Wikipedia:Reference desk/Archives/Science/2008 July 30

= July 30 =

Redefining the metre
Shouldn't the scientific community redefine the metre so that the speed of light in vacuo is exactly 3 x 10^8 ms^-1? If not why not? —Preceding unsigned comment added by 79.76.156.194 (talk) 00:00, 30 July 2008 (UTC)


 * No. It would give a small advantage when remembering and calculating with the speed of light, but such calculations are usually done by people who know what they do, and does it matter how accurately other people can remember the speed of light? It would give huge disadvantages in many other situations, for example uncertainty about which definition is used in a given situation. PrimeHunter (talk) 00:06, 30 July 2008 (UTC)


 * You'll note that in the history of the metric system, the various units were defined based on natural and seemingly unchangable measures for convenience' sake (using the circumference of the Earth, density of water, etc). That the speed of light is very close to 3x10^8 was really just a fluke. But in all the redefinitions of units thereafter, the focus has been on finding a more consistent measure that is very close to the one that has been used, again, for convenience' sake. Seeking to actually change a unit of measure would not be very convenient, considering everything that would have to be reconfigured and recalculated. Someguy1221 (talk) 00:44, 30 July 2008 (UTC)


 * And even more devastating, the smoot would then require redefinition :-( hydnjo talk 02:24, 30 July 2008 (UTC)


 * Couldn't we just say it faster? Relativistic contraction would then supply the necessary correction. Thx for the link btw :) Franamax (talk) 02:35, 30 July 2008 (UTC)
 * He-he, excellent idea! hydnjo talk 10:45, 30 July 2008 (UTC)


 * The speed of light is 299 792 458 meters per second exactly. It's just as good as any other number.  Besides, it makes the permeability of free space exactly 4π × 107.  Wily D  02:19, 30 July 2008 (UTC)
 * It's the definition of the ampere that fixes μ0, not the metre. Algebraist 12:18, 30 July 2008 (UTC)
 * Err, this are not independent quantities. Wily D 13:27, 30 July 2008 (UTC)


 * The physical constraint is that μ0*ε0*c2 = 1. However, even with fixed c, there is a further choice of definition of the Ampere that fixes μ0 = 4π × 107 (effectively this is a choice of definition for the charge of the electron).  There is no physical reason one can't have both c = 300,000,000 m/s and μ0 = 4π × 107, provided you are willing to play with the definition of charge units and the value of ε0.  However, messing with the definition of units is generally undesirable for the forementioned reason that it confuses people.  Dragons flight (talk) 23:41, 30 July 2008 (UTC)


 * You might like natural units which often set the speed of light at 1. J kasd  04:50, 30 July 2008 (UTC)


 * Instead of making the meter shorter, we should concentrate on making light faster. APL (talk) 12:49, 30 July 2008 (UTC)


 * You missed your chance. The speed of light may have been up to sixty times faster in the early universe (see Variable speed of light).  I guess it wore out over the last fifteen billion years. :D TenOfAllTrades(talk) 19:38, 30 July 2008 (UTC)


 * The proposal you refer to apply to variation during the first fraction of a second of the universe's existence (i.e. the era of cosmic inflation). The speed of light can not have changed more than a few parts per million since the earliest stars were formed.  Dragons flight (talk) 23:41, 30 July 2008 (UTC)

Diamagnetic materials
What is the most easily obtainable diamagnetic material that has a high negative value of permeability? Ive seen pyrolytic carbon and bismuth mentioned, but where can I get these or some thing similar? —Preceding unsigned comment added by 79.76.156.194 (talk) 02:32, 30 July 2008 (UTC)
 * Pyrolytic carbon and ebay is likely your best bet. Mac Davis (talk) 05:02, 30 July 2008 (UTC)
 * Bismuth is sold as environmentally-friendly lead shot. If you're in the U.S., try going to a gunstore and asking for it.  --Bowlhover (talk) 07:10, 30 July 2008 (UTC)


 * Hey thanks Bowlhover. Thats just ideal. I think I can get bismuth shot locally. Its 97% bismuth and 3% tin so hopefully it would not lose much of its diamagnetic strength. Im going to have to melt the shot down so I can cast some plates from it. Any ideas on a safe way to do this? —Preceding unsigned comment added by 79.76.156.194 (talk) 16:57, 30 July 2008 (UTC)


 * Bismuth has a melting point of 272 degrees Celsius. Lead turns into liquid at 327 degrees Celsius, yet I easily melted it with a propane torch from Walmart.  Perhaps you can fill your cast with lead shot, heat the cast in an oven used for baking, and use a torch to melt the bismuth.  Make sure, of course, that you keep the torch well away from the heated oven.  --Bowlhover (talk) 19:24, 30 July 2008 (UTC)


 * This site describes using either a propane torch or a regular kitchen stove. (Don't use eating utensils for your crucible.)  Melting bismuth shot isn't particularly difficult.  Note that molten metal – lead or bismuth – is extremely dangerous if handled carelessly. TenOfAllTrades(talk) 19:33, 30 July 2008 (UTC)


 * Thanks for the warning TOAT. We wouldn't want to get our fingers (or other bodily parts) burned would we? I know it can be very painful 8-) —Preceding unsigned comment added by 79.76.157.54 (talk) 00:21, 31 July 2008 (UTC)

Grizzly bear
Since the grizzly bear is not always grey, why does it have the name grizzly? —Preceding unsigned comment added by 79.76.156.194 (talk) 02:51, 30 July 2008 (UTC)
 * The article suggests the grizzly has a silver tipped pelt and is a subspecies of the Brown bear, so maybe when it's brown, it's not a grizzly. Julia Rossi (talk) 05:26, 30 July 2008 (UTC)
 * Contrarily, the article also states: Their coloring ranges widely across geographic areas, from blond to deep brown or red.  due to diet variations. ?! Julia Rossi (talk) 05:29, 30 July 2008 (UTC)


 * Because the name, like the bear, is badass. --Shaggorama (talk) 08:29, 30 July 2008 (UTC)
 * Indeed. The grizzly will make a grisly mess of his gristly victim.  --Sean 14:45, 30 July 2008 (UTC)

Faraday vs. Lenz
Hi, It is the night before the physics exam (the best time to ask emergency questions), and I have a question. I don't know on which problems I should use Lenz's Law, and on which I should use Faraday's Law. Lenz's appears to be exactly the same, but multiplied by negative 1. How do I know which formula to apply? Thank you oh great desk :) Mac Davis (talk) 04:59, 30 July 2008 (UTC)


 * Whell now, good Q. Does this help?
 * ''Lenz's law (pronounced /ˈlɛntsɨz ˌlɔː/) gives the direction of the induced electromotive force (emf) and current resulting from electromagnetic induction. The law provides a physical interpretation of the choice of sign in Faraday's law of induction, indicating that the induced emf and the change in flux have opposite signs. Heinrich Lenz formulated the law in 1834.

''
 * This tells me that Lenz law also gives the direction of the emf. So if the exam Q asks for direction youll have to use Lenz's law. Otherwise yould be ok with Faraday's Law —Preceding unsigned comment added by 79.76.156.194 (talk) 05:13, 30 July 2008 (UTC)

Fleas on Horses or Cows
Do Horses and Cows get fleas?. If they don't why don't they? 202.92.75.130 (talk) 05:42, 30 July 2008 (UTC)


 * You need to further define "get fleas." Human can have fleas on them and get bit if they are in an infested area, but that is rarely referred to as "getting fleas."  Small animals often carry an infestation with them - which is what is often meant by "getting fleas."  Cows, horses, and other large animals rarely carry an infestation with them.  I grew up around a lot of cow farms and fleas were never an issue.  However, it is possible, just as it is possible for a human to take fleas from one building to another.  Any warm-blooded animal is capable of providing a safe home for fleas.  They just prefer certain animals over others. -- k a i n a w &trade; 06:06, 30 July 2008 (UTC)


 * I think there are a couple of reasons why horses and cows don't have fleas. First, their skin is too thick for the penetration of a flea's mouthparts to suck blood. Secondly, and probably more important, horses and cows don't have a nest or home area in the same way that dogs and cats do. The home area is important in the life cycle of the flea to allow the eggs to drop into an area where they can hatch to larvae, pupate and then climb aboard the animal to take in blood to start the next generation. Richard Avery (talk) 07:27, 30 July 2008 (UTC)


 * I believe they do get ticks, however. I wonder what's different that allows ticks to feed on them but not fleas ? StuRat (talk) 13:36, 30 July 2008 (UTC)


 * I know cows get ticks on their ears. Do they often get ticks on the rest of their body? -- k a i n a w &trade; 13:41, 30 July 2008 (UTC)


 * Only if they are fully checked out. —Preceding unsigned comment added by 79.76.185.178 (talk) 00:15, 1 August 2008 (UTC)


 * Ticks differ from fleas in two respect that may be pertinent to this discussion. They tend to burrow into the skin thus overcoming the problem the flea encounters. (Why a tick is able to do this and a flea not is beyond my primitive grasp of this topic) The spread of ticks is achieved by the adult, after hatching, looking for and ascending a stalk of grass or a plant to put itself in a position where it can grasp a passing animal, cow, deer, dog or indeed human. This strategy gives it a singular advantage over the flea by allowing it to bridge a much larger vertical space and not having to rely on a central point to board the host. Richard Avery (talk) 14:40, 30 July 2008 (UTC)

Ocean smell
I've lived for 30+ years in the Arctic. For the first time ever we are noticing a strong "smell of the sea". In other years you would almost have to be on the shore to actually smell it. However, this year it can be smelt quite well at my house, about .4 km (1/4 mi), away and I noticed it the other morning about 2 km (1.2 mi) inland. Any ideas why the smell would be stronger this year than other years? CambridgeBayWeather Have a gorilla 09:40, 30 July 2008 (UTC)
 * Warmer water leading to higher growth rate of microorganisms? In the article you cite you can read the mechanism stays off until decaying plankton are around. From this it's not far to a testable hypothesis. --Ayacop (talk) 10:10, 30 July 2008 (UTC)
 * Thanks. I should have thought of something like that. Especially as it was only yesterday I was looking at videos of some young people in Ulukhaktok, Northwest Territories jumping their bikes off the dock into the ocean. It's the first time I've ever seen anybody go into the ocean without a suit on. As an aside we've noticed some other changes this year. The ponds which were drying up, similar to the one shown here but not as extreme, are completely full. Also the vegetation, which on our side of the island is usually brown, is very green. CambridgeBayWeather Have a gorilla 13:03, 30 July 2008 (UTC)

PLZ GIVE ME THE FORMULAE
What is the formula for calculating "port pressure drop" for water passing through a port hole at certain "port velocity"? What is the formula for calculating "wall shear stress" in a heat exchanger? Please give me simplified formulae. I will be grateful.

Chandra 30.07.08 —Preceding unsigned comment added by 117.193.161.16 (talk) 10:49, 30 July 2008 (UTC)

Does the photon exist?

 * Reference_desk/Archives/Science/2007_December_3

Answer:

 * Q: "Does the photon exist?"
 * A: Yes.

Pure dogma aimed at perpetuating the popular myth.

Why should nature behave with such exuberant extravagance instead of simple elegance? The photon, no doubt, is the greatest mistake of twentieth century physics and will eventually join its predecessor the Aether. —Preceding unsigned comment added by 84.69.94.168 (talk) 08:40, 2 August 2008 (UTC)

rember?
Does anyone know of any recent publications that mention the exact (or even approximate) chemical composition of the new anti-Alzheimer's drug 'rember'? According to the BBC article Rember = Methylene Blue, according to other AP stories Rember = Methylene Blue + Other stuff. My quandary is that if the first statement is true then it should probably be merged into Methylene Blue, if not then it should probably have its own article. And yes, I am aware that this question is a thinly veiled article improvement drive ;) VectorPotential Talk 13:27, 30 July 2008 (UTC)


 * http://www.bestsyndication.com/?q=20080729_rember_active_ingredient_alzheimers_disease.htm Identifies methylene blue as the active chemical, no where else can I find any mention of any other active ingredients, (so the rest is probaly water+flavourings), maybe they add some colouring too (joke).87.102.86.73 (talk) 13:44, 30 July 2008 (UTC)
 * I was really hoping for a journal article. I have full journal access but for some reason I just can't turn up a recent publication on the subject. The most recent paper I can find published by Professor Wischik that even mentions methylene blue is "Selective Inhibition of Alzheimer Disease-Like Tau Aggregation by Phenothiazines", and that was published in 1996.--VectorPotential Talk 13:53, 30 July 2008 (UTC)
 * Started with journal articles and found this one; it mentions combining methylene blue with "other diaminophenothiazines". (Paired methylene blue with Alzheimer's instead of Rember. This search also turned up two others after the Wischik article you mention; this one from 2007 and this one from 2005). But maybe this is better: the conference report says "Methylthioninium chloride (MTC, or brand name remberTM)" and here's the press release - cheers, WikiJedits (talk) 14:59, 30 July 2008 (UTC)

The abbreviations "T.C." and "T.C.D." on a plot plan
In a plot plan, what might the abbreviations "T.C." and "T.C.D." stand for? I found a series of labels of the form
 * T.C. xxx.yy
 * T.C.D. xxx.yy

along the curb of a street block in a plot plan. In the labels, xxx and yy are three- and two- digit numbers respectively. When interpreted as decimal numbers, those xxx.yy numbers are close to each other, but no two of them are the same, and they are not in numerical order. It is not clear whether they are identifiers or whether they are measurements of some kind. —Preceding unsigned comment added by 71.162.242.76 (talk) 14:09, 30 July 2008 (UTC)


 * I don't know, but it is quite common for spot levels to be measured along a curb, so perhaps they are heights above a datum such as sea level (in either metres of feet). Is this plan from an English-speaking country?--Shantavira|feed me 14:32, 30 July 2008 (UTC)


 * Yes, the plan is from an English-speaking country. --71.162.242.76 (talk) 14:51, 30 July 2008 (UTC)


 * In construction, T.C. commonly means "Target Completion" and T.C.D. means "Target Completion Date". It is also common to represent a date in Julian format - a 3-digit number 0 to 366 followed by a 2 or 4 digit year.  Does that format fit with your xxx.yy numbers? -- k a <font color='#990066'>i <font color='#660099'>n <font color='#3300cc'>a <font color='#0000ff'>w &trade; 14:38, 30 July 2008 (UTC)


 * The xxx.yy numbers don't make sense when interpreted as dates in Julian format. Here's another bit of information: there's a T.C. label and a T.C.D. label in front of each property. The two are quite close together. There are only T.C. labels along the parts of the curb not directly in front of a house, and those labels are farther apart. --71.162.242.76 (talk) 14:51, 30 July 2008 (UTC)


 * How about elevations? Top of Curb, Top of Curb at Driveway. Have look at this, page 5, Section G, #7. Franamax (talk) 19:35, 30 July 2008 (UTC)


 * Judging from the context, I think you're right. Thanks. --71.162.242.76 (talk) 19:47, 31 July 2008 (UTC)

The shortest research paper abstract
Years ago I read about a physics paper which had the shortest abstract possible — just one word: "no". (The paper's title poses a question and the abstract answers it in the negative.) I don't remember enough about the title to look it up. Does anyone know what paper I'm talking about?

Update: I found the answer. The paper was:
 * Hajdukovic, D and Satz, Helmut, "Does the one-dimensional Ising model show intermittency?", 1992 (a pre-print from CERN's theory division).

—Preceding unsigned comment added by 71.162.242.76 (talk) 14:28, 30 July 2008 (UTC)


 * A well deserved attaboy for extreme finding. -hydnjo talk 01:52, 1 August 2008 (UTC)


 * Unfortunately, when the paper was finally published in a journal, the abstract became much longer: "We give an analytical proof that the general d-dimensional Ising model in an external field does not lead to intermittency." . --Itub (talk) 13:14, 11 August 2008 (UTC)
 * The traditional example of "the shortest abstract ever written" is "e=mc2". -- <font color='#ff0000'>k <font color='#cc0033'>a <font color='#990066'>i <font color='#660099'>n <font color='#3300cc'>a <font color='#0000ff'>w &trade; 14:31, 30 July 2008 (UTC)
 * What paper had that abstract? Not Einstein's, which seems to have no abstract at all. -- BenRG (talk) 19:01, 30 July 2008 (UTC)
 * Probably just another silly scientific myth. Einstein's paper of course doesn't even have E=mc2 in it at all in that particular form. (Scientists love to pretend they care about truth, but clearly their understanding of the term doesn't extend to history.) --98.217.8.46 (talk) 19:56, 30 July 2008 (UTC)
 * Nothing like an sweeping generalization to brighten the day, huh? -- Coneslayer (talk) 20:01, 30 July 2008 (UTC)
 * I know what you're talking talking about, but I can neither remember nor find it. This is a tough one to google.  The paper title was along the lines of "Does the blah blah blah blah?" and the abstract was, as you say, "No."  -- Coneslayer (talk) 14:46, 30 July 2008 (UTC)


 * It reminds me a bit of this paper, Are crystal structures predictable?, which starts with "No". However, it's not an abstract. --Itub (talk) 17:21, 30 July 2008 (UTC)


 * I seem to remember that the question posed is about a certain property, something along the line of "Is symmetry preserved ...?" (I don't actually remember if any of those specific words are in the title. I just have a vague feeling that that's the type of question posed.) --71.162.242.76 (talk) 18:10, 30 July 2008 (UTC)
 * I tried searching for this abstract in the database Scopus, but I didn't have any luck. I think Web of Science may have better coverage, but I don't have access. Can someone else try? ike9898 (talk) 20:31, 30 July 2008 (UTC)


 * The paper was mentioned in Science along with a number of other curiosities such as most authors on a paper and shortest title ("!"):
 * Frustratingly though it doesn't give the title. All I can figure out is that it must have been published before 1988, but I'm having no luck finding it. the wub "?!"  22:49, 30 July 2008 (UTC)
 * Frustratingly though it doesn't give the title. All I can figure out is that it must have been published before 1988, but I'm having no luck finding it. the wub "?!"  22:49, 30 July 2008 (UTC)


 * A couple of amusing close contenders I found are "Guaranteed margins for LQG regulators" (abstract: "There are none") and "How good is Morse Code?" (alleged abstract: "Not bad!")  the wub  "?!"  23:09, 30 July 2008 (UTC)


 * Someone on another site asked this question a few months ago: . Some of the more interesting responses included
 * Title: Guaranteed margins for LQG regulators
 * Abstract: There are none.
 * and
 * Title: On the zeroes of the Riemann zeta function
 * Abstract: The paper proves the Riemann Hypothesis.


 * Good hunting, folks. TenOfAllTrades(talk) 23:06, 30 July 2008 (UTC)


 * Note that the abstract is presumably incorrect, since the Riemann hypothesis is still an open problem. —Lowellian (reply) 00:50, 2 August 2008 (UTC)

Kind of related to the subject, but I remember learning in undergraduate physics that the shortest PhD dissertation was probably submitted by Louis DeBroglie. It was 2 pages. His dissertation committee was bothered by that (just two pages? for a PhD?), so they showed the paper to Albert Einstein. Einstein said it's a very good paper, so they awarded deBroglie a PhD. This dissertation eventually led to deBroglie winning a Nobel prize for introducing the theory of electron waves. I imagine with 2 pages of text, the abstract was probably rather short too. I wish I could find references for that story. Wikipedia doesn't mention it. ~Amatulić (talk) 23:59, 30 July 2008 (UTC)
 * A little googling suggests that's complete nonsense, I'm afraid! is a site selling his thesis as a 127 page book. --Tango (talk) 01:05, 31 July 2008 (UTC)


 * I can't find any verification for that. says his Recherches sur la théorie des quanta was 127 pages long.  This corresponds to WorldCat and ScienceDirect, as well as here ("over 100 pages").  Even so, smart guy.  --Bennybp (talk) 01:04, 31 July 2008 (UTC)


 * This translation of De Broglie's thesis spans 73 pages, and French is less concise than English. --Bowlhover (talk) 01:05, 31 July 2008 (UTC)


 * Did they translate the references section? --Carnildo (talk) 20:50, 31 July 2008 (UTC)


 * There references (as one can see) only fill up one page (like most Physics theses of that time). --98.217.8.46 (talk) 00:36, 2 August 2008 (UTC)


 * Carnildo: I was actually the first user to reply to Amatulic's post, so I was demonstrating that De Broglie's thesis is much longer than 2 pages, not that it's shorter than 127.  --Bowlhover (talk) 06:04, 3 August 2008 (UTC)


 * Note that length questions aside (which I suppose are spurious), it is true that his committee was very dubious of DeBroglie's thesis (not because of its length, but because of its content) and did show it to Einstein who did not only approve it but suggested it was of immense importance. So there is an aspect of truth to the story, even if parts of it are, well, dubious. --98.217.8.46 (talk) 00:36, 2 August 2008 (UTC)


 * Wow. Thanks for the clarification on deBroglie. I guess my physics professor embellished the story regarding the length of the paper, but the other details were correct. Either that, or my own memory has modified the story after 25 years. ~Amatulić (talk) 01:01, 2 August 2008 (UTC)


 * Actually, it's likely that neither your professor embellished the story nor you remembered incorrectly. http://www.math.niu.edu/~rusin/known-math/00_incoming/thesis is an example of another person making similar claims about De Broglie's PhD thesis; it seems that the misconception is widespread.  --Bowlhover (talk) 06:04, 3 August 2008 (UTC)

Cat behavior
A stray cat had kittens in my carport and mother moved them across the street when I cleaned the carport up. Occasionally one of the kittens would stay close and follow back over. They found several spots in the yard to sleep. Even though I fed the kitten while it was in the carport it would run like crazy an leave the mother behind who let me hold her all of the time. One morning when I returned from the store, however, to my surprise each cat demonstrated the reverse behavior. The mother slipped away but the kitten stayed behind and did not run away. The impression I had was that they had exchanged personalities as in sort of like who is who. Where can I find information about this type of behavior? 71.100.9.68 (talk) 15:48, 30 July 2008 (UTC)


 * This doesn't answer your actual question, I know, but still: I can pretty much guarantee that the cats did not exchange personalities. -- Captain Disdain (talk) 17:09, 30 July 2008 (UTC)


 * Maybe what you're looking for is something like imprinting. --98.217.8.46 (talk) 17:32, 30 July 2008 (UTC)
 * Perhaps on that day the mother cat simply didn't want to be friendly, while the kitten, after watching you and the mother interact, decided to be bold and investigate. 20I.170.20 (talk) 19:37, 30 July 2008 (UTC)


 * Expanding on what 20I.170.20 said, I would think the mother cat was once a house cat, so it initially reacted fondly to you as a human. Then, while you weren't with the mother, another human might have frightened her (e.g. by throwing water on her to get her to go away or yelling at her), which might have put her in a temporary bad mood toward humans. Or she might just be fickle like most cats and tomorrow she'll be fine with you. Since the kittens interacted with you at a very young age, they might have started to trust you and understand you do not want to hurt them but care for them, so they're letting you handle them. I can't base anything I have said on something encyclopedic, just on my own experience with feral cats.--El aprendelenguas (talk) 20:29, 30 July 2008 (UTC)


 * Maybe the mother just needed a break and was happy that her kitten finally let someone else take care of it (I am half serious). Maybe the mother needed to go take a call of nature. BTW, you seem to switch between kittens and kitten. If only one kitten was with you, perhaps the mother decided she needed to go look after the other kittens Nil Einne (talk) 14:30, 31 July 2008 (UTC)

Maximum size of a star
I was reading about VY_Canis_Majoris, and it's said that "the largest possible star is approximately 2,600 times the radius of the Sun." Does anyone know why this is or what happens at that size? Thank you. <font style="color:#955619;">Louis Waweru <font style="color:#FFFFFF;background:#955619;"> Talk 21:42, 30 July 2008 (UTC)


 * I was wondering about that too. I'm not sure... The only other objects that are larger are supermassive black holes. OJ 287 is the most massive at 18 billion sollar masses. Maybe if a star becomes too massive, the core pressure forces the density into a black hole perhaps? ScienceApe (talk) 22:30, 30 July 2008 (UTC)


 * Stellar evolution has a link to the Eddington limit, saying "Stars cannot be more than about 120 solar masses because the outer layers would be expelled by the extreme radiation." -- 128.104.112.147 (talk) 22:41, 30 July 2008 (UTC)


 * Star formation also has some information - it appears the topic isn't particularly well understood. --Tango (talk) 22:50, 30 July 2008 (UTC)


 * (two edit conflicts) I think if a star were so massive, the pressure of gravity would cause it to collapse onto itself. That's what happens to massive but stable stars after they expand beyond a stable point; they collapse and form a black hole.--El aprendelenguas (talk) 22:51, 30 July 2008 (UTC)


 * Bah, see Eta Carinae for the most massive known star. Even at the maximum mass, it's often shedding due to its instability. If you're talking about maximum radius, however, see Hayashi limit. More mass in formation means pressure tends to overwhelm gravity, not the other way around. The only way to get a black hole is a large implosion caused by a sudden drop in thermal pressure which occurs when fusion in a stellar core ends. Even in core collapse, though, degeneracy pressure holds the majority of stars as a white dwarf or neutron star. Please read stellar evolution. SamuelRiv (talk) 23:11, 30 July 2008 (UTC)

Thanks for the information guys. The maximum radius of a star is the Hayashi limit, which varies for a given mass. The maximum mass of a star is the Eddington limit. If a star exceeds that limit, the intense energy from the nuclear fusion will create stellar winds that expel mass until that the star returns to within the Eddington limit. And I guess someone calculated that largest possible radius to be 2600 solar radii. In a broad sense, is that a decent view for the laymen to hold? <font style="color:#955619;">Louis Waweru <font style="color:#FFFFFF;background:#955619;"> Talk 02:20, 31 July 2008 (UTC)

The Development of Oxygen
What does the eventual development of oxygen mean? Isn't it that most environments were not suitable for anaerobic prokaryotes? Or is it because a large portion of the history of life was devoted to eukaryotic evolution?Crazymaniac15 (talk) 22:37, 30 July 2008 (UTC)Crazymaniac15
 * Wasn't this answered already? Someguy1221 (talk) 23:12, 30 July 2008 (UTC)


 * Yes, but three contradictory answers were given. According to History of the Earth, "Oxygen was toxic; probably much life on Earth died out as its levels rose."  However, according to Oxygen Catastrophe, oxygen provides energy much more efficiently than other sources.  This would presumably facilitate evolution of complex organelles like the nucleus, but I could not find a source.  I would say that A is the best answer because D is doubtful, and the others are utterly ridiculous.  --Bowlhover (talk) 07:14, 31 July 2008 (UTC)

Rubber band plane.
Looking for stuff to entertain my young son, I saw a rubber band powered plane kit (cardboard) for some ridiculous price in a toy-shop the other day, and I thought I could make that from scratch without too much hassle. However I can't find a decent pattern for such a device anywhere on the net, they all seem to require balsa. I want to make it cheaply as possible, using cardboard (cereal packets, 2+ ply if required), maybe coke cans for the propeller, that kind of thing. Can anyone help with a decent link? Jooler (talk) 23:10, 30 July 2008 (UTC)


 * I've made these before for Science Olympiad, and it's really difficult to get going right. My first suggestion is to order online - you can get a great plane for $20 (in 2003, at least). If you don't want to do that, you'll definitely need to order a proper propellor, wing paper, and rubber band online. My "test" plane was the Delta Dart from TurnerToys, which won't get you anywhere but gives you a good 10-second flight with no modifications. The better ones, though, will require you to shave down the propellors with an exacto-knife or sandpaper. SamuelRiv (talk) 23:20, 30 July 2008 (UTC)


 * Also see FAI Model Supply. SamuelRiv (talk) 23:24, 30 July 2008 (UTC)


 * When I was a kid, balsa rubber-powered planes were available in any convenience store, for usually less than a dollar. These were planes with a stick for a body, and slots for inserting the wings and stabilizer parts. Not really a kit, as they took no skill to assemble. The big brands I remember were Guillows and North Pacific (no article on that, 'cause Guillows bought it out). I never understood the popularity of Guillows planes, as they always had heavy propellers, whereas the North Pacific propellers were thin, light, well-balanced, and had the correct aerodynamic twist.
 * Guillows, however, made much more elaborate kits (and still does). I just never liked their propeller design. Look in a hobby shop. ~Amatulić (talk) 23:40, 30 July 2008 (UTC)


 * $1.79 at Toyworld (kids love 'em and will save you much time).  -hydnjo talk 23:53, 30 July 2008 (UTC)
 * $1.95 at Megahobby for the Guillows brand. -hydnjo talk 00:13, 31 July 2008 (UTC)


 * They're both Guillow's, actually. They both have the fat heavy props. The better North Pacific props can't be found on toy planes anywhere. I liked the Sleek Streek and Skeeter myself. Picture is here.
 * Look at this, I think it's perfect for your kid: free plans for building a reproduction Sleek Streek. That page also confirms my memory that the Sleek Streek was a better flyer than anything Guillows made. ~Amatulić (talk) 00:57, 31 July 2008 (UTC)


 * As I originally stated, I am looking for plans that do not use balsa, just cardboard, and I'm looking for just plans, not commercially available kits. Thanks anyway. Jooler (talk) 07:34, 31 July 2008 (UTC)
 * I trawled through a number of Google searches on this and found nothing good, so I haven't posted yet. Pretty much everyone wants some money. You can buy a book to tell you how to do stuff for free. You can buy a kit and try to make some direct copies. Or, if you want to teach your boy something good, you can just wing it (nyuk) and try making the whole thing by yourselves. The major problem with cardboard is that it doesn't have good stiffness (compared to balsa wood, that's why it's used so often). In order to sustain the tension of a wound elastic band, you are likely to need a stiffener of some kind, even if you fold the cardboard. I spent an hour searching this, if it was that easy I expect I would have found a good result. I did find some book reviews with bold promises, perhaps they are at a library close to you. Bottom line - if you want to do it for free, just start trying. We might be able to help with specific advice on wing shape or propeller twist or ways to stiffen individual bits. As far as designs for cardboard planes - sorry, I personally couldn't find any free ones. :) Franamax (talk) 10:51, 31 July 2008 (UTC)


 * These types of planes are tough to get off the ground, especially when you're not using ultralight materials, but there's no harm in trying. Here are a few suggestions: To make a propeller from a coke can, cut your figure-8 shape at a slight angle from the vertical axis of the can. Punch a hole in the center and see if you can smooth the edges of the hole, then fit snug around a thin dowel for your axle. Since you're using cardboard, you won't have much of any compression strength, so I suggest rolling a small piece into a tube for the fuselage and then having a paperclip hook fixed at one end to hold the rubber band *inside* the tube. To hook to the propeller axle, I'd say just drive a small, thin nail into the end of the wood dowel and bend into a hook., letting the dowel rest free inside the fuselage. My last tip is that you should make sure the wings are bent into a small arch, and that they make a slight "V" shape when viewed head-on. This will ensure that the plane is stable in flight. SamuelRiv (talk) 14:04, 31 July 2008 (UTC)