Wikipedia:Reference desk/Archives/Science/2010 February 12

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February 12

Apollo 13 and teflon

The article on Apollo 13 says:

"...Damaged Teflon insulation on the wires to the stirrer motor in oxygen tank 2 allowed them to short and ignite the insulation. The resulting fire ..."

"...power passed through the bare wires which apparently shorted, producing sparks and igniting the Teflon."

First of all teflon will not burn. Even in an oxygen atmosphere. So that can't be true.

Now, while teflon does decompose at about 350 °C, the analysis said that:

"... This raised the temperature of the heater to an estimated 1,000 °F (540 °C)."

So if the teflon was going to do anything it already did, and a spark is not going to have any additional effect.

So what actually happened? A short maybe? I have a hard time believing they had no fuses though. Ariel. (talk) 00:00, 12 February 2010 (UTC)

NASA Spacecraft Incident Investigation, Panel 1, MSC Apollo 13 Investigation Team (June 1970) report states: "The first short-circuit might have contained as much as 160 joules of energy, which is within the current-protection level of the fan circuits. Tests have shown that two orders of magnitude less energy than this is sufficient to ignite the polytetrafluoroethylene insulation on the fan circuits in the tank." Your assertions about Teflon do not match the statements made by the official accident report, or any of its followups. As far as circuit-breakers or fuses, as just cited, the energy was sufficiently low as to not trip a fuse or over-current sensor, but still enough to ignite the fire. If you're interested in details, these accident reports are a great place to start - they are publicly available in their entirety, and you can see all the ground test data, recorded telemetry and spacecraft measurements, and speculations to fill in the rest of the gaps. Some amount of uncertainty will forever plague all accident investigations, but NASA spent a lot of effort tracking down what happened here, and had the good forethought to instrument everything possible on their Apollo spacecraft to assist in diagnostics. Nimur (talk) 00:16, 12 February 2010 (UTC)

Well, that calls for a test. So I took some teflon put it in a fire on my stove - and it doesn't burn (it does decompose and glow, but it doesn't burn). Obviously they said what they said, but it doesn't make sense. Just by looking at the chemistry of teflon you can see that trying to burn it consumes energy, it doesn't release it. And if there was anything flammable there (besides the teflon), why didn't it burn when the tank was heated to 1000 °F? Ariel. (talk) 00:27, 12 February 2010 (UTC)

I wonder why you've completely ignored the previous answer by Nimur which says that Teflon was not involved? 89.243.182.24 (talk) 00:50, 12 February 2010 (UTC)

Hu? Where did he say that? If teflon was not involved that would moslty answer my question - but he didn't say that. Perhaps you don't know that polytetrafluoroethylene and teflon are the same thing. Ariel. (talk) 01:04, 12 February 2010 (UTC)

My apologies for misunderstanding. Sorry. 92.29.136.128 (talk) 15:33, 12 February 2010 (UTC)

That's right - PTFE is teflon. As far as your experiments, I hardly advocate burning teflon, or even trying - because it can release some really toxic fumes - but if you're going to test this, you need to get yourself a supercritical oxygen tank at high pressure to replicate the conditions at hand. I've said it before and I'll say it again (only lightly exaggerated) - everything burns in the presence of strong oxidizer. Do you want to look at the room-temperature chicken combustion video again? Now imagine that oxidizer at thousands of psi instead of atmospheric pressure. Strong oxidizers have very unusual, unintuitive chemical behaviors. At some point, after igniting the teflon insulation, it seems that the tank walls also ignited. It may seem "impossible" to you, but this is a major problem for spacecraft or any other oxidizer-carrying tank. When you have 100% cryo oxygen at high pressure, solid steel burns like gasoline. All it takes is a small spark. Nimur (talk) 01:08, 12 February 2010 (UTC)

You are right that I need an oxygen environment to test this properly. But you are ignoring something: teflon will not burn! Teflon is carbon burned with fluorine. Oxygen will do nothing to it. Fluorine is much more electronegative than oxygen (4 vs 3.44). Ariel. (talk) 01:14, 12 February 2010 (UTC)

(ec)It occurs to me that your argument is addressing whether the oxygen would replace fluorine, but it doesn't address whether oxygen would attack the C-C bonds. Why shouldn't (CF₂)_n react with oxygen, giving carbonyl fluoride? I'm not a chemist and this could easily be nonsense, but if it is, I'd like to know why it's nonsense. --Trovatore (talk) 01:27, 12 February 2010 (UTC)

The exothermic reaction is replacing the carbon-carbon bonds with carbon-oxygen bonds. You can do that quite easily with liquid oxygen, but generally doesn't happen spontaneously in air because the rate at which oxygen gets around the fluorine to attack the carbon backbone is too low at atmospheric pressures. Dragons flight (talk) 01:23, 12 February 2010 (UTC)

So much for my being sure teflon will not burn. Thank you (both of you). Ariel. (talk) 01:35, 12 February 2010 (UTC)

Maybe the teflon is not 100% PTFE - it may contain any number of binders, polymers, adhesives, etc. In any case, unless you have a sample of the exact material used on the Apollo 13 Service Module, (which WAS tested by NASA, and DID burn in post-accident tests), your test results are of limited use for comparison. As the accident report spells out, the teflon (or whatever the insulation was actually made of) burned for about 80 seconds; after this, the inconel began to burn (yes, that's not something we typically think of as flammable, but it did burn), and ultimately, the vacuum dome failed structurally (a combination of burnthrough and overpressure) - even though the heat was insufficient to over-pressure an intact tank, the structurally damaged tank was less sturdy and may have had a gas leak as a result of the fire at the insulator entrypoint to the tank interior. Nimur (talk) 01:19, 12 February 2010 (UTC)

Page 82 of the accident report I linked above goes through a very rigorous breakdown of every likely, possible, and unlikely burn source, ignition source, mechanical stress, etc. If you're unconvinced of the teflon burning, there are dozens of other "unlikely" options to choose from, and a few "possible" options; it will be productive to read through that report and bring yourself up to speed on what NASA concluded was possible/probable. These guys are counting the number of milli-Joules of energy available from every possible source - chemical, mechanical, propulsion, RF... in order to account for every wobble measured by the spacecraft's roll, pitch, and yaw sensors. If you're absolutely sure that teflon is chemically inert, you'd best check your numbers against the extraordinarily thorough accident report. After Apollo 13's disaster, NASA sunk a lot of man-hours in to this investigation. Nimur (talk) 01:24, 12 February 2010 (UTC)

I wasn't trying to challenge, I was trying to understand. And yes, I'm quite sure teflon is inert. I'll have to read the report when I have a bit more time. When I asked this I thought it was an error in the article, not something from the report. Ariel. (talk) 01:30, 12 February 2010 (UTC)

I hope I'm not sounding dismissive. It's good that you're scientifically skeptical. I wouldn't expect you to take NASA's word on faith alone - but the report really is a good read. It will give you some perspective about how many decimal-points-after-the-zero they investigated. For example, the spacecraft was observed from at least three independent ground observatories (optical telescopes!) who measured a brightness change corresponding to the nebulous cloud of oxygen that was vented; from this, a rate and quantity of vented oxygen were calculated. These images were compared with a 1/6th scale model which was suspended and photographed with a variety of different damage simulations. The strength of the RF signal from the high gain antenna (destroyed) was used to tweak the numbers on the roll and pitch rate and extrapolate data following the loss of telemetry. I would hope that with all this diligence, with so much investigation into miniscule details, that something as obvious as "that material wouldn't burn" has not been overlooked. If it does turn out that teflon will not burn under any such circumstances, then I would apply Occam's razor and suggest that the terminology "teflon" refers instead to "a mostly teflon-based insulator which contains other materials, that, as a whole, can burn, and burns with a measured rate confirmed by ground experiment." Nimur (talk) 01:41, 12 February 2010 (UTC)

Turn out I was wrong about teflon not burning. (See higher up in this question.) I still might read the report. Ariel. (talk) 01:47, 12 February 2010 (UTC)

Time Travel question

I was booking a flight recently and i noticed that one on of the sites i could pick a return flight that was earlier than my departing flight this seem to create paradox in that i can return before depart and prevent self from departing in the first place (Dr hursday (talk) 00:07, 12 February 2010 (UTC))

What exactly is your question? If you are wondering how this could be, it is because of time zones. For example, 12pm in the eastern US is exactly equivalent to 5pm in England - they are the same time. Things going on in New York at this time are not occurring before those in London, it is just the local expressions of time being normalized to the daylight. (I renamed the section since there has already been a time travel section recently) —Akrabbim^talk 00:16, 12 February 2010 (UTC)

Isn't the answer simply that flight booking software is stupid? Dragons flight (talk) 01:03, 12 February 2010 (UTC)

To avoid confusion, flight depart/arrive times are always printed in local time. So, I wouldn't call it stupid. It is just to avoid confusion. -- kainaw™ 01:19, 12 February 2010 (UTC)

I'm not sure what the original post is referring to, but I took it to mean that when taking a return flight on the same day as the outgoing flight, the user may be presented with flights that are genuinely earlier than the original flight arrives. I've seen this happen with day trips on regional flights (i.e. my intent is to fly into LA in the morning and fly out in the evening, but the software will happily inform me about the very cheap flights leaving LA at 6 AM even though my incoming flight doesn't get there until 9 AM.) Dragons flight (talk) 05:02, 12 February 2010 (UTC)

Oh, on second read, it seems you are right. Never mind my answer then. —Akrabbim^talk 15:09, 12 February 2010 (UTC)

Moon Question

astronaunts traveling to the moon in a spacecraft that travels at the rate of 6,260 km per hour, at this rate, how long will it take for the astronaunts to reach the moon, while assuming a straight line and average distance. —Preceding unsigned comment added by 72.85.214.110 (talk) 00:29, 12 February 2010 (UTC)

Sorry, we don't do homework questions. APL (talk) 00:57, 12 February 2010 (UTC)

Two options:

• • find out how far the Moon is away (look it up; try Moon) and find out (look it up; your math(s) teacher may be available) how to calculate a time from a velocity over a given distance.
  • Give the answer "about 162 years" (then complain about the complete uselessness of Wikipedia as a research tool).

By the way, it's "astronauts". An astronaunt is your mother's cosmic sister. Tonywalton ^Talk 02:09, 12 February 2010 (UTC)

Well, if the Moon were 12,520 km away (2 X 6,260) it would take about 2 hours to get there, assuming we didn't stop too many times at rest areas for peanut butter and jelly sandwiches. How far away is the Moon? Answer: I don't know. But if we could find out how far away the Moon is, we could divide that distance by 6,260 (assuming that distance were expressed in units of kilometers). The answer (to that calculation) will be the number of hours (possibly including a fraction of an hour) of travel time. What we really need to know is how many kilometers the Moon is away as an average distance. Bus stop (talk) 02:25, 12 February 2010 (UTC)

While we're at it, assuming a straight line and constant velocity for travel from the earth to the moon is a bad approximation - even if it is the homework assignment. Orbit makes such a trajectory very difficult - not impossible, but very difficult to achieve in practice. Nimur (talk) 04:07, 12 February 2010 (UTC)

Don't let these smart people and their sandwiches distract you. You will get the answer by dividing one number by another number, and you already have one of the numbers. Good luck. Cuddlyable3 (talk) 13:35, 12 February 2010 (UTC)

It will depend on where you are. If you are sitting on the launchpad, then you would never get there, and if you were 2 miles from the moon, you will reach it momentarily. Even if we wanted to answer this HW question for you, we don't have enough information. Googlemeister (talk) 13:59, 12 February 2010 (UTC)

The indicated speed would be under the Earth's escape velocity assuming that the spacecraft is travelling at a near-constant velocity, and you'd never get off the Earth. To escape from the Earth's gravity requires a speed of over 40,000 km/h. ~AH1^(TCU) 23:44, 13 February 2010 (UTC)

No, the OP specified the velocity, not that it was a ballistic trajectory after a rocket motor had shut off. Perhaps God or Xenu or Lex Luthor is maintaining the spacecraft at a constant velocity from the beginning to the end of the voyage. The article Moon confuses the issue. Did the astronaunts depart from the center of the Earth to go to the center of the Moon? Then they have to travel 384,403 km. If they left from the surface of the Earth to travel to the surface of the Moon, then the distance will be decreased by the mean radius of the Earth (6,371 km) and the mean radius of the Moon (1737 km). If they departed from the highest or lowest point on the Earth's surface and arrived at the highest or lowest point on the Moon's surface, that would require a small correction. Edison (talk) 05:03, 14 February 2010 (UTC)

Capacitors

Yes, this is a homework question, but I have no idea where to even begin. Can someone at least point me in the right direction and give me a few useful equations please?

Two 13.0 cm -diameter electrodes 0.59 cm apart form a parallel-plate capacitor. The electrodes are attached by metal wires to the terminals of a 15 V battery. What is the charge on each electrode while the capacitor is attached to the battery? --24.207.225.13 (talk) 01:26, 12 February 2010 (UTC)

This is nothing that Capacitor doesn't answer. It really isn't all that complicated, so giving you an equation directly would practically be akin to doing the problem for you. —Akrabbim^talk 01:29, 12 February 2010 (UTC)

First, you need to figure out the capacitance of the capacitor from its geometry and the dielectric constant of the material separating the plates. In a steady state, the voltage across the terminals of the capacitor must equal that of the battery—that's how you get zero current flow in a steady state. With that knowledge, you can use the relationship between stored charge and voltage in a capacitor to work out the answer you're looking for. --173.49.16.103 (talk) 02:05, 12 February 2010 (UTC)

You will certainly be expected to assume for simplicity that the area of the plates is so much larger than the space between them that edge effects can be ignored. Treat the electrical field as though it is uniform over the whole plate area. Cuddlyable3 (talk) 13:30, 12 February 2010 (UTC)

The charge on one electrode is minus the charge on the other electrode.. —Preceding unsigned comment added by 79.76.205.40 (talk) 23:33, 12 February 2010 (UTC)

What tickles my fancy is what happens to the voltage across the capacitor if the battery is disconnected after charging the capacitor, and the spacing between the plates is changed to 10 times or 1/10 the original spacing. Quite amazing, and there are demo devices which do this. (Assume charge is conserved, since there is no path for current between the plates). Edison (talk) 04:50, 14 February 2010 (UTC)

Yes, this appears to be the principle of operation of the condenser microphone —Preceding unsigned comment added by 79.76.197.2 (talk) 11:42, 14 February 2010 (UTC)

It is also the principle of the Electrophorus which could tickle Edison's fancy. Cuddlyable3 (talk) 23:26, 14 February 2010 (UTC)

mic

i wanna know how does a mic work? or just tell me how to change sond energy into electrical energy.? does mic contains piso crystle( a crystal that can change pressure into electricity)? cant this idea be used to change sound energy aroun' us into electrical energy- put mics on the muffer tip of car or infront of horn. ^{- answer my first question dont start telling me about piso crystle! i dont want to know abot it now}-§§§§§§§

Have you checked microphone? -- kainaw™ 03:25, 12 February 2010 (UTC)

Also, microphones do not create energy. They alter an electrical signal according to sound waves. -- kainaw™ 03:27, 12 February 2010 (UTC)

Some microphones use piezoelectric crystals, but others use a solenoid or a mass-spring system, and still others use a capacitor diaphragm. Each of these has advantages and disadvantages; each works according to a different principle; but in general the idea is to convert pressure changes in the air (sound waves) into a time-varying electric signal. Most microphones also need an amplifier to boost and condition that electric signal for later use and eventual playback. Nimur (talk) 04:11, 12 February 2010 (UTC)

Kainaw: Some microphones do create electricity. You can use a mic to generate electricity from the sound around you - but not very much. It's not enough to be worth it. If you scream into headphones you can measure electricity in the jack. Ariel. (talk) 04:22, 12 February 2010 (UTC)

Yes, they all create electricity, but they do not create energy. Kainaw was referring to conservation of energy; it's unlikely that a microphone could harness waste energy from a car's exhaust or air-drag in any meaningful or productive way. Nimur (talk) 04:40, 12 February 2010 (UTC)

Mics do harness energy, i.e. convert energy from sound to electricity. I assumed Kainaw was saying mics only vary resistance (meaning they must be externally powered), and I was saying some can generate their own signal. Maybe that's not what he was saying, sorry if I misunderstood him.

Anyway, the energy they convert is in tiny amounts. Mainly because the mic is very small. Wave power is exactly the same thing, except with water instead of air. Ariel. (talk) 05:35, 12 February 2010 (UTC)

See also Carbon microphone which works on the principle of slightly varying resistance, so requiring a current to be supplied to them to work. —220.101.28.25 (talk) 07:10, 12 February 2010 (UTC)

In every case a microphone absorbs some energy from the sound. Yes, microphones could extract tiny amounts of power (energy) from noisy parts of cars. The power would be tiny but it could be maximised if the microphone resonated at a frequency related to the engine r.p.m. Similar attempts are made to extract power from a radio antenna. Cuddlyable3 (talk) 13:23, 12 February 2010 (UTC)

The complete answer here is that yes, it should be possible to harness energy from sound as you describe...and yes, with some (but not all) kinds of microphone, you could do that. However, the amount of energy would be so amazingly tiny - and the efficiency with which it could be converted would be so poor that it would certainly not be worth the effort to do so. There just isn't much energy there to be had in the first place. SteveBaker (talk) 17:13, 12 February 2010 (UTC)

Thomas Edison in the 1870's built a device called the "Phonomotor," which collected sound energy in a horn, cause a diaphragm to vibrate, used the vibration to operate a fine gear train via a ratchet to create rotary motion. It got some press around the world, with humorous comments about the power of a mother-in-law's voice to bore a hole in a piece of wood, but had no practical application. (Maybe people lost interest because it was a "boring machine"). If you had a device which converted sound to electricity with 100% efficiency, and it had a 1 square meter collector, it would require 138dB (deafeningly loud) to power a 60 watt light bulb, per [1], which says that would require the combined voices of a million people. Edison (talk) 03:01, 13 February 2010 (UTC)

Strategically placed Phonomotor's could convert noise pol-pol-pol-pollution into useful energy. Cuddlyable3 (talk) 18:08, 13 February 2010 (UTC)

Sunscreen and acne

Does sunscreen increase acne? My dermatologist told me not to use sunscreen and he told it increase acne. Don't want to seek any medical advice, just want to know the scientific basis behind this claim and the physiological mechanism through which sunscreen increases acne. --Qoklp (talk) 04:09, 12 February 2010 (UTC)

Oil-based sunscreens can increase acne. It isn't complicated. Putting oil on your face can increase acne if you are already prone to it. There are many oil-free sunscreens that will have a noticeably less increase in acne compared to the oil-based ones. How your specific face will react to any specific sunscreen will not be known until you try it. -- kainaw™ 04:13, 12 February 2010 (UTC)

The term to look for is "noncomedogenic". (Hmm, it looks like we don't have that page yet. Okay, try Comedogenic instead.) -- 174.21.247.23 (talk) 04:17, 12 February 2010 (UTC)

Hmm, Comedogenic redirects to Acne cosmetica. Perhaps Noncomedogenic and Non-comedogenic should as well. 58.147.58.179 (talk) 04:42, 12 February 2010 (UTC)

Dr Kevorkian

where can i watch i tried google when he videotaped himself performing a lethal injection on some old dude on 60 Minutes, he was charged and convicted with murder in the second degree. —Preceding unsigned comment added by 67.246.254.35 (talk) 05:24, 12 February 2010 (UTC)

The 60 Minutes video and reactions from the MDA and in comedy(1), comedy(2) Cuddlyable3 (talk) 13:10, 12 February 2010 (UTC)

Scar removal/ Erase Scars

Hi,not medical advice, but is it absolutely impossible to remove a scar.

A while ago, about ten years back, I went to touch a pie but the filling got stuck on my hand and when my hand went back as a natural jerk reaction the pie filling stuck to it and was flung on my face, leaving a small scar.

I was wondering if there was anyway to remove a scar in the future or will it be impossible forever.

Also, I what causes scars to be scars and normal skin doesn't form after injury.

Scar should contain an explanation for why you get scars and not normal skin. There are certainly methods to reduce scarring, but I believe it's on a case-by-case basis - your doctor will certainly be able to give you the information you need. Vimescarrot (talk) 06:46, 12 February 2010 (UTC)

You already asked about removed on on the 8th. Was there are problem with TenOfAllTrade's answer? You're certainly not going to get anyone here to comment on your specific case. APL (talk) 08:09, 12 February 2010 (UTC)

About burden of proof and scientific method

Burden of proof#Burden of proof in epistemology and scientific methodology says that it is "the responsibility of the person who is making the bold claim to prove it".

On the other hand, Scientific method#Introduction to scientific method says that "Note that this method can never absolutely verify (prove the truth of) 2. It can only falsify 2.[8] (This is what Einstein meant when he said "No amount of experimentation can ever prove me right; a single experiment can prove me wrong."[9])"

It seems to me that there is a mismatch between two. Like sushi (talk) 08:22, 12 February 2010 (UTC)

Your confusion stems from two different interpretations of the word "proof". In the first sentence, it doesn't mean "proof" in the absolute, mathematical sense, but rather "provide sufficient evidence for his claim". On the other hand, a single experiment can indeed disprove (in the absolute mathematical sense) a hypothesis. (note that theories that have been proven wrong in this way do not always lose their usefulness, not if they were good theories that had lots of "proof" in the first place, classical physics being the prime example of this) —Preceding unsigned comment added by 157.193.173.205 (talk) 08:31, 12 February 2010 (UTC)

Thank you. Then it is that the defender must provide enough evidence, while the accuser must disprove it (in the absplute sense). Like sushi (talk) 09:00, 12 February 2010 (UTC)

You might also be interested to know that when a "single experiment" appeared to prove Einstein wrong (I think it was some measurement of the transit of Mercury, or something), he wrote, and I quote loosely from memory: "I can't understand why some people are so impressed by these measurements and figures; the elegance of the theory is enough to convince me it must be right." And of course, we now know Einstein was right and the measurement was in some way wrong, but at the time it was a serious result that a lot of serious scientists thought meant serious trouble for relativity. That is to say, it's never really very clear-cut what constitutes a disproof and what can be simply brushed aside, and many scientific theories have been abandoned without ever being "absolutely" disproved. There are also any number of other possible complications that violate supposedly sacrosanct principles of scientific inquiry: sometimes an experiment is so expensive it can't be freely reproduced elsewhere (detecting neutrinos with a giant underground tank); sometimes the mathematics is so dense that even many experts get it wrong or just take it on faith (as in the early days of general relativity, and possibly string theory today?), etc. etc. All in all: any very broad generalization in the philosophy of science should be taken with a pinch of salt. But they can still serve as useful guides.--Rallette (talk) 10:01, 12 February 2010 (UTC)

(edit conflict) When someone makes a claim to truth, it is their responsibility to offer some evidence or justification that makes the claim seem reasonable - that is the 'burden of proof' in the first case. it doesn't mean they have to 'definitively' prove it (in fact, it's impossible to definitively prove anything outside of pure mathematics), it just means they have to do something more than say it's true, so that other people might be convinced by it. --Ludwigs2 10:06, 12 February 2010 (UTC)

"a pinch of salt", and "so that other people might be convinced by it".

How can I become able to say so? I seem to have to learn a lot to convince other people, and the amount of salt is so difficult (I don't still have something to convince other people of, in the first place). Well, it is just a useless complaint, never mind!

Like sushi (talk) 10:45, 12 February 2010 (UTC)

Like sushi, yours is not a useless complaint. "How can I be able to say (that the person has provided sufficient evidence for his claim)" is a question that deserves an answer. In order of priority the claim should 1) be demonstrable by repeatable experiments with unambiguous interpretations, 2) have an impact on the current theories in an explicable way, 3) add to the total understanding of the field and 4) achieve this in a way that is "elegant" in the sense of Occam's razor. Cuddlyable3 (talk) 12:42, 12 February 2010 (UTC)

Rallette's response is absolutely excellent. These are broad guidelines that serve to shape some kinds of activity and belief, but are more often applied in retrospect than they are at the time. We tell very nice compact histories of science in which a single experiment disproves a century's worth of theory, but this is the exception, not the rule, and even when that does happen, it can take a long, long time for everybody to agree that is what happened. Example: August Weismann cuts the tails off rats, disproves Lamarckism, etc. Problem: True Lamarckians would never have thought that what Weismann was doing actually violates Lamarckism—it only falsifies a very straw-man version of the theory. Example: John Snow shows with a single map that cholera is obviously water-borne. Problem: Almost no doctors actually believed that Snow's experiment was correct, and after a century of coming up with other complicated explanations for cholera (misasma, morality, etc.), they dismissed Snow's theory and evidence very easily. It took a good generation for the turn-over in thinking about cholera to happen, great evidence be damned.

All of which brings up the quotation of Max Planck: "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it." None of which says that falsification is incorrect or that the burden of proof shouldn't lie with those making the stronger claim. But in practice, disagreement about whether something has truly be falsified, and these question of who is making the stronger claim, are both somewhat subjective properties. Scientists are not pure logic in vats—they are human beings, organized into professional communities, and bear all of the handicaps of psychology and sociology just like the rest of us. --Mr.98 (talk) 13:22, 12 February 2010 (UTC)

I agree that there are two meanings of the word 'proof' being used here. If you have a totally wild and crazy hypothesis - then it is without doubt your reponsibility to provide enough proof to convince other people to take you seriously. So, for example, if you claim that you can teleport objects across the room with the power of thought alone - then serious scientists are not even going to bother to talk to you until you can provide a pretty serious demonstration of that happening. But if you are an established astronomer and you claim to have found yet another extrasolar planet orbiting some distant star - then there would be only a small amount of skepticism and you could probably get other astronomers to double-check your results so you can publish your findings in a serious journal and have them come to be accepted as fact. A better way to think about this is "Extraordinary claims require extraordinary evidence". The more outrageous the thing you're claiming, the harder it is to get the attention of others and the better the evidence you have to provide. But this doesn't have to be mathematically perfect proof. If you walk into the office of a serious scientist and demonstrate your ability to teleport a pencil from one end of his desk to another - then that's probably enough proof to get him interested enough to do a controlled experiment and either prove or disprove it to a higher standard.

A practical example was the case of the Mpemba effect - which is the very odd finding that cold water freezes more SLOWLY than warm water. This is a pretty outrageous claim - and worse still, it was made by a high school student in Tanzania. It took six years of work to just to get that result published - and it's still not widely accepted.

On the other side though - it is true that there is very rarely absolute proof of anything. Einstein was right - it would only take one scientist to demonstrate how to make a golfball travel 10% faster than the speed of light to demolish relativity theory overnight. However, each experiment that confirms relativity pushes it asymptotically towards complete acceptance. But this does happen. Prior to Einstein, everyone assumed that Newton's centuries old laws of motion were correct - but one experiment which established the constant speed of light (plus a good deal of clever thinking on behalf of Einstein) was all it took to demolish it utterly in a matter of just a few years. Newton's laws were never proved conclusively - they never could be because at any time, one more experiment could bust them wide open.

However, what gives us confidence in well-established laws (Thermodynamics, Evolution, etc) is that if they are wrong - then just like Newton's laws of motion, they can only be a little bit wrong over the domain that they've been tested. Maybe thermodynamics breaks down inside a black hole - maybe evolution turns out not to be true amongst yet-to-be-discovered life under the ice of Europa - but that doesn't make them useless. Sure, Newton was wrong - but he was sufficiently right to allow almost all of modern technology to successfully rely on his laws.

SteveBaker (talk) 17:05, 12 February 2010 (UTC)

Strictly speaking, a golf ball traveling at 1.1c would not disprove relativity (it requires infinite energy to accelerate a massive particle from sub-light speed to the speed of light, but there is no instantly obvious reason it couldn't always have gone faster than the speed of light). But it would have other highly problematic consequences, assuming relativity still worked. The one you seem to be hung up on is that the usual formulas would imply that its rest mass was an imaginary number (assuming its energy is a real number) — that one doesn't much bother me; the derivations for the energy-mass relationship don't go through above the speed of light anyway, or at least none of the ones I've seen go through, so maybe it's just a different equation in that regime.

The more serious consequence is that if you could modify the behavior of such golf balls, and detect the effect of someone else's modification, and assuming relativity were still true (so that all this worked the same in every reference frame), then you could send signals back in time, as per the tachyonic antitelephone. Then you get the grandfather paradox and all that. These are seriously counterintuitive consequences. But I would not take them as "disproving relativity" in and of themselves. --Trovatore (talk) 05:03, 13 February 2010 (UTC)

Theory of justification might be worth a look. Quite a lot of people in this thread are being justificationists, I think, and Karl Popper would probably disapprove. I'm never very at ease with trying to guess what he would say, but he might propose a burden of showing how your new theory could be disproved if it was wrong, rather than a burden of proof. This is certainly the case in Occam's razor situations like the celestial teapot, where the problem with theory is not a lack of proof but a lack of testability. Epistemology is a work in progress, anyway, so it's not all that surprising if wikipedia articles contradict each other. 213.122.51.100 (talk) 04:41, 13 February 2010 (UTC)

Also, it is worth noting that epistemologically speaking, people often arrive at "truths" through different modes of understanding. On a personal level, there are certainly experiential truths, that is stuff that you know to be true because you personally expienced or witnessed them. But there are also truths "by proxy", or "by authority", that is truths we personally accept as true because we trust the person who asserts them. Most of us never performed or witnessed the experiments which supported "General Relativity", but on a personal level we accept them as true because we place trust in the source of those facts, either the person who taught us about them or the books they were recorded in, or whatever.

Take the example of crossing a street. Most people accept that there is a proper method of crossing the street (The Truth) which is to, say, cross at a crosswalk, look both ways, obey the traffic signals, etc. etc. However, many people may arrive at this personal truth by differing means:

• They were taught to do so by their parents
• They have read and obey local traffic laws
• They were hit by a car when they didn't obey the rules

Each person constructs their own truth-seeking aparatus, and as such, sets their own requirements for "proof" of a true fact. The same person often sets differing standards for different modes as well (for example, seperating scientific truths from behavioral truths or moral truths or religious truths or legal truths), each having their own standards of "proof". --Jayron32 20:49, 14 February 2010 (UTC)

Popping ears

If you inhale, block your nostrils and wait, there is a sensation of 'popping' from both ears, not necessarily simultaneously. What is happening please? If, in fact, one ear does not 'pop', over a long period, does that indicate a blockage? How does that relate to hearing ability? With many thanks. —Preceding unsigned comment added by 93.24.238.214 (talk) 08:39, 12 February 2010 (UTC)

Ears pop to equalize the pressure between the outside of the ear and the inner ear. Unequal pressure can potentially lead to damage in the ear, along with general discomfort, so ear popping is the body's way of resolving the pressure difference before it becomes an issue. Colds can cause ear popping because mucus secretions block the Eustachian tubes, making it difficult to normalize the pressure. When someone with a cold blows his or her nose, clearing the sinuses of mucus, the Eustachian tubes can open up so that the pressure will normalize and the ears pop. Incidentally, it is a very bad idea to pinch the nose shut and blow hard to pop ears if they are uncomfortable, because this can cause mucus to blow up the Eustachian tubes, causing an infection in the ear. Source: Wisegeek. -^Avicenna_sis @ 09:02, 12 February 2010 (UTC)

See also Valsalva maneuver. TenOfAllTrades(talk) 14:48, 12 February 2010 (UTC)

--79.173.235.183 (talk) 18:14, 12 February 2010 (UTC)

Civil Engineers Only .....reinforced concrete column behavior under load

we all know how to reinforce a concrete column by arranging steel bars around the perimeter and confining steel bars using stirupps ..the question is how steel work in columns ... i tried to figure it out and this is the result :

when start loading the column it respond by getting short,by other words its began to shrink and as we all know strain could'nt happen in one direction (poissons ratio) so the concrete must expand horizontally in order to allow vertical shortening ... so that in order to stop vertical strain we have to prevent lateral strain .

now let's think about it ... steel bars around the perimeter can resist compression loads alot more than concrete which leeds to the same relation between strain value for both materials ... according to that steel will held the concrete around it in position depending on adhesion between concrete and steel forming something like a fence wich can hold the concrete within as the load increased the concrete in the middle is subjected to a big load and is forcing the fence to deform so the inner concrete can expand laterally .... here where stirupps can work .... it transfer the lateral deforming in the fence into tensile strain in the stirupps so it helds the fence in position preventing lateral strain which preventing vertical strain which in the result will prevent the column to collapse ....

will ... the question is ... am i right ...? and anthor question why is there a maximum reinforcement ratio for column...? --Mjaafreh2008 (talk) 09:58, 12 February 2010 (UTC)

Remember that concrete is strong under compression. The steel reinforcement is there to provide strength under tension. Astronaut (talk) 15:16, 12 February 2010 (UTC)

Incidentally: Insisting that a question is only answered by Civil Engineers pretty much guarantees you'd get no answers because the odds of there being such people here on any given day is small. However, the questions you are asking could be answered by almost anyone with an engineering background. SteveBaker (talk) 16:29, 12 February 2010 (UTC)

Maybe he just wants the engineers to be well behaved? Googlemeister (talk) 21:35, 12 February 2010 (UTC)

Hi there .... I look for the answer in other places , and in some civil eng sites without any good .... I'am already thankful for any help i can get .--79.173.235.183 (talk) 18:14, 12 February 2010 (UTC)

Could be something to do with the shear strength of concrete! —Preceding unsigned comment added by 79.76.205.40 (talk) 00:57, 13 February 2010 (UTC)

Does a flame cast a shadow?

Well, does it? It's kinda hard to tell because the flame itself generates a lot of light that would tend to light up any area that it would shadow - but just how opaque is the flame itself to (say) sunlight? SteveBaker (talk) 16:31, 12 February 2010 (UTC)

Well it depends on the relative brightness of the two light sources. I have certainly seen the shadow of a candle flame cast by bright sunlight, but it's a kind of translucent shadow. It's very easy to check this out for yourself if the sun is shining and you have a candle.--Shantavira|^{feed me} 16:46, 12 February 2010 (UTC)

I guess the question here is this: does flame absorb light? This is an excellent question, and I suspect that the answer is yes, but this is pretty far out of my comfort zone. Is there a plasma physicist in the house? – ClockworkSoul 16:54, 12 February 2010 (UTC)

A yellow flame consists of glowing soot. Soot is black. Go figure. Cuddlyable3 (talk) 16:57, 12 February 2010 (UTC)

I've observed the "shadow" from a flame as well. I assumed it was not from the flame blocking light, but from the hot gas inside the flame acting as a lens, redirecting the light. Whatever portion of light is not absorbed should certainly be refracted. If you take a flame into bright sunlight, look for a brighter fringe of light around the flame's "shadow." 146.186.131.95 (talk) 17:05, 12 February 2010 (UTC)

A fundamental law of physics says that probabilities of absorption and emission of a photon are strictly related. Anything that can emit light can also absorb light at the same wavelengths. Anything that can absorb light can also emit light at the same wavelengths. Flame -- hot mixture of chemically reacting gases -- emits light (mostly in infrared and in visible range), therefore it also absorbs visible and infrared light. So yes, any flame can cast a shadow. It may not always easy to technically visualize and record that shadow, though; but it can always be done in principle. Steve certainly knows this, but for the general audience it is important to make the science clear first. Now, if you want to visualize the shadow of the flame, you can take a candle out into the sunlight - it will make a clear shadow of the flame. Some of that shadow will be because of the refraction rather than absorption, though. --Dr Dima (talk) 18:07, 12 February 2010 (UTC)

Steve, you should be ashamed of yourself... get a candle and a torch and find out for yourself... (The answer, however, is "yes" - a flame is a plasma, meaning there are lots of free electrons floating around. Those electrons will absorb light.) --Tango (talk) 20:30, 12 February 2010 (UTC)

It does depend if the flame is sooty and yellow versus premixed and blue so I think it is the soot not the electrons which do most of the absortion. Certainly if you pick the right laser there is enough transparency in premixed flames for laser tomography. Flames also have a massive temp difference therefore density difference across them. I have seen the flame and violin demo a few times (sound has a huge impact on flame structure) and even tried probing flames ultrasonically. The violin one you could do in a school lab with a big floppy bunsen I reckon. --BozMo talk 20:48, 12 February 2010 (UTC)

I don't have a candle anywhere in the house...but in any case, I was hoping perhaps for some kind of quantitative feel for how much a flame is likely to attenuate the light passing through it...sooty yellow and unsooty blue flames are both interesting. FWIW, I'm doing some computer graphics fires and things like rocket exhausts and trying to understand at what 'density' to draw the shadow of a flame (if at all). If it were possible to estimate the ratio of light emitted by the flame to that passing transparently through it, I could make a call as to when the shadow would be negligably visible and save a bunch of computer time by not drawing it when it's too tenuous to be noticable. The smoke produced by the flame is a different matter - that obviously does cast a shadow - and I have that much nailed. I just can't think of any source that tells me the transmissivity of a flame...and it's insanely difficult to measure (even assuming I could set a building on fire to get a nice BIG flame to measure)! SteveBaker (talk) 05:15, 13 February 2010 (UTC)

You can have the entire range of absorption, from fully opaque flame of poorly burning oil to practically invisible flame of pure ethanol. As you said, experiment is crazy hard, but it may be the only option. Take a green laser pointer and try to measure if something comes through. There is not much green in the flame (unless you add some copper compound to the fuel), but the eye is most sensitive to the green; so shadow for green is like shadow for white. You will need to find a bandpass filter for your photovoltaic cell that blocks most light from the flame but allows the green to pass. And a cell big enough to compensate for the refraction of light by flame. I never tried this, so I'm not sure it will work at all. --Dr Dima (talk) 06:11, 13 February 2010 (UTC)

Since eclipsing binary stars cause a dimming of the overall brightness of the system when one star passes in front of the other, I'd say that the opacity of fire and plasma are enough as to cause a "shadow" in the way that it blocks some of the light from the other light source. ~AH1^(TCU) 23:34, 13 February 2010 (UTC)

thoracentesis

As a practicing general surgeon, I am asked to do thoracentesis regularly. I go for a complete drainage of the pleural space, removing all the fluid I can, safely. This is often amounts over the 1 liter your article notes. This causes consternation among my patients. Your article does not describe the cough reflex associated with reinflation of the alveoli (as a newborn does during the immediate inflation of the lungs (wah wah cough cough, waaahhh), a native, protective reflex to airbreathers, nor does it mention the pleuritic pain associated with reapproximation of the separated pleural surfaces. It is that second pain that caused the patient most recent in my memory to look at your article and come in all hot and bothered. The chest x-ray showed persistent clearing of the pleural effusion with no infiltration or pneumothorax. Exam did show decreased inspiratory effort (pain) and slight rb. I ask that your editors make some mild changes. That business of "removing more than 1 liter at a time associated with complications" needs modifier that not removing all means having to repeat the procedure, also at increased risk. —Preceding unsigned comment added by Tlfmd (talk • contribs) 17:41, 12 February 2010 (UTC)

We have a guideline here called Be Bold, which says: Go ahead and make the changes yourself! You're the expert. Click "edit this page" at the top of any article and go ahead and make any changes that are needed. Normally we want "inline citations" on every claim. Formally it is preferred that articles have inline citations from top to bottom, but in practice on Wikipedia this is rare — though it's needed if the article is to be considered high enough quality to be a "Good Article" or a "Featured Article". Comet Tuttle (talk) 17:52, 12 February 2010 (UTC)

I'd just like to add a note that Wikipedia Talk:WikiProject Medicine (aka WT:MED) is an excellent place to bring up concerns of this sort. Looie496 (talk) 19:03, 12 February 2010 (UTC)

Tlfmd, thanks for pointing that out. Although I'm surprised that you, as a general surgeon, are performing thoracentesis. My experience (in the UK) is that general surgeons do not deal with pleural effusions (indeed they shouldn't deal with pleural effusions). Axl ¤ [Talk] 09:43, 13 February 2010 (UTC)

From the British Thoracic Society guidelines: "The amount of fluid evacuated will be guided by patient symptoms (cough, chest discomfort) and should be limited to 1–1.5 litres." "Large pleural effusions should be drained in a controlled fashion to reduce the risk of re-expansion pulmonary oedema." Axl ¤ [Talk] 09:54, 13 February 2010 (UTC)

ant poison methanol

im allergic to boric acid i have a ant problem can i use methanol to kill them i heard it tastes sweet i dont want to use any regular ant poison —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 20:18, 12 February 2010 (UTC)

can i get an answer please i dont want to call an exterminator —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 21:09, 12 February 2010 (UTC)

Methanol? As in the poisonous alcohol (AKA wood alcohol)? Do you mean menthol maybe? Either way, get some bait traps instead. Or remove the food source. Ants are attracted to food. You can use tons of traps and poison and they'll keep coming back till you get rid of the food source. Ariel. (talk) 21:45, 12 February 2010 (UTC)

yes i mean Methanol, As in the poisonous alcohol. i already removed the food source. im not going to use bait traps i want to use methanol will it work , is it toxic to ants? and will they eat it? —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 21:52, 12 February 2010 (UTC)

Perhaps you'd like to tell us why you think it might be poisonous to ants? And by the way, demanding an answer from the volunteers who frequent this desk fifty-one minutes after you originally posed the question is not a good strategy for encouraging people to answer you. --ColinFine (talk) 23:12, 12 February 2010 (UTC)

Please sign your posts. It's the sweet thing to do. Cuddlyable3 (talk) 23:21, 12 February 2010 (UTC)

The practicality of methanol will be limited because it is volatile and will quickly evaporate. I think it is highly unlikely that they will eat it anyway. If you are insistent on using methanol, your best results will come from simply drowning them in it. (But don't inhale the vapors due to the toxicity!) —Preceding unsigned comment added by 72.94.164.21 (talk) 23:24, 12 February 2010 (UTC)

WILL THEY EAT IT —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 23:39, 12 February 2010 (UTC)

Orange oil and neem oil are far safer than methanol, and may work better, too. Of the two oils, orange oil smells much better :) . However, you will absolutely need to inquire if any one of those oils are recommended for use against ant infestations. I do not and can not give you an advice what to use; but I strongly suggest you do NOT use methanol indoors. --Dr Dima (talk) 23:49, 12 February 2010 (UTC)

I second that. Methanol is not only highly toxic, but its volatility is troublesome for this application -- its vapor pressure is high enough to allow it to give off hazardous toxic vapors (and to evaporate too quickly to have any effect on ants), but low enough to allow traces of the stuff to persist for a long time. (I know this firsthand, we use methanol at the refinery to scrub sulfur out of the flue gases, and we actually have to wear gas masks any time we're working with the stuff!) Worse, it's also water-soluble and can soak into the soil, so using it anywhere near water supplies or even household plants (or even on your lawn) is a very bad idea (quite apart from the fact that it's a violation of at least three EPA and OSHA regulations). Also, methanol is highly flammable -- not quite as flammable as gasoline, but pretty close -- so you should be careful using it around electrical equipment, because it's particularly prone to ignition by sparks. My advice to you and to everyone else is, don't screw around with methanol unless you REALLY know what you're doing. And last but not least, it prob'ly won't even work against ants because (1) it will evaporate too quickly, and (2) its toxicity to humans is due to it oxidizing to formic acid, which ants make naturally and therefore have immunity to it. Oh, and did I mention that it could damage furniture and wood floors by dissolving the lacquer coating? 24.23.197.43 (talk) 00:29, 13 February 2010 (UTC)

Firstly, even if they are inside your house - they don't live there. If you can wipe out the nest (which is outdoors someplace) then within a day or two, there won't be any more ants indoors. Knowing that gives you more treatment options. Sure, you're allergic to boric acid - but if you wear a mask and gloves, you can apply it outdoors without coming into contact with it. There are many other options too. I had good luck with vicious Texas fire ants by kicking the top off of the nest and pouring a gallon of boiling water mixed with washing up liquid (to help it get into the small burrows). Merely warm water won't do. And, yes, you need to be sure that all of your food is in proper containers or they'll come back. SteveBaker (talk) 02:52, 13 February 2010 (UTC)

i dont want advice on other things to use just will methanol kill them —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 04:49, 13 February 2010 (UTC)

It seems like you already got a clear "NO!" on that - we're just trying to offer alternatives that you may not have thought of. SteveBaker (talk) 05:05, 13 February 2010 (UTC)

or, as pointed out above, the answer could be "yes" if you pick up the ants and hold them under the surface of your methanol. Plain water would be safer but would take longer. Seriously, though, take advice and look for alternatives. We think that methanol might do you more harm than real ant killer, despite your allergy. Dbfirs 22:14, 13 February 2010 (UTC)

If methanol vapor were so deadly, I doubt Sterno would be so widely used in chafing dishes or alcohol lamps supplied in chemistry sets. Just don't try to drink it. Edison (talk) 04:44, 14 February 2010 (UTC)

In the days before photocopiers, methanol was widely used in schools for "spirit duplicators" (no, they worked using merhanol spirit, they didn't duplicate spirits in any form!). Good ventilation was advised, but the vapour was not considered dangerous for occasional use. As pointed out above, because methanol evaporates rapidly, it would be necessary to use a large quantity to maintain a supply for the ants, and, even if it did work, this might be dangerous to humans with prolonged breathing of the vapour in a confined space. Perhaps a greater problem would be the fire risk in leaving large quantities of a flammable liquid lying around in open containers. Dbfirs 08:01, 14 February 2010 (UTC)

Human field of view

How many degrees of view can humans see horizontally and vertically? 92.29.82.48 (talk) 20:48, 12 February 2010 (UTC)

Our Field of view article claims it's about 180 degrees horizontally, and that "it varies" vertically. The article could use some improvement. Comet Tuttle (talk) 22:29, 12 February 2010 (UTC)

The article Peripheral vision is in poor shape too.Cuddlyable3 (talk) 23:19, 12 February 2010 (UTC)

180 degrees is the statistical average for most people, but some folks can see as many as 240 degrees horizontally. (My own field of view, BTW, is about 220 degrees.) FWiW 24.23.197.43 (talk) 00:33, 13 February 2010 (UTC)

Our area of distinct vision, in which we can see details or read normal print, without eye movements, is tiny, confined to the Fovea of the eye, subtending less than 2 degrees of visual angle horizontally (or about twice the width of the thumbnail at arm's length) and less vertically. The edges of the claimed 180 degree field would be nearly blind, only to detect things like movement of objects or flashing lights, whereupon we would normally direct the fovea to that region of visual space by eye and head movements. The horizontal field of view is obviously greater if you combine the fields of view of the two eyes. Prey animals like rabbits or horses have their eyes set more to the side than to predator aniimals like cats, so they have a 360 degree horizontal field of view, at the expense of depth perception in the forward direction the predators enjoy. As an experiment, look at the computer screen with your two thumbs extended next to each other, at arms length, below a line of text. Without eye movements, can you read words to the left and right of the thumbs? Now turn your chair at a 90 degree angle to the computer screen, and move your fingers in front of the screen, at about 90 degrees from your visual fixation point. Rotate until the movement disappears. You have mapped your visual field. Eye doctors do tests for the extremes of the visual field called Perimetry. Some diseases cause the visual field to shrink. Edison (talk) 02:16, 13 February 2010 (UTC)

There are many numbers here because there are many ways to measure it. From extreme head-turn plus eye swivel to opposite head turn plus eye swivel is very close to 360 degrees. With eye motion only, it's more like the 220 that '24 suggests. Without eye motion - and including the outer regions of the retina where we can only see in monochrome (but are very sensitive to motion), it's more like 90 degrees - and for full color vision, more like 50 to 60 degrees. But our ability to conentrate our gaze on a smaller region still comes from brain function rather than actual vision so it's possible to concentrate only on (say) the middle 10 degrees - without noticing what's going on outside of that small region (eg when reading). These numbers are all slightly variable from individual to individual - and also depend on your eyesight (and whether you wear glasses). SteveBaker (talk) 02:08, 13 February 2010 (UTC)

At 90 degrees or so from fixation, only gross changes are seen, so glasses are less important than in the areas nearer fixation. The lens does not focus that sharply nor is the retinal that acute at visual angles far from fixation. Edison (talk) 02:29, 13 February 2010 (UTC)

Your coloured field of view is also smaller than your black and white field of view. You don't normally notice as your brain is very good at making up what colours things in you peripheral vision are. To test this, take a few coloured pens or pencils, hold one behind someone so that they don't know which colour you are using, then with the person still looking forwards bring the pencil round slowly round the side of their head towards the front of their head. You can only accurately describe the colour when its about 45 degrees away from your front. If you do the same thing but show someone which pencil you're using they'll be able to tell you the colour much sooner than before. Maybe someone can remind me as to why this happens. Smartse (talk) 17:42, 13 February 2010 (UTC)

Chemistry diagrams

http://en.wikipedia.org/wiki/Penicillin

On the right hand side of the page there is a diagram depicting the structure of penicillin. Between the HN and C atoms there is a black shaped wedge. Between the c and H bond (top middle) and the C and C bond (bottom right) there are wedges with parallel lines. Please could you explain the meaning of these bonds - I can't find reference to them anywhere90.216.189.67 (talk) 20:56, 12 February 2010 (UTC)

Thank you

Our article Skeletal formula describes how this type of chemical structure depiction can be interpreted. -- Ed (Edgar181) 21:03, 12 February 2010 (UTC)

Put simply the black wedge shows that the molecule is 3D and that that bond is coming out of the paper/screen towards you. Smartse (talk) 17:44, 13 February 2010 (UTC)

Minor quibble - all molecules are 3D. The wedges are there to indicate chirality - that is, how the molecule is structured around the atom with the wedges matters. Chiral compounds can have very different properties from their mirror image compounds. The classic example is thalidomide, where one compound is effective against morning sickness, where the other causes severe birth defects. -- 174.21.247.23 (talk) 19:25, 13 February 2010 (UTC)

Cryogenics

Hello i was wondering what has been in the field of cryogentics sucessfully done have scientist been able to freeze mice and revive with full function? i read article on cryogentic but did not see information about current ability our science is in area? (Dr hursday (talk) 22:53, 12 February 2010 (UTC))

The article you want is Cryonics.Cuddlyable3 (talk) 23:14, 12 February 2010 (UTC)

The short answer to your question is "No". The reason is, when mice are frozen, all the water in the tissues freezes and forms ice crystals -- and since ice expands during freezing, those crystals usually poke holes in cell membranes, killing the cells. It's the same reason why you don't put fruits and veggies in your freezer -- the ice crystals destroy the cells and make the veggies (or fruits) soften when thawed. In the case of mice or other animals, the blood also freezes and its expansion bursts blood vessels -- sort of like a water main bursting in sub-zero weather. You could of course put chemicals into the blood that would keep it from freezing, but the problem is, those chemicals are toxic enough to kill or to cause irreversible damage. So far, the only living organism to have been successfully frozen in dry ice and revived with full function is Han Solo in Star Wars; but it's only a movie, it's not anything like real life. 24.23.197.43 (talk) 00:55, 13 February 2010 (UTC)

Wood Frogs freeze solid and thaw out with no apparent ill effects all the time. Perhaps we could learn from them. Edison (talk) 01:49, 13 February 2010 (UTC)

I have fixed your link, Edison - internal links inside of external links confuse the MediaWiki engine. Nimur (talk) 16:49, 13 February 2010 (UTC)

Well, those few animals that can do this have a natural antifreeze in their bodies. It might be possible to do some genetic engineering and gain that benefit. However, it's not clear how well things like higher brain functions would survive, for example. If a frog lost all of it's memories through the process, it wouldn't really matter a damn - but with humans...not so good! I don't think it's impossible that we could do that one day - but don't bank on it. SteveBaker (talk) 02:03, 13 February 2010 (UTC)

There are quite a few memories I would not mind losing. Edison (talk) 04:37, 14 February 2010 (UTC)

I have seen no references that say the wood frogs lose their memories each time they freeze and thaw. If the memories are stored as new synapses, they might survive. Edison (talk) 04:39, 14 February 2010 (UTC)

This article in 2008 discussed work that Israeli scientists were doing on pig livers that could be frozen and then still functioned in another pig. Maybe read some papers in Rejuvination research if you want more up to date information. Smartse (talk) 17:55, 13 February 2010 (UTC)

As Steve says, it's the brain that's the tricky bit. Livers have amazing regenerative capabilities. --Tango (talk) 19:31, 13 February 2010 (UTC)

You be be thinking about the successful cloning from a frozen mouse, which was reported a few years back. [2] See also this interesting, if somewhat tangential, story about super-cold squirrels. [3] Rockpocket 02:21, 14 February 2010 (UTC)

21 years ago?? There simply must be more on this matter. 77.18.91.253 (talk) 19:41, 14 February 2010 (UTC)

Cloning from a frozen animal is entirely possible - you don't need to revive the animal - all you have to find is some intact DNA. In all of those trillions of cells, you only have to find one that didn't get destroyed. If 1% of the cells survived, you could clone without difficulties - but if 99% of your cells are ruptured then you're very, very dead! There are serious discussions of cloning a mammoth from frozen tissues found in northern siberia. SteveBaker (talk) 23:17, 14 February 2010 (UTC)

You can read more about it here. Rockpocket 19:20, 15 February 2010 (UTC)