Wikipedia:Reference desk/Archives/Science/2006 October 13

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Chromosomes

Chromosomes are not generally observed in nondividing cells. Does this mean that they are newly formed for each cell division?

Nope. It's not that they are not present in nondividing cells, but rather that they cannot be observed. When not replicating, they are not neatly arrayed and separated from each other, so all one sees is a non-distinct nuclear blob of "all the chromosomes together". There's an overview explaining it in the intro to the chromosome article. DMacks 00:40, 13 October 2006 (UTC)

Threat to human race

What do editors think is the biggest currently percieved threat to the survival of the human race and why?--Light current 00:41, 13 October 2006 (UTC)

Bad spelling? Clarityfiend 00:42, 13 October 2006 (UTC)

Yes I know I cant spell!--Light current 00:45, 13 October 2006 (UTC)

Without trying to be too flippant - ourselves? People always seem to find reasons to want to kill other people. One day, it'll probably all go too far and someone will start something *very* nasty that no-one can stop. --Kurt Shaped Box 00:52, 13 October 2006 (UTC)

I vote for global worming. A big enough temperature change could destabilize the ecology and trigger an unstoppable chain reaction of species extinction. (Damn those hot giant underground worms.) Clarityfiend 01:01, 13 October 2006 (UTC)

Bullets kill, but it takes basically a trigger pull per death. Retail killing, little better than bare hands assault. Nukes kill faster, but the effect is geographically and temporally limited. Wholesale killing. For real extermination of the human race, think of biological weapons, the Gift that keeps on killing. Self-replicating killer nanomachines are also a plausible method for the demise of the human race, as is nudging a large asteroid to a collision course with Earth. The best case would be the replacement of the human race by the next phase of hominid evolution, just as humans theoretically replaced neanderthals. Edison 04:31, 13 October 2006 (UTC)

Climate change is by far the biggest clear and present danger to mankind. But not to its survival. Over the next century or so, millions if not billions of people will die, even if we stop producing greenhouse gasse now (I'm not kidding). But some people will always survive somewhere. It would take something even bigger than that. Forget about nuclear weapons, they're nasty but not big enough. An asteroid impact (caused by man or not) would have to be pretty big to wipe us all out (we're pretty resourcefull). 'Something nano' is probably the most likely cause of our extinction, if that is to happen in the near future. Like a very infectious lethal disease with a very long incubation period. But it would have to be lethal to everyone, which is rare. Genetic engineering could make something more alien our bodies don't have an answer to (made intentionally or by accident - both are an equally serious threat). But even that is biological and some might survive. Self-replicating adaptive nano killing machines (a hardware version of intelligent computer viruses) might be harder to find an answer to and are something we could probably build within a century (less even). Nano engineering isn't as serious a threat as genetic engineering because it is not as (commercially) developed yet. But that time will come. My own thoughts are starting to scare me now. DirkvdM 10:21, 13 October 2006 (UTC)

About the nuclear boms, let me rephrase that. The total arsenal would be big enough if it was employed with that single goal, but in reality it would be used by competing forces targeting only military targets, leaving enough room to hide. For some.... DirkvdM 11:47, 13 October 2006 (UTC)

You are assuming of course the humans that do survive will not be killed off by the nuclear winters and the radioactivity and the like after the bombing stops. It also depends on your viewpoint of what leaders will do. It is my opinion anumber of leaders if they feel their country is facing eminent destruction will say to hell with it and not just target military targets but try to destroy as many people as possible. I'm not saying I think this is likely to happen but it could Nil Einne 12:20, 13 October 2006 (UTC)

I don't think that an atomic war would be capable of killing off *all* humans. Most of us, certainly - but there will be a select few who saw it coming (or at least figured that 'something bad is going to happen one day') and made preparations. I do get a feeling that one day, those 'crazy survivalists' that documentary makers like to sneer at will end up having the last laugh. I don't fancy the chances of the world leaders after they emerge from the shelters when the whole thing is over - coming up for air and being faced by mobs of *very, very* angry and most likley heavily-armed (post-apocalyptic man will be a hunter/gatherer/farmer and he *will* have a gun) people... --Kurt Shaped Box 00:14, 15 October 2006 (UTC)

I think the biggest threat is to the survival of humans is humans. A quick look at this page should prove that to you. I'm actually quite surprised we made it this far... Nil Einne 11:14, 13 October 2006 (UTC)

There have been sci-fi scenarios, such as H.G. Wells The Time Machine (and movies adapted from it) in which nuclear war drives humans underground to escape the radiation. They have an underground civilization, perhaps with hydroponic agriculture and nuclear power, and survive indefinitely without blue skies and sunshine, perhaps mutating into Morlocks. The human race theoretically consisted of a few thousand people at the smallest, before modern humans expanded their range and replaced the neanderthals. With some radiation exposure and a small population, rapid evolution would be likely.Edison 13:40, 13 October 2006 (UTC)

I think humans are the biggest danger to themselves. Philc _T^E_C^I 17:47, 13 October 2006 (UTC)

Well my personal opinion is that its something beyond human control that will wipe everything out instantaneously. I can think of only one thing that would do it 8-)--Light current 02:33, 15 October 2006 (UTC)

The gulls? ;) --Kurt Shaped Box 02:35, 15 October 2006 (UTC)

I really can't think of one at all. And agreeing with Dirk (hehe), humans are damn good weeds and we won't go out easily or quietly. — X [Mac Davis] (SUPERDESK|Help me improve)04:23, 15 October 2006 (UTC)

A professor from Stanford mulls them all over here.[1] — X [Mac Davis] (SUPERDESK|Help me improve)07:42, 17 October 2006 (UTC)

Looking for medical term...

What is the actual medical term for the situation where someone bursts an artery in their brain whilst pushing too hard on the toilet when constipated? Anyone know? C'mon - doctors must've given this one an offical name... --Kurt Shaped Box 01:05, 13 October 2006 (UTC)

Drain Brain Strain. Anchoress 01:07, 13 October 2006 (UTC)

A stroke of bad luck? Or maybe just hard shit! 8-)--Light current 01:14, 13 October 2006 (UTC)

"You had a stroke while sitting on the can? Tough shit!" DMacks 01:28, 13 October 2006 (UTC)

Is there an echo box under the Ref desk? I could have sworn I just said that! 8-|--Light current 13:02, 13 October 2006 (UTC)

An aneurysm? Not necesarily the brain and not necesarily on teh tolit either, but does meet both criteria at times. Hyenaste ^(tell) 01:28, 13 October 2006 (UTC)

This cause of death was featured in the X-Files episode War of the Coprophages. --JWSchmidt 02:39, 13 October 2006 (UTC)

The Elvis effect.Edison 04:33, 13 October 2006 (UTC)

There is no specific name that I know of. If you find a name, it is likely to be an attempt at humor and not truly in medical usage. InvictaHOG 09:36, 13 October 2006 (UTC)

The lesson is of course to eat lots of fibre and cut out the sat fats. You then reduce the chances of stroke etc. 8-)--Light current 12:59, 13 October 2006 (UTC)

Could be called a minor brain scanning event 8-)--Light current 17:38, 13 October 2006 (UTC)

See Valsalva maneuver.--Mark Bornfeld DDS 21:30, 13 October 2006 (UTC)

It is a cerebral aneurysm you are thinking of. Unspecific to constipation though. — X [Mac Davis] (SUPERDESK|Help me improve)04:28, 15 October 2006 (UTC)

Oxygen

What happens when Oxygen is burnt(chemically)? Pure oxygen on it's own (O2 i assume...) is very flammable (like in Oxygen tank for medical or scuba use). When It is burned what does it form? I read the Oxygen article and it didn't give me much help. Can anyone else tell me or point me in the right direction? --Agester 01:20, 13 October 2006 (UTC)

Pure oxygen is not flammable in the usual sense of the word. Rather, it makes it very easy for other things to burn--burning as we usually experience it is a reaction in which the thing that's burning is combining with oxygen. DMacks 01:23, 13 October 2006 (UTC)

Im not a chemist, but I would think that oxygen has to oxidise something. So its the 'something' that is burnt , not the oxygen. 8-|--Light current 01:24, 13 October 2006 (UTC)

Oxygen by itself does not burn. Instead, it is a potent oxidizing agent that will readily combine with other materials; that chemical reaction is what we usually refer to as fire when it's fast, but as oxidation or even good old rusting when it's slow.

Atlant 01:26, 13 October 2006 (UTC)

For oxygen to burn, it would have to combine rapidly with oxygen. Well, it is already oxygen, so it has no urgent need to combine with itself. Thus oxygen doesn't burn, but flammablke substances will indeed burn rapidly in the presence of oxygen. Edison 04:35, 13 October 2006 (UTC)

The most common things we 'burn' would be carbon and hydrogen in various forms, carbohydrates(like wood and paper) and many various hydrocarbons. When these substances burn in oxygen (which is very different from "air"), the most common by-products formed are ordinary water "dihydrogen monoxide ;)", carbon dioxide, carbon monoxide.

This is not so much a faq but a frequently given answer (fga): fire requires three things: fuel, oxygen and heat. Having said that, ozone is formed by oxygen reacting with itself. I don't think that can be called 'burning', though. DirkvdM 11:56, 13 October 2006 (UTC)

The pedant in me notes that the requirement is an oxidizer, not necessarily oxygen, though oxygen is by far the most common one in most people's everyday experience. I wonder if O₂+2F₂→2OF₂ could be reacted directly and to give a visible effect enough to be considered "burning" and not just "oxidation of oxygen". DMacks 12:34, 13 October 2006 (UTC)

If I recall correctly Scientific American once (decades ago) had an amateur scientist column on building apparatus where "inverse" flames burn, in the sense that a small glass tip was used to introduce oxygen into a container of flammable gas, where the oxygen appeared to burn like a gas jet does in air.(Don't try this at home, since explosions would result if too much of the mixture combined unburned before ignition). The point is, that in that demonstration, it did appear that the oxygen was "burning" in the sense that heat and light were given off at a steady rate when it was introduced into the gas and a spark or ignitor lit it. Edison 13:46, 13 October 2006 (UTC)

You recall correctly.

Atlant 14:13, 13 October 2006 (UTC)

(sorry if i'm incorrect somewhere i'm still a student!) So oxygen we do know is highly flammable when it is with other substances(not chemically combined yet!)! But what i'm having trouble understanding is: oxygen on it's own isn't flammable?? --Agester 19:25, 13 October 2006 (UTC)

Let's put it this way: steak and fish are highly edible substances. They won't be consumed spontaneously, but combining them with your cat may result in the steak or fish being consumed. This does not mean that your cat is highly edible, but you'd better be careful with edible substances that you want to keep in the presence of your cat (and the other way around – it's really the combination that is riskly). Now read steak = cotton, fish = paper, edible = flammable, your cat = oxygen.  --Lambiam^Talk 20:33, 13 October 2006 (UTC)

Oxygen is flammable in a reducing atmosphere (say, methane). The oxygen and the methane combine to produce the flame; there's no obvious reason for preferring to say it's the methane burning, rather than the oxygen. But no, oxygen on its own is not flammable (the 3O₂→2O₃ reaction is endothermic, I think), unless you're talking about nuclear combustion (fusion), which requires extremely high temperature and pressure. --Trovatore 21:01, 13 October 2006 (UTC)

haha trovatore that's why i specifically mentioned chemically in my posts 8) but thanks for the feedback lambiam that certain helps a bunch! thanks to everyone for their input!--Agester 00:58, 14 October 2006 (UTC)

Ah, that answers my question. But can I reverse that? Is 2O₃ → 3O₂ therefore exothermic and can it therefore be called 'burning'? After all, ozone is a form of oxygen, right? DirkvdM 09:21, 14 October 2006 (UTC)

Yes, it's exothermic. Under normal conditions, ozone decomposes slowly to O2. But I just googled for an MSDS for ozone, an there, it says "At elevated temperatures and in the presence of certain catalysts such as hydrogen, iron, copper and chromium, this decomposition may be explosive." Simon A. 16:52, 14 October 2006 (UTC)

Wow, oxygen can be explosive. Don't tell any terrorists. :) DirkvdM 08:21, 15 October 2006 (UTC)

It can be toxic too... if i read correctly --Agester 12:31, 17 October 2006 (UTC)

Alpha level and power for a hypothesis

Hi:

I am sitting on my desk, trying to figure out the following statistics problem: if the alpha level increases power also does. Now, I wonder whether power can be less than the alpha level for a hypothesis test. I think it cannot be less as they are somewhat related and depend on each other. But I am not 100% sure. Does anyone know anything that would illuminate my mind and refresh my brain cells a little? I would be thrilled. Thanks much.Hersheysextra 02:00, 13 October 2006 (UTC)

Think of f(x)=mx+b. x is the alpha level. — X [Mac Davis] (SUPERDESK|Help me improve)04:33, 15 October 2006 (UTC)

Stored energy in tempered glass pellets

I threw a squiggly piece of metal at an oven today. The tempered glass shattered on impact, but when I went closer for inspection, I heard and saw the fragments continuing to break apart for minutes after the glass pane initially broke. The glass pellets were actually breaking apart with enough force to send them several cms in opposite directions. How does tempered glass manage to hold that much energy for so long? Hyenaste ^(tell) 03:01, 13 October 2006 (UTC)

The article has a pretty good description, although a diagram would be nice. The outside of the glass solidifies first, leaving too much room for the inside, and then the inside solidifies and contracts, pulling the outside inward. Think of it as a rigid box with a bunch of springs inside, under tension. The springs can't contract because they're attached to the rigid box. Then when you break the box, the springs contract and release their stored energy. See also Prince Rupert's Drop. —Keenan Pepper 05:34, 13 October 2006 (UTC)

Mystery writer Dick Francis wrote "Shattered" (2000) ISBN 0-399-14660-1 the plot of which focuses on the dangers of improper annealing of masses of glass.Edison 13:54, 13 October 2006 (UTC)

One day I shut the door on my old van, and the rear glass window completely shattered. For a second I thought there was a shooter! Apparently this was happening with all the vans of the same make and vintage. --Zeizmic 14:17, 13 October 2006 (UTC)

I was building something with a glass plate in it. The glass was on two hinges to act as a door. After I screwed everything in and such I tapped the glass with my screwdriver and it exploded into a million tiny little pieces all over me. To my astonishment some of the million little pieces just kept jumping. I guess the hinges were too close together!! There was so much compressive stress that my little tap sent it over the edge. — X [Mac Davis] (SUPERDESK|Help me improve)04:39, 15 October 2006 (UTC)

Microbiology math?

Would a course in pre-calculus be important for a microbiologist? 129.15.131.247 03:38, 13 October 2006 (UTC)Razma Dreizehn

Most post-secondary institutions require it, or some other math. It can't hurt to have some basic mathematical knowledge. -- Consumed Crustacean (talk) 03:51, 13 October 2006 (UTC)

Yes, definitely. Calculus is indispensable for all research in natural sciences. Whether it is of use to already aquire some knowledge before starting your university courses, or whether you may depend on them to lead you gently enough into the subject in the introductory courses, depends on the school, of course. But most freshmen in science and engineering subjects notice that in the first year, the math courses are the hardest and show the steepest increase in difficulty as compared to high school, and hence, being prepared may make your live much easier. (Note: I am German, but I assume this advice holds for most countries.) Simon A. 09:20, 13 October 2006 (UTC)

For microbiology, I'd recommend studying some statistics; stats is probably the most useful field of maths in Biology, as although you can never work out mathematically exactly what an organism will do, perfoming something like a Chi-square test or the Pearson product-moment correlation coefficient can allow you to find the likelyhood that something is related (such as the death of bacteria when exposed to different temperatures), rather than just a random occurance, very accurately. Laïka 18:25, 13 October 2006 (UTC)

Don't forget that pre-calculus and calculus cover things like difference equations and differential equations which can be used to model, for example, organism populations. Confusing Manifestation 02:40, 14 October 2006 (UTC)

Education

I am a doing my MA Education in a pakistani international university.The teacher has assigne me to write on the topic of "Mental heath of the teacher",for which i search many web site but found nothing. Now i requesting you to send me on the tpic of "Mental Health of the Teacher". Thanks in anticipation and best regards. (Muhammad Hussain)

Generally speaking, when doing research for postgraduate courses (actually even normal Bachelor's level courses) your expect to rely on primary sources i.e. journals and the like. Perhaps some good books etc as well from the library. Websites are usually a poor source. For a specialised topic like the one you mentioned, it will definitely be the case that you should be relying on journals and books not websites. BTW, I personally suspect the mental health of your teacher is rather poor if he/she has to put up with students doing Masters who think they can rely on websites for their essays/assignments Nil Einne 11:12, 13 October 2006 (UTC)

I suggest that you start with this question: what is special about the mental health of university professors that they would be singled out as a topic for study? You've found what I'd suspect, that there is little if any research focusing specifically on professors. One good place to start would be Occupational Psychology and studies such as these and this will allow you to evaluate instructors mental health relative to other professions. For example, you might ask: 'is the work of university teaching more or less stressful than other occupation?' and 'what positive mental health benefits does teaching provide?'. If you're really feeling ambitious, you could design or locate mental health questionnaires and ask professors to complete them, possibly comparing them to another occupational group. Learning how to conduct your own research is an essential skill in most graduate programs. Antonrojo 12:51, 13 October 2006 (UTC)

I'm not sure but I think he mean's school teachers not university professors but your post mostly still applies. BTW I would assume there must be at least some studies on the mental health of school teachers Nil Einne 13:08, 13 October 2006 (UTC)

I certainly had several who were nuts, and I probably did my share of harm to the sanity of others. One area of teacher sanity to look at would be the wierdness of teachers in their 20 or 20's who throw away their career to have sexual escapades with young teenage students. The teachers' mental health or lack thereof is often presented as an excuse at the trial.Edison 14:21, 13 October 2006 (UTC)

a short brief essay

Hi, I am a student and for one of my major essay projects-I chose 'is HPPA useful ,has it changed things much....a link to an article from a medical journal or any other reliable source talking about HIPPA's shortcomings or merits and demerits would be of immense help...I'd appreciate any help, thanks

• Make up your mind. Is it HIPPA or HPPA? - Mgm|^(talk) 07:53, 13 October 2006 (UTC)

So the purporse of this essay project was for you to learn how to get other people to find references for you? What course is this? "Users 101"? I'll tell you what I'll write your whole essay for you, see below:

I'm very lazy and can't be bothered doing the work that is expected of me. Please give me an F

That's it. The essay will be enough for an A+ I guarantee it. Nil Einne 11:06, 13 October 2006 (UTC)

This might be one starting point and oddly typos seem to help in this case. Antonrojo 12:54, 13 October 2006 (UTC)

Don't forget this too... Nil Einne 13:06, 13 October 2006 (UTC)

Double-slit experiment aiming

I find it incredible that single electrons on their own have the statistical probabilities of waves (weirdly phrased, but bear with me), but in the entire of Double-slit experiment I can't find out, why isn't it possible to perform this kind of experiment with anything bigger than a proton or an electron? 213.161.190.228 08:42, 13 October 2006 (UTC)

I think it might be, but the wavelength of bigger things is smaller so the interference pattern gets so compressed (to a small area) that you can't really see it's there anymore… I think. —Bromskloss 09:54, 13 October 2006 (UTC)

I don't see it in the article, but I remember one of my physics professors in college saying they'd managed to measure the interference pattern with helium. Or maybe it was hydrogen. But it was definitely an atom. --Allen 12:12, 13 October 2006 (UTC)

Here ya go: Carnal, O. (1991). "Young's double-slit experiment with atoms: A simple atom interferometer". Phys. Rev. Lett. 66 (21): 2689–2692. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) DMacks 15:12, 13 October 2006 (UTC)

OH, now I found it! The largest theoretically possible is just under the size/weight of a large bacterium, but should be very difficult to find out. Just scan the related Wave-particle duality for "bacterium", and it'll jump to it. Should've searched before asking. :) Thanks! (this is the original poster) 81.93.102.3 15:59, 13 October 2006 (UTC)

this[2] probably interests you too, it has been achieved with buckyballs. Xcomradex 23:17, 14 October 2006 (UTC)

How does the transferrin and ferritin be cleared in human body, respectively?

== How does the transferrin and ferritin be cleared in human body, respectively? Thank you. ==

• You might find this useful: Iron Transport and Cellular Uptake. --JWSchmidt 03:33, 16 October 2006 (UTC)

196.200.9.253 14:05, 16 October 2006 (UTC)== Chemical Engr/Production and application of CaCO.3 filled PVC ==

Hi,I'm a student of chemical Engineering & ve been working on the production and application of CaCO.3 filled PVC.I've done home work and got some knowledge,that inorganic CaCO.3 filler and particulate filled polymer are blended together;

• because CaCO.3 reinforce polymer(PVC)
• CaCO.3 has a toughening effect in the PVC/CaCO.3 binary composite

And they most applicable in,

• Coating/car underbody painting
• Plastics
• Rubber.

So,please i don't know if can get some help on the following;

• what is the method/procedure of production of CaCO.3 filled PVC
• What other application do we ve apart from that mentioned above.
• What are the effect of CaCO.3 blended with PVC

Please can i get a name of a reference material/textbook to me in my study for this topic

• What are the reason and advantages for such blend of CaCO.3 filled PVC.

Please I need your help,and will be waiting for your reply,till then thanks for your kind gesture and assistance.196.200.9.253 14:39, 16 October 2006 (UTC)

I fixed your post to make it more readable. Also please Wikipedia:Sign your posts with 4 tidles (~~~~) Nil Einne 11:22, 13 October 2006 (UTC)

Flu shot

I wonder if there is data concerning the time between getting a flu shot and being immuned (partly, as I understand) by it.

I assume you mean an influenza vaccine? I don't know specifically but it would be within a few days (to reach maximum immunity) I would suspect. Do you know how vaccines work? Nil Einne 12:14, 13 October 2006 (UTC)

definition of the word "plaxing"

I am trying to help a friend out with her child's vocabulary lesson at school. The teacher has raised the question as to the meaning of the word "plaxing" in relation to computers. I have not found any clear definitions or usages on any site. Does anyone have a definition and/or usage for this word?

Given the Google results, I'm doubtful whether plaxing is a word. Are you sure you got the word right? Nil Einne 13:04, 13 October 2006 (UTC)

Plaxing is, of course, the process of fulmagrating the tardyons in the central time and space dilator module of the Tardis. I thought everyone knew that. 8-)--Light current 13:16, 13 October 2006 (UTC)

Plaxing has something to with gambling. Google found plaxing poker, plaxing blackjack etc - Wikicheng 13:36, 13 October 2006 (UTC)

Multiplexing--Light current 15:17, 13 October 2006 (UTC)

I belive the spelling is correct as the teacher relayed it. In order to confirm, I will have to wait until next week's class. I do really appreciate all of responses at this point.

Urban dict. sez "The usher didn't notice the kids plexing, because he was looking at an attractive girl while they snuck ... If you plexing wit me you aint havin good luck". More senses on any search eng. -- DLL ^{.. T} 19:41, 13 October 2006 (UTC)

All examples I see of "plaxing" using Google search are typos for "playing" or "placing". My conclusion is that this is an unknown word, in relation to computers as well as otherwise.  --Lambiam^Talk 22:18, 13 October 2006 (UTC)

Black Hole

In wikipedia, under the paragraph "Recent Discoveries" we find a black hole discovered which is about 12.7 billion light years away which means it "really" existed 12.7 billion years ago.But the alleged Big Bang started about 15 billion years ago which shortens the life of the star to only 2.3 billion years.But we know a star should be highly massive and should be atleast 10 billion years to form a black hole which means the is an error with the dating of the big bang.Please give me an explainaton.

Highly massive stars actually have shorter lifespans than smaller stars. (Their greater mass and consequently stronger gravity cause them to compress and burn fuel much more rapidly.) Very massive stars (tens of solar masses and up) will exhaust their fuel in millions of years, rather than billions. Hope that clears things up. TenOfAllTrades(talk) 14:33, 13 October 2006 (UTC)

You expect a bit much of us Wikipedians. The black hole article says: In June 2004 astronomers found a super-massive black hole, Q0906+6930, at the centre of a distant galaxy about 12.7 billion light years away. This observation indicated rapid creation of super-massive black holes in the early universe. [6] And in the article of reference [6], they say A team of astronomers have found a colossal black hole so ancient, they're not sure how it had enough time to grow to its current size, about 10 billion times the mass of the Sun., asking the same question as you did. The discovery is recent and surprising, and the obviuos answer to your qeustion is: We don't know yet. That's why the discovery is so interesting. However, the hypothesis that some black holes have not formed from a star but already during the big bang is discussed a lot and we even have an article on this: primordial black hole. Simon A. 14:47, 13 October 2006 (UTC)

The article Age of the universe lists the best current estimate as 13.7 ± 0.2 billion years, making the universe even considerably younger at the supposed moment of black hole formation.  --Lambiam^Talk 18:19, 13 October 2006 (UTC)

Yeh but the point was that black holes dont just appear, a star has to die first, and woould a star have had enough time to live and die in the time given, considering its huge mass. I dont know the answer myself, but you may (or may not) have missed the questioners point. Philc _T^E_C^I 19:18, 13 October 2006 (UTC)

Supermassive black holes can, according to present theory, also result from a large gas cloud collapsing into a star of supersized mass, like wow. The star is unstable and may collapse directly into a black hole without going through the usual process ending with a supernova.  --Lambiam^Talk 23:15, 13 October 2006 (UTC)

Food pyramid

you know you have to eat 6 servings or more of carbohydrate foods such as bread a day, up to 3-5 servings of vegetables a day and 2 recomended servings of meat and alternatives each day. But how can you tell how much is each serving? for bread i know a slice is a serving, but what about a bowl of rice? there's different sized bowls for carrying rice.I asking this because i think i'm overeating. And also when it says two recomended servings does that mean i should only eat two servings of meat per day?

A serving of rice is 3/4 cup prepared. Most foods you buy at the grocery store have nutritional guides on the side somewhere. But isn't the food pyramid currently considered a poor guide to nutrition? If you're considering losing weight/keeping weight off, you might want to cut down on the carbs (especially processed flours and sugars) and incorporate exercise into your routine. See Mypyramid for more info. Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 20:59, 13 October 2006 (UTC)

It's supposed to be 5-10 servings of veggies and fruit, and a serving is 1/2 cup packed, 2/3 of a cup of juice, or 1 cup of salad. And contrary to the above post, reducing carbs is not a guaranteed way of losing weight, and not a proven positive choice for health (although reducing or even eliminating sugar and highly processed foods is definitely good). There are good and bad carbs and lots of people aren't sensitive to them. The only guaranteed way of losing weight is to take in fewer calories than you burn. As for protein, serving size depends on the type of protein. IIRC the meat serving size is approximately the size of a deck of cards, fish and soy is somewhat larger (6 oz), 2 eggs = 1 serving, and about a cup of beans = a serving. Anchoress 21:08, 13 October 2006 (UTC)

As for whether the recommended number of servings is a maximum or minimum, use it as a min for good foods, like fruits and vegetables, and a max for bad foods, like meat. StuRat 21:57, 13 October 2006 (UTC)

I think the food pyramid servings would seem incorrect with it's carb intake because some-most people aren't as active as they were in the past when this pyramid was suggested to them! --Agester 01:02, 14 October 2006 (UTC)

I wasn't guaranteeing weight loss (I said might). Burning more calories than you consume often takes more than just reduced input since your input can affect your metabolism. Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 07:38, 14 October 2006 (UTC)

It's certainly true that drastically reducing calorie intake can reduce set point, but I've only heard rumours about foods and food groups that actually affect metabolism. Were you thinking of any food in particular? Anchoress 07:49, 14 October 2006 (UTC)

No, I was more thinking about basal metabolism and how meal frequency and size can affect it, but apparantly this has been debunked. I vaguely recall a conversation with a health-conscious friend about carbohydrates but it was a while ago and he also believes that his car ("Laura") talks to him, that he speaks French well, and that his name isn't short for Francis. Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 23:18, 14 October 2006 (UTC)

Above all, don't stop listening to your body and don't over eat, if you've had your 5 servings of carbs by 7pm and you are not hungry, don't stuff another slice of bread in just because your pyramid says to.. ;) Vespine 05:03, 16 October 2006 (UTC)

Calculating wavelength of radio waves at a given frequency

I know it says not to give homework problems, so i'll just change the numbers. I'm having a problem where I can't seem to calculate the wavelength of a particular wave in megahertz, and I suspect i'm just not getting the concept, because I can't get any of the other problems which have anything to do with calculating wavelengths, de Broilegh or otherwise. For example, if there was a bunch of radio waves moving at, say, 100 MHz, I start by changing that to hertz to make it 1,000,000 hertz, then divide 2.998x10^8 by that value, and that should be my wavelength in meters, yet somehow i'm still wrong. (And it doesn't appear to be signifigant digit errors either) Can anyone tell me what i'm doing wrong? Homestarmy 21:53, 13 October 2006 (UTC)

First off, 100 MHz is 100,000,000 Hz, not 1,000,000. StuRat 22:00, 13 October 2006 (UTC)

So is the mega 10^6 and not 10^4? :/ Homestarmy 22:01, 13 October 2006 (UTC)

Yes. StuRat 19:31, 14 October 2006 (UTC)

SI prefix has a table. -- Consumed Crustacean (talk) 22:04, 13 October 2006 (UTC)

Or you can just look at mega or even mega-. In fact, also megahertz and MHz lead to this information.  --Lambiam^Talk 23:24, 13 October 2006 (UTC)

Nuclear fission (in nuclear weapons)

It seems to me that the amount of released neutrons in an atom-bomb grows exponential. How does it slow down? Why won't the neutrons just crash into other atoms and split them? (Henningklevjer 22:28, 13 October 2006 (UTC))

Why do you think it does slow down? In a "perfect" bomb, every single fissionable nucleus is fissioned; in practice the bomb is violently dismantling itself as it works, so a proportion of the fuel is cast off before it can be fissioned. One of the design goals for any practical fission device is to maximise the yield for a given mass of fuel, and minimise the waste. -- Finlay McWalter | Talk 22:44, 13 October 2006 (UTC)

Thanks. I guess I just thought every neutron hit another atom. (Henningklevjer 22:54, 13 October 2006 (UTC))

Ideally that's just what happens, but of course the bomb has only so many fissile atoms and (just like most other exponentially growing things in the real world) it soon runs out of new atoms to recruit into this subatomic Ponzi scheme. -- Finlay McWalter | Talk 22:56, 13 October 2006 (UTC)

That's why it is so difficult to make a really good atomic bomb that can fit in a missle, and why the North Korea 'bomb' may have been a dud (or never attempted). --Zeizmic 00:12, 14 October 2006 (UTC)

Decompression

If a person suffers sudden decompression, as in an airplane at high altitudes, does one pass out? If so, how long might such a condition persist? I imagine it isn't around the same time for everyone, even if they all suffer the same decompression. What is the cause of passing out in this manner? Thank you. --Demonesque 23:14, 13 October 2006 (UTC)

Uncontrolled decompression may cause air embolism, which can be fatal. See also Decompression sickness.  --Lambiam^Talk 23:32, 13 October 2006 (UTC)

Hypoxia (insufficient partial pressure of oxygen) is the cause of one passing out. And the condition persists until you reach a lower altitude, obtain an alternative source of oxygen, or die.

Atlant 00:05, 14 October 2006 (UTC)

Someone told me she hit that problem when a window broke. It was not too awful, only everyone had their ears bleeding ... the eardrums were better some days later. -- DLL ^{.. T} 18:40, 14 October 2006 (UTC)

In aviation the term is Time of Useful Consciousness. See the article, note that altitudes quoted in flight levels (eg FL180) are quoted in hundreds of feet, so FL180 is 18,000 feet. Over 30,000' it's measured in seconds. 203.22.236.14 10:23, 18 October 2006 (UTC)