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May 17

what spider is this?

what species? i saw it in my back yard the picture is [1] i posted it earlier but a picture of spiderman showed up since it had the same name as the commons picture, spidey.jpg. anyways any help identifying it would be awesome. —Preceding unsigned comment added by Spideygonnagetu99999 (talk • contribs) 03:47, 17 May 2009 (UTC)

I have never seen that before (I am in the UK), but I am assuming by the time stamp that you are more West from me, and therefore probably North America. Try this database. They have photos. Good luck.--KageTora - (영호 (影虎)) (talk) 04:37, 17 May 2009 (UTC)

My intuition tells me it's in Linyphiidae family, but I can't be sure. Sorry. --Dr Dima (talk) 07:30, 17 May 2009 (UTC)

I'd go for an Orb-web spider, possibly a Barn spider, it would help to have some idea of size. Mikenorton (talk) 12:02, 17 May 2009 (UTC)

Can you please describe the web of the spider you are asking to identify? That will help a lot. --Dr Dima (talk) 22:24, 17 May 2009 (UTC)

This spider is in my yard in Richmond, California its about 2-3 inches from front feet to back feet, the main part of its body being 1.5-2 inches, and its about 1-1.5 inches wide. the web is big and roughly hexagonical but more than six, like 18 to 20 ended shaped. —Preceding unsigned comment added by Spideygonnagetu99999 (talk • contribs) 23:38, 17 May 2009 (UTC)

This sounds a lot like an orb-weaver indeed. Orb-weaver webs are rather large (usually 1-3 feet across), near-vertical, and look something like this. Individual linyphiid webs, on the other hand, are small and sheet- or tent-like. Also, 1.5" size is about right for Araneus sp. (a typical orb-weaver), but huge for a linyphiid. --Dr Dima (talk) 04:40, 18 May 2009 (UTC)

Variable Frequency Sine Wave Generator

I need to create a sine wave generator circuit, whose frequency output f will be proportional to the input voltage/current. In a Wein-bridge oscillator, if in place of the resistance, a transistor is used, operating as an amplifier, with the gate connected to the frequency control terminal, will it suffice? —Preceding unsigned comment added by 218.248.80.114 (talk) 06:30, 17 May 2009 (UTC)

You are wanting a voltage controlled oscillator or VCO. You can buy ICs with this built in, or as you suggest a MOSFET or field effect transistor could be a resistance controlled by a voltage. If you want to you can use a capacitor controlled by a voltage, such as a reversed biased diode (varicap), this can very quickly change the frequency. Graeme Bartlett (talk) 08:08, 17 May 2009 (UTC)

You may consider designing an Arbitrary waveform generator to produce a sine wave output. The only active analog circuit this requires is a Digital-to-analog converter which is available as a single fully-specified component. It would receive from memory (RAM or ROM) at a relatively high clock rate samples of the wave to be generated. The memory would be loaded, or the clock rate controlled, by a digital controller that includes an ADC for the input voltage/current. Cuddlyable3 (talk) 13:16, 17 May 2009 (UTC)

I've used a varac diode to tune the resonance of a voltage-controlled oscillator. This is conceptually the simplest VCO, because your applied voltage directly changes the resonant frequency of the LC-tank, but it is complicated by the nonlinear and uncooperative behavior of a varac. Nimur (talk) 19:59, 17 May 2009 (UTC)

Human digestive system - top speed? ;-)

So I was curious how fast the human digestive system works, and read the article - apparently 40~50 hours? A lot longer than I'd have guessed. What I'd really like to know, though, is how fast something can run through you... I'm clearly thinking about really bad diarrhea here...

Surely I'm not the only one who has ever had really bad diarrhea and began to think back over what all they'd eaten trying to pinpoint the source?

I did an archive search for "diarrhea speed" but only got lots of discussion about traveling at the speed of light, you sickos! ;-) —Preceding unsigned comment added by 61.189.63.198 (talk) 07:28, 17 May 2009 (UTC)

A patient preparing for a Colonoscopy must stay on a clear liquid diet for a day, followed by a day of purging using laxitives and lots more clear liquids. -Arch dude (talk) 09:04, 17 May 2009 (UTC)

Ever had a barium meal? It takes less than two hours for that stuff to come out and you need to make sure you are near a toilet when it starts!--KageTora - (영호 (影虎)) (talk) 09:36, 17 May 2009 (UTC)

I think some gastric infections (e.g. Norovirus) may affect other parts of the digestive system, in that something might stimulate strong peristalsis to get whatever is causing it out of the system. Digestive Transit (for which we don't have an article!) is the name given to the time taken for food to pass out of the system. It varies between people: if you don't drink enough and/or are constipated, things will take longer to leave you (if at all!). --TammyMoet (talk) 10:55, 17 May 2009 (UTC)

For estimating normal speed, eat some sweetcorn and time thje result. 78.146.103.200 (talk) 16:48, 17 May 2009 (UTC)

Also, the GI tract is not a FIFO queue. Different types of food have different characteristic time-scales. It's possible for a faster item (like soup) to pass faster than a slow item, like steak. By the time it's in the intestine, everything's pretty soupy anyway. Nimur (talk) 17:04, 17 May 2009 (UTC)

A search for "diarrhea speed" gets stuff about the speed of light? Sounds like a joke from Spaceballs (Sure glad they called it "ludicrous speed" instead. :-) )Somebody or his brother (talk) 00:23, 18 May 2009 (UTC)

3 PHASE IN ELECTRIC POWER SYSTEM

I want to know why the electric powe generator is designed to be 3 phase not more than this? in other way why is the angle between Phase and the other must be 120 degree?~ thank u —Preceding unsigned comment added by 3ateka (talk • contribs) 10:13, 17 May 2009 (UTC)

The article for this is Three-phase electric power. This is an engineering decision. It isn't impossible to use fewer, or more, phases, but using three phases is most cost-effective. It is the solution that needs the least conductor material, and if you're going to build a power line across hundreds of miles, conductor material (copper) will be the decisive cost factor. --dab (𒁳) 10:34, 17 May 2009 (UTC)

Nikola Tesla used two phase power pretty effectively to run his induction motors. But when you add the third phase, starting the motor is easier and the flow of energy to the motor is steadier. There is little benefit to adding more phases, considering the higher cost of conductors, insulators, and structures, not to mention circuit breakers, transformers, etc. Edison (talk) 20:52, 17 May 2009 (UTC)

In the US, most residences only have one 60hz phase. We use both poles of one phase to get to "pushes" per cycle, so flourscent bulbs flicker at 120hz. the high-voltage is delivered to the transformers in the neighborhood via a single conductor, and each home is connected to teh transformer with two power conductore (the phase nad the anti-phase) plus a neutral. In industrial areas, the powe company delivers all three phases using three high-voltage wires that are 120deg out of phase with each other. I think motors can use both poles of each phase, for a total of six "pushes" per Hz. So in industrial areas, more capital is spent on the wires but less is needed for the big motors. for residential-type applications (motors below about 2hp), the cost differnce between the more expensive single-phase motors and the cheaper three-phase motors is small-to-nonexistent, so the whole thing makes economic sense. -Arch dude (talk) 23:18, 17 May 2009 (UTC)

With three phase, the torque is continuous. With single phase, (and maybe 2 phase, like Tesla's early installations) the torque pulses. Edison (talk) 19:02, 18 May 2009 (UTC)

Egg crystals?

I left a little bit of whisked egg in a bowl overnight in a warm, dry room, and it has formed what appear to be crystals, although they are a little cloudy (photo at http://www.benjamin-mills.com/photos/2009/egg-crystals.jpg). Is this really a crystalline solid, or just a kind of flaky amorphous solid?

Ben (talk) 16:39, 17 May 2009 (UTC)

Looks like a beautiful set of radial cracks caused by the drying out of the egg, like dessication cracks in mud. The radial symmetry comes from the shape of the bowl and the thickness of the layer. On a completely flat plate the cracks would have been roughly hexagonal, like in the basalt of the Giant's Causeway (though of course they're a result of cooling rather than drying). Mikenorton (talk) 17:27, 17 May 2009 (UTC)

I agree - not all geometric patterns are due to crystal lattice structures. This appears to be uniform fracturing due to dessication. Nimur (talk) 19:56, 17 May 2009 (UTC)

OK, thanks guys.

Ben (talk) 22:58, 17 May 2009 (UTC)

This also looks like the basis for a really good science-fair project for elementary school kids to demonstrate dessication cracks. -Arch dude (talk) 23:24, 17 May 2009 (UTC)

Little gas poker

What do you call the hand-held wand used for lighting candles and gas stoves? It has a liquid gas container and a piezo ignition. I thought it was a gas poker, but Googling suggests that that is a more heavy-duty device for starting fires. I want to find one on line but I don't know what they're called (in the UK.)--86.25.195.233 (talk) 17:55, 17 May 2009 (UTC)

Piezoelectric gas lighter or static electricity generator. Axl ¤ [Talk] 19:03, 17 May 2009 (UTC)

(e/c) Could it simply be known as a lighter? Lakeland (that nirvana of kitchen goods) currently has on sale something called a Handy Lighter which performs that function, although it doesn't mention what ignition method is used. Kitchen lighter also produces some relevant results on Google. --Kateshortforbob 19:09, 17 May 2009 (UTC)

What is the name of this bird?

Does anyone know the name of this bird, photographed in Austria? Thanks a lot... --Edcolins (talk) 18:48, 12 April 2009 (UTC)

• 
  Unknown bird, first picture.
• 
  Unknown bird, second picture.

It looks like a Common Blackbird. Axl ¤ [Talk] 19:17, 17 May 2009 (UTC)

From the size of the eye, its posture and the rather fluffy plumage at the base of the breast I'd go for an Alpine Chough. Mikenorton (talk) 19:29, 17 May 2009 (UTC)

Yes, you're right, Mike. The colour of the legs also fits. Axl ¤ [Talk] 19:32, 17 May 2009 (UTC)

Many thanks! Great! --Edcolins (talk) 19:44, 17 May 2009 (UTC)

HIV and preeclampsia

I have been trying to get a dissertation topic for Part II FMCOG relating to HIV and preeclampsia since 80% of antenatal patients I attend to are HIV positive. Please, could you suggest some topics.41.219.251.119 (talk) 20:51, 17 May 2009 (UTC)

LOL

I've just been watching a comedy show on TV. I notice that at the funny bits all the audience laughs at the same time, and rarely at other points. Are funny things just funny, or do we accept cues from other people that encourage us to laugh at the same time out of some kind of evolutionary advantage. When I watch comedies alone I often find that I never laugh througout the whole programme, but appreciate which situations are humourous. Also, I have heard that laughing benefits us in bearing our teeth, which is an aggressive response to a situation as seen in many primates. Your thoughts, please, russ (talk) 20:58, 17 May 2009 (UTC)

Most TV shows have a "laugh track" with recorded laughter, or a "live studio audience" including the writers and friends of the cast who laugh predictably at the appropriate places. In 1939s when NBC in the U.S. started their experimental broadcasting, there was a concern that theatrical movies would not play well on TV if comedies, because in the theater, as in live theater, there is a range of latencies for people to figure out the joke and laugh, and the movie actors would pause after a gag (as on stage) to allow for that before the action moved on. Laughing out loud may be something of a group phenomenon. The concern was that the solo home viewer would be put off by the resulting slow pace, but it would be less of a problem with group viewing. The "laugh track" can act as a filler to avoid the latency problem. It also helps the clueless understand that something funny happened. The humorist Mark Twain had a standard joke he used at the beginning of an appearance to measure an audience. Their latency in getting it and laughing told him whether to dumb down his material and use broad humor for a dullard audience, or to use his more demanding material. Edison (talk) 21:25, 17 May 2009 (UTC)

Most shows with live audiences employ applause signs to tell the audience when to applaud and when to laugh. The audience also never goes in "cold" - before the action starts the stage manager or someone similar will always stand in front of the live studio audience and give them directions on when it's appropriate to laugh, etc. Frequently for comedy shows, (especially the late night shows like the Tonight Show) they will also have a warm-up comedian* to get the studio audience in a good mood. (* Amazing - Wikipedia doesn't seem to have an article on warm-up act)-- 128.104.112.117 (talk) 21:52, 17 May 2009 (UTC)

We do laugh more openly when there are others to hear it. And as for the way primates bare their teeth, it is apparently more to do with a reassurance that you mean no harm. A fear grin.Popcorn II (talk) 22:40, 17 May 2009 (UTC)

I think we take cues from others, but I have some admittedly personal observation that shows that there are always those who are slower and faster, even if not warmed up. The warm-up guys are there mostly, I think, to get the slower ones up to speed. Otherwise, you'll have a situation like what happened with a friend. He's the stoic kind who always tries to keep his cool and usually only grins or chuckles. Well, we were all laughing at one of those silly B movies and making fun of it and he sits there reall quiet for about 20 minutes, then suddenly bursts into a laughing fit that's like all his laughter came out at once. He kept getting the cues, but something in his personality was holding him back, till all those cues caught up with him.Somebody or his brother (talk) 00:34, 18 May 2009 (UTC)

yes, there are laugh tracks and prepared audiences, but also laughter is strongly contagious. Looie496 (talk) 02:28, 18 May 2009 (UTC)

After a performance has been recorded with a live audience the sound track can be "sweetened" by adding laughter or applause to the genuine reactions. It is hard to detect when that is done skilfully but on occasions audience reactions seem suspiciously mistimed. Cuddlyable3 (talk) 13:11, 18 May 2009 (UTC)

You know that this laughter is totally faked in at least some shows because it's added to shows where no live audience is present - and it sounds exactly the same. I recall, for example, that when we watched M*A*S*H (TV series) in the UK, it was broadcast without the canned laughter. I couldn't believe it when I first came to the US and watched the exact same shows with canned laughter...it totally changed the show from something rather pointedly anti-war to just another sit-com. Weird. SteveBaker (talk) 13:33, 18 May 2009 (UTC)

Magic and illusion

I have several questions about magic: 1- What's the difference between magic and illusion?

2- Is their a true magic? I mean is it true what the media says and what is sometimes posted on wikipedia about magicians such as David Copperfield and the Liberty Statue? If so how can we explain it physically?

Thanks awfully..--Email4mobile (talk) 21:00, 17 May 2009 (UTC)

1. "Magic" generally refers to one of two things: illusionism, which is essentially the art of fooling people into thinking that they're seeing something that appears to be impossible or supernatural, whereas in reality it's all done with trickery and clever misdirection, or paranormal magic, which actually is supernatural -- that is to say, it actually violates the known laws of reality. The latter, it should be stressed, is something that a lot of superstitious people certainly believe in, but of which there exists no actual evidence. The former is illusion and the latter is delusion, you could say. (It's particularly important to understand that there's no evidence of someone actually performing supernatural acts of magic, but there are many, many instances of people claiming to have magical powers and being exposed as liars and frauds. That in itself doesn't prove that there's no supernatural magic, of course, but when there's no evidence for something and a lot of the people who claim that there is are exposed as liars, it doesn't exactly make an argument for its existence.)

2. I don't know what you mean when you refer to what the media says and what is sometimes posted on Wikipedia. I can tell you, however, that David Copperfield did not actually make the Statue of Liberty disappear, he just made it look like it did. That's an illusion. We don't know exactly how he did it, though, because like most magicians, Copperfield likes to keep his tricks to himself, but William Poundstone's explanation for how it was done (explained in general terms in the article I just linked to) seems fairly sensible. If that's how he did it, it's a classic example of misdirection, an illusionist's most important tool: the idea that Copperfield would actually move the audience instead of the statue without anyone noticing is just so audacious that most people would never even consider it! But it could certainly be done.

So no, I don't believe that there's any magic in the supernatural sense. There certainly isn't any hard evidence of magic -- just stories people like to tell, but as the Copperfield example above illustrates, even if people really believe in something, that doesn't mean it actually happened. It's easy to fool people when you know how, and in many cases, the more outrageous the trick, the more willing people are to believe it. -- Captain Disdain (talk) 21:38, 17 May 2009 (UTC)

Some think there's a difference, some don't. -RunningOnBrains 00:41, 18 May 2009 (UTC)

I think that one of the most convincing reason to disbelieve these 'magic' acts is that if the magician could truly perform them, he'd be able to do so in much clearer, testable situations. The industrial value of being able to make objects weighing hundreds of tons simply 'vanish' - or to have people who could fly or create coins out of thin air would be extensive and revealing the techniques involved would earn the performer billions of dollars. The fact that they restrain themselves to a simple stage presentation is very telling. All of this quite aside from the violations of scientific laws of all kinds that would be required. So we can be VERY confident in saying that (without exception) magic tricks are tricks - and most magicians are only too happy to admit that. SteveBaker (talk) 00:43, 18 May 2009 (UTC)

The method David Copperfield used to make Lady Liberty disapear is a known, if rather elaborate conquerors' trick. This Article explains it, if you really want to know. APL (talk) 02:26, 18 May 2009 (UTC)

I refer to the same method above (except in our own article), but our article says that it's speculation, not actual proof of how he did it. I agree that it's probably how it was done, but in the interests of the accuracy of our article -- is it actually sure that this is how it was done? -- Captain Disdain (talk) 07:41, 19 May 2009 (UTC)

Thank you very much, gentlemen for this valuable emphasizing. --Email4mobile (talk) 06:53, 18 May 2009 (UTC)

• Magicians generally refer to large stage effects (tricks) using big boxes and large props as illusions, although some smaller tricks can also be called illusions. - Mgm|^(talk) 11:30, 18 May 2009 (UTC)

As the aforementioned Gob puts it... "It's an illusion, Michael. A trick is something a whore does, for money." -- Captain Disdain (talk) 14:05, 18 May 2009 (UTC)

Lye in a swimming pool

(Caution: do not try this at home.) On CSI Miami, in Dissolved (CSI: Miami episode) someone added enough sodium hydroxide to a swimming pool to make the pH a bit above 12.3 (per the CSI Ph meter). How many kilograms of sodium hydroxide would have to be added to a home swimming pool of say 100,000 liter capacity to achieve that alkalinity? How many liters of supermarket vinegar (say 8% acetic acid) would it take to get the pH back down to 7.0? It did not look like they poured very many gallons of vinegar to neutralize the lyewater. Would the high alkalinity solution instantly break a glass beaker if poured into it as in the episode? Would concentrated lye water have a strong smell? Edison (talk) 21:16, 17 May 2009 (UTC)

NaOH is awfully strong, but dilution in 100,000 liters is no small effect. If my calculations are right, to make a pH of 12.3, you only need a molarity of 0.02, or about 0.8 grams of NaOH per liter of water. In a 100,000 liter swimming pool, that gives you about 80 kilograms of NaOH. More to the point, how did somebody add the NaOH? It's much more likely that it was not added as a pure solid, but added as a more concentrated liquid (like Lye). Since lye is only about a pH of 13, you would basically need to fill most of the swimming pool with it to reach a pH of 12.3. Nimur (talk) 21:51, 17 May 2009 (UTC)

Glass, especially chemical lab beakers made of pyrex, does not react with sodium hydroxide. Lye does have a distinctive smell, and if the pool were full of it, it ought to be obvious. Nimur (talk) 21:54, 17 May 2009 (UTC)

And, while we are debating the validity of the scientific events in a TV show whose extent of scientific reality falls somewhere between "just making shit up" and "faking it", droping that much NaOH into a swimming pool will likely be exothermic enough to boil the water, and spatter everyone in the area with a nice boiling, skin dissolving solution of sodium hydroxide. Yum, yum. --Jayron32.talk.contribs 23:04, 17 May 2009 (UTC)

Nimur, the paper-thin things I've accidentally left in base-bath overnight or flasks etched with melted NaOH would disagree. Now of course that's not how the typical person would use such a material:) DMacks (talk) 02:33, 18 May 2009 (UTC)

That analysis only works if the pool water is not buffered. If the owner has added a pH buffer to the pool water, or simply lives in a region where the tap water naturally contains buffering agents, you'll need to add additional NaOH to overcome the buffering effect. How much extra is hard to say, as water buffering capacity is usually measured by alkalinity, which assumes that you're adding acid, not base. -- 128.104.112.117 (talk) 18:16, 18 May 2009 (UTC)

Why would they use such a weak acid as vinegar to neutralise it? You can get "Muriatic Acid" (weak Hydrochoric acid) at pool supply stores - it would be much better at the job than vinegar! SteveBaker (talk) 00:19, 18 May 2009 (UTC)

Red Devil is nearly pure crystalline sodium hydroxide, you can buy it in any grocery store, and it's cheap -- on the order of a dollar a pound to the best of my recollection. So based on the numbers above you could probably do it for around $500 or less. Looie496 (talk) 02:43, 18 May 2009 (UTC)

Saturated NaOH will etch glass over time, but does not react violently. And making a pH 13 solution of NaOH by dumping pure solid into water is nowhere near exothermic enough to cause boiling (unlike sulphuric acid!), possible just because it takes to long to dissolve. A higher concentration of a weak acid probably would be just as good for such a neutralisation, as the act of neutralising would pull the equilibrium to one side, so the lower dissociation constant in water is not a factor. Was the pool being used to kill people, or just dispose of bodies? Pure NaOH is corrosive, but can still be picked up without gloves (not recomended though!), so i'd guess wouldn't kill people quickly enough.YobMod 08:00, 18 May 2009 (UTC)

• 100,000 liters is more than even some large aquariums. It's not a reasonable size for a home swimming pool. - Mgm|^(talk) 11:27, 18 May 2009 (UTC)

One cubic meter is 1000 liters, so a pool 10mx10mx1m would have 100,000l, as would one 10mx6mx1.5m (well, close enough). Large, but not impossible for a home pool.--Stephan Schulz (talk) 12:14, 18 May 2009 (UTC)

Yeah - our home pool is 26,000 gallons - that's 98,000 liters. It's not by any means a huge pool - if you had a part that was deep enough for diving (which many of my neighbours do) then it could easily double that. SteveBaker (talk) 13:21, 18 May 2009 (UTC)

On the show, they neutralized the lye with a few gallons of vinegar. But a lab beaker shattered when the lye solution was poured in it and a live human was "boiled" to death. Edison (talk) 18:59, 18 May 2009 (UTC)

Meh. I use 3 M NaOH on a daily basis, which is 15 times as concentrated as here. Spilling it on the skin has no effect, except the usual soapy feeling from bases (not even peeling the next day, like most acids), so i very much doubt it could kill someone unless they are held in it for a while. And the 3 M solution i use is poured from Schott bottles to measuring cylinders to beakers - none of them ever break or even crack slightly. Overall seems a poor murder method indeed!YobMod 07:38, 19 May 2009 (UTC)

May 18

Dry skin itch

Why, precisely, does dry skin cause itching? What physical or chemical factors are involved? 69.224.113.202 (talk) 02:22, 18 May 2009 (UTC)

OR: What causes itching is people asking about itching on the Ref Desk - damn you! --Tango (talk) 02:26, 18 May 2009 (UTC)

Desquamation. I would say that the itching is an allergic reaction to dead epidermal cells, but researchers put it like this. Cuddlyable3 (talk) 11:45, 18 May 2009 (UTC)

Evidence of a civilization a billion years ago

Just a thought exercise: Assume that a civilization existed a billion years ago (and continued for about the same length of time as our own achieving roughly the same level of technology that we now have). Then, for some mysterious reason, this civilization disappeared. My question is: would there be any evidence that this imaginary civilization ever existed? —Preceding unsigned comment added by 209.161.213.227 (talk) 04:18, 18 May 2009 (UTC)

Well, sure. There'd undoubtedly be some physical artifacts left, even though much of it would be destroyed by the ravages of time. They'd show up in the fossil record, one way or another. More importantly, the ecological impact would probably be detectable. (A similar civilization couldn't have existed back then, though, because at the time there was really no ecosystem that civilization could've had an impact on, so the parameters would just have to be different.) I don't know if it would be anywhere near enough for anyone to actually be able to tell what the civilization was like, but I think there'd be evidence of its existence if one knew where to look and how to interpret what they were seeing. Actually, come to think of it, perhaps the most obvious piece of evidence would be that life on Earth would be completely different from what it is now: whatever bacteria and whatnot those people would leave behind would be the basis for our own life. Our primordial soup could literally be someone's leftover soup. -- Captain Disdain (talk) 09:42, 18 May 2009 (UTC)

Anything 'they' might have had or made back then would not likely be visible on the surface of the planet. Everything would be way underground buried deep in rock, as would any fossils of the creatures which had this civilisation. Life was around at that time, and had been around for at least 1.5 billion years before that, so it is certainly not impossible that some creature or another developed some sort of civilisation, which then got wiped out in some way or another. Changing the time frame to just 500 million years ago, we could say the same. It would, however, be very hard to detect, unless you knew what you were looking for. On a related note, you may want to look at this and see what you make of it. --KageTora - (영호 (影虎)) (talk) 11:13, 18 May 2009 (UTC)

Suppose the ancient civilisation having technology similar to ours did the same things (why not?). Expect aliens to arrive about now, attracted by the Arecibo message and asking if we want our probes back, like this. Cuddlyable3 (talk) 11:21, 18 May 2009 (UTC)

As the oldest fossils are "several billion years old", it seems likely that some evidence of human life would certainly remain. As many man-made objects are less susceptible to decay than living organisms, this would present evidence for our technological achievments (even simple mass-produced trash is dependant on a huge infrastructure). This, along with the planet-wide climate effects would make deduction of a widely-spread technological society pretty conclusive, imo.

Off course, none of this necessarily applies to any past civilisation, as they could easily have been entirely arable/biodegradable. Civilisation does not require an industrial revolution.YobMod 11:28, 18 May 2009 (UTC)

Having said that, there are a number of "ooparts" which bear consideration. I'm not saying I am a believer, but it would be interesting if we could find an explanation for them which fits our current 'knowledge' of history, or maybe we would have to rethink what we 'know'.--KageTora - (영호 (影虎)) (talk) 11:41, 18 May 2009 (UTC) I fixed the oopart link. Cheers.Cuddlyable3 (talk) 12:32, 18 May 2009 (UTC)

Cheers. I wondered why it wasn't working.--KageTora - (영호 (影虎)) (talk) 12:36, 18 May 2009 (UTC)

The book The World Without Us and the Discovery channel documentary that comes from it: "Earth Without People" follows the unlikely scenario where all humans suddenly vanish. That's not a very likely one - but if there were some kind of mass extinction due to (say) a massive meteor strike - then the story it tells of what remains of us after thousands of years is applicable - and it's pretty chilling. Aside from artifacts left on the moon, mars and out in deep space - there doesn't seem to be much that would survive. If that's true - then it might very well be that a sufficiently ancient civilisation would be very hard for us to detect. The fact that we find fossilised bones from the time of the dinosaurs (for example) leaves us with the impression that we'd also find fossilised Internet Routers and other indicators of civilisation. However, in reality, fossils are extremely rare - if a civilisation like ours were only to last (say) 100,000 years - then the probability of finding something within that window would be pretty tiny...the fossil record simply isn't that reliable. We have actually discussed this question before - and my opinion remains that the best place to look for such evidence would be out in space at places called Lagrange points - which would be a natural place to leave things that you wanted people to find a hell of a long time into the future. 13:16, 18 May 2009 (UTC)

Are even L-points stable on scales of a billion years? --Tango (talk) 14:54, 18 May 2009 (UTC)

I'm reading a book that depicts a similar scenario where aliens come to visit Earth 200 million years from now...and the only evidence they find of a past civilization is on the Moon (but it is difficult to tell if the artifacts were left there from a civilization on Earth or from another intergalactic traveller). Also, it really isn't a mystery why past ancient civilizations collapsed, leaving behind their ruins as if they disappeared suddenly: the biggest factors are war, famine, environmental depletion (think Easter Island), and climate change. The Arecibo message was aimed at the globular cluster M13, but it would take about 50,000 years for any reply message to reach Earth, assuming that the message actually arrives at its target, which it probably won't, because the motion of the cluster around the galaxy would likely have carried it away from the path of the message by then. ~AH1^(TCU) 16:06, 18 May 2009 (UTC)

A billion years ago all life was microscopic life, with stromatolites about the only macroscopic evidence of life. So, essentially any macroscopic fossil would stand out as evidence of the unexpected. If you are positing a civilization of people that spring up out of nothing (e.g. aliens landing on the Earth) and lasts for only 10000 years, then the duration of their existence and their spread might well be very hard to find in the fossil record. On the other hand, if you are imagining a civilization that arises organically, then it is hard to imagine doing that without developing a wider ecology of macroscopic life. For example there are far more trees on Earth than people. A naturally developed macroscopic ecology would be expected to have taken many millions of years. If you include all of those associated forms of life and their long history, then it would be shocking not to have some evidence of that in the fossil record. If we assume macroscopic life is a prerequisite for civilization, then I think we can rule out the development of civilization a billion years ago. Dragons flight (talk) 17:28, 18 May 2009 (UTC)

coefficient of volume elasticity

is there anything called coefficient of volume elasticity?? —Preceding unsigned comment added by 122.50.137.137 (talk) 05:10, 18 May 2009 (UTC)

I don't think there is anything called volume elasticity and I am sure there is nothing called coefficient of volume elasticity - DSachan (talk) 11:16, 18 May 2009 (UTC)

Possibly you are thinking of the elasticity tensor or one of the elastic moduli such as the bulk modulus. Gandalf61 (talk) 12:51, 18 May 2009 (UTC)

Here is a definition of the coefficient of volume elasticity. The term is also used in biophysics, as in this abstract. Isn't Google great? Looie496 (talk) 18:44, 18 May 2009 (UTC)

dimensional analysis

my teacher set me this question:

using dimensional analysis, check whether the relation is correct.

S_nth = u + a/2(2n - 1)

where the symbols have their usual meanings

i know that u stands for initial velocity and a for acceleration, but what about n and S_nth??? —Preceding unsigned comment added by 122.50.137.137 (talk) 05:16, 18 May 2009 (UTC)

This is a formula in Kinematics ( study of spped, distance, tima and acceleration ) for the distance traveled in the nth second. Say you are dropping a ball from a cliff. If it has fallen 5m after 1s, 20m after 2s, and 45m after the third second, the distance travelled in the first second is 5m, the distance travelled in the second second (ignore the pun) is 20 - 5 = 15m, and the distance travelled in the third second is 25m. So your Snth has the same dimension as S, distance. n is the number of seconds, so you should be able to tell its dimensions. Also don't forget to sign your posts by typing 4 '~'s in the end...Rkr1991 (talk) 05:29, 18 May 2009 (UTC)

I don't like this business of "where the symbols have their usual meanings" because 'n' isn't often used as a symbol for 'time' and S_nth isn't a "usual" symbol at all (although 'S' is conventionally used for a distance travelled). That makes this question very hard to answer definitively.

Does the constant '1' have a dimension (like '1 second' or '1 hour')? No - because if 'n' is a time - then (2n-1) is only dimensionally correct if '1' is also a time. As Rkr1991 explains it, the equation is only valid if the units happen to be seconds. If you were to provide 'n' in hours - then it would tell you the the distance travelled in the n^th hour...but only if that magic '1' constant is now assumed to be in hours.

But as Rkr1991 explains it, there is a 'get out' clause here. If the equation is truly stated to describe: the distance travelled "in the n^th second" then that leaves open the possibility that 'n' is "the number of seconds elapsed" - not "the elapsed time" (a subtle distinction that leaves n dimensionless and makes (2n-1) work). Using 'n' as a dimensionless number is certainly reasonable here because 't' would be the more usual symbol to use for a 'time'...but then the dimensions of 'u' and 'a/2(2n-1)' don't match anymore because u is a velocity (distance.time^-1) and a is an accelleration (distance.time^-2) so (2n-1) MUST be in units of time or else you can't add u to a/2(2n-1) legally. So that says that the units of 'n' MUST be time - and that constant '1' has to be in the same units as 'n' - which is unspecified in the equation. Furthermore if S_nth has units of distance - then the equation fails again because 'u' is a velocity and 'S' is a distance. If 'a' were zero then you'd have 'S_nth = u' - which doesn't work if S has units of distance. But if we believe Rkr1991's description of what the equation means then "S_nth is the distance travelled over a second" - which is a velocity - not a distance.

I think the equation is dimensionally incorrect - although the way Rkkr1991 explains it, there is some wiggle room. It would produce a meaningful answer providing that 'n' is defined as 'the time in seconds' and not 'the time' - and providing that '1' is really '1 second' and that S_nth can truly be construed to be a velocity. I think the question could have been better phrased - but the answer should be "No". SteveBaker (talk) 13:00, 18 May 2009 (UTC)

I agree with you, but to play devils advocate - the 2 could have units of time, and the (2n-1) not. The presence of constants in things like this always creates room for confusion. --Tango (talk) 15:00, 18 May 2009 (UTC)

Is this equation meant to be a discrete time version of kinematics? I really really don't like this "symbols have their normal meanings." That's a very meaningless statement. In the papers I've been reading lately, s is "slowness" (reciprocal velocity). And a is the anisotropy vector. And n is the Normal Move Out operator, or it can be almost anything else. You should verify the meaning of all of these variables, or you're really lost. "Conventional" variable names are only relevant in very specific contexts. Nimur (talk) 15:55, 18 May 2009 (UTC)

Well let me tell you that this equation is perfectly correct, both dimensionally as well as physically. S_nth is the distance traversed in the nth second, not the average velocity. Note the distinction. So it has dimension L. The only trick in the question is the first term on the right hand side. It is not velocity. It is Velocity seconds. Velocity multiplied by one second. This will have been given in the question, because it is not the usual meaning. n is a number, dimensionless. So now the rest should be obvious. Though it is not mentioned here, i'm quite confident the teacher would have mentioned that u is velocity seconds in class. This is a standard equation for distance traveled in the nth second, so it is obviously right. Rkr1991 (talk) 05:27, 19 May 2009 (UTC)

The notation is far from standard, so I'm guessing "usual meaning" means usual meaning in that class, so we can't really tell if the question is right because we don't know the notation. Sure, we can come up with interpretations that make it correct, but that doesn't mean those interpretations are the "usual" ones. --Tango (talk) 15:52, 19 May 2009 (UTC)

Well, Rkr1991 can hypothesise that our OP has miscommunicated the question to us - but for absolute 100% certain, 'u' is not "velocity seconds" in it's "usual meaning" in the context of dynamics/ballistics questions. The usual meaning is found in equations like:

S = ut + at²/2

...where the meaning of 'u' is "the initial velocity"...and our OP even tells us that explicitly. If the meanings of these terms are not "the usual ones" then all bets are off. 'u' could be the phase of the moon, 'a' the dissolution rate of resublimated Thiotimoline, 'n' the airspeed an unladen swallow and 'S' the amount of wood a woodchuck could chuck if a woodchuck would chuck wood. So either our OP has the question wrong - or the question was written incorrectly - or the answer is "No". Pick any one - but the answer isn't "Yes". SteveBaker (talk) 20:24, 19 May 2009 (UTC)

The reason i say the equation is dimensionally right because of two reasons : (i) Any equation which is right is also right dimensionally. You can derive the given equation yourself, writing the formula S = ut + at²/2 for t = n seconds and t = n+1 seconds and then subtracting. Note that the n seconds part cancels out in the first term, which is why u here represents velocity seconds, not velocity. This equation is pretty much standard, and it would be against my senses to call it wrong just because the teacher has told usual meanings. (ii) The OP has said usual meanings. For this particular formula, this is the usual meaning. Now, since the dimensions of each quantity has not been explicitly stated, there is a very high chance that the teacher has actually mentioned this in class. Ya, you guys are right, for the exact question the OP has asked, the answer is NO, but i am pretty confident that u here refers to velocity secons and NOT velocity. So if this question was asked to me in an exam, i would right YES as the answer. Having known a formula, my instincts bristle at having to write it as not correct. But i think this question really doesn't require so much debate. You got to ask the teacher what she meant by u. The other confusions, regarding n and 1, should be quite obvious by now. n is a number. So is 1. Rkr1991 (talk) 04:52, 20 May 2009 (UTC)

I disagree. If you derive the equation the way you suggest then 'n' has the dimension of time and the '1' in(2n+1) is really 1 second - I don't see a unit against that constant in that equation - which means that it's dimensionally incorrect...not because the equation is incorrect per-se but because the person who wrote it down omitted the 'time' dimensionality for the constant '1'. You certainly can't argue that the "usual meaning" of the symbol '1' is "1 second" - so the equation is quite simply wrong. If I take it as written and choose 'hour' as the unit of time for 'n' and whatever contorted units you then arrive at for 'S', 'u' and 'a' then it produces the wrong answer. It's a fundamental precept of dimensional analysis that you can't add a dimensionless constant to something that is not itself a scalar. This equation (as written) is therefore incorrect...and I'm quite sure that's what the teacher expects you to point out. SteveBaker (talk) 11:58, 20 May 2009 (UTC)

Can you please explain how n will refer to time here ? Remember the formula is for distance in the nth second. n here is clearly a number. When you substitute t in the equation, do not make the common mistake that t is n. t is n seconds. Catch the subtle difference. But to accept whether the equation is right dimensionally or not lies with each individual, but certainly it should be clear that n and 1 are numbers. Rkr1991 (talk) 12:35, 20 May 2009 (UTC)

'n' has the dimension of time because of the way you derived this equation. Look above - you said it yourself: "You can derive the given equation yourself, writing the formula S = ut + at²/2 for t = n seconds and t = n+1 seconds and then subtracting. - you can ONLY substitute t=n and t=(n+1) if 'n' (and '1') is in the same units as 't'. Hence if 't' is time - then so is 'n' - and so must be '1'. So your derivation of the equation is wrong unless both 'n' and '1' have time as their dimensions. You may be about to claim that you aren't setting t=n but t=nseconds - thereby making 'n' into a scalar - but that's just introduced a non-scalar constant so that 't=n.k' where k=1second (it has to be like that in order to make your 't=n' substitution be dimensionally correct) - but then the problem is that when you do the subsitution, you get "S = u.n.k + a(n.k)²/2" - which would leave the equation our OP gave us littered with k's which would be carrying these '1 second' constants and making it dimensionally correct...but it most certainly doesn't have those...which is why it's incorrect. SteveBaker (talk) 18:16, 20 May 2009 (UTC)

Well, i'm sorry, but there appears to be a lot of confusion over nothing. Lets forget for now whether the equation is dimensionally right or wrong. Lets just analyze n and 1. First question. What is this formula for ? Ans : It gives the displacement covered is the nth second of motion. That's it, I'm through. Just think about it, how can n possibly be in seconds ? The whole formula wouldn't make any sense. Second, think physically. As i had explained in my very first post, you substitute t as n seconds. Now you tell me this formula would be littered with ks. Unfortunately, while writing equations, we don't have the practice of writing units along with the numbers. You just write the numbers. So in the formula you just substitute k = 1, assuming it is in seconds. You might argue now that see it is not the usual convention. But now you're coming to analysis of the whole equation. Personally, i think this is a standard enough formula to be asked as a trick question, but its up to the teacher, there's really not much point in arguing about that. But remember, the whole physical meaning of the formula is lost if you put t = n. When the question is how many meters has the ball traveled in the 5th second, then you must substitute n as 5. There is no meaning in substituting n as 5 seconds. All the ks are left out because of conventional convenience. Another earlier confusion was whether Snth is distance or velocity. Its distance, as can be clearly seen from the physical meaning of the formulaRkr1991 (talk) 03:39, 21 May 2009 (UTC)
Let me just Give an example. Say there are a set of 5 vectors. I want to know the magnitude of the 5th vector. Is 5 a vector here ? Or is it just a number ? Think about it in relation to this question. Rkr1991 (talk) 04:59, 22 May 2009 (UTC)

Brain health

Is there any explanation for a condition that brings a headache when a person is studying or trying to focus on a taskBotosh (talk) 05:48, 18 May 2009 (UTC)

Eyestrain causes headaches, and can be caused by "tedious visual tasks". -RunningOnBrains 07:01, 18 May 2009 (UTC)

See Tension headache.71.236.24.129 (talk) 09:40, 22 May 2009 (UTC)

Houseplant identification please...

I've looked on the internet and on W, and the best I can do is narrow these down to Succulents. I understand that's not much help, but I'm an amateur ornithologist, not a botanist.

Just bought this pair today in China and they were completely unlabeled...

Thank you!

succulents maybe?

--61.189.63.170 (talk) 07:04, 18 May 2009 (UTC)

try Kalaonchoe (spelling?) Sorry, gotta run. 67.193.179.241 (talk) 07:51, 18 May 2009 (UTC)Rana sylvatica Spelling Kalanchoe

Aloe aristata? --Dr Dima (talk) 08:25, 18 May 2009 (UTC)

More probably a Haworthia species, pretty. To the right is an Agave, I think. --Ayacop (talk) 17:02, 18 May 2009 (UTC)

Earth Rotation Effects

I asked this question few weeks ago but couldn't get an answer, so I will rephrase my question in another way:

If a rocket is initially launched (or an object thrown at very high initial speed) normal to the Earth (Vertical) at the equator for example then what would be the path it flows with respect to its origin on Earth (recall that earth is spinning and the rocket was initially having the same spin)? I'd appreciate it if the governing equations are included.--Email4mobile (talk) 07:21, 18 May 2009 (UTC)

Sorry, doctor said no equations this late at night for me :-D

In all seriousness, a rocket which appears stationary to an observer in the rotating frame has an initial tangential velocity v=[omega]xr (I never did learn how to make wikiequations). Thus if you add thrust normal to the surface of the sphere, its velocity will be v=at^2+v_0, with the a being in the, say, x-direction and v_0 being that initial tangential velocity in the y-direction. A few considerations when considering Earth: add an atmosphere and you have drag accelerations as well, and don't forget that "normal to the surface" isn't always necessarily what you think of as "up": Depending on latitude, the sum of the gravitational force and the centripetal "force" will not point to the center of the earth, but rather a small, but significant deflection away from the center.-RunningOnBrains 07:46, 18 May 2009 (UTC)

Thanks -RunningOnBrains, but I'm only curious about this stage when the rocket or any trajectory is being thrown 90o normal to the Earth surface and assuming ideal conditions where no air effects or any other kind of friction. This is because my original question was how the Earth rotation or spin would affect the released bodies from its surface (i.e. how it would be different from doing the same experiment at the Arctic or Antarctica). Indeed this question arose when a friend of mine was reading an entertainments physics book and asked us the following question: "Assume you're ideally jumping up and down, continuously at the Equator, can you slip from the Earth surface due to its spin? " His answer according to that book was No, never! But to me it wasn't convincing because I analyzed it starting with the initial conditions (same spin velocity and same angular speed) and so I realized their must be a slight slip in every jump due to the increase in the new radius (Earth's radius + height). When I used simple equations and approximations I concluded a full circle slip every 58000 years if the jump is around 0.5 m height (I eventually reached this formula, ::$T_{r}=3T{\frac {R_{e}}{2h_{max}}}\,$ , where Tr is the required time for full circle slip, T is the normal 1 day time, Re is the standard Earth's radius and hmax is the max height of the jump. For this reason I wanted some one to help me justify this answer. --Email4mobile (talk) 08:25, 18 May 2009 (UTC)

OK - so you have an equation - what's the question? Do you not trust your equation? If your math is right - then the amount of 'slip' is proportional to the radius of the earth divided by the height the object reaches - which certainly fits with the idea that the effect is essentially negligable for things like people jumping and rocket launches. When you add in the atmospheric drag effects, then with a perfectly calm atmosphere, it would act such as to reduce the effect you are describing - when you add in wind speed, then the randomness of the result will completely dominate the results. 12:28, 18 May 2009 (UTC)

I'm sure the OP is aware about those caveats. He wants to confirm his calculations. I got an extra factor of 1/2.

$T={\frac {3}{4}}{\frac {R}{h}}T_{Earth}$.

But I didn't double check it, so I may be the one that made a mistake. Dauto (talk) 14:55, 18 May 2009 (UTC)

Conserve angular momentum. Roughly speaking, the stationary rocket begins on the ground, "orbiting" with a circular orbit equal to the radius of the Earth. When you add an impulse to kick it to a higher orbit ("flying vertically from the surface of the earth"), you have not changed its angular momentum, but you have moved it to a new orbital radius. You will find that the rocket is now traveling in an elliptical orbit which intersects the surface of the earth (crash!). Eventually, the rocket will return to the Earth and crash, unless you give it sufficient velocity to escape orbit. If you wanted to get into a useful orbit, you would need to add some angular momentum, which can only be done with a non-vertical launch trajectory. (Also, you should account for atmospheric drag, which will have an important effect on the orbit anywhere near Earth). Nimur (talk) 16:04, 18 May 2009 (UTC)

name that snake

Near San Francisco Bay, my cat killed a little snake, about a foot long, brown back, light beige belly. Should we worry? —Tamfang (talk) 07:49, 18 May 2009 (UTC)

This site and this site can help you a great deal in the identification of the snakes of California. Hope this helps. I'm actually curious what species it is. --Dr Dima (talk) 08:32, 18 May 2009 (UTC)

I wouldn't worry. I'm sure the snake didn't feel a thing :) --KageTora - (영호 (影虎)) (talk) 11:00, 18 May 2009 (UTC)

Alas that I didn't photograph it. The leading candidate is rubber boa. —Tamfang (talk) 17:10, 18 May 2009 (UTC)

Are you worried about the snake (species) or the cat or your family/self? Nil Einne (talk) 12:56, 18 May 2009 (UTC)

Yes, maybe it's just a phase the cat's going through. She'll grow out of it. Just stop playing GTA IV in front of her.--KageTora - (영호 (影虎)) (talk) 13:39, 18 May 2009 (UTC)

He is four years old and I think this is the first prey he has brought home other than leaves. —Tamfang (talk) 17:10, 18 May 2009 (UTC)

Mostly about the cat. It's futile to worry about the safety of vermin in the city. —Tamfang (talk) 17:10, 18 May 2009 (UTC)

Well I would question whether a snake in what is potentially its native habitat and which from the discussion appears to be non-posoinous is unlikely to, for example, get into your house and chew your food etc and is not know as a carrier of disease can be called a vermin especially since the snake may help to kill rats and mice which may get into your house and chew your food and are known as carriers of disease. And definitely it seems to me it's worth worrying about endangered snake species (I don't know if this one is). As for the cat, well to be honest if you're asking on the RD by the time you get an answer your cat is likely to be either dead or out of danger. If your worried your cat may make a habit of catching snakes, well to be honest as with birds, there's not so much you can do. You could try putting a bell on your cat but I don't expect it will help much Nil Einne (talk) 05:54, 19 May 2009 (UTC)

There are only a few venomous snakes in California and they are all pretty unpleasant (rattlesnakes—relatively large, mean-looking, lots of warning signals, don't generally live near populated areas) —I doubt your cat would try to mess with them. The smaller snakes cannot do any damage to your cat. Psychologically, your cat is both having fun and trying to please you. There's no reasoning with it about such things. --98.217.14.211 (talk) 18:39, 18 May 2009 (UTC)

Don't rule out a house cat going after a rattler. For example check this out [2] (Otherwise I can only offer OR.) Males seem to be generally less inclined to do so, but females, particularly the unfixed ones, will tackle snakes. As with other prey there seems to be a size limit, but that can get thrown to the wind if a litter of kittens gets threatened. The good news is that by the time kitty brings one home it is very unlikely to still be alive. (Other than more harmless trophies like mice or rabbits.) Look at the bright side, you'd probably rather have your cat deal with snakes than meeting them yourself while they are alive. BTW. I've never heard of a house cat that got killed by a rattlesnake, so they seem to know what they are doing or stay away if they don't. 71.236.24.129 (talk) 23:05, 18 May 2009 (UTC)

I did lose a cat to unknown causes but a snake bite was a potential candidate. It died frothing at the mouth. This was in Malaysia however so no rattlers, it could have been a python or something. This ref [3] suggests rattlesnake bites are definitely not unheard of and often fatal but this site seems to suggest rattlesnake bites don't usually kill cats [4] and this one is in between [5] Nil Einne (talk) 05:54, 19 May 2009 (UTC)

Pythons do not have venom, they are constrictors. 65.121.141.34 (talk) 13:09, 20 May 2009 (UTC)

8D type batteries

Explain about 8D type Lead acid batteries —Preceding unsigned comment added by Kumar3214 (talk • contribs) 09:30, 18 May 2009 (UTC)

Explain what? Perhaps you would care to read our article on lead-acid batteries? -- Captain Disdain (talk) 09:47, 18 May 2009 (UTC)

8D is a standard size of lead-acid battery for marine use [6] [7] that fits within a space 11-1/2 x 21-1/4 x 12-3/4 (height including cables) inches[8]. Do not confuse 8D with 8 D-cell batteries. Cuddlyable3 (talk) 11:04, 18 May 2009 (UTC)

I don't think D-cell batteries come in lead-acid form. Hence our OP is certainly talking about the 8D marine batteries. These appear to be pretty serious bits of equipment. Prices range from $250 to $700 and those seem to assume you're returning an old battery for recycling - otherwise they stick you with another $70 charge. They look a bit like longer car batteries - but according to the various web sites that deal with them, they have all sorts of specialisations such as vibration protection. Google "8D marine battery"...there's a ton of information out there. SteveBaker (talk) 12:17, 18 May 2009 (UTC)

Name that fluffy white lint bug!

I'm looking for an ID on this lint-like bug. I'm not the photographer by the way. Thanks. 152.16.223.48 (talk) 18:21, 18 May 2009 (UTC)

A location would be great if you have one.Popcorn II (talk) 19:37, 18 May 2009 (UTC)

The photograph was in southeastern Ohio, and I've seen them in North Carolina's Appalachians. 152.16.223.48 (talk) 21:01, 18 May 2009 (UTC)

It is an Eriosomatid, a kind of aphid. We have article on Eriosomatinae. --Dr Dima (talk) 20:37, 18 May 2009 (UTC)

An after-thought: Eriosomatidae family is better known as Pemphigidae. I'll update the Wiki pages for Eriosomatinae and Eriosomatidae if no objections land on my talk-page today. --Dr Dima (talk) 21:08, 18 May 2009 (UTC). Done. --Dr Dima (talk) 20:26, 19 May 2009 (UTC)

I'm not so sure. It doesn't look much like an aphid in my opinion. The antennae make it look more like a moth to me - no idea whatsoever what type though I'm afraid! Smartse (talk) 23:54, 18 May 2009 (UTC)

No, Smartse, it is definitely an Eriosomatid (a "woolly aphid"). The picture on the Eriosomatinae page is not so good though, that's probably what's confusing you. I wish we could use the Original Poster's picture... In the meanwhile, you can look at the pictures of Eriosoma sp. at this site. --Dr Dima (talk) 00:12, 19 May 2009 (UTC)

Here is the original image. I suppose someone could ask the user for wikipedia appropriate rights. Sifaka ^talk 01:44, 20 May 2009 (UTC)

Radios in tunnels

Why does my car radio continue to work all the way through the Rotherhithe Tunnel? It usually soon dies to static in much smaller motorway tunnels. Do they have a leaky feeder or something down there? Why do you need to know what I was listening to to answer the question? Radio 4 on FM if you must know. SpinningSpark 19:22, 18 May 2009 (UTC)

"Drivers will be able to listen to normal radio programmes including BBC and commercial radio programmes on FM, AM and LW and also on the increasingly popular DAB (Digital Audio Broadcasting) channels while travelling through the [Rotherhithe] tunnel." -- Press release. Cuddlyable3 (talk) 21:46, 18 May 2009 (UTC)

I bet there are few of the drivers using that tunnel in rush hour who realise how much technology went into that, if they even noticed anything at all. SpinningSpark 22:52, 18 May 2009 (UTC)

That is a sign of good technology - people not noticing that it exists. --Tango (talk) 00:23, 19 May 2009 (UTC)

fuel stability

In reference to storing fuel, Our article on gasoline states that it will go stale in time frames of 3-24 months. How long can you store Avgas before it will go stale? 65.121.141.34 (talk) 19:43, 18 May 2009 (UTC)

According to this page, the answer is 1–2 years, but that doesn't look like a very reliable source. Bovlb (talk) 22:02, 18 May 2009 (UTC)

The reason regular gasoline 'goes stale' is because the lighter fractions evaporate to a greater degree than the heavier stuff - but it's the lighter fractions that produce much of the engine power. Avgas has more of the lighter fractions to start with - but if you're going to use it to fly a plane, then you need that. So it doesn't really surprise me that the times are comparable. SteveBaker (talk) 01:22, 19 May 2009 (UTC)

It would depend on how big a container it is in and how well it is sealed and whether there is oxygen or just pure nitrogen filling the rest of the space. Well anyway I don't believe if it is well sealed that it will go off it is just that it is very volatile so you need a very good container or a huge amount to keep it a long time. I dfon't know what the times quoted are for but I'd guess it's for those small containers people sometimes carry petrol around in rather than tankers. Dmcq (talk) 10:10, 19 May 2009 (UTC)

Does space feel cold?

I recently got into a discussion with some friends about enduring the vacuum of space. I mentioned that this article states that, because of the lack of a surrounding environment, heat doesn't transfer out very quickly, so freezing to death isn't an "immediate risk". This makes sense, but what then does outer-space feel like, if there's little transfer of heat going on? -- MacAddct1984 ^{(talk • contribs)} 21:39, 18 May 2009 (UTC)

There is a significant pressure difference between the outside pressure your body is adjusted to and the vacuum of space. My guess would be that your body would use existing sensors for heat/cold and pain to signal that. Extreme pain is often felt as extreme chill. A 'burning" sensation is also possible, though. 71.236.24.129 (talk) 22:28, 18 May 2009 (UTC)

One of the few to have experienced this was Joseph Kittinger during Project Excelsior when his hand was exposed to low pressure. His main reported symptom was severe pain due to swelling. See also Vacuum#Effects on humans and animals. SpinningSpark 23:30, 18 May 2009 (UTC)

That's not really comparable; the rest of his body was pressurized. Essentially the pressure on the rest of his body was trying to squeeze his insides out through his hand. With full-body exposure to vacuum, obviously you have other problems, but you don't have that one. --Trovatore (talk) 23:47, 18 May 2009 (UTC)

Keep in mind, I'm asking specifically about the perceived temperature of space, ignoring, if it's even possible, the other effects, such as a the body's reaction to a vacuum. I'm thinking a true vacuum is temperatureless? -- MacAddct1984 ^{(talk • contribs)} 00:06, 19 May 2009 (UTC)

That's correct, the temperature of a true vacuum is undefined. Space, even without the few particles dotted around, is not a true vacuum though, since it is filled with radiation. It is possible to define a temperature of that radiation (for example, the cosmic microwave background radiation has a temperature of about 3K). --Tango (talk) 00:14, 19 May 2009 (UTC)

A quick google search turned up Phil Plait's article[9] which states:

Space doesn't feel like anything, because there is nothing to feel! Space is a vacuum (or near enough). It's a common question to ask how hot space is (or how cold), but space itself has no temperature. However, the Sun is hot, and radiates that heat in the form of light. You absorb that light and feel heat. Near the Earth, a person floating in space would actually not receive enough light to keep from freezing! You yourself would radiate away your heat, and that's why spacesuits have heaters in them.

-Phil Plait

--MacAddct1984 ^{(talk • contribs)} 15:53, 19 May 2009 (UTC)

That doesn't sound right. Of course you radiate heat, but you also produce heat metabolically. Black body#Radiation emitted by a human body says you radiate about 100 W (oops, see below), which is roughly what you produce (100 W × 1 day ≈ 2000 kcal). So I'd think you'd be reasonably comfortable temperaturewise. That's ignoring heat from the Sun. Insolation at 1 AU is around 1400 W/m². I don't know what the human cross-section is, but I guess you'd be getting about a kilowatt. I also don't know how much of that you'd absorb (it depends on the color of your clothing/skin), but at any rate it looks like overheating is your problem, not freezing. I guess sweating would help—it would evaporate instantly and at least carry away the heat that was in it at the time (like Tango, I'm unclear on whether it would draw any extra heat as it evaporated). I don't know if it would be enough. Note the Apollo suits were cooled, not heated, and they were white, which seems to support this analysis. (They were in fact evaporatively cooled—I'm not sure what that says about the sweating issue.) -- BenRG (talk) 18:54, 19 May 2009 (UTC)

Never mind, I just realized that the figure in the article is net radiated heat, not σT_body⁴, for which I get around 1 kW. So Phil Plait is probably right. -- BenRG (talk) 19:21, 19 May 2009 (UTC)

I thought space suits have refrigeration units in them, not heaters. Insolation from the Sun is, indeed, about 1400 W/m² and the side of the person facing the Sun is probably about 1 m², so that is 1400W from the sun. There is also about 100W from metabolism. By my calculations, completely exposed to vacuum one would radiate about 1000W. That's about 500W left over that needs to be dealt with by refrigeration. --Tango (talk) 19:37, 19 May 2009 (UTC)

The extreme vacuum would be sucking the moisture out of your skin. I'll bet you'd get frostbite as your sweat boiled away. APL (talk) 02:44, 19 May 2009 (UTC)

Would you get any evaporative cooling in a vacuum? The sweat wouldn't need any heat in order to evaporate since the boiling point in a true vacuum would be absolute zero, wouldn't it? --Tango (talk) 15:46, 19 May 2009 (UTC)

You have to supply the latent heat of vaporization in any case, so yes, there would be cooling.

Water doesn't really have a "boiling point" in a vacuum. At pressures below the triple point there is no liquid phase — it simply passes directly from solid to vapor (see sublimation (chemistry)). If this picture is accurate, it appears that the solid phase continues up to almost 200 K even at zero pressure. I suppose every now and then you'd lose a molecule to space and it wouldn't come back, so it doesn't seem like a true equilibrium, but I gather that there isn't any tendency for this to happen quickly. --Trovatore (talk) 19:37, 19 May 2009 (UTC)

Excellent point, I completely forgot about the latent heat! Thank you for that. If the loss of pressure were gradual (a leaking spacecraft/spacesuit say), then the sweat would presumably boil before the pressure reached the triple point (if I'm reading that graph correctly), so the lack of a liquid phase isn't an issue. If the loss of pressure were more sudden, what would happen? What happens if you put a liquid into conditions in which there isn't meant to be any liquid? Presumably it would boil as well. Once the sweat that was produced prior to the loss of pressure is all gone, does anyone know what would happen? Are sweat glands capable of producing sweat in a vacuum? The pressure of the skin would allow liquids to exist inside the body, but how would pores behave? --Tango (talk) 19:51, 19 May 2009 (UTC)

I think if you put liquid water into a vacuum it would simultaneously boil and freeze. As it boils, giving taking up its latent heat, the temperature drops and the remainder freezes.

As for the human body, I don't really know. At some point I'm going to go challenge the information in the articles about "skin swelling to twice its normal size" or whatever it claims now. There isn't a cite for it (or wasn't last I checked), and I suspect that someone may have extrapolated from Kittenger's experience. I explained above why that's not a valid inference. --Trovatore (talk) 20:07, 19 May 2009 (UTC)

My understanding is that the elasticity of the skin is sufficient to keep internal pressure normal with only minimal swelling. Death is from suffocation (air gets "sucked" out of the lungs [assuming you don't try and hold your breath and make them explode], oxygen then defuses from blood to empty lungs very quickly and you lose conciousness within seconds). What happens to your corpse, I don't know. I would guess not a great deal at first and it eventually freezes or burns depending on whether or not you are in sunlight. --Tango (talk) 20:22, 19 May 2009 (UTC)

The pressure axis on that diagram is logarithmic. I suspect that only the gas phase exists in the limit of zero pressure, because of the irreversibility of casting a molecule out into the infinite void. Of course, at absolute zero the solid phase kinda has to prevail. --Tardis (talk) 22:11, 19 May 2009 (UTC)

Those molecules would only be cast out very slowly, though, there would be a solid for a long time. --Tango (talk) 22:30, 19 May 2009 (UTC)

I'm a latecomer to the party, I know, but remember that the temperature of human skin is much greater than 200 K, so a great deal of evaporation/sublimation would occur initially, until the skin cooled to well below what we'd consider "frozen solid". -RunningOnBrains^{(talk page)} 17:19, 20 May 2009 (UTC)

Plastics, Playdough and thermoelastisity

Several questions here.

What is the melting point of #2 plastic (used in milk jugs in usa)

What is the melting point of playdough

If I make an object with #2 plastic using a playdough mold, how much smaller would the final object be from the original thing pressed into the playdough after the plastic cools?

thankyou and have a nice day. —Preceding unsigned comment added by 173.25.242.33 (talk) 21:52, 18 May 2009 (UTC)

According to Plastic recycling, a #2 cycle code is for High-density polyethylene - and according to that article: "HDPE has little branching, giving it stronger intermolecular forces and tensile strength than lower-density polyethylene. It is also harder and more opaque and can withstand somewhat higher temperatures (120 / 248 °F for short periods, 110 °C /230 °F continuously)". According to playdoh, "Play-Doh's current manufacturer, Hasbro, reveals the compound contains water, salt, and wheat flour. While its 2004 US patent indicates its composed of water, a starch-based binder, a retrogradation inhibitor, salt, lubricant, surfactant, preservative, hardener, humectant, fragrance, and color.[7] A petroleum additive gives the compound a smooth feel, and borax prevents mold from developing.". This seems like a bad thing for your idea - the plastic won't melt until 110°C to 120°C - but the water in the playdoh may well be boiling by that point...that might not be a good thing. The RepRap Wiki says that: "HDPE Is one of the more finicky plastics...It does not stick together well, and...it shrinks a lot when it cools tends to distort readily."...unless you REALLY specifically want to do recycling, you'd be better off heading to an art supply store and getting some Polycaprolactone - which is sold under various trade names as stuff to make jewellery out of. It softens in warm water and melts at about 60°C - so you can even mold it with your fingers. SteveBaker (talk) 01:16, 19 May 2009 (UTC)

Maybe another modeling clay would be better, like the polymer based Fimo (can be heated to higher temps, and is harder).YobMod 07:16, 19 May 2009 (UTC)

One warning from the palycaprolactone article... "PCL has been known to become brittle, lose its tensile strength and fall apart after several months so is not suitable for permanent or critical applications." So I wouldn't make anything too important out of it. Low density polyethylene might be a better answer as it has a melting point of 95 C. 65.121.141.34 (talk) 13:06, 19 May 2009 (UTC)

Yeah - I noticed that. But I have stuff that I made of polycaprolactone (specifically the "Polymorph" brand) that's at least 16 years old that hasn't obviously degraded (I know it's that old because Polymorph is the British name for the stuff - so I must have made it while I still lived in the UK - which must be more than 16 years ago). I suspect that our article is referring to the plastics based on polycaprolactone that have starch mixed in with them specifically to make them biodegradable. The article mentions this - but I wonder whether the authors have correctly put two and two together. SteveBaker (talk) 19:58, 19 May 2009 (UTC)

Identifying some Australian animals from Sydney Wildlife World

Hi all. I'm looking for help identifying the following Australian animals that I photographed at Sydney Wildlife World in April 2007 so that I can upload them to Commons:

• Some kind of skink
• Some other kind of skink
• Some kind of spider
• Some nocturnal creature in its nest (maybe spotted-tail quoll, Spinifex Hopping Mouse, or bilby?)
• This grasshopper
• This large bird

Thanks for any help. :-) Dcoetzee 22:11, 18 May 2009 (UTC)

We don't have a page, but the Psudocheirus cinereus - Daintree Ringtail Possum [10] looks like the "nocturnal creature in its nest" I'm not into creepy crawlies so I'll leave those for others. 71.236.24.129 (talk) 23:58, 18 May 2009 (UTC)

o.k. one more: Your "Grashopper" may be a migratory locust [11] the wings are a bit short which would indicate it's not an adult or another species.

May 19

Tree questions

Is tree really absorbed CO2 and release O2 in day time, and the contrary at night? Are all kind of trees have the same characteristic? And what species of trees produce the largest amount of O2? When we sleep in the forest at night, can we suffered from lack of oxygen? Thanks for the responds. roscoe_x (talk) 01:46, 19 May 2009 (UTC)

All plants perform cellular respiration, which consumes oxygen and releases CO2. However, this effect is completely overwhelmed by the action of photosynthesis, of which oxygen is something of a side-effect. Because plants manufacture their own oxygen, the "drain" on atmospheric oxygen is minimal. Go ahead and sleep outdoors; it'll do you good! Incidentally, there is an urban legend that you shouldn't bring flowers to people in hospitals because the plants supposedly suck the oxygen out of the room. Complete nonsense. Matt Deres (talk) 03:10, 19 May 2009 (UTC)

(EC) Matt, I'm no scientist, but I think there is something wrong with that last post. It implies that plants take in oxygen, then release CO2 (contrary to what I and the OP have been told in primary school) and yet still have enough oxygen to release that too, on account of photosynthesis. So, the idea of the Amazon rainforest getting depleted adding to the CO2 level(or at least not reducing it) and thus causing global warming is nonsense? Planting more trees would not help, because they suck oxygen from the atmosphere and not CO2? Are you sure about this? Question asked in all good faith - not sarcastically --KageTora - (영호 (影虎)) (talk) 03:22, 19 May 2009 (UTC)

Ha! Either I misread the answer or someone changed it while I was writing my query. Forget it. Been a long night.--KageTora - (영호 (影虎)) (talk) 03:25, 19 May 2009 (UTC)

Yeah - exactly - the amount of O2 they produce (and CO2 they absorb) during the day more than makes up for the small amount of O2 they consume and CO2 they produce at night. Also, it's not just trees - all green plants from the teeny-tiniest green algea to the giant redwoods do that. SteveBaker (talk) 03:17, 19 May 2009 (UTC)

This kind of question keeps coming up. The Plant article seems to be hopelessly lost in taxonomy and basic plant concepts like what parts do what and the question above get one on a wild goose chase through highly specialized articles. If one can find anything to begin with, that is. Thinking of the post about organizing information in a tree structure earlier this month maybe someone with enough knowledge could sort out an article for the non-specialists. I don't feel comfortable starting something, because my last biology lesson was a couple of decades ago and in my experience any article started without enough ooomph just gets deleted. 71.236.24.129 (talk) 06:53, 19 May 2009 (UTC)

I think your idea is good. I think Wikipedia should have a FAQ page on each of its article. roscoe_x (talk) 14:25, 19 May 2009 (UTC)

There is always the Simple English Wiki - although in this case, their plant article is probably waaay TOO simple. SteveBaker (talk) 02:53, 20 May 2009 (UTC)

Not all plants absorb CO₂ and release O₂ in day time and do the opposite at night. Keeping it simple, CAM Plants take in CO₂ during the night and convert it to oxygen during the day as a way to keep the plant from losing too much water. I'm not sure when most of the oxygen is released, but my hunch it happens mostly during daylight hours. As to what plant produces the greatest net O₂, I'm not sure, but it is likely not a species of tree. Someone answering a similar question stated that "the largest fraction of the planet's molecular oxygen is not produced by tree and other landbased plants but photosynthetic organisms in the world's oceans." I can't validate their answer, but I wouldn't be surprised if it was true. Sifaka ^talk 03:31, 20 May 2009 (UTC)

dimensional question

when a wave traverses a medium, the displacement (Y) of a particle located at x at time t is a*sin(bt- cx), where a, b and c are constants. what are the dimensions of b??

the dimension of Y is [L], and that of t is [T]. but should i write the dimensions of x as [L} or ... something else? 122.50.135.154 (talk) 05:44, 19 May 2009 (UTC)


Ya you're right. x is [L]. Which means c must be [L^-1], as you can't take the sine of anything except a number. Similarly, b is [T^-1], and the sine of anything is just a number, dimensionless. So a is [L].... There seem to be a lot of questions on dimensional analysis :-)..Rkr1991 (talk) 07:28, 19 May 2009 (UTC)

Almost right. "c" is actually radians/L, and b is radians/T, assuming your sine function is in radians, as it usual in mathematics. If your sine function is in degrees, replace "radians" with "degrees". The "a" is an amplitude, "b" is frequency, and "c" is phase shift.-Arch dude (talk) 20:31, 19 May 2009 (UTC)

Radians are generally considered to be dimensionless. They are the ratio of two lengths (a radius and an arc length). --Tango (talk) 20:38, 19 May 2009 (UTC)

explosive force calculation based on weight.mythbusters??

Hi

I am confused about something I saw on mythbusters the other day, they make a cannon that launches a 6 pound bowling ball 1500 feet. Yet the cannon itself barely moves backwards. shouldnt a force that can move 6 pounds 1500 feet move a cannon that weighs around 150 pounds about 50 feet? or does something else effect this ? I mean i would think that a force powerfull enough to push a 6 pound cannonball 1500 feet would have at least enough force in the other direction to move a 150 pound cannon about 20-30 feet, but the cannon just rolls back like a foot and falls over.

how does the calculation for the amount of pressure needed to move heavier and heavier objects work?

Thank you. —Preceding unsigned comment added by 79.68.210.245 (talk) 08:23, 19 May 2009 (UTC)

The canon would move a distance at a ratio inversely proportional to the ratio of masses, if there were no other forces acting (eg in space). But in this case, the frictional force between the canon and ground would presumably be much higher than that between the canon and ball, by design. So the reaction force is mostly balanced out by this frictional force, leading to little acceleration. Friction is dependant upon both mass and the friction coefficients of the materials used, hence heavier objects need more force to move on Earth than a simple momentum calculation would suggest. Recoil might have more info (it might have had a recoiling barrel on springs for example, so the momentum is aborbed by that and prevents large backwards movement).YobMod 09:22, 19 May 2009 (UTC)

AAAh thank you, your suggestion of friction, plus the recoil article helped. apparently some cannons and guns can be designed to have more chemical energy tranferred to the projectile than the gun. That would explain it. this is the quote "bullet fired from an M16 rifle has approximately 1300 foot-pounds of kinetic energy as it leaves the muzzle, but the recoil energy of the gun is less than 5 foot-pounds. The reason mechanical energy is not conserved is because much more of the chemical energy released during powder combustion is transferred to the bullet than is transferred to the gun."

How would they do that? —Preceding unsigned comment added by 79.68.210.245 (talk) 10:08, 19 May 2009 (UTC)

Actually, nearly any gun will do that by the simple laws of physics. Action=reaction applies to impulse - the gun and the projectile (plus the escaping gas, if we want to nitpick) have to have a total impulse that is zero - in other words, the impulse of projectile and the gun will have the same magnitude but opposite directions. Since impulse is mass times velocity, but the gun is a lot more massive, the projectile is much faster than the gun. Kinetic energy is mass times velocity squared, so that higher speed translates to a much higher kinetic energy. --Stephan Schulz (talk) 11:22, 19 May 2009 (UTC)

Working through the equations for parabolic motion and conservation of momentum, if the cannon were on frictionless wheels, it would move backward at somewhat less than 5 mi/hr after the shot. If it isn't on wheels, and considering that the shot is probably angled upward at about 45 degrees resulting in a strong downward push, friction would probably keep it from moving.

I am surprised that no one on refdesk spotted that, "The reason mechanical energy is not conserved is because much more of the chemical energy released during powder combustion is transferred to the bullet than is transferred to the gun." is a non sequitor that makes no sense.

• "The reason mechanical energy is not conserved is because" there is no law of conservation of "mechanical energy". In any case, energy is not a vector quantity and the energy of the gun moving backward will not somehow cancel the kinetic energy of the bullet.
• In a gun/cannon, chemical energy (from the explosive) is converted into mechanical energy (+ heat, sound etc), and total energy is of course conserved.
• More importantly, for understanding recoil: Momentum is also conserved. The "positive" momentum (mass*velocity) of the bullet is matched by the "negative" momentum of the gun + shooter + earth + exhaust gases.

Can someone take a stab at rewriting the Recoil section ? Abecedare (talk) 16:27, 19 May 2009 (UTC)

What we're missing here is that the total momentum of the entire system is constant - that includes bullet, gun AND the gasses produced by the propellant. So in a "recoilless" gun (well, they have some recoil - but less), some of the propellant is sent sideways and backwards at very high speeds - and this removes some of the momentum from the recoil. But certainly the bullet's mass is much less than the gun - so the force acting on the gun is the same as the bullet - but the resulting acceleration is much lower. In the case of the Mythbusters' cannon - the friction with the ground is transferring some of that momentum to this big planet that has a REALLY big mass and consequently hardly accelerates at all. It's also common to have some kind of elasticity in the system (eg a padded shoulder stock) that spreads the recoil's energy out over a longer period of time - thereby reducing the instantaneous force to something much easier to handle. SteveBaker (talk) 19:52, 19 May 2009 (UTC)

Also, what everyone is forgetting is that the cannon is not fired straight parallel to the ground. If it were, it would likely roll backwards some distance. The cannon is usually fired at an upwards angle, which means much of the recoil force is directed into the ground. Much of the energy therefore goes into deforming the ground under the cannon rather than pushing the cannon backwards. --Jayron32.talk.contribs 00:56, 20 May 2009 (UTC)

cats landing on their feet

House cats always seem to land on their feet. Does this self righting reflex extend to other members of the cat family, such as jaguars, cougars, or tigers? 65.121.141.34 (talk) 14:09, 19 May 2009 (UTC)

Probably only if they are habitual tree climbers, like leopards and unlike lions. - GlowWorm. —Preceding unsigned comment added by 174.130.252.35 (talk) 14:15, 19 May 2009 (UTC)

As an interesting sidenote: Cats can only self right if the height from which they fall gives suffivient time to execute the reflex. Some studies (and i wish i still had that link!) showed that cats falling from either very low or high altitudes survived the fall more often then cats falling from heights in which they cannot execute the full reflex - The writers of course noted that there was a maximum height in which cats tended to survive more then cats falling from lower heights. Excirial ^{(Contact me,Contribs)} 14:35, 19 May 2009 (UTC)

No, Wikipedia does not have one page for this...it has two!

The High-rise syndrome article has some good cites supporting the number-of-floors effect. Might want to copy them to the Cat righting reflex article, which presently only cites Straight Dope. DMacks (talk) 15:37, 19 May 2009 (UTC)

The question could be rephrased "Can big cats right reflexively, or is this just a 'little cat feat?'" See also Buttered cat paradox. Edison (talk) 16:44, 19 May 2009 (UTC)

Cats I have known could all right themselves when dropped from amazingly low heights, like 1 foot. Edison (talk) 18:36, 19 May 2009 (UTC)

The height from which cats suffer the highest fatality rate, ie. heights higher or lower than this are more likely to allow the cat to right itself properly and survive, is approximately seven storeys. This is because acceleration due to gravity causes the cat to become rigid, but once the terminal velocity is reached, the cat has an easier time trying to right itself. ~AH1^(TCU) 01:59, 20 May 2009 (UTC)

So does this work with the big cats too? 65.121.141.34 (talk) 15:09, 20 May 2009 (UTC)

I suspect that some big cats have a righting reflex, but that it is less effective because big cats are more massive and so must absorb considerably greater force of impact for the same velocity. Small wildcats probably pull this off better. Dcoetzee 05:55, 21 May 2009 (UTC)

Which is worse, a drop-bear or a drop-tiger? DMacks (talk) 06:27, 21 May 2009 (UTC)

In reading through this, I checked out the Buttered Cat Paradox which led to the Irresistable Force Paradox. My question is about this latter. IF an irresistable force and an unmovable object did exixt and were to meet, wouldn't they simply cancel each other out (i.e. annihilate each other)? Why or why not (other than these forces/objects can't exist)? —Preceding unsigned comment added by 209.161.223.123 (talk) 03:42, 22 May 2009 (UTC)

mass increase or mass energy equivalence

which one did einstein formulate first? mass increase in relativity or mass energy equivalence? if he formulated mass energy equivalence first, can some one give the derivation first?--harish (talk) 14:59, 19 May 2009 (UTC)

Both came in 1905 papers, but the mass increase came first, in "On the Electrodynamics of Moving Bodies". Mass-energy equivalence was first directly presented, I believe, in the later 1905 paper "Does the Inertia of a Body Depend upon its Energy Content?". See special relativity and mass-energy equivalence for more information. Looie496 (talk) 15:31, 19 May 2009 (UTC)

Weren't the units of work or energy (such as the joule in the MKS system) given in kilogram meters² per second² before 1905? This meant that energy was already in units of mass times velocity squared. Was Einstein the first to notice this? Edison (talk) 17:06, 19 May 2009 (UTC)

$KE={\frac {1}{2}}mv^{2}$ was known long before Einstein, that gives you the units. --Tango (talk) 17:15, 19 May 2009 (UTC)

Right, but having the same units is not the same as being interchangeable. (Think about how much pathological physics would result...) Einstein not only noticed the units, but explained a correct equivalence relationship. Nimur (talk) 05:44, 20 May 2009 (UTC)

Of course, I was just pointing out that Einstein wasn't the first the notice the units, they were common knowledge long before he came along. --Tango (talk) 12:06, 20 May 2009 (UTC)

artifact hoaxes

Which scientific or historic artifact was accepted as genuine for the longest period of time before it was later discovered to be a hoax or forgery? 65.121.141.34 (talk) 15:08, 19 May 2009 (UTC)

This is totally unauthoritative, but:

• I think it must be a religious artifact of some sort, like a church claiming it has part of the True Cross or some other relic — at this point these claims are probably being made in good faith but human nature suggests that most of them involve somebody lying at some point. Does this still comprise a hoax?
• The Talpiot Tomb is around 2000 years old and was discovered in 1980; some claim that one inscription reads "Yeshua bar Yehosef", or "Jesus son of Joseph". Hoax? Concidence? Who knows.
• More contemporaneously, the 1934 "Surgeon's Photo" of the Loch Ness Monster was revealed as a hoax in 1994. That's sort of an artifact.

The right answer may be some hoax that is as of yet undetected. Tempshill (talk) 15:39, 19 May 2009 (UTC)

Piltdown Man is one that creationists often point to that "discredits evolution". It was exposed as a hoax in 1953, but some scientists were skeptical from the start. Also, what about those inscribed balls found in South America? The name is eluding me... -- MacAddct1984 ^{(talk • contribs)} 16:02, 19 May 2009 (UTC)

The consequences of Piltdown Man went on long after the hoax was exposed. I wasn't born until 1955 - and I clearly recall being taught that Piltdown Man was 'the missing link' - and that must have been around 10 years later! It takes a long time for syllabuses and school books to get rewritten! If you ever get the chance to visit the little village of Piltdown - be sure to drop into their pub: "The Missing Link" - it serves some of the finest Real Ale I've had the pleasure of sampling. SteveBaker (talk) 04:07, 20 May 2009 (UTC)

I'm betting it's a book of some kind. As I recall, there are works that were attributed to writers like Aristotle for over two thousand years but eventually demonstrated by textual analysis to be forgeries. Unfortunately I have only the vaguest recollection of any of this, not enough to dig up sources. Looie496 (talk) 16:55, 19 May 2009 (UTC)

Klerksdorp Spheres? --Sean 17:39, 19 May 2009 (UTC)

Our literary forgeries article says One of the longest lasting literary forgeries is by Pseudo-Dionysius the Areopagite a 5-6th century Syrian mystical writer who claimed to be a disciple of Paul the Apostle. Five hundred years later Abelard expressed doubts about the authorship, but it was not until after the Renaissance that there was general agreement that the attribution of the work was false. In the intervening thousand years the writings had much theological influence. Looie496 (talk) 17:47, 19 May 2009 (UTC)

Turin shroud? The Bible? 89.242.109.25 (talk) 09:16, 20 May 2009 (UTC)

I have not seen anything proving that either of those are hoaxes or forgeries, though the church does not seem to allow much in the way of testing such relics as the shroud. 65.121.141.34 (talk) 15:07, 20 May 2009 (UTC)

See Radiocarbon 14 dating of the Shroud of Turin. 78.146.198.122 (talk) 20:50, 20 May 2009 (UTC)

Why would the Bible be a hoax? It's pretty well researched when it's specific books were written, and I've never heard of anyone claiming that it was written a lot later. --131.188.3.21 (talk) 20:51, 20 May 2009 (UTC)

momentum and relativity

take two coordinate systems K and K' . K' is moving with a velocity of v relative to K. An object is moving with a velocity of u relative to K'. will the observers in K and K' agree with the momentum and velocity of the object?--harish (talk) 16:11, 19 May 2009 (UTC)

Looks like a homework problem (which we don't do). Looie496 (talk) 16:57, 19 May 2009 (UTC)

It looks too general for a homework problem to me. --Tango (talk) 16:58, 19 May 2009 (UTC)

No. Velocity and momentum are always relative to a coordinate system, different systems will get different values for them. What velocity observers in K will measure depends on whether you are talking about simple Galilean relativity, in which case you can just add the velocities, or Special Relativity, in which you need the appropriate velocity addition formula. --Tango (talk) 16:58, 19 May 2009 (UTC)

biomedical projects?

i am applying for a scholarship for which i am supposed to do a BIOMEDICAL PROJECT.i need some information regarding this.what is a biomedical project?what am i supposed to do?is any paper work included?is it all about collection of some data or woking out something new? —Preceding unsigned comment added by 115.241.146.220 (talk) 17:25, 19 May 2009 (UTC)

:Pardon me for this observation, but if you don't know what a biomedical project is why are you wasting your time applying for the scholarship? --TammyMoet (talk) 19:01, 19 May 2009 (UTC)

BIO stands for Biological, while Medical stands for MEDICINE. In short, i assume that you will have to do some medicine related project. As for paperwork and working data out: How could we know? A project can be anything; it all depends on how you define the goals of the project. However i tend to agree with the user above me - If you don't even have a basic clue about the mere meaning of the word is it wise to apply for such a project? Most times at least some background knowledge is required to successfully complete a project Excirial ^{(Contact me,Contribs)} 19:08, 19 May 2009 (UTC)

Most likely "doing a biomedical project" means finding a mentor who has a lab that does biomedical research, working out with the mentor a project that involves lab work, and then writing up the results. Beyond that, the details may vary. Looie496 (talk) 19:41, 19 May 2009 (UTC)

The best advice is to contact the people offering the scholarship directly. They aren't trying to mess with you; they will answer your questions directly. It's always best to contact the people directly involved rather than random strangerz on deh intrawebz. Those people will be able to answer your question directly. --Jayron32.talk.contribs 00:51, 20 May 2009 (UTC)

I've gotten a few scholarship before, which required having a project planned out. I basically just wrote to a (large) number of professors whose web-pages looked interesting, explaining the requirements for the scholarship. Most profs are very happy to help if you will be be bringing your own funding. However, i also had all the qualifications needed - for a biomed project scholarship, i would think the applicant should have experience in biology or medical research, at least at the undergraduate level.YobMod 09:49, 20 May 2009 (UTC)

Number of individual lifeforms on this planet?

Is there an estimate of the number of individual lifeforms on our planet? Meaning, all 6 billion humans, every individual insect, arachnid, invertebrate, blade of grass, etc. My second question is, are there more galaxies in the universe, than there are individual lifeforms on our planet? ScienceApe (talk) 17:58, 19 May 2009 (UTC)

If you're just counting lifeforms, virtually all of them are bacteria or archaea. They're hard to count, but one estimate is on the order of 5 x 10³⁰. Looie496 (talk) 18:19, 19 May 2009 (UTC)

As for the amount of galaxies: As estimate is that there are between 10 billion and 1 trillion stars, all which may or may not have planets orbiting them. If we were to count every metheorite, planet and star then the numbers would be drastically higher. Higher then the amount of lifeforms we have? Possibly - the galaxy is a massive place and our knowledge about it is still very localized. Excirial ^{(Contact me,Contribs)} 19:01, 19 May 2009 (UTC)

Sorry, you didn't ask for the amount of stars, but for the amount of galaxies. If i remember well the last estimate i saw was between 60 and 110 billion galaxies. Far less then the amount of estimated lifeforms. Excirial ^{(Contact me,Contribs)} 19:03, 19 May 2009 (UTC)

It is necessary to clarify the word "universe". The entire universe may well be infinite and, thus, contain infinitely many galaxies. The observable universe is finite and our article says it contains "more than 80 billion galaxies". --Tango (talk) 19:11, 19 May 2009 (UTC)

Excirial, I think your stars estimate is way off. Our galaxy itself contains 100 billion stars. It's a hundred thousand light years side to side. It bulges in the middle, 16 thousand light years thick; but out by us it's just 3 thousand light years wide. We're 30 thousand light years from Galactic Central Point; we go 'round every 200 million years; and our galaxy is only one of millions of billions in this amazing and expanding universe. Tempshill (talk) 00:02, 20 May 2009 (UTC)

Has life got you down, Mrs. Brown? --Jayron32.talk.contribs 00:49, 20 May 2009 (UTC)

100 billion is between 10 billion and 1 trillion. Excirial initially misunderstood the question and thought it was about the number of stars in our galaxy, rather than the number of galaxies. --Tango (talk) 00:31, 20 May 2009 (UTC)

Since regardless of how you do it there are millions of times more bacteria on Earth than stars in the entire universe, it's all sort of irrelevant. Looie496 (talk) 02:44, 20 May 2009 (UTC)

Observable universe. --Tango (talk) 12:07, 20 May 2009 (UTC)

Film speed vs. digital gain?

I understand that film speed and signal gain in photography are about the same thing: sensitivity to light, and work pretty much the same way. Greater sensitivity allows for shorter shutter speeds while still keeping the image lightness identical, but produces noisier and grainier images. My question is, because once the light gets through the shutter (how much and for how long the shutter is open is identical), what happens then is fundamentally different between film and digital photography. The sensitivity is labelled with the logarithmic ISO scale in both anyway, using the same numbers. How well do these correspond with each other? How is it determined which film speed corresponds to which signal gain? Are even the bases of the logarithms the same? JIP | Talk 19:34, 19 May 2009 (UTC)

Film speed answers your question. In short, yes they should correspond with each other. --antilived^{T | C | G} 05:06, 20 May 2009 (UTC)

Amount of vegetable fat in ml

I've been rather surprised to learn that recent medical advice is that consuming reasonable amounts of vegetable oil (but not hydrogenated or trans fats) is better for you than trying to avoid all fats. http://heartdisease.about.com/cs/cholesterol/a/raiseHDL_2.htm "The best advice regarding fat in the diet appears to be this: 1) reduce the fat intake to 30 - 35% of the total calories in the diet - but probably no lower than 25% of total calories". How much in ml of vegetable oil is 1% of total calories in one's diet going to be? 78.149.232.7 (talk) 23:44, 19 May 2009 (UTC)

According to this page, vegetable oils contain about 120 calories per tablespoon (15 mL). Caloric intake will vary from person to person, but USDA/FDA standards are based on a 2000-calorie daily diet. 1% of 2000 calories would be 20 calories, so 2.5 mL of vegetable oil would supply about 1% of a typical diet's caloric intake, assuming vegetable oil is mainly fat, which it is. 4.242.147.206 (talk) 00:36, 20 May 2009 (UTC)

As a side note, why did you think a completely fat free diet would be healthy? This reminds me of the overly-simplified definition of healthy food 'low as possible in fat, high as possible in fibre' which would make paper the healthiest food. 80.41.33.31 (talk) 07:37, 20 May 2009 (UTC)

Involuntary digestive organs?

Is there a common English term for the part of the body where food goes after being swallowing and before being felt as a need to poo? If we had to use anatomical terminology, I guess that would be from the pharynx to the... wherever the threshold of feeling a need to poo is. I was thinking of calling it "involuntary digestive organs" or similar... basically including oesophagus, stomach and the guts. Or is there a better term or even a non-medical plain English term?--Sonjaaa (talk) 23:45, 19 May 2009 (UTC)

Gastrointestinal tract. Dauto (talk) 23:51, 19 May 2009 (UTC)

Teenagers in school would call it the digestive system in Biology lessons - the link shows it's the same thing, so take your pick. 90.193.232.41 (talk) 18:05, 20 May 2009 (UTC)

Climate Variation

Is there any kind of technology on the internet that lets you take a climate chart of a particular location, provided by the site, and do a search to come up with all the climate charts around the world that correspond most closely with the initial chart? This climate chart would include average monthly highs and lows and average monthly precipitation. —Preceding unsigned comment added by 189.4.53.90 (talk) 23:52, 19 May 2009 (UTC)

You could start at the Weather Underground, http://www.wunderground.com/, which has all sorts of great climate and historical weather information from many many cities around the world. Oh, and dispite the name, they have nothing to do with these people. --Jayron32.talk.contribs 00:46, 20 May 2009 (UTC)

May 20

What labs, books, and conferences are there about research on the neuroscience of empathy?

I want to make this list more complete.

Specifically, what are the: a) labs or primary researchers b) books c) conferences d) one-off papers

... which have to do with the neuroscience of empathy?

Please include only primary academic sources - i.e. not popular press, unscientific publications, or the like. (Exception: popular-format books by people who are in fact real researchers are OK, e.g. most of Paul Ekman's recent books.)

Most important to me is the list of labs / researchers, preferably with links to pages where I can directly download PDFs of their papers, as the primary use for this list is as a list of places I should apply to for my PhD.

Thanks!

Sai Emrys ¿? ✍ 00:26, 20 May 2009 (UTC)

You could start here. --Tango (talk) 00:29, 20 May 2009 (UTC)

The Society for Neuroscience annual conference is in Chicago, October 17-21. You may consider attending and finding out for yourself what you like and where you should apply. I don't know if you have to be a member to attend (I'm a member anyway), but it's easy to find out. The SFN homepage is at http://www.sfn.org/ . Also, Tango's advice is really good. Just google or google-scholar for "empathy", "neuroscience", "mirror neurons", "insula", "anterior cingulate", or any combinations thereof, and you will find all you are looking for and more. And, good luck! Empathy is really a fascinating research topic. --Dr Dima (talk) 01:35, 20 May 2009 (UTC)

Hmm, I wouldn't really recommend going to SFN in order to find a school, it's kind of an overwhelming experience. Anyway, if I had to recommend a place to somebody who could get in anywhere, I would recommend University College London, with the Friths, Ray Dolan, etc. It's a hot topic, though, and there are people all over the place working on it. Looie496 (talk) 02:38, 20 May 2009 (UTC)

I'm afraid the $550 (+ hotel & travel) non-member price is a bit too steep for me; otherwise, it looks interesting... but very general. I'm only interested in (dedicating my life to) limited parts of the field of neuroscience; I feel a general conference would be a bit too shotgun. (FWIW, I'm very disappointed I missed the Berkeley conference on mirror neurons recently - I heard of it too late. I live in Berkeley, it was exactly on MNs, and it was free to boot! Sigh.)

Yes, I know how to use Google Scholar; my hope was to find somewhat more personal pointers, as GS can be a bit like finding a specific kind of needle in a stack of popularity-ranked hay. I'd love to, but practically speaking there's no way I can actually read through all the stuff there to find out the handful of people whose research is really what I want. This is something that domain knowledge is very helpful for making a lot easier. Thanks! Sai Emrys ¿? ✍ 02:48, 20 May 2009 (UTC)

Many conferences use student volunteers to man the doors, check badges and such like. When you do that, you can generally hang out at the back of the conference hall while sessions are in progress and catch most of the event for free. Obviously travel and accommodation is still an issue. But it's worth calling the conference organizers - expressing your enthusiasm and interest for this narrow field - they may be able to cut you a deal - or even offer a small grant/scholarship to help to get you there. It's definitely worth a try - especially with such a tightly focussed conference. SteveBaker (talk) 03:59, 20 May 2009 (UTC)

Ah, you're in Berkeley -- and I see from your resume that you got an undergrad degree there. The best advice I can give is to try to get a "technician" job in a lab that does something similar to what you're interested in -- there are several people there interested in social neuroscience, and all of them are top notch. There's nothing better than hands-on experience for getting a good fix on who is doing the stuff you care about most, and it's also a big plus for getting into a top-notch program. (To Steve: SFN is one of the largest academic conferences in the country, with typically about 50,000 attendees -- tightly focused is not what I would call it. It's a circus. They do provide a bit of support, but they wouldn't support somebody who isn't currently in an academic program.) Looie496 (talk) 04:26, 20 May 2009 (UTC)

Throwing a ball of wool (or twine) to a lion/tiger...

What happens? Do big cats also find it entertaining to play with suchlike? --Kurt Shaped Box (talk) 02:22, 20 May 2009 (UTC)

The Desert Museum puts ice in the mountain lion cages for their enjoyment if I remember correctly. A google of zoo lion enrichment found this website which says: "To stimulate predatory behavior, keepers toss hay-filled burlap sacks or cardboard boxes into the lion and tiger enclosures, which the cats pounce on and shred as if they were prey. Keepers may add olfactory interest to these items by scenting them with zebra or camel urine, perfumes, hunting lures, and herbs. In the tiger yard, keepers can hook up to a tree a giant spring covered with PVC pipe to which they attach a hard plastic Boomer Ball® or burlap sack. The tigers attack and tug at the unyielding item as if it were struggling prey. For the small cats, keepers hide meat and prey items throughout the enclosures. In the summertime, the fishing cats hunt for live goldfish released into their pools." A search for zoo enrichment might yield some more results. My guess is that a suitably sized ball of twine would generate interest from a large felid, but a zoo might not put an object which might present a tangling or choking hazard in their enclosures. If they could keep them from unravelling it enough to choke or tangle it might work. A zoo keeper would be a good person to ask. Sifaka ^talk 03:10, 20 May 2009 (UTC)

Certainly I've seen balls in big cat zoo exhibits - so I presume they play with them. I doubt it matters much whether it happens to be a ball of wool or a plastic soccer ball or whatever. Of course this is all about zoo animals - who need all of this 'enrichment' to keep them interested in life in their tiny enclosures with all of their natural instincts being effectively turned off. Whether a wild Lion or Tiger out there in it's native habitat would give a ball of wool a second glance is an entirely different matter...I suspect the very young ones would - but not the adults. SteveBaker (talk) 03:52, 20 May 2009 (UTC)

Genus

Where can I find information describing when a genus split from others in its family? Specifically I am writing about genus Abramites, though specific information isn't neccesarily needed, just how to find it.Drew Smith What I've done 07:13, 20 May 2009 (UTC)

First a remark: I'm no expert in fishs or phylogenetics, just a geneticist. I think, there is no clear answer to your question. Even for families that are "hot research topics" like hominidae the exact time points of speciation are unknown. All you can do is apply a model of the time course of genetic changes, and then come up with some rough estimate how much time it took to accumulate the differences you see. A quick googling didn't bring up any research paper that did this for Abramites, though, so I think the answer is: No one really looked into this. TheMaster17 (talk) 09:14, 20 May 2009 (UTC)

Meh. I came to the same conclusion, just wondered if anyone knew of a site or book that specialised in this kind of thing.Drew Smith What I've done 11:17, 20 May 2009 (UTC)

So, for the taxobox, is it ok to use the time period that the order first appeared?Drew Smith What I've done 11:19, 20 May 2009 (UTC)

Butterflies/moths identification

• 
  Diacrisia sannio
• 
  Pyrgus (species uncertain)
• 
  Hamearis lucina?

I took some pics of butterflies a couple of days ago and I wasn't able to fully identify them. I have some hints about the genus/species for two of them, but I can't be sure. The pics were taken in southern Romania, in a forest along the Dâmboviţa river. Can anyone help? bogdan (talk) 09:45, 20 May 2009 (UTC)

The first is a Diacrisia sannio, the second probably a Pyrgus armoricanus or a Pyrgus malvae and I can't be sure about the last. BTW I used this amazing website to do the identifications [12]. Mikenorton (talk) 15:45, 20 May 2009 (UTC)

Thank you, both for the identification and for the link. bogdan (talk) 20:43, 20 May 2009 (UTC)

Work = Force*Distance or = Force*Time?

I have a textbook saying the work done is the product of the force applied and the distance the object moved. But is this ultimately right? Because if I apply the same force for the same time to a faster-moving object, it would result in more work done. Or the distance moved by initial speed of the object must be subtracted from the distance? Work = Force*Time seems better to me. Like sushi (talk) 11:44, 20 May 2009 (UTC)

No, it's right. Force*Time is momentum. Kinetic energy ("work" just means "energy added") is proportional to the square of velocity, rather than velocity itself, that is the key point. The energy required to make a 1kg object go 1m/s faster depends on the initial speed - if it starts off stationary you need 1/2mv²=1/2J, if it starts off at 10m/s you need 1/2m(11²-10²)=10.5J. --Tango (talk) 12:13, 20 May 2009 (UTC)

Thank you. Then the same force applied for the same time could mean different work done?Like sushi (talk) 12:25, 20 May 2009 (UTC)

Yes. Consider a constant 10N force applied to a 1kg mass starting from rest. In the first second the mass accelerates from rest to 10 ms^-1, so the work done is 50 J. In the next second the mass accelerates from 10 ms^-1 to 20 ms^-1, so the work done is 150 J. Gandalf61 (talk) 12:36, 20 May 2009 (UTC)

Does that mean the object moving, no force applied, also, well, having work?

Like sushi (talk) 13:09, 20 May 2009 (UTC)

An object moving with constant velocity has constant kinetic energy. Work is the increase in energy, which would be zero. --Tango (talk) 13:19, 20 May 2009 (UTC)

We must note that the formula Work = Force x Distance is not exactly right. There are two..erm.. errors. (i) It should be displacement, not distance. Note the difference. Distance is the total length of the path traversed. Displacement is just the distance between the initial and final points alone. For example, if you move on a semicircle, the distance is the length of the path, namely pi*radius. But the displacement is merely the distance between the initial and final points, which is twice the radius. (ii) This formula is valid only for a constant force. For a time varying force, this must be integrated along the path to get the work done, so keep it in mind to apply this formula only for constant forces. Rkr1991 (talk) 12:46, 20 May 2009 (UTC)

Even though I have no doubt about the formulas, it has always bugged me that KE is quadratic in velocity, and that (as a result) it's not force times duration. What your intuition is picking up on is momentum, not work; the (change in) momentum is the product of force and time, and is called impulse. --Tardis (talk) 13:09, 20 May 2009 (UTC)

There's one more problem. It should be the dot product, not the cross product. The cross product will get you torque. — DanielLC 15:15, 20 May 2009 (UTC)

Did anyone say cross product? I think we were all talking about the 1D case. --Tango (talk) 15:18, 20 May 2009 (UTC)

Still, it doesn't cost any extra to adapt it for the more general case. I was having the same thought as DanielC. —Tamfang (talk) 02:24, 21 May 2009 (UTC)

It costs understanding for people that aren't familiar with vectors. You don't know if the OP knows anything about vectors or not. --Tango (talk) 14:54, 21 May 2009 (UTC)

How to best boil water?

If we try to heat something by burning fuel, common sense tells us that there is a certain most suitable magnitude of fire. Setting aside the effect of incomplete combustion, (if we use a mixed gas of combustable and oxygen,that will be avoided) Is it better for energy efficiency to make the fire as large as possible, or as small as possible, or there is a golden middle? If we heat it too slowly, the heated object seems to cool down while heating, on the other hand, if we are not trying to heat all the surroundings, the heated gas seems to drive away the gas still not having cooled down yet, and thus, a loss of energy. Like sushi (talk) 12:16, 20 May 2009 (UTC)

It's not really the size of the fire, but the efficiency of getting the heat from the fire to the water. Storm kettles are very good in that regard. The most efficient way to boil water is, I believe, with an electric kettle, though. --Tango (talk) 12:40, 20 May 2009 (UTC)

My mother's coffee-making device heats the water as it's coming out. This has the distinct advantage of not having to heat more of the water than you're going to use. This is somewhat off-topic, though, since you're asking about fire.... 90.193.232.41 (talk) 18:02, 20 May 2009 (UTC)

To efficiently use a kettle or pan of water on the gas range (or "hob"), adjust the flame so that the bottom of the vessel is heated without excess heat escaping around it. This will not make it boil faster, but will get the job done with less fuel. A larger vessel may need a larger flame. A covered pan will boil faster than an open one. The use of water from the "hot" tap is to be avoided for cooking, since it may have more dissolved undesirable substances. With an electric Calrad type burner, select a setting which again matches the size of the heated area to the size of the bottom of the pan. The same quantity of water should boil quicker in a broad pan than a narrow one due to the larger heated surface. A pan with copper cladding might heat quicker than an all steel or thick cast iron one. I suspect that a black or dark bottom pan would absorb heat faster than a white or reflective metallic one, unless the dark coating is thick enough to act as insulation. Edison (talk) 23:06, 20 May 2009 (UTC)

You would be better off just moving to a country with a mains voltage that allows decent electric kettles. In the UK you can easily get 3kW kettles that boil water far more quickly that you would on a hob. --Tango (talk) 16:25, 21 May 2009 (UTC)

Yes, those can be extremely efficient. I'm not entirely sure how they work, do they need time to charge inbetween uses? --Tango (talk) 16:25, 21 May 2009 (UTC)

Unability to lose fat?

I have been working out for the past six months and I have lost a lot of body fat and gained muscle which I am very happy. I am female and have naturally very thin arms and legs so, as you can guess, I tend to gain weight in my torso. However, all these months, my stomach and back fat have remained the same. It doesn't matter how many miles I jog, sit ups and push ups I do, kickboxing (one hour session - 5 days a week) AND playing basketball and volleyball per week. FYI - doc said at my checkup that I am healthy and eat right but I need to lose weight in my middle. He said something about women who are apple shaped are likely to have heart attacks when older. I know that I am genetically predispositioned (mom is short and pudgy) to have a pot belly but it possible for some people to never lose that fat? --Reticuli88 (talk) 12:50, 20 May 2009 (UTC)

Your question appears to be asking if there is a medical justification for your inability to lose fat. That requires a medical diagnosis. It is impossible to give a medical diagnosis over the Internet. If you simply want information on medical studies about fat loss, please ask specifically for information about medical studies. Do not include personal medical information. As it is, your question is too much a request for medical advice to be answered. See the guidelines at the top of the page - we will not provide medical advice. -- kainaw™ 12:56, 20 May 2009 (UTC)

(Non medical oppinion). A lot of the health freaks at my gym talk about hitting "plateau", for either weight loss or gain. Seems the human body gets used to certain level of regular exertion and calorie intake. They generally suggest changing your regime to suprise the body again - so either a further reduction in calorie intake (booo!), or mixing up your excercise for a while, such as swimming / lifting weights, while giving the running a rest.

Does anyone know how much the body adapts to a diet (or can point to a journal)? I know i can reduce by 500 Cal/day from the average 2500 and it makes no difference, but reducing by 1000 Cal/day causes weight loss (and 500 Cal/day extra gives weight gain). There must be research on the calorie level when these things happen on average.YobMod 08:18, 21 May 2009 (UTC)

This article [[13]] may point you towards the research that prompted your doctor's comments. Also see Adipose tissue#Visceral fat. It is reportedly harder to get rid of than the one stored in other tissue. When starting an exercise program or going on a diet a lot of excess water is often lost from tissues. This is frequently mistaken for "loosing fat". Miracle diet ads create unrealistic expectation as to how fast health weight reduction can be achieved. 71.236.24.129 (talk) 10:54, 21 May 2009 (UTC)

CO₂

The en:wiki (:en:Carbon dioxide) has for the meltingpoint of CO₂: -78.5 °C, the german de:wiki (de:Kohlenstoffdioxid) tells us it (called Schmelzpunkt) is: -56.6 °C.
The en:wiki states for the boiling point of CO₂: -56.6 °C, the german de:wiki gives for the same (called Siedepunkt) -78.5 °C.
Why did it go so wrong, and how to fix it? --VanBurenen (talk) 12:53, 20 May 2009 (UTC)

FWIW, Wolfram Alpha says the melting point is -56.56C and the boiling point -78.5 C. -- Aeluwas (talk) 13:05, 20 May 2009 (UTC)

When heating a solid first it will melt, then boil. Thus the boiling temperature has to be the higher of the two. The -56C is higher (hotter) then the -78C. So I think the en:wiki is (now) right and all the other wiki's (and Wolfram Alpha) are wrong... (Or I am nuts?) --VanBurenen (talk) 13:23, 20 May 2009 (UTC)

Don't ask me, I'm about as reliable as... uh, not sure what, today. I did think that it looked pretty odd when I wrote it, but I'm sure that's what Alpha says. I'm NOT sure that it's correct, on the other hand! -- Aeluwas (talk) —Preceding undated comment added 13:53, 20 May 2009 (UTC).

Under typical lab conditions (~1 atm pressure), solid CO2 sublimes directly to the gas at -78°C, and has no liquid form. Liquid CO2 only exists under certain pressure conditions, so separate melting/boiling points only make sense at high pressures. See File:Carbon dioxide pressure-temperature phase diagram.svg. I think the problem with the en:wiki article is that is uses "melting point" as a standard field, which is incorrect in this case. So the melting point given is really the sublimation point, and note the boiling point is given for a particular high pressure.YobMod 14:51, 20 May 2009 (UTC)

Hubble Propulsion

Greetings, giant brains! Please tell me where I begin to veer off course during the following series of postulates: A) The Hubble Space Telescope has a mechanism that allows it to change direction so that it can track pieces of the sky for long periods of time, and turn to other subjects when its ground-based masters desire. B) Since the Hubble cannot store years worth of propulsive material to eject and change direction, it must use forces generated by the movement of internal battery-powered mechanics to accomplish this trick. C) It is therefore possible to create a giant solar-powered, wing-flapping, bird-like spaceship to travel all over the solar system. No ejection of propulsive material required. Sappysap (talk) 13:28, 20 May 2009 (UTC)

Birds can use flappers because they push against air. In space there is no air. --VanBurenen (talk) 13:31, 20 May 2009 (UTC)

Changing orientation is easy since it only requires a temporary change in angular momentum (which can be offset by an opposite temporary change in angular momentum in another part of the craft). Moving around (at least, moving further than the size of the craft) requires a change in linear momentum which cannot be offset by part of the craft, it needs to be offset by something leaving the craft (generally exhaust gasses from a rocket engine). --Tango (talk) 13:37, 20 May 2009 (UTC)

Hubble can't move itself from one place to another without propellant. It can ROTATE by moving its gyroscopes around. Gyroscope goes clockwise, Hubble goes counter-clockwise. And vice versa. You can't move around like that. (Sure you could throw the gyroscope out the back and the Hubble would move forward slightly, but then you'd just be using gyroscopes as propellant.) APL (talk) 13:51, 20 May 2009 (UTC)

You might be interested in ion propulsion, which can indeed create a great deal of thrust with only a little bit of ejected matter simply by ejecting it at very high speeds. --Sean 16:26, 20 May 2009 (UTC)

Hubble definitely uses gyroscopes - those can be powered from the solar panels. The basic idea is that if you spin a gyroscope's wheel in one direction - equal and opposite reaction means that the even bigger, heavier satellite spins in the opposite direction. With three sets of wheels at right angles - you can rotate in any direction. Hence, no (C) - sorry. You can use this trick to rotate a spacecraft - but to accelerate it bodily - you need some reaction mass. The faster you can throw the mass away - the less fuel you need - hence Ion drives which send a very small amount of material out at extremely high speeds. You could also use a solar sail - which uses light, bouncing off of a very large mirror as the 'reaction mass'. However, Hubble doesn't need anything like that. The little propellant it has left is being conserved in order that it can be used for its final de-orbit burn at the end of its life. SteveBaker (talk) 17:57, 20 May 2009 (UTC)

You might be interested, however, in the idea of solar sails. TastyCakes (talk) 18:03, 20 May 2009 (UTC)

Get a rotating office chair and a bowling ball. Put chair in center of room, self in chair and hold the ball. Keep your feet off the ground. Demonstrate that you can achieve B) rotary motion by swinging the ball. Try to achieve C) linear motion by any amount of flapping etc. If it's not possible in two dimensions it won't be possible in three dimensions. Cuddlyable3 (talk) 20:56, 20 May 2009 (UTC)

The trouble is that there is friction involved in the office chair scenario - and because you get different amounts of static friction than dynamic friction, you can move your arms slowly forward without the chair moving because of the high static friction - then fling them back violently and move forwards a few inches. This process can be repeated as often as needed to propel oneself around the room. However, in the almost fictionless environment of space - this trick doesn't work. SteveBaker (talk) 01:42, 21 May 2009 (UTC)

The engineer Eric Laithwaite thought he could use gyroscopes for reactionless propulsion, but other scientistis seem to think he was mistaken. 89.242.85.248 (talk) 19:38, 22 May 2009 (UTC)

Setup to play music in apartment

I am looking for a way to listen to music / podcasts in multiple locations in my apartment. All my music / podcasts are on my PC - in my old place I could hear the music from the speakers next to the PC anywhere in the apartment, but in my new (bigger :) ) apartment the PC sits at one end of the apartment, so as soon as I enter another room I can no longer hear it.

I am willing to lay down some cables, but wireless solutions would be wonderful (especially as the distance from my PC to the kitchen would be a good 25-30m of cable, to go around doorframes etc). I would love to have sound in two locations (in addition to the speakers next to the PC).

I have thought about just taking the audio signal from my PC and running it through some y splitters and feeding it to multimedia speakers which I would install in the other rooms. Unfortunately, this involves wiring (a lot of it, I'd have to run wires from my PC to two locations), and I'm not sure what splitting the signal like this (not to mention the 25m of cabling!) would do to the sound quality. I have also thought about feeding the signal to an amp, which would then output to two independent sets of stereo speakers - but, again with the cabling, and some cursory shopping around has revealed no amps with several speaker outputs, does this even exist? Lastly, a colleague has mentioned using some kind of internet radio, which would listen wirelessly (over my WLAN) to a stream from my PC, but I don't know where to start with such an idea.

What would be good solutions that I should look at? Any pointers would be appreciated! — QuantumEleven 15:24, 20 May 2009 (UTC)

Wireless devices specifically intended for this do exist. A quick bit of googling found this, but I make no recommendations. I believe there are various such devices on offer, so you'll need to do your own research to find what is right for you. --Tango (talk) 15:58, 20 May 2009 (UTC)

Apple's Airport Express allows wireless streaming of iTunes music. You can download add ons that let the system stream other things - Airfoil I think is one of the products. I personally have an Airport Express and it works really well for linking your iTunes up to another set of speakers - and with my laptop on the network I can use that as 1 (admittedly giant) remote control for my stereo. I must warn, however, that user reviews on the product have been mixed with many reports of the product dieing after a year or two. ny156uk (talk) 16:27, 20 May 2009 (UTC)

I dont' know if this is what you have in mind, but if you would be happy playing it through your television/whatever speakers are hooked up to your television, I bought a WDTV this weekend and have been very happy with it. You plug in any kind of USB drive and it'll play it on your television over composite or HDTV cables. It's primarily for playing computer videos on your tv, but it will play mp3s (and pictures) as well. The only problem (for music) is it doesn't seem very good at splitting up by album: you have to go by artist or folder, and then it gives the files in those folders by alphabetical order. I'm not sure if it can play playlists... Also it doesn't have a network card. You could conceivably hook up a networked drive to it (such as the My Book World Edition) but it probably makes more sense to just put all your music on a separate hard disk and attach it. I got one for $150 Canadian at Best Buy, on Amazon they are $105 US.TastyCakes (talk) 16:56, 20 May 2009 (UTC)

This inexpensive gadget is a tiny FM transmitter that plugs into the sound output of your PC. Then you can hear the sound on any FM radio within range. Cuddlyable3 (talk) 20:43, 20 May 2009 (UTC)

If you don't mind headphones you should get a pair of decent wireless headphones. I love my Sennheiser HDR-130, super comfy with good sound quality, but tend to fall down at the slightest tilt from my head (so far it has survived what, 50 1.8m drops?). --118.90.137.39 (talk) 04:58, 21 May 2009 (UTC)

My suggestion is a receiver with a multi-room output. This mean that you will plug 2 (or more, but 2 is common) pairs of speakers into the receiver, and then you can choose which of the pairs are on at any given time, regardless of the signal coming in (you can have none, either or both on at a time). I have this set up at my house: My iPod plugs into the receiver, and I can listen to it in my basement. If at any time I want to walk into my backyard and keep listening, I can hit the zone 2 button on my receiver and the outside speakers will turn on and mirror what's playing while the music continues in my basement. This also fixes your costly wiring problem, since you just need 2 speaker wires for each pair, and speaker wire is generally pretty cheap if you get it in bulk. I would stay away from many wireless devices, ESPECIALLY those fm radio transmitters, because the quality is horrible, which really really bothers me (but if you don't mind horrible sounding fuzzy music than that's the easiest solution). -Pete5x5 (talk) 16:07, 21 May 2009 (UTC)

• I've been successful before in installing an audio driver that allows you to transmit audio output over Ethernet from one PC to another. I combined two programs, one that allows you to digitally redirect a virtual audio output back into a virtual audio input channel (you can also do this with a 1/8" male-male cable and your speaker output/mic in), and one that allows mic input to be broadcast over a LAN. Combine this with standard wireless Ethernet and cheap netbooks, and it's quite easy to get audio from one place to another. Dcoetzee

Human Skulls

Do people with different face shapes have different shaped skulls? Or is the difference made by skin, muscles and cartilage? —Preceding unsigned comment added by 82.44.54.169 (talk) 16:59, 20 May 2009 (UTC)

See Forensic facial reconstruction. The skull, otherwise they wouldn't have much hope doing it. Dmcq (talk) 17:18, 20 May 2009 (UTC)

Well, I think it is a combination of factors. I agree that the skull does play a significant role. I remember when I was reading about the first face transplant the doctors saying the recipient would end up with a face that is somewhere between their old face and the donor's face since they kept the same bone structure but got new skin, etc. --Tango (talk) 17:44, 20 May 2009 (UTC)

The bones make an enormous difference. The triangle formed by the eyes and mouth are essential in both natural and machine facial recognition, and that triangle is determined almost entirely by the skull. If the skull wasn't a big deal, you could put facial prosthetics on a person to make them look just like anyone larger than themselves, but that's just not the case -- Mission Impossible to the contrary. --Sean 17:49, 20 May 2009 (UTC)

Cartilage and soft tissue attaches to bone at some points and vessels feed through holes. There used to be a saying in paleontology that the fossil of an Elephant would be reconstructed to look like a Hamster because the soft tissue didn't leave a trace. This has been changed with the more recent developments in the field where similarities in fine bone structure of (recently dead) living creatures is compared to pits and holes and attachment ridges left in the fossilized bones. Bone is not a stable structure. It grows and cells get replaced. Soft tissue differences leave a trace on the bone. 71.236.24.129 (talk) 07:08, 21 May 2009 (UTC)

All the tissues impact the appearance of the face. Notice that if a person gains or loses a lot of weight, the appearance of their face changes substantially, without their bone structure changing - this shows that the face isn't determined entirely by bone structure. Dcoetzee 10:46, 21 May 2009 (UTC)

mt doom

I am drawing a satirical comic parodying Lord of the Rings. Basically Sam and Frodo get into a fight at the top over who has to buy the beer back at the Shire and Frodo gets pushed in. I need to know if it is likely that his hair would catch fire before he hits the lava, assuming hobitts have a similar terminal velocity and hair burning properties as humans would and that the fall distance to the lava is sufficient to achieve terminal velocity. 65.121.141.34 (talk) 20:17, 20 May 2009 (UTC)

Does it really matter? Dauto (talk) 20:47, 20 May 2009 (UTC)

Hair won't catch on fire because of the free fall itself. Terminal velocity for a flailing human is too slow - it won't generate enough friction, as evidenced by all the skydivers which reach terminal velocity without catching fire. In the absence of a spark, you need to get a substance to the autoignition temperature in order for it to catch fire. I couldn't find a figure for the autoignition temperature of hair, but for paper it's around 450 F (230 C - although some sources claim it's higher, around 840 F/450 C. It of course depends on the type of paper, etc). Lava can get up to 2,200 F (1,200 C), so it might be reasonable to claim that at some point above the lava the temperature reaches the 450-840 F range for autoignition of paper. If hair's autoignition temperature is similar to paper, hair should spontaneously ignite at that point. How long it'll be on fire will depend on how far away from the lava the temperature reaches the autoignition temperature. But a satirical comedy featuring hobbits in a magical universe probably can take some license with the facts ;-). -- 128.104.112.117 (talk) 20:50, 20 May 2009 (UTC)

Did you get the 450F from Fahrenheit 451? TastyCakes (talk) 20:54, 20 May 2009 (UTC)

I actually got it from averaging and rounding the 424-474 F range listed in the autoignition temperature. But I knew about Fahrenheit 451 - in fact footnote 1 in that article is where I got the "some sources claim it's 840 F" info. -- 128.104.112.117 (talk) 15:56, 21 May 2009 (UTC)

True, I don't think my crazed LOTR fan friend is too big into real science anyways. 65.121.141.34 (talk) 20:53, 20 May 2009 (UTC)

Things that one need to know about are where to find food, water and shelter. But flaming hairy hobbits? Cuddlyable3 (talk) 21:04, 20 May 2009 (UTC)

Have you read Bored of the Rings? -Arch dude (talk) 01:43, 21 May 2009 (UTC)

Draw whichever you think is funnier. DJ Clayworth (talk) 18:06, 22 May 2009 (UTC)

Professional sport gamblers

Is it possible to be good at sport gamble or is it just good luck? Since a player is competing against the mob and the mob is always right, is it possible?--88.6.117.202 (talk) 20:52, 20 May 2009 (UTC)

The "mob" isn't always right. The odds are based on what the mob thinks is likely to happen, if you know more than the mob then you can profit (consistently - anyone can profit inconsistently with just luck). You usually can't know more just by being clever, you need better sources of information. If you have contacts involved in the sport feeding you information (eg. "so-and-so's injury is worse than they're making out, he probably won't last the whole match") you can get an advantage. Personally, I prefer to gamble on things where I can increase my own chances using skill - eg. poker. --Tango (talk) 21:13, 20 May 2009 (UTC)

Umm, regarding the above tantalizing comment, and this little tidbit and reviewing Poker, Betting (poker) and Bluff (poker), I think there is an article opportunity here: Poker, how to play intelligently. Sorry about the short notice but I just saw your comment and thought that with all of the trivial articles we have around here that this one would stand as non-trivial, for sure. I think that you've got something to add but, that's just a guess. Ya think? -hydnjo (talk) 03:14, 21 May 2009 (UTC)

Wikipedia is not a how-to guide. There are plenty of websites offering tips on how to play poker, many of them are quite good (for a complete beginner wanting to get good enough to win money off their friends, you would need something a bit more than google to learn how to win major tournaments). --Tango (talk) 14:51, 21 May 2009 (UTC)

Like the stock-market, there are a few anomolies, but in reality it is unlikely to be worthwhile. See the efficient markets hypothesis. Sports gambling is a kind of market, and a lot of academic research by economists has been done. Anomolies include the favorite-longshot bias. It used to be possible to sometimes exploit the tote in the past, but the rules have been changed. You might in theory be able to develop a handicapping system that gave you a small advantage over chance. But, if you are smart enough to be able to do all this, then you would certainly be able to earn far more money doing something else. In reality, you will almost certainly lose money in the long run. 78.146.198.122 (talk) 21:17, 20 May 2009 (UTC)

Wouldn't consistently losing money be just as hard as consistently winning? — DanielLC 05:02, 21 May 2009 (UTC)

The house gets a cut, the vig. If someone bets randomly on sports, over time that will erode his capital down to nothing. Dragons flight (talk) 05:30, 21 May 2009 (UTC)

The trick is always to exploit inefficiencies in the market. In this case, the fact that not everyone has the same information. --Tango (talk) 14:51, 21 May 2009 (UTC)

You could search the bookies for Arbitrage (spelling) opportunities whereby you bet on all outcomes and are guaranteed a (usually small) win. E.g. A league football (soccer) game has 3 outcomes. Home win, draw, home loss (or away win if you prefer). If site X has odds of 4/1 for home win, site Y has odds of 4/1 for the draw and site Z has odds of 4/1 for home loss you can put money on all possible outcomes and be guaranteed a return. These sorts of situations will occasionally come up but given the difficulty and effort of finding (and taking advantage) of them they're not really viable as a 'pursuit'. Lots of betters will use statistical tactics to hedge bets and reduce down their odds of losing, whilst trying not to reduce the value if they do win. Professional Gamblers certainly do exist, I know one. I don't know what you mean by the mob but bookmakers certainly arrange their odds so that they win regardless of the event outcome. ny156uk (talk) 21:40, 20 May 2009 (UTC)

In fact we have an Arbitrage betting article, guess that's worth a read! ny156uk (talk) 21:41, 20 May 2009 (UTC)

Tango means that the odds you can get (or the line) depends on the alleged wisdom of crowds. If the Patriots are favored by 8 points over the Rams, and masses of bettors ("the mob") put money on the Patriots, then, as Ny156uk implies, the bookmakers will adjust the odds so that the Patriots are favored by 8 and one-half points, and then by 9, and so forth until the betting is roughly equal on both sides, so the bookmaker is finally sure to profit no matter who wins because he's only paying out $10 for every $11 that was bet (or so).

To answer the original anon's question, it's possible to win, yes, which can be illustrated easily if you consider illegally bribing players or referees, which certainly has happened many, many times. Unfortunately I don't know any references that discuss how many people are able to do this (more legally) for a living. Tempshill (talk) 22:35, 20 May 2009 (UTC)

Yes, one of the most effective ways of getting more information than the "mob" is to bribe people so you have a key piece of information others don't have - that so-and-so is going to throw the match. --Tango (talk) 14:51, 21 May 2009 (UTC)

When you are thinking of placing a bet of any kind, it is wise to consider the multi-billion dollar casino the "house" has managed to build - and how they raised the capital to build it. The stakes are always against you; the Bellagio didn't get built by having the odds in your favour, right? Matt Deres (talk) 01:46, 21 May 2009 (UTC)

For random games, like roulette, that is absolutely correct. There is no way to win at roulette other than getting lucky (or cheating!). The results of a horse race aren't random, though, which opens up possibilities. --Tango (talk) 14:51, 21 May 2009 (UTC)

You can win at horse racing if you base your bets on the speed of each horse rather than its form. AFAIK horse speeds are not published (presumably because that would spoil the fun), and you have to work them out for yourself. But this does work; success has everything to do with spending a few hours on your homework and very little to do with luck.--Shantavira|^{feed me} 08:20, 21 May 2009 (UTC)

The speed of a horse is not constant, otherwise you would just have to go through results for the last few weeks and find out which horses in the race you are betting on have beaten which other horses in the race previously. You don't need much of an advantage to get profitable in horse racing, the house edge isn't particularly great. It doesn't matter if you lose the occasional bet, as long as you win more than your lose. --Tango (talk) 14:51, 21 May 2009 (UTC)

I sometimes get junk mail about horse racing betting systems - where for a large subscription you get sent betting tips which have been produced by some secret system. Is there an article about thse? I'm confident that such systems do not work, but I'm curious about what the secret system may be. Similarly with other secret money-making schemes that I also get sent junk mail about. 78.146.67.27 (talk) 12:16, 21 May 2009 (UTC)

The secret system will just be a load of nonsense, if you receive anything at all after giving them your money. It is obviously a scam because anyone knowing such a system could make far more money just using it themselves than they could make selling it. --Tango (talk) 14:51, 21 May 2009 (UTC)

One "secret system" (which a sometime-gambling friend once experienced) works as follows (numbers are for example only). The scammer identifies by adverts or otherwise 400 receptive gamblers (unknown to each other), and sends each a free "exclusive" prediction of the outcome of a race. If there are 4 horses in the race he'll send 100 a prediction of horse A winning, 100 horse B and so on. After the race, 100 will think he called it correctly. He then repeats the process with another race (perhaps for a small fee), then another (for a larger fee), until he's got about 6 marks who think he really knows his stuff. Now he offers to sell them the next "prediction" either for a fairly hefty sum, or on the condition that they put on a sizeable additional bet on his behalf, or both. Assuming they fall for it, he's assured of 6 hefty fees, and/or the proceeds of at least one large winning bet that he didn't have to stake. I'm glad to say that my friend figured out the scam before committing himself to the last step. 87.81.230.195 (talk) 23:58, 21 May 2009 (UTC)

See Derren Brown, The System. 89.168.85.22 (talk) 10:32, 22 May 2009 (UTC)

Ah! An interesting corroboration I was unaware of as I avoid most TV. FWIW, the experience I recounted occurred around 1980, but I'm sure the method (or System) has been around for a lot longer. 87.81.230.195 (talk) 11:42, 22 May 2009 (UTC)

Early primate Darwinius shown at keyboard?

Why does our supposed ancestor, "Ida" Darwinius,

look like she is sitting and working at a keyboard? Edison (talk) 21:17, 20 May 2009 (UTC)

This?Popcorn II (talk) 21:32, 20 May 2009 (UTC)

She seems to have better posture, and a shorter tail, in photo number 2. Edison (talk) 22:49, 20 May 2009 (UTC)

Ya, and at the moment, she is trying to google why she is suddenly so famous after 47 million years. More than that she is surprised at why her food is taking so long to digest. Unfortunately she cannot write anything in her own article at Wikipedia because of conflict of interest. But expect a question or two here at refdesk in few days maybe, because she will know many more startling things about herself in coming days and more temptation to come and ask here. - DSachan (talk) 23:10, 20 May 2009 (UTC)

Then does WP:BLP apply? We would not want to embarrass her. Computer geeks have feelings, too. Edison (talk) 04:57, 21 May 2009 (UTC)

She's waiting for 999 Shakespeare-loving friends to show up? Clarityfiend (talk) 05:34, 21 May 2009 (UTC)

On a more serious note: Rigor mortis may help explain some of the position of the limbs. The creature was using Arboreal locomotion. When in pain or near death many creatures curl up in a near fetal position. Humans tend to recognize known images in non related visual input (google "Face on Mars" "Devil in the smoke") Evolutionary this enabled us to recognize hidden predators. But sometimes a primate fossil is just a primate fossil.71.236.24.129 (talk) 06:57, 21 May 2009 (UTC)

We have an article for spurious pattern recognition by humans: pareidolia. Dcoetzee 09:31, 21 May 2009 (UTC)

They laughed when she sat down at the piano. Deor (talk) 11:56, 21 May 2009 (UTC)

May 21

Coraline and Real-D

Coraline was easily one of my favourite films of the past year. Even after seeing it in normal 2-D, it was well worth the price of seeing it again in Real-D (if only for the folded paper mice at the very, very end, after the theatre was empty!). Our article says that the DVD release will include both versions, but our article about Real D Cinema indicates that that process requires some pretty heavy duty specs to show in 3-D. Are those specs only applicable to projected films (i.e. a theatre) or will the normal DVD/Blu-Ray versions be the same quality as the film? Matt Deres (talk) 01:38, 21 May 2009 (UTC)

I don't see how they can show the 3D version on a standard or HD TV screen. In movie theatres, the 3D effect is produced by displaying the left eye and right eye images with different planes of polarization - and the 3D glasses filter out the undesired image for each eye. But a TV screen can't do that. There are 3D technologies that do work with TV - for example by drawing the left-eye image in red and the right-eye image in cyan and using glasses with colored lenses - but that produces nasty flicker and weird color fringing. Alternatively, they can display left and right eye images in alternate frames and use rather expensive 'LCD shutter glasses' which alternately blank out the left and right eye images alternately - but those have to be synchronised to the video stream somehow - which entails special electronics in the video player (or in the cable between the video player and the TV) to send a signal to the glasses (typically via infra-red) to tell it which eye to blank out for the following 1/60th second (1/50th in the UK). Some company once did a similar thing with a little gadget with a rubber suction cup that you stick onto the bottom-left corner of your TV screen that picks up light from a flickering black or white square and relays it to the glasses. But the cost of shutter glasses is pretty steep - and the red/cyan glasses suck - so I can't see how they plan to do this for the DVD/BluRay market. SteveBaker (talk) 12:50, 21 May 2009 (UTC)

It will probably be red/cyan. Other films shot in the Real-d process have been released to Blu-ray in red/cyan. (example: My Bloody Valentine 3D)

Personally, I enjoy movies in red/cyan, but a lot of people have trouble converging the image, get headaches, etc. APL (talk) 16:45, 21 May 2009 (UTC)

It seems as though doing polarization-based 3D on an LCD screen would be pretty easy. LCDs require an outer polarizing layer anyway, and if you replaced it with alternating horizontal and vertical polarizers then ordinary viewing would be unaffected but H-V polarized sunglasses would send each pixel to only one eye. If they'd shipped LCDs like that from the beginning then there'd be a huge installed base of 3D ready screens now. Seems like a sad missed opportunity. -- BenRG (talk) 20:40, 21 May 2009 (UTC)

It would be pretty expensive to do that in the absence of a market demand. So many good technological ideas fail because of this kind of chicken-and-egg situation. There are no 3D TV's - so there are no 3D movies for TV - so there are no 3D TV's. It's not that we don't want 3D movies on TV - it's that we can't figure out how to get there from here. Personally, I think the LCD shutter approach is a better one for the home - it requires no change to the TV whatever - so you don't have to throw away your $3,000 80" flatscreen plasma in order to see 3D movies. But it does require an IR transmitter (about $10) and actively switching glasses (maybe $30 a pair). That would be relatively expensive if you want a lot of people to be able to watch the movie at the same time (which is why they don't do that in the 3D movie theatres) - but much MUCH cheaper than a new TV set for situations where only 3 or 4 people need to be able to watch at the same time. Also they work equally well for non-LCD TV's such as plasma, DLP, CRT, OLED, etc. But it's still a chicken-and-egg situation. Unless a whole bunch of movie-makers release video's in that format on the same day that the hardware manufacturers release the glasses - it's just not going to happen. SteveBaker (talk) 14:50, 22 May 2009 (UTC)

There are already LCD monitors (not TVs) that do that. E.g. iZ3D and the Zalman Trimon. See also [14]. There is also a small number of movies released in field sequential or sensio 3D, see [15]. You may also be interested in the Meant to be Seen 3D forums although primarily about gaming, they do have a forum for movies [16]. Most 3D rendered games can of course be played in (stereo) 3D albeit with some potential issues such as related to aiming, mouse cursors and 2D interfaces. For a long time nVidia had semi decent drivers (which they inhereted from someone I forget at the moment) supporting a variety of 3D modes. They didn't survive the Vista switch nor the switch to general purposes shaders i.e. Geforce8/9 very well and were relaunched eventually along with nVidia's shutter glasses with more limited hardware support. However now that nVidia is actually paying some attention perhaps game developers will too. There are also some decent drivers for shutter glasses from iZ3D for both ATI and nVidia although these are not free. Previously there were a variety of poor quality drivers from others that sometimes worked with ATI. Nil Einne (talk) 21:39, 22 May 2009 (UTC)

Yeah - it's really tough to do that well without help from the game programmers - the driver just doesn't have enough information to get it right. But adding it into a game isn't tough - the real problem is that it halves your frame rate - and serious gamers don't like that. Casual gamers might go for it - but they don't generally want to pay the money for high-end hardware. As games programmers, we'd rather use that horsepower to make a nicer non-stereo game than to make a 3D game for 1% of the market. Of course there is always the Virtual Boy. SteveBaker (talk) 23:32, 22 May 2009 (UTC)

Red/Cyan glasses work for me - but the color is a problem. Either you have to have very monochromatic video - or you have to strongly avoid putting bright red or cyan color into the image. If you draw a bright red bouncing ball against a black background and view it with Red/Cyan glasses, the left eye sees the ball OK - but the right eye sees nothing and the 3D effect is destroyed. Worse still, if there is (say) a flashing red light in the scene - it can make things alternately pop into and out of 3D which is enough to make you want to puke! The solution is to desaturate the video so that red becomes pink...that reduces the 3D artifacts - but makes for a less vibrant image. Red/Cyan is a gimmick - it's not a proper solution to the problem. SteveBaker (talk) 14:50, 22 May 2009 (UTC)

Velocity profile of typical 12V DC electric motor

Hi, I'm wondering what the velocity profile is of a typical 12V electric motor? I've noticed (just empirically) that relatively low speed electric motors get up to speed pretty much straight away but I'd like a slightly more quantified estimate if possible. I think this question is best expressed in an example. So lets say I buy this motor and use it to run a little car. Approx how long would it take to get to its maximum speed of ~500 RPM? For arguments sake the load is approx 2kg.

Also on a related note, how do you convert the torque specification of 5 kg-cm to Nm?

Thanks --118.139.3.77 (talk) 03:02, 21 May 2009 (UTC)

Consider the moment of angular momentum versus the torque. This should answer your question. If a motor were trying to spin up a rotor of large moment, it would take longer than if the motor were spinning free of any load. More torque would get the system up to a given rotational velocity quicker. Edison (talk) 04:55, 21 May 2009 (UTC)

Would the load make that much difference? Wouldn't the load just make it run slower? At any rate I'm not sure on how you relate the moment of angular momentum to the torque of the motor to work out the time it would take to get to the maximum speed. Because say the output shaft of the motor was attached to a solid cylinder with a moment of inertia of 1 kgm^2, wouldn't that give a constant angular acceleration: T_motor = I_cyl*alpha_cyl => alpha_cyl = T_motor/I_cyl. And since the alpha is constant wouldn't that mean it would keep on spinning at ever increasing angular velocity? When surely it has to peak out at 500RPM? And it wouldn't really make sense to say it accelerates according to alpha_cyl until it reaches 500RPM and then suddenly stops because then what is balancing out the torque of the motor? Thanks, --118.138.152.143 (talk) 07:27, 21 May 2009 (UTC)

The motor isn't lifting the weight of the vehicle vertically. Assuming you're on level ground: You need to know the frictional forces (both static and dynamic) and the air resistance (if it's significant at the speeds you expect to travel). Once you know how much force the motor has to apply to overcome those things - you can take the torque and the wheel diameter and figure out how much force there is left over to accelerate the vehicle. You know the mass of the vehicle and the force available from the motor - so you can calculate that acceleration. Then you can turn linear acceleration back into rotational acceleration (again, knowing the wheel diameter) and you'll know the rate of rpm increase. SteveBaker (talk) 12:38, 21 May 2009 (UTC)

Was the ice age cold enough?

According to Quaternary_glaciation, The earth was 8 degrees (C) cooler at the peak of the last ice age. This sent glaciers all the way down into in Upper Midwest. But such a temperature change doesn't seem to me to be enough to cause such glacial expansion. Consider Minneapolis, for instance, whose geology is influenced by past glaciation. According to Minneapolis#Geography_and_climate the average high in July is 29 C. If it were 8 degrees cooler it would still be a warm 21 C, more than enough for the snow to melt through the year. The average year-round temperature would fall to -1 C. Seems cold enough, but Fairbanks, Alaska is colder at -3C [17] and is not currently covered by glaciers. What am I missing?

140.247.125.9 (talk) 04:27, 21 May 2009 (UTC)

Who in Minneapolis talks about temperature in centigrade/Celsius? Edison (talk) 05:44, 21 May 2009 (UTC)

nobody, but Wikipedia's graphs are all in celsius. 140.247.125.15 (talk) 17:06, 21 May 2009 (UTC)

The temperature changes more at the poles than at the equator so currently the poles are melting whereas the temperature has only changed a little at mid to equitorial latitudes. In an ice age the poles get much colder and the effect spreads down but the equator isn't all that much colder. The big expanse of ice causes a feedback effect cooling the area that is iced up. Dmcq (talk) 07:50, 21 May 2009 (UTC)

(edit conflict) Temperature change is not uniform. The number you reference, presumably from the plot, was for Central Antarctica. The global average change during the ice age was ~3 C, with the tropic changing much less than the poles. Central Greenland, by way of contrast saw a temperature change of ~30 C. Ice sheets grow by starting at places that are very cold and spreading outward. As they spread, the effect of covering more areas with ice and snow for more of the year often causes further cooling by reflecting sunlight into space (an albedo feedback). In addition, ice sheet growth also requires an available supply of moisture to allow for regular snowfall. Fairbanks, to use your example, is far enough North that the prevailing winds are polar easterlies. This means most of its weather comes from dry Canadian air rather than from the Pacific. As a result it is harder to form glacier there than on the East coast of North America at similar latitude, where one will get snow from Atlantic moisture. Hence ice sheet in North America start in the far northeast and grow out and down as temperatures fall. Dragons flight (talk) 07:52, 21 May 2009 (UTC)

When birds sleep...

Why do they usually turn their heads through 180 and tuck their beaks into their back feathers? Is it just to keep their faces warm, or is there a physiological reason for it? —Preceding unsigned comment added by 81.77.140.54 (talk) 08:42, 21 May 2009 (UTC)

Perhaps, it acts as a natural and ready to use pillow for them, which provides comfort (in the sense of softness) and warmth both. - DSachan (talk) 09:23, 21 May 2009 (UTC)

In Britain, for example, during the winter a large proportion of birds are killed during the nights from the cold, particularly when they are short of food and hence the energy to keep them warm. Anything that reduces their surface area will help them survive. (I remember hearing or reading that the dawn chorus intensity is in proportion to the left-over energy budget from the night). Plus, I imagine that they save energy by being able to relax the neck muscles which are no longer working to hold up the head. And like humans, when they sleep their head would droop if not supported. 78.146.67.27 (talk) 10:53, 21 May 2009 (UTC)

I suspect that it helps keep the biting insects at bay. If you've ever seen a bird on the nest being swarmed by mosquitoes and black fly. You would understand. 67.193.179.241 (talk) 20:44, 21 May 2009 (UTC) Rana sylvatica

On the topic of thunderstorms and humans

I am personally very fond of thunderstorms. They bring about a certain "charged" smell in the air, a heated and moist atmosphere and indeed, the rumbling from afar is tad soothing. I know a dozen more of my friends share this with me, and while lightning striking nearby does affect us all in similar way, I was keen on asking a question more related to thunderstorms from afar: Shouldn't I feel less enthusiastic when I know a thunderstorm is about to come? Most animals seek shelter, I can't imagine too many of them enjoy the ordeal, but while some humans retain the fright of thunderstorms, many (most, according to my original research) don't. The precautionary signs come off in a comfortable way. What is to be attributed for my experiences? Simply that I've never experienced anything to teach me otherwise, or that a more built-in switch has been dulled over generations of having shelter? Thank you in advance. 90.149.144.55 (talk) 10:34, 21 May 2009 (UTC)

I'm just speculating here, but it seems to me that if you're a human-sized animal, you really don't worry about thunderstorms too much. The chance of encountering a lightning strike in our natural habitat (the savannahs) is very small, and there isn't much shelter to speak of around. It's probably even a good time to hunt for certain animals. Dcoetzee 10:39, 21 May 2009 (UTC)

Well, one of the cool (and really comparatively advanced) things about us humans is that we are capable of ignoring or overriding our instincts based on the circumstances and rational thinking. Animals aren't very good at that. I mean, when we get angry, horny or scared, we can still function properly -- we don't start fighting, screwing or running away at the drop of a hat as soon as the urge strikes us. (Well, some people do, but people with that poor impulse control are generally trouble, and in trouble.) I was a little scared of thunderstorms when I was a kid; these days, like you, I love 'em. A part of it is probably the fact that I know I'm safe, and while I haven't examined my feelings very closely, I wouldn't be surprised to find that I'm still a little scared somewhere deep inside, but knowing that I'm safe, I can enjoy the thrill -- not unlike going on a roller coaster ride at an amusement park. -- Captain Disdain (talk) 11:17, 21 May 2009 (UTC)

Captain, i respectfully disagree with "animals aren't very good at that". Any plant or animal can be aclimatized, habituated or get used to, any stimulus within thier physiological limits. Again, HUMANS ain't so special. 67.193.179.241 (talk) 20:51, 21 May 2009 (UTC)Rana sylvatica

Sure, animals can get used to all kinds of things, but there's a great conceptual -- and cognitive -- difference between becoming acclimatized to something and making an actual case-by-case decision to disobey the instinct. The latter tends to require abstract reasoning skills. -- Captain Disdain (talk) 23:32, 21 May 2009 (UTC)

I suspect (without evidence) that we're 'wired' to seek shelter in the case of storms - which means that something in our brains makes us feel uncomfortable out in bad weather and comfortable when we reach shelter. If our emotional systems "reward" us for achieving an instinctual goal, that would be no surprise. We feel similarly comfortable after eating, sex and other such activities. It seems reasonable then that when we hear a storm and are sheltered - that we feel good about that. SteveBaker (talk) 12:31, 21 May 2009 (UTC)

Maybe I'm not like other people, but personally I like being outside rather than in when a big storm is coming. Then again, I also want to go tornado chasing, so I think my fight-or-flight instinct is broken.-RunningOnBrains^{(talk page)} 14:18, 21 May 2009 (UTC)

I just got myself thinking: maybe more of us are adrenaline junkies than we give ourselves credit for. Maybe that sense of impending danger is what gives you a pleasurable rush. -RunningOnBrains^{(talk page)} 14:22, 21 May 2009 (UTC)

I think all the answers above are very good. I would only add that thunderstorms may engage our higher brain functions as well. We live in an age that allows us unprecedented communications abilities; we can vicariously experience almost anything we care to imagine, but there's something to be said for the first hand, totally immersive experience of being within a powerful thunderstorm. For an old atheist like myself, it's probably as close as I'll ever come to experiencing something of that kind of terrible power. The kind of awe that power can elicit is probably not too far from an old-time fire-n-brimstone religious experience. Matt Deres (talk) 13:38, 21 May 2009 (UTC)

The "charged" smell you sense is probably ozone. It is said that some people react positively to the ionised air before thunderstorms. Cuddlyable3 (talk) 14:04, 21 May 2009 (UTC)

The fear factor is partly situational, I think. I ordinarily don't have any fear of thunderstorms, but I've been caught in exposed positions a couple of times -- once on a mountain pass with lightning striking all around and numerous lightning-blasted trees beside the trail -- and it definitely got my adrenaline going. Regarding the smell, I think it comes more from rain on dry ground than from ozone. Looie496 (talk) 16:31, 21 May 2009 (UTC)

Rain on dry ground happens in any sudden downpour. If the smell is unique to thunderstorms then it is more likely from the ozone. That would require lightning to be nearby, though, you wouldn't get any ozone from a thunderstorm several miles away. --Tango (talk) 23:25, 21 May 2009 (UTC)

There is some element of instinct going on here. When the weather outside is utterly diabolical - storm, rain, etc. I feel very good about curling up on the sofa with a good book or vegging out watching TV. When it's gorgeous weather outside, I find it very difficult to do those things - even though I have no intention of going outside. That's not the rational part of my mind doing that - because if you're indoors anyway, what the heck does it matter what's going on outside? SteveBaker (talk) 14:36, 22 May 2009 (UTC)

Avoiding sexual arousal

I'm not sure if this is science or not. I took a guess. Anyway, my friend has two problems. One, she gets aroused very easily by vibrating buses - something which she finds intensely uncomfortable, especially as she has to take a bus to university every day. Secondly, she has wet dreams, which again, she doesn't enjoy. Is there any way to control or prevent either of these? Vimescarrot (talk) 10:28, 21 May 2009 (UTC)

Some people just happen to be very easily sexually stimulated by certain stimuli. I'm not aware of any treatment for this, although she can talk to her doctor about it if she feels comfortable doing so (I do know that there are some drugs that decrease libido - this is generally listed as a negative side effect - but I don't know if she'd want it to be impeded all the time). Generally, we can't give medical advice here. The only suggestion I can think of is to bring along a book or a music player or something to help divert her attention, and if possible to seek a more comfortable alternative to the bus. Dcoetzee 10:35, 21 May 2009 (UTC)

Maybe she just needs more sex, duo or solo? Or does she have religious reasons for abstaining? If you are a male friend, are you sure this is genuine and isnt just a come-on? 78.146.67.27 (talk) 10:56, 21 May 2009 (UTC)

She has reasons for abstaining, but she won't tell me what they are. Vimescarrot (talk) 11:09, 21 May 2009 (UTC)

Generally, if someone is abstaining from sex for reasons they aren't willing or able to disclose and gets very disturbed by arousal or wet dreams, I would consider that a kind of a warning sign. I could speculate, but what with the information available to us being second-hand and especially that whole medical advice thing, I'm gonna pass. Instead, I would recommend that she talk to a good therapist. -- Captain Disdain (talk) 11:23, 21 May 2009 (UTC)

Why the hell wouldn't she enjoy sexual dreams?? As for the bus thing,, see PSAS —Preceding unsigned comment added by 82.44.54.169 (talk) 11:23, 21 May 2009 (UTC)

82.44 - Just because you enjoy your sexuality, doesn't mean everyone does. Vimescarrot (talk) 11:33, 21 May 2009 (UTC)

True enough, but when the body and mind are at odds, it's an indication that one side or the other needs to be brought into alignment. The one requires a therapist, the other requires a physician; neither would benefit particularly from strangers on the internet making guesses based on second-hand information. The anon's comment was a little insensitive, but speaks to the general truth that the mind is often confused while the body seldom is. Matt Deres (talk) 13:43, 21 May 2009 (UTC)

I have heard two advices given to celibate monks troubled by sexual desire: A) Imagine that everyone is your brother or sister, and B) Picture everyone without their skin. Cuddlyable3 (talk) 13:42, 21 May 2009 (UTC)

The OP's friend isn't being aroused by specific people, though. Avoiding being sexually stimulated by the bus could be as simple as sitting it a different position. Cross or uncross your legs, maybe. Being made uncomfortable by wet dreams isn't something we can help with, though, that needs a therapist. --Tango (talk) 14:29, 21 May 2009 (UTC)

Check to see if she's figiting with her legs; bouncing one leg up and down is a common indication that someone is sexually aroused. It's considered by some to be an almost unconscious form of masturbation. If she's moving her legs all the time then she's likely sexually aroused more often than just on her way to school, and it's not just the bus (although that would indicate that the bus does a better job at pleasing her than her own legs). -Pete5x5 (talk) 16:07, 21 May 2009 (UTC)

Restless leg syndrome, though an invented reason to sell a drug, is not an unconscious form of masturbation. Tempshill (talk) 16:08, 21 May 2009 (UTC)

Unconsciously figiting is not restless leg syndrome. --Tango (talk) 16:27, 21 May 2009 (UTC)

Check to see if she's figiting with her legs; bouncing one leg up and down is a common indication that someone is sexually aroused. It's considered by some to be an almost unconscious form of masturbation.

Wikipedia articles are fine. Vimescarrot (talk)

Actually, I don't know why I responded to that. I don't need to know when she's sexually aroused (she tells me anyway), and we already know why. I was just after how to stop it. Thanks for trying, though. Vimescarrot (talk) 17:02, 21 May 2009 (UTC)

To me, this looks like a request for medical advice, right? Axl ¤ [Talk] 21:09, 21 May 2009 (UTC)

At least partially, yes, which is why people have been suggesting going to a therapist. --Tango (talk) 23:23, 21 May 2009 (UTC)

Rules of thumb to identify wildflowers?

The rules of thumb I know are that if its got four petals, its a member of the mustard/cabbage family, and if its got five petals then its a member of the Mallow family. Are these two rules of thumb reliable, and are there any more? I am in the UK, but such rules of thumb might apply worldwide. 78.146.67.27 (talk) 11:01, 21 May 2009 (UTC)

No, they are not reliable in that form. For example, a flower with four petals may belong to a plant in Papaveraceae and not only in Brassicaceae (=Cruciferae), and a flower with five petals may belong to a plant in Rosaceae, Oxalidaceae, Violaceae, Geraniaceae, etc., and not only Malvaceae. --Dr Dima (talk) 19:58, 21 May 2009 (UTC)

Those are not reliable rules and to each rule there are exceptions, BUT if the flower consists of many "florets" it is generally in the composite family. If the stem of the plant is roughly squared, then it is usually in the mint family. Can't think of exceptions to either rule but learning to use botanical keys quickly, is learning to cheat. That is, if you recognize that a plant is in family "X" then you can go to the index and find where that family is in the key. Good luck and have fun. 67.193.179.241 (talk) 21:19, 21 May 2009 (UTC) Rana sylvatica.

Thanks. "The family Asteraceae or Compositae (known as the aster, daisy, or sunflower family) is the second largest family of flowering plants, in terms of number of species." Cleavers or Goose grass is one of the exceptions to the square-stem rule. 78.146.162.232 (talk) 11:30, 22 May 2009 (UTC)

Biology - water

In cold countries such as Alaska, the surface of the sea freezes first or becomes solid ice, while the bottom of the surface still remains in liquid state. Why? —Preceding unsigned comment added by 60.53.212.205 (talk) 11:12, 21 May 2009 (UTC)

Because ice floats. 78.146.67.27 (talk) 12:07, 21 May 2009 (UTC)Rkr1991 (talk) 13:04, 21 May 2009 (UTC)

Exactly. Ice has a density of only approximately 9/10th of water, and hence when water freezes, ice being lighter rises to the top. This is of vital importance to the survival of fish and other aquatic animals. If ice had frozen from the bottom, they would have been pushed to the top, an a more dangerous environment. Now since ice freezes from the top, they can swim underneath the ice sheet. Also, don't forget to sign your posts by typing 4 '~' signs at the end :) Rkr1991 (talk) 13:04, 21 May 2009 (UTC)

Also, the sheet of ice on the top tends to insulate the water underneath and prevents total freezing. If it froze from the bottom up you would end up with the whole thing frozen. This peculiar feature of water (most substances constantly contract as they cool, water has a little bump in the graph near its freezing point) is one of the things that makes it so good for life. They have been theories about life on the moons of the outer planets based on ammonia, but ammonia doesn't have this advantage (it also lacks certain other advantages). --Tango (talk) 14:33, 21 May 2009 (UTC)

A crucial point is that (for fresh water) the maximum density of water occurs at 3.98 °C (39.16 °F), that is, several degrees above freezing. This means that the deep water is never colder than that, because colder water will rise. The same thing holds for sea water, except that the temperatures are different. Looie496 (talk) 16:40, 21 May 2009 (UTC)

Is that point of maximum density universal, or does it depend on pressure? --Tango (talk) 16:43, 21 May 2009 (UTC)

Here is a graph of water density vs. temperature and pressure and based on the maximums, the point of greatest density does indeed depend on pressure. Regarding ice density, there are some other forms of ice made using varied temperatures and pressures which have higher densities than liquid water like Ice III (1.16g/cm3 (at 350 MPa)). I'm not sure if Ice III is more dense than water at 350 MPa though. Sifaka ^talk 00:35, 22 May 2009 (UTC)

No, the same thing does not hold for sea water. For sea water, due to its salt content, the maximum density of the liquid is at the freezing point. Dragons flight (talk) 17:31, 21 May 2009 (UTC)

Interesting. I didn't know that. I wonder what's the minimum amount of salt necessary in order to make the point of maximun density coincide with the freezing point. Dauto (talk) 23:01, 21 May 2009 (UTC)

If what you are saying is true D.F., I'm not sure that implies that saltwater ice is equally or more dense than the saltwater it's in. To rule out the brine effect (the tendency for ice to exclude solutes as it freezes), I'm making a solid icecube of 125mM NaCl and I'm going to see if it floats or sinks in the same liquid solution it is made from. I'll report the results once the cube freezes entirely solid. (Later Edit:) I went and spilled my liquid solution and was too lazy to make some more so I tested my salty ice cube in tap water and it still floated, just barely. Sifaka ^talk 00:35, 22 May 2009 (UTC)

The solid is still less dense than liquid. It is just that the point of maximum density of the liquid shifts to the freezing point of the liquid rather than several degrees above the freezing point as is seen for pure water. It is also worth noting that the solid-to-liquid density shift is very large in all cases. By contrast the temperature dependence of density within the liquid state is relatively quite small. Dragons flight (talk) 00:51, 22 May 2009 (UTC)

DF, are you saying tha the maximum density of saltwater is precisely at the freezing point, or just much nearer the freezing point than freshwater? Is there a graph for the salinity/density/freezing point relationship? I'm asking because of my fascination with the very weird properties of water in all its phases. Franamax (talk) 09:34, 22 May 2009 (UTC)

AFAIK Freezing also changes the concentration of salt because it gets squeezed into channels and oozes out. You then get water with less salt in it which again floats. Drift ice. 71.236.24.129 (talk) 09:49, 22 May 2009 (UTC)

Self-suggestibility - link to confabulation?

I'm sure I'm not the first person to say the suggestibility article reads poorly and looks to be mostly about hypnotic suggestibility. (Or, maybe the editors are just very suggestible and have been told it's god like it is. :-) )

I was wondering how it was that some - especially children - are able to think that things they imagine are actually real. Is this self-suggestibility due to confabulation? Do their minds naturally envision that, "Since I thought/envisioned it, it must be true?" What about adults? I'm not talking necessarily about the criminal who - desipte all the evidence they did it - convinces him or herself they didn't, though that may be part of it.

I would even be tempted to try to edit the article to include mention of confabulation, but I wouldn't have real sources. But, there has to be more to suggestibility than hypnotic states, doesn't there? 209.244.30.221 (talk) 13:29, 21 May 2009 (UTC)

I'll give this a shot. First off, when you say above that editors have been "told it's god" - have you been staring at any rotating coins lately? ;)

The confabulation article seems to be about manifestations of neurological impairment. This is not the case with children, rather there is an ongoing process of distinguishing imagination from reality. Recall that for the first several months of a human life, the baby is not able to even recognize the difference between itself and its environment. For many years, one depends on one's parents to explain that your dreams were only that, that the scary movie you watched was all made up, and that it's OK to walk down the stairs into a dark basement. It takes a long time for a brain to settle down and get on with the boring process of plain old living a life. Even then, many people are still compelled by their imagination and they imagine crazy realities like light bulbs and microprocessors. That's just normal neural development,

Looking at the Suggestibility article, I'm struck by the section discussing the differences between suggestible, susceptible and gullible. Confabulation may play a part there too as a pathological manifestation, but yes, you would need to assemble some sources. If you do find them, please be bold and edit away! Franamax (talk) 08:54, 22 May 2009 (UTC)

Carbon Monoxide Poisoning

Hi, I've always been curious about some of the specific points relating to carbon monoxide poisoning and have been unable to find answers elsewhere, I have five questions, any help or answers would be greatly appreciated:

1. Many of the long term effects of co poisoning(CoP) can take several weeks to show up, I've read that this is due to the long term effects being caused by CO debinding from hemoglobin, then becoming toxic. Is it true that this is the cause of longterm effects, and if so would being treated with hyperbaric oxygen after 48 hours, but prior to several weeks, have any benefit?(HBO has a large benefit if administered within 48 hours)
2. CoP can have permenant/long term effects of cognition and memory formation; in the event that these effects occur, how often are they permenant?
3. Related to the above, I've read that some cases of CoP present mild symptoms so that the victim is unaware that have been poisoned; supposing that such a case did cause cognitive/memory problems, would the victim be aware that they had such problems? In other words, would the person be able to tell that they something was wrong, or would they be oblivous to such things, perhaps thinking that they have become somewhat absented minded...in short, how obvious are the brain based effects of CoP?
4. Again relating to the above; I've read that CoP causes demylination to occur in the white matter of the brain, and I've also read that their are medicines for other disorders that can reverse the effects of demylination; given that this medicine was developed for other disorders, would it be effective in reversing the effects of CoP also?
5. My final question, again related to the above; in the event of long term cognitive impairments would a CT/MRI be able to detect such damage? Are there any means to estimate the ammount of damage, the possiblity of recovery, or the chance of further degradation? I've read that in the first few weeks after exposure that small pockets of atrophy can be detected in the brain, though I would imagine that in time these atrophied cells would be removed by the body; is this accurate?

Thank you for any help. P.S. I do realize that this question could be considered "medical" in nature, to avoid giving the wrong impression; I am asking out of curiousity, not because I think I may have CoP or any other such thing:) Phoenix1177 (talk) 14:43, 21 May 2009 (UTC)

I have adjusted the formatting of your question slightly, I hope you don't mind! --Tango (talk) 16:30, 21 May 2009 (UTC)

To answer question 1: Carbon monoxide washout follows a biphasic pattern due to myoglobin binding. From this article, half times while breathing air are 236 minutes and 302 minutes; breathing 100% oxygen they are 87 minutes and 160 minutes. The CO level will be back to baseline within a couple of days. Our article "Carbon monoxide poisoning" describes the mechanisms of toxicity. The main effect is binding to haemoglobin, which reduces the oxygen-carrying capacity of blood, leading to tissue hypoxia. The other mechanisms are (probably) less important. Release of CO bound to myoglobin does indeed slow the rate at which CO in the blood falls. However this is not enough to actually raise the blood CO level. I am unconvinced that hyperbaric oxygen has "a large benefit". This study did not demonstrate superiority over high flow oxygen (FiO₂ 100%) at normal barometric pressure. Axl ¤ [Talk] 21:42, 21 May 2009 (UTC)

Scanning western blots randomises results...

Is there an advantage to using built-for purpose gel/blot scanners from biotech companies over a regular scanner for the purpose of scanning in western blots stained with AEC stain?

We've been using an ordinary scanner, and then quantifying the bands but I notice that the same band from two different scans of the same blot divided by the first band in the blot (for normalisation purposes) can differ by as much as two-fold. It depends on the contrast settings used. Default settings don't always result in fair representations of the actual blot. How does one overcome this? ----Seans Potato Business 15:03, 21 May 2009 (UTC)

If you mean an ordinary scanner in the sense of an off-the-shelf document scanner, I think that's a remarkably bad idea. Their nonlinearities are hideous. Looie496 (talk) 16:47, 21 May 2009 (UTC)

You shouldn't need anything fancy to scan in your gels and quantitate the bands. The commercial scanners are usually bundled with software that facilitates the analysis process and they come with other bells and whistles that make it worthwhile for some people to buy them. You can test for nonlinearity by just scanning the same gel a few different times and checking to make sure that you're getting similar results. Granted, if you're doing ultrasensitive measurements, Looie has a good point.

However, I think you already have a clue about why you're getting disparate results -- it sounds to me that the software you're using to adjust contrast is actually changing the information content of the image instead of just representing it differently on your display. This can be a huge problem because you're basically saturating the darkest bands to be able to see the lightest ones. If your image software is doing this, you need to either perform the quantitation on the unmodified image (you may not be able to see the band very well but the computer will be able to count up the gray levels for each pixel without a problem), or get new software!

If you just want to contrast the blot for the purpose of presentation or publication, you can do so but you should be honest and report that the image was contrasted using such-and-such program. Image manipulation can be very misleading and is pretty rampant in the scientific literature! --- Medical geneticist (talk) 16:57, 21 May 2009 (UTC)

Energy from walking feet

I read somewhere that now-a-days, many scientists have developed methods to produce and use energy in many forms, from walking human steps! Can anyone tell me how is this done? many thanks. 59.103.63.74 (talk) 23:08, 21 May 2009 (UTC)

I'm not sure what you are talking about, but I know that some wrist-watches use energy from a person's movement to self wind. This is not a new technology. Dauto (talk) 23:17, 21 May 2009 (UTC)

There are two technologies you could be describing. There are some devices that are powered by being shaken as a person moves. I also recall a design for a floor that uses the vibrations caused by people walking over it to generate power (possibly the floor of a subway station...). Which one are you interested in? --Tango (talk) 23:21, 21 May 2009 (UTC)

I think he is thinking of piezoelectrics which generate a tiny amount of electricity when mechanically compressed. Placed in everyday areas subject to compression, such as the sole of your shoe, and rectified in the right way this can be used to do small amounts so work. The available energy is usually quite small though. See also: Energy harvesting. Dragons flight (talk) 00:58, 22 May 2009 (UTC)

There are also floors that generate energy from the friction of those walking around on it. http://www.groovygreen.com/groove/?p=1867 has more info on them. 194.221.133.226 (talk) 09:08, 22 May 2009 (UTC)

It's not friction, it's impact. That's the kind of thing I was trying to describe above. --Tango (talk) 11:08, 22 May 2009 (UTC)

The compression technique is one method, but the questioner might have been think about something like the backpack that generates power. There were a bunch of news stories about this a couple of years ago. Looie496 (talk) 17:48, 22 May 2009 (UTC)

The anon I replied to gave a link to a description of what they were talking about, it is clearly talking about piezoelectrics. --Tango (talk) 18:23, 22 May 2009 (UTC)

May 22

does THC cause weed's smell?

I'm curious. If it doesn't, I imagine there's some future genetic engineering in the works that will be the delight of young people everywhere, and I imagine it could be very lucrative for street hustlers with biotech qualifications. John Riemann Soong (talk) 02:55, 22 May 2009 (UTC)

The large leaves have little THC content but still have the herb smell, so I'd say no, the smell is due to other chemical compounds. Of course, that's only what I've heard through my church group, I never touch the stuff. :) One of the attractions of cannabis is that it is a natural plant product that springs from the earth all by itself and delivers a gift of nature - I'm not so sure there is a big market for GMO's in that space. There are already lots of synthetic chemical products to whack your head with if you're so inclined. (I'm not) Franamax (talk) 08:19, 22 May 2009 (UTC)

If you're thinking of sniffing dogs, I would imagine expect they could be trained to smell THC if they're not already. In any case, removing every single compound likely to be detected by humans is an extremely difficult task. In other words, you could change the smell but it would likely still have a fairly unique smell. Indeed, I would expect the current smell is a combination of a large number of compounds not one single one although some may be more important then others. Most importantly perhaps, removing most of the compounds giving it a smell is likely to result I would expect in a product that doesn't 'taste' as good when the marijuana is smoked or whatever Nil Einne (talk) 08:52, 22 May 2009 (UTC)

As an analogous scenario, think about decaffeinated coffee. While some enthusiasts insist it's as tasty as regular coffee, I can tell the difference. However, removing the caffeine does not create a colorless, odorless liquid. Many other constituent chemicals contribute to the total flavor and aroma. Nimur (talk) 09:54, 22 May 2009 (UTC)

Hypermetropia

How to find power of corretive lens? why do we consider normal near point as object distance and the defective near point as image distance while calculating the power of convex corrective lens for Hypermetropic eye? —Preceding unsigned comment added by 61.2.178.70 (talk) 03:10, 22 May 2009 (UTC)

I assume you are asking this question with some knowledge of lenses and optics. Now consider a hypermetropic eye. The problem is that things too close are not focused on the retina. The objective is to give normal vision, where the least distance of distinct vision (D) is about 25cm. That is, if an object is placed in front of the eye as close as D, even then the eye must be able to see it. That is the limiting case, so if we satisfy for the limiting, we (theoretically at least) satisfy for all cases. So now the object is at D. But the eye can see only its own least distance of distinct vision (d) which is greater than D. Therefore, the image must be formed there. So now applying the lens formula, as you correctly suggested, we consider normal near point as object distance and the defective near point as image distance. Also don't forget to sign your posts by typing four '~'s at the end. Rkr1991 (talk) 05:07, 22 May 2009 (UTC)

Lilac bushes

I have a few lilac bushes in my front yard. I'd like to have more. Is there an easy way for me to take a cutting from one of the bushes and get another bush out of it? Dismas|^(talk) 05:15, 22 May 2009 (UTC)

I have no answer for you (other than talking about all my different-coloured lilac bushes) but I will say that if you're in the northern hemisphere, this is probably the time to clip off some green shoots and test directly. You could also try using a rooting hormone in the water, and while you're at the garden centre buying it, ask one of those helpful people. Franamax (talk) 09:42, 22 May 2009 (UTC)

Buddleia seeds can be easily bought, where I am at least, and grow into shrubs that look very similar to lilac bushes in my opinion. Perhaps you could harvest some lilac seeds from your bushes and grow those in pots of compost before planted them out. Other shrubs with lots of blossom also exist - I sometimes see for example a shrub that is completely covered in blue, no idea what its name is. Edit: I have looked at The Tree And Shrub Expert by D. G. Hessayon, published in the UK. Buddleia - propagate by sowing seeds in spring or sowing cuttings outdoors in autumn. The blue bush seems to be Ceanothus or 'Californian Lilac' - propagate by planting cuttings in a cold frame in summer. Syringa or 'Lilac' - also propagate by planting cuttings in a cold frame in summer. But as the UK is mostly in hardiness zone 8 or 9, and where the OP comes from is in zone 4 I think, then that advice may not apply. 78.146.162.232 (talk) 11:50, 22 May 2009 (UTC)

The usual way to propagate lilacs is from shoots, not seeds. See [18] - Nunh-huh 12:12, 22 May 2009 (UTC)

Lilacs grow most successfully from suckers. At the base of every lilac bush you will see shoots emerging. Get a mattack and detach the shoot from the rootstock below the soil level, then put it in a plastic bag until you are able to plant it (don't wait too long though). Then it's easy enough to just plant it and it should grow. And then you will find that, before too long, you want to get rid of said lilac bush because it's about to take over your garden! --TammyMoet (talk) 13:04, 22 May 2009 (UTC)

BTU'S produced by a conventional 4 or 6 cylinder engine

Can anybody advise how much heat is produced on the exhaust system of a conventioal 4 -6 cylinder engine at the exhaust pipe near the catalytic convertor? —Preceding unsigned comment added by Sustain6996 (talk • contribs) 07:36, 22 May 2009 (UTC)

List of longest rivers in Poland

List of rivers of Poland (edit | visual edit | history) · Article talk (edit | history) · Watch

I have only found top 29 longest rivers in Poland. Do you know top 50 longest rivers in Poland? —Preceding unsigned comment added by 213.158.197.100 (talk) 11:44, 22 May 2009 (UTC)

There are 123 pages in Category:Rivers of Poland. You might find what you are looking for there, but we don't have them as an organised list. SpinningSpark 14:00, 22 May 2009 (UTC)

When you get to the smaller rivers - you start running into the "How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension" problem. When precisely does the river start? Maybe water trickles over some fields before it starts to look like a river? If the river is very crinkly, then issues of fractal dimension start to become a problem. So I doubt very much that you can say with any authority which of those 123 rivers are longer than which others...except for the biggest and most obvious ones - which we've already covered. SteveBaker (talk) 14:27, 22 May 2009 (UTC)

Eating too little fats

What would be the long term physiological or medical effects of an adult eating say only 10% of their calories as fat, instead of the 25 to 35% that is recommended? I understand that fat-deficiency was a problem in Victorian times, before margarine was invented. 78.146.162.232 (talk) 13:11, 22 May 2009 (UTC)

See rabbit starvation. It does not discuss the American West in the article, but apparently this was a condition suffered by some pioneers, even though they had a high calorie intake and the native Americans around them on the same diet were not suffering. The difference - the pioneers were discarding the fat from the meat. SpinningSpark 13:25, 22 May 2009 (UTC)

Thanks, but it does not mention anything about the physiological effects. 78.146.162.232 (talk) 14:30, 22 May 2009 (UTC)

From the lede paragraph of the article: Symptoms include diarrhea, headache, lassitude, a vague discomfort and hunger that can only be satisfied by consumption of fat or carbohydrates, and low blood pressure and heart rate. Are those not physiological effects? SpinningSpark 14:49, 22 May 2009 (UTC)

Thanks again, but those are the symptoms. I'm wondering what physiological pathways are involved, how it might for example affect the nerves or the brain which I understand include a lot of fat, or if something like ketosis or its opposite is involved. 89.242.85.248 (talk) 19:03, 22 May 2009 (UTC)

It is discussed in detail in this article from The American Journal of Clinical Nutrition. SpinningSpark 14:55, 22 May 2009 (UTC)

Thanks, but that link only seems to be a description of hunter-gatherer diets. 89.242.85.248 (talk) 19:14, 22 May 2009 (UTC)

See Essential fatty acid. There may also be some links you can track down in the articles on Omega-3 and Omega-6 fatty acids. I'm not convinced that someone taking in only 10% of their calories in fat would have any adverse physiological effects unless the fat source was completely deficient in Omega-3 and Omega-6 fatty acids. The body can otherwise make other lipid molecules it needs. Do you have any references for fat-deficiency in Victorian times? Also, the issue of "rabbit starvation" applies to a special condition of a diet largely composed of "lean meat coupled with a lack of other sources of nutrients" (i.e. presumably also lacking in carbohydrates and certain vitamins) which isn't really directly related to what the OP is asking. --- Medical geneticist (talk) 13:36, 23 May 2009 (UTC)

Question

What would happen if a man with a double-barreled name married? What would the woman be named? If they had a child, what would the child be named? 143.238.237.25 (talk) 13:39, 22 May 2009 (UTC)

It's up to the couple. There may be legal restrictions on what they can choose, though. A German court has recently upheld a ban on triple-barrelled names [19]. --Tango (talk) 13:50, 22 May 2009 (UTC)

This isn't a science question - it belongs on the language desk IMHO. SteveBaker (talk) 14:28, 22 May 2009 (UTC)

Question 2

Are there any double-barreled names that are not one of a kind? Are there any people with triple- or quadruple-barreled names? 143.238.237.25 (talk) 13:40, 22 May 2009 (UTC)

You may find this article interesting. What do you mean by "one of a kind"? --Tango (talk) 13:51, 22 May 2009 (UTC)

Double-barrelled name has some examples of multi-barreled names, such as the Anstruther-Gough-Calthorpe family, the Plunkett-Ernle-Erle-Drax family and Richard Temple-Nugent-Brydges-Chandos-Grenville and his descendants. Also worth a mention, although not an inherited name, is John Desmond Lewis who changed his name by deed poll to Tarquin Fin-tim-lin-bin-whin-bim-lim-bus-stop-F'tang-F'tang-Olé-Biscuitbarrel when he stood as a candidate in the Crosby 1981 by-election. Gandalf61 (talk) 14:12, 22 May 2009 (UTC)

This also isn't a science question - it belongs on the language desk IMHO. SteveBaker (talk) 14:28, 22 May 2009 (UTC)

Why are not all elements of Tarquin's name capitalised? Oh yeah, I know, this is not a science question. SpinningSpark 14:40, 22 May 2009 (UTC)

I'm sorry - can you rephrase that in the form of a falsifiable hypothesis? SteveBaker (talk) 18:52, 22 May 2009 (UTC)

Tarquin's name is not all capitalised because he felt like it. Discuss. --Tango (talk) 18:53, 22 May 2009 (UTC)

How long before the earth runs out of food?

The world population is still increasing, even though not quite as fast as previously forecast. How long will it be using current population projections before the earth can no longer produce enough food for its inhabitants? I heard David Attenborough say on tv that the worlds population was only about 2 billion when he was born rather than the 6 or approaching 7 billion now. A world packed with the maximum number of people would be like hell. 78.146.162.232 (talk) 14:35, 22 May 2009 (UTC)

Are you going to assume even food distribution, or status quo? 65.121.141.34 (talk) 14:49, 22 May 2009 (UTC)

You may want to read Malthusian catastrophe. People have been predicting that the Earth won't be able to sustain the growing population for years and we've haven't had a problem so far. Improved agricultural technologies allow increase yields that will probably keep up with population growth until the population levels out. There are plenty of people going hungry in the world but that isn't due to lack of food, it is due to food not getting where it is needed (generally due to politics). --Tango (talk) 14:57, 22 May 2009 (UTC)

The Mathusian catastophe article has red error messages where some maths formulae ought to be. 89.242.85.248 (talk) 19:24, 22 May 2009 (UTC)

Fixed (by purging). --Tango (talk) 19:55, 22 May 2009 (UTC)

With enough technology applied to the problem I guess we could have many times the current population of the earth fed so if things go on as they are the earth will be utterly and totally devastated and all other non-food species above microbes extinct except as some genes saved in a bank. The earth won't run out of food but there is some very high limit on the ultimate carrying capacity of the earth, certainly 30 billion and possibly much more than a hundred billion. Most food will be grown in vats or in trays and a few cows will be kept to feed the very rich. If the population could be reduced to less than a billion, maybe 500 million, then they would be able to have good lives without constantly worrying about destroying everything. Dmcq (talk) 17:39, 22 May 2009 (UTC)

"With enough technology applied to the problem" - if that includes artificial fertilizer or fossil fuel products, then they will run out at some time. 89.242.85.248 (talk) 19:18, 22 May 2009 (UTC)

The crisis is likely to come not from the earth as a whole running out of food, but specific regions. The two greatest danger points, in my opinion, are India and sub-Saharan Africa. In India, the population continues to increase rapidly while the Green Revolution yields diminishing results and the supply of usable land has been pretty much exhausted. In Africa, the population is projected to more than double before stabilizing, and already there are continual flare-ups of famine. Looie496 (talk) 17:41, 22 May 2009 (UTC)

But a large percentage of people in S-SA are HIV positive as well, which should mitigate a lot of famine potential in the 10-20 year range right? 65.121.141.34 (talk) 19:21, 22 May 2009 (UTC)

Not necessarily. Plenty of people have children despite being HIV+, so there might not be a significant long term reduction in population. --Tango (talk) 19:57, 22 May 2009 (UTC)

Are their children born infected? 65.121.141.34 (talk) 20:03, 22 May 2009 (UTC)

Yes perhaps a quarter of the children born to HIV infected mothers are infected. Dmcq (talk) 20:55, 22 May 2009 (UTC)

(EC) With access to certain drugs the chance is greatly reduced. See [20]. Of course for a variety of reasons many pregnancies in sub-saharan Africa don't get such drugs [21] Nil Einne (talk) 21:04, 22 May 2009 (UTC)

(EC) Another big concern in a number of places including IIRC China, India and sub-Saharan Africa is the diminishing availability of fresh water caused by a variety of reasons including ground water that's being overused (deeper and deeper wheels need to be dug, contamination of water supplies, diminishing reservoir (lakes, rivers etc) levels, climate change. We may be able to partly or completely solve this by engineering crops able to grow in sea water. We may not. Only time will tell. Nil Einne (talk) 21:04, 22 May 2009 (UTC)

There are other high-tech ways to get fresh water - if you have power, a desalinization plant will work - if you are close to the sea, you could tow a gigantic iceberg into a convenient harbor and 'mine' it for water. If you have enough energy, there isn't much you can't do. SteveBaker (talk) 23:16, 22 May 2009 (UTC)

I think the 'enough energy' is a big if. I suspect if we really had unlimited energy, terraforming Mars, the moon, or a few other places would be a piece of cake. We could even build giant stations to grow food. In other words, we don't have to restrict ourselves to earth if we don't consider practicalities. While these may be several orders of magnitude more difficult then having sufficient energy to desalinise sufficient water for 7 billion people, the basic issue is the same IMHO. It's pointless talking about possibilities which even if we devote all our current efforts to them we probably couldn't achieve in 50-100 years. Nil Einne (talk) 08:49, 23 May 2009 (UTC)

By sufficient technology I mean sustainably the world could probably support many many times its current population using solar panels and wave power plus using some fast breeder reactors as backup. Fertilizer can be generated from power and of course suitably treated waste from people would also be used. I wonder what the earth would look like from space with every last spot covered with farm or power machinery of one sort or another Dmcq (talk) 20:55, 22 May 2009 (UTC)

I recommend The Mote in God's Eye which I won't discuss any more for fear of spoiling it for you. Tempshill (talk) 22:12, 22 May 2009 (UTC)

On the subject of climate change, the area of arable land is forecast to decrease within the century. Although CO2 fertilization may have the effect of temporarily increasing crop productivity, as well as more arable land being produced in Northern Canada and Siberia, major "breadbaskets" today are forecast to decline. For example, the American Midwest is predicted to suffer major desertification with a further warming of just 1C (2F), Southern Mediterranean Europe is forecast to become much drier and hotter, the Kalahari desert is expected to expand south, the Gobi desert to expand east, and the water supplies from the Himalayan glaciers, which support farming in otherwise dry areas, are expected to nearly dissapear before the end of the century. In addition, crop and insect diseases could increase, and major staple grains, especially rice, suffer a dramatic drop in yields above a certain threshold temperature. Population load, once it increases past global supply, reaches the "final point of sustainability". After such, both supply and load must start to decrease, until load decreases sharply below the level of supply, although not everyone predicts this. Clean drinking water supplies could decrease as well, which would hinder farming. ~AH1^(TCU) 23:13, 22 May 2009 (UTC)

The answer has a political as well as a scientific component. Many things that are scientifically possible won't be done. Someone would have to allocate the resources. (e.g. money, energy, water, raw materials, medication). In an ideal scenario humans would all be altruistic and distribute those to benefit all. That is unrealistic, though. Despite the fact that there are mass die-offs due to war, pandemics, starvation and drought the human population in general seems to keep multiplying. There is no free lunch, though. Scientific scenarios to feed and water ever increasing numbers come at a cost. Either environmentally or in loss of life or reduced lifespans or quality of life of some populations. The more artificial components the system gets the more fragile it becomes. If you feed your entire population with food grown in vats, one good bug could wipe our a significant portion or them. BTW. Last I checked Egypt had a higher birth rate than sub-Saharan Africa. Just because s.o. is e.g. in the U.S. they should not develop the attitude "It can't happen here." Example: Atlanta, which is in an area with lots of rainfall, has grown so much that in years that have less rainfall there's water rationing. Cases of people dying because they can't pay their water bill are rare, but not unheard of. People in industrialized nations have a higher chance of having their food supply ensured, but there's no guarantee. There is also an inverse relationship between wealth and population increase. 71.236.24.129 (talk) 10:28, 23 May 2009 (UTC)

food web

Why we have to study food web, food chain and food pyramids? —Preceding unsigned comment added by Lakshmibp (talk • contribs) 14:42, 22 May 2009 (UTC)

Because questions about them will be on the test. -- kainaw™ 14:59, 22 May 2009 (UTC)

Because education about ecology and food production is beneficial to society. Nimur (talk) 15:11, 22 May 2009 (UTC)

They are a good way of understanding how an ecosystem fits together. Such understanding is important whenever you have to consider the environmental impact of something, which we have to do quite often. --Tango (talk) 16:36, 22 May 2009 (UTC)

Same reason for studying anything else. Knowlege is useful. Now quit being lazy and do your homework. Dauto (talk) 16:48, 22 May 2009 (UTC)

So you don't grow up like one of the dumb people some on the Internet laugh about, like ones who think food just comes from the supermarket, and who don't understand how the stuff grows and has to be shipped. So you understand the importance of farmers and don't grow up to build huge subdivisions with homes that cost a lot of money, but which deplete the available land to grow food.Somebody or his brother (talk) 18:13, 22 May 2009 (UTC)

Food web / pyramid does not mean food distribution or even growing, so learning them would have little or no impact on ignorance on such topics. It is a schematic representation of ecological interactions, like cats eat fish eat flies plant eggs in cat corpses/faeces, which can be useful in practical application such as ecological planning (eg, releasing ladyirds to control aphids may simply cause an increase in ladybird predators, if understanding of the food-web is insufficent) and in understandig various food scandals and recomendations (like why heavy metals appear in fish, or why DDT is banned). As with most school sciences, it is essential for anyone undertaking further scientific education, and is the sort of thing that any typically educated person should know.YobMod 09:03, 23 May 2009 (UTC)

Phlegm and vocal range

This morning I woke up with a laryngitis, and was able to sing a loud and clear (mf) B♭1, a note I had only been able to sing ppp in Mahler's Eight and the All-Night Vigil. I even could sing down to F1, although that was very hoarse and open to interpretation. Now that I've been up for a while, my lower range has moved up, too, but my electronic tuner still recognizes my A1. Is this because the phlegm acts as a weight on the vocal chords? — Sebastian 15:28, 22 May 2009 (UTC)

Just speculation, but since I'd think that phlegm would be rather mobile when you start singing... It may be the swelling of the mucosae that adds weight to the vocal chords, and causes the frequency to drop. --NorwegianBlue ^talk 18:10, 22 May 2009 (UTC)

Would swelling of the mucosae be the reason that, the morning after drinking heavily, some people speak in a lower tone of voice and are able to reach lower notes? Tempshill (talk) 21:14, 22 May 2009 (UTC)

Hey, when I have a bad cold, I can sing "Ol' Man River" or "Asleep in the Deep" (or the bass part of the Marcels' version of "Blue Moon") in a way that will bring tears to your eyes. Otherwise, not so much. Deor (talk) 02:46, 23 May 2009 (UTC)

Calulating the Surface Area of the Human Body

I'm curious how could one most easily calculate the surface area of a person's body? Would men or women have more than the other and would tall, thin people have less than a short, fat person?TheFutureAwaits (talk) 16:30, 22 May 2009 (UTC)

The easiest way, which should be exact enough for what you need, would be to measure length and average circumference of your body parts - torso, arms, legs, and head - and add them up (neglecting the areas of your feet and the top of your head). Roughly speaking, you can think of your surface as your height times your average circumference. Since girth can easily vary by a factor of 2, while length only varies within a much narrower range, it is easy to see that a short, fat person has more surface than the tall, thin one. — Sebastian 16:45, 22 May 2009 (UTC)

See google:"body surface area" nomogram. There are various formulas in use, and discrepancies between them sometimes make it difficult to compare clinical studies that depend on body surface area. --NorwegianBlue ^talk 18:18, 22 May 2009 (UTC)

If you have access to a corpse, you could try peeling off a small section of skin, weighing it and measuring its surface area, then weighing the whole skin and scaling up the previous surface area accordingly. Vimescarrot (talk) 19:43, 22 May 2009 (UTC)

Not sure if this qualifies as "most easily".  ;) --- Medical geneticist (talk) 20:29, 22 May 2009 (UTC)

Bottom of feet is much thicker skin then the rest of you. Might be pretty uneven in other places too. Could throw off the calculation. Might be a decent approximation on someone who does not walk, though. I would think that perhaps you could cut up a wetsuit and measure the area of that? Also include some socks with toes and gloves made of a material that is not very stetchy. No cadavers involved. 65.121.141.34 (talk) 20:02, 22 May 2009 (UTC)

Just as a general principle, the more "spherical" the body shape, the less surface area in proportion to mass. In other words, of two people who weigh the same, the "rounder" one will generally have less skin surface. Looie496 (talk) 21:01, 22 May 2009 (UTC)

Hip anatomy

Hi is there any way in which the ilium on either side of the pelvis is referred to differently in a clinical setting? My question is how would you know what side of the ilium someone was talking about if it is only one bone? If there was for example a fracture on one side of the ilium but not the other would doctors talk about the left/right ilium? Hope this makes sense. Is there a similar way of differentiating which side of pubis or ischium someone was talking about? Thanks in advance to anyone who can help! —Preceding unsigned comment added by 139.222.240.161 (talk) 16:53, 22 May 2009 (UTC)

Take a look at Anatomical terms of location. There is a precise term for each orientation or position (e.g. the anterior distal portion of the ilium). These terms avoid the use of terminology which would be vague based on how somebody is standing/moving the limb, etc. Nimur (talk) 16:57, 22 May 2009 (UTC)

When did fruit bearing plants first evolve and what was the first fruits?

When did fruit bearing plants first evolve and what was the first fruits?Capitalistroadster (talk) 00:06, 23 May 2009 (UTC)

Evolution of plants doesn't cover this terribly well, but as far as I can tell, the Gingko is a good candidate. According to our articles, the first gingkos evolved around 270 million years ago, and were among the first seed-bearing plants. And having lived next to a female Gingko tree for a few years, I can tell you from unpleasant experience that they do bear fruit. Looie496 (talk) 19:43, 22 May 2009 (UTC)

According to our article: "The apricot-like structures produced by female ginkgo trees are technically not fruits, but are seeds that have a shell that consists of a soft and fleshy section (the sarcotesta), and a hard section (the sclerotesta)." --Tango (talk) 19:50, 22 May 2009 (UTC)

Thanks Loie496 and Tango.Capitalistroadster (talk) 00:06, 23 May 2009 (UTC)

Dendritic cells

The Wikipedia article on dendritic cells says that these phagocytes are unique to the mammalian immune system. However, things like this and this seem to suggest other groups of animals have DCs as well. Which is right? If other groups of animals have DCs, which have them: all amniotes? all tetrapods? all jawed vertebrates? Thanks a lot. --Leptictidium (mt) 20:12, 22 May 2009 (UTC)

The adaptive immune response goes back to jawed vertebrates as you suggest, and it seems likely that would be true for dendritic cells. I don't know for how many of the more "primitive" jawed vertebrates they've been demonstrated, though. Your reference for Langerhans cells in reptiles is a good one, though. --Scray (talk) 00:15, 23 May 2009 (UTC)

What is the average pushing power of a man in psi

Can anyone tell me the amount of pushing power a man who weighs 90 kgs and has 7 inch by 7 inch hands in psi (pounds per square inch) ? my brother says its something like 20psi but that doesnt seem right to me. Is there a way to roughly work this out?

Thank you —Preceding unsigned comment added by 79.68.219.232 (talk) 21:13, 22 May 2009 (UTC)

It depends on what they are pushing...the world record for weight-lifting is around 260 kg - and that's over a length of cylindrical bar the width of the guy's hands (let's say 20cm) by maybe 4cm wide...so 260kg over 80cm² - which is about 46 psi. Obviously that's the world record - I'd say that less than half that is perhaps reasonable. SteveBaker (talk) 23:11, 22 May 2009 (UTC)

(Edit conflict)Yes, if you first define what "amount of pushing power" really means. Since you've mentioned psi you (or the teachers who set this poorly worded homework question?) are presumably thinking of how much pressure the man can exert through his hands (since psi is pounds per square inch, a measure of pressure).

An accurate figure will depend on how well muscled he is, how he applies the pressure, and in what direction, but let's assume he's moderately strong and can push with flat hands with a total force equal to his own weight - does that sound reasonable? Think of a wrestler holding his opponent above his own head preparatory to a body slam, not an unlikely scenario, and certainly below world-class weightlifting standards.

Now, you know the linear measurements of his (two) hands, so you should be able to work out their area in square inches - you should find that the answer comes close to a round figure useful for approximate calculations. you know how much he weighs in kilos, which we've assumed is about the same as the maximum force he can exert (weight being a force). You need to convert this force to pounds, which I'm sure you can manage. You should find this comes close to another convenient round figure.

Now you need to work out how how that total force is distributed over the total area he's using to push with, how many pounds he's exerting on each square inch. The answer may surprise you, and should show that your brother has made a minor error in his working. 87.81.230.195 (talk) 23:24, 22 May 2009 (UTC)

If a 200 pound man does a hand stand then he is supporting his whole weight on the area of his two hands, which I reckon is a pressure of about 4 psi. However, as pointed out above, a weighlifter can support the same weight on a much smaller area, so they are exerting a higher pressure. And a 100 pound ballet dancer en pointe is supporting her weight on probably 2 square inches, so she is exerting a pressure of around 50 psi. So pressure is not a useful measure of "pushing power". Gandalf61 (talk) 09:45, 23 May 2009 (UTC)

What would the best way to measure pushing power , if not pressure? —Preceding unsigned comment added by 79.68.229.253 (talk) 10:48, 23 May 2009 (UTC)

Force. --Tango (talk) 10:52, 23 May 2009 (UTC)

Actually, since the original question was actually for pushing power, the correct answer is "power", e.g. force times velocity, or rate of energy expended per second. I think the original questioner may want to review some basic physics terminology like force, energy, power, and pressure, to decide which quantity is actually the one he/she is trying to inquire about. Nimur (talk) 12:06, 23 May 2009 (UTC)

Fancy Guppy Reproduction

I have a femal fancy guppy and a male gold swordtail, among other things. It appeared that my guppy was pregenant, and seeing no other possible candidate, assumed the swordtail was the father. I took the neccessary steps to prepare, and even moved her to a seperate breeder when I assumed she was close (before it would be to dangerous to move her though). There she sat, for nearly a month. Then one day she was skinny again! There was no evidence of a miscarriage, and there were no babies in the other compartment. The only change is that I was better able to control how much she ate, so she probably cut back on some calories, but if this were the cause, I assume she would have lost weight over time, instead of so suddenly. What happened? And now she's starting to show pregnancy signs again. This is very troubling.Drew Smith What I've done 23:59, 22 May 2009 (UTC)

Do fish get phantom pregnancies? I know other mammals (than Humans) do, so could be. I also read that Guppies can store sperm, so can have multiple pregnancies from one mating - but this doesn't explain the spontaenous loss by itself, uness followed by multiple miscarriages.YobMod 08:35, 23 May 2009 (UTC)

Guppies sometimes eat their young. 71.236.24.129 (talk) 09:41, 23 May 2009 (UTC)

May 23

Solar-powered vending machine indoors?

Could a low-cost photovoltaic cell mounted to the top or side of an electronic vending machine provide enough power to run it reliably? The machine would be indoors, but in a vestibule with glass double doors and overhead lighting during the evening (at least during the hours when it would need to run). NeonMerlin 02:25, 23 May 2009 (UTC)

One important question is whether this vending machine needs to have a refrigerator in it, as it would if it's vending cold soft drinks. Tempshill (talk) 03:33, 23 May 2009 (UTC)

No fridge. This is for trading cards. NeonMerlin 06:05, 23 May 2009 (UTC)

There are Mechanical vending machines, condom machines are often just a place to put cash, pull a handle and get your prize. Zero electricity - the room that it is in is already lit up so no need for electricity. Similarly there are apparently 'eco' vending machines but not sure how good they are (from a brief read - not entirely free of grid-electricity use - the link from google is 'blacklisted' but search for 'eco vending machine'). ny156uk (talk) 10:02, 23 May 2009 (UTC)

If the panels are directly driving the machine - then I'd say no. But if they are charging a battery that operates the machine - then perhaps if the machine is used sufficiently infrequently, it'll have time to recharge fully between 'vends' - in which case you'd be OK. But if you had a whole bunch of kids arrive at once - all wanting to buy trading cards - then you'd run the risk that the battery would go dead. I agree with Ny156uk - there have been plenty of purely mechanical vending machines where the weight of the coin against a spring releases the ratchet on of a wheel - allowing it to rotate. The purchaser drops in the coin - then turns a knob to rotate that wheel and thereby to release the product. When the wheel rotates past a certain point, it reveals a slot through which the coin drops - allowing the ratchet to re-engage against the wheel and prevent it from rotating again until another coin is dropped in. This approach is much more practical than messing around with solar panels and rechargeable batteries. SteveBaker (talk) 15:21, 23 May 2009 (UTC)

Insect identification

This tree in Bavarian countryside was entirely covered in a kind of web and had caterpillars crawling all over it, yellow to light brown with two dotted black stripes down their backs, thin, about 1.5 - 2 cm long (I think, I didn't measure them). Can anyone tell me what the caterpillars are? N p holmes (talk) 08:25, 23 May 2009 (UTC)

• 
  The caterpillars.
• 
  The tree.
• 
  Another view.

Try Small Tortoiseshell The German page has a pic with the "web" de:Kleiner Fuchs 71.236.24.129 (talk) 09:38, 23 May 2009 (UTC)

Thankyou. I looked at some pictures: the Small Tortoiseshell caterpillars look fatter and hairier than these (and the web was only a little thing on a couple of nettle leaves). So I'm slightly doubtful. Any other suggestion? N p holmes (talk) 10:13, 23 May 2009 (UTC)

I think I've narrowed it down now to some kind of Ermine moth. I don't know how to distinguish the kinds. N p holmes (talk) 10:38, 23 May 2009 (UTC)

Most likely the Bird-cherry Ermine, yponomeuta evonymella, from the images of the larvae on this website (9th out of 30) [22]. Mikenorton (talk) 14:33, 23 May 2009 (UTC)

Air vortex force calculation

If an air vortex has enough force to move a 150lb object 1 foot from 30 foot distance from the launcher. Is there any way to estimate how far it will be able to move the same object from 5 foot? Or is the degredation of force within a vortex unique for each vortex depending on the speed of the spin of the vortex, and the speed which it is traveling?

Thank you —Preceding unsigned comment added by 79.68.229.253 (talk) 11:12, 23 May 2009 (UTC)

Some information that may help is that the starting pressure within the vortex is 14,7 psi and the speed is mach 1 and the size of the vortex is 2ft (24 inches) in diametre —Preceding unsigned comment added by 79.68.229.253 (talk) 11:43, 23 May 2009 (UTC)

Well - the air vortex is going to dissipate sideways - so the pressure will decrease as you get further away at a rate that's proportional to the increase in cross-sectional area. Probably a good estimate would be an inverse-square-law kind of thing - as you double the distance from the source, the pressure decreases by a factor of four. However, it's going to depend critically on the size of the object being moved. For an object who's cross-sectional area is small compared to the diameter of the air vortex, the area over which that pressure is exerted doesn't change as the air flow diameter increases - so the inverse-square drop in pressure equates to an inverse-square decrease in force applied. But for an object that's much larger than the airflow, as the pressure drops off, the area it's exerted onto increases at the same rate - so the force is about the same no matter how far away you are. But in truth, this is a very rough estimate. The details matter a lot. SteveBaker (talk) 15:11, 23 May 2009 (UTC)

Hmmm that helps a little but wont the slowing down of the air due to the distance decrease the impact as well? If the vortex grows at a very small rate the area effected would not change much, but the air speed would slow due to drag. how much does drag decrease air flow?

User: Robin (talk) 16:24, 23 May 2009 (UTC)

Fancy swordcraft and damaged clothing...

I'm guessing not, BUT...

is it actually possible to damage clothing but not the wearer in a controlled manner ala Zorro (or many other films & shows)?

61.189.63.185 (talk) 11:49, 23 May 2009 (UTC)

It is possible, but unlikely - especially at the speeds Zorro slashes at. Fine motor skill is handled by small muscles, while quick slashing motions is gross motor skill. The two processes are handled by different parts of the brain and executed by anatomically different muscle and tendon groups. Nimur (talk) 12:13, 23 May 2009 (UTC)

Calculating oversteer/drift in a car

Hi all. I'm trying to calculate the amount of oversteer of a car, based on one main variable, the centre of mass, and forward velocity. The main result I want to achieve is to be able to calculate, for a set numbers of degrees of drifting, how the center of mass affects the forward speed and stability of the drift, so the car doesn't slide out.

I've tried to solve it in terms of opposite torques. For the front tires, I've assumed they aren't slipping, so have used the force into the drift as (coeffient of static friction)(normal force of tires)(center of rotation), and taking the centre of rotation as the intersection of the normals of the inside tires (think that's right, haven't derived it.)

The rear tires are where I'm having the most trouble. Assuming they are slipping, the only force I can think to use is mv^2/R, but I don't think that's right because there should be a force straight on, since the car is angled? And I'm not sure what figures to use for R, the center of rotation, and r, the length of the lever arm for the torque equation.

The end result I think I want it (coeffient of static friction)(normal force of tires)(center of rotation) > (mv^2/R(?))(r) so the car doesn't slide out.

So if anyone can make sense of that, and can help, thank you very much :) 203.206.34.183 (talk) 11:50, 23 May 2009 (UTC)

On second thoughts, mv^2/R may be not a valid equation for this, instead using the kinetic friction force. But then velocity doesn't come into it at all, and it should... I think I need to use both, on thinking that sounds better.203.206.34.183 (talk) 14:07, 23 May 2009 (UTC)

I think you are dramatically underestimating the complexity of the system you're trying to analyse. In real cars, the weight is not evenly distributed over the wheels - and as the car accelerates or turns, that weight shifts as the suspension takes up the strain and the car leans or pitches. In some cars, one wheel may actually lift off the road altogether. Chassis flex and the effect of anti-sway bars change this weight shift in complicated ways. Front wheel drive versus rear wheel drive makes a difference. Static versus dynamic friction and side-wall flex in the tires complicates the answer too. This is an insanely complex thing to try to analyse mathematically. SteveBaker (talk) 14:52, 23 May 2009 (UTC)

Today's featured pic

Hi, in todays (23) featured pic, it shows a volcano erupting. There's a curious thing; the smoke from the volcano is drifting to one side, while the clouds around the volcano seem to be drifting to another side. What is the explanation for this? What is happening here? 202.129.232.137 (talk) 13:56, 23 May 2009 (UTC)

My guess is that the clouds are actually flowing in the same direction as the smoke - and are being constrained by the other two islands. But as the cloud reaches the volcano, the air temperature rises steeply. Since the amount of water that the air can hold increases with temperature, the water vapor in the clouds simply evaporates.

Alternatively - if your theory as to the direction the clouds are travelling is true - then perhaps it's merely that the smoke is at much higher altitude than the clouds - and that perhaps the wind at those altitudes are blowing in a different direction from the winds at lower altitudes.

SteveBaker (talk) 14:31, 23 May 2009 (UTC)

Looking for a quote by Taiichi Ohno

At some point in the past few weeks I have read a quote by Taiichi Ohno that Lean Production should not be separated and codified as tools, but should be adopted by organisations as a whole system. Now that I'm writing my dissertation I can't find it, and it's driving me bonkers. Can anyone who has read any of Ohno's books identify the quote, and give me a citation for it please? Otherwise I'm going to have to re-write my dissertation in order to not miss the deadline. -- role^player 13:59, 23 May 2009 (UTC)

Breaking stength of an extension cord.

Someone at my car club spotted a pickup truck towing an Accura using a yellow extension cord!! I was wondering whether this was really as foolhardy as it sounds. Does anyone have any idea of the breaking strain on one of those things? Some way to get a rough estimate? SteveBaker (talk) 14:23, 23 May 2009 (UTC)

Mystery sea creature

What is the sea creature that appears at about 0:52 in this video, which the speaker calls a "flying turkey"? 69.224.113.202 (talk) 15:25, 23 May 2009 (UTC)