Wikipedia:Reference desk/Science

Wikipedia:Reference desk/headercfg

September 16

Carbon based fossil fuel

Is the supply of fossil fuels like crude oil, coal, etc, diminishing? If so, when will the supply run out? And why is combustion of carbon fuel still the most popular method to obtain energy? Are there many alternatives available? Thanks for answering. Oidia (talk) 02:31, 16 September 2007 (UTC)

Yes - see the lead section of Fossil fuel.

It's hard to tell, but some people suggest we're already on the downward slope - see Peak oil.

Because it's (currently) cheap, easy and plentiful enough that people haven't been too bothered to seriously look into alternatives until somewhat recently. See Energy economics.

Yes, but they are generally eiter expensive, inefficient, or in some cases still purely theoretical. See, for example Nuclear energy and Renewable energy. Confusing Manifestation 03:52, 16 September 2007 (UTC)

As fossil fuels become more scarce, their price will go up, and the more expensive of the alternative fuels will be more on par with the cost of fossil fuels. So I think eventually things will even out. --24.147.86.187 13:09, 16 September 2007 (UTC)

Note that peak oil is about the rate of production which is related to things like how much of the supply we have found and how much we have used. I think even most of the more extreme 'optimists' in the area agree that overally supply is diminishing. They just argue there is still so much out there we don't have to worry and/or we will always find a way whatever happens. The only way the overall supply could not be diminshing is if more was being produced then we are using which is supported by virtually no evidence Nil Einne 20:36, 19 September 2007 (UTC)

Fossil fuels are being used, so naturally the supply is diminishing (possibly, some is still being produced the way it used to be, but that will be negligible compared to the amount that is used). When the supplies 'run out' depends on how you define that. It will become ever more difficult (read: expensive) to extract the oil (or whatever). The low hanging fruit has already been picked. The murky oil fields in Canada that didn't receive any attention in the past because the oil was too hard to extract, are now receiving large investments because there is nothing else left. So oil won't 'run out' until we decide it's become too expensive - which is never, because our societies are so dependent on energy that we will pay any price. Unless alternatives become cheaper. But that requires investment in those, of which there hardly are any (in comparison). Fossil fuels are still popular because a lot of money has been invested in the knowledge and infrastructure (think of the many petrol stations, for example), so there is a huge (really, really huge) invested interest in maintaining the use of those. Even now, the amount of money invested in fossil fuels is more than ten times (for got the exact figures) larger than in other energy sources, and the biggest usurper of that remaining money is still nuclear energy. If, say, the development of solar cells had received the same level of investments as oil, then we probably would have stopped using fossil fuels years ago, when the low hanging fruit was all picked. DirkvdM 10:47, 16 September 2007 (UTC)

• Is the supply of fossil fuels like crude oil, coal, etc, diminishing? Yes
• If so, when will the supply run out? It will become more expensive to extract as its deposits are used up - eventually other fuels will be cheaper.
• And why is combustion of carbon fuel still the most popular method to obtain energy? It's the least expensive, given the current industrial infrastructure.
• Are there many alternatives available? Yes, see Ethanol fuel in Brazil, Nuclear power, Fusion power and Future energy development for examples. --Duk 14:55, 16 September 2007 (UTC)

Fossil fuels are still the most popular because, in their way, they're still the cheapest. They are, in effect, a conveniently-stored form of millions of years' worth of accumulated solar energy.

Suppose you inherit $1,000,000 from your rich uncle. You know that the money won't last forever, especially if you indulge in expensive pastimes. But on the other hand, it's fun to indulge in expensive pastimes, much more fun than, say, working for a living.

On any given day, you have a choice: (a) get a job, or (b) play some more (and spend down your inheritance some more). If you're like most people, you'll keep choosing (b) until it's almost too late, or maybe even actually too late. And the situation is (I believe) exactly the same, on a macro scale, with human society and our inheritance of fossil fuels. —Steve Summit (talk) 16:05, 16 September 2007 (UTC)

But there's not just the added cost of having to develop alternatives faster in the future if we don't start (seriously) investing in it already. There's also climate change, and the cost of that could dwarf all that. The problem is that large companies have too many invested interests in fossil fuels and small companies don't have the money to invest. So governments should step in, but the democratically elected ones won't do that because their electorate is brainwashed with the help of the big money from the big companies (funding 'scientists' who spread all sorts of doubt about climate change). As usual, a disaster has to happen before anything is done about it. Such as the North Sea flood of 1953 that led to the Delta Works in the Netherlands. Except that it's worldwide now. DirkvdM 08:19, 17 September 2007 (UTC)

• That's a great analogy. --Sean 14:02, 17 September 2007 (UTC)

We had this question (about oil specifically) the other day. At present rates of consumption, we expect to run out of oil in 500 years. Coal and natural gas would be available for much longer. Nuclear fuels would also eventually run out - but we don't know how large the reserves are - possibly tens of thousands of years. Fusion power (if we ever manage to get the technology right) will last until we've boiled the oceans dry - there is no practical way to run out. Solar, Wind, Tidal....same deal. However, it's a completely academic question. We now know that throwing carbon-dioxide (an inevitable by-product of burning oil, gas or coal) into the atmosphere is going to kill the planet LONG before we run out of oil (let alone gas and coal) - so we absolutely have to cut back on our consumption at least 4-fold, possibly 10-fold. This stretches our reserves out to a point where it no longer matters because improved technology will push down consumption faster than our supplies are shrinking. However, we DO have to cut back on our consumption somehow - and that's not easy. At this point, running out is NOT the issue. SteveBaker 15:02, 17 September 2007 (UTC)

It's nonsense to talk about 'when we will run out'. Using up all fossil fuels would be total madness, because at one point it would be so hard to retrieve that it would cost more energy than it would yield. The question is when it would run out economically, and that depends on how fast alternatives are developed (ie when do they become cheaper than oil). As for Uranium (and other fission fuels - not too many of those), some wild numbers are given for how long that would last (billions of years), but for that all Uranium would have to be used up and most of that is spread all over the Earth's crust, so we'd have to completely overturn the entire Earth's crust, down to 10 km or so. So same story there.

Btw, you're overstating the effect of climate change. It's probably going to be sheer misery for the next milennia at least if we don't act quickly and most life on Earth might disappear. But not all of it. Some life will survive, even if only bacteria. It'll be just another catastrophy hitting the planet, and life will overcome it. What matters more is that we will probably survive too, as a species - we're resilient enough. But it's likely to not be a lot of fun for the next few generations (or 10 or 100 (1000 anyone?)). DirkvdM 18:41, 17 September 2007 (UTC)

I don't think it will be miserable for everyone. Those living in Canada, Alaska, Russia, Finland, Norway, and Sweden will likely benefit in some ways (such as the Northwest Passage opening up in Canada). Also, Greenland and Antarctica may become habitable. However, those in equatorial climates or with major population centers on ocean coasts (and/or near sea level) will suffer, such as Bangladesh. The most important thing is that the climate change happens slowly enough for us to adjust. As for plants and animals, they will generally do better with a warmer climate, although there will be many exceptions (like polar bears). StuRat 03:52, 18 September 2007 (UTC)

The major problem with climate change lies not in the new climate but in the change. First of all, life in general and human infrastructure in particular are not adapted to the new climate, so most animals will die and humans have to rearrange their economies and infrastructure (to what extent is a great unknown). Shorelines will change and agriculture will have to look for new foodcrops. Humans will adapt, but those living during the adaption will not have it easy, to say the least. Nordic countries indeed have an advantage in that the most likely new climate will be better for humans in general (if it really will be warmer - mind the regional variations) and that most are among the top ten richest countries on Earth, which will make the transition a lot easier.

But a second factor is that we don't suddenly jump to a new climate. Only after the greenhouse gas concentrations have settled to a certain level (which will take a long time) will the climate(s) settle to a new equilibrium. In the meantime, the climate will go all over the place. Climate is consistency in weather patterns, so effectively there will be less climate, however odd that may sound. Farmers need to know what weather to expect when, so they will know what to do when (plough, plant, harvest, what have you). If they don't, crops will fail or not be optimal and there will be less food. So we're increasing our luxuries at the expense of our basic necessities, which is downright silly, if you think about it.

As to the speed of change - the Permian–Triassic extinction event killed some 90% of life on Earth but that took thousands of years (if not millions). It looks like we're recreating that, but in just a few hundred years. Note that I say this based on the theory that that event started with a temperature rise of 5 C, which led to the freeing of frozen methane (such as on ocean floors), which raised the temperature by another 5 C. And that initial rise of 5 C is not unlikely to happen even in the next century - just one century! And it is quite likely to happen in the next few centuries. It's actually the incredible speed at which this might happen that is so scary. Note that I say 'might'. We don't really know what we are doing, and that might just be the scariest part. We're doing this wild experiment, but we have only one test tube - and we live in it. Sorry about the shouting, but that has to do with the huge importance of this. DirkvdM 08:16, 18 September 2007 (UTC)

Delicious but dangerous

What foods are the most dangerous to eat? Not as in "highest probability of harm", but as in "most serious worst-case scenario". I'm especially looking for foods that are deadly if prepared incorrectly, like fugu and false morel. —Keenan Pepper 04:42, 16 September 2007 (UTC)

Raw manioc is bad for you. A.Z. 05:43, 16 September 2007 (UTC)

I think the most serious worst-case scenario is probably beef infected with mad cow. Frankg 07:32, 16 September 2007 (UTC)

Rotten meat > food poisoning. DirkvdM 10:50, 16 September 2007 (UTC)

Not what I'm looking for, because you can just get fresh meat instead. I'm looking for foods that are intrinsically dangerous. Many foods become dangerous when spoiled, but they also become less palatable. —Keenan Pepper 17:35, 16 September 2007 (UTC)

Well, Death Cap is poisonous, it even came out in Eragon. Just out of curiosity, is it just a regular question or are these stuff meant to be put in someone's meal? --Zacharycrimsonwolf 14:09, 16 September 2007 (UTC)

Um, I don't think you understood the question. You can't eat death caps at all, if you want to live. On the other hand, fugu is served to people every day, and they are perfectly safe unless the fugu is incorrectly prepared. That's the kind of thing I'm looking for. —Keenan Pepper 17:35, 16 September 2007 (UTC)

Probably not that much help, but I do remember reading a long time ago about a type of mushroom that was perfectly edible and pleasant, unless consumed with alcohol - at which point it becomes deadly poisonous... --Kurt Shaped Box 17:43, 16 September 2007 (UTC)

That sounds like Coprinopsis atramentaria, though that one does not appear to be actually deadly. Unpleasant, however ... --Pekaje 12:25, 17 September 2007 (UTC)

Interesting - thanks. It's always good to fill the gaps in the pieces of knowledge I attained as an 8 year old... :) --Kurt Shaped Box 14:38, 17 September 2007 (UTC)

Anything from a dented tin can. TenOfAllTrades(talk) 14:14, 16 September 2007 (UTC)

Again, that's not an intrinsically dangerous food, just spoilage. —Keenan Pepper 17:35, 16 September 2007 (UTC)

Hmmm. Steak tartare? Probably not deadly but I know that you *can* get sick off it... --Kurt Shaped Box 17:38, 16 September 2007 (UTC)

Good, that's much closer to what I'm looking for. I had never heard of a dish containing raw beef before. —Keenan Pepper 17:55, 16 September 2007 (UTC)

I had some once (without knowing exactly what it was). It was actually quite nice. As I understand it, it's pretty safe it it's prepared with carefully-selected, properly-stored-and-handled muscle meat. --Kurt Shaped Box 18:02, 16 September 2007 (UTC)

Eating the liver of a polar bear will actually cause you to OD on Vitamin A, although polar bear livers are large enough that they can be easily removed without leaving too many traces (unlike the poisonous parts of fugu). Potatoes are also poisonous if you forget to cook them (they contain glycoalkaloids, especially if you eat wild or over-ripe ones). Laïka 19:33, 16 September 2007 (UTC)

Oh yes, and bitter almonds contain hydrogen cyanide, which must be thoroughly removed before eating. Laïka 19:35, 16 September 2007 (UTC)

Note that the toxins in potatoes are less from aging than from exposure to sunlight, and that cooking does not necessarily inactivate them. See solanine, and always peel all the green bits off your spuds. --Sean 14:12, 17 September 2007 (UTC)

Frankg said eating beef with mad cow disease is bad. To my knowledge there is no proven connection between it and the similar disease that infects humans. Laïka said raw patatoes are poisonous. I've eaten them many times before and I don't think I ever got sick soon after. What's this for? Are you writing a story? Are you just curious? — Daniel 20:07, 16 September 2007 (UTC)

Variant Creutzfeldt-Jakob disease has been linked to eating nerve tissue from cattle infected with Mad Cow (which was caused by Scrapie prions the cows got from eating meal made from leftover sheep parts). -- Kesh —Preceding signed but undated comment was added at 20:31, 16 September 2007 (UTC)

The Spanish Blood Donation Service declined my offer on the grounds that I am English and had eaten British beef during the 90s, so they think there's a connection. Richard Avery 21:56, 16 September 2007 (UTC)

Ditto for the US Blood donation folks. Proving a causal link is very tricky indeed. However, the incidence of CJD in the UK spiked at exactly the time you'd expect from the incubation period starting at the time when BSE became prevelant. CJD and BSE are more or less identical diseases. Whilst this doesn't prove a link - it's enough to warrant a strong reaction and in my mind it shifts the onus from "prove that CJD is caused by BSE" to "prove that it isn't" - and there is no proof of the latter. SteveBaker 14:12, 18 September 2007 (UTC)

Humans ... not sure about the 'delicious' part though. --Duk 20:48, 16 September 2007 (UTC)

Pork, if not sufficiently cooked, can give you trichinosis. (In the US, this is less of a danger than it used to be.) Cardamon 03:50, 17 September 2007 (UTC)

Which might be part of the reasoning behind prohibiting the eating of pigs in the old testament. Which reminds me of an anecdote I read in Time about a famous Jewish scholar at a religious conference, waiting in line, who got frustrated and called out "I hope you all get trichinosis and come to believe in the god of Moses", wherin someone replied, "And if we don't get such diseases, will you believe in the god of Jesus?". Ah, witty religious scholars... (the article was about his book and how the Pope actually cared enough to write a rebuttal) Kuronue | Talk 23:01, 21 September 2007 (UTC)

Nutmeg in large quantity, if you consider it delicious. --antilived^{T | C | G} 04:40, 17 September 2007 (UTC)

Brain (as mentioned by Duk) is an interesting food stuff. It doesn't have much taste, but the texture is quite interesting. But as the article points out, there are some risks involved. DirkvdM 08:27, 17 September 2007 (UTC)

Nardoo accroding to this and this. Here is more information on Nardoo. Cardamon 09:22, 17 September 2007 (UTC)

Honey that is just fine for everyone else can be deadly to infants due to botulinum spores. --Sean 14:16, 17 September 2007 (UTC)

Condensed milk is supposed to be A Bad Thing to give to babies. I'm not sure why - but it tells you not to do so on the side of the tins. --Kurt Shaped Box 14:37, 17 September 2007 (UTC)

Chickpeas contain varying levels of antinutrients and can be dangerous in large quantities.

Atlant 14:28, 17 September 2007 (UTC)

Water will kill you if you drink enough of it. (Water intoxication) SteveBaker 14:54, 17 September 2007 (UTC)

Won't just about every single substance in existence kill you if you consume enough of it? --Kurt Shaped Box 15:04, 17 September 2007 (UTC)

Mr Creosote would be the best authority on that. "One little tiny wafer-thin mint..."

Atlant 18:15, 17 September 2007 (UTC)

KP, are you writing a murder mystery? —Tamfang 01:14, 18 September 2007 (UTC)

While I can't answer the specific question, you might want to take a look at the somewhat similar question related to toxic foods a few weeks back. From memory amongst the things mentioned where tapioca (cassava), cashew nuts, bamboo shoots and various stuff containing Oxalic acid. Of these, the only one that may come close to a level of concern of something like fugu is probably tapioca. If we are speaking of specific people here, obviously you should consider allegies. Even a peanut shell could be deadly to someone who is severely allergic. There are of course various interactions e.g. grapefruit and some other fruit could be deadly to someone on certain medications as they inhibit the cytochrome P450 isoform CYP3A4 (which is also essential for the metabolism of these drugs and therefore you end up with a much higher level then you are supposed to have). There are also various other stuff relating to people with various conditions and a variety of food you could probably pick up from case reports in medical journals. E.g. someone who ended up with a potassium overdose from eating durian (I don't know but I suspect durian would be on a list of forbidden food for someone with a low potassium diet in SEA) Nil Einne 19:06, 18 September 2007 (UTC)

Chaya leaves are poisonous until cooked. Cardamon 09:12, 19 September 2007 (UTC)

ackee fruit. - Nunh-huh 21:25, 20 September 2007 (UTC)

Fusing vertebrae

When do vertebrae stop fusing in humans? ←Ben^B4 13:26, 16 September 2007 (UTC)

Well, I'm not sure I understand the question entirely. It is my understanding that vertebrae do not normally fuse in humans, except in abnormal circumstances. If vertebrae fused together - one to another - I assume that's what you mean, the spine would lose its flexibilty. There are a group of fused vertebrae at the lower end of the spine they are called the sacrum and they form the posterior part of the pelvic girdle, they show no flexibilty in adulthood although they are not completely fused in the prepuberty period. There is a pathological condition called ankylosing spondylitis(have a look) which causes the vertebrae to fuse together and this results in considerable mobility problems for sufferers.Richard Avery 21:50, 16 September 2007 (UTC)

Vertabrae#Sacral says those are "fused in maturity" but there is nothing in the ssociated article -- when do the sacral vertebrae usually fuse? ←Ben^B4 02:51, 17 September 2007 (UTC)

Uh, huh, I see what you mean. From my meagre knowledge of a twenty year nursing career I reckon they fuse at about the same time as the shafts of the long bones fuse with their extremities. This happens during puberty and a little after. It's a variable proces, depending on each individual. I think it is unlikely that there is much separation between the sacral bones in infancy, the spaces may show on a radiograph, but for general physical examination they would feel solid. Richard Avery 21:49, 17 September 2007 (UTC)

Re:The Sun and Moon

How does the Sun's gravity make stuff orbit around it? I only have a rough metaphor (made by me) for the phenomeneon, but I don't really understand it. Also, are there any pictures of the Moon's orbit around Earth? My sister asked me a question about the phase of the Moon and I need it to answer her. Zacharycrimsonwolf 14:06, 16 September 2007 (UTC)

Have you seen Orbit#Understanding orbits and Lunar phase#Names of lunar phases? --Wirbelwindヴィルヴェルヴィント (talk) 15:45, 16 September 2007 (UTC)

For the "how", are you starting from "gravity exists and pulls objects towards each other", or something else? If you start from there, then the link above to the Orbit article should be a reasonable explanation. Otherwise, you're looking at a slightly more complicated explanation. Confusing Manifestation 12:43, 17 September 2007 (UTC)

How gravity makes things orbit? Well, normally, an object (let's say a space ship) in deep space with no stars or planets nearby will travel in a straight line at constant speed (no friction) forever. When it's near a star (or a planet or something big and heavy like that), gravity will pull the spaceship towards the star. Now - imagine if the spaceship was already moving at right angles to the line between it and the star. It's tendancy to go in a straight line (in the absence of gravity) would make it gradually move further from the star. Now, if (by a amazing coincidence) the distance it would normally move away from the star in one second were EXACTLY equal to the amount it would fall towards the star in one second because of the gravity - then it would end up staying the exact same distance from the star...moving around it in a perfect circle forever. That's a perfect circular orbit. Now, it turns out that if things aren't exactly right for a circular orbit (for example if the gravity were a bit stronger or the spaceship were moving a bit slower) then you get an elliptical orbit...but the exact "why" of that is hard to explain in words without resorting to a lot of math.

The phases of the moon are something different. The moon moves in a roughly circular path around the earth - and the sun is a very long way away with the earth going around the sun in a roughly circular path with the moon constantly looping around it. The resulting path of the moon around the sun looks like a spirograph pattern. What this means is that as we watch the moon from the earth, the moon is being lit by the sun from all sorts of different directions - sometimes, the sun is on the opposite side of the earth from the moon - and the whole of the 'front' of the moon is lit up. Other times the sun is off to one side of the earth as the moon is overhead and the side of the moon nearest the sun is lit up. As the position of moon goes through this 'spirograph' pattern the relative position of sun, moon and earth changes gradually over a month or so and the moon is lit first from 'behind' (the moon looks dark because only the far side is lit), then from one side (a 'new' moon), then from in front (a 'full' moon), then from the other side (a 'waning' moon) and then from the back again. SteveBaker 14:46, 17 September 2007 (UTC)

Quibble: The Moon's path is always concave toward the Sun, because the Sun's gravity at that distance is 2.5 times Earth's. I don't know if it can be drawn with standard Spirograph parts. —Tamfang 01:12, 18 September 2007 (UTC)

I know - but let's keep the complexity of the answer commensurate with the complexity of the question. Someone who needs to ask this question isn't going to understand a more complex answer than the one I gave without another page of explanation. Hence spirograph rather than epicycloid. SteveBaker 14:05, 18 September 2007 (UTC)

Many thanks all, especially to Steve. Well, since there isn't any straight explanation to the gravity question, then I'll just take what I understand. By the way, how far does the Sun's gravity go? I know comets go really far away, but they come back in an orbit aeons later. --Zacharycrimsonwolf 14:53, 20 September 2007 (UTC)

Well, strictly, gravity goes on for ever, but it gets weaker the further you go. It follows an inverse-square law, so if you go twice as far away, it's a quarter the strength, and if you go a thousand times as far away, it's a millionth of the strength. So your question doesn't really have an answer: it depends at what level you want to count it as negligible: one hundredth? one thousandth? one millionth? --ColinFine 20:14, 22 September 2007 (UTC)

Relative Age of Races

Is it true that the Negroid race is approxiamately 225,000 years, the Caucasoid race is approximately 110,000 years old and the Mongoloid race is about 40,000 years old? 4.242.18.225 14:37, 16 September 2007 (UTC)

There might be answers in our article on Race (although in an initial skim I didn't spot any). —Steve Summit (talk) 16:18, 16 September 2007 (UTC)

That doesn't really sound right to me. For one thing, it assumes a very old and now fairly discredited tripartite racial model. It also falsely assumes that the "older races" have not been differentiated at all in that time, which is not true in the slightest. That is, it sounds like a misunderstood interpretation of the recent single origin hypothesis. As an example of the falsity of this assumption, the Kennewick man, for example, looks very little like the "native" residents of that particular area that he was found in, even though very little time had passed between them. "Racial" characteristics are largely superficial and are fairly malleable as populations merge and separate. "Race" on a genetic level is a set of relatedness between various populations (at best—most of what we assign to "race" colloquially is culturally constructed mixed with a little bit of superficial biology), and are never static. --24.147.86.187 16:37, 16 September 2007 (UTC)

I have answered here: [1]. StuRat 01:29, 17 September 2007 (UTC)

Cute that you copied the question there so that you could disagree but not have people argue with you. Smooth move. Anyway, you really don't know what you are talking about, and the disparagement of the answers here as "politically correct" (and somehow tying affirmative action to that) is both insulting and intellectually dishonest. --24.147.86.187 14:40, 17 September 2007 (UTC)

You are certainly welcome to follow links to Wikiversity to leave information there. Personally I would appreciate it if you could leave your inter-personal squabbles from Wikipedia here at Wikipedia. They add little to Wikiversity. mirwin@wikiversity —Preceding unsigned comment added by 70.110.44.165 (talk) 03:45, 18 September 2007 (UTC)

I just responded there so it wouldn't be deleted by someone who disagrees. You are free to respond here, there or in both places, if you wish. I stand by my statement. StuRat 03:06, 18 September 2007 (UTC)

When you use terms such as 'Race' there are a lot of touchy concepts raised. There is no defined genetic definition of Race as is commonly used, it is simply a set of common characteristics in a population. Genetic studies have found that humans have an unusually low amount of variation between diverse populations. In fact, some studies have found that two people of the same "race" might differ, genetically, more than between two people of different "races". However, there has been speculation as to how humanity spread across the globe, and were subsequently isolated enough such that each subpopulation to develop independently, which you'll see in the Subspecies as clade section of the Race article. -- JSBillings 12:10, 17 September 2007 (UTC)

Dacryocystorhinostomy in the UK

In the UK (England, in fact), does the NHS tend towards the use of external or endoscopic dacryocystorhinostomies, or do they use both procedures in equal preference to eachother? I found a NICE document from 2005 (ish), saying that it was basically "ok" to use the endoscopic method, but I was wondering if anyone here had any experience of the same? Martinp23 16:25, 16 September 2007 (UTC)

Science blog

Hello. Could you recommend a daily science blog or news site? Someone pointed me to gizmag.com but they seem to be mainly interrested in cars and phones. Any recomendation for a general science news site? Thank you 81.242.81.35 16:30, 16 September 2007 (UTC)

Nature News —Keenan Pepper 17:38, 16 September 2007 (UTC)

http://www.sciencedaily.com/ - they are just an aggregator, but they do a great job. ←Ben^B4 18:01, 16 September 2007 (UTC)

http://www.scienceblogs.com - Several blogs by various scientists and academics hosted by Seed Magazine. PZ Meyers has a very good one called "Pharyngula." -- Kesh 20:54, 16 September 2007 (UTC)

Scientific American has a good blog and they cover the gamut of science & technology. — Scientizzle 15:37, 17 September 2007 (UTC)

In a similar vein, New Scientist also has several blogs [2] Nil Einne 21:25, 19 September 2007 (UTC)

Radio brightness of this or other earths

Looking at the radio rather than the visible spectrum,

1) how bright is the earth compared to stars (including the sun)? I vaguely remember hearing it would be very bright due to the great amount of radio transmision.

2) If there was another earth identical to ours in 2007, but placed near the hub of our galaxy the milky way would it stand out and be easily spotted? (So either the answer will be "no" or we are alone at least in this galaxy).

3) Would the radio spectra of earth be different in quality from stars and stand out?

4) Are there any objects in the sky which have a similar radio spectrum? (Presumably answer will be "no".)

5) How far away from earth could you be and still (if you were very clever and had unlimited resources) watch tv or listen to the radio?

80.0.135.165 18:12, 16 September 2007 (UTC)

1) Not sure. 2) and 5) I'm often told that a typical high power radio transmitter can transmit far enough that a very sensitive radio receiver could pick it up from 4 light years away (well, that's all very general isn't it, so a good deal of range depending on how good equipment you're talking about). However, if you're using this baby as your radio receiver or transmitter, that thing can reach far. Not sure how far, but easily many thousands of light years. 3) The radio spectra of the Earth would noticably different from those of any star, so informs me a planetary scientist. 4) He also tells me that no radio signals have ever been detected not-of-earth-origin that were undoubtably intelligent communication. Further, only a handful of radio signals have ever been detected that have not been explained by natural phenomena presently understood. Someguy1221 19:43, 16 September 2007 (UTC)

Also, detecting Earth from a distance would be difficult except within around 70 light-years or so. Much more than that and there'd be no radio signals from here at all. Richard B 23:04, 16 September 2007 (UTC)

Thanks for answers so far. Its the first question that particular interests me - ignoring the fact that radio started about 80 years ago, are we a bright beacon in space that would stand out in the radio spectrum sky? Perhaps this could be estimated by adding the total amount of radio and tv transmitter power and taking away the proprtion absobed by the earth. Would this be greater than the radio power of the sun? 80.3.42.129 13:53, 17 September 2007 (UTC)

No, I don't think we are a large radio beacon at all. I read someplace (I think it was on the SETI web site) that the amount of normal radio/TV/radar we humans emit is less than we could detect with our most sensitive radio telescopes at a distance of 4 lightyears (the distance to the nearest star). So it's very, very feeble indeed. The thing with radio waves is that their energy decreases as the square of the distance. Remember that your local radio or TV station starts to fade out at maybe 100 miles from the source - at 200 miles, it would be 1/4th as loud, at 400 miles, 1/16th as loud, at 800 miles, 1/256th as loud...at 4 light years...it's too feint to detect, even with our most sensitive devices. This is one of the problems with SETI (looking for alien civilisations by listening for their radio transmissions) - it's only going to work if the aliens have some INSANELY powerful radio transmitters. So it would take aliens quite close by (cosmologically speaking) with much more advanced radio telescopes than we have to be picking up "I love Lucy" (1951) out at 50 lightyears. SteveBaker 14:26, 17 September 2007 (UTC)

And of course, we point our power towards earth-bound receivers using directional antennas and the skywave effect. The vast majority of our transmitted radio frequency signals never leave our planet. Nimur 01:04, 18 September 2007 (UTC)

So nobody knows the answer to 1). ;-( 80.0.122.151 21:39, 18 September 2007 (UTC)

Nope, but I can look it up. ;-) The problem is, "radio" is a big place. It covers a lot of frequencies, and you can look either at broad-band emission, or narrow lines. Here are a few references to start you off. Check out figure 1 of Man-made radio noise: Part I [3] It's on page 23. You can find the definition of F_a in the introduction. This shows man-made radio noise in various environments is comparable to the galactic center around 10-200 MHz. The galactic center's radio emission is strongest around 1-10⁴ GHz [4], at about 1 Jansky. The sun is much louder, about 10⁵-10⁷ Janskys in the range 1-1000 GHz. (Be careful about comparing spectra in F_a with spectra in Janskys, I think there must be a factor of λ² to give a different frequency dependence). Remember that all of these are as seen from earth. I conclude that the Sun and the galactic center are intrinsically *much louder* above 10 MHz or so, and probably at lower frequencies too. However, man-made radio signals aren't a continuous spectrum. I believe it is true that the Earth outshines the sun at certain radio frequencies, and that you could see these from ~a few light years away. As far as I can tell, you would not see the Earth next to the galactic center. --Reuben 23:14, 18 September 2007 (UTC)

The colour of Light

Further to the above question on 'Green', I am a bit confused about all this colour being to do with light waves that are reflected. If I was to switch on a red lamp, surely it is giving red light off, not absorbing green and blue light inwardly and reflecting magenta out? How does this work? Is it something to do with the red glass absorbing the green and blue light energy? --russ 19:07, 16 September 2007 (UTC)

Precisely. Red glass only permits red light to pass through (for visible light, anyway). Other colors are absorbed. However, you can have a light emitting diode or a laser that only emits one color (a narrow band of wavelengths). An important distinction from the above question is that the lamp is generating its own light, and not simply reflecting light from another source. Someguy1221 19:26, 16 September 2007 (UTC)

Also, neon lamps emit an orange light, and many other types of lights emit a characteristic color. StuRat 23:08, 16 September 2007 (UTC)

What's the colour of love? —Bromskloss 19:28, 16 September 2007 (UTC)

You can have a red lamp - that emits red light. If you look directly at the lamp, it looks red because it's EMITTING red light. But things that are not light sources (a table or something) are only visible by the light they reflect. When you see objects illuminated by that light, you see the light reflected by that object. White light (which is the normal thing we experience - from the sun or 'white' lamps) contains all of the colours. When lit by white light, the colours of objects depends on the colours they reflect. A green object reflects green light and absorbs everything else - so we see green light reflected off of it. However, if you were to view the world in light from a red lamp, the green object would absorb the red light and reflect...nothing...there is no green light there to reflect. So a green object will look black when lit with red light. In actual fact, it's rare for a green surface to literally only reflect green light - it'll usually reflect a little red and blue also...but nowhere near as much as it does green. So when you actually use a red light, green objects will just be very dark - not literally black. If you go out at night into a street that's lit with orange 'sodium' lights, you'll see that everything is in shades of orange depending on how much orange light they reflect. Some objects that are really bright colours in daylight will look very dark indeed if they aren't reflecting orange light. SteveBaker 14:14, 17 September 2007 (UTC)

And Energy, too

At school, we were always told that energy took several different forms: potential, kinetic, light, sound, nuclear and so on. My question is that if light has something to do with moving photons, sound to do with moving atoms bouncing on the eardrum, nuclear to do with emitted particles and so on then surely they are varieties of kinetic energy and not forms in their own right? Furthermore, if you are deaf, then does sound energy exist? If there are other forms of energy that our senses are not able to detect then how would we ever know to look for them? russ 19:13, 16 September 2007 (UTC)

Sound energy (the energy stored in sound waves, which is really just the kinetic and elecrostatic potential energy of the particles carrying the wave) exists whether or not you can sense it. Further, there are forms of energy we are incapable of sensing on our own. Nuclear energy was unknown until the discovery of radioactive materials, and not understood until quantum mechanics existed. Gravitational waves carry energy, but were themselves unknown to exist until the theory of relativity. However, scientists still came up with ways to try to detect them, and might actually succeed one day. Someguy1221 19:35, 16 September 2007 (UTC)

(edit conflict) Nuclear energy is a form of potential energy. Other than that, all of your examples are forms of kinetic energy (although I think it might be arguable with light). Every particle is energy, although only massless ones (such as photons) can be considered kinetic energy. Sound energy exists whether or not you can hear it. People can't detect most forms of energy directly. One way to know to look for a form of energy is if the energy in a system doesn't appear to be constant, such as the sun radiating more energy than can be explained by chemical energy (this was noticed before nuclear energy was discovered). — Daniel 19:44, 16 September 2007 (UTC)

Sound waves can be detected by the deaf. Low frequency waves can be felt as vibrations and higher frequencies will cause waves to form on water. And, of course, they can see the volume meter move on an amplifier. So, there are other forms of energy (like dark energy) which are much harder to detect than sound is for the deaf. StuRat 22:18, 16 September 2007 (UTC)

Sound is just vibrations. The vibrations are there whether you are deaf or not - and deaf people can still feel very low frequency sounds vibrating in their stomaches or if their fingertips are resting lightly on a flexible surface...just like hearing people can. So the energy is still there - even if it's not being heard. SteveBaker 14:16, 17 September 2007 (UTC)

If you're technical enough about it, thermal energy in opaque electrical insulators tends to travel as sound, as well. It's inaudible, but it heats up your skin, which allows you to sense this form of energy indirectly. Of course, it's indistinguishable from heat energy which has traveled as light or as diffusing electrons. Also note that sound is quantized; a particle of sound is called, unsurprisingly, a phonon. —Preceding unsigned comment added by 128.115.27.10 (talk) 17:56, 17 September 2007 (UTC)

Ozone effects

If the ozone layer disappeared, would blacks have a better chance of surviving than whites? I remember hearing somewhere that white people have a higher chance of UV poisoning.--130.126.67.144 21:33, 16 September 2007 (UTC)

If I recall correctly, blacks have an almost-nil incidence of skin cancer, so yes, I would think that might be the case. Vranak 21:56, 16 September 2007 (UTC)

• This document says whites have about 10 times the chance as blacks of getting melanoma, so not quite nil, but still a pretty good adaptation for spending time in Africa. --Sean 14:26, 17 September 2007 (UTC)

But don't forget that sunscreen exists. This would mean that those living in poverty (who couldn't afford it) would likely fare worse. StuRat 22:11, 16 September 2007 (UTC)

And also don't forget those living within a couple thousand miles of the poles; not much sunlight reaches there anyway, comparitively. Someguy1221 23:08, 16 September 2007 (UTC)

See this about biological effects. If the ozone layer disappeared completely, there could be a breakdown in the entire foodweb, and getting skin cancer may be the least of our worries while we starve to death. --jjron 07:09, 17 September 2007 (UTC)

Diagram

Do you know of any scientific diagram shaped roughly like some kind of bird, perhaps a bat? Would probably be named after the man who invented it. Thanks. —Preceding unsigned comment added by 88.111.107.4 (talk) 21:51, 16 September 2007 (UTC)

Rorschach inkblot test? -Arch dude 22:50, 16 September 2007 (UTC)

Penguin diagram? Half on the ball :-) Someguy1221 23:07, 16 September 2007 (UTC)

Butterfly diagram? Relates to Fast Fourier transforms. SteveBaker 14:00, 17 September 2007 (UTC)

Smith chart? The diagram itself is circular, but the patterns inside always struck me as sort of Thunderbird-like. Saturn 5 20:44, 20 September 2007 (UTC)

September 17

Recycling plants

I was wondering if you could point me in the right direction online as to where I can educate myself about recycling plants. I would be extremely grateful! thank you —Preceding unsigned comment added by 195.250.91.198 (talk) 00:05, 17 September 2007 (UTC)

What are you interested in recycling ? Metals ? Plastic ? Paper ? StuRat 00:48, 17 September 2007 (UTC)

You might try Materials recovery facility and Recycling. At first I thought the OP wanted to know about how to recycle his azaleas, and was a bit confused. -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 00:54, 17 September 2007 (UTC)

Recycling azaleas? Look at composting. -- 22:26, 17 September 2007 (UTC)

Rotating liquids

My kid is doing a project for an upcoming science fair, and I was thinking about helping her build something like this:

It looks cool and it's more original than a baking soda volcano, so I like it :) Would basically any two non-mixing substances work (I assume they have to have different densities)? Like cooking oil and water? Any other suggestions? How fast would it have to rotate? I guess you could experiment to find that out (depending on the amount of fluid, I'm assuming), but some equations would be neat. Me and my offspring would be very grateful and if she wins a prize or something, you're all getting barnstars :) Thanks in advance! 83.249.113.29 01:16, 17 September 2007 (UTC)

Dunno about the physics, but the fluids are easy: I believe it's traditional to use mineral oil and water in all such non-mixing-fluids gadgets. You can use any old water-based food coloring to give the water a pretty color, and/or a nonpolar dye for the mineral oil. --Steve Summit (talk) 01:35, 17 September 2007 (UTC)

1. Remember the rule "like dissolves like." i.e. Nonpolar substenses will not disolve/mix with polar substenses. (yes, in other words) 2.(see below). A pratical use for this is that a parabola will focus light, so if one of the liquids were mercury, you could have a realy big mirror, like for a telescope. (sombody did this once) 3. when a liquid is spun, the surfice will become a parabola, just like in the photo. a parabola can be expressed mathamaticly 4. you will get a parabola no matter what speed it would be spun at, but the greater the speed, the deeper the curve. (one could also do a study about rotation speed and curve steepness/depth) 5. Youre welcome. hacky 03:51, 17 September 2007 (UTC)

On the topic of reflective parabolic liquid surfaces, see liquid mirror, mercury mirror. TenOfAllTrades(talk) 12:33, 17 September 2007 (UTC)

In the context of the original question, I think we should say that a real mercury mirror is not a suitable candidate for a science fair project because of the dangers of mercury poisoning (although building a demo model with a safe liquid would be fine). Gandalf61 13:30, 17 September 2007 (UTC)

The speed you'd need to rotate it would depend on the ratio of the densities of the two liquids and the diameter of the tank. But I'd guess that a really low speed would work quite well. I would grab an old bicycle with a set of Derailleur gears. The bicycle frame should simplify the mechanical construction. I'd attach the pedal end to the tank and the back-wheel end to an electric screwdriver (those have fairly low speeds and lots of torque - so probably better than an electric drill. The bearings on the pedal end are strong enough to support a person standing on the pedal - so it should be plenty strong enough to support the weight of the water tank. Placing the chain onto the smallest gear first would give you the slowest speed of rotation - which will give the drill the extra torque needed to get the tank started - and also be slow enough not to slosh liquid everywhere. If you find you need more speed, you can move the derailleur up to a larger gear wheel. If you need less speed, you could put the back wheel back on the bike and use an electric drill with the chuck pressed against the tyre to spin the thing REALLY slowly. Tell us how it goes! We need pictures! SteveBaker 13:56, 17 September 2007 (UTC)

One thing to watch out for is creating an emulsion. If you accelerate the liquids too quickly, you will end up with a mess that looks like a bottle of salad dressing which has just been shaken. The layers will eventually settle out, but probably not until well after it stops moving. StuRat 02:57, 18 September 2007 (UTC)

With a big tank like the one in the picture, that's unlikely to be a problem - the tank will need a LOT of torque to get it moving, so a violent startup would be unlikely - and even when it is started, the tank will be spinning but the liquid inside will mostly be stationary. I agree though that with a much smaller tank, and some nice wine vinegar replacing the water, you might have just built the world's greatest French dressing maker...which might still make for a good science project! SteveBaker 13:57, 18 September 2007 (UTC)

Stu might be thinking of a stationary round Plexiglas tank where a paddle at the bottom is used to spin the liquids, in which case if the paddle is very thin and spinning at a high enough speed then it might be possible to use egg whites instead of water and produce mayonnaise instead of salad dressing, oh wait, mayo is salad dressing, what am I thinking? Clem 02:31, 23 September 2007 (UTC)

looking for the name of something

what would the "study of the relationship between the mind and the body" be called? I know it will end in "olgy" but I don't think it is psycology. —Preceding unsigned comment added by 76.19.185.11 (talk) 03:47, 17 September 2007 (UTC)

It depends on what you mean by "mind." If you're talking about the physical aspects of the brain, that would be covered by neurology. If you're talking about "that which does the thinking," that would be psychology. If you want to know the relationship between mental processes and physical/chemical interactoins in the brain/body, you're thinking of neuropsychology. If you want to know the true distinction between the mind and the brain, you'll have to look towards philosophy. Someguy1221 05:04, 17 September 2007 (UTC)

Could science genetically engineer an organism which can survive for extended periods of time in outer space?

Let’s say a being which can work and move in outer space for about 36 hours without need for special gear, and for even longer on terrain at almost zero Kelvin, with very thin atmosphere. 5 hurdles as far as I can see.

1. Zero pressure. Could be insuperable, I thought, but then we have sea bed creatures that live in pressures hundreds of time greater than at sea level. If they can do it, why could we not design a creature that can do with one less than us. Just a case of having a very sturdy casing with pluggable orifices and insulation for eyes etc.

2. Zero Gravity. Big problem with terrestrial animals, but fish exist in what is virtually zero gravity.

3. Cold. Well insulated skin would be needed, perhaps like a polar bear’s. Also the type of anti-freeze found in salamander blood.

4. No air. Whales can dive for hours without air. Organism would have to be able to super-saturate blood and organs with oxygen, to be released gradually.

5. Damage by cosmic rays. Genetic code would need to be double coded with extra checking bits to overcome radiation damage.

All in all, I can’t see huge problems here. In the next 50 years we will have the technology to do this. Why do I ask? Because this being, which I see as some kind of beaver with tentacles, will have HUMAN DNA, it will be our homogenobased descendant (my coinage). Let’s face facts. We will not conquer space and other planets looking like tourists from Sydney. Extreme conditions will require radical modifications to the morphology and genetics of the human organism. Yet virtually all the commentators on humans in space ignore the fact that what is happening now in Genetics is far far more important than progress in the rockets, ray guns and robots fields that so entrance sci fi addicts to the exclusion of all else. What say you? Are we going to be carrying bits of earth environment around with us forever, like deep sea divers, or am on the right track? A new man who can live in extreme conditions with a minimum of special gear. Myles325a 05:28, 17 September 2007 (UTC)

But the whole point of sending humans to space is that it is actual humans that go. If you're not going to send actual humans, why not just send robots of some type and cut out all the mucking around (hell, they could even carry some human DNA with them if you really want the DNA out there)? Or am I missing your point? --jjron 07:01, 17 September 2007 (UTC)

1) Good luck. 2) This one is easy, humans can already operation in zero gravity. 3) Near 0 Kelvin, seriously? Consider that there is almost no motion at such temperatures, so you couldn't do it with anything resembling a known life form. The insulation required would be incredible, just keeping something at 70 Kelvin for long periods requires an extremely well built thermos. And antifreezes don't work even at 200 Kelvin; I've confirmed this myself. 4) Yes, giant air supply is possible somewhere...in theory. Not that genetic engineering is at the point where we can add new organs to an organism, aside from making mice grow human ears. But I guess if you're starting with something that can already do that, good for you. 5) Biologists still haven't fully figured out how organisms naturally control their genes, so genome-wide alterations aren't even in the scope of speculation yet.
Now, I hate to have been a pessimist, but it's simply that a lot of people have a distorted view of what genetic engineering can do. Genes aren't the blueprints for the body that the press and popular culture often make them out to be. Individual genes just code for chemicals, and it is individual chemicals that are the targets of current genetic engineering projects. Someguy1221 08:25, 17 September 2007 (UTC)

Cold isn't that big of a short-term problem because there's not much anything to leak heat to. However, over the long term...it's a huge problem. -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 08:43, 17 September 2007 (UTC)

Note that making organisms that are resistant to even extremely high doses of radiation is possible—nature has already done it with Deinococcus radiodurans. D. radiodurans will survive a dose of radiation a hundred times that which would kill a human being. Nicknamed 'Conan the Bacterium', it is also resistant to heat, cold, dehydration, vacuum, and acid in addition to intense radiation. Of course, scaling that up to anything bigger than a bacterium is an exercise left to the reader. TenOfAllTrades(talk) 12:29, 17 September 2007 (UTC)

I don't see why you'd bother. It's much simpler to provide a life-support suit of some kind. I could certainly imagine a suit that would keep you safe in vacuum/zero-g for 36 hours - existing space-suits can keep you alive for 8 to 9 hours - quadrupling that shouldn't be too big of a challenge. The insanely low temperatures you talk about are not relevent in a vacuum. The whole concept of temperature is meaningless in a vacuum - deep space doesn't have a temperature because there is nothing there to measure the temperature of! A big problem may well be shedding heat - not retaining it. The creature you envisage would probably be totally crippled in a 'normal' environment - this seems like a ridiculously drastic step compared to wearing a space-suit. If you insist on thinking about it this way, far from being a "beaver with tentacles" (where the heck did THAT idea come from?!) - that seems like the worst possible design! If you are really concerned about unprotected survival in low temperature and vacuum, you'd want something close to being spherical so as to minimise surface area and maximise the ability to contain internal pressure sufficiently to prevent liquids from boiling...tentacles are definitely out! But operating in almost absolute zero environments is just not going to happen. SteveBaker 13:39, 17 September 2007 (UTC)

I, for one, support our new tentacled space beaver overlords. --Sean 14:48, 17 September 2007 (UTC)

File:TentacledSpaceBeaver.jpg

All hail!

See pantropy, and I think you really want to read a book called The Seedling Stars. --Reuben 16:54, 17 September 2007 (UTC)

Quite do-able, but it might be more than 50 years. Edison 01:47, 18 September 2007 (UTC)

We probably have life forms now that could survive those conditions, like some seeds, I imagine. Getting life forms that can actually do anything besides hibernate under those conditions is entirely different, however. StuRat 02:46, 18 September 2007 (UTC)

double acting gasoline engines

hey friends i ve designed a double acting gasoline engine.i really want to know that whether such engines r availaible.if not then it would be a great matter for me.

regards Reveal.mystery —Preceding signed but undated comment was added at 06:22, 17 September 2007 (UTC)

There are an awful lot of alternative configurations that have been invented already. The Bourke engine might be what you are thinking of - or perhaps Split Cycle Engine, or Twingle engine, or the Stelzer engine. I strongly recommend looking at all of the links in the table at the bottom of those pages that contains links to dozens of articles to alternative kinds of gasoline engine. SteveBaker 13:22, 17 September 2007 (UTC)

"violotion" of law of conservation of energy ?

According to special relativity the mass of any object or particle increases with increase in speed . is'nt that a violation of law of conservation of energy ? because we know mass is a form of energy .

Except that you have to supply an object with that same increase in energy to make it speed up. Conservation achieved! Someguy1221 08:11, 17 September 2007 (UTC)

Actually it's more common now not to talk of mass changing at all, but to modify the formula for energy. If you want to think of mass energy equivalence, it is easier to think of the extra kinetic energy acting to cause the extra mass, rather than vice versa. Cyta 08:52, 17 September 2007 (UTC)

The concept of invariant mass (as distinct from relativistic mass) is probably useful to mention here. TenOfAllTrades(talk) 13:53, 17 September 2007 (UTC)

Yes. When physicists talk about "mass" in a relativistic context, they almost invariably mean invariant mass. Relativistic mass is relatively uncommon. In popular books and articles, it's the other way around, and this leads to a lot of confusion. I believe the physicists switched over some time around 1950, as it was gradually decided that invariant mass is a more useful concept. So now physicists don't often talk about mass changing with velocity. --Reuben 16:50, 17 September 2007 (UTC)

Field Maple

I have some large field maples (20m) in my garden one of which needs to be felled. They are old slow growing trees (the garden has been cultivated since the thirteenth century). The tree has a good straight trunk but I want to know whether the timber will weather outside well (e.g. can I season it and then use it for raised beds). All I can find on google is the same couple of texts repeated endlessly about it being good for musical instruments, mallet heads and bird's eye veneers, not the weatherability of large planks. --BozMo talk 09:03, 17 September 2007 (UTC)

Generally, maple is too expensive for that kind of usage - that's probably why there is no information about weathering outdoors. You might want to investigate whether you can sell the trunk and use the money to buy some (much cheaper) pressure-treated lumber which will last for a very long time. SteveBaker 12:55, 17 September 2007 (UTC)

I'm curious: why are you taking them down? Are they unhealthy? --Sean 14:54, 17 September 2007 (UTC)

Only one. Planted too close to other trees (or they were planted close to it) and is dying back from the top. There are more magnificent ones I won't touch. --BozMo talk 19:17, 17 September 2007 (UTC)

Heron

A Heron like bird

At the risk of sounding hopelessly naive, I would like to ask: what bird is this ? and whether this photograph I took, may be added to the relevant article. I would appreciate any help. I am sorry in advance if it is not too useful. :) Vijeth 09:42, 17 September 2007 (UTC)

Do we have any Asian ornithologists here? It should be emphasized that the picture was taken in Hyderabad. TenOfAllTrades(talk) 13:56, 17 September 2007 (UTC)

I think I'd start looking under cranes Richard Avery 21:31, 17 September 2007 (UTC)

Or ask at Wikipedia talk:WikiProject Birds.--Jude. 13:58, 19 September 2007 (UTC)

aerodynamics

can an aeroplane be stand still at a place like a helicopter?203.94.231.74 10:42, 17 September 2007 (UTC)

Depends on the aeroplane. Most cannot but see Harrier Jump Jet as an example. —Preceding unsigned comment added by BozMo (talk • contribs) 10:48, 17 September 2007 (UTC)

In general, not unless they've been specially designed to do so (as the Harrier was) - but aside from that, with the right conditions (if the wind speed is equal to the air-speed of the aircraft), a plane will appear to be standing still from the point of view of someone on the ground. Hence, some aircraft have a low enough stall speed that they can 'hover' in fairly modest winds. Also, aside from the Harrier, there are also the Tiltrotor craft that blur the line between a fixed-wing plane and a helicopter. SteveBaker 12:52, 17 September 2007 (UTC)

Other designs that allow fixed-wing aircraft to hover and/or land vertically are tiltwing and the (not very practical) tailsitter design. All designs are based around the requirement to smoothly change the direction of thrust between horizontal in normal flight and vertical in a hover. Our article on VTOL gives a good overview. Gandalf61 12:59, 17 September 2007 (UTC)

I wonder if a jet with enough horsepower to accelerate straight up, and thrust vectoring for control could point upwards and hover for a bit? That would be a neat trick. --Sean 15:00, 17 September 2007 (UTC)

I believe Sukhoi has created models of aircraft that could do just that. StuRat 02:19, 18 September 2007 (UTC)

Actually - quite a lot of modern fighters have the power to do that. You only have to be able to accellerate at >1g which lots of modern planes can do. The problem for hovering with those aircraft is that as the airspeed over the control surfaces drops you start to lose control over the beast - if you are literally hover, you have no control whatever over the aircraft. Depending on what happens next, this can be rather dangerous. If the aircraft has thrust vectoring, then a modicum of control is still possible - but whilst they proudly show it at air shows, this is hardly a practical manouver! SteveBaker 13:49, 18 September 2007 (UTC)

Prototypes of the flying flapjack could hover vertically if the wind was just right. Someguy1221 18:44, 17 September 2007 (UTC)

You might also check out the F-35. -Wooty [Woot?] [Spam! Spam! Wonderful spam!] 23:55, 17 September 2007 (UTC)

Symmetry

What is the likelihood of getting a wart in the exact same spot on each index finger? Clem 12:08, 17 September 2007 (UTC)

Warts are caused by a viral infection through the skin. If you spend time with your two index fingers pushed against each other symmetrically the chances might be quite high... --BozMo talk 12:11, 17 September 2007 (UTC)

When I was a child, I had a small plantar wart in the exact center of my fingerprint whorl. I have always considered this to be non-random, so maybe there's something to it. --Sean 15:03, 17 September 2007 (UTC)

Reminds me of ol' Dan Tucker, who died with a toothache in his heel :-) --Trovatore 18:09, 17 September 2007 (UTC)

• Haha, I just noticed that a plantar wart is foot-only by definition! OK: I had a thing that looked just like a plantar wart in my finger. :) --Sean 19:26, 17 September 2007 (UTC)

There is said to be a psychological aspect to warts, so if your brain makes a connection between two symmetrical parts of your body then that might just cause a new wart. Just a wild (and only slightly educated) guess. DirkvdM 08:51, 18 September 2007 (UTC)

Naming of electronic components

What is the basis of naming electronic components?
for eg:1N 4001 etc? Its kind of a homework question. But googling 'naming of electronic components' wasn't very helpful (yet). For zener diodes I think that the name incorporates the breakdown voltage; right? the page Electronic_component does'nt seem to have it. Still searching If someone knows a link or something where it is discussed in detail It would be helpful. 59.93.41.117 14:15, 17 September 2007 (UTC)

I think JEDEC were responsible for categorising and maybe naming in conjunction with the manufacturers--88.111.135.162 15:46, 17 September 2007 (UTC)

railway semaphores

Why did I.K. Brunell device and built semaphores on the GWR that indicate clear in a downward position? This construction is more expensive and more prone to failure than the everywhere else used signalling by which the arm is pointing upward to indicate clear. wally. 82.173.141.164 14:46, 17 September 2007 (UTC)

"Why" is a tough question to ask when it comes to GWR, I've found. :) Brunel also thought a 7' rail gauge was a good idea too. But yes, the Lower Quadrant signalling does seem like it could fail to a dangerous condition. Saturn 5 20:39, 20 September 2007 (UTC)

Mama seagull - will she recognise her own offspring?

It's getting to about that time of year when this year's fledgling gulls are cut loose by their parents to fend for themselves. Just wondering - will the mother/father gull treat her/his 'grown up' offspring any differently to any other gull when if/when they encounter each other in the future - or will they be seen as just more gulls to squabble with over food and perches? I know that magpies tend to stick together in family groups but it's quite hard to tell with gulls - as they never really obviously interact with each other in a friendly social manner (they just kinda stand near each other if they don't want to fight). --Kurt Shaped Box 15:03, 17 September 2007 (UTC)

Well, you're our resident seagull expert, I doubt if anyone here knows more about them than you. Maybe you should mark some seagull families (dye, perhaps ?) so you can identify them and see if they react differently in subsequent years. If you were in the US, you could probably get a million dollar grant to do so. :-) StuRat 02:09, 18 September 2007 (UTC)

You *could* ring the gulls in question and observe their interactions. That sounds like something that someone may have already studied... --Kurt Shaped Box 16:46, 18 September 2007 (UTC)

steam engine advantages at high altitude

"Steam locomotives are especially advantageous at high elevations as they are not adversely affected by the lower atmospheric pressure. This was inadvertently discovered when steam locomotives operated at high altitudes in the mountains of South America were replaced by diesel-electric units of equivalent sea level power. These were quickly replaced by much more powerful locomotives capable of producing sufficient power at high altitude."

In reading that I thought it to be dubious for these reasons Studying the statement that asserted that steam engines are advantageous at high altitude is a partial truth. While it does satisfy Carnot's cycle by having high pressure steam coming into the engine, and exhausting the steam at very low pressure. (thermodynamically efficient) it does not take into account the combustion of the fuel used to heat the water to make the steam. Any engine that derives its power from chemical energy (diesel, jet, gasoline) requires a certain amount or ratio of fuel to air to operate properly. Recall that the supercharger was used in war to maintain sea level pressure so that aircraft would maintain power at all altitudes (turbochargers). The locomotive style boiler has no means of forced induction and as a result the air is "rare" and thus the sociometric ratio is compromised. I think this issue should be addressed. Spencer —Preceding unsigned comment added by 199.17.91.22 (talk) 15:10, 17 September 2007 (UTC)

This sounds like something that should be addressed on the talk page of whichever article you are referring to. If you return to that article and click on the "discussion" tab at the top, you will be able to address your concerns to an audience that is more specifically interested in and informed on the topic. --LarryMac | Talk 17:44, 17 September 2007 (UTC)

That assumes that the availability of oxygen is going to be a limiting factor for a locomotive at any reasonable altitude. Is that a reasonable assumption?

In a (non-turbo, non-supercharged) internal combustion engine, the amount of fuel that can be burnt (and therefore the amount of energy that can be extracted) per unit time is a function of the total amount of fuel and air that fits in the cylinders and engine revs (more revolutions per second means more combustion cycles). As you decrease the atmospheric pressure, the amount of air that the engine ingests per cycle falls, reducing the amount of fuel that can be burnt and limiting the available energy. The maximum speed of the engine is limited by its mechanical strength, so you can't restore the lost power by cranking the engine faster.

In a steam locomotive, coal is shovelled into the firebox, where it is burnt in available air at atmospheric pressure. Air is continuously drawn into the firebox, and combustion products are continuously vented through the smokestack. As long as it's possible to draw air through the firebox drafts then the coal will continue to burn. (In other words, at any reasonable atmospheric pressure, the coal in the firebox will be able to suck in as much air as it needs at any given time. Contrast this with an internal combustion engine, where each volume of air has to be drawn in mechanically.) Will the combustion of each lump of coal proceed more slowly with the lower partial pressure of oxygen? Possibly—but you can get around that by adding a bit more coal (increased combustion surface area) to maintain the same total amount of heat per unit time. TenOfAllTrades(talk) 21:35, 17 September 2007 (UTC)

What's wrong with an ATOMIC powered steam engine. No requirements for minimum oxygen levels, just boil the water to make lots of steam. 202.168.50.40 00:56, 18 September 2007 (UTC)

Thanks that really clarified it. I failed to take into account the draft produced and the constant supply of air to support combustion of the coal. Spencer —Preceding unsigned comment added by 69.42.233.219 (talk) 04:42, 18 September 2007 (UTC)

Freaking out. (Bio/Med Q.)

I'm freaking out. I clean my desk and other surfaces in my room with alcohol which seems to 96% ethanol and i presume 4% methanol. When its all evapourated the room usually has a fairly strong odour to it. Is the amount of methanol in the air enough to do any damage to my body? i probably only use a small amount of the liquid each time and its only %4 anyway and by the time its dispersed amongst my room it probably woulndt be in any concentration that would do any noticeable damage... Right??? any im only exposed to it for 5minutes until diffused out windows/other rooms ect and no longer noticeable. I know this is probably silly but thanks anyway. Lolfalroflealal 15:31, 17 September 2007 (UTC)

Standard alcohol formulations such as this are 95ish% ethanol and the rest is primarily water not methanol (but only you have the actual bottle to read the ingredients on this particular product). See azeotrope to learn why 95% is a convenient concentration. DMacks 17:02, 17 September 2007 (UTC)

Wikipedia does not give medical advice. I have never heard of a cleaning/sterilizing solution containing so much methanol that its vapors do harm. That said, it couldn't hurt to leave a window open. Plasticup ^T/C 20:27, 17 September 2007 (UTC)

Contrary to popular belief, ethanol itself has an odour (from Ethanol: "Ethanol, like most short-chain alcohols, is flammable, colorless, has a strong odor, and is volatile."). When using a significant amount of it (say in cleaning), it can get quite overpowering, especially if the room is poorly ventilated. -- 22:26, 17 September 2007 (UTC) —Preceding unsigned comment added by 72.33.121.200 (talk)

Where are you? The alcohol that I use for cleaning is isopropyl. —Tamfang 00:54, 18 September 2007 (UTC)

I'm told that ethanol is a better disinfectant. I think isopropanol is just cheaper. But I have to agree, I doubt the other 4% is methanol. That's something that would probably be written on the bottle. Someguy1221 03:35, 18 September 2007 (UTC)

don't worry about it, remember, ask yourself this question when in fear of methanol: what is the antidote to methanol poisoning? Ethanol. have a beer, imagine how the ethanol is competitively using up the same enzymes that methanol would fuck with, and relax. —Preceding unsigned comment added by 12.217.199.246 (talk) 02:05, 18 September 2007 (UTC)

If you want to avoid methanol poisoning, just take a shot of ethanol ;O
Mrdeath5493 03:47, 18 September 2007 (UTC)

Alcohol based cleaning fluids sometimes contain ethanol and a surfactant such such benzyl alkonium sulponate.. Read the label it should tell you what exactly is in it - ie if there is methanol or not and any possible dangers - it is possible that the fumes themselves are making you high and paranoid..87.102.7.192 09:46, 18 September 2007 (UTC)

Cosmological Redshift and the conservation of energy

Consider a photon created shortly after the era of recombination. At the time its wavelength would likely be about 966 nm, corresponding to an energy of 1.28348270 eV. Now say that it travels along, not interacting with anything, for 13.5 billion years or so. During that time the Universe expands significantly and the photon's wavelength is increased to 1,900,000 nm. It now has only 6.5255*10^-4 eV of energy. So it lost 1.28283015 eV without any interactions. When I asked my physics professor to explain this he replied "under the most general forms of general relativity, energy is not conserved". True? False? Plasticup ^T/C 20:51, 17 September 2007 (UTC)

Strange but true! In fact, there's no good way to define the total energy of the universe in general relativity! --Reuben 20:55, 17 September 2007 (UTC)

Break out the Stress-energy-momentum pseudotensor! It's controversial and some people think it's hand-wavey, but it lets you conserve something like energy in general relativity. Damned if I know how to use it, though. See also "Is Energy Conserved in General Relativity? for a summary and some good references. (The nutshell answer from that site is "In special cases, yes. In general -- it depends on what you mean by 'energy', and what you mean by 'conserved'.") TenOfAllTrades(talk) 21:14, 17 September 2007 (UTC)

What does "hand-wavey" mean ? StuRat 01:49, 18 September 2007 (UTC)

Lacking rigor. Which seems inappropriate here, since it's a rigorous idea, just not a generally covariant one. -- BenRG 02:08, 18 September 2007 (UTC)

Some people find the lack of general covariance...disturbing. TenOfAllTrades(talk) 03:27, 18 September 2007 (UTC)

Conveniently, we have an article on handwaving. TenOfAllTrades(talk) 03:27, 18 September 2007 (UTC)

The photon appears to be gaining gravitational potential energy. I don't know if that's the same amount as it's losing from decreasing wavelength, though. — Daniel 23:01, 18 September 2007 (UTC)

Understanding Motion

My question is:

How do I calculate the velocity and accelaration of a free falling object if the object is 45 meters above the ground and free falls to the earth?

Have a look at the Acceleration article, and then Newton's law of universal gravitation. Probably what you are looking for though is Equation of motion. — RJH (talk) 22:40, 17 September 2007 (UTC)

If it's 'free falling' and we are neglecting air resistance, the only force is gravity - so the acceleration must be 'g' (the accelleration due to Standard gravity) which is about 9.8ms^-2 (although it varies a bit depending on where you are on the earth). The equation you need from the classical equations of motion is: v²=u²+2as (where u is the initial velocity, v is the final velocity, a is the accelleration and s is the distance travelled). We know that s=45m, u=0ms^-1 (assuming the object was stationary at the start), a=g=9.8ms^-2 - so substituting into the equation and taking the square root of both sides, we get v=sqrt(2x9.8x45) which gives us roughly v=29.7ms^-1. SteveBaker 13:36, 18 September 2007 (UTC)

Comparator input capacitance

Anyone know (or make a guess at) the input capacitance of the SE521 comparator? The data sheet doesn't say.--88.111.135.162 23:22, 17 September 2007 (UTC)

That's surprising, but you're certainly correct: it doesn't say. But we can infer, based on the speed of the part and the fact that the inputs are bare transistor bases, that it can't be much, a few pF at most. If you had an LCR meter, a network analyzer, or a TDR, you could measure it. Or you could just call NXP/Philips and ask them.

Atlant 12:46, 18 September 2007 (UTC)

I do have a meter that can measure down to about 1pF but Im not sure if the part should be energised when making the measurement as I suspect the capacitance will vary with the state of bias of the input stage. Any thoughts?--88.111.135.162 13:55, 18 September 2007 (UTC)

Yes, energized, but LCR meters don't like applied DC voltages so put a DC blocking capacitor in series with the meter and the DUT. You can either make the blocking capacitor largish (say, 1nF) so its effects are immaterial or you can do the series-capacitor calculation to mathematically remove its effects later. Either way, connect the test circuit, short the LCR meter's inputs, energize the test circuit (so the blocking cap charges), and ONLY THEN unshort the LCR meter's inputs and make your measurement.

Atlant 15:38, 18 September 2007 (UTC)

Looking at other comparator data for fast comparators, it seems to be about 3-4pF. I'm gonna take this as a guess and trim my compensator for best looking i/p w/f on the input pin somehow.--88.111.135.162 15:08, 18 September 2007 (UTC)

Sounds like a good plan! Don't forget, though, that your 'scope probe has a pF or ten as well.

Atlant 15:38, 18 September 2007 (UTC)

Ah yes. I thought of that. Im gonna try using my home made low C probe (Zo probe): 450 ohm series R feeding a 50 ohm cable into 50 ohm scope i/p giving 10:1 attenuation. (my planned source resistance is only 10 ohm)--88.111.135.162 22:50, 18 September 2007 (UTC)

September 18

soil conservation

how does science and technology benefit soil conservation

Science and technology are very important to soil conservation. Without science and technology, soil conservation would be much more difficult. Many scientists and technologists around the world are working very hard to contribute to soil conservation, including Illinois. In conclusion, I think science and technology benefit soil conservation in many important ways. The end. —Tamfang 00:52, 18 September 2007 (UTC)

Well it all starts with doing your own homework... Plasticup ^T/C 00:53, 18 September 2007 (UTC)

Welcome to Wikipedia. You can easily look up this topic yourself. Please see soil conservation. For future questions, try using the search box at the top left of the screen. It's much quicker, and you will probably find a clearer answer. If you still don't understand, add a further question below by clicking the "edit" button to the right of your question title. --Shantavira|^{feed me} 07:31, 18 September 2007 (UTC)

Fuzzy Logic

Is Fuzzy Logic science or mathematics? 202.168.50.40 03:11, 18 September 2007 (UTC)

Math(s). —Tamfang 03:29, 18 September 2007 (UTC)

I'm not sure I'd call it either science or math. It seems to be used solely by industry; I can't recall a pure mathematician ever expressing interest in it. The mathematician's version of fuzzy logic is Bayesian inference, which has different rules. -- BenRG 10:01, 18 September 2007 (UTC)

Isn't Defuzzification the same as Collapsing the Probability Wave in Quantum Mechanics? What about the similarity between Fuzzy Logic and Quantum Wave Theory. Both seems to deal with "All possible worlds" before collapsing into one observed result. 202.168.50.40 05:24, 18 September 2007 (UTC)

Not really - fuzzy logic is just probability based decision making under another name, wave function collapse is something else that can be related to probability.87.102.7.192 09:41, 18 September 2007 (UTC)

The collapse of the wave function does look like a Bayesian update. This was noticed by the founders of quantum mechanics, and led to a lot of rather embarrassing speculation about consciousness and mind-over-matter (because the Bayesian update is about subjective knowledge, but the wave function collapse is a physical effect). Eighty years later, the connection between quantum statistics and Bayesian inference seems to still be unclear, like everything else about the foundations of QM. But I can say with some confidence that fuzzy logic has nothing to do with QM. -- BenRG 10:01, 18 September 2007 (UTC)

It's applied mathematics. It's a branch most often used in practical technology (mostly computer software) rather than in pure mathematics. SteveBaker 13:16, 18 September 2007 (UTC)

Adjusting to high altitude

I understand that if you go up to 6,000 or 7,000 ft above sea level you can dehydrate and get headaches, and that it can require as much as 6 weeks for your body to adjust. My question: what exactly is the body's adjustment? Do we create more hæmoglobin? Thanks. PaulTanenbaum 04:12, 18 September 2007 (UTC)

Yes (more red blood cells). --> Altitude training. Someguy1221 04:41, 18 September 2007 (UTC)

After many years at altitude, you create too many. --> Polycythemia. --Mdwyer 14:40, 18 September 2007 (UTC)

I don't quite understand. Why is it "too many"? The article doesnt seem to discuss any disadvantages. Yet is calls people with the condition "sufferers". Is the article of poor quality? Capuchin 14:47, 18 September 2007 (UTC)

Polycythemia vera lists many nasty reasons you wouldn't want that particular brand of it. Someguy1221 16:08, 18 September 2007 (UTC)

Suspension of Disbelief

This is a question of psychology. As I am not a psychiatrist or a psychologist, please keep your answers on the simple, non-technical side. Thanks. I don't quite understand this. Can someone please explain? When I watch a film or a TV show, my brain knows and understands that the whole thing is "fake" and not truly happening in real life. A physical example: when I see a character get stabbed ... my intellectual side knows that it is just an actor, reading from a script, with a fake knife and fake blood as props. That is, a real person did not just suffer a real stab wound from a real murderer with a real knife and is now bleeding real blood. An emotional example: when I see a husband/wife argue and fight and get a divorce on a soap opera ... my intellectual side knows that it is just a group of actors, reading from a script, with no real fight or real divorce involved. So, this is my question. If the intellectual / intelligent part of my brain knows and realizes and accepts this, how exactly is it that a film or TV show can get me scared or nervous or happy or sad or whatever? In other words, why do people get scared / nervous / frightened / upset when they see the shark attacking in Jaws and they "know" that the whole scene is a fake / a sham? What is happening with the brain that allows us to experience "fear" in such an irrational manner? (Irrational = "I know that this is all fake and not really scary, yet I am still scared.") Why do people get happy / sad etc. when fake characters on a soap opera engage in a fake wedding or a fake divorce or a fake fight or a fake death or whatever? (fake=fictitious) How is it that the rational / thinking side of our brain / intellect gets "fooled", if you will, by the film or TV show or acting or writing, etc.? Thanks. (Joseph A. Spadaro 05:00, 18 September 2007 (UTC))

Well, I found a paper on it. Here. Someguy1221 05:12, 18 September 2007 (UTC)

I think empathy has a lot to do with it. We are able, and all too willing, to put ourselves in the shoes of the protagonists and "experience" what he or she is going through emotionally. Rockpocket 06:16, 18 September 2007 (UTC)

Our brain hasn't evolved to deal with actors. Capuchin 11:42, 18 September 2007 (UTC)

As with most systems of any complexity, the brain has layers of interpretation from the lowest level perception of colours, shapes, motion, sounds, etc - though the level that recognises people, sharks, water - then into the level that produces 'gut reactions' of surprise, fear, etc - then the higher levels of 'what to do about this'. It's likely that only the highest levels of processing are able to assemble enough context together to realise that this is all fake - the lower levels of processing having already acted on the basis of the information being real. SteveBaker 13:13, 18 September 2007 (UTC)

I am not sure how much empathy comes into play, I have a marked lack of empathy and I don't think I enjoy movies any less than the next person. Although I admit I do prefer action to romance, but that may be more to do with my gender. If you can identify with the situation the actors are in it may illicit more of an emotional response perhaps. Lanfear's Bane 15:42, 18 September 2007 (UTC)

Our article on empathy is a little, ahem, uneven to put it politely, but there are several definitions of empathy. The common one I knew about growing up was, as you suggest, being sympathetic (compassionate) about someone's situation. A wider definition is more about identifying with the other person, putting yourself "in their place", which might be more like what Rockpocket was talking about. You become scared or sad not because you feel sorry for the characters, but because you see yourself in their predicament. Also see Emotional contagion, though the article needs a lot of fact-checking and referencing, etc. Matt Deres 16:28, 18 September 2007 (UTC)

Methanol poisoning

If ethanol treats methanol poisoning, why is alcoholic beverages that contain a small amount of methanol dangerous? Jack Daw 14:20, 18 September 2007 (UTC)

Ethanol DOES NOT treat methanol poisoning.87.102.7.192 14:25, 18 September 2007 (UTC) The article on methanol states that ethanol may be used in cases of methanol poisoning to compete with the methanol for the 'enzyme' that breaks down methanol into harmful components.. This assumes that the breakdown products of ethanol are less harmful than those from methanol. This doesn't stop methanol and ethanol from being poisonous it's just than ethanol is less worse.87.102.7.192 14:29, 18 September 2007 (UTC)

Considering that ethanol is a widely socially accepted form of intoxication and not comparably a poison at all, which methanol is, we can quite safely assume "that the breakdown products of ethanol are less harmful than those from methanol". Jack Daw 15:32, 18 September 2007 (UTC)

A lot depends on the concentrations required to achieve the effect. Ethanol is most definitely toxic in sufficient quantities - we normally drink the stuff heavily diluted with water. SteveBaker 16:46, 18 September 2007 (UTC)

acetaldehyde and acetic acid are far less toxic than formaldehyde and formic acid, because they are more reactive.--134.76.234.75 17:28, 18 September 2007 (UTC)

So what's the answer to this question, are alcoholic beverages containing small amounts of methanol dangerous or not? —Preceding unsigned comment added by 12.217.199.246 (talk) 23:06, 18 September 2007 (UTC)

Yes. In fact all alcoholic beverages are dangerous. In fact everything is dangerous.

Just how dangerous depends, among other things, on how small is small. Poorly made moonshine can definitely contain enough methanol to be a problem. The mere fact that it also contains ethanol is not something you can rely on to protect you, because the ethanol may not monopolize the alcohol dehydrogenase for long enough for your kidneys to remove the methanol from your blood. --Trovatore 02:51, 19 September 2007 (UTC)

Breast size

How many years after first period do the breasts stop growing? --124.254.77.148 14:41, 18 September 2007 (UTC)

They never stop.87.102.7.192 15:06, 18 September 2007 (UTC)

It's going to depend on the individual, of course. We have an encyclopedia article on puberty that may prove useful. Friday (talk) 17:04, 18 September 2007 (UTC)

Both of the above answers are considering different issues. The female breast will mostly stop increasing in size some time after puberty. However as with all living body parts, it does not stop growing until you die. There is constant cellular regeneration as well as some specific changes during pregnancy. Even the size fluctuates somewhat outside of pregnancy. Breast covers this in some detail Nil Einne 21:16, 18 September 2007 (UTC)

erm breasts do get bigger with age (after puberty whatever that is) - that is I haven't yet seen teenage girls with 54DD breasts yet is not uncommon in women of a mature age..87.102.116.240 17:12, 19 September 2007 (UTC)

Read my response carefully. I said sometime after puberty. The precise time varies but it would AFAIK usually be in the late teens of perhaps early adulthood. (This ref [5] suggests you will usually know the final size by 17-18 although obviously there will be some who continue past then) An actually I'm pretty sure natural 54DD breasts are quite uncommon in women of a mature age (although more common then in teenage girls obviously) Nil Einne 20:20, 19 September 2007 (UTC)

Also, remember that breast size fluctuates with weight - if you lose a lot of weight your breasts often shrink in proportion, and similarly, if you gain weight, you gain breast size, as more fat is stored in them. My grandmother has giant ones - but she's a very large woman (and apparently had thyroid cancer, so that could be a cause). Mine fluctuate from a 36D to a 34C when I go from around 170lbs to 150 or so. It's all in how much fat is behind them, sort of pushing them out. Kuronue | Talk 23:38, 21 September 2007 (UTC)

Daisies and temperature

Can real daisies alter a planet's surface temperature the way they can in DaisyWorld? If so, could we theoretically reduce global warming by seeding large areas with white daisies, or delay the early stages of the next ice age using black daisies? NeonMerlin 15:57, 18 September 2007 (UTC)

I suppose so - the effect of the polar ice (white, shiney!) melting and being replaced by seawater (dark) is measurable in terms of increasing the effect of planetary warming...so I guess if you could plant enough daisies, it would have an impact too. It's obviously not a particularly practical scheme though - the areas covered would have to be enormous - and the consequential impact on biodiversity would undoubtedly be serious. SteveBaker 16:44, 18 September 2007 (UTC)

I dunno, but it's similar to a Snowball Earth. I wonder, though, how reflective white daisies are to IR. --Reuben 19:46, 18 September 2007 (UTC)

Yeah - it's hard to say. I'd hazard a guess that they were more reflective than green plants though - leaves are designed to absorb sunlight - petals aren't. SteveBaker 20:54, 18 September 2007 (UTC)

If they are like in Daisyworld, planting daisies won't change the temperature. The numbers of each shade of daisy will move towards equilibrium. — Daniel 22:43, 18 September 2007 (UTC)

That's just because it's a contrived example though. They set it up so that black daisies grow better in cool temperatures and white ones prefer the warm. As the temperature rises, the number of white daisies goes up and the number of black reduce - this causes the white ones to reflect more heat away resulting in the temperature dropping. No matter which way the temperature swings, the daisy growth rates will adjust and pull the temperature back to something they can both tolerate. This doesn't really mimic anything in the real world because the black daisies might very well evolve to be more heat-tolerant in order to out-perform the white daisies on warm days, which would allow the temperature of the planet could spiral upwards in an uncontrolled manner. Still, as a teaching tool, it's not bad. SteveBaker 14:33, 19 September 2007 (UTC)

It's not entirely contrived. After all, the black daisies themselves absorb more heat from sunlight than the white ones. So if both types had the same limits on their absolute heat tolerance (perhaps due to hard physical limits), the white daisies would be expected to do somewhat better at high temperatures and vice versa. Of course, it's still an extremely simplistic model. —Ilmari Karonen (talk) 20:25, 19 September 2007 (UTC)

Liver

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

Treating methanol poisoning with IV vodka/whiskey?

Does this actually work in the real world? I've seen this used as a plot device in shows like Casualty and Holby City on several occasions. --Kurt Shaped Box 17:46, 18 September 2007 (UTC)

I cannot imagine any reputable medical facility would use something intravenously that wasn't meant for this route of administration. Surely medical grade ethanol would be preferable? Friday (talk) 17:51, 18 September 2007 (UTC)

In the storyline, it's usually the case that they've run out of ethanol - so they have to raid the drinks cabinet/go down the off-licence. Makes more interesting TV, I guess. There was a scene in House M.D. where Dr. House downs a bottle of whiskey with a methanol victim in order to flush the toxins from his system - instead of say, just hooking a bag to the guy's drip... --Kurt Shaped Box 17:54, 18 September 2007 (UTC)

Well, it'd be sterile... -- Flyguy649 ^talk _contribs 17:58, 18 September 2007 (UTC)

Not saying that this is a healthy thing to be doing (or even a good idea - so don't try it, kids) but I used to know of someone whose party trick was to shoot whiskey into his veins. It didn't kill him - well he was still alive a couple of years ago, at least. He was a roadie for my friend's band - it was all very rock 'n' roll... --Kurt Shaped Box 18:30, 18 September 2007 (UTC)

To answer the question: it's possible, but I'm not sure. I know ethanol is used to treat isopropyl alcohol poisoning, so it's quite possible that it would be used for methanol poisoning. The reasoning behind ethanol's use in isopropyl is that ethanol is competitive to alcohol dehydrogenase. Alcohols, by themselves, aren't nearly as toxic as what they're broken down into (i.e. aldehydes), so the reasoning behind using ethanol in cases of isopropyl poisoning is to simply keep alcohol dehydrogenase busy while isopropyl is being naturally excreted by the kidneys (since it's a small enough chemical and since ethanol is also a diuretic). So, while the person will get ridiculously drunk, he'll live. Also, as far as I know, that's the only prescribed treatment if I remember correctly. So, it would make sense that the same approach would be used in cases of methanol poisoning, but again, I'm not certain. As to the IV route, I haven't heard of it being used. From what I've seen in the ethanol-countering-isopropyl route, it's just given PO (by mouth), since alcohol is irritating to connective tissue and it's readily absorbed from the gastrointestinal tract. --slakr^\ talk / 18:44, 18 September 2007 (UTC)

... which also reminds me. Everything from the GI tract gets first-pass at the liver, so it's a more direct route than IV/IM anyway. --slakr^\ talk / 18:49, 18 September 2007 (UTC)

I think you're thinking of ethylene glycol, not isopropanol. Isopropanol is not really all that poisonous I think; mostly it makes you sick (alcohol dehydrogenase turns it into acetone, which is not all that bad). That makes it a somewhat less vicious way of protecting the government's revenues than denaturing with methanol.

By contrast ethylene glycol turns into oxalic acid, which destroys your kidneys, and methanol turns into formic acid, which makes you go blind. As you say, a little bit of alcohol (a "beer" as an earlier poster put it) will not protect you from this. You need to tie up all the alcohol dehydrogenase until all the ethylene glycol or methanol is removed by the kidneys, which could take some time. I think there's now a less damaging pharmaceutical for doing this, without the brain damage involved in staying hammered for a day or so. --Trovatore 19:10, 18 September 2007 (UTC)

Fomepizole is what you are referring to, but in veterinary medicine it's still fairly common to use ethanol (usually vodka) IV for ethylene glycol poisoning. This is due to the cost of fomepizole and the fact that not everyone keeps it on hand. Interestingly, ethanol, not fomepizole, is the treatment of choice in cats. --Joelmills 19:40, 18 September 2007 (UTC)

Acetone is toxic through ketoacidosis, a condition one wants to avoid. Beer is of far too little of a concentration of ethanol, so whisky (or another high-proof spirit) is used instead. Saturation of alcohol dehydrogenase occurs rather easily with oral absorption of ethanol, as referenced by the linear breakdown curve that countless law enforcement agencies and learn-to-drive schools love to parade around. --slakr^\ talk / 19:22, 18 September 2007 (UTC)

I'm not claiming that isopropanol, or acetone, is exactly good for you. The isopropanol article says While large quantities of isopropanol can be fatal if left untreated, it is not nearly as toxic as methanol or ethylene glycol. The acetone article says Relatively speaking, acetone is not a very toxic compound; it can, however, damage the mucosa of the mouth and can irritate and damage skin. Accidental intake of large amounts of acetone may lead to unconsciousness and death. So I still sort of doubt that you're thinking of ethanol being used to treat isopropanol poisoning. It's much more likely that you're thinking of ethylene glycol, or methanol. --Trovatore 02:19, 19 September 2007 (UTC)

Batteries

Hi all,

If I hook a battery up to an LED, with the appropriate resistor in series, and leave it on, the battery will eventually run out. If I hook up a bigger battery (more volts, say, a 12 Volt battery), and change the resistor so that the correct amount of current is flowing, will the battery last longer? Or will the increase in resistance mean that the battery will be doing more work so there would be no difference?

Thanks! --Mary 18:05, 18 September 2007 (UTC)

See Ohm's law and Power (physics). --slakr^\ talk / 19:02, 18 September 2007 (UTC)

Perhaps more accurately, you'll want to check the amp-hour rating (generally expressed in milliamp hours, or mAh) to estimate battery duration. Voltage really has nothing to do with this, as not all 1.5V batteries are created equal -- do a quick comparison of an AAAA battery with a D-cell. Anyway, to estimate your battery use, divide the battery's mAh rating by the current pulled by your circuit. Note that stacking batteries in series does not mean that you add their mAh ratings together. — Lomn 20:07, 18 September 2007 (UTC) —Preceding unsigned comment added by Lomn (talk • contribs)

Take a look at Battery (electricity) for some averages. Note that although it'll be useful to predict how long your battery will last with a given load (the LED case), it doesn't directly tell you how much energy the battery stores (as explained in the linked page). For example a latern battery which usually AFAIK has 4 F type cells has a mAh of an F type cell. However it's delivering 4x the voltage so has a store of 4x the energy. Assuming you have a perfect voltage regulator (obviously such a thing can't exist) you could power a device for 4 times the length you could with a single F type cell. When you're simply using a current limiting resistor obviously the mAh is all that really matters Nil Einne 21:00, 18 September 2007 (UTC)

Iris Color Change

Are there any reported cases in which a person's iris color had changed from say, dark brown to blue or green, without any diseases involved? --WonderFran 19:30, 18 September 2007 (UTC)

Yep—this came up at the Ref Desk a few months ago (link to archive). There's some good information in Eye color#Eye color change and Iris (anatomy)#Color. TenOfAllTrades(talk) 20:26, 18 September 2007 (UTC)

Want to buy a new parrot/parakeet - suggestions?

I already have a Sun Conure, which is a lovely bird. But she can be a handful at times and very strong willed and independent. I want to get another parrot (to keep alongside her) but I want one that's a lot quieter, tolerates being held and stroked more and doesn't bite without warning as much. Anyone know of any species like this? Thanks. --90.240.248.51 20:57, 18 September 2007 (UTC)

Don't forget to investigate whether your two pets will get along well. It sounds like there is a risk the Sun Conure might attack any new pet. Also, while I've never kept birds as pets, I would presume that as with most pets their temperaments can be quite variable. Although certain breeds may be much more docile, there is no guarantee the temperament will be what you want. You might want to consider adopting an adult from someone who has kept the bird for a while and say knows the temperament Nil Einne 21:11, 18 September 2007 (UTC)

Yep, temperament varies from parrot to parrot - though in my experience, most of them are prone to fits of pique (i.e. sudden biting) if you unwittingly annoy/scare them. The fight/flight response is never too far below the surface in these birds. I've heard that Bourke's Parrots and Lineolated Parakeets are generally pretty calm and quiet as far as psittacines go - but it's all relative. Don't get a Lovebird - it's a complete misnomer. As scrappers and biters go, they're right up there (don't let the cuteness fool you). Separate cages for the Conure and your new bird are a must - at least at the beginning. --Kurt Shaped Box 21:29, 18 September 2007 (UTC)

Color of beta-Carotene

I noticed that beta-carotene is used to color margarine and vanilla ice cream - which are yellow, not orange like carrots which are said to get their color from beta-carotene. Does anyone the real color of beta-carotene? Icek 22:31, 18 September 2007 (UTC)

you can use this to find the exact color of beta-carotene

http://www.ch.ic.ac.uk/wiki/images/0/0d/SpectraCarotene.jpg —Preceding unsigned comment added by 12.217.199.246 (talk) 23:10, 18 September 2007 (UTC)

Carotene, like many other complex pigments, has different colors at different concentrations. "Carotene is a common ingredient used in commercial colored oleomargarine to impart a yellow color. A typical useage level is five (5) milligrams beta-carotene per pound of oleomargarine, or 0.0011%. At this level, the color is light yellow. At 0.011% the color is still yellow. At 0.11%, the color is orange-brown and at 1.1%, the color is reddish-brown." [6] —Keenan Pepper 02:58, 19 September 2007 (UTC)

An interesting side note is that for many years it was illegal in most places to color margarine yellow (thanks to dairy industry lobbying), and in some places they even forced producers to dye it some unappetizing color. --Sean 16:27, 19 September 2007 (UTC)

The things one can learn around here! "Bootleg colored margarine became common, and manufacturers began to supply food-coloring capsules so that the consumer could knead the yellow color into margarine before serving it." margarine#History. DMacks 00:33, 20 September 2007 (UTC)

Hang on, vanila ice cream is white...not yellow

Depends what type you buy, here in the UK it's invariably yellow. Capuchin 10:59, 21 September 2007 (UTC)

September 19

Is this what it appears to be?

Just seen this video. Is this actually a gull seeing a female mallard being attacked (raped?) and deciding to intervene and save her? Hmmm. Opinions? --Kurt Shaped Box 00:17, 19 September 2007 (UTC)

Rape is a form of assault where one individual forces another to have sexual intercourse against that person’s will. I don't think rape really applies outside of humans. Lanfear's Bane 09:31, 19 September 2007 (UTC)

An interesting little scenario. The little I know about gulls leads me to believe that their goals in life are driven by food, territory, food, sex and food. (depending on the time of year) The setting here is some sort of pond or lake where the birds are obviously habituated to human presence and thus probably are used to human food handouts. I think the gull is more interested in the possibility of free food which she/he thinks might be available within the scrabble of bodies. Even the Canada goose has a gander. (ooh, pardon my pun!) I have noticed in places like this where there are largish numbers of birds all looking for a bit of free fodder, whenever there is a bit of a kerfuffle or argy-bargy between a couple of birds all the others tend to gravitate to that point as they maybe associate it with the frantic activity involved in filling your gizzard before anyone else and thus the presence of food.

It also crossed my mind that the gull may have been looking to take the opportunity to finish the stricken duck off itself and dine on some fresh meat. I've seen gulls mercilessly (mercifully? I don't think that the gull really cares either way) dispatching injured pigeons on several occasions. --Kurt Shaped Box 12:48, 19 September 2007 (UTC)

With regard to the the above comment about rape only being a human concept, mallard rape has been referred to for many years and is characterised by the absence of precopulatory behaviour normally seen in these birds and by the additional perceived reluctance of the female to engage in copulation evidenced by her attempts to escape. What is more interesting is that this behaviour often stimulates other nearby males who attempt to join in. Look at this http://elibrary.unm.edu/sora/Wilson/v092n03/p0409-p0409.pdf for further information.Richard Avery 10:17, 19 September 2007 (UTC)

Still, as this does not involve humans it cannot be categorised as rape. Neglect to perform a mating ritual before copulation does not constitute rape. As for other male mallards joining in to classify this as mallard gang rape is bordering on ridiculous. Sounds like we are straying into the realms of anthropomorphism on this topic. Lanfear's Bane 10:32, 19 September 2007 (UTC)

Assumming an animal has the cognitive skills to form an intent to have sex (or not), then in my opinion, rape can exist in that species. Obviously most animals can't tell us their intent, but we can make an educated guess based on behavior, and some animals (e.g. primates, some birds, and dolphins) have mastered enough basic language skills to directly communicate simple desires. 76.231.189.193 17:33, 19 September 2007 (UTC)

Language isn't really required. If the female sticks her rear end up and waits, she's giving consent. If she runs away, she's not. Pretty simple. StuRat 05:49, 20 September 2007 (UTC)

I remember reading about the mallard rape. It did raise a lot of questions as to whether "rape" can occur outside of Homo sapiens. I guess it comes down to whether murder, theft, incest or other human crimes also count. You can find equivalents in nature of many human crimes. This really isn't a Science question but rather Ethics. -- JSBillings 11:49, 19 September 2007 (UTC)

I wish that I hadn't mentioned the 'r-word' now. I didn't mean to start another one of these circular debates... :( --Kurt Shaped Box 12:39, 19 September 2007 (UTC)

My take on the use of 'rape' is that in this context it is an ornithological term to describe a specific pattern of behaviour which appears analogous to the human activity of this name. My sympathies KSB, like Forrest Gump said "Life is ..... Richard Avery 18:15, 19 September 2007 (UTC)

If you, as a human had seen that happening in front of you, you'd have tried to stop it, wouldn't you? Because preventing cruelty and suffering would be the right thing to do if it was within your power to prevent it. Are we that arrogant as a species that we really do believe that we are the only ones with views on what is acceptable and unacceptable? —Preceding unsigned comment added by 84.71.180.141 (talk) 19:39, 19 September 2007 (UTC)

Well I will be very interested when this case hits the duck courts to hear the outcome. How do you punish a duck anyway? Are duck judges severe? As for animals 'desiring' and 'consenting' these are again human emotions and actions. They do not exist outside in the animal kingdom. It's not a case of being so arrogant that humans believe their views are the only acceptable ones - it is however a form of arrogance to project human qualities onto animals and label their actions or instincts with human terms and equivilents. It also doesn't come down to ethics, again, these are human traits. Rape does not exist outside of humans. Or, if I am wrong, feel free to bring one of these thinking, talking, feeling, desiring ducks to me to explain duck law in regard to rape and then I will retract all of my recent comments. Lanfear's Bane 09:33, 20 September 2007 (UTC)

So the only way you'd accept that any animal has thoughts, feelings, desires or agency independent of some kind of mechanistic "instinct" is if it could articulate these qualities to you in English? Hmmmm, talk about arrogant. Maybe you could learn sign-language and find a signing chimp to communicate with, meet 'em halfway... 38.112.225.84 15:02, 20 September 2007 (UTC)

Chemical Nomenclature

When considering the hydrogen in a bond, is it treated like a non-metal or a metal? For example, with the compound HF, would it be called "Hydrogen fluoride" (ionic conjugation) or "Hydrogen monofluoride" (covalent conjugation)? Thanks. Acceptable 01:57, 19 September 2007 (UTC)

Hydrogen is named as a metal in compounds with a more electronegative element (for example hydrogen fluoride) and as a non-metal in compounds with a less electronegative element (for example sodium hydride). —Keenan Pepper 02:24, 19 September 2007 (UTC)

Quantum physicist's name?

Someone suggested that I should look into the work of a certain quantum physicist, but now I can't recall the scientist's name. All I can remember is that it sounded something like Muset or Mussay, but I'm not sure. I looked on the list of physicists and no one there sounds like the right one. I know it isn't Harrie Massey or Amédée Mouchez — I was told this man was a contemporary of Star Trek creator Gene Roddenberry. (I hope I'm not waaaaay off on the name, but it's possible!) Thank you kindly. — Michael J 02:25, 19 September 2007 (UTC)

Could maybe be Albert Messiah (last name pronounced roughly mess-ee-yah, not messEYEah)? He wrote a standard graduate or advanced-undergrad text on QM, I think. --Trovatore 02:31, 19 September 2007 (UTC)

Maybe it could be a first-name, Murray Gell-Mann? --Taktser 04:25, 19 September 2007 (UTC)

Archaea or Bacteria, which came first?

Greetings! I finished reading the articles archaea and bacteria, but I still have a doubt as to which domain appeared first on our planet? From what I can gather, the species of the domain archaea tend to be hyperthermophiles living near geysers, that Earth during the Archean eon was much warmer than today, that species adapted to survive at lower temperatures evolved later than the hyperthermophiles, and that the species of the domain bacteria can adapt to a much wider range of temperature environments. Would this mean that archaeon appeared before bacterium? In the article archaea it also states that the archaea are more closely related to the more advanced eukaryotes, would that mean it was bacteria first followed by archaea? Thanks in advance! --Taktser 04:07, 19 September 2007 (UTC)

I think there is no conclusive evidence for one or the other. Studying different genes suggest a lot of gene swapping occured and there is no simple tree structure of organisms. There are more than just extreme thermophiles! Graeme Bartlett 12:30, 19 September 2007 (UTC)

As far as I'm aware, archaea are usually believed to be more closely related to eukaryotes then bacteria. I.E. bacteria diverged first. However I don't know whether there is really an answer to which appeared first. It's a bit like asking which appeared first humans or chimpanzees (or orangutans or something)? The answer is neither since both are modern species. It will depend on your definition of what's a human and what's a chimpanzee. Nil Einne 20:11, 19 September 2007 (UTC)

What is the long term result of electrolysis of water?

During electolysis of water stand alone hydrogen and oxygen gas are split from the water compound. My question is what happens to these gases after this? Can they ever get together again? Or is the process which occurs everywhere lead acid batteries are used, especially in motor vehicles, reducing the global supply of water and accelerating droughts and climate change generally?Vorc 04:57, 19 September 2007 (UTC)

From Hydrogen: "In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by identifying the gas from a metal-acid reaction as "inflammable air" and further finding that the gas produces water when burned."

Another word for burning is combustion:

"A simpler example can be seen in the combustion of hydrogen and oxygen, which is a commonly used reaction in rocket engines:

2H
₂ + O
₂ → 2H
₂O + heat

The result is simply water vapor."

See also Fuel cell, in which hydrogen can be oxidized to produce electricity and water.

(ec)They can get together again. Actually, if you put hydrogen gas and oxygen gas together at room temperature, they will spontaneously reform water. This is a slow process however, unless you provide some spark for the reaction to speed up, in which case you might get something like The Hindenburg. Someguy1221 05:07, 19 September 2007 (UTC)

This was one of my science teachers favourite tricks. As far as I recall, we mixed oxygen and hydrogen in a tin can, pressed the lid on, and somehow ignited it. There was a bang, the lid flew off, and inside the can were a few drops of water.--Shantavira|^{feed me} 07:23, 19 September 2007 (UTC)

Please be careful or people might copy your bad memory... The Hindenburg was lots of nitrogen from the atmosphere to slow things down. If you mix pure hydrogen and oxygen together in a tin you have got a potential gas detonation on your hands which is potentially seriously dangerous (to your hearing in particular)>> some people do it in a balloon but I still wouldn't recommend it. The tin can trick is normally to fill the can with hydrogen (or methane) and light the gas diffusing out of a small hole: you get a brief flame because the mixture in the can is too rich to burn but then enough air gets into the can to mean the flame goes back into the can. Heat generated increases pressure and unless the tin lid can keep about 8 bar in (no, it cannot) you get a loud pop. Any, not the pure gases (the oxygen comes with the rest of air). --BozMo talk 11:42, 19 September 2007 (UTC)

The Hindenburg wasn't helped by the flammable chemicals that they used to paint the thing - if the problem had only been the hydrogen, it would have been a much smaller problem. Hydrogen (being very light) would have carried the fire upwards and away from the passengers and crew - and that would have prevented all of the gas-filled cells from burning, allowing the craft to drift more slowly towards the ground. The flames you see in that infamous newsreel are far too luminous to be hydrogen flames - what you are seeing is the envelope burning. Indeed only about a third of the people on board died - most of those because they jumped from the gondola - the remainder being crew members up at the nose of the craft. Every person who stayed on board inside the gondola, survived. It's unfortunate that this was such a notorious event because a properly designed hydrogen-based Zepplin is a perfectly reasonable aircraft that would be vastly cheaper to run than modern helium-based craft. With modern materials for the gas bags - proper monitoring of oxygen levels inside those bag - construction techniques to isolate a disaster in one gas bag from destroying the others in a chain-reaction - and control of arcing due to static buildup, there is no reason why we couldn't still fly craft like the Hindenburg with at least the degree of safety that we fly jumbo jets. SteveBaker 14:15, 19 September 2007 (UTC)

I disagree. The main safety risk of blimps, dirigibles, zeppelins, and hot air balloons (or any other lighter-than-air craft) is that they can't be controlled in strong winds, which are common and not always predictable. The risk from containing an explosive gas is secondary to this risk. (I do agree that hydrogen-filled craft are not as dangerous as they appear, however.) StuRat 03:23, 20 September 2007 (UTC)

I agree that wind is a major issue when these gizmos are close to the ground - but they have so many advantages in some applications that this problem can be worth circumventing. Forget about carrying passengers - think about freight. Ships are an efficient way to carry goods around the world - but you run into trouble when there are no convenient oceans nearby. Replace a ship with a truly gargantuan airship and suddenly that restriction has gone away. The dramatically smaller drag factor in moving through air rather than water should make airships cheaper to operate and a lot quicker too. But yes - landing and taking off again is a tricky thing (but then so is docking a ship in a heavy current). Lowering cables to the ground and winching the thing down seems like the smart solution. There are also applications for airships in replacing communications satellites and terrestrial radio antennae. The relative cheapness of Hydrogen compared to Helium - and the vastly improved lift capability per unit volume is what is needed to make these things economically feasible - but the "Hindenburg factor" means that nobody wants to invest money in them...which is a shame because the problems that caused the demise of the Hindenburg are easily overcome. Also, only about 36 people and two dogs died in the accident - two thirds of the passengers and crew survived - compared to the 89 that died (just 30 survived) in an MD-80 airliner as it attempted to land in Bangkok a couple of days ago. I guarantee that the Hindenburg disaster will be remembered around the world 100 years from now - but One-Two-GO Airlines Flight 269 will largely be forgotten in...well, come to think about it, I think it's pretty much already been forgotten everywhere outside Thailand. SteveBaker 14:03, 20 September 2007 (UTC)

When you electrolyse water with direct current electricity, you get oxygen coming off of one of the electrodes and hydrogen coming off of the other. This enables one to capture the hydrogen safely without oxygen mixed into it - and if you do that, there is no immediate danger of the gas exploding. SteveBaker 14:15, 19 September 2007 (UTC)

Most of the hydrogen and oxygen will eventually become water again. However, some of the hydrogen may rise to the upper atmosphere and be blown away from the Earth by the solar wind. Of course, nobody would be able to convert enough water to hydrogen and oxygen for this to have any noticeable effect. However, if they could, we would eventually have more oxygen in the air and less water in the oceans, yes. StuRat 03:33, 20 September 2007 (UTC)

It is important to note that there is a very large activation energy for the combination of H2 and O2. Without an ignition source the reaction is very slow — Preceding unsigned comment added by Shniken1 (talk • contribs)

Wouldn't lightning provide the needed activation energy ? StuRat 04:33, 21 September 2007 (UTC)

With deep-cycle lead-acid batteries you can use caps with a catalyst (platinum?) that reforms the gases into water, so that the batteries need less water added later.Polypipe Wrangler 15:08, 20 September 2007 (UTC)

Methanol and Ethanol

If ethanol is used to treat methanol poisoning, is it possible to mix the two at a ratio so that it's no longer toxic (as in methanol toxic)? --antilived^{T | C | G} 05:15, 19 September 2007 (UTC)

Get it into your thick head. Ethanol is poison. Methanol is poison. A mixture of ethanol and methanol is poison. Ever wonder what happens to young people when they drink a lot of alcohol? That's right, they get alcohol poisoning. So whether you drink ethanol or you drink methanol, you are putting poison into your body. The idea that you can mix ethanol with methanol and come up with a solution which is "no longer toxic" is utter rubbish. 210.49.155.132 13:20, 19 September 2007 (UTC)

Yes - agreed. Methanol is horribly toxic - it causes blindness in even quite small doses. Ethanol is less toxic - but it's still nasty stuff in high concentration. If you have life-threatening methanol poisoning then ethanol (being the lesser of two evils) might save your life (but probably not your eyesight)...but the idea that these two poisons somehow cancel out is ludicrous. SteveBaker 13:55, 19 September 2007 (UTC)

I think the question antilived was trying to ask was whether you could create a mixture of the two so that the methanol poisoning would be "treated" by the ethanol consumed with it. From what I can understand from this website [7] Methanol is toxic because it is broken down by the enzyme alcohol dehydrogenase in the liver to form formic acid and formaldehyde. Ethanol in large quantities is administered to a methanol poisoned patient because it will compete for the enzyme with the methanol. This slows down the metabolism of methanol allowing doctors to haemodialysis it away or clear the body through the kidneys (which occurs much slower than being broken down in the liver). Just drinking a mixture of ethanol and methanol is not enough because some of the methanol will still be metabolized in the liver, just over a longer period of time, meaning you are still going to be poisoned. You could try to design the solution so that the amount of methanol metabolized would be minimal and would avoid side affects, but since everyone's body chemistry and alcohol metabolizing ability are different it would be difficult to predict the severity of the poisoning. **DISCLAIMER:** I am not an expert, and trying this would be REALLY REALLY REALLY dumb. Sifaka ^talk 15:27, 19 September 2007 (UTC)

Actually the idea that these two cancel each other out is about the easiest explanation you could give to someone who doesn't understand how methanol poisoning works. Methanol in and of itself doesn't cause the toxic effects. The effects come from byproducts of the breakdown of ethanol in the liver (by the enzyme alcohol dehydrogenase). These cause initially blindness, but it is not necessarily permanent. If treated with ethanol, the ethanol competes with the active site of the enzyme and is broken down into harmless by products. You could probably handle an intake of ~100 times more ethanol than methanol depending on how much methanol you have in you system (which would at least reduce the break down of methanol by a factor of 10^2). This does not take into account the fact that alcohol dehydrogenase has much more affinity for ethanol than methanol. So you can essentially stop the breakdown of methanol into toxic molecules by drinking/injecting enough ethanol. Then methanol is removed only by the kidneys (like 10000:1 Kidneys:Liver) and viola no lasting effects if caught early. If someone had a serious case of methanol poisoning, you really wouldn't be worried about their sight anyway. You would be more worried about keeping formic acid and formaldehyde out of their blood and lungs.
Now I'm certainly not suggesting that it is as simple as getting drunk. You need to go to the hospital so your vital signs can be monitored. CNS depression from both alcohols can cause bradycardia and hypoxia, but this would be easily compensated for in a hospital setting.
And if at this point your still thinking, "But ethanol is toxic too!?" Well, in terms of toxicity, methanol is an F5 tornado and ethanol is a dust devil. The risks of this treatment are essentially negligible in comparison to the almost certain death of someone with a serious case of acute methanol poisoning.
There was apparently an editing conflict.
Mrdeath5493 15:29, 19 September 2007 (UTC)

Ethanol is not some sort of cure that neutralizes all effects of methanol rendering it harmless - you're thinking like it's some sort of acid base reaction, it's not.87.102.116.240 16:36, 19 September 2007 (UTC)

Why are there suddenly so many questions about ethanol being used to treat methanol? — Daniel 22:24, 19 September 2007 (UTC)

You read stuff here and it makes you think of other, related stuff to ask that you never, ever thought that you wanted to know before? --Kurt Shaped Box 22:58, 19 September 2007 (UTC)

Perhaps they are writing a fiction book and need a "home cure" for methanol poisoning ? StuRat 04:56, 20 September 2007 (UTC)

I thought my explanation was pretty clear, but obviously I'm talking over your heads. It is true that ethanol doesn't immediately neutralize methanol's toxic properties, but you really wouldn't know the difference by observing someone being treated with ethanol for methanol poisoning. It will make them better, almost immediately. Even if there was permanent damage, proper treatment will pretty much completely reverse the course of the pathology within 36 hours. There is only one other option for treating methanol poisoning and it is Fomepizole. I live in Arkansas and know for a fact that there are regional ER's that protocol ethanol as a remedy. Sorry to everyone out there that thinks they know what they are talking about, but this treatment works, very well.
Mrdeath5493 05:51, 20 September 2007 (UTC)

But that wasn't the question. What was asked was whether you could mix them from the start in such a way that the methanol wouldn't poison you. The treatment you're talking about requires administration of ethanol on an ongoing basis, until the methanol is out of the system; it's not good enough, I think, to give one dose up front.

All the more so if, as you said, "alcohol dehydrogenase has much more affinity for ethanol than methanol". Because that means the ethanol will get used up, and the body will make more alcohol dehydrogenase, and now the methanol is still around to be turned into formaldehyde (kidneys haven't had time to get rid of it), and the ethanol isn't there to prevent it anymore. --Trovatore 21:07, 20 September 2007 (UTC)

Trovatore, other than being completely wrong in your assumptions you are right. Notice the words "proper treatment" above. One dose probably wouldn't do it. The obvious solution is to add more ethanol (if what was there is gone). Normal saline + diuretic rings a bell too (increased action of kidneys). Also, dialysis can be used. I'm pretty sure that any competent Physician understands the basic concepts of biochemistry anyway.
Mrdeath5493 21:41, 20 September 2007 (UTC)

I don't believe you carefully read the original question. --Trovatore 21:46, 20 September 2007 (UTC)

Well, I don't think you read the Science help desk every day. There have been 2 other similar threads to this one and if read chronologically, you obviously see that most of the users that usually answer questions on the desk don't think ethanol is a good treatment. So, I decided to do some extra homework. Here is a Quote from Current Medical Diagnosis & Treatment. 2007. Stephen J. McPhee et al.

Treatment [for methanol poisoning]

Emergency and Supportive Measures

For patients presenting within 30–60 minutes after ingestion, empty the stomach by gastric lavage (see Antidotes & Other Treatment-Gastric Lavage). Charcoal is not very effective but should be administered if other poisons or drugs have also been ingested.

Specific Treatment

Patients with significant toxicity (manifested by severe metabolic acidosis, altered mental status, and markedly elevated osmolar gap) should undergo hemodialysis as soon as possible to remove the parent compound and the toxic metabolites. Treatment with folic acid, thiamine, and pyridoxine may enhance the breakdown of toxic metabolites.

Ethanol blocks metabolism of the parent compounds by competing for the enzyme alcohol dehydrogenase. The desired serum ethanol concentration is 100 mg/dL. To achieve this, administer a loading dose of approximately 750 mg/kg orally or in a dilute intravenous solution (available from the pharmacy in 5% and 10% solution), and then provide a maintenance infusion of 100–150 mg/kg/h. The infusion will have to be increased to about 175–250 mg/kg/h during hemodialysis to replace dialysis elimination of ethanol.

Fomepizole (4-methylpyrazole; Antizol), blocks alcohol dehydrogenase and can be used instead of ethanol. A regional poison control center (800-222-1222) should be contacted for indications and dosing.

My regional poison control office just happens to be on the same floor as the college of pharmacy I attend. They said they recommend ethanol...Imagine that.
Mrdeath5493 22:03, 20 September 2007 (UTC)

If you read the threads carefully you'll see that few posters have said otherwise. There was one anon who said "ethanol DOES NOT treat methanol poisoning" but then immediately contradicted himself. Everyone else has argued against other aspects, such as injecting a non-medical-grade spirit or trying to make methanol "safe" by including enough ethanol with it. --Trovatore 22:46, 20 September 2007 (UTC)

So I should probably just pretend that you didn't offer an opinion directly contradictory to mine 5 posts up? All that stuff about ethanol leaving the system and methanol breaking down faster... If you hadn't, of course, I would not have pushed my point. On top of the doubts you raised earlier concerning my position, I was referring to this specific comment
"Ethanol is not some sort of cure..."
You are correct in your analysis of the previous posts; almost no one contradicts me there. It does seem, however, that the people who initially said something to the effect of "Treating methanol poisoning with ethanol is stupid..." have retroactively erased their initial statements or just edited them. So, I guess I am preaching to the choir even now.
Mrdeath5493 01:05, 21 September 2007 (UTC)

You shouldn't pretend anything. I never said ethanol was not a treatment for methanol poisoning. I said you couldn't drink a mixture of ethanol and methanol and expect the ethanol to protect you. If you read my comments otherwise, you read them wrong. --Trovatore 01:15, 21 September 2007 (UTC)

So this:
"the ethanol will get used up, and the body will make more alcohol dehydrogenase, and now the methanol is still around to be turned into formaldehyde (kidneys haven't had time to get rid of it), and the ethanol isn't there to prevent it anymore."
was in reference to a mixture of eth/meth in a glass and not about treating methanol poisoning?
My bad.
Mrdeath5493 01:34, 21 September 2007 (UTC)

Purpose of review articles from writer's perspective

Apparently scientists not working for a corporation have to publish in order to recieve grants. Does the publishing of review articles count towards this? If not, why do people write them? --Seans Potato Business 15:25, 19 September 2007 (UTC)

Publishing a review (depending on what it is) can count towards 'recognition' but won't really help to get grants (which need evidence pf original research usually).

However like all published written work payment is usually included.

Plus maybe they just like writing reviews - I'd do that for nothing on a topic that interested me.87.102.116.240 17:07, 19 September 2007 (UTC)

Surprising though it may seem, scientists actually do science - they don't just seek grant money. Publications are there to move science along - not just to get grant money. If publishing a review will help people to get closer to whatever it is they are working on - then writing one is a valuable use of a scientists time. Grants are a means to an end - they aren't the goal of science! (Although sometimes it seems like that). SteveBaker 17:53, 19 September 2007 (UTC)

"However like all published written work payment is usually included." Really? I've never paid nor gotten paid for journal articles. Maybe in some fields or some journals, but certainly the minority in the sciences I know. DMacks 18:20, 19 September 2007 (UTC)

I meant book reviews rather than literature reviews in journals.87.102.116.240 18:29, 19 September 2007 (UTC)

Further to DMacks, the authors often pay a "per page charge" to have articles published or to have colour figures. -- Flyguy649 ^talk _contribs 18:27, 19 September 2007 (UTC)

Note that when they do pay, it will usually be mentioned at the end of the article Nil Einne 20:03, 19 September 2007 (UTC)

When it comes to writing review articles, remember that this requires them to familiarise themselves with the literature and the work they're reviewing. While most scientists writing reviews AFAIK usually work in that specific area already so would already be fairly familiar with the literature, I suspect they would still learn something out of the process. Remember one of the best ways to test how well you understand something is to try and teach it. It may also be an opportunity for them to consider things to teach at university. Writing reviews aren't the only things they do for 'free'. Peer reviewing journal articles is also something most experienced scientists will do but they aren't paid for it. It's considered part of being a scientist. This is actually covered fairly well in Peer review Nil Einne 20:03, 19 September 2007 (UTC)

From a more political (and perhaps cynical) perspective, scientists will often have different hypotheses about scientific fields. Similar data can be interepreted in different ways and an experienced scientist may have a number of papers published in a field that supports one hypothesis, while another scientist may have a body of work that supports a conflicting interpretation. Review articles can help "sway" the scientific consensus towards one of these interpretations. Its no co-incidence that review articles will often contain many, many citations of the author's own original research papers. In a recent review (PMID 15985310) I read, 42 of the 113 citations were by the authors of the review. This has the added bonus of boosting the the impact factor of the journals the authors have published in, and the authors' own H-indices. Rockpocket 21:31, 19 September 2007 (UTC)

Regarding specifically whether you get "credit" for review articles: In my institution, which is a government lab, we have specific minimum requirements for number of original research papers per year. For us, review articles don't count towards this. ike9898 17:25, 20 September 2007 (UTC)

Developmental term I have forgotten

In some organisms, the presence and subsequent contact with of a large number of peers triggers a developmental change causing the individual to become larger than its peers and engage in cannibalistic behavior. I forget what it is called. Any ideas? Sifaka ^talk 15:32, 19 September 2007 (UTC)

Can you suggest one or two species that do this? It might make the search a little easier. SteveBaker 17:48, 19 September 2007 (UTC)

Sorry, I can't remember any in particular, although I think some examples were fish or lizard-shaped amphibians. I read about it so long ago... Sifaka ^talk 18:32, 19 September 2007 (UTC)

GOT IT!!! Cannibalistic Polyphenism It's now a redirect to polyphenism for now... Sifaka ^talk 19:14, 19 September 2007 (UTC)

I changed it to a redirect to the Cannibalistic Polyphenism section of polyphenism. — Daniel 22:17, 19 September 2007 (UTC)

Basic Axioms of Physics

I read somewhere that you could write the basic axioms of physics, which would describe much of the universe around us, on a single index card. I assume that by axioms, the meant the fundamental underlying assumptions. So, 1. Is this true? and 2. What would these axioms be? Czmtzc 20:29, 19 September 2007 (UTC)

I wouldn't really use the term 'axiom' with 'physics'. The axioms of arithmetic or euclidian geometry could certainly be expressed in so little space - but physics is about measurement and experiment. The idea of something being so self-evident that you don't need to prove it is kinda alien to that concept. Perhaps you don't mean 'axiom'...the basic equations of physics are certainly fairly compact - and indeed some physicists suggest that we can finally boil a 'theory of everything' down to an equation that you might fit in so little space - but that's the opposite of an axiom.

As an example, here are the axioms around which all of Euclidean geometry is based:

1. Any two points can be joined by a straight line.
2. Any straight line segment can be extended indefinitely in a straight line.
3. Given any straight line segment, a circle can be drawn having the segment as radius and one endpoint as center.
4. All right angles are congruent.
5. Parallel postulate. If two lines intersect a third in such a way that the sum of the inner angles on one side is less than two right angles, then the two lines inevitably must intersect each other on that side if extended far enough.

SteveBaker 20:52, 19 September 2007 (UTC)

• This might be relevant: Hilbert's sixth problem. --JWSchmidt 21:02, 19 September 2007 (UTC)

We do sometimes use "axiom" in physics to mean the fundamental equations that define a particular theory. For instance, you could say that the Schrodinger equation is an axiom of non-relativistic quantum mechanics. You don't prove it in a mathematical sense, you prove it by empirically confirming the predictions of quantum mechanics. I would choose the Einstein equation and the standard model lagrangian. You could write them both on an index card, if you have small handwriting for the standard model lagrangian! --Reuben 21:26, 19 September 2007 (UTC)

In so far that mathematical axioms are considered to be "true" they are empirically derived, just like physical axioms. They are also based on measurement; counting for example is clearly a measurement procedure. The predicitons of the "addition" axiom can be empirically tested by counting. Just count two heaps of apples, put them together, count again, and compare with the prediction by addition. You see - mathematics *is* physics. —Preceding unsigned comment added by 84.187.37.196 (talk) 22:21, 19 September 2007 (UTC)

I'm not sure a pure mathematician would agree with you. I think they would argue that arithmetic is a set of theorems that depend on the axioms and the axioms are just assumptions built into the thing at the beginning. If, as a result, addition appears to be applicable to the problem of counting things in the real world then all well and good - but the math doesn't depend on it. Notably, the axioms of Euclidean geometry that I posted earlier are not things that are necessarily true in the real world. Mathematicians have a lot of fun by denying one or other of the axioms - or negating one altogether and seeing what pops out. Denying Euclids parallel postulate results in all sorts of interesting non-Euclidean geometries that are interesting but do not necessarily represent 'real world' stuff. In fact, in normal 3-space in our universe, several of those postulates aren't true because of the bending of space-time due to gravity. That in no way invalidates any of Euclids theorems because they only apply in the event that you assume the axioms are true. SteveBaker 22:31, 19 September 2007 (UTC)

As a pure mathematician myself, I suggest the axioms of ZFC (especially replacement and choice) as an antidote to the idea that all mathematical axioms are closely derived from physics. While some would still argue that all mathematics is empirical in nature, most of it has to be extremely indirect. Algebraist 22:57, 19 September 2007 (UTC)

There is a fundamental difference of opinion among pure mathematicians on this point. Oversimplifying wildly, there are two basic schools, the "realists" (or "Platonists"), and the "formalists" (in which camp, just for now, I'm including fictionalists and people like George Lakoff). For a realist, mathematical objects are real (though non-physical) objects, and axioms are not arbitrary but are supposed to describe those things. For example ZFC should describe the von Neumann hierarchy (note that the von Neumann hierarchy is much more intuitively "natural" than ZFC itself). I lean to the realist school myself, and would argue that there is an empirical component to the discovery of axioms, particularly where it comes to things like large cardinals. --Trovatore 23:09, 19 September 2007 (UTC)

Hmmm - interesting! So do you assert that it is somehow wrong to pick a set of axioms that don't match reality and then attempt to prove theorems based on them? Is it perhaps merely so pointless that you don't think it's worth doing? Or are you just saying that the standard set of axioms around which most of mathematics is based is based upon 'reality'? SteveBaker 13:39, 20 September 2007 (UTC)

A little bit of 2, but mostly 3. Certainly there's nothing "wrong" with investigating the consequences of arbitrary axioms, and once in a while it even turns out to lead somewhere. But the importance of the axiomatic method as a whole is somewhat overestimated by most interested outsiders and even a lot of mathematicians. Most proofs are not really axiomatic per se. We tell ourselves that we could, if we had to, convert them into axiomatic proofs by routine methods, and this is probably true, but is almost never actually checked. --Trovatore 17:18, 20 September 2007 (UTC)

OK - I'll buy that. It's a pretty reasonable stance. But we know that not all theorems are provable - but we try to build new theorems on top of older ones that we 'know' were correctly derived from yet older ones - and somewhere at the bottom of the whole pile are a handful of axioms that we can't prove. The iffy part happens if you are pretty certain that some unproven theorem is true - and therefore rely upon it. This effectively introduces another axiom - but one that you hope can be removed at a later date. The only question is whether you argue that those axioms are some kind of self-evident 'truth' or whether you say "this huge pile of theorems is only true if you assume these axioms are true". My view is that the former is a bit limiting because it prevents you from doing things like denying Eulers parallel postulate (even though you generally believe it to be a self-evident truth) - and thereby figuring out non-Euclidean geometry - which would be a shame because it subsequently became very useful in other areas. On the other hand, denying that 1+1=2 might well generate a huge pile of interesting theorems - but if none of them apply to reality, what's the point? Both ways are relevent. SteveBaker 20:03, 20 September 2007 (UTC)

If you want to model a solar system (which can't be modeled accurately with quantum physics) down to the atom (which can't be modeled accurately with general relativity) you'd have to use a theory of everything. As far as I know, any of them can model the universe relatively accurately. No computer is powerful enough to run such a model, and I don't think it's even theoretically possible to make one that can, as it would be modeling itself, but that wasn't your question. — Daniel 02:57, 20 September 2007 (UTC)

It's not always necessary to model the entire universe - there is merit to using a theory-of-everything in order to model something simple. But it bothers most people to have to pick the set of fundamental laws (relativity or quantum theory) depending on the nature of the thing they are trying to figure out. There are cases (such as the Hawkings radiation from a black hole) that are simple enough to simulate in a computer and which require both sets of laws - and they don't agree. The consequences of picking the wrong set of theories in order to solve a particular problem is to get the wrong answer. So there is certainly merit in seeking the theory-of-everything - if only as a way to fix these corner-cases. SteveBaker 13:40, 20 September 2007 (UTC)

You can certainly write some axioms of some of the forms of physics on a card. But that wouldn't get you much. All of Special Relativity, for example, falls out of the following two axioms: 1. Galilean relativity holds for all frames of reference and all forces; 2. the speed of light is seen as constant from all frames of reference. Now that looks pretty simple but it took a lot of big brains (starting with Einstein, but others too) to figure out all of the implications of those two things and it takes a lot of explanation and extrapolation to show how inside those two, simple axioms are things like time dilation and length contraction. General Relativity can almost completely be summed up in the single axiom that gravitational acceleration can be described by the curvature of space and time, but knowing just that gets you almost nowhere in terms of actual physics or calculations.

It should be noted for historical purposes that both of the above are care of Einstein, and that Einstein was himself an explicitly axiomatic thinker, believing that if you started out with the correct axioms (and often a reexamination of simple concepts like "space" and "time" and "acceleration") then everything else would fall out. As an approach it worked very well for things like SR and GR but not well at all for things like quantum mechanics. --24.147.86.187 15:04, 20 September 2007 (UTC)

It sounds to me you may actually be asking for Hamilton's principle which arguably has the whole of physics in a single equation? --BozMo talk 16:30, 20 September 2007 (UTC)

September 20

Plant has its own division?

Apparently, there is one plant that has it's own division, does anyone know what this plant is? TheCoolestDude 13:35, 20 September 2007 (UTC)

Ginkgo biloba. Polypipe Wrangler 15:14, 20 September 2007 (UTC)

Our Ginkgo article agrees...although we should be careful to say that it's the only modern plant in that division, there must have been a number of others that are now extinct. It's likely that the modern Ginkgo is also extinct in the wilds - now only existing as a cultivated plant. SteveBaker 17:18, 20 September 2007 (UTC)

How can I jam a radio controlled car? (In the USA)

can I purchase a device that would jam my neighbors remote controlled car so he would use it elsewhere? his toy is causing problems for my dog as the sound aggravates her.

thank you

rob neal

irvine,ca —Preceding unsigned comment added by 216.154.252.184 (talk) 23:34, 19 September 2007 (UTC)

Someone into electronics correct me if I am wrong, but buying the same type of remote control car and using its remote should work because the two are on the same frequency. Personally I would talk to the neighbor about it first if possible, and if that fails try to move the dog elsewhere where the sound wouldn't bother her before going so far as to attempt to jam the remote controlled car. Another solution you could try if you can't get the neighbor to change his behavior would be to get a source of white noise for your dog. 71.226.56.79 00:36, 20 September 2007 (UTC)

Of course, it depends on the type of radio system. Some modern wireless systems are difficult to jam - especially with such a simple attack as a frequency tone jam. (For example, you can think of wireless mouse and keyboard - both are wireless systems but the communications protocol enables multiple access of some type or other. You should probably seek a non-technical solution to this, lest you escalate the conflict (or turn it into a systematic game of cat and mouse to see whose counter-counter-counter-measures are most effective). Nimur 02:42, 20 September 2007 (UTC)

On the other hand, if he can jam the radio secretly, then his neighbor may just think there's some type of interference and go elsewhere. For certain neighbors, even suggesting that they change their behavior may result in hostility, so that might not be the way to go.

I would think the first step is to find the proper frequency. Using some type of scanner when he uses his remote control might be the way to find the frequency (listen for some frequency where the sound changes when the car turns, for example). Then you would need something that jams that frequency. The car might use an adjustable frequency, though, in which case he might just go on to another. StuRat 03:11, 20 September 2007 (UTC)

The cheapest solution is to buy another radio controlled toy that operates on the same frequency. You'll of course need to find out the frequency it operates on...that would require some detective work. Most toys operate in the 27Mhz or 35MHz range. In the UK, I believe that only model airplanes are allowed to use the 35MHz band - in the US, it seems that both are used. However, within those two bands there are a dozen or more 'channels' - each at a slightly different frequency, you'd need to find the right channel. Some recent remote-controlled toys use infrared (like a TV remote) instead of radio - which will be almost impossible to 'jam' unless you are close to the toy at the time. SteveBaker 13:22, 20 September 2007 (UTC)

In the US, 27 MHz and 49 MHz are both common.

Atlant 16:18, 21 September 2007 (UTC)

You have overlooked the simplest route, beat him up and take it! That, or buy a faster one and run him off the road. Don't work harder, work smarter--Jmeden2000 15:29, 20 September 2007 (UTC)

Doggy issues aside, do bear in mind that generating "Malicious Interference" in the radio spectrum is a crime that the FCC doesn't appreciate much. Saturn 5 20:28, 20 September 2007 (UTC)

Holographic Lightsabre

Can a holographic projector be used to create a safe lightsabre blade? --Ecyrblim 01:09, 20 September 2007 (UTC)ecyrblim

Sure. But can that kind of holographic projector be made in the first place? — Kieff | Talk 01:13, 20 September 2007 (UTC)

Holograms only work when you're looking at them. You can't "project" an image of a blade from the hilt unless the hilt, the blade, and your eye are all collinear, which only happens when you're looking at the blade end-on. -- BenRG 02:46, 20 September 2007 (UTC)

But what they could do is have you hold the hilt of the "light sabre", and see your reflection in a "mirror" which has the light blade added. This would make for a nice illusion at an amusement park. They could even give you a movie of you with the light sabre (for a suitable fee, of course). StuRat 03:03, 20 September 2007 (UTC)

How about just a regular "bright and focused" light and a room with a lot of dust in the air? Light projects out of hilt, reflects off dust in its path. DMacks 05:40, 20 September 2007 (UTC)

The problem with that is making the light stop abruptly three feet from your hand...there is no way to do that without some physical object being in the way. FYI: in the early StarWars movies they filmed the lightsabres by using a solid tube covered with a 'retro-reflective' material that was lit by a light next to the camera. Since retro-reflectors reflect light back towards the source, you ended up with a bright reflection from the lightsabres with very little light reflected off of anything else. In the later movies they used computer graphics (of course). Trust me, if there were any way at all to make a 'real' lightsabre, the toy makers (or at least the StarWars fanatics) would have done so LONG ago. SteveBaker 13:16, 20 September 2007 (UTC)

Most sources I've read state that the light sabers were done by rotoscoping.[8]. DMacks 13:37, 20 September 2007 (UTC)

• Our lightsaber article says: The lightsaber first appeared in the film Star Wars Episode IV: A New Hope (1977). At first, the effect was created by a handle with a motorized spinning reflector and pointing high-intensity light in their direction. The outcome was not satisfying, so in post-production the effect was augmented through rotoscoping. For episodes V and VI the use of reflective tape was abandoned and the effect was achieved by rotoscoping rods made of aluminum and later carbon fiber rods. For the prequel trilogy, the effect was created using computer animation. I have read that in the original Star Wars, right after Darth Vader kills Obi Wan Kenobi, his lightsaber is the original retro-reflective white, rather than red. The rotoscopers missed that scene. No doubt the bastardized re-releases have it colored in. --Sean 15:43, 20 September 2007 (UTC)

• Oh, look! This video shows the shiny spinning saber: [9]. --Sean 15:52, 20 September 2007 (UTC)

Socks

Do they mainly were out from the inside or the outside? —Preceding unsigned comment added by 88.109.106.146 (talk) 03:47, 20 September 2007 (UTC)

They usually fail when my townails chop a hole through! So that would be inside. Graeme Bartlett 12:07, 20 September 2007 (UTC)

There's lots of variables to consider, including: How you wear them, e.g., only with shoes, or often just as socks with no shoes; the manufacture of the socks, e.g., whether they are lined, the quality of construction; personal hygiene, e.g., the length of toenails, how often and how the socks are washed. You'd need to define some of these before you could make any type of definite answer. --jjron 12:19, 20 September 2007 (UTC)

One hint, tube socks last longer because the heavy wear doesn't occur in just one spot, but rather in a ring, since you put them on in a different rotation each time. (They also avoid having the heel on the top of your foot when you get dressed in the dark.) StuRat 16:19, 20 September 2007 (UTC)

Engineering Projects

I have just begun with my first year of the four year engineering course in mechanical engineering... i was interested in making a research project... how do i start of?? I haven't a special interest in a particular field, i just follow a particular boom in the field.. as in nanotech,cad,automobile... how do i help myself out of this sitution developing an interest and the research part??? —Preceding unsigned comment added by 210.212.44.7 (talk) 06:32, 20 September 2007 (UTC)

You know, I was in a very similar situation once, and I eventually solved it by switching majors. Uh, but on a more helpful path, I went and found out what professors at my school were researching, and eventually found a project that just seemed really cool to me. I asked the guy, and he invited me on to the project. Someguy1221 06:43, 20 September 2007 (UTC)

So you have to decide on a research project in your first year? I don't think so. Wait until you need to decide. You'll have some ideas by then! —Preceding unsigned comment added by 88.109.4.191 (talk) 00:10, 21 September 2007 (UTC)

Aeroplane Speed -advantage when flying east?

Please consider: a) the earth ratates on its axis at around 2000 kmph b) two airplanes takes off at same time and from same point in opposite direction (east & west) and fly at same speed. c) whether the one flying east will have any advantage over the one flying west because of earth's rotation ? Or whether both the planes will return the same start point at the same time ? If so, why? —Preceding unsigned comment added by 59.182.61.89 (talk) 08:45, 20 September 2007 (UTC)

The planes are flying at the same speed relative to the atmosphere, so what is important here is to understand how the atmosphere moves relative to the surface of the Earth. At low levels (and ignoring local weather conditions) the atmosphere is carried around at the same rate as the surface (we don't experience continuous 2000 kph winds at ground level, do we ?). At higher levels in the atmosphere things become more complicated - see our articles on atmospheric circulation and the jet streams. Gandalf61 09:11, 20 September 2007 (UTC)

My physics teacher explained it that they sort of kept the motion of the earth with them, so their absolute speed included the rotation of the earth - therefore, relative to the earth below, they went the same speed, and if you take the rotation of the earth into account, they also have that same motion in that same direction at that same speed as part of their overall speed, so it cancels out. Which is why when you go up in a hot air balloon, you don't end up traveling laterally - you stay "stationary" because you're really still moving at the same speed as on the ground - the speed of the Earth. Kuronue | Talk 00:00, 22 September 2007 (UTC)

• When I visited the US last year, the plane took significantly less time to return home (east) than it took to get there. If you consider transatlantic travel at about 11 km, there's definitely an advantage. If only JFK wasn't congested at the time, I might actually have reaped the benefits of the whole thing... - Mgm|^(talk) 09:41, 20 September 2007 (UTC)

This is most likely the effect of the Jet stream rather than the rotation of the earth. -- JSBillings 11:50, 20 September 2007 (UTC)

In Australia it's generally considered a cross-country west->east flight (say Perth-Melbourne or Perth-Sydney) will commonly take around half-an-hour less than the same east->west flight (average flight time is about 4hrs). However the reason for this is the prevailing winds rather than the Earth's rotation. The flight speed is commonly varied to allow for the winds, rather than having the planes arriving at unexpected times due to varying winds. --jjron 11:57, 20 September 2007 (UTC)

Any east/west bias in travel time is entirely due to the prevailing wind. It's reasonable to say that the velocity of the aircraft over the ground is it's velocity through the air plus the wind velocity. The rotation of the earth only has an effect to the degree that the coriolis effect affects the winds. Mostly we have to be concerned with large scale weather patterns at a particular altitude (eg the Jet Stream). SteveBaker 13:07, 20 September 2007 (UTC)

Be sure you are measuring true elapsed time for the flights, not comparing starting and ending times in local time zones. It's even possible the arrive before you leave, if following time zones (have we discovered time travel here ? :-) ). StuRat 16:28, 20 September 2007 (UTC)

Any advantage from being carried east by planetary rotation is exactly nullified because the target point is carried east at the same rate. —Tamfang 21:25, 20 September 2007 (UTC)

Indirectly (at least in North America and over the North Atlantic; I haven't flown elsewhere). The prevailing winds blow from west to east, due to the rotation of the earth; that gives flights from west to east a boost in speed over flights from east to west. Look at flight times listed on airline schedules.Gzuckier 13:50, 21 September 2007 (UTC)

differentiator

what type of the wave form pattern we get in case of of differentiator? —Preceding unsigned comment added by Patelshiv (talk • contribs) 12:54, 20 September 2007 (UTC)

The differential of the input signal? —Preceding unsigned comment added by 88.109.4.191 (talk) 15:34, 20 September 2007 (UTC)

The wave form out depends on the input naturally, if the input is rising the output is poisitive, if it is falling the output is negative. If you look at it in the Fourier domain, the output is multiplied by the frequency, so the higher the frequency the more it is amplified, and the lower frequencies are reduced in level. The opposite is the integrator. Graeme Bartlett 11:22, 21 September 2007 (UTC)

A sine wave will turn into a phase shifted sine wave, a triangular wave turns into a square wave. A square wave turns into non physical alternating infinite pulses. Graeme Bartlett 11:31, 21 September 2007 (UTC)

Chest clicking. Not medical advice?

I'm just wondering what interaction is going on here. When I stretch my arms and chest (like the stereotypical tired stretch), I sometimes click something in the front centre of my chest. I'm assuming it's similar to cracking joints. But I don't know of any joint in the front center of my chest that it could be! Any ideas? Please feel free to delete if you still feel this constitutes medical advice. Capuchin 13:03, 20 September 2007 (UTC)

I click sometimes when lying on one side, I understand one of my false ribs is detached at the end. DuncanHill 13:06, 20 September 2007 (UTC)

I'm not going to give you medical advice. This is information relevant to the phenomenon to which you refer;-) Have a look at this http://upload.wikimedia.org/wikipedia/commons/8/85/Human_skeleton_front.svg

and you will see that between the sternum and the ribs are connections of cartilage. These are not bendy articulations but they facilitate a little expansive movement to the ribcage and probably enough movement to produce a little bubble to cause the 'crack'. Thank God, really, because if these cartilage connections weren't there I've got a feeling everyone who underwent commpressive cardiac massage would need to get along to the orthopoedic department afterwards to get their ribs fixed. Richard Avery 14:21, 20 September 2007 (UTC)

I can feel the rib move. DuncanHill 14:58, 20 September 2007 (UTC)

You can dislocate ribs from those joints as well. I've done it twice. First time, I was hit by a bus. Second time, same rib, I woke up and somehow it just dislocated and hurt like hell. -- kainaw™ 15:04, 20 September 2007 (UTC)

There's a joint between the xyphoid process and the rest of the sternum that can apparently "pop" in some individuals, for example when taking a deep breath (so says my doc). To my delight (and others' disgust) I can pop mine on command. --David Iberri (talk) 23:44, 20 September 2007 (UTC)

aquatic plants

what is the most favourable form of nitrogen for aquatic plants? —Preceding unsigned comment added by 202.141.78.125 (talk) 13:42, 20 September 2007 (UTC)

It is possible that Nitrification will provide some insights, although it doesn't mention aquatic plants in particular. It seems that the nitrogen-fixing bacteria are soil-dwellers, so there is probably an equivalent version for water-borne ecosystems (either in the form of aquatic bacteria or other nitrogen fixers). Nimur 15:22, 20 September 2007 (UTC)

I think the asker means either nitrate, ammonia as well as possibly nitrite and urea - I think it may depend on the plant which is most readily absorbed - but it is almost certainly one of the first two..87.102.87.157 15:15, 21 September 2007 (UTC)

Props go to any fan fan who answers this Q

Why aren't cooling fan blades shaped like an airfoil ? That is, why are they constant thickness instead of thicker near the leading edge ? I was asked this question and didn't know for sure, but this was my speculation:

• Airfoils are more expensive and more efficient. While this additional cost is justified for aircraft props it is not for electrical cooling fans, where it would be difficult to ever recoup the additional cost.

Was my speculation correct ? StuRat 16:14, 20 September 2007 (UTC)

The Sukhoi 29 is the probably most aerobatic aircraft in the world - as you can (just about) see, it has a symmetrical wing cross-section, showing clearly the myth of 'airfoil' shapes being responsible for generating lift SteveBaker 17:10, 20 September 2007 (UTC)

I don't think so. It's an alarmingly common myth that the cross-section of an airfoil is what causes an aircraft to gain lift...it has a very small effect but the major part of it is the angle of the wing to the airflow. The airfoil cross-section has more to do with controlling turbulance at low speeds - and getting the wing strong enough and yet still have a low drag coefficient. Consider a typical Ceiling fan. Those have flat, rectangular, plank-like blades - and they work very well. A desk fan, on the other hand has fat, more steeply angled blades. The choice of shape probably depends on the ratio of motor torque to blade diameter. A desk fan has to be compact - a ceiling fan doesn't. A desk fan is (typically) enclosed in a safety cage so the blades can spin much more quickly than a ceiling fan can. There are lots of little decisions that go into the design of such things. I would say that the blades of a desk fan more closely resemble a ship or submarine propeller - and the demand for small diameter with a high-torque motor probably drives both designs. SteveBaker 17:03, 20 September 2007 (UTC)

Thanks, but that doesn't seem to address why an airfoil shape is never used for fan blades. Are you saying that avoiding turbulence isn't important in fans ? I do think that turbulence occurs, since I note a small distance from the leading edge is clean, but after a half-inch or so, the fan blades become filthy. I take it that little dirt is deposited by laminar flow but turbulent flow "dashes dirt particles against the blades", causing them to stick. I would also reason that this turbulence would necessarily lower efficiency, since energy is being used to move air chaotically, not in the desired direction. StuRat 17:12, 20 September 2007 (UTC)

In aircraft, you need that thick part of the wing to contain the main structural spar (basically just a girder) - which supports the entire weight of the aircraft in the air and has to flex the other way and support its own weight against massive leverage when the plane is on the ground. This spar is at the center of gravity of the plane (in most designs anyway) - and it's wrapped in that teardrop shape merely to get the air to slip past it efficiently and to promote stability by placing the center-of-pressure as close as possible to the center-of-gravity. By virtue of smaller scale, fan blades can be simple thin plates that are mostly being flung outwards by centrifugal force and are not likely to break from the aerodynamic stresses alone. Hence no big fat girder running down the middle of the blade. So they can have a lower coefficient of drag than an aircraft wing that needs a fat bit in the middle to contain that chunky structural member. Turbulance isn't necessarily such a terrible thing in a fan blade whose main function is to stir up the air - so whilst it's probably undesirable, it's not a serious design issue. With ceiling fans, the cost of the things must be a lot less with flat wooden blades than with curved ones. I guess that with desk fans, which mostly have cast metal or plastic blades, you can have them be any shape you want - so they are more efficiently curved. Another issue with the design of fan blades is the range of speeds they have to operate at. It's possible that you are getting non-laminar air flow at the speed you happen to run your fan - but you'd get smoother airflow if it were running faster. The most likely thing is that aircraft are designed VERY carefully with wind tunnels and such - where ceiling and desk fans are designed as much for looks and cost as for efficiency. SteveBaker 17:33, 20 September 2007 (UTC)

(Come to think of it - if you look at one of those large modern windmills (which are just fans running backwards), the do have aerofoil shaped blades - presumably for the same kinds of structural considerations as aircraft wings). SteveBaker 17:35, 20 September 2007 (UTC)

Another consideration is that, given the RPMs of a desk fan on high, you probably don't want the blades generating lift, or your desk fan soon becomes a floor fan. Saturn 5 20:24, 20 September 2007 (UTC)

I believe "for every action there is an equal and opposite reaction" dictates that if you push air forward with a given force you also push the fan backwards with the same force, regardless of the means used to propel the air. I've definitely had fans fall over as soon as they are turned on. They need sturdy, weighted bases, or to be secured in some way, to prevent this. StuRat 02:01, 21 September 2007 (UTC)

Was my speculation correct ... partially, but I think it misses half the story:

• Airfoils act on the Bernoulli principal, which is a form of reaction - see Newton's third law.
• Curved blades, with no airfoil crossection, are usually designed to work with impulse - they change the direction of fluid flow without airfoil action - see Newton's second law.

Fans can benefit from both these concepts, depending on the design. Also, just guessing, a curved or angled blade made of stamped sheetmetal can probably be designed to act as an airfoil.

Cheap fans use simple shapes because they are cheap, even if an airfoil crossection could improve performance. In other cases, the fan might be an impulse design that doesn't benefit from an airfoil shape. I once saw a high performance fan - it had a stator and a rotor - that put 10 horse power in to the flow. It was less than twelve inches in diameter and only a couple of inches thick, and it could knock you over. It didn't have air foil shaped blades, just cheap stamped curved sheetmetal blades. --Duk 21:58, 20 September 2007 (UTC)

It really annoys me that just about every 'how things work' book says that Bernoulli's principle explains how airplanes fly - it really has almost nothing to do with it. This is one of the biggest pieces of misinformation in even quite serious publications. I offer as evidence the photo of the Su29 I posted above. It has a symmetrical wing cross-section and therefore has ZERO Bernoulli lift...yet it's one of the most nimble aerobatic aircraft in the world! Notice that something like a simple Cessna light aircraft that has a classic 'airfoil' cross section wing can fly inverted - with the Bernoulli effect pushing downwards on the wing. I've flown model planes with planks for wings (a rectangular cross-section). They fly just fine - again no Bernoulli lift whatever. Truly - this is a misconception that is perpetuated everywhere and it needs to be screamed and shouted from the rafters: THE BERNOULLI EFFECT IS NOT WHAT MAKES AIRPLANES FLY!!! SteveBaker 00:19, 21 September 2007 (UTC)

THIS SECTION IS NOT ABOUT WHAT MAKES PLANES FLY, IT'S ABOUT FAN BLADES!!!--Duk 00:51, 21 September 2007 (UTC)

Well, it has everything to do with the angle of attack of the wing. It's funny, just last week I performed an experiment in a wind tunnel using a NACA 0012 airfoil; its primary characteristic is that it is symmetric, yet it still produced lift. It still presents a typical $C_{L}$ v. $\alpha$ graph like the one shown on Lift coefficient, but the only difference is that it has a y-intercept of zero. It still presents stall, whether you are flying upright or upside down. What Bernoulli's effect does is that it generates a non-zero intercept for the graph. Titoxd^{(?!? - cool stuff)} 02:14, 21 September 2007 (UTC)

It seems to me that these discussions about "symmetrical cross sections" are all using the wrong frame of reference. The axis about which one should calculate whether aerodynamic symmetry exists is the air direction line that intercepts the center of gravity for the wing, is it not ? If the wing is symmetrical using this frame of reference, I would indeed expect there to be zero lift. StuRat 02:24, 21 September 2007 (UTC)

Not really. The calculations needed in fluid dynamics turn really ugly if you try to calculate them using a wind-based coordinate system. You always calculate them using a wing-based coordinate system, then do a simple transformation employing the angle of attack to bring them to the other coordinates. If the wing is completely parallel to the wind, there will indeed be zero lift; however, any deviation from that will cause air (or whatever the working fluid is) to have a longer displacement path on one surface, which causes higher speeds and lower pressures on that surface, generating lift. Titoxd^{(?!? - cool stuff)} 02:37, 21 September 2007 (UTC)

It sounds to me like you're saying the same thing as I did, just in a different way. Instead of starting with a wind-based coordinate system, they merely start with a wing-based coordinate system, then do a simple transformation, to get to a wind-based coordinate system. StuRat 04:14, 21 September 2007 (UTC)

Answering the original question: A flat blade at a good angle to the air provides more than enough wind without using much power. There is no need to increase the cost by planing down the blades into airfoils. The higher-quality blades are not airfoils. They are simply curved to better direct the wind in the preferred direction - a process that requires flexible blades, but is still cheap. As for the question about how much lift a simple air foil gives, consider common helicopters. The blades are airfoils for stability. They tilt to create lift. To touch briefly on two other subject mentioned: Stunt planes have wings curved on both sides to provide better stability for flying upside down. The wings (and the plane) feel the same to the pilot either way. For larger planes, such as passenger jets, the body of the plane provides a lot of lift. This goes back to TWA's first airplane purchase. They required the passenger jet to fly from Denver to Kansas City with one wing (I've also heard that it didn't have a tail, but I'm not sure about that). The wings are rather important though because most of the fuel is inside them. When it comes to jets though, keep in mind that they cannot fly at low speeds. As I was told when I started flying TWA's 727 and 747 simulators, jets don't glide when the engines stop. They drop like a rock. -- kainaw™ 02:52, 21 September 2007 (UTC)

 Are you kidding us Kainaw? Just a few years back, some large commercial jet 'glided' for over 100 miles, if I remember correct. The plane ran out of fuel because of a metric/standard error. The tanks were filled with litres instead of gallons! I can`t remember the exact flight, but, the 'emergency' glide was to a small set of islands in the Indian or Pacific ocean. Sorry if I can`t remember more particulars, but this was BIG news, at the time. To conclude though, jets CERTAINLY can glide... with a glide-rate of around 16:1 to boot!  64.230.233.222 19:44, 21 September 2007 (UTC)Dave

No I am not kidding. The event you are referring to is Air Transat Flight 236. It "glided" at a fall rate of about 2,000 feet/minute. Note that the pilot knew about the fuel leak (not a metric conversion error) before he ran out of fuel. So, he descended and punched the remaining engine to get forward momentum. Then, he basically fell onto the runway. There is a huge difference between gliding along and falling at 2,000 feet/minute. But, you can define "gliding" however you like. -- kainaw™ 19:54, 21 September 2007 (UTC)

Kainaw, I certainly don`t want to be argumentative since 'falling' at 2000ft/min is surely quite a 'fall', but one must remember that while 'falling' at such a rate, that craft in question was also travelling forward at around 32,000ft/min. What I`m trying to get at is that given both numbers, the craft was far from "drop(ing)like a rock", as you put it. I`m quite certain with that forward speed, that aircraft surely was able to flare some, further decreasing its 'fall' rate. Looking up 'glide ratio' right here on Wiki gave some interesting values: Cessna 150 7:1, modern sailplane up to 60:1, hang "glider" around 12:1, paraglider around 7:1, airliners around 17:1, Space Shuttle 1;1! So, with those numbers in mind, wouldn`t you say THAT craft 'glided' pretty well? Thanks for finding those particulars that I missed,,,,I read the link. I found it very interesting. Thanks again. Dave64.230.233.222 21:00, 21 September 2007 (UTC)

The glide ratio is only half the need for gliding. The other half is the sink rate. Unfortunately, Wikipedia doesn't have an article on sink rates (yet). A good glide ratio and good sink rate make a glider. While a large passenger jet may be able to get a somewhat reasonable glide ratio, the sink rate stinks. So, the longer the jet is "gliding", the less forward momentum it has. The less forward momentum it has, the worse the glide ratio gets. The worse the glide ratio, the faster it falls. That is why the few cases where engines have completely gone out but the jet survived were cases where the pilots had warning and lowered the altitude while increasing speed. Lower altitude means less glide time to the ground. Higher speed means longer glide ratio. I'm sure someone will say that they can nose-dive and pull out to get forward momentum. Large jets are not constructed to handle that maneuver safely. (Although, I've seen a 747 do it in a simulator.) Then, there's the whole issue of the jet going into a crippled mode due to power failure. The little turbine that pops out gives only the basic necessities - not enough for a comfortable flight. All in all, if you set a rock in flight at the same height and speed as a jet, the rock will take a ballistic course. The jet will do a little better, but be much closer to the rock than a glider. -- kainaw™ 04:49, 22 September 2007 (UTC)

Thanks for the extra 'work' Kainaw...good job. A quick 'calculation' shows that the plane 'fell', just taking the vertical aspect of the fall into consideration, at an average speed of about 22-23 mph. I think an ordinairy, i.e. no 'special' aerodynamic qualities, rock would fall with a terminal velocity of, just a guess, 120-150 mph. The high-performance modern glider would 'fall' at about 5-6 mph, I think. Refering to your last sentence above, I believe that 22-23 mph, if correct, and if all other guesstimates are close to accurate, then the jet glided much closer to the rate of the glider than an ordinairy rock. Please correct me if I`m wrong. This will be my last post to this FAN question. Apologies to those 'forced' to listen to these side-tracks. Thanks all. Dave 64.230.233.222 09:07, 22 September 2007 (UTC)

What gives airplanes lift

HEY, STEVE BAKER, WHAT GIVES AIRPLANES LIFT ?????????--Duk 00:58, 21 September 2007 (UTC)

Steve, aren't you kind of splitting hairs? The pressure difference between the upper surface of the wing and lower surface create lift. If the aggregate of vectors of lift and thrust are sufficient to overcome gravity then the plane will rise. The Bernoulli equation can be used to estimate lift from airflow over the wings if the geometry of the wings and the angle of attack are known. The longer streamlines generate lower pressure since the air must flow faster from the leading edge normal to airflow, specific location controlled by the angle of attack, to meet back up at the trailing edge. If this condition fails then you have flow separation and a resulting stall. Most standard airfoils have greater curvature on the "top" to increase the lift when flying right side up. If you fly with your symmetrical airfoils at an angle of attack of zero then you have identical streamlines both above and below, zero pressure differential and thus zero lift as predicted and calculated by the Bernoulli equation. Your inverted Cessna better have a proper angle of attack to make the streamlines on the undersurface of the wing longer while upside down or your "Bernoulli lift" will indeed be down rather than up. The reason the airfoil on your aerobatic plane, photo above, is symmetric is because it is designed to give equal "lift" either up or down as per the angle of attack selected by the pilot while flying aerobatically. Large subsonic widebody jets on the other hand will have asymmetric cross sections to maximize lift (greater curvature on top and flatter on bottom) when flying right side up. Indeed, they also have flaps to further extend the asymmetric curvature and maximize lift while landing ... as predicted and calculated using the "Bernoulli Effect". Lazyquasar 01:00, 21 September 2007 (UTC)

And to the Su29 wing design, they are shaped that way so as to provide equal lift regardless of which side is up, as LQ said above. Aerobatic planes tend to spend alot of their time upside down. The wing shape lets them get the same lift from the same alpha (angle-of-attack) in either orientation. Couple that with the massively overpowered engine which essentially "drags" the aircraft through the air regardless of lift, and you get the nimbleness that Mr. Baker described. Yes, Cessnas CAN fly upside down, but to maintain level flight as such requires a very aggressive alpha angle, and a steadier nerve from the pilot (if you've ever done this, you know how easy it is for the aircraft to "fall off" its lift...). I guess my point is that, while the wing angle is a significant element in maintaining lift, it is incorrect to say that Bernoulli Lift from the wing shape plays no part, or even an insignificant part. Saturn 5 14:36, 21 September 2007 (UTC)

Well as "steve baker" says - it's not the bernoulli effect - because the force downwards on the wind due to the curve on the leading top edge of an airfoil does not offset any force gained by having faster air above.

It's the angle of attack that gives lift. Consider "For every action there is an equal and opposite reaction" (newton).87.102.87.157 15:12, 21 September 2007 (UTC)

To be perfectly fair, it is a combination of Bernoulli and Newton that give lift. It is ignoring much physics to say that either Bernoulli or Newtonian lift play no part. Consider this: a "normal shaped" airfoil wing (what we refer to as a NACA 4415 shape, if you want to look it up), will still generate lift even when it is angled 3 degrees down relative to the airflow (3 degrees negative α ). At 4 degrees negative α, the Bernoulli lift is cancelled out by the downward Newtonian (so called Reactive) lift. Saturn 5 15:21, 21 September 2007 (UTC)

Does "bernoulli lift" violate the conservation of momentum principle? or not.87.102.87.157 15:41, 21 September 2007 (UTC)

For example this shape

   >>>>>          XXXXX
   >>>>>        XXXXXXXXXXXXXXXXX
air>>>>>      XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
   >>>>>    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
   >>>>>  XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

In an horizontal airflow would it get lift, and what would be the forces on it?87.102.87.157 15:52, 21 September 2007 (UTC)

Actually, Bernoulli is a special case restatement of Newton, for a fluid. In your drawing, the air flowing over the top of the wing has further to travel due to the curvature, than the air flowing across the bottom. Therefore it must move faster than the air flowing over the bottom. Since Newton requires conservation of Energy, the faster moving air must be at a lower pressure than the bottom air. The pressure difference between top and bottom results in a net upward force on the bottom surface of the wing. All as a result of Conservation of Energy. Saturn 5 16:04, 21 September 2007 (UTC)

Rubbish - you seem to be assuming that two molecules starting at the front have to meet at the back at the same time. More worryingly what about the forces required to make the air move along the upper surface - total rubbish now fuck off87.102.87.157 17:05, 21 September 2007 (UTC)

Wow.... Sorry you feel that way, but I'm not making this stuff up. Read any physics book, its all in there. Oh and by the way, please also read WP:CIV. Saturn 5 17:11, 21 September 2007 (UTC)

I would like to make it clear that I'm not disputing that a wing with the cross-section shown in 87.102.87.157's post will generate lift. Yes, it will - as more or less every book on "How Airplanes Fly" will be sure to tell you. However, that's grossly misleading when you consider what keeps most airplanes in the air most of the time. This 'Bournoulli lift' effect is simply NOT a large part of the total lift in a normal aircraft and the wing cross-section has more to do with support structure and drag minimisation and stall-safety than it has to do with lift generation. The picture above misleadingly suggests that in normal flight, the flat bottom of the wing is parallel to the airflow. That's simply not true for almost every aircraft at almost every speed. For most planes, there is a well-defined "angle of attack" which is the angle that the flat bottom of the wing makes to the incoming airflow. You'd think that the air pressing against the bottom of the wing would immediately tip the plane's nose down until the wing sliced though the air nice and flat - like in the diagram...but airplanes are more cunningly designed than you perhaps think. Find a nice side-on photo of your favorite 'typical' airplane (try not to pick something weird) and look at the angle of the wing to the fuselage - and also at the angle of the tailplane to the fuselage. Notice how the wing is tilted upwards at the front compared to the tailplane. That's because in normal, level flight, the tailplane (being stuck WAY out the back of the plane, far from the center of gravity) exerts a downward force on the tail that pushes the front of the plane up. This results in the flat underside of the wing deflecting the air downwards just like it does on a typical slab-bladed ceiling fan. That's what's making the lift. There are exceptions...but as a general rule the whole business of the air taking a longer path over the top isn't what's generating the vast majority of the lift - the Su29 shows that elegantly by having a wing that's rounded on the bottom as well as on the top. If it's pointed directly into the airflow as per the diagram above, the air travels the exact same distance above and below - so no pressure differential - and no Bournoulli-effect lift...yet the plane flies perfectly well (in fact AMAZINGLY well in that case - it's one of the most manouverable aircraft in the world). If you are still not convinced, ask yourself why an aircraft points it's nose up at the sky on takeoff? If Bournoulli effect was getting it off the ground, it would keep the flat bottom of the wing parallel to the airflow and take off with the wings parallel to the runway. If we are dualing with references, read Angle of attack which says: The amount of lift generated by a wing is directly related to the angle of attack, with greater angles generating more lift. THAT is what makes (almost all) airplanes fly. There are some exceptions. SteveBaker 18:24, 21 September 2007 (UTC)

Please allow me to clarify a few things. First, before the other gentleman decided to cease having a civil discussion, my explanation of the wing diagram was deliberately simplified because dropping too much physics at one time, before some basic concepts are agreed to, tends to cause heads to explode. In fact, had we proceeded civilly, I would have gone into how, yes, the air molecules do NOT in fact arrive at the trailing edge at the same time. But anyway, you see how that went.

Second, if you notice, I have not said that the lift generated by deflection of airflow off an angled wing does not play a significant part in airfoil lift. In fact, at cruise (30,000 feet, 500kts or so), I'd guesstimate that a good 70-75% of total lift is produced that way. At takeoff, that goes even higher. I'm not arguing that point!!! My comments have been to simply point out that completely discounting the Bernoulli effect is not correct. Bernoulli lift is important because the Reaction lift (equal-opposite reaction from the deflected air molecules), while more powerful than the Bernoulli, is rather unstable by itself, and very sensitive to the slightest change in airflow such as one would find in the turbulent atmosphere. The way one's hand reacts when held out the car window on the highway gives a good example of this.

I'm not duelling with references... the only reference I've cited was CIV, for obvious reasons. :-) Saturn 5 18:41, 21 September 2007 (UTC)

Yes - so we don't actually disagee. In cruise you say that at least 70% of lift comes from the angle of attack - and the rest from the airfoil effect - and I'd probably agree with that (for at least most 'normal' aircraft - we'd have to argue about the Sukhoi and the Stealth fighter for example). Up until a few months ago I used to design flight simulators - mostly for military aircaft - and I could probably quote you some exact numbers - but one never knows what's classified - so I won't. Of course in the case of the Su29, the figure is 100% and I'm pretty sure we could find some kind of a weird-assed plane for which the number was much smaller (although I'm finding it hard to think of one right now). My problem is not denying the existance of this airfoil effect - it's that without fail almost every single book on the subject (especially for kids) says that the airfoil effect is "What Makes Airplanes Fly" - which is to completely miss the point! The measure of misinformation is a crisis level! Go to your local library and take a look at books on the subject and I guarantee that 95% or more get it wrong. In discussion of this subject one should FIRST talk about the angle of attack effect - discussing how that angle is maintained by the tailplane and how the elevators work by pushing up and down on that long lever arm (which is why aircraft have such long tails) to adjust the angle of attack. Someplace way back in Appendix Q of the most erudite books on aeronautics, it should mention the airfoil effect. Issues of stability and flight through turbulant are are VASTLY more complicated - effects such as lift from the fuselage, dihedral/anhedral, tailplane lift...it's all insanely complicated - and it would be oversimplifying to say that this is why we need Bournoulli lift. However, it is true to say that in aircraft where stability is NOT desirable (fighters, Su29's, etc), a symmetrical wing is desirable...so there is clearly some contribution to stability from having a flat-bottomed airfoil. But no matter what - can we PLEASE fix the textbooks?! SteveBaker 19:02, 21 September 2007 (UTC)

(Ok, 8 indents is plenty I think):-) Yes, my 70-75% was based on the 4415 sort of shape, and more specifically the 747-400. Something like 1000 lbf/sq-ft from Reactive lift, 240-ish for Bernoulli. At least my textbook got it right. :) Saturn 5 19:16, 21 September 2007 (UTC)

Then of course we have the F16 which exhibits 'black magic' vortex lift...no Bernoulli and kinda perpetually in stall...weird. Works great just so long as your computer keeps running! SteveBaker 19:59, 21 September 2007 (UTC)

I believe many of the pre-Wright-brothers aircraft were designed around the assumption of pure Bernoulli lift -- which is why they tended not to fly very well. --Carnildo 22:33, 21 September 2007 (UTC)

Yep. One thing that can be said without excessively simplifying the subject is that an unsymmetrical airfoil will have an initial lift at $\alpha =0$. However, that lift is much smaller than lift caused by angle of attack. Then, of course, you have to worry about flow separation and all those nice things... Titoxd^{(?!? - cool stuff)} 22:50, 21 September 2007 (UTC)

Ooooohhhh! I forgot to tell the skeptics to try my poor-mans wind tunnel demonstration! The next time you are riding shotgun in someone's car - take along a paperback book - preferably an nice slim 200 pager - not a 1000 page Stephen King monster! Open the window when the car is going nice and fast and hold the book out into the airflow with the spine pointing into the wind - hold it up high enough to get out of the turbulance caused by the door mirror. You now have a 'wing' with a rectangular cross-section. If you tilt the spine of the book up - you'll easily be able to feel the lift caused by the "angle of attack" effect. OK - so now, push on the pages on the top of the book to make an 'airfoil shape with a flat bottom and a slight bulge on the top. Hold the book so that the flat, bottom surface is parallel to the airflow and see how much 'Bournoulli effect' lift you get. When I tried this, it was hard to tell that there was any lift at all - but if you curve the top edge just right, you can kinda-sorta feel it. If this demonstration doesn't convince you, you're a lost cause! SteveBaker 19:02, 21 September 2007 (UTC)

• For those who are wondering what on Earth is the NACA xxxx, there's the NACA airfoil article. Titoxd^{(?!? - cool stuff)} 22:50, 21 September 2007 (UTC)

Dominant and recessive

Why human genes are dominant and recessive? Is it because of their chemical structure or something else? And is it possible to interchange their properties? --85.132.14.38 17:02, 20 September 2007 (UTC)

This question is answered in the Dominance relationship article. To put it simply, it has to do with the fact that we carry two copies of each gene (for the most part), one chromosome from your father and one from your mother. -- JSBillings 17:47, 20 September 2007 (UTC)

Come now, anyone who asks about gene dominance already knows about diploidy. To put it still rather simply: if one allele produces a functioning enzyme and the other doesn't, usually the presence of the former is enough to have full effect; presence dominates absence like light dominates darkness. —Tamfang 21:21, 20 September 2007 (UTC)

It is important to remember the genes themselves do not create the phenotype, it is the proteins (and RNA) they produce which ultimately causes the differences in organisms we call phenotpyes. Dominance and recessiveness are often (but not always) correlated with how the respective alleles' protein products function (or not). There are many ways that dominance or recessiveness can be "created" through mutation so I will give some protein related examples. 128.196.149.20 00:56, 21 September 2007 (UTC) (This is User:Sifaka who can't sign on right now)

• Reccesiveness can be caused by a loss of function mutation. Suppose you have two alleles A (normal) and B (mutated) that make some protein. Allele B is mutated so that its protein can not function properly. If allele A produces enough normal protein to make up for allele B's defective protein resulting in a normal phenotype, Allele A would be considered dominant to B. If allele A alone can't produce enough protein to make up for the deficiency so an intermediate phenotype results, then A and B might be incompletely dominant.

• Imagine if the gene encodes for a red pigment in petals and the mutation in B causes a noncolored protein causing white petals in double recessive individuals. A normal phenotype is red. If allele A can make up for B completely, the flowers are still red. If A doesn't make enough protein though, the flower might be pink.

• Dominance of a mutant allele can be caused if the mutant protein fails to be regulated properly. Imagine a gene with two alleles C (normal) and D (mutated). Allele D has a mutation so that the protein produced has a defect in a regulatory region which controls its activity so that it can't be "turned off". The Allele D is dominant over Allele C because only one copy of allele D is needed to make mutant protein which causes the mutant phenotype.

• Imagine the gene encodes for a red pigment in a flower whose normal phenotype is red on the edges and white in the center. There is a regulatory protein produced in the cells in the center of the flower where it is normally white which tells the red protein not to work here. The mutant protein created by allele D doesn't respond to that signal creating the mutant phenotype of an entirely red flower.

• A gene has a part that encodes for the protein, and also regions to regulate its transcription. A mutation need not be in the parts encoding for a protein (thereby creating a mutant protein), a mutation to a key part of the regulatory region may drastically change the the gene's expression, causing a mutant phenotype.

FTL and the size of the universe

Begging your pardons if this is the wrong place but I couldn't find the information or answers anywhere else on Wikipedia.

I need a logic and reason check on this statement, please:

"If faster-than-light travel is possible, then the universe is not infinite."

Or, if you prefer:

"If the universe is infinite, then faster-than-light travel is impossible."

The logic is as follows:

If the universe is infinite, then there has been infinite opportunity for an advanced intelligence to develop FTL travel and visit us. As we see no evidence for extra-terrestrial intelligence, then at least one of the following must be true:

1. The universe is finite.

2. FTL travel is impossible.

"An infinite universe and faster-than-light travel are mutually exclusive." (corrected stupid typo in this statement AJKGordon 18:28, 20 September 2007 (UTC))

Therefore if experiments conclude that FTL travel is possible, then the conclusion that the universe is finite is automatically deduced. And vice-versa, of course. —Preceding unsigned comment added by Ajkgordon (talk • contribs) 17:54, 20 September 2007 (UTC)

Anyone care to correct or confirm? AJKGordon 17:46, 20 September 2007 (UTC)

There's a clear and fundamental flaw in your logic. An infinite universe (presumably you mean in size) does not necessitate that everything which might happen has happened. — Lomn 18:04, 20 September 2007 (UTC)

Yes, there are indeed quite a few problems with that assumption. First of all, it assumes that advanced intelligences CAN exist and are not somehow eliminated by the laws of physics. Secondly, it assumes that an advanced intelligence would WANT to search the universe for other life - maybe not. Thirdly, it assumes that this has not already happened (maybe they visit suitable planets, seed them with unicellular life and stand back and wait until WE find THEM!). It assumes that FTL travel means infinitely fast travel...maybe you can go faster than light but only twice as fast. Also how long does it take an infinite number of intelligent species, flying at infinite speeds to search an infinite number of stars in order to find an infinite number of less intelligent species like ours? The answer is something like infinity divided by infinity - which can be any number you choose...including zero or infinity. So it's perfectly possible for there to be infinite everything but for there still to be only a one in a trillion chance of us ever being reached and communicated with. There are plenty of holes in your argument that make it perfectly possible to have an infinite universe with infinitely fast travel and no alien visitations whatever. A similar argument to yours (without the need for FTL travel) would say that there are an infinite number of black holes in the universe so how come we haven't been swallowed by one of them? Well, there might be an infinite number of them - but they are spread over infinite distances - so the actual density of them can be whatever you could imagine. So, sadly, your argument is without merit. For the record, we believe that the universe is finite and FTL travel is impossible. However, because space can expand (as a result of the big bang) faster than light (this is NOT the same thing as travelling faster than light) - there are parts of the universe that are receding faster than we could fly towards them - so we can never reach them...which means nothing from those regions can reach us. In that sense, it doesn't matter whether the universe is infinite or not - in either case, we cannot possibly ever reach all of it. SteveBaker 18:05, 20 September 2007 (UTC)

Thanks both. Just want to make it clear it's not my logic! Kids sometimes ask difficult questions! I will reflect on your responses. Thanks again. AJKGordon 18:17, 20 September 2007 (UTC)

Ah - In that case, the short-form, kid-safe answer is: The trouble is that infinity is a slippery concept. If the universe is infinite then it also contains an infinite number of cats - so by your logic, there must be one sitting on my lap right now - and there isn't (you'll have to take my word for that!). That's because those infinite cats are spread over an infinite volume - so the distance between them is infinity divided by infinity which could be any number at all. We know the universe isn't infinite - in fact, about 13.7 billion years ago it was a mere 'dot', then we had the big bang and it's been expanding ever since - but it's not expanding infinitely quickly or we wouldn't be able to see any distant galaxies - so it must still be finite in size. Hubble's law says how fast it's expanding and that gives us an idea of the size - which is most likely about 78 billion light-years. SteveBaker 19:24, 20 September 2007 (UTC)

Hmmm... predicting his response...

A finite but infinitely old universe and FTL travel are mutually exclusive." AJKGordon 18:26, 20 September 2007 (UTC)

Hmmm - I misunderstood that comment initially. No - even if the universe was finite but infinitely old, the aliens might not be here. A finite (spatially) universe only contains a finite number of civilisations at any given point in time - although over the entire past history there must have been an infinite number of them. Because a civilisation doesn't necessarily last forever (wars, etc) - each civilisation might last long enough to look everywhere in the finite universe using their super-fast spaceships - but we weren't there at the time, we were still in our 'primordial ooze' stage and now (millions of years later) maybe the aliens are all dead. Now we are here and they aren't - so they might never find us because we never overlapped in time. But still, it's an academic point because..... SteveBaker 19:51, 20 September 2007 (UTC)

A finite (in size) but infinite (in age) universe is already a mutually exclusive proposition...forget FTL. We KNOW the universe is expanding (even a very basic telescope+spectrometer can show the red-shift in more distant galaxies) - and we know that if it ever stops expanding, gravitation will force it to shrink again and then nothing can stop it from ending in a 'big crunch'. If the universe was INFINITELY old then either it crunched already (it didn't or we wouldn't be here) - or it has already expanded to infinite size. So infinite in size and infinite in age are possible - and finite in both size and age are possible. But besides, we can already look back at the universe as it was soon after the big bang (Cosmic microwave background, etc) - we know for sure it's not infinitely old - hence we know it's finite in size - and we're pretty much 100% certain that FTL travel is impossible. So, sadly, we have finite everything and boring old spaceships that are forever going to be too crappy to let us see much of it. Gene Roddenberry would roll in his grave. SteveBaker 18:48, 20 September 2007 (UTC)

Infinite in size but finite in age is also possible. In fact it's what follows from the simplest models having negative or zero asymptotic curvature.

Of course the observable universe is finite. --Trovatore 18:55, 20 September 2007 (UTC)

Human history is only 10000 years old or so (much less if you limit it to people capable of productively processing the concepts of space and aliens). Even if space was chock full of species with warp drives, maybe they just haven't been interested in making their presence known to a boring backwater civilization like ours. 76.231.189.193 19:52, 20 September 2007 (UTC)

OK thanks, Steve and others. Not sure I get your logic about finite age = finite size and I think that "[virtually] 100% certain that FTL travel is impossible" is over-cooking it a little but that's enough to keep the offspring entertained. Thanks again. But I may be back! AJKGordon 20:18, 20 September 2007 (UTC)

Oh - that's an easy one. The universe is 13.7 billion years old. Back then, the universe was a dot - zero sized. Then we have the big bang and it starts growing. It doesn't grow infinitely fast - the growth rate is finite and approximated by the Hubble's law. So if it started off at zero size and grew at a finite rate for a finite amount of time - then the universe has to be finite in size...and we estimate it's 79 billion light years across right now. Hence finite age means finite size (assuming finite growth rates - which is what we see when we look out there and watch distant galaxies rushing away from us). If there was at some time a brief moment of infinite expansion before things settled down to where they are now then we'd be in deep trouble because the finite amount of matter that was in the universe shortly after the big bang would be spread out over infinite space - and things would look kinda empty around here! So we can be reasonable sure the universe is finite size and finite age. But that's not 100% for sure. Anything further away than 13.7 light years is too far away to see because it would take longer than the life of the universe for the light to get to us...so there is a good fraction of the universe that we'll never be able to examine...maybe it's a lot different from our bit and maybe those parts ARE moving infinitely fast...it doesn't seem likely though. FTL travel is fairly certain to be impossible...sadly...the experimental results testing Einsteins theory of relativity have absolutely all shown it to be 100% correct - and it most certainly says that faster-than-light travel is out of the question. It's not looking likely. SteveBaker 00:01, 21 September 2007 (UTC)

The part of the finite-universe reasoning that you can't check is the "the universe was a dot" part. What we actually get by running the equations backwards to the big bang is that the universe had infinite density, not that it had zero volume. Certainly, if its mass is finite, then it would follow that it had zero volume, but that's begging the question.

I also think you're assuming too much about Einstein's work applying in regimes in which it's never been tested (why don't you like possessive apostrophes, BTW?) but we already know we disagree on that one. --Trovatore 00:29, 21 September 2007 (UTC)

• Fermi paradox. --JWSchmidt 22:36, 20 September 2007 (UTC)

Couple of things I understood differently, Steve. 13.7 billion light years is simply how far light has travelled since the Big Bang, not how far away the furthest objects in the observable universe are away from Earth - that works out as 47 billion years. The 79 (or 78) billion light year size is simply the lower limit of the size of the universe, i.e. the furthest that can be seen with no repeating patterns - repeating patterns suggesting that the universe might be curved and finite within observable limits. (I think I got that right). I was also under the impression the question of whether the universe was infinite or not was still pretty open. (No pun intended). AJKGordon 00:54, 21 September 2007 (UTC)

What about the Fermi paradox, JW? AJKGordon 00:57, 21 September 2007 (UTC)

I pointed to Fermi paradox because this section started with, "....opportunity for an advanced intelligence to .... visit us. As we see no evidence for extra-terrestrial intelligence, then.....", which is the starting point for the "Fermi paradox". People have been thinking about this for a long time and some of the resulting chains of thought are outlined at Fermi paradox. --JWSchmidt 03:06, 21 September 2007 (UTC)

The trouble with the Fermi paradox is that it's not really paradoxical. There are some rough calculations as to the number of possible alien civilisations out there. The numbers have vast error bars on them - so it's possible that the answer is 1 (vis, Us) - and suddenly there is no paradox. Also, (as previously discussed) we shouldn't be surprised that we aren't visited by aliens because of the limitations of the speed of light - and the lack of radio transmissions is unsurprising if their radio technology is on a par with ours because our strongest transmitters would be undetectable by our most sensitive receivers at 4 light years distance (the distance to the nearest star system). The universe could easily have a human-level civilisation on every single planet of every single star and there would still be no possible way for us to figure this out. SteveBaker 04:07, 21 September 2007 (UTC)

Technological civilizations might have developed on other planets of our galaxy hundreds of millions of years ago, providing what strikes some people as plenty of time for evidence of their existence to have reached Earth. Some people have speculated about panspermia and other possible forms of "contact" that might not be easy for us to detect. --JWSchmidt 06:25, 21 September 2007 (UTC)

They may have developed, and they may have died out, like many civilizations have done on this planet. Our own Western civilization has seemed precariously teetering on its own destruction for the last century, and we've only made it to our moon a handful of times. (I also want to just add, that even if we had FTL travel, it would have to be pretty significantly FTL to make interstellar travel something people really wanted to spend the time doing. Even if you were traveling at c it would still take you a long-ass time to get anywhere beyond our solar system. A four-year trip to the next nearest star is still a bit too long for casual travel, even if those on the ship didn't experience any time as passing—you wouldn't want to go on a long trip and come home to find your kids grown up, family dead, etc.) --24.147.86.187 13:09, 21 September 2007 (UTC)

It's impossible to say what FTL travel might do to human perception since all of the math and physics say it can't happen. But the effects of time and distance dilation have a massive effect on this stuff. If we could travel very close to the speed of light, distances between stars would contract and we could move between them in less elapsed time. You don't need FTL travel to zip around the universe like on StarTrek - 99.9999999% of 'c' is plenty. However, this has the side-effect of speeding up time around us so whilst the occupants of a fast ship would live long enough to travel between stars - the remainder of their civilisation would die of old age waiting to hear the results of their travels. At exactly the speed of light, the universe shrinks to an infinitesimally thin two-dimensional object - which is too small to contain your spacecraft - while time speeds up to an infinite degree so the universe ends (big crunch or heat-death...either way) before you can press the "OFF" button on your hyperdrive...never a good thing for crew morale! Beyond the speed of light - we are "in mathematical la-la-land" (a new phrase that I'm becoming fond of) in that lengths, time and masses all become complex numbers (like the square root of -1) - which is simply not possible in our universe...so speculation as to what FTL travel might or might not do is pointless - it can't happen so we can't say what would happen if it did. Things would get plenty freaky at 99.99999% of 'c'. SteveBaker 15:14, 21 September 2007 (UTC)

Science fiction writers have come up with various imaginative ways of side-stepping the Fermi paradox and explaining why our galaxy is not overflowing with alien civilsations. In the Culture novels of Iain Banks, sufficiently advanced civilisations become bored with the material universe and join the Sublimed. In Vernor Vinge's novels FTL travel (and other advances such as sentient computers) is only possible if you are more than a certain distance from the galactic centre - which the Solar System, unfortunately, is not. Gandalf61 13:33, 21 September 2007 (UTC)

I don't think they NEED to do that. The Fermi paradox relies on the Drake equation for it's prediction of the number of civilisations within reasonable distance of us. According to our article, the Drake equation states that:

$N=R^{*}\times f_{p}\times n_{e}\times f_{l}\times f_{i}\times f_{c}\times L$

where:

N is the number of civilizations in our galaxy with which we might hope to be able to communicate;

and

R* is the average rate of star formation in our galaxy

f_p is the fraction of those stars that have planets

n_e is the average number of planets that can potentially support life per star that has planets

f_l is the fraction of the above that actually go on to develop life at some point

f_i is the fraction of the above that actually go on to develop intelligent life

f_c is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

L is the length of time such civilizations release detectable signals into space.

Some of these numbers we have good estimates for. We know R*, we have enough evidence about f_p to guess, but so far, the value if n_e is unknown. We've found maybe a hundred stars with planets (and it starts to look like f_p is maybe 0.1 or so) - but so far, none of them have planets remotely like earth. So n_e could be very close to zero. It could be 1.0 divided by the number of stars in the universe - which would mean we are utterly alone here. As for L and all of the f_whatever terms - we have literally no clue about those. We can guess - but the answer could be wildly wrong. So where is this paradox? It's not paradoxical for n_e to be a very tiny number - we don't know enough about planetary formation to say whether Earth is an amazing flook of nature - a unique result of a spectacularly unlikely series of coincidences. So it's not a paradox - it's a result of some of those numbers being rather smaller than we estimated. Science fiction writers don't need to come up with elaborate reasons why the universe is or is not full of aliens - it's simply the result of some assumptions about some unknown numbers in an equation. If you want a Star Wars universe where every tiny little rock (including asteroids) is teeming with life then crank n_e to around 5.0 and f_l to 1.0 and put f_i to maybe 0.5 or so. If you want StarTrek - where most of the universe has been colonised by just a few intelligent species but where most planets are colonisable - then set n_e to a bit less than 1.0 but f_l to a very small number. If you want Asimov's Foundation series where humans are everywhere but no alien life of any kind exists - then push f_l to a smaller number still so that everywhere is livable but all life comes from earth colonisation and set f_i to 1.0 so the one place that has life has intelligent life. By playing around with the unknown numbers in the equations you can get any science fiction setting you like. The Fermi paradox is nonsense until/unless we somehow prove that the f_whatever terms should somehow be big numbers - and yet we still find no life. But how would scientists show that the probability of a civilisation developing technology is a big number when we only have one example (ourselves) to use as evidence? Nah - forget the Fermi paradox. SteveBaker 15:35, 21 September 2007 (UTC)

Steve, I think you might be making the same mistake that many many people have made in the past - claiming that something is impossible when we don't really understand it. Sure, travelling conventionally in accordance with Einstein's famous equations, it seems fairly bullet-proof that FTL is impossible. But we also know, through those very same equations, lots of stuff about folding space and so on that could, theoretically, allow some of these hard and fast rules to be bypassed. Even though we have no idea how to generate exotic matter and other fanciful notions for, say, worm-holes, or indeed if it's even possible, that's "just engineering". Science and technology are two very different things. And the latter doesn't necessarily need to understand the former! AJKGordon 18:35, 21 September 2007 (UTC)

The trouble comes when you add infinite variables to a question... infinite sets can act and interact in funny ways. Probably a bit too complicated for young children, but these discussions of infinite sets and events can be good brain candy (depending on your sweet tooth). --SB_Johnny | ^PA! 19:57, 21 September 2007 (UTC)

Thanks Johnny. 84.98.245.216 20:51, 21 September 2007 (UTC)

Finding Average Acceleration from a Position-Time Graph

So there's this physics question which I can't seem to get. There's a bus, it's got a varying speed along its 3.5 hour trip. From t = 0 to t= 1 hour it position changes from 0 to approx. 25 (the graph is small). Then on leg B of it's journey, it goes from t=1 hour t~2.2 hours. Its position changes fromm x = 25 to x = 33. Then, on leg C of the journey, from t = 2.2 to t =3.5, the bus's position changes from x = 33 to x = 28. Now, I have to find the average acceleration. The answer I know, -8.3km/h². However, the process I don't. I first began by calculating the velocity's (using the slope) of A, B, and C.

So then I got answers such as V(a)= (25km-0km)/1hr = 25km/hr, V(b) = (33km-25km)/(2.2hr-1hr) = 6.6km/hr, and V(c) = (28km-33k)/(3.5h-2.2h) = -3.84km/hr.

Now I proceed to find the average acceleration of each segment, by diving the change in velocity of each segment by the change of time. a) (25km/hr-0km/hr)/(1hr) = 25km/hr². b) (6.6km/h²-25km/²)/(2.2hr - 1hr) = -15.33km/h². c) (-3.84km/h-6.6km/h)(3.5hr-2.2hr) = -8.03km/h².

That adds up to a grand total of of + 1.64km/h²....which is well far from the answer. If any could help me, I'd really appreciate it. Thanks.

207.161.45.29 22:48, 20 September 2007 (UTC)

It seems odd to ask for average acceleration, rather than average velocity, in a problem like this. That said, look at the first equation in velocity, which says how to calculate average velocity; acceleration is to velocity as velocity is to position, so you should be able to use a very similar equation for your problem. (Hint: you'll need some but not all of the numbers you've given here, and some but not all of the ones you don't need to use are wrong.) --Tardis 23:32, 20 September 2007 (UTC)

I do use that same equation, in the second part where I wrote avg. a = (v2-v1)/(t2-t1). I'm not really sure what you mean by the last sentence.. I need to use some of the numbers I came up with, but some of those are wrong? —Preceding unsigned comment added by 207.161.45.29 (talk) 23:42, 20 September 2007 (UTC)

No...this is wrong, wrong, wrong. You've approximated the position curve by three straight lines. A straight line in position means a constant velocity which means zero acceleration. But at the precise point where the two straight lines meet, the velocity changes instantaneously. That's an infinite accelleration for zero amount of time - which throws the math off into la-la-land. SteveBaker 23:48, 20 September 2007 (UTC)

I know the acceleration is zero from Point A to point B, from Point B to C and zero from C to D, but as a whole the acceleration changes because the velocity changes. How would I work this out? —Preceding unsigned comment added by 207.161.45.29 (talk) 23:58, 20 September 2007 (UTC)

No - you don't understand. You have approximated the position-versus-time curve as a straight line from A to B - right? So you can calculate the average velocity over that time from the slope of that line. But if you assume the velocity is constant - then what is the acceleration? Acceleration is the rate of change of velocity over time. Well, if the velocity is constant then there is no change - so the acceleration is zero. OK - so from A to B there is ZERO acceleration. If B-C is also approximated by a straight line (albeit one with different slope from A-B) then the same argument applies - a straight line for position-versus-time means constant velocity and zero accelleration. The velocity changed at point B. So let's plot a graph of velocity versus time. It's a horizontal line from A to B - then the graph goes up vertically and you get another straight line from B to C. Acceleration is the slope of the velocity/time graph. So you had zero acceleration most of the time - but at precisely time B you had...infinite accelleration. So for most of the journey, there was zero accelleration - but at time B there was infinite acceleration. SteveBaker 00:09, 21 September 2007 (UTC)

Okay that does makes sense...but then why in the world does my textbook (wiley 7th edition) give an answer of -8.3km/h²? I've tried nearly every way to get that number pop up in my calculator but it won't. Is the textbook wrong then?

Well, let's assume that your approximation of the three sections of the graph as straight lines is wrong. I think the average accelleration should be the velocity at the very end of the graph minus the velocity at the start of the graph - divided by the time. The rate of change of velocity over time. I don't care what happens to the position and velocity between those two points...right? So measure the slope of the curve at time A (that's the initial velocity), measure the slope at time C (that's the final velocity), subtract one from the other and divide by the total time. SteveBaker 00:25, 21 September 2007 (UTC)

Ahh, and there it is. Thanks for devoting so much time and effort. Thanks again! 207.161.45.29 00:34, 21 September 2007 (UTC)

Please do point out to your instructor that the illustration is crap, in that infinite acceleration is needed between the flat lines, which, of course, is impossible. StuRat 02:17, 21 September 2007 (UTC)

Indeed - yes. I'm a little dissatisfied with the definition of an 'average' - in a situation where you have zero acceleration throughout the period being sampled - with the exception of an infinite acceleration for a zero amount of time...I'm not sure that the mathematical concept of an 'average' can actually be calculated. However...it looks like we answered this one to at least some degree of satisfaction. SteveBaker 14:44, 21 September 2007 (UTC)

The notion of average is actually one of the motivations for introducing such things as the Dirac delta function. If you work at a goldsmithy and get paid in the form of a continuous trickle of gold from the casting pot, we can talk about your wage as a literal instantaneous derivative of value in the gold that's yours, and that derivative is constant (at least over the work day). If your company decides to instead give you weekly paychecks via direct deposit, and the average rate of payment is the same, then the paychecks (which are instantaneous adjustments to your wealth) must each have the value of the week's worth of trickle. The checks can be seen as the limiting process of giving you a larger portion of the "flow" for a shorter period of time: you could have all the output for, say, 3 minutes a week instead of having the trickle. Then the plot of your wealth-rate over time looks like a series of top hats corresponding to those 3 minutes each week. The paychecks are just the limit as the paying-time tends to 0 while the paying-rate grows without bound in such a fashion that their product (integrated over the longest time interval involved, like a week) is constant. On longer time scales (like calculating your yearly salary) the average is all that matters, and the divergent instantaneous values are unimportant.

In the OP's problem, the discontinuous changes in velocity merely correspond to changes that are fast enough that we don't worry about them. A bus could easily change speeds from 25 to 6.6 or from 6.6 to -3.84 kph in a very short time compared to an hour or more of travel at each speed, so (in terms of its overall position) the details of how it changed speeds are unimportant (except to the passengers, who do not want to experience the conceptual infinite acceleration). The average acceleration is quite well-defined, so long as we are sure that we don't cut the graph off in the middle of a change: if the bus came to a stop at the 3.5 hour mark, our value for the average acceleration changes drastically if we include that change or not (or include half of it!) in the analysis. The reason for the trouble is that we are told to evaluate the average acceleration on a precise time interval, so if there's a change at one end or the other there's no way for it to be so fast that we don't have to worry about its precise duration and shape. --Tardis 19:33, 21 September 2007 (UTC)

There is something else confusing about "average acceleration", how to deal with negative acceleration (deceleration). For example, if you accelerate at 1 g to the half-way point of your journey to the Moon, then turn around and decelerate at 1 g for the second half of the journey, does that mean your average acceleration is 1 g or 0 g ? There are different ways of looking at it. I suppose we can call the 1 g answer "the average of the absolute values of accelerations" and the 0 g answer "the average acceleration", to avoid this confusion. In this case, the 1 g answer is definitely more useful, when considering the effects on humans. (Note, this isn't how actual Moon trips have worked, but would provide the most comfortable, quick journey, if energy was not a constraint.) StuRat 16:08, 22 September 2007 (UTC)

Heat Absorbtion

Please go in depth on the following question. Do different colors absorb heat diffently? If so, why? —Preceding unsigned comment added by 208.61.108.71 (talk) 23:06, 20 September 2007 (UTC)

Yes. A coloured object looks coloured because it's absorbing some frequencies of light and reflecting others. The light energy it absorbs turns into heat (in almost all materials). So a black object (which absorbs all frequencies) gets hotter than a white object (which reflects most of it). However, it's not quite a simple as that because lots of the sun's energy comes in the form of Ultraviolet and InfraRed light - and two objects might appear to be the same colour but in fact absorb different amounts of UV and IR making one get hotter than the other. Beyond that, it's a complicated matter to actually predict the total energy gain because when an object gets hotter, it sheds energy by emitting IR radiation too. So some objects emit energy better than others - which greatly confuses matters. SteveBaker 23:45, 20 September 2007 (UTC)

To clarify on Steve Baker's answer, a black object absorbs all visible light frequencies, but not necessarily those outside our vision range. User:Sifaka who is currently IP 128.196.149.20 01:27, 21 September 2007 (UTC)

People never seem to mention that darker objects emit energy easier, too. Because of this, when objects are cooling down, darker object will cool faster and end up being colder than light objects. — Daniel 01:46, 21 September 2007 (UTC)

Are you sure about that ? Why would it's color in the visible frequency be related to it's ability to radiate heat (in the infrared frequency) ? StuRat 02:05, 21 September 2007 (UTC)

I think he assumes that darker objects in the visible spectrum are also typically darker in other wavelengths. --Spoon! 02:38, 21 September 2007 (UTC)

Well, if they were then they'd cool off slower. No - what's going on here is that EMISSIVITY is not necessarily correlated with REFLECTIVITY. The former is associate with shedding heat - the latter in absorbing it. Whilst it is commonly the case that visible colour and IR reflectivity and emissivity are correlated - it's not necessarily true. SteveBaker 03:54, 21 September 2007 (UTC)

Kirchhoff's law of thermal radiation --Spoon! 04:21, 21 September 2007 (UTC)

And Black-body radiation. --jjron 09:01, 21 September 2007 (UTC)

September 21

GEarth blue streaks

I was playing around with the sky part of Google Earth when I came across these really odd parallel blue streaks. Here's a .kmz link to the location: BlueStreaks.kmz. I was wondering if those are actual astronomical thingamabobs or if they're just a glitch that somehow got into the photo-ing stuff.

For those of you who don't feel like opening the .kmz file, here's a picture of the view: Blue Streaks Foxjwill 02:35, 21 September 2007 (UTC)

Satellites can leave streaks like that on astronomy pictures- the camera takes three different color snapshots of each section, so things that move really fast (like satellites) only show up in one color and as streaks because of the long exposure time. Galaxyzoo has a good explanation in section 3. Except that there are two parallel lines here, so it might be something else. 68.231.151.161 03:42, 21 September 2007 (UTC)

Satellites with a complicated cross-section (say, a pair of solar panels) can leave parallel streaks like that. There's a certain lack of scale there, so it could also be something more prosaic, like UFO running lights. --Carnildo 22:36, 21 September 2007 (UTC)

Hypotheticals in chemistry

I posted this question in talk:sulfonic acid 3 weeks back but got no nibbles, so I thought I'd ask it here...

I can guess—but I cannot find a definitive explanation of—what is meant by calling these babies [the sulfonic acids] hypothetical. I suppose it's OK to use a bit of jargon that's well known in chemistry, but I'd suggest creating an entry for it on the "hypothetical" page because at least one reasonably well educated person (me!) cannot fully understand the first sentence of the article, and that's poor design form in Wikipedia.

PaulTanenbaum 02:42, 21 September 2007 (UTC)

Ball-and-stick model of methanesulfonic acid

Chemical structure of sulfonic acid.

I think what it means is that the sulfonic acid shown on the top does not exist in this form (see tautomer). It would convert to sulfurous acid (bottom) in solution because that would a better bonding configuration for the sulfur. However, if rather than a not very electron donating hydrogen were swapped out for a methyl, butyl, etc. group, the six bonded sulfur configuration found in sulfonic acid would be stable enough to exist. Even if it weren't especially stable, it wouldn't have much choice anyway. Unlike the hydrogen attached to the sulfur, an organic group could not be transposed to an oxygen form a err... sulfonylester? (not sure what to call it) because the intermediate would involve an extremely thermodynamically unfavorable carbocation. Methanesulfonic acid certainly exists. Here is the MSDS. http://physchem.ox.ac.uk/MSDS/ME/methanesulfonic_acid.html Sifaka ^talk 05:04, 21 September 2007 (UTC)

Chemical structure of sulfurous acid.

I'll take a stab: if we consider a zwitterionic resonance form of O=S ↔ O^–1–S⁺¹, then we have an H on a partially-positive S (see sulfoxide for a dramatic example). Tautaumerizing puts it on the O instead (quenches partial negative) and leaves a lone-pair on the S (quenches the partial positive). The protons on the carbon attached to S in an alkylsulfonate are particularly acidic, further support for S being non-stabilized by having a non-electron-donating H attached to it. Interestingly though, if you deprotonate sulfurous acid to get bisulfite, then you do get a structure with H on S. Note that carbocationic rearrangements are quite common but they are more often occurring by concerted migrations instead of a carbocation popping off and then later reattaching somewhere else. And they usually need a pretty strong driving force (a preexisting carbocation, a strained ring, etc). DMacks 06:28, 21 September 2007 (UTC)

Much clearer explanation than mine DMacks. Thanks, Sifaka ^talk 07:12, 21 September 2007 (UTC)

building downtown nyc

I heard that south of greenwich st. in nyc there used to be ocean, but it got filled up over the years and reclaimed as land. how can you build skyscrapers on a man-made landfill? Don't you need some strong bedrock to support them? —Preceding unsigned comment added by 12.217.199.246 (talk) 06:12, 21 September 2007 (UTC)

You drive piles down through the fill into the bedrock, below the water line if that's where the bedrock is. —Tamfang 08:08, 21 September 2007 (UTC)

What will happen to this molecule?

While answering the question two above I wondered about the stability of this molecule. After querying NIST Chemistry WebBook and google, I couldn't find any examples of anything like this as a functional group. I figure it must spontaneously react with itself. Assuming 2 molecules reacting with one another, I pushed arrows as shown to produce two Organosulfonic acids. Is this a reasonable assumption for what would actually happen? Organic chem buffs, what do you think? Sifaka ^talk 07:07, 21 September 2007 (UTC)

It is a reasonable explaination of what might happen if you had that radical in a jar...but of course that doesnt mean anything like that will occur :DShniken1 11:59, 21 September 2007 (UTC)

It's a sulphite ester. In genereal no this reaction won't occur because the R-O bond is much stronger than the R-S bond - so the equilibrium constant would prevent the reaction occuring to any noticeable degree.87.102.87.157 15:01, 21 September 2007 (UTC)

I don't have experience with the electronics/stability/reactivity of sulfite esters themselves, but in related structures such as DMSO, the sulfur-bound oxygen, not the sulfur itself, often acts as the nucleophile. HSAB is an interesting way of comparing relative stabilities of these structures. Perhaps by choosing an electrophile (Lewis acid, in HSAB terms) that is particularly soft, one could get reaction at the S or migration of something from O to S? Acid hardness is yet another way of explaining the relative stability of sulfonic acid vs sulfurous acid: H⁺ is a hard acid, O^– is a hard base, S^– is a soft base. A bit of caution here: relative stability is about which structure would be preferable, not whether or how one structure could convert to a more stable one…lots of things are "stuck" in less stable forms because there's no viable mechanism for the change. DMacks 16:14, 21 September 2007 (UTC)

Good point, if R was Br (bromine) I would expect that change, but R often means an alkyl or other hydrocarbon group - I made that assumption.87.102.87.157 17:00, 21 September 2007 (UTC)

After sitting on it for a night I found what appears to be a more plausible multistep reaction which is sort of analogous to a decarboxylation reaction but forms sulfur dioxide gas and some sort of alcohol depending on what the R group is. The most unstable intermediates are protonated oxygens and oxyanions in neutral reaction conditions although this reaction would be catalyzed by acids or bases. Seems more likely to me. Sifaka ^talk 17:25, 21 September 2007 (UTC)

Yup, now we're talkin'! Hydrolysis (cf. R migration O→S) is a well-known process among many types of esters. For alkyl sulfates, both the C–O and O–S bonds are labile under various conditions (loss of an intact sulfate or hydrolysis of the ester bond, respectively), though some of the mechanisms are still being investigated (doi:10.1021/ja0279747 S0002-7863(02)07974-X for example). Sulfite haloesters are also highly reactive at the C–O bond (see thionyl chloride#Use in organic chemistry). Then there are also the various sulfite ester hydrolysis mechanisms (see [http://pubs.nrc-cnrc.gc.ca/cgi-bin/rp/rp2_abst_e?cjc_v77-413_55_ns_nf_cjc Can J Chem. 55 1977 2971-2976). DMacks 17:49, 21 September 2007 (UTC)

mitosis,meiosis in humans

what takes place in mitosis in the human body? what takes place in gamete formation in humans? —Preceding unsigned comment added by 82.206.143.13 (talk) 07:15, 21 September 2007 (UTC)

I would suggest reading the articles mitosis and meiosis to answer your question. Sifaka ^talk 07:21, 21 September 2007 (UTC)

Colourblindness

Are all animals colourblind?124.7.82.159 09:05, 21 September 2007 (UTC)

I would think it unlikely. It might be a good start to think about why animals, in it's broad sense, are coloured. Off the top of my head I'd say there are three drivers for colour in animals.

Camouflage, defensive and offensive.

Attraction for mating or territorial defence.

Chance, as when the animal has other features that don't require specific colouration, e.g. elephants or rhinos.

Clearly perception of colour is important and thus presumably visible in a wide range of animals, birds (of paradise, for example) lizards and cephalopods are three groups that come immediately to mind where colour is used to transmit information. If it transmitted we must assume it is received. Richard Avery 09:21, 21 September 2007 (UTC)

See our articles on color vision and monochromacy where this topic is discussed in (a little) more detail.--Shantavira|^{feed me} 11:26, 21 September 2007 (UTC)

No - most animals aren't colour blind - although that term is a horribly inaccurate one and requires clarification before we can proceed to answer the question.

First let's establish a baseline for comparison. Humans can see only three colours - red, green and blue - and we have other cells in our eyes that detect brightness (without responding to colour) and which are really sensitive to motion. Everything else we see is a mixture of those colours - yellow is a mixture of red and green for example - even 'normal' humans are colour blind in that we are completely unable to distinguish between a mixture of red light and green light (such as is produced by your computer screen when it displays "yellow") and a pure yellow light such as would be found in a rainbow or being emitted by sodium street-lamps. This makes us 'trichromats' - we see everything in terms of three colours plus an overall average 'brightness' value that's mostly useful at night.

People who are "colour blind" are sometimes dichromats with one set of colour detection cells completely missing...or (like my son) they may be trichromats who have weak colour perception in one or more sets of colour detectors making some colours hard to distinguish. Those people don't see things in black and white - they see them in a different range of colours depending on which set of detectors are missing or weak. It's wrong to call such people "colour blind" because they do see colours - but that's the term we use. My son can correctly identify all of the colours in a rainbow - but cannot pass a colour blindness test.

A really unfortunate person might have one or zero colour detectors - and they will truly only see in shades of grey and might truly be called 'blind' to colour.

There are also a very, very few women who are tetrachromats (in fact only one such person has been clearly identified and tested) - they can see colour even better than a typical human...compared to them, we are ALL "colour blind"!

OK - so with those things in mind - how does animal colour perception stack up against us humans:

• Some animals (such as owls) need really good vision at night - they don't bother cluttering up their eyes with useless (to them) colour sensors - but instead pack them with brightness/motion detectors. They see in amazingly low light levels - but they are utterly colour-blind. Their eyes are also somewhat sensitive to Infra-red so they can see 'heat' from warm, furry mice...but I believe that's still a monochrome sense. The world for them must be a lot like using military night-vision devices is for us.
• Some animals (like dogs and cats) are dichromats by nature. The can see in colour - much like a dichromat human - but not with as much colour sensitivity as a trichromat human. I wouldn't call them 'colour blind' so much as 'colour deficient'. We think that humans probably evolved to see in three colours in order to be able to distinguish red and green so that we could tell the difference between ripe and unripe fruit. Dogs and cats are carnivores - they don't care about that - so dichromaticity is fine for them - and the extra space in their eyeballs allows for better night vision - which is good for a carnivore.
• Some animals (such as the goldfish) have as many as seven different colour detectors in their eyes (heptochromats)!! Their world must be just alive with subtle colour because they see colour incredible better than humans. I have no clue why they evolved this ability.
• I read a while back about a species of freshwater shrimp which may have even more than seven colour detector types...perhaps as many as twelve!
• Bees can see in ultra-violet light - beyond the range of our eyes. Otherwise plain-coloured flowers often have elaborate patterning in the UV part of the spectrum specifically to attract bees. I don't know whether they can see different 'shades' of UV light or not...I suspect not.

So, no - animals aren't all colour blind. Some are, some aren't, some see colour better than us, some worse - some can see light outside of the "visible spectrum" that we can see in. But there isn't a simple distinction between being able to see in colour or not - there are huge ranges of colours that humans cannot distinguish - and some things we think of as 'colours' (like magenta) that aren't true colours at all - but merely an artifact of our (relatively poor compared to goldfish) colour vision.

SteveBaker 14:35, 21 September 2007 (UTC)

For a really interesting and thorough discussion of colour-blindness with respect to (scientific) presentations, see this link. The website shows what people with different colour deficiencies see. -- Flyguy649 ^talk _contribs 20:02, 21 September 2007 (UTC)

Have a read of this thread from a couple of months back, WRT to the colour perception in birds too... --Kurt Shaped Box 02:44, 22 September 2007 (UTC)

photons and gravity

Are photons affected by gravity? According to the article on Newton's (outdated?) law on gravity, the force must be equal to zero since photons have no mass. If so, how do black holes "trap" photons? (I have almost no knowledge of quantum mechanics and similar things). Thanks. --wj32 ^{talk | contribs} 09:57, 21 September 2007 (UTC)

In general relativity, mass curves spacetime. In this model, straight lines across spacetime are curved near masses. Since photons travel in straight lines, they will also curve. Black holes curve space time so much that a straight line going out from a black hole (or any straight line that enters the event horizon) enters back into the black hole. A photon following this straight line cannot escape. (I am, of course, vastly simplifying here). Capuchin 10:14, 21 September 2007 (UTC)

You can't use Newton's laws to talk about black holes—the latter are a prediction of General Relativity and have nothing to do with Newton. General Relativity supercedes Newton. --24.147.86.187 13:01, 21 September 2007 (UTC)

That's not entirely true. Somewhere between the periods of "Newton develops theory of gravitation" and "Scientists decide the particle theory of light doesn't work too well", someone pointed out that if light were subject to gravity - and there was no actual reason at the time to suggest that it wouldn't be, even if it were some strange kind of effectively massless particle - then it would be possible to have an object of such a size and mass that its escape velocity would exceed the speed of light, hence creating a black hole. Confusing Manifestation 13:38, 21 September 2007 (UTC)

Indeed. John Michell predicted the existence of black holes in a letter to Henry Cavendish in 1783. The text of the letter is here - the part dealing with black holes is paragraph 16. Gandalf61 13:48, 21 September 2007 (UTC)

So an idea based on a misunderstanding of gravity and a misunderstanding of light counts as a prediction of something rooted in different conceptions of both? Not in my book. --24.147.86.187 00:35, 22 September 2007 (UTC)

Depends on what it means to know/predict something. Someguy1221 00:47, 22 September 2007 (UTC)

Certainly photons are bent by gravity - check out Gravitational lens - in which the bending of light by the gravitational field of some large body out in space is used to magnify the image of more distant objects in exactly the same way that light is bent by a glass lens. There is a photo there showing it actually happening - so it's hard to deny! SteveBaker 16:52, 21 September 2007 (UTC)

• And you don't even need something as massive as a black hole to visibly bend the path of a photon. Light curving around extrasolar planets has been used to discover them. See gravitational lensing. --Sean 17:05, 21 September 2007 (UTC)

The odds of having a planet lens some distant object is really small - as our article points out, it's only been recorded once - and the alignment was too brief for anyone to double-check it. Large objects like galaxies and black holes bend light by so much that a chance alignment is not really needed - so while it's true that you can do this with planets, it's much easier to demonstrate with bigger objects. SteveBaker 17:24, 21 September 2007 (UTC)

Gravitational microlensing had found three planets as of this two-year-old paper. --Sean 20:00, 21 September 2007 (UTC)

I don't really buy that photons have no mass. Experimentally, all they could determine is that they have no mass above a certain threshold which they can measure. But, let's say they are right and photons have no "mass". That really means photons have no rest mass, which is a useless bit of data since photons are never at rest. They do have relativistic mass, however, when moving (which is always), that explains why they are pulled by gravity and why they can exert a pressure on a solar sail. (This may not be the current way of stating things, but I find it useful in explaining photon behavior under Newtonian mechanics.) StuRat 15:43, 22 September 2007 (UTC)

Physics

So this is sort of a bullshit question. As it seems mathematically simple. The question goes something like this: An automobile starts from rest and accelerates to a final velocity in two stages along a straight road. Each stage occupies the same amount of time. In stage 1, the magnitude of the car's acceleration is 3 m/s². The magnitude of the car's velocity at the end of stage 2 is 2.5 times greater than it is at the end of stage 1. Find the magnitude of the acceleration in stage 2.

a1 = v1/t1 (that's obvioius)

a2 = v2/t2 (obvious as well)

v2 = 2.5v1 (seems obvious)

t1=t2 (probably the most obvious)

So given that a1 = v1/t1....v2 = 2.5v1, one can say that a2 = 2.5v1/t1

Since v1/t1 = 3m/s². Now one could play with equations and get a2 = 2.5 (3m/s²) = 7.5 m/s²

However, this is stated as being wrong. Either I made a complete mistake or something else is up. Anyone know what? Thanks HERODOTUS 14:22, 21 September 2007 (UTC)

Your second equation should be a2 = (v2-v1)/t2, and thus a2 = (1.5)v1/t1. Gandalf61 14:39, 21 September 2007 (UTC)

Oh there we go... forgot about getting the change in v. thanks. HERODOTUS 14:45, 21 September 2007 (UTC)

Sky and Planet Earth

What makes the sky and our planet appear blue from outer space?24.91.219.166 14:59, 21 September 2007 (UTC)

Water molecules in the atmosphere refract ("scatter") blue light more than other colors, due to the wavelengths involved. Similar to how a prism refracts a beam of light into a rainbow - some colors are "bent" more than others. Saturn 5 15:35, 21 September 2007 (UTC)

See Diffuse sky radiation. DMacks 16:19, 21 September 2007 (UTC)

See Mie scattering and Raleigh Rayleigh scattering. SteveBaker 16:40, 21 September 2007 (UTC)

Yeah. "Raleigh scattering" is what Hurricaines fans do after the game. DMacks 17:23, 21 September 2007 (UTC)

And the oceans appear blue from above because they reflect blue sky; without atmosphere I guess they'd look muddy green. —Tamfang 19:24, 21 September 2007 (UTC)

No, water is actually blue. It's very faint though, which is why you have to look through a lot of it to really notice. Someguy1221 22:22, 21 September 2007 (UTC)

If you want proof, go to Crater Lake sometime. It's incredibly pure water a few thousand feet deep -- and incredibly blue. The pictures in the article don't do it justice. --Carnildo 22:41, 21 September 2007 (UTC)

Air appears to be slightly blue also - when I looked at the dome of a nuclear reactor from a long distance away it was pale blue, as I walked towards it the colour changes to bright white. 80.0.114.206 13:52, 22 September 2007 (UTC)

INCORPORATION OF INTERMEDIATE FREQUENCY

DEAR SIR. I AM LIAQUAT JAWED FROM KARACHI PAKISTAN. SINCE LAST FIFTEEN DAYS I AM IN A SEVIER CONFUSION THAT AS GIVEN BELOW;

1) WHAT ARE THE BASIC RANGES OF INTERMEDIATE FREQUENCIES FURTHER THAT VHF/UHF DOES COME UNDER THE RANGES OF INTERMEDIATE FREQUENCIES .

2) WHETHER CATV DISTRIBUTION AMPLIFIER OR CATV LINE AMPLIFIERS DO INCORPOATE THE INTERMEIDATE FREQUENCY.

3) WHETHER CAN WE CLASSIFY THE CATV DISTRIBUTION AMPLIFIERS OR CATV LINE AMPLIFIERS UNDER THE CATEGORY OF INTERMEIDATE FREQUENCY INCORPORATING AMPLIFIERS.

WAITING FOR YOUR AN EARLY REPLY.

THANKS AND BEST REGARDS.

LIAQUAT JAWED —Preceding unsigned comment added by Lachi9 (talk • contribs) 16:12, 21 September 2007 (UTC)

Ow! Please type in mixed upper and lower case in future - typing in ALL CAPITALS seems rude to most people. SteveBaker 16:37, 21 September 2007 (UTC)

I suggest you start by studying our articles on radio frequency and CATV. (I'm not sure what you mean by "intermediate frequency").--Shantavira|^{feed me} 18:30, 21 September 2007 (UTC)

We have an article on intermediate frequency - but it doesn't list the UHF and VHF IF's. SteveBaker 20:03, 21 September 2007 (UTC)

fish in water

take a bucket of water full to the brim(water about to overflow) add a fish any type dead or alive,no water will become displaced why is this? —Preceding unsigned comment added by 83.71.37.244 (talk) 18:07, 21 September 2007 (UTC)

Because what you just stated doesn't happen. Water is displaced. If you put something very small in a very large container of water, it is possible for surface tension of the water to bulge upward without overflow - but the bulge is still displaced water. -- kainaw™ 18:09, 21 September 2007 (UTC)

See meniscus for a little more info. That article could do with some more info, but that is the phenomenon you would observe. Saturn 5 18:12, 21 September 2007 (UTC)

If you toss a fish into a bucket of water then the water level goes up. If it's "full" beforehand then it overflows (if there was room for a little more water because of meniscus effects then the bucket wasn't full yet). The questioner is incorrect. Is this some kind of urban legend you read someplace? SteveBaker 20:02, 21 September 2007 (UTC)

If you toss a struggling live fish (or a dead fish from a sufficient height) into a bucket, it may splash it's own volume of water out of the bucket, in which case the waterline on the bucket would remain the same. StuRat 15:27, 22 September 2007 (UTC)

Sleepless early-hours mulling over past bad events

It seems common for many people to involuntarily mull over past bad events if they are sleepness and half-awake in the early hours of the morning. Does anyone know why there is a psychological tendency for humans to do this? Or how to stop it? Thanks. 80.2.199.116 20:05, 21 September 2007 (UTC)

See cognitive behavioral therapy for the field of techniques on controlling negative thoughts. --Sean 22:05, 21 September 2007 (UTC)

To stop it, you refute those thoughts and think of something pleasant/interesting to you. Alternatively, you can refuse to accept any words in your thoughts, only pictures. Eventually the pictures will fade and you will lose consciousness. —Preceding unsigned comment added by 88.110.12.8 (talk) 02:21, 22 September 2007 (UTC)

Useful advice, but why do humans suffer this in the first place? 80.0.131.244 08:53, 22 September 2007 (UTC)

Very shortly and simply put: our defense mechanisms are not as strong during the night as they are during the day, so unpleasant thoughts have a stronger impact on us. Lova Falk 09:14, 22 September 2007 (UTC)

One theory of sleep is that the brain uses this opportunity to review past events, consider where mistakes were made, and formulate a plan on how to do things better in the future. A semi-sleep state may take on some of these characteristics, too. StuRat 15:24, 22 September 2007 (UTC)

how old is stone bone

Many years ago i found a petrified bone in the bad lands of South Dakota, it appears to be a femar of a four legged animal. The bone has become brittle stone. The bone marrow has become crystalized. Any idea how long it would take for that to happen? Hundreds, thousands, or millions of years? —Preceding unsigned comment added by 69.254.44.75 (talk) 20:20, 21 September 2007 (UTC)

If it's still bone, it's probably not too old, as actual preserved tissue from the distant past is extremely rare. If it's stone, it could be anywhere from thousands to hundreds of millions of years old. See fossils. --Sean 22:09, 21 September 2007 (UTC)

I'd take it to a natural history museum and ask them to tell you what it is. It's probably just a 1000 year old wolf or something similarly worthless, but you never know, it may be some type of dinosaur bone. (Make sure you obtained it legally, though, as some areas, like National Parks, don't let you take fossils home.) Also, how big is it ? (A 10 foot long femur would definitely make it a dino bone.) StuRat 15:15, 22 September 2007 (UTC)

Any Aussies here?...

I was just at a local bar. We were 'discussing' fall/autumn. Some were saying that TODAY, September 21st was the first day of fall. I said, "No. The official date of fall this year is Sunday, September 23rd." Ok, that`s not a question. One of the patrons said that he lived for several years in Australia, here`s the "Aussie" connection, and that THEY 'celebrate' the changing of the seasons ALWAYS on the 1st of the month of the 'official' change. Of course, they would have 'celebrated' spring, and not fall, but the question is this: Is it true, that they, the Australians, celebrate these 'changes' at the first of their respective months? Seems quite strange to me. Sorry for posting here on the science desk but, I was already 'here', and it DOES have an Astronomy bent! Thanks Dave. 64.230.233.222 21:32, 21 September 2007 (UTC)

The four seasons are more relevant in the southern part of Australia than the northern part. Here in Melbourne:

Summer is Dec, Jan, Feb

Autumn is Mar,Apr,May

Winter is Jun,Jul,Aug

Spring is Sep,Oct,Nov

I'm not sure what you mean by "They celebrate the changing of the seasons" as I certainly do not celebrate the changing of the seasons nor do I know of anyone who does. However the snow bunnies do celebrate the starting of the ski season but not everyone is a snow bunny. 210.49.155.132 22:59, 21 September 2007 (UTC)

Thanks for the reply, umm, 210. To simplify, the aforementioned patron, who spent some time in Australia, said that Australians consider the 1st of the month, 'their' official start of a particular season, be it fall or spring or whatever, rather than the equinoxes and solstices as the official beginnings of said seasons. No REAL celebrating implied. Perhaps I should have utilized the term 'observe', rather than 'celebrate'. Is that TRUE? Sorry for any misunderstanding, and ty again. Dave 64.230.233.222 23:19, 21 September 2007 (UTC)

So you might have heard that the summer solstice (roughly speaking the "longest day of the year", even if it isn't always exactly) used to be called "midsummer", whereas in North America we think of it as the first day of summer. The reason is that average daily temperature somewhat lags the length of the day (it takes a while for the ground and the oceans to heat up), so the hottest three months of the year are roughly the ones between the summer solstice and the autumnal equinox. That makes the summer solstice a convenient marker for the start of summer.

As I understand it, in Australia, for whatever reason, the lag time is a bit less, and they find it convenient to use the first day of the month in which the solstices and equinoxes appear. --Trovatore 00:46, 22 September 2007 (UTC)

I'm in Sydney, and we change seasons on the first day of the respective month, in fact until a few minutes ago I used to think the entire world changed seasons on the first day of the month... As for the lag time of temperature changes and what not, I think the reason we change on the first day is simply because it is easier to remember, given that often the weather does not match the season I'd say the lag times etc are not taken into account. Still that's just my opinion 124.183.147.134 01:24, 22 September 2007 (UTC)

Thanks for the replies folks. And 'Sydney', 124; You`re probably just as surprized to hear that the whole world doesn`t change on the 1st of the respective months as I am to hear that you, in fact, DO change at those times. As I said earlier, seems strange to me. Just as an aside, for the Aussies: What do your calendars say? Is your first day of spring actually written on your calendars as occuring on September 1st? Thanks again all. Dave 64.230.233.222 04:27, 22 September 2007 (UTC)

When it's written on the calendars, yes. However, given that often we get calendars that are actually sourced from overseas, most often produced for the mass market in the US, we will actually find out that September 23 for example is the first day of Autumn (or even worse, Fall), when we're actually three weeks into Spring; d'oh! BTW, I don't mean to enter into a 'your culture is stranger than ours debate', but it always strikes me that starting the season on the first of the month is far simpler - you started this post saying you had a debate about which day was the start of Fall; you never get that debate in Australia as everyone knows it's the first of the month, the only trick can be knowing which month. Cheers, --jjron 12:50, 22 September 2007 (UTC)

Well, except months are arbitrary, fixed by human convention; solstices and equinoxes are not. Aligning our seasons to the solstices and equinoxes makes it look like the seasons aren't arbitrary either. Of course it's really just a trick. If we wanted summer to be the fourth of the year with maximum insolation, it would run from early May to early August (or, I suppose, early November to early February for y'all). --Trovatore 17:15, 22 September 2007 (UTC)

Number of neurons in the human brain

What is an estimate of the number of neurons in the human brain? Please cite a research source.72.75.96.28 21:30, 21 September 2007 (UTC)superiorolive

Neurons#Neurons_in_the_brain: "One estimate puts the human brain at about 100 billion (10¹¹) neurons and 100 trillion (10¹⁴) synapses." This review says "Estimates for the human brain range between 10 billion and 1 trillion. The imprecision in these estimates is due almost entirely to uncertainty about the number of granule cells in the cerebellum, a problem that can be traced back to a study by Braitenberg & Atwood (1958). More recent work by Lange (1975) makes a reasonably accurate estimate possible: The average human brain (1350 gm) contains about 85 billion neurons. Of these, 12 to 15 billion are telencephalic neurons (Shariff 1953), 70 billion are cerebellar granule cells (Lange 1975), and fewer than 1 billion are brainstem and spinal neurons." Rockpocket 21:52, 21 September 2007 (UTC)

Thank you for this72.75.96.28 02:21, 22 September 2007 (UTC)superiorolive

Is there any way to stop melanin production in humans?

Is there any way to stop melanin production in humans? And please dont say death or aging or idk. —Preceding unsigned comment added by 81.99.218.58 (talk) 22:28, 21 September 2007 (UTC)

There are chemicals that will permanently depigment human skin. Or so Vitiligo#Treatment would have you believe. Vitiligo, by the way, is a natural condition in which the body has no ability to produce melanin over patches of skin. Someguy1221 22:32, 21 September 2007 (UTC)

September 22

Are there chemicals that will permanently depigment human hair?

Are there chemicals that will permanently depigment human hair? —Preceding unsigned comment added by 81.99.218.58 (talk) 00:06, 22 September 2007 (UTC)

Yes, but such a chemical would have to be cytotoxic, as to do so one needs to destroy the stem cell niche of the hair follicle. There is not a known chemical that can do that specifically without harming other cells. Similarly exposing your head to high doses of ionizing radiation would permanently depigment your hair. It would probably also give you cancer though. The alternative would be to permanently inhibit the melanogenic enzymes, such as tyrosinase. There are chemicals that can do that in a temporary manner, but doing so permanently, and without serious adverse effects, is not currently possible. So if what you really wish to know is if there is a chemical that can safely and permanently depigment human hair, the answer is no. Rockpocket 01:32, 22 September 2007 (UTC)

Colors

So, I was reading the question above on colorblindness, and I had a startling thought. You said we don't perceive real yellow, just red + green, right? So if we were to meet an alien with yellow receptors, they could see REAL yellow, and what we call yellow they'd call redgreen (or whatever)? so we never really see Yellow at all (or any color other than red, green, and blue) in the pure forms? After all, people with no green receptors see red+blue for green, right, which looks TOTALLY different... am I on to something here? Kuronue | Talk 00:47, 22 September 2007 (UTC)

In terms of colour perception, it doesn't really matter whether we see "real" yellow when we can perceive it so well using our three types of cones. A yellow cone could certainly provide an alien with a richer yellow hue perception, but they would all still be variations of the same "yellow" that we see (assuming, of course, the same processing system of perception is in place). The reason we don't need a yellow cone is because its redundant to the three that we have. Rockpocket 02:06, 22 September 2007 (UTC)

Yes, but like, someone who is partially colorblind can distinguish between colors, but they look totally different to them. Just because we can distinguish yellow from blue doesn't mean what we're seeing is anything like actual yellow, right? I mean, green looks like brown to people with a defective cone, so maybe some brownish colors to us are actually shades we can't see properly, things like that... Kuronue | Talk 03:01, 22 September 2007 (UTC)

Well, what is "actual yellow"? Its a wavelength of light. Notwithstanding the the "red" receptor actually has its peak sensitivity in the yellow part of the spectrum anyway, the actual detection mechanism is simply a action potential along an axon in response to the detection of a certain wavelength. The information is processed in the parvocellular layer where certain neurons process red-green differences, and others process blue-yellow differences. Its here that we "see" yellow. If an alien had a different cone, then it would fire in response to the appropriate wavelength, but still need to be processed in some manner. Depending on how these inputs are wired, the alien brain could "see" exactly same yellow as we do or it could interpret the wavelength as any pseudo-colour its brain evolved to conjour up. What is likely is that it could use such a receptor to distinguish multiple shades around that wavelength that would be beyond what we can distinguish. I guess what I'm trying to explain is that a fourth receptor type in the visible spectrum doesn't really offer "new" colours - our system evolved to have that well covered - it simply expands the subtles hues within those we already see. Rockpocket 04:27, 22 September 2007 (UTC)

You could try getting your hands on a yellow light - or a white light with a pure yellow filter, as well as two lights with red and green filters - then try illuminating things - you should be able to tell the difference between the things that are yellow for different reasons.. As an aside I remember that some insects can see ultraviolet light - this lets them see patterns on plants that we humans can't see - for instance flower petals look striped to insects87.102.89.127 12:37, 22 September 2007 (UTC)

Right - there are (at least) two "yellow" colours - one is a mixture of red+green and the other is 'true' yellow - light which has a frequency halfway between red and green. Our eyes can't tell the difference - but you can do experiments to see the difference. Put the 'yellow' light through a prism to spread out it's spectrum. Yellow light from your TV or computer monitor will split into two lines (red and green) but true yellow (from a sodium lamp for example) would form a single line (well, more or less). So these two colours look identical to us - but they are NOT the same colour. In order to get an idea how an alien (or your goldfish) would see these colours, we can try some analogies:

• The analogy of sound: On a piano, you can play two notes 'C' and 'E' together - or you can pick a note midway between C and E ('D'). Does C+E sound the same as D? Nope - not by a mile! But that's the exact same thing as the difference between the two yellows.
• We see three colours - red, green and blue. Green is a frequency between red and blue. So we can ask: How different is red+blue from a frequency halfway between red and blue? Well, halfway between red and blue we have green. What does red+blue look like? Magenta! So for our alien/goldfish, the difference between those two versions of "yellow" might look as different as magenta and green!!! That's a very powerful indication about how poorly we percieve colour. What I find most mind blowing is the little old lady in England who is a tetrachromat - she sees colours that almost nobody else in the world can see. She works in a store selling knitting yarns and she remarked to researchers how she was much better at matching colours than other people...no surprise if others were 'matching' magenta and green and calling them "the same exact colour". WOW!

I talk about the problems with "yellow" - but the same problems are there with "cyan" (midway between blue and green or a mixture of blue and green?). The third colour pair that might be problematic would be "magenta" - but we have a green sensor so we can tell the difference between red+blue and green. But in general, for colours that are more complex mixtures of frequencies - there are colours like a mixture of red, green and true-yellow that are yet different from the other two versions. Even our goldfish friend can't get the full subtlety - for that you'd need a spectrum analyser.

SteveBaker 15:22, 22 September 2007 (UTC)

Finally, one should mention that there might be people who can distinguish the two yellows by means of having two different kinds of cones for the red colour, one shifted towards yellow or orange. More at tetrachromacy. Simon A. 16:00, 22 September 2007 (UTC)

Special Relativity and Mass Defect

This was a question that came to me during a physics class. Einstein's special theory of relativity states that as an objects velocity approaches the speed of light its mass approaches infinity, and that increasing amounts of the input energy used to accelerate (eg from combustion of liquid fuel) is converted into matter. The processes of nuclear fusion and nuclear fission produce energy due to the mass defect where the products have less mass than the reactants. However, as the total mass of the system approaches infinity it follows that the mass defect will also approach infinity, which could possibly overcome one of the problems with fast travel and allow us to come closer to the speed of light than if we used conventional fuels. However, wouldn't this also violate the law of conservation of energy (the total energy of the system must remain constant, with mass being recognised as energy according to E = mc²) as both the mass and thrust of the system would increase without any additional input energy?

I only study basic physics, but it would be great if someone could cast some light on whether or not this would be possible 124.183.147.134 01:19, 22 September 2007 (UTC)

• Short answer: no. There are no such defects in special relativity theory, which has been experimentally confirmed many times. --Sean 02:07, 22 September 2007 (UTC)

Um, I think you might be misinterpreting the word "defect" here. "Mass defect" is not a defect in the theory. --Trovatore 02:19, 22 September 2007 (UTC)

Perhaps I should clarify. The theory of special relativity states that as velocity approaches the speed of light mass will approach infinity (although I'm not sure if this has been proved experimentally). The mass defect is not related to the theory of special relativity, but is observed in nuclear reactions (eg in nuclear fusion two hydrogrens fuse to form a helium, the mass of the helium is less than the combined mass of the hydrogen, and this mass defect explains the energy released). I was wondering what would happen if the two separate situations were combined, as the velocity approaches the speed of light the mass of the system should approach infinity, but if a nuclear reaction is occurring then the mass of the hydrogen and helium will approach infinity, meaning the mass defect of the reaction will approach infinity resulting in the energy produced approaching infinity. If this nuclear reaction was used to accelerate the vessel then it would overcome some of the problems with high speed travel (increasing amounts of energy released from conventional fuels would be converted into mass reducing the effective acceleration and restricting the practical obtainable speeds below that of the speed of light, however if the nuclear reaction produced increasing amounts of energy this would allow the system to continue accelerating at a higher rate) however intuitively it seems to violate the law of conservation of mass-energy... 124.183.147.134 02:47, 22 September 2007 (UTC)

Well, think of it this way. Your spacecraft takes off. Its own mass is an upper limit on how much energy it could possibly generate, ever. That is a very finite value. Therefore, it can never supply an infinite amount of energy. The energy lost in accelerating two hydrogen molecules before fusing them will nullify any increase in energy they will produce thanks to being in a very fast reference frame, relative to whoever is measuring it. Someguy1221 04:56, 22 September 2007 (UTC)

From the point of view of people on the space craft (e.g. in their inertial frame), the fuel isn't moving and hence the mass defect remains constant. Thus from their point of view, the energy they have available to generate thrust doesn't change. However, from an external point of view, it is actually more complicated. Because of time dilation, the apparent rate of the reaction (as measured by an outside observer) would slow down. Hence they would actually be generating less thrust per unit external time as their speed increased. 136.152.153.120 03:42, 22 September 2007 (UTC)

Dear physics student, you may have learned that the mass increases as an object accelerates towards the speed of light. This is true if you're talking about a definition of mass called relativistic mass, which is often discussed in popular works on relativity and sometimes in physics textbooks. Early in the history of relativity, that's what was usually meant by "mass." But it's quite misleading if you start to think about things like nuclear reactions in those terms. Instead, you can use invariant mass, which is more useful for a lot of purposes (it's exactly what you want for thinking about a nuclear reactor on a relativistic spaceship!). Since the 1950's or so, physicists have come to use this definition of mass instead. As you accelerate your nuclear fuel, its invariant mass doesn't increase, and that's what you need to convert to energy. --Reuben 04:03, 22 September 2007 (UTC)

• Saying that nuclear fusion and fission "produce energy due to the mass defect" is putting the cart before the horse; it reminds me of Feynman's complaint about wakalixes. There is necessarily a mass decrease of E/c² in any system that releases energy E in some reaction, but that's not why it releases the energy. Chemical power sources work by forming and breaking chemical bonds, and nuclear power sources work by breaking (fission) and forming (fusion) nuclear bonds. There's no difference between them as far as E=mc² is concerned. —Preceding unsigned comment added by BenRG (talk • contribs) 12:26, 22 September 2007 (UTC)

Right. The mass defect bit of fission, for example, is often used just to calculate the energy released, but it is not a good way of explaining the energy released. And the "energy" released isn't some sort of magical burst of lightning as it is usually shown in little diagrams—it relates to the velocities of the various components expelled from the fission reactions themselves (the fission products and the neutrons). I find a better way of explaining the fission reaction (and calculating much of it) to be in the form of thinking of the two split nuclei as being two extremely positively-charged objects placed right next to each other (just out of range of the nuclear force), and then calculating what the electrostatic repulsion is going to be from each of them. --24.147.86.187 14:16, 22 September 2007 (UTC)

I'm drunk - how to sober up quick

it's nearly 4am in the UK now and I'm drunk after a night out. I'm meant to be in work at 8am. Is there any way of sobering myself up quickly? —Preceding unsigned comment added by 81.79.171.12 (talk) 02:50, 22 September 2007 (UTC)

Not really, there isn't a whole lot you can do as "there are currently no known drugs or other ingestible agents which will accelerate alcohol metabolism" See Blood_alcohol#Metabolism and excretion. The best you can do is try to limit the damage, see Hangover#Possible remedies. Rockpocket 03:21, 22 September 2007 (UTC)

I suggest drinking lots of water or rehyrating sprorts beverage about once every two hours, which will minimize the hangover's effects. 128.196.149.25 03:25, 22 September 2007 (UTC)

Exercise helped me when I was in the Marines. After drinking all weekend, I'd show up on Monday morning drunk, but be nice and sober after a 6-mile run. I attributed it to sweating out alcohol while pumping more blood through the liver and kidneys where it gets cleaned. Then, it could just be that the time it took to run was enough for me to sober up. -- kainaw™ 04:54, 22 September 2007 (UTC)

Was the 6-mile run by any chance your punishment for showing up drunk ? StuRat 15:05, 22 September 2007 (UTC)

I also used to run even after wet nights but I was warned that exercising with alcohol in your blood means a serious health risk. I can't remember the details though. Lova Falk 15:44, 22 September 2007 (UTC)

I never had a hangover, because drinking heavily just made me vomit (my body's defense mechanism in action, I suppose). I do NOT suggest that you induce vomiting, however, since that can damage the esophagus and teeth. In severe cases of alcohol poisoning, hospital stomach pumping can help, if they catch it early enough. You might want to call in sick to work, as that likely won't get you fired, but showing up drunk might. You also need to learn not to drink so heavily that you can't function normally (like going to work). Your pores will likely give off alcohol for several hours yet, so even if you clean up you won't fool anyone with a working nose (that's just about all nonsmokers). StuRat 15:05, 22 September 2007 (UTC)

When I have a hangover, I usually take a headache pill, drink a cup of hot black coffee, and go out into the fresh air as soon as possible. Staying indoors will make the hangover remain. It is most important to go out into the fresh air and stay there for many hours. JIP | Talk 16:13, 22 September 2007 (UTC)

matter and anti-matter .

is the total amount of matter and anti-matter in our universe same ? —Preceding unsigned comment added by Shamiul (talk • contribs) 04:21, 22 September 2007 (UTC)

No, there is far more matter than antimatter thanks to baryon asymmetry. Someguy1221 04:23, 22 September 2007 (UTC)

Well, far more matter has been observed than anti-matter, but the article you linked to mentions that distant regions of the universe may well have large amounts of anti-matter so that there could be equal amounts of both in the universe as a whole. Bistromathic 15:41, 22 September 2007 (UTC)

I read the link in full only after I pasted it here, but now I have another one that might satisfy. Experiments win. Someguy1221 15:58, 22 September 2007 (UTC)

It is now considered very unlikely that a balancing amount of antimatter is somewhere far because at the boundary between the matter and the antimatter region, there should be a violent bright emission of gamma rays, and it is now considered excluded that we would have missed such a thing with our gamma-ray observatories. Hence, the origin baryon asymmetry is considered one of the very big open question in physics. Simon A. 16:06, 22 September 2007 (UTC)

are there any chemicals that can permanently inhibit the melanogenic enzymes, such as tyrosinase

are there any chemicals that can permanently inhibit the melanogenic enzymes, such as tyrosinase, stoping the production of melanin, in animals? —Preceding unsigned comment added by 81.99.218.58 (talk) 08:27, 22 September 2007 (UTC)

Link. Someguy1221 15:18, 22 September 2007 (UTC)

Note that none of these permanently inhibit tyrosinase, they simply do so, to a greater or lesser extent, for as long as they are applied. Note they also only work on skin, not hair, as delivery to the hair follicle is an issue. Rockpocket 17:31, 22 September 2007 (UTC)

Retail trend in America

20 year ago Home Depot was able to displace local hardware stores by offering lower prices and better customer service. Years went by. Then Home Depot raised its prices, got rid of even minimal customer services like cutting and threading a piece of galvanized pipe. Anything and everything that did not fall within one standard deviation of average got canned. If you needed 4mm x 12mm screws forget it. Only high profit items like stainless remote control barbeque grills and fancy riding mowers now occupy the entrance to the store. My question is are retail stores now looking to stay in business by selling only the icing off the top of the cake and if so where does that leave the consummer who might need a 4mm x 12mm machine screw or a piece of galvanized pipe cut to 2-1/2 ft and threaded on both ends? Clem 12:01, 22 September 2007 (UTC)

Where does it leave the consumer? Up the creek without a paddle I suppose. But seriously, if major stores are starting to offer such a paltry level of service, presumably that opens up the opportunity for smaller businesses to exploit the market niche that does provide what the consumer wants - and then it's up to the consumer to support those stores by shopping there. Or you might be able to find these types of things in stores that specialise as trades outlets. Unfortunately in our first world consumption obsessed societies it seems that fixing or making things yourself has become very unpopular, as its far easier and quicker (and sadly often cheaper) to go down the Home Depot or equivalent and just buy a new one. BTW, is this a 'Science' question? --jjron 13:06, 22 September 2007 (UTC)

It's the law of supply and demand. If there is high demand for one kind of screw - the prices will be good and everyone will stock them. When the demand is low, the volume is low but the cost of the shelf space to stock them is the same - so either the price goes up steeply or they stop stocking them. You'll still find specialty stores that'll sell you those items - but you'll pay through the nose. Here in Texas, there is a vicious turf war between Home Depot and Lowes - and there are WAY too many of these stores for the amount of business they do - sooner or later one of them is going to disappear. The cut-throat nature of their business means that they have to look at everything they stock and to devote shelf space and staff to those areas that are the most profitable. As for cut and threaded galvanised pipe - geez - get a hacksaw and a set of taps and dies and do it yourself - it's not difficult. SteveBaker 14:53, 22 September 2007 (UTC)

What you describe is the classic result of one business (or a small number of businesses in collusion) taking control of an industry. At first, while they are "on their best behavior", to steal customers from the competition and avoid any consumer wrath, everything is great. But then, once they force their competitors out of business, they turn the screws on the consumer to extract the maximum profit. If any other business tries to compete they are likely to temporarily go back to "good behavior" mode just long enough to regain market dominance. Eventually, other businesses know what's in store for them if they try to compete, so nobody ever tries. It would take a new store with even deeper pockets to knock them out of their dominant position.

One hope for the future is Internet sales. That allows low-volume items to be sold without the need for the huge infrastructure of a brick-and-mortar store which would make such sales unprofitable. I'd see if you can find what you need online. StuRat 14:37, 22 September 2007 (UTC)

The future is now. Buy commodity items at fairly low proces at Home Depot or Lowe's. Buy weird stuff on the web. The web prices are reasonably low because of web competition, but you pay for shipping. You can find really unusual stuff on the web that is not otherwise available. -Arch dude 16:09, 22 September 2007 (UTC)

Thrust sea level/vaccum

Hello

The thrust of the same rocket engine is not the same at sea level and in vaccum, why? The divergent nozzle is adaptable at different pressure?

Tank you —Preceding unsigned comment added by 74.13.154.170 (talk) 13:35, 22 September 2007 (UTC)

I would think the thrust is the about the same.. Maybe because of the added pressure at sea level it is harder for the gas to be pushed out of the engine. Also obviously friction would be greatly increased in an atmosphere, although this wouldn't reduce the thrust it would reduce accelerationShniken1 14:14, 22 September 2007 (UTC)

100% thrust (sea level / vacuum): 1670 kN / 2090 kN (375,000 lbf / 470,000 lbf) 104.5% thrust (sea level / vacuum): 1750 kN / 2170 kN (393,800 lbf / 488,800 lbf) 109% thrust (sea level / vacuum): 1860 kN / 2280 kN (417,300 lbf / 513,250 lbf)

The difference is notable, 25%..... —Preceding unsigned comment added by 74.13.154.170 (talk) 16:04, 22 September 2007 (UTC)

Parts of the USA that have a similar climate to Scotland

Living in England I envy the amount of space people have in the USA - in England land is very expensive and even wealthy people live in small houses on small plots compared with the US.

But in Scotland there is more space, land is cheaper. So if I wanted more space I could in theory emmigrate to the US. But could I achieve the same goal by just moving to Scotland? In many parts of the US the climate is much colder than in Scotland.

So what parts of the USA have similar winter temperatures to winter in Scotland please? And what parts have similar summer temperatures to summer in Scotland please? (These two things are unlikely to be the same places as there is far greater seasonal temperature variation due to the continental climate in the US, and the maritine climate in Scotland). Thanks 80.0.114.206 13:47, 22 September 2007 (UTC)

You might consider the Pacific Northwest, near the coast, particularly Oregon and Washington state. They also are warmed by the Pacific currents, and therefore have a climate similar to England and Scotland (small variation, lots of rain and fog, etc.). See Seattle#Climate for a description of the climate there. And, if you want to include Canada in your list of possibilities, Vancouver Island is a large island warmed by the Pacific version of the Gulf Stream, almost identical to Great Britain in that respect. StuRat 14:01, 22 September 2007 (UTC)

Our article on Köppen climate classification classifies Seattle as type Cfb which is what our article on Climate of Scotland says that region is. This climate is considered unusual in the U.S. though. Rmhermen 14:09, 22 September 2007 (UTC)

Land prices are pretty high around Seattle though. The places in the US with the most temperate climate tend also to be the ones with the steepest property prices. I'm a Brit who lives in Texas - land is pretty cheap (as low as $1000 per acre far from civilisation - more like $15,000 per acre within commutable distances of cities - much, much more in city centers of course). The Texas winter climate is gorgeous - but in the summer, the heat gets rather crazy. My present house (which I designed myself) is on a gorgeous tree-covered 1.2 acre lot - with a view over a nearby lake. But I'm moving down to Austin and I'm probably going to build my new house on a 10 acre 'virgin' lot. There is absolutely no way to do that in England on a programmers' salary. There are a lot of jobs in my particular line of work in California (I'm a Game programmer) - but I can't afford to live there precisely because of insane land prices anywhere within commutable distance of a decent sized city. SteveBaker 14:26, 22 September 2007 (UTC)

Land prices might be high right around Seattle, but I'm sure land can be had cheaply somewhere in the coastal region of Oregon, Washington state, and British Columbia. The search could even be extended to the coastal regions of Northern California and Southern Alaska, which have similar climates. One caution, though, the entire region has some major fault lines, so earthquakes are a possibility. StuRat 14:54, 22 September 2007 (UTC)

Thank you for interesting answers so far, and apologies for not stating the question very well, but what I would like to know are which areas of the USA have a) winter temperatures, and b) summer temperatures, that are similar to those in Scotland. I imagine these would be in a band stetching across the US, somewhere between the cold north and the hot south. I recall seeing in the past climate charts that gardeners use, where the climate is given numbers, and these did have belts stretching from coast to coast. 80.3.44.82 16:24, 22 September 2007 (UTC)

If you want to match both the winter and summer temps, you don't get a band crossing the US, since, as you had noted, there is far more temperature variation within the interior of a continent than on an island. Your only choices are then ocean islands and coastal areas where the temperature is moderated by the oceans. Aside from the area given in the Pacific Northwest your only other choice would be on the Atlantic side. However, since the currents flow south there, not north, you would need to go considerably farther south to match temps with Scotland. Also, since the prevailing winds in the continental US go east, you would need an actual island there, as coastal areas would still be subject to quite high temps in summer, except for those on peninsulas extending well into the ocean. Islands or peninsulas off the coast of the North Carolina and Virginia might work, for example. I suppose you could go as far north as Long Island, New York, and still be close to the climate in Scotland. Earthquakes are less of a concern on the Atlantic side than on the Pacific side, but now you also have to deal with the occasional hurricane. StuRat 17:26, 22 September 2007 (UTC)

Hello... I'm Frank Necrosis

What is frank necrosis? How does it differ from plain necrosis? JIP | Talk 16:11, 22 September 2007 (UTC)

The term "frank" usually refers to something that is plainly visible, as opposed to covert (I think that's the medical opposite term...) where they have to go looking for it. Saturn 5 17:29, 22 September 2007 (UTC)

human eye

Re: Wikipedia:Reference_desk/Computing#Wide_screen_Vs_Full_screen

Anyone know what the 'human vision aspect ratio' is?87.102.89.127 16:21, 22 September 2007 (UTC)

This link might help you. I just glanced at it and it looked like what you needed.–Sidious1701_{(talk • email • todo)} 17:37, 22 September 2007 (UTC)