Wikipedia:Reference desk/Archives/Science/2007 August 3

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August 3

Finite Photons?

Would there be any upper bound on the amount of photons in the universe, and what (extremely vague) order of magnitude would it be? 10^1000, 10^10^10... Each carries some amount of energy so it seems like it should be finite, but the amount of energy they carry can drop lower and lower, is there some lower bound of energy one can carry? Does anything exist that can radiate photons with wavelengths of a galaxy? -- atropos235 ✄ (blah blah, my past) 01:46, 3 August 2007 (UTC)

Protons without electrons that orbit the galaxy will radiate at a very low frequency. Intuitively, I would say that it would be on the order of the size of the orbit. It's a consequence of Maxwell's equations that accelerating charge radiates EM energy. --Tbeatty 03:19, 3 August 2007 (UTC)

I'd just point out that we can't possibly have an upper bound on the number of photons in the whole universe, because as far as we know, the universe could be infinite. Maybe you mean the observable universe. In that case I don't know. --Trovatore 04:44, 3 August 2007 (UTC)

Light coming from near the event horizon of a black hole, or from the very edge of the observable universe can have quite extreme redshift, so quite a low frequency, and so very low energy per photon. I'm not sure if there's a minimum frequency for a photon...possibly that who's wavelength is on the scale of the observable universe? Someguy1221 04:49, 3 August 2007 (UTC)

The absolute temperature of the Cosmic microwave background radiation is known. From this number you can compute the energy density of the radiation, using the Stefan-Boltzmann law. Divide by the mean photon energy of radiation of that temperature to get the number of photons per cubic meter. The age of the universe is also known. Multiplying this age with the velocity of light gives the radius of the observable universe, and then the volume can be computed. Multiply the volume by the photon number density to get the total number of photons in the observable universe. The number of photons from stars and galaxies and black holes etc is relatively small. Bo Jacoby 19:45, 5 August 2007 (UTC).

Latex discoloration

Any ideas as to why my latex gloves often slowly show deep yellow patches after putting them on? The only chemical they commonly encounter is ethanol, although I believe the discoloration appears even without that. Human sweat? 151.152.101.44 06:35, 3 August 2007 (UTC)

This article explains,

If discoloration occurs during use, it is termed staining and may be caused by chemicals from the glove reacting with chemicals secreted by the wearer. For example, carbamate, the least sensitizing of the accelerators used in latex processing, reacts with lactic and uric acid from human perspiration to cause an amber or brown stain. Nicotine from the skin of smokers turns gloves brown, as do copper and iron, excreted to varying degrees through the skin by healthy individuals. Some illnesses and the use of specific medications may also result in glove staining.

Rockpocket 07:22, 3 August 2007 (UTC)

calculation

Gandhiray 08:59, 3 August 2007 (UTC)I am having volume of an Aluminium piece. I want to calculate the weight of this article. How, please advice. VirendraGandhiray 08:59, 3 August 2007 (UTC)

With a Weighing scale? Am I missing something? Capuchin 10:08, 3 August 2007 (UTC)

Ah Yes, I think I am missing something. You look up the density of aluminium in our Aluminium article. Then you multiply the volume that you have by this density to get the mass. Then you apply F=ma using a=g to get the weight. Capuchin 10:49, 3 August 2007 (UTC)

But usually what we describe as weight is really mass (e.g. grams or kilograms). No one is interested in knowing how many Newtons they weigh. Flyguy649 ^talk _contribs 14:25, 3 August 2007 (UTC)

Let me put it in plain English in case the questioner doesn't want the amusing details. You take the volume of the piece in cubic centimetres, multiply that by the density of aluminium which is 2.70, and you get the weight in grams. --Heron 21:25, 4 August 2007 (UTC)

silver plating

I cannot find any reference to the term 'microns' in connection with silver plating (of silverware, cutlery, flatware etc.) Is it a measure of the thickness of the silver plate? Does the higher the number of microns indicate the better quality? Edgbaston1968 12:51, 3 August 2007 (UTC)

See Micrometre.Yes, more is better. -Arch dude 13:07, 3 August 2007 (UTC)

Unless thinness is desired of course --froth^t 15:47, 3 August 2007 (UTC)

Which it wouldn't be, in this case. Aaadddaaammm 00:57, 4 August 2007 (UTC)

It might not be if you had too much money. Silver is expensive and performs worse at the eating utensil-functions than steel. It may one day have been useful as a means to prevent rust (in which case a thin layer would have been sufficient), but nowadays with stainless it just adds to the cost and makes knifes blunt, so it only makes sense as an investment, in other words for people with more money than they need. But then why bother going through the process of silver-plating utensils? You might as well buy a block of silver. In which case, if you really want to use it for a utensil, you might use it for a hammer. In which case it would add to the functionality because silver is heavier. To prevent silver chipping off, it could be steel-plated. So why do we have silver plated steel cutlery and not steel plated silver hammers? A case of showing off, I suppose. DirkvdM 07:55, 4 August 2007 (UTC)

As a eating utensil buyer I can tell you that silver plated cutlery is practically non existant these days - even at the expensive end of the market.87.102.89.203 14:22, 4 August 2007 (UTC)

molecular biology

what are different kind of DNA its structure function & differences

I suggest reading DNA, wikipedia isn't for doing your homework for you and the answer is far too long for a reference desk note. Briefly, if you are doing A level biology (which I'm assuming by the way your question is phrased), you will be looking for DNA or RNA, DNA is a double helix made up of four base pairs, A T G and C, which pair up as "bAtTle star GalaCtica" or "A - T and G - C" it is stored in the nucleus and gives basic coding for the construction of amino acids (i.e. proteins). RNA is a duplicate of one strand of a DNA double helix, which is able to leave the nucleus to enter the endoplasmic reticulum (rough ER to be precise) in order to be translated into such amino acid groups, with a sequence of three letters (say A T G) coding for one particular amino acid. Try Transcription (genetics) and Translation (biology) :) SGGH ^speak! 15:15, 3 August 2007 (UTC)

Heart rate

I was just wondering, is the rest heart rate affecting by body size? Would a broad shouldered 6"5 man in good shape have a resting rate of around 80bpm whereas a slighter man in good shape have a resting beat of 70bpm? Or am I just out of shape having a resting beat of 80bpm? The Heart rate doesn't seem to have this particular info SGGH ^speak! 15:15, 3 August 2007 (UTC)

Across species, heart rate falls as you get bigger. So much so that a humming bird's heart may beat hundreds of times a minute while blue whale's heart may beat only four or five times. So, I'd expect that if there is any difference, and the people are in the same relative shape, that the large person would have a slightly slower heart rate. I don't have a source for this, however. --Cody.Pope 16:55, 3 August 2007 (UTC)

Maybe I'm just unhealthy then, though I read that the a good heart rate for my age group does include 80ish. SGGH ^speak! 18:44, 3 August 2007 (UTC)

I was told by my doctor and nurse (on separate occasions), that anything below 100 bpm is considered normal. Anything above is called tachycardia--SpectrumAnalyser 21:21, 3 August 2007 (UTC)

Dogs and milk/chocolate

Why do dogs get so sick from eating chocolate or drinking milk? Is it a natural defense developed by chocolate milk cow parents? --froth^t 15:45, 3 August 2007 (UTC)

For chocolate: dogs, and other animals, metabolise theobromine more slowly than humans, and thus suffer theobromine poisoning more readily. I dunno about milk; really it's not natural for adult mammals to eat milk, so maybe the question should by why can some humans tolerate it? -- Finlay McWalter | Talk 15:49, 3 August 2007 (UTC)

Lactose intolerance explains how and why (some) adult humans are unusual in their ability to drink milk without adverse effects. Rockpocket 17:21, 3 August 2007 (UTC)

Apparently humans had to develop a tolerance to (cows,goats etc)milk--SpectrumAnalyser 21:24, 3 August 2007 (UTC)

Yea, the dog is probably just lactose intolerant. I feed my cat lactose-free milk, and she does fine (even cats are often lactose intolerant). --Wirbelwindヴィルヴェルヴィント (talk) 22:15, 3 August 2007 (UTC)

• It is rather surprising that people feed their fully-grown cats milk, or fully-grown dogs. There is a trick-question that children sometimes play, where the participant says "milk" 7 times, and is then asked "What do cows drink?" - the correct answer is actually "water". Cows drink water. Cats drink water. Dogs drink water.
  

(My dog doesn't eat meat. I don't give him any. <Boom tish...>Myles325a 03:41, 9 August 2007 (UTC)

But to clarify, dogs can't handle chocolate because of the theobromine as Rockpocket mentioned, and I believe some dogs will probably get away with drinking milk, but know well that to look after your pets properly you should always have a good supply of water available for them. Rfwoolf 05:35, 5 August 2007 (UTC)

My dog will hapilly drink milk with no ill-effects. We only give him a little bit of skimmed, so it's practically water anyways ;) Capuchin 06:53, 6 August 2007 (UTC)

Black Iron Pipe

I can't seem to find any articles (or sections) on black iron pipe. The closest thing I found to it is Black lacquered steel, but I don't think it's the same. Black iron pipe is greased; does the function of the grease reduce electrical conduciveness because black iron is gas only? LCecere 17:53, 3 August 2007 (UTC)

I believe the oil or grease is to inhibit rusting, and/or as a residual result of the cutting and threading process.

I wouldn't imagine that it's intended to affect the conductivity, or that it does affect the conductivity, since black iron pipe is never used for its electrical conductivity.

Black iron pipe is not only used for gas -- surprisingly enough, it's also often used for some of the piping in forced hot water heating systems. Since the water in these systems circulates continuously, with little or no replenishment, it becomes completely de-oxygenated, and doesn't cause rusting.

(It's too bad we don't have any articles on this sort of thing, though -- I've wanted to write one on various pipe fittings and materials, but I've never gotten around to doing the research.) --Steve Summit (talk) 18:33, 3 August 2007 (UTC)

The lacquer or the grease from forming the pipe would not be relied on at all for any electrical insulating properties. I have heard that black iron pipe is preferable to galvanized pipe for natural gas, but no one seemed to know why. Is it just to save the cost of galvanizing? Or does the zinc do something bad in the presence of gas? I have seen black iron pipe used on hot water heating systems. It never seemed to make much sense, since the systems get drained and refilled occasionally. Edison 18:44, 3 August 2007 (UTC)

I've always assumed that the main reason to use black iron was to save money when the galvanizing wasn't needed. But under some circumstances, the zinc galvanizing can just plain get in the way. User:Duk mentions one reason below. I've speculated (though I don't know for sure) that another reason to avoid galvanized pipe in gas work is to avoid the hazard of bits of zinc flaking off (if only during the original installation process) and then traveling along the pipe until they pass into and clog the orifices of the various gas appliances downstream.

gas supply line trap (lower left)

As a side point, gas supply pipe installations often include little traps to catch foreign materials (of any kind) before they can clog up appliances. Here's a picture (at right) of the trap on the gas supply to the water heater I was installing two nights ago. —Steve Summit (talk) 00:18, 4 August 2007 (UTC)

I found a section on black iron pipe in pipe fitting under the section "Steel pipe." The definition of black iron pipe (in that article) matched the definition of black lacquered steel (in Domestic water system): best used in fire sprinkler systems; also used for gas and propane. I'm in the middle of learning rough plumbing, and it's really hard because Lowes has discontinued all the plumbing and electrical department manuals--and I'm the new plumbing associate. I think I'll find a complete book on plumbing on Amazon LCecere 20:10, 3 August 2007 (UTC)

My hat is off to you for working so assiduously (despite obstacles) to learn this stuff. It is a credit to you that you care so much to seek this information out on your own (and no credit, I'm afraid, to your employer for not providing this training as a matter of course). —Steve Summit (talk) 00:26, 4 August 2007 (UTC)

Iron is naturally grey/silvery. If you want black, it has to be oxidized (like when its just cooled down after the rolling mill etc). The other way of getting it black is to paint it.--SpectrumAnalyser 21:29, 3 August 2007 (UTC)

"Black Pipe" refers to regular steel pipe that isn't galvanized. This is commonly available and used when the pipe needs to be welded (welding galvanized steel releases toxic fumes), or where you can't have zinc flaking off. The oil (I'm guessing here) is probably just a standard mill P&O coating (pickled and oiled). --Duk 23:41, 3 August 2007 (UTC)

It is impossible to weld galvanized pipe. Black pipe is not regular steel pipe. LCecere 06:33, 5 August 2007 (UTC)

1) It is possible to weld galvanized pipe, though not preferable. You just need to handle the toxic fumes. PS. to all you backyard mechanics out there, don't weld galvanized steel unless you want to catch "metal fume fever".

2) "Black pipe" and "Black Iron Pipe" is steel pipe. The "Iron" in "Black Iron Pipe" is old slang - it's steel pipe. Same dimensions and material as galvanized pipe except, of course, the coatings. You can also buy iron pipe. "Black malleable iron pipe" is iron, not steel. --Duk 16:07, 5 August 2007 (UTC)

OK what causes the black color then?--SpectrumAnalyser 01:54, 4 August 2007 (UTC)

I suspect that it is an outer layer of the pipe that is slightly chemically altered by the pickling process that User:Duk referred to. I suspect (though I am not at all sure) that it is a form of hematite or Iron(III) oxide, Fe₂O₃, or perhaps Iron(II,III) oxide, Fe₃O₄. There are black oxides of iron which end up inhibiting the more familiar (and more destructive) red rust by having "gotten there first", so to speak. If anyone knows more about this, please post! —Steve Summit (talk) 03:23, 4 August 2007 (UTC)

It's almost certainly not parkerization

http://www.keidel.com/mech/pvf/pipe-blksteel.htm (as mentioned above black rust+oil) - think like an iron skillet.87.102.93.50 15:26, 4 August 2007 (UTC)

Not sure what the original poster was asking but if it's stove pipe it might be black lacquered also.87.102.93.50 15:27, 4 August 2007 (UTC)

I asked a plumber (who has been doing it for 40 years) about the specs of black iron pipe. Black irong pipe is NOT used for any kind of water transport. It is GAS ONLY, as I originally knew; this pipe will rust out if used with water--use galvanized pipe for water. The greased coating is used to keep the pipe from heating up as black iron is often used in exposed areas; it deflects sun rays--the coating has nothing to do with threading because the threading machine constantly pours oil onto it while revolving (I can cut and thread now). The black pipe used in the picture above is the pipe in question, for those who are unsure what I meant. Galvanized pipe is used for transporting water and must never meet a copper pipe. And about copper piping: Type M is used for above ground and Type L (or K) is used for below ground, period. All of these facts have have been confirmed. I don't know why this is such a vague subject. But thanks to everybody. LCecere 06:33, 5 August 2007 (UTC)

I'm glad you're getting some answers, but I'm not sure your 40-year plumber is an infallible source!

• It may or may not be a good idea, but black iron pipe does regularly get used for the boiler connections in forced hot-water heating systems. If I have a chance I'll take some pictures of some installations I'm familiar with. I suspect black iron is used in steam systems, as well.
• That notion that the greased coating is for deflecting the sun's rays is, I'm afraid, pure nonsense.
• Saying "type L (or K) is used for below ground, period" is too simplistic. No, you'd never want to bury type M, but both of the heavier types are used above-ground all the time, where their extra strength and robustness are needed for various reasons.
• (But if all you're concerned with is pipe being sold to homeowners in a home-improvement store, saying "black iron is for gas, galvanized is for water, type L is for below-ground, type M is for above-ground" are probably all appropriate simplifications.)

The reason good information on this subject can be hard to find (and also that a certain amount of misinformation is present) is that plumbing, like many crafts, still retains vestiges of the old guild systems; practitioners are assumed/expected to receive much of their training on the job, as apprentices, so it's not necessarily all written down and organized in a form that's easy for us duffers on the internet to search for. —Steve Summit (talk) 12:58, 5 August 2007 (UTC)

Biology/ snakes

Would it be correct to say a "quiver of cobra"?

If you are referring to the cobra snake, I would say "no" because the collective nouns are not based on the type of snake, just the group of snakes. See List of collective nouns by subject I-Z for proper collective nouns. -- Kainaw^(what?) 22:06, 3 August 2007 (UTC)

I'd say right answer, wrong reason. It's fine to say "a herd of mustang" even though a mustang is a type of horse instead of the generic name. But quiver doesn't seem to be a word for a group of snakes --froth^t 00:49, 4 August 2007 (UTC)