would be a good example of the existence of black in nature, if you take "light" to mean just the visible frequencies of electromagnetic radiation, but in such a situation there would still be infrared radiation, so it wouldn't count as black if you're considering all frequencies of electromagnetic radiation. The sky, as seen from space in a direction other than in the direction of a star, would be a purer absence of electromagnetic radiation, although even then there would at least be the cosmic microwave background radiation. But the blackness of the sky is beat hands down by the blackness of a black hole, which is indeed extremely black. The only electromagnetic radiation coming from a black hole is Hawking radiation, but a reasonable-sized black hole emits far less power per area in the form of Hawking radiation than even the cosmic microwave background radiation. Red Act (talk) 00:27, 12 November 2012 (UTC)

There's no such thing known to science as truly black light, but undoubtedly there is black pigment, especially a blackbody. To confuse you further, blackbodies can glow red hot or white hot --- indeed, to within a small approximation, the Sun is black! (And with that, everybody in Colorado or Washington has to take a toke) Wnt (talk) 04:17, 12 November 2012 (UTC)

My reading of black body is that this is a very useful theoretical approximation: an idealized description that does not occur in physical objects on earth. It even opens with "A black body is an idealized physical body." SemanticMantis (talk) 13:48, 12 November 2012 (UTC)

Well, the taste of maple syrup and the sound of an oboe also lack all hue, but we don't therefore call them white or black or grey. There are different ways to perceive color: from reflective surfaces like coal, from luminous surfaces like computer monitors, through transparent object like rose-tinted glasses, or even without focused dimension, like the red one sees through closed eyelids, or the utter black of an unlit cave. Developmentally we first conceptualize colors as perceived on reflective surfaces, fundamentally the colors of a crayon box, including ROYGBIV as well as white, black, grey, brown, silver, gold, etc., all equally as "colors" and all falling within certain ranges where two slightly different blacks still count as black.

It's only when we gain some scientific or artistic sophistication that we learn there is no way to make black light, that grey and brown lights don't exist in isolation, but only in contrast to brighter or more saturated hues, that the colors gold and silver are identical in hue to yellow and white--that their properties are based on the coherent reflectivity of their surfaces, and painters have to use the trick of painting highlights to portray them. All this requires making finer distinctions and expanding our vocabulary. Simply saying black is not a color, rather than, say, explaining in detail how black is different from green, doesn't achieve that. μηδείς (talk) 18:15, 12 November 2012 (UTC)

See here. Count Iblis (talk) 18:48, 12 November 2012 (UTC)

As it happens, on my laptop the change in display color according to change in viewing angle is just sufficient to counteract the optical illusion so that they actually do look the same color. Wnt (talk) 19:48, 12 November 2012 (UTC)

November 12

Size of Eliminated Dendritic Spines

Hello. Can an eliminated dendritic spine have a size? If so, why can such spines classified as "eliminated"? --Mayfare (talk) 01:32, 12 November 2012 (UTC)

If it has been eliminated, it no longer exists. It is possible that at least in some cases spines are actually reduced to a nub rather than eliminated, but such a spine could not properly be said to be eliminated. Was there some statement somewhere that created this confusion for you? Looie496 (talk) 03:21, 12 November 2012 (UTC)

The only occurrence of this phrase coming up on straight Google was at [7] - see figure 1H, in which the yellow square (lower row of panels) marks the eYFP signal corresponding to a single dendritic spine that goes away. As you see, the spine itself disappears, but it still occupies space in terms of the length of dendrite that is now unmarked by a spine. I assume this is what is meant by that, but could easily be wrong. Wnt (talk) 04:13, 12 November 2012 (UTC)

The last full sentence of the second page in http://www.nature.com/neuro/journal/v15/n7/abs/nn.3134.html --Mayfare (talk) 05:56, 12 November 2012 (UTC)

I guess you mean this sentence: "Measures of the relative size of eliminated spines—a measure of synaptic strength—showed no differences across groups (Fig. 2c), indicating that our stimulation paradigm was not causing the loss of a specific subgroup of spines.". My take on that is that they mean the size of a spine before it was eliminated. Looie496 (talk) 07:18, 12 November 2012 (UTC)

IQ and artists

I know that there's a correlation between IQ and performance in professional careers, like medicine and law. Have any studies explored the correlation between IQ and artists? 65.92.7.202 (talk) 03:45, 12 November 2012 (UTC)

We have a section, IQ#Social_outcomes. I looked at some of the studies linked there in, but the best ones are paywalled so you probably won't have access to them. The gist is that IQ is a better-than-random predictor for performance at virtually every entry-level job, and usually the best. This is assuming you have controlled for variables such as education, age, and socioeconomic origin. As far as music goes, the research discussed in our article looks at it from the other direction, asking the question "Does learning to play music make you smarter?" The answer seems to be yes. Someguy1221 (talk) 04:15, 12 November 2012 (UTC)

Do we have any substances or pills that are the opposite of anti-depressants?

Specifically, I would mean depressants in the mood or emotional sense, not in the CNS or respiratory sense. Do we have a pill that can make you sad, or less happy? If anti-depressants are SSRI (Seratonin reuptake inhibitors), do we know of any seratonin reuptake promoter, or dopamine reuptake inhibitor?

I ask out of curiosity, because it seems like an interesting field of research as to its possibility and effects, and possible treatments for extreme cases of narcissistic personality disorder or mania fits (or insert other potential uses here). Is this even possible? Is there research into it? Ehryk (talk) 06:12, 12 November 2012 (UTC)

See depressants. StuRat (talk) 06:57, 12 November 2012 (UTC)

No no no - I don't mean CNS depressants, as I said, and I don't mean depressants as opposed to stimulants. I'm talking about 'a pill that makes you feel sad', the opposite of 'a pill that makes you feel happy.' Ehryk (talk) 07:02, 12 November 2012 (UTC)

(ec) That's the wrong article -- depressogenic is the one that refers to mood. Adding to it: (1) There is a drug called tianeptine that works as a selective serotonin uptake enhancer, but strangely, it seems to have antidepressant effects rather than prodepressant effects. (2) Dopamine reuptake inhibitors do not have depressive effects, rather the opposite -- in fact, cocaine is a dopamine reuptake inhibitor. Looie496 (talk) 07:05, 12 November 2012 (UTC)

The way tianeptine works doesn't seem completely strange, the brain tries to keep the homeostasis, so a push in one direction can have an effect in the opposite direction. Philoknow (talk) 18:23, 12 November 2012 (UTC)

The nearest that I find: Recreational_drugs#Depressants. Comploose (talk) 19:01, 12 November 2012 (UTC)

Transmission of radioactive rays through glass

Can alpha, beta and gamma rays pass through glass ? Sunny Singh (DAV) (talk) 07:40, 12 November 2012 (UTC)

Alpha: no, beta: no, gamma: generally yes, with the added bonus of often colouring the glass through prolonged exposure. Fgf10 (talk) 07:54, 12 November 2012 (UTC)

It isn't really a case of each ray being able to penetrate or not penetrate. How much gets through depends on the energy of the radiant particles and the thickness of the glass, as with any media. For a thick piece of glass, the rays suffer attenuation per unit distance. Sufficiently energetic (ie.e, accelerated) betas (ie electrons) will penetrate glass without too much attenuation if it is not too thick. If it were not so, linear accelerators and other sorts of accelerator could not work. Floda 120.145.138.192 (talk) 12:36, 12 November 2012 (UTC)

The electrons also suffer energy loss due to their ionising effect so for any given energy there is a maximum distance they will penetrate. Dmcq (talk) 14:48, 12 November 2012 (UTC)

square ring falling through magnetic field

Suppose you have a square loop falling through a circular loop through which a current flows. Is there an equation relating the position of the square loop to time? Widener (talk) 07:42, 12 November 2012 (UTC)

You can write a system of differential equations for this problem. However I am not sure that it has the exact analytic solution. Ruslik_Zero 18:40, 12 November 2012 (UTC)

Mil Mi-24

Is the Mil Mi-24 attack helicopter equipped with infrared camera?--Wrk678 (talk) 10:51, 12 November 2012 (UTC)

This undated article (December 2008 or later) states "Russian Army Mi-24s are being upgraded with new avionics including thermal imagers." This article, also undated, mentions an "upward hinging cover for IR sensor" for the Mi-24K. Clarityfiend (talk) 11:11, 12 November 2012 (UTC)

Although if this is connected with your previous question; Noveber 4: Syria Rebels, then that is a different matter. Alansplodge (talk) 18:20, 12 November 2012 (UTC)

Yep. Buying a helicopter is much like buying a car in that nearly any accessory can be added -- provided you're willing to pay for it. Even if there was no integrated infrared camera option for an Mi-24, a bolt-on camera and an independent controller/screen for the cockpit can't be all that difficult to add if "getting it done" is more important than "doing it right". — Lomn 23:53, 12 November 2012 (UTC)

What is "matter" according to modern physics?

In classical Physics essential feature of "matter" was "mass". Right? Now since "mass" and "energy" are same so what is the defining characterisic of "matter"? :: Vineet Chaitanya 14.139.82.7 (talk) 13:18, 12 November 2012 (UTC)

Unsurprisingly, there's an answer in our article on matter: Matter is whatever possesses mass and occupies space. This is then linked to the Pauli exclusion principle. AlexTiefling (talk) 13:32, 12 November 2012 (UTC)

Can you just have one of this features? For example, occupy space but not have mass, or have mass but not do not occupy space? Philoknow (talk) 18:10, 12 November 2012 (UTC)

Both I believe. There are particles with no rest mass, like the photon, which presumably occupy space, and massive objects which have no volume, like the gravitational singularity in a black hole. StuRat (talk) 19:25, 12 November 2012 (UTC)

Per the Simpsons, "What is mind? No matter. What is matter? Never mind." μηδείς (talk) 23:23, 12 November 2012 (UTC)

Stu, photons do not occupy space (in the sense that if it is there nothing else can be there). They are bosons and thus are not bound by Pauli's principle, which is a fermionic statistic. On those scales the laymam's ideas of "mass" and "occupy space" as we know them are not really meaningful. 24.92.74.238 (talk) 01:45, 13 November 2012 (UTC)

Aren't photons a type of imaginary particle whose entire existence is defined purely by its history? History includes: absorption, emmision, and gravitational interaction. Plasmic Physics (talk) 02:54, 13 November 2012 (UTC)

"Hey this mass has lost some energy, lets call it a photon." Plasmic Physics (talk) 03:09, 13 November 2012 (UTC)

Getting a given wavelength radio signal given an antenna with real-world constraints

Wavelength is related to transverse distance between peaks, not axial displacement of charge carrier.

Supposing you are given a transmitting antenna of whatever type of metal is most commonly used these days, and supposing that you are applying an AC current with the intent of transmitting a 1 m wavelength radio signal, about how far is one electron likely to make it in one direction along the antenna conductor in one half cycle from a negative peak to a positive peak, factoring in the likelihood of the presence of antenna material atoms affecting the electron's path? Can individual charge carriers actually make it very far (on the order of meters) through metal?

But if the answer is that individual charge carriers actually only make a microscopic or very small displacement in space, how could a 1 m electromagnetic wave be produced? I don't see how a large number of charge carriers each only making a very small displacement in space can add up to a 1 m wave.

This site, especially Fig. 2 there, is where I'm getting my basic understanding of how alternating current gets an EM wave transmitted. From that is where I got the feeling that charge carriers would actually need to make a displacement in space on the same order as the intended EM wave. Peter Michner (talk) 16:43, 12 November 2012 (UTC)

The individual electrons will only move a very small distance - see drift velocity. In the example on that page, the electrons only move a couple of nanometres (that's ignoring the random motions the electrons have anyway and just includes the motion induced by the electricity). It may help to think of it like a Newton's cradle. The balls in the middle hardly move at all, but they are still able to pass the energy along. One bumps into the next, which bumps into the next and so on. Electrons carrying current through a wire do roughly the same thing (it's not a great analogy, but it might help to see that lots of things moving a very small distance can add up to result in large movements). --Tango (talk) 18:25, 12 November 2012 (UTC)

I think I get it now after looking at this visualization. The radiated field wavelength doesn't have to do with the physical displacement of the charge carriers in the direction of the conductor, but is related to the transverse distance perpendicular to the conductor with the waves emanating out at the speed of light (in a vacuum, and only slightly slower in a medium such as air) as shown by this picture which I just made to try to explain it to myself. Peter Michner (talk) 19:32, 12 November 2012 (UTC)

Long time effect of drugs

Some people lose their mind after too much use of recreational drugs, and their brains never get tuned again, even if they stop to take drugs. Is the opposite case also possible? Could someone who goes through a controlled therapy change the chemistry of his brain long term but in a positive direction? Comploose (talk) 17:46, 12 November 2012 (UTC)

First of all, we need to figure out what we mean by changing the chemistry of the brain in a positive direction. We tend to consider any deviation from the norm to be a bad thing (evolution tends to do a pretty good job of finding a fairly optimal norm, so that's not a bad definition). I can imagine situations where someone has some kind of neuro-chemical disorder that is permanently cured by medication - would you count that? Or are you specifically looking for improvements above the norm? --Tango (talk) 18:29, 12 November 2012 (UTC)

Nope, no improvement above the norm. Just if, for example, a schizophrenic or depressive patient goes through a treatment with psychoactive drugs, can his brain chemistry be changed for ever, or for a long term, after he stop taking the medication. Comploose (talk) 18:45, 12 November 2012 (UTC)

• To begin with, the claim that people may lose their minds after overuse of recreational drugs is very dubious, unless they overdose to a degree that causes brain damage due to the heart or lungs shutting down and depriving the brain of oxygen. But to address the main question, ECT is a therapy that is supposed to change the chemistry of the brain long term in a positive direction, for people who are depressed. There is some recent evidence that ketamine also can cause long-term positive changes in depressed people. Looie496 (talk) 18:50, 12 November 2012 (UTC)

• "Lose their minds" might be overstating it, but many drugs can cause negative long-term brain changes. StuRat (talk) 19:27, 12 November 2012 (UTC)

• There are a lot of neurotoxic recreational drugs, that could cause Olney's lesions among other things. I don't know exactly what is meant by "lose your mind". Has someone suffering from Parkinson lost his mind? He will be able to think, but not to control completely his movements with his brain. OsmanRF34 (talk) 21:02, 12 November 2012 (UTC)

I'd be more optimistic of changing the brains of children in a positive way than adults. In adults, the basic way the brain works is already established, and only incremental improvements are normally possible. StuRat (talk) 19:29, 12 November 2012 (UTC)

Drugs are used as part of successful therapies to overcome such things as alcoholism and acute psychological traumas, PTSD and OCD with varying success rates. See librium, valium, antabuse and so forth. It's also certainly not dubious that people become psychotic or terribly damaged long-term after drug abuse and some don't recover. μηδείς (talk) 23:21, 12 November 2012 (UTC)

Evidence of filamentation of the milky way

Given that dark matter sculpts the galaxy clusters into filament structures I would assume that this is also an effect at smaller scales such as our Galaxy itself.

Is there any evidence of filamentation of the 1) Milky way galaxy and also 2) The gas in our solar system.

I can visualize the dark matter as tiny chargeless particles flying towards more massive objects and causing a sort of "gravitational current" effect which causes the filament structures . Am I on the right track? :) --Ap-uk (talk) 18:52, 12 November 2012 (UTC)

I'm not sure it's correct to say dark matter is what "sculpts" the galaxies into the formation they take. It would certainly play a part, if it even exists, which I don't doubt very much, but it's not certain yet. Whatever effect dark matter has, it's quite weak, so weak that it is difficult to measure on sub-galactic scales. That's why we didn't notice it for so long. Looking for it inside our galaxy is hard, we really notice the effect when we look at whole galaxies or on groups of galaxies. Looking for an effect of dark matter on gas in our solar system would probably be a waste of time at this stage. Also most of the current best theories don't describe dark matter as "tiny" particles. Maybe you should give our dark matter article a good read. Vespine (talk) 21:37, 12 November 2012 (UTC)

plastic PE discoloration

hello i was asking about the plastic PE film tube discoloration to reddish or yellowish since it will be changed after putting in a warehouse or even inside the plant and this matter will happen after only few days. thank you — Preceding unsigned comment added by 77.31.104.159 (talk) 20:55, 12 November 2012 (UTC)

It's not clear what you are asking. Do you want to know what caused it, how to prevent it, how to repair it, or what ? And what's a PE film ? StuRat (talk) 20:57, 12 November 2012 (UTC)

I assume PE = Polyethylene. Perhaps if it's being stored at high temperature it could be loss of plasticizer? or some sort of side reaction? I agree though, more information would help. (+)H₃N-Protein\Chemist-CO₂(-) 21:36, 12 November 2012 (UTC)

cornstarch and water experiment

I have been looking everywhere for this. I am doing a science project and I don't have a good idea for my research draft.It has to be 1-5 pages.what I mean is that it can be 2-4 or 1-3 or 2-5.So what I need is a good research draft.Can I have help? — Preceding unsigned comment added by 99.32.182.192 (talk) 22:31, 12 November 2012 (UTC)

It is difficult for us to answer with regards to the expectations of your teacher. As a teacher myself, I wouldn't object if a student asked me for a clarification on my requirements regarding an assignment. Length requirements are a secondary issue: the teacher wants you to write enough to completely cover the topic of the paper, but to not drift into off-topic writing. Remember that longer is not better, but incomplete is also bad. Your goal should be completeness but not excess. Still, your best option is to ask your teacher directly. A smart student with initiative gets their assignment done several days in advance, and asks their teacher to look it over briefly to see if any adjustments need to be done before the due date. A good teacher will give constructive feedback to a student that does this. --Jayron32 22:35, 12 November 2012 (UTC)

Well, length should be a secondary issue, but, depending on the teacher, it may very well be their primary concern. I've had teachers grade almost solely based on length, and I shoveled lots of "filler" into everything I wrote for them, accordingly. StuRat (talk) 22:55, 12 November 2012 (UTC)

So, the one thing we can be certain of is that Jayron never taught StuRat? μηδείς (talk) 23:11, 12 November 2012 (UTC)

No, that does not follow. Stu had at least two other teachers other than Jayron, that much is certain. --Stephan Schulz (talk) 23:22, 12 November 2012 (UTC)

Nobody can predict how grade school teachers will act. But we have a piece of an article on "oobleck" under Non-Newtonian fluid and Wikiversity has some resources also. (Those are in an unusually advanced condition for Wikiversity, which is to say, it looks like a rough draft of something even if you're not quite sure what yet) Wnt (talk) 23:58, 12 November 2012 (UTC)

Jayron must be an exceptionally helpfull teacher if he gives students a pre-mark off the record assessment, just because individuals ask for it. Whether it is fair to all students is debatable. Remember, there are 3 basic reasons for marking assignments: 1) So the teacher and the teacher's superiors can asses his success at teaching; 2) to ensure students actually do the assignments; 3) Gating - i.e., only let thru students who have a demonstrated level of capability - knowledge, ability to think, and the ability to get work done. Would you be comfortable with a student asking another student look over a draft paper? That is sometimes done, but is generally considered a bad thing unless it is only to get help where you are stuck. It it always a bad thing if the student pays the other student. How is getting the teacher to give a pre-mark off-the-record assesment different? The teacher would need to be VERY carefull how he does this. Having said that, it is quite normal for university staff to provide such help with post-grad thesis papers - but this is done in very controlled ways, is acknowledged to be the norm, and when the thesis is marked, it's usually done by at least 2 people. I agree that it is quite acceptable for a student to ask in general terms what length is expected, just as it is acceptable to get any ambiguity in the assignment question resolved.

Particularly in 1st year university and college courses, there is another reason why teachers/lecturers set a required length for assignments. 1st year students sometimes come with an intense interest in certain topics and may be poor time managers. A student might, for example, happilly spend all week writing a most splendid longish paper on a subject he/she loves, and leave minimal time to do that difficult math assignment - but in fact the big picture is that he/she should have spent the time pondering the math and mastering it. It's not very good if at the end of semesterm you got an A in subject you love and a FAIL in subjects you didn't like - not good for you, and not good for the college or university. It's better to get a whole lot of B's and C's if that's what it takes to avoid any FAILS. Setting a max length on assigments helps prevent students not do more than is required and maitain a balance of effort.

Another reason for setting a maximum length is to force the students to be concise - that keeps the teacher's marking work load down, and sets the student up for his future - being concise is essential in employment. So, look at what you have been asked to write on. If you feel you can cover the subject quite well in 2 pages when 5 have been asked for, perhaps there's an aspect to the topic you haven't thought of?

Wickwack 121.221.32.50 (talk) 00:49, 13 November 2012 (UTC)

Your experiences must be very different from mine. I've never had a teacher who wasn't willing to look over drafts. Most of them refuse to give preliminary grades, but they do give detailed and helpful feedback. I've also never had a teacher who objected to students proofreading each others' essays. In fact, my school has a student-staffed writing center specifically for the purpose of proofreading other students' essays. --140.180.252.244 (talk) 02:12, 13 November 2012 (UTC)

Could be. You (140.180.252.244) geolocate to Princeton University (a very good university incidentally). Where you refering to Princeton or to a highschool? Certainly in my experience, getting such assistance from teaching staff in undergrad courses is just not possible due to their workload. I remember doing first year engineering math - about 2000 students from all engineering & science courses together in a large hall - and way down the front was the lecturer with a microphone. After presenting his weekly 2-hour excited no-stopping-for-anything recital, he would hang around another 10 minutes or so for questions, then nick off - we wouldn't see him until the next week. Each week during the 2 hour lectures in each subject they would set an assignment. We were required to submit them to the department clerk on or before the required date, along with a cover sheet and signed statement that it was all our own work and references credited. The clerk date-stamped them and gave us a receipt. A day or so later, the lecturer got all the assignments from the clerk, took them somewhere (home? his office?) and marked them. At the next lecture, he brought the marked assignments with him, and put them on the table for us to collect during the break. That was pretty much all the contact we had. If only (say) 1% of students somehow made contact and asked for advice, that would obviously take up more of the lecturer's time than his official commitment would. If you wanted him to advise you on a draft, you'd have to give the draft to to the clerk, and there was no reason why the lecturer would turn up until he needed to collect the assignments for marking. However, once you got past first year, the teacher-to-student ratio progressively improved considerably and much more contact/interaction happened. Wickwack 121.221.90.241 (talk) 02:42, 13 November 2012 (UTC)

Off label use of drugs

How can it happen that some drugs are used off-label? If someone has reliable information about one use, it should be included among the normal uses of a medicine. If no one knows it it's reliable, why is someone using it? Comploose (talk) 22:50, 12 November 2012 (UTC)

Getting "reliable info" about a new use of a drug requires years of research and millions of dollars. It would also be difficult to prevent off-label use. StuRat (talk) 22:56, 12 November 2012 (UTC)

What Stu said. We have an article on off-label use, by the way. Someguy1221 (talk) 22:59, 12 November 2012 (UTC)

November 13

my camera for my experiment recorded video with a 0.80x resampling factor. When calculating centripetal acceleration and curvature, how do I scale?

I run the video through a program and it plots the trajectories of tracked objects over time (based on timestamps). The only issue, my video is 25% faster than reality. Video is taken for 5 min and 35 seconds, but only 4 min 30 seconds of video is recorded. The video is being time-scaled to match, i.e. it is not truncation. I have since corrected this problem, but I have two months of data that were taken in this "time-compressed" fashion.

Am I right to assume that curvature will remain unchanged, that is, the scale corrections applied to velocity and x' * y - y' * x will cancel out?

However for centripetal acceleration, since it is v^2 / r or v^2 * curvature, and curvature will not change with time scale, my values that I am calculating for centripetal acceleration will be (1.25)^2 faster, that is I have to apply a correction factor of 1/1.56 to my values. 137.54.63.225 (talk) 00:12, 13 November 2012 (UTC)

(EC) Why would you assume that that the time scaling would cancel out? Have you tried the calculus yourself? I think to say anything definitively, you'd have to know exactly how the camera samples the frames in time. Can you document that it's uniform? If not, then we cannot say for sure without knowing how frames are sampled over time. Also, is this the fruit fly project that IP questioners have discussed here before? SemanticMantis (talk) 02:13, 13 November 2012 (UTC)

Chemistry problem

I was wondering how to do part B of the following problem.

1) A saturated solution of sulfur dioxide was prepared at 27 °C and 760 torr (millimeters of mercury). A 5.00-milliliter sample of this solution was diluted and an excess of potassium iodate solution was then added. The iodine liberated was equivalent to 32.80 milliliters of 0.100-molar sodium thiosulfate solution. The reactions that occur are given in the equations below:
5 SO2 + 2IO3¯ + 4 H2O --> 5 HSO4¯ + 3H+ + I2
2S2O32¯ + I2 --> 2I¯ + S4O62¯
(a) Calculate the moles of I2 liberated.
(b) Calculate the volume of sulfur dioxide needed to prepare 1.00 liter of the saturated sulfur dioxide solution.

I got .00164 moles of I2 for part a (I am almost positive this is correct, if someone would like to double check feel free to do so and let me know).

NOTE:

• The answer for part B is 40.3 L, but I am not sure how to do this.
• Part B is not a limiting reaction, it is a gas law problem, and may or may not involve stoichiometry.
• You don't need to write a detailed explanation for your steps, if you just write the equations as you progressed and the answers for them, I should be able to figure it out on my own. If I need more help I'll contact you. Or you can just write the steps you'd take.

Alternatively, if someone can't solve it but can just explain what Part B is asking, that'd be appreciated. SO2 and sulfur dioxide are the same, so isn't 1.00 Liter of satured sulfur dioxide the same as the volueme of SO2? I don't understand what they're looking for.

Please, if anyone can solve Part B and explain their steps here, it would be much appreciated! Or offer even some steps or help. I've tried this multiple times, but have never been able to get 40.3 (and I know this is the answer). --Jethro B 02:45, 13 November 2012 (UTC)