Wikipedia:Reference desk/Archives/Science/2010 April 12

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April 12

I know why the sky is blue...

..but why does it feel so far away? Aaronite (talk) 00:35, 12 April 2010 (UTC)

Perspective. --Jayron32 00:46, 12 April 2010 (UTC)

That was a whole lot simpler than I expected. Aaronite (talk) 01:01, 12 April 2010 (UTC)

Simple...but not true. The sky seems far away even when there are absolutely no clouds or anything. How can clear air have "perspective"? Nah. The deal is that our visual system has five ways to judge distance - in order of increasing range:

• The amount of muscle tension needed to distort the lens to form a sharp image.
• The amount by which our two eyes have to point inwards to make the two images form a single image.
• The amount by which the object moves as our heads move.
• The relative size of things whose size we know well (trees, houses, people, etc) - and that one thing is in front or behind another.
• The amount of color change due to Rayleigh/Mie scattering (far mountains look purple-ish, etc).

Things that show none of those effects appear (effectively) infinitely far away...which includes the sky. We don't see any of these 3D cues for the blue or black of the sky - we can somewhat judge the distance for clouds - but even then it's tough because we don't have "reference" for how big they should be, and they transmit and filter light rather than reflecting it. Things like sun, moon, planets and stars all appear to be infinitely far away.

SteveBaker (talk) 02:19, 12 April 2010 (UTC)

Don't forget relative brightness. But, of course, this also assumes you know the absolute brightness, to gauge the distance properly. I don't think the Moon seems infinitely far away, because it contains familiar sights, like mountains, which we can see and compare with the size of mountains on Earth. StuRat (talk) 02:30, 12 April 2010 (UTC)

Relative brightness comes under the category of color change. SteveBaker (talk) 13:18, 12 April 2010 (UTC)

How is the frequency of a wave the same as the magnitude ? StuRat (talk) 14:24, 12 April 2010 (UTC)

On computers. Using the RGB system, a pure red colour (typically 255,0,0) would presumably have the same frequency as an apparently duller red, but will have an RGB value of something like (128,0,0) and is therefore a "different colour". --Phil Holmes (talk) 15:51, 12 April 2010 (UTC)

In that example, I'd say the magnitude was decreased, but the frequency remained the same. StuRat (talk) 16:43, 12 April 2010 (UTC)

"Color" is not at all the same thing as "frequency" - if it were then "lime green" and "forest green" would be the same "color" and "pink" wouldn't be a "color" at all because it's not representable by a simple frequency - and if you were to argue that it was a color then you'd have to admit to "white" and "dark grey" being the same "color" - which is stretching the meaning of the word to breaking point! The correct word for what you are thinking of is "hue" which is the nearest approximation that our eyes can perceive to the "frequency" of the light. SteveBaker (talk) 17:52, 12 April 2010 (UTC)

I wouldn't call white, black, or gray "colors" at all. I see the problem. I'm using def 3 at Wiktionary:color, while you are using def 2. StuRat (talk) 21:29, 12 April 2010 (UTC)

I think basically the reason the sky seems so far away is that it doesn't move as you move around -- no parallax, in other words. For what it's worth, having lived in both the west and east of the USA, it has often struck me that the sky seems much farther away in the west. I expect this is somehow a result of the lower humidity. Looie496 (talk) 18:13, 12 April 2010 (UTC)

high altitude training chamber levels blood acidity

its my understanding that as the carbon dioxide levels in our blood go up so does blood acidity. many pilots go through high altitude training chambers with high levels of nitrogen to adjust to hypoxia. in a high nitrogen environment does blood acidity go up or down or stay the same? —Preceding unsigned comment added by Jonny12350 (talk • contribs) 01:07, 12 April 2010 (UTC)

High nitrogen environments can lead to the bends. I am not sure what effect, if any, it has on blood pH. --Jayron32 01:57, 12 April 2010 (UTC)

High nitrogen environments can;t cause the bends, as the nitrogen has no way of entering the bloodstream as bubbles (recall that hemoglobin, the O₂-carrying compound in RBCs, cannot bind to elemental nitrogen). @OP It may interest you to know that our atmosphere is ~80% nitrogen, and less than 20% O₂. While true that respiratory acidosis can be caused by hypoventilation (not breathing enough), a high nitrogen environment would likely have little, if any, effect on this. Acidemia is caused by an imbalance of CO₂ and O₂ in the blood; it has nothing to do with other gases in the air. --Anonymous 02:13, 12 April 2010 (UTC)

Almost totally wrong about the bends. It is caused by dissolved inert gases such as nitrogen (or helium when used in some diving mixtures). See Decompression sickness#Mechanism. Dragons flight (talk) 02:43, 12 April 2010 (UTC)

To avoid confusion, the above poster is not me. My "--Anonymous" signature is done manually and does not have parentheses as in "(UTC)". (Yeah, I know, this is what I get for being anonymous.) --Anonymous, 05:23 UTC, April 12, 2010.

But you aren't anonymous - you're User:64.231.232.179, posting from somewhere around Toronto, Canada. If you want to be anonymous, create a user account. SteveBaker (talk) 13:25, 12 April 2010 (UTC)

Don't imagine that an IP address identifies a person. I have contributed to WP from several IP addresses, all of them shared by other people. However, I am the only one posting here with the form of signature I use. --Anonymous, 18:53 UTC, April 12, 2010.

High nitrogen does not have any effect on acidity either way. And the bends are caused by high pressure, not high <any specific gas>. The high altitude effects the partial pressure of oxygen - basically oxygen is not "pushed" into the blood as effectively. The altitude training gives the body time to adjust to this by making more red blood cells and some other changes as well. The acidity of the blood is very very very carefully managed by the body, so even if the high altitude changed it, the body would adjust it to compensate. But I don't know if high altitude will have an effect on it. Ariel. (talk) 18:57, 12 April 2010 (UTC)

Decreased pressure of carbon dioxide in the atmosphere seems like it would cause more of it to diffuse out of the blood, which would raise the pH. Except blood is buffered, so you are just stressing whatever system maintains that buffer (and losing some of whatever precursors are involved)--see carbonate#Biological significance. DMacks (talk) 15:22, 13 April 2010 (UTC)

Gold

Dude, I checked the various elements and noticed that Gold has a higher density than most of the elements that are even higher on the table. What is the deal? I'm sure I can handle the scientific stuff, but give me the simple answer so I can explain it to my friends. —Preceding unsigned comment added by 68.28.104.239 (talk) 02:22, 12 April 2010 (UTC)

Density is mass per unit volume, so there are two ways to increase density of a collection of object: Make the objects heavier, or pack them closer together. In the case of gold, you rightly note that its density is higher than elements which have heavier atoms; so that leaves the second method of varying density, which is the organization of the gold atoms in the solid form. There are two effects going on, the atomic radius of gold, and the crystal lattice of the gold atoms in the solid form. Lets deal with atomic radius first.

Periodic trends#Atomic radius is some basic background, but basically heavier atoms are not automatically larger atoms in terms of volume. The gas-phase atomic radius of an element actually decreases as you move to the right along any row of the periodic table. In other words, though a gold atom is heavier than say, a cesium atom, it is also smaller in size than a cesium atom. This is because of something called effective nuclear charge. To simplify it, as you move right through a row of the periodic table, you are adding more protons to the nucleus of an atom, but you are not adding more energy levels to the electron cloud. The electrons that match those protons are added to existing energy levels, not to new energy levels, so the effect is such that the additional protons are exerting a greater pull on the outermost energy levels of the atoms to the right, making them progressively smaller and smaller in radius. If you move down in the periodic table, you add an additional energy level, which causes a large increase in radius. Thus, gold is going to be denser than elements below it on the periodic table, despite having lighter atoms. With gold, the radius is even smaller than expected because of something called the Lanthanide contraction.

Gold also has a face centered cubic crystal lattice, which is a very efficient way of packing atoms into a crystal. The face centered cubic crystal has the highest Atomic packing factor among the standard cubic crystal shapes. This means that in any given unit cell of the gold crystal, there is very little "empty space" and thus, a higher density.

Hope that helps some! --Jayron32 02:48, 12 April 2010 (UTC)

Hey, that made perfect sense to me, but my friends are lost. I sent them packing. Next time they come over, we will try to figure out something way easier. —Preceding unsigned comment added by 68.28.104.234 (talk) 02:58, 12 April 2010 (UTC)

Just tell them that the gold atoms, while lighter than atoms lower down on the periodic table, are packed together in such a way as to minimize the empty space between them. That makes a higher density than other elements whose atoms are packed together in a less efficient manner. --Jayron32 03:00, 12 April 2010 (UTC)

Thanks Jason...don't you have to teach tomorrow? —Preceding unsigned comment added by 68.28.104.244 (talk) 03:07, 12 April 2010 (UTC)

I no longer work in the classroom. I work mostly as a private tutor right now. --Jayron32 03:19, 12 April 2010 (UTC)

Hey dude 68.28.104.239, your friends may enjoy hearing Archimedes' bathtime story about the weight of a gold crown. Cuddlyable3 (talk) 09:17, 12 April 2010 (UTC)

Read this as well for more about the size of the gold atom, and how special relativity makes gold yellow. Ariel. (talk) 19:01, 12 April 2010 (UTC)

Organic crops and contamination

How can a farmer protect organic crops from being contaminated by non-organic crops? Also and more specifically, how can a farmer protect non-GMO crops from being contaminated by crops of genetically modified organisms? -- Wavelength (talk) 03:58, 12 April 2010 (UTC)

The first one is relatively easy, just don't grow your crops adjacent to a non-organic farm. I don't think crop-dusting planes are used much any more, as it's too expensive and unhealthy for the pilots and farmers. So, that leaves hand-spraying, which isn't likely to over-spray nearly so much. Chemical fertilizers aren't much of a problem, either, although a bit might blow onto adjacent farms. Only if the organic farm was downhill would major run-off be a problem.

The 2nd one is a real problem, though. If the GMO crops really are more fit, as the makers claim, then they will naturally spread to adjacent farms and displace the natural crops. The GMO companies try to stop this by making farmers destroy the seed, but there's no way to do that 100%. And, since GMO crops may look identical to their organic cousins, there's no way to remove them without genetically testing every one. Perhaps the GMO crops need to have a gene inserted which will make them fluoresce under UV light, so organic farmers can find them and remove them. StuRat (talk) 05:23, 12 April 2010 (UTC)

Actually, there's a third problem. While some genetically modified crops, like Maize, require people for fertilization, there are other crops which spread pollen via the air, or which use, say, honeybees to spread pollen. So, if my farm is certified organic, and its next to YOUR farm, which uses genetically modified crops, and your pollen drifts over to my farm (who's gonna stop it?) or the two farms are visited by the same honeybees, then what's to stop my organic crops genetic material from being contaminated by YOUR genetically modified genome? The big problem would seem to be the spread of the genetically-modified genome via pollenation. The second-generation hybrid crops can no longer be considered organic, so the organic farmer may have legal standing to sue for damages (indeed, I believe this has already happened). Its a thorny issue. --Jayron32 05:36, 12 April 2010 (UTC)

Hey, what's the big deal? About genetically modified crops, I mean? 24.23.197.43 (talk) 07:58, 12 April 2010 (UTC)

Hay ? Cuddlyable3 (talk) 09:10, 12 April 2010 (UTC)

Organic farming is more than avoidance of GMO, it relies on crop rotation, green manure, compost, biological pest control, and mechanical cultivation, with limited use of synthetic fertilizers and synthetic pesticides, plant growth regulators, livestock antibiotics and food additives. Because the harmfulness of GMOs remains disputed we may see marketing of "organically grown GMOs".Cuddlyable3 (talk) 09:10, 12 April 2010 (UTC)

Variety Genetic use restriction technology would greatly limit any second generation problems and is advocated for this reason (amongst others). Well there is a slight possibility according to an article there may be some limited spread with the sterility only becoming apparent in later generations. However they have had limited use out of concern of food security, farmers rights and other such issues. Nil Einne (talk) 20:15, 12 April 2010 (UTC)

Contamination was an issue in Monsanto Canada Inc. v. Schmeiser. -- Wavelength (talk) 14:05, 12 April 2010 (UTC)

Actually AFAIK, we don't really know what happened in that case. The farmer claims that is was accidential contamination that he wasn't aware of or something of that sort, but that was dismissed by the court, not surprising given the evidence. Either it was accidential contamination and the farmer in that case then "identified, isolated and saved" the GM seeds or the contamination part was simply untrue. P.S. Note that the article also says "While the origin of the plants on Schmeiser's farm remains unclear, the trial judge found that "none of the suggested sources [proposed by Schmeiser] could reasonably explain ..... Schmeiser's crop" Nil Einne (talk) 20:15, 12 April 2010 (UTC)

No, I mean, why would the spread of GMO crops would even be an issue at all? I mean, all of the "ordinary" crops we already grow have been subjected to a lengthy process of artificial selection, and quite a number have been crossbred with plants of some different but related species -- why would genetic engineering be any different than this "conventional" kind of crossbreeding? For example, I've never heard of people making a big fuss because the wheat we grow had been crossbred with wild rye way back when; so why is this "new" crossbreeding suddenly such a big deal? Personally, I think that this whole debate about GMO crops "contaminating" other crops is just a big tempest in a teacup. 24.23.197.43 (talk) 05:02, 13 April 2010 (UTC)

Correction: wheat was crossbred with goatgrass, not with wild rye. I stand corrected. :-) 24.23.197.43 (talk) 05:25, 13 April 2010 (UTC)

The main concern with GMO crops is that we aren't sure that all of the alterations to the genetic code of these crops are perfectly safe. The most widespread example of this in the states is "Bt corn". Bt, or Bacillus thuringiensis , is a naturally occuring soil bacteria that is used in forestry and agriculture to prevent crop damage by killing off larvae of moths and butteflies (lepidoptera). Thing is, they figured out how to splice the genes from the bacteria into good "old fashioned" corn. So...people may worry about all their pet moth collections dying off, or they might not like eating high doses of naturally occuring pesticides. Bt has proven overwhelmingly safe for humans in its historic uses, but that was before our food started making its own pesticide. I'm terrible at linking in here...but Bt has it's own page you can look up. 68.153.29.23 (talk) 07:44, 13 April 2010 (UTC)

Please see Co-existence of genetically modified and conventional crops and derived food and feed. -- Wavelength (talk) 15:19, 13 April 2010 (UTC)
[I am revising my comment. -- Wavelength (talk) 15:40, 13 April 2010 (UTC)]

Is there a term for that shimmery border you get where two vibrant colours meet?

... bright light purple spots on a bright green field for example, as on one of my daughter's dresses?

Ta Adambrowne666 (talk) 05:42, 12 April 2010 (UTC)

I know the effect you are talking about, unfortunately the article Complementary color does not discuss it. --Jayron32 05:47, 12 April 2010 (UTC)

Maybe the term that your hunting for is Chromatic aberration.--Aspro (talk) 12:15, 12 April 2010 (UTC)

Since this is a subjective observation it would be helpful if anyone can link to an image. Cuddlyable3 (talk) 08:54, 12 April 2010 (UTC)

It might be caused by the afterimage of the pattern as the motion of the eye or the subject moves it out of sync with the image, creating colored fringes. Paul (Stansifer) 12:01, 12 April 2010 (UTC)

I know why it happens in television pictures - but you're talking about "reality"?

The only thing that I can imagine that would cause such a thing with naked eye vision would be due to the fact that your eyes focus each of the three primary colors at a slightly different 'depth' - so it's hard to keep the boundaries between very pure complementary colors (green and magenta, for example) in sharp focus. Personally, I don't see a shimmery border in such cases...and I'm a little surprised to hear that you do.

On television it happens because of the way they added color to the pre-existing monochrome television standard by encoding the color on a higher frequency carrier and using the phase of the signal to encode color. When you switch the signal from green to magenta, the phase changes 180 degrees and that has the effect of producing a momentary drop in frequency that allows the color signal to briefly depress or raise the overall signal level in the 'brightness' channel - so you get either a bright or a dark vertical line where the colors change. On PAL format television, it shimmers because of the phase of the color signal being reversed on every alternate line.

SteveBaker (talk) 12:33, 12 April 2010 (UTC)

You may be seeing an iridescence effect? Comet Tuttle (talk) 13:43, 12 April 2010 (UTC)

Complementary colors "clash." Found here:

"Complementary colors are on opposite sides of the color wheel -- they are each half of a pair of contrasting colors. For example, blue is a complementary color to yellow. Green is complementary to purple and magenta. A pair of complementary colors printed side by side can sometimes cause visual vibration (clash) making them a less than desirable combination. However, separate them on the page with other colors and they can work together. Note the spelling. These are not complimentary colors. They don't always flatter (compliment) one another but they do complete (complement) each other."

Note that purple and green fall into the category of complementary colors. Bus stop (talk) 13:54, 12 April 2010 (UTC)

I'll just note that I see the effect as well, though most often where red and blue come in contact. The colours (in my experience) have to be deeply saturated and flat (no shading or borders of any kind). For some reason children's colouring books often get printed with those colours and I often see the bright red letters shaking against the blue background. Matt Deres (talk) 14:28, 12 April 2010 (UTC)

The Bank of America signs have this effect on me. This one isn't as bad as some of the ones around here (since adding white outlining around the letters reduces this issue), but does somewhat show the problem: [1]. StuRat (talk) 14:50, 12 April 2010 (UTC)

It is called scintillation. Probably it happens because even when the eyes seem to be still, they are constantly making tiny movements called microsaccades. These cause the receptive fields near the edges to fluctuate back and forth between the two colors. A similar thing happens in the so-called grid illusion. Looie496 (talk) 17:28, 12 April 2010 (UTC)

That's a likely name for the phenomenon, but that's not a useful article to point to in this case. Matt Deres (talk) 00:53, 13 April 2010 (UTC)

Good answers, all - thanks - yes, makes sense that it's due to microsaccades. Adambrowne666 (talk) 08:14, 15 April 2010 (UTC)

Biological pest control for Fruit fly

Are there any Biological pest control for Fruit fly ? --yousaf465' 08:37, 12 April 2010 (UTC)

Yes, baby chameleons. Chameleons Online--Aspro (talk) 12:03, 12 April 2010 (UTC)

One approach that has been tried is to breed a vast number of fruit flies of the same species - treating them (eg by irradiation) to make them infertile - and then to release them into the area. If you can outnumber the local (fertile) population with infertile flies (by a factor of 10 to 1, for example), you'll reduce their breeding effectiveness to near zero as the probability of a naturally born fertile male happening to meet a naturally born fertile female drops dramatically (in this case to about 1%). Since fruit flies don't live very long, their population crashes within one generation. Repeating the treatment on the (much reduced) initial population should pretty much eradicate them. SteveBaker (talk) 13:06, 12 April 2010 (UTC)

That was used to stop the spread of the Medfly. See Medfly#California_medfly_crisis. However, I'd expect people to object to releasing all those fruit flies, year after year, to combat normal fruit flies. Also, is irradiation 100% effective at sterilization ? If not, you could end up increasing their mutation rate and making them more of a threat. StuRat (talk) 14:34, 12 April 2010 (UTC)

It's pretty effective, and I've never heard of mutation being a significant problem (the odds of said mutation also being beneficial is fairly low as well). I'm not sure people would object to the released fruit flies. The only reason fruit flies are a pain is because they lay eggs in the fruit... sterile males won't do that (and they would be released over croplands anyway, so it's not like we're talking about fruit flies being dropped into your iced tea). Anyway, Sterile insect technique is the full article... --Mr.98 (talk) 14:44, 12 April 2010 (UTC)

Obviously, even a beneficial mutation won't be a problem if the irradiated flies are infertile and therefore unable to pass this wonderous gene onto the next generation. The odds of an animal happening to avoid being sterilized AND getting a beneficial mutation AND mating with a rare fertile animal are very low indeed. (Unless of course you end up with 50' tall mutant fruit flies with laser eyes and an unaccountable craving for human flesh...albeit infertile!) SteveBaker (talk) 17:42, 12 April 2010 (UTC)

Sounds something like the Drake Equation:

Nb = Ni × Ff × Fs × Fm × Fb

Nb = Number of Beneficial mutant fruit flies which reproduce
Ni = Number of surviving Irradiated fruit flies
Ff = Fraction of Ni which remain Fertile
Fs = Fraction of Ff which Successfully mate with other fertile fruit flies
Fm = Fraction of Fs which undergo a Mutation in their sex cells
Fb = Fraction of Fm where the mutation is beneficial

And, just like the Drake Eq., depending on the values you plug in, we can get zero or huge numbers. StuRat (talk) 21:22, 12 April 2010 (UTC)

...and we should probably toss in:

Fc = Probability that the beneficial gene is passed on to a given offspring.
No = Number of offspring produced from one successful fruit fly mating.
Fo = Fraction of newly hatched fruit flies surviving to maturity.

N_o and F_o might be kinda large given that we've just wiped out most of the competition for resources from other fruit fly. SteveBaker (talk) 23:53, 12 April 2010 (UTC)

Some gardening stores sell mantis ootheca for bio pest control. Mantis larvae eat fruit flies. Also, Metarhizium anisopliae or similar entomopathogenic fungi may be effective against medfly, but I don't think they are actually used against medfly. The end result of entomopathogenic fungus action is a pure Nightmare Fuel for some people, so I can imagine their commercial success may be somewhat limited. --Dr Dima (talk) 17:10, 12 April 2010 (UTC)

The usual difficulty with introducing predator species is that in many cases, the predators themselves become a pest - either eating beneficial species when they've finished consuming all of the pests - or consuming so much that they starve out other natural predators higher up the food chain (birds, for example). Hence. this is an extremely risky strategy. SteveBaker (talk) 17:42, 12 April 2010 (UTC)

True, especially when the predator is a non-native species or an apex predator. The ootheca I mentioned are of either Mantis religiosa or Tenodera sinensis. Neither is native to US, however, both are present in US in the wild since around 1900, with not much -- if any -- ill effect. It's not like releasing Africanized honeybees in America or cats/foxes/rabbits in Australia. --Dr Dima (talk) 18:55, 12 April 2010 (UTC)

Actually one of these methods will be used in melon farm.--yousaf465' 07:37, 15 April 2010 (UTC)

three phase electric energy meter

give construction, working and principle of a three phase electirc energy meter

Three-phase electric power
Electricity meter. Cuddlyable3 (talk) 23:13, 12 April 2010 (UTC)

Cholestasis in humans and animals

Hello all.

I'm currently working on a bio for toxicologist Gabriel L. Plaa. For talking about his primary research, I'm basing mostly on doi:10.3109/03602539709037571, an account by himself of his career. There's one aspect regarding his research on cholestasis I'm quite unclear about. Basically a significant interest for him was the elaboration of a protocol to detect cholestatic properties in drugs by animal test, but this was made difficult because, I think, the common lab animals (he specifically discuss rats and mentions hamsters and rabbits) are much less susceptible to cholestasis than human. Is that correct? I'd ask on that article's talk page, but it is little edited (and the article is currently rather... curt).

As an aside, has such a protocol been devised since Plaa's retirement? Since I'm no medical student, I wouldn't quite know where to look regarding the state of the art of this subject.

Thanks in avance, Circéus (talk) 12:40, 12 April 2010 (UTC)

You might find this helpful. Target organ toxicity, Volume 1; By Gerald M. Cohen. Page 102 Second paragraph down: “Foreign compounds whose administration to animals leads to intrahapatic cholestasis show some interesting specie variations.... etc., etc. “ I don't know about any successful protocols. In vitro human cell studies might be better today but even they are not definitive.--Aspro (talk) 14:39, 12 April 2010 (UTC)

It does confirm the state of the art at the time, but is not, unfortunately, really useful for current aspects fo the topic: it was published in 1986. 14:44, 12 April 2010 (UTC)

I've dug up a few refs that indicate that the issues with prediction of human hepatotoxicity based on animal models are well-known and still not solved (Chem. Biol. Interact. 150(1)115-128 doi:10.1016/j.cbi.2004.09.011), though I'd still appreciate a better informed opinion. Circéus (talk) 16:41, 12 April 2010 (UTC)

is it possible to "work off" cholesterol?

Is it possible to "work off" cholesterol? What about "after the fact" (ie when it's clogging your arteries). If you switch to a low-cholesterol diet after years of high cholesterol, do the clogs slowly undue, or are your veins and arteries difigured for life? If it IS possible to "undo" over time, Approximately what time frame are we talking about for this? Thank you. 84.153.204.187 (talk) 14:34, 12 April 2010 (UTC)

The Atherosclerosis article reports some mixed findings on this, so "maybe, a bit" seems to summarise. -- Finlay McWalter • Talk 16:00, 12 April 2010 (UTC)

The body also makes cholesterol, so even if you ate none at all, you can still have high levels simply because that's what your body wants. In general cholesterol is not absorbed particularly well, and most is created in the body, not from food. The problems are caused by a bad diet in general, not specifically eating cholesterol. Since cholesterol is (indirectly) made from fat, and fat is made from sugar (via insulin). So just eating lots of sugar can raise your cholesterol level. If you want to reduce the effects you need to fix your diet in general and not focus just on cholesterol. Ariel. (talk) 19:12, 12 April 2010 (UTC)

Or to practice regular exercise, according to our article (unsourced, though). --NorwegianBlue ^talk 17:28, 13 April 2010 (UTC)

Printing on aluminum cans

How (the process) and what (ink? something else?). 20.137.18.50 (talk) 15:24, 12 April 2010 (UTC)

This paper by someone at Coors has a section on aluminium can printing, curing, and ink-sealing. -- Finlay McWalter • Talk 15:58, 12 April 2010 (UTC)

Old television smoky exploding madness!

An old television (Ferguson TX 37340) was brought into service on 2010-04-11 at 2020 hours and after a few minutes made some loud crackly banging noises and smoke emanated from the vents at the rear. The television was quickly decommissioned and the area ventilated. The picture was apparently unaffected until the moment at which the electrical supply was terminated. What components in the television are likely to cause such noises and smoke and yet allow the television to continue operating, with sound, as it did? --92.25.206.9 (talk) 15:24, 12 April 2010 (UTC)

Persuade a responsible adult to take the back off and have a look. A coating of old (damp?) dust may have provided a conduction path from the HT circuit to the chassis. Track marks (burns) may be visible. Had it just been brought into the room from a colder place? – One should always give electrical equipment of this type, time to equalise with the ambient temperature, so that condensation (forming from the humid warm air) can evaporate.--Aspro (talk) 16:34, 12 April 2010 (UTC)

Another possibilities is insects nesting in there, which managed to short out an electrical connection. StuRat (talk) 16:40, 12 April 2010 (UTC)

As stated. high voltage arcing (perhaps across dust) could make noise and smoke. This could be around the flyback transformer. Some resistors make smoke when they fail. Capacitors sometimes are a ceramic cylinder with a roll of paper and foil inside, and arcing in it can cause the end to blow off. Failed insulation in a transformer or coil winging can cause smoke and popping noise. The problem is that things like this would usually be accompanied by disturbances in the picture. If the picture was unaffected until the end, the faults could be in the audio circuitry, where the extremely high (several kilovolt) voltage is not found, but where small problems can cause loud "crackly banging" noises from the speaker, since it could be at a level where there is yet much amplification before it reaches the speaker. Edison (talk) 18:46, 12 April 2010 (UTC)

I would also advise caution in removing the back. Old TV's often have large capacitors inside and even though the TV is physically unplugged from the wall - there is still enough energy there to give you a nasty shock or high voltage burn - maybe even kill you! I agree that the likely cause was dust & fluff inside causing the thing to arc. It may be that you got lucky and all that happened was an arc that burned up some of the accumulated fluff. Ideally, you'd want to get that stuff out of there - maybe with some gentle vacuuming - maybe with some of that aerosol "canned air" that electronics stores sell (it's not really "air") that allows you to blow the dust out of tight spaces. But like I said - avoid prodding around inside with anything metallic - and keep your fingers out of the circuitry, even if the TV is turned off and unplugged at the wall. SteveBaker (talk) 19:18, 12 April 2010 (UTC)

I had planned on waiting a week, but I couldn't and removed the back this afternoon. I found no obvious damage/burn marks. I do plan to take it outside tomorrow, weather permitting, spray with canned air duster and see if it will operate safely again. I've no need to put anything near any of the capacitors but I will be wearing rubber gloves while I take it outside and clean it. 92.25.112.212 (talk) 22:02, 12 April 2010 (UTC)

Err... in that case, this might be a good time to check your building and contents insurance policy. If you are going to leave the back off when you switch on, have the curtains draw and the lights off to see the sparks more easily... and a CO2 extinguisher to hand. Do let us know how it went. Good luck.--Aspro (talk) 18:10, 13 April 2010 (UTC)

Household dishwashing type rubber gloves would be of no particular use when dealing with a capacitor holding a charge of 10 thousand or 20 thousand thousand volts. Edison (talk) 16:19, 14 April 2010 (UTC)

How long is safe ?

Regarding a TV capacitor, how long would it take to fully discharge after it's unplugged ? A minute ? An hour ? A day ? A year ? StuRat (talk) 20:53, 12 April 2010 (UTC)

I think it depends on the circuitry and on air humidity, but I certainly wouldn't touch it for half an hour, and I would be nervous up to two hours. The capacitor will take much longer to fully discharge because voltage reduces with exponential decay, in theory never quite reaching zero. Dbfirs 22:03, 12 April 2010 (UTC)

A reference I've just read says, for HV, anywhere between days and indefinitely. Here it is. --Tagishsimon (talk) 22:08, 12 April 2010 (UTC)

It says "In the case of old TV sets using vacuum tube HV rectifiers, the leakage was essentially zero. They would hold their charge almost indefinitely.". If they're that good, maybe we need to replace the batteries in our electric cars with vacuum tubes. :-) StuRat (talk) 01:41, 13 April 2010 (UTC)

Charge isn't energy. —Preceding unsigned comment added by 92.17.233.94 (talk) 10:29, 14 April 2010 (UTC)

Nobody said it was. StuRat (talk) 18:59, 14 April 2010 (UTC)

You need the HV discharge tool, a long insulated rod (which you hold) with grounding clip wire attached. Graeme Bartlett (talk) 22:14, 12 April 2010 (UTC)

In a phenomenon which is counterintuitive, a high voltage capacitor which has been thoroughly grounded and discharged can recharge itself over time. Utility workers who lived to a ripe old age have a motto "If it ain't grounded, it ain't dead." I have been very savagely "bit" by TV set high voltage terminals quite a while after they were turned off and unplugged. Edison (talk) 01:45, 13 April 2010 (UTC)

How long after ? StuRat (talk) 13:32, 13 April 2010 (UTC)

Certainly several minutes, perhaps over an hour. A capacitor can store charge longer than that. Edison (talk) 16:17, 14 April 2010 (UTC)

I had some old 70v (4700uF ?) electrolytic capacitors that I was going to use in a power supply. The supply never got built and the capacitors were left open circuit in the cupboard for over 20 years. Recently I needed one for something and measured the voltage out of curiosity. It was about 4v! Never trust a cap to be discharged unless its shorted out and kept shorted.--79.76.250.218 (talk) 16:39, 13 April 2010 (UTC)

Assuming they were fully charged to start, and that the energy loss works like the half-life of radioactive elements, that gives us about a 14% loss per year. (If the loss was linear, it would be more like a 5% loss per year.) Either way, that sounds like a good way to store a charge long-term. StuRat (talk) 19:08, 14 April 2010 (UTC)

"Neutron-activatable elements"?.. I'm inventing terms because I don't know English well.

Hello! I have a problem with a term. I need to translate help file for our program into English. It concerns neutron-gamma spectrometry in well-logging. The closest topic I found here is Neutron activation analysis. In our program we have a list of elements that are subject to neutron activation (I, B, Al, H, Si, Ca, Fe etc.). How can I call them as a whole? Neutron-activatable elements?.. Neutron-capturing elements?.. Elements, subject to neutron activation?.. Shorter is better. For instance, I need to translate a sentence saying something like "To convert channels to energies, you must specify at least two peaks of neutron-activatable elements..." - you see, it needs a short term, and of course I can't just say "peak" because it can't be just any peak - it can't be a Compton peak or escape peak. Thanks in advance.94.41.62.121 (talk) 15:54, 12 April 2010 (UTC)

It's hard to answer your question. Perhaps something like 'detectable element' would work. You don't necessarily need to say 'neutron detectable element', since if that's what your product does it's implied. Ariel. (talk) 19:16, 12 April 2010 (UTC)

about generators

iam planning to convert mechanical energy in to electrical energy. in our daily life, in many ways ,we use many electrical devices and machines. in those, considering ideal conditions, some energy is being wasted. many devices operated by rotatory motion. so,iam planning to attach some required number of small generators.which does not affect the motion of the devise or machine non ideally. for example, arranging small generators to fan. in which the generators(4 or 6) are attached to the down rod carrying the fan, avoiding their weight on the fan. after collecting some current in to battery, fan collects current from battery and spontaneously battery is recharged. in this way we could minimise the usage of electricity. i would like to know, is it possible to construct so. and modifications i need. please give me some sugessions to plan better. thank you. iam waiting. could any one respond to me.

iam k. kumar raja. mechanical engineering(first year, b.tech), aditya engineering college, suram palem, near kakinada, india.

As near as I can tell, you're talking about getting energy from a fan by putting magnets on the shaft, and using the rotation of the magnets to generate electricity. This should work, but the law of conservation of energy means that you would lose more energy, due to the increased mass being rotated along with the fan, putting more strain on the motor. StuRat (talk) 16:31, 12 April 2010 (UTC)

I'm not sure exactly what is being asked either, but it sounds a bit like a dynamo. Perhaps that article can help you out. Matt Deres (talk) 16:42, 12 April 2010 (UTC)

Yep, StuRat is correct. Here's the problematic phrase:

attach some generators which do not affect the motion of the device

I've bolded the part that doesn't work. If the generators don't affect what they're attached to, then they're not generating anything. Conversely, if they're generating something, then they're increasing the load (and affecting the device). This is just a restatement of a perpetual motion machine, and it doesn't work. What you can do is try to make the initial device more efficient.

Now, to branch off a little bit, there are options along the lines of regenerative braking, which quite clearly add to the load of an axle in order to generate electricity. The distinction here, though, is that it doesn't operate concurrently with the motor -- a car does not both speed up and slow down at the same time. But this is a means of recovering some energy under limited circumstances. — Lomn 17:26, 12 April 2010 (UTC)

I'm very skeptical about this proposal. Certainly in the case of the fan, adding these small generators to the blades will make it harder to spin the fan and would result in either (a) the fan spinning more slowly and therefore being less effective or (b) consuming more electricity than your generators are able to recover. The energy you waste that way will (with 100% certainty) exceed your gains through these generators. There are a few places where wasted energy can be regained (and, as someone already mentioned, regenerative braking on motor vehicles, bicycles, etc is one of them). But in most cases, you only end up making things worse. So, sadly, I have to say that your idea is not workable. SteveBaker (talk) 17:33, 12 April 2010 (UTC)

A wind turbine is essentially a fan with magnets on the shaft to generate electricity, so if you operate your fan by allowing the wind to turn it (or even a person or animal), then maybe you could get some "free" electricity, but otherwise, as stated above, you will get less electricity out than you put in. Dbfirs 17:53, 12 April 2010 (UTC)

I don't know why the OP thinks there is a reason to add generators to a battery-powered fan. When the wind can drive the fan faster than the battery then you already have a wind turbine generator that charges the battery. Whichever of the power conversions DC-to-mechanical or mechanical-to-dc is happening there are losses, which rules out any possibility of making a perpetual motion machine by combining the two conversions. However a big wind turbine can usefully supply power enough to run a small fan. Cuddlyable3 (talk) 13:34, 15 April 2010 (UTC)

Air ducts

Why is a lot of ductwork in large HVAC systems square, whereas in things like natural gas pipes, the are circular in cross section? I would think that production costs are lower for a circular pipe, so why is HVAC square? Googlemeister (talk) 19:18, 12 April 2010 (UTC)

There is less worry for leak in HVAC; leaks are undesirable, but not disastrous or dangerous. As such, HVAC ducts can be made of cheap, lightweight, and "flimsy" material. Natural gas pipes must resist corrosion, impact damage, and pressure, so they must be constructed of sturdy pipe. Sturdy metal is easier to roll into tubing or piping than it is to create straight rectangular boxes and weld or roll a seam on each edge. "Flimsy" (by comparison) HVAC ducts do not need pressure- and impact-resistant pipe, so their shape can be whatever is easy to manufacture and install. Nimur (talk) 19:36, 12 April 2010 (UTC)

Also, a rectangular cross-section allows you to have the maximum cross-sectional area which fits in a rectangular region, such as between support beams in a wall. StuRat (talk) 20:43, 12 April 2010 (UTC)

In my house, the air conditioning ducts are circular cross-section insulated/flexible pipe where they travel through the attic space - but switch to box-section as they travel through walls and places like that. I agree with StuRat that the box-section simply fits better into the spaces available. Circular tubes use less material per unit-cross-section - and resist pressure better - but they waste a lot of volume when going through square/flat things like walls and ceilings. SteveBaker (talk) 21:32, 12 April 2010 (UTC)

Hollywood has decreed that high security buildings shall be equipped with unsecured HVAC ducts that are large enough for secret agents to creep through, with grilles that are handy for spying through and are lightly held by spring clips for covert access, especially over priceless jewels in museums. The consequencies for civilisation of people suspecting that any of this is unbelievable are too ghastly to imagine hence the need for square ductwork. Cuddlyable3 (talk) 13:52, 15 April 2010 (UTC)

Using imaging software to determine the length of a section of coiled apparatus

I want to determine the length of the highlighted portion of the tool in this photograph. I know that the total length of the tool is 130 cm. My idea was to import it into Inkscape or GIMP and then trace over it and use some tool to tell me how long the trace is, but I don't know if any such tool exists. I want to compare this flexi shaft with a number of others, because I need to drill in a rather tight place. The low-tech solution might be to print it out and use a piece of string... what's the less-low-tech solution? --92.25.112.212 (talk) 20:20, 12 April 2010 (UTC)

No need to print it out, just make it as large as possible on the screen and use a string there. Note that this wouldn't work if some parts were farther away than others, though. I tried it myself, and got that the ratio of the length of the handle to the overall length is about 1:6.2. Thus, if the overall length is 130 cm, the handle is about 21 cm long. StuRat (talk) 20:28, 12 April 2010 (UTC)

I don't know of a feature to do that in any art tools I own - but here is a way that should work:

• In a paint program like Photoshop or GIMP (which is a free download)...I'll use GIMP terminology - but if you use Photoshop, you'll know what I mean.
• Make two transparent layers over the top of the image - copy the image to both layers - delete the white background.
• Cut the image where the coiled part overlaps itself so that you have two non-overlapping sections - one in each layer.
• Erase the "handle" part whose length you wish to measure - and the bit that sticks out at the other end so you have nothing but the shaft itself, split over two layers.
• Measure the width of the shaft in pixels using the measurement tool.
• Use the "histogram" tool to figure out the percentage of pixels in the image that are not white/transparent in each of the two layers - add those two percentages and multiply by the height and width of the total image to determine the total area of the shaft of the tool.
• Divide the number of non-transparent/white pixels (which is the area of the shaft) by the width of the shaft in pixels.
• Now you know the length of the shaft in pixels.
• Measure the length of the other part of the tool (in pixels) directly using the measurement tool.
• Length of curled shaft + length of tool = 130cm - so now you know how many pixels there are per centimeter - and now you can calculate the length of the bit you're interested in.

...or do it StuRat's way with string - which is MUCH better! SteveBaker (talk) 21:20, 12 April 2010 (UTC)

Save your string. From the image the highlighted length is 14.3x the width of the cable. If that is 1cm (you CAN measure that, yes?) then the length would be 14.3cm. But you need more clearance to use the tool because the cable cannot bend sharply. Cuddlyable3 (talk) 23:01, 12 April 2010 (UTC)

If you have access to MATLAB, you can use the Image Processing Toolbox to generate a generalized 2D spatial transform and unwrap that coil. You can register the image to create a pixel-to-meters transform; this way your transform will yield a directly readable measurement of length in meters. MATLAB and the Image Processing Toolbox are unfortunately not free, and as far as I know, GNU Octave does not have free alternatives to the image processing toolbox utilities, but you can manually program those features if you have a solid grasp of image processing. Nimur (talk) 23:08, 12 April 2010 (UTC)

Thomas Edison's lab supposedly needed to determine the volume inside an early light bulb. Francis Upton, a gifted mathematician, used calculus to approximate the volume, based on the shape of the bulb and the thickness of the glass. Thomas Edison supposedly filled the bulb with sand or water and weighed it, using the density of sand to determine the volume in an analog fashion. The string/analog method and the photometric/mathematical method should agree in general in the present case. Edison (talk) 01:38, 13 April 2010 (UTC)

Instead of overcomplicating things with software and reducing accuracy in the process, why not use software to improve the accuracy of the result? Use GIMP's perspective tool to turn the image into what an overhead view would look like, then print out the result & measure with a string. --99.237.234.104 (talk) 01:29, 13 April 2010 (UTC)

The pic already shows the device head-on. StuRat (talk) 01:34, 13 April 2010 (UTC)

Thomas Edison's lab supposedly needed to determine the volume inside an early light bulb. Francis Upton, a gifted mathematician, used calculus to approximate the volume, based on the shape of the bulb and the thickness of the glass. Thomas Edison supposedly filled the bulb with sand or water and weighed it, using the density of sand to determine the volume in an analog fashion. The string/analog method and the photometric/mathematical method should agree in general in the present case. Edison (talk) 01:38, 13 April 2010 (UTC)

It seems to me that the mathematical methods should be used only in cases where the simpler method wouldn't work, like determining the volume of a battleship. This is both because the mathematical methods, being more complex than direct measurements, take longer, and have a higher probability of error. StuRat (talk) 11:25, 13 April 2010 (UTC)

Applying the mathematical methods incurs a higher probability of human error but you can't blame math for that. Cuddlyable3 (talk) 12:52, 13 April 2010 (UTC)

In the case of measuring the volume of a battleship, mathematical or analytic methods are probably prone to less error than "filling with sand and measuring the mass." You can imagine the logistics challenges associated with filling a battleship with sand, and massing it afterwards... the only way I can think to measure the mass of such a large object is using an analytic method with prior knowledge about the material properties, volume, densities, and so on. Nimur (talk) 16:25, 13 April 2010 (UTC)

Yes, and that's why I gave finding the volume of a battleship as an example of a case where a "simpler method wouldn't work". StuRat (talk) 17:14, 13 April 2010 (UTC)

Measuring the mass of a battleship is probably an accountancy problem: What is the cost of a ton of steel? What is the value of a ton of steel scrap? How much did we spend on steel? How much did we recoup from selling the left-over bits? SteveBaker (talk) 18:28, 13 April 2010 (UTC)