Science desk
< May 28	<< Apr \| May \| Jun >>	May 30 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

May 29

Black Body Radiation

At what rate do things like man-made satellites, space ships, and planets radiate electromagnetic energy?

I know that's a very general question, so I'll give some background. I was thinking about man-made satellites and space probes. Satellites have electronics in them, and in those electronics are batteries and resistors. So since batteries have a resistance and current runs through them, there will be a certain amount of heat energy coming from those electronics. So it seems to me that since there's no air for the satellites to radiate their heat energy into, they'd either overheat or they'd have to radiate electromagnetic energy to cool down. So for something like a satellite, how much power can they radiate in the form of electromagnetic energy? Is this referred to as albedo? And do satellites have to run on very low current or can they run with current similar to personal computers? Jolb 00:53, 29 May 2007 (UTC)[reply]

Satellite electronics are similar to ground electronics with a few major differences. They must be radiation tolerant; they must be low-power; and they typically have failsafe mechanisms built in to "reboot" in case of failure. What this typically means is that the upper boundary of available components for satellite applications are a few months or years behind the "cutting edge" ground systems (slower processors, less memory, etc). What they lack in "benchmark" performance specs, they make up in reliability, low-power consumption, and ability to function in space. As far as cooling: some amount of heat is clearly radiated away (see thermal radiation, which can occur even in total vacuum). Some satellites also have cooling systems or heat exchangers. Although it varies for each spacecraft, it is probably safe to say that there is more heat gained due to solar radiation than due to the internal electronics. Nimur 00:58, 29 May 2007 (UTC)[reply]

Mmm... I think heat exchanger doesn't describe what goes on in vacuum. Satellites, manned or otherwise, can have some very elaborate radiators, however. Gzuckier 19:09, 29 May 2007 (UTC)[reply]

You're right that that's a very general question, and the answer, as you might expect, is also very general.

Satellites usually have a heat rejection system, not only because their internal circuits etc. generate heat but also because the side that's facing the sun tends to get very hot. Heat is generally lost using a space radiator (redlink! that needs fixing!) which rejects heat to deep space even if it's subject to an environmental heat input on its surface. Electrical equipment is mounted on cold plates and heat transferred from these to the radiators using heat pipes. The heat rejection of a space radiator can be estimated using:

G_{s}\alpha \cos \theta +{\frac {Q_{w}}{A_{r}}}-\sigma \epsilon T^{4}=0

where

G_{s}=

solar flux

$\alpha =$ surface absorptivity

$\theta =$ angle between surface normal and solar vector

$Q_{w}=$ waste heat rejected by radiator

$\sigma =$ Stefan-Boltzmann constant

$\epsilon =$ infrared emissivity

T=

operating temperature of radiator (Kelvin)

Satellites tend to use a little power as possible, because more power usage means more weight of power generation and control systems, which means more cost (both development cost and launch cost are dependent on weight). Satellite powers range from very low (a couple of hundred watts or less) to very high (multiple kilowatts). An average medium-sized spacecraft consumes about 1kW in total, which accounts for the requirements of the instruments plus propulsion, stabilisation/control, communications, thermal control etc. Hope that helps a bit. --YFB ¿ 01:30, 29 May 2007 (UTC)[reply]

There is abundant energy available to a satellite from the sun via photovoltaic panels which receive over a kilowatt per square meter, and which weigh from .5 kg to 10 kg per kilowatt per Solar power satellite. 12% efficiency would yield over 100 watts per square meter. Our article on the International Space Station says nothing about the amount of power available, but [[1]] says it has about an acre of solar panels and [[2]] says the solar panels plus rechargeable batteries for when they are in the shade make 110 kilowatts available. The ISS uses liquid ammonia radiators to eliminate the waste heat from the systems. Edison 15:43, 29 May 2007 (UTC)[reply]

The whole topic of cooling in a vacuum is a nontrivial subject. I recall an SF story from my youth with the somewhat inept hero on the moon cheerfully mixing up an entire barrel of epoxy at one time. All the experienced hands run for cover because a few minutes later... kablooie. Heat of the chemical reaction in that volume built up too fast for radiation to keep it down to a non-kablooie level. Gzuckier 19:09, 29 May 2007 (UTC)[reply]

My cooler pump???

hey friends i,ve bought a water cooler pump but it isint working well.at times when required supply is given then also it dosent works and produces some humming sounds or moves with low speed.after giving it a break of about 15mins it again starts working.can any1 give me wats exactly wrong with it.. as a solution should i fix some timer circuits in it(i do have timer of 1 minute cycle) 0663Sameerdubey.sbp

Could it be overheating, which causes it to shut down to protect itself from damage ? StuRat 04:29, 29 May 2007 (UTC)[reply]

That's a reasonable suggestion - but I don't think it works because the pump is humming and/or moving slowly. If it was a thermal cutout or an overvolt protection circuit or some kind of stall protection, it would just shut off. I think we need more information. What is this water cooler pump for? Can you give us an idea of how big it is - what current it draws, etc?

Does it need to be primed? --Tbeatty 05:15, 29 May 2007 (UTC)[reply]

If it did, why would waiting 15 minutes help? SteveBaker 13:43, 29 May 2007 (UTC)[reply]

exactly it is a 240V water pump with no overheating cutoff type circuits in it.actually it is a simple ac motor with a long shaft and veins fitted on the other end to lift water.such motors are sometimes used in small ventilator exhausts. Sameerdubey.sbp0663

It's probably an "induction" electric motor. Such motors can fail for several reasons:

Failed bearings; they may overheat and thermal expansion causes them to "sieze up". Later, when they cool, there may be enough clearance to allow the motor to turn again for a while.
Failed starting circuitry. Single-speed induction motors often have a centrifugal switch that controls the starting. If thaat fails, the motor won't start turning, will usually hum loudly, and will rapidly overheat, tripping the termal protection device.
Too much load (but this seems unlikely in a pump)
Too little voltage (leading to a higher-than normal current draw and no starting or overheating). This may also be caused by too long a mains lead causing too much voltage drop in the wiring.

In an existing application that used to work, I'd guess that the fault is bad bearings or a lack of lubrication of the bearings.

Atlant 16:27, 29 May 2007 (UTC)[reply]

Space Elevator

I was reading the Space Elevator article and stumbled upon the fact that as the cable increases in hieght it mus increase in diameter, then it goes on to explain this could be avoided many various ways, but one the fact which intrigues that if you had a tower 100km tall then this would reduce Diameter increase. I was curious if an airship station was 100km in the air could the cable be attached to that?67.127.167.131 04:53, 29 May 2007 (UTC)[reply]

The problem with cables is that attach point/top of the cable has to support the weight of the cable. Think of the top layer of molecules of the cable being pulled on by the entire weight of the cable below it. there is a material science problem with creating a cable that could support 100 km of weight. How much does a 100 km of cable weigh and what is the tensile strength of the material? --Tbeatty 05:10, 29 May 2007 (UTC)[reply]

100km is far too high for any type of airborne object to support a large weight. The atmospheric density in 100km is so low, that you can do orbital flight in that height. I really dislike the space elevator article, it gives a lot of "back of an envelope" calculations concerning the physics, but it has little consideration of engineering. For example 100km is more than two orders of magnitude larger than the highest tower ever built, and that tower had to support some radio dishes, not a giant cable.

The odd thing about the space elevator (at least in it's most common incarnation) is that the cable is self-supporting. The idea is that centrifugal force one one end of the cable (which is higher than geostationary orbit) exactly counterbalances the gravitational forces on the section that's below geostationary orbit. There is an equation (see Space_elevator#Cable taper) that relates the tension in the cable to the distance above the ground - and in order to make the thing work at all, the cable has to have a fairly complex shape such that it tapers just enough to take the strain at each point - this is called the "taper". A cable supported entirely under gravity also has a variable tension - but it's not the same as in the elevator. Certainly you can dangle a cable under an airship - but the size of the airship needed in order to support 100km of cable would be utterly immense (not to mention that there isn't any atmosphere at 100km - so you can't possibly fly an airship that high). With a tower, the entire structure is in compression - so the structure has the most weight to bear at the bottom - so tall towers are commonly thicker at the base than at the top. But a cable dangling under an airship is different - it's in tension and the most tension is at the top - so ideally you'd want a cable that thick at the top and very thin at the bottom. The space elevator is a completely different beast - in an idealised form, it just floats there - it doesn't have to be anchored to anything at the top, middle or base! In practice, they'll probably shorten the segment that's above geostationary orbit and replace most of it with a counterweight - but the counterweight is a waste of resources - it might be better to have the elevator simply stretch out further and be it's own counterweight. Consider how the elevator would be constructed: The entire cable would be spooled up into a large satellite and launched into geosynchronous orbit using a conventional rocket - then the satellite would proceed to unspool the cable symmetrically - both up and down at the same time(!) - allowing the outer end's increasing centrifugal force to counteract the lower end's increasing gravitational tug in order to keep the satellite balanced in geosynchronous orbit. As the cable unspools, either a ground station (or more likely, a ship) would see the cable end literally drop out of the sky! In principle - there would be no tension whatever on the lower end of the cable. In practice, the effect of the wind on the cable would be considerable - so a large mass is needed on the bottom end in order to stop it flapping about and causing nasty instabilities. SteveBaker 13:23, 29 May 2007 (UTC)[reply]

Wouldn't the point at the middle of the cable (from where this satellite would unspool it) be under a massive amount of tension (with the half above pulling upward and outward, and the half below pulling downward)? Or is that fixed by the taper? Neil (►) 17:38, 29 May 2007 (UTC)[reply]

No, you're correct. The tension would be highest in the middle, and lowest at the two ends. The cable must taper to its widest point there. TenOfAllTrades(talk) 19:15, 29 May 2007 (UTC)[reply]

Yep - exactly - the cable (which is actually generally imagined to be a flat ribbon so that the elevator cab can get a grip on it) gets widest at geosynchronous orbit - and thinner at either end. The snag is that there are no existing materials that can do the job. We need carbon nano-tubes of sufficient length to be woven into some kind of a composite material - but we can't make them long enough or cheaply and in sufficient quantities yet. There are numerous other problems with the Space Elevator concept - not the least being that it's unlikely that humans will ever be able to ride in it because it moves too slowly and we'd be slowly cooked as we passed through the radiation belt. The necessary amount of shielding would weigh too much for the cable to support. Incidentally - if you think the space elevator is a daring and exciting piece of technology - check out the space fountain and the space rotor (for which we don't appear to have an article?!) SteveBaker 22:43, 29 May 2007 (UTC)[reply]

I can just imagine how it'd be to be in that elevator when it malfunctions. "Hi, Mr. *beep*, we can't get a support team up there. Sorry. *click*" --Wirbelwindヴィルヴェルヴィント (talk) 01:46, 30 May 2007 (UTC)[reply]

I suppose you could parachute out of the thing wearing a suitable spacesuit - remember - you aren't travelling at ungodly orbital velocities and you aren't in zero G until you approach the altitude at which the cable is in a geostationary orbit - but as I explained before - humans can't use the elevator because it takes too long to travel through the dangerous radiation belts and so you'd be cooked on the way up. The issue is only whether a cargo elevator might get stuck. I don't know what they've planned for that. SteveBaker 19:13, 30 May 2007 (UTC)[reply]

Parachuting from space involves the minor problem of burning up like a meteor when you reach the atmosphere. You would keep accelerating until you hit air – there is nothing else to slow you down – so by that time you would be moving quite fast and the parachute would be of no use at all. Think about the insulating tiles on the underside of the space shuttles, and how they glow red on re-entry. Also, if your jump-off point was high enough, you would find yourself in an elliptic orbit and never reach Earth at all. --mglg_(talk) 21:15, 30 May 2007 (UTC)[reply]

Allergies

Ok, so I'm not supposed to ask medical questions. But answer me with something, resources, or whatever you please.

One of my friends as a strange type of allergy—doctors said they were normal, seasonal allergies, like to pollen. But she has them year-round, and they involve total body itching, as well as inside the ears and throat. That doesn't seem like any type of normal allergy that I know about that isn't from food, or more exposure. Perhaps she is just extra-sensitive? [Mac Δαvιs] ❖ 06:37, 29 May 2007 (UTC)[reply]

Total body reactions are not so uncommon, see Atopy. If you are exposed to the allergen all around the year, you will have the symptoms all around the year. This can happen for example if you react to the excrements of the House dust mite. If your friend is in doubt about the source of her allergy she can do a RAST test. This test is more reliable than skin tests. Oh, and please don't ask me why I know all this (*sneeeeeze*).

If the RAST test does not work, try the homeopathic remedy: the QX machine. This is an amazing machine based on NASA technology that can pick up allergens in your body (amongst a whole host of other problems) and can help you to treat yourself. Of course if your environment contains something like toxic mould, just be glad that you identified it and you could run away from it in time. Sandman30s 13:53, 29 May 2007 (UTC)[reply]

Amazingly there is an article (not a very good one) on that here: Qxci - could an admin please rename this to QXCI and I will edit the article? Sandman30s 14:06, 29 May 2007 (UTC)[reply]

"Based on the principles acupuncture, homeopathy, quantum physics, and electronics". Are these people for real, or is it a genuine hoax?

It is a very real, and very good machine. My family and many others have made use of consultations with homeopaths who use this machine. Sandman30s 14:39, 29 May 2007 (UTC)[reply]

Wonderful. That text has everything. Health, latin terms, experts, statistics, contradictions, spirituality, quantum mechanics, brain waves. The list is endless. Nobody will *ever* believe me that I didn't made that up myself.

I sent it to Quantum Xrroid Consciousness Interface per style. Nothing links there and the machine is obvious quackery, but it does get 10,000 G-hits, so I can give it the benefit of a doubt on being encyclopedic. Incidentally, pages may be moved by any logged in user - be bold! Eldereft 17:11, 29 May 2007 (UTC)[reply]

Well, thanks to the first guy. Any other comments? [Mac Δαvιs] ❖ 20:10, 29 May 2007 (UTC)[reply]

I resent all these comments about hoaxes and quackery. I am being totally serious when I say that I have had first hand experience with this machine. You people can carry on going back to your allopathic doctors and stuff yourselves with antibiotics and drugs, but I know what has worked for my family. We have not had antibiotics for two years. This is from a point when my hyper-allergic son was getting pumped with antihistamines, steroids and antibiotics every two weeks. Those who refuse to believe that there is "alternative healing" can remain in their un-enlightened state for all I care. Sandman30s 08:26, 30 May 2007 (UTC)[reply]

Sandman30s You aren't allowed to give medical advice on Wikipedia - especially on the help-desks - even hoaxes and quackery like this one. The machine is obviously completely bogus - I don't know whether you have a financial interest in promoting this bullshit - or whether you are simply experiencing a placebo effect - but you aren't allowed to do it here. Promoting pseudo-science is definitely not what we're here for. SteveBaker 11:49, 30 May 2007 (UTC)[reply]

I can't believe I'm getting this reaction. Somebody ASKS for advice on allergies. I GIVE advice that has worked for me. And I get summarily dismissed as a quack. What's more, how can you people dismiss this as bogus/quack whatever? "Sufficiently advanced technology is indistinguishable from magic". Or quackery as you put it. So what if Star Trek science is here today? Dismiss it and call it bogus? I am NOT promoting a product otherwise it would have a brand name. I am merely telling the OP what has worked for me. Interesting you talk about the placebo effect - funny that doctors who cannot understand how alternative medicine WORKS always call it that. Allopathy vs homeopathy will ALWAYS be a debate because it boils down to economic competition. But you just cannot shout out that homeopathy does not work? My aunt is an allopathic doctor with MbChB but she readily admits that alternative medicine works better in SOME cases. I am NOT saying this QX machine is a panacea! It works for SOME THINGS like allergies! Do some research first before making closed-minded comments. Sandman30s 14:06, 30 May 2007 (UTC)[reply]

And something further that all you scientific critics might be interested in. This machine was invented by a NASA engineer. This machine was used in the original space programme to scan astronauts at cellular level before they entered space and after they returned from space. They had to invent this technology because NASA had a need for it. Now decades later this technology has gone mainstream and is being used by homoepaths. Personally I am one of the biggest critics of technology, but the when I saw the results of the machine's scan, I was amazed. The proof was in the pudding. How can a diagnosis be related to placebo effect? It told me about my energy levels, hydration levels, etc, etc, and conditions that I had - by scanning at the cellular level and beyond. Sandman30s 14:34, 30 May 2007 (UTC)[reply]

Don't feed the trolls...

Now, what did you mean with "other comments". Are you looking for other possible causes for an itching body or more information on allergies?

Heat and Waves ??any relation

hey friends ...in waves the energy disappears at trough and appears at crest ... if sound waves are made to travel in a heat transfer pipe then can we expect any change in heat transfer rates by the pipe. we may consider equal energy appears and disappears at crest and trough but crests might be thought to transfer energy to boundary of tube.and troughs interact with fluid in the vessel. orr if i perform the experiment in a open vessel ment for transferring heat. a double chambered vessel in series

                                              _ _ 
                            sound waves->----1 1 1
                                             1-1-1

0663Sameerdubey.sbp

(Fixed formatting so we can read the question!) SteveBaker 12:55, 29 May 2007 (UTC)[reply]

I disagree with your very first premise - energy doesn't "appear and disappear", it just changes form. Consider a water wave. At the peak of the wave the water is almost stationary - and it's higher than the average level of the water. It has gravitational potential energy. As the wave moves on, the water rushes downwards and forwards into the trough - at which point it's moving quickly - but now below the average level of the water. It's lost gravitational potential energy and gained kinetic energy. No energy is lost in the process - it's merely transformed from one form to another. The effect is much like a pendulum swinging - gravitational potential energy at the ends of the swing when the pendulum bob is moving slowly - kinetic energy in the middle of the swing when it's moving quickly. In sound waves, the trade-off is between kinetic energy and pressure. It's always just energy changing form - not being gained and lost. In the case of sound waves moving along your heat pipe, when the air (or whatever fluid you are using) is compressed, it'll heat up - when it decompresses again, it'll cool down. If you take away heat from the high pressure regions then I guess you'll dampen down the sound wave because as you cool the fluid the pressure will decrease making it less able to gain kinetic energy. So I suppose you could (in principle) deaden the sound and extract a little energy from it in the form of heat. But it's going to be tricky (or perhaps impossible) in practice because as the sound travels along the pipe it's alternately heating and cooling your heat pipe. Thermal inertia being what it is, I don't think your apparatus would work as a practical device. SteveBaker 13:04, 29 May 2007 (UTC)[reply]

I think it might-- see [3]

Yup. I used to read about these kinds of things in Popular Science 50 years ago. Gzuckier 19:13, 29 May 2007 (UTC)[reply]

A psychological experiment where half of the subjects took on the role of a guard and the other half the role of prisioners

I believe, if I am not mistaken, that several psychological experiments took place at major universities where 1/2 of the test subjects were given the role of guards and the other test subjects that of prisoners. To pinpoint exactly what I am looking for the experiment I am seeking was held in the confines of a prison-like atmosphere. 1/2 of the test subjects acting as "guards" (I believe, they were taking on the role of a brown shirt within the now defunct Nazi Regime). The other 1/2 of the test subjects were their prisoners. I recall, that the controls of the experiment were very loose allowing the test subjects acting as "guards" many freedoms over their prisoners.

The experiment showed how easily one can be manipulated in whatever direction the researchers wished them to be.

I am sorry as I cannot supply any more information than the aforementioned, nor the universities where these experiments took place. The experiments took place a number of years ago perhaps in the 90's.

The experiment would be similar to Golding's study of human behavior in his novel: "Lord of The Flies."

I thank you for your time and effort.

Antony baekeland 12:02, 29 May 2007 (UTC)[reply]

See Stanford prison experiment and Milgram experiment. There may be others. Anchoress 12:08, 29 May 2007 (UTC)[reply]

You might want to read around Jane Elliott who did a similar exercise (although a lot less violently) showing how discrimination can so easily come about based on almost ANY criteria you could come up with. Her experiment has been repeated dozens if not hundreds of times. Also, see The Third Wave for another kind of experiment. What's chilling about these things is not just that they work - but that they work so strongly that they tend to get wildly out of control. SteveBaker 12:24, 29 May 2007 (UTC)[reply]

Also Strip Search Prank Call Scam - very weird. SteveBaker 13:41, 29 May 2007 (UTC)[reply]

I remember seeing a film (Das Experiment) that fitted the criteria, and lo' and behold, it led me to the Stanford prison experiment. Icthyos 20:30, 29 May 2007 (UTC)[reply]

Seagulls

Recently I saw 2 seagulls. One was standing on the others back and sqwaking loudly, the one under neath was sqwaing more quitly in higher pitch. The on on the top was balancin using its wings. What were they doing?

This question should be moved to the Seagull Reference Desk, but that seems to be missing. Also, they were making more Seagulls. --Cody.Pope 14:00, 29 May 2007 (UTC)[reply]

They were 'making fuck', as an old friend of mine from India used to say... --Kurt Shaped Box 14:37, 29 May 2007 (UTC)[reply]

If the original poster is correct in saying the one gull was only standing on the other, and no mating was occurring, could this be some type of dominance display ? StuRat 16:33, 29 May 2007 (UTC)[reply]

Do you realize just how much blood would be spilled if a gull tried to climb on the back of another gull without permission? ;) --Kurt Shaped Box 16:36, 29 May 2007 (UTC)[reply]

No, it's los mating. 81.93.102.185 16:38, 29 May 2007 (UTC)[reply]

The gull on top didnt seem to be accessing the rear of the the lower gull and I watched them for about 2 minutes (perhaps he was having erection problems?). How long does it take for a gull mating?

I don't think theirs even go erect. They have a thin twisty tube that deposits sperm. And it doesn't take very long, because like most other animals, they mate to mate, not to have orgasms. --Wirbelwindヴィルヴェルヴィント (talk) 01:39, 30 May 2007 (UTC)[reply]

About twenty seconds and neither party seems to have much fun, if they are like chickens. So far as I know, birds do not enforce dominance or restrict flock membership as social mammals do. Here and here are some pictures of gulls, including some voyeuristic ones. Eldereft 11:09, 30 May 2007 (UTC)[reply]

This is roughly what I saw with lots of Squawking. [4]

So they were just courting?--Tugjob 15:07, 30 May 2007 (UTC)[reply]

It may have been a post-mating thing. I've sometimes seen the male stand on the female's back for a while after the 'physical act of love' - sometimes he waits a while, gets his mojo back and has another go. --Kurt Shaped Box 21:40, 30 May 2007 (UTC)[reply]

Opposite of helium?

I was at a "mad science"- -type presentation, and the man demonstrated the effect of helium on his voice (making it higher). After that, he ingested another gas that had something of the opposite effect. However, I forgot the name of that gas. Would anyone have a clue what that may be? Ab e g92contribs 14:05, 29 May 2007 (UTC)[reply]

See xenon. --Kainaw ^(talk) 14:26, 29 May 2007 (UTC)[reply]

Sulfur hexafluoride? Video here - cool, huh? --Kurt Shaped Box 14:40, 29 May 2007 (UTC)[reply]

(double ec!) Anything heavier than air would work: xenon, argon, sulfur hexafluoride. Safety first! Even helium has killed people (although Darwin was an accomplice). --TotoBaggins 14:45, 29 May 2007 (UTC)[reply]

It's probably a bad idea to try it with radon... --Kurt Shaped Box 14:48, 29 May 2007 (UTC)[reply]

Or xenon. It's an anesthetic. Argon should be cheaper anyway: it makes up almost 1% of the air. --Anonymous, May 29, 2007, 23:03 (UTC).

Argon wouldn't work, as it is only marginally heavier than air (Molecular weights of Ar: 18, O₂: 16, N₂: 14). You wouldn't hear the difference. Sulfur hexafluoride on the other hand makes a dramatic difference (molecular weight 70). --mglg_(talk) 23:39, 29 May 2007 (UTC)[reply]

Thanks, silly of me to forget that argon is monatomic. The correct numbers there are 40, 32, and 28 respectively (you forgot the neutrons), but they'd still be close enough not to make much difference, I guess. (Anyone ever seen it done with argon?) --Anon, May 30, edited 03:47 (UTC).

Is there a heavier gas that's relatively safe to inhale, as a matter of interest? --Kurt Shaped Box 23:42, 29 May 2007 (UTC)[reply]

There is no gas heavier than SF6 apart from radon. CO2 is relatively safe to inhale. —The preceding unsigned comment was added by 88.109.29.179 (talk • contribs) 00:39, 30 May 2007 (UTC)

Well, "relatively" compared to, say, cyanide, sure. But you won't enjoy it. Concentrated CO2 is pretty nasty. --Trovatore 00:48, 30 May 2007 (UTC)[reply]

Yes as our article says:

Carbon dioxide content in fresh air varies and is between 0.03% (300 ppm) and 0.06% (600 ppm), depending on location (see graphical map of CO2 in real-time) and in exhaled air approximately 4.5%. When inhaled in high concentrations (greater than 5% by volume), it is immediately dangerous to the life and health of humans and other animals. The current threshold limit value (TLV) or maximum level that is considered safe for healthy adults for an 8-hour work day is 0.5% (5000 ppm). The maximum safe level for infants, children, the elderly and individuals with cardio-pulmonary health issues would be significantly less.

Indeed; please avoid inhaling pure carbon dioxide. You'll very rapidly lose consciousness, as the high concentration of CO₂ in the lungs will tend to displace oxygen from hemoglobin in the blood. It will also be a rather unpleasant experience during your few seconds of consciousness, as carbon dioxide will dissolve in the water coating your mucous membranes to form carbonic acid. (Think 'coating your lungs with a layer of club soda' unpleasant.) TenOfAllTrades(talk) 04:41, 30 May 2007 (UTC)[reply]

(outdent) Thanks, sulfur hexafluoride was what I was thinking of. Actually, after the guy inhaled it, he bent over to get it out of his lungs (he learned that the hard way, after he passed out ten seconds after he inhaled it in his first show). Ab e g92contribs 13:48, 30 May 2007 (UTC)[reply]

The Earths Atmosphere

Dear Sir or Ma'am,

IN your article on the Earth's Atmoshpere you wrote...

"For this reason, the Earth's current environment is oxidizing, rather than reducing, with consequences for the chemical nature of life which developed on the planet."

If hydrogen is able to escape the earths gravity and leek into outer space, thus oxidizing the Earth's current environment, what would those consequences be, specifically, for the chemical nature of life on earth as we know it.?

Thank You,

Eugene Rosenquest

H₂ does in fact rise to the top of the atmosphere and escape permanently, so the consequences would be... that things are the way they are now. Did you mean to ask what would happen if H₂ could not escape? —Keenan Pepper 15:28, 29 May 2007 (UTC)[reply]

The consequences of oxygen for life is major. It means that there is a high energy way to metabolise food using aerobic respiration. Without oxygen only microorganisms can cope. Some of these can make use of sulphur or other compounds containing oxygen instead, but less energy is derived. GB 06:53, 30 May 2007 (UTC)[reply]

ARUUN ques. about clitoris

what is the maximum size of human clitoris?

Read Clitoromegaly. Anchoress 14:39, 29 May 2007 (UTC)[reply]

The normal volume of it expanded from arousal is a little bit less than what it can be. [Mac Δαvιs] ❖ 20:13, 29 May 2007 (UTC)[reply]

Heavy gases and speaker enclosures

Is there any record of the use of 'heavier than air' gases being used in loudspeaker cabs to make them appear acoustically bigger?--Tugjob 14:55, 29 May 2007 (UTC)[reply]

Well, short answer: I never heard of such. Longer answer: would be difficult; obviously, cabinet would have to be completely gastight, and that causes problems as the outside atmospheric pressure rises and falls. Even sealed enclosure cabinets need a tiny hole to allow them to equilibrate. Otherwise, nobody could use them in Denver, for instance, unless they assembled them there. Gzuckier 19:17, 29 May 2007 (UTC)[reply]

If you enclosed the gas within flexible gas tight bags what then?--Tugjob 20:36, 29 May 2007 (UTC)[reply]

It seems to have been done: [5]. Search within the page for "gas". --Reuben 20:55, 29 May 2007 (UTC)[reply]

Puking up turds?

What's the medical term for the condition that causes the digestive tract to work in reverse, leading to the patient vomiting faeces from the mouth? I used to know someone that had this happen to him as a result of alcoholism and cancer. --Kurt Shaped Box 15:18, 29 May 2007 (UTC)[reply]

Copremesis. There's an article at fecal vomiting. --Joelmills 15:29, 29 May 2007 (UTC)[reply]

Antiperistalis [6]

Thanks guys. I've created a redirect for that redlink... --Kurt Shaped Box 20:52, 29 May 2007 (UTC)[reply]

This happened on an episode of [House]Llamabr 20:59, 29 May 2007 (UTC)[reply]

I don't remember watching that episode. I know that fecal vomiting was mentioned on South Park... --Kurt Shaped Box 21:11, 29 May 2007 (UTC)[reply]

Vented cabinet.

In a bass reflex cabinet, what importance does the cross sectional area of the port have? I thought it was just the volume of air in the duct that was important.--Tugjob 20:41, 29 May 2007 (UTC)[reply]

See diffraction for some details on wave interaction with an aperture. Nimur 22:11, 29 May 2007 (UTC)[reply]

I cant see how that applies to my question. Can you explain?--Tugjob 23:03, 29 May 2007 (UTC)[reply]

"Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. It occurs with any type of wave, including sound waves...." In other words, the size of the hole that the sound waves must travel through will "shape" the outgoing wave. Does this help clarify? There are mathematical treatments of this subject, which are discussed in the articles I linked (sorry, my aperture link was misspelled). Strictly conceptually, a different size hole will allow different frequency waves to pass in different ways. Nimur 03:02, 30 May 2007 (UTC)[reply]

Yes although diffaction is possibly going to occur, i dont see that as a problem to the operation of a vented box. Its only the lower frequencies (below driver resonance) that come out of the hole. So whats with the area as opposed to the volume?--Tugjob 11:03, 30 May 2007 (UTC)[reply]

Phase diagrams for mixtures of ethanol and water.

I recently asked a question about the boiling point of a mixture of ethanol and water, and its dependency on pressure. After some googling, I realised that what I actually was asking for is a binary phase diagram for a mixture of ethanol and water. The best I could find on an image search was this one (middle panel), which is what I'm looking for, but with very low resolution in my region of interest. This exellent tutorial explains how to read the diagram.

Is anyone able to provide pointers to a similar diagram, with better resolution in the range 78-100°C?
Is all the information I need for calculating boiling points and vapour composition at various pressures in the phase diagram, or does the phase diagram itself depend on pressure? The fact that the diagram ends at 100°C for pure water suggests the latter, since water would have boiled at a higher temperature if the pressure were higher than 1 bar. If indeed several phase diagrams are needed, does anyone have information about where to find them? My region of interest for pressure is from atmospheric to approx. 1.5 bar. --62.16.173.45 20:48, 29 May 2007 (UTC)[reply]

Sorry, I don't have a table to point you to. But the following may be conceptually helpful for the pressure question: At any given temperature, a given mixture of ethanol and water has a well-defined vapor pressure (or partial pressure) of ethanol, and a different vapor pressure of water vapor. The vapor pressures are defined as the gas concentrations that the fluid would be in evaporation/condensation equilibrium with. The vapor pressures do not depend on the actual external pressure. The fluid(s) will evaporate or condense until the actual concentrations of each gas is equal to the fluid's vapor pressure for that gas (which may itself change during the process because evaporation/condensation can affect the temperature and fluid mixing ratio). At a certain temperature, the total vapor pressure will equal the ambient pressure; this temperature is the boiling point, at (or above) which evaporation can take the form of bubbling. Increases in pressure by addition of a third, more-or-less inert gas (such as air) does not in principle change the vapor pressures, just the boiling point. --mglg_(talk) 21:37, 29 May 2007 (UTC)[reply]

Thanks again! Regarding the total pressure and partial pressures, I make the assumption that the only gases present are water and ethanol vapour. I made a phase diagram with better resolution based on the one I linked to. The blue curve is the boiling point of the liquid mixture, the red curve is the composition of the gas mixture. Based on the diagram, I can see that 40 vol% ethanol in water boils at appox. 81°C, and that the mixture in the gas phase then contains about 65% ethanol. This is valid, I presume, only when the sum of the partial pressures of ethanol and water vapour equals 1 bar. Is it possible to determine the corresponding data at 1.1 bar by using this diagram, or by combining it with the graph of water vapour pressure shown below? --62.16.173.45 10:08, 30 May 2007 (UTC)[reply]

Hmm. Did some calculations to check this out, using these calculators: Water vapour pressure, Ethanol vapour pressure, created by Shuzo Ohe. The vapour pressure of ethanol at 81°C is 844.8 mmHg = 1.126 bar, and that of water is 369.8 mmHg = 0.493 bar. I was wandering whether the pressures would add up to 1 bar, and see that they don't. Am I correct in thinking that the exact purpose of the phase diagram is to correct for this discrepancy? And again, is there some way of reading my phase diagram, in order to calculate boiling points for higher pressures than atmospheric? --62.16.173.45 11:33, 30 May 2007 (UTC)[reply]

The values don't add to one atmosphere because they represent the vapor pressures above pure ethanol and over pure water; the partial pressures over a mixture of water and ethanol are different from these. What you need for complete understanding is a set of curves or tables that show the partial pressures of the two gases above a mixture of ethanol and water, as a function of temperature and of the mixing ratio in the liquid. The boiling point at any given pressure is the temperature at which the two partial pressures add to the given pressure. --mglg_(talk) 16:14, 31 May 2007 (UTC)[reply]

Thank you again, mglg! I think I understand it now. I'll see if the library can help me with some tables. --62.16.173.45 19:38, 31 May 2007 (UTC)[reply]

(outdent) I found a random old reference (Phys. Rev. 57, 1040–1041 (1940)) that contains partial pressure graphs for low temperatures (20-40°C). They got the data from the International Critical Tables, which might contain data for higher temperatures (more relevant for you) as well. You can find out in the online edition, but you may have to pay to use it. --mglg_(talk)

Thank you for the book reference. It probably has the data I'm looking for, but the website wouldn't even let me read the index without paying! However, I'll check it out at a library workstation, they may have a subscription. -62.16.173.45 10:08, 30 May 2007 (UTC)[reply]

Which do you think is more likely to happen first?

A) Developing a spacecraft capable of carrying humans to Proxima Centauri and back within a reasonable time period (decades, as opposed to centuries).

B) Developing technology that allows humans to be preserved (cryogenically or otherwise) for a journey to Proxima Centauri and back that may take several centuries.

--Kurt Shaped Box 21:30, 29 May 2007 (UTC)[reply]

Probably annihilation of our species will occur before either of these is feasible enough for even an eccentric, self-funded enthusiast-investor to implement. Nimur 22:10, 29 May 2007 (UTC)[reply]

I would say (A) - but my personal belief (which I've gone into in some detail here before) is that the correct answer is more likely to be (C) That we'll first figure out how to scan the 3D structure of the brain in enough detail to place our psyche's into computers and dispense with these dangerous organic bodies. Once that happens, we can say several things about interstellar travel:

Since (as a block of digital data) we would be able to be transmitted at lightspeed - we could send a very slow ship anywhere we really wanted - and transmit our minds via radio or laser to the onboard computer when it eventually arrived. No time would seem to pass for us during the trip - and it would only take four years to travel four lightyears. In effect we could teleport anywhere where there was a sufficiently powerful computer at lightspeed. Very 'Star Trek'!
We could slow down the clock rate on the computer simulating our minds and time could be sped up to any degree desirable to make a fairly conventional trip happen with as much or as little time as we wanted it to. You might want to speed up your clock to normal speed (or perhaps even faster) for a minute or soe every day - just to check up on your craft - then fast-forward through the next 23 hours 59 minutes. Forty years would zip by in about ten days of perceived time.
With effective immortality - and a more or less unlimited ability to 'fast-forward' through time by slowing down our system clocks, our 'long view' of events would make use pay much more attention to these kinds of long-range goals than we do at present. Stuck here on earth would be a dangerous thing indeed for an immortal being - the odds of being squished by an asteroid or something nasty would certainly have me demanding that a backup copy of my mind be kept a nice safe distance away and updated by laser transmission at least annually. Proxima Centauri would do nicely.
Without the demands of a physical body - we wouldn't need oxygen, food, water, recycling or anything else like that - just a nuclear power cell good for the duration of the trip. So maybe this craft could be extremely small - perhaps the size of a coffee can - yet it could easily contain a virtual reality world of whatever size we needed to keep ourselves amused during the trip. A tiny craft like that could be accellerated to high speed much more cheaply than a honking great life-support system!

I believe we'll have the computing and scanning technology to do this for a few (rich!) people in 40 years and for everyone else in 50 years. It might be dangerous to be scanned and limiting to be 'stuck' in cyberspace - but if you were near death anyway, it would be worth it. SteveBaker 22:18, 29 May 2007 (UTC)[reply]

(B) could be a real downer for the human involved. Imagine setting off as THE FIRST HUMAN TO LAND ON AN EXTRASOLAR PLANET!, being frozen, getting there 500 years later and being unfrozen only to discover that spacecraft technology improved leaps and bounds in the time you were in stasis, the ships built after yours got there much faster than yours and the system was already teeming with humans. Not only are you now 500 years out of your time, instead of being a pioneer, you are now just a historical curiosity. --84.68.104.115 22:30, 29 May 2007 (UTC)[reply]

A.E. Van Vogt wrote a story like that ("Far Centaurus" I think). Clarityfiend 22:46, 29 May 2007 (UTC)[reply]

And Bill Roper wrote a song, "Space Is Dark". I've read one novel, I think Kevin O'Donnell's Mayflies, in which it's mentioned that humanity graciously refrains from leapfrogging the first sublight ship, since there are plenty of other stars to be visited in the meantime. —Tamfang 04:09, 1 June 2007 (UTC)[reply]

This question asks for speculation and is therefore disallowed under the present guidelines.--Tugjob 22:59, 29 May 2007 (UTC)[reply]

When we achieve that, most likely both technology will be used. A spacecraft that reaches there, say about 150-200 years; and some bio-chemical ways to slow down the human metabolism perhaps in a hibernation or dormancy state so that he can last the journey, to conserve energy, and also to prevent him from being bored to death. I don't think Cryogenics will work, but increasing lifespan to 200 years is feasible. Afterall, we have doubled our life expectancy in the last century. --Vsion 00:19, 30 May 2007 (UTC)[reply]

B, I think. I saw on this show that a researcher is developing a blood-substitute (using fluorocarbons, I think) that will enable medical teams to immediately shut down an injured patient (e.g., after a 911 call or on a battlefield) and them revive him/her at the hospital. The point, I think, was that many patients die in between the arrival of medical care and entering a hospital. They called it "temporary death." They're not far away from developing this right now, and I imagine that it could be extended to space travel if needed. Getting spacecraft up to an appreciable fraction of the speed of light, however, is still far, far away. zafiroblue05 | Talk 01:21, 30 May 2007 (UTC)[reply]

There's also an episode of Naked Science where they talk about space travel. Scientists know of genes that allow some animals to survive being frozen (Wood Frog, for example), as well as animals that can withstand higher temperatures than other animals (some reptile, IIRC). They speculated that if those genes were put into humans, that humans might be able to survive the trip as well as the conditions at other planets. However, they did raise the question if those humans are still humans. --Wirbelwindヴィルヴェルヴィント (talk) 01:31, 30 May 2007 (UTC)[reply]

What would happen

What would happen if I ate a cactus. Not like a cooked cactus, I mean if I just went to some desert and knifed a cactus into bitesize pieces and shoved it down my throat taking painkillers if needed cause of the barbs.

Seemingly some cactus varieties are edible (http://www.foodreference.com/html/f-cactus.html, http://www.rawguru.com/cactus.html). I suspect that some are not edible/could cause harm so (as with any 'eating wild food') you should always be 100% sure before eating produce in the wild. ny156uk 23:18, 29 May 2007 (UTC)[reply]

You can eat raw nopales, assuming you remove the spines. If you ate the spines too, I suspect you would tear up your mouth and esophagus, but as I don't know anyone who's tried it, I can only speculate. You don't have to go to a desert, either - prickly pears grow in a lot of places. They're even common in Florida. --Reuben 00:48, 30 May 2007 (UTC)[reply]

Haven eaten both nopales and prickly pears, you obviously take the spines off. Nopales are eaten raw, and it's rather slimey, so a lot of people don't like it from what I gather. Prickly pears are eaten raw like a fruit, where the seeds aren't chewed, and are quite tasty. --Wirbelwindヴィルヴェルヴィント (talk) 01:23, 30 May 2007 (UTC)[reply]

mmm, nopales. Amazes me that some people might not like 'em. It's not like we're talking natto or something. --jpgordon^∇∆∇∆ 01:28, 30 May 2007 (UTC)[reply]

I regularly eat cactus pear, which grows in open spaces, road-sides, and people's yards - practically anywhere (at least here in California; I've also eaten it all over Texas and New Mexico). The worst effect is, of course, the spines, which inevitably end up on my hands and mouth. There are large spines, which are easily removed with a cloth; but no matter how much peeling and careful cleaning, tiny micro-spines manage to stick to me. I've also found that people around me find it strange to eat road-side plants, especially cacti, so the social consequences can be fun / problematic. Nimur 03:07, 30 May 2007 (UTC)[reply]

I've never had natto, nor do I intend on trying it either. A lot of people don't like okra either, and I guess that's pretty similar to the sliminess of napales. --Wirbelwindヴィルヴェルヴィント (talk) 04:25, 30 May 2007 (UTC)[reply]

I also found nopales a lot like okra in texture, color, and taste, minus the seeds from okra. --Reuben 05:36, 30 May 2007 (UTC)[reply]

Yes - we eat cactus in Texas - you can buy it in the supermarket - although it grows wild everywhere, the ones in the supermarket always look nicer than the beat-up ones we see in our back yard. Obviously you have to remove the spines (I take them out with an apple-corer) - then you boil it in water (we generally microwave them in a shallow pot of water). When we cook them at home, we change the water at least once during cooking because otherwise it gets very slimy and (to my mind) not too appetizing - from reading other responses (above), I guess that's not what everyone else does. Then we slice the big oval "leaves" thinly and serve it just like any other vegetable. To my mind, it tastes a lot like raw 'snow peas' - pea pods in other words. I like it because it's a nice change from other vegetables - although preparing it the way we do is a bit of a hassle. SteveBaker 11:36, 30 May 2007 (UTC)[reply]

A cell's life?

Do you agree that a cell (any cell) leads only one kind of life - either a mitotic or a meotic life? Or are there cells known to exhibit both?Arun T Jayapal 23:25, 29 May 2007 (UTC)[reply]

I would check mitotic to start with.

I would start with your textbook.... --Wirbelwindヴィルヴェルヴィント (talk) 01:24, 30 May 2007 (UTC)[reply]

Consider where the germ cells originally come from. An organism forms from a single cell resulting from fertilisation (this includes the germ cells that ultimately undergo meiosis). So the cells that end up undergoing meiosis had to originally form by mitosis. --jjron 08:38, 30 May 2007 (UTC)[reply]

So all germ cells have this cycle - a mitotic start and a meotic division later on? deostroll 13:18, 30 May 2007 (UTC)[reply]

In organisms with a gametic lifecycle, such as humans, that is the case. There are other possible lifecycles - you could read the section that talks about different types of life cycles here.

To give a simplified answer, no cell can simply undergo meiosis as it results in a halving of the number of chromosomes. So if every time the cell divided it ended up with half the chromosomes, it wouldn't take long for there to be none left (unless it each time it underwent meiosis it then recombined with another cell to replenish the chromosome number). That's why mitosis is the typical method of cell division, as it retains the correct number of chromosomes. --jjron 01:32, 31 May 2007 (UTC)[reply]

Biology

what chemical the white blood cells produce that makes it functional?

Quite a few, in fact. You might want to start by looking at White blood cell, and return here if you have any questions. You also might be thinking of antibodies. Someguy1221 02:52, 30 May 2007 (UTC)[reply]