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May 2

Moth Help

I live in Boston, MA---my apartment is flooded with these tiny little moth type creatures.

They're incredibly easy to kill, but their numbers are becoming worrisome!

Is there a common moth that infests in this time of year, or mayhap a well known reason to be surrounded by them? We don't leave out food!209.6.54.248 (talk) 00:40, 2 May 2010 (UTC)

You may want to check your pantry, if you have one. If they are flour moths, you don't have to leave food out to have a problem. Looie496 (talk) 01:35, 2 May 2010 (UTC)

(edit conflict) Are you sure they are moths? I haven't known moths to swarm like that. Having grown up outside of Boston, swarming insects include mosquitos, gnats, and mayflys. The only one of those that may be confused for tiny moths may be mayflys. Do you live near a swampy area or wetlands like the Back Bay Fens or something like that? --Jayron32 01:40, 2 May 2010 (UTC)

Moths don't usually accumulate for food. Light is the more usual source. At university accomodation we have lots of them about where light is abundant. Regards, --—Cyclonenim | Chat  02:54, 2 May 2010 (UTC)

Make sure they aren't eating your clothes. If so, wash any clothes they've started on, with bleach. Then store them in an air-proof container (those Space Bags are a good choice). I had a problem with moths and found tiny brown worms (their larval stage) at the top my walls, adjacent to the ceiling. I went around the whole house and killed any that I found there, and they went away. StuRat (talk) 10:55, 2 May 2010 (UTC)

When I lived in an apartment, pest control was the landlord's responsibility. You might want to talk to your building superintendent or whatever that job is called these days. --Anonymous, 20:23 UTC, May 2, 2010.

Re-engineering the universe for increasing computational capacity

In "Computational capacity of the universe" (Phys Rev Lett 88 (23):237901), Seth Lloyd estimates the storage and cumulative data-processing capacity of the universe to be proportional to ρc⁵t⁴/ħ, where t is the age of the universe, ρ is its density, c is the speed of light and ħ is the reduced Planck constant.

From Moore's law#Other formulations and similar laws, I gather that human needs for data processing and storage are increasing exponentially, which means that eventually they'll outpace the polynomial growth that Lloyd's formula implies. This means that if our needs for computation are to be satisfied, the universe will eventually have to be re-engineered to accommodate them; and if that's to be done in a way that keeps the equation valid, either ρ or c has to start growing exponentially, or else ħ has to start decaying exponentially. (NB: I'm extrapolating to its logical conclusion the general observation that when reality and human needs come into conflict, it's reality that gets changed, at increasingly fundamental levels.) Has it been studied which constant would be best to manipulate, assuming equally straightforward ways are someday found to manipulate all of them? (I'd tend to favour c, given that it would have the side effects of lowering communication latency and extending the raange of interstellar travel, but I'm probably not aware of all the considerations.) NeonMerlin 03:35, 2 May 2010 (UTC)

You're not going to manipulate any of these constants; first of all there is no need given the size of the numbers involved. Humans are in no danger of exceeding the computational capacity of the universe, however defined, for any timescale measured in units smaller than billions of years. Secondly, your statement "when reality and human needs come into conflict, it's reality that gets changed, at increasingly fundamental levels" is patently rediculous. Fundemental physical constants, like the speed of light or planck's constant, can't be manipulated to magically "create" new computational capacity. Its just silliness. --Jayron32 03:51, 2 May 2010 (UTC)

I think he's trying to say that as scientists run out of technology to explain the universe they will almost be forced to make up elaborate stories to perpetuate their point of no return theories that constantly alter previous realities to compensate for the lack of human knowledge. —Preceding unsigned comment added by 98.221.254.154 (talk) 04:19, 2 May 2010 (UTC)

C is in that equation because of it's connection to energy. The amount of calculation a particle can do is related to it's energy, and the energy of a particle is related to c. The implication of this is that to change c you are also changing the energy content of every particle in the entire universe - and where would you get such energy? Ariel. (talk) 04:19, 2 May 2010 (UTC)

I don't buy this anyway - forget about the underlying technology and think only about speed-of-light issues.

What use is computational power if it's situated in the next solar system? A computer has to shuffle data around - and if it takes 4 years to ask for a number from Alpha Centauri and four more years to get the answer back, that's going to be a pretty spectacularly slow machine. In any computation, there is a trade-off between storing something for later use - and recalculating it when needed. As the size of the machine grows, the balance tilts towards recalculating rather than storing. So as your computer grows to the size of a planet (which, in effect, is what the Internet has become), you get a 'law of diminishing returns' where you have to cache information locally rather than reaching out across the network to get it. The bigger computer can store much more information - but it becomes so slow to fetch it that you have to store it locally.

When you think about a computer that's distributed between (say) here and Neptune - the round-trip time to ask for and get back some information is around 8 hours. So the result of any calculation that takes less than 8 hours is better computed locally than being distributed over the larger computer. We might want to use the storage system on neptune (for example) for storing all of the DNA sequences of long-dead people - on the grounds that we seldom need that within 8 hours of asking for it...but if Wikipedia were stored 8 hours away - it would be useless to us.

Now consider storage on Alpha Centauri. At 8 years access time, we can't even store the results of major research programs over there. If we stored the DNA sequence of some obscure plant over on that part of the system - then it would be simpler to re-sequence the DNA of the plant than it would be to fetch it from way over there. If we stored the design for an airplane over on Alpha Centauri, it would be faster to redesign it from scratch than it would be to fetch the old design from storage in memory outside of our solar system!

When you get to the scale of a galaxy - the round-trip time exceeds the duration of an entire civilisation. It's hard to envisage a question that a human might ask where the answer could still be useful to us when it gets here 100,000 years later. There would be no point in storing things in memory on the other side of the galaxy since there would be no way for any future member of your civilisation to get it back again!

When you get to the size of the universe, you have many more problems. You ask the question of a far distant galaxy - and by the time the answer gets back, we've evolved into a different species - or the sun has exploded and we've all moved someplace else. What possible storage or computational needs could we possibly have where the answer could be useful so much later? Why store something that your species could never possibly retrieve again in the future?

While we might want something with more power than we can reasonably fit into a few planets - we simply can't have that. Our present exponential growth of computing needs will ultimately be cut short. However, the amount of growth we have left with nanotech computers, quantum computers and biological computers leaves us an immense amount of headroom before we really start to hit these limits. Humans run into these kinds of resource limitations all the time...and ultimately, we cannot grow forever.

SteveBaker (talk) 14:01, 2 May 2010 (UTC)

I guess you make another point in favour of raising c, as soon as a way is found to do it. NeonMerlin 15:52, 2 May 2010 (UTC)

You can't just arbitrarily alter the value of c. By what means would you go about changing the way the Universe works? What part of the word "constant" escapes your understanding! --Jayron32 00:48, 3 May 2010 (UTC)

Indeed. E=m.c². So if you change 'c' you've either got to find enough energy from somewhere to keep the mass of the universe the same - or if you're stuck with a finite amount of energy - then the mass of everything in the universe would decrease as the square of the change in 'c'. So if, for example, you decided to increase 'c' so that you could get to Alpha Centauri in a few months, you'd need to increase 'c' by (let's say) a factor of 10. That would decrease the mass of everything in the universe by a factor of 100 - which would instantly cause all of the stars to explode because they wouldn't have enough gravity to withstand the radiation pressure. You can't just tinker with fundamental constants without causing major upsets. Changing 'c' is premium-quality craziness! SteveBaker (talk) 13:46, 3 May 2010 (UTC)

NeonMerlin, you should ignore Seth Lloyd; he's silly. And when you see growth that looks exponential, you should fit a logistic curve to it, not an exponential curve. -- BenRG (talk) 17:39, 2 May 2010 (UTC)

Aztec knives

What are these Aztec knives made of? Flint? --The High Fin Sperm Whale 04:58, 2 May 2010 (UTC)

The image description says that they're made of flint. Is there some reason you don't believe this? Dismas|^(talk) 05:07, 2 May 2010 (UTC)

This site [1] has one made of chalcedony from the Ethnologisches Museum (berlin). The light coloured ones in the picture in question (rhs) to me look like quartz, but it may simply be the light shining off them. --220.101.28.25 (talk) 05:26, 2 May 2010 (UTC)

Sorry, I missed the image description. However, there is such thing as lightly-coloured flint (see this). --The High Fin Sperm Whale 20:14, 2 May 2010 (UTC)

Quartz is very difficult to knap due to its prominent grains. Quartzite is sometimes used, but even that makes for a very rough finished product. When I first saw the question, I assumed they were going to be obsidian, which the Aztecs put to good use in making weapons, but these are indeed flint or chert. Matt Deres (talk) 23:35, 2 May 2010 (UTC)

Another spider question

How many spiders does one eat while sleeping during the course of one's life? Alaphent (talk) 09:41, 2 May 2010 (UTC)

A quick Google search suggests as little as 4 but as many as 7-8. Although this page suggests the whole thing is a load of rubbish. Dismas|^(talk) 09:54, 2 May 2010 (UTC)

"For a sleeping person to swallow even one live spider would involve so many highly unlikely circumstances that for practical purposes we can rule out the possibility. No such case is on formal record anywhere in scientific or medical literature," says a spider expert at the Burke Museum: http://www.washington.edu/burkemuseum/spidermyth/myths/whileyousleep.html Rimush (talk) 10:31, 2 May 2010 (UTC)

One such case is in a Post mortem report (video): Misadventurous ingestion of Musca domestica by geriatric female was initially treated by a chelicerate arthropod taken orally, with consequent evolution of treatments until equine injestion and consequent termination. Cuddlyable3 (talk) 15:21, 2 May 2010 (UTC)

I woke up once when a spider lowered itself onto my cheek, which was a close call. StuRat (talk) 10:45, 2 May 2010 (UTC)

The Straight Dope : Does the average person consume four spiders per year in his sleep?. This article discusses it a bit. In it, he explains why the chances of swallowing a spider during your sleep is virtually zero, except in the case where an egg-sac hatches nearby. In that case you might inhale a few new-born spiders. But new-born spiders are so tiny that you wouldn't even notice if you were awake. APL (talk) 16:12, 3 May 2010 (UTC)

Stupid insects and spiders

I've had numerous times when an insect or spider walked right up to me, or even on me, and then I promptly killed it. Can't they see me ? Don't they have an instinct to avoid animals a million times their size ? StuRat (talk) 10:45, 2 May 2010 (UTC)

We're so massively beyond their scale and world-view that I doubt that they (the ones that don't seem to react to our movements, that is - it may be different for the ones that feed upon us) even see us as lifeforms, nor possess the intelligence to see us as such. --Kurt Shaped Box (talk) 12:26, 2 May 2010 (UTC)

Isn't there a story in the Odyssey or Sinbad the Sailor of a ship's crew landing on the back of a floating turtle and thinking it's an island? If a human sailor, albeit mythical, with some 100 billion neurons in his brain, can conceivably make this mistake with a turtle a few hundred times his size, I can't see a spider, with a brain of a mere 100 thousand, could make such a distinction when walking on a human a few hundred thousand times its size. Tonywalton ^Talk 00:07, 3 May 2010 (UTC)

StuRat, what is your opinion of this? Count Iblis (talk) 14:28, 2 May 2010 (UTC)

(Baker's law of website design: Large fonts, too many colors strange placement of text on page == Nut-job - you don't actually have to read the text to know this with 95% certainty) SteveBaker (talk) 14:41, 2 May 2010 (UTC)

And actually, this is no place to discuss people's opinions of such things. This is a Reference Desk. --Mr.98 (talk) 20:01, 2 May 2010 (UTC)

I think being concerned with the lives or deaths of insects and spiders is silliness, except when they are helpful to us. I also find myself saving the lives of pretty insects, like butterflies and ladybugs (ladybirds), but most creepy crawlies can join each other in the tread pattern on my shoes. I was upset to find that a magnificent praying mantis, living at the entrance to my work, was killed. StuRat (talk) 18:20, 4 May 2010 (UTC)

A spiders' brain is a very tiny thing indeed. They don't have a lot of space to store all of the kinds of behaviors that might turn out to be useful. The have to prioritize. Web building - yep, that's necessary. Mating behavior - yep. Feeding - yep. Avoiding being eaten by a bird - maybe. But the probability of an individual spider being killed by a large animal is so amazingly small that the evolutionary benefit to carrying that around doesn't make it worth-while to do so. Spiders who somehow gained that ability would have to expend more energy to support the growth & maintenance of that larger brain - and (evidently) that extra 'cost' would exceed the statistical benefit. It's worth remembering that the spider couldn't "learn" this human-avoidance behavior - because the first failure means death. It also can't be taught the behavior from it's parent because spiders lack language and they don't hang out with their parents for very long. So this would have to be an 'instinctive' behavior...and that means that it has to be contained in the spider's DNA. So we're not only talking the cost of having a brain big enough - but also the cost for every cell in the spider's body of storing the "instinct".

Worse still, how many large animals actually go out of their way to kill spiders? Cows don't, sheep don't. I bet most large animals don't. That means that many species of spider didn't evolve with large spider-killing animals around them. Humans spread across the planet very rapidly in evolutionary terms - and many species are still playing catch-up. Even large, smart animals haven't evolved the necessary fear of humans. A large bear that might attack a human hasn't evolved to realise that we carry guns - or that if you do kill one of us, a posse of humans will come along the next day and hunt you down - or that if bears in general pose a problem for humans in general, we're going to round you all up and relocate you somewhere you don't want to be. Bears aren't stupid - they simply haven't had time to evolve to cope with the rapid pace of change on the planet.

A bigger question is why are you (an otherwise intelligent human) indiscriminantly killing spiders? All but a few species are harmless to us - and help keep the population of other insects (like flies and wasps) to a minimum. Flies and wasps are harmful to humans (flies spread diseases and wasps sting us). So we should perhaps ask instead: "How come large, super-smart animals like StuRat don't have an instinct to carefully avoid killing beneficial spiders?"

SteveBaker (talk) 14:39, 2 May 2010 (UTC)

That would be because, even if there's only a small risk of a spider bite, this risk isn't worth the even smaller benefit. Also, waking up with a spider crawling on you is just as unpleasant as an insect. StuRat (talk) 14:56, 2 May 2010 (UTC)

However here in the UK there are no harmful spiders at all, yet people still squash them, Perhaps people just don't like spiders. Tonywalton ^Talk 00:07, 3 May 2010 (UTC)

Some sources state that the factoid about eating spiders in your sleep is a myth, but while awake people eat more spiders and insects in food (example). As for killing spiders, there's a Russian superstition that killing 40 spiders brings a person good luck, and on the other hand some people eat fried spiders. ~AH1^(TCU) 23:47, 2 May 2010 (UTC)

@ StuRat so you don't ever do things with a small risk like driving, or crossing the road? These activities are way more risky than an encounter with a wee spider in the UK. Why not just say they frighten you because you've never taken the time to understand them. There must be a law somewhere that states that fear is directly proportional to the individual's ignorance of the feared object. Caesar's Daddy (talk) 07:57, 3 May 2010 (UTC)

I suppose you could call it ignorance, in that not knowing which spiders are harmful, we tend to just kill them all to be safe. As for driving, there's a huge benefit to driving, like allowing me to hold a job, while there's no such huge benefit to tolerating spiders on me. StuRat (talk) 13:48, 3 May 2010 (UTC)

Well, there are no harmful spiders in the UK - so if that's where you live, you can stop killing them without any additional risk. There is some benefit to tolerating them - so on balance, that's the rational thing to do. The main problem for the spiders, however, is not the rational - it's the irrational. Of course, here in Texas...not so much. We have quite a few nasty little buggers who certainly need to be squished on sight if found in your home. I've had one hand swell to twice it's normal size following a spider bite...it's no fun! But still, it doesn't take buy 10 minutes to dig out a list of venomous spiders and learn to recognize them. Brown Recluse and Black Widows get squished without a fair trial - but even so, some - like the pink-kneed tarantulas are quite magnificent animals and get treated to a half mile car trip in nice cosy box to someplace I can safely release them. SteveBaker (talk) 20:04, 3 May 2010 (UTC)

Steve, don't you know I'm from Detroit, by now ? Was that injury from a spider you were trying to save ? StuRat (talk) 18:25, 4 May 2010 (UTC)

Then, of course there is Cochineal - which is an insect from which red food coloring is made. Take a look at all the foods containing "E120" - 70,000 crushed insects per pound of coloring. SteveBaker (talk) 13:41, 3 May 2010 (UTC)

Burning fat without burning muscle

Hi. I've been working hard in the gym over the last few months, and I have developed quite big arms and chest muscles. Now, I would like to burn some fat which has accumulated in my belly in order to start developing a six-pack. Which kind of exercise is best to burn fat, without burning any of my hard-earned muscles? Is aerobic or anaerobic exercise better? Should I eat before the exercise, or not (so that the body burns fat faster)?

Thanks a lot! --81.44.96.96 (talk) 09:45, 2 May 2010 (UTC)

Keep excercising but eat less calories. 89.242.97.110 (talk) 11:11, 2 May 2010 (UTC)

Fewer calories is one thing, but the source of those calories is also important. For example, you wouldn't want to cut protein, as that's needed to maintain those muscles. StuRat (talk) 12:20, 2 May 2010 (UTC)

Western eat far more protein than they need anyway. 89.242.97.110 (talk) 12:26, 2 May 2010 (UTC)

On average, yes, but we still get many people on crazy diets who don't get enough. StuRat (talk) 13:09, 2 May 2010 (UTC)

The reverse is more likely. Excessive protein is bad for you, see Protein (nutrient) 89.242.97.110 (talk) 20:44, 2 May 2010 (UTC)

(ec) No, that ("Keep excercising but eat less calories") is not the answer. The answer is, be absolutely certain to eat 0.7-0.8 grams of protein per pound that you weigh to keep your muscle. For example, if you weigh 180 pounds, then 180 * 0.8 = 144 grams of protein. That's a lot! It's equivalent to the protein from 28 egg whites per day (ie two and a half cartons of eggs). Or a steak like this. If you eat less than that while continuing to exercise, you will lose muscle, period. (Of course, the easiest way to get your protein intake may be a protein powder). Now as for losing FAT while you exercise and retain MUSCLE, yes, it is true that if you eat fewer calories you will lose weight, but that is not the right way to lose weight while keeping muscle, as your body will realize you're only getting, say, 900 calories, and you will just lose fat and muscle and everything. The correct thing to do is to keep a normal intake, say 2500 calories, including, crucially the amount of protein that I listed (150 grams, say, if you weigh 180 pounds), absolutely continue to do weight training (if you don't use your muscles, they will disappear), do this weight training, say, every 3-4 days. Then, every day, get on the elliptical machine, and use it until it shows that you have expended 3500 calories. The elliptical machine, on a fair resistance setting, is a monster at burning calories. Now, you might not FEEL like you've just burned more calories than your whole daily intake (2500) but you did: the machine does not lie, as calories are a measure of physical work (ie a physics concept) and if you've done that physical work (moved resistance) by definition you have burned those calories.

So, that is where the fat-burning comes in. Now you must keep very strictly to a 2500 calorie diet, and every day burn 3500 on the elliptical machine on a fair resistance level. At that rate, you will lose 1000 calories per day. 1 pound of fat is 3500 calories, so every three and a half days you will lose a pound of pure fat. If you continue doing this, while not stopping with either the weight training, the proper amount of protein, and the 2500 calories of real good food, you can have a real six-pack, totally toned and defined everything, etc. I have personally developed a six-pack using the above methodology and can attest to it. Hope this helps. 84.153.248.35 (talk) 12:31, 2 May 2010 (UTC)

Even for a body-builder, I don't think your protein requirements would be as high as that. Exessive protein is just used as calories. Do you have any quality independant scientific sources for the above please? I imagine the sellers of high-protein supplements are going to try to convince you that you need a lot of it. 89.242.97.110 (talk) 13:03, 2 May 2010 (UTC)

Please refer to this [2] Science Desk question regarding protein intake and "strength training", from ≈4 days ago. It has references that look "quality independant scientific". (I must admit that I answered this question!). 89.242.97.110 is quite right to ask for references, they should always be provided. Ref.Weight_lifting_and_training
♥ Recommended 'normal protein' RDA (Recommended Dietary Allowance) is 0.8 grams per kilogram of lean bodyweight (1 kilogram=2.2 pounds) ie. Higher than what you thought was a high figure! exactly the same as I provided - see below.
♥ For muscle building an intake of 1.6-2.2 grams per kilogram of bodyweight is recommended.
Aerobic exercise would be best for 'fat burning' as it can be carried on far longer than anaerobic exercise. Short, high intensity exercise is not as good at calorie burning as moderate 'long term' exercise. See also Weight Loss/Dieting--220.101.28.25 (talk) 13:38, 2 May 2010 (UTC)

Particularly see the "Fat loss versus muscle loss" Section--220.101.28.25 (talk) 13:46, 2 May 2010 (UTC)

hey, we're saying the exact same thing! You just said "For muscle building an intake of 1.6-2.2 grams per kilogram of bodyweight is recommended" and your figure of 1.6 grams per kilogram is exactly the same 0.72 grams per pound that I listed!! So my number is the same as your number, 1.6 (in per kg). Now, your range goes higher, it goes up to 2.2. grams per kilogram you weigh. That is 0.99g per pound that you weigh. Even while you are trying to really body-build and gain muscle mass, I think that is just a teeny bit too much. You won't have any use of the extra amount over 0.8 grams per pound you weigh. But the low end of your range is 0.72, just like I said (0.7-0.8), and the high end of your range, 0.99, is just a little bit over what I said. So basically we are in total agreement. The original poster can go ahead and "play it safe" and take 0.99g per pound he weighs daily, or he can follow my advice and take 0.7g-0.8g per pound that he weighs. But we both agree that any more than that and he will not benefit, and any more than that and he will lose protein. 84.153.248.35 (talk) 14:23, 2 May 2010 (UTC)

Burning 3500 kcal on the elliptical each day is absolutely insane. That would take about 5.5 hours at normal resistance. And advising our OP to sustain a deficit of 1000 kcal a day without first talking to a doctor is NOT appropriate. This is why we have the no-professional-advice rule. Btw, the RDA for protein is (as 220 says) 0.8g per kg of lean body mass. Also, a lot of the energy your body burns is through normal metabolism - see Basal metabolic rate. Zain Ebrahim (talk) 14:59, 2 May 2010 (UTC)

To the OP: to get a handle on what 84 is talking about I recommend you read Basal metabolic rate and the article on Harris-Benedict equation might also be interesting. As for your question, I suggest talking to the personal trainers at your gym. Zain Ebrahim (talk) 15:06, 2 May 2010 (UTC)

← ← @84 No real need to whisper! ;-) I think here I have seen 0.8 gm and read it as per Kg not per pound. Perhaps not a good idea to mix 'imperial' and 'Metric' quantities ie 0.8 grams per pound is not as 'scientific' as we should try to be. I was actually answering 89.242.97.110s' comment that they thought the protein requirement was too high. So yes we are basically in agreement, with the references!. Throw a few conversions in here, 800 grams (1.8 lb), 1,600 to 2,200 grams (3.5 to 4.9 lb), the upper figure does seem high! But, everyones metabolism is different. Arnie Schwarzenegger could probably, once, have done that easily. And if it's not 'used' it will just be er, 'excreted'. Wasteful.

I was mainly trying to provide references, very important here. Doesn't matter what you know/believe to be true, must be wp:verifiable! Has been some real turmoil caused by editors, in all Good Faith, giving rather wp:POV opinions.

As Zain says (beating me to it) talk to a 'pro', though I'd suggest a nutritionist/ dietician or similar. We can't give specific advice for a person, we can't even see them! Guten Nacht! 84 and all. :-) --220.101.28.25 (talk) 15:53, 2 May 2010 (UTC)

Protein (nutrient) suggests 0.8g per kg for a mature adult, and the relevant reference from there also says that extreme amounts of protein is harmful. 0.8g per kg for a person weighing 180lbs is about 65g of protein. 100g of raw peanuts contains nearly this amount according to High protein diet, but many foods in the everyday diet already contain some protein so there may be no point in deliberately eating protein-rich food as the excess is just used as calories by the body. 89.242.97.110 (talk) 20:49, 2 May 2010 (UTC)

@81.44.96.96: This Men's Health article (entitled "how to lose muscle") has some very sensible suggestions. It amounts to eat, sleep, rest, and exercise sensibly; to break any of these you'd have to be behaving fairly immoderately . Unfortunately every gym has a few people who think progress is made only by suffering. -- Finlay McWalter • Talk 17:22, 2 May 2010 (UTC)

Good advice there, Finlay McWalter. Moderation in all things. This seems a good reference for Protein intake:"Contemporary Issues in Protein Requirements and Consumption for Resistance Trained Athletes", Journal of the International Society of Sports Nutrition. 2006; 3(1): 7–27. Published online 2006 June 5. doi: 10.1186/1550-2783-3-1-7. Retrieved 3 May 2010. --220.101.28.25 (talk) 15:05, 3 May 2010 (UTC)

Take your finger out of my butt, please...

With MRI and other technologies, are we getting any closer to eliminating the highly invasive digital rectal exam and colonoscopy ? The MRI seems to carry far less risk, so that would be another advantage. What's the current limitation preventing replacement, a lack of resolution in the MRI images ? StuRat (talk) 12:25, 2 May 2010 (UTC)

If you know another way of removing prostate fluid for microcellular examination post it here! MRI doesn't resolve down to cellular level AFAIK. --TammyMoet (talk) 13:00, 2 May 2010 (UTC)

I can think of one more enjoyable way to produce prostate fluid... However, I don't believe "removal of prostate fluid" is a normal part of either of the procedures I listed as candidates for elimination. StuRat (talk) 13:12, 2 May 2010 (UTC)

DRE is obviously cheaper and easier than any kind of other technique—it takes five minutes and a greased finger, and the analysis happens "in real time" without any money spent on fancy machines or their operators. So I doubt that's going away anytime soon, even if it isn't the most fun medical procedure in the world (it's hardly the worst, though—I don't find it as bad as getting blood drawn, personally). Colonoscopy is a different thing altogether. I suspect the problem is that current MRI tech doesn't allow the fine-grained manipulation of the colon itself, or resolve in color, that makes a big difference. The colonoscopy can also remove polyps in realtime as well during the procedure, and the tissue can be analyzed in the lab later—that's handy. An MRI is going to maybe tell you there are things in there, but still require you to go in and get them. So that's not as useful. --Mr.98 (talk) 13:48, 2 May 2010 (UTC)

Is the OP's dislike of the colonoscopy procedure based on imagined or actually experienced discomforts? I tolerated the examination easily and found the experience interesting. I was able to watch my inside view on a TV screen and discuss what was going on with the nurses. I was surprised to see that the colon bore is more triangular than round, and of course am reassured that nothing untoward was discovered. The only significant discomfort came as flatulence on my way home after the colonoscopy. MRI is slow to give a result, needs a major expensive installation, and this video may persuade the OP that it has its own risks: "There are obvious potential hazards to people and equipment in the area (of the MRI)...The magnet environment under certain circumstances can be a dangerous place...Complacency can be fatal." Cuddlyable3 (talk) 14:54, 2 May 2010 (UTC)

The other thing about a colonoscopy is that you can remove tissue samples at the same time, thus removing the need for two procedures. I had an MRI scan last year, and the procedure itself wasn't unpleasant. However, the recovery took days: I was disoriented and dizzy immediately, I couldn't drive home, and I couldn't sleep properly. Comparing it with the gastroscopy I had a few years previously, of the two procedures I prefer the gastroscopy! --TammyMoet (talk) 15:36, 2 May 2010 (UTC)

TammyMoet your account is interesting because there seems to be no reliable information about persisting aftereffects of MRI. If yours was not a (rare) reaction to the contrast agent you may have been given, I would ask whether you suffer from claustrophobia. Cuddlyable3 (talk) 17:18, 2 May 2010 (UTC)

No it wasn't a reaction to gadolinum, and as I had some free time after the procedure I spent some of it on the internet looking for the cause of my reaction. It doesn't appear to be that rare, and I left my experiences on a particular website which was set up by a radiologist in the UK collecting such experiences. I don't suffer from claustrophobia. I have my own explanation as to what happened, which as it falls into an area called by some "pseudo-science" or "woo woo" doesn't belong here. --TammyMoet (talk) 18:25, 2 May 2010 (UTC)

This is NOT MEDICAL ADVICE but you might find this article by Harriet Hall over at SBM interesting. Vespine (talk) 22:39, 2 May 2010 (UTC)

According to a couple of web links I dug up on the spur of the moment, the cost of an MRI ranges from $400 to over $2500 depending on the details of the procedure. Enough said, I think. Looie496 (talk) 22:52, 2 May 2010 (UTC)

That makes it more expensive than DRE, but I don't know about colonoscopy. Googling around seems to indicate that colonoscopies range from $1K to much more depending on what is done (assuming uninsured, in the US). --Mr.98 (talk) 23:38, 2 May 2010 (UTC)

CT and MRI are being evaluated as alternatives to colonoscopy (see virtual colonoscopy). There several significant limitations, however. For one, they're newer technologies, so we don't have studies showing that they are good screening methods (do people undergoing CT colonography have a lower mortality rate after 20 years? 30 years?). Also, the resolution is not nearly as good as direct visualization. CT involves ionizing radiation. MRI is quite expensive and wouldn't really afford a cost savings over colonoscopy. One of the major drawbacks is that the patient still must drink the preparation the night before (and in my experience, the part about colonoscopies that patients usually dislike is taking the preparation, not the procedure itself), so the virtual colonoscopy isn't necessarily more comfortable than actual colonoscopy. And then, finally, imaging studies have no way to obtain samples (until we develop a Star Trek–style transporter), so if there is any abnormality seen, the next step is to to a full colonoscopy (and another round with the preparation). Since polyps are seen on a fair number of colonoscopies, this would mean that a number of people would have to undergo two preparations and twice the expense. Regarding the digital rectal examination, it's fast, cheap, and safe. It's going to be very difficult to develop a replacement procedure. — Knowledge Seeker দ 00:17, 3 May 2010 (UTC)

The above answer is quite good. To add to it, virtual colonoscopy (VC) may also have a higher occurrences of false positives in polyp detection. The inside of the colon has to be reconstructed digitally from 3D scans and thus depend greatly on the quality of the "raw" image (image contrast, patient movement, image artifects, distribution of contrast media, etc.) and also what computer algorithm was used do the digital reconstruction. Since the digital image cannot definitively tell you if you have something "bad" and quite often tells you that you "may have" something, it is likely that you will STILL get something stuck up your rectum after a VC session. My cynical side thinks that currently VC is just another wayfor clinics (who plaster ads everywhere) to generate revenue based on patient fear ($ from VC then onwards to possible $$ from follow-up exams), however I think that with continued development in more reliable VC techniques a tool like this could be of great benefit to patients in the future.Sjschen (talk) 15:32, 5 May 2010 (UTC)

soy

it seems overnight every fast food place in America switched to soybean oil and soy flour ect. im allergic to soy. what am i supposed to do? —Preceding unsigned comment added by Tom12350 (talk • contribs) 13:30, 2 May 2010 (UTC)

Cook yourself, or don't eat fried food, or eat at a restaurant where they use different ingredients. Or perhaps you can desensitize yourself. Graeme Bartlett (talk) 13:41, 2 May 2010 (UTC)

Might this constitute medical advice? Consult with a physician to determine what would happen if you eat soy from a fast-food restaurant. If the consequences are serious (and we aren't qualified or able to tell you), then you should not eat at fast food restaurants (or anywhere that you can't verify soy-free ingredient lists). Nimur (talk) 13:43, 2 May 2010 (UTC)

not just fast food places use soy every restaurant does including places like chilies tgf Fridays, moes ect. they also put it it hot pockets. —Preceding unsigned comment added by Tom12350 (talk • contribs) 13:47, 2 May 2010 (UTC)

Yes, eating prepackaged foods will require reading the label carefully for soy/soya. Making foods from scratch, like cutting up potatoes and frying them yourself, using an oil you choose, is a lot safer. StuRat (talk) 15:03, 2 May 2010 (UTC)

They will have made a decision based on profit margins. What you can do is write to them and explain that this means you can no longer eat there, since they do not offer a safe option for you. You can alert friends and family to your inability to eat at these places, so social events are held elsewhere (maybe someone's house): any enthusiastic friends might be encouraged to write to these places and explain that they are no longer able to hold their social events there, since they do not offer a safe option for you. Essentially, you make it clear to the companies that this decision has lost them custom. They might still consider it a good decision (who knows how this affects their profits), but you are adding weight to the other side.

I do sympathise: I've lived most of my life with someone extremely allergic to peanuts, and this sort of thing can accumulate. Luckily, things have changed over the years so that companies consider it in their interests to warn for nuts and peanuts, and some companies work hard to offer safe options precisely because there is a market for them. But eating out is still difficult, and always subject to change.

And, I hope it doesn't need saying, but absolutely do not follow Graeme's advice to attempt desensitizing yourself: people have died doing that. Any attempt at exposing yourself to something you are allergic to should be carried out under medical supervision, as advised by a doctor, so that you can be treated and even resuscitated if needed. 86.178.225.111 (talk) 15:08, 2 May 2010 (UTC)

My daughter has a sensitivity to both soy protein and cow milk protein, so I can sympathize. Who knew that virtually all brands of hot dog weiners have milk in them? Not I, until I had to start reading the labels on frigging everything. We have an article on soy allergy which helpfully contains a list of additives that do or may contain soy. Hope that helps. Some fast food places list ingredients and nutritional information on their websites, but beware of corporations that just don't give a crap about your health and lie to you. Matt Deres (talk) 01:24, 3 May 2010 (UTC)

I thought that desensitization was a medical procedure rather than something to try on your own. From examples I have heard, it is not very successful. Graeme Bartlett (talk) 21:39, 3 May 2010 (UTC)

It is: Allergen immunotherapy. Buddy431 (talk) 00:16, 4 May 2010 (UTC)

Indeed, but that's not the same as "desensitize yourself". That is "talk to your doctor about the possibility of being desensitized, and hear them explain whether that is typically successful for people your age with your allergy, and consider whether the procedure (carried out under medical supervision) is a good idea in your case". It's the difference between the babysitter feeding a toddler a peanut butter sandwich because she'd heard that a little bit of peanuts helped, and a medical procedure carried out starting with minuscule amounts of allergen under controlled conditions. The person I know with peanut allergies had to abort a similar procedure under medical supervision, because they reacted too much to skin contact with peanuts: the medical staff didn't consider it safe to proceed. Forgive the jumping in, but people thinking it's a good idea to try desensitizing themselves instead of as a medical procedure is a really bad thing. 86.178.228.18 (talk) 22:23, 4 May 2010 (UTC)

Deepest part of ocean

Mariana Trench says that "[it] is the deepest known part of the world's oceans". I would like to know:

1. What are the odds that there is a deeper part? (I admit that this can be seen as inviting wild speculation, but perhaps it can be quantified based on the percentage of as yet unsurveyed area.)
2. I understand that the entire World Ocean has been measured from space using gravity-based algorithms, but would this be accurate enough to detect narrow trenches?
3. If not, would finding a deeper part be down to essentially luck or are there ongoing efforts to systematically measure the entire World Ocean? (I believe various navies were quite active in this respect in the 1960s but they probably have better things to do now.)

Thank you in advance. 83.81.60.233 (talk) 15:35, 2 May 2010 (UTC)

Trenches are formed by subduction zones, hence they are very special parts of the sea floor. Common sea floor is much shallower. Given that we know pretty well where all the subduction zones on this planet are and that there is great interest in studying them in detail, I would guess that it is pretty certain that the Mariana trench is the deepest part of the ocean without actually knowing what fraction of the general sea floor has been measured. --Wrongfilter (talk) 16:31, 2 May 2010 (UTC)

We have actually had quite accurate maps of the sea floor for fifty years, after the advent of Side-scan sonar. Widespread seafloor mapping was what led to our modern understanding of plate tectonics. It is highly unlikely that a large seafloor feature on scale with the Mariana Trench would have been missed by this point. --Jayron32 00:42, 3 May 2010 (UTC)

All the trenches are known, e.g. Oceanic trench#Major oceanic trenches. They are hundreds or thousands of kilometers long, and not easy to miss given even cursory surveys of the ocean floor. However, finding the specific deepest point in a given trench requires detailed mapping. I wouldn't be shocked if there happened to be a spot in one of them that was a little deeper than Challenger Deep (the deepest known part of Mariana), but the longer that record stands the less likely it becomes that we will find anything deeper. Dragons flight (talk) 05:19, 3 May 2010 (UTC)

More to the point, the size of such a place would have to be very small in order to evade our surveys - there comes a point where you'd have to be talking about a narrow crack or hole smaller than the precision with which we're surveying the ocean bottom.

If we found a five centimeter wide crack that went down deeper than Challenger Deep - would we count that? What about a one meter wide cave that wiggled down deeper - would that count? Assuming the answer to that is "No" then it's safe to say that Challenger Deep is the deepest spot of any reasonable size - and that we won't find anything that big and that deep in the future. Of course, these ocean trenches are extremely geologically active (that's why they are the way they are) - so it's quite possible that some future submarine earthquake could open up a deeper spot - or perhaps even fill the deepest bit with lava or an avalanche and thereby make some not-so-deep place become the new record holder. On balance though - I think it's pretty safe to say that Challenger Deep is truely the deepest spot within reasonable criteria. SteveBaker (talk) 13:35, 3 May 2010 (UTC)

Also, it's not clear whether it would be possible to have a tiny (e.g., 5 cm wide) crack that extended several kilometers in depth. Material properties of rock and sediments don't favor such an unstable structure. (If it existed, it would soon cave or deform and fill in). This is another reason why we don't expect such features except in large-scale subduction zones. Nimur (talk) 14:39, 3 May 2010 (UTC)

The important points have been touch on, but to add one thing, space gravity surveys can and do resolve trenches - they are still several tens of kilometers wide, much larger than the resolution of the free-air gravity maps. Awickert (talk) 17:14, 3 May 2010 (UTC)

5 cm? We don't even have maps of most of the Earth's dry surface that are that well resolved. The best available maps of most of the deep ocean are about 1-5 square km per pixel. As high priority targets, the trenches may be better mapped than that (though extreme depth also makes it harder to get good resolution). However, in general I think you are being overly optimistic about how well surveyed the oceans are. Could a canyon or fissure be hiding down there? Certainly. Are any deep enough to matter? Perhaps not. Dragons flight (talk) 18:45, 3 May 2010 (UTC)

The best worldwide maps are probably the digital elevation model from the Shuttle Radar Topography Mission, which has resolution of about 30 meters per pixel worldwide (although I don't believe it actually has any ocean coverage - I'll have to check). It is available for free. I have also worked with airborne LIDAR data for small regions (e.g., an entire county) which has 1-cm accuracy per pixel. At this scale of map detail, we have to design optimization algorithms to determine whether we're looking at laser returns from plant-leaves, stems, or ground, etc. You can imagine the difficulties and the data volumes involved! I am not aware of any LIDAR technology that works underwater; but you can create very high-resolution SONAR, seismic, or bathymetry imagery; such data tends to be proprietary and there is definitely not full coverage of the Earth's entire seafloor. Again, if you can resolve to 5 cm, you have to worry about 5-cm-sized interference - like sediments swishing around on the seafloor, plant and animal life, and so on. The bottom of Challenger Deep is probably fairly rocky, and the water is probably fairly still, which might help, but there could still be time-variations of the sea bed. Nimur (talk) 11:11, 4 May 2010 (UTC)

Incidentally, I also work with SRTM and LiDAR :-). Neither are usable for bathymetry because of attenuation in water. Global bathymetry is from free air gravity anomalies, and goes down to 1 arc minute (a little under 2 km). More precise bathymetry is given from ship tracks, and I imagine that this is used to ground-truth the free air gravity maps, but as others have said, this is not anywhere near global in extent. Awickert (talk) 02:03, 5 May 2010 (UTC)

Activating the Deepwater Horizon blowout preventer

Is there some intrinsic reason why this has been so difficult so far? Couldn't a blowout preventer be designed for wireless activation -- just press a button on a command ship and it stops flow? Or is there some fundamental reason that this is not an option when designing these things? Vranak (talk) 17:20, 2 May 2010 (UTC)

Wireless signals (radio) does not work under water. Radio waves are pretty much totally blocked by seawater. But take a look here - there are acoustically activated devices, since sound travels pretty well. Ariel. (talk) 18:39, 2 May 2010 (UTC)

Wireless signals do work under water, but not well. They are used to communicate with submarines: [3]. --Phil Holmes (talk) 10:26, 3 May 2010 (UTC)

My understanding of this event is that any such equipment on the rig itself would have been destroyed in the initial large explosion, subsequent fires, and the sinking of the rig's wreckage, and that no such intact and working equipment is still in place on the seabed, even if it was there in the first place, bearing in mind that at the time of the blowout the well was being modified rather than being in routine production. 87.81.230.195 (talk) 21:39, 2 May 2010 (UTC)

When the rig blew up, that did sever the communications with the preventer, but within the first 48 hours there were remotely operated subs at the site trying to trigger it. Apparently, the preventer isn't closing even when told to do so. Failure to activate, even when told to do so, indicates a more fundamental problem than just a communications issue. Dragons flight (talk) 22:11, 2 May 2010 (UTC)

I think that the valve itself may have been wrecked by the explosion. FWiW 67.170.215.166 (talk) 02:17, 4 May 2010 (UTC)

Thanks very much guys. Vranak (talk)

Bacon curling

Why does bacon curl up when you cook it on a grill? I presume it'd be due to drying out, so there's less hydrolysed protein and thus curling would occur (the opposite to when your hair gets straighter when you shower) but I'm not sure if that's the actual reason. Regards, --—Cyclonenim | Chat  20:39, 2 May 2010 (UTC)

I don't know chemically what's happening but I've cooked a LOT of bacon I have thought about it so I'll tell you what I've observed:) I believe it is not the "meat", not the fat and not the rind that causes the curling, I think it is the sinewy connective tissue between the fat and the meat. I think it shrinks when it cooks and this is what causes the curling. I bake my bacon now because I like it really crispy and it's much easier IMHO in the oven and curling doesn't matter so much. But when I used to fry it, there was 3 spots on the bacon, where the fat "meets the meat" that I would cut through to stop it from curling. Vespine (talk) 22:29, 2 May 2010 (UTC)

I am pretty sure the curling comes from differential heating of the bacon. As noted, bacon consists of at least 3 different tissues: fat, meat, and connective tissue. All three of these will cook at different rates, and as they cook will contract or expand at different rates. Also, when you fry bacon, you set up a LARGE temperature differential, as the part of the rasher in contact with the pan is a LOT hotter than the rest of the bacon. Since baking bacon tends to evenly distribute the heat over all parts of the rasher, there is less curling. They make a device called "bacon press" designed to counteract this curling; you see them alot at diners where they make a lot of bacon on a griddle. See this Google Image search which shows you the many different styles of bacon press. The ones I have seen most often look like heavy rectangular trowels, but they come round and pig shaped as well. --Jayron32 23:56, 2 May 2010 (UTC)

I agree with Jayron; it's the temperature difference. And forget using a "bacon press" - cook your bacon on a cookie sheet with a rack. Place the bacon in a cold oven, set the thermostat for 400F, and cook until done (time will depend on thickness). Yum! Matt Deres (talk) 01:30, 3 May 2010 (UTC)

I endorse the oven method, and I'll add that the oven temperature is not at all critical... anything from 325–425 F works (at least), so if you're baking something else, you can probably throw the bacon in and it will be fine. The cooking time will, of course, vary with temperature. I've read that higher temperatures result in more bitter-tasting compounds, so I tend to use the lower end of the range, but I'm not sure it actually makes much difference. -- Coneslayer (talk) 13:11, 3 May 2010 (UTC)

To be honest the actual curling has never caused me any bother :P I tend to just grill mine plain and simple -- comes out curled but very tasty. Thanks for all the interesting answers. Regards, --—Cyclonenim | Chat  14:49, 3 May 2010 (UTC)

Electron excitation - discrete?

In A level physics, we are taught that an electron can be excited to a higher energy level by means of absorbing a photon, on condition that its energy exactly matches the energy difference between the levels. This makes sense, there doesn't seem to be a mechanism for where the "excess" energy goes. However, this can't really be correct, surely? I mean, you could never get it exactly the same. And this sort of thing happens all the time in the real world (e.g. in fluorescent tubes' outer coating). What actually happens? (Unusually, excited state seems to be written for the layperson, and hence fails to approach the issue.) 92.23.14.145 (talk) 20:43, 2 May 2010 (UTC)

I'm by no means a trained physcist so I'll let others rip apart my answer in due course, but this seems to me like just a fallacy in human logic rather than questioning whether it's actually true or not. "...get it exactly the same" - There is no "getting", there are stupidly large numbers of photons (and electrons) around, the chance of some being of the same energy is, I imagine, pretty high. Also, because energy is distributed in packets (quanta), the possibilities are slightly limited as the energy values have to be a certain factor of some constant (someone remind me which?). Regards, --—Cyclonenim | Chat  00:20, 3 May 2010 (UTC)

Ok, so in A level physics you have learned that atoms have precisely defined energy levels and that transitions between these levels are possible by absorpion/emission of photons which in this picture would ahve to have exactly the energy difference between the energy levels. You have correctly noted that this picture cannot be exactly correct.

What is wrong with this picture is the idea that an atom can both have an infinitely precisely defined energy level and be in a state that changes as a function of time. The precisely defined energy levels only appear if you ignore the coupling of the atom to the electromagnetic field. If you take this approximation serious then the atom cannot make any transitions as no interaction with the electromagnetic field means that it will not interact with photons at all.

The moment you take into account the fact that atoms do in fact couple to the electromagnetic field, then what you see is that the "energy levels" are no longer states with a precisely defined energy. The spread in energy of a state is inversely proportional to the spontaneous decay time of that state. One can heuristically unbderstand this using the time-energy uncertainty relation.

In practice this means that atoms can absorb photons that are within the the energy spread. Now this energy spread is quite small, but then each atom will have some random velocity causing its energy levels to appear to shift due to the doppler effect. This causes a gas of atoms to be able to absorp photons of a larger range of energies. This is called doppler broadening. Count Iblis (talk) 01:29, 3 May 2010 (UTC)

It's also worth pointing out that it is quite possible for photons of exactly the right energy to exist. Where the electromagnetic radiation (typically light) is created by an incandescent source (i.e. one that uses heat to produce the light), then the light produced is a broadband of every wavelength within the band. So the atoms only absorb the light whose wavelength exactly matches their energy gap. Hence Spectral line. --Phil Holmes (talk) 09:39, 3 May 2010 (UTC)

Spectral broadening is the article that should help see Spectral_line#Spectral_line_broadening_and_shift - the lines in practice are non-zero width.Sf5xeplus (talk) 10:46, 4 May 2010 (UTC)

hot water

recently my hot water tastes and smells like scouring powder. my cold water is fine. can someone explain this? —Preceding unsigned comment added by Tom12350 (talk • contribs) 20:57, 2 May 2010 (UTC)

It might help someone to answer if you give some details about how your particular hot water system works: mains-fed instant gas heater, electrically heated hot water cylinder, hot rocks in a leather cauldron? (OK, the last isn't very common these days.) 87.81.230.195 (talk) 21:26, 2 May 2010 (UTC)

its a hot water heater tank. heated by either gas or electricity. —Preceding unsigned comment added by Tom12350 (talk • contribs) 22:12, 2 May 2010 (UTC)

The hot tap water in your tank may contain extra chemicals to treat the water. ~AH1^(TCU) 23:35, 2 May 2010 (UTC)

It may be water softeners? --Jayron32 23:43, 2 May 2010 (UTC)

That would be my guess, particularly if they just added a new batch of salt to the water softener or if it's been sitting for a while unused. Under those conditions you can get excess salt in your water. If the water softener is hooked up after the water heater, try bleeding some water directly off the hot water heater to see if it's good. If so, that would seem to implicate the water softener. It could just be a bad batch of salt in there, which isn't sufficient compacted, and thus dissolves too readily in the water. StuRat (talk) 01:53, 3 May 2010 (UTC)

"The magnesium corrosion control rod present in many hot water heaters can chemically reduce naturally occurring sulfates to hydrogen sulfide." [4]. You can change the rod to aluminium (they just unscrew out, although it might be hard to do in an old tank), or add a carbon filter before the water. If you choose a filter make sure you get one designed for it - otherwise it will clog up very fast. Ariel. (talk) 02:18, 3 May 2010 (UTC)

Infrared rainbow

Yesterday I took a near-infrared picture of a double rainbow. As expected, the two arcs are displaced towards each other relative to a visible-light rainbow. Is there a frequency at which the two arcs merge, and if so, what is it? --Carnildo (talk) 21:21, 2 May 2010 (UTC)

This region is called Alexander's band, and is discussed in both that article, and in the article Rainbow. Presumably, there will be some point at which the wavelengths of light from the two bows are identical as they pass one another; however I see no reason why this overlap point would be identical for every rainbow; it may be unique for each observer. --Jayron32 23:42, 2 May 2010 (UTC)

I can't see any reason why the overlap point wouldn't be the identical for every rainbow. The critical angles for total internal reflection are determined by the properties of water and air, I believe, which are essentially constant (on Earth, at least - other planets, eg. Titan, have different angles). --Tango (talk) 01:28, 3 May 2010 (UTC)

The two rainbows may very well never meet since the refractive index of water is not a monotonic function of the light's wavelength. Dauto (talk) 04:48, 3 May 2010 (UTC)

May 3

Plutonium

In the Simpsons, Homer's bag has plutonium in it and the police dynamite it, causing a nuclear explosion. Would this happen in real life? --75.33.219.230 (talk) 00:13, 3 May 2010 (UTC)

It wouldn't cause a nuclear explosion, but it would disperse toxic plutonium into the air. Think dirty bomb, not nuke. A decent real-life analog would be the 1968 Thule Air Base B-52 crash. Messy and expensive to clean up. Few if any immediate deaths; maybe some long-term health problems if plutonium was inhaled. Bad, but not as bad as a full nuclear explosion. (Making plutonium detonate in a full nuclear explosion is not easy—see Fat_Man#Technology for a decent description of why.) --Mr.98 (talk) 00:45, 3 May 2010 (UTC)

To explode a nuclear bomb you need to have enough material in one piece to reach the critical mass for the element. That's more or less it. The trouble is that when you have anywhere near that amount it starts to get really really hot and radioactive. So what you go is make a number of small pieces, and when you need it to explode shove them all together into one piece (like imagine a pizza, pull all the slices apart, then when it's time to explode push them all back together into a circle). Just exploding the plutonium will not make a nuclear explosion - it will just send plutonium everywhere, which will do exactly the opposite, since now you have lots of small pieces instead of one big one. Ariel. (talk) 02:26, 3 May 2010 (UTC)

This is not, in fact, how plutonium bombs work (so far as we know), but is a common misconception. Plutonium weapons use a solid piece of plutonium that is then compressed to a a high density. If you split plutonium into multiple pieces and then tried to combine it, you would have a fizzle, because the combination speed would be slower than the reaction speed. Nuclear weapon design has more detail on implosion physics. It is not the "small pieces" model, though this is often how it is erroneously explained in textbooks or encyclopedias (but not Wikipedia). --Mr.98 (talk) 12:02, 3 May 2010 (UTC)

Ummm, actually that is how Gun-type fission weapon operates. Implosion types mentioned above are more powerful, and are most likely the design used by the developed nuclear powers. Googlemeister (talk) 14:10, 3 May 2010 (UTC)

The article you linked to says plutonium CANNOT be used for gun-type fission weapons. --99.237.234.104 (talk) 20:15, 3 May 2010 (UTC)

From my reading it was because of the Pu240 impurities that were not removed in 1940s technology plutonium enrichment (with results similar to Helium 3 contamination), not that it was an inherent property of plutonium itself. Perhaps even with today's production methods we still can not remove the 240, or it is not cost effective? Googlemeister (talk) 20:55, 3 May 2010 (UTC)

This is getting a bit tangential, but while we're all here... the reason you don't remove the Pu-240 is twofold:

1. It is not cost effective. If you can remove Pu-240, then you can also enrich uranium (both require the same level of technical development). So in that case, you have a product flow that looks like this: uranium metal -> reactor -> processing fission products -> enrichment. If you have the technology for enrichment, you can make it just uranium metal -> enrichment and skip the whole reactor phase. (To your credit, you don't have to enrich as much as you do with the uranium. Though it might be harder from a physics point of view... I don't know if the 1 neutron difference between Pu-239 and Pu-240 would change things a bit, as compared to the three neutrons between U-235 and U-238.) You can reduce the Pu-240 levels by varying the way you have your reactor make plutonium, but not to levels that it will work in a gun-type weapon without fizzling, I don't think.
2. More importantly, plutonium is nasty and messy. It is more volatile and toxic than uranium, especially in a gaseous form. I'd think the last thing you'd want to do with plutonium is to make it into a gas and then spray it inside your enrichment machines. The contamination level would be much higher than with uranium and require a lot more expense and effort.

To my knowledge no nation has tried to use plutonium in a gun-type weapon. When they did want gun-type weapons (say, for artillery shells), they used U-235. For everything else, implosion is a far more efficient use of material.

Separate from this is whether the "pizza" design (which is in fact how the plutonium implosion is sometimes depicted and was even considered as a possibility very early on in the project before implosion was invented) would work. It's basically a spherical gun-type design. I don't think any powers ever made weapons this way, probably because the amount of symmetry necessary is probably quite difficult to pull off. (Implosion is hard, too, but if you get it working correctly, it is almost certainly more efficient than any variation of the gun-type design.) Anyway, it is not how any plutonium bombs have ever worked, as far as anyone knows. True implosion is much more efficient. There are ways to do it that involve imploding spherical shells of plutonium (you can fill the center with DT gas for boosting), but again, this is real-deal implosion and not spherical gun-type. --Mr.98 (talk) 00:02, 4 May 2010 (UTC)

Voice

I was wondering, hypothetically, if is it possible to prevent a boy's voice from breaking at puberty. I saw something on TV that put this question in my mind. Of course, I mean without surgeries, medications, etc. Thank you. 76.230.212.190 (talk) 01:07, 3 May 2010 (UTC)

I think you have ruled out the two methods that would work. Castration works (see Castrato for a description of precisely that) and I would expect hormone treatments (well, some kind of hormone suppressant) to work too. I can't think of any other way to do it. --Tango (talk) 01:31, 3 May 2010 (UTC)

(e/c) You'll need one or the other, unless the boy just happens to naturally keep his boyish voice - rare, but not unheard of. See our article about castrati and Kallmann syndrome for a semi-natural way this sometimes occurs. Matt Deres (talk) 01:34, 3 May 2010 (UTC)

You're missing another possibility: Don't speak for the entire length of puberty. Then your voice wouldn't break "at puberty". Of course, it'll probably break constantly when you start speaking again due to atrophy from disuse, but you didn't ask us to solve that problem. —ShadowRanger ^(talk|stalk) 20:56, 3 May 2010 (UTC)

Joke aside, voices crack for a lot of reasons. Puberty makes it nearly inevitable that it will occur sometimes, but you can do things to reduce the frequency. Tensing up makes cracking more likely, so try to relax. Cold water can temporarily constrict the vocal chords, so don't speak for a few seconds after taking a sip of ice water (or drink lukewarm or room temp water). The longer you speak, the drier your throat will get, increasing cracking, so you should drink, just avoid the really cold stuff. You can find other examples online; these tips are generally useful to public speakers of all ages. —ShadowRanger ^(talk|stalk) 20:56, 3 May 2010 (UTC)

River Geometry

There are rivers with various depth and width of flow.How do these parameters get fixed in the nature.Which laws of nature governs them ?.Are there any mathematical relationships? —Preceding unsigned comment added by Amrahs (talk • contribs) 02:23, 3 May 2010 (UTC)

I would assume the depth is related to how hard the material on the land is - soft earth will wash away and make a deep river, while rock won't (at least at first, the longer the river runs, the deeper it gets). The width of the river is related to the topology (elevations) of the land. Gentle hills will make a wide river, steep ones will make a narrow ones. Next the amount of water in the river depends on whatever is feeding that river. Once you know the amount of water, and the size of the river you get the flow rate. See Meander for information on why rivers make those strange winding shapes, it's quite interesting. Ariel. (talk) 02:29, 3 May 2010 (UTC)

Oddly enough, Wikipedia has an article that covers much of this, in some detail. See River. WHAAOE! --Jayron32 03:47, 3 May 2010 (UTC)

There is some maths or 'laws' associated with the branching of rivers, but I do not recall where to find it. 92.28.253.63 (talk) 11:02, 3 May 2010 (UTC)

Rivers are also somewhat fractal in nature, meaning that the rivers are similar to the rivulets which feed them, which are in turn similar to the creeks which feed them, other than scale. StuRat (talk) 13:20, 3 May 2010 (UTC)

Some of the early fractal work was developed by some colonial English engineer whose name I forget, H.... I think, who collated and studied time series for the periodic flooding of the Nile. Edit: it was Harold Edwin Hurst. 92.28.253.63 (talk) 15:22, 3 May 2010 (UTC)

Most of the properties of a river depend on its sources, the distance it has to travel to get to the sea - and the nature of the terrain in between. The ultimate source of a river is rainfall or snow-melt on high ground someplace. Because the water has run downhill, it tends to gather together to make small streams - and those streams merge to make a river. Because the water can only flow downhill, it will fill in hollows in the land to make ponds and lakes - and generally run down the bottoms of valleys. The nature of erosion means that over geological time, the river will make it's own valleys by wearing away the soil and rock and carrying the resulting sandy stuff down-stream. Rivers also get twisty because if (for example) there is a large, hard rock on one side of the river bed - it'll deflect the water off to the side, towards the other bank. If that bank is softer, it'll get eroded - allowing the river to make a diversion around the rock. That diversion points the flow of the water towards another bit of ground - and that too erodes.

These processes are sufficiently complex - and so sensitively dependent on things like precisely where a particular (now completely eroded) rock was half a million years ago - that although we understand all of the processes very well, and can make pretty good mathematical models - we can't predict the precise shape or flow rate of any particular river from first principles.

SteveBaker (talk) 13:24, 3 May 2010 (UTC)

Isnt that all obvious? 92.28.253.63 (talk) 15:20, 3 May 2010 (UTC)

Although most of what Steve says is pretty much correct and very straightforward, I will disagree with him on two counts. I think that we can pretty well figure out what shape a river will have (braided, meandering, etc.) based on a combination of bank cohesion, sediment flux, and aggradation rate. And although what Steve says about being deflected around rock and boulders is probably correct in itself, it is not generalizable in that way. Meandering in itself is actually a self-forced phenomenon by which any irregularity in the channel will cause the flow to become nonuniform and focus high shear stresses in one location and lower ones in the others. This in turn focuses zones of erosion and deposition in a positive feedback that gives the meandering river patterns that we see. (Likewise, this gives the patterns of bars in braided streams.) Awickert (talk) 20:48, 3 May 2010 (UTC)

There's a useful introduction to fluvial geomorphology here [5]. DuncanHill (talk) 13:27, 3 May 2010 (UTC)

(outdent) I actually work as a sedimentologist / fluvial geomorphologist, so I might be able to help!

1. First, the river article is really bad in terms of geomorphology and doesn't mention hydrology much. Fixing it up has been on my mental to-do list for a while, but you know how those things go...
2. River channel morphology is controlled by events that are large enough to move sediment and/or erode the bed or banks. Most flows do not change the channel.
3. There are downstream relationships (empirically-derived) that give the depth, width, and slope of rivers as a function of discharge. See river regime. But this doesn't answer your question.
4. The width of a river channel with noncohesive/nonvegetated banks is given by a critical value of shear stress against the channel banks. If the river is narrow (relative to the difficulty of its flows to carry bed sediments), the shear stresses on the channel walls will be higher than a critical value to move these sediments. Therefore, the banks will erode. But as a channel widens, bank shear stresses decrease. If it overwidens, this will result in deposition on the banks. This is how a channel maintains its width as well as its width:depth ratio. There are a whole ton of theoretically-sound (i.e., not just empirical) equations that describe this, but the end product is what I wrote here.
   • This changes with the application of bank cohesion (e.g., vegetation), but the same principle applies. It is just much harder to erode the banks, so the flows are deeper and narrower.
5. An endmember of bank cohesion would be a bedrock channel, and results in a completely different morphology because bedrock channels are sediment-supply-starved. Here, the channel is able to incise a deep canyon (much deeper than its flow depth) because it erodes its bed, but doesn't have a sufficient sediment supply for much deposition to occur.

Hope this helps, Awickert (talk) 17:34, 3 May 2010 (UTC)

space-time continuum

Do anybody 'feel' the 4-dimensional space-time continuum in everyday life? —Preceding unsigned comment added by Amrahs (talk • contribs) 02:28, 3 May 2010 (UTC)

Space time? Then yes - everyone. 3 dimensions space, 1 of time. Do you mean 4 space dimensions? Then no. Ariel. (talk) 02:32, 3 May 2010 (UTC)

If you're talking about 4 spatial dimensions (plus time), then the question is a slightly tricky one. Obviously nobody directly perceives anything more than 3 spatial dimensions, but if string theory is correct and we actually have over a dozen dimensions - then in a sense, the mere existence of everything around us would be a consequence of all of those dimensions - and because we 'feel' all of those things, we are all feeling the consequences of those additional dimensions. String theory claims that these extra dimensions are "small" so we can't detect them. Think of this as being stuck inside a long, narrow tube - the length of the tube allows use to move freely along it - but it's so narrow that we can't move sideways or up and down. In this situation, we have one 'large' dimension, and two 'small' ones. Of course, in such a situation, we can see the sides of the tube and be aware of their proximity because even though those dimensions are small, they are still larger than our bodies. But the extra dimensions in string theory are very small indeed - much, MUCH smaller than the size of an atom. So small, that we don't even notice that they are there - and so small that we have been unable to devise a means to measure or even detect them. SteveBaker (talk) 13:13, 3 May 2010 (UTC)

Isopropanol, Peroxides can Result in Explosion & Injury?

i was reading the article on here and it says Isopropanol can form Peroxides? i keep my bottle with out the cap on. does that help? how can i test for peroxides? also if it forms them wouldent that make it caustic? i use it on my skin. —Preceding unsigned comment added by Tom12350 (talk • contribs) 03:03, 3 May 2010 (UTC)

See Peroxide, especially the safety section. I am not sure isopropanol itself is much of a problem, but acetone can spontaneously form acetone peroxide and many ethers can form ether peroxides. It generally takes a pretty powerful oxidizer to oxidize an alcohol to a ketone, but from the ketone or ether to a peroxide, something as simple as excess oxygen and a radical initiator, like UV light, could do it. You could also run into serious trouble if you mix ANY organic compound with hydrogen peroxide, and many households have both hydrogen peroxide and several common organic compounds together. Not sure it's a huge problem in your bathroom cabinet, but it may be. --Jayron32 03:45, 3 May 2010 (UTC)

Here's the article, if anyone's interested: Isopropyl alcohol. The sources cited for the peroxide claim include a materials safety data sheet [6] and an incident report [7]. The MSDS claims that it "may react with oxygen in the air to form peroxides", while the incident report claims that "The probable cause of this explosion/injury was peroxide formation associated with Isopropanol, perhaps accelerated by grease metal/solvent reactions". It further elaborates that "Literature review indicates that Isopropanol, with air contact, can develop peroxides, which can explode when concentrated". However, the big thing to note in the incident is that the isopropyl alcohol was concentrated overnight, making a probably insignificant concentration of peroxides into an explosive concentration. Jayron's probably right that it's hard to oxidize isopropyl alcohol to acetone, so the concentration of peroxides built up in most cases will be extremely low. However, the moral of the story is:

1. Keep your isopropyl alcohol in a closed container, and don't open/close it frequently.
2. Don't concentrate any potential peroxides by allowing a large amount of isopropyl alcohol to evaporate.
3. If you are going to concentrate or heat the alcohol, test for peroxides first.

I don't think it's a big deal for households with isopropyl alcohol: if it was, we'd hear a lot more about it. This incident had a lot of factors that made an explosion possible (keeping it uncovered overnight, evaporating it to concentrate peroxides, and heating), none of which should be present at home. Furthermore, when reading the incident report, it appears that even the suppliers and lab workers were unaware of the danger, indicating that it doesn't happen very often, even under these more favorable conditions. Buddy431 (talk) 05:31, 3 May 2010 (UTC)

The peroxides are usually formed in small amounts - typically around the cap - the danger (in addition to the damage caused to a person by the exposion) is that when they explode they will break the bottle and/or ignite the rest of the liquid.

An additional precaution is to keep the bottle in a dark place (no light). Sf5xeplus (talk) 10:51, 4 May 2010 (UTC)

Before big bang

What was there before big bang ????????? --Extra999 (Contact ^me + _contribs) 10:50, 3 May 2010 (UTC)

A black hole according to an article "It's black holes all the way down" by Ben Gilliland in the Metro (Associated Metro Limited) of 30 April 2010, pages 22-23. It mentions an URL www.cosmonline.co.uk but I have not been able to find it yet. dit: You could see it here http://e-edition.metro.co.uk/home.html but it requires giving an email address (which is not verified). In the e-edition, its on pages 24-25. 92.28.253.63 (talk) 11:03, 3 May 2010 (UTC)

What was where before the Big Bang? --KägeTorä - (影虎) (TALK) 11:12, 3 May 2010 (UTC)

In fact, there may not even be a "before", as both time and space came into being at the big bang (but that's only one possibility, per A Brief History of Time). --Stephan Schulz (talk) 11:40, 3 May 2010 (UTC)

See also (seriously) Turtles all the way down, which does discuss the issue. --Jayron32 12:13, 3 May 2010 (UTC)

I usually respond with the question: "What was there bewhat the Big Bang?" :-) - DVdm (talk) 12:35, 3 May 2010 (UTC)

There are quite a few possibilities - and we don't know which is true, and (worse still) there are reasons to believe that we may not ever be able to know which is true. Certainly one possibility is that both time and space were created at the instant of the big bang - hence there is no "before" and no "there". Other possibilities are that the universe is cyclic with big bang leading to expansion, then slowing, then collapse and finally a big crunch that would be the source of the next big bang. Another possibility is that the universe is symmetrical in time - with the history of the universe being played out backwards before the big bang. Right now, most of this stuff is speculation. The best answer is "We don't know" - and I'd say that Occam's razor suggests that time and space both started at the big bang - so there simply was no "before". This is hard to get your head around - but there is no guarantee that physics will be readily comprehensible to human minds. SteveBaker (talk) 12:52, 3 May 2010 (UTC)

The other posibility is that the big bang represents a sort of "cosmic censorship" (see cosmic censorship hypothesis) in that, since it represents a singularity, that is everything is in the same place at the same time, there is no means of extrapolating anything earlier than the point of the big bang, meaning that while we may idly speculate as to what (or when) anything (or anytime) existed before the Big Bang, its moot because the nature of the big bang makes it impossible to verify any hypothesis about what may have existed before it. --Jayron32 12:56, 3 May 2010 (UTC)

A big mind-boggling question is why is there any universe(s) rather than just nothing. 92.28.253.63 (talk) 16:37, 3 May 2010 (UTC)

Depends on what you mean by why. If you mean "what processes brought the universe about instead of nothing happening at all" then see anthropic principle. At worse, its a meaningless question because we are here to ask the question in the first place, if the universe did not exist, there would not be an us to question why it did not exist. If you mean "for what purpose was the universe created instead of leaving behind nothingness" then you are starting to veer into territory that religion or philosophy rather than science is equipped to answer. Immediately below this post, SteveBaker will come saying that science is perfectly well equipped to answer questions of grand purpose, and then give no qualifying statement, or propose any experiment or method which would show how science could answer such questions. --Jayron32 18:25, 3 May 2010 (UTC)

That's a little unfair. I've already said that we may not ever be able to know the answer to this. The reaction that you are referring to happens when someone says that it's not science's business to be investigating these matters - or that this is a subject only for philosophy or religion or UFO researchers or some other bogus field. That's something I do take objection to. If there is a way to investigate something, science should absolutely do that - there are no areas that are "off limits". However, there most certainly are situations (and this may well be one of them) where it is not possible - even in principle - to know the answer. But the proof of that applies just as well to philosophers and religious types. Proof of impossibility is still proof. SteveBaker (talk) 21:22, 3 May 2010 (UTC)

Sorry about mischaracterizing your standard arguement. I fully agree that there are no areas of which science should be "off-limits". Still, there is some stuff which science is clearly not equipped to answer. You seem to agree on that as well. However, we disagree that that then means there can be no answer. There can be one, just not one which science can provide. As such, it may be a very personal answer, over which people can respectfully disagree, but it still can be a very real answer which is useful in informing people's lives, and upon which people may act. --Jayron32 21:29, 3 May 2010 (UTC)

Without evidence of any kind, the more normal word for "answer" is "guess". So sure, if we can't figure out what (if anything) caused the big bang - then we are at liberty to guess - but we shouldn't go around suggesting that this guess is of much value. That being the case, you might as well say that the universe was sneezed into existence by the Great Arklesiezure as that it came from a black hole in some older universe - or any other guess you might come up with. The trouble is that with a literal infinity of possible causes - all of which are equally probable - the odds of your guess being correct are essentially zero. SteveBaker (talk) 23:27, 3 May 2010 (UTC)

That's Great Green Arkleseizure, Steve. Mustn't forget the colour. --Psud (talk) 05:20, 6 May 2010 (UTC)

You are still confusing cause with purpose, and confusing the Big Bang with creation. There's no problem in concept with using science to discover the cause of the Big Bang. Again, it may not be possible due to the laws of physics, but the concept is sound. Discovering the cause of the universe doesn't add to my understanding of the purpose of the universe, or of my life. Knowing the details of the process that created me doesn't grant me any insight into the knowing the purpose for which I was created. Furthermore, even if a furtherback cause for the Big Bang were discovered, it wouldn't change the nature of "creation", it pushes the date farther back, if you will, but still doesn't answer the fundemental questions of creation itself. Changing the identity of the creation event doesn't eliminate the questions surrounding creation itself. I understand you don't spend much time pondering things of this nature, things like "purpose", but can you atleast concede that they are valid matters for human discourse and reason, and as such, there are going to be valid discussions regarding them, even if you yourself have no interest in such discussion? --Jayron32 14:39, 4 May 2010 (UTC)

Buddha said that creation was a false concept, that creators don't exist. Why should "nothingness" ever exist without somewhere there being something? 67.243.7.245 (talk) 20:33, 4 May 2010 (UTC)

Human centipede - possible in real life?

Apologies in advance if this question causes you to consider concepts that you'd rather not have considered...

In the movie The Human Centipede, the mad doctor character creates the titular outrage against nature by attaching three people together by their digestive systems (i.e. sewing person B's mouth to person A's anus, then person C's mouth to person B's anus - the idea being that it is then sufficient to feed only person A, with B and C being nourished by poop and second hand poop, respectively). Nasty, huh?

Now, the movie advertises itself as '100% MEDICALLY ACCURATE!' (granted, which may be one of those standard horror movie marketing things intended to further disturb the audience) and the director says that he actually consulted with a top surgeon to design a feasible series of operations by which the human centipede creation could be accomplished.

Question is this (for the medically-qualified here, mainly) - quite simply, would someone *really* be able to do carry this out in real life? If so, how long would the human centipede realistically be able to survive and what sort of medical complications might arise? I'd imagine that there would be a whole host of things that could go very badly wrong, very quickly.

I do hope that my question doesn't fall afoul of the RDs 'no medical advice' rule... :) --Kurt Shaped Box (talk) 12:24, 3 May 2010 (UTC)

Coprophagia ——but this not address the nutritional value to humans, which I suspect is inadequate. Graeme Bartlett (talk) 12:29, 3 May 2010 (UTC)

Just as an aside, I really was expecting that article to contain an user-created image of a man eating faeces. --Kurt Shaped Box (talk) 12:37, 3 May 2010 (UTC)

Apologies if you are a lady coprophagiac for the Male chauvinism exhibited by the above poster. Cuddlyable3 (talk) 20:58, 3 May 2010 (UTC)

As with many "based on a true story" films, there is no requirement for any claims the films make about their own accuracy to be true. Vimescarrot (talk) 12:51, 3 May 2010 (UTC)

The professional in the article you linked to mentions the necessity of an IV drip, essentially making the whole procedure redundant (you're just pointless making faeces go through two more digestive systems to no effect - you may as well attatch a fifty-foot tube to Person A's anus). Obvious complications would be the myriad diseases you can pick up from excrement (cholera is my first thought, there are dozens more) and, without an IV drip, malnutrition. Vimescarrot (talk) 12:58, 3 May 2010 (UTC)

The key phrase here is "based on" - meaning that they started with a perfectly normal story with nothing unusual or unexpected about it - and blew it out of all proportion. If you imagine a real-life doctor who did a study on the efficiency of the human gut and discovered (not unreasonably) that some percentage of nutrients remained on excretion. A movie "based on" that true story could certainly contain this much nonsense. Sadly, there are no legal requirements for the correctness of movie blurbs! SteveBaker (talk) 13:01, 3 May 2010 (UTC)

I bet there is some implied legal requirement for a movie advertisement to be accurate, as with other ads. If they put out a blurb for a movie claiming it's a kid's movie and it's really a porno, I think they could get in trouble, for instance. The movie Kindergarten Cop seemed close to that line, being advertised and titled as if it were a cute kid's movie, but actually being a violent movie no child should see. StuRat (talk) 13:09, 3 May 2010 (UTC)

(after ec)Thanks for the answers so far, guys. FWIW, I don't believe that it was ever stated that the movie is 'based on a true story' - just that the director asked a surgeon how *he* would go about sewing three people together, ass-to-mouth, if he was an insane doctor... --Kurt Shaped Box (talk) 13:10, 3 May 2010 (UTC)

Since most the nutritional value has been removed after the first run, starvation would be an issue for the 2nd person and even moreso for the third. A more realistic way to have one person medically feed others might be to splice their circulatory systems together, although this would require compatible blood types. If only one person was fed, they would then get hungrier, because much of the nutrition would be used by the other people. In this way, it might be similar to having a tapeworm. The other people, who would be denied food, would still be hungry due to an empty stomach, but might not starve, if enough nutrition was received through the shared blood. The person who does eat might eat 3x the normal food and still not gain weight. Have I just invented a new fad diet ? :-) StuRat (talk) 13:05, 3 May 2010 (UTC)

I haven't seen the movie, but the article on it seems to imply that the nutritional needs of the people are not met and that one of them begins to suffer from blood poisoning as a result of the arrangement. That sounds about right to me. Not only would the nutritional value of feces be very low, it would be full of all sorts of gut flora that is quite toxic to humans, and not nearly enough water to survive on. Person #2 in the conga line would probably get quite sick, which would probably mean that person #3 would get... less than nutritional byproducts as well. I think the centipede would not survive long—numbers 2 and 3 would probably get quite ill, and at the very least would dehydrate themselves. --Mr.98 (talk) 13:23, 3 May 2010 (UTC)

Source: "100% MEDICALLY ACCURATE" at 2:17 (video). The standard for Wikipedia is verifiability not truth. Cuddlyable3 (talk) 20:51, 3 May 2010 (UTC)

I'm a little surprised no one has mentioned E.coli.. I read once somewhere that even if you are starving to death, don't eat human poop. Bad effects will far outweigh any benefit. Vespine (talk) 22:43, 3 May 2010 (UTC)

Well, I did mention gut flora, the larger category of stuff in yer guts of which E. coli is a distinguished member... --Mr.98 (talk) 23:39, 3 May 2010 (UTC)

This film happens to be medically inaccurate. The writer's claim that some un-named Dutch doctor supposedly gave some sort of medical "approval" concerning the "medical accuracy" of the procedure, is obviously nothing more than a crude advertising hoax or false-hood. Otherwise, where is this supposed doctor's name listed in the advertising? There is no known medical instance of anyone ever successfully stitching two people together.

In fact the only account I have been able to unearth of such a gruesome experiment comes from the annals (no pun intended) of the infamous Nazi doctor, one Dr. Josef Mengele. This doctor once attempted to permanently stitch two twins together, only to find that they both promptly contracted gangrene at their suture point, and could not "grow together". In the writer's fantasy of a "human centipede", in addition to the certain gangrene that would have been induced at the suture points, there is the question of asphyxiation. Certainly the middle and tail members of the trio would have reflexively regurgitated at the time of their first forced "meals", and then quickly suffocated in their own vomit. The entire proposition is ludicrous at best, and a new genre of sadistic snuff films at worst. Scott P. (talk) 21:00, 6 September 2010 (UTC)

"Man-made global warming can cause volcanoes"

There was a documentary on C4 last night called "The Volcano that stopped Britain". Near the end they claimed that man-made global warming caused volcanos to erupt by melting the ice on top of them. How do they get away with spreading such nonsense? I like to think I'm pretty liberal but i've lost most of those views since seeing this. Aren't there laws against knowingly spreading lies?--92.251.130.74 (talk) 14:16, 3 May 2010 (UTC)

That's interesting, I was watching a program last night on National Geographic about the same volcano, and it spent a fair amount of time covering the mind boggling amount of ice that the volcano its self melted, though not nearly the amount of an event in I think 1996. Definitely seems like a major flaw in the program if they think man made warming could even approach the heating effects of a volcano. Beach drifter (talk) 14:30, 3 May 2010 (UTC)

Even if hte ice was melted, that wouldn't cause the volcano to spontaneously erupt would it?--92.251.130.74 (talk) 14:42, 3 May 2010 (UTC)

Perhaps it was a phreatomagmatic eruption, i.e. one pertaining to the contact between magma and water (from melted ice?) Regards, --—Cyclonenim | Chat  14:48, 3 May 2010 (UTC)

After reading several articles, it seems there are phreatomagmatic components to the eruption, but they are side effects due to the location, and not the cause. Beach drifter (talk) 14:54, 3 May 2010 (UTC)

I think the idea is that GW could cause ice sheets to melt, which causes post-glacial rebound which in turn could release pressure on volcanoes causing an eruption. I agree that its not really necessarily to scare monger like this with relation to GW - its bad enough as it is - but I guess it makes for exciting TV. 131.111.30.24 (talk) 16:03, 3 May 2010 (UTC)

Almost correct, but nothing to do with post glacial rebound (though both have the same cause). Awickert (talk) 17:40, 3 May 2010 (UTC)

(outdent) Removing ice sheets reduces the vertical confining pressure on a magma chamber, increasing deviatoric stresses and causing an eruption. This is also well-documented in a study in Iceland of lava flow volumes during the last deglaciation. To the original poster of this: if you've changed your views by calling something "nonsense" and "lies" without knowing what you're talking about, I suppose that's your call. Though I admit: modern-day documentaries can over-dramatize to the absurd, and sometimes bungle the facts, making skepticism natural. Awickert (talk) 17:40, 3 May 2010 (UTC)

(edit conflict) It's a real theory that melting glaciers can trigger eruptions due to decompressing active magma chambers. Basically, by removing the pressure of 100 m of ice (for example) you cause more of the superheated rock to melt and more gases to escape and this might cause an eruption to happen hundreds of years earlier than it would have otherwise. It is important to note that this is about triggering volcanoes and not causing them. Melting ice certainly doesn't cause a magma chamber to form. At best it might provoke an existing magma chamber into erupting a little bit early. It's not specific to global warming either, people argue about changes at the end of the last ice age triggering eruptions. Dragons flight (talk) 17:43, 3 May 2010 (UTC)

Even if that were true, the resulting eruption would be less explosive then it would otherwise have been, and therefore cause far less trouble then one that goes Krakatoa. Googlemeister (talk) 19:27, 3 May 2010 (UTC)

How do you know that? Awickert (talk) 19:57, 3 May 2010 (UTC)

Simple thermodynamics. If you have a pot on you stove filled with boiling water and place the lid on (for the purposes of this experiment you can assume this makes the inside of the pot airtight), as the water boils, it forms steam. Steam has a volume far larger then that of water, so without anywhere to go, the pressure increases. If the lid is lightweight, this pressure will force the lid up, and steam will escape and some water may boil out of the pot. Inconvenient perhaps, but not a catastrophe. If you make the lid heavy, or better yet, weld it to the pot, when failure finally occurs, the pressure differential will be far greater, and so will the damage. Googlemeister (talk) 20:42, 3 May 2010 (UTC)

Ah, OK. Thanks for your answer! Unfortunately, volcanoes aren't that simple, largely because there is no constant "burner" and the "lid" is both nonuniform in its material properties and evolving through time. So for example, with a heavier lid, the lava may freeze before it gets to the top, making less of an eruption. Or conversely, to bring in another issue, the eruption may be less damaging without the glacial lid because it won't trigger jokulhaups. (Also, as an aside, Icelandic volcanoes don't have the right composition to go Krakatoa...) So what you say is an interesting idea; when I get a chance I'll see if I can find anything published about it. But I would caution against making authoritative claims about complex systems based on simple models in the meantime (unless you do a little research and find out that you are indeed correct). Best, Awickert (talk) 21:00, 3 May 2010 (UTC)

OK - our OP needs to calm down and do the tiniest scrap of background research.

I don't see any problem (in principle) with the idea that (a) global warming melts glaciers and other ice deposits...which (b) reduces the pressure on the top of glacier-encrusted volcanoes...and (c) that it is possible that reducing the pressure on the top of the magma chamber of a volcano could trigger an eruption. Imagine a volcano that is just on the edge of having built up enough internal pressure so it's on the verge of exploding...just on the tipping point...then melting the glaciers could be enough to cause an eruption that might not otherwise have happened for another 100 or 1000 years. It might also change a slow oozing magma flow into a full scale explosion - as water from the melting ice could be flashed into steam inside the magma chamber, increasing it's ability to overcome the reduced pressure on top.

So this isn't nonsense (meaning non-sense) because it does actually make some kind of sense. I just don't know whether that's really what happened.

Whether that is specifically what happened in this case would require some considerable study. So I googled it. :-) It turns out that it's not just C4 the BBC who are saying this - this article in the Daily Telegraph newspaper claims the same thing. It turns out that their claim (and therefore, probably, C4's the BBC claim) is based on a study by the Royal Society who are a rather prestigious bunch of scientists.

Hence, I think our OP is WILDLY overreacting. C4 The BBC is most definitely not lying because a lie is a deliberate untruth - and they are only repeating what some extremely reputable scientists are saying. So it's not a lie. Channel 4 The BBC are doing their job - and in this case, they are doing it well...so quit complaining about that!

The guys at the Royal Society may be mistaken (a mistake is a non-deliberate untruth) - but they too are not lying. This is properly published, peer-reviewed work, in "The Philosophical Transactions of the Royal Society". That journal has been the gold standard for scientific reporting for 300 years (Sir Isaac Newton was published there!). So C4 the Beeb didn't say anything that's in any way unreasonable.

Now - if you wish to place your own extensive scientific training your privately obtained data and your own in-depth study into this subject matter against people who were published by the Royal Society - please feel free to do so...but don't expect us to be wildly sympathetic to your cause because the odds are very good that you're guessing! So, IMHO, you should assume that (like most BBC documentaries) this was well researched and based upon solid scientific sources. Certainly, the idea that there might be some law you could invoke is WAY out of the question!

SteveBaker (talk) 19:43, 3 May 2010 (UTC)

I thought it was channel 4 and not the BBC? C4 don't have the best track record on documentaries (The Great Global Warming Swindle springs to mind) so perhaps the OP was correct to be sceptical. 86.7.19.159 (talk) 19:58, 3 May 2010 (UTC)

I'm sorry - you're right. I'll fix my response. SteveBaker (talk) 20:39, 3 May 2010 (UTC)

Using the phrase "I like to think I'm pretty liberal but..." suggests the OP considers the issue a political not a vulcanological one.Cuddlyable3 (talk) 20:09, 3 May 2010 (UTC)

And if this were the rabid right-wing politics reference desk, I'd have answered accordingly...but since this is science - and AFAICT, they nailed the science perfectly - we have to take an appropriately offended stance. SteveBaker (talk) 20:39, 3 May 2010 (UTC)

Dare I suggest, Steve, that a more effective approach would be to explain what the paper suggests would happen, without the command to take it as verbatim truth because it's from the Royal Society. I think you'd be more persuasive if you yourself didn't seem so defensive about it, and if the alternative you offered was more varied than "take it on faith because of who said it". I don't think responding to a polarized view with an even more polarized view generally accomplishes much. Just my two cents. --Mr.98 (talk) 23:34, 3 May 2010 (UTC)

You mistake what I'm saying. The question before us is: Was Channel 4 lying (as our OP so vociferously alleges) when they said that this global warming theory is a true possibility? No!! Clearly they were not lying because (like Wikipedia and other responsible journalists) they relied upon 'reliable sources'. Nobody can seriously doubt that one of the oldest and most respected scientific journal on the planet is a reliable source!

Now, it might be that there is an error in the paper in that journal - nobody claims that their peer-review system is infallible. Or it might be that the journal (for some utterly bizarre reason) faked the entire thing and there is a gigantic secret conspiracy. But what we cannot doubt is what Channel 4 said. They reported results from a reliable source...they absolutely, 100% certainly, did not lie. If the documentary is wrong (which seems really unlikely under the circumstances) then Channel 4 is not to blame. They can't even be accused of making a mistake...they honestly reported a reliable source - and that's the very best we could hope they'd do.

As for the Royal Society - for sure, they occasionally make mistakes - no journal is ever 100% infallible. After all, we had 200 years of everyone reporting that Newton's Laws were right - then Einstein came along and proved them all (very slightly) wrong. But given the choice - and given that you aren't a vulcanologist - should you believe your own guesses about how volcanoes work? Or should you believe a paper published in one of the most respected journals in the world? By all means be skeptical - by all means dig out the paper and read it yourself - but PLEASE don't go off on a major rant about some Channel 4 documentary without at least some sort of evidence beyond "gut-feel".

SteveBaker (talk) 00:45, 4 May 2010 (UTC)

Regarding Aren't there laws against knowingly spreading lies? No - OFCOM decided that it is outside of their remit to punish broadcasters over the accuracy of their programs - see this, only news reports have to be factually accurate. 131.111.30.21 (talk) 12:24, 4 May 2010 (UTC)

Internal and external cell conditions - source?

I need to find a source (preferably in table form but I can always form one from the data) which provides cell conditions for Na+, Ca++, Cl- and K+ ions with respect to their concentrations internally and externally? Anyone know of such a source? Regards, --—Cyclonenim | Chat  15:50, 3 May 2010 (UTC)

Articles Nernst equation or Resting potential may help. Cuddlyable3 (talk) 17:02, 3 May 2010 (UTC)

Membrane potential also would be useful. The lede mentions all 4 ions. See also ion channel and Ion transporter and Plasma membrane Ca2+ ATPase and Na+/K+-ATPase. Cytosol#Ions discusses actual concentrations, and has a handy chart that lists difference between intracellual concentrations and blood concentrations. Extracellular fluid has some figures as well, though not in a handy chart. --Jayron32 18:19, 3 May 2010 (UTC)

Supporting ladder on stairs - sideways

I need to position a ladder on some stairs, sideways so that it leans against the wall at the side of the stairs. The stairs are eight inches deep, but the ladder is about 15 inches wide. Thus one foot of the ladder will dangle unsupported.

What is the best practical way to support the ladder firmly and safely? The stairs are not very wide either, and are covered in carpet. Thanks 92.28.253.63 (talk) 16:31, 3 May 2010 (UTC)

You'll need to find a device which extends the leg of the ladder on the downstairs facing side. Something like this, but I'll let more knowledgeable people give you advice on specific products. Note that this stabilises the ladder to the usual extent like it would on the floor, but particular care should be taken not to wobble the ladder whilst you're on it. Regards, --—Cyclonenim | Chat  16:34, 3 May 2010 (UTC)

Cut out a big block of wood and fix it to the lower stair, although obsiouly in a maner which you can remove it.--92.251.141.43 (talk) 16:40, 3 May 2010 (UTC)

In a professional setting, those needing to carry out work on stairs usually construct a scaffolding platform, as I myself have seen done on several occasions while employed in facilities maintenance: indeed, in the UK it is contrary to Health & Safety Regulations to carry out actual work more than 2 metres above the ground from a simple ladder, which should only be used for access and inspection; also, ladders should always be secured in place at top and bottom (the latter can be done by a workmate rather than mechanically). What an individual chooses to risk doing in a private setting is, of course, up to him/her, but you may wish to balance the worth of your intact neck against the cost of getting the job (whose specific setting, scope and duration we do not know) done by a trained professional.

As an alternative to both a straight ladder and to constructable scaffolding (i.e. tubes, clamps and boards), you might be able to buy, or more economically hire, a small mobile scaffold tower with the two sides adaptable to different base heights supporting a horizontal working platform, which are designed for this sort of work: I suggest you make enquiries at a local equipment hire firm, if you can find one. 87.81.230.195 (talk) 19:18, 3 May 2010 (UTC)

Buy a ladder like this one. Then you put the ladder sideways like this. You can get different sizes for that ladder, and there are other brands, which might be less expensive. Ariel. (talk) 21:03, 3 May 2010 (UTC)

No liability whatsoever is assumed by providing this information, but I have seen painters wishing to work on the wall high above a short run of stairs place a ladder against the wall at the bottom of the stairs, then run a scaffold or plank from the ladder to a step at the same level. See "How to use a scaffold on stairways."An old 1906 solution in Popular Mechanics is seen here and some modern solutions are shown http://books.google.com/books?id=RTC8yFaw7ioC&pg=PA32&dq=ladder+stairs&lr=&as_brr=3&cd=6#v=onepage&q=ladder%20stairs&f=false here]. Some modern ladders are made with the two sides independently adjustable as Ariel pointed out. Edison (talk) 21:38, 4 May 2010 (UTC)

Moment of Inertia

My textbook says that moments of inertia about principal axes are constant to the first order for small angular displacements. Is there any way to prove this? Thanks. 173.179.59.66 (talk) 16:53, 3 May 2010 (UTC)

Wikipedia's relevant articles are Moment of inertia and List of moments of inertia. A consequence of the definition of the Sine of an angle x (in radians)

${\begin{aligned}\sin x&=x-{\frac {x^{3}}{3!}}+{\frac {x^{5}}{5!}}-{\frac {x^{7}}{7!}}+\cdots \\[8pt]\end{aligned}}$

is that for small x

${\begin{aligned}\sin x&=x\end{aligned}}$ approximately. Cuddlyable3 (talk) 19:59, 3 May 2010 (UTC)

Great, thanks. 173.179.59.66 (talk) 23:59, 3 May 2010 (UTC)

(edit conflict) Cuddlyable3 is deriving the Small-angle approximation, an often used approximation in physics, and quite accurate for small angles: i.e. an error of less than 0.15% for angles smaller than 5 degrees, about 0.5% for angles smaller than 10 degrees, and still only about 5% for angles up to 30 degrees (yeah, you have to convert to radians when working with it...) Buddy431 (talk) 00:07, 4 May 2010 (UTC)

Don't worry, I understood. Actually, I was aware of the small angle approximation. I just realized that I was using addition when I should have been multiplying. —Preceding unsigned comment added by 173.179.59.66 (talk) 02:29, 4 May 2010 (UTC)

Alcohol for stage fright

Is alcohol an effective treatment for stage fright? Are there any other non-prescription drugs that are as good as or better? Thanks 92.28.253.63 (talk) 17:19, 3 May 2010 (UTC)

Wikipedia cannot offer medical advice. Alcohol is not a prescribed treatment for any known medical or psychological condition. If you are having trouble, please seek advice from a qualified professional, such as a psychologist, who works in this field. The internet, and random strangers that hang out there, is not the proper place to ask such questions. --Jayron32 18:13, 3 May 2010 (UTC)

How is stage fright a condition needing medical advice? I intensely dislike preforming in front of people, but it doesn't require a "qualified professional" to treat. Ks0stm ^(T•C•G) 18:29, 3 May 2010 (UTC)

Stage fright isn't a medical condition - but as soon as someone starts to ask us to suggest drugs to treat it - it becomes a request for medical advice...and our only answer is "If this concerns you - go see a doctor." In this case, it's possible that a doctor might prescribe something. SteveBaker (talk) 19:08, 3 May 2010 (UTC)

I'm not suffering from stage fright, and I do not like alcohol. I was asking in general terms, not medical advice. 92.28.253.63 (talk) 18:23, 3 May 2010 (UTC)

In that case, I reiterate that Alcohol is not prescribed for any known medical or psychological condition. Some people self-medicate using alcohol, usually to less-than-desirable results (alcohol-related violence, cirrhosis, drunk driving, addiction.) Anxiolytic are the class of drugs prescribed for anxiety problems, which stage fright certainly qualifies. None are actually availible over-the-counter, unless you count "herbal" remedies, or "off-the-label" remedies. --Jayron32 18:29, 3 May 2010 (UTC)

That is not strictly true. Ethanol is occasionally prescribed for poisoning by ethylene glycol or methanol. The latter two substances are very toxic, but not terribly toxic in themselves — rather, the damage is done by their metabolites. Ethanol competes for the enzyme that oxidizes or dehydrogenates them, giving the kidneys a chance to eliminate the substances before the toxic metabolites can be formed. --Trovatore (talk) 23:21, 3 May 2010 (UTC)

What you are describing is a result of abuse or over-consumption of alcohol. You can get nasty results if you overdose on pretty much any other chemical, from cough syrup (toxic psychosis), vegetable oil (Cardiac Arrest) or even water (Water intoxication). Googlemeister (talk) 19:23, 3 May 2010 (UTC)

I'm sorry, people have never abused alcohol before. Statistically speaking, there is not a significant number of people to have every overconsumed alcohol to even mention. I apologize for misleading people to thinking that there are ever negative consequences from using alcohol to excess. (as an aside, I am not a teatotaller. I regularly consume responsible amounts of alcohol.) --Jayron32 19:42, 3 May 2010 (UTC)

I'm not going to say anything about its effectiveness, but alcohol is very frequently used for such things. See Dutch courage. --Tango (talk) 19:24, 3 May 2010 (UTC)

So you are going on stage and feel nervous? Then Break a leg !. Cuddlyable3 (talk) 19:36, 3 May 2010 (UTC)

A well-known symptom of alcohol intoxication is the loss of social inhibitions, so it's reasonable to assume that stage fright would be reduced. However, whether the lack of stage fright would outweigh the decreased mental capacity caused by alcohol and make the show better overall, I can't say. --99.237.234.104 (talk) 20:08, 3 May 2010 (UTC)

However, we should not be advising people to treat an anxiety disorder by drinking. Such irresonsible medical advice is exactly what the medical disclaimer is about. Yes, people do drink because they have anxiety. However, to recommend that as a reasonable course of action, to actually state "Yes, it would be a good idea to drink alcohol to combat stage fright" is a fantasticly irresponsible thing to do. If anyone is seeking genuine advice on how to handle stange fright or any other anxiety disorder, see someone who knows how to treat anxiety disorders. Period. --Jayron32 20:28, 3 May 2010 (UTC)

I hardly think it's proper to call stage-fright an "anxiety disorder". This medicalisation of normal feelings is a pernicious trend in late 20th and early 21st century western society. I'd ask an actor or an acting coach for advice about stage fright. DuncanHill (talk) 21:04, 3 May 2010 (UTC)

I didn't advise anybody to do anything. My answer was a scientifically valid statement of well-known facts. --99.237.234.104 (talk) 21:12, 3 May 2010 (UTC)

I agree. "Anxiety disorder" means being anxious about things a normal person wouldn't be anxious about. Almost everyone is anxious about appearing on stage in front of hundreds of people. --Tango (talk) 22:37, 3 May 2010 (UTC)

Before trying this, be sure to watch The big bang theory episode The Pants Alternative (the link has a small spoiler, don't click on it). Ariel. (talk) 21:18, 3 May 2010 (UTC)

If you've gone a way down the path to becoming an actor then you have contemplated the awesome responsibility of addressing an audience from a stage. That you continued along this path probably indicates that you've worked "stage fright" into the equation of what you bargained for. It is unlikely that the fear of going onstage only cropped up at the last minute. You can take heart from your own decision, made time and time again in preparation for your role as stage actor, that this is something that you calculate you can do. Bus stop (talk) 21:31, 3 May 2010 (UTC)

For discussion of the "piss artist" in acting see [8]. There is a danger that an actor may feel he is doing his best work, when his fellow actors and the audience see someone whose timing is off, who muffs lines and stumbles around. Even one instance of showing up tipsy for a public performance can stick for a lifetime, as happened to Andrew Johnson at his vice presidential inauguration. Edison (talk) 21:29, 4 May 2010 (UTC)

construction, coal

During excavation for a new house, a seam of coal was uncovered. will the coal hold up to a foundation placed on top or is it too soft and will require pilings drilled through the seam and filled with rebar and concrete? It will be a large house and the foundation for the fireplace will be close or on the seam. thanks for any help on this. —Preceding unsigned comment added by Lhirsche (talk • contribs) 18:43, 3 May 2010 (UTC)

Really? You want to ask people on the internet about how to safely build your house? The answer almost certainly depends on the size, extent, and type of deposit. You need to talk to a structural engineer, geologist, or someone similar who can inspect the site and give you a professional evaluation. Dragons flight (talk) 18:52, 3 May 2010 (UTC)

There are lots of different foundation approaches for modern houses. No matter the type of soil or subsurface conditions, you'll need a proper foundation design. So even if there had been no coal there - you'd still be crazy not to have someone design you a proper foundation that's appropriate to the conditions. Specifically, I'd expect coal to be a pretty good rock to build onto - but if an expert says otherwise then there are other options beside the 'pier and beam' approach you are describing. My house is build on some of the soggiest clay imaginable with the bedrock 30' below the house...we have a floating 'waffle slab' that floats on the soil...and that's despite it having foot-thick concrete walls! But you have to consult an expert - the consequences of a foundation/slab failure can be utterly catastrophic. SteveBaker (talk) 19:05, 3 May 2010 (UTC)

There is more then one type of coal, from bituminous to anthracite. They would not have the same structural properties, so expert help is strongly recommended. Googlemeister (talk) 19:14, 3 May 2010 (UTC)

How convenient to have a coal mine under the fire place. What could possibly go wrong? Edison (talk) 19:48, 3 May 2010 (UTC)

Do you live in Centralia, Pennsylvania? Googlemeister (talk) 20:25, 3 May 2010 (UTC)

Just in case you are simply looking for a second opinion, and not actually relying on random people on the internet to build your house, coal is pretty strong and you should be able to build on it. I'd worry about gases being released from the coal though. Methane, and Radon specifically. Radon especially is pretty bad, be sure to handle it properly, either active venting, or some sort of construction technique to make sure it doesn't enter the basement. Also, you may have legal issues. In many parts of the country, you don't own mineral rights under your land, so that coal may not be yours, and I have no idea what that would mean to your house. If it is yours see if it's worth mining that coal (well, selling it to a mining company) instead of building on it. Ariel. (talk) 23:29, 3 May 2010 (UTC)

I doubt if mining the quantity of coal that would be found on a typical house lot would be cost effective. StuRat (talk) 00:21, 4 May 2010 (UTC)

My understanding is that coal mining often starts by finding a seam on the surface, then following it underground. The bulk of the coal is underground, and not limited to the size of a house lot. Ariel. (talk) 00:35, 4 May 2010 (UTC)

Sure, but what's the advantage to you if they pull up coal from your neighbor's yard? APL (talk) 03:13, 4 May 2010 (UTC)

I don't think it's necessarily a non-profit endeavor to extract coal from a neighbor's yard -- there was an answer on this topic posted some time ago, but it's certainly profitable to extract coal even if you have to pay others for the coal you get from under their property. DRosenbach ^{(Talk | Contribs)} 16:48, 4 May 2010 (UTC)

I don't know if you can build a house on it (see a licensed architectural engineer), but I do know you can build a house from it: Coal House (Williamson, West Virginia). -- 174.21.225.115 (talk) 15:30, 4 May 2010 (UTC)

Wouldn't it be a fire hazard? 146.74.230.104 (talk) 00:24, 5 May 2010 (UTC)

No more then a wood house I should think. Googlemeister (talk) 13:29, 5 May 2010 (UTC)

Less actually. Coal is really hard to ignite. I took a blowtorch to a piece of coal once (I don't know what type, but it was very hard and shiny), and it sparked but would not ignite. Ariel. (talk)

Must've been anthracite, it's very hard, black and shiny and notoriously hard to ignite. Bituminous coal is also black and hard, but not shiny, and it ignites a lot easier, burning with a smoky yellow flame. 67.170.215.166 (talk) 00:38, 6 May 2010 (UTC)

how much is $280,000 per year (inflation-adjusted) for 40 years worth today?

How much is $280,000 per year, but adjusted for inflation, ie this value goes up from year to year to account for inflation, and to be paid out for 40 years, worth today? Thank you. 84.153.250.110 (talk) 19:30, 3 May 2010 (UTC)

Do you mean, how much would being paid $280,000 per year, adjusted for Cost of living annualy, be worth if the first $280,000 payment was made 40 years ago? Or do you mean that you are going to be paid #280,000 this year, and want to know what the COLA payments will do to the money over the next 40 years? I am unclear on what you are asking. --Jayron32 19:35, 3 May 2010 (UTC)

Numerous websites will calculate the inflation adjusted values of money, a simple Google search will find them for you. This one shows that $280,000 in 1969 was equivalent to $1,620,160 in 2009. TastyCakes (talk) 19:38, 3 May 2010 (UTC)

Future inflation cannot be predicted. 40 x $280 000 = $11 200 000. Cuddlyable3 (talk) 19:41, 3 May 2010 (UTC)

Well it can be predicted, it just can't be predicted correctly ;) TastyCakes (talk) 19:45, 3 May 2010 (UTC)

Of course, even if you had a true figure, most people time discount; that is, they'd take 90% of something this year than 100% of it next year (rightly or wrongly). So it might be "worth" more or less today than it is in the future, depending on how you look at it.- Jarry1250 ^{[Humorous? Discuss.]} 19:56, 3 May 2010 (UTC)

If it's adjusted for inflation - then isn't the answer just $280,000 x 40 ? SteveBaker (talk) 20:11, 3 May 2010 (UTC)

If the question was asked correctly, then I agree, that's exactly what it is. Vimescarrot (talk) 20:28, 3 May 2010 (UTC)

The question above (which is different from the one below) asks for today's value of a stream of payments of $280K (adjusted for expected inflation) paid annually for 40 years. Even though inflation is adjusted for, you also have to adjust for the time-value of money. So the answer will be lower than $280K x 40, unless the discount rate is equal to (or less than) the expected inflation rate - but there would be no sense in using a discount rate like that. Zain Ebrahim (talk) 11:49, 4 May 2010 (UTC)

Um, I'm the original questioner and your answers don't make sense to me. Let's simplify and say that you will be paid nothing until 40 years from now, at which point you will be paid the then-equivalent of $1,620,160 in today's dollars. How much would you pay for that to happen? Obviously it has to be far LESS than a million, since why would you tie your money up for 40 years for nothin'? What I want to know is exactly how much less. I think it has to do with the prime rate. This isn't homework.... 84.153.250.110 (talk) 20:54, 3 May 2010 (UTC)

That's actually impossible to answer. Inflation is a very tricky thing, people have a very hard time agreeing on what historical inflation has been, that is how to calculate inflation based on what we know has happened to values over the past 40 years. To predict with any certainty what will happen in the next 40 years is literally an impossibility. Inflation has little to do with the Prime rate. The Prime rate is part of monetary policy which is the means by which central banks hope to control inflation. Inflation itself is measured in very different ways; see producer price index and consumer price index for a couple. If anyone definitively knew how to predict inflation reliably, they'd be fantasticly rich. --Jayron32 21:21, 3 May 2010 (UTC)

No, he said it was the then-equivalent of $1,620,160 in today's dollars, which means 84.153 has removed inflation from the equation. In this revised question, 84.153 is asking what would be a good price for a fixed rate bond which matures 40 years from today for the then-equivalent of $1,620,160 in today's dollars, issues no coupon payments, and is not callable. I am going to venture an answer, based on the current price of 30-year TIPS bonds that sold about a month ago for 2.125%. If we use this as the answer, then your answer will be somewhere under US$720,000 (because you're selling a 40 year instrument instead of 30). The main critical assumption I am making here is that your bond would be backed by the US government and not some company; else a higher interest rate would be demanded. Comet Tuttle (talk) 21:29, 3 May 2010 (UTC)

mm if I'm reading this right, is this now a net present value/time value of money question? If it is, the net present value will depend on what discount factor you use, and that's really up to you. You could use the historical average of a big bond rate like Comet Tuttle says above, or you could use the average stock market growth over the last 50 years, or the average inflation rate or any number you think represents how much more money in your pocket right now is worth than money maybe in your pocket next year. TastyCakes (talk) 21:42, 3 May 2010 (UTC)

Yes, it sounds like a time value of money question. The challenge with these questions is working out an appropriate discount rate. --Tango (talk) 22:41, 3 May 2010 (UTC)

Yes — and 84.153 also didn't specify whether this bond can be sold to another party. If not, and you're already 70 years old and in poverty, there may not be any appropriate discount rate, because you may not want to tie up even $1 in a scheme that will not pay off during your lifetime. Comet Tuttle (talk) 00:02, 4 May 2010 (UTC)

This restated question becomes a question of what interest rate you can earn versus how inflation grows. If you can get an interest rate that consistently out-paces inflation, then take the money now - and invest it. If inflation out-paces interest rates - then let someone else pay the price and take the money in the future. Which of those things wins is utterly unknowable. It depends on how interest rates change - how the stock-market grows (or shrinks) - how much risk you're prepared to take. That last thing is the real problem. Historically, the stock market grows about 5% per year and the inflation rate isn't that high for long. So the stock market ought to be a no-brainer...except for risk. As a lot of people have recently discovered, there is not such thing as a safe stock. Who knows what happens to the major markets of the world over the next 10 years - let alone the next 40! Uncertainly increases exponentially with time. So, we can't reliably answer your question. Risk is the big issue here. If you want to take the money and invest it now - and you expect a 99% chance of beating inflation - then you're forced to take such low-risk choices that you can't make any money. If you only want a 50/50 chance of beating inflation - then you can probably find a set of stocks that will give you a 50/50 chance of winning big-time over inflation. So if you are risk-averse, take the money in 40 years and let whoever is paying it to you take all of the risk. Of course if the person/organization/government who is supposed to do that fails over the next 40 years then you may be completely screwed - so there is no such thing as a 0% risk. SteveBaker (talk) 00:14, 4 May 2010 (UTC)

Here are some thoughts for determining a discount rate. Assuming you give the money to an insurance company, you can use the following sum:

Required return = real risk-free rate + credit-risk premium + liquidity-risk premium

• Risk free rate: You can use Comet Tuttle's suggestion above for the first part: 2.125% (these are ususally quoted as nominal rates).
• Credit premium: Look at the long term (e.g. 10-year) credit spread on highly rated insurance companies. Insurance companies don't typically issue very long term debt so you can also look at banks that might have issued 30 or 40 year bonds.
• Liquidity might not be an issue for you if you don't intend to sell this. There are many many ways to try and estimate this - if you're interested, you can try google.
• You don't need to add anything for inflation if you assume that whatever you get in 40 years will compensate you for whatever inflation did over that period.
• There may be other special circumstances that you would need to allow for.

Then just add them up and discount at that rate. Alternatively, insurance companies sell this kind of product all the time - just call your local insurance broker and ask him how much this would cost. Zain Ebrahim (talk) 12:27, 4 May 2010 (UTC)

Nothing

In the bits of space between the molecules, atoms, ions, &c., do forces still apply? What exists in the space between them in which gravity, magnetism and so on exist to allow the potential forces to exist. I suppose what I am asking is what nothing is, or what 0 actually means. If you could suck all the matter completely out of a given area does it still exist because there is no matter in it to describe it? -russ (talk) 19:54, 3 May 2010 (UTC)

Gravity, magnetism and other such forces are not transmitted by real physical particles that require a "something to exist between here and there" to work. DMacks (talk) 19:59, 3 May 2010 (UTC)

It was once thought that a medium called the luminiferous aether was required to transmit the electromagnetic force, but this idea was incorrect. The gravitational and electromagnetic forces propagate just fine through a vacuum. -- Coneslayer (talk) 20:00, 3 May 2010 (UTC)

There is almost nothing between the stars and planets - but the force of gravity still operates perfectly well. Gravity can be shown to operate between galaxies too - and the space between them has so little 'stuff' in it that we're down to one atom per cubic meter or so! So clearly forces can operate through a vacuum. On a smaller scale, the strong and weak nuclear forces operate at the scale of individual atoms - and (as you say) the atoms are separated by a nice, hard vacuum. The earth's magnetic field is responsible for deflecting charged particles from the sun - and that too operates out beyond our atmosphere - so you can tell that magnetic forces also propagate just fine through "nothing". SteveBaker (talk) 20:18, 3 May 2010 (UTC)

For people that have a problem with forces propagating through nothing, there's field theory. Fields are by no means necessary to explain or understand force propagation through empty space (see Action at a distance), but they do provide a helpful framework for understanding how things like "light waves" propagate through empty space (i.e. Q: "what" is vibrating in a light wave? A: the electromagnetic field). Insofar as concepts like "energy" are "real" so are fields. --Jayron32 20:25, 3 May 2010 (UTC)

But doesn't that mean that a vacuum must exist, which according to Wikipedia is 'only a philosophical concept and never is observed in practice'? -russ (talk) 20:12, 3 May 2010 (UTC)

Well, I don't have much time for philosophers - they cause more confusion than they do clarity. The question here is whether you should have a name for nothingness. A 'vacuum' is defined as the absence of matter - does that make it a useless concept? Not at all, it's an exceedingly handy word - and for beings who live in a world surrounded by air, the concept of a 'vacuum' is sufficiently different from normal existence that it makes sense to have a word for it. Beside, we use 'black' to mean an absence of light - and 'silence' to mean an absence of sound - are those also "only philosophical concepts"? SteveBaker (talk) 20:22, 3 May 2010 (UTC)

(also reply to pierhead above, EC with him below) Vacuum is an asymptotic condition, not a philosophical concept. Science is filled with concepts which are physically impossible to achieve, and yet are very real, such as absolute zero, big bang, speed of light, etc. etc. Being impossible to achieve is not the same as saying its only a "philosophical concept". Things like ontology and eschatology and epistemology are philosophical concepts. A vacuum is a very real, if physically unobtainable, condition. --Jayron32 20:37, 3 May 2010 (UTC)

Classically, you can have real, hard vacuum. Out there between the galaxies there is only about one atom per cubic meter of space. If the atom happens to be in the top-left corner of that cubic meter - then you have almost an entire cubic meter of perfect vacuum. However, from a quantum-theoretical viewpoint, there are two problems with that. One is that fundamental particles don't have exact positions - they are probability clouds - so even if the atom is nominally considered to be in the top-left corner - there is a vanishingly small probability that you'd detect it over a meter away in the bottom-right corner. In a sense, the atom is everywhere at once - so no place in the universe is truly empty. Beyond that, you have the issue of virtual particles where a particle and an anti-particle will pop up out of nowhere - then vanish again just as fast - and this makes it tricky to define precisely what we mean by "empty". Also, there would be a lot of photons and neutrinos out there too...so if you count those, then there is quite a lot of 'stuff' contained in that cubic meter. SteveBaker (talk) 23:04, 3 May 2010 (UTC)

Does not the absence of sound and light constitute an entity in which they are void? The void must surely still exist as those properties which propogate them still exist and are absorbed by their terminal entities? Is there, therefore no (realistic) nothing or zero? -russ (talk) or am i just being needlessly foolish? —Preceding undated comment added 20:34, 3 May 2010 (UTC).

I think you're confusing the existence of stuff with the existence of a concept to describe the situation. "Vacuum" is a concept that exists, even though nothing exists in a vacuum. That's not contradictory. We can label any concept we want. But more importantly, this is a philosophical issue that doesn't have much to do with understanding the science. Rckrone (talk) 21:39, 3 May 2010 (UTC)

May 4

learning skills

On one of the Nat Geo documentaries that I watched, I saw why one messes up when they get nervous. It seems that there are two parts of the brain that learns a skill. One is a learner that is very clumsy and a learned part that executes the technique. When one needs to perform and cannot overcome their nervousness, the very clumsy "learner" part takes over and the resulting performance is bad. I think they used an amateur soccer player for this experiment and tricked him by saying that he was being watched by talent scouts. Anyone can direct me to its wiki article? --121.54.2.188 (talk) 00:39, 4 May 2010 (UTC)

I've never heard this idea before and am very sceptical. It doesn't make much sense to have your brain learning something twice, once not very well. We have an article on Anxiety and also the Yerkes–Dodson law which may be useful to you. --Tango (talk) 02:20, 4 May 2010 (UTC)

I think I wasn't very clear. One part of your brain learns the skill while the other part executes the learned skills. Anyways, it seems to be Procedural memory and messing up due to choking. I was able to get to them from muscle memory.--121.54.2.188 (talk) 02:26, 4 May 2010 (UTC)

(edit conflict)Its probably closely related to concepts like working memory vs. short-term memory vs. long-term memory. The article The Magical Number Seven, Plus or Minus Two specifically discusses on theory of Working memory and also contains some great links to related articles. I think there is a specific term related to this sort of performance-learning connection. As a teacher, you'd think I remember the term. I'll do some digging and get back to you. --Jayron32 02:22, 4 May 2010 (UTC)

The article Procedural memory also discusses learning procedures and processes, and the normal way in which procedures are learned. May offer some insight into the OP's question. --Jayron32 02:27, 4 May 2010 (UTC)

How long does that 'one part of the brain' learns? —Preceding unsigned comment added by 125.21.50.214 (talk) 11:38, 5 May 2010 (UTC)

Molar mass of Aluminium

What is the molar mass of Aluminium? Thanks in advance, --The High Fin Sperm Whale 01:45, 4 May 2010 (UTC)

It is in the article, in the infobox, under the title "Standard atomic weight". --Jayron32 01:59, 4 May 2010 (UTC)

dumbest idea in the world

So this has to be the dumbest idea in the world, but please confirm that it is. They have done various nuke tests in the desert where after the bomb goes off, the sand underneath is fused into glass, maybe dozens of feet thick. The dumb idea is: what if they do that underwater, as a way to seal the burst oil well in the gulf of Mexico? Would it exchange one environmental catastrophe for another? Radiation, tsunamis, etc.? Test ban treaty issues? There was at least one deep-water test in the 1950's (Operation Wigwam) whose effects weren't all that severe. 69.228.170.24 (talk) 01:57, 4 May 2010 (UTC)

Would the explosion fuse the sand into glass, or would it rupture the entire oil deposit, and send the entire contents of the deposit into the sea instantly, making the situation MUCH worse. Its a nice line of thinking, but beware of unintended consequences. --Jayron32 02:01, 4 May 2010 (UTC)

I think most of the heat would go into evaporating the water, rather than melting the sand. --Tango (talk) 02:06, 4 May 2010 (UTC)

Controlled frac is done all the time during drilling and enhanced oil recovery. It never needs nuclear weapon sized explosions. Most of the time, just pumping saltwater or steam down the bore is sufficient to frac the entire formation. In some cases, chemical frac (chemical fracture) is used - e.g., injecting an acidic drilling mud to intentionally break up the reservoir rock. Frac often increases permeability, rather than decreasing it - though the geomechanics is very complicated and depends on the circumstances. See, e.g., Hydro Frac at the Schlumberger oilfield glossary. Blowing stuff up in the borehole will more likely increase fluid flow; but there's a possibility of plugging the hole. Remember also that there's a pressure gradient - the oil is flowing up because it is at higher pressure than the water (and the rock) above it. That is why it blew up in the first place. Nimur (talk) 02:23, 4 May 2010 (UTC)

FYI the technical term for intentionally plugging the well to stop fluid flow is "bridging" the borehole. Nimur (talk) 02:32, 4 May 2010 (UTC)

You might find this article a good description of the likely consequences. Clear skies to you 67.170.215.166 (talk) 02:48, 4 May 2010 (UTC)

I can't believe I forgot to link to Completion (oil and gas wells). This is the term for the general set of techniques to manage a well, including casing, cementing, safety valves, and so on. I don't believe any completions use explosive of any type. Most use downhole tools and careful control of fluid/mud pumping. Nimur (talk) 14:39, 4 May 2010 (UTC)

Apparently it's not such a dumb idea, because if this article can be believed, the russians actually used nukes 5 times to seal leaks. Ariel. (talk) 19:59, 4 May 2010 (UTC)

For what it's worth, the article is from the Komsomolka, which is every bit as credible as our own National Enquirer. 67.170.215.166 (talk) 01:46, 5 May 2010 (UTC)

The U.S. government in 1964 proposed to use a series of nuclear explosions in Missisippi to excavate the "Divide Cut" portion of the Tennessee Tombigbee Waterway. These would have been excavation explosions of hydrogen bombs, which would have created ground shock waves and air blast as well as radioactive fallout according to the book cited. The Corps of Engineers at the time said there would be "[no fallout or radiation problems" because the explosions would be underground. This was part of "Plowshare," a program for the peaceful use of atomic energy, in which the U.S. government also proposed to set off nuclear explosions to dig harbors. Trying to seal up an oil leak a mile below the surface far out in the ocean sounds way more acceptable. Edison (talk) 19:46, 5 May 2010 (UTC)

It also requires a lot more precision than you get from your typical nuke -- as Jayron correctly pointed out, this method is more likely to actually make the leak worse. 67.170.215.166 (talk) 00:42, 6 May 2010 (UTC)

refrigerating foods

I have heard from some people that refregerating some foods spoil them.Is it true?amrahs (talk) 04:24, 4 May 2010 (UTC)

Never heard that before. See Refrigerator for details. There are some issues, such as freezer burn if meat is not packaged properly before freezing. Additionally, if the fridge is not cleaned properly, food may become contaminated through a process known as "cross contamination". But a properly maintained fridge and/or freezer should be perfectly safe for all foods, so long as the foods themselves are properly packaged before storing. --Jayron32 04:39, 4 May 2010 (UTC)

Actually, some foods will indeed spoil, not in the sense of becoming contaminated or rotten but in the sense that they will turn into something I wouldn't want to eat. Bananas, for instance become pretty disgusting when placed in the refrigerator. Dauto (talk) 04:45, 4 May 2010 (UTC)

Generally speaking, foods with a high water content (like bananas) are susceptible to "freezer burn" -- since water expands on freezing, any ice crystals that form tend to burst the cell membranes and thus degrade the food item's texture. Likewise, if frozen items (like ice cream) are thawed and then refrozen, large ice crystals can form that degrade the texture. In both these cases, however, the items involved are still safe to eat (though less appetizing). Foods made from grain, though, tend to have a different problem if refrigerated -- since they have very low inherent moisture content, they tend to exhibit hygroscopic tendencies at near-freezing temperatures, which makes them soggy and also could promote mold growth. (Incidentally, I store bananas in my fridge all the time, and I hardly ever observe any degradation in texture from it.) FWiW 67.170.215.166 (talk) 04:57, 4 May 2010 (UTC)

Correction: the phenomenon I described where ice crystals burst the cell membranes is not the same as freezer burn -- the latter is caused by dehydration from contact with the air. 67.170.215.166 (talk) 05:01, 4 May 2010 (UTC)

Not really refrigeration as much as freezing but an interesting fact is the founder of the modern method of freezing food was Clarence Birdseye, founder of the Birds eye company. Until I discovered this I always assumed "Bird's eye" was just a arbitrary name. Vespine (talk) 05:52, 4 May 2010 (UTC)

Potatoes and other foods that are rich in starch will go off faster in a 'fridge than at room temperature. The temperature promotes the conversion of starch to sugar. CS Miller (talk) 11:08, 4 May 2010 (UTC)

Not correct. Warmth drives the starch to sugar conversion, not cold; cold temperatures put the spud into hibernation. Potatoes actually have a longer shelf life when kept near 0C (Please don't just take my word for it, but I do work in a huge foodservice distribution centre where we routinely have to store hundreds of different products to maximize shelf-life.) The problem with taters in the fridge is that they are not kept uniformly chilled; every time you open the door, you introduce more warm air and humidity and this fluctuation is what kills the spuds. If you have potatoes that you're planning on using, keep them cool, dry, and dark - slightly less than room temperature if you can. If you want to keep them for more than a couple of weeks, keep them cold, dry, and dark (you know, like in a root cellar), just let them warm up before you try to make fries with them.

It doesn't have anything to do with starch to sugar conversion, but certainly breads and other baked goods don't keep as long cool. Refrigerating breads causes them to go "stale" faster. (Staling in breads has more to due with rearrangement/recrystallization of the gluten network, rather than drying out per se.) Freezing baked goods, on the other hand, doesn't have the same problem. Cookwise and Bakewise by Shirley Corriher are good reads, if you are interested in the topic. -- 174.21.225.115 (talk) 15:25, 4 May 2010 (UTC)

You're right, placing fruits and vegetables that are grown in warm regions into the fridge damages them. It is due to their plasma membranes being susceptible to chilling. Basically the membrane stops being a fluid and turns into a gel, this creates holes in the membrane allowing the cell contents to mix. This is obvious with bananas as they go black but it also happens with tomatoes (and others - not sure which). It's not due to ice crystals forming as 67.170 says. Temperate fruit + veg are used to the cold and so are preserved by the fridge - their membrane lipids are less saturated and longer, so the Van der Waals forces between the lipid tails are weaker and the membrane remains fluid and intact at lower temperatures. 131.111.30.21 (talk) 12:34, 4 May 2010 (UTC)

See Banana#Storage_and_transport - it might only be when they are unripe that the fridge damages them. Also see Tomato#Picking_and_ripening - they remain edible but lose their taste when refridgerated. 131.111.30.21 (talk) 12:41, 4 May 2010 (UTC)

Chilling also causes decreased binding of ethene to its receptor, thereby slowing down ripening as well ([9]). It looks like this may also be the same in tomatoes. 131.111.30.21 (talk) 12:56, 4 May 2010 (UTC)

Note - "if frozen items (like ice cream) are thawed and then refrozen, large ice crystals can form that degrade the texture. In ...these cases, however, the items involved are still safe to eat" - is not true.

"The third and most important reason not to refreeze is increased risk of spoilage due to microorganisms. Many people thaw food by letting it sit at room temperature for several hours, giving the microorganisms in it time to get busy and partially spoil the food before it's refrozen. The problem is particularly pronounced in large pieces of meat such as a turkey, some parts of which may be at or near room temperature for hours during thawing. That's why turkeys should be thawed in a sink filled with water--the water equalizes the temperature and makes for faster thawing. Alternatively, you can thaw in the refrigerator, which is slower but retards spoilage by keeping the meat cool. Even so you're likely to have some multiplication of microorganisms. If you refreeze and rethaw, you've subjected the food to double the microorganism growth and double the fun.

If you must refreeze food that has been thawed in a warm place (or which has remained thawed in a cold place for a long time), you should cook the food properly first, then refreeze it. Even under the best circumstances, however, multiple freezing cycles aren't recommended. If you can't finish the food yourself, you're better off giving it to your household garbage disposal--ideally the one that barks or meows."[10] Exxolon (talk) 16:06, 4 May 2010 (UTC)

Ice cream that's been allowed to warm to a few degrees above freezing and then refrozen is no more dangerous than the food in your fridge. Clearly warmer is worse than colder (up to room temperature) but lets be reasonable. Rckrone (talk) 16:27, 4 May 2010 (UTC)

"Refrigeration" is not the same as "freezing." The OP did not ask about the freezer. Bananas turn dark quickly in the refrigerator, but refrigeration is claimed to leave them edible longer[11]. Some books claim that refrigerating tomatoes [12] and avocados [13] adversely affects the flavor and texture . A refrigerator is kept in a range of perhaps 34 to 38 degrees F (1-3 C). A freezer might be at 0 degrees F( -17C).A "self-defrosting" freezer causes worse freezer burns than older manual defrost ones, because of the low relative humidy needed to remove the frost from the walls. Edison (talk) 21:11, 4 May 2010 (UTC)

Tomatoes and bread are two things that tend to suffer from refrigeration -- tomatoes turn mealy, and bread dries out. Looie496 (talk) 00:55, 5 May 2010 (UTC)

Older refrigerators, before the "self-defrosting/no-frost" feature became so common, had higher humidity and baked goods, lettuce, etc did not dry out so quickly. An ice box was probably even better at keeping a high humidity in the refrigerator. Edison (talk) 19:33, 5 May 2010 (UTC)

Air navigation

What is an aperiodic compass, and how does it work? I've seen it mentioned by both Amelia Earhart and Charles Kingsford-Smith in their writings, but neither of them explains in any detail how it works or what advantages it has (if any) over an ordinary magnetic compass, Earth inductor compass, directional gyro or any other such device. Also, is it still used for navigation, or has it been completely replaced by other devices? Thanks in advance! 67.170.215.166 (talk) 05:12, 4 May 2010 (UTC)

Aircraft are very different to ships in that they can change heading rapidly, so ideally an aircraft compass can retain a reasonable degree of accuracy during a turn, without excessive overshoot. Prior to development of the gyroscopic compass, many aircraft were equipped with a magnetic compass specially developed for use in aircraft. This was more complex than the simple magnetic compass used for surface navigation. It was called the aperiodic compass. There is some good information available HERE. In modern aircraft the magnetic compass is used primarily as a back-up for the gyroscopic compass, and to ensure the gyroscopic compass is correctly aligned. Consequently, in modern aircraft the magnetic compass is simple and inexpensive because it is not relied on when maneuvering.Dolphin (t) 05:49, 4 May 2010 (UTC)

I wouldn't call the magnetic compass a "backup". It's the reference for the gyro, which has no sense of direction of its own. The gyro is set to the mag compass on the ground, and checked periodically when it level flight. It is, as you say, used for navigation and maneuvering, because it's easier to read and interpret that the mag compass. PhGustaf (talk) 06:19, 4 May 2010 (UTC)

So essentially it's a magnetic compass with an advanced magnetic damping system that prevents oscillation and overshoot (but also makes it lag behind the aircraft when maneuvering); and there's no longer any need for it because the gyrocompass is the primary instrument when maneuvering. Thanks for the info, and clear skies to you! 67.170.215.166 (talk) 06:14, 4 May 2010 (UTC)

I wasn't clear. All the gyro can do is point the same way all the time, with a little drift and precession. It has no idea which way is north. So the pilot sets it so it's pointing North, or whatever direction the magnetic compass says. The mag compass is the primary direction reference. The gyro has a bigger dial and is easier to interpret if the aircraft is turning, because is isn't sensitive to second-order issues, as is the mag compass. You mostly watch the gyro and check every so often to make sure it agrees with the mag. PhGustaf (talk) 00:26, 5 May 2010 (UTC)

I would imagine magnetic compasses on aircraft these days are electronic, e.g. using flux gates or other such devices. 69.228.170.24 (talk) 20:23, 4 May 2010 (UTC)

Could be. My pilot's license dates from 1976, and I might have missed stuff since. But even a plane with a flux gate compass would surely have a mag compass along: it doesn't weigh much, works even when the electric system fails, and doesn't break often. Modern pilots use GPS a lot. PhGustaf (talk) 00:26, 5 May 2010 (UTC)

It isn't correct to imagine that modern magnetic compasses in aircraft are electronic. If a modern general-aviation aircraft has a magnetic compass it will only be for orienting the gyroscopic compass. It wil be of the basic variety as used in boats, not even an aperiodic one. (Modern aircraft of the highly sophisticated jet-powered variety are likely to have no magnetic compass. Modern Inertial Reference Systems, GNSS and area navigation systems render the humble magnetic compass redundant.) Flux gates are linked to the gyroscopic compass to keep it aligned correctly - they are not linked to the magnetic compass.

Back to the original question. I believe the word aperiodic was intended to refer to the expectation that the compass needle would not follow the aircraft as it maneuvered but would remain accurately in the north-south alignment. Dolphin (t) 01:33, 5 May 2010 (UTC)

That is what Dolphin51's link says. According to it, an aperiodic compass is a magnetic compass like a ship's compass, but with better damping to keep the needle from swinging erratically.

As for highly sophisticated jet aircraft having no magnetic compass and instead relying exclusively on R-NAV, personally I find it extremely disturbing -- what if there's a total electrical failure? Or if lightning strikes the plane and fries the electronics? On some aircraft, all electronics are powered by engine-driven generators without any battery backup worth the name, so if there's a double-engine failure then all the electronics fail too and the pilot has no way to determine his/her heading. Didn't the Air France disaster teach the designers anything? It's high time that the pilots got together and demanded more stand-by instruments in the cockpit as well as full manual backup for all the primary flight controls! 67.170.215.166 (talk) 02:00, 5 May 2010 (UTC)

The magnetic compass on a 747

Relax. Of course modern aircraft have magnetic compasses -it part of the CIAA regulations. For instance: Smith's Industries used to make many of them and SIRS has taken over.[14]. Look on WC and you'll see them on other aircraft types. A peculiarity of the magnetic compass, that has not been mentioned yet, is acceleration error. Meaning: that when the compass is acceleratingly, the rose tilts up and towards the nearest pole. Decelerating the effect is reversed. Anyone who has a magnetic car compass will be very familiar with this. Reading a magnetic compass (on an aircraft) in unstable air to maintain a steady course can therefore be a trying exercise. --Aspro (talk) 09:14, 5 May 2010 (UTC)

Good, at least they're not totally oblivious to the need for low-tech backups for all them high-tech gadgets. Whew! As far as acceleration error, I'm actually perfectly aware of that -- it's prob'ly one of the big reasons why the DG is the primary heading reference and the magnetic compass is used only to reset the DG. Which leads me to my second question: would an aperiodic compass be less susceptible to acceleration error because of its heavier damping, or does it not make a significant difference? 67.170.215.166 (talk) 00:49, 6 May 2010 (UTC)

shadows, mirror images?

Are shadows mirror images? Are they superimposable? At times, i noticed the images of shadow and mirror being alike, for ex.: a word printed on a glass shows shadow (behind the glass)similar to that of the original (not reversed) and similar image is also seen when a mirror is placed behind the glass on which the word is written. Hope i am clear..- anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 05:15, 4 May 2010 (UTC)

No, shadows are caused by an object blocking light rays, while a mirror image is caused by light rays reflected from the object being reflected a second time by the mirror. FWiW 67.170.215.166 (talk) 05:36, 4 May 2010 (UTC)

Regarding your second question, shadows are not actual things. A shadow is a place where there is less light - but it isn't no light at all. There is still some light, but less. If you have a second shadow on top of the first, then you have even less light then before. Ariel. (talk) 06:17, 4 May 2010 (UTC)

If you're facing the writing on the same side as the light source, the shadow looks "normal" (i.e. you can read it easily). The mirror on the other side of the glass shows you the mirror image of the other side of the writing (i.e. the inverse of the inverse) so it looks the same as the shadow. This doesn't mean that the shadow is a mirror image - but in this case they are superimposable. Hope this helps. Zain Ebrahim (talk) 13:07, 4 May 2010 (UTC)

FORTRAN Programming (Lahey Compiler)

I am trying to run one old fortran program (1980's). I compiled it using Lahey Compiler and i removed all errors and warnings. It is not running properly, if i give some print or write commands at some particular locations in some subroutines, it starts running. I am not able to understand without making any change in the code how is it running just due to some print or write commands and the results are still some what away from expected.203.199.205.25 (talk) 07:12, 4 May 2010 (UTC)

You will probably find a more receptive audience at WP:Reference desk/Computing. I suggest you delete your message from the Science Reference Desk and paste it into the Computing Reference Desk. Dolphin (t) 08:16, 4 May 2010 (UTC)

Cross-posted at Computing desk. Nimur (talk) 12:14, 4 May 2010 (UTC)

is it HF that kills? or F-?

I'm a little confused by the articles. Is F- toxic because it can form HF, or is HF toxic because it can form F-? Ignoring acidity, which is the more toxic species here? Is it because F- is a potent nucleophile, or binds with Ca2+ to form calcium fluoride? John Riemann Soong (talk) 07:26, 4 May 2010 (UTC)

It looks like the F- reacts with the Ca++ to form CaF2, but the H+ in the HF seems to function as a carrier ion (it carries the acid into the skin); even though any F- (or fluorine gas) is toxic in itself. --Chemicalinterest (talk) 11:05, 4 May 2010 (UTC)

see Fluoride#Toxicology F- is 'mildy toxic' and poisonous by hypocalcemia at relativly high doses. Hydrogen fluoride causes burns - in addition to any toxicity caused by flouride present.

In both cases the 'solution' is Ca2+ ions (ie as calcium gluconate / hydroxide / chloride) to precipitate F- as CaF2.

HF is more toxic because it both burns and poisons.77.86.70.220 (talk) 11:35, 4 May 2010 (UTC)

Is fluoride really a potent nucleophile? It holds on to its electrons tightly, so I don't think it's very happy to donate them to electrophiles.

Ben (talk) 00:17, 5 May 2010 (UTC)

The peculiar thing about F- is that although it indeed holds on tightly to its electrons, it has a high charge/size ratio because of its small size, which causes it to bind irreversibly to both calcium and magnesium to form insoluble salts. Living cells can't function without either, so they die off. This is why HF can cause such deep burns -- it soaks into the skin due to the action of the H+ ion, and the F- ion then kills the cells by precipitating the calcium. (Which is why the folks at our alkylation unit have to wear neoprene coveralls at all times while on duty.) 67.170.215.166 (talk) 02:08, 5 May 2010 (UTC)

An additional effect is that HF isn't a strong acid, so it doesn't necessarily cause serious "acid burns" (only 1-2 pKa units stronger than acetic acid I think). But because it's not highly ionic, it would be more able to penetrate skin and other water-tight membranes. So the H+ assists getting the HF in, where F- then can do some serious damage. Glacial-acetic poured on your hand? Wash it off right away, will be red/itchy for a few hours. Dilute HF few drops on your hand? You're in for a world of hurt for a long time. DMacks (talk) 02:18, 5 May 2010 (UTC)

A few drops of dilute HF wouldn't cause a serious burn, provided that you wash it off promptly with soap and water. It's the concentrated stuff (such as what we use at the refinery) that can kill you or burn you to the bone (yes, even a few drops of concentrated HF can burn you down to the very bone, I'm not kidding). Not to mention that concentrated HF can also give off poison gas when exposed to moist air. 67.170.215.166 (talk) 04:39, 5 May 2010 (UTC)

Is it maybe a mix of effects? Someone said that you need high doses of Na+ F- to get poisoned. So why does a few drops of HF hurt so much? It looks that HF is a good skin-soluble acid, so after F- binds calcium or magnesium, maybe the remaining H+ protonates bicarbonate buffer to form carbon dioxide? I mean I've spilled 1M HCl solution on myself before ... it didn't burn at all, except for a mild sting(I washed it off within 10-15 seconds). I assume HF would be way less acidic. John Riemann Soong (talk) 04:47, 5 May 2010 (UTC)

It's the skin permeation and cellular toxicity that cause it to hurt so much. HCl just attacks your skin by acid-catalyzed protein hydrolysis, and human skin is pretty resistant to that (especially the skin of an amateur chemist). HF, on the other hand, soaks into the skin and kills the living cells underneath by calcium precipitation, and it is this destruction of living cells that causes deep, painful burns (sometimes even to the very bone, as I said before). It's all the difference between scraping your skin on rough concrete vs. falling on some punji stakes. In the first case (concrete/HCl) only the outer layer of skin is damaged, whereas in the second (spikes/HF) there's damage to the underlying tissue (which hurts a whole lot more). 67.170.215.166 (talk) 05:09, 5 May 2010 (UTC)

It seems that ingesting 1 mmol of NaF would be worse than spilling 1 mmol of HF on your skin. Apparently it's the other way round. But wouldn't 1 mmol F- have the same effect, regardless of counterion? John Riemann Soong (talk) 17:54, 5 May 2010 (UTC)

Yes. 1 mmol F- would have the same effect, but the H+ ion has certain properties, such as ability to penetrate skin and put the F- ion into your system. Na+ ion does not have any toxic effects generally. For example, HNO₃ is much more reactive than NaNO₃. One can oxidize copper quite easily, while the other one can only with difficulty (or not at all). The "carrier" ion has an effect on toxicity, too. --Chemicalinterest (talk) 18:22, 5 May 2010 (UTC)

Are Kepler's laws rigth?

Hi, I hope this is the rigth corner to open this discussion.So I copy-pasted my former talk from other wikicorners.I claim:

Planetary orbits are not elliptical,but spiraled,with the Sun at the barycenter.Newton's universal attraction force formula F=G*M*m/r^2 gives the masses a tangential velocity so that each masses have to orbit one around the other (attraction force=centrifugal force). This tangential velocity Vp is constant:Vpm for m and VpM for M until the masses reach to the barycenter.Kepler says the contrary. According Kepler the tangential velocities are variable and the areal velocities are constant.But,when you draw the polar graph of two bodies you find, according Newton's F*dt=m*dV,the motion's equation r=-a*t*(t-tmax) which shows no sign of ellipse.No ellipse,no focus,no aphelion,no perihelion,nor equality of swept out areas in equal interval of time.Consider Nasa's photos of the galaxies: you will see the spiraled orbits of celestial bodies.Newton does not confirm Kepler; except for period's law (P1/P2)^2=(r1/r2)^3 which is valid only and only for circular orbits.Does Kepler has changed his reasoning;(elliptical orbits in 1609 and circular orbits in 1618)? Yes.He wanted to say, the elliptical orbits will be transformed to circular orbits with time.How does a solid elliptical shape could be transformed to circular shape,unless the orbits are not elliptical? This is possible when the orbits are spiraled: expanding and then compressing, billions of spirals. TASDELEN (talk) 07:35, 4 May 2010 (UTC)

Think about conservation of energy and see how your proposal fits in. Graeme Bartlett (talk) 10:22, 4 May 2010 (UTC)

Kepler's laws are simplified, empirical observations that are valid to a certain level of accuracy for certain cases that are valid to describe planet-like orbits. I don't follow your description about spirals; but in any case, there are other types of orbit, including non-elliptical orbits (such as those of a non-returning comet, or the orbit of a ballistic missile, which intersects the planet it orbits). These cases require mathematical treatments using the more general laws of Newtonian gravitation (and eventually, general relativity's even more complete description of gravitation). Your polar-form equation of planetary motion is not correct in the general case - I'm not sure where you got that equation from, but it looks kind of like an equation for a parabolic orbit - only one of many possible paths. Kepler's laws are applicable only if the orbit is closed and unperturbed. Our articles are extraordinarily descriptive of all possible cases. Nimur (talk) 12:22, 4 May 2010 (UTC)

TASDELEN, you are mistaken. Kepler's laws are completely consistent with Newton's law's within the "two body problem" approximation - That is, provided any pertubations introduced by other planets are negligible. Dauto (talk) 14:40, 4 May 2010 (UTC)

Science can not prove that something is true. All that it can say is that is has not been disproved. Googlemeister (talk) 14:23, 5 May 2010 (UTC)

Coefficient of drag at hypersonic speeds

Hi,

I was wondering how C_D varies with Ma at hypersonic speeds? Must graphs of C_D I have seen only go up to Ma 2.0, I'd like to know how it varies up to Ma 20 (eg what the Falcon Hypersonic Technology Vehicle experiences). Thanks! --58.175.32.19 (talk) 08:36, 4 May 2010 (UTC)

At hypersonic speeds, the linear model described in drag coefficient is totally inapplicable, so there's no real need for these charts. The shape and geometry become significantly more important than the total effective surface area. This is why an aerospike reduces drag, even though it adds surface-area exposed to the fluid flow. Consider this paper, Numerical Solution of the Hypersonic Viscous Shock-Layer Equations (AIAA, 1970). Nimur (talk) 11:31, 4 May 2010 (UTC)

Newton's cradle question

I recently bought an inexpensive Newton's cradle. Much to my dismay, it is not operating as nicely as I had expected. When the outside ball hits the remaining four, the middle three do not stay perfectly still, they wiggle quite a lot - and very quickly start swinging back and forth. This causes the motion to deteriorate very quickly. If I start by putting two balls into motion, it is even worse. Are there any simple adjustments that can be done to improve it? Thanks, decltype (talk) 10:19, 4 May 2010 (UTC)

Make sure that the row of balls is precisely in a straight line. Should be able to adjust the supporting cords. Graeme Bartlett (talk) 10:24, 4 May 2010 (UTC)

Also make sure that the surface on which the cradle sits is completely level. caknuck _° needs to be running more often 05:15, 5 May 2010 (UTC)

Curvy tunnel

On Balfour Beatty's website there is a tunnel image http://www.balfourbeatty.com/bby/segments/business-intro/ - ( Image url ) can anyone identify what project this is from, and what the tunnel is for?

More importantly - can someone explain why the tunnel is so crazily curved - is this trick photography or real. Thanks. Sf5xeplus (talk) 10:59, 4 May 2010 (UTC)

Balfour Beatty's website gives a contact e-mail address. Have you tried asking them about the tunnel? Cuddlyable3 (talk) 12:05, 4 May 2010 (UTC)

No I haven't contacted them.Sf5xeplus (talk) 13:41, 4 May 2010 (UTC)

The convoluted nature, the lack of a flat foor, and the diameter, would suggest it was for carrying water. It looks like a pipe inside a hydroelectric power plant, or a pumped storage plant like Dinorwig Power Station. These typically feature wire-bore tunnels for water to pass through, either for power generation or as part of the overflow system (see these pictures for the Hoover Dam's overflow tunnels). That said, every tunnel of that nature I can find pictures of has a smooth surface (either concrete or stone). Balfour Beatty does just that kind of business, but then they do lots of large civils in general. -- Finlay McWalter • Talk 14:17, 4 May 2010 (UTC)

I was wondering about sewage (google images show some similar page 4 and 5 - but most are smooth) - The shape doesn't make a lot of sense - appears to be a S bend followed by a turn to the right - more suitable for a water slide - anyone think the image has been distorted? Sf5xeplus (talk) 15:03, 4 May 2010 (UTC)

I'd suggest that it's the pedestrian part of an underground railway station, without the floor. Bank Underground station has at least one tunnel which is essentially the shape shown, with a staircase on the bit that's not horizontal. AlexTiefling (talk) 00:13, 5 May 2010 (UTC)

Addendum: although I can't be certain, I'd suggest that it might be the new access tunnel leading to the Northern Line platforms at Kings Cross St Pancras. AlexTiefling (talk) 00:34, 5 May 2010 (UTC)

Thanks, a passenger access tunnel makes much more sense. Sf5xeplus (talk) 08:50, 5 May 2010 (UTC)

Gloria Allred

Question moved to Wikipedia:Reference_desk/Miscellaneous#Gloria_Allred

substitute for peanut butter

I initially became a big nutritional fan of peanut butter when I read that it had no cholesterol and twice the protein of calves liver. Boy was I excited - peanut butter the perfect food. Then I started gaining weight only to realize 40 lbs later that even though peanut butter had no cholesterol it had plenty of fat. Not only did it have fat but it had saturated fat but alas I could not stop eating the stuff because I also loved the taste. Now my doctor says stop eating peanut butter or die so I have to find a substitute. What tasty treats with unsaturated oil can I find that will take the place of squshed gubbers? 71.100.1.71 (talk) 15:52, 4 May 2010 (UTC)

ask your doctor. Dauto (talk) 15:56, 4 May 2010 (UTC)

I did and he said that for a longer list to consult the Wikipedia. —Preceding unsigned comment added by 71.100.1.71 (talk) 15:58, 4 May 2010 (UTC)

All right then. Here's my suggestion: Eat more fruits and vegetables andexercise more frequently. Dauto (talk) 16:17, 4 May 2010 (UTC)

While finding an unsaturated fat alternative is probably better, the real problem here is that consuming excessive fat whether it's unsaturated or saturated is likely to increase your weight, simply because fat's energy density is so much higher than protein/carbs. You need to find an alternative that's both lower in saturated fat and lower in calories! Exxolon (talk) 15:59, 4 May 2010 (UTC)

The calorie thing is under control by limiting myself to 11 grams of peanut butter per meal (3 meals per day) for a diet plan of 21% fat, 67% carbs and the rest protein. So what unsaturated substitutes do you suggest? 71.100.1.71 (talk) 16:12, 4 May 2010 (UTC)

Typing the words "peanut butter substitute" into Google returned this search result: [15]. There's lots of options. --Jayron32 16:18, 4 May 2010 (UTC)

LOL... I told my doctor that when I asked the Wikipedia they said to Google. 71.100.1.71 (talk) 17:19, 4 May 2010 (UTC)

I was surprised to find almost instantly a link to waht is being called "soynut butter". I guess this idea already took off due to peanut butter "allergy's". 71.100.1.71 (talk) 16:55, 4 May 2010 (UTC)

• However, in comparing the labels of great value brand peanut butter and peanut free soynut butter the soy actually fairs worse with 14% instead of only 10% saturated fat and 4 grams of sugar instead of only 3. 71.100.1.71 (talk) 17:12, 4 May 2010 (UTC)

Why the " " on "allergys"? 86.178.228.18 (talk) 21:20, 4 May 2010 (UTC)

You eat peanut butter with every meal? One of the key features of a good diet is that it be varied, otherwise it is easy for it to be deficient in something (there are plenty of nutrients that you only need a small amount of but that aren't in all foods, eating lots of different foods means you will probably be eating at least one with each of the essential nutrients in it). --Tango (talk) 17:30, 4 May 2010 (UTC)

Ignoring the obvious problems involved with a diet high in any fat, I personally enjoy SunButter. It has multiple varieties, which are more or less similar in taste to a comparable type of peanut butter. That said, it still has saturated fat, about 2/3 the amount in peanut butter. And its overall fat content (saturated plus unsaturated) is close to peanut butter. —ShadowRanger ^(talk|stalk) 17:17, 4 May 2010 (UTC)

To be clear, there are a whole lot of varieties of SunButter, and the similarity to peanut butter varies. Natural Crunch is the only one I buy regularly (I like crunchy over creamy), and it's a very close match (a little sweeter and less oily to my taste). I can't say how close the other varieties are to their equivalent peanut butter. Also, if I didn't make it clear, the primary ingredient in SunButter is sunflower seeds plus some sugar. —ShadowRanger ^(talk|stalk) 17:20, 4 May 2010 (UTC)

I suggest you try either "organic" or "natural" peanut butter. In both cases they won't contain the added trans-fats, which make it creamy, and will have somewhat lower saturated fats, too. Without that it will separate and need stirring, but that's a small price to pay for avoiding trans-fats. You might wonder why the label says 0 trans fats on traditional creamy PB. They just keep the amount low enough that they are allowed to "round down" to zero. In the US, anything under 0.5 gram can thus be classified as 0, even though getting that much trans fat in every serving is unhealthy. Look for partially and/or fully hydrogenated vegetable oil in the ingredients, that means they added trans-fats. StuRat (talk) 17:33, 4 May 2010 (UTC)

As a side note yes I am aware of the round down problem which Congress can eliminate by requiring all nutrients be stated as grams per 1000 versus grams per serving and then let the customer do the serving math. 71.100.1.71 (talk) 18:54, 4 May 2010 (UTC)

Focusing on saturated fat for weight loss is simply wrong. It won't help in the slightest. Saturated far affects cardiovascular health, but not weight. And switching to unsaturated fat for cardiovascular health is also wrong. Because the ratio of the various types of unsaturated fat matters (the various Omega types) too. And cutting fat out entirely won't help either, because aside from being bad for you because you need essential fatty acids, carbohydrates can be converted into fat by the body. If you really do want to fix your health then for starters stop eating sweetened peanut butter, switch to unsweetened (it's harder to find though). Second stop eating a lot of any one food. There are some foods that historically have worked as the main source of calories (staples), but most are not suited for that. Ariel. (talk) 19:44, 4 May 2010 (UTC)

Even with lots of available variety, the problem of staples is taste. People have a tendency to eat over and over again only the tastes they like. 71.100.1.71 (talk) 20:20, 4 May 2010 (UTC)

My 2 roommates and I consumed 40 pounds of peanut butter one school year in college. So I consumed about 6 kilograms, or 40,000 calories, or 190 servings in 223 school days, and that seemed like a lot at the time, but we really never got tired of it. Peanut butter is the most caloric portion of a PBJ: 190 calories in a serving of peanut butter, 140 in 2 slices of white bread, and 50 in a serving of preserves, 380 total.Calories vary with variety and quantity of ingredients. Edison (talk) 19:28, 5 May 2010 (UTC)

Meteorological deposition of carbon dioxide snow or frost

Seeing as the coldest temperatures on earth (eg Vostok Station) are often well below the freezing point of carbon dioxide, do these areas see deposition of solid carbon dioxide from the atmosphere, such as CO2 snowfall or frost? If not, why not? —Preceding unsigned comment added by Btxtsf (talk • contribs) 16:39, 4 May 2010 (UTC)

The CO2 content of the atmosphere (around 0.05%) is so low that the snow probably would be unnoticeable. And the size of the miniscule amount of CO2 would decrease much more when solidified, since solids are generally smaller than gases. --Chemicalinterest (talk) 16:51, 4 May 2010 (UTC)

But, on the other hand, you get very little traditional snow there, due to the low water vapor content in the air, so any dry ice would therefore be a larger component of the total. An interesting Q, I wonder if you can easily tell the difference between the two. StuRat (talk) 17:45, 4 May 2010 (UTC)

An easy way to tell the difference: water snow feels wet in your hand, CO₂ snow doesn't. Clear skies to you 67.170.215.166 (talk) 02:13, 5 May 2010 (UTC)

I'm assuming the reason the massive block of CO₂ ice I touched felt wet was because of the condensation of the water vapour in the air nearby, then? Vimescarrot (talk) 06:00, 5 May 2010 (UTC)

Yeah, that's right. 67.170.215.166 (talk) 00:55, 6 May 2010 (UTC)

Another way to tell the difference between ordinary snow and CO₂ snow is to squeeze a handful in your glove -- water snow sticks together into a snowball, CO₂ snow doesn't, and also makes a whistling or shrieking sound when squeezed very hard. FWiW 67.170.215.166 (talk) 00:58, 6 May 2010 (UTC)

Fill a Teflon sample bag with CO2 and seal it and the Vostokians may see some, but otherwise no. As to the 'why'. That has already been answered elsewhere, so I'll just link to it.[16]--Aspro (talk) 17:49, 4 May 2010 (UTC)

Vostok Station is over 11,000 feet above sea level, giving an atmospheric pressure only about 2/3 of the sea level value. That's enough of a difference to drop the sublimation temperature of CO2 by at least a few degrees, meaning that the sublimation point has never been reached in recorded data even there. Looie496 (talk) 00:49, 5 May 2010 (UTC)

Chemical element lists

I'd like lists for the following:

1) The state of matter (gas, liquid, solid) of each of the 118 chemical elements at STP.

2) The names from which the chemical symbols are derived, for those which are not derived from the English name. For example, W = Wolfram = Tungsten.

I could eventually figure them out by reading all 118 articles, but I hope lists are already available. StuRat (talk) 17:53, 4 May 2010 (UTC)

List of elements by name, List of elements by boiling point, List of elements by melting point might help.--Stone (talk) 18:02, 4 May 2010 (UTC)

List of chemical element name etymologies should help with 2 ? —Preceding unsigned comment added by 77.86.70.220 (talk) 19:49, 4 May 2010 (UTC)

Just to note, you are only going to find state-of-matter information for about 100 or so of the elements. Many of the largest elements have only existed briefly as a very small sample, sometimes of as little as a few hundred atoms; far too small a sample to say anything reliable about its "state". --Jayron32 19:55, 4 May 2010 (UTC)

Also, the heaviest elements are either named after famous scientists, or not named at all yet. Clear skies to you 67.170.215.166 (talk) 02:16, 5 May 2010 (UTC)

Mercury and bromine are liquids. Fluorine, chlorine, oxygen, nitrogen and the noble gases (with the possible exception of ununoctium) are gases. Rubidium, cesium, probably francium, and gallium are liquids near room temperature. The rest of the elements that can be observed are solids.--Chemicalinterest (talk) 15:16, 5 May 2010 (UTC)

Na-Latin natrium, K-latin kalium, W-german wolfram, Fe-latin ferrum, Cu-latin cuprum, Ag-latin argentum, Au-latin aurum, Hg-latin hydrargyrum, Pb-latin plumbum, Sb-latin stibium These are names of elements whose symbols do not correspond. --Chemicalinterest (talk) 15:46, 5 May 2010 (UTC)

PhD programs and mental health

Can a PhD program be harmful to your mental health?--Mr.K. (talk) 17:57, 4 May 2010 (UTC)

Most academics would deny it, while a lot of PhD students would say that they suffered mentally during their slave work like thesis.--Stone (talk) 18:04, 4 May 2010 (UTC)

I'm not sure that most academics would deny it. Most that I know (which is many) would say, "yes, of course." They might say it is worth it (they might not), they might say it weeds out the less fortified (but they might also think it weeds out the non-crazy, as well). Academics are surprisingly straightforward about how crappy their overall career system is, even if they at the same time are likely to be less straightforward about whether or not that implies that academia is not all it is cracked up to be. Just my anecdotal experience. --Mr.98 (talk) 21:44, 4 May 2010 (UTC)

Can anything be harmful to your mental health? Yes. It is hard to attribute it specifically to a PhD program. Consider my PhD experience. I worked full time as a software engineer. I was raising two babies. I had to teach up 80 students (including grading homework and exams). I had to write not only a thesis, but also a readiness paper. I was also pestered with attending one symposium after another. Basically, I had about 30 hours of responsibility each day for about 3 years. So, did the PhD program cause mental health issues or was it the kids or dealing with idiots as a software engineer or dealing with students who claim their grandmother died three times each semester or simply never getting more than 4 hours sleep per day (and not 4 hours of continuous sleep)? I don't think you can blame the PhD program itself. It is an entire lifestyle that easily contributes to poor mental health. -- kainaw™ 18:11, 4 May 2010 (UTC)

There has been suicides of graduate students ,for example Jason Altom. How closely this is connected to his supervisor was disputed and will never be known.--Stone (talk) 18:14, 4 May 2010 (UTC)

As an addendum, I thought it important to point out that I believe my experience of three months of boot camp in the Marines was far easier than any particular 3 month period of my PhD program. It doesn't take much to mindlessly follow orders. However, being able to mindlessly do tasks until they are done does help a great deal when you have something like 80 programs to grade, each submission about 20 pages of source code, and you would much rather be doing anything else other than read through tons and tons of code that doesn't compile, doesn't make sense, and looks like random snippets of code pasted from various websites. -- kainaw™ 18:16, 4 May 2010 (UTC)

The answer is of course yes, as can school, the army, work etc... PhD's are notorious for their stress-levels (not for everyone of course) - WP:OR and it's quite suprising the percentage of PhD students who express a hate for their supervisor, or a deep unhappiness with the process..

In particular the transistion from primarily taught courses to self propelled is a factor, as it will be also the first experience for many of truly individual responsibility for their actions.

There's some results under http://www.google.co.uk/search?hl=en&ei=gXvgS5C3KJuTsQauqYzoBA&sa=X&oi=spellfullpage&resnum=0&ct=result&cd=2&ved=0CAYQvwUoAQ&q=phd+student+stress&spell=1 —Preceding unsigned comment added by 77.86.70.220 (talk) 19:56, 4 May 2010 (UTC)

One possible form of stress release for suffering grad students is write a comic strip. 69.228.170.24 (talk) 20:27, 4 May 2010 (UTC)

Yes, that is generalizable. (rolls eyes) --Mr.98 (talk) 21:44, 4 May 2010 (UTC)

Being in a Ph.D. program can be stressful, and stress can "harm your mental health." Being up for tenure can be stressful, too. Trying to get admitted to a good college can be stressful, as can trying to "do more with less" in the deliberately stressful environment of a large (or small) business, where years invested in a career can suddenly go "poof" due to corp reorg. I would expect that being in a modern war or occupation zone is rather more stressful. Being unemployed or underemployed is pretty stressful. I would not rate a PhD program as being the highest stress level I have encountered. Edison (talk) 21:05, 4 May 2010 (UTC)

You have to consider your initial susceptibility, general stress level, and lifestyle choices. If you're already inclined to depression or anxiety, for example, even the stress of high school or undergraduate university work might be enough to induce a full-on crisis. A person who is trying to juggle single parenthood, a full-time job, and graduate work is probably going to have a harder time of it emotionally than someone who has no major responsibilities and nothing else to do but concentrate on academic work. Knowing how to manage your time and how to de-stress yourself is an important factor. And making the right lifestyle factors is crucial, especially if you're already susceptible or stressed in the first place. Eat good healthy meals, get plenty of sleep, exercise regularly, have a supportive social network, and try to find time for things you enjoy, and you'll give yourself the greatest chance to get through a Ph.D. program - or college admissions or unemployment or almost anything else - with your sanity intact. 71.104.119.240 (talk) 01:08, 5 May 2010 (UTC)

Stress in a PhD student depends on many things, though I would say it is more related to the competitiveness of a field, the funding resources available, and most importantly, the political environment of the lab. Your stress will be greatly compounded by the latter. Life can be hell if your lab-mates are leeches or backstabbers and your supervisors are abusive or incompetent. It is likely that more labs have split or died due to politics alone than any other factor. However, if you work well, know your research field, having funding, and work in a relatively tame lab environment the stress is not that bad. Sjschen (talk) 15:07, 5 May 2010 (UTC)

HTPB

Our article on Hydroxyl-terminated polybutadiene says it is a polymer of butadiene terminated at each end with a hydroxide radical. So does the reaction to make it go like this?

nC₄H₄(OH)₂ → nH₂O + (C₄H₄O)_n

Also, do the all the C₄H₄ have oxygen between them? Thanks, --The High Fin Sperm Whale 19:20, 4 May 2010 (UTC)

The Os are at the end only (if in between it would be a polyether).

One synthesis uses hydrogen peroxide [17] US patent 5159123

The link probably has much of the answers you want.

The wikipedia article Hydroxyl-terminated polybutadiene incorrectly described it as a polyol - I've corrected that. —Preceding unsigned comment added by 77.86.70.220 (talk) 19:47, 4 May 2010 (UTC)

So do you use C₄H₆ and H₂O₂? --The High Fin Sperm Whale 20:10, 4 May 2010 (UTC)

Any radical initiator should work to start the polymerization reaction. --Jayron32 21:30, 4 May 2010 (UTC)

It needs to be convertable to OH - hence why H2O2 is used.77.86.70.220 (talk) 23:02, 4 May 2010 (UTC)

So are the bonds C-C? --The High Fin Sperm Whale 00:57, 5 May 2010 (UTC)

Yes they are. 67.170.215.166 (talk) 02:17, 5 May 2010 (UTC)

Clarification: the bonds in polybutadiene are a mixture of C-C (single) and C=C (double) bonds; what I meant was they're carbon-carbon bonds as opposed to carbon-oxygen. Clear skies to you 67.170.215.166 (talk) 03:58, 5 May 2010 (UTC)

Gravity

Let's imagine I'm riding my bicycle in a frictionless world. Taking into account the following:

a) If I'm riding forwards on a completely flat road, I'll have to fight no gravity force at all (exactly 0 g), since gravity only hinders upward movement.

b) If I try to ride up a 90º wall, I'll have to fight all of the gravity force (exactly 1 g), since all my efforts will be directed towards movind upward.

Therefore, if I am riding up a 18º climb, I'll have to fight exactly 0.18 g, and if I am riding up a 23º climb, I'll have to fight exactly 0.23 g. Is that correct, or is my reasoning flawed? If so, what is the mistake? Thanks.

Leptictidium (mt) 19:32, 4 May 2010 (UTC)

The first mistake, surely, is that if 0º = 0g, and 90º = 1g, then 18º = 18/90 rather than 18/100. --Tagishsimon (talk) 19:34, 4 May 2010 (UTC)

I think force due to gravity = mgsinθ might be of use here. sin 90 = 1 and sin 0 = 0, but sin(18) degrees is not 0.18 (it's closer to 0.3, I think). - Jarry1250 ^{[Humorous? Discuss.]} 19:36, 4 May 2010 (UTC)

Not sure where this line of questioning is leading, but no, you can't even ride a bicycle on a flat road without friction. DMacks (talk) 19:38, 4 May 2010 (UTC)

What about a rocket powered bicycle? A kite attachment? A gun to fire backwards? - Jarry1250 ^{[Humorous? Discuss.]} 19:41, 4 May 2010 (UTC)

The OP is missing the necessary trigonometry to calculate the gravity force vector relative to the direction that he is traveling. I think Jarry1250 has it, you need to take the sine of the angle relative to the ground to get the portion of gravity you have to combat. --Jayron32 19:46, 4 May 2010 (UTC)

And, for completeness, you should consider the normal force of the incline. Without friction, you will experience a horizontal force, because the normal force is perpendicular to the incline, and only its vertical component is canceled by gravity. The remaining horizontal component will cause you to slide. Most often, that horizontal force is counterbalanced by static friction. Nimur (talk) 19:49, 4 May 2010 (UTC)

Sorry, yes, that was a lapsus and I was thinking along those lines. My question can be summarised as whether the force of gravity one must fight is directly proportional to the angle on which one is moving. Leptictidium (mt) 19:52, 4 May 2010 (UTC)

It is proportional to the angle in a sense. If you make a triangle such that the base is flat (zero degrees) and the angle you are riding is the hypotenuse, the height of the triangle is the amount of "upward travel" that will be fighting gravity in your example. You use trigonometry to calculate the length of the height based on the angle. Assuming that the hypotenuse is set to a length of 1, sine of the angle is the length of the height of the triangle - which is the amount of upward travel. -- kainaw™ 20:03, 4 May 2010 (UTC)

I've tried riding a bicycle on ice, which is a bit like the OP's problem statement. In a frictionless world, the driven wheel will spin without providing any forward motion whatsoever when you operate the pedals, so if stationary you will remain stationary, and if in motion you will remain in motion. You will not be able to accelerate or brake. Second, due to a lack of traction, the instant the center of mass is not directly over the center point of the line connecting the points of contact of the tires with the ground, the tires will slide sideways dumping you on the ground. Steering will not correct the condition, as it does in normal bike riding, even if you are moving forward. Any gyroscopic effect of the spinning tires is negligible (unless you get the the driven wheel spinning very fast indeed). The only ability to climb an incline would be due to the initial forward motion, since there is by definition no traction. Edison (talk) 20:53, 4 May 2010 (UTC)

"Can't Burn Your Skin"

i aw this

http://www.amazon.com/CERTOL-INTERNATIONAL-LLC-USA-128-1/dp/B000KKQ8LA

how can they say "Can't Burn Your Skin," —Preceding unsigned comment added by Tom12350 (talk • contribs) 20:46, 4 May 2010 (UTC)

That description isn't for the Muriatic acid (hydrochloric acid is the more formal name), its for something called "Acid magic" , which is described as buffered hydrochloric acid. See buffer solution for a description of what a buffer is and what it does. I can't find a full ingredients list anywhere; the best I can find is that its a "proprietary blend". Here is an FAQ about the product: [18]. --Jayron32 21:14, 4 May 2010 (UTC)

Here's a forum discussion on it http://www.troublefreepool.com/acid-magic-as-an-alternative-for-muriatic-acid-t16607.html it doesn't look like anyone has an answer. Ariel. (talk) 21:36, 4 May 2010 (UTC)

As the FAQ says to always use gloves and goggles when using it, and they also insist on good ventilation, it doesn't look like they have much confidence in their non-burning non-fuming claims. DuncanHill (talk) 01:52, 5 May 2010 (UTC)

The buffer is prob'ly a weak base such as ammonia or an amine of some sort. But c'mon, if the acid's supposed to be strong enough to do its job instead of HCl, it's gonna be strong enough to burn your skin -- that's just a fact of life, deal with it. 67.170.215.166 (talk) 02:21, 5 May 2010 (UTC)

Not necessarily. A sufficiently concentrated buffer of the appropriate pH could be very mild on the skin, and still be able to efficiently lower the pH of your swimming pool if it is too basic. Remember, the purpose of this stuff is to lower pH. There are lots of ways to do that using chemicals which aren't going to burn on contact. --Jayron32 03:12, 5 May 2010 (UTC)

Having spilled 1M HCl on myself before ... I should say H+ doesn't burn if you wash it off immediately. I take keratin is a pretty tough thing to hydrolyse. (I assume hydrolysis of skin is the main hazard of skin contact with HCl solution). You could buffer it with a very weak base like phosphate or biphosphate. This changes the dominant H+ species. HCl is a chemically mild acid... it's only hazard is H+. With H2SO4 or HNO3 on the other hand, you risk redox reactions, turning your skin a nice healthy black. Mmm, I love the smell of burnt skin and organic ash in the morning. John Riemann Soong (talk) 04:58, 5 May 2010 (UTC)

Actually, HNO₃ turns your skin yellow by oxidation (I know from personal experience). H₂SO₄ doesn't oxidize human tissue -- it dehydrates it, essentially turning it to charcoal (good thing it hadn't happened to me yet). 1M HCl wouldn't burn even if it stays on the skin a while; 3M HCl, however, will burn just a little bit (even if promptly washed away) and more concentrated HCl will burn a whole lot more. Buffering the HCl will reduce the effect by raising pH, but by the same token it will increase the amount needed to do the job required. FWiW 67.170.215.166 (talk) 05:26, 5 May 2010 (UTC)

You see the clever marketing ploy by the folks at Certol, don't you? By buffering plain ole HCl, they accomplish 3 things in 1 fell swoop: (1) they make a product that's almost as cheap as plain HCl, keeping their costs down; (2) they make something that allegedly "won't burn your skin" (but still requires rubber gloves, according to the fine print), thus justifying a higher price; and most brilliantly, (3) they also make this product less effective than ordinary HCl, so it will take more of this product to do the job than if you use plain HCl. Low production cost + higher price + greater quantity required = more moolah for the company. Good job, Certol, and may y'all rot in hell for swindling your customers! 67.170.215.166 (talk) 05:38, 5 May 2010 (UTC)

Again, not necessarily. The purpose of the stuff is to lower the pH of your swimming pool if the pH is too high due to excess chlorination. A highly concentrated buffer solution whose pKa was something close to the target pH of what you want your swimming pool to be, could sufficiently correct your pool's pH problems at volumes similar to what you would need if you tried to do the same with straight hydrochloric acid. It claims a one-to-one volume correspondance with straight conc. HCl, and also claims to be less harmful to skin and fumes much less. The only reasonable solution would be a highly-concentrated buffer system, which could in theory work exactly as described. Since the stuff does actually contain HCl (the MSDS confirms that much), then we'd need a weak base to serve as the other part of the buffer system. I with the above assessment that its like ammonia or another amine. --Jayron32 05:37, 5 May 2010 (UTC)

Yeah, they claim all this, but you don't really know unless you read the fine print on the bottle... 67.170.215.166 (talk) 05:42, 5 May 2010 (UTC)

Normally they use a weaker acid (or less concentrated) such as sodium bisulfate to prevent burns. The buffered HCl may be just a dilute solution. --Chemicalinterest (talk) 12:04, 5 May 2010 (UTC)

Um, the amine is certainly too strong a base to be a buffer for HCl. (You'd get NH4+ and not H+ as the dominant species). What you want I think is to create an acidic species with a pKa of around 0 or 1 (instead of say, -1.7). Much weaker bases like bisulfate and biphosphate come to mind. John Riemann Soong (talk) 14:28, 5 May 2010 (UTC)

I think you may be on the money - did you mean sulphate as a base? - the pkA of hydrogen sulphate is ~2 compare somewhere between -4 and -7 for hydrochloric acid - this means that an sulphate would be almost completely protonated to HSO4- (still a strong acid) - the FAQ for the product notes that it reduces the level of fuming (usually due to free HCl excaping as gas in concentrated hydrochloric acid) - in the presence of 1 mol equivalent of sodium sulphate this would almost certainly acchieve the "90% fume reduction" advertised.. whilst still having a low pH (easily 1) .. also sodium sulphate is dirt cheap. 77.86.70.220 (talk) 19:28, 5 May 2010 (UTC)

Sodium hydrogen sulfate, not sodium sulfate, which is not acidic. --Chemicalinterest (talk) 01:32, 6 May 2010 (UTC)

Digestive Cycles

I've read on several websites that the human digestive process follows a specific cirdadian rhythm that has three distinct phases. The appropriation cycle begins around noon (in most people) and continues until 2000 (8 pm). During this time the body is naturally predisposed to dispense plenty of energy to the digestive tract, and a person is most likely to feel hungry (the body's way of indicating it's the right time to take in food). The assimiliation cycle lasts from 2000 to 0400 and during this time the body is most efficient at the later stages of the digestion process: the absorption of nutrients from the intestines and delivery to the cells. The elimination cycle lasts from 0400 to noon and is the time when the body is most efficient at removing from circulation the byproducts of the metabolic process. Eating during the assimilation or elimination cycles is not recommended, as the body is not prepared to devote its energy to digestion at that time, and if one forces one's body to divert energy from the intestines, liver and kidneys, and/or other parts of the body to the stomach, all processes are performed less efficiently and this can result in health problems, weight gain, restless sleep, etc. The exception is fruit, which can be consumed at any time because it doesn't take a great deal of energy to digest. (Water is another exception of course.) I may have described it a bit too simplistically and yet in rather too much detail, but what I want to know is, is any of this true? —Preceding unsigned comment added by 71.104.119.240 (talk) 21:42, 4 May 2010 (UTC)

The body will adjust to whatever food cycle it is given. If you always eat, exercise or do other events at the same time of day, that's what the body will expect. There is no fixed cycle. Ariel. (talk) 00:54, 5 May 2010 (UTC)

Food, drugs and other rewards can entrain the circadian clock in the absence of light cues (e.g. constant light / constant dark). If I remember my Circadian clocks class correctly, you can lesion the SCN in a mammal (under normal light conditions) and other cues will start to entrain the clock.

There have been circadian clock studies carried out with methamphetamine. For the purpose of circadian clock entrainment, meth is basically a more powerful version of a food cue. The clock period can be lengthened to as much as 38-44 hours (for both mice and humans), when allowed to "free run". (It also explains meth users' strange behaviours). You can also entrain the clock to shorter periods (i.e. by controlling when meth is administered).

I really disagree with the whole idea that eating/exercising during an elimination or absorption cycle results in you being less healthy. The whole "energy diversion" thing is crock. Digestion is energetically-intensive, but it doesn't consume a lot of oxygen. Blood sugar is easily produced from fat. I'd go so far to say that exercising after eating, provided you don't do anything stupid that would cause you to throw up, would increase blood sugar levels available to organs. Muscles tend to use glycogen stores (which are local) before drawing on blood sugar. There are clock effects, but they are with respect to entrainment/efficacy, etc. As a student, the thing I'm most concerned about is my alertness, i.e. studying at the optimum time.

You should be worried about efficacy when efficacy is of the utmost importance. You can administer botulism toxin via injection to mice at a time when livers are "optimised" to handle it -- generally at a time after eating. The mortality rate is around ~8%. Inject it 12 hours out of phase and the mortality rate skyrockets to 90+%. Regular food isn't like a toxin -- it doesn't hurt for its metabolism to wait. John Riemann Soong (talk) 18:08, 5 May 2010 (UTC)

Btw, "inefficient digestion" implying "worse health" sounds like a twist on colon cleansing crap. In general, slower digestion is better. Also, absorption is generally not that energetically-intensive -- it's mostly passive diffusion combined with maybe a few active transport pumps for certain ions or minerals. John Riemann Soong (talk) 18:17, 5 May 2010 (UTC)

Humans eating pet food

Is it possible to eat cat and/or dog food? What about other kinds of pet food? ScienceApe (talk) 22:25, 4 May 2010 (UTC)

Humans are potentially omnivores although vegetarians object. Cuddlyable3 (talk) 22:32, 4 May 2010 (UTC)

Chap I knew at college ate a tin of dog food for a bet once. Mind you, he also used to drink gin by the half-pint, so it is possible his judgement was somewhat impaired. DuncanHill (talk) 22:34, 4 May 2010 (UTC)

(ec)Generally, yes. We might not like them very much, having less taste for innards than dogs or cats do, but we could probably subsist on them reasonably well. It's possible to eat birdseed or fish food (it's possible to eat dirt, too) but it would be hard to derive much nutrition from them. Note, though, that dogs and cats make their own Vitamin C and we don't. There may be other such differences. So if you want to live on them, you might need some supplements. PhGustaf (talk) 22:40, 4 May 2010 (UTC)

Although pet food bags are generally labeled "Not For Human Consumption," there's nothing in cat or dog food that's really going to hurt the average person. Pranksters, mischievous older siblings, and pet-loving parents can all tell you stories of humans who ate dry pet food once or twice and lived to tell the story. It's also been reported in the past that some elderly or disabled individuals, struggling to get by on their government handouts, would eat canned wet dog food because it was cheaper than meat considered fit for human consumption. I would guess that dog food would be more nutritious for a human than cat food, because humans, like dogs, are omnivores (yes, even the vegetarians; being an omnivore is a fact of human biology and refers to what the body is equipped to chew and digest, whereas vegetarianism is a lifestyle choice), whereas cats are carnivores. Some columnist, I forget who, once said that if you could only eat one food for the rest of your life, dog food wouldn't be a bad choice - it's specially formulated to meet the complete nutritional needs of an omnivorous mammal. 71.104.119.240 (talk) 00:46, 5 May 2010 (UTC)

The reason they say "Not For Human Consumption" is because the factories that make it don't follow the same food hygiene/food safety procedures as are required by law for food intended for human consumption. That means there is a slightly increased risk of food poisoning compared to eating human food, but that's about it (and given that dogs aren't always getting food poisoning, I think we can assume the risk is still minimal - it's probably just the paperwork they don't bother with rather than the actual hygiene). --Tango (talk) 01:08, 5 May 2010 (UTC)

But don't for get the Melamine Pet Food Recall of 2007 a lot of cats and dogs wound up in veterinary hospitals over that. APL (talk) 03:12, 5 May 2010 (UTC)

Not really comparable. That was a contamination issue. It doesn't prove anything about the healthfulness of pet food in general, any more than the occasional E. coli outbreak proves that human food is inherently unsafe. 71.104.119.240 (talk) 08:14, 5 May 2010 (UTC) I've been told that the average dog or cat has a "hardier system" than the average human, which is why they can eat things that aren't labeled for human consumption. Whether or not this is true I can't say. You'd have to have a pretty hardy stomach to handle some of the things I've known dogs to gulp down their greedy gullets, but I don't know it would affect the average human to eat insects, burrs, and day-old things, so it's hard to say for sure whether dogs have some kind of systemic advantage. Humans are fussier than they used to be, so it's possible we can't handle some of what our pets consume, and our ancestors consumed, on a regular basis. 71.104.119.240 (talk) 01:15, 5 May 2010 (UTC)

It would be remiss not to mention Ann Hodgman. Her article on the subject is pretty funny. (Note that there are a lot of things that don't kill people but carry some kind of risk of long-term effects. I doubt that anyone has any interest in doing studies on the subject.) Paul (Stansifer) 02:04, 5 May 2010 (UTC)

Comedy Answer : The Monkey Chow Diaries] <-- Man decides to eat only monkey kibble for a week. APL (talk) 03:15, 5 May 2010 (UTC)

Record Maximum

http://climate.weatheroffice.gc.ca/climate_normals/results_e.html?Province=NU%20%20&StationName=&SearchType=&LocateBy=Province&Proximity=25&ProximityFrom=City&StationNumber=&IDType=MSC&CityName=&ParkName=&LatitudeDegrees=&LatitudeMinutes=&LongitudeDegrees=&LongitudeMinutes=&NormalsClass=A&SelNormals=&StnId=1774&

How can the record max for Pond Inlet, NU, be 25.7C recorded in March when the temp has never reached that even in July? —Preceding unsigned comment added by 78.32.155.164 (talk) 23:50, 4 May 2010 (UTC)

Options include a) the weather event on 5 March 1993 was a freak b) the data is wrong c) you're imposing expectations on the data which are not entirely supported by the data. We had 22 degrees in July, but 21.5 in February. How much of a problem is 25.7 in March, given the February value? Sure, it's counter-intuitive, but non the worse for that. --Tagishsimon (talk) 00:01, 5 May 2010 (UTC)

Surely you've answered your own question? Nil Einne (talk) 00:10, 5 May 2010 (UTC)

May 5

Fucking Magnets!

HOW DO THEY WORK? —Preceding unsigned comment added by 69.180.172.142 (talk) 00:12, 5 May 2010 (UTC)

Are you asking how magnets fuck? Or are you just interested in magnetism? 71.104.119.240 (talk) 00:27, 5 May 2010 (UTC)

Both. —Preceding unsigned comment added by 69.180.172.142 (talk) 00:37, 5 May 2010 (UTC)

It has to do with all the electrons in the magnet being aligned a certain way so the subatomic forces don't cancel each other out. Why it is that the subatomic forces exist in the first place, I can't say. 71.104.119.240 (talk) 00:53, 5 May 2010 (UTC)

They exist because if they didn't we wouldn't be here to notice it. (See anthropic principle - it's the best answer to "why" questions we have. Science is good at "how" but it doesn't really do "why".) --Tango (talk) 01:09, 5 May 2010 (UTC)

Sure you're not just interested in ICP lameness? DMacks (talk) 01:22, 5 May 2010 (UTC)

For those not in on the joke, see Miracles (Insane Clown Posse song). Incidentally the New York Times had an amusing article on this meme. Regarding magnets:

VIOLENT J: I think we might have misused the word miracle. These things we mentioned in the song, they can all be explained. But what we’re doing is appreciating them. Even the infamous line “Magnets, how do they work?” I mean, yeah, we know how magnets work. But they’re still incredible. You can push something across the table without touching it.''

SHAGGY 2 DOPE: Come on, man. The North and South Pole makes a rock magnetic, and if you touch a piece of metal with it, that becomes magnetic? That’s crazy.''

I kind of agree, to be honest. I find magnetism pretty magical, scientific explanation be damned! --Mr.98 (talk) 01:54, 5 May 2010 (UTC)

The reason a magnet attracts iron/steel is basically because when you bring it toward an iron/steel object, it induces an electric current in the object, which interacts with the object's magnetic domains (if they're lined up right) such as to produce a magnetic field of the opposite polarity, which creates an attracting force. As for your question specifically about how fucking magnets work, I got no clue -- I'm pretty conventional in my love life, so I've never tried using magnets for it. Perhaps you could find out more on this use of magnets if you take a look at the article Sex toys...  :-D 67.170.215.166 (talk) 04:11, 5 May 2010 (UTC)

I thought only a moving magnetic field induces a current. When a magnet is motionless near a piece of iron, there is still the same attractive force present. DMacks (talk) 05:04, 5 May 2010 (UTC)

I think that's because the magnetic lines of force are a different density at different points in the metal object. But honestly, I'm not so sure about the induction part anymore... 67.170.215.166 (talk) 05:45, 5 May 2010 (UTC)

It's not usually induction (eg magnet/metal attraction). The Magnetic reluctance / Permeability (electromagnetism) are the factors in whether or not a material is attracted to a magnet (see below).Sf5xeplus (talk) 09:04, 5 May 2010 (UTC)

As for fucking magnets, I've checked out the article on sex toys -- there's no mention of magnets anywhere in it. I suppose you could put a pair of magnets on your cock for more female stimulation, but I don't think it would give much of an advantage vs. all those other toys, or simply improving your technique. FWiW 67.170.215.166 (talk) 05:52, 5 May 2010 (UTC)

Motors that are present in vibrators contain magnets. This would potentially make these magnets "fucking magnets" ;) Sjschen (talk) 15:45, 5 May 2010 (UTC)

Well, I've known more than a few guys who thought they were magnetically fuckable. And despite my asexuality, these losers seem to hit on me constantly. Subatomic forces aside, sometimes opposites just don't attract. 71.104.119.240 (talk) 08:11, 5 May 2010 (UTC)

One route to the explanation: Magnets in their interactions will move the position of lowest energy (like everything else - gravity, electric fields etc) - this explains both magnet-magnet and magnet-metal interactions - for 'part 2'; an explantion of how energy levels change with magnetism is required...Sf5xeplus (talk) 08:57, 5 May 2010 (UTC)

When two magnets meet at opposite poles, is their overall magnetic field lowered than when they were separated? John Riemann Soong (talk) 18:23, 5 May 2010 (UTC)

Also I'm curious in the thermodynamics of how magnets reproduce, i.e. magnetise other materials. Generally delta-S is negative. How about delta-H? Do the calories expended in moving your arm provide the free energy required? John Riemann Soong (talk) 18:23, 5 May 2010 (UTC)

delta H is negative for magnetic attraction - energy levels are split into opposed and alligned states (eg for paramagnetic materials) - electrons will tend to drop from opposed states to alligned states (emmitting hv) and creating a net magnetic property.

As you note - delta S is negative - so thermal energy tends to demagnetise in general.77.86.70.220 (talk) 19:20, 5 May 2010 (UTC)

As a better attempt at a (simple) answer - a big strong magnet will magnetise a smaller weaker magnetic substance.. any energy required (from your hand/arm combination) will be to separate them afterwards..! 77.86.68.186 (talk) 20:18, 5 May 2010 (UTC)

Is delta-H negative for magnetic induction? And is delta-S still negative when two magnetic poles come together by attraction, without induction? John Riemann Soong (talk) 21:00, 5 May 2010 (UTC)

Gulf war oil spill

Is the claim that 36 billion gallons of oil was released in the Gulf War oil spill as ridiculous as it sounds to me? I'm ready to remove the quotation, reliable sources be damned, considering how silly it sounds. Thoughts? Magog the Ogre (talk) 01:04, 5 May 2010 (UTC)

As our article says, it is orders of magnitude bigger than all the other estimates we have. My guess is that the Times article is getting confused between the Gulf War oil spill and the Kuwaiti oil fires. The latter may well have burnt 36 billion gallons of oil, but I don't think that much has ever been spilt at sea. --Tango (talk) 01:15, 5 May 2010 (UTC)

For the record, it takes the entire US a month a half to consume that much oil. Magog the Ogre (talk) 01:22, 5 May 2010 (UTC)

Medical question

What is the name of the disease when the body has trouble keeping fat and storing it, and the sufferer is underweight as a result? I saw it describled on a medical TV show, but I didn't quite pick up the name. ```` —Preceding unsigned comment added by 76.229.150.6 (talk) 01:34, 5 May 2010 (UTC)

You may be thinking of Cachexia. Dauto (talk) 02:55, 5 May 2010 (UTC)

You might also be thinking of hyperthyroidism. Dismas|^(talk) 05:11, 5 May 2010 (UTC)

None of the above. You saw a description of lipodystrophy which occurs in both congenital and acquired forms, and both generalized and partial. Quite striking and in the severe forms associated with several other severe problems. alteripse (talk) 10:38, 5 May 2010 (UTC)

Silver mineral

How does this type of silver form? 149.169.218.250 (talk) 01:49, 5 May 2010 (UTC)

By precipitation from hot sulfurous solution (such as in geysers, fumaroles, those kinds of places) due to the action of the dissolved hydrogen sulfide (generally upon cooling of the solution -- the stuff is slightly soluble in hot water, but completely insoluble in cold water). FWiW 67.170.215.166 (talk) 02:29, 5 May 2010 (UTC)

aka Hydrothermal synthesis 77.86.70.220 (talk) 15:58, 5 May 2010 (UTC)

as well as Ore_genesis#Hydrothermal_processes 77.86.70.220 (talk) 16:00, 5 May 2010 (UTC)

What is the current state of Computer text to speech compare to human readers?

Two question: is good/modern computer TTS system better reader then "average Joe" who is a human native speaker reading same text aloud? If yes, is computer TTS as good as professional announcer (TV, radio etc.)? 1) Sounds as good as human pro. 2) Very close. 3) Still far away, but better then average Joe.

As to give an example of good TTS, I generated mp3 on my computer from reading few paragraphs of introduction to Bird article. http://www.autohotkey.net/~TePe/BirdsIntro.mp3 TTS I used probably not the best one out there, but still quite good IMHO. And the reason I'm asking, I'm very curious, but ESL here, and computer sounds totally perfect for me. But my judgment could be clouded, plus once again, mine English is far from perfect. PS. Lets not go into acting and emotion, sure computer could mimic them, but there is too much room for good or bad taste opinions etc. Lets stick with reading informational articles like most on Wikipedia etc. 70.48.64.135 (talk) 01:52, 5 May 2010 (UTC)

It still sounds like a computer to me, regarding the tone. It still has something of a Stephen Hawking quality, and the timing of some words is off. Some of the words are a bit wrong to my ear (e.g. the second "i" in "fertilizer" is pronounced wrong), but it's not bad. What throws it off is the pitch at the end of words, and the timing between words, which is not very natural. It is definitely not as good as a professional announcer to a native English speaker. I have definitely heard better text to speech than that, though. --Mr.98 (talk) 02:29, 5 May 2010 (UTC)

I don't think the bird recording comes anywhere near to even an average native speaker in terms of quality. --99.237.234.104 (talk) 02:38, 5 May 2010 (UTC)

Thank you Mr.98! Much appreciated! Could you please point me to the system that sounds more natural then the one I choose as an example? Sure, if it is available online. Or, if that is not possible, make a recording of the same paragraphs for comparison. Thank you once again. 70.48.64.135 (talk) 03:26, 5 May 2010 (UTC)

I'm not a linguist, but I believe that getting the timing and emphasis perfect is AI-complete. Consider the sentence "Fruit flies like a banana.". To read that sentence aloud correctly requires recognizing that "fruit flies" is one noun phrase, and needs to be grouped tightly, so that it doesn't get parsed the same way as "Time flies like an arrow.", in which "flies" is the verb, not "like". (Time flies like an arrow; fruit flies like a banana) So, in order to get a sentence to sound just right, it's necessary to understand it. Paul (Stansifer) 02:50, 5 May 2010 (UTC)

The point is valid but the example is not a very good one. One of the reasons Chomsky chose "fruit flies like a banana" is that it actually sounds the same for both parsings, even though the meanings are completely different. Looie496 (talk) 03:00, 5 May 2010 (UTC)

I say the two parsings differently, although you would only notice if you were listening really carefully. The difference is in the pauses between the words "fruit" and "flies" and between "flies" and "like". --Tango (talk) 03:05, 5 May 2010 (UTC)

I'm with Tango. I say them they way he does. --Jayron32 03:08, 5 May 2010 (UTC)

They can be said the same if you're trying to make a point, but a normal human reading that line would emphasize it for clarity, depending on the intended meaning. APL (talk) 03:14, 5 May 2010 (UTC)

Interestingly, system I used got the phrase from |TTS article "My latest project is to learn how to better project my voice" right, but ""Time flies like an arrow. Fruit flies like a banana" was very unnatural. 70.48.64.135 (talk) 03:30, 5 May 2010 (UTC)

I just noticed that spellchecker highlighted the word "fertiliser" from bird article. The phrase is "Some species, particularly songbirds and parrots, are popular as pets. Other uses include the harvesting of guano (droppings) for use as a fertiliser." Could it be misspelled? When I have changed it to "fertilizer" TTS sounded much more natural :( 70.48.64.135 (talk) 03:39, 5 May 2010 (UTC)

You can pick even worse examples: "Green flies like a lettuce", for example is semantically reasonable spoken both ways. You need a much bigger context than that sentence. Since there are no such things as "Time flies", you'd at least have a chance at that one. SteveBaker (talk) 18:39, 5 May 2010 (UTC)

How does the colour green flying make any more sense than fruit flying? I would say it makes less sense - at least fruit is tangible. --Tango (talk) 20:21, 5 May 2010 (UTC)

See American_and_British_English_spelling_differences#-ise.2C_-ize_.28-isation.2C_-ization.29. The -ize/-ise are both equally acceptable spellings. Americans tend to exclusively use -ize endings, while the British tend to have a much more nuanced approach towards deciding when to use each of them. --Jayron32 03:55, 5 May 2010 (UTC)

(ec)Fertiliser is the British spelling and is just as correct, and is also consistent with the rest of the article (see the words specialise, characterise, categorise... in the same page). If your software can't read British-English spelling, it isn't very good. --Lgriot (talk) 04:02, 5 May 2010 (UTC)

So if a human make mistake while reading an article you will also claim that "humans are not very good"? Or just particular person? Have you tried to listen to WikiProject Spoken Wikipedia articles? Even on the project page they are talking about "incorrect pronunciation" in the problem section. And BTW, could you please point at better software? Thank you in advance. 70.48.64.135 (talk) 04:17, 5 May 2010 (UTC)

We've come a long way since the "Stephen Hawking" era of text-to-speech. He's been offered vastly better voice synths (some, even based on analysis of recordings of his own voice before he lost the ability to speak) - but he turns them down because he's become used to it. My Amazon Kindle has pretty good text to speech (the male voice seems superior to the female for some reason). There are a few words it gets wrong - but they are pretty rare and it seems to react to punctuation better than some that I've heard. Some of the best stuff I've heard is done by analysis of actual, specific people talking - and some of those are incredibly lifelike. But the limit comes (as others have observed) when the text doesn't contain enough information by itself to convey how it should be read. Since it would take a full-scale AI system with a vast knowledge of humanity and all of it's quirks to get that right. Figuring out when something should be read sarcastically - and when it's real requires a lot of smarts. The way you read "The dog was wearing pink and green spotted hat!" is quite different from "The man was wearing a pink and green spotted hat!" - my emphasis helps - but the reason that sentence is surprising is different because dogs don't often wear hats - but men do - and because pink and green spots would be remarkable on a man - but relatively unremarkable on a dog. The amount of culture, knowledge and so forth needed to artificially generate the highlighting I added to those sentences is incredible - way beyond the current ability of our best AI systems. SteveBaker (talk) 18:39, 5 May 2010 (UTC)

The example sounds like sampled speech (recorded speech) played back as a collection of phonemes, with rising and falling inflections added manually or by a clever program. It is better than early purely synthesized text-to-speech, which to Americans sounded a bit like a Russian reading from phonetically written Scottish English. It was full of unusual phonemes, and this sample is less so. Perhaps the earlier system sounded more natural to inhabitants of some other English speaking countries. Edison (talk) 19:04, 5 May 2010 (UTC)

File:Sirius A and B Hubble photo.jpg

On this File's description, it says "The cross-shaped diffraction spikes and concentric rings around Sirius A, and the small ring around Sirius B, are artifacts produced within the telescope's imaging system.".

Hadn't the mirror been replaced, and the battery replaced, by this time?174.3.123.220 (talk) 04:24, 5 May 2010 (UTC)

Diffraction spike has half your answer. Also, I don't think the mirror was actually replaced, our Hubble Space Telescope article describes what was done to correct the spherical aberration present in the original mirror. I suspect the concentric rings are also an artifact of part of the telescope's design, or limitation of the design, rather then a "fault" with some part of it. There is an example of a star imaged with the "uncorrected" mirror in the HST article, it looks a lot worse then the photo you link. Vespine (talk) 05:42, 5 May 2010 (UTC)

I think the other half of your answer might be Diffraction it self. Vespine (talk) 06:05, 5 May 2010 (UTC)

More specifically, see Airy disk. TenOfAllTrades(talk) 12:35, 5 May 2010 (UTC)

Using TNT or dynamite instead of smokeless powder in guns

According to this, http://en.wikipedia.org/wiki/Trinitrotoluene#Energy_content TNT and dynamite contain more energy per unit of mass than gunpowder. I don't know if the article means modern day smokeless powder or old day black powder. But why don't we use TNT or dynamite in smaller quantities (so energy content released is the same while mass used is reduced) instead of smokeless powder as propellant? Or maybe even gasoline?

Or perhaps to rephrase the question, what advantages does smokeless powder have over those other explosives when used in guns? Presumably reduced smoke is one. Is it possible to make guns using those propellants? ScienceApe (talk) 04:27, 5 May 2010 (UTC)

High explosives would blow the gun to bits and pieces instead of propelling the projectile. 67.170.215.166 (talk) 04:32, 5 May 2010 (UTC)

Smokeless powder deflagrates, while dynamite detonates. That is, the first goes "whoosh" while the second goes "bang". See USS Vesuvius (1888) for an unusual approach to keeping projectiles from going "bang" in the barrel. PhGustaf (talk) 04:40, 5 May 2010 (UTC)

TNT or any other higher explosives hav got a very high burning rate sometimes it being a few hundred meters per second! Now at such high speeds you have to provide small length barrels to maintain the pressures. just refer to this.. http://thefiringline.com/forums/showthread.php?p=2351433 Prady.. —Preceding unsigned comment added by 116.73.242.109 (talk) 05:16, 5 May 2010 (UTC)

Consistent, safe, controllable burning is important in a firearm. Modern smokeless powder can already easily produce the maximum allowable pressure (if desired) in any particular cartridge, so there is little advantage to a propellant with more power. Friday (talk) 15:14, 5 May 2010 (UTC)

Put another way: If you have an explosion then all of the explosive gets converted into gas pretty much instantly. The pressure in the barrel goes up insanely high and the bullet gets an extremely violent initial acceleration. As the bullet moves along the barrel, the space behind it gets bigger - and since no more gas is being produced, the pressure can only drop. The bullet is therefore no longer being accelerated as fast as it could be. For relatively slow burning propellants, the gas pressure builds up more slowly (although still pretty darned fast!) and the bullet gets a chance to start accelerating more slowly - and as the volume behind it increases, the propellant generates enough gas to fill it and keep the pressure up. So the bullet gets a more smooth and gradual acceleration down the barrel. For a given muzzle velocity, you need much lower pressures with a slow burning charge than with an explosive. So the gun doesn't have to be as strong - and can therefore be lighter and easier to handle. As far as the user of the gun is concerned, you can get the same muzzle velocity with a lighter weapon if you use a slower burning charge...or to put it another way - for the same pressure-resistance in the gun, you get a higher muzzle velocity with gunpowder than with dynamite - which gives you a longer range and better accuracy. A perfect charge would be one that produces exactly constant pressure from the moment it's triggered until precisely the moment when the bullet leaves the end of the barrel, and no more after that. Since the volume to be filled is at it's largest at the end, you ideally want a charge that gradually increases the amount of gas it produces until the bullet leaves the barrel...pretty much the opposite of an explosive. SteveBaker (talk) 18:18, 5 May 2010 (UTC)

An analogy might help. Think of a bow and arrow instead of a gun. The string of the bow accelerates the arrow over a distance of a foot or two. How hard would you have to hit the end of the arrow with a hammer to make it go as far? If I were to hit the end of the arrow as hard as I possibly could, it might go a few feet - but that would be it! But whacking the end of the arrow hard enough to make it go 100 feet would certainly smash it to bits! So a gentler (but more prolonged) force is better. SteveBaker (talk) 18:22, 5 May 2010 (UTC)

So even if the cannon or gun were invincible and wouldn't blow up, the gunpowder is still better to use? ScienceApe (talk) 00:00, 6 May 2010 (UTC)

The answer to that isn't very meaningful though. How much dynamite am I allowed to use versus how much gunpowder? Dynamite is an energetically more concentrated explosive than gunpowder - so if there is zero risk of harming the gun then stuff the barrel almost full of dynamite and get a really HUGE bang! But if you have a gun with a limited tolerance for pressure - then you can do better with gunpowder than dynamite. SteveBaker (talk) 03:35, 6 May 2010 (UTC)

Proximity of brain structures?

How close is the hypothalamus (especially the suprachiasmatic nucleus) to the hippocampus and amygdala? —Preceding unsigned comment added by 71.104.119.240 (talk) 10:02, 5 May 2010 (UTC)

Fairly close. There is a good schematic drawing on this page. --Dr Dima (talk) 10:31, 5 May 2010 (UTC)

Since the hypothalamus and hippocampus/amygdala don't actually touch, what is it exactly that's between them? 71.104.119.240 (talk) 19:34, 5 May 2010 (UTC)

Parts of hypothalamus are bounded by the third ventricle, optic tracts, and cerebral peduncles. Hypothalamus is fairly compact. Hippocampi, on the other hand, are fairly large, curving structures in the human brain. They go almost all the way around the thalamus, and join up in a fornix, adjacent to the third ventricle. The fornix projects down towards mamillary bodies, which are the part of the hypothalamus. So they do actually touch. --Dr Dima (talk) 23:19, 5 May 2010 (UTC)

Well, they are connected, but I wouldn't say that they touch. Looie496 (talk) 23:37, 5 May 2010 (UTC)

From Grey's anatomy (29th American edition), page 863: "The body of the fornix lies above the tela choroidea and ependymal roof of the third ventricle... Anteriorly, above the interventricular foramina, the body [of the fornix] divides again into the columns or anterior pillars of the fornix. They bend downward, forming an anterior boundary of the interventricular foramina, become buried behind the wall of the third ventricle and end in the mamillary bodies". So they do touch. --Dr Dima (talk) 01:15, 6 May 2010 (UTC)

Yes, the fornix touches the hypothalamus, but the fornix is not usually considered part of the hippocampus. It is a nerve bundle connecting the hippocampus to the hypothalamus and septum. Looie496 (talk) 03:51, 6 May 2010 (UTC)

Sleep before Exams

I feel more sleepy whenever I wish to avoid sleep the night before my exams. Why is that so? 'Interest' matters? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 10:51, 5 May 2010 (UTC)

Perhaps this is because studying at night is more demanding for the brain than going out with your friends at night or watching a movie? Count Iblis (talk) 13:57, 5 May 2010 (UTC)

Wait, wait, waaaiiit! Staying up late the night before an exam is really seriously dumb! It's much more important that you are relaxed and well rested than that you cram facts into a sleep-deprived brain! You won't retain much of what you revise that late at night anyway - and being alert through the exam is critical to your performance. SteveBaker (talk) 18:06, 5 May 2010 (UTC)

Usually, yes. Although if you've just found that you only had access to half the course over the last couple of months, and the exam is in the morning, and you slept the night before, you might consider hours spent cramming outweighed hours sleeping. But usually, yes, it is much better to sleep than do last-minute revision. 86.178.228.18 (talk) 21:07, 5 May 2010 (UTC)

Well, We will speak about last minute preparation and not last minute revision! Why do i feel sleepy when i intend to avoid it? Not just in case of sleeplessness and exams but at many occasions, "I should not do that...Oops, I did that" happens. Something which I wish to avoid is mostly confronted. Why? —Preceding unsigned comment added by 125.21.50.214 (talk) 03:51, 6 May 2010 (UTC)

Plastics & half-life periods

DO all entities have half-life periods? Why do they say that plastics are non-degradable (non-biodegradable)? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 10:56, 5 May 2010 (UTC)

Theoretically, the entire universe has a "half life" in that it itself is degrading (see heat death of the universe). So yes, anything in the universe is, by definition, "temporary" and "degrading". If the half-life of a substance is, say, measured in the millions of years, its going to be here a while. Even though it may be "technically" degrading, on any scale reasonable for human life, it isn't. --Jayron32 13:23, 5 May 2010 (UTC)

Yeah...I once had a comb that said indestructible on it, and I made it my business to destroy it. In your case, perhaps it's supposed to be like a plastic bag in relation to, like, an apple core. The latter will be gone way before the former. DRosenbach ^{(Talk | Contribs)} 17:33, 5 May 2010 (UTC)

Plastics do degrade in sunlight, and you may find that some are slowly degraded by fungi or bacteria over thousands of years.. Also In theory proton decay could destroy all the matter you like. Graeme Bartlett (talk) 22:22, 5 May 2010 (UTC)

Right-hand writing & Left-leg tumbling

It is easy to write/draw (not with pen or pencil) using the right leg for a right-hander/right-hand-writer even though the one has never been exposed to practice for writing using legs. BUT, It is difficult for the same person to use the left leg for writing/drawing (not with pen or pencil). Does the left-brain hemisphere train the right-leg covertly when one practices to write using right-hand? - anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 11:08, 5 May 2010 (UTC)

I can't answer your question directly, but suggest that, to the extent that the left side of the brain does exercise preferential control over the opposite side of the body - bearing in mind (Ha!) that theories of brain lateralization have sometimes been exaggerated - the pre-existing brain functions for controlling the right hand to write and draw will be more easily applied to the novel use of the right leg for those tasks than to the left. A brief self-trial seems to indicate that this is true even for someone like myself who is naturally right-handed but also naturally left-footed. 87.81.230.195 (talk) 16:33, 5 May 2010 (UTC)

Can light be heard?

Can light be heard by any creature? What is the essential factors for an organism to 'hear' light? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 11:56, 5 May 2010 (UTC)

Sound is caused by mechanical vibrations in the air, which is detected by an organ (usually in the ear) which is designed to detect those vibrations. See hearing. On the other hand, light is caused by electromagnetic radiation and does not cause mechanical vibrations, so no organ which can be described as a "hearing" organ would be able to detect it. See sight. --Jayron32 13:19, 5 May 2010 (UTC)

In certain ways, yes. When pulses of light at select frequenciecs strikes certain objects, the interaction may cause the object to emit sounds (photoacoustic effect). However you can't really "hear" the sound the the traditional sense of the word. Sjschen (talk) 14:42, 5 May 2010 (UTC)

Another "not really" answer... Some people with brain damage have a side effect of hearing noise when they see certain lights (or seeing light when they hear certain sounds). This is not hearing light. It is brain damage causing signals caused by perceiving light to trigger sensations in the part of the brain that should only be activated by hearing something. -- kainaw™ 14:46, 5 May 2010 (UTC)

Well...it both can and can't be heard...radio waves, microwaves, and I'm assuming visible light (as it's in the same spectrum) can be converted into sound, but cannot be heard outright. Also, some forms of synaesthesia may cause light to be heard, but this is, again, not hearing them in the true sense. Ks0stm ^(T•C•G) 15:11, 5 May 2010 (UTC)

You get on a slippery slope with some of these answers:

• Sound and light are very different things - organs designed to pick up vibrations in the air (our ears) can't pick up electromagnetic waves (which is what light is). So in truth, it's impossible to use an organ of hearing to detect light.
• However, light can sometimes cause sounds - which you could hear. If you attach a sensitive microphone to a tree - then as the sun rises and lights up the leaves, they will start to transpire water and you can hear the flow of that water up the trunk. Are you "hearing light"? Well, not really - you're hearing the consequences of the light.
• But then, our ears don't exactly transmit sound to the brain - they convert the sound waves into the vibration of little hairs which in turn create nerve impulses that are a combination of electrical signals and chemical reactions. In a sense, we aren't really "hearing" the sound - we're hearing the consequences of the sound hitting our ears.
• People who have synesthesia mistakenly interpret one sense as another - so they might get the sensation of sound from light - or vice-versa - but they aren't truly hearing the light. If you blindfold them, so their eyes can't see the light - but leave their ears wide open - then stop "hearing" the light immediately. So this doesn't count.
• There is a demonstration of sound being carried by a laser beam in the Dallas Science museum - but that's not really "hearing light" either because the light has to be converted back into sound by a bunch of electronics.

Short, direct answer: "No". SteveBaker (talk) 18:01, 5 May 2010 (UTC)

A few thoughts on this

• We don't know how bats and dolphins interpret their sonar.
• Some blind people report feeling an object in front of them brushing their face, before they actually touch it; it is believed that they hear the echos from their footfalls, see Human echolocation.
• There has been an experiment with a blind person. They wore a camera, connected to a computer. It scanned the image in horizontal lines, top to bottom. Pixels on each line were converted to a pure sine wave, low frequency to the left, high frequency to the right. The brightness of each pixel. controlled the intensity of each sine wave. Thus a thin vertical line gave a continuous pure tone, a thin horizontal line gave a short burst of white noise, a diagonal line gave either a rising or lowering tone. The subject could recognise simple shapes after a little practise. I'm not sure how successful the experiment was in the long run.

CS Miller (talk) 18:28, 5 May 2010 (UTC)

I'd be inclined to say the answer is just: no. I think it's a primarily semantic question. By definition, "hearing is the sense by which sound is perceived", I'd argue it doesn't matter if you do that with your eyes, visual cortex, or your backside; you hear sound, not light. Synaesthesia is a neurological condition which does "funny" things to perception, if EVERYONE was synesthetic, then our definitions of normal sight and hearing would be different. Vespine (talk) 22:50, 5 May 2010 (UTC)

Chromate Reactions

The chromates I formed by the reaction of chromium hydroxide with sodium hypochlorite were yellow. When I reacted them with hydrogen peroxide (3%), they immediately turned dark purple-black. After a while, the hydrogen peroxide started sizzling (from catalytic decomposition), and the solution began lightening. It turned into a shade of yellow just darker than the previous one (more purple). I added more hydrogen peroxide and it repeated the reaction. The hydrogen peroxide was not finished up when it turned yellow again, because an addition of sodium hypochlorite made it fizz oxygen gas still. What is the purple-black substance. It is about as dark as solid potassium permanganate. --Chemicalinterest (talk) 11:59, 5 May 2010 (UTC)

Could it be something like or related to Potassium tetraperoxochromate(V) which is red-brown?77.86.70.220 (talk) 12:58, 5 May 2010 (UTC)

or Chromium#Chromium(VI) : "Chromium(VI) compounds in solution can be detected by adding an acidic hydrogen peroxide solution. The unstable dark blue chromium(VI) peroxide (CrO5) is formed, which can be stabilized as an ether adduct CrO5·OR2" 77.86.70.220 (talk) 13:05, 5 May 2010 (UTC)

It could be the chromium peroxide. It was dark blue and decomposed soon. --Chemicalinterest (talk) 13:44, 5 May 2010 (UTC) The formula would be CrO6 though, because the chromium is 6+ and 3 peroxide ions would be 3 O2(2-). --Chemicalinterest (talk) 14:37, 5 May 2010 (UTC)

I did some figuring and got these reactions.

Na₂CrO₄ + 3 H₂O₂ + 2 HCl → CrO₆ + 12 H₂O + 2 NaCl

CrO₆ + 6 NaCl + 2 H₂O → 4 NaOH + Na₂CrO₄ + 3 Cl₂

4 NaOH + 2 CrO₆ → 2 Na₂CrO₄ + 2 H₂O + 3 O₂

Overall reaction:

3 Na₂CrO₄ + 9 H₂O₂ + 6 HCl → 3 Na₂CrO₄ + 12 H₂O + 3 Cl₂ + 3 O₂

As you can see, the Na₂CrO₄ is not consumed. It is a slow acting catalyst for the reaction of H₂O₂ with HCl. They do not react normally. That is why the yellow color comes back after the reaction is over.

Thanks for the information on the chromium peroxide. It helped me figure out what I wrote here. --Chemicalinterest (talk) 14:37, 5 May 2010 (UTC)

What I mean by slow acting is that the intermediate states do not instantly decay, as in an ordinary catalyst. --Chemicalinterest (talk) 14:38, 5 May 2010 (UTC)

If it is CrO5 that would be 2 x O₂^2- (peroxide) and 1 x O^2- (oxide) - that's the often reported structure eg - explaining why it is two peroxide and not three is quite difficult.77.86.70.220 (talk) 15:33, 5 May 2010 (UTC)

So its not a pure peroxide, its chromium peroxide oxide? --Chemicalinterest (talk) 16:32, 5 May 2010 (UTC)

Then I have to refigure my reactions. --Chemicalinterest (talk) 16:33, 5 May 2010 (UTC)

Collagen-proline-triple helix

Might be an old question. Collagen is rich in proline. Collagen is triple helical for which the three strands should be 'tightly' wounded to each other, at the same time, proline distorts the structure (tertiary) of a protein. Paradoxical??? Are prolines present in the periphery of the helical structure? - anandh, chennai —Preceding unsigned comment added by 125.21.50.214 (talk) 12:09, 5 May 2010 (UTC)

The article collagen discusses this, and the picture in the article (unfortunately in French, so you'd have to translate it), this one [19], clearly shows the formation of crosslinking between collagen triple helices. Thus, coupled with the non-standard amino acids present in the chain probably explins the tertiary structure yoy note. --Jayron32 13:14, 5 May 2010 (UTC)

Proline does not disrupt the tertiary structure of a protein - on the contrary, the unique structural properties of prolines can be critical for a protein to fold into its final conformation. And it's not that prolines disrupt all secondary structure. For example a polyproline helix is actually remarkably stable. Proline is thought of as "secondary structure disrupting" because it does disrupt the two most common secondary structures (the alpha helix and the beta strand). -- 140.142.20.229 (talk) 22:48, 5 May 2010 (UTC)

What proline does is force the protein chain to adopt the right amount of twist, thus actually stabilizing the collagen triple helix. Note that the triple helix must also contain hydroxyproline to be adequately stabilized. BTW, the hydroxylation of proline requires vitamin C as a cofactor -- not having any vitamin C in your system weakens your collagen, which is responsible for the symptoms of scurvy. FWiW 67.170.215.166 (talk) 01:12, 6 May 2010 (UTC)

Space random movements vs planets

While every object in space moves in a random manner, how are planets and satellites moving in orbits? - anandh, chennai. —Preceding unsigned comment added by 125.21.50.214 (talk) 12:26, 5 May 2010 (UTC)

Macroscopic objects in space never move in a random manner. Perhaps you are thinking of thermal motion. Macroscopic objects (satellites, planets) are too massive to move in such a random manner, there is insufficient thermal energy available. 157.193.175.207 (talk) 12:37, 5 May 2010 (UTC)

You might want to read Formation and evolution of the Solar System. Dismas|^(talk) 12:55, 5 May 2010 (UTC)

The only force big enough to move large objects like this is gravity. Because gravity is an attraction force that acts as if the source is a point (at the "Center of gravity"), that forces nearby objects into elliptical orbits (strictly, they are conic sections). However, even gravity gets weak at intergalactic scales so you'd expect galaxies to have motion that's all over the place - except that at those colossal scales, the expansion of the universe starts to dominate motion and is seems like everything at those distances are moving directly away from wherever you happen to be. It's only at really small scales (around the size of dust grains, bacteria, stuff like that) where the forces involved are much more complex (electromagnetic, weak and strong nuclear forces) and truly random quantum effects come into play that the motion is truly random. Between those limits, there are some things (like winds and storms and stuff) that are not strictly random - but so complicated that they are "chaotic" (in the mathematical sense) and are therefore unpredictable beyond very short intervals of time...so they might as well be random for all practical purposes. SteveBaker (talk) 17:52, 5 May 2010 (UTC)

Gravity only acts as though from a point-source if the source is a shell (including spheres). At sufficient distance, any object is roughly spherical, so it is actually at large scales that you would expect elliptical (and other conic sectional) orbits. The reason you don't get that is because a conic section is the solution for the 2-body problem. At large distances you usually have to consider more than just two objects, which can result in very complicated motions. Within a cluster of galaxies, they do sometimes move in roughly elliptical orbits. At larger scales it can be difficult to determine the movement beyond current speed and direction (and even that isn't easy) - all paths are approximately straight on a small enough scale, and you don't need a very small scale when you are talking about clusters of galaxies. --Tango (talk) 20:34, 5 May 2010 (UTC)

Grass cuttings

I know stuff about slow and fast baterial decomposition of compost and the like but I have noticed that newly cut grass gets very warm very quick (e.g. in 15C ambient reaching 50C+ in the time it takes to finish mowing the lawn, so say an hour). Whether this cools off quick depends on the heap size, it can stay hotter for a few days. An hour seems very fast for bateria to multiply, is it possible that there is direct oxidation of some of the chemicals in the grass sap on that timescale? It is much more pronounced when (as at this time of year) the grass is fast growing and sappy. --BozMo talk 17:40, 5 May 2010 (UTC)

Are you sure its bacterial growth and not merely absorbing sunlight which is causing the additional heating? --Jayron32 18:25, 5 May 2010 (UTC)

Yes, sunlight causes much heat addition. Probably some oxidation is occurring, but there would need to be large quantities of a strong reducing agent in the phloem of the plant, which I don't hear of. --Chemicalinterest (talk) 18:38, 5 May 2010 (UTC)

There was no sun this afternoon. The grass was cut cold and went hot in a heap in about an hour, possibly two from the first blade cut. The pile of lawn cutting from cutting the lawn once must be at least 200 kg with an incident surface area in the pile of say 4 sq metres. So say 200 kg of grass contains what 100kg of water heated by 0.5C a minute I make about 20kW of heat. Also the heat is much more pronounced from about 10cm deep in the surface, the very surface is losing heat to air and feels about ambient. Not sun. Very fast fermentation of some sort or direct oxidation? --BozMo talk 18:50, 5 May 2010 (UTC)

Could be. Each blade of grass has a cut end and smashed cells of fatty acids, phospholipids, oils and enzymes splashed all over the place. Perhaps it could simply be due to the rapid oxidation of these volatile components taking place, multiplied millions of times. --Aspro (talk) 18:50, 5 May 2010 (UTC)

The O2 isn't present deep in the grass pile though, limiting the amount of oxidation and the heat. It would be used up very quickly (only a little can seep through the grass), limiting the heat output. --Chemicalinterest (talk) 18:59, 5 May 2010 (UTC)

Diffusion and the partial pressure of oxygen will insure will ensure there is no shortage (after all, an anaerobic heap would become black and stagnate -would it not).The smell of cut grass is due to a rapid chemical reaction [20]--Aspro (talk) 19:25, 5 May 2010 (UTC)

Nitrates and sulfates are other potential electron acceptors. You could culture the bacteria on an agar plate to see what type of species you get ... John Riemann Soong (talk) 19:01, 5 May 2010 (UTC)

Bit technical for me culturing something. And is it definitely a bateria not, say, a yeast? Only really smells grassy mind you. But certainly there will be a lot of nitrates. --BozMo talk 19:06, 5 May 2010 (UTC)

If it is oxidising something then I reckon it needs to release about 70MJ for my 200kg pile in an hour say which corresponds to oxidising a bit over a kg of sugar, or 1% of the total weight being an oxidisable mixture. S'pose thats vaguely plausible. --BozMo talk 19:10, 5 May 2010 (UTC)

If it's a yeast, you should see some of the colonies too. Why don't you smash up some of the cuttings and put it in a little bit of water in a test tube (or some sort of small see-through container). Cover the top of the solution with oil to prevent O2 entry. Or have two containers and cover one to see what oxygen presence does. (Seal both.) I'm a bit curious if any gas will evolve. (You could make a homemade gas test... basically any evolved N2, NO2, SO2, H2S etc. will bubble into an overturned glass dome inside the container and show up as a bubble.) John Riemann Soong (talk) 19:10, 5 May 2010 (UTC)

Getting dark here. Might have to wait until the next cut next week. Should I warm the crushed grass in water? Couple of centrimetres thickness of pestled grass? Presumably I don't need to use boiled water because disolved gas will be negligible? --BozMo talk 19:20, 5 May 2010 (UTC)

I don't think you have to warm it. Lukewarm water might do (25C - 37C), but plain tap water will work. I've never done a microbiological experiment in a drinking glass. Basically enough water to make a liquid suspension. We're being really unrigourous about the concentration and skipping buffering the solution, but I'm just curious what type of things will show up.

I wonder if you could also do a pH sample across time. Sample the pH of freshly cut grass, grass in a grass heap after 1h, 4h, 24h, etc. (Use a large sample of cuttings per time period to prevent sampling error). and use the same amount of liquid each time. John Riemann Soong (talk) 19:25, 5 May 2010 (UTC)

I don't think boiled water is necessary. The gas solubility for produced gases will be very low. On the other hand, dissolved O2 in water might retard the growth of any microbes causing the heat. You have a large sample of grass, I assume.

Some species causing the heat, e.g. Pseudomonas can turn a previously yellow/colourless culture a nice green. ;-) John Riemann Soong (talk) 19:27, 5 May 2010 (UTC)

Silage#Fermentation says fermentation takes 48 hours to establish. If that's true the heat might be respiration [21]. For some reason although I googled "grass" first googling "silage" did not immediately occur to me. But I have not found what "respiration" is beyond that it is immediate, heat releasing and uses carbohydrates. --BozMo talk 19:34, 5 May 2010 (UTC)

Note the reference refers to "a potential silo fire" from allowing too much respiration. This all sounds quite plausible now. --BozMo talk 19:37, 5 May 2010 (UTC)

The only issue is the oxygen. Maybe it's microbes using nitrates / sulfates. Fermentation might not be in full swing for 48 hours, but other forms of anaerobic respiration might be used before then. John Riemann Soong (talk) 19:59, 5 May 2010 (UTC)

Interesting. Hmm. I didn't know the browning reaction reduced the amount of available protein. I thought it just made proteins tastier by glycating them to sugars. John Riemann Soong (talk) 20:02, 5 May 2010 (UTC)

The initial heating may not be due to microbes at all but due to the living (about to die) grass. This is metabolising too, and it suddenly has a lot of repair work to do, so there will be a lot of activity in the damaged cells. Graeme Bartlett (talk) 22:13, 5 May 2010 (UTC)

Copper oxidation

When copper metal is added to a solution of copper(II) nitrate, does the copper(II) nitrate oxidize the copper metal? The silver-potassium nitrate discussion in the reference desk archive is similar. If a small amount of HCl is added to it, does it oxidize it? Thanks. --Chemicalinterest (talk) 18:16, 5 May 2010 (UTC)

If it is of sufficiently low pH, then yes it will. See Standard electrode potential (data page) and find the half reaction for the reduction of nitrate. The reaction requires H⁺ ions, which means that at low enough pH, the nitrate ion will sufficiently oxidize additional copper metal. One could calculate the necessary concentration of H⁺ necessary to do so; converting the E^o for the overall reaction to an equilibrium constant is trivial, and from the equilibrium constant and the concentration of copper nitrate, you can calculate the concentration of H⁺ needed to oxidize additional copper. I suspect you will need a small amount of additional acid, either HCl or H₂SO₄ should be sufficient. You should see the brown NO₂ gas as a product; the counterion of the acid (either chloride or sulfate) effectively replaces the nitrate in the solution as the additonal copper is oxidized. --Jayron32 18:23, 5 May 2010 (UTC)

Does the counterion for the nitrate really matter for the oxidation to work? I assume that existing Cu(II) will tip the equilibrium slightly towards the reverse reaction. Unless the reaction is autocatalytic -- Cu2+ oxidises copper metal? (But two Cu(I) ions I recall, are less stable than Cu(0) and Cu(II). But maybe this represents a good intermediate...) John Riemann Soong (talk) 18:29, 5 May 2010 (UTC)

See above. The Cu(II) is irrelevent, excepting that it will lower the pH of the water by forming complex ions via lewis acid-base reactions. Basically, you will get some Cu(OH)₄^2- complexes in any solution with Cu(II) ions, and thus will also produce an excess of H⁺. I am not certain this excess H⁺ is of sufficient concentration to be useful in the nitrate reduction half-reaction, which is why you probably need a little bit of extra acid. --Jayron32 18:36, 5 May 2010 (UTC)

I don't have any nitrates, but I saw a demonstration of a Daniell cell using copper nitrate and copper electrodes, and I wondered if the copper got oxidized. --Chemicalinterest (talk) 18:41, 5 May 2010 (UTC)

Copper seems to need an acidic environment to oxidize. When copper metal is added to hydrogen peroxide, no black CuO is formed; but when HCl is added, green CuCl₂ solution is formed (green because of HCl prevalence). --Chemicalinterest (talk) 18:43, 5 May 2010 (UTC)

I'm wonder if it's out of a need to have a counterion more than anything. You're generating Cu2+ from Cu(0) -- you're generating OH-, which will accumulate unfavourably. What if you add a weak acid like ammonium chloride or acetic acid? John Riemann Soong (talk) 18:52, 5 May 2010 (UTC)

My possibly incorrect reaction on paper was: Cu(NO₃)₂ + Cu → 2 CuO + 2 NO₂. In this reaction, the OH- as O2- is precipitated from solution. --Chemicalinterest (talk) 18:57, 5 May 2010 (UTC)

I wonder if you can "guide" the reduction to other things, e.g. nitrogen, imines, amines... Also NO doesn't last long by itself in solution. In the presence of oxygen it becomes NO2. John Riemann Soong (talk) 18:59, 5 May 2010 (UTC)

In general yes - adding a reagent that will complex the oxidised copper helps - one v. good example from old A level course if the use of thiourea - it complexes Cu+ strongly enough to allow the reverse disproportionation reaction to happen. For Cu2+ - yes amines et al help - eg Copper and water - fairly non 'rusty' , but copper + water + ammonia - increase rate of corrosion.77.86.70.220 (talk) 19:45, 5 May 2010 (UTC)

I said before that I didn't complete this reaction, so it might not occur. --Chemicalinterest (talk) 19:04, 5 May 2010 (UTC)

No, your reaction is wrong. For the correct reaction, you need to use the correct half-reactions from Standard electrode potential (data page). The relevent half reactions are:

• Cathodic: NO₃⁻(aq) + 2 H⁺ + e⁻ ⇌ NO₂(g) + H₂O
• Anodic: Cu(s) ⇌ Cu²⁺ + 2 e⁻

Now, just balance the electrons by doubling the nitrate half reaction, and combine the two reactions, to get:

• 2 NO₃⁻(aq) + 4 H⁺ + Cu(s) ⇌ 2 NO₂(g) + 2 H₂O + Cu²⁺

Notice that the reaction equilibrium depends on the concentration of H⁺ on the reactant side, so you need a sufficiently low pH to drive the equilibrium to the product side. As I noted above, Cu²⁺ will generate some acid via lewis acid-base reactions with the water; however this is probably not sufficient to make the reaction extensive if you are just adding copper metal to copper nitrate solution. Remember, there is already Cu²⁺ ions present in the solution, so via the common ion effect, the equilibrium is unlikely to move forward. What you need to do is to overcome the common ion effect by adding something additional to the reactant side. Adding more copper metal does no good, since solids do not effect equilibrium, so you need to add either additional nitrate OR additional acid. The acid is easy enough to do, and you could easily figure out for yourself what the maximum pH is to have an extensive reaction by converting the total E^o for the above reaction to an equilibrium constant, and then using your initial concentration of copper(ii) nitrate. If doing that gives you trouble, I can help you with that too. --Jayron32 19:38, 5 May 2010 (UTC)

One of two things ie either Cu2+ or NO3- as the oxidant.

1.

Cu + Cu2+ >>> 2Cu+

This is called Symproportionation (opposite of Disproportionation)

This reaction doesn't happen in water - the reverse reaction does..

The overall reaction doesn't occur in major amounts in water ... but this is mainly due to hydration energy, right? But I wonder if Cu(I) can form intermediates. e.g. Cu + Cu2+ ---> 2 Cu(I) ---> 2 Cu(II). John Riemann Soong (talk) 19:56, 5 May 2010 (UTC)

2.

Cu + NO3- + H+ >>> yes ... products vary can be NO2 , N2 , N2O maybe others.

Jayron already covered this above - it only happens if you add acid (in general enough and strong enough to generate some free nitric acid).77.86.70.220 (talk) 19:45, 5 May 2010 (UTC)

Chromate reduction

What is a good chemical to reduce chromates to Cr₂O₃? --Chemicalinterest (talk) 19:03, 5 May 2010 (UTC)

Just about metal will do. Chromates have a very high standard reduction potential, see Standard electrode potential (data page), Cr₂O₇^2- has a reduction potential of +1.33 volts, more than sufficient to oxidize most any metal. The end product is Cr³⁺, which in a base will precipitate Cr(OH)₃. A hydroxide is just the hydrated oxide, If you heat a hydroxide in a crucible, you can drive off water and generate the oxide, in this case Cr₂O₃. --Jayron32 19:27, 5 May 2010 (UTC)

On the organic side, if you find metals a little expensive, you could try sugar, alcohols (vodka comes to mind), formaldehyde ... Organic reactions might be a little more chaotic though. If you don't care about the identity of what spread of sugar products you might get, e.g. you care only qualitatively about the production of Cr2O3 (or black/brown products from oxidation of sugar), then you're good. John Riemann Soong (talk) 19:35, 5 May 2010 (UTC)

endodermal cell solution

My biology question paper has the following multiple choice question: Four solutions, with different water potentials are listed. 1 endodermal cell solution 2 root hair cell solution 3 soil water solution 4 solution in a xylem vessel Which list has the solutions in order from the highest (least negative) water potential to the lowest (most negative) water potential? highest-----> lowest A 1 2 3 4 B 2 4 1 3 C 3 2 1 4 D 4 1 3 2

Link: http://www.xtremepapers.net/CIE/International%20A%20And%20AS%20Level/9700%20-%20Biology/9700_w08_qp_1.pdf Question no. 23 —Preceding unsigned comment added by 116.71.40.176 (talk) 20:20, 5 May 2010 (UTC)

I cant seem to find anything regarding the endodermal cell solution in either my textbook or the internet. What is it? And what would be the answer to the question? This is not a homework problem, and I have tried it. Thanks. --116.71.40.176 (talk) 20:18, 5 May 2010 (UTC)

heat capacity units and calculation

I find heat capacity units are confusing. (K = kilogram or K for Kelvin?. °K instead of °C.)

I would appreciate if someone would check if I have interpreted and calculated this correctly.

According to this table Heat capacity#Table of specific heat capacities, the heat capacity of water (under constant pressure) at 25 degrees C is 4.18 J/(g·K). Same at 100 degrees C.

Suppose I want to heat water from 25 to 75 °C, at atmospheric pressure

So to heat a gram of water takes 50 x 4.18 = 209 joules.

And to heat a kilogram of water takes 50 x 4.18 x 1000 = 209,000 joules.

And 1 kWh = 3.6 x 10**6 joules. So 1 kWh would heat 3.6 x 10**6 /209000 = about 17 kilograms of water. And 17 kilograms of water is 17 litres.

So to heat a 175 litre tank of water requires just over 10 kWh of energy.

Therefore a water tank that was one cubic meter in volume could be heated from 25 to 75 °C with 1000/175 = 57 kWh of energy. Please is this all correct?

Thank you, Wanderer57 (talk) 21:36, 5 May 2010 (UTC)

According to Google, your calculation is correct, (with a slight rounding error). [22]

Three points, the specific heat capacity of water is slightly dependant on the temperature, the units are normally 4.18 kJ/kg/K (kg is the base unit of mass, but its the same as J/g/K. Lastly K is kelvin, kg is kilogrammes. CS Miller (talk) 22:11, 5 May 2010 (UTC)

... and °K is just wrong. (While Celsius, Fahrenheit and Rankine get degree symbols, Kelvin does not.) -- 140.142.20.229 (talk) 22:42, 5 May 2010 (UTC)

It's wrong now, that is. The kelvin (no capital letter, symbol capital K) was previously called the degree Kelvin (with capital K, symbol °K) just like all the other "degrees" of temperature. It changed in 1968, but some people took a long time to notice. --Anonymous, 01:50 UTC, May 6, 2010.

(edit conflict) :The calculations seem correct, but how many liters (or litres) are in a 1 m³ tank? --Chemicalinterest (talk) 22:15, 5 May 2010 (UTC)

1 liter = 1 cubic decimeter. Since a decimeter is 1/10th of a meter, 1 liter is 1/10^3 = 1/1000 of a cubic meter. --Jayron32 22:25, 5 May 2010 (UTC)

Electric spacecraft drives

Why do Variable Specific Impulse Magnetoplasma Rocket drives have the ability to get spacecraft around the solar system better than Ion thrusters? The articles go on about the workings of each, but the main advantage claimed in the VASIMR article is less electrode erosion. Is that really the basis for the recent wild hype about VASIMR that it could get astronauts to Mars in 45 days? If they were both operated for the same burn duration in spacecraft of similar mass, would the VASIMR drive produce greater acceleration? Edison (talk) 23:45, 5 May 2010 (UTC)

May 6

epson salts

how come the epson salts article dosent explain how it helps sore joints. —Preceding unsigned comment added by Tom12350 (talk • contribs) 00:57, 6 May 2010 (UTC)

Curvature of the earth

Not a big deal, but I was wondering just now if it is known how much a certain area of earth's surface (assuming a perfectly flat area) is curved. Is there any measurable curvature within, say a mile? –Juliancolton | ^Talk 01:19, 6 May 2010 (UTC)

Divide the number of miles in the circumference, about 24000, into 360°. This will tell you how many miles it takes to produce one degree of curvature. --Chemicalinterest (talk) 01:29, 6 May 2010 (UTC)

That makes sense. Thanks! –Juliancolton | ^Talk 01:39, 6 May 2010 (UTC)

Not quite. That assumes the Earth is perfectly spherical, but it is actually a bit of a flattened sphere. Over a small distance like a mile, this imperfection can be discounted, but on a large scale it has to be considered. 76.199.153.83 (talk) 01:49, 6 May 2010 (UTC)

Look at a map of one of the plains states in the US, like North Dakota or Nebraska, and you will see lots of places where a road, or a series of successive county boundaries, forms a straight north-south line that jogs to the west every so often as you go north. In Canada the boundary between Manitoba and Saskatchewan is an even better example, having the same sort of shape for hundreds of miles with no further irregularities. The reason for this is that both the Public Land Survey System in the US and the Dominion Land Survey System in Canada were based on dividing the land into squares with specific sizes -- squares whose boundaries run north-south and east-west. For example, a 1-mile square on this system was called a section.

But of course that's impossible on a curved planet. The way it was really done was that they made the shapes almost square, with true north-south sides, running north and/or south from an east-west baseline until they got too far from the desired size; then they jogged all the boundaries to one side (by an amount that depended on how far they were from a principal meridian) and continued north or south from there. So for example each of the stairstep points in the Saskatchewan-Manitoba border is the same distance west of a principal meridian that runs north and south more or less through Winnipeg. The jogs in this case are about 24 miles apart. Look at a map of Manitoba and you can see how much the curvature of the Earth affects things. --Anonymous, 02:15 UTC, May 6, 2010.

To really get a gut feel for it - imagine you're standing on the end of a long, straight, "flat" road (we have to put "flat" in quotes - because it follows the earth's curvature). Over the distance between where you're standing and where the horizon is - the difference between a 'flat earth' and the real curved earth is exactly the height of your eyes from the ground. Within a mile, this "curvature" distance is about 8 inches...which is quite measurable. It gets bigger fast though! Within 3 miles, it's about 6 feet of curvature...which is why (if you happen to be a little over 6' tall) the horizon is about 3 miles away on dead flat, level ground. SteveBaker (talk) 03:18, 6 May 2010 (UTC)

Pages 774-779 of an old science book from 1887 give an approchable understanding of the Earth's curvature. If the diameter is 8000 miles, then in 1 mile there is 8 inches of curvature. The "drop" increase more than 8 inches in the 2nd mile,to 32 inches, and to 72 inches at 3 miles, and 128 inches at 4 miles, 66 feet at 10 miles. Observers watching a ship see it go "hull down" with only the mast or superstructure visible, through a telescope, when it is several miles away. One old source claims "optical depression" of only 6 inches in the first mile at sea, with similar geometric increases in dip per mile. Only the top of a tall hill or mountain will be visible from a distance. If you note the setting of the sun from the ground floor of a skyscraper, then ride the elevator to the top floor, you might see it once again partly above the horizon. Edison (talk) 03:38, 6 May 2010 (UTC)

Another example of this effect is to look at a city skyline from across a wide body of water; if you're familiar with the relative heights of the different buildings, you can tell that their bottoms are missing. I have noticed this when riding toward Hamilton over the Garden City Skyway on a day when the air was clear, and observing the Toronto skyline across part of Lake Ontario. --Anonymous, 04:20 UTC, May 6, 2010.

can Blue cheese produce penicillin?

Just curious. If the cheese could produce penicillin then it might be bad to those that are allergic to penicillin. --121.54.2.188 (talk) 05:20, 6 May 2010 (UTC)