Wikipedia:Reference desk/Archives/Science/2009 January 26

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January 26

Air pressure or surface tension

Have any of you ever noticed this? Let's say you have a plastic cup and a large basin of water. You put the cup in the water sideways so that some water goes into it. Then you turn the cup upside-down and submerge it. When you try and pull it out again (keeping the cup upside-down), it sticks a little at the surface and you have to apply a little extra force in order to pull it out completely. Is that due to surface tension, or have I somehow decreased the amount of air inside the cup (perhaps having displaced some of the air with water), creating a slight vacuum effect? howcheng {chat} 02:51, 26 January 2009 (UTC)

Surface tension is probably a factor. Another factor could be that the water falling out of the cup creates a vacuum behind it, that vacuum is going to try and hold the water in. It could be the combination of the two, actually - surface tension tries to hold the water together, the air pressure tries to keep the water in the cup, so you have to add extra force to overcome that. --Tango (talk) 03:36, 26 January 2009 (UTC)

The water you let into the cup is staying in there while the upside-down cup is part way out of the water, because of the pressure of the surrounding air. The force you're feeling is simply the weight of that water. The reason you didn't notice it before you lifted the cup out of the water was that it was buoyant while it was submerged. If you try filling the entire cup with water and lifting it out udside-down, the force at the moment you lift it out of the water will be exactly the same as if you lifted it out right-way-up, also full of water. Surface tension is not involved in any significant way. --Anonymous, 05:24 UTC, January 26, 2009.

Interesting. Will have to try that when bathing the kids tonight. Thanks. howcheng {chat} 19:25, 26 January 2009 (UTC)

Catching the milk

Resolved

 – Fat can be good

When heating milk for cocoa, I have noticed that skimmed or semi-skimmed milk is more likely to catch (burn on the bottom of the pan) than full-cream. Why would this be? DuncanHill (talk) 04:13, 26 January 2009 (UTC)

Because the fat in the cream provides some burning protection to the milk solids (mostly sugars and proteins). Without the fat coating these particles, they are much more susceptible to being affected by the heat. The burning of the milk is a varient of the Maillard reaction, though in this case, its a rather unwanted one. --Jayron32.talk.contribs 04:49, 26 January 2009 (UTC)

Fat/oil has a much higher boiling point, so I figure this is part of the reason. BTW, try microwaving the milk to avoid burning it. StuRat (talk) 17:00, 26 January 2009 (UTC)

Just last night, I was reading some related advice in Cook's Illustrated. They suggested putting a small amount of water to cover the bottom of the cold pan, heating that water (to boiling, if I recall correctly), and then adding the milk. This method is supposed to prevent the problem you describe. -- Coneslayer (talk) 14:04, 27 January 2009 (UTC)

There's even a device to do just that, called a double boiler, where water boils in the bottom part, and the steam then heats the milk in the top part, but not hot enough to burn it. Before microwave ovens, this was the best way to heat milk. StuRat (talk) 16:46, 27 January 2009 (UTC)

We call them bain maries in English :) DuncanHill (talk) 16:57, 27 January 2009 (UTC)

Actually - we call them bain marie's in French - even though we're English! SteveBaker (talk) 18:05, 27 January 2009 (UTC)

A double boiler is a similar idea, but not quite the same thing, since the top pot sits in boiling water in a bain marie, while the top pot is held out of the water in a double boiler. StuRat (talk) 21:14, 27 January 2009 (UTC)

Or just stir constantly - always works for me. --Tango (talk) 14:12, 27 January 2009 (UTC)

• Thanks for all the answers - very interesting. I prefer full cream milk because it tastes nicer, but circumstances sometimes dictate the use of the watery stuff. I've tried using a microwave, but it is hard to get the milk boiling without it overboiling. DuncanHill (talk) 16:57, 27 January 2009 (UTC)

• I don't think you need to boil it, just get it hot enough for hot cocoa. Does your microwave have variable power levels ? If so, use the lowest setting. StuRat (talk) 15:37, 28 January 2009 (UTC)

The car of the future!

I remember reading back in high school about guys that had developed engines with unheard of efficiency and gas mileage and such. This was usually in magazines such as Popular Science and Popular Mechanics. I haven't picked up either magazine in quite a few years but I would guess that they still publish these stories from time to time. What happened to these engines? I was told by various cynical and pessimistic people over the years "The oil companies bought the patents to keep people buying more gas!" although, I've never been one to believe in too many cabals. So what's the story with these things, these wonder engines? Where are they? Were they always just figments? Or were they not commercially viable for one reason or another? Dismas|^(talk) 06:24, 26 January 2009 (UTC)

What you're remembering is known as the "Pogue carburetor." This is what Snopes has to say about it. Also read about the Pogue patents. Interestingly, the only article we have for a Charles Pogue is not this Charles Nelson Pogue. 152.16.59.190 (talk) 09:41, 26 January 2009 (UTC)

Well now we have Charles Pogue (disambiguation), so if someone writes an article about the Pogue Carburator or that Pogue, it can hang off there. DMacks (talk) 04:30, 27 January 2009 (UTC)

Free energy suppression and fuel saving devices are an interesting read. DMacks (talk) 14:33, 26 January 2009 (UTC)

A lot of the inefficiency in car engines comes from running them at variable speeds and temperatures. If an engine could be run continuously, at a constant speed, and was tweaked to perform optimally at that speed and temperature, it would get much better efficiency numbers. Electric/gasoline hybrids, which run the engine at a constant speed to charge the batteries, do get better mileage, but still suffer from temperature changes from starting and stopping the engines periodically. StuRat (talk) 16:54, 26 January 2009 (UTC)

One point of clarification, as StuRat's commas make this unclear: Hybrids which run the (gasoline) engine at a constant speed, which are presently a very small subset of all hybrid cars, are applicable to this statement. These "series hybrids" include models like the not-yet-released Chevrolet Volt. They do not include the Prius or any other mass-distributed hybrid, in which the gasoline engine still connects directly to the drivetrain. — Lomn 18:27, 26 January 2009 (UTC)

Thanks for the clarification. Your right, my wording didn't make that clear. StuRat (talk) 21:38, 26 January 2009 (UTC)

Some of those things have definitely made it - the Wankel engine, for example, had horrible lubrication problems when it was first described (probably in Popular Mechanics!) - but that was solved after maybe 30 to 40 years of engineering effort - and now you can buy several Mazda's that have Wankels in them. But many of these ideas (the Scuderi engine for example) fall by the wayside for reasons of practicality that the original inventor didn't consider: Cost of manufacture, reliability, wear, pollution, noise, smoothness, overheating on hot days, failure to start on cold days...many of those ideas simply didn't prove practical. Also: If you see some engine that seems impressive because it did 55mpg back in the early 1960's - remember that lots of engines could do that when pulling cars of that era. My 1963 Mini does 55mpg with it's little 37hp engine. My 2007 MINI does barely 40mpg...which is considered pretty good by modern standards. That's not because some mysterious magic thing happens in the 1963 engine - to the contrary, it's crude and horrible in many ways. It's because the '07 car is exactly twice as heavy and can do 140mph and 0-60 in 6.5 seconds with it's 170hp engine, while running the airconditioner, the radio, the computer and so on. The '63 can just barely break 70mph and has a 0-60 time around 12 seconds - no radio, not much of a heater, no A/C, etc. The '07 car needs its first service at 20,000 miles - the '63 requires the owner to do work every 1,000 miles with an oil change and full service every 3,000. So you have to be careful. MPG numbers from old magazines probably have to be halved before you can compare them with modern engines - and MPG is not the only consideration. SteveBaker (talk) 19:08, 26 January 2009 (UTC)

What's this about cars being heavier today? It was my impression that they were considerably lighter, unless you count things like SUVs and Hummers as cars. You know, to economize on fuel and all that. I remember hearing 2 tons as the typical weight of an ordinary car circa 1970 and 1 ton today. Am I that far off base? --Anonymous, 09:40 UTC, January 27, 2009.

This depends on the location and date, of course, in that those things effect the price of fuel. Europe was known for small cars, and the US for large cars, traditionally, but they are becoming more similar now, due to globalization. As would be expected, large cars were common where and when fuel prices were lowest (as adjusted for inflation): [1]. The biggest cars in the US were perhaps from the early 1970's, right before the 1973 oil crisis, which stopped all our fun. Also, you can't exclude SUVs, minivans, trucks, etc., as more people drive those now than did back then. StuRat (talk) 15:30, 27 January 2009 (UTC)

The first generation VW Polo was below 700kg and the newest version is 1100kg.--Stone (talk) 10:24, 27 January 2009 (UTC)

My '63 Mini comes in at 1300lbs - my '07 MINI Cooper weighs 2600lbs - exactly twice as much - and until the SmartCar came on the scene, the modern MINI was the smallest car on sale in the USA. Ironically - there is more luggage space AND more rear legroom in the '63 car...and it handles better. Most cars that were around 20+ years have gained about 50% in weight. Most of that is because of the legal requirements for crash survivability, plus air conditioning, plus higher performance expectations (it really is a pain driving a car with a 72mph top speed on a Texas freeway!), plus luxury, plus emissions control. I'm not saying that the weight gain is necessarily a bad thing - but it does explain why the performance numbers for these bizarro-engines tend to look so good from a modern perspective. Some of them genuinely DO have better power-to-weight or fuel efficiency than conventional otto-cycle engines - but many are not that great. Those that are better on a purely fuel/power basis tend to have other (fatal) practical problems. The Scuderi engine for example has twice the usual number of cylinders - set up in pairs so that one is hot and the other cold. The latter collects water and corrodes - and the temperature difference between them causes stresses in the engine block which cracks very easily - also, the conduit between the two cylinders gets fouled easily and is almost impossible to clean. So while the Scuderi gets almost twice the power than a conventional engine - it would cost close to twice as much to make and it would fail very easily. SteveBaker (talk) 15:22, 27 January 2009 (UTC)

With twice the power, it seems like you could use some of that extra power to heat the cold cylinders, using the exhaust, and cool the hot cylinders, using air and unburned fuel, to equalize the temps. Has this been tried ? StuRat (talk) 20:57, 27 January 2009 (UTC)

As I understand it, the reason the Scuderi cycle is more efficient (on paper) than the Otto cycle is precisely because the exhaust condenses in the cold cylinder so you aren't robbing the engine of power when you push the exhaust gasses out - but rather get benefit from the exhaust gas condensation dropping the pressure in the exhaust cylinder and extracting power on the up-stroke. If you let it get hot, you lose all of that benefit. But the details are sketchy because companies who have been working on these split-cycle engines are pretty secretive.

Interestingly though (looking at the references in our article) it looks like the technology (which has pretty much languished since the 1890's(!)) is undergoing something of a revival - with serious efforts to make a workable/manufacturable engine as recently as the middle of last year. One thing that is really interesting about the Scuderi is the ability to shut down the combustion cylinder and use the exhaust cylinder as an air pump. So you can make an 'air-hybrid' engine where you run the engine at it's most fuel-efficient RPM all the time - using excess power to compress either inlet air or exhaust gas into a pressurized cylinder. Later, when you need more power you use the pressurized gasses to produce extra power by injecting it into the combustion cylinder. If you compress air (from 'active braking') and exhaust gasses (when storing unused engine power) into separate tanks then you can use the pressurized exhaust to produce pneumatic power from the same pair of cylinders and any pressurized air you may have accumulated to supercharge the engine when more power is needed. But for all of those cool things to work out, there are a lot of the more annoying fundamental things to iron out first...like not having the engine block crack! IIRC, there are also issues about what happens to oil that may get into the exhaust cylinder when the engine gets old and the piston rings start to wear. In a normal engine, the excess oil gets burned off (which is not great - but at least the engine still runs) - but in the Scuderi, there is no place to go. If it starts to fill up the cylinder - you'll eventually get a 'hydrolock' and the engine will self-destruct. That kind of annoying practical problem is what always makes these fancy engines take decades to perfect (cf. Wankel engines). SteveBaker (talk) 14:35, 28 January 2009 (UTC)

To keep the engine block from cracking, how about using a material with little or no coefficient of thermal expansion ? (Is there something cheaper than a platinum-iridium blend, perhaps some type of ceramic ?) You could also occasionally heat up the cold cylinder to drive out accumulated water and oil, say when the car engine is turned off. StuRat (talk) 15:28, 28 January 2009 (UTC)

The car of the future? It's time for a new bug; a light weight, cheap, simple hybrid that stays the same for several decades, so you can actually find inexpensive parts for it and maintain it yourself. Imagine how cheap it could be made - stripped of whistles and bells and with half the parts count. Also, each wheel hub should be an electric motor for traction control, regenerative braking and to eliminate the traditional power train. It should have a 10-20 mile range on batteries. The IC engine should be a small ultra-high efficiency diesel that runs at 40%+ thermal efficiency, and only at its most efficient settings. TungstenCarbide (talk) 01:38, 30 January 2009 (UTC)

I've thought of many of those items, too, like the car model that never changes (except for actual fixes). I'd predict that sales would drop off after the model got "old", but would later rebound after it became "classic", especially when the lower cost and higher reliability became apparent. I'd also change the way such cars are "sold". The manufacturer could supply the car, full service (including replacement models as needed), and insurance, etc., leaving the consumer only responsible for electricity. This could all be done for a fixed annual fee. The removal of risk in transportation costs would be a selling point, too.

I'd also thought of a small electric motor on each wheel. This, hopefully, would allow one person to replace the motors as needed, without special equipment to "lift the engine". StuRat (talk) 06:00, 30 January 2009 (UTC)

I think the wheel/motor hub has a lot of potential - it's an unexplored area in the consumer automotive industry. The problem is getting a mature and simple design with the economy of scale required to make it cheap. But the advantages are big; eliminate 300 pounds of drivetrain as well as the associated costs. All time 4 wheel drive with active traction control that's potentially superior to anything in existence. Regenerative braking. Redundancy. I wonder if it could be an induction design, fully encapsulated with no brushes. The controller would have to be pretty sophisticated. --TungstenCarbide (talk) 17:24, 30 January 2009 (UTC)

Actually, that's even better than 4-wheel drive, that's all wheel drive. StuRat (talk) 00:12, 2 February 2009 (UTC)

Einstein Field Equation

Is the Einstein field equation G_ab=8πKT_ab or G_ab=8πT_ab or G_ab=T_ab(G is the Einstein Tensor, K the Gravitational constant and T the Strees-Energy Tensor)?The Successor of Physics 06:43, 26 January 2009 (UTC)

Doesn't really matter, does it? You can get rid of K through a redefinition of your units, see Natural units and Geometrized unit system. In SI units, the factor is actually 8πK/c⁴ and you seem to have set c=1 already. You could get rid of 8π by a redefinition of either G_ab or T_ab or both, if you wanted to, but that's rather uncommon, I think. There's no "wrong" or "right" here, it's just a matter of convention. Check in your text book what convention they use. --Wrongfilter (talk) 17:52, 26 January 2009 (UTC)

Remember, if you remove a pi from the field equation, it will be at the expense of adding pi's to other equations. --Tango (talk) 23:28, 26 January 2009 (UTC)

Thanks!!!The Successor of Physics 04:50, 27 January 2009 (UTC)

Drake equation with infinite L

I think I've found a flaw in the Drake equation.

Suppose that it is possible with non-zero probability for a civilization to break the law of entropy and continue to exist and release radio signals forever. Then the term L in the Drake equation, as an average, is infinite. Since the existence of Earth rules out a zero value for any other term in the equation, this in turn implies that N must be infinite as well. But in reality, this will be true only once the universe is infinitely old.

Would it be possible to adjust the Drake equation to account for the finite age of the universe? NeonMerlin 09:34, 26 January 2009 (UTC)

I don't think you need to adjust anything. The maximum L cannot be infinity; max L is equal to the age of the universe, although in my unprofessional opinion it is unlikely anything got started for at least the first billion when everything was getting settled out into galaxies and such. If 1% of alien civilizations builds a broadcaster that lasts for 10 billion years and the rest will communicate for 1000 years on average then we get an L of 10,000,990. 152.16.15.23 (talk) 10:14, 26 January 2009 (UTC)

Reading your question over again I realize that I may have not given you the answer that you wanted. Are you looking for a way to express the Drake equation as a function of time passed since the first possible civilization could have formed with the assumption that a fixed fraction of the civilizations that form continue broadcasting for the rest of eternity and thus accumulate? 152.16.15.23 (talk) 10:29, 26 January 2009 (UTC)

That's not even the big effect. If civilizations are arising at a uniform rate (in fact, you'd want to tie it to the star formation history of the universe in some entirely unknown way - life as we know it won't arise until you produce some metals), you'd just use half the hubble time as an average age. WilyD 15:03, 26 January 2009 (UTC)

This is a problem with most predictive mathematical models — they can lead you astray if you don't pay attention to their limitations. In the original Drake formulation, there are just two terms that aren't unitless constants: L, which is the average lifetime of a broadcasting civilization; and R^*, the average rate of star formation in our galaxy. (Note that Drake only contemplates civilizations within our own galaxy, not across the entire Universe.)

Implicit within those terms is the assumption that L will be less than the age of our current galaxy (civilizations require some time to evolve), or at the very least, less than the age of the Universe. Pushing the formula back further in time (with a larger L) would imply that civilizations had been developing around stars that had not yet formed. The alternative form of the Drake equation (Drake equation#Alternative expression) described in our article incorporates this restriction a bit more explicitly. There, the final term L/T_g – the average lifetime of a communicating civilization divided by the age of the galaxy – should end up as not more than 1. (Give or take some fudging I don't want to get into, if that ratio is 1 then every civilization that starts broadcasting continues to do so forever.)

Of course, that formulation falls down on very long time scales, too — as L approaches the lifetime of the average star, species with interstellar capability begint to settle 'new' stars (increasing the odds that a given star system will harbor life). Species without interstellar capability, meanwhile, will tend to get wiped out as their stars go out. TenOfAllTrades(talk) 14:46, 26 January 2009 (UTC)

The trouble with this hypothesis is the setting of the other attributes to 1.0 because Earth represents one example. Doing that tells you that either:

• Earth is eventually able to learn to broadcast radio forever...hence WE are the cause of L=infinity...but N_e (the average number of civilisations per suitable planet) could still be one-over-infinity (there are an infinite number of planets and we are the only one with life). Then the equation boils down to infinity over infinity - which tells you nothing...we may still be alone in the universe.

• The various 'N' terms in the equation strictly refer to the number of suns/planets/civilisations THAT ARE CAPABLE OF ACHIEVING LIFESPANS OF DURATION 'L'. Now, you can't count the Earth as 1.0 for any of those N terms because we may never defeat entropy - so any one of the N's could go to zero - and we're back with no aliens out there.

But the Drake equation really needs be used to count the number of civilisations that are NOT us - otherwise it's not very interesting. If you exclude Earth from the math - then the answer can still be zero - even with L=infinity.

But in any case, the idea of a civilisation being able to 'defeat entropy' is kinda silly...as far as we know, entropy can no more be defeated than time travel or superluminal travel be achieved. If you assume that science-fiction physics is allowed - then you need to rewrite the equation to include time travel and instantenous travel. If we aren't talking about "known physics" - but instead "unknown physics" (in which entropy can be defeated for example) then the Drake equation itself is incorrect and would have to be severely amended. The whole POINT of the equation was to estimate the number of civilisations we might hear from given our present knowledge of the universe. Once you start throwing in alternative physics models - all bets are off.

SteveBaker (talk) 15:54, 26 January 2009 (UTC)

There seem to be several flaws, all dealing with levels of technology reached by other civilizations:

1) I agree with your concept, that, if a civilization survives beyond some length of time, they may have overcome all the problems which tend to cause extinction, like warfare and living on a single planet.

2) They may also develop ways to communicate instantly with other civilizations, over vast distances, and in different times, say by using wormholes.

3) There seems to be an implicit argument in the Drake Equation that only our galaxy matters, while I can imagine a civilization in another galaxy that could spread to ours, either physically, or virtually.

4) There may also be life forms in other dimensions/parallel universes, which manage to develop a technology which allows them to communicate with us. StuRat (talk) 16:46, 26 January 2009 (UTC)

I would argue that if communication between "parallel universes" is possible, then they aren't really separate universes. I can't think of a reasonable definition of "universe" which would consider them separate. --Tango (talk) 00:53, 27 January 2009 (UTC)

We may indeed want to redefine the word "universe" at some point if that happens, but my point is that the Drake Equation doesn't consider this possibility. StuRat (talk) 15:18, 27 January 2009 (UTC)

For a civilization to survive the possibility of extinction, it must be far more advanced than us, and it must also have learned how to keep its civilization alive if its own actions start destroying its environment. Our own species might not even survive 3 million years, and most scientists agree. The Fermi paradox really isn't such a paradox. ~AH1^(TCU) 18:17, 27 January 2009 (UTC)

Whether civilizations self-destruct has a lot to do with what nasty weapons science brings us in the future. Nuclear weapons may be capable of destroying all human life on a planet. And perhaps more powerful anti-matter weapons (which may be available in a century or so) might be capable of destroying the planet itself. However, once people have spread to many planets, moons, asteroids, and space-stations, in many solar systems, and floating between them, even this won't be enough to wipe us out. So, we might be safe, unless there's some new super-weapon that will allow anyone to wipe out the galaxy or universe, then self-extinction will become virtually inevitable. StuRat (talk) 20:52, 27 January 2009 (UTC)

In dogs, say a Great Dane and a Chihuahua were to breed through artificial insemination...

What would the offspring look like? Would this even be possible? This article shows how big the size difference can be. So what might be the effect if the mother was a Great Dane and the father was Chihuahua, and vice versa?--'Cause It's No Good (talk) 11:25, 26 January 2009 (UTC)

I don't think it is possible to say what they look like, we simply don't know enough about the genetics. Besides it will almost definitely vary a fair amount from cross to cross. I don't however see any reason why it would be impossible if the mother was a great dane. I'm somewhat doubtful the mother and/or puppies will survive if if the chihuahua is the mother however. Nil Einne (talk) 11:51, 26 January 2009 (UTC)

Couldn't they be prone to sympatric speciation, where the two dogs, currently physically incapable of mating, eventually become speciated where they cannot reproduce genetically? Or does them being in the environment of dog breeders prevent this from happening? -- MacAddct1984 ^{(talk • contribs)} 14:43, 26 January 2009 (UTC)

I think this is just another example of why the standard definition of "species" doesn't really work. Breeding between Great Danes and medium sized dogs and Chihuahuas and medium sized dogs (which will presumably occur naturally) means there will be an exchange of DNA between the two breeds even though they can't breed together easilly. --Tango (talk) 19:38, 26 January 2009 (UTC)

I think it is fair to say that the size would be somewhere in between the two, though I doubt it be right in the middle, I'd assume the hight would take after one more than the other. That being said, the father would have to be the Chihuahua since if the Chihuahua was the mother it would not be big enough to carry a baby that potentially would be so much larger than itself. It does matter which one is the mother as you keenly asked. We know some human traits we have are more from our mothers, like baldness in males (That is why they tell men to look at their mother's father to see if they'll be bald). I assume there are similar gender specific attributes in dogs, though there probably hasn't been as much research on it. Anythingapplied (talk) 20:40, 26 January 2009 (UTC)

I wouldn't be quite so fast to say it's all in the genes. It has been found that many features in fetal development are heavily influenced by conditions in the womb (do you also call it that in dogs?) like e.g. available nutrition, what chemicals are released to trigger certain cellular activities. It may still be that a Great Dane mix cub might grow too big for a Chihuahua mother, but I'd consider it more likely that it would fail to develop because something in the fetus growth pattern would not be compatible it might even be that the cub would drain resources the mother could not afford to lose. Another possibility might be that instead of carrying a litter of several pups most of the fetuses would fail to develop and only one would be carried to term. If the mother then can't birth it and no vet is available to do a C section they'd both die. Her birthing one rather big, but still manageable pup that then grows to something odd looking and significantly larger than a Chihuahua. A lot of a puppy's growth, size wise happens after it's born. So, a Chihuahua as mother has fewer chances, but it's not all because of genes. 76.97.245.5 (talk) 21:51, 26 January 2009 (UTC)

I think it's unlikely the bitch would die, I would expect the fetus to be aborted if it got bigger than was safe. I guess it's possible the bitch's body wouldn't notice the fetus was too big to be delivered until too late (since it can probably fit in the womb without being able to fit through the cervix), but it seems unlikely to me. --Tango (talk) 23:24, 26 January 2009 (UTC)

OOhhh. If I ask a question about donkeys, can I use the word "ass" in a totally non-ironical way too? --Jayron32.talk.contribs 15:04, 27 January 2009 (UTC)

If you want, although donkey is the more common term. --Tango (talk) 15:48, 27 January 2009 (UTC)

Throw the British term for a Rooster into the question for maximum linguistic titillation on this side of the pond. Edison (talk) 17:45, 27 January 2009 (UTC)

As for the OP, see a report of such a mix at [2]. This is certainly not a confirmed report, and I could find no such reports at Google News archive or Google books. Might be some discussion in the veterinary literature. Edison (talk) 17:53, 27 January 2009 (UTC)

Progesterone receptor A - isoform

I would like to know what is the molecular weight of (human) progesterone receptor A (PR-A)? There are a lot of reports that looked at PR expression using western blotting but it is for me still unclear what the 'real' molecular weight is. Some studies report 94 kDa, others 81-82kDa (in both cases there is a single PR-A band visible). Many thanks in advance. Ana. —Preceding unsigned comment added by 131.211.166.194 (talk) 14:37, 26 January 2009 (UTC)

Estimating the molecular weight of a protein on a western blot is a bit dicey. First, the molecular weight markers that are run alongside the sample are just meant to give an approximate reference point to estimate the sizes of the bands of interest. Second, a gel can run unevenly, throwing off the size estimates. Third, the size markers would typically be invisible on a western blot (since you're using an antibody that should only react with your protein of interest) so in practice one marks the position of the MW standards on the transfer membrane after visualizing the transferred proteins using a stain like Ponceau S. Fourth, the lanes containing the size standards are usually cropped out of the published photos and replaced manually with the approximate molecular weights. Fifth, sometimes only the band of interest is shown and reported to be at some particular MW for which you just have to take the author's word on it.

Now, if you were talking about a protein gel stained with Coomassie or Silver stain to visualize all the proteins, then you would only have the first 2 problems. However, you would still have the universal problem of post-translational modifications, which can either increase the apparent molecular weight (by adding on a phosphate, acetyl, ubiquitin, or lipid side chain, etc.) or decrease the molecular weight by cleaving the protein.

The "real" molecular weight of the A isoform of the progesterone receptor? You can get a predicted MW based on the weight of each individual amino acid in the chain (see http://ca.expasy.org/ for a good set of proteomics resources). In this case, the predicted MW of PGR-A is ~99 kDa. Of course, then you have the final problem with proteins... sometimes they don't behave themselves and they run out on the gel faster or slower than you expect them to. --- Medical geneticist (talk) 15:26, 26 January 2009 (UTC)

greatest possible scientific progress 40 years ago from single twitter?

thinking of working scientists with a 50+ year career:

if they could, today, send back 1 twitter's worth* of information (a clue) to themselves of 40 years ago regarding what to explore, what is the greatest progress they possibly could have made (early) as a result?

Actually I am interested by discipline: chemistry; biology; physics; mathematics; economics; medicine

Thank you!

* (140 characters) —Preceding unsigned comment added by 82.120.111.130 (talk) 17:37, 26 January 2009 (UTC)

Thats an interesting question. My first inclination would actually be for social purposes. Instead of giving them what we value the most, give them what they could use the most at that time in history. To me, the answer to that question would be something to try and prevent the cold war or any of the other wars that have occured in the last 40 years. Science will always move on. The fact that we would be sending them something we now know is proof that we would have will be eventualling have been going to learn it, and thus isn't necessarially of a crucial need to transmit, where as the lives lost in wars or the recources lost in economics collapses maybe of more importance. That said: In the field of math I'd probably transmit hints to the proof for Fermat's Last Theorem. Anythingapplied (talk) 17:56, 26 January 2009 (UTC)

I doubt you could get a significant amount of useful information about FLT into 140 characters. Wile's proof built upon large amounts of recent work - all Wiles actually proved was "All elliptic curves are modular." (although one shouldn't diminish the significance of that proof), that only proves FLT because of lots of work done before. I guess you could say "The proof of Fermat's Last Theorem involves modular forms." so people have an idea of what stuff to study, but that's about it. --Tango (talk) 18:14, 26 January 2009 (UTC)

I have a truly marvellous hint to give you which this SMS sized mesasge is too small to contain. --LarryMac | Talk 18:35, 26 January 2009 (UTC)

I think I'd go with "Fermat's last theorem didn't fit in the margin!"...well, if I were sending back something about Fermat...which I think would be a waste. 40 years ago is 1969 - that's around the time when most of the fundamental physics stuff had already been figured out. Look at the MANY Wikipedia timelines - it's tough to find a suffiently compelling single breakthrough since the mid-1970's. Using our one super-valuable 'twitter' to save them 5 years by mentioning Quarks or Dark Matter seems like a wasted opportunity. I wonder if there is enough space in our 140 characters to tell them how to send twitters back in time - it would be good to tell Newton to give up Alchemy or to tell Einstein about Quantum theory while he was still young enough to work on it...but if we're really stuck with 40 years then neither of those things is any good. I'd be awfully tempted to say "Make REALLY SURE that the 'twitter' standard allows unlimited-length message attachments" - then go on to dump all of Wikipedia and the results of the Human genome project onto the end of the message. But I sense you're not going to let me do that...so we're down to: "Arrest G.H.W.Bush'sOldestSon&BillGates.GlobalWarmingCausedByCO2-SERIOUS!!TellSteveBaker:BuyGoogle,DiseaseOfRobert R. don'tLetItSpread.". But specific scientific advice is tricky in so few characters. SteveBaker (talk) 18:48, 26 January 2009 (UTC)

The OP let us have one twitter per discipline, so you don't need to be quite so careful about what you choose. I'm struggling to think of good things, though - it seems there have been disappointingly few major discoveries in the last 40 years... There has been lots of incremental development, but few major breakthroughs. The biggest development in the last 40 years has to be computers, but even the major breakthroughs for that were made more than 40 years ago, it's just been incremental development since (pretty rapid incremental development, sure, but not anything a twitter is likely to help with). You could send back warnings about various disasters, of course, but I don't think that's really what the OP had in mind. --Tango (talk) 19:03, 26 January 2009 (UTC)

How about a message on the importance of the Internet, using words they would understand at the time, like "ARPA-NET, on home personal computers, will revolutionize how people communicate". Be sure to send it to Al Gore, so his claims to have invented the Internet will then become true. :-) StuRat (talk) 20:47, 26 January 2009 (UTC)

Would knowing how important the internet will become actually help develop it? It moved pretty quickly as it was... --Tango (talk) 21:45, 26 January 2009 (UTC)

It took from the 1960's to the 1990's for the Internet to become widely available for home users. I suspect that this could have happened a couple decades earlier, although, due to bandwidth limitations on dial-up modems, that text-only pages would be all that could be passed easily between computers at that time. Still, that could have been quite useful, and Wikipedia could have even started in the 1970's. StuRat (talk) 03:41, 27 January 2009 (UTC)

I think the essentials of the Polymerase chain reaction could be boiled down to 140 characters.-gadfium 23:07, 26 January 2009 (UTC)

"Useful fluorescent protein for tagging in Aequorea victoria" => Win Nobel Prize. Dragons flight (talk) 23:16, 26 January 2009 (UTC)

Apparently I need a better time machine. GFP was first isolated in 1962. Dragons flight (talk) 23:19, 26 January 2009 (UTC)

I'm also partial to sending lottery dates and numbers but that's not very scientific. Dragons flight (talk) 23:16, 26 January 2009 (UTC)

Computer science: "32 bit network addresses are too small, but go for a flat 32 bit memory model for RAM. Emacs, not vi, and never NotePad!" --Stephan Schulz (talk) 23:26, 26 January 2009 (UTC)

Er - you mean "vi, not emacs" - right? SteveBaker (talk) 00:18, 27 January 2009 (UTC)

Will all of the women please leave the audience? Now where did I put that bag of stones... --Stephan Schulz (talk) 10:20, 27 January 2009 (UTC)

Eighty Megs And Continually Swapping - Ha!! (Oh - it's OK - the chicks have left - we can just pretend like we're doing a bunch of macho/geek posturing).OW! That rock really stung!<wink, wink> SteveBaker (talk) 15:07, 27 January 2009 (UTC)

Plastics. -- Coneslayer (talk) 12:46, 27 January 2009 (UTC)

Nylon:1935, Polystyrene:1839, Polypropylene:1951...nope. (Oh, wait - I just followed your link - Hahahaha!). SteveBaker (talk) 15:11, 27 January 2009 (UTC)

What about 200 years?

Since we seem to be struggling with 40 years, how about 200 years? "The speed of light in a vacuum is constant for all inertial observers." has to be pretty high on the list of options for physics - once you have that, you can work out most of special relativity in an afternoon. Is there a similarly short statement that sums up quantum mechanics? What about for other disciplines? --Tango (talk) 19:15, 26 January 2009 (UTC)

Forget pure science. Go for technology: "Wires carrying current have a magnetic field. Conductor cutting through magnetic field gets voltage induced. Build motors and generators." Edison (talk) 19:54, 26 January 2009 (UTC)

I certainly would not send anything back. Humanity has teetered on the edge of self-annihilation too long for me to be comfortable making sweeping changes in the discipline that has defined the last 200 years. 200 years isn't long at all anyway; let them work it out for themselves. Who knows what kind of other advances were made trying to solve problems that we might spoil for them. The key article here is Serendipity. And don't even think of trying to avert wars or disasters; I'd argue confidently that nothing has more impact on the future than war. For one, the modern large-scale conflicts have marked remarkable leaps in manufacturing technology, not to mention paradigm shifts in popular culture- billions of people thinking and behaving differently. Yes the price was unimaginable suffering and the blood of millions, and the world might be better if things had happened differently, but we're not talking about a stable, post-scarcity world culture; we're talking about an era in which the world is stockpiling enough nuclear weaponry to turn the earth into molten slag, we're talking about progressive changes positively straining at the fabric of society to change slavery and torture into equality and humanitarianism and to accept radical changes in our way of life. That may be the best or the worst time to confront Earth with a greeting from the future, but it's certainly not the best time to meddle with things. .froth. (talk) 21:06, 26 January 2009 (UTC)

And anyway don't assume the message has to tell the truth.. Seldon lies to the Foundationers to great effect, and telling them the truth would have destroyed them, although a little 40- or 200- year hop is hardly comparable. .froth. (talk) 21:06, 26 January 2009 (UTC)

I'd go with disease prevention: "Boil water before you drink it and surgical instruments before you use them; eat fruits, veggies, grains, milk, and meat to be healthy." Alternatively: "Don't poop into rivers you drink from, bury it instead" (although they might have figured that out by then). StuRat (talk) 20:51, 26 January 2009 (UTC)

Except those things aren't sufficient. The link between peaches and cholera was real when they were being washed in contaminated water; someone who knows eating fruit has an unhealthy effect will discount the rest of your advice. You'd need to give them some clue as to what your motive was for boiling the water; it's not just something you do before drinking it. And sticking to the old-fashioned American food pyramid groups might make healthy eating easier in modern-day America, but it isn't an absolute healthy diet guide. There's no reason to add milk to an adult's diet if they're already getting what they need elsewhere, particularly if they don't retain the ability to digest lactose into adulthood. There's no need to tell them to eat meat if they're eating enough protein without it, and if they aren't they probably can't afford meat anyway. If they're getting enough carbs elsewhere there's no need for grains. Etc. Find an influential person and seed them with germ theory instead - "Miasma theory is onto the right idea, but it's tiny creatures not bad smells and they can travel through water too. Look into it." 79.66.105.133 (talk) 21:53, 26 January 2009 (UTC)

I believe germ theory goes back further than 200 years, and the invention of the microscope allowed people to actually see bacteria. Saying "boil water before you drink it, wash food with it, or wash dishes with it" might be a good addition, though. StuRat (talk) 03:36, 27 January 2009 (UTC)

Yes, but it wasn't taken seriously until the mid 19th century. Seeing micro-organisms doesn't tell you they cause disease. By giving someone the reassurance it would prove to be right 40 years before it was being seriously explored, you could provoke research that would save thousands of lives. 79.66.105.133 (talk) 18:38, 27 January 2009 (UTC)

Once you have the microscope, it's relatively straightforward to determine that some diseases are caused by microbes. If someone is sick, and their sores, spittle, blood, etc., show a microbe not present in healthy people, and when someone else gets the same sickness they get the same microbes showing up in them, it's a pretty simple jump to label that microbe as the germ theory vector. Yes, there could be other explanations for the microbes, like an opportunistic infection that only thrives once the immune system is compromised, but the simplest explanation is that they caused the disease. StuRat (talk) 14:12, 31 January 2009 (UTC)

"Marie, use a much longer stick when stirring the pitchblende" . DuncanHill (talk) 16:47, 27 January 2009 (UTC)

obviously this isn't working - so how about without a length limit

obviously I'm not getting answers about physics, chemistry, etc, and 40. So what if you can only relate one discovery, but without length limit. What discovery of the past 40 years would have the biggest impact 40 years ago?

We're talking about biggest impact now? Hm, I'd have to go with "you can't tell now, but the sun has become unstable and will destroy the entire earth in 40 years and there's absolutely nothing you can do about it. make your peace." 72.236.192.238 (talk) 22:09, 26 January 2009 (UTC)

I think you mean you have no chance to survive make your time. --Trovatore (talk) 23:13, 26 January 2009 (UTC)

"Rub sticks together"? --Tango (talk) 23:16, 26 January 2009 (UTC) Sorry, I wasn't reading properly... --Tango (talk) 00:21, 27 January 2009 (UTC)

I really don't think 40 years is enough. It's not the length of the message (well, not within reason) - even with a couple of pages, I doubt we could make a big impact. Part of the problem is that most of the work we do these days requires modern technology. It's no use telling them to look for the Higgs boson because the technology to do that simply wasn't there in the 1970's. Even if we tell them that computers are seriously important and the internet matters and to use open systems to allow scientists (and laymen) to collaborate on writing an encyclopedia...they simply couldn't do that back then because first you had to make smaller/cheaper computers - then you could use those to push the technology - which in turn allows still smaller/cheaper computers - which means that more people have them - which turns computer networking from a cliquish "UseNet" into the Internet and thence into the world-wide-web. Back when I was in college in the mid 1970's, we couldn't have built the internet if our lives depended on it. Sure, we can tell them about the rise of text messaging - but without the battery technology and the mass-production of tiny RAM chips - they couldn't make the cell phone to exploit that. Some things just have to evolve slowly.

That's why Tango's idea to stretch the time limit to 200 years has started to provoke some interesting answers while increasing the message length has not. If we had something important to say - I'm sure we could figure out a way to say it in 140 characters and add enough information to speed up the work...but we just don't have anything profound to say. I think a global warming warning would be the best thing we could do. What we're trying to do now would have been so much easier if we'd had another 40 years to do it in.

So (within limits) it's not the length of the message - it's the amount of time we can send it back. If the limit TRULY is 40 years - then the idea of telling some scientists how to make a ridiculous amount of money on the stock market isn't so silly - lack of funding has probably done more to limit our technological progress than anything else...fix that and everything moves faster. SteveBaker (talk) 00:18, 27 January 2009 (UTC)

Re the Higgs boson: the theory was pretty well understood forty years ago. I don't think there's much we could send. Algebraist 00:22, 27 January 2009 (UTC)

If there's no size limit to the message, perhaps the people of the late sixties would enjoy a copy of the human genome. APL (talk) 06:14, 27 January 2009 (UTC)

Physics and chemistry like most technical things advance gradualy and if you lift somebody up 200 years in knowledge in a small area he has no foundation to stand on. The design of a microchip is usles in 1809, same with airplanes. Penicillin extraction from fungus might work even with technics in 1809 and this will make the differnce in the growth of the nations. The ammonia synthesis of Haber Bosch is complicated, but if you get this running in 1809 the food production would increas drastic. To chnge the outcome of the wars in the 19th century would have the largest impact. Machinegun design to one of the fighting groups in a war done in the old fashoned way would make clear winners. The French under Napoleon would be my choice before or after Watergate the map of Europe would be a lot different than. The composition of sulfur mustard or chlorine gas might be a good tip to the armies of the world too. --Stone (talk) 10:15, 27 January 2009 (UTC)

I believe the main threat to humanity is our technology outpacing the social structures necessary to survive it (nuclear weapons in the last century, probably nanotech and biotech in this one). I would send something like "it is a sin to put the tools of adults into the hands of children", and then maybe some lotto numbers so they'd know I wasn't just some goofball. --Sean 13:51, 27 January 2009 (UTC)

You're just guessing, though, they can do that just as well. We've had nuclear weapons for over 60 years and haven't destroyed ourselves yet, so the benefit of hindsight should make you less concerned about such things than someone 40 years ago rather than more. --Tango (talk) 14:10, 27 January 2009 (UTC)

The problems of technology outpacing our ability to deal with it were well known in the late 1960's - there is nothing we can possibly tell them about that except, perhaps, "You were right about that". That's not going to change anything that happened. As for the nuclear weapons thing - it was only the presence of all of those nukes that prevented a third world war. Trust me, I was there. Everyone was so freaking terrified that the end of the world was coming that we were forced to work with the 'enemy' to make sure that it didn't. The result was exactly what the pre-nuclear weapon people said: A policy of mutually-assured destruction works. That surprised me at the time - but hindsight helps a lot! If we told them it would all turn out OK in the end - they might have caused one side or the other to drastically scale back weapons production before the moment of reconciliation - and THAT could easily cause the very thing we'd be trying to avoid. Besides - we're talking 1969 - by which time the worst of the madness was over. We were much more concerned then about the Soviet's conventional army nibbling away at the edges of Europe and our inability to prevent that OTHER than by starting a nuclear exchange that would end the world. Fortunately, the soviets had much the same concern...(see how that works?!). 14:59, 27 January 2009 (UTC)

In what way were they "right about that"? People fear problems with too advanced technology all the time (and have done for centuries), but can you give an example of a time they were actually right? --Tango (talk) 15:13, 27 January 2009 (UTC)

Internal combustion engines and global warming? SteveBaker (talk) 16:40, 27 January 2009 (UTC)

That's still a fear about the future - global warming hasn't done any major damage yet (a few extra hurricanes, maybe, but nothing on a global scale) and we may yet get emissions under control and prevent a complete disaster. --Tango (talk) 16:45, 27 January 2009 (UTC)

Just a guess - you aren't a polar bear are you?

It's completely UTTERLY incorrect to say that global warming hasn't done any major damage yet. There is strong evidence that the number of hurricanes is increasing due to global warming - and that means that the victims of Katrina and the total annihilation of Galveston could easily be suffering those consequences. Low lying island communities all around the world are actually starting to notice the sea level rise and a few are losing crops due to salt water getting into the groundwater beneath their fields. Plants that live on mountain slopes are vanishing from the lower slopes and being found at higher altitudes. Migratory birds are being found further North than they've ever been seen before - and in other areas, whole populations of animals and plants have simply 'vanished' because one species growth spurt or breeding cycle that is triggered by temperature are appearing out of sync with other species who time their young based on day-length - so one species thrives to 'plague' proportions while the other starves. Heck - find a photo of ANY glacier in the world as it was 10 years ago and as it is today! If that's not "major damage" - I don't know what is! SteveBaker (talk) 17:50, 27 January 2009 (UTC)

Oh - and to your other comment: getting emissions under control ain't enough. A big climatology study that came out a few weeks ago reported that the timescale for the atmospheric CO2 level to return to 'normal' even if we went back to a pre-fossil-fuel economy overnight (yeah...right!) would be on a scale of thousands of years and that indeed CO2 levels will continue to climb slowly for decades - even after we stop making matters worse. That's because of the knock-on effects of the temperature rise slowly feeding back into CO2 release from the oceans. Even if we "get emissions under control" - we are still in for a disaster. At this point it's more about the depth of the disaster we're just starting to head into than whether it gets worse or not...it's definitely going to get worse no matter what we do. SteveBaker (talk) 17:58, 27 January 2009 (UTC)

Well, if the human race gets wiped out in the next 50 years, I'll buy you a pint! ;) I take all claims of impending doom with a very large pinch of salt - none of them have been correct so far, what makes this one any different? Once it gets bad enough that people can't get away with just doing it lip service, we'll find a workable solution - we always do. --Tango (talk) 18:04, 27 January 2009 (UTC)

I guess it depends on your definition of "major". None of those things are even remotely comparable to a nuclear winter, which was the main fear regarding technology getting out of hand 40 years ago. Also, such statements are only meaningful if compared to non-global warming figures - there are always lots of hurricanes, there are always lots of species going extinct, glaciers have been melting for the past 10,000 years, etc.. There is undeniably an increase in those things and it is undeniably getting worse, but it isn't easy to actually make a meaningful comparison which you need to do before you can claim that global warming (particularly, man-made global warming) has already caused major damage. --Tango (talk) 18:04, 27 January 2009 (UTC)

Displacement, s

Why is displacement notated with the letter s? Any particular reason, or just what ended up as convention in the end? --80.229.152.246 (talk) 19:49, 26 January 2009 (UTC)

Not much more than guessing: Latin la:spatium denotes the length of a path. v is velocitas, t is tempus. --Wrongfilter (talk) 20:02, 26 January 2009 (UTC)

Thanks, that sounds extremely plausible. --80.229.152.246 (talk) 22:50, 26 January 2009 (UTC)

I'm also going to pipe in with my opinion. Notation varies from place to place, but in my experience, the most uniform and consistent systems always use "X,Y,Z" as the standard Cartesian grid, because they are the last letters of the English alphabet. When we do a $\mathbb {R} ^{3}$ to $\mathbb {R} ^{3}$ mapping to some other abstract coordinate system, we generate other coordinates in $\mathbb {R} ^{3}$, so we just count back three more letters and get "U,V,W". These are common notations in computer graphics - "UVW" Mapping. Now, we're running out of letters at the end of the alphabet, (U-Z are taken), and t is usually reserved for "time", so we now have to step back one more letter... "S" - for a mapping of $\mathbb {R} ^{3}$ to $\mathbb {R} ^{1}$. I actually came up with this explanation for myself; I had a similar question about this notation during my first vector-calculus classes. This explanation seems to make the most sense to me. Nimur (talk) 18:01, 27 January 2009 (UTC)

Not really. Computer graphics mostly uses 'homogeneous' coordinates - (X,Y,Z,W) - with 4x4 matrix math that can accomodate translation, scaling, skewing and perspective operations in a single matrix.

We originally used (U,V) for texture coordinates - but when 3D textures came along maybe 10 years ago we needed a third coordinate, we'd already used 'W' - and homogeneous 3D texture coordinates proved useful - so we needed a fourth letter anyway), it was necessary to dump (U,V) - but somehow (S,T,U,V) or (U,V,S,T) didn't work out and most modern API's use (S,T,P,Q).

R is right out because we need (R,G,B) for color and (R,G,B,A) to conveniently roll in 'Alpha' or transparency. But with high-dynamic-range (HDR) rendering, we used 'S' for intensity - so we have (R,G,B,S) - which clashes with (S,T,P,Q)...

But in the end - the whole sorry mess and lack of foresight has evaporated. We have so many different things that are groups of three or four numbers that increasingly we talk about 'Position', 'Color', 'TexCoord', 'Normal', etc - and toss them around as 4-vector objects without looking too carefully at what's inside. Both PC and GPU hardware can do operations on 4-vectors in parallel - and C++ lets you 'overload' operations so you can say "Position += Velocity * Time;" - and all of the (X,Y,Z,W) stuff 'just works'. So that's the simplest answer. In shader languages, a 4-vector is a fundamental unit of calculation - and the underlying shader language lets you access it interchangeably as (X,Y,Z,W), (S,T,P,Q), (R,G,B,A) or [0],[1],[2],[3]. So it's common to see people accessing (say) the Red component of a color using 'Color.x' rather than 'Color.r'. I never use either (U,V) or (S,T,P,Q) for textures anymore - it's just TexCoord.x .y .z and .w as needed. SteveBaker (talk) 02:08, 28 January 2009 (UTC)

Anyway, in my experience, X, Y, Z are quite uncommon variable names for Cartesian coordinates. Usually it's x, y, z. The uppercase variables are more likely to be sets, or random variables, or something other than Cartesian coordinates. --Trovatore (talk) 02:11, 28 January 2009 (UTC)

Well, yes - but for programmers (who are NOT mathematicians, in general), capitalisation or not is a separate matter and often depends simply on local programming practices. Hence (to pick some silly examples to illustrate some common conventions):

#define X 1234.0f

const float x = 1234.0f ;

class X () { ... } ;

inline float x ( float *vector ) { return vector [ 0 ] ; }

In every case, we're talking about a single, simple number.

SteveBaker (talk) 19:39, 28 January 2009 (UTC)

Another guess: since r (for radius) is used as the symbol for the vector position of a point relative to the origin, s might have been chosen as the next letter to represent the subsequent displacement of that point. --Heron (talk) 10:41, 28 January 2009 (UTC)

Actually, I don't think we have to guess - the first answer from User:WrongFilter was the correct. Newton wrote his laws of motion in Latin - and 's' stands for 'spatium'. SteveBaker (talk) 19:39, 28 January 2009 (UTC)

viscosity vs. temp

Is it safe to assume that the viscosity of an aqueous solution will drop as its temperature goes up? ike9898 (talk) 20:21, 26 January 2009 (UTC)

Temperature dependence of liquid viscosity. But I'd keep an eye on Evaporation, Vapor pressure.76.97.245.5 (talk) 21:30, 26 January 2009 (UTC)

I think the watch-word is "solution"; if raising the temperature takes the solution to a new phase, e.g., liquid crystalline, the viscosity could rise significantly.GVB012009 (talk) 19:56, 29 January 2009 (UTC)

Alternating current outlet

Why do outlets have one hole larger or different than the other so you have to put the plug in a certain way? I thought that alternating current, well you know, alternates; the only difference between putting it in one way or the other is a tiny (1/60 second in america I believe) phase change.. I read Neutral_wire and it confused me. It seems to suggest that AC comes in on a live wire and out on a neutral wire, like direct current. I thought the relative safety and interesting electrical properties of AC were precisely due to it not flowing in any particular direction for more than a tiny fraction of a second.. 72.236.192.238 (talk) 20:30, 26 January 2009 (UTC)

Here, I think, is an explanation, from our article on AC power plugs and sockets:

Polarised plugs and sockets are those designed to connect only in the correct orientation, so the hot and neutral conductors in the connected equipment are connected to the hot and neutral poles of the outlet. Polarisation is maintained by the shape, size, and/or position of plug pins and socket holes to ensure that a plug fits only one way into a socket. This is so that switches, for example, interrupt the live wire of the circuit. If the neutral wire were interrupted instead, although the device would deactivate due to the opening of the electrical circuit, its internal wiring would still be energised. This can present a shock hazard if the device is opened, because the human body would create a circuit — a path to a voltage different from that of the live wire. In toasters and other appliances with exposed heat elements, reversed polarity can cause the elements to be electrically live even when they are cool to the touch, posing the risk of electrocution even if the device is not deliberately disassembled or otherwise tampered with.

Reverse polarity can also create a hazard with screw-in light bulbs, where the shell of the socket may be energized even though the lamp is switched off.

Interchange of the live and neutral wires in the behind-the-walls household wiring can defeat the safety purpose of polarised sockets and plugs; a circuit tester can detect swapped wires. ike9898 (talk) 20:49, 26 January 2009 (UTC)

That can't possibly be right. If you interrupt the circuit then there's no current, correct? It doesn't matter where you interrupt it. And again, how is there a hot lead and a neutral lead if alternating current just goes back and forth through the whole circuit? Every lead is hot, or rather each lead alternates between being the + and the - 72.236.192.238 (talk) 21:14, 26 January 2009 (UTC)

The hot lead alternates, yes. But both + and - will flow to ground. It doesn't have to be the ground in that particular socket. It could be the ground from some other socket, or can be the ground in the actual ground. APL (talk) 21:27, 26 January 2009 (UTC)

I understand that both leads (1 and 2) flow to the ground (3) but why are 1 and 2 different sizes as if it matters which is which? ( http://img220.imageshack.us/img220/2696/782455zp3.jpg ) 72.236.192.238 (talk) 21:39, 26 January 2009 (UTC)

Because only one lead is "hot" (Alternating from + to -). The other is neutral, similar to ground. APL (talk) 22:01, 26 January 2009 (UTC)

There is one hot lead which alternates between positive and negative. The other lead remains at (or near) 0v, so the effective voltage and current change directions (signs), but the second lead is never hot. You could theoretically implement a system where both leads changed voltages, but it wouldn't provide any real advantages and it wouldn't allow simple safety measures like polarised plugs. --74.137.108.115 (talk) 21:53, 26 January 2009 (UTC)

How can the other lead remain at 0v? Volts are electric potential, it has to be measured between two different points. So the hot lead is +120v relative to neutral, then -120v relative to neutral. Which should be another way of saying hot is +120v relative to neutral, then neutral is +120v to hot. Which should be another way of saying the two leads are identical except for phase, so it shouldn't matter which is which. We can ignore the additional grounding lead since it isn't used unless there's a problem. I really don't know where you're coming from saying "the effective voltage and current change directions (signs), but the second lead is never hot" ... if the current is flowing into the hot lead that means it's coming out of the neutral lead, and uh isn't current coming out of a lead the definition of hot? The electrons have to come from somewhere; you're not pumping charge into and out of a giant tank, you're dealing with a giant electrical circuit starting and ending at the power plant. 72.236.192.238 (talk) 22:05, 26 January 2009 (UTC)

You just explained it well, actually. Ground really can act as a "giant tank". The neutral wire does not go back to the power plant. It is simply connected to ground. (There is no 'complete circuit' between your lamp and the power station.) So if you imagine two hoses, one constantly vibrating between pressure and suction, and another connected to the infinite "tank" of ground-water at neutral pressure, you can see how it makes a difference which "hose" you accidentally tap into. APL (talk) 22:30, 26 January 2009 (UTC)

Hm ok it's not a circuit But if ground can act like a giant tank then -120v on the hot (relative to 0v on the neutral) really is equivalent to 120v on the neutral (relative to 0v on the hot). That's the only thing I was worried about being wrong about, but apparently I'm not. Think about it... if the live wire is alternating between 0 and 120 relative to ground, and the neutral is equivalently alternating between 120 and 0 relative to ground, then they're the same.. :( 72.236.192.238 (talk) 22:49, 26 January 2009 (UTC)

Oh oh oh I see. As explained above it's useful for breaking the connection before the appliance instead of after. I was assuming that it's a circuit and it wouldn't matter which side, but I see now that I learn that one end is just ground, not a circuit back to the power station: your body could be that one end! Whew that was a doozy. I have no non wikipedian training in electricity and it shows im afraid 72.236.192.238 (talk) 22:55, 26 January 2009 (UTC)

There is a hot lead, a neutral lead and often a ground. The voltage is from hot to neutral or ground. Where there is a power switch, it must interrupt the hot line; interrupting the neutral would turn the device off, but would leave live power. Devices such as a GFCI work by detecting residual current; reversing the leads render them useless. --—— Gadget850 (Ed) ^talk - 20:48, 26 January 2009 (UTC)

Of course, I usually just file those polarized plugs down so that they'll fit into older sockets. APL (talk) 22:02, 26 January 2009 (UTC)

Let me try to clear this up a bit. If you live in the U.S., you have 2 lines coming into your house: One is at +120 V (relative to ground) and one is at -120 V (relative to ground). Now, in your house, there are two types of plugs. You major appliances, which draw lots of current, like the dryer, are likely hooked up to the +120, -120, and ground. This supplies a net voltage of 240 V across the appliance. These are those funny round fat plugs. The normal "frowny-face" outlet is hooked up to one of the two "hot" wires (either +120 or -120, it doesn't matter which) a "neutral" wire (which is hooked up to ground at the breaker box) and a "ground" wire, which is generally grounded firectly at the junction box. So, at this outlet, the net voltage is 120 V, because the appliance you attach is hooked into the hot wire and the neutral wire, and the two are 120 V apart relative to each other. The deal with alternating (rather than direct) current, is that the "direction" or "sign" of the current flow doesn't matter. The sign only effects the wave function of the current (i.e. a +hot wire has a mirror image wavefunction profile to a -hot wire) and as such, all that usually matters is that the hot wire is hooked up to where the appliance expects it to be. It doesn't matter whether its the +hot or -hot. In fact, for some applications (like a regular incandescent bulb, or a toaster) it doesn't even matter which wire gets the hot, and which gets the neutral. --Jayron32.talk.contribs 22:10, 26 January 2009 (UTC)

There is no + or - in an AC line. If you measured across +120 and -120 DC, you would get 0. Residential U.S. power is two 120 volt hot leads and a neutral. In a standard breaker box, odd numbered breakers tap onto one hot and even the other hot, balancing the load. 220v breakers are double and tap into both hots. --—— Gadget850 (Ed) ^talk - 23:29, 26 January 2009 (UTC)

I'm sure he meant instantaneously one is + while the other is - (on a sine curve), even though overall both average 0 .froth. (talk) 00:29, 27 January 2009 (UTC)

As I actually explained in my own words, the +120 and -120 refer to the sign of the wavefunction. The neutral, of course, is a flat line at 0. The two lines have an alternating wave function which are mirror images of each other, so arbitrarily one can be called + and one -. Tapping into these two lines will give a net difference of 240 V relative to each other, which is used for high demand appliances like you drier. --Jayron32.talk.contribs 16:38, 27 January 2009 (UTC)

Nit: US breakers aren't "odd-breakers one hot, evens the other". It would sure make running the two internal bus-bars easier (one feed to the left column, other to the right), but makes it much harder to configure a "two-hot" (240V) breaker. See Breaker box#Breaker arrangement. DMacks (talk) 17:25, 27 January 2009 (UTC)

Ah, that helps a lot. But doesn't that prove my point? Like you said it doesn't matter for frowny face sockets which house line you connect the hot lead to. Equivalently it doesn't matter which direction you plug your power cord into, for any application, not just lamps and toasters. By connecting to only one house line (and the neutral goes to 0v, ground) you change nothing except the net voltage. Instead of 240v you have 120v. But it can't matter which side you connect the live wire to, because electrically the live and neutral are only distiguishable by phase, exactly the case with the two lines coming into the house! One end of the cycle the live is +120 (relative to the neutral being 0v) the other end of the cycle neutral is +120 (relative to the live being 0v). 72.236.192.238 (talk) 22:42, 26 January 2009 (UTC)

The holes are different sizes so that if you plug in a device the off switch, fuse and breakers are interrupting the circuit on the live side. If you have a short in the device and the off switch only disconnected the neutral line you could still get power flowing from your hot lead to whatever ground (e.g. your body) was available. If the disconnecting element is where the hot line connects to the device and will effectively interrupt the circuit. Some devices are designed to disconnect both poles. For those it would not matter which way you plug in the plug. So don't reshape your plugs or widen your outlet holes.76.97.245.5 (talk) 22:16, 26 January 2009 (UTC)

Let's say you have a toaster. The lever on the toaster turns on the hot lead. When it is off, you can jam a fork in it all you want to get that last bit of bagel off. If hot and neutral are reversed, then the lever only turns off neutral. If you stick that fork in while you are grounded (touching the fridge, oven, sink, etc.) then you are going to get toasted by that hot lead. --—— Gadget850 (Ed) ^talk - 23:29, 26 January 2009 (UTC)

As an added precaution to the polarized plugs, you should install the sockets with the grounding plug *up*, not down (i.e., not a frowny face). That way when a picture frame or some other metal object slides down the wall it won't have any chance of being energized. --Sean 16:51, 27 January 2009 (UTC)

That may or may not be good advice. Wall-warts, heavy-duty line or extension cords with low-profile plugs, and other devices, depending on their design, may be much more prone to leaning/falling or being inadvertently pulled partway out of a wall socket with grounds up rather than down or sideways. But whether it's good advice or poor, it doesn't really belong here; Wikipedia is not a how-to manual. —Scheinwerfermann ^T·_C02:26, 30 January 2009 (UTC)

Compact fluorescent light bulb hooked up backwards

If a CFL is hooked up with the hot and neutral wires reversed, would it work correctly? I have a lightbulb socket that causes otherwise normal CFLs to light up dimly and flash. I'm wondering if reversed wiring is a possible explanation. ike9898 (talk) 20:45, 26 January 2009 (UTC)

Do you have it on a dimmer switch? Sometimes if you have an ordinary fluorecent tube fixture in the same circuit this can also happen.76.97.245.5 (talk) 21:06, 26 January 2009 (UTC)

No but it is on a circuit with a GFCI breaker (a breaker, not an outlet). Does that matter? ike9898 (talk) 17:26, 27 January 2009 (UTC)

Reversing hot and neutral wires cannot possibly affect operation of any device. It can only increase safety hazard for some (improperly designed) devices. -Yyy (talk) 07:51, 27 January 2009 (UTC)

Certainly reversing the hot and neutral can affect the operation of a device. My home had some light fixtures with an obsolete scheme of three-way switching which could energize the light socket with the tip of the bulb connected to neutral and the shell of the socket at 120 volts from neutral. The hot part was separated from a grounded metal outer surround of the socket only by paper, as in the normal construction of such a socket. One time when it was switched on, the 120 volt potential difference arced across the old paper insulation and before the breaker operated a glob of molten metal fell on the carpet. Had the phase and neutral been connected to the socket properly, such a large voltage difference from shell to surround would have not occurred. I rewired the circuit for modern 3-way switching, which required an additional conductor, and replaced the light fixture. Edison (talk) 17:32, 27 January 2009 (UTC)

Why do octane raings vary?

Why do unbranched hydrocarbons have lower octane ratings that branced or cyclic ones. Andy (talk) 22:01, 26 January 2009 (UTC)

They are easier to burn, probably due to more surface area exposed to oxygen. Graeme Bartlett (talk) 23:11, 26 January 2009 (UTC)

Cheers Graeme. Andy (talk) 07:11, 27 January 2009 (UTC)

Skin temperature and freezing

Hot water freezes faster than cold water.[3] Does the same hold true for flesh? In other words, if you were to sit in a sauna for a while and then go out naked into crazy cold temperatures, roll in the snow, etc. would you develop frost bite FASTER than you would with a normal skin temperature? --S.dedalus (talk) 22:09, 26 January 2009 (UTC)

I read that article and it looks like most of the proposed explanations are specific to it being a jar of water. Anyway, I'm certain that the determining factor in this case is how the wind flows past your body, which parts of yourself you rub deepest and more often into the snow, which parts of the snow are colder, which parts of your body were warmer than others to start with... the effect you referenced is only reliably measurable in consistent laboratory conditions; there's no way you could possibly roll around in the snow consistently. .froth. (talk) 22:25, 26 January 2009 (UTC)

The effect that makes hot water freeze faster almost certainly doesn't apply to flesh. However, other effects could cause you to get frostbite quicker after being very hot - your body will be adjusted to stay cool, so when you suddenly go outside it will take just time for your body to adjust to staying warm and you will lose a lot of body heat very quickly (I'm not sure how much "a lot" is - it depends on how quickly the body can adjust). --Tango (talk) 23:18, 26 January 2009 (UTC)

Your body works hard to maintain its temperature - going into a sauna makes it work harder to do that - but if you take your body temp with a proper core-temp thermometer - it's not going to vary by so much as one degree between the sauna and the snow...at least not until you're in a lot of distress. Also, the thing about hot water freezing faster than cold isn't REALLY true...at least not in a proper controlled experiment where the ONLY difference between the two pots of water is their initial temperature. If you think about it, it couldn't be any other way. Hot water has to first turn into cold water before it freezes! There are some rather specific circumstances where the nature of the stuff dissolved in water boils off and the nature of the cooling happening from the outside in when something is cooled rapidly rather than slowly CAN make it happen - but none of those special effects are true of your body. So not directly. However, one of the CRUCIAL things they tell you about being out and about in very cold conditions is not to work up a sweat - because as soon as you stop exercising, the sweat freezes and puts you in a lot of danger. So while a hot/dry body should do no worse than a cold/dry body, a hot/sweaty body will indeed be WAY more susceptible to the cold than a cold/dry one. SteveBaker (talk) 00:01, 27 January 2009 (UTC)

But the initial temperature apparently changes something about the chemical properties of the water to make it freeze faster. Or as the article said, convection currents (as parts of the water cool, the warmer water rises.. aka closer to the surface, so it can be more efficiently cooled) could play part .froth. (talk) 00:18, 27 January 2009 (UTC)

Yes indeed - all kinds of things that are not true 'in general' (and certainly aren't true for the human body). SteveBaker (talk) 00:48, 27 January 2009 (UTC)

The Mpemba effect really is true, you don't need really obscure circumstances, just two beakers of water and a freezer. --Tango (talk) 00:08, 27 January 2009 (UTC)

Actually - if you read the acticle - you'll find that 'special' circumstances are indeed needed. It just happens to be that the 'special' conditions are two cups stuck in a freezer! "The Mpemba effect is the observation that, in certain specific circumstances, warmer water freezes faster than colder water" - it's definitely not true in general. SteveBaker (talk) 00:46, 27 January 2009 (UTC)

Sure, but they aren't obscure circumstances, which is what I said. In fact, they are exactly the circumstances you would first use if you wanted to test for such an effect existing. --Tango (talk) 00:50, 27 January 2009 (UTC)

Yeah - I absolutely agree that the conditions aren't "obscure" (in the sense that you don't need a titanium klein-bottle in a helium/neon atmosphere with exactly 3.4 parts per million of iodine dissolved in the water) - but they are SPECIFIC - in that if you vary the conditions of the test to even a fairly small degree - the effect completely goes away. It's one of those odd coincidences that the simplest possible test of the effect works just fine - but any significant variation on the experiment fails to demonstrate it...and that's what matters here. An exposed human body out in the snow is not at all like a cup of tap water placed into a freezer (it's salty - it has an irregular shape - the liquid inside can't use convection to move around - it has an internal homeostatic heat source...you name it). Hence it's exceedingly unlikely to meet the SPECIFIC (but not OBSCURE) conditions of the Mpemba experiment and we can be reasonably confident (certainly to the degree required in a WP:RD response) in saying that the Mpemba effect does not apply in the situation our OP describes. SteveBaker (talk) 14:46, 27 January 2009 (UTC)

So can we say with confidence that, when thoroughly dried with a towel, a person immerging from a sauna will take slightly longer too developed frostbitten than a person with a normal skin temperature? --S.dedalus (talk) 19:31, 27 January 2009 (UTC)

Perhaps very, VERY slightly...but my best guess would be "No". There is another thought which does occur to me though. When you're hot, your body expands the blood vessels close to the skin to allow the blood to cool - and contracts them to keep the blood warm at your core when it's cold. Coming out of the sauna MIGHT have the effect of giving you an initial period of time while the body adapts when the blood would cool faster than for the person who is already kinda chilly. This is the reason given for NOT warming people with hypothermia up too quickly - and also for not drinking alcohol to warm yourself up in a cold situation. So the sauna would (I think) tend to cause hypothermia (because the skin is getting all of the blood supply and cooling it down dangerously quickly) and perhaps HELP the frostbite (because the warm blood is still getting to the extremities rather than being pulled back into your core. But I think the body would adapt before either of those things would be too terrible - so the judges are still out on this one. 21:59, 27 January 2009 (UTC)