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April 10

Is there and hand-powered or foot-powered laptop charger?

XO-1 clamp charger. If you had an OLPC XO-1 laptop, you could use this hand-crank. I'm not sure it'd be practical to be cranking on this thing in economy-class, though. APL (talk) 03:42, 10 April 2011 (UTC)

Whenever I go to anyplace far from a plug outlet (like some campgrounds or an economy-class section of an airline), a thought I always have is "Are there any manually-powered laptop chargers anywhere on Earth?"

Now I hope you can solve this thought once and for all. Where would I find those kinds of chargers? (By the way, it would help me lose weight.) --70.179.169.115 (talk) 21:35, 9 April 2011 (UTC)

I think that the electricity requirements for a laptop are a bit too high for that to be practical. Maybe one with a tiny screen and a stationary-bicycle-type charger might work, but that wouldn't be very portable. Perhaps multiple pre-charged batteries would be more practical, although airlines might not like those.StuRat (talk) 22:01, 9 April 2011 (UTC)

A minute on a stationary bike will get you about 5 minutes of laptop power (assuming 100 W from biking and 20 W as a typical laptop power drain for CPU-light activities). OLPC has specialized laptops that can be powered by a hand-crank for the developing world, but they've gotten down to only 2 W under normal usage. Dragons flight (talk) 22:17, 9 April 2011 (UTC)

Well apparently power requirements have improved, because I distinctively remember doing this thought experiment in physics class in 2000 (yes, I'm old), It was an Apple desktop from the early nineties. In any case, only one person in class was fit enough so as to even get the computer through bootup (which -as you other old folks might know - was pretty freaking long for early 90s Apples). Magog the Ogre (talk) 03:20, 10 April 2011 (UTC)

Um, holy shit, if taking physics in the early 2000's is old, what does that make me who was teaching physics in the early 2000's? --Jayron32 03:52, 10 April 2011 (UTC)

All these kids with their technology... why, back in my day we used Windows Vista! And us old-fogeys still knew how to make a computer run smoothly, even though we had to fit all our programs into a mere 1 gigabyte of RAM! Nobody ever complained about battery-life either, because we still plugged the computer into the wall! Nimur (talk) 19:39, 10 April 2011 (UTC)

We never had a wall, a wall would have been luxury to us. if we wanted to divide 3200 by 365 we had to double 365 repeatedly until the largest possible multiple of 365 was reached, which is smaller than 3200. In this case 8 times 365 is 2920 and further addition of multiples of 365 would clearly give a value greater than 3200. Next we noted that (2 / 3 + 1 / 10 + 1 / 2190) times 365 gives us the value of 280 we needed. Hence we found that 3200 divided by 365 must equal 8 + 2 / 3 + 1 / 10 + 1 / 2190 (ref). Cuddlyable3 (talk) 12:30, 11 April 2011 (UTC)

Not practical for flying, but on camping grounds you could use a solar charger - although I have never used one and have no idea how well they actually work -- Ferkelparade π 03:28, 10 April 2011 (UTC)

Mars Science Laboratory landing criteria

This news article discussing the landing criteria for the Mars Science Laboratory says: Being nuclear-powered, Curiosity cannot go to a location that has either water or ice within one meter of the surface, Golombek noted, due to planetary protection guidelines. What is the basis for this guideline and what then is the purpose of Curiosity's DAN instrument? Are they hoping to find what they are trying to avoid? -- 110.49.234.239 (talk) 00:38, 10 April 2011 (UTC)

I haven't been able to confirm that claim on any sites with a better reputation for science reporting than msnbc, so I wonder if it's even true (in the rest of the article, they gave exact quotes from this Golembek, but not in that paragraph, so it is possible they misunderstood). It is important to note that "nuclear-powered" really isn't a good description. There is no nuclear reactor, there is a radioisotope thermoelectric generator. That's just a lump of radioactive material giving off heat as it decays and that heat is turned into electricity to power the lander. The risk from the radioactivity is fairly low. --Tango (talk) 11:31, 10 April 2011 (UTC)

I wonder if it was an unfortunate collision of two unrelated sentences - the "planetary protection" thing is generally a biological concern. Though it seems rather absurd, considering my impression that any given Mars probe is, in all probability, going to end up smashed all over the landscape. Wnt (talk) 15:59, 10 April 2011 (UTC)

By "in all probability", did you mean "as likely as not", given the historical success rate of Mars landings and orbital insertions? -- 110.49.248.162 (talk) 23:37, 10 April 2011 (UTC)

Heh, we have an article for that? Well, a 50% success rate is better than I thought, and some of those are launch failures that won't touch Mars. Wnt (talk) 02:11, 11 April 2011 (UTC)

Here the answer from a real planetary protector! (no this is not a joke) The problem wit the RTG is that it produces heat. After a crash landing the heat and the subsurface ice would form a habitable zone. Any microbe on the rover outside might find enough food to grow and than you have a small area which is full of evolving earth life. This would rendering any further mission to Mars useless because you find earth based life and not Matian life. Areas where this can happen are listed as special regions and belong in a special category for missions. So MSL is not designed to reach special regions as a whole, only the small drilling tool is sterile and might be clean enough to touch a special region. As a crash landing is possible they are not allowed to land in an area with possible special regions. They will drive to the interesting places, they have the lifetime to do so.--Stone (talk) 19:25, 11 April 2011 (UTC)

Sound in space

What would be the implications if it were possible for sound to propagate in space? Would it be possible to hear hellish supernovae explosions and other stuff?--89.76.224.253 (talk) 01:20, 10 April 2011 (UTC)

Eh. First, interjecting something like Earth's atmosphere into the interstellar medium would have wide-reaching effects such that whether or not we heard a distant supernova wouldn't be terribly significant (for instance, we'd collapse into a black hole in pretty short order). Generally, though, I think it's a fairly safe principle to derive from how light behaves: supernovae may objectively be hellishly bright, but they're so far away that they are not subjectively bright. Sound will have a similar rate of dissipation (the same in ideal conditions, probably higher in terms of power lost to the medium), and so I feel pretty confident that supernovae wouldn't be subjectively loud, either. As with light, the sun would probably dominate the local soundscape.

On the other hand, if you don't like putting an actual sound transmission medium in place and are instead just asking "but what if we could hear through space?", then you're rewriting physical laws and the answer can be more or less what you like. — Lomn 03:12, 10 April 2011 (UTC)

In the most broad definitions of "sound" and "space", you can technically make a sound in space, but there are real physical limits to the property of that sound. The basic principle is that sound may only propagate if the molecules doing the propagation are close enough together. The exact minimum spacing of the molecules is dependent on the desired frequency of the sound, or if you prefer to think of it the other way, there is a minimum frequency of sound which may be transmitted by any medium, and that minimum frequency is dependent on how close together the molecules of the medium are. This relationship doesn't have a bounds to it; so hypothetically you could generate a sound even in a medium where the molecules were spaced kilometers apart, if, for example, the sound wave was similarly huge, say millions of kilometers in wavelength. That's a fairly low-frequency sound, but its still a sound. So yes, you can generate a "sound" in "space", but you cannot generate a sound which human ears (or indeed, any means of sound detection we have on earth, be they natural or artificial) could detect. --Jayron32 05:32, 10 April 2011 (UTC)

Indeed, there are even real, measureable consequences to the speed of sound in space. The termination shock, for instance, occurs at a point about 80 AU from the Sun where the solar wind is slowed by its interaction with the thin stuff in space to a subsonic speed (about 100 km/s); this results in measurable local compression and heating. TenOfAllTrades(talk) 19:37, 10 April 2011 (UTC)

Of course, the word "local" needs to be interpreted relative to the size of the wavelength involved. The termination shock is sort of a "region" with extent on the order of AUs. When Voyager II passed through the heliopause, the astrophysical community debated the actual timing of the crossing over a span of several years. (There are still some scientists who believe that the relevant instrument readings are at levels that indicate Voyager II is still inside the heliosphere). It's a bit difficult to intuit, but you have to think of a boundary zone whose size is determined by the effective wavelength - which is enormously huge. See our article Heliosphere#Heliopause, and especially the section about detecting the effects. The "sonic shock" is measured as a gradual decrease in particle density (from "almost-total-vacuum" to "almost-completely-totally-vacuum"), accompanied by an effective difference in average particle incidence energy. But, if you were to draw a diagram scaled by the relevant scale-length, this hundreds-of-millions-of-miles-wide zone would be a "clean" boundary line between solar heliosphere and interplanetary space. Nimur (talk) 19:50, 10 April 2011 (UTC)

Question: for a sound as long as Jayron is proposing: wouldn't we eventually hit some sort of limit to the length of the wave? I simply cannot fathom that a wave could exist with a length of millions of kilometers. My knowledge of physics is not good enough to answer any of the following, so I'm asking for clarification:

1. Would it require an obscene amount of energy to produce such a wave, one that humans cannot produce, in order to try to monitor this possibility?
2. Would Planck's law in some way require that the length of the wave be an intermediary length, for which the desired distance is simply too long?
3. Even if the above concerns were somehow addressed, isn't sound based off of molecules getting close enough to each other to interact on an electromagnetic basis (i.e., they bump into each other)? Thus the precision required for having one molecule hit another at such a distance is outstandingly high, correct? I suppose it wouldn't be an issue if there was a flood of molecules, e.g., a supernova which somehow created low frequency sound. Magog the Ogre (talk) 20:41, 10 April 2011 (UTC)

1. I don't see that there would be any clear lower limit to the energy of such a wave. It might be hard to detect such waves no matter what their energy are, but that's a different matter from whether they can exist.

2. Um, why would it?

3. True, at least in areas of interstellar space where the matter is not ionized. Within the galactic disk, there's usually not more than a few centimeters between neighboring atoms, but they hardly ever hit each other. That is why the wavelengths have to be that large, because the wavelength needs to be many times the mean free path before a wave can propagate. –Henning Makholm (talk) 21:25, 10 April 2011 (UTC)

Theoretically, there's no reason you can't have a wavelength of light-years. Practically, we have to ask: what transducer could be so large that it could radiate that low frequency? You would literally need a vibrating membrane the size of the galactic disc. As such, it's best to think about these waveforms as wave-like descriptions of the material in the galactic disc, rather than as a propagating sonic "signal." The size- and time-scales relevant to such waves are cosmological in scope, so this analysis might actually be useful for analyzing galactic formation and early universe cosmology. For example, density wave theory explains one such formalization. Nimur (talk) 22:17, 10 April 2011 (UTC)

It is probably worth noting for interest sake, that prior to decoupling, indeed sound was the only way that information could propagate significant distances through the universe. —Preceding unsigned comment added by 92.20.198.146 (talk) 01:33, 11 April 2011 (UTC)

Question about the lightcone?

As we all know that when a flash of light is released from source, light-rays spread out isotropically in space, tracing out a cone on a space-time diagram. As "cone" is expanded at the speed of light, and light emitted at the apex and moves on the surface of the cone, therefore, at any instant “t” say one light second, the radius, edge and the vertical axis of cone represent a right angle triangle in which

Vertical axis is the perpendicular of triangle = t = time

Edge of the cone is the hypotenuse of triangle = st = space-time diagram of a pulse in one second

Radius of cone is the base of triangle = c = speed of light in one second

Thus c² + t² = (st)², where (st) > c, so is this possible?

Q1: Why the space-time diagram [edge of light-cone/ light like curve] of light in light cone is greater than speed of light?

Similarly, nothing can travel at or greater than the speed of light therefore

Q2: How come space forward in time in its space-time diagram [upward direction] at the speed of light? [Space include we all including nature at present]

Q3: Is light forwards in time in two directions horizontally [moves on the surface of cone] as well as vertically [upward direction in time] ?

Q4: Isn’t time dilating even in a stationary light clock because a pulse covered a greater distance in its space-time diagram?68.147.41.231 (talk) 02:46, 10 April 2011 (UTC)Eclectic Eccentric Khattak #1

The quantity you call "st" has no physical meaning. The geometry of spacetime does not follow the Pythagorean formula (you can stick numbers into it if you want, of course, but the result will not have any physical meaning). What one must use instead is

$s^{2}=t^{2}-x^{2}$

where x is the distance, t is the time coordinate, and s is something called the space-time interval. It is always 0 between two events connected by a lightspeed path.

If I understand your numbered questions correctly, they are all mooted by this initial misunderstanding. –Henning Makholm (talk) 03:08, 10 April 2011 (UTC)

Hennings equation above assumes c=1. for more general choice of units you should have :: $s^{2}=(ct)^{2}-x^{2}$

The basic error is the statement that nothing can travel faster than the speed of light. The physics of relativity only assert that no physical object can move faster than the speed of light. Abstract events don't obey any speed limit. Looie496 (talk) 03:12, 10 April 2011 (UTC)

Not quite, causality requires that no information can travel faster than the speed of light. This is much more restrictive than applying the rule to merely physical objects. —Preceding unsigned comment added by 92.20.198.146 (talk) 01:38, 11 April 2011 (UTC)

Carburator.......mystry......

hi... I know the basic functioning of a normal carburator(generally used in single cylinder 4 stroke motorcycle).....but have some doubts... as i know when vehicle is in nutral gear (idling condition)it needs rich mixture of air and fuel and at the same time throttling valve is in fully closed condition. when we drive uphill it needs more fuel and when we drive downhill it needs less fuel.

I want to know that when we drive down the hill and if motorcycle is in top gear and we put throttling valve in close condition (as in idling condition), will it consume more fuel than normally driving with throttling valve in open condition. —Preceding unsigned comment added by 220.225.96.217 (talk) 03:39, 10 April 2011 (UTC)

You want to know if the vehicle uses more fuel coasting with closed throttle than normal driving (with throttle partially open). That, is more complicated than it ought to be, since carburetors have gotten more complicated. (Let's assume the same speed in both cases)

Obviously, coasting itself doesn't require input of energy the way normal driving does. Closed throttle, however, generates a large degree of drag. But, if you are actually coasting with actually closed throttle at that fixed speed, then the acceleration from gravity must by definition be larger than the drag of the closed throttle, so theoretically you would need no fuel, even to keep the engine turning, since gravity is doing that. In practice, there are complications: crude old carburetors will suck a lot of fuel with the throttle closed under these conditions but not burn it because the air is shut off, because the throttle shuts down the air but the fuel is sucked through the idle passages which open below the throttle and they now see a big vacuum . You see this in race cars decelerating, for instance, when big flames come out of the exhaust when the hot unburned fuel hits the open air. But modern carbs may have gimmicks to cut that out, to reduce fuel consumption, to reduce emissions, and to stop raw fuel being poured into the catalytic converter overheating it. For instance the throttle might be rigged (electronically, for instance) to not close all the way when speed is nonzero, thus reducing the vacuum that sucks the gas through the idle passages. Alternately, all those air passages and bleed holes and what not in the carb might serve to reduce idle fuel flow when vacuum is super high, as when coasting compared to idling.

So, to sum up, the answer to your question would be, the vehicle wouldn't "use" any fuel when coasting but a simple carburetor may waste quite a bit, if you want to draw the line between using fuel and wasting it; whether it would waste more than it would need while driving on the flat depends on a million things such as, obviously, speed and the steepness of the slope, for two. However, more complicated carburetors can be designed to waste less fuel in these conditions. This probably doesn't actually answer what you want to know at all. Gzuckier (talk) 04:20, 10 April 2011 (UTC)

Throttle valves never close. At idle the throttle is slightly open, as set by an idle screw, and fuel enters the air stream from a small jet. If the vehicle is in gear and rolling down a hill in idle, more air and fuel are sucked in but the extra fuel is wasted because the idle arrangement is not dimensioned to give the stoichiometric gasoline-to-air ratio 14.7 However the amount of fuel involved is small. When the throttle is opened two things happen: A) an accelerator jet briefly injects extra fuel. This occasionally produces an over-rich mixture so some fuel can be considered "wasted" but only briefly, and B) the main fuel jet(s) come into play when the throttle is open and much more fuel is consumed. Whether any is wasted depends on whether the carb is adjusted to deliver a richer than stoicchiometric mixture. See the Wikipedia article Carburetor. Cuddlyable3 (talk) 11:04, 10 April 2011 (UTC)

how are methane and CO2 greenhouse gases?

On the basis of polarity, that is. I understand how H2O is a greenhouse gas, while O2 and N2 aren't, on the grounds of H2O's notorious polarity, but CO2 is symmetrical. I'm totally guessing that it's the internal polarities of the CO double bonds that might do it, but then were does methane come in? Not only is it symmetric, but isn't the CH bond pretty nonpolar? Gzuckier (talk) 04:03, 10 April 2011 (UTC)

An informative discussion can actually be found at a related article to the greenhouse effect, namely Infrared_spectroscopy#Number_of_vibrational_modes. IR spectroscopy and the greenhouse effect work on the exact same principle; the ability of a molecule to absorb energy in the infrared region of the spectrum. Infrared absorbtion is associated certain types of molecular vibrations that are active in the in the absorbtion (and in the greenhouse effect especially) re-emission of infrared photons. The specific effect that governs how CO2 works as a greenhouse gas is called the Renner–Teller effect, that article is very jargon-laden and inaccessible to the average reader, however to break it down simply, CO2 has the ability to vibrate assymetricly, that is you can get vibrations where one C=O bond is shortening and the other C=O bond is lengthening. This mode of vibration is (called "wagging" in the Infrared spectroscopy article) is exactly why otherwise symmetrical molecules exhibit IR-dependent absorbtions and emissions. Since two-atom molecules cannot "wag" like this, they are invisible to IR. Three-atom molecules are the smallest molecules which have this mode of vibration, and so they are capable of absorbing infrared radiation, and thus have the ability to cause a greenhouse effect. If you look at Atmosphere_of_Earth#Composition, you'll see that the two most abundant gas you'll find in dry air, which have at least 3 atoms, are CO2 and CH4. --Jayron32 04:50, 10 April 2011 (UTC)

Oh, and regarding Methane and the C-H bond; the C-H bond isn't nonpolar, its just that the bonding symmetries present in hydrocarbons make hydrocarbons as a molecule nonpolar. CH4 is a nonpolar molecule for the same reason that CO2 is, the dipoles present in the molecule all cancel out. Some basic trigonometry will prove that to you. In even more complex hydrocarbons, all relevent C-H dipoles almost always end up cancelling, which is why hydrocarbons, even really complex ones, end up being non-polar. --Jayron32 04:58, 10 April 2011 (UTC)

what kind of spider is this black one with a red butt?

What kind of spider is this? I found it in my backyard in Richmond, California This is in the San Francisco Bay Area. She was black but not jet black very slightly almost fuzzy looking with an oblong red butt almost brick colored. She seemed to like the shade.Thisbites (talk) 04:47, 10 April 2011 (UTC)

I live in the SF Bay Area and I've seen lots of these. It's a jumping spider, possibly Phidippus johnsoni or Phidippus californicus. -- BenRG (talk) 06:56, 10 April 2011 (UTC)

Salticidae are quite amazing spiders. They have extremely good eyesight, and use advanced hunting techniques. Whenever they come up here, I like to post this excellent article [1]. SemanticMantis (talk) 15:00, 10 April 2011 (UTC)

What is the best store-bought equipment to clean soot out of the fireplace walls?

Since soot seems incredibly hard to clean out of the fireplace brick wall, what would be some equipment needed to do it adequately?

Sand blaster. Cuddlyable3 (talk) 10:37, 10 April 2011 (UTC)

Calories burned from cleaning fireplaces

Also, since I prefer to lose weight by doing chores for others, I wonder how many calories per hour (or 10 minutes) I would burn by cleaning out a fireplace. Some suggested that I run instead, but it doesn't help anyone else like cleaning a fireplace would, nor is that as fun as exercising on an XBox Kinect or zipping to class on a bike.

On the other hand, how many calories get burned from jogging at 5 MPH?--70.179.169.115 (talk) 04:50, 10 April 2011 (UTC)

Note: The OP has a long history of asking pointless/trolling questions on the ref desks. Looie496 (talk) 05:17, 10 April 2011 (UTC)

There is no way for us to know how much of your body you'll use. Probably akin to playing tennis or something, if you go at a high speed. Just try it out and compare it. Magog the Ogre (talk) 20:46, 10 April 2011 (UTC)

Calories per pound?

I never got around to finding out how many calories are in one pound of body weight. When you state the answer, please also cite the source. Thanks! --70.179.169.115 (talk) 04:50, 10 April 2011 (UTC)

Are we talking about the human body ? The would depend on how much flesh they have, especially body fat, since it has the most calories per pound, followed by protein, with bone and water having basically zero calories. StuRat (talk) 04:57, 10 April 2011 (UTC)

If it helps anything, I weigh ~195, and am 5'11.5". Would that bring us closer to figuring out how many calories I'd need to burn to lose 14 lbs? 182 is the overweight threshold, so I'll "finish" once I weigh 181. Thanks. --70.179.169.115 (talk) 05:11, 10 April 2011 (UTC)

To the OP: Are you asking "How many dietary calories will I get from eating person" or are you asking "How many calories do I have to "burn" to lose 1 pound of body weight". The first question is pretty simple to answer; the edible parts of you are essentially all protein and fat, protein will provide 4.1 calories/gram and fat will provide 9.4 calories/gram of food energy, see the table at Food_energy#Nutrition_labels. If you can work out how much fat and protein are in your body, you can figure out how many food calories you can provide (presumably to someone else, since autocanibalism is rarely a long-term survival strategy). If you want the second question answered, its really impossible to answer even in very broad terms. The amount of calories you burn doing various activities, AND the effect of burning those calories on your body weight, are really uniquely dependent on you and own body chemistry. It is a complex melange of Basal metabolic rate, Body Mass Index, your own muscle mass, your own unique muscle composition (such as the ratio of fast twitch/slow twitch type muscle fibers, see Skeletal_muscle#Muscle_fibers, how active or sedentary you are, your base heart rate, etc. etc. Its way too complicated to say, for you specifically "If I run ten miles, how many calories will I burn" or "If I burn XXX calories, how much weight will I lose". You can, of course, do the experiment, and say calculate a ratio of activity levels to weight loss, but you will quickly find that the relationship is dynamic and feeds back on itself; i.e. as you work out, you actually affect how fast you lose weight, and it isn't even easy to predict how the changes themselves will change, i.e. as you work out, you change your basal metabolic rate, which means you may lose more weight; but you will also build muscle mass, which will conversely cause you to gain some weight. Its a complete and utter mess working out the specific numbers. We can speak in general trends; i.e. if you consume less food calories and you are more active, you will tend to be healthier and have more positive health outcomes (irrespective of your weight) and the reverse is also generally true. --Jayron32 05:11, 10 April 2011 (UTC)

The IP asking this question has a history of ref-desk trolling, it should be noted. Looie496 (talk) 05:18, 10 April 2011 (UTC)

I dunno, these seem like legitimate, answerable questions. The questions themselves do not seem to beg for controversial answers, nor are they in-and-of-themselves disruptive. The IP address may have asked disruptive questions in the past, but I see no reason not to answer these questions for that reason. I am will to extend good faith so long as the questions themselves are benign. --Jayron32 05:24, 10 April 2011 (UTC)

are there calories in water?

i know calories are something measure by something making a drop of water go up by one degree, so water has a tiny amount of calories right?Thisbites (talk) 04:58, 10 April 2011 (UTC)

No, pure water will have zero calories, meaning you don't get any heat produced from it by burning it. StuRat (talk) 05:00, 10 April 2011 (UTC)

No, you're both sorta wrong. A calorie is just a unit of energy, like a Joule. In fact there are 4.184 chemical calories in a joule, or 4.184 food calories in a kilojoule 4.184 joules in a chemical calorie, or 4.184 kilojoules in a food calorie. The way a calorie was originally defined was the energy needed to raise the temperature of water (1 gram for a chemical calorie, and 1 kilogram for a food calorie) from 24.5 degrees celsius to 25.5 degrees celsius, but we now define it more rigorously by relationship to the Joule, and thus from the base definitions of the SI system. The choice of water is arbitrary, and has nothing to do with the energy in the water, or the energy you can get from "burning" water, or anything else having to do with water. Its just a unit, used to measure energy/work, and that is all. In other words, the "Calorie" unit has no more connection to water than the "foot" as a unit has a connection to actual feet, excepting as a historical definition. Also, you can burn water, in the sense that if you put enough heat energy into it, you can cause it to change chemically into hydrogen gas and oxygen gas; this is what happened in the Fukushima I nuclear accidents; the extreme heat of the uncontrolled reactors basically "burned" the water, releasing hydrogen and causing explosions which damaged the plant. --Jayron32 05:21, 10 April 2011 (UTC)

Your conversion factors are the wrong way - it's 4.18 joules in a calorie. Zain Ebrahim (talk) 12:54, 10 April 2011 (UTC)

fixed --Jayron32 17:46, 10 April 2011 (UTC)

It seems to me the original poster is more or less correct. If you're on a calorie-counting diet, you may as well say that a liter of water at 10°C has 10 more (kilo)calories than a liter of water at 0°C, since the body has to burn an extra 10 kcal to heat the latter up to body temperature. Although they both have negative calories overall. -- BenRG (talk) 06:43, 10 April 2011 (UTC)

Our articles related to the power-plant hydrogen explosions, supported by refs, state that the hydrogen comes from water undergoing redox with zirconium metal, not pyrolysis of water itself. DMacks (talk) 10:12, 10 April 2011 (UTC)

The disassociation of water is endothermic (absorbs more energy that it releases), so it can't be described as "burning". Burning refers to combustion, which is defined, in part, as an exothermic reaction (releases more energy than it absorbs). --Tango (talk) 11:37, 10 April 2011 (UTC)

The notion that you can burn water is a little silly. Any substance can be disassociated into its constituent atoms at a high enough temperature. In the case of water this does not amount to burning, more energy has to be put into the system to cause disassociation than is released. This is clear from the large amount of energy that is released when the opposite reaction - the burning of mixed hydrogen and oxygen gases - produces water as an end product. The answer to the OPs question is a simple "no" - water does not contain any dietary calories. SpinningSpark 09:08, 10 April 2011 (UTC)

You can burn water just fine. It's simply a matter of finding a more powerful oxidizer than oxygen: I've heard that chlorine trifluoride works well. --Carnildo (talk) 22:53, 13 April 2011 (UTC)

OK, let me clarify my response:

A) Do you gain any calories by consuming water ? No, unless you consider that drinking hot water may mean you can burn less food to maintain proper body temperature.

B) Can water contain energy in the form of heat ? Yes, and this energy can be measured in calories or other units. StuRat (talk) 06:59, 10 April 2011 (UTC)

While the OP's question has been answered (there are no dietary calories in water), it is still interesting to consider some theoretical limits of using pure water as an energy source. If I have one kg of water at room temperature and the relative humidity is, say, 50%, then the water will evaporate all by itself: The Gibbs energy of the 1 kg of water is more than that of the water vapor. So, I can extract work from pure water, and it isn't difficult to compute how much. However, the maximum power that one can extract is, I think, not so easy to compute. I guess there is no hard theoretical limit to this, you can think of making the evaporation rate arbitrarily high by using larger and larger surfaces... Count Iblis (talk) 16:53, 10 April 2011 (UTC)

Evaporative cooling like this, that is using water spread over large surface areas, is a common enough; the work you do in evaporation is essentially work you do in cooling (i.e. removing heat from) something; in the Old South of the U.S., prior to air conditioning, it was common to sleep with wet sheets; the evaporation of the water from the sheets kept the sleeper cooler than dry sheets would. --Jayron32 17:50, 10 April 2011 (UTC)

Yes, it's an effective way to keep cool. Count Iblis (talk) 17:03, 11 April 2011 (UTC)

Water can interfere with the intake of calories from food, see here. Count Iblis (talk) 17:03, 11 April 2011 (UTC)

Energy source graph

I remember seeing on Wikipedia a line graph showing how the percentages of the amount of energy by source used by the muscles vary with hours of exercise, in red/orange/yellow, but can't seem to find it anymore. Can anyone help? Thank you 85.138.123.142 (talk) —Preceding undated comment added 08:20, 10 April 2011 (UTC).

I believe I know the type of diagram you mean, and I can't find one on WP either(yet). Here is an external link to some graphs.
The 'sources' being in this case Aerobic respiration, Anaerobic respiration and ATP-PC biological energy systems. - 220.101 talk^\Contribs 12:00, 10 April 2011 (UTC)

Canine teeth and monkeys

If herbivores generally don't have canine teeth and if humans evolved from herbivore monkeys, what caused humans to gain such teeth?--89.76.224.253 (talk) 13:10, 10 April 2011 (UTC)

What makes you think that herbivores don't have canine teeth? DuncanHill (talk) 13:18, 10 April 2011 (UTC)

Check out the fearsome canines on baboons here [2]. SemanticMantis (talk) 14:29, 10 April 2011 (UTC)

It's not accurate to say that humans evolved from monkeys. more that primates (including humans) had common ancestors. Actually the predominance of cannine teeth is one of the more important factors in distinguishing the line of hominids to humans. Earlier hominids had much larger canines. There's a lot of evidence that most of our ancestors were definitely not herbivores.190.56.14.159 (talk) 13:58, 10 April 2011 (UTC)

What makes you think monkeys are herbivores? With very few exceptions, primates are omnivores. Of all the primates humans have the most "degenerate" canine teeth. A leading theory to explain it is the idea that our ability to prepare our food manually before eating has allowed our teeth and jaws to reduce. Roger (talk) 15:45, 10 April 2011 (UTC)

Canine teeth are useful for fighting as well as prey capture -- rhesus macaques are almost exclusively vegetarian and they have pretty fearsome canines -- I have a scar to prove it. Baboons, by the way, are definitely omnivores -- they will even prey on other types of monkeys if they can catch them. Looie496 (talk) 16:19, 10 April 2011 (UTC)

This does raise a question in my mind. We've all seen movies of chimps preying on monkeys, but (other than insects),are there any documented instances where monkies/apes have been feeding on more common food species like small rodents etc.190.56.16.100 (talk) 16:57, 10 April 2011 (UTC)

If they only prey on monkeys, then perhaps it has less to with food sauce and more to do with dominance over competitors for food.190.56.16.100 (talk) 17:08, 10 April 2011 (UTC)

There are many reports of monkeys preying on small mammals, birds, lizards, etc. I'm not going to take the time to look up sources, but they wouldn't be difficult to find. (Our baboon article gives some information along with a reference.) Looie496 (talk) 17:18, 10 April 2011 (UTC)

I believe one factor in the diminished size of human canines is that they are no longer used as weapons, since we developed more useful external weapons (rocks, spears, arrows, etc.). StuRat (talk) 17:10, 10 April 2011 (UTC)

A prim Victorian lady was heard to say "I don't know whether Mr. Darwin is correct to say that humans have chimpanzees as ancestors, but if he is right then I hope it does not become widely known." Cuddlyable3 (talk) 10:32, 11 April 2011 (UTC)

Electron resonance and tapping

Say if a electron orbiting inside of a magnetic field gets hit by a wave with the same frequency as the electrons circular frequency. Could the electrons be made to make a electrical current flow with their new energy. —Preceding unsigned comment added by 82.38.96.241 (talk) 18:04, 10 April 2011 (UTC)

Isn't that close to what generators do. (details not withstanding).190.56.16.100 (talk) 19:32, 10 April 2011 (UTC)

I don't really understand the idea underlying the question, but the concept of stimulated emission may be at least vaguely related. Looie496 (talk) 19:42, 10 April 2011 (UTC)

Based on the OP's prior questions, I'm pretty sure he is asking about Electron cyclotron resonance.

The electron orbit is already a current. Any change in the electron energy, due to incident radiation or any other source of energy, will cause a corresponding change in both the magnitude and the vector of the current. You might want to read about current density for a proper overview of a three-dimensional mathematical description of current. Interactions between radio-waves and gyro-resonant electrons are very complicated. Nimur (talk) 20:36, 10 April 2011 (UTC)

Fog

I notice yesterday in the sky a weird type of fog. it was quite brownish yellow kind of colour. It was also quite high in the sky and didn't look like any cloud formation I ever have seen. What was it. --109.76.36.208 (talk) 18:53, 10 April 2011 (UTC)

Were you in L.A? Mexico city? etc190.56.16.100 (talk) 19:35, 10 April 2011 (UTC)

Sounds like smog, perhaps a fire provided the smoke ? If you give us your location, we will look for fires in your area. StuRat (talk) 19:38, 10 April 2011 (UTC)

I was going to say that it might be the current "worst ever" Texas wildfires,^[3] but that IP geolocates to Dublin. The smoke couldn't go that far... could it? Wnt (talk) 02:16, 11 April 2011 (UTC)

No im down here in Cork if that helps. --109.76.7.143 (talk) 15:07, 11 April 2011 (UTC)

I couldn't find any news of a big fire there. Could it be pollution from a factory in Cork ? Or perhaps from the port or airport ? The color you describe makes me think of sulfur. Did you notice a "rotten eggs" smell that day ? StuRat (talk) 07:20, 12 April 2011 (UTC)

Chemical bonding

Is there any compound with a P-S-H bond? Nirmos (talk) 20:01, 10 April 2011 (UTC)

Yep. (Among several other dithiophosphates.) TenOfAllTrades(talk) 20:13, 10 April 2011 (UTC)

Thank you so much! Nirmos (talk) 20:24, 10 April 2011 (UTC)

Electron configuration orbitals

If nobody has ever actually seen an atom, how do they know that after all the 3p orbitals are filled, the next orbitals are 4s instead of 3d? If the answers to this question reference spectral lines as the indicator, how does the position of a line on the electromagnetic spectrum tell you that the shape of the next electron cloud density is spherical and not butterfly shaped? 76.27.175.80 (talk) 21:18, 10 April 2011 (UTC)

I'm no expert on this, but the shape of orbitals is determined mathematically by solving the wave function- not by "actually seeing" it. Staecker (talk) 01:25, 11 April 2011 (UTC)

My gosh you're certainly not a scientist, are you a mathematician by any chance? To contradict the previous poster, in physics we like to find out if the hodge podge we concoct in mathematica has any relation to the real world, one way in which one could go about tackling this particular conundrum would be to like a the splitting of the emission spectra of atoms with the relevant number of electrons. As if indeed we are right, and after 3p we fill 4s, thus after filling 3p, if we add a further two electrons we should have filled a whole new shell, and thus since closed shells have no angular momentum this would be reflected in the spectrum. See Fine Structure, Spin–orbit interaction and Hyperfine structure for the effect of angular momentum on emission spectra. —Preceding unsigned comment added by 92.20.198.146 (talk) 01:47, 11 April 2011 (UTC)

In physics we like to understand the connection between the mathematical 'hodgepodge' and the real world. Unfortunately, this is one of the greatest problems with quantum mechanics, string theory, and the like. Quantum mechanics is accurate is describing many things, but imagining the universe as a wave function just doesn't correlate. So the wave function description is the best you can get. ManishEarth^{Talk • Stalk} 04:01, 11 April 2011 (UTC)

One of the things about the wavefunction model for orbital shapes is that the system works across disciplines to explain lots about the behavior of electrons around atoms. Various models of molecular bonding, such as valence bond theory and hybridization theory and molecular orbital theory all work nicely with the standard spdf quantum mechanical model of electron configurations because the shapes of the orbitals as described by the quantum mechanical model mesh nicely with, for example, the bonding angles predicted by hybridization theory and with behavior predicted by molecular orbital theory. And behaviors of substances generally confirm the predictions of these theories regarding molecular shape and electron organization. Just some examples:

• Bonding geometries predicted by valence bond theory and hybridization theory present molecular shapes which allow predictions of allowable and unallowable chemical reactions, for example in E2 Elimination reactions in organic chemistry, the leaving group must be able to take a specific orientation relative to the acid hydrogen in order to eliminate; this is predicted by knowing the shapes and orientations of the molecular orbitals, and confirmable by real reactions, where molecules that lack the ability to take the correct geometry do not undergo the reaction.
• Perhaps simpler to understand, molecular orbital theory predicts the O₂ to be a diradical, something not very evident from just counting the electrons. The magnetic properties of O₂ confirm its diradical nature, something which is only understandable in the context of what the quantum model predicts the organization of the electrons orbitals to be around the O₂ molecule.

So yes, we cannot "see" orbitals in the same way I can see my own hand; but that doesn't mean that they don't exist, or that the models that depend on them don't have fantastic predictive power regarding the actual properties and behavior of substances. Indeed, the entire thing is that its the predictive power of the model which makes it useful; understanding how electron configurations (and the underlying theories) works is important to understanding why the substance that makes up the world around you behaves the way it does. --Jayron32 04:49, 11 April 2011 (UTC)

Many orbitals have been visualized more directly (not "seen" obviously, but STM and related techniques), so there is fairly direct evidence for "an upper-level electron-density that matches the p dumbbell shape" on an atom expected to have p near the HOMO and "an electron-density that matches various d shapes" on atoms that have occupied d levels, etc. Spectroscopy tells you the energy levels pretty directly. The only step in the process not as easily answerable is how we match energy level (from each one's energy) to its shape--OP is on the right track that this is a more complicated analysis ("how do we know a dumbbell comes after a sphere" regardless of what energies and symbols you use to identify them). I don't have time to comment more, but figured better help distinguish some issues first. DMacks (talk) 13:08, 11 April 2011 (UTC)

Four-winged vs. two winged flight

What is more stable for powered flight in an animal, four winged or two winged? And if there was a four-winged animal, is it more efficient to have them both flapping in opposite cycles or does this create turbulence? And does anyone know of any four-winged animals, apart from insects? --T H F S W (T · C · E) 21:52, 10 April 2011 (UTC)

Am I dreaming this, or was there a Pterodactyl that had four wings (i.e. its arms *and* legs were wings)? I could swear down that I read that once... --Kurt Shaped Box (talk) 22:01, 10 April 2011 (UTC)

(EC with The High Fin Sperm Whale below)I don't think any discretely 4-winged Pterosaurs (aka Pterodactyls) are yet known: in some the flight membrane or patagium may have stretched back to rear-limb attachments, and some may have also had a further membrane between the hind limbs, similar to some Bat species.

However, some of the flying therepod dinosaurs closely related to, though not in, the Avialae clade which includes true birds, such as Microraptor, are thought from the forms of the attached feathers to have used their hind limbs as an additional pair of wings. I believe discussion of possible wing-beat patterns is ongoing in paleontological academia.

Some Flying fish glide using enlarged pelvic (rear) as well as pectoral (front) fins, but this doesn't quite qualify as powered flight, although the configuration is obviously stable. The OP might find further leads in the article Flying and gliding animals. {The poster formerly known as 87.81.230.195} 90.197.66.111 (talk) 22:46, 10 April 2011 (UTC)

I think I can also vaguely remember having even seen a picture of one ... but might also have been from some sci-fi. As for 2 vs. 4 wings, it is not uncommon for insects to have four wings. 77.3.170.46 (talk) 22:11, 10 April 2011 (UTC)

Not true flight, but some gliding animals use all four legs, and the skin stretched between them, like the flying squirrel and sugar glider. StuRat (talk) 22:20, 10 April 2011 (UTC)

OK, I don't think there are any that meet the description I'm looking for. But what I really want is some clue as to efficiency, stability, etc. of a four-winged creature. And do most insects fly with two seperate wing cycles or flap in unison? --T H F S W (T · C · E) 22:25, 10 April 2011 (UTC)

Can't say about all insects. That's an enormous field, but the emperor dragonfly uses four wings and they do not flap in unison. According to research each wing is individually controlled. Yes, this seems like an impossibly complex system but mother nature allways is. The muscles that do this make up fully one third of the dragons body weight and have infinitely perfect flight control. Some insects are comically clumsy in flight. there are an infinite number of variations in between. some use only two wings, some use a second pair of wings only as balancing "pendulums" or "gyros". It's an extremely wide field of study and very difficult to study. there is no simple answer to your question. You cannot simply compare insects with aircraft. carefully controlled turbulence can be an asset, as with some modern computor controled airecraft, and with some four winged insects. good luck figuring it all out.190.56.17.78 (talk) 01:02, 11 April 2011 (UTC)

Many other creatures called flying something or other (foxes, squirrels, frogs etc.) do not actually fly. They glide. pteredactyls, as mentioned, did not "according to fossils" have four wings. they had an elastic membrane stretched between the fore and aft limbs, like a bat. Again, some bats have membranes that stretch between the extremities of the limbs, in others the membrane stops short on the rear limbs. different hunting techniques. I hope that helps.190.56.17.78 (talk) 01:30, 11 April 2011 (UTC)

Insects started off with (at least) six wings (two per thoracic segment), though only two pair were large - see [4]. There are several situations in which insects have evolved from four wings to (effectively) two - (Diptera, Coleoptera, Blattodea for example, or Lepidoptera where the wings work together as one. Then again, many insect lineages lose or greatly reduce all their wings, which likely does not improve flying ability. Saying which is the best number of wings is a difficult philosophical question. Certainly dragonflies are awesome fliers, difficult even to photograph. Wnt (talk) 02:39, 11 April 2011 (UTC)

April 11

Past oxygen

In the past, oxygen levels were at times much higher than they are today. One would think that at 22% higher levels of oxygen and forests covering most of the land, whole continents would go up in smoke. Was there anything back then that we do not have now that helped to stop the effects of forest fires? I just don't see how a fire in such conditions could ever be stopped. --T H F S W (T · C · E) 00:13, 11 April 2011 (UTC)

Fires probably would have started earlier in the season (before the plants were quite so dry), burning up most of the fuel, so later fires wouldn't be much bigger than now. StuRat (talk) 00:58, 11 April 2011 (UTC)

Actually, I have read that you did have huge forest fires in the carboniferous era. This is also mentioned in this BBC discovery program. Count Iblis (talk) 01:18, 11 April 2011 (UTC)

Today there is a great deal of forest fragmentation due to human habitation. If the forests of the period you're referring to were continuously dense across the land then certainly the fires would have burned until they ran out of fuel. The fires today are usually curtailed by forest fragmentation and heroic human efforts, but as sturat says, the damage to the forest would be somewhat minimised by frequent burning of the fuel. Very hot, destructive fires of the recent past were largely aggravated by misguided human protection causing a build up of fuel. Yes, the fires would have raged far and wide but forests would bounce right back almost immediately.190.56.17.78 (talk) 03:57, 11 April 2011 (UTC)

One other thought, the burning depends on what type of forest it is. Having experience with central american jungle, you almost can't make it burn if you want it to. If those forests were damp tropical jungle,then the fires would not have gone far.190.56.107.103 (talk) 04:07, 11 April 2011 (UTC)

Continuing that thought, and as a response to "the fires would have burned until they ran out of fuel", rain would also have stopped them. HiLo48 (talk) 05:10, 11 April 2011 (UTC)

Even in the modern world, some plants clearly require fire for their own life cycle; fire is a natural and normal thing, and some ecosystems go beyond tolerating it to actually depending on it. See Chapparal#The_chaparral_and_wildfires for one ecosystem for which regular burning is part of normal life. --Jayron32 05:36, 11 April 2011 (UTC)

Ancient oxygen levels were at times so high that even swamp plants, which would never ignite at current levels, evolved natural flame retardants. This is part of the evidence for high ancient levels. Nick Lane's Oxygen: The Molecule that Made the World, is a fun book with a lot on such questions, which could be of use at Geological history of oxygen. IIRC, don't remember the whole story, the frequent fires were part of an eventual paradoxical effect involving carbon sequestration that increased atmospheric oxygen levels even more.John Z (talk) 11:00, 13 April 2011 (UTC)

List of American northward-flowing rivers?

Does Wikipedia, or does the internet, have a list of rivers in North America that flow northward? I think some people like to say that the Red River of the North is the only one. But that seems moderatly far-fetched. Michael Hardy (talk) 02:02, 11 April 2011 (UTC)

OK, I may have found it:

Red River - Minnesota and Dakota.

St. John River - Jacksonville, FL.

Saginaw River - Michigan.

Shiawasee River - Michigan. (slightly easterly)

Kishwaukee River - Illinois.

Monongahela River - WVA and PA.

Youghiogheny River - WVA and PA.

Willamette River - Oregon.

Maumee River.

Little Big Horn River - Montana.

Jordan River - Utah

Mojave River - Southern California

Tennessee River - Kentucky-Tennessee

Cumberland River - Kentucky-Tennessee

Reese River (spring only) - Nevada

Michael Hardy (talk) 02:09, 11 April 2011 (UTC)

See Wikipedia:Reference desk/Archives/Language/2009 June 2#Downtown, uptown

and Wikipedia:Reference desk/Archives/Miscellaneous/2010 October 7#Rivers.

—Wavelength (talk) 02:18, 11 April 2011 (UTC)

What might however be true is that the Red River of the North is the only significant waterway to flow from the US into Canada. Looie496 (talk) 02:20, 11 April 2011 (UTC)

The Saint Lawrence River meets both requirements. If you launch your boat from the south bank near Lake Ontario, you are unambiguously in the U.S. If you then proceed to the mouth of the river, you cannot help but pass into Canada. Also, the mouth of the Saint Lawrence is at a considerably more northern latitude than the source is. Also, the Saint John River has its source in Maine and flows into New Brunswick. --Jayron32 02:25, 11 April 2011 (UTC)

Surely all the rivers on Canada's and Alaska's northern shores flow generally northwards. Yes, I know they will be frozen often enough, but when they do flow, they flow north. HiLo48 (talk) 02:29, 11 April 2011 (UTC)

Indeed, see List of rivers of Canada--Shantavira|^{feed me} 08:26, 11 April 2011 (UTC)

So could the Red River and its tributaries be the only ones originating in the USA that ultimately drain into Hudson's Bay? Michael Hardy (talk) 15:18, 12 April 2011 (UTC)

Not necessarily; the Great Lakes watershed appears to have outlets to Hudson's Bay via the Albany River, however the connections may be "man made", so I'm not sure if you wish to count that; but you can currently get from the Great Lakes to Hudson's Bay via water connections the whole way, meaning that any of the rivers from the U.S. side that drain into the Great Lakes would qualify as well. Before these connections were made, you'd probably be right regarding the Red River, but human intervention has changed how water flows substantially. --Jayron32 15:44, 12 April 2011 (UTC)

Double Recombination II

Hello. A wild-type female fruit fly mates with a yellow, chocolate, cut male (all traits recessive). The percentage of progeny of various types is as follows:

• 40.53% cho, y⁺, ct⁺
• 7.85% cho, y, ct⁺
• 1.84% cho, y, ct
• 0.05% cho, y⁺, ct
• 0.03% cho⁺, y, ct⁺
• 2.08% cho⁺, y⁺, ct⁺
• 8.07% cho⁺, y⁺, ct
• 39.55% cho⁺, y, ct

I determined that the ct gene is in the middle. Why is the distance between y and ct the sum of the single recombinant between the two genes and the double recombinant frequencies? Why must I add the double recombinant frequencies? I add the single recombinant frequencies because the distance between y and ct will affect the number of single recombinants. Why would the double recombinant frequencies affect the distance between ct and cho? Thanks in advance. --Mayfare (talk) 05:31, 11 April 2011 (UTC)

I should like back to Wikipedia:Reference_desk/Archives/Science/2011_March_26#Double_Recombination where these data were first examined.

The reason to add the double recombinant frequencies is that in a fly with two recombination events, the first recombination event doesn't "know" that you can measure the second. If you're measuring the distance between y and ct you want to tot up every fly with a recombination between the two, no matter what else happened, so that you have a total figure.

However, as I linked from there, there is a more meaningful calculation to make with the double recombinants: you want to make sure that they really are uncommon relative to what you think are the single recombinants. Because there's a chance your data could just be inaccurate - maybe you can't score flies right, maybe a gene reduces viability, maybe two genes crossed together reduce viability. In such a situation the recombination rates you measure between pairs of genes might put the genes in the wrong order, and only double recombinants will set you straight. Wnt (talk) 00:18, 12 April 2011 (UTC)

Photon travel time during stellar collision

I was reading an article last week about a recent gamma-ray burst, which was thought to be a star crashing into a galactic black hole. The Sun article says "...Therefore it takes a long time for radiation to reach the Sun's surface. Estimates of the photon travel time range between 10,000 and 170,000 years." Since the physical substance of the core is disrupted once the star passes the Roche_limit do we see that 10 to 170 thousand years of photon generation more-or-less all at once? Tdjewell (talk) 16:01, 11 April 2011 (UTC)

sure, more-or-less. Not only that, but the star matter also gets heated as it spirals down the accretion disk. Dauto (talk) 20:47, 11 April 2011 (UTC)

Rabbit death

Resolved

This is the death of humans who eat nothing but rabbit, supposedly due to a lack of fat:

A) Do we have an article ?

B) Is this condition real ?

C) Is it really due to a lack of fat in the rabbits ?

D) Can't humans produce fat, like other animals ? StuRat (talk) 16:40, 11 April 2011 (UTC)

Rabbit starvation APL (talk) 16:47, 11 April 2011 (UTC)

It isn't just about fat: rabbit (or any meat) is also entirely lacking in carbohydrates. Humans can produce fat from carbohydrate, but not, I believe, from protein. I hadn't heard of this condition before, but I have little doubt that it is real -- it's pretty well known that it is dangerous for too high a fraction of the diet to consist of protein. Looie496 (talk) 17:55, 11 April 2011 (UTC)

Don't tell that to the Inuit. Matt Deres (talk) 18:02, 11 April 2011 (UTC)

Eh? Most of the meat eaten by the Inuit contains a lot of fat. You can get by on either fat or carbs, but you can't live long with neither of them. Looie496 (talk) 18:13, 11 April 2011 (UTC)

Indeed, which is why it is the lean-ness of rabbit that creates the problem. It's not that I'm necessarily disagreeing with with what you said; I'm just trying to point out that your point could be misconstrued. The OP asked if it was due to absence of fat - and that's exactly the problem. Matt Deres (talk) 18:24, 11 April 2011 (UTC)

Traditionally (back in the old days), at least in the South, easily obtainable wild game, like rabbit and squirrel, were often prepared in a vegetable based stew with a lot of starchy wild plants that would contain carbs. Quinn ^☂THUNDER 19:13, 11 April 2011 (UTC)

How much less fat does rabbit meat have than its nearest common competitor—perhaps chicken meat? I mean, rabbit meat contains some fat. Bus stop (talk) 19:15, 11 April 2011 (UTC)

I'm at work and cannot do much in the way of research, but that info is probably pretty easily available. I think the problem isn't the particular meat per se, it's the reliance on that meat. If you're living off of rabbits and other small game, it could be that that's practically all you're living on (consider trappers and furriers), but if you're eating chicken, you're pretty much assured of also having eggs in your diet - and eggs have fat. Matt Deres (talk) 20:09, 11 April 2011 (UTC)

Thanks, all. I've now added a redirect from "rabbit death". StuRat (talk) 19:22, 11 April 2011 (UTC)

"Rabbit Death" also brings to mind Elmer Fudd and the Bunny Man...but I guess no one technically died in those examples. Quinn ^☂THUNDER 20:45, 11 April 2011 (UTC)

What are you doing?! Rabbit death should redirect to the most foul, cruel, and bad-tempered rodent you ever set eyes on! Clarityfiend (talk) 04:16, 12 April 2011 (UTC)

I don't know the answer, but the catabolism of proteins produces acetyl-CoA which can be used by fatty acid synthase, so it's not true that fat cannot be made from proteins in humans. However, note that certain unsaturated fatty acids cannot be synthesized in humans but must be eaten (essential fatty acids). Icek (talk) 23:08, 11 April 2011 (UTC)

I find this: "Domestically produced rabbit meat contains less fat than other meats. Again, beginning with the rabbit we see only 10.2% fat per pound compared with chicken at 11.0%, turkey at 20.2%, veal at 14.0%, good beef at 28.0%, lamb comes in at 27.7% and once again pork has a whopping 45.0% fat per pound." [5] What I don't understand is that rabbit seems to have only slightly less fat than chicken. Bus stop (talk) 01:21, 12 April 2011 (UTC)

What I don't understand is what kind of measurement "% per pound" is. Apparently a three-pound pig will contain 135% fat? Where does it store the last 35%? –Henning Makholm (talk) 02:34, 12 April 2011 (UTC)

I would take that to be a way of saying "percent by weight", as opposed to "percent by volume" or "percent of calories". StuRat (talk) 07:11, 12 April 2011 (UTC)

The mammalian hemoglobins will eventually kill you. Stay away from red meat. Imagine Reason (talk) 16:11, 12 April 2011 (UTC)

Are you suggesting that Sturat is not a mammal? 86.164.75.102 (talk) 20:08, 15 April 2011 (UTC)

Thanks everyone, I will mark this resolved. StuRat (talk) 18:17, 15 April 2011 (UTC)

Photons

How can photons only travel at the speed of light if they have no mass what slows them down if there they are massless? why don’t photons how come photons gain mass as they are going the speed of light does E=mc2 not apply to photons as they are light? —Preceding unsigned comment added by 82.38.96.241 (talk) 22:31, 11 April 2011 (UTC)

There are two kinds of masses, rest mass and relativistic mass. The difference between rest mass and relativistic mass is the mass difference provided by E=mc². What that means for photons is that they have no rest mass, but they do have a relativistic mass. This means that (in broad approximation), so long as they have kinetic energy (are moving) they have a mass and can interact with anything that has an effect on masses. Thus, photons can interact with other massive objects and undergo gravitational red shift. Photons can interact with matter (being absorbed and emitted by electrons as described in the Bohr model); this interaction with matter is what "slows" light down when it isn't in a vacuum. I'm sure I made some mistakes in presenting my best understood, laymen's approximation to reality. Someone who actually knows physics will be along shortly to tell you where I went wrong. --Jayron32 22:41, 11 April 2011 (UTC)

Photons are always moving at the speed of light. Photons either move at the speed of light, or do not exist. Sometimes, we describe a wave packet of light as an aggregate of many photons; and in the case of a significant interaction with certain types of matter, the speed of the wave packet is less than c. But the speed of any individual photon is always exactly c. The wave packet can be slower because of delays and statistical effects related to the emission and re-absorption of individual photons as they interact with atoms. For brief periods of time, a photon may be absorbed (at which point it ceases to exist as a photon, and the energy exists as some elevated state of the atom), and later, a new photon is re-emitted. Nimur (talk) 23:53, 11 April 2011 (UTC)

Once again, that's not right. There is no "emission and re-absorption of individual photons as they interact with atoms" when a photon moves through matter (as say, a photon moving through glass). If that happened, the photon would follow a random path and would exchange energy with matter changing its energy and frequency. That's What happens for instance to a photon as it finds its way out from the sum which can take tens of thousands of years and by the time it comes out it has completely thermalized (reached thermodynamic equilibrium with matter). That doesn't happen to a photon moving through glass. The photon that is moving through glass is indeed moving at a speed smaller than the speed of light. Dauto (talk) 01:09, 12 April 2011 (UTC)

Here's another description, published by Argonne National Lab: Photon Re-Emission. After all, these are merely theoretical models of actual physical processes. Which model is the best description depends on your specific experimental conditions. I'm very sure that emission and re-absorption is both a widely-used and very applicable model for photon/matter interaction. This is the approach described in several of the E&M and condensed-matter books I've read. A photon doesn't actually know it's in the vicinity of an atom (or inside glass) until it interacts with an atom; so it is by definition either scattered or absorbed/re-emitted. I have seen this approach for photon-matter interaction formalized using compton scattering, raman scattering, and with classical electrodynamic interactions in plasmas. The frequency is changed; dispersion is by definition a non-linear optical phenomenon. Statistically aggregated over a large number of photons, the result is a distortion of the wave packet envelope; equally well described as a frequency-dependent index of refraction, a dispersive medium, and so on. There are surely circumstances where this formulation of statistical photon absorption/re-emission doesn't apply very well, but I disagree with Dauto's assertion that it's "wrong." Nimur (talk) 02:32, 12 April 2011 (UTC)

A quantum mechanical description of photons requires you account for the small probability that the photon is absorbed / reemitted from each atom. This causes the photon's wavefunction to evolve, which affects the probabilities of observing the photon at later points. This is true even though in general you don't see the photon being absorbed and the actual probability of it being absorbed on any specific atom is quite low. More generally, one should keep in mind that ALL photon interactions in quantum mechanics can be understood as some flavor of absorption / reemission event (even scattering events get described this way if you look close enough). Quantum mechanical photons really don't do anything else.

Personally though, I consider using absorption and reemission to describe the propagation of light through matter to be something of a red herring. The retardation of light moving through a dielectric (such as glass) can be understood in purely classical terms without ever resorting to quantum mechanics or absorption / reemission. An electromagnetic plane wave impinging on a dielectric excites a counter oscillation in material. Because this involves accelerating charges, the counter oscillation will emit electromagnetic radiation. In the steady state, the superposition of the incident and excited radiation leads to a wavefront whose apparent velocity is lower than the velocity of light in free space. All of this can be worked out in detail and you get essentially the right answer using mesoscale properties and classical electromagnetism without the need to consider either photons or atoms. So, yes, the quantum mechanical description is correct, but using that formulation actually tends to obscure the underlying process since you tend to overlook the counter oscillation excited in the dielectric. Dragons flight (talk) 04:35, 12 April 2011 (UTC)

Yes, that is the correct description. Now, some phenomena do require quantum mechanics for a proper description in which case the wave you described is quantized, and the counter oscillations you described are included in the quantization. The whole thing becomes the photon that propagates down the medium without interaction. (Unless it does interact in which case the photon is scattered or absorbed which is what happens in the example I gave of a photon inside the sun). That photon includes the oscillation of the electromagnetic field as well as the oscillation of the medium itself, all within one particle. Sometimes people call that a quasi particle but that's just nomenclature. Physically, there is no difference between a "real particle" and a "quasi particle". Dauto (talk) 05:33, 12 April 2011 (UTC)

Right; and, physically, there is no difference between the first photon that got absorbed and the one that gets re-emitted after a delay; they are identical particles, and for purposes of nomenclature, you can call them "the same particle." There's no meaningful way to determine experimentally whether one single photon got slowed down, or if a new photon was created after the first one got absorbed/destroyed. Individual photons have no uniquely-identifiable features. Nimur (talk) 14:34, 12 April 2011 (UTC)

Yes, and a photon moving through vacuum also gets "absorbed" and "reemited" by vacuum quantum fluctuations (see vacuum polarization) and the final photon is indistinguishable from the original one. Nobody has a problem with identifying the final photon with the initial photon in this situation and the consistent thing to do is to identify the final photon with the initial photon for the case of a photon moving through matter as well unless the photon changes somehow, becoming distinguishable from the original one, which happens when it gets scattered or actually is absorbed and reemited. Dauto (talk) 15:11, 12 April 2011 (UTC)

April 12

DNA samples and testing time

Two sets of multi-part questions on the subject of DNA testing:

—SeekingAnswers (reply) 02:44, 12 April 2011 (UTC)

(1) How easy is it to get DNA samples?

In some films and television shows, the police find DNA everywhere. They can get it by dabbing the inside of a person's mouth with a swab, or from a cup that a person has drunk out of. I think I've even seen cases of police getting it from surfaces that a person has touched with the tip of his or her finger.

On other films and television shows, getting DNA samples seems to be really hard: the police have to draw blood from the person they want to test, and samples seem to get corrupted and become unusable all the time. (In fact, the difficulty of getting a DNA sample seems to be most correlated to whether the plot demands a successful or unsuccessful DNA test...)

Are dead skin cells scraped off with casual contact with any surface sufficent for a DNA sample, or are bodily fluids necessary? Which bodily fluids? (That is: saliva? urine? blood? semen? vaginal lubrication?)

If getting DNA samples is very easy, then in cases of rape, even if the rapist used a condom so that semen could not be collected for DNA testing, it should be easy for the police to get DNA samples from skin cells left on the body of the victim, correct?

—SeekingAnswers (reply) 02:44, 12 April 2011 (UTC)

You can DNA samples from any of the above; however the chance of recovering enough usable DNA is slimmer the smaller and deader the sample. DNA tends to degrade over time; however since the advent of PCR, even the most minute amount of DNA can be replicated and magnified into as much as you need to do tests. Very recently, there have been a few studies on extracting DNA from samples as small as fingerprints, and work is being done to reliably extract DNA from a single hair, but the work has not been expanded into clinical viability (i.e. tested and retested to the level where the method is reliable enough to stand up in a court of law). However, DNA has been extracted from cigarette butts and coffee cups before. If you've touched it, you've left your DNA on it; the question becomes whether you've left enough to be useful. We're very close to that point; it may be likely that within the next decade or so we'll have perfected the "DNA from fingerprints" technique, making actual fingerprinting moot. --Jayron32 04:07, 12 April 2011 (UTC)

I give a thumbs-up to Jayron32's response above, with a few twists. Actual fingerprints will remain useful in situations where DNA would be poorly preserved; some circumstances will favor the long-term survival of the prints, others may better protect DNA. I suspect that databases of fingerprints are larger and more comprehensive than databases of DNA, though the difference is probably eroding. Collecting and processing fingerprints still generally requires less-costly equipment and can be done faster than DNA typing. Finally, DNA plus fingerprint may perform better in court than either test alone (particularly if someone ever successfully mounts a Daubert challenge against fingerprint evidence).

While it is technically possible to extract utterly miniscule amounts of DNA from samples – with modern PCR techniques, a single cell's worth from a suspect should in principle suffice – the risk of error or cross-contamination also rises as one becomes able to amplify smaller and smaller amounts of DNA. Consider a hypothetical case where a cigarette butt is recovered from the crime scene. DNA on the butt matches one of the suspects, but there is also DNA from a second unidentified individual. Defence attorneys get the evidence excluded as unreliable, or insist that the mysterious second person is the actual murderer. What happened? A single skin cell was shed by a cigarette plant worker; the cell settled on the cigarette packaging and fell onto the outside of the cigarette filter, from which it was eventually recovered by forensic investigators.

Sound far-fetched? Something similar has already happened in Germany: story. DNA at forty different crime scenes over a span of more than a decade was linked to the same woman, dubbed 'The Phantom of Heilbronn' by the press. The Phantom's DNA never matched any of the suspects in any of the cases; police were stumped. Investigators eventually came to believe that The Phantom was just a careless worker in a factory that manufactured cotton swabs used by forensic investigators. Sloppy manufacturing processes allowed traces of the employee's DNA to contaminate the swabs, causing her DNA to 'appear' at crime scenes across Germany.

Biochemists and molecular biologists who do high-sensitivity proteomics experiments are familiar with this problem. Labs routinely ignore any hits for keratin as irrelevant in their mass spec results, because that protein is abundant in skin, hair, and nails and contamination with it is virtually impossible (or horrifically inconvenient and expensive) to avoid. TenOfAllTrades(talk) 16:18, 12 April 2011 (UTC)

For extra credit, you can visit Murder of Meredith Kercher and associated talk archives... Wnt (talk) 21:10, 12 April 2011 (UTC)

(2) How long does DNA testing take, and why?

On television shows like CSI: Crime Scene Investigation, DNA tests take just a few hours, or sometimes just minutes.

In the real world, I've seen news articles about police, lawyers, and/or suspects waiting for months for DNA tests. Are these cases unusual?

How long do DNA tests usually take in real life? And why would they take so long? The chemical reactions involved surely can't be so slow that they take months to run their course.

—SeekingAnswers (reply) 02:44, 12 April 2011 (UTC)

It is strictly a matter of economics and priorities (or lack of them). Some jurisdictions are requiring DNA testing for shoplifting;^[6] others set very low priorities on testing of rape specimens when no immediate suspect is known. Evidence can sit around for years untested.^[7] I'd love to see these statistics broken down by the race and income of the victim. Wnt (talk) 03:24, 12 April 2011 (UTC)

The actual DNA test can be done in hours. It consists of a) isolation b) PCR c) DNA fingerprinting. The entire sequence can be completed by a technician within a few hours; the average DNA analyst can, by staggering procedures, probably churn through several in a day. The reason that real cops and prosecutors wait weeks or months for results is that there is a backlog of submitted evidence. Occasionally, a high-profile case will get rushed, but generally it is first come-first served, and everyone waits in line. It just takes time for the DNA analyst to get through all of the cases that got to his/her office before yours did. It doesn't matter how much you want your case done; the 50 other prosecutors and sherrifs and whatnot that submitted evidence before you did want their evidence just as much, and you're not any more important than them... --Jayron32 04:12, 12 April 2011 (UTC)

So...why aren't jurisdictions hiring/training more technicians and buying more equipment? That DNA testing can take months for a process that should only take hours and thereby clogs up the entire criminal justice system shows that DNA testing facilities are grossly understaffed, to an extreme degree, worse than any understaffing of police, prosecutors, prison guards, etc. No doubt criminal justice systems have many inefficiencies, but this has to be one of the worst. If police and prosecutors are all waiting months for DNA tests, then it would seem that DNA testing is the obvious limiting factor in the criminal justice system, and therefore one of the most pressing problems that needs more budgeting. —SeekingAnswers (reply) 05:55, 12 April 2011 (UTC)

They would love to. I'm am certain that if you have several million dollars, and would like to donate it to start a trust fund with which to provide both the capital investment in new equipment, and ongoing funding for both its maintenance, and for more technicians to do this work, your local crime lab would LOVE to work with you. Most places in the world, and especially in the U.S., are so strapped for cash that they are actually furloughing or outright laying off workers in these areas just to avoid having to file bankruptcy. In North Carolina, where my wife works as a forensic chemist, there's been a hiring freeze; they can't even replace the analysts who they've lost through deaths, retirement, or quitting, never mind expanding capacity... --Jayron32 06:07, 12 April 2011 (UTC)

Yeah, but what I don't get is this. In the news, I constantly hear about plans to "add a hundred more officers to the streets next year" (for mid-size cities) or "add a thousand more officers to the streets next year" (for large cities). It would seem that some of the money going to those hundred/thousand extra officers for next year would surely be better served hiring more technicians and buying more equipment. There's no way that it's cheaper to hire and arm a thousand police officers than it is to hire and equip ten more technicians, so clearly, money can be found from somewhere. The problem doesn't seem to be (or at least, not just) a lack of money; it's that the money is going into the wrong places and being inefficiently allocated. —SeekingAnswers (reply) 06:16, 12 April 2011 (UTC)

Putting more officers on the streets is often more about politics. Politicians in the UK are always boasting about how they are going to put more police on the "frontlines" (instead of doing office/paperwork) because when people are asked what they what from the police force, it's always more police on the streets. Recent suggestions that budget cuts will lead to reductions in the number of police have led to a furore in local press. No-one ever says, "But what about the evidence processing?!" Technical work is not high-profile (unless something goes very wrong), and tends not to get funding. In fact, the UK's government-owned Forensic Science Service is being shut down, and the work contracted out to private companies, which (sorry, personal opinion here) is going to be an absolute disaster.--Kateshortforbob _talk 09:23, 12 April 2011 (UTC)

As I hinted above, even if the police have somewhat sufficient capacity, it's likely to be wasted. It takes only a stroke of the pen to demand that all shoplifters be tested, that people be tested on arrest simply to fill a database, etc. I suppose there's a feeling that if you actually do budget for increased capacity, it will only be wasted anyway. (In fact, I think that by collecting too much DNA information, countries greatly harm themselves, because in future generations it may be impossible for them to send a spy to another country without the target finding out who they sent, who the agent's family is, etc.) Wnt (talk) 00:59, 13 April 2011 (UTC)

Efficiency of fixed wings vs. rotors

Long-distance aircraft tends to be fixed-wing aircraft rather than rotary. Is this because fixed wings are inherently more efficient than rotors?

—SeekingAnswers (reply) 04:09, 12 April 2011 (UTC)

Fixed-wing aircraft can run on jet engines, which are orders of magnitude more efficient than propellers are. Helicopters are propeller planes, by necessity, which is why they aren't as efficient. --Jayron32 04:18, 12 April 2011 (UTC)

On a fundamental level, how does a jet engine differ from a propeller? Both are big fans that generate thrust by spinning rapidly and pushing air behind them, so what exactly is the basic difference between them?

Would it be possible to attach a jet engine to the back of rotary aircraft to generate thrust and counter torque from the main rotor while that main rotor generates lift?

—SeekingAnswers (reply) 04:37, 12 April 2011 (UTC)

A jet engine is a Reaction engine it is fundamentally completely different to a propeller engine. The fans inside certain types of jet engine are NOT what actually cause the thrust, they are the intake, compression and exhaust stages; they move the fuel and gas around but it is the combustion gas that creates the actual thrust. There are several jet engine designs which completely lack any kind of propellers or fans. Vespine (talk) 04:53, 12 April 2011 (UTC)

As for rotary aircraft, the main problem is the rotating wing has to travel "backwards" at some point. When the aircraft begins to approach a speed comparable to the speed of the blades, in essence when the blade is traveling backwards it has a zero airspeed and generates no lift. If you strapped a jet on for speed, you'd also need to use it for lift beyond na certain velocity, at which point, your whole "rotor" mechanism just becomes dead weight to a conventional jet aircraft. We have tilt rotor aircraft which combines the benefits of rotary aircraft and fixed wing aircraft, but if you haven't noticed, there aren't many around in civilian use because they have their own whole set of challenges and difficulties. Vespine (talk) 05:02, 12 April 2011 (UTC)

Fundamentally different? Large airliners universally use turbofan engines, essentially a ducted many-bladed propeller driven by a gas turbine in the middle. The fundamental difference between that and a turboprop is just that the latter has a gearbox between the turbine and the propeller and no duct. Modern helicopters also, as far as I understand, tend to be driven by gas turbines. –Henning Makholm (talk) 12:16, 12 April 2011 (UTC)

Hmm, well I'm not an expert but I think you are wrong. In a turbofan engine, it's NOT the "fan" that creates the thrust but the exhaust gasses. The exhaust gasses are NOT created by the fan but by fuel combustion, which is what creates the thrust AND also powers the fan. The fan is there to provide compression and exhaust stages to the engine. Read the turboprop article again: The engine's exhaust gases contain little energy compared to a jet engine and play a minor role in the propulsion of the aircraft. A turboprop is powered by a jet turbine, that's like a jet engine except the primary role of a turbine is to turn a shaft (like in a helicopter), not create thrust like a jet engine. Fundamentally different methods of propulsion. Vespine (talk) 23:00, 13 April 2011 (UTC)

Maximum carrying capacity of aircraft

Our article on the Airbus A380 says that it is certified to carry up to 853 passengers, almost a thousand people. That got me wondering, just how big can we theoretically make aircraft, assuming that cost-benefit-risk ratios were not much of a factor? (What sort of actual physical limits would there be on the size of aircraft?) What would be a good estimate for the upper limit on the number of passengers a long-distance airplane could theoretically carry (again, assuming cost-benefit-risk ratios were not much of a factor)? Could an airplane for 2,000 people be built? 5,000? 10,000? 20,000? 50,000? 100,000? Would such an enormous airplane fly more efficiently with fixed wings or with rotors?

—SeekingAnswers (reply) 04:09, 12 April 2011 (UTC)

Roughly speaking, larger aircrafts need larger engines and more fuel to operate; and they must be able to lift their own engines and their own fuel. What this means is that the larger an aircraft is, all other things being equal, the larger the proportion of its weight will be taken up fuel and engines, and thus the smaller the proportion of its weight will be availible for passengers and cargo. Given a set of materials and general construction mechanisms, there is an upper limit for any aircraft design, in terms of size. This probably varies depending on the exact aircraft type, but there is a limit. --Jayron32 04:16, 12 April 2011 (UTC)

The above comment needs sources. While the first part – that larger aircraft will require larger engines – is reasonable, the second assumption – that larger aircraft must use proportionately more mass for engines and fuel – doesn't (ahem) fly. Fuel efficiency in transportation#Aircraft notes that a 747 uses about one-sixth the fuel per passenger mile of a Gulfstream business jet. I strongly suspect – though I would welcome a search for valid numbers – the thrust-to-weight ratio of turbofan engines generally improves slightly as the engines get more powerful, and not the other way around. Upper limits on aircraft size are governed by the maximum capacity of airport facilities (including gate and taxiway spacings) and the amount of time it takes to load and unload passengers and cargo from a hypothetical extremely large passenger aircraft, rather than physical limitations on aircraft efficiency. Few routes carry enough traffic to justify aircraft carrying more than five hundred passengers, and even on high-traffic shorter-haul routes an airline my prefer to use two fast-loading jets instead of one big craft that spends a long time at the gate. Aircraft manufacturers have no incentive to design aircraft that won't be able to land at existing airports and which airlines won't want or need to buy. TenOfAllTrades(talk) 16:41, 12 April 2011 (UTC)

Airports preparing for the A380 had to extend and widen runways, and modify terminal facilities so people could get on and off the plane in a sensible time. The same would apply for bigger planes, only more so. HiLo48 (talk) 06:01, 12 April 2011 (UTC)

So, assuming you have unlimited budget and no concern for profit, does anyone have any actual maximum passenger estimates? My thinking is that at some size, even with unlimited budget and no concern for profit, you would still encounter insurmountable problems because of fuselage stress issues (as in, compressive stress, tensile stress, etc., would make aluminum and titanium no longer viable options for construction), and you would have to turn to increasingly exotic construction materials. —SeekingAnswers (reply) 06:27, 12 April 2011 (UTC)

I'm not sure that there is an upper limit, if we ignore costs/benefit analysis. After all, you could just chain multiple airplanes together and call it a single airplane. As for a large, single fuselage plane, perhaps a ground effects airplane (no article ?) that launches and lands in water would work best, since that would eliminate the need for runways, and would limit fuel req's. See Spruce Goose (if we made this out of aluminum or composites it would be far more practical). StuRat (talk) 06:55, 12 April 2011 (UTC)

There is an article at ground effect vehicle, and I've now created a redirect from "ground effects airplane". But yes, my question regarding an estimate for the upper bounds of passengers is for a single-fuselage plane. I'd also be interested in any comments people have for the type of construction materials to use for this theoretical maximum-size aircraft. —SeekingAnswers (reply) 09:53, 12 April 2011 (UTC)

According to this there is a worldwide limit at air terminal gates of 80 meters wing span. The A380 fits at 79.8 meter wing span but the "Spruce Goose" is too large at 97 meters wing span. Cuddlyable3 (talk) 13:07, 12 April 2011 (UTC)

I've seen a documentary about 10 years ago in which it was pointed out that flying wing designs become more efficient for very large planes and that an optimal design for a plane capable of carrying many thousands of passengers would look like a giant flying saucer. Count Iblis (talk) 14:24, 12 April 2011 (UTC)

You might want to read about the Antonov An-225 which is the world′s heaviest aircraft and also longer than the Spruce Goose (although not as wide). Our article says it can carry 640 tonnes, so I guess you could equip it to carry more people than the A380 can if you wanted to. SmartSE (talk) 15:15, 12 April 2011 (UTC)

A regulatory limitation, as opposed to a physical limitation, is the requirement that the airplane be capable of evacuation in 90 seconds, limiting travel distance and requiring increasing numbers of exits. Acroterion (talk) 17:05, 12 April 2011 (UTC)

Giant Sequoia

How long do Giant Sequoias live up to? 174.114.236.41 (talk) 04:19, 12 April 2011 (UTC)

According to our Giant Sequoia article, the "oldest known Giant Sequoia based on ring count is 3,500 years old." —SeekingAnswers (reply) 04:38, 12 April 2011 (UTC)

Taxonomy/Etymology question...

Opossum

Possum

I understand that the Australian Possum and the North American Opossum are only very distantly related; they belong to different orders. Still, I have a question about the etymology of the Australian Possum name specifically. It seems that the North American Opossum gets its name from an Algonquin word. That makes sense; they were here before the English speakers, and lots of native New World animals and plants have derived their English name from Native American names. I am quite sure that is also true about Australian animal and plant names; many of them derive from Aboriginal names of the same critters. Still, I am thus confronted with an interesting conundrum: How is it that these two marsupials should have similar names at such a geographic distance. I am left with some unsatisfying possibilities:

• That the Australians took the name of the American animals and applied it their own. This doesn't seem to make much sense; other than being marsupials, Possums and Opossums don't look all that much alike; Opossums are more rodent-like in appearence, Possums more resemble primates like Lemurs or Bushbabys. Furthermore, the entire idea that Australians would appropriate a Native American name, to describe a native Australian species seems a bit weird, if you ask me, and any path that would take the name from North America to Australia seems quite convoluted.
• The Australian Possum is derived from an Aboriginal name after all. This seems equally weird; Aboriginal languages and Native American languages are linguisticly so far apart, I can't imagine one influencing the other, and yet this would be an example of the most bizarrely close False cognates I;ve heard, how random that both Aborigines and Native Americans would have given similar names to small marsupials.

So, to sum up this insanely long question: What is the actual etymology of the Australian Possum's name? --Jayron32 05:28, 12 April 2011 (UTC)

Dictionaries that I consulted are unanimous in stating that "possum" is derived from an abbreviation of "opossum." I don't find this puzzling at all, actually. The Americas were settled by Europeans much earlier (by centuries) than Australia was (late 18th century), so the word "opossum", and its informal abbreviation of "possum", would already have been well-established in the English language. Thus, while it would be strange for Australians to appropriate a Native American name, it would not be strange for them to appropriate an American or a common English language name, which is probably what they thought it was. I doubt the first Australian settlers were even aware that the word "opossum" was of Native American origin; they probably just thought of it as another regular word in the English language. They're both marsupials. And to the layman, opossums and possums look very much alike. Just look at the photos (File:Opossum_2.jpg and File:Trichosurus vulpecula 1.jpg, which I also posted to the right) in the infoboxes at the top of the articles (as of this current writing) for the two respective animals; those photos look a lot alike at a casual glance. —SeekingAnswers (reply) 06:08, 12 April 2011 (UTC)

My Australian Macquarie Dictionary suggests that the two words are connected and interchangeable, so yes, Australia did borrow the American word. HiLo48 (talk) 06:11, 12 April 2011 (UTC)

Just by the way, hardly anyone actually says opossum in the States, at least outside of a scholarly context. In normal colloquial speech they are called possum. Using the two words distinctively is likely to lead to confusion. --Trovatore (talk) 19:07, 12 April 2011 (UTC)

According to Wiktionary, the phrase "playing possum" is documented back to 1822. I think the Australian possum does the same thing but I'm not sure. Actually, the Australian Possum doesn't look like an opossum to me - because of its face it makes me thing more of kangaroos and koalas than the opossums I've seen - I suspect it's the creature's behavior that has given it its name. Wnt (talk) 21:25, 12 April 2011 (UTC)

Note that although only one species of opossum is found in the United States, several dozen species can be found in South America. (A few extend as far north as Mexico.) Some of the South America species, such as the Gray Short-tailed Opossum, look quite a bit more like an Australian possum than the Virginia Opossum does. Looie496 (talk) 21:35, 12 April 2011 (UTC)

The power of noise

What proportion of the power of a jet engine or car engine is wasted in producing noise? My notion is that the most efficient engine would be silent. In other words, by how much would the ratio of output/input power increase if all noise energy was redirected to the output power? Do high efficiency modern engines tend to be quieter? Thanks 92.15.21.224 (talk) 13:23, 12 April 2011 (UTC)

Only a very small portion of the energy goes into sound itself. However, a loud engine may be indicative of other inefficiencies, such as friction, turbulence, cavitation (on prop attached to boat engine), an unbalanced engine, or missing cylinders (internal combustion engine), which tend to waste most energy as wear, heat, and vibration. So, a silent engine likely would be more efficient, yes. (Note that this logic doesn't apply to noise which is produced by the engine but then muffled in some way; this actually reduces engine efficiency.) StuRat (talk) 17:26, 12 April 2011 (UTC)

Before starting, I should say that so far as I've seen, measurements regarding sound are nearly always dishonest or actively misleading. Either a manufacturer wants you to believe something is more powerful than it is, or a polluter wants you to think it is weaker. Numbers are usually given in "decibels", but the decibel is a relative unit, i.e. meaningless on its own, tied to one of many different arbitrary reference levels - the article gives some of the many sub-definitions used. A particularly obnoxious trick is the usage of a "filter" (dBA) which supposedly reproduces the characteristics of human hearing - by means of a simple mathematical curve which underestimates the impact of low frequencies. And even that is relative to a curve generated by psychoacoustic measurements... I take particular exception to the low-frequency business because people do hear infrasound and suffer physiological effects from it, but it is claimed, not "consciously" (i.e. they don't call the vibration/sensation they feel a sound); for those deemed unable to hear things which are plainly audible, psychology rapidly wears out its welcome. Another use of psychoacoustics is frequently seen when a polluter takes data that people surveyed on a form said that a 10 dB increase is only a 2-fold increase (even though it's more), and uses it to say that their newest proposal will only "sound" twice as loud.

Now that hopefully I've emphasized the need for you to take such data with a truckload of salt, I'll point you to sound power, which gives some energy figures. Though I am quite suspicious that an excavator is quieter than a heavy truck, for example. To convert these to a few other sound measures, see [8]; probably there are others. But the bottom line is that if the figures in the article can be trusted, vehicles generally emit less energy, perhaps much less, by sound than from their headlights. Wnt (talk) 22:05, 12 April 2011 (UTC)

Yea, that 1/100 of a watt for helicopter noise seems particularly low. That article needs some work. StuRat (talk) 22:12, 12 April 2011 (UTC)

A jet engine delivers "noisy" i.e. irregular thrust. Longitudinal pressure variation in the output stream is just the way it delivers useful power and all the jetstream is good, though not for your ears if you stand behind a jet aeroplane. The only wasted sound power is that emitted radially (and, at subsonic speed, forwards) from the engine. A car's reciprocating combustion engine cannot be silent because of its pulsing exhaust. By dimensioning the intake and exhaust tracts to resonate at particular engine speeds, high efficiency (which can be variously defined) is obtainable with the inconvenience of loud noise. (Formula One racers are very noisy.) Two-stroke engines can only work with a resonant exhaust so they are always noisy, while four-stroke car engines are usually muffled in a compromise with efficiency but will not be completely silent. Cuddlyable3 (talk) 22:14, 13 April 2011 (UTC)

What will happen if bicycle tyre will be filled using Helium gas?

What will happen if bicycle tyre will be filled using Helium gas? — Preceding unsigned comment added by Mayank3 (talk • contribs) 13:37, 12 April 2011 (UTC)

It's an interesting question! What sorts of effects do you expect might happen? DMacks (talk) 14:05, 12 April 2011 (UTC)

The compressed helium in the tire would weigh slightly less than the compressed air when the tire was inflated to the same pressure. One would have to know the volume of gas contained in the inflated tire to calculate the exact weight difference. The weight of the gas in the tire might be very insignificant compared to the weight of the tire and the bicycle: helium in the tires would not make the bike lighter than air, for instance. The helium would likely leak out of the tire quicker than air leaks out, since it is monatomic compared to the larger and heavier molecules of the component gases in air. It might have a lower viscosity, and circulate more freely inside the tire. It would have greater thermal conductivity than air. Being an inert gas, it would not react chemically with the rubber of the tube or tire as would the oxygen in air. Edison (talk) 14:10, 12 April 2011 (UTC)

To expand a bit on Edison's response, the helium in the tire will weigh proportionally quite bit less than the same volume and pressure of air: about 85% less, in fact. In absolute terms, however, the mass of air in the tires makes a negligible contribution to the bicycle's – or even the tire's – weight; there's only a few grams of air in each tire, accounting for something like 0.1% of the total weight of the bike. TenOfAllTrades(talk) 15:17, 12 April 2011 (UTC)

Furthermore, the tire would go flatter much faster; Edison lights on this but fails to name the effect, which is called Graham's law of diffusion. A mathematical treatment of Graham's law is covered in that article if you are interested. --Jayron32 15:34, 12 April 2011 (UTC)

Filling it with hydrogen gas instead may give spectacular effects in case of an accidental tire puncture :) Count Iblis (talk) 14:16, 12 April 2011 (UTC)

Only if punctured with something that is also on fire. Hydrogen is not spontaneously combustable; perhaps you are thinking of the Hindenburg disaster, whose explosion cause was unknown, however given the properties of hydrogen all of the serious hypothesis revolve around a source of either fire or electricity as the initial cause. Hydrogen itself will not explode without sufficient cause, and merely puncturing the tire is not sufficent cause. --Jayron32 15:34, 12 April 2011 (UTC)

Yes, but then the so-called "inversion temperature" of hydrogen is lower than room temperature. This means that when under pressure and then expanding into the environment, it will heat up, not cool down like most other gasses, due to the Joule-Thomson effect (the temperature of an ideal gas will not change. While due to exansion it would cool down , the energy goes into kinetic energy of the gas; it shoots out of the puncture, that kinetic energy is subsequently dissipated and heats up the gas again). This is why hydrogen is never stored under pressure at room temperature (which complicates implementation of green energy technologies that depend on hydrogen to store energy, e.g. generated from wind energy). Count Iblis (talk) 15:48, 12 April 2011 (UTC)

Er, hydrogen is frequently stored (and readily available) as a room-temperature compressed gas; see for example hydrogen tank for some specs. Google offers lots of additional pictures: [9]. And a bicycle tire – starting at perhaps six atmospheres of pressure – is never going to reach the autoignition temperature of hydrogen through simple expansion. TenOfAllTrades(talk) 17:00, 12 April 2011 (UTC)

I see! I blame my old Prof. for giving a misleading homework problem on this issue a long time ago, although I should have been able to see that you don't get problems with tires. Count Iblis (talk) 01:45, 13 April 2011 (UTC)

What eventually happens to a beam of light?

Does it keep getting red-shifted for eternity? Imagine Reason (talk) 16:09, 12 April 2011 (UTC)

If the red shift doesn't get it, extinction will. --Sean 17:19, 12 April 2011 (UTC)

How could the photon change? Where would the energy go? Metric-expansion red shift never really made sense to me, so I don't really understand how it happens. My best guess is that it's only the relative difference in velocity between the objects in space and the photon that changes (so it only redshifts relative to you), but I'm not clear on how the energy budget is worked out. Ariel. (talk) 01:53, 13 April 2011 (UTC)

Do the articles Red shift and Photon help? Cuddlyable3 (talk) 14:07, 13 April 2011 (UTC)

Your guess is right. The redshift happens because the source of light and the detector are moving away from each other. The energy at emission will not be the same as the energy at detection because they are measured in two different inertial frames. Dauto (talk) 18:35, 13 April 2011 (UTC)

Eliminating sex

(sorry my English) One of the common themes in a lot of science fiction tales is a society that no longer repruce by bilogical sex. I wonder to wich extent that would be possible with current technology. For example, suposse a relatively isolate community (something like the Amish) Then imagine this community decide to apply chemical castration to all its male babys and oly reproduce by artificial insemination. Could this community efectivily erase both the desire and the need of sex in a generation or two? --83.59.47.204 (talk) 17:43, 12 April 2011 (UTC)

How is chemically castrating all the males (which probably would erase the desire in all males anyway, simply greatly reduce it) going to erase the desire in females? In addition, I'm doubtful chemical castration has ever been tried on male babies and even ignoring the ethical considerations I would guess given the way most forms of chemical castration work it's going to cause a great degree of feminisation of the males as they develop to the point where you will have trouble getting sperm for the artificial insemination and who knows what other problems. Nil Einne (talk) 17:53, 12 April 2011 (UTC)

Many science fiction tales seem to be based on the idea that you can't totally erase the human instinct to have sex and/or reproduce naturally. See the film THX 1138 for example. I don't know about eradicating human sexual desire...but I imagine that, in theory, it is possible to sustain a human population through artificial reproduction, and that over many generations, we might evolve to a point where we have no sexual desires. But that's just speculation. Quinn ^☂THUNDER 18:03, 12 April 2011 (UTC)

I expect that removing testes and ovaries at birth (or before), then reproducing by cloning, would pretty much eliminate sexual desire. You could also have all males or all females, and thus at least eliminate any hetero sex. StuRat (talk) 19:00, 12 April 2011 (UTC)

That all presumes that the sexual drive is a purely reproductive one, but the sexual act itself is done for all sorts of reasons, social, emotional, etc. To eliminate the reproductive desire does not necessarily eliminate the other sorts of reasons why people have sex; its why efforts to sterilize or chemically castrate males who have committed sex crimes have limited success in stopping them; they aren't committing sex crimes because of a desire to reproduce; as often as not its about establishing power relationships or other issues which have nothing to do with reproduction. --Jayron32 19:23, 12 April 2011 (UTC)

That's where the "at birth (or before)" part comes in. If you wait until adulthood to remove them, then the hormones will have already altered the brain in a sexual way. You must remove them before the brain becomes sexualized. All other sexual stimuli, like porno movies and pictures, would also need to be removed. If your brain has no concept of sex, then it can't have any concept of rape, either. (Of course, there are many other ways to humiliate people, like defecating on them, which might then become more prevalent.) StuRat (talk) 19:30, 12 April 2011 (UTC)

Well, you hit on one big point there; sexual abuse is in many ways the symptom of other social problems; removing sex as an option would not necessarily change rapists into fine people. It may very well just change the mode of abuse without altering the underlying causes that make some peopel want to be abusive. --Jayron32 19:39, 12 April 2011 (UTC)

Every life form currently living on Earth has excelled at one thing: reproducing. In vertebrate species, reproduction is usually sexual. If any behaviors are determined by evolution and genetics, copulation (i.e. 'having sex') is the most likely. Lastly, in order for some sort of asexuality to be 'evolved' it would have to be advantageous under selective pressure. You may be interested in the species which have evolved parthenogensis. This is common among the insects, such as aphids, and even some lizards and fish can reproduce this way. We suspect that this lack of sexual recombination may lead to an evolutionary bottleneck, and ultimately the extinction of the species. SemanticMantis (talk) 20:57, 12 April 2011 (UTC)

UV emission from electric arcs

What is the actual mechanism of ultra violet emission from electric arcs.--92.28.38.62 (talk) 18:05, 12 April 2011 (UTC)

Electric arcing causes a lot of non-specific excitation of electrons, across a broad spectrum of wavelengths. Generally, certain types of wavelengths are closely associated with certain types of excitation (for example, the infrared wavelength is particularly correlated with vibrational modes, while radio waves are found in the range of nuclear magnetic resonance). In a situation like an electric spark, you are basically exciting electrons non-specifically, so they tend to promote to higher energy levels, and re-emit photons as they relax, between nearly every allowable transition within the material. Basically, they don't just emit in the ultraviolet, they emit in the ultraviolet along with emitting in just about every frequency from radio waves through to the UV. Radio waves emitted by simple electric sparks was, for example, one of the cornerstone areas of research that eventually led to modern radio technology, see Heinrich Hertz. --Jayron32 19:18, 12 April 2011 (UTC)

Farmer's action plan?

There is a large farm located on the Eastern shore and the farm grows corps, and to many bugs is destroying the crops and the farmer last year sprayed heavy doses of pesticides, this year the farmer was asked not to use the same chemicals and wants to control the amount of soil that is being washed into the stream. What is an action plan that will help the Bay and the farmer —Preceding unsigned comment added by 71.191.176.79 (talk) 22:07, 12 April 2011 (UTC)

Sounds suspiciously like homework, but, in case it's not, here's some thoughts:

1) Plant crops which are more resistant to "bugs".

2) Introduce natural predators of those "bugs".

3) Utilize "no till" planting methods.

4) Plant trees at the edges of fields to limit both wind and rainwater losses of soil. StuRat (talk) 23:30, 12 April 2011 (UTC)

Don't forget Bt corn. This would be easier to answer if we knew the crop, the bug, and the pesticide. Wnt (talk) 00:54, 13 April 2011 (UTC)

The farmer could also plant cover crops in the fall (like alfalfa, which, aside from simply reducing weather-based erosion, restores favorable levels of nitrogen in the soil). Juliancolton (talk) 02:14, 13 April 2011 (UTC)

Just for the benefit of the readers who aren't familiar with Atlantic Seaboard of the U.S. geography, the Eastern Shore refers to the Maryland and Virgina parts of the Delmarva Peninsula. The Bay referenced would then be the Chesapeake Bay. The region is known for agriculture, large industrial chicken farming, and crab fishing. --Jayron32 05:32, 13 April 2011 (UTC)

light-bulb

hows the glass attached to the metal in this http://www.traderscity.com/board/products-1/offers-to-sell-and-export-1/mr16-gu10-halogen-light-bulb-240-volt-energy-saver-gu10-lamp-50w-189861/ — Preceding unsigned comment added by Wdk789 (talk • contribs) 23:32, 12 April 2011 (UTC)

Since the late 19th century a substance called "vitrite" was used to join metal of the incandesent lightbulb shell to the glass bulb. Edison (talk) 05:14, 13 April 2011 (UTC)

Wikipedia does have a brief article on it: Vitrite. --Jayron32 05:25, 13 April 2011 (UTC)

Mining of thick seams

some of the ways of mining thick seams are :

• blasting gallery method
• inclined slicing method
• horizontal slicing method
• sublevel caving

can anybody explain the methods? — Preceding unsigned comment added by Him.12.pat (talk • contribs) 23:33, 12 April 2011 (UTC)

I just looked on Google, there are websites which cover this. I think you could find out most of this information yourself. Your question sounds like homework.217.158.236.14 (talk) 12:24, 13 April 2011 (UTC)

April 13

wrong named structure

• 

To my mind the structure shown on the picture should be named 3-Methyl 4-propyle-octane because you have to choose the main-chain with the most branches. I dont participate very often in the en wp so id like to ask sb from here to either correct the structures name or to (let) deleate it. Greetings --Oliver s. (talk) 23:38, 12 April 2011 (UTC)

Straight from the IUPAC themselves:

The longest chain is numbered from one end to the other by Arabic numerals, the direction being so chosen as to give the lowest numbers possible to the side chains. When series of locants containing the same number of terms are compared term by term, that series is "lowest" which contains the lowest number on the occasion of the first difference. This principle is applied irrespective of the nature of the substituents.

See also IUPAC_nomenclature_of_organic_chemistry#Alkanes. Your rule (main-chain with the most branches) is used only when there are two or more possible main chains of the same length. Buddy431 (talk) 23:51, 12 April 2011 (UTC)

3-methyl 4-propyl is lower numbered than 4-(1-methylpropyl), so far as I know. When I search for "3-methyl 4-propyl octane" I get a few serious-looking mentions, whereas the other name only gets me derivatives with a lower numbered substituent, and Wikipedia hits. (including a talk page discussion about someone being wrong for naming the compound that way) Wnt (talk) 00:52, 13 April 2011 (UTC)

The OP is correct. I assume the molecule is being used to demonstrate how to name a molecule with a branch off of a branch, but it doesn't work because there ARE two main chains of the same length (both octanes) and in that case you choose which octane has the most branches. So the 3-methyl-4-propyloctane is a better name for that reason. It also works with the rule quoted above, because the alternate name, being 4-(1-methylpropyl)octane has the "occasion of the first difference" on carbon 4, whereas the 3-methyl-4-propyloctane has it on carbon 3. Since it has the lowest number of first difference (3 vs. 4) its the better name. Using either rule, that's still a badly named compound. --Jayron32 01:23, 13 April 2011 (UTC)

Good catch Jayron. I was counting 7 carbons on the chain the OP wanted to be the main one. They say organic chemists only need to be able to count to 8, but it doesn't even look like I can do that. Buddy431 (talk) 03:20, 13 April 2011 (UTC)

• :-) --Oliver s. (talk) 14:19, 13 April 2011 (UTC)

Speed of Earth's orbit around the sun

I read that earth orbit's the sun at a speed of 107,000 KM/H, which seems mighty fast. Given this imense speed, I find it somewhat surprising that we do not feel any wind resistance here on earth. I mean if you stuck your head out of a car window travelling at 100 KM/H you would feel a strong gust of wind in your face, yet we are tearing through space at 107,000 KM/H without so much as a feint breeze? Perhaps somebody might be able to enlighten me as to why this is! Kind Regards. Paul —Preceding unsigned comment added by 79.71.91.21 (talk) 02:09, 13 April 2011 (UTC)

If you keep your head inside that car window, and keep the window closed, you also don't feel any breeze, yet you're still travelling at 100km/h relative to the road surface, because the air in the car is also travelling with you at 100km/h. Same with the Earth. Its air comes with us as we hurtle along, so we don't feel a thing. — Preceding unsigned comment added by HiLo48 (talk • contribs) 02:22, 13 April 2011

Yes, the speed of the Earth relative to the sun is very fast, but the sun is a very long way off. The sun is at such a great distance that even though the relative speed is 107 km.hr^-1 it takes the Earth one whole year to complete one trip around the sun. That is an angular speed of only 0.0411 degrees per hour which is extremely slow. There is no atmosphere between Earth and the sun, and no atmosphere means no wind when moving relative to the sun.

Earth's linear speed relative to the other planets in our solar system is also extremely large, but the angular speed is extremely small so we experience no effects from our speed relative to those planets.

A jet airliner might pass overhead at a speed of 1000 km.hr^-1 and a height of 40,000 feet (12 200 m) but you experience no effects because of the great distance between you and the airliner. If the jet airliner passed near you (close to ground level) you would experience many effects! Dolphin (t) 06:48, 13 April 2011 (UTC)

Paul you may be interested in the Michelson–Morley experiment that was carried out in an attempt to detect some kind of "wind" due to the Earth's motion, and is famous for having completely failed. (I simplified this story). Cuddlyable3 (talk) 13:52, 13 April 2011 (UTC)

Those experiments strongly (and unexpectedly) demonstrated a phenomenon that the then-current theories were totally unable to explain. For a physical experiment, that counts as a spectacular success -- the opposite of a complete failure. –Henning Makholm (talk) 16:14, 13 April 2011 (UTC)

Once again proving that there are no failures in science; a negative result is still a result, and it is all data. --Jayron32 18:56, 13 April 2011 (UTC)

No Henning Makholm. Lorentz-Fitzgerald length contraction was a theory that explained the negative result of the MM experiment. If Albert had not come along later with his special relativity we would probably still find Lorentz's aethereal hypotheses plausible. Cuddlyable3 (talk) 21:31, 13 April 2011 (UTC)

I would like to point out that the diameter of the Earth is 12,750 km, so the planet takes seven minutes to travel its own width. Meanwhile, your car travels its own width in a tenth of a second and a turtle walks its own width in maybe five seconds. If you were watching the Earth from above, it would look very slow. —Preceding unsigned comment added by 205.193.96.10 (talk) 16:03, 13 April 2011 (UTC)

Using decay heat in a nuclear reactor to spin a turbine

I did a presentation in a class of mine, and part of it discussed nuclear energy. The professor asked me if it was possible to use the decay heat produced in a nuclear reactor in a scram situation to spin a turbine which would power a water pump to cool the reactor. I was fairly certain that this idea was not possible simply because it does not generate enough steam to spin a turbine, but I'm not entirely sure. I'm pretty sure they disconnect the reactor from the turbine anyway during a scram for safety reasons. Can anyone confirm my guesses? ScienceApe (talk) 02:33, 13 April 2011 (UTC)

In principle the waste heat could be used to turn a turbine, though probably not the main turbine(s) used for regular electrical generation (the initial decay heat will be less than 10% of the reactor's regular output, and this will decline in the days following the scram). In practice, adding a second turbine (with all of the associated mechanical complexity and necessary preventive maintenance on parts that would be in working contact with radioactive coolant) isn't worth the complexity and cost over other solutions to drive the pumps. (Generally, grid power as the first option, and backup diesel generators as the second.) TenOfAllTrades(talk) 03:27, 13 April 2011 (UTC)

Wasn't that a system in place at Chernobyl that they were testing when the accident occurred? And I thought they referred to s similar system at the Fukushima 1 plants. A scrammed reactor should produce plenty of steam for a while to ruin emergency cooling pumps. Nuke plants are all about complexity and cost, with backups to backups. Edison (talk) 16:14, 13 April 2011 (UTC)

The system being tested at Chernobyl was to run the cooling pumps off the residual kinetic energy of the turbine for the 60 seconds it would take to activate the emergency generators. --Carnildo (talk) 00:17, 14 April 2011 (UTC)

whey gel

what exactly is whey gel? —Preceding unsigned comment added by 80.1.216.243 (talk) 03:39, 13 April 2011 (UTC)

It is a gel formed from Whey protein. You can read both of those articles to learn both what a "gel" is and what "Whey protein" is. --Jayron32 04:03, 13 April 2011 (UTC)

Universe = black hole, for some of time... or wait, only in the sideways version of time, which is length (*confused mumbling*)

OK I've been doing some thinking about the universe. Let's say there's this guy, and he's just chilling looking at our universe from the outside right before the big bang. Now, because the universe is ridiculously massive and small, it will appear to him like a black hole. And he is sitting right outside the event horizon (naturally this is the mother of all black holes - being the mass of the universe at ~1.6×10^55 kg and a Schwarzschild radius of approximately a two trillion light years [10] [11] - can this be right?!).

Now do I understand properly, that because he is outside the event horizon, everything that occurs within will be unobservable to him? Time on the surface of the event horizon is frozen for him, and time inside is on an entirely different plane of existence (piece of trivia: I heard one theoretical physicist put it this way: time bends on the fourth dimensional level, and length becomes time, and time length). As such, the big bang will never exist for our friend on the outside of the black hole. At best, current theories indicate he might (or might not) be able to deduce what occurs inside only from an extremely accurate reading of the Hawking radiation (see Holographic principle#Black hole information paradox).

Thus, if I understand properly, it is entirely possible that we live in a universe which is encapsulated within another universe, but the second universe will remain forever unattainable to us. No matter how much the universe expands, because we are dealing with infinitely small meters and units of time (on the event horizon, from the perspective of the outside... god knows what the hell happens inside), we will never reach that universe. I realize this isn't an entirely new concept (I saw Leonard Susskind explain it similarly), but it... kind of made sense to me for the first time tonight, when I thought it up on my own.

So I have some questions about all this:

1. If something were to enter the black hole from the outside, when and how would we perceive it on the inside?
2. Could it be, with the super-screwed-up-ness of time and space, that tracing back to the big bang is really just tracing back to the beginning of the existence of the black hole? And we would experience it entirely backwards (instead of matter falling in, vice versa), in a mad confusing turn of events because time is all goofed up.
3. Addendum to above: possibly all matter that can fall in has already fallen into the black hole before the big bang? And the entire external universe has already all ended, because it took infinite time for even a second to pass within? I'd have to assume Hawking radiation turned out incorrect. Thus we experience the big bang as the beginning of time, but really it's the end of time for the external universe. Much in the same way as someone traveling on a photon would have the entirety of time pass before experiencing even a second.
4. My understanding is that, given the right conditions of a spinning black hole, the singularity can be exposed to the outside world. What would happen then? What would it look like?

OK, I hope I haven't textwalled here too much, and I've stated this clearly enough that you all can understand it. I know I haven't stated it clearly. Anyway, am I making any sense at all?Magog the Ogre (talk) 06:37, 13 April 2011 (UTC)

Unlike some of the people here, I'm no expert, but aren't there a couple of problems with treating the big bang as a black-hole style singularity. I believe time and space came about in the big bang, standing outside it makes no sense. (unlike standing outside a black hole, of course) Isn't the concept of observing anything flawed with no concept of time and space? Grandiose (me, talk, contribs) 08:18, 13 April 2011 (UTC)

I have two questions:

1) can black hole return to expand or exploding to produce new objects?

2) about the big bang and expanding of universe ,there is no boundary and centre for universe , is there remnant matter in first point which big bang started?(this helps imagining )-78.38.28.3 (talk) 08:37, 13 April 2011 (UTC)

[Fixed your formatting for clarity, 78] In brief:

1) It is thought that, given long enough, all black holes will eventually evaporate by giving off Hawking radiation, but the time this takes is in some inverse proportion to their size, so black holes of star-mass or larger might take longer than the Universe itself will exist to evaporate (from the first link: "For a black hole of one solar mass . . . we get an evaporation time of 2.098 × 10⁶⁷ years"). Otherwise (we think), no.

2) There is no one "first point where the Big Bang started" because that point itself has now expanded to form the whole of the Universe. The Big Bang was also an expansion of space (and time) itself, not just of some matter within pre-existing space. To put it another way, everywhere is that "first point". This is, of course, very difficult for us to visualise. {The poster formerly known as 87.81.230.195} 90.197.66.111 (talk) 12:53, 13 April 2011 (UTC)

The error in your hypothetical scenario is subtle—it presumes that there is somewhere for an observer to sit outside the Universe, where he can watch the show. (That scamp Douglas Adams can be blamed for this perception, as he offered us the Big Bang Burger Bar as the natural complement to Milliways, The Restaurant at the End of the Universe.) Outside the Big Bang singularity, there just isn't any space to be in, and no way to watch the big...bang as it happens. TenOfAllTrades(talk) 15:10, 13 April 2011 (UTC)

4 It look like black hole from outside —Preceding unsigned comment added by 77.127.207.138 (talk) 15:47, 13 April 2011 (UTC)

Outside ? It's confusing to think about these things because of the tendency to think of the metric expansion of space being like a 2-sphere expanding into 3D space....but it isn't. Sean.hoyland - talk 16:10, 13 April 2011 (UTC)

"Big bang theory". Phewy, bah humbug, hogwash. I can think of no other scientific postulation which has received such resounding, universal acceptance based on such flimsy empirical evidence(other than perhaps the flat earth theory). Oh yes another one might be "god done it". The big bang is no more an explanation than the bible is. Think about it.190.149.154.194 (talk) 17:08, 13 April 2011 (UTC)

Perhaps I should clarify. Befor the existance of time or space or the universe,(something?) went bang and brought everything including itself into existance. What? Metaphysical mumbo jumbo.190.149.154.194 (talk) 17:21, 13 April 2011 (UTC)

Read Big bang#Observational evidence for the empirical evidence for the big bang. Dauto (talk) 17:48, 13 April 2011 (UTC)

The Big Bang theory is one of the best-evidenced scientific theories in the world, provided you understand its inherent limitations (briefly, that it describes effects and not cause). — Lomn 17:50, 13 April 2011 (UTC)

Thanks guys. I have no difficulty with hubble's expansion conclusions or with penzias and wilsons observations of residual electromagnetic radiation. I do however have a problem with the general assertion that the logical back track of those observations indicate the origin of the universe. It seems clear that what is being learned is part of the history of the universe, not neccessarily the origin. I think that basically sums up my argument.190.148.132.153 (talk) 19:07, 13 April 2011 (UTC)

I think that most (if not all) cosmologists would agree, these days. -- BenRG (talk) 20:38, 13 April 2011 (UTC)

Contrary to popular belief, you can put a big bang cosmos inside a larger universe that didn't start at the big bang, at least in classical general relativity. From the outside, the big bang cosmos has the same gravitational field as any other object with that mass. (This means the mass has to be finite—which means that the homogeneous cosmos that we find ourselves in has to have an edge out there somewhere—but that's consistent with observations if the edge is far enough away.) The big bang appears from outside as a white hole. In a black hole there's an event horizon that can only be crossed from outside to inside, and anything that does cross it ends up at the singularity, while anything that doesn't cross it ends up at future infinity. A white hole is the time-reversed version of that: there's an event horizon that can only be crossed from inside to outside, and anything that crosses it started out at the singularity (the big bang singularity, in this case), while anything that doesn't cross it started out at past infinity. The big bang singularity is inaccessible from the outside universe, but all of the matter that originates from it crosses the event horizon, after which there are no restrictions on two-way travel between the big bang and non-big-bang regions.

However, if there's a positive cosmological constant, then long-distance travel eventually becomes impossible. In the real world, assuming future expansion is dominated by the cosmological constant, I think that it's already too late to reach the edge of the visible universe, much less the edge of the whole big bang cosmos (if there even is one). Also, I don't know how quantum gravity alters this picture. Classically, the white hole has to have existed forever from the outside universe's perspective, but I don't see why it wouldn't Hawking-radiate away once you add quantum effects. It may be that nothing I said above makes sense in quantum gravity. (And all of it is almost certainly wrong in any case, even if it works in theory.) -- BenRG (talk) 20:38, 13 April 2011 (UTC)

Bear pit

The article says that a bear pit trap can deter bears from approaching a cabin. How could that be? If bears are smart enough to avoid falling in it, wouldnt they be smart enough to simply walk around it? Thanks 92.15.19.232 (talk) 13:11, 13 April 2011 (UTC)

Perhaps bears are just smart enough to keep away from anything that looks dangerous or smells human, but not up to complex route planning. Here is the editthat added the information to the article Bear pit. You might leave a message to the editor on their Talk page or raise the question at the article talk page. Cuddlyable3 (talk) 13:37, 13 April 2011 (UTC)

It's unreferenced and sounds pretty questionable to me. I'd just remove it and maybe leave a note about it on the talk page. --Sean 19:32, 13 April 2011 (UTC)

Mass-energy conversion of the human body

One of the sources I've read claims that the conversion of the human body mass to energy would produce a 200-300 TNT megaton explosion, Another source, however, states that because the basic human body components - carbon, hydrogen, oxygen and nitrogen - have low molecular weight and a lower proportion of internal energy, the released energy would be far less than that from the nuclear weapons. Which is right?--89.76.224.253 (talk) 16:17, 13 April 2011 (UTC)

My suspicion is the difference is in how you are proposing to convert the mass to energy. If you're talking about throwing a human into a human-sized chunk of anti-matter (a more or less pure conversion of mass into energy), then you'd get something like a massive nuclear explosion. If you're talking about any other, more conventional method (e.g. burning alive), you're getting considerably less than that. --Mr.98 (talk) 16:20, 13 April 2011 (UTC)

Going by the mass–energy equivalence, the human body would be around 4.5 to 11 EJ (ballpark estimate for adults - ~50 to ~120 kg). That is, very roughly, between 1000 and 2600 megatons of TNT. By comparison, the biggest bomb ever created by humans was around 50 megatons of TNT. --Link ^(t•c•m) 17:10, 13 April 2011 (UTC)

Evaporated Water Consumption

If one consumes water with absolutely no salts, what are the major disorders one might run into? Most of the disorders found in wiki and google search are caused by a single salt/mineral deficiency. Also what specifically does the body go through when there are no salts present in the water consumed? Does this affect kidneys? Is it true that salt deficiency causes body to borrow salts from bones resulting in calcial erosion of bones in process? —  Hamza  ^{[ talk ]} 17:29, 13 April 2011 (UTC)

Does this help? --TammyMoet (talk) 18:12, 13 April 2011 (UTC)

Actually, I think Water intoxication is more relevent; water intoxication is caused when consumed water causes the electrolytes (salts) in the bodies fluids to become diluted to a dangerous point. --Jayron32 18:53, 13 April 2011 (UTC)

Water intoxication can (and in practice usually does, as it's what people usually drink) involve regular tap water and mineral-containing spring water; it's not confined to demineralized or distilled water, and indeed the trace minerals present in most water don't make an appreciable difference to body or blood electrolyte levels. TenOfAllTrades(talk) 19:39, 13 April 2011 (UTC)

How did the hills of Rwanda form, and how old are the soils?

Rwanda is the "land of a thousand hills", but I can't work out how they were formed. In the UK, AFAIK, most hills were formed by the last glaciation - how do hills form on the equator? On a related note, can anyone find out roughly how old the soils in the south of Rwanda are (we'll be talking millions of years)? _{(google is not being my friend today)} SmartSE (talk) 18:35, 13 April 2011 (UTC)

Rwanda lies in the western branch, pretty much right under those two red triangles

Rwanda lies on the western fork of the Great Rift Valley, see the map to the right. The hills in Rwanda are thus caused by Plate Tectonics, i.e. in this case the area is literally being torn into two pieces as the Somali Plate seperates from the African Plate. Along plate boundaries, you get a lot of geologic activity, from volcanism to subduction to folding, and I suspect that, given where Rwanda is, despite being such a small country, you can find ample evidence of all of this. In geology, all of these process are called Orogeny, which roughly means "mountain birth". Sadly, I cannot find any articles on the Geology of Africa or of the Rwanda region. The template below, filled with redlinks, shows that this is likely a MUCH needed area of Wikipedia. Alas, I hear there is a new Pokeman coming out soon, so I think this is going to be pushed to the back burner for a bit longer while more important work gets done.--Jayron32 18:48, 13 April 2011 (UTC)

The geology of Rwanda is pretty complicated so it probably depends on which hills you are talking about. Generally speaking though, in the tropics like elsewhere, landforms like hills are formed by climate+the nature of the rocks+the biological activity...only much faster. Rock can be turned into soils through chemical weathering and high rainfall, transported away somewhere else either by water or landslides/soil creep/slow flow processes etc pretty quickly in the tropics. Well, that and whatever else is going on geologically that could effect the landscape like rifting, volcanic activity etc etc. Sean.hoyland - talk 19:12, 13 April 2011 (UTC)

I was going to go start linking the geography articles of those respective countries, then I realized... Not the same thing at all. Falconus^{p t c} 22:41, 13 April 2011 (UTC)

Follow-up on cleaning apple juice bottles for recycling

Referring to this question, I am happy to say I finally threw out the first of about half a dozen apple juice bottles.

Using hot water and dishwashing liquid, but mostly repeating the process of filing the bottle with water and adding dishwashing liquid and shaking it up every now and then when I prepared my bottles for recycling, I finally looked at one bottle and realized it was clean enough to go.

The others still look a mess. I suppose I could take them, but someone would have a lot of work to do and they might just reject them at whatever facility processes them.

Yes, it has been over a year. I had no idea.Vchimpanzee · talk · contributions · 18:40, 13 April 2011 (UTC)

It seems that you may have the wrong idea about what recycling is. It's true that if you wash out a bottle and put something else in it you can say that you recycled it, but that is not how a recycling facility does it. At a commercial recycling facility the sorted plastics are melted down and reformed into other products. Any contaminants (such as apple juice and other stuff) are iliminated by processing and melting. Therefor a simple rinse out one time with water will aid the processing slightly. It is not neccessary to make them clean enough to put food into.190.56.16.167 (talk) 20:18, 13 April 2011 (UTC)

Another thought. If your bottles are made of glass the same thing applies. The glass will be smashed up and melted down to make other bottles or maybe a window. You dont need to make them clean enough for food. Germs will not survive the melting process.190.149.154.28 (talk) 21:00, 13 April 2011 (UTC)

Where I live the recyclers say to just recycle the item without any cleaning at all, just leave remaining food or juice on it. I suspect it will get washed later anyway. Graeme Bartlett (talk) 21:39, 13 April 2011 (UTC)

My understand was the washing of recycling was more to prevent Rats or Cats or whatever other street creature from making a mess of your recycling box to get at that last bit of baked beans your tin didn't get clean (similarly to reduce smell given that my recycling is only collected once a fortnight). ny156uk (talk) 22:06, 13 April 2011 (UTC)

Do we feel heat from the sun because of Infra Red, or because of the energy in the entire spectrum?

Whenever people talk about being warmed by infra red radiation from the sun, I always grumble and say that the entire spectrum of light contains energy, and that infra red just happens to be the frequency that warm bodies on earth emit, and so we think of that as heat.

However, I recently read in [12] that "Far infrared waves are thermal. In other words, we experience this type of infrared radiation every day in the form of heat." So this NASA site seems to be saying that there really is a difference between IR light and other light when we are feeling heat from the light source. Is that right? Have I been confused all along? Can we not get warm from just the visible/UV spectrum of the sun (if there is enough of it)?

Thanks! — Sam 71.184.188.110 (talk) 22:30, 13 April 2011 (UTC)

You are not wrong. The sentence you quoted is about perception, we experience some frequencies as vision, and others as heat. But both can cause warming. However there is a somewhat more light energy available as infrared than as visible light (from the sun), so most warming is from the infrared. Ariel. (talk) 22:41, 13 April 2011 (UTC)

But you can have very bright, but "cold" light right? Vespine (talk) 22:44, 13 April 2011 (UTC)

I think the reflectance characteristic of each frequency is very relevant. See Spectral reflectance curve. The frequencies we associate with visible light are readily reflected from opaque surfaces and that is one of the reasons we can see things with the naked eye, but little of the energy with those frequencies is transmitted into the opaque surface to raise its temperature. The frequencies we associate with the infra-red band are not so readily reflected from opaque surfaces so most of the energy in the IR band is transmitted into the opaque surface and so raises its temperature. Also see Infrared#Heat and Thermal radiation. Dolphin (t) 22:55, 13 April 2011 (UTC)

The so called "cold" light is a light bulb that produces little Infrared while producing visible light. Of course, visible light is also a form of heat so "cold" light does produce heat. Dauto (talk) 23:58, 13 April 2011 (UTC)

"But you can have very bright, but "cold" light right?" Not if the source is blackbody radiation. The spectrum emitted because of thermal energy is a well-defined function, and the intensity is rigidly bound to the frequency-distribution. Both of those parameters are determined by the source object's temperature.

A non-thermal source of radiation can provide any spectral distribution; it can radiate at specific frequencies (observable as individual spectral emission lines), or can radiate over a wide range of frequencies, with continuously varying intensities.

But again, if the source is due to thermal emission, then the total amount of energy radiated is defined by the temperature of the source (which also defines the spectral distribution that gets radiated). The mathematical formula that defines this relationship is Wien's displacement law. Loosely speaking, it's not possible to have very bright radiation from a very cold source: decreasing the temperature decreases the total amount of radiated power and changes the shape of the spectrum. Nimur (talk) 00:17, 14 April 2011 (UTC)

Just as an aside - "cold" lightbulbs, such as a cold cathode fluorescent lamp, are not thermal radiators: they fluoresce (producing photon-emission via a totally different physical process), and thus are not a blackbody radiator. This is very different than an incandescent lightbulb. Nimur (talk) 00:20, 14 April 2011 (UTC)

Procession of the Perihelion

Prior to the acceptance of GR what other attempts had been made to explain the peculiar mercurial motion. So far I have:

1. Planet Vulcan
2. Gravity as an $r^{2.00000016}$ instead of $r^{2}$ law

Please add to the list if you know of any! Thanks. —Preceding unsigned comment added by 92.20.205.185 (talk) 22:46, 13 April 2011 (UTC)

For one thing, gravity is a $r^{-2}$ law, not a $r^{2}$ law. (Sorry for the nitpicking). Dauto (talk) 00:07, 14 April 2011 (UTC)

Why not at all, Newton claimed the mass required to produce a unit force at a distance $r$ scaled as $r^{2}$. —Preceding unsigned comment added by 92.20.205.185 (talk) 00:46, 14 April 2011 (UTC)