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February 25

Shine-Dalgarno sequence

How is this pronounced? "Shine" as in the word "shine"? Nadando (talk) 00:02, 25 February 2011 (UTC)

The Wikipedia article on John Shine, for whom the sequence is part named, gives no pronunciation guide, which weakly suggests that it is indeed not out of the ordinary for someone of apparently Anglo-Saxon heritage, as can be seen here. 87.81.230.195 (talk) 01:18, 25 February 2011 (UTC)

Greenhouse effect from producing methane

If you plant trees, you are extracting CO2 from the atmosphere. What would happen, in terms of greenhouse effect, if you produce methane with this biomass from the trees and release it into the atmosphere? I know that burning the methane would bring you back to the CO2, but this is a hypothetical question. Quest09 (talk) 01:51, 25 February 2011 (UTC)

Methane is also a green house gas. And it is pound for pound much stronger than CO2. Dauto (talk) 03:31, 25 February 2011 (UTC)

(ec)Methane has a much stronger greenhouse effect than co2, but it doesn't last long. It reacts with oxygen and essentially burns. See Global warming potential. Ariel. (talk) 03:34, 25 February 2011 (UTC)

Yes, I know, but since you are also removing a green house gas from the atmosphere, even if it's to produce other, the question remains, is the balance positive, or negative - in terms of greenhouse effect? Quest09 (talk) 12:17, 25 February 2011 (UTC)

Because methane decays faster than carbon dioxide, you need to specify a timescale. Global warming potential is the time-dependent factor used to compare different gases. It is calculated by mass. One mole of CO₂, molar mass 44g, would presumably be converted to one mole of CH₄ (methane), molar mass 16g. So one mole of methane has 0.36 the mass and over 20 years around 72*0.36=26 times the global warming potential. Over 500 years one mole of methane has around 7.6*0.36=2.76. So even over 500 years, converting the CO2 to methane would be worse. Unless my sums are wrong, which is fairly likely! --Colapeninsula (talk) 15:31, 25 February 2011 (UTC)

It doesn't matter, because methane decays to carbon dioxide. You'll have a certain period with a much more potent greenhouse gas, and then you'll get back the original greenhouse gas that you were trying to avoid. Releasing methane is always worse than releasing an equivilent amount of CO₂. Buddy431 (talk) 17:53, 25 February 2011 (UTC)

Methane does not decay to carbon dioxide. It reacts with hydroxyl radicals and forms CO2 and water. 212.169.176.233 (talk) 22:21, 25 February 2011 (UTC)

I'm just using the terminology that user:Colapeninsula. Maybe "react" or "degrade" is a better term in this case, but it's really just semantics. The point is, methane (a greenhouse gas) doesn't last long in the atmosphere, but in being destroyed, it produces another, less potent but longer lived greenhouse gas, carbon dioxide. In fact, that gas is the same gas that would have been produced if the tree had been burned, and is produced in the same quantities, assuming that carbon is not converted into other compounds. Buddy431 (talk) 01:06, 26 February 2011 (UTC)

Methane capture technology is useful for electricity generation. Anoxic decay (better links available?) of plant matter (for example submersed in water) produces methane, as do methane clathrates. ~AH1^(TCU) 19:55, 26 February 2011 (UTC)

Rest mass

Okay, so suppose two electrons initially at rest begin to repel each other. They will evidently speed up, but the total momentum will remain zero. The total mass will remain zero as well, so that energy is conserved. That means that each electron's mass will remain constant. But $m={\frac {m_{0}}{\sqrt {1-v^{2}}}}$. So does that mean the electron's rest mass decreases? 74.15.137.130 (talk) 06:29, 25 February 2011 (UTC)

Why would the total mass of the system be zero? The electron has a non-zero rest mass, see Electron#Fundamental_properties. --Jayron32 06:37, 25 February 2011 (UTC)

Erm, I meant remains constant, sorry! 74.15.137.130 (talk) 07:15, 25 February 2011 (UTC)

Let me answer the question I think you are asking. In the initial state both electrons have potential energy - and the potential energy shows up as mass. Once they repel each other the potential energy gets converted to kinetic energy, which also has mass. So it's not enough to just calculate the mass due to velocity, you also need to include the mass due to potential energy. (Which BTW is almost impossible to do in practice - if someone on the other side of the planet turns on an electromagnet my magnet here suddenly has more potential energy since it could in theory be drawn toward that electromagnet, this is also true of a magnet on the other side of the universe, so in practice it's impossible to include all sources of potential energy.) Ariel. (talk) 07:18, 25 February 2011 (UTC)

Wanting to be able to work out the potential energy without considering all possible long-distance interactions is one good reason that we set the 0 of potential energy at infinity: then if that electromagnet turns on, your magnet merely has the possibility of negative potential energy. (Potential potential energy, I guess.) Its current potential energy doesn't change. Another reason to set that 0 is that it lets us (at least approximately) localize the potential energy within the mass of the object. (It's approximate because the EM/gravitational fields have some of that energy; see my further reply below.) If electrons were defined to have, say, 1 eV of potential energy even at infinite separation, we'd have to count up all the electrons in the universe and subtract that many eV from the measured mass of the electron to find its "true" mass without all of those interactions. --Tardis (talk) 15:53, 25 February 2011 (UTC)

Momentum staying zero doesn't imply that mass is constant. In this case, the momentum vectors are opposite and equal in magnitude, so the mass of the two particles is the same at any point in time (assuming velocities same--which you get from symmetry) but it can decrease or increase. So the mass of the electron decreases, but the rest mass is a constant, like the speed of light in a vacuum. Similarly, you can pass light through water, and its speed decreases, but that doesn't affect the speed of light in a vacuum. ManishEarth^{Talk • Stalk} 09:37, 25 February 2011 (UTC)

This is one of the many questions where "mass" merely causes confusion. Just say energy, and then throw in $c^{-2}$ if you don't like the units. I don't know what definition of mass you're using when you say it decreases: maybe some sort of "apparent rest mass" derived by removing the kinetic energy and supposing the rest to be rest mass. But in this case that's just the true rest mass plus the electrostatic potential energy, so we can just say that the latter is decreasing and be done with it. If we simplistically assume that the electrons do not radiate, then by simple symmetry the total energy (aka relativistic mass) of the electrons must remain constant because the total over both is conserved and each must always bear half of it. Yet another way of looking at it is that the electrons have their rest masses and the electric field in their vicinity has additional energy (mass/whatever). If you work out the energy of that field (which requires some care around infinities), you'll find that it drops as the charges separate, such that the process may be described as the electrons absorbing some of the energy from the electric field and manifesting it as kinetic energy. --Tardis (talk) 15:53, 25 February 2011 (UTC)

Hmmm, what's sort of odd about that is that when, say, an electron raises or drops a few levels in a nucleus, the light that mediates this is quantized and can be expressed as a particle. But how is the energy stored in the electric field quantized and described? (It has to be photons, but it seems hard to figure out where they are, how many there are, what frequency, and above all what prevents them from escaping) Wnt (talk) 04:01, 27 February 2011 (UTC)

medicine gaity-400

details about medicine gaity-400 —Preceding unsigned comment added by 220.225.96.217 (talk) 07:33, 25 February 2011 (UTC)

Gaity is a brand name for Gatifloxacin, 400 is the dosage in mg. See the linked article on it for more info - in particular note that it is considered unsafe and has been taken off the market, but still seems to be available in China and India. Unfortunately the article neglects to say what it's used for but it seems to be an antibiotic. Also, I've created a redirect for Gaity. Ariel. (talk) 07:51, 25 February 2011 (UTC)

pvc

is Vinyl Flooring pvc or another plastic — Preceding unsigned comment added by Wdk789 (talk • contribs) 09:01, 25 February 2011 (UTC)

Yes, PVC, but with Plasticizers to make it flexible (unlike white PVC water pipes which don't have any). Ariel. (talk) 09:19, 25 February 2011 (UTC)

Surge Protection

Hi, how much surge protection in power adaptor of consumer electronic devices like a TV or STB should be enough? Thanks? Dearkundan (talk) 10:06, 25 February 2011 (UTC)

It depends entirely on the stability of your AC power. I currently live in a residential area of California, and we "never" have power spikes - the electric current out of our wall plugs is pristine. So I consider surge-protection redundant, (in a sense because I'm trusting my power company). But I've lived elsewhere on other power grids, and also on a home electric generator; in those times, I would pay a lot more attention to the surge protector and/or invest in a uninterruptable power supply for important/expensive electronics. Surge protector explains some of the parameters to worry about - clamping voltage, total surge energy dissipation capacity. Larger total-energy capacity will mean that you can sustain multiple, repeated surges, or one very large surge, but let's be honest - if lightning strikes your transformer or distribution box, no surge-protector has the capacity to absorb and dissipate that level of energy. It's been my experience that a UPS is the best way to keep nasty power lines (particularly, if the power is coming from a generator) from zapping my equipment, but UPSes are much more expensive. Nimur (talk) 16:16, 25 February 2011 (UTC)

how to find hot and cold temp

calculate hot and cold temprature after 25 orbit .assume a 100kg sherical spacecraft is in an equatorial orbit.How is calculation different for a spacecraft in a 90 degree polar orbit 124.124.247.141 (talk) 11:19, 25 February 2011 (UTC)

Sorry, the Reference Desk will not answer your homework for you. The clues you need will probably be in your textbook or in your notes from class. Matt Deres (talk) 11:38, 25 February 2011 (UTC)

EM wave and magnetic field

Can a em wave and a magnetic field create a stream of electrons. Like the opposite of a cavity magnetron like when a magnetic field and a stream of electrons creates a em wave —Preceding unsigned comment added by 82.38.96.241 (talk) 11:50, 25 February 2011 (UTC)

Yes. Like most physics, Maxwell's equations are invariant under T-symmetry. 213.49.110.245 (talk) 18:41, 25 February 2011 (UTC)

Is there a example of it happening naturally or artificially. —Preceding unsigned comment added by 82.38.96.241 (talk) 19:19, 25 February 2011 (UTC)

Electron precipitation might count. A radio-signal from Earth (usually man-made, but sometimes caused by lightning), sends an electromagnetic wave or disturbance into the Earth's magnetosphere. The electromagnetic wave interacts with the steady-state magnetic field and the magnetically-confined plasma at high altitudes; and sometimes, electrons "squirt out" and rain down to low altitudes. It's a very complex process, though. Various ground experiments, atmospheric remote-sensing experiments, and satellites have investigated this phenomenon: here's a sensationalized (but scientifically accurate) account of killer electrons from space. Nimur (talk) 19:43, 25 February 2011 (UTC)

Sorry to bother you again but what does 'gyroresonate' mean in this context 'Some of the VLF waves from these transmitters will leak through the ionosphere, couple into the magnetosphere, and gyroresonate with trapped particles leading to particle precipitation.' — Preceding unsigned comment added by Lufc88 (talk • contribs) 19:58, 25 February 2011 (UTC)

The term "gyro-resonance" is a short-name for electron cyclotron resonance. This gyro-resonance describes the most simple type of electron motion in a magnetic field. The electron cyclotron resonance article describes it in more detail, but very briefly, it means that an electron (or other charged particle) flies in a circular or helix-shaped orbit around the magnetic field-lines. This is due to the Lorentz force, which describes how a charge moving through a magnetic field experiences a force perpendicular to the direction it is traveling - causing a circular-shaped orbit. In Earth's magnetic field, the magnetic field lines are non-uniform, because of the shape of the Earth's magnetic field. Also, the exact value of the magnetic field strength varies at any specific location, due to complicated interactions with radio waves and plasma. As a result, the path that each electron "flies" can be very strangely-shaped. Due to gyro-resonance, electrons spiral around in "circles", and due to field-parallel motion, these "circles" get stretched into "coil-shapes" (a helix). The size of those spirals ranges from a few meters, to more than a kilometer in radius. As the electrons also move parallel to the field-lines they follow a curved path along the Earth's dipole field, so they also bounce back and forth between the north- and south- polar regions of the earth, tracing out thousands of kilometers of motion. If, during any of these motions, the electron ever reaches a "very low" altitude (say, about a hundred miles above the ground), it's very likely it will "knock" into a gas molecule in our atmosphere. This causes the electron to lose energy, and so it can no longer sustain its magnetic-field interaction, and falls to earth (usually "zapping" a gas molecule in the ionosphere and creating new electromagnetic waves).

I should say - when a radio wave is in gyro-resonance, it means that the radio wave is at the same frequency as the electron's circular orbit frequency. This is a bit like a matched impedance - it means that energy can flow from the radio signal into the electron. Nimur (talk) 21:18, 25 February 2011 (UTC)

Thanks — Preceding unsigned comment added by Lufc88 (talk • contribs) 21:28, 25 February 2011 (UTC)

Malaria - could I be infected with malaria and not know about it?

I wanted to donate blood today, but I was sent away to take a test for malaria instead. I lived in India 15 years ago and according to Polish law I have to be tested for malaria before I am allowed to donate blood. Does this regulation make any sense? I assume I would have found out a long time ago if I had been infected with malria so this test will be just a waste of my time and the taxpayers money. Mieciu K (talk) 15:46, 25 February 2011 (UTC)

Makes some sense AFAIK Plasmodium vivax is capable of surfacing after quite long dormancy periods (many years) although the one I had Plasmodium falciparum is not. --BozMo talk 15:56, 25 February 2011 (UTC)

(e/c)P. vivax and such don't go away until you get cured. Chances are you would have noticed, but it's theoretically possible. It's worth noting that blood donation controls are a little on the paranoid side, mostly because people have this irrational fear of diseases from blood transfusion that leads them to refuse transfusions that might save their lives. SDY (talk) 15:57, 25 February 2011 (UTC)

Given that there have been notable instances of diseases transferred by contaminated blood products, a little healthy paranoia is probably warranted: Contaminated haemophilia blood products, HIV-tainted blood scandal (Japan), [1]. Recently, there's been some scare about people getting donated blood from people who later developed vCJD. It's unclear how well (if at all) CJD is transmitted through blood, but most blood officials are erring on the side of caution (rightly so, in my opinion). The BBC article I linked to above details the case of what's believed to be the first vCJD transmittion through contaminated blood (though symptoms never showed themselves, and the man died of other causes). Buddy431 (talk) 17:50, 25 February 2011 (UTC)

Here in Spain, you can donate your blood no matter what, but you also get asked lot of question, including in which countries you have been. It gets tested only after the donation. I don't know if this is a better system, but it seems evident that you need to test for possible hidden risks. 212.169.184.39 (talk) 16:29, 25 February 2011 (UTC)

Well, the blood can only be tested after the donation, can't it? Here in the US, one interesting feature of blood donation is that there's a big box that you can check on one of the forms telling them: "Destroy my blood after I leave". I think the reason for the box is in case a donor hears all the questions ("Have you had homosexual sex in the last X years"; "have you ever traded drugs or money for sex"), and answers "Um, no, certainly not" out of embarrassment or shame, then the donor may be insecure enough to actually go through with the entire donation so the questioner won't detect the donor has done these things. And then make sure not to endanger others. (Yes, some of these questions are becoming a bit controversial.) Comet Tuttle (talk) 18:31, 25 February 2011 (UTC)

No. There's a difference of about 400 ml between a donation and a simply extraction. For testing your blood, they only need a little. Homosexuals are still considered a risk group, although the most logical question would be: how many partners/with or without condom/anal or not. But, I suppose that's too personal for most donors. Anyway, I doubt that blood contaminated with HIV gets through the system. 212.169.176.233 (talk) 22:14, 25 February 2011 (UTC)

Well, to give an idea of the absurdity of it, the U.S. and many other countries ban blood donations from any man who has had sex with a man since 1977. Several countries making reforms to this policy have reduced this period to one year.[2] Such policies, no matter what they turn out to be, are probably a combination of public relations and defensiveness against liability suits, representing largely the relative political power and social status of each group affected, with only a small element of medicine involved. Wnt (talk) 01:55, 26 February 2011 (UTC)

You should read this explanation of why exactly the UK excludes men who have sex with men as donors, which the Terrence Higgins Trust currently supports. It is based on the body of evidence, although the current review of recent evidence may lead to changes. Blood contaminated with HIV can indeed get through the system, even though every donation is tested for it, especially if the donor is only recently infected: this is why they go to such lengths to discourage donations from people who might be infected, and include information on how to get tested for HIV if you think you might be infected (rather than treating blood donation as a test). 86.166.42.200 (talk) 13:59, 26 February 2011 (UTC)

The word I have been looking for is Asymptomatic carrier "a person or other organism that has contracted an infectious disease, but who displays no symptoms." Are there any human asymptic carriers of malaria? I have already donated 4 or 5 times in Poland always stating in the questionare that I lived in India for over 6 months but until today nobody took notice of this. Mieciu K (talk) 16:50, 25 February 2011 (UTC)

Vivax malaria isn't nearly as dangerous as falciparum, which causes almost all of the malaria-related deaths, and the symptoms of malaria aren't very specific and could theoretically be mistaken for some other illness if mild enough or if misdiagnosed. Here in the states, a blood donor is considered "at risk" for one year after travel to a malaria risk area and is not allowed to donate, with the exception of Korea (longer deferral due to some unusual strains in that area). No testing is ever done. Honestly, malaria, especially non-falciparum, is not a big deal for a well-equipped medical system (compared to, say, other transfusion-transmitted infections), as there are several fairly cheap and reliable cures available, so even if someone "got through" it's easy to fix. The tragedy of malaria is that "cheap" cures, like a $4 course of an ACT or the even cheaper synthetic quinine derivatives, are too expensive for many of the people affected. Presumably they use the testing instead of forcing donors to wait after traveling, which means you get more donations if your donor pool is mostly people who travel (most notable in the US with the Armed Forces Blood Program). SDY (talk) 20:47, 25 February 2011 (UTC)

Note that is you carry one sickle-cell anemia gene, you may have a partial resistance to malaria, but still be a carrier. This gene is more common among blacks. See Sickle-cell disease#Genetics. StuRat (talk) 22:50, 25 February 2011 (UTC)

As detailed in the Plasmodium article, the hypnozoite stage can lie dormant for many years, but is less common in the falciparum form. Wnt (talk) 03:20, 26 February 2011 (UTC)

In 2004 after about 25 years of blood donation in the UK my blood was declined in Spain because I had lived in the UK during the 90s. I was told that I was at risk of carrying bovine spongiform encephalitis prions (the incorrectly named mad-cow disease) At that time Spain was free of that disease. Richard Avery (talk) 08:21, 26 February 2011 (UTC)

water survival

Assuming that you did not drown, die of thirst, or be eaten by sharks, how long could a person survive in the ocean if the water is 85 degF? Googlemeister (talk) 16:03, 25 February 2011 (UTC)

There may be some links leading to a specific answer to that at Hypothermia#Water. WikiDao ☯ 17:56, 25 February 2011 (UTC)

Not at 85F. If you had water to drink and a buoyancy jacket I would imagine starvation would be the next barrier at that temp. --BozMo talk 17:59, 25 February 2011 (UTC)

According to this chart, that is correct. :) WikiDao ☯ 18:12, 25 February 2011 (UTC)

A question related to this was discussed last year. To recap, the longest authenticated record of survival in open water is 5 1/2 days, by a shipwrecked Japanese sailor in World War II. Looie496 (talk) 18:37, 25 February 2011 (UTC)

I would think that overheating could be a problem during the day. If the water is 85°F, how hot is the air ? And add to that sunlight in the day. If overheating wasn't an issue, then sunburn might be. This could eventually lead to ruptures in the skin and then infections. StuRat (talk) 22:41, 25 February 2011 (UTC)

Sunburn would be a problem. Overheating would impossible in those conditions.

I think overheating might be possible. Specifically, if the air temperature is well over body temperature, humidity is 100%, and if the Sun is shining brightly, and if the people have short, dark hair and maybe dark skin, then their brains might overheat. They could continually dunk their heads underwater to cool off, but might not do so if they fall asleep during the day or if their flotation device prevents this. Splashing water on themselves might help, but as their energy gets lower, from lack of food, they may stop doing this. StuRat (talk) 21:07, 27 February 2011 (UTC)

Excessive jellyfish and any exposure to marine pollution (depending on location) may be another concern. ~AH1^(TCU) 19:06, 26 February 2011 (UTC)

Round and round the cell pellet goes.... how fast do you spin yours?

Is 1000 g not a rather large force to subject cells to in culture? Will it cause many cells to burst? Sigma Aldrich (at a course I went to) and Invitrogen (here) suggest 100-200 g, yet the place where I work routinely uses 1000 g. I'm planning on investigating the effects by counting cells before and after centrifugation, to see if many have "disappeared". In fact, I think I'll go and do it right now. --Seans Potato Business 19:07, 25 February 2011 (UTC)

Didn't seem to make a difference. *shrug* ----Seans Potato Business 19:59, 25 February 2011 (UTC)

Because the cells are inside water (fluid) they don't really experience the full effects of that force. Cells and water have nearly the same density, so while they feel a downward force, so does the water, which counteracts it. The only thing left is the small difference in density from water. Ariel. (talk) 20:02, 25 February 2011 (UTC)

Carbon dating

On Wikipedia today, I came across a claim that carbon dating once showed that two volcanoes from Hawaii that erupted in 1800/1801 erupted millions/billions of years ago (and that presumably, carbon dating is discredited). A quick websearch showed that this claim was repeated on various young-earth creationist websites. This had me wondering - what is the actual scientific explanation for this phenomenon, as I'm not as willing to dismiss carbon dating out of hand? Kansan (talk) 20:34, 25 February 2011 (UTC)

Carbon dating doesn't work for millions or billions of years anyway. But assuming you mean tens of thousands then if the sample is in water it can mess with the results, making the sample appear to be older than it really is. I've read that if your sample is, or ever was, in water, you can not use carbon dating on it. And unfortunately people are not always careful about this. Ariel. (talk) 20:41, 25 February 2011 (UTC)

How do you carbon-date a volcano, anyway? Doesn't that process require once-living material? APL (talk) 21:07, 25 February 2011 (UTC)

I'm pretty sure all you need is some trapped atmospheric CO2. Although I'm not sure you could get that with volcanic rock, since the gases are from the volcano, not the atmosphere. Ariel. (talk) 21:10, 25 February 2011 (UTC)

See uranium-lead dating and my comment below. Nimur (talk) 21:30, 25 February 2011 (UTC)

Carbon dating measures the carbon in things that use to be made out of plants or use to eat plants. It's used to measure the age of fabrics in archeological sites, frozen mammoths, mummies, etcetera. It is not used on things that are made out of rock, like dinosaur fossils or volcanic rocks, because they never breathed in any carbon isotopes.

Maybe they are dating plants that lived and died on the slopes of the volcano? Ariel. (talk) 21:12, 25 February 2011 (UTC)

Except nobody would do that since they already knew when the volcano erupted - and presumably with a much better margin of error than they'd get with even calibrated carbon-dating. Matt Deres (talk) 21:21, 25 February 2011 (UTC)

That may be a perfect reason to do it: To calibrate the tests. Ariel. (talk) 02:33, 27 February 2011 (UTC)

Comment - it's very common to see the term "carbon dating" used incorrectly. Radiocarbon dating measures the ratio of Carbon-14 to Carbon-12, and is "scientifically useful" only over a few thousands of years. Many other types of radioactive dating exist - our top-level article is radiometric dating. In all cases, the idea is to compare ratios of isotopes measured in a sample against those of a control-group. The assumption is always that the relative abundance or ratio of an isotope depends on the condition the object was in - so if it were buried underground, its expected isotope mix is different than if it were exposed to air (for example). Pop-science publications rarely get the subtleties correct - and often just say "carbon dating" when they really mean some other scientific radiometric assay. Nimur (talk) 21:25, 25 February 2011 (UTC)

It's also common for creationists to use a straw man argument, that by finding one discrepancy in a field, they then claim that the entire field of science is thus discredited. For example, one misidentified fossil is used to "prove" that all fossil evidence is bunk. This is, of course, total nonsense, as a complete T-Rex skeleton is definitely not a deformed elephant, or whatever else they claim. Now, I have no idea if anybody mis-dated a volcano by that long, but, if so, it certainly doesn't invalidate the method, just that particular measurement. StuRat (talk) 22:36, 25 February 2011 (UTC)

Thank you very much for the excellent answers. Kansan (talk) 21:42, 25 February 2011 (UTC)

In my view it is a blunder to try to explain what is wrong with a claim without having a clear and specific statement of the claim in the first place. Could you give a pointer to where on Wikipedia you saw the claim you are talking about? Looie496 (talk) 03:37, 26 February 2011 (UTC)

Fortunately, it isn't in mainspace. It was on Talk:Behemoth, but was removed as a rant unrelated to the page. See here: [3] Kansan (talk) 21:41, 26 February 2011 (UTC)

These two deal with the problem.

• doi:10.1016/0012-821X(69)90160-5
• doi:10.1007/BF02597188

And these are creationists trying to interpret the 40 year old measurments :

• 200 Year Old Lava Dated 2.96 Billion Years Old?
• How do you date a volcano?
• The Cause of Anomalous Potassium-Argon

--Stone (talk) 11:30, 26 February 2011 (UTC)

You might want to check Mark Isaak's Index to Creationist Claims, in particular this page that debunks the claims. [4] and [5] are about similar claims, but the first page has links to where I assume the claim mentioned byt the OP comes from.Sjö (talk) 11:42, 1 March 2011 (UTC)

Singular Value Decomposition and prediction

I'm working on a project where I have an existing dataset where each record contains some textual data and a metric relating to that data. My plan had been to represent this as a matrix where columns were records and rows were 'terms' (n-grams) - so that each element was the frequency of that term in that record.

I'd then hoped that I could augment this with the metric as an additional row, and use the incremental SVD to determine a relationship between the terms and this metric such that, when given an new (i.e. not in the training dataset) incomplete record where I have only the textual data (which I can represent as a vector of frequencies of terms), I could attempt to predict the metric for that record.

However, whilst I'm more-or-less okay with the SVD in principle, I'm unsure of its use for prediction (so my question here is 'how do I do this?'). Looking at various papers, particularly on product/movie recommendation, it looks like I'd have to add the incomplete record to my matrix and then compute the SVD, then... do something. However, this seems like it would be incredibly slow to work. 131.111.255.9 (talk) 22:08, 25 February 2011 (UTC)

All SVD does is decompose the input vector into a different set of coordinates (an output vector), with the intent that most elements in the output vector are close to zero. The SVD algorithm will produce a matrix that transforms between input- and output- coordinate spaces. The output vector is now in a new coordinate-space, whose unit-vectors are usually pretty abstract (they don't necessarily correspond to any observable property of the input-space).

If your input vector represents word frequency, what exactly are you trying to predict? Nimur (talk) 22:19, 25 February 2011 (UTC)

Yes, please tell us what data you have and what you are trying to predict, then we can recommend an extrapolation or interpolation method. StuRat (talk) 22:29, 25 February 2011 (UTC)

I'm trying to predict the metric. The text field explains an idea, and the metric is a retrospective numerical assessment of the quality of that idea. So, given a dataset of ideas and their qualities, can I discover some relationship between some aspect of the text and the potential quality of the idea it represents. Sorry for the vagueness, I'm not sure precisely what I can disclose. We've tried a few methods so far, and the SVD was recommended to us as an avenue to pursue. 131.111.255.9 (talk) 23:01, 25 February 2011 (UTC)

Singular Value Decomposition can be used to reduce the number of dimensions of the problem se [6] so other methods can be used on the reduced problem but I do not know how it can be applied directly. I think a naive implementation would just reduce to a least square algorithm. You need a Supervised learning algorithm such as Support vector machines. I think the software Weka (machine learning) can be useful to you.--Gr8xoz (talk) 14:30, 26 February 2011 (UTC)

If you can't disclose the actual data, could you come up with a similar example, so we can tell what kind of data you are working with ? StuRat (talk) 21:01, 27 February 2011 (UTC)

February 26

Entropy Quote

Resolved

 – Smallman12q (talk) 04:00, 26 February 2011 (UTC)

Entropy currently has the following unreferenced quote:

Any method involving the notion of entropy, the very existence of which depends on the second law of thermodynamics, will doubtless seem to many far-fetched, and may repel beginners as obscure and difficult of comprehension.

— Willard Gibbs, Graphical Methods in the Thermodynamics of Fluids (1873)

Unfortunately, it doesn't seem like their is a digitized version of the 1873 Graphical Methods in the Thermodynamics of Fluids. Can anyone confirm this quote with a reliable source?Smallman12q (talk) 02:30, 26 February 2011 (UTC)

The same quote appears in the collection of his scientific papers vol 1 (Relevant area of Graphical Methods.. is on page 11) available on archive.org here (record overview here). Nanonic (talk) 02:52, 26 February 2011 (UTC)

Thanks!Smallman12q (talk) 04:00, 26 February 2011 (UTC)

"Graphical Methods in the Thermodynamics of Fluids (1873)" looks like a reference to me. Just because there isn't a link to an online version doesn't make it unreferenced... --Tango (talk) 23:42, 26 February 2011 (UTC)

Sucking the wind

Once upon a time, the waters of the earth were thought to be infinite, and we poured all manner of crap into them because we did not know that the crap didn't just get diluted to oblivion, and eventually caused damage.

Are we on a similar path today with wind energy?

A few windmills here and there certainly don't have a noticeable impact on anything. But, if a few hundred of them become a few thousand or a few tens of thousands, will converting the energy of the wind to motion and thence to electrical power "slow down" the wind enough to have an impact on something else? What if the wind, like the water, is not an infinite resource, for us to use up as much as we can?

Seems inconceivable -- but we once thought that of the oceans, too. DaHorsesMouth (talk) 04:26, 26 February 2011 (UTC)

It's not inconceivable at all. Large objects, such as mountains, do have a profound impact on weather and climate, see Rain shadow and we are well aware how man-made structures affect weather and climate (see Urban heat island, which notes that one side benefit of these manmade hot spots is how they decrease the likelyhood of tornadoes; which is why it is rare that tornadoes will hit major cities). It is not inconcievable at all that large-scale windfarms could alter weather and climate patterns in many ways; indeed I don't think anyone is claiming that they wouldn't. The question over their usage isn't that they are zero-impact; literally NO power source is to be zero-impact; its that the negatives of windfarming, while very real, are also very much smaller than the negatives of burning fossil fuels. I don't think anyone claims that the technology is harmless, just less harmful than what we are doing now. Environmental effects of wind power would be a good place to look at some of the real concerns with windfarming. --Jayron32 04:46, 26 February 2011 (UTC)

The impact of wind power on climate has been studied in [7]. They found that over 100 years the magnitude of the impact is one fifth of that of current power production. Wind power gives a direct effect on the climate while CO2 will accumulate and the effect will increase with time. They also showed that the impact will partly be the opposite of that from C02. Wind power slows down the heat transport from the equator towards the poles while the polar regions (not sure about definition.) will be most effected by CO2 warming. They calculated simulated wind power usage at the same scale as the current total energy usage, 15 TW.(All fuels, renewable power, nuclear and so on, excluding the the solar energy used by plants in farming and so on.). This [8]article suggests that the oceanic heat transport could also be sensitive to differences in wind patterns.

It is interesting to compare the scale of the different energy flows:

• Total solar power: 3.8*10^26 W
• Solar power hitting the earth: 174 000 TW (1 TW=1*10^12 W)
• Total wind power :1000-4000 TW (conflicting estimates, better figures probably known)
• Total photosynthesis 75-2250 TW (Depends on if you count energy used by the plant it self and other issues with the definitions.) (approx. 25% of the photosynthesis are used or directly affected by humans.[9])
• Geothermal power from radioactive decay and cooling of the inner parts of the earth: 44 TW
• Total human power consumption: 15 TW (In technological systems, not solar energy or non fuel biomass in e.g. agriculture, forest.)
• Total tidal power: 3.75 TW
• Total wave power: 1-10 TW
• Total human electricity production: 2 TW (uses about 5 TW primary energy.)
• Total human wind power production in year 2009: 0.04 TW

If human power consumption continues to increase with 3% a year or 20 times in a century (Approximately the increase year 1900 to 2000) it is obvious that wind power is not unlimited but it can make a significant contribution to power usage at today's level. With 3% yearly increase in power consumption not even the total solar power on earth is enough year 2350.

--Gr8xoz (talk) 12:44, 26 February 2011 (UTC)

Depending on the scale of wind production, large-scale wind farms could potentially slow local/global wind speeds by a measurable amount according to numerical modelling studies. See the following articles from LiveScience: Nov 2004 Nov 2008 Oct 2010. ~AH1^(TCU) 18:40, 26 February 2011 (UTC)

Availability of the generic Adderall XR

"In 2009, Barr and Shire reached a settlement agreement permitting Barr to offer a generic form of the drug beginning April 1, 2009."[8] I just read the above quote in Wikipedia. Last month I was told by three pharmacies in my home town that the company is no longer going to make the generic capsule. I have ADHD and the capsule was working well for me. The price was right too. Does anyone else make a generic capsule? The brand is too expensive for me even with the help of insurance. Thank you. —Preceding unsigned comment added by 24.197.183.193 (talk) 06:00, 26 February 2011 (UTC)

Barr is owned in a roundabout way by Teva who still have generic Adderall listed as a product on their website. Global Pharma still have generic Adderall XR listed on their website. The best people to contact for confirmation of continued availability would be those companies. Nanonic (talk) 06:27, 26 February 2011 (UTC)

Humbucking pickups and 60Hz hum

I have an electric guitar with humbucker pickups, which are designed to cancel out 60 Hz hum. I am thinking about getting a guitar with P-90 pickups, with are not humbucking. I have a lot of compact fluorescent in the house and I am worried about picking up hum (from them and any other sources). Will these cause hum on the guitar? Will any compact florescent bulb in the house cause hum, or only ones on the same circuit breaker? Bubba73 ^{You talkin' to me?} 06:39, 26 February 2011 (UTC)

Compact fluorescents put out electromagnetic interference, but mostly in radio frequencies interfering with radio reception. Your main problem with guitar pickups will be magnetic fields. You should keep any power cords away from the pickup leads or guitar. Electric motors will have a much bigger effect than lights. SO keep these away too. If cords have to cross, do this at right angles. Keep the cords short. Do not create earth loops. Graeme Bartlett (talk) 22:28, 26 February 2011 (UTC)

Then I'll probably be OK. No motors except when the A/C or an appliance is running, and they aren't close. Not too many power cords running around. Thank you. Bubba73 ^{You talkin' to me?} 00:31, 27 February 2011 (UTC)

Modern florescent lights use electronic ballasts (both CFLs and tubes), but old ones used magnetic ballasts - those will probably interfere. One way to tell is simply to listen - the old ones hummed a little. A second way to test is wave your hand under the light. With modern fixtures your hands will simply "smear" out, with old one you will see a sort of strobe effect and you'll see images of your hand in various positions. (The old ones flashed at 60hz, modern ones at many thousands of hz.) Ariel. (talk) 01:29, 27 February 2011 (UTC)

Thanks. Some of the CFLs are up to 7 or 8 years old. Sometimes they start making a sound when they are going bad. There are a few long tube florescents in the kitchen that make noise - they may be the old type, but they are not on most of the time. (BTW, I ordered a guitar with non-humbucking pickups tonight.) Bubba73 ^{You talkin' to me?} 05:19, 27 February 2011 (UTC)

What's the problem with non-native species?

Why are conservationist groups so concerned about the introduction of non-native species to new environments? It's not like it's a new phenomenon (species have been migrating around the planet for hundreds of millions of years, e.g. the Great American Exchange) and it actually seems quite unnatural to try and prevent non-native species from taking hold on new territories. I know new species may be detrimental to the survival of native ones, but that's what natural selection is all about, no? Who are we to get in its way? --Leptictidium (mt) 10:50, 26 February 2011 (UTC)

The funny answer would be: Than have fun with the tigers in your suburb and the crocodiles in the public pool. Frogs do not migrate from Africa to Australia and rats were unable to cross over to New Zealand so why should humans help them. Humans are simply stupid to know what they are doing and at the end they do harm to their environment that it become less providable to live there.--Stone (talk) 11:11, 26 February 2011 (UTC)

"but that's what natural selection is all about, no? Who are we to get in its way?" -> http://en.wikipedia.org/wiki/Naturalistic_fallacy#Other_uses 213.49.110.245 (talk) 11:53, 26 February 2011 (UTC)

Rabbits in Australia. Vimescarrot (talk) 12:23, 26 February 2011 (UTC)

In the Sahal the sourthern part of the sahara desert people use non native herds of cattle and goat which unlike camels strip the grass right down to there roots this leaves the ground bare and the soil gets blown away and eventually it causes desertification which is land turning into desert this is a real damaging effect on the enviroment. Also non native goats and wildboar have been extremely damaging to the enviroment and wildlife populations. —Preceding unsigned comment added by 109.77.244.8 (talk) 12:34, 26 February 2011 (UTC)

Humans can speed-up the introduction of new species many times the natural rate. The human activity in an area is adapted to the historical environment there, it can be costly to adapt to handle the consequences of new weeds, or other spices. Evolution is most efficient when there are many weakly connected habitats and high biological diversity. If all habitat with the same conditions get the same ecosystem then it is mush more sensitive to changes, say fore instance that a new pest develops. --Gr8xoz (talk) 13:16, 26 February 2011 (UTC)

See non-native species and invasive species for more examples of the damage they can cause.--Shantavira|^{feed me} 13:37, 26 February 2011 (UTC)

However, non-native species do not always cause damage. They may simply take over from an equivalent native species. Concern about this (such as concern over the loss of the red squirrel to the grey squirrel and its associated pox) seems to me to be conservatism rather than conservation (unless, perhaps, conservation is its sub-category). See damage for a discussion of the different meanings that the word takes on when used within different value systems - oh wait, that doesn't work (it's just a disambig page). Well, imagine it did. 213.122.25.248 (talk) 14:39, 26 February 2011 (UTC)

The main problem is that invasive species tend to fill an occupied ecological niche and outcompete the original species in a way that alters the proportions of predators and prey. The introduced species often creates a rapid directional selection in the other species within that ecosystem and those species cannot evolve quickly enough to adjust to this new state. Notable examples of invasive species include the emerald ash borer, dandelion (especially New Zealand), large blooms of Nomura's jellyfish (not strictly invasive but oceanic changes are encouraging blooms), purple loosestrife, the common reed, and the historical Y. pestis. ~AH1^(TCU) 18:31, 26 February 2011 (UTC)

While the mechanism is true it is not necessarily clear that it is a problem. It can be a problem if it affects human activity in a negative way or if for some other reason the old ecosystem is valued higher than the new one.--Gr8xoz (talk) 23:29, 26 February 2011 (UTC)

Another problem with invasive species is that they may hybridize with native forms. This is important with things like killer bees, coy-dogs and mosquitoes transmitting West Nile virus. Hybrids have a larger gene pool to draw upon, and can evolve rapidly, e.g. hybrid speciation. Though measures of environmental damage usually focus on the loss of species, I would suggest that the evolution of new species could also be a major environmental challenge. Wnt (talk) 00:53, 28 February 2011 (UTC)

Did we just call speciesation and rapid evolution an environmental challenge? What else is the biosphere supposed to do? Mac Davis (talk) 14:19, 28 February 2011 (UTC)

It would be an environmental challenge for us. Clearly the biosphere is free to do as it "wishes" - even extinction represents a natural reaction to circumstances - but when such change is imposed on a rapid timescale by human action, it doesn't seem all that natural or benign. Wnt (talk) 16:35, 28 February 2011 (UTC)

Scientific American did a short interview in the Feb '11 issue with Mark A. Davis, who argues that invasive species aren't all that bad, in general. Certain examples, such as the brown tree snake in Guam, aside, the introduction of exotic species to new locations isn't necessarily a negative thing, he says. The interviewer summarizes by saying "the field needs less emotion and more science." The interview leaves me with about 100 questions, though, because it's very short and superficial. Davis does have a new book out called Invasion Biology, which might be more informative. -IceCreamAntisocial (talk) 18:10, 28 February 2011 (UTC)

Change isn't necessarily bad, and even changing an area into a desert is only bad by human standards, since most humans don't get much out of a desert. Environmentalists tend to hold values that say we should keep all environments as they were, before human intervention. Also, they value biodiversity, while, given free movement around the world, you tend to get a smaller number of "most successful" species, which wipe out the less competitive ones that accumulated on isolated islands. Thus, less competitive species, like many marsupials, might be doomed to extinction. One exception is that some environmentalists think the cure for an out-of-control non-native species is to introduce the predator which controlled it in it's native environment. StuRat (talk) 17:04, 2 March 2011 (UTC)

Converting % and ppm to g/kw-hr

I am working on a project, to determine the level emissions from generators. The values from the Gen. sets using an exhaust gas analyzer are in % and ppm, which has to be compared to international standards,which are in g/kw-hr. what is therefore the conversion rate. For example,CO and CO2 are in percentage (%), while HC and NOx are in parts per million (PPM).I will be most gratefull to be assisted in converting to g/kw-hr. Sample:

                                                CO=6.62%;4.71%;3.67% etc
                                                CO2=5.63%;7.27%;7.84% etc
                                                HC=136ppm;145ppm;152ppm
                                                NOx=40ppm;60ppm;68ppm

Thank you in anticipation —Preceding unsigned comment added by 41.78.80.94 (talk) 12:40, 26 February 2011 (UTC)

You need to know the mass of the exhaust gas produced then generating 1 kWh. If you know the amount of fuel and fuel type used to produce 1 kWh then that could be used to get a rough estimate. --Gr8xoz (talk) 12:56, 26 February 2011 (UTC)

Victoria waterlily

Why do these have a high raised lip? I presume it isn't for buoyancy, since they seem to stay afloat even when pushed partly underwater (they have some sort of air pockets, don't they?) ... and if it was for buoyancy, what would happen when it rains? Besides, there is a cleft at one point on the circumference (to let rainwater out?), which would be a poor design for a boat. 213.122.25.248 (talk) 14:46, 26 February 2011 (UTC)

I think you answer your own question. The lip aids in buoyancy, but the cleft prevents filling with rainwater. SemanticMantis (talk) 16:48, 26 February 2011 (UTC)

I guess. I suppose the lip helps a bit, despite the unlikeliness of a human designing a boat with a big hole in the side. It's an odd-looking evolutionary compromise. I'm not even sure it makes logical sense. If, when there is some water inside, the pad is buoyant enough for the water to run out the gap, wouldn't this still be the case with no lip? I can only think its purpose is to prevent sudden flooding, like in the case of being jumped on by one of those giant Amazonian otters ... but the article says the leaves are very fragile, so the leaf would be punctured by the otter's feet anyway. Maybe the point is to protect against being splashed by animals? 81.131.21.81 (talk) 16:57, 26 February 2011 (UTC)

Ok, here's a few other things to consider.

• The leaf doesn't need to be a boat; it doesn't 'want' or need to have much Draft_(hull).
• Under no load, the 97% rim is quite effective at keeping out all kinds minor slosh/ ripples of water, regardless of the source. This is good for the plant in terms of gas exchange and photosynthesis.
• If the leaf submerges for any reason, it can more easily drain and resurface due to the gap compared to a full rim.
• The 97% rim allows allows the leaf to stay afloat under small dry loads, such as frogs, insects, and detritus.
• A full rim would not be much advantage over 97% rim in most circumstances, and is worse in a the case of submersion.
• There may be genetic limits to the leaf#morphology, wherein a full rim is more difficult to achieve than it's worth. Most traits do indeed strike some sort of balance or trade off, i.e. as described with respect to shade tolerance here [10].

In short, I conclude that the 97% rim is a benefit due it its effects on buoyancy. Also, the cleft is not a big problem, and in fact provides additional benefits. I don't think a trait this distinct is ecologically neutral. Indeed if there are any suggestions for benefits aside from buoyancy issues, I'd be interested to hear them :) SemanticMantis (talk) 17:56, 26 February 2011 (UTC)

Oh OK, that's very good, particularly the part about needing to stay dry, rather than avoiding a risk of sinking. Thank you. 81.131.21.81 (talk) 17:59, 26 February 2011 (UTC)

It's an interesting question. On the other hand, if the lip is so great, we might wonder why it's not more common among water lilies... SemanticMantis (talk) 18:37, 26 February 2011 (UTC)

I did wonder that. It might be a thing which is only needed at large scales for some reason (*waves hands*). It might be that the non-Victoria waterlilies have better water-repelling surfaces (this is achieved by tiny hairs, or some amazing quantum effect and/or goretex). It might be (this is my bet) that there is much more detritus (particularly falling twigs, or falling branches which could cause splashes) in the Amazon than in your typical pond elsewhere in the world. 81.131.21.81 (talk) 18:53, 26 February 2011 (UTC)

I think you're on to something with scale. Those leaves are huge. For species with smaller leaves, surface tension plays a relatively larger role in keeping the leaf afloat, so the rim isn't as useful. A small needle can float on surface tension, but a large nail can not. SemanticMantis (talk) 20:06, 26 February 2011 (UTC)

This picture of Victoria amazonica would argue against that. Ariel. (talk) 02:28, 27 February 2011 (UTC)

While we are speculating wildly, what about preventing the leaves from overlapping? That seems like a simpler explanation; overlapping would have a big impact on photosynthesis, obviously. -- Scray (talk) 02:02, 27 February 2011 (UTC)

Sure, preventing leaf overlap is probably another slight benefit. SemanticMantis (talk) 17:07, 27 February 2011 (UTC)

Electrons circular orbit frequency

Can a electrons circular orbit frequency be changed or altered — Preceding unsigned comment added by Lufc88 (talk • contribs) 18:08, 26 February 2011 (UTC)

Do you really expect anybody to know what you are talking about without a little more context?? Dauto (talk) 19:57, 26 February 2011 (UTC)

It is asked in the context of my question above called EM wave and magnetic fields — Preceding unsigned comment added by Lufc88 (talk • contribs) 20:37, 26 February 2011 (UTC)

Do you mean Electron cyclotron resonance? If you do, as you can see by yourself in the linked article, the frequency depends on the magnetic field. Dauto (talk) 00:57, 27 February 2011 (UTC)

Thanks sorry about that i did not see that bit — Preceding unsigned comment added by Lufc88 (talk • contribs) 12:44, 27 February 2011 (UTC)

Ruhmkorff lamps

"Finally we had all the necessary chemicals for the Ruhmkorff lamps."[11] -- Jules Verne. Journey to the Centre of the Earth

How do you make a Ruhmkorff lamp? I saw the foreign languge links in Heinrich Daniel Ruhmkorff, but I'm looking for some simple step by step procedure. And what chemicals are used? Thanks. -- Uzma Gamal (talk) 20:09, 26 February 2011 (UTC)

As the article states, you need a Geissler tube and a source of electricity. Apparently they were powered either by a battery or a portable generator (which maybe fed the battery?). DMacks (talk) 20:27, 26 February 2011 (UTC)

The Google link didn't work for me, but from s:Journey_into_the_Interior_of_the_Earth/Chapter_XI:

"Ruhmkorff's apparatus consists of a Bunsen pile worked with bichromate of potash, which makes no smell; an induction coil carries the electricity generated by the pile into communication with a lantern of peculiar construction; in this lantern there is a spiral glass tube from which the air has been excluded, and in which remains only a residuum of carbonic acid gas or of nitrogen. When the apparatus is put in action this gas becomes luminous, producing a white steady light. The pile and coil are placed in a leathern bag which the traveller carries over his shoulders; the lantern outside of the bag throws sufficient light into deep darkness; it enables one to venture without fear of explosions into the midst of the most inflammable gases, and is not extinguished even in the deepest waters. M. Ruhmkorff is a learned and most ingenious man of science; his great discovery is his induction coil, which produces a powerful stream of electricity. He obtained in 1864 the quinquennial prize of 50,000 franc reserved by the French government for the most ingenious application of electricity."

The same page says "all the articles needed to supply Ruhmkorpff's apparatus", but doesn't specify what they were. (it lists "a row of phials containing dextrine, alcoholic ether, liquid acetate of lead, vinegar, and ammonia drugs which afforded me no comfort" just before that, but I think these are actually intended for human use???) I have to assume that the unspecified ingredients are the material needed to supply the Bunsen pile. Wnt (talk) 21:05, 26 February 2011 (UTC)

Looking over it, I still can't be sure - probably you'd need zinc anodes, sulfuric acid, and the potassium dichromate mentioned; with the sulfuric acid being used to convert that to chromic acid in the Bunsen pile. Such a pile wouldn't emit NO₂ - I'm not sure what sort of chromium salt would come out of it, but I think it would avoid the noxious fumes, hence the "makes no smell" in the text. Note however that hexavalent chromium has quite a bad reputation nowadays. Wnt (talk) 22:06, 26 February 2011 (UTC)

The Ruhmkorff coils would be called "induction coils" in publications from the early 20th century onward. Such a device has a primary coil fed at a low voltage, such as 6 volts, which coil acts as an electromagnet to attract the armature of an interrupter switch, which on being attracted breaks the current for a bit. A spring then recloses the primary circuit. This is the same as how a DC doorbell or buzzer works. Wound around the same magnetic core of a bundle of steel wires is a secondary coil with hundreds of times more turns which produces impulses of several thousand volts every time the primary circuit makes and breaks. The device is a transformer fed by pulsating DC. This is how primitive spark wireless telegraphy got its high voltage in the early Marconi days. The Geissler lamp is like a fluorescent lamp, but without the white phosphorescent coating which generates the nice white light. A basic Geissler coil would have been a dimmer light with less of a broad spectrum than a fluorescent light. Such a coil is rather a current hog, and a substantial and thus very heavy battery would have been needed to run it for extended periods. Short battery life and low light output are arguments against the basic system Verne described. So an induction coil, or a Model T spark coil, would be the "Ruhmkorff" device, and an evacuated tube like a neon sign would be the light emitting element. The battery described would be a complex 19th century wet cell, but as a demo you might use a modern rechargeable battery of the voltage the coil primary is designed for, such as 6 volts. A fluorescent tube, even a "dead" one, will glow brightly when connected to one output terminal of the induction coil. Note: painful and possible dangerous shocks from the high voltage generated are very likely., even from the primary circuit. I found it helpful to ground the primary circuit, a difficult task if the device is carried around. Further caution: High voltage can produce xrays from the light tube connected to the high voltage, so don't try this at home. A battery powered fluorescent lamp would be a modern and safe analog of the Vern lamp. Edison (talk) 02:36, 27 February 2011 (UTC)

Though to be fair, we have altogether lost the artistry of the Geissler tubes depicted in the article, especially as one considers the light such intricate baubles would shed in caves of fantastic minerals in the unknown depths of the Earth. I do concede, however, that whatever Verne said, such a high voltage circuit seems quite likely to involve sparks that would set off firedamp, especially if it truly used a buzzer mechanism. (though would it possible, in concept, for a well-crafted Bunsen pile to reach the needed voltage simply by using thousands of cells cleverly linked to be filled from common reservoirs?) Wnt (talk) 03:04, 27 February 2011 (UTC)

Verne did not suggest that a battery of 2000 cells, like Humphrey Davy's Great Battery of the Royal Institution, circa 1808 was carried on someone's back. Much easier to carry a primary battery which could produce 6 volts at several amps for several hours, and an induction coil with an interrupter to produce 4 kilovolts or so to make the Geissler tube glow. He might also have imagined an incandescent lamp powered by the battery, since one passage in the book says the battery was connected to the "filament" of the lamp. All he needed was an 1860's carbon filament in vacuum lamp, with a late 1870's vacuum pump. Then they would simply have had flashlights. Edison (talk) 06:18, 27 February 2011 (UTC)

You're right on this one. I was only speculating at a way to try to avoid the sparks, but among other problems you point out such a massive pile would not use the induction coil Verne specified. (Alternatively, maybe there's a way to encapsulate the entire relay/transformer mechanism to prevent contact with the air ...?) Wnt (talk) 16:33, 28 February 2011 (UTC)

Tricky physics problem

Dear Wikipedians:

I am working on the following tricky physics problem:

a 0.234 kg shoe is dropped onto a vertically oriented spring with a spring constant of 104 N/m. The shoe becomes attached to the spring upon contact and the spring is compressed 0.117 m before coming momentarily to rest. What work is performed by the weight of the shoe while the spring is being compressed?

My first approach is the gravitational approach:

W = mgh = 0.234×9.8×0.117 ≈ 0.268J

My second approach is the spring approach:

W = ½kx² = ½×104×0.117² ≈ 0.712J

I would tend to the 0.268J answer, but the computer system is rejecting both of my answers as wrong! I have only one more try left and I am desperate to see where I went wrong.

Your help is much appreciated.

174.88.35.131 (talk) 21:02, 26 February 2011 (UTC)

The gravitational approach doesn't consider any kinetic energy the shoe had upon hitting the spring. Not sure about the spring method, looks OK to me. Grandiose (me, talk, contribs) 22:18, 26 February 2011 (UTC)

The question is a little odd. I can't quite work out what it wants. Since your two answers don't work, the only other thing I can think of is to take the difference between the two. That is, calculate the work done by the resultant force on the shoe. That's not how I would have interpretted the question, but you've already tried my other ideas. --Tango (talk) 23:55, 26 February 2011 (UTC)

How many significant digits your answer is required to have? The data of the problem has three significant digits, and given that the average value of earth's surface gravitational acceleration is actually 9.81m/s^2, I'm getting W = 0.269J. If that turns out to be the correct answer to this problem I would say that this computer program is too picky. Dauto (talk) 00:08, 27 February 2011 (UTC)

It sounds like the shoe free-falls, then continues to drop as it compresses the spring. Both these things must add up to account for the force that the spring absorbs when compressed. Hmmm, on second thought, that should simply be the .712 figure, since all the force of the shoe goes into the spring (with typical frictionless assumptions and one-dimensionality it could rebound endlessly). But the question doesn't ask about the force of the shoe, only the work done by the weight of the shoe. That's just (F=mg=2.2955) x distance = (0.117 m) = 0.269 after all. Hmmm... Wnt (talk) 03:07, 27 February 2011 (UTC)

Is there a documented possible link between gender identity to sexual orientation?

Ya know, in a superficial way it seems that indeed there is, i myself don't agree and i think that even if there is, it ain't that robust...

but, what does the research shows to us?, is there a link?, and if there is, how significant it is by this stage of the research?

thanks and blessings,

Beni —Preceding unsigned comment added by 109.66.8.242 (talk) 22:56, 26 February 2011 (UTC)

I think it is rather well established that most persons that identifies them self as male primarily are sexually attracted to women and vice versa. I think almost every one agree that this is true in at least 80% of the cases, is it this correlation you want documented or did I misinterpret the question?--Gr8xoz (talk) 23:09, 26 February 2011 (UTC)

The question only makes sense if you ask: if my gender identity doesn't match my biological gender, which sexual orientation do I have? Normally that of the biological gender you wish to have... —Preceding unsigned comment added by 212.169.187.124 (talk) 00:08, 27 February 2011 (UTC)

Yes, normally but not always. Dauto (talk) 00:58, 27 February 2011 (UTC)

My guess is that the intended question is something more like this: If all you know about someone is that they are cisgender, what (if any) information does that give us about the statistical likelihood that they are also heterosexual? And I don't know the answer. --Allen (talk) 08:14, 27 February 2011 (UTC)

What does it mean to say that this transgender person is heterosexual? Is that according to his biological or intended gender?Quest09 (talk) 00:11, 28 February 2011 (UTC)

Presumably the term "transgender heterotsexual" would apply to person born with male sex characteristics, living as female gender identified, who is attracted to the male gender. Just a terminology note: Biological traits determine sex, but gender is a socio-cultural construct."Intended gender" would probably be considered a loaded term to some. The OP's entry needs clarification if s/he wants more help. SemanticMantis (talk) 00:39, 28 February 2011 (UTC)

I agree with SemanticMantis about what someone would probably mean if they said they were transgender and straight. But either way, that wouldn't change the numbers involved in answering the OP's question, if I'm correct about the interpretation. --Allen (talk) 13:31, 2 March 2011 (UTC)

February 27

Why is blood iron test taken from finger?

When one donates blood, at least in the UK, they first test your blood to make sure you're not anaemic. To do this, they prick your finger and deposit a couple of drops of blood in cylinders of fluid - if a drop sinks, you have enough blood iron and you're okay to donate. Out of curiosity alone, this leads me to a couple of questions:

1. Can someone point me to a description of the actual mechanism of this test (the sinking blood bit) - what's in the cylinders, etc. Wikipedia's article about blood iron/haemoglobin tests seem to all be about fancier lab tests not this rough-and-ready one.
2. Why must they take blood from a finger (as Penfield's homunculus shows, one of the most nerve-ending-rich places in the body)? I asked the technician if they could take it from elsewhere, and he said they had to use the finger, but didn't know why.

Thanks. 91.125.171.235 (talk) 00:42, 27 February 2011 (UTC)

Re: 2; This is a fairly rough test for your Haemoglobin (Hb) level; sadly neither the WP article on Haemoglobin or blood test covers it in any detail, but fingerprick does mention that it's "typically quicker and less distressing than venipuncture".

The Hb level in blood from your fingertip won't be significantly different from that from anywhere else. The "technician" probably had no idea.

Probably the real answer is "fingertips are easy to get at without removing any clothing". Though fingertips are sensitive you'll hopefully have found that by the time you've given your blood donation, had your cup of tea and removed the sticking plaster from your fingertip the sharp prick of the sample is but a distant memory.

I've an appointment to give my 38^th unit next month - I'll be sure to ask about the above (particularly 1 above as I've always wondered too). If I get an answer I'll put it on my userpage. Tonywalton ^Talk 01:10, 27 February 2011 (UTC)

The blue solution is copper(II) sulfate (see this section), and here PMID 2646909 is a reliable source referring to the screening procedure. That paper is more than 20 years old, and I presume that since then the cutoff (i.e. the specific gravity of the solution used for the screening) has been adjusted to improve the test's performance. Entries here and here describe the procedure in more detail. -- Scray (talk) 01:34, 27 February 2011 (UTC)

Interesting that the specific reagent is available for sale here . -- Scray (talk) 01:37, 27 February 2011 (UTC)

(ec) I'd thought it looked like CuSO₄, however the system in the UK is that the blood drop goes into a blue (sulphate)- looking tube for males but a green (looks more like copper carbonate) tube for females. I'll be sure to read the refs above tomorrow (it's 1:44AM here, and I need some sleep!) Tonywalton ^Talk 01:47, 27 February 2011 (UTC)

It could just be that they add dye so people don't mix them up and they are the same thing just in different concentrations because the acceptable iron level is different for males and females (is it? If it isn't, that would invalidate my theory! I know women often have lower iron levels due to menstruation, but I can't see how that would make the safe level different). I've never seen this green liquid you describe, but then I've never donated blood as a woman! Are you sure they use different ones? --Tango (talk) 02:14, 27 February 2011 (UTC)

More recent, showing the cost-effectiveness of CuSO₄ screening: PMID 20808648 -- Scray (talk) 01:39, 27 February 2011 (UTC)

Additional detail on the performance and characteristics of the test here. -- Scray (talk) 01:42, 27 February 2011 (UTC)

Regarding site: this PMID 11274589 suggests that use of earstick (rather than fingerstick) tends to under-estimate anemia. -- Scray (talk) 01:46, 27 February 2011 (UTC)

Further, this page discusses "microcollection" (about 80% of the way down the page) and the issue of pain receptors in fingertips, stating that despite this problem it's preferred. -- Scray (talk) 01:50, 27 February 2011 (UTC)

Its easier to get a small drop of blood of the size used for this hematocrit test that can be dropped into the tube of solution from the fingertip with a stick from a micro lancet than if, say the forearm were stuck, but it should be possible to use alternate sites as is now done for diabetic blood sugar testing. Maybe they just like to keep using this early 20th century technology because it is cheap compared to some new meter and test strips which could measure iron in smaller droplets. But If the pain of the fingerstick is too much to bear, then the pain of the blood donation would be worse. Edison (talk) 14:23, 27 February 2011 (UTC)

Measuring iron concentration from a small volume of blood might be feasible, but it will not accurately assess degree of anemia. There are multiple carriers of iron in the blood other than hemoglobin. The question is not iron level - it's hemoglobin level. Iron deficiency is only the most common of many causes of anemia, and they don't want to take blood from any anemic volunteer. -- Scray (talk) 00:58, 28 February 2011 (UTC)

Destroy secret papers

I think I've been watching too many spy movies and so I've got this weird question in my head; here goes. Suppose I have a stack of (secret) papers in my super-secret attaché case that is airtight with a perfect vacuum inside and with the temperature of the contents maintained at -5 C. What would be a good chemical reaction (with reactants contained in some mechanism in the case) that could be used, if the case falls into enemy hands, to destroy all the contents of the case beyond possible recovery as quickly as possible, and that could be triggered by a button, remotely, or by an internal timer (or all three)? Assume this reaction might be needed at an arbitrarily long time into the future. 72.128.95.0 (talk) 03:48, 27 February 2011 (UTC)

I have a few ideas:

• Chloroform is pretty good at lifting ink off paper, as I found out when I accidently erased a paragraph in my laboratory manual.
• Concentrated sulfuric acid carbonise paper, it turns paper into a handful of carbon dust. (not that I'd encourage using your hands, for fear of acid burns). With enough paper, it may catch on fire, as the reaction can get very hot.

Plasmic Physics (talk) 05:51, 27 February 2011 (UTC)

Well you could try concentrated perchloric acid, but with these sort of destructive acids, you will not be allowed to carry it on board a plane. Graeme Bartlett (talk) 10:15, 27 February 2011 (UTC)

I believe codebooks carried by the navy in WW2 were designed to be destroyed by dumping them in a bucket of salt water. Dmcq (talk) 13:14, 27 February 2011 (UTC)

If all the documents were on flash paper (the nitrocellulose kind), you could possibly set them alight with an electrical spark, although it would probably best if the case wasn't under vaccuum (needs oxygen to burn completely). Alternatively, you could spray the papers with a mist of pyrophoric liquid, which would ignite upon contact with oxygen (although the enemy could just open the case in a nitrogen filled glove box, if they knew about your countermeasures). -- 174.31.194.183 (talk) 18:40, 27 February 2011 (UTC)

It seems to me that destroying papers is trivial, but doing so without any outward sign (like a flaming/exploding attache case) is more of a challenge. Using magnetic media instead of paper provides for a possibility of wiping them with a strong magnetic field, without any outward sign, if a Faraday cage is constructed inside the case, to keep the field from escaping (does the Faraday Cage work to keep a field inside, instead of outside ?). StuRat (talk) 20:55, 27 February 2011 (UTC)

There is a scene in Cryptonomicon, I vague recall, where various Wikileaks-style hackers had rigged up their office so that any media passing through the door would be subjected to a strong magnetic field, so that if they were ever raided, the police would find themselves with completely scrambled hard disks. --Mr.98 (talk) 17:45, 28 February 2011 (UTC)

I guess they have never heard of CDs, DVDs or flash drives then. Googlemeister (talk) 17:32, 1 March 2011 (UTC)

Have something that releases pure oxygen into the case, and make a spark. In pure oxygen, things burn very rapidly (for example the tragic example of the Apollo capsule interior that caught fire in pure oxygen). The oxygen could come from a small cylinder or a chemical reaction. To prevent the burnt remains of the papers being read, then you could have something such as large loose nuts and bolts in the case that would pulverise the ashes when you shook it. Or perhaps you could have "plastic" paper that would melt as well as burn. 92.24.189.108 (talk) 00:35, 28 February 2011 (UTC)

Ability to understand accents

I've always had a problem (more than most people) hearing what people are saying in a noisy environment(nightclub/factory/party). Tonight I was out with some friends and a bunch of their friends who were from various locations around the UK (so they had a variety of accents). Even in the quiet pubs I was constantly having to ask them to repeat what they'd said even though they could understand each other. Is there a term to describe why some people can't understand accents and is it connected to the ability to filter out background noise? --BlackberryPicking (talk) 04:03, 27 February 2011 (UTC)

Any fault in binaural hearing (such as a very slight blockage in one ear) will increase the difficulties in picking out individual voices from a noisy background. It is also possible that a slight under-development or slight damage to the Primary auditory cortex will have the same effect. I don't think that this causes specific difficulties with comprehension of unfamiliar accents, but it will increase the problems that we all have in converting sounds into words that we recognise, especially when the sounds don't follow the pattern we expect. (I have difficulties with the Glasgow accent, and I live less than a hundred miles away.) The more one hears of an accent, the easier it becomes to decipher the words, so perhaps it was just the noisy environment combined with unfamiliar accents, but you might wish to undergo a simple hearing test to rule out the possibility that one ear is less sensitive than the other (we can't give medical advice here). Dbfirs 10:08, 27 February 2011 (UTC)

I don't have a source for you, but in my work as an Audiologist, I often hear these two complaints together from people with even very mild high frequency hearing losses. Some people seem to have these problems with normal hearing thresholds on audiogram; no-one really fully understands why, though it is thought there may be some neurological/cortical involvement Si1965 (talk) 11:54, 27 February 2011 (UTC)

I think there is a natural difference. I've never really had much trouble understanding any English accents, as opposed to many of my friends, who sometimes have trouble understanding my accent. On the flip side, while I can understand people's accents, I often can't recognise them. Chipmunkdavis (talk) 12:15, 27 February 2011 (UTC)

In addition to the other causes listed, the McGurk Effect may come into play here. That is, you may be better able to understand somebody if you watch their mouth as they speak. If you are in a dark nightclub with flashing lights, it may be more difficult to get any visual cues. I've noticed this effect on TV news. When I watch the reporter speak, I understand what they say, but when I turn away, I often misunderstand what they say.

Also, context also plays a part in speech recognition. If somebody says "My favorite fruits are apples, orangutans, and bananas", you will likely hear "oranges". Those with accents may also use different words, or use the same words differently, and this could throw you off. For example, when somebody says they are going to "eat tea" or "wash their hands in the toilet", this doesn't make sense to Americans, so they might hear it differently. StuRat (talk) 20:41, 27 February 2011 (UTC)

Regarding the role of context: I'm not sure you'd hear oranges. You'd guess oranges. I have a friend who is very prone to malapropisms, such as saying "pacific" instead of "specific" and "bi-curiously" instead of "vicariously". These don't escape my attention at all, quite the reverse, they tend to distract me from whatever he's trying to say. 81.131.30.247 (talk) 00:45, 28 February 2011 (UTC)

The same thing applies to reading. The first time I read that, I got oranges. Googlemeister (talk) 14:30, 28 February 2011 (UTC)

Good point. StuRat (talk) 22:35, 28 February 2011 (UTC)

Wow, over 20 years in Audiology and I've never heard of the McGurk Effect. Thanks! Si1965 (talk) 23:31, 27 February 2011 (UTC)

You're welcome. I hope it helps with your job. StuRat (talk) 22:34, 28 February 2011 (UTC)

I can only offer anecdotal evidence: I share your inability to understand people over background noise, but I am quite good at understanding accents. I think the main thing that affects how well you understand an accent is how familiar you are with it. I am quite well-travelled, so I'm used to a wide variety of accents. That probably helps me. --Tango (talk) 00:57, 28 February 2011 (UTC)

I think that a lot of it has to do with traveling and being exposed to many different accents or ways of speaking a language. Mac Davis (talk) 14:16, 28 February 2011 (UTC)

(OP here) Thanks for all the responses, as always they are an education! I'd thought there might be a term to describe it but maybe it's too non-specific a problem. I kinda assumed it was probably a 'processing' problem rather than a physical problem (mainly because I'm 36 and have had the background noise problem since I was in my teens, maybe younger). Understanding accents wasn't really a problem until this night out so I think I will book a hearing test as well. --BlackberryPicking (talk) 18:45, 28 February 2011 (UTC)

Flavored condoms and infections

This page claims that flavored condoms can cause yeast infections if used during vaginal sex. Is there a source for this info? I'm a development worker in HIV prevention in the Philippines; if anyone can help me find an authoritative source linking flavored condoms to vaginal yeast infections, I'd appreciate it. You can email me at <email redacted>. Cheers, Casey.

I do not have a good source for you, but I work in HIV prevention in America and India. I have heard that flavored condoms can cause this problem but I have also seen condoms which specifically state that they are made for intercourse. On disreputable sites found by searching Google it seems that many people say that yeast infections can be caused by flavoring or chemicals in the condoms.

I recommend that you consult with a doctor in your area as condoms manufactured in different parts of the world may be made to different specifications. Also, I just sent a note about this post to your email address. Blue Rasberry (talk) 05:39, 27 February 2011 (UTC)

And is Blue Raspberry one of the flavors ? :-) StuRat (talk) 20:31, 27 February 2011 (UTC)

I suspect that the mechanism of infection is that flavored condoms are first used for oral sex, where they pick up yeast, then are used in vaginal intercourse, where they deposit the yeast. Much like Q-tips are supposedly "not for use in the ears", despite being on the end of a long stick so they fit inside ears, the same skepticism should be aimed at flavored condoms "not meant for oral sex". StuRat (talk) 20:31, 27 February 2011 (UTC)

polycarbonate

how can i tell the difference between polycarbonate, acrylic, and abs plastic ? — Preceding unsigned comment added by Wdk789 (talk • contribs) 09:43, 27 February 2011 (UTC)

Is destructive testing allowed? (i.e. break a piece off and run tests on it) Ariel. (talk) 10:37, 27 February 2011 (UTC)

no --Wdk789 (talk) 11:25, 27 February 2011 (UTC)

I don't know but I suspect it's quite difficult from visual inspection alone. Can you find some hints in our articles on polycarbonate, acrylic, and ABS plastic?--Shantavira|^{feed me} 16:37, 27 February 2011 (UTC)

The three plastics have different densities. ABS is 1.04, Acrylic 1.18, Polycarbonate 1.20. They also have different hardness levels and tensile modulus - if you have other plastics to compare it to you should be able to tell just from the feel. A pretty definitive test is their refractive index. You can try various colors of light and compare. (That's how they do it in recycling facilities BTW.) Ariel. (talk) 18:30, 27 February 2011 (UTC)

what do u mean by " refractive index You can try various colors of light and compare." — Preceding unsigned comment added by Wdk789 (talk • contribs) 03:52, 28 February 2011 (UTC)

Do you know what a refractive index is? It's a measure of how much light bends when it passes through a material. Different materials bend light by different amounts, and by comparing you can distinguish them. You can google for some methods of how to measure this. Additionally different plastics absorb different frequencies of light that is passed through it. See Spectrometer and spectroscopic analysis. Ariel. (talk) 04:13, 28 February 2011 (UTC)

how can i pass light thru if its a thick plastic and if its not clear? — Preceding unsigned comment added by Wdk789 (talk • contribs) 08:23, 28 February 2011 (UTC)

You'll need a sensitive spectrometer, but you can probably check the light that reflects from it. You've reached the limit of what I know on the subject though. Research how recycling stations do it - they have this exact same problem when dealing with mixed plastics. Ariel. (talk) 08:35, 28 February 2011 (UTC)

u mean how shiny it is? — Preceding unsigned comment added by Wdk789 (talk • contribs) 13:10, 28 February 2011 (UTC)

I don't mean that, but checking the shinnyness level may give you a clue of which plastic it is. What I mean is that different plastics reflect specific colors of light in varying amounts. Probably not visible to the eye, but if you measure it you can see a "notch" or "peak" in the reflection curve that is different for each plastic. Ariel. (talk) 03:55, 1 March 2011 (UTC)

Weak interaction: figures

I'm attempting to improve the referencing and clarity of the weak interaction page. The commonly quoted range is ~10^-18m; carrier mean lifetime ~3x10^-25s and W-boson mass ~80 GeV (80.4 GeV/c2). I'd like authoritative sources for these numbers if you know of them, and also which ones are calculated from which ones. The first two appear to be related by the maximum velocity of c (although not quite), but I don't know which one is actually measured. I did once see an equation linking mass to mean life for virtual particles, but I can't remember it and it doesn't seem to be on an obvious page here. If this does exist, then the same question applies. Thanks! Grandiose (me, talk, contribs) 14:07, 27 February 2011 (UTC)

The authoritative source for anything related to particle physics is the PDG page. Go to that page, click on "Summary Tables" and then click on "gauge and Higgs bosons". There you will find information about the W and Z masses MW = 80.399 ± 0.023 GeV, MZ = 91.1876 ± 0.0021 GeV. You will also find their full widths ΓW = 2.085 ± 0.042 GeV and ΓZ = 2.4952 ± 0.0023 GeV. The widths are related to the carries lifetimes through the formula Γ = ħ/τ as you can see on the page Resonance (particle physics) which unfortunately for you is still only a stub. Finally, as you pointed out, the range of the interaction is roughly given by multiplying the particle's lifetime by the speed of light. Dauto (talk) 15:51, 27 February 2011 (UTC)

Thanks, does one find the width first and use it to calculate the lifetime, or vice versa? Grandiose (me, talk, contribs) 16:48, 27 February 2011 (UTC)

Either thing can in principle be measured but in practice the width is often easier to measure. Dauto (talk) 16:57, 27 February 2011 (UTC)

Actually, rethinking what I said above I realized that the distance obtained through the formula I gave : d=cħ/Γ is the average distance traveled by carrier particles after they are produced in collisions. In a interaction virtual particles carry the interaction and the average distance traveled by those is given by d=cħ/M which is about two orders of magnitude shorter for the weak interaction. See for instance the first paragraph of Yukawa potential. Dauto (talk) 16:49, 27 February 2011 (UTC)

Sorry. There is still a mistake above. I forgot a time dilation factor in the expression for the average distance traveled by carrier particles after they are produced in collisions. Dauto (talk) 03:44, 28 February 2011 (UTC)

Thanks. I have most of the key factual information now reasonably referenced. I was attempting to get some grasp of the strength of the weak interaction force, but have suddenly realised I have no idea of what a force means in this context [a mechanism]. (I should point out I'm in above my head and thus treading carefully.) Possibly the force preventing decay? In any case here has a couple of useful comparisons, but do we have anything more detailed/a better source? Some sort of formula or graph, for instance? I might be missing some facet or other, so do bear with me! Grandiose (me, talk, contribs) 18:02, 27 February 2011 (UTC)

In a fundamental level the strength of an interaction is given by the coupling constant. I'm busy now so I won't be able to give you a better explanation. I will try to post again later today. Dauto (talk) 19:04, 27 February 2011 (UTC)

cloud formation

I watched a video about global warming they say that cosmic rays forming with water droplets is what creates clouds and they say when the sun is more active fewer particle get through to make clouds so this is why it is colder. Is this true do cosmic rays create clouds — Preceding unsigned comment added by Lufc88 (talk • contribs) 14:34, 27 February 2011 (UTC)

The main cause of cloud formation is Cloud condensation nuclei, but it is true that a more active sun could alter the stage and altitude at which clouds form (see Solar variation). The exact process and the interpretation of the observed correlations has not been agreed on, but the effect is probably small compared with other causes of cloud formation. Did you mean more particles from a more active sun? Dbfirs 17:26, 27 February 2011 (UTC)

No, it isn't. That's a load of bull, that's what that is. Dauto (talk) 17:12, 27 February 2011 (UTC)

Then please change our articles and add appropriate references (though I agree that the effect is disputed and probably small). Dbfirs 17:27, 27 February 2011 (UTC)

What articles? Dauto (talk) 03:18, 28 February 2011 (UTC)

Well they do only suggest a possible effect. I've just re-read the OP's post about what the video claims, and I agree with you that cosmic rays are not "what creates clouds", so I'm with you on the bull call there. Dbfirs 10:08, 28 February 2011 (UTC)

no it said when the sun is more active fewer rays get through so there are less clouds so things warm up quicker. But my intial question was so cosmic rays form with water to make clouds and if so how? — Preceding unsigned comment added by Lufc88 (talk • contribs) 17:32, 27 February 2011 (UTC)

One possible process is that increased solar activity interacts with the earth's magnetic field to deflect more of the galactic cosmic rays that are the main cause of ionisation in the atmosphere. Whether this ionisation affects cloud condensation nuclei to any significant extent is not currently known. Dbfirs 18:07, 27 February 2011 (UTC)

You're very quick to say that Dauto. Henrik Svensmark is the primary researcher of cosmic rays' effect on atmospheric nucleation. It's new research, and it could turn out well--we don't know yet. Mac Davis (talk) 14:11, 28 February 2011 (UTC)

I'll eat my hat if that turns out to be an important factor. Dauto (talk) 15:17, 28 February 2011 (UTC)

Is there any special reason you're driven to make this pledge, or is it just a hunch? 213.122.11.147 (talk) 22:25, 28 February 2011 (UTC)

Clouds form when relative humidity reaches 100% Nucleation is not necessary or effective. Dauto (talk) 04:20, 1 March 2011 (UTC)

Well the lead to our article on Cloud condensation nuclei disagrees with your opinion (though I'm less sure about the exact effects of cosmic rays because the process seems to be complex and not fully understood). Dbfirs 08:20, 1 March 2011 (UTC)

No it doesn't. As you can see by yourself that article doesn't mention the need of cosmic rays in order for the condensation nuclei to work. As I said, Cosmic rays are neither necessary nor effective. Nucleation happens when humidity reaches 100% because the cloud condensation nuclei are already present and quite effective by themselves without any need of cosmic rays or anything else. Dauto (talk) 18:45, 1 March 2011 (UTC)

Are we reading the same article? The way I read it, nucleation is both both necessary and effective (and opinion differs on the importance of cosmic rays). Dbfirs 23:48, 1 March 2011 (UTC)

Probably the best thing to do is let the OP make his own mind up on whether or not comic-rays might have a noticeable effect on the climate. As CERN points out, there is satellite evident that which shows a possible correlation between cosmic-ray intensity and the amount of low cloud cover. A study of the link between cosmic rays and clouds with a cloud chamber at the cern ps--Aspro (talk) 19:38, 1 March 2011 (UTC)

Thanks for that paper. I may have to eat my hat after all... :). Dauto (talk) 20:39, 1 March 2011 (UTC)

mass & motion of earth

Is there any effect on the mass and motion of the earth from taking mass from the earth (mostly satellites and space probes that never come back to earth)? and also, the fact that more and more of the earth's mass (airplanes ships cars trains) moves around where before (1000 years ago) it was all stationary in the earths crust? How much does meteorites counter this effect? —Preceding unsigned comment added by 98.221.254.154 (talk) 16:22, 27 February 2011 (UTC)

The mass will change but by a very small amount. It could be offset by meteorites hitting the earth or add to the loss in mass we get as the atmosphere drifts off (slowly) into space. The force of gravity between ourselves and the moon (and the sun etc) is directly proportional to our (and their) mass, but you need to look at the mass of the earth and see where the decimal point is, compared with satellites that might be of the order of 1000 kg. (See Wikipedia for facts on mass) Victuallers (talk) 16:37, 27 February 2011 (UTC)

Our article on Micrometeoroids suggests that the mass of the earth might be increasing by around ten million kg per year from the inflow of Cosmic dust alone, so a few satellites are not going to make a measurable difference. Moving vehicles that don't go beyond the atmosphere will have an effect that normally cancels out to zero ( though if the whole human population with all their transportation converged on one island, there would be be a measurable effect on mass distribution and the orbit of the moon would change). The eruption of a large volcano can change the length of the day by a very tiny but measurable amount, so having many aeroplanes high in the sky, and many satellites in orbit might also slow the rotation very slightly (because angular momentum is conserved), but the effect will be very small because the earth "weighs" nearly six million million million million kg. Dbfirs 17:54, 27 February 2011 (UTC)

The entire Earth's crust (which is the only part we can have any impact on) makes up less than 1% of the mass of the Earth. There is no way anything we do could have a noticeable effect on the Earth's mass. The total mass of everything launched into space is perhaps a few tens of thousands of tonnes (that's a guess, but it's probably about right - it's more if you include fuel, but that's mostly burnt early in the launch, so the resulting CO2 and water probably remains part of the Earth). The total mass of the Earth is 6 thousand billion billion tonnes. As you can see, our impact is minimal. --Tango (talk) 01:09, 28 February 2011 (UTC)

While humans are not able to significantly change the mass of the earth, we are able to shift its distribution a bit, thus changing its moment of inertia. This NASA article mentions that filling the Three Gorges Dam reservoir (which can hold 40 cubic kilometers of water, at a maximum of 175 metres above sea level) could increase the length of a day by 0.06 microseconds. In comparison, the 2004 Indian Ocean earthquake was calculated to effect a 2.68 microsecond decrease in the length of the day. To what precision are astronomers able to measure our rate of rotation? Sidereal day#Exact duration and its variation would suggest that such measurements are made to the fraction of a nanosecond. -- ToE^T 02:37, 28 February 2011 (UTC)

Bond angle of water

At Water (data page), I read this:

Bond angle 104.4776° (equilibrium)

Not being ignorant of geometry, I put that into the cosine function on a calculator and got −0.250001484. So arccos(−1/4) ≈ 104.477512186 and that got rounded. If it's not exactly arccos(−1/4) then the three consecutive 0s are an odd coincidence, and Occam's razor favors such a simple thing. So I edited it to say this:

Bond angle 104.4776° = arccos(−1/4) (equilibrium)

I find various web pages explaining why the bond angle is not 109.47°, which is the arccosine of −1/3, and is what would result from a certain kind of tetrahedral symmetry. Instead of just explaining physical reasons why it should be smaller than arccos(−1/3) ≈ 109.47°, shouldn't it also explain why it's the angle whose cosine is such a simple fraction?

Can someone here explain that? Michael Hardy (talk) 17:13, 27 February 2011 (UTC)

A google search for "cosine of the bond angle of water" gets 0 hits! Michael Hardy (talk) 17:19, 27 February 2011 (UTC)

that's just a funny coincidence. You should revert your edit. Dauto (talk) 17:57, 27 February 2011 (UTC)

If it's a "funny coincidence", then why does it agree to seven decimal places? Getting the same decimal digit seven times in a row happens once in 10 million trials if it's "just a coincidence". Michael Hardy (talk) 18:03, 27 February 2011 (UTC)

....and how do they actually measure it so accurately that they get seven digits? Could it be that they concluded it's arccos(−1/4) and then computed that to seven places, rather than actually doing a physical measurement that's so phenomenally accurate? Michael Hardy (talk) 18:05, 27 February 2011 (UTC)

Think what you will. It is a coincidence. Besides, the second page you linked has the figure 104.45 degrees. Dauto (talk) 18:07, 27 February 2011 (UTC)

The page Properties of water also has the figure 104.45 degrees. Dauto (talk) 18:08, 27 February 2011 (UTC)

(ec)The lack of Google results probably means that the correspondence to the arccos might be a coincidence. The reason why arccos(-1/3) is the bond angle of, say, methane, is because of the tetrahedral symmetry of the molecule. Water doesn't have that symmetry, or any other symmetry which would constrain the bond angle. You have a plane of reflection that splits it down the middle, you have another in the plane of the three atoms, and you have a 2-fold axis splitting the angle in the plane of the three atoms. There is absolutely no geometric reason why the angle would be exactly arccos(−1/4). Indeed, anyone rounding arccos(−1/4) ≈ 104.477512186 to 104.4776° is off (you would round it down to 5, not up to 6). 104.47759732 (which also rounds to 104.4776) is not equal to arccos(−1/4), no matter how hard you squint at it. I would *not* put the correspondence in there unless you were able to cite a reference for it (no original research and all that). Frankly, there is a heck of a lot of precision in that angle measure, and I am slightly uncomfortable with the absence of a citation mentioning how it was derived (from experimental measurements - how precise were they? From quantum chemical calculations - what level of theory? From geometric considerations - what was actually calculated?). Looking at the history [12], it looks like the reference was for (Hoy 1979), which was then removed [13] with the edit summary of "fix references". I'm not sure what paper was meant by (Hoy 1979) (no further specification was given), but the edit summary mentions the CCCDBD, which currently lists the experimental equilibrium bond angle as 104.48 [14]. -- 174.31.194.183 (talk) 18:25, 27 February 2011 (UTC)

The figure we give would appear to come from this paper, assuming this is the Hoy (1979) that was meant in the edit [15]:

A. R. Hoy and P. R. Bunker, A precise solution of the rotation bending Schrödinger equation for a triatomic molecule with application to the water molecule, Journal of Molecular Spectroscopy 74(1), 1--8. (January 1979). doi:10.1016/0022-2852(79)90019-5

The abstract gives a figure of 104.48, and says it was the result of least-squares fitting a model with 7 parameters (one of which was the equilibrium bond angle) to 375 spectroscopically observed vibration mode energies.

I don't have access to the full paper, so I can't confirm whether or not it contains the 4 d.p. number inside. You're right to be suspicious that this is so close to such a round number as arccos(−1/4), and it's not impossible that there might be some hidden symmetry underlying this (cf the virial theorem etc). It's also possible that somebody has said "Ooh, that looks close to arccos(−1/4)", and simply made up the extra figures. But there doesn't seem to be any immediately obvious reason to expect it.

We give the bond angle for ammonia as 107.8°, which would be about arccos(-0.306); but that doesn't seem to reflect any numerology -- unless there's something you can see there too? Jheald (talk) 18:41, 27 February 2011 (UTC)

I do have access to the full paper: the value given is indeed 104.4776(19) degrees. Buddy431 (talk) 21:07, 27 February 2011 (UTC)

This is clearly a coincidence. Look at for instance the angle of the Hydrogen sulfide molecule which has a structure very similar to water. Dauto (talk) 18:45, 27 February 2011 (UTC)

FWIW, ab initio calculation (as of 2005) gives 104.50°; the discrepancy between that and the observed value is said to be accountable for, by various factors not included in the basic calculation. [16] Jheald (talk) 19:13, 27 February 2011 (UTC)

It may also be worth noting that the current value for the bond length is 95.777 pm, not 95.84 -- this should be updated. I'd change the [:File:H2O 2D labelled.svg SVG] but someone's changed all the text elements to drawing paths, so somebody else can have the fun of working out what the fonts and sizes are meant to be.

It's a bit alarming that (1) we were showing out-dated information; and (2) that when somebody updated it, they only updated one data-element not the other; that they may have added spurious digits; and that we didn't spot any of this till Mike got suspicious of the numerology. Jheald (talk) 19:45, 27 February 2011 (UTC)

The quoted value is indeed the one given in the paper (they didn't add spurious digits), though there's a not insignificant amount of uncertainty in the final two digits. Wikipedia, and indeed any reference source, will always have out of date information. There's not much we can do about that (although I am suspicious of the article cited, seeing that it's over 30 years old). Buddy431 (talk) 21:07, 27 February 2011 (UTC)

Someone has now changed it to say 104.48 degrees, citing the paper by Hoy. That's more credible since it's not so many decimal places. When I put 104.48 into a calculator and hit the cosine key I get −0.250042041528. It still seems suspiciously close to −1/4, since it has two 0s immediately after −0.25. Michael Hardy (talk) 22:13, 27 February 2011 (UTC)

It is just a coincidence. Dauto (talk) 03:27, 28 February 2011 (UTC)

Decay products (further questions)

Further to my question above, I have a couple of questions about the data given in this document. As I read it something like 10% of W- bosons should decay into e- and electron antineutrinos. However, explanations of beta minus decay always gives this outcome – is there a reason why? I'm also a little bemused by the numbers given. The first four (all leptons) given are ~10%, hadrons are listed at 67% and 67+40>100. My reading of the numbers below this suggests they don't total to 67% either. Can you assist? Grandiose (me, talk, contribs) 20:17, 27 February 2011 (UTC)

β⁻ decay can't produce heavy particles because there isn't enough energy available (the nuclear energy only decreases slightly), but that energy is available in spades when a "free" W boson decays. There are three leptonic decay modes (eν, μν and τν) and those together with the hadronic modes add to 100% within the margin of error. The "ℓν" decay on the first line must come from a different measurement or calculation that didn't distinguish the lepton generations. Likewise, the lines below "hadrons" are limited by the experimental data that happens to be available. It's a bit confusing because this summary document doesn't cite its sources. -- BenRG (talk) 20:58, 27 February 2011 (UTC)

Thanks, that's that pretty much cleared up. Grandiose (me, talk, contribs) 21:01, 27 February 2011 (UTC)

Circuit of Unique Equivalent Resistance

Hello. Is it possible to design a circuit that has a unique equivalent resistance regardless of the order in which resistors are connected? Thanks in advance. --Mayfare (talk) 23:17, 27 February 2011 (UTC)

Please clarify. Surely you are asking for something harder than the fact that the equivalent resistance of a string of series resistors is independent of the order in which they are connected. Similarly the sum of a series of numbers does not depend on their order (commutative property). Edison (talk) 23:47, 27 February 2011 (UTC)

February 28

Spaying and neutering of feral animals

I know that there are groups in America who trap feral animals (cats mostly, but sometimes dogs) and have them spayed/neutered and then return them to their ranges. I just had my cat spayed and she must wear bandages and a funnel for about 10 days, as per the vet's orders. How does this work for feral cats? Do they stay at the vet for a week or so, or are they turned loose early with some sort of slowly-degrading bandage? The Masked Booby (talk) 00:58, 28 February 2011 (UTC)

I think they're just kept for a couple of weeks in a cage. This site looks like it has all the answer but you have to go through a free registration process requiring an email address to access it. Vespine (talk) 01:17, 28 February 2011 (UTC)

Not to be insenstive, but wouldn't a .22 have a similar effect on population control at a tiny fraction of the cost? Googlemeister (talk) 17:31, 1 March 2011 (UTC)

Yes but it's insensitive. Vespine (talk) 21:39, 1 March 2011 (UTC)

where do aliens come from

where do aliens come from ? — Preceding unsigned comment added by Joshuad95 (talk • contribs) 04:06, 28 February 2011 (UTC)

Presumably the same place humans come from. But no one has even seen an alien, so it's hard to know. Ariel. (talk) 04:16, 28 February 2011 (UTC)

We have articles on these kinds of aliens, these aliens and even a list of aliens. Vespine (talk) 04:58, 28 February 2011 (UTC)

"Alien" is a word derived from the Latin words aliēnus (“belonging to someone else, exotic, foreign”) and alius (“other”). Basically, an "alien" is a word for someone or something from elsewhere. Hence the terms "illegal alien", "resident alien", and even "alienation" are literal usages of the term "alien", and are in no way metaphorical. So the answer to the question "where do aliens come from" is simply "somewhere (anywhere) else". -- 174.31.194.183 (talk) 05:01, 28 February 2011 (UTC)

If you mean extraterrestrial life, the general assumption seems to be that it would need an environment similar to that of Earth, which would mean a small, terrestrial planet/asteroid or a moon of a larger, Jovian planet. Planets like Venus, which at first seem inhospitable to life, due to extreme temperatures and pressures, may support life in a manner similar to that found at undersea volcanic vents on Earth. But, alien life could also be "totally alien", perhaps evolving in deep space or as magnetic currents inside stars. We don't know anything about such life, though, so it would be difficult to judge whether it's possible and what it requires, making it impossible to pick probable locations. StuRat (talk) 22:27, 28 February 2011 (UTC)

Pureed Food

Do vegetables and fruit lose their vitamins and nutrients if they are pureed? And if they don't if you added the puree into food like spaghetti or meatballs and then cooked the meatballs, would that cause the vegetables or fruit to lose their vitamins and nutrients, would it still be just as healthy as if you ate the veggies steamed or the fruit raw? —Preceding unsigned comment added by 70.141.255.136 (talk) 06:07, 28 February 2011 (UTC)

Vitamins and nutrients aren't destroyed by macroscopic mechanical stress. You can crush a cucumber with a hammer, steamoll a pumpkin, the vitamins and nutrients will stay intact. They are however destroyed or ruined by chemical attack, thermal damage, or excessive air pressure. Plasmic Physics (talk) 06:57, 28 February 2011 (UTC)

It may be a bit more complicated than that - vitamins and the like are stored inside cells where they are protected to some degree. Pureeing them breaks the cell wall exposing them to further damage. But in general I think it's not something to worry about. Ariel. (talk) 07:00, 28 February 2011 (UTC)

Yes, and breaking those cell walls makes it easier for our body to absorb the vitamins. No point in protecting the vitamines so that they can be flushed down the toilet. Dauto (talk) 15:12, 28 February 2011 (UTC)

Some of the water-soluable vitamins, such as Vitamin C, may dissolve into the cooking water. But if you use the cooking water when making the sauce etc, then that is not a problem. 92.15.3.182 (talk) 11:11, 28 February 2011 (UTC)

Something else to consider is that pureed fruits and veggies may oxidize and decompose more quickly, so don't puree until right before you consume them. StuRat (talk) 07:55, 2 March 2011 (UTC)

Pureed fruits and veggies are able to retain their contents and original compsition depending on the way in which they are processed, wheter at home or purchased from outside vendor. Like, while cooking at one particular stage, if tomato puree is needed, then it is possible to smash tomatoes and make puree out of it, however, most of the times it depends on the approach, way and method in which a puree is to be made. Making puree is a part of cooking process, however, puree can be made seperately and stored and then also routine cooking process can be started. Thus if vegetables and fruits when they are in their original form are converted into puree then they will retain their contents and add taste and flavor to the food that is been cooked. aniketnik (talk) 11:43, 2 March 2011 (UTC)

UV-A, UV-B, UV-C of metal halide lamp

Hello,

I wanted to ask here how dangerous the UV radiation of a 150w metal halide lamp can be, compared to the sun( i have the numbers of the lamp they are:

• UV-A:6.1
• UV-B:0.003
• UV-C:0.006. microwatt/cm2/500 lux

I cannot find the numbers for the suns radiation on earths surface (average, temperate climate)
TY
DST — Preceding unsigned comment added by DSTiamat (talk • contribs) 09:59, 28 February 2011 (UTC)

Sorry, I couldn't find anything. And if you get no other replies it means no one else found anything either. Ariel. (talk) 23:23, 28 February 2011 (UTC)

Of my interest would be the numbers of the sun, I have the numbers of the lamp and can make my own conclusions, TY Ariel, anyone?
  DST  — Preceding unsigned comment added by DSTiamat (talk • contribs) 08:17, 1 March 2011 (UTC) 

solar spectrum

The Thekaekara Spectrum shows the amount of radiation at different wavelengths from the sun. Graeme Bartlett (talk) 11:46, 1 March 2011 (UTC)

Birds and eyelashes

Random question, but something I was thinking about. How common is it for birds to have eyelashes? --95.148.106.158 (talk) 10:34, 28 February 2011 (UTC)

Birds do not have eyelashes. Some have bristles, which are feathers that lack barbs, around the eyes which appear to be similar to eyelashes. That feature is primarily only in insect-eating birds. -- kainaw™ 13:34, 28 February 2011 (UTC)

And do they serve to keep insects out of the eyes ? StuRat (talk) 22:13, 28 February 2011 (UTC)

view full size - not easy to see, but they're there

Budgerigars have eyelashes. The one in the pic doesn't have particularly prominent/thick lashes, but that's the only pic I could find on here with sufficient resolution to show them at all. I think (IIRC) that Cockatiels do too. --Kurt Shaped Box (talk) 22:57, 28 February 2011 (UTC)

They're also mentioned in our articles on the Hornbill and some of the Vulture species. Our Eyelash article mentions that they are barbless feathers as Kainaw describes, rather than true hairs as in mammals, but I don't think that that excludes them from being defined as eyelashes. 87.81.230.195 (talk) 23:39, 28 February 2011 (UTC)

It appears that ornithologists refer to those bristles as "eyelashes". --Sean 16:44, 1 March 2011 (UTC)

Yeah, I don't see anything particularly wrong with taking an 'eyelash is as eyelash does' attitude towards this... --Kurt Shaped Box (talk) 22:00, 1 March 2011 (UTC)

So, having a look at another couple of parrot species...

• 
  African Grey Parrot appears to have (very fine) 'eyelashes'
• 
  as does this Umbrella Cockatoo
• 
  Whereas this macaw seems to have a ring of 'nodules' (dunno) that may serve a similar purpose

--Kurt Shaped Box (talk) 23:53, 28 February 2011 (UTC)

The close up of that macaw is going to give me nightmares! lol.. Vespine (talk) 02:00, 1 March 2011 (UTC)

Reminds me a bit of elephant skin up close... --Kurt Shaped Box (talk) 22:00, 1 March 2011 (UTC)

It is tempting to look at such pictures and think that there must be a common basis for eyelashes. But this means tracing back from birds through the dinosaurs and other sauropsids to the synapsids, and supposing that hair and feather patterning (and perhaps, at least in most basic concept, the hair/feathers/scales themselves) have been conserved throughout all that evolutionary distance. Is it possible that basal amniotes possessed the ability to pattern eyelashes around the eye, or even to mount them on eyelids? There's a discussion of comparative homology between eyelids of amphibians, frogs, turtles, and crocodiles here [17] - there is a certain amount of uncertainty on major points, but the overall consensus seems to be that the structure could indeed be so ancient. But eyelashes won't be pulled out of the literature (nor, I suppose, the rocks) quite so easily. A person can look at things like the eyelash viper and crested gecko and wonder, but admittedly, it's not the same thing. At least to a quick search, the secret remains undiscovered. Wnt (talk) 23:44, 1 March 2011 (UTC)

Can holograms work in broad daylight?

Does it need to be very dark for them to be clearly visible? ScienceApe (talk) 13:26, 28 February 2011 (UTC)

It depends on what you mean by hologram. Ones that are generated by lasers must be brighter than the surrounding light. However, white-light holograms (seen commonly on credit cards) work best in daylight. -- kainaw™ 13:30, 28 February 2011 (UTC)

Yeah I was talking about the holograms that are suspended in midair, presumably generated by lasers. ScienceApe (talk) 14:19, 28 February 2011 (UTC)

Such holograms does not exist. A hologram can show objects in front of or behind its surface but only in the direction of the hologram as seen from the viewer. --Gr8xoz (talk) 17:33, 28 February 2011 (UTC)

I have seen laser-generated holograms that you could walk around 360 degrees. They are expensive. The one I was was being licensed by a popular magician for his stage show - which should give a general idea of the cost. -- kainaw™ 17:35, 28 February 2011 (UTC)

That seems interesting, do you have any idea of where to get more information. Are you sure it was a hologram? not every 3D projection is a hologram. Was there any transparent materials between you and the background? --Gr8xoz (talk) 18:50, 28 February 2011 (UTC)

I have never been able to find the manufacturer online. I was paid through a company named "Magic Stage", which I also cannot find online. I did computer programming - which was the easy part. The setup required a lot of lasers on little pivots. The best I could tell, the lasers do not produce noticeable light until the beams cross. I programmed vector lines in 3D space, which the lasers "drew" in the air - oscillating quickly to keep it visible. The program I wrote just drew a little red apple with a green leaf on top. The demonstrator had a transmitter on his wrist that relayed the position to another computer so as he moved his hand around the apple moved with it - looking like he was holding it. That's about all I remember - and it was a good 20 years ago. I'm sure that the technology is much better now. -- kainaw™ 19:11, 28 February 2011 (UTC)

Was it something like this? http://www.aist.go.jp/aist_e/latest_research/2006/20060210/20060210.html 83.134.177.173 (talk) 19:53, 28 February 2011 (UTC)

Yes. It was just like that with two exceptions. First, I never heard anyone mention plasma. Maybe the plasma in your example makes it much easier to see in normal lighting. Second, the one I saw used three colors (red, green, blue) to produce nearly real-color images. Now that I think of it - I may be mis-remembering the existence of blue since the only example I saw used red and green. I've always meant to get two laser pointers to see if they make a dot of light when you cross the beams, but just never think to try it when I actually have two laser pointers on hand. If it works, then there's no "plasma" involved - just a disruption of the laser beam. -- kainaw™ 19:58, 28 February 2011 (UTC)

That isn't a hologram BTW. Ariel. (talk) 20:31, 28 February 2011 (UTC)

I think the plasma involved is just air made very hot by pointing multiple lasers at it, rather than the plasma of neon that's used in a plasma globe - if that was what you were thinking. 81.131.17.66 (talk) 20:59, 28 February 2011 (UTC)

The air would not get hot! If the laser was strong enough to do that it would burn holes in the walls. Ariel. (talk) 23:15, 28 February 2011 (UTC)

The lasers are focussed, with the focal points in mid-air, and there it gets hot. After that point, the beam diverges. Icek (talk) 23:51, 28 February 2011 (UTC)

Reading it again, it seems it only uses one laser, focused through a lens. 81.131.65.79 (talk) 12:32, 1 March 2011 (UTC)

That sounds like an incredible amount of effort to go to, just to make an apple appear or disappear; something any magician could do with a regular apple. Maybe there's important information missing from the descriptions above. Light is not cohesive, the main "problem" with holograms is you can see THROUGH them. That might work if it is kept in front of a black curtain with the audience only to your front, but in other situations it would fail. Lasers also definitely do NOT make a visible "point" of light where beams intersect in air, they need something to reflect off, (the little balls of plasma are definitely not "rgb"). I'm not calling anyone a liar, but I smell something very fishy, IMHO something doesn't add up. Vespine (talk) 00:23, 1 March 2011 (UTC)

I made an apple disappear today for lunch and I'm not even a magician. Dauto (talk) 02:12, 1 March 2011 (UTC)

http://www.youtube.com/watch?v=thOxW19vsTg What's going on in this video? It seems like it's a legit 3D hologram. ScienceApe (talk) 03:03, 1 March 2011 (UTC)

Despite what they call it, it has absolutely nothing whatsoever to do with holograms. It's just computer graphics. They have a bunch of cameras (in a circle) that record the reporter, then they add that to the outgoing television stream - the person physically there does not see her. The "new" thing, is that the computer can dynamically adjust the look of the outgoing stream based on the motion of the camera. But otherwise it's not much different than the special effects shot of a hologram in Star Wars. Ariel. (talk) 03:22, 1 March 2011 (UTC)

Yeah, I looked into it and it seems like that is in fact the case. Really deceptive especially when it's coming from a damn news source. ScienceApe (talk) 03:30, 1 March 2011 (UTC)

I agree, they should not have called it a hologram, maybe call it a virtual presence or something. A true real time hologram would be a pretty big deal - it requires an enormous amount of computing to generate one on the fly. No ones done it yet as far as I know. Ariel. (talk) 03:50, 1 March 2011 (UTC)

MOND or MOG theory

If MOND or Scalar–tensor–vector gravity turns out to be correct, will any changes need to occur to other physical laws apart from gravity? Would it ever have any effect on everyday life? Thanks 92.29.122.72 (talk) 15:33, 28 February 2011 (UTC)

No, and No. Dauto (talk) 16:07, 28 February 2011 (UTC)

The second one seems to be answered in the article anyway:

On the scale of the solar system, the theory predicts no deviation[7] from the results of Newton and Einstein. This is also true for star clusters containing no more than a maximum of a few million solar masses.

Nil Einne (talk) 17:29, 28 February 2011 (UTC)

Just to answer the last question; when scientists tweak existing laws, it doesn't actually change the nature of the universe. The universe keeps doing what it always has, so there's no change to what happens to you. What changes is our understanding of how the universe works. Just because Copernicus figured out that the earth moves around the sun doesn't mean that it hadn't been doing that before he figured that out! Its the same deal here; if our understanding of gravity changes, it doesn't mean that it hadn't been doing the same thing even before we changed the laws... --Jayron32 17:43, 28 February 2011 (UTC)

No, really? I am not a three year old, thanks. 92.24.179.104 (talk) 22:18, 28 February 2011 (UTC)

You asked if it would have an effect on everyday life, and Jayron answered that question. --Sean 16:46, 1 March 2011 (UTC)

Modified Gravity Makes Galaxies Brighter Count Iblis (talk) 22:41, 28 February 2011 (UTC)

Snake venom myokymia

I saw on a TV program that some type of snake can cause this.

1) Which is it ?

2) Also, could this venom be used (in low dosages, of course), to exercise the muscles of patients who are either comatose or immobile, to prevent muscular atrophy ?

StuRat (talk) 19:35, 28 February 2011 (UTC)

Timber rattlesnake?[18] DMacks (talk) 20:46, 28 February 2011 (UTC)

Thanks, I updated our article on Crotalus horridus. Any comments on part 2, anybody ? StuRat (talk) 05:15, 1 March 2011 (UTC)

Christchurch volcano

Following the recent quake there, a noticeable increase in the temperature of water in the harbor has been measured, leading to speculation that the earthquake may have either triggered, or been triggered by, an increase in volcanic activity in the area. So, then, which volcano(es) are involved and do we have article(s) on them ? StuRat (talk) 19:38, 28 February 2011 (UTC)

New Zealand has a lot of volcanoes. It's right on the Ring of Fire, and Volcanism of New Zealand lists quite a number. The map shows that most of them are on the North Island, not the South. But List of volcanoes in New Zealand has 4 candidates on the South Island. And of those, the first two are exactly in the right spot: Akaroa and Lyttelton Harbour. However those are very old, so it may also be a new unnamed volcano. Ariel. (talk) 20:56, 28 February 2011 (UTC)

Right, so which one is the likely candidate ? Also, do we have any articles on those volcanoes ? (The links you provided aren't to volcano articles.) StuRat (talk) 21:11, 28 February 2011 (UTC)

If it's an existing one, then most likely is Lyttelton Harbour I guess. But I think more likely is that it's a new opening that may or may not eventually become an underwater volcano. And I know those aren't links to volcano articles, but that's what was there. We don't seem to have anything else, probably because those volcanoes are so old. Ariel. (talk) 23:19, 28 February 2011 (UTC)

As the volcanoes are there a result of the subduction zone, it may just mean that the earth moment has provided new crevasses for sea water to peculate down to the hot rock in the zone (and then rise again). So I think it might be less to do with volcanism more to do with popular fear-mongering. In a few months/years time, the sea temperature may return to its former levels. Crack in the overburden around the volcano aren't going to afford easier passage for magma to rise. If it wants to rise - it will regardless of the overburden and the upage will have been noticed before now. Also, the quake was in the wrong place and over the subduction area --Aspro (talk) 21:21, 28 February 2011 (UTC)

The volcanoes on the South Island are not subduction-related as there is no subduction zone, the plate boundary being of transform fault type. The volcanoes are examples of intraplate volcanism that happened more than about six million years ago. Mikenorton (talk) 22:28, 1 March 2011 (UTC)

Chromosome numbers and speciation

We have articles about how an individual can have a different number of chromosomes than its parents, but how does this change occur to an entire species? When the first proto-human was born with 46 chromosomes instead of the 48 of chimps and gorillas, how did that individual produce viable offspring with its 48-chromosomed mates? If it happened gradually over many generations, why don’t we see species with fractions of a chromosome as part of their speciation? —Arctic Gnome (talk • contribs) 19:46, 28 February 2011 (UTC)

It seems that this individual must have reproduced with "normal" individuals matching one of his chromosomes to two of the "normal" ones. What is a fraction of a chromosome anyways? Dauto (talk) 19:54, 28 February 2011 (UTC)

Chromosomes do sometimes break: [19]. StuRat (talk) 02:02, 1 March 2011 (UTC)

When the number of chromosomes changes, it is usually because either one chromosome has split in two or two chromosomes have merged into one. As long as all the genes are still arranged in the same way, with just an extra split/join, then reproduction is still possible (although fertility would probably be greatly reduced). Women with Down syndrome can (with difficulty) reproduce, for example, despite having an duplicate chromosome. --Tango (talk) 20:03, 28 February 2011 (UTC)

There are people right now who carry abnormal chromosomes yet are phenotypically normal and reproduce -- albeit with a higher chance of having an offspring with severe birth defects. See Robertsonian translocation and balanced translocation. There are some rather complicated models of how primate chromosomes evolved - see [20] and [21]. --- Medical geneticist (talk) 20:11, 28 February 2011 (UTC)

Not an 'answer' but you might find Chromosome 2 interesting. I think the questions you are asking are one area which isn't fully understood yet. why don't we see fractions of a population with different numbers of chromosomes is a very interesting question... Different number of chromosomes occurs above the level of species. All Hominidae have 24 pairs of chromosomes, so it's possible to see many "speciation" events before you see any "chromosome count altering" events making them relatively rare, we struggled to find "speciation events" in action so it might be even harder to find the chromosome events. Also, if you think about scenarios where such an event might take place, they might take place relatively "fast", so it might make such events very hard to "catch in the act" so to speak. Vespine (talk) 23:23, 28 February 2011 (UTC)

We are Hominidae and we don't have 24 pairs of chromosomes... --Tango (talk) 23:53, 1 March 2011 (UTC)

We do, in fact, see species where interbreeding members of a population have different numbers of chromosomes. The phenomenon is called chromosomal polymorphism. In addition to the linked article, the phenomenon is discussed at Karyotype#Chromosomal_polymorphism. One observation which to me is pretty convincing that the evolving human species must have gone through a long period of chromosomal polymorphism (involving chromosome 2 and the two corresponding ape chromosomes), is the fact that a large number of molecular polymorphisms in the Major histocompatibility complex, by far predate the split between humans and chimps. This observation has been called the trans species hypothesis by Jan Klein. See also Jan_Klein#Trans-species_Polymorphism. --NorwegianBlue ^talk 21:58, 1 March 2011 (UTC)

Sorry, I did actually mean all Hominidae except us. Vespine (talk) 00:16, 2 March 2011 (UTC)

Toxorhynchites?

I was discussing mosquitoes with another entomology student, and he mentioned a blood-feeding Toxorhynchites species in Panama. I was quite certain that all Toxorhynchites species were nectar-feeding only and not one species was hematophagous. He mentioned that the mosquito was metallic, and thus he inferred it was a Toxorhynchites species. Can anyone find information on what mosquito species he may be referring to?130.127.130.191 (talk) 20:55, 28 February 2011 (UTC)

Well I can't find anything in google scholar searching for 'Toxorhynchites blood panama'. If it was true I'd imagine it would be mentioned somewhere in this or this which I can't access unfortunately. SmartSE (talk) 22:30, 1 March 2011 (UTC)

According to the first article, all Toxorhynchites species are not blood-feeders, as I suspected. Thank you for finding that.130.127.108.23 (talk) 04:54, 2 March 2011 (UTC)

Relativity and nuclear bombs

Did Einstein's theory of relativity have anything to do with discovering how to build and explode nuclear bombs? Could the later have been done without the former? 92.24.179.104 (talk) 22:25, 28 February 2011 (UTC)

There have been previous Ref Desk threads about this. Certainly the role of special relativity (and "E=mc²") in nuclear physics is grossly oversold, and I think that the Manhattan Project could have succeeded without any understanding of special relativity, but that doesn't mean that special relativity wasn't helpful to them. -- BenRG (talk) 22:51, 28 February 2011 (UTC)

(EC)No, not directly. Off course relativity is one of the pillars of 20th century physics so it is a fundamental part of the science of physics as a whole including nuclear physics. Dauto (talk) 23:00, 28 February 2011 (UTC)

Einstein's other, "more important contribution", led to our understanding of modern atomic theory, and probably had more direct impact on the line of research that eventually led to nuclear fission. General relativity has more direct application to astronomy and gravity than it does to atomic or nuclear physics. Lawrence, Fermi, and Oppenheimer all made theoretical contributions that had far more direct impact on the discovery of nuclear fission than any work by Einstein. And even these contributors were primarily theoretical. Most physicists concede that experimental radioisotope research predated modern nuclear theory; but I don't think anyone could have discovered the energetic applications of fissioning radioisotopes without the development of theoretical nuclear physics. Nimur (talk) 00:09, 1 March 2011 (UTC)

Not forgetting the earlier work by Ernest Rutherford. 92.24.191.30 (talk) 12:48, 1 March 2011 (UTC)

Einstein's main contribution to the bomb was writing a letter to Franklin Roosevelt. Edison (talk) 01:47, 1 March 2011 (UTC)

... see Einstein–Szilárd letter (although, according to that article, Szilárd wrote most of the text). Gandalf61 (talk) 13:06, 1 March 2011 (UTC)

There is some good discussion of the ways in which it does and does not apply here. It's hard to ask ahistorical questions about what would have happened without something, but if you could somehow have quantum and nuclear theory without Einstein (only somewhat imaginable), then you could have a bomb without him. But you can say the same thing about Newton. --Mr.98 (talk) 03:00, 1 March 2011 (UTC)

E=mc² tells us that a large amount of energy is potentially available from nuclear reactions, but it does not address the issue of how to access this energy in practice. Uranium-235 is the only isotope that occuipes the narrow gap allowing it to be sufficiently fissile to sustain a chain reaction but at the same time having a long enough half-life to be naturally occuring on Earth in macroscopic quantities. Without U235, is not clear to me that we would have any mechanism to tap significant amounts of energy from nuclear reactions with current technologies. Gandalf61 (talk) 13:29, 1 March 2011 (UTC)

You can describe the energy release from U-235 entirely without recourse to relativity, though, which I think is Serber's point in the link I gave. If you calculate the electrostatic repulsion of two Barium-sized nuclei that happen to be right next to each other (but outside of the Coulomb barrier), you end up with the majority of the energy released in a fission reaction. (Some things don't work so easily, like the energy of the neutrons that result from it, at least as far as I know.) Presumably you could have discovered nuclear fission without the knowledge that E=mc^2. Your knowledge would be incomplete, to be sure, but seeing it as just an electrostatics problem gets you most of the way there.

As for fissile material without U-235... you could use particle accelerators to generate LARGE amounts of neutrons which would then be used to "seed" U-238 or thorium to create either plutonium or U-233. Such an idea was actually pursued by the U.S. government in the late 1940s and early 1950s, when they thought that they might have a uranium shortage. It was code-named the "Materials Testing Accelerator", and was the original basis for Lawrence Livermore National Laboratory (before it was a bomb design lab; our article is sadly deficient on this point, but if you Google around you can find a lot of info on it), even though it was cancelled when it became clear that the US had abundant uranium for its nuclear programs. It's a very inefficient neutron source, though, compared to a nuclear reactor (huge amount of electrical energy, gignormous facility, for not a lot of neutrons by comparison). But if we were imagining a hypothetical universe without U-235, that's one way you'd go about making other fissile materials. --Mr.98 (talk) 19:27, 2 March 2011 (UTC)

March 1

Modified Newtonian dynamics

I've read 3/4 of the article and still don't understand what the theory/idea is, other than it seeks to explain the Galaxy rotation curve. My question: Can someone explain MOND simply? Albacore (talk) 01:04, 1 March 2011 (UTC)

It's a modification of Newton's theory of gravity in which the usual gravitational force law, G M m / r² = m a, is replaced by G M m / r² = m a μ(a/a_o), where a_o is a new constant and μ is tanh or another function with a similar shape. Does that help? -- BenRG (talk) 01:41, 1 March 2011 (UTC)

Useful as if a classical limit that explains away the dark matter problem, then a relativistic field theory can be constructed with the relevant weak field limit. —Preceding unsigned comment added by 129.67.37.227 (talk) 10:24, 1 March 2011 (UTC)

In popular science, MOND is stated as "That Newtons laws of gravitation does not hold over large distances, such as a galaxy". It introduces a fudge-factor into Newtons law of gravitation, which makes the law fit with observations of galaxy rotation. Adding invisible dark matter to the galaxy solves the problem too. The wikipedia article is a hard read but that's partly MONDs own fault. The theory does now answer the "why's" we are accustomed to in other theories, like "why would gravitation change?" It just states that this fudge factor works for the galaxy rotation problem. EverGreg (talk) 09:30, 2 March 2011 (UTC)

The univers is cycla in time and at the age the arrow of time flip ' and it affect gravity , thanks water nosfim —Preceding unsigned comment added by 77.127.25.82 (talk) 10:36, 2 March 2011 (UTC)

How do oral ansthestics with benzocaine work?

Yes I have read the articles but I still dont understand how they work.Accdude92 (talk) 01:18, 1 March 2011 (UTC)

There's a brief explanation at Benzocaine#Mechanism_of_action. Basically Benzocaine blocks the sodium ion channels that, when opened, propogate a signal down the nerves. Since the sodium channel stops working, no signals can get sent down the nerve. --Jayron32 01:34, 1 March 2011 (UTC)

Then what makes the numbing fealing? If it cant transmit a signal, the why dont you feal nothing at all?Accdude92 (talk) 01:36, 1 March 2011 (UTC)

It only blocks certain nerves, those which reach the surface of the skin and sense pain there. You also have nerves whose endings stop some distance under the skin; these nerves sense pressure but not touch. The "numb" sensation you feel when you use benzocaine comes from the fact that you've deadened the surface nerves, but not the deep nerves. Other "caines" like novocaine operate in the same manner; however they are usually injected subcutaneously, thus you tend to lose ALL sensation from the deadened region. With a topical anesthetic, however, you are only deadening the surface nerves. --Jayron32 01:58, 1 March 2011 (UTC)

ear piercing

Is there ever a time when its impossible for an ear piercing to heal?Accdude92 (talk) 02:04, 1 March 2011 (UTC)

Check out wound healing, it should work as with any wound. Constantly traumatizing the site can at least slow the process, also infection probably would do the trick.But frankly cases of non-healing wounds, I've heard about are rather discusting 84.52.32.149 (talk) 02:56, 1 March 2011 (UTC)

Because I know girls that have left their earrings out for quite a while, and the piercing remained open.Accdude92 (talk) 03:25, 1 March 2011 (UTC)

Oh, in that case it has acctualy healed i.e. there is no wound, but a miniature hole in ear, therefore I believe it can stay open indefinetly, though it usualy disapears 89.235.200.28 (talk) 03:37, 1 March 2011 (UTC)

I dont understand how a piercing isnt a wound.Accdude92 (talk) 03:42, 1 March 2011 (UTC)

Look at wound. A wound is when the skin (specifically, the dermis) is damaged. When an ear is pierced, there is initially a true wound: the skin is broken. Soon, though, skin regrows, not covering the hole (because theres an earing there), but rather around the inside of the hole. Compare it to, for example, losing a finger in an accident with a table saw. Initially there's a wound: skin is broken, and blood spurts everywhere. Soon, though, a clot forms, and a scab develops. Before too long, skin regrows, and the finger is the same as before, though a bit shorter, and with some possible scarring. The wound healing article really is pretty good. Buddy431 (talk) 04:08, 1 March 2011 (UTC)

In other words, the tunnel through the earlobe is now lined with surface epithelium. DRosenbach ^{(Talk | Contribs)} 05:42, 1 March 2011 (UTC)

It could be useful to look into process that causes holes to disapear in the first place. Perhaps wounding the site anew can cause it to close up (i.e. if skin is removed from within the hole and there is no earing, nothing would prevent wound from closing), I also figure that since something is inserted in ear initial wound could be healing little bit longer than normal, also if earrings are from material that person is alergic to could do the trick, especialy if alergic reaction is light and person dosen`t notice it right away, also removing and puting back earings might hurt the ear or if it hasn`t been moved at all it could grow into ear, which might cause new wound when removing the earing. So one might still have an unhealed wound by the time earings are removed for good. However I don`t think any of this is what normaly happens when these holes disapear, especialy if person has worn earings for long time 89.235.214.5 (talk) 11:34, 1 March 2011 (UTC)

That would probably work. I have heard that you have to be careful with burn patients because if they have burns on their fingers and the fingers are not wrapped individually, they can sort of grow together when they heal. Googlemeister (talk) 17:25, 1 March 2011 (UTC)

The secret magic of color intensity?

I am taking an arts related course in university as an elective, it is meant for people studying audiovisual media. The teacher has been trying to make a point that something happens, if you put two colors of similar intensity together, but she can't explain what and when I tried to make her clerify this she said that I would see. What I see is that any two colors look difrent when put together, but frankly the particular combinations she sugests look dull. Also she seems to have discovered this effect on her own (she's a painter), so I can't find anything on this. What I want is someone to explain what effect this could posibly have 84.52.32.149 (talk) 02:45, 1 March 2011 (UTC)

A color will look different juxtaposed to one color as opposed to another color. Neighboring colors cause the perception of each to be altered, vis-a-vis what would be the case if they each had different neighbors. Josef Albers did work in this area. Our article Munsell color system may be worth taking a look at. The terms used have to be defined. You refer to colors of "similar intensity". The term "intensity" doesn't appear in the Munsell article. But there may be a different term referring to that aspect of color. "Hue", "value", and "chroma" are terms used in that article. I'm not sure if one of those might be the approximate equivalent of "intensity". Bus stop (talk) 03:13, 1 March 2011 (UTC)

For the record - she uses "similar lightness or darkness" 89.235.213.2 (talk) 03:30, 1 March 2011 (UTC)

I believe that would be value in the Munsell system. Deor (talk) 03:44, 1 March 2011 (UTC)

In the absence of further information, it's difficult to interpret what, exactly, your teacher may be referring to; but the entries for "halation" and "vanishing boundary" here may be relevant. Deor (talk) 03:44, 1 March 2011 (UTC)

What makes this hard is that two colors that have equal luminance on one monitor may have different luminances when shown on a different monitor. See if this demo works for you. Looie496 (talk) 05:18, 1 March 2011 (UTC)

What I learnt from experience, is that when two pigments of a given saturation are mixed, the resulting mixture is of less saturation than either of the constituent pigments.

Just for clarification:

• Hue is the absolute colour on the spectrum.
• Saturation is a measure of how vivid the natural colour is, ranging from a dull grey to perfectly vivid.
• Luminosity is a measure of how bright the natural colour is, ranging from black to white.

Brown is equivalent to vivid (saturation) orange (hue), of low brightness (luminosity). Plasmic Physics (talk) 09:00, 1 March 2011 (UTC)

She has been demonstrating by putting together solidly colored pieces of paper, rather than mixing paint. I think she means vanishing boundry, thanks, now I know what I am supposed to look for 89.235.214.5 (talk) 11:44, 1 March 2011 (UTC)

This (the mixing problem) is explored on the level of particles of pigment in a book called Blue and Yellow Don't Make Green. 81.131.65.79 (talk) 12:38, 1 March 2011 (UTC)

I did this with silly putty once. I bought the bright neon green and pink (came together in a 2-pack) and of course ended up mixing them together. To my amazement the resulting color was the regular old dull-skin peach color of the original silly putty! They "cancelled" each other out. —Preceding unsigned comment added by 165.212.189.187 (talk) 13:53, 1 March 2011 (UTC)

84.52.32.149, you might wish to ask at the following online reference desk.

• Ask a Color Scientist!

—Wavelength (talk) 15:51, 1 March 2011 (UTC)

GPS suction cup problem

I've had three or four automobile GPS units, all different brands, and I've had the same problem with all of them. The suction cup works fine until it gets hot - then it won't stay on but a few minutes. (This is even when the inside of the car is cool.) If you wet the suction cup before sticking on the windshield, it holds. But once it the weather gets hot then you can't remove it properly.

Is there a way to get the suction cups to work properly in a hot environment? Bubba73 ^{You talkin' to me?} 05:17, 1 March 2011 (UTC)

(I think you have a typo in the last sentence of the first paragraph.) Suction cups work by having one part of the suction cup "pull" against a different part of the suction cup. If the pull is not strong enough it falls. So what happens in the heat is that the rubber softens which reduces how springy it is, and it doesn't pull. What you need is one of those suction cups that have a mechanical lever to press it, instead of just relying on the elasticity of the rubber. Or find one with very very stiff rubber which will hopefully stay elastic even in the heat. Ariel. (talk) 06:08, 1 March 2011 (UTC)

But the suction cup has to be in the mount for the GPS, so I don't see any way to change it. Bubba73 ^{You talkin' to me?} 06:25, 1 March 2011 (UTC)

By typo I meant: In one case you say it falls off in hot weather, then you say you can't remove it in hot weather? Isn't that what you want? Anyway, you may be able to buy an aftermarket alternative GPS holder. Either one specifically for your model, or a generic type. Ariel. (talk) 06:55, 1 March 2011 (UTC)

When it is new, it works. It holds it on until I want to take it off. But once the weather gets hot, it falls off every few minutes. Years ago someone suggested wetting the suction cup before putting it on. But once that is done and it is out in the heat, I can't get it off properly (it sticks to the windshield). I want it to stay on until I want to take it off. I take it off to move to the other car or to hide it. Bubba73 ^{You talkin' to me?} 14:11, 1 March 2011 (UTC)

My Dad has a beanbag like thing that is glued (with a weak non-marking adhesive) to the dashboard of his car. It's intended to hold things like satnavs, glasses, and phones. He just puts his satnav down on this, and the satnav is held pretty effectively in place (due to the saggy nature of the bag and the clingy fabric). When he's done, he can return the satnav to the glove compartment just by lifting it off. It's proven to be much more successful than a variety of dashboard and screen-mounting suction cups. -- Finlay McWalter ☻ Talk 13:02, 1 March 2011 (UTC)

Can we assume that you are also cleaning the windscreen and cup surface with alcohol to remove any greasy film. Greasy fingerprints (even if you can't see them) attracts dust which provides an easier access for air to creep in between the two surfaces. This is what a liquid film stops, but it also, as you have found, makes it very difficult to brake the air tight seal again. Also a little trapped air is going expand as the temperature rises so you might still have to re-stick if you first apply it in cooler conditions. On a different application, I stuck a disc of reflective film (just half again as big) on the outside and that helped enormously. But you must keep both surfaces clean!--Aspro (talk) 14:38, 1 March 2011 (UTC)

No I have not been cleaning the surfaces. I'll try cleaning the glass with a glass cleaner and the suction cup with alcohol. Bubba73 ^{You talkin' to me?} 17:02, 1 March 2011 (UTC)

Physical Examination and Vital Signs

Is "pulse oximetry" and "oxygenation" one and the same thing as far as the patient's vital signs on physical examination are concerned? — Preceding unsigned comment added by Aniketnik (talk • contribs) 09:47, 1 March 2011 (UTC)

Yes, probably. But there is also Arterial blood gas which is related but not the same. Ariel. (talk) 10:36, 1 March 2011 (UTC)

From practical stand point, most likely. However any -metry means mesuring something, rather than the stuff being messured, in this particular case pulse pulse oximetry is used to messure oxygenation, and note that the article on it says that it is not just any kind of oxygenation, but oxygenation in hemoglobin 89.235.214.5 (talk) 12:01, 1 March 2011 (UTC)

Phenobarb level

What is the normal phenobarb level in a patient? What are the effects of a high phenobarb level in a patient, in what way does it affect the patient's health? — Preceding unsigned comment added by Aniketnik (talk • contribs) 10:07, 1 March 2011 (UTC)

Assuming you mean Phenobarbital, then the normal level is zero. It's a drug, it's not naturally in a patient. Do you mean what is the typical therapeutic level? If so, then I don't know. For high doses see Phenobarbital#Overdose and Barbiturate overdose. Ariel. (talk) 10:32, 1 March 2011 (UTC)

Incomputable things.

Title is a bit unclear, so here we go:
British mathematician Alan Turing proved that there are true statements in mathematics that are incomputable, meaning beyond the reach of computers, no matter how new and powerful, how can it be explained that limited human mind came to know this statements?Intuition? Is Human intelligence something apart, never to be reached for machines?

TY(again)

DST —Preceding unsigned comment added by 194.138.12.167 (talk) 10:30, 1 March 2011 (UTC)

I think you mean Gödel's incompleteness theorem not Undecidable problem. They are related but not the same. A barebones answer to your question is that we know it, but can't prove it. So that means while it seems correct whereever we check, we can't know that it's correct everywhere. This section and Mechanism (philosophy)#Gödelian arguments talk about it as well. Ariel. (talk) 10:44, 1 March 2011 (UTC)

It is true that there are incomputable functions, but we, humans, can not compute them either. 157.193.175.207 (talk) 10:51, 1 March 2011 (UTC)

so that's a red link, just look here http://en.wikipedia.org/wiki/Uncomputable_function#Incomputable_functions_and_unsolvable_problems 157.193.175.207 (talk) 10:52, 1 March 2011 (UTC)

I meant , that if such things cannot be logically proven , how did the human mind(intelligence) understand the concept? should it not be not understandable then? Is human intelligence something never to be reched by machines, something apart? DST —Preceding unsigned comment added by 194.138.12.167 (talk) 11:43, 1 March 2011 (UTC)

The statement "uncomputable or undecidable statements exist" is not itself an uncomputable or undecidable statement. It can be "reached" by machines. 157.193.175.207 (talk) 13:04, 1 March 2011 (UTC)

The entire trick here is that humans have wonderful abilities to express illogical statements. Human language has no requirement for being self-consistent (ergo the common graffito in college men's rooms: "This sentence is false."). Computability/completeness/etc. all require you to express things that are logically self-consistent. It's not so much that the human intelligence is "something apart," so much as we define machine intelligence as something logically consistent. Such is my meager understanding of these things, anyway. --Mr.98 (talk) 12:41, 1 March 2011 (UTC)

No, that's not quite it. Gödel proved that for any formal system that is powerful enough to describe peano arithmetic, there is a statement that is true, but not provable in the formal system. We can, however, step outside the system and prove (some of) these statements on a meta-level. Of course, our meta-system will have its own unprovable truths, and so on. But in general, a proof of something does not have to be constructive. I can prove that some x with property P exists without being able to produce the x. This frequently happens with with a proof by contradiction, where I assume no such x exists and show that this leads to nonsensical conclusions. --Stephan Schulz (talk) 14:36, 1 March 2011 (UTC)

Turing himself addressed this objection, which he called the Mathematical objection, in his famous essay Computing Machinery and Intelligence, as follows:

“ The short answer to this argument is that although it is established that there are limitations to the powers of any particular machine, it has only been stated, without any sort of proof, that no such limitations apply to the human intellect. But I do not think this view can be dismissed quite so lightly. Whenever one of these machines is asked the appropriate critical question, and gives a definite answer, we know that this answer must be wrong, and this gives us a certain feeling of superiority. Is this feeling illusory? It is no doubt quite genuine, but I do not think too much importance should be attached to it. We too often give wrong answers to questions ourselves to be justified in being very pleased at such evidence of fallibility on the part of the machines. Further, our superiority can only be felt on such an occasion in relation to the one machine over which we have scored our petty triumph. There would be no question of triumphing simultaneously over all machines. In short, then, there might be men cleverer than any given machine, but then again there might be other machines cleverer again, and so on. ”

Looie496 (talk) 17:43, 1 March 2011 (UTC)

Cantor's diagonal argument might be an interesting example of something similar. Basically it proves that all the irrational numbers can't be counted, if you can't count them all, how can you prove they can't be counted? This is as opposed to natural numbers which even though there's an infinite number of them CAN be counted. It would take you an infinite amount of time but you could count all the natural numbers, however even if you count for an infinite amount of time, you'll never count all the irrational numbers. :)Vespine (talk) 02:40, 2 March 2011 (UTC)

Contorting the human body

The image of the woman at this page is confusing me. (Note: Image is of a woman bent over backwards. She's clothed in a... something... but the image may not be entirely work safe) It's really the hump between her legs that has my reviewing my basic knowledge of the human skeleton. I'm of two minds about it, really. If it's a Photoshopped image, then why would the 'shopper put in such a distended hump? But if it's real, what's causing the hump? Her coccyx? Someone care to enlighten me? Dismas|^(talk) 10:59, 1 March 2011 (UTC)

This will help. Scroll down a bit and you can see the original, which has been deleted from the source, but tineye still has a cache of the thumbnail. Ariel. (talk) 11:24, 1 March 2011 (UTC)

I think it is called Mons pubis. Dauto (talk) 16:28, 1 March 2011 (UTC)

PhL, Ph1, Ph2

What are the PhL, Ph1, Ph2 settings on a microscope supposed to do? ---Seans Potato Business 11:10, 1 March 2011 (UTC)

Which kind of microscope? My one doesn't. Plasmic Physics (talk) 11:53, 1 March 2011 (UTC)

You might find Phase contrast microscopy ansewers all your questions--Aspro (talk) 14:56, 1 March 2011 (UTC)

The article fails to mention that PhL is simply the phase-plate on the Left-hand side as you sit before the microscope. Usually, the plate for the lowest useful magnification goes here so that you always know where it is by touch, rather than having to move your head away to check where each plate is by sight all the time. You can then get in to a rhythm of moving around the specimen slide(s) and going up through the magnification range with ease. You choose phase-plates 1 & 2 to suit the whatever higher mag ranges your using.--Aspro (talk) 15:54, 1 March 2011 (UTC)

3 questions of the nature of electricity

What happens to a electron in a magnetic field and a magnet in a electric field? is there any difference between negative and positive charges? Why do interacting magnetic fields create electricity? — Preceding unsigned comment added by Lufc88 (talk • contribs) 17:02, 1 March 2011 (UTC)

For the first question, see Lorentz force; the simplest answer is "it tends to move in circles". For the second, see C-symmetry; the answer is "yes, via the weak interaction". (If you don't include antimatter, then they are more different because of the differences between the proton and the electron.) For the third (assuming you mean "changing" by "interacting"), see The Maxwell–Faraday equation; I'm not sure there is a good "why" answer, though. --Tardis (talk) 17:58, 1 March 2011 (UTC)

Tardis' answer is correct ("yes, via the weak interaction"), but I worry that a non-physicist will not understand what he means; so I will elaborate a bit. Negatively-charged electrons have an antimatter "counterpart," the positively-charged positron. Positively-charged protons have an antimatter counterpart, the negatively-charged antiproton. "For most purposes", these are "exactly the same particle but with opposite charge." They have identical mass and spin, and opposite charge. (Those are pretty much the only properties of an electron or proton). However - if you "zoom in" for a closer look and analyze the way that each particle/anti-particle experiences the Weak interaction, it is clear that they are not just equal-but-opposite-charge particles. Physicists call that property "violation of the charge-symmetry" (or "C-symmetry") by the weak interaction.

This symmetry breaking is a very complicated and subtle effect; it leads some theoretical high-energy physicists to postulate that the Universe fundamentally has a preferred coordinate system - which is an altogether unappealing idea, in the context of the rest of modern physical theory. Nimur (talk) 21:41, 1 March 2011 (UTC)

Oh, but please elaborate! I'm a great fan of a preferred coordinate system, but I don't see how to get there from symmetry breaking. Wnt (talk) 19:55, 2 March 2011 (UTC)

I neglected to answer the second half of the first question: nothing significant happens to a magnet in an electric field, although I wouldn't be surprised if the electric polarization of the atoms produced some small effects on their magnetism. --Tardis (talk) 17:34, 2 March 2011 (UTC)

Are phosphate esters chiral?

Are phosphate esters (R¹, R², R³ all different in the image to the right) chiral? If so, are natural organophosphates enantiopure or racemic? —Preceding unsigned comment added by 148.177.1.215 (talk) 18:04, 1 March 2011 (UTC)

Some phosphate esters are chiral, see page 4 (labelled p. 28) of this for example, but it depends on what groups the Rs are as to whether it is or not. I can't find a source for your second question, since information about nature is drowned out by chemical information, but I would guess that they will be enantiopure, since compounds that are synthesised by enzymes have to be. SmartSE (talk) 22:17, 1 March 2011 (UTC)

Thanks, that's a useful document. 148.177.1.215 (talk) 22:42, 1 March 2011 (UTC)

Yes, as long as there are two R group that are unique, it is chiral. Plasmic Physics (talk) 22:29, 1 March 2011 (UTC)

Don't you mean three R groups need to be unique? With only two different groups, it will have a plane of symmetry and therefore not be chiral, right? 148.177.1.215 (talk) 22:42, 1 March 2011 (UTC)

Well, but if two of R1, R2, R3 are unique, can the third be a duplicate? ;) Wnt (talk) 22:44, 1 March 2011 (UTC)

It could, but the P wouldn't be a stereocenter. DMacks (talk) 13:40, 2 March 2011 (UTC)

In general it is possible to isolate and study enantiomers,[22] though I'm not sure what the rate of inversion actually is. There has been some study of chiral phospholipids in biological systems. Wnt (talk) 22:43, 1 March 2011 (UTC)

Rate of spontaneous inversion seems fairly low for all sorts of XYZP=O structures...what's more interesting is the same is true even for XYZP: (unlike tertiary amines, which undergo pyramidal inversion easily). (CH₃)(t-Bu)(Ph)P ΔG^‡=136.9 kJ/mol at 130 °C. Chiral phosphonyl chlorides undergo clean inversion in S_N2 reactions. The geometry is pretty solid--ligands don't migrate while bound to the P center--but rather the racemization for alkoxy-substituted P appears to be generally by an acid-catalyzed ligand dissociation/reattachment (S_N1-like) or other multistep mechanisms involving planar intermediates. (ref: ISBN 0854042466 §3.2.11 "Racemization, Enantiomerization and Diasteriomerization: Silicon, Phosphorus and Sulfur Compounds"). One extreme example that demonstrates intrinsic stability of the oxy (and halo and amino...) phosophorus center is the configurational stability (and study-ability and multistep reaction sequences involved with) monoalkyl phosphates. CH₃OPO₃H₂ is a rock: the protons can dissociate/reassociate (no control over which two O are formally OH and which is =O) but the O do not come off or invert at the P center. DMacks (talk) 03:13, 2 March 2011 (UTC)

Thanks DMacks. That is very helpful. 148.177.1.215 (talk) 16:08, 2 March 2011 (UTC)

Weak interaction: help

As to my previous questions have alluded, I am attempting to improve the Weak interaction page. (A vital article.) I've pretty much got what was there to how I'd want to be; however, if there isn't more to add, I'm the Queen of Sheba. So perhaps you have something to add or improve? Thanks. Grandiose (me, talk, contribs) 20:27, 1 March 2011 (UTC)

A diagram plotting mass against charge for the six quarks of the standard model, and depicting the various decay routes due to the weak interaction and some indication of their likelihood.

Queen of Sheba? I don't get it. That Article needs improvement. That picture from the article for instance is wrong. Dauto (talk) 21:45, 1 March 2011 (UTC)

In short, I'm not the Queen of Sheba. I've corrected the image. If you have any suggestions for the article, I'll act on them as best I can. Grandiose (me, talk, contribs) 22:01, 1 March 2011 (UTC)

The picture is still not right. The line connecting b and c should be solid and so should the line connecting s and u. Dauto (talk) 00:43, 2 March 2011 (UTC)

The diagram is adapted from information presented by Stanford, and as such could we find a (better) source to suggest the change? Grandiose (me, talk, contribs) 17:43, 2 March 2011 (UTC)

That's a sloppy job done by whoever did it in Stanford. For instance the s-quark can only decay to a u-quark. No other decays are allowed. So that decay must be characterized as very likely (100% chance in fact). Dauto (talk) 19:54, 2 March 2011 (UTC)

No, as the likelihoods are for a specific interval, not for an infinite one. s to u is a slower rate decay than those listed as very likely.

Short English People

Everyone knows that the English people (and presumably other peoples) used to be short a few hundred years ago. I have never seen any published article regarding this, however it is reinforced whenever you visit someone’s quaint 15th century cottage and hit your head on the 5 foot ceilings, or walk round a country house and notice a suit of armour is particularly diminutive.

What caused this sudden increase in height, or alternatively, what caused the stunting in growth?

I have often heard that it was because of either a) diet or b) childhood disease c) starting work earlier.

If diet, what did they lack or were being poisoned by? Surely at least some parts of society was well fed but it seems to across all classes (citation needed) 92.28.85.122 (talk) —Preceding undated comment added 21:58, 1 March 2011 (UTC).

Nutrition accounts for a huge amount of height. See Human_height#Determinants_of_growth_and_height for a lot of discussion of this. It isn't "poison" so much as "you eat only one staple or two, don't get enough protein, are lacking several major vitamins." Note that it's not necessarily whole life nutrition — nutrition as a child can affect overall height by a huge factor, even if later you end up with a more improved diet.[23] --Mr.98 (talk) 22:11, 1 March 2011 (UTC)

But surely most or many people were not malnourished even if they did not have a huge excess of calories?, especially those who lived in the country, on farms etc (i.e. where these tiny cottages are. My impression is that people over 5”4 are almost unknown.

Are there any studies that show when this sudden increase in height happened and what specifically was added, i.e. more protein, vitamins etc?

Oh, another question. Are these deficiencies pre-natal or in early childhood? Thanks. 92.28.85.122 (talk) —Preceding undated comment added 22:19, 1 March 2011 (UTC).

Yes, most people were malnourished, at least during part of their childhood, by modern standards (back then they would likely have said that if you didn't die, your diet was adequate). No, people over 5'4" were not almost unknown. The range of heights was similar then to what it is now, although the average was shorter. Protein is likely the major factor, as poor people rarely got meat, then, and didn't know how to get all the amino acids needed for their bodies to build proteins without meats, with combos of nuts, beans, and grains. Deficiencies which affect adult height could be prenatal, early childhood, or late childhood, up to when adult height would have been reached. Also note that there would be a class difference, with upper classes being the same height as modern people, due to getting plenty of protein (they might also have had gout and other diseases, from too much animal fat, BTW).StuRat (talk) 22:56, 1 March 2011 (UTC)

While you may not have intended to suggest so, to avoid confusion I would note gout isn't caused by animal fat Nil Einne (talk) 15:04, 2 March 2011 (UTC)

No, I meant that other diseases are caused by excess consumption of animal fat.StuRat (talk) 17:08, 2 March 2011 (UTC)

Eating a diamond

can sucking or eating a diamond can kill a human being, how much average mass of diamond can kill a normal human and why.--True path finder (talk) 22:52, 1 March 2011 (UTC)

It's not going to dissolve and release toxic chemicals, so the only dangers are mechanical:

1) If large enough, it could cause a blockage. This would be a multi-million dollar diamond.

2) If the cut has sharp edges, it could cut the walls of the digestive tract, leading to infection, etc.

So, unless it's huge or sharp, I'd expect it to pass through without a problem. As for sucking on a diamond, I see no problem with that, as long as it's sterilized first. If it has some rather deadly microbes on it, that could be a problem, of course. StuRat (talk) 22:58, 1 March 2011 (UTC)

You might also want to read our article on the syndrome called pica. Most often, pica is associated with mental health issues. Nimur (talk) 01:37, 2 March 2011 (UTC)

Eating an intact diamond is unlikely to do any harm. Eating a small quantity of diamond that has been ground to powder can be fatal, though -- it gets into the walls of the digestive tract (as mentioned above) and causes bleeding. (Full disclosure -- I don't know for certain that this actually works. I learned about it from the Autobiography of Benvenuto Cellini, who is not an entirely reliable source.) Looie496 (talk) 01:56, 2 March 2011 (UTC)

Snopes says "no", not that they're an entirely reliable source. --Sean 19:33, 2 March 2011 (UTC)

Centre of the Universe

Just wanted to pose a question which has been puzzling me. Apparently galaxy UDFj-39546284 is the most astronomical object/galaxy ever to have been observed from earth, which lies 13.2bn light years away from us. Now assuming that scientists are correct in their assertion that the big bang occured 13.7bn years ago, then I assume it is theoretically impossible to observe anything beyond the range of 13.7bn lightyears from earth. Now here is my question... if we are able to observe a galaxy 13.2bn LY away from earth does that mean that we must be situated pretty near to the centre of the universe in order to see it? Or could it be that we are 6.6bn lightyears east of the centre of the universe observing something which might be 6.6bn lightyears west of the centre? Or is there even a centre at all? I understand there is a fair chance that the answer to my question might be that we just dont know! —Preceding unsigned comment added by 79.74.240.134 (talk) 22:59, 1 March 2011 (UTC)

The metric expansion of space enters heavily into this sort of thing -- while the Horrendous Space Kablooie happened less than 14 bn years ago, expansion means that our theoretical horizon for observation is something like 40 bn light years, even though we'd only be seeing things 13 bn years old or so at that distance. As for the "center" -- it's everywhere. The Big Bang encompassed the entire observable universe, and it's expanded to everything we can now observe (and all but certainly plenty that we can't). The cosmic microwave background radiation is an incredibly strong piece of evidence supporting this -- in all directions, we observe the remnants of the Big Bang, and the intensity is the same in all directions. We are at the center. But if we measured it 10 bn light years distant, we'd be at the center there, too. — Lomn 23:23, 1 March 2011 (UTC)

In other words, there is no center. Dauto (talk) 00:47, 2 March 2011 (UTC)

The center is like, everywhere, and nowhere. Heavy, dude. Say, you gonna bogart that thing all night? :-) --Trovatore (talk) 00:49, 2 March 2011 (UTC)

I actually lolled.Vespine (talk) 01:26, 2 March 2011 (UTC)

I found the centre of the Universe, its in the sock which I lost in the dryer. Now if only I could find that sock... Plasmic Physics (talk) 04:04, 2 March 2011 (UTC)

The answer is 42. Roger (talk) 09:48, 2 March 2011 (UTC)

Remember, the Big Bang isn't something you could "watch" from the outside. Most people think that if you were present at the time, you could take a box of popcorn and SPF 10¹⁰⁰ suntan lotion and watch the world go boom. The fact is, there was no "Outside", as the entire universe, including the fabric of space (and time) was scrunched up in a tiny ball. So the center is everywhere. ManishEarth^{Talk • Stalk} 12:05, 2 March 2011 (UTC)

(EC)Exactly, so all those CG representations of the Big Bang, where everything starts off black and then you see a big explosion of flames and particles (similar to the Death Star exploding), just ain't accurate. For a start, even if there was a TV camera present at the time, it would have no way of being outside the 'explosion' beforehand - there was no space outside. It could not be viewed from outside. The explosion was more of a rapid expansion, and may have been viewable (theoretically with the right hot-suit) from the inside (the centre), but that's what we're doing now - viewing the explosion from the inside (the centre), just with no need for a hot-suit. --KägeTorä - (影虎) (TALK) 12:45, 2 March 2011 (UTC)

That is also the reason why questions that contain the phrase "before the Big Bang" are totally meaningless. Roger (talk) 12:42, 2 March 2011 (UTC)

A little note: If you were to measure the speeds of all galaxies from Earth, it would appear that they are all moving away from us, which would make it apparent that we are the "center of the universe". But, this will happen on any galaxy'. This is because, if you view the universe as a rubber sheet, with dots representing galaxies, stretching the sheet would best describe the motion of the galaxies, as here all intergalactic distances get magnified, and everything moves away from everything ManishEarth^{Talk • Stalk} 12:56, 2 March 2011 (UTC)

Technically speaking, the universe is multiple dimensions (I don't remember the exact number - 10 or 11 maybe?) in a 1 dimensional space. Tis 1 dimensional space is called the "Multiverse". In that regard, it cannot have a center, as its laws of physics only apply to it, and nowhere else. Therefore, as observed from the outside of this universe, our universe is simply a "membrane", or "brane" for short, that folds in on itself countless times. If you COULD observe from an outside position, which is impossible for two reasons: 1 - photons don't exist "outside", and 2 - the concept of mass doesn't exist "outside", (so you would either cease to exist, or die in some way so horrific that it can't be described in modern physics), you would see that any and every point is the "center" because any point is "0", with 0 being on each side of the universe, and adding those up and dividing them by two gives you zero. Verba et Acta. -Aholb 14:41, 2 March 2011 (UTC) — Preceding unsigned comment added by Aholb (talk • contribs)

This is all M-Theory stuff you're talking, which has no experimental backing at all. --Sean 19:39, 2 March 2011 (UTC)

March 2

measuring and irrational numbers

I've been thinking about measuring and I was curious to know if it's OK to think of it this way:

Imagine we want to measure the length of an object.first we get 2m.and then with a more accurate measurement we get 2.1 ,2.12, 2.129 ,.... It's almost like an irrational number, because the decimals can't be predicted, and it also has an algorithm to be calculated more accurately (which is "measurement").so, which sentence is right?

1.the decimals never end and the object doesn't have a true, accurate length.

2. the decimals end somewhere and the object has an accurate, rational length. — Preceding unsigned comment added by Irrational number (talk • contribs) 13:00, 2 March 2011 (UTC)

Since 1983, (1) has been correct, except that stuff can only be measured with so much precision. See accuracy and precision. Before that, there was just one thing that was, by definition, exactly a metre in length.--Shantavira|^{feed me} 13:25, 2 March 2011 (UTC)

I think you must be referring to the definition of the meter in terms of the speed of light, as described here Meter#Speed_of_light. However, I don't see how this definition of meter has anything to do with the claim that an objects don't have 'true, accurate' lengths. We could change the definition of a meter many of times, and this would never affect the material nature of e.g. the pencil on my desk. That is, the number used to quantify its length may change, but the pencil will not. SemanticMantis (talk) 15:33, 2 March 2011 (UTC)

Where I live, pencils get shorter.--Shantavira|^{feed me} 16:41, 2 March 2011 (UTC)

I think this question is not about science, but about philosophy_of_physics, specifically regarding how to interpret the real numbers as a model for aspects of physical objects. I don't think there is a purely scientific basis for choosing to believe 1), 2), or other alternative interpretations. Perhaps someone else can shed more light on the philosophy involved here. SemanticMantis (talk) 15:33, 2 March 2011 (UTC)

Also, we should be careful with terminology 'accuracy' applies to measurements, not lengths. SemanticMantis (talk) 15:44, 2 March 2011 (UTC)

Having an unending decimal representation is not the same as being irrational – e.g. 1/3 = 0.333.. – so (1) and (2) don't cover all the possibilities even in an idealised situation. AndrewWTaylor (talk) 15:44, 2 March 2011 (UTC)

If the OP is talking about measuring real physical objects, then the answer is that a physical object does not have a "true", infinitely precise, length because the "length" of a physical object is a macroscopic concept and is not well defined at, say, picometre scales due to thermal motion, quantum effects etc. If the OP is talking about measuring ideal objects then the ratio of the lengths of two ideal objects may be either rational or irrational, depending on the objects involved. But I don't see how an irrational ratio is any less "true" or "accurate" than a rational ratio. Gandalf61 (talk) 15:45, 2 March 2011 (UTC)

I think it's better to ask my question this way:Is there any such thing as "the true length" or "the true value" for a certain object?Imean that we can do measurements more and more accurately, but is there any "end" for this process? — Preceding unsigned comment added by Irrational number (talk • contribs) 16:09, 2 March 2011 (UTC)

As Gandalf wrote, "length" for a physical object is a macroscopic concept that breaks down as you start measuring at the quantum level. In other words, you can only ever get to a certain precision (and you can always find a rational number expressing the length to that precision). On the other hand, if you talk about ideal mathematical objects, there are things that have irrational length (the diagonal of a square with sides of length 1) or even transcendental (the circumference of a circle with radius 1). --Stephan Schulz (talk) 19:35, 2 March 2011 (UTC)

In thought experiment only, couldn't the photon sphere around a black hole or neutron star be measured with arbitrary precision, by looking at the number of wavelengths of an arbitrarily high-frequency light source? Wnt (talk) 19:50, 2 March 2011 (UTC)

True or false? (about frogs)

"if you boil a pot of water and throw in a live frog that that frog will hop right out, saving his life to croak again another day (ha, ha)? If, on the other hand, you place a frog in a pot of cold water and turn the heat up slowly, that frog will stay in the pot." Quest09 (talk) 14:05, 2 March 2011 (UTC)

Talking from specific personal experience on this, if you boil a pot of water and throw a fish in, the shock will kill it instantly, or at least render it immobile. I believe the same would be true of frogs. --KägeTorä - (影虎) (TALK) 14:28, 2 March 2011 (UTC)

Isn't that animal cruelty? Quest09 (talk) 14:52, 2 March 2011 (UTC)

We have a well-referenced article on the Boiling frog anecdote, which says: "According to contemporary biologists the premise of the story is not literally true; an actual frog submerged and gradually heated will jump out. However, some 19th century research experiments suggested that the underlying premise is true, provided the heating is gradual enough." WikiDao ☯ 14:30, 2 March 2011 (UTC)

Incredible that WK has an article even on that. Quest09 (talk) 14:52, 2 March 2011 (UTC)

Wikipedia has an article on everything! Of course we do!

Getting to the point of course, I doubt any animals at all (with a few exceptions) can withstand boiling water. Crimsonraptor • (Contact me) Dumpster dive if you must 15:04, 2 March 2011 (UTC)

The question is if every animal will try to escape or if it will just numb and die. Quest09 (talk) 15:25, 2 March 2011 (UTC)

In truth, as someone who worked on getting that article into shape in 2009, we were spurred on to make it a good article (rather than just a bad anecdote and some biologists saying "not true") after being asked about it on the Ref Desk, if I recall. (I believe I was the one who really looked into the 19th century physiological literature for boiled frogs, which I happened to know was a very 19th century physiological thing to do with one's research time. But I may be mistaken.) It has been significantly edited since then, but bears the same hallmarks of the original '09 improvements. --Mr.98 (talk) 19:36, 2 March 2011 (UTC)

dimensions

Could matter, motion, thought, energy, light, etc. possibly be dimensions? For example 4-d spacetime could exist and not result in matter or thought. —Preceding unsigned comment added by 165.212.189.187 (talk) 16:19, 2 March 2011 (UTC)

If you redefine what "dimension" means, then anything can be a dimension. As for the standard definition of "dimension", they are not dimensions. -- kainaw™ 16:20, 2 March 2011 (UTC)

In physics, we use generalized coordinates to describe the complete state of a system. Anything can be defined by a "coordinate" - but only a few are useful coordinates that help us simplify a description of an observed physical system. In addition to your typical "x,y,z" coordinates, physicists often use velocity, angular displacement, and energy as a "coordinate" of a system. Typically, we seek to use a linear transform to convert from an orthonormal coordinate scheme (like a cartesian grid or a polar coordinate system) into a generalized coordinate space; this makes the math much simpler. It is sometimes, but not always, possible to obtain "energy" via a differentiation of a spatial coordinate; (for example, kinetic energy is related velocity squared - which is a nonlinear operation on the first derivative of a spatial coordinate). So, "energy" is rarely a useful coordinate in most physical treatments.

For a concrete example: consider a robot arm. Its hand has an "x,y,z" position; but this is not the easiest set of coordinates to "control the robot." Instead, you want to design a coordinate-system based on the position-values and velocity-values for each "joint" or "elbow" in the robot-arm, so that you can send motor control commands. This approach is called Forward kinematics and is an elementary part of robot theory. More advanced robot control will use other coordinates to design an objective function: for example, you could have a robot-arm who is aware of a coordinate called the "value" of a position, and thus prefers to move to "high-value" coordinates (independent of their x,y,z coordinate). You can thus introduce a new "coordinate" and call it anything you like. This "coordinate" or "dimension" might be the pixel-value at some location in a computer vision camera; or it could be the result of a complex algorithm, or any other thing you want. The reason I bring this up is because advanced robotic theory is mostly concerned with the matrix-mathematics needed to find optimal solutions in high-dimensional spaces. Nimur (talk) 16:37, 2 March 2011 (UTC)

OK, then I guess my question is can current physics describe information and thought the way it describes light and heat? —Preceding unsigned comment added by 165.212.189.187 (talk) 16:58, 2 March 2011 (UTC)

No. See information theory and artificial intelligence for the overview of how "information" and "thought" are modeled scientifically using current theories and technology. Nimur (talk) 17:04, 2 March 2011 (UTC)

But a true "theory of everything" would have to describe them, right? —Preceding unsigned comment added by 165.212.189.187 (talk) 18:13, 2 March 2011 (UTC)

I should just mention Kaluza-Klein theory, M-theory, string theory and so on where the modeling of matter, energy, and light is concerned. Typically information is thought of in terms of other quantities - when you measure the position of an electron and such - I don't know if there's a way to quantify it in such a theory independently of specific forces and particles. But thought, or the "when's dinner?" kind of information, is really not well understood and quite macroscopic (even to the point that no specific part of the brain is certain to affect it when damaged). I'm sure that there are some chip makers who daydream about shrinking their transistors down to the scale of a compactified dimension and using them to operate artificial intelligence, but (probably luckily) this is not on the drawing board yet) Wnt (talk) 18:30, 2 March 2011 (UTC)

There is a theory that all information is retained in the universe in just two dimensions and that any concept we have of a third dimension is nothing more than how our brains perceive the two dimensional information. I haven't read anything on this theory in a few years and I'm certain it has been completely discredited by now. This is an old paper on it by someone who knows what he is talking about. -- kainaw™ 19:04, 2 March 2011 (UTC)

The Holographic principle seems to a mainstream (if highly theoretical) idea of this type. - Jarry1250 ^{[Who? Discuss.]} 19:32, 2 March 2011 (UTC)

I just want to point out that when physicists say theory of everything they mean a theory of all matter and forces, nothing else. Dauto (talk) 19:30, 2 March 2011 (UTC)

(ec) Well, and the reductionist, materialist world-view is predicated on the belief that all complex processes (including sentient thought, consciousness, reason, and sophisticated intelligent life) are fundamentally nothing more than extremely large numbers of simply-interacting objects that behave according to fundamental physics. This is a philosophical position - it is neither correct nor incorrect; it falls outside the realm of "falsifiable" or "provable." But if you hold this world-view, then intelligent thought and complex information storage can be completely described as the ensemble definition of all applicable rules and the state of a complex material representation of information. For example, the bits inside a computer are represented by voltage on microscopic capacitors; those voltages exist because of electrons in a semiconductor-material that obey fundamental rules of electrodynamics. It doesn't matter how complex the computer is behaving - the information it contains is still governed by basic rules of elementary physics. Unfortunately, we are not as close to understanding the way that psychology and memory works in living creatures; so it is much harder to apply a materialist/reductionist worldview as a description of human intelligence. Nimur (talk) 19:54, 2 March 2011 (UTC)

If time can go backwerd , and it can , it can go proprate to matter,or any thing we want to relate to , matter too will be dimensions . thanks water nosfim —Preceding unsigned comment added by 212.199.175.104 (talk) 19:49, 2 March 2011 (UTC)

Maxwellian conflict

Paradigm shift talks about the contest between Maxwellian electromagnetism and Einsteinian relativistic theory. However my understanding was that prior to Einstein, Maxwell's equations were one of the few bits of physics which did, prior to Einstein, already Lorentz transform correctly. Certainly the equations I was taught at university to be Maxwell's equations, are the same as those which are pulled out by considering the force resulting from the EM-Stress energy tensor. So where was there conflict between the two? —Preceding unsigned comment added by 129.67.37.227 (talk) 19:58, 2 March 2011 (UTC)