Wikipedia:Reference desk/Science

August 10

Death - turning on back

Why do some animals and insects turn on their back when they die? Is it the death causing the turnover, or the turnover causing the death (for the insects)? PitchBlack 04:09, 10 August 2007 (UTC)

I'm hypothesising here, but I always assumed this happened in animals that weren't necessarily stable on their legs as far as a natural state. So say you spray a fly, as it's dieing it will tend to buzz and bounce around and at some stage flip onto its back, which is physically a far more stable position that its feet/legs, or it's side. As it no longer has the strength to resume it's preferred, but less stable, position on its feet, it will remain and die in this most stable position on its back. I can't imagine many animals that would die simply by being on their backs, unless they couldn't right themselves, such as with a turtle. --jjron 08:51, 10 August 2007 (UTC)

Sounds right, but it raises the question as to why are "these" animals more unstable when on their legs than on their back. I think it could be because being unstable makes moving around easier, better mobility. I may be wrong, any comments ? -- Myth (Talk) 15:19, 10 August 2007 (UTC)

Well, and think about a dead fly. Their legs contract inward. Even if they were somehow not on their back, they would quickly fall over. Insect legs most likely end up contracting like that when they dry out, for reasons I know not. In any case, I think it is pretty clear that it is not the turnover which causes the death — you can turn beetles over all day long and they won't care. --24.147.86.187 17:43, 10 August 2007 (UTC)

And the reason flies are more stable on their backs is that they are "top heavy". StuRat 05:45, 12 August 2007 (UTC)

I've seen spiders roll over and contract their legs (playing dead) when attacked. And then spread out their legs and take off a few minutes later. Surely, sometimes they actually die after attempting this, and maybe stay in that position (there may also be a reason for contracting the legs after dying, but I do not know). I always figured they were trying to make themselves look as small as possible, while simultaneously taking advantage of an instinct in many predators not to eat things that are already dead. 151.152.101.44 19:27, 10 August 2007 (UTC)

The Eastern Hognose Snake will roll onto its back and lie there defacating,with its mouth open oozing blood, playing dead, when attacked [1]. If turned onto its stomach, it rolls again onto its backs, genetic programming overcoming logic. Edison 00:10, 11 August 2007 (UTC)

Apparently, instead of using muscles, spiders force blood and other fluids into their legs to push them outward. When a spider dies, they lose the hydraulic pressure necessary to keep their legs extended, and thus they contract. I'm not sure if this is true of other anthropods, though. Vsst 18:47, 16 August 2007 (UTC)

Headaches

Headaches are of different types and have different causes - but I have always wondered - what ACTUALLY happens in our body or head so that our head starts 'aching'. For example, many times hyperacidity leads to a headache (which I have experienced myself). But what is actually happening in my head during hyperacidty so that my head starts aching? In other words why is head pain caused (thought not always and also not to everybody) due to hyperacidity?

Forml 11 04:57, 10 August 2007 (UTC)

Headache#Pathophysiology. More specific causation of pain is explained in articles on individual types of headaches, listed at headache#Types. Someguy1221 05:06, 10 August 2007 (UTC)

As for hyperacidity, are you referring to acidosis or heart burn?. Someguy1221 05:10, 10 August 2007 (UTC)

I was referring to Heart burn Forml 11 08:04, 10 August 2007 (UTC)

Heart burn can apparently irritate the sinuses (sinusitis), which can be felt as a headache, but I don't see an explanation on Wikipedia as to how this happens. Someguy1221 06:54, 10 August 2007 (UTC)

Thanks for the responses. Even I could not find any references to it. When I take medicines to prevent hyperacidity, my incidents of headaches go away. Hoever, my question is *not* about hyperacidity or about preventing hyperacidity or about medical treatment for acidity or headache. What is bugging me is this - what does the excess acid in my stomach do to my head so that it starts 'aching'? Forml 11 08:04, 10 August 2007 (UTC)

Well, there are no pain nerves in your brain or skull, it's all in the scalp. Very likely muscle cramps from unconsciously contracting your scalp muscles due to the pain in your stomach. Similar to the caffeine-withdrawal headaches, where withdrawal from caffeine causes the blood vessels in the scalp not to expand enough, causing the muscles to complain. Gzuckier 15:24, 10 August 2007 (UTC)

I've always been amazed that there are different kinds of headaches, I can feel the difference, and when I talk to my doctor about headaches, he always asks "where in your head is it?".Evilbu 18:51, 10 August 2007 (UTC)

WHICH BIRD CAN FLY IN BACKWARD DIRECTION ALSO?

BIRD WHICH FLIES IN BACKWARD DIRECTION61.11.76.116 06:01, 10 August 2007 (UTC)

Hummingbird? Make a new section if you want to ask a question using ==Title==. --antilived^{T | C | G} 06:02, 10 August 2007 (UTC)

Or use the handy "ask a new question" link at the top of the page. And don't type in all-caps, it's considered shouting. And wash your hands before you eat. --LarryMac | Talk 14:23, 10 August 2007 (UTC)

Does being able to glide backwards with wind assistance count? --Kurt Shaped Box 18:02, 10 August 2007 (UTC)

Let's take the air surrounding the bird to be our frame of reference. Anything else would just be silly. Plasticup ^T/C

I don't know about that. In the case of gulls (I'm sure that other birds can do it too - I've just noticed the gulls doing it when I feed them), they deliberately adjust the angle of their wings in relation to the wind in order that they may glide backwards (or glide backwards and upwards at the same time). It's a conscious decision to reverse - it's not as if they just go wherever the wind blows them. --Kurt Shaped Box 12:22, 11 August 2007 (UTC)

Flying backwards relative to the ground is easy with a wind strong enough. Even aircrafts can do it, with a stall speed small enough, for example the Antonov 2. Flying backwards relative to the air is something different, and the seagulls can't do it. The hummingbirds can certainly do it, as they can hover, so it' very close to a slow backwards flight. --V. Szabolcs 18:12, 11 August 2007 (UTC)

To clarify what the others just said (perhaps our reader doesn't understand frames of reference) - if the wind is blowing strongly at (say) 30mph and the bird flies into the wind at (say) 20mph then it would appear to someone standing on the ground as if it were flying 10mph backwards. I have also seen gulls doing that - but it doesn't really count as flying backwards because as far as the bird is concerned, it's still flying forwards into the air flow. Gulls can only do that when they have a reasonably strong headwind. Hummingbirds, on the other hand, can truly fly backwards even in still air because they can rotate their wings at all sorts of strange angles to direct thrust slightly forwards while hovering. This makes them fly more like a Harrier Jump Jet aircraft (well, sort-of).

Doh! Yes, I understand it *now*. Hehehe. :) --Kurt Shaped Box 19:07, 11 August 2007 (UTC)

It's my un-studied impression that all birds can hover to at least a small degree. Obviously, some birds, for example, hummingbirds, are very good at it and can do it for sustained periods of time, but for most of the birds I've seen, the have the ability to abruptly stop their forward motion in flight, hold still for a moment, and then change direction.

Atlant 11:54, 13 August 2007 (UTC)

Not exactly. Most of the larger birds even need a long runway to take off. Larger birds of prey were used to be captured in traps made by a bait and a fence around it. The bird did not have a runway long enough to take off, so it would be trapped in the fenced area. --V. Szabolcs 13:47, 14 August 2007 (UTC)

Citation? I recently watched a Great Blue Heron take off several times. No runway needed; it simply flapped downwards and lifted its feet. Perching birds certainly don't need a runway. I don't know of any North American "land-based" bird that needs a runway. And we're not talking about "takeoffs" anyway; I was talking about hovering and the original question was talking about reverse flight.

Atlant 12:14, 15 August 2007 (UTC)

Exact reason for the gender difference in essential body fat percentage

What, precisely, causes the essential percentage of body fat for women to be eight percent higher than that of men? In the body fat percentage article, it states that it's "due to the demands of childbearing and other hormonal functions", but does not elaborate; in particular, exactly what role does it play in childbearing? Does it merely serve to shield the woman's other organs from the mechanical stresses of hosting and delivering a developing fetus, or is there an additional reason (such as to serve as a source of nutrients)?

I'm asking because I'm trying to develop a fictional alien race of oviparous humanoids, and I'd like to know what, if any, adjustments I need to make to their figures because of their reproductive system.

CameoAppearance ^orate 07:19, 10 August 2007 (UTC)

Breasts and breastfeeding? An alien race is completely up to your imagination however, so you are only limited by what you can imagine. Lanfear's Bane

One of the key reasons is that fats are the most convenient way to store energy in the body. If I remember correctly (I can't find an immediate link to the figures), in the old money fats store 9 calories per gram compared to proteins and carbohydrates which only store 4 calories per gram. If you want to carry around the most energy for the least weight, you store it in fats. It takes a lot of energy to grow and sustain another human being from conception. --jjron 08:40, 10 August 2007 (UTC)

I'm a complete amateur, so take my hypothesis with great caution. I've always thought that women have a "base" or "normal" level of muscle mass and it's men who have an "abnormally higher" level due to the anabolic effects of testosterone. This sexual dimorphism is also seen in related species, and it's maybe caused by physical competition for females or more physically demanding duties, such as hunting. To sum up, I conjecture that the level of body fat in women has no particular reason for being the way it is and maybe it's men's level who has one. --Taraborn 21:01, 10 August 2007 (UTC)

Childbearing is one explanation. Indeed, having a child grow inside you, and nursing it afterwards require large energy reserves. But from an evolutionary point of view, I suppose that women were the ones who sat around raising the childring while the men were hunting. The hunting men, being outdoors, could eat as soon as they made a kill, if needed. The women would be left without any food. And any food they did have, would likely have gone to children of various ages. So the women (and therefore the children) would greatly benefit from them being able to last with little food. I think.81.83.82.123 20:56, 13 August 2007 (UTC)

light intensity

i was just generally thinking about light and its intensity, i was just wondering, about how would the intensity of light passing through a glass container containing a liquid vary when the height of the liquid in the container is changed. i really cannot understand what kind of relation would exist between the height liquid in the container and the light intensity?? please answer my queries, i have broken my head on this for quite some time and still cannot find an answer.

If the light is passing in a vertical direction then the liquid may scatter or absorb it. however it is passing horizontally then that will not differ, however you may get reflections from the top of the liquid affecting your result. Also if the glass is not a cylinder then the path length in the liquid would change as the height increases. The liquid is not fluorescent or luminescent by any chance is it? Graeme Bartlett 11:54, 10 August 2007 (UTC)

Did you mean passing through a glass horizontally (eg half full vs full), or passing vertically (up/down) though the column of liquid?87.102.35.197 11:56, 10 August 2007 (UTC)

You may find the photic zone article of use. Also try the underwater article, especially the section down near the second photo. --jjron 14:26, 10 August 2007 (UTC)

Mr. Graeme Bartlett the light is passed perpendicular to the liquid therefore the direction of the light will be parallel to the normal therefore there is no scope of reflection takeing place. And when i performed some experiment related to this i found that the intensity of light increases with the increase in height. i have no idea how to get convinced by the results i got. Can you please help me out.

Still not sure exactly of what you are looking at here - just as a guess if you are measuring the light reaching the bottom of a tall glass - could it be that increasing the fullness of the glass causes more light to be trapped in the cylinder by total internal reflection (catching light coming from the side). (this would apply if you have light coming from all around..)

If thats not what you are thinking of can you clarify again - is the light coming through the glass (sideways) or down (though the top surface and down to the bottom)?87.102.74.130 20:40, 10 August 2007 (UTC)

ya i ment that the light was coming from the top of the glass container.

If the liquid is coloured the Beer-Lambert law applies - this always means that the amount of light is reduced for longer columns.

I'm guessing that your liquid is clear - and you mentioned that the light seems to increase - in which case I'd suggest the answer I gave above - that is that the liquid filled portions are acting as a sort of funnel - since the light reflects from the inside of the glass when it's full of water - place the glass in strong sunlight and you might be able to see this effect - for example see the images in Caustic (optics) for a rough approximation of what I'm suggesting.87.102.8.162 21:34, 11 August 2007 (UTC)

For a compressible fluid, the density will increase with the depth/pressure, and the more dense the fluid, the more light it will absorb. StuRat 05:36, 12 August 2007 (UTC)

Sleeping feet

I was wondering, just what IS the condition of a "sleeping foot" (or hand, etc) called? That is, when it's under something for long enough that it starts to tingle and often be unable to be felt (and something hard to walk on it). Is there an article on this condition? ♫ Melodia Chaconne ♫ 14:08, 10 August 2007 (UTC)

Try Paresthesia. Mdwyer 14:13, 10 August 2007 (UTC)

Yes, that's it. Thanks. ♫ Melodia Chaconne ♫ 15:09, 10 August 2007 (UTC)

AIDS enquiries

Hi, I'm just wondering where does AIDS arise from? I mean, if 2 people do not initially have HIV (or at least they are not aware of it) and one of them have touched the other's bodily fluid, say, blood; is there a chance that one of them will get HIV, and subsequently AIDS?

Also, does kissing transmit AIDS/HIV?

If neither has the virus, they're not going to get it no matter what they do between them. If one has the virus and doesn't know it, that's different.... As for kissing, most reputable authorities put the possibility very very low. However, if there are open sores of some kind, such as bleeding gums, cold sores, etc. in one or both persons the likelihood goes up. (similar for actual sex; if there are sores from other STDs, for instance, likelihood of infection goes way up.) Gzuckier 15:29, 10 August 2007 (UTC)

You should consult your doctor for any medical advice, particularly when it comes to diseases. -- JSBillings 17:23, 10 August 2007 (UTC)

However, if you're speaking purely in the hypothetical, then no, you can't become infected with HIV without the presence of HIV. There are AIDS/HIV Denialists out there who might say otherwise, but there isn't any real science behind it. -- JSBillings 17:27, 10 August 2007 (UTC)

Yes, there was an early theory that AIDS was caused by repeated assaults on the immune system, such as by drugs and other venereal diseases, but that theory was discredited with the discovery of HIV. StuRat 05:30, 12 August 2007 (UTC)

Try reading our article on AIDS. Plasticup 17:57, 10 August 2007 (UTC)

Fading of photogaphic prints

Are there published data on the fading rates of the different dyes in a photographic print (over time, and under various conditions)? I believe manufacturers of photographic supplies must have done detailed studies on their own products but I couldn't find any published data. What I'm hoping to get is a quantitative characterization of the color shifting in a faded photograph. Thanks.

Digital_versus_film_photography#Archiving claims "Gold or platinum toned prints probably have a lifespan limited only by the lifespan of the base material, probably many hundreds of years." - I imagine that is the upper limit for film?

For a few values try this http://www.wilhelm-research.com/ist/WIR_ISTpaper_2002_02_HW.pdf (page 2)87.102.74.130 20:34, 10 August 2007 (UTC)

Microbiology/statistics

write the name of 100 types of bacterial,giving 10 examples of it structural types and indicate whether gram negative or gram positive.

Distinguish between Normal scale,Ordinal scale,Equal scale and Ratio scale.Show a graph interpretation of their relationship

and DO YOUR OWN HOMEWORK. --LarryMac | Talk 18:07, 10 August 2007 (UTC)

Here's what I don't get. What kind of person would be in a course that would ask that kind of question, yet be unable to read and follow simple directions? How is he/she going to be able to wade their way through microbiology textbooks? Are they planning on asking us new questions with every assignment? And for what? So they can become a microbiologist who still has to come to the reference desk every time they do research? Bizarre. Matt Deres 20:08, 10 August 2007 (UTC)

Maybe we should add "... and your own doctoral thesis" to the admonition. --Sean 13:32, 13 August 2007 (UTC)

This is the reference desk - yet the question reads like some sort of fuhrer-order. Were you aware that as it reads the question is pushing the boundarys of politeness? The main page asks that you 'do your own research'87.102.74.130 20:20, 10 August 2007 (UTC)

The page bacteria has links to lots of species, (look in the info box on the right for lists of phyla and you could easily find many from there. Also the page bacteria has info on structural types. Typing gram negative into the search box, or google etc may also help...87.102.74.130 20:23, 10 August 2007 (UTC)

Did anyone read the original question carefully? "write the name of 100 types of bacterial,giving 10 examples of it structural types and indicate whether gram negative or gram positive." That's quite a lot of useless work! --Bowlhover 22:19, 10 August 2007 (UTC)

Maybe the question is designed to increase general knowledge in the bacteriological subject area - by neccessitating a lot of background reading.??87.102.5.144 10:14, 11 August 2007 (UTC)

The Reference Desk staff is unable to do you homework for you because we are suffering from a staff infection. 05:18, 12 August 2007 (UTC)

about sea monkeys

i have some sea monkeys that are in the process of reproducing and there is a big black ball shaped thing on the bottom of the tank is that a baby sac or something different?

I'm not sure, but have you fully read Sea monkey and brine shrimp?

I seem to recall that the male sea monkey carries the fertilized eggs in a pouch, rather like a kangaroo. I don't know if this makes it a marsupial, but it would suggest that the "big black ball shaped thing" is not a sac of babies. Perhaps it is faeces. Plasticup ^T/C 02:35, 11 August 2007 (UTC)

Male seahorses keep babies in a pouch too - but they definitely aren't marsupials! In marsupials, it's the female that has the pouch - and there are nipples down inside the pouch for the baby to suckle on. Hence marsupials are all mammals. SteveBaker 18:05, 11 August 2007 (UTC)

changing the demand for electricity in a 24 hour period

how is it possible to change the demand for electricity in a certain period (either increase it or decrease it).thanx i appreciate your help 203.31.216.248 21:07, 10 August 2007 (UTC)

If you want to change demand for something, change the price. Many electrical utilities charge less for electricity used at night (when the natural demand from homes, offices, and factories is lower). Their customers (generally it's industries, but sometimes even domestic users with more sophisticated metering setups) can then choose to use electricity at night that they might otherwise use during the day. So the night shift at the steelmill might make more steel than the day shift. -- Finlay McWalter | Talk 21:13, 10 August 2007 (UTC)

If I recall my economics course, artificially changing price does not change demand (economics); it will change the quantity sold. This is a matter of semantics and the definition of "demand." To actually change demand, you will need to market or advertise the service differently, or change its quality, or otherwise affect how much people want it. Nimur 18:17, 11 August 2007 (UTC)

Or you might do your laundry during the day when prices are low rather than in the evening when prices are high. Plasticup ^T/C 02:36, 11 August 2007 (UTC)

In UK, we had this dual metering as an option for electricity customers for the past 35 years (at least) - it used to be called "White metering" because the electricity meters where white instead of the usual black. Since then it's gone through several incarnations - "Cheap rate electricity", "Off peak metering", etc. The deal is that you can opt to have white metering rather than the usual flat rate - that's your choice. If you opted for this scheme then electricity was significantly cheaper during the off-peak nighttime hours - but much more expensive than usual during normal daylight hours. The meter had two separate sets of dials and some kind of timer inside that switched over from one set of dials to the other at the prescribed time of day so it measured the amount of daytime and nighttime usage separately. Many people use them in conjunction with timers that set washing machines, dishwashers and water heaters to run during the night - and "Night Storage Radiators" for heating. Night storage radiators consist of a steel case containing a huge pile of thermal bricks threaded through with heating elements. During the night (when electricity is cheap), the radiators turn on, the bricks heat up - then in the morning, the heating coils turn off and the heat stored in the bricks gradually radiates out into the house to keep you warm. If you get it right, they are still sufficiently warm when the cheap rate cuts in again the next night. Used correctly, this system can save you a ton of money compared to normal electrical use. Used badly, it could cost you a packet! From the perspective of the electricity suppliers, this made a great deal of sense since this lightened the load on their generators during the day - and used some of the idle capacity during the night. Overall, this enabled them to operate with fewer power stations. This approach only really works in places where people aren't running air conditioning. SteveBaker 18:01, 11 August 2007 (UTC)

I seem to remember reading that the time-of-day switchover was actually triggered by a special tone embedded in the Radio 4 long-wave broadcast, and picked up by a receiver in the meter using the wiring as an aerial. Makes a certain amount of sense since independent clocks could be wrong - either accidentally, or deliberately in order to get night-rate power during the day. What wonderful things you could do in the 70s when all this stuff was run by quasi-government agencies :-) 62.56.81.182 23:47, 11 August 2007 (UTC)

Check out Economy_7 81.144.241.244 14:12, 15 August 2007 (UTC)

One advantage to encouraging solar power in homes and businesses is that energy production occurs during daylight hours, thus reducing demand for power from the grid during peak hours, especially during summer when A/C power use is at it's max. This "encouragement" can take the form of government subsidies, tax deductions, etc. StuRat 05:08, 12 August 2007 (UTC)

Melarsoprol - sorting fact from fiction

Has anyone here had experience with the drug Melarsoprol? I've been doing a bit of reading about it tonight and it sounds like pretty horrific stuff. Kills 5-10% (depending on what you read) of patients outright, may cause permanent nerve damage to those it cures, will eat straight through regular plastic IV tubing/syringes, corrodes veins, causes burning agony on administration, etc. This is of course 'stuff what I read on the internet'...

So, what's the straight dope with this stuff? Anyone ever been injected with it? --Kurt Shaped Box 23:15, 10 August 2007 (UTC)

Well, I imagine when the alternative is death, you're willing to try anything. :( I don't think it was this same compound, but I recall seeing a patient at a cancer clinic receiving an IV that sounded like it had similar effects. They had to be very careful when administering it (directly into a port instead of a conventional IV needle), and they covered the skin surrounding the port with self-adhesive plastic, to protect the patient in case of spills. I'm like you: I'm terribly curious how something so hazardous could actually be a good thing when injected! --Mdwyer 23:52, 10 August 2007 (UTC)

I think the general idea is that they inject it, cross their fingers and hope it kills off all the parasites before it kills the host... --Kurt Shaped Box 23:57, 10 August 2007 (UTC)

Yes, remember the way most tests of drugs are conducted is to determine if the outcome is on average better then the outcome without the drug. Nil Einne 10:08, 11 August 2007 (UTC)

Don't you reckon that there's just something "oldschool" about Melarsoprol, though? Reading about it kinda makes me think of a bottle of the stuff on a shelf next to the ether, leeches, blood-lettting equipment and various 'tonics' back in the day. --Kurt Shaped Box 12:38, 11 August 2007 (UTC)

My mom has blood-letting done on her. As bizarre as it sounds, it is still an accepted treatment for polycythemia caused by chronic mountain sickness. No leeches, though, thank goodness! --Mdwyer 22:58, 11 August 2007 (UTC)

It looks like Eflornithine is a much better treatment. Plasticup ^T/C 02:39, 11 August 2007 (UTC)

August 11

Questions about hydrogen/oxygen ratio in Eternal Tank, Kourou launch site and inclination

Hello,

I have a couple of questions :

1. I was taught (or maybe I misunderstood) that two hydrogen molecules and one oxygen molecule combine to make two water molecules. Now from this I conclude that 1 kilogram of hydrogen and 8 kilograms of oxygen give you nine kilograms of water. But when I check this official site : [2], it turns out that they have a 616/102 ratio). Does anyone understand why?

Probably has something to do with the fact that hydrogen is the lightest element. If you had a kilogram of ping pong balls and a kilogram of tennis balls, would you expect the numbers to be the same? Matt Deres 00:16, 11 August 2007 (UTC)

I don't see where you got the ratio from. Two moles of hydrogen masses 2.01g. One mole of oxygen masses 16.00g. When they meet, you should get 18.01g of water. The mass can't change, but the volume -- the amount of space it takes up -- can change. --Mdwyer 00:27, 11 August 2007 (UTC)

The ratio comes from the weight/weight ratio given on Nasa's website. Someguy1221 00:34, 11 August 2007 (UTC)

I thought two moles of hydrogen would mass 4.02 g or something like that? I still don't understand the ratio though?Evilbu 00:42, 11 August 2007 (UTC)

I suspect they rely on natural oxygen in the atmosphere. It makes sense to take more hydrogen than necessary to burn all the oxygen since it is very heavy to waste oxygen. Also any burn from the atmosphere is free. --Tbeatty 04:40, 11 August 2007 (UTC)

You are right in your mass calculations - the data I found on the site was

Liquid oxygen:

616,496 kilograms

(1,359,142 pounds)

Liquid hydrogen:

102,619 kilograms

(226,237 pounds)

that's about 6:1 (not 8:1) as you find - I can't explain the descepancy.87.102.5.144 09:39, 11 August 2007 (UTC)

The 8:1 ratio of Oxygen:Hydrogen for combustion is correct (ignoring Isotopes). So there are IMO only two possible explanations for the 6:1 ratio in the external tanks:

• Atmospheric oxygen is pulled-in mid-flight (very unlikely)
• There is unburned hydrogen either remaining in the tank, or expended due to incomplete combustion.

Note that the NASA website states, "The now nearly empty tank separates and falls", so I vote for the second option. Speculation: One reason for the tanks not being "completely" empty could be that the fuel intake system for the shuttle's engines requires the oxygen/hydrogen to be available at a particular partial pressure, which cannot be maintained once a certain % of the fuels have been consumed. Calculation of how much fuel remains unused will depend upon detailed design specs. of the tank, "fuel-injection-system" and engine. Abecedare 12:00, 11 August 2007 (UTC)

Let me rephrase the answer as I don't think I was clear. 8:1 is the theoretical limit with a perfect burn. Perfect burns are impossible. So they have a choice: they can stack the equation to either burn all the hydrogen or burn all the oxygen. Since oxygen weighs significantly more, it makes sense to add more hydrogen to consume all the oxygen. It is a huge waste to expel unreacted oxygen, but not nearly the amount of waste to expel unreacted hydrogen. They are engineering the combustion to consume all the oxygen by carrying extra hydrogen. By mixing in a 6:1 ratio, they make sure all the heavy item is burned. As an added benefit, the excess hydrogen will burn in normal air and provide additional thrust. Simply doing the math of increasing the oxygen to get to 8:1 (~200,000 kg) vs. the amount of hydrogen that brought it to 6:1 (25,000 kg) shows how effective it is to scale with excess hydrogen --Tbeatty 06:40, 12 August 2007 (UTC)

Tbeatty, I agree with everything you said, but I did not understand how the burning of the excess hydrogen in the atmosphere provides additional thrust.

That aside, the unburned hydrogen in the rocket engine exhaust may also have the additional benefit of reducing the average molecular weight of the exhaust gases -> increasing the speed of sound in that medium -> allowing for higher exhaust velocities (i.e. greater thrust) as mentioned in the rocket engine and choked flow article. I am no rocket scientist, so I can't say if this effect is quantitatively significant, especially since the unburned hydrogen will also reduce the average temperature of the exhaust. Abecedare 07:11, 12 August 2007 (UTC)

2. I read that many critics complain that the inclination of the ISS is too high, raising costs each time something is launched by NASA from Cape Canaveral. But why is the inclination 51.6 degrees? The Baikonur Cosmodrome lies at a latitude of about 46 degrees, so why the unnecessary five degrees?

3. Am I correct that nothing has been launched to ISS from the Kourou base? I was just wondering about the costs and others problems. Does ESA have lots of experience when it comes to docking in low earth orbit? And won't the it be really expensive to give their Automated Transfer Vehicle a huge inclination like that, while they are situated near the equator?

Thanks,Evilbu 23:42, 10 August 2007 (UTC)

The oxygen might reacte with the rocket combustion chamber, and additional hydrogen will create a reducing condition and might protect the wall.--Stone 16:33, 11 August 2007 (UTC)

I would assume that those numbers are maximums for each tank. After the rocket is fuelled, it's got to sit there on the laumch pad for hours before launch. During this time the tanks are often vented to atmosphere for various reasons (pressure/temperature control perhaps). Our article on Space Shuttle external tank also mentions some venting that happens after launch. Maybe they need to vent more of one gas than the other under some complicated set of conditions - and therefore one tank is larger than would be expected. SteveBaker 17:38, 11 August 2007 (UTC)

What is the fate of insulin molecules in the body?

What happens to a typical molecule of insulin after it has been produced in the pancreas? It circulates in the blood and attaches to an insulin receptor to do its job, and then what? Thanks, AxelBoldt 02:43, 11 August 2007 (UTC)

Insulin enters the cell after binding to its receptor, and is rapidly degraded by insulin-targeting cytosolic enzymes[3]. Someguy1221 03:16, 11 August 2007 (UTC)

name of Middle Eastern herb?

I'm trying to figure out the English or preferrably Latin name for this Arabic herb: مرمية

Another name is wild miramiya, meramiya, mariamiya, as in in mariam.. or meryam .. virgin Mary. They say she had tea made from this herb while pregnant with baby Jesus. It's calming to drink, soothes the body, and if you take a lot you can for sure sleep like a baby. It can be used to alleviate stomach pain. Or it can be put in baby's milk bottle when he's teething to reduce pain.

I Googled it and it showed pictures of common sage, but I'm told by my informant that the herb in question is definitely not common sage, nor is it rose of Jericho, which were my two first guesses. Apparently it's popular in Israel and in the Levant.

Picture: http://www.kisa.ca/lj/herb.jpg

--Sonjaaa 03:46, 11 August 2007 (UTC)

I created the stub Salvia libanotica, because this might be it. But I'm not positive.--Sonjaaa 04:46, 11 August 2007 (UTC)

From living in Egypt I believe it's actually another member of the mint family, marjoram. Bendž|Ť 09:53, 11 August 2007 (UTC)

Although after looking it up it seems the dictionary gives مريمية (with an extra ي, so pronounced mariamiya, "belonging to Mary") to mean "sage" while marjoram is ṣa3tar sha2i3, which, if you can read that awkward transliteration, you could ask your informant about. If it turns out to be a different sage species, it may also be Salvia lanigera, "wrinkle-leaved sage," which makes sense looking at your picture. Bendž|Ť 10:18, 11 August 2007 (UTC)

Toe Nails

Can anyone hazard a guess as to the growth rate for a complete "cycle" of a typical toe nail? In other words ... say, you are examining the "newest" portion of the toe nail (the section closest to the skin from which it has protruded). How many days/weeks/months will that part of your toenail take to grow out to where it is at the "end" of the toenail -- i.e., ready to be clipped? Thanks. (Joseph A. Spadaro 04:04, 11 August 2007 (UTC))

A study of 70 individuals suggested an average toenail growth rate of 0.050 mm per day, with significant variation from person to person. The "cycle" time would then depend on the size of your toenail. [4] Someguy1221 04:10, 11 August 2007 (UTC)

So... if your toes are 1 cm long, it takes about six months. —Keenan Pepper 19:49, 11 August 2007 (UTC)

biology --- moth question

Why is there no Wikipedia page about the moth genus(?) Phalaena ? Is it an outdated term? If so, what is the modern equilavent(s)? What did it originally mean or span?--Sonjaaa 04:22, 11 August 2007 (UTC)

Phalaena was originally a subdivision of lepidoptera, created by Linnaeus, and included moths in general. It is now obsolete, having been replaced by the various families currently under lepidoptera (shown below). Someguy1221 04:32, 11 August 2007 (UTC)

So Phalaena means all lepidoptera? Or only certain subgroups of lepidoptera?--Sonjaaa 04:48, 11 August 2007 (UTC)

To my knowledge it included only identified moth species (not sure if it contained all of them). This classification has not been used in contemporary taxonomy in two centuries though, to my knowledge, and the distinction between moths and other members of lepidoptera has changed significantly in that time. Finding a comprehensive, internet-ready source for this may be a difficulty, but I'm going to search trough entomology journals right now. Someguy1221 05:04, 11 August 2007 (UTC)

Correction, I have found papers using this term in their title as late as 1910 (needless to say, these might be somewhat difficult to actually find and read). However, it's use in more recently printed papers (last 40 years) seems to be only as an historic artifact of the original taxonomy, and these papers make no attempt at actually defining the term. Someguy1221 05:10, 11 August 2007 (UTC)

nano tech

Is it possible to synthesise nanoparticles of CuS

Almost certainly - probably by preciptiation with a copper (II) salt and a sulphide salt - it may be neccessary to introduce additives into the mix to prevent the CuS agglommerating - I can't give more details.87.102.5.144 09:41, 11 August 2007 (UTC)

Here http://nanotechweb.org/articles/news/1/5/7/1 shows nanowires have been made - do nanowires count as nanoparticles?87.102.5.144 09:43, 11 August 2007 (UTC)

or here http://www.informaworld.com/smpp/content~content=a759267176~db=all but chains again87.102.5.144 09:47, 11 August 2007 (UTC)

Or just do a search for "copper+sulphide+nanoparticles" http://ww.google.co.uk/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=copper+sulphide+nanoparticles&spell=1 - which gives syntheses in the first few results. 87.102.5.144 09:55, 11 August 2007 (UTC)

AC Adapter

I ordered a Linutop, which of course came with a europlug. I live in the US, so the europlug won't work. However, it says on the back that the output is 9V 1.5A. I've looked through my AC adapters, even universal ones, and they only go up to 300mA. Where would I be able to get a 1.5A one? Can I find one in this country? 172.135.153.217 04:52, 11 August 2007 (UTC)

You'd want a switching power supply here, most adapters your looking at are probably just plain old transformers (although a switching power supply doesn't have to be able to supply a high current of course, most mobile phone chargers are switching nowadays). Your best bet would be to look at the kind of adapters suitable for laptops and stuff. However are you sure the power supply isn't universal? Many are so all you would need is a passive plug adapter. Check the ratings carefully of course before you try anything Nil Einne 09:50, 11 August 2007 (UTC)

When I accidentally left my adaptor behind on one trip, I found a 'univeral' adaptor at Fry's for my laptop that provides that amount of power - they definitely exist - but they aren't cheap (I think mine was about $45) and most places like WalMart and Radio Shack don't carry them. One thing though - read the label on the thing REALLY carefully - some of them only provide that much current at lower voltages.

Bit does the existing adaptor work at 110v/60Hz? If it's designed to work in Europe, it should - 110v/60Hz is what they use in France (for example). If that's the case then all you need is a different plug - you can just cut the old one off and put a new one on. Screw-on plugs are not exactly common in the USA - but I've found them in DIY stores (the one I found was for garden tools - it's huge and bright orange - but it works). Alternatively, there are adaptors that accept a Europlug and plug into a US-standard wall socket. I've only ever seen those on sale at airports though - they might be kinda hard to find. SteveBaker 17:15, 11 August 2007 (UTC)

Where did you get the information that France uses 110V/60Hz? As far as I know and according to various "voltage charts" I can find it uses 220V/50Hz (or 230V/50Hz, which, I think, is the official value these days), just like the rest of Western and Central Europe. And I second Nil Einne's question: perhaps the AC adapter is universal? My laptop's power supply is rated "100-240V 50-60Hz", and has a Schuko plug; with a simple adapter, I could easily use it in the US. --Dapeteばか 10:54, 12 August 2007 (UTC)

IF your adapter is rated for "universal voltages" (120 volt operation as well as 230 volt operation), then any Radio Shack in the United States can sell you the adapter you need to plug a Europlug into an American NEMA 5-15 outlet. And if you will be mostly using this in the United States, any hardware store, Home Depot, or Lowe's home center can sell you any of ten different types of plugs that you could rewire onto your adapter's power cord (assuming it has a cord and doesn't plug directly into the wall).

Atlant 12:05, 13 August 2007 (UTC)

Intracranial pressure

My EEG revealed a slightly high intracranial pressure. However IMHO after downing the pressure to normal I will a bit more passive and slow. Does it make much sense? --Vado

Wikipedia cannot offer medical advice, please ask your doctor. However, did your doctor tell you why you had high ICP? Or could you tell us how it was reduced? Knowing these might allow us to offer you some insight. Someguy1221 06:17, 11 August 2007 (UTC)

I've responded to your question here: [5]. StuRat 04:13, 12 August 2007 (UTC)

anxiety disorders

im having a habit of impressing everybody since childhood..this is leading me to a variety of problems such as social phobia and gynophobia..what can be done to overcome this?

Find a psychiatrist. I got over my own social phobias by deciding the whole world could go fuck itself if it didn't like me. I think it's a good personal philosophy ;-) WP:DGAF. Someguy1221 06:17, 11 August 2007 (UTC)

Or, with mad skills like that, you would fit in perfectly among the Ref Desk regulars ;) But seriously, impressive as we are, we can't give medical advice, you should ask a mental health professional for direction. Rockpocket 06:53, 11 August 2007 (UTC)

Given the difference between psychiatrists and psychologists, it follows that you probably need to see a therapist (which could range from anything from a counsellor, to a psychologist, to a pschiatrist, etc). To my knowledge the psychiatrists are more the ones that dispense medication, so a psychologist is probably the one to see. You probably just need to talk to someone (in addition to talking to a professional). By "Gynophobia" do you mean "fear of women", or "fear of women's sexual anatomy"? Articles you should probably look at include Genophobia and Erotophobia and definitely have a read through of Social Anxiety - a great article which should really help you analyse yourself (even you're going to be paying for someone like a psychologist).

Other than that my personal advice is to definitely consider seeing a psychologist, and socialisation is extremely important (even if you feel that you "don't get it right" or "aren't comfortable" in social situations, maybe keep trying because through socialisation you learn a lot about yourself, and you observe how everyone else behaves, you can put forward and develop whatever 'personality' or 'persona' that you want to. In life you should have a variety of friends that feed different aspects of your personality. For example there might be friends that really make you laugh, and other friends that think everything you say is funny, or you have friends where you are always serious with and have very mature and 'deep' conversations, and other friends that seem to be unable to talk about anything of seriousness or importance. Through these you learn to develop certain social skills. Mirroring for example is where you mirror the behaviour of the person you're with - if they put their hands in their pocket, do the same, or if you're both at a table and they lean forward, copy them, or they lean back, so do you, or if they talk and use a lot of expression, don't answer back in a monotonous voice (unless of course you're tryin to specifically not mirror them). Another piece of advice is to try maintain self esteem. Spending time in the sun for example helps me a bit. Getting a good haircut helps a lot of people. Meditation can keep you focus on yourself and your objectives. Seeing a movie can really help motivate you.

Finally, as for the gynophobia, that's something you and your therapist can try and find the cause of. However in my persuit to try and help, here are some ideas: befriend a female (i.e. become friends with a female not because you're interested in her romantically, but rather as someone you feel relaxed with - and by befriend it can be anything you're comfortable with); consider whether you want your therapist to be male or female (note that Tony Soprano of The Sopranos had a female therapist) on the one hand you might feel very embarassed imparting your personal feelings to a woman, on the other hand it might be just what you need to get honest feedback from a woman and perhaps break through your problem.

If you like you should check if there are any newsgroups on the web of other people with social phobia or social anxiety, other people with gynophobia, and I know for sure that there are mens groups out there that discuss mens issues where some people could talk to you about it.

Good luck! Hope this helpsRfwoolf 15:18, 11 August 2007 (UTC)

First thing to do is go discuss it with your normal doctor. He/she will then prescribe something and/or refer you for further treatment to psychologist etc.--SpectrumAnalyser 23:15, 11 August 2007 (UTC)

I'm wondering what the OP meant by "impressing". —Tamfang 23:54, 14 August 2007 (UTC)

How to find out the caffeine content thropugh experiment

Hello

Im a student and i have tried to find out about how to detect caffeine in coffee and tea. I know that we require sulphuric acid and chloroform but havent found the way to find out how much caffeine a particular tea has or which of the provided samples have more caffeine 122.163.203.2 14:12, 11 August 2007 (UTC)Tarush

Feed it to a spider and observe the web it builds. See Spider_web#Spider_webs_and_drugs - the photograph is even of a cafeine-induced web. Funny thing is, I made this up and the short section actually mentions this as a method of determining the toxicity of substances. Every now and then I find out my thoughts aren't as weird as one (including myself) might think. :) DirkvdM 19:09, 11 August 2007 (UTC)

There is a funny video about spiders on various drugs on youtube [6] I have no idea how much, if any of it is true. Theresa Knott | The otter sank 07:55, 12 August 2007 (UTC)

Except the spider trick doesn't measure the quantity of caffeine. I've also got to remind Tarush that there is a lot of argument about tea not actually having any caffeine. Some argue that tea instead has a similar chemical called theobromine, most often discussed with chocolate, which is gentler than caffeine. --Mdwyer 22:52, 11 August 2007 (UTC)

I have no personal direct knowledge of the caffeine content of tea, but I have trouble believing that there can be an argument about it -- any decent lab should just be able to take a sample of tea and assay it, and find out. If tea really contained no caffeine, that ought to be common knowledge; since it isn't, I much doubt that it's true. --Trovatore 23:02, 11 August 2007 (UTC)

Yeah, it sounds kind of sketchy to me, too. But I came across it when I was doing some research earlier. A quick google found this and this which seem to contradict each other somewhat. 'Course now I'm getting tea and chocolate confused... --Mdwyer 03:40, 12 August 2007 (UTC)

It could be less simple than that if (for example) the theobromine is metabolized into caffeine in the body. I don't think this reaction actually occurs, but similar things confound food science when studying many complex transient phenomena (like browning reactions). --Sean 13:37, 13 August 2007 (UTC)

I don't know if it counts as "experimental," but I think that caffeine content is typically determined quantitatively using something along the lines of HPLC. For both quantitative and qualitative determination, maybe something along the lines of LC-MS. Although I'm sure there's a titration of some sort for a non-instrumental determination. --Bennybp 00:40, 12 August 2007 (UTC)

This is from my recollection of a school science project from a long time ago. I cannot attest to the safety of the procedure or the accuracy of the results. (In general, I recommend against trying it.) The procedure goes like this: the content of several (e.g. 10) teabags are emptied onto a container; the net weight is measured accurately using an electronic scale. Concentrated tea solution is obtained by boiling in water and filtering. Residue of the first filtration is boiled a second time to allow more of the remaining constituent compounds to be extracted. Lead acetate solution is then added to the solution to cause tannins to precipitate. The precipitate is removed by filtration. Solvent extraction (using chloroform) is performed to extract caffeine (and possibly other organic compounds) from the aqueous solution. The chloroform is evaporated in a hot water bath (and recovered, for safety reason). The solid that remains is supposedly mostly caffeine and is weighed using an accurate electronic scale. (Warning: This experiment involves fire, explosion, lead poisoning, and other hazards. Do not attempt unless the experiment has been cleared for safety, authorization, and regulatory compliance. And do not attempt without adequate safety precautions, and expert guidance and supervision. The information here may be incomplete or inaccurate, and is not to be relied on.)

There is a slightly different method in my organic chemistry lab book. I think it's a common experiment for undergraduate organic or separations lab. It basically involves boiling tea bags in hot water with sodium carbonate (to help keeps the tannins water soluble), extracting the solution with dichloromethane (I'm guessing this is used as a slightly safer replacement for chloroform), boiling off the dichloromethane, and recrystallization of caffeine in hot acetone and ligroin. That would extract it, but would only probably give a rough idea of how much is in the tea, due to some impurities and yields. The details should be in any undergrad lab book (This is in "Macroscale and Microscale Organic Experiments", 4th edition, by Kenneth L. Williamson, pg 148). But again, this should not be attempted without the proper safety equipment (fume hood, hazardous waste collection, etc) and supervision by a professional. --Bennybp 17:19, 12 August 2007 (UTC)

Term for an aggressive signal used by animals

My girlfriend has a bird (Quaker parrot) that doesnt really like me, and times moves its head side to side. I'm the type of person that likes to explain behaviors with psychology and evolution. So I figured him doing this meant some kind of signal of being aggressive.

What's funny is while my girlfriend would hold him, I would make the same signs (such as turning head side to side, and making bird calls) and he would respond right after I did with the same thing I used. So right there I figured that those signals had something to do with a competition to show ability to fight.

Last night, around 6 AM, I watched the Science channel, and in one of the documentaries it showed that the side-to-side behavior being done by a chameleon right before fighting with another. And that it was done to show off its swiftness and the like to intimidate the competitor. It was a very small part, so it didnt go into details, which I wanted. But when I saw that, I thought "Eureka!"

I want to know if there is a term for that. And I also want to know if I was right about my assumption, and also if that signal is used for anything else, such as a normal social reason. I looked around on a few pages and couldnt find a mention of it. I looked it up on google and they only said the signal, and hardly on why it'd done. Sorry for the long explanation, but I thought you guys would appreciate the story. =) PitchBlack 16:33, 11 August 2007 (UTC)

When an animal puts on a show without necessarily acting on it, this is called a "display" (as you suspected, here an "agressive display"), which is a part of its inherited evolutionary stable strategy. This theory explains behaviour from an evolutionary perspective. In this case, the bird is sizing you up as an opponent rather than taking a lunge at your eye straightaway as it realises you may be capable of doing more grievous harm to him than he to you. Where fighting for dominance does occur within a species, it is rarely "red in tooth and claw", as the mutual costs in terms of injury and time are too great and the outcome can be decided with restraint. Needless to say, his jealously is misdirected (or is it?), and when harmless, the neuroticism of an animal outside of its natural environment is a big part of the fun in keeping a pet. Don't take it personally! Bendž|Ť 17:38, 11 August 2007 (UTC)

Thank you for the response! I have some responses myself though. If my girlfriend were to actually let the bird down on the couch, it would come to me and bite/attack me, it TRIES to attack me if I touch or hug her (starts chirping like hell too). So its not just sizing me up, I think it might be using its signals cause it really wants to do something. And when I let it bite me, I put on a little show and everyone starts laughing. And when my girlfriend takes it away and picks it up, the bird actually laughs with her. Can you tell me if maybe the bird is doing this not only for a jealous/territorial reason, but maybe a humorous reason too? And can you explain more about how an animal can be jealous? PitchBlack 19:01, 11 August 2007 (UTC)

I think that bird is trying to steal your girlfriend, dude. Someguy1221 07:39, 12 August 2007 (UTC)

Sure, displays often indicate intent, but you can see the difference between the show that is swinging its head back and forth (unless its trying to hypnotise you) and actually biting you, a more utilitarian action; it's taking aggression to the next level. Many beaks are designed primarily to crack nuts and seeds rather than disembowling adversaries. Nevertheless, among polygynous chickens, where the stakes are much higher (all the females or none), fighting is wanton and beaks are used to their full capacity, leaving the loser to choose his final resting place. You can take it on good faith that your girlfriend's parrot is actually being quite gentle with you really and that there's still a signaling element to its behaviour. Many parrots pair up for life, so you can imagine how in the absence of a conspecific (member of its own species), it's grown quite attached to your girlfriend. As a seeming loner arriving on the scene, you're clearly a threat. I'm quite positive birds experience a wide range of emotions, including jealousy, although self-pity is a luxury only humans seem to indulge in. Humour, also, is a fairly recent innovation that is probably only shared in a true sense with some of our closest relatives. Remember parrots are talented mimics, and laughing may not be something they do in the wild. A book you may be interested in is Alexander F. Skutch's The Minds of Birds. A good chunk of it can be sampled on Amazon. (I should say that no, I'm not the author, nor have I even read the book myself.) Bendž|Ť 09:47, 12 August 2007 (UTC)

Oh, ok. Yeah, I know theyre great mimics, that's why I asked if it was doing it for a humorous reason. I didn't know if it was actually laughing or just mimicing (sp?) the others laughing. Thanks for all the answers, but I have one more question. The bird was biting her cusion for a while, but then stopped. Why? Also, when my girlfriends presence around the bird is gone (like in vacation) it'll be much nicer to the people around. PitchBlack 03:44, 14 August 2007 (UTC)

New fish in an ecosystem

Oftentimes when people create artificial pools or lakes, I know a whole ecosystem can move in - frogs, birds, insects, subsequently tadpoles, etc. However have there not be times when fish have somehow shown up? Or how could fish migrate from one pool to another pool without water as a medium? Or do these ecosystems just make do without fish? Any input is appreciated Rfwoolf 17:18, 11 August 2007 (UTC)

I don't have a source for this, but I remember being told that fish eggs are transported between ponds on birds' legs. 80.169.64.22 17:45, 11 August 2007 (UTC)

Flooding also can help fish to migrate.

Also when an artificial lake is created it's almost inevitable that a human will put fish fry in there..87.102.8.162 21:29, 11 August 2007 (UTC)

I read that as "fried fish". Oops. It is also somewhat conceivable that the ecosystem was already there, just dormant. Cryptobiosis explains that some organisms stay dormant until water appears. Sea monkies are an example. --Mdwyer 22:46, 11 August 2007 (UTC)

And some fish can walk using their fins. They can cross land from one pond to another. Graeme Bartlett 10:47, 12 August 2007 (UTC)

I’ve heard the fish eggs on birds’ legs explanation as well. I’m pretty sure it’s a standard ecological phenomenon. Most ecology text books should have it. --S.dedalus 21:04, 12 August 2007 (UTC)

Slow vcr power-up

More of a technology question, but I suppose the science community is most likely to have an answer.
My old vcr has started to develop the problem that when I turn it off for a while, it takes a long time to power up again. When I leave it off for a few days I have to hold the power button down for a minute or so until it 'comes alive'. When I left it off for about a month recently it even took several days (in case you're wondering - I kept the power button down with sticky tape). On stand-by there is no problem, but in power-save mode I get the same problem. Now this isn't too much of a problem if it remains the same (though still annoying), but if it gets even worse (as seems to have happened over the last year or so), it might not power up at all if I turn it off too long. I only occasionally need it when I play an old tape, but then I do need it. And I don't want to have it powered up all the time just for that. DirkvdM 19:34, 11 August 2007 (UTC)

Leaky electrolytic capacitors?--SpectrumAnalyser 20:27, 11 August 2007 (UTC)

Sounds like a good reason. Heat causes some electronics -- especially capacitors -- to slowly degrade. Once they get to a certain level, they no longer function at the ranges they are supposed to. A few years ago, there was a problem where a particularly bad set of capacitors were manufactured and turned up in a great number of consumer goods. I personally had these show up in computers, DVD players, and cable modems. If the VCR was built in the last few years, it might contain these capacitors. In that case, unless it is still under warantee, there is probably very little you can do about it, I'm afraid. --Mdwyer 22:43, 11 August 2007 (UTC)

If you have a soldering iron handy you can still replace the capacitors with a blown cap. --antilived^{T | C | G} 02:46, 12 August 2007 (UTC)

I've got a soldering iron, but I don't know which one to replace - there are about seven capacitors near the power inlet section (assuming a code like 'C904' means a capacitor). Btw, there is a writing saying 'HOT' between two capacitors - a big round one (400 V 120 μF) and a small blue 'blobby' one. Notice that I barely have a clue what I'm talking about. But then again, if the alternative is to give up on the vcr then that is a wonderful excuse to completely take it apart (ignoring the 'shock hazard' warning :) ).

Another thing is, how do I find out how much power it consumes in the various states it can be in. If it consumes less than 1 W on standby then I'll just do that. 1 W would cost me less than 2 euro per year (at today's electricity prices).

Or, more importantly, is there a chance that if I disconnect the power and try to start it up again in 10 years, it will not? DirkvdM 09:09, 12 August 2007 (UTC)

If this is indeed a leaky electrolytic, you can probably distinguish it from the non-electrolytic capacitors because electrolytics are normally marked with a '+' at one end and a '-' at the other - where non-electrolytics are not. Electrolytics are generally bigger, and cylindrical rather than disk-shaped - but that's not such a 'for sure' thing as the +/- markings. Hopefully, that will narrow it down to a small number that you could replace one at a time. SteveBaker 04:23, 13 August 2007 (UTC)

You can distinguish them by plugging them in backwards. The electrolytic ones will explode.  :) --Tbeatty 04:28, 13 August 2007 (UTC)

Can you see any cylindrical capacitors with some goo on the top or its cap is not flat? Those are the faulty ones and you can try replace them with approximately same spec'd ones. Remember to discharge the capacitors (shove some maybe scissors across the two pins and wait for the spark) first. --antilived^{T | C | G} 06:04, 13 August 2007 (UTC)

Ah, so that's what you meant with 'blown cap'. I thought you meant 'broken capacitor'. :) No, I don't see any blown caps or goo. But now I hear a ticking sound coming from the power section, with a frequency of just over 1 Hz. IT'S A TIME BOMB! :) Or rather, it sounds like something a capacitor might do - build up a charge, not able to hold it and then discharging it somehow, resulting in a tick. Of course, that would happen at very regular intervals. QED. I hadn't noticed that tick before, so I assume it wasn't there.

Anyway, accessing the big capacitor (which might be the faulty part) from the top is a bit tricky because I'd have to dismantle the recorder-section, which is rather delicate, and I couldn't figure out how to remove the bottom plate, so I cut out a section (right next to the 'Warning: shock hazard, do not open' sign :) ) and when I put the blade of my knife across the prongs I got the fireworks you promised. Strangely, all the electronics parts shops are at the other side of town - where I work, so I'll look for a replacement tomorrow. Thanks for the help so far. DirkvdM 08:28, 13 August 2007 (UTC)

Oh, and something I had forgotten to mention so far - at the top of the cylindrical thingies, which I assume to be capacitors, there is a symbol that looks like a 'K'. Or a 'V' with a line at the bottom. Which looks rather like the symbol for a diode, which I find rather confusing. The '+' and '-' are on the circuit board, though, as indicated. And there appear to be only two connectors to the board, which isn't very diodish. :) DirkvdM 08:37, 13 August 2007 (UTC)

(Diodes also have two pins). The term 'blown cap' does mean 'blown capacitor' - but frequently, when they blow, the contents (which is a nasty chemical paste) may boil - either forcing some of the contents of the capacitor out of one end or actually bending the metal can. Similarly the term 'leaky electrolytic' doesn't necessarily mean that it's leaking fluids - it means that it's leaking voltage. But it's perfectly possible for the capacitor to fail in ways that don't cause those obvious signs - and since your VCR does EVENTUALLY turn on, I doubt the capacitor has completely failed - it's just leaking voltage and therefore not charging as fast as it should. If you can't completely remove the dead capacitor - perhaps you can just solder a wire across it's pins to short it out - then cut one of the tracks leading up to it and solder the new capacitor across the gap you made (making sure the +/- of the new electrolytic are in the same order as the old one!) - you can use a couple of short lengths of wire to connect your new capacitor to the circuit board so you can position it someplace more convenient. SteveBaker 12:11, 13 August 2007 (UTC)

Why would you want to replace a cap with a blown one? 68.39.174.238 23:04, 13 August 2007 (UTC)

Yeah, that had me puzzled for a moment too, but of course he didn't mean replace the capacitors with others with 'a blown cap', but replace 'the capacitors with a blown cap' with a good one. Which led me to think that 'blown cap' meant something other than 'blown capacitor'. As per above. DirkvdM 07:39, 14 August 2007 (UTC)

Digital vs Analog Television Broadcasting

What are the real CURRENT facts regarding the alleged discontinuance of analog television broadcasting in favor of analog by 2009? What is the now-intended timing of this change if revised? What does it mean for the future of our fifteen year old TV (without HD capability, of course)?----Bob

You didn't specify the country. Your WHOIS information points to the US, however (I live in the UK, and so know nothing at all about the US switch off, and post this merely for the sake of someone else who might) Angus Lepper^{(T, C, D)} 21:20, 11 August 2007 (UTC)

For the time being at least, TVs do not need to be high-definition to receive a digital service; the UK offers Freeview (terrestrial), Sky Digital (satellite) and Virgin Media (cable) digital services which will work just fine on any TV with just a small set-top box to show for it. The US offers similar services, although they are currently slightly less advanced; according to our article on digital television "The FCC has determined that an external tuning device can simply be added to non-digital televisions to lengthen their useful lifespan. [Although] external tuning devices are not widely available, are relatively expensive, and require bulky AC power supplies, starting in 2008, the government will take requests from households for up to two coupons to reduce the price of some converter boxes by $40". These will make your TV perfectly digital compliant if you live in the US. Laïka 22:07, 11 August 2007 (UTC)

On the point of switchoff, the FCC will switch off the analogue signals on 17 Feb 2009 and sell the old analogue stations to other companies; this will render your TV screen completely blank on this date onwards, although analogue cable will continue for the forseeable future. Laïka 22:10, 11 August 2007 (UTC)

(Assuming USA/FCC NTSC, etc) Well, sort of. The stations will still exist, they'll just have moved to digital signals. The frequencies are being sold off -- mostly to cell phone companies. The FCC intends to have a voucher program, that will put money towards a new TV or an adaptor. You'll still be able to use your 15yo TV, assuming the correct adaptor. Your picture may even be better, since problems like ghosting will go away. But depending on where you are, you might have to invest in a UHF antenna, instead of a VHF antenna. --Mdwyer

However, don't expect an old analog TV with a converter to give a picture anywhere near as good as an HDTV, especially one with 1080i resolution. I'm personally planning on upgrading rather than spend more money on bad TV, but I am waiting and hoping the HDTV prices will come down first. StuRat 02:11, 12 August 2007 (UTC)

Note though, that correlating the analog switch off to the advent of HDtv is far from necessary. StuRat's approach to this makes the whole thing seem like a major cost and investment to households, and may very well create far more opposition to the switch than what's really warranted. Yes, digital terrestrial tv will not be as good as HDtv, but the existence of HD does not mean you need it. The cost to continue watching tv if you use an old tv set and your own antenna for reception can be as low as $30 US. ([7] Swedish appliance store, 1 USD = 7 SEK)/Kriko 08:21, 12 August 2007 (UTC)

In Australia the government keeps delaying the switch off, of analogue TV, as very few viewers have changed to digital. Only in the last year or so have TVs with a digital tuner been available as standard. It is now difficult to buy a plasma or LCD screen with only an analogue tuner. The set top box has been getting cheaper and cheaper. Graeme Bartlett 10:53, 12 August 2007 (UTC)

Health,

Has anyone heard about the study being done at the Mayo clinic using DNA testing to have a extremely early detection of cancer throughout the body? Cory Nelkin 21:06, 11 August 2007 (UTC)Cory Nelkin

Are you sure it's all cancers? Or is it a particular cancer? Recurring dreams 23:49, 11 August 2007 (UTC)

The Mayo clinic offers many types of screening for many types of cancer. You'll have to be more specific. Someguy1221 03:55, 12 August 2007 (UTC)

Enzymes releasing products after the reaction.

Whenever I read about enzymes things talk about substrates being brought together, reactions happening, and then the product is released. Nowhere have I found a description of what chemical/structural changes occur that cause the product to be released.

My assumption is that the product somehow changes the enzyme shape so that it can no longer hold the product. Is this correct? Additionally in competitive inhibition how does the inhibitor get out of the active site (and when)? Thanks Caffm8 22:35, 11 August 2007 (UTC)

(Oy, where are my Bio notes when I need them) The enzyme generally returns to its original conformation after catalyzing a reaction (the product cannot hydrogen bond or ionically bond to the enzyme exactly as the substrates did, being a different chemical), and in doing so the product unbinds. As for competitive inhibitors, these can just randomly bind and unbind from the reaction site (as hydrogen bonds and ionic/ionic or ionic/polar bonds can form and break in solution quite easily). It's also possible that it can't be removed, and the enzyme is rendered useless (mode of action of penicillin and similar antibiotics). Some substrates involved in signal transduction (such as acetylcholine and insulin) are removed from their receptor enzyme through another enzymatic reaction. It's possible some products and competitive inhibitors must be also, but I know of none. Someguy1221 23:55, 11 August 2007 (UTC)

Funny thing is that the product doesn't so much change the comformation of an enzyme. It's the change of conformation of the enzyme that produces the product. An enzyme will have a certain affinity for a substrate but an even higher affinity for the transition state (the state between substrate and product). So as the enzyme is catalysing the reaction it will take on a conformation that is ideal to match the transition state. But because the transition state is unstable it won't last very long, leading to a product. Of course the enzyme has a very low affinity for the product, so it is released. If an enzyme would have an extremely high affinity for either the substrate or the product no reaction would ever occur. Because either de product or the substrate would be permanently stuck to the enzyme. PvT 18:44, 12 August 2007 (UTC)

CO2 levels

Is there a simple way to measure the level of CO2 in a given gas sample that would be accessible to the at-home scientist? I don't need to know the exact quantity, just compare one sample with another. 69.123.113.89 23:52, 11 August 2007 (UTC)

Do you have sensitive balance? CO2 is heavier than air for example.--SpectrumAnalyser 23:57, 11 August 2007 (UTC)

That wouldn't really work in this situation (I should have been more specific). I need to measure the CO2 in a sample, and then measure the same sample again at a later time. 69.123.113.89 00:02, 12 August 2007 (UTC)

I think I've thought of a way to do what I need, but I'm not sure it will work. My Idea: I pass the gas sample through a tank of water to which a pH indicator, like Red Cabbage juice, has been added. Hopefully, some of the CO2 will disolve and form Carbonic acid, which will cause a pH change. Then, later, I can pass the gas sample through a second tank, and compare the pH changes of the two.
My Question is - will this work? 69.123.113.89 01:25, 12 August 2007 (UTC)

The basic concept sounds good, but the problem is that the sensitivity of the cabbage juice indicator probably isn't up to the task of detecting the minute changes in atmospheric carbon dioxide levels. It would also be critical to bubble the exact same quantity of air through the cabbage juice both times. StuRat 02:00, 12 August 2007 (UTC)

The CO2 would be absorbed by a strong base like NaOH.. if you can get that to happen then the amount of gas would be reduced by the fraction of CO2 present in the air - you'd need to be able to measure the volume - not easy for small amounts of CO2 though.87.102.1.234 10:36, 12 August 2007 (UTC)

Or you could attempt to measure the increase in weight of the NaOH. Although it would absorb water as well. A more exotic method may be to grow a seed and see how much dry weight the final plant ends up with. Graeme Bartlett 10:57, 12 August 2007 (UTC)

In high school chem lab, we looked at absorbing CO2 from a given amount of air in a given amount of water. You could use an indicator directly but you'd need to standardize it against known amounts (how dark or what color corresponded to how much CO2). See [8] for a way that might work for you. Alternately, you could titrate the dissolved CO2. Finally, you can measure the turbidity after passing the air through lime water. DMacks

The conventional grade school test for CO2 is to bubble the gas through Kalkwasser/Lime water (a saturated Calcium hydroxide solution). Carbon dioxide gas will precipitate as calcium carbonate. You may be able to quantitate the precipitate either volumetically, or by dry weight. Alternatively, here's a NASA webpage that may help: [[9]] -- 20:33, 12 August 2007 (UTC)

There's a commercial gadget that measures CO2 content in gas by the reduction in the temp of a target heated by IR beamed through the gas. Sort of a reverse greenhouse effect. Gzuckier 15:50, 14 August 2007 (UTC)

August 12

Need help with another link - hair pulling obsession

I'm looking for an article or reference for an assertion that in some instances, the syndrome (pathology? mental illness?) that causes an irresistible urge to pull out head hair may be caused by or related to food sensitivities (allergies). However, I don't even know the name of the syndrome. Any help is appreciated. Also interested in any studies or articles that correlate this syndrome to Demodex or other microbe/spore/parasite infestation. Anchoress 00:52, 12 August 2007 (UTC)

Trichotillomania is strictly an obsessive compulsive disorder, to the best of my knowledge. StuRat 01:33, 12 August 2007 (UTC)

Oh, thanks for the link to the name of the disorder, I can do some searching now. I don't know if the associations with the outside contributors I mentioned have been proven or are mainstream, but I'd like to see any documents on the topics if they exist. Anchoress 02:11, 12 August 2007 (UTC)

Silicate Lattice - edges?

So... theoretically, we have an infinite array of Si-O-Si bonds. But realistically, a crystal will end. So.. what happens at the end? Do we have OH or O(1-), with what sort of cation, and so on?

Yes - OH or even Si-O-Si bridges can happen, and the H in OH can be replaced by a cation as well as you suggest, in fact the OH groups can be reacted with compounds such as Me₃SiCl to give O-SIMe₃ terminal groups etc.

Actually, now that I think about it.. what happens in diamond? I suppose CH3 groups or even vinyl groups are possible at the edge.

It's a similar situation - what you find on the edges depends on how the diamond was made/ it's history - in air C-OH groups or C=O groups are most likely.

If you cleave a diamond to get two new surfaces - there will be Radical (chemistry) at the new edges - these will react with air (or water) to form C-O bonds - reaction with N2 in air can also happen/

If you make diamond from chemical vapour deposition of say methane then yes - CH3 or vinyl end groups are likely.87.102.66.187 10:43, 14 August 2007 (UTC)

The topic is known as surface science more specifically surface chemistry see surface functionalization - we don't seem to have a lot on it. A web search might turn up more info..87.102.66.187 10:46, 14 August 2007 (UTC)

Concentrated acids - definition, calculations?

how are concentrated acids defined?... I know pure sulfuric acid is impossible to have, since it combines with itself to form pyrosulfuric acid and water, so is 98.5% sulfuric acid the highest concentration you can have?... What about other concentrated acids, like nitric, hydrochloric, and phosphoric? And finally... how would one do calculations involving mass equations (I suppose the H20 term in the acid dissociation equation is no longer negligible)

The concentrations of laboratory conentrated acids usually comes from the composition of the free distilling azeotrope - in the case of nitric this is 68%, in HCl the figure is about 20% but more HCl can easily be dissolved in water - the usual conc. is about 35-38% see Hydrochloric acid

Other acids such as acetic acid can be obtained esily pure 100%.

You can have 100% sulphuric acid - by adding a small about of SO3 to 98.5% sulphuric. As you know there is an equilibrium between sulphuric acid, pyrosulphuric acid and water - in the case of 100% sulphuric acid most of the substance will be in the sulphuric acid form.

(See also oleum) and look at Sulfuric acid for more info on the equilibriums.

I'm not sure about phosphoric acid - see Phosphoric acid "Pure anhydrous phosphoric acid is a white solid that melts at 42.35 °C to form a colorless, viscous liquid."

As for calculations you would need the equilibrium constants (see also Chemical_equilibrium) of the various species present in the liquid. Ask if you need more info etc.87.102.1.234 10:28, 12 August 2007 (UTC)

Fear of reading text books

Im doing mbbs..i cant study anything before the exams..because of this i've failed many exams...as soon as i start reading,my heart starts pounding..ill get precordial pain..this is since 4years

I would suggest consulting your medical practitioner; I don't believe there's much that we can do. Seriously, if this has been a long-standing issue for you, perhaps you need to consult? Splintercellguy 12:06, 12 August 2007 (UTC)

Certainly we cannot give medical advice, and you should consult a doctor about any chest pains. That aside, to get started doing something which seems odious and unbearable, such as reading your assigned textbook, try establishing a time when you are going to do it (initially) and a place and a duration. Try setting a kitchen timer for 15 minutes (you can endure the agony of reading for that long, right?) then open the book at the assigned start page and start reading. Next time, set the timer for longer, to build up your tolerance. Possibly, you will find after the 15 minute timer dings that it isn't as bad as you expected. Edison 03:06, 13 August 2007 (UTC)

See panic attack. This is a rather common problem that I've seen. Each year that I was teaching, I'd find many students suffer from panic attacks due to various things such as taking an exam or being required to give a presentation. One girl fainted every time she'd be asked to answer a question. The article suggests treatments, but they will only work if a medical professional diagnoses you with this specific disorder. Do not assume that an article on Wikipedia can diagnose your specific problem. I only mention the disorder (and frequency of it) to try and reduce your anxiety that is must be something severe. -- Kainaw^(what?) 03:44, 13 August 2007 (UTC)

I know quite some students who failed year after year due to problems of this kind, and this is so unnecessary given that these are medical problems that can be treated suprisingly well. So, please, go and seek professional advice, it could change much. There are lots of mental techniques to overcome such fears, and even drugs that support the process. It may, however, be not the best idea to only ask a general practitioner. Overcome any bad feeling you may have about it and ask a psychiatrist and/or a psychotherapist -- they are much more experienced with such problems. Simon A. 06:36, 17 August 2007 (UTC)

mitosis

i'm just wondering..what do you guys think will happen if a cell undergoes nion-stop mitosis? and what do you think will happen if a cell can't undergo mitosis? thanks! :)

What kind of cell? Any single celled organism could be said to be undergoing non-stop mitosis (although mitosis might not be the exact correct word for it). A single celled organism that can't divide is one that is going to die. For multicellular organisms, let's just look at humans. Cells that can't undergo mitosis are in a state called senescence. Cancer is a disorder in which cells in humans or other animals mitose uncontrollably. There are some cell types that naturally mitose constantly, however (Some cancer treatments indiscriminately target all dividing cells, resulting in loss of hair and compromised immune systems, as some of the cells related to these naturally divide near constantly). Someguy1221 06:25, 12 August 2007 (UTC)

That was a great explanation. You might also want to read section 9.5 of this page [10]. Cells can labile, stable or permanent, and permanent cells only very rarely replicate. Recurring dreams 09:36, 12 August 2007 (UTC)

Recharging batteries

I've heard that one has to fully charge a rechargeable battery in a new appliance, otherwise it'll not be fully charged in future charges...is this true? or is it a myth?

Do you mean using old batteries in another appliance? Or do you mean new batteries? I recently bought some and it stated on the package that the first time they should preferably be left in the charger for a whole day. Is that what you were thinking of? Don't know the reason, but if the manufacturer advises it, it'll be for a reason. DirkvdM 09:25, 12 August 2007 (UTC)

I mean the new batteries. But why does the manufacturer advise so? won't the battery get overcharged?

The manufacture does not want a flat battery to give the impression that the appliance does not work. Followed by a return of the product. Batteries can take a bit of overcharging with out destroying them. Batteries sitting around for a long time self discharge. Your statement is mostly myth, unless you chuck them in the bin thinking they are dead! Graeme Bartlett 11:02, 12 August 2007 (UTC)

At any rate, a proper battery charger will not overcharge. —Steve Summit (talk) 11:40, 12 August 2007 (UTC)

The first couple of charges with a new rechargeable battery help to "condition" the battery for use. These batteries have a memory of sorts, as it will remember how much it was charged and recharge to that point again. That is why it is important to fully charge and fully discharge before charging again the first few times. It is also helpful to fully discharge and charge your battery every so often, say once every month or so. This link gives a small amount of information regarding the first battery charge. You can also do a google search for "first battery charge" and get a wealth of information on it. http://www.cellpower.com/FAQs.cfm#How%20should%20I%20charge%20my%20battery

thx!

Overcast Days

Why do I feel so lazy and tired on overcast days even when I know I have had enough rest? my guess would be that the weather slows my metabolic rate...thus the lack of energy...but why does it slow my metabolic rate while it doesn't seem to affect anyone around me?

Seasonal affective disorder? --antilived^{T | C | G} 10:10, 12 August 2007 (UTC)

This helps, thanks!

Fractional charges on quarks

we know that charge has a QUANTIZED property,meaning that it exit in discrete packets rather than continuous amounts then why QUARKS has charge values in fraction? ..........usman

I don't really understand your question. It's not like they can have any fractial charge. It has to be be either 1/3 or 2/3. So it seems to me that the "quanta" of charge is 1/3 the charge of en electron. We choose the electron charge as a convention. We could just as easily choose the d quark. Then that would have charge -1 the u would have charge 2 the e would have charge -3. Theresa Knott | The otter sank 14:18, 12 August 2007 (UTC)

But quarks don't wander around by themselves - they come in threes - and I believe that the combinations always have a charge that adds up to a whole number. (Someone may want to correct me on that - this is not my subject.) SteveBaker 23:10, 12 August 2007 (UTC)

Pseudocodes, DFDs and Flowchart

Guys, its ADIDS.

Well i have another problem.

My Computer Studies teacher can't give detailed diagrams for how DFDs work and for diagrams for it. I dont also have flowchart examples. I am just doing my O levels so all I want is a non technical examples. Can any one post a link here for me?

PSEUDOCODES

Well. I had a problem writing a pseudocode/algorithm (formal) for i)finding out the avg,highest,lowest no.s from a set. ii) using various loop constructs (like for-next, loop-until,while-do,etc)

Can any one find me a review about such pseudocodes.

Wikipedia gives a much more difficult technical overview on such topics. SO HELP ME!!!!!!!!!!

ADIDS

Please don't spam questions across sections. Check computing :). Splintercellguy 14:35, 12 August 2007 (UTC)

Magic cleaning liquid

A 'magic' substance is called "sugar soap" in de Commonwealth countries. I could not find any information on a bottle as to its chemical contents. Is it farfetched to call it a Trisodium phosphate solution, considering what is written in the "sugar soap" article? VanBurenen 15:43, 12 August 2007 (UTC)

Good question. It appears that Liquid Sugar Soap is a TSP based. But to confuse the issue more, I found an article that suggests adding sugar (sucrose) to your homemade soaps to make them lather more. I've also seen "sugar scrubs", which are sugared oils which soften skin. this article might be the best answer, though. "It is sodium carbonate and sodium phosphate, and sometimes sodium silicate as well."

Note that phosphorus-based cleansers are difficult to find in America due to their environmental problems. Many cleansers NAMED "TSP" may actually not contain any trisodiumphosphate. --Mdwyer 17:56, 12 August 2007 (UTC)

I rewrote the sugar soap article. I think it is safe to say, "If you are in the US and are looking for something to clean your paint, then you are looking for TSP." --Mdwyer 18:11, 12 August 2007 (UTC)

Hmmm - that's really interesting. Being a Brit, I've always use 'Sugar Soap' to clean paintwork prior to repainting it. Here in Texas, I've never been able to buy any - and nobody seems to have heard of it, so it's been hard to find an equivalent. When I buy it in UK, it always came in a gallon tub filled with small granules of this soapy stuff. Being granulated, it dissolves quickly in warm water. I had always understood it was called Sugar Soap because it has the texture of sugar crystals. But that doesn't make much sense if it's available in liquid form too. SteveBaker 22:52, 12 August 2007 (UTC)

The double pendulum...

does the double pendulum have a time period as such....and if so...how do we practically find it out...and if so then the time period is dependant on the intermediate mass or the main bob?

It's common to use a Lagrangian mechanics approach; this will allow you to solve the system in a straightforward way via conservation of energy. Depending on the arrangement, the double pendulum may be stable, and may even be well-approximated by a simple harmonic oscillator, but since it has two degrees of freedom, you must generalize what you mean by the "periodicity," as many types of complicated oscillations may have periods that do not return to identical initial conditions. Nimur 16:19, 12 August 2007 (UTC)

We even have an article about the double pendulum, which mentions that it can exhibit chaotic motion (in the technical sense, not the colloquial "wow, that's crazy":). DMacks 19:05, 12 August 2007 (UTC)

Since you specifically asked, both the stability and any form of periodicity would depend on both masses and both pendulum lengths; but the equation for the period would probably not yield a simple relationship with these values. Nimur 21:31, 12 August 2007 (UTC)

But nimur, how do i derive or get to this equation and what is this equation.....could you please elucidate?

The math is given in Double pendulum (of course). But what you are asking for is impossible. A double pendulum doesn't have a 'period' - a period implies periodicity. ie The object is at some position, moving at some speed - then sometime later, it's at the same exact position, moving at the same exact speed - the "period" being the time elapsed between those two events. A double pendulum may move in such a way that it will NEVER return to the exact same position and speed - no matter how long you watch it for. Without periodicity, there can be no equation for the period. It's a classic example of a 'chaotic' system. You can't predict a double pendulums' motion over the long term - except under the simplest of starting conditions. This seems amazing because it's such a simple thing to look at - and that's why they are officially "cool"! SteveBaker 18:57, 14 August 2007 (UTC)

Urinal etiquette

Could someone explain the various rules of 'polite urinal use' in the mens' room to me? Thanks. I know the obvious 'never use the urinal directly next to another guy' thing. Thanks. --84.64.182.39 23:11, 12 August 2007 (UTC)

1) Don't splash.

2) Unzip and zip back up facing the urinal, not facing other men.

3) Don't look at anyone while urinating, stare at the urinal or wall in front of you.

4) Flush after.

5) Wash your hands after.

6) No snacking on the urinal cake. StuRat 23:46, 12 August 2007 (UTC)

If there are (say) ten urinals in a row, go 1-3-5-7-9 (i.e. keep one urinal between each user). In an empty three-urinal mens' room, *never* got straight to the middle one (effectively, it means that you're bogarting all three and causing other users to wait until you've finished). Never use a urinal next to another man, or between two other men. If you have a choice, use the urinal furthest from the door (to avoid other men walking behind you whilst you're urinating). Do not use the urinal for solid waste. --Kurt Shaped Box 23:56, 12 August 2007 (UTC)

And, perhaps, most important of all: Dont try doing any George Michael impressions while you're in there (an I don't mean singing). You never know who's in the next stall. BTW, whats scientific about this query? —Preceding unsigned comment added by 88.109.93.168 (talk • contribs) 00:29, 13 August 2007

Hmmm. The psychology behind it might be interesting to discuss, come to think of it. I'm in the UK and it (the urinal spacing thing, that is) seems to be a pretty universal, unspoken thing. I don't remember anyone ever explaining it to me either - it's just something that guys 'do'. --Kurt Shaped Box 07:43, 13 August 2007 (UTC)

Some may disagree with me, but I say don't talk in the men's room, even to your friends. It can wait until you're finished. Talking in the restroom is something girls do. —Keenan Pepper 00:46, 13 August 2007 (UTC)

The disturbing part is what girls talk about when they're in the bathroom. Someguy1221 02:39, 13 August 2007 (UTC)

http://www.drinknation.com/urinaltest.php - I got a perfect score! Yeay me! ←Ben^B4 00:52, 13 August 2007 (UTC)

Why not use the urinal next to one in use? What is it there for then? Sure, if there is enough room I usually observe some spacing too, but if the only available urinal is between two other guys, I'll use it. If I weren't 'allowed' to, it shouldn't be there, right? And why not talk? That's actually one of the few times I engage in small talk, just to pass the time. I haven't noticed anyone being bothered by either breaking of the 'taboos'. I suppose this is a cultural thing (I'm Dutch, btw). DirkvdM 08:53, 13 August 2007 (UTC)

Yeah, it must be cultural. I've found myself in situations where someone is using the middle urinal of three and bunch of grown men are hanging around at the back of the restroom (that's another 'unwritten rule', I guess - 'don't stand directly behind your fellow urinal users') waiting for him to finish before they can go forth and pee. It sounds really lame when you write it down... :) Perhaps the most important rule of all, as yet unmentioned - is that you must never, ever attempt to use a urinal that is already in use. Breaking this rule *may* get you stabbed. --Kurt Shaped Box 09:32, 13 August 2007 (UTC)

Additional etiquette rule: 7)"Stand close. The man behind you may be barefoot." Edison 15:07, 13 August 2007 (UTC)

• Dave Barry's Complete guide to guys has a good section on this. The real deal is just Leave each other alone - as any Nervous peer can attest. WilyD 15:20, 13 August 2007 (UTC)

Speaking of different cultures, I once ended up in a gay bar. When I went to the toilet it was pitch black - suppose that was the 'dark room'. I walked a few paces, felt 'splash splash' under my feet and decided to relieve myself there. Go with the flow, so to say. :) DirkvdM 17:28, 13 August 2007 (UTC)

O_O I would burn those shoes. Anyway, I agree with all the above but want to add that it's not really as necessary to observe spacing if there are nice big privacy barriers between the urinals. But if there's no barrier the spacing becomes extremely important- with no barriers I for one am completely incapable of relaxing enough to "go" if there's not more than 2 urinals between me and the next guy o_O --froth^t 20:07, 13 August 2007 (UTC)

I believe that's a sign of inadequate beer intake. If you really have to go, you can probably manage it under almost any circumstances. Friday (talk) 20:12, 13 August 2007 (UTC)

What the heck do you scared boys do when confronted with a place that has only one big trough? Or at a sports venue that is packed with guys trying to go during a break in the action? Or even better, the combination of the two? Heck, it's only a penis. Roughly half of all humans have one. --LarryMac | Talk 20:14, 13 August 2007 (UTC)

Easy. The users space themselves appropriately at the trough. In the case of a sports game, they patiently wait in line (they really do!). There is *no* excuse for poor urinal etiquette. --Kurt Shaped Box 20:55, 13 August 2007 (UTC)

What about changing rooms at sports parks? Do you guys use them in turns, or what? Or does the fear of same-sex nudity not apply there for some reason? DirkvdM 07:46, 14 August 2007 (UTC)

Honestly, I think you should as at the Humanities desk. ←Ben^B4 03:41, 15 August 2007 (UTC)

Huh? DirkvdM 14:57, 17 August 2007 (UTC)

Dirk, I don't think the posters above worry about same-sex nudity. This is rather a question of personal space -- a concept in psychology that there is a minimum distance (depending on relation of the people) that people need around them to feel comfortable. Well, and urinals are a rather striking violation of this principle because they are commonly spaced closer than people who don't know each other would stand even in normal social situations. Simon A. 06:58, 17 August 2007 (UTC)

Then there are those of us who prefer not to be so close that we get splashed with each other's tinkle. StuRat 06:40, 18 August 2007 (UTC)

August 13

BaBar Experiment

What is the consensus on the mysterious particle produced by the BaBar experiment a few months ago? Thanks *Max* 00:21, 13 August 2007 (UTC)

Japanese Vehicle Horsepower Restrictions

I know that Japanese auto manufactuere's adhere to a 280bhp horsepower limitation. Does that apply to foreign vehicles as well? Could I import a vehicle into Japan that exceeded that 280 bhp or does it just apply to domestic models?

Hmm, I read somewhere that they only advertised powers up to 280 hp, but that the cars in reality could develop more. I'm not sure, though. —Bromskloss 10:43, 13 August 2007 (UTC)

Yeah, I've heard the same thing, if I remember correctly I've read it in quite reputable car magazines. They have a gentleman's agreement if you like (or perhaps it's a government sanctioned agreement) that cars can only have a limited maximum horsepower. If the cars are over that horsepower then they simply understate it to the agreed limit, or usually just below the maximum. I believe they stick with these stated figures on exported models in other countries as well, I spose it would look a bit suss if the exported models had more horsepower than the identical domestic product. Kind of contrary to manufacturers in many other countries that tend to overstate their horsepower. It is an interesting question on what they do on cars imported to Japan that are known to have greater horsepower; do they pretend it's less, really limit it, or just not worry? As far as I know they just leave them at whatever they really are, but I could be wrong. --jjron 13:18, 13 August 2007 (UTC)

On the subject of Japanese manufacturers sticking with stated figures on exported models, the Mitsubishi GTO (sold as the 3000GT and Dodge Stealth in North America) was rated at 280 PS in Japan but 300-320 PS (depending on model year) in North America. I don't think there were hardware differences, though I could be wrong. I think Japanese manufacturers only stuck to the 280 PS "limit" in Japan and rated cars at their true output for export.

Here is a little news blurb from Car and Driver titled Japan Dumps 276-hp Pact]. It appears that, as Jjron says, it's a gentleman's agreement, not a law. I don't know anything about Japanese import laws, so I don't know how practical it would be to import a powerful car, but I don't think there's any law requiring that cars sold in Japan have no more than 280 PS. TomTheHand 14:38, 13 August 2007 (UTC)

I believe some of them have a restrictor plate installed somewhere in the intake that limits the amount of air and fuel the engine can receive. Once you purchase the car, you can take the restrictor off. I might be crazy, though. --Mdwyer 14:45, 13 August 2007 (UTC)

I don't have a source, but I'd be surprised if a modern car did something like that. Generally when they tune an engine to different outputs for different applications, it's done by tweaking the engine control software. Friday (talk) 16:53, 13 August 2007 (UTC)

I realize this is probably a dead topic and nobody will read this, but I found an article on Japanese Wikipedia that appears to discuss the 280 PS "limit". Here's the article: [11] and here's a Google translation: [12]. The translation is iffy, and the article seems to be unsourced, but maybe it's of some use to someone. It seems to imply that the 280 PS limit was actually set by the Ministry of Transport. TomTheHand 04:07, 16 August 2007 (UTC)

Ohm's law

We know that Ohm's law is valid only when the temperature of the system is constant but we can observe that the temperature of the wire through which the current passes,changes with timei.e heat liberated =i²R.dt where dt is the time interval.How can we say that Ohm's law is valid in our real world conductors.218.248.2.51 08:04, 13 August 2007 (UTC)Ecclesiasticalparanoid

You are not taking into account that heat will be lost by the wire via conduction, convection and radiation. The conductor will reach as state of equilibrium very quickly. In most situations the conductors do not get sufficiently warm for there resistance to be markedly affected and so Ohm's law is seen to hold. In some situations of course the conductor does get very hot. A filament light bulb comes to mind. In that case Ohm's law certainly does not hold. Theresa Knott | The otter sank 08:27, 13 August 2007 (UTC)

You're saying Ohm's law doesn't hold for a light bulb filament, even in a steady state? Why not? —Keenan Pepper 09:04, 13 August 2007 (UTC)

Ohm's law relates resistance, current, and voltage, where voltage and current are variable. A "steady state" would involve all three being constant, so the law becomes meaningless if you confine yourself to looking at steady states. Someguy1221 09:29, 13 August 2007 (UTC)

I think you got it a bit wrong. Voltage, current and resistance are all variables, but neither have to vary with time. Steady state just means that things don't vary with time. —Bromskloss 10:41, 13 August 2007 (UTC)

It's not wrong. If you only look at a particular steady state, you can't see the variation, and so Ohm's law remains meaningless. If you're comparing steady states, that's something different. Someguy1221 20:27, 13 August 2007 (UTC)

Oh whoops, I see I wrote it slightly wrong the first time. Someguy1221 20:31, 13 August 2007 (UTC)

What Theresa Knott meant (I suppose) was that Ohm's law doesn't hold for the bulb unless you restrict yourself to steady state. (Alternatively, you could introduce a model for the resistance as a function of the current that has so far flown through the filament.) —Bromskloss 10:41, 13 August 2007 (UTC)

Ohms law doesn't hold through transient conditions. If you make a sudden voltage increase - and there is an inductor in the circuit - then Ohms law won't hold until the circuit reaches steady state. Ohms law does apply to light bulbs - providing the value for 'R' that you plug into the equation is the resistance of the bulb at the actual operating temperature. If you plug in the resistance when the thing was cold, you'll obviously get the wrong answers.

Ohm's Law always holds true: V always equals I x R. What doesn't hold true is any assumption that resistance is a constant.

Atlant 12:15, 13 August 2007 (UTC)

With real-world electrical wiring, the conductors may be loaded to say 80% of their rated current. Insulated wires will not reach an equilibrium temperature anything like instantaneously. The wire temperature will increase for an extended period, from several minutes to several hours, depending on how well ventilated the conduit, raceway, or cabinet containing them is. The resistance will change over the same period. At any point in time, Ohm's Law will apply, just as it applies when a variable resistor is included in a circuit. In some conductors, resistance increases with temperature, while in others it decreases. Edison 15:03, 13 August 2007 (UTC)

Ohm's law is an approximation, even in the best of circumstances. Of course, R can change with temperature. But even if I keep the temperature constant, and vary currents and measure voltage very carefully, I will find that the linear approximation is just that; an approximation. It might be a very good one, depending on the material, and the range of voltages and currents considered and so on. Why would anyone expect that this would not be true?--Filll 16:57, 13 August 2007 (UTC)

No, Ohm's Law is not "an approximation", at least once you're above the current levels where quantum effects (such as shot noise) start to matter. If you've correctly analyzed your circuit (and in doing so, accounted for every source of resistance and every source of EMF {voltage}), Ohm's law will apply essentially exactly.

Atlant 17:02, 13 August 2007 (UTC)

Ohms Law is a Law. It is always true. R, V and I can be a funtion of frequency, time and temperature but Ohm's law is always correct. Capacitors have a resistance that varies as a function of frequency/time. Same for inductors. The Law is always correct and the other variables will be modified so that it is true. Ohms law is provable from first principles. It is as fundamental and F=ma. --Tbeatty 17:14, 13 August 2007 (UTC)

Ohms law is true BY DEFINITION - because the definition of an ohm is: the electrical resistance offered by a current-carrying element that produces a voltage drop of one volt when a current of one ampere is flowing through it.. If some strange physical effect is happening at some voltage and current in some weird material or other then it doesn't matter because the definition of an ohm is "that thing that makes Ohms law work" - and therefore the resistance of the material (as measured in ohms) will always be what Ohms law predicts. The mistake that many respondants are making is in assuming that resistance is a fixed property of a material when it's clearly not. Resistance can change in all manner of weird ways as a function of any number of physical parameters - but Ohms law cannot possibly be untrue. SteveBaker 18:55, 13 August 2007 (UTC)

Hmm, interesting take but I am not sure I fully agree. Here is my understanding:

• Ohm's Law states that the relationship between the applied voltage and induced current is linear and calls the proportionality constant (whatever it may be) "resistance". As has been sated above, this constant may depend upon many other factors, including temperature, frequency of applied voltage etc and none of this constitutes any violation of the law.
• However the law does break down (or rather is considered inapplicable) for non-ohmic devices, such as a simple P-N diode in which the V-I curve is non-linear. Of course one can technically still keep saying that V=IR with R now also depends upon V, but IMO that semantic defense is not very valuable, because on the same basis I can define a new Abecedare law which says, $V=I^{2}R$ that by definition holds true as long as I allow R to be a function of V.

In summary my main points are, (1) Ohm's law is fine as long as the resistance depends on factors other than the voltage and the current, (2) It is not a universal fundamental law, but a empirically derived observation that AFAIK (but I am not sure about this) can be justified on the basis of Maxwell's equations for conductive materials and some voltage/current regimes. A final note: I know that there are several versions of (so-called) non-linear Ohm's laws and generalized Ohm's law that are used in several disciplines, but in my comment here I am referring solely to the $V\propto I$ formulation. Abecedare 20:58, 13 August 2007 (UTC)

Certainly Ohm's law was formulated for conductors as that is the easiest to measure. However, the proof of Ohm's law is not limited to simple conductors and from that derive the more complex impedances that give rise to the I-V curves of diodes and other such devices. --Tbeatty 22:30, 13 August 2007 (UTC)

You can always make Ohms appear law true if you postulate varying resistance--SpectrumAnalyser 19:54, 14 August 2007 (UTC)

But by doing so you completely lose the value of it. Theresa Knott | The otter sank 19:57, 14 August 2007 (UTC)

seperation of sugar solution from pure water

(reformatted since I think this is supposed to be a new question from an anonymous user SteveBaker 11:57, 13 August 2007 (UTC))

One way to separate sugar from solution is to boil the solution - the water boils off - the sugar stays behind. You can condense the steam back into water and you'll be left with a bunch of sugar crystals. You need to turn the heat off as soon as all of the water is gone or else you'll burn the sugar. SteveBaker 11:57, 13 August 2007 (UTC)

Then it becomes the separation of caramel from a sugar and water solution. :P Lanfear's Bane

Yeah, I've done this, you just get a sticky toffee mess, not sugar crystals. You can boil off the water with ionic solutions like salt and get left with the crystals, but not with sugar. Perhaps if you just left the water to evaporate naturally it would be more likely to work, but not sure. --jjron 13:21, 13 August 2007 (UTC)

You can boil off some of the water and then chill the remaining solution and/or let more evaporate without heating to get rock candy. Just gotta avoid caramelization, which is certainly doable if you don't get it too hot—"boiling" represents an increasingly higher temperature as the water evaporates. DMacks 14:56, 13 August 2007 (UTC)

I have no idea if this would work, but what if you used a double boiler, such as those fondue pots, with the sugar water in the inner pot? This would probably waste a ton more energy but not burn the sugar, assuming the inner pot will still have evaporation? --Wirbelwindヴィルヴェルヴィント (talk) 17:59, 13 August 2007 (UTC)

If I understand correctly, heating the sucrose-water will cause some of the bonds to break, converting sucrose into simpler sugars (glucose? fructose?). Eg, you create a simple syrup, which is chemically different than sugar water. So, evaporating off the water isn't not going to make sucrose again. I'm just guessing, here, but I suppose it is possible that you could put the solution in a vacuum, and evaporate off the water without heat. That might work to get sucrose back out of sugar water. --Mdwyer 18:56, 13 August 2007 (UTC)

According to the caramelization page and the page it cites when talking about the temperature of caramelization of sucrose, sucrose does not appear to decompose appreciably below 160 °C. The double-boiler trick might work (ref says that 100 °C what happens to a sucrose solution is water-evaporation), and of course one can speed evaporation by reducing the pressure at a given temperature. DMacks 22:49, 13 August 2007 (UTC)

The process of refining sugar from sugarcane involves pulling it out of solution a number of times. As suggested above, the industrial separation process involve placing it in a vacuum, where the solution is boiled at a low temperature and begins to evaporate, forming a syrup. The syrup is then fed into a large, sterile pan and further slowly evaporated in a very controlled way, resulting in crystalisation. The crystals are then spun down and collected. Its true that the exact ratio and types of sugars you put into the solution is lightly to be altered though. Rockpocket 23:01, 13 August 2007 (UTC)

Gravitation

1.hoe does the force of gravitation between 2 objects change when the distance between them is reduced to half?

I fixed it. See Newton's law of universal gravitation. - Capuchin 13:29, 13 August 2007 (UTC)

G is inversely proportional to the square of the distance between the masses. Do your own homework? Plasticup ^T/C 14:05, 13 August 2007 (UTC)

Erm? G is constant? Did you mean gravitational force? :) - Capuchin 14:08, 13 August 2007 (UTC)

Oh, how embarrassing Plasticup ^T/C 18:31, 13 August 2007 (UTC)

Plasticup means 'g' - not 'G'. But even that is wrong because 'g' is the accelleration due to earth's gravity - not between two arbitary bodies. The force due to gravity is G x M₁ x M₂ / R² - where G is the universal gravitational constant (not the same thing as 'g'!), M₁ and M₂ are the masses of your two objects and R is the distance between their centers. So the force decreases as the square of the distance. So if you halve the distance, you quadruple the gravitational force. SteveBaker 18:45, 13 August 2007 (UTC)

No, Plasticup was just wrong. Plasticup hasn't taken a physics class in rather a long time. Plasticup ^T/C 18:49, 13 August 2007 (UTC)

Infinite light box

Consider a box with all six internal sides being mirrors or another highly reflective material with no imperfections. Suppose you shone a light into this box, then closed it up so that none of the light could escape (of course this can't be done because the speed of light is too fast, but imagine it could be), would the light remain in the closed box forever, reflecting from mirror to mirror, or would the light dissipate over time because it is expending energy by reflecting from place to place? Think outside the box 13:43, 13 August 2007 (UTC)

A perfect reflection would require no engery loss, so I suppose the light would bounce around forever. Assuming perfect mirrors, perfect construction, etc. Plasticup ^T/C 14:07, 13 August 2007 (UTC)

That perfect mirror is a bit of a practical problem. And you'd have to choose a wavelength that doesn't interact with whatever fills the empty space inside the box. OTOH, closing the box isn't the problem that Think seems to think. Light is fast but not instantaneous. With a big enough box, slamming it shut while a bright light is shining in would still trap a lot of photons. See also the last time we pondered a question like this. DMacks 14:15, 13 August 2007 (UTC)

Thanks for the link DMacks, interesting stuff Think outside the box 14:28, 13 August 2007 (UTC)

To me, this is a sort of paradox. Once the box is shut, how do you know if there is any light in it? You could have a sensor in it, but that would absorb light and mess up the whole thing. The only way to check is to open it and try to grab a few photons as they race out. If you fail to grab any, you would claim that there was no light - which may not be the case. If you do grab some, how do you know they came out of the box and not from the surrounding environment? So, you could just get any old box and put on a shelf and tell people that it holds some photons, but they can't open it to look because they'll let the photons out. -- Kainaw^(what?) 14:45, 13 August 2007 (UTC)

Schrödinger's light box? Lanfear's Bane

Well, you could theoretically use such a box for long-term storage of light. Strobe lights are too complicated, lets store bursts of light in tiny mirrored boxes. 69.95.50.15 16:04, 13 August 2007 (UTC)

Assuming we're quite familiar with the box beforehand, we can weigh it to determine if it has an above-thermal amount of photon energy in it, although we won't be able to count the photons unless we also know their spectrum. The interesting bit is that in theory we could do this without any advance knowledge, as I believe the effective inertial and gravitational masses of photons differ (because of their intrinsic momentum; see this relevant question from May). --Tardis 16:23, 13 August 2007 (UTC)

This opens up a whole new question... The photons would expectedly be bouncing all sides of the box equally. They don't sit on the bottom of the box. So, the collision with the sides of the box should not create extra downward force to measure as an increased weight in the box. The photons that are floating around inside the box aren't propelling themselves against the box or atmosphere inside the box, so they won't increase the weight of the box. There cannot any sort of heat/radiation discharge to measure - or it wouldn't be perfect mirrors. So, there's nothing to measure there. -- Kainaw^(what?) 17:07, 13 August 2007 (UTC)

The weight comes about because photons fall. They will strike the bottom of the box more directly and the top more obliquely (or even fail to strike it at all if they are travelling very nearly horizontally at the bottom); moreover, they will have more energy when striking the bottom because of gravitational redshift, although I'm not sure that the redshift's effect on the weight isn't a fiction caused by combining Newtonian mechanics for the box with GR for the photons. --Tardis 21:29, 13 August 2007 (UTC)

This question comes up over and over again here on the science desk (at least once a month!) - some people specify a spherical container - others just want a pair of precisely aligned parallel mirrors - other a cuboid box. But the answer is always the same - no surface is a 100% perfect mirror - they always absorb some small percentage of the light at each reflection. Hence the light bounces around inside the box for a while - gradually being absorbed and turned into heat. For reasonable sizes of box (ie one the order of a few meters), the light will be gone within a few microseconds - if you make a box that's a few light-years across, the light would be around for thousands of years before being absorbed. But with a hypothetical perfect mirrored interior, yes, the light bounces around forever. As the original light 'beam' disperses, gradually the individual photons will all be heading off in utterly random directions - and their wave-like behavior will result in interference and such - but since there is nowhere for the energy to go - the light would still be there centuries later. But there are no perfect mirrors - so it's not a particularly useful concept! SteveBaker 17:24, 13 August 2007 (UTC)

See Optical cavity. We have some of the most perfect mirrors in the world here at the 40-meter LIGO prototype lab, so that "optical ringdown" measurements become possible. The optical cavity is filled with laser light, and then the laser is turned off. The light immediately begins leaking out of the cavity, but the half-life of a photon in the cavity can be several milliseconds. If you keep making the mirrors better and better you can increase this ringdown time arbitrarily. There's no fundamental limit, just a practical one (no one knows how to make mirrors that good). —Keenan Pepper 19:52, 13 August 2007 (UTC)

Electrons in String Theory

In string theory, are electrons represented by open strings, or closed strings? MrRedact 15:00, 13 August 2007 (UTC)

As I recall, all strings of known particles are open. The theoretical graviton is alleged to be a closed string. 151.152.101.44 20:19, 13 August 2007 (UTC)

That's not correct, some theories posit that (at least) all bosons are closed strings (e.g. photons). Whether or not an electron is necessary open or closed, I don't know. Dragons flight 21:01, 14 August 2007 (UTC)

A string physicist I know is fond of explaining how he can concoct a theory complicit with all observations of quantum phenomena, but in which particles are actually elephant shaped (one of the reasons he gave up on string theory). Make any claim about the strings, there is probably a theory somewhere to match it. Now if only we could observe these little buggers...Someguy1221 22:12, 14 August 2007 (UTC)

box fan

I have a symmetrical box fan that takes in air from one side and blows it out the other. Why is it that when I put it in the middle of a room I can feel a strong airflow on the "blow" side of the room but feel no airflow on the "suck" side of the room? Shouldn't they be equal? --froth^t 19:16, 13 August 2007 (UTC)

I've noticed this too - I believe it's because on the inlet side, the air is being sucked in over a wide angle - but on the output side, it's coming out in a fairly narrow-angled 'cone'. Hence the volume of air going in is the same as going out (well, more or less) - but the speed of the air on the outlet side is higher because that same volume of air is coming out of a smaller area. Using a small length of thread held between your fingertips to visualise the airflow will quickly convince you that this is the case. SteveBaker 19:40, 13 August 2007 (UTC)

SteveBaker says that the volume is "approximately" equal on intake and outflow. I disagree; the conserved quantity is of course mass flux. Applying the standard equations (PV=nRT) and noting that pressure is inversely proportional to velocity squared... an equal mass flow in and out, but at significantly different velocities, may have a huge difference in volume. I do agree with the conical flow-shaping hypothesis, that seems to explain the perceived difference in flow. Nimur 19:48, 13 August 2007 (UTC)

Well the change in volume is irrelevant once the fan has been running for a few seconds and the velocity is the same on both sides. I guess the cone theory makes sense though- but what would cause it to do that? The shape of the blades? --froth^t 20:01, 13 August 2007 (UTC)

I think the basic issue here is that it's possible (and rather easy) to create a directed stream of a fluid, but there's no such thing as a "directed suck".

There's nothing magical about the shape of the fan blades, other than that they create a directed flow. Imagine a tall tank of water with a small hole on the side, at the bottom. Water shoots out of the hole at high velocity in a concentrated stream. But if you were swimming inside the tank, you probably wouldn't be aware of any significant flow towards the hole unless you were right next to it. (At which point you might get sucked against it and trapped and drown, so don't try this at home. :-) ) The reason you're not aware of much flow is that water is migrating towards the hole from all directions, to supply the flow exiting via the hole. And the same holds for the air in the room on the "suck" side of the box fan. --Steve Summit (talk) 23:16, 13 August 2007 (UTC)

Indeed. If you wanted to create a strong airflow on the intake side, the way to do it would be to force the air into a narrow channel by enclosing the fan in a pipe of the same shape. Then the flow would not arrive from all directions, but only through the pipe -- in fact, you would have a wind tunnel. But the effect outside the pipe would be no different than before. --Anonymous, August 13, 2007, 23:40 (UTC).

Hm? For the analogy to hold, the hole at the bottom would have to be the entire floor of the tank. Like I said it's a symmetrical box fan so the "hole at the bottom" is the same size as the "tank of water". --froth^t 02:02, 14 August 2007 (UTC)

The analogy's not perfect, no, but I'm not sure what you're talking about with respect to "the entire floor of the tank". For the analogy to hold perfectly, you'd need a wall down the middle of your room, with a box-fan-sized hole in it, with the box fan in the hole.

But ignore the analogy, if you like: the point is that on the "suck" side, air can and does flow from all directions to supply the flow through the fan, while on the "blow" side, it's concentrated into a relatively narrow and well-defined stream. --Steve Summit (talk) 02:09, 14 August 2007 (UTC)

My gut feeling tells me that the air flow would still be different in the tube. Suppose there were a tube on both sides. Wouldn't the airflow be smoother on the suck side? Alas wind tunnel doesn't seem to cover this. DirkvdM 08:03, 14 August 2007 (UTC)

Btw, could this be seen as a proof of the irreversibility of time? If you'd turn time around, physics would no longer apply because the behaviour of air before and after the fan is reversed. DirkvdM 08:03, 14 August 2007 (UTC)

Not really: reversing time once the fan was running smoothly would involve blowing a strong wind at what was previously the output side of the fan and driving the fan with it, creating a turbulent, slow-moving mess on the other side (exactly as before). --Tardis 15:11, 14 August 2007 (UTC)

Realistic deaths in films?

How realistic are TV/movie death scenes? I know that the closed eyes are pretty implausible, but what else? Like, shouldn't the sphincter relax upon death, and wouldn't that be messy? And what about the speed of it all? People are often seen dying from a single gunshot, say to the abdomen, is this realistic? Wouldn't dying -- especially from a gunshot -- hurt a hell of a lot more than shown on TV? And last, but not least, are there any realistic death scenes at all?

Actually been meaning to ask this, but as a follow up question, what would the rate of blood loss be? It seems a lot of film tone down blood flow, or unrealistically increase ala Kill Bill. Is there a good example of blood loss in media? Zidel333 20:21, 13 August 2007 (UTC)

Well this resource (http://www.moviedeaths.com/deaths/) and its forums may help. I haven't looked much but I suspect it will go into detail about the variety of ways. Without science/medical reasoning I would say that no deaths in movies are not very real. I heard the sphincter-part was a myth so might be worth checking on snopes (quick search couldn't find anything on it). I think gun wounds vary in movies ranging from the somewhat odd seeming "no affect at all" style 'hero gettng shot' to the 1-shot-kill no matter where in the body 'hero does the shooting' variations. I expect the people that slip away do so in a similar style to movies. Blood loss wise i've no idea - though I understand exit wounds for bullets are much larger than entry wounds and this is rarely the case in movies (just like hiding behind a wood crate is enough to stop a bullet - to that end (http://www.intuitor.com/moviephysics/) is a good site). ny156uk 21:34, 13 August 2007 (UTC)

Deaths in film are rarely there to depict death. They are there for plot momentum. The hero has to kill a bunch of thugs. The bad guys have to kill a lot of innocent people. The head bad guy has to survive multiple deadly hits and, usually, blow up in the end. If you want to see real death, volunteer at your local emergency room. You'll see very little comparison between real trauma and what is on television or the movies. -- Kainaw^(what?) 22:33, 13 August 2007 (UTC)

The mechanisms of bullet wounds have been extensively discussed; I bet we've covered it on the RDs once or twice. Here's a quick synopsis by our mentor Cecil Adams.

Blood loss can be pretty alarming. Rob Cockerham investigates this in his characteristic style at "How much is inside?". I once saw the aftermath of some poor guy on a motorcycle who had done battle with an eighteen wheeler and lost, and there was at least that much blood on the pavement. --Steve Summit (talk) 23:09, 13 August 2007 (UTC)

Some war movies attempt to recreate realism, Saving Private Ryan is one example which has been both praised and criticised for it's often gruesome realistic depiction. Vespine 23:35, 13 August 2007 (UTC)

If you watch the video where politician Budd Dwyer shoots himself in the mouth, I think you'll find that it's very bloody indeed. --Sean 23:43, 13 August 2007 (UTC)

Well that answers my question quite well. Thank you ...I guess? 00:45, 14 August 2007 (UTC)

That is both disturbing and fascinating (not to mention tragic). I'm amazed that I had never even heard of Dwyer before now. In addition the the amount of blood, the speed of the whole thing is remarkable - I guess we are so used to slow-mo, and dramatic staggers before falling, after gun-shot wounds to the head in the fictional media. Rockpocket 07:22, 14 August 2007 (UTC)

No relation... --Mdwyer 14:11, 14 August 2007 (UTC)

Fire diamond

I had long been under the impression that numbers on fire triangle diamond warning labels only went up to 4, but to my utter shock last week, I saw one with warning numbers as high as 7 and 8 on the side of a large container. I even went and looked through the fire safety manual after seeing this, to find out what those numbers mean, but the manual only listed hazards up to number 4. What the heck was in there? 151.152.101.44 20:38, 13 August 2007 (UTC)

NFPA 704 is explicit that the numbers go up only to 4. The signs you saw were noncompliant. Perhaps someone was trying to underscore the danger involved? ←Ben^B4 21:52, 13 August 2007 (UTC)

Maybe the container contains a corpse that is dissolving and is on fire? That way it would exceed the 4s since they are all about potential for harm. DMacks 22:01, 13 August 2007 (UTC)

Do you remember what it was? Also, is this "Fire triangle" the NFPA 704 one? If not, it could easily be something else which does go that high. Alternately, someone may just be incompetent. 68.39.174.238 23:18, 13 August 2007 (UTC)

I posted the original question logged out. The fire diamond was in the format of the NFPA 704, aside from having such high numbers. Although maybe it was just to underscore the danger, as Ben suggested, "If you open this container, you will die." I was sort of hoping someone else saw something like this before...Someguy1221 23:32, 13 August 2007 (UTC)

Oopsie, I meant to say "diamond," and not "triangle." That's how well I can think when I only have 5 hours sleep. Someguy1221 23:35, 13 August 2007 (UTC)

The only time I've seen this I believe is in that Seinfeld episode The Pothole. The only reason I remember that episode at all is because the barrel of turpentine at the end has a flammability rating of "8", which is impossible. Yeah my brain is full of useless stuff like that. Comes in handy sometimes, like on this desk :) Of course, I have trouble remembering where I parked my car... --Bennybp 00:33, 14 August 2007 (UTC)

I've seen something like this a couple of times - in both cases with chemicals shipped directly from overseas. I think (this is a reasonable conjecture but YMMV) we eventually determined that the issue was most likely an incorrect merging/grafting of the DOT Classification of Hazardous Materials coding system into the NFPA diamond. For example, one of the chemicals was a batch of granular polymer beads; the white NFPA box had a numeric "9" in it (obviously not NFPA approved). -- MarcoTolo 00:33, 14 August 2007 (UTC)

You know, on second thought, I think it might have been DOT warnings arranged in a diamond. Thanks! Someguy1221 00:50, 14 August 2007 (UTC)

Health fairs at libraries

How many libraries have done health fairs in the last two years? May I have a name of a few?

I'm thinking you will need to say where, i.e., your locale; what city you're in, before anyone is likely to be able to help you with this. Having said that, see http://www.google.com/search?&q=library.health.fair ←Ben^B4 22:50, 13 August 2007 (UTC)

Skin pigmentation in higher latitudes.

I was wondering why such non-Caucasoid peoples that live in relatively high latitudes aren´t light-skinned, like the high Arctic people like the Chukchis, Evenks, and Inuit, and the Aborigines that live in Australia. While I know that the Asians that live in the high arctic are obviously lighter-skinned than the Aborigines, my question was why they don´t have blond hair and blue eyes. While I have read of some high arctic peoples having blue eyes, freckles, and relatively blond hair, those are only rare genetic mutations, or contributions from the Scandinavians who explored the Arctic. I have also read that the reason they aren~t lighter skinned is because the mongoloid race doesn~t have the capacity to change like the Caucasoid race has. Oh, and about the Aborigines, they lived below 40 S Latitude longer than anyone else did, so why aren~t they at least lighter than the rest of the Australian aborigines. —The preceding unsigned comment was added by 200.176.110.253 (talk • contribs) 22:32, 13 August 2007 (UTC)

There is selection against light skin in the tropics, but there is no selection against dark skin elsewhere, other than self-selection based on tribal instincts, xenophobia, etc. among the light skinned. Dark skinned migrants from the tropics to higher latitudes are likely to stay dark skinned if there are no indigenous light-skinned inhabitants. ←Ben^B4 22:55, 13 August 2007 (UTC)

We don't actually know for sure, as Ben suggests, that there is "no selection against dark skin elsewhere", although it is true in the skin pigmentation loci studied there was no evidence for positive selective pressure for pale skin alleles. However, there are other genes effecting skin pigmentation so far undiscovered, and until we can study those in the human population, we can't be definitive in that answer. We don't even know why Europeans do have blonde hair and blue eyes, so its beyond our current knowledge to know why other groups at Northern latitudes don't. It may simply come down to genetic drift and sexual selection. Rockpocket 23:16, 13 August 2007 (UTC)

Dark skin in low UV environments would be selected against because they would develop Vit D3 deficiency, surely? Aaadddaaammm 00:44, 14 August 2007 (UTC)

That's what I've always heard. I've heard that vitamin D deficiency is actually occasionally a problem for people with dark skin growing up in, for example, Britain. Skittle 00:52, 14 August 2007 (UTC)

That is "widely assumed". We know that variations at MC1R result in pale skin and we know that pale skin can generate more D3, but there is no evidence to support the fact the MC1R was under such evolutionary pressure. To quote the most extensive study :

There is a popular hypothesis that fair skin in Europeans has been positively selected to increase sensitivity to UV radiation and that, in northern latitudes, this adaptation is needed to increase UV radiation–induced vitamin D synthesis and to prevent rickets... However, we found no statistical evidence that MC1R diversity has been enhanced by selection, either in its apparently high levels or in its haplotype frequency–distribution patterns. [13]

The vitamin D deficiency story is nice, but the facts don't back it up. Rockpocket 01:04, 14 August 2007 (UTC)

Light skin is an adaptation to allow sufficient vitamin D3 to be produced during periods of lesser amounts of sunlight. However, most of the peoples of the extreme north have diets that are heavy in seal and fish oils. Fish oil is an excellent source of vitamin D. Hence, people who evolved in an environment where they have a fish-heavy diet did not need to evolve light coloured skin. SteveBaker 03:58, 14 August 2007 (UTC)

Wouldn't fish have been a (the?) major food source for the lightest-skinned people around, the Nordic peoples? (Of course, that doesn't disprove what you say, but it is somewhat salient.) DirkvdM 08:18, 14 August 2007 (UTC)

People living on the tundra get plenty exposure to UV as the snow refracts it everywhere. That's why you see polar explorers wearing sunglasses to prevent snow blindness. Inuits still have to cover their skin, so its not a great source of vitamin D, which fish oil takes care of. Bendž|Ť 09:53, 14 August 2007 (UTC)

August 14

weather - humidity

what does relative humidity tell me that dew point does not tell me? what does dew point tell me that relative humidity does not tell me? Csnewman 00:26, 14 August 2007 (UTC)

I think you can calculate one from the other (given a known temperature and maybe pressure). So, they are just two different ways of presenting the same info. The two interesting values in each case are that you expect it to rain when it reaches 100% relative humidity (although this is at the clouds, not necessarily where you are) and expect dew when the temperature drops to the dew point. StuRat 07:50, 14 August 2007 (UTC)

Relative humidity is the ratio of the quantity of water vapor in a gas to the quantity that would saturate that gas at the same temperature. RH is expressed as a percentage of saturation at a certain temperature. It can also be defined as the ratio of the partial pressure of water vapor to the Saturated Vapor Pressure at the same temperature multiplied by 100. (to give %)

Dew point is the temperature at which condensation of water vapor in a gaseous atmosphere takes place.

--SpectrumAnalyser 20:15, 14 August 2007 (UTC)

Ice

Say you have a spherical container completely filled with water, completely closed, and you freeze it. If the material of the container was strong enough, would the ice compress when it expanded? How strong would a material have to be to withstand ice expanding without breaking? 68.231.151.161 00:38, 14 August 2007 (UTC)

If the material is strong enough, then the pressure within the container will rise as the ice 'tries' to expand. As you cool the container, the pressure will rise and the water will stay liquid at lower temperatures than normal. Eventually, the water will freeze into ice (at a lower temperature than normal), but it will be denser ice than would form at normal, atmospheric pressure. As to how strong the material would have to be, I'm afraid I don't have a definite answer, so you'll have to wait for someone else. It will have to be strong enough to resist the pressure difference between the inside and the outside of the container, and will depend on the volume of the spherical container, the thickness of the walls, etc. Skittle 00:50, 14 August 2007 (UTC)

You'd need to look at a Phase diagram for water. DMacks 00:51, 14 August 2007 (UTC)

Interesting question. This page says that what you are talking about is called "isochoric cooling" and can produce pressures up to 25 MPa (about 250 atmospheres) in a water pipe. But if the temperature continues to be lowered, the pressure will increase further, until at about -22°C (about -7°F) it reaches a maximum of almost 210 MPa (2,070 atmospheres)! If the temperature is lowered still more, one of the high-pressure phases of ice will then form. Obviously you would need a very strong container to withstand such pressures. This page (requires JavaScript enabled) will tell you how thick it would have to be, depending on the size, For example, for a design pressure of 40,000 psi (about 2,720 atm), a maximum stress of 60,000, and an inside radius of 2 inches, the pressure vessel would need walls 3.33 inches thick. Note: This is not professional advice! Do not consider obtaining a 3.33-inch-thick, 2-inch-inside-radius pressure vessel and conducting this experiment without consulting a suitably qualified professional engineer! --Anonymous, August 14, 2007, edited 04:20 (UTC).

That page seems to not mention what material the pipe needs to be made out of. Someguy1221 05:50, 14 August 2007 (UTC)

There, see what I mean? --Anon, 06:51 (UTC).

Some old story we had to read in school a century ago, about a guy who had a stock of cannonballs after the civil war he wanted to melt into scrap, but couldn't because of the residual gunpowder inside them which he couldn't clean out. Solution was to fill them completely with water and leave them outdoors in the winter until he ice broke them into pieces which could be thoroughly washed. Gzuckier 15:56, 14 August 2007 (UTC)

I never knew that cannonballs were hollow! --Dweller 16:45, 14 August 2007 (UTC)

They aren't - but seige mortar/bombard "shells" of the period probably would have been - which might be how the story originated. However, I'm doubtful that it would work because there wouldn't be an easy way to block up the hole you filled it through. You could possibly consider welding it shut - but if the things were full of gunpowder, that would definitely be ill-advised! Probably the easiest way would be to set them off and collect the shrapnel. SteveBaker 18:31, 14 August 2007 (UTC)

Remember, ice formes OVER water. So as ice forms, it will seal itself in.

No, actually. 2000 atm is quite enough to push the ice out of the way before busting through steel. 151.152.101.44 20:57, 14 August 2007 (UTC)

Yep. Those of us who used to get milk delivered in bottles in places with a real winter will remember that if it was delivered when nobody was home to move it inside, you would find the bottles with their caps elevated like this. --Anonymous, August 14, 2007, 22:13 (UTC).

about scientist of friction

hello i want to know about scientist of friction

Um, friction? If not, perhaps you need to be more specific. --jjron 09:07, 14 August 2007 (UTC)

I believe that article is about the science of friction, not about the scientists who study friction. As friction is generally well understood (with the exception of a few specific areas, like acoustic lubrication), it has largely moved out of the realm of science and into engineering, where civil, mechanical, automotive, aeronautical, and naval engineers spend a great deal of time evaluating the coefficient of static and dynamic friction of various material combinations, and study lubricants, fluid dynamics drag, etc. StuRat 10:14, 14 August 2007 (UTC)

A scientist of friction is usually called a tribologist, after tribology, the study of friction. Most these days are technically not tribologists but lubrication engineers (they come up with ways to use existing knowledge to produce new systems, rather than developing new knowledge). Laïka 11:12, 14 August 2007 (UTC)

On the other hand, maybe he means frictional scientists like Tom Swift or Buckaroo Banzai.

Effects of gravitation from and on an object near light speed

Hello, I've got of the following question. Does an object (which is not a photon, thus has mass) which is traveling at relativistic speeds, have a higher effect on spacetime's curvature (since its mass is higher that it's rest mass). Also, if said object, was traveling at relativistic speeds, but towards a massive object, say a black hole, since it's accelerating and thus it's mass is increasing, at what I imagine some rate related to it's acceleration, can it also become a singularity before it passes said black hole's event horizon, since it's mass is increasing and its length is contracting ? 62.48.159.19 09:27, 14 August 2007 (UTC)

Yes, a moving object has more energy, and thus more gravitation. (It's not particularly useful to talk about it having more mass as if the motion caused mass increase; rather, the absurd amount of kinetic energy it must have to be moving at, say, 0.99c has inertia too which is simply added to its normal inertia.) However, I believe that the other relativistic effects (particularly time dilation) and the finite speed of gravity (c) would alter the dynamics around, say, a 1-centimeter-square rod with the mass of the Earth moving so as to have a measured length of 1cm so as to prevent it from acting like a black hole. After all, if we move ourselves fast enough it would appear that everything had become a black hole if that could happen, which would be completely inconsistent with still being able to see it all! --Tardis 15:19, 14 August 2007 (UTC)

An object wouldn't shrink from its speed when moving into a black hole. It would be shorter from the point of reference of the black hole than from the object, but the tidal forces would cause spaghettification and stretch the object and make it is significantly longer (and thinner) than normal. It would look like it's getting shorter from an outside observer due the light taking longer to get to them, and it would never appear to pass the event horizon. I don't think this is related to what you're talking about. — Daniel 02:15, 16 August 2007 (UTC)

Swirling Water

I've noticed that when I drain a tub of water, the water kinda spirals...why? I understand that there are lots of water molecules converging towards the 'drain hole', but then what happens?

Basically there will be non uniformities in the surface of the tub, and these make the water channel in a specific direction. There may also be currents set up in the tub from when you were using it, which would influence the water to drain in a particular direction. Be sure to understand that it is NOT due to the Coriolis effect (It has a tiny tiny influence compared to the others). Capuchin 10:02, 14 August 2007 (UTC)

Once a small preference to swirl in one direction starts, as the water approaches the drain, the conservation of angular momentum thing kicks in to make it swirl faster and faster. (The classic description of this is "Like when an ice-skater pulls his or her arms inward to spin faster.") Once the water is swirling down the drain in a particular direction, the viscosity of the water tends to make the stationary water further away want to spin in that direction too. So it only takes the tiniest of initial circular motion in the water to build up into that violent spiral vortex - and once the spiral forms, it becomes a self-sustaining thing. The story about the Coriolis effect making water spiral down in one direction in the Northern hemisphere and the opposite direction in the south is indeed an urban legend, although theoretically, if you did have a large body of water that was truly, utterly, stationary - with no initial preference to spin in either direction, it's possible that the Coriolis effect might have enough of an effect to make it tend to spiral one way or the other. However, in practice, it never does - even the slightest thing will cause motion in the water that carries on for hours afterwards and eventually determines which way the swirl will form. SteveBaker 18:17, 14 August 2007 (UTC)

I'd compare your swirling effect to any effect with many particles. If you throw a lot of marbles down a hill towards a drain they'll bounce around like crazy but then run in a motion around the drain due to gravity, surface anomolies, and to angular momentum. Consider also that a bathtub is designed to drain water when the plug is pulled, i.e. it's at an angle which will affect the water flow.

Car's rim

HI guys...I am a graduate in physics.I love physics for life...but I'm embarrased to say that I don't know some of the key concepts in it.....so please all those who read this ahead just give your idea...EVErybody has seen the automobile's rim rotating w.r.t tire RPM. When it slowly accelarates, the wheel's rim looks like its spinning in clockwise direction..With further increase in speed, the rim looks like its spinning in anti-clockwise direction..With varying RPM, the rim looks spinning in clock and anti clock direction rapidly...I hope you get the picture...What's the trick behind this?, that fools our brain?...Thanks in advance

It's more to do with the frequency of the lights illuminating the wheel or the camera taking the movie or the monitor playing the movie. You don't see this effect outside in the sun. It's a stroboscopic effect. When one frame is taken, the wheel might be in one position, then when the next frame is taken, the wheel may have rotated a whole 11/12ths of a rotation forwards, but our brain interprets this as a 1/12 rotation backwards, because that's a smaller change. This is how the illusion is made. With wheels which have a high rotational symmetry (due to spokes), which effect you see is highly dependant on the speed at which the wheels are turning, which is why you see the effect sometimes and not other times.

Also, please sign your posts using 4 tildes (~). Capuchin 11:24, 14 August 2007 (UTC)

Capuchin didn't monkey around, he spoke the truth. I would also add that a few cars come equipped with spinners, which do, indeed, rotate the rims at different rates and/or directions from the rest of the wheel. StuRat 16:51, 14 August 2007 (UTC)

But rarely backwards! (Unless reversing I think, I'm not hip enough to have some of my own). Yay for those little guys. They make my day. Capuchin 07:19, 15 August 2007 (UTC)

The effect is properly called 'temporal aliasing' - but it can only happen when there is some kind of stroboscopic light or something. You see it under electric lights because those flicker on and off at the frequency of the power source (50 or 60 times per second depending on where you live). You also see it on the TV and in movies where the camera only takes a few dozen pictures per second. Under either of those situations, you are only seeing brief moments of the motion - it's not really a continuous motion but a bunch of still snapshots - which your brain tries to turn back into continuous motion for you. When something like a spoked wheel rotates, imagine what happens if it one spoke of the wheel were to be pointing (say) straight upwards in one snapshot - then in the intervening fraction of a second, the wheel were to turn exactly enough so that the next spoke would be pointing straight up. Since one spoke looks pretty much the same as the next, it would look as though the wheel hadn't turned at all during that fraction of a second. If the wheel were rotating just a bit too slowly for that to happen, then the next spoke would be just a little behind where the first spoke was in the first picture. Each new picture that we see has the top-most spoke be just a little more behind each time. The net result is that the wheel seems to be spinning slowly backwards. This effect happens with other things too - a picket fence for example may appear to be moving forwards at the same speed you are...anything with a repeating pattern built into it will do this. But it can't happen in normal daylight when you see the scene with your own eyes - although many people I've met will swear up and down that they've seen the effect - when you have them actually go outside and look, they have to admit that they aren't seeing it. But at night and on TV, it's a common phenomenon. You can easily destroy the effect by (for example) painting one of the spokes of a car wheel a different colour - then your eyes can latch on to the true motion and the illusion goes away. SteveBaker 18:07, 14 August 2007 (UTC)

Two small corrections. Incandescent lights don't flicker perceptibly, but that doesn't matter here because it's rare for them to be used for street lighting; most street lights are of types that do. And the flicker frequency is 100 or 120 per second, twice the power frequency. --Anon, August 14, 2007, 22:12 (UTC).

I always like to argue a bit. I don't think this is a purely stroboscopic effect, although that does happen. The human eye has a fixed refresh rate, I believe at about 10 times per second so it is perfectly possible to see this effect in constant sunlight, and I am sure I have done, although SteveBaker has put doubts in my head now! Cyta 07:24, 15 August 2007 (UTC)

NO! BIG MISCONCEPTION! The human eye does not have a 'fixed refresh rate' - completely the opposite in fact. If it did have a fixed refresh rate then maybe this strobe effect would work in daylight - but it doesn't so it doesn't. This is a very simple experiment - step outside - in daylight - and look at a car! SteveBaker 11:51, 15 August 2007 (UTC)

Agree with steve. Measurements of the "FPS" of the eye are done by flashing something on a screen for a few tens of ms and asking the subject if they noticed it. It isn't a measure of how the brain refreshes the image of the eye. The eye refreshes in a much more fluid way than the operating principles of monitors and other technology. And seriously? Have you ever watched somethign going at 10 fps. It's a very very discernable juddering effect. I know that some people can notice 60Hz monitors flickering - my dad does and makes me change it to 75Hz, so it's probably somewhere around that range. But the strobe effect won't work with just the eye because it doesnt "strobe" like that when it "refreshes". (I feel filthy trying to explain the eye in mechanical terms) Capuchin 13:21, 15 August 2007 (UTC)

I think the confusion comes about because each rod/cone photodetector in the eye has about a 1/10th second recovery time after it fires. That gives people the impression that all of the detectors simultaneously grab an image and send it off to the brain - and cannot take another one for 1/10th second. The truth is that each rod or cone fires and recovers independantly - out of sync with the others - so that while one individual detector has a 10Hz-ish response rate, the eye as a whole is seeing the world more or less as a continuum. What the eye sends to the brain isn't a 'picture' in the normal sense - it's a set of basic shape information like "a vertical line, half the height of the retina is moving left to right at 5 degrees per second". That information doesn't have a frame rate at all because it's described in terms of how fast things are moving and in which direction. That enables the brain to understand the scene presented to the eye in high level terms and cuts back on the amount of data that would otherwise need to be transmitted over the optic nerve.

The nature of that information flow also allows us to perform the important trick of interpolating the position of a moving object when it briefly vanishes from view. If you are primitive man, chasing a prey animal through trees, attempting to throw a rock at it so you can have it for supper, it's vitally important that you know where the animal is - even in the brief moments when it's hidden behind a tree. So you can imagine the in-between motion between the brief glimpses when you know where it truly is (this is called 'object constancy'). That same mechanism is what allows us to fuse together separate frames of a movie or TV show. But once again, people hear that we can use 'persistence of vision' (a poor term) to envisage a 10Hz flickery image as smooth motion - and go on to assume that the eye operates at a 10Hz rate - which is not the case. 1/10th second is just the right interval for the task we originally needed it for - imagine a rabbit running at 5mph - if it passes behind a 9" diameter tree trunk - then it'll be out of view for just about 1/10th second. SteveBaker 17:16, 15 August 2007 (UTC)

Sounds like I am wrong, strange I am sure I remember seeing a similar effect, ah well, the power of the memory to play tricks I guess. Is there some average focusing time though? Because as you move your head it isn't a smooth movement of vision, but a series of small focuses with jumps. Could this produce the effect under discussion? Cyta 07:13, 16 August 2007 (UTC)

Human body drinking issue

HI! I have one doubt in my mind for a very long time...we use to piss whenever we feel that sensation.Either by drinking more water or by taking liquid food stuffs, we can keep our body under cool conditions...At those periods our urine color remians almost whitish..But when we reduce the water intake and control our urination for several hours, the color of the urine changes from normal whitish(close to that) to yellowish...And when our body gets more heat and if we subject to piss less often, then we use to feel pain(only males I think) at the tip of our organ..Why is that?...And also how much a normal human should drink water(in litres)?...

Urine is clear when we drink a lot of water because it is less concentrated (there's more water per unit of urea). Like when you put a bit of orange squash in a glass, as you put more water in the color of the orange squash becomes clearer and clearer. The pain (pain?) to pee you are refering to is probably just the sensation that your bladder is full and you need to empty it, the sensation gets stronger and stronger until you do pee. If it is very painful you should see your doctor. Healthy adults should drink somewhere around 2-3 liters of water over the course of a day, but i'm sure most people don't manage that much, it depends on the excercise and electrolyte intake you have, too.

I hope I managed to answer most of your questions, but It was hard to work out what some of them were so please reply if you have further questions. Also, please sign your posts with 4 tildes (~). Capuchin 11:32, 14 August 2007 (UTC)

Qualification: Healthy adults should take in 2-3 litres of water over the course of a day; this can be from food as well as drink. If urine is very dark in colour, there is a good chance of dehydration. If someone is experiencing pain after a certain action, they should probably avoid the action if possible and definitely see a doctor. Skittle 22:30, 15 August 2007 (UTC)

The pain is at "the tip of the organ". I'd see a doctor about that, it could be a sign of a disease which is aggravated by hot conditions, such as herpes. StuRat 16:41, 14 August 2007 (UTC)

It could just be pain from holding up urine in your bladder for one er... "big release" which comes out quicker that your anatomy can handle? SGGH ^speak! 22:18, 14 August 2007 (UTC)

Speaking of bladders, can the bladder get tired from holding in a large quantity of urine for too long, even if very little is still trickling in? I'm afraid to do the obvious home experiment...Someguy1221 22:20, 14 August 2007 (UTC)

I believe that "holding it in" when your body is telling you to pee will increase the risk of urinary tract infection. In fact it's mentionned in that article as something that "seems sensible but has not been tested" to avoid UTI. No medical advice and all that, but don't do it ;) Capuchin 13:14, 15 August 2007 (UTC)

Mouldy bread

I've noticed that recently the incidence of bread mould seems to have increased drastically; formerly bread kept in our kitchen only went mouldy in exceptional conditions (if it was kept for weeks in damp conditions for example), but recently, virtually every loaf of bread, produced in a number of different factories, bought from several different shops, and in a number of different varieties, becomes spoilt by mould before reaching the end of the loaf; sometimes, even bread sealed in unopened plastic packets becomes mouldy, days or even weeks before "best before". Bread consumption rate has not changed, nor have the conditions in our kitchen to the best of my knowledge. Is there any reason for the rapid increase in bread mould; someone suggested maybe removal of a banned preservative or change in recipe is causing this; have any anti-mould agents been banned recently? Laïka

You might want to try buying two identical loaves at the same shop at the same time, then giving one to a friend to monitor in his kitchen. That should reveal if it's the bread or your kitchen. 147.197.230.174 12:02, 14 August 2007 (UTC)

You should simply buy freshly baked bread, and eat it within a 48hour period. Factory made bread not only tastes foul, it also contains all sorts of crappy preservatives to make it last longer. "Days" or "weeks" before the "best before" date suggest to me that you are indeed referring to this poor excuse for bread. Still, it should not go mouldy that fast. Make sure the temperature isn't too high, that no sunlight can get to the "bread" and the cupboard isn't, well, mouldy. If none of that is the case, then there's something seriously amiss with the shop you're getting the bread from. Maybe they're tampering with the best before dates, maybe they're printed in error, or maybe they have indeed done something to the recipe.81.83.82.123 12:09, 14 August 2007 (UTC)

I have had great tasting as well as lousy tasting factory made bread, home-made bread, and "artisan" made bread. Maybe your "crappy" tasting "factory made bread" got too close to your soap box. Why buy a loaf of bread every 2 days if your household cannot consume a pound of bread in 48 hours? Edison 15:05, 14 August 2007 (UTC)

Buy a smaller loaf? Or freeze half? Seriously, it's not rocket science. You don't buy 100lbs of meat and then spend the rest of the month eating it without putting it in a freezer, do you?

Which jurisdiction do you live in? If we know that, we can perhaps see if the laws on preservatives have changed. It might also be good to see the type of mold. Perhaps you can e-mail or call the bakery company and ask. -Arch dude

A small increase in temperature or humidity will encourage the growth of (most types of) mould, sometimes dramatically--going from the winter heating season with its tendency towards low humidity to spring and summer may be responsible. Note as well that mould is the result of spores that settle on the bread and then grow; if your kitchen has accumulated a large load of spores from previous contaminated loaves, then subsequent loaves are likely to pick up spores more rapidly and mould more quickly. TenOfAllTrades(talk) 14:56, 14 August 2007 (UTC)

I suppose we could add a disclaimer about "Ask a baker" or "Ask a mycologist" for bread mold advice. I claim no expertise in this area and only cite info found on the net or from general reading, including a baking textbook, and from baking various types of bread in the home. The surface of fresh-baked bread is generally free of microorganisms because of the heat of baking, but ropy mold may survive in the interior of bread. The surface can become contaminated while the bread is cooling or being wrapped, while it is sliced, or while it is stored. [14]. Bread can be attacked by various types of mold. There are over 600 varieties of bread mold. Some of them are listed at [15]. Note that the same mold may grow on bread and other substances, and some of these are toxic to humans. In general, some spores are just part of nature. But if mold from bread or other sources has left a high concentration of spores in an area such as your kitchen or your breadbox, it stands to reason that a loaf of bread placed there subsequently might get moldy quicker than if the mold spores were not drifting around. See Black bread mold, [16] at Madsci.org. Edison 14:59, 14 August 2007 (UTC)

I'd go with humidity. It has been exceptionally humid where I live recently (Detroit), and, as previously mentioned, that has a dramatic effect. I've seen bread last indefinitely without getting moldy in dry climates, where it just mummifies instead. StuRat 16:08, 14 August 2007 (UTC)

Benzodiazepine

please list all possibilities for testing positive ie;..urinalysis, for Benzodiazepine. please list all known drug and chemical relatives associated with this subject.

Please list all chemical associations and or any and all reasons to test positive for Benzodiazepine. all known narcotics...etc. all biological refrances. — Preceding unsigned comment added by Jamdmp1850d (talk • contribs)

Wikipedia:Medical disclaimer: The medical information provided on Wikipedia is, at best, of a general nature and cannot substitute for the advice of a medical professional (for instance, a qualified doctor/physician, nurse, pharmacist/chemist, and so on). Wikipedia is not a doctor. -- JSBillings 13:48, 14 August 2007 (UTC)

Judging by the wording, a "do your own homework" is more in order. 147.197.230.174 13:53, 14 August 2007 (UTC)

I didn't want to be too snarky, but I had also considered adding, "... or consult your parole officer." -- JSBillings 14:17, 14 August 2007 (UTC)

The Tour de France is over, you are not going to get that medal back... Lanfear's Bane

In all seriousness, have you looked at Benzodiazepine? -- JSBillings 18:12, 14 August 2007 (UTC)

Detection Periods can be found here. Why would one test positive for benzos? Almost certainly because they had taken one. Mrdeath5493 04:05, 15 August 2007 (UTC)

Electromagnetic Waves

Can someone please define clearly, how electromagnetic waves are related to magnets.

Does magnetism explain this ? StuRat 15:04, 14 August 2007 (UTC)

Sorry, not really. That just tells me that all magnets are electromagnets which Im aware of. I was thinking more of how electromagnetic waves are related to magnets. And do all magnetic fields generate electromagnetic waves?86.139.54.68 15:08, 14 August 2007 (UTC)

The simple but not very enlightening answer is the Poynting vector: if integrating that vector's flux through very large surfaces surrounding your system gives a non-0 answer, you have produced EM waves. Since it involves ${\vec {E}}$, any purely magnetic field will not radiate. However, since changing magnetic fields produce electric fields, in most cases a changing magnetic field (e.g., a spinning magnet) will radiate. We don't seem to have magnetic dipole antenna, but dipole has some discussion of them radiating. --Tardis 15:30, 14 August 2007 (UTC)

(I may have to award another platinum plated spork for that answer! I think the OP wants a SIMPLE answer!

Simply: A magnet produces a magnetic field - you know that. If you put a compass onto the table and spin a magnet around or wave it about in some way - then the compass needle will also move around. This shows that the magnetic field is changing. When the magnetic field oscillates, then a magnetic wave is produced - just like if you move the cone on a loudspeaker you get changes in air pressure - or sound waves. Magnetic waves are what light, radio, X-rays, etc are. Unfortunately, you'd have to spin your magnet around very fast before you'd get any light out of it - 10,000,000,000,000,000 times per second would just about do it - but a mere million times a second would be enough to generate radio waves that an AM radio could pick up. We talk about electromagnetic waves rather than just magnetic waves because electrical fields and magnetic fields are actually different aspects of the same underlying thing. You can see that is the case if you spin a magnet around inside a coil of wire, then you'll generate some electrical current in the wire - and if you apply some voltage to the wire, you can make the magnet move. (That's how electrical generators and motors work.) Since it's a lot easier to change the voltage in a wire than it is to spin a magnet around, we make radio transmitters with rapidly varying voltages instead of spinning magnets - but the end result is the same. SteveBaker 19:25, 14 August 2007 (UTC)

This is my first attempt at helping out on WP so apologies in advance for any errors or over-simplification... SteveBaker may be correct but in my more simplistic explanation I understand that magnetism is a magnetic force exerted on materials (most notably on metals) while electromagnetism is a combination of the electric field and the magnetic field and is a fundamental force. Maybe this will help in conjunction with Steve's answer above:

Radio waves can cause nuclei of some atoms to change their magnetic orientation. This is known as nuclear magnetic resonance (nmr) spectroscopy and is the basis of the new medical application magnetic resonance imaging (MRI). Atomic nuclei, e.g. hydrogen nuclei or proton, behave like little magnets and can align themselves with or against an applied magnetic field. It is possible for the nuclei to "flip" between the "with" and "against" states; the energy diffrence between the two states is quite small and corresponds to radio frequency waves and 60 or 90 MHz radio waves are commonly used to effect the "flip". The precise radio frequency required depends on the chemical environment of the atomic nucleus as the magnetic field felt by a nucleus is influenced by neighbouring atoms which of course are potential magnets. NMR spectroscopy can be used to deduce the chemical environment of atoms and hence the structure of molecules. The nmr spectrum of bromoethane CH3CH2Br has two signals corresponding to (i) the methyl CH3 protons and (ii) the methylene CH2 protons.

Because radio waves represent small amounts of energy they represent little hazard. Radio waves from radio transmitters are passing through our body all the time. When analog radio waves are picked up by an antenna they result in the formation of a tiny electrical signal which is amplified and converted into sound and/or vision and is the basis for radio and television reception and other forms of telecommunication.

Sorry for potentially hijacking this thread but then how are photos created if it's just a spinning magnet? I thought photos were more than merely particle models for light. --antilived^{T | C | G} 06:08, 15 August 2007 (UTC)

The electromagnetic wave carries energy. When that energy hits something - there may be some change to the thing it hits as the energy is absorbed. In the case of photographic film, there is a chemical change that is caused by light (an electromagnetic wave) of an appropriate frequency hitting it. That chemical change can then be exploited to trigger more chemical reactions when you develop the film to change the colour of a pigment which ultimately forms the photograph. The light energy could also hit a carefully designed piece of electronics in a digital camera - ultimately resulting in a signal being sent to a computer and a picture being stored. SteveBaker 13:09, 15 August 2007 (UTC)

Why does a hand in warm water while asleep cause bed wetting?

Is there a scientific reason for the above? Everything I google comes up with rubbish reasons along the lines of "it just happens" there must be a biological reason. SGGH ^speak! 18:06, 14 August 2007 (UTC)

I guess the first question is: Is it even true? That sounds like an urban legend. SteveBaker 22:21, 14 August 2007 (UTC)

I have only anecdotal evidence, but I believe this to work. Not only did this work on me (sadly), but it has worked on a couple of friends too. I have no clue what the cause is. Mrdeath5493 04:01, 15 August 2007 (UTC)

The Straight Dope's Cecil Adams addressed this on 28 June, 1991:

Insofar as it works at all, the pan trick depends on the power of suggestion--simply thinking about water, or in this case dreaming about it, makes you want to go to the bathroom. The effectiveness of the stunt is a matter of debate. Some urologists scoff at the idea. But other medical types have been known to tell patients having a tough time urinating after rectal surgery to put their hands in warm water. Merely letting the water run in a nearby sink sometimes works, too. I tried it once without success, perhaps because my richly deserving would-be victim was dead drunk. But I've gotten too many testimonials from satisfied perpetrators to think the whole thing's a fraud. The suggestion need not be tactile. Recently I heard a talk by an architect who was trying to deal with the problem of men unable to perform in public restrooms. His solution: mount pictures of waterfalls over the urinals. Audio stimuli work too. Rockpocket 05:20, 15 August 2007 (UTC)

Is the warm really necessary for this 'trick' to work other the fact if you put your hand in cold water particularly freezing cold water you may not fall asleep? Also, um BTW, is there any particular reason you and your friends wanted to urinate in bed? BTW were you all males? Nil Einne 16:11, 15 August 2007 (UTC)

In my experience, this trick does not work. DuncanHill 16:13, 15 August 2007 (UTC)

Lanthionine

I need a small amount of a chemical called lanthionine. Although it is not expecially exotic, I can't find it in any catalog I have or on by searching Google. Any help? Or can you think of some good reason this chemical wouldn't be available? ike9898 19:16, 14 August 2007 (UTC)

TCI has it. And Acros used to, maybe call 'em and ask what happened to their supplier? DMacks 19:47, 14 August 2007 (UTC)

Thanks, you saved the day. ike9898 19:55, 14 August 2007 (UTC)

Adoption

How do I go about adopting my wifes 36 year old daughter

That's not really a question for the science desk! But in any case, it's a legal question and we aren't allowed to answer those. SteveBaker 19:34, 14 August 2007 (UTC)

You would need to consult a lawyer, as the process will be different depending on your constituency. If you are the from the USA, http://www.adoption.com/ might be a good place to start. Rockpocket 19:42, 14 August 2007 (UTC)

There are several websites that give general information about adult adoption like here http://adoption.about.com/od/typesofadoption/a/adultadopt.htm, but that does not take into account that you are already the person's step father. As above, information off the internet can not be used as legal defence, you will need to talk to a lawyer. Vespine

Perfectograph

i have a perfectograph made in new york city dated 1925 what is it and what did it do?

HMM! Does it look like this [17]?--SpectrumAnalyser 20:44, 14 August 2007 (UTC)

Cool! A gizmo for training morse code operators by the look of it. SteveBaker 22:20, 14 August 2007 (UTC)

Plato on third region beyond true and false, fuzzy logic precursor

Hello all, in a wikipedia article about founder of fuzzy logic, Lofti Zadeh, there is a following claim: "Plato laid the foundation of what is now known as fuzzy logic indicating that there was a third region beyond true and false." Does anybody know more specifically about Plato's opinion on this? Thnx, Mel

Maybe that's a reference to Plato's analogy of the divided line? Not sure. ←Ben^B4 20:37, 14 August 2007 (UTC)

No, its not got to do with it, although its kind of intriguing. mel

Well, if it was Plato, it wasn't exactly a deep insight. We're all pretty aware that there is "True", "False" and "Er...kinda". SteveBaker 22:59, 14 August 2007 (UTC)

yes, you´re right, but i must say that internet is sparkling with the attribution that i brought out above, and none quote the source. it seems to me a little bit like this case: http://www.geniebusters.org/915/04e_ex01C.html

I've taken the claim out of Lofti Zadeh based on this discussion. Of course if a reliable source turns up, it can go back in. --Allen 23:39, 14 August 2007 (UTC)

You should ask on the humanities desk - the experts there are more likely to know87.102.4.73 08:23, 15 August 2007 (UTC)

Physics?

Just wondering, but would it be possible to make a copy of the keystrokes + cpu instructions when you're 100m away from the said computer? Not with current technology, but wondering if this is possible. 206.77.151.206 20:38, 14 August 2007 (UTC)

From EM radiation? I don't think so, it isn't distinct enough to recover the system state (if it was then WiFi could be unlimited speed.) But see TEMPEST. ←Ben^B4 20:49, 14 August 2007 (UTC)

Maybe better placed on computing desk.--SpectrumAnalyser 20:50, 14 August 2007 (UTC)

Eavesdropping a video signal remotely has been possible for some time - see van Eck phreaking. With a suitable directional detector I imagine monitoring a USB cable and retrieving keystrokes would be a similar task. Doing so from a distance like 100m will require a more sophisticated detector with a highly directional waveguide and a sensitive detector, perhaps (sf authors would have us dream) a SQUID). I would be surprised if major intelligence agencies didn't already have this capability, although perhaps not at that range. Doing the same for the CPU is a whole other matter - you're not detecting the emanations from one wire or two or four, but tens or hundreds of thousands, all right beside one another and signalling at insanely high frequencies. -- Finlay McWalter | Talk 20:51, 14 August 2007 (UTC)

The OP says "Not with current technology" - so we're mostly interested in the physical limits of what's possible - not what we could actually built tomorrow. I think that some technique involving not one van Eck detector but a huge array of them surrounding the building might get enough spatial/holographic radio detection data to extract useful information from the PC. Personally - I'd bet on being able to hack into the PC via an unused wireless port - or perhaps to send a nanotechological flying robot into the building and to have it sneak into the PC's case and latch itself onto some interesting data lines.

Got a follow up - Would it be possible to read contents of a cd/casette through the paper casing? 206.77.151.206 20:53, 14 August 2007 (UTC)

That seems almost impossible. Unlike the phreaking above, where the video/usb signals are stretched out and time and space (and are comparatively large, because they're actively emanating) a cd or magnetic tape would be very hard to examine. The data is stored in very small locations, they're entirely passive, and they're physically smushed together making picking one from all the others almost impossible. -- Finlay McWalter | Talk 21:12, 14 August 2007 (UTC)

I would think that reading a CD through a paper envelope might be possible - paper will transmit some amount of laser light - with the right lenses...maybe. Also, the data on a CD has levels of error protection that would mean that even if you could only read a portion of the disk, it might be possible to reconstruct the data. SteveBaker 22:14, 14 August 2007 (UTC)

Well, you could always beef up the laser output to flash burn the paper away...you know...if you were really didn't feel like take the thing out and doing a nice resealing job on the sleeve once you were done. Someguy1221 22:17, 14 August 2007 (UTC)

I think the paper will diffuse the light far too much (you're aiming for pits 100nm deep and only a few times that apart). Similarly I thought about using ultrasound, but that would have to be of an extremely high frequency to get the wavelength down low enough to detect a 100nm pit. Perhaps a scanning x-ray probe would work? -- Finlay McWalter | Talk 22:24, 14 August 2007 (UTC)

I think reading cassettes with paper in between would work without major problems though... --antilived^{T | C | G} 06:05, 15 August 2007 (UTC)

Even a simple twisted-pair would preclude radiation (to a sufficient level) that it isn't likely to eavesdrop on a signal inside of it. I think the hard part would be discerning which detected emissions corresponded to which signals. Inside a modern computer, thousands of independent wires, solid-state connections, and data bus cables all have unique signals on them simultaneously. Even if each were perfectly and noiselessly radiating towards your ideal eavesdropping antenna, the interference would prevent any sort of meaningful interpretation. Crosstalk is enough of a problem even inside the microcomputer, since signal levels are being pushed to ever lower voltages and power levels. Furthermore, you would need a very nice "ideal antenna" that can pick up radiation across a huge bandwidth - from kilohertz for some of the video and audio signals, up to gigahertz for the CPU clock and the RAM access. Nimur 15:05, 15 August 2007 (UTC)

Not strictly related to the question at hand, but close, and still fascinating : http://applied-math.org/optical_tempest.pdf 69.95.50.15 15:23, 15 August 2007 (UTC)

This one blows my mind [18] it's a camera that works by figuring out how all of the light in the visible scene got where it finally ended up. With some clever math, the camera can take photos around corners. Their math effectively allows them to interchange the position of the camera with the position of the light source. In their example, they show a picture of a hand of cards - taken from the back side of the cards, calculating what's on the front of the cards by inferring how they scattered light onto the wall behind!! If you can do that - it's hard to believe that you couldn't do similarly amazing things with an array of RF detectors. Think about how CAT scanners image the interior of solid objects. These kinds of technique are what convince me that you could decypher a CD-ROM through a paper sleeve. SteveBaker 17:53, 15 August 2007 (UTC)

SteveBaker might want to amend his quote to: "With some clever math, a large number of images, and total control over the scene lighting conditions, the camera can take photos around corners." It's still amazing; there's a very nice video of the technique which is probably comprehensible in a non-technical way. Nimur 23:50, 15 August 2007 (UTC)

Well - that's perhaps overstating it. You do need some special lighting - lighting that 'scans' the scene - and you need to take a lot of photos, but that's not difficult. The presentation at SigGraph a few years ago included a comment from the author that it is possible that the light from a TV screen or computer monitor might suffice to perform this trick - since the raster scan produces light that moves relative to the scene (albeit very quickly). In a dimly lit room with a single CRT-type display showing a nice, bright image - it might be possible to reconstruct the scene without having additional control over the light source - given enough time to integrate the images. It definitely wouldn't be easy though. SteveBaker 11:58, 16 August 2007 (UTC)

Not a question!

A WikiCookie for you!

This isn't a question, it's a cooKie of appreciation for Sci Ref Desk people. I've gotten some great help here recently; keep it up! ike9898 21:08, 14 August 2007 (UTC)

Well, thank you so much...but we've got to share it? There's at least 23 regular contributors and the average mass of a chocolate chip cookie is 30g which at about 8kcal per gram means we only get...oh well, perhaps if we weighted the cookie share according to the number of bytes of response normalised and tracked as a moving average over the period...oh...sorry. THANK YOU! IT WAS DELICIOUS! :-) SteveBaker 21:58, 14 August 2007 (UTC)

Quick! Eat it before the seagulls get to it! — Scientizzle 22:49, 14 August 2007 (UTC)

Don't see Kurt around here... bibliomaniac15 00:46, 15 August 2007 (UTC)

Awww... it's great to be thought of! --Mdwyer 01:26, 15 August 2007 (UTC)

What about those who don't provide great help? -- Kainaw^(what?) 01:42, 15 August 2007 (UTC)

Bran cookies with raisins. SteveBaker 01:45, 15 August 2007 (UTC)

Since this isn't a question, I propose that tasty looking cookie should be removed from the desk. But, y'know, so not to clutter up the talk page, I'll volunteer my page for it... Rockpocket 01:45, 15 August 2007 (UTC)

The reference desk does not provide gustatorial advice or services. Please contact me in real-life to resolve this cookie. DMacks 03:18, 15 August 2007 (UTC)

Alas, I've turned off cookie support in my browser (black helicopters and tinfoil hats, doncha know), so I can't enjoy it at all. :-( --Steve Summit (talk) 20:47, 15 August 2007 (UTC)

Do you still have granola bar support enabled? I'll trade you for your share. Confusing Manifestation 02:21, 16 August 2007 (UTC)

Laser Cutter in Woodshop

For those of you familiar with laser cutters...

I want to cut some 1" thick hard wood boards on the school laser cutter. The policy says that we can not cut over .5". I am wondering if this is a technical limitation or not. After reading the article on laser cutters it sounds like running the cutter slower would allow you to scale up the thickness of the material. Or Running the entire cut pattern twice.

Anyone want to chime in on this?

Thanks,

E

Have you considered asking whoever is in charge of that fantastical piece of destruction, or consulting its manual? Your teachers probably won't appreciate your setting the building on fire ;-) But why not use a table saw? Someguy1221 22:03, 14 August 2007 (UTC)

Laser cutters can cut all sorts of interesting shapes that a table saw can't touch. But seriously - there is a reason why they said the limit was 0.5" - if it could actually cut 1" safely/effectively then the limit would be 1".

There may be a physical reason -- the optics might not be able to focus the laser any farther than .5" from the cutting head. --Mdwyer 01:24, 15 August 2007 (UTC)

I did ask, the .5" limit was quoted as "we have never tried anything thicker". Thats why I am looking for technical reasons- to see if I should pursue the issue. The optics may play a roll and I hadn't considered that.

My reason for using the laser cutter is as stated, you can design some really funky shapes, I am making a bookcase with interlocking sections of mahogany and maple and the joints I designed would be hell to cut on a table saw.

Thanks for the feedback

Well, you could – with permission – try cutting a thicker piece. I wouldn't be surprised if the limit was due to the maximum working distance of the optics. Note that if you set up your patterns very carefully, you could (in principle) do a thicker piece by cutting a 0.5" from one site, turning the piece over, and cutting another half inch from the other side.

Your best bet, however, might be to jot down the manufacturer and model number and look up the specs online. I suspect that any company that's selling laser cutters these days will be hip and trendy enough to have a web site. Even if the specific information (product manuals, specifications sheet, etc.) isn't on the site, with any luck they'll have an email address or other contact. A politely-worded email can work wonders.

By the way, how the heck did you get a laser cutter in your wood shop? Back when I was your age, we had to use saws! TenOfAllTrades(talk) 01:56, 15 August 2007 (UTC)

Saws? You were lucky to have saws, we had to use our teeth! DuncanHill 11:01, 15 August 2007 (UTC)

Ah-hah! Then get permission to try something thicker. Bring a fire extinguisher! SteveBaker 01:57, 15 August 2007 (UTC)

Band-saw and/or router might work (depending on the pattern) assuming they are available to you; if not, keyhole hand-saw, chisel, and drill-press can suffice. stack the two pieces together when cutting so the results will interlock even if your hand slips or whatever. DMacks 02:06, 15

August 2007 (UTC)

Heh, we have a laser cutter in the shop because I am in college. We have a couple of them actually, and a water jet cutter, (and a rapid plastic prototyper, which is particularly cool!). Anyways, Ill do the spec thing and see what I can dig up. I have been trying to use all of this high-tech equipment for one thing or another. I realize that I can make a book shelf using a variety of manufacturing techniques, I specifically designed this one to be laser cut, there is something attractive about going from CAD to glue-able pieces in one step!

(Im sold on the fire extinguisher thing though..)

Ahh, now I see:) Well put the precision to the test...cut the 1-inch piece it as if it were .5 inch, turn the piece over in reality and in CAD, cut it again, and see how well the two cuts align. DMacks 02:16, 15 August 2007 (UTC)

The laser cutter at my school has software where you can set the thickness and material of what it's supposed to be cutting, and adjusts the speed, etc automatically. Have you tried playing around with the options to see if yours can do that? (Also, I'd advise checking with a scrap piece of wood before you try the real thing - the edges can end up a bit burnt) 147.197.230.174 09:02, 15 August 2007 (UTC)

Kids these days. "If you can't do it with electromagnetic radiation, then it ain't worth doing." Capuchin 09:38, 15 August 2007 (UTC)

When you say school, are your referring to secondary school/high school or university/tertiary level college (higher education)? Nil Einne 16:37, 15 August 2007 (UTC)

If you mean me(147.197.230.174), secondary school. 80.169.64.22 19:10, 15 August 2007 (UTC)

August 15

xenalights

information on xenalights as a air cooling technology — Preceding unsigned comment added by 72.222.165.50 (talk • contribs)

Xenalight makes a type of fiberoptic light. I do not know of any other product they produce. I do not know of any means of cooling with fiberoptic lights. -- Kainaw^(what?) 03:04, 15 August 2007 (UTC)

Hmm - I agree - it's a fibreoptic light. One claim for such lights is that they can deliver a lot of light without producing a lot of heat becaused the hot lamps can be placed a long way away and the light they generate carried to where you need it down the fibre bundle. So they don't cool the air, but they presumably do a great job of avoiding heating it up. SteveBaker 03:53, 15 August 2007 (UTC)

Cardio and Barfing

I have been doing a lot of intense cardio for the past 6 months, and recently I feel like barfing while running and I cant figure out why. I think its because I drink too much water before and during, but I have always drank a lot of water. Any ideas as to why I'm feeling like this? Thanks — Preceding unsigned comment added by 76.167.145.55 (talk • contribs)

... perhaps there is a difference between "intense" and "too intense" ...? something to consider ... (Joseph A. Spadaro 03:16, 15 August 2007 (UTC))

Motion sickness? Um, don't ask medical advice here, talk to your doctor. ←Ben^B4 03:44, 15 August 2007 (UTC)

I think we are getting a little too broad in our categorizing of questions under medical advice. This issue could certainly be discussed from a theoretical standpoint. Why would one feel nauseous while exercising? Mrdeath5493 04:09, 15 August 2007 (UTC)

I used to play soccer at a fairly competitive level and our coach would often make us run to the point where people would vomit. There's also anecdotal evidence linking intense cardio and vomiting with lactic acid build-up. Heat exhaustion, altitude, or simply overdoing it could also be relevant factors. Also, maybe read this [19]. The preceeding does not constitute medical advice, consult your physician, etc. -- 38.112.225.84 04:52, 15 August 2007 (UTC)

The cardio I used to do was way more intense, actually thinking about it, what I'm doing right now isn't really intense. I never really had this problem before, I think if it was motion sickness, it would have been present in the past.

I know when pushing too hard I use to get nauseous, but never when I was not pushing too hard or too long.

Same altitude in an air conditioned gym (I dont really even sweat a lot, well not excessively. Thanks for the article and everyones help.

I seriously disagree. When someone says "I'm exercising and I'm having these problems" they really need to see a doctor and we should tell them that. Discussing stuff from a 'theoretical' viewpoint in a case where someone needs to see a doctor it a very bad idea! Perhaps if the poster had said "I was speaking to a person I met in the gym and he said he was exercising a lot and..... This got me thinking, what could have caused this person's problems", then probably discussing things from a theoretical view point would be okay. (but please don't take this as an example to phrase your question so). Nil Einne 11:15, 15 August 2007 (UTC)

It could simply be a bad case of acid reflux from all that water, indeed.

This could be a brain tumor, too. Again, see a doctor. ←Ben^B4 17:49, 15 August 2007 (UTC)

You are telling us that something has changed which could have a serious cause. You really need to see a doctor so it can be checked out. Skittle 18:56, 15 August 2007 (UTC)

See this. Of course he needs to see a doctor, but that doesn't mean that the topic is off limits, does it? Are we to never mention nausea and exercise together again? Does it need a new thread? After 3 people declare that we can't give this person specific medical advice and to see a doctor, it seems perfectly acceptable to discuss this exact topic theoretically. I personally have nothing to add, because I'm not familiar with why this would happen. However, I fear that others who might be able to contribute something are being improperly discouraged.

Furthermore, if you actually read the Medical Disclaimer, you might notice that it does not prohibit such discussion. It just warns users to seek professional advice and not to rely on information submitted by users. It certainly seems to license theoretical discussion, rather than forbid it.
Mrdeath5493 19:31, 15 August 2007 (UTC)

The medical disclaimer applies to articles - the ref desk has different rules - one of which is: "The reference desk is not a place to seek professional advice on medical or legal matters, nor analyses, diagnoses or solutions to questioners' health or legal problems, and responses that could be construed as such must not be given." - so, nothing that could be construed as a diagnosis is allowed - which would obviously include "It could simply be a bad case of acid reflux". Writing a referenced article about some medical matter is OK - but issuing a diagnosis of a particular patient is to practice medicine without a license - which is illegal in many places in the world. SteveBaker 19:57, 15 August 2007 (UTC)

There must be some circumstance under which we could theoretically discuss cardio and barfing. What are the boundaries? Not under this thread? Not within so many days of the asked question? Is some sort of disclaimer at the beginning of an answer required? Or is it just off limits forever since someone asked about it in a way that seemed to be seeking medical advice (certainly not, I assume)? Don't think I'm being snarky, either. Discussing this can not be completely off limits. There just needs to be some explicit way of indicating that we are not giving medical advice. (I think the medical disclaimer is enough, but whatever.) I'm not sure anyone wants to diagnose or treat OP's that ask questions like this. These sorts of questions raise curiosity (at least they do in me) and I would like to see some sort of educated response. I think that people that are capable of answering such questions (from a standpoint that in no way diagnoses or treats the OP) are being unjustly discouraged

Mrdeath5493 00:19, 17 August 2007 (UTC)

Journal Cell Publication Period

Is the journal "Cell" published biweekly or bimonthly? The disambiguation page for the word "cell" says it is bimonthly, but I understand it to be biweekly, which is what the main article says. Is there a difference I am missing, or can I change this? 131.215.240.27 03:28, 15 August 2007 (UTC)

It's published biweekly (every two weeks). I'll change the disambiguation page. Flyguy649 ^talk _contribs 03:32, 15 August 2007 (UTC)

There is general confusion over bi-, some people using it as "twice-" and some using it as "every two". There is a similar confusion over semi-. It might be worth avoiding using these prefixes where possible. Capuchin 08:16, 15 August 2007 (UTC)

For biweekly you could use fortnightly I guess but what about bimonthly? Every two months? Bimestrial is probably more confusing. The confusion may partial arise from biennially I guess Nil Einne 11:06, 15 August 2007 (UTC)

Glazing

what is segar formula,please elaborate — Preceding unsigned comment added by Naray2007 (talk • contribs)

Do you mean agar? Lanfear's Bane

Or sugar? Capuchin 11:49, 15 August 2007 (UTC)

A quick google turns up that it's something to do with the chemical composition of pottery glazes. Nothing stands out as being particularly enlightening, though. 147.197.230.174 11:58, 15 August 2007 (UTC)

According to [20]:

Segar Blue Glaze - cone 9-10

(KPG)

3360 G-200 feldspar

1440 whiting

1040 ball clay

2160 flint

240 rutile

320 red iron oxide

----------------------------------------------

8560

(I hope this means more to our OP than it does to me!)

SteveBaker 12:42, 15 August 2007 (UTC)

I was thinking more of glazed doughnuts (mmmmmm). Capuchin 13:09, 15 August 2007 (UTC)

If you like your doughnuts glazed in ground up flint and red iron oxide...go ahead. If you're hungry, I think there is still some of that cookie left - about five posts up from here. SteveBaker 13:13, 15 August 2007 (UTC)

READING BURRETTES IN TITRATION

Assuming you are given a 50litres burrate which are not callibrated stepwiselly i.e each location isnt labeeled, can u take the burrete reading in the opposite direction knowing well that you will arrive at thesame answer. i.e

INITIAL READING 50.00 35.00

FINAL READING 35.00 15.00

Knowing well that the reading of a callibrated burette is

00.00 15.00

15.00 30.00

BUT IT IS STILL THEASME VALUE OF ANSWER.

OKEWOLE OLUWASEYI

— Preceding unsigned comment added by 80.88.140.24 (talk • contribs) 10:51, 15 August 2007 (UTC)

If you mean what I think you do, yes, it's the difference between the values that's the titre. (Also, a 50 litre burette?) 147.197.230.174 10:57, 15 August 2007 (UTC)

I somehow think a mili was missing from somewhere. Nil Einne 11:00, 15 August 2007 (UTC)

Wow! A coral atoll (click on the link) was missing? Maybe you mean a milli...? :-) Carcharoth 16:22, 15 August 2007 (UTC)

One half of a lip-synching vocal duo? Edison 17:59, 15 August 2007 (UTC)

Internet in Africa

I'm looking for a map that shows the distribution of internet access (or something along those lines) in Africa. My dream would be to find something about cross-border internet connections in Africa (who's communicating with whom, etc.), but I doubt there's anything about this topic in particular. So any type of map in that direction would be interesting: Internet access, internet usage, possibly the most important internet cables (i.e. hardware), you name it.

Do you have any idea where to find that kind of materials? Thanks, Ibn Battuta 16:55, 15 August 2007 (UTC)

PS: I'd rather use materials that do not just display information for each country; if possible, I'd like to prevent using political borders as sorting criteria. Thanks, Ibn Battuta 17:02, 15 August 2007 (UTC)

Many areas in Africa are not well served by terrestrial Internet, but there are at least ten separate providers of satellite IP service taht covers all of Africa. When you use satellite service, each terminal is topologically "closer" to the hub and the the Internet core than they are to each other: the ping time from such a terminal to Wikipedia is approximately half the ping time to a terminal in a village 20 km away, and the IP addresses reflect the IP address space of the hub, not the African country. Each ISP's hub can be anywhere that is visible to the satellite, e.g. in Europe. Of course, much of the population will be in larger towns and cities with terrestrial internet connections ranging from poor to excellent. -Arch dude 17:21, 15 August 2007 (UTC)

The Internet isn't like the telephone network. You can't tell who is talking to whom by looking at a wiring map of the Internet - there is no way to know whether the bulk of the traffic from (say) South Africa is going to Wikipedia's servers or in local communications or in communications with users in (say) Kenya. Even if people in Kenya and South Africa were talking to each other in great numbers, the odds are good that they'd be using Gmail or MySpace to do it - so the actual communication pathways would probably still go to big servers outside of the African continent even if two people in the same town were talking to each other. For example - my sister and I use the same mail server (my Webhosting company gives me 700 free email accounts - so why not?) - but she lives in UK and I live in USA. When she emails her neighbour, the email travels from UK to USA, where it sits on the server and is then sent off to the neighbour in UK - how could you possibly tell the difference between a communication between two people in the UK and a communication to a location in the USA? You are asking a question that cannot be answered - even in principle. SteveBaker 17:37, 15 August 2007 (UTC)

Maybe I didn't express myself clearly enough: I'm looking for maps, not just general information. :o) And yes, I'm very aware that the internet doesn't work like the phone, that's why I said the information is probably not available. (It would require extensive surveys, which are probably not even available for industrialized nations.) So the other option are maps of 1.) hardware (e.g., those hubs -- are there maps about their distribution? Else I've found so far only this map) or 2.) statistics (how many households use the internet, how many hours/week or /month do people spend online on average etc.). Thanks, Ibn Battuta 18:18, 15 August 2007 (UTC)

Hole in a spacesuit

An astronaut doing a spacewalk had to return to the shuttle early today because of a tiny hole in the outer layer of his glove. That got me thinking -- just what would happen if that tiny hole had penetrated through all the layers of the glove? Would the astronaut had suffocated (as would happen with no spacesuit at all)? -- Mwalcoff 22:46, 15 August 2007 (UTC)

A micrometeorite, a sharp edge from a broken piece of metal or a tool, or even the end of a piece of wire could cause a puncture. The NASA Extravehicular Mobility Unit, the space suit used on extravehicular activities is apparently one large pressurized system, and a leak anywhere would soon bleed away the oxygen needed to sustain life.[21] The life support system would release stored oxygen, so the size of the hole which cause a leak would be an important factor. A pinhole would lead to a sudden end to an EVA and a race for the airlock. A large cut might be catastrophic. In sci fi stories, there were devices such as pressure cuffs in space suits which could be suddenly inflated to seal off the hand, foot, arm or leg which had the leak, preserving life at the cost of injury to or loss of the isolated part. Again, time would be of the essence. The suit reportedly has only 4.7 pounds per square inch, less than 1/3 of normal Earth air pressure, so direct pressure on a puncture would slow the leak. A sticky patch (think NASA quality duct tape) held on with pressure could seal many leaks, but I have not seen that they have that readily available. They do have a rule to inspect the gloves every half hour because of tears found in the past which penetrated the outer layer. Self sealing suit and glove materials have been developed which have in the lab sealed 2 mm holes, with research ongoing to extend the capability to 4 mm holes [22]. This self-sealing capability would add 15 pounds or 5% to the EMU mass, an would increase the mass much less if only applied to the gloves, but making the gloves thicker without losing dexterity might be a challenge. I would at least go with Space Duct Tape. Edison 23:11, 15 August 2007 (UTC)

Michael L. Gernhardt was aked this question. [23] His response:

"If we got a small hole [in our spacesuit], our oxygen would start coming out of the spacesuit, and the pressure would start to drop. If the pressure drops too far, then you'll get the bends, and if it drops below about 2.5 psi, then you don't have enough oxygen to maintain useful consciousness. Now, we have a device called the Secondary Oxygen Pack on the back of our backpack, and it's got a whole lot of oxygen in it, and it would be able to support a small leak for—depends on how small it is—but for at least 30 minutes. So for a small leak, we'd have our secondary-oxygen system kick in, and we'd be heading back to the airlock and repressurizing, and we'd be fine. A big leak—like a big hole in the suit, say a half-inch hole or something like that, or if your glove blew off—would pretty much be a real bad day for you." Rockpocket 23:15, 15 August 2007 (UTC)

I'm sure I remember reading that very small holes to appear in suits and they are not noticed until returning to the space craft, because they are too small (i mean bordering microscopit) to notice or to have much effect. SGGH ^speak! 00:17, 16 August 2007 (UTC)

I'm not answering the initial question here but you may want to google self healing polymers which can potentially heal damage to their structure many times... try [24] for a bit of interesting info. --Cosmic joker 00:47, 16 August 2007 (UTC)

In the movie Event Horizon, one of the crew members goes into an airlock and floats out into space without a suit. Blood comes out of his eyes and stuff. They get him back and he survives. Is that survival realistic? --Seans Potato Business 00:36, 16 August 2007 (UTC)

See Vacuum#Effects_on_humans_and_animals, Human_adaptation_to_space#Effects_on_humans and Explosive decompression. Exxolon 00:50, 16 August 2007 (UTC)

Something similar happens in various moments throughout the Gundam franchise, Generally someone closes their eyes and covers their ears, opens something suddenly enough that the oxygen rushes out and 'manages to survive' by staying within the oxygen stream until they get to whatever they were jumping to (which generally is only a few seconds) --Lucid 02:35, 16 August 2007 (UTC)

So the aptly named scientist Robert Boyle put small animals in a vacuum and observed the effects. Perhaps they felt "ebullient." The scene from "2001 Space Oddesy" is plausible, in which a man survives brief vacuum exposure. Edison 04:04, 16 August 2007 (UTC)

You would think that NASA could just have astronauts wear a standard high altitude type masks insider their helmets. Then even if there suite was punctured they’d still get oxygen. Yes, the person might suffer decompression sickness and might eventually freeze to death after a long while, but they would have a much greater chance of making it back to the lock or being rescued. --S.dedalus 06:19, 16 August 2007 (UTC)

S.dedalus, that's exactly what I'm wondering: Can you survive in vacuum as long as you can breath and don't freeze to death? If so, I really don't understand why they don't have a two-part suit, with a mask for oxygen, and mere heating for the rest (plus a bit of pressure as long as necessary). I'm sure that NASA debated that at some point and apparently rejected the idea. So is a vacuum just below the pressure that a human body can survive? Or what is the problem? --Ibn Battuta 07:53, 16 August 2007 (UTC)

The standard NASA and Russian suits have been filled throughout with one zone of breathable gas, pure oxygen at relatively low pressure. The low pressure may make it easier to move around, since the curse of space suit design has been that if bending reduces the total volume, the gas pressure resists the movement. A lot of cleverness has gone into making joints such that bending the arm or leg does not cause a volume change. A new proposal, "skin tight suits" is discussed in Space suit. These would have a skin tight pressure garment (with heating or cooling, naturally) surrounding the body with a gas supply only to the face. That way, movement would not be opposed by the gas pressure. If such a suit were punctured, there could be tissue damage from fluid exposed to the vacuum boiling, or from simple blood loss accelerated by the lack of external air pressure, but see the "space duct tape" notion above for possible repairs. There are sharp edges from rocks on the moon and mars as well as when working with equipment in extravehicular activities. If there is ever conflict in space, it would be useful to not have an impact from a small projectile not be inevitably quickly fatal. A Mars explorer with a hole in the arm of the skintight suit (which did not threaten the continuity of the breathing air supply) could rescue himself much more easily than if the oxygen were rushing out at a rate which dropped the breathing supply to too low a pressure to sustain life, or which quickly used up the supply in the tank. Such a suit would have to have a moisture absorbing layer, to allow the skin itself to "breath" by expelling moisture. The present suits have a life supprt system which absorbs this moisture. Edison 16:10, 16 August 2007 (UTC)

The only known suit puncture was partly sealed by the astronaut's own blood (on STS-37 [25]). And wasn't noticed until examination back on Earth so a puncture need not be catastrophic. Rmhermen 01:18, 17 August 2007 (UTC)[26] Rmhermen 01:18, 17 August 2007 (UTC)

August 16

Stupid pharmaceutical names..

Where do the ridiculous names like 'Gemtuzumab ozogamicin' come from? It it's a Calicheamicin-(another one!)-bound anti-CD33 antibody then call it that! Don't tell me that Gemtuzumab ozogamicin is less cumbersome! --Seans Potato Business 00:30, 16 August 2007 (UTC)

Monoclonal antibodies for therapeutic use have a specific nomenclature. See Nomenclature of monoclonal antibodies. I agree it looks crazy, but the name is actually quite inforamative. I imagine IUPAC has rules for naming other compounds, but I'm not sure. Flyguy649 ^talk _contribs 00:40, 16 August 2007 (UTC)

Full IUPAC names would be a terrible mess for drugs—while they would describe the drug structure completely, they'd never fit on the label for any but the very simplest molecules. Instead, standardized generic names are created based on a set of standardized stems, prefixes, and suffixes to create International Nonproprietary Names and United States Adopted Names. TenOfAllTrades(talk) 01:25, 16 August 2007 (UTC)

Wikipedia has an article List of chemical compounds with unusual names about real chemicals with funny names, such as "curious chloride," "traumatic acid," "moronic acid," and "draculin, an anticoagulant found in the saliva of vampire bats." There was a strange scientific paper which sought to determine "Is an Arsole aromatic?" Edison 04:17, 16 August 2007 (UTC)

The names are choosen to be stupid and long and hard to remember! The producer with patent for the medicament (chemical substance) is allowed to choose two names, one for the own business, mostly easy to remember, and than an second name used for the other producers after the patend has run out or the product is licenced to somebody else.--Stone 09:37, 16 August 2007 (UTC)

How long would you retain consciousness/awareness if your head was cut off?

Simple enough question. If your head was severed from your body, (for the sake of argument lets say this is almost instantly), how long would a person retain consciousness/awareness (assuming the shock didn't kill them instantly). Could someone cut your head off and show your headless body to you before you lost consciousness for instance? Exxolon 00:46, 16 August 2007 (UTC)

Have a read of the articles decapitation and guillotine, they answer those questions. Since the effectt is always quickly fatal, there is no real way of knowing, movement and supposed reaction has been observed in severed heads immediately after the act, but no one can tell if they were purely physical/reflex or conscious movement. For quite obviousl reasons there has been a lack of research in this specific field. Vespine 00:57, 16 August 2007 (UTC)

au contraire our fascination with death has, in fact, lead to some experimentation on the subject. Plasticup ^T/C 13:47, 16 August 2007 (UTC)

I think this more a humanities question but there have been arguments about how long it takes for brain death to REALLY occur when oxygen is cut off from the brain for a long time. If your head is cut off I'd guess you would lose 'consciousness/awareness' as opposed to brain death in fractions of a second of the spinal cord being severed. If you've ever had a really nasty knock/shock you lose all awareness. When I was a child I fell off a roof and was knocked unconscious (big surprise) so I had no awareness, I could have died that day and would have had no awareness that I was lying starfished on the ground so my awareness would have ended when I hit the ground. But (and I said this was a humanities question) the perception of how long it takes you to lose awareness may be very different. --Cosmic joker 01:13, 16 August 2007 (UTC)

Part of this question borders on a sort of philosophical / semantic debate about what it means to be conscious. To simplify the issue, we could define a standardized test for responsiveness of some type. Then, simply perform that test on the head. Such a test might need to be specifically crafted given the uniquely limited communications capabilities of a severed head. Nimur 01:48, 16 August 2007 (UTC)

Henri Languille responsiveness was measured by his opening and closing and focusing his eyes. Carcharoth 03:29, 16 August 2007 (UTC)

Nobody has yet mentioned Mike the Headless Chicken?! For shame! You should all have your Wikipedia editing privileges revoked D: --Lucid 02:04, 16 August 2007 (UTC)

The question has also been covered by the great Cecil, briefly in this article and more extensively in this followup. —Steve Summit (talk) 02:15, 16 August 2007 (UTC)

Ooh. That last story is horrible! It should be possible to carefully decapitate without using a large impact that would render someone unconscious, but then you get into the realms of science fiction and 'heads in a jar' type things. Carcharoth 03:37, 16 August 2007 (UTC)

More specifically, don't miss Guillotine#Living heads! :-) Carcharoth 03:37, 16 August 2007 (UTC)

nickle silver alloy

nickle silver alloy combination is 55% CU 27% ZN 18% NI my question is what is the withstand temperature of this alloy (that is in which temperature itss colour will be change

Does Nature utilize prime numbers (qua prime) for any reason?

I know that the American periodical cicada has two sub-species, one which resides underground for 13 years and the other for 17. Apparently, these numbers were selected by evolution because, being prime, they make it difficult for any predator species to correlate their own life cycles to those of the cicada. For example, had the cicada’s periodicity been 12 years, then any predator species having cycles of 2, 4, or 6 years could prey on them. I am wondering if this is the only example of prime number utilization in Nature, whether it is in the organic or inorganic domains. Humans now use primes in encryption, a practice broadly analogous with that of the cicadas. But, before computers, was there any practical use for primes. Myles325a 04:25, 16 August 2007 (UTC)

Could predators could evolve to be in sync with one of the sub-species and thus have a predictable food supply? An alternative explanation I've heard is that having several reasonable-sized prime-number periods keeps more than one of the sub-species from appearing at the same time, thus preventing them from competing with each other for food or territory or whatever resources the noisy critters use. DMacks 04:36, 16 August 2007 (UTC) Meh, off-topic...scientists have apparently been arguing about the evolutionary reason for the length and primeness for a long time and don't appear to have good consensus. DMacks 04:46, 16 August 2007 (UTC)

If you count the number of seeds in a circle around a pineapple you will get a prime number. Also look at the sunflower seed head. This sort of thing happens when things are arranged in a spiral growth pattern on a plant. Frequetly the prime mumber is 2, or 5 but the large plant objects like fruit or flower heads could have larger prime numbers in use. Graeme Bartlett 05:56, 16 August 2007 (UTC)

OP myles325 back. Yep, Graeme, that's interesting, but I did specify "prime(qua prime)", in other words prime numbers BY VIRTUE of their primemess. Now, is this the case here? Do we find primes in spiralling entities, and if so why? Myles325a 06:14, 16 August 2007 (UTC)

Actually, I think in the case of natural spirals the tendency is more towards Fibonnaci numbers, it's just that four of the 6 smallest of them happen to be prime (counting the repeated 1 only once), and then after that the numbers are getting too big to be particularly likely to occur naturally. Confusing Manifestation 06:26, 16 August 2007 (UTC)

Yup, the Fibonacci number page (note spelling:) has some examples from nature. DMacks 06:35, 16 August 2007 (UTC)

The OP's example sounds like one given by Marcus du Sautoy in The Music of the Primes, and his Royal Society Christmas lectures. You may have access to this already and have got the example from there, but if not, it may well have more details. Cyta 07:18, 16 August 2007 (UTC)

Hibiscus

How is hibiscus distributed?

It is normally proagated by taking a cutting and sticking it in the ground with rooting hormone. Graeme Bartlett 06:09, 16 August 2007 (UTC)

Source of non-copyrighted image of plants

Could someone help me to find a non-copyrighted picture of guar bean and processed guar gum? E.g. are there any federal institutions having photos of plants? Thank you in advance, Timur lenk 06:13, 16 August 2007 (UTC)

Can you fault my logical and scientific proof for personal immortality?

It’s based on the Schrödinger’s Cat thought experiment. Suppose you have a person in that box instead of a cat. ( “Schrödinger’s Friend”). As before, random events determine whether the box is flooded with poison gas or not. As before, Quantum Theory says that BOTH possibilities exist until an observer looks at it, and then it snaps into one option or the other. Suppose YOU are the guy in the box, and you are recording what happens. You notice an INCREDIBLE THING! Each time the random event occurs, it always comes out in your FAVOUR! It’s like betting Heads on a coin toss a hundred times in a row and never losing once. That’s becoz it is logically impossible for you to observe and record your own extinction. The scenario where you live is the one you will always experience. Thus, if quantum theory is true, and it appears to be rock solid, I will ALWAYS and forever be observing and recording my own continued existence. I will see everybody else die, but never myself.

And what goes for me goes for all the other people too. In the Universe they end up in, they will see me die, but never themselves. Can anyone put a hole in this? You will need to know a little about Copenhagen Interpretation of Quantum Theory.

It’s a bit like the basic idea in the film “The Prestige”. SPOILER ALERT! When the magician gets access to a cloning machine, he makes a clone of himself each night as part of his act, and destroys the clone during the act. Now, the two versions of the magician are identical, but each night one of them dies. Nevertheless, the magician’s life and memory carry on unimpeded, because there is always ONE of him left over. Now think of the man in Schrödinger’s box. He would see the experiment that has a 50/50 chance of killing him played over and over, and yet each time he finds himself alive. Like tossing a coin hundreds of times and always coming up heads. In the wider reality, a version of him perishes each time the experiment is done. The existential reality of his life has continuity because if is carried forward by the surviving copy. Myles325a 06:46, 16 August 2007 (UTC)

Sounds something like Wigner's friend. DMacks 06:53, 16 August 2007 (UTC)

Take a look at quantum immortality. It all depends on how you interpret quantum mechanics. It's a clever idea, by the way, even though other people have thought of it before. --Reuben 07:03, 16 August 2007 (UTC)

Actually sounds more like Russian Roulette. You can play and write down whether you live or die. You will never write down that you are dead. But that doesn't mean you live. Plus, you treat death as a single event rather than a sequence of discrete failures of body systems. What you will see in your scenario is your body and brain failing in sequence on a march until death (i.e. heart fails, levier fails, muscles fail, stomach fails, etc). Your scenarios is most likely a fate worse than death as you continue to live in a less and less capable shell. --Tbeatty 07:06, 16 August 2007 (UTC)

I don't know about the quantum mechanics aspect, but one thing seems hard to deny, "I will see everybody else die, but never myself." Still, never seeing yourself die doesn't necessarily mean "I will ALWAYS and forever be observing and recording my own continued existence." As an analogy, consider falling asleep. Replace "dying" in this thougt experience with "falling asleep". Does it follow that not observing your own falling asleep means you are forever awake? Pfly 07:20, 16 August 2007 (UTC)

You might also be interested in solipsism. It's perfectly rational that I am immortal --Lucid 11:23, 16 August 2007 (UTC)

I've thought a lot about this - and certainly what you describe seems possible within our present understanding of quantum mechanics. There are other interpretations of what we know that says it isn't true - but I'm not aware of any science that says it's impossible. A way to have personal immortality without messing around with all that religious stuff about after-lives initially seems very attractive and comforting. But remember that the 'anthropic principle' is the only thing that ensures that "you" always end up in the universe where you are still alive. But you only have to be sufficiently alive to "observe" events - and things around you would go on as normal. This principle won't prevent non-fatal injury so expect to lose arms and legs in car accidents - but to somehow always survive. You can lose your eyesight - your hearing - your sense of smell and touch. Everyone and everything around you can fizzle out. So you could be the only thing left alive in the universe - with just a portion of your brain operating and essentially nothing else - you could be in continual anguished pain and have no way to end it because anything you could possibly do to kill yourself will always fail. You're being kept alive by a continual series of increasingly unlikely coincidences - you can be starving and on the point of dying of thirst - and every thousandth of a second (say) just enough nutrition and water will appear (somehow) to just keep you alive for another thousandth of a second. After a couple of hundred years of life - you are going to be in the most terrible state imaginable. This is more like the classical vision of a personal hell than it is of immortality "the good way". We'd all better hope this isn't true. But read quantum immortality, quantum suicide, Final anthropic principle for more information. SteveBaker 11:44, 16 August 2007 (UTC)

Well, that's obviously wrong, your claiming its impossible to die if nobody is recording it. Also, you'll die of natural causes anyway, even if the box doesn't kill you you'll still die. ΦΙΛ Κ 18:20, 16 August 2007 (UTC)

Closed Time-Like Loops

Hypothesized to exist philosphically/physically when the big bang(big crunch) creates(destroys) time due to the nature of anything leading up to the big bang not affecting our current universe, and in the negative radius of of a spinning black hole's circular singularity, closed time-like loops go-on and reapeat to infinity. If relative time, or true time, were to play back a "recorded version" of a seemingly infinite loop, one would find a beginning other than the one seen repeated infinitely in the loop. As in the case of the black hole, it would be the infalling energy or space in our real universe outside the horizon. My question is, in the case of the universe, what would I find? Borahborah 10:15, 16 August 2007 (UTC)

Iron pentacarbonyl

What technique is used to detect trace level of Iron pentacarbonyl in gases ? 71.199.170.8 10:53, 16 August 2007 (UTC)

Mass spectroscopy might be a easy one.--Stone 11:01, 16 August 2007 (UTC)

FT-IR is another.87.102.66.173 12:05, 16 August 2007 (UTC)

Depends how trace is "trace", what else is in the gas, whether it needs to be on-line or can be an off-line sample, whether it can be destructive testing, etc. Googling for "iron pentacarbonyl" detection gives some good refs for some applications. DMacks 15:06, 16 August 2007 (UTC)

cities

which is the worlds most technologically advanced city — Preceding unsigned comment added by 41.207.68.129 (talk • contribs) 12:05, 16 August 2007 (UTC)

Tehachapi, California.

(That's a wrong answer, btw, but it's not much more wrong than any of the "right" answers you're likely to get. The question is impossible, of course; there's no one right answer. We can't even say what the world's longest or tallest bridge is; how can we possibly determine the "most technologically advanced" city?

What do people think they're looking for when they ask these questions? There's an implicit notion that any attribute of any entity can be reduced to a simple, objective, linear scale. It's at best a goofball, and at worst a dangerously misguided notion -- why is it so prevalent?)

—Steve Summit (talk) 12:30, 16 August 2007 (UTC)

It's prevalent because most mainstream educational systems are very effective at destroying the capacity for original thought, and insist on a single "right" answer for any question. DuncanHill 12:43, 16 August 2007 (UTC)

Is this a reference desk or a pie throwing contest? Bendž|Ť 14:56, 16 August 2007 (UTC)

...KERSPLAT!!! - gotcha! Hehehehehe! SteveBaker 16:37, 16 August 2007 (UTC)

There are things for which a simple one-dimensional scale is possible - but this isn't one of them. It's not even clear what the question is. For example, are we asking which city produces the most advanced technology - or the city that uses most? Are we looking for the most widespread use of technology (measured, say by the city with the highest cellphone usage) - or the single most advanced single use (eg: Which city has the most advanced Particle accelerator)? It's really not a very answerable question. SteveBaker 16:37, 16 August 2007 (UTC)

While I agree with the above, about never being able to answer the question fully, since we don't know what that even means [27], I'm going to have a go at offering some examples.

• According to the BBC, Tallinn appears to be among the most technologically advanced cities in Europe. [28], While Birmingham ranked top for "eGovernment" [29]
• Popular Science "weighed dozens of variables, from the number of homes with wireless internet to the number of robotic surgeries performed at local hospitals, to rank U.S. cities by tech quotient". Their overall ranking was [30]:

1. Minneapolis-St. Paul
2. Atlanta
3. Washington D.C.
4. Boston/Cambridge
5. San Diego

• Some magazine list Shanghai or Tokyo as the most advanced, wile others cite purpose built "cities" (although most of them are really towns or suburbs, certainly much smaller than a regular city) like New Songdo City and Cyberjaya. Rockpocket 18:39, 16 August 2007 (UTC)

Redmond, it has Microsoft. :-) --S.dedalus 22:27, 16 August 2007 (UTC)

Dream question

I remember a little bit of a dream I had last night in which I was going to say the name of a running back who plays for the Chiefs (I would explain why, but it would make even less sense) and another guy in the dream said "Priest Holmes!" before I could think of his name. And that's who it was! I kind of assume that my thoughts in dreams are at a more conscious level than whatever it is that is making all of the other stuff (other people, places, events, etc.). Is that a good assumption to make? If so, how did my subconscious know before I did? Are there Wikipedia articles that address the difference between "self" and "other" in dreams? Recury 13:39, 16 August 2007 (UTC)

I think that's a really good question. Dream_interpretation says that Jung considered others in dreams to represent parts of the self. But I'm not aware of any discussion about how the brain seems able to simulate multiple others with enough complexity as to seem conscious and with access to memory, all without these others sharing the consciousness of the dreaming person. --Allen 14:47, 16 August 2007 (UTC)

Unless of course Recury knows the other guy in real life, which means his brain would not have needed to create too much SGGH ^speak! 19:44, 16 August 2007 (UTC)

Inhibited self control is a common dream issue. It is usually an inability to walk. It can also be an inability to do things such as open a door or start a car. Similarly, it can be an inability to speak. When this occurs, it is normal for other entities in the dream to continue as normal. Therefore, you had an inability to think of a name while another entity in the dream could think of the name normally. All in all, it is a normal dream. As for what it means, that is debatable. I've usually heard it interpreted as a lack of self esteem. -- Kainaw^(what?) 19:12, 16 August 2007 (UTC)

Nero mammoths

These beasts appear in the Prehistory section of two articles, History of Kansas and History of Arizona, and seem to have sprung from the same source. Would anyone have any idea what "Nero" refers to? (The answer may have nothing to do with any kind of science, in which case I apologize for the intrusion on this reference desk.) - Mu 15:52, 16 August 2007 (UTC)

No idea; the only google links are Wikipedia. Probably should be removed. Geologyguy 16:06, 16 August 2007 (UTC)

The phrase was added to the Kansas article on September 27, 2005 by User:Reddi, who is a major contributor. I will remove the instances in both articles, and leave a note for Reddi. Flyguy649 ^talk _contribs 16:20, 16 August 2007 (UTC)

"Sashimi Grade" fish, and parasites and other nasties

About once a week I go past a prominent fish-shop and ask them if they have any "Sashimi Grade" salmon or tuna- and when they say they have stock, I order, and they go into the back and come back with my order. However, what is totally killing the fantastic sashimi experience, is my paranoia over parasites and other nasties.
Some questions not addressed in the sashimi article:

• If something is "sashimi grade" fish, does that sort of guarantee that it's been frozen, or just that the fish is of a high quality? Or does it only refer to the "cut" of fish - the part of the fillet with the most oil (as one fishmonger I spoke to claimed "It's just about the cut")?
• After buying "sashimi grade" fish, are you still expeced to thoroughly check the meet for any sign of parasites?
• Is there some resource that I can use to educate myself on all the possible little things to look out for?
  

Any knowledgeable answers would be appreciated.
Rfwoolf 17:36, 16 August 2007 (UTC)

Banana skins

I would like to know why banana's are typically eaten without their skins, as I prefer to eat them whole, as I don't like the mushiness/softness of them without the hard skin to contain them. Could anybody tell me why the skins are not eaten? Thanks 81.110.75.212 17:48, 16 August 2007 (UTC)Steven

This may vary with both the eater and the variety of banana - I personally have tasted banana skin and found it bitter. DuncanHill 17:53, 16 August 2007 (UTC)

Thanks, so it's just a matter of taste rather than there being anything poisonous to humans in them?81.110.75.212 20:44, 16 August 2007 (UTC)Steven

Just make sure to wash them thoroughly. Since the skin isn't generally eaten, I suspect handlers and vendors are less concerned about cleaning the fruit than might otherwise be the case. But then, washing fruit before eating is always a good idea :) GeeJo ^(t)⁄_(c) • 22:15, 16 August 2007 (UTC)

cytochrome c measurement

Hi, my question is related with the measurement of cytochrome c from canine blood. So far we have tried using HPLC but because of the high amount of proteins on it the life time of the columns gets short. Besides the results are variables and so the standar peaks. ELISA would be a good idea but seemenly there are some proteins binded to cytochrome c and its use could not be meaningful. according with some papers we should have to dilute the samples and at the same time dilute the cytochrome c. What do you advice me? Thank you very much,

Pedro Vargas — Preceding unsigned comment added by Pitvarpin (talk • contribs)

troubleshooting

i would like to now hints on how to troubleshoot an electrical line.≠41.219.216.183 21:17, 16 August 2007 (UTC)

Very carefully. You should probably not troubleshoot an electric power line if you are not a trained electrician because high voltages and currents in electric power lines can kill you. Call an electrician. If you are seeking a long-term solution, you might consider one of the various engineering disciplines or a vocational training as an electrical technician. Nimur 21:34, 16 August 2007 (UTC)

You may wish to document carefully what is the problem - eg no power form a power point - which ones, circuit breaker popping, lights too dim, overheating in part of the line. You can unplug all your appliances from power points and then plug in one by one to see when the problem appears. (Divide and conquer algorithm) What kind of electrical line are you talking about? Graeme Bartlett 23:37, 16 August 2007 (UTC)

Most stores (Walmart, KMart, Target, Home Depot, Lowes...) sell a device that looks like a pen. When AC current is near the tip, it will flash and beep. This is handy (and relatively safe) for non-technicians to use. Buy one (they are not expensive). Put it near an outlet that has power. Notice that it beeps. Now, go to an outlet that you don't think works. If it beeps, the outlet is working - it is some other problem (perhaps the outlet is wired wrong). If it doesn't beep, go to the switch for the outlet. Does it beep? If so, the switch is most likely bad. If not, follow the line to the next part - usually the breaker box. Note that this can also be used to see if there are power lines behind the wall. You can follow a live line by tracing the beep along the wall. Since you never actually touch a wire, it isn't too dangerous. -- Kainaw^(what?) 23:47, 16 August 2007 (UTC)

Birth of a seagull

Does anyone know where I can find a video of a seagull egg hatching? --84.65.110.20 22:36, 16 August 2007 (UTC)

Youtube here [31] DuncanHill 22:45, 16 August 2007 (UTC)

Man, I was looking on YouTube for more gull hatching vids and I found this one. That's just pure evil. Why the hell would someone do that - *and* be stupid enough to post it online? Does anyone live in Gibraltar here? The person who made that video should be reported to the local police. F-ing dirtbags. --Kurt Shaped Box 23:19, 16 August 2007 (UTC)

I too found that one. I reported it to Youtube as inappropriate. Was really rather vile. DuncanHill 23:23, 16 August 2007 (UTC)

I'm honestly shocked. I mean, what was the point of that? Those kids belong in a detention home. If those were British kids, I'd be forwarding that video to the authorities - people have gone to jail here for doing that sort of thing. --Kurt Shaped Box 23:29, 16 August 2007 (UTC)

They appear to be breaking Section 3 of the Nature Protection Act 1991. [32] DuncanHill 00:45, 17 August 2007 (UTC)

And the Royal Gibraltar Police have now been notified. DuncanHill 00:54, 17 August 2007 (UTC)

Damn right. See my post on your talk... --Kurt Shaped Box 01:03, 17 August 2007 (UTC)

Dangerous love

Is there any evidence of a link between sexual/romantic activity and immanent physical danger in humans? Judging from books like “For Whom the Bell Tolls” there is a positive link. Are there any real world examples of, for instance, a surge in marriages during The blitz, or a surge in sexual activity in people suffering from the early stages of terminal diseases? Last question, does Wikipedia have an article on this, and if not what could it be called? Thanks! --S.dedalus 00:35, 17 August 2007 (UTC)

Anthony Burgess touches on this idea repeatedly in many of his novels, but I don't know if there is a formal term or even if there has been any scholarly research. DuncanHill 01:53, 17 August 2007 (UTC)

Shape of the eye

I was told that prolonged wearing of glasses would cause the eye to bulge due to the eye's adaptation to the peripherial lenses. However, there is this thing I don't get. Glasses are supposed to fit your degree of near/far-sightedness, and should not require your eyes to deform to achieve focus. What's more is that (well, this I base on a speculation) if the eyes deform due to their seeking for the focus, people who are near/far-sighted and who don't wear glasses should have more or less the same problem shouldn't they?

Uh... I think whoever told you that is probably wrong. Sometimes people's poor vision is caused by bulging eyes, but I'm pretty sure that glasses themselves don't make the eyes bulge. --24.147.86.187 01:45, 17 August 2007 (UTC)

Chemistry and Botany

Dear Wikipedia,