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March 8

Radiative transport?

Does the "Radiative transport" linked in the Sievert integral article mean the same thing as "Radiative transfer"? Or is this "Radiative transport" referring to some physiological aspect of radioactivity? I can't tell from the references. Thank you. Praemonitus (talk) 00:21, 8 March 2013 (UTC)

The former. The integral pertains to a layered medium, with $\varphi =0$ normal to the layers, such that $x\sec \varphi$ is the distance along a line at angle $\varphi$ to the normal to a point x away in the normal direction. Then the exponential decay of radiation over distance (in the simple case) is invoked. I'm not sure what should be taken from the weighting by angle; there may be compensating terms involving solid angle subtended at each end of the line segment. I think "radiation transport" (as it says: note the first word) is a common synonym for "radiative transfer"; it might deserve a redirect. --Tardis (talk) 03:08, 8 March 2013 (UTC)

Thank you for the clarification, Tardis. Praemonitus (talk) 05:23, 9 March 2013 (UTC)

Mixing chemicals

Hello. Can you tell me what would complete the following reaction, which I added together into a beaker. I have noted the solution is both black, and very acidic.:

C3H6O + H20 + NaCl + HCL + C3H8O + KCL + BaCl2 + HNO3 + CoCl2 + K2Cr2O7 + K2CrO4 + H2SO4 + K4Fe(C2O4)4·2H2O → ?

Thanks, Albacore (talk) 03:07, 8 March 2013 (UTC)

It depends on the initial concentration of the hydrochloric and nitric acids, many of the reagents in that reaction aren't reagents at all, and may only at best act as catalysts. The final solution is black because of colloidal carbon. Plasmic Physics (talk) 03:41, 8 March 2013 (UTC)

Also, barium sulfate may crash out of the solution, and if the chromate/dichromate is concentrated enough, they may oxidize the isopropyl alcohol to acetone. Of course, if the sulfuric acid is concentrated enough, it will dehydrate all organic compounds in the mixture to carbon like Plasmic said -- but if the nitric acid is highly concentrated, then it might in turn oxidize the carbon to CO2 (which will bubble out of the solution because of its low solubility in acid)! So if I had to guess, I'd say your solution contains the following: H2O (solvent), C(s), C3H6O(aq), Na+(aq), Cl-(aq), H3O+(aq) (lots of), K+(aq), BaSO4(s), NO3-(aq), Co+2(aq), Cr2O7(aq), HSO4-(aq), CO2(g), and Fe+2(aq). 24.23.196.85 (talk) 06:43, 8 March 2013 (UTC)

Oh, I forgot the oxalic acid H2C2O4(aq) (which will be fully protonated because of the acidity). 24.23.196.85 (talk) 06:48, 8 March 2013 (UTC)

A biological question about myself

we cannot offer diagnosis or medical advice
The following discussion has been closed. Please do not modify it.
I once took an otc pill was for Common coldness (it was in 2011) and contained: Dexchlorpheniramine maleate Pseudoephedrine for an unkown reason, it maid my hand-skin very dry !!!, so much so, that after 5 days some of the skin on the middle of the upper hand (next 2 where the fingers start-out), and also, in some cushions of the hand, skin could be easily ripped off from this areas (and it wasn't painful). other Antihistamine drugs didn't do that 2 me (except 2 one which i think contains the same AH molecule mentioned above, but don't take my word for it). could you at least try 2 tell me about this very interesting mechanism? thanks 4 your time. Ben-Natan (talk) 05:50, 8 March 2013 (UTC) The drug is a common antihistamine decongestant combination. Your skin changes were either (1) an effect of the respiratory infection for which you took the drug-- several of them can cause late skin desquamation and peeling; (2) an allergic reaction to either component of the drug; or (3) due to something completely unrelated. Note that an allergic reaction to a drug is different than a "side effect"-- what you describe is not a recognized side effect of either drug. I suspect the first possibility is most likely. The only way I can think of for you to determine whether it was a drug effect would be to take it again for a few days: if it didnt happen again, it probably wasnt the drug. Note that this is speculation because you asked for it and not medical advice. alteripse (talk) 12:41, 8 March 2013 (UTC) This is a one-off trial with a sample size of one person and no double-blind control. Literally nothing can be deduced from it. Without other information, there is zero reason to assume that the effect on your skin had anything whatever to do with the medication - rather than some chance encounter with some chemical or biological agent over some several days before you skin condition popped up - or as a side effect of the disease that caused you to take the drug in the first place. To even credit the question as something worth answering, you'd first have to take a thousand people, give half of them the medication and the other half a placebo, count the number that have skin problems and see if the result is higher for those taking the medication than those that didn't. If that's a big enough difference, then it's a side effect and you can start to ask why it happens. But if not...then this is not a meaningful question. Since the manufacturers most certainly did some kind of a trial like this for all of the active ingredients, then if this were a reasonably common side-effect, it would be printed on the label someplace. So check the label - and if it describes this symptom, then we can probably find the cause somehow. If not - then it was almost certainly something else that caused your skin issues. SteveBaker (talk) 14:20, 8 March 2013 (UTC) Hi. For the first answerer, anytime i take the drug, the exact thing happen, i took it again before and after the aforementioned time. thanks. Ben-Natan (talk) 17:16, 8 March 2013 (UTC)

the human singing voice - effects of age

Until age 50, I had a soprano voice and could sing a high A without difficulty. In the 15 years since, it has dropped an octave. I now sing (croak) lower than my husband does. I am aware that voices change over time and that women's voice generally get lower. What physical changes account for this please? And does it matter? There have been no illnesses which might explain it and my speaking voice has not much changed. Thank you. — Preceding unsigned comment added by 109.12.62.161 (talk) 07:59, 8 March 2013 (UTC)

One of the illnesses that affect voice, and that affects many females over the age of 50, is hypothyroidism. I presume you've ruled that out. --TammyMoet (talk) 10:25, 8 March 2013 (UTC)

Firstly, we're not allowed to diagnose medical issues here on the Wikipedia reference desk - that's a huge "No-no" for use! So our advice has to be limited to "Go see a doctor"...and something like this does have the potential to be indicative of medical issues that you might not otherwise have noticed (see Vocal cord dysfunction for a range of alarming possibilities), so that's especially good advice in this case.

Our vocal cord article suggests that menopause can specifically change a woman's singing voice, and since this evidently happened in your early 50's (which is plausibly the age when menopause happened for you) the timing is right for that to be the cause here.

If all else fails...there is always helium! :-)

SteveBaker (talk) 14:37, 8 March 2013 (UTC)

And menopause causes a lowering in the voice frequency due to changing hormone levels (a higher testosterone to estrogen ratio, which also can cause facial hair). I wonder if anyone has studied if hormone replacement therapy reduces or reverses this effect ? StuRat (talk) 16:14, 8 March 2013 (UTC)

Does the concept of a "quantum speed" make any sense?

I am currently taking a Quantum Chemistry class at university and to test our knowledge on quantum mechanics, the professor just posted a rather interesting question. The question is:

"Does the concept of a 'quantum speed' make any sense?"

I thought this question in two ways:

1) Speed as a continuous variable is not quantizable. This means a "quantum of speed" doesn't exist, and therefore the concept of a "quantum speed" does not make any sense.

2) Since speed is the magnitude of velocity and velocity is the time derivative of position, the speed of a particle trapped in a box (say, a 1-D infinite square well potential) is represented by || d/dt [xΨ(x,t)] ||. Taking the position operator on the wave function yields a position with an imaginary part, and taking the magnitude of the time derivative of a complex position should be able to yield a real solution. Would the real solution represent the "quantum speed"

Am I at all on the right track with these two approaches? Hope to hear you guys' insights! — Preceding unsigned comment added by 169.232.187.44 (talk) 08:28, 8 March 2013 (UTC)

What evidence do you have to support your theory that "speed as a continuous variable is not quantizable"? It might be true, but is it established as a fact? See Planck length and Chronon. Also see [ http://arxiv.org/pdf/quant-ph/0004086.pdf ]. --Guy Macon (talk) 10:19, 8 March 2013 (UTC)

The Planck length is just a distance at which quantum gravitational effects should become large. There's no particular reason to think that distances are quantized in units of the Planck length. Anyway, there's no Planck speed—or rather the Planck speed is c, which isn't particularly helpful in this context. -- BenRG (talk) 23:09, 8 March 2013 (UTC)

Perhaps an overly simple approach: aren't speed and temperature essentially the same thing, on a quantum scale? Isn't temperature quantized? --Mr.98 (talk) 12:50, 8 March 2013 (UTC)

Sorry for the digression, but no, absolutely not. Speed and temperature are not remotely the same thing. In fact temperature has nothing directly to do with kinetic energy. Temperature is a measurement of the relationship between entropy and internal energy. This is the statistical mechanics approach to temperature, and it is far more fundamental than the kinetic approach. Temperature can even be negative, that is, below absolute zero, which is obviously not possible for speed or kinetic energy. --Trovatore (talk) 17:13, 8 March 2013 (UTC)

Define a linear speed operator S by defining it on the functions exp(i k x) (which form a complete set), as

S exp(i k x) = hbar |k|/m exp(i k x)

Then S is defined for all states. You then need to check to see if S is a Hermitian operator. Count Iblis (talk) 15:51, 8 March 2013 (UTC)

In physics, I believe there are some massless particles which can only go the speed of light, while particles with rest mass can go speeds below, or, theoretically, above the speed of light, but not precisely that speed, as getting there would require infinite energy. A complicating factor is that the speed of light itself varies, depending on the medium. StuRat (talk) 16:04, 8 March 2013 (UTC)

If you're implying that particles can't travel faster than the speed of light in a medium, that's absolutely wrong. They can and do break the "light barrier" in water all the time, and the result is Cerenkov radiation. --140.180.243.114 (talk) 18:53, 8 March 2013 (UTC)

(Mostly responding to StuRat) The speed of light in a medium is just the speed of light in a medium and has nothing intrinsically to do with the speed of anything else. The universal constant c has nothing intrinsically to do with light, even though it's often called "the speed of light in vacuum" or even just "the speed of light". So your second sentence isn't a complicating factor in any physical sense. It's just a pun on the phrase "the speed of light". -- BenRG (talk) 23:09, 8 March 2013 (UTC)

To the OP: maybe I'm missing something here, but why can't you apply the momentum operator to the wavefunction, calculate the inner product of the result and the wavefunction, and integrate over all space? That would give you the expectation value of momentum. Divide that by mass and you'll get the classical analogue of velocity for a wavefunction. --140.180.243.114 (talk) 18:53, 8 March 2013 (UTC)

I wonder if this question had some specific context—i.e. there was something in the lectures or readings recently that looked like it was about "quantum speed", and the question is whether that's accurate or misleading. Without context it's hard to know what to say. Speed is an observable in quantum mechanics, as other people have already said. It's not quantized in general (though it can be in particular cases like the particle in a box), but not being quantized doesn't mean it's not quantum—"quantum X" and "quantized X" generally mean different things. -- BenRG (talk) 23:09, 8 March 2013 (UTC)

There isn't a really specific context that I can provide I'm afraid. We just wrapped up 3D particle-in-a-box and moved onto the harmonic oscillator approximation. The professor is pretty big on the interpretation of Quantum Mechanics though. I suppose the context for a "quantum speed" comes frmo the latest Verizon adverts where they allow the users to upgrade to a faster internet speed called "quantum." I think that's where he based the problem off of. In regards to 140.180.243.114, taking the momentum operator and then dividing it by the mass does seem to be a much quicker way to determining the velocity! — Preceding unsigned comment added by 169.232.187.164 (talk) 00:22, 9 March 2013 (UTC)

See also group velocity and phase velocity ? Jheald (talk) 10:11, 11 March 2013 (UTC)

Something about coelomates

In here (page 95), the classification chart of animals into different phyla is given. I'm having trouble understanding how coelomates are further divided. Can anybody help? Thank you. --Yashowardhani (talk) 09:30, 8 March 2013 (UTC)

The chart on that page clearly shows that coelomates are divided into Annelida, Mollusca and Arthropoda on one branch and Echinodermata and Chordata on the other. Wikipedia uses a 'superphylum' notation to name those two branches - so the Echiondermata and Chordata are both "Deuterostomes" (with a couple of other phyla tossed in that your chart doesn't mention) and the Annelida and Mollusca are all in the super-phylum "Lophotrochozoa". Wikipedia's chosen classification places the arthropoda in the "Ecdysozoa" super-phylum.

The trouble with these classifications is that they are changing rapidly as we discover more about the animals involved - and the entire structure of the tree is a matter of heavy debate with some biologists preferring a DNA-based approach, others an evolutionary approach - and with both laboring under some horrific mis-classifications made by observation of body structure alone dating back to Victorian times. Your book looks like it was probably published about 8 years ago...and things are changing faster than that!

SteveBaker (talk) 15:04, 8 March 2013 (UTC)

Some of the clades you mention, are fairly certain and stable such as the crown deuterostomes and the ecdysozoans. The big problem is the protostome/deuterostome dichotomy has turned out to be as flawed as the dicot/monocot dichotomy, with protostomy and dicotyledony turning out to be non-diagnostic symplesiomorphies. The linked information Yashowardhani provided would have been considered simplistic and out of date decades ago--it's basically suitable merely as an introduction to the fact that such concepts exist, as might be okay for non-science majors. There are plenty of popular books like Assembling the Tree of Life that are slightly more updated and at least bring up the issues that are at question. (Even that will be outdated, however--the field is in a huge flux, see Afrotheria for an unexpected recent yet now undoubted grouping.) μηδείς (talk) 01:25, 9 March 2013 (UTC)

The solubility of francium hydroxide: is it OR?

In Chinese article of francium hydroxide it is claimed that francium hydroxide is soluble in water along with this source:Maddock, A. G. (1951). "Radioactivity of the heavy elements". Q. Rev., Chem. Soc. 3 (3): 270–314. doi:10.1039/QR9510500270.. In English article of francium there is a similar claim using the same source says"Nearly all francium salts are water-soluble." But in the DOI page all I can say is an abstract of the research focusing mainly on the actinium series. So does this article actually describe the solubility of francium salts?

The article says "nearly all francium salts are soluble". That's it; no further details are given. It doesn't say water-soluble, though this is implied by the context. Chris (talk) 15:29, 8 March 2013 (UTC)

After all, the article might mean "soluble in molten tungsten"... :) --Guy Macon (talk) 17:05, 8 March 2013 (UTC)

What??? The wikipedia article did say water-soluble. You mean the doi article?--Inspector (talk) 23:57, 8 March 2013 (UTC)

Cinnamon Wattle

Hi!

How has the plant Cinnamon Wattle got its scientific name Acacia leprosa? Does it have something to do with leprosy? --213.214.155.24 (talk) 12:13, 8 March 2013 (UTC)

The word indeed derives from the original Latin word for leprosy (as of course does the English word itself), and in biological nomenclature is sometimes used to indicate a spotted or blotched appearance (as a sufferer of leprosy might have). Although it's not obvious in the pictures in our article on the Cinnamon Wattle, it looks as if the 'leaves' do have a slightly mottled appearance due to their texture. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:42, 8 March 2013 (UTC)

This says: "Acacia; from Greek acis, a thorn. leprosa; having a whitish, mealy or scaly surface, presumably referring to the phylodes.". And according to leprosy: "The word leprosy comes from ancient Greek Λέπρα [léprā], "a disease that makes the skin scaly"". So the name basically refers to the scaly nature of the plant - and both "leprosa" and "leprosy" come from a common base term for scaliness. The plant itself has nothing whatever to do with leprosy. SteveBaker (talk) 14:45, 8 March 2013 (UTC)

Drat, I misread the title, and now I'm hungry for cinnamon waffles. StuRat (talk) 16:10, 8 March 2013 (UTC)

This here's the wattle, the emblem of our land,
you can stick it in a bottle, or hold it in your hand

— Monty Python

Amen. -- Jack of Oz ^[Talk] 04:27, 9 March 2013 (UTC)

specilization of the cell wall of epethilia

please i want it very soon

specilization of the cell wall of epethilia — Preceding unsigned comment added by 41.37.24.186 (talk) 16:07, 8 March 2013 (UTC)

See Epithelium, but "the epithelia" includes every type of tissue in the body, apart from muscles, nerves, and tendons. Without knowing the specific type of epithelium you need information about, it's not really possible to answer the question. Tevildo (talk) 18:07, 8 March 2013 (UTC)

Why azane, not nitrane?

All the examples listed at Substitutive nomenclature are constructed as main part of element name + "ane": borane, oxidane, phosphane. So why is azane not called "nitrane"? — Sebastian 16:44, 8 March 2013 (UTC)

It's named after azote which is an alternate name for nitrogen which has now fallen out of use. Dauto (talk) 18:58, 8 March 2013 (UTC)

Cool, thanks! BTW, German "Stickstoff" expresses the same idea, meaning "suffocating substance". — Sebastian 19:33, 8 March 2013 (UTC)

There's also Guns 'n' Roses copyright. μηδείς (talk) 01:13, 9 March 2013 (UTC)

Which they stole from Roy Acuff. 24.23.196.85 (talk) 03:37, 9 March 2013 (UTC)

Weird chemistry dream: The scent of a proton

I had an odd dream last night in which I was back in chemistry class. The teacher had a device which could strip the electron from atoms of hydrogen, leaving positively charged protons, which we sniffed via a tube stuck up the nose. They had an unpleasant acrid smell. Now in reality, would such a gas of low energy low density hydrogen atom stripped of electrons have a smell? I know that normal hydrogen is odorless. This is quite distinct from proton beam therapy. The Proton article in the section "Interaction of free protons with ordinary matter" says that such protons might combine with another atom or molecule to make "Bronsted acids," which makes the "acrid" scent in the dream plausible. Is such an experiment possible (however inadvisable)? Edison (talk) 17:56, 8 March 2013 (UTC)

It must have been an awesome dream! 140.254.121.60 (talk) 19:30, 8 March 2013 (UTC)

Maybe you were smelling ozone. The protons can also be called ionized hydrogen, and ions are generated during lighting storms which also makes ozone, which you can smell. Ariel. (talk) 20:18, 8 March 2013 (UTC)

Acrid: "Smells like Akron". :-) StuRat (talk) 22:51, 8 March 2013 (UTC)

Didn't you mean this Akron? 24.23.196.85 (talk) 03:40, 9 March 2013 (UTC)

Nope, Akron, Ohio, with that lovely rubber volcanization scent. StuRat (talk) 04:20, 9 March 2013 (UTC)

To be smellable, a substance must be volatile and soluble. (Volatile to get to your nose, soluble to penetrate the aqueous and lipid layers that surround the olfactory nerve cells.) I'm guessing that by the time a proton reaches your olfactory receptors, it's hydrogen, though as you point out other substances might be possible. - Nunh-huh 03:48, 9 March 2013 (UTC)

If a number of low energy protons were introduced to the olfactory area of the nose, they might steal an electron and become odorless hydrogen as you suggest. They might also latch onto another atom or molecule and share its electrons. The stray low energy proton would likely not combine with the nucleus of another atom, increasing its atomic number. Most air molecules would be nitrogen, followed by oxygen. What compound would nitrogen or oxygen plus a proton be? (For me, a chemistry or physics dream is interesting and thought provoking, while a math dream is literally a nightmare). Edison (talk) 03:20, 10 March 2013 (UTC)

A protonated oxygen molecule O₂H⁺ is called the hydroperoxyl ion.[1][2][3] The hydroperoxyl anion is O₂H^- the opposite charge. (but this may also just be called the hydroperoxyl ion too, casuing confusion) N₂H⁺ is rather boringly called protonated nitrogen.[4][5] The links I provided also list some reactions. There is also a protonated nitrogen dimer: N₂H⁺N₂ with two nitrogen molecules bridged by a proton.[6] There looks to be just enough material to justify articles. Graeme Bartlett (talk) 04:21, 10 March 2013 (UTC)

Thanks much. Edison (talk) 20:32, 10 March 2013 (UTC)

Actually, protonated oxygen is called dioxidanylium, and deprotonated hydrogen peroxide is called hydroperoxide, or dioxidanide. Plasmic Physics (talk) 06:10, 11 March 2013 (UTC)

Another name for dioxidanylium is hydroperoxonium. Hydroperoxyl is not an ion, it is the HO₂^• radical. Plasmic Physics (talk) 06:15, 11 March 2013 (UTC)

I'm thinking that you can't spray air full of protons without a counterion. A simple example would be H+ and Cl- ions. Of course these would be in equilibrium with HCl gas, which upon reaching moist nasal membranes will largely dissociate, and by the time the H+ affects an olfactory receptor, the Cl- is surely long gone. Since you have Cl- ions in your nose, i.e. sodium chloride, the very small amount of HCl gas you can smell without your olfactory epithelium falling out in clumps shouldn't have much of a smell. So HCl has a recognizable "sharp" smell, which should be roughly equivalent to the smell of a proton. Of course, you can argue that this isn't the "real" smell, since it probably reacts with something to create whatever scent you perceive, just as the smell of iron isn't its "real" smell, but that seems like excessive sophistry. Wnt (talk) 15:55, 12 March 2013 (UTC)

caffeine ==> adenosine receptors

Is caffeine a competitive agonist for ATP on the adenosine receptors? ATP stands for adenosine triphosphate, and it is used by cells as an energy source. Similarly, caffeine somehow gives you energy. Is it possible that they work the same way? 140.254.121.60 (talk) 19:27, 8 March 2013 (UTC)

The chemical that activates adenosine receptors is adenosine, not adenosine triphosphate. I am unaware of any evidence that ATP acts as an agonist at adenosine receptors. So I believe the answer to all these questions is no. You can look at our article on caffeine for more information. Looie496 (talk) 23:23, 8 March 2013 (UTC)

Adding water causes liquid soap to gel

We decant liquid dish soap from a large commercial bottle into a pump-action dispenser beside the kitchen sink. Recently in rinsing out the liquid remaining in the bottle by adding water, I found the resulting diluted soap lathered up well on the sponge and was then easier to rinse off the dish being washed. However, when I added water to the dish soap in the dispenser (about 1:3 ratio), I was dismayed to discover the lower part in the dispenser turned into a gel that resists dilution with water. What's going on here? -- Deborahjay (talk) 19:49, 8 March 2013 (UTC)

If you put the dispenser in warm water for a while, does the gel dissolve? --Guy Macon (talk) 20:00, 8 March 2013 (UTC)

I can't try that without recreating the original problem - I poured the entire contents of the dispenser into a large bowl and combined it with my fingers, then added much more water so it's highly diluted now. -- Deborahjay (talk) 20:23, 8 March 2013 (UTC)

I think what Guy is getting at is that the water temperature might make a big difference, with the water mixing much better if hot. Was the water a uniform temperature in both cases ? The other big difference might be the surface area. Presumable, on the plate, there was much more surface area available for mixing than in the dispenser. Next time, you might want to just add a little hot water to the dispenser, mix that in, then add a bit more, until it's all mixed. StuRat (talk) 22:48, 8 March 2013 (UTC)

March 9

Why do ceiling and walls get darker except for the corners

My room used to be white but darkened because of smoke, etc. Except for the very corners that seem to be unaffected. A professional painter tells me this is very common. How would smoke even know it's in a corner? Joepnl (talk) 00:00, 9 March 2013 (UTC)

Just a WAG, but my guess is that it has something to do with the way that air currents distribute the smoke around the house; the corners may present perturbations to air flow that prevent as much smoke from getting into the corners as along the surface. --Jayron32 00:05, 9 March 2013 (UTC)

In that case I'd expect a big white spot in the "very 3D-corners", where there are three angles at the same time giving reason to the smoke to not stick to the wall. The white stripe seeminglingy has the same width everywhere. I was thinking that it might have to do with the way the paint was applied (using a paint roller for the large areas and a brush for the corners), but the white stripe also appears next to lights that were installed after the painting was done. Joepnl (talk) 01:19, 9 March 2013 (UTC)

Doesn't laminar flow decrease exponentially with proximity to a surface? Wouldn't that imply airflow in room corners is minimal, and that wsmoke would more likely escape a room before getting into its extreme corners? I am reminded of H. P. Lovecraft. μηδείς (talk) 02:03, 9 March 2013 (UTC)

It's an effect called ambient occlusion. SteveBaker (talk) 05:00, 9 March 2013 (UTC)

An optical illusion? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:29, 9 March 2013 (UTC)

No, neither of these. I've observed exactly the same effect and it is real and independent of paint and light (it happens to wallpaper, too). Jayron's and Medeis' answer of airflow must be correct one, though there will sometimes be a bit of turbulence. I'm not sure how airflow behaves at the intersection of room right-angles, but presumably one could make some deductions from the lighter areas. The pattern might depend on the temperature difference between the room air and the walls, thus creating constant convection currents unless the walls are really well insulated. Dbfirs 15:50, 9 March 2013 (UTC)

• This phenomena is certainly not Ambient occlusion. As the professional painter informed Joepnl, it is is very common. It becomes apparent in a room by the temperature differential on the surfaces. If Joepnl looks around s/he will notice it is less worse in the outer corners of the house which loss the least heat if the roof if the roof is uninsulated but worst if it is. A quick, off the top of my head, physics explanation, is that the colder places, the Brownian motion of the dust particles, loose their energy fastest here and thus are more likely to get stuck on those surfaces (the surface may also change its electrostatic charge in the process – in comparison to the rest of the room- leading to even more dirt to be deposited). It is no optical illusion or anything like that. As Joepnl can problem come back and testify – it is a very noticeable and up-close inspection discoloration. Particulate are more likely to stick to colder surfaces -period. No mystery.--Aspro (talk) 21:45, 10 March 2013 (UTC)--Aspro (talk) 21:45, 10 March 2013 (UTC)

I can't vouch for this unequivocally, as I am not in the mood to think it trough properly (unless someone wants to pay me loads of dollars). Yet this appears to support my thinking as well. www.google.com/url?q=http://www.nbslgt.com/designbuild/pdf/18Ghosting.pdf&sa=U&ei=dfc8UZrYN8vA7Ab814CgCw&ved=0CBgQFjAA&usg=AFQjCNEbn0bL19bdERgriI-4vrmsAxhv7A

--Aspro (talk) 22:17, 10 March 2013 (UTC)

There is no apparent difference between the outer wall (on the right on the picture) and an inner wall (to the left) which I would expect if it has to do with a temperature difference. (It's not due to removing spider webs either, it's the same at the top and bottom). But Brownian motion might still be the solution. If the particles were huge (like tennis balls) and shot them randomly at the wall they wouldn't even be able to reach to corners. Making them gradually smaller still would make it harder to get to the exact corner. All the way to the smallest particle. But then again, I thought Brownian movement would only be visible under a microscope, but the stripes are about a centimeter in width. Joepnl (talk) 23:30, 12 March 2013 (UTC)

• Indeed, it is not ambient occlusion. As our images at Cornell box or Radiosity (computer graphics) show, the way the light falls tends to make edges and corners appear darker, as it is more difficult for light to bounce into them off a wall. But the contributor here is observing that actually the edges and corners are appearing lighter, with less dirt apparently settling there. Jheald (talk) 23:32, 10 March 2013 (UTC)

science writing

Why is science writing usually done in the third person, passive, past tense? — Preceding unsigned comment added by 99.146.124.35 (talk) 02:52, 9 March 2013 (UTC)

Because it's always done that way. I'm serious. That's what my high school science teachers told me almost 50 years ago. Oh, there's also the fact that we lost marks if we did it any other way. HiLo48 (talk) 02:59, 9 March 2013 (UTC)

Well, there is actually a reason: to maximize objectivity. First-person writing brings ego into the picture, and when ego comes in, objectivity goes out. Looie496 (talk) 03:10, 9 March 2013 (UTC)

My impression is that most papers are written in the present tense, first person plural (even if there's only one author). Popular books about science are written in the past tense insofar as they're histories, in the third person insofar as the author wasn't involved, and in the first person insofar as he/she was involved. I think the passive voice is used mainly where the subject would otherwise be "scientists in our (sub)discipline" and it would be silly to keep repeating it. You do often see "our results are summarized below" instead of "we summarize our results below", but there's nothing wrote with that. -- BenRG (talk) 04:58, 9 March 2013 (UTC)

This does actually vary a little. A friend told me in psychology, the first person is becoming more common, even (I think) normal or expected in some journals. This is true of qualitative and quantitative research. I do not mean to suggest applies across the board in psychology, and it was just what one psych PhD told me. In IT I was told to use the third person, but the reason given was just because my supervisor had seen things done that way himself, not because he had any ideology about it. I think those that have strong feelings get their opinions heard, and others play along. In science, as might be suggested by Looie's post, more people are strongly against the "I" than strongly in favour. I'm in favour, but wouldn't make a drama over it. Also, past tense for your methods section (this is what you did) and present for the conclusions (where the conclusions apply to a general case, rather than reasoning about specific factors in the experiment). So "Method: 33 subjects were recruited....Discussion: It seems from the data that some of the results may have been confounded by the subjects talking on mobile phones and drinking too much beer ... even so, it seems (present tense) that safety lessons improve driver behaviour... " etc IBE (talk) 02:04, 10 March 2013 (UTC)

About 1970 my high school biology teacher said to write up the lab report in the "third person". He meant "passive voice". So I wrote things like "he made the incision in the frog". "She saw the intestines." To address the original question, I think that it is because it is more about the object and procedures than the person doing them. Bubba73 ^{You talkin' to me?} 04:23, 10 March 2013 (UTC)

Papers in the natural sciences usually have a number of authors. Using "I" would be weird: which of the authors is speaking. And using "we" would also jar, because it was actually just one person minding the experiment in the lab, another one crunching the results on the computer, etc. In the social sciences and humanities most papers have one or two authors, so it sounds more natural to write "I" or "we". Itsmejudith (talk) 10:00, 10 March 2013 (UTC)

Journals do ask authors to avoid this old habit of using the third person, see this style guide, section 9 on page 14 and 15. Count Iblis (talk) 23:58, 10 March 2013 (UTC)

But (2) in that section says "The passive voice is often the most natural way to give prominence to the essential facts." Active voice is almost nonexistent in wikipedia. Bubba73 ^{You talkin' to me?} 02:06, 11 March 2013 (UTC)

Glomerular Pore Radius

Hello. Given the filtration coefficient, how can one find the pore radius in order to calculate the "pore surface area to pore length" ratio? I am referring to the formula: $K_{f}={\frac {r_{0}^{2}S}{8\mu l}}$ where $r_{0}$ is the pore radius and ${\frac {S}{l}}$ is the ratio. A link to a journal article would be appreciated. Thanks in advance. --Mayfare (talk) 03:28, 9 March 2013 (UTC)

Eggs and potatoes

Eggs and meat cook from the outside in, but potatoes and root vegetables cook evenly (if that's the right way to put it). I suppose that it has something to do with the fact that eggs and meat contain more protein, but what is the reason for that difference? Sjö (talk) 08:27, 9 March 2013 (UTC)

There might be a small difference in thermal conductivity as you suggest, but the main difference is that potatoes and root vegetables are normally cooked for much longer at only 100C, so the difference between inside and outside is not really significant because the whole object has been at a constant temperature for a long time. Eggs are normally cooked for a short time so delays in heat flow are noticeable, with the yolk never reaching 100C in some cases. Meat is normally cooked for longer, but at a higher temperature, and not covered in water, so low thermal conductivity and restricted heat flow becomes very important. Those who like their meat "rare" never allow the inside to reach 100C, even if the outside has reached several hundred degrees. If you try grilling potatoes and root vegetables, you will see that they also cook from the outside in. Dbfirs 09:44, 9 March 2013 (UTC)

I can assure you that potatoes and root vegetables do indeed cook from the outside in, and I really have no idea where you got the notion that the inside of a potato cooks at the same rate as the outside. Do you have any references to that effect? --TammyMoet (talk) 10:53, 9 March 2013 (UTC)

As Dbfirs notes above, while they do cook from the outside in, the difference in cooking time between the outside and inside is small, relative to the overall cooking time. I've cooked potatoes, carrots, etc., for hours, while that would ruin eggs or meat, in many cases. In the case of exceptions, like a pot roast, where meat is cooked for a long time, you don't find a noticeable difference in how well the inside and outside are cooked. StuRat (talk) 15:46, 9 March 2013 (UTC)

... and as Tammy mentioned, if you try boiling a large potato for less than five minutes, you will see that the inside is still starchy and uncooked. Dbfirs 15:57, 9 March 2013 (UTC)

Does vitamin D insufficiency known as a potential Obesity cause?

My Nutritionist told me that there may be a connection. my endocrinologist told me: "take at least 10 drops !!! (off 400 IEA)"). is there a connection between being with bmi like 29 (near obese) to this vitamin? thanks Ben-Natan (talk) 08:49, 9 March 2013 (UTC)

That seems unlikely. New Zealand is pretty close to the ozone hole, and apparently we're the sixth fatest country in the world. Plasmic Physics (talk) 10:38, 9 March 2013 (UTC)

Vitamin D is involved in many more process than bone health. E.g. without enough vitamin D, your muscles will have a more difficult time accessing energy, see here:

"Conclusions: Cholecalciferol therapy augments muscle mitochondrial maximal oxidative phosphorylation after exercise in symptomatic, vitamin D-deficient individuals. This finding suggests that changes in mitochondrial oxidative phosphorylation in skeletal muscle could at least be partly responsible for the fatigue experienced by these patients. For the first time, we demonstrate a link between vitamin D and the mitochondria in human skeletal muscle."

Count Iblis (talk) 13:48, 9 March 2013 (UTC)

Also note that just about any vitamin or mineral deficiency may be linked with obesity, in the Western world, as the most frequent cause of such deficiencies (where food is plentiful) is solely eating junk food, which also causes obesity.

In the case of a vitamin D deficiency, since this vitamin is produced by exposure to sunlight, as well as obtained from nutritional sources, a lack of D also implies a lack of time spent outside, which can mean a lack of exercise, which is also linked to obesity.

So, a vitamin D deficiency may or may not cause obesity, but may also indicate an unhealthy lifestyle which is associated with obesity. StuRat (talk) 16:34, 9 March 2013 (UTC)

The likelihood of finding vit D deficiency in obese adolescents and young adults is >90%. The association of vit D deficiency and obesity is strong. However association does not prove causation, and there not yet strong evidence that vit D deficiency actually causes obesity. alteripse (talk) 16:45, 9 March 2013 (UTC)

Both StuRat and alteripse need to provide some sources, especially as they are in disagreement with each other. Bielle (talk) 17:09, 9 March 2013 (UTC)

Read our posts again. We're both saying that, while there's a correlation, that doesn't necessarily means it's the cause. StuRat (talk) 17:12, 9 March 2013 (UTC)

No disagreement. Just emphasis that association does not prove direct causation. alteripse (talk) 17:24, 9 March 2013 (UTC)

Exactly, we're fat, and we don't have a D deficiency, if anything, have a D surplus. Plasmic Physics (talk) 22:44, 9 March 2013 (UTC)

Unless you take something of the order of 5,000 IU/day of vitamin D or if you happen to live in some African tribe in the wild, you are vitamin D deficient, if not severely vitamin D deficient. See here for some actual measuremnts of vitamin D levels of people who live in the way we all lived until about 10,000 years ago. Count Iblis (talk) 23:33, 9 March 2013 (UTC)

OK, so we are deficient, but certainly less so than most other areas. Plasmic Physics (talk) 23:41, 9 March 2013 (UTC)

Actually Count Iblis frequent claims about vitamin D deficiency are usually lacking in good sourcing compliant with WP:MEDRS standards. In this particular case, the very source they linked to says that the measurements do not establish a vitamin D deficiency for people living a more modern lifestyle:

Whether this concentration is optimal under the conditions of the current Western lifestyle is uncertain, and should as a possible target be investigated with concomitant appreciation of other important factors in Ca homeostasis that we have changed since the agricultural revolution.

unless I guess you use a rather odd definition of deficiency where someone with an optimal concentration of vitamin D is 'deficient'

Nil Einne (talk) 18:58, 11 March 2013 (UTC)

You have to see this in the context of the current discussion in the scientific community. A number of scientists in the field have argued that there is no rigorous proof that for optimal health you need to be above 50 nmol/l. The Institute of Medicine has argued this way in their latest report from 2010. Then, this does has the effect of setting the bar a lot higher for claims that you need to have higher levels for optimal health, despite many other scientists disagreeing with some of the basic issues here. They will argue that it is foolish to just assume the null hypothesis that that 50 nmol/l is ok. (because this is what indoor living Westerners can easily achieve) while demanding that this has to be proven wrong in randomly controlled trials where you e.g. show that higher levels significantly reduce the risk of heart disease, cancer etc.

Vitamin D is not some manmade drug designed to cure some specific disease, so you don't know a priori what to look for in a randomly controlled trial. It may e.g. have benefits in an indirect way, e.g. there is some evidence that higher levels help with recuperation from exercise. Then, if this is indeed the case, it would be beneficial for people to supplement to higher levels, because that may help them to stick to some exercise program, stay fit and lower the risk of heart disease. However, it is then possible that there are no benefits for the heart due to the higher calcidiol levels at all, so in an RCT you could well see nothing at all. This (potential) irrelevance of RCTs has been argued about in the literature a lot, but vitamin D is still treated more like a drug than a nutrient where we typically don't impose this standard.

Even within the well established issue of bone health, there is a lot of controversy about the 50 nmol/l level, see e.g. here, note also that the endocrine society advices people to have levels between 100 nmol/l and 150 nmol/l, because they do find sufficient evidence of benefits beyond bone health. Count Iblis (talk) 23:25, 11 March 2013 (UTC)

You're basically making my point for me. You frequently present one view as the correct one without making it clear it's much disputed and even when you do provide sourcing such as here, you're frequently relying on a very selective reading of the sources. Note that I've never taken sides on whether or not people are commonly deficient OR the recommendations you present are correct or the current common recommendation is correct. That's beside the point in a lot of the questions you reply to. Ultimately what we need good scientific analysis and sources that provide that, not personal POVs or half baked theories based on what people 10k years ago got or overtly simplistic analysis based on one possible benefit ignoring the plenty of possible conflicting factors at play both positive and negative. Nil Einne (talk) 16:23, 12 March 2013 (UTC)

what is Nec?

in many scientific words like Necrosis, Adiponectin, and also in such as Necromancer there is the morpheme Nec. what is the meaning? Ben-Natan (talk) 10:15, 9 March 2013 (UTC)

It comes from the Greek prefix necro, meaning death. Don't know whether Adiponectin uses that particular meaning though. --TammyMoet (talk) 10:46, 9 March 2013 (UTC)

The etymology of the nect element in adiponectin is from Latin nectere meaning to connect or to bind. SpinningSpark 11:47, 9 March 2013 (UTC)

And to avoid using the word to define the word, "connect" means "to bind together".[7] ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:29, 10 March 2013 (UTC)

How can we predict properties of an element and its compounds when that element is not available or too unstable to experiment?

One early example of those might be Mendeleev's prediction for germanium and its compounds, which includes some densities and melting points. How are those kinds of predictions made? Just simple linear regression, and in some cases by theoratically calculating the Van der Waals Force? Do we know how accurate it can be? Can we apply such methods to other elements and their compounds? Is it original research to make such predictions?--Inspector (talk) 10:10, 9 March 2013 (UTC)

For putative properties that we don't measure but derive, this is the realm of disciplines such as computational chemistry. The modern methods are more rigorous (as we have more data and better equations) than Mendeleev used in filling in the holes in his table, but the principles are the same. The prediction of these properties is roughly the field of Ab initio quantum chemistry methods, which basically involves deriving putative properties from purely mathematical principles: You start with what you know of the laws of physics as they apply to all smaller atoms you already know, then you extrapolate that data (it's probably a LOT more complex extrapolation than mere linear regression) and predict the likely properties of the unknown element. --Jayron32 16:14, 9 March 2013 (UTC)

Planck derived units

What is the difference between one Planck length per Planck time; and one Planck length per second? Isn't the latter one meaningful when describing quantum speed? Plasmic Physics (talk) 10:49, 9 March 2013 (UTC)

One Planck length per Planck time is simply another way of saying C: the speed of light in a vacuum. It is the equivalent of measuring speed in light-years per year. --Guy Macon (talk) 14:25, 9 March 2013 (UTC)

So, one is the fastest speed, and the other is the slowest measureable speed? Plasmic Physics (talk) 21:47, 9 March 2013 (UTC)

The latter is not the slowest measurable speed. It can't be, because the second is a human invention, and there's no reason for the universe to depend it. Since momentum is not quantized, there's no such thing as a slowest speed. --140.180.243.114 (talk) 21:53, 9 March 2013 (UTC)

Note, I adjectived 'measureable'. Plasmic Physics (talk) 22:01, 9 March 2013 (UTC)

It's important not to get hung up on the Planck units as imposing some sort of limitation on physical phenomena. The Planck mass is a perfectly ordinary macroscopic mass, well within the measurement capabilities of, if not a set of kitchen scales, certainly a cheap education-grade analytical balance. Nothing special happens at that mass - it's not a lower or upper limit to anything. The Planck length and Planck time are outside the range of (practically) measureable quantities, but they have no special significance otherwise. Tevildo (talk) 22:51, 9 March 2013 (UTC)

Planck Time article says it is a theoretical limit due to effects of quantum mechanics. manya (talk) 03:46, 11 March 2013 (UTC)

That's not true. I removed it. -- BenRG (talk) 05:55, 11 March 2013 (UTC)

The Answer to "Relaxing Voices"

This is from January 2011; my original question was deleted because it was too "medical" sounding, and my follow-up question was therefore poorly explained on my part because I didn't want it removed. Anyway, from this thread: "Why do some voices, e.g., Bob Ross's, cause people to relax? I've read on other forums that people will watch his show to help them fall asleep." I didn't know how else to explain this. well just now, some random video on YouTube was being pushed on me ("featured"?), so finally I watched it and I noticed all these "ASMR" videos that seem to be a thing now. I Googled ASMR and it took me to Autonomous sensory meridian response—that's precisely what I've been looking for for decades (long before people discovered this on the Internet). It's a "dizzy" feeling one experiences when certain individuals talk quietly.Reflectionsinglass (talk) 11:59, 9 March 2013 (UTC)

You should look at Bitching Betty. Shadowjams (talk) 12:33, 9 March 2013 (UTC)

Venus flytrap and meteors

Is it true that following meteor impacts, large numbers of venus flytraps can often be found growing around the craters and no-one is really sure how they got there? And that their main habitat is located near what was once a crater left by a huge meteor strike from millions of years ago? — Preceding unsigned comment added by 87.113.139.192 (talk) 17:41, 9 March 2013 (UTC)

Carnivorous plants typically grow where the soil is missing some needed nutrient, which they then get from whatever they digest. I suppose the area where a meteor has struck might be depleted in some nutrients, if it blew away the topsoil. This would make it difficult for normal plants to grow there, but the Venus flytrap could survive. StuRat (talk) 17:56, 9 March 2013 (UTC)

However, none of that answers the question about venus flytraps being mysteriously co-located with impact craters. The answer to that question is firmly "no". Flytraps are native (only) to the Carolinas, which are not notable impact basins, and are not natively found elsewhere. — Lomn 18:04, 9 March 2013 (UTC)

I think we need to link to Little Shop of Horrors. Rmhermen (talk) 20:18, 9 March 2013 (UTC)

What about a link to Dr Quatermass or even The Night of the Triffids. Oh, I'm not going to sleep tonight. I can see the wife's rubber plant looking at me right now and it's licking its lips.--Aspro (talk) 22:32, 10 March 2013 (UTC)

March 10

Social interaction and levels of cognitive activity

I read an interview with French neurologist Pierre Bustany that neural activity was greatly heightened in social interaction, much more than, say, when doing a crossword. The conclusion was that social interaction is much better for the mind than puzzle solving. That last part may be obvious anyway, but I'm not so curious about that - I just want to know if anyone can point me to any interesting references (books or key papers) that establish the claim about the level of neural activity/ excitement in social interaction, especially compared to puzzles/ games/ etc. Thanks in advance, IBE (talk) 02:09, 10 March 2013 (UTC)

The entire concept of doing a brain scan, then assuming, because glucose is being used in many areas of the brain, that that somehow indicates more thought is occurring, seems like a stretch, to me. I suspect that glucose is used for other things, too, like repairing damage. Or, even when it does indicate brain cells "working", it's not necessarily useful thinking. For example, an epileptic seizure probably lights up the scan, but this doesn't indicate that quality thought is occurring. StuRat (talk) 02:51, 10 March 2013 (UTC)

No worries, and by all means point me to a reference on this line of thinking. It's for a PhD lit review, although there is only a marginal chance I'll be able to squeeze it all in anyway. Totally peripheral aspect, but I like to paint a broad picture, even at the risk of sounding frightfully amateurish. IBE (talk) 03:26, 10 March 2013 (UTC)

I'm skeptical of that statement, and it doesn't seem to be a topic that he has actually worked on. As far as I know the greatest difference in brain activity is between sleep and waking, and across the range of normal waking states the variations in activity level are pretty limited. Also as far as I can see the literature, such as PMID 18381770, does not give any support, although of course there are specific brain areas that are activated by social cognition. Looie496 (talk) 03:59, 10 March 2013 (UTC)

I think you're right that he hasn't worked on this area, or at least my own googling says it isn't his primary field at all. I was under the impression it was something that was maybe generally well known, but you have convinced me otherwise. At any rate, it isn't going in the "lit" review ;) IBE (talk) 04:32, 10 March 2013 (UTC)

I highly doubt that any non-crackpot neurologist would draw a conclusion like "social interaction is much better for the mind", as if the mind were a monolithic entity instead of a collection of interacting components with different functions. That simply doesn't follow from "more brain areas are active". --140.180.243.114 (talk) 08:42, 10 March 2013 (UTC)

It turns out I've overstated it slightly. I was just looking for a paper on it, and assuming it was some well known thing, so I wasn't too precise about it. The full quote is this (French with my Fr-2 translation, interview in Ca M'Interesse, Jun 2012):

Les cablages formes dans la jeunesse sont-ils effectifs toute la vie?

Ces associations de neurones se maintiennent a peu pres vingt ans. Apres, si elles ne sont pas utilisees, elles disparaissent.

......

Comment eviter cette impasse?

Il faut stimuler son cerveau a toute age. Pour cela, rien de mieux que les relations sociales. Avoir des contacts avec les autres impose de devoir discuter, echanger, decrypter les non-dits, les gestes, les hesitations...Et aussi d'anticiper, de s'organiser pour arriver a l'heure a un rendezvous. Tout cela met en jeu des reseaux de neurones differents. Bien plus nombreux que lorsque vous faites des mot croises! Rien de pire, a la retraite, que de quitter le lieu ou l'on a toujours vecu pour se retirer sur la Cote ou l'on ne connait personne. C'est l'atrophie cerebrale assuree.

My translation:

Are the neuronal connections formed in our youth effective throughout the lifespan?

These connections last for about 20 years. After that, if they are not used, they disappear.

How do you avoid this?

One must stimulate one's brain throughout one's whole life. For that, nothing is better than social relationships. Social contact imposes the need to discuss, interact, and interpret non-verbal cues...And also to anticipate, to prepare oneself to arrive on time for a meeting. All this activates a variety of networks of neurons. Many more than when you do a crossword puzzle! There is nothing worse, upon retirement, that leaving the place where you have always lived, to retire to the Cote (d'Azure?) where you know no one. That is guaranteed to produce cerebral atrophy.

So I had overstated it, partly from trying to weave it into my own knowledge/ interests. Does it sound more reasonable in this form? IBE (talk) 18:12, 10 March 2013 (UTC)

Can plants grow on lunar soil given enough water and air?

--Inspector (talk) 04:33, 10 March 2013 (UTC)

No, because lunar soil has no organic matter, and therefore no nutrients needed for growth. See [8]. In fact, even on Earth, plants will die if the concentrations of the 6 macronutrients and 8 micronutrients are too high or too low, or if the soil is too coarse/tight, or if the soil PH is too low or high.

It is possible to grow plants on the Moon if you provide the required nutrients, using hydroponics. If you plan to do that, you might as well ditch the soil, because it doesn't help. --140.180.243.114 (talk) 08:35, 10 March 2013 (UTC)

This appears to disagree with the above. --Guy Macon (talk) 09:04, 10 March 2013 (UTC)

In that experiment they added bacteria to the lunar soil simulant, which by the looks of it leached nutrients from the rock. It notes that the plants "fared very badly" in neat soil simulant. Fgf10 (talk) 09:37, 10 March 2013 (UTC)

Also lunar night is too long (354 hours). This makes moon unsuitable for Earth's plant life. --PlanetEditor (talk) 08:45, 10 March 2013 (UTC)

In places like Murmansk or Hammerfest, the night can sometimes be two months long, but does that make these places unsuitable for plant life? 24.23.196.85 (talk) 04:40, 12 March 2013 (UTC)

The OP may find the Soil article useful. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:02, 10 March 2013 (UTC)

What is happening here?

what is happening here?112.209.165.87 (talk) 11:29, 10 March 2013 (UTC)

It's an electric fence. The first four people are insulated from the ground, so don't get shocked. As soon as the last guy joins the chain, a connection is made to earth, current flows, and everybody gets zapped. Rojomoke (talk) 13:25, 10 March 2013 (UTC)

It looks like very high power. Somebody told me that you have to increase the power from horses, cows, goats to sheep. The horses are very sesitive while the isolating capabilities of sheep make it hard to shook them.--Stone (talk) 21:58, 10 March 2013 (UTC)

Wool is a reasonably good insulator, so sheep (and sometimes goats) will push under an electric fence without feeling much of a shock. Horses and cows tend to investigate with their mouths first, so are more likely to avoid a low-power fence. Dbfirs 10:30, 11 March 2013 (UTC)

Don't try this at home, folks! 24.23.196.85 (talk) 00:16, 11 March 2013 (UTC)

inactive ingredients (excipients) in prescription and otc drugs

I have a question not writing an article: individuals who have celiac disease or other sensitivities such as milk allergy such as myself find it very difficult without a physicians desk reference to determine what the binders are in drugs when they are being manufactured. When researching the drug Ultram for a friend I determined per the site www.ehow.com: (I am copying and pasting)"The starch ingredients in Ultram are used in the manufacturing process. Grain Processing Corporation indicates that various starches are used for thickening and binding applications as well as water absorption. Individuals with allergies could have an adverse reaction to tablets containing starches. One example is patients with celiac disease, an allergy to gluten that results in intestinal inflammation. According to Steven Plogsted, clinical pharmacist, the U.S. Food and Drug Administration is not as strict about inactive ingredients, called excipients. They dictate which ingredients may be used but do not stipulate the quantity and type. Lactose, milk sugar and microcrystalline cellulose from fibrous plants are also used as filler." I cannot find any information on wikipedia any information re excipients in any drugs or information re any binders. Can you suggest a better way for me to search your site for further information. Thank you. — Preceding unsigned comment added by 68.61.198.89 (talk) 14:16, 10 March 2013 (UTC)

If you have a medical condition which requires you to be careful about excipeints used, do not trust Wikipedia regarding that information. Any information we have could be out of date, not applicable to the particular pills you're interested in, or just plain wrong. Instead, talk to your pharmacist. Since they're the ones handling the pills, they'll have the best information regarding inactive ingredients, and may be able to talk to the manufacturer if the desired information is not listed. -- 71.35.100.68 (talk) 18:23, 10 March 2013 (UTC)

Terms in QSAR / medicinal chemistry

Hello. I am struggling with a scientific paper in the field of medicinal chemistry, and would be happy to get basic explanation and/or links to websites that explain about the the terms "matrix of biological response", "score matrix", "block matrix", and about the use of the regression methods MLR,PCR,PLS in the context of QSAR. Thank you! 94.159.214.106 (talk) 19:13, 10 March 2013 (UTC)

This seems like a homework question. Therefor follow this link [9]--Aspro (talk) 22:42, 10 March 2013 (UTC)

As I wrote explicitly it is not a homework question but an attempt to understand basic terms in a paper that I am not familiar with. I did search in Google and other sources and did not find anything. I wrote that I would be happy to get a simple explanation and/or references. It is the declared aim of this page. You would probably notice all that if you would read my question properly, but apparently your "answer" is only an excuse for this stupid, not funny link. 94.159.214.106 (talk) 04:49, 11 March 2013 (UTC)

science so far outside experience / experiments that no one bothers

can you suggest areas of science that are so far outside of experience, experiments, or the subject of current theories that nobody has really bothered to do all the science and therefore it is relatively easy to be first to truth and nab a nobel. For example, in biology maybe nobody has thought about Evolution on the scale of organisms evolving to deal with the Heat Death of our Universe, simply because it seems like it's something that can wait. Still it's bound to happen, so this has to come up sooner or later. This is the type of thing that I mean, and I was prompted by the fact Einstein thought of relativistic speeds at a time when even cars were pretty slow if not outright horses. No rockets or GPS or anything that needs relativistic effects, still he thought of it. 178.48.114.143 (talk) 22:08, 10 March 2013 (UTC)

How about you give that 'heat death of the universe' thing a try, and then get back to us with your results? Seriously, the Reference Desk is here to help find sources of information to solve specific problems; we're not a chat forum. TenOfAllTrades(talk) 22:16, 10 March 2013 (UTC)

Yes. As above. The advancement of science is everybody building up in little increments on what has been discovered and been explained before. Even Professor Einstein drew on what was already known but in his case he was just too stupid to realise it was too difficult to formulate in mathematical terms -so he went on and did it anyway. In other words there is no short cut. --Aspro (talk) 22:54, 10 March 2013 (UTC)

I thought maybe there were references like a list of problems no one is working on because they don't seem relevant to anything. 178.48.114.143 (talk) 23:12, 10 March 2013 (UTC)

I don't think such a s list exists. There are not so much unsolved problems but areas of wonder that scientist have on their back burner... that they would develop if only they had the time and funding. An astronomer said to me in passing, that the most useful letter he received back as a child from writing to 'famous” astronomers was to look at part of the sky where there was nothing to see (!). The Hubble telescope has now seen billions of galaxy in that part of the sky. If it had been simply a dust cloud obscuring that part of the sky that niggling little thought would not have played on the mind. But one has to have a thorough understanding of the subject to inquire into these thing and that requires much preparation. A 'problem' is where the 'knowns' don't add up and thus there are often many other scientists working on that same 'problem'. That makes one's own chances at solving it not good. It seems (too me) that the big jumps in knowledge comes, from long study of a subject that comes to ignore the 'next problem' and the enquire thinks: Uhmm!!? There are several thing that don't add up here. Very often it come with the benefit of cross pollination from other scientific disciplines that give the key to the back-burner puzzlement. Lets go back to Einstein. He was a patent examiner in his day job. He was not a specialist. He was exposed to many different ideas, theories, and hypotheses. He made interconnections. A scientist has to feed his family (yes, some times -believe it or not- they find time to have sex and end up with children to feed and wives that want new dresses etc.). If he should get an inkling of an a promising avenue of research, he ain’t going to breath a word to anybody else. He'll want to keep it to himself in the hope that he can get funding. So, from that point of view he would not add to such a list. Blame the American's, they have turned universities into patent generators where every professors have to justify their jobs by publishing as many scientific papers as possible, regardless of the quality. If you want a Noble forget the academic rat-race.--Aspro (talk) 00:10, 11 March 2013 (UTC)

I agree the question is without much substance, but the OP might like to check out Ig Nobel Prizes for a bit of amusement. It was originally awarded for achievements "that cannot, or should not, be reproduced", although this has changed a little. IBE (talk) 02:04, 11 March 2013 (UTC)

March 11

Why does water spray out of a tap quicker if you almost completely cover it with your thumb?

The title pretty much says it. I was wondering because I always assumed it increased the pressure but thinking about it it shouldn't affect it because with a smaller volume exiting the force will be proportionally less due to constant pressure.--Gilderien Chat|List of good deeds 00:23, 11 March 2013 (UTC)

Read the article Bernoulli Principle. 24.23.196.85 (talk) 00:34, 11 March 2013 (UTC)

Strictly speaking, Bernoulli's principle is not relevant because it is only valid in situations where fluid friction is zero. In flow in a pipe, fluid friction exists throughout the flow profile across the pipe's diameter. See my response below regarding fluid friction. Dolphin (t) 02:07, 11 March 2013 (UTC)

With a rapid flow of water there is a substantial amount of fluid friction which exerts a shear force on the water in the pipe, retarding its speed and causing the pressure to fall along the pipe. (See Boundary layer.) When you reduce the flow of water by using your thumb there is less fluid friction and consequently less fall in pressure along the pipe. The pressure of the water at the end of the pipe is highest when the flow of water is almost reduced to zero. Torricelli's law explains why the water sprays out quicker and higher when the pressure of the water at the end of the pipe is highest. Dolphin (t) 01:45, 11 March 2013 (UTC)

The correct answer is simpler than the answers above. Friction does indeed affect the exit speed but that speed increases even if friction is completely negligible. The speed is given by dividing the flow by the cross section area of the pipe. If you reduce the latter, the speed will increase. Dauto (talk) 15:06, 11 March 2013 (UTC)

I'm pretty sure that's wrong. In principle the utility company supplies a constant pressure to the big pipe to your home. Assuming no friction from there to the tap is equivalent to assuming the pipe length is zero, and your thumb is blocking the utility company's supply at its source. When you do that you will just get proportionally less water. In practice I suppose the flow rate and pressure will change slightly, but it will be averaged over many homes. The water can't know to flow at twice the speed through your opening specifically if you block half of its area. -- BenRG (talk) 17:14, 11 March 2013 (UTC)

Dauto's explanation is correct, its an equal volume through a smaller cross section requiring a faster speed. If the water pressure's not too high then you can get to the point of actually blocking the flow by pressing hard enough which would be what BenRG is suggesting--in effect turning of the tap, just as with a valve. μηδείς (talk) 18:11, 11 March 2013 (UTC)

You can also experiment with this if you have an adjustable flow shower head. At one setting it will offer a slow flow through all the spigots. Tighten it a little and you will get the same flow but at a faster speed through fewer spigots. Tighten it some more and you'll reach a maximum speed with the total flow decreasing, eventually to zero. But you can always adjust it to get a full flow at a faster speed with a certain amount of restriction, but no more. μηδείς (talk) 18:19, 11 March 2013 (UTC)

I don't see why BenRGs point is incorrect, it is along the lines I was thinking. Will the "narrowing" caused by my thumb increase the pressure at the end? --Gilderien Chat|List of good deeds 22:44, 11 March 2013 (UTC)

If there's no friction, a narrowing of the pipe has to be accompanied by a decrease in pressure just because of energy conservation (the water moves faster in the narrower pipe, so its kinetic energy is higher, and that extra energy can only come from the pressure). In practice there is a substantial pressure increase when you block the end of a garden hose, for example, but that's because there's less friction in the hose (as Dolphin51 said). -- BenRG (talk) 00:21, 12 March 2013 (UTC)

It's true of course that if you narrow the aperture while keeping the flow rate constant then the speed will increase. But there's no reason for the flow rate to remain constant, and in most cases it doesn't, as you can check by doing the experiment. The water company supplies a fixed pressure, not a fixed rate of flow. -- BenRG (talk) 00:21, 12 March 2013 (UTC)

Dauto's simple explanation makes no sense. The water company supplies a pressure that varies very little, not a fixed rate of flow. The thumb over the end of a garden hose is a classic experiment any student can perform at home to demonstrate the existence of fluid friction. In an hydraulics laboratory the same demonstration is performed using pipes of different lengths, different internal diameter, and different internal surface roughnesses; a pressure gauge is at each of the upstream end of the pipe and the downstream end. Plotting pressure difference versus flow rate for these different pipes yields a lot of useful information but it is all an illustration of the phenomenon of fluid friction. Dolphin (t) 04:59, 12 March 2013 (UTC)

Catalan Talgo

Did the passengers have to disembark for the gauge change at the Spanish border, or was the operation performed with them still aboard the train? 24.23.196.85 (talk) 00:41, 11 March 2013 (UTC)

Cosmic ray

I know cosmic rays exist in interplanetary space and interstellar space. Do cosmic rays exist in the intergalactic space? --PlanetEditor (talk) 06:36, 11 March 2013 (UTC)

I don't see why not. Plasmic Physics (talk) 06:41, 11 March 2013 (UTC)

• Yes, since active galactic nuclei are a source of cosmic rays. -- Scray (talk) 07:01, 11 March 2013 (UTC)

That is still speculation. Existing evidence suggests supernova remnants are the origin of cosmic rays (90% protons and 10% atomic nuclei and electrons). [10]

If supernova remnants are the origin of cosmic rays, it will be present in the interstellar and interplanetary medium within a galaxy. But will it be able to escape the galaxy? --PlanetEditor (talk) 07:37, 11 March 2013 (UTC)

Why not? Plasmic Physics (talk) 07:42, 11 March 2013 (UTC)

If we want to take a strict observationalist approach, we can trivially state that we have no idea, because we have never sent a probe to experimentally measure the presence or absence of cosmic rays in extragalactic space. Or, we can take the more useful, albeit less provable, stance: we have a pretty good idea that many high-energy things originated outside our galaxy. One of my favorite muon detectors, AMANDA, was intentionally "pointed down" so that it would detect incident radiation that was not along the Ecliptic or the galactic equator. That implies, in my opinion, that the neutrino sources would be extrasolar and probably extragalactic. (Though, this 1998 paper suggests that South Pole Station was one of many worldwide detectors and could be used for holographic triangulation of neutrinos from any direction; and AMANDA II had improved angular resolution for mapping purposes; but, to steal a quote, the full scientific implications are far too broad to discuss in this limited forum. Nimur (talk) 08:14, 11 March 2013 (UTC)

Thanks. --PlanetEditor (talk) 08:33, 11 March 2013 (UTC)

Nimur, perhaps a followup question. It occurs to me that if the rays are coming from within our own galaxy, there should be some kind of relationship between the trajectory with which the ray reaches the Earth, and the density of rays coming along that trajectory, that makes sense given the number of potential intragalactic sources along any given trajectory. Is any such thing elucidated by the available evidence? Someguy1221 (talk) 08:46, 11 March 2013 (UTC)

The second paper I linked talks about a knee-point in the spectrum at 10¹⁵ eV. Below this energy, the authors believe neutrinos are generated by point-sources - supernovae, "micro quasars"... - so the incident raditation is expected to have a directionality. Above this energy, there are far fewer events, or at least far fewer detections, so statistics are not as clear; but it seems possible that these very-high energy neutrinos are not generated by point-sources. If so, there are a few questions about their origin that are unanswered: we expect the cosmic microwave background radiation to be much lower temperature based on everything we know about the evolution of the early universe. My response, as an enthusiast for muon detectors, is that we clearly need to fund and build more such detectors so we can collect better data; I don't think there are enough observations to be really really sure of very much about these high energy incidents. Nimur (talk) 15:40, 11 March 2013 (UTC)

There is now strong evidence that the ultra high energy cosmic rays come from Centaurus A, see e.g. here. Count Iblis (talk) 12:47, 11 March 2013 (UTC)

Chemical egg

What are those things that look like glass boiled eggs, filled with various reagents, resting in an egg cup? Are they some sort of ampoule? Plasmic Physics (talk) 07:16, 11 March 2013 (UTC)

Possibly. Where have you seen them? Can you post an image of one of "those things" to give us a better idea of what you have in mind?--Shantavira|^{feed me} 16:50, 11 March 2013 (UTC)

[11] Plasmic Physics (talk) 21:49, 11 March 2013 (UTC)

[12] Plasmic Physics (talk) 21:53, 11 March 2013 (UTC)

They look to me like round-bottom flasks (okay, actually a pear-shaped flask - [13], but at least for organic synthesis use those fall into the general "round-bottom flask" category, at least when used in semi-microscale chemistry) that have been stoppered (with a specialized stopper) and inverted. Laboratory flask mentions "Powder flasks, for drying of powdered substances, pear shaped, with socket" which may be more apropos, but I've never heard of those before, the link redirects to Musket, and searching the term either returns nothing related (in Sigma-Aldrich's search engine) or black-powder related results (in Google). -- 205.175.124.30 (talk) 18:18, 12 March 2013 (UTC)

What are these lights?

What are those flashes of light seen in this video at 1:24, at 1:28 to 1:29 and again at 1:52. --PlanetEditor (talk) 08:27, 11 March 2013 (UTC)

Some of those flashes are lightning, and others are errors of exposure in the photograph, either due to operator error or due to digital post-processing. Previous montage-videos and time-lapses from the ISS have used long exposures and multiple captures to produce the high dynamic range you see in the final video imagery. Here are more videos, including videos with less post-processing than your link: ISS Crew Earth Observation videos from NASA Johnson Space Center. The video linked in the original question was produced by a film student, not by NASA; and was composited from NASA's image database using what are termed "browse quality" photos. FAQ #2: "Because of the number of images that are added to our database each day, we cannot do publication-quality color corrections on each image. For some scientific purposes those corrections even destroy information (even though they make the picture look prettier)." Nimur (talk) 08:37, 11 March 2013 (UTC)

Freezing point

I just read our article on Melting point (to which Freezing point redirects). I understood some of it, but not too much, which is unsurprising given how little Science I got away with studying at school. From what I could gather, the article only mentions pressure as being a factor in setting the freezing point of a substance, which seems like a big gap, as different substances at the same pressure (say water and mercury) will have different freezing points.

Some questions - please be gentle with the layest of laymen:

1. Why do different substances have different freezing points? Is it their physical properties, chemical properties, both, something else?
2. I know that salt lowers the freezing point of water. What substances that might lie around a typical house would raise it? And if so, is there anything that is edible?
3. I'd guess that British tapwater would have a different freezing point than distilled water. What's the difference and what additives are making the biggest contribution to that difference?

Thanks.

Yours curiously (I always liked the curiosity bit of Science, just not the intellectual rigour/need to remember things bits) --Dweller (talk) 11:01, 11 March 2013 (UTC)

1. In broad terms, there are two competing set of forces that hold subnstances together. Intermolecular forces are the electrostatic forces between the positive and negative charges. Thermal energy is the energy of motion that tends to want to encourage molecules to fly apart. If the thermal energy exceeds the energy of the intermolecular forces, the particles that make up the substance fly apart, and the substance will be a gas. If it is the other way (intermolecular exceeds thermal) then the substance will be a condensed phase (either a solid or liquid). The actual process of melting itself (the transition from solid to liquid) is mostly based on a specific types of thermal energy: those of molecular vibration and rotation. The third mode of thermal energy is "translation", which marks the distinction between gases and the condensed phases of solids & liquids. All of the various modes of thermal energy together are known as a molecule's degrees of freedom, and those degrees of freedom are important towards understanding properties like this. Melting itself is a far more complex and difficult to model behavior, but that's roughly it.
2. Roughly speaking, any substance you dissolve in water will lower its melting point. That's because freezing-point depression is one of the colligative properties, which primarily depend on the number of dissolved particles, but not (to a first approximation) their identity. That is, the fact that anything is mixed in the water will cause its freezing point to lower, but the amount of lowering isn't dependent on what that substance is, only on how much there is. Now, there are some liquids which if you add enough of them to water, may raise the freezing temperature, but what you have there is a eutectic system, and at that point what you would have isn't that substance dissolved in the water, but rather the water dissolved in the other substance, and then we'd be basing our colligative relationship on that rather than on a water-based solution.
3. Tap water will have a very marginally lower freezing point than absolutely pure distilled water. Even the worst tap water is still very mostly water; the stuff that isn't water in tap water can be measured in the parts per million range, which will have a very small effect on the freezing point, probably not noticeable on the average household thermometer. --Jayron32 12:42, 11 March 2013 (UTC)

(ec) Q1. All substances that we can see are of two types: elements and compounds. A compound is a substance made up of multiple elements. Water is a compound because it is made up of oxygen and hydrogen. In nature, most of the substances that you see or feel everyday, such as water, oxygen etc. are compounds. Only the noble gases and noble metals are found in elementary form or monoatomic form (i.e. they consists of one atom). Here we will be dealing primarily with compounds.

Any substance, whether it is an element or a compound, is composed of particles. In case of elements, this particle is called atom. In case of compounds, this particle is called molecule. A molecule is made up of two or more atoms. (The atoms are made up of multiple subatomic particles, but that is not relevant to this discussion.) This particles are attached to each other by a force or attraction. This is called chemical bond. Without chemical bonding, the particles will be separated. If the particles are separated, then the substance will cease to exist.

Now, when you heat a substance (say water), then what happens? When the temperature reaches 100 degree Celsius, the molecules within water possess enough energy and they overcome the intermolecular attractions that bind the molecules. When they overcome the intermolecular attractions, the distances between the molecules become greater. This turn the liquid into gas. In solid, the distances between the molecules are smallest, in gas the distances between molecules are greatest.

Now, what we can see? The freezing point or melting point of a substance (whether an element or a compound) is dependent on the strength of the bonding between the particles. So if the bondings are stronger, you will need more energy (heat) to break them, so the boiling point rises. If the bondings are weaker, you will need less energy (heat) to break them, so the boiling point falls.

I explained the mechanism in terms of boiling point. In case of freezing point, a liquid turn into solid. So if the bondings are strong, melting point will increase and freezing point will decrease. If the bondings are weak, melting point will decrease and freezing point will increase. Helium has weakest bonding. This is why its boiling point is lowest, near absolute zero.

This is the explanation why different substances have different freezing points, melting points and boiling points. --PlanetEditor (talk) 12:49, 11 March 2013 (UTC)

Thanks, chaps. Enlightening. I particularly liked Jayron's answer to Q2 and PlanetEditor's excellent "keep it simple without patronising" style of writing. One last thing - am I right that the information was missing from the article, or was it there, but just impenetrable to me? --Dweller (talk) 12:54, 11 March 2013 (UTC)

Actually, it's there in the section labelled "Carnelley's Rule", which I've never heard the name before, but knew the principle well. The deal with that "Rule" is that molecules which are more symmetrical don't have as many "degrees of freedom" (see above), so have less modes by which to vibrate. Consider the geometry of something like a sphere, versus a cylinder, versus say a human body. With a sphere, you have zero vibrational modes; the sphere cannot vibrate because there are no parts that can vibrate relative to each other. In a cylinder, you have one vibrational mode: the cylinder can vibrate in-and-out along the axis between the molecules at the end. In the human body, there are LOTS of vibrational modes: every limb can move in and out, around, bend at angles, etc. The same is true of molecules. Furthermore, the more symmetrical a molecule is, the less ways it can be arranged, so the more efficiently you can "pack them" together. Spheres pack very efficiently, cylinders less so (because cylinders arranged at angles won't match up positive and negative bits well) while something shaped like a person would be a complete nightmare to get to randomly arrange properly. Because of both of these factors, more symmetrical molecules (by definition, those with less vibrational degrees of freedom: those are coincident properties) are those that will melt at higher temperatures, all other factors being equal (such as molecular weight, polarity, molecular volume, etc.) --Jayron32 17:33, 11 March 2013 (UTC)

Missing quantity

Consider an underground water source whose free surface is 60 meters below ground level. The water is to be raised 5 meters above the ground by a pump. The diameter of the pipe is 10 cm at the inlet and 15 cm at the exit. Neglecting any heat interaction with the surrounding and frictional heating effects, and assuming a steady flow of water at a rate of 15 liters per second, and that the water remains at atmospheric pressure and temperature. Determine the power input at the pump.

I have this equation

${\frac {dE}{dt}}={\frac {dQ}{dt}}+{\frac {dW}{dt}}+{\stackrel {\circ }{m}}(u_{2}+P_{2}v_{2}-u_{1}-P_{1}v_{1}+{\frac {1}{2}}(V_{2}^{2}-V_{1}^{2})+g(z_{2}-z_{1}))$

Where we need to find ${\frac {dW}{dt}}$, of course. I believe all of those quantities are given or are easily derived, except I don't know how to work out $u_{2}-u_{1}$. How do you do that?

150.203.115.98 (talk) 14:26, 11 March 2013 (UTC)

get the flow (in cubic meters per second) and divide it by the cross section area of the pipe (in squared meters) to get the speed (in meters per second). Dauto (talk) 14:53, 11 March 2013 (UTC)

That's $V_{2}$ and $V_{2}$. I suppose I should have said what these symbols meant. $u_{2}$ and $u_{1}$ are specific internal energy. 150.203.115.98 (talk) 23:45, 11 March 2013 (UTC)

In that case their difference vanishes since all heat is considered negligible. Dauto (talk) 14:33, 12 March 2013 (UTC)

productivity of 120 hour weeks

my personal impression is that if pressed a single person can perform the work of 5 (the skeleton crew of a company), including marketing business sales design engineering biz dev (contacts and so forth) and so forth for a very short period of time.

is this a fallacious impression?

or could three things work together here:

1) Granted productivity must drop off precipitiously after 40 hour. But perhaps for some kinds of "work" even a productivity of 0.01 person-hours per hour is enough, for example when waiting for an email response that must simply be OK'd once received. Either someone is sitting there waiting or they're not. Thus perhaps some of the work of the 5 people can be interleaved as interrupts and does not require a full amount of time added to the workload.

2) Perhaps there is some kind of "economy of scale" that comes from many, many hours. That is to say, perhaps 20 hours of trying to close a deal are 80 times more effective (in an all-or-nothing situation) as 3 hours of doing that (rather than only seven times as we might expect based only on the time). If so then the precipitious drop in productivity - a 97% drop in productivity, say - between hours 112-120 in the week, could still, leave the remaining 3% of productivity highly productive due to this reason.

3) Perhaps there is some kind of "economy of scale" that can come from serializing work that would otherwise (in a larger team) be parallel, or bringing all aspects (e.g. design and programming) into the same brain: that is, there is now no interprocess communication or delay waiting for someone else to acknowledge something, nor is there repetition of:

- Several people waiting one after the other

- Blocking conditions that create a bottleneck

- Repetition of the same information being read, stored, etc.

- Copying information or results from one person to another.

- Work that continues even though instant serial communication would already be pursuing a different path. (For example, engineering working on something that marketing has decided should be among the last things done, if this decision has just been made: the 5 people take some delay communication it)

In other words, the single-person doing 120 hours might be something like a single-core processor at 3 GHz versus the 5-member team being a 4-core processor at 666 MHz. The former can potentially do a LOT more, for some types of workflows. This might further compensate for the precipitious drop in productivity.

So, the question remains. If normally the 5-member team is putting in 200 hours, can a single person pulling in 120 hours do the work of all of them for a few weeks before burning out? Even if we assume an incredible loss of productivity at the margin of that many hours? --91.120.48.242 (talk) 15:49, 11 March 2013 (UTC)

It seems plausible to me that it could be possible (perhaps not with the exact figures, but the general idea is correct). This is actually related to the question of why all animals need to sleep. Of course, one can consider this from biochemistry, but it can be argued that this was always the inevitable outcome of evolution. If you have two systems that have equal performance, and they both have uniform performance as a function of time, then you can take one system, cut down on its internal maintainance to let it temporarily outperform the other system and then have a period of lower activity so that it can do more internal maintainance. In the context of biology, this typically leads to a better performance (e.g. if you can run faster, you are much more likely to catch more prey). Count Iblis (talk) 16:13, 11 March 2013 (UTC)

There are several fundamental problems that I can see with this:

• You're assuming that this one person is some kind of super-human who possesses the skills and knowledge needed to do all 5 jobs. Engineering requires a set of skills and abilities that someone who is an expert salesperson does not have...and vice versa. Those 5 people may have overlapping skill sets - but finding one person who knows enough to do all 5 jobs seems really unlikely.
• When you suggest that someone might be able to do a second task while waiting for an email response or something - thereby getting more work done by 'interleaving' task, you're assuming that the original employee wasn't simultaneously working 20 streams of email, responding to one while waiting on the others. Your 5 separate employees might already be 100% busy (or at least a lot more than 20% busy) just doing their individual jobs.
• Humans are not very good at multitasking. Our article Human multitasking cites multiple studies showing that people are actually very bad at multitasking - no matter what they may claim. It's interesting to note that they discuss the 'cost' of 'context switching' - the time it takes your brain to switch between tasks - which is strongly analogous to computer operating systems that multitask. The "context switch time" is something that's critical to the efficient operation of multitasking computers - so computers have hardware and software that's specifically designed to make that more efficient. Humans (especially males) seem not to have much in the way of specialization to make that work well.

So I very much doubt that one person could adequately do the work of five - even for very short periods of time...not effectively. But (of course) it depends on your definitions of "adequate" and "effective" - and on how busy those five people were in the first place. SteveBaker (talk) 03:21, 12 March 2013 (UTC)

However, our market economy has no problem valuing the work of one person at a rate five times higher than another person. This is not strictly equivalent to doing five times as much work. I find statistics such as revenue per employee interesting: for example, corporations who specialize in petroleum pipelines average several million dollars per employee, while grocery stores average just a few thousand dollars of revenue per employee (as shown in this 2007 survey. From a purely pragmatic point of view, the work and skill level required to operate a pipe valve might actually be easier than operating a cash-refister; and yet one of these jobs produces, on average, thousands of times more value. Perhaps this is a stunning indictment of the inequity inherent in market valuation, or perhaps it is proof that supply-and-demand "works correctly" - I think the conclusion you draw is dependent on your views of economic. Nimur (talk) 15:09, 12 March 2013 (UTC)

In support of the OP's hypothesis, I offer a couple of observations from the belly of the corporate beast:

1) most employees' 40 hour week contains about 20 hours of productive work, max. Maybe more during emergency situations.

2) don't forget, the answer to the question "If 1 programmer can write a program in 1 day, how many days would it take 5 programmers?" is "5 days". Gzuckier (talk) 17:32, 12 March 2013 (UTC)

I can sympathize with the sentiment that one person is often more productive than a team, provided that one person has all of the skills needed for the job. One cost of teamwork is all the time that must be taken for each team member to communicate with all the others and reach agreements, while you also have the potential for slackers. (If one person is responsible for the job, he will be blamed if he doesn't meet the schedule, while a slacker on a team might escape blame if the other team members cover for him.)

That said, 120 hours per week is rather extreme. Figuring on 7 days of work, that's still over 17 hours a day, leaving less than 7 hours for sleep, not counting time to get to and from work, eat, etc., which will leave you seriously fatigued and unproductive. It turns out that being able to sleep in the office, have your meals and clothes brought to you, shower there, etc., can make a huge difference (Edison slept in a cot in the office). I find my practical limit is around 80-90 hours, and I try to do heavy brain work in the mornings, when I'm still fresh, and leave rote jobs for later, when I'm "on autopilot". I'm a computer programmer, so would do new coding in the mornings, and leave testing, which is mostly repetitive, for last.

Note that another hidden benefit of working long hours may be being alone in the office. I find the constant interruptions of others seriously impedes my ability to concentrate on a problem. StuRat (talk) 17:49, 12 March 2013 (UTC)

Reference material for physics/chemistry of vegetables

I'm not sure if something like this exists, but I'm looking for some information on the physics, chemistry and biology of a range of vegetables. For example, what makes garlic sticky and odorous, why are avocados creamy, what is the underlying cellular structure of a pepper. Questions like that. Images of cells, molecules, etc, would be fantastic too. So... is there anything out there like this? Goodbye Galaxy (talk) 18:30, 11 March 2013 (UTC)

This is not quite what you're asking for, but it is close, and very good --"On Food and Cooking" by Harold McGee (amazon link [14]) has a lot of information on the physics and biochemistry of veggies. It is mostly focused on traits of culinary importance, and also has material on meats, eggs, etc. I highly recommend it to anyone with an interest in the combination of cooking and science. SemanticMantis (talk) 19:25, 11 March 2013 (UTC)

Alton Brown used to produce an excellent and humorous show, Good Eats, with strong emphasis on the science - physics and chemistry and everything else - of food and cooking. Nimur (talk) 21:14, 11 March 2013 (UTC)

hydraulic

Moved from the Entertainment desk.
Why must a liquid and not a gas be used as the fluid in a hydraulic machine? — Preceding unsigned comment added by 70.39.187.167 (talk) 12:42, 11 March 2013 (UTC)

In general because most liquids are virtually noncompressible. If you use a gas you'll lose a lot of energy to compressing and decompressing the gas. APL (talk) 12:47, 11 March 2013 (UTC)

Although steam engines and steam turbines still have their uses. OsmanRF34 (talk) 22:08, 11 March 2013 (UTC)

You have to use liquids in a hydraulic machine because if you used gases, it would be a pneumatic machine. Matt Deres (talk) 15:05, 11 March 2013 (UTC)

Pneumatic and hydraulic / gas and liquid. So, what would you call a machine that uses solids? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:18, 11 March 2013 (UTC)

... A solid state device. For obvious reasons, solid state devices operate on totally different physical principles and have totally different applications, most commonly as semiconductor electronics. Nimur (talk) 21:04, 11 March 2013 (UTC)

There are certain rare situations where a "hydraulic" system with no liquids is used, with large numbers of small ball bearings used as a working fluid. The main advantages are the ability to withstand both very hot and very cold temperatures (enough to boil and freeze liquid systems), a total immunity from any sort of leaking causing contamination, and no cavitation erosion. Disadvantages include large size, having to custom make everything, not being suitable for pilot valve / piloted valve operation, and limited working pressure (too high and you shot peen the interior surfaces and dent or shatter the balls.) --Guy Macon (talk) 21:54, 11 March 2013 (UTC)

I thought such things existed, but couldn't find them with cursory searching (I did find systems for hydraulic transport of powders...) What are they called, or do you have any refs? SemanticMantis (talk) 22:36, 11 March 2013 (UTC)

I took a look too and didn't find anything. The one I saw was at a customer facility where I was doing some unrelated consulting, and I don't have permission to disclose any specific information from that job. I don't know what they called it. :( --Guy Macon (talk) 23:58, 11 March 2013 (UTC)

Wouldn't a cable-operated tube-type system be considered "solid" -- as in a bicycle brake-cable? ~:74.60.29.141 (talk) 23:08, 11 March 2013 (UTC)

BFKP

What is the meaning of BFKP, referring to a boring and milling machine such as this? bamse (talk) 22:20, 11 March 2013 (UTC)

Well, it might not meaning anything in English, but given that the website is in Polish, it could very well be an acronym for a Polish term. You may do well to find a Polish speaker and ask them, or perhaps ask on the Polish Wikipedia reference desk, which is here, presuming of course that you speak Polish. --Jayron32 22:26, 11 March 2013 (UTC)

I think it's just part of the model name, e.g. one particular model made by that manufacturer is the BFKP-110. Apparently these are CNC machines. Looie496 (talk) 22:38, 11 March 2013 (UTC)

(edit conflict) That's a CNC Horizontal Boring & Milling Machine, Model# BFKP-110. Nice tool if you can get the one with the Siemens controller. --Guy Macon (talk) 22:40, 11 March 2013 (UTC)

(ec) This is on the topic of "My BFKP". It’s about gopeds and is written in English, but it may as well be in Urdu for all the sense I can get out of it.

This suggests it’s something that happens to girls, but exactly what is not specified. This tells me it’s a sort of joint acronym for Brandon Flowers (BF) and Katie Perry (KP). Maybe that’s the girl thing. Whatever, it hasn’t been given official status at Urban Dictionary yet.

Elsewhere I see it can mean:

• Bionic Fuel Knowledge Partners
• Binary Fractional Knapsack Problem
• Barack, Ferrazzano, Kirschbaum & Perlman (who seem to have changed their name [15]). -- Jack of Oz ^[Talk] 22:51, 11 March 2013 (UTC)

Interesting, but it's still a BFKP-110 CNC Horizontal Boring and Milling Machine. --Guy Macon (talk) 00:11, 12 March 2013 (UTC)

Yes, you already told us that. But are you saying they chose those four letters at random, and they stand for nothing specific? -- Jack of Oz ^[Talk] 01:12, 12 March 2013 (UTC)

I'm fluent in Russian but not in Polish, but let me take a guess: "F" might stand for "milling" ("frezerovaniye/frezerovochny" in Russian, probably a similar word in Polish), and "KP" probably has to do with computer control ("komputerny pravleniye" or something like that). FWiW 24.23.196.85 (talk) 00:23, 12 March 2013 (UTC)

Is the panda the only herbivorous carnivoran?

I don't have much to add beyond the title. The article Carnivora mentions the panda as among "a few primarily herbivorous species", but that's not cited. Are there in fact any others? If so, what are they? ± Lenoxus (" *** ") 23:47, 11 March 2013 (UTC)

The bearcat is another Carnivora species that's mostly vegetarian. 24.23.196.85 (talk) 00:13, 12 March 2013 (UTC)

Sloth bears, perhaps. Even pandas can eat meat. Claims that something only eats meat or only eats plant matter tend to be exaggerated. Wnt (talk) 02:02, 12 March 2013 (UTC)

Nope -- the sloth bear mostly eats insects (especially termites). 24.23.196.85 (talk) 04:27, 12 March 2013 (UTC)

According to Red panda (a species not closely related to great pandas and closer related to racoons and mustelids) it is primarily herbivorous, though like great pandas do eat some animal products like fish and eggs. --Jayron32 05:57, 12 March 2013 (UTC)

Gorillas are primarily herbivores, but sometimes they eat ants and termites. --PlanetEditor (talk) 08:13, 12 March 2013 (UTC)

• Here's the answer, if you restrict to Carnivoran species that have been documented to consume at least 95% vegetable matter, from this study, titled "Shape at the cross-roads: homoplasy and history in the evolution

of the carnivoran skull towards herbivory", available here [16].

" As a

result, five species were considered as specialized herbivores in this study: the giant panda ( A. melanoleuca , Ursidae), the red or lesser panda (A. fulgens , Ailuridae), the bushy-tailed olingo ( Bassaricyon gabbi , Procyonidae), the kinkajou ( Potos flavus , Procyonidae) and the specta- cled bear ( Tremarctos ornatus

, Ursida "

-- So, there are five primarily herbivorous carnivorans, and we had the two pandas picked out. (Also note that the Gorilla mentioned above is largely herbivorous, but not a Carnivoran.) SemanticMantis (talk) 15:07, 12 March 2013 (UTC)

SemanticMantis, gorillas sometimes eat ants and termites, this make them occasional insectivores. And insectivory is a type of carnivory. --PlanetEditor (talk) 15:26, 12 March 2013 (UTC)

Thanks Planet editor. But in this case, Carnivoran does not mean "is a carnivore" (as we've illustrated with the pandas et al.) What it means is "a species in the Order_(biology) named Carnivora". So not all carnivores are Carnivorans, and not all Carnivorans are carnivores. This is an unfortunate turn of language, but there it is. Using standard definitions, Gorillas are neither Carnivoran nor carnivores. SemanticMantis (talk) 15:57, 12 March 2013 (UTC)

Hmm, thanks for the clarification. --PlanetEditor (talk) 16:05, 12 March 2013 (UTC)

March 12

Why light does not hurt us

Light travels at, well, the speed of light. If it were possible to accellerate a tennis ball to the speed of light and the tennis ball were to hit me in the chest, the results would be disasterous. So, why do light particles not hurt us when then hit us? Even though they are very small, there is a lot of them . . . 99.250.103.117 (talk) 01:49, 12 March 2013 (UTC)

Their mass is very small. How small? Well, consider what a small fraction of the mass of a lump of plutonium can do to a city. E=mc² Wnt (talk) 02:05, 12 March 2013 (UTC)

Light at ultraviolet frequencies and above does hurt us. It's ionizing radiation. Photons at lower frequencies don't individually have enough energy to break chemical bonds, and the aggregate energy doesn't matter (see photoelectric effect) unless it's enough to heat body tissue to the point of damage (which is why you shouldn't put your cat in the microwave). -- BenRG (talk) 02:15, 12 March 2013 (UTC)

Light is made of photons and (barring semantic pedants), unlike tennis balls, photons are massless particles. They do not have mass, not even very small mass, they have momentum. Vespine (talk) 02:23, 12 March 2013 (UTC)

Yes, but photons have energy, which is the exact same thing as mass, at least for the point of this discussion. The fact that photons are in motion and have relativistic mass means that photons can, say, move electrons (that's the idea behind the Bohr model and all more modern models of how light interacts with electrons) and photons can even move objects, see Radiation pressure and solar sail. Light, all by itself, can move an object. Photons do not have rest mass, but they have energy, and there's no functional difference between mass and energy for the point of calculating the effect of a photon striking an object. One low energy photon is not going to move a massive object, but a whole shitload of high energy photons absolutely can move objects. --Jayron32 02:51, 12 March 2013 (UTC)

Most skin cancer is caused by (sun)light. HiLo48 (talk) 02:25, 12 March 2013 (UTC)

Nope, it's caused by UV rays, not visible light. 24.23.196.85 (talk) 04:29, 12 March 2013 (UTC)

I would argue that most of us mean "sunlight" to include all wavelengths bombarding our bodies that are present on a sunny day. Beach drifter (talk) 04:38, 12 March 2013 (UTC)

• Even infrared radiation can bake us to death, and radio waves can induce incredible, killing heat in certain metal conductors. FYI. μηδείς (talk) 02:55, 12 March 2013 (UTC)

A tennis ball, moving at literally the speed of light would have infinite mass and would rapidly become a black hole that would (at the very least) swallow the entire universe. Photons have a "rest mass" (if they were stationary) of zero. They only have mass at all because they are travelling at the speed of light. A photon with enough energy could be extremely damaging - but a low energy photon is utterly unnoticable. Stick your hand in front of a 200 watt visible light laser beam and it'll burn your skin off, stare at the sun for any significant amount of time and you'll blind yourself - so even visible light can most certainly hurt you if it has enough energy. SteveBaker (talk) 03:05, 12 March 2013 (UTC)

Thanks all. Clearly, I was referring to the kind of damage a tennis ball could effect at relativistic speeds (IF that were possible). I am well aware that light can harm us as outlined above (i.e. sunburns, etc.). 99.250.103.117 (talk) 03:48, 12 March 2013 (UTC)

The direct answer to your question is simple: An arbitrarily fast-moving tennis ball has arbitrarily high energy. Close to the speed of light, getting hit by it would be like getting hit by a nuclear detonation (if you are interested in precisely what would happen, the best source i can recommend is actually this xkcd). But a photon does not necessarily have such high energy. Since a photon has zero rest-mass, it does not have infinite energy at the speed of light. So that's the answer - it's not a matter of speed, it's a matter of energy. And a relativistic tennis ball has a hell of a lot more energy than a square meter of sunlight. Someguy1221 (talk) 03:59, 12 March 2013 (UTC)

Energy of a photon is Plancks constant times the frequency: E = ħ ⋅ f. Einstein won his Nobel prize in 1921 for physics related to the frequency and energy of photons in a 1905 paper related to the minimum frequency to emit an electron,see Photoelectric effect (like dunking a basketball, if you can't reach the rim, no amount of jumping will help). More precisely, accelerating a tennis ball to the speed of light would require all the mass of the universe. Using relativity, arbitrary speeds and the corresponding energy/mass can be calculated as mass and energy are equivalent. --DHeyward (talk) 08:15, 12 March 2013 (UTC)

Why is milk homogenised?

When I was young, milk came in bottles with a layer of cream on top, something most consumers seemed to enjoy, and others my age reminisce about. Then it started to arrive in cartons, and it had been homogenised. The cream was no longer floating on the top. I know there's many choices now, but the most common product is still sold that way, homegenised. Why? NOTE: I'm talking about Australia, and customs elsewhere will obviously vary, but the basic question is, why is most milk homogenised these days (when I'd prefer it wasn't)? HiLo48 (talk) 02:44, 12 March 2013 (UTC)

Why would you prefer it that way? If you want skim milk, you can buy it. If you want cream, you can buy it. Why buy something that makes unnecessary work for you regardless of what you do with it? Looie496 (talk) 02:53, 12 March 2013 (UTC)

Per Looie496, milk is homogenized because people didn't want to have to shake the heck out of the milk every time they wanted to drink it. I'm not sure why that is hard to understand; that you don't mind shaking it is irrelevent; others found it easier not to have to shake it every time, where it became economically more viable to homogenize milk before it was sold to the public than to make the public have to do it every time they wanted to drink it. --Jayron32 02:55, 12 March 2013 (UTC)

Looie - where is the evidence that "people didn't want to have to shake the heck out of the milk every time they wanted to drink it", and that this was really the reason for the change? I can remember lots of people asking, why the change, at the time. I can't recall anyone saying thank you. HiLo48 (talk) 03:06, 12 March 2013 (UTC)

Milk is also homogenized so that consumers can know what they are buying. Without homogenization, milk can vary greatly in fat content, taste and consistency. I, probably like you, don't have a problem with natural variation, but it's the way market forces and regulation have progressed. Vespine (talk) 03:01, 12 March 2013 (UTC)

Surely fat content, taste and consistency can be managed just as easily without homogenisation? HiLo48 (talk) 03:06, 12 March 2013 (UTC)

No because the cream at the top is most of the fat and taste. Rmhermen (talk) 03:35, 12 March 2013 (UTC)

In fact, I have seen one person who was so used to homogenized milk look at a cup of unhomogenized milk, and believe that it had gone bad. Someguy1221 (talk) 04:04, 12 March 2013 (UTC)

Is there a science question in here somewhere? This seems like a discussion of preferences and business practices. -- Scray (talk) 03:45, 12 March 2013 (UTC)

Well, "when I was a kid, the world was better. Damn innovation!" That isn't a science question? --Jayron32 04:11, 12 March 2013 (UTC)

• But, if we want to really answer with a reliable source, the basic question, the "purpose of homogenization is to make more permanent and uniform suspension of the fat by reducing the fat globules to a very small diameter" and "Homogenization is used for making milk more stable against creaming and for giving the product a richer mouthfeel due to a slight increase in viscosity" per the Ohio State University. I don't know that we need any better answer than that. That should satisfactorily answer the question "Why is milk homogenised?" As to the implied commentary which is couched as the subtext of the question, I'm not sure that needs any more response than has already been given. --Jayron32 04:15, 12 March 2013 (UTC)

Jayron - I take your point about this perhaps not being a Science Desk question. I did ponder it before I posted. Obviously the answer is going to be part scientific and part something else. (Marketing?) I'm happy to post it elsewhere (Miscellaneous?) as well, but expected that if I posted there first someone would be bound to tell me to take it to the Science Desk. And if I posted in two places.... Well, we all know what THAT leads to. HiLo48 (talk) 04:25, 12 March 2013 (UTC)

If you want the marketing answer, then Vespine gives the best answer above, which is "consistency" of product. Food marketing and distribution over the past umpteen years has been focused on providing a "consistent product". It is the ubiquitous mantra of the factory-food industry, the entire system is geared to producing a product which is universal for the customer. If I buy a hamburger at, say, a McDonalds anywhere in the world, McDonalds wants it to taste exactly the same. That's how mass produced food tries to work. Milk is certainly no different than that. Homogenization of milk means that every gallon of milk from the same dairy should be exactly the same taste every time. Homogenization helps do that. It is also undoubtedly more convenient, as I noted above, it's what the market seems to want: convenient and consistent. If you doubt that the food industry has those as its primary goals, you haven't been paying attention. That you don't value those things as an individual is irrelevent: the market does, and the evidence that the market does is that food companies aren't in the business of making less money. Milk companies wouldn't homogenize their milk if it meant they sold less milk doing so. I'm sorry if this is unsatisfactory, because you don't hold the same values that the preponderance of the milk buying public does. If the milk-buying public only bought milk that wasn't homogenized, that's what would be produced. That's the answer as to why some types of products are sold instead of others. The answer is that companies try to maximize profit, and will produce the products that do that, while at the same time also creating that market for the product in the first place. To some extent, dairy companies may have convinced people that not shaking their milk was something they wanted out of their milk product, and the milk-buying public agreed with them (or was convinced to agree with them). --Jayron32 04:39, 12 March 2013 (UTC)

Here in the UK, I bought non-homogenised milk for as long as it was available because I preferred the taste, and I knew that there was a difference in digestion of finer globules of fat. That option is no longer available, and milk is now also "standardised" (that's how they achieve "consistency", by mixing lots of batches to bring the total fat content to a standard level). I'm not sure whether I've gradually adapted, but modern homogenised milk doesn't seem to taste so much of "machinery" as it used to. Homogenisation and standardisation are different processes, but they seem to go together. I've never seen one without the other. Our article Homogenization (chemistry) is was in error. Dbfirs 09:39, 12 March 2013 (UTC)

My milkman still delivers pasteurised milk in bottles, which has a layer of cream floating on top. So it's still done. (UK) --TammyMoet (talk) 10:23, 12 March 2013 (UTC)

I can remember when my milkman delivered unpasteurised milk (green-top), but, sadly, we have no local milkman now. I'm glad to hear that "silver-top" (with cream) is still available. I expect I could still obtain it if I travelled to the appropriate farm or dairy. Can you still get "gold-top" (with extra cream from Jersey and Guernsey cows)? Dbfirs 16:58, 12 March 2013 (UTC)

Here in NZ, you don't need a local milkman for unhomoginised milk, it's available at many supermarkets and even some dairys. I believe it's the same in Australia where the OP is from although they use gold tops instead but I believe their milk fat concentration is closed to here in NZ (see also Milk bottle top). Of course the price is a lot higher but I don't believe this is the only reason why you'll find far fewer people purchasing these then the blue and light blue tops. Nil Einne (talk) 17:59, 12 March 2013 (UTC)

Also, never underestimate the ability of marketing to sell you something that helps the business as "for your convenience" (as in the frequently seen by me around here at least, "for your convenience we are now open 9-5 instead of 8-6"). In this case, imagine how much more convenient it must be for the dairies if big tanks of the stuff didn't have to be stirred up vigorously to keep it from separating before it was removed? Might be not too much of a problem or even might be fun to have to shake a quart before pouring out a glass, but 2,000 quarts, not so much. Gzuckier (talk) 17:42, 12 March 2013 (UTC)

Re: Relativistic Baseball

Up above, the thread on tennis balls at light speed pointed me to this page. Particle accelerators accelerate particles until they're close to the speed of light; why don't we see this effect? Is it simply that the particles they accelerate are just as tiny as the air particles around them, and thus unable to pick up molecules in the air (or leave them behind) in the way that molecules in the 0.9c baseball would be doing? Nyttend (talk) 05:09, 12 March 2013 (UTC)

Particle accelerators are evacuated very close to vacuum before anything is accelerated in them. otherwise, yes, I suspect the accelerated particles would just be smacking into air molecules all the time. Vespine (talk) 05:24, 12 March 2013 (UTC)

But surely they are still hitting a fair amount of "air" molecules. Any data on that? Probably boring to the scientist at the facility but maybe interesting to us normal folks. Beach drifter (talk) 05:54, 12 March 2013 (UTC)

The entire purpose of a particle accelerator is to smack small particles into each other at relativistic speeds (or sometimes a small particle into a large, stationary object). To make the collisions occur in a controlled manner, the air is necessarily evacuated from the tunnel. But in essence, nearly all particle accelerator data is the result of particles colliding with at least one moving near the speed of light. Someguy1221 (talk) 07:16, 12 March 2013 (UTC)

why do optics use IR and not UV?

why do optics (remote control, laser mice, whatever), Microsoft Kinect etc prefer to work with IR if you dont want to bother with distracting people with whatever dots or lines or whatever you're doing - and not with UltraViolet which wouldn't it have the same effect?

Also range sensors etc. Lots of stuff is Infrared. Why? 91.120.48.242 (talk) 09:42, 12 March 2013 (UTC)

Infrared LEDs are cheap and invisible to the human eye, and plastic covers that look black to us but are transparent to IR are easy to make.

Ultraviolet LEDs are expensive and the human eye can see a violet glow, and plastic covers that look black to us but are transparent to UV are hard to make. --Guy Macon (talk) 09:55, 12 March 2013 (UTC)

This just deepens the mystery. Are you saying there is no usage benefit, dangerousness benefit, to being outside visible range via IR but simply is a matter of price and appearance? This completely does not explain why I wouldn't see it in very expensive vision research setups. It's just not used. Would it work if you changed everything that was currently IR to UV instead or would it not work for some other theretical reason? (Other than appearance of the LED's).

Secondly, following up on just your statements: just why are these LED's or cameras more expensive? Is there something about UV that makes it harder? 91.120.48.242 (talk) 12:13, 12 March 2013 (UTC)

Also: why do UV lights cause a violet glow but IR lights don't cause a red glow? If the wavelength is outside human sight, shouldn't we see nothing in both cases? 91.120.48.242 (talk) 12:14, 12 March 2013 (UTC)

UV lights, if they only emit ultraviolet radiation, are not visible to the human eye. Any violet glow from UV-lights is the result of it emitting a range of wavelengths, including visible (violet) light. Infrared LEDs and lasers are not only cheaper, but also safer. Ultraviolet light is Ionizing radiation and can therefore be both destructive to equipment and harmful to people. One might of course argue that low-intensity UV-radiation has negligible effects, but even then the the mere possibility of harmful effects and any resulting negative publicity is enough to deter manufacturers from implementing UV optics, especially when IR works just as well and is cheaper. - Lindert (talk) 13:10, 12 March 2013 (UTC)

does everything glow precisely because uv is ionizing, so that it will always have a relatively wide-spectrum glow? (Meaning it is not a good source for a signal as random things will glow under uv light as well, causing reflection and noise)? I find the 'negative publicity' aspect of your argument very unconvincing as we use lasers that are literally dangerous in all kinds of CD readers. researchers use things that are literally non-safe. people solder with lead. so if it's (in actual reality) not dangerous, then researchers won't care and people such as myself don't know anything about this subject anyway. I have no idea what's in a tv remote. so, there must be some other reason it simply doesn't work for the same applications. — Preceding unsigned comment added by 91.120.48.242 (talk) 15:51, 12 March 2013 (UTC)

Actually, there really doesn't have to be some other reason. IR works. UV wouldn't intrinsically overcome IR's limitations nor would it be cheaper (the first LEDs were IR, and creating LEDs in new frequency ranges tends to be expensive). These drawbacks don't say that UV wouldn't work, but more relevant is that they also don't present any reason why the established technology should be replaced. See also reinventing the wheel. — Lomn 16:09, 12 March 2013 (UTC)

doesn't answer why things were as they were before the Current Era, but as far as I know, modern image sensors are naturally sensitive to IR as well as visible, so that IR filters need to be installed to make them perform like the eye/film, right? so that kind of constitutes a solid bias towards IR instead of UV. Gzuckier (talk) 17:46, 12 March 2013 (UTC)

Species Identifcation..

2 Butterflies for identifcation:

Species identification desired so these can be re-titled approrpriately prior to Commons transfer. Sfan00 IMG (talk) 12:06, 12 March 2013 (UTC)

Can't immediately contribute (being at work), but it might help if you narrowed down the location from "India" to a particular locality - the State, say (not trying to dig out your personal details!) {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 15:06, 12 March 2013 (UTC)

Bihar, india according to the uploaders detail on another upload. Sfan00 IMG (talk) 16:57, 12 March 2013 (UTC)

How much nucleus/nuclei are present in the eggs of birds such as hen? What is the structure of those big cells?Ganesh Mohan T (talk) 14:39, 12 March 2013 (UTC)

I have heard that the egg of ostrich is the biggest cell in the world.So, if eggs are so big, how much nuclei are present in it.I know nucleus is present as a white dot in the yolk of an egg. So how much nuclei are present in an egg(which is a cell)? I think the egg contains only one nucleus. But I want to make sure that. Also are there any kind of cell that contains two or more nuclei?(other than during the process of reproduction) I think it only happens during the process of reproduction in micro-organisms. If I am wrong, please correct me.

The other thing I want to know is that If a single cell can be that much big, what is the outer shell made of(i.e what is it really)? Is it the cell membrane or plasma membrane? What is the yolk made up of? Do the eggs contain cytoplasm,vacoules, lysosomes, etc.., which are found normally in an animal cell?

If the yolk is not made up of cells, what is it made up of?

A ostrich egg is not a single cell, though at some stage it might contain a single cell that then develops into an embryo, then an ostrich chick. You might like to read the article on Egg (biology), but it includes other senses of "egg" that are single cells. The article Ovum explains this sense. The article Egg (food) explains a little bit about the make-up of yolk, white and shell. Dbfirs 17:19, 12 March 2013 (UTC)

Use of laxatives in Anorexia/Bulimia

I am writing a paper on Anorexia/bulimia and I'm trying to understand use of laxatives. Wikipedia's articles say they are a method of getting rid of the food from the system just as vomiting is, but they don't go one farther and say how that works. My lack of understanding is that, whereas with vomiting, it is obvious that undigested food is purged, it is not obvious to me that the same would be true with laxative use. I would guess, actually, that the body would digest the food just the same as it normally would in the small intestine, but that the end product would be expelled more quickly from the large intestibe and in the form of (sorry) diarrhea, but it must have some actual effect on lack of digestion in the small intestine. So what actually happens with laxatives? Sorry if this question is a gross out. I want to get an A and want to describe the scientific matters in detail, with good sources.--108.27.62.131 (talk) 14:58, 12 March 2013 (UTC)

Scissors VS Paper

Why do sharp objects cut through things? 203.112.82.129 (talk) 14:59, 12 March 2013 (UTC)

In the instance of scissors, consider shear action. Sfan00 IMG (talk) 15:04, 12 March 2013 (UTC)

We have an article on cutting that covers the basics. The short answer is that cutting "occurs only when the total stress generated by the cutting implement exceeds the ultimate strength of the material of the object being cut". — Lomn 15:06, 12 March 2013 (UTC)

Energy

Hi Noosphere, If the universe is infinite, the quantity of available energy is thus infinite? Thank --YanikB (talk) 15:12, 12 March 2013 (UTC)

Of course. --PlanetEditor (talk) 15:17, 12 March 2013 (UTC)

Hmm. Depends on what you mean by "available". I would say that only energy within the observable universe can be considered "available", even in the most theoretical sense. And the observable universe is always finite. Gandalf61 (talk) 15:21, 12 March 2013 (UTC)

Black hole

What black hole are made up of? For example, the composition of neutron stars are known. I want to know what is the composition of a black hole? What is the internal structure of a black hole? --PlanetEditor (talk) 15:22, 12 March 2013 (UTC)

Current theory believes that black holes have only 3 meaningful physical properties: mass, charge, and angular momentum. In terms of your question, then, there is no meaningful answer. The black hole information paradox further discusses ongoing efforts to resolve what happens to our knowledge about stuff that enters a black hole. — Lomn 16:02, 12 March 2013 (UTC)

Instead of "there is no meaningful answer", a more accurate description is "we don't know". There is no theory of quantum gravity that can describe what happens at the singularity; that's why there's a singularity at all. --140.180.249.27 (talk) 16:15, 12 March 2013 (UTC)

No, my understanding of the matter (which is admittedly amateur) is that, from the perspective of an observer external to the black hole, there really is no meaningful answer, and that we know (within the limits of present understanding) that that is the case. Even in the case of the holographic principle, which I understand to be the best current presentation for preserving information about what goes into a black hole, that information is believed to be encoded at the event horizon rather than within it. — Lomn 18:08, 12 March 2013 (UTC)