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June 29

Glasses

Why do so many people wear glasses the older people get. In school at early ages, only a few people wear glasses but every year in school this increases and by the time people are in college or start working, so many people wear glasses. Sometimes it seems like over half the population does. Why?
— Preceding unsigned comment added by 90.194.55.177 (talk • contribs) 00:38, 29 June 2014 (UTC)[reply]

First, some forms of nearsightedness (myopia) develop gradually over one to three decades. Also, there have been suggestions that frequent use of near vision can activate a genetic tendency to nearsightedness, and frequent use of near vision is a feature associated with reading in school. Second, after approximately 40 or 45, presbyopia sets in, requiring reading glasses for reading. Robert McClenon (talk) 02:15, 29 June 2014 (UTC)[reply]

One more point: unless eye tests are arranged by the school or the child's parents, myopia might go unrecognized for a while, because the child simply thinks everybody sees that way. I did. How long it takes for someone to realize might depend on how things are done in the particular school, i.e. how often a child has to read written text from a distance. --70.49.171.225 (talk) 05:45, 29 June 2014 (UTC)[reply]

By the way, in a complex human society with division of labor but without glasses, nearsightedness is not actually a disadvantage. Nearsightedness in adolescence would steer a person into a trade or craft involving near vision, such as weaving or woodworking, and a naturally nearsighted person continues to have good near vision after the onset of presbyopia. In a complex human literate society without glasses, nearsightedness may have actually been beneficial, because one could become a scribe, a high-status occupation. So evolution in humans never selected against nearsightedness. Robert McClenon (talk) 02:15, 29 June 2014 (UTC)[reply]

This presupposes that the nearsighted actually see better up close than those with normal vision. Is this true ? StuRat (talk) 15:55, 29 June 2014 (UTC)[reply]

What it presumes is that the nearsighted can see better up close after age 40 than those with normal vision. Robert McClenon (talk) 19:54, 29 June 2014 (UTC)[reply]

Purely OR, but I'm short sighted (as we say over here) and 55; I have been wearing glasses since I was 5. I can easily read tiny text as long as it's only two or three inches from my nose. My previously normal-sighted contemporaries all hold things at arms length to read things now, but I just take my glasses off. Alansplodge (talk) 12:20, 1 July 2014 (UTC)[reply]

Of course, a lot of scribes were nominally celibate. —Tamfang (talk) 03:27, 29 June 2014 (UTC)[reply]

See Human eye#Effects of aging and Presbyopia. Red Act (talk) 02:21, 29 June 2014 (UTC)[reply]

I've read speculation that nearsightedness was more prevalent among long-settled agricultural societies like China and much of Europe than areas where hunting or pastoralism required one to see animals is the distance rather than the crops at your hands and feet. Probably read this in Discover, it's not something I'd have seen in a technical source. My nephew, BTW, was fitted for glasses before he was three, his squinting and refusing to sit as far away as the couch to watch TV was a dead giveaway. μηδείς (talk) 18:06, 29 June 2014 (UTC)[reply]

If limiting career options and one's ability to participate in certain recreational activities isn't a "disadvantage", then I don't know what is. It is a categorical error to confuse what is beneficial to a Society with what is beneficial to an individual. You could (obviously) argue that having no education isn't a disadvantage because some jobs (like toilet cleaner) will always be open to the illiterate and uneducated. Saying that something isn't "necessarily" disadvantageous because there are certain situations where it might be useful is less than honest. I'm near-sighted. I don't especially mind it. My glasses cost me $500-$1000, and contacts also cost money which without my disadvantage I could spend on other things. I have to put them on in the morning, not lose them, not break them, and keep them clean. When I swim, I am certainly at a disadvantage. With water sports, the possibility that I'll lose them is a restriction. When I'm traveling, especially away from "civilization" their loss would be a nuisance at best and life-threatening at worst. By the way, the "disadvantage" post is OPINION. I was told that as children's head grow, some eyes deform leading to an inability of the lens to focus - a simple matter of optics. Most people's lenses also harden with age which also limits the ability of the lens to focus. The human lens is a "bag of gel" which changes focus by stretching and relaxing. http://en.wikipedia.org/wiki/Lens_%28anatomy%29 — Preceding unsigned comment added by 173.189.75.163 (talk) 14:50, 2 July 2014 (UTC)[reply]

NML Cygni

Move from Portal talk:Astronomy by -- Moxy (talk) 08:17, 29 June 2014 (UTC) ...user notified[reply]

i've got a question concerning the radius of NML Cygni: this article http://arxiv.org/abs/1207.1850 has been quoted as the source of the radius of 1650 R_☉. however, i could not find 1650 R_☉ in the article. all i could find was the following sentence on page 10: NML Cyg’s stellar size of 16.2 mas from Blöcker et al.(2001) was derived using the Stepan-Boltzmann law, adopting Teff=2500 K and a distance of 1.74 kpc. Rescaling this stellar diameter with our distance of 1.61 kpc gives 15.0 mas. well, mas are milli arc seconds, i suppose.

using http://www.wolframalpha.com/input/?i=1.61+kpc*sin%2815+milliarcseconds%29 i get a diameter of 3.613 billion km. this is far from the 2.29 billion km quoted for NML Cygni. can anyone explain, how the 1650 R_☉ were calculated? many thanks --Agentjoerg (talk) 08:01, 29 June 2014 (UTC)[reply]

Note to readers who don't recognize the symbol next to R (or whose browser doesn't render it): it`s the Sun; R_☉ is its radius, about 700,000km on a sunny day.

The Stepan[sic]-Boltzmann law (yahoo only found it in that source) is the Stefan–Boltzmann law.

The 2001 figures return 4.2 billion km, or about 6000R_☉; a factor of 1.8 compared to 2*1650R_☉. - ¡Ouch! (^{hurt me} / _{more pain}) 09:23, 30 June 2014 (UTC)[reply]

Shortcut to balance redox equations

I am trying to find a shortcut method to balance redox equations.

(There is one such method for the simple (non-redox) chemical equations. source: http://www.nyu.edu/classes/tuckerman/adv.chem/lectures/lecture_2/node3.html) (I know the original method to balance an equation by oxidation numbers, but just trying to find if there exists an shortcut method for this. This is not my homework. I can balance these equations, but the original method is too long and boring.)

The problem with this type of equation is - we are not always given H₂O and H⁺ on any of the sides. If we were given all of the resultants and the products, we could solve the equation simply by the algebraic method. (see the link above)

I think that the main thing I have to figure out is - how to determine the side, on which H₂O or H⁺ is, at first sight.

e.g. 1) S + HNO₃ ---> H₂SO₄ + NO
   2) P₄ + NO^3-  ---> PO₄^-3 + NO₂
   3) FeS + H₂O₂ ---> FeO + SO₂

The answers to the above equations is respectively -- 1) S + 2HNO₃ ---> H₂SO₄ + 2NO 2) P₄ + 20NO^3- 8H⁺ ---> 4PO₄^-3 + 20NO₂ + 4H₂O 3) FeS + 3H₂O₂ + 5Fe⁺² + 2H₂O ---> 6FeO + SO₂ + 10 H⁺

Ravishankar Joshi

The algebraic method expresses the problem as a set of simultaneous equations. Your boring job of solving them can be delegated to a computer programmed to perform Gaussian elimination which is a well known routine. Balancing any given chemical equation makes a nice exercise in any programming language; simple BASIC will do because calculating speed will be insignificant. 84.209.89.214 (talk) 11:27, 29 June 2014 (UTC)[reply]

If you're allowed to use both H⁺ and H₂O, then because the hydrogen ions are an oxidizing agent, you can use them to balance the equation. What I remember about them is that on the left side, you use them if the solution the reaction is in is acidic (it's been a while since I've done this).--Jasper Deng (talk) 18:34, 29 June 2014 (UTC)[reply]

The steps for balancing these are as follows:

Step 1) Split the reaction into 2 half reactions (an oxidation and a reduction)

Steps 2-5 apply for each half reaction separately

Step 2) Balance all NON-H and NON-O atoms with coefficients for each half reaction
Step 3) Balance the O with extra water molecules. Simply find the side of the reaction that has too few O atoms, and add that number of water molecules (H₂O) to that side.
Step 4) Balance the H with extra hydrogen ions (H⁺). Simply find the side of the reaction that has too few H atoms, and add that number of H⁺ ions to that side.
Step 5) Balance for charge by adding extra electrons to the side whose charge is too positive.
Step 6) Multiply the half-reactions by some whole number ratio to get an equal number of electrons in the two reactions
Step 7) Recombine the two half reactions, and eliminate any common items on either side of the reaction arrow.

Easy peasy, lemon squeezy. Here's how to do it for #2 above, just for example:

Step 1

split to half reactions

Oxidation half reaction: P₄ --> PO₄^-3

Reduction half reaction: NO₃^- --> NO₂

Step 2

balance for non-O and non-H atoms:

Oxidation half reaction: P₄ --> 4PO₄^-3

Reduction half reaction: NO₃^- --> NO₂

Step 3

Balance O using water

Oxidation half reaction: P₄ + 16H₂O--> 4PO₄^-3

Reduction half reaction: NO₃^- --> NO₂ + H₂O

Step 4

Balance H using hydrogen ions

Oxidation half reaction: P₄ + 16H₂O--> 4PO₄^-3 + 32H⁺

Reduction half reaction: NO₃^- + 2H⁺--> NO₂ + H₂O

Step 5

Balance for charge using electrons

Oxidation half reaction: P₄ + 16H₂O--> 4PO₄^-3 + 32H⁺ + 20e^-

Reduction half reaction: NO₃^- + 2H⁺ + e^- --> NO₂ + H₂O

Step 6

Equalize electrons by multiplying

Oxidation half reaction: P₄ + 16H₂O--> 4PO₄^-3 + 32H⁺ + 20e^-

Reduction half reaction: 20NO₃^- + 40H⁺ + 20e^- --> 20NO₂ + 20H₂O

Step 7

Recombine and eliminate common terms

P₄ + ~~16H₂O~~ + 20NO₃^- + 40 8H⁺ + ~~20e^-~~ --> 4PO₄^-3 + ~~32H⁺~~ + ~~20e^-~~ + 20NO₂ + 20 4H₂O

What you are left with is:

P₄ + 20NO₃^- + 8H⁺ --> 4PO₄^-3 + 20NO₂ + 4H₂O

There ya go. --Jayron32 19:04, 29 June 2014 (UTC)[reply]

Should "12" be "16" at steps 3 and 4? Tevildo (talk) 20:22, 29 June 2014 (UTC)[reply]

So fixed. Wikimarkup makes debugging rather difficult on the fly. --Jayron32 23:15, 29 June 2014 (UTC)[reply]

No, I think that I have not properly explained the question I have. I already know to balance the equation by Jayron32's method. I just want to know if it is possible to determine the number of H⁺ or H₂O (and their side) just by looking at the equation. Please tell me if that is possible. Ravijoshi99 (talk) 10:43, 2 July 2014 (UTC)[reply]

? "Just by looking" implies you think that intelligence is unnecessary in the solution of a problem. BTW, the word is "reactant" not "resultant". I am not sure why you think (IF you do) that Red-Ox reactions all involve H(+) and H2O ?? H(+) → H2O is NOT a redox reaction, which I hope you understand. Hence they have no net contribution to a redox process (although can be part of the chemical reaction chain). You also seem to think that WE can tell you whether you can, just by looking, know what the roots are for the polynomial equation (x-1)² = 0... or x²-2x = -1...Perhaps a moment's thought will lead you to the realization that it depends on YOUR mental acumen. The best way to improve your acumen is to practice the boring stuff. My suggestion is to NOT spend a lot of time on this, as virtually no one does that type of equation balancing for a living. Don't misunderstand, a chemist SHOULD be able to balance a chemical (redox) equation, and an scientifically educated layperson should be able to recognize when an equation is not balanced, but developing speed at this trivial task is probably not time well spent. I can tell you about several times in my career as a chemist where other chemists got it wrong. Once, a company I worked for sold a test kit to analyze water and the reaction they THOUGHT was occurring with their chromate redox reaction, was WRONG! (They thought the product was CrO4(=) and not Cr2O7(=) ) They'd been wrong for years, until I pointed it out. It took several weeks for them to actually realize that I was right. Changing someone's mind is either hard or impossible, unless you go about it diplomatically. They had to change all of their literature, instructions and what a mess it was. As I said, its important that you can mass balance, ballance atoms, and electrons but the reason why you are being drilled is so that you'll retain enough of the skill so that 10 or 20 years from now you won't just accept what some know-it-all says is "right". Without more information on what exactly the reactants and products - all of them - are, how could we possibly answer you? You could always include electrons, e(-) as a reactant in the reduction half-equation and as a product in the oxidation and balance them separately, but as far as I know there's no fool-proof short-cut (nothing is fool-proof, fools are too clever by far). I'm guessing your equations use a lot of H2 → 2H(+) because the book (or instructor) is too busy (or too lazy) to give you more variety. Try this one ClF3 + F2 → ClF5 (product chlorine pentafluoride). — Preceding unsigned comment added by 173.189.75.163 (talk) 15:24, 2 July 2014 (UTC)[reply]

Organs alive outside the body.

I'm curious to know if organs are able to be supported outside the body on a long term basis? We know that organs require a healthy blood supply and circulation in order to survive. With modern medicine and science could this not be achieved? Perhaps technology could go a step further in the form of a machine that actually simulates the environment of the body.

Building on this, could we then support a fully functioning female reproduction system? Infants could be spawned without the need for a human host. How feasible would all all this be?

And whilst we're at it, I know during brain surgery the brain is actually exposed with the patient conscious. So what would happen in a scenario with a large portion of the skull missing, exposing the brain. Would the said individual be able to function normally for a period of time (beside the distress of having your brain exposed of course) If not, what would be the cause of death?

Liver dialysis, artificial hearts, and even hemodialysis remain crude stopgaps that range from inadequate to laughable as substitutes for the actual organs. Parenteral nutrition is not so good either. Wnt (talk) 12:50, 29 June 2014 (UTC)[reply]

This chap (the Daily Mail, I'm afraid, but it's reliable enough in this sort of situation) has survived for a year without half his skull, and isn't at imminent risk of death. He's by no means alone in his predicament, as a Google image search for "missing skull" will confirm. See also human skull, trepanation and craniectomy. Tevildo (talk) 13:16, 29 June 2014 (UTC)[reply]

Note that scientists are working on ways to grow replacement organs for implantation, and this, of course, requires that those organs survive outside the body for an extended time. There was the famous pic of a human ear being grown on a mouse's back, for example. StuRat (talk) 17:09, 29 June 2014 (UTC)[reply]

Don't know if it counts as an example to your satisfaction, but a hernia in the abdominal wall can allow theintestines to escape the inside of the wall and roll around just under the skin of the belly like sausage links on the run. That's a very dangerous condition, but yo can live that way indefinitely. Advertisements for Truss (medicine) were common when surgery was less available. μηδείς (talk) 17:57, 29 June 2014 (UTC)[reply]

You might want to read this. A lot of scientific detail on organ preservation, but not too incomprehensible to regular people. InedibleHulk (talk) 18:18, June 29, 2014 (UTC)

Okay, back to my second question regarding brain exposure, I mean literally an exposed brain, no tissue or flesh covering it. Is it possible to function normally in this condition? Obviously, aside from the somewhat obvious mental distress. If not, what would be the cause of death?~~

Infection - specifically, encephalitis - would be the big risk in that situation. However, unless Jeffrey Dahmer was responsible for your treatment, some sort of scar tissue would form over the exposed brain (probably from the dura mater, if that was damaged - see this fascinating article about an experiment with rats) to provide an adequate barrier to bacteria. Tevildo (talk) 21:03, 29 June 2014 (UTC)[reply]

Maybe goes without saying, but you'd want to keep large objects off of it, too. And the sun, rain and snow (at least until your scar grows in). Not sure of the physiology, but it seems like a recipe for strokes and seizures, especially in autumn. Unless your hypothetical guy can wear a helmet. Then it's mainly the dirt and swelling. InedibleHulk (talk) 21:22, June 29, 2014 (UTC)

This equally-fascinating article would appear to indicate that keeping the sun off isn't a major consideration. Incidentally (and perhaps one for the language desk), I note that vivisectionists were using "sacrificed" as a - euphemism? - in 1949. When did this usage first come in? Tevildo (talk) 22:34, 29 June 2014 (UTC)[reply]

Hey, if a priest can get the genetics ball rolling, it's only fair that scientists can appease the Lord of Light every 28 days, if that's their hobby. But yeah...a bit weird. Maybe we can still trust them with our exposed brains, though. Good find! InedibleHulk (talk) 00:49, June 30, 2014 (UTC)

What would happen if you were sweating in the sun, and it leaked in? Saltwater's no good for metal electronics. Same deal? InedibleHulk (talk) 00:58, June 30, 2014 (UTC)

Aside from irrelevant aquarium stuff, a quick Google finds this charming brain-eating amoeba. Seems freshwater isn't great, either. InedibleHulk (talk) 01:01, June 30, 2014 (UTC)

(see primary amoebic meningoencephalitis for that --catslash (talk) 00:17, 1 July 2014 (UTC))[reply]

There's an interesting report http://www.bbc.co.uk/news/health-28061265 on how to chill livers to keep them viable for longer, up to 3 days instead of the normal 24hours. It also hints that the organ is supplied with oxygenated fluid. However, I do not have a Nature subscription to read the full article. CS Miller (talk) 12:25, 1 July 2014 (UTC)[reply]

How to remove rust from stainless steel

I have a pair of spoons that, well, "spooned" in the dishwasher. One apparently has a flaw in the surface that allowed iron to escape, and the area between the spoons stayed wet and formed a rust ring on both spoons. I tossed out the one with the flaw, but can the other be saved ? So far I tried using steel wool on it, which removed some, but not all, of the rust stain. Obviously I want to avoid damaging the surface. StuRat (talk) 17:01, 29 June 2014 (UTC)[reply]

Try this. --Jayron32 17:06, 29 June 2014 (UTC)[reply]

(ec) You could try citric acid. - Lindert (talk) 17:09, 29 June 2014 (UTC)[reply]

Toothpaste is a very fine abrasive. You could polish out the corrosion pits on top with it if these spoons are worth the work. --Kharon (talk) 20:57, 29 June 2014 (UTC)[reply]

No, the spoon with the corrosion pit is in the trash. It's the other one I'd like to save, so my set of flatware isn't so short of spoons that I have to buy another set (you can never find an exact match to replace the missing ones). StuRat (talk) 14:58, 30 June 2014 (UTC)[reply]

I dread to think how long they were left like that for a rust ring to form, weeks at a guess. Anyway the sad thing you have learned is that cheap stainless steel isn't stainless. Greglocock (talk) 22:23, 29 June 2014 (UTC)[reply]

As with cheap copper-based utensils with a coating to make them look like silverware. Used by low-income Irish, when the veneer wore off and the underlying metal became corroded, the folks would discuss "The greening of the ware". ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:26, 29 June 2014 (UTC)[reply]

^{[clarification needed]} Bugs, you're going to have to explain; I don't get it. Nyttend (talk) 02:58, 30 June 2014 (UTC)[reply]

The color copper turns when it oxidizes + "The Wearing of the Green". (Blame Johnny Carson for this one.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:20, 30 June 2014 (UTC)[reply]

I thought maybe you were getting at the oxidising, but I'd never heard of "The Wearing of the Green". I thought maybe it was "wear" in the sense of "wow, that's worn; it needs replacement". Nyttend (talk) 03:32, 30 June 2014 (UTC)[reply]

I was told that, at least with acetic acid (vinegar), you have to heat the reactants to start the acid-base reaction. I'm not sure of it, but it may also be possible to use electrolysis to reduce the iron back to the free element (the main problem I can think of is that water might be too easily reduced instead); my book mentions the untarnishing of antique silverware this way.--Jasper Deng (talk) 03:13, 30 June 2014 (UTC)[reply]

I use Bar Keepers Friend to clean rust off my stainless steel sink and burnt spots off of cookware. It's a mild abrasive and an acid. I've never tried it on utensils though. Mr.Z-man 19:00, 1 July 2014 (UTC)[reply]

How to identify quality stainless steel ?

This brings up the obvious Q, how do I find stainless steel flatware that won't have flaws in the surface ? Or do I just buy a really expensive brand and hope they are good ?

1) Is there no way to tell before I make the purchase ?

2) Is there a test I could do immediately when I get them home, so I could return them if defective ? (I'm thinking submerge them in bleach so any corrosion will happen far sooner.) StuRat (talk) 14:58, 30 June 2014 (UTC)[reply]

No, there is no easy way to tell. I'd use either salt water or whatever it you usually use to rot your utensils. Even with engineering grade stainless steels, such as 304, their life in seawater is supplier dependent. 316 is generally pretty good wherever it comes from. Greglocock (talk) 22:16, 30 June 2014 (UTC)[reply]

What does 304 and 316 mean ? Also, are some stainless steel items solid, as opposed to just the surface layer ? StuRat (talk) 16:42, 1 July 2014 (UTC)[reply]

The numbers relate to the ratio of metals in the alloy; see: [1] -Or this interesting PDF —71.20.250.51 (talk) 17:18, 1 July 2014 (UTC)[reply]

Per Stainless steel#Types of stainless steel, stainless steel flatware is usually made from austentitic steel, which is not magnetic. Mild steel (your basic cheap steel), on the other hand, is magnetic. If it doesn't stick to a magnet, it's probably stainless. --Carnildo (talk) 23:38, 2 July 2014 (UTC)[reply]

RGB colour model

In the diagram here, is "Area of triangle / Area of grey shape" a sensible estimate of the proportion of the colour space of human vision that can be represented by the RGB colour model? 86.179.117.18 (talk) 20:23, 29 June 2014 (UTC)[reply]

No, that diagram isn't perceptually uniform. This diagram, which uses CIELUV instead of CIE xy, is better. Surprisingly, I couldn't find an appropriate image on Commons. Note that there are many color spaces called RGB. The diagrams above show sRGB, which is the de facto standard. Adobe RGB and CIE RGB cover more colors than sRGB. -- BenRG (talk) 22:20, 29 June 2014 (UTC)[reply]

Thanks, by the way, in the theory of RGB colour models, is it assumed that the intensity of a colour can vary continuously from zero to any desired brightness? (I understand, of course, that in any practical implementation the intensity of light is limited to what the device can physically pump out). 86.179.117.18 (talk) 22:59, 29 June 2014 (UTC)[reply]

The RGB color model is typically applied to a set of 3 primary color lights whose intensities are each separately controllable in 256 steps from zero to a maximum whose absolute intensity need not be specified. However the relative peak intensities represented by [RGB] = [255 255 255] are in proportions that give a reference White point. 84.209.89.214 (talk) 00:52, 30 June 2014 (UTC)[reply]

sRGB has a nonlinear intensity curve which is only defined for values from 0.0 to 1.0 (or 0 to 255). If you use a linear (energy) scale then the values can be arbitrarily large or even negative. If they are allowed to be negative then any set of three primaries is equivalent to any other, since they are just different bases for the same space of colors. -- BenRG (talk) 02:26, 30 June 2014 (UTC)[reply]

June 30

Live and Neutral

Why does the resistance becomes almost zero when a live wire touches a neutral wire? — Preceding unsigned comment added by 182.66.60.246 (talk) 03:14, 30 June 2014 (UTC)[reply]

Resistance between what two points? But assuming a wire has little resistance in general, obviously connected wires still have little resistance. Do you mean potential (voltage)? That's a more surprising case. Again assuming low-resistance conductors, the voltage of a "high voltage" line drops when it touches a ground/neutral line. But then remember that voltage is a difference not an absolute value, and the ground/neutral is the usual reference point. And it's not surprising that connecting two wires causes them to have the same voltage as each other. Attaching a live wire to ground causes (almost) all the current to flow that way, so it doesn't seem that unusual that connecting a wire to neutral causes it to have little or no measurable voltage with respect to neutral. DMacks (talk) 03:21, 30 June 2014 (UTC)[reply]

See Short circuit. 24.5.122.13 (talk) 04:16, 30 June 2014 (UTC)[reply]

Rephrasing DMacks, the resistance is almost zero because the resistance of any wire (in this sense) is almost zero. Touching 2 wires together just completes the circuit, where previously there was an air gap (which has very high resistance). That one is live and the other neutral is irrelevant. cmɢʟee⎆τaʟκ 19:23, 1 July 2014 (UTC)[reply]

Current Induction

What happens at atomic level in a coiled wire when a bar magnet in moved in and out of coil which induces curret in the wire? — Preceding unsigned comment added by 182.66.60.246 (talk) 03:22, 30 June 2014 (UTC)[reply]

In the frame of the wire, the magnetic field strength changes as the magnet moves around; an electric field is produced according to Faraday's law of induction. In the frame of the magnet, it's just the Lorentz force on the charges moving along with the wire. --Tardis (talk) 03:52, 30 June 2014 (UTC)[reply]

Although your question specifically requests an explanation at the atomic level, a conduction electron in a piece of metal isn't actually closely associated with any particular atom at any given time. So it works reasonably well to think of the conduction electrons as forming an "electron gas" that's confined to the wire, independent of any atoms. For details, see Free electron model and Nearly free electron model, or if you're super interested study a beginning book on solid-state physics, which will require an understanding of quantum mechanics as a prerequisite. Red Act (talk) 05:50, 30 June 2014 (UTC)[reply]

Passenger Aeroplane

What happens to those carbon dioxide which are exhaled by passengers of a passenger aeroplane and there is no accomodation of it although the plane is totally airtight? — Preceding unsigned comment added by 182.66.60.246 (talk) 03:39, 30 June 2014 (UTC)[reply]

Passenger aircraft aren't totally sealed. As our article cabin pressurization explains, in most passenger jet aircraft bleed air extracted from the engine compression stages is fed to the cabin, and subsequently exits via an outflow valve. Boeing have recently gone over to using electrical pumps to provide inlet air instead - reducing the risk of introducing contaminated air into the cabin. AndyTheGrump (talk) 03:51, 30 June 2014 (UTC)[reply]

That's true - but even if it were not, a person can live on about 16 cubic feet of air per hour (see calculations here, for example) - limited by the amount of exhaled CO2 rather than the amount of oxygen used. According to Boeing, the 747-8 has a cabin volume of about 30,000 cubic feet for around 450 passengers...which is 66 cubic feet each. So without the air being replaced at all, the passengers could survive for around 4 hours on just the air in the cabin.

Put another way, you only need to replace 16*450=7200 cubic feet of air per hour...which is 120 cfm. The extractor fan in my bathroom is rated at 110 cfm - so if the passengers are mostly just sitting quietly or sleeping, it could probably exchange enough air to keep the entire 747 ventilated.

SteveBaker (talk) 04:17, 30 June 2014 (UTC)[reply]

For reference, a cubic feet is 28 litre in proper units. 131.251.254.110 (talk) 07:45, 30 June 2014 (UTC)[reply]

The 16 cubic feet Steve cited would be at sea level. In a pressurized aircraft the internal air pressure is only around 3/4 to 4/5 of sea-level pressure, which suggests that a somewhat larger volume of air per hour would be needed. (Not necessarily 4/3 to 5/4 as much, because it depends on human response to oxygen and CO2 at those pressures. But probably something like that.) Of course this is just a detail and does not invalidate Steve's comment, or for that matter, Andy's. --70.49.171.225 (talk) 08:05, 30 June 2014 (UTC)[reply]

I don't trust first-principles calculations on matters like this because biology has a way of surprising us. But my guess (and anything other than literally looking at data from a submarine accident or something is just a guess) is that the partial pressure of CO2 ought to be the more limiting factor, and would not depend on atmospheric pressure. Wnt (talk) 11:26, 30 June 2014 (UTC)[reply]

"Totally airtight?" Passenger airplanes with pressurized cabins cannot be accurately described as totally airtight. For much of a flight, the air in the passenger cabin is at constant pressure but not because the cabin is airtight. The pressure is constant because air is allowed to escape from the cabin at the same rate as fresh air is introduced by the cabin pressurization system. There is a significant amount of fresh air being introduced to the cabin every hour, and the same amount escaping. The escaping air contains a slightly higher-than-normal amount of CO2 and water vapour, and a slightly lower-than-normal amount of oxygen; and the introduced air contains normal CO2, water vapour and oxygen. Dolphin (t) 12:43, 30 June 2014 (UTC)[reply]

Some comments:

1) People with breathing problems, like asthma, might die far sooner from excess carbon dioxide.

2) Everyone would be made uncomfortable far earlier.

3) Ironically, "bad air" is more of a problem for planes stuck on the tarmac, as the air exchange system depends on running the engines, and they don't want to do that on the ground for an extended period, or they need to return to refuel before take-off. StuRat (talk) 14:51, 30 June 2014 (UTC)[reply]

They can use the APU, or run the ventilation using external power. 24.5.122.13 (talk) 21:40, 1 July 2014 (UTC)[reply]

Interstitial tear of the Posterior cruciate ligament

What is a Interstitial tear of the Posterior cruciate ligament in the knee? Is is classified as a grade 1, 2, or 3 tear? Just to clarify I do not have a knee injury and I am not asking for medical advise, I just like learning about the anatomy of the knee. --Sara202020 (talk) 07:13, 30 June 2014 (UTC)[reply]

See Posterior cruciate ligament. An interstitial tear is one which occurs in the body of the ligament, rather than a tear where one of its ends detaches from the bone. (See this article about the rotator cuff for an explanation of the terminology). The grade of a tear depends on its severity, rather than its location, so an interstitial tear can be any of the three grades. Tevildo (talk) 11:45, 30 June 2014 (UTC)[reply]

Trimix (injection)

Trimix (injection) talks about Trimix injections, but http://finance.yahoo.com/news/ed-patients-now-60-days-123000584.html talks about Trimix gel. Is Trimix gel even a thing, or is it a scam like like "herbal Viagra". Either way, the Wikipedia page should mention it. 76.194.214.123 (talk) 09:07, 30 June 2014 (UTC)[reply]

"Trimix gel" is a registered trademark of a company that can easily be located via your favourite search engine, and who have some ~~ultra-yiffy~~ videos on their website which appear to demonstrate their product's effectiveness. It seems to be a form of Trimix that's suitable for topical application. On the other hand, they don't give the impression of being a well-established pharmaceutical firm. Anyone suffering from erectile disfunction should contact his doctor for reliable advice, of course. Tevildo (talk) 21:47, 2 July 2014 (UTC)[reply]

Colour space and spectrum colours

What proportion of the colour space of human vision is covered by the spectrum colours (rainbow colours)? Since human-perceived colours are described by three numbers, and spectrum colours by two (wavelength and intensity), it seems to me that the mathematical answer to this question should be zero, but can that actually be correct? 86.179.117.18 (talk) 13:12, 30 June 2014 (UTC)[reply]

It's more-or-less true that the spectral colors, distinguishing different intensities, form a 2-D surface within the 3-D color space that humans perceive, and it's true that a 2-D surface has zero volume. However, in reality humans have a non-zero just-noticeable difference in color perception, such that there's a small but non-zero volume within the 3-D color space that's perceptually indistinguishable from the spectral colors. Red Act (talk) 14:47, 30 June 2014 (UTC)[reply]

One useful way of characterizing a color is in terms of hue, saturation, and intensity. In that scheme, the "spectrum colors" are the colors that have maximum saturation. Looie496 (talk) 15:20, 30 June 2014 (UTC)[reply]

An actual numeric answer to your question may be hard to come by, but I'd think that 1% would be a good order-of-magnitude estimate, given that the number of distinguishable colors increases by roughly a factor of 100 for each additional dimension in an animal's color space, according to Color vision#In other animal species. The Color difference article talks about some of the complexities involved in trying to come up with color space models such that just noticeable differences between two colors are equivalent to the same Euclidean difference between points in the color space model, anywhere within the color space. A big part of the difficulty with perceptual non-uniformities in the models is due to the human eye being more sensitive to some colors than others; see Color vision#Physiology of color perception. Red Act (talk) 16:11, 30 June 2014 (UTC)[reply]

Thanks for the replies. 86.179.117.18 (talk) 16:33, 30 June 2014 (UTC)[reply]

A color is a mixture of many frequencies, each at different intensities - as such, there are an enormous number of them. However, since our eyes are only really telling us how much each of three sensors is stimulated, we're really perceiving that as just three numbers. Some species of shrimp have twelve sensor types - so their color perception should be represented by 12 numbers...so right there, you know that we're missing out on a lot. If we could distinguish 100 different brightness levels (which is a very roughly reasonable statement), then we can see 100x100x100 = one million distinct colors. If the shrimp can see 10 different brightness levels then it can hypothetically see 100x100x100x100x100x100x100x100x100x100x100x100 = 1,000,000,000,000,000,000,000,000 colors....and some hypothetical animal with yet more sensors would be able to distinguish even more. Of course whether it's brain is equipped to use that information is very doubtful...but in principle, it's vastly more capable than we are.

However, you used the word "spectrum" - and that changes things. A spectrum (such as you'd see in a rainbow or as spread out by a prism) has at each point the intensity of light at one single frequency. There are definitely colors that we can easily distinguish (like the color we call "magenta" that is a mix of red and blue) that aren't in the spectrum at all. At each point in the spectrum, there is a single frequency at some particular intensity. But how many "colors" that is depends on how finely you measure that. If you sliced the spectrum into 100 frequency bands - and measured the intensity of each one to one part in one hundred - then there would be 10,000 distinct colors - and we could perhaps argue that humans (being able to see a million colors) can see 100 times more colors than there are in the spectrum. But that's a bogus argument. Suppose we sliced the spectrum into a hundred thousand bands - each with 100 intensity steps. Now we're saying that there are 10 million colors in the spectrum - and humans can only see a million colors (some of which, admittedly, aren't even IN the spectrum).

So I don't think this is a very meaningful question. It's all about precision of measurement - and that's not an apples-and-apples comparison because you have to decide the precision of frequency measurement and compare it to the precision of intensity measurement.

It's just like asking: Can you throw a ball further than the weight of an elephant? If you measure the distance in millimeters and the weight in kilograms - then yes. But if you measure the distance in meters and the weight in micrograms - then no. It's truly meaningless.

SteveBaker (talk) 19:31, 1 July 2014 (UTC)[reply]

The question isn't really comparing apples to oranges, because the question effectively does specify the measurement precision to be used. The OP explicitly specifies "human perceived colors", so dividing the visible spectrum into 100,000 frequency bands is clearly not what the OP is intending, because the human visual system can't distinguish that many different frequencies.

Conceptually, the product space of the set of all frequencies in the human-visible spectrum with the set of light intensities the human eye can handle is a two-dimensional manifold. There exists a map from each point on that 2-D "spectral manifold" to a point within the 3-D human color space. (Whether or not that map has a well-defined inverse is irrelevant.) The image of that map forms a 2-D submanifold of the 3-D color space. One can then define a 3-D "spectral subspace" of the color space as being the set of all points in the color space which humans are incapable of distinguishing from some point on the 2-D submanifold. You can then make an apples-to-apples division of the volume of the 3-D spectral subspace by the volume of the whole color space, if you first introduce on the color space a metric such that the color difference using that metric between any pair of colors that are just noticeably different to humans is the same no matter where that pair of colors are within the color space. That ratio is what the OP is asking for. The answer can't be very precise, because color perception involves biology and psychology, not just physics, but the question is indeed asking for a meaningful number. Red Act (talk) 23:26, 1 July 2014 (UTC)[reply]

regarding species

I always wondered: if a biological variety A of a species X can have offspring with variety B (of X), and B with C (of X), A need not be able to with C. So, if A and C don't produce offspring, is A a species with respect to C? - SCIdude (talk) 14:26, 30 June 2014 (UTC)[reply]

Our article ring species addresses this. -- ToE 14:51, 30 June 2014 (UTC)[reply]

Yes. As the article says, A and C would be considered the same species if they can have fertile common descendants, even if not directly. However in practice things can sometimes get a bit tricky. I read an article a couple of years ago (can't remember how to find it) about a case involving two varieties of fish that were classified as distinct species because they did not interbreed. However, when a third variety of fish was introduced into the environment, it was capable of breeding with both of them. What this sort of thing really points out is the arbitrariness of the "species" concept. Many modern biologists no longer take it very seriously. Looie496 (talk) 15:11, 30 June 2014 (UTC)[reply]

Well, we can take the concept of "species" seriously, even if we acknowledge the species problem. Systematics and cladistics seem to be replacing taxonomy, and there are ontological problems with the notion of defining species by ability to produce fertile offspring -- but for most purposes it's just fine to talk about Apis mellifera or Carduus nutans or other common species. Yes, there are ring species and cases where species don't make a lot of sense (e.g. archaea). But just because there are corner cases and tough calls doesn't mean species designations are completely arbitrary. Unless your goal is to resolve evolutionary relationships, species work just fine for most biological applications. SemanticMantis (talk) 15:51, 30 June 2014 (UTC) (p.s. Dialect continuum is a nice analogy for ring species.)[reply]

Beyond this, remember that some types of individuals are universally considered the same species, despite what's likely an inability to reproduce together; an Irish Wolfhound and a Chihuahua aren't really going to be able to produce puppies, but nobody's going to say that they're separate species. Nyttend (talk) 11:52, 1 July 2014 (UTC)[reply]

Members of the same species don't need to be able to reproduce together directly, they only need to be able to have overlapping trees of descendants. As a rather obvious example, a pair of males or a pair of females cannot reproduce together. Dogs, by the way, seem like an excellent example of a "ring species". Looie496 (talk) 12:18, 1 July 2014 (UTC)[reply]

I understand; I was attempting to provide a very simple example that everyone assumes. Not trying to denigrate your more scientific approach; it's just that considering the dogs a single species is much more intuitive to me, and it may be likewise for SCIdude and others as well. Nyttend (talk) 12:58, 1 July 2014 (UTC)[reply]

Micro SD type of and how many GBs

How many types of micro SD cards there are and how many gigabytes can they carry? — Preceding unsigned comment added by 162.219.184.233 (talk) 15:04, 30 June 2014 (UTC)[reply]

This question belongs on Wikipedia:Reference desk/Computing. Looie496 (talk) 15:13, 30 June 2014 (UTC)[reply]

Yes, and the questioner should ask a more specific question there if they don't find what they want in our Secure Digital article. -- ToE 21:08, 30 June 2014 (UTC)[reply]

Water plant in Dutch nature reserve

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Hello, would anybody be able to identify the water plant shown on this picture? Someone found it in a wetland reserve in the North of the Netherlands. A quite long discussion in the nl.wiki Biology café gave no satisfying result, though Ludwigia and Salix were mentioned. Regards, Apdency (talk) 15:42, 30 June 2014 (UTC)[reply]

Are you sure it's a water plant at all ? Those usually don't grow up beyond the waterline much, but just float on the water and spread out, as that's a more effective way to increase the amount of sunlight that hits the leaves. See water lily or lotus flower for examples. I'm wondering if this isn't a terrestrial plant which is in an area that's been flooded. StuRat (talk) 16:08, 30 June 2014 (UTC)[reply]

Uhm, having read that, I was planning to propose Vaccinium corymbosum, but now I see that on Commons, EB Doulton already did the work. Apdency (talk) 16:55, 30 June 2014 (UTC)[reply]

But that's a North American plant, so it would have to be an invasive species, if present in the Netherlands. StuRat (talk) 17:08, 30 June 2014 (UTC)[reply]

I learned that it has been imported there from North-America in the 1940s. This Dutch language page is one of the sources; it also shows other pics of Vaccinium corymbosum in that particular reserve ('Fochteloërveen'). Apdency (talk) 19:07, 30 June 2014 (UTC)[reply]

Our article on that plant should be updated accordingly. Are you up to it ? StuRat (talk) 16:45, 1 July 2014 (UTC)[reply]

Uhm, I hope this will be a challenge to anyone more used to writing on biology topics than I am. Apdency (talk) 19:47, 1 July 2014 (UTC)[reply]

RGB colour triangle

In an RGB colour triangle, such as the one here, I understand, of course, that the corner points are R, G and B, and that the RGB values of the interior points are somehow related to the distances to the corners. However, this "somehow related" calculation can be done in numerous different ways, and the resulting triangles will contain different subsets of all the possible RGB colours. Even if it is desired to have (255, 255, 255) at the centre of the triangle, there will still be many ways to do it. What is the reason (if any) for choosing one method over any other? Is there one particular method that makes special sense? 86.179.117.18 (talk) 17:00, 30 June 2014 (UTC)[reply]

File:GammaFunctionGraph.svg

Example of CRT gamma correction. The dotted line indicates a linear transfer function (γ=1); the solid line shows how a typical CRT behaves; the dashed line represents the inverse function.

Points in the RGB color space corresponding to linear steps in each coordinate i.e. 0% 25% 50% 75% 100%. The actual intensity steps depend on the gamma of your display.

The corner points have [RGB] coordinates [255 0 0] [0 255 0] and [0 0 255]. The sides are the locii of coordinates [0 n n] [n 0 n] [n n 0]. Ideally the intensity of each primary light is proportional to its coefficient 0...255 and the white point is at the Centroid of the triangle. However a typical CRT has a power-law luminance response, typically gamma=2.2, so will not respond proportionally to [RGB] coordinates. The solution is to apply Gamma correction. This color list attempts to show the difference gamma correction makes but will be constrained by the display you actually use. 84.209.89.214 (talk) 18:05, 30 June 2014 (UTC)[reply]

Ultimately, the choice of color-coordinates (and the various ways that you can plot them) are heuristics guided by data collected during several landmark perceptual psychology experiments. For example, CIE 1931 uses data that was collected by the world's preeminent psychologists in 1931; CIE 1976 uses essentially the same methodology and new data collected in 1976... Now, if I understand correctly, humans didn't evolve very much during those decades, so if the data was actually representative of the human population using sound scientific methodology, these color spaces should be exactly the same.

To be perfectly honest, the whole concept of projection into "perceptual" colorspace is, in my opinion, a lot of false precision puffed up by people who call themselves color scientists. (I have yet to meet a "color scientist" who is an optical physicist but I've met plenty who studied art or film or photography - they're really interested in the artistic side of science). Since I started off my career as a pedigreed optical physicist, I am incredibly frustrated by these silly color spaces: all I want is an imaging spectrometer and an intensity-versus-wavelength or frequency spectrum plot across the visible spectrum. That is a precise methodology: we can build machines (spectrum analyzers and photon counters) that exactly tell us everything that matters with respect to the color. We can build other machines (monochromators and tunable lasers, for example - or even just regular illuminants and calibrated color filters) to precisely reconstruct any combination of colored light, with arbitrary precision. Any sufficiently-well-sampled reconstruction of a scene that produces the same spectrum is guaranteed (as a side-effect) to also have the same coordinates when projected into a 3-element perceptual colorspace - which is, at the core, nothing but an obscenely under-sampled coordinate-transform of the frequency spectrum. With a bit of linear algebra, you can construct any color space you like, subject to any constraint you wish to impose, and produce a brand new n-element colorspace; and if your linear algebra exactly matches that used by the CIE or the ITU or any of the other prestigious consortiums, then you get one of their numerous "standard colorspaces." Nimur (talk) 18:21, 30 June 2014 (UTC)[reply]

Correct, but encoding an movie with a seperate spectrum stored for each pixel will take a lot more storage/bandwidth, and making a display that reconstructs that spectrum at at each pixel doesn't sound cheap. The reason three dimensional color spaces work pretty well are because in the end that spectrum gets broken down to responses from three (technically four) types of receptors in the eyes so, like you say, it's all linear algebra from there. Katie R (talk) 19:18, 30 June 2014 (UTC)[reply]

....linear algebra based on an approximate, implementation-dependent, somewhat-standards-compliant heuristic. I don't mind the imprecision; I don't mind the psychology-based perceptual heuristics... what irks me is the phony pretense of numerical accuracy - which is, I think, the same thing that the OP's question is getting at. Nimur (talk) 19:25, 30 June 2014 (UTC)[reply]

For tasks such as paint mixing and textile production, a precision no less than the ability of a critical eye to distinguish a difference between colours is justified and, in practice, is paid for in a commercial system such as Pantone's which samples thousand(s) of colours. According to Pantone, the colour of 2014 shall be Radiant Orchid! One sympathises with Nimur's disdain for the arty fashion designers and other consumer-oriented companies that don't care much about electromagnetic spectral analysis of that shade. 84.209.89.214 (talk) 00:19, 1 July 2014 (UTC)[reply]

Thanks for all the replies. Let me put it another way. Is there anything special or significant, either physically or perceptually, about the subset of RGB colours that are displayed in the colour triangle? I apologise if this question has actually been answered above, but if it has, I'm sorry, I can't pick it out. 86.179.117.18 (talk) 19:33, 30 June 2014 (UTC)[reply]

The color triangle has no utility until 3 practical phosphors (for a CRT) or dyes (for a positive film) are formulated that can reproduce a generous Gamut of colours. The article Phosphor shows the plethora of chemical formulations that have been investigated. Development of color TVs took a long time due to the long search for a red phosphor; for this purpose a rare earth phosphor YVO4,Eu3 was introduced in 1964. The RGB triangle is thus dictated by the state-of-the-art of additive colour reproduction, just like the subtractive CMY (Cyan, Magenta, Yellow) triangle for printing is limited by practical ink formulations. In this case, 3-ink colour printing is incapable of showing a deep black and in practice a fourth ink is needed for good quality images, see CMYK color model. 84.209.89.214 (talk) 23:49, 30 June 2014 (UTC)[reply]

Phrased another way: we know how to build tri-color-filter-arrays - "red/green/blue" combinations - for things like television displays and camera sensors and printer inks, such that the "greenish" color matches the average human eye's perception of green; and the "reddish" color filter matches the average human eye's perception of "red"... or can be emulated by some combination of those inks/phosphors/dyes. This lets us use only three numbers - we can call them "R,G,B" or "X,Y,Z" or "n1,n2,n3", or {z[0],z[1],z[2]} to approximate a full color spectrum. This is possible because researchers and industrialists have spent years experimenting with various printable inks, chemical dyes for phosphors and LCD panels, and so on. The color triangle is just a plot that idealizes the possible combinations.

The subset of RGB values inside the color triangle therefore correspond to all the possible combinations of (printer ink, or LCD pixel brightnesses on your computer screen, and so on). The "size" of the triangle, loosely speaking, shows the extent to which such inks/dyes/phosphors can reproduce all possible colors that humans can normally see. A standard colorspace can be compared, in triangle-form, to the calibrated colorspace of any machine, enabling designers to determine how one set of chemical dyes compares to another; or how one brand of television hardware corresponds to another, and so forth. Nimur (talk) 00:13, 1 July 2014 (UTC)[reply]

Inks for Color printing are normally the subtractive primaries cyan, magenta and yellow, not RGB. 84.209.89.214 (talk) 00:39, 1 July 2014 (UTC)[reply]

Different coordinates, different color limitations, exact same methodology. Let me emphatically reiterate: when you represent the complete spectrum, everything is incredibly simple. There's no such thing as "additive" or "subtractive" color. All that matters is the intensity at each wavelength. Nimur (talk) 01:37, 1 July 2014 (UTC)[reply]

"The subset of RGB values inside the color triangle therefore correspond to all the possible combinations of (printer ink, or LCD pixel brightnesses on your computer screen, and so on)." -- Now I am totally confused. How can this be true? Surely numerous RGB combinations -- in fact most combinations -- are not present in the colour triangle??? This is the whole basis of my question: Is there anything fundamentally significant about the subset of combinations that are present? 86.179.117.18 (talk) 02:13, 1 July 2014 (UTC)[reply]

Okay, let's disassemble this a different way; my intent was not to add confusion. When you look at one of these color-space gamut plots, you're looking at a two-dimensional plot of a three-dimensional color space. What's worse, three dimensions isn't really even enough to capture every possible combination of photons in the real, physical world!

So what the "color scientists" have done is take one slice out of the three-element model. Usually, they do this by selecting "constant brightness" - by decomposing their color model into a luminance and chrominance space. This means that they intentionally pick one coordinate to be a parameter that they think looks like brightness, (what-ever that means); and that leaves two coordinates to describe what they think looks like color. Now, the physicist deep within all of us is just fuming over this decomposition: "brightness" is a vague and fuzzy description of radiometric intensity. In other words, total number of photons. But, perceptual psychology experiments seem to indicate that not all photons look as bright. Green photons look brighter! It's weird, but it's a real effect that's mostly determined by the anatomy of the human eye (the cells in our eye that are more sensitive to green are shaped differently than the other types); consequently, this affects the way our brain's visual cortex interprets the signals that the retina produces. "Green" photons not only look "green," but they also look "bright."

When you look at this 2-D plot, you are seeing one single slice - usually a slice of constant "brightness" (Z) - and so the X,Y positions in the chart correspond to the "color" part of the photons. This is totally not-physical. It is a mathematical transformation: a projection onto a new set of coordinates, defined by integrating the incident light, premultiplied by a spectral sensitivity curve, to result in a number. That number is called "X" for one of the curves; and "Y" for another curve... you get the idea. And now, they graph the "X vs. Y" plot - and draw a triangle in it for the region that they believe corresponds to the visual range. By construction, there exists a gamut in this plot that corresponds to all possible nonnegative combinations of certain primary colors. Keep in mind that the position of the primaries in X,Y,Z space is determined by the same math, so it's definitionally true that the triangle (or the convex hull) between them must contain all possible nonnegative combinations of primaries - for this particular Z slice.

This is a whole lot of linear algebra, involving a whole lot of singular matrices and crude pseudoinverses... which is why, as I said earlier, things are so much easier if you stick to pure physics - total photon count, and optical spectrum - which can totally and uniquely define the color of any object in the scene. This is the purist, spectroscopic approach, and it is what chemists, optical scientists, and astronomers use. It is sometimes called radiometry. Contrast it to perceptual photometry, with all the XYZ color-spaces and weird gamuts... which is what photographers, filmmakers, and "color scientists" use (or, at least, they pretend to use it so they look busy, while a chemist designs their camera-film, or a physicist designs their digital camera sensor, or so on). Nimur (talk) 03:34, 1 July 2014 (UTC)[reply]

...And Nimur's optical physics experience (and bias ;) show clear! Very good explanation, but I think you're a bit hard on some of the systems we use to describe color. I take your points that the "pure physics" approach to "color" is somewhat conceptually simpler. As you say, it's just "intensity at each wavelength" -- but that's not very useful for a person who uses colors for designing print, fabric, user interfaces, and other things that IP 84... mentions above. I mean, that's an infinite dimensional Hilbert space your talking about (or is it a Banach space? -- even worse). If I want to make a poster to look similar on my monitor, your monitor, and when printed, shall we discuss it in terms of a specific Fourier series? And if so, to what end? As you also point out, human color perception does weird things, with "bright" greens etc. RGB, CMY(K) and other systems do have some problems, but they also serve many purposes that cannot be achieved with spectral descriptions and analysis (even if we could pass elements of L2 around, we'd have still have to translate that information into instructions that a printer or monitor could use). It can be confusing to go back and forth between different systems, and RGB et al. can never suffice for representing all colors/wave forms, due to the projections, singular matrices and other lossy parts of the process that you mention. But I won't be disparaging RGB or CMYK for being "non-physical" -- it is not their goal to be physical, but to offer a systematic framework that can be used to describe and manipulate colors, in a variety of contexts. At that, they succeed, at the cost of using transformations that make it hard for the average person to follow the math of an RGB code, through display technology, back to the spectrogram.

To answer OP's recent follow-up questions explicitly: in concept, all RGB combinations of a certain brightness are in that triangle. No monitor or printer can display all (infinitely many) of them, but as a mathematical concept (i.e. as a projection of the span of the basis vectors), they are all there. The significance of that triangle is that it represents the boundaries of everything describable in that system, even if that system cannot describe every wave-form of light that some human eye can distinguish. SemanticMantis (talk) 04:08, 1 July 2014 (UTC)[reply]

Nimur, physical spectra and human perceptual models are both essential in different contexts. You can't specify RGB primaries as physical spectra. An LCD or OLED display can't practically produce the exact spectrum of the YVO4,Eu3 red phosphor in an old CRT, and shouldn't have to. You define primaries using CIE xy coordinates or something analogous so that the engineers are free to pick the cheapest method of producing that psychological color. It isn't realistically possible to capture or store images with complete physical spectra at visible wavelengths either. Color photography and color TV would be impossible in practice if we "stuck to pure physics". DVDs and streaming video wouldn't be possible without lossy video compression that's closely tied to properties of the human visual system.

You said "There's no such thing as 'additive' or 'subtractive' color" when you deal with physical spectra rather than XYZ coordinates. That's wrong. RGB displays produce light, so they work additively. Inks absorb light, so they work subtractively. Subtractive color is more complicated because it depends not only on the absorption spectra of the inks but also on the spectrum of the illuminant. This is all "pure physics".

The CIE xy plane is a 2D projective representation of the 3D space of perceptual colors. There's one point in the xy plane for every line through the origin in XYZ space. It's not a slice of constant brightness; points in the xy plane don't have a brightness.

Perceptual brightness is zero in the infrared and ultraviolet and positive in between. It has to have a maximum somewhere. The maximum happens to be at around 555 nm, which is perceptually green. This is no more strange than if it were anywhere else, as far as I can tell. -- BenRG (talk) 06:29, 1 July 2014 (UTC)[reply]

Photons don't remember how they were produced: when light hits your eye or your camera, the photon doesn't magically know that it came from an additive combination of spectral light sources, or a subtractive absorption/reflection of photons from a pigmented surface. By the time the light gets to you, the only state the photons carry that is relevant to their color is their wavelength. How the photons got that wavelength is irrelevant, because the photon doesn't carry that kind of information. What matters is the intensity and wavelength: these are the most general possible way to describe the color of a scene.

All the various color models exist to help approximate this completely general representation of color using as few numbers as possible. That is, again, why I call these color models "obscenely undersampled," but as BenRG and SemanticMantis point out, these models are good enough to fool most human eyes, and therefore they have some utility. Nimur (talk) 16:01, 1 July 2014 (UTC)[reply]

The cones in the eye don't know where the light came from either, so there's no difference between additive and subtractive psychological color either, from that perspective.

Low-frequency (radio) astronomy works by direct sampling of the electromagnetic field, but the frequency of visible light is on the order of 10¹⁵ Hz. Even astronomers use color filters at those frequencies, much like animal eyes. I think it's unavoidable. -- BenRG (talk) 03:34, 2 July 2014 (UTC)[reply]

Thanks, at last we have got to the actual question that I asked. "all RGB combinations of a certain brightness are in that triangle." So, I take this to mean f(R, G, B) = const? What is the function and what is the constant? Thanks for your patience with this. 86.179.0.75 (talk) 11:17, 1 July 2014 (UTC)[reply]

In this case, that function would be one way to represent the color space conversion matrices. For example, if you were using MATLAB to perform your image processing, you could use this reference to review the matrix multiplication that would define f. If you were using CoreGraphics ColorSpace, you could create and pass in your own function and define your own colorspace. Many standard color-spaces exist - and they would therefore have a standard function: for example, Rec. 601, Rec. 709, and Rec. 2020 all standardize the format conversion mathematics, including a colorspace definition. You can represent them as 3x3 matrices of standard coefficients, and you should always look those coefficients up in a reliable reference (like the technical specification itself). Speaking from experience - many implementations claim to use one of these standards, but fail abysmally if measured against calibrated equipment. Many more times, I have seen software implementations that report a standard colorspace but use a home-made set of coefficients. So, tread with caution: the standardized colorspace might not be the one that's in common use and commonly called "standard." Nimur (talk) 16:07, 1 July 2014 (UTC)[reply]

See Chromaticity - it has a good description of the diagram. The CIE color spaces attempt to make perceptual brightness one of the 3 axes in their system. For example the L in the Luv system is luminance, and by setting that constant and varying u,v you can create the CIELUV chromaticity diagram. CIE_1931#CIE_xy_chromaticity_diagram_and_the_CIE_xyY_color_space explains the transformation from the XYZ to the xyY color space that is used for the commonly seen CIE 1931 diagram. Katie R (talk) 13:24, 1 July 2014 (UTC)[reply]

"in concept, all RGB combinations of a certain brightness are in that triangle" -- This seemed to be the answer to my question, but now I am having doubts that it can be true. When I look at the triangle in question, it seems to me that the vertices are (255,0,0), (0,255,0) and (0,0,255), and the centre is (255,255,255). I can't understand how (255,255,255) can possibly have the same brightness as, say, (255,0,0) in any sensible physical or perceptual sense, since the former has all the brightness of the latter (R = 255) plus a whole lot extra. 86.167.19.242 (talk) 17:45, 1 July 2014 (UTC)[reply]

The vertices represent the chromaticity of each primary, independent of the luminosity. It is possible for all three primaries to have vastly different luminosities, but the slice of the color space represented by the diagram sets the luminosity value constant on all three. Katie R (talk) 18:30, 1 July 2014 (UTC)[reply]

A 3D rendering of the edges of an RGB color cube projected to the xyY color space with the CIE 1931 diagram drawn slicing through it could be interesting, showing how the RG and B vertices are projected onto the plane. Unfortunately I have no idea where to find one, and I don't have the time to make one. — Preceding unsigned comment added by Katie Ryan A (talk • contribs) 18:37, 1 July 2014 (UTC)[reply]

Sorry, I don't understand how your reply resolves my question. Are you saying that (255,0,0) and (255,255,255) have the same luminosity? Is this the same as saying that they have the same brightness? 86.167.19.242 (talk) 19:24, 1 July 2014 (UTC)[reply]

Luminosity is pretty much the same as perceived brightness - it's the term the CIE uses when talking about how their standard observer perceives brightness. I'm saying that (255,0,0) and (255,255,255) might not both exist on that diagram. The red corner of the triangle has the same x,y coordinates as the (255,0,0) color, but the point on that plane of equal luminosity may actually be something like (200,0,0) or (300,0,0) which gets limited to (255,0,0) for display. Katie R (talk) 19:59, 1 July 2014 (UTC)[reply]

The first response in this thread, above, stated that "The corner points have [RGB] coordinates [255 0 0] [0 255 0] and [0 0 255]". I have been assuming that this information was correct. 86.167.19.242 (talk) 20:44, 1 July 2014 (UTC)[reply]

The animated diagram presents the only real color space that your screen can show. Identify the one bright spot that is not rotating. That is the (255,255,255) white point. The 3-D array is rotating about the "greys" axis from the white point to black (0,0,0). Looking along that axis towards the origin you see the rotating triangle of [RGB] points. We can speak of an analytical brightness variation only along that greys axis. Surfaces of constant perceptual brightness (PB) cut across the axis. The corner coordinates [RGB] need not lie on exactly the same PB plane and certainly do not lie on the same PB plane as the (255,255,255) white point. However the CIE 1931 color space and RGB triangles drawn on it are 2-D representations that hide the PB dimension (greys axis) that disappears "into the paper". 84.209.89.214 (talk) 00:07, 2 July 2014 (UTC)[reply]

The two-dimensional chromaticity diagram is a projection of the 3D color space, not a slice through it. Each point on the 2D diagram represents a line through the origin in the 3D space, not a point in the 3D space. The line through the origin consists of all possible brightnesses of a particular color (hue and saturation). The RGB values (1,0,0), (2,0,0), ..., (255,0,0) all map to the same point in the 2D diagram (one of the vertices of the triangle). Likewise the RGB values (1,1,1), ..., (255,255,255) all map to the same point (the "white point"). The white point is in the interior of the triangle, but it doesn't have to be at any of the centers of the triangle, and generally it isn't. You can project the 3D space into 2D in many different ways, and depending on which one you pick, the white point will be in a different location relative to the vertices. But in every projection, the same colors are inside the triangle and the same colors are outside. -- BenRG (talk) 02:34, 2 July 2014 (UTC)[reply]

July 1

Superconductor critical temperature graph

What do the markers' shapes and colours mean, and what is FeAs's T_c?

I would like to redraw File:Sc_history.gif to address the misleading axes (the year axis before 1980, and temperature axis above 50 K are compressed).

Could anyone familiar with the subject please tell me what the colours and shapes of the markers for each substance denote? I tried searching for a legend of the graphic online but couldn't find anything. It's no longer available at the original US government site.

Secondly, FeAs appears under 50 K in the top part of the graph, yet doesn't appear in the bottom part (which is under 50 K), so what is its critical temperature? Iron-based_superconductor lists many FeAs compounds but no plain FeAs.

Thanks, cmɢʟee⎆τaʟκ 19:17, 1 July 2014 (UTC)[reply]

Not an answer, but rather a suggestion: If you redo that chart, I'd take the chemical formulas off the graph and place them in a legend, instead, and just put a number in place of each on the graph. This will make the graph less busy and easier to read. Also, ideally the legend would have links to the articles on each chemical. StuRat (talk) 23:30, 1 July 2014 (UTC)[reply]

..."easier to read" is often in the eye of the beholder. Replacing all the formulas with numbers means that at a single glance it is impossible to identify important compounds or chemical families. Someone wanting that sort of basic information would have to constantly shift their focus from the graph to the legend and back again. (Note, as well, that the "formulas" already present are, in many cases, abbreviated; for example, the XBaCuO and XCaCuO compounds are most assuredly not actually present in anything like 1:1:1:1 quantity.) Stripping out too much information can cause as much confusion as putting too much in.

Arguably, one might be able to label the families of compounds in some cases (the blue diamonds are all YBCO-related structures, for instance) and add smaller notations for the individual family members, but there's limited gains to be made there. Some of the 'families' are pretty tenuously related. TenOfAllTrades(talk) 07:58, 2 July 2014 (UTC)[reply]

I'd love to see the original legend for the categories. As I note above, the blue diamonds are YBCO/LBCO-related compounds. The dark red triangles are "3D"-carbon compounds (conjugates to carbon nanotubes or buckyballs, or diamond), the black triangles are "2D"-carbon compounds (intercalated graphite structures). The red circles seem to be mostly metals and simple binary compounds...except for the ones that aren't(?) The red squares are..."weird-ass actinide compounds"? Note that FeAs doesn't likely refer to a straight-up "iron arsenide" binary compound; presumably it is a catch-all for the ferropnictide [FeAs] layered structure, of which the best have (as you've seen in the linked article) critical temps just above 50 K.

As for adjusting the vertical and horizontal scales, do be careful. You can linearize the vertical scale without too much harm if you're willing to accept a much taller figure; it works well if the point you want to convey is that the YBCO compounds were an astonishing leap forward in the field. If you try to keep the figure the same height, though, you squish together all the lower-Tc points. Similar crowding problems arise if you try to linearize the date axis. There are only eight points in the eighty years (one point per decade) between 1900 and 1980, whereas there are nearly thirty points in the subsequent thirty (almost one point per year). If the point you want to make is that the field was relatively quiet until the mid-1980s, that's fine; if you want the reader to be able to read approximate date and Tc information for particular compounds or classes...then completely linear date and Tc scales may not be as effective. TenOfAllTrades(talk) 07:58, 2 July 2014 (UTC)[reply]

Looks like FeAs is ~54K, according to the introduction of [2].

I would suggest trying out a semilog plot format for the Tc, since temperature practically wants a log before it anyway. Also a cool aspect of that plot is that you could have room temperature taunt the reader from the top of the graph. Wnt (talk) 14:45, 2 July 2014 (UTC)[reply]

I second that suggestion for a semilog plot. This is a far more natural way to squeeze this information into a graph, compared to the current cut axes. The jumps in the axes essentially hide what the graph is trying to communicate, which is the progression in time. Crowding can be dealt with via fine lines from data points to the individual labels. —Quondum 16:13, 2 July 2014 (UTC)[reply]

I agree (I almost suggested this myself). I'd also like to see the temperature of dry ice on there, as that will make those superconductors accessible for home experiments. StuRat (talk) 16:19, 2 July 2014 (UTC)[reply]

That may be a bit busy on a semilog graph - remember, from 1 K to 150 K is 2⁷ and it's only 2¹ to get all the way to room temperature. So on the graph it will look like they're just about there already. Wnt (talk) 05:34, 3 July 2014 (UTC)[reply]

Plastic in the Sun

I live in the Mojave Desert. I regularly find old plastic soda and water bottles out in the sand. Often, the bottles are so thin and brittle that the side facing up (in the sunlight) turns to dust when you touch it. This is, to me, degraded plastic. However, I am strongly into recycling and one common claim that I've read (and I use in my writings) is that it takes about 500 years for plastic to degrade. I know that these soda bottles are not anywhere near 500 years old. So, is this dust state of plastic not considered degraded plastic? If it is degraded, what is the justification for the standard "500 year" time for plastic degradation? I want to sound as though I have some knowledge of the matter because I'm sure others around here have seen plastic turned to dust as well. — Preceding unsigned comment added by 209.149.113.71 (talk) 19:54, 1 July 2014 (UTC)[reply]

See the articles Biodegradeable and Biodegradable plastic for information. 84.209.89.214 (talk) 22:57, 1 July 2014 (UTC)[reply]

The UV light causes this degradation in polymers such as plastics and rubber, unless they take precautions, such as adding dye to absorb the UV. This is why, incidentally, they quickly stopped making white rubber tires, as they rapidly degraded in sunlight, too. So, the 500 year time frame is for buried plastics, kept safe from UV light. StuRat (talk) 23:26, 1 July 2014 (UTC)[reply]

Plastics degrade at differing rates depending on the composition of the material and on the environment it is in, such as exposure to UV. Some contain stabilizers to resist UV, others do not. The book "Green plastics" says (p53) that some polyolefins basically do not degrade, while more recently biodegradable plastics have been introduced which break down after use via the action of moisture, daylight, heat or biological activity. But I have seen tables which imply that it is bad to use plastic because it takes 500 uers to break down, without considering the composition and the environment it is exposed to. Edison (talk) 02:32, 2 July 2014 (UTC)[reply]

I was too lazy to look it up but certainly "turning to dust" is not the same as degradation; see microbeads. :( Some of the "biodegradable" plastics of the past simply broke up into fibers. Of course, plastic will still degrade faster in the sun, while even newspapers might remain readable in landfills on a paleontological time scale. Wnt (talk) 14:37, 2 July 2014 (UTC)[reply]

YES. I could take a new plastic bottle and run it through a shredder a few times, but it would not be decomposed, just broken into little pieces. As with microbeads, these small particles can still be potentially harmful. Though some depolymerization may occur in the desert sun over a few years, those small particles are still plastic, and in some ways even more harmful, since they can be easily dispersed and cannot be picked up and recycled the way an intact bottle can. I'd encourage the OP to tell friends and neighbors that picking up bottles before they disintegrate is the best option for avoiding environmental contamination. See also Plastic_particle_water_pollution and Microplastics. Most of the documented damage is in marine environments, but remember everything eventually gets washed to the sea. SemanticMantis (talk) 14:57, 2 July 2014 (UTC)[reply]

Most Plastic is actually brittle in its raw form. That was a major problem with early plastic like Bakelite (1907). Today Plasticizers are used widely to put it in the state we are so familiar with that we take it for its oiginal state. Unfortunately these additives evapurate or degenetate rather fast over 20 - 30 years and much faster under exposure of Light, especially ultraviolet wavelength. So actually plastic "degenerates" much faster in 20-30 years. The 500 years are needed to decompose plastic completely. --Kharon (talk) 20:56, 2 July 2014 (UTC)[reply]

The brittle plastics are thermoset plastics. Thermoplastics, on the other hand, despite the similar name, are soft and flexible at a certain temperature (typically room temperature), how we normally think of plastics. StuRat (talk) 21:19, 2 July 2014 (UTC)[reply]

Good distinction. The problem that apparently none of us want to invest time in researching is: what exactly constitutes decomposition of a plastic? Small pieces of e.g. HDPE (commonly used for bottles) are still HDPE, and that can cause problems in both natural ecosystems, and in human health. When is HDPE no longer HDPE? It sounds like a koan, but that is the type of question we need to research to fully answer this question. I'm no good a this kind of detailed chemistry, but I suspect the long-chain molecules must be cut/broken until the constituent ingredients no longer have the physical and chemical properties of the parent plastic. UV light can apparently break such bonds, but that is similar to dilution -- how many drops of water must I add to my coca cola before it no longer coca cola? I think in the OP's description of bottles turning to dust some chains are broken, but many more remain. SemanticMantis (talk) 21:41, 2 July 2014 (UTC)[reply]

Thanks for all the comments. This sent me off to do more research. Water bottles are normally HDPE, which degrades quickly in UV light, and still degrades quickly without UV light. The 500 year statement is the average time for LDPE plastic to degrade. I found a nice chart that relates the recycle number to breakdown estimates. I don't feel that this negates my work in trying to limit plastic use. It helps focus on bad plastics and worse plastics. The site with the chart is http://www.brighthub.com/environment/green-living/articles/107380.aspx 209.149.113.71 (talk) 20:09, 3 July 2014 (UTC)[reply]

July 2

Enthalpy of formation

Is it possible to calculate a vapoural heat of formation of when IR spectroscopic data is the only experimental data available? Plasmic Physics (talk) 00:23, 2 July 2014 (UTC)[reply]

Maybe, but I don't see how that would be possible. For measuring heat of formation, calorimetry is the normal technique. 24.5.122.13 (talk) 01:11, 2 July 2014 (UTC)[reply]

You mean if the ONLY thing you know is a single ir spectrum? No. But IR does capture TEMPERATURE information - I hope that is clear to you. So, theoretically, there are probably some gas phase reactions which have sufficiently strong and sufficiently sensitive peaks in the IR so that you could determine the initial and final composition and temperatures. Generally, IR is only semi-quantitative, meaning that its good for composition to 5% (optimistically) and maybe ½% in very good circumstances. This means that IR would be a poor method if you wanted accuracy to 1% or better. (And this ignores the issue, which I am not competent to deal with of the accuracy of the temperature measurement using IR. I know that IR guns are commonly used to measure temp., and I know they can be calibrated to within a couple of degrees, but I don't know how much more accurate a calibrated lab IR spectrometer can be (since a couple of degrees is probably not good enough).) Could you get "an answer" ? Sure. How accurate would it be? Depends, but without a lot of calibrating, I doubt it would be more than plus or minus a factor of 10 of the right Hf...maybe a factor of +/- 5X ... Your question basically doesn't give sufficient context for an answer. A lab IR uses IR to excite various modes, while temperature is all about the existing modes (or black-body radiation emission). Meaning if you want to see if something in a room is giving off light, you don't turn on more lights, you turn all the lights off... — Preceding unsigned comment added by 173.189.75.163 (talk) 15:54, 2 July 2014 (UTC)[reply]

What a shame, thanks though. Plasmic Physics (talk) 04:23, 3 July 2014 (UTC)[reply]

Will Ebola become a global pandemic?

There are about 600 Ebola cases in West Africa and it seems that the number of cases is doubling every month. At this rate, in about a year there could be a million cases and in two years time there could be more than a billion cases. With an incubation period of up to 21 days, what is going to stop this virus from getting to Asia, the US or Europe? Count Iblis (talk) 18:11, 2 July 2014 (UTC)[reply]

Our Ebola article states that "The potential for widespread EVD epidemics is considered low due to the high case-fatality rate, the rapidity of demise of patients, and the often remote areas where infections occur". It also says that "Due to lack of proper equipment and hygienic practices, large-scale epidemics occur mostly in poor, isolated areas without modern hospitals or well-educated medical staff". Your 'doubling every month' prediction (which isn't actually borne out by the latest data - see 2014 West Africa Ebola outbreak#Temporal evolution) is predicated on the same lack of appropriate medical care occurring elsewhere. AndyTheGrump (talk) 18:25, 2 July 2014 (UTC)[reply]

As Andy says, Ebola epidemics are usually more or less self-contained because of the rapidity of the death of patients, and because the epidemics tend to occur in isolated areas, where the patients are unlikely to go to the US, Europe, or Asia. If the patients come in contact with visitors from an industrial country who then return home and develop Ebola, they will be treated in isolation units to control the spread. Influenza is far more of a pandemic threat than Ebola or similar hemorrhagic fevers. Get your flu shot this coming fall. (If you are in the Southern Hemisphere and haven't gotten your flu shot yet, it isn't too late.) Robert McClenon (talk) 18:54, 2 July 2014 (UTC)[reply]

Yes. Ebola kills hundreds per year and may expand to thousands. Flu kills hundreds of thousands and has sometimes expanded to millions. Our OP is relying on news to guide action. A disease makes news when it is interesting, thus odd, thus small. Newspeople aren't in the business of guding action. Jim.henderson (talk) 19:06, 2 July 2014 (UTC)[reply]

Also note that increasing at a rate, were it to continue, which would rapidly infect the entire human population, is a feature of the early stages of many diseases or disease strains. That rate of increase inevitable slows down, as it moves out of the most vulnerable populations, survivors develop immunity, and people start taking precautions, like breathing masks, in the case of SARS. Of course, we should avoid getting lazy and just assuming it will slow down, but rather study it and actively find ways to slow it down. StuRat (talk) 19:11, 2 July 2014 (UTC)[reply]

See Richard II Act II Scene 1:

John of Gaunt:

...His rash fierce blaze of riot cannot last,

For violent fires soon burn out themselves;

Small showers last long, but sudden storms are short;

He tires betimes that spurs too fast betimes;

With eager feeding food doth choke the feeder:

Light vanity, insatiate cormorant,

Consuming means, soon preys upon itself.

μηδείς (talk) 19:30, 2 July 2014 (UTC)[reply]

(Reminding all of WP:NOTCRYSTAL) -- the question in the header cannot be answered with references. I will not answer this question, but instead provide references relevant to the topic.

If OP would like reliable information on the current Ebola situation, he should look at WP:RS such as the USA's CDC page on the topic [3], or the UK's HPA [4]. If you prefer an NGO perspective, check out info from Doctors without borders here [5], [6]

Since this is "breaking news" in the field of epidemiology, there are very few peer-reviewed papers published on the current outbreak, and reports from those agencies are probably the best sources. If you want to see some of the science of Ebola-specific control and mitigation, here's a paper on an Ebola vaccine and vaccination strategies [7]. For the general topic of control strategies for multiple outbreaks, see this nice paper on epidemic control in a more disease-agnostic sense [8]. SemanticMantis (talk) 19:53, 2 July 2014 (UTC)[reply]

Hygiene, communication and medicine are advanced enough today to contain any epidemic virus that spreads tru physical contact and/or exchange of body fluids. Only airborne contagious Vira have a high potential to cause a Global pandemic. Thus not Ebola. --Kharon (talk) 21:24, 2 July 2014 (UTC)[reply]

"Viruses" if you're writing in English, "virus" (plural) if you're writing in Latin. "Vira" is entirely beyond the pale, as there is no Latin declension that has "-us" in the singular and "-a" in the plural. "Virii" (the most common error) has at least the excuse of being plausible. Tevildo (talk) 21:59, 2 July 2014 (UTC)[reply]

Virus isn't originally Latin. It is originally Greek. I don't know Greek plurals. However, Tevildo is right about the Latin. If virus is fully naturalized in Latin, it is fifth declension, and its plural is virus. So if it is fully naturalized in English, and it is, its plural is viruses. Any other plural is just a misguided attempt to use a classical language without understanding the classical language. Fortunately, this has not been litigated, so that no one needs to be warned of discretionary sanctions. But do not edit war over the plural. It is viruses, unless the rest of the article is in Latin. Robert McClenon (talk) 03:22, 3 July 2014 (UTC)[reply]

No and no. Vīrus is not from Greek (how could it be? - classical Greek had lost its w sound before the Roman period). It's a native Latin word. The equivalent Greek word is īos, both the Latin and Greek forms representing regular development from something like like *wīsos. And it's not fifth declension. The genitive singular is documented as vīrī, making it second declension. In fact it's an almost unique example of a second declension neuter noun in -us: nominative and accusative both vīrus, dative and ablative apparently not found, and more relevant to the current question, it never occurs in the plural. --rossb (talk) 16:14, 3 July 2014 (UTC)[reply]

To answer the original question, it's not as if the locals are doing nothing; in Liberia, the legislature appropriated a huge portion of the national budget to fight it (if I remember rightly), and although the news outlets currently aren't talking as much about Ebola as they were a few months ago, it still sometimes makes the headlines; this story, for example, is on the main page of the Heritage website, while the Liberian Observer hasn't been running any above-the-fold stories about it in the last few days. A big contributor to the spread of such a disease is ignorance — people who are aware of it will be more careful, and that alone will reduce transmission rates, especially with a disease like this that requires some sort of contact with a patient. Nyttend (talk) 02:06, 3 July 2014 (UTC)[reply]

Air conditioner settings

I have a window air conditioner that has only two dials. One is a dial that can be turned from max cooling (7) to min cooling (1). The other dial has four settings, labeled "low cool", "high cool", "low fan", and "high fan". What is the difference between "low cool" and "high cool" (the manual is slim and gives no useful information on this)?

One of my friends argues that the words "low" and "high" in "low cool" and "high cool" refers to the fan, so that compressor usage is the same in both settings, with only fan speed differing. In other words, he argues that the settings mean:

"low cool" - compressor on; low fan speed
"high cool" - compressor on; high fan speed
"low fan" - compressor off; low fan speed
"high fan" - compressor off; high fan speed

Another of my friends argues that the words "low" and "high" in "low cool" and "high cool" refers to compressor usage, and that "high cool" uses the compressor more than "low cool" does. In other words, he argues that the settings mean:

"low cool" - compressor on less; fan off
"high cool" - compressor on more; fan off
"low fan" - compressor off; low fan speed
"high fan" - compressor off; high fan speed

Who is right?

—SeekingAnswers (reply) 21:54, 2 July 2014 (UTC)[reply]

We can't predict the response of an unknown model of air conditioner. You could specify the model, but I don't understand why you can't just listen to what the fan sounds like (surely it is more than loud enough, and even a deaf person would feel it blowing and also feel the vibration of the compressor) Wnt (talk) 22:14, 2 July 2014 (UTC)[reply]

Re: "We can't predict the response of an unknown model of air conditioner." Googling suggests these setting labels are fairly standard for many air conditioners. There would be a standard meaning to them, then, no? And no matter what the setting, there is sound, there is air, and there is vibration, so I can't tell the difference between them that way. —SeekingAnswers (reply) 22:20, 2 July 2014 (UTC)[reply]

(e/c) Top option. The compressor is only 'On' or 'Off'; the fan has 2 speeds in this case. (In my case, it set so that when the compressor is on, the fan is high, and when the compressor is off, the fan is low; for circulation, air filtering and even distribution of temp/humidity). This link provides some general info: [9] (A web search can easily find plenty of other links). BTW, the fan doesn't use much electricity, especially when compared to the compressor. —71.20.250.51 (talk) 22:26, 2 July 2014 (UTC)[reply]

Agreed on top option. However, on a car, I might suspect that "High cool" would mean recirculate mode, while "Low cool" means fresh air. But, I believe most window A/C units only have recirc mode, as fresh air would require screens/filters, etc. StuRat (talk) 02:23, 3 July 2014 (UTC)[reply]

Okay, after changing around the settings and listening carefully as User:Wnt suggested, I agree with User:71.20.250.51 and User:StuRat that top option is correct: when set to "high cool", I can hear the compressor periodically automatically turning off, presumably due to the thermostat detecting that it has reached the desired temperature set by the other dial, at which point it sounds exactly like "high fan". But now I have a new question. When initially turning the air conditioner on, the manual recommends "high cool" to cool down the room to the desired temperature as quickly as possible. My question, however, is about what to do once the room cool downs to the desired temperature: given that the compressor automatically turns off when it detects that the desired temperature has been reached, at that point, would it be more energy-efficient / cheaper for my electricity bill to leave the air conditioner on "high cool" or to switch to "low cool"? First of all, everyone agrees that the compressor comes on or off automatically based on the thermostat, and that the compressor costs far more electricity than the fan. However, that still leads my friends to different conclusions:

Friend #1 argues that once you only want to maintain a temperature rather than cool further, "high cool" is more energy-efficient and cheaper than "low cool", because the fan uses so little electricity in comparison to the compressor that all that matters is how often the compressor comes on. He argues that "high cool", with the fan running at high speed, will do more to circulate the cool air, therefore doing more to maintain the cool temperature, and therefore causing the compressor to automatically turn on less often and thereby saving more electricity.

Friend #2 argues that once you only want to maintain a temperature rather than cool further, "low cool" is more energy-efficient and cheaper than "high cool", because the fan is running at a lower speed, which obviously consumes less electricity. He rejects friend #1's argument about the fan running at high speed doing anything to maintain a cool temperature to cause the compressor to turn on less often. In other words, friend #2 believes how often the compressor automatically turns on/off is entirely unaffected by fan speed.

Friend #3 agrees with friend #2 that once you only want to maintain a temperature rather than cool further, "low cool" is more energy-efficient and cheaper than "high cool". However, he differs from friend #2 in also accepting friend #1's argument that the fan running at high speed will cause the compressor to turn on less often -- but he ultimately still agrees with friend #2 that "low cool" is more energy-efficient and cheaper than "high cool" because he believes the effect of greater circulation is very small and he does not believe that the compressor will turn on less often enough to compensate for the higher cost from running the fan at high speed.

Now who is right among these 3 viewpoints?

—SeekingAnswers (reply) 04:07, 3 July 2014 (UTC)[reply]

It depends on the size and layout of your room. In a small square room, with the A/C in the center of one wall, and nothing in the way, the low fan is probably adequate. But in a large, irregular shaped room with obstacles, like a big-screen TV in the center, more fan speed might be required to distribute the "coolth". I've even supplemented the anemic fan in my window A/C unit with a box fan blowing across the vents.

I'd try "low", and if it isn't getting the job done, then switch to "high". If that still results in a cold spot by the A/C and it being hot in the rest of the room, then you might want to consider my solution. StuRat (talk) 04:29, 3 July 2014 (UTC)[reply]

My experience based on a lot of motels with that sort of air conditioner is that "high" is usually too damn noisy, and that's enough reason to prefer "low" if possible. --50.100.189.160 (talk) 19:47, 3 July 2014 (UTC)[reply]

I think this depends on where the thermostat actually is (the part taking the measurement) and if it is drawing in outside air, the temperature of the air. If the air outside is hotter and being drawn in, the more you have the fan on the more you're drawing in the heat from outside. If the air is from inside, the metal is probably still transmitting more heat in from outside when more air is blowing through it but I doubt it is much. Now when the air passes over the compressor, it warms it up, and a warmer compressor should be able to cool by 1 degree using less energy than a cold compressor, per Carnot cycle. OTOH who knows what really is going on inside it? But if the thermostat measures the exact temperature of the compressor gas then the compressor will be the same temperature when on no matter how much air is passing over it; it just will be warmer in the room when the setting is to a lower fan. (I doubt that's the case, but again, who really knows?) That said, the choice of fan setting for many might have more to do with the amount of noise it produces (some of us don't even use those things because the heat is less annoying), or what it feels like to stand directly in front of it, or whatever. Wnt (talk) 04:38, 3 July 2014 (UTC)[reply]

While the compressor is running, its efficiency depends (in part) on how many air molecules contact the heat exchanger (coils w/fins, like a car's radiator) –which, of course, depends on the fan speed. So, while the compressor is running, the fan should be 'high'. I'd suggest finding the manual for your specific thermostat model, which is probably online if you don't have a copy. There might be an automatic mode where the fan continuously runs at low speed and switches to high speed when the compressor comes on. Something like 'Auto low'; ('Auto high' would have the fan always on high). The "best" setting depends on a lot of things. For example, if you live in a very hot location (e.g. Phoenix) and you have an older home with non-insulated ducts in a very hot attic, then having the fan run continuously would not be recommended -at least not during mid-day. However, when the compressor turns off, the heat exchanger is still cold (and probably has some ice on it) -and if the fan shuts off at the same time, then this "thermal mass" is wasted, and literally goes down the drain as the ice melts. This effect only lasts for a few (5~10?) minutes with the fan on, so efficiency also depends on how often the compressor turns on/off. —I hope this helps, ~E:71.20.250.51 (talk) 05:35, 3 July 2014 (UTC)[reply]

Iron as essential nutrient, rust, and water pipes

Two parts to this question:

If iron is an essential nutrient, does that mean people can just eat things like iron bolts? Yet no one eats iron bolts, and eating pieces of iron instinctively seems to me to be a very bad and unhealthy idea. Similarly, rust is just iron and oxygen, the former of which is an essential nutrient and the latter which we need to breathe. So, again, wouldn't that mean it would be a good idea to eat rust? But again, no one eats rust, and eating rust instinctively seems to me to be a very bad and unhealthy idea.

If water pipes are made of iron, doesn't that mean they would rust? And wouldn't that mean our drinking water is full of rust? Wouldn't that bad for people's health, if indeed the answer to the previous question is that eating rust is a bad/unhealthy idea?

—SeekingAnswers (reply) 22:09, 2 July 2014 (UTC)[reply]

One could get dietary iron by eating iron or rust in bulk. But it will likely damage the person. Consult your doctor if you need more iron or not. Some people need to consume less iron. But you don't need that much that you need a bolt's worth. If you get a breakfast cereal wheat biscuit and run a magnet through it you should be able to extract the iron added by the manufacturer. Too much iron degrades the water quality, leading to bad taste and staining. Graeme Bartlett (talk) 22:59, 2 July 2014 (UTC)[reply]

(1) Generally, eating pieces of metallic iron is a bad idea because of the physical damage they can cause to interior organs. However, some prepared foods contain "reduced iron", which is essentially just very finely powdered iron that dissolves rapidly in stomach acid.

(2) Yes, steel water pipes DO rust (sometimes pretty rapidly, if used for very hot water), so your drinking water MAY be full of rust. This, however, does NOT impact people's health, because the rust particles are very small and dissolve in the stomach -- but it DOES impact your home repair bill when the pipe eventually rusts right through and floods your whole house with scalding hot water (as happened to me on one occasion). 24.5.122.13 (talk) 23:05, 2 July 2014 (UTC)[reply]

I don't know how common the practice actually was at the time, but at least in the "Law of the Land" episode of Dr. Quinn, Medicine Woman, Dr. Quinn tells someone suffering from iron-deficiency anemia to boil rusty nails in water and then drink the rusty water.[10] Red Act (talk) 00:36, 3 July 2014 (UTC)[reply]

Note that an Iron overload can be quite dangerous, so eating an entire iron bolt could be very bad for that reason, too. Also, an iron bolt probably contains additives that are toxic. And if you've every tasted rust, you probably spit it right back out. It tastes horrid.

You might also be interested in pica (disorder)#Causes, a condition in which people eat strange things, like bolts, at times due to a deficiency in some mineral like iron.

As for pipes rusting, they often accumulate scale (minerals that come out of solution from the water and stick to the pipes), so that can protect the iron from the water and slow down rusting. But, if your water is shut off, when it comes back on you may very well notice a rusty color for a bit. StuRat (talk) 01:09, 3 July 2014 (UTC)[reply]

The Iron poisoning article talks about how much iron you can eat before it has toxic effects. From the numbers that article gives, it sounds like even a rather small iron bolt, finely ground up to aid in digestion and to avoid poking a hole in your throat or something, would be too much to safely eat at once. Monsieur Mangetout ate a lot of bolts during his lifetime, but he was a rather special case who shouldn't be emulated. Please don't eat bolts, kids.

As much of iron goes to blood, blood is a good nutritional source, or for the more Mosaic palette, liver (food) provides a more solid relative. I dare say even in the wild west they must have had liver now and then when they shot something. Wnt (talk) 05:46, 3 July 2014 (UTC)[reply]

As strange as it may seem, placing a piece of iron in cooking vessels does actually help fight iron deficiency. See this article about an iron fish used in Cambodia for that purpose [11]. --Xuxl (talk) 08:22, 3 July 2014 (UTC)[reply]

Yeah, cast-iron cookware has been known for some time to contribute nutritionally significant quantities of iron to food, which is why people thought to create the lucky iron fish to provide the same benefit. Red Act (talk) 08:52, 3 July 2014 (UTC)[reply]

Why the hell haven't bacteria evolved to eat plastic by now anyway?

The question above about plastic degradation and plastic particle water pollution by microplastics reminds me of an old mystery: why haven't the bacteria evolved to eat this stuff? I mean, polyethylene is basically fatty acid, minus the ends. And living organisms routinely chow down fatty acids two carbons at a time (beta oxidation) for variable distances; there's no special mechanism for just a certain length (well, OK, I'm sure there is if you look hard enough but it's not the main metabolic pathway). Discarded in every possible environment, all the necessary nutrients are close at hand to at least some of the pieces of plastic. I've been expecting to see news reports of bacteria dissolving plastic in landfills for decades now, and it dawns on me suddenly that I'm still waiting. Why? Wnt (talk) 22:40, 2 July 2014 (UTC)[reply]

You may be interested in Nylon-eating bacteria, although it's actually byproducts of nylon manufacture that that bacterium eats. Red Act (talk) 22:50, 2 July 2014 (UTC)[reply]

You are probably more interested in [12]. EllenCT (talk) 22:54, 2 July 2014 (UTC)[reply]

There are plenty of search examples for "plastic eating bacteria", many referencing: Nature —71.20.250.51 (talk) 23:02, 2 July 2014 (UTC)[reply]

That "minus the ends" bit is pretty critical. Polyethylene in the form of plastic isn't water-soluble, and beta oxidation, like almost every chemical reaction, takes place in solution. In order to digest it, a bacterium would first need to evolve a way to dissolve it. --Carnildo (talk) 00:11, 3 July 2014 (UTC)[reply]

Hmmmm... there's some merit to this, although I'd think that in some sense the plastic is already dissolved in plasticizer, I'm getting the impression that truly dissolving polyethylene requires elevated temperatures. [13] Though I know that polyethylene terephthalate (bottle cap) doesn't need to be all that warm to dissolve into olive oil (it's amazing what I've had to resort to during power outages). Bacteria clearly can form biofilm on fat globules and somehow use them for energy; but the devil may indeed be in the details. To begin with I should admit that upon RTFA I note that beta oxidation of lipids over 22 carbons actually has to take place in peroxisomes for some reason (which may be a clue?). But also, there's the question of whether a fatty acid has to get into the cell before beta-oxidation in order to be used for energy. It doesn't seem like that ought to be an inflexible requirement, but it is hard to picture how to separate the cycle from the external environment otherwise. And for all the marvels of bacterial design I have to admit I've never read about one with teeth to bite off and chew little bits of plastic. Wnt (talk) 05:24, 3 July 2014 (UTC)[reply]

Maybe they already have, and we just don't know it yet? There are a lot of landfills, and prospecting is slow and tedious. Granted, this is "just" a science fair project, and I haven't looked yet for follow up since 2008, but this kid thinks he's found a bacteria (from a landfill) that can speed plastic degradation [14] [15]. Also, recall that it took fungi a long time to figure out how to eat dead wood, that's why we had the carboniferous era. So like you, I've expected to hear more about this by now, but I also think such a discovery and serious scientific investigation will take place long after bacteria have started munching our plastic bags. SemanticMantis (talk) 16:37, 3 July 2014 (UTC)[reply]

July 3

Mach's Principle

I am wondering if there has been an experimental confirmation of Mach principle? I am wondering also it such an experiment makes sense? Well, one of the formulations of Mach principle is as follows: "Events in local inertial frame are dependent on mass distribution of distant stars."

A few questions: how distant is "distant?" Can it be defined in terms of the parsecs? Ten parsecs? One hundred? A kilo parsec or what? Where does the influence end?

Our Sun is located on the periphery of the Galaxy, off center, thus it can be surmised that the gravitational pull of the "distant stars" that determine local inertial frames should be one sided to an extent. Can it be verified?

Imagine a plank rotating around its center, sort of a carrying pole. The two shoulders of the plank must be absolutely symmetrical of course. While rotating they will generate centrifugal force. Provided the angular velocity is stable, can it be measured if the force is absolutely the same over the 360 degrees of circumference? Or the pull toward the center of our Galaxy is stronger than in other directions? Thanks, --AboutFace 22 (talk) 01:24, 3 July 2014 (UTC)[reply]

That plank length (pardon the pun) would have to be many light years long to have any measurable effect of being pulled more towards the galactic center when on the side closer to it. However, closer stars might have an effect on somewhat smaller scales, enough to noticeably perturb Oort Cloud objects, for example. StuRat (talk) 02:29, 3 July 2014 (UTC)[reply]

StuRat, I am at a loss. I cannot understand what you are talking about. What does Plank Length have to do with my question? --AboutFace 22 (talk) 02:39, 3 July 2014 (UTC)[reply]

That part was a pun, related to your example of a rotating plank. The serious part followed that. StuRat (talk) 03:10, 3 July 2014 (UTC)[reply]

Mach's principle by itself is really too vague to be testable. From the article, "... because the principle is so vague, many distinct statements can be (and have been) made which would qualify as a Mach principle, and some of these are false." On the other hand, general relativity was to a certain extent inspired by Mach's principle, although it isn't 100% compatible with it, and general relativity certainly is precise enough to be testable; see Tests of general relativity. Red Act (talk) 02:56, 3 July 2014 (UTC)[reply]

StuRat, thanks. I must have been tired last night, I did not notice the pun when I typed my question. I guess Planck and plank are separated by many convolutions in my brain. Anyhow, RedAct says Mach's Principle is too vague to be tested, so what? What about the centrifugal force? Is it caused by the whole mass of the Universe or not? --AboutFace 22 (talk) 13:39, 3 July 2014 (UTC)[reply]

The only way you could answer that question scientifically is by extracting a numerical prediction from Mach's principle that's different from a prediction of general relativity, but Mach's principle is too vague for that. At best you might "predict" something totally different from GR, in which case it's probably ruled out by existing data.

You can alternately ask "how Machian" general relativity or some rival theory is, philosophically. People have argued about this for the last century. On the one hand, in GR the gravitational field is spacetime and does completely determine inertial behavior, and massive objects are sources of the field, at least in the conventional terminology. On the other hand in the Kerr solution for a rotating massive object, the object rotates relative to the vacuum despite being the only object in the universe, which seems quite non-Machian.

Brans–Dicke gravitation may still be consistent with experiment, and I seem to recall that it was promoted as more Machian than GR by its creators. I'm not sure what they meant by that or whether anyone else agreed with them. -- BenRG (talk) 15:43, 3 July 2014 (UTC)[reply]

Flush survivors

In general, which of the following will survive a flush down the toilet if healthy before the flush?

(Before you animal lovers get up in arms, the question is hypothetical.)

—SeekingAnswers (reply) 05:23, 3 July 2014 (UTC)[reply]

Rats will drown, and goldfish would suffocate from toxic methane gas. Some insects might survive, though, but I'm not sure about that. 24.5.122.13 (talk) 05:31, 3 July 2014 (UTC)[reply]

Flushing is a brief, transient event. What would really matter is where the results of a flush end up.Sewerage systems vary a lot from place to place. Some would be not much different from open flowing water. Some would be far worse. HiLo48 (talk) 05:40, 3 July 2014 (UTC)[reply]

My thought was that a rat ought not to go gently into that good night. Fortunately, through the use of YouTube one can obtain objective data, with a certain risk of fraud. [16] seemed persuasive enough that the second flush is enough to put a mousy-looking "rat" down the hole - that I never expected. On the other hand, sometimes the rat makes it the other way. [17] According to the Daily Mirror even a puppy can survive the trip, though I don't think it would do well in the sewers. (With alligators YMMV) Wnt (talk) 05:58, 3 July 2014 (UTC)[reply]

@@ Line 407: / Line 407: @@
 :::::The brittle plastics are [[thermoset plastic]]s.  [[Thermoplastic]]s, on the other hand, despite the similar name, are soft and flexible at a certain temperature (typically room temperature), how we normally think of plastics. [[User:StuRat|StuRat]] ([[User talk:StuRat|talk]]) 21:19, 2 July 2014 (UTC)
 ::::::Good distinction. The problem that apparently none of us want to invest time in researching is: what ''exactly'' constitutes [[decomposition]] of a plastic? Small pieces of e.g. [[HDPE]] (commonly used for bottles) are still HDPE, and that can cause problems in both natural ecosystems, and in human health. When is HDPE no longer HDPE? It sounds like a [[koan]], but that is the type of question we need to research to fully answer this question. I'm no good a this kind of detailed chemistry, but I suspect the long-chain molecules must be cut/broken until the constituent ingredients no longer have the physical and chemical properties of the parent plastic. UV light can apparently break such bonds, but that is similar to [[dilution]] -- how many drops of water must I add to my coca cola before it no longer coca cola? I think in the OP's description of bottles turning to dust some chains are broken, but many more remain. [[User:SemanticMantis|SemanticMantis]] ([[User talk:SemanticMantis|talk]]) 21:41, 2 July 2014 (UTC)
+:Thanks for all the comments. This sent me off to do more research. Water bottles are normally HDPE, which degrades quickly in UV light, and still degrades quickly without UV light. The 500 year statement is the average time for LDPE plastic to degrade. I found a nice chart that relates the recycle number to breakdown estimates. I don't feel that this negates my work in trying to limit plastic use. It helps focus on bad plastics and worse plastics. The site with the chart is http://www.brighthub.com/environment/green-living/articles/107380.aspx [[Special:Contributions/209.149.113.71|209.149.113.71]] ([[User talk:209.149.113.71|talk]]) 20:09, 3 July 2014 (UTC)
 = July 2 =