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November 10

Antimatter paradox

In a particle accelerator, a matter particle and the corresponding antiparticle are created simultaneously out of nothing. Why doesn't this violate the law of conservation of matter? The only resolution that I can think of is that antiparticles would have negative mass, but scientists generally consider this very unlikely. Is there something that I'm overlooking? --75.33.217.61 (talk) 01:01, 10 November 2010 (UTC)[reply]

There is no law of conservation of matter, only conservation of energy. The Sun converts matter to energy all the time. Clarityfiend (talk) 01:54, 10 November 2010 (UTC)[reply]

Mass and energy are different ways of looking at the same thing, due to the whole E=mc² thing. In pair production of an electron-positron pair from a photon, for example, the rest mass of the electron and positron comes from the energy of the incoming photon. The total energy, or mass, depending on how you want to look at it, is conserved. See Mass–energy equivalence#Conservation of mass and energy. Red Act (talk) 02:06, 10 November 2010 (UTC)[reply]

Of course there is a law of Conservation of matter. I think the rest of what is said is pretty right. Vespine (talk) 02:55, 10 November 2010 (UTC)[reply]

The individual conservation laws of matter and energy (seperately) work for ordinary transformations which occur in the course of most people's experience, such as chemical reactions, or the like, at least to a first approximation. The combined matter+energy conservation law is more scrupulously true in all cases, but changes from matter to energy, or visa-versa are usually unmeasurable by normal means except in the cases of very high energy nuclear reactions. Most people don't work in that realm. Of course, even in a chemical reaction, there are (with sensitive enough measurements) real changes in mass due to energy changes, for example in an exothermic reaction the products are slightly less massive than the reactants due to the release of binding energy during the reaction as heat. This loss of energy will result in a tiny change of mass, which is usually unmeasurable using the kinds of scales which most people will have experience with. --Jayron32 07:33, 10 November 2010 (UTC)[reply]

Quite right. From a semantic standpoint, one is also permitted to say that in pair production relativistic mass is always conserved (for a given observer). Some might say that this is a cop out, as relativistic mass incorporates terms for kinetic energy and even accounts for particles (like photons) that have no rest mass whatsoever. On the other hand, fast-moving particles really are measurably more massive (to a suitable observer, with appropriate instruments), and photons really do have momentum — so if it quacks like a massive duck, then it must have mass. In other words, 'Conservation of matter' is a rule of thumb that applies in most 'normal' situations, whereas 'Conservation of (relativistic) mass' is the law. TenOfAllTrades(talk) 14:52, 10 November 2010 (UTC)[reply]

You say "In a particle accelerator, a matter particle and the corresponding antiparticle are created simultaneously out of nothing". But they are not created out of nothing, they are created out of other particles in interactions that obey certain conservation laws including conservation of energy and conservation of momentum - see pair production. You may be thinking of virtual particles, which can exist for short periods of time because of the uncertainty principle. Gandalf61 (talk) 15:49, 10 November 2010 (UTC)[reply]

A noob rock question

What rock is this and how did it get that way? [1] Thanks. Imagine Reason (talk) 01:42, 10 November 2010 (UTC)[reply]

It's not a great picture but it resembles granite. And what "way" are you referring to? Do you mean the relatively flat side or the slant? Either way, it could be from many things. Where did you find it? That might lend some clues. Dismas|^(talk) 01:48, 10 November 2010 (UTC)[reply]

It looks like some sort of granitic or metamorphosized granitic rock. The surface of the rock is heavily weathered, so you would need to break off a piece and examine the clean, broken face to positively identify the rock; that's why geologists carry a rock hammer, since identifying rocks which have been exposed to the elements, covered in lichens, out in the rain for thousands of years, etc. etc. are hard to identify. A freshly broken rock is essential to identification. Some other options, if it isn't granite, would perhaps be gabbro or diorite or gneiss, but these are just shots in the dark. It is quite impossible to positively identify the rock from that picture. --Jayron32 02:01, 10 November 2010 (UTC)[reply]

It's just a random rock on a trail. I was wondering about the surface of the rock. Weathering...of course. Thanks for the responses. Imagine Reason (talk) 04:59, 10 November 2010 (UTC)[reply]

The vertical surface and cracks are joint (geology) planes, formed when the rock is under stress, but not too much pressure. The green stuff may be lichen or green algae, but resolution in the image is not good enough to tell. Graeme Bartlett (talk) 08:00, 10 November 2010 (UTC)[reply]

History of SR

When you plug in the Lorentz transformations into Maxwell's equations, they remain in the same form. 1) How did he (or whoever) arrive at the form of the transformation? Was it worked out or done by blind luck? 2) How did Lorentz interpret this? When we was suggesting Lorentz contraction, I appears that he though length contraction was purely an electromagnetic effect. Did he ever suggest that it might be more general? 76.68.247.201 (talk) 01:53, 10 November 2010 (UTC)[reply]

Have you read History of Lorentz transformations and Lorentz ether theory#Historical development yet? Red Act (talk) 02:35, 10 November 2010 (UTC)[reply]

a disconnected capacitor and dielectrics....

When I add a dielectric into a capacitor do I change the energy stored? Or does the potential energy remain constant? I'm guessing constant but I am not entirely sure.... I usually don't have large enough capacitors to play with so I can't tell if it costs more energy to put a dielectric in or take it out.

From what I get, putting a dielectric in can't change the charge stored, so while the capacitance increases and voltage decreases, this basically increases the amount of charge that could be stored. The voltage drops in the sense that it now costs less energy to separate the same amount of charge .... but wouldn't this reduce the potential energy stored by the capacitor? Or does adding the dielectric only make it possible to store more?

The article really isn't clear on this. John Riemann Soong (talk) 04:55, 10 November 2010 (UTC)[reply]

What would happen if you removed it? You now have "too much" charge. But actually, I believe it would take energy to insert a dielectric (which would show up as voltage, not charge), and presumably the capacitor would constantly be trying to expel the dielectric, converting the stored energy (voltage) into kinetic energy in the process. (I wonder if you can make a motor this way.) I'm not 100% sure about this, but after "simulating" this in my head it's the only option that made sense. Ariel. (talk) 06:34, 10 November 2010 (UTC)[reply]

Actually, I believe the energy stored will decrease. If you take an air-gap capacitor, charge it, and then put some dielectric (with a higher dielectric constant than air) between the plates, Q will remain the same, C will increase by the ratio of the dielectric constants because C=εA/d, V will decrease by the same factor because V=Q/C, and the available stored energy W will decrease because W=VQ/2. Red Act (talk) 07:04, 10 November 2010 (UTC)[reply]

So that will mean the dielectric is attracted to the capacitor, just like a charged plastic rod can attract paper. Graeme Bartlett (talk) 07:52, 10 November 2010 (UTC)[reply]

Well I guess if I charged the capacitor (with dielectric) with a 10V battery, then removed the dielectric, the voltage will be higher than the battery's. It will have a higher potential than the battery, so now it will put energy back into the battery. This is how I understand it. The dielectric "stabilises" the built-up charge. It's kind of like how hyperconjugation or hydrogen bonding stabilises a high-energy intermediate or transition state? John Riemann Soong (talk) 20:08, 10 November 2010 (UTC)[reply]

What if there is no battery connected? No, I believe that the capacitor is constantly trying to expel the dielectric, and if it manages to do so, the "extra" energy is converted to kinetic energy. Ariel. (talk) 04:00, 11 November 2010 (UTC)[reply]

You've got that backwards, Ariel.

As the dielectric is inserted, the potential energy stored on the capacitor decreases, as per my previous post. For conservation of energy to hold, that means that in the absence of any additional external forces, the kinetic energy of the dielectric increases as it moves into the capacitor, which means its velocity is increasing, which, since the velocity of the dielectric is toward the capacitor, that the capacitor basically sucks the dielectric into it. I.e., the dielectric is attracted to the capacitor, as Graeme said.

As another way of looking at it, look at the picture on the right at Capacitor#Theory of operation. As shown in the picture, the electric field between the plates produces a surface charge on the dielectric such that the charge on the dielectric's surface is opposite in polarity to the charge on the adjacent plate. The opposite charges result in an attractive force. Red Act (talk) 04:43, 11 November 2010 (UTC)[reply]

Could be, could be, the part that's bugging me is what happens if you remove the dielectric from a fully charged capacitor? It now holds more electrons than it can. Ariel. (talk) 06:01, 11 November 2010 (UTC)[reply]

It now holds more separated charges, creating a higher voltage than the battery that created it. Normally a capacitor stops when its voltage drop equals the battery because if it went any higher the capacitor would start charging the battery. I suppose it's a situation of equilibrium. John Riemann Soong (talk) 06:53, 11 November 2010 (UTC)[reply]

Yeah, I made my comment below while assuming that the capacitor was disconnected, in which case removing the dielectric would greatly increase the voltage on the capacitor, likely resulting in exceeding the breakdown voltage. But if the capacitor was connected to a rechargeable battery while the dielectric was being removed, then current would flow "backwards" back into the battery, charging it back up slightly, and reducing the charge stored on the capacitor, with just a tiny increase in voltage. Red Act (talk) 07:56, 11 November 2010 (UTC)[reply]

If the capacitor's breakdown voltage is exceeded, it will short out briefly. Red Act (talk) 07:19, 11 November 2010 (UTC)[reply]

Got it. The dielectric is removed, the farad(s?) goes down so the voltage goes up (which may or may not breakdown), since the coulombs is constant - it's not holding more electrons than it can, like I mistakenly wrote, it's holding them at a higher potential. Thanks. Ariel. (talk) 16:51, 11 November 2010 (UTC)[reply]

cotton pants

i bought some new cotton pants and washed them and afterrwards they have a strong pesticide smell. wtf? and why didnt they smell like that while dry? —Preceding unsigned comment added by Kj650 (talk • contribs) 09:52, 10 November 2010 (UTC)[reply]

When articles get wet it seems to release some latent odours, I'm thinking 'dog' at this point But hey, look on the bright side, it'll keep the ants out. Caesar's Daddy (talk) 23:33, 10 November 2010 (UTC)[reply]

Something from Nothing

Quantum fluctuations arise because of the Heisenberg's uncertainty principle. Our universe is said to evolve from such a fluctuation, big enough. So does that mean that the Heisenberg's uncertainty principle is the ultimate driving force of all the universes in the multiverse? Or is there another explanation that I am missing?--Lightfreak (talk) 10:17, 10 November 2010 (UTC)[reply]

Mu. Either a "yes" answer or a "no" answer to your question would be unfalsifiable, because the phrase "ultimate driving force" has no established scientific definition. The word multiverse is also problematical, because that can mean too many different things, all of which are hypothetical. Red Act (talk) 11:27, 10 November 2010 (UTC)[reply]

Also, the Big Bang seems to have created the fabric of space along with matter and energy. It's not the same as a quantum fluctuation happening within the existing universe. Heisenberg does, however, imply that our current models lose predictive power for the very first moments of the Big Bang. --Stephan Schulz (talk) 17:27, 10 November 2010 (UTC)[reply]

Yes. I agree. But Stephen Hawking says in his new book, The Grand Design, that these fluctuations are the reason for the formation of our universe. So how does it all add up??--Lightfreak (talk) 09:50, 19 November 2010 (UTC)[reply]

what'ts this lake called?

[2] ? —Preceding unsigned comment added by Hemanetwork (talk • contribs) 11:13, 10 November 2010 (UTC)[reply]

Are you talking about the *type* of lake, or the name of that particular body of water?

To my eyes, it appears to be man-made in an effort to drain the water from the surrounding land that would otherwise be some sort of salt-marsh. I believe that the appearance of the land on the other side of the railway suggests this. (Am in on 'the wrong track'?) Darigan (talk) 11:48, 10 November 2010 (UTC)[reply]

On Wikimapia, it's labeled "Pinole Lake", but I'm not finding much independent confirmation of the name. Deor (talk) 13:01, 10 November 2010 (UTC)[reply]

I see no streams or such feeding the lake, so this is most likely some sort of man made pond. Perhaps a landscaping project for a business park or housing development being built in the area. Googlemeister (talk) 15:12, 10 November 2010 (UTC)[reply]

It might be an old gravel quarry. 92.24.187.248 (talk) 15:45, 10 November 2010 (UTC)[reply]

I was wondering about the name, there is a complex creek system throughout the area actually, I believe it is fed by Garrity Creek. What government agency would be able to tell me what it is, what its named or who owns it? —Preceding unsigned comment added by Hemanetwork (talk • contribs) 07:17, 11 November 2010 (UTC)[reply]

I'd think that the city of Richmond, California would be the first place to contact. Deor (talk) 03:27, 12 November 2010 (UTC)[reply]

can you strangle someone with your own intestine?

I saw a fight scene where someone was eviscerated, i.e. their gut was sliced open, but in the seconds before they died, they used their own intestines to strangle their assailant. Is this remotely possible??? Could you survive for even seconds with your guts out, and are your guts tensile enough to choke someone? Thank you. 84.153.247.200 (talk) 11:30, 10 November 2010 (UTC)[reply]

No. Dolphin (t) 11:35, 10 November 2010 (UTC)[reply]

You can survive for a short while with your guts out. Hence disembowelment was historically used as a particularly gruesome form of capital punishment, and the Japanese rite of seppuku involved having a second stand by to behead the person as soon as the abdomen had been sliced open (harakiri). However, a person who has been disembowelled is hardly likely to have the strength (because of blood loss and extreme pain) to be able to strangle another person even if they had a piece of rope handy, let alone with their own intestines. Physchim62 (talk) 11:42, 10 November 2010 (UTC)[reply]

A person with guts exposed would not automatically lose all strength, and the blood loss would not necessarily be all that quickly incapacitating merely from the front of the abdomen being sliced open, as opposed to an abdominal injury which sliced arteries and internal organs and caused massive blood loss. Edison (talk) 18:32, 10 November 2010 (UTC)[reply]

Maybe it would help if they were on drugs, like PCP or something else with strong analgesic properties. There's cases of people undertaking "injurious activities" oblivious to the harm they are causing themselves. As for whether it is strong enough, my purely speculative answer is yes, they're pretty strong. Vespine (talk) 21:37, 10 November 2010 (UTC)[reply]

There are horrifying accounts from bullfighting [3], accounts of animal mutilation [4], [5] the American Civil War and World War 1 of horses in a battle trying to gallop away with their guts hanging out. They did not all just fall over when they suffered a fatal abdominal wound which caused the gut to fall out.Edison (talk) 18:18, 12 November 2010 (UTC)[reply]

This is implausible for an additional important reason: Intestines released from the abdomen are on a pretty short tether - the mesentery (and mesocolon for the colon). Think of the intestines as the piping on the edge of the mesenteric apron. The mesentery won't stretch far, but could be torn (with plenty of additional vascular damage). The intestines are also fairly stretchy, so it would take some work to pull them taut enough even if they could be made to reach the intended victim. -- Scray (talk) 12:32, 11 November 2010 (UTC)[reply]

A quick Google reveals the movie in question to be Riki-Oh: The Story of Ricky [6], just in case anyone was interested. Alansplodge (talk) 16:48, 11 November 2010 (UTC)[reply]

Species identifcation for File:Orange-shelf-fungus.jpg

I'm not familar with my local fungi species here in the UK , let alone those of Australia which is where the uploader of the image appears to be based, hence this request.

In order to expand on the image description, so the image can be moved to Commons, Is anyone on the Science Reference desk able to provide a more specific species identifcation? Sfan00 IMG (talk) 13:45, 10 November 2010 (UTC)[reply]

Looks vaguely like Polyporus squamosus, but it's too blurry to make out details of the cap surface, and there's no image of the underside. Not a useful picture, really; deletion would be a suitable fate. Sasata (talk) 22:14, 10 November 2010 (UTC)[reply]

Might be laetiporus sulphureus, but with so little detail... Richard Avery (talk) 23:26, 10 November 2010 (UTC)[reply]

Yes, it looks more like Laetiporus sulphureus to me. @Sasasta: I don't think it needs to be deleted, if it's identified. --The High Fin Sperm Whale 03:13, 12 November 2010 (UTC)[reply]

Pycnoporus coccineus? A lot of fungus species are cosmopolitan as are ferns - spores are extremely light and easily wind-borne all over the world Androstachys (talk) 20:44, 14 November 2010 (UTC)[reply]

energy from antimatter

If one was to calculate energy from an antimatter reaction, one would use the famous E=mc² formula, but is m equal only to the mass of the antimatter, or to 2x the antimatter mass to account for the equal amount of matter that is annihilated? Googlemeister (talk) 15:17, 10 November 2010 (UTC)[reply]

The total mass converted, which is both standard and antimatter. — Lomn 15:26, 10 November 2010 (UTC)[reply]

Antimony oxidation

Would oxidation of antimony by a mixture of dilute hydrogen peroxide and concentrated hydrochloric acid form the pentachloride or the trichloride? --Chemicalinterest (talk) 15:33, 10 November 2010 (UTC)[reply]

It might depend on your concentrations. (The redox potential cited for H2O2 is only for standard state conditions after all.) It might form a mixture of them, even. Have you tried doing any free energy calculations with redox potentials? John Riemann Soong (talk) 23:21, 10 November 2010 (UTC)[reply]

I haven't done any calculations about it. I only put a little powdered antimony in the solution and it dissolved. It did not dissolve when only the hydrochloric acid was there. From the solubility charts, when the small amount of powdered antimony turned whitish in hydrogen peroxide, antimony pentoxide was formed. I would expect it to form the pentachloride when mixed with hydrochloric acid but didn't know whether the pentachloride was stable in that solution. (It was very dilute). --Chemicalinterest (talk) 11:39, 11 November 2010 (UTC)[reply]

Meteorites in mammoth tusks?

I was watching a TV program (National Geographic?) about scientists who were proposing that North American mammoths went extinct ~13,000 years ago because of a meteor impact in what is now northern Canada. One of the scientists scoured collections of mammoth tusks with a magnet looking for small pieces of meteor-derived metal shrapnel in the tusks. This seemed to me like an extraordinarily unlikely thing to be looking for. The chance that fragments of a meteor would end up embedded in a mammoth tusk must be infinitesimal. And the chance that if such as thing did occur that the mammoth involved would end up fossilized and collected must also be infinitesimal. But the scientist did find fossilized mammoth tusks with supposed meteor fragments in them, according to the show. They just turned out to be from an older age (~30,000 years ago), and were said to be evidence of another earlier meteor event. Can this be true, or has this story somehow been embellished and dramatized for a television audience? Edgeweyes (talk) 15:39, 10 November 2010 (UTC)[reply]

Well, it probably wouldn't be fragments per se. However, stuff you breath in and stuff you eat will end up in trace amounts in your hair, teeth, and fingernails, things like that. So what was probably being looked for was elemental evidence of meteoric impact; unique elements and isotopes that would have been in the air and water which would have been ingested by the mammoths and would have shown up in their teeth and bones. Such a meteoric impact would not have likely killed the mammoths instantly, instead it would probably take a few generations for the species to go extinct. Animals which grew up in the years shortly after the meteor impact would possibly have signs in their teeth and bones which would have been indicative of that. See Isotope analysis for the likely work that was done on the mammals. Look especially at the "oxygen isotopes-tissues affected" especially the paragraph on teeth. What applies to oxygen there also applies to other elements in teeth, so any unusual isotopes introduced to the environment of the mammals, such as by a meteor impact, would show up in the animals teeth (tusks are teeth, after all) and remain "locked in" throughout the animals life. I have not seen the program in question, but I suspect what you are interpreting as "fragments" is really chemical elements. --Jayron32 15:56, 10 November 2010 (UTC)[reply]

Actually, the show depicted the scientist looking for visible fragments. He was dangling a magnet on a string and moving it slowly over the surface of the tusks, watching and feeling for a tug from metal fragments. They showed images of small pieces (hard to judge exactly how small), but clearly pieces visible without magnification. Edgeweyes (talk) 16:08, 10 November 2010 (UTC)[reply]

I think I identified the show (by searching Wikipedia, of course): National Geographic Explorer, "Mammoth Mystery" from 2007. Edgeweyes (talk) 16:10, 10 November 2010 (UTC)[reply]

This sounds like the research of Allen West. Here is an abstract of a scientific presentation about this research: http://adsabs.harvard.edu/abs/2007AGUFM.U23A0865F —Preceding unsigned comment added by 148.177.1.210 (talk) 16:32, 10 November 2010 (UTC)[reply]

No shit? Well, strike my comments above. You learn something new all the time. --Jayron32 16:41, 10 November 2010 (UTC)[reply]

I consider this "extraordinarily unlikely" - but that doesn't mean it's false. Skepticism about meteorites is nothing new. It's worth repeating the classic quote from Thomas Jefferson: "I would more easily believe that a Yankee professor would lie than that stones would fall from heaven."[7] Jefferson's skepticism has since been proven wrong, and meteorites are now widely accepted scientific facts; rocks occasionally do fall from the sky (as unlikely as that seems!); and if they survive to the ground intact, they have to land in something. From a certain point of view, it's probably easier to identify a micrometeorite in a tusk (where it stands out clearly as a mineral of foreign origin), as opposed to finding it in the ground. What I find amazingly extraordinary is that the bison survived the impact - in the case of the rest of the tusks, the micrometeorite could have impacted at any time during or after the animal's life - but at least one observation indicates that the micrometeorites hit the animal while it was still alive, and the bison managed to heal and regrow new bone-material! Nimur (talk) 22:39, 10 November 2010 (UTC)[reply]

Wow, that seems to match exactly. I have to say that I'm really surprised. Edgeweyes (talk) 23:33, 10 November 2010 (UTC)[reply]

I'd just like to note that the majority view at the moment is that the impact hypothesis for the North American mass extinction has been pretty definitively rejected, with the last nail in the coffin coming out last month; see PMID 20805511. Basically none of the things that were claimed to support it have stood up to detailed examination. Looie496 (talk) 00:23, 11 November 2010 (UTC)[reply]

The original paper from 2007 Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas coolin is nice to read. Especially if you know how heated and controversial the discussion became in the following three years. --Stone (talk) 07:55, 11 November 2010 (UTC)[reply]

Can you describe how West's work has been criticized? Edgeweyes (talk) 13:50, 11 November 2010 (UTC)[reply]

This PNAS paper is representative of most of the literature. As the abstract says, "We report the results of an independent analysis of magnetic minerals and microspherules from seven sites of similar age, including two examined by Firestone et al. We were unable to reproduce any results of the Firestone et al. study and find no support for Younger Dryas extraterrestrial impact." The basic story is that none of the authors of the original paper were experts in the techniques they were using, and when people who were experts have tried to replicate the observations, they have generally been unable to. Looie496 (talk) 17:26, 11 November 2010 (UTC)[reply]

Thanks, Looie. That is interesting reading. Edgeweyes (talk) 19:26, 11 November 2010 (UTC)[reply]

Species identifcation for File:Flower2294.JPG

File:Flower2294.JPG

The image in question

In order to expand on the image description, so the image can be moved to Commons, Is anyone on the Science Reference desk able to provide a more specific species identification? Sfan00 IMG (talk) 13:45, 10 November 2010 (UTC)[reply]

Looks like some kind of Helianthus (aka sunflower), not sure on the exact species, but you could hunt around. --Jayron32 15:58, 10 November 2010 (UTC)[reply]

My suggestion would be Calendula officinalis. Being a popular garden plant, this comes in a range of cultivars with varying appearances (double heads, different colours, etc), but the leaves (which are also subject to some variations) look consistent. 87.81.230.195 (talk) 22:18, 10 November 2010 (UTC)[reply]

There are so many types of aster that all look generally similar, that you really gotta be a specialist to be able to name a specific one (modulo a few distinctive exceptions). Looie496 (talk) 00:12, 11 November 2010 (UTC)[reply]

Yes, it is definitely Calendula officinalis. Cacycle (talk) 08:59, 12 November 2010 (UTC)[reply]

Molecular geometry

Hello, I would like to find a reference that clearly and concisely describes the geometry of ideal polyhedra. For example, in a molecule formed of X and O units in 4-fold coordination, the ideal O-X-O bond angle for a tetrahedral unit is cos-1(-1/3)=109.47 degrees. This is quoted in the article Molecular_geometry. However I would like to understand, in simple terms, where this formula comes from. And hence how I would go about calculating the O-X-O bond angle in other types of polyhedra, specifically for octahedra or cubic geometry. I know this is quite basic geometry but I find it quite difficult to visualise and am sure there must be a reference out there somewhere that describes how to calculate this angle for ideal polyhedra. Thanks in advance for your help. 88.219.44.165 (talk) 22:06, 10 November 2010 (UTC)[reply]

The technical term for this value is the central angle of the polyhedron. My bookmark for looking them up is [8]. Here goes my understanding of the math. In general, one considers inscribing the polydedron in a sphere, and the edges of the polyhedron are therefore chords. Now you've got a triangle (center, and the two ends of the chords) and you know all three side-lengths (from the dimensions of the polyhedron and the sphere, respectively), so you can solve the angles of it with simple trig. And the dimensions of the sphere are also based on the dimensions of the polyhedron. So "all you have to do" is figure out how to derive the sphere size for a given polyhedron. I don't remember how. DMacks (talk) 01:11, 11 November 2010 (UTC)[reply]

Okay, it appears maybe related to the "miter angle" (angle between the two faces joined by the edge that is the chord). I still don't know how to find that, but lots of woodworking sites have applets or links to calculators for at least some forms. DMacks (talk) 01:15, 11 November 2010 (UTC)[reply]

Thanks DMacks for the reference that gives the table of central angles, that helps for a start. In terms of the calculation yes it just fundamental geometry so must be described in a text book or a good online reference somewhere but thus far I have not been successful finding anything.88.219.44.165 (talk) 07:55, 11 November 2010 (UTC)[reply]

Equilibrium -- only at 109.47 degrees are all four bonds equally spaced from each other. Or is this not what you were asking? John Riemann Soong (talk) 03:03, 11 November 2010 (UTC)[reply]

Yes, although often there may be some distortion from these ideal values. Nevertheless my question is how do you actually calculate the angle (termed central angle as DMacks points out) for various ideal polyhedra. It's "basic" geometry but I'm looking for a reference that describes the procedure in simple terms. I have spent a long time (a few hours) searching on google but can't find a straightforward explanation. 88.219.44.165 (talk) 07:55, 11 November 2010 (UTC)[reply]

Since calculating the central angles of various polyhedra is really purely a math problem, you might have better luck with getting a thorough explanation if you ask about it at the math reference desk. Red Act (talk) 09:14, 11 November 2010 (UTC)[reply]

Thank you, I have posted my question here: Wikipedia:Reference_desk/Mathematics#Calculating_the_central_angle_in_polyhedra. Best wishes 88.219.44.165 (talk) 11:03, 11 November 2010 (UTC)[reply]

Species identifcation for File:Marouxlynx.jpg

In order to expand on the image description, so the image can be moved to Commons, Is anyone on the Science Reference desk able to provide a more specific species identification?

Sfan00 IMG (talk) Sfan00 IMG (talk) 22:26, 10 November 2010 (UTC)[reply]

Looks like a canadian lynx to me (Felinae canadensis), but I'm not an authority. -- Scray (talk) 01:42, 11 November 2010 (UTC)[reply]

The same image appears here and here, both of which treat it as a Lynx canadensis. WikiDao ☯ (talk) 14:17, 11 November 2010 (UTC)[reply]