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October 14

H1N1 vulnerability after infection?

My local television news just aired an interview with a studio staffer who had recently recovered from H1N1. According to the producer, he believed that he was still vulnerable to the virus despite having just fought it off; no explanation was offered for this statement. How could this be possible? Or is the staffer simply mistaken? I couldn't find anything on our article about the virus; I can't imagine how immunity would not be conveyed by having the infection. Nyttend (talk) 03:13, 14 October 2009 (UTC)

According to our article on the influenza vaccine, each particular vaccine cocktail is only good for about a year. Since that's largely due to mutation, I'd guess similar caveats would apply to folks who'd had the actual flu (i.e. yes, you could get it again next year if you'd like). This brings up the basic problem of what is meant by "same" when it comes to something that mutates as quickly as the flu bug does. Compound that by the fact that most infections and diseases are not properly identified in a lab and you're left with the unhelpful non-answer of "If he did get it again, how would he know? Matt Deres (talk) 03:38, 14 October 2009 (UTC)

I don't think it is really mutation like that. This year's seasonal flu isn't a mutated version of last year's, it is a different strain (well, combination of strains) that has reached significant levels. Immunity to the current pandemic strain of H1N1 should offer at least partial immunity to mutated versions of it, unless you get a really rapid mutation (which is possible, but unlikely), but it won't necessarily offer immunity to other strains of flu (including other strains of H1N1 - that code refers to a whole family of influenzas). However, as you say, the current strain is just a strain of flu like any other strain of flu, without detailed lab tests there is no way to tell it apart. Unless he was actually tested there is no way to know he ever actually had the pandemic strain and even if he did he could easily catch a different strain of flu in the future. --Tango (talk) 08:42, 14 October 2009 (UTC)

If I remember rightly, the TV guy said something like "I could still get it again"; it was definitely an imprecise statement such as this. I do know that he was tested and was told that the lab confirmed that it was H1N1. Nyttend (talk) 18:07, 14 October 2009 (UTC)

Well, what it means is he could get the flu again, and he could even get H1N1 Influenza A again. But it is unlikely he will get this one strain of H1N1 flu (the 2009 Swine flu) again. Look at it this way. Influenza describes a grouping of viruses which, on the Linnaean scale, would be something like Class. Influenza A would be something like a Order and H1N1 Influenza A would be something like a Family. See, even something like "H1N1" describes a large grouping of related, but distinct, viruses. Specific strains of H1N1 would be something like at the genus or species level, and vaccines are specific to the specific strain only. In fact, the standard cocktail of vaccines given every year to combat the "seasonal flu" usually contains some vaccines against some strains of H1N1 flu, just not the one specific strain being called the "swine flu". Since that strain was only discovered this past spring, it did not have time to make it into that cocktail of vaccines, so a seperate vaccine has to be initiated to catch it. Had the virus been discovered a few months earlier, it likely would be part of the standard annual seasonal flu shot. --Jayron32 20:03, 14 October 2009 (UTC)

A friend of mine actually has the swine flu and she says that she has gotten sick twice. It's been over two weeks now, and she's still very sick. I saw her after a week and she looked fine, then she got really sick again. Maybe it can relapse and then return, like malaria? It's also common to catch a cold after you catch the flu, due to your weakened state. That happened to me once. So that could be another explanation. Swine flu sounds like a very bad virus. Her husband and her brother are both in the hospital right now because of the pneumonia brought on by swine flu. So, I imagine her immune system must be pretty weak right now. I'm terrified of swine flu!--Drknkn (talk) 07:45, 15 October 2009 (UTC)

It could be a relapse (don't overdo it as soon as you start to feel better!) or it could be really bad luck and she's gotten ill twice in a quick succession. Don't be terrified - it really is just the flu. Unless you have an underlying medical condition the chance of you having any complications is really low. --Tango (talk) 11:07, 15 October 2009 (UTC)

Big Bang

Where did Georges Lemaître first use the phrase "a day without yesterday" ? Was it in the 1927 paper or the 1931 letter to Nature, or somewhere else ? Lord Labak Daas (talk) 07:42, 14 October 2009 (UTC)

I don't have access to the 1927 paper, but in the 1931 letter to Nature, which I do have, he does not use the phrase. The closest he gets is to say that "If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time." --Mr.98 (talk) 14:42, 14 October 2009 (UTC)

This book about him says: He would later refer to this ultimate origin in his 1950 collection of essays The Primeval Atom as "the now without a yesterday", which has been translated as "the day without yesterday", a quote often associated with Lemaître's letter to Nature. --Sean 15:35, 14 October 2009 (UTC)

Why is the original paper on the big bang not easily accessible? Something is wrong. Weepy.Moyer (talk) 19:44, 17 October 2009 (UTC)

Antimatter fuel

Does matter/antimatter collision produce enough energy that it could be a viable power source for applications such as space travel once technology is developed to produce antimatter at a significantly lower cost? --Jean-Luc Pikachu (talk) 16:29, 14 October 2009 (UTC)

It produces enormous amounts of energy. The trick is producing antimatter using less energy than would be created - that is rather difficult. --Tango (talk) 16:37, 14 October 2009 (UTC)

See Antimatter rocket and the website How Stuff Works. —Preceding unsigned comment added by Nigelpackham (talk • contribs) 16:39, 14 October 2009 (UTC)

Antimatter utterly annihilates matter, converting all of the mass into energy. Mass-to-energy is given by $E=mc^{2}$, which yields joules if mass is given in kilograms and the speed of light is given in meters per second. The speed of light is 300,000,000 meters/second, so 500 grams of antimatter "exploded" with 500 grams of matter (1 kg total) would produce 90,000,000,000,000,000 ($9x10^{18}$) joules, approximately equivalent to a nine thousand-megaton nuclear bomb, and enough energy to run a 100-watt light bulb for almost 30 million years. In reality, a good portion of the energy would be lost to neutrinos, but yes, antimatter would make a fantastic energy source, assuming 1) we can find a way to produce it cheaply, and 2) we can find a way keep it from spontaneously destroying itself (and everything else around it for a very long distance). J.delanoy^gabs_adds 16:43, 14 October 2009 (UTC)

Since the previous posts didn't say it, I will: there is no prospect of antimatter being a viable fuel in the foreseeable future. Our antimatter article says: "According to CERN, only one part in ten billion of the energy invested in the production of antimatter particles can be subsequently retrieved." There are some schemes floating around to harvest it from cosmic ray interactions with the solar wind, but they are all extremely speculative. --Sean 16:56, 14 October 2009 (UTC)

Being a viable fuel and being a viable energy source are two different things. Obviously it's not a viable energy source since there's not really antimatter sitting around and creating it necessarily takes at least as much energy as it would release when annihilated. But as a way to efficiently store energy for vehicles where carrying around bulky fuel is an issue, it has the highest usable energy content per mass possible if the problems of creating it and storing it could be addressed. Rckrone (talk) 17:41, 14 October 2009 (UTC)

Basically, unless you can find a big pile of antimatter somewhere - AND figure out how to collect it - AND figure out how to store it without spontaneous annihilation with the walls of the container, then you aren't going to be able to use the stuff. It seems unlikely that antimatter exists anywhere in the universe in a 'natural' form...and if it does exist - it's pretty clear it won't be in our galaxy. So we fail at the first hurdle there - there isn't any of this stuff just lying around! We can make tiny amounts of the stuff - but (as others have pointed out) the amount of energy that takes is spectacular. So antimatter as either a primary fuel - or as a way to store energy is pretty much a non-starter, and is likely to remain that way for a very long time to come. However, IF you had a means to produce it with more like 100% efficiency than 0.0000000001% efficiency (which is about what we have right now) - and a way to store it (presumably in some kind of magnetic containment arrangement) - then it would certainly be the densest possible way to store energy - which (in principle) makes it useful for spaceflight - or aircraft or even cars. But we're just so very far from being able to do that - we have to say it's "impossible" until we know whatever it is that we don't already know! SteveBaker (talk) 17:49, 14 October 2009 (UTC)

An exotic application like powering interstellar flight might be one of the earlier things it could be used for, and that is not near term. Might have weapon applications as well. With respect to practical applications of antimatter, we are at the level of people experimenting with static electricity in the 1700's and speculating about electricity's possible use to run motors, for fast communication, or for lighting. Theoretically possible but not even close to practical. Edison (talk) 19:06, 14 October 2009 (UTC)

That's not entirely true. The 'P' in PET scan stands for positron, a form of anti-matter. Dauto (talk) 19:40, 14 October 2009 (UTC)

In a PET scan, we are not technically creating antimatter. We are letting an element undergo beta decay. J.delanoy^gabs_adds 21:00, 14 October 2009 (UTC)

The element undergoing beta decay is not found in nature. I is a man made element in a particle accelerator. Dauto (talk) 00:53, 15 October 2009 (UTC)

Which bit of Steve's post does that contradict? A few positrons is a tiny bit of antimatter and we use a large amount of energy (in the particle accelerators you mention) to make it (indirectly). --Tango (talk) 12:35, 15 October 2009 (UTC)

If a massive space based solar power station was created to power a space based anti-matter production machine, then once enough anti-matter had been produced (even if it took a thousand years) this matter could be taken back to earth for power production. It might be an alternative to beaming solar power down to earth using microwaves, or space elevators, which might not be practical.Trevor Loughlin (talk) 12:58, 16 October 2009 (UTC)

But you still have to solve the containment issue - that's decidedly non-trivial for any significant quantity of the stuff - remember, you can't allow your antimatter to come into contact with ANY normal matter. But in any case - with our best efforts at turning electricity into Antimatter having an efficiency of 0.0000000001% - you'd be better off leaving your space-based solar power station on the ground and connected to the power grid directly! The amount of energy you'd lose due to atmospheric absorption, poor orientation of the collector to the sun, clouds and nighttime would still be irrelevent compared to the horrific inefficiencies of turning electricity into antimatter. SteveBaker (talk) 13:33, 16 October 2009 (UTC)

ko kaaf

I want to know a little about the "Kohkaaf". given the name of the place/home land of Ghost(jin). Please tell me its answer. Thanks Mohsan saleem —Preceding unsigned comment added by Mohsan saleem143 (talk • contribs) 18:00, 14 October 2009 (UTC)

The name is usually transliterated as Koh-e-Qaf (Persian: کوہ قاف), which refers to the Caucasus mountains. See Paristan. Red Act (talk) 18:18, 14 October 2009 (UTC)

Global warming vs. record lows/snowfall

I am getting tired of my friends telling me that because their town in Saskatchewan just had a record snowfall, ipso facto global warming is made up. Is there a response for this specific kind of reasoning? Gohome00 (talk) 19:39, 14 October 2009 (UTC)

Global warming is a climatic effect, not a weather effect. See climate and weather for some differences. The big deal is that climate is the average atmoshperhic conditions over a long period of time. Weather is what is happening in one specific place at one specific point in time. Weather says "It's raining now". Climate says "It rains here a lot". The deal is, global warming says that, on average, the earth is warming up. On a local level, in specific places, on specific days, you can still have cold weather. Global warming does not mean that it will never be cold ever again anywhere. It does mean that there will be less cold days in any given period of time (measurable probably over a year or a decade); and that those "cold" days are a few degrees warmer than cold days used to be. The deal is, that things like polar ice caps grow and shrink very slowly, on the order of decades or centuries, so they will respond to conditions on the scale of decades or centuries, which is why we care about climate rather than weather. So, just because it snows in Saskatchewan today doesn't mean that global warming isn't happening. What you would need to look at is the average temperatures in Saskatchewan over a long period of time, and see what the general trend is; in the case of climate a moving average is probably the best way to judge this. --Jayron32 19:50, 14 October 2009 (UTC)

You can also direct them to the Climate Normals compiled by the Meteorological Service of Canada. They might be interested in looking at local trends over the span of decades, rather than specific days, years, or weather events. Note the important difference between local and global climate, also. I would also like to point out global climate change as opposed to global warming - which are related but distinct phenomena. Nimur (talk) 19:59, 14 October 2009 (UTC)

Riding on what Nimur said, in my neck of the woods (Central NC), a lot of people are rejecting the Global Warming phenomenon and discussing instead Global Climate Change. Global Warming makes it sound like the entire globe is going to heat up. On average, it will, but while it may get hotter in country X, it may get to be a mini-ice age in country Y. Also, Global Warming doesn't begin to cover the ideas of droughts and floods, which are also cited as being major factors associated with this event. Falconus^{p t c} 22:13, 14 October 2009 (UTC)

Am I alone in reading Opie's question as How do you argue against an arguer taking statistically insignificant facts and using them as evidence?"...He asked about this specific kind of reasonining, not this argument. 90.208.3.84 (talk) 23:14, 14 October 2009 (UTC)

A response to the OP's tiresome friends is to invite them to read the article Statistical significance. Cuddlyable3 (talk) 15:13, 15 October 2009 (UTC)

Ah, good point. I would say that the argument that I would use is that 1) it is an average trend over time, not that tomorrow is automatically going to be warmer today, and that 2) Global warming is somewhat of a misnomer as it will warm some places and cool others. The overall general trend however is to get warmer.

Yes - the response is that changing and unusual weather are precisely what proves that there is something weird going on. As we discussed a few days ago, Texas has gone through one of the most prolonged hot periods on record - and is now getting the highest rainfall on record. The key things here are that:

• The "weather" (what's happening here and now at whatever specific place you are at) is getting crazier - sometimes crazy hot, sometimes crazy cold, sometimes crazy windy, othertimes crazy rainy - or droughty. Records are being broken at a much higher rate than in the past - which is quite contrary to expectations - which is that the longer we keep records, the lower the probability that they will be broken.
• The "climate" (what's happening on average over a few years over the entire globe) is getting hotter.

As the climate warms up - the weather will get crazier. Sure, on the average that weather will be warmer than usual - but it's very possible for climatic warming to cause cool weather locally. An unusually cold spell in Saskatchewan is more than balanced by an even more unreasonably hot summer in Texas.

SteveBaker (talk) 00:31, 15 October 2009 (UTC)

good point. not only is the mean temp rising, but the standard deviation is rising as well, meaning an increase in the frequency of record lows as well as an increase in the frequency of record highs (but more of the latter). also more record wind velocities, precipitations, dry spells, etc. what you'd expect if more energy is being entered into the system, but it isn't being entered uniformly over space and time. Gzuckier (talk) 20:27, 18 October 2009 (UTC)

Plate movement rvsals

Removed question from sock of banned User:FreewayGuy. Please take any debate to the discussion page. SteveBaker (talk) 23:41, 14 October 2009 (UTC)

Oops! No wonder I never got complete answer. They even mention it on Pangaea Ultima artilce which I never bother to study it. And North American is attach with Eurasian plate. See the green and the brown boundarys and Pacific Plate is yellow. Theose tools have answer my questions. Those questions is probably sound alot like homework questions to normal peoples.--209.129.85.4 (talk) 19:01, 15 October 2009 (UTC)

average size of a penis

laugh all you want, because i am too right now. but i want to know, whats the average size of a mans penis age 18-25? i know im going to be laughing about this one all day --Talk Shugoːː 20:49, 14 October 2009 (UTC)

The NSFW article Human penis size will tell you all you want to know. And more. Just makes sure the kids have gone to bed and/or your boss is not lurking around your cubical. --Jayron32 20:54, 14 October 2009 (UTC)

Well i am at work so I won't be clicking the link. It is probably discussed there, but I find it a really amusing anecdote how there was an old study, IIRC from the 60s or 70s that asked men to measure them selves and record the result. That results of that study were used for decades as the basis for "average" penis size. What they neglected to factor in is that most men when measuring them selves were, lets say, generous with their result, pretty much systematically adding half to a whole inch to the actual result. This probably accounted for a whole generation of "average" men suffering penis envy because they thought they were really an inch below average. A more recent study in which men were measured by nurses revealed a more accurate, and not surprisingly lower figure. Vespine (talk) 23:42, 14 October 2009 (UTC)

About that last sentence you wrote there... Did they get a figure that was lower than the original figures and this was not surprising, or did they get figures that were not far enough below the original figures to surprise anyone? APL (talk) 02:42, 15 October 2009 (UTC)

Sorry probably needs a comma after "surprisingly", as in it didn't surprise anyone that the figure was lower, especially after they realised the error in the method used for the first study. Vespine (talk) 03:14, 15 October 2009 (UTC)

You need two commas: "and, not surprisingly, lower". --Tango (talk) 08:50, 15 October 2009 (UTC)

I'm surprised it wasn't a bit bigger if it was measured by nurses. Interesting to read how they managed that. :) Dmcq (talk) 11:53, 15 October 2009 (UTC)

These days I believe they administer Viagra (or similar) to ensure consistency in that respect. --Tango (talk) 12:57, 15 October 2009 (UTC)

but what if thay didnt have viagra then lol? kinda would make you wander. and thanks jayron for the link, luckly i dont have kids yet but i am at work. --Talk Shugoːː 17:27, 15 October 2009 (UTC)

I think some poeple might be falling for the stereotype, a Nurse in no way implies they were female. And so what if they didn't have viagra? A sperm bank manages just fine without viagra, and there would already be nurses on hand, wouldn't there? "While you're doing that do you mind if we measure your jhonny?" I don't think that's the way they did it since that would also introduce a bias, under average people might be less likely to agree, but i'm just using it as an example why i think "not having viagra" isn't an issue. Vespine (talk) 23:02, 15 October 2009 (UTC)

To be honest, there were so many music hall assumptions in Dmcq's answer that it's about a century out of date with reality. Simpler just to move along than try to unpick it. 86.140.149.215 (talk) 23:16, 20 October 2009 (UTC)

Which parts of the USA have a climate similar to London?

Particularly in terms of the summer and winter temperatures. Many parts of the US have I think extremely hot summers and extremely cold winters compared with those in London. Thanks. 92.29.126.121 (talk) 21:40, 14 October 2009 (UTC)

No part is quite the same, but the Pacific Northwest is most similar -- the area around Seattle. Looie496 (talk) 21:44, 14 October 2009 (UTC)

Given that England is surrounded on all sides by water, it's climate tends to be a lot more moderated. Most of the islands in the US (Alaskan islands aside, for which I do not know the weather patterns) are rather far south, so their climates tend to be far warmer on average. Since none of the continental US is a small island in the North Atlantic, the weather patterns will tend to be more varied and more extreme. Falconus^{p t c} 22:18, 14 October 2009 (UTC)

"Most of the islands in the US...are rather far south" I wonder which islands you had in mind and am not sure the "most" part is correct. Certainly we have a number of islands here in the Great Lakes rather far north and the Seattle area has several as well. 75.41.110.200 (talk) 15:05, 16 October 2009 (UTC)

I agree with Looie, the Pacific NorthWest is pretty similar. TastyCakes (talk) 22:23, 14 October 2009 (UTC)

I'm in Vancouver here and although the general regime is comparable, the 'type' of precipitation, the type of sunny day, the type of frigid air mass, is rather dissimilar. Vranak (talk) 14:03, 15 October 2009 (UTC)

In what way are these things different from London please? And, another item, I've always been suprised that somewhere as far north as Vancouver (and not maritime) could have a nice climate. 78.151.108.233 (talk) 11:46, 18 October 2009 (UTC)

Vancouver is actually closer to the equator than London. Being near an ocean moderates climate - London, where it never, ever, ever gets really cold, is further north than Winnipeg, where actual real authentic cold occurs. This is in part because London is close to the ocean. --NellieBly (talk) 12:03, 18 October 2009 (UTC)

In London it you usually get some snow on two or three days a year. Does not that count as cold? 78.151.114.229 (talk) 09:58, 19 October 2009 (UTC)

The US is farther south, but London (and most of western Europe) gets heated by ocean currents flowing from the tropics. That's why Ireland is considered to have a temperate climate, while southern Labrador, at a similar latitude, is considered subarctic. --Carnildo (talk) 23:19, 14 October 2009 (UTC)

Agreeing with all of the above, at London, you will find a link taking you to Oceanic climate. The map, will show the NW as in the same range as London, with Portland and Seattle listed alongside London in the Notable Cites of Oceanic Climate. --Preceding unsigned comment 02:39, 15 October 2009 (UTC)

On a pedantic note, England is not surrounded on all sides by water (see above). It has two land borders: Wales to the west, and Scotland to the north. If you're visiting, then it's good to not upset the natives. Bazza (talk) 14:28, 15 October 2009 (UTC)

That's actually quite relevant to the question, as Wales and Scotland, being mountainous areas and bordering a large expanse of water, suffer much higher rainfall and lower temperatures than London does. London is in the East Anglian rain shadow, and has a climate more comparable to Brussels or Paris than to Cardiff or Edinburgh. OR it's a good layer of clothing warmer than Wales or Scotland. --TammyMoet (talk) 15:17, 15 October 2009 (UTC)

October 15

Higgs Boson sabotages Large Hadron Collider.

Is this [1] as silly as it sounds? This is a discussion of a hypothesis that the failures of the super-conducting-super-collider and the large hadron collider to actually function is due to the laws of physics acting backwards through time to retroactively prevent a Higgs boson from being formed! The couple of papers I've read here seems to suggest that the authors are reasonably well-respected and that they are actually quite serious! But isn't there a gigantic loophole in their argument for a test of their theory? They say that if the LHC management were to promise to shut down the machine on a one in a million random chance - then if that unlikely event actually happens, then it's extremely strong evidence that there are influences travelling back in time to shut down the LHC!! But surely the odds are good that if the one-in-a-million chance comes up, then there is a high probability that the governments who paid all of those billions of dollars to build the machine would simply fire the LHC management who make this stoopid agreement - and have their replacements turn on the machine despite the result of the random trial? Hence a negative result of the experiment is proof of nothing - and we have an unfalsifiable proposition. Am I missing something? SteveBaker (talk) 03:31, 15 October 2009 (UTC)

I'm sure this isn't really an answer to your question, but I don't see how what they are proposing implies anything traveling 'backwards through time'. Instead, if what the collider produced would be destructive to the universe, then the anthropic principle / many worlds interpretation would imply we are only here to witness it because the collider malfunctioned. 149.169.106.83 (talk) 03:55, 15 October 2009 (UTC)

Reading the article, that seems to be exactly what their argument is, even though the science reporter phrases it as time travel. Basically that if the LHC leads to a paradox, then that can't be part of a consistent timeline that we're experiencing. It seems pretty doubtful to me that the laws of physics could lead to a paradoxical outcome, although I guess I can't think of any reason why not. Quantum mechanics seems like it could grant enough leeway for the universe to be steered away from certain outcomes and we probably wouldn't be able to notice most of the time. Rckrone (talk) 04:29, 15 October 2009 (UTC)

From a general relativistic point of view, the universe is not evolving form initial conditions, it exists as a solution to a system of equations that appears to its inhabitants as if it were evolving. Solutions where a Higgs boson create a time paradox cannot exist, because they would be self contradictory. Therefore, only the solutions where, for example, the LHC malfunctions, will be observed. Also, if the one-in-a-million chance did come up, I think we would try harder to find the Higgs boson, so it would, according to their theory, actually be less likely. 76.67.73.166 (talk) 05:02, 15 October 2009 (UTC)

At the very least, the hypothesis is falsifiable in that if the LHC gets started up successfully, and successfully detects a Higgs boson, then the hypothesis was incorrect. Red Act (talk) 04:25, 15 October 2009 (UTC)

And if we spend 100 years trying to set up this experiment and something always seems to go wrong, then that's pretty strong evidence to confirm the hypothesis. Rckrone (talk) 04:34, 15 October 2009 (UTC)

Really? That's like saying that you hypothesize a magic purple elephant exists in a particular jungle. Each expedition you set out to explore for the magic purple elephant fails. The conclusion, by analogy, would be that (a) the magic purple elephant exists; and (b) it is directly responsible for staging the interferences with your expeditions. Both (a) and (b) are ridiculous. Nimur (talk) 05:34, 15 October 2009 (UTC)

The analogy would be that you hypothesize that no expedition to find a purple elephant will ever even be carried out. Suppose then that every time someone plans an expedition, something unexpected happens that prevents it from even getting off the ground. If enough expeditions fail to happen and you can somehow calculate the probability of all those expeditions failing to happen given the null hypothesis, and that probability is sufficiently low, then you have a good reason to reject the null hypothesis, and conclude that something weird is going on whatever that may be. If the only plausible explanation of that phenomenon were that purple elephants were somehow sabotaging the expeditions, then you might conclude that was the cause, but there would certainly be room for other explanations if others were plausible. Rckrone (talk) 06:01, 15 October 2009 (UTC)

An infinite series of indents to this thread can be generated by remorselessly applying the spell "Absence of proof is not proof of absence". Nature provides one unavoidable reason that this series, as all non-abstract series, must like life be truncated. Sic transit gloria mundi. Cuddlyable3 (talk) 15:04, 15 October 2009 (UTC)

I think you are misunderstanding what I'm saying. Maybe I'm not saying it clearly. There are two experiments going on, not to be confused with one another. There's an experiment to find or not find the Higgs boson, and there's the meta-experiment to see if all attempts at carrying out the first are doomed. Hypothesis 1 is that the Higgs boson exists. Hypothesis 2 is that experiment 1 can actually be run without something against all odds melting it first.

• If experiment 1 is conducted and produces the Higgs boson, that's confirms hypothesis 1 and 2.
• If experiment 1 is conducted and doesn't produce the Higgs boson, that's evidence against hypothesis 1, but confirms hypothesis 2.
• If experiment 1 against the odds fails to be conducted, that offers no evidence for or against hypothesis 1 because there was no experiment, but it is evidence against hypothesis 2.

If enough attempts at the experiment produce the second result, without any producing the first result, then we probably have to conclude there's no Higgs boson. If enough attempts at the experiment produce the third result, without any producing the first or second result, then we probably have to conclude that something we didn't expect is dooming these experiments. That seems pretty far fetched, so there would need to be very strong statistical evidence to rule out just bad luck. But as you said, at some point absence of proof that the experiment can be conducted has to suffice as demonstration of absence of the possibility. Rckrone (talk) 18:10, 15 October 2009 (UTC)

There is a flaw in your logic. If I devise an experiment for detecting a Higgs Boson that involves nothing more than standing on my head and singing "the star spangled banner" (hypothesis 1 says that this will produce a higgs boson) - then if that experiment fails (which, I suspect it will), then it confirms hypothesis 2? Well, yes, it confirms that my stupid experiment can indeed be conducted - but if my experiment is useless in the first place, it doesn't confirm that the universe cannot unexpectedly cause a GOOD experiment to fail. So if the LHC fires up and doesn't produce a Boson - then nothing of any significance really happened and we still don't know whether the universe would have caused it to blow up if it had been sufficiently well designed that it could have produced a Boson. SteveBaker (talk) 20:36, 15 October 2009 (UTC)

That's not a flaw in the logic, although I think it is an important point. Hypothesis 2 relates to a particular experiment which may or may not be a good experiment for finding the Higgs boson. In fact the Higgs boson really has nothing to do with hypothesis 2 (except in motivating it). It's possible that hypothesis 2 could be confirmed and yet it's still true that the universe is conspiring against us, just in a way we haven't detected. As you say, maybe the universe "lets" the experiment happen because it's crappy, or the universe forces a certain result in a case where it could go either way. That's not something the meta-experiment can test. But if the experiment in question does always fail to happen, then we can say something more definitive. In other words, confirming hypothesis 2 wouldn't prove the universe isn't conspiring, but refuting hypothesis 2 would prove that it is.

If every single time someone stood on their head and began singing the star spangled banner the building collapsed or they had a heart attack and died, that would be quite a result. Rckrone (talk) 21:29, 15 October 2009 (UTC)

On reading through the few relevant publications at arXiv, I feel like the original authors (who may be respected physicists) are pretending to publish physics in order to make a political statement. I think this is disingenuous; they are protesting political and economic pressure in the wake of recent troubles at the LHC; but rather than address these issues straightforwardly, they are suggesting throwing caution to the wind and flipping a coin to decide the project's fate - they would prefer to see the LHC fail by random chance - preferring that "...LHC is stopped by our proposed game than if it just failed for some technical or political reason."[2]. Nimur (talk) 05:52, 15 October 2009 (UTC)

Taken as read, that last line is not completely off the wall. If the God Of The Future has to stop the LHC from generating Higgs particles, It would be preferable to do it in a way that doesn't destroy all the equipment or put all the scientists out of work. APL (talk) 13:36, 15 October 2009 (UTC)

I wish I could remember the name of a short science fiction story I read some time ago that sounds like this. A scientist had discovered a contradiction between two laws of physics, but in fact all physics laws had been generated in response by nature to contradictions been found like for instance between the wave and particle nature of light. He was warned not to do the experiment as other such experiments had bad effects but did so and disappeared in a flash of light. Many details are probably left out or wrong as it has been a while Dmcq (talk) 12:19, 15 October 2009 (UTC)

We need to miniaturize a Higgs Boson generator. My plan is to buy 36 of them. I will let them sit on my work bench for a few weeks. Then, based on the 6-bit binary representation of 6 numbers from 1 to 60 I will turn some of the generators on, and smash the rest with a hammer.

I'm being silly, of course, but the papers in question [3] do seem to be seriously proposing reverse causality. However, scientific humor is often so dry that outsiders don't spot it, so it's difficult to guess whether this is intended seriously or as some sort of satire. APL (talk) 13:36, 15 October 2009 (UTC)

Oh wait, My plan is too complicated. I'll just buy a lotto ticket and turn a single generator on if I don't win. Through this means I can take the universe hostage and make it do my bidding. APL (talk) 13:38, 15 October 2009 (UTC)

That's a good idea, I think I'll do it too ;-) Dmcq (talk) 14:05, 15 October 2009 (UTC)

Be wery wery careful. Larry Niven wrote a story called Rotating Cylinders and the Possibility of Global Causality Violation in which a mathematician tried just such a scheme to twist the universe's self-protection to his personal benefit and that of his species. For his trouble, he wound up getting himself and his race fried in a nova. --Trovatore (talk) 22:14, 15 October 2009 (UTC)

This is why we need to miniaturize our high energy reseach facilities. Sixty years ago, the common knowledge was that "nobody needed computers except the Government, the military, and a few nutcase physicists." Today, every desktop in the developed world (and a surprisingly large number in the un-developed world) is home to a miniature, personal, network-attached computer. We have found ways to make the computer usable and useful to everyday people. Meanwhile, the common knowledge has transitioned to "nobody needs high energy large hadron colliders except the Government, the military, and a few nutcase physicists." Imagine the possibilities when every man, woman, and child has access to a hadron collider! Nimur (talk) 14:10, 15 October 2009 (UTC)

Well, we don't really need to miniaturize the LHC. If the universe would care to make a few trillion dollars materialize in my bank account - I promise to use half the money to buy the actual LHC (I'm sure they'd sell it if I offered enough!) and then I'll smash it with a hammer. Hmmmm...nope...no money yet...any time now, I'm sure. SteveBaker (talk) 20:36, 15 October 2009 (UTC)

A hammer might be ineffective at destroying such a large piece of equipment. If the universe conspires to give me super-powers I will use them to destroy the LHC once and for all. APL (talk) 20:47, 15 October 2009 (UTC)

This whole business reminds me of quantum suicide. --Sean 14:21, 15 October 2009 (UTC)

It also reminds me of the Transactional interpretation of quantum mechanics and the Wheeler–Feynman absorber theory of electrodynamics, which require time travel in the form of electromagnetic radiation moving backwards through time. --Carnildo (talk) 21:53, 15 October 2009 (UTC)

I read the paper (the first one). It's... pretty stupid. They start with what I think is supposed to be the Feynman path integral, $\int _{\gamma }e^{i\,S(\gamma )/\hbar }D\gamma$. Here $\int _{\gamma }\,D\gamma$ is an integral (i.e. a sum) over all "paths" (i.e. histories of the system) and S(γ) is the action associated with the path γ. ħ has the same units as action, so S/ħ is unitless, and e^iS/ħ is a unit complex number pointing at an angle of S/ħ (in radians). The result of the integral is called an amplitude, and the square of the absolute value of the amplitude is basically the probability of the system going from a particular initial state to a particular final state. This is all standard physics. If you've read the book QED by Feynman, this is what those little arrows are—unit complex numbers pointing in different directions—and when he adds them up he's doing the path integral. As he explains, when you're near a critical point of S the arrows point in roughly the same direction and so combine to make a large arrow. Away from the critical points the arrows point every which way and don't add up to much; therefore those histories don't matter much and you may as well imagine that they don't happen. This is where the principle of least action comes from.

So, these authors say, what if S is complex rather than real? Then after multiplying by i you still have a real part, so the arrows are no longer all of unit length; they may be smaller or larger. Paths where they're smaller don't count for much, and they think paths with Higgs bosons in them might yield very short arrows. The first problem with this is that if S isn't real then you lose unitarity, and quantum mechanics pretty much falls apart completely without unitarity. The total collapse of the quantum formalism isn't necessarily fatal, but you'd think they'd have something to say about it. It's not apparent that they even know there's a problem. Secondly, they seem to think this modification of the path integral leads to retrocausality somehow, and I can't figure out why. Their whole reason for this seems to be the idea that the path integral is holistic since it treats the whole history at once and any unlikely event in any part of the history makes the whole thing not count. Okay, but that's true in standard quantum theory too, and it (provably) doesn't lead to retrocausality there. Consider proton decay. Proton decay is exceedingly uncommon if it happens at all. To put it another way, "the universe likes to avoid histories where proton decay happens". So, we build a machine to look for proton decay and we don't find any. The machine isn't plagued by technical problems, it just doesn't see what it's looking for; histories where it sees proton decay don't happen. That's not retrocausality, it's life as usual.

A lot of other crazy stuff in the paper. For example, they suggest that one of the options in their card game be to turn off the LHC after seeing 10 Higgs particles. That makes no sense. You don't turn on a particle accelerator and watch exotic particles fly out one by one. The LHC's solid-state detectors produce on the order of a petabyte of raw data per second. The overwhelming majority of that is thrown away almost immediately on the basis of simple heuristics, and the remainder, around a gigabyte per second, is stored in CERN's datacenter and subjected to subtle statistical tests over a period of months or years to tease out a signal. Even if you find a Higgs signal you don't know how many Higgs events there were or which ones they were, you only know that there were enough events of a certain type that it's statistically unlikely that none of them involved the Higgs. It's bizarre that two professional physicists would think that you could just count Higgs particles in real time at the LHC.

In short, they're crackpots or it's an elaborate joke, I'm not sure which. -- BenRG (talk) 21:54, 15 October 2009 (UTC)

Alternatively, it could be their effort to erode the credibility of arXiv, which has become notorious for releasing a variety of un-reviewed literature unto the masses (who seem unable to differentiate between "draft" and "publication" - let alone "peer reviewed"). As I noted above, I feel like the authors are attempting to make a point, but in a very roundabout way. Whether they have a prior history of research prestige is irrelevant - this publication series looks nonsensical. Nimur (talk) 23:43, 15 October 2009 (UTC)

I created some Higgs bosons in my backyard, but Schrodinger's cat ate them all. Matt Deres (talk) 17:11, 16 October 2009 (UTC)

It is not as crazy as it looks. They also mention superdeterminism in their paper. If Nature really is deterministic then you cannot rule out conspirationally looking events leading to some outcome. This can look the same as backward causation in some cases. Count Iblis (talk) 21:26, 20 October 2009 (UTC)

Ethanol / isoproyl alcohol

My mom is doing the experiment of extracting DNA from cheek cells (I'm not sure of the exact details, but whatever the usual way for a highschool biology class do it would be), and she only has isopropyl alcohol, not ethanol. Will this give comparable results? 149.169.106.83 (talk) 03:49, 15 October 2009 (UTC)

I'm terrible at Orgo; but, even if I can't answer your question, I'll state some facts facts from the article we have on it. The relevant subsection on our article Isopropyl alcohol says here that it dissolves a wide range of nonpolar compounds, and says it's safe and relatively non-toxic. If your mother is a teacher, can she just run the experiment one time and check to see if it gives comparable results? I don't know the answer, but I would assume the answer is yes. 윤리윤리윤리 (talk) 06:05, 15 October 2009 (UTC)

Using isopropanol throughout will result in a lower quality final product (more salt), although it may still be usable. For the purpose of washing a pellet of DNA (but not precipitating the DNA from solution into a pellet), 70% ethanol is the norm, which you can find in most drug stores (and if she's performing this experiment through a school, she may be able to acquire the higher quality ethanol from biochem providers). Someguy1221 (talk) 06:08, 15 October 2009 (UTC)

couldn't you use Bacardi 151 in a pinch? Gzuckier (talk) 20:22, 18 October 2009 (UTC)

quartz thermometer

what is the calibration,uses,advantages,disadvantages and applications of quartz thermometer —Preceding unsigned comment added by Derrickinlove (talk • contribs) 04:47, 15 October 2009 (UTC)

The resonant frequency of a quartz crystal depends on temperature, thus a quartz crystal oscillator plus a frequency counter can serve as a thermometer. Some advantages of this arrangement are small size, ruggedness, the display can be remote from the sensor, small thermal inertia gives fast response and the calibration is completed when the crystal is cut (cutting angle defines its frequency/temperature coefficient) and ground (for center frequency). An example application is an ingestible thermometer. A disadvantage is the electrical power needed for the oscillator and counter. Cuddlyable3 (talk) 13:42, 15 October 2009 (UTC)

Cosmological Constant

Doesn't a nonzero cosmological constant violate (or at least spontaneously break) time-translational symmetry? 76.67.73.166 (talk) 05:06, 15 October 2009 (UTC)

There are at least one or two sci ref desk regulars who are more knowledgeable about GR than I am, so they may (hopefully) come along and provide a more complete and unequivocal answer to this than I am able to. However, I'm fairly certain that the answer to the question is "yes". This of course implies via Noether's theorem that energy isn't conserved, but total energy isn't conserved in general in GR, except in certain cases like an asymptotically flat spacetime. For more information that may be valuable to you, see ADM energy, vacuum energy and cosmic inflation. Red Act (talk) 06:25, 15 October 2009 (UTC)

The big bang violates time-translational symmetry, so the cosmological constant is neither here nor there. --Tango (talk) 08:57, 15 October 2009 (UTC)

A cosmological constant by itself doesn't break time translation or time reversal symmetry. Roughly speaking a cosmological constant behaves like a repulsive acceleration that's proportional to distance, d²x/dt² = (Λ/3)x. This is time translation invariant since there's no explicit dependence on t, and it's time reversal invariant since acceleration doesn't flip sign when you reverse the direction of time. Of course, there are no nontrivial time-independent solutions to that differential equation. The solutions look like combinations of $e^{\pm t{\sqrt {\Lambda /3}}}$, and that's why the cosmological constant is said to cause "exponential expansion". But that kind of violation exists even without a cosmological constant, because the matter will gravitate together. In fact to avoid time dependence in a universe with matter you need a nonzero cosmological constant to counter the gravitational attraction, which was the idea behind Einstein's static universe. -- BenRG (talk) 12:42, 15 October 2009 (UTC)

Proper acceleration

Can anyone explain the following phrase to me, please?

"This first leg takes about 2 years if the acceleration's magnitude is about 1-gee."

I've read it in the proper acceleration article (Select, show for the Animation: high speed trip up then down), and couldn't understand the meaning of "1-gee".--Email4mobile (talk) 08:19, 15 October 2009 (UTC)

"1-gee" is another way of writing "1 g", which means 1 times g, where g is the acceleration of gravity at the Earth's surface. See g-force. Red Act (talk) 08:32, 15 October 2009 (UTC)

Thank you very much, Red Act! I will have to add it in my dictionary :). —Preceding unsigned comment added by Email4mobile (talk • contribs) 08:44, 15 October 2009 (UTC)

I presume this is in the context of some kind of space travel. If you could devise some kind of rocket that would keep you accelerating at 1 g for two years, you'd be moving pretty fast! 9.8 meters per second of speed increase for every second is 9.8 x 2 x 365 x 24 x 60 x 60 meters per second which would be 620,000,000 meter per second...but that's twice the speed of light - so long before you get to that speed, relativity is gonna get in your way and limit you to some significant fraction of the speed of light. Since relativity is involved, your perception of time and space will be distorted and your two year-long "leg" of this epic journey will take you a very long distance indeed! I'm sure someone with more time than me will be able to calculate just how far - but it's a long way. If you are thinking of hypothetical rocket engine designs, choosing an acceleration of 1 g is convenient because your crew would be able to experience earth-normal gravity for the entire ride. SteveBaker (talk) 20:05, 15 October 2009 (UTC)

Perhaps the OP is describing a theoretical acceleration of a massless particle to the speed of light followed by deceleration back to stationary. Cuddlyable3 (talk) 22:39, 15 October 2009 (UTC)

Massless particles can only travel at the speed of light. At any other speed they would have zero energy, which is pretty much the same, as far as we know, as not existing physically at all. (Abstract objects, like the number 2, can exist without having energy, but they don't exist physically.) --Trovatore (talk) 22:49, 15 October 2009 (UTC)

The whole question is about proper acceleration, not coordinate acceleration. So there's no problem with a rocket or other massive object maintaining a constant proper acceleration for arbitrarily long, without ever reaching the speed of light. Red Act (talk) 23:58, 15 October 2009 (UTC)

Relativistic Energy!

Is there a future probability that scientist might also discover Energy will be also relativistic like mass? I mean if they encounter a similar phenomenon to light someday that will account for the start and end of this universe?--Email4mobile (talk) 09:43, 15 October 2009 (UTC)

I'm not sure what you mean; it's already known that all energy is relativistic. Two different observers that are moving relative to each other will in general disagree about how much energy a given photon has. The frequency of light will red shift or blue shift depending on the velocity of the observer, and the energy of a photon is proportional to its frequency.

As far as predicting what may happen in the future, we don't do that here. See the top of this page. Red Act (talk) 10:17, 15 October 2009 (UTC)

Crystal Field effect

how the crystal field theory help us to understanding coordinating bonding and how it link with Jahn-Tller theorem ?Supriyochowdhury (talk) 10:32, 15 October 2009 (UTC)

The question is outside of my areas of expertise, but do the following articles help you?: Jahn–Teller effect, Crystal field theory, Coordination complex Red Act (talk) 11:02, 15 October 2009 (UTC)

Energy crisis and environment

what is energy crisis?and how energy crisis is related to environment —Preceding unsigned comment added by 203.196.249.171 (talk) 11:31, 15 October 2009 (UTC)

"Energy crisis" usually refers to an anticipated problem where energy demand is greater than supply. This can cause environmental problems because the energy gap may well be filled by using fossil fuels, pumping lots of CO₂ into the atmosphere. --Tango (talk) 11:41, 15 October 2009 (UTC)

Wouldn't they just increase the price until the supply and demand are equal? — DanielLC 13:47, 15 October 2009 (UTC)

Yes, but that's not always tenable. If it costs $300 to drive a car to the store, and you have a society based primarily around automobile transportation, it has very real effects. If the cost of food becomes unaffordable, then people starve. Yes, the economy stabilizes out eventually, but that can have horrific consequences, especially since affecting the price of fuel, energy, heat, etc., affects the prices of so many other commodities (increased transportation costs = increases goods costs, etc.). "The economy will correct itself" works to a certain degree, but "correcting itself" can mean "crashing". --Mr.98 (talk) 16:40, 15 October 2009 (UTC)

That's not enough to avoid a crisis. Suppose the supply of oil plummets, and as a result gasoline goes to $20 / gallon. Many economic activities that exist today would be totally untenable under those conditions, leading to drastic changes in the economy. Dragons flight (talk) 16:42, 15 October 2009 (UTC)

I think at $20 / gallon we would just adapt without many changes in activities (the price is not that far off in the UK!), but at $200 / gallon there would be drastic changes. Dbfirs 17:55, 15 October 2009 (UTC)

I don't think petrol in the UK has ever gone over $10/gal (I'm not sure how fuel price variations have corresponded with exchange rate variations, so I can't be sure). At double that, it would make a difference. People would use public transport more, travel less, etc. --Tango (talk) 18:14, 15 October 2009 (UTC)

Not to mention, USA is bigger than UK. Far more goods and services need to be trucked across country, and they need to be trucked longer distances. The cost of gas effects the cost of a lot of other things, not just your price at the pump. Groceries are a big one. APL (talk) 18:40, 15 October 2009 (UTC)

Also, the UK has significantly more infrastructure that does not depend on an individual automobile then in the US. Especially outside of major metropolitan areas. Googlemeister (talk) 20:53, 15 October 2009 (UTC)

And our cars are about a third the size of American cars. --Tango (talk) 21:00, 15 October 2009 (UTC)

Have a look at Energy crisis for an overview and Category:Energy crises for a list of specific crises. Regarding the environment, it could be argued that energy crises force people to use less energy or develop innovative ways of conserving energy which may benefit the environment in the long run. This search might help. Zain Ebrahim (talk) 11:54, 15 October 2009 (UTC)

Of course, if the energy crisis was caused by the sun becoming 10% dimmer, that would be very bad for the ecosystem. Googlemeister (talk) 15:34, 19 October 2009 (UTC)

Hydrogen fusion

The fusion of two hydrogen atoms produces a helium atom. But where do the two required neutrons come from? --Leptictidium (mt) 17:49, 15 October 2009 (UTC)

See the proton–proton chain reaction. In short, ¹H + ¹H ≠ ⁴He — Lomn 17:52, 15 October 2009 (UTC)

And note that saying "two hydrogen atoms" does not necessarily mean ¹H₁... it can mean, for example, ²H₁ or ³H₁. --Mr.98 (talk) 18:16, 15 October 2009 (UTC)

And the helium produced doesn't need to be ⁴He₂, it can be ³He₂. --Tango (talk) 18:23, 15 October 2009 (UTC)

Given the "but where do the two neutrons come from", it seems clear that the original question meant standard hydrogen and helium. If deuterium or tritium were involved, then there are your neutrons. If helium-3 was involved, then you don't need two neutrons. On a tangential note, though, why are you guys (and the pp article) specifying the atomic number of hydrogen and helium? Isn't that utterly redundant? — Lomn 19:11, 15 October 2009 (UTC)

The fusion of two ¹H ₁ atoms does not produce helium (standard or otherwise), though (not directly, anyway). D and T are both "hydrogen"; I think that's worth pointing out for someone confused. (And the proton-proton reaction explains how you get D from regular H). As for the notation—yes, technically it is redundant, but I've found personally that keeping track of protons helps students when thinking about nuclear reactions, especially when we are talking about isotopes. --Mr.98 (talk) 19:35, 15 October 2009 (UTC)

Kid in the balloon thing

If you have heard about the kid in Colorado who allegedly went for an unauthorized balloon ride, What volume of helium would be required to lift him off the ground if we assume that he weighs 50 lbs? I suppose we would need to know the pressure and temperature of the helium as well, but do not have a good estimate other then the altitude was something like 6500 ft above sea level and the temperature in the 60s F. Googlemeister (talk) 20:51, 15 October 2009 (UTC)

Helium has a density of .18 g/L at 1 atm, air a density of 1.2 g/L at 1 atm (and reasonably standard temperatures). The lifting capacity of helium is (roughly modeled) the density of air minus the density of helium, times the volume of helium. At altitude, the density of air drops -- it's ballpark 1 g/L at 6500 feet. Additionally, you have to put enough helium to create more than ambient pressure to inflate the balloon (but the sea level density is probably enough to suffice here). So, you get about .8 g/L of lift in the given conditions. To lift 30 kg (a low estimate of kid plus balloon materials), you'd need nearly 37500 L of helium, or a spherical balloon about 13 feet in diameter. The news photos I see don't show a spherical balloon, but it looks like a reasonably close estimate. Incidentally, the lifting power of helium has been discussed here repeatedly; there should be lots more in the RD archives. — Lomn 21:40, 15 October 2009 (UTC)

Turns out that the kid was hiding above his garage, and never flew, so I guess that while it may have been possible, it didn't happen. 152.7.20.66 (talk) 22:54, 15 October 2009 (UTC)

If I'm not mistaken, the balloon had absolutely no room for any children, unless he could breath helium. Vranak (talk) 01:14, 16 October 2009 (UTC)

Wonder what the density (lifting power) of Trimix is? DMacks (talk) 05:17, 16 October 2009 (UTC)

See also cluster ballooning.--Shantavira|^{feed me} 07:14, 16 October 2009 (UTC)

For Trimix you can work out the average molecular weight using the proportions given. The oxygen and nitrogen will dominate the mass since their molecules are so much more massive than helium. Using lighter gasses than Helium will not make much difference in lift either. eg Helium-3 would be more pricey. Graeme Bartlett (talk) 11:52, 16 October 2009 (UTC)

The New York Times reported that in a Wolf Blitzer interview on CNN, the kid said the reason he did not answer when he heard people calling his name was “You guys said… that, um, we did this for the show.” Mr. Heene denied that this meant it was all a publicity stunt. Local law enforcement has indicated they do not believe it was a hoax. Has there been any indication that the balloon ever had a gondola which could have carried the boy, or that the boy could have been inside the silver mushroom or the little stub below it? How long after the family called a TV station to report the balloon was away did they call 911? Edison (talk) 14:12, 16 October 2009 (UTC)

In a press conference that evening, Mr. Heene said the balloon was an experimental vehicle which was supposed to rise and descend via helium, but that it was supposed to move laterally via million volt pulses of electricity it would emit. Heene said that an egg timer on board was supposed to regulate the million volt emissions while it was tethered, before it escaped. Where was the electricity supposed to come from? Various accounts have mentioned a video of the actual launch, but I can only find coverage of the flight, pursuit and landing. Are there any images of the intact balloon and gondola prelaunch or of the liftoff? Edison (talk) 14:39, 16 October 2009 (UTC)

Found the launch video at CNN.com.[4] No sign of any basket or gondola other than the apparently sealed silver nub below the gasbag. Edison (talk) 14:53, 16 October 2009 (UTC)

I believe that's the wrong link and/or it changed. [5] gives the launch video for me called "'Balloon boy' story unfolds" (it's near the end) Nil Einne (talk) 20:00, 16 October 2009 (UTC)

given that the dad was a "scientist" who was building the "saucer" as part of his research into extraterrestrials..... Gzuckier (talk) 20:20, 18 October 2009 (UTC)

According to [6] they did check with someone to see if it was plausible it would lift the boy, and he suggested based on the dimensions given it was. However based on the real dimensions now available it was not possible for it to lift the boy. It's worth remembering that they had little choice but to err on the side of caution. Also accurately estimating the size of the balloon in the air is probably not so easy. In other words, even though it may be easy to say now, they should have realised at the time it couldn't lift the boy it probably wasn't so easy at the time, particularly since they apparently didn't have initial reason to suspect the father/family may have been fibbing on the dimensions which given it was apparently a hoax, he may have been. Also the weight for the kid was 17 kg (I was expecting it to be something like that). No info on the weight of the balloon but 7 kg seems a reasonable estimate to me. So 25 kg not 30 kg. And when you're just estimating (say 15kg for the child, 5kg for the balloon), 20 kg seems reasonable to me to err on the side of caution. Remember no one ever claimed the balloon was a supersturdy thing designed to carry a child. Nil Einne (talk) 19:29, 18 October 2009 (UTC)

more proof that the media is irresistably mesmerized by shiny objects. Gzuckier (talk) 20:20, 18 October 2009 (UTC)

Tree trunks painted white

Upon visiting certain developing countries, it is immediately noticeable that the bases of many tree trunks have been painted white, or with some form of whitewash. This usually occurs with cultivated trees or those at the edge of a forest area, and in some areas this is a very common practice. Regarding this subject, I have some doubts.

First, what purpose does this practice serve? In what way is this beneficial to the tree or to the ones who planted it? Is it done for biological protection, or merely for aesthetic purposes (despite the fact that I find it a bit of an eye-sore)? If effective in any way, to what degree is it recommendable?

Second, how prevalent is this practice? Upon mere observation, and from the experiences I can immediately recall, I cannot remember having observed this practice in developed countries, namely those with Western civilizations. However, upon visiting developing countries such as Brazil, Colombia, Mexico, and Kazakhstan, I have noticed that this practice is prevalent in varying degrees. Unfortunately, my inquiries into this subject with the natives have turned up fruitless.

Third, has this practice ever been used in developed countries in the past? —Preceding unsigned comment added by 201.21.180.57 (talk) 21:34, 15 October 2009 (UTC)

Not sure about Brazil etc., but when I've seen tree trunks painted white in temperate climates, it's been to prevent Sun scald (see section "Painting"). It's a form of sunscreen for trees. -- 128.104.112.179 (talk) 22:11, 15 October 2009 (UTC)

Trees along a road side sometimes have painted white stripes to guide traffic, e.g. in France. Cuddlyable3 (talk) 22:32, 15 October 2009 (UTC)

In some circumstances, might it be a way of marking trees selected for felling? 87.81.230.195 (talk) 23:31, 15 October 2009 (UTC)

If I remember correctly (I never paid attention to these things while I used to live in Mexico), it is to prevent sun scald, like 128.104.112.179 said. Titoxd^{(?!? - cool stuff)} 23:39, 15 October 2009 (UTC)

Roadside trees in WW2 London were often painted white because of the blackout. Some were still white during my 1960s childhood. Didn't seem to do them any harm.

In the U.S. I have seen foresters use "safety yellow" paint to mark trees to be felled for timber production. Some on the very base of the tree and some higher on the trunk. This way the harvesters know which trees they are to cut. Could the white paint be intended to provide the tree some protection against dog urine, when in parks or next to sidewalks? Edison (talk) 23:47, 15 October 2009 (UTC)

Second, how prevalent is this practice? China does it. 218.25.32.210 (talk) 00:52, 16 October 2009 (UTC)

When I used to live in downtown Manhattan as a kid, tree trunks were painted white -- and included those in the backyard parks with no access by car. Explanation for the white paint was that it was some form of protection against infestation of some sort. DRosenbach ^{(Talk | Contribs)} 02:34, 16 October 2009 (UTC)

In Spain, especially Andalucia, tree trunks in patios and to some extent street tree trunks are whitewashed partly for decoration and partly to discouraged ant and thus aphid infestation. The practice seems to be confined largely to citrus trees. It doesn't prevent infestation. Caesar's Daddy (talk) 06:22, 16 October 2009 (UTC)

My next door neighbor here in rural California paints her young fruit trees' trunks white. See tree paint. --jpgordon^{::==( o )} 18:48, 16 October 2009 (UTC)

Used to be quite common in former USSR for apple trees etc. Apart from sunburn protection already outlined above, another benefit is that it somewhat delays development of flower buds, relieving the risk of frostbite in case of spring frost. The practice used to apply to ordinary (not fruiting) trees as well but, for example, city of Moscow banned it, except for apple trees, in 1997. NVO (talk) 20:23, 17 October 2009 (UTC)

October 16

Wy does refraction occur?

What is the cause of refraction? I know about change in speed of light, but why does the speed of light change in different media? --shanuu (talk) 05:06, 16 October 2009 (UTC)

To quote our Speed of light article: "Light travels more slowly in a transparent material than it does through a vacuum due to interaction of the light with the electrons in the material." The Refractive index article explains it in terms of other intrinsic properties of the material. DMacks (talk) 05:12, 16 October 2009 (UTC)

In addition to what what DMacks said, the book QED: The Strange Theory of Light and Matter by Richard Feynman is an excellent (advanced) secondary-school-level treatment of the physics of optical phenomenon. I'd highly recommend it to everyone. -- 128.104.112.179 (talk) 14:30, 16 October 2009 (UTC)

That's sort of like asking, "I know that's it's harder to swim in maple syrup than in water, but why?" Perhaps it's difficult to conceive how light has to "act," so to speak, like a moving body, but the "viscosity" of the medium can have an effect on the light -- while this may not be the most precise way to describe it, it sure makes it more easy to understand for those whose name doesn't rhyme with "-eynman." :) DRosenbach ^{(Talk | Contribs)} 13:05, 23 October 2009 (UTC)

Special relativity.

I am currently reading a book on theoretical physics called, "The Elegant Universe, by Brian Greene". I've just finished reading the section on special relativity, and I had a question.

According to special relativity, every observer sees the speed of light at the same speed, regardless of their state of motion. This raised a question in my mind. I've read that light can be slowed down when it's in different media, eg rubidium gas. So, my question is this: If we always see light travelling at the same speed, how do we know that it changes speed in different media?Unique and proud of it (talk) 08:38, 16 October 2009 (UTC)

There is a constant called c, which is the speed of light travelling though a vacuum, as observed by all observers. If instead the light is travelling through a medium, all observers will instead observe the speed of the light to be less than c. Furthermore, if the light is travelling through a medium, the observed speed of the light depends on the velocity of the medium relative to the observer. It's only in a vacuum that the speed of light is the same for all observers. Red Act (talk) 09:09, 16 October 2009 (UTC)

Just as with the question right before this one, the speed of light and refractive index articles will provide a more thorough explanation. Red Act (talk) 09:17, 16 October 2009 (UTC)

I don't think it's correct to say "according to special relativity, every observer sees the speed of light at the same speed". The constancy of c is an empirical result (e.g. from the Michelson-Morley experiment), and Special Relativity examines the consequences. AndrewWTaylor (talk) 13:44, 16 October 2009 (UTC)

Right—Special Relativity comes out of assuming c is constant for observers. It does not prove it or even argue for it (and it's unclear how attentive Einstein was to experimental results like M-M, anyway). Of course, confirmations of SR's predictions further lend themselves towards believing the assumption is correct. An easy way to explain SR is that it is to say that it's the combination of two assumptions—that Galilean relativity is generalizable, and that c is constant. Everything else in SR just falls out of those two assumptions and what they imply about physical reality. --98.217.71.237 (talk) 14:24, 16 October 2009 (UTC)

No, it isn't entirely right. Special relativity gives rules for transforming space and time coordinates for an observer in motion. Those rules were formulated with the aim of making Maxwell's equations valid in moving reference frames. The constancy of the speed of light is a consequence of them. Looie496 (talk) 17:13, 16 October 2009 (UTC)

Yes,the Special theory of Relativity was inspired from Maxwell's equations, how they referred to a specific speed of light, c. Rkr1991 ^{(Wanna chat?)} 05:14, 17 October 2009 (UTC)

The "coordinate" approach to SR was not inherent to Einstein's original work, but is a later development by Minkowski (which Einstein originally was skeptical of, but later embraced totally). Einstein's original papers do not explain the constancy of the speed of light, but take it as a given. I am aware this is not how SR might be taught in a modern physics classroom, but as an assessment of its historical development, it is correct. As our article on the Annus Mirabilis papers puts it: "First, he applies the classic principle of relativity, which states that the laws of physics remain the same for any non-accelerating frame of reference (called an inertial reference frame), to the laws of electrodynamics and optics as well as mechanics. In the second postulate, Einstein proposes that the speed of light has the same value in all inertial frames of reference, independent of the state of motion of the emitting body." This is very clear from reading his 1905 paper on the subject. --Mr.98 (talk) 16:44, 17 October 2009 (UTC)

nuclear reactor model

i want to make a pressurised heavy water reactor for a science exibition to be held on 30th october. i need to complete my model till 26th october. i have find many a thing about its theory. but i'm unable to make the model of nuclear reactor of this type. i've the full explanation.

i'm in trouble in making its inside structure through which i can explain its working and its components. (full working,coolent used,its component) i'll also be including india's advanced heavy water reactor theoratically to enhance this project.

this project cannot be a working one but somehow we can use some goodoies to make it a attracting one.

can you please help me out in making this project i've very less days left with me. so pls help me. —Preceding unsigned comment added by Sunny kuchya (talk • contribs) 12:35, 16 October 2009 (UTC)

What materials are you using to make the model, and how large is it going to be? Our article on the CANDU reactor has a pretty nice schematic of one; this page gives a more clear explanation of the core area. Perhaps others will have concrete ideas as to what could be done to make something similar on a small scale without too much work? --Mr.98 (talk) 12:43, 16 October 2009 (UTC)

black hole

How do we know that a black hole is in fact a singularity and not simply an object where all dimensions are smaller then the event horizon, but not zero (say where all the mass is in a volume the size of a grape)? Googlemeister (talk) 16:24, 16 October 2009 (UTC)

We don't, as we have no way to retrieve information from beyond a black hole's event horizon. However, general relativity predicts the existence of a gravitational singularity, and since GR holds up well where we can observe and test it, it's reasonable to expect the math here to be a good model as well. It may also be worth noting that my understanding of the singularity is that it expresses the unavoidable eventuality that all matter within the event horizon will converge to a point. This statement does not preclude that, at the present time, the matter still has some non-zero volume (such as a grape). — Lomn 16:54, 16 October 2009 (UTC)

I'm afraid "at the present time" doesn't make much sense here. I don't believe there's a natural coordinate system in which you can talk about events inside the event horizon with the same time coordinate as events outside. In the usual coordinate system — I think they're called Schwarzchild coordinates or something like that — the time dilation means that, at the event horizon itself, time completely stops. --Trovatore (talk) 19:00, 16 October 2009 (UTC)

There are coordinate systems that cover the whole space except the singularity itself, but the timelike coordinate doesn't really coincide with what we would call "time" - the whole point of relativity is that there isn't really a global concept of "time". It makes sense to talk about the time things near you happen but if they happen somewhere else (and the other side of an event horizon definitely counts as "somewhere else") then it gets complicated. See Relativity of simultaneity. --Tango (talk) 09:06, 17 October 2009 (UTC)

Apparently the Penrose–Hawking singularity theorems prove it, but I don't understand that article. --Sean 17:01, 16 October 2009 (UTC)

Those are mathematical theorems, they just prove that the basic assumptions of GR imply singularities at the centres of black holes, they don't prove that those basic assumptions hold. I think most (if not all) scientists agree that those assumptions are perfect, since they don't explain quantum effects. --Tango (talk) 09:06, 17 October 2009 (UTC)

It isn't actually presumed that there physically exists a gravitational singularity at the center of a black hole. The singularity predicted by general relativity is commonly perceived as signaling the breakdown of the theory near that point. In particular, in some volume near that point, the extremely high density should result in quantum mechanical particle interactions that are not yet understood. To date it has not been possible to combine quantum and gravitational effects into a single theory. It is generally expected that a theory of quantum gravity will feature black holes without singularities. (Borrowing some from Black hole#Singularity.) Red Act (talk) 07:06, 17 October 2009 (UTC)

Perhaps for all we know the black hole, singularity or whatever else cease to exist inside the event horizon, but the effects still occur on the outside because the information about this non-existance cannot be transmitted to the outside without exceeding the speed of light?Trevor Loughlin (talk) 08:42, 17 October 2009 (UTC)

That sounds a little like the holographic principle. --Tango (talk) 11:30, 17 October 2009 (UTC)

Does "dark gravity" exist?

Scientist talk about "dark matter" and about "dark energy". They say that gravity "pulls the Universe together", while dark energy "pushes the Universe apart". But there are weird results from the formulas. So does "Dark Gravity" exist? Are any scientists investigating dark gravity? Lemonyjuicy (talk) 17:38, 16 October 2009 (UTC)

It's not clear what sort of concept "dark gravity" would be. Have you read our articles on dark energy and gravity? Our dark energy article in particular discusses its relationship with gravity and the rationale behind its proposal. — Lomn 17:55, 16 October 2009 (UTC)

We unfortunately don't yet have an article on dark gravity, not even a stub. Dark gravity just redirects to dark matter, which is incorrect.

It is not yet known whether dark gravity "exists" or not, i.e., whether a dark gravity theory will wind up matching experimental data better than a dark energy theory. Dark energy, in some form or another, is currently the most popular way to explain the acceleration of the universe's expansion. And general relativity is generally taken to be a very solid part of the foundations of modern physics, so any idea like dark gravity that involves tweaking general relativity faces an uphill battle.

Yes, scientists are investigating dark gravity, in that some theoretical physicists are playing around with trying to find an appealing dark gravity theory to fit the available data. Whether some complete, self-consistent dark gravity theory will be developed, which will hold up to theoretical scrutiny to the point where experimental physicists will start to get involved in testing the theory, is at this point a matter of speculation. Red Act (talk) 06:27, 17 October 2009 (UTC)

Really? I've never heard the phrase "dark gravity". There is lots of work going on trying to find new theories of gravity to explain various things, but do any of them use the term "dark gravity"? "Dark matter" and "dark energy" are just names, the word "dark" doesn't have a specific meaning, it just sounds good in applications for research funds. --Tango (talk) 09:08, 17 October 2009 (UTC)

Agreed. Some theories that try to explain the effects we ascribe to dark matter by modifying gravity are called Modified Newtonian Dynamics or MOND. They can explain some of the discrepancies in the rotation rate of galaxies, but not e.g. the Bullet Cluster. --Stephan Schulz (talk) 09:20, 17 October 2009 (UTC)

Yeah, MOND and some other older alternate gravity theories couldn't explain the gravitational lensing in the Bullet Cluster. But there are a couple newer alternate gravity theories, STVG and TeVeS, that supposedly can. Red Act (talk) 09:57, 17 October 2009 (UTC)

Yeah, I'd never actually heard of dark gravity either, before I started researching this question. But Google turns up tons of hits. It's basically modifications of the Einstein field equations in ways that would explain the acceleration of the universe's expansion, in ways that don't fit the form of the cosmological constant or an additional contribution to the stress-energy tensor. It's rather new; I think the oldest date I saw on anything was 2001 or 2003, with most stuff being since 2005 or 2006. I'm sure the "dark gravity" name arose as a contrast to "dark energy", which it's an attempt to avoid hypothesizing. Dark gravity basically differs from earlier alternative gravity theories like MOND in that it's addressing a different problem. Dark gravity addresses the expansion of the universe; MOND was developed to address the much smaller scale problem of galaxy rotation curves. However, very recently there are also alternate gravity theories like STVG and TeVeS, that address both cosmological and galactic gravitational problems. Red Act (talk) 09:51, 17 October 2009 (UTC)

I don't think the recent appearance of the term "dark gravity" in place of "modified gravity" means much; it's just become fashionable to put "dark" in front of everything in cosmology. I don't think the bullet cluster can be explained without dark matter. STVG and TeVeS introduce new vector and scalar fields, and their explanation of the bullet cluster, if it works at all, involves independent motion of those extra fields. Scalar and vector fields are also known as "particles", and particles introduced to explain gravitational anomalies are known as "dark matter". There are lots of other dark matter candidates, so it's hard to get excited about one more. MOND was interesting because it didn't have those extra degrees of freedom. -- BenRG (talk) 00:27, 18 October 2009 (UTC)

Chewing gum or no chewing gum on the pavement

Are these marks on the pavement of every city which look like chewing gum, really chewing gum? I read somewhere they were something else, like dirt getting clumped together with oil rests, but I am having trouble in finding the article. --Quest09 (talk) 17:57, 16 October 2009 (UTC)

If it looks like this picture, then it's chewing gum. If it looks like this on the other hand, it's still chewing gum, but after Ben Wilson has dealt with it. SpinningSpark 19:21, 16 October 2009 (UTC)

Could these be some kind of bird excrement or perhaps treesap blobs? What about insect residue like snail trails or worm matter? 66.102.199.179 (talk) 14:31, 17 October 2009 (UTC)

no dude, its gumm. smails and worms would have a trail not splotches and sap would have a shine to it, normaly. —Preceding unsigned comment added by DanielTrox (talk • contribs) 17:38, 19 October 2009 (UTC)

Water supply in developing countries

Why is it that in many developing countries, it is not safe to drink water from the mains supply but yet it is safe to use it for washing etc? Clover345 (talk) 18:49, 16 October 2009 (UTC)

Because it is far more easy for a pathogen to infect you if you directly consume it. You are far less likely to get infected from using infected water to wash your clothes as most of the nasties will die when the clothing dries, or from soap you use while washing. Of course, it would be better to use uninfected water for washing as well if it is available.

To put it another way, drinking the infected water would be like making out with someone who has the flu, vs washing would be like entering a room that someone with the flu exited 10 minutes ago. Which is more likely to give you the flu? Googlemeister (talk) 19:11, 16 October 2009 (UTC)

Similar to the reason you (well, children anyway) wipe your hands on your clothes before eating - the dirt and grime is a drag to get on your cheeseburger, but it won't do too much harm on your shirt sleeve. ~ Amory (u • t • c) 21:00, 16 October 2009 (UTC)

I understand that in many parts of India, for example, the water supply drawn from wells and acquifers (sp?) is naturaly contaminated with low levels of arsenic - not enough to kill you, buy enough to cause health problems. 78.151.108.233 (talk) 11:42, 18 October 2009 (UTC)

that said, volatile toxic contaminants are often more easily acquired by inhalation than by ingestion, meaning that you wouldn't want to shower in water that was too polluted to drink, either. [7] although most of the work, at least the well publicized work, done appears to be studying chlorinated compounds in the First World water supply. Gzuckier (talk) 20:13, 18 October 2009 (UTC)

Oxygen production in the dark?

Can photosynthetic organisms produced oxygen in the dark?

Aaadddaaammm (talk) 20:43, 16 October 2009 (UTC)

Yes. Photosynthesis is technically two reactions, and only the first requires light energy. The second requires the products of the light reaction, not light itself, so it is not directly dependent on sunlight. Often plants will perform this second reaction (called the "dark reaction") during the daytime, when the reactants made from the light reaction or readily available, although in climates where water is scarce they will often wait until after dark to prevent water loss. ~ Amory (u • t • c) 20:56, 16 October 2009 (UTC)

Thanks for the reply. But only the first reaction generates oxygen, doesn't it? The light reactions produce proton gradient (then ATP), NADPH and O2, and then the dark reactions use the ATP and reducing power to fix CO2. So in the very basic scheme, oxygen shouldn't be evolved in the dark, but are there certain circumstances or other processes known?? Aaadddaaammm (talk) 21:06, 16 October 2009 (UTC)

In general terms yes, most of the oxygen is likely to be released during the day. Some crassulacean acid metabolism plants uptake most of their CO₂ during the night but oxygen release is still during the day [8]. I'm not aware of any plant that releases significant amounts of oxygen in the dark Nil Einne (talk) 09:32, 17 October 2009 (UTC)

October 17

Spin quantum number

Why do they have the two possible values for the spin quantum number be -1/2 and 1/2 rather than -1 and 1? --76.211.91.59 (talk) 00:43, 17 October 2009 (UTC)

Spin quantum numbers are a measure of a particle's intrinsic angular momentum, in units of ħ, the reduced Planck constant. In other words, the component of an electron's intrinsic angular momentum, as measured along any direction, can be either +1/2 ħ or -1/2 ħ. That begs the question of why the reduced Planck constant was chosen to be defined as it is, instead of defining a unit of angular momentum that's half as big. Why that happened was really a matter of notational convenience in other places in quantum mechanics where ħ shows up. I'm not sure of the original equation(s) for which ħ were historically used first, but as an example, the energy of a photon with angular frequency ω is given by E=ħω. If instead of ħ, a constant was instead defined which had the value of ħ/2, then the equation for the energy of a photon as expressed using that different constant would have to have an extra factor of 2 in it. Red Act (talk) 03:15, 17 October 2009 (UTC)

Masturbation and a teen

Hi, if a 17 year old boy masturbates, could that affect his physical growth? --FromSouthAmerica (talk) 02:04, 17 October 2009 (UTC)

No. Masturbation is a normal, healthy practice, and even has some health and psychological benefits. See Masturbation#Benefits. Red Act (talk) 02:23, 17 October 2009 (UTC)

Yes but the growth is only temporary. Cuddlyable3 (talk) 10:46, 17 October 2009 (UTC)

What Red Act said goes for 17 year old girls too. Unfortunately many so called "civilized" cultures have indoctrinated us with various moral taboos on this subject (and sex in general) resulting in taking a 100% natural part of life and adding in artificial components of guilt, shame, and even horror to the idea of masturbation. Thus we get wive's tales of "If you do that it will stunt your growth". As we enter the 21st century we are just now (as a society) beginning to finally realize that such negative components are psychologically harmful and that masturbation (in moderate use) has physically and mentally beneficial effects. 66.102.199.179 (talk) 14:00, 17 October 2009 (UTC)

The primary factor behind stunted growth, worldwide, is malnutrition. Masturbation doesn't have anything to do with it. --Mr.98 (talk) 15:20, 17 October 2009 (UTC)

Why do some people so eagerly promote a self abuse (that was an accepted term) that is indisputably debilitating, un(repro)ductive, messy and not the sort of thing a competitive athlete does before the Olympics? Cuddlyable3 (talk) 16:32, 17 October 2009 (UTC)

I don't think I'd promote it, but it's a bit like defecation: don't talk about it in polite society, but don't deny that it exists or that it happens or that it's a perfectly normal part of the human experience. SDY (talk) 16:37, 17 October 2009 (UTC)

I'd promote it, sure. I think people coming to terms with their own sexuality, the reality of orgasm, and things of that nature are perfectly healthy. It is not debilitating in the slightest, it is not much messier than blowing one's nose, and does in fact relieve quite a bit of mental stress and allows many a young man to focus on things other than trying to have actual sex. Compared to teenage intercourse, masturbation is downright healthy and a social good. I promote it, sure, why not? I don't see any evidence that moderate masturbation does any harm, whereas self-denial, self-shame, fear-of-sexuality, marrying-at-too-early-an-age, having-children-at-too-early-an-age, and many of the mental and social activities that have gone along with the discouragement of masturbation have done legions of harm across the ages. If you don't want to do it, then don't, but don't make it out like it is not a perfectly natural human activity. --Mr.98 (talk) 23:23, 17 October 2009 (UTC)

Something to keep in mind next time you're in the Olympics. APL (talk) 23:22, 18 October 2009 (UTC)

I should remind all posters of the Ref Desk prohibition on giving medical advice - some of the above comments are getting dangerously close to it... Tevildo (talk) 20:31, 17 October 2009 (UTC)

Stating factual information isn't media advice. —Preceding unsigned comment added by 82.44.55.2 (talk) 20:43, 17 October 2009 (UTC)

This is common sex education information that anyone who paid attention in health class should know. It's not medical advice in the slightest. --Mr.98 (talk) 23:23, 17 October 2009 (UTC)

I still think there's a difference between "Masturbation doesn't stunt your growth/make you blind/put hair on the palms of your hands" and "Masturbation is good/bad for you" - however, the line has not been crossed, and I withdraw my remark. Tevildo (talk) 00:32, 18 October 2009 (UTC)

There must be nearly 98 strawman arguments in Mr.98's promotion. Masturbation is also socially preferable to running naked through the streets molesting little children but so what? Mr.98 seems to have discovered Sigmund Freud's once-liberating model of Psychosexual development a century late. Mr.98's claim that (his?) masturbating does not delibilitate in the slightest sounds more like a boast of solo virility than a prowess that can stand up to testing. IMHO Tevildo's line has been crossed and I agree with Tevildo's original post. Cuddlyable3 (talk) 13:17, 18 October 2009 (UTC)

Go back to the 16th century. —Preceding unsigned comment added by 129.67.39.44 (talk) 14:32, 18 October 2009 (UTC)

Cuddlyable, you seem to be arguing from old fashioned superstition and/or ignorance. And are definitely assuming bad faith. The Masturbation article has four separate references providing scientific data that frequent ejaculation increases fertility, not decreases it. It also has a reference indicating that masturbation can lower blood pressure. And a couple of conflicting reports that it may (or may not) reduce the likelihood of prostate cancer. And that's just for males. There a couple of other references to health benefits for females.

If you're going to go around pushing old fashioned prejudices (ie:"that was an accepted term"), then you could at least provide a modern reference that back up your claims. This is the reference desk. APL (talk) 23:37, 18 October 2009 (UTC)

Set of 4 questions: Nanotech, astrophysics, and structural engineering related.

This is basically a set of mostly math-based questions but to answer them also requires knowledge of other advanced scientific subjects (see the Subject above).

The core of this question set is based on a hypothetical proposal, to wit:

Build a simplified Niven ring made entirely of carbon nanotubes and set it in an equatorial orbit around the Earth.

Two major types of nanotubes are required:

• Type One are to be engineered for use as a rigid frame for the ring structure, perhaps formed like a belt of interlocked large (2m) triangular or hexagonal cells).
• Type Two are to be engineered for use as a optical screen mesh mounted across the frame in panels.

Dimensionally the "belt" must be wide enough to fully shadow the Thermal equator during peak periods of insolation. That dimension will in turn depend on the belt's diameter which is open for discussion (see below).

So here is my question set...

1. Ideally this belt would be located in the upper atmosphere between 100km and 300km above sea-level. However, at that altitude the belt would be exposed to a large amount of atmospheric turbulence and might not be able to sustain orbit. Nanotubes should be well suited to such stresses but in the event that this is not a practical location what is the next best location (altitude/radius) to accomplish the desired shadow area?

2. Having selected an altitude what is the full set of dimensions for such a belt? Thickness obviously will be negligible unless structural design mandates a frame depth of more than nano dimension.

3. Based on the answer to #2, what is a rough estimate of the total mass of the ring? That is, how much nano carbon material would be needed to build this structure?

4. According to the WP article on optical properties of carbon nanotubes, it states:

"Their unique feature is not the efficiency, which is yet relatively low, but the narrow selectivity in the wavelength of emission and detection of light and the possibility of its fine tuning through the nanotube structure."

So, assuming you couold create the Type Two nanomaterial to filter only certain frequencies, what optical frequencies would need to be filtered to create a shadow effect that reduces the thermal energy of insolation by approximately 2% in the belt's shadow zone, but leaves the visible and botanically important sunlight frequencies unaffected?

66.102.199.179 (talk) 06:02, 17 October 2009 (UTC)

I don't see why you need carbon nanotubes. The Ringworld needs to be really strong because it rotates really fast to create artificial gravity. Your ring could rotate at orbital velocity, so there would be no forces on it at all (beyond the turbulence, etc., that you mention, but that is manageable). The problem with your idea is that the visible and botanically important sunlight frequencies make up the vast majority of the sun's emissions - that is why our eyes and plants have evolved to use those frequencies. You can't block out the thermal energy without blocking those frequencies because the energy is carried by those frequencies. --Tango (talk) 09:18, 17 October 2009 (UTC)

... and don't forget (a) to account for tidal forces due to Moon and (b) you'll need some sort of stabilising mechanism. Gandalf61 (talk) 11:14, 17 October 2009 (UTC)

I'm not sure it would be too unstable - you can consider each molecule separately as being in a stable orbit, the forces within the body will be fairly small (how big they are depends largely on the size of the body) and shouldn't affect the stability. --Tango (talk) 11:34, 17 October 2009 (UTC)

For a discussion of the dynamic instability of Niven rings see Why Niven rings are unstable by Erik Max Francis. Gandalf61 (talk) 14:17, 17 October 2009 (UTC)

Yes, but this isn't a Niven ring - it would be travelling at orbital velocity, which should make a difference. If a regular satellite can orbit stably then lots of them joined together should be able to - is the problem that the orbit needs to be able to become elliptical? If so, I've made some suggestions below to allow that. --Tango (talk) 13:40, 18 October 2009 (UTC)

Tango: As for "why nanotubes?", simply because I believe that (or some other nano structure) would be the material that would be lightest and least resource consuming yet still able to maintain structural integrity (thus my interest in answering Q#3). The inspiration for its use came from Bradley C. Edwards' idea of using a nanotube ribbon for a space elevator cable. 66.102.199.179 (talk) 13:28, 17 October 2009 (UTC)

Since making nanotubes is so difficult, I don't think it would be the best choice. They are necessary for a space elevator because of the tensions involved, there shouldn't be any tension in your design. --Tango (talk) 13:38, 18 October 2009 (UTC)

On Q#4: If we are only trying to reduce thermal energy, what about reducing of the infrared and/or the ultraviolet? What about selectively filtering out a motled sampling of the spectrum using a wide variety of freqency atuned nano-devices in low quantities? Recognize that we only need to filter about 2% of the energy, not all of it. The end-intent should be to ensure we don't make the days "always grey" and piss off the local tourist industries. :) 66.102.199.179 (talk) 13:28, 17 October 2009 (UTC)

Both infra-red and ultra-violet do serve a purpose (for example, UV is used in producing vitamin D in humans). I think blocking them entirely would be a bad idea. Just reducing intensity throughout the spectrum by 2% would probably be easiest - it is a fairly small amount compared to natural variations due to latitude and weather. --Tango (talk) 13:38, 18 October 2009 (UTC)

Gandalf61: Agreed, the belt would need a set of basic attitude actuators just as any satelite does for station keeping. This may be a huge belt shaped object but it is still an artificial satelite in the end. The issue of orbital stability does however have great bearing on the answer to Q#1. 66.102.199.179 (talk) 13:28, 17 October 2009 (UTC)

It might be best to have lots of co-orbital satellites rather than a continuous ring - that might improve the stability. Alternatively, having the ring be reasonably flexible could help. I think the instability, if there is any, would be a result of the orbit not being able to become elliptical - a series of individual satellites or a flexible ring would be able to. --Tango (talk) 13:38, 18 October 2009 (UTC)

Certainly separate satellites have better stability than a ring. The problem with a ring is that if it moves off-center by a tiny amount, the gravitational force on the side that is now nearer to the planet is greater than it was - and the gravitation on the side further from the planet is weaker - so the ring tends to move even more off-center. The inverse-square law makes this a worse-than-linear issue, so things get bad quickly. Furthermore, if the ring is even moderately rigid, parts of the ring are now under nasty stresses that are going to be tough to control. There are modes of lateral instability too - the ring can start to wobble, and again, there are feedback effects to consider that make it very tough to control. With computerized thrusters, running somewhat continuously - you could MAYBE avoid these problems - but then you have to consider where the energy and reaction mass is coming from. Solar panels would get you plenty of energy - and some kind of ion drive would minimise (but not eliminate) the amount of reaction mass needed. The killer is that with the sun and (especially) the moon involved, the tidal forces on a rigid ring would be spectacular - fighting the tides would require vast expenditure of energy. SteveBaker (talk) 15:49, 18 October 2009 (UTC)

indeed, a ring has NO orbital stability whatsoever, and thus shows no advantages over just flying a bunch of planes or balloons or some such, since it would need to be actively steered all the time. it's nothing like a satellite which just needs a nudge every now and then. the closest thing would be a couple of satellites at the Trojan points which probably wouldn't supply what you need.Gzuckier (talk) 20:45, 18 October 2009 (UTC)

Could Alain Robert have escaped the Twin Towers?

The survival prospects of those above the Twin Towers explosion were limited. Would someone with the "French Spiderman" Alain Robert's near superhuman climbing skills have escaped by climbing down the outside of the building, rather than take the lethal alternative of jumping?Trevor Loughlin (talk) 08:32, 17 October 2009 (UTC)

We can only speculate and the ref desk doesn't do speculation. Sorry. --Tango (talk) 09:20, 17 October 2009 (UTC)

Ask him. His website has a contact page. Cuddlyable3 (talk) 10:36, 17 October 2009 (UTC)

If he had been in the building above the burning portion, there would be absolutely no way that he could have climbed down through the fires. If he had been below the burning portion, he could have taken the stairs down like the other survivors. 72.94.164.21 (talk) 10:44, 17 October 2009 (UTC)

I would be hesitant to rule it out as impossible. There may well have been a path around or through the fires, any reply we can give would be guesswork. --Tango (talk) 11:32, 17 October 2009 (UTC)

Philippe Petit might have stood more chance, but...--Shantavira|^{feed me} 12:27, 17 October 2009 (UTC)

On September 11, 2001 this could have happened: 8:46 a.m. plane hits WTC North Tower. Philippe Petit rushes to the roof and throws a line and anchor that he happened to have stored "just in case" to WTC South Tower. By 8:55 a.m. he is balancing on the line between the towers. Just before 9:03 a.m. he arrives on the roof of WTC South Tower and breathes a sigh of relief "Mon dieu, I am - how you say - out of zat frying pan! Cuddlyable3 (talk) 16:25, 17 October 2009 (UTC)

One question would be whether he would have time: the South tower lasted 55 minutes after the impact, the north tower about 100 minutes. Climbers like this seem mainly to go up buildings not down, although Robert has been up and down a few, e.g. the RBS Tower in Sydney, but it's hard to estimate how long it would take to climb down (especially as he normally stops to chat on the way). --82.41.11.134 (talk) 13:58, 17 October 2009 (UTC)

Right, this is what I imagine the question is. How far could he have gone in 55 minutes? The towers are pretty tall—I doubt he could do them from the very top. If one had some idea of what his speed is climbing down, you could calculate around where the cutoff would be for feasibility. --Mr.98 (talk) 15:24, 17 October 2009 (UTC)

I thought about the timing too as well but once finding out the time it took for the buildings to collapse I decided it was impossible to rule it out with that. No one said it had to be the south tower right? According to Alain Robert it took him about 100 minutes to climb the Petronas Twin Towers. This is climbing up not down but I don't see any reason to presume he would definitely take longer to climb down, in fact it's possible it would be faster therefore it seems you can't rule it out Nil Einne (talk) 15:44, 17 October 2009 (UTC)

I would personally suspect down to take longer, but I don't really know. Climbing up a tree is easy. Climbing down is hard—you've got to limit your own momentum, and you are somewhat going against the orientation of your body (you can't use your upper arms as well, and you can't see what your feet are doing as well). But I'm no climber. --Mr.98 (talk) 16:40, 17 October 2009 (UTC)

I don't know much about climbing buildings, but it seems like the facade of the trade towers would be difficult. I don't think there were any horizontal elements to grip. Rckrone (talk) 16:54, 17 October 2009 (UTC)

Take a look at his photo gallery, he doesn't actually need very much to hold on to at all. A rock climbing friend of mine can lift himself up holding on to a beam with just the tips of the fingers of one hand. This is a difficult thing to do but possible with training. SpinningSpark 14:26, 18 October 2009 (UTC)

The so-called skyscraper climbers usually just use a dedicated window washing equipment track. Descending would be far faster than ascending, and if there were a track not swept by flame or enveloped in extreme heat, it would have been a piece of cake to make the descent. Once below the fire, he could have broken a window, entered the building, and run down the stairs. Easy-peasy. Edison (talk) 00:11, 19 October 2009 (UTC)

Cold Fire

Hello I'm looking for info on cold fires i.e. fires that have unusually low temperature they don't burn, just glow. I could not find anything about it in Fire. I've been told that such fires are possible but how? Aurora sword (talk) 12:29, 17 October 2009 (UTC)

will o the wisp or ghost light is a natural kind. Does cold fire have anything? (No) Graeme Bartlett (talk) 12:33, 17 October 2009 (UTC)

Burning methane clathrate is a sort of cold fire. It's like burning ice. It does have a regular flame, though, not just glowing. Red Act (talk) 12:41, 17 October 2009 (UTC)

Interesting, is this the kind of thing commonly used in chemistry demos? Aurora sword (talk) 12:46, 17 October 2009 (UTC)

"Fire" is just a self sustaining reaction between something and oxygen which generally generates heat. It self sustained by the local diffusion of both heat and radicals, but there is no reason why in absolute terms it has to be hotter than room temperature say. The heat generated will tend to heat things up but if the starting material is naturally cool (for example has latent heat associated with a phase transition at a cool temperature) then it is possible for the fire to stay cold. But it needs to be fairly reactive to burn cold. So if you burn something which boils at body temp (Diethyl ether for example) the liquid under the flame will not get to above its boiling point, and you can pour it over your hands and light it without burning yourself (although not recommended, jugglers use it but it needs skill to avoid the flame itself burning you). A solid which sublimes but is reactive enough could surface burn cold but personally I cannot name one. Methane Clathrate seems a plausible candidate. --BozMo talk 12:53, 17 October 2009 (UTC)

In that case, what is actually burning is just methane so it is just like any other methane flame - the source of the methane is cold, but the fire itself is hot. --Tango (talk) 13:02, 17 October 2009 (UTC)

The light from a flame is usually because it is hot, so you're not going to get a bright orange flame like you get with a candle without it being hot. Any light will be from chemical emissions, like the blue flame you get from complete combustion of natural gas (eg. a gas cooker or Bunsen burner). I don't know of any chemical reactions that result in emissions at low temperatures. --Tango (talk) 13:02, 17 October 2009 (UTC)

Well, there's bioluminescence and other chemiluminescence. Red Act (talk) 13:13, 17 October 2009 (UTC)

Have a look at "pyrophoricity". Plutonium is one of the classic examples. Axl ¤ [Talk] 13:25, 17 October 2009 (UTC)

To have a visible flame - you need enough temperature for the blackbody radiation to be in the visible range. When the temperature is below the 'Draper point' (Huh! No article?!?) - which is at about 500 degrees Centigrade - there is no light emitted. So that's pretty much the coldest a visible flame can possibly be. There may be other chemical reactions that produce light as a byproduct that could kinda look like a flame - but those aren't properly 'flames'. There may be cooler oxidation reactions that produce the characteristic plume of a flame - but with no visible light. Methane clathrates look like a lump of ice - if you set light to it, it looks like you're burning an ice-cube - which is surprising and interesting - but the flame is just a normal methane flame - it's plenty hot! SteveBaker (talk) 13:26, 17 October 2009 (UTC)

I thought the OP asked for no visible flame but surface burning? So why are you suddenly all talking about flames? Surface burn cold was the request, my flame bit was intended to be an analogy. --BozMo talk 14:07, 17 October 2009 (UTC)

I think the glow from white phosphorus in damp air pretty much fits the bill of what is being asked for. The reaction is essentially a kind of fire, in that it's ultimately a gas phase oxidation process, but it merely glows instead of burning normally with a flame. And the reaction is cold, because it's a form of chemiluminescence, not a form of incandescence, in which the Draper point of black body radiation would be a consideration. Red Act (talk) 14:16, 17 October 2009 (UTC)

I may be interpreting the OP's question incorrectly, but perhaps they'd be interested in coal seam fires that often simply smoulder for years and years, but don't "flame up" in the usual manner. Smoulder has more information on that kind of topic. Matt Deres (talk) 21:15, 17 October 2009 (UTC)

The OP specifically asks about COLD fires. The combustion of Coal requires more temperature than that. Recall the Fire triangle. For a fire to be maintained requires heat, oxygen and fuel. Remove the heat and the fire goes out. Even smoldering (which is just a small fire) requires - and produces - heat. So - either what you have is some kind of exotic combustion at temperatures so cool that no light is produced (below the Draper point) - or it's some other luminescent chemical reaction which would not normally be described as a "fire". SteveBaker (talk) 15:35, 18 October 2009 (UTC)

How do deleaved trees breathe?

How do trees that have lost all their leaves in the fall breathe through the winter? 71.161.59.133 (talk) 15:36, 17 October 2009 (UTC)

Trees don't breathe like you or me. See the article Leaf. During tree growth, leaves absorb carbon dioxide from the air. When the tree is not growing it needs little or no carbon dioxide, and the article implies that if the concentration of carbon dioxide in the atmosphere were higher than it is now, a tree could absorb all its needs through its branches or roots. Cuddlyable3 (talk) 16:06, 17 October 2009 (UTC)

Trees only use CO2 for photosynthesizing. The rest of the cells consume oxygen.

The living tissue of the woody stems (the cambium) breath through organs in the bark called lenticels. --SB_Johnny | ^talk 16:26, 17 October 2009 (UTC)

I'm not entirely sure but perhaps this interesting [9] conference paper I found yesterday about common misconceptions taught in school including on the difference between breathing and respiration will help. While it's directed at educators it may help clear up any misconceptions Nil Einne (talk) 10:17, 18 October 2009 (UTC)

How to make my doorbell ring for longer

I find that people tend to politely press doorbell buttons for just a microsecond, which is difficult to hear. Is there any simple circuitry that could turn a brief closing of the circuit into a ten-second bell ring? My doorbell is I think 6 volts, off a mains transformer. I'd prefer somthing with rugged relays rather than transistors. This explains why bad-taste musical doorbells are popular. Thanks 92.29.130.77 (talk) 17:31, 17 October 2009 (UTC)

You could put together something using a 555 timer IC, a couple of resistors and capacitors, and a relay. See the "Monostable mode" section of the article for the circuit diagram. If your transformer is AC/AC, you'll also need a rectifier pack and voltage regulator. A good introductory electronics project. :) Tevildo (talk) 20:36, 17 October 2009 (UTC)

No need to mess around building electronics. You can buy a timer relay that does the job straight away. You can get different voltages ac/dc and timing ranges so there's bound to be one that suites your doorbell. Here's a data sheet. Tevildo's idea is a more interesting project though, if you are trying to learn electronics. SpinningSpark 21:09, 17 October 2009 (UTC)

That is a nice data sheet but none of the relays shown are rated for control by 6V. It is unsafe to connect mains voltage to a doorbell button. Cuddlyable3 (talk) 21:25, 17 October 2009 (UTC)

Ah, I missed the OP requires 6V. Those ones go down to 12V and I certainly was not suggesting connecting it to the mains (as a paperboy while still at school I once got a shock from someones doorbell) agreed that is highly dangerous. 6V is a lot less common for relays but I will see if I can find something, are you sure you need 6V? SpinningSpark 22:21, 17 October 2009 (UTC)

To press a button for literally a microsecond or 10^-6 second is practically impossible. Cuddlyable3 (talk) 21:15, 17 October 2009 (UTC)

You and your pointy-eared logic, Spock.[[Special:Contributions/Dr. Leonard McCoy|209.244.187.155]] (talk) 00:04, 18 October 2009 (UTC)

Maybe the gross motion of the button mechanical system is slower than a single microsecond event; but the electrical contact may be as short as 1 microsecond, and may actually twitter back and forth on that sort of timescale (usually due to micromechanical behavior of the switch contact plate or spring). Digital samplers often need to correct for this on any mechanical user-interface button. Nimur (talk) 21:44, 17 October 2009 (UTC)

How about a little sign that says "Please press the doorbell for at least 10 seconds". Low-tech, but effective! SteveBaker (talk) 22:16, 17 October 2009 (UTC)

Obvious answer - replace the chime with one that plays for much longer - common ones here in the UK play the opening chimes of Big Ben for instance - around 6 seconds. Exxolon (talk) 04:30, 18 October 2009 (UTC)

I am reminded of the TV show WKRP in Cincinnati, where the character Jennifer had a doorbell that played the opening notes of Fly Me to the Moon. --Anonymous, 07:02 UTC, October 18, 2009.

I've had a closer look at the old "Friedland" transformer and it has a choice of 4v, 8v, or 12v. Currently it is set up for 8v, which I recall is the current required by the bell itself. So it could be possible to draw off 12v, although the transformer does have fuses on the low-voltage side which I expect are far too old to be replaceable. Thanks 78.151.108.233 (talk) 12:05, 18 October 2009 (UTC)

That is the voltage required by the bell. The current is something else. Cuddlyable3 (talk) 12:27, 18 October 2009 (UTC)

Thoughtless typing error. The "microsecond" above was hyperbole. Relax, do not take everything so literally. You must have great difficulty reading novels or magazines. Jokes must be completely meaningless. 78.151.108.233 (talk) 12:36, 18 October 2009 (UTC)

In that case you should have used the correct technical term, which is tick, as in the expression "just a tick". You want this to be increased to "just a mo". SpinningSpark 14:38, 18 October 2009 (UTC)

That was an unfortunate choice of link! For many people, a tick has a very specific meaning. SteveBaker (talk) 15:27, 18 October 2009 (UTC)

Mixing up current and voltage is a good way to get electrocuted. And stating the time duration with six orders of magnitude error is a good way to confuse us if you're asking a technical question about circuitry (where such time units are very common). As Steve has just pointed out, these are technical terms which mean something - if you don't know what they mean, we will gladly explain them or point you to the articles - but you can't fault us for correctly interpreting the words which were actually written by the OP. We have no a priori knowledge of the OP's expertise level or technical background. Nimur (talk) 15:37, 18 October 2009 (UTC)

So, ignoring the ridiculous pedants for a moment (you know who you are!). In order to stretch the amount of time that the existing bell rings for a brief press on the button requires the addition of some sort of a timer.

You could build a piece of electronic circuit with something like a 555 timer chip - but that's likely to be difficult for anyone who actually needed to ask this question. You would change the system so that instead of directly powering the bell, the button would trigger a circuit which would count down the 10 seconds and keep applying power to the bell for all of that time. You can google "Monostable multivibrator" or check out this site. If you understand enough to build this, you can use the 555 timer output to drive a small relay and use the relay to power the doorbell - and you're done. It would be more elegant to do this without the relay and use a power transistor or something to drive the bell - but for that, you need to know a lot more about the voltage & current that the bell mechanism needs. Relays are better because they aren't so fussy about the nature of what they are switching.

If you don't have the skills for electronics but like to tinker with mechanical systems - why not build a crazy mechanical system? Have a ball-bearing balanced on a little wooden platform at the top of a ramp - pushing the doorbell mechanically nudges the ball so it rolls down the ramp. The ramp has a v-shaped cross-section with the two arms of the V made of metal strips which don't touch and which are connected to the wires where the old door bell button was connected - as the ball bearing rolls down the ramp - it connects the two metal strips just as if the button was being pressed. Make the slope of the ramp gentle enough that the ball takes 10 seconds to roll down and fall off the end. After you answer the door, pick up the ball-bearing and put it back at the top of the ramp. I'm sure you could use your imagination to make a yet cooler mechanism.

But if you are one of those sad (but all too common) people who couldn't build anything to save their lives - then you're going to have to do what you do when anything else goes wrong...spend money. Go buy a new doorbell...it's your only option.

SteveBaker (talk) 15:27, 18 October 2009 (UTC)

Dear Steve, Thank you for your question "Why not build a crazy mechanical system?". It is an excellent question for the Ref. Desk. What happens in your proposed ramp system after someone rings the bell while the OP is not at home? Signed Sad-too-common-ridiculous pedant. Cuddlyable3 (talk) 14:18, 19 October 2009 (UTC)

Bah! Anyone with an ounce of mechanical imagination could come up with a fix for that. A tube filled with about a hundred ball-bearings sits above the button - you push it, the bottommost ball bearing rolls down the ramp, ringing the bell and when the person releases the (spring loaded) button, another ball drops down to replace the first one and you're ready to go for the next visitor...easy! Plus you can count the ball bearings on the floor when you get home and figure out how many visitors you had while you were away! Vastly superior than some crummy electronic system.  :-P Come to think of it - you could dispense with the electric bell and place a series of carefully spaced and tuned chimes alongside the ramp where the rolling ball would just gently tap them on the way down - you could have it play a tune just like an electronic doorbell. A simple rearrangement of the chimes would allow a wide range of tunes to be programmed when you get bored with "La Cucaracha". Think "wind chimes".

When I was a kid, my parents had a clockwork doorbell - it had a big round bell with a couple of bulges in it that rotated against a small hammer when it rang. You wound it up by rotating the bell a dozen or so turns. All that the button did was to release the ratchet on the clockwork. However, it did have the problem you describe - if you had more than a handful of visitors while you were out - nothing. SteveBaker (talk) 02:10, 20 October 2009 (UTC)

What I need is something that, when the button is pushed, will close another path in parallel with the button, and then open it again after a few seconds. (Hmmmn, electro-magnet, leaking capacitor....) 78.151.108.233 (talk) 18:14, 18 October 2009 (UTC)

That won't work if your bell is AC, and, even if it's DC, getting a reasonably accurate 10 second delay with a simple RC circuit is going to be quite tricky. You're going to need some sort of active electronic/mechanical compoments, as discussed above - or just buy a new doorbell. :) Tevildo (talk) 18:27, 18 October 2009 (UTC)

It would be extremely difficult. You're expecting the capacitor to charge up sufficiently in the tiny fraction of a second that the button is pressed to sustain powering the bell for 10 seconds! That would take a pretty huge capacitor - and the current required to charge it in a fraction of a second would be impressive! SteveBaker (talk) 19:54, 18 October 2009 (UTC)

Well, the capacitor would just be discharging through the relay coil, not through the bell itself - it _could_ be done, but a 555 would be more reliable and cheaper (because big capacitors are expensive). Tevildo (talk) 19:58, 18 October 2009 (UTC)

Trying to drag this conversation away from the 555-timer-home-electronics-enthusiasts (guys, not everyone thinks its fun to spend their evening soldering minuscule bits together, some people just want the answers). The answer in this case being a pneumatic time delay switch example, example, example. Sorry, I could not find a slimline version suitable for fitting on a door jamb, but I think they exist. Make sure you buy a pneumatic or mechanical version, the electronic models are no good to you as they will require mains powering. SpinningSpark 20:29, 18 October 2009 (UTC)

i believe there are mechanical, or at least "black box" timed relays available that will stay closed for a set period when triggered; whether they can be used with your voltages is another question. if you don't get lucky that way, then getting some high school kid to throw something together with a 555 is the second easiest bet. if not that, then get a yappy dog. if not that, then a doorbell that plays "la cucaracha" or whatever.

another point: the OP hasn't specified whether his/her doorbell is something that buzzes/rings continuously, or is the bing.....bong type ubiquitous in the US. Gzuckier (talk) 20:38, 18 October 2009 (UTC)

Oh a 555 timer, what a great idea, I wonder why no one else mentioned that. Obviously it won't work with a bing-bong, but the whole context of the OPs post is that it is a continuous bell. Of course, if you are going to use a 555 timer, you could build a timed multivibrator, which would work with a bing-bong. SpinningSpark 00:21, 19 October 2009 (UTC)

The doorbell is a continuous one. Bear in mind that the button and the bell could be on two seperate parallel circuits powered from the transformer, only connected by some sort of relay. What I was thinking of above was something like this: 1) button pressed briefly 2) electromagnet relay closes, which starts bell ringing 3) hazy fog obscuring what happens next 4) capacitor charge leaks away through a resistor, which means the electromagnetic opens, so the bell stops ringing. The capacitor and the relay could have a diode etc to overcome the AC problem. The capacitor could be powered by another cicuit from the transformer. Are there not any simple low-voltage relays available that are designed to open after a delay? 78.151.114.229 (talk) 10:19, 19 October 2009 (UTC)

Well, the timer relays in the data sheet above have coil voltages down to 12V, and the existing transformer can be stepped up to provide the 12V needed by the relay. You can just run the bell off of the same 12V, with a resistor in series with the bell in order to drop the voltage down to the 8V it needs. You'd only need to wind up buying two parts. Red Act (talk) 10:48, 19 October 2009 (UTC)

                           \
        |Co                :\
        |Co--------------^   o-------------------        C = Electrolytic capacitor
        |Co   |                                 |        D = Silicon diode 1N4003-6
        |C    |___|\|____                    -------     RL= Small relay 
-------c|C        |/|+ | V                   | bell |          with DPDT contacts
       C|C         D   |  \                  |______|          & 1000 ohm coil
mains  C|C     ________|   \                    |
       C|C    |            :\                   |
-------c|C_   |___   ____î   o--------          |
           |     ----- |             |          |
           |       |   |             |+         |
           |     push  |___        ----- C      |
           |               C       |___| 4700µF |
           |               C             25V    |
           |           RL  C       -----        |
           |               C         |          |
           |_______________C_________|__________|

Cuddlyable3 (talk) 15:03, 19 October 2009 (UTC)

It might be an idea to put a small resistor (10R should be enough) between the supply rail and the diode, but otherwise that circuit would be adequate. Make sure you get the diode and capacitor the right way round. :) Tevildo (talk) 17:16, 19 October 2009 (UTC)

In the above circuit, there's nothing limiting the current while the capacitor is charging. My guess is the diode would get smoked, although the transformer's at risk, too. Also, with only half-wave rectification, you're basically counting on the relay's operate time being less than 1/2 cycle (about 8ms), whereas a typical operate time of a relay is actually about 20ms. You could fix those problems by sticking in an extra resistor to limit the current through the capacitor while it's charging, and change to use full-wave rectification. But both of those add to the circuit complexity. It's easier to just buy a timer relay. Red Act (talk) 17:29, 19 October 2009 (UTC)

At switch-on the current in the diode is limited by the secondary resistance of the transformer but adding a resistor as Tevildo suggests can add some safety margin. Charging time for the capacitor is too short to cause significant heating of the transformer. The drive that energises the relay is initially about 12V from the charged capacitor. The half-wave rectified supply sustains current in the relay after it has built up enough magnetic field to set the contacts in motion. Inertia of the contact armature and the relay coil inductance together ensure that both contacts close. I tweaked the artwork slightly to clarify the lower relay contact. Cuddlyable3 (talk) 23:36, 19 October 2009 (UTC)

I'm still a little dubious about inertia being enough to keep the armature moving long enough to ensure the NO contacts close. Assuming the relay is the more common break-before-make, the charged capacitor wouldn't help between the time the NC contacts open and the NO contacts close. However, there are a couple simple ways to avoid any possible problem in that regard, without needing to go to full-wave rectification as I had earlier suggested. One possibility would be to simply specify the relay as being make-before-break. Another simple possibility would be to have the side of the pushbutton that's connected to the diode in the diagram instead connect to the + lead of the capacitor. That second option would also have the advantage of the ring duration always being the chosen duration (as long as the button isn't pushed longer than the chosen duration), instead of the ring duration varying depending on how long the button is pushed.

I still think just buying a timer relay would be the simpler, more reliable way to go. But the circuit above does have the advantage of only needing parts that can be readily picked up at Radio Shack, instead of having to be ordered. Red Act (talk) 02:58, 20 October 2009 (UTC)

Modifying a mobile phone / cell phone to use only as a computing device.

I do not like mobile phones. But some mobile phones can be used as a miniture computer. Is it possible to tinker with its insides and stop it being usable as a mobile phone but keeping it working as a computing device? 92.29.130.77 (talk) 17:39, 17 October 2009 (UTC)

Why not just put it in airplane mode? --Cameron Scott (talk) 17:44, 17 October 2009 (UTC)

Not OP, but not all phones have "airplane mode". Indeed, I've never seen a phone that had that, although I've not seen many newer model phones recently. —Preceding unsigned comment added by 82.44.55.2 (talk) 17:47, 17 October 2009 (UTC)

Well, many do. Mine does, and I use the feature frequently. See flight mode --NorwegianBlue ^talk 18:21, 17 October 2009 (UTC)

Actually I suspect most phones probably have airplane mode or something similar. It's not actually new at all, or uncommon. My bet is that your phones have had it but you didn't know how to use it. --Mr.98 (talk) 19:07, 17 October 2009 (UTC)

Pretty sure they don't, then again I'm talking about very old (5 years) phones here.

My 3.5 year old phone (Panasonic VS2) did not have a flight mode although it supported (limited) video playback, most audio formats, had a 1.3 MP camera, infrared, a good (for the time and price) colour 320x240 screen and had 32mb of memory. I would expect most new model phones in that price range to have a flight mode but I'm pretty sure it wasn't unusual for the time and it was in the low mid to mid price range (IMHO). It didn't have bluetooth, 3G, or expandle memory (the later being the biggest limitation). The ~2 year old Nokia 1110 I use occasionally since my Panasonic VS2 broke which is a fairly basic phone with a monochrome screen, no camera etc also lacks a flight mode. It's replacement model, the Nokia 1200 also does not have a flight mode I'm pretty sure. The usefulness of a flight mode for such a basic phone is of course fairly questionable. Of course if you're intending to use your phone as a computer you're unlikely to be using either a basic phone or a 3+ year old model however I would suspect when we think in world wide terms they do represent a substanial percentage of the market so I think it's questionable if 'most phones' have an flight mode Nil Einne (talk) 07:32, 18 October 2009 (UTC)

Probably... but the phone's computer is NOT very powerful. It strikes me that anything you might want to do on a cell phone could be EASILY better done on a machine better suited to that purpose. I mean, I use mine as a calculator. It's not the best calculator and it's a pain to use. It is ONLY convenient as a calculator because it is also a phone, and I am already bringing the phone with me. If I didn't have a phone, and I needed a calculator, I'd just carry a regular calculator around—it'd be a lot easier to use. --Mr.98 (talk) 19:07, 17 October 2009 (UTC)

The phone indicated by NorwegianBlue above has a higher memory and storage spec than a DOS laptop I had a few years ago. If it has an operating system that allows the introduction of other programs, then it should be able to do a lot. Perhaps the drawback would be the difficulty of using the tiny 'keyboard'. 92.29.130.77 (talk) 19:35, 17 October 2009 (UTC)

Perhaps, but for the price of the phone (probably a few hundred dollars) you can just get a netbook and skip all of the hassle and the very tiny monitor, no? --Mr.98 (talk) 20:04, 17 October 2009 (UTC)

It might help if you explained why you don't want it to work as a phone. You can choose not to make any phone calls without disabling the feature. --Tango (talk) 19:52, 17 October 2009 (UTC)

Obviously for situations like being on an airplane or not wanting a phone without a sim card to radiate you with signals when it's not being used for calls. —Preceding unsigned comment added by 82.44.55.2 (talk) 20:05, 17 October 2009 (UTC)

Obviously for situations like being on an airplane which if it is powerful enough to add as a small computer is going to have an aircraft mode for.. --Cameron Scott (talk) 20:10, 17 October 2009 (UTC)

The OP hasn't mentioned aircraft and there can be other motives for disabling the call function on a mobile phone, such as lending it to child for game playing only. Cuddlyable3 (talk) 20:55, 17 October 2009 (UTC)

Rather than modify a phone, why not just get a PDA? Does about the same thing... SDY (talk) 20:17, 17 October 2009 (UTC)

For those who wonder why anyone would want to do this, mobile phones have a very good performance / power consumption ratio so it could be seen as some kind of a green act and a cheap way to waste time to build a cluster of recycled phones. Why you would want to disable calling I do not know. --194.197.235.240 (talk) 20:48, 17 October 2009 (UTC)

If I just threw away the "sim" card, would that be the solution? Do all these phones have sim cards? I'd like to use such a device because its probably easy to get one cheaply or perhaps even for free as people upgrade, and because they are very light. PDAs or netbooks weigh 500g+ (weight of a jar of jam) as far as I recall and would be no fun to carry around in your pocket for any length of time. And because its fun getting something to work like that, particularly for little or no cost. I like to work things to the max. 92.29.130.77 (talk) 21:29, 17 October 2009 (UTC)

I'm not sure what you think of when you think "PDA", but most PDAs are the size of a phone. A PDA is something like a PalmOS device. PDAs are not the same thing as a netbook. APL (talk) 22:52, 17 October 2009 (UTC)

If I just threw away the "sim" card, would that be the solution? Depends, you are in the UK, so yes, you could just remove the SIM card, the only problem is that some smartphones will not operate for long without the presence of a SIM card. As for the weight and size, well as the size decreases, so does the screen size. --Cameron Scott (talk) 21:32, 17 October 2009 (UTC)

Actually some phones won't operate at all without a sim card (well they will just say "no sim card" or "emergency calls only" and won't let you do anything). You can get wiped sim cards from places like Deal Extreme may avert this problem however if the phone is sim locked they probably won't work. Also this won't necessarily stop the phone from transmitting so there may still be battery life and other such issues. So I have to agree a PDA of some sort would be a better bet. Why get something with the phone part if you don't want it? Nil Einne (talk) 07:36, 18 October 2009 (UTC)

I'm surprised the no one has mentioned the iTouch yet. It's essentially an iPhone without the telephone stuff.

I'd also like to mention the Open Pandora which will eventually ship its first unit. That's going to be the size of a NintendoDS which can fit your pocket, depending on the kind of pockets you have. APL (talk) 22:52, 17 October 2009 (UTC)

One of the reasons why I'd like to try using a mobile phone as a computing device is for the same reason that I keep a minature radio all the time in my bag: the radio is extremely light so I do not notice the weight, it is very small so takes up no space, and it is very cheap so I'm not worried about it being lost damaged or stolen. If I find I've got some time to waste while on a journey then the radio is there if I want to play with it. For similar reasons I wear a cheap digital watch rather than walking around with an antique grandfather clock strapped on my back. 78.151.108.233 (talk) 12:20, 18 October 2009 (UTC)

There are a number of PDAs on the market that are the same size as a phone. Those would be far better options than buying a phone and disabling the telephone. Obviously the iTouch is the same size as the iPhone. Personally I like PalmOS for PDAs. here is one current offering in that line. APL (talk) 17:17, 18 October 2009 (UTC)

Thanks, but thats at least ten times more than what I would want to spend. As I mentioned above - and surprisingly nobody here seems to "get it" - is that it would be fun to get an old phone for very little from eBay or for nothing from Freecycle, and do a "mod" (probably involving soldering irons)to get it to do what I want at little or no cost. Someone is trying to get a very old computer to run in the Computer section of the Referance Desk in the same spirit. 78.151.108.233 (talk) 18:22, 18 October 2009 (UTC)

Um, folks..... the default state of a cell phone is to be only a computing device with no phone capabilities unless you do a bunch of things including, but not limited to, paying a cell phone bill every month. I keep my old retired cell phones as free calculator/cameras, without doing anything special other than not having them on an account with a cell phone provider. Gzuckier (talk) 20:34, 18 October 2009 (UTC)

Ah. I see what you mean now. I had the impression that you were trying to buy a new phone for use as a pda, which would be crazy. I think Gzuckier is mostly right here, most phones you won't have to do anything special as long as their subscription is canceled. (Though, in my experience, they seem to keep the radio circuits turned on, apparently just to update the current time. Perhaps some tinkering could save you some electricity there.)

Don't be surprised if you need to purchase a new battery for the thing. (Perhaps it could be modded to take a battery you have on hand.) APL (talk) 21:16, 18 October 2009 (UTC)

Sorry, I don't meen to keep harping on PDAs, but I just noticed that used older model Palm devices are really cheap on ebay. [10] [11] APL (talk) 21:18, 18 October 2009 (UTC)

Gosh, you are right, thanks. I've asked a question about the best old PDAs for my old-fashioned preferances on the Computing desk. I'd appreciate people's expertise there. 78.144.243.47 (talk) 19:50, 19 October 2009 (UTC)

stomach pressure in vomiting

What pressure (mm/Hg) is needed for the stomach to eject its contents? Please cite authoritative reference. —Preceding unsigned comment added by 72.75.125.231 (talk) 23:43, 17 October 2009 (UTC)

The stomach must merely apply positive pressure to its contents while the pyloric sphincter is tensed and the esophageal sphincter is relaxed. Stomach contents will then be brought to the oropharynx via esophageal reverse peristalsis. It's not as though the stomach has to pump its contents through a conduit of static/merely elastic vessels like the heart must do to sustain blood pressure. DRosenbach ^{(Talk | Contribs)} 00:29, 18 October 2009 (UTC)

Physiology and pharmacology of vomiting, (1953), discusses the ability to induce vomiting by applying pressures to various sections of the gastrointestinal tract. Vomiting was induced by 300 mm-Hg applied to the biliary ducts; or 30 to 35 mm-Hg applied to the pyloric pouches. These experiments were conducted on dogs. Nimur (talk) 00:45, 18 October 2009 (UTC)

Respiratory mechanics of vomiting in decerebrate cats, (1974), states that "the respiratory muscles provide the motive force in vomiting..." and that "the retching pulses were generally 0.5 s or less in duration, and at their peak amplitude often exceeded minus 75 mmHg in the thorax coincident with 125 mmHg in the abdomen, adding up to transdiaphragmatic pressures greater than 200 mmHg." This paper presents time-versus-pressure plots, as well as EMG plots of the control signal, so you can actually see the vomiting process as a dynamic event (rather than an approximate average pressure). It also might explain why human studies are more or less impossible - decerebrate cats were used in this study. I would like to comment for the record that the procedures described in this paper are not necessarily pleasant. We can hope that the useful scientific data may help (or may have already helped) the medical and biological community; hopefully, assisting our understanding of the neurological issues which motivated the original research and spurning medical progress. Nimur (talk) 00:52, 18 October 2009 (UTC)

October 18

Voltage drop in an extension cord

So, here's a break from relativity and black holes and all that high-powered stuff...

My "good" 14-ga, 100-foot extension cord wasn't really that good, and finally died today. Bought a new one, CostCo had 12-ga cords for less than 14-ga cords at the local home repair store. I swear that my leaf blower is running faster on the new cord than the old -- speed being indirectly perceived by the racket it makes.

(1) Is this actually possible, or am I suffering from too much observer bias? (2) Can I safely measure the voltage at the end of the cord with a simple V-O-A meter, just sticking the prongs into the outlet holes?

Thanks to the electricians in the audience! --DaHorsesMouth (talk) 01:09, 18 October 2009 (UTC)

Certain voltmeters are designed for probing high-voltage, AC sources. However, this is categorically not safe - even if you are a trained electrician, it is still not safe. But, there is an alternative - and a better one, actually.

First of all, you don't care about the "resting" voltage - there will be virtually no voltage drop unless the leaf-blower is on, since no (net) current is flowing through the extension cord. So, you need to measure the voltage when operating the leaf blower. Consider buying one of these plug-in outlet voltage monitors. They are much safer to use, and you can use them while operating the leaf blower - to see whether turning it on causes a voltage drop at the end of the cord. Nimur (talk) 01:15, 18 October 2009 (UTC)

Here's a digital one, for ~ $25. Nimur (talk) 01:22, 18 October 2009 (UTC)

Calculating from the values in American wire gauge, using the 14 AWG cable instead of the 12 AWG should introduce an extra resistance of 0.1874 Ohms. Assuming it's a 20 amp circuit, that means the voltage drop could be at most 3.748 volts, and is actually something less than that. So the voltage to the appliance is being dropped by only about 3% or less, which one wouldn't think would be noticeable. Extra resistance due to corrosion on the contacts of the old extension cord, however, could make a much bigger difference. Red Act (talk) 01:42, 18 October 2009 (UTC)

OK, that'll do nicely. Nimur, I promise not to do something patently stupid -- today.

Do a proper scientific experiment. Have a friend or family member operate the leaf blower - you stand at a suitable distance away with your eyes closed. They flip a coin and plug the leaf-blower either directly into the wall outlet or into the old extension cord without telling you which they did. Repeat the experiment 10 times. Can you reliably tell where the leaf blower was plugged in from the noise alone? Repeat the experiment with the new extension cord. (I'm fairly certain you won't be able to tell which is which at a rate better than chance - but if you can, you need a higher gauge wire for your extension cord.) SteveBaker (talk) 15:01, 18 October 2009 (UTC)

My experience, strictly unscientific although I have a good handle on my volts and amps, is that the connections at the ends of the wire to the plug and socket tend to be the weakest link; for instance, on a high load, they will get warm while the wire itself is still ambient temperature, and they will fail frequently, while the wire itself never does. Gzuckier (talk) 20:02, 18 October 2009 (UTC)

Not tried running an extension cord fully wound up on high load then (e.g. doing the ironing as a relative of mine did)? Nice fire. The wiring in them is often pretty rubbish and loss of power seems quite plausible to me. --BozMo talk 20:29, 18 October 2009 (UTC)

Yes, I've seen one melt when used coiled, but inductive impedance contributes when coiled. Dbfirs 21:28, 19 October 2009 (UTC)

Inductive impedance may contribute much less than you think because there is virtually no external magnetic field coupling to the extension cord which is a Balanced line unlike the conductor of a solenoid, and the AC power frequency is low at 50 or 60Hz. A lamp on the end of an extension cord does not get dimmer when the cord is coiled. Cuddlyable3 (talk) 23:08, 19 October 2009 (UTC)

I would expect to hear an easily descernible difference between a 12 gauge and a 14 gauge 100 foot extension cord when driving a motor rated near the stated limit for the 14 gauge cord. How many amps is the motor rated at at 120 volts? You could also use a splitter at the motor end of the cord to measure the voltage under load for the two cords, if you have such a meter and understand how to make voltage measurements safely. Edison (talk) 00:07, 19 October 2009 (UTC)

OP here. I marked this as {{resolved}} about 48 hours ago, as I had enough information. Baker: it's bad form to remove somebody's tag and signature. If you wanted to continue the discussion, fine, but next time Don't edit others' comments, except to fix formatting errors that interfere with readability. --DaHorsesMouth (talk) 02:22, 20 October 2009 (UTC)

Not trying to take sides, but so you know: there's an opinion that those "resolved" tags are a bad idea. See this discussion. —Steve Summit (talk) 03:14, 20 October 2009 (UTC)

Hychlorite?

File:Clorox Bleach Bottle.jpg

Dilute Sodium Hypochlorite! SteveBaker (talk) 14:53, 18 October 2009 (UTC)

I toured George Eastman's house today and in his bathroom was a bottle labeled "Hychlorite". After doing a search, I see that there's a Flickr image of the bottles. I never expected to see an image of the exact same bottle on the net but okay... What was this? The closest I can find here or on Google seems to be Hypochlorite. Are these the same thing? From what I gather, hychlorite was used as an anti-septic. Can anyone confirm this? Dismas|^(talk) 02:59, 18 October 2009 (UTC)

From this, it appears that hychlorite is another name for sodium hypochlorite. Red Act (talk) 03:17, 18 October 2009 (UTC)

Looks like Hyclorite was a brandname for a commercial sodium hypochlorite preparation. See TALK:Sodium_hypochlorite#Hychlorite_and_Zonite for a link that supports this. 66.102.199.179 (talk) 03:22, 18 October 2009 (UTC)

External Speaker Noise Problem

Very recently my external speakers (5.1) connected through its own amp, has started making really huge buzzing noise. The noise starts if I just turn on the speakers. I have tried disconnecting the audio in cables, but the problem persists. Any help ? —Preceding unsigned comment added by 59.93.204.61 (talk) 04:12, 18 October 2009 (UTC)

I'm no audio engineer but two things spring to mind - the first is inteference - have you plugged in/installed new appliances either nearby or on the same ring main as the speakers/amps? Try disconnecting them/switching off if so. Secondly could be poor connections - check all plugs and sockets, then look for loose wires or poor solder joints. Exxolon (talk) 04:26, 18 October 2009 (UTC)

To figure out if interference is the problem, try using the speakers in another part of the house, or in a different house altogether. If the problem goes away, next try moving the speakers around your house to identify when the buzz is the loudest, and that should lead you to the interference source.

Also, do these speakers have their own volume control ? I've had lots of trouble with the rheostats used to control volume levels, although an intermittent crackling when changing volume is more typical of that issue. If this is the problem, you can either replace the rheostat or bypass it, using the volume control at the source instead of at the speakers.

Another thought is the power supply. Does the power cord have a wall wart ? If so, maybe you need to replace that. If the power supply is internal, then it may be more difficult, but still possible, to replace. StuRat (talk) 13:46, 18 October 2009 (UTC)

Strictly from practical experience, buzz or hum in an amplifier almost always comes from a "bad" power supply. What this means can vary; the power supply unit may have experienced hardware damage (e.g. a capacitor that has fizzled via dielectric breakdown) or it might just be picking up EMI interference. Check for other "high power" equipment nearby (physically or electrically - sometimes things like the refrigerator can be far away but on the same mains circuit). Anything with a motor or compressor will create EMI and power fluctuations in the audible range; but so can a variety of other electronic devices like televisions and other amplifiers. If the noise is not "hum-like", check the signal pathway for any unusual wiring; consider switching to a digital audio connection; consider physically moving or changing the orientation of the wiring to avoid passing near sources of electromagnetic interference. Nimur (talk) 14:34, 18 October 2009 (UTC)

You might try threading the cable through a ferrite bead (you can buy them in good branches of Radio Shack for example). SteveBaker (talk) 14:48, 18 October 2009 (UTC)

From past experiecne. noise in an audio system implies a grounding problem. Edison (talk) 00:03, 19 October 2009 (UTC)

Regulation of cholesterol in blood

Hi everyone I am a little confused about how cholesterol levels are regulated. The article on Cholesterol says that fat intake, especially that of saturated fats, plays a large role in blood cholesterol. My question is why? Surely our bodies can choose not to convert the fat we eat to cholesterol? I realise that fatty foods contain cholesterol but if my understanding is correct our bodies produce cholesterol from fat as well - why would it do this if the cholesterol levels were already high enough? Can't the process be inhibited in some way? Thanks in advance for any contributions! RichYPE (talk) 10:29, 18 October 2009 (UTC)

When humans (and their primate ancestors) evolved, the problem of excess fat and cholesterol consumption was so rare that there was almost no evolutionary pressure to developed a mechanism for dealing with this problem, because the portion of people who were unable to pass on their genes due to high cholesterol was almost zero. Had we evolved from predators, instead of mostly herbivores who eat meat only on rare occasions, then perhaps such a mechanism would have been passed on to us. StuRat (talk) 13:33, 18 October 2009 (UTC)

True. It's very rare to see arterial disease in dogs and cats, even when they're grossly overweight from being fed a high-fat diet. On the other hand, since cholesterol is involved in regulating the fluidity of cell membranes, which is crucial, our bodies have evolved with an emphasis on avoiding ever being too low on cholesterol, without ever facing much evolutionary pressure to keep the levels down. Until now. Gzuckier (talk) 19:58, 18 October 2009 (UTC)

The trouble with comparing typical human conditions with similar things in animals is that most animals don't live long enough to exhibit the problems. A 14 year old human would probably not have noticable cholesterol problems no matter how bad his/her diet has been...and not many dogs or cats live much longer than that. If you had dogs and cats living until 50 to 60 years old - then their fatty, cholesterol-laden diets might well cause them similar problems to humans - but we'll never know. SteveBaker (talk) 11:32, 19 October 2009 (UTC)

I'm not convinced by that argument. Cats and dogs eat more relative to their mass/volume (due to the square/cube law), which ought to counteract the difference in lifespan. I don't know which factor would be larger, but it is worth noting that cats and dogs get other age related problems (arthritis, for example) at similar ages to humans relative to lifespan, not in terms of absolute age. --Tango (talk) 11:41, 19 October 2009 (UTC)

FWIW I am with Tango on that one. Vast swathes of age related diseases in humans (cancer for example) have significiant mortality in shorter lived mammals past child bearing age. Nothing is as simple as a kettle furring up and all creatures will have evolved to have mechanisms to push progressive illnesses on average to an age where they have less evolutionary impact. The fact we sit on sofas eating burgers (not that I eat burgers) for decades after we were evolved to die is to blame. --BozMo talk 11:46, 19 October 2009 (UTC)

I don't think I agree with your "evolved to die" time - there hasn't been a large change in when people die of old age. The increases in life expectancy are primarily due to a reduction in infant mortality. If you reached adulthood you would probably reach your 50s or 60s, often older, even before the birth of modern medicine. There is evidence that evolution has made changes to make us more successful in middle/old age (eg. the Grandmother hypothesis), so you can't blame age related problems on evolution not caring what happens to us after we've had our children. (Yes, I'm anthropomorphising evolution, it's just easier to express it that way. I know it isn't accurate.) --Tango (talk) 12:00, 19 October 2009 (UTC)

You are right of course on the Grandmother hypothesis, and I don't know enough about whether people 100,000 years ago really ever lived to their seventies (after child bearing in their late teens) to contradict that so I leave, a little humbled! --BozMo talk 12:09, 19 October 2009 (UTC)

British museum website suggests aged 35 to 40 as a ceiling for Iron Age man but with no real evidence. --BozMo talk 12:12, 19 October 2009 (UTC)

Look at the list of Roman emperors. A fair number of them seemed to live to 60 or even 70, despite the fact that they also had to watch out for assassinations. Googlemeister (talk) 20:31, 19 October 2009 (UTC)

Seedless pepper

I bought a red pepper at a farmer's market and it doesn't have any seeds. Is this a mutant or a new breed ? I'd like to grow more of these myself, but, of course, have no seeds to do so. Is there another way to make the existing pepper grow ? StuRat (talk) 15:07, 18 October 2009 (UTC)

See seedless fruit. --Tango (talk) 15:18, 18 October 2009 (UTC)

It's likely a result of cross-breeding and selection. Obviously consumers like seedless varieties for convenience - and farm supply companies like them because farmers cannot simply use some percentage of their crop to provide seeds to replant the next generation of plants. For you, it completely sucks because there is no way to grow another plant from the pepper itself. Your best chance would be to somehow getting a cutting from one of the original plants, using rooting compound and producing a new plant that way. If you bought it from a local grower, that might not be impossible. SteveBaker (talk) 15:57, 18 October 2009 (UTC)

See also F1 hybrid. But the seed would probably not have grown true to type anyway.--BozMo talk 11:49, 19 October 2009 (UTC)

LNB Power

Does LNB consume the power from the receiver and also send its signals on the same coaxial cable? If so, how usually is it implemented (I.e.: is it like modulating the filtered signals on the same DC power)?--Email4mobile (talk) 16:33, 18 October 2009 (UTC)

Yes, the cable carries both the DC power and the IF signal, with a DC block between the RF and power sections at both ends. See DC bias#Remote power. Tevildo (talk) 17:02, 18 October 2009 (UTC)

The use of signal cabling to carry power is also used in other applications, see phantom power. --Jayron32 18:38, 18 October 2009 (UTC)

... and USB uses the same technique. Dbfirs 19:44, 18 October 2009 (UTC)

No, USB has separate power and signal conductors - they just share a common ground wire. Tevildo (talk) 19:51, 18 October 2009 (UTC)

Sorry, you are correct. My error! Dbfirs 16:53, 19 October 2009 (UTC)

Erie Canal

What would happen if all the locks on the Erie Canal were opened at once? Is it dangerous that this could occur? TheFutureAwaits (talk) 18:41, 18 October 2009 (UTC)

There may be local flooding, probably not much of any other effect. The Erie Canal is no longer a contiguous water way; large sections have either silted over naturally or have been filled and paved over as roadways. Some sections are maintained as recreational waterways, and do see some boat traffic; other sections have been added to the more modern New York State Canal System and do see some commercial barge traffic. See Erie Canal. --Jayron32 18:51, 18 October 2009 (UTC)

thioketone thioester?

What do you call an ester where it's RCS2-R' rather than jus R-COS-R' ? John Riemann Soong (talk) 19:51, 18 October 2009 (UTC)

It's a dithioester. Someguy1221 (talk) 20:31, 18 October 2009 (UTC)

why is phenol toxic?

Is it because it's a good nucleophile? How does its toxicity compare to methanol? John Riemann Soong (talk) 20:02, 18 October 2009 (UTC)

I don't seem to have access to any relevant journals, but Burns Volume 32, Issue 4, June 2006, Pages 517-521 should answer the question based on the outline. Someguy1221 (talk) 20:39, 18 October 2009 (UTC)

That source mostly discusses skin burns from phenol, which it says are due to its "caustic and defatting (hydrophobic effect of phenol) properties." No more specifics. Without giving a mechanism, it also mentions "systemic toxicity and poisoning usually occur by skin absorption, the main route of entry for solid, liquid or vapor phenol; the result can be lethal" with seizures, coma, and dysrhythmia. Pulmonary complications can include tachypnea, pulmonary edema, bronchospasm, and stridor, which to my medical student ear sounds potentially fatal also. - Draeco (talk) 05:38, 19 October 2009 (UTC)

Is there any accessible reason based on its aromaticity? I mean, it's separate from why benzene is toxic, right? John Riemann Soong (talk) 00:34, 19 October 2009 (UTC)

Aromaticity affects solubility and other hydrophobic interactions, and also the stability/reactivity of the hydroxyl. DOI:10.1016/S0009-2797(00)00171-X suggests toxicity is related to a radical formed from PhOH. Toxicity is always an interesting issue, and often the result of dozens of complicated and/or inter-related effects (is tyrosine highly toxic?). DMacks (talk) 00:42, 19 October 2009 (UTC)

Isn't it a suspected carginogen or am I years out of date? --BozMo talk 11:51, 19 October 2009 (UTC)

Isn't everything? More seriously though phenol says it is so either you're both out of date or is still is. I think it's supported by the ref [12] although I only partially understood it Nil Einne (talk) 15:37, 19 October 2009 (UTC)

Which population clock is better?

There are several of them. I assume that (unlike in the US Census) they add uncounted people, which would make up a lot of the disagreements, and error. Sagittarian Milky Way (talk) 21:02, 18 October 2009 (UTC)

They add people that don't get counted during censuses and they estimate growth rates and use them to add people born/subtract people that died since the last census. I don't think there is any way we can really say which is best. I expect the margin of error is big enough to contain any disagreement. --Tango (talk) 21:14, 18 October 2009 (UTC)

Most countries, I suppose; but it is archaicly illegal to do that for the official US Census value for America that determines representation. The US Census' version of the clock number would not be under that requirement though. Sagittarian Milky Way (talk) 21:54, 18 October 2009 (UTC)

A woman delivers a baby approximately every second. By now she must be sick of it. Cuddlyable3 (talk) 13:49, 19 October 2009 (UTC)

See Lilith... Tevildo (talk) 17:55, 19 October 2009 (UTC)

Why ? Cuddlyable3 (talk) 22:53, 19 October 2009 (UTC)

A cat breastfeeding another adult cat?

What causes a queen to breastfeed another adult cat? No, the cat who is suckling is not a larger kitten or the queen's offspring. The queen breastfeeds another cat and the two cats are not related. Surtsicna (talk) 21:25, 18 October 2009 (UTC)

Please provide a reliable source to document that this phenomenon actually occurs. Sounds dubious/bogus/made up. Edison (talk) 00:01, 19 October 2009 (UTC)

He may not have one. The questioner could have simply witnessed this unusual phenomena and been curious about it. APL (talk) 00:11, 19 October 2009 (UTC)

Grr. Phenomenon. --Trovatore (talk) 01:48, 19 October 2009 (UTC)

Funny. Wiktionary says that "Phenomena" is the plural of phenomenon, but Merriam Websters says that it's a nonstandard but "borderline" singular (with its own plural.). Huh. In the future I will try to restrict myself to the most commonly accepted written form. APL (talk) 18:48, 19 October 2009 (UTC)

phenomenon comes from Latin phænomenon from Greek phainomenon "that which appears or is seen", a noun derived from phainesthai "to appear". Plural is phenomena. Cuddlyable3 (talk) 22:47, 19 October 2009 (UTC)

Adult cats I have known love milk , and there is no reason to suppose they would not like cat milk. It seems less likely the female would want to provide milk to an adult cat. Edison (talk) 00:55, 19 October 2009 (UTC)

OR. We had 3 kittens over a year ago, one girl two boys, and when the mother refused to let them nurse any longer they all started nursing on the girl. She sucked on her own nipple, and the two brothers also sidled up for some cuddle time. They eventually quit, and it never seemed like she was lactating, so I suspect it was a comfort issue rather than a "we totally want more milk" issue.218.25.32.210 (talk) 05:52, 19 October 2009 (UTC)

Don't male cats have nipples? Axl ¤ [Talk] 07:46, 19 October 2009 (UTC)

OR. Lactating mother cats are very tolerant of who sucks. Zoo keepers know this and often seek a lactating cat to be a wet nurse for a variety of orphaned baby animals. Cuddlyable3 (talk) 13:46, 19 October 2009 (UTC)

I've seen it. My own cat (who has just stopped breastfeeding her kittens) breastfed a stray cat several times. I have a picture of the suckling cat trying to grasp a nipple while my cat is sitting. The cat was lying and breastfeeding another cat as if it were her own kitten just seconds before I took the picture. I really don't have a reason to make this up; cats are known to breastfeed a variety of animals. I just want to know what made my cat breastfeed another adult cat. Surtsicna (talk) 18:02, 19 October 2009 (UTC)

This practice is known as beastfeeding. (Just joking.) Bus stop (talk) 22:54, 19 October 2009 (UTC)

October 19

abu hureyra

what language is abu hureyra? what in the world does it have to do with the world we call earth? —Preceding unsigned comment added by Mia9013 (talk • contribs) 01:02, 19 October 2009 (UTC)

Tell Abu Hureyra is a earthen mound which is believed to be the site of a stone-age settlement which is probably the earliest example of agriculture. That's what it has to do with the "world we call earth". The language is arabic, but I don't know the actual english translation. --Jayron32 01:29, 19 October 2009 (UTC)

Tell is specifically an archaeological mound. Abu Hurairah was a specific person (that was his name); this archaeological site is named in his honor (though he probably has nothing to do with it). Literally, it means "Mound of the Father of the Kitten." (But this literal translation of peoples' names is unusual/uncommon - it would be more appropriate to say "Mound of Abu Hreira"). This is a tough topic for an elementary-school project - being both a recent find and in Syria, it is difficult to do research at even a university level (for political reasons); not much research work is published in English; and since the site was flooded during the construction of the Tabaqah Dam, it's probably never going to be excavated again. This site in particular seems to predate any other major finds in the Levant region - it's important because evidence of seeds and agriculture were found there and dated to around 11,000 BC. Nimur (talk) 04:41, 19 October 2009 (UTC)

Ficin and adjuvants

Ficin is a reagent that is used in blood banking to enhance or modify certain immunological reactions. Is there any relationship between this enhancement and the effect enhancement produced by Immunologic adjuvants? SDY (talk) 02:47, 19 October 2009 (UTC)

electrophilic halogenation

So going over last semester's stuff for a problem set... ok why does the iron in say, FeBr3 end up being electronegative enough to pull electrons from dibromide?

Is this sort of related to an alkane that already is partially fluorinated becomes even more reactive to fluorinating agents? It seems kind of paradoxical to me on how an electron donor ends up being an electron acceptor ... if Fe is too electronegative, why doesn't it just kick out a bromine? Basically how can Br(+1) and Fe(II) be better than Fe(III) and Br(0)? John Riemann Soong (talk) 03:34, 19 October 2009 (UTC)

I think you are taking the wrong perspective. I am pretty sure the reaction presents the formation of the FeBr₄^-, aka the tetrabromoferrate (III) ion. There is no reduction of the iron atom; its a coordination reaction with the bromine; if you want to think of it in redox terms, you are disproportionating the Br₂ molecule into Br⁺ and Br^-. The article Electrophilic halogenation actually covers the mechanism pretty well. --Jayron32 04:12, 19 October 2009 (UTC)

Oh, and the Iron (III) bromide is an electron acceptor (Lewis Acid) in this reaction. It really has little to do with electronegativity, and a lot more to do with the fact that Iron (III) has empty "d" orbitals which are of an appropriate energy to accept electron pairs from Bromine. --Jayron32 04:15, 19 October 2009 (UTC)

Aren't those d orbitals really high in energy? Why in the world would a halogen such as chlorine or bromine donate its bonding electrons to those orbital? John Riemann Soong (talk) 04:32, 19 October 2009 (UTC)

Oh, I see. Is it that Br+, Br- is normally bad combination compared to the covalent bond combination, but if Br- can chelate to the Fe, the additional stabilisation drives the formation of Br+? John Riemann Soong (talk) 04:35, 19 October 2009 (UTC)

The 3d orbitals are actually very close in energy to the valence level. That's one of the properties of transition metals that helps them participate in coordination chemistry. The deal is, its probably an equilibrium between Br₂ + FeBr₃ <--> Br⁺ + FeBr₄^-; and I wouldn't doubt if the K value for this were very small (i.e. favors the left side a LOT). However, since the small amount of Br+ reacts with the aromatic ring, Le Chatelier's Principle tells us that the equilibrium will keep generating the Br+ no matter how little of it there was to start with, and the reaction will go to completion even if the initial equilibrium provided only a negligible amount of Br+. In fact, since the reaction generally takes place in non-protic solvents (water or other protic solvents will prevent the tetrabromoferrate (III) complex from forming), there is very little to stabilize the ions on the right side of the equilibrium, so it is likely a very small amount indeed. However, since you have a mechanism to quickly remove any Br⁺ that forms as soon as it does, the actual stability of the Fe-Br coordination bond, vis-a-vis the standard Br-Br covalent bond, is moot. It's stable enough to catalyze the reaction. The FeBr₄^- ion provides the "base" (Br^-) to for the deprotonation step as well, so you only need catalytic (much less than stoichiometric) amounts of the iron (iii) bromide anyways. --Jayron32 04:46, 19 October 2009 (UTC)

Electrophilic halogenation indicates (and all organic texts I've seen agree) that the electrophilic species is "Br2 coordinated to FeBr3": the Lewis acid induces a large dipole along the Br-Br bond, making the bromine atom that is not directly bound to Fe have a large partial-positive. There is not a pure "Br+" ion, merely something that is positive enough to induce the reaction. The Fe-coordinated bromine atom of Br2 does not break off immediately, but rather helps pull off that bromine atom in an SN2-like process. DMacks (talk) 05:16, 19 October 2009 (UTC)

superacids and aromatic compounds

So .... if I use a superacid (magic acid) on an alkane, can I use it to alkylate an aromatic ring? Let's say I have pure benzene. The acid won't react irreversibly with the benzene (or interfere with the alkylation), while the carbocation will go on to perform an electrophilic aromatic substitution, right?

(Just trying to come up with an imaginative way to alkylate benzene on paper.) John Riemann Soong (talk) 05:01, 19 October 2009 (UTC)

If you can get a cationic carbon that has an open valence site (unsatisfied octet), or at least something very close to that, a pi bond will in principle be able to attack it and go down the Friedel-Crafts pathway. But "[super]acid won't react irreversibly with the benzene (or interfere with the alkylation)". DMacks (talk) 05:07, 19 October 2009 (UTC)

Well the way I see it, benzene will kick out the proton, because of the lack of a good nucleophile from the magic acid conjugate base... and isn't an alkyl carbocation more preferable over a benzene carbocation (which has lost lots of resonance stabilisation?) John Riemann Soong (talk) 05:37, 19 October 2009 (UTC)

But the very meaning of a strong acid is that it provides a large equilibrium amount of H+, and can therefore push protonation reactions far forward even if they are not normally favorable. DOI:10.1021/jo00342a015. DMacks (talk) 05:48, 19 October 2009 (UTC)

Is there any way to stop overalkylation? I'm supposed to come up with a total synthesis of ibuprofen ... from benzene. I don't know how to alkylate the benzene ring (I can then turn to the green chemistry synthesis yayyy) without overalkylating it at multiple sites. John Riemann Soong (talk) 05:34, 19 October 2009 (UTC)

What sorts of substituents have what effect on the rate of alkylation? DMacks (talk) 05:37, 19 October 2009 (UTC)

Well okay I wanted to do the alkylation first so I could basically copy the green synthesis. But I guess I have to do the green synthesis first and then alkylate the ring...? My big worry is that I have this carboxylic acid and that will also be alkylated too, in some fashion. I mean I know carboxylic acids aren't very reactive, but then again an aromatic ring with a deactivating substituent might be less reactive than a carboxylic acid, right? John Riemann Soong (talk) 05:45, 19 October 2009 (UTC)

The end of the green synthesis does not have a "carboxyl on the ring" in a way that strongly deactivates it (check your textbook for the origin of the deactivation). If the carboxylic acid is alkylated also, what is the product there, and do you know a way to solve it by an additional reaction? On the other hand, suppose you put the alkyl group onto benzne in two steps: first as "something" and then "convert something into alkyl". What are functional groups that you know how to convert to alkyl? Especially think about ones that would also prevent additional alkylations. DMacks (talk) 05:54, 19 October 2009 (UTC)

Oh whoops. Yeah, convenient that the carboxylic acid is actually an additional carbon away. So .... is this this alkyl chain (with the acid group) an o,p director or an m-director? On one hand, that electropositive carbon might make the benzylic carbon electropositive, (though it's got a pi cloud partially delocalised over it), but on the other hand, alkyl groups tend to be weak activators. Which effect wins?

Let me think about your other suggestions. I'm really inconfident with protecting group strategies, namely because of my fear of side reactions. John Riemann Soong (talk) 06:03, 19 October 2009 (UTC)

Okay here's my synthesis plan for "alkylating first".

alkylating first

• React benzene with an acyl chloride.
• Reduce the carbonyl to an alcohol via Wolf-Kishner. This is a benzylic alcohol ... umm, it won't hydrogenate benzene rings right? Is it compatible with aryl carbonyls?
• Eliminate the alcohol to create a secondary-aryl alkene.
• Hydrogenate the alkene. The alkene is however, conjugated with the benzene ring. Is there any way to break this pi-cloud interaction with a strong enough catalyst without hydrogenating the benzene ring? John Riemann Soong (talk) 06:14, 19 October 2009 (UTC)

Oh hey, I guess is the perfect reaction for the Clemmensen reduction? John Riemann Soong (talk) 06:20, 19 October 2009 (UTC)

Good idea! DMacks (talk) 06:28, 19 October 2009 (UTC)

W-K also reduces C=O to CH2. There's no practical difference in this case. Tim Song (talk) 06:57, 19 October 2009 (UTC)

tractionsystems

can you tell about how track is used as return conductor using earthing– —Preceding unsigned comment added by 122.252.241.54 (talk) 06:01, 19 October 2009 (UTC)

See Third rail. Red Act (talk) 07:29, 19 October 2009 (UTC)

radioactive labelling and fatty acid synthesis

I totally don't get this part at all. I guess I get fatty acid synthesis, with iterative aldol condensations, but I don't get why radiotopic labelling ends up on so many carbons of a fatty acid. Basically it's like almost every carbon atom ends up labelled (but even-numbered atoms are labelled differently from odd-numbered ones). John Riemann Soong (talk) 06:29, 19 October 2009 (UTC)

"even-numbered atoms are labelled differently from odd-numbered ones" is the key. That pattern tells you which carbons come from which parts of which starting materials. DMacks (talk) 06:32, 19 October 2009 (UTC)

Okay now I have to admit myself I don't really get fatty acid synthesis besides the carbonyl/enol(ate) chemistry, not at least when I look at the fatty acid synthesis article. It seems that the most optimal reaction sites lead to branched-chain fatty acids, not straight-chain ones. John Riemann Soong (talk) 06:45, 19 October 2009 (UTC)

So basically I'm labelling the CH3 group of acetyl CoA. This time, the malonyl CoA isn't labelled. Is the malonyl CoA used once? Once a fatty acid chain is going, is malonyl CoA needed? Is the malonyl CoA and acetyl CoA used in alternate elongations? Basically I don't get how after one elongation, how to iteratively work up the product to make it reactive for the next elongation. John Riemann Soong (talk) 07:01, 19 October 2009 (UTC)

You always use a malonyl-ACP to grow the chain. Expelling CO2 drives the reaction along. Tim Song (talk) 07:03, 19 October 2009 (UTC)

My instructions say "indicate the pattern of radioactive labeling if derived from 14CH3-12C-O2H enriched acetate". So how does that translate to radioactive sites on malonyl-ACP? I also am a loss at how to figure out radioactive labelling sites when it comes to rings, steroids and unsaturated compounds. Help! John Riemann Soong (talk) 07:06, 19 October 2009 (UTC)

OK, how do I make unconjugated unsaturated fatty acids, and what would their labelling patterns be? Like say, arachidonic acid. My big problem is that if for example I keep the alkene bond, I get conjugated pi systems instead ... John Riemann Soong (talk) 07:09, 19 October 2009 (UTC)

Engine braking - NA vs forced induction

Hi. Archive search brought up SOME results, but nothing exactly answering my question. Simply put: do you get less engine braking from a turbo-charged, super-charged or naturally aspirated car? Say for the following 2 scenarios:

1. All 3 engines have identical torque curves, all 3 engines have identical gear ratios (e.g. a 1.4L turbo vs. 1.4L SC vs. 2.0L NA). I would assume that the braking torque of the NA engine would be the "full" 2L worth of braking, whereas the turbo would only give "1.4L worth" of braking that the un-forced engine would have given give. Not sure what the SC engine would do? Is my intuition correct?
2. Engines with different characteristics: my favourite examples are the Honda S2000 (NA) vs. a Seat Leon Cupra (turbo) - both 177kW but with 208Nm vs 300Nm respectively. At a gear ratio that gives them the same nett torque at the wheels at the same road speed (but not at the same engine speed obviously, the Honda would be revving much higher), which one would experience more braking torque?

Second question, is the braking torque the same as the full-throttle accelerative torque (both in the actual value and also the mechanism by which they are generated)?

Thirdly, our articles engine braking and maximum brake torque are in serious need of attention from someone knowledgeable. Regards. Fourthly, I'm expecting Steve to go to town on this question :) Zunaid 09:06, 19 October 2009 (UTC)

Typically, forced aspiration engines have a lower compression ratio than NA engines (since the charge is forced in, and therefore already somewhat compressed) and this lower compression ratio reduces the engine braking. Therefore TC engines lose engine braking effect owing to 2 factors - the engine is smaller, and the compression ratio lower. I don't know how SC engines would fit into this, but I would guess similarly - the only extra factor may be a slightly greater braking than the TC engine owing to supercharger losses. Engine braking torque is way lower than accelerative torque - it's caused by friction and pumping losses, whereas acceleration is caused by combustion - a series of explosions - and generates much more power. --Phil Holmes (talk) 13:47, 19 October 2009 (UTC)

Interesting question - and not one I've really thought about. On all of the reasonably modern Turbo and Super-charged cars I've owned, the air injection system has gate valves that turn off when you take your foot off the gas - so the pump is essentially turned off when you're engine-braking. So I'd expect the results to be essentially identical on otherwise identical non-supercharged engines. I guess on the supercharged motors, the supercharger itself eats about 5% of the horsepower (although it gives more than that back in return when it kicks in). That suggests that perhaps a supercharged engine would be able to provide about 5% better engine braking just because of that loss. Not so with turbo's though. SteveBaker (talk) 19:57, 19 October 2009 (UTC)

PRECISE mechanism of HMG-CoA synthase (how in the world do you replace a methyl group with an oxygen atom?)

There seems to be a lot of hand-waving in this article. I need to do radioactive labelling of a huge amount of terpenes, starting with the labelling of the methyl group of acetate (which presumably becomes the methylene group of malonyl-CoA). So which atoms in 3-hydroxy-3-methylglutaryl-CoA would be labelled? How in the world do you replace a methyl group with an oxygen atom? John Riemann Soong (talk) 09:25, 19 October 2009 (UTC)

The three labeled carbons would be the two CH2 carbons and the CH3 carbon in HMG-CoA. Now, I don't know what you mean by "replacing a methyl with an oxygen". This reaction pathway does the opposite, it changes acetate to acetone; which requires the replacement of an oxygen with a methyl. So I am confused by your second question. --Jayron32 13:55, 19 October 2009 (UTC)

Go read the literature. What makes you think the exact reaction mechanism is known? It usually isn't. --Pykk (talk) 17:35, 19 October 2009 (UTC)

SMART Transmitters

I'd like to know whether SMART Transmitters used mainly in Oil and Gas plants can be categorized under S.M.A.R.T. technology? I tried lately to search the internet for the meaning by SMART in such transmitters. These transmitters usually support the HART , FOUNDATION. ™ fieldbus, Modbus, and/or Profibus protocols. I was even wondering why there is no Wiki article about SMART Transmitters! I can write some but will need someone to correct my language later.--Email4mobile (talk) 09:52, 19 October 2009 (UTC)

Do you know which company or contractor makes these SMART transmitters? It looks like a brand-name, but it could also be a generic description of field sensors with extra features (similar to "smart" phones). I suspect the contractor or operator's website would be the best place to look. For example, Omega manufactures a "SMART Transmitter" which is not specifically for oil and gas (it's a general purpose line of wireless transducers), but could certainly be used to instrument an E&P field site. This product does not use S.M.A.R.T. for hard-disk drives, though. Nimur (talk) 15:01, 19 October 2009 (UTC)

STS Sensor also makes a "Smart Transmitter" to wirelessly convey transducer signals. Again, not to be confused with the S.M.A.R.T. technology. Nimur (talk) 15:05, 19 October 2009 (UTC)

Also Honeywell [13] Nil Einne (talk) 15:52, 19 October 2009 (UTC)

SMART transmitters are a new standardized replacement for the pneumatic, and electronic transmitters used in almost all industrial plants (as a part of control loops) that utilize the 4-20mA signal and HART or any communication signal associated with the dc signal. There are many manufacturers, among them: Rosemount (EMERSON), Honeywell, Yokogawa. Althou I studied enough about them but never tried to ask myself if the word "SMART" means "S.M.A.R.T" or "intelligent".--Email4mobile (talk) 17:25, 19 October 2009 (UTC)

Well, I've just read some information in the "Instrumentation Reference Book" and understood the meaning is referring to "intelligent". I think that should be, not S.M.A.R.T. Thank you very much for your interaction.--Email4mobile (talk) 17:53, 19 October 2009 (UTC)

Fainting

Why things look blurry and yellow when you're about to faint, or when you nearly paint?--Mikespedia (talk) 10:34, 19 October 2009 (UTC)

I would recommend reading Syncope (medicine). The effects you are describing are known as brownout, and is most likely caused by low blood pressure in the brain. Googlemeister (talk) 13:16, 19 October 2009 (UTC)

See also paint mask.--Shantavira|^{feed me} 15:28, 19 October 2009 (UTC)

Sorry,it is should be "or when you nearly faint".--Mikespedia (talk) 00:02, 20 October 2009 (UTC)

Fusion Reactor Image..

I'm trying to track down a (somewhat iconic) image of a fusion reactor firing; the image appears to be taken from above the reactor assembly, and has multiple bots of electricity arcing across the metal. However, I'm stuck at work on a rather slow connection and my google-fu is weak and I've been unable to find it (trawling through wikimedia didn't produce it either). Can anyone help? Plus which reactor did the image come from? Thanks! NeoThermic (talk) 12:59, 19 October 2009 (UTC)

Is this a fantasy photo you are looking for? As far as I know, there aren't any fusion reactors sitting around for us to take photos of. -- kainaw™ 13:11, 19 October 2009 (UTC)

Not at all. There's been many fusion experements that would require some description of a fusion reactor to actually experement with. Granted, we've not had any reactors that have produced a positive power output over the input, but that's why they're all experemental reactors. NeoThermic (talk) 13:16, 19 October 2009 (UTC)

here is the image of Z machine which I think you are talking about. --Dr Dima (talk) 13:38, 19 October 2009 (UTC)

YES! Many thanks! That's the exact image I was trying to find! Thanks again! NeoThermic (talk) 13:51, 19 October 2009 (UTC)

Here it is in high-res, if you want it. It's a crazy image. --Mr.98 (talk) 13:57, 19 October 2009 (UTC)

That's a high energy X-ray and plasma physics experiment, not a fusion reactor. (Though, plasma physics is closely related, and research from this project often applies to fusion research. Still, it's not a reactor in the analogue of a fission reactor). You might want to read about tokamaks. Nimur (talk) 18:02, 19 October 2009 (UTC)

It's not that unrelated to fusion reactor research. You can use z-pinch (and even Z machine itself) to induce DT fusion, and they are working on prototype power plant designs. --Mr.98 (talk) 22:15, 19 October 2009 (UTC)

Bilingualism and Inner Monolouge

Do bilingual people think in just their native language or does it switch depending on usage/context? Does the brain change in someway to accommodate not just speaking another language but actually instinctively thinking in that language?TheFutureAwaits (talk) 13:54, 19 October 2009 (UTC)

My understanding from talking to a lot of people about this is that it varies. Some people only think in their native language. Some get accustomed to thinking in other languages. An American professor of mine (English as first language) told me that she generally thinks in German now because she finds it better at expressing what she's thinking about. I'm not sure all people "think" the same way, either (I don't generally think in "words", for example, unless I am trying to actually compose language in my head). --Mr.98 (talk) 14:00, 19 October 2009 (UTC)

My first language is Portuguese, but I've been speaking mostly english long enough that I think in english most of the time to the point that I find myself thinking in english and translating it back to portuguese whenever I have to speak portuguese for short periods. Dauto (talk) 14:15, 19 October 2009 (UTC)

OR. It switches depending on context where the dominant context is the people around one. THere is a tendency to be confused when one "thinks" an expression in the other language that does not readily translate. Cuddlyable3 (talk) 15:13, 19 October 2009 (UTC)

Most language acquisition data shows that you don't "think" in a language; thought and cognition is independent of language. You can disable language centres and still think and rationalise perfectly fine (but your communication skills suffer). You can also severely impair cognition and have perfectly fine language. Cognition and language are separate. Now, cognition may be rapidly translated into a favourite language (like a native language), but this does not imply "thinking in a language". Notably, you think in a language only when you wish to communicate. Sure, talking to yourself is useful, but is not necessary, for cognition. John Riemann Soong (talk) 16:40, 19 October 2009 (UTC)

Go back and read the title. "Inner monologue" certainly does involve using language. --Pykk (talk) 17:30, 19 October 2009 (UTC)

I have to agree. I was thinking about this several times and just before I answered it. I was definitely thinking in English. In fact I'm one of those people who tends to think about all sorts of stuff stuff all the time and lets their mind wander all over the place, quite often I know it's in English. Technically this may simply be my mind analysing my thoughts in a manner I can understand but that seems to be to be mostly a moot point. Perhaps I'm just a freak of nature but I doubt it. This doesn't mean you need language to think nor does it mean your thought process is limited if you don't have language. Nil Einne (talk) 19:02, 19 October 2009 (UTC)

Ah, but speech isn't a medium for thought. It's simply a byproduct of thought. John Riemann Soong (talk) 00:44, 20 October 2009 (UTC)

Feral children who never learn language. Deaf people before and after people established schools/institutes where they invented/learnt sign languages. Learning a language is something that has to be done in a certain window in a child's life or never, and is necessary for certain types of reasoning. As Nil said, your thought process is limited if you don't have language. 86.140.149.215 (talk) 01:06, 20 October 2009 (UTC)

Did Nil really say that? Steven Pinker argues in the The Language Instinct that language is a biological machine, independent from consciousness and cognition. Witness the stroke patient with Broca's aphasia struggle with language even though he knows *exactly* what he wants to say in terms of ideas, but is at loss for words. Deaf people who never learnt a native language but mime out scenes enthusiastically to others and know how to pick locks and do complicated sums. A near-adult who with mental handicaps who struggles with everyday tasks but yet talks with the sophistication of a British noble at tea. This is a case where again correlation does not imply causation. Simply because language is frequently correlated with thought doesn't mean language is necessary for thought. John Riemann Soong (talk) 03:00, 20 October 2009 (UTC)

My wife (who is French) has spent more than half of her life in English-speaking countries and is pretty much fluent in English. She says she thinks in English when she's around English people - and in French when she's with French people. However, one thing is startlingly clear - she can't do mental arithmetic in English...you hear her muttering numbers in French - then translating the answer to English at the end. Presumable rote-learning of multiplication and addition tables is the cause of that. English word order occasionally trips her up and there are a few metaphors she messes up - also she ALWAYS screws up the names of the letters G ("gee") and J ("jay") - saying things on the phone like "No, that's 'jay' as in 'George'."...much to the confusion of the poor person on the other end of the line! Another peculiarity I've noticed is that when she's been on the phone with her french-speaking family, her English accent "goes away" and she sounds incomprehensibly French for about 15 minutes after. SteveBaker (talk) 19:36, 19 October 2009 (UTC)

Ah, I did the same thing the other day! But your wife has a better excuse: French and English J and G are exactly reversed! — Sebastian 03:42, 20 October 2009 (UTC)

Well, not exactly, no. The article you linked gives the French pronunciation of G as "jay" in the respelling-pronunciation column, but as "zhay" in the IPA column. If I remember correctly, the "zhay" is closer (I was going to say "correct", but not really, because they "ay" sound in English is a diphthong). --Trovatore (talk) 03:56, 20 October 2009 (UTC)

Oh, but of course that's not a problem with the IPA column of the article, but with my respelling as "zhay". --Trovatore (talk) 03:57, 20 October 2009 (UTC)

By "exactly" I meant to point to the amazing fact that two conditions apply: (1) the exchange is symmetric (J->G and G->J) and (2) the pronunciation is the same with the exactness of the phonemes of the language used (i.e. English. In English, neither initial /ʒ/ nor /e/ are phonemic). — Sebastian 06:35, 20 October 2009 (UTC)

While there is definitely debate in the scholarly community as to the interdependence of language and thought (as the previous comments alluded to) what you are referring to, which I would describe as using language internally to mediate thought, is a well-recognized phenomenon, which psycholinguists often refer to as "inner speech."

When searching to an answer for your question, I googled "second language acquisition "thinking in a language"" and found a review for what looks to be a very comprehensive book on the topic:

http://linguistlist.org/issues/17/17-1309.html

The book is called: Inner Speech -- L2: Thinking words in a second language. By Maria C. M. de Guerrero.

(this is how I learned that thinking in a language is called "inner speech")

de Guerrero is a professor at the Inter American University of Puerto Rico, and is a prominent researcher on this topic.

I then searched for this title in SpringerLink (Since this book is published by Springer), which is an electronic research database that many libraries and universities subscribe to. I was able to read portions of this book, and Chapter 3 "Thinking Words in a Second Language" is especially informative on this topic. I would recommend searching for this book at your local library or school, either through the catalog or using an electronic database such as SpringerLink.

I'll summarize some of the main points from this chapter:

Bilingual people do think in their second language at times. Whether an individual does and how much they do seems to depend on a variety of complex factors, including:

1) the level of proficiency in the second language ("inner speech" in a second language increases and changes purposes from that of mere mental rehearsal to true private thinking as a person becomes more fluent in the language)

2)The content/subject of the thoughts (for example, if someone goes to school in a second language and studies medicine, when they are thinking about medicine, they may more naturally think in the language in which they learned about it. OR, if someone is thinking about an event that happened while they were using one language vs. another (e.g. when someone lived in one country vs. another), they are likely to thinking the language that the event occurred in))

3)the purpose that the thought fulfills (e.g. praying, doing mental math, planning/organizing, remembering life experiences) - some people display a preference for one language or another when thinking for different purposes.

As to your question about what happens in the brain when people are able to think in a second language, the best answer is probably found somewhat indirectly, by looking at how multiple languages are represented in the brain and how this is affected by proficiency in a language, since we know that people are better able to think in a second language when they are more proficient in it.

While some research shows that a second language will be represented in a different part of the brain unless you learn it before a certain age, most research shows that level of proficiency is more important - that is, for people proficient in a second language, the second that language is processed in the same part of the brain as the first language regardless of the age that the person learned the second language.

So it seems that the more proficient you are in a second language, the more likely you will be to think in that language in certain contexts, and, the more likely your two languages will use same part of your brain.

Here is another book chapter written by this Maria C. M. de Guerrero that is available via google books preview: It is called "Form and Functions of Inner Speech in Adult Second Language Learning" from the book "Vygotskian approaches to second language research"

http://books.google.com/books?id=QbB-CGkx4hwC&pg=PA83&lpg=PA83&dq=%22inner+speech%22+in+second+language&source=bl&ots=FPvpPtgPiO&sig=8o_JIQJopy_UnOQ1n19boMbu-VA&hl=en&ei=qcPcSri5IYGN8AaGqK23BQ&sa=X&oi=book_result&ct=result&resnum=3&ved=0CBgQ6AEwAg#v=onepage&q=%22inner%20speech%22%20in%20second%20language&f=false

This chapter discusses the nature of inner speech in second language learners, its proposes, and how these might vary with proficiency in the second language.

I found this source with a google search for ""inner speech" in second language"

Finally, here is a discussion of various viewpoints on the relationship between language and thought that other posts have referred to:

http://www.d.umn.edu/~dcole/hearthot.htm

It's called "Hearing Yourself Think: natural language, inner speech and thought" by David Cole, Head of the Department of Philosophy at the University of Minnesota. Coming from a philosopher, this naturally offers a somewhat different perspective on the issue, but nonetheless raises some of the main points of debate.

I found this with a google search for "second language acquisition "inner speech""

I hope this helps answer your question. --Kristin Good (talk) 20:42, 19 October 2009 (UTC)

I talk in my sleep, and according to my wife I have had Spanish dreams on a few occasions when I've been immersed, even for only a few weeks. I know this doesn't answer your question, but I think it supports the notion that the brain can "switch over" on a very deep level. - Draeco (talk) 01:08, 20 October 2009 (UTC)

I used to think to myself on occasion in Spanish. That was when I used Spanish everyday. Now that it has fallen into disuse, I only think in English.--Drknkn (talk) 04:07, 20 October 2009 (UTC)

Quantum mechanics free particle - follow-up question

Hi all:

I posted the following question a while back:

http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_September_18#Energy_eigenfunctions_of_a_free_particle

and just had one further question on it.

I asked about the limit as ${\text{L}}\to \infty$ - I believe i am meant to recover the spectrum of a free particle on an infinite line when I take such a limit.

Currently I have $\psi _{n}=A\,\cos({\frac {2\pi \,n}{\text{L}}}x)+B\,\sin({\frac {2\pi \,n}{\text{L}}}x)\,$ and $E_{n}={\frac {2}{m}}({\frac {n\,\pi \,h}{L}})^{2}$ with h the reduced Planck constant, and the wavefunction of a free particle on an infinite line would be $C\,{\text{exp}}({\frac {2\,\pi \,n}{\text{L}}}i\,x)$ for some constants A,B,C - however, for the limit, unless I'm mistaken I'd need $B\to Ai$ - why does this occur in the limit? I can't see any mathematical reason why it would.

Thanks! Spamalert101 (talk) 14:38, 19 October 2009 (UTC)

First let me get a minor notation neatpick out of the way. The standard notation for the reduced Planck constant is $\hbar$. To answer your question: The first equation assumes a non-negative n. That is n=0,1,2,3,.. etc. The second equation assumes any integer value for n (even negative values). So you cannot compare the two equations without first performing some manipulation. To directly compare the two equations you must write the second equation as $C_{1}\,{\text{exp}}({\frac {2\,\pi \,n}{\text{L}}}i\,x)+C_{2}\,{\text{exp}}(-{\frac {2\,\pi \,n}{\text{L}}}i\,x)$ where now n is assumed to be a non-negative integer. Does that answer your question? Dauto (talk) 15:28, 19 October 2009 (UTC)

Yes, thanks, and I did know the standard notation - just not how to LaTeX it: should have tried the obvious I suppose! :) 82.6.96.22 (talk) 17:52, 19 October 2009 (UTC)

precise chemical composition of butterish products

So ... I need to somehow obtain the precise chemical composition (percentage breakdown by fatty acid, etc.), including the precise structural formula of every major constituent of the following products: Land o' Lakes butter, Crisco all-vegetable shortening, I can't believe it's not butter spray, ghee, liquid corn oil, partially hydrogenated soybean oil, whey, sweet cream buttermilk, and sweet cream butter.

Unfortunately, as you can see, manufacturers have this irritating tendency to give me vague mixtures that doesn't tell me what their exact chemical compositions are... help? Should I call the Better Business Bureau or something? John Riemann Soong (talk) 16:36, 19 October 2009 (UTC)

Or maybe the Butter Business Bureau? --Trovatore (talk) 03:26, 20 October 2009 (UTC)

GC-MS?!? --Jayron32 18:21, 19 October 2009 (UTC)

Food that is Generally recognized as safe (in the legal sense of that phrase) is not subject to detailed chemical or agricultural scrutiny. It may be impossible to get chemical contents from the manufacturers. Nimur (talk) 23:13, 19 October 2009 (UTC)

Are we getting taller

Now, it seems (and I think is proven) that younger people tend to be talle than their parents. (From my experience, I'm not!) I was wondering, is it nutrition, evolution, genetics or some other factrs that influences or height? Also, will this trend continue, so say in many years, the avarage height may be 6 foot something! Cheers. AtheWeatherman 16:59, 19 October 2009 (UTC)

Parents live longer and start shrinking. Cuddlyable3 (talk) 17:08, 19 October 2009 (UTC)

Yes, in general over the past few hundred years people have been getting taller and taller (see this article). The usual reason given is nutrition, critically at young ages and even a mother's nutrition while the child is in the womb. However, it appears that Americans in particular may be getting shorter on average, particularly compared to Europeans. The reasoning given is that there is greater health and nutrition inequality in the US than Europe, with more poor people living on junk food. I'm not sure if immigration from "short countries" (ie Mexico) is also part of the story. TastyCakes (talk) 17:15, 19 October 2009 (UTC)

Over several generations we (in the west - it is just starting in Asia, although I believe there is a genetic component involved there as well) have gotten taller due to better nutrition. (That is somewhat based on folk wisdom - I'll try and find some reliable sources in a minute.) I've never heard of any significant general change over one generation - children are usually roughly the average of their parent's heights (after accounting for gender differences). --Tango (talk) 17:20, 19 October 2009 (UTC)

One of the links I put above claims that German children raised during the two World Wars were shorter than their parents, due to chronic food shortages. Anecdotally, I would say a lot of the males I know are taller than both their parents, and a lot of the females are taller than their mothers. I'd also say there is less of a genetic component than generally presumed. The type of food and amount of protein in the regions diet seems to be a big factor, and the reason many American (or Canadian) born Chinese are much taller than their relatives in China (even Hong Kong, which has been a "first world place" for more than a generation). I have also heard, again anecdotally, that people from the north of China are taller than those in the south because their staple food is wheat rather than rice (and presumably they eat more protein). TastyCakes (talk) 17:30, 19 October 2009 (UTC)

I believe Asians born and living outside Asia typically have a height somewhere between the average where their parents are from and the average where they grew up. That suggests the height difference is partly environmental and partly genetic (although it is also possible that the Asian sub-culture in other continents still has worse nutrition than other people there). --Tango (talk) 18:40, 19 October 2009 (UTC)

I'm not sure I agree that Asians have "worse nutrition", as much as they have different nutrition. Smaller meals with more carbohydrates (rice) and less meat is common in many Chinese families, wherever they live and however well off they are. Personally, I would put this as the reason behind Chinese people being somewhat shorter than average even when they're born and raised in the West, rather than genetics (I haven't found data one way or the other in my brief google search). That is also why I'd say Japanese people remain somewhat shorter than westerners. TastyCakes (talk) 19:28, 19 October 2009 (UTC)

little of everything, maybe. prenatal and childhood nutrition has a big effect; also reduction of childhood diseases. this has presumably plateaued in the middle and higher classes of the first world by now. but on a longer time scale, there is a tendency for species to evolve larger and larger in times of plenty, as larger individuals are better able to compete with their own species for territory, food, shelter, mates, etc. that's not exactly 100% relevant for humans, but I still can't shake the unscientific observation that more women will mate with a football player and more men with a supermodel than with a little person. also, i wonder about the effects of our unnatural diet on growth, both in terms of really huge doses of fat (and increasing body fat) and trace hormones in the food, the former probably more significant than the latter. certainly, it's caused a much earlier onset of puberty; however, that might be expected to cause people to be shorter, since that typically starts to terminate physical growth. on a tangential note, the average bust size of american women has gone from 34B in my youth to 36C now. Brassiere. Gzuckier (talk) 17:42, 19 October 2009 (UTC)

More attractive humans tend to mate with other more attractive humans, but I don't think they generally have fewer children. In fact, poorer families are usually larger, and there is some positive correlation between attractiveness and wealth. --Tango (talk) 18:43, 19 October 2009 (UTC)

Don't you mean 'I don't think they generally have more children' or 'I think they generally have fewer children'? Nil Einne (talk) 18:56, 19 October 2009 (UTC)

From anecdotal evidence it seems to me that pretty much every german male (and most females) in my generation (born late 60s/early 70s) is taller than both parents. There is certainly a drastic difference in a generation. Of course our parents generation has been directly affected by WWII and its aftermath, so they were likely exceptionally short. Somewhat jokingly, I have always favoured the "dutch cheese" theory: according to which the dutch fed growth hormones to their cows in the 70s which then got passed on to cheese eating Europeans. I base this on (again anecdotal) perceived correlation between height and consumption of dutch cheese in peoples childhood. I know this is likely nonsense, but I have failed to find another explanation why the Dutch are (or seem to be) that much taller than say the Belgians (can't believe that nutrition was that much different).195.128.251.194 (talk) 22:52, 19 October 2009 (UTC)

Sharpless epoxidation, dihydroxylation

So, in each of these, the catalytic metal complex gets released by hydrolysis... but isn't hydrolysis SN2? Doesn't that reverse the enantiomeric stereochemistry of the intermediate? John Riemann Soong (talk) 17:27, 19 October 2009 (UTC)

Testicle sweat

Why does the sweat of my testicles smell quite differently than that from other parts of my body? --Belchman (talk) 17:45, 19 October 2009 (UTC)

It's explained in Sweat_glands#Apocrine sweat glands. --NorwegianBlue ^talk 18:00, 19 October 2009 (UTC)

Your perception may be biased. Do you have independent confirmation of this difference? 87.81.230.195 (talk) 00:32, 20 October 2009 (UTC)

Odds of skin color and features in children of multiracial couples

Excuse my relative ignorance of the subject, but I didn't find the answer to my question in the miscegenation or admixture articles. Assuming that in a multiracial couple, there are a black and a white person, what will be the odds of the offspring's skin color and features, considering that the children can either seem white, black, or mixed ? Also, is it a regressive trait, or the aforementioned couple can have one child that looks white and the other black ? Rachmaninov Khan (talk) 17:55, 19 October 2009 (UTC)

Human skin color isn't a simple matter of one or two genes; it's quite complicated. See Human skin color. Also, trying to define the terms "black", "white", and "multiracial" isn't nearly as straight-forward as you might think, either. "Race" is basically a social construct, not a scientific one. See Race (classification of human beings) Red Act (talk) 18:27, 19 October 2009 (UTC)

I'm not sure if I understand your last comment but [14] [15] [16] may interest you Nil Einne (talk) 19:19, 19 October 2009 (UTC)

I'm not sure whether the "your last comment" is in reference to the OP's last sentence, or to my last sentence. If it was in reference to my last sentence, my last sentence was basically a shortened paraphrase of the following sentence in the Race (classification of human beings) article: "The academic consensus is that, while racial categories may be marked by sets of common phenotypic or genotypic traits, the popular idea of 'race' is a social construct without base in scientific fact." See the article for more information; it's a very interesting article. Red Act (talk) 20:03, 19 October 2009 (UTC)

The "odds" cannot be easily calculated because the genetics are more complicated than just one gene, and people who label themselves "black" or "white" are often to some extent "mixed race" themselves. Personally, I object to all three labels, and to the concept of "race" (as explained by Red Act above). Nil Einne's second reference estimates the probability as one in a million, but this is just a rough estimate and should not be taken too seriously as an accurate calculation. Dbfirs 21:04, 19 October 2009 (UTC)

coffee and weight gain

I hope this doesn't count as "medical advice". A couple years ago I started a job where they had very good free coffee (I guess the costs were justified by the increased typing speed of caffeinated workers). I'd never been much of a coffee drinker before, but I developed a 1-2 cup a day habit which I thought of as being pretty moderate. I've also never been much of a weight watcher (I've been skinny most of my life) so was very surprised when I recently stepped on a scale for the first time in a couple years, and found I had gained about 15 pounds. I'm still not fat by most standards, but I'm a bit perturbed by this, and wonder if the steady coffee consumption might have anything to do with it (e.g. by causing appetite increase). Any thoughts? 66.127.54.181 (talk) 19:15, 19 October 2009 (UTC)

Correlation does not imply causation. Lots of people gain weight as they age - for many reasons. It might have been the coffee - but at such low rates of consumption, I kinda doubt it. It might have merely been the change of job. Maybe you don't walk around so much in your new job? Maybe you've changed your lunchtime eating habits? Maybe the building is a few degrees warmer so you're not burning energy that way? There are all sorts of other possibilities and it's almost impossible to guess which of them it is. SteveBaker (talk) 19:28, 19 October 2009 (UTC)

Well, my first thought was how you're taking your coffee. Plain black coffee has a fairly negligible calorie count (5 calories or so a cup, and I'm using the US convention where a food calorie is really a kilocalorie). Say you use a tablespoon of sugar, though -- that's 50 calories. Creamer appears to be another 20 or so. Two cups a day like that becomes an extra 150 calories, 5%-10% of your daily intake. So that could be a contributing factor. As for the extended effects... that gets trickier to answer. Lots of websites suggest that caffeine contributes to weight gain, but I don't find them to be all that reliable. The Mayo Clinic has a page on the links between caffeine and weight gain/loss, but it avoids making far-reaching statements. — Lomn 19:34, 19 October 2009 (UTC)

Thanks. I drink the coffee with no sugar but with some creamer. Yeah, I figured the coffee and creamer didn't add many calories but I have generally noticed increased appetite and only today it occurred to me that coffee might have something to do with it. The Mayo Clinic page actually says coffee may promote weight loss. I also read somewhere recently that diet soda promotes weight gain by increasing appetite. Anyway I used to trust my metabolism and eat whenever it told me to. I'll have to start being a bit more careful (whether or not coffee is involved) but I think I can handle it. 66.127.54.181 (talk) 20:23, 19 October 2009 (UTC)

Caffeine inhibits cAMP phosphodiesterase, causing the increased hydrolysis of glycogen, and that process happening in the liver eventually causes a higher blood glucose level. Low blood glucose would make you hungry, so that's the theoretical background to weight loss caused by caffeine. I think that only works if you do not eat too much after the time of day when you had a high caffeine level; otherwise the glycogen will be replenished for the time when you are less active, and then - I guess - fat would be created from part of the glycogen. Icek (talk) 02:40, 20 October 2009 (UTC)

Of course for the same reason it's often recommended not to eat much before going to sleep (no matter how much caffeine you ingest). Icek (talk) 02:47, 20 October 2009 (UTC)

I think stimulants in general suppress appetite, right? On the other hand I believe it's well-established that sleep deprivation promotes obesity. So it could be a lot like the vicious cycle some of us are familiar with regarding alertness and ability to concentrate: We consume caffeine to enhance these, and it works, but then we can't get to sleep that night, and the next day it's worse. So we either up the dosage, or suffer the consequences.... Do I get more done with coffee, in the long run, than I would without it? Who knows. --Trovatore (talk) 02:54, 20 October 2009 (UTC)

Hidden variable theories and T-symmetry

I am not a scientist and pose this question at severe risk of it going way above my head lol, so I apologise in advance if it's the most stupid thing you've ever heard.

My interest is in philosophy and I've been wondering to what extent quantum mechanics and modern physics preclude the possibility of a deterministic existence. In previous discussion at the Reference Desk (thank you, by the way!) I've been pointed in the direction of the Bohm interpretation and hidden variable theories, which I realise are not by any means accepted, but are at least not technically impossible. My question is about the relationship of these theories to the idea of T-symmetry, elements of physics that would appear the same whichever direction time was moving. The way my mind was moving was, if these theories can account for quantum theory in a deterministic way, do they also account for it in a way that wouldn't break any physical laws if the Universe was played out in reverse, so to speak?

I realise that thermodynamic laws and similar would obviously not work in this way- but my understanding of these is that they are probability on such an enormous scale that they are always demonstrated true. If we were able to account for asymmetrical laws in this way, would that help?

Like I say, I have an absolutely lay understanding of physics, I haven't even studied it for A-level (High School, if you're across the pond) and so am bound to be wrong about this. I just thought that it was no good speculating about things like this without any expert insight. Dan Hartas (talk) 19:36, 19 October 2009 (UTC)

I don't know much about hidden variable theories, but the Many-worlds interpretation is an alternative to the Copenhagen interpretation that dispenses with a lot of the problems of wave function collapse like being time irreversible. In MWI, states tend to decohere and branch apart as time goes forward, but there's nothing stopping previously non-interfering states from coming together except that it's statistically unlikely, just like with the second law of thermodynamics. The Bohmian mechanics article mentions that it's isomorphic to MWI and consistent with decoherence, so it sounds like it also doesn't have a problem with time symmetry. You might also look at Arrow of time and Entropy (arrow of time). Rckrone (talk) 22:18, 19 October 2009 (UTC)

(ec)All complex natural processes are irreversible. That has been expressed in the Second law of thermodynamics and the principle of entropy. This law is true not only on an enormous scale; it is true for any isolated system, large or small. The philosophical view Determinism cannot be disproven by logic because it can maintain that perception of logic is pre-determined. Thus identifying any reversible processes neither supports nor defeats the determinist proposition. Cuddlyable3 (talk) 22:23, 19 October 2009 (UTC)

On the subject of determinism, calling hidden variable interpretations deterministic is sort of questionable. The future is depends on information that necessarily can't be known until after the fact. I'm not sure that really counts. More generally, determinism isn't a requirement for time symmetry, just as long as the theory is non deterministic in the same way in both directions (which wave function collapse isn't, but quantum decoherence is).

One more unrelated point is that technically T-symmetry can be broken in the Standard Model, but CPT-symmetry holds. Rckrone (talk) 00:37, 20 October 2009 (UTC)

Chaos theory means that determinism doesn't exist as a practical matter. You can come up with mechanisms and other systems which are infinitely sensitive to their initial conditions. In theory - if you knew the initial conditions to literally infinite precision, then you could predict the outcome - but the slightest error (even an infinitely small error) - and you'd have no idea what the result might be. Imagine a metal-tipped pendulum suspended over a pair of magnets such that when you swing it, it ends up poised over one or other magnet. This is a chaotic system. If you plot the position from which you release the pendulum and color that point red if it ends up over one magnet and blue if it ends up over the other, and do that over a whole range of positions, the picture you'd get as a result is a fractal - there are places where releasing the pendulum from one point leaves it over the red magnet - and releasing it from another position that's INFINITELY close to the first results in it ending up over the blue magnet. Such systems are mathematically deterministic - but in the real world, are most certainly not. SteveBaker (talk) 01:40, 20 October 2009 (UTC)

OK, somebody's gonna ask, so might as well be me: What exactly do you mean by "infintely close" in this context? --Trovatore (talk) 03:15, 20 October 2009 (UTC)

Palladium

Why is palladium considered to have five electron shells, even though the outermost shell is empty? Dogposter 20:00, 19 October 2009 (UTC)

1. All elements have an infinite number of electron shells. They may only have enough electrons to fill a certain number of these shells in the ground state, but the shells are still there.
2. That being said, Palladium has the following electron configuration: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶4d¹⁰. The expected ground state, based on the location in the periodic table would be ... 5s²4d⁸, however the actual configuration occurs due to the slight energy lowering caused by electrons which have paired spins. The deal is, that the difference in energy between an empty s orbital and the d orbital of the level below it (say, 4s & 3d or 5s & 4d in this case) is very small, they are almost the same energy. Thus, small changes in energy can effect them, and the net result of the paired spins of the ...4d¹⁰ state more than compensates for the difference in energy for moving those two electrons from the 5s to the 4d orbital. So, you are technically correct that Palladium only has 4 filled energy levels in the ground state. --Jayron32 20:51, 19 October 2009 (UTC)

Wait, so because small changes can affect the electrons around palladium, they consider it to have 5 electron energy levels? Dogposter 21:18, 19 October 2009 (UTC)

What Jayron is saying is that small energy changes can easily knock electrons from 4d (or other levels) into the 5s. Because atoms in real materials are constantly in thermal equilibrium with their surroundings, and receiving photons and gaining and losing thermal energy, these electrons are regularly knocked into and out of the 5s "shell", even though that is not their "resting" shell. This is characteristic of many large atoms classified as transition metals. Other types of atoms, where the energy gaps are larger, do not have such a dynamic equilibrium of valence electrons. Nimur (talk) 22:51, 19 October 2009 (UTC)

That's true, but its not exactly what I was saying. All atoms have 5 energy levels, even hydrogen. They all have an infinite number of energy levels. Its just that the ground state electron configuration may not place any electrons on the fifth energy level for atoms. The second part of my explanation was about the fact that there is a "rubric" for determining the ground-state electron configuration of an element based on its placement in the periodic table. Based on the location along, palladium would be expected to have the [Kr]5s²4d⁸ electron configuration; thus its valence level would be taken to be n=5; which would fit with it being located on the 5th period of the periodic table. HOWEVER, experimental evidence shows that palladium does not obey the expected result; its electron configuration is actually the non-standard [Kr]4d¹⁰ configuration. The explanation for this is the additional stability generated by spin-spin coupling of electrons in THAT configuration compared to the expected configuration, which would NOT have spin-spin coupling. To make a very long story short, the description of Palladium as having it's valence level is n=5 since it is located on period 5; but experimental evidence shows this to not actually be so. Palladium does not actually have any ground-state electrons in the n=5 level, so technically its valence level is n=4. Still, the entire set of 5s-4d-5p energy levels are so close in energy as to make them all practically identical. The "fact" that Palladium does not have any ground state electrons in level n=5 isn't all that important, since it does not much affect the behavior of the element, chemically speaking. Such is the nature of transition metals; one can really understand their chemistry much better if you just consider the whole set of ns/n-1d/np orbitals as roughly the same energy. That's how coordination chemistry works anyways. --Jayron32 04:38, 20 October 2009 (UTC)

mercury as an element

I have these few questions which i will be glad to get positive answers to.They are as follows;

1. can a mobile phone torch light or a normal battery torch light be used to confirm that a mercury(element) is still active and good 4 industrial use?
2. When exposed,how long does it take for it to get inactive and no longer good 4 industrial use?
3. Is it really used in making the old pendulum wall clocks,analague telephones,old wooden black and white televisions?
4. What are its functions in this machines since some of them still works when the mercury(element) has been removed?
5. What other related items is it used in?

Thanks...Emma —Preceding unsigned comment added by 41.217.1.3 (talk) 20:24, 19 October 2009 (UTC)

What do you mean by "mercury(element)"? Mercury is a chemical element, it can't be "active" or "inactive". --Tango (talk) 20:38, 19 October 2009 (UTC)

(edit conflict) See Mercury (element) for more info, especially the "applications" section for specific uses. Mercury doesn't "go bad" in the sense you seem to think it does. It is actually quite stable in open atmosphere, it slowly evaporates, but not on any time scale that would make it disappear. When heated, it will react with oxygen in the air to form mercury oxide compounds; but it generaly does not so react at room temperature, so its pretty stable stuff. Mercury in devices like, say, one of those old mercury tilt-switches used in many devices, will last pretty much indefinately, or at least longer than the useful life of the device. --Jayron32 20:41, 19 October 2009 (UTC)

Two uses that the OP asks about aren't covered in the Mercury article. Mercury was used in the Bob of a pendulum clock to provide temperature compensation - as the temperature rises, the length of the pendulum rod increases, making the effective length of the pendulum greater and slowing the clock down. The expansion of the mercury in the bob raises its centre of gravity, reducing the effective length of the pendulum and keeping the clock's speed accurate. An alternative way of doing this without using mercury is to make the pendulum rod out of two metals with differing expansion rates, arranged to cancel out thermal expansion (see Bimetallic strip). In electronics, apart from the simple tilt switches mentioned in the Mercury article, it was used in the Ignitron rectifier, to produce DC power from an AC source. However, these were big industrial-scale devices, and wouldn't have been used in a domestic telephone or television. Tevildo (talk) 21:11, 19 October 2009 (UTC)

(edit conflict)... and in answer to Q5, you will find much larger quantities of mercury in old thermometers and especially old barometers. The amounts in your list at 3 will be minimal (or zero) and not worth trying to recover (except for ancient pendulum clocks that are worth much more with the mercury in place). Dbfirs 21:17, 19 October 2009 (UTC)

The OP might be asking about mercury battery - some of these questions seem like non-sequitors. Can you rephrase some of these questions? It might help us answer them better. Nimur (talk) 23:01, 19 October 2009 (UTC)

Restriction of Hazardous Substances Directive (the new electronics chemical safety standards) might be helpful (if not to the OP, maybe to some other responders). Mercury has been used in electronics, specifically in certain lights (I think some types of fluorescent bulbs and halogen bulbs used a mercury oxide coating inside the glass bulb). See also, Mercury-containing lamps and mercury-containing equipment from the US Environmental Protection Agency. Nimur (talk) 23:05, 19 October 2009 (UTC)

Mercury was also frequently used in switches and mercury-wetted relays - these were used in telephones and thermostats and such. In a regular switch, the metal-on-metal contacts would wear out - but if one of the contacts is liquid mercury, there is almost no friction and the switch lasts MUCH longer. I can't think why it would be used in an old black & white TV - but it's possible it was used in the manufacture of the tube or something. These days, the toxicity of mercury is causing a steep decline in the number of places it's used. SteveBaker (talk) 01:21, 20 October 2009 (UTC)

DNA contains entire human genome?

I was told that all humans possess the same exact genes and that the only difference is the sequences of nucleotides that account for physical differences. So I was wondering if it were possible to have a person like Shaquille O'Neal and if had a son with a woman, to make the son look exactly like Brad Pitt the only we need to do is get different nucleotide sequences? —Preceding unsigned comment added by 139.62.166.238 (talk) 23:17, 19 October 2009 (UTC)

I don't understand - the nucleotide sequences are the genes. About 99.9% of human DNA (for a particularly way of measuring it) is the same in all humans (see Human genetic variation), the other 0.1% accounts for all the variation we observe. Turning one person's DNA into another person's would probably be beyond our genetic engineering abilities (but if you have the other person's DNA you could just try and clone them - we don't have that ability yet, but we aren't far off), it also wouldn't be enough - physical appearance is determined by a combination of genetics and environmental affects, you would end up with someone similar looking, but not identical. --Tango (talk) 23:39, 19 October 2009 (UTC)

As a gross comparison, you might get someone that would look like Jose Canseco and would hit like Ozzie Canseco. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:52, 20 October 2009 (UTC)

It's also worth mentioning that a lot of information is also extra-genetic - promotor sequences can determine how much of a gene is produced, methylated genes can be turned off and on, and some genes code for RNA products that can regulate gene expression, to name a few. ~ Amory (u • t • c) 02:41, 20 October 2009 (UTC)

October 20

Vacuum Ablation

I've heard of a concept called Vacuum Ablation in which given enough time the atoms in a substance boil away into space. Is there such a thing? Josh Parris 02:54, 20 October 2009 (UTC)

Googling "vacuum ablation", it looks like the term refers to a situation where there is a substance in a vacuum, and the substance is ablated by pulsing a laser on it. It's not a matter of just waiting for the ablation to occur, without supplying any source of energy. However, see also Outgassing#Outgassing in a vacuum, which is closer to the situation you're thinking of. Red Act (talk) 03:17, 20 October 2009 (UTC)

You might also want to read Pulsed laser deposition, which is what vacuum ablation is used in. Red Act (talk) 03:21, 20 October 2009 (UTC)

So, in summary: No, Vacuum Ablation is not something extremely long-lived space structures need to worry about due to the high energies required to cause it. Josh Parris 03:34, 20 October 2009 (UTC)

Resolved

largest possible Black Hole

What is the largest possible Black Hole and how long would it take to form? 71.100.9.185 (talk) 03:23, 20 October 2009 (UTC)

I don't think there's any theoretical limit on the upper size of a black hole. Josh Parris 03:34, 20 October 2009 (UTC)

Black holes have a minimum size, in that if they're too small, Hawking radiation will make them evaporate. But the only limit on maximum size is how much matter in the universe gets close enough to get sucked in. The supermassive black hole in OJ 287 is currently the largest black hole known, with a mass of about 18 billion times the mass of the sun. But AFAIK there's no theoretical reason why a black hole couldn't be much larger than even that. Red Act (talk) 04:35, 20 October 2009 (UTC)

Size in terms of mass is one thing. Another is size in terms of diameter. But given the nature of black holes, is "diameter" a meaningful term? If so, do scientists have any clue about the "widest" black hole? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:42, 20 October 2009 (UTC)

For a black hole (or more pedantically precisely, a nonrotating, uncharged black hole), the mass and "diameter" are equivalent. The Schwarzschild radius of a black hole, which is the radius in Schwarzschild coordinates of the black hole's event horizon, is directly proportional to the black hole's mass: r=2Gm/c². So the aforementioned black hole in OJ 287 has a Schwarzschild radius of about 5x10¹³ m. There is no more a theoretical maximum on the Schwarzschild radius of a black hole than there is a theoretical maximum on a black hole's mass. Red Act (talk) 05:09, 20 October 2009 (UTC)

I don't follow how they're "equivalent", but "proportional" makes sense. 5 times 10 to the 13th meters is apparently on the order of an Astronomical Unit, yes? (Distance from sun to earth) That would be sufficiently large. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:15, 20 October 2009 (UTC)

What about the amount of time it would take to form the largest possible Black Hole and how long did it take to form the supermassive black hole? Also after the largest possible Black Hole sucks up all the matter in the Universe could it then suck up all of the empty space? 71.100.9.185 (talk) 04:51, 20 October 2009 (UTC)

That's kind-of one hypothesis about the end of the universe, but there's a lot of distance between black holes. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:15, 20 October 2009 (UTC)

That is one theory. However the currently accepted theory is that the expansion of the universe is accelerating, despite gravity pulling everything together. Under that theory a black hole could conceivably suck up all the matter nearby given enough time, which could be quite a lot of stuff, like a galaxy cluster, but not everything in the universe. Rckrone (talk) 05:30, 20 October 2009 (UTC)

Not a single black hole, maybe, but all of them together could theoretically eventually consume everything that wasn't a black hole, just through random drifting? Or most of it. Then all you would have is drifting black holes, which might eventually drift into each other - or might not. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:35, 20 October 2009 (UTC)

There isn't a supermassive black hole; there are a bunch of them. It's believed that most galaxies have a supermassive black hole at the center of them.

Black holes have existed and have been growing since shortly (in cosmological terms) after the big bang. So they've been around, and growing, and occasionally merging, for about 13 billion years now.

A big crunch, in which the universe recollapses down into one black hole singularity, is one possible ultimate fate of the universe. But it's not really known whether that will ever happen. If that does happen, it will be billions of years from now. Red Act (talk) 05:29, 20 October 2009 (UTC)

And, possibly, create another big bang, yes? With a new universe and possibly new laws of physics? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:36, 20 October 2009 (UTC)

Well, there is the Big Bounce possibility. It's highly speculative, as would be any theory that extrapolates past singularities in both directions. And thinking that there might be different laws of physics in each bounce is even much more wildly speculative.

Again, heat death is the currently preferred theory, although I wouldn't take heat death as being engraved in stone, since predictions of the fate of the universe depend heavily on the nature of dark energy, about which we know next to nothing. The field of physical cosmology has changed drastically in the last few decades, and I don't think there's any good reason to expect that it won't continue to change drastically in the next few decades. We just don't have all the answers yet, which makes it an exciting time to be watching the progress as it's being made. Red Act (talk) 06:31, 20 October 2009 (UTC)

P.S.: Although collapsing into one big black hole hasn't been completely ruled out, the preponderance of the evidence at this point is that that probably isn't what will happen. Instead, the ultimate fate of the universe appears more likely to be heat death. Red Act (talk) 05:37, 20 October 2009 (UTC)

Meaning essentially a vast nothingness? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:43, 20 October 2009 (UTC)

an inherently flawed workup to a Grignard synthesis?

So ... my lab synthesis prescribed to me worked like this. First we form phenylmagnesium bromide in ether in situ, then react it with methyl benzoate (in more ether). We hydrolyse the alkoxide salt with dilute sulfuric acid, discard the aqueous layer then dry the organic layer with brine and magnesium sulfate, then evaporate, then recrystallise the crude product with hexanes.

How likely is it that an explanation for a yield of say, 34%, comes from the fact that the magnesium (soft) alkoxide salt ends up forming a carbocation that is then even more soluble in water? The carbocation escapes into another phase, driving carbocation formation to the right ...

Secondly, I notice there isn't a lot in this workup that separates methyl benzoate and bromobenzene from the product ... is it reasonable that they all get consumed to near completion (I had an MP depression of about 5 C); their BPs are really high but the product is a solid; maybe bromobenzene and methyl benzoate form an azeotrope that can be evaporated easily...? (But on a totally different scale than evaporating ether.) Would acid-catalysed hydrolysis of the starting reagent into methanol and benzoic acid help significantly? John Riemann Soong (talk) 04:22, 20 October 2009 (UTC)

Does elevated oxygen allow adjusted respiratory rates?

People who are suddenly at unusually high altitudes tend to feel short of breath. Is the opposite true if we hyper-oxygenate a room?

Let's say respiratory rate is R, and respiration volume is V. Is it as simple as saying that in a room with an oxygen level X times normal at sea level a human will be able to breath at a rate of R/X? Or would the blood oxygen levels fall too low between breaths? Assuming constant respiratory rate, could we instead inhale V/X - taking shorter breaths to satisfy the body's need?

I'm envisioning a dude sitting in a room with 3X average oxygen and breathing *really* infrequently!218.25.32.210 (talk) 05:00, 20 October 2009 (UTC)

Breathing serves two purposes; the intake of oxygen, and actually more importantly, the exhaling of CO2. The body produces CO2 at roughly the same rate, regardless of how much oxygen you are taking in, so there is a minimum required breathing rate necessary to expel CO2 from your system before it builds up to toxic levels. Even in a pure-oxygen atmosphere, you'd still need to breath at roughly the same rate you do in standard 20% oxygen atmosphere, in order to get the CO2 out of your body. --Jayron32 05:16, 20 October 2009 (UTC)

Interesting! In such a situation would you be introducing potentially harmful levels of oxygen into your bloodstream, or can the lungs autocompensate by reducing uptake per inhalation?218.25.32.210 (talk) 06:54, 20 October 2009 (UTC)

It's a bit more subtle than stated above. If you are untrained, your reflex to exhale will kick in long before CO2 becomes critical, and your breathing rate is unaffected by elevated oxygen levels. If you go SCUBA diving, you are breathing an atmosphere that contains increased levels of oxygen in absolute terms - every 10m under the surface doubles the atmospheric pressure and hence oxygen content. Untrained divers will use up their air supply at correspondingly increased rate, but trained divers can slow down their breathing somewhat and hence stay underwater much longer. And indeed, if the oxygen partial pressure exceeds certain values, it does become toxic. IIRC, the upper limit for recreational diving is 1.4 atm. You cannot reach this with plain air under normal depth restrictions, but you can with Nitrox, easily - with Nitrox 36, you can only go 29m down. Military divers seem to dive reasonably safely with up to 2 atm, but that leaves little room for errors. --Stephan Schulz (talk) 07:41, 20 October 2009 (UTC)

IFT TRANSFORMER

WHY IF=455 INTERNAL CIRCUIT DIAGRAM & WORKING..........???????????

Neutronium

Science fiction has loved to use neutronium for all sorts of purposes, plating on shields for instance. Is it possible, even in principle, to use neutronium as an engineering material in small components? Or will it immediately return to "normal" matter in a spectacular reaction if by some magical means it is suddenly removed from a neutron star? SpinningSpark 07:01, 20 October 2009 (UTC)

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Featured Article - Diamond

In todays featured article it explains that synthetic diamond is used in heat sinks. But in the heat sink article, under 'construction and materials' there is no mention of diamond. When would synthetic diamond be used for a heat sink?91.109.234.25 (talk) 08:20, 20 October 2009 (UTC)