Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

February 24

Crushing

I remember reading about the study of crumpling or crushing paper or another two-dimensional object. But we don't seem to have an article on this. Are there any sources giving information on how well paper crumpled within a cylinder can support a weight above it? Thanks. μηδείς (talk) 02:25, 24 February 2013 (UTC)

I don't quite understand. The more weight you place on it, the more it will compress, until it reaches a point where it can't compress much more (about the density of wood, I imagine). StuRat (talk) 08:08, 24 February 2013 (UTC)

The question has relevance and merit if the crumpled paper is used for packing fragile products. There's bound to be someone who has studied it from that angle - what density of object can be protected by crumpled paper packing. What is the optimum crumpling density for use in packing? Of course, whether or not this is what Medeis had in mind - who knows? Wickwack 60.228.244.46 (talk) 10:56, 24 February 2013 (UTC)

My interest is in the abstract. I remember reading about ten years ago that researchers had found some sort of fractal constant that would predict how much a two-dimensional sheet of material--say paper or aluminum foil of the same thickness--would crumple within a confined space, like a tube, before it would cease compressing under a certain weight. If I remember properly, it turned out the actual material being crumpled didn't matter, the effect was a geometrical one. μηδείς (talk) 16:25, 24 February 2013 (UTC)

The place to start on the engineering properties of crumpling would be to look up the physics of crumple zones that are the structural safety feature of modern cars. The point is that the crumpling action itself absorbs energy -- if the structure it is already partly crumpled, much of that absorbing potential is lost. So thin supports such as those inside cardboard are in an ordered honeycomb structure instead.

An interesting place to look at the fundamental physics of crumbling is in newer research on mathematical origami. An artist makes the incredibly-complex fold pattern on a computer, prints the pattern and burns the perforations on paper. But instead of assembling fold-by-fold, the artist finds that they can get most of the folding in place immediately by gently crumpling the sheet. SamuelRiv (talk) 16:39, 24 February 2013 (UTC)

Yes, both crumple zone and mathematical origami are interesting articles, and I have watched a documentary on the latter. But I am looking specifically for some sort of fractal treatment of the random crumpling of paper and other two-dimensional substances. μηδείς (talk) 21:33, 24 February 2013 (UTC)

I'm not familiar with that research. You said you saw an article on it somewhere - can you try again to find anything on it? I'd be interested, and from there maybe I can lend guidance from there.

For now, if I were to make such a model, I'd start with finding folding arrangements that make all triangles, after which one might find a small set of transformations that collapse each triangle into smaller ones and maybe find a volume limit from there. But see if you can find an article. SamuelRiv (talk) 19:21, 25 February 2013 (UTC)

The only thing I can say for sure is that it was in Discover or Scientific American or American Scientist or the New York Times Tuesday Science section (about 60/34/5/1%) and that it included the words paper and fractal and something about crush or crumple or fold or bend, and what I have said above. Had I written the hook, it would have been, "Did you know that according to the new science of folding, fractals mean more than packaging?" But I didn't write the hook and my searches haven't worked. μηδείς (talk) 02:59, 28 February 2013 (UTC)

Quantum mechanical stability of historical timelines

"The Moving Finger writes: and, having writ,

Moves on: nor all thy Piety nor Wit

Shall lure it back to cancel half a Line,

Nor all thy Tears wash out a Word of it."

- Rubaiyat of Omar Khayyam

How well does that stand up against quantum mechanics?

Is the past in any way fixed or is it instead a swirling storm of uncertainties that we don't notice simply because we're just the product of the current history and so can't see the pasts that used to be? Hcobb (talk) 03:53, 24 February 2013 (UTC)

It's impossible to tell. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 04:28, 24 February 2013 (UTC)

Further reading I found while looking for this: Transactional interpretation. Hcobb (talk) 04:44, 24 February 2013 (UTC)

I've got two tests for the thread of history being in a vibrational state.

• Dark Matter might be echoes of past states of the past and so its fine scale structure could have certain harmonics.
• The Big Bang if connected to the present could have its structure influenced by the current configuration of the universe.

Hcobb (talk) 04:55, 24 February 2013 (UTC)

• You may want to check your ideas against this standard. --Jayron32 05:49, 24 February 2013 (UTC)

I think this is a deep and important question. We live in an indeterminate universe, and just as one present might be mapped to many futures, it might be mapped to many pasts. It seems like the religion of causality seems to suppose that a Watchmaker God decreed the past in some arbitrary and uninformative way, and the present is random, and the past is set in stone; but it would seem to me that the past is indeterminate, and the present is what we know. Indeed, I suspect you could argue solipsistically that whatever consciousness is - if it relies on some algorithm to somehow provide it with input - that it is impossible to distinguish the nature of the universe beyond what is consistent with the input of the present moment, and all the rest of the physical certainty, even memory, is an illusion, no? Wnt (talk) 07:58, 24 February 2013 (UTC)

There is no backward causality in quantum mechanics. -- BenRG (talk) 22:44, 24 February 2013 (UTC)

Would german V-2 rocket left earth orbit?

If a V-2 rocket would have been launced straight vertically with a 100 kg payload. Would it stay in space or fallen down ?, in particular would it left earth gravity for planetary space? Max altitude is specified as 206 km. Electron9 (talk) 05:50, 24 February 2013 (UTC)

This sounds like homework, but here's a hint: find out what the maximum velocity would be with a 100 kg payload and compare that with the escape velocity at your launch latitude. Zoonoses (talk) 06:59, 24 February 2013 (UTC)

Data on height vs velocity and escape velocity at specific height is missing.. Electron9 (talk) 07:53, 24 February 2013 (UTC)

You might like to read our Low Earth orbit article. Alansplodge (talk) 09:23, 24 February 2013 (UTC)

The article you link states that 206km is the maximum altitude if launched vertically. If it were capable of leaving the Earth's orbit, there would not be a maximum altitude, so it must fall down. Someguy1221 (talk) 09:26, 24 February 2013 (UTC)

So no secret Nazi base on the Moon? Clarityfiend (talk) 11:23, 24 February 2013 (UTC)

The first rocket reaching a low orbit with such payload was an R-7 Semyorka (280 tons) with its payload Sputnik 1 (83.6 Kg) in 1957. A V-2 was only 12,5 tons. --Kharon2 (talk) 21:31, 24 February 2013 (UTC)

Some book I read in high school many years ago said that the Germans in WW2 could theoretically achieved orbit with a V2 as the 1st stage, a cluster of some type of antiaircraft rockets as the 2nd stage and one such antiaircraft rocket as the third stage, implying that one stage to orbit was impossible for the V2. Getting the timing and steering to work is a different problem than thrust or specific impulse. Edison (talk) 22:15, 24 February 2013 (UTC)

A V-2 rocket couldn't possibly reach orbit -- but the proposed V-10 "Amerika-Rakete" two-stage version just might have. 24.23.196.85 (talk) 00:33, 25 February 2013 (UTC)

Something to remember is that V-2 is designed for a 1000 kg payload. If this is reduced, other orbits should be possible. Electron9 (talk) 02:37, 25 February 2013 (UTC)

No, to "reach orbit" means to stay there. Reaching the same height does not suffice. ForLow Earth orbit you need to accelerate into a trajectory with roughly 8 Km per second speed around the planet in addition to the height to stay there for a while. If a V-2 had been capable of that, the first satellite in orbit had been one of United States origin because they where the ones that actually captured all the remaining V-2's and their science- and engineering staff including Wernher von Braun. But as already pointed out the Russians won hat part of the race into space 12 years (1957) after WWII (1945). --Kharon2 (talk) 10:57, 25 February 2013 (UTC)

Think of it this way. Firing a V2 straight up means it moving up a gravity well as far as 206 km, where it stops going any higher. Now that it has stopped going up there is no kinetic energy left for it to resist the pull of Earth's gravity, which will cause it plummet back to earth. Fired straight up -on say the equator- and it will have a suborbital velocity of about a 1,000 mph, yet, fall back to Earth it will do ... quickly. To stay up, it will either have to have enough orbital velocity or perpendicular velocity or a good thick coating of Cavorite.--Aspro (talk) 19:35, 25 February 2013 (UTC)

Liquid nitrogen and frostbite

The image on the right shows liquid nitrogen is boiling and a person put his hand in the gas. Since the boiling point of liquid nitrogen is −196 °C, I am wondering why the person is not getting frostbite in his hand? The temperature of the newly formed gas is supposed to be −196 °C. --PlanetEditor (talk) 06:44, 24 February 2013 (UTC)

They might, eventually. However, being a gas, it has a low density and doesn't have much heat capacity. If he submerged his hands in the liquid, he'd get frostbite quickly. Try putting your hands in the refrigerator at 40 degrees F, then submerging them in water stored in the same refrigerator (which has reached 40°F), and you will notice how much quicker your hands get cold in the liquid. That said, having bare hands that close to liquid nitrogen is foolhardy. He should wear thick leather gloves. One slip and he could be seriously injured. StuRat (talk) 07:46, 24 February 2013 (UTC)

(ec) There are two important things about liquid nitrogen that make this less likely. First, low heat capacity - it doesn't store as much "cold" as it would seem - I'm getting "1.341j/g/K (gas), 2.042j/g/K (liquid), enthalpy of vaporization: 198.8j/g" from [1]. Our article properties of water says water has heat capacity 4.2 J/g/K around the freezing point, so you heat up the boiled nitrogen gas 3.1x faster than water, plus it absorbs the equivalent of 152 degrees when boiling, so it's sort of like "3.5 times colder than ice water" in terms of the energy it absorbs from your hand, in terms of hypothetical heat absorption.

But second, the liquid nitrogen surrounds itself in gas which rapidly pushes away from the skin, making it very hard to bring that full cooling to bear on it; there's poor heat conduction in a gas. It's a bit like a firewalk in that regard. I've held little drops of liquid nitrogen in my hand, but as the skin cools, they start to bite a little. If some prankster loaded a container of ethanol into the vessel holding the liquid nitrogen so that the demonstrator dipped his hands into that, I think there would be immediate injury. Wnt (talk) 07:52, 24 February 2013 (UTC)

The ethanol would freeze, of course. It melts at 159 K, whereas nitrogen boils at 77 K. Maybe you mean it would get cold enough to cause immediate injury before it froze? I suppose that's possible. But the violently boiling nitrogen around the container should be a clue. --Trovatore (talk) 08:00, 24 February 2013 (UTC)

You have a good point there. I suppose I was thinking that ethanol that has been sitting on dry ice is already quite cold enough! Wnt (talk) 08:44, 24 February 2013 (UTC)

Well their hand isn't really in the liquid nitrogen, probably just in the boiled off nitrogen and water vapour from the air. Making icecream with LN2 is very safe providing you know what you are doing. Your hand can get a bit cold when making ice cream like this over the minutes but unlikely to be so cold so as to cause any damage. When dipping your bare hand into liquid nitrogen you are protected by the Leidenfrost effect for several seconds so it feels cold but little heat transfer takes place. Damage is much more likely if the nitrogen gets stuck next to your skin for a longer period such as if it gets accidently poured in your glove or shoe and these can't be removed quickly. JMiall₰ 10:23, 24 February 2013 (UTC)

Thanks everyone. --PlanetEditor (talk) 13:26, 24 February 2013 (UTC)

One more interesting and important concept: the Leidenfrost effect. It's how people can stick their hand into boiling lead, for example. SamuelRiv (talk) 16:20, 24 February 2013 (UTC)

T-90 tank shtora system

Can Shtora system disable javelin missile ? 87.236.232.97 (talk) 08:19, 24 February 2013 (UTC)

It seems not, because Shtora "disrupts semiautomatic command to line of sight (SACLOS) antitank guided missiles, Laser rangefinders and target designators." The FGM-148 Javelin uses "an imaging infrared seeker". According to the China Defense Blog, "the Shtora is less effective against the more advanced third generation of ATGM such as the US Javelin or the German PARS 3 which relies on laser or electro-optical imager for guidance". Alansplodge (talk) 09:20, 24 February 2013 (UTC)

String or Higgs boson

Which fundamental particle give mass to all other particle? Is it string or Higgs boson? 106.215.104.44 (talk) 10:04, 24 February 2013 (UTC)

See higgs boson, higgs mechanism. "String" is not a particle, but a hypothetical model for all known particles. See string (physics). The higgs boson could hypothetically be a string. Someguy1221 (talk) 10:15, 24 February 2013 (UTC)

I guess you mean gives mass to other fundamental particles rather than all other particles i.e. not composite particles like a proton for the most part (see Proton#Quarks_and_the_mass_of_the_proton). Sean.hoyland - talk 10:33, 24 February 2013 (UTC)

Name of all 11 dimensions of space

I read in M-theory article that there are 11 dimensions of space. What is the name of all 11 dimensions? One is time and other 10 are ........ I read further in an another article that elementary particles are zero-dimensional. Then, what is the number of dimensions of an atom? 106.209.220.49 (talk) 11:58, 24 February 2013 (UTC)

To answer the first part of the question, space is four dimensional with the three spatial dimensions we are familiar with — you can call them length, width, and height or X, Y and Z — and time being the fourth dimension — see: Dimension (mathematics and physics)#Additional dimensions. It is not known whether any others exist, different theories posit 10, 11 and 26, so they haven't been named yet. Richerman (talk) 15:07, 24 February 2013 (UTC)

Also, it's useless to try to assign them names when we don't still know what they "look like". For example, they could be circular, so that walking along the "Q-axis" (a dummy name: t,x,y,z,q,l, etc) will quickly bring you right back where you started. For anything larger than the tiniest particles (e.g. gravitons), this "Q" is virtually non-existent. Or it could be like a sphere with "L" and "M" corresponding to latitude and longitude, again only fat enough for tiny particles to experience. One thing an extra dimension almost certainly is not, however, is like normal spatial length-width-height. If it were, we'd have seen it by now. SamuelRiv (talk) 16:18, 24 February 2013 (UTC)

This "names" thing is fairly silly in my view.

For spacetime (@Richerman: only spacetime is four-dimensional; space is still three-dimensional), you have one distinguished dimension which may be called "time". More precisely, there are "timelike" and "spacelike" intervals, and all observers will agree on which is which.

The remaining three, however, have no fixed "names". The names all correspond to a choice of (possibly local) coordinate system. For example, on the surface of the Earth, you'll probably use up/down for one axis, but whether you use left/right forward/backwards, or port/starboard fore/aft, or north/south east/west, depends entirely on your immediate purpose.

For what it's worth, and it isn't worth much, a writer by the name of Charles Howard Hinton proposed the names ana and kata for opposing directions in a fourth spatial dimension. How, or even whether, he proposed to distinguish between them, I am unaware. --Trovatore (talk) 00:05, 25 February 2013 (UTC)

In computer graphics, we use 'w' for the fourth dimension - hence x,y,z,w - but we rarely use more than 4 spatial dimensions. Isn't it the case with some varients of M-theory that there might be multiple time dimensions? That hurts my head! SteveBaker (talk) 21:02, 25 February 2013 (UTC)

Food energy

The standard food energy values, as given in our article and appears in most publications, are as follows:

• carbohydrate: 4 kcal/g
• protein: 4 kcal/g
• fat: 9 kcal/g

On the other hand, as given here and mentioned this journal article, energy value of fat is 9.3, and that of protein is 4.2 for meat protein and 4.3 for vegetable protein.

Now, this article published by the USDA says (p.4) energy value of protein is 5-6 kcal/g. This also describes the energy value of protein is 5.6 kcal/g. Why so many variations? I cannot understand the reason for the differences. --PlanetEditor (talk) 13:13, 24 February 2013 (UTC)

• I found this book which says "in vivo, the oxidation of protein is only party complete .... calorific value of protein, in vivo, is less, i.e. 4.1 Kcal/gm". The the book does not cite any reference. Definitely the USDA article is the most reliable. --PlanetEditor (talk) 13:20, 24 February 2013 (UTC)

• The main point here, is there any way to know whether the energy value of a food, as determined by bomb calorimeter, is different from energy value of the same food in human body? --PlanetEditor (talk) 13:36, 24 February 2013 (UTC)

It obviously is not. A bomb calorimeter can burn sawdust. A human body can not. The ash that a bomb calorimeter leaves behind cannot be ignited and burned. Dried dung can. The question is what the calorimeter operators do to compensate for these sources of error. See [ http://www.fishersci.com/ecomm/servlet/cmstatic?href=Scientific/researchAnalytical/ProductsServices/Food_Diagnostics/food_beverage_newsletter_bombcal.jsp&store=Scientific&storeId=10652 ]. --Guy Macon (talk) 19:49, 24 February 2013 (UTC)

Very interesting question; my first instinct would be that the caloric values given are for proteins/carbs/etc. which have already been digested and are being oxidized in the mitochondria, but I can't find a reference for that; note that the efficiency of digestion, for lack of a better phrase, varies between species and foodstuffs; cats don't extract as much from their food as goats, for instance. Gzuckier (talk) 06:26, 25 February 2013 (UTC)

I believe the caloric values are reference for calories available to humans. --DHeyward (talk) 05:27, 28 February 2013 (UTC)

Our mirror image is chiral or achiral

What is the nature (chiral or achiral) of our image formed in a mirror? 106.209.220.49 (talk) 13:25, 24 February 2013 (UTC)

This question indicates that you don't understand the meaning of the words "chiral" and "achiral". A chiral object is an object whose mirror image can't be superimposed on the original. An achiral object, in contrast, has a mirror image that matches the original. Looie496 (talk) 16:13, 24 February 2013 (UTC)

Then, what about our image formed on mirror? I want to know whether this image is able superimpose our body (achiral) or it isn't (chiral). 106.209.220.49 (talk) 16:56, 24 February 2013 (UTC)

If you are chiral, then your mirror-image is chiral. If you are achiral, then your mirror-image is achiral. --catslash (talk) 17:34, 24 February 2013 (UTC)

You may be interested in Julian Wolkenstein's Symmetrical Portraits series and his echoism.org site. Sean.hoyland - talk 17:46, 24 February 2013 (UTC)

If you part your hair on the right, the person in the mirror parts his hair on his left. If you take a picture of yourself and take a picture of yourself in the mirror, when you try to superimpose the pictures on each other the parts of the hair will be on opposite sides. So you are chiral. Even if you part your hair in the middle, you are still asymmetric and therefore chiral. Duoduoduo (talk) 18:14, 24 February 2013 (UTC)

Vegetarian Experience

Last summer I decided to be a vegetarian, and since then, something weird happened to me, I began to have dreams of me eating meat, and after a while I began to feel guilty about it in the dream, and in the last dream I had I actually spitted out the meat. I was just curious is it common/normal? Is it a way for my body to tell me I need meat? (Probably like sexual dreams?) I'm interested to know what's happening in my brain... Thanks!--Irrational number (talk) 15:15, 24 February 2013 (UTC)

I have taken the liberty of removing the first two copies of this question. It looks like something got screwed up with the post. Falconus^{p t c} 15:17, 24 February 2013 (UTC)

Thank you, I clicked on the "save page" button more than once, very slow connection here this is embarrassing... I feel like a cave man... — Preceding unsigned comment added by Irrational number (talk • contribs) 15:22, 24 February 2013 (UTC)

This falls into the category of "wish fulfillment" dreams -- a major type. (Freud thought that all dreams are of that type.) It simply indicates that you had a strong desire to eat meat. Looie496 (talk) 16:15, 24 February 2013 (UTC)

To continue using Freud, the desire to eat the meat comes from your id, while the desire to avoid it comes from your superego (which aims for perfection), and these are mediated by the ego. This conflict is being fought out in your dreams. StuRat (talk) 16:48, 24 February 2013 (UTC)

I think it might have been more normal if you had spat out the meat, rather than sticking it on spits. Food cravings are usually conscious. If your dreams are bothering you you need to see a medical professional. We can't do oneiromancy here. μηδείς (talk) 16:17, 24 February 2013 (UTC)

There's nothing in the question that would indicate that this is a wish fulfillment dream, or that Irrational number has a strong desire to eat meat. The only emotional reaction to eating meat that was expressed in the question is guilt, and the dream behavior of spitting out the meat would be consistent with disgust. Red Act (talk) 18:12, 24 February 2013 (UTC)

I believe it's normal. My own experience tells me that - I once gave up meat for Lent, and by Good Friday I was getting phantom roast chicken smells. Also my vegetarian friends tell me they still get cravings for meat, most commonly bacon. As to why this happens, I don't think there's any research into it that will tell you. So don't worry about it. --TammyMoet (talk) 16:37, 24 February 2013 (UTC)

There's no mystery about the attractiveness of the smell of roast chicken or bacon. See Maillard reaction. Bacon is a superstimulus, it's basically the essence of meat all in one high-fat crunchy protein package:again, Maillard reaction as well as Monosodium glutamate, etc. μηδείς (talk) 18:23, 24 February 2013 (UTC)

I would take the desire to eat meat as a sign that you're not getting enough protein (or possibly some other nutrient, like iron or Vitamin B12). If you want to remain a vegetarian, I suggest beans and nuts. (You might want to get some Beano, if you plan on getting your protein from beans without offending everybody you know.) If your version of vegetarianism permits eggs and/or dairy products, those are other options. My (extremely lax) version also permits fish. If iron or B₁₂ is the deficiency, there are other nutritional sources of those, too. StuRat (talk) 16:58, 24 February 2013 (UTC)

Re: "We can't do oneiromancy here", sure we can. We aren't allowed to give medical or legal advice, but oneiromancy, like other forms of divination, is certainly allowed, despite the control issues some folks here have concerning what other people post. And who better to interpret your dreams than some random stranger on the Internet? I agree with StuRat that cravings for meat and/or dreaming about meat may very well be a sign of an inadequate diet. It is a well-known fact that, while a vegetarian or even vegan diet can be healthy and balanced, you have to work at it. Wikipedia has some excellent info on this issue at Vegetarian nutrition#Potential nutrient deficiencies and Vegan nutrition#Nutrition. --Guy Macon (talk) 18:01, 24 February 2013 (UTC)

However, if the OP starts growing towards the light, he should see a doctor. Or maybe a gardener. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:17, 24 February 2013 (UTC)

I quit smoking at the start of the year and I've had a few dreams of me just chain smoking. Vespine (talk) 21:46, 24 February 2013 (UTC)

Actually, the OP is asking for medical advice, which is not allowed. However, any kind of change can lead to what I can "anxiety dreams". But if you're really concerned that there might be something wrong with you, see your doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:17, 25 February 2013 (UTC)

Correct me if I'm wrong but I think the definition of medical advice in the reference desk is getting wider. I didn't ask what I should do, I was just curious about how common this is and what is happening in my brain and why. Is any question about human body a request for medical advice? I think a request for advice must at least have a part in which the OP asks what they should do, which I didn't.--Irrational number (talk) 10:40, 25 February 2013 (UTC)

I agree. You wouldn't go to a doctor to ask him to explain your dreams, so it's not medical advice. (Of course, there are some things you might ask a doctor that don't require a doctor to answer, like "How can I reduce my sodium intake". They would likely refer you to a nutritionist.) StuRat (talk) 15:47, 25 February 2013 (UTC)

"What's happening in my brain?" is a question only a doctor can answer, through diagnosis of the OP. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:44, 26 February 2013 (UTC)

Since all learning happens in the brain, then all academic questions, according to your criterion, should be referred to a doctor. StuRat (talk) 17:20, 26 February 2013 (UTC)

Why stop at academic questions? Let's make it about all questions, period. Here's an idea: We don't allow anyone to ask a question on the Ref Desk, until they produce a certificate from a doctor or a lawyer saying they've attended and asked their question but were advised to seek external help from the Wikipedia Reference Desk. Yes, that ought to fix it. -- Jack of Oz ^[Talk] 22:51, 26 February 2013 (UTC)

stereoscopic images

How much did it cost to make them in the 1800s' — Preceding unsigned comment added by 172.218.36.253 (talk) 20:45, 24 February 2013 (UTC)

About twice as much as it took to make a normal photograph. Back then the one-time equipment costs were much higher (new technology) and the per-image costs comparatively lower (they re-used plates instead of buying more film). --Guy Macon (talk) 21:42, 24 February 2013 (UTC)

Refs for stripping the emulsion off plates and re-using them? I thought plates were mostly one-time use. Edison (talk) 03:54, 25 February 2013 (UTC)

There really isn't any reason why they shouldn't be exactly the same price as two normal photographs - that's really all they were. They'd either use a special camera with two lenses that could expose two images at the same time...or for things like landscapes that don't move much, they'd take two consecutive photos - moving the camera sideways by some amount between. They'd develop the two images separately and either print them onto one piece of paper or make two slides - depending on how the viewer worked. But throughout the process - it's nothing more than taking two pictures...it ought to be cheap. Of course they may have charged extra to do it just because that's what the market would stand...but I don't see any particular reason why it should cost more to make them. SteveBaker (talk) 20:59, 25 February 2013 (UTC)

Rate of exothermic reaction

Let's assume one wishes to measure the rate of reaction for an exothermic reaction in aqueous solution. Would measuring temperature of the reaction and graphing the temperature at given intervals be an accurate way to measure this? Is there a given point where the reaction would be able to be determined "finished"? And if this is a viable method, what type of container would be most useful? Must one use a calorimeter, or just any beaker or flask? 66.41.216.19 (talk) 22:36, 24 February 2013 (UTC)

Well, the temperature will be cumulative, ignoring cooling to the environment, so you might want to graph the change in temp versus time, rather than the temperature itself. An insulated container would be best, to minimize the effect of cooling to the environment. However, beware that some reactions might get out of hand, leading to an explosion, in such a situation, as the insulated container may increase the temperature, and thus the reaction rate. The reaction is finished when the temperature change is zero (smaller time increments provide better data). StuRat (talk) 22:57, 24 February 2013 (UTC)

So you're saying I should record the change in temperature over each, say, 5 second period until the temperature ceases to change? I was only planning on reacting zinc with 3.0 M HCl, so an explosion risk is low. However, I am not sure if a calorimeter would affect the rate of reaction as you just said. If so, how so? Would I have to know the calorimeter constant? Or would I be better off with a beaker? I'm just trying to find a way one could measure rate of reaction between these particular compounds. 66.41.216.19 (talk) 23:06, 24 February 2013 (UTC)

Well, most reactions are sped up by higher temps, but there may be a few exceptions (say if the higher temperatures cause one of the reactants to change into a gas, and leave the reaction vessel). Now, why exactly do you want to know the speed of the reaction ? If there was a Q you were trying to answer, like "does the color change take place during the reaction or after it has completed", then speeding it up wouldn't matter. If, on the other hand, your question is "how long does the reaction take to complete at STP", then you not only need to avoid an insulated container, but you might want to cool it to standard temperature during the reaction, depending on how you interpret the Q.

Also note that in any sealed reaction vessel, you may also need to account for the effect of a change in pressure, as that can change the reaction rate, too.

Is every 5 seconds the fastest you can measure temps ? If you are doing it manually, that's about right, but automated temperature probes/recorders ought to do far better than that. StuRat (talk) 23:38, 24 February 2013 (UTC)

Maybe once per second with the technology I have available. I want to find out the rate of the reaction to investigate the effect of surface area of Zn(s) on rate. I would use solid lumps of zinc, zinc filings, and zinc powder in a constant amount (molarity) of HCl. Rate is my dependent variable, and form of zinc is my independent variable. The rate of reaction, I thought, might be the initial number of moles of Zinc (constant for each trial set) divided by the amount of time before the temperature ceases to change. Is there an easier way? 66.41.216.19 (talk) 23:46, 24 February 2013 (UTC)

About how long does this reaction take, in the slowest case ? The only problem with the open reaction vessel is that, when the reaction is trailing off, the small amount of heat produced may equal that lost to the environment, so it will appear that the reaction ended earlier than it did. You might want to try it both in the bomb calorimeter and in the open vessel, to see if the ratio is different between the fastest and slowest reactions. If not, just stick with the open vessel. StuRat (talk) 23:52, 24 February 2013 (UTC)

I have a styrofoam calorimeter with a small hole in the lid to permit gases to escape, therefore keeping temperature loss at a minimum while keeping pressure constant. Is this OK? (thnx for ur patience) 66.41.216.19 (talk) 23:54, 24 February 2013 (UTC)

Sounds reasonable to me (provided that nothing will react with the Styrofoam). Of course, keep in mind that any experiment is only a model of "the real world case". So, for example, if you want to know which is faster for designing an industrial reaction process, then you'd want to set up your experiment as closely to the industrial process as possible. StuRat (talk) 00:03, 25 February 2013 (UTC)

Better quality safety glasses

I noticed when I buy clear safety glasses they don't have very good clarity to them and seem to stop light transmission to some degree. They also get a lot of glare on them. I don't wear prescription glasses but I have friends that do I have looked through their glasses and the plastic they are made from has very good light transmission and is extremely clear. They also seem to get almost no glare. I'm wondering if you can buy safety glasses with the same quality lenses that they make prescription glasses from. --Tommythehook (talk) 23:47, 24 February 2013 (UTC)

Well, plastic will get tiny scratches over time, which will make them look foggy. Glass won't do that. Of course, glass could be quite dangerous, if it shatters. So, there are special types of glass which are less likely to shatter, which would be suitable for safety glasses. StuRat (talk) 23:57, 24 February 2013 (UTC)

Most prescription glasses are not made from glass. Also my safety glasses have problems brand new, its not due to scratches.--Tommythehook (talk) 00:11, 25 February 2013 (UTC)

There are 2 reasons why presciption specs are better: 1) anti-reflection coatings, and 2) frames for prescription use have the lenses closer to the eye - thus making surface imperfections further out of focus and so less noticeable. This question has come up before, for a possible solution - see http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2012_June_15 Ratbone 124.178.54.230 (talk) 01:12, 25 February 2013 (UTC)

I'm pretty sure it's the same banned sockpuppet so I guess the previous answers didn't help. Nil Einne (talk) 05:11, 25 February 2013 (UTC)

is it possible that prescription glasses are simply made from a higher quality polycarbonate?--Tommythehook (talk) 16:05, 25 February 2013 (UTC)

Depends on what country you live in. In Europe one can buy safety glasses that meet standards suitably matched for your intended use. [2]. All you need to do is google standards,safety glasses and local retail out lets, etc.--Aspro (talk) 20:13, 25 February 2013 (UTC)

We also have to be super-careful about what kind of safety glasses we're talking about. My most-often-worn safety glasses are to protect my eyes from infrared light from a CO2 laser. They are made from high-quality polycarbonate - cost close to $100 and they are very different beasts from the $10 ones I use when operating a table saw to prevent wood chips from hitting my eyes. The $100 pair are indeed very clear and I don't get problems with glare with them - I'm fairly sure that they'd stop a fast-flying wood-chip - but that's not what they are designed to do. SteveBaker (talk) 20:49, 25 February 2013 (UTC)

One might say from the above post that: you get what you pay for. Just a thought: if the OP belongs to a trade union or similar organization he may be able to get good eye protection where he can offset the cost against his income tax. This is common in Europe were you can get eye protection for nothing if it is in connection with your employment. Being a safety concern, one only has to provide the slightest reason why you qualify. Are you ever (even once in 12 months) in an area where your company’s delivery vehicles are are maintained? Right, you might be passing by when a mechanic is toping up the battery with dangerous sulphuric acid – you need eye protection. Your company/government may pay for this. Self employed? Do you ever have to (in connection with your trade) go near any dangerous chemicals – Strong vinegar is a nasty substance if it gets in your eyes. After reading the official safety warnings, why they allow supermarkets to sell it -I don't know. You need googles – even if your an accountant and never come across anything stronger than a letter form IRS. Mind you, when I look at my accountant's bills, I feel like I could do with some super eye protection.--Aspro (talk) 23:29, 25 February 2013 (UTC)

The thing is I have looked at some expensive safety glasses like $100 Oakley safety glasses and they don't look very clear to me. What brand are your laser safety glasses? --Tommythehook (talk) 15:21, 26 February 2013 (UTC)

February 25

Pot stats in USA

Hello all, I'm trying to find a comparative breakdown of the marijuana abuse rate trends state-by-state from 1998 to present. Here are the requirements I have for this data: (1) it must be from a reputable source; (2) it must show the marijuana abuse rates separately for each of the 50 states; (3) it must show these rates over several years, preferably over the entire period from 1998 to present; and (optional but preferred) it wouldn't hurt if it indicates which of the states have legalized pot, and in what year. I've been trying to find it for days, but all the studies I've found either aggregate the data over the entire country, or else they only have the data for one year (two at the very most). Thanks in advance! 24.23.196.85 (talk) 00:44, 25 February 2013 (UTC)

Not that I have an answer in any case, but I think you need to specify what you mean by "abuse". Do you mean, say, (1) any recreational use, (2) recreational use in violation of state law, (3) usage that causes medical harm or makes it difficult for the user to discharge his ordinary responsibilities? The most justifiable sense of the word "abuse" is number 3, but it's also a bit vaguely defined, so precise stats would depend on who is judging. --Trovatore (talk) 00:58, 25 February 2013 (UTC)

Because marijuana is largely illegal, it's almost impossible for precise figures on anything to do with its use to be collected. HiLo48 (talk) 01:15, 25 February 2013 (UTC)

Yes, that's true. Still, there is an extra layer of ambiguity added by the term abuse. On the other hand, I suppose it's possible that there are avenues to track genuine abuse (sense 3 in my list) that are not available for private use that doesn't cause obvious harm. For example, you could interview doctors and ask them to provide aggregate statistics, without identifying any individual. --Trovatore (talk) 01:20, 25 February 2013 (UTC)

I actually meant "abuse" in sense (1). 24.23.196.85 (talk) 01:28, 25 February 2013 (UTC)

Since that's not the normal use of the term "abuse", I suggest you use the term "recreational use", instead, when doing searches. StuRat (talk) 01:31, 25 February 2013 (UTC)

Anti-drug warriors are probably the only ones who use "abuse" in sense (1). ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:14, 25 February 2013 (UTC)

or sense 4, insulting and belittling the substance until it feels bad about itself, or sense 5, physically injury to the substance Gzuckier (talk) 06:32, 25 February 2013 (UTC)

I remember a girl who would look for any opportunity to use the phrase "that's alcohol abuse!". Examples might be spilling beer or dropping a bottle of champagne. --Trovatore (talk) 08:19, 25 February 2013 (UTC)

Getting into off-topic politicizing, sprinkled with personal attacks. Let this one go, mmmkay? — The Hand That Feeds You:Bite 00:02, 28 February 2013 (UTC)
The following discussion has been closed. Please do not modify it.
To Mr. Bugs: Since when is there anything inherently wrong with being an anti-drug warrior? 24.23.196.85 (talk) 06:52, 25 February 2013 (UTC) Ever since it became blatantly obvious to all rational people that the war on drugs was never going to reduce drug usage. HiLo48 (talk) 07:19, 25 February 2013 (UTC) Well, that's not really all that logically connected — you could be a crusader in a hopeless cause and still be right. But the more pertinent question is, why should we consider all recreational use of marijuana to be "abuse"? Is there any decent evidence that the people who so consider it are right? --Trovatore (talk) 08:18, 25 February 2013 (UTC) The key here is that we should avoid words that place a normative value on behavior. Instead, as most researchers do in areas such as this, we need use terms that themselves don't contain values; abuse implies a negative connotation, while a word like "use" does not. "Use" is not debatable: either a person has or has not used marijuana. Abuse, on the other hand, requires us to place values on which kinds of uses (if any) are allowable or not, and as such, words like that should be avoided. --Jayron32 16:06, 25 February 2013 (UTC) To HiLo48: There are plenty of rational people who support the War on Drugs (or in any case oppose legalization), so your implication that their views automatically make them irrational is a flat-out lie! Now get lost, you America-bashing pothead! 24.23.196.85 (talk) 01:22, 26 February 2013 (UTC) "Rationality" means, at the minimum, being able to draw valid conclusions from given premises. While HiLo may or may not be an America-bashing pothead, your conclusion that he is doesn't follow from the evidence available, making your rant a good example of irrationality. I also suggest that you read WP:CIVIL and WP:NPA before posting again, remembering that all of us are unpaid volunteers. If you're not able to follow these policies, I think you're the one who should get lost. --140.180.254.250 (talk) 01:48, 26 February 2013 (UTC) It DOES follow from the derogatory statements about my country that he makes on his user page, AND from some of his previous comments! (Like, for example, the following: "I also find it necessary to protect Wikipedia against, again, mostly American editors who want to impose conservative, middle American Christian values here. Apparently Conservapedia isn't enough for them.") And as an American patriot, I don't HAVE to be civil to America-haters like him! So I say once again: HiLo48, fuck off! 24.23.196.85 (talk) 06:25, 26 February 2013 (UTC) A rational person would realise that my comments are not criticism of a country. In fact, to criticise a whole country would be pretty weird. HiLo48 (talk) 06:32, 26 February 2013 (UTC) And yet I remember you calling all Americans stupid a while back! 24.23.196.85 (talk) 00:02, 27 February 2013 (UTC) Please point out where, in WP:CIVIL or WP:NPA, it says that "American patriots" are exempt from its proscriptions, or that "America-haters" are exempt from its protections. By editing Wikipedia, you agree to be bound by its policies. I would also note that you are reinforcing common negative stereotypes about Americans, and as such, are hurting your patriotic cause more than HiLo ever could. --140.180.254.250 (talk) 08:07, 26 February 2013 (UTC)

Nothing wrong with it, but I wouldn't look for unbiased statistics from anyone with a particular political agenda. I also wouldn't trust any figures from the participants in the Hash Bash. If you want reliable stats, look for them from uninvolved scientists, who won't tend to use subjective terms like "abuse". StuRat (talk) 07:20, 25 February 2013 (UTC)

That's what I'm trying to do -- but the problem for me is not finding reputable and unbiased sources (I've already found quite a few on my own), it's finding sources that track pot abuse separately in each state instead of aggregating the data for the whole nation. What I need are comparative statistics among the different states, not just one rate for the whole country. 24.23.196.85 (talk) 01:29, 26 February 2013 (UTC)

Until you lose that politically-charged term "abuse", you're not likely to get a good answer here. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:42, 26 February 2013 (UTC)

And I still can't see how realistic statistics can be collected on the use of something illegal. HiLo48 (talk) 20:47, 26 February 2013 (UTC)

Indeed. The best data anyone is likely to get would be what are technically known as "guesstimates". ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:27, 26 February 2013 (UTC)

Lithium ion batteries

Can electronics with lithium ion batteries be damaged if you don't use it enough or don't charge it fully before taking it off the charger? Clover345 (talk) 01:58, 25 February 2013 (UTC)

No, not if the battery is working correctly, but you can potentially shorten the life of the battery. Looie496 (talk) 02:57, 25 February 2013 (UTC)

How often does it need to be used or charged fully to prevent this? Clover345 (talk) 10:32, 25 February 2013 (UTC)

That's not right Looie. Removing a lithium ion batteries from the charger before it's fully charged doesn't shorten the life of the battery. In fact, the opposite is true. Charging the battery up to 100% shortens the life of the battery. Dauto (talk) 14:45, 25 February 2013 (UTC)

So which is it and why? Don't most electronic manufacturers recommend that you charge up to 100% at least once a month? Clover345 (talk) 16:38, 25 February 2013 (UTC)

(edit conflict)Yes, Li-on cells behave differently from other rechargeables. They must never be deeply discharged, and the control circuitry normally protects against this by cutting off the power when the voltage falls to a minimum level. For this reason, they can become unusable if left discharged for a very long period. Other than this, it probably doesn't make much difference to the life if you charge from half-discharge or give a quick boost charge to less than full. Dbfirs 16:42, 25 February 2013 (UTC)

I would guess that the reason is to ensure that the battery never becomes fully discharged. My camera battery has been left without charging for many months and still works perfectly and holds a good charge. Dbfirs 16:44, 25 February 2013 (UTC)

... later note: ... I'd forgotten about recalibrating the power gauge for discharge monitoring. (Failing to do this might give an apparent shortening of battery duration, but this will be corrected when next fully charged.) See Guy's links below. Using Li-on cells without control circuitry is not to be recommended unless you really know what you are doing. Dbfirs 08:21, 26 February 2013 (UTC)

I have designed several Lithium-Ion Battery chargers. I have prototyped several different approaches, but I always end up going back to using a subset of the Atmel ATAVRBC100 battery charge management reference design ( http://www.atmel.com/Images/doc8088.pdf http://www.atmel.com/images/doc8080.pdf ) using an Atmel ATtiny25 ( http://www.atmel.com/Images/doc2586.pdf ). As you can see from the datasheet, this is a smart charger design which allows the user to just connect the battery and walk away without worrying about overcharging or undercharging. In most cases (laptops, cellphones), there is another smart battery management circuit handling the discharge cycle, which allows the user to just let the device run until it stops working without worrying about overdischarging or underdischarging. That being said, if you don't have smart chips managing your battery (handheld power tools often just run the battery flat and cheap chargers just let the battery cook) you should manage the charging and discharging yourself. Here are some pages with good advice for doing that: http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries http://preview.powerelectronics.com/mag/504PET23.pdf http://www.techrepublic.com/blog/five-apps/five-tips-for-extending-lithium-ion-battery-life/289 --Guy Macon (talk) 19:27, 25 February 2013 (UTC)

Does exercise really result in weight loss?

Science writer Gary Taubes says exercise has no effect on weight loss. On the other hand, the mainstream medical establishment believe in "calorie in-calorie out" theory of adiposity, i.e. if you spend more energy than you eat, you will be lean, if you eat more than you spend, you will be fat. Is it really true exercise does not result in weight loss? If so, then why do we see so many people who claim they lost weight after exercising? I could not find any scientific criticism of Taubes' claim regarding exercise. Is his claim right or wrong? If Taubes' theory is right, then how could the heaviest person Manuel Uribe lose 400 kg (597 kg to 200 kg) after diet and exercise program? And if Taubes is wrong, why there is no scientific criticism? --PlanetEditor (talk) 03:42, 25 February 2013 (UTC)

This is very individual. I personally have definitely had periods of long-term weight loss success based mainly on exercise. But it all depends how your calorie intake responds to an exercise program. Some people may get hungrier and eat more; other people may find that the exercise relieves stress that they had been treating with food, so they actually eat less (or at least not much more). --Trovatore (talk) 03:46, 25 February 2013 (UTC)

It very much depends on your assumptions:

1) If you start to exercise, without changing anything else, specifically your diet, then you should lose weight (or at least gain it more slowly than before), as the same number of calories are going in, and some of those are now being burnt by exercise.

2) If you also increase the calories you consume, because the exercise makes you hungrier, then you might still lose weight, see no change, or even gain weight, depending on if the additional calories consumed are more or less than those burned by the exercise.

However, in any case, exercise should make you healthier, by converting fat to muscle, etc. (assuming you don't pick a dangerous or injury-prone exercise). Also note that the fastest way to lose weight is to both cut calories and exercise, although such rapid weight loss may not be healthy. StuRat (talk) 03:49, 25 February 2013 (UTC)

This is a common question on Ref Desk, and StuRat has given you a good common sense answer. For lots of discussion on this, search Ref Desk archives for "exercise weight loss" (see the search filed at the top of this page). See for example http://e.wikipedia.org/wiki/Wikipedia:/Reference_desk/Archives/Science/2010_July_1#Weight_loss. I'll summarise here: If, over a sustained period of time, you eat the same calorific value as you did before, but increase your physical effort, then the increased mechanical energy you expend has to come form somewhere - if not from the food, then it MUST come from metabolising body mass - there is no other source.

I worked for a few years for a large company who had a large office tower. Floors 1 and 2 were a calls centre - about 200 women sitting at desks answering phones. Floor 3 was the staff canteen. Call centres are renowned for fat workers, due to sitting on their arse for hours at a time doing nothing but talk and click the mouse, maybe push the odd keyboard key. But some women were trim and remained trim. Some women were fat and just got fatter the longer they worked there. Guess which ones walked up the stairs to go to the canteen to eat their subsidised food? Guess which ones always took the lift, just to go up or down one or 2 floors?. Guess which ones parked their cars in free parking a kilometer away and walked the remaining distance? Which ones used paid parking next door? Yup - you got it - its the fat ones who didn't do any walking - every time.

Wickwack 124.178.143.40 (talk) 04:38, 25 February 2013 (UTC)

Since nobody seems to have mentioned it, note that replacement of fat with muscle might not result in "weight loss", in that muscle is heavier than fat. Probably less important for a 400 pounder than for somebody trying to get from 175 to 170. Gzuckier (talk) 06:35, 25 February 2013 (UTC)

That will occur if the degree of exercise and food intake are sufficient. However, it does not, and can not, change what StuRat and I said above: If food intake is not increased, then over a sustained period of time, increased exercise MUST reduce your weight. In fact, weight will go down whenever a regime of food digestable calorific value greater than body metaboloic need + mechanical energy produced is sustained. The ratio of muscle mass to fat mass might well change, but total body mass MUST go down. In theory, there are a couple of factors StuRat and I did not cover (they were covered by people posting in response when this question was asked before - did you check the archives?): 1) Expelled faeces contain unburned calorific value; and 2) the metabolic uptake of the brain is dependent of how hard it works (including how hard you think/concentrate on problems). However, variation in brain metabolic uptake is not in practice great enough to make a noticeable impact on total body mass, unless you do silly thinks like use drugs to sleep most of the 24 hours in a day. The body also has minimal ability to improve digestion efficiency - and the reason why faeces have calorific value is becasue that calorific value is in things like celulose fibre that humans cannot digest. Wickwack 60.230.230.154 (talk) 07:06, 25 February 2013 (UTC)

And another minor factor is how well hydrated the person is. If they sweat heavily as a result of the exercise, and don't drink more fluids to replace those fluids, they may also lose weight by being dehydrated. Not healthy, of course. StuRat (talk) 07:14, 25 February 2013 (UTC)

True. And taking a duretic (herbal or prescription dug) will reduce weight. Eating more salt will, by causing water retention, increase weight. although in healthy people gnerally middle aged or younger, the kidneys are very effective in getting rid of excess salt. However, significantly modulating your weight by any of these methods will eventually cause other medical issues - as you said - not healthy. Wickwack 60.230.230.154 (talk) 07:24, 25 February 2013 (UTC)

What being physically fit does is that it makes your weight less dependent on your calorie intake. E.g. my weight has been stable at 60 kg during the last 4 years or so. I eat approximately 3500 Kcal per day. If I eat 200 Kcal per day more or less, it would have zero effect on my weight, because my body is working much harder than the average body to maintain itself in its present super fit state. I can quit exercising for a week and eat 4000 Kcal per day and still have no weight gain at all. Some people are naturally thin and have a constant weight (without necessarily being very fit), see here. Count Iblis (talk) 13:10, 25 February 2013 (UTC)

Muscle weighs more than fat, so some types of exercise for some people may actually increase their weight. The thigh muscles, for example, can be particularly heavy when well developed. --Dweller (talk) 13:19, 25 February 2013 (UTC)

Yes, that's what Gzuckier said above, but how is it relevant? More correctly, muscle is more dense than fat. But how much extra muscle mass do you gain by exercising more, over a sustained period? For reasonable exercise levels, not a lot. Think about it - an average office worker does not need to grow any muscle to go walking - he already has it. His muscles will just run at a higher metabolism to provide the mechanical energy. And muscle is only about 15% denser than fat anyway - not enough to matter much - See http://en.wikipedia.org/wiki/muscle (last para under heading Types of tissue). Unless you eat more, fat will have to be burned - you will get thinner - and you'll weigh less, because the energy storage value of fat is abou 32 kJ/g whereas muscle build is about 12 to 16 kJ/kg. I did weight training in my 20's. And I did put on a lot of muscle mass. But I ate twice as much food too. Wickwack 60.230.197.212 (talk) 15:08, 25 February 2013 (UTC)

Thanks for explaining it, however I have problem understanding the energy storage value concept. the energy storage value of fat is about 32 kJ/g whereas muscle build is about 12 to 16 kJ/kg. please explain. Thanks. --PlanetEditor (talk) 17:24, 25 February 2013 (UTC)

You may be referring to the fact that I accidentally typed "kg" where I meant "g". Muscle isn'y that cheap to make. If you meant your question as written, here's the answer: In the case of fat, it's simple. When the body is storing energy in fat, 1 gramme of fat mass is added for each 32 kJ stored; for each 32 kJ recovered for use, fat mass goes down by 1 gramme. To build 1 gramme of muscle, energy is required, which must come from either food or fat, to the extent of 12 to 16 kJ/g. However this is a rough guide only, and the body is not able to build or tear down muscle as well as it can make/consume fat. Wickwack 60.228.241.158 (talk) 23:44, 25 February 2013 (UTC)

Also note that the amount of calories burned by aerobic excercise, while not negligible, is quite small. An hour of a typical aerobic exercise is worth less than a whopper - see [3]. There are side benefits to training, like increased fitness and more muscle mass, which have a second- or third-order effect on weight, but it is very hard to exercise against an overly rich diet. --Stephan Schulz (talk) 14:01, 25 February 2013 (UTC)

Thank you everyone. --PlanetEditor (talk) 17:24, 25 February 2013 (UTC)

The "muscle weighs more than fat" statement is very relevant to dieters whose only goal is to lose weight, such as the subscribers to programmes such as "Slimming World" or "Weight Watchers". I've seen many women lose several inches from various points of their bodies, only to be dismayed at the weigh-in because the actual numbers of pounds lost has not met expectations. This causes more severe dieting and more exercise, which in turn results in more muscle mass, which in turn results in fewer pounds lost, which results in more severe dieting and more exercise... which may tip a younger person over into anorexia nervosa. Other diet plans such as Rosemary Conley's emphasise inches lost over pounds lost. So it's important to emphasise to (especially) young women dieters that poundage lost is just one of the ways in which diet and exercise plans work. --TammyMoet (talk) 21:34, 25 February 2013 (UTC)

The "muscle weighs more than fat" is one of the most missunderstood statements around. Check proper scientific literature - there is in fact only a slight difference as I said earlier - did you check the Wiki article I cited, or scientific literature?

One should be very carefull when considering "facts" given by anyone associated with the weight loss or dieting business. In the case of women, you need to take into account that under dieting, especially rapid dieting or the early stages of a sustained calory restricted diet, the female body is very selective in where it consumes fat. Usually "spare tyre" fat and breast fat (unless the woman has inherited very small breasts) goes first, giving them a smaller clothing size. Fat at the top of the legs goes next. Fat in all sorts of hidden places of the body, such as within the chest, goes last. This means that waist measurement and clothing size goes down faster than total fat loss, even if muscle mass remains the same. Fat consumption in men is also selective, but the distribution of fat consumed first is different.

Wickwack 60.228.241.158 (talk) 00:05, 26 February 2013 (UTC)

I'm sure there is plenty of scientific literature regarding this. What I'm telling you is how this is perceived by dieters and how they use the statement (or not) in their lives. Some companies (such as the two I mentioned) will play on this to hook gullible dieters into their programmes and carry on paying their money every week to be publicly humiliated at the weighing scales. As with everything, where there's money there's charlatans. --TammyMoet (talk) 09:10, 26 February 2013 (UTC)

Exercise Is an Effective Intervention in Overweight and Obese Patients, Alansplodge (talk) 01:47, 26 February 2013 (UTC)

Ozone hole over Antarctica

We all know that there is a ozone hole over Antarctica. But Antarctica doesn't have any industry, factory, refrigerator, etc. Despite there is hole over Antarctica. Why is it so? Technologous (talk) 15:30, 25 February 2013 (UTC)

Because CFCs don't float straight up and stay still, they float around, until they are approximately evenly distributed. The good news is, since they've been banned, the ozone hole seems to have largely closed, as the CFCs gradually dissipated. StuRat (talk) 15:37, 25 February 2013 (UTC)

Have a look at Ozone_hole#Ozone_hole_and_its_causes. Basically, the CFCs get transported from their sources around the world to polar regions, and then get trapped there due to a polar vortex. Once there, they remain concentrated for a long time, and facilitate ozone destruction. SemanticMantis (talk) 15:41, 25 February 2013 (UTC)

(post WP:EC, I do not believe that the CFCs are evenly distributed, I believe they are concentrated at the poles, as outlined in our article. I welcome referenced information to the contrary. Stu is right that the the ozone hole is not the problem that it once was. This is largely due to the Montreal protocol.) SemanticMantis (talk) 15:41, 25 February 2013 (UTC)

Actually, while it had stopped growing, it has not yet shrunk significantly. --Stephan Schulz (talk) 15:58, 25 February 2013 (UTC)

You will notice that the Ozone Hole (!)^TM was discovered in the same year the first satellite that could detect it was launched. In other words, we have no reason to believe it didn't always exist. Its cause is unknown. μηδείς (talk) 02:10, 26 February 2013 (UTC)

Not true. () It was 320 in 1956. Sagittarian Milky Way (talk) 03:45, 26 February 2013 (UTC)

As an aside, I believe there is a typo in this diagram: -- shouldn't it read anthropogenic instead of antropogenic? I do not know how to change it, sorry. DRosenbach ^{(Talk | Contribs)} 18:21, 26 February 2013 (UTC)

You've given as a source for a 1950 stat a graph without refs that goes back to 1980? I am old enough, Sag, to remember when this so called discovery was announced in the mid-late 80's. μηδείς (talk) 02:43, 28 February 2013 (UTC)

Why protein requirement is calculated on the basis of total body weight?

The daily protein intake, RDA or other protein requirement calculations, are based on g/kg or g/lb of body weight basis. But protein is required mainly for muscle, the fat mass of the body has nothing to do with dietary protein. They why the daily value is not calculated on the basis of the weight of lean body mass? Why is it calculated on the basis of total body weight (lean body mass + weight of fat)? --PlanetEditor (talk) 17:38, 25 February 2013 (UTC)

Just because most people don't know their lean body mass. Note that people with a lot of fat on them do also tend to have more muscle, in order to be able to lift all that fat. So, it's not as bad of a method as it sounds. If we really wanted to be precise, we should probably also increase protein requirements for growing children and pregnant or nursing women. StuRat (talk) 17:53, 25 February 2013 (UTC)

Do you have any reference for that? --Jayron32 18:09, 25 February 2013 (UTC)

For what ? StuRat (talk) 18:10, 25 February 2013 (UTC)

For anything you just wrote. --Jayron32 18:14, 25 February 2013 (UTC)

I don't think needing more muscle to support more weight needs a reference. How many 100 lb people can lift 300 pounds ? Just about none. How many formerly (adult) 100 lb people who now weigh 300 lbs can lift themselves up ? Just about all. Do you imagine they developed psychokinesis to lift themselves up, if not muscles ?

Or, look at it this way: If you wore weights around all day, would you gain muscle mass ? Of course you would. (Although there may very well be an exception for those who are bed-ridden, but that's a small portion of the obese.) StuRat (talk) 18:17, 25 February 2013 (UTC)

I'm not saying your statement is right or wrong, just that you shouldn't make assumptions on what people will and won't find self-obvious. Mainly because a) if it was so obvious it didn't need a reference, there's no need for you to say it in the first place and b) if it's not obvious enough that you had to mention it because you thought the OP didn't know it, you should include a reference to it. I can find at least one source that says the opposite: "Obese people tend to have a lower percentage of muscle mass because of muscle atrophy and lack of exercise." and later in the same source "obesity can alter the neural pathways in a way that accelerates skeletal muscle loss." So, we have at least one source that indicates that obesity can cause muscle loss. --Jayron32 18:31, 25 February 2013 (UTC)

You're looking at percentage of muscle mass, not total muscle mass. Yes, the obese will have a somewhat lower percentage of muscle mass, but the actual amount will be higher. Just to toss some wild numbers out, if the 100 lb person had 50 pounds of muscle, then, when they gain weight to become 300 lbs, they might have 100 lbs of muscle mass. The percentage dropped from 50% to 33%, but the amount of muscle actually doubled. So, if the OP was thinking the 300 lb person would only have the original 50 lbs of muscle mass, and therefore only need the same amount of protein to support that as they did when they weighed 100 lbs, this helps to clarify the situation.

As for your point a, there are many things which are obvious once mentioned, but which you don't tend to think of yourself. For example, if you asked "How do we know that ice is less dense than water ?", many people wouldn't think to answer "Because ice floats", but, once you tell them that, they would understand and agree. StuRat (talk) 18:40, 25 February 2013 (UTC)

The article says "obesity can alter the neural pathways in a way that accelerates skeletal muscle loss. (bold mine). You have not addressed this. As I said before, I'm not terribly interested in what you find obvious or not. I'm interested in what you can find verification for. Telling me that you find something obvious doesn't help the OP find references to answer his questions. You shouldn't be arguing with me, as that doesn't help the OP find references to his questions. You should be finding references to the OPs questions. And if the OP wants to know why ice floats, it would help to provide a link to articles like density so they can learn more. --Jayron32 18:44, 25 February 2013 (UTC)

You have yet to produce a source which says the actual amount of muscle stays constant as people gain weight. Our lean body mass article lists formulas which estimate lean body mass, being roughly proportional to total weight and height. StuRat (talk) 18:45, 25 February 2013 (UTC)

Look, I've never said you were right or you were wrong. I've said that you're the one, when making statements, upon which the burden of evidence lies. You could be right for all I know. All I am asking for is a little bit of evidence. Not a lengthy argument about why you should be exempt, among everyone, from providing evidence. --Jayron32 18:54, 25 February 2013 (UTC)

You said I have not addressed your source, as if your source says something counter to what I claimed, when it does not. See that article I linked to for references supporting my claim. However, requests for references should be limited to cases where you genuinely question the accuracy of a statement. Otherwise, we waste our time hunting down sources to prove the obvious. StuRat (talk) 18:57, 25 February 2013 (UTC)

Again, forget everything I have said which is distracting your from this core concept: We have no way of knowing one way or the other if what you say is correct if you don't provide a reference for it. I'm not saying what you have said is wrong, what I am saying is that we don't know if it is correct. Those are not the same thing. Everything else I said above was my mistake, and not in any way should be addressed. The only thing I want addressed is a source or reference for your statement, so that we can know one way or the other. You made the positive assertion, it's your responsibility to provide some evidence. --Jayron32 20:03, 25 February 2013 (UTC)

As I did. Now, would you like me to challenge you to provide sources for everything you say, no matter how obvious it is ? StuRat (talk) 20:46, 25 February 2013 (UTC)

You both know this "discussion" should go someplace else. But since the train has derailed, and we're discussing references, I'll note that a very high percentage of Jayron's answers contain at least one useful and relevant reference. I try to do the same myself, and I think we would all benefit if we used tried for the modest goal of one useful and relevant reference in each answer. SemanticMantis (talk) 20:56, 25 February 2013 (UTC)

I think you two should get a room. (smile) --Guy Macon (talk) 19:38, 25 February 2013 (UTC)

Nelson Mandela Bridge

What impact does the Nelson Mandela Bridge have on the lives of people living and working in Newton and surrounding areas — Preceding unsigned comment added by 37.228.107.19 (talk) 18:00, 25 February 2013 (UTC)

I added a title. StuRat (talk) 18:05, 25 February 2013 (UTC)

I've hear this question before: What impact does the Nelson Mandela Bridge have on the lives of people living and working in Newton and surrounding areas Well, they no longer get wet when crossing the river – unless they forget to use the new bridge.--Aspro (talk) 23:42, 25 February 2013 (UTC)

You might like to read City regeneration and the making of an urban experience : The Nelson Mandela bridge as sculpture. Alansplodge (talk) 01:37, 26 February 2013 (UTC)

Child cognitive development - how old does a child have to be to realize that money has worth?

How old does a child have to be in general to realize that money has worth in the sense that that child will say that "I choose the two quarters over the eight pennies, because two quarters is worth more, even though the eight pennies may look like a lot of money."? 140.254.121.34 (talk) 20:23, 25 February 2013 (UTC)

If it is explained to them at three or four, thay may well grasp the concept. Left to their own devices it may take until seven. They need practical experience of buying and selling things (trade and commerce) to realise that the little silver things are worth more (by size) than the bigger copper things and that the paper-stuff is valued more by their older sibling -for vacuuming up coke. Be prepared for a lot of awkward questions along the way - which must answered honestly. --Aspro (talk) 20:44, 25 February 2013 (UTC)

They'd need actual math skills to compare 2 quarters to 8 pennies, but knowing a small dime is worth more than a larger penny they can learn at a fairly early age. StuRat (talk) 20:50, 25 February 2013 (UTC)

I assume you'll provide a link somewhere where we can read more about that? --Jayron32 20:58, 25 February 2013 (UTC)

Now you want sources to prove that comparing 2 quarters to 8 pennies requires math skills ? Shall I also include proof that 2 and 8 are, in fact, numbers ? StuRat (talk) 21:02, 25 February 2013 (UTC)

Its a fair question:This doesn't give any references but I suppose it is also based on the authors hard learned experience with his own kids. [4] Providing the sum doesn’t come to more that 10 units, even very child can grasp 10 cents = one silvery small dime, and ten of those equal one dollar. This holds even if they can't yet count up to one hundred. If we had eight fingers on each hand and hexadecimal coinage they might be able to cope with 16 units – who knows. It's the 1,1's and 1,2's that come after 10 that throws them. So it that sense, StuRat is correct. As Jane Jane Goodall et, al, have found, even chimpanzees can count – maybe, one day my time will come where I lean to master division and square roots of irrational numbers. Try and short change your four year old on his pocket money and you may find you have your proof - however, if you can, then blame his parents.--Aspro (talk) 22:05, 25 February 2013 (UTC)

Any 4-year old worth his salt will accuse you of shortchanging him no matter what. :-) StuRat (talk) 22:16, 25 February 2013 (UTC)

What maters most is weather s/he or it, can give you a logic reason to challenge your creative accountancy (to use the current professional term). The argument based on “ I'll tell mom” though-often-very-effective, is not a display of numeracy and must fearlessly be resisted; unless you’re having to sleep on the sofa for some transgression that even your ex-girlfriends can't figure out.--Aspro (talk) 22:39, 25 February 2013 (UTC)

Any small child can be fooled by giving them some of these. They think themselves instant rich and no silly coins to deal with. CambridgeBayWeather (talk) 00:46, 26 February 2013 (UTC)

At least the pater doesn't have to sleep in the doghouse, during bad "whether". :-) StuRat (talk) 00:44, 26 February 2013 (UTC)

I don't think Canadian Tire money will solve the sofa problem. I do a mental check every, every time, of everything I've said... Nice dress, like the new hair style; wow, that baked potato was as good as anything I've had in Wendy's® . Then I might help her out by telling how my mom cooked stuff. I can also commiserate by saying things like “Gosh., I wish I could revers into a parking space like that, (pity about the fire hydrant and I have got to admit is was in the way..etc) . So no problems there. So, I just don't understand where she's coming from.--Aspro (talk) 02:43, 26 February 2013 (UTC)

I think I was thinking of a different situation in which a child would count a limited number of coins on the table, but when the coins were spread out, the child thought that there were "more coins" or somehow it was "bigger" than it was, even though there were the same number of coins on the table. A similar situation would be when a child was given one cookie, and an adult was given two cookies. The adult broke the child's cookie into two pieces, and the child said it was "fair", even though those cookies were smaller portions. 140.254.121.34 (talk) 20:54, 25 February 2013 (UTC)

(edit conflict) According to Piaget's theory of cognitive development, a child would need to be in the "concrete operational" stage of development, which is where they start to form logical connections and also begin to understand the concept of money, though the ability to understand money abstractly, and to be able to plan correctly and make wise purchases based on weighing comparative values and being able to consider worth abstractly (rather than merely accepting "price" as equal to "worth") is something that may have to wait until "formal operational" stage. Of course, there are other theories of child development out there, but I suspect that they would all broadly agree on the ages when these milestones would occur in children. Wikipedia has an article titled Child development stages which states that a 5 year old "Recognizes and identifies coins; beginning to count and save money." however that article is fairly poorly referenced. If you want some reading outside of Wikipedia on the development of a child's money sense, I did find this work which has a LOT of good research on this exact topic. It provides a general overview of scientific research into a child's understanding of economic concepts, including money and worth. --Jayron32 20:58, 25 February 2013 (UTC)

Yes, specifically Piaget's_theory_of_cognitive_development#The_intuitive_thought_substage discusses some examples very similar to the OP's question, and I conclude that a child who knows 2 quarters is more money than 10 pennies has left Piaget's "intuitive thought" stage behind. SemanticMantis (talk) 21:09, 25 February 2013 (UTC)

I see your point. A child has three ways of learning. Experience, what it learns through guidance and explanation, observing and copying actions of others. If parents assume that 'schools' are the only place their children should learn the academic things, then progress may be slower than it was before schooling became compulsory...Deschooling Society; 4-Year-Old Girl with Sky-High IQ Joins Mensa (I wonder if she can help me sort out my tax returns?) --Aspro (talk) 22:20, 25 February 2013 (UTC)

As far as I can tell, every child nowadays goes through this stage, where the parent says something like "We can't go to Disneyland, buy a big house, buy an airplane, whatever, because we don't have enough money", and the kid says "Why can't we just get more from the ATM?" Gzuckier (talk) 07:38, 26 February 2013 (UTC)

ATM confusion just does not apply to uninformed children. A friend's in-laws (or some such relatives) came over from India and wanted to be immediately show the nearest ATM that gave 'free' money. He explained (via his wife) that 'free' referred to the fact that these ATM's (they had read about) were referred to as 'free” because did not charge for crash withdrawals.... but that the withdrawer had to have an account that was in the black to benefit from this arrangement. “But you have told us you have £20,000 pounds worth of free credit (about seven years salary for them). We will be back home, long before before, we get can get forced to pay it back! “ That had arrived expecting their investment on a flight to the UK would prove a money making bonanza. They went home realising the streets of London where not paved with gold and they had a son in-law that was a tight fisted b@%&'d for not letting them access to his free credit card.--Aspro (talk) 18:01, 26 February 2013 (UTC)

Wang, A. (2010). Optimizing Early Mathematics Experiences for Children from Low-Income Families: A Study on Opportunity to Learn Mathematics. Early Childhood Education Journal, 37(4), 295-302. doi:10.1007/s10643-009-0353-9 states "It was found that after controlling for a number of variables, the extent to which teachers emphasized activities that build on skills such as telling time, using measurement tools accurately, estimating quantities, and knowing the value of coins and cash was a significant predictor of kindergarten mathematics achievement for both African American and Caucasian students from low income families," implying that by the age of five or so, children should be able to understand the value of coins.

Saxe, G. B., Guberman, S. R., & Gearhart, M. (1987). SOCIAL PROCESSES IN EARLY NUMBER DEVELOPMENT. Monographs Of The Society For Research In Child Development, 52(2), 1-137. doi:10.1111/1540-5834.ep11865217, discussing developmental processes in 2 1/2-4 1/2-year-olds includes a table with "Activities entailing numerical comparisons of at least two sets. Money equivalences.—I show him that five pennies are the same as a nickel. Sometimes I try dimes and quarters and their relations to the other coins." --some jerk on the Internet (talk) 20:25, 26 February 2013 (UTC)

February 26

4K resolution tv

Does an 84 inch 4K tv have a similar ppi to a 32 inch Full HD tv? If not, are the differences insignificant due to limitations with the human eye? Clover345 (talk) 00:58, 26 February 2013 (UTC)

I'm not quite sure what a "4K tv" is, but I imagine you mean it interpolates between the pixels in a 1080p signal, and adds new pixels, accordingly. While this could make it look less blocky, it will make it more fuzzy. The only way to make an 84 inch screen look good with a 1080p signal (or, God-forbid, a lower res signal), is to sit a long way away from it. (Incidentally, the Computer Desk might be better for this type of Q.) StuRat (talk) 01:13, 26 February 2013 (UTC)

Stu, you might at least look it up in Wikipedia before replying: 4K resolution. It refers to TV (and other devices) designed to display ultra high definition television signals. This technology is just emerging and most people won't yet have access to UHD sources. Dragons flight (talk) 01:23, 26 February 2013 (UTC)

I didn't find an article under 4K resolution television, which is what I looked for. Looking at that article, they apparently have switched from labeling resolutions by vertical lines to horizontal, no doubt to trick people into thinking they are getting more than they are. How annoying. I'm aware that such a signal isn't likely to be available anytime soon, hence my comments on interpolation to upconvert a lower res signal. StuRat (talk) 01:29, 26 February 2013 (UTC)

UPDATE: Someone has now added a redirect so that link now works. StuRat (talk) 16:22, 26 February 2013 (UTC)

To answer the original question, a 4K UHD TV will have similar PPI to HD TV that is 1/2 its size. So a hypothetical 84 inch 4K TV will have similar pixel density to a 42 inch 1080p HD TV. Dragons flight (talk) 01:26, 26 February 2013 (UTC)

Regarding whether your eye can resolve such detail, you might read the technical section in Retina display; or the more generic angular resolution article. Nimur (talk) 02:22, 26 February 2013 (UTC)

1920 minutes of arc is only 32 degrees, and some can see up to 20/10 (twice as sharp) so not insignificant. With the 84" 4K set you can start seeing pixels at $84/((sqrt(16^{2}+9^{2}))/16*3840*2)*tan(90-1/120)$° inches away — 89.5% of the screen's width, even up to 1.79x the screen's width if you have Chuck Yeagar's eyes. And I want a monitor that remains pixeless as I walk 4 times closer than the couch like it's the future, the 8K TV is for me. Sagittarian Milky Way (talk) 03:29, 26 February 2013 (UTC)

A 4K tv has 4,000 pixels per scanline. A regular "1080p" tv has 1,080 pixels per scanline. So an 84" 4K TV has the same per-pixel angular resolution as a 21" 1080p TV when viewed at the same distance.

HOWEVER: There are no good sources of 4K content. The highest resolution you get from a bluray disk is 1920 pixels (and that's either interlaced or at a reduced frame rate - so the "quality" is arguably no better than 1080p) - but I doubt that many disks are mastered at that resolution. Broadcast & cable TV tends to top out at 1080p.

What this means is that your 4K tv has to stretch the lower resolution image to fit the screen - and almost certainly, that will result in an image that is no sharper than a 1080p tv of the same size viewed at the same distance.

Right now, the only use for a 4K TV might be as a computer display...some graphics cards can generate signals at that resolution. Probably there are video games out there that would benefit from being displayed on a 4k TV versus a 1920 pixel computer screen...but even that is highly problematic because the amount of calculation needed to compute a video image that large tends to degrade the frame rate - making for a worse experience overall.

I could imagine someone who edits digital movies from finding a benefit in this technology - but otherwise 4K TV is a solution looking for a problem.

SteveBaker (talk) 14:46, 26 February 2013 (UTC)

Steve, apparently you didn't read the article or my comment on it above. From the lede: "The term 4K refers to the horizontal resolution of these formats, which are all on the order of 4,000 pixels". My comment: "Looking at that article, they apparently have switched from labeling resolutions by vertical lines to horizontal, no doubt to trick people into thinking they are getting more than they are. How annoying.". StuRat (talk) 16:25, 26 February 2013 (UTC)

There's content and GPU problems with 4K screens. That's why it's future tech instead of current tech. I'm using a 23.625" 1080p TV as a monitor and I wish it was 4K so I could stop seeing pixels. That is one reason to use 4K now, if you can afford it: my pixels look honking huge, and I don't want to go back to a small monitor for smaller pixels again. My crappy 0.6 gigapixel per second graphics card feeds 2 million pixels at 60Hz with no problem, except for intensive graphics like Google Earth with lots of icons to draw. Crysis 3 at 4K would test even very good modern cards, but you could always turn the resolution down if need be. Sagittarian Milky Way (talk) 18:57, 26 February 2013 (UTC)

I don't think TVs make very good computer monitors, since they are designed for more distant viewers. While they are fine if you're sitting across the room, they're not if your face is right in front of them. I have an only slightly better res 1600×1200 monitor, and it's 24 inches diagonally, and I sit close to it, too, but I don't see individual pixels. I believe this is because the gaps between the pixels are intentionally kept smaller on computer monitors. StuRat (talk) 22:50, 26 February 2013 (UTC)

That was true in the past, when computer monitors and TV's were CRT based, and TV was analog TV. One of my computers is an old PC (bought in 1995). I pusrchased with it back then an NEC Multisync 1600 x 1200 monitor - a top model in its' day. It had a dot pitch of 0.25 mm and a video bandwidth of >100 MHz. This is way way outclassing a CRT based analog TV of same diagonal size (21 inch) the old top of the line Philips I have has a dot pitch of 3.3 mm and an RGB video bandwidth of only 5.5 MHz. But the NEC monitor cost a lot more than the TV too - about $2000 vs ~$600, equivalent to about $8000 today. Recently the NEC monitor stopped working. I replaced it with a 19" diagonal LED digital TV Teac model LEDV19U83 Full-HD. It has a "VGA" input and so can be used as a computer monitor. It cost $139.99, cheaper than the cheapest 1600 x 1200 monitor the shop had, and does 1600 x 1200 @70 Hz. I can't tell you what the dot pitch and video bandwidth is, as it is not specified in the manual. But it clearly outperforms the old NEC monitor. Why is it so? Because it was difficult and costly to make high resolution CRT's, and high power electronics was required to drive them. But LED screen manufacturing cost is mainly a function of the screen area, and not the resolution. The driving electronics are low power and simplified. Ratbone 121.221.5.16 (talk) 02:32, 27 February 2013 (UTC)

In what respect two protons (or any two fermion) are not identical?

No two electrons of the same atom are identical. If we choose two electrons of two different atoms having same orbit, same subshell, same spin, same quantum numbers, would they be identical? I know two protons (or any two fermions) are not identical. In what respect two protons (or any two fermion) are not identical? Is it mass, charge, shape, size, or anything else? 106.218.233.58 (talk) 03:00, 26 February 2013 (UTC)

I'm certainly no expert but according to Identical particles, electrons ARE in fact identical, as are the other fermions and bosons. Vespine (talk) 03:17, 26 February 2013 (UTC)

Then, what about Pauli Exclusion Principle 106.218.233.58 (talk) 03:23, 26 February 2013 (UTC)

As you say, they're part of orbitals of (and have quantum numbers with respect to) different atoms (coordinate systems or frames of reference for the wavefunctions). Whatever equation you use to describe 1s, for example, is based on an origin at the center of the nucleus. If you expand your perspective to include two different atoms, there's an offset for the actual position of that center, which is different for different atoms in your world. DMacks (talk) 03:53, 26 February 2013 (UTC)

Protons/electrons are not identical. The concept you're referring to is distinguishability (no article?), which has a very specific meaning. Each electron is described by a wavefunction, and any system of two electrons can be described with a system wavefunction that's a combination of the two electrons' wavefunctions. Electrons are indistinguishable because if switch their wavefunctions, the system wavefunction remains identical.* This property is called exchange symmetry. Nobody, not even God, can tell if the two electrons were exchanged or not; an exchanged system behaves exactly the same as an unexchanged system. Distinguishability doesn't hold for classical particles, because if electrons were classical, you could always mark one of them with chalk, or paint one of them red, and you'll always be able to distinguish them.

*Actually, this is not true. Since what matters for any measurement is the square of the wavefunction, the wavefunction itself can either stay the same or switch sign. Bosons do the former; fermions do the latter. --140.180.254.250 (talk) 07:42, 26 February 2013 (UTC)

Not sure if it's what 250 was looking for above regarding distinguishability, but we do have an article on indiscernibility. It's framed more philosophically, going back to Leibniz, but I think it is relevant for the current question as well. If someone has more confidence on the matter, perhaps they could be bold and add a redirect. SemanticMantis (talk) 16:03, 26 February 2013 (UTC)

The article I linked quite plainly says: indistinguishable or indiscernible particles, are particles that cannot be distinguished from one another, even in principle. Am I misunderstanding or is the article wrong? Vespine (talk) 21:49, 26 February 2013 (UTC)

I think this is just a nomenclature issue. I think the party line is that protons are not identical (i.e. there is more than one proton), but that they are indistinguishable (or perhaps indiscernible). I only linked the indiscernibility article for background context, not to say anything written here is in error. Basically, in physics and philosophy, identity and discernability are separate issues. As discussed in the linked article, identity of indiscernibles is philosophically (or perhaps physically) debatable, while indsiscernibility of identicals is a (relatively) settled issue. SemanticMantis (talk) 14:47, 27 February 2013 (UTC)

T-90 tank Shtora system

What is the reason that Shtora was able to disrupt 6 kornet missiles from a total of 10 http://fofanov.armor.kiev.ua/Tanks/TRIALS/19991020.html 87.236.232.97 (talk) 08:10, 26 February 2013 (UTC)

I have to admit that I'm confused as to the exact thrust of your question. Are you asking why Shtora is at all effective against 9M133 Kornet missiles? Because Shtora is an electro-optical countermeasure and the Kornet is laser-guided. Are you asking why it's not 100% effective? Broadly, because countermeasures rarely are. Specifics probably depend on the nature of the test. Our article suggests that while it has a 360° field of use, it may not cover all 360° with equal effectiveness simultaneously. Additionally, there is a time delay to deploy its aerosol screen, and said screen also dissipates in a fairly short amount of time. It's also possible that the system wasn't being run in fully automatic mode, which introduces the possibility of operator error. Finally, you might be asking why specifically 6 of 10 missiles were disrupted, in which case little can be said except that that's how probability worked out in that particular test on that particular day. — Lomn 14:39, 26 February 2013 (UTC)

How much sensation does a tortoise/turtle have in its shell?

I've heard of occasional occurrences of people graffiting the shells of living large tortoises at wildlife parks - sometimes by carving into the shell with a knife (and also the repair attempts afterwards, using polyfilla type stuff and silicone sealant). I gather that it's more common for people to write stuff on the shell with marker pen or tippex or something, but anyway...

To what extent would the tortoise feel someone cutting their name into its shell? Or are the whole outer layers of shell pretty much dead tissue and sensation-free? --Kurt Shaped Box (talk) 08:46, 26 February 2013 (UTC)

Turtle shell does not seem to address this question. I googled [can turtles feel their shells] and well as [can turtles feel pain on their shells], and a variety of contradictory answers turned up. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:09, 26 February 2013 (UTC)

I searched google scholar for /turtle shell innervation/ and found this paper [5], titled "Carapace and plastron sensitivity to touch and vibration in the tortoise." :It seems to address your question rather rigorously and scientifically, but you might need to get to a library to read it. The abstract says "Neural impulses in response to tactile stimulation of the shell were recorded from afferent nerve fibres in tortoises (T. graeca and T. hermanni). It was found that there is a mechanoreceptive innervation in the superficial layers of the shell which is sensitive to transient stimuli, particularly to vibration at frequencies up to 100 Hz. Receptive fields pertaining to single and small groups of individual afferent fibres were mapped: the fields were sharply circumscribed and distributed in relation to the scutes of the shell. The tactile innervation that was found would be consistent with a capacity for recognition and accurate localization of innocuous stimuli and may play a central role in courtship and mating behaviour."

So, it seems that at least one tortoise can feel at least some touch on its shell. To get into more detail, I'd look to see what papers have cited that one. SemanticMantis (talk) 14:19, 26 February 2013 (UTC)

But vibration is a funny thing. If my hand is on the table and I can feel you bang on the table 4 feet away, just because I can detect superficial vibration on the table top of on its legs inches or feet away doesn't mean that the vibration receptors (perhaps Pacinian corpuscles, as in mammals) exist in the shell. My point is this -- the shell is firmly attached to the living tissues of the tortoise and so the organim can feel when you tap on the shell, for instance, but detecting pain would require free nerve endings or other end bulbs that I'm not qualified to respond about -- but perhaps this distinction ought to be made rather than confusing the two very different things of "can a tortoise feel its shell being manipulated" vs. "is carving a living tortoise's shell a painful stimulus to the tortoise." DRosenbach ^{(Talk | Contribs)} 18:12, 26 February 2013 (UTC)

I had similar thoughts, but this line " It was found that there is a mechanoreceptive innervation in the superficial layers of the shell which is sensitive to transient stimuli"- seems to indicate that there are nerve endings in the shell. That being said, the scutes are mostly (entirely?) keratin, which has no innervation. So, as to the two questions you pose, my guess (based on the linked readings) is that a turtle could sense being carved on, but would not feel pain unless the scutes were penetrated. SemanticMantis (talk) 20:10, 26 February 2013 (UTC)

Big Tortoises (Aldabras,etc) that are too heavy to lift can be "steered" quite readily by slapping on the side scutes to steer and on the rear scutes to get them to move forward. Zookeepers commonly use this to move them from one exhibit to another, or bring them inside at night. They will usually only move about 2 metres, then you have to let them rest for a few minutes before they will respond to more signals. 124.191.176.235 (talk) 05:44, 27 February 2013 (UTC)

Not that I doubt you, but you know this how? μηδείς (talk) 02:39, 28 February 2013 (UTC)

From a long and varied career as a zookeeper. I know there's a massive body of knowledge in past and current zookeepers, much of which is unrecorded and will die with them. 124.191.176.235 (talk) 07:06, 28 February 2013 (UTC)

I read the paper Semantic linked to. Quite on topic is the following:

“ The level of sensory endings within the shell was determined by testing the effect of progressive abrasion of the outer horny scute. Complete penetration of the scute caused abolition of the locally elicited response (Fig. 6). Partial abrasion, however, led to an increase in response (Fig. 7). These results support the view that the receptive surface under examination lies near the underside of the scute. ”

An accompanying diagram of the experiment helps elucidate their conclusions - basically, they assert that sensory nerve endings may be found a mere 0.5mm beneath the surface of the shell. They show earlier in the paper that stimuli as gentle as a brush stroking over the shell can be felt by the tortoise. They also show that not all areas of the shell are equally sensitive. Someguy1221 (talk) 03:05, 28 February 2013 (UTC)

About the gravity field of black hole

Some time we see news about black holes in center of galaxies, but nothing is there in references about exact properties of black holes gravity field. When the black hole in center of galaxy creates strong gravity field how is space time shape or figure of such field? Does it never done calculating or drawing such field. Is the potential diagram 1/r? --Akbarmohammadzade (talk) 09:19, 26 February 2013 (UTC)

A black hole is nothing special on the outside other than being a big lump of mass in a very small area. Its gravitational potential indeed drops as 1/r, as with any planet or star. Near the surface of a black hole, however, you start seeing the neat tricks of gravity when you can orbit a supermassive body at extremely tight radius: relativistic effects like frame dragging, tidal forces that lead to spaghettification, etc. SamuelRiv (talk) 15:28, 26 February 2013 (UTC)

thank you

With shortages have been monitored in theories and existing explanations it can not be considered that any central black hole be able to tide whole galaxy members !!!A.Mohammadzade — Preceding unsigned comment added by 2.187.66.54 (talk) 21:04, 26 February 2013 (UTC)

endosymbiotic theory of prokaryotic evolution

how can natural selection explain why, after the anaerobic primitive cell ingested aerobic bacterium to become its mitochondrion been able to divide so that after mitosis, both daughter cells have mitochondrions? it is like me ingesting a worm but not digezsting and when i divide to reproduce, the worm also replicate so that i and my sons could have worms inside our bodies.TTLOAFH (talk) 10:26, 26 February 2013 (UTC)

Cells can have loads of mitochrondria inside them though many only have one, they reproduce inside the cell. What would have evolved is a way of properly regulating the number rather than having them reproducing unchecked inside the cell. Dmcq (talk) 13:25, 26 February 2013 (UTC)

In a recent BBC documentary it was mentioned that sexual reproduction might have evolved 1.5 billion years ago to deal with this problem. Count Iblis (talk) 14:18, 26 February 2013 (UTC)

Unless I am missing something, that doesn't make sense. Mitochondria have their own DNA, so they are unaffected by sexual recombination. The fact that mitochondria reproduce asexually even in cells that reproduce sexually is what has made mtDNA a useful tool for tracking ancestry (on the maternal side). Looie496 (talk) 16:13, 26 February 2013 (UTC)

Or even simpler to counter Count Iblis's comment, sexual reproduction does not affect mitochondrial reproduction. Instead of a cell doubling and the daughter cells doubling and so on and so forth to create new life forms, sexual reproduction merely allows for the separation (haploid state) and combining of alleles (diploid state) to further mingling within what amounts to a gene pool -- but the first new diploid cell then undergoes mitosis to form its own diploid, multicellular organism and the mitochondria in each of these cells must split. DRosenbach ^{(Talk | Contribs)} 18:04, 26 February 2013 (UTC)

See about ten minutes into this programme. Count Iblis (talk) 18:34, 26 February 2013 (UTC)

Seems extremely unlikely to me, there are large numbers of such cells that never bother with sex and there are other much better reasons for sex. If you listen to that - where did this neighbouring cell with mitochrondria come from if not from straighforward splitting instead of sex? Splitting happens far more often. Dmcq (talk) 18:11, 27 February 2013 (UTC)

Reversing light-emitting diode

Can a LED work in reverse order, transforming light into electricity instead of electricity into light? OsmanRF34 (talk) 14:14, 26 February 2013 (UTC)

That would be a solar cell, which is not a form of diode. So no, you can't have an LED that does this (because it wouldn't be light-emitting), nor can you have another form of diode that does this (they don't do that), but you can have a semiconductor-based circuit that does this. — Lomn 14:27, 26 February 2013 (UTC)

Not correct. LEDs and photovoltaic cells are all semiconductor PN diodes. Shining light on any semiconductor diode will generate electrical power. However, the efficiency of LEDs in converting light into electrical power is abyssmal, and of little if any practical use. Googling "LEDs as photodiodes" will give you a multitude of web pages describing experimental results. Ratbone 120.145.40.231 (talk) 14:37, 26 February 2013 (UTC)

Ratbone is correct, as a bit more thought and searching would have told me. In fact, here's a recent article discussing a new high-efficiency LED-type solar cell design. — Lomn 14:49, 26 February 2013 (UTC)

A reversed LED might make a poor power generator, but it works well enough to make quite a decent light detector. I saw a great project once that used alternating rows of LEDs configured to emit and detect light respectively. The sensitivity was set so the detectors wouldn't trip until an object, such as your hand, came close enough to reflect a significant portion on the light emitting LEDs, making a pretty decent close proximity, 'touch less' switch. I searched for a couple of minutes but I can't find it. Vespine (talk) 23:28, 26 February 2013 (UTC)

Why "Hornblower's Sign?"

A test for injury to certain shoulder muscles is called "Hornblower's sign." Is it named after some Doctor Hornblower, or is the particular arm position involved thought to resemble that used in "blowing a horn?" Edison (talk) 15:53, 26 February 2013 (UTC)

I couldn't find a specific statement about this, but in the literature it is commonly used as "hornblower's sign" or "hornblower sign", and combined with the fact that this (inability to rotate the shoulder joint) is a problem that would naturally occur in somebody holding a horn for hours a day, the answer seems reasonably clear. Looie496 (talk) 16:07, 26 February 2013 (UTC)

A thorough search of Google has failed to turn up any famous medical people called Hornblower, although Hornblower is an English surname. However, I found Orthopedic Physical Assessment, by David J. Magee (p.313), which for some reason also gives the name of the test in French, "Signe de Clairon" which translates as "Bugle Sign". This seems to confirm your second suggestion. Alansplodge (talk) 16:15, 26 February 2013 (UTC)

One photon at a time

Is it possible to connect a light emitting diode to a battery in such a way that light is only emitted one photon at a time? Either one photon for each push on a switch or a continuing series of photons with significant time gaps between.

Thanks, Wanderer57 (talk) 16:27, 26 February 2013 (UTC)

Yes - see this news report from 2001. But it does not sound easy - for example, the prototype device had to be cooled to 5K. Gandalf61 (talk) 16:43, 26 February 2013 (UTC)

You might also find shot noise enlightening. You can use any method to reduce the intensity of photons down to one photon per unit time, where one unit of time is a completely arbitrary duration. If you observe for n units of time, you expect to see n photons; but in practice, you actually observe n photons on average. The error is due to shot noise. If you expect to emit (or observe/absorb) exactly one photon, you will actually sometimes see zero photons, and sometimes one photon, and sometimes some other number of photons. The better that you can control your experiment, the less shot-noise will affect your measurement. This is a good thought-experiment that can help develop intuition about the statistical interpretation of quantized observations. It's also very easy to set up as a real experiment, in a simple lab, using very common equipment - like a digital camera and a dark shoe-box. Cooling the device will help eliminate thermal noise. Thermal noise is a different physical effect that superimposes on the shot noise, contributing to the experimentally-measured value. What do you know, there's an MIT OpenCourse lab detailing this exact experiment! Nimur (talk) 17:12, 26 February 2013 (UTC)

It is relatively easy to get a low number of photons per time by e.g. start with any light source and put enough absorbing material in front of it. Getting exactly one photon on the push of a button (not just one on average) is more difficult. In quantum mechanics this is called a Fock state with one photon and there is some information on how to create these in Fock state#Source of single photon state. Ulflund (talk) 17:33, 26 February 2013 (UTC)

I don't see how the "quantum mechanical case" is any different from the "classical" case, except that one uses the somewhat obtuse bra-ket notation. Shot-noise describes quantized events, whether they are microscopic or macroscopic in origin; the arrival of a single photon is still a single quantized event, whether the origin of that photon is described using a bra-ket equation or by putting several ND filters in front of a light-bulb. The photon doesn't know the difference. If I put a thousand ND filters in front of an incandescent bulb, and used a button to turn on the bulb, I might see one photon at my detector. Haven't I constructed a "macroscopic quantum-mechanical system" that can emit one photon at the push of a button? It's the same system, whether you use difficult mathematics to describe it or not. Nimur (talk) 17:58, 26 February 2013 (UTC)

Well, as you said, your approach is not very reliable; that section of the article appears to be about reliably getting one photon and not 0 or 2. -- BenRG (talk) 02:50, 27 February 2013 (UTC)

Is there reason to believe the signal-to-noise ratio would be any different at all? The OpenCourseWare paper I linked above derives the signal-to-noise ratio of shot noise, from first principles; if we are concerned with only one photon, then we are definitionally in the limiting-case of a Poisson distribution, and no matter what system you construct to determine when the emission happens, - quantum-mechanical or otherwise - the signal-to-noise-ratio is always the same. "According to Poisson statistics, the variance of n is the mean... [6]." Or, to put it another way, when your expected value is one photon, your variance is also one photon. Nimur (talk) 04:07, 27 February 2013 (UTC)

You seem to misunderstand, the research grade single photon sources are specially designed so that releasing two photons is simply not an option (typically for a specific wavelength and interval). For shot noise, there is a Poisson distribution such that the probability of seeing n photons p(n) is always greater than zero for all n. One can tune such a system so that the probability of getting two photons within a given time interval is arbitrarily low (at the expense of reducing the one photon rate), however the one-photon research sources are different. They are physical systems such that the probability of getting n photons is exactly zero for all n greater than 1. For example, you might be watching a quantum dot in its lowest excited state, and it can only collapse once (and emit one photon) without the researcher intervening to re-excite it. Dragons flight (talk) 04:36, 27 February 2013 (UTC)

Log laws

Log laws tell me that the integral of dx/x is lnX + C so why is the integral of adT/T equal to aln(T2/T1)? Clover345 (talk) 16:48, 26 February 2013 (UTC)

You're looking at the difference between taking the antiderivative (the indefinite integral) and evaluating a definite integral. (Bear in mind that one property of logarithms is that log(A)-log(B) = log(A/B). ) TenOfAllTrades(talk) 17:07, 26 February 2013 (UTC)

Shouldn't this be on the Math Desk ? StuRat (talk) 17:08, 26 February 2013 (UTC)

I know the integral of dT is T2-T1 but won't that mean the integral of adT/T is a(T2-T1)lnT? Clover345 (talk) 17:11, 26 February 2013 (UTC)

(EC)You are confusing indefinite integrals with definite integrals. The first expression you gave is for an indefinite integral, and the C is the constant of integration. In the second expression, you are effectively integrating a dT/T from the limits of integration (T1,T2). Integrals don't notice scalar multiples, so you pull that outside. When integrating dT/T, over (T1,T2) you first get Log(T2)-Log(T1). Then, the Log identities (Logarithm#Product.2C_quotient.2C_power.2C_and_root) tell us that the difference of two Logs is the Log of the quotient. Remembering we took the scalar out, that gives us \int_T1_T2 (adT/T)=a Log(T2/T1). Make sense? (I am at work and busy/lazy. If anyone cares to pretty print my math, feel free :) SemanticMantis (talk) 17:13, 26 February 2013 (UTC)

Further detail, you are making a very common mistake of trying to treat the factors of the integrand separately. To handle (non-scalar) factors correctly, you'd need integration by parts. But this problem doesn't need that, it is just a simple application of the fact that \int dx/x = log x + c, and fundamental theorem of calculus (version applied to definite integrals). SemanticMantis (talk) 17:18, 26 February 2013 (UTC)

The indefinite integral of adT/T is aln T + C. The definite integral of adT/T, evaluated from T1 to T2, is found by first plugging T2 into the indefinite integral, to get aln T2 + C, and then subtracting from that what you get when you plug T1 into the indefinite integral, which is aln T1 + C. Performing the subtraction gives a ln T2 - a ln T1 = a(ln T2-ln T1) = a ln(T2/T1). Duoduoduo (talk) 18:18, 26 February 2013 (UTC)

Angiosperms

The article on peppers doesn't indicate that this species (and its many member cultivars) are angiosperms, even though the various peppers are flowering seed-producing plants, which according to how I understand it, should rank them as angiosperm spermatophyes. Nonetheless, the pepper article calls them eudicot instead of angiosperm, and the eudicot article refers to the term 'eudicot' as a clade along with 'angiosperm', which seems to mean that one clade is not contained within the other -- so are eudicots (and therefore peppers) angiosperms? DRosenbach ^{(Talk | Contribs)} 17:52, 26 February 2013 (UTC)

Eudicots are a subset of angiosperms. Basically angiosperms divide into monocots, dicots, and a few weird things such as the magnolia. Monocots can be thought of as grasses and things that are similar to grasses. Dicots are the other major group, with over 100,000 species, and the great majority of existing dicots are eudicots (which basically means "true dicots"). Looie496 (talk) 18:43, 26 February 2013 (UTC)

To further explain, a clade is simply a group containing all the descendants of a given ancestor species, and nothing that is not descended from that single ancestor species. It is entirely possible for one clade to be contained in another clade. Looie496 (talk) 18:46, 26 February 2013 (UTC)

Eudicots are a subbracnh of angiospems, the largest, and containing what we might consider typical flowering plants with two seed-leaves, flowers usually with five, or sometimes four petals, and leaves with branching veins. Think rose, oak, poinsettia, sunflower, chili peppers, and even cactuses. Monocots are a large branch of angiosperms distinguished by one seed leaf, leaves with parallel veins, and three-part flowers. Think grasses, orchids, [[[lilies]], onions, bananas, palm trees. There are various other more primitive angiosperms, including the magnoliales, that generally resemble dicots but are more primitive, and inlcudes magnolias, laurales, and black pepper. This very simplified diagram of all the angiosperms is a little easier to understand than the cramped diagrams we have at our own article.μηδείς (talk) 18:58, 26 February 2013 (UTC)

when a capacitor discharges, is it all converted to heat + light? what percent light? if light can't escape, is it all converted to heat?

I don't understand something. could a single charged capacitor in theory heat a room just as well as the equivalent amount of charge going into any other radiator/heater occupying the same space, in terms of heat generated? I realize that the discharge could produce light - but if you enclose the whole thing in something (like tiles) then doesn't the light also have to convert to heat as it dissipates from bouncing around?

What I mean to say is this: look at this answer

http://answers.yahoo.com/question/index?qid=20110416105219AALeYzb

THe guy (first response) does a calculation which shows that a "large" 100000µF 100 volt capacitor in the end stores "500 joules" as compared with 5400 joules in an AAA battery.

However if you short the AAA battery it still won't instantly discharge 5400 joules as heat. Whereas a capacitor has very low inherent resistance and I imagine causes a big spark and instant discharge.

So my question is this: if you tried to use a "500 joule" power source (of any kind) to heat, for example an AAA battery that is 9/10th drained :), then is it guaranteed to do just as much heat as instantly discharging a "500 joule" capacitor inside a container where light has to bounce around?

Or is there some kind of extra inefficiency (with respect to trying to turn charge into heat, which is our goal) due to the instant discharge? I can think of one off-hand: the noise if it makes a spark noise is mechanical energy some of which would leave before it turned into heat.

is that hte only loss? otherwise is a capacitor an "optimal heater" for that many joules (as compared with a power source discharging that many joules over some time into some heating-device) when instantly discharge? How much are the losses from the nosie? THanks. 178.48.114.143 (talk) 19:00, 26 February 2013 (UTC)

Any sound and light produced from the spark will be negligible compared to the heat, and most of this will end up as heat anyway. The capacitor resistance will not be quite zero, but, even if the capacitor takes half a second to discharge, 500 joules in 0.5 seconds is just the equivalent of a 1Kw heater switched on for half a second -- not very much heat to heat a room, but possibly sufficient to damage the capacitor or its leads. Dbfirs 20:19, 26 February 2013 (UTC)

It seems from your question that you are thinking of discharging the capacitor or battery by short-circuiting it. If you short a battery, the energy is almost entirely dissipated in its' internal resistance (assuming it isn't damaged, which for many batterries it will be). In doing so, almost all of the energy is converted directly into heat, raisning the temperature of the battery. However, with capacitors, compared with batteries of similar size in terms of energy storage, the internal resistance is a lot less. This means that the inductance of of the "short circuit" must be taken into acount. It means that shorting a capacitor results in emission of significant amounts of electromagnetic energy - in laymans' terms, short-circuiting a capacitor results in practice in a brief emission of a radio wave.

If the desire is to confirm that energy is energy and can regardles of source be converted into heat, a better way is to discharge either the capacitor or the battery into a resistance, sized in both cases so that the discharge time is long enough to avoid inductive effects so that conversion to radio wave energy is negligible. Then, in both cases, virtually all the stored energy will go into heating the resistor and then be transfered to the surrounding room. In this case, a capacitor large enough to store the same as a battery will heat the room to the same degree. In discharging into a resistance, there is no need to cause sparks and light or sound. Keit 58.170.129.186 (talk) 01:30, 27 February 2013 (UTC)

As regards the light produced by a discharging capacitor: any light which is trapped (for example, by putting the capacitor in a box) will be converted into heat (in our example, it's absorbed by the walls of the box which heats them up). As for what percentage of energy becomes light, this depends on how the discharge occurs. Light will be created if the discharge causes a spark though this is technically because the spark heats the air it passes through and anything sufficiently hot will radiate light. Even if there is no spark, small amounts of light will be emitted because the capacitor itself will be hot. The power emitted as electromagnetic radiation depends on the temperature of the capacitor (and the spark if present) and can be calculated from the Stefan-Boltzmann law. Some of this radiation will be light but much of it may be elsewhere in the electro-magnetic spectrum (e.g. infra-red). How much of the radiation is actually visible light can be calculated from Planck's law. Again I stress: the discharging of the capacitor produces heat and then light is emitted because it is in the nature of hot things to emit light in order to achieve Thermal equilibrium with their surroundings. Eaglehaslanded (talk) 03:10, 27 February 2013 (UTC)

All good theory. But, if you actually DO the calculations, you'll find that in just about every possible real life non-sparking case, and ignoring deliberate light creating strageies like discharging into a light globe, LED, etc, the amount of light so emitted is a negligible fraction of the system energy. It's a bit like saying light is emitted from the hot water when you make a cup of tea. Keit 121.221.5.16 (talk) 03:39, 27 February 2013 (UTC)

What kind of fish is this

The BBC news story Giant 6ft long ling fish caught off Shetland doesn't say what kind of fish it is. Can anyone identify it? -- Q Chris (talk) 19:14, 26 February 2013 (UTC)

Yes she does, she identifies it as a ling (although not the specific species) in the first sentence. μηδείς (talk) 19:21, 26 February 2013 (UTC)

interesting phenomena - I, too, missread and fused ling long' to long. Just like 'Paris in the the spring', I guess. Zarnivop (talk) 03:23, 27 February 2013 (UTC)

I'm sure the 'ling' in the strapline was not there when it was originally posted (BBC English is riddled with errors) because I read it deliberately, several times, wondering why they used just the word 'fish' without any sort of identification. 6ft long isn't big for many fish, but of course very big for a shore caught ling. Richard Avery (talk) 08:07, 27 February 2013 (UTC)

I can confirm it was not. -- Q Chris (talk) 12:40, 27 February 2013 (UTC)

You are correct, Ave, it wasn't, or I would not have bothered even to listen. Shows how much you can trust the BBC are doing the honorable thing. μηδείς (talk) 02:37, 28 February 2013 (UTC)

T-90 Shtora System

It seems that you understood my question more than me , but what I meant from the question is why the Kornet was expected to be not harmed by Shtora as stated in the conclusion of that page "Report of Shtora-1 EOCMDAS trials is confusing. Being laser-guided, ATGM Kornet should not suffer any interference from Shtora as it only affects IR SACLOS ATGMs" 149.200.151.156 (talk) 20:54, 26 February 2013 (UTC)

You should edit the earlier question to maintain context rather than posting new questions. Our Shtora article indicates that it is effective against lasers, at least in some wavelengths, so perhaps your report is in error. Alternately, your report suggests that flawed test procedures could be the reason. Finally, I note that I find any technical military details highly suspect when provided by a site labeled "Sauron's Creations" -- that's not exactly Jane's. For instance, elsewhere on his site (on the Shtora page he specifically says it's effective against laser-guided missiles, in agreement with our article. — Lomn 00:23, 27 February 2013 (UTC)

Anisotropic aquifers

What are some factors that make àn aquifer ísotropic?

Have you intentionally misspelled isotropy? You will need to specify what you're looking for in a little more detail. When I think about isotropy and reservoirs, I think of two general categories: porosity/permeability, which can be anistropic, and affect fluid flow; and stress/strain tensors, which can be anisotropic, and affect propagation of sound waves during a seismic survey. There are dozens of other characteristics that could be anisotropic. I'm surprised that we have no article on reservoir mechanics, but we have rock mechanics, Reservoir modeling, reservoir simulation, and so forth. And, whenever I find something missing on Wikipedia related to water wells, I go straight to the Schlumberger reservoir and geology encyclopedia website: here's a query for isotropy, which prompted me to recall that electromagnetic surveys are also used in the study of water and hydrocarbon reservoirs, and electromagnetic properties are frequently anisotropic. Nimur (talk) 23:12, 26 February 2013 (UTC)

Meat tastes

Why do cheaper meats tend to have less of a taste compared to more expensive high quality meats? Some of the low cost meats, especially minced, can have very little taste. Clover345 (talk) 23:02, 26 February 2013 (UTC)

Virtually all of the taste in meat is in the fat, and cheaper cuts have less marbling. You can make burger out of lean pork and beef fat or lean beef and and lamb fat and it tastes like the meat the fat came from. --Guy Macon (talk) 23:06, 26 February 2013 (UTC)

At the cheapest end, we have pink slime, where the citric acid or ammonia fumes they are exposed to in order to kill the bacteria may also denigrate the flavor. StuRat (talk) 23:11, 26 February 2013 (UTC)

People prefer meat with more taste and pay more for this. Cheaper meats are the same phenomenon in the opposite direction. OsmanRF34 (talk) 23:59, 26 February 2013 (UTC)

Yeah - exactly, it's a market-demand matter. If cheaper meat tasted better than the expensive stuff, more people would buy cheaper meat and fewer would buy the expensive stuff. Laws of supply and demand would then cause the cheaper cuts to get more expensive and the expensive stuff would get cheaper. So no matter which parts of the animal are better tasting, those are always going to be the most costly. It's economics rather than biochemistry that's at work here! SteveBaker (talk) 14:47, 27 February 2013 (UTC)

Agreed, although "tasting better" is subjective. In the case of fish, for example, most people like them to taste "less fishy". Lobsters used to be cheap, until they became fashionable to eat. Similarly, chicken wings were cheap, until preparation methods were developed allowing people to get a maximum amount of salt and fat with each, by frying them and serving them with ranch dressing, etc. StuRat (talk) 16:28, 27 February 2013 (UTC)

Or, in the case of red meat, some people actually prefer the tougher, leaner (and therefore milder-tasting) cuts. 24.23.196.85 (talk) 00:42, 28 February 2013 (UTC)

I think this is only true in limited cases. For example, the most traditionally expensive beef cuts are the very tender cuts with 'subtle' (i.e., little) flavour, whereas the cheaper cuts were the tougher cuts (usually stewed or similar, to render them tender) which were much more flavourful. Lobster is much less strongly flavoured than the cheaper crab.

However, fresher, less processed meat, from animals that have exercised and eaten a more interesting diet, and which has not subsequently been injected with water, tends to have more flavour. And that does cost more. 86.129.248.199 (talk) 21:33, 27 February 2013 (UTC)

Homosexuality in identical twins

If one twin is gay, what is the likelihood of an identical twin being similarly gay versus that of a non-identical twin? — Preceding unsigned comment added by 82.132.236.194 (talk) 23:35, 26 February 2013 (UTC)

See Biology_and_sexual_orientation#Twin_studies. OsmanRF34 (talk) 23:55, 26 February 2013 (UTC)

Also see Homosexuality#Cause. The bottom line is, nobody really knows at this time -- so please remember to check back in ten to twenty years. 24.23.196.85 (talk) 23:59, 26 February 2013 (UTC)

February 27

practically, how many joules does it take for a helicopter to lift itself?

for a given weight, practically, how much power is required for a helicopter to ascend, say, 50 meters? 178.48.114.143 (talk) 00:11, 27 February 2013 (UTC)

It is not easy to answer this question without knowledge of other things like the helicopter's efficiency (how much of the energy goes to producing lift). However, we can make a rough estimate of how much work that needs to be done by it to rise 50 meters using the definition of work (power is different in this context; it's the rate at which this work is done, which would depend on how much time you give the helicopter to ascend).

The work is done against the force of gravity. If we can ignore the initial acceleration required to start the helicopter moving upwards, then the force exerted by the helicopter on the air is equal to its weight plus air resistance. If we can neglect the work done against air resistance, then the work is the work done against gravity only, $W=-W_{gravity}=-(-mgh)=mgh=50m\cdot mgJ$, where m is the mass of the helicopter and g is the acceleration due to gravity.

Whether this reflects reality, I don't know, because this is only the work done in lifting the helicopter, and does not include the work done to overcome friction in components like the bearings, nor air resistance.--Jasper Deng (talk) 00:34, 27 February 2013 (UTC)

Specifically, that assumes that a helicopter is a 100% efficient machine - and it's VERY far from that! Energy efficiency in transportation says "The Sikorsky S-76C++ twin turbine helicopter gets about 1.65 mpg-US (143 L/100 km; 1.98 mpg-imp) at...260 km/h" - but when hovering, miles-per-gallon is zero! However, the helicopter probably uses about the same amount of power per hour at hover as at speed - so we can get another estimate by assuming that 143 L/100km at 260 kph - means that it consumes 143 liters every 20 minutes...or around 400 liters an hour. Gasoline says that gasoline contains 35 MJ/L - so the helicopter is consuming around 14,000 MJ per hour.

That's likely to be an over-estimate because there is no air-drag in hover. Also, when close to the ground, the helicopter uses less energy than when flying at high altitude because of "ground effect". But we could probably say that the number is between 5,000 and 10,000 MJ per hour in low-altitude hover. If it takes maybe 20 seconds to get to 50m altitude then (for the Sikorsky) the number is between 2.8MJ and 5.6MJ. Interestingly, Jasper's calculations for a 5,000kg Sikorsky suggests 2.5MJ is required just to overcome gravity. But a lot depends on the time it takes to get up to 50m...it's complicated!

SteveBaker (talk) 14:43, 27 February 2013 (UTC)

Solar powered garden fountains - suitable latitudes?

I'm interested in getting a solar powered garden fountain, but am concerned about it's performance because I live in a rather high latitude (40+° N). Are there solar panel suitability/performance range maps available? I am imagining something like how the USDA maintains plant hardiness/suitability zone maps for North America. The Masked Booby (talk) 02:12, 27 February 2013 (UTC)

Some questions:

1) Will the solar panels point straight up, or be tilted towards the south ? Will they all point in the same direction ? (I assume they won't actually track the Sun.)

2) How big are the solar panels, or, alternatively, what's their peak output ?

3) I assume the fountain only needs to run during the day, but what hours, specifically ? (Trying to run the fountain near dusk might be difficult.)

4) When will you shut the fountain down for winter, and start back up in spring ?

5) Will the solar panels be in shade for any part of the day ?

6) What's the weather like there ? Are there many cloudy or rainy days ? And do you care if the fountain runs at those times ? StuRat (talk) 02:33, 27 February 2013 (UTC)

Would an article like this help? Vespine (talk) 02:43, 27 February 2013 (UTC)

The point here is about how much efficiency you need. It may be that the pump will work even with the panels pointed in the wrong direction, etc - or it may be that you have to have so many solar panels to make that work that way that you have to do something better. But let's talk about how to get good efficiency.

The efficiency of a panel as a function of the angle between the surface and the suns' rays varies a bit depending on the kind of panel - but straightforwardly, the number of photons you intercept depends on the area of the panels as seen from the direction of the sun...to put it another way - it's proportional to the area of the panel multiplied by the cosine of the angle between the direction the panel is pointing and the direction of the sun. Some panels have reflective glass or plastic that reflects the sun rather than absorbing it when the sun is coming from an extreme angle - which make it much more important to point the panels towards the sun.

But the sun moves across the sky throughout the day - and through the year - and it depends on the latitude of the place where you live.

So, echoing SutRat's answers:

1. Will the solar panels point straight up, or be tilted towards the south ? Will they all point in the same direction ? (I assume they won't actually track the Sun.) -- You get solar panels built into other equipment that points straight up, or that you can fix at some specific angle, or that you can manually adjust, or that are driven mechanically to preserve maximum output through the day.  ::#* If you want to position the panel once and never change it - then you'll presumably want to aim it where it points towards the sun at midday in mid-spring/mid-autumn. That'll produce less power at noon in summer and winter and less still in early morning and late evening...but it's a compromise.
   • If you're prepared to go out there and reposition the panel every few months to account for the changing position of the sun at zenith...then you'll get optimum power each day at noon - but worse in morning and evening.
   • If you don't mind popping outside to adjust your solar panels a few times a day to compensate for the motion of the sun across the sky - then you'll get better still output from your panels.
   • If you have a fancy motorized mount with a computer that knows where the sun will be minute by minute through the day - then you'll do even better.
2. How big are the solar panels, or, alternatively, what's their peak output ? -- This depend on how much power does the motor requires - but also on how many batteries you have (if any).
   • If you don't have any batteries in the system, then the panel has to be large enough to collect diffuse energy from the sky even when it's a cloudy day in mid-winter. That's a LOT of solar panels!
   • If you have have batteries that can accumulate power when the sun goes behind a cloud, then you don't need as many solar panels to continue to generate power when that happens.
   • If you have enough batteries to run the pump for 24 hours without discharging, then you don't need so many solar panels because the excess power that they generate at noon makes up for the deficiency at morning and evening.
   • If you had very, very large batteries, you could charge them in the summer and you wouldn't need such large panels to get your through the winter. Clearly that's unreasonable - but in many places you can feed the excess solar power that you generate in the summer back into the electricity grid and get a reduction in your electricity bill. You can use that money to buy electricity in the winter...so (in effect) the entire electricity grid becomes a giant year-long-capacity battery!

I assumed no batteries and no operation in winter, when presumably ice will form. StuRat (talk) 16:21, 27 February 2013 (UTC)

I live in the north of England at a latitude of 53 degrees. My sister had a small, solar powered fountain in her garden. When the sun came out the fountain ran and when the sun went behind a cloud it stopped. Unless the panels are connected to batteries I suspect this would always be the case although they don't tend to mention it when they advertise them. Richerman (talk) 10:35, 28 February 2013 (UTC)

At 41 degrees at the equinox and kindof mid day it can be stopped by your body (or was it hand?) from a few feet or meters away. Also clouds. This was at least an 8 year old model, though. Sagittarian Milky Way (talk) 12:35, 28 February 2013 (UTC)

Dark matter?

I don't pretend to understand the fine points, but for those here who do, what would be reasonable conclusins to draw from this article,[7] which posits that there may be no such thing as dark matter? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:46, 27 February 2013 (UTC)

The long-and-short of it is this: There's a prediction about how the universe should behave given a) what we know about the laws of physics and b) how much matter we can reliably identify in the universe. The problem is that the universe does not obey the predictions in certain ways; and that means that either a) or b) is wrong: That is either the laws themselves are incorrect, and need tweaking or revising, or that there's some large amount of matter which is previously (and still) unaccounted for which is throwing off the observations. B) is what is meant by Dark matter, which just means "matter which, if it existed, would allow us to match theory to observation without having to rewrite the laws of physics". There's been lots of complex proposals as to what this dark matter is, but nothing has ever definitively been proven. The article is about looking at the problem from the other perspective: that instead of trying to come up with some "Dark matter" which is unobserved (and maybe unobservable) to explain the problems, instead the article is proposing that tweaks need to be made to the theory instead. --Jayron32 05:04, 27 February 2013 (UTC)

The problem with many articles like that is they select the bits that support MOND without touching on the parts that indicate a theory like that is wrong. What one should try and do in science is try and falsify a hypothesis not just calculate more of the thing you set the theory up to explain in the first place. See the criticisms section of the MOND article. It may be something like it will work but there's definite difficulties with the straightforward versions. Dmcq (talk) 11:10, 27 February 2013 (UTC)

That's a bit much. The criticisms section there goes on about the Pioneer anomaly being explained by MOND, whereas that is explained very well by the pressure of reflected heat radiation, so what's happened to the extra MOND should have contributed? Does one then just ignore that it predicted yet more deviation? Dmcq (talk) 11:16, 27 February 2013 (UTC)

MOND isn't promoted as a full theory of gravity by anyone, not even its creator (I heard him lecture). Basically, it fits one system, that of galactic rotation, perfectly, where dark matter explanations are rather inadequate. It does not do well in explaining larger-scale dark matter phenomena. Basically, the founder of the theory said this: because the current theory that is used to explain this phenomenon (galactic rotation) is pretty bad at it, and because MOND is really good at it and can put up decent fitting for some larger-scale stuff, then MOND is worth researching more.

That is, it is an incomplete theory by any standard and hardly offers a replacement for the dark matter explanation. That said, both dark matter and MOND still lack a mechanism – a particle or something that can drive it. Dark matter has some ideas for that particle, while MOND has none. SamuelRiv (talk) 18:02, 27 February 2013 (UTC)

How are dark matter explanations inadequate for galactic rotation? It's hardly surprising that MOND explains rotation curves accurately; they were designed specifically with that purpose in mind. In the Bullet Cluster, dark matter passed right through a galaxy and is significantly offset from the galaxy's core. That's very hard to explain with MOND, and completely consistent with dark matter.

One other thing that hasn't been mentioned is that one can directly measure, from the cosmic microwave background and distant supernovae, the density of baryonic matter (protons + neutrons) AND the total density of matter in the universe. The baryonic density can also be measured by looking at galaxies and summing up their masses. All these measurements indicate baryons only comprise 17% of total mass. So it's not the case, as Jayron implied, that dark matter allows us to avoid rewriting the laws of physics. The laws of physics have to be rewritten no matter what, because if dark matter exists, it cannot be made of any known particle. That would require a fundamental rewrite of the Standard Model likely much more drastic than MOND. --140.180.255.158 (talk) 21:43, 27 February 2013 (UTC)

American and Russian Tank Designs

Which tank is better in your opinion , the cheap Russian tank which can be prodeced in large numbers , or the expensive American and German tanks of fewer numbers - if we assume that military budget is equal for both sides- or in other words which is more important the numbers or quality ? — Preceding unsigned comment added by Tank Designer (talk • contribs) 07:46, 27 February 2013 (UTC)

It isn't a straightforward question but I think it is generally agreed that in the case of the German tanks the best was the enemy of the good. I have a suspicion that some of the high up German technocrats actually wanted Germany to lose the war. I think you have a bit of a misapprehension though. The main Russian and American tanks were good designs and better than the earlier German tanks. Dmcq (talk) 10:16, 27 February 2013 (UTC)

Well thank you for this information , but I am asking about the tanks in present time (M1 Abrams , T90 and Leopard 2A6 ,) it is known that T-90 is lighter and carry lower amount of ammunition -22 rounds- , and M1 Abrams can carry 42 rounds , so what case is better : larger number of T-90s or better quality of M1 Abrams-also Leopard 2A6-? It is known that they are similar in armour and firepower , but the difference is in safety and comfort of tanks . — Preceding unsigned comment added by Tank Designer (talk • contribs) 11:29, 27 February 2013 (UTC)

Your recent questions, including this one, have asked for opinions for which whole books can be written, which may, but most probably not, provide a definitive answer. This Reference Desk is intened to help people with specific questions about science subjects. The Reference Desk is capable of coming up with very good answers and assistance on questions on specific science topics. It is not intended to provide opinions on intangibles and broad subjects. Though some may offer opinions, you are likely to form a much better opinion if you do your own research. If you have a deep interest in tanks, why not visit your State Library? You can probably get books on inter-library loan from a military college in your country, or even visit the college library yourself. What you need is not restricted information.

There is not likely to be one "best" tank - what sort of tank is best for any country depends on a myriad of variables, a lot of which will be intangible. For example, what sort of tank is "best" depends on what sort of battles will occur - small, large, against tanks or against other systems. And what sort of battles, or applications for the tanks depends on military planning. For instance, in the military planning of my country, (Australia), it has been anticipated that military operations may involve long penetration deep into other country's jungles, where the ability to tow trucks out of bogs & rivers, rapidly construct bridges, and be largely field repairable is more important than accurately firing dirty great shells. So tanks were purchased that look very different to that of other countries that wanted tanks for a rapid shock and awe penetration (firing shells) across open terain or deserts. The cost of a tank is not at all closely related to its complexity, capability, or sophistication. For example, factory labour cost in Russia and China is well below that of the USA. Depending on Govt policy, whole of life cost may be more important, or less important, than ex-factory cost. Another factor is that the purchase of expensive military hardware is always a political decision - will it provide jobs in a senator's or minister's home State? Will it provide technology experience transferable to other industries? - always an important reason. One strongly supects that, on purely objective operational grounds, countries such as Australia, and perhaps even the USA, would like to purchase Russian equipment. But that is never going to happen for obvious political and "face" reasons - on both sides. These factors are always at least just as important, and usually more important, than straight technical merits of military hardware design. This is why Australia builds its own submarines - they aren't as good as Russian subs, they aren't as good as USA subs, they aren't as good as other subs - we know that. But it means $billions injected into local industry, and not $billions injected into some other country. Economic strength is important, wins wars, and prevents wars.

Finally, just like the strength of a patent is unknown until tested in court, what tank or any other sort of military hardware is "best" cannot really be known until it is used in a major war, and we found out who won, and we have the oportunity to post mortem research and figure out why they won. I'm sure that if you were to ask 5 American generals and 5 Russian Generals in a off-the-record free discussion which is the best tank, you'll get 10 different answers with 10 sets of different reasons.

Wickwack 58.170.157.73 (talk) 13:15, 27 February 2013 (UTC)

I agree with all of what Wickwack has pointed out, but I'll also note that the premise of the question seems flawed. The T-90 and the M1 Abrams aren't that different in unit cost (perhaps a factor of 2 or 3), but more importantly, the T-90 isn't "produced in large numbers" relative to the Abrams; there are roughly 4 Abrams for every T-90. Generally, it looks like you might be interested in reading on "quality vs quantity" topics with respect to the military. Certainly there are some good case studies like the air war in Vietnam. — Lomn 13:38, 27 February 2013 (UTC)

These questions don't have black-and-white answers. : For example, suppose "team A" in a conflict has a vehicle which has a "worth" in battle that is twice that of the vehicle that "team B" manufactures at half the price. Which is best?

• If you have to ship your army halfway around the world (as the USA did for wars in Iraq and Afghanistan) - then it's clearly a bad idea to have to ship twice as many vehicles, provide them with fuel, feed and provide sleeping quarters for their crews, maintain them...etc. So for "long distance" wars, team A's approach with fewer, high quality vehicles is clearly a good idea.
• For a war that's close to home, a simpler design that needs less technical sophistication and training from the crew, probably less maintenance too - is clearly a good thing, so maybe team B's approach is better. Short supply lines make it easy to get the extra fuel, food, etc to the battle front.
• You also have to consider that tanks have to do other things than fighting other tanks. If you need to have forces spread over a long border with a hostile neighbor to protect against incursions from light-weight forces - then you might just need a large number of cheap vehicles just to have them spread along the entire length of the border...so again, team B have the best approach.
• There are other less tangiable considerations too - cultural matters: Team A will have half the number of people out there in harm's way than team B. If team B's people place a lower value on human lives than team A - then they may not care much about that...but team A might well believe that having half as many people killed or injured in battle more than justifies the more costly vehicles.
• High-tech vehicles require more training for crew and maintenance people than lower-tech vehicles. That's justified if your army is staffed by career professionals who stay in service for decades. But if you rely on conscripts or part-time soldiers who come into the military, get brief training and only work out a short stint before returning to daily life, then team B's K.I.S.S approach is clearly better. Issues as fundamental as how good your nations' educational system is has an impact on what kind of tanks you make!

I'm sure I've missed many arguments here - but the point is that there are a huge number of trade-offs. Simple calculations about ammunition capacity and armor thickness are an overly-simplistic way to look at this problem. The success or otherwise of team A & B's approaches depends on much, MUCH more than that! To couch this in purely military terms: In modern warfare, you need to consider "strategy" - not just "tactics".

SteveBaker (talk) 13:43, 27 February 2013 (UTC)

You have made very good points, and you have remined me of another important factor: In anticipation of a future time of major war, where a rapid acquisition of large numbers of tanks may need to occur, military planning may involve the conversion of truck and car factories to large scale tank production. Any tanks made under such circumstances will be a design, retrieved from the files, that is compatible with existing or easily adapted factory tooling, standard available engines, compatible with assembly line floor widths and crane load capacities and the like. The rationale may be to settle on a tank design that is not the best possible, whatever that means, but one that can be made in a hurry. A good tank you have in quantity now is better than a perfect tank you won't get until the war is long over. Wickwack 121.215.21.148 (talk) 14:38, 27 February 2013 (UTC)

The current Russian tanks seem pretty good to me! The tanks have developed in an arms race and it isn't over yet. I'd guess in the future people will only have a few of the heavy tanks and go more for lots of drone tanks which don't have to bother with armour quite so much - but who am I to guess? Perhaps they'll make them even more impregnable if they don't have to worry about frail humans inside.. But as the contributors before said - best really depends on what's cost effective for the circumstances. Dmcq (talk) 13:46, 27 February 2013 (UTC)

In the 1991 Gulf War, the "quality over quantity" argument went in strongly favour of "quality" - the Iraqis lost a total of 4,000 of 4,230 tanks deployed, the Coalition lost 4 of 3,360 tanks deployed.[8] Of course many of these were lost to aircraft; however 180 British tanks destroyed 300 Iraqi tanks without loss (BTW, it's not only the Americans and Germans who know how to make tanks). To qualify that, many of the Iraqi tanks were of very old designs, and as Dmcq says above, the latest Russian tanks are firmly in the "quality" bracket too. Alansplodge (talk) 15:03, 27 February 2013 (UTC)

On the other hand, if you can make them cheap enough, and no human lives are involved, why bother with armor at all? There was a time in the first war against Iraq where the cost of the missiles the US were using to shoot down Iraqi aircraft cost twice the price of their targets. When there are humans in the conflict, you have to concern yourself with the ethics of under-protecting the crew of your vehicle - but in some future "drone war", the economics of the situation start to matter. SteveBaker (talk) 15:13, 27 February 2013 (UTC)

Apocryphal story about the Russians in WWII; an American advisor sees them chaining three tanks front to back before crossing a frozen river and asks why. The Russian commander answers "So that in case one tank breaks through the ice and sinks, the other two can haul it back up again." the American asks, "Won't the crew be already drowned?" The Russian answers "Oh, we can always get a new crew." Gzuckier (talk) 17:21, 27 February 2013 (UTC)

Note that most Russian tanks are equipped to drive underwater, e.g. for crossing deep rivers. 24.23.196.85 (talk) 00:49, 28 February 2013 (UTC)

Recommended reading on the subject: [9]. Gzuckier (talk) 17:21, 27 February 2013 (UTC)

Thank you every one for this valuable information and for your patience too.

Why is sleep associated with "scary"?

After reading the Night terror and Sleep paralysis articles, I was wondering, why is sleep almost always associated with the frightening, even unconsciously? Why aren't sleep problems more often associated with, say, feelings of bliss or, instead of an "intruder in the room", maybe being in a celestial location? What is it that the body is trying to tell us that it needs to make such drastic and terrifying emotions?

Bonus question: These scary sleep problems have names, but are there names for ultra-realistic dreams that sadden you to the point where you wake up drenched in tears (or anything similar—just not scary)? – Kerαunoςcopia^◁_galaxies 09:50, 27 February 2013 (UTC)

Where do you get the 'almost always' from? Have a look at the percentage occurrences mentioned in the articles. Dmcq (talk) 10:04, 27 February 2013 (UTC)

A lot of people find being awake a lot more scary.--Shantavira|^{feed me} 10:28, 27 February 2013 (UTC)

Our brain has been shaped by the hunderds of millions of years long arms race where animals try to eat other animals and try to avoid being eaten themselves. Count Iblis (talk) 12:23, 27 February 2013 (UTC)

You're more vulnerable while asleep, as the Count says. A couple of counterargument quotes:

"Sleep... the most beautiful experience in life... except drink!" -- W.C. Fields

"Sleep is wonderful. You're alive... and unconscious!" -- Rita Rudner

←Baseball Bugs ^{What's up, Doc?} carrots→ 12:56, 27 February 2013 (UTC)

And another quote...

"There is not any book

Or face of dearest look

That I would not turn from now

To go into the unknown..."[10]

Edward Thomas, "Lights Out" (1914) Alansplodge (talk) 14:45, 27 February 2013 (UTC)

One possible reason is that sleep requires darkness, and, being diurnal, people can't see well in the dark, and thus fear what might be lurking out there (hostile people or animals). StuRat (talk) 16:13, 27 February 2013 (UTC)

Note that ~3/4 of dreams are unpleasant [11]. However sleep paralysis is a different thing altogether; the emotional/frightening component is kind of logical, considering the predicament of being more or less conscious and yet incapable of voluntary movement. Hard to imagine how that could NOT be considered scary; but it's just a software timing failure in the old meat-computer, the reticular activation system not properly turning off the muscle inhibition circuit before it turns the sensory awareness circuit on. Similarly, there is no reason why true night terrors, not associated with any bad dream, could not be just the result of a misfire of the brain's terror circuit in the absence of a valid stimulus. (Seems like sleep is a time of frequent brain malfunctions). Similar to deja vu; no reason to think of that as anything more than a misfire of the "hey I recognize this" circuit without valid stimulus, no need to invoke past lives etc. On another note, those "I'm falling!" jerk-awake dreams (somtimes accompanied by the belief "Hey, I levitated in my sleep!") might have something to do with our ancestors sleeping in trees for a zillion years, and the evolutionary benefit of being hypersensitive to a fall and snapping immediately awake. Gzuckier (talk) 17:30, 27 February 2013 (UTC)

Is that 3/4 of all dreams, or 3/4 or remembered dreams ? (Presumably traumatic dreams will be easier to recall.) StuRat (talk) 18:41, 27 February 2013 (UTC)

Stagnation pressure

Does stagnation pressure only exist at stagnation points? Clover345 (talk) 13:40, 27 February 2013 (UTC)

According to the first line in that article, yes. StuRat (talk) 16:02, 27 February 2013 (UTC)

but the article also says its the static pressure + dynamic pressure. Both pressures exist everywhere in a fluid doesn't it? Doesn't this contradict that first line? Clover345 (talk) 18:55, 27 February 2013 (UTC)

First is a theoretical model view for calculation. In reality Dynamic pressure is added (or subtracted if negative). --Kharon (talk) 20:40, 27 February 2013 (UTC)

Total pressure exists everywhere, and stagnation pressure only exists at stagnation points, but total pressure and stagnation pressure are equal (except in the vicinity of shock waves.) Seeing total pressure and stagnation pressure are equal, many authors who write about incompressible flows, and low speed flows, don't complicate things by talking about total pressure. Those authors only write about stagnation pressure and they say it exists everywhere. Dolphin (t) 07:23, 28 February 2013 (UTC)

Space Travel Time Dilation Chart

I remember reading a book in the library about the history of space travel & the possible future of space travel & I remember that on one page that there was a chart showing the velocity of a space craft, if using current technology & the amount of time dilation for each step. For example if the space craft was travelling at 0.1c (or 10% light speed) than there will be this much time dilation or if travelling at 40% then there will be this much time dilation. And the chart showed you all the way up to I think 99.9... something %. I can't remember the title of the book so I couldn't find it again in the library so does anyone know where I can find a similar chart from somewhere else. Scotius (talk) 14:52, 27 February 2013 (UTC)

Our article on Time dilation contains such a chart, I believe. Zzubnik (talk) 15:58, 27 February 2013 (UTC)

That contains a graph (which, unfortunately, is linear, so doesn't show much detail beyond .95 c). For a chart, see Lorentz_factor#Numerical_values. StuRat (talk) 16:08, 27 February 2013 (UTC)

Calculating Shaft Power

I had some marine engine data which mentioned the ship's maximum speed at maximum engine power at the maximum rpm. e.g. 13 knots at 9000kW at 120 rpm. Is it possible to calculate shaft power with this data? If not, then what other data is required for such calculation? —  Hamza  ^{[ talk ]} 16:25, 27 February 2013 (UTC)

I think you do need more info. You could either go from engine power to shaft power if you knew the efficiency of the transmission of power from the engine to the shaft (you could just guess at this efficiency) or you could look at the speed of the ship, along with the size, mass, hull design, prop efficiency, wind, water salinity/density, etc., and try to determine the shaft power that way. This later method has far more variables, and is likely to be less accurate. StuRat (talk) 16:33, 27 February 2013 (UTC)

1) No 2) Displacement (ship) 4) Fluid mechanics are extremely complex and ship construction is never sure their new designs work as intended like reaching planned max speed. Engine results are far more exact to estimate just from design as are Transmissions. Therefor shaft power is considered given aka can be estimated exact enough just by giving engine power. --Kharon (talk) 20:30, 27 February 2013 (UTC)

The writers of the IQ tests are the smartest persons on earth?!

Hi,
let suppose that IQ measures the human intelligence;
That means that to challenge another personin the test whoever writes those tests should be smarter, isn't it?Exx8 (talk) 17:42, 27 February 2013 (UTC)

No, since writing a question when you already know the answer is far simpler. For example, you can easily come up with a sequence of numbers that follows some pattern too complex for most people to guess. Try this one: 429,-75,-100,-36,-99,384,-75,-100,96,125,300,-36,-19,96,-51,-100,300,125,-100,-64,-75,-99,224,-100,-96,341,300,-100,-64,-75,-99,224,-100,-19,300,261,-75,44. What's the next number in the sequence ? StuRat (talk) 17:48, 27 February 2013 (UTC)

Answer

To find the answer, add 100 to each number, take the square root, then look it up in a table of letters, where 0 = space, and 1-26 = a-z: x x+100 sqrt(x+100) letter ---- ----- ----------- ------ 429 529 23 w -75 25 5 e -100 0 0 -36 64 8 h -99 1 1 a 384 484 22 v -75 25 5 e -100 0 0 96 196 14 n 125 225 15 o 300 400 20 t -36 64 8 h -19 81 9 i 96 196 14 n -51 49 7 g -100 0 0 300 400 20 t 125 225 15 o -100 0 0 -64 36 6 f -75 25 5 e -99 1 1 a 224 324 18 r -100 0 0 -96 4 2 b 341 441 21 u 300 400 20 t -100 0 0 -64 36 6 f -75 25 5 e -99 1 1 a 224 324 18 r -100 0 0 -19 81 9 i 300 400 20 t 261 361 19 s -75 25 5 e 44 144 12 l Lookup table ------------ 0 a 1 b 2 e 5 f 6 g 7 h 8 i 9 l 12 n 14 o 15 r 18 s 19 t 20 u 21 v 22 w 23 Now can you determine the next number in the sequence ? StuRat (talk) 18:36, 27 February 2013 (UTC)

I can't answer that question. You must be smarter than I. Gzuckier (talk) 18:00, 27 February 2013 (UTC)

Or maybe StuRat just found it in a book somewhere and copied it out. Wickwack 124.182.57.146 (talk) 01:06, 28 February 2013 (UTC)

I think there are some problems of this nature - it's known that the most intelligent people sometimes have trouble with intelligence tests because they can think of perfectly valid reasons to pick a answer other than the one that the person who framed the question didn't think of.

For example, I might ask what the next letter in this series is: A,H,I,M,O,T (it's "U") - but who is to say that if you converted each letter into a number 1,8,9,13,15,19 that someone couldn't come up with an equation that would produce something 21 instead of 20 as the next in that series? Maybe converting the letters into morse code produces a pattern who's obvious next letter is "R". Maybe the first letters of the names of the first six days of the week in the Kx'a language of southern africa are A,H,I,M,O and F?

Once these kinds of alternative answers come up, this super-smart person now has to decide which of the possible answers is the most likely to have been in the mind of the (clearly less intelligent) question writer. Avoiding those kinds of accidental alternative answers is not a trivial matter - and it most certainly it doesn't help if you already know which answer you think is "most correct". SteveBaker (talk) 18:09, 27 February 2013 (UTC)

It's easy to develop questions that are more difficult to answer than they are to conceive and verify (there are tons of examples in mathematics). Also, almost all (maybe all) aptitude tests have some sort of time limitation (even if only practical... the researcher has other things to do with their life). There's also Steve's point, that sometimes you can think yourself out of an answer, or know so much more that the obvious answer seems just too obvious. Shadowjams (talk) 18:16, 27 February 2013 (UTC)

Clever sequence, Steve, but a cinch with google: t, u, v, w, x, y. Not the point of the question exactly, but try this one (if I've got it right): class, rate, world, estate, element, sense, .. IBE (talk) 18:22, 27 February 2013 (UTC)

Heaven! 80.254.147.84 (talk) 00:07, 28 February 2013 (UTC)

I have got a feeling that as soon as I post this others will come in with support. '[Smart] is the wrong term. In tests I have always come well up in the upper percentiles – but I am not what I consider smart. I've come across countless people, like those depicted a TV soaps as hill-billies and trailer-trash and self- made millionaires that still have trouble reading and writing -but who are really smart... but they are just not good at IQ tests. Think Henry Ford and his court case about him being ignorant pacifist [12] If you teach a kid how to do the tests they just become good at doing the tests. I don't think their intelligence comes to match mine after all that effort (as a tutor) because – to use a phrase – Old age and cunning will always triumph over youth and skill so I still have the advantage. Our only 'equality' is now that we can also amaze but doing things like reciting pi to twenty decimal places. But tell you folk out there.. 3 decimal places does for almost every thing including designing jet engines. The ability for remembering the signs and cosigns for 10-30-40-50-60 degrees extra is just something we happen to be good at. But what good is that in trying to get over to our accountant, lawyer etc. that their bill is too high (“we have looked in to your consernse Mr Aspro but our billing is in line with blah-blah-blah”). In other word 'intelligence' is is a much broader attribute than (say) a child psychologist can objectively measure with the simple analytical tools at his/hers disposal. If the IQ examiners are smart at anything, then it is to get paid well for what their doing - which is not a lot.--Aspro (talk) 19:25, 27 February 2013 (UTC)

Writing tests like this one is more difficult than a standard IQ test. Count Iblis (talk) 21:42, 27 February 2013 (UTC)

A fun test written by someone who doesn't know the difference between your and you're, plus it turns into a chain letter at the end. – Kerαunoςcopia^◁_galaxies 23:10, 27 February 2013 (UTC)

Being able to write an IQ test does not mean that the author is really smart - he could be really dumb. Two factors: 1) He could have spent his whole career figuring it out, but you and I tried to do the test in half an hour; 2) A specialist in any trade, be it wood working, electronics, dentistry, or devising IQ tests, can, and should be able to, outperform a lay person or non-specialist. I make my own furniture and can join boards, as in making table tops, so that it is almost impossible to see the join - it has always impressed my wife, and never fails to impress other women. It often doesn't impress men, though, because they, like me, learnt the simple secret to it in high school woodwork class. Wickwack 124.182.57.146 (talk) 01:18, 28 February 2013 (UTC)

Engineering and medicine

Could one claim that engineering is physics applied to real world situations and that medicine is biology applied to real world situations? If this is true, what's applied chemistry? Clover345 (talk) 18:52, 27 February 2013 (UTC)

Hummm! Medicine is a 'discipline' often avoid of any proven science/effectiveness. With engineering/physics, its clear if it works or it doesn’t work.--Aspro (talk) 19:30, 27 February 2013 (UTC)

All of the advances of medicine of the last century have been forms of applied science, and have been justified by the methods of science, and have been consilient with biology. One of the main differences between medicine and engineering is the importance of the personal interaction with between patient and doctor. This is not science (though it can be studied scientifically). There is a perfect controlled experiment of history. Homeopathy was a very popular form of medicine in the 19th century. It was completely unable to adopt the methods of science and its theoretical underpinnings are completely incompatible with biology (despite desperate fantasies). Homeopathy really is medicine without the science. alteripse (talk) 19:36, 27 February 2013 (UTC)

Engineering includes virtual world application (like CAD) and theory (like Patents)as well. --Kharon (talk) 20:11, 27 February 2013 (UTC)

What about vets? Clover345 (talk) 21:33, 27 February 2013 (UTC)

One form of applied chemistry might be materials science. StuRat (talk) 00:40, 28 February 2013 (UTC)

Is there a request for references here? This is the reference desk, not a discussion forum. μηδείς (talk) 01:02, 28 February 2013 (UTC)

Um - I only have one reference for this...and well...[13].  :-) SteveBaker (talk) 05:12, 28 February 2013 (UTC)

February 28

Emotional impact of surveillance

Suppose the following three alternative scenarios: (1) A person is placed under surveillance and told beforehand that he/she is under surveillance (without being told how, where or when); (2) The same person is placed under surveillance and not told about it, but rather is left to find out about it for himself/herself (or not); (3) The same person is not placed under surveillance, but falsely told that he/she is, for the purposes of intimidation/behavior modification/etc. My question is, of these three scenarios, which one do you think will be emotionally the hardest for the person in question, and which will be the easiest? 24.23.196.85 (talk) 05:40, 28 February 2013 (UTC)

As it says at the top of this page, we don't answer requests for opinions, predictions or debate. --Guy Macon (talk) 06:24, 28 February 2013 (UTC)

That sounds like stalking and harassment to me. Dmcq (talk) 11:36, 28 February 2013 (UTC)

increasing white blood cell count

My brother recently discovered he has cancer of the gullet(osophagus)- he has started receiving chemotherapy which is causing his white blood cell count to reduce to an unhealthy low level.Does anyone know of natural food stuffs that increase white cells in the blood system?62.6.188.162 (talk) 06:45, 28 February 2013 (UTC)

The reference desk, and Wikipedia editors in general, cannot offer medical advice.--Jasper Deng (talk) 06:58, 28 February 2013 (UTC)

The desire that individual foods also function as medicines to specifically cure certain serious diseases goes back to prehistory. While spectacular benefits may accrue when one eats a food that supplies a specific deficient nutrient (like citrus fruits for scurvy, or cod liver oil for vitamin D rickets, or iodine for endemic goiter) I cannot think of a single food that has more than a marginal specfic benefit for a serious dysfunction of a major organ or system. This is a fantasy that underlies the transfer of billions of dollars, however, as there are an unlimited number of quacks out there willing to take the money of those wanting to buy hope. Please understand thst a healthy diet with all needed nutrients is essential to health. It is just that I cannot think of a single major organ dysfunction (like bone marrow or lymphocytes or liver or skin or parncreas) that a particular food will reverse. Best wishes to your brother. alteripse (talk) 11:29, 28 February 2013 (UTC)

Oldest extant species

What is the oldest extant species? I know the horseshoe crab has been there for 450 million years. Is there any other species which is older? --PlanetEditor (talk) 10:58, 28 February 2013 (UTC)

No extant species of horseshoe crab has been around that long, though xiphosurans in general have. You may want to take a look at the article Living fossil for some insight into the matter. Deor (talk) 12:01, 28 February 2013 (UTC)

It's difficult enough defining where one species ends and another begins when dealing with two extant species. Trying to decide when one species goes extinct and becomes another species is almost impossible, so the standard species descriptions will be highly arbitrary. --Tango (talk) 12:35, 28 February 2013 (UTC)

two questions about flight. 1) why do helicopters have 4 blades?

1. My first question is this:

In talking about the top rotor only, why do helicopters have 4 blades, instead of just 2? (i.e. in an X configuration instead of a simple / configuration). In googling, I do see quite a few that have one long pair and one relatively short pair, but there are still 4 blades in total in an X. Why do the designs always need that? 91.120.48.242 (talk) 11:56, 28 February 2013 (UTC)

Helicopter rotors don't always have four blades - most only have two. Compare the Bell 212 and Bell 412. (The small rotor at the tail end of the fuselage is called the tail rotor. It serves to stop the helicopter from spinning around; it doesn't contribute to the lift necessary to support the weight of the helicopter.) Dolphin (t) 12:23, 28 February 2013 (UTC)

I am extremely confused as when we look at the TOP rotor only (which is what my quesiton is about; please ignore tail rotors), on both of your pictures I see *four* blades in an X configuration! The first one (Bell 212) shows the long pair/short pair combination I mentioned in my question, while your second picture is an X such as all the other ones I see. Googling Helicopter, I see only exclusively 4-blade designs, with a very very occasional / (two blade) instead of X (four blade) design of the top blades. Why is this? What is the role of the two short blades when it is two long + two short X design? 91.120.48.242 (talk) 12:28, 28 February 2013 (UTC)

There is something sticking out perpendicular to the blades, but I don't think they are blades themselves. They don't look like they'll provide any significant lift. I'm not sure what their purpose is. --Tango (talk) 12:43, 28 February 2013 (UTC)

second theoretical question about aerodynamics

my second question about flight. this is a purely theoretical question intended only to further my understanding of aerodynamics and is not intended to have any practical application, be something i publish build or offer for sale or anything like that (indeed it is practically impossible as described in the end). it's just aerodynamics question I am asking here to further my understanding.

2. as a purely theoretical question.

• imagine a glider similar to this: http://en.wikipedia.org/wiki/Eta_Aircraft_eta

Now imagine the following changes.

1. the wings are actually attached above (not in line with) the body
2. the body can turn under the wings via the power plant - (if it did the tail would bump into the wings if the tail didn't get out of the way)
3. one wing can turn around 180 degrees and back, along its long axis
4. the angle of attack of both wings can be changed
5. the tail is, in fact, 3 layers: two flaps and a rotor inside...
6. ...which normally enclose a rotor which is hidden.
7. ... however, which can each open (change yaw) 90 degrees (to point toward the sides of the plane), exposing the rotor inside.

The question is this. Suppose the plane goes through these steps:

1. the one wing turns around 180 degrees along the long axis
2. the angle of attack of the two wings is changed
3. the rudder flips 180 degrees along the forward-aft axis of the plane to get out of the way of the (geometrical plane of the) wings
4. the rotor on the tail is exposed by unhinging the flaps to change their yaw
5. the rotor can turn to counteract the turn produced by the power plant, thereby keeping the body of the plane straight while the wings turn.

Would this be enough to turn the glider into an efficient climbing machine (like a helicopter)? Or would the characteristics that make the wings good gliders make it a terrible "helicopter" at ANY angle of attack and the design could not possibly work (theoretically, this isn't intended to be practical but just to further my understanding of aerodynamics) for this reason.

(I imagine it might be possible that this would NOT theoretically work because the glider is designed with wings that go long distances while losing very little altitude. Conversely, it would have to spin many many many times to gain very little altitude. However, my idea is that changing the angle of attack is enough to counteract this)?

This is not intended to be practical in any way. I am simply interested in understanding aerodynamics better through this exercise in whether such a glider would be able to climb efficiently, or, if not, what the problem would be with this?

I am really only interested in the climbing efficiency / aerodynamics, not practical problems with this machine such as the obvious one that a glider could never support a helicopter engine, fuel, and so forth. For the purposes of this question, you could even assume that a long tether from ground feeds the glider compressed air to turn the engines. My question is about how efficiently it can use that power in the configuration described.

Thanks for furthering my theoretical understanding of aerodynamics. 91.120.48.242 (talk) 12:25, 28 February 2013 (UTC)