Wikipedia:Reference desk/Archives/Science/2006 December 30

= December 30 =

Vegetarians and Meat
If a human that only eats vegetables is a vegetarian, than whats a human that only eats meat??? —The preceding unsigned comment was added by 67.10.213.12 (talk) 01:01, 30 December 2006 (UTC).


 * A carnavore. StuRat 01:03, 30 December 2006 (UTC)


 * I used to wonder this. The term for a species that only eats meat is carnivore, which can also mean a specific 'group' of animals. However, calling humans that choose to eat only meat 'carnivores' would be like calling those who choose to eat no meat 'herbivores'. When I used to write stories about intelligent apples, I used the term 'meatatarian' (translated into 'Pommes' as 'meatatatarian', but you didn't want to know that), but I suspect there is no generally accepted term. If you and I use 'meatatarian' enough, maybe it will become accepted. :-) Skittle 01:11, 30 December 2006 (UTC)
 * Langmaker and the Urban Dictionary (somewhat jokingly and with typos) suggest meatarian. I have heard this term used to describe human omnivores who criticize vegetarianism. ---Sluzzelin 01:39, 30 December 2006 (UTC)
 * What does that make a humanitarian? Tbeatty 06:45, 30 December 2006 (UTC)
 * Are there humans who only eat meat? --JWSchmidt 01:45, 30 December 2006 (UTC)
 * Maybe in an experimental setting? Due to the scarcity of their environment's vegetation, Arctic people, such as some Inuit tribes, follow a very meaty diet (including fish, of course), but they supplement it with seaweed, and also with berries and herbs during the short summers. ---Sluzzelin 01:59, 30 December 2006 (UTC)


 * Vilhjalmur Stefansson consumed nothing but meat (0.3 lbs. protein, 0.67 lbs. fat per day) and black coffee for a year with no apparent ill-effects.EricR 02:42, 30 December 2006 (UTC)


 * Meatatarian is becoming quite well accepted - it's what my boyfriend has called himself for years (none of the sites listed are his, BTW!). He eats meat, dairy products, potatoes, peas, wheat, rice and some fruit. I'm pretty sure I recall an article on the topic here, but I can't seem to find any record of its deletion now. Natgoo 10:57, 30 December 2006 (UTC)


 * I think it is called an Atkinsarian. ;-) --24.147.86.187 15:59, 30 December 2006 (UTC)

Vegetarians do not eat meat. To be approved by the Vegetarian Society, they must be:
 * 1) Products have to be free of animal flesh, meat or bone stock, animal carcass fats, gelatine, aspic, or any other products resulting from slaughter.
 * 2) Products and ingredients should not have been tested on animals
 * 3) Eggs used must be free range
 * 4) Products must be GMO free
 * 5) Products must also be free from cross contamination with non vegetarian products/ingredients in the production process.

Paul Silverman 12:26, 31 December 2006 (UTC)


 * Reread the question, Paul. The OP is asking for the name given to someone who only eats meat. Natgoo 13:02, 31 December 2006 (UTC)


 * A person who eats meat/wants to get his teeth into something/A person who eats no meat/wants to get his teeth into something else/If these thoughts interest you for even a moment/you are lost. -- Leonard Cohen --jpgordon&#8711;&#8710;&#8711;&#8710; 16:01, 31 December 2006 (UTC)

As for those wondering who in the world may only eat meat, I've heard that the Masai people are an interesting example. --Taraborn 22:50, 3 January 2006 (UTC)


 * Don't the Maasai also drink cows' blood? Is the word "eat" in the question used in the general sense of ingesting anything including drinking liquids, or in the specific sense of ingesting solid or semi-solid foods?  I rather doubt that one can live on meat and nothing else at all for very long (Stefansson at least had black coffee to vary his diet). JackofOz 04:36, 4 January 2006 (UTC)

fluorescent tubes
how do fluorescent tubes give advantage and disadvantage to our environment? —The preceding unsigned comment was added by 67.71.121.123 (talk) 01:53, 30 December 2006 (UTC).
 * The articles on Fluorescent lamp and Compact fluorescent lamp list some advantages (environmentally speaking, mainly the overall lower energy consumption) and disadvantages (mainly waste disposal) in comparison to incandescent lamps. ---Sluzzelin 02:11, 30 December 2006 (UTC)
 * This is definitely not a homework question. (Please do not ask homework questions here) X ['Mac Davis '] (DESK |How's my driving? ) 02:59, 31 December 2006 (UTC)


 * For disadvantages it is probably worth noting that the tubes have mercury in them as well, which is a rather toxic heavy metal. It isn't much per tube though I imagine it adds up. In the end though you'd have to consider that in comparison to other types of waste (I imagine the amount in a bulb is almost nothing compared to the amount in a computer or any other piece of discarded consumer electronics) and the benefits saved in terms of energy requirements. --24.147.86.187 16:07, 30 December 2006 (UTC)

Vomiting reaction to endives in children
I heard that some children have a gene that causes a vomiting reaction to endives which they outgrow in adulthood. Could anyone please provide more information on this and the gene that might be involved? 216.194.22.39 03:07, 30 December 2006 (UTC)
 * I can find no mention of endive or chicory at OMIM, where one would expect a published gene with a such a phenotype to be listed. There is also nothing mentioned at PubMed (the closest I can find is a report of an allergy ). So It sounds like you may have been misinformed. The only related thing I can think of is the recent reports about the TAS2R38 bitter taste receptor . However, endives do not contain large amounts of glucosinolates, and so they would not be expected to drive evolution of this gene. Rockpock  e  t  02:50, 31 December 2006 (UTC)

Thanks for your research. I thought I had read it in an anthropology course.

Stem cells
Is it possible that Stem cells could be used to prolong life indefinitely instead of creating new life from the start? 71.100.6.152 03:13, 30 December 2006 (UTC)


 * Not in the foreseeable future. We cannot do very much of anything useful yet with stem cells, and we have not even begun to extend life with biological manipulations. alteripse 03:33, 30 December 2006 (UTC)

Extend life: yes. Indefinitely: no. StuRat 07:04, 30 December 2006 (UTC)


 * I can imagine replacing almost every organ in the human body, but the brain would be tricky. How do you replace brain cells without tampering with the brain's functions?  --Bowlhover 14:25, 30 December 2006 (UTC)


 * You could, in theory, replace each cell with another which has all the same connections. In reality, however, you're right, we have no way to do that. StuRat 16:31, 30 December 2006 (UTC)

Tarantula found in San Francisco Bay Area
Hello!

A friend of mine found a tarantula recently hiding under her bed. The room was attached to a nice cool, dark garage. She gave the tarantula to another friend who better appreciates him/her. He says he found one just like it but slightly smaller in San Diego. It is black or grey and "not very hairy" (he thought for a moment it might be a wolf spider). He isn't entirely sure it is a true tarantula.

I'm having a difficult time finding any sort of reliable guide, and wonder if it is actually a tarantula, and if so if perhaps it was an escaped or released pet.

Any help would be much appreciated!

Russia Moore 04:35, 30 December 2006 (UTC)


 * Pretty hard to say without so much as a picture. Tarantulas as a common name are pretty widespread as a family, as the article will tell you, but as far as the popular usage seen on TV/movies this doesn't sound like one. Can I suggest you take it into your friendly local museum or university entomology department for identification if you are really keen to know for sure (or at least put up a picture here which someone might be able to take a shot at identifying). --jjron 04:56, 30 December 2006 (UTC)


 * Even if it is a tarantula, I would think it more likely to have arrived on a recent shipment of fruit than to be an escaped pet. - Nunh-huh 14:53, 30 December 2006 (UTC)


 * That sounds more likely. After all, Harry Belafonte says it's so in the Banana Boat Song, and such reports do seem to turn up in the news from time-to-time.


 * Atlant 13:53, 2 January 2006 (UTC)


 * Tarantulas are native to the San Francisco Bay Area. They are quite common in some areas such as Mount Diablo, though seen most often in certain seasons. That of course doesn't necessarily mean that your particular spider is a tarantula. --mglg(talk) 23:05, 2 January 2006 (UTC)


 * Thanks for the help, I actually volunteer somewhere that might be of use, and will ask the more spider-oriented there...

Russia Moore 01:46, 5 January 2006 (UTC)

Lightsabers?
Is it possible, that one day we'll have the technology to make real lightsabers? I'td be some cool stuff to see a bunch of soldiers fighting with sabers. PitchBlack 06:43, 30 December 2006 (UTC)


 * Perhaps, but why bother? It's cool to watch a good swordfight too, but that went out of vogue when one of the combatants started pulling out a gun and shooting the other guy from a distance. Why would they go back to this close combat? And not to moralise, but do you really want to see REAL soldiers killing each other (with light sabres or anything else)? --jjron 07:03, 30 December 2006 (UTC)


 * Probably not, since lightsabers are based on their own, fictional physics that seems very much against everything we currently know about our real world physics. For that, see Lightsabers - In Reality.
 * But really, I'd hope that if we could and if we ever achieved such level of technology, we would use it better than for creating such a silly melee weapon! There's nothing cool about it, as I see it. It'd just be silly and a terrible waste of technology. &mdash; Kieff 09:07, 30 December 2006 (UTC)
 * If wielded by someone who can forsee and block projectile attacks, a lightsaber makes a decent weapon. --Carnildo 02:17, 31 December 2006 (UTC)


 * Yeah, that goes even further, and into the realm of pseudoscience. &mdash; Kieff 05:47, 31 December 2006 (UTC)


 * Read The Science of Star Wars: An Astrophysicist's Independent Examination of Space Travel, Aliens, Planets, and Robots as Portrayed in the Star Wars Films and Books by Jeanne Cavelos. There is a long section on this subject included in the book. S.dedalus 05:45, 31 December 2006 (UTC)

immunology
how does Aids virus escaps from antibodies?


 * I suggest reading the article on HIV. Splintercellguy 11:12, 30 December 2006 (UTC)

Spinning and orbiting
How are the Force of gravity, Centripetal force and Centrifugal force conceptually related in classical physics to Spinning and Orbiting? (How would they be used to describe the Moon falling toward the Earth yet moving away?) 71.100.6.152 08:42, 30 December 2006 (UTC)


 * You can leave spinning out – it has little to do with the others, except that a spinning body might come apart as a result of centrifugal force, while gravity will help to hold it together. Gravity is the fundamental thing here, and may cause orbiting. Orbiting may be a form of rotation. When you have rotation, you have curved motion, which means there is acceleration, which means some force is acting. The name for the force acting on whatever is rotating, thereby causing the curved motion to be maintained, is "centripetal force". A way of thinking of a falling body is that it commences to orbit (the common barycentre with) the Earth, usually in a highly elliptic orbit, but in most cases it doesn't get very far because the Earth (or some other large body) is in the way. How gravity relates to orbits is well explained in the section Understanding orbits of the article Orbit (celestial mechanics). In relation to orbits, the terminology of centripetal force is best reserved for the case of (almost) circular orbits, as only those have a clear "centre" of rotation for the orbiting body. In that case the centripetal force acting on the orbiting body is the force of gravity. A diametrically opposed force is exerted on the Earth. It would be unusual to call this a centrifugal force; that term is reserved for the asymmetric case in which a second rotating body pulls the first body along in the same rotating movement, such as the drum of a centrifuge pulling on matter inside. In orbiting, we have a symmetric situation. --Lambiam Talk  10:27, 30 December 2006 (UTC)


 * I'm not just thnking of the Moon moving away from the Earth in terms of an elliptical orbit but rather the expansion of the eliptical or (circular) orbit such that the Moon slowly moves away. Would centripetal force also be the cause of this expansion of orbit? 71.100.6.152 13:34, 30 December 2006 (UTC)


 * If you are referring to the Moon moving away farther away from the Earth as an effect of tidal forces, read our article on Tidal acceleration. Newton's laws of motion and gravitation are fundamental and universal laws; the laws for orbits, and notions like centripetal force, are derived laws and notions, and are valid and useful only in specific contexts. The effect of tidal acceleration follows from Newton's laws. Trying to explain it by means of centripetal force, if possible at all, would be awkward and strained. --Lambiam Talk  18:39, 30 December 2006 (UTC)


 * Thanks. The Tidal acceleration article explains the cause of the Moon's expanding orbit very well. Thanks. 71.100.6.152 20:11, 30 December 2006 (UTC)

EMERGING TECHNOLOGIES
hai people!, hey, thought u guys could help me out with this assignment i was given at college. i was asked to collect as many as 15 emerging technologies in the field of electronics. anything comparatively new would do125.22.49.187 10:04, 30 December 2006 (UTC)


 * Emerging technologies is a good starting point.--Shantavira 10:24, 30 December 2006 (UTC)


 * Read a few months' worth of EE Times or some similar trade journal.


 * Atlant 13:57, 2 January 2006 (UTC)

retrovirus and telomerase
Hi.
 * What are the major difficulties in reactivating the telomerase enzyme in order to reset the cell's clock and gain a better anti-aging product?
 * Is there a way to infect the entire body with a new gene code, using a retrovirus that reproduce without killing the host (does this thing exist in nature?)
 * or maybe one that only combine its code and do not reproduce (we'd need to inject large amounts of viruses into the patient that way).
 * Is there a difference between this genome reprogramming and general gene therapy?
 * thank you. --Procrastinating@ talk2me 12:14, 30 December 2006 (UTC)


 * I think that is basically gene therapy, as you describe it. Some comments:


 * Lengthening the telomeres likely wouldn't extend human longevity as much as you think. This is because we've adjusted our diets, risk exposure, etc., so that they kill us in about 100 years, anyway.  We would need to radically change our behaviour to extend our lives, say, to 200.


 * If we could significantly increase our life-spans this would cause massive overpopulation, especially in countries where people still have as many children as possible. This, in turn, would lead to starvation, pollution, war, etc.


 * I don't mean to discourage you, I believe this will ultimately happen, but we do need to consider the consequences, too.


 * For any responders, I would like to add the question: "How long before we can extend telomeres using gene therapy ?"


 * StuRat 13:00, 30 December 2006 (UTC)


 * Worth noting: The re-activation of telomerase – which allows cells to evade the Hayflick limit and continue to divide in perpetuity – is a key step in carcinogenesis. (Depending on whom you ask, anywhere from three-quarters to nine-tenths of all human tumours have telomerase active.)  While the reactivation of telomerase is not the only step required to transform a normal cell to a malignant one, it is an important one.  Having telomerase active in all the body's cells is apt to significantly increase the risk of cancer. TenOfAllTrades(talk) 14:59, 30 December 2006 (UTC)


 * I don't agree. While telomerase is used by cancers to increase their ability to reproduce, this only promotes cancer growth in that it gives them a relative advantage over normal cells.  If, for example, stems cells which produce white blood cells also have an unlimited ability to reproduce via telomerase, this will "even the playing field", especially for the elderly, where their immune system might be otherwise depressed due to age.  So, activating telomerase throughout the body potentially could help to fight cancer, where telomerase is already activated within the tumors. StuRat 16:17, 30 December 2006 (UTC)


 * In medicine, there is a term for overproliferation of white blood cells: leukemia. Bear in mind that even in hematopoietic (blood-forming) and other 'immortal' adult stem cells in which telomerase is active, cell division is necessarily very tightly regulated by the body.  Maintaining a population of rapidly-dividing, immortal cells is a very 'risky' thing for the body to do.  It is only tolerated in the bone marrow (and a few other places, like the intestinal lining) because it's the only way to maintain tissues subject to lots of 'wear and tear'.  Note that these same areas are also prone to malignant transformation: cancer.


 * Encouraging the proliferation of normal tissue won't fight cancer; it will encourage hyperproliferation of normal tissue. 'Immortalizing' normal non-stem cells (that is, giving them the ability to divide indefinitely) through activation of telomerase is a dangerous game; encouraging terminally-differentiated tissues to divide without the 'safety valve' of telomere shortening seems to be asking for trouble. TenOfAllTrades(talk) 18:41, 30 December 2006 (UTC)


 * I'm not talking about overproliferation of white blood cells, but rather restoring the balance when white blood cell count is suppressed. And, if someone already has terminal cancer, anything is worth trying. StuRat 19:52, 30 December 2006 (UTC)


 * Sturat, you write: "So, activating telomerase throughout the body potentially could help to fight cancer, where telomerase is already activated within the tumors". Do you have are reference for such a claim?  David D. (Talk) 22:19, 31 December 2006 (UTC)


 * No, do you have a reference disproving such a claim ? StuRat 16:59, 1 January 2006 (UTC)


 * Plenty, but I'm not going to get into a pissing match with you. How about you stop making answers up as you go along? David D. (Talk) 03:31, 2 January 2006 (UTC)


 * How about you only challenge answers if you have some actual proof that they're incorrect ? StuRat 02:13, 3 January 2006 (UTC)


 * Huh? StuRat, you are making stuff up. Don't write down your hunches on ref desk. Have a reference to back it up or don't write it here. Thank you. David D. (Talk) 16:12, 3 January 2006 (UTC)


 * There is no requirement that all answers must have references, and you're assumption that I'm "making stuff up" is unwarranted, as you have no proof that my statements are incorrect. StuRat 03:26, 5 January 2006 (UTC)

You guys did not even try to answer a even one of my questions !--Procrastinating@ talk2me 14:42, 1 January 2006 (UTC)


 * Yes I did. You asked "Is there a difference between this genome reprogramming and general gene therapy ?".  And I responded "I think that is basically gene therapy, as you describe it".  In other words, no, there's no difference. StuRat 16:56, 1 January 2006 (UTC)


 * Your first question assumes certain correlations, which makes a single answer impossible. There are many unanswered questions about telomerase, about the so-called "cell clock" (whatever that may be), and about "ageing" (however that may be assessed). There are as yet no answers adequate enough to guide safe use of telomerase de-repressors, and for every fact found, there are many more questions generated. Some responses about "difficulties" would be: 1. The question assumes that telomerase de-repression would "reset the cell's clock". This is not entirely true, since: this does not always happen; telemerase sometimes needs other factors to function; even when telomerase is active, cell division does not always occur indefinitely. 2. The question implies that telomerase function is causally and sequentially related to "ageing". This may be partly true, but we do not know for sure. 3. "Resetting the cell's clock" is not all there is to ageing, i.e. increasing the number of possible cell divisions will not necessarily reduce cumulative tissue wear and tear. The question cannot be answered until a whole lot more about the telomerase system is known. It may turn out that it is a highly dangerous and lethal therapy (though the circumstances differ, cf the case of Jesse Gelsinger). Overviews of what we know about telomerase are difficult to find, but you may check out Human Telomerase and Its Regulation and Genetic and Epigenetic Changes in Human Epithelial Cells Immortalized by Telomerase for what has been known for quite some time. Some observations to think about: The Human papillomavirus is quite efficient at de-repressing telomerase; repression of telomerase is associated with arrest of growth in estrogen dependent breast cancer. One would think very deeply before subjecting intact humans to treatments which we have no thorough experimental basis for.  While speculation can be fun, my own view is that the illusion that we know enough about telomerase de-repression to confidently predict effects in humans is just that, an illusion. The difficulty is that we do not know enough about the effects, not that technically it cannot be done.
 * Your other questions: Q2 and Q3: not possible (in vertebrates) with present knowledge. Q4 is a matter of semantics - one can argue that all therapy using genes is gene therapy. Others may argue that it is not directed therapy for a "condition", and should be called by some different name (not yet known, since the technique is not yet possible) - something like "whole organism genome modification"? —The preceding unsigned comment was added by Seejyb (talk • contribs) 20:10, 1 January 2006 (UTC). Oops --Seejyb 22:40, 1 January 2006 (UTC)

British broad-based cloud physicist Frank Ludlam
In an article by Cloudman there is a mention of British broad-based cloud physicist Dr. Frank Ludlam who wrote a scientific paper on English poet Shelley's poem 'The Cloud'.This paper was written somewhat before 1971. Can anyone kindly provide the full text of the original paper or its whereabouts from where I may obtain it? I'd also be interested on Dr. Ludlum's other works. Thank you. —The preceding unsigned comment was added by 59.94.113.128 (talk) 15:36, 30 December 2006 (UTC).


 * Wikipedia doesn't have an article about Frank Ludlam, but here is a link to a paper that he co-authored with fellow meteorologist Keith Browning about supercells. Gandalf61 16:04, 30 December 2006 (UTC)

Veg food
I was traveling in Europe with my friends and whenever they ask for veg-food in restaurants and in plains they serve you fish and if you want pure veg then you have to ask for Asian veg. So my question is that why a fish is considered as veg food?


 * Because fish is so easy to digest, like (cooked) vegetables, and unlike meat. Vranak 17:09, 30 December 2006 (UTC)


 * And also healthier than meat. StuRat 17:24, 30 December 2006 (UTC)


 * I used to use that line a lot too, but it will convert nobody. :) Vranak 22:13, 30 December 2006 (UTC)

There's some more information under Pesco/pollo vegetarianism. ---Sluzzelin 22:37, 30 December 2006 (UTC)


 * That's an odd experience. I just returned to the US from Germany on United Airlines, and they made the opposite assumption: because I asked for vegetarian that I would not eat eggs or cheese.  In Germany, fish was never included as a dish marked as "vegetarisch".  --best, kevin [kzollman][talk] 00:21, 31 December 2006 (UTC)


 * Ok, since we're exchanging experiences, here's one I had while living in Stuttgart (Germany) a while back. My workplace's canteen had a vegetarian dish (marked vegetarisch) on the menu, but I only asked for it once, because that day it was actually a salad with bacon bits sprinkled over it. ---Sluzzelin 00:47, 31 December 2006 (UTC)


 * Most bacon bits used in such bastions of fine dining are made from soy and 100% vegetarian. If they're the really crunchy ones, they're definitely soy. Did you ask or just assume? Speaking of experiences and in response to the questioner, I've travelled extensively in Europe and have never been served fish or had to specify 'Asian vegetarian'. Where did you go? Natgoo 12:57, 31 December 2006 (UTC)


 * This was the real deal. I did ask what this brown stuff was on top of my vegetarian meal, and the answer was: Speckwürfel (diced bacon) - I guess my usage of the term bacon bits was misleading, I'm not even sure the vegetarian substitute was cheaply available around there and at that time. ---Sluzzelin 19:36, 31 December 2006 (UTC)


 * Heh. That sucks. I ordered a burger in Australia once asking for "egg, cheese and salad - no meat" and it came with bacon. I haven't had a negative vege experience in more than 10 years, though - it's far more widespread than in years past. Natgoo 21:19, 31 December 2006 (UTC)


 * In other words and getting back to the question, vegetarian has several definitions (though none of them should include bacon bits, in my opinion) and can mean different things to different people. Several varieties are discussed in the article on vegetarianism. As for the term Asian vegetarian, I have never heard it used the way you mentioned, and am curious in which country you encountered this. ---Sluzzelin 01:06, 31 December 2006 (UTC)


 * Well, I suppose asking for "Asian vegetarian" food probably does often work, in the sense that you're likely to get either some stir-fried vegetables (with no bacon bits) or a blank stare. —Ilmari Karonen (talk) 07:30, 31 December 2006 (UTC)


 * Used to be in Germany, if you were a vegetarian, you'd get pretty much blank stares ("Es hat nur ein bischl Speck") until you explained that you were "on a cure" ...on the other hand, last time I was in Paris (in 2000), I was amused by the ads for "McDonald's Hippie Toast", which turned out to be some sort of veggie burger. --jpgordon&#8711;&#8710;&#8711;&#8710; 15:55, 31 December 2006 (UTC)


 * And here I thought they finally found a use for hippies -> cook them and serve them on toast. (But then again, you'd keep getting the pony-tail caught between your teeth, wouldn't you ?) StuRat 20:57, 31 December 2006 (UTC)

North Star
If you shoot night sky then you see that the north star is still and all other stars are revolving around it. The explanation teachers give about this in school is that "Its because north star is right above the north pole and when earth rotates around its axis, it seems to be still." But then i thought that earth also revolves around sun even though the north star seems to be still all the time!? Then I got the answer by myself that its like even though you walk for a long distance on earth the moon seems to be still at its place because the change in angle is so less that we cant notice it. So my question is that How long the North Star has to be from earth's north pole so that it seems still all the time? Manasmdk 17:13, 30 December 2006 (UTC)


 * See stellar parallax. To summarize, even the closest stars vary by less than one arcsecond (1/3600th of a degree) when the Earth orbits halfway around the Sun.  This is far too small to make out with the naked eye, but can be used with accurate equipment to measure the distance to nearby stars via triangulation. StuRat 17:19, 30 December 2006 (UTC)


 * Polaris (i.e. the North Star) is 431 lightyears from Earth. Dragons flight 18:36, 30 December 2006 (UTC)


 * Which is about 100 times further than the closest star (excluding the Sun, of course), Proxima Centauri. StuRat 18:51, 30 December 2006 (UTC)


 * And it's about 27 million times farther than the Sun. --Anonymous, December 31, still 2006, 01:54 (UTC).


 * If we suppose 5 degrees is accurate enough for direction finding, then the pole star only needs to be 11 AU away before parallax causes a problem (tan(5 degrees)=1 AU/11.4 AU). That's just outside Saturn's orbit.  Pluto, at 39 AU, only appears to move 1.5 degrees as Earth orbits the Sun.


 * The problem is not parallax; it's proper motion. Stars move relative to each other, sometimes at hundreds of kilometres per second.  If we assume a normal proper motion is 90 km/s, and that you don't want the pole star to move more than 5 degrees in 300 years, then the pole star has to be at least a light year away. --Bowlhover 10:05, 31 December 2006 (UTC)


 * Note that Bowlhover's response relates to the previous, unsigned, one (in effect asking how close the pole star could be and still be useful as a pole star) and not to Manasmdk's original question. Manasmdk wrote, "But then i thought that earth also revolves around sun even though the north star seems to be still all the time!? Then I got the answer by myself that its like even though you walk for a long distance on earth the moon seems to be still at its place because the change in angle is so less that we cant notice it", and this is precisely talking about parallax (and is correctly reasoned). --Anonymous, December 31, still 2006, 20:47 (UTC).


 * But the original poster also said "So my question is that How long the North Star has to be from earth's north pole so that it seems still all the time?", to which I gave two approximate answers. --Bowlhover 06:26, 1 January 2006 (UTC)


 * The quickest factor that does change which star is the North Star is precession, which will give us a new North Star in 1000-2000 years. See precession of the equinoxes. StuRat 12:54, 31 December 2006 (UTC)

RBMK
Regarding the RBMK1000 reactor, what is the purpose of the tall, braced, red and white stack at the center of reactor #4, and I suppose all other RBMK reactors?

Thanks, Spencer


 * I assume you've already read our RBMK article ? StuRat 18:54, 30 December 2006 (UTC)


 * It's not in our article. Interestingly, the Ignalina Nuclear Power Plant in Lithuania – which operates RBMK-1500 reactors, a descendent of the RBMK-1000 design used at Chernobyl – also features large stacks over the reactors.  I don't know what its stacks are either (ventilation? exhaust?) but the answer for Ignalia will probably be the same as that for Chernobyl.


 * I will note that both Chernobyl and Ignalia used water from an adjacent body of water for cooling, and that neither site had cooling towers: . (I suppose it might be possible that the tower was for cooling some smaller piece of equipment, but I'd tend to think that unlikely.)  TenOfAllTrades(talk) 20:06, 30 December 2006 (UTC)


 * It looks like a cooling tower to me, though it is hard for me to find anything that says specifically. --24.147.86.187


 * OK — it is a chimney. From this page:
 * Chimneys of the plant, including the famous one of the third and fourth blocks, can be seen from here. People frequently ask what these chimneys are for, as the nuclear plant does not emit smoke.


 * They are intended for ventilation. Most of the premises like the reactor hall, turbine island, etc. are connected to them. The air of a nuclear reactor goes through special tarred filters, which intercept radioactive particles. Spent decontamination filters are stored in nuclear waste depositories.


 * Two ventilation chimneys overlook the Chernobyl nuclear power plant. One of them is a usual brick one and services the 1st and 2nd power units. The second originally shaped chimney, which has become a symbol of the Chernobyl plant, services the 3rd and 4th power units.


 * First photos taken after the accident show this chimney painted white and red. Over the twenty years it has lost colors and is grey now. Like the “Shelter” installation this chimney has a high ionizing radiation background. The order to send two people up there and mount a flag on top of it after the accident was the most idiotic idea. At that time pieces of highly radioactive graphite from the reactor still laid on the chimney paces. The chimneys are 150 meters high.


 * Sounds plausible to me. --24.147.86.187 21:35, 30 December 2006 (UTC)

Aerogel properties
If you impregnate Aerogel with Hydrogen or Helium instead of Nitrogen or Air will it be lighter than air and if so could it be used to make an Aerogel/Helium or Aerogel/Hydrogen Blimp? Adaptron 20:14, 30 December 2006 (UTC)


 * I'm pretty sure the answer is yes it could, but with normal aerogel costs at ~$500/pound the resulting blimp would be outrageously expensive. Dragons flight 20:41, 30 December 2006 (UTC)
 * Actually - since it's so light in the first place, a pound is a pretty big volume... And is that pre-filled-with-helium or post-filled-with-helium?  If it is post, they'd have to pay *you* at that rate!  (remember, pounds are force :p ) —AySz88\^ - ^  07:09, 31 December 2006 (UTC)
 * Well the Helium is ~$10/pound, and the Helium + Aerogel will undoubtedly be heavier per equal volume, so you have still raised the cost of filling your airship some 50 fold. Dragons flight 08:53, 31 December 2006 (UTC)
 * Here is a calculation showing it would. Let p be the fraction (in volume) of the gas, and q the fraction of the solid matter (so p+q = 1). Let further dair, dHe, dsol and dgel-G be, respectively, the densities of air, helium, the solid matter in the aerogel, and the areogel when the gas is G (air or He).
 * We have
 * dgel-air = pdair + qdsol,
 * dgel-He = pdHe + qdsol.
 * Your Heliogel® blimp will float if the inequation dgel-He < dair is satisfied.
 * I don't have a value for dsol, but fortunately we can eliminate it by substracting the equations, giving:
 * dgel-He – dgel-air = p(dHe – dair).
 * We can now eliminate dgel-He from the inequation determining flotation:
 * p(dHe – dair) + dgel-air < dair.
 * "Solving" this for p gives (using also the fact that dHe < dair):
 * p > (dgel-air – dair) / (dair – dHe).
 * Using dair = 1.186 kg/m3, dHe = 0.1786 kg/m3, dgel-air = 1.9 kg/m3, we calculate for the requirement: p > 0.71. According to the article Aerogel, aerogels are composed of 90-99.8% air, so, assuming that the percentage given refers to volume (otherwise the material would be even lighter than it already is), the inequation is satisfied. Please donate to Wikipedia if this invention makes you a billionaire. --Lambiam Talk  21:05, 30 December 2006 (UTC)

I suspect it might work, but only for a little while. My understanding is that helium can pass through just about any substance. The walls of each cell would be so thin that I doubt that it would take very long for much of the helium to escape. Hydrogen? Haven't a clue. Bunthorne 04:46, 31 December 2006 (UTC)


 * My understanding is that aerogels have to be at least a little bit porous during their manufacture&mdash;otherwise you would never be able to get the liquid out and the air in to them in the first place. I suppose you could use an aerogel as the filling for a rigid airship envelope, as long as you wrapped it in with something airtight.  Heck, load up chunks with hydrogen, seal them on the outside, and load them into a big bag: presto, a balloon that doesn't leak. TenOfAllTrades(talk) 05:07, 31 December 2006 (UTC)


 * Our article claims aerogels are "open celled" so they are quite porous, and won't be trapping any gasses inside.


 * Atlant 14:01, 2 January 2006 (UTC)


 * Helifiltergel®?! Adaptron 04:14, 3 January 2006 (UTC)

Snowfall and Sir Isaac Newton
I've heard many, many times that the reason the temperature goes up a couple of degrees after snow starts falling is because of the huge release of energy, but I don't understand why/how this happens. Is it the energy expended turning the rain into snowflakes? Anchoress 20:26, 30 December 2006 (UTC)


 * That's the way they protect citrus, by spraying water. See  for a good scientific explanation.  I'm not a scientist, and I think of it like this:  when water turns to ice, the heat (energy) is released into the air as the water goes from warm to cold. -THB 20:36, 30 December 2006 (UTC)

The temp doesn't always go up when it snows, but sometimes goes up when a warm front comes in, triggering both the snow and warmer temps. StuRat 20:40, 30 December 2006 (UTC)

Nothing to do with physics, everything to do with climatology.

Here in Vancouver, arctic outflows contend with warm semi-tropical air moving in a prevailing west-to-east direction. If the temperature goes up after snowfall, it's because the semi-tropical air has 'prevailed' over the arctic airmass. The mixing of the two is what produces snow. Vranak 22:11, 30 December 2006 (UTC)
 * Thank you all for your answers, and Happy New Year. Anchoress 19:42, 1 January 2006 (UTC)
 * There is a large amount of energy released as sensible heat, but it happens before the snow falls and at higher altitudes. When moist air rises and cools it releases latent heat as the water vapor condenses and freezes. If the air mass is then somehow forced back to the surface there can be a dramatic rise in temperature, see: föhn wind and chinook wind.EricR 17:03, 2 January 2006 (UTC)

What was your question about Isaac Newton? JackofOz 04:25, 4 January 2006 (UTC)