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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

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| 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): . 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/c 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 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 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 . 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 Misplaced Pages 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 Misplaced Pages 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 Misplaced Pages 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 ${\displaystyle \mathbb {R} ^{3}}$ to ${\displaystyle \mathbb {R} ^{3}}$ mapping to some other abstract coordinate system, we generate other coordinates in ${\displaystyle \mathbb {R} ^{3}}$, 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 ${\displaystyle \mathbb {R} ^{3}}$ to ${\displaystyle \mathbb {R} ^{1}}$. 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 ,,,. 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  ; }

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)  - 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)  - 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)  - 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; Misplaced Pages is not a how-to manual. —Scheinwerfermann ·_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. 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)

January 27

Errors in casting plastics

Hi - I need a piece of terminology - what's it called when a mold produces a bad casting and you get something that's not the shape you intended?

Thanks,

Adambrowne666 (talk) 00:55, 27 January 2009 (UTC)

A dud ? I'm not sure if a malformed plastic casting has a specific name. StuRat (talk) 03:28, 27 January 2009 (UTC)

One type of imperfection in casting is flash, though this may be removed to obtain the shape you intended. -- KathrynLybarger (talk) 03:39, 27 January 2009 (UTC)

Thanks, yeah, probably there's no global term - I'm gonna go for a 'miscast', I think. Adambrowne666 (talk) 04:14, 27 January 2009 (UTC)

Id call it a blob--GreenSpigot (talk) 13:52, 28 January 2009 (UTC)

I read through two rather large online glossaries to do with metal casting, and although there were lots and lots of words for the particular defects, I couldn't find a general one. There were many places where they might have used such a word if it existed, but they always just called it a defective casting. I expected to find some nice, slangy wordling, something like "glippet" or "pfnisch", but no dice. (I should imagine that the terminology of metal casting would have transferred to plastic casting more or less entire.) --Milkbreath (talk) 14:11, 28 January 2009 (UTC)

I don't know officially, but I would say 'dud', 'reject' or 'miscast' (to repeat 2 already-mentioned terms) - I actually doubt they would coin a new term for it because there are very common words that would be suitable. I know in anything that I've ever manufactured (computerised engraving, plastics assembly, signage) we could just say 'dud' or some expletive. Rfwoolf (talk) 22:30, 2 February 2009 (UTC)

Spontaneous absorption of water waves

What is the formula for the rate at which deep water surface waves (both gravity and capillary) are absorbed by the water and the air above it, if they do not run into anything?

129.2.43.42 (talk) 01:22, 27 January 2009 (UTC)Nightvid (unregistered)

Well, I was really hoping you'd get a good answer - because it's great question. But I've looked all over for an equation and I don't see one. From reading around the subject, some things become evident:

• Water waves at different frequencies and directions can be considered independantly.
• Waves move at different speeds and are attenuated at different rates depending on their frequency.
• Higher frequency waves are attenuated more rapidly than low frequencies.
• Wind has a huge effect on energy transfer into and out of waves.
• Tides make a big difference too...even in deep water.
• Breaking waves behave very differently from 'smooth' waves.
• When the water is more than 1.5 wavelengths deep - it may be considered to be a 'deep water' wave.

But I couldn't find a single, simple equation anywhere...which is surprising.

SteveBaker (talk) 01:30, 28 January 2009 (UTC)

soap

Good day!

I would like to ask what is a germicidal soap and what are its effects?! or shall we say what are its applications-for what and for whom...

Your answer would be greatly appreciated.

Thank you and God bless! —Preceding unsigned comment added by 125.5.144.109 (talk) 02:50, 27 January 2009 (UTC)

An antibacterial soap is one that tends to kill bacteria. This is usually unnecessary, as washing bacteria off your hands is sufficient. There are some negatives, as well:

1) It can kill off helpful bacteria that control other health threats, like fungus.

2) It can kill off helpful bacteria in septic tanks, which decompose waste.

3) It can cause bacteria to develop a resistance, which makes it more difficult to kill them when they really do pose a threat. StuRat (talk) 03:23, 27 January 2009 (UTC)

That's why there's an increasing move to switch to bacteriostatic rather than antibacterial soap. 76.97.245.5 (talk) 03:46, 27 January 2009 (UTC)

Although the evidence is still being generated, I believe that while washing of hands will suffice for reducing the microbial load (primarily through friction), there are some pretty nasty pathogens that require stronger means to more greatly ensure reduction in their counts. Case in point -- you want to definitely "nuke" Salmonella and MRSA, not just reduce their respective counts. I also believe that the levels of antimicrobials that would go from your hands to the septic tank are far below those needed to effectively reduce those bacteria. Lastly, the potential of antimicrobial resistance is a real issue -- and the jury is out on that. However, when you consider the degree of action needed to hold a microbe in stasis (e.g., bacteriostatic), rather than killing it (e.g., bacteriocidal), the probability of building up resistance to bacteriostats would far exceed the ability to develop resistance to bacteriocides! GVB012009 (talk) 19:53, 29 January 2009 (UTC)

Soap was invented around 3000 BC, During the 1970's someone thought "why don't we make soap that's BAD for bacteria." Apparently up to that time soap was enjoyed by bacteria as a nutritious food stuff. Bacteria fought back, hiring lobbyists who argue that use of antibacterial soaps should be restricted. —Preceding unsigned comment added by 76.125.8.141 (talk) 13:42, 27 January 2009 (UTC)

That was entirely unhelpful. Matt Deres (talk) 20:10, 31 January 2009 (UTC)

antibiotic resistance

Something has long bothered me about the antibiotic resistance discussions as applied to hand soap. The active ingredients usually used in antibacterial soap are triclosan or ethanol. However, it is physically impossible to use either of these compounds as internal antibiotics. The ratio required for ethanol (>60% by volume) would be fatal in the bloodstream, and triclosan is too insoluble in water to reach bactericidal concentrations in blood (normally it is suspended in an nonpolar solvent). Further, my understanding is that their chemistry and method of action is simply not related to any of the widely used internal antibiotics, so the risk of cross-resistance ought to be very low.

Hence my question is: Should people really worry about bacteria developing resistance to triclosan or ethanol? Would it matter? It would appear that even if bacteria developed resistance to hand sanitizer it would have little to no relevance in deciding how to fight an infection of that bacteria. Sure, it might be a little bad if hand soaps and the like lost their edge, but in the grand scheme of things being resistant to hand soap would appear to be independent of and far less troubling than resistance to things like methicillin. Dragons flight (talk) 05:36, 27 January 2009 (UTC)

No, the issue of resistance doesn't pertain, as the agents in hand soaps are antiseptics rather than antibiotics. - Nunh-huh 06:05, 27 January 2009 (UTC)

I think it's just a case of mislabeling. What they probably mean is that any surviving pathogens are likely to be very hardy and might be harder to kill with conventional methods. I agree that there is a lot of confusing (confused?) info out there. I read an article (reputable science site) where the interviewed researcher within 4 sentences first complained that increasing use of antibacterial cleaning agents in households would influence bacterial susceptibility to drugs, then he stated that although that had been shown in a petri dish an experiment conducted on an actual kitchen countertop failed to yield the same result. He followed that by saying if it were up to him he would only advocate use in hospitals because in a household you wouldn't need it anyway because the bacterial load was rather low whereas in hospitals it was high. Somewhere lower down was a comment that hospitals are breeding grounds for drug resistant strains. (So he advocates use of chemicals he suspects of increasing drug resistance in a place that already has a lot of that, instead of where it could not be shown to develop?) I read it several times, and then actually went and looked the guy up. He really was a researcher in a university lab. 76.97.245.5 (talk) 10:01, 27 January 2009 (UTC)

I have to disagree with both of the two previous posters.

@76.97.245.5: Sure - that was a bad report - but it doesn't mean that what the guy is saying isn't true - and it CERTAINLY doesn't mean that the reverse of what he says IS true!

@Nunh-huh: Your distinction between antiseptics and antibiotics is irrelevent.

But in general:

Whenever we provide some kind of stress factor in the life of a creature (be it a bacterium or an aardvarq), we're going to be affecting it's evolutionary development in such a way that it'll tend to be better at surviving in that stressed environment in the future. That's absolutely unavoidable - and it doesn't matter whether it's an "antiseptic" or an "antibiotic" - the result is the same. (From the lead paragraph of our Antiseptic article:

"Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction. They should generally be distinguished from antibiotics that destroy bacteria within the body, and from disinfectants, which destroy microorganisms found on non-living objects. Some antiseptics are true germicides, capable of destroying microbes (bacteriocidal), whilst others are bacteriostatic and only prevent or inhibit their growth. Antibacterials are antiseptics that only act against bacteria. Microbicides which kill virus particles are called viricides."

But it really doesn't matter. Antiseptics, antibiotics, disinfectants, germicides, bacteriocides, bacteriostatics, antibacterials, microbicides AND viricides - all apply stress to their intended targets and if they are anything less than 100% effective at preventing their chosen victims from ultimately reproducing - they WILL cause evolutionary pressure. (It's tough to be 100% effective because at the boundaries of the area the substance was applied over, there is guaranteed to be some place where it's present in non-lethal doses - and right there, a creature can survive and evolve tolerance)

Once you have evolutionary pressure - you'll tend to get resistant strains developing.

Hence, the rule is that you shouldn't use ANY of those things unless you actually need to. We got along just fine without antibacterial/whatever soaps, baby-wipes, TOYS(!), etc - and introducing them is a bad idea regardless of whether you happen to be able to induce evolutionary effects in the lab. Evolution is a valid scientific theory and you don't need to keep doing experiments to prove it. Just as we know that brand X bowling balls will fall if you let go of them without having to do the experiment - so we know that creatures will tend to evolve without doing the experiment. If you can't reproduce it in the kitchen but you can make it happen in the petri dish then you certainly need to ask why that is and set up experiments to find out why - but it shouldn't lead you to conclude that evolution doesn't work in the kitchen because extraordinary claims require extraordinary evidence. We should behave as if the hypothesis that evolution doesn't work on kitchen countertops is false until such time as someone proves it and manages to explain why.

So, with what we currently know (which is all we ever have to go on) - we shouldn't use these products in the kitchen because the consequences of failing to do so are not severe. But we may be forced to use them in hospitals where the consequences of infection are vastly more serious because of all of the sick people spreading nasty bacteria everywhere - and all of the open wounds and so forth. Resolving the issue of bacterial and viral resistance to antimicrobials in hospitals is a serious one - but it's not relevent to the question of whether we should make matters worse by using them when we don't need to in our own homes.

SteveBaker (talk) 14:24, 27 January 2009 (UTC)

Steve, There's some kind of flaw in this argument, in its most general form, isn't there? I see some sort of assumption that organisms have an unlimited capacity to cope with any number of evolutionary pressures. In practice if you put a pressure on a zillion parameter system sure it will adapt to that pressure but the adapted point will not be as optimal at some other things as the unpressured system. So your bacteria may adapt to survive repeated exposure to 55% alcohol when it couldn't before but it will be worse at something else. Which depending on your reliance on the hard soap may or may not be a worse situation than before. Sure if you are talking about an antibiotic you need to cure someone you don't want to stress it that way but if you are talking about something which doesn'r really matter I find it hard to buy the argument.--BozMo talk 15:03, 27 January 2009 (UTC)

Sure - the bacterium that's resistant to dilute alcohol will be worse at something else - but in evolutionary terms, it only has to be better off than it's competition. So every time you use dilute alcohol, you'll wipe out more of the 'capable' bacteria and give the resistant (but otherwise worse) ones room to grow and thrive. The problem is that the 'worsening' may be (say) the loss of the ability to metabolize pink food coloring or something. That loss isn't measurably to our gain - and we can't control or (easily) predict what that 'worsening' might be. Worse still, when you set loose a new set of genes, you don't know WHAT the effect will be. It could just as easily result in a change of the 'coating' of the bacteria and thereby cause all of us humans to lose our antibody-resistance to the darned thing. SteveBaker (talk) 16:36, 27 January 2009 (UTC)

Agree but AFAICT in general "big" stresses (e.g. surviving in salt water or Dettol) seem to take a lot out of bacteria: they don't seem to ever manage one of these and still be able to compete with other bacteria well when the stress is absent. --BozMo talk 21:05, 27 January 2009 (UTC)

Lots and lots of things can place an evolutionary pressure on bacteria though, and almost no one worries about their impact. For example, ordinary (non-bactericidal) bar soap, dish soap, and laundry detergent will all remove bacteria. Presumably this creates an evolutionary pressure for bacteria that cling more firmly to their environment to avoid being washed away. However, you'll never hear people advocate that we stop using soaps entirely. Similarly, the wide spread use of food preservatives presumably encourages "preservative resistant" bacteria, but I've never seen people get crazy about preservative resistance the way some people do about hand soap. It just strikes me that the way some people focus on antibacterial hand soap is way out of proportion to the danger. Dragons flight (talk) 15:41, 27 January 2009 (UTC)

That's true - but the things you've described are truly necessary to us. Antimicrobial washing up liquid is of negligable benefit - it's purely an advertising bullshit thing - and we don't need to use it. Food preservatives, however are necessary to our way of life. SteveBaker (talk) 16:36, 27 January 2009 (UTC)

For an example of where antibacterial soaps should be used, hand-washing in areas prone to MRSA comes to mind: MRSA#Hand_washing. StuRat (talk) 15:14, 27 January 2009 (UTC)

Despite SteveBaker's assertions and theoretical dissertation, the facts are: there are no significant clinical effects that can be attributed to "antiseptic resistance", and there are significant clinical consequences of "antibiotic resistance". - Nunh-huh 07:26, 28 January 2009 (UTC)

Of possible relevance: Hand washing with soap significantly reduces the spread of pneumonia and diarrhea, the two leading causes of death worldwide among children younger than age ive. In a study funded primarily by P&G Beauty, a division of Proctor & Gamble, researchers examined 900 households in squatter settlements in Karachi, Pakistan. Although the public health benefits of clean hands are clear, whether poor communities by themselves can afford to purchase soap regularly remains uncertain.

Number of pneumonia cases (per 100 person-weeks) among households that washed-

With antibacterial soap: 2.42

With plain soap: 2.20

Without soap: 4.40

Number of diarrhea cases among households that washed-

With antibacterial soap: 2.02

With plain soap: 1.91

Without soap: 4.06

(Source: The Lancet, July 18 2005) (as reported in Scientific American, October 2005) —Scheinwerfermann ·_C01:57, 30 January 2009 (UTC)

Interesting. That shows that antibacterial soap isn't quite as good. I wonder why ? Either some bacteria are killed which helped to control the baddies, or perhaps people don't wash their hands as thoroughly, thinking the antibacterial action will do the job for them. StuRat (talk) 05:36, 30 January 2009 (UTC)

question about HIV/AIDS

how does science, technology and communications address issues of HIV/AIDS and gender mainstreaming —Preceding unsigned comment added by 196.33.11.13 (talk) 12:21, 27 January 2009 (UTC)

This sounds like a homework question to me. On the off chance it isn't, perhaps you would care to provide a little more information about what, specifically, you're interested in? -- Captain Disdain (talk) 12:47, 27 January 2009 (UTC)

Writing a college essay involves first determining what the question means. College professors are often not models of clarity. I think they sometimes get fed up and try to trip the class up. Sometimes they actually think what they wrote makes sense, not realizing that they're begging the question. Sometimes they're drunk when they write it, I suppose, which would explain a lot. The second step is to guess what the professor wants to see. This is important only to the extent that your grade is important. You can learn the material thoroughly and become the most proficient person in the world in your pursuit and still get only a "C" if you don't follow this second step. Often, too, your paper will be graded by a graduate student with a checklist looking for key concepts and facts, and you should try to guess what these will be. In this case, we start at a disadvantage because the grammar of the question is bad ("does" should be "do"), so we can look forward to getting marked off for correct English, always frustrating. Another problem is the jargon. What is an "issue"? Professors love that word. I've never been able to tell whether they use it because they think it has a meaning, because they want to leave things open-ended, or because they're just being bloody-minded. And good luck figuring out what "gender mainstreaming" is. That really pisses me off. I'll bet your professor just got done having a big argument with his mistress over the term, and he wants to see what you'll all say about it so he'll have more arrows in his quiver the next time it comes up in a symposium. Anyway, good luck, and don't sweat it. Think it's easy, and it will become easy. --Milkbreath (talk) 12:57, 27 January 2009 (UTC)

...OR...

You could just say:

Please do your own homework.

Welcome to the Misplaced Pages Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

SteveBaker (talk) 14:03, 27 January 2009 (UTC)

There's nothing wrong with telling people generally how to go about thinking of how to answer questions when it is clear that's probably what is at stake here. Saying "do your own homework" is concise but it isn't always the most useful answer (and I mean "useful" here in the true sense, not in the sense that giving them the answer would be "useful" in the long run). Teach a man to fish, and all that. --140.247.241.150 (talk) 17:51, 27 January 2009 (UTC)

I too thought "gender mainstreaming" was just meaningless jargon, but truly we have an article on everything. Gandalf61 (talk) 17:01, 27 January 2009 (UTC)

Silly me. Now that I know it's about differential implications.... --Milkbreath (talk) 17:28, 27 January 2009 (UTC)

If it was about differential integrations it would be much easier, by the Fundamental Theorem of Calculus. You could probably submit the question, (+C), and not get a C+ ... Nimur (talk) 18:32, 27 January 2009 (UTC)

Vines climbing around a tree

Why do vines climb upwards around a tree in a clockwise direction(if looked from above)? —Preceding unsigned comment added by 202.70.74.137 (talk) 15:15, 27 January 2009 (UTC)

You may have selection bias. I spent three years trying to tame the wisteria on my trees. It grows wherever it likes, in whatever direction it likes. -- kainaw™ 15:17, 27 January 2009 (UTC)

Apparently this is an active area of research; try googling "vines clockwise". It seems most vines twist counterclockwise, but that we haven't figured out why yet. Perhaps something to do with the chirality of biological molecules. --Allen (talk) 15:37, 27 January 2009 (UTC)

Why are 90% of people right handed? Why do most sea shells twist in one direction? Why do (nearly) all of us have our hearts, livers and pancreases on one particular side? Why do ALL animals and plants have the same chirality of biological molecules? If there is not advantage to one asymmetry over the other - why isn't there a 50/50 mix? The reason is that we're all descended from a single individual. So in this case, once the gene for a particular direction of twist got to become the ancestor of all modern vines - only an evolutionary change in the twist-direction gene could cause opposite-direction-twist to happen. Since there is likely to be ZERO evolutionary benefit to twisting in the opposite direction to all of the other plants - that gene would not reproduce preferentially to the 'normal' direction and could easily simply fade from the gene pool because it's so rare. Genes only spread when there is some benefit to the creature that possesses that gene. Left-handedness in humans is a bit different - it is thought to hang around because we are tribal creatures and there is a benefit to every community of humans to have a few left-handed people because our brains are wired up differently. Hence communities in which left-handedness dies out are at a disadvantage compared to those where it remains - and hence there are always a few lefties around (including an unreasonably large percentage of US presidents, architects and 3D computer graphics people!). SteveBaker (talk) 16:23, 27 January 2009 (UTC)

Before we compare to handedness, we could at least provide a non-google reference that it's intrinsic to the plant and not the environment. There seem to be a lot of news stories re-hashing this same research. APL (talk) 17:12, 27 January 2009 (UTC)

I agree with APL. Steve's explanation sounds plausible, with the quibble that vines are not a monophyletic group, so any shared twist-direction gene would probably be doing more than determining twist-direction. But most researchers seem to agree that vine twining is an unsolved question. Same with handedness... there seem to be multiple active hypotheses for the proportion of left-handedness. And Steve's explanation requires group selection, which is controversial. --Allen (talk) 20:24, 27 January 2009 (UTC)

I wonder if the OP is from a hemisphere opposite Kainaw's, though; there's part of me that remembers an experiment with toilets flushing a different direction in the northern hemisphere from the southern, and wondering if vine growth has to do with the rotation of the earth. —Preceding unsigned comment added by DTF955 (talk • contribs) 17:59, 27 January 2009 (UTC)

Er - you do know that the toilet-flushing thing is a myth don't you? The coriolis forces are VASTLY too tiny to produce either that - or the vine rotations...so no. SteveBaker (talk) 18:31, 27 January 2009 (UTC)

Ohh, now I donno about that…surely if the Coriolis forces are strong enough to create left- rather than right-hand traffic in Australia and New Zealand, they're strong enough to make water spiral the wrong way down the sink. ← The preceeding text is a joke. It is not intended to inform or educate. —Scheinwerfermann ·_C21:01, 27 January 2009 (UTC)

Vine-twisting direction seems to have been noticed only quite recently. I wonder why botanists did not notice it generations ago. What else is being overlooked in botany? And what is being overlooked in other branches of science? Medical school students are told to pay attention to details about a patient and his ailment; but that does not seem to be stressed for college students in other areas of learning. In everyday life we ignore many, many, small details - we would go nuts if we paid great attention to everything. But in science, and in professions, attention to details within the area of interest is needed. (The transistor was discovered by investigating a small detail in the action of diodes.) On the other hand, a scientist should not become so immersed in details that he overlooks the big picture. In this regard, details may be sought in order to support a pre-existing conjecture. For instance, Darwin studied details in biology with a predetermined objective. He wasn't just accumulating facts (though that can be useful to aid further work in science by others). Darwin's predetermined objective was to place evolution on a firm basis. Thus, there are two goals in science. One is to accumulate facts. The other is to put 2 and 2 together to make 5 (idea synthesis). Sometimes the "accumulating" approach in science leads to the other approach – the very act of accumulating related facts can bring to light an overall concept that was not seen at all before. Even in everyday life a serendipitous juxtaposition of seemingly unrelated facts will occasionally reveal an overall concept not seen before. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:22, 27 January 2009 (UTC)

It's not a recent discovery, Charles Darwin wrote about it. I always thought it was because the plant was phototropic following the sun as it went around the sky. Graeme Bartlett (talk) 20:12, 27 January 2009 (UTC)

Surely that would only work if they were growing an entire loop around the tree each day? I don't think they grow that fast. --Tango (talk) 20:19, 27 January 2009 (UTC)

No, it could just be that they're influenced at some critical point. But the articles I link indicate that the influence of the sun's motion has been ruled out as the cause. APL (talk) 20:25, 27 January 2009 (UTC)

Yeah - I mean it would work during the summer at the North or South polar regions where the sun doesn't set for months at a time - and it couldn't possibly work near the equator where the sun doesn't "circle" a tree but ascends pretty much vertically into the sky - across the zenith and vertically back down again on the opposite side. The acid test would be whether the same plant would coil in the opposite direction when planted in the southern hemisphere...that's worth thinking about...just so long as nobody else says the word "coriolis"! SteveBaker (talk) 21:51, 27 January 2009 (UTC)

Actually -- and it's surprising to me, too -- the effect was one of the hypotheses of these Australian researchers. --Allen (talk) 22:08, 27 January 2009 (UTC)

Puh!...botanists...what'ya gonna do? They aren't even proper biologists. May I refer you to this handy chart and invite you to place botanists on that scale! That effect relies on the magnitude of two properties - speed of motion and North/South distance travelled - two properties that a vine has in astoundingly negligable quantities! Bozo's. :-) SteveBaker (talk) 01:03, 28 January 2009 (UTC)

Botany is scorned because it has not progressed much beyond description and classification. The reason it has not progressed much is because it is very difficult. Physics is child's play compared to botany. – GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 16:42, 28 January 2009 (UTC)

It's not a matter of difficulty. We were talking a few days ago about economists and I was saying that what they do isn't really science. That doesn't make economics 'easy' - it just means that they aren't doing science while they are doing it. Botany is indeed mostly a matter of 'stamp collecting' with relatively little actual science going on. That doesn't make it less worth-while or less difficult - it just means that it's mostly not 'science'. Hence, it comes as no surprise to me that some botanist would make the incredibly stupid suggestion that coriolis forces caused this when the briefest glance at what that force actually IS would make it blatently obvious that it cannot be the culprit. A proper scientist might do an experiment - but when a back-of-envelope calculation shows the effect has to be utterly negligable, one would not consider doing THAT experiment until all other reasonable lines of inquiry had been excluded. If it we're me, I'd want to try to make one grow the other way by having artificial lighting that moved in the opposite direction to the real sun in the vine's habitat. I'd look to see if there were EVER a vine that grew the opposite way and do a DNA study to try to isolate the 'clockwise' gene. I'd try a whole bunch of much more likely things before I'd EVERY go on record as saying that coriolis was even the remotest possibility. So this particular botanist is not behaving like a proper scientist and is showing a lamentable lack of scientific knowledge. SteveBaker (talk) 19:27, 28 January 2009 (UTC)

Botanists are just a cross-section of humanity, and as with reference desk authorities you get the whole spectrum from awesomely wise to thick as two bricks. Left- and right-handedness in creepers has been known since our ancestors started oozing around on dry land. Even Flanders and Swann wrote a ditty celebrating the phenomenon
Said the right-handed Honeysuckle to the left handed Bindweed
oh let us get married if our parents don't mind we'd
be loving and inseparable, inextricably entwined we'd
live happily ever after' said the Honeysuckle to the Bindweed..
Rotational (talk) 09:48, 29 January 2009 (UTC)

Help on Forces

Does Contact force exist even when there is no gravity. Bold text CAN YOU DIFFERENTIATE NORMAL CONTACT FORCE FROM CONTACT FORCE??? And further more...what is the newtons third law pair for contact force acting on the feet of a gecko that clings to a wall which is perpendicular to the ground??? —Preceding unsigned comment added by 123.49.43.236 (talk) 17:52, 27 January 2009 (UTC)

Certainly. Gravity is just a force - you could substitute a different force. Magnetism, say. Also, that nice Mr Einstein told us that acceleration and gravity are indistinguishable for all laws of physics - so in deep space an object accelerating at 1g would produce exactly the same effect. The teeny-tiny hairs in the gecko's foot are sticking to the glass through Van-de-Waal's forces at the atomic level. SteveBaker (talk) 18:30, 27 January 2009 (UTC)

See Sticky Secrets of the Gecko and van der Waals force ciao Rotational (talk) 10:04, 29 January 2009 (UTC)

It seems really unlikely that in any circumstance, the Contact Force would be in any other direction than normal. Does anyone know of any counter-examples? If there are any, they are probably not in macroscopic, "standard" situations. Nimur (talk) 18:39, 27 January 2009 (UTC)

I think there is some confusion here between contact force and normal force. Our contact force article explains the difference as follows: "A contact force has two components. The part of the force that lies within the plane of contact is friction ... The part of the force that is perpendicular to the plane of contact is called the normal force." For example, an object in equilibrium on a rough sloping surface experiences a contact force that is not normal to the surface (the contact force must be vertical so that it is equal and opposite to the object's weight), but the normal force is always, by definition, normal to the surface. Gandalf61 (talk) 10:36, 28 January 2009 (UTC)

I'd better review my basic physics terminology... Nimur (talk) 15:15, 28 January 2009 (UTC)

Most stuff eaten at once and eating things whole

Since I'll be gone on April Fools Day, I ask this question now that was on my mind.

The song about the old lady who swallowed a fly has her eating huge amounts of things at once, apparently whole (though it's not said for sure; she's likely nuts as it is, so she could have odd ideas about what can catch what, but anyway...).

My questions are: 1. How much is the most one person has eaten at one time? I've heard of ten-pound burgers someplace, I think. 2. I doubt one could even get a cat down one's throat, so we'll go with a bird; suppose someone was able to swallow a very small bird whole; how long would it survive in the stomach before being attacked by the stomach fluids and killed? Long enough to find the spider?

Take note - anyone who claims this question is asking for medical advice will be laughed at for days. :-)Somebody or his brother (talk) 18:08, 27 January 2009 (UTC)

Well, our stomach article states "in humans, the stomach has a relaxed volume of about 45 ml, it generally expands to hold about 1 litre of food, but can hold as much as 4 liters." Certainly the limiting factor is the circumference of one's esophagus. According to this article average diameter is 2-3cm (.78-1.1 in), so 6.3-9.4 cm (2.4-3.5 in) circumference. -- MacAddct1984 18:30, 27 January 2009 (UTC)

Surely the esophageal cross-section is not of fixed size? Nimur (talk) 18:37, 27 January 2009 (UTC)

Yeah, it must expand to a point, I couldn't find much about it though. If a bird did manage to get down someone's throat, I'm sure finding and eating an already decomposing spider is the last thing on its mind. Also, we happen to have an article on There Was an Old Lady Who Swallowed a Fly. -- MacAddct1984 18:43, 27 January 2009 (UTC)

Wow, there is an article on everything here. :-)Somebody or his brother (talk) 19:21, 27 January 2009 (UTC)

Not forgetting 'a waffer thin meent' Laughed at for days, eh? - ooh, blimey!! Richard Avery (talk) 19:41, 27 January 2009 (UTC)

66 hot dogs in one sitting. You might also want to check competitive eating. Clarityfiend (talk) 20:04, 27 January 2009 (UTC)

Please see the International Federation of Competitive Eating Records List. These guys are pretty much the authority. The most impressive item on the list in my opinion is the 21 lbs of grits eaten in 10 minutes. Anythingapplied (talk) 20:51, 27 January 2009 (UTC)

Hmmm...less than 2 pounds of chocolate in 7 min.? On the other hand, 65 hard boiled eggs, and by a woman. In your face, Cool Hand Luke. Clarityfiend (talk) 00:13, 28 January 2009 (UTC)

In my old school times a guy tried to eat two krapfen at once, but suddenly became red and almost died.--pma (talk) 00:55, 28 January 2009 (UTC)--pma (talk) 00:55, 28 January 2009 (UTC)

Does this count as "whistling"?

Hi. I know a method of "whistling" different from conventional whistling. Place the tip of your tongue loosely on top of your lower teeth, then place your upper teeth loosely on top of your tongue, and very slightly behind your lower teeth. Pucker your upper lips up towards your nose, close your jaws slightly, then blow a steady stream of air through your upper teeth and the gap in your lips, while slightly puffing your central and upper cheeks. It should make a high-pitched sound. Now, I find that using this method, I cannot control the pitch of the whistled note, and it isn't always continuous. However, would this still count as whistling or not? Thanks. ~AH1 19:17, 27 January 2009 (UTC)

See Whistling#Types. Seems to me like it's still whistling, unless by "still count" you mean you're planning to enter a whistling contest and don't want to be disqualified. Coreycubed (talk) 19:50, 27 January 2009 (UTC)

Whistling can be done lots of ways, even with a whistle, your hands, or a blade of grass. To decide if something is whistling or not all depends on the noise that is made. If it makes that high pitch whining "whistling" noise then it is indeed a whistle regardless of how you do it. Even when a teapot makes that noise it is considered to be whistling. Anythingapplied (talk) 22:43, 27 January 2009 (UTC)

Autoclaving liquid

When autoclaving liquid, one is always instructed to use an oversized container so that the liquid will not escape if it starts to boil. When you use the 'liquid' cycle on the autoclave, at the end of the cycle the pressure drops slowly to prevent boiling over.

My question is, in practice does liquid (an aqueous solution such as microbial media) commonly boil in a autoclave run on the liquid cycle? That is, is the oversized container really just a redundant precaution, and the liquid will not boil as long as the autoclave works correctly? ike9898 (talk) 21:08, 27 January 2009 (UTC)

There might be some liquid expansion issues but I think you've answered your own questions. In practice many things can go "wrong". Preparation can determine if the "wrong" event is a) of no consequence or b) requires the process to be repeated without getting anything "wrong". If a redundancy doesn't cost anything, for example grabbing a moderately larger dish over a smaller one, than there is no reason not to take the extra precaution.--OMCV (talk) 01:21, 28 January 2009 (UTC)

Usually the problem with boiling is that the pressure drops much faster than the temperature does. Theoretically if the autoclave is working and designed properly it wouldn't happen, but in practice people get antsy and try to open the door too soon or the control isn't exactly 100%. I know with the media I've autoclaved (been a few years, though!) it wasn't unusual to see it churning a little bit when I took it out, albeit not enough to boil out of anything. I may have been a little trigger-happy with the door, though. SDY (talk) 01:17, 28 January 2009 (UTC)

I used to make LB all the time and, while I couldn't tell what was going on once the doors shut, I would often see evidence of broth that had crept up the inside of the flash. Also, after taking out the flasks, the slightest movements would cause it to bubble up rather violently. -- MacAddct1984 18:14, 28 January 2009 (UTC)

Thanks, all. I'm basically being cheap and trying to avoid bigger flasks, but I think I'm going to just bite the bullet buy them. It's better than making a mess and/or ruining an experiment. ike9898 (talk) 19:36, 28 January 2009 (UTC)

From my experience, the liquids boil anyway even on the liquid setting in an autoclave. When autoclaving agar mix I avoided boiling over by only filling the bottle half full. When removing a freshly autoclaved bottle, it is completely normal that the liquids are superheated and will boil when disturbed. Put your bottles of media in one of those heavy duty plastic autoclave-safe bins to keep boiled over liquid from spilling inside the autoclave. Bigger flasks are nice because the extra volume keeps the liquid piping hot while pouring plates. (Cleaning out congealed agar from inside a bottle is no fun) Something to keep in mind is that when choosing a large size container, pick one that is easy to pour while wearing something to keep your hands from being burnt. The typical 1L glass bottles can be difficult to handle while wearing oven mitts. I would suggest donning a mitt and visiting the lab next door, filling up a bottle with water so it mimics the weight of a full bottle and practice holding and pouring to get a feel for what you can grip. Sifaka 20:06, 29 January 2009 (UTC)

osmole confusion

I`m just reviewing some renal stuff, and I`ve realized I`m confused on a pretty question:

If I took 500 sodium molecules and put them in 1 L in one container. In another contained, I put 500 glucose molecules.

Which would have the greater osmolality?

--Cacofonie (talk) 21:39, 27 January 2009 (UTC)

Did you review osmolarity? The first paragraph has a discussion of a similar question. See also molality within the concentration article. On a related note, you probably mean "sodium chloride" or some other sodium salt since pure sodium would be pretty reactive in water (which is what I assume you are dissolving in, since you didn't specify). --- Medical geneticist (talk) 23:27, 27 January 2009 (UTC)

Besides the fact that sodium doesn't really form molecules. If you're talking about sodium chloride I guess you could consider a pair of Na+ and Cl- as one "molecule", at least for the purpose of molarities. Confusing Manifestation(Say hi!) 04:16, 28 January 2009 (UTC)

Actually, see Van't Hoff factor. Sodium chloride has a colligative molarity double its measured molarity because it is not a molecule, but rather, an ionic substance. Strong electrolytes like NaCl have Van't Hoff factors equal to the number of discrete particles they form in solution, for sodium chloride each "NaCl" formula unit (which are not molecules) results in TWO discrete particles, an Na+ and Cl-. Non-electrolytes, like glucose, have a Van't Hoff factor of exactly 1, since they don't dissociate at all in solution, so one mole of glucose molecules produces exactly one mole of particles in solution. So a 1 molar solution of NaCl will have double the osmolarity of a 1 molar solution of glucose, because dissolving 1 mole of NaCl in a liter of solution will produce double the number of particles that dissolving 1 mole of glucose will. --Jayron32.talk.contribs 04:41, 28 January 2009 (UTC)

January 28

Can one guess the mass of a dice?

Suppose we have a cube with labeled faces (e.g., one of those objects called dice), with (possibly) inhomogeneous mass. Given the probabilities of the outcomes 1,..,6, (say that we have thrown it so many times that we agree on them), can we at least locate the baricenter? Or conversely: besides the symmetric case, is there a distribution of mass in a cube for which we can guess the frequencies of the outcomes? (Disclaimer: I am not planning to cheat people) --pma (talk) 00:43, 28 January 2009 (UTC) hopefully fixed

There is no such thing as "a dice". --Trovatore (talk) 00:58, 28 January 2009 (UTC)

You can make a guess, but only within certain statistical parameters. Note that casino dice have the pips filled so as to maintain symmetry of mass. — Lomn 01:02, 28 January 2009 (UTC)

He never did say "a dice", he quite correctly and grammatically said "one of those objects called dice" (objects dice plural). Don't be pedantic and wrong. Rotational (talk) 13:40, 29 January 2009 (UTC)

He did say (correctly) "a dice", but has since edited the original question to avoid confusing Americans. DuncanHill (talk) 14:57, 29 January 2009 (UTC)

My mistake......sorry Rotational (talk) 17:19, 29 January 2009 (UTC)

What Trovatore is saying is that "dice" is the plural form of "die". Saying "a dice" is like saying "a cars" or "a books", it doesn't really make sense. -- Mad031683 (talk) 01:21, 28 January 2009 (UTC)

Surely the OP means a die. Surprised no one linked this--GreenSpigot (talk) 01:51, 28 January 2009 (UTC)

Well, the relevant article is at dice, which is far and away the most common form of the word. I'm more surprised that three of four responses ignored the question. — Lomn 01:54, 28 January 2009 (UTC)

OK die redirects to dice. But die is the singular.--GreenSpigot (talk) 01:57, 28 January 2009 (UTC)

We're not really supposed to correct the OP's grammar/vocabulary. If you can't answer the question...don't. SteveBaker (talk) 02:19, 28 January 2009 (UTC)

Correction in this case gives the OP more of a chance of finding what (s)he was looking for: therefore it is legitimate.--GreenSpigot (talk) 02:27, 28 January 2009 (UTC)

Dice is perfectly acceptable as a singular. DuncanHill (talk) 02:32, 28 January 2009 (UTC)

No, it isn't. It sounds seriously uneducated. --Trovatore (talk) 02:34, 28 January 2009 (UTC)

Dice is the normal singular, and the old singular die is confined to a few fixed phrases and certain mathematical contexts. DuncanHill (talk) 02:43, 28 January 2009 (UTC)

No, it isn't. A dice is substandard English, like a bacteria or a criteria. Absolutely unacceptable in formal writing. --Trovatore (talk) 02:45, 28 January 2009 (UTC)

Will you write and tell the OUP that or shall I? DuncanHill (talk) 02:47, 28 January 2009 (UTC)

The Brits do seem to see these things differently. They're wrong, of course. But I'd be surprised about Oxford; I'd need to see evidence there. --Trovatore (talk) 02:51, 28 January 2009 (UTC)

Edmund Weiner, Andrew Delahunty, Oxford Guide to English Usage, 2nd edition 1993, page 130. That do you? DuncanHill (talk) 02:55, 28 January 2009 (UTC)

What does it say, exactly? --Trovatore (talk) 02:56, 28 January 2009 (UTC)

"dice is the normal singular as well as the plural (one dice, two dice); the old singular, die, is found only in the die is cast, straight (or true) as a die, and in mathematical discussions, e.g. Rolling a die will generate a string of random numbers." Further down the same page it has "die (noun); see dice." DuncanHill (talk) 03:00, 28 January 2009 (UTC)

Boy, good thing we Americans are around to save the language. Y'all aren't taking care of it at all.

Anyway, you should be aware that a dice is seriously grating on American ears. In shared situations, if you can't bring yourself to say a die, it would be better to rephrase. --Trovatore (talk) 03:04, 28 January 2009 (UTC)

(ec)God forbid Americans should have to put up with English as She is Spoke in England :) David Crystal in The Cambridge Encyclopedia of the English Language, CUP, 1995, makes a similar point to the Oxford, at page 201. DuncanHill (talk) 03:08, 28 January 2009 (UTC)

Both 'die' and 'dice' are unacceptably vague here, and 'cubic die' sounds unnatural to my ears. The object in question is a d6. Algebraist 03:07, 28 January 2009 (UTC)

I second d6. All Dungeons and Dragons players know that the only acceptable way to reference dice is to day 'd' followed by the number of sides on the dice (die) in question, most commonly d20. -04:00, 28 January 2009 (UTC) —Preceding unsigned comment added by Pete5x5 (talk • contribs)

English is defined solely by how it is used (we don't have an equivalent of the Academie Francaise, for example), dictionaries just report what is used. If enough people make the same mistake, as in this case (or the case of "begging the question", for example), it becomes correct. --Tango (talk) 15:10, 28 January 2009 (UTC)

An easier way than relying on random movements and outcome while rolling the die/dice would be to build yourself a contraption where you could stand/clamp the thingy in question in by 2 diagonally opposed corners and give it a controlled push with a known and repeatable force and speed. Dice with centered mass should spin at the same rate and slow down to a stop within the same time no matter which corners you used. Dice instead of die is common because most of us encounter them before we get to school. (Even in the US.) I learned about a die for casting before I found out it was also (officially) the singular for dice.76.97.245.5 (talk) 03:54, 28 January 2009 (UTC)

Yes, well, that's sort of why it sounds uneducated. --Trovatore (talk) 05:27, 28 January 2009 (UTC)

Thank you everybody! So, I understand that the singular of dice is not so used, like in latin. Maybe I tried the Language desk for the mechanical side of the question...--pma (talk) 09:36, 28 January 2009 (UTC)

Some interesting discussions on two subjects!! The grammar bits were especially entertaining, but neither the title nor the question referred to "a dice". Bazza (talk) 13:41, 28 January 2009 (UTC)

Yes it did. It's been changed. Algebraist 13:44, 28 January 2009 (UTC)

And now I'have re-corrected at least the title so as to keep memory of the lucky occasion that gave origin to this debate. Note that, as a non-native english speaker, I am really glad to be corrected. In fact, I started writing here also to improve my english. And, of course, because I believe in sharing the knowledge with people from different countries. pma (talk) 14:39, 28 January 2009 (UTC)

Determining the centre of mass for the die by how it rolls is probably impossible in practice. The actual way to do it is to attach a string to the die to a bunch of points, one point at a time. The centre of mass will lie along the line that extends downward from the string (to maintain no torques on the die). Do this twice and the intersection of the two lines reveals the location of the centre of mass, but in practice, you're best to do several measurements to beat down the experimental error. WilyD 14:45, 28 January 2009 (UTC)

If we could all just use impeccable grammar, it would be a pair o' dice. Edison (talk) 16:20, 28 January 2009 (UTC)

Thanks Wily. Yes, we can determine geometrically the baricenter, but what I had in mind is another issue: is there a relation between the frequencies and the position of the baricenter? Roughly, the dice will stop more often with their baricenters in the lower position; I just wonder how this can be made quantitative. I had in mind a kind of approach via statistical mechanics and... no matter. I found interesting the linguistic aspect, and even more the anthropological one ;) --pma (talk) 17:42, 28 January 2009 (UTC)

Err, realistically, you'd never work out the relationship theoretically. Depends on the details on the friction in the die roll, the non-cubicity of the die, many unpleasant bits. You could make a simplified model, but the devilish details would cause me, a theorectical physcists to say "This problem is impossibe" - the easiest way to do it would be a bunch of dies with known baricentres, an undergraduate and some money from NSERC (or the NSF or whatnot). WilyD 18:13, 28 January 2009 (UTC)

Ok, that's what I also suspect; too many details are to be fixed. Now, trying to answer by myself, a simple model is: an cubic die with sharp edges, rolling under the effect of impulses randomly distributed. The six positions are local minima for the energy, and a 90 degrees rotation from one face (i) to another (j) needs a small amount of energy, δ_ij -it's how much the baricenter has to be raised. This should give a transition probability p_ij for any pairs of adjacent faces; p_ij is related to δ_ij according to the distribution of the random impulses. Now we have a Markov chain and I may think that the corresponding stationary distribution is the probability distribution for the stopping positions. The idea is that at a certain moment the die just decides to stop for reason of his own (otherwise, in alternative one may think of a slowly decaying energy, acting till the die can't move any longer). Anyway, my interest about it is just linked to dinner conversations; I'm not a physicist nor a probabilist and can't say how fool is this picture. pma (talk) 19:59, 28 January 2009 (UTC)

(Thanks for hiding the off topic!) The problem is there are even more details than just the dice itself. Even consider the initial position as random, the initial hight and spin have an impact. If it drops from a large hight with little spin, it is much more likely to make it into some equilibrium position before hitting the ground. It also depends on how much the die bounces on the surface it is being dropped. A lot of bouncing would again lead to more randomness and less predictability which would mean you'd have to use a die with a weight even more from the center. If you wanted to make a situation where the dice would land more predictably I may suggest dropping into a large tank of undisturbed water with sand at the bottom. The large decent would give it enough time to reach its equilibrium state and its landing would be slow because of the water so it'd probably just stick into the sand the same direction that it was falling. Even for a dice that was just off a little, you may find that you get the same number almost every time in this situation. Anythingapplied (talk) 21:40, 28 January 2009 (UTC)

Yes, the way it's thrown is clearly relevant. For the slow die in water that you are describing, the probability to land on a face should be proportional to the solid angle subtended by that face at the baricenter, I think. Anyway, I would expect just a rough correspondence between a true die and a mathematical model. Thanks again pma (talk) 22:10, 28 January 2009 (UTC)

I think you're model is solid. If you use some sort of machine to throw dice consistantly and fit variables to the model, I think it'd work quite well for a controlled situation. If you could use a high speed camera to record the initial side that hit the ground, the number of bounces, and all the intermediary sides to be face up when making contact with the ground you'd be able to fit your variables with much higher relaibilty and far fewer experimental throws. Determining what probability distrabution to use for the amount of initial energy would be the most difficult part in my opinion. Anythingapplied (talk) 22:23, 28 January 2009 (UTC)

Actually, I think one could get an approximate answer that while far from complete might none the less be interesting. If you watch a die, then at any given instant there is nearly always one side that is more approximately "up" than the others, and the die will either settle on that side or rotate to another. The question of whether it rotates to another side is dependent on whether it has enough angular momentum to carry its center of mass against gravity across a pivot point. A higher center of mass is easier to flip than a lower one. If one chooses to consider only the "last flip", when the angular momentum of the die is sufficient to rotate over once more but no further, one should be able to state roughly how much easier it is to flip the die in one configuration versus another based on the position of that center of mass. If one assumes that the last part of the roll, when the die is about to settle, is the most important, then this would give a rough way of estimating. Obviously there are a lot of other details that could modify that conclusion, but I think there is nonetheless a tractable (though still complicated) starting point for making such estimates. Dragons flight (talk) 22:35, 28 January 2009 (UTC)

Hey! Someone deleted my answer!! (restoring it) I've been thinking about this for the past day or so while all of the babble about die/dice was going on. I think we don't have enough information. Think about the mechanisms by which a 'weighted' dice ends up being 'unfair':

• If it were being tossed in a vacuum, then while it was in the air, it would rotate about it's center of gravity (which would be off-center) but that would only affect it's rate of rotation because of the changed moment of inertia of an off-center center of gravity compared to a dice with the CofG in the middle. So the initial force imparted to roll the dice would have a different resulting spin rate - but once launched, it would still land (essentially) randomly depending on the precise speed and height it was thrown from...and (of course) what orientation it was in at the start of the toss. But a dice with a heavy weight just under the '1' face wouldn't preferentially come up '6' for this reason.
• In the presence of air resistance, there would be a tendency for it to slowly stop rotating and to fall 'heavy-side-down'. But the degree to which that happens would have to depend on the lightness of the body of the dice. Imagine something like a shuttle-cock - those lightweight feathers result in it's flight rapidly stabilising to a 'heavy-end-first' approach. But if you imagine a 4 ton solid steel dice with a similarly off-center weight, you'd imagine that air resistance would be negligable. So this tells us that the weight, size, aerodynamics of the dice will affect the degree to which the thing will or will not tend to stabilise.
• Then, when the dice hits the ground and starts rolling there will be the question of whether the corner of the dice has enough friction to allow it to flip over onto the next face instead of merely sliding along the table without rolling. Offsetting the weight further from the point where the friction is applied gives it a greater turning moment when the weight is high up - and reduces the turning moment when the weight is at the bottom - so that's going to increase the probability of it ending up heavy-side down rather than managing to rotate another 90 degrees. The degree to which this effect works depends on how steeply the dice is dropped (if it's vertical - then this has little effect - if it's rolled horizontally - such as as a casino 'craps' table - then it's very significant).

So here's the problem. The degree to which weighting the dice affects the outcome depends on (at least) the air resistance, the moment of inertia of the unweighted version of the dice, the frictional forces between dice and table and the angle from which the dice is thrown. All of those things will alter the probability of the dice to be 'unfair'. If the degree of unfairness (statistical irregularity) depends on something OTHER than the placement of the weight in the volume of the dice - then you can't use statistical methods to determine how far the weight is from the center. You almost certainly can determine the direction in which it's displaced because that's just the degree of asymmetry in the statistics. But the AMOUNT of displacement would require knowing an awful lot about the detailed physics.

SteveBaker (talk) 00:38, 29 January 2009 (UTC)

Very clear. By the way, now I understand why casino dice have sharp edges: one good reason is that rounded corners would make it easier to stop on the lower position of the baricenter, if it's not perfectly centered - as extreme case, a ball would do it certainly. --pma (talk) 07:36, 29 January 2009 (UTC)

PS: It seems it was me the vandal... sorry Steve.pma (talk) 11:58, 29 January 2009 (UTC)

Yes - I wondered the same thing. It does make sense that square-cornered dice would be somewhat less prone to weighting - but on the other hand, they might be more prone to not being so random by virtue of not rolling so well. If you imagine some kind of dice that would somehow not roll at all (maybe it has spikes on the corner that dig into the table!) - it would be pretty easy to cheat by tipping it out of your hand - or perhaps the dice cup - in some kind of carefully controlled manner. An almost spherical dice seems less problematic in this regard. Going back to the 'dungeons & dragons' dice - a 20 sided icosahedral dice rolls forever - but a d4 (which is a tetrahedron) really doesn't roll at all. I have a set of d4 dice that are cylindrical 8-sided things with each number printed on them twice. They are much nicer to play with. I often suspect people of kinda gently tipping the tetrahedral ones onto the table to get the number they want. However, that may not be an issue for casino's where they make you roll the dice the entire length of that L-O-N-G table. SteveBaker (talk) 19:12, 29 January 2009 (UTC)

Backwards FET operation

Can I use a FET backwards to generate the square root of the drain current by looking at the Vgs?--GreenSpigot (talk) 02:05, 28 January 2009 (UTC)

It won't work if you just use the FET on its own, which is what I think you mean. The FET won't 'know' that you want the Vgs to vary with the drain current. You can, however, put the FET in the feedback loop of an amplifier and reverse its operation that way. There's an example here. --Heron (talk) 09:55, 28 January 2009 (UTC)

Yes but the opamp in that cct is only used to generate a drain (actually source current in that config) current proportional to the signal voltage. Id rather not use an op amp as Im considering very high frequencies. So if I was to force a drain current and use the developed Vds to act on the gate as feedback, do you think it may work?--GreenSpigot (talk) 13:33, 28 January 2009 (UTC)

In essence, you can't "reverse" the FET but you can ask the question "What voltage, when squared, would equal this voltage?" - and that is the answer you want. Hence User:Heron's idea of using a feedback approach. So (effectively) you compare the output of the FET to the voltage you are trying to take the square root of - and adjust the input of the FET up or down until they match. (Or if you don't need to do it too quickly you could use a $5 microprocessor that has A/D and D/A and do it in software!) SteveBaker (talk) 14:01, 28 January 2009 (UTC)

Its ok I modelled it on spice and it works.--79.75.56.52 (talk) 17:14, 28 January 2009 (UTC)

BTW thats SPICE--GreenSpigot (talk) 01:13, 29 January 2009 (UTC)

intensity light

SteveBaker, You said if I'm on Mars I won't notice the vermilion color becasue my eyes is in vermilion color, and the color I'll see is just tranparent light. Then why on Earth, on foggy day the I still notcie white, I see sky everyday, they always look azure (light blue). The yellow (signal light), I think way inside, humans can notice the yellow colour. But on Saturn/Titan, the problem is the light we get is 1/100 that of Earth, that is only light of a thunder hit our house at night. If I orbit around looking down, would Saturn look almost black? When I descend in Titan's atmosphere, you said I won't see the orange color because orange colour is in my eyes. I thought the color won't burn my eyes blind, just turn my color vision off? is strong color not rich just burn off vision?--69.226.46.118 (talk) 02:00, 28 January 2009 (UTC)

You seem to be referring to this thread. Be aware that if you show up here continuing a discussion from a week ago, and speaking directly to an unspecified person (who are you talking to, anyway?), most people here will wonder what on earth you're talking about. Algebraist 03:12, 28 January 2009 (UTC)

I think it's a steganographic message of some sort. Taking 1=color and 0=colour, it comes out 111010111. Not very good steganography — low information density; easily broken. Reminds me of this. --Trovatore (talk) 03:21, 28 January 2009 (UTC)

To avoid confusion the OP modified the post, original was here . To the OP, it is usually considered poor form to modify your post in such a way that you make proceeding discussion meaningless. You should at least mention it was modified or better still, if modifying your post will confuse the situation, just reply to your post with the additional information Nil Einne (talk) 11:16, 28 January 2009 (UTC)

• Trova, What??--69.226.46.118 (talk) 04:26, 28 January 2009 (UTC)

He's referring to the fact your original message was fairly cryptic. Nil Einne (talk) 11:16, 28 January 2009 (UTC)

Unfortunately, he feels very bad when he finds mis-spells and typos, and goes crazy. Usually these are results of a severe education... --pma (talk) 11:55, 28 January 2009 (UTC)

(Background: The OP had been asking a lot of questions - with a lot of follow-ups about the general topic of the color that planets would seem to be if you were really there. (S)he started asking more of these questions over on my UserTalk: page - and I requested that they not be posted there - but here, where they belong. IMHO, between several L-O-N-G answers here - and more on my UserTalk: the question has already been fully answered and there is little (if anything) more to be said on the subject. IMHO, the OP should carefully read the previous replies and desist from further posting on the subject until all of that material has been properly absorbed. At any rate - I've had enough.) SteveBaker (talk) 13:54, 28 January 2009 (UTC)

What matters isn't what colour the things you're seeing are, but rather what colour the ambient light is. On Earth, the ambient light is almost always white (that's why our eyes see the frequencies they do) - while the sky is blue, the sun is yellow, and they add together to make white (in fact, the light from the sun started out as white and was split into blue and yellow by the atmosphere). On Mars, the ambient light is going to be more red because the dust in the atmosphere absorbs other colours (this is different from the scattering that makes our sky blue - that just makes different colours seem to come from different places, it doesn't absorb anything so the result is still white), and your eyes would very quickly get used to that and you wouldn't notice (if it was too red you would notice because certain colours (eg. blue) would appear extremely dark, even black, but on Mars it wouldn't be that severe). --Tango (talk) 15:05, 28 January 2009 (UTC)

This reminds me of the Goethe vs. Newton dispute on the theory of colours... even Newton had enough of it, at a certain point ;) pma (talk) 18:18, 28 January 2009 (UTC)

Newton avoided the worst of that dispute by dying two decades before Goethe was born. Algebraist 15:13, 29 January 2009 (UTC)

...as everybody knows, as I assume... as a joke was a disaster :( pma (talk) 18:55, 29 January 2009 (UTC) I'm talking of my post, the silly one with ";)"

Feed the sailors with carrots so they'll have better eyesight.

The Japanese battleship Yamato was the last serious and also the largest navy battleship ever built. It was sunken by U.S. navy pilots in 1945. In 1941, it had a very traditional battleship vs. battleship configuration. In 1944, they removed two 155 mm turrets and installed 138 25 mm AA guns.

Nevertheless, Yamato was still sunken. They had too few AA guns. The first wave of attack consists of 280 planes and the second one over 100. It had taken 386 airplanes to bring down Yamato which only had 162 25 mm AA guns and a very small fleet of 9 escort ships. The special AA ammunitions for the 18.1" guns were found useless. Yes, they used the 18.1" guns as if they were shotguns.

The 25 mm AA guns, clustered around the bridge, were mostly destroyed by the bombs before Yamato's demise. Then the battleship had taken 10 torpedo hits (1 starboard, 9 port, the U.S. navy was very clever) and went off-balanced.

Since the Japanese Empire did not have the resources to build additional aircraft carriers and more airplanes in 1944, air support was out of the question. From a 20-20 hindsight point of view, how many 25 mm AA guns were required to defend against 386 U.S. airplanes? How many anti-torpedo weapons did it take? How many 18.1" turrets needed to go to make room for all these self-defense weapons? Did Yamato still have a chance if it cleans up the whole deck and give each of its sailor a 25 mm AA gun? -- Toytoy (talk) 09:58, 28 January 2009 (UTC)

Japan did not have the proximity fuse at that time, using time fuses or barometric fuses as always, and nobody had radar-guided anti-aircraft guns on their ships. It's surprisingly hard to hit a moving airplane from a moving ship with a projectile by eye, and it's almost impossible to set a fuse so it goes off near an approaching plane. If the entire deck of the Yamato had been covered in AA guns, it would still have taken only one well-placed bomb to sink her. The battleship was a doomed dinosaur even before the Yamato was commissioned. (It was a beautiful ship, though, wasn't it?) --Milkbreath (talk) 12:37, 28 January 2009 (UTC)

Also, if it was sufficiently well defended from air attack, it would have been attacked in other ways, such as a submarine torpedo attack or even a traditional battleship-to-battleship "crossing the T" engagement. High altitude bombers, which are out of range of anti-aircraft guns, would be another option, although their low accuracy means that many more bombs would need to be dropped. They also might not destroy the battleship directly, but could disable most of the anti-aircraft guns, allowing for low-altitude torpedo plane attacks. Mines could also be laid in it's path. If, by some miracle, the Yamato managed to survive all such attacks, the US might have even used an atomic bomb on it, when they became available, but, having only 2, they were in short supply. Still, if an "unsinkable" ship could be sunk instantly, especially if close enough to Japan to provide a sufficient demonstration, it might be a good use, perhaps sparing the 2nd city bombed, Nagasaki, of it's fate. Some of these approaches would have required a "strategic withdrawal" of the US fleet, to give time to prepare an adequate "reception". StuRat (talk) 14:51, 28 January 2009 (UTC)

I don't know that nuking a battleship would have done much. The US didn't know at the time (and so it can't really be used to justify the theoretical decision), but Crossroads Able wasn't much of a ship-killer, and that sort of airburst is a good approximation of how an attack would have gone. — Lomn 18:25, 28 January 2009 (UTC)

It sank 5 ships, despite having missed the target, and disabled many more. Also, I'm not sure if an air-burst is the best way to sink a single ship; a surface burst might be more effective, by swamping the ship. StuRat (talk) 15:07, 29 January 2009 (UTC)

Incidentally, in reference to your topic heading, the idea that carrots significantly boost eyesight is a myth . The myth was created intentionally by the British during WWII as a cover story to explain why the British were able to locate approaching German bombers so easily at night. The real answer is that the British had a top secret new invention: radar! Dragons flight (talk) 16:08, 28 January 2009 (UTC)

Indeed. As I understand it carrots are only going to improve your night vision (day vision is completely unaffected) if you actually have a vitamin A deficiency (which cases nightblindness). If you have reasonable night vision already, it's not going to get any better. --Tango (talk) 18:11, 28 January 2009 (UTC)

To take a different tack, I'll address the US Army Air Corps' approach to this problem. Faced with bombers that were outranging their fighter cover (and being mauled by the Luftwaffe for it), the AAC decided that the Flying Fortress, with its 10 or so antiaircraft guns, was insufficient to hold fighters at bay. They rebuilt B-17s into YB-40s, flying gunships that eschewed bomb loads in favor of additional powered turrets, ammunition, and armor. The effort, in short, flopped. YB-40s could not keep fighters at bay, could not keep up with the standard bomber formations, and could not drop bombs to salvage any cause for their inclusion in the flight line. It seems likely that the same sort of result would have come of a full conversion of a battleship to an antiaircraft platform -- as far as I know, no modern air assault has ever been substantially ablated by fixed-position fire (and yes, I'm lumping aerial and naval gunships into "fixed" -- relative to the attacking aircraft, they're effectively immobile), and a potentially effective battleship would have been lost in the process to boot. — Lomn 18:25, 28 January 2009 (UTC)

The combination of radar gunlaying and radar proximity fuses permitted an 82% kill rate for antiaircraft guns defending against the V-1 cruise missile during World War II. --Carnildo (talk) 02:19, 29 January 2009 (UTC)

Without a radar-controlled AA system, you can hardly hit any airplane with no matter how many guns. And without a radar system capable of tracking and engaging dozens of targets at once (good computers + phase-array antennas), your defense can be saturated in a matter of seconds. But just how good were these WWII planes and their ammunitions? The steel hull of Yamato was very thick. It was designed to take serious punishments. Its sister ship Shinano was sunken by torpedos because of some poor design mistakes. If the design and manufacturing were perfect, could these outdated heavy weight battleships survive non-nuclear air attacks? Could a thick-shelled turtle return home? -- Toytoy (talk) 18:31, 28 January 2009 (UTC)

Given that the Yamato and the Musashi were both sunk via aerial attacks, the answer is quite obviously "no". By 1944, US Naval bombers were lugging around one-ton bombs or torpedoes -- about the same throw weight as battleship shells. Since this wasn't an era where armor reigned supreme (contrast with the Battle of Hampton Roads for such a case]]), it's not controversial to say that any conventional ship* of the era could be sunk by any conventional aerial attack.

*See Project Habakkuk for what could have been an interesting exception. — Lomn 21:18, 28 January 2009 (UTC)

Organ donor records

Who is the youngest organ donor? And who holds the record for being the oldest at the time of organ donation? In multiple organ donors, what is the maximum number of organs that have been donated by a person? Or is there any article similar to World records in medical science? Jay (talk) 10:03, 28 January 2009 (UTC)

Youngest? Stillborn babies can become organ donors . If you want to get technical, I guess you should count from conception. I'm somewhat doubtful anyone has records of that sort of thing Nil Einne (talk) 11:11, 28 January 2009 (UTC)

Does destroying a few day old embryo in order to harvest embryonic stem cells count as "organ donation"? Technically, I suppose there weren't any "organs" yet. But in general, I believe finding the youngest organ donor is mostly a question of how one chooses to define "organ" and "donor". Dragons flight (talk) 16:01, 28 January 2009 (UTC)

If you accept it, younger than this seems difficult! pma (talk) 22:30, 28 January 2009 (UTC)

Making the queries more specific, I would like age to mean post live childbirth, and organ donation in the context of organ transplantation. Rather than the exact answers, what I'm looking for, in the absence of an available article, is ideas on which articles these details can be inserted into, or suggestions on title of a new article. Jay (talk) 08:36, 29 January 2009 (UTC)

That sounds like a miscellaneous fact; in light of the objections raised above regarding ambiguous definitions, you might want to reconsider adding such information to any article. We have a trivia guideline information page; that page may help you decide the applicability of this policy. Nimur (talk) 18:40, 29 January 2009 (UTC)

Osmole Confusion Part II

I asked a previous question (here) here, that was partially answered, but I find myself still confused.

The question was (edited a little): If I took 500 sodium ions and put them in 1 L in one container. In another contained, I put 500 glucose molecules. which has the greater osmolarity?

The answer that I found most helpful was this one, by Jayron32: So a 1 molar solution of NaCl will have double the osmolarity of a 1 molar solution of glucose, because dissolving 1 mole of NaCl in a liter of solution will produce double the number of particles that dissolving 1 mole of glucose will.

What I`m really confused about is the plasma osmolality equation. Posm=2xNA+GLUC/18+BUN/2.8 or something like that. Why does the concentration of sodium atoms contribute 36 times more to the osmolality than glucose?

Thanks! --Cacofonie (talk) 16:16, 28 January 2009 (UTC)

The sodium does not contribute 36x more than the glucose -- you have to pay attention to the units. The short-hand calculation for plasma osmolality corrects for the different units that are given for the measurement of sodium (mEq/L), glucose (mg/dL), and BUN (mg/dL).

1. The mass of glucose is ~180g/mol. Let's say you measure a typical plasma glucose of 90 mg/dL. First, let's convert to g/L for a plasma glucose of 0.9 g/L. Divide by 180g/mol and you get 0.005 mol/L or 5 mM. This is the same thing as dividing the plasma glucose by 18. A similar calculation is made for BUN. (corrected numbers... oops... stupid math... --- Medical geneticist (talk) 19:37, 28 January 2009 (UTC))
2. Jayron already stated this, but again, in a biological context, sodium is never present on it's own but as a sodium salt, predominantly sodium chloride (but also, importantly, sodium bicarbonate). When in aqueous solution (as in blood), one mole of sodium chloride dissociates into a mole of sodium and a mole of chloride. Thus, in the calculation, you just double the amount of measured plasma sodium milliequivalents to account for the fact that the other (unmeasured) components (chloride and bicarbonate) of the sodium salts are present in solution.
3. Adding together the molarity of sodium+chloride, glucose, and BUN gives a decent approximation of plasma osmolality.

--- Medical geneticist (talk) 18:31, 28 January 2009 (UTC)

It should also be noted that bicarbonate, being a weak electrolyte, introduces some serious complications should you want to be scrupulously correct in your calculations. Because bicarbonate, in a water solution, produces small amounts of SEVERAL different kinds of particles, it has a non-integer Van't Hoff factor, and as such, makes the calculations quite messy. However, as a first approximation, assuming sodium bicarbonate has a Van't Hoff factor of "approximately 2" usually gets things close enough for government work... Thus, as noted, you can assume "sodium" in this context to mean "sodium, and whatever negative ions it is draging along". So, we have some assumed NaX compound, which produces 2 moles of ions (Na+ and X-) and we just take it to mean that the identity of X (be it chloride, bicarbonate, or melange of several different kinds of ions) to be moot for colligative purposes. --Jayron32.talk.contribs 04:56, 29 January 2009 (UTC)

Wearing a coat inside making the cold outside feel colder.

I wear my winter jacket inside a lot of the time. I'm told that doing this will make the outside "colder" (it's winter) when I go outside. People recommend that I take off my coat when inside so that I don't get as cold outside.

Is this true? If so, how/why is this?

141.117.29.242 (talk) 16:40, 28 January 2009 (UTC)

Perhaps it is because sweat glands, our natural cooling system, adjust to current conditions. When a coat is worn indoors, the glands open to produce more cooling. If the coat wearer then goes outdoors, it takes a little time for the sweat glands to adjust to the new condition. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 16:58, 28 January 2009 (UTC)

I agree with the above, in that if you're so hot you're sweating indoors, you should definitely take the coat off indoors. However, if you are cold enough to feel you need it indoors, then wear it. StuRat (talk) 17:04, 28 January 2009 (UTC)

See Thermoregulation in humans. 76.97.245.5 (talk) 17:07, 28 January 2009 (UTC)

That sounds about right, thanks a lot. 141.117.29.242 (talk) 17:17, 28 January 2009 (UTC)

The article on thermoregulation says, "Horses and humans are two of the few animals capable of sweating." I wonder whether monkeys and apes sweat. It is also surprising that two creatures as unlike as horses and humans both sweat. Where did it start in the evolutionary chain? Did the same thing crop up twice in evolution? Also, sweating is one of those things that are a stumbling block to the theory of evolution - an organ cannot perform its function unless it is already perfected, or nearly perfected. – GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:21, 28 January 2009 (UTC)

Dogs have things that are essentially sweat glands in the their paws. This appears to be so that they can leave a scent trail for their pack-mates to follow rather than to cool themselves. That suggests an evolutionary means to adapt that kind of capability into something for cooling through relatively simple genetic changes. These "stumbling blocks to the theory of evolution" almost always turn out to be something like that. Some piece of biological machinery that was originally intended for one purpose gets re-purposed in some unexpected manner. The business about it only being in horses and humans sounds unlikely - but bear in mind that it's possible for the common ancestor of humans and horses to have had functioning sweat glands and that all of the other species descended from that point didn't need them anymore and lost the capability. Evolution is just as capable of deleting a feature as adding one. SteveBaker (talk) 18:48, 28 January 2009 (UTC)

Or, it could be convergent evolution, although that seems even more unlikely. Interesting, sweat gland says that mammary glands are often considered modified sweat glands, which would suggest sweating pre-dates the evolution of mammals. --Tango (talk) 20:26, 28 January 2009 (UTC) --Tango (talk) 20:26, 28 January 2009 (UTC)

The use of sweating for thermoregulation is rare, but many organisms, including mammals, reptiles and insects, all excrete pheromones for various purposes, and it would not surprise me if scent glands developed for that purpose were modified to produce sweat glands. Dragons flight (talk) 20:42, 28 January 2009 (UTC)

Sweat glands in dog's feet still had to be nearly perfected if they were to work at all. Sweat glands have to perform the complex function of converting bodily fluids, probably blood, into sweat. A duct to the surface also had to be developed. The same requrements apply to mammary glands. - GlowWorm —Preceding unsigned comment added by 98.17.34.148 (talk) 19:31, 28 January 2009 (UTC)

Sweat could have started off as just blood plasma or interstitial fluid and still served a purpose, so there it doesn't have to be one big leap. --Tango (talk) 20:26, 28 January 2009 (UTC)

I still think the organ-specialism problem presents a serious difficulty to the theory of evolution. Those who wish to deny this difficulty say, in any particular case, that there was adaptation of something else. But they cannot show a partially-adapted organ (midway between two functions) in living things or in fossils. Their denial of the difficulty seems to me to be in the same category as the original denial of evolution itself. There was immense opposition to the theory - in England especially - when Darwin's work was first published. However, by now a great mass of supporting evidence for the theory of evolution has been adduced. There is so much supporting evidence that the main thrust of the theory cannot be denied except by religious fundamentalists, who take a nonscientific approach. But I think there is more to be said - in a scientific manner - about evolution. And it is something important. – GlowWorm

One major part of the problem may just be that soft tissue doesn't fossilise particularly well so it is very difficult to tell when organs an extinct creature had. Even if these missing links exist, we would probably struggle to find them. --Tango (talk) 22:47, 28 January 2009 (UTC)

Organs are never "partially adapted". To suggest such a thing implies a teleology to evolution — as if an organ starts out performing function A, but then somehow decides that it should instead be performing function B and starts moving that way. The only way organs can be repurposed is if, at every single step along the way, the changes provide a larger advantage (in performing function B better) than they do disadvantage (in performing function A worse). Every organism in the evolutionary chain that leads to us was a successful reproducer in its own right, there are no inferior halfway points between well-adapted creatures. Maelin (Talk | Contribs) 00:50, 29 January 2009 (UTC)

That's not entirely true - as long as there isn't a significant disadvantage to the change it may spread just by random chance, especially in a small population. Advantageous mutations are more likely to spread, but that doesn't mean that all neutral mutations die out. --Tango (talk) 14:00, 29 January 2009 (UTC)

Another simpler explination is that if you wear your jacket indoors you will sweat in it (not necessarially because you are hot but because you normally sweat a little in most of your normal daily activities). When you go back outside this slight dampness will make you significantly colder. It is the same effect if you've ever worn the same socks two days in a row and notice that on the second day your feet are colder. This is also why they advice changing cloths before bed when doing winter camping, to make sure the cloths are dry and clean to keep you as warm as possible. Anythingapplied (talk) 20:36, 28 January 2009 (UTC)

Not just sweat; we have a variety of ways to regulate our temperature, such as dilating blood vessels. Someone who has adapted to live in Scotland is likely to feel rather hot in Miami, and someone adapted to Miami is probably going to feel chilly in Scotland. Even if the two people wear the same clothes in the same places. We adapt to regulate our temperatures so our internal body temperature stays constant. On a smaller scale, if you wear more clothes than strictly necessary inside in the winter you'll get used to being snuggly and warm while regulating your temperature for warmer conditions. When you go outside, you need to shift to working harder at keeping warm. In particular, if you wear your coat inside you're likely to have more warm blood flowing near the surface of your skin. When you go outside you're suddenly in a situation where your skin is much warmer than the outside air (far more so than if you hadn't kept your coat on), so you quickly lose a lot of heat. Losing heat feels cold. 79.66.105.133 (talk) 20:35, 29 January 2009 (UTC)

Synthesis of Benzene

Hi, I was told you cannot "make" benzene from cyclohexane as Benzene cannot be treated as a molecule with 3 isolated double bonds- as bond lengths indicate equal bond lengths. So is the following not possible then? Because you can Birch reduce Benzene to cyclohexane.
Notify me of a response by copying and pasting the following on my talk page, Thanks --DFS454 (talk) 17:12, 28 January 2009 (UTC)
{{newmessages|Misplaced Pages:Reference desk/Science#Synthesis of Benzene}}

Birch reduction of benzene gives cyclohexadiene, not cyclohexane, and dissolving-metal reductions don't usually touch simple alkenes at all. That's two bits of evidence that benzene is something other than "cyclohexatriene". DMacks (talk) 18:36, 28 January 2009 (UTC)

The alternating-double-bond model that makes benzene appear to be "cyclohexatriene" is largely an artifact of the diagrams used to draw benzene, or reliance upon models of molecular bonding which fall short of fully explaining the situation. There are several good models of bonding which actually reliably predict that benzene will NOT behave as "cyclohexatriene" would be expected to. For example, hybridization theory shows that every carbon atom is "sp2" hybridized, and its just not possible to justify having 6 identical atoms bonded to each other with alternatingly different length and strength bonds. It just doesn't make sense. Likewise, Molecular Orbital Theory, sort of a "hybridization theory on steroids", makes a perfect prediction of the "correct" structure of benzene. The problem is that the standard "stick and ball" model, or the condensed structural formula model shown above, do not allow themselves to easily represent the reality of the delocalized pi-bonding system present in benzene. Its a case of inadequate models more than anything. Once you realize what benzene really is, as explained by hybridization theory and MOT, then its properties and reactions make MUCH more sense. --Jayron32.talk.contribs 04:48, 29 January 2009 (UTC)

Such excellent answers have rarely benzene at the Ref Desk. StuRat (talk) 14:56, 29 January 2009 (UTC)

ha! DMacks (talk) 18:22, 29 January 2009 (UTC)

Yeah, without MO theory, it's hard to explain why benzene is like this, but cyclooctatetraene is really just cyclooctatetraene alternating single and double bonds. DMacks (talk) 18:22, 29 January 2009 (UTC)

• One of the issues would be the comformation of the cyclohexane. It has a chair or boat conformation while the benzene ring is flat. - Mgm| 08:52, 30 January 2009 (UTC)
  • Thanks for the explanations everyone! DFS454 (talk) 13:32, 2 February 2009 (UTC)

Letter to the BMJ

While reading, with some amusement, about the cello scrotum hoax, I noticed the original letter to the editor finishes, "... — I am, etc. <signed>" It appears, from the other letters on that page and Ghits, that this is a standard sign off for letters published in this journal. What does the etc replace and why is it used by all correspondents? Rockpocket 18:10, 28 January 2009 (UTC)

I'm guessing - but I get the impression that somewhen in (roughly) Victorian times, there was a large amount of flowery crap you had to put on the end of a letter ("I am yours faithfully") with the complexity of the protocol required to say 'faithfully' on business letters unless it's to a loved one ('eternally') or to a lawyer ('respectfully') or a government official or some minor royalty ('loyally'). Keeping all of that straight - especially when writing (in effect) to a large number of unknown people in a journal - got so bothersome that people would just stick an 'etc' in there an let people figure it out for themselves! It's come a long way from there to ~~~~ or '-- Steve' which is what I use on email! SteveBaker (talk) 18:36, 28 January 2009 (UTC)

Yes, you are correct. I just looked at some of the letters from the first issues in the 1840s and, back then the standard sign-off was "... — I am, gentlemen, your very obedient servant,<signed>." The "gentlemen" are the editors of the journal to whom the letters are addressed. Rockpocket 19:11, 28 January 2009 (UTC)

Note, "yours" in "yours faithfully",etc., is short for "your servant" (as in "I'm at your service", not necessary actually employed to scrub floors!). We do, of course, have an article: Valediction. --Tango (talk) 19:35, 28 January 2009 (UTC)

Which somehow fails to mention the Italian form sono vostro schiavo, "I am your slave"; a flowery formula of the highborn that somehow morphed into today's extremely informal ciao. --Trovatore (talk) 23:26, 28 January 2009 (UTC)

Misplaced Pages - the 💕 that anyone can edit. SteveBaker (talk) 00:29, 29 January 2009 (UTC)

Well, true. I can't be bothered at the moment to look up sources and so on. I wasn't really criticizing the article, just remarking on the fact itself, which seemed germane to the discussion. --Trovatore (talk) 01:44, 29 January 2009 (UTC)

Isn't the "etc." put in by the editors? the original letter would still have a valediction.124.176.236.32 (talk) 07:41, 29 January 2009 (UTC)

Such letters to the editor are always published in exactly the same format, so I would expect people to just write them in that format to start with. If they don't, it might well be edited to fit the standard format (there is usually a disclaimer somewhere saying they might edit your letters). --Tango (talk) 13:49, 29 January 2009 (UTC)

Hmmm - that might make sense. If the author wrote TO the editor using a valediction appropriate to the editor - then the editor might wish to redact it when printing the letter to be read by others to whom that valediction was not appropriate. This stuff mattered a lot more 35 years ago than it does today. I'm fairly sure we'd have been taught the correct way to address a letter to a person of importance when I was in high school around about then...sadly, that's exactly the kind of thing I forgot about a nanosecond later! SteveBaker (talk) 18:59, 29 January 2009 (UTC)

I don't think it's a matter of appropriateness, they're just abbreviating it because it's very long. These days "Yours faithfully" would be standard (since letters to the editor are usually addressed "Dear Sir"), but publications like the BMJ have been around so long they probably like to stick to old fashioned versions just for the hell of it. --Tango (talk) 20:08, 29 January 2009 (UTC)

Autodidact: how to prove that you learned something

How can an autodidact prove that he learned something about this or that science? Is there any independent examination out there?--80.58.205.37 (talk) 18:16, 28 January 2009 (UTC)

Well, you could try answering 10 questions a day on the WP RefDesk and if you get through a month without getting ripped to shreds by the other editors then you've probably made it! But seriously: I don't know at what level you are working - but you could take a look at the resources available to parents of home-schooled children...somehow they must be able to do it. SteveBaker (talk) 18:39, 28 January 2009 (UTC)

Actually, if you answer enough Q's here you will get ripped to shreds, even if the answers are correct, if they lack references to expert sources (even though they agree with the experts). If, on the other hand, your answers are correct, but disagree with the current experts, then God help you. StuRat (talk) 14:51, 29 January 2009 (UTC)

Well the reason you get ripped to shreds is because without references no one has a way of knowing if they really agree with the experts. That is after all the wikipedia way. Trust no one. (Okay maybe I'm mixing up my metaphors but it works) Nil Einne (talk) 19:45, 1 February 2009 (UTC)

In the same line: General Educational Development certifies that the taker has American or Canadian high school-level academic skills. For more advanced skills you could try the GRE. It is done before graduate school, however, I don't think you have to have a Bachelor degree to apply for it. There are also several IT certificates that don't require that you follow an specific path. Mr.K. (talk) 18:58, 28 January 2009 (UTC)

You could make and publish ground-breaking discoveries. --NorwegianBlue 19:36, 28 January 2009 (UTC)

For jobs at my organization, experience can be substituted for formal education. The idea being that if you have done a type of work sucessfully for a long time, that is as good as or better that a degree saying that you know how to do the job. ike9898 (talk) 19:48, 28 January 2009 (UTC)

I think we would be better able to address your question if we know: (1) the (equivalent) education level; (2) area of study; and, (3) country you are interested in, since there is a huge difference between being a "certified" autodidact in, say, web-design vs surgery. Abecedare (talk) 20:08, 28 January 2009 (UTC)

No, I don't have any interest in becoming a certified surgeon or certifying my knowledge in another highly regulated profession. I only have an interest in certifying my knowledge in some natural sciences above undergraduate level without putting a huge amount of money and time into a degree program. So far I found Graduate_Record_Examination#GRE_Subject_Tests. --88.0.97.125 (talk) 10:43, 29 January 2009 (UTC)

edit conflict

The GRE Physics subject test is a good start, but even some physicists consider it "irrelevant" because it emphasizes certain areas of research over others. (If only I had known ahead of time!) This is a general problem of any testing methodology.

Whether you are an autodidact or a formally trained scientist, you are fundamentally trying to establish credibility, if not expertise, in a specific subject area. The best way to do this is to participate in mainstream discussions with your specific community of interest. In modern science contexts, such conversations take the more structured format of journal publications, conference presentations, and grant requests. In the (slightly less formal) Misplaced Pages community, you can follow SteveBaker's advice - the Reference Desk is a cut-throat community of hardened misanthropic science-enthusiasts who will gladly correct your errors until you learn the ways of its in-crowd. It's not so very different from regular academia. Nimur (talk) 18:45, 29 January 2009 (UTC)

January 29

Parallel Universes' Laws of Physics

Hello,

According to String Theory ("M" theory in particular), there is the possibility of many other parallel universes just out of our "dimensional reach". Interestingly, The Elegant Universe by Brian Greene, gives rise to the possibility that these universes (if they exist) could reasonably have different laws regarding physics as we know it. My question is how is this possible?

Why would other universes have completely different laws? I can understand that there may be different parameters than ours (temperature, structure, makeup, etc...) but I don't understand that there can be a universe with laws that wouldn't make any sense! For example, if our universe had different laws, such as "F=m/a" or "E=mc", it would fall apart quite quickly, correct? Can universes really exist if they, say, violate the Laws of Thermodynamics? Or am I reading too much into the hypothetical implications to a hypothetical theory?

On a side note, could anyone please provide links or reading from a respectable (read "scientifically accepted") journal, website, book etc... for either the acceptance or denial of the Laws of Physics changing over time? Multiple sources or conflicting viewpoints are fine as well!

Thank you for your time, additional reading or information would be greatly appreciated!

Cheers! ❦ECH3LON❦ 00:28, 29 January 2009 (UTC)

Scroll up and read Cosmic gods Rotational (talk) 13:52, 29 January 2009 (UTC)

I suspect a lot of assumptions are hidden here under the term "laws of physics". Are we talking about "laws" like E=mc^2 or "F=m/a" or are we talking about, say, the number of quarks in existence, the relative strength of gravity, the same bestiary of particle physics? It's easy to imagine a universe where gravity is more powerful than it currently is; it's hard to imagine a universe in which simple relationships were not the same. --98.217.14.211 (talk) 00:43, 29 January 2009 (UTC)

The problem is that any parallel universe which is 'inaccessible' to us is inaccessible to our theories too. So we have no way (even in principle) to probe the other universe to figure out what its' laws are. Do we have any reason to assume the laws ARE the same? Npt really. Heck, we don't even know for 100% sure whether the laws we've worked out apply everywhere in OUR universe. We don't know - we can't know - so the safe assumption is that they could be different. SteveBaker (talk) 00:48, 29 January 2009 (UTC)

Well, I don't know if it's a "safe assumption." I hate invoking anything resembling the anthropic principle, because I find it less than explanatory, but from an issue of pure incidences, we certainly know that our particular configuration seems to work and appear fairly steady. We have no evidence that anything else could be. We have no evidence (and no reason to assume) our particular universe is anything special, that our particular place in it is particularly privileged. So it seems to me like we'd have more reason to assume that things elsewhere are similar to the way they are here. That's no rigorous proof, obviously. But I'm not sure there's any reason to assume they are different elsewhere. I don't see why, in the absence of evidence, it makes sense to assume that something is different than the case we know, even though the sample size is blindingly small (n=1). --98.217.14.211 (talk) 01:41, 29 January 2009 (UTC)

(Edit Conflict) By "laws of physics" (sorry for the vague term), I meant the relationships (mathematically) that we understand. For example, F=ma,

E=mc^2, Laws of thermodynamics, Maxwell's equations, etc... Does this help? Cheers! ❦ECH3LON❦ 00:51, 29 January 2009 (UTC)

If I recall that book correctly, he was talking about different values for physical constants such as c, μ₀, and particle masses, though I might be wrong. They say that if the strong nuclear force were only a few percent stronger than it is, then tetraneutrons could exist, which would make for an interesting universe (and would also throw our notions of radioactivity to hell). There are actually theories that some physical constants might change over time. It's a fun thought experiment to imagine a universe where the speed of light is only a few hundred miles an hour. But I digress.

Any notion of different laws of physics would be completely incomprehensible; asking how other physical laws are possible in other universes is like saying "how is it possible that God exists"? We only say it's "possible" because its outside of the realm of physics to say it's impossible. It's all a thought experiment anyway, like working with four-dimensional geometry. It doesn't exist in any way that we could ever observe it, so it isn't worth worrying about.-RunningOnBrains 01:31, 29 January 2009 (UTC)

Heh, I'm reading that book at the moment too. I wonder if I know you ;) —Cyclonenim (talk · contribs · email) 07:45, 29 January 2009 (UTC)

Unfortunately, I lost my copy of that book years ago (I should buy another one...), so I'm not sure quite what he was talking about. However, things like the inverse square law are easy to change - in a universe with 4 spacial dimensions, you get an inverse cube law (which messes with things like orbits to the point where everything either flies apart or crashes together). --Tango (talk) 13:55, 29 January 2009 (UTC)

Centripetal vs. Centrifugal

Could someone please explain to me the difference between centripetal acceleration and centrifugal acceleration? Also, what is the dostinction between centripetal acceleration and centripetal force? Yakeyglee (talk) 01:58, 29 January 2009 (UTC)

If you swing a mass round in a circle, there must be a force acting on the mass to stop it flying off in a straight line (as per Newton). This force is directed toward the center of rotation and is called the centripetal force. Every action has an equal and opposite reaction (some one called Newton again) so the centripetal force is balanced by the centrifugal force (which is what you feel when in a centrifuge. Force = mass*acceleration (that Newton chap again)--GreenSpigot (talk) 02:17, 29 January 2009 (UTC)

That last part isn't entirely correct. Every action has an equal and opposite reaction, yes, but you're confusing where the reaction is. The string is pulling the mass inwards, and the equal and opposite reaction is the string pulling your hand outwards. (When you're wondering about equal and opposite reactions, it's always best to consider that the forces are almost always applied to different objects, because if they were applied to the same object the equal forces would mean that nothing would ever move). For a better explanation of centrifugal force, see the article linked. It's a tricky one, because many over-zealous physics teachers will tell you that centrifugal forces "do not exist." This isn't quite true, it's just that they only exist in the frame of reference of the object being spun. — Sam 146.115.120.108 (talk) 03:40, 29 January 2009 (UTC)

Our article on inertial frames of reference has a nice explanation too. Basically, if you have to invoke forces that have no obvious physical origin and that act on all particles within a body (like centrifugal force and Coriolis force) then this shows that you are working in a non-inertial reference frame. A hypothetical Foucault pendulum at the North pole illustrates the difference nicely - what causes its plane of oscillation to rotate through 360 degrees every 24 hours ? Non-inertial frame answer - Coriolis force. Inertial frame answer - the plane of oscillation doesn't rotate, the Earth rotates around it. Gandalf61 (talk) 12:20, 29 January 2009 (UTC)

Obligatory xkcd reference. — DanielLC 16:48, 29 January 2009 (UTC)

According to Newton's first law, in the absence of an external force, a body will continue to move with uniform velocity in a straight line. The force that causes a body to deviate from a straight line and move along a circular path is called a centripetal force. However when you make measurements in a frame of reference that is intself rotating (such a frame of reference is called a non-intertial frame of reference), you get a "fictitious force" which is experienced in that non-intertial frame. This fictitious force is called the centrifugal force. So, if you you use an inertial frame of reference you experience a body getting deviated into a circular path due to a centripetal force. If on the other hand you are using a non inertial force which is rotating (revolving?) along with the body, you experience a centrifugal force on everything in that frame of reference. Gosh I always think I will be the first to answer some easy question I can answer but get beaten to it everytime :-( ReluctantPhilosopher (talk) 09:25, 30 January 2009 (UTC)

Actually - it's not a matter of being first - or even being the first to be correct - it's a matter of being the first to be both correct AND sufficiently lucid for the OP to understand what you're saying. I think you nailed that this time. There were other explanations ahead of yours - but I think you was the first that was really clearly explained. Sadly, there are no prizes being handed out (I need to make a T-shirt: "I made 15,000 useful posts and all I got was this lousy barnstar.")!! SteveBaker (talk) 12:28, 30 January 2009 (UTC)

Yes seems a very good answer to me. Perhaps some of the text of this answer could actually be incorporated in the relevant articles as a non technical explanation of this misunderstood topic?--GreenSpigot (talk) 18:42, 30 January 2009 (UTC)

Seeing bubbles on a leaf in water

If I put a leaf in water for a while, I see lots of bubbles. "Weeee!!! The plant is photosynthesizing!" I think, "I'll demo this for my students!" But... then I put a pen in water for a while, and I see just as many bubbles. Hmmm....

1) Why do bubbles build on the pen? Yes, I know there are dissolved gasses in the water, but why to they build on the pen?

2) Does anyone know a good lab that makes it clear that the bubbles on the leaf are being produced by photosynthesis?

Thanks! — Sam 146.115.120.108 (talk) 03:17, 29 January 2009 (UTC)

1) Nucleation

2) Not right off, since leaves are not exempt from nucreation you'd have to separate that out. The article hints that pure water might work, but then how do you prove to your students that they are seeing two different effects. Someone probably has a nicer set up up their sleeve. 76.97.245.5 (talk) 04:01, 29 January 2009 (UTC)

It might work if you degas the water immediately before. I can't comment on if you'd actually see the bubbles from photosynthesis - I'm not much of a biologist. --Bennybp (talk) 04:07, 29 January 2009 (UTC)

I think the water can be degasified by boiling it. Then, of course, let it cool before putting the leaf in. — GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 04:24, 29 January 2009 (UTC)

The leaf will need CO2 to be in the water, so you can't de-gas it. --Milkbreath (talk) 11:50, 29 January 2009 (UTC)

You're right, Milk. Boiling the water will remove the CO2. But that could be the basis of another classroom demonstration. Put a leaf in an inverted test tube full of unboiled water in a beaker of unboiled water. Put another leaf in the same situation with boiled water. Put both beakers under a strong light. I think oxygen bubbles will appear only on the leaf in the unboiled water. This will demonstrate that the leaf takes in CO2, extracts the carbon and keeps it, and exhales the oxygen. Perhaps it could be demonstrated that the gas which collect at the top of the unboiled water test tube is actually oxygen, though I don't know of an easy way to do that. The leaf being under water is not its natural conditiion, but still... - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:34, 29 January 2009 (UTC)

You could show that the gas in the test tube is probably oxygen by putting a heat-glowing stick or cotton swab in the test tube. The glowing item will burst into flame. - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:51, 29 January 2009 (UTC)

(ec)I like it, but how do you convince the kids that boiling removes gasses? (I once lost an eyebrow demonstrating fractional distillation for my step-daughter with a saucepan, some vodka, and a match.) Maybe you could boil some seltzer water and show that it's flat. Also, you'd need to seal the boiled water against the air to keep CO2 from getting into the water, and the plain water, too, for equivalency, which would put a time limit on the effect. I've seen a simple test for oxygen done by introducing a glowing splint of wood, which flares up in the presence of it. If you use a small enough test tube and let it go long enough to get a good amount of oxygen, you could evacuate the water by bubbling air into it through some tubing, leaving the air-oxygen mixture in the tube, hopefully concentrated enough to test positive for O2. --Milkbreath (talk) 18:59, 29 January 2009 (UTC)

(ec)1) Dunno. Maybe the air is coming out of the plastic as the water cools it; maybe the rough surface of the pen is providing nucleation sites for dissolved gases that are coming out of solution as the water comes up to room temperature.

2) Fill a test tube with water and place a sprig of elodea inside. Invert the tube in a pan of water. You might have to set up a clamp or something to keep it from falling over. Do the same with a fake plastic sprig of elodea as a control. Keep the rig well lit and the live elodea should outpace the plastic one in bubble production by quite a lot. --Milkbreath (talk) 04:12, 29 January 2009 (UTC)

I think that nailed it pretty neatly. Does anyone know if the Lotus effect would also work in reverse, i.e. would gas bubbles in water on a lotus leaf behave like water in air? 76.97.245.5 (talk) 04:25, 29 January 2009 (UTC)

Thanks! That sounds like a great setup. — Sam 146.115.120.108 (talk) 12:08, 29 January 2009 (UTC)

The plant doesn't just generate oxygen from nowhere - it converts CO2 to O2 in the presence of light - and reverses the direction of the reaction (O2 to CO2) in the dark. So there needs to be dissolved oxygen in the water in order for you to see CO2 bubbles. De-gassing your water seems like it's going to prevent photosynthesis. SteveBaker (talk) 18:39, 29 January 2009 (UTC)

Atomic Bombs and Radiation Burns

On the recent episode of Lost, they make reference to the fact that several people suffered radiation burns/radiation poisoning from an unexploded nuclear weapon (a hydrogen bomb). I was under the impression that the uranium/plutonium used in nuclear weapons is comparatively inert and relatively not that radioactive, at least up to the point it goes supercritical. Given the amount and type of radioactive material in an unexploded nuclear bomb, how close would you have to be to the bomb, and how long would you have to stay there to get enough radiation for acute effects to occur? (The bomb was depicted as leaking, so figures for both with and without typical shielding are appreciated.) -- 76.204.94.153 (talk) 04:46, 29 January 2009 (UTC)

You won't get radiation burns from the core of a nuclear weapon unless it is having some sort of criticality accident (i.e. if a gun-type weapon was submerged in water it could basically become a light-water reactor). But that doesn't sound like the case here—just Hollywood B.S. (no h-bomb would use a gun-type design). (Something similar happens in the film version of Sum of All Fears, if I recall.) To be sure, a hydrogen bomb contains a lot of unpleasant and exotic material, but until it goes critical its hazards are not radioactive (they are toxic, but that's a different issue). If just being near a nuclear weapon would burn you up, you can be sure that a lot of photos would probably indicate that. --98.217.14.211 (talk) 05:02, 29 January 2009 (UTC)

When the last poster writes "its hazards are not radioactive", I'm sure the intended meaning is that there is not enough radioactivity to be an immediate hazard. I mention this because it might be taken as saying that there is no radioactive material in the bomb; and since it contains a fission bomb, that would of course be wrong. --Anonymous, 07:25 UTC, January 29, 2009.

Well, right. What I meant is, "radioactivity is really not your biggest problem in a situation like that." There are far more dangerous materials in an unexploded bomb (high explosives, beryllium, etc.). The radioactivity of an unexploded bomb will only be a problem if, say, the high explosives go off and litter the surrounding area with a nice mist of plutonium, but even that won't give you radiation burns, per se, which is characteristic of highly radioactive material. (Materials of low radioactivity are still dangerous, mind you, but not because they will burn you or give you radiation sickness—they'll get in your lungs and bones and just radiate for ages, and eventually you'll get cancer and die. hooray.) --98.217.14.211 (talk) 12:37, 29 January 2009 (UTC)

But given the timetravel and other such events on the show, I think its safe to say the laws of physics as we know them do not apply to the island and therefore anything is possible. I try to turn the scientific portion of my brain off when watching, since its more of a fantasy setting than sci-fi. I'm not quite sure why bad science doesn't bother me on "Lost" but it does on "Fringe". Maybe its because Fringe acts like it is based on real science while Lost is so far out there they don't even try. -- Mad031683 (talk) 18:21, 29 January 2009 (UTC)

We don't have to even assume different laws of physics, though. We can just assume that it's a really poorly made hydrogen bomb, one that they happened to shove a bunch of raw fission products into. --140.247.243.29 (talk) 18:56, 29 January 2009 (UTC)

Oh lord fringe is so bad. They look at the guy's browsing history or something and get the street address of someone downloading the same thing right now? The platters of the hard drive are fused together but it's ok they have a special program that can recover data? °_o .froth. (talk) 18:44, 29 January 2009 (UTC)

Loss of memory cells

If you lose a lot of blood, will you also lose the immunological memory contained in those memory B cells you lost? Will you be once again susceptible to some diseases you've suffered in the past? Thanks for your answers. --Leptictidium (mt) 10:56, 29 January 2009 (UTC)

Typically you will retain more than one memory B cell per pathogen, so the odds of all of one of a particular type being flushed out – even with extended bleeding and multiple transfusions – is low. Further, at least some cells will likely remain in areas that won't drain readily, including the spleen and lymphatic system. TenOfAllTrades(talk) 14:20, 29 January 2009 (UTC)

Another thing to consider is the distribution of B lymphocytes in your body: Only roughly 2% of your total B cells are at any timepoint in your blood, 98% are in your tissues and lymphatic system. So the chance of completely eradicating a specific memory clone is rather low. In addition, even a heavy blood loss normally leaves several liters of blood even in a smaller human body (otherwise you will die rather quickly). So even the 2% that actually swim in your blood will not be drained completely. TheMaster17 (talk) 14:45, 29 January 2009 (UTC)

The new blood will contain Immune memory of diseases the donor has had. Will the recipient of the blood acquire those immunities? - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:55, 29 January 2009 (UTC)

The "new blood" as you call it is not typically whole blood, but only plasma and/or red blood cells. But even in cases where whole blood is given, the few remaining living cells in the "new blood" are quickly eradicated by the recipient's immune system, because they are recognized as foreign antigen. So no "transfer of immunological memory" is possible simply by blood tranfusion. :-) PS: It is considered polite on wikipedia to sign your posts by adding four tildes at the end. TheMaster17 (talk) 19:52, 29 January 2009 (UTC)

(edit conflict)

Donated blood is usually split into two or three components in the blood bank - the red cells, the plasma and often, but not always, the platelets. The plasma may be used either for producing plasma-derived proteins for treatment of specific diseases, or as whole plasma, which is used for stopping bleeding. When asking about the "immune memory" in the blood , you could refer to the T and B lymphocytes, and possibly also to the antibodies in the plasma.

First, the T and B cells: When these are transfused, they do not under normal circumstances transfer any useful immunity to the recipient - on the contrary, they act as antigens in the recipient, and are destroyed. This will lead to the recipient producing antibodies against the Human Leukocyte Antigens of the donor. Such antibodies can cause problems in subsequent transfusions, both febrile transfusion reactions and poor response to platelet transfusions. Very rarely, the transfused lymphocytes survive, and attack the cells of the recipient, causing graft versus host disease. Because of the problems the lymphocytes cause, it is mandatory in many countries to remove the white blood cells by filtering the red cell and platelet concentrates. In addition, for patients that are especially vulnerable (immunosuppressed), the blood bank will irradiate the blood to ensure that white cells that have managed to get past the filter cannot multiply in the recipient.

Second, the antibodies in the plasma: As said above, whole plasma (as well as platelets) is used for stopping bleeding. The amount of antibodies in whole plasma is too small to have any significant beneficial effect in the recipient, and again, it may cause problems. Plasma from a donor of blood group A has antibodies against blood group B, and would cause a transfusion reaction if transfused to a recipient of blood group B. However, as mentioned above, plasma is also used as raw material for industrial production of specific proteins, such as concentrated amtibodies. Such antibody concentrates are used to treat patients with immune deficiencies, and transfer immunity in a passive way.

The procedure of intentionally transferring functional immune cells is called stem cell transplantation, and the stem cells are either harvested from the bone marrow (bone marrow transplantation), or from the blood. However, to get stem cells in any significant amounts to enter the blood stream requires that the donor is treated beforehand, and it also requires that the donor is carefully selected to match the tissue types of the patient. --NorwegianBlue 20:27, 29 January 2009 (UTC)

Doctors in Médecins Sans Frontières

When Médecins Sans Frontières sends a doctor to say Rwanda, Sierra Leone or whatever, what is the status of this doctor? Does he have a degree to be a doctor in these countries? Is he illegally working as a doctor but since nobody cares, he can get away with it?--Mr.K. (talk) 11:06, 29 January 2009 (UTC)

From the article Médecins Sans Frontières:

Medical volunteers include physicians, surgeons, nurses, and various other specialists, all of whom usually have training in tropical medicine and epidemiology. In addition to operating the medical and nutrition components of the field mission, these volunteers are sometimes in charge of a group of local medical staff and provide training for them.

So the doctors definitely have degrees at least in the own countries. I would assume that they don't have degrees in the countries they are flying to, but I'm not sure why you would call this "illegal." They are not prescribing drugs, and I don't think there are laws that prevent anyone at all from giving medical care, or even performing surgery. If you wanted to reset my broken arm, and I was ok with you doing it, there is no legal reason that you couldn't. — Sam 146.115.120.108 (talk) 12:18, 29 January 2009 (UTC)

This string is a bit off topic but I think the word "volunteers" is a bit misleading since although hats off to them for volunteering to go, AFAICT they are still paid a salary comparable to an expat doctor for a multi-national? However since they are paid by MSF in whatever offshore location they may not have to be qualified to practice (meaning doing paid work) locally. I know plenty of people who were medically qualified in the UK who couldn't work for pay as a doctor in whatever non-Commonwealth country Africa but were welcomed to work as unpaid volunteers there. Paid by an offshore NGO is probably similar--BozMo talk 12:31, 29 January 2009 (UTC)

It should also be noted that MSF tends to operate in areas which are often described as "Failed states" or "failing states". In many of these areas, there are may be so few qualified doctors that there does not exist any real regulatory apparatus; or the government has so little control that any regulation on paper, especially one as esoteric as the regulation of doctors (which the country may not have many of to begin with), is essentially unenforcable. Even if the doctors are not technically "certified" in the states in which they are working, its hard to imagine that, if someone showed up and said "Hey, we want to cure your 3-year old kids of Diphtheria" that anyone would turn them away. It happens (in Rwanda, for example) that sometimes the doctors are unwelcome, and are murdered as such; however in general many places recognize the charity they provide for what it is and raise no objections.--Jayron32.talk.contribs 14:48, 29 January 2009 (UTC)

@Sam 146.115.120.108: I do believe there are laws in many countries regulating medicine in general and not just people prescribing drugs.

There is still a third possibility: there may be a special UN regulation for the case of catastrophic events, and doctors working for a specific international institution only have to be certified at home. MSF - and other international institutions like Red Cross- often works in failed stated, but also in war-torn regions, earthquakes...80.58.205.37 (talk) 15:20, 29 January 2009 (UTC)

AFAIK if there is an de facto government then that gets to decide what foreign help to accept and what not. There have been cases in the past where the local government has turned away help despite their people suffering. (e.g. Myanmar, ) Most countries regulate entry of people wishing to work in their country via visas. A government that accepts help from an international aid organization and issues visas to their employees will probably also accept their qualification. 76.97.245.5 (talk) 04:47, 30 January 2009 (UTC)

About Ocean Tides

Moon has less gravitational pull when compared to Earth's gravity.But how it is possible for moon to pull the water body(ocean) of the earth? —Preceding unsigned comment added by 117.200.112.103 (talk) 13:09, 29 January 2009 (UTC)

It's not the gravitational "pull" itself that causes the tides, it is the difference between the pulling forces at that side of the Earth that faces the moon, the centre of the Earth, and the side that faces away from the moon. Those differences are large enough to cause the tides as we see them (locally the effect can be enhanced by resonant and even interferometric effects due to the shape and size of ocean and sea basins). --Wrongfilter (talk) 13:32, 29 January 2009 (UTC)

But, if the Moon had comparable oceans, it would indeed have tides. StuRat (talk) 14:39, 29 January 2009 (UTC)

Even without oceans, the moon can have "solid" tides in the crust or mantle. That's how the moon's rotational energy dissipated to the point that now the moon always shows the same side to earth. Dauto (talk) 15:19, 29 January 2009 (UTC)

Perhaps the easiest way to think about it is that the ocean water that's closest to (vertically below) the moon feels the earth's gravity MINUS the gravity of the moon. That makes the effective gravity (and therefore the weight of the water) be a bit less there. That reduces the pressure of the water - and the higher pressure water off to the sides and further away that aren't feeling the moon's gravity quite so much are able to push inwards towards the point of least "gravity". That causes a bulge in the ocean vertically beneath the moon. It's actually more complicated than that because there are actually TWO high tides per day - one when the moon is overhead and ANOTHER when it's vertically beneath your feet.

That second tide is harder to explain:

Because the earth and the moon are rotating about a common point that's at the center of gravity of the two bodies, the earth doesn't spin perfectly about it's center - it orbits about a point that's a bit closer to the moon than the true center of the globe. So the part of the ocean that's furthest from the moon experiences centrifugal force that's a little higher than for the rest of the ocean. This results in an outward centrifugal force that ALSO causes the water to bulge outwards - but opposite from where the moon is.

To add to the complication, the sun also causes tides - but much smaller ones than the moon. So depending on the time of year and the time of the month and day - the sun's tidal force may add to or reduce the height of the tides. It ends up being rather complicated!

SteveBaker (talk) 18:32, 29 January 2009 (UTC)

Are you sure about that? I don't think it has anything to do with centrifugal force, it's just tidal forces (ie. the difference between the strength of gravity on different parts of the object due to different distances). The bit of Earth closest to the Moon feels the most gravity, the centre of the Earth feels a little less and the bit on the far side of the Earth feels even less, that causes the Earth to be stretched along the line joining the Earth and Moon. Both tides are caused by exactly the same thing. (Low tides are caused by each side of the Earth being pulled towards the centre of the Moon, so they are pulled at slightly different angles, the net result is that they get pulled towards each other.)--Tango (talk) 18:45, 29 January 2009 (UTC)

The viscosity of water has to be taken into consideration. As the moon pulls the ocean toward it, water flows from all parts of the earth to be closer to the moon. But viscosity slows down the flow. This will not produce a high tide on the far side, but it will lessen the high-tide effect. - GlowWorm.

That's not true, the moon doesn't pull the ocean towards it. The Earth and Moon orbit each other, that means they are in free-fall so are weightless. It's tidal forces (the difference in gravity between different points), not gravity itself, that cause the tides. It does take time for the water to move, though, which means the tidal bulges are offset slightly from the line joining the Earth and Moon - this is what causes tidal locking (gravity pulling on the bulge pulls against rotation, slowing it down). --Tango (talk) 19:32, 29 January 2009 (UTC)

It's just a matter of terminology. "Pull" in this context signifies the difference between the earth's gravitation and the moon's gravitation. - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 21:44, 29 January 2009 (UTC)

It's not the difference between the Earth's gravity and the Moon's, it's the difference between the Moon's at one point on Earth and the Moon's at another point on Earth (because they are different distances away from the Moon, or the Moon is in different directions). It isn't pulled towards the Moon, it's pulled away from the centre of the Earth in the direction towards the Moon and towards the centre of the Earth in the perpendicular direction. There is absolutely no difference between "directly towards the Moon" and "directly away from the Moon" - the ocean is pulled the same amount in each direction. Our article, Spaghettification, has some good explanation (with diagrams) - the tides caused by the Moon are far less extreme than those described in the article (which is about black holes), but the principles are the same. --Tango (talk) 22:46, 29 January 2009 (UTC)

Crystal violet staining for cell-counting

In a lab where I'm an intern, we perform crystal violet staining of cells for subsequent assessment of cell-growth inhibition of certain compounds. My problem is thus: the current protocol requires the removal of the medium (DMEM, 10% FBS, 1% P/S antibiotics) before addition of the crystal violet/ethanol solution. The methods for currently employed for medium removal are a) shake the (96-well) plate in a large beaker or b) pipette the medium off the bottom. Option a) results in the cell culture leaving the bottom of the plate in a more or less random pattern, leading to large irregular patches of cells disappearing. Option b) results in small marks in almost every well where abrasion by the pipette tip has resulted in removal of cells from the bottom of the plate. My solution is to add 100% formaldehyde directly to the medium without removing first (intended end concentration 10% = 20 ul formaldehyde + 200 ul medium), fixing the cells and preventing them from leaving the plate during the exercise of medium-removal-option a) (shaking the plate). Thus, my question is: will formaldehyde be able to fix cells to the bottom of the plate in the presence of the DMEM? ----Seans Potato Business 14:17, 29 January 2009 (UTC)

Not an answer to your Q, but have you considered using a needle and syringe instead of a pipette ? An even better option may be to put a sterile paper towel at the lower corner of the plate, to absorb the solution. StuRat (talk) 14:37, 29 January 2009 (UTC)

You haven't stated what kind of cells you're working with, but from your description of the experiment and medium removal techniques, it sounds like they are adherent cells. I don't know about formaldehyde, but paraformaldehyde is often use for fixation of cells in suspension before doing flow cytometry. In that setting, the paraformaldehyde does not make the cells stick to the plastic walls of the 96-well plates (or the tubes) that you're working with, at least not to an extent that causes problems. Why don't you try it out experimentally? Take three plates, seed out equal cell numbers in a couple of concentrations with several replicates for each concentration, and then try the three techniques for medium removal, and compare the variances between the methods? It doesn't sound like a difficult or expensive experiment, and you're the one who is in the position to perform it. If the reproducibility is poor, I would consider a redesign of the technique you use for getting a readout, using a staining method that doesn't require that the medium be removed. --NorwegianBlue 21:41, 29 January 2009 (UTC)

The DMEM probably isn't going to be a problem; the FBS might be. (Typical DMEM composition is here: .) Protein in the serum - mostly bovine serum albumin (BSA) - is going to be crosslinked and fixed by the formalin/formaldehyde. This may affect the degree of fixation of your cells, and may also result in a noisy result in your assay (as large amounts of precipitated, crosslinked protein is left behind). You may have to try it and see.

In lieu of violent shaking over a beaker, can you get an equally effective result - that doesn't detach cells - by gently inverting the plate over a stack of paper towels or other absorbent material? Gently refilling with PBS and dumping a second time may be required to clear most of the media before fixation. One last thought - perhaps you could look for 'stickier' plates. Different manufacturers offer tissue culture plates with different coatings; some will hold cells better than others. TenOfAllTrades(talk) 23:32, 29 January 2009 (UTC)

Swollen abdomen in Kwashiorkor

From the article "One important factor in the development of kwashiorkor is aflatoxin poisoning. Aflatoxins are produced by molds and ingested with moldy foods. They are toxified by the cytochrome P450 system in the liver, the resulting epoxides damage liver DNA. Since many serum proteins, in particular albumin, are produced in the liver, the symptoms of kwashiorkor are easily explained. "

Does this albumin deficiency causes the abdomen to swell? Why does it happen? 80.58.205.37 (talk) 16:32, 29 January 2009 (UTC)

According to the german language WP, albumin is mainly responsible for the colloid-osmotic pressure of blood, i.e., its content of solved substances. If that goes down, tissues near the blood will draw water, and this water can't be reuptaken by the veins---which are the most numerous in the belly. --Ayacop (talk) 17:08, 29 January 2009 (UTC)

Cause of death in the ocean

I’m curious as to what the frailest part of a person is while in the ocean. In particular say a person is in the ocean, perhaps a few miles off the coast of Florida, I’m wondering what factor would kill them if they don’t or can’t get help/swim to shore. Presumably the person would be able to float sufficiently well to not drown. And they probably don’t look enough like food to be eaten by something. So I would guess that either hypothermia, dehydration or salt overdose would be the actual killer. Any ideas as to which would come first, or how I would figure this out? Thanks 130.127.186.172 (talk) 17:41, 29 January 2009 (UTC)

In cold water, hypothermia is probably your primary concern. In extremely hot conditions, dehydration would be a problem. In more temperate conditions, exhaustion, leading to drowning, would probably be what gets you (while people float pretty well in salt water, it does take a certain amount of effort to keep your head above water, particularly in rough seas). This is just off the top of my head, though, we don't seem to have a relevant article (at least, not one I can find)... --Tango (talk) 18:00, 29 January 2009 (UTC)

Without flotation aids, I'd expect that both hypothermia and salt ingestion lead to drowning as the immediate cause of death, since those conditions would cause on to lose the ability to keep one's head above water before they actually become fatal. With a life jacket, I'd guess hypothermia is the killer for large portions of the ocean. Dragons flight (talk) 18:16, 29 January 2009 (UTC)

I've often heard "exposure" as a cause of death in those cases, which I would guess is by a combination of severe sunburn, dehydration, and exhaustion (since it would be tough to sleep while keeping your head above water). A lot of times desperately dehydrated people with no survival skills will drink seawater, which leads to confusion, hallucinations, and a fairly quick death.-RunningOnBrains 20:23, 29 January 2009 (UTC)

Guidance required.

Hello all, most initially, sorry for putting such an odd question here. But I want to create a new Project about Development of Science in Ancient India. Can anyone please tell me how should I proceed since I am new to this site? Anirban16chatterjee (talk) 17:50, 29 January 2009 (UTC)

Try the Misplaced Pages:Help desk for advice on how to contribute to Misplaced Pages (the Ref Desk is more about helping people get the most out of what is already written). It sounds like an interesting topic to write about - good luck with it! --Tango (talk) 17:54, 29 January 2009 (UTC)

Thank you very much, for rendering your kind hand of cooperation. And, thank you for your best wish! Best Regards. Anirban16chatterjee (talk) 18:09, 29 January 2009 (UTC)

Do you really mean "Project" (as in WikiProject) or do you just want to write an article? Writing an article is very easy and there are lots of tutorials out there. However, if you really do want to start a project (as in a collaboration between a number of editors to write, grade, produce standards and maintain a body of articles relating to a common topic) then I STRONGLY recommend that you write some articles in the areas of your interest, gradually find out who the active editors in those areas are - get to know them and gradually form a consensus to start a 'Project'. If a relative newcomer just dives in and starts trying to do such ambitious things - well, let's just say that it won't end well!

If you do actually just want to write an article then I recommend starting with Misplaced Pages:Introduction, then Misplaced Pages:Introduction_2, then go to the full Misplaced Pages:Tutorial. There are lots of quick guides out there - I'm going to recommend the one on my own off-site Wiki: http://www.sjbaker.org/index.php?title=The_simplest_possible_guide_to_writing_MediaWiki

There are already a couple of dozen WikiProjects relating to India Misplaced Pages:WikiProject_Council/Directory/Geographical/Asia#India and also a fairly large and active project that handles issues relating to the history of science in general: Misplaced Pages:WikiProject_History_of_Science. You might want to talk to the people on those projects about your ideas...I'm sure you'll find them a helpful and useful resource.

SteveBaker (talk) 18:18, 29 January 2009 (UTC)

Tons to kN conversion

I've found a source relating to the collapse of a bridge saying that the wind "applied an estimated lateral force of 90 tons (40 kN)" I pretty sure "kN" is kilonewtons, but which type of ton (short ton-force, long ton-force ect) is given? I have tried converting them myself, but I couldn't get the numbers to match up. --​​​​D.B. 17:58, 29 January 2009 (UTC)

Unresolved

Resolved

Resolved

Dmcq (talk) 00:45, 31 January 2009 (UTC)

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